Ultrafast and Compact Fiber-Optic Temperature Sensor for Unmanned Underwater Vehicles

PI: Han, Ming (Michigan State University)
Co-PI(s): Hou, Weilin (Naval Research Laboratory – Stennis Space Center)
Start Year: 2019 | Duration: 3 years
Partners: Michigan State University, Naval Research Laboratory Stennis Space Center

Project Abstract:

Unmanned underwater vehicles (UUVs) are key enablers for current and future Naval operations. To gain undersea and maritime dominance, persistent sensing and situational awareness requires next generation sensors to advance the data to knowledge, and improve ocean forecast capabilities. Oceanic turbulence is key to material and energy transfer over all spatial scales, throughout the water column and at air-sea interface. Limitation in sensor response time and accuracy hinders our capability in adequately sampling in spatial and temporal domain. The goal of the research is to develop a field worthy, compact, ultrafast, standalone temperature sensor instrument for UUVs, capable of measurement at a sampling rate of 2 kHz and a resolution better than 1 mK or 0.001 °C (over the bandwidth between 1 Hz – 1 kHz). The finished sensor instrument will have a dimension of ~5′′(diameter) × 10′′(length), a weight of less than 5 lbs, and a depth rating of 500 m as initial configuration. The sensor is based on a silicon (Si) Fabry-Perot interferometer (FPI) attached at the tip of an optical fiber. The excellent thermal, mechanical, and optical properties of the sensor material and the small size of the sensor head afford us with a time constant of < 0.5 ms and a spatial resolution of < 0.1 mm in all three dimensions. This unprecedented temporal and spatial resolution will be sufficient to resolve both the smallest scales and highest frequencies contained in the temperature gradient field of ocean turbulence.

To achieve the research goal, we will execute the following research objectives: (1) design and fabricate Si-FPI temperature sensors with integrated fiber Bragg gratings for increased dynamic range; (2) design and develop miniaturized, high-speed spectrometers optimized for demodulation of the proposed sensors; (3) develop a circuit board and software for optical system control, power management, data acquisition, storage, and transmission; (4) design and develop a miniaturized and ruggedized package suitable for ocean deployment particularly for UUVs that can also be integrated into other configurations; (5) characterize and test the sensor instrumentation in the lab and outdoor environment; and (6) test the sensor package in the ocean by leveraging the cruise opportunities from ongoing NRL base programs.

The outcome of the project is a new generation of temperature sensor instrument suitable for ocean deployment with ten times improvements in measurement speed. The availability of such an instrument to oceanographers, especially naval researchers, will not only advance our modeling with better spatial and spectra information, but also improve sensor performance estimation of myriad Navy assets, especially those affected by thermal structures in the ocean such as acoustic color and scattering cross-section assessment. The faster sampling speed also allows quicker characterization with large coverage of the ocean field, which is critical for future autonomous sensing and decision making. Higher sampling rate also opens new opportunities to allow aerial-based sensing of the top ocean layers, and offer possible means of better wake detection.

BAA: N00014-18-S-B007