Abstract: An asymmetric Fabry-Perot modulator comprises a multiple quantum well (MQW) p-i-n diode (8, 10, 12) defined by a front surface of reflectivity 0.3 and back surface of reflectivity 0.95. The cavity length L is such that resonance occurs close to the long wavelength side of the unbiased MQW absorption edge so that application of a bias signal to the MQW (12) causes the reflectivity of the cavity to become close to zero. This arrangement provides a high contrast modulator less sensitive to temperature variations and deviations from ideal reflectivities of the front and back surfaces than high-finesse Fabry-Perot modulators.

Abstract: A surface emitting photonic switching structure includes an intermediate semiconductor structure having pn junction is sandwiched between a first semiconductor multi-layer film mirror (DBR1) and a second semiconductor multi-layer film mirror (DBR2). A pair of electrodes are provided to the intermediate semiconductor structure and the pn junction therein is applied with reverse bias voltages for changing the effective optical length of the intermediate semiconductor structure so as to change transmission wavelength of light incident on the second multi-layer film mirror or the first multi-layer film mirror. The structure can be two-dimensionally integrated, be compact and is capable of operating with low voltages.

Abstract: An object of the invention to vary a light absorption coefficient within wider limits in a light absorption control semiconductor device. The device includes at least three quantum wells Q1, Q2, Q3. The width of the respective quantum wells and barriers is set such that wave functions of electrons in the respective quantum wells interact in a resonance state where the quantized energy levels in either one of conduction and valence bands are matched. In addition, the width and material of the respective quantum wells are set so that one of the bands is brought into the resonance state where the quantized energy levels at the respective quantum wells are matched in a state where no electric field is applied or a state where a suitable electric field is applied in a direction perpendicular to the junctions. The light absorption is changed by controlling components of the electric field perpendicular to the junctions.

Abstract: A spatial light modulator includes a multiple quantum well (MQW) device. Unlike MQWs of the prior art, this MQW is made semi-insulating. As a result, individual picture elements can be defined entirely by the placement of electrodes in an array on a surface of the device. Them is no need to etch trenches for electrical isolation of the picture elements.

Abstract: An opto-electronic semiconductor device including a variable strained layered quantum well structure having at least two superimposed heavy- and light-hole triangular bottom valance band quantum wells with mutually opposite slopes. Upon the application of a bias potential across a thickness dimension of the quantum wells, an electric field is generated therethrough which produces an interchange of the confined energy levels of heavy-holes and light-holes in the quantum wells which causes a change in the transmission characteristics of light passing through the device as a result of the heavy- and light-hole energy bands having different light absorption anisotropy.

Abstract: Integrated electrooptic modulator and process for the production thereof. This modulator comprises a substrate (2), a guide structure having a guiding layer (14) defining a microguide (16) for the propagation of beams, interposed between the lower and upper layers (12, 18) having indices below that of the guiding layer, a cavity (20) made in the upper layer, an active material such as an active, solid, organic polymer (26), whose index can be electrically modified and which fills the cavity and serves as an optical guide, a confinement layer (28) covering the polymer and the guide structure, the indices of the upper layer and the confinement layer being below that of the polymer, two electrodes placed on either side of the polymer, an electrode (6) being positioned between the lower layer and the substrate and the other electrode (30) is located on the confinement layer.

Abstract: An optic modulator having a transparent piezoelectric substrate, an active multiple quantum well (MQW) epilayer with bottom electrical contacts bonded to the substrate, wherein the substrate is cut such that its thermal expansion coefficient is matched or roughly matched to that of the MQW epilayer in the direction parallel to the long axes of the bottom contacts and so that the piezoelectrically-active direction of the substrate is normal to the long axes of the bottom contacts. In order to control the bias of the MQW epilayer a transparent contact is disposed over the MQW epilayer. In operation, the piezoelectric substrate, when activated, will displace an anisotropic strain on the MQW epilayer which will break the rotational symmetry in the plane of the MQW. This will result in anisotropic mixing of the heavy and light holes in the MQW epilayer and thus, will result in an anisotropic excitonic absorption of light normal to the MQW epilayer.

Abstract: The present invention is a spatial light modulator which uses an uniaxially trained multiple quantum well (MQW) structure with an anisotropic absorption to rotate the polarization of light normal to the MQW structure. The anisotropy which produces this rotation is the result of a thermally induced in-plane anisotropic strain. The MQW light modulator based on this process has a high contrast ratio of 7000:1 and increased speed as compared to other similar modulators.

