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PhD Thesis Defense

Tuesday, August 18, 2020
2:00pm to 3:00pm
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Active Flat Optics Wavefront Manipulation for Imaging, Ranging, and Sensing
Seyed Mohammadreza (Reza) Fatemi, Graduate Student, Electrical Engineering, California Institute of Technology,

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https://us02web.zoom.us/j/88300269319?pwd=MTFMT21UWk5oMWFGRTRhQWFMa2RyZz09

The emergence and maturity of integrated photonic platforms over the past decade allowed for reliable integration of a large number of photonic components on a single substrate. This ability to process and control coherent light on a chip is a potential pathway for the realization of novel low-cost systems capable of non-conventional functionalities for optical wavefront engineering. In this thesis, integrated active flat optics architectures for generation, manipulation, and reception of optical wavefronts are investigated. In particular, the application of such systems for imaging, ranging, and sensing are studied and multiple photonic systems including a large scale transmitter, a high-sensitivity receiver, and a high-resolution transceiver are demonstrated.
For generation of optical wavefronts, solutions for engineering a radiative optical waveform via emission by an array of nano-photonic antennas are studied and a chip-scale photonic transmitter is implemented. The transmitter forms an optical phased array with a novel architecture in a CMOS compatible silicon photonics process which not only dispenses with the limitations of previously demonstrated systems but also yields a narrower beamwidth leading to a higher resolution. Moreover, an integrated adaptive flat optical receiver architecture that collects samples of the incident light and processes it on-chip with high detection sensitivity is implemented. To detect the optical samples with a high signal to noise ratio, an optoelectronic mixer is proposed and designed that down-converts the optical signals received by each antenna to a radio frequency signal in the electronic domain, provides conversion gain, and rejects interferers. This system allows arbitrary wavefront manipulation of the received signal by adapting itself to new conditions — a capability that does not exist in conventional cameras. Using this system, we realized the first high-sensitivity optical phased array receivers with one-dimensional and two-dimensional apertures and the functionality of the chips as ultra-thin lens-less cameras were demonstrated. To achieve a high-resolution integrated photonic 3D imager with low system complexity, a double spectral sampling method is developed through a special wavefront sampling arrangement on the transmitter and receiver apertures. This transceiver architecture includes a multi-beam transmitter and a high sensitivity receiver that can distinguish the illuminated points separately and process them simultaneously using a digital signal processor.
Moreover, novel ultra-low power architectures for generation and reception of short RF/microwave pulses are explored. Such systems have a broad range of applications including imaging and ranging. In this study, the capability of generating and receiving orthogonal Hermite pulses of various orders using a capacitor-only time-varying network is demonstrated.

For more information, please contact Tanya Owen by email at tanya@caltech.edu.