When light dances with sound, teases the molecules, and plays an important role in green energy!

Shuffling among many eye-opening technical sessions and CLEO’s Market Focus & Technology Transfer Showcase, I simply realize adventures with light are everywhere:

An amazing imaging technique called photoacoustic imaging/microscopy (JTuG) caught my full attention on Tuesday. It is a perfect example of light collaborating with sound to achieve something fascinating.  Think about it, light and sound are siblings. They are governed by similar natural laws. You might argue that light can propagate in vacuum while the sound needs media to do so. But again, they are siblings, not twins. So this argument does not really hold. Anyway, taking that into account, isn’t it fun to see them hold hands and work on something new together!?

The principle behind this new imaging technique is actually straightforward. The pulsed laser light (MHz repetition rates) is focused into the tissue; the tissue of interest absorbs the light and expands. This process is repeated with laser repetition rate. The pulsed expansion creates the ultrasonic sound wave, and we detect this by transducers. We then reconstruct the image of the tissue through some complex algorithm. We know that ultrasonic can penetrate deep tissue, while the resolution of ultrasonic is not as great as optical imaging. On the other hand, optical imaging can only go to a few millimeters deep. By endeavors of the researchers in improving this technique, photoacoustic imaging actually combines the strength of these two – it can do deep tissue imaging with optical imaging resolution – optical resolution photoacoustic microscopy.

An experimental layout for photoacoustic microscopy.

Fast-forward to Wednesday, a wonderful QELS session (QWB) focusing on laser cooling and its further applications on quantum computations and simulations are really hardcore stuffs. Using light to produce ultra cold molecules is definitely pushing the frontiers of science. We all heard of atoms cooled by lasers and a Nobel Prize was given to this achievement. But for molecules, things are more difficult. They have inertial structures and as a result, complicated processes are involved when cooling them by laser light. However, diatomic molecules are being cooled to sub micro Kevin through Sisyphus and Doppler cooling (check this article for more). If you missed today’s presentations, it is totally ok. On Thursday, sessions like QThJ, QThM, QThN, and QThO will feed your quantum hunger.

Talking about green energy, Laser Inertial Fusion Energy (LIFE) is discussed during CLEO’s Market Focus. Due to human mankind’s need in energy, we turn to fusion, and we intend to do so by using extremely high power lasers. LIFE utilizes 384 powerful lasers to create pulses with the energy of 3.1 mega Joule in IR and 2.2 mega Joule in UV per pulse. Each laser has the size of a truck and can be swapped in and out as a unit if the lifetime is reached or malfunction is found. This kind of gigantic project requires the state-of-art techniques and actually drives the development of the optical industry, such as glass productions. If you dig even further, the diode pumped helium cooled mercury amplifier inside each laser is just breathtaking. The helium is blown through the gain media with 0.1 Mach speed to cool down the laser. In other words, you even need aerospace technology to prevent the turbulence inside the laser.

Finally, also thanks to CLEO’s Market Focus & Technology Transfer Showcase, I just learned that an animated website created by JDSU called Photovoltaic for generating and measuring energy is a good starting point to know how light plays the role in green energy. Enjoy it and do not forget to check out CLEO’s Technology Transfer Showcase program tomorrow.

DISCLAIMER

The opinions expressed herein are those of the author and do not represent the Optical Society of America (OSA) or any OSA affiliate.

Behind every successful conference!!!

An exciting conference is mainly composed of two parts – technical sessions and exhibition. We enjoy the technical sessions because that’s where we learn from our peers, get our brainstorms, and have a quick update on the scientific frontiers. These are addicted as you can tell me about it. However, ask yourself about the definition of a successful conference. Most of us will say a conference will not be complete without stopping by the exhibition hall to see the zoo of new products and technologies presented by numerous companies. Well, the souvenirs we gather from each booth are attractive too!