Abstract: An optical modulator in which waveguide regions are disposed at opposite ends of a modulation region to reduce the capacitance of the device and prevent pn junctions from exposure to air. On an n-side electrode there are laminated a substrate, an n-type clad layer and an optical modulation waveguide layer. A modulation region lies at the center of the optical modulation waveguide layer along the direction of travel of light, and two waveguide regions are disposed at opposite ends of the modulation region, respectively. On the optical modulation waveguide layer which constitutes the modulation region there are laminated a non-doped layer, a p-type clad layer and a p-side electrode, and a semi-insulating semiconductor is formed on the optical modulation waveguide layer which forms the two waveguide regions.

Abstract: A wide band optical modulator is grown on a substrate as tandem Fabry-Perot resonators including three mirrors spaced by two cavities. The absorption of one cavity is changed relative to the absorption of the other cavity by an applied electric field, to cause a change in total reflected light, as light reflecting from the outer mirrors is in phase and light reflecting from the inner mirror is out of phase with light from the outer mirrors.

Abstract: A surface-normal optoelectronic device is provided which includes a first semiconductor layer of a first electroconductive type, a second semiconductor layer of a second electroconductive type having a polarity inverse to that of the first electroconductive type, a semiconductor active layer, a third semiconductor layer of the first electroconductive type, and a fourth semiconductor layer of the second electroconductive type, formed on a semiconductor substrate. The second and third layers are larger in forbidden band width than the active layer, said second layer is smaller in forbidden band width than a part of the first layer contacting the second layer, and the third layer is smaller in forbidden band width than a part of the fourth layer contacting the third layer. High resistance regions are formed vertically passing through the active layer, to surround its light-emitting region and to have a resistance higher than that of that region.

Abstract: An optical apparatus consisting of a laser for producing a coherent polarized beam of electromagnetic radiation of a preselected wavelength. A substrate of silicon has a first transparent cover layer for receiving the polarized beam substantially normally incident thereto, and a second transparent guide layer for receiving the polarized beam from the first layer and for supporting at least one resonant mode. The first and second layers have a preselected index of refraction and a grating is interposed between them, having a grating period less than half the preselected wavelength. The layers and grating interact to produce a standing wave resonance by Bragg reflection. A control obtains a resonance wavelength in the guide layer equal to the predetermined radiation wavelength and thereby high reflectance to modulate the polarized beam.

Abstract: A device that frequency up-shifts an impinging electromagnetic wave, facilitating signal pulse compression, consisting of a semiconductor block or waveguide with an optically-induced relativistic plasma wave which interacts with an applied or self generated electromagnetic signal.

Abstract: A multiple quantum well optical modulator comprising a multiple quantum well structure embedded in the intrinsic region of an s-i-n+ semiconductor. The s-i-n+ structure causes an electric field to be applied to the multiple quantum well structure which causes uncoupling of the el energy confined level of one layer and the x level of the adjacent layer, thereby changing the absorption of the light and causing modulation thereof.

Abstract: An asymmetric Fabry-Perot reflectance modulator (AFPM) consists of an active region between top and bottom mirrors, the bottom mirror being affixed to a substrate by a buffer layer. The active region comprises a strained-layer region having a bandgap and thickness chosen for resonance at the Fabry-Perot frequency. The mirrors are lattice matched to the active region, and the buffer layer is lattice matched to the mirror at the interface. The device operates at wavelengths of commercially available semiconductor lasers.

Abstract: A planar semiconductor optical device for modulating an optical beam includes an active layer provided on a substrate, the active layer having a quantum structure and being laterally surrounded by an optical confinement region which has a refractive index smaller than the effective refractive index of the active layer.

Abstract: An article that comprises novel means for modulating the transparency of a semiconductor body in accordance with a modulating signal is disclosed. The body comprises one or more quantum wells (QWs), and the modulation mechanism comprises changing the free carrier distribution function in the QWs. An important feature of the inventive article is the use of (relatively long wavelength) inter-subband radiation (ISBR) to change the transparency of the body for (relatively short wavelength) inter-band radiation (IBR). In preferred embodiments the modulating signal is an electric field applied across the QWs, such that ISBR absorption can be tuned by means of the Stark effect. One embodiment of the invention makes it possible to rapidly modulate IBR, and another embodiment can form narrow (typically less than 10 ps) IBR pulses.

