Integrated Photonic Analog Link on Si: This program is affiliated with the AIM Photonics program. Previously, we have demonstrated discrete modified uni-traveling carrier photodiodes with high saturation current/RF output power and. In this program we have initiated research on high-power MUTC waveguide photodiodes heterogeneously integrated on SOI. To date, these photodiodes have achieved the highest power reported for any waveguide photodiode on any platform. This program has been extended to fabrication of high-performance photodiodes on III-V compound epitaxial structures grown directly on Si substrates. This represents a new approach to Si photonic integrated circuits.
Fundamental Studies of Single Photon Detection with Avalanche Photodiodes: The goal of this program is to develop a fundamental, quantum-based model for single photon detection and number resolution in avalanche photodiodes. The experimental device work is being conducted in collaboration with a quantum theory study in the University of Virginia Physics Department and materials support at the University of Texas. The device effort is focused on two strategies: (1) using several nano-detectors in series, i.e., a segmented detector, and (2) placing the detector material inside a resonator so as to affect multiple passes across a thin absorber.
AlInAsSb Photodetectors: Recently, in collaboration with the University of Texas we have demonstrated, for the first time, that high-aluminum-content AlxIn1-xAsySb1-y lattice matched to GaSb can be grown within the miscibility gap using a digital alloy approach. This material has been used to demonstrate the first working staircase avalanche photodiode (APD), a low-voltage, high-gain gateless tunneling phototransistor, and a separate absorption, charge, and multiplication (SACM) APD that achieves ultra low noise in the short-wave infrared (SWIR). The goal of this program is (1) to conduct fundamental studies on these novel materials and (2) to realize the full potential of the AlxIn1-xAsySb1-y-based photodetectors. For high-sensitivity optical receivers, AlxIn1-xAsySb1-y separate absorption, charge, and multiplication avalanche photodiodes have been successfully demonstrated. The detectors have the potential to achieve 5 dB to 7 dB improvement in receiver sensitivity. High-speed configurations can enable improved performance of 100 Gb/s and 400 Gb/s Ethernet.
Integrated Optically Modulated Scanner: The goal of this program is to develop an integrated high frequency, near-field measurement probe. The probe will function as a calibrated reflector and return power to the antenna under test. The photodiode is a component of a resonant circuit that can be switched with a modulated laser (~100 kHz). The net effect is to modulate the return signal so that the large, unmodulated background signal can be filtered. In order to achieve the requisite performance two novel photodetector structures are being developed: (1) a reach-through photodiode with a charge layer adjacent to a lightly doped absorption region and (2) an optical varactor.
InGaAs Photomultiplier Chip photon counting array for 1550 nm operation: In collaboration with LightSpin Technologies, Inc. this program is developing tight pitch arrays of single photon avalanche diodes for 1550 nm optical communications applications. Scaling InAlAs/InGaAs to small area devices has the potential to achieve an advantageous tradeoff between gain and after pulsing, enabling improved performance.
Portable optical frequency comb systems for the generation of ultralow phase noise microwave signals: Microwave oscillators based on optical frequency division provide phase and timing noise performance that is orders-of-magnitude better than any other system. The characteristics of the photodiode significantly affect the performance of these oscillators. In order to achieve the most stable performance it is essential that the photodiodes operated at very high optical input power with low amplitude to phase conversion. This program has developed detectors with very high RF output power, for example 2 W at 10 GHz and 10 mW at 100 GHz, and record low non-linear response. Work continues to extend the bandwidth to higher frequencies and achieve even higher linearity through fundamental device physics studies, detailed modeling and simulations, and advanced fabrication and characterization techniques.
Ultraviolet III-N/SiC Photodiodes: High sensitivity deep ultraviolet (DUV) photodetectors operating at wavelengths shorter than 280 nm are useful for various applications, including chemical and biological identification, optical wireless communications, and UV sensing systems. SiC avalanche photodiodes have achieve excellent performance as visible-blind, high-sensitivity detectors. However, it is beneficial to extend their operation to longer wavelengths for some applications. This is being accomplished by using GaN in tandem with SiC. A parallel approach employs the AlGaAs material system with high Al content. Further, AlGaN on SiC shows promise to push the response toward deep UV.