If we take a step back, we realize that convention center is a very busy host. Every week it is embracing a new show and new people with crazy ideas. This makes me wonder, what kind of preparation is required to host a welcoming conference? For technical sessions, things are easier to picture since most people had the opportunity to observe or organize a symposium either in the school or in a research institute. We need to multiply everything by at least a hundred. These are OK, we can have more rooms, chairs, projectors, laser pointers, and most importantly, more coffee and labor. So we can make this happen. Now, if we think about the preparation of an exhibition hall, a blank image usually emerges. I did not even know how an exhibition hall looks like before all the companies fight for the space and start to build their own territories, not even mention about how to set it up. Thanks to my job duty and helps from the colleagues, now I have observed the way it happens…^_^


The convention center is moving at a very fast pace as we mentioned. The first thing we have to realize is the time you have to build a booth. Normally, each company has a full day working with the labor of the union to set up everything. In other words, people are working under great pressure. The very first scene I saw is that everyone on the floor was tense since all they faced is a concrete floor marked by chalk to specify the territories of each company. Phones were ringing all the time because on the other side of the exhibition hall, hundreds of trucks were waiting to ship the equipments into the hall. In the meanwhile, experienced workers maneuvered loaded carts, and crates were shuffling among people. These would go on for several hours, and step by step, each big and small cargo reached the right destination, while small hassle was happening all over the place (such as some trucks got lost, according to the workers, this is quite normal).

Small carts moving around the cargos and magically they all arrive at the right destinations.

After this was all set, locating the power jackets and building tiny power grids on the floor were next. We can fairly say, without the electricity, the exhibition hall would be like a haunting house rather than a technology showcase. But for the beauty of the exhibition, we want to hide these power grids. So we make them lying comfortably on the floor and covered by carpet later on. By doing so, we will never spot them unless you come to the hall before the grand opening. At the same time, small hydraulic trucks were busy putting the overhead canvas slogans and signs above company’s booth. From this moment on, we would not get lost, since the flag (well, the slogan) was waving on each and every corner of the hall.

The power grids (shown in orange) on the floor are taped down nicely and distributed very efficiently for the booth use. 

Time to do some makeup. The “base foundation” was the carpet. It covers all the power grids and jackets, all the chalk signs, and marks the lanes of the traffic. Putting the carpet represents an important step – “the equipments are ready to get some fresh air.” Knowledgeable technicians started to open the crates (always with complaining, since equipments had legs, they moved around after staying in the trucks for so long), tried to do preliminary assembling, and finalized the floor plans. They spent another several hours to put optical tables together, made the equipments up and running, and arranged and cleaned the surfaces of each components. These are tedious work, and work was again under great pressure.

This booth is about 50% done. Technicians have been working for hours, and there are still al of of crates need to be opened and arranged on the optical tables.

Just like LEGO we played when we were young, setting up the booth was like intense LEGO works, except they are much bigger and you cannot quit if you feel tired. It is not uncommon to see people work way beyond midnight because they want to present the best to the researchers and the students the following day. After technicians and the product line managers were satisfied with the setups, final cleanup was required. Final vacuuming on the floor, tearing open the plastic wrapping of the carpet, and covering the equipments and tables with blanket were essential works not to be omitted.  Everyone wanted to keep every link neat and flawless.


After a detailed inspection on the booth, we can call it a day. Hmmm, time for bed or time for a drink?! I would like to thank Mr. Hoang Hung and John Carter, the men who are in charge of the booth setup. Without his help and explanation on the details, I will not be able to peek through this new window to see how to dress the conference!

Another successful show!!! After seeing so much traffic, all the efforts and sweats are just sweet!

DISCLAIMER

The opinions expressed herein are those of the author and do not represent the Optical Society of America (OSA) or any OSA affiliate.

From the smallest lasers to the biggest ones!!!

With so many different kinds of lasers play essential roles in modern researches and daily life, it is tempting to find out what are the extremes among them. Thanks to this conference, this question intrigues me once again during a talk (QMF3) where a gigantic free electron laser (FEL) was mentioned and used to probe the atomic structures. Searching with the conference program brochure and within my memory, here is what I can find.

The winners of “the biggest” prize go to the FELs. Taking the one in the U.S. soil as an example, a FEL powered by a two-mile-long linear accelerator (linac) in Stanford Linear Acceleration Center (SLAC) has a grand name associated with it  -- Linac Coherent Light Source (LCLS). Technically speaking, it is a laser of more than two miles in length and many many tons in weight (I don’t think people actually weight this monster, figure 1). Basically, after SLAC’s linac accelerates very short pulses of electrons to 99.9999999 percent of the speed of light; the LCLS takes them through a 100-meter stretch of alternating magnets that force the electrons to undulate back and forth. This motion causes the electrons to emit X-rays. Since the electron motion is in phase with the field of the light already emitted, the fields add together coherently.  As many as 10 trillion X-ray photons can be produced and squeezed into a bunch that’s a mere 100 femtoseconds long. This giant laser has a sibling across the Atlantic. In Europe, an x-ray free electron laser (European XFEL) shared by 14 countries is powered by a 2.1 km long superconducting linear accelerator.

