Demodulation of DBR Fiber Laser Sensors With Speckle Patterns

A multimode fiber (MMF) speckle pattern is proposed to demodulate a distributed Bragg reflector (DBR) fiber laser sensor. DBR light source emits a highly coherent laser, and the speckle pattern is caused by intermodal interference in the MMF. The speckle change induced by salinity and temperature is identified using the image correlation algorithm through the alteration of the speckle pattern. Zero mean normalized cross correlation (ZNCC) is used to process the speckle data, and the test range was extended by adjusting the reference speckle. In the temperature range of 25 °C–75 °C and 75 °C–100 °C, the speckle sensitivity is −0.0150/°C and −0.0148/°C, respectively. The salinity sensitivity is −0.0158/ ‰, compared with nearly no spectrum shift in the optical spectrum analyzer (OSA) under the same conditions. The proposed sensor can be applied in environmental monitoring and other fields.