Experimental Studies On Active Frequency Stabilization Technique For Distributed Feedback Laser Diodes

Distributed feedback semiconductor laser（DFB-LD）has become a popular optoelectronic device in laser application field because of its advantages of direct high speed modulation,low cost and mass production.However,the output optical frequency of DFB-LD is easily affected by operating temperature and noise of injected current,and there is usually a frequency drift of several hundred MHz in operation,which limits the application of DFB-LD.Therefore,it is significant requirement to keep DFB-LD with high frequency stability.The work of frequency stability for the DFB-LD in 1.5μm band is described as follows.（1）Based on reviewing the research status of active frequency-stabilized semiconductor lasers and various frequency-stabilizing systems,a closed-loop DFB-LD frequency-stabilizing drive circuit is designed by the absorption spectrum frequency-stabilizing technology to achieve DFB-LD frequency stabilization.（2）Using the principle of side-frequency locking,a frequency stabilization system based on analog circuit is built.In the frequency stabilization system,（1）the custom low-pressure H¹³C¹⁴N gas cell（2.4 Torr）is used as the frequency reference,（2）the analog divider is used instead of the conventional subtractor to generate a high-sensitivity frequency discrimination signal,（3）the DFB-LD,drive circuit and frequency stabilization photoelectric feedback circuit are integrated into the frequency stabilization drive circuit integration module,which greatly improves the frequency stabilization effect.The above three points are also the three novelties of the frequency stabilization system scheme in this paper.（3）In order to quantitatively characterize the frequency stability of the DFB-LD frequency stabilization system in the closed loop,the beat signal is produced by mixing the fiber femtosecond optical frequency comb with our stabilized DFB-LD.The results show that the second level frequency stability of the output light of stabilized DFB-LD at the wavelength of 1548.958 nm is 2.34×10^-10.Compared with the second level frequency stability of 3.67×10^-8 before frequency stabilization,it is improved by two orders of magnitude,and the goal of frequency stabilization of DFB-LD is realized.