Abstract: Method and apparatus for casting metal strip in which molten metal is introduced between a pair of parallel casting rollers (16) via a tundish (18) and delivery nozzle (19). Casting rollers (16) are cooled so that shells solidify on the moving roller surfaces and are brought together at the nip between them to produce a solidified strip product (20) at the roller outlet. The tundish (18), delivery nozzle (19) and a pair of side closure plates (56) to confine the pool of metal on the casting rollers are separately preheated to working temperature and then rapidly brought into an operative assembly and casting is started before detrimental uneven or localized cooling of the preheated components can develop. To avoid material deterioration and metal flow irregularities due to oxidation on preheating, the delivery nozzle (19) and side closure plates (56) are provided with oxidation retarding coatings, for example in the form of ceramic glazing, or are preheated in an inert atmosphere.

Abstract: A graded index lens having one end-surface thereof adapted for connection to an optical fiber or the like characterized by an axially asymmetrically tapered end portion terminating in the end-surface.

Abstract: A simple variable optical attenuator or the like suitable for printed circuit board mounting has an optical filter slab positionable between the arc-rounded aligned ends of two optical fibres. The filter slab is mounted on the wiper carrying reciprocating part of an adjustable potentiometer. The resistance value corresponds to the position of the filter slab, i.e. to the attenuation or other optical index as the case may be, once the unit has been calibrated.

Abstract: A passive fiber optic device and optical fiber connected to it are packaged in a solid block of a bismuth containing fusible alloy. The alloy exhibits appreciable expansion on solidification, negligible dimensional change after solidification, and a low thermal expansion coefficient. Coupled with its low melting point and glass wetting ability, the alloy is uniquely adapted for forming a hermetic seal with glass. By molding as a solid block, the packaging operation is rendered simple and rapid.

Abstract: An optical switch having a light input side and a light output side where there are a plurality of optical waveguides with light collimating lenses on one of the sides with the lenses in spaced positions and, on the other side there is an optical waveguide with a light collimating lens. To enable light to be transferred between the latter waveguide and any of the other lenses, it is movable to bring its lens into any of a plurality of switch positions, each corresponding to the position of one of the other lenses, and means is provided to move the lens selectively between positions. In preferred arrangements, the plurality of lenses are arranged around at least one pitch circle but a linear arrangement of lenses is also possible. An electric stepping motor is ideally used for the switching operation.

Abstract: A variable attenuation electro-optic device has a lens for collimating light from an input fiber and for focussing light into an output fiber. The optical path of light passing through the device passes through a dynamic scattering liquid crystal cell whose optical transmissivity can be varied by varying an AC electric field applied across it. Reflective and transmissive embodiments are described using one or two lenses of the Selfoc.RTM. type. The applied AC introduces a frequency component into the attenuation which is suppressed to particularly adapt the device for use as an attenuator or enhanced and modulated to particularly adapt the device for use as a modulator.

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.