Book Description
The goal of the proposed research is to develop new photodetectors that are capable of high power operation at high frequencies for microwave fiber optic link applications. Conventional high frequency photodetectors have low saturation power because of the small absorption volume required to reduce transit time and parasitic capacitance. We have proposed a novel velocity-matched distributed photodetector (VMDP) that can achieve high bandwidth and high saturation power simultaneously. During the performance period, we have successfully demonstrated three generations of long-wavelength VMDP's operating at 1.3 and 1.55 mm fiber optic communication wavelengths. The VMDP consisting of metal-semiconductor-metal (MSM) photodiodes serially connected by an optical core optical waveguide and an coplanar strip microwave transmission line that is velocity-matched to the optical waveguide. The MSM phodiodes have been patterned by both optical and e-beam lithography. We have demonstrated a bandwidth of 18 GHz and a quantum efficiency of 0.42 A/W. The maximum linear photocurrent measured is 12 mA. The distribution of photocurrents inside the VMDP has also been measured using a novel split contact structure. Test patterns on nanoscale MSM photodiodes show a bandwidth> 50 GHz (measurement limit). The research results achieved in this program has been transferred to TRW, Focused Research, and BAE. TRW has provided additional funding for transfer the technology to TRW. Focused Research has obtained a Phase II SBIR to commercialize VMDP.