Figure 1. The aerial view of the monster FEL laser in SLAC.

The runner-up would be FELs powered by the synchrotrons. Although there are huge ones such as LHC, the ones that are used to pump FELs are smaller, such as Japan’s SPring-8 and France’s SOLEIL (on Wednesday, a presentation (CWG5) utilizing this instrument will be discussed). Well, maybe Synchrotron has a bigger surface area than linear accelerator, since I am naming the prizes, let’s say, the length is what we compare.

Just a bit digression, an instrument (or experiment) involved 192 high power lasers is an unusual contender for this prize. Apparently, researchers in Lawrence Livermore National Laboratory’s (LLNL) National Ignition Facility (NIF) are trying to fulfill the dream of fusion by focusing many lasers in a capsule of size equivalent to a peanut. By squeezing so much energy in so little space (with the existence of hydrogen), they are optimistic about that the fusion is bound to happen.

Let’s swing to the other extreme. Nano-lasers with many different designs can proclaim the winners of the “smallest” prizes. A quantum cascade laser embedded in a microcavity and emitting THz radiation is one of the smallest lasers available (with a size of a few tens of microns). But the 44-nanometer "spaser – surface plasmon laser" will be very hard to beat. The device is a hybrid -- A bluish-green laser beam is shined into a suspension of gold nanoparticles.  A layer of sodium silicate and an outer silica shell containing dye molecules surrounds each of these particles. When the gold is excited by the laser photons, collective oscillations of electrons on the surface, known as surface plasmons, are excited. The plasmons then excite the dye molecules, and subsequently the photons released from the dyes stimulate more plasmons on the gold at the same wavelength, causing the device to emit green laser light. How amazing is that!

DISCLAIMER

The opinions expressed herein are those of the author and do not represent the Optical Society of America (OSA) or any OSA affiliate.

CLEO/Laser Focus World Innovation Award endorses the recent triumph of Terahertz (THz) spectroscopy and applications.

This year, the award goes to Applied Research and Photonics Inc. for its endeavor in THz device and applications. This is indeed another sign saying that THz will be a hot topic for the following few years thanks to many people’s efforts over the past two decades. Besides, we are very happy to see this field has grown into a vibrant society with its own conference – Optical THz Spectroscopy and Technology (OTST). I was there, learned many news things from researchers all over the world, and enjoyed the nice breeze from the Pacific sea in Santa Barbara.

Thinking about THz, most of us immediately connect it with a couple of concepts, including the wavelength of it is long compared with the familiar optical and even mid-IR wavelength (a wavelength of 1 micron is 300 THz while 1 THz is 300 um), the property of great penetration to soft materials like tissues, plastics and, card boards, and its application in security screening due to the sensitivity of many explosives. In addition, its low energy and non-invasive feature is perfect for authenticity test on artwork and biomedical imaging. With this field burgeoning like never before, it is worth to take a quick look on the methodologies of generating THz.

The most orthodox way to create THz laser is to find a suitable gain media and pumping source. Just like a dye laser in which an electronic transition of dye is directly related to the lasing frequency, the transitions between the rotational states of methanol gas falls right into the THz region. A very good white paper using methanol and pumped by a CO2 laser can be found in here. Of course, the gain media is not restricted to methanol; even water vapor is actually a good THz source.

Mixing two lasers with the frequency difference in the THz regime is another neat way. Considering mixing two lasers in the optical fiber, the beating that is produced by the frequency difference of these two lasers is just the source of the THz. If we can filter out the pumping lasers, then we have a useful THz radiation. A more efficient way of doing so will be mixing two lasers in the nonlinear crystals (GaAs, LiNbO3, … etc). Depending on the nonlinearity of the crystal, frequency conversion is achieved with different efficiencies. In this case, the efficiency of THz generation is proportional to how strong the nonlinearity of the crystal is. This principle is adopted by Applied Research and Photonics Inc. to the extreme. The core of its THz device is based on a polymeric nanomaterial that has very strong nonlinearity.

