研究目的
To characterize the Allan deviation and phase noise of the beat note generated using different pairs of highly coherent lasers for phase-sensitive optical distributed sensing applications.
研究成果
The EOM-facilitated heterodyning technique allows for accurate measurements of instantaneous laser linewidths and frequency drifts, confirming that Φ-OTDR performance at kilohertz repetition rates is mostly limited by the Lorentzian laser linewidth. The technique is suitable for benchmarking highly-coherent lasers for integration into Φ-OTDRs and other interferometric optical sensors.
研究不足
The measurements are limited by the frequency stability of the ESA time base and the electronics noise of the amplified detector and spectrum analyzer. The technique's ability to measure Lorentzian linewidth is limited to 100 Hz due to electronic noise.
1：Experimental Design and Method Selection:
The study employs a new heterodyning scheme facilitated by an electro-optic modulator (EOM) to measure the Allan deviation and phase noise of beat notes from highly coherent lasers. The methodology includes theoretical models for laser phase noise and spectral analysis.
2：Sample Selection and Data Sources:
The study uses several ultra-narrow linewidth lasers of different types, including diode lasers with external WGM micro-resonators and planar waveguides, and fiber lasers.
3：List of Experimental Equipment and Materials:
Equipment includes a zero-chirp intensity modulator (Oclaro Powerbit SD-40), a radio frequency generator (Hewlett Packard synthesized signal generator 8672A), a fast InGaAs amplified detector (Tektronix Optical Receiver System ORS20), and an 8 GHz Rhode and Schwartz FSW-8 Electronic Spectrum Analyzer (ESA).
4：Experimental Procedures and Operational Workflow:
The output of the laser under test is combined with a reference laser using a beam splitter, directed to the EOM, and then analyzed using the ESA in quadrature analysis mode. The beat note signals are processed off-line using MATLAB software.
5：Data Analysis Methods:
The Allan variance and phase noise power spectral density (PSD) are calculated from the recorded ESA I/Q data. The phase noise PSD is calculated using detrended phase processing.
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