The Developing Of Light Source And Receiver In Continuous Variable Coherent System

The secret channel of classical communication based on mathematics can be safeunder conditions, whereas quantum cryptography communication based on thequantum mechanics principle is absolutely safe, which core part is quantum keydistribution. Continuous variable quantum key distribution with characteristics ofsimple equipment and higher channel capacity has become a hot topic. This paper iscommitted to study the laser light source and receive cell circuit of continuousvariable coherent system, in order to satisfy the need of the research of continuousvariables quantum key distribution. Main contents are as follows:This paper briefly introduces the continuous variables coherent light experimentscheme and light modulation principle about existed light modulation equipments,and analyzes the method of balanced homodyne detection, but also introduces thereceiver system of data acquisition and control designed by virtual instrument.Laser light part adopts domestic semiconductor lasers AL0808T500to outputhighly stable coherent light. The stability of power output depends on injectioncurrent and working temperature two factors. Drive current source can output stabilitydegree0.012%current by using current series negative feedback technology. Withcooling device, temperature control circuit used proportion integral (PI) algorithm canmake laser output stability degree than0.06%within four hours. The drive not onlyuses single-chip microcomputer control and DVM display, but also uses a seriescircuit protection for laser.Receiving cell circuit consists of two parts: the piezoelectric ceramics (PZT)driving power which is used to control phase synchronization and coherent lightreceiving circuit improvement. According to the characteristics of domestic PZTdisplacement, the type of driving power is designed by DC amplifier, a low-pass filteris used to improve the stability of output voltage, and photoelectric isolating devicefor used to protect acquisition card and computer. The static ripple voltage of drivepower is less than45mV. The mechanical component of PZT phase shift is used toimprove the telescopic performance, and the relationship between input voltage anddisplacement is measured. On the improvements of coherent light receiving circuit, photoelectric diodeS1223-01is used to increase effective photosensitive area, in order to reduce thespace alignment difficulties; active band-pass filters is used to extract carrier, so thatthe signal-to-noise ratio can reach60dB; In the same sampling rate, a distortion of thediode envelope demodulation inert is adopted, improved the circuit to collect the dataof precision. A simple process of gathering information can effectively restoreinformation. The experimental BER was below0.1%. The improved circuit can beused to apply to the joint experiment measurements of amplitude modulation andphase modulation.