NASA 1998 SBIR Phase I


PROPOSAL NUMBER: 98-1 26.01-6000

PROJECT TITLE: Large-Area Transmission-Line Resonant Optical Cavity Photodiodes

TECHNICAL ABSTRACT (LIMIT 200 WORDS)

Spire proposes to make resonant optical cavity (ROC) photodiodes shaped in the form of a transmission line with an upper transparent conductor plate, incorporating the photodiode junction capacitance as part of the transmission line, lowering this limit to the photodiode speed. The goal is to achieve a very high-speed (~32GHz), large-area detector (>1 sq. mm). Currently, high speed photodiodes are restricted to very small areas (~50 micron diameters) to limit their capacitance and RC time constant. Photodiode speed is then limited by photogenerated carrier transit time through the diode space-charge region (SCR). Photodiodes with resonant optical cavities (ROCs) address this limitation. Their short SCRs have faster transit times while the ROC allows several light passes through the SCR, maintaining good quantum efficiency even with short SCRs. Unfortunately, the shorter SCR also means ROC photodiodes have higher capacitance than photodiodes with long SCRs. The proposed transmission- line ROC photodiodes (T-ROCs) should overcome this RC limitation, since the distributed photodiode capacitance and transmission line inductance balance each other, resulting in only a transit-time limit on the photodiode speed.

POTENTIAL COMMERCIAL APPLICATIONS

The proposed large-area high-speed T-ROC photodiodes are a unique product that can greatly aid optical communication system robustness and lower cost by reducing the required optical coupling precision to a high-speed photodiode. Such photodiodes now have diameters of ~50 microns, where as the proposed T-ROC photodiodes could have diameters of >1 mm while maintaining a high speed.

NAME AND ADDRESS OF PRINCIPAL INVESTIGATOR

Steven J. Wojtczuk, Ph.D.
Spire Corporation
One Patriots Park
Bedford , MA 01730-2396

NAME AND ADDRESS OF OFFEROR

Spire Corporation
One Patriots Park
Bedford , MA 01730-2396