How about generating ultrashort THz pulses to cover a wide THz spectrum at once. A very exciting way of doing so is through air plasma. The principle is quite straightforward although there are several variations of it (figure 1).  Basically, you create air plasma in the air (by focusing intense laser pulses in air), drift the electrons away from the nuclei through different bias methods, and then the nature law takes over. Since the electrons will recombine with the nuclei through coulombic force, this process creates a transient current (or a oscillatory dipole). An oscillatory dipole/transient current in this process creates radiation that covers THz regime. Before the advance of intense lasers, researchers focus laser beams onto photoconductive antenna chips to create transient current. Actually this is still the most popular way to generate ultrashort THz pulses.

Figure 1. THz generation based on air plasma. In all scenario, air plasma is generated by intense laser pulse (red). Electrons are accelerated in the direction of laser pulse . This process creates THz in a cone fashion.  Electrons are drifted away by external DC source (b), by another laser pulse (c), and by the laser pulse itself (d). Courtesy of Thomson M., Kreb M., Loffler T., and Roskos H. in Laser & Photon Rev. 1. No. 4. 349 (2007).

Just a reminder, on Monday, CLEO has an entire session focusing on TH Sources. Besides, the award presentation will be during the Plenary Session in the same day evening. This is definitely another power boost for you to learn how it goes in this field. Hopefully, next time when we encounter THz research, we all know a bit more in their business. You can also explore THz quantum-cascade lasers, THz generation by pulse front tilting in the crystal, and more through the power of the Internet…^_^.

DISCLAIMER

The opinions expressed herein are those of the author and do not represent the Optical Society of America (OSA) or any OSA affiliate.

From quantum Zeno effect to all optical switch, part II.

In the last blog, we took a trip starting from quantum Zeno effect and reached to one of its applications -- all-optical switch -- at a quick pace. This time, we will look into more phenomena that researchers use in order to achieve this all-optical switch future.

We discussed about photonic crystals (PCs) and their versatility in a recent blog. We learned that by changing the patterns of the PCs, it is able to select which color of light that can travel within it or be rejected. While the patterns play the crucial role in PCs, we have to realize that it is the modulation of the refractive index produced by the patterns that give PCs their unique physical properties. With this being said, it is not difficult to understand that if the refractive index of the material that PCs are made of can be changed, we are able to affect (or tune) PCs’ properties. This is exactly what researchers are trying to do recently:

Considering the silicon PC shown in figure 1a, there are two colors of light allowed to propagate in it (mode c and mode s). Now, it is known that putting some free electrons in the conduction band of Si would change its refractive index. To use this feature, researchers shine this PC with some light (pump) such that a few electrons in the Si can be kicked to the conduction band. Changing the refractive index shifts the center frequencies of mode c and mode s directly. In addition, since PC is so sensitive to its refractive index, just a few hundred fJ of energy is required to tune the transmittance property of the PC. The all-optical switch is then realized by the following: Let’s input two colors of light into the PC -- one is very close to mode s and one is right at mode s (figure 1b). Without the additional pumping light, mode s is transmitted. With the pump, mode s is suppressed and the other color now is able to transmit since the transmittance property is shifted. So by pump-on/pump on, we will have different colors of light coming out -- an all-optical switch, as we expect.

Figure 1. an all-optical switch based on a silicon PC. (a) The structure and the transmittance curve of this specific PC. (b) with/without pump, the transmittance of the PC is shifted. Here we use mode s as an example. Courtesy of T. Tanabe, M. Notomi, S. Mitsugi, A. Shinya, and E. Kuramochi on APL 87 151112 (2005).

Another example is a PC made of polystyrene. The pump beam can also control the transmittance of it. The structure and the transmittance curve are shown in figure 2. By pumping this PC with femtosecond laser pulses of a few nJ, it is found that the transmittance can be changed by more than 60%. And this feature definitely makes it a strong candidate for all-optical switch application.

Figure 2. (a) A SEM image of a PC made of polystyrene. (b) The transmittance curve of this PC without being pumped by optical pulses. Courtesy of Y. Liu, F. Qin, Z. Wei, Q. Meng, D. Zhang, and Z. Li on APL 95 131116 (2009).

