Experiment Research On Drive And Measurement Of AL808T500 Type Semiconductor Laser Diode

Light source, modulator, fiber and photo-detect devices are absolutely necessary for optical communication system. Light source is the most important part of transmitter, which can produce carrier wave for optical communication system. Its specialty can directly affect the performance of communication system.The semiconductor laser is a kind of high power density device. A certain input current is corresponding to a certain output power, and the input current can directly affect the stability of output power, therefore it is an essential factor to design a certain control circuit with high stable constant current sources to guarantee the stabilities of light power. Besides this, constant temperature is also indispensable. Because when inject current is transited into heat, the temperature of LD will be uprising, thus the threshold current, V-I curve, output wavelength and P-I curve will change accordingly. This paper introduces the method of driving laser diodes with different encapsulation, based on the laser driver and laser temperature controller. The characteristics of L131T5m produced by HTOE corporation are: TO-5.6 encapsulation, wavelength 1310nm, output power 5mW; the characteristics of AL808T500 produced by AOE company are: TO-5 encapsulation, wavelength 808nm,output power 500mW. This paper also designs a device to simulate laser module, and supplies the module with constant temperature and constant current. In order to study and analyze the output light signal, we should firstly change it into electrical signal. The current device is photo-detector (PD). The common points of photoelectrical conversion are: the information is modulated on carrier wave through all kinds of domino effects (engine, thermal, sound, electronic, magnetic), and then demodulated, through this course we can realize photoelectrical conversion. Photoelectrical circuits are most important during the conversion. In practice applications, the photocurrent (or signal voltage) is very slight, which make the SNR is low accordingly, so it cannot be used in measurement and control. This paper studies the problems of amplifying the photo-current and restraining the noise. The designed detection circuits can efficiently monitor the power stability under automation temperature control (ATC).In optical communication, we should firstly solve the problem of adding the light signal on carrier wave, that is to say, light modulation. According to the relationships between modulation and light source, light modulation includes direct modulation and indirect modulation. The method of direct modulation is: change the ready information to current signal and then inject the LD or LED to obtain the corresponding light signal, thus the idea is source modulation. When directly modulating LD, it will present complicated transient characteristics: photoelectrical delay, surge, self-pulse and so on.This paper designs a kind of automation power control circuit (APC) to restrain the phenomenon of surge, and gives a theory analysis.Electronic noise is the fluctuation of LD voltage, also called TEN. It is caused by the fluctuation of charge carriers. We can monitor many parameters and characteristics by measuring TEN, such as surge frequency, spectrum width, threshold current, mode jump and stability of output light power. This paper studies and analyses TEN of 808nm high-power LD by noise measurement system. By the experiment we get the relationship of noise and frequency, relationship of noise and inject current.Experiment study on the drive and measure of different semiconductor lasers has active significance in optic-electronic techniques.