Sunday, November 6, 2011

Getting it together

Hey everyone..

Recently I met up with some friends from undergrad and we were discussing life and times in engineering school. You have a lot of good friends. You study and learn, yes, because there are classes and homeworks and tests and exams. But a large part of my memories are of time spent with friends, little comments and jokes cracked just before an exam. I valued my friends and classmates for their friendship and their company through those times. And yet, all these years I had never credited them with teaching me everything I have learnt!

This one is a 5 minute introduction of the problem

Someone recently pointed me to a very good talk on education by Professor Eric Mazur who teaches Physics at Harvard. He spoke about the problem with the common lecture-homework-exam approach. He says that it is not the teachers alone that enable a student's learning and understanding. Real learning, be it in engineering or any other discipline (his own examples are from physics), largely happens outside the class when we do homeworks with friends, discuss problems and questions, and study for exams with others.

Monday, October 31, 2011

FiO 2011 - part 6 (final)

Hey everybody..  this is going to be the last post with my notes on Frontiers in Optics 2011.

Sergio Carbajo and Ying Geng won the Hilbert Grant award in
 optical engineering, lens design and illumination. Pic courtesy OSA.

Sergio Carbajo, from Colorado State University, who won the Hilbert Grant (in pic above) showed some amazing movies taken for nanoscale moving objects at near wavelength resolution. They have built an EUV tabletop laser and use repetitive nanosecond pulses from the laser with a zone plate objective to image the nanoscale moving object.

Ying Geng from Rochester, who also won the Hilbert Grant (in pic above), showed clear and sharp images of the mouse retina obtained using an adaptive optics scanning laser ophthalmoscope. The mouse imaging is very important for disease detection, diagnosis and cure because it is easier to find transgenic and knockout models of various eye-diseases in mice. But mice have notoriously poor vision. One would assume this should make for terrible images. But Ying managed to modify the beacon used for wavefront sensing to adapt to the unusually thick retina of the mouse (compared to humans). The beacon is now an annular shape instead of the conventional full uniform beam at the pupil and gives a tight sharp wavefront sensing spot allowing her to do adaptive optics sensing and correction. She showed images of the photoreceptor mosaic, blood capillaries, nerve fiber bundles. She also showed fluorescence labeled ganglion cells and even some results of classifying the ganglion cells into bi-stratified and mono-stratified classes which have dendrites (like roots) in two layers or one layer respectively. Very cool!

In the animal optics session.. 

Monday, October 24, 2011

FiO 2011 - part 5

Hey everybody.. FiO is officially over. But I am still processing the information from the sessions. In this post I'm going to summarize some of the talks I thought were interesting work. More will come later..

David Brady at the Hot Topics. Pic courtesy: OSA
In the Hot Topics session for information sensing and processing David Brady emphasized that optics is increasingly penetrating digital systems. Compressive measurement has started being used in optics and is increasingly more practical. Compressive measurement has now been demonstrated for projection tomography, snapshot hyperspectral imaging, OCT, holography, digital superresolution, etc. This year FiO had a tutorial talk by Rebecca Willett and a whole session dedicated to the topic. 

Serhan Isikman and M. J. Lee from the Ozcan group talked about...

Thursday, October 20, 2011

FiO 2011 - part 4 Eday

Hey everyone.. All is going great at FiO. Yesterday and today were full and busy days. But I do have some pics for you.

I went to Eday yesterday evening. This is an event the OSA organizes every year at FiO. They have volunteers, students and various chapter members from all over the world come in and give optics demos to teachers who wish their students to explore optics in their classrooms. This year's event was well attended.

They had lots of tables with various demos and a crowd of folks checking out the easy, inexpensive and interesting experiments these enthusiastic volunteers had come up with! I just took a couple of pics, here they are..

This is an undergrad student member, Denys Zaikin from Naples, Italy.

Denys had a demo for sustainability. He told us..

Tuesday, October 18, 2011

FiO 2011 - part 3

Hey everyone..! Another busy day.. let me tell you about some interesting folks I met today.

Animated discussions at the VIP meeting. Pic courtesy OSA.
In the morning I attended the VIP networking session. They had some very inspiring people from the optics industry – Karl Koch from Corning, Jean-Michel Pelaprat of Vytran, Michelle Holoubek, patent attorney at SKG, Richard Smart from Oclaro, Colin Seaton from Fianium and Ken Ibbs from LanTian Photonics. It was great to meet them in person and hear about their experiences and advice for working in the optics industry. Some of their advice included trying out places through internship programs so you can figure out what you want, making sure you fit in well with the work and culture of the team, and when you start working, try to learn the most you can from positions in your career. 

