| High stability of semiconductor lasers have been shown useful in many applications areas, such as optical communication, high-resolution spectroscopy, quantum metrology, laser cooling and trapping. With the rapid development of fiber optic dense wavelength division multiplexing system, we require laser source with high frequency stability in 1.5μm band. In this paper we demonstrate a modulation-free frequency locking scheme based on acousto-optic frequency-shifting method. As a result, laser frequency of external-cavity semiconductor is locked to the acetylene transition.The primary content includes in the following aspects:Firstly, the principle and several common approaches of laser frequency locking are researched, Furthermore, the principle of modulation-free frequency locking based on acousto-optic frequency-shifting method is analyzed in detail, and the line broadening and how to choose the absorbing gas are also studied.Secondly, a complete laser frequency locking system based on acousto-optic frequency-shifted method is designed. The working principle of FBG external cavity semiconductor laser is described in detail. And focus on illustrating the frequency-shift characteristic of acousto-optic modulator. Gas cell suitable for system is studied. In addition, electrical devices used in system are briefly introduced, such as optical isolator, photodetector, preamplifier, differential amplifier and PID control which is achieved by computer.Finally, it is clear that temperature, cavity length and injection current have effects on frequency stability of FBG external cavity semiconductor laser by simulation experiments. Besides that, the frequency stabilization system is adjusted. Therefore, the frequency jitter spectra before and after locking are given and the experimental results are analyzed. The results show that after locking laser the typical frequency jitter is significantly improved comparing with frequency fluctuation in the condition of free running. |
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