Proposal And Implementation Of A Frequency-Locked Scheme For Two Distributed Feedback Laser Diodes With High Stability And Wide Bandwidth

Realization of high-precision time-frequency transfer system has been one of theimportant topics. Also it is one of the key techniques in our nation’s BeiDou navigationsystem. At present, fiber based DWDM (Dense Wavelength Division Multiplexing)bi-directional time-tranfer scheme due to its high-precision, high-stability and stronganti-interference attracts quite a lot of research attention. However, the lasers’ outputfrequency stability is vulnerably affected by the accuracy of their injection current andtemperature controlling. Besides, the signal transmission for the fiber dispersive effectinduces different dispersive delay results. Therefore the relative drift between the lasers willresult in transmission delay variance, which affects the resulting time delivering precision.This thesis proposed and realized a scheme to lock the frequency difference betweentwo distributed feedback (DFB) laser diodes with high stability. It can be used not only inthe DWDM fiber time delivery scheme but also in fiber-optic sensing field. The maincontent includes the following aspects:(1) The basic principle of the semiconductor laser is presented. The effects of currentand temperature on the stability of a single laser driving circuit are investigated. A singleDFB laser’s driving circuit is designed and realized. The stabilities of its current andtemperature are tested. The experiment result shows that the single laser’s outputwavelength has a well stability. Based on this, two DFB lasers with independent drivingcircuits are preliminarily tested for the feasibility of frequency locking.(2) The factors determining the jitter of the beating frequency are analyzed, and thepreliminary frequency locking circuit is optimized. A frequency locking feedback ring issetup based on LabVIEW software so as to implement coarsely and finely tuning one of thelaser’s temperature and current by proportional-integral-derivative (PID) control algorithm. The experimental result indicates that the net difference of the two lasers’ outputfrequencies can be locked with high stability in the wide frequency range of from50MHzto11GHz. The two-hour measurement shows that the RMS is below5MHz, whichapproaches the theoretical estimation that the beating frequency accuracy is limited by thelasers’ linewidth.