Excellent Linearly Frequency-Swept Light Source for Sensing System Utilizing FMCW Technique (Special Issue on Electromagnetic Theory)

概要

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We propose and demonstrate an excellent linearly frequency-swept laser diode (LD) for sensing system utilizing frequency-modulated continuous-wave (FMCW) technique. In order to linearly sweep the optical frequency, we adopt a reference interferometer and an electric phase comparator. The interference beat signal of the reference interferometer is phasecompared with an external reference rectangular signal having a fixed frequency near the interference beat signal ferquency by a lock-in amplifier. The error signal from the lock-in amplifier is fed back to the modulating signal of the injection current of the LD. Thus, a phase-locked loop composed of optical and electric circuits can be established, and the beat signal frequency is locked to the frequency of the reference signal. The optical frequency of the LD is, therefore, excellently linearly swept in time. In order to experimentally confirm the linearlity of the proposed method, we apply this light source to the FMCW reflectometry. Resultingly, the improvement of the linearity is estimated to be about 10 dB. And the theoretically limited spatial resolution of the FMCW reflectometry is achieved.
社団法人電子情報通信学会の論文
1994-11-25