Abstract: In dual wavelength equipment such as a combined read/write unit for an optical disc system, read light of wavelength .lambda..sub.1 is directed through an isolator and a combiner, is reflected from a target back through the combiner and, at the isolator is directed out of the incident beam path to photodetectors. Write light of wavelength .lambda..sub.2 is directed from a position off the read beam path to the combiner where it is re-directed into the read beam path and onto the target. The isolator has a linear polarizer, a polarizing beam splitter, and a retarder functioning together to ensure that at the polarizing beam splitter reflected light is linearly polarized in a direction perpendicular to the incident light. The combiner is typically an interference filter inclined both to the read and write beam path, which transmits .lambda..sub.1 and reflects .lambda..sub.2.

Abstract: At each of a pair of linked terminals, an image is generated at local and remote input devices. The generated image is projected onto a viewing screen and, while exhibited, further locally or remotely generated data is used to alter the generated image and, consequently, to alter the projected image. Data can, for example, be generated by means of a document scanner and a manually operated X-Y pen digitizer.

Abstract: To secure accurate control over rapid diffusion such as the diffusion of zinc into gallium arsenide, the source and slices to be processed are isolated from one another during an initial warm-up period. This is done using one vessel for the crystal slice and a second vessel for the source. The source vessel initially blocks an opening in the slice vessel while the source and slice are brought to the desired diffusion temperature. The source vessel is then slid through the opening to a diffusing position in which a trailing part of the source vessel again plugs the opening in the slice vessel and in which an open part of the source vessel is now in the interior of the slice vessel. Use of this arrangement avoids the uncontrolled diffusion which occurs in current diffusion capsules during initial heating of the capsule.

Abstract: In an arrangement of two keyboards or other lamellar input/output devices for a computer or telecommunications terminal, one keyboard is integral with a cabinet of the terminal and the other keyboard normally fits within a housing in an undersurface of the cabinet and is masked by the integral keyboard. To enable withdrawal of the keyboard housed within the housing for use, a rear part of the cabinet undersurface is configured to allow the cabinet to be tilted bodily backwards to allow access to the keyboard. This is then pulled from under the integral keyboard and the cabinet is returned to its stable position. The keyboard housed within the housing is returned to its stored position in a converse manner.

Abstract: A method for screening double heterostructure laser diodes before mounting and packaging is disclosed. At a normal laser diode operating temperature, a range of pulsed current is passed through the laser diode and the lasing threshold current and slope efficiency of the laser diode are monitored. The laser diode is then subjected to a burn-in process in which it is driven at a high junction temperature for an extended time period. Subsequently the lasing threshold current and slope efficiency are again monitored by applying the same range of pulsed current at the normal operating temperature. If either the threshold current or the slope efficiency have changed by more than a predetermined amount, the laser diode is rejected. Otherwise, the laser diode is gauged as likely to have a lifetime greater than a predetermined value at normal operating conditions so warranting further testing prior to installation into a laser package.

Abstract: During production of laser diodes, crystals on which the laser diodes are formed are subjected to two high temperature processes: diffusion and alloying. These steps are performed in a quartz process tube in an oxygen free atmosphere. At some stage in the process the crystal must be moved from a cool zone to a hot zone within the tube and this is done by means of a push rod which extends through an aperture in the diffusion tube. The conventional arrangement for sealing around the push rod acts to clamp the push rod in position. Thus, temporarily, while the push rod is being moved the seal must be partly released and its sealing action is inferior. To maintain the process atomsphere free of reactive gas there is proposed by the invention a mechanism for flooding the sealing area between the push rod and the process tube with an inert gas while the sealing means is temporarily released.

Abstract: In a stacked metal-oxide-semiconductor (SMOS) transistor, the transistor source, drain and channel each have a lower part formed in a silicon substrate and an upper part composed of recrystallized polysilicon. The device gate is located between the upper and lower channel parts. By vertically integrating a MOS transistor, performance limitations imposed by the direct scaling approach to device miniaturization are avoided.

Abstract: A device for accurately positioning an optical system element uses an array of electromagnets to alter fluid pressure distribution in a mass of ferromagnetic fluid. The pressure redistribution causes movement of an optical system element positioned adjacent to the ferromagnetic fluid. The invention is concerned with particular arrangements of fluid and energizing electromagnets to ensure combined rectilinear and angular movement of the optical system elements. The device has neither the complexity nor the delicacy of known structures used for moving optical system elements.

