Abstract: A method and assembly for frequency stabilisation of an optical signal especially from a laser, the assembly (11) comprising beam splitter (15), a passive frequency discriminator (16), and a pair of photodiodes (17 & 18). The beam splitter (15) in use receives a collimated optical beam (B) and diverts a sample beam (B1) which is directed towards the discriminator (16) which transmits a portion (B2) of said sample beam to one of the photodiodes (17) and reflects a second portion (B3) of said sample beam to the other photodiode (18). A control signal (S3) is derived from the respective intensities of the transmitted and reflected portions of the sample beam, and utilised to operate the electronic control to adjust the frequency of the laser output signal, if required, to maintain a specified frequency.

Abstract: A modulator arrangement for modulating an optical signal using a differential quadrature phase shift key for use in an optical wavelength division multiplex (WDM) optical communications system comprising a laser for producing an optical signal of a selected wavelength, which signal is split by a splitter (4), each part of said split signal being applied to a respective phase modulator (6, 8). The phase modulators (6, 8) are adapted to modulate the phase of the signal in dependence on a respective drive voltage and the phase of the output of at least one modulator is shiftable. The split signals are recombined by an optical recombiner (12) to form an optical phase shift key output. The arrangement further comprises a phase modulator (20) adapted to chirp the optical phase shift key output.

Abstract: The RF power passing through a given position in a monolithic microwave integrated circuit (MMIC) is determined using the Seebeck effect. The MMIC includes at least certain components of a voltage creating circuit, including a first Seebeck junction on the MMIC at a given position and a second Seebeck junction at a different position. The voltage generated between the two junctions as a result of differential heating caused by the passage of RF power through the given position is measured with a voltmeter. By calibration, the RF power is related to a measured Seebeck voltage created when the circuit is in operation and hence can be determined. The Seebeck circuitry may be independent of the MMIC circuitry or be integrated into the active circuitry of the MMIC itself.

Abstract: To make a grating substructure in semiconductor material for use in a DFB laser, a first layer of semiconductor material is doped at a first doping concentration. A second layer of the semiconductor material is formed over the first layer. The second layer is doped higher concentration than the first layer and sufficiently different to change the refractive index of the semiconductor material. A third layer doped at a concentration comparable with the first layer is formed over the second layer. An etch is performed through a mask to form spaced etched regions extending at least through the second and third layers. Then a further layer of the semiconductor material doped at a doping concentration comparable the first and third layers is overgrown on the wafer.

Abstract: An optical modulator comprises first and second optical waveguides having first and second electrodes respectively associated therewith, and an electrically conductive region associated with both waveguides. The electrodes have inputs for an electrical signal at input ends thereof, and outputs for the electrical signal at opposite output ends thereof. The conductive region is electrically connected to the output ends of the first and second electrodes such that an electric field created by the electrical signal between the first electrode and the conductive region is substantially equal in magnitude to an electric field created by the electrical signal between the second electrode and the conductive region. The balancing of the electric fields experienced by the waveguides enables the modulation of light in the two waveguides to be balanced.

Abstract: A Mach-Zehnder interferometer modulator for modulating a beam of laser light includes a pair of separate waveguides (115, 116) through which the laser light is passed after splitting in a splitting zone and after which the light is recombined in a merge zone, the waveguides being formed of a material having electro-optic properties and there being provided opposed pairs of electrodes (120, 114a, 121, 114b) electrically located so as to be able to effect optical changes within the material of the waveguides. The waveguides are formed in a semiconductor material with one of the electrodes of each pair being formed in a doped layer (114), the doped layer being of relatively high conductivity compared to the semiconductor material, buried within or below the waveguide material whilst the other electrode, the top electrode (120, 121), is a surface metalisation.

Abstract: An optical assembly includes a photodetector for detecting light signals. An optical fiber receives an input signal and has a light-emitting portion extending in front of the photodetector. A MEMS actuator is located between the light-emitting portion of the optical fiber and the photodetector. The MEMS actuator is controllably deflectable to partially obscure the photodetector and thereby vary the amount of light received.

Abstract: A system (10) comprises a carrier (1) which is adapted to carry an optical fiber (9) and an optical chip (3) having a circuit element (4). The carrier and the optical chip are provided with co-operable alignment features (13,14) for aligning the carrier with the optical chip so that the optical fiber and the circuit element are optically coupled.

Abstract: An optical spectral filtering device and associated method for selectively directing a portion of a wavelength multiplexed input signal, entering through an optical fiber, into one or more output signals provided to one or more optical fibers and/or electronic outputs. The optical filtering is accomplished using free-space diffractive wavelength demultiplexing optics combined with a fixed (permanent) patterned structure located in the spectrally dispersed image plane. The structure can block or direct a selected spectral portion of the optical signal to one or more separate outputs, such as an optical fiber or power detector. A single active element in the optical path is used to spatially shift, or steer, the entire input spectrum at the dispersed spectral image plane, to control the portion of the input spectrum illuminating specific features on the permanent patterned structure.

