| Research Abstract |
The current optical communication systems are using the intensity modulation method, but it will be difficult for this method to handle the high speed and large capacity communication needs in the near future. We intended to develop the optical frequency modulation method for the next generation systems. This needs the frequency stabilization of a semiconductor laser. So, we stabilized the oscillation frequency of a semiconductor laser under the direct frequency shift keying (FSK) using the Rb-D2 absorption lines at 780 nm wavelength. The high frequency stability was obtained in the PEAK method, which is the system using the simple envelope detection circuit, under the direct FSK. We, then, investigated the stabilization method applicable to 1.5 μm wavelength for the optical communication systems. We intended to use the inner second harmonic generation (SHG) of the semiconductor laser to get the control signal for the frequency stabilization, because this SHG wavelength is around 780 nm. We also tested how to use two frequency references, I.e., the Rb-D2 absorption line and an etalon, for Stabilizing the 1.5 μm wavelength semiconductor laser, because they have different and supplementary characteristics as a frequency reference. We finally investigated the estimation method of the frequency stability using the beat note between two laser frequency.
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