Laura, Donna, Jannick and Liz. Pic courtesy OSA.
In the afternoon I was at the Minorities and Women in OSA event where the panelists included very accomplished women in optics. Donna Strickland is a Professor at the University of Waterloo and works in ultrafast short-pulse intense lasers and non-linear optics. Jannick Rolland is a Professor at the University of Rochester and does very interdisciplinary and applied work in the areas of head mounted displays, augmented reality, illumination and freeform optics. Laura Weller-Brophy has vast experience working in industry at 3M, Kodak, and Corning. She is presently the founder of a start-up in Rochester, FluoroLogic Inc., which is developing devices for screening cervical cancer using fluorescence detection. Fluorologic has won several awards for their technology and business plan in Rochester. Elizabeth Rogan is the CEO of the Optical Society and has strong management experience in the corporate, federal and non-profit sectors.

It was great to hear these extraordinary ladies speak about working in academia, industry and management. They talked about the importance of support from family, mentors, colleagues and peers, gave advice for making choices in careers and a work-life balance.  

It was fantastic that the panel members in both events took the time and effort to reach out to us and gave us their best advice. Such interaction and support is amongst the greatest benefits of being in a professional society with a strong sense of community. 

Monday, October 17, 2011

FiO 2011 - part 2

Hey everyone..

Silicon Valley

Today was a busy day. I missed much of the morning plenaries. Apparently the organizers are uploading a lot of these talks online accessible to technical registrants. So I am hoping I can catch up with these things online later.

The afternoon had some exceptional sessions. Let me tell you about a few.

There was a session called "Phase". Sounded straightforward.. and as expected, all the works discussed in this session contained phase information in some way or other. Manuel Guizar-Sicairos from the Swiss Light Source in Switzerland talked about X-ray phase imaging. He discussed coherent diffractive imaging, ptychography, and 3D phase tomography. A coherent x-ray illuminated object is imaged in the far-field and algorithms such as used in phase retrieval approaches with suitable support, translation and Fourier constraints are used to recover object information. He showed some cool pictures of objects they have imaged such as bacteria in plant root nodules, nanostructure in bones and nanostructure in cement.. (Cement and bones in the same line sound odd, no?)

There were several other very interesting talks in the session. Adam Zysk from Illinois Instiitute of Technology talked about using task based assessment of phase contrast mammography. He had an interesting Bayesian decision maker that gives the best "discrimination" of calcification or other anomalies that may be identified by radiologists from mammograms.

Donald Duncan talked about extracting phase and amplitude from DIC images. Varun Raghunath showed some interesting work on non-linear imaging of phase and amplitude at the focal plane using heterodyne four wave mixing microscopy. Chien-Hung Lu from Princeton talked about using phase retrieval methods modified to adapt to non-linear media.

Later I attended the Compressed Sensing session I discussed in my earlier post. This session was good fun with a packed room full of enthusiastic and interactive audience. Rebecca Willet (Duke), Kenneth MacCabe (Duke), Lei Tian (MIT) and Sehoon Lim (Duke) gave interesting presentations on their work. 

That's all for today! Cheerio and thanks for reading!

Sunday, October 16, 2011

FiO 2011 - part 1

Hey everyone.. it's Sunday and the FiO crowd is starting to trickle into CA. I plan to meet some friends today, catch up and hang out a bit. Might attend a couple of sessions... if possible..

If you are visiting the Bay area for the first time.. there's plenty for tourism..

.. a stroll or hike through some of the woody trails.. maybe a picnic lunch..

.. and good eats!

Looks like OSA is also organizing visits to the Winchester Mystery House, Santana Row on Monday, 10/17 and to the Tech Museum on Tuesday, 10/18. Seems open for all OSA members, family and friends.

Look forward to a great week!!

Wednesday, October 12, 2011

Astronomical Scintillations

My first trip from grad school had been to the University of California at Santa Cruz for the Adaptive Optics Summer School held by the Center for Adaptive Optics (CFAO). I was very excited and the visit did not disappoint. We had learnt lots of adaptive optics and met a lot of people doing great work in the area.

Lick Observatory on Mount Hamilton. Picture from Wikipedia

And the best part of the trip had to be the trip they organized to the Lick Observatory at Mount Hamilton. The winding roads and breathtaking views led to domes that housed the most amazing optics and astronomy. Elinor Gates, a scientist at the observatory, was the most knowledgeable host we could have hoped for! She showed us around their adaptive optics setup, their telescopes, and narrated some very engaging ghost stories whilst setting up a smaller telescope on the night sky! It was an absolutely starry and spectacular night!

So some weeks ago, when the N-Cal OSA committee here asked for local speakers, I immediately thought of Elinor! Would be good to catch up with her and see what’s new at the Lick Observatory! Elinor kindly agreed to give us a talk on “Untwinkling the Stars.”

