Experimental Investigation of Power Distribution in Distributed Balanced Photodetectors

A distributed balanced photodetector with high saturation photocurrent and excellent linearity has been experimentally demonstrated. Distributed detection is shown experimentally to be important for the high saturation photocurrents. High-speed photodetectors with high saturation photocurrents are essential for high performance analog fiber optic links. In externally modulated links, the link gain, noise figure, and spurious free dynamic range (SFDR) improve with increasing optical power of the link [l]. This improvement will eventually be limited by the relative intensity noise (RIN) of the laser source and/or the amplified spontaneous emission noise (ASE) from erbium-doped fiber amplifiers (EDFA). It is known that the laser RIN and EDFA-added noise can be suppressed by balanced receivers [2]. Therefore, balanced receiver with linear photocurrent under high input power is a critical component of highperformance analog fiber optic links. Previously, we reported a novel monolithic distributed balanced photodetector based on velocitymatch distributed photodetector (VMDP) structure [3]. Broadband (1 to 12 GHz) noise suppression has been achieved. The maximum noise suppression of 24 dB was observed at the relaxation oscillation frequency of the laser [4]. However, the maximum DC photocurrent was limited to 12 mA. In this paper, we report on an improved distributed balanced photodetector with continuous optical waveguide and strong optical confinement. It exhibits superior DC and AC linearity as well as maximum linear photocurrent. The distribution of photocurrents in distributed photodetector was also measured for the first time. The distributed detection is shown to be very important for high saturation photocurrent. This project was supported by Office of Naval Research under a MuRI on RF photonics, National Radio Astronomy Observatory and the University of California Microelectronics Innovation and Computer Research Opportunities (UC MICRO). The authors are with the Department of Electrical Engineering, 63128 Eng IV, University of California, Los Angeles, CA 90095, USA. Tel: (310) 794-9309, Fax: (310) 794-5513. e-mail:[email protected]. 'D. L. Sivco and A. Y. Cho are with Lucent Technologies, Bell Laboratories, Murray Hill, NJ 07974. 0-7803-5634-9/99/$10.00019999 IEEE 806 I Optkal waveguides veguide Optical Input