Metaphotonics revolution: Engineering light for tomorrow’s technologies

Who speaks in this episode?

• Professor Yuri Kvar (Plenary speaker (keynote) and referenced collaborator)
• Dr. Canuda Sharta (Host)
• Professor Hongup Park (Panelist and main speaker (Talk #3))
• Professor Wun Ragunatan (Panelist and main speaker (Talk #2))
• Dr. UNU (Host)
• Dr. Chiminga (Host)

What is discussed, and when

1. 0:00 – 10:00: Cell Press, Professor Yuri Kvar, Dr. Canuda Sharta, Australian National University
2. 10:00 – 20:00: Nature Photonics
3. 30:00 – 40:00: Nonlinear Optics, Dr. Canuda Sharta, Professor Wun Ragunatan, Indian Institute of Science
4. 40:00 – 50:00: Nonlinear Optics
5. 50:00 – 1:00:00: Nonlinear Optics, Indian Institute of Science
6. 1:00:00 – 1:10:00: Professor Yuri Kvar, Professor Hongup Park, Photonic Crystals
7. 1:10:00 – 1:20:00: HBT Measurement
8. 1:20:00 – 1:30:00: Nonlinear Optics
9. 1:30:00 – 1:35:15: Nonlinear Optics, Cell Press, Professor Wun Ragunatan

Notable quotes from "Metaphotonics revolution: Engineering light for tomorrow’s technologies"

• It's it's my pleasure to host this webinar today organized by Cell Press. As you may know, Cell Press is an all science publisher of over 50 scientific journals across the life,.

  about Dr. Canuda Sharta · at 0:03

• So, it is my great pleasure and honor to pro welcome our professor Yuri Kvar from the Australian National University as our plenary speaker. Joining him are panelists, Professor Wun Ragunatal from IAC Bangalore, India and Professor.

  about Professor Yuri Kvar · at 4:11

• Science in Bangalore in India. his research group works in the areas of nonlinear optics, integrated photonics, resonant metaurfaces, optical communication and quantum…

  about Nonlinear Optics · at 35:23

• The title of Warren's talk today is nonlinear metaphonics with two-dimensional lead materials. Warren, please take it away. Thank you.

  about Professor Wun Ragunatan · at 36:14

• Professor Park received their PhD in physics from Kais in 2004 and completed their post-doal training at Harvard University. He's currently a full professor in the department of physics.

  about Seoul National University · at 1:00:06

• Generating way characteristics. So to address this issue just my group is focused on the topological features especially topological discolination state. So this is very interesting feature. First starting point is C4 lattice four-fold.

  about Professor Hongup Park · at 1:03:38

• Using that similarity we designed the photonics version of a discolination cavity. So our design strategy is very simple. So starting point is again C4 lattice and using…

  about Photonic Crystals · at 1:05:43

• So fabrication is very simple. just disperse chyro golden particle onto the silicon dioxide substrate and measure the second order correlation function simply G2 factor G2…

  about HBT Measurement · at 1:15:07

Who and what is mentioned in this episode?

People

• Professor Yuri Kvar — Person · Plenary speaker (keynote) and referenced collaborator · 3 mentions · first at 4:14
  Introduces the field from metamaterials to metaphotonics and provides foundational framing for the rest of the webinar; later referenced as a co-corresponding author on Park’s 2024 paper.
• Dr. Canuda Sharta — Person · Host / moderator · 3 mentions · first at 0:03
  Hosts the Cell Press webinar, introduces speakers, manages Q&A, and represents iScience as scientific editor.
• Professor Hongup Park — Person · Panelist and main speaker (Talk #3) · 2 mentions · first at 4:27
  Presents work on strong nanophotonic interactions for lasing and single-photon emission, including disclination nanolasers and chiral single-photon emitters; participates in Q&A on practical challenges.
• Professor Wun Ragunatan — Person · Panelist and main speaker (Talk #2) · 2 mentions · first at 35:14
  Presents research on nonlinear metaphotonics using 2D layered materials (e.g., MoS2 disks) and answers technical Q&A about nonlinear conversion and experimental parameters.
• Dr. UNU — Person · Co-host / Cell Press editor (introduced) · 1 mention · first at 1:03
  Introduced as a Cell Press colleague from the journal Device; present as part of the editorial hosting team though not speaking in the provided excerpt.
  I am Dr. Canuda Sharta the scientific editor at I science an open access broad scope interdicciplinary journal. Joining me are my colleagues Dr. UNU from device a journal that…
• Dr. Chiminga — Person · Co-host / Cell Press editor (introduced) · 1 mention · first at 1:15
  Introduced as a Cell Press colleague from Cell Reports Physical Science; part of the editorial hosting team though not speaking in the provided excerpt.
  Multid-disciplinary research on applied technologies and Dr. Chiminga from cell reports physical sciences an open access journal dedicated to cutting edge research across the…

Books & papers

• Cell Reports Physical Sciences — Book · Referenced work · 2 mentions · first at 1:15
  Mentioned as a journal by Cell Press dedicated to cutting-edge research in physical sciences.
  I am Dr. Canuda Sharta the scientific editor at I science an open access broad scope interdicciplinary journal. Joining me are my colleagues Dr. UNU from device a journal that…
• Matter and Light — Book · Referenced work · 1 mention · first at 2:13
  Mentioned as a new journal by Cell Press focusing on materials and light interactions.
  Press Blue that will have their first issues online in 2026 itself and are already open for submissions. As you see on this slide, matter and light will publish illuminating…
• Nature Photonics — Book · Referenced work · 1 mention · first at 19:52
  Mentioned as a journal where the term metaphotonics was introduced.
  That's somehow shaped the field which we now call mi resonant photonics or metronics interesting story the term was introduced around 2019 by editors of photonics nature photonics was kind of sudden discussion and discoveries when we were.

Companies & orgs

• Cell Press — Company · Organizer · 4 mentions · first at 0:10
  Host of the webinar, publisher of scientific journals related to the discussed topics.
  It's it's my pleasure to host this webinar today organized by Cell Press. As you may know, Cell Press is an all science publisher of over 50 scientific journals across the life, physical, earth, and health sciences. We publish.
• Seoul National University — Company · Affiliation · 4 mentions
  Affiliation of the speaker, Professor Hongup Park, discussing nanopotonic interaction.
• Australian National University — Company · Affiliation · 2 mentions · first at 4:18
  Affiliation of the plenary speaker, Professor Yuri Kvar, discussing metaphotonics.
  So, it is my great pleasure and honor to pro welcome our professor Yuri Kvar from the Australian National University as our plenary speaker. Joining him are panelists, Professor Wun Ragunatal from.
• Indian Institute of Science — Company · Affiliation · 2 mentions · first at 35:21
  Affiliation of the speaker, Professor Wun Ragunatan, discussing nonlinear metaphotonics.
  And the following talks. So moving on let me introduce speaker number two professor Wun Ragunatan. Wun is currently an associate professor at the department of electrical…

Concepts & topics

• Nonlinear Optics — Concept · Core topic · 13 mentions · first at 35:29
  Central theme of the episode, discussing advancements and applications in nonlinear optics.
• TMD Materials — Concept · Key argument · 4 mentions
  Discussed as a material platform for studying nonlinear optics and metaphotonics.
  So thanks for this opportunity to present some of our work. so I'll be talking about a specific application of metaphotronics in the area of nonlinear optics and also choose a specific material system.
• Quantum Dots — Concept · Key argument · 4 mentions
  Discussed in the context of quantum communication and single photon emission.
• Photonic Crystals — Concept · Key argument · 1 mention · first at 1:03:16
  Discussed as a platform for demonstrating nanopotonic cavities.
• HBT Measurement — Concept · Framework · 1 mention · first at 1:15:19
  Mentioned as a method to measure single photon emission features.

Full transcript with timestamps

0:00 Uh good day everyone. Uh it's uh it's my pleasure to host this webinar today um organized by Cell Press. As you may know, Cell Press is an all science publisher of over 50 scientific journals across the life, physical, earth, and health sciences. We publish both independently and in partnership with scientific societies. Our forum today metaphotonics revolution engineering light for tomorrow's technology will explore current edge cutting edge advancements in metaphotonics. We will focus on the remarkable capabilities of meta surfaces. Discovering how engineered nanoructures can manipulate light to control polarization, enhance the color coral responses and enable innovative optical functionalities.

