Abstract: An optical intensity modulator for high-speed RZ and NRZ data modulation based on a balanced three-arm Mach-Zehnder interferometer. The three arms are joined at the input and output sides of the device by three-way couplers. The input coupler is structured to couple approximately equal powers into the first and third arms and no more than 50% power into the second arm. In the straight sections of the arms, there is arranged an AC electrode structure for applying an RF modulation signal and a DC electrode structure for biasing the device at a working point. The AC electrode structure is arranged so that an applied modulation signal induces a negative phase shift (−&Dgr;&PHgr;) in the first arm in relation to the second arm and a positive phase shift (+&Dgr;&PHgr;) in the third arm in relation to the second arm. Large notch widths of up to 12 times the notch width of a conventional two-arm Mach-Zehnder modulator are achievable.

Abstract: An optical window signal generator which begins generation of an optical output signal in response to an optical activation pulse, and terminates generation of the optical output signal in response to an optical deactivation pulse. The rise time of the optical output signal is equal to the rise time of the optical activation pulse, and its fall time is equal to the rise time of the optical deactivation pulse.

Abstract: An apparatus for gating an optical signal comprising: an input stage arranged to receive and combine first and second optical control signals (ON, OFF) of first and second wavelengths, and an optical signal (SIGNAL IN) to be gated of a third wavelength. A gain medium is arranged to receive the signals SIGNAL IN, ON and OFF from the input stage. The gain medium (e.g. YAG) comprises a transition metal dopant (e.g. Cr4+) that has an excited state populatable by the first control signal and depopulatable by the second control signal to allow selective amplification of the optical signal to be gated by stimulated emission from the excited state responsive to the control signals. The amplification process has a very fast switch-on time that is several orders of magnitude faster than in prior art devices based on the rare earth dopant Er3+. This allows the apparatus to be used for high-speed optical switching applications, such as routing of data packets in an optical packet switching network.

Abstract: An optical device for providing threshold and comparison functions. The device comprises first and second SOA's having respective first and second propagation paths along which the first and second optical signals, input as signals Pin1(&lgr;1) and Pin2(&lgr;2) travel in first and second forward directions. A feedback path is provided using couplers to interconnect the outputs of the SOA's. As a result, a portion of the optical signals output from each SOA is supplied backwards into the output of the other SOA as feedback optical control signals Pfeedback1(&lgr;1) and Pfeedback2(&lgr;2). The feedback optical control signals modulate the gain of the forwards travelling optical signals by cross gain modulation (XGM). In contrast to prior art devices, the optical control signal is supplied backwards into the SOA's in a counter-propagating configuration. This allows much shorter feedback path lengths to be achieved in comparison to what is possible with prior art co-propagating configurations.

Abstract: An optical device having a first input for at least one input optical signal having a random state of polarization and a first optical element capable of dividing, in space, the input optical signal into a pair of optical signals which are substantially parallel and have a predetermined state of polarization perpendicular to each another. The optical device also having a first crystal element for propagation, in free space, of at least the pair of optical signals coming from the first optical element, and the first crystal element being devoid of internal separation planes, and having electro-optical properties and being associated with electrodes so as to apply a voltage in a direction substantially perpendicular to the direction of propagation, along the first crystal element, of the at least one pair of optical signals.

Abstract: In an interferometer configuration, a retarder in the form of a half-wave plate (125) and a phase shifter in the form of a glass plate (120) are arranged in one arm (114). The phase shifter provides an optical path difference between the interferometer arms which needs to be greater than the coherence length of the input light to be polarization stabilized. A polarizer in the form of a linear polarizer (118) aligned at 45° to the half-wave plate is arranged across both interferometer arms (114 & 116). Polarization stabilization action is achieved by the retarder in combination with the polarizer. More specifically, for at least one input polarization state, the polarization states in the two interferometer arms are rendered orthogonal by the retarder, the polarizer being aligned to allow only one of the two orthogonal states to be transmitted, the other being absorbed. The device is expected to find application for WDM networks based on broadband sources, such as superluminescent diodes.

Abstract: An optical device for processing a digital optical signal in parallel and in free space, the said device comprising:

Abstract: An optical device is provided for processing a digital optical signal in parallel and in free space. A device consistent with the invention provides for inputting a digital optical signal in guided propagation, converting the digital optical signal to n digital optical signals in guided propagation, and converting the n digital optical signals to n digital optical signals in free space. In addition, the invention provides for selecting a bit preselected from the at least one temporal series of n bits of each of the n digital optical signals, modifying optically, at least one bit of the spatial figure of the n bits, and outputting the at least one bit of the spatial figure of n bits.