Elinor Gates chatting with folks after the talk

The Lick Observatory is an astronomical observatory on the summit of Mount Hamilton, east of San Jose, founded in 1888 by the bequest of James Lick. They have several telescopes like the 3m Shane Reflector which has adaptive optics on it, the 1m Nickel Reflector and a couple of smaller telescopes and accessory equipment.

Monday, October 3, 2011


Holography has been a technology that has fascinated people for many years. It has featured in movies, books, comics, cartoons.. it’s like a technology that’s just got to be!

Bad hair day..

A hologram is a recording of the interference between light reflected from an object and a pristine reference beam. If later you illuminate the recording with a beam similar to the reference beam, it re-interferes and re-creates the appearance of the original object. The benefit of a hologram compared to a 2D picture is that you can look at the object from different angles and the object retains depth information.

Recording a Hologram. Figure from Wikipedia.
Film or photographic emulsions are common media for recording simple holograms. Lately much progress has been made in Digital Holography where the film is replaced by a sensor like a CCD. This allows us to reconstruct the hologram entirely digitally, without illuminating it with an actual beam of light.

Computer Generated Holography is when you digitally create a hologram of an object; there’s no reference beam illumination, no actual interference of light. That makes it possible to create holograms of completely unreal objects.

The most basic holography (shown in the figure above) is done with coherent laser light. But it is also possible to do holography with white, incoherent light. For instance, techniques like Scanning Incoherent Holography and FINCH (Fresnel incoherent digital holography) give incoherent light holograms. It is also possible to capture multiple images of the object from different angles using a normal digital camera, no reference beam, no interference and then digitally generate a hologram from a combination of those views.

There seem to be several good sessions on holography at Frontiers in Optics this year on Tuesday and Wednesday morning - FTuF, FWJ. They have some of the best speakers giving invited talks on this topic. There is also quite a bit of recent research in holographic microscopy, computer generated holography, synthetic aperture digital holography that I can see in the sessions. Surely worth a dekko!!

Cheers and thanks for stopping by!

Saturday, September 24, 2011

Measuring the eye

Our eyes are like windows, I’ve been told. We use them to look out at the world, and doctors use them to look into our body; a non-invasive health check. But our window is not really top-quality, which blurs the seeing in both directions. Glasses and contact lenses have long been used to better see the world. They correct low order errors, like defocus and astigmatism, and give improved vision.

Of course, some glasses just serve as inexpensive identity props
 more funky ones let you see wrackspurts.
For doctors to look into our eyes, we turn to imaging systems that compensate these aberrations and image the retina, blood vessels and other features in the eye. The efficiency of correction both ways depends much on how accurately the aberrations are measured.

In 1961 Mikhail Smirnov developed a subjective technique to measure the aberrations of the eye. The individual would look at two incoming beams of light, use the on-axis beam as reference and change the position/angle of the off-axis beam to try and fuse the two beams at the retina. This gave the slope of the wavefront and allowed step-by-step measurement of the eye’s aberrations.

Monday, September 19, 2011

Compressed Sensing and other stuff

Hey everyone..

I have registered for FiO 2011, and have started looking into the schedule. There are many events this year and I don’t want to put off looking at the schedule till the last moment and miss out on the more interesting ones. 

The first day, Sunday 10/16, 4-6pm, seems to have a very good What’s Hot in Optics session that should be interesting. Usually a start-off session like this provides a very good overview of things to come, so I will surely be there. 

Sunday evening (7.30-8.30pm) has meetings for OSA technical groups. I had signed up for a couple for groups and got emails from them inviting anyone interested to join the meetings. There should be discussions for areas like Optical Design and Instrumentation, Holography, Information Acquisition, Biomedical Optics, etc. Meetings like these help people get involved with OSA in these technical areas.

Monday has a great session on Compressed Sensing (FMM, from 4-6pm). Rebecca Willet from Duke is going to have a 45 minute tutorial style talk on compressed sensing for optical imaging; she mentions IR and focal plane arrays in her abstract. There is much work being done to minimize the data being sensed as well as transmitted. Her group works on compressed sensing, exploiting sparsity in the nature of data to obtain compression. She has worked on compression in the presence of Poisson noise, coded aperture imaging, multi-aperture imaging for thin imagers, and more. So the tutorial talk should be a good overview.

There are also talks from George Barbastathis' group at MIT, and some from David Brady’s group in this session that should be interesting. There is one by K. MacCabe that takes advantage of aliasing high spatial frequencies, folding them into the lower spatial frequency region which is more resistant to loss during defocus. In my opinion, turning around aliasing to your advantage is always brilliant! This session certainly promises to be very interesting.