0:58 I am Dr. Canuda Sharta the scientific editor at I science an open access broad scope interdicciplinary journal. Joining me are my colleagues Dr. UNU from device a journal that publishes groundbreaking multid-disciplinary research on applied technologies and Dr. Chiminga from cell reports physical sciences an open access journal dedicated to cutting edge research across the physical sciences and related interdicciplinary fields. We are excited to host this discussion today with our keynote speaker and panelists and address questions from the audience.

1:36 Our panel will specifically focus on the theme of caral and nonlinear metaphotonics of meta surfaces, two-dimensional layered materials and ultra compact lasers. I would like to highlight that many of the journals within the cell press portfolio including device matter Newton cell reports physical sciences and I science regularly publish research related to the topics discussed today. Moreover, in addition to our premium journals, Jewel Cam Matter Newton joining our our new journals Matter and Light and Cell Press Blue that will have their first issues online in 2026 itself and are already open for submissions. As you see on this slide, matter and light will publish illuminating science and build community around materials and light interactions across scales fundamentals to technologies in association with matter journal editors with its first issue online in spring 2026.

2:43 CPress blue is a is another journal with uh publishing research with infinite potential and is a highly selected journal open access uh publishing cutting edge research across all the topics mentioned and applied sciences which is a platform carefully selected for curated articles with the potential of impact in academia, industry and practice and beyond. Before we begin the talks, I would like to share a few practical points. Each speaker will present their latest research for approximately 15 to 20 minutes. Following the presentations, there will be a lively Q&A providing an engaging platform for discussion. If you have a question for any of the speakers, please use the Q&A box on the right hand side of your screen. You can submit questions at any time and you can also upvote the questions you would like to see answered by clicking the thumbs up icon beneath each question. We will do our best to pass on as many questions as

3:49 possible during the Q&A. It would be helpful if you include include the name of the speaker to whom your question is directed. Also, this event is being recorded to watch later. Finally, at the top right of your screen, there is an option to turn on closed captioning. Click the CC button and select your preferred language. So, it is my great pleasure and honor to pro welcome our professor Yuri Kvar from the Australian National University as our plenary speaker. Joining him are panelists, Professor Wun Ragunatal from IAC Bangalore, India and Professor Hongup Park from Seol National University in South Korea. And kicking off with our sp first speaker, distinguished professor Yuri Kishir.

4:39 Thank you for joining us today. Uh, Professor Kvisher received their PhD degree in 1984 in Kao, Ukraine. From 1989 to 1993, he worked at several research centers in the US and Europe. And in 93, he moved to Australia where he created the nonlinear physics center at the Australian National University. His research interests include nonlinear physics metamaterials and nanopotonics. He's the fellow of the Australian Academy of Science, Optica, APS, SPIE, and IOP. received many awards for his distinguished research including L medal in Australia, libertal in Russia, the state prize of the Ukraine in science and technology, Harry Mas medal in the UK, Humboldt research award in Germany, SPI Spiote award in USA, Maxorn award optica and more recently the 2025 met Metu Fenders Medal a top award for the Australian Academy of Science. The title of Yuri's talk today is from metamaterials to metaphotonics.

5:46 Yuri, the stage is all yours. Thank you very much. I just uh try to get connected. Um Oh, this is the wrong one. Sorry. Yes. Okay. Um I I I thank u uh cell cell editors for organizing this event and for attracted attention uh to many subject on physics in particular the um this fascinated new um directions on metaphatonics and um my job today is um uh to start from the very beginning introducing the field because it's definitely not subject which you can find textbooks uh and also give a platform for uh to following talk by my young enthusiastic and outstanding uh colleagues on specific areas of this field. Uh I'm trying to Yeah. Yeah. Yeah. First I start from the very very beginning.

7:47 Um so many of you know about light just easily switch on and switch off light in a room or anywhere else using torch. So light is something what every everyone sees their everyday's life. Uh but light is actually it's a physical object. It's a part of so-cal electromagnetic waves family. So visible light which all of you know understand is a very small or very restricted um um part of the so-cal spectrum of electromagnetic waves which cover a lot of different phenomena started from radio waves up to gamma rays and x-rays which you use for medical examinations.

8:41 Electromagnetic waves um appeared um concept of electromagnetic appeared long time ago and uh um from theoretical mathematical point of view um um uh we may say that the origin of all these ideas was finalized was specified by introducing of Maxwell equation. This is a simplified form of Maxwell equation on a Maxwell stat in the Edinburgh. Uh basically this is a one of the most important concept in physics uh with a multiple demonstration and application every everyday life. uh some of the application of optics and photonics uh particular light which part of electromagnetic waves it's uh already well known and you definitely had the chance to uh meet with this application and enjoy this application through optical fiber network communication with the photons then data storage um this less less common laser machinery in which used for different for different fabrication of different devices and

10:06 also for medical application. There are many different manifestations of application of optical lasers and um eye therapy and everyday's life. So it's very well established that optics is a is extremely important for for our future life and future development of our technologies. The question is how to implement the optical functionalities in the specific devices which you may actually uh use in everyday life. uh this is related to so-called photonic integration revolution is already ongoing for some years and initially it was kind of a relatively large expensive devices based on electronics then optics came into play and optics on the chip the silicon photonics type of devices were started to be important introduced in ultra high bandwidth technologies and telecom applications And this is devices which can be integrated in a cheap of order of cm.

11:16 And the question is how to use this functionalities even in smaller devices with many more different type of applications. So our future actually suggest that we should reduce all this u functionalities to the scales of order of micron and then um take photons um to replace electrons for different type of um application and actually achieve some disruptive um technologies for different for different areas of uh of subject and of course the size becomes very important because you you need to have a smarter devices on much smaller scales.

12:04 uh question is how to get everything uh scaled to smaller sizes. And of course this is a big question because we need to apply different knowledge and different approaches to um make a next revolutionary step and these approaches are associated with a so-cal concept of meta materials. So my job is to actually provide you background of what um I will be presenting later today and also my colleague will be presenting today and this is not very common knowledge which you can't find in textbook. So that's why I started to to introduce a very very first concept which actually um started to be developed about 20 20 25 years 20 25 years ago. Of course, meta these days everybody knows meta because it's associated with a media platform.

13:05 But uh in our contents uh meta is somehow used to define something less usual. Meta actually the direct Greek word which word which means beyond. So in the concept of meta materials uh meta was introduced about 25 years ago and to basically um define materials which can mimic what is actually nature uh does with normal materials. So basically all materials consist of atom molecules and with a particular packaging. So meta materials operate with a bit larger object a few 100 nanometer so called meta atoms or even larger object if you're talking about microwave application. So these are artificial structures usually artificial type of resonators which are composed in different latises periodic or a periodic and basically this uh structure um is controlled by properties of individual elements which we call meta atoms. So by changing meta atoms we may change properties of entire structure and of course size of that

14:26 several hundred nanometers will not be visible. It's exactly what's happening in nature. You don't see atoms. You don't feel them. And the same with meta materials. But in reality just to give you impression what's happening there. These are structures which are consist of these smaller elements. So basically this structuring of materials is now new type of trend to change properties microscopics properties of this object. This is basically uh the very general concept of uh meta different meta materials meta surfaces meta devices and different type of things because we are engineering elementary units. How it's happened actually it's happened that people in for electromagnetic application they we they combine different type of resonances. First resonance is a so-cal plasmonic resonance which in when excite um strongly localize hybrid waves um of combining electrons and electromagnetic waves on the interface

15:37 of electro metal dialectric material. So we have this kind of plasmonics reson associated resonance associated with so-cal electric atoms. But what was a big discovery some years ago that that we can actually control magnetic component of electromagnetic waves by introducing another type of element so-called magnetic atoms. This is so-called magnetic resonances which are in this simple geometry are excited by oscillating electrons and combining magnetic and electric responses we can actually engineer response of both electric and magnetic um properties of metamaterial. That was a concept which was created around 2,000 years and then 2025 was a uh special celebration of 20 years of discovery of metamaterials. A lot of interesting properties. This is one of the first structures. One of the properties was a so-cal uh uh invisibility clock possibility to engineer both electric and magnetic responsive to create a kind of shielding

