Abstract: A wavelength filter for use with optical fibers comprises a plurality of filter units, each unit comprising first and second collimating lenses separated by a filter element, the filter elements of the two units being capable of passing first and second wavelengths respectively, and each unit being such as to reflect light transmitted by the filter element of each of the other units. A first of the units has its first lens connected to an input optical fiber and also connected to a first connecting optical fiber positioned so that one of these optical fibers is capable of receiving light from the other fiber reflected off the filter element of the first unit. The first unit has its second lens connected to a second connecting optical fiber carrying light of a first wavelength transmited from the input optical fiber through the first filter unit.

Abstract: A bandpass optical filter is provided that is formed within an optical fiber in the form of a Bragg grating. The grating includes multiple Fabry Perot cavities disposed along the waveguide. Each of the cavities includes a pair of reflectors. Each reflector comprises alternating high-low index regions within the waveguide, each region having a thickness of one quarter-wave at a bandpass wavelength, each alternate region being of a different index of refraction than an adjacent region. A multiple odd quarter-wave or quarter-wave high or low index region is sandwiched between each pair of reflectors. The number of high/low regions within a reflector is selected in accordance with the refractive index difference between two alternate adjacent regions.

Abstract: An optical filter is provided having first and second graded index (GRIN) lenses preferably disposed in a coaxial relationship so that they have a common optical axis. Each of the GRIN lenses have an endface providing a port at predetermined location. The ports are disposed on opposite sides of the optical axis and each of the ports are substantially equidistant from the optical axis, so as to be oppositely offset from the optical axis by a same amount. The filter also includes an optical interference filter disposed between other endfaces of the first and second graded index lenses. By changing the location of the ports by a same small amount, the center wavelength of the filter changes by a small amount, thus in manufacture, the filter is tunable. After tuning the filter to a desired wavelength, the locations of the ports are fixed.

Abstract: A non-reciprocal optical device for interconnecting single mode optical fiber waveguides so that a light beam can pass between the fibers in a forward direction but a reverse beam, such as might be caused by unwanted reflections, is displaced away the input fiber, includes a focussing lens unit and at least one non-reciprocal optical element in series between respective ends of an input optical fiber and an output optical fiber. The focussing lens unit has a focal length such that a light beam from the input optical fiber will be focussed onto the end of the output optical fiber. The focussing lens unit may comprise, for example, a half-pitch grin-rod lens. The non-reciprocal device is positioned adjacent one or other of the foci of the focussing lens unit. The focussing lens unit may comprise several lens elements, for example a pair of quarter pitch collimating lenses, allowing additional optical elements, such as filters, to be interposed.

Abstract: A device for splitting an optical beam into two beams propagating along different optical paths, is provided. The device includes a pair of graded index collimating lenses having their planar collimating ends aligned such that they are both inwardly facing and share a common optical axis. A partially transmitting partially reflective material is disposed between the lenses. At least one of the planar endfaces of the collimating ends are wedge shaped such that a non-zero angle is formed between the two endfaces. This non-zero angle reduces the effect of unwanted optical interference.

Abstract: An tunable optical filter of the kind used, for example, in wavelength-division multiplexing (WDM) optical communication systems and tunable source applications, has an interference filter element which is pivotable to adjust the operating wavelength of the filter. In order to reduce polarization dependency as the angle of the interference filter element changes, the light beam to be filtered is passed through the filter element twice, the second time with its polarization state shifted, specifically orthogonal, relative to the polarization state during the first pass. As a result, polarization dependent effects are equalized.

Abstract: In order to reduce the number of components and avoid relatively long optical lengths, a non-reciprocal device such as a circulator comprises a plurality of ports at one end of the device, a mirror at an opposite end of the device, and a series of optical elements disposed between the ports and the mirror. The optical elements include a first element which spatially separates first and second orthogonally-polarized components of a light beam leaving one of said plurality of ports and passing through the device in a forward direction, and recombines the first and second components as they pass through the device in a reverse direction after reflection. A second optical element, disposed between the separating and recombining element and the mirror, selectively displaces and rotates the light beam components such that the recombined light beam is coupled to a different one of the plurality of ports.

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: 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: Low loss directional coupling of optical fibres is obtained by wrapping a tap fibre round a trunk fibre. Any cladding is first removed and then the tap fibre wrapped round the trunk fibre. The tap ratio can be varied by a variation in the number of turns or twists of the tap fibre around the trunk fibre. Signals can be abstracted by the tap fibre and also inserted.