Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2002-05-13
2004-09-14
Lee, John D. (Department: 2881)
Optical waveguides
With optical coupler
Switch
C385S015000, C385S017000
Reexamination Certificate
active
06792173
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a device and a method for switching optical signals and particularly relates to an optical switch for selectively establishing pathways for light beams which enter and leave the optical switch through conduits which are distributed over two parallel planes thus allowing the selective direction of a light beam in three dimensions from an incoming to an outgoing optical fibre.
BACKGROUND OF THE INVENTION
According to Jerry D. Gibson,
THE COMMUNICATIONS HANDBOOK
, CRC PRESS, Boca Raton 1997, chapter 37, pages 513-528 the migration of photonics into switching is occurring in a variety of ways. This is happening because of the large variety of switching tasks to be performed in a modern communications network. The different switching tasks range from ensuring that major trunks have the ability to be switched from one route to another when a catastrophic accident destroys a route, to the real-time switching on a per call basis. Two generic switching applications that are in use in present networks are protection switching and call-by-call switching. Both of these applications will preferably be realised in the future with optical switching techniques.
Most of the switches currently in use require conversion of the optical signals received through optical fibers into electrical signals which are routed for example in an electronic switching fabric from an incoming line to an output line which is selected according to the corresponding signalling information. Electronic switching fabrics are described in the aforementioned Gibson reference, chapter 32, pages 425-432.
A fiber optic communications network typically operates at data rates from a few megabit per second to beyond 2.5 Gb/s. At the 2.5 Gb/s rate, several thousand digitised voice channels, each operating at 64 kb/s, can be transmitted along a single fiber using time-division multiplexing. Electronic switching fabrics which can handle the traffic in fiber telephone networks require therefore transfer capacities which are costly to realise. Electronic switching fabrics in fiber optic communications networks will therefore be replaced in the near future by optical switches acting as cross-connects which allow the bit transparent data transfer between data systems such as public telephone exchanges.
An optical switch for the transparent transfer of data is described for example in PCT Patent Application publication number WO 00/79311. This optical switch comprises, mounted on a base, at least one controllable actuator used for positioning of an optical element designed to guide an optical signal on a selected free space switching path, within an optical path plane arranged parallel to said base, from an input optical fiber to an output optical fiber. Switching therefore takes place in two dimensions over the optical path plane along which on two sides opposite to each other optical fibers are arranged in rows. The size of the optical path plane and therefore of the optical switch rapidly increases with the number of optical fibers installed. Further the lengths of the switching paths also increase so that the optical elements require a more precise adjustment. The mounting and precise alignment of each of the optical elements, mounted perpendicular to respective upright on the base and parallel to opposing optical elements by means of hinges and a carrier panel, results in corresponding production costs. Imprecise alignment may however cause transmission losses. It would therefore be desirable to improve the described optical switch. It would be desirable in particular to provide an optical switch of smaller size while allowing the connection of an increased number of optical fibres for switching purposes. It would further be desirable to design an optical switch which can be manufactured at reduced cost. Further, it would be desirable to design an optical switch which easily allows correct geometrical positioning of the optical elements and therefore avoids adjustment problems. It would also be desirable to provide an optical switch comprising simple means for precisely aligning selected optical paths between optical fibers. It is further desirable to provide a method for establishing, optimising and correctly maintaining established optical paths between optical fibers.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is now provided a device for directing an optical signal from a first optical fiber along one of a plurality of selectable switching paths each terminating in a corresponding one of a plurality of second optical fibers via an optical element, the optical element being moveable by a controllable actuator (
60
) from a first to a second position to change the switching path of incident optical signal, characterised in that the optical element is slideably mounted in parallel to a first mounting plate comprising a conduit through which the optical signals from the first optical fiber can be directed by the optical element along the selected one of the switching paths to one of a plurality of conduits in a second mounting plate parallel to the first mounting plate, and further to the corresponding one of second optical fibers.
In a preferred embodiment of the present invention, the first mounting plate comprises a plurality of conduits each for communicating optical signals with a corresponding one of a plurality of first optical fibers and each corresponding to a different one of a plurality of optical elements slideably mounted in parallel to the first mounting plate for selectively directing optical signals passing through the corresponding conduit.
Optical elements may be mounted in parallel to the second mounting plate for adapting an optical signal arriving over the switching path to the second optical fibers. The optical elements mounted in parallel to the second mounting plate may be slideably moveable relative to the conduits in the second mounting plate for directing optical signals arriving from the second optical fibers to the optical elements of the first mounting plate and further to the first optical fibers.
Each of the slideable optical elements is preferably coupled to an actuator subsystem for sliding the optical elements between different positions within a plane. The actuator subsystem preferably moves the slideable optical elements based on forces generated by any one or more of piezoelectric, electrostatic, acoustic and thermal effects.
The actuator subsystem may hold the slideable optical elements in position by friction. Each slideable optical element preferably comprises a flat part which is supported by the actuator subsystem and at least one of a reflective part and a refractive part. The reflective part may comprise a mirror and the refractive part may comprise a lens.
In a particularly preferred embodiment of the present invention, the actuator subsystem and light sensitive elements are arranged near the conduits of the first and/or the second mounting plate and are connected to a control unit which adjusts the position of the slideable optical elements such that signals caused in the light sensitive elements by improper alignment of optical signals are reduced to a minimum. Two or more light sensitive elements are preferably placed at regular distances on a circle concentric to a conduit. The slideable optical elements are preferably designed to provide optical signals with a main lobe and at least one side lobe which is directed toward a light sensitive element. The control unit may sense data carried by the signals received from the light sensitive elements.
The slideable optical elements may be designed to have a fan-out of at least two optical beams which are guided along different switching paths. The slideable optical elements are preferably mounted between the corresponding mounting plate and a holding plate comprising apertures for the passage of optical signals.
The first and second mounting plates may be connected to each other by spacers or side-walls.
Viewing the present invention from
Bona Gian-Luca
Despont Michel
Cheung Wan Yee
Hughes James P.
International Business Machines - Corporation
Lee John D.
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