New frequency stabilization method of a semiconductor laser using the Faraday effect of the Rb absorption line

We normally apply a precise amount of electrical. feedback into the laser injection current, to stabilize the oscillation frequency of a semiconductor laser. This feedback method usually needs 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, benefit from, and in fact require narrower oscillation linewidth. We obtain the error signal, and stabilize the laser oscillation frequency in narrower oscillation linewidth, using the Faraday effect of the Rb absorption line. Our next task involves frequency-stabilization, which we accomplish, using a large frequency discrimination gain (G(d)). By incorporating our "PEAK" circuit, which utilizes the envelope detection method to determine the switching points between two different absorption signals corresponding to the different magnetic fields and different polarization conditions, we increases the G(d) in our stabilization system.