Let’s change the gear and look at something that will also be presented in CLEO 2011. A phenomenon called inverse Raman scattering (IRS) is utilized for all-optical switch application. We are all very familiar with Raman scattering, in which a material is pumped with a strong light, and you can detect some other colors of the light in the output due to inelastic scattering of the pump light in the material. If now we input two frequencies of light -- one is pump, the other has bluer color such that the frequency difference between these two are equal to the energy loss of the inelastic scattering, IRS would drain the energy from the high frequency light to the pump. So by putting pump or not in to the material, we can actually decide we want to drain the energy from the high frequency light out or not. This is actually realized by using a optical fiber or a silicon ring resonator. Excitingly, these will be presented during the conference. So, do not forget to check it out if you are interested.

There are more to say on this topic, such as using “four wave mixing on a silicon photonic chip” or “quantum dots coupled with a PC” to achieve the all-optical switch goal. The pool of exploration is open, just get ready and jump in!

DISCLAIMER

The opinions expressed herein are those of the author and do not represent the Optical Society of America (OSA) or any OSA affiliate.

From quantum Zeno effect to all-optical switch, part I.

Needless to say, scientists have been puzzled and fascinated by the quantum nature of the physical law for more than a century. The history of science is all over it and evolves with it. Having this in mind, it is very reasonable to see that the Science magazine has named the discovery of the quantum machine as the most significant scientific advance of 2010. It is the first quantum mechanical resonator that can actually be seen by bare eyes and deserves another detailed blog by itself.


How about in the optical world? Have we successfully implemented or utilized the quantum nature of materials for cool applications? The exciting answer is YES, and we will be looking at some of them in this short blog:


Let’s start from one of the most bizarre behavior that quantum mechanics can do – Quantum Zeno Effect. It states that if your observation of an event is frequently enough, its decay to the natural state of equilibrium will be affected significantly, either being slowed down, frozen, or accelerated. In fact, scientists call it anti-Quantum Zeno Effect, if the process is being accelerated (by the way, you will be able to hear the talk from its explorer -- Gershon Kurizki in CLEO 2011: QELS Fundamental Science).


The name “Quantum Zeno effect” adopts a broader meaning when it enters the optical world. We now use this term to describe manipulating the evolutions of the populations of different quantum states (or photons with different colors) by external perturbation.


If you feel the aforementioned is hard to digest, I promise the following will be not. We will be looking at some real examples and these are aiming for a high goal -- all-optical switches. If you wonder why all-optical switch is important, just think about how hot your CPU can get most of the time and how fast light can travel compared with electrons.


Take a look at figure 1. Two optical fibers connected by a microdisk made of GaAs. As shown in the figure, the signal light is shown in green. The disk couples the signal weakly. It comes in from the lower left (upper right) side, coupled to the disk, to the second fiber, and leaks to the upper left (lower right). Now if we carefully put in another pump light, marked as blue, it would perturb the property of the disk such that the ability to couple the signal light will be ceased completely. As a result, no signal light can be coupled to another fiber through the disk. In other words, you can detect signal from the upper left by putting it from the lower left with the pump-off. With pump-on, you detect no signal into the second fiber. This is a switch controlled by pump light.

Figure 1. one model of all-optical switch utilizing a microdisc. Courtesy of Y. Huang and and P. Kumar in Optics Letters Vol. 35 2376 (2010).  

In terms of quantum mechanics, the pump light opens a new channel of interaction inside the microdisk. It affects the existence of signal photons in the disk by draining them into another wavelength of light (shown in red in the figure). So the populations of photons with different colors are rebalanced. Virtually no signal photons are found in the disk when pump is on, and as a result, no leakage of it on the second fiber can be found.


Yu-Ping Huang, Joseph B. Altepeter, and Prem Kumar also present another similar methodology utilizing second harmonic generation (SHG) principle, as shown in figure 2. When there is no pump in the waveguide (WG-I), SHF process dominates. You put in signal with frequency ws; you get 2ws in the output. If the pump light is in, then every moment you have 2ws in the waveguide, it will interact with the pump and be drained to another frequency. So light with 2ws never builds up, and intensity of ws is not affected too much. The net result is that you still have the ws as the output. In summary, you have 2ws (ws) as output with pump-off (on). This is indeed another neat way of doing optical switch.

Figure 2. an all-optical switch based on SHG principle. Courtesy of Y. Huang, J. Altepeter, and P. Kumar.