16:53 and hide an object. That was a lot of media attention. Invisibility clocking is a very interesting concept and people were very exciting with many journal publication. That was a basically one of the development of metamaterial in addition to negative refraction but everything was a for much larger scale and the question was how to bring all this development to uh optics and visible light. This came to the concept of solo meta optics. Idea was that currently currently currently using that time structures which were based on metallic component. We needed to actually move to platform of dialectric to actually um in to actually have this magnetic properties of excited magnetic resonances. That took a bit of time to actually move from metallic structures with lossy elements to dialectric structures. An idea to actually replace resonances and metallic structures to resonances of dialectric structures was

18:01 to use so-cal um uh mi resonances. So basically the the the ideas which happens around 201011 was that for meta optics for visible uh realization visible realization of metamaterials um we need new platforms. So to create meta optics which will absorb different knowledge of metamaterials and will provide new elements and new functionalities which people discovered from meta materials. uh this meta optics actually uh based on dialectrics is uh uh was possible due to rediscovery of so-cal MI or functionalities of MI resonances. MI theory is very well known and describe um how sphere made of any type of material uh uh actually react to external electromagnetic waves. So mi solve for max equation exactly and describe this mod which known like mi resonances and people did not realize for a long time that this mi resonances may be associated with both electric and magnetic responses and then if you

19:20 excite individual elements made of high index resonances you basically come to the simple techn platform which allows you similar to metam materials combine electric and magnetic response of materials and that's somehow shaped the field which we um which we now call mi resonant photonics or metronics interesting story the term was introduced around 2019 by editors of photonics nature photonics uh was kind of sudden discussion and discoveries when we were interviewed with Mark progma from Stanford University by that time editor of nature nature photonics Rachel W and that came to the idea that this field somehow relies on this elementary exitation produced by me resonances it's very interesting direction which allows you to actually create structures with a very control responses of to electric and magnetic field and the most impressive manifestation of all the developments were of course not individual particle

20:32 But the structures if you now put um this resonator on the surface as you see this is artistic image of the some structures we fabricate uh we create so meta surfaces. Meta surfophysices are usually flat uh structures composed of resonators. Meta surfaces actually led to another revolution. revolution in optics. Uh this is very fascinating development which has a many different manifestation and basically idea is to actually replace all uh lenses which exist and um produce through polishing of uh pieces of glass to something flat.

21:20 This flat um structure is composed of resonators and it allows you to introduce the same functionalities for entirely flat surface. How it works? Uh if you now look at the conventional less into the concave on convex type of surfaces which are usually polished and met with the surface we have a very flat surface which are composed of resonators as you see shown here by this stripes and this replace lenses which are with sizes several millimeters to structures which are actually engineering along the surface. It's not very thin but still it's of order of hundred of nanometers or several hundred nanometers.

22:06 Basically you achieve similar functionalities like for normal lens which are um hard to fabricate and polish by creating structures with a specifically designed surfaces composed of resonators. That's a um revolution which associated with the word of meta optics and now many many applications of different types and um several years ago with my colleagues from Singapore National University we presented very recent in that time development of the concept of meta surfaces showing that way it can be applied for biosensing hybridization with two-dimensional materials which will be mentioned today because we surfaces are both flat and also with many other things like generation of uh photons from structures and quantum meta surfaces and computational and information meta surfaces for decode and unquote information. So it's a lot of a lot of things and I just mentioning me mention only this most recent

23:18 developments and even now we have already more different interesting things. The basic knowledge associated with meta surfaces is a ways to control response and that people um uh in last years we realize that you can control response of metaurfaces either engineering individual resonators and then we call such metaurfaces local metaurfaces or engineering longer structures longer response of a collective response and then we call them non-local meta surface. ES um this is different type of strategies uh which allows you achieve different functionalities. I will mention only about uh a few of them uh as examples.

24:07 For example, for resonances we actually explore so-called bound state in a continum. interesting concept introduced for quantum mechanics long time ago without understanding that how it may be affected how can be realized and can how it will affect optical application. Um this is um very interesting concept which allows you for quantum particles sitting in a in a potential actually introduce a states which will be fully localized and will coexist will exist in a continuum but it would allow you to actually cup light with this localized states and decoup light and that's what we use for resonances and meta surfaces. this example. So we engineer elements in these elements have some asymmetric profile allows you to create a very sharp resonance and these are examples of fabricated structures. You see is that these are meta surfaces with specific design elements and this elements uh have this

25:16 as symmetry introduced and this is also a symmetry and the sharp resonance allows uh to do many different things with the structures and with their uh with their response to light. One of the example I want to mention is so-cal uh biosensing application. We create a meta surface consisting of smaller meta surfaces. Each of them has a resonators and each of them has a particular sharp resonance. This is scale. So we have 10x 1000 pixelated metaurface meta surfaces composed of smaller meta surfaces. We have a combo of resonances.

25:59 And then if you use it for sensing, we just put the analyte and coupled with um uh midair oscillations of um particular substances and what we can see without any spectrometer we can record it and uh create so-called barcoding and associate particular substances with barcoding library. And this is one of the original ideas how to use this sharp resonances for biosensing. There are many other ideas and ideas how to expand it to hyperspectral biosensing and now there are many application interrogates and demonstration of the similar ideas with multi-ressonant type of metaurfaces.

26:50 uh very recent developments. is based on um efforts to actually combine local response from particular meta atoms and non-local response to create very sharp and high Q collective resonances and create a so-cal metal lasers which will allows you in a flat surface covered by gain material to produce any laser beam of any type of shape that was demonstrated and recently published in nature and probably still will take a moment real to realize particular different application. Uh finally I'd like to mention that this ability to engineer meta atoms allows you to control kyal responses of meta surfaces and metapatonics. This is a very hot topic and the idea associated with the possibility to achieve a very uh very sensitive kyal sensing separating of molecules by their chyal characteristics. And this basically comes to the very old days of um of um uh pioneers in uh um in in kyal properties and uh

28:18 knowledge is associated with intro in introduction of circular diorism. response of materials and substances to light of different circular polarization and people initially try to enhance circular uh the kyal response because kality in natural materials are very weak through introducing this you know plasmonic structures you see with spirals. So spirals pitch of order of fa length of light and actually make different response to right and left polarization. Uh but of course this plasmonic structures are very lossy and it was not clear how to actually make a lossless and uh highly sensitive structures uh which will react to different types of circular polarization of light that became possible. Um uh this is Kyle plasmonic is even seven seven years ago it became possible um through introduction of this bound state in a continum sharp resonances this is a very first theoretical paper which predicted that type of response

29:31 which will be highly sensitive to uh type of circular polarization of light right and left you see that transmission depends very much of a type of circular polarization and one of the application was demonstration of kyal laser which will emit light of particulous uh polarization and that is achieved through interesting engineering meta surfaces that uh give you example how we can actually operate and engineer this elementary units initially we start from symmetric meta surface compos of symmetric resonate resonators and then basically we change profile and incline them making slantic resonators. And this uh control of vertical dimension allows you to actually achieve preferential interaction with particular circular polarization. And then what we can do we can basically achieve uh lasers which will be uh with relatively low thresholds but will separate right and left circular polarization. uh meta meta

30:42 surfaces based on um um lazing based on meta surfaces will be presented by professor park later on but uh I just wanted to show you that there are different approaches but all these approaches actually based on the simple idea that we can manipulate with this individual units achieving particular um particular functionalities. uh this is a slide which gives you idea which may give you idea of um scope of different application. I pick up directions which are uh uh associated with my former students and my former poss.

31:26 So uh just to see to show you variety of possibilities. So we can with metamaterials we can control invisible solar panel contact. This is important uh important for for industry of uh solar energy harvesting because contacts produce several percentage of uh losses and this is very important uh meta materials can be used for security screening. This is prototype um for security screening which will completely replace the currently arrange huge delay and bottlenecks in airports. And this is stealth technology apparently based on the metamaterial concept is a race of antennas which make um uh uh aircraft invisible. Of course you can't read about that in normal journals. um MRI can be enhanced signal quality and reducing time may be enhanced with this particular metamaterial pads and there's already companies which produce that and more recent developments in hologram holograms created in your iPhone and of

32:39 course sensors created installed in your iPhone that's all this technology uh is coming and it it will be based it's so heavily based on this concept of metam material. Coming to the end, I just wanted to make a very few general statements. So meta materials is a new excited field of research and basically the concept is that we we create artificial structures based on some units, engineer units, they change properties of entire structures. That's a very very basic concept of everything. And of course when we managed to move from microwaves we managed to move to optics this reshape or rebranding that field and now we talking about meta optics beyond optics and metaphotonics beyond photonics.

