International Standard Electric Corporation

Nortel Networks Corporation

Northern Telecom Limited

Itt Industries, Inc.

Stc, Inc

Itt Gallium Arsenide Technology Center, a Division of Itt Corporation

Standard Telephones and Cables Public Limited Company

Itt Gallium Arsenide Technology Center

George H Thompson

David F Lovelace

James E Whiteaway

Terry Bricheno

Piers James Dawe

Mark Acton Gibbon

Richard E Epworth

John C Greenwood

Alan Fielding

Jun Yu

Peter Richard Selway

Claude Rolland

Igor K Czajknwski

David A Spear

David Owen Yevick

A planar dispersion compensator for an optical signal is provided. The compensator decomposes an inputted optical signal into N component signals separated by a fractional wavelength &dgr;&lgr;. Each component signal has its path-length adjusted to induce a sufficient phase shift between input and output to change the group delay of the optical signal when recombined from each of the component signals. In this manner, pulse broadening can be compensated by selectively varying the induced phase shifts to produce the desired level of opposite group delay.

Planar waveguide dispersion compensator

Arrayed waveguide grating

An optical comb filter is constructed from a monolithic arrangement of two identical integrated optics format arrayed waveguide diffraction gratings connected back-to-back via a star coupler incorporating a field stop (spatial filter,Alternatively, only one of the diffraction gratings is employed in conjunction with a combined field stop and retro-reflector, the other end of the diffraction grating being optically coupled with one port of an optical circulator.

Optical comb filter

Optical multiplexter/demultiplexer

An monolithic version of optical multiplexer/demultiplexer with an improved spectral characteristic is provided by two diffraction gratings arranged optically in tandem and with a field stop in the coupling between them, the gratings also being arranged to provide free spectral ranges differing by a factor of at least two, and having a coupling between them that carries over into the second grating information concerning the dispersion afforded by the first grating. The field stop is constituted by a pair of etched troughs arranged in the pattern of an open chevron.

Optical multiplexer/demultiplexer

Semiconductor lasers

A MQW semiconductor Mach Zehnder phase modulator is formed by two Y-junctions (12, 32), each having a single waveguide (14) optically coupled with two branch waveguides (18, 20). The branch waveguides of the two Y-juntions are optically coupled in Mach-Zehnder configuration that, under zero bias conditions, has one interferometric arm longer than the other to provide a .pi. phase shift. The additional length is preferably accommodated in the branches of the Y-junctions. The phase shift, in combination with voltage dependent absorption properties and non-linear phase variations of the MQW guided regions in the Mach-Zehnder modulator results in a negative chirp and high extinction ratio for an equal, push-pull device configuration.

Semiconductor modulator with a .pi. shift

The saturation effects observed in an MQW electro-absorption modulator are reduced by modifying the composition of the MQW structure so that the barrier layers, that are interleaved with the quantum well layers, are in tension.

Electro absorption optical modulators

An integrated optics polarization state converter comprises optically in series a first TM.sub.0 to TM.sub.1 mode converter that is substantially transparent to TE.sub.0, a concatenation of total internal reflectors and a second TM.sub.0 to TM.sub.1 converter, similarly substantially transparent to TE.sub.0, which is connected the way round so as to operate as a TM.sub.1 to TM.sub.0 converter. Each TM.sub.0 to TM.sub.1 converter may comprise a tandem arrangement of a 2.times.2 TE.sub.0 /TM.sub.0 polarization beam splitting coupler and a mismatched, 3 dB maximum, 2.times.2 beam splitting coupler. The place of the TM.sub.0 to TM.sub.1 converters substantially transparent to TE.sub.0 may be taken by TE.sub.0 to TE.sub.1 converters substantially transparent to TM.sub.0.

Polarization state converter

A technique for achieving a substantially planar structure incorporating embedded vapor phase epitaxial growth involves the use of a window-frame shaped mask 40 of epitaxial growth resistant material to define a well in which embedded growth is to occur, and subsequently to ease mask registration problems in the location of a mask 60 employed while selectively removing unwanted material epitaxially grown on regions surrounding the well. Complementary format structures may also be formed in which epitaxial growth is provided up the sides of a mesa to substantially the same height as material grown on top of the mesa itself.

Semiconductor device manufacture

A one-dimensional reflective-type diffraction grating is formed in a slab waveguide by a one-dimensional array of wells formed with substantially perpendicular walls.

Diffraction grating

A photo-detector in the form of an optical field effect transistor comprig a semi-insulating InP substrate (1), a p.sup.+InP gate region ( 2) an n.sup.- InGaAs channel region (3) and source and drain contacts (5,6). Light incident on the bottom face of the substrate is detected. The channel region is thicker and reduced in doping in comparison with a normal JFET in order to achieve efficient light absorption and low gate to source capacitance. The source and drain contacts are interdigitated to increase the area for optical absorption (FIG. 1). Alternatively, (FIG. 2), the channel region is a composite structure including a lowly doped layer (11) for directing photogenerated carriers to a more highly doped layer (12) (active channel layer) of reduced dimensions of reduced area and upon which strip-like source and drain contacts (9,10) are disposed. The optical FET structures proposed facilitate integration with other circuit elements.

Heterojunction photo-detector with transparent gate

A coupled waveguide injection laser is provided with two waveguiding ridges (36,37 or 60,61) that are configured such that the coupling between them produces a first order supermode for which a signal current modulation produces optical amplitude modulation with substantially no attendant frequency modulation. In a related structure the configuration affords the facility of providing for the zero order supermode optical frequency modulation with substantially no attendant amplitude modulation.

Coupled waveguide injection laser

A photoconductor comprising an optically sensitive FET in which an abrupt heterojunction (18) is inserted in the channel (11) at a certain distance from the gate contact (16). This provides a potential barrier (17, FIG. 4) in the valence band that accumulates minority carriers (carriers of the lower mobility type) and controls their release. A gate bias resistor which is conventionally used in a receiver circuit including the FET is no longer required, instead the potential barrier height determines the time constant and a response comparable in length with an input optical pulse is achieved. This overcomes the problems of integrated manufacture, and slow response, associated with the large value of the bias resistor which is needed to reduce noise.

FET photoconductor with a heterojunction in the channel

An injection laser array has 2.sup.n output elements (1) coupled by Y couplers (2, 4, 6) and (n-1) in sets of intermediate elements to a single element (7) in a tree configuration. The face end of the single element is provided with a high reflectivity coating (8) while those of the 2.sup.n output elements are provided with low a reflectivity coating (9).

Growing community of inventors

Sawbridgeworth, United Kingdom

George H Thompson