Abstract: Apparatuses and methods for optical code-delay reflectometry (OCoDR) are disclosed. An apparatus includes a modulator, a receiver, and control circuitry. The modulator is configured to receive incident electromagnetic (EM) radiation at a substantially fixed frequency generated by one or more EM radiation sources. The incident EM radiation includes continuous-wave EM radiation. The modulator is configured to impart a sequence onto an amplitude, a phase, or both of the incident EM radiation to generate modulated EM radiation. The modulated EM radiation includes continuous-wave EM radiation. The receiver is configured to receive reference EM radiation. The receiver is also configured to receive reflected EM radiation from an optical system responsive to the modulated EM radiation and generate interfered EM radiation responsive to the reference EM radiation and the reflected EM radiation. The receiver is further configured to generate a continuous interferogram responsive to the interfered EM radiation.

Abstract: Apparatuses and methods for optical code-delay reflectometry (OCoDR) are disclosed. An apparatus includes a modulator, a receiver, and control circuitry. The modulator is configured to receive incident electromagnetic (EM) radiation at a substantially fixed frequency generated by one or more EM radiation sources. The incident EM radiation includes continuous-wave EM radiation. The modulator is configured to impart a sequence onto an amplitude, a phase, or both of the incident EM radiation to generate modulated EM radiation. The modulated EM radiation includes continuous-wave EM radiation. The receiver is configured to receive reference EM radiation. The receiver is also configured to receive reflected EM radiation from an optical system responsive to the modulated EM radiation and generate interfered EM radiation responsive to the reference EM radiation and the reflected EM radiation. The receiver is further configured to generate a continuous interferogram responsive to the interfered EM radiation.

Abstract: Multi-spectral feature sensing techniques and sensor and related digital signal processing circuitry and methods. A method of operating a digital signal processing circuitry includes acquiring optical frequency domain reflectometry (OFDR) data from an interferometer operably coupled to a tunable laser and a sensing fiber, separating sensor signals corresponding to sensors of the sensing fiber from the OFDR data, and inferring a relative shift of a separated sensor signal. A digital signal processing circuitry includes a front end circuitry and a back end circuitry. The front end circuitry is configured to isolate sensor responses from an input signal including OFDR data. The back end circuitry is configured to determine a phase shift corresponding to each isolated sensor response.

Abstract: The various embodiments described here comprise an OFDR system and technique that may be used for inference of strain or temperature over a large dynamic range using a narrow wavelength range. Embodiments of the sensor fiber may be composed of one or more multi-spectral-feature sensors, each sensor exhibiting several spectral features that together offer coverage over a wavelength range corresponding to the desired system strain and or temperature dynamic range.

Abstract: Various embodiments of sensors are described that exhibit several spectral features that together offer coverage of a wavelength range corresponding to the desired strain dynamic range (or temperature range) of a system. The spectral features arise from a Fabry-Perot interferometer formed by two overlapping chirped FBGs, the free-spectral range (FSR) of which varies with wavelength. The spectral features may be differentiated due to a combination of spacing and slope of the overlapped, chirped gratings.

Abstract: Multi-spectral feature sensing techniques and sensor and related digital signal processing circuitry and methods. A method of operating a digital signal processing circuitry includes acquiring optical frequency domain reflectometry (OFDR) data from an interferometer operably coupled to a tunable laser and a sensing fiber, separating sensor signals corresponding to sensors of the sensing fiber from the OFDR data, and inferring a relative shift of a separated sensor signal. A digital signal processing circuitry includes a front end circuitry and a back end circuitry. The front end circuitry is configured to isolate sensor responses from an input signal including OFDR data. The back end circuitry is configured to determine a phase shift corresponding to each isolated sensor response.

Abstract: Various embodiments of sensors are described that exhibit several spectral features that together offer coverage of a wavelength range corresponding to the desired strain dynamic range (or temperature range) of a system. The spectral features arise from a Fabry-Perot interferometer formed by two overlapping chirped FBGs, the free-spectral range (FSR) of which varies with wavelength. The spectral features may be differentiated due to a combination of spacing and slope of the overlapped, chirped gratings.

Abstract: A tunable laser system includes a tunable laser to be scanned over a range of frequencies and an interferometer having a plurality of interferometer outputs. At least two interferometer outputs of the plurality of interferometer outputs have a phase difference. A wavelength reference has a spectral feature within the range of frequencies, and the spectral feature does not change in an expected operating environment of the tunable laser. Processing circuitry uses the spectral feature and the plurality of interferometer outputs to produce an absolute measurement of a wavelength of the tunable laser and controls the tunable laser based on a comparison of the absolute measurement of the wavelength of the tunable laser with a setpoint wavelength.

Abstract: The various embodiments described here comprise an OFDR system and technique that may be used for inference of strain or temperature over a large dynamic range using a narrow wavelength range. Embodiments of the sensor fiber may be composed of one or more multi-spectral-feature sensors, each sensor exhibiting several spectral features that together offer coverage over a wavelength range corresponding to the desired system strain and or temperature dynamic range.

Abstract: A tunable laser system includes a tunable laser to be scanned over a range of frequencies and an interferometer having a plurality of interferometer outputs. At least two interferometer outputs of the plurality of interferometer outputs have a phase difference. A wavelength reference has a spectral feature within the range of frequencies, and the spectral feature does not change in an expected operating environment of the tunable laser. Processing circuitry uses the spectral feature and the plurality of interferometer outputs to produce an absolute measurement of a wavelength of the tunable laser and controls the tunable laser based on a comparison of the absolute measurement of the wavelength of the tunable laser with a setpoint wavelength.

Abstract: A tunable laser wavelength measurement system includes an interferometric wavelength tracking system that uses a combination of interferometric and wavelength reference measurements to directly measure the laser output wavelength, The measurement exhibits the following desirable error signal characteristics: directional information, continuity, low latency, absolute information, high accuracy, high precision, and little or no drift, A tunable laser wavelength control system additionally incorporates electronics to compare the measured laser wavelength to a desired wavelength or wavelength function, and to generate a feedback control signal to control the wavelength of the laser output based on the comparison. In one non-limiting example implementation, the desired wavelength function is repetitive.

Abstract: A tunable laser wavelength measurement system includes an interferometric wavelength tracking system that uses a combination of interferometric and wavelength reference measurements to directly measure the laser output wavelength, The measurement exhibits the following desirable error signal characteristics: directional information, continuity, low latency, absolute information, high accuracy, high precision, and little or no drift, A tunable laser wavelength control system additionally incorporates electronics to compare the measured laser wavelength to a desired wavelength or wavelength function, and to generate a feedback control signal to control the wavelength of the laser output based on the comparison. In one non-limiting example implementation, the desired wavelength function is repetitive.

Abstract: The technology described here enables the use of an inexpensive laser to measure an interferometric response of an optical device under test (DUT) at reflection lengths significantly greater than the coherence length of the laser. This is particularly beneficial in practical interferometric applications where cost is a concern. In other words, inexpensive lasers having shorter coherence lengths may be used to achieve very high interferometric measurements at longer DUT reflection lengths. The technology also enables the use of such inexpensive lasers to measure Rayleigh scatter in commercial-grade, single-mode optical fiber.