A method detects discontinuities in an optical channel using two laser units that respectively have a laser and an electroabsorption modulator. The reference frequencies of the two lasers have a predetermined reference frequency difference. The optical ports of the electroabsorption modulator are fed to the two inputs of a polarization beam splitter and the output of the polarization beam splitter is connected to the optical channel. A test pulse is applied simultaneously to the two electroabsorption modulators and laser light from the lasers is thus transmitted through the respective electroabsorption modulators during the time of the test pulse. The test pulse is divided into two time periods, and during the first time period the lasers are operated with their respective reference frequency, and during the second time period the emission frequencies of the lasers are detuned with respect to the reference frequencies, by a predetermined detuning frequency difference.

According to examples, a fiber-optic testing source for testing a multi-fiber cable may include a laser source communicatively coupled to a plurality of optical fibers connected to a connector. The fiber-optic testing source may include at least one photodiode communicatively coupled to at least one of the plurality of optical fibers by at least one corresponding splitter to implement a communication channel between the fiber-optic testing source and a fiber-optic testing receiver. The communication channel may be operable independently from a polarity associated with the multi-fiber cable. The fiber-optic testing receiver may include a plurality of photodiodes communicatively coupled to a plurality of optical fibers. The fiber-optic testing receiver may include at least one laser source communicatively coupled to at least one of the plurality of optical fibers by at least one corresponding splitter to implement the communication channel between the fiber-optic testing receiver and a fiber-optic testing source.

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 optical fiber array includes a support, a single-mode optical fiber and a plurality of multimode optical fibers, the single-mode optical fiber and the multimode optical fibers being arranged on the support, and a polarizing plate provided on an end face of the support, wherein the single-mode optical fiber has polarization maintaining characteristics, an end face of the single-mode optical fiber and end faces of the multimode optical fibers face the end face of the support, and the polarizing plate covers the end faces of the multimode optical fibers.

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 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.

An optical frequency-domain reflectometer (OFDR) capable of estimating the transfer matrix of a multimode optical fiber using mode-selective measurements performed from a single end of the fiber. In an example embodiment, the multimode optical fiber includes distributed reflectors designed to generate relatively strong light reflections along the length of the fiber at a desired spatial resolution. The embodiments may employ a signal-processing algorithm to estimate the fiber's transfer matrix by estimating segment transfer matrices corresponding to the fiber segments located between different ones of the distributed reflectors. Different embodiments of the disclosed OFDR can beneficially be adapted for use in different applications, such as fiber-optic component and module characterization, distributed optical sensing, biomedical imaging, OCT, etc.

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.

The present invention provides an ellipsometry device and an ellipsometry method whereby measurement efficiency can be enhanced. In this method, an object is illuminated by spherical-wave-like illumination light Q linearly polarized at 45 (S1), and an object light O, being a reflected light, is acquired in a hologram I.sub.OR using a spherical-wave-like reference light R having a condensing point near the condensing point of the illumination light Q, and a hologram I.sub.LR of the reference light R is furthermore acquired using a spherical-wave reference light L having the same condensing point as that of the illumination light Q (S2). The holograms are separated into p- and s-polarized light holograms I.sup.K.sub.OR, I.sup.K.sub.LR, =p, s and processed to extract object light waves, and object light spatial frequency spectra G.sup.K(u, v), =p, s are generated (S3) (S4). Ellipsometric angles (), () are obtained for each incident angle from the amplitude reflection coefficient ratio =G.sup.p/G.sup.s=tan .Math.exp(i). Through use of numerous lights having different incident angles included in the illumination light Q, data of numerous reflection lights can be acquired collectively in a hologram and can be processed.

A method detects discontinuities in an optical channel using two laser units that respectively have a laser and an electroabsorption modulator. The reference frequencies of the two lasers have a predetermined reference frequency difference. The optical ports of the electroabsorption modulator are fed to the two inputs of a polarization beam splitter and the output of the polarization beam splitter is connected to the optical channel. A test pulse is applied simultaneously to the two electroabsorption modulators and laser light from the lasers is thus transmitted through the respective electroabsorption modulators during the time of the test pulse. The test pulse is divided into two time periods, and during the first time period the lasers are operated with their respective reference frequency, and during the second time period the emission frequencies of the lasers are detuned with respect to the reference frequencies, by a predetermined detuning frequency difference.