112results about "Reflectometers detecting back-scattered light in frequency-domain" patented technology

A method and a system for Uniform Frequency Sample Clocking to directly sample the OCT signal with a temporally-non-linear sampling clock derived from a k-space wavemeter on the external sample clock input port of a digitizer.

A CW lightwave modulated by a continuously reiterated psuedorandom code sequence is launched into an end of a span of ordinary optical fiber cable. Portions of the launched lightwave back propagate to the launch end from a continuum of locations along the span because of innate fiber properties including Rayleigh scattering. This is picked off the launch end and heterodyned producing a r.f. beat signal. The r.f. beat signal is processed by a plurality (which can be thousands) of correlator type pseudonoise code sequence demodulation and phase demodulator units, operated in different time delay relationships to the timing base of the reiterated modulation sequences. These units provide outputs representative of phase variations in respective unique spectral components in the r.f. beat signal caused by acoustic, or other forms of, signals incident to virtual sensors at fiber positions corresponding to the various time delay relationships.

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

Optical fiber lines of a PON system can be monitored with the remote fiber test system having a practical structure, comprising a branch-type optical fiber line constituting the PON system and test equipment connected to the branch-type optical fiber line on the central office side. The test equipment comprises a light source, an optical splitter, a detecting part, and a control unit. The light source outputs light having an optical coherence function of a comb shape that is formed as a result of the optical frequency being modulated by a modulation signal of period p. The optical splitter receives light output from the light source and splits the light into probe light and reference light. The detecting part detects interference light that occurs from mutual interference between the reference light and reflected light arising while the probe light propagates through the branch-type optical fiber line. And, upon detection of the interference light, the detecting part converts the interference light into an electrical signal. The control unit changes the period p, and on the basis of the period p and the electrical signal output from the detecting part, obtains reflectance distribution along the direction of the probe light propagation in the branch-type optical fiber line.

Complex data is obtained from OFDR backscatter measurements for an optical device under test (DUT). That complex scatter pattern data may be used along with a previously-determined fiber segment pattern to identify the fiber segment within the DUT, even when the DUT is an optical network DUT that includes multiple fibers coupled to perform one or more functions. In other non-limiting example applications, the OFDR scatter pattern data can be used to identify where in the DUT a loss occurred and where in the DUT a temperature change occurred.

Light is coupled into two polarization modes of a waveguide, e.g., an optical fiber. The spectral response of Rayleigh backscatter in the waveguide segment for the two polarization modes is measured, e.g., using OFDR, OTDR, OLCR, etc. The autocorrelation of the spectral response is calculated. The spectral (wavelength) shift from a main autocorrelation peak to a side autocorrelation peak, corresponding to one of the two polarization modes of the waveguide segment, is determined. The spectral shift, corresponding to a beat length of the waveguide segment, is multiplied by an average index of refraction to determine a birefringence of the waveguide segment.

A portion of a polarization maintaining (PM) optical fiber having two polarization states is analyzed. First and second spectral responses of the PM fiber portion are determined. In a preferred implementation, the spectral responses are determined using Optical Frequency Domain Reflectometry (OFDR). Each polarization state of the PM fiber portion has a corresponding spectral component in the first spectral response. First and second spectral analyses of the PM fiber portion are performed using the first and second spectral responses. Based on those spectral analyses of the PM fiber portion, a first physical characteristic affecting the PM fiber portion is determined that is distinct from a second different physical characteristic affecting the fiber portion. Example physical characteristics include temperature and strain. An output signal related to the first physical characteristics affecting the fiber portion is provided, e.g., for display, further processing, etc.

A CW lightwave modulated by a continuously reiterated pseudorandom (PN) code sequence is launched into an end of a span of ordinary optical fiber cable. Portions of the launched lightwave back propagate to the launch end from a continuum of locations along the span because of innate fiber properties including Rayleigh scattering. This is picked off the launch end and heterodyned producing a r.f. beat signal. The r.f. beat signal is processed by a plurality (which can be thousands) of correlator pseudonoise code sequence demodulation and phase demodulator units operated in different delay time relationships to the timing base of the reiterated modulation sequences. Pairs of outputs of the units are connected to respective substractor circuits, each providing a signal representative of a differential signal between acoustic, or other forms of, signals incident the bounds of virtual increments of the span.

In order to identify an optical cable for optical communication from a remote place, a Sagnac interferometer including two strands of an optical fiber is formed in the optical cable, and a worker in the remote place applies a disturbance of a popping sound to an optical cable to be identified. The disturbance applied by the worker is detected and regenerated in the form of a sound. The optical cable can be easily identified by comparing the regenerated signal and the disturbed signal in the remote place to thereby prevent an incorrect optical cable from being cut. In addition, the optical cable can be more precisely identified by selecting a different light detecting frequency component in accordance with environment conditions.

