Rhode Island Board of Education, State of Rhode Island and Providence Plantations

Gerald Hefferman

Tao Wei

Zhen Chen

The present disclosure provides a novel distributed coaxial cable strain sensor that can measure a strain profile over the entire length of a cable. Individual strain sensing elements are constructed using Fabry-Perot interferometers, coaxial cable Bragg gratings, or other reflectometry-based sensing structures. By assembling three or more strain sensors together in a bundle, a coaxial cable shape sensing device can be constructed which is capable of accurate three dimensional position measurement.

Coaxial cable sensor device for distributed strain measurement and shape sensing applications

The present disclosure provides methods and apparatus to improve the dynamic coherent length of a sweep velocity-locked laser pulse generator (SV-LLPG) in an all-electronic fashion. A digital SV-LLPG is disclosed with two operation modes, i.e., unidirectional and bidirectional sweep modes; self-adaptive and time-dependent loop parameters (gain and location of poles/zeros); and, self-adaptive initial input curve. High frequency locking architectures, both single-side band (SSB) modulation method and direct phase measurement method, are provided to suppress the linewidth, or improve the coherent length, of the swept laser. A combination of high and low frequency locking, or a combination of multiple architectures disclosed in this invention, is utilized to achieve a higher level of linewidth reduction. The enhanced laser coherence extends the measurement range by at least one order of magnitude for applications including frequency-modulated continuous wave (FMCW) light detection and ranging (LiDAR) and optical fiber distributed sensing applications.

Method and apparatus for coherence enhancement of sweep velocity locked lasers via all-electronic upconversion

The present disclosure provides a novel fiber optic sensing device using ultra-weak, terahertz-range reflector structures. A fiber optic sensor device for distributed measurements (strain/temperature) includes an optical fiber detection arm having an inner core extending along a length of the optical fiber, an outer cladding surrounding the inner core, and at least one ultra-weak, terahertz-range reflector structure. Each reflector structure is comprised of two or more ultra-weak range reflectors (gratings) written at a spacing corresponding to the terahertz range and formed along a length of the inner core of the optical fiber. A narrow bandwidth, tunable laser interrogation system interrogates the optical fiber and measures changes in reflections and interference patterns caused by physical changes in the optical fiber.

Weak reflection terahertz fiber optic devices for distributed sensing applications

The present disclosure provides a sweep velocity-locked laser pulse generator (SV-LLPG) controlled using a digital phase locked loop (DPLL) circuit. The SV-LLPG is utilized for the interrogation of sub-terahertz-range fiber structures for sensing applications that require real-time data collection with mm-level spatial resolution. A laser generates chirped laser pulses via injection current modulation and a DPLL circuit locks the optical frequency sweep velocity. A high-quality linearly chirped laser pulse with a frequency excursion of 117.69 GHz at optical communication bands using a distributed feedback laser is provided.

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Warwick, RI, United States of America

Gerald Hefferman