Oh.. I just found an old video of Rebecca Willet giving a talk at some CS workshop at Duke; summarizes compressed sensing to some extent. Here are the slides for her talk, do check out the slides because the video below does not display them. Also, audio-video here are a bit out of sync, but with the slides it's a pretty good talk. Her talk at FiO will probably have more recent stuff, but this should give you a flavour of what to expect at the CS session.



Ooh, just spotted this, Kevin Kelly from Rice seems to have a 30 minute talk (LTuC3) Tuesday morning, on their work on single pixel compressive imaging where they use a fast DMD to time multiplex and compress the object information and then capture only the minimum required on a single pixel! 

That's it for now. I'll post more about other sessions and events over the next few weeks. Cheers and thanks for reading!

Monday, September 5, 2011

Fun weekend, cool jellies!

Hey everyone!

The weekend was good. We did some fun things. Drove to Monterey, CA, and got stuck in lots of traffic en route. But the scenery around us was so beautiful, we loved the drive!! We were surrounded by some of the most fragrant tall Eucalyptus trees. Then slowly drifting past artichoke farms, we could see the artichoke-heads up close near the highway. Around Gilroy, we could smell Garlic!
At the Monterey Bay Aquarium, we saw the coolest jellies. These are called Comb Jellies. They propel themselves through the water using their hairy cilia. And light diffracts off their hairy-cilia-comb making an amazing rainbow! Check out this video from that exhibit (uploaded by someone with a fairly steady hand). And you can read more about Comb Jellies here.


I don't think the one below was at the Aquarium when we went, but I spotted the next video browsing through the aquarium website - the Bloodybelly Comb Jelly.


Nature is astonishing!

Cheerio and thanks for stopping by!

Friday, August 12, 2011

Ideas, start-ups and Milton Chang

Hey everyone..

It’s been busy past couple of days, resulted in fewer posts. I’ve been working on a project at RII, trying to make an idea work. Some of it was in my area of expertise. Some was new to me. And some of it was completely unknown (this is research after all). After some crazy tinkering, finally it seems to work!! :)

In the Silicon Valley everybody has good ideas. Everybody is ambitious. It’s very common for casual conversation to get around how we should take this or that idea and start a new business. Surely, people would pay good money for XYZ.. Start-ups here are many. And so are folks working in them. Life in a startup seems to be hard, but very rewarding if you thrive on learning and every day being new.

Milton Chang is a well-known name in the optics community. He was the President/CEO of Newport and New Focus, later an angel investor and is now at Incubic, his venture capital firm. Milton’s story of building Newport and New Focus, bringing them to IPO and making them “household” names is recounted to every rookie in our world.

Naturally, I was very excited to hear that Milton Chang is going to meet us for dinner and give a talk at our local N-Cal OSA meeting. What would he be like?

Milton Chang (coffee-ing) just before the talk
The first thing that struck me, he’s incredibly down-to-earth and nice. He went around the table, talked to absolutely everyone at dinner. He also hung out at the talk, giving advice and suggestions, sharing some of the lessons learnt from his experience in startup and venture capital.

Milton's simplest advice was – don’t rush. Do your best, put all of yourself in your idea.. but don’t rush into getting outside funding. He said that startups don’t have to be so risky. Yes, there is always a risk. But the risk can be mitigated if we put in enough effort up front. Make sure the idea is solid. Know what will be involved in developing the idea. Have a clear plan. And in order to develop a strong plan, spend time at the outset to clarify the unknowns in your idea.

Another important thing he cautioned was that the business plan should not be taken lightly. A strong technical idea could fail miserably if the market and business aspects are overlooked. An early team shouldn't have only technical strength but also a strong business component. Whether this comes in the form of a fulltime business person on the team, a part-time consultant, or you doing it all yourself, it needs to be done, and done well.

It was very good to get this balanced perspective about startups in optics and photonics, with his positive experiences as well as cautionary advice. Certainly got everybody’s entrepreneurial wheels churning

Note: If you got to this post looking for entrepreneurship guidance, a good reference would be Milton Chang’s book that has just come out – Toward establishing a successful technology business entrepreneurship. We just got a copy!

Cheerio and thanks for stopping by!

Update 09/22/2011: Just spotted the following notice on OSA's website.

"Milton Chang has partnered with the OSA Foundation to offer his new release, Toward Entrepreneurship: Establishing a Successful Technology Business to the OSA community with sales proceeds benefiting the OSA Foundation. 

All sales proceeds from the book will be donated to the OSA Foundation, and will be matched 100% by OSA through its contribution to the OSA Foundation General Fund.

Through this special offer you can purchase Toward Entrepreneurship for $20 (USD) minimum donation, or more if you like, for a limited time. The retail list price for the book is $35. There is no additional charge for shipping."

Wednesday, July 20, 2011

Looking forward..

Hey everyone..!