An optical fiber includes primary optical core(s) having a first set of properties and secondary optical core(s) having a second set of properties. The primary set of properties includes a first temperature response, and the secondary set of properties includes a second temperature response sufficiently different from the first temperature response to allow a sensing apparatus when coupled to the optical fiber to distinguish between temperature and strain on the optical fiber. A method and apparatus interrogate an optical fiber having one or more primary optical cores with a first temperature response and one or more secondary optical cores with a second temperature response. Interferometric measurement data associated with each primary and secondary optical core are detected when the optical fiber is placed into a sensing position. Compensation parameter(s) is(are) determined to compensate for measurement errors caused by temperature variations along the optical fiber based on a difference between the first temperature response of the primary cores and the second temperature response of the secondary cores. The detected data are compensated using the compensation parameter(s).

There is provided an apparatus for measuring the characteristics of an optical fiber in which a frequency difference between first and second coherent light respectively generated by first and second light sources can be accurately set and wherein preferable coherent detection can be carried out in accordance with frequency components of returned light. First coherent light at a frequency f1 is converted into a pulse light which is output to the optical fiber to be measured. The characteristics of the optical fiber are measured by multiplexing returned light from the optical fiber to be measured and second coherent light at a frequency f2 and by detecting the multiplexed light. A component |f1-f2| is detected from an optical signal obtained by the multiplexed light and is mixed with a signal at a frequency fr to decrease the frequency. An electric signal at a voltage level corresponding to a differential frequency |f1-f2|-fr included in the mixed signal is generated, and a predetermined voltage level is generated which corresponds to a set value for an optical frequency difference between the first and second coherent light. The second light source is driven based on the difference between the two voltage levels to correct the frequency of the second coherent light.

The invention discloses an optical frequency domain reflectometer with optical wave frequency shift modulation, which comprises a narrow linewidth scanning laser, a first optical fiber coupler, an optical circulator, a to-be-measured optical fiber, an optical wave frequency shifter, a second optical fiber coupler, a first polarization beam splitter, a second polarization beam splitter, a first balanced photodetector, a second balanced photodetector, a third optical fiber coupler, a first Faraday rotating mirror, a second Faraday rotating mirror, a reference optical fiber interferometer, a photodetector and a signal acquisition and processing unit. Through frequency shift modulation on measurement light and reference light, interference signals produced by superposition of scattering signal light of the to-be-measured optical fiber which is symmetrical about zero delay and local oscillation light are separated on the spectrum. According to the optical frequency domain reflectometer with optical wave frequency shift modulation, mutual interference among the interference signals of the to-be-measured optical fiber scattering signal light which is symmetrical about zero delay can be suppressed, measurement of the scattering signal light which is symmetrical about zero delay can be realized, and the maximum optical fiber measurement length can be improved.

A method of simultaneously specifying the wavelength dispersion and nonlinear coefficient of an optical fiber. Pulsed probe light and pulsed pump light are first caused to enter an optical fiber to be measured. Then, the power oscillation of the back-scattered light of the probe light or idler light generated within the optical fiber is measured. Next, the instantaneous frequency of the measured power oscillation is obtained, and the dependency of the instantaneous frequency relative to the power oscillation of the pump light in a longitudinal direction of the optical fiber is obtained. Thereafter, a rate of change in the longitudinal direction between phase-mismatching conditions and nonlinear coefficient of the optical fiber is obtained from the dependency of the instantaneous frequency. And based on the rate of change, the longitudinal wavelength-dispersion distribution and longitudinal nonlinear-coefficient distribution of thee optical fiber are simultaneously specified.

Optical frequency domain reflectometry (OFDR) circuitry to perform tasks on an optical fiber to generate calibration or correction data for calibrating or correcting a reference OFDR data set. A segmented technique is used which permits precise and accurate determination of the correction data for even initial and long fiber lengths. Correction information for each segment is stitched together to generate the correction data for the fiber.

A method for conducting fast Brillouin optical time domain analysis for dynamic sensing of optical fibers is provided herein. The method includes the following stages: injecting a pump pulse signal into a first end of an optical fiber and a probe signal into a second end of the optical fiber, wherein the probe and the pump pulse signals exhibit a frequency difference between them that is appropriate for an occurrence of a Brillouin effect; alternating the frequency of either the probe or the pulse signals, so as the alternated signal exhibits a series of signal sections, each signal section having a predefined common duration and a different frequency; measuring the Brillouin probe gain for each one of the alternating frequencies; and extracting physical properties of the optical fiber throughout its length at sample points associated with the sampled time and the frequencies, based on the measured Brillouin probe gain.