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 optical coupler includes at least one input waveguide and a plurality of output waveguides. The optical coupler spatially disperses optical signals carried on the input waveguide according to wavelength to the output waveguides. The input waveguides and the output waveguides are arranged to provide crosstalk between optical signals carried on the output waveguides.

Multiplexed microvolt sensor systems and methods are described. An example system may include a pulsed light source, a first optical waveguide segment operatively coupled to the pulsed light source, an optical circulator including a first port, a second port, and a third port, the first port being operatively coupled to the first optical waveguide segment, a second optical waveguide segment operatively coupled to the second port of the optical circulator, and an array of sensor elements. Each of the sensor elements may include a detector and an electro-optical modulator, the electro-optical modulator being operatively coupled to the second optical waveguide segment. The example system may further include a third optical waveguide segment operatively coupled to the third port of the optical circulator, a compensating interferometer operatively coupled to the third optical waveguide segment, and a time division multiplexed demodulator operatively coupled to the compensating interferometer and the pulsed light source.

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).

An waveguide on access tube (WOAT) system measures soil moisture by sensors placed at various depths of a medium, such as soil. The WOAT system includes a rigid tube into which an inflatable tube with various sensors bonded to it is inserted. Once in place, the rigid tube is removed and the inflatable tube and its sensor are inflated to the diameter of the hole or channel in which it is positioned. The ability to inflate the inflatable tube allows for the sensors on the inflatable tube to be force fit against the interior wall of the hole or channel for proper soil or ambient environment measurements.

An waveguide on access tube (WOAT) system measures soil moisture by sensors placed at various depths of a medium, such as soil. The WOAT system includes a liner tube into which an inflatable tube with various sensors bonded to it is inserted. Once in place, the liner tube is removed and the inflatable tube and its sensor are inflated to the diameter of the hole or channel in which it is positioned. The ability to inflate the inflatable tube allows for the sensors on the inflatable tube to be force fit against the interior wall of the hole or channel for proper soil or ambient environment measurements.

The present invention is the optical fiber sensor, that laser pulses from a laser source are separated into a reference path and a measurement path by the second optical coupler via the first optical coupler, the first FRM is provided at an end of the reference path, the second FRM is provided at an end of the measurement path, and the reference reflected light of the first FRM and the measurement reflected light of the second FRM are interfered at the second optical coupler and are converted into three phases. The first phase pulses are transmitted to the optical synthesis section via the first optical coupler, second phase pulses are transmitted to the optical synthesis section via the first delay section, and third phase pulses are transmitted to the optical synthesis section via the second delay section. The time division pulse train is outputted from the optical synthesis section.