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.

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 integrated system for detecting a red palm weevil (RPW), farm fire, and soil moisture includes an optical fiber configured to be extending to a tree, and a distributed acoustic sensor (DAS) box connected to the optical fiber. The DAS box is configured to process first to third different optical signals reflected from the optical fiber, to determine a presence of the RPW from the first optical signal, a temperature at a location along the optical fiber from the second optical signals, and a moisture at a location around the tree from the third optical signal.

An environmental property measurement apparatus includes a unit configured to receive probe light in a desired mode from one end of a measurement optical fiber, a unit configured to receive, from the other end of the measurement optical fiber, a light pulse in the desired mode as a pump light pulse with respect to the probe light, the light pulse having a frequency difference corresponding to a Brillouin frequency shift of the measurement optical fiber relative to the probe light on a high frequency side, and a unit configured to receive second probe light having the frequency difference corresponding to the Brillouin frequency shift of the measurement optical fiber relative to the probe light on a low frequency side from the other end of the measurement optical fiber, the second probe light being probe light with respect to the probe light in another mode different from the desired mode.

An optical fiber characteristic measurement apparatus (1) includes: a light source (11) configured to output a laser beam of which frequency is modulated; an incident part (12, 13, 14, and 15) configured to make the laser beam output from the light source be incident from one end and another end of an optical fiber (FUT) as continuous light (L1) and pulsed light (L2), respectively; a light detector (16) configured to detect light projected from the optical fiber and output a detection signal (D1); and a detector (17 and 18a) configured to detect, in a first period (T1) in which scattering light based on the continuous light and the pulsed light is projected from the optical fiber and a second period (T2) shorter than the first period, in which the scattering light is not projected from the optical fiber, the scattering light based on integrated values acquired by integrating the detection signal for a predetermined time.

A multi-dimensional spatial positioning system and method for disturbance source. The system includes a distributed-optical fiber sensor, a sensing optical fiber, a coordinate system, a disturbance source to be monitored, a first signal group, and a second signal group. The disturbance source is positioned by combining an array signal processing method with the distributed optical fiber sensor, using different laying manners for the sensing optical fiber and a certain number of flexibly selected sensing units distributed a certain distance from each other along a line, and combining with a special signal processing method, thereby realizing a function of being capable of monitoring multi-dimensional spatial position information of the disturbance source in real time in both short and long distances.

A monitoring humidity measurement system includes: a humidity measurement optical fiber including a first optical fiber and a humidity detection layer provided so as to annularly cover the first optical fiber; a reference optical fiber including a second optical fiber; a plurality of optical communication cables; and a signal processing device configured to, with a laser beam entering into the first and second optical fibers, calculate and obtain Brillouin frequency shift and Rayleigh frequency shift of backscatter light from the first and second optical fibers based on the entering laser beam, and store predetermined constants, wherein reference data and target data are measured from the Rayleigh frequency shift and an initial humidity value calculated from the Brillouin frequency shift, and the value of humidity at the present time is calculated on the basis of Rayleigh frequency shift per unit humidity calculated from a difference between the above two data.

In some examples, a temperature distribution sensor may include a laser source to emit a laser beam that is tunable to a first wavelength and a second wavelength for injection into a device under test (DUT). A first wavelength optical receiver may convert a return signal corresponding to the first wavelength with respect to Rayleigh backscatter or Raman backscatter Anti-Stokes. A second wavelength optical receiver may convert the return signal corresponding to the second wavelength with respect to Rayleigh backscatter or Raman backscatter Stokes. Bending loss associated with the DUT may be determined by utilizing the Rayleigh backscatter signal corresponding to the first wavelength and the Rayleigh backscatter signal corresponding to the second wavelength. Further, temperature distribution associated with the DUT may be determined by utilizing the Raman backscatter Anti-Stokes signal corresponding to the first wavelength and the Raman backscatter Stokes signal corresponding to the second wavelength.

The present invention provides novel apparatus and methods for fast quantitative measurement of perturbation of optical fields transmitted, reflected and/or scattered along a length of an optical fibre. The present invention can be used for point sensors as well as distributed sensors or the combination of both. In particular this technique can be applied to distributed sensors while extending dramatically the speed and sensitivity to allow the detection of acoustic perturbations anywhere along a length of an optical fibre while achieving fine spatial resolution. The present invention offers unique advantages in a broad range of acoustic sensing and imaging applications. Typical uses are for monitoring oil and gas wells such as for distributed flow metering and/or imaging, seismic imaging, monitoring long cables and pipelines, imaging within large vessel as well as for security applications.

An optical fiber characteristics measurement apparatus (1) includes: a light source (11) configured to output continuous light (L1) of which frequency is modulated; a first optical splitter (12) configured to split the continuous light into pump light (LP) and reference light (LR); a pulser (13) configured to pulse the pump light; a second optical splitter (14) configured to cause the pulsed pump light to be incident from one end of an optical fiber (FUT) and output backscattered light (LS) generated due to Brillouin scattering in the optical fiber; a detector (17) configured to detect interference light between the backscattered light and the reference light; a cutout unit (18, 20a, 34, 41, 42a) configured to cut out a detection signal output from the detector at predetermined time intervals; and a measurer (19, 35a, 35b) configured to measure characteristics of the optical fiber individually using the detection signal for each of the predetermined time intervals cut out by the cutout unit.