33:33 We are dealing with quantum light and that's majority of all this effect are based on resonances because resonances are important to specifically control particular um particular responses and of course meta surfaces is implementation of metamaterials um for so-called flat optics uh and that will help to replace bulky optical elements ments particularly in conventional lasers. There are 22 companies right now which actively research all this application. Of course the most important as always in any scientific discovery it to get it relatively cheap. uh so as soon as we we create something cheaper you can apparently expect that it will be it it will be it will be going to market and people will enjoy all this technologies which already developing in the scientific labs. Thank you very much for your attention and thanks uh cell people who actually arranged that um that webinar to um make this activities more

34:44 available for public. Thank you very much. Thank you. Thank you so much for the insightful talk, Yuri. Uh I'm sure uh you have formed a solid understanding to follow up fundamentals but also updated everyone of us to follow on the research applied and to the latest technology and and the following talks. So uh moving on uh let me introduce speaker number two uh professor Wun Ragunatan. Uh Wun is uh currently an associate professor at the department of electrical communication engineering at the Indian Institute of Science in Bangalore in India. Uh his research group works in the areas of nonlinear optics, integrated photonics, resonant um metaurfaces, optical communication and quantum communications. He received his PhD a degree in electrical engineering from the University of California and Los Angeles in 2008 working in the areas of uh silicon photonics from 2009 to 2012 he was a post-docctorate fellow uh at

35:52 the department of chemistry in university of California air working in nonlinear optical microscopy from 2012 to 2016 he was a research scientist at Agelant research laboratories in Santa Clara working in the areas of infrared micro spectroscopy and applications of optical techniques to tissue imaging. The title of Warren's talk today is nonlinear metaphonics with two-dimensional lead materials. Warren, please take it away. Thank you.

36:24 Okay. Uh thank you very much uh Canuda. Uh so thanks for this opportunity to present uh some of our work. uh so I'll be talking about a specific application of metaphotronics uh in the area of nonlinear optics and also choose a specific material system uh two-dimensional layered materials and also may try to make a convincing case why this is an interesting material to study right um so uh this is the outline of what I have planned so just to make sure everybody is on the same page I'll talk about some basics of nonlinear optics and then why study nonlinear optics in nanos scale or subwavelength scale platforms uh and then move on to a specific work we have done recently in the enhancement of nonlinear processes specifically second harmonic generation in isolated malibdinum dulfide discs so I'll take you through uh some of the design fabrication and also the experimental work uh to understand some

37:22 of these structures as well the work I'm going to talk about is uh something we published in 2025 uh in the journal advanced materials Uh so basics of nonlinear optics. So what are we talking about here? We talking about light interaction with matter at high optical intensities. Uh so what happens is that when I shine light of uh high optical intensity on a material uh I can understand the individual atoms kind of responding to that uh high intensity. So in essence it's the electric field which drives the oscillators. the atom and the uh electrons uh the valence electrons respond like a harmonic oscillator for a linear optical process and if I drive it hard enough then it becomes anharmonic.

38:06 The consequence of that in electromagnetic theory I would be able to write it down as a polarization field which is made up of not just a linear term which is directly proportional to the electric field but now I have interesting wave mixing terms because of the quadratic dependence, cubic dependence and so on. Right? So that uh creates lot of interesting optical processes. I can look at wave mixing, frequency conversion, intensity dependent changes to refractive index and lot of other interesting properties can be studied. U where is nonlinear optics used? There are lot of practical applications for nonlinear optics. Uh for example, if you at all use a green laser pointer, invariably it is a harmonic like a doubling crystal which is used inside it to generate green wavelength. uh there are also a lot of interest in photon pair generation for quantum applications as well. The heart of it is a nonlinear crystal right and

38:58 two important considerations when you talk about nonlinear optics is energy conservation which directs the direction uh or the energy of the photon which is being generated and momentum conservation which decides the direction of photons or its dispersion properties of the structure in which it propagates and so on. So what are the nonlinear processes we study? Uh just again very high level overview we study different uh processes like harmonic generation uh with two photons combining to give rise to a second harmonic or three photons combining to give rise to third harmonic. There are also wave mixing processes where I have two different uh energy photons. We give rise to a third photon at a higher or a lower energy.

39:39 And uh all these three processes are parametric in the sense nothing is lost to the medium. But there are processes where energy is also taken up by the medium. For example, multifoton fluosence is a very important process there. And also there are ramen optical nonlinearities. You can drive phonon modes or vibrational modes in materials as well and study their nonlinear optical response as well. Right? So all these processes find useful applications. For example, ramen nonlinearities are used to build ramen amplifiers. Multifoton fluoresence is used as an imaging technique to look at tissue samples and so on. So there are there are whole uh array of applications which have emerged over the years in studying or leveraging these nonlinear processes for uh for something useful basically right so then moving on to what are the kind of material platforms in which nonlinear processes are studied. uh if you look at some of the

40:31 uh popular work you find uh long interaction materials like optical fibers where people use kilometer long nonlinear media to study optical nonlinearity and that has been something which has been uh popular since I would say the 80s where people have studied a whole range of nonlinear processes then if you look at a even smaller scale like bulk crystals then we find that the length scale gets reduced to maybe few centimeters maybe tens of centimeters so there's a huge hit in uh length right the interaction length and the way that is often comp compensated is by going for materials with strong optical nonlinearity going for crystals going for non-entroymmetric materials like lithium nibate KTP BBO and lot of other bulk crystals are have been used uh to build useful devices and then if you look at maybe around '90s and early 2000s there was interest in shrinking the optical mode to a much smaller

41:26 spatial scale and then still guide it in guided wave structures for example silicon photonics and more recently thin film lithium nibbate photonics has also come up where the lengths of interaction are even going down to maybe centimeters or millimeter and you compensate for it by an increase in the optical intensity due to tight optical confinement so if you follow the same trend what do we expect uh to come up then I can expect devices which are going down to maybe micron scale in length and then u there's a huge hit in terms of interaction length and the way we try to compensate for this is by going for materials with uh even higher optical nonlinearities or probe uh materials at wavelengths where it will respond resonantly or the other approach to take would be to enhance the electric field right it's the electric field and its quadratic and the cubic terms which drive the nonlinearity so if I can

42:17 enhance the electric field by a factor of maybe 10^2 or 10^ 3 then that can have a huge impact in enhancing the optical nonlinearities basically and then if you see what has been happening in this field over the last decade or so. People are exploring material platforms especially meta surfaces like what uh Yuri was talking about like leveraging the field enhancement right what you get in resonant meta surfaces to enhance optical nonlinearities as a direction of interest and in terms of exploring novel materials there's been interest in uh exploring 2D layered materials and then studying their nonlinear optical properties and hopefully these will also find device applications in the future.

42:58 So what what are the work that has happened in studying nonlinear optics in uh metaphotonic structures. So one of the earlier work u I think professor Yuri was also part of this they were looking at isolated silicon uh disc structures and then relying on the intrinsic mi scattering modes for example magnetic dipole type resonant modes from these structures and then using this to enhance resonantly enhance third harmonic generation processes in these kind of structures. In fact, the third harmonic is so bright that you can even see the blue color in a camera image which was taken uh from this uh sample. Uh subsequently people have started looking at arrays coming up with interesting resonance mechanisms. I think quasi bic is one popular resonance mechanism to achieve high quality resonances. So even that has been used to enhance uh optical nonlinearities. So this is a silicon meta surface with an

43:50 intentional asymmetry which has been introduced and that creates very sharp high quality resonances. So this has been used to study both sec third harmonic and also second harmonic from centroymmetric silicon structures. Uh and then there's also work on studying higher harmonic generation from interesting platforms. For example, these are like holes instead of uh discs which have been patterned. This is a membrane of silicon where you see arrays of holes. Again, it supports interesting uh scattering modes and then one looks at collective effect between arrays of these scatter scatterers and then you you can you can make use of the strong field enhancement in the silicon material and then look at lots of odd harmonics which are being generated all the way to ninth harmonic and so on. Uh and then there's also interest in applications right how to how to use this for useful frequency conversion. So

44:44 one area of interest which has taken off is this kind of projecting images onto this meta surface and then wide field like the large area whatever is being projected trying to upcon convert it to uh other frequencies. Uh a driver here is like if you have infrared images which are difficult to detect with an infrared sensor then one could potentially convert it to a wavelength where I can use a standard silicon sensor to do imaging and all that right. So all these are areas which are uh which have come out of this meta surface and understanding the meta uh meta structure physics and then applying it to nonlinear frequency conversion type applications. U so if you look at all these structures a general trend which you see is that some of the scattering modes which are supported in these structures are strongly influenced by the refractive index of the medium.

