An encoder scale includes a tabular base material and an optical pattern provided above one surface of the base material, a first region and a second region being disposed side by side above the optical pattern. The first region includes a resin layer disposed above the base material and including photosensitive resin and a metal film disposed above the resin layer and formed of a metal material. The surface of the first region is configured mainly by a first surface having a normal line in the thickness direction of the base material. The surface of the second region is configured mainly by a second surface inclined with respect to the first surface.

A measurement system may be enabled to detect properties within an enclosure based on information detected using optical fiber sensors. The measurement system may include an enclosure having at least one wall with an inside surface and an outside surface; at least one silica-based optical fiber comprising at least one functional optical fiber core and at least one cladding layer; at least one optical fiber interrogation member; at least one transducer arranged to output energy; a controller; and a processing element configured to communicate with the optical fiber interrogator and the controller. The silica-based optical fiber is associated with a wall of the enclosure. The controller is configured to control the optical fiber interrogator and the transducer. The processing element is configured to process information from the optical fiber interrogation member.

A detection system according to the present disclosure includes: an optical fiber (30) embedded in or near an embankment (20) of a river (10); a communication unit (41) that receives, from the optical fiber (30), an optical signal including a pattern indicating that the optical fiber (30) is exposed; and detection unit (51) that detects breakage of the embankment (20) based on the pattern.

Apparatus and associated methods relate to determining the wavelength of a narrow-band light beam. The narrow-band light beam is passed through an optical filter. The optical filter has complementary and monotonically-varying transmission and reflection coefficients within a predetermined band of wavelengths. The predetermined band of wavelengths includes the wavelength of the narrow-band light beam. A first photodetector detects amplitude of a first portion of the narrow-band light beam transmitted by the optical filter. A second photodetector detects amplitude of a second portion of the narrow-band light beam reflected by the optical filter. The wavelength of the narrow-band light beam is determined, based on a ratio of the determined amplitudes of the first and second portions of the narrow-band light beam transmitted and reflected, respectively.

An optical fiber includes multiple optical waveguides configured in the fiber. An interferometric measurement system mitigates or compensates for the errors imposed by differences in a shape sensing optical fiber's response to temperature and strain. A 3-D shape and/or position are calculated from a set of distributed strain measurements acquired for a multi-core optical shape sensing fiber that compensates for these non-linear errors using one or more additional cores in the multicore fiber that react differently to temperature changes than the existing cores.

A personnel monitoring system. The personnel monitoring system includes a host node having an optical source for generating optical signals, and an optical receiver. The personnel monitoring system also includes a plurality of fiber optic sensors for converting at least one of vibrational and acoustical energy to optical intensity information, each of the fiber optic sensors having: (1) at least one length of optical fiber configured to sense at least one of vibrational and acoustical energy; (2) a reflector at an end of the at least one length of optical fiber; and (3) a field node for receiving optical signals from the host node, the field node transmitting optical signals along the at least one length of optical fiber, receiving optical signals back from the at least one length of optical fiber, and transmitting optical signals to the optical receiver of the host node.

A method of dynamic change detection using an optical fibre arrangement in disclosed. The optical fibre arrangement can include a forward optical path and a second optical path. The optical fibre arrangement can be configured into a plurality of spans by a plurality of nodes between first and second ends of the optical fibre arrangement. At least one of the nodes includes a feed from the forward path to the second path such that forward propagation of the light signal from the forward path feeds the second path. The method can include transmitting a light signal into the forward path; receiving a response signal from the second path, wherein the response signal includes a loop back signal that includes a light signal fed into the second path via the feed; and detecting dynamic changes along a span associated with the feed from the loop back signal.

An apparatus, including: an optical sensor fiber having a first end optically couplable to receive light from a light source, wherein the optical sensor fiber is a multimode optical fiber configured to carry light in different spatial propagating modes, wherein the optical sensor fiber is constructed such that environmental fluctuations couple light energy between some of the spatial propagating modes; a spatial propagating mode demultiplexer optically coupled to a second end the optical sensor fiber and configured to separate a plurality of light signals received from different ones of the spatial propagating modes; and an optical receiver configured to process the separated light signals and to estimate a longitudinal position of one of the environmental fluctuations along the optical sensor fiber based a measured delay between arrival times of the separated light signals.

A distributed acoustic sensing (DAS) system may include an optical fiber, a phase-sensitive OTDR (-OTDR) coupled to the optical fiber, and a processor cooperating with the -OTDR. The processor may be configured to generate a series of covariance matrices for DAS data from the -OTDR, and determine an acoustic event based upon comparing the series of covariance matrices with a corresponding Toeplitz matrix.

Methods and apparatus for fast sweeping a spectral bandwidth in order to distinguish among signals received from effectively wavelength division multiplexed (WDMed) and time division multiplexed (TDMed) optical components on a single fiber. For some embodiments, a method for interrogating optical elements having characteristic wavelengths spanning a sweep range is provided. The method generally includes introducing a pulse of light, by an optical source, into an optical waveguide to interrogate at least a first set of optical elements having different characteristic wavelengths by performing a sweep of wavelengths over a period of the pulse, wherein the period is less than a round-trip time for light reflected from an optical element closest to the optical source to reach a receiver and processing the reflected light to determine a parameter based on the times at which signals are received.