Abstract: A semiconductor-insulator-semiconductor (SIS) structure diode device for providing fast optoelectronic switching with stimulated emission. The device includes a substrate which has a buffer layer disposed on top thereof. An n-type cladding layer is disposed on top of the buffer layer. An undoped i-region is disposed on top of the buffer layer. The i-region includes at least one quantum well disposed between two waveguide layers. A lightly doped p-type cladding layer is disposed on top of the i-region. A contact layer is further disposed on top of the p-type cladding layer. First and second contact terminals are included for providing a two-terminal device. The diode advantageously provides good lasing performance, significant negative differential resistance and strong light sensitivity. In an alternate embodiment, a third terminal is connected to the undoped i-region to thereby form a three terminal device.

Abstract: A non-linear optical device utilizes laterally asymmetrical quantum dot structures (D1-D5) that are tunable in terms of their lateral asymmetry by bias potentials (V1, V2) applied to laterally extending electrode structures (13, 14).

Abstract: In a semiconductor element is shown having a silicon layer, a waveguide comprising silicon and a diode structure connected with external, conductive contacts. The diode structure is provided in such an arrangement to the waveguide that the diode structure can be influenced by electron hole pairs generated by photons in the waveguide. In order to create a semiconductor element with an optical waveguide and an integrated diode structure, in which high losses in the optical waveguide are avoided, the waveguide is weakly doped, and a germanium-rich layer is a component of the diode structure. The semiconductor element is well suited as a component in integrated optics for optical-electrical conversion.

Abstract: A multiple quantum well arrangement which achieves significantly improved third order optical nonlinearity in a semiconductor device by way of spatially periodic electrodes applied to the semiconductor device. The spatial period of the applied electrodes and the resulting exciton confinement dimension is improved over that of previous multiple quantum well structures and to the Bohr radius range of dimensions for the semicondcutor material by way of avRIGHTS OF THE GOVERNMENTThe invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.

Abstract: An optic modulator which employs strained multiple quantum well structures which are fabricated and spaced from one another such that the stress perpendicular to the direction of the spacing is released leaving only a uniaxial stress along the direction parallel to the spacing. The multiple quantum well structures are then sandwiched between two optic polarizers which are aligned perpendicular to one another. At zero electric field, polarized light passing from the first polarizer is further polarized such that the polarization of the light is rotated to pass through the second polarizer. When an electric field is applied across the heterostructure, light passing through the heterostructure is not further polarized and therefore, the optic signal is interrupted. Thus, optic signals may be modulated with the contrast of polarizing modulators at the speed of superlattice heterostructures.

Abstract: A combined bipolar junction transistor and an optical modulator comprising a plurality of semiconductor layers providing an optical mirror for the modulator, a collector for the transistor formed upon the plurality of semiconductor layers, the collector also forming an optical absorber of the modulator, a base of the transistor formed upon the collector, an emitter of the transistor formed upon the base and a metallic contact for the base, the metallic contact providing a function of an optical reflector for the modulator.

Abstract: A quantum well wave modulator comprises a central well sandwiched by two lateral wells. The central well is populated with electrons and the two lateral wells, having different constitutions, are coupled to the central well so as to modulate two light waves under the effect of the application of an electrical field perpendicularly to the structure in one direction or in the opposite direction.

Abstract: An optical modulation apparatus includes a semiconductor element having a quantum well structure, a unit for applying an electric field to the quantum well structure of the semiconductor element, a unit for supplying polarized probe light to the semiconductor element, the probe light emerging from the semiconductor element such that a polarization state thereof is changed by an electrooptical effect in the quantum well structure, a unit for causing the semiconductor element to receive pump light which causes virtual charge excitation in the quantum well structure, the virtual charge excitation screening the electric field applied to the quantum well structure, and a polarizer for converting a change in polarization state of the light emerging from the semiconductor element into a change in intensity.

Abstract: A photodiode array composed of sharply tuned at consecutively different wavelengths are disclosed with the vertical resonance cavity. Semiconductor superlattice distributed Bragg reflectors can be used as the resonance cavity to achieve sharp tuning and monolithic integration, and the wedged distributed Bragg reflector configuration resonance cavity provides a sequential wavelength detection range. A linear array having resolution a fraction of the photodiodes bandwidth and a square-matrix array with a wedged etalon for high resolution, are disclosed. The disclosed photodiode array make a pocket-type wavelength meter feasible and can be used as a substitute for a spectrometer.