45:32 Right? So what I show here are two different prominent scattering modes. The one on the right side is because of the magnetic dipole type resonance and one on the left is because of the electric dipole type resonance. And as you can see as I increase the refractive index, this is just a standard disc, an isolated disc. As I increase the refractive index of the disc, these resonances get sharper and sharper. Uh the reason being that uh light wants to confine itself into a high refractive index medium, strongly interact and correspondingly scatter more efficiently through that. And a as light strongly interacts with high refractive index medium, there's going to be a higher electric field which is going to be set up in this material. Right? So that is something which I would like to leverage if I'm studying the nonlinear properties coming out of these kind of isolated meta atoms. Um so the if you study

46:19 nonlinear optics in any material right it's the it's the material it's the interplay between the material and the electromagnetic field which is of interest. So if I want to select materials I want to go for materials with high refractive index. Right? But nature is generally not so kind that we find that when I go to high refractive index material, the band gap of the material starts reducing. Right? So that could be a problem because when I generate my harmonics, it could be at a wavelength where the material will start absorbing and then now I cannot efficiently collect that light coming out of my meta surface. Right? So then uh then there is interest in exploring materials or new materials which kind of beat this rule that what is shown here is uh essentially the refractive index versus band gap. So as I go higher in refractive index the band gap of the material reduces. Then I want to look at

47:07 outliers which which do not follow this trend. Right? So people are looking at materials. So this is this trend. Whatever is shown here is what is known as MOS law and which has been published in the past. And then people are looking at materials which violate this rule which are called as super motion materials. Two of the popular materials which were identified are shown here. One is iron pyite FAS2. The other are these whole class of uh transition metal dalcogenates like MOS2 and so on. Right? So there's lot of interest in studying or building metaurfaces out of this and then studying the light interaction and for for our interest we are trying to explore the kind of nonlinear photonic properties which these kind of material platforms will offer.

47:50 So moving on why why do we study nonlinear optics in these kind of layered materials? One motivation is to violate this MOS rule and then go beyond that to achieve wide band gap materials with high refractive index. But then if you look inherently at these kind of layered materials especially I'm I'm focusing here more on the transition metal dalcogenides monochalcoenide like platforms the transition metal atom is essentially made up of these dshells of electrons and then uh they essentially screen the valence electrons quite a bit right. So when you drive these oscillators nonlinearly there you can create strong polarizations at these non uh which respond nonlinearly and then you generate enhanced nonlinear response from these kind of materials.

48:35 So inherently these transition metal dalcogenate systems especially in its crystalline form exhibit strong optical nonlinearity just because of the way these electron shells are arranged in these atoms basically right so I would like to leverage that property the combined properties of having very good linear optical properties and the way that I can drive these nonlinear oscillators with uh quite a bit of strength that I want to combine these two effects and try to make use of this for useful device applications right uh on top of that there's also this whole field of using these 2D layered materials both in monollayer and also multi-layer form for electronics applications as probably potential replacement or maybe an addition to a standard silicon transistor. So that's also an emerging area which is coming up. So as uh as more and more investment goes into this in fabrication and all that we we can we can leverage that when

49:27 we study these uh the photonic properties of these materials as well. So our group has been focused on uh studying nonlinear properties of layered materials for almost last six to seven years. So I broadly categorize some of our research efforts into these four categories. We have been studying layered materials just trying to understand the nonlinear properties right no patterning or nothing but just study like if there is a new material which comes up then is this good for nonlinear optics or not is an area is something we work on. So trying to characterize like how strong is the optical susceptibility is something of interest. Uh this for this we collaborate with lot of groups uh around the world who send us samples. We study their properties and so on. And then now a basic level of integration would be to build multi-layer stacks. So you can think of it like a DBR reflector or a fabriero kind of very simple stack which

50:21 can be used to enhance light uh interaction with these kind of structures. So I can design this stack carefully so that uh there will be a strong electric field which is set up within the layered material. So that is a promising direction we have explored. And then one more area of interest are these hybrid integration or hybrid metaurfaces where there could be an underlying uh silicon metaurface platform on top of which I can transfer layered material. So a lot of groups around the world are also exploring these kind of ideas where I leave the high quality resonance to the underlying silicon meta surface while I leverage the nonlinearity offered by the layered material and then build these kind of composite platforms for nonlinear applications. And then one more area which has come up over the last uh 2 three years I would say is to have the ability to pattern these layered materials and build resonance structures

51:10 out of these. Right? So this is an example. This is just a cartoon schematic of a disc malibdinum dulfide disc uh which we have been also working on. Lot of groups around the world are also addressing this uh where one can leverage the high refractive index to enhance the scattering properties and then use this for nonlinear photonic applications. Right? So what is the workhorse like how do we do experiments in the lab? Uh the workhorse what we have is this nonlinear microscopy system whatever is shown here. Um so we use pulse laser systems to kind of excite these samples. Uh it's like a microscope fairly generic system. So all the four samples I showed you can be put on the on the sample plane of a microscope excite with different colors and then try to look at their nonlinear response.

51:55 It's a fairly uh robust system. So these are couple of examples of uh how nonlinear microscopy is very useful if you want to study layered materials. So this is an example where we have looked at twisted uh billayers. These are uh these are essentially MOS2 and WS2 which are intentionally twisted a little bit to create these moss or moay potentials and a golden standard to measure the twist angle is to make use of second harmonic generation. So we look at the intentional uh we look at the polarization response in the second harmonic and the slight twist whatever is shown here in the polar plot gives me an accurate estimate of how much is the twist angle between the two layers. And similarly we have also looked at different poly types of materials you can grow. So this is an example of a three poly type of MOS2 which is supposed to show layer independent nonlinearity which is also something we

52:46 have characterized and uh this is a collaboration with a group uh here in India. So moving on uh uh so in terms of metaphotics we have been looking at these kind of MOS2 disk structures. I've already motivated why we study this. It offers very good optical properties like broad optical transparency, high refractive index. Uh some of the refractive index numbers which have been reported in the visible are like refractive index in the range of 5 to six. While in the near IR wavelengths people have reported refractive index of about 4 4.5 type numbers. So they are fairly high while the band gap wavelength is about 750 to 800 nanometer. So, so it's a it's a fairly good material if you want to use this for frequency conversion harmonic generation type applications. Uh the kind of structures we have been looking at are very simple disc resonator structures. If I look at an isolated disc resonator, we design the dimensions

53:38 of these discs to support scattering modes which are called as anopole resonances in literature. So what what these resonances are are essentially the kind of scattering modes which are supported in a individual disc but now it's made up of an electric dipole mode and a tooidal mode which essentially interacts with each other and at a particular dimension or a particular wavelength for a fixed dimension you get kind of a destructive interference between the two in the far field that you essentially get like a dark state that you you wouldn't see any scattering come out coming out of it but locally there is a strong field enhancement because of the interaction between the to the electric dipole and the tooidal mode. So these are typical field profiles which we we obtain when we look at these kind of resonances and then we design these structures by choosing an appropriate diameter where you can park

54:27 one of these dark bones which is shown by these bands at a particular wavelength of interest basically right so then what we do is we introduce the underlying layers right I cannot study a dis hanging in air so I have to support it by a silicon dioxide layer and a silicon substrate so when we build these stacks we we find that uh there's some interesting ing effects which occur. The silicon dioxide layer is a low index medium sandwiched between the MOS2 disk which is of a high index and a silicon substrate at the bottom. Then there are going to be interesting fabric modes which are going to be set up in the silicon dioxide layer. And what we find is that there these bands whatever I showed in the previous slide they become lot more pronounced in the sense that there are specific diameters where there is a strong enhancement in the energy which is stored within the disk. The reason why this occurs is that there's

