Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-11-05
2002-09-17
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
Reexamination Certificate
active
06452704
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for generating an optical bit slot window comprising N bit slots, all the N bit slots representing the same logical state, and uses thereof.
In the field of all optical processing, optical signal streams are used for data processing applications. These optical streams consist of an optical pulse train that is divided into a series of bit slots. Each bit slot, which has a predetermined length within the pulse train, represents a single bit of data, with the presence or absence of an optical pulse within a bit slot representing complementary logical states. Thus, for example, the presence of a pulse may represent a binary “1”, whilst the absence of an optical pulse may represent a binary “0”, or vice versa.
It has long been a goal to produce devices capable of carrying out all optical processing. In order to achieve such devices, it is necessary to produce, using only optical manipulations, optical signal streams with certain predefined characteristics. One such signal stream that is required for many applications is a window which comprises an optical stream with a predetermined number of bit slots all having the same logical state so as to represent a predetermined number of binary “1”s, or “0”s, in sequence.
According to a first aspect of the present invention, we provide a method of generating an optical bit sloth window comprising N bit slots, all the N bit slots representing the same logical state, using an all-optical switching device, the switching device having an input coupled to an optical pulse source which generates optical pulses in successive bit slots, each optical pulse representing a logical state, an output which generates an output stream defining the bit slot window, and a switching input coupled to a source of optical switching signals, wherein the application of switching signals to the switching input selectively switches a connection between the input and the output so as to change the logical state of the output, the method comprising applying a first switching signal to the switching input and, after a time interval corresponding to N bit slots, applying a second switching signal to the switching input.
According to a second aspect of the present invention, we provide apparatus for generating an optical bit slot window comprising N bit slots, all the N bit slots representing the same logical state, the apparatus comprising an optical pulse source which generates optical pulses in successive bit slots, each optical pulse representing a logical state; a source of switching signals which generates first and second switching signals separated by a time interval corresponding to N bit slots; and, a switching device, the switching device comprising a switching input coupled to the source of switching signals, an output which generates an output stream defining the bit slot window, and an input, coupled to the optical pulse source, wherein the application of switching signals to the switching input selectively switches a connection between the input and the output so as to change the logical state of the output.
We have designed a method and apparatus for generating an optical bit slot window comprising N bit slots, all the N bit slots representing the same logical state, thus providing a sequence of bit slots representing a predetermined number of binary “1”s, or “0”s, in sequencers
The apparatus comprises an optical switching device to which is input a continuous stream of optical pulses. By applying switching signals to the switching input of the switching device, a connection between the input and the output of the switching device can be opened or closed, allowing the transfer of optical pulses from the input to the switching device output to be controlled.
These optical pulses are used to generate an output stream and, as the presence or absence of an optical pulse represents complementary logical states, the logical state of the output stream can be controlled by controlling the transfer of the optical pulses to the output of the switching device.
As the application of a switching signal causes the connection to switch from open to closed, or vice versa, by applying two switching signals separated by a predetermined time interval corresponding to N bit slots, the output stream will represent one logical state for N bit slots and the complementary logical state outside the N bit slots.
Typically the source for generating optical switching signals comprises a source for generating a single optical switching signal; a delay line; and, an optical combiner, the optical combiner comprising first and second combiner inputs coupled to the single optical switching signal source and a combiner output, wherein the first combiner input is connected to the single optical switching signal source via the delay line such that the single optical switching signal is input to the first and second combiner inputs separated by a time interval corresponding to N bit slots such that first and second optical switching signals are output from the combiner output separated by N bit slots. This allows the predetermined number of bit slots to be altered by altering the time interval introduced by the delay line.
Preferably each switching signal comprises a single optical pulse in a bit slot, although a bit slot containing no optical pulse could be used, situated within a streamed bit slots containing optical pulses.
Typically the switching device comprises an all-optical non-linear gate, the non-linear gate comprising a gate input coupled to the switching device input; a gate output which generates a gate output stream; a gate switching input coupled to the switching device switching input, wherein the application of a switching signal to the gate switching input selectively switches a connection between the gate input and the gate output so as to change the logical state of the gate output stream for a time interval corresponding to a single bit slot; and, a feedback loop with a single bit slot delay for feeding back N bit slots of the gate output stream to the gate switching input to maintain the logical state of the gate output stream. Whilst any form of switching device may be used, an all-optical non-linear gate is preferable as it is compact and easy to use whilst still providing all optical operation with fast switching properties.
Typically the switching device further comprises an optical combiner, the optical combiner comprising a first combiner input coupled to the switching device switching input; a second combiner input coupled to the gate output via the feedback loop; and, a combiner output connected to the gate switching input, wherein if a bit slot having the same logical state as the switching signal, and a switching signal are received at the first and second combiner inputs at substantially the same time, then no switching signal is output from the combiner output. This allows the gate output stream to be fed back as a switching signal without there being problems of interferometric mixing of the switching signal and the output stream.
It will be realised that provision of no switching signal upon the reception of a switching signal and a bit slot having the same logical state may be achieved by simply ensuring there is no output from the combiner. However, preferably this is achieved by ensuring that any output from the combiner is not detectable as a switching signal, i.e. it is of a different format.
Typically, each of the N fed back bit slots in the gate output stream preferably comprise a single optical pulse in a bit slot. Although again a bit slot containing no optical pulse could be used.
Typically, the gate output is coupled to the switching device output such that each of the N optical bit slots contains an optical pulse. Alternatively however, the optical gate may further comprise a second gate output which generates a second gate output stream which is the logical complement of the gate output stream. In this case, the second gate output may be coupled t
Blow Keith James
Manning Robert John
Poustie Alistair James
British Telecommunications Public Limited Company
Nixon & Vanderhye PC
Pascal Leslie
Singh Dalzid
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