23 March 2005 Oscillation frequency stabilization of a semiconductor laser using the Faraday effect of Rb absorption lines and the double optical feedback
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Currently in the initial stages of development, the endeavor aims to use satellite-to-satellite tracking laser interferometer-based optical technique, to document fluctuations in earth’s gravitational field indicating other critical changes in the environment. This system must be able to measure infinitesimal changes in the relative velocity of the two satellites, using a laser light source, which oscillates at frequency stability better than 10-13 in the square root of the Allan variance. We have stabilized the laser’s oscillation frequency using the Faraday effect of Rb absorption lines. This method modulates the reference frequency of the stabilization system by modulating the magnetic field applied to the Rb absorption cell, instead of the oscillation frequency of the laser diode. Furthermore, we have adapted the “double optical feedback” to the laser diode for narrowing its oscillation spectrum and improving its frequency stability. In recent years, a “femtosecond optical comb generator” has been developed as a new reference frequency source for absolute frequency measurement. This optical comb generator is controlled by the microwave frequency standards systems and provides stability of 4x10-13 at an averaging time of 1s and at the order of 10-15 at 1000s averaging time. We have measured the frequency stability of our system using the optical comb. We obtained the best spectrum narrowing effect using two gratings as external reflectors in the double optical feedback setup. The obtained results were 6.269x10-11 ≤ σ ≤ 1.516x10-10 (24.11kHz ≤ f ≤ 58.31kHz) from 1s to 39s in the averaging time.
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Hiromichi Kobayashi, Toshiya Nimonji, Shinya Maehara, Takashi Sato, Masashi Ohkawa, Takeo Maruyama, Taizoh Yoshino, Hiroo Kunimori, Mizuhiko Hosokawa, Hiroyuki Ito, Ying Li, Shigeo Nagano, Seiji Kawamura, "Oscillation frequency stabilization of a semiconductor laser using the Faraday effect of Rb absorption lines and the double optical feedback", Proc. SPIE 5710, Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications IV, (23 March 2005); doi: 10.1117/12.590396; https://doi.org/10.1117/12.590396

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