55:14 an inter interaction between the fabric mode and the anopole scattering mode supported in the disk and that's what enhances the overall energy much further than what you would uh see for an essentially an isolated disc. So this is something we would like to leverage in in whatever we are doing subsequently for studying the nonlinear properties. So we went ahead and fabricated some of these structures in uh the Indian Institute of Science clean rooms. So what you see here is an exfoliated MOS to flake and then we do electron beam lithography to define discs of different diameters and then study initially their linear properties. So this is just looking at the reflectance which is an equivalent measure of looking at the scattering though we don't collect all the angles but still we can get a good uh spectral feature which resembles the dark state and then the other uh uh sign what we are looking for is that as I

56:04 increase the diameter of these disc there's a clear shift in these resonances right which is also shown and then the other feature is that the contrast in these resonances tend to go up uh as well uh for an optimum disk diameter which is also of interest to us because we have intentionally designed for a specific disk diameter where I get this constructive interference between the fabropo and the anapole scattering mode basically right so then we went ahead put these samples in our microscope system and started looking at the second harmonic response and what we found was that uh corresponding to the dips what we what we saw in the reflectance spectra you can see peaks in the SG spectra because those are the wavelengths where the second harmonic response is going to get enhanced and then when we quantitatively compared this with an unpatterned uh layer right I can go outside these discs and then

56:53 measure the SG we do obtain significant enhancements in SG for one of these diameters we obtain like nearly 160 times enhancement and the other interesting thing also we observed is that we can also compare this with a monollayer right a monollayer is like just a single layer of MOS2 there again we obtain a significant increase like nearly 100 times increase in the response I'll explain why this is interesting in the uh the two slides I have subsequently. So these are not done only across few discs. We have tried it across like nearly 40 to 50 disk and then we we observe a clear trend in the sense that the diameter of these uh uh scatter plot shows the strength of the SSG signal that is being enhanced for a optimum value of uh the uh the disk dimension and then we also see clear trends for different diameters and so on. Right? So uh the reason why I was comparing with monollayer is that uh if

57:47 you look at the particular poly type or the way these layers are stacked the dipoles the nonlinear dipoles tend to cancel each other out. So it's the monollayer which gives the highest second harmonic and anything even you get a cancellation in the dipoles and then as I stack them bigger like thicker and thicker there's going to be a reduction in the SG signal right but then we were in fact able to observe an increase in the SG signal with stacking and fabricating the disk. The reason for this is very interesting that you not only create a strong field enhancement within the structure but you also create a strong field gradient right the consequence of the field gradient right because there's a rate of change of field with respect to the height of the structure I find that those dipoles right no longer cancel each other out so that that makes it even more interesting because that lack of cancellation

58:36 enhances the overall second harmonic significantly when compared to if I were to choose only a monollayer of these materials. So the the disc structure not only helps in increasing the field strength which is used to study optical enhancement nonlinear optical enhancement but uh it is also very useful in creating field gradients which are used to essentially break the asymmetry in the way these dipoles are oriented. So that makes it even more interesting. Right? So then we went ahead did some modeling uh with comsol and then tried to compare it and all that. We were able to get very good agreement with this as well. Right. So I think my time is running out so I'll stop here. Um I hope I have convinced you that 2D layered materials is an interesting platforms to study nonlinear optics and particularly patterning them is a promising approach to leverage some of the advancements in metaphotonics the

59:26 individual scattering modes and also if you were able to realize arrays that also makes it that much more interesting. I I discussed one particular application of second harmonic enhancement in these MOS2 discs but then this field is just starting up. Lot of interesting things are coming up around the world as well. Right. Thank you. I'll stop here. Yeah.

59:45 Thank you. Thank you very much. Thank you Arun for the insightful talk and your latest research. Our best wishes with you. So moving in in the interest of time, it's my pleasure to introduce our third and the final speaker and it's my privilege to introduce Professor Hongu Park from Seol National University from South Korea. Uh, Professor Park received their PhD in physics from Kais in 2004 and completed their post-doal training at Harvard University. He's currently a full professor in the department of physics and astronomy at Seol National University. He's a fellow of the Korean Academy of Science and Technology and an Optica fellow. His research focuses on topological nanoasis and nanoscale photonic and plasmonic devices as well as optical applications in lowdimensional materials. The title of professor pug's talk is strong nanopotonic interaction for lasing and single photon emission. Please

1:00:46 thank you very much for your nice introduction and just my name is Park. I'm from Soul National University and first of all I'm very happy to give a talk in such a great webinar series and thank you very much and thank you uh Dr. Sharta for your thoughtful invitation and today the title of my talk is strong nanopotonic interaction for lagging and single photon emission. So my talk will consists of two part and first one is nano laser and the other is single photon emitters and first part is a nanoer and this part will be uh presented based on this paper published in 2024 and the uh yuri is co corresponding author of the paper and I want to briefly introduce nano timeline first of all And around 2000 photonic crystal as you know very well consists of periodic array of two dialectric materials and photonic crystal laser can exhibit high quality factor and small mode volume and around 2010 plasmonic cavity

1:02:05 or metallic cavity can support very uh strong light confinement within a defraction limit around uh Since then, since 2010, more fundamental physics uh mechanism have been uh included to demonstrate nanopotonic cavities. For example, parity time symmetry breaking, bound the continum and photonic topological insulate mechanism have been included to demonstrate photonic cavities. uh more recently more inspired nano laser and discolination nanoer have been successfully demonstrated so today I'm going to focus on this culination nano laser first I want to explain just orbital angular momentum of light simply is very good quantum number and particularly useful for generating different degrees of freedom for specially distinguishable channels in data transmission The coherent OEM light sources have been demonstrated successfully using micro ring resonators, photonic crystals and pillar chains. But these are all some bulky

1:03:22 size and micron size. So substantial scattering loss and high ling threshold cannot be uh uh avoided. In addition, there is no report about intrinsic vortex mode generating way characteristics. So to address this issue just my group is focused on the topological features especially topological discolination state. So this is very interesting feature. First starting point is C4 lattice four-fold rotational symmetry and cut into four sectors like that and add one sector or remove one sector. So we can generate C3-fold rotational symmetry or five-fold rotational symmetry structures. More interesting thing is four corner charges originally in the C4 lattice can be confined in the bound state in the core as a result of this culination procedure.

1:04:31 So also that corner charge uh called bound topological bound state can have angular momentum. So we want to mimic this feature to uh to generate uh discolination nano cavity. So we design photonics version of this colination cavity generating vector vortex state such as optical vortex and optical antiortex. In addition we use similarities between tightbinding simulation and optical simulation. In tight binding simulation, chargy density is confined in the atomic side uh shown like a black dust and also periodicity of these atomic site uh energy band gap can be generated.

1:05:23 Similarly in optical simulation the uh black dots correspond to air holes and magnetic field can be confined in the air hole region if we consider transverse electric case and also photonic band gap can be generated uh due to the periodicity of air holes. So using that similarity we designed the photonics version of a discolination uh cavity. So our design strategy is very simple. So starting point is again C4 lattice and using voltage process or discolination procedure we can make C3 C5 and C6 discolination structures and then these black dust can be replaced into air holes to make photonics version of discolination cavity and then just like fractional charge photons can be confined in the core region and fractional charge can have angle momentum. So also photons can have angular momentum. So we can uh check this feature by comparing uh type binding simulation and optical simulation in two-dimensional case. So

1:06:39 there is one trunk correspondence between type binding simulation and optical simulation in C5 discination cavity. You can see L0 L plus minus1 and N plusUS five in state in type binding simulation. And similarly in optical simulation there are five resonance mode L0 L + minus1 and L+US2. This one correspondence between geometric and photon inf state with the same angular momentum is originate from the similarities between type binding simulation and optical simulation. In C3 and C6 there is strong one correspondence. There are three in gap state in C3 and there are six inap state in C6 discolination structures.

1:07:25 So we further interest in these two mode L0 and L plus minus 2 in C5 discolination cavity because they have central singularities in the electric field. So we can drive exact form of electric field just like that L0 and L+US 2. There are two degenerate mode in L+ minus2 electric field. In addition, we calculate topological charges using this equation. And then L0 mode has topological charge of + one and L +2 have topological charge of minus1. So L0 mode is vortex mode or in conventional optics it is called admiss polarization state and L+US 2 mode anti vortex mode.

