Optical fiber strain sensor system and method

An optical fiber strain sensor system comprising:

• a signal generator that generates a modulated electrical signal;
• a first light source that receives the modulated electrical signal and produces a first modulated optical signal having a first phase;
• a second light source that receives the modulated electrical signal and produces a second modulated optical signal having the first phase;
• at least first and second optical fibers, wherein at least the second optical fiber is fixedly secured at multiple locations along the second optical fiber to a structure;
• an optical coupler that receives the first and second modulated optical signals and couples the first and second modulated optical signals into first ends of the first and second optical fibers, respectively;
• a three-dimensional (3-D) pixel sensor having at least first and second pixels, the first and second modulated optical signals passing out of second ends of the first and second optical fibers, respectively, and being received by the first and second pixels, respectively, and being converted by the first and second pixels into first and second electrical sense signals, respectively, the first and second pixels having first and second pixel circuits, respectively, the first and second pixel circuits receiving a clock signal that is used by the signal generator to generate the modulated electrical signal, the first and second pixel circuits cross-correlating the clock signal with the first and second electrical sense signals to produce first and second cross-correlation results, respectively;
• an analog-to-digital converter (ADC) that receives at least the first and second cross-correlation results and converts the first and second cross-correlation results into first and second digital cross-correlation results, respectively;
• and
• phase difference determination logic that receives at least the first and second digital cross-correlation results from the ADC, the phase difference determination logic processing at least the first and second cross-correlation results to determine changes in the phases of the first and second optical signals, respectively, and to determine, based on the changes in the phases of the first and second optical signals, changes in lengths of the first and second optical fibers, respectively, and wherein the change in the length of the second optical fiber is indicative of stress or strain in the structure to which the second optical fiber is secured.

A method for using an optical fiber to measure strain or stress in a structure, the method comprising:

• with a signal generator, generating a modulated electrical signal;
• driving at least a first light source with the modulated electrical signal to cause the first light source to produce a modulated optical signal having a first phase;
• with an optical coupler, coupling at least a measurement optical signal portion of the modulated optical signal into at least a first end of a measurement optical fiber, the measurement optical fiber being secured at multiple locations of the measurement optical fiber to a structure;
• in a three-dimensional (3-D) pixel sensor, receiving the measurement optical signal portion passing out of a second end of the measurement optical fiber on a first pixel of the 3-D pixel sensor;
• with the first pixel, converting the measurement optical signal portion into a first electrical sense signal;
• in a first pixel circuit of the first pixel, receiving a clock signal used by the signal generator to generate the modulated electrical signal and cross-correlating the clock signal with the first electrical sense signal to produce a first cross-correlation result;
• converting the first cross-correlation result into a first digital cross-correlation result;
• and
• in phase difference determination logic, processing at least the first digital cross-correlation result to determine a change in the phase of the measurement optical signal and to determine, based on the change in the phase of the measurement optical signal, a change in a length of the measurement optical fiber, and wherein the change in the length of the measurement optical fiber is indicative of stress or strain in the structure to which the measurement optical fiber is secured.

A method for using an optical fiber to measure strain or stress in a structure, the method comprising:

• with a signal generator, generating a modulated electrical signal;
• driving at least first and second light sources with the modulated electrical signal to cause the first and second light sources to produce first and second modulated optical signals, respectively, the first and second optical signals having a first phase;
• with an optical coupler, coupling the first and second modulated optical signals into first ends of the first and second optical fibers, respectively, wherein at least the second optical fiber is fixedly secured at multiple locations along the second optical fiber to a structure;
• in a three-dimensional (3-D) pixel sensor, receiving the first and second modulated optical signals passing out of second ends of the first and second optical fibers, respectively;
• with a first pixel of the 3-D pixel sensor, converting the first optical signal into a first electrical sense signal;
• with a second pixel of the 3-D pixel sensor, converting the second optical signal into a second electrical sense signal;
• in a first pixel circuit of the first pixel, receiving a clock signal used by the signal generator to generate the modulated electrical signal and cross-correlating the clock signal with the first electrical sense signal to produce a first cross-correlation result;
• in a second pixel circuit of the second pixel, receiving the clock signal used by the signal generator to generate the modulated electrical signal and cross-correlating the clock signal with the second electrical sense signal to produce a second cross-correlation result;
• converting the first and second cross-correlation results into first and second digital cross-correlation results, respectively;
• and
• in phase difference determination logic, processing at least the first and second cross-correlation results to determine changes in the phases of the first and second optical signals, respectively, and to determine, based on the changes in the phases of the first and second optical signals, changes in lengths of the first and second optical fibers, respectively, and wherein the change in the length of the second optical fiber is indicative of stress or strain in the structure to which the second optical fiber is secured.