I'm back home again! Last week at COSI was such good fun! Next I look forward to Frontiers in Optics in October. This year FiO is in the Bay area. It's usually a big enough meeting that plenty of people travel to make it. So it's nice to have it in sunny California!

Although a large part of conferences involves checking out the latest and best in optics, much of it involves meeting new people and building strong professional relationships. Networking lunches, dinners and receptions are ideal for these. Most meetings also host exhibitions and poster sessions that let you connect with people who may have interests in your field.

In the past couple of years there have also been plenty of activities that are specifically targeted toward students and the somewhat younger crowd in optics. My favorite at FiO had been a couple of years ago in Rochester, they had Jorge Cham of PhD comics talk about procrastination! :) Some time back there was also the most awesome laser tag event and some cool eday demos. Young optics professionals from all over had come together to showcase all the cool and innovative stuff you can do with optics. Check out Nicole Moore's demo of a pinhole camera.

Ref: OSA E-day 2008,

This year's conference has quite a few fun events. I was just having a look at the Young Professionals and Student Activities link. The Entrepreneurs International Network (EIN) Workshop and VIP Industry Leaders Networking Event certainly look very useful! There's a Minorities and Women in OSA Tea that I'll attend.

Also, check out this Student Chapter Competition. It's going to be a contest - Mission Optical, where Student Chapters from all over the world will do optics demos for youth optics education using only ordinary household items.. under 25$.

I was thinking about the household items bit and you know, there actually are plenty of household items that can be used in optics experiments! A TV screen makes for an amazingly bright object with built-in illumination, plastic spoons show excellent stress birefringence, water and glass are always the good old reliable light-benders, jello can be cut out to be shaped like lenses, and as Nicole pointed out, even a Folger's coffee can is reusable as a lensless, pinhole camera! 

Promises to be highly imaginative, right? I'll be sure to check it out! Hope they take videos at this event.. or maybe I will!  

Thursday, July 14, 2011

COSI 2011 - part 3 (final)

Hey everyone.. 

Today was the last day. A lot more relaxed. I got to hang out with some friends and do some fun stuff.  

Sunny and blue!
Wish I had taken more pictures of us! Next time..
There is so much in terms of talks I haven’t written about. I’m going to mention just a few things next.

This year’s meeting included quite a few talks on areas related to Lithography. I liked that because I don’t often go to conferences that are focused only on lithography. But it’s an interesting area and very relevant to anybody interested in imaging. So it was good to find some talks on this topic here.

Mehdi Vaez Iravani from KLA Tencor spoke about metrology in the semiconductor industry – mainly inspection of patterned and unpatterned wafers and related issues. There was also a very nice talk on model based metrology for resist patterns by Arie Boef from ASML. I also got to meet Dr. Alan Rosenbluth from IBM, T. J. Watson Research Center. His work on identifying a correction factor for source radiance in photolithography is an example of how much depends on “little” details in lithography. Clearly speed and accuracy are so very important in this industry.

Kenny Kubala from Five Focal gave an interesting talk on improving yield in wafer level cameras. He talked about measuring errors in manufacturing. They have their own fast, model-based algorithm for measuring post-assembly errors such as decenter and air-gaps. 

There was a very interesting talk on superresolution due to spatial non-linearity effects in non-linear material by Christopher Barsi from Princeton. He showed increased resolution and wider FOV.

There was also an interesting talk from Marc Christensen’s group on using structured illumination for optical superresolution using active illumination in cameras. Manju, the speaker at COSI, told us they are starting off a company called SLIC Technology which is trying to productize this work. And hey, startups for superresolution are always cool in my book! 

There is much I may have skipped here. These conference posts are written in some haste. Hopefully no one will mind typos and misspelled names. And then there was so much good stuff that I just couldn’t attend because of parallel sessions that I needed to be in. There was lots of Fourier Transform Spectroscopy, Wavefront Sensing, Adaptive Optics, 3D imaging, localization imaging.. it goes on. I attended some, but lots, I missed! I am hoping my colleagues caught it and will give me an update. 

The best part of conferences is always people! I am really glad I got to catch up with old friends again, meet new folks! The enthusiasm and excitement everyone has for their work is always infectious. And at conferences we get it all in one concentrated dose! :)

Now it’s time to go home. Am at the gate now and super-happy that Toronto airport has free WiFi!! :)

Cheers and thanks for reading!

Wednesday, July 13, 2011

COSI 2011 - part 2

Hey everyone..!

Yesterday and today were packed. We met lots of people, heard lots of talks, had lots of discussions. At smaller meetings like this there is plenty of opportunity to meet people and chat. The breaks tend to be well spaced, and then yesterday there was a networking lunch and an evening reception. So it’s been interesting, intriguing, sometimes highly entertaining, and finally exhausting! :) There is still another morning’s worth of events to go. But most of the conference is almost over. Has been such good fun!

