Abstract:
A frequency-modulated light signal is introduced into an input 12 of a Mach-Zehnder interferometer 1. The light signals at the outputs 17 and 18 are converted into electrical signals and subtracted, giving an output signal in which the effect of the frequency-modulation is not overwhelmed by the effect of amplitude-modulation of the input signal.
Abstract:
This invention is a new type of Fabry-Perot cavity, and an optical communication system using such a cavity. The inventive Fabry-Perot cavity comprises both a waveguiding portion (43) and a nonwaveguiding portion (52,53). In this manner, tunable cavities of desirable mid-range length, necessary to obtain required free spectral ranges, may be fabricated with minimal diffraction losses otherwise associated with cavities of such length. The cavity length may be varied using, for example, piezoelectric elements, and the various cavity elements may be aligned and connected, using fiber connector technology.
Abstract:
Le procédé, et le dispositif correspondant, de détection des variations de temps de propagation dans l'anneau d'une interféromètre utilise une modulation de phase des ondes contra-rotatives parcourant l'anneau par des créneaux asymétriques à une période double d'un temps de propagation initial, qui créent des paliers à décalage de phase nul dans la modulation de la différence des deux ondes émergent de l'anneau. Ces paliers se traduisent par des impulsions dans le signal détecté de sortie dont la largeur est variable avec le temps de propagation. L'invention s'applique, notamment au contrôle de la longueur d'onde de la source de l'interféromètre, particulièrement du fait des variations de température de la source.
Abstract:
L'invention a pour objet un capteur interférométrique à fibre optique, du type comprenant une source laser, un interféromètre dont les bras sont de fibres optiques, l'un de ces bras comprenant une cellule de mesure, et un détecteur à la sortie de l'interféromètre, caractérisé en ce qu'il comprend: - un premier coupleur (2) séparant l'onde émise par la source laser (1) en deux. - un bras de référence (3) à fibre optique transmettant une des parties de l'onde à un deuxième coupleur (4), - un bras de mesure (5) à fibre optique comprenant au moins une cellule de mesure (6) et parcouru par l'autre partie de l'onde, ce bras de mesure (5) étant terminé par une surface réfléchissante (7) qui renvoie une onde réfléchie vers le premier coupleur (2),
- un bras de renvoi (8) à fibre optique transmettant l'une des parties de l'onde réfléchie depuis le premier coupleur (2) vers le second coupleur (4), - ainsi qu'un détecteur (10) sur lequel interfère l'onde transmise par le bras de renvoi (8) et l'onde transmis par le bras de référence (3).
L'invention trouve en particulier une application dans la mesure des températures.
Abstract:
A closed loop optical fiber interferometer is used in sensing a quantity, Q, by applying a time varying or modulated measure of, Q, asymmetrically to the closed loop (24) and detecting phase shift between two counterpropagating optical signals in the closed loop. The closed loop (24) can be used as the sensing element or a separate sensor (68, 70) can develop a time varying signal which is then applied to the closed loop interferometer.
Abstract:
A system and method for phase-readout/control and active stabilization on arbitrary interferometric phase in the optical interferometer platform is disclosed. The method makes use of a bi-colored polarization-multiplexed reference laser scheme. The disclosed scheme is based on two phase-locked reference signals with different frequencies that together remove the phase ambiguity. The two signals are polarization-multiplexed (either in free-space or optical fiber implementations) to enable easy separation and combining of these two signals through the use of polarization beam-splitters. The disclosed scheme provides a one-to-one map between phase and feedback signal levels, and enables phase- readout and stabilization even when one of the feedback-signals is at a maximum/minimum.
Abstract:
In some example embodiments there is provided an apparatus. The apparatus may include a first delay line passing a first portion of an optical signal to produce a first input signal. The apparatus may further include a second delay line passing a second portion of the optical signal to produce a second input signal. A combiner may combine the first input signal and the second input signal to produce a plurality of output signals. An analyzer may determine from the plurality of output signals at least a wavelength of the optical signal.
Abstract:
An illustrative interferometric system with high-fidelity optical phase demodulation includes a receiver having a fiberoptic coupler that produces optical mterferometry signals having mutual phase separations of 120° and balanced photo- detectors that each produce an electrical difference signal based on a respective pair of said optical mterferometry signals. The system further includes circuitry that converts the electrical difference signals into measurements of an interferometric phase.
Abstract:
A waveguide spectrum analyser comprises an input waveguide (10) for receiving a beam of electromagnetic radiation to be spectrally analysed, a plurality of output waveguides (14, 16) which are single mode for wavelengths longer than a certain minimum, a substantially wavelength independent splitter (18) for splitting the input radiation between the single-mode output waveguides, and an array (24) of radiation- sensitive detector elements (30). Each output waveguide has a respective exit port (20, 22) facing the detector array so that radiation from the exit port is diffracted onto the array. The separation of the exit ports and the distance to the detector array is selected such that at least for a range of wavelengths longer than the certain minimum a plurality of interference fringes are produced at the array each extending across sufficient detector elements to allow spatial sampling of the fringes above the Nyquist rate. Data processing means (26) is provided for sampling the detector array to capture an image of the fringes and transforming the captured image data to the frequency domain, preferably using HTP and/or DFTS processing techniques.
Abstract:
Wavefront sensing apparatus comprises a beam splitter (106) for combining a wavefront to be characterised (105) with a frequency-shifted plane wavefront (111) and a bundle of optical fibres (112) arranged to detect the combined beam at a plurality of positions across the combined beam. Output from individual fibres of the bundle are detected to produce corresponding heterodyne signals, the phases of which are extracted by demodulation. By fitting the extracted phases to an assumed functional form for the phase of the wavefront to be characterised, the piston, tip, tilt and radius of curvature phase parameters of the wavefront to be characterised may be found at the position of the fibre bundle. In contrast, prior art methods of wavefront characterisation only allow the piston phase of the wavefront to be characterised to be obtained.