Abstract: A non-linear semiconductor optical device comprises a first quantum well layer having discrete quantum levels of carriers including a first quantum level for electrons and a second quantum level for holes with an energy gap corresponding to a wavelength of an incident optical beam; a pair of barrier layers provided above and below the first quantum well layer in contact therewith with a thickness that allows a tunneling of the carriers therethrough for defining a potential well in correspondence to the first quantum well layer; and a second quantum well layer provided in contact with the barrier layers for accepting the carriers that have been created in the first quantum well layer upon excitation by the incident optical beam and escaped therefrom by tunneling through the barrier layer. The second quantum well layer comprises a material that has a conduction band including therein a .GAMMA. valley and an X valley, wherein said .GAMMA.

Abstract: An optical logic operation apparatus includes an optical induction refractive index crystal having first and second planes parallel to each other and a device for inputting a coherent probe light from the first plane of the crystal. At least one of the first light output from the first plane of the crystal and the second light output from the second plane of the crystal is taken out so that one of the first and second lights is amplified by the two-wave coupling of the probe light reflected by the second plane and the probe light inputted from the first plane and the other light is attenuated likewise by the two-wave coupling. The inputted image is projected onto the crystal by use of light incoherent to the probe light. With the incidence of the incoherent light, a gain distribution corresponding to the inputted image is generated in the crystal so as to modulate the first and second lights spatially.

Abstract: An electric-signal amplifying device is provided which includes a light source and an opto-electronic element for amplifying an input signal by use of light emitted from the light source. The opto-electronic element includes a semiconductor substrate and a multi-layered structure disposed thereon. The multi-layered structure has a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and a third semi-conductor layer of the first conductivity type in this order. The second and third semiconductor layers form a first p-n junction for modulating the amount of light to be absorbed thereinto with a change of bias voltage applied thereto in accordance with the input signal, while the first and second semiconductor layers form a second p-n junction for generating a current as an amplified output signal by absorption of the light transmitted through the first p-n junction.

Abstract: A non-linear optical device having the TBQ structure comprises an active layer forming a quantum well for interacting with an incident optical beam, an electron removal layer provided adjacent to the active layer at a first side thereof with a first barrier layer intervening therebetween for removing the electrons from the active layer; and a hole removal layer provided adjacent to the active layer at a second, opposite side of the active layer with a second barrier layer intervening therebetween for removing the holes from the active layer; wherein the first and second barrier layers have respective thicknesses determined such that the probability of tunneling of the electrons through the first barrier layer and the probability of tunneling of the holes through the second barrier layer are substantially equal with each other.

Abstract: A semiconductor light amplifier is driven by a drive device, and selectively amplifies one of a TM mode component and a TE mode component of input light. For example, TE mode light is selectively amplified by making thickness of the active layer of the semiconductor light amplifier not more than 0.05 .mu.m, or by tilting at least one of the entrance and exit faces of the semiconductor light amplifier by 10 to 16 degrees. An another type of light amplifying polarizer, input signal light and excitation light are combined by a half mirror or an optical coupler, and combined light is input to a rare-earth-element doped, polarization maintaining optical fiber.

Abstract: An electro-optical component defined by a substrate which is coated in the growth axis direction with a periodic stack of semiconductor layers suitable for defining a superlattice whose quantum wells are fairly strongly coupled together. By applying a control electric field to the superlattice parallel to its growth axis, the optical absorption threshold is varied, and the direction of variation is towards higher energies.

Abstract: A one-dimensional or two-dimensional transmission mode spatial light modulator (SLM) includes one or more heterojunction acoustic charge transport (HACT) channels 18 with surrounding layers 16,20 vertically adjacent to a multiple quantum well (MQW) region 14, grown above a thick semiconductor substrate 10 thick enough to allow a surface acoustic wave (SAW) to propagate and transparent to the incident light 40. The SAW is injected by a transducer 24, charge is carried to and from the HACT channel 18 by electrodes 32,34,36, and light 40 is applied to a surface 44 perpendicular to the MQW region 14. Each charge packet 19 in the HACT channel 18 invokes an electric field 52 within the MQW region 14 which determines the optical absorption and index-of-refraction thereof, thereby determining the intensity and/or phase of each output light beam 45. Light modulation is achieved by modulating the amount of charge injected.

