A method of detecting removal of a maintenance hatch includes transmitting an optical pulse along an optical fiber, wherein a first portion of the optical fiber is proximate to the maintenance hatch. The method further includes detecting backscatter light from the optical fiber using a sensor. The method further includes determining information related to the first portion of the optical fiber based on a comparison of the detected backscatter light and a trained model. The method further includes identifying whether the maintenance hatch has been removed based on the determined information.

A displacement detection device is capable of stably and accurately detecting an amount of displacement. A polarization maintaining fiber has a length not to be equal to a length obtained by dividing, a product of an integral multiple of twice a length of a resonator times a refractive index of the resonator and a beat length obtained from a difference between propagation constants of two polarization modes, by a wavelength of the light source, is selected from a range including a length equal to the above length. The polarization maintaining fiber includes multiple polarization maintaining fibers fitted to each other by removable connectors.

Fiber optic sensors are described for detecting the operational position of a downhole moveable device. In one example, an electric or magnetic field is emitted into the wellbore and interacts with the moveable assembly, thereby producing a secondary electric or magnetic field. The secondary field is detected by a fiber optic sensor which produces a corresponding response signal. The response signal is then processed in a variety of ways to determine the operational position of the moveable device. In another example, the operational position is determined using fiber optic temperature or acoustic sensors. A temperature or acoustic vibration reading is acquired before and after actuation of the moveable device. The two readings are then compared to determine the operation position of the moveable device.

An optical fiber sensing range limiting device comprises: a blocking unit that, on the basis of a control signal and for a prescribed period, causes probe light that has been sent to an optical fiber used in optical fiber sensing and has returned from the optical fiber to be blocked from being transmitted to a light detection unit, or causes a detection signal that is detected with respect to the return light to be blocked from being transmitted to a downstream processing unit; and a control unit that outputs the control signal to the blocking unit. The prescribed period includes a period corresponding to the positional range for which acquisition of information from the detection signal is prohibited or for which it is undesirable to acquire the information.

An aircraft and method of operating an aircraft. The aircraft includes a temperature sensor and a processor. The temperature sensor that obtains an optical signal indicative of a temperature at a selected location of an outer surface of the aircraft. The processor is configured to determine the temperature at the selected location from the optical signal, and operate the aircraft based on the temperature at the selected location.

An optical sensor includes a tube-shaped base formed from a metal, an optical fiber member received inside the base, and a sensor head formed from monocrystalline alumina and bonded to the base to be optically connected with the optical fiber member. The sensor head is provided with a first cavity including a first reflection surface configured to reflect a part of light introduced through the optical fiber member and a second reflection surface provided facing the first reflection surface and configured to reflect a part of the light reflected by the first reflection surface. A first interference light produced by an interference between the light reflected by the first reflection surface and the light reflected by the second reflection surface is output from the first cavity.

There is described a method of determining a position of a pipeline inspection gauge (PIG) in a fluid conduit. While the PIG is moving through the fluid conduit, one or more sensors positioned along the fluid conduit are used to detect one or more signals. Parameter data is extracted from the detected one or more signals. The parameter data includes one or more parameters of the detected one or more signals as a function of time and position along the fluid conduit. PIG movement data indicative of a position of the PIG in the fluid conduit as a function of time is generated using the parameter data.

A production monitoring system includes a distributed acoustic sensing subsystem that includes a first optical fiber for a distributed acoustic sensing signal and a distributed temperature sensing subsystem that includes a second optical fiber for a distributed temperature sensing signal. The production monitoring system, also includes a cable positioned in a wellbore penetrating through one or more subterranean formations. The distributed acoustic sensing subsystem is communicatively coupled to the cable through the distributed temperature sensing subsystem. The cable includes one or more optical fibers used to obtain optical fiber measurements pertaining to the distributed acoustic sensing signal and the distributed temperature sensing signal. The optical fibers include a sensing fiber that is common between the distributed acoustic sensing subsystem and the distributed temperature sensing subsystem. The distributed acoustic sensing subsystem, receives at least a portion of the optical fiber measurements from the sensing fiber through the distributed temperature sensing subsystem.

An optical cable (31) includes: a stress wave detection optical cable (30) having an optical fiber (7) and a plurality of first steel wires (8) which are helically wound so as to surround the optical fiber (7) and which are surrounded by a flexible material (9); and second steel wires (32) different from the first steel wires (8). The stress wave detection optical cable (30) and the plurality of second steel wires (32) are helically wound to form one annular body as a whole, and a winding angle (α) of the stress wave detection optical cable (30) with respect to the axis is determined by a property value prescribed by Lamé constants of the flexible material (9).

A method and a system for arbitrary optical waveform generation from an optical input, the system comprising an optical shaper comprising unbalanced interferometers with at least one delay, the delay being selected of at least 0.1 ps, an optical sampling readout selected for measuring optical waveforms of at least 0.1 ps; and an electronic processing unit; wherein the optical input is a picosecond pulse; with a minimal pulse duration before the optical shaper equal to a minimal delay of the optical shaper; the optical shaper splitting and interfering optical pulses; the optical sampling readout collecting data at an output of the optical shaper; and the electronic processing unit comparing the collected data with a preset target and updating the optical shaper from results of the comparison until a maximal match between the output of the optical shaper and the preset target output, wherein the maximal match is determined iteratively using one of: machine-learning, optimization algorithms and iterative search algorithms.