Semiconductor nonlinear optics
At HP Labs, we are interested broadly in computing in the post-Moore's Law era. While optical computing has been investigated for many years since shortly after the invention of the laser, recent advances in nanofabrication (the development of optical microcavities with very high quality factors and very small mode volumes) open up new opportunities to study logic devices utilizing a small number of "particles" per operation. How should we build our circuits when intrinsic quantum fluctuations play a large role in determining their dynamics?
On an experimental front, we have been developing optical devices in hydrogenated amorphous silicon (a-Si:H). Interestingly, a-Si:H seems to have superior nonlinear optical properties compared with crystalline silicon at wavelengths near the 1550-nm telecom band. In recent work, we have demonstrated pump-probe optical switching in a-Si:H microring resonators using cross-phase modulation (based on the optical Kerr effect), where the switching speed (14.8 ps observed) is determined by the photon lifetime of the cavities.
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| Scanning electron micrographs of a-Si:H devices after etching: (a) layout of microring device with bus waveguide and grating couplers; (b) close-up of grating coupler for TM-polarized light; (c) a 5- μ m-diameter a-Si:H microring and bus waveguide. (c) OSA. |
Design and fabrication of PPLN waveguides
Much of my research in the Fejer group at Stanford has revolved around the design and fabrication of devices for efficient frequency conversion of optical signals. The concept here is that we can use a strong laser beam to take an optical signal and change its color, one photon at a time, with efficiencies greater than 99.99%. This idea was cool enough to get me to work on these devices for 5+ years, from ~2007 to 2012.
Upconversion single-photon detectors
Single-photon detectors, particularly in the telecom band with wavelengths near 1550 nm, have a number of applications. Commercial detectors in this spectral region based on III-V avalanche photodiodes have a number of drawbacks compared with Si devices for the near-visible spectral range. An upconversion single-photon detector leverages a high-efficiency frequency converter to "boost" the optical frequency of an incident telecom-band signal to a frequency above the Si bandgap where a Si detector can then be used. We've developed two upconversion detector systems, the first optimized for high-efficiency and low-noise detection using a thick-junction Si APD, and the second using a novel cascaded upconversion approach to achieve high efficiency with very low timing jitter.
There remain a number of exciting research opportunities in this field. Frequency conversion enables the integration of additional functionalities into a detection system, including fast switching, time-to-frequency conversion, spectral sensitivity, and so on.
There remain a number of exciting research opportunities in this field. Frequency conversion enables the integration of additional functionalities into a detection system, including fast switching, time-to-frequency conversion, spectral sensitivity, and so on.
Other projects
For a Stanford class on classical mechanics I did projects on:
I played keyboard in a band called Tin Whiskers for a while.
