107results about "Reflectometers dealing with polarization" patented technology

The present invention discloses simple and yet highly efficient configurations of optical coherence domain reflectometry systems. The combined use of a polarizing beam splitter with one or two polarization manipulator(s) that rotate the returned light wave polarization to an orthogonal direction, enables one to achieve high optical power delivery efficiency as well as fixed or predetermined output polarization state of the interfering light waves reaching a detector or detector array, which is especially beneficial for spectral domain optical coherence tomography. In addition, the system can be made insensitive to polarization fading resulting from the birefringence change in the sample and reference arms. Dispersion matching can also be easily achieved between the sample and the reference arm for high resolution longitudinal scanning.

In order to characterize the optical characteristics of a device, a source of light having a variable frequency with a polarization state which varies linearly with frequency is provided as an input to the device under test. The input light is also passed through a known reference path and is added to the light output from the device under test in a beam combiner. The combined light for the frequencies of interest is split into two orthogonal polarizations which are then detected in a spectral acquisition apparatus and supplied to a microprocessor. The spectral measurements are digitized and curve-fitted to provide optical power versus optical frequency curves. Fourier transforms of each of the curves are calculated by the microprocessor. From the Fourier transforms, the four arrays of constants are calculated for the Jones matrix characterizing the device under test.

The invention discloses a fully distributed optical fiber strain and vibration sensor comprising a laser (1), a first coupler (2), a pulse modulation module (3), an optical amplifier (4), a circulator (5), a sensing optical fiber (6), a fiber bragg grating (7), a polarization scrambler, a second coupler, a balance photoelectric detector, an analyzer, a photoelectric detector (12) and a signal processing unit. Continuous light output by the laser (1) is split into two paths through the first coupler (2), wherein one path is used as reference light and is accessed to a first input end of the second coupler (9) through the polarization scrambler (8); and the second path is processed by the pulse modulation module (3) and the optical amplifier (4) and then used as detection pulse light to be injected into a first port of the circulator (5). In the invention, Brillouin optical time domain reflectometry (BOTDR) and polarization optical time domain reflectometry (POTDR) are simultaneously utilized for respectively and correspondingly carrying out fully distributed measurement on strain and vibration on a signal optical fiber, the defects of a system with single BOTDR or POTDR are overcome, and the false alarm rate or missed report rate of the system is decreased.

In a method of polarization optical time-domain reflectometer (P-OTDR) for measuring a parameter of an optical transmission path, for example an optical fiber, by transmitting pulses of light into the path and measuring the state of polarization of backscattered light against distance, statistical analysis of the degree of polarization (DOP) of the backscattered signal is used to detect sections of an optical transmission path for which mode-coupling behaviour (long h) leads to high PMD. Preferably, successive DOP measurement are taken with different state of polarization, SOP, for the P-OTDR light source.

A polarization-related characteristic of an optical path is determined from a predetermined function of the mean-square of a plurality of differences between polarization-analyzed optical power parameters corresponding to pairs of wavelengths mutually spaced about a midpoint wavelength by a small optical frequency difference. At least some of the said differences correspond to wavelength pairs measured under conditions where at least one of midpoint wavelength, input state of polarization (I-SOP) or analyzed state of polarization (A-SOP) of a pair is different.

A telecommunications optical fiber is secured against intrusion by detecting manipulation of the optical fiber prior to an intrusion event. This can be used in a non-locating system where the detection end is opposite the transmit end or in a locating system which uses Fresnel reflections and Rayleigh backscattering to the transmit end to detect and then locate the motion. The Rayleigh backscattering time sliced data can be stored in a register until an intrusion event is detected. The detection is carried out by a polarization detection system which includes an optical splitter which is manufactured in simplified form for economic construction. This uses a non-calibrated splitter and less than all four of the Stokes parameters. It can use a polarimeter type function limited to linear and circular polarization or two linear polarizers at 90 degrees.

The invention relates to an optical fiber sensor. The invention discloses an optical fiber destabilization detecting method combining based on a phase sensitivity light time domain reflection and a polarization sensitivity light time domain reflection method and distributed optical fiber sensing system thereof to improve the detecting accuracy and reliability of the optical fiber destabilization. The method comprises: a. injecting an optical signal with determined polarization state into the optical fiber; b. receiving the back rayleigh scattering light in the optical fiber; c. diving the rayleigh scattering light into two bundles to perform the Phi-OTDR data acquisition and the POTDR data acquisition; d. determining the destabilization and position thereof based on the distortion points of the Phi-OTDR data and the POTDR data. The invention also discloses an optical fiber destabilization detecting device. The technical scheme of the invention is used for monitoring and protecting the optical cable lines, thereby greatly improving the precision and the sensitivity of the monitoring system and reducing the erroneous judgment rate and the missing report rate.

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 method for screening fiber polarization mode dispersion using a polarization optical time domain reflectometer. A pulse radiation is emitted into the fiber under test, and the backscattered radiation is measured by the POTDR and used to obtain a POTDR trace. The POTDR trace is then analyzed to compare the variation of signals along the length of the fiber, the variation in signals relating to the level of PMD along the length of the fiber. Because high levels of PMD correspond to localized levels of low variability, by setting the variability of signal threshold sufficiently low, fibers having unacceptably high localized PMD can be identified and removed.

