According to examples, a temperature or strain distribution sensor may include a photodiode to acquire a beat frequency between a first laser beam and a second laser beam. A modulator may modulate the first laser beam that is to be injected into a device under test (DUT). A coherent receiver may acquire a backscattered signal from the DUT, and use the second laser beam as a local oscillator to determine a Brillouin trace with respect to the DUT. The Brillouin trace may be used to determine a Brillouin frequency shift and a Brillouin power for the DUT to implement an absolute referencing of a Rayleigh reference trace. The coherent receiver may determine, relative to the Rayleigh reference trace, a further Brillouin frequency shift and a Rayleigh frequency shift to determine a temperature or a strain associated with the DUT.

An optical line testing device for measuring at least a cutting position of an optical line according to the present invention includes: a first wavelength tunable laser source configured to generate a first optical signal in which a plurality of wavelengths appear alternately and periodically; a second wavelength tunable laser source configured to generate a second optical signal which is identical to the first optical signal but has an adjustable delay time; and an interferometer configured to cause interference between a reflected optical signal, corresponding to the first optical signal, which is returning after having been emitted to the optical line, and the second optical signal to output an interference signal.

A cable identification system is provided. The cable identification system may include a laser pulse generator configured to emit laser pulses into the first optical-fiber cable segment. The cable identification system may include a polarization disturbance device configured to induce a change in polarization of a second optical-fiber cable segment via changing a position of the second optical-fiber cable segment. The cable identification system may include a polarization detection device configured to determine measures of polarization based upon backscattered light received from the first optical-fiber cable segment when the second optical-fiber cable segment has different positions. The polarization detection device may be configured to determine whether the first optical-fiber cable segment is connected to the second optical-fiber cable segment based upon the measures of polarization.

A multi-core fiber includes multiple optical cores, and for each different core of a set of different cores of the multiple optical cores, a total change in optical length is detected. The total change in optical length represents an accumulation of all changes in optical length for multiple segments of that different core up to a point on the multi-core fiber. A difference is determined between the total changes in optical length for cores of the set of different cores. A twist parameter and/or a bend angle associated with the multi-core fiber at the point on the multi-core fiber is/are determined based on the difference.

A method for distributedly measuring polarization transmission matrices of an optical fiber includes steps of: inputting a fully polarized pulse into the optical fiber with linear birefringence only; and demodulating polarization states of Rayleigh backscattered light at different points on the optical fiber from a pulse input end; after demodulating, dividing the polarization states of the Rayleigh backscattered light into Q groups in sequence, wherein every three polarization states are divided into one group; calculating a transmission matrix of Group N; and solving the equation set using a numerical analysis method for obtaining multiple solutions, and screening the multiple solutions according to characteristics of the polarization transmission matrix, wherein each time of screening provides a unique solution M.sub.x(N) of the equation set; continually updating M.sub.A values for iteration, so as to obtain the distribution of polarization transmission matrices of the optical fiber.

The disclosed technology in this patent document includes, among others, methods and apparatus for distributed measuring at least one of fiber bend or stress related characteristics along an optical path of a fiber under test (FUT) using both a light input unit and a light output unit connected to the FUT at one single end.

The disclosed technology includes, among others, methods and devices for measuring distributed fiber bend or stress related characteristics along an optical path of fiber under test (FUT) uses both a light input unit and a light output unit connected to the FUT at one single end.

The disclosed technology in this patent document includes, among others, methods apparatus for distributed measuring at least one fiber bend or stress related characteristics along an optical path of fiber under test (FUT) uses both a light input unit and a light output unit connected to the FUT at one single end.

An accurate measurement method and apparatus using an optical fiber are disclosed. A total change in optical length in an optical core in the optical fiber is determined that reflects an accumulation of all of the changes in optical length for multiple segment lengths of the optical core up to a point on the optical fiber. The total change in optical length in the optical core is provided for calculation of an average strain over a length of the optical core based on the detected total change in optical length.

The present disclosure concerns a photonic integrated circuit (10) and a method for interrogating a ring resonator (3) comprised therein. The circuit (10) comprises an optical port (4) for coupling light (L) into and out of the circuit (10). The circuit (10) further comprises a first waveguide (1) for receiving light (L1) from the optical port (4), and a second waveguide (2) for sending back light to the optical port (4). The ring resonator (3) is arranged between the first waveguide (1) and the second waveguide (2) for coupling a resonant wavelength () of the light therein between. The optical port (4) comprises a polarization splitting coupler for coupling light of a first polarization (P1) to and from the first waveguide (1) and coupling light of a second polarization (P2), orthogonal to the first polarization (P1), to and from the second waveguide (2).