My colleagues - Prasanna, Jorge, David and Kathrin had a talk on design for better depth estimation. It was very well received. I think this was a really good meeting to present work from our group.

Now let me give you all an update on some of the interesting talks we saw past few days. This post is going to get terrifically newsy now.

Ravi Athale and David Brady gave some interesting talks dedicated to the memory of Dennis Healy and his vision for sensors and imaging. Ravi proposed all sorts of ideas and visions for the future. History and vision go very well together.  Certainly got everyone thinking.

There were many talks on Holography. They started out with Oscan’s group discussing LUCAS, an incoherent holography technique to image cells. Some of his results use prototype attachments for compact cell phones.

George Barbastathis’s group showed much work on 3D optical imaging. He gave a very interesting talk on quantitative reconstruction of phase objects, visualizing 3D flow, bubbles, etc. using digital holography including ideas for compressive sensing.

My own (earlier) group from Rochester, Jim Fienup’s research lab, showed results by Abbie Tippie on lensless synthetic aperture digital holography for gigapixel imaging. This work involves generating a digital hologram of an object and building up the hologram by scanning the detector to effectively obtain a larger aperture and more resolution. Abbie talked about sampling conditions, propagation approximations, defocus, aberrations, drift and other mosaicking errors and how to handle them all.   

David Brady’s group also collaborated on this project. They too showed results, by Sehoon Lim, on the corrections they have implemented for their system. Both groups had slightly different implementation issues. I love that this collaboration got so much research work done on that front.

Optical superresolution, as some of you may know, is the area of my thesis research. So I love work on superresolution. Zeev Zalevsky was at COSI today and gave a great talk on recent advances in superresolution imaging. This was a very nice review style talk with tons of info. He had so many slides to show. Even a 40 minute slot is sometimes not enough. I’ll put in a link here if I find his material or paper somewhere online.

Alden Jurling from the Fienup group talked about some interesting approximations that they found worked for them and helped to speed up broadband phase retrieval. He actually blurred some of his data to get rid of high frequencies (treating them like noise), which allowed him to quickly zero-in on a reasonable estimate. Speeding up algorithms is often critical for practical implementation. So it’s good to see them explore the regime of speed versus accuracy to try and find a balance.

Sam Thurman showed a useful method to estimate the OTF of an imaging system – phase and magnitude, using a binary Siemens Star Target. The cool thing is that his technique works even for undersampled images. This is probably because the Siemen’s Start Target has repetitive identical lines which, in my understanding, gives him multiple “measurements” and allows him to get around the sampling limits.  

Fredo Durand gave a very nice talk on computational photography, briefly describing the work on light fields, coded imaging, feature matching, SIFT, blind deconvolution and superresolution as done in the computational photography community.  

His talk was followed by another great talk by Edward Adelson where he demo-ed as well as talked about an elastomer they have developed, called GelSight, that easily deforms when touched by a feather, brush, thumb, even bubbles. This deformation can be seen on the other side of this skin-like Gel and imaged in 3D using photometric stereo. The images were impressive.

Ref: and

Ramesh Raskar’s group had an interesting talk on their picosecond camera – a streak camera that can capture picosecond phenomena, as long as they are repetitive events, using pulsed light and strategically sampled frames. They demonstrated images of light traversing a bottle, bouncing off of objects, etc.

Ed Dowski gave an interesting perspective on how optics may one day be manufactured like chips. Scalable, cost effective and easy to design.

Oh, and there was much work on CASSI and other such spectroscopy techniques, a lot of good talks from the Brady and Gehm groups.

It’s getting late now. But there is still more I want to note here. I’ll write again soon. 

Till then, cheerio and thanks for reading!

Monday, July 11, 2011

COSI 2011 - part 1

Hey everyone!

Quick update.. I am in Toronto for the Computational Optical Sensing andImaging (COSI), OSA meeting. This conference is held once every couple of years, usually collocated with Signal Recovery and Synthesis, Applied Industrial Optics, Adaptive Optics and Wavefront Sensing, Digital Holography and some other interesting meetings as part of the Imaging and Applied Optics Congress.

The two buildings on either side of CN tower 
look tilted in my pic!  What does that say 
about my cell phone's camera?

Today is our first day here. The whole Ricoh Innovations Inc. (RII), Digital Optics Research group is here. We have two talks at this meeting. One was today, Kathrin Berkner's and my submission on “Optimization of Spectrally Coded Mask for Multi-modal Plenoptic Camera” (CMD4) I'll put in a link to the paper once it gets online. Some people at the conference had already shown interest in the work. So despite being pretty late in the day we had a decent crowd. We had been looking forward to this for a while now and were glad to see the response.

