Physics & Informatics (PHI) Lab Distinguished Scientist, Dr. Robert Byer, recently won another well-deserved accolade. Optica (formerly OSA), a global society for optics and photonics, named him Honorary Member. Byer is the William R. Kenan, Jr., Professor Emeritus of Applied Physics at Stanford University. He has been a part of the PHI Lab and the NTT Research leadership team since 2019. Honorary Membership in Optica is awarded by unanimous vote of its Board of Directors and is limited to two-thousandths (2/1000) of total membership of the Society.
“Bob Byer has made extraordinary contributions to laser science and technology through his work as a researcher, educator, mentor and leader. His exceptional contributions to our field and Society will have a lasting impact,” Michal Lipson, Optica’s 2023 President, said in a statement. “It is a great pleasure to welcome Bob into this group of distinguished Optica Members.”
The Optica statement furthermore notes that Dr. Byer has served as President of Optica, the American Physical Society and the IEEE Photonics Society. He has also served Optica and the field in a wide range of other roles. “He is a Fellow of Optica, the American Association for the Advancement of Science, the American Physical Society, the California Council on Science and Technology, IEEE Photonics Society, IBM, the Laser Institute of America and the National Academy of Inventors,” the Optica statement continues. “He is the recipient of several awards and honors, including Optica’s Frederic Ives Medal/Jarvis W. Quinn Prize, R. W. Wood Prize, and Adolph Lomb Medal, the Photonics Award, the Willis E. Lamb Award for Laser Science and Quantum Optics, and the A.L. Schawlow Award.”
As a scientist, Dr. Byer’s contributions include the demonstration of the first tunable visible parametric oscillator; the development of the Q-switched unstable resonator Nd:YAG (neodymium-doped: yttrium aluminum garnet) laser; remote sensing using tunable infrared sources; and precision spectroscopy using Coherent Anti-Stokes Raman Scattering. The green laser pointer (an infrared laser, co-packaged with a nonlinear optical crystal that up-converts infrared photons to green light) was invented because of a question he was asked while teaching his optics class. The sodium-yellow guide star (see these images) was also made possible by contributions from his group at Stanford. More recent research includes the development of nonlinear optical materials and laser diode-pumped solid-state laser sources for applications to gravitational wave detection and laser particle acceleration.
Working with Professor (and now PHI Lab Director) Yoshihisa Yamamoto, Dr. Byer developed the idea of the Coherent Ising Machine (CIM). Specifically, he proposed replacing the laser in previous attempts with an optical parametric oscillator (OPO). Alireza Marandi, then one of Byer’s students working on OPOs, took the idea from concept into practice. The use of CIMs for solving hard optimization problems is now one of the core research directions within the PHI Lab.
Dr. Byer’s personal impact has been significant, especially among those who were graduate students at Stanford University. PHI Lab Scientist Marc Jankowski met him at Stanford, worked with many of his students in the lab and served as his teaching assistant for several years. “It was great to learn about optics through his perspective,” Dr. Jankowski said. For more on Professor Byer’s achievements and influence, please see Dr. Jankowski’s extended reflection:
There’s a common refrain in science attributed to Isaac Newton: ‘If I have seen further, it is by standing on the shoulders of giants.’ For those of us in the PHI Lab who work on thin-film lithium niobate, Bob is one of those giants. Everything we use has been influenced by Bob in a deep way. The material we use, lithium niobate, is notoriously finicky; if you hold it wrong, or heat it up wrong, or use the wrong tweezers, it can misbehave, and your device will stop working. In the early days of nonlinear optics, little was known about how to grow crystals of this material, and it turns out that everyone working with lithium niobate had different crystals. The growth techniques commonly used at the time led to crystals with chemical compositions that varied throughout the material, with correspondingly different optical properties depending on where your crystal was cut from the boule. Robert Feigelson, working with Professor Byer, developed a technique for growing crystals known as the congruent melt, which made every crystal the same. Congruent lithium niobate is still the standard material used in nonlinear optics today, and Professor Byer was one of the first scientists to build nonlinear optical systems using the congruent material.
Professor Byer’s group then went on to develop new techniques for controlling nonlinear interactions in lithium niobate, a technique called periodic poling. You can think of poling as being a method of taking any nonlinear crystal and programming what it will do: We can take an input frequency and double it, we can sum together or subtract two frequencies, or we can make amplifiers. Periodic poling is an electronic process that selects which of these optical processes happens. His group, working with others at Stanford, then developed a technique called reverse proton exchange, which can be used to make waveguides in lithium niobate. This technique takes the bulk material and turns it into a circuit, like an optical fiber, that can confine and guide the light. This technique is now one of the standards in the field, and several companies sell products based on it.
For our generation, scientists working in nonlinear optics now use a recently developed material called thin-film lithium niobate to build nanophotonic devices, also called photonic integrated circuits. These devices are built on all these previous techniques. Thin films are made from the congruently grown bulk material, and we pole the material to program in our nonlinear interactions. The main challenges for the new generation of scientists have been how to pole these thin films with high fidelity, and how to make waveguides in these thin films. When these things go well, we can make circuits that outperform proton-exchanged waveguides a thousand-fold, but at heart, all the design strategies we use today are inherited from people like Professor Byer.
In parallel, Professor Byer’s group has developed many of the lasers that are used to drive these nonlinear crystals. In other words, he hasn’t just laid the groundwork for these recently developed optical circuits, but also their power supplies. You can see this reflected in his achievements beyond the PHI Lab. Lasers and other optical components developed by Professor Byer’s group have been used for gravity wave detection at the Laser Interferometer Gravitational-Wave Observatory (LIGO), and laser-driven fusion at the National Ignition Facility (NIF), part of the Lawrence Livermore National Laboratory.
