A resonance fiber-optic gyro (RFOG) with quadrature error reducer is provided. The RFOG with quadrature error reducer includes a laser assembly, a fiber resonator assembly, a resonance tracking loop and a quadrature error reducer circuit. The resonance tracking loop, coupled to an output of the finder resonator assembly, is used to generate a resonance frequency signal that is coupled to an OPLL mixer in one of a CCW OPLL or the CW OPLL of the laser assembly. The quadrature error reducer circuit includes an amplitude control loop and a second harmonic phase control loop. The amplitude control loop is used to generate a common modulation signal. An output of the amplitude control loop is coupled to a common phase modulator in the laser assembly. The second harmonic phase control loop is used to selectively adjust a phase of a second harmonic modulation signal in the amplitude control loop at startup.

A method comprises receiving a first optical signal and a second optical signal at or near an optical resonator, where the first optical signal includes a clockwise (CW) optical signal and the second optical signal includes a counter clockwise optical signal; injecting the first optical signal and the second optical signal into a resonator loop closure optics system of the optical resonator; sampling a portion of the first optical signal and a portion of the second optical signal; combining the portion of the first optical signal and the second optical signal; converting the combined optical signals to an analog electrical signal; digitizing the analog electrical signal; storing an estimated frequency of a beat signal created by a combination of the CW optical signal and the CCW optical signal; and using the stored estimated beat signal frequency, digitally phase lock to a frequency of the beat signal.

A device includes an optical resonator having four ports including a first port, a second port, a third port, and a fourth port. A first electronic circuit is configured to calculate a first information representative of a power difference between optical signals supplied by two of the four ports. A method of operating a device is also disclosed.

A fiber-optic interferometer is designed to receive and propagate a first single-mode wave along a first optical path and, respectively, a second single-mode wave along a second optical path, the second optical path being the reverse of the first optical path, and to form a first output wave and, respectively, a second output wave, having a modulated phase difference .sub.m(t). According to the invention, the modulated phase difference .sub.m(t) is equal to sum of a first periodic phase difference .sub.(t) having a level equal to , a second periodic phase difference .sub.alpha(t) having a level equal to alpha and a third periodic phase difference .sub.beta(t) having a variable level between beta and +beta, said modulated phase difference .sub.m(t) comprising per modulation period T at least eight modulation levels among twelve modulation levels and said modulated phase difference between such that: .sub.m(t+T/2)=.sub.m(t).

A passive ring interferometer sensor includes an electromagnetic ring path configured to receive a pair of electromagnetic waves from an electromagnetic radiation source and to direct the waves to be counter-propagating within the ring path toward respective ends of the path. A combination junction receives the waves from the respective ends and combines the waves to be co-propagating within a coupling path. Polarization elements are configured to set the waves to be mutually co-polarized within the electromagnetic ring path and to be mutually cross-polarized within the coupling path. A detector is configured to receive the mutually cross-polarized waves from the coupling path and to detect second-order coherence. Embodiments can sense rotation rate as fiber-optic gyroscopes or serve as other types of sensors such as gravitational wave sensors. Embodiments may have greatly increased unambiguous range and decreased sensitivity to any centroid wavelength shift.

An optical fiber ring interferometer is provided, which is based on a common light path for two or more light beam pairs preferably originated from two or more light sources of a substantially different spectrum or from a single light source split spectrum and whereas each light beam of a specific pair is propagating in relative opposite directions, wherein at least one pair of light beams is utilized to detect acousto-mechanical events and to provide information regarding location and other characteristics of detected environmental disturbance.

An interferometric optical fibre sensor comprises optical fibre defining an optical circuit configured to propagate a first optical wave via an environment in which the optical fibre can be exposed to a stimulus that modifies the first optical wave, and a second optical wave, and to combine the first optical wave and the second optical wave to create an interference signal containing information about the stimulus, wherein optical fibre propagating either or both of the first optical wave and the second optical wave comprises hollow core optical fibre configured to propagate the optical wave or waves by an antiresonant optical guidance effect.

An optical gyroscope includes, in part, an optical switch, a pair of optical rings and a pair of photodetectors. The optical switch supplies a laser beam. The first optical ring delivers a first portion of the beam in a clockwise direction during the first half of a period, and a first portion of the beam in a counter clockwise direction during the second half of the period. The second optical ring delivers a second portion of the beam in a counter clockwise direction during the first half of the period, and a second portion of the beam in a clockwise direction during the second half of the period. The first photodetector receives the beams delivered by the first and second optical rings during the first half of the period. The second photodetector receives the beams delivered by the first and second optical rings during the second half of the period.

An optical resonator is provided. The optical resonator comprises: an optical resonator coil comprising a first port and a second port; wherein the optical resonator coil comprises antiresonant nodeless fiber; a resonator loop closure optics system; and wherein the antiresonant nodeless fiber has a length such that the resonant frequencies the optical resonator of the desired polarization state of light and of the undesired polarization state of light are separated by between a tenth of a free spectral range and nine tenths of a free spectral range to minimize gyroscope errors.

A method comprises: receiving a first optical signal and a second optical signal; injecting a portion of the first optical signal into an optical resonator; injecting a portion of the second optical signal into the optical resonator, where the first optical signal and the second optical signal propagate in opposite directions in the optical resonator; emitting a portion of the first optical signal; emitting a portion of the second optical signal; coupling, by free space optics, a portion of the emitted first optical signal to a first power detector; coupling, by free space optics, a portion of the emitted second optical signal to a second power detector; adjusting the power level of the received first optical signal based upon a first detected power level detected by the first power detector; and adjusting the power level of the received second optical signal based upon a second detected power level detected by the second power detector.