Using two-photon absorption for the optical switch is yet another exotic way. Considering the design in figure 3, a toroidal resonator couples two fibers. The input light E1A (E1B) on fiber 1 (2) has frequency wA (wB). The resonator has strong two-photon absorption of wA + wB but nearly no absorption for wA, wB, 2wA, or 2wB. It is found out that, with the existence of strong E1B, you cannot find any E1A in the second fiber. In other words, by inputting E1B or not, we can control the existence of E1A on the fiber 2. The principle behind it is very similar to what we just discussed. With strong E1B in the resonator, any light of E1A will be destroyed through two-photon absorption process, so only strong E1B remains in the resonator. With the non-existence of E1A in the resonator, none of it can be coupled to the fiber 2. In addition, we can also use the strength of E1A to control the existence E1B in the first fiber! So a multi-functional optical switch emerges.

Figure 3. An all-optical switch based on two-photon absorption resonator. iR and T are coupling coefficient and transmission coefficient of the system. Courtesy of B. Jacobs and J. Franson in Physical Review A 79 063830 (2009).

Since two-photon absorption plays a core role of optical switches, researchers like Seth R. Marder and Joseph W. Perry are trying very hard to synthesize new organic compounds with desired two-photon absorption. You can learn about it in the morning section of QELS Fundamental Science.


We will look into more different kinds of all optical switches in the next blog.

DISCLAIMER

The opinions expressed herein are those of the author and do not represent the Optical Society of America (OSA) or any OSA affiliate.

The best resource I can find to learn your first “optical fiber” lesson!

When trying to search for more information about CLEO 2011 plenary speaker – Dr. Donald Keck, a pioneer and veteran in optical fiber technology, I realized that the best online resource to learn about optical fiber is not Wikipedia this time. It is actually the website of Corning. Apparently, as a company, Corning has a different standard in educating his customers. It puts a lot of efforts and resources into the contents. What impresses me about this website is that – it does not just pile the information day after day for you to dig in. It organizes the information so well that you just absorb the knowledge without noticing it. It contains knowledge for the beginners, amateurs, and serious researchers. All you need is a cup of coffee/tea and a nice break to enjoy it.

I will start with the “Fiber 101”. Almost all the technical terms you need to know (such as core and cladding, single/multimode fibers, and mode field diameter) will be explained with beautiful illustrations here. I will call it “fiber for dummy” section.

If you are interested in the history of optical fiber, make a little digression and feel it through “The History of Corning's Optical Fiber Innovation”. Over the past 40 years, the technology of fiber has advanced so much that we now have an optical fiber of more than a few thousand kilometers transmitting the information at the rate of terabits/s! Intriguingly, you can also see Dr. Donald Keck’s video clips and his historic photos scattered in this timeline-type-of-presentation.

Let us shift back to more scientific and technological points of views. If you want to know what and how the optical fiber can carry the information around the world and what the emerging technologies are, you might not miss this link “Long-haul Networks”. In this short report, concerns and solutions about transmitting information through fibers, new technologies to advance optical fiber’s applications are well discussed. All of us are fascinated by the fiber to the home (FTTH) for sure. Learning about it is straightforward through the following two links – “Broadband Technology Comparison” and “FTTH benefits”. I really hope soon we can have this technology at each corner of the country.

Time for the hard cores! You can find numerous application notes and conference papers in “here”. You can easily get lost if you do not know what you are looking for. This section is like a database for serious researchers. It also proves that Corning is intimately connected with the scientific community. With this being mentioned, do not forget to check Wikipedia now! After a quick power boost from the Corning website, I believe everyone can have a fundamental ideas about what optical fibers are and can surf through the heavy materials presented by wiki much easier.

Of course, the devotion of this website raises my expectation on Dr. Donald Keck’s plenary talk. I really look forward to learning the stories of the advances of optical fibers through a person who dedicates himself into this field for more than thirty years!

Finally, I found a very amazing video clip online to end this blog. It is an inspiring one made by Corning – A day made of glass, made possible by Corning – shows you that optical fiber is just a link or part of the technologies made possible by glass. Combing glass with chemistry, material sciences, and physics, the life is with unlimited potential!!!

DISCLAIMER

The opinions expressed herein are those of the author and do not represent the Optical Society of America (OSA) or any OSA affiliate.