Reaserch On Photodetectors With Flat-Top And Steep-Edge Response For Wavelength Division Multiplexing System

Wavelength-division multiplexing which makes full use of fiber bandwidth can solve the transmitting deficiency problem of communication networks, and has wide promising prospect. Besides, in the aspects of network expanding, upgrading and the realization of ultra-high speed communications, WDM also has significant meanings. Photodetector is the key device of wavelength demultiplexing and receiving technology in WDM system. Photodetector with flat-top and steep-edge response can reduce the crosstalk between wavelengths and improve the rapidity and accuracy of channel optical detection. The key content of the paper is on photodetector with flat-top and steep-edge response. The research findings are as follows:1,Research on variable filter cavity length (RCE) photodetector indicates that the flat-top and steep-edge response can be realized by the filter cavity with two kinds of lengths and selection of appropriate lenghs. The principle and structure of dual-absorption (RCE) photodetector are discussed. Compared with conventional (RCE) photodetector,dual-absorption (RCE) photodetector has higher quantum efficiency.2,A RCE photodetector with flat-top and steep-edge response based on variable filter cavity and dual-absorption structure is designed. The flat-top and steep-edge response with high quantum efficiency is obtained by variable filter cavity with two different lengths and dual-absorption structure. The quantum efficiency and the effection of the critical parameters are analyzed. Simulation results show that the quantum efficiency value in bandpass are about 68%, the extent of flat top is about 0.38%; 0.5dB,3dB, and 20dB bandwidth are 0.1 nm,0.14nm, and 1.13nm respectively. The photodetector has high quantum efficiency, and good flat-top and steep-edge response.3,A circuit control method achieving the flat-top steep-edge response of photodetectors is researched. The response is realized using three wavelength selective photodetectors and the circuit which consists of amplifiers,comparators and a AND gate. The work principle of the circuit control method is detailedly analyzed and the design of the circuit is completed.4,Experimental verification of the circuit control method is carried out. In group 1, the flat-top steep-edge response is from 1546nm to 1549.3nm and 0.5dB,3dB,20dB bandwidths are 2.76nm,3.29nm, 4.58nm respectively. In group 2, the flat-top steep-edge response is from 1554.8nm to 1557.6nm and 0.5dB,3dB,20dB bandwidths are 3.19nm, 2.89nm,3.06nm respectively. The results of experiments show that the desirable flat-top steep-edge response can be gained.