1:08:12 This is called even and hybrid polarization state. So we extend our uh simulation to real three-dimensional case. So we employ the photonic crystal slap structure and repeat the same uh simulation. The results are exactly same. So electric field intensity and vector distribution indicate admissial polarization state with a singularity at the center and phase distribution indicate counterclockwise closure loop which indicate topological charge plus one. More important thing is high quality factor and wavelength scale mode volume and also that core region is the uh singular point. So we can modify freely to excite another resonant mode. So we shrink the core. So we can excite degenerate antivax mode like that. In this case topological charge is minus one while the mode volume is very small.

1:09:20 So based on these welldesigned optical cavities we actually fabricate the samples using uh 280 nanometer thick Indian gallium marinite slab with three quantum wells. So uh the cavities are optically pumped at room temperature and each cavity exhibit clearing features including sharp single mode peak and super linear increase above the threshold. So this vortex mode has just a single uh pig and this antiortex cavity support uh two doubly degenerate uh lazing uh mode to identify this lazing mode. We measured polarization result mode images without the polarizer first case and all three mode uh exhibit donut shaped intense profile which is a unique feature of vector vortex mode.

1:10:16 But with polarizer the images are very very different very distinguishable. The vortex mode exhibit the aim of polarization state and these two doubly degenerate antiortex mode exhibit the odd and even hybrid polarization state and those measurement result uh shows excellent agreement with the simulation result to uh identify the lazing mode in more detail. We also performed specially resolved struct parameter experiment. To do that we need complete set of polarization result mode images including horizontal, vertical, diagonal, antid-diagonal, right circular and left circular polarization images.

1:11:01 And these are row data and using the equation we obtain stocks parameter images and S01 2 and S3. And these STOs parameter confform the lazy mode with topological charge plus one and two doubly degenerate minus one values. And I want to highlight this table because uh we want to compare the our discolination laser with other vortex nano and micro lasers. I want to highlight the very low threshold value just 100 times smaller than the previous cases because the cavity size is thousand times smaller than the previous uh nano lasers. More recently we successfully demonstrate C6 six-fold rotational symmetry photonic discretation in a laser and we added two more sectors in this C4 largest cavities and we fabricate a sample and we successfully observe single mode lazing pig. More important thing is polarization result mode profile. So with rotating the uh polarizer interesting thing is laser mode complete

1:12:13 just half rotation that is unique feature of rotation order of two or topological charge of two. So we successfully demonstrate C5 and C6 this clinician nano lasers. So I want to uh make a transition to the second topic single photon emitters based on the uh this paper published in 2024 also. So you know very well quantum communication and that quantum communication is typically based on banned and brasad protocol simply BB-84 and BB-84 consists of three parts. First one is sending polarized single photon through quantum channel. Second is confirmation through public channel and last one is sharing the secretive key chains. But most important and difficult part is generation of polarized single photons.

1:13:09 In addition, the quantum emitter should be strongly integrated with high quality optical cavities for practical single photon emitters. And then this as shown in this equation radiative rate of quantum emitter can be controlled. So to enhance pel factor the emitter should be controlled in their position spectrum and polarization. But these are all always very difficult. So people try to use 2D materials because 2D materials with inherent mechanical flexibility and strength can provide an ideal and robust platform for practical single photon images via strain engineering. So my group successfully demonstrate the single photon array using monollayer tons and dicelonide.

1:14:01 First nano gap should be fabricated underneath the monollayer tonselonide and this nano gap induced tensile strain and localized extern rise from a confined potential caused by a local strain gradient which lead to quantum funneling and single photon emission and also two dimensional in this case one-dimensional photonic crystal cavity is placed onto the monollayer tungsten iselani single photon emitter and then post cell factor can be increased but still manipulation of polarization properties especially so polarization properties of single photon emitters remain challenging. So we want to combine the monollayer tonselonide with chyro gold particle and strained tonselonide monollayer coupled with chyro plasma golden particle can emit right circular polarization or left circular polarization depending on the coupling orientation.

1:15:07 So fabrication is very simple. just disperse chyro golden particle onto the silicon dioxide substrate and measure the uh second order correlation function simply G2 factor G2 value using HBT measurement setup and then we successfully demonstrate single photon features very narrow emission P and G2 value below 0.5 especially uh in our experiment G2 value range from 0.1 to 0.23 3 which is shows high single photon purity and then more important thing is interesting thing is polarization resolved uh spectra so in this sample so we observed dominant left circular polarization spectrum while single photon emission feature is still observed so G2 value is below 0.5 but only red cup left circular applyation is dominantly observed and black hop rice polyization spectrum is strongly prohibited to identify to analyze more quantitatively that feature we obtained we measured uh stocks parameters and in

1:16:28 this case at three value is more important because s3 is intensity of right circular polarization minus intensity of left circular polarization so we measured at three value of minus 0.8 and that means left circular polarization is dominant and the other sample indicate just right circular polarization dominant single photon emission. So in this case at three value or degree of circleization dcp value is 0.5 which indicate rolopization is dominant but interestingly just if you use uh gold nano cube without chronop particle just uh there's no difference between right circular polarization and left circular polarization. So chyon nanop particle is uh real origin to generate uh rirolization or lap circle polarization.

1:17:31 So to understand that issue so we performed optical simulation. So key origin is dipole moment generated by tensile strain on the core corner of the kyal nanop particle. So if this dipole moment is oriented along the horizontal direction, left circular polarization is dominantally radiated but uh dipole moment is aligned along the vertical direction right circular polarization is dominant. That dipolement is aligned along the 45 degrees angle and linear polarization is dominant. But in the nano cube case only uh only linear polarization is dominant regardless of the orientation of dipole moment.

1:18:22 So we also uh demonstrate the particle array and also single photon array uh was successfully demonstrated the generation yields is very high 75%. So I want to conclude my talk. So I talked about two topics vortex and laser based on a photonic discrimination cavity and second topic is manipulation of polarization properties of single photonimeters. And so I want to thank uh my old team and current members and especially uh thank professor Yuri Kubisha for his strong support and collaboration and very much. Thank you very much for your insightful talk. Uh I'm really happy to um that we all name this webinar as metaphotonics revolution because indeed as our all speakers described we are in the revolution phase and it's so exciting to see everything happening. Um once again I would like to thank all the speakers for their valuable contributions and um I would like to hand over the floor for

1:19:38 um Q&A and discussion with the audience. So please keep your questions coming in and invite all the speakers back on stage with your cameras on. Hello. Yes. So if there's no additional questions from the audience, uh I guess we'll just ask uh a general questions for professor KFR. Uh so uh we can see in the Q&A session here. Uh so the question is what are the strategies uh that can be used to improve the conversion efficiency of nonlinear optical processes in the meta services? Do you have any thoughts?

1:20:47 Okay. Uh I can take a shot at that. uh so uh often uh uh yeah to to improve conversion efficiency it's good to uh use uh lower optical nonline orders of optical nonlinearity. So in general second order nonlinear processes tend to have higher conversion efficiency than third order and fourth order and as you go up the order the efficiencies can't go down. So often the second order processes seem to work well if you were pushing the efficiencies then choosing materials with strong u uh optical susceptibilities is good to have and that's where uh lot of the 35 semiconductors lithium nabbate all all that is becoming popular uh these days and uh then in from a meta structure perspective it's also good to design resonances with high quality so that there is going to be huge field enhancements uh within the structure and And that's what we want to uh make use of right uh I hope you I have answered your

1:21:50 question anything to add uh professor park and professor kchar. Well if there's nothing then uh let's move on to the next question. Uh so is it prefer to have resonance at the extension uh frequency or the emission frequency for this?

1:22:21 I think professor Kishure can take this if it's okay. Yes. Anybody want to take a shot at?

1:22:29 Uh you're you're muted, Professor Kure. Oh sorry, sorry if the reception is not very good. Can you please repeat the question?

1:22:43 Yes. So uh the question is uh is it prefer for these uh uh devices to have uh the re resonances at the uh exitation frequency or the emission frequency? I will pin also the question at the top of the Q&A as well.

