According to examples, a Brillouin and Rayleigh distributed sensor may include a first laser source to emit a first laser beam, and a second laser source to emit a second laser beam. A photodiode may acquire a beat frequency between the two laser beams. The beat frequency may be used to maintain a predetermined offset frequency shift between the two laser beams. A modulator may modulate the first laser beam. The modulated first laser beam is to be injected into a device under test (DUT). A coherent receiver may acquire a backscattered signal from the DUT. The backscattered signal results from the modulated first laser beam injected into the DUT. The coherent receiver may use the second laser beam as a local oscillator to determine Brillouin and Rayleigh traces with respect to the DUT based on the predetermined offset frequency shift.

An improved technique for acoustic sensing involves, in one embodiment, launching into a medium, a plurality of groups of pulse-modulated electromagnetic-waves. The frequency of electromagnetic waves in a pulse within a group differs from the frequency of the electromagnetic waves in another pulse within the group. The energy scattered by the medium is detected and, in one embodiment, the beat signal may be used to determine a characteristic of the environment of the medium. For example, if the medium is a buried optical fiber into which light pulses have been launched in accordance with the invention, the presence of acoustic waves within the region of the buried fiber can be detected.

There are proposed an optical fiber property measuring device and an optical fiber property measuring method which can enhance spatial resolution more than before. In the present invention, in synchronization with frequency modulation applied to x-polarized light, intensity modulation is also applied to the x-polarized light by an intensity modulation means. This makes it possible to increase or decrease the intensity of the x-polarized light at a specific frequency, thereby allowing the effective length of a Brillouin dynamic grating formed by the x-polarized light to be adjusted. As a result, the shape of the reflection spectrum obtained when y-polarized light is reflecting by the Brillouin dynamic grating can also be adjusted optimally, which leads to enhancement of spatial resolution with the y-polarized light.

A Brillouin backscattered spectrum is obtained in such a way that two optical pulse pairs each composed of two pulses of different durations and of the same phase and n phase difference are launched into a sensing optical fiber; Brillouin backscattered lights produced by the optical pulse pairs are detected into signals for the respective optical pulse pairs; the signals are sampled with two window functions whose time widths are equal to respective pulse durations of the optical pulse pair and whose delay time is variable; each sampled signal is transformed with a predetermined transformation; products of the transformed signals are calculated; and subtraction between the products is performed.

Methods of measuring an anomaly, any induced change in physical parameters such as strain, temperature, and so forth, in an optical fiber. One method may include launching a plurality of probe pulses from a probe source; recording a Brillouin scattering spectrum from a plurality of reflection signals generated in the optical fiber, responsive to the plurality of probe pulses; determining a relative motion between the optical fiber and the anomaly during the recording the Brillouin back-scattering spectrum; and dynamically adjusting the Brillouin back-scattering spectrum according to the relative motion, or performing an adjustment of the Brillouin back-scattering spectrum after acquisition of the Brillouin back-scattering spectrum.

In a TDM- and WDM-based FBG sensor array system, a source emits a light covering a selected wavelength range. The light is amplified and then used to generate a series of pulses that are fed into an array of sensor gratings. The propagation of a pulse through the sensor array results in a time-domain-multiplexed output, comprising a series of output pulses in which each output pulse comprises a reflection of the input pulse at a respective grating in the sensor array. Raman amplification is used to amplify both the pulse input into and the time-domain multiplexed output from the sensor array, which is then coupled into an output processing stage for receiving the sensor output and for reconstructing the wavelength output of each grating in the sensor array. The wavelength change for each grating is then used to calculate a physical parameter(s) to be measured, such as temperature and/or strain.

The subject matter of this specification can be embodied in, among other things, a method that includes separating, from a few mode optical fiber, a collection of backscattered Rayleigh signals based on a vibration of the few mode optical fiber at a vibration frequency at a first location along the few mode optical fiber, separating, from the few mode optical fiber, a collection of backscattered Stokes Raman signals and Anti-Stokes Raman signals based on a temperature of the few mode optical fiber at a second location along the few mode optical fiber, detecting the separated Rayleigh signals and Raman signals, determining, based on detecting the collection of backscattered Rayleigh traces, at least one of the first location, the vibration frequency, and an amplitude of the vibration, and determining, based on the detecting the collection of backscattered Raman signals, the temperature at the second location.

The present invention is to provide a backscattered light amplification device, an optical pulse test apparatus, a backscattered light amplification method, and an optical pulse test method for amplifying a desired propagation mode of Rayleigh backscattered light with a desired gain by stimulated Brillouin scattering in a fiber under test having the plurality of propagation modes. The backscattered light amplification device according to the present invention is configured to control individually power, incident timing, and pulse width of a pump pulse for each propagation mode when the pump pulse is incident in a plurality of propagation modes after the probe pulse is input to the fiber under test in any propagation mode.

Aspects of the present disclosure describe amplifier dynamics compensation through feedback control for distributed fiber sensing systems, methods, and structures employing Brillouin optical time-domain reflectometry.

An apparatus for digitizing an optical signal comprises: an optical detector to detect an optical signal and to generate an electric signal corresponding to the optical signal; an envelope curve detector to determine the amplitude of the electric signal or a modified electric signal resulting from the electric signal, and to supply an amplitude signal corresponding to the amplitude; an analog to digital converter to digitize the amplitude signal and to supply a corresponding digitized amplitude signal; and a variable voltage source to calibrate the envelope curve detector.