The present invention relates to a method for detecting or inferring a physical disturbances on a communications link, in particular by using distributed backscattering. The method includes the steps of: transmitting test signals onto a link; receiving test signals returned from a remote portion of the link; performing a function on the returned test signals; and in dependence on at least one characteristic of the combination signal, inferring the presence of a disturbance. The test signal are returned by a process Rayleigh backscattering along the fibre, so existing fibre installations can be used without requiring a mirror to be specifically introduced.

An accurate measurement method and apparatus are disclosed for shape sensing with a multi-core fiber. A change in optical length is detected in ones of the cores in the multi-core fiber up to a point on the multi-core fiber. A location and/or a pointing direction are/is determined at the point on the multi-core fiber based on the detected changes in optical length. The accuracy of the determination is better than 0.5% of the optical length of the multi-core fiber up to the point on the multi-core fiber. In a preferred example embodiment, the determining includes determining a shape of at least a portion of the multi-core fiber based on the detected changes in optical length.

A method for characterizing an optical link by its beat length, coupling length and polarization mode dispersion is disclosed. A pulsed signal is sent along said optical fiber link and the backscattered signal (being a POTDR signal) is measured after passing through a polarizer. The length of said optical fiber, the average power difference between two successive minima of said backscattered signal and the number of maxima per unit length are derived. In an iterative way a beat length interval and an interval for the polarization mode coupling parameter are determined until the length of said intervals is below a predetermined value, yielding a value for the beat length and the coupling length, and the polarization mode dispersion is calculated.

A measurement precision is improved and a measurement range is extended by efficiently suppressing a noise level of integrated unnecessary components from non-correlation positions. Measuring means 33 detects the Brillouin gain of a probe light output from a measurement-target optical fiber FUT while sweeping a frequency difference between the pump light and the probe light, and measures the distribution of strains of the measurement-target optical fiber FUT. An optical intensity modulator 4 performs intensity modulation on output light in synchronization with frequency modulation performed on a light source 1. Accordingly, the spectrum distribution with respect to the frequency of light from the light source 1 can be adjusted arbitrarily, and a noise spectrum shape generated at a position other than a correlation peak position and spreading over a frequency axis can be adjusted, and the peak frequency of a Lorentz spectrum generated at the correlation peak position can be measured precisely. Moreover, a measurement range d_m can be extended.

A polarized lightwave reflectometry method including the steps of sending at least two polarized light signals into the optical fiber to be tested, the signals presenting a determined angular offset relative to each other so that the polarization mode dispersion coefficient remains independent of any rotation of polarization in the optical fiber under test; extracting a scalar parameter of the relative noise type for each trace obtained by back-scattering of the light signal; and estimating the polarization mode dispersion coefficient by a function having a single scalar input, which function is of the type based on exponentials and has the form exp (a+bP+cP⁻¹).

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.

An apparatus and method for measuring characteristics of optical fibers that enable accurate measurement of characteristics of optical fibers (distribution of polarization mode dispersion and distribution of magnitude of birefringence) are to be realized. This invention is an improvement of an optical fiber characteristics measuring apparatus in which pulse light is inputted to a subject optical fiber, back scattered light of the pulse light from the subject optical fiber is detected by a photodetector to find a Stokes vector, and polarization mode dispersion in a longitudinal direction is measured. The apparatus comprises a light source unit for outputting the pulse light having at least three different angular frequencies, and an arithmetic operation unit for calculating the magnitude of linear polarization components and the magnitude of a circular polarization component of a polarization dispersion vector on the basis of the Stokes vector and thus calculating polarization mode dispersion.

In a method of measuring cumulative polarization mode dispersion (PMD) along the length of a fiber-under-test (FUT), a polarization-sensitive optical time domain reflectometer (POTDR) is used to inject into the FUT plural series of light pulses arranged in several groups. Each group comprises at least two series of light pulses having different but closely-spaced wavelengths and the same state of polarization (SOP). At least two, and preferably a large number of such groups, are injected and corresponding OTDR traces obtained for each series of light pulses by averaging the impulse-response signals of the several series of light pulses in the group. The process is repeated for a large number of groups having different wavelengths and/or SOPs. The PMD then is obtained by normalizing the OTDR traces of all of the groups, then computing the difference between each normalized OTDR trace in one group and the corresponding normalized OTDR trace in another group, followed by the mean-square value of the differences. Finally, the PMD is computed as a predetermined function of the mean-square difference. The function may, for example, be a differential formula, an arcsine formula, and so on.

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.

A method for determining at least one optical property of an optical device comprises providing an optical input signal that includes first and second signal components that are modulated at first and second frequencies, respectively, and that have first and second polarization states, respectively. The optical input signal is passed to an optical device. An optical output signal from the optical device is separated into first and second output signals that have third and fourth polarization states, respectively. The first and second output signals are each compared with reference signals at the first and second frequencies to provide four phase shift and amplitude measurements that can be used to determine the at least one optical property of the optical device as a function of wavelength.

A method for measuring fundamental mode cutoff wavelength of single polarization fiber comprising: (i) launching pulsed light of at least one wavelength λ_i into one end of the single polarization fiber; (ii) measuring backscattered light intensity corresponding to said wavelength to obtain the backscattered light intensity as a function of fiber position, wherein the backscattered light propagates through the same end of the fiber; and (iii) determining at least one cutoff wavelength and the corresponding position within said fiber for the cutoff wavelength, based on a specified threshold light intensity level.