Abstract: In an optosemiconductor device including a superlattice configuration (TBQ) of first and second quantum well layers and a potential barrier therebetween, photo-excited carriers are formed in the first quantum well layer and are tunnelled through the potential barrier toward the second quantum well layer, so that the tunneled carriers are accumulated in the second quantum well layer. An electric field is applied to the superlattice configuration to expel the tunneled carriers from the second quantum well layer.

Abstract: A one-dimensional or two-dimensional transmission mode spatial light modulator (SLM) includes two different mediums, one medium being a semiconductor comprising one or more heterojunction acoustic charge transport (HACT) channels 28 with surrounding layers 26, 30 vertically adjacent to a multiple quantum well (MQW) region 22, and the other being a transparent piezoelectric insulating substrate 10 thick enough to allow a surface acoustic wave (SAW) 13 to propagate therein. The SAW 13 is launched in the substrate 10 by a transducer 12 and generates electric fields which propagate the charge along the HACT channel 28 in the semiconductor medium 18. Electrodes 32, 34, 36 carry charge to and from the HACT channel 28, and light 40 is applied to a surface 44 perpendicular to the MQW region 22.

Abstract: A crystalline silicon 1.1-20 micron spatial light modulator has an X-Y array of p-i-n pixels which are selectively foward biased at low voltages to induce substantial phase shifts in the optical wavefront, by the dual injection of holes and electrons through the silicon body and parallel to the light being modulated. The easy-to-fabricate SLM, is less sensitive to changes in temperature and wavelength, and can modulate light regardless of its state of polarization.

Abstract: An optical apparatus consisting of a laser for producing a coherent polarized beam of electromagnetic radiation of a preselected wavelength. A substrate of silicon has a first transparent cover layer for receiving the polarized beam substantially normally incident thereto, an a second transparent guide layer for receiving the polarized beam from said first layer and for supporting at least one resonant mode. The first and second layers have a preselected index of refraction and a grating is interposed between them, having a grating period less than half the preselected wavelength. The layers and grating interact to produce a standing wave resonance by Bragg reflection. A control obtains a resonance wavelength in the guide layer equal to the predetermined radiation wavelength and thereby high reflectance to modulate the polarized beam.

Abstract: An optical switch comprises a substrate, a lower cladding layer, a waveguide layer, and an upper cladding layer each formed of a semiconductor, and in which at least one of the three layers except the substrate has a quantum well structure at a quantum confined potential. The well plane of the quantum well structure is symmetrical with respect to the center position thereof, and varies in proportion to the square of the distance from the center position. If an electric field is applied perpendicular to the well plane, the respective changes in the absorption coefficient and refractive index in the vicinity of the absorption edge are influenced by absorption peak shifts attributable to both 1e-1hh and 1e-11h transitions. Thus, the optical switch operates in response to both TE and TM mode light without depending on polarization.

Abstract: An electron wave interference device controlled by a light is disclosed. The electron wave interference device includes a first channel to propagate an electron wave, a second channel arranged with an interval from the first channel for propagating an electron wave, and an magnetic field application device for applying a magnetic field into the first and second channels and a region sandwiched by those channels so as to traverse them. The electron waves which are respectively propagated in the first and second channels mutually interfere, and when the light is irradiated to those channels, a distance between peaks of wave functions of the electron waves which propagate in the channels is changed, so that a phase difference occurs in the electron waves.

Abstract: A switch matrix which comprises non-linear optical (e.g. bistable) elements each consisting of an optically active layer applied to a substrate. The surface of the substrate has a microstructure composed of pillars each of which functions as a switch element and has at least one optically active layer. The pillar structure prevents interaction due to thermal contact and diffusion of charge carriers across the optically active layer and the substrate. The lithographic-galvanic (LIGA) process described is suited to the mass production of these structured substrates my moulding plastics. Both transparent and opaque substrates with high aspect ratios and adequate stability can be advantageously manufactured in this way.

Abstract: A semiconductor-to-metal optical switch or device for power limitation in the infrared spectral region includes two thin semiconductor layers sandwiched between two transparent electrodes. An electrical voltage is applied across the two semiconductor layers to produce an active device for blocking incident light in the 8 to 12 .mu.m spectral region. The material composition and thickness of the two semiconductor layers are such that enough photo-excited electrons are generated in the first semiconductor layer so that the second semiconductor layer undergoes a rapid semiconductor-to-metal transition at a predetermined light intensity. The semiconductor layers remain transparent below the predetermined light intensity and the second layer will become metal-like at a light intensity above a threshold level. Upon becoming metal-like, the second semiconductor layer will block the incident light.

