Frequency Stabilization of a Semiconductor Laser by Moditied Direct FSK Using the PEAK Method

We stabilized the oscillation frequency of a semiconductor laser under direct FSK. The frequency stabilization of a semiconductor laser under direct FSK is difficult because of its unavoidable sideband spectra. Therefore, we have devised the peak-hold method and improved the frequency stability under direct FSK. However, a direct rectangular wave modulation of the injection current of a semiconductor laser does not provide the complete FSK in some modulation frequencies because of the frequency chirping effect. Therefore, we modified the rectangular wave modulation and obtained the better FSK signal. We also report this better FSK signal improves both the frequency stability and frequency deviation.