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.

Provided is an apparatus for generating an incident light, the apparatus including an input light generator configured to generate an input light by changing an intensity of an operational signal at intervals of a predetermined period, a filter configured to change a wavelength of the input light through an electrical change, and a light amplifier configured to amplify an intensity of the input light having the changed wavelength to emit an incident light.

The application describes methods and apparatus for distributed fibre sensing, especially distributed acoustic/strain sensing. The method involves launching interrogating radiation in to an optical fibre and sampling radiation backscattered from within said fibre at a rate so as to acquire a plurality of samples corresponding to each sensing portion of interest. The plurality of samples are divided into separate processing channels and processed to determine a phase value for that channel. A quality metric is then applied to the processed phase data and the data combined to provide an overall phase value for the sensing portion based on the quality metric. The quality metric may be a measure of the degree of similarity of the processed data from the channels. The interrogating radiation may comprise two relatively narrow pulses separated by a relatively wide gap and the sampling rate may be set such that a plurality of substantially independent diversity samples are acquired.

An apparatus for measuring state variables with at least one fiber-optic sensor, containing at least one optical coupler, at least one filter element and at least one photoelectric converter, where the optical coupler, the filter element and the photoelectric converter are integrated on a substrate, and the filter element contains at least one Bragg grating which is designed to supply the light portion reflected by the Bragg grating to the photoelectric converter.

To provide an OFDR device and an OFDR method capable of measuring a large strain distribution or a large temperature distribution within a narrow measured wavelength range by using an FBG. A measured optical fiber 13 includes a plurality of gratings that is overlappingly formed in order to reflect a plurality of different wavelengths. An OFDR device 1 measures a strain distribution or a temperature distribution of the measured optical fiber 13 on the basis of the result of detection by a measuring range non-inclusion detector 26 that detects gratings of the plurality of gratings of which the reflected wavelengths are not included in the measured wavelength range from the peak wavelengths detected by a peak wavelength detector on the basis of measured wavelength range non-inclusion detecting condition data (Ds) in which a predetermined measured wavelength range is set in the direction of the axis of the peak wavelengths.

A pressure sensing assembly (1), comprising: an elongate, axially extending tube (100), having a flexible tube wall (102) that encloses an inner pressure chamber (106); and at least one sensor unit (200), including: two tube wall fixation devices (210), connected to the tube wall (102) at respective axially spaced apart positions, and configured to fix respective diameters (D, d) of the tube wall at said positions; and a first strain sensing element (220), connected to the tube wall (102) at a first position axially in between said two tube wall devices (210), and configured to provide a first signal indicative of an axial elongation of the tube wall resulting from a change in axial curvature of the tube wall when a pressure differential between the inner pressure chamber (106) and an outside environment (108) of the tube is applied across the tube wall at said first position.

The invention relates to a fiber-optic sensor comprising an optical waveguide having at least one first core and a cladding surrounding the first core, wherein the first core extends substantially over the entire length of the optical waveguide, wherein the sensor has at least one second core which is at least partly surrounded by the cladding, wherein the longitudinal extent of the second core is less than the total length of the optical waveguide and at least one Bragg grating is introduced into the second core. Furthermore, the invention relates to a use of the fiber-optic sensor.

Embodiments of the present invention relate to determining temperature, pressure, strain, or other changes of an optical fibre (250) having Fiber Bragg Grating (FBG) patterns provided in at least one portion (Portion 1) of said optical fibre (250), said optical fibre (250) being connected between a first detector arrangement (210) and a second detector arrangement (220).

A method for interrogating an FBG sensor includes lighting the FBG sensor with a broadband excitation optical radiation, conveying the optical spectrum transmitted or reflected by the FBG sensor to a tunable optical BPF having a first extraction port and a second transmission port, tuning the optical BPF at a constant operating wavelength, depending on nominal operating wavelength of the FBG sensor, detecting a first optical signal exiting the first extraction port, converting, by a first opto-electronic receiver, the first optical signal into a first electrical signal, representative of a wavelength shift of the spectrum transmitted or reflected by the FBG sensor, detecting a second optical signal exiting the second transmission port, converting the second optical signal, by a second opto-electronic receiver, into a second electrical signal, representative of an optical reference power, and determining the wavelength shift of the spectrum transmitted or reflected by FBG sensor, based on detected first and second electrical signals. A system for interrogating an FBG sensor is also provided.

A spectral interrogation device, including: an optical source for emitting a light signal, a measurement optical fibre comprising a series of successive Bragg gratings for reflecting the light signal in different wavelength bands, a reflective optical fibre comprising a total reflection element, a wavelength detector, and an optical switch for switching between a sequence of three operating modes. In a first mode, the light signal emitted by a given optical source is guided from the optical source to a corresponding measurement optical fibre. In a second mode, the light signal is guided to make a predetermined number of return trips in a line formed by a coupling between the measurement optical fibre and a corresponding reflective optical fibre, generating a predetermined delay between the successive gratings. In a third mode, the light signal is guided to a corresponding detector to successively measure the wavelength bands associated with the gratings.