Plenoptic imaging systems have been around for a while and promise to be very useful for digital refocusing, angular imaging, multimodal imaging, etc. Lately there is a lot of industry interest in exploring the potential for these kinds of applications. Our group works on the optics side of it - design, tolerancing, etc. Being in industry, these things are important to us. The research culture at RII is strong and we greatly value the opinion of the diverse academic research community. We got some great feedback and good discussions after the talk today. Thanks folks, for all your interest!

We have one more talk from RII coming up on Tuesday afternoon - 3D Imager Design through Multiple Aperture Optimization (JTuD4). Do stop by if you are at COSI 2011!   

Thursday, July 7, 2011

Meeting Jay Sharping - Fiber Optical Parametric Oscillators

Hey everyone!

Meeting time! I recently went to the dinner and meeting hosted by the N-Cal OSA chapter. This month the guest of honor was Professor Jay Sharping from the University of California at Merced. 

We were joined by a whole crowd of optics locals. Dinner with this group of people is always fun. I get to hear much about what else is going on with other groups and areas of optics. Here’s Jay (front) with Rick Rairden, Olaf Korth, Yujun Deng, Eric Hansotte and I’m-not-sure-who-that-is? I forced everyone to stop their discussion so I could click this pic and they kindly obliged! :) I couldn’t manage to get the whole table in one click. Need one of those 180 degree panoramic viewing cameras!

Fig.1. Dinner with Jay Sharping (front)
Afterwards we drove over to Xerox PARC where Jay talked about his work at UC Merced. UC Merced is a relatively new school, started around 2005, located about 90 minutes South-East from the Bay area. Jay is on their Physics faculty and heads the Applied Photonics Research Group.

Most of his research revolves around Optical Parametric Oscillators. OPOs are essentially used as tunable light sources. An OPO uses the principles of nonlinear optics i.e. the nonlinear influence of the electric field of light on the dielectric polarization of a material such as nonlinear crystals or fibers. 

In an OPO, an input pump frequency is passed through an optical non-linearity such as a nonlinear crystal or fiber to output a pulse at a different frequency. You can change the output frequency by tuning the phase matching properties of the nonlinear material. Jay’s team works specifically in the area of OPOs that use photonic crystal fiber to provide the non-linearity.  Photonic crystal fibers show similar nonlinear effects as ordinary optical fiber, along with the benefit of greater chi(3) nonlinearity. Here and here are two of his papers that elaborate a little more.

My interest in OPOs and femto second/pico second lasers stems from their use in two-photon microscopy, CARS (Coherent Anti-stokes Raman Spectroscopy) and other such non-linear imaging modalities.

Two-photon emission results from the absorption of two photons which are at twice the wavelength of absorption of a fluorescent dye. i.e. If your dye would fluoresce on the absorption of one photon at 350nm, instead it will fluoresce the same emission w/l if it is bombarded with two photons, each at 700nm. So effectively one ends up using much longer w/ls for two photon excitation. Longer w/ls penetrate deeper, so one can image deeper. Longer w/ls are also usually safer for living tissue. The nonlinear emission process is generally localized to the center of the beam where the intensity is maximum, hence it naturally imparts some amount of sectioning. Non-linear emission processes are less efficient for longer pulse widths (or continuous beams) since they require high peak intensities which can typically be achieved only in short pulse widths.

Pulsed lasers are commonly used as sources for non-linear imaging when a narrow band of wavelength tunability is sufficient. In cases where a broad range of tunable wavelengths are required, OPOs offer significant advantages. 

Jay showed some good results using their Fiber-OPO for CARS imaging. I also liked his one-line description of CARS, “If you tune two frequencies to coincide with the Raman mode of a material, you can efficiently excite that mode and use it to image!” That’s succinct! Well, CARS sure makes for useful images! 

OPOs do have other uses in probing material properties, quantum states, etc. I haven't written much about that here. But you can look up his work at UC Merced as well as his earlier collaborators, the Gaeta Group at Cornell for more details if you are interested.

Cheers and thanks for reading!

Saturday, June 25, 2011

Invisibility Cloaks – when light images nothing

Fig. 1. The blue stuff is the polymer
and golden stuff is gold used to SEM
image the structures. The upper one as
they point out is for reference while the
polymer in the lower rectangle contains the
3D features that give invisibility.
Ref: Joachim Fischer, Tolga Ergin, and Martin
Wegener, "Three-dimensional polarization
-independent visible-frequency carpet
invisibility cloak,"
Opt. Lett. 36, 2059-2061 (2011)

Invisibility cloaks are always interesting; no matter how they do it. Some people use ideas for camouflage like imaging and then displaying the background behind the invisible person on the cloak, effectively rendering the individual see-through.  Others use optical metamaterials.

