Wavelength Stabilization and Control of a Semicondutor Laser Using the Faraday Effect and Saturated Absorption Spectroscopy

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The frequency stabilization of a semiconductor laser using a saturated absorption line of atoms of morecules has been performed usually by applying a small modulation directly to the injection current. We demonstrated a few frequency stabilization methods without a direct small modulation, i.e., without a frequency broadening, here. We applied both biased and modulated magnetic fields to the Rb atoms and modulated the absorption and refractive index profiles by the Zeeman and the Faraday effects. These modulated absorption and refractive index profiles provide the modulated transmitted light intensity signal as an indirect modulation signal for obtaining a control signal. This cintrol signal is fedback to the injection current for stabilization. The method using the Faraday effect provided the better stability than the direct modulation method in a certain modulation condition in our optical setup. We also investigated two other optical setups which used the Faraday or the Zeeman effects for applying the indirect modulation and confirmed the superiority of these indirect modulation methods over the direct modulation methods in the stability and the spectral width. These indirect modulation methods provided not noly the good stability and the narrow oscillation bandwidth but also the frequency controlability within the absorption spectrum range by changing the biased magnetic field strength which is used for improving the frequency stability.