Abstract: An electron-wave coupled semiconductor device, in particular a semiconductor switching device, comprises a first layer of semiconducting material having a first bandgap, and a second layer of material formed on said first semiconducting layer and having a second bandgap greater than the first said bandgap. First and second electron waveguides are formed alongside but spaced apart from each other in the first semiconductor layer adjacent the boundary between this layer and said second layer. A gate region extends over said second layer transverse to and over said electron waveguides. First contact means provides input connections to said first and second electron waveguides on one side of said gate region and further contact means provides separate output connections from said first and second electron waveguides on the opposite side of the gate region from said first contact means.

Abstract: A semiconductor optical device for focusing an optical beam includes a substrate doped to a first conductivity type, a semiconductor layer doped to a conductivity type different from that of the substrate, a recombination region formed between the substrate and the second semiconductor layer, a first electrode provided on a bottom surface of the substrate, and a second electrode provided on a top surface of the second semiconductor layer. The first electrode is transparent to the optical beam which passes freely therethrough. The second electrode is provided with a passage for the optical beam. The passage has a size which exceeds the carrier diffusion length in the semiconductor layer. A profile of refractive index is thus created in the recombination region such that the refractive index is at a minimum at the center of the circular passage and is at a maximum at an edge of the passage.

Abstract: An optical deflection device for manipulating optical beams employs a set of layers having the configuration NUPUN . . . , where the N and P symbols refer to N-type and P-type dopants and the U symbol refers to an electrooptically active optical guide layer having an index of refraction sufficiently higher than that of the N- and P- layers that light is guided within it and a free electron concentration low enough that the guide layers are depleted, so that light is guided within the layers with low loss, while the N- and P- layers have an appropriate bias applied to establish a differential phase shift between layers to deflect emitted radiation along a desired angle.

Abstract: An optical intensity modulator includes a compound semiconductor substrate of a first conductivity type having first and second surfaces, and a compound semiconductor active layer of the first conductivity type formed on the first surface of the compound semiconductor substrate. An incident laser beam to be intensity-modulated is applied to the compound semiconductor active layer. The modulator further includes a compound semiconductor layer of the first conductivity type formed on the compound semiconductor active layer, an opposite conductivity type compound semiconductor layer of a second conductivity type opposite to the first conductivity type, a first electrode formed on the opposite conductivity type compound semiconductor layer, and a second electrode formed on the second surface of the compound semiconductor substrate.

Abstract: A coupled quantum well electro-optical modulator, whose semiconductor structure is composed of one or of a plurality of successions formed by two layers capable of forming quantum wells, of a barrier layer which separates the two layers and of an intrinsic layer which separates the succession from other possible successions, where in presence of an electric field the absorption threshold of the light radiation shifts towards shorter wavelengths.

Abstract: An optically bistable device is disclosed. The device includes a uniformly thick layer of amorphous silicon to constitute a Fabry-Perot chamber positioned to provide a target area for a probe beam. The probe beam has a maximum energy less than the energy band gap of the amorphous semiconductor. In a preferred embodiment, a multilayer dielectric mirror is positioned on the Fabry-Perot chamber to increase the finesse of switching of the device. The index of refraction of the amorphous material is thermally altered to alter the transmission of the probe beam.

Abstract: An optical light beam position control system utilizes Kerr cells and Lummer-Gehrcke plates to produce sets of optical phased linear arrays for beam positioning and beam monitoring. The system controls a light beam in the vertical and horizontal axes by the means of two optical phased linear array generators with associated monitoring and positioning optics.

Abstract: An infra red radiation modulator comprises a p type silicon substrate 1 having spaced n type and p type doped regions 2, 3 having respective doping concentrations of approximately 10.sup.20 and 10.sup.16 /cm.sup.3. A signal source 11 provides a bias voltage between the doped regions 2,3 via electrodes 4 for modifying the concentration of free carriers in the substrate between the doped regions and therefore the response of the modulator to incident infra red radiation. By appropriate control of the bias voltage the modulator can be caused to modulate, chop, filter or spectrally scan the incident radiation.