Some embodiments of the disclosure provide a demodulation system for obtaining phase change parameters by a fiber-optic Fabry Perot sensor. In an embodiment, the demodulation system includes a transmitting module, a fiber-optic Fabry Perot sensor, a light splitting module, a filter module, a receiving module, and a processing module. The transmitting module transmits a beam with a predetermined wavelength range. The fiber-optic Fabry Perot sensor receives the beam and forms a reflected light beam. The light splitting module is arranged between the transmitting module and the fiber-optic Fabry Perot sensor. The filter module obtains the first light beam, the second light beam, and the third light beam. The filter module has a broadband filter. The receiving module receives the first light beam, the second light beam, and the third light beam and converts them into the first signal, the second signal, and the third signal.

An optical sensor readout Interrogates an optical sensor and includes: a microcavity sensor that receives an optical frequency comb, produces a post-sensor optical frequency comb from the optical frequency comb based on a physical perturbation subjected to the microcavity sensor, and communicates the post-sensor optical frequency comb to a photo detector; an electro optic modulator in optical communication with the microcavity sensor and that receives input light and a radiofrequency drive signal, produces the optical frequency comb from the input light based on the radiofrequency drive signal, and communicates the optical frequency comb to the microcavity sensor; and the photo detector in optical communication with the microcavity sensor and that: receives the post-sensor optical frequency comb from the microcavity sensor; receives frequency shifted light; and produces a radiofrequency interferogram from interference between the post-sensor optical frequency comb and the frequency shifted light.

Example embodiments add an optical amplifier to a multi-channel, continuously swept OFDR measurement system, adjust amplified swept laser output power between rising and falling laser sweeps, and/or utilize portions of a laser sweep in which OFDR measurements are not typically performed to enhance the integrity of the OFDR measurement system, improve the performance and quality of OFDR measurements, and perform additional measurements and tests.

The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

A method for measuring a response from an optical fiber providing distributed back reflections using a system comprising an optical source comprising a laser, an optical receiver and a processing unit is disclosed. The method comprises generating an interrogation signal and an optical local oscillator using the optical source, the interrogation signal being represented by an interrogation phasor and the optical local oscillator being represented by a local oscillator phasor; transmitting the interrogation signal into the optical fiber; and mixing the optical local oscillator with reflected light from the optical fiber and detecting a mixing product with the optical receiver to achieve a receiver output signal. The method further comprises performing a measurement that characterizes fluctuations in the local oscillator phasor; processing the receiver output signal based on the measurement result to provide a corrected receiver output signal such that an effect of fluctuations in the local oscillator phasor on the corrected receiver output signal is reduced; and applying distributed back-reflection processing on the corrected receiver output signal. Finally, the method comprises extracting the response from the optical fiber from the distributed back-reflection processing output. A system for measuring a response from an optical fiber providing distributed back reflections is also disclosed.

A long-distance optical cable physical safety monitoring system, including a light source module, a light interference module, a sensing module, a reflection module, a photovoltaic conversion module, and a data processing module. The light interference module is use for dividing a light beam into multiple light beams; the sensing module is use for transmitting the multiple light beams; the reflection module is used for reflecting the multiple light beams to make the light interference module to output an interference signal; the photovoltaic conversion module is used for converting the interference signal to obtain a data signal; the data processing module is used for processing the data signal. The long-distance optical cable physical safety monitoring system is passive, low in energy consumption, anti-jamming, low in false positive rate, simple in construction, and convenient in maintenance.

A displacement measuring apparatus, a displacement measuring method and a photolithography device are disclosed. The displacement measuring apparatus includes a light source module (300), a diffractive member (200), a reader head assembly (100), an optical detection module (410, 411, 412, 413) and a signal analysis module (500). The reader head assembly (100) is configured to receive two input light beams (610, 611) from the light source module (300) and guide them so that they come into contact in parallel with the diffractive member (200) and are both diffracted. The diffracted input light beams are guided and combined to form at least one output light beam (612, 613, 614) each containing diffracted light signals respectively of the two input light beams (610, 611), which exit in the same direction from the same light spot location of the diffractive member (200). Displacement information of the diffractive member (200) can be derived from phase change information contained in an interference signal produced by each output light beam (612, 613, 614). The displacement measuring apparatus and method can be used to achieve independent displacement measurements in different direction, with adaptivity to a wide angle and reduced nonlinearity errors. The photolithography device includes the displacement measuring apparatus.

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.

There are described methods, systems, and computer-readable media for detecting events in a conduit. A first length of optical fiber, positioned alongside the conduit, is interrogated to obtain interferometric data from the first length of optical fiber. A second length of optical fiber, positioned alongside the conduit, is interrogated to obtain interferometric data from the second length of optical fiber. The interferometric data obtained from the first length of optical fiber is compared with the interferometric data obtained with the second length of optical fiber. Based on the comparison, whether an event has occurred in the conduit is determined.

The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.