The present disclosure relates to a device, including: a first light source for outputting incident light to a measured optical fiber or optical device; a second light source for outputting local light for being multiplexed with transmitted light through the measured optical fiber or optical device; and a signal processing unit for performing digital signal processing on a light-receiving signal I(t) obtained by multiplexing the transmitted light and the local light, wherein the signal processing unit is configured to calculate an autocorrelation function between the light-receiving signal I(t) and a signal I(t+) obtained by shifting the light-receiving signal by a time , and to measure a delay time difference between propagation modes in the measured optical fiber or optical device, from a peak position of the autocorrelation function.

A method for inspecting a wafer, includes: rotating the wafer about an axis of the wafer, emitting from a light source, two pairs of incident coherent light beams, each pair forming, at the intersection between the two beams, a measurement volume, a portion of the main wafer surface passing through each of the measurement volumes during the rotation, collecting a light beam scattered by the wafer surface, capturing the collected light and emitting an electrical signal representing the variation in the collected light intensity, detecting in the signal, a frequency, being the time signature of a defect through a respective measurement volume, for each detected signature, determining a visibility parameter, on the basis of the visibility determined, obtaining an item of information on the size of the defect, and cross-checking the items of information to determine the size of the defect.

A multi-core fiber includes multiple optical cores, and for each different core of a set of different cores of the multiple optical cores, a total change in optical length is detected. The total change in optical length represents an accumulation of all changes in optical length for multiple segments of that different core up to a point on the multi-core fiber. A difference is determined between the total changes in optical length for cores of the set of different cores. A twist parameter and/or a bend angle associated with the multi-core fiber at the point on the multi-core fiber is/are determined based on the difference.

Apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre 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. Advantages of this technique include 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.

An accurate measurement method and apparatus using an optical fiber are disclosed. A total change in optical length in an optical core in the optical fiber is determined that reflects an accumulation of all of the changes in optical length for multiple segment lengths of the optical core up to a point on the optical fiber. The total change in optical length in the optical core is provided for calculation of an average strain over a length of the optical core based on the detected total change in optical length.

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.

An interferometer apparatus for an optical fibre system and method of use is described. The interferometer comprises an optical coupler and optical fibres which define first and second optical paths. Light propagating in the first and second optical paths is reflected back to the optical coupler to generate an interference signal. First, second and third interference signal components are directed towards respective first, second and third photodetectors. The third photodetector is connected to the coupler via a non-reciprocal optical device and is configured to measure the intensity of the third interference signal component directed back towards the input fibre. Methods of use in applications to monitoring acoustic perturbations and a calibration method are described.

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 device for detecting optical loss includes a first light-guiding cable, a second light-guiding cable, a light detector, at least one angle-adjusting bracket, and a first emission microscope. The first light-guiding cable is connected with a light generator. The light detector is connected with the second light-guiding cable. When the light generator generates a light beam, the light beam is emitted to a semiconductor light-guiding chip through the first light-guiding cable. The semiconductor light-guiding chip guides the light beam to the second light-guiding cable. The light detector receives the light beam through the second light-guiding cable to retrieve the energy of the light beam. The first emission microscope captures the leakage position of the semiconductor light-guiding chip where the light beam is emitted from the semiconductor light-guiding chip.

An apparatus is provided. The apparatus includes: a first main waveguide, configured to input and output a first optical signal; a first to-be-tested waveguide, configured to couple the first optical signal to generate a second optical signal, and transfer the second optical signal, an optical signal that is reflected by a second fiber Bragg grating, and an optical signal that is reflected by a first fiber Bragg grating. The apparatus also includes the first fiber Bragg grating, configured to totally reflect the optical signal that is reflected by the second fiber Bragg grating; the second fiber Bragg grating, configured to partially transmit and partially reflect the second optical signal and the optical signal that is reflected by the first fiber Bragg grating; and a first photoelectric detector, configured to receive an optical signal that is transmitted by the second fiber Bragg grating of the corresponding first to-be-tested waveguide.