1:23:01 Oh wow. Yeah, that's a that's a good question because uh for for nonlinear processes uh somehow people believe that we should have a resonant exitation of uh modes or particular resonators at the fundamental frequency. But it turns out that some of the effect can be better controlled by designing resonances and the harmonic field. Um the same valid for emission. For example, if you if you pump structure and then see emission at different frequency um in the like like in the case of luminousense. So resonance should be carefully designed but it there is no general answer yet. It's there are several example. So it's a it's a rapidly developing field and people trying different approaches but it turns out that um if you design resonances at harmonics it may sometimes much better in terms of efficiencies but it's not very well understood yet. So it's a it's a field when uh more people require it to actually work

1:24:24 on this. So it's a lot of fresh directions possible here. Yeah. Thank you. Mhm. The other two speakers anything to add?

1:24:40 Well, there's nothing. Let's move on to uh we have a question from the audience. So uh the Akil Romesh would like to thank all the speakers for the wonderful talks and uh they have a question for professor Barun. Uh can you please let us know the laser spot size used on the nano desk in your presentation?

1:25:00 Yeah. So uh we we normally use microscope objective lenses to focus the light. uh if you're addressing an individual meta atom then uh we want to be comparable the the spot size should be comparable to the diameter of the meta atom. Um so we typically make use of maybe two micron or three micron spot uh spot diameter on the sample. But if it's a meta surface with many like an array of meta atoms then it's better to uh if you're looking at collective effects then it's good to spread that energy across uh across the array right so maybe a lower numerical aperture and a larger beam spot size would be preferred so I guess next up uh we'll have a question for professor Park uh more suitable for the journal of device of course. Uh so what are the key challenges in making these single photon emitters more practical for real world applications and what sort of applications have I guess the most

1:26:03 demand for these uh uh materials and devices? Yeah, just key challenge is not just generating single photons but efficiently coupling the emitter to a cavity to achieve posal enhancement and also just more practically the collecting single photons to an optical fiber is more important and high brightness and collection efficiency and indistinguishably should should be uh maintained in this case. So that is most uh challenging issues and so but my group is focused on the some integration of single photon emitters to high quality optical cavities for practical applications.

1:26:56 So is there any specific practical applications I guess that is driving most of this demand? I'm

1:27:08 is there what kind of specific applications that's driving the demand of these devices of these single photons emitters? I'm just asking uh that from kind of like a the industry or commercial point of view,

1:27:23 right? So, so just there are several quantum technologies including just quantum sensors and quantum communication and quantum computers. But just quantum computer to uh demonstrate and just just photon cubing is not is not easy just always challenging but quantum sensors and quantum communication especially quantum communication the single photon is very good candidate also and combination with single photon and a single scheme and just photon can serve as a flying cubit. So just we can transfer the uh information to the uh other people just with very high security and that will be some some future technology for industry in my person.

1:28:19 Thank you. Uh so the next questions I think is for uh professor Raganthan uh and the question is what role does material absorption play in the efficiency of the nonlinear optical process?

1:28:35 Yeah. So often when we do frequency up conversion uh through nonlinear process there is a like a good chance that it uh the the energy of the photon may fall above the band cap and then the photon will be absorbed right so that so then one has to look at the thickness the interaction length and then how does it compare with the the skin depth of this material and then see if it is uh going to be absorbed significantly or not. uh but often absorption is a parasitic effect it would be good to avoid and that's why materials with wide band gap are generally preferred and uh that's what we try to find high refractive index wide band gap materials which uh are always good for doing nonlinear optics especially when we are doing frequency up conversion

1:29:24 yeah okay next I think we have a more technical question uh uh which is can cavities with higher rotational symmetry enable the generation of higher order optical vortices.

1:29:40 Yeah, that is my part and it's possible and just in technically n rotational symmetry gener generally restrict the some angular momentum to maximum value is half of the value. So by increasing the rotational symmetry yeah it's totally possible. So designing cavity with higher rotational symmetry can generate higher order vortaces. So just we uh on study to make higher rotational symmetric cavities.

1:30:21 Very nice. So uh just to close out the Q&A qu uh session the last question is uh open to any of the speakers who want to hop on uh is what kind of optical intensities are used for the incident exitation and so are the meta services prone to damages at these intensity levels? You have to consider the intensity.

1:30:54 So for for nonlinear optics we do use uh high optical intensities. It could be on the order of uh few hundred megawatt per centime squared to maybe few hundred gawatt per centime squared. Um right. So u so that is required uh as a way to compensate for the reduced interaction length. But one good thing with working with dialectric materials like silicon uh or uh or even 35 materials is that they have a fairly high optical damage threshold. Uh so they're able to withstand uh the high optical intensities. But eventual goal uh beyond proof of concept demos is like when we improve the conversion efficiencies higher we can go to uh lower exitation intensities as well.

1:31:39 Right? So that would be required if uh for any of these uh uh demos to find some useful applications. So uh definitely the the field as a whole is going towards improving conversion efficiencies and reducing the incident light intensity.

1:31:56 Thank you. Uh we do have one more question from the audience uh for professor park. Uh the question is what about tuning the emission wavelength of single photon emitters with TND material and also is the stability of the emission. Uh so how long it will make how long will it make the same quantum state I guess using the strategy. Yeah, that's very important question and very good question but yeah that is hard to say. So TMD material is very great to make a uh well localized uh quantum dot artificial quantum dot but there is some still problem. So the uh that is challenging how to control the emission wavelengths because the PM defect can uh emit single photons and also stability is not very good. So that is the key challenges to single photons from PMD materials with some high quality optical cavity. These are also very challenging. So still people think about that or more recently other types

1:33:15 of uh two dimensional materials for example guide or boron nitrite and other candidate are now under study. So yeah that is still we should about that. Oh, thank you again uh for all three speakers for their time. Uh and I think uh I'll hand it back to Penuta for any closing remarks.

1:33:43 Sure. Thank you. Thank you. cuz uh over and over again we have iterated that 2D materials are our favorite but it remains challenging to do the research uh stably and solidly but yeah we are excited and then we follow up um you know in the in the next occasion. So I would like to uh say that we have come to the end of our session today and again would like to thank all of our speakers and coordinators to um organize this webinar for Cell Press, Professor Yubir Kishir, Professor Wun Ragunatan and Professor Hungu Park. It had been an immense pleasure to um listen to you and uh for your presentations and engaging discussions. Uh I would to like to thank the audience for tuning in today to learn more about metaphonics. If you have missed anything during this webinar or would like to listen to it again, a recording will be emailed to you shortly and posted on cell.com events. Please take a few moments after this webinar to

1:34:50 complete a brief survey that will be emailed to you momentarily. Your comments help us improve our service and value our your feedback. Thank you so much again everyone and we hope to see you at a future selfpress event.

1:35:06 Thank you. Thank you very much for organizing that. Thank you so much. Thank you. Thank you. Thank you.

Questions about this episode

Who speaks in "Metaphotonics revolution: Engineering light for tomorrow’s technologies"?

Professor Yuri Kvar (Plenary speaker (keynote) and referenced collaborator), Dr. Canuda Sharta (Host), Professor Hongup Park (Panelist and main speaker (Talk #3)), Professor Wun Ragunatan (Panelist and main speaker (Talk #2)), Dr. UNU (Host), Dr. Chiminga (Host).

What is discussed in "Metaphotonics revolution: Engineering light for tomorrow’s technologies"?

In order: 0:00 Cell Press, Professor Yuri Kvar, Dr. Canuda Sharta, Australian National University; 10:00 Nature Photonics; 30:00 Nonlinear Optics, Dr. Canuda Sharta, Professor Wun Ragunatan, Indian Institute of Science; 40:00 Nonlinear Optics; 50:00 Nonlinear Optics, Indian Institute of Science; 1:00:00 Professor Yuri Kvar, Professor Hongup Park, Photonic Crystals; 1:10:00 HBT Measurement; 1:20:00 Nonlinear Optics; 1:30:00 Nonlinear Optics, Cell Press, Professor Wun Ragunatan.

What is mentioned in this Cell Press episode?

18 people, works and ideas are mentioned, including Professor Yuri Kvar, Nonlinear Optics, Dr. Canuda Sharta, Cell Press, Professor Hongup Park, Professor Wun Ragunatan. Each one on this page links to its own page with every episode that mentions it.

How long is "Metaphotonics revolution: Engineering light for tomorrow’s technologies"?

The episode runs 1 h 35 min; the transcript is about 13,079 words in 108 timestamped sections.

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