Abstract: An optical device to perform an asynchronous and parallel processing of a N bits serial stream of an optical digital signal comprises a) a serial to parallel converter which converts the serial stream of N bits into a first parallel pattern of N bits carrying the same information as the serial stream of N bits; b) an optical system to produce, from the parallel pattern of N bits, a first two-dimensional (2-D) image made of N rows and M columns (N×M) of bits, each column being associated to the digital optical signal by a predetermined relationship; c) a logic device to perform logic operations on the bits of the first 2-D image; and d) a device to send to an output the results of the logic operations.

Abstract: There is provided an optical wavelength converter which allows the rapid and efficient shifting of information modulated on a light signal of one wavelength to a light signal of a second wavelength without the negative effects of noise and other disturbances which have proven to be problems in the prior art. The device splits a CW probe signal of a first wavelength into two components, which propagate with opposite orientations through a Kerr leg. Also propagating in the Kerr leg is a modulated drive signal at a second wavelength. These signals interact in the Kerr leg, and are recombined at an output coupler so as to create interference between the two probe components. An intensity modulated probe signal is output.

Abstract: There is provided a method and apparatus for measuring the optical properties of bulk samples. A probe laser beam is fed into the two arms of the apparatus, a reference arm and a measurement arm, both of which contain optical fiber to conduct the laser lights. The measurement arm includes a free space area for mounting a sample to be tested. The probe beam is directed into the sample in free space. The sample also receives light in free space, rather than via the optical fiber, from a second, pump laser. The interaction of the sample and the pump laser affect the optical properties of the sample. This change in optical properties can be detected by comparing the output signals from the measurement and reference arms.

Abstract: Optical switching device comprising:a) first elementary switching module which in turn comprises i) a crystalline element without internal planes of separation and which is capable of rotating the plane of polarization of a polarized optical signal by a predetermined angle under the action of an optical control beam, and ii) a polarization analyzer capable of selecting, according to a predetermined plane, the said polarized optical signal issuing from the said crystalline element, b) first means for supplying the said polarized optical signal to the said elementary switching module, and c) second means for supplying the said optical control beam to the said elementary switching module, in which the said first and second means route at least two different polarized optical signals and at least one optical control beam in the said crystalline element such that the said at least one control beam is substantially collinear with and superimposed on the said at least two polarized optical signals.

Abstract: A superluminescent source emits a wide-band light beam, that is frequency modulated by a filter with a pass band centred on a frequency that is made to vary according to a predetermined law so as to frequency modulate the light beam. Means for splitting and recombining beams determine a mutual phase shift between two components of the beam that depends on the physical magnitude to be measured and is detected by a detector as an indication of the value of the magnitude itself.

Abstract: In a laser apparatus for measuring the velocity of a fluid, a measurement laser light beam (M) fed into the fluid and scattered by a particle within the fluid is made to interfere with a reference laser light beam (R) to generate an interference signal based on the velocity of the particle; the apparatus comprises a low-coherence laser source (10) and interferometric means (11, 12) which split the light beam of the laser source (10) into the stated reference light beam (R) and measurement light beam (M), and cause the reference light beam (R) derived from the laser source (10) to interfere with the backscattered component resulting from the scattering of the measurement light beam (M).

Abstract: In a polarimetric fibre-optic sensor using a polarization-maintaining optical fibre with two light propagation modes, a reference light signal is fed to propagate along the optical fibre in accordance with one propagation mode, a series of measurement light signals being induced by a series of optical fibre deformation elements, to propagate along the optical fibre in accordance with the other propagation mode, each being unbalanced in time with respect to the reference light signal by an amount which is different from that of the other measurement light signals; by using particular interferometric techniques, compensating the unbalances and analyzing the signals resulting from the interference between the measurement light signals and the reference light signal it is possible to determine and locate a physical phenomenon which disturbs the optical fibre.

Abstract: The detector comprises an electro-optical section for the signal analysis, a transmission fibre-optic, a fibre-optic coupling of high immunity to environmental noise, and a fibre-optic sensor terminating in a reflecting element. It can be provided in either homodyne or heterodyne version (phase or frequency modulation). This latter version has the advantage of detecting phase modulations exceeding 2.pi. radians. Both the versions have the advantage of enabling measurements to be made which are not influenced by environmental disturbances affecting the transmission fibre-optic.

Abstract: The invention relates to an inerferometer based on the exploitation of an optical fibre through which both the phase signal which is of interest for the measurements concerned and a reference signal are simultaneously forwarded in order that in the differential measurement the noise introduced by the optical fibre for both thermal and mechanical reasons is ruled out.