Abstract: Semiconductor lasers exhibit transient relaxation oscillation on start-up and specific lasers often exhibit sustained spontaneous pulsations caused probably by crystalline defects. These fluctuations are suppressed in a laser having an integrally formed light emitting diode (LED) which generates spontaneous light which is coupled into the laser by virtue of the close proximity of the laser and the light emitting diode.

Abstract: In fabricating a III-V compound, for example, GaAs, having a layered structure a first layer is grown on a planar substrate by a vapor deposition process adapted to produce differential growth while a subsequent layer is grown by a deposition process which restores planarity. In this way, a uniformly thick combination layer is produced with a non-planar junction between its composite layers. Particularly in the fabrication of channelled substrate double heterostructure lasers, a channelled blocking layer is grown by organo-metallic pyrolysis (OMP) and a subsequent confining layer is grown using liquid phase epitaxy (LPE). The OMP process produces a channel with flanking shoulder portions which permit LPE growth of a very thin confining layer immediately above the shoulder portions thereby improving linearity of the device.

Abstract: A latching lever for aiding insertion, retention and removal of PCB's is pivoted on a PCB and has an operating handle, a pair of arms which straddle the PCB and latch the PCB within the frame when fully inserted, and a camming piece which pivotably engages the frame to permit the PCB to be levered into and out of the frame. An effective, simple latch mechanism is provided by domed pips on the legs which engage in a hole through the PCB.

Abstract: An optical modulator has two closely spaced optical fibre end surfaces, the optical path length between which can be altered in response to an applied modulating signal. Light is partially reflected from the two surfaces, the two beams interfering according to their phase difference. Alternatively the modulator may be operated in a transmissive mode. To obtain modulation either the refractive index of material between the fibre end surfaces is altered or one of the fibres is longitudinally vibrated. A method of operating a modulator in a wavelength selective mode is also described.

Abstract: A printer has a print head on which a series of individually-heatable printing resistors are linearly arranged. The print head is mounted on a carriage for stepwise reciprocation in a direction parallel to the line of resistors, paper being stepwise movable in a transverse direction. The printing sequence is designed to permit the carriage stepping motor to be operating in the slew mode for maximizing print speed.

Abstract: Semiconductor lasers exhibit transient relaxation oscillations on start-up and specific lasers often exhibit sustained spontaneous pulsations caused probably by crystalline defects. These fluctuations are suppressed by coupling laser emission into a 0.3 to 2 cm. length of waveguide and coupling light reflected from the end of the waveguide back into the laser. Embodiments disclosed include one utilizing a length of optical fibre, while others are integrated optical structures.

Abstract: An electro-optic device for stabilizing the output level of a Burrus-type light emitting diode (LED) utilizes a photodiode to monitor side emission from an active region of the LED. Side emission closely tracks top emission, which is launched into an output fiber. An electrical analog is derived from the monitored side emission and is applied in a feedback loop to control modulation level or bias current to the LED. In this way, peak optical output (for digital systems) or r.m.s. output and linearity (for analog systems) is stabilized. The monitoring photodiode and the LED may be spatially separate or may form a unitary structure.

Abstract: An integrated optical wavelength demultiplexer has deposited on a waveguide layer a pair of Luneburg lenses, the first for collimating light from an optical fiber, the second for focussing light at an array of photodetectors formed under the waveguide layer. Between the lenses is the dispersive element, a thin-film prism of a highly dispersive low-loss material such as arsenic trisulfide. A known integrated optical demultiplexer, which uses a chirped diffraction grating to spatially disperse (rather than angularly disperse) the optical wavelengths, would suffer a greater insertion loss particularly for wavelengths coupled out at a later point in the grating. Demultiplexing with a thin-film prism should also result in the capability to handle a larger number of channels, for a given channel isolation and substrate area.

Abstract: A guidance system suitable for use in burying cable uses a previously buried signal-emitting cable to produce a signal along the cable path. A vehicle mounted plow used to plow a second path has a receiver which analyzes signal from the buried cable and determines from it both the lateral direction and the extent of vehicle movement in order to maintain a predetermined lateral spacing of the two paths.

Abstract: The invention uses the phenomenon of self-coupling by which light emitted from, and reflected back into, a laser produces self-coupling with consequent change in lasing activity. The invention proposes using the laser as a detector by inducing the self-coupling and monitoring the change in lasing activity. The invention enables fibre length, and the position of a reflective discontinuity in a fibre to be determined without the sophisticated and costly equipment required by current optical time domain reflectometry techniques.