Abstract: Before splicing optical fibers having cladding and core of differing refractive index, the cores are axially aligned. The fiber ends are held apart with the fibers approximately coaxial. The fiber end surfaces are then illuminated and reflected light is monitored. Since reflectivity is a function of refractive index, the position of the core in the reflectivity profile of each surface can be readily identified. The fiber ends can then be manouvered transverse of the fiber axes to bring the fiber core centers into registration with a datum line. The fiber ends are then brought close together for splicing. Previously, fibers having nominally identical outside diameters were aligned simply by pressing them into a common V groove, the optical transmission efficiency then depending on fiber/core concentricity. Alternatively, light was injected into the far end of one fiber, monitored at the far end of the other fiber, and the fibers at their near end manipulated to maximize monitored optical power.

Abstract: In a known optical cable, optical fibers are loosely laid in a number of grooves formed within an elongate plastics extrusion. Typically the grooves follow a helical path with periodically reversing pitch, the helices centered on a central longitudinal axis of the cable. A primary reason for the helical lay is to prevent the fibers from becoming stressed should a bend occur in the cable. A further benefit of loose laying of fibers in a helical groove of periodically reversing pitch is that any elongation of the cable core is not immediately transmitted to the fiber supported by it. The fiber will move from its initial loose laid position both in a direction towards the inside curve of the helix and in a direction towards the base of the grooves. When it bears against the cable core over an appreciable length, the fiber will then be subjected to tensile stress.

Abstract: A thin film transistor has a semiconductor layer, an insulating layer and source, drain and gate electrodes. The improvement comprises creating an enhanced conductivity layer in the semiconductor by ion implantation or diffusion on phased deposition. The benefits of the enhanced conductivity layer are that transistor action is obtained without the conventional annealing step and DC stability is much improved.

Abstract: A telephone for a physically handicapped person has a transducer which is selected for easy actuation by the handicapped person. The transducer may, for example, be operated orally. When the transducer is first operated, a switch under the control of the transducer causes the telephone line switch to go "off hook" and, after a suitable delay, causes outpulsing of a zero signal to alert the operator. Once contact with the operator is established, the caller who has access to a telephone microphone, asks the operator to place the call and subsequently participates in it. Following the termination of the call, the transducer is operated again to reactuate the line switch and return the telephone set to its "on hook" condition. A similar procedure is followed when a call is received by the handicapped person. However, in this case, since no zero dialling is required, ringing voltage on the line is detected and, while present, zero dialling in response to transducer actuation is prevented.

Abstract: Optical fiber wound onto a take-up reel after production is invariably tensioned such that results of characterization tests performed on the wound fiber are markedly different from such results obtained when the fiber is untensioned. Doubly winding the fiber to minimize tension is a laborious procedure. The invention covers a reel which has an adjustable hub circumference. Adjustment can be made with the fiber wound onto the hub so allowing rapid characterization of the fiber prior to restoring the fiber and the hub to their normal storage positions for fiber shipment.

Abstract: Light transmitted by an electro-optically variable cell on application of a voltage actuates a photoconductor which controls the voltage. Voltage is, for example, applied across both a liquid crystal and a photoconductor, control then deriving from a relative change in impedance of the liquid crystal and photoconductor. High contrast and a hysteresis effect permit multi-cell adaptation using a high order of multiplexed addressing.

Abstract: Surface relief analyzing equipment comprises a turntable and an audio frequency pick-up including a stylus. A substrate bearing the surface relief is rotated on the turntable at a fixed frequency and and analogue electrical signal produced at a pick-up transducer is passed through an a-d converter. Digital data is processed to produce an input to a display for registering a pictorial representation of the surface relief.

Abstract: An electret microphone has a metal shield around it in order to guard against electromagnetic interference. Acoustic waves reach the electret element through a passage in the shield. The electret response is undesirably affected by an electric field produced by body capacitance when the microphone is brought close to a user's mouth. To overcome this effect, the microphone has a conductive film, transparent to acoustic waves, positioned between the passage and the electret element, the film contacting a grounded part of the casing. The conductive film can form an integral part of a microphone moisture barrier.

Abstract: A thin film transistor has a semiconductor layer, an insulating layer and source, drain and gate electrodes. The improvement comprises creating an enhanced conductivity layer in the semiconductor by ion implantation or diffusion on phased deposition. The benefits of the enhanced conductivity layer are that transistor action is obtained without the conventional annealing step and D.C. stability is much improved.

Abstract: A telephone user who cannot hear the telephone ringing is alerted, other than audibly, to the fact that the telephone must be answered. A radio transmitter at the telephone is driven by ringing voltage supplied to the instrument. The transmitter emits a radio signal which is picked up by a receiver carried by the telephone user. Upon detection of the received signal, a tactile transducer is actuated and alerts the telephone user to the fact that the telephone must be answered.