Metamaterials are artificial materials that could be made to demonstrate un-natural properties like a negative refractive index, unusual optical frequency tuning capabilities, non-linear properties, etc. Optical metamaterials used to obtain invisibility are made up of sub-wavelength structures that bend light away from the object so as to render it “invisible”.

Earlier work on metamaterials started off at microwave frequencies. For optical wavelengths much finer nano-structure was needed. Soon the technology progressed to optical frequencies, but provided invisibility only along 2 dimensions. So if you looked along the 3rd dimension, the person wouldn’t be invisible. Then last year someone managed to do it for 3D. But it was still in a restricted range of wavelengths of 1000s of nanometers.

But I recently read articles here and here, that report a group at Karlsruhe Institute of Technology's Center for Functional Nanostructures (CFN) that have managed to write small enough features in their cloak that they can now guide light around it. Their team uses a combination of Stimulated Emission Depletion (STED) with direct laser writing to produce the polymer based, fine 3-D nano-structure. Their cloak works in non-polarized red light.

I realize one gets a lot of coverage for research like this. But we rarely hear about the effort. There is a lot of detail involved in work like this.. math, derivations, calculations, fabrication, chemistry, SEMs, microscopy.. Here is their paper in Optics Letters (finally out) for more detail. They show angle dependence, wavelength dependence, comparisons with ray-tracing simulations...

Fig. 2. This figure taken from their paper demonstrates the visibility
and invisibility of the vertical bars in the center of each rectangular
block for different wavelengths. The bars are visible in the reference
(upper rectangles) and invisible in the cloaked rectangles (lower ones).
Ref: Joachim Fischer, Tolga Ergin, and Martin Wegener, "Three
-dimensional polarization-independent visible-frequency
carpet invisibility cloak," Opt. Lett. 36, 2059-2061 (2011)

All that effort condensed into a 3 page easy-to-read optics-letter! But this is really the kind of work engineers and scientists do.. and love to do! So it's way cool to see coverage of the kind of work we love! :) Check it out! (If you can.. I wish every research paper were open and unlocked.)

Three cheers for all the good news coverage scientists and engineers get! And some more cheers for absolutely every individual involved in the effort!

Friday, June 17, 2011

Imaging Rods In-vivo

Rods are the retinal cells that we use to see in dim light conditions. They are much smaller than cones which are used to see during the day and in bright light settings. The Williams lab at the University of Rochester pioneered the use of Adaptive Optics to image and resolve cone photoreceptors, blood vessels, retinal pigment epithelial cells and ganglion cells. They have shown much work in the areas of color vision, light sensitivity and disease detection. But rods were hard to image, and when then were seen there was much jubilance.

Recent work by the Rochester team shows repeatable imaging of rods in the human retina! How did they do it? Better design! Alf Dubra’s design has reduced astigmatism in both the pupil and image planes for better adaptive optics wavefront correction and improved imaging performance. They have two papers (here and here). The first shows a lot of good imaging results. The second one is super for system details.

The Williams Lab is where I did much of my PhD research. So any fun stuff from there is always interesting to me! And an actual online video with interview and all!!! Now that I simply have to put on my blog! :)

Friday, June 10, 2011

Maskless Lithography

One of the benefits of living in Silicon Valley is the number of events and activities in the area. One recent addition to my regular talk schedule is the monthly meeting held by the Northern California Chapter of OSA.

Last month they had invited Eric Hansotte from Maskless Lithography to give us a talk. When I looked him up online (of course that's what everyone does).. the first thing that showed up was - this Lasers Rock concert at CLEO/QELS in 2010! A guitar-playing scientist certainly rocks!

It was cool to meet Eric over dinner and listen to him speak about his work at Maskless Lithography. ML makes direct-write digital imaging lithography products for the PCB manufacture industry. Digital Lithography eliminates the need for a mask.

At ML they use a Digital Micromirror Device (DMD) based system which performs multiple exposure scans of the PCB, producing an effective gray-level "dosing" of the exposures. Stronger exposures have a tighter impulse response whereas low level exposures have a broader impulse response. These widths control the exposed feature width and lets them obtain features with finer spacing.

What is interesting is that a super-sharp impulse response would not provide enough variation in its base width (at different gray-levels) for this technique to work. So they actually prefer some amount of blur in their system. 

Good resolution + good speed + flexibility to update the pattern on a whim! Now who might own a projector we can take apart...

Hello World!

I am Sapna Shroff. I'm a Research Scientist at Ricoh Innovations Inc., Menlo Park, CA, a research lab for Ricoh Company Limited, Japan. I graduated from the University of Rochester and work in optics and imaging. I was recently asked by OSA to consider writing a blog. So here we are! I hope to write about Optics and Imaging, experiences working in the field, general news, and fun stuff. Let's see how this goes.

Hope your time spent here is fun. Else click away on one of the links on my blogroll! ;)