A transmitter generates a first electrical signal comprising a first low-frequency signal, an empty period, and a pump pulse having a first frequency; and a second electrical signal comprising a second low-frequency signal and at least two probe pulses, each probe pulse having a second frequency that differs from the first frequency. The transmitter modulates first and second optical subcarriers having different polarizations using the first and second electrical signals, respectively. The transmitter generates an optical signal from the first and second optical subcarriers, wherein the first and second low-frequency signals overlap in time, wherein the empty period overlaps in time with one of the probe pulses, and wherein the pump pulse overlaps in time with another one of the probe pulses. The optical signal is detected at a receiver over an optical link, and the receiver uses the optical signal to estimate nonlinear phase shift in the optical link.

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 fiber sensor system includes a light source, a modulation unit, an optical coupler, a polarization separator, a first polarization controller optically coupled to the polarization separator, and a first detection unit that includes a first optical detector that receives the first component, converts the first component into a first electrical signal, and detects stress. The first polarization controller controls a polarization state of light input to the polarization separator so that the first electrical signal exhibits a first-order response to the stress.

The invention provides a measurement system to interrogate at least one birefringent optical sensor and a method to interrogate birefringent optical sensors at high speed and high resolution. The system and method detects, at least, a first and a second spectral feature that are polarization dependent, wherein the detected first and second spectral features correspond to different responses of at least one birefringent optical sensor.

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).

A first optical path and a second optical path have a common path branching point. An OTDR sampling optical signal is emitted into the first optical path and into the second optical path through the common path branching point. At least one predefined optical property of the OTDR sampling optical signal emitted into the second optical path is altered and/or of a reflection of the OTDR sampling optical signal received from the second optical path is altered. An OTDR reflected optical signal resulting from a reflection of the OTDR sampling optical signal on the first optical path and/or from a reflection on the second optical path is detected. The OTDR reflected optical signal is analyzed to determine, based on the at least one predefined optical property, whether the OTDR reflected optical signal resulted from a reflection on the first optical path and/or on the second optical path.

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 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.

Various embodiments relate to a method including: coupling one or more optical spatial pilot signals into a first end of optical fiber, wherein the optical fiber is a multimode optical fiber; Reflecting and modifying each mode of the optical pilot signals at a second end of the optical fiber; receiving a reflected portion of the one or more optical spatial pilot signals at the first end of the of the optical fiber in response to the reflected portion having propagated through the optical fiber in both directions; processing the reflected spatial pilot to determine components of one of a round-trip transfer matrix of the optical fiber and a single-direction transfer matrix of the optical fiber.

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.