New Frequency Stabilization Method of a Semiconductor Laser Using the Faraday Effect of the Rb-D2 Absorption Line

Abstract

We have applied a precise amount of electrical feedback into laser injection current to stabilize the oscillation frequency of a semiconductor laser. This feedback method usually requires a small direct modulation to the laser injection current to obtain an error signal. This broadens the oscillation width of the laser diode, but certain applications, such as those related to coherent optical communications and measurements, require a narrower oscillation linewidth. Thus, we have attempted to obtain the error signal and stabilize the laser oscillation frequency in a narrower oscillation linewidth using the Faraday effect of the Rb absorption line. Our next task for the Faraday-effect-based method involves frequency stabilization, which we accomplish using a large frequency discrimination gain Gd. By incorporating our “PEAK” circuit, which utilizes the envelope detection method to determine the switching points between two different absorption signals, we increase Gd in our improved PEAK methods.