Research On Differential Phase-Shift Keying Demodulator Based On Delay-Interferometer

Laser communication links between satellites, which adopts laser as the information carrier wave, is a promising solution for the increasing requirements of higher data rate and capacity as an alternative to conventional microwave. Satellite optical terminals possesses the advantages of less volume and better security. Hence laser communication technology is an attractive method to establish satellite links. Since last century 60th the satellite laser communication has been researched in countries, including America, Japan, Germany, France and so on. Space experiments have been performed for intersatellite and satellite-to-ground link. And these countries are preparing to promote this technology to commercialization.Optical communication scheme based on differential Phase-Shift Keying(DPSK)modulation/demodulation technology has already commercially applied to ground fiber communication systems. Comparing with intensity modulation/direct detection (IM/DD), for the same desired BER the required optical signal-to-noise ratio (OSNR) would be 3dB less, which means the receiver sensitivity increasing 3dB more. DPSK system has high sensitivity, which can compare with coherent detection, relatively simple configurations and especially large channel capacity by adopting dense wavelength division multiplexing technology (DWDM). Therefore, DPSK is one of the most promising ways to approach high speed and large capacity satellite laser communication.The DPSK method is achieved by comparing the phase two sequential bits, which needs to be transferred into intensity information through the demodulator before direct detecting. The DPSK demodulation technology is one of the critical technologies for DPSK communication systems. Prior typical demodulator method is 1bit delay interferometer based on all fiber or plane waveguide technologies, which have some disadvantages including temperature sensitivity and unstable output characteristics. In this paper two kinds of temperature-stability delay interferometer are proposed, and major work includes:First the principle of DPSK demodulator is introduced and mathematical analysis is also reviewed.The demodulator method of an double-core fiber Mach-Zehnder interferometer is proposed, whose temperature characteristic is studied theoretically.The demodulator method of an Michelson interferometer based on space delay line is proposed. The theoretical analysis of related parameter is given, and the demodulator is developed. The characteristic of this demodulator is exhibited according to the experimental data. Results show that this kind of demodulator owns outstanding advantages comparing to the existent equipments. A set of back-to-back DPSK modulate/self-homodying system, in which the proposed demodulator is applied, has been conducted with demodulating rate of 40Gbps. The eye graph shows comparative advantages with abroad experiments.The subject studies in this paper can benefit the DPSK modulate/self-homodying system, and would be helpful to the ground fiber DPSK communications.