Research On Narrow Linewidth Semiconductor Lasers

In recent years, the semiconductor laser develops rapidly. For its high reliability, longlife, low cost, small in size, high performance, it’s widely used on the optical fiber sensing,optical communications, radar and so on. Generally semiconductor laser linewidth reaches afew hundred KHz and its phase noise is very high, which limits application in all fields. Soreduction of laser linewidth becomes the focus of research. To get the stable power andnarrow linewidth, the design need have good drive circuit, well structure, and reduce phasenoise, frequency noise. This paper mainly devotes to the research of laser drive circuit andnarrow linewidth, simultaneously conducted a series of theoretical and experimentalresearch.The main content of this article is as follows:1. The current situation of the semiconductor lasers development, working principleand working characteristic were described. The methods of narrow linewidth laser weresummarized.2. Temperature control methods was put forward by analyzing the temperatureproperties of semiconductor lasers. The system used temperature control chip LTC1923todrive H bridge circuit. Working principle is through changing the direction of the current tocontrol the temperature of the laser. In order to guarantee the temperature stability,difference signal amplify was added to the circuit. Through the PID control output signal torealize refrigeration and heating.3. The ways of laser power control were proposed. Comparing temperaturecompensation with automatic power control, the system chose the last. We test the laserlong-term stability at the condition of room temperature and changed temperature. Theexperiment results showed that the output power of laser was stable, and stability is0.1%.4. A stable narrow linewidth structure based on electronic feedback was raised. Thismethod used the π-PSG as frequency discriminator. The feedback signal was injected intothe photoelectric detector, and compared with internal signal of laser. The difference signalthrough loop filter was feed into laser. The key of this method is the design of loop filter andselection of frequency discriminator. In order to restrain the ripple of the difference signal,the experiment used three order passive loop filter, and choose π-PSG as frequencydiscriminator. The linewidth after adding electronic feedback was0.08nm, which comparedwith the input laser, linewidth was reduced significantly.