Abstract: A current tuned optical attenuator includes a Mach-Zehnder interferometer that relies on the creation of free carriers to create a phase difference in an optical signals along two waveguide arms.

Abstract: A modulator arrangement adapted to use a differential quadrature phase shift key for use in an optical wavelength division multiplex (WDM) optical communications system, comprising a precoder (16), which is adapted to generate drive voltages for first and second phrase modulators (6, 8) in dependence upon first and second data streams. The respective drive voltages for the first and second modulators (6, 8) are fed back to the precoder inputs with a delay related to the line speed of the data system, wherein the length of the delay corresponds to n bits.

Abstract: A signal time-scaling arrangement utilises a known configuration comprising the use of a laser which has its wavelength varied over time, a modulator coupled to the laser and to a modulating analogue electrical source and a dispersion means coupled to the output of the modulator and providing at its output a signal which is a stretched version of the analogue modulating signal, but provides for the modulator to be a single-sideband modulator instead of double-sideband. The effect of this is to enable the use of a much simple laser-control system involving a CW laser output which is wavelength-ramped continuously between quite narrow wavelength limits, while allowing the use of a dispersion means having a wide dispersion characteristic in order to provide the required degree of time-scaling. The invention is application to an ADC system or to a Doppler system.

Abstract: Semiconductor laser diodes, particularly high power ridge waveguide laser diodes, are often used in opto-electronics as so-called pump laser diodes for fiber amplifiers in optical communication lines. To provide the desired high power output and stability of such a laser diode and avoid degradation during use, the present invention concerns an improved design of such a device, the improvement in particular consisting in a way of suppressing the undesired first and higher order modes of the laser which consume energy and do not contribute to the optical output of the laser, thus reducing it's efficiency. Essentially, the novel effect is provided by a structure comprising CIG—for Complex Index Guiding—elements on top of the laser diode. These CIG elements consist of one or a plurality of layers and must contain at least one layer which provides the optical absorption of undesired modes of the lasing wavelength and preferably contains an insulating layer as a first contact layer to the semiconductor.

Abstract: A device comprises a tapered semiconductor optical waveguide which tapers, at an angle of taper with respect to a longitudinal axis of the waveguide, from a relatively wide region to a relatively narrow region, wherein the angle of taper varies along the length of the tapered waveguide such that at all points along the taper it is no greater than, and within a substantially constant angular separation of, the adiabatic limit of the fundamental mode of the waveguide at that point along the taper.

Abstract: A thermo-optic semiconductor device has one semiconductor region providing an optical waveguide and an adjacent semiconductor region providing a resistive heater between two doped regions, current may be passed through the resistive heater within the adjacent semiconductor region to heat it and thereby vary the optical characteristics of the waveguide.

Abstract: A glass fixative composition for bonding glass materials to non-glass materials is provided. The fixative composition is selected for its thermal expansion coefficient, its viscosity, its adhesion to glass, melting point, and bond strength. The glass fixative is in particular useful for bonding optical fibers to metallic materials such as Kovar. The low melting point of the glass fixative enables localized heating methods to be used, in particular, as Kovar is a ferromagnetic material, induction heating can be used to form a bond. The bond formed provides a compressive joint which enables the fiber to be hermetically fixed in position.

Abstract: An asymmetric MEMS thermal actuator device includes a base portion, typically a pair of bond pads, and an actuator element connected to the base portion by a flexure portion. The actuator element has a first arm and a second arm alongside the first arm and spaced from the first arm. The second arm is wider than the first arm so that the actuator element deflects about the flexure element due to differential heating in the first and second arms when an electrical current is passed therethrough. A cut-out portion is provided in the second arm adjacent the first arm so as to increase the spacing therefrom over at least a portion of the second arm. Preferably, a heat sink is also provided laterally adjacent the second arm.

Abstract: A semiconductor device such as a buried heterostructure semiconductor laser includes a semiconductor substrate supporting an active region comprised of a multiple quantum well active region and confinement layers having defined gratings and grating overgrowth regions to produce a laser device. The device also includes a current confinement layer including a sequence of doped n-p-n-p semiconductor layers to produce a n-p-n-p blocking structure and a semi-insulating semiconductor material deposited over the n-p-n-p blocking structure.

Abstract: A method of assembly is presented for a multi-wavelength optical monitor (MWOM) for use in fibre optic telecommunication networks. The method allows coarse optimisation to be used to align an input optical fibre and detector array relative to a wavelength division demultiplexing element. The detector array output data are transformed with a digital signal processor into relative intensities of the components of the spectrum or spectral parameters of telecommunication channels.

Abstract: An optical link is operative for transmitting a microwave signal in modulated optical form over an optical fiber. The optical link has a transmitter and a receiver. The transmitter splits and converts the microwave signal into two separate optical signals, each of which represents either the positive varying part of the microwave signal or the negative varying part of the microwave signal. The receiver combines the two separate optical signals and converts them back into the microwave signal.