Fiber-optic sensor using an injection-locked local laser

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Abstract
An interferometric fiber-optic sensor using a local laser is proposed. An Er-doped-fiber ring-laser is injection locked to a signal carrier using a fiber coupler, and the extracted carrier is directly homodyned with the signal light at the output of the coupler. With a feedback loop suppressing the local laser instability, demodulation linearity over two decades and minimum detection in the 10/sup -3/ rad range are attained. The Er-doped fiber ring laser constructed for this work has a linewidth of less than 1.4 kHz. Acceptable signal frequency ranges and the linearity and sensitivity of the proposed sensor are examined. Also discussed is the applicability of this configuration to simple, long-spanned sensors.