Phase-contrast enhancements to a speckle based fiber optic sensor

Speckle based fiber optic sensors have been developed and used in laboratory and field settings for a number years. In the case of a speckle-based fiber optic vibration sensor, optical signal processing of the field emerging from a multimode fiber has been performed through the use of intensity modulating masks. In such cases, portions of the speckle pattern are not allowed to illuminate a photodetector thereby performing forms of statistical selection of modal patterns. While this technique is robust, it does inherently reduce the sensor's operational dynamic range, and signal-to-noise ratio, due to the simple fact that a portion of the light field is not used. By contrast, it is possible to use phase-contrast enhancing techniques found in microscopy to phase-modulate the fiber's speckle pattern. The performance of a multimode fiber optic sensor using these techniques is compared with the more traditional intensity-modulating fiber optic sensor.