Major Funding Defense Advanced Research
National Science Foundation (NSF):
|
Research Interests
Single Photon Detectors: Avalanche-free Single Photon Detector Arrays:
 |
Motivation: There are numerous applications for single photon detector arrays with low dark counts and high quantum efficiency. Currently, silicon avalanche photodiodes are the only devices with acceptable performance. However, their wavelength is limited to below ~1000 nm, and the maximum array size is limited to a few tens of pixels per side. This is a new project. The idea is to create novel single photon detectors that can operate at wavelengths beyond the silicon limit. The novel device we are working on is based on a nano-transistor, and unlike avalanche detectors, will not produce any "excess noise." |
Novel Infrared Detectors: Infrared Detectors based on Type-II Superlattices:
 |
Motivation: type-II superlattices provide a unique opportunity to produce highly performance IR detector arrays in the long and very long wavelength IR (LWIR, VLWIR). Also, higher operating temperature is expected due to the low Auger recombination rate. Results: type-II superlattices with excellent structural, optical, and electrical quality have been grown. Some of the results shown here are: P-i-N photodiodes at a cutoff wavelength of 15.5 um showed background limited performance (BLIP) at nearly 60 K with a current responsivity of about 3.5 A/W. Devices for room temperature operation were designed. These devices showed a cutoff wavelength of about 9 um and a detectivity of 1.3E9 (cm.Hz^0.5/W) at room temperature. A wide wavelength tuning range was demonstrated by changing the layer thickness of the superlattices. The longest cutoff wavelength is more than 30 um. |
Electrooptical Modulators: High Performance Phase Modulators based on Stepped QWs:
Motivation: optical modulators are enabling technology for photonic systems. Although semiconductor-base modulators can be integrated with other photonic components, they have a low figure of merit due to the high loss and low electrorefraction.
Results: A novel quantum well was designed and optimized to enhance material electrorefraction at a low loss. Measured figure of merit is about one order of magnitude better than the best reported modulators.
Electrooptical Modulators: Highly Linear InP-based Phase Modulators:
Motivation: high linearity is a key feature required for analog photonic systems, such as analog RF photonics. Unlike lithium neobate, semiconductor modulators have a poor linearity which limits their performance for integrated photonics.
Results: a novel linearization method is developed.This method is only based on modification of the quantum wells and doping, and no feedback or feed forward signal is involved. Therefore, the speed of the device is not affected. Measured linearity is more than two orders of magnitude higher than the best reported devices, while the device maintains a very high efficiency.
Electrooptical Modulators: High-performance Surface-normal Modulators:
  |
Motivation: surface-normal modulators are attractive for a wide range of applications including optical computers, high density 2-D interconnects, ultra-low power free-space communication for mobile platforms, and optical tags. Results: novel stepped quantum wells are used to produce extremely efficient surface-normal modulators around 1550 nm. These devices are 5-6 mm wide and can be electrically tuned to operate over a 100C temperature range, and with a +/-60 degree field of view. They show higher efficiency, higher extinction ratio, and wider operating temperature than any reported surface-normal devices. |
Photonic Integrated Circuits and Nano-Photonics
Motivation: similar to electronic devices, integration will provide the ultimate functionality of the photonic systems. Integration is a mandatory step for realization of ultra-high capacity photonics with a very small footprint and low cost. High index contrast nano-photonics provide the necessary platform to manipulate light in micron range for a highly dense integration.
Photonic Integrated Circuits and Nano-Photonics: Arrayed Waveguide Grating (AWG) Based Multi-wavelength Lasers:
 |
Results: a novel integration method is developed. Active and passive photonic components can be integrated without regrowth. This reduces the cost significantly, as the process is much simpler than regrowth and has a potentially higher yield. As a proof of concept for this method, single-chip multi-channel (wavelength) lasers based on AWGs and SOA has been demonstrated. |
Photonic Integrated Circuits and Nano-Photonics: Chip-Scale Wavelength Division Multiplexing (WDM):
 |
Results: deeply etched submicron waveguides are used to produce integrated multi ring-resonators that are individually tunable. Independent modulation of each WDM channel was demonstrated. |
Photonic Integrated Circuits and Nano-Photonics: High Index Contrast Nano-Photonics:
 |
Results: ultra-low loss deeply-etched waveguides with electrical contacts were demonstrated. Nano-ring resonators with a very small diameter showed a quality factor Q of ~100,000. A ring-resonator with such a high quality factor provides an electrically tunable filter with FWHM of only a few gigahertz, a very high tuning speed, and an extremely small footprint. Many other interesting photonic components such as highly dispersive waveguides, single-mode lasers, and high-order filters can be realized with this deeply-etched semiconductor platform. |