Optical: systems and elements – Optical computing without diffraction
Reexamination Certificate
1998-06-12
2001-09-18
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Optical computing without diffraction
C359S108000
Reexamination Certificate
active
06292280
ABSTRACT:
The present invention relates to an optical device and a method of processing a digital optical signal in parallel and in free space.
Further to the widespread development of optical communication systems, the need is felt for devices capable of performing, at high speed, various operations on those bits which constitute the digital information of an optical signal and of creating advanced “super computers” and network nodes suitable for modern methods of information transfer (e.g. ATM).
The equipment currently used for processing optical signals is inadequate to manage the ever increasing transmission speeds possible in transmission systems of optical fibre type. In fact, such equipment consists of digital electronic devices with a limited band in comparison with the optical band available in optical fibre transmission systems based on serial information processing.
Furthermore, the equipment which enables the signal to be maintained in optical form, e.g. intensity or phase modulators, processes signals under the control of an electrical signal and suffers from the inherent limitations of electronic devices.
Consequently, there is still a great need to obtain the full benefit of the optical band available in optical fibre transmission systems, processing the signal by means of purely optical control signals and thus overcoming the inherent limitations of electronic devices.
U.S. Pat. No. 5,589,967 describes a method and a device for transmitting and switching packets in an optical network which carries out multiplexing by a synchronous time division system, in which the packets are transmitted at a given speed and the transmission rate is determined by line occupancy time.
Patent EP 0 742 660 A1 describes a signal processor for processing digital signals in the physical domain (e.g. optical). A symbol flow is conducted towards different delay branches. The number of delay branches is such that at any given time, in at least one of the branches, a “1” symbol and a “0” symbol are available. By controlling the opening and closing of the on/off switches, the symbol values can be changed. Furthermore, extra light sources are not necessary and the processor is transparent, that is the processor output symbols possess exactly the same physical characteristics as the processor input symbols. Processing of the optical signals takes place in a serial way and in guided propagation.
Boffi P. et al. [“Optical time-to-space converter”, Optics Communications, 123, 473-476 (1996)] describe an all-optical time-to-space converter of free propagation type which translates time-coded binary words of an optical communication signal of 1550 nm to equivalent space-coded words. Conversion is carried out by means of four optical gates, one for each of the four polarized optical signals. Each optical gate comprises a first and second indium-doped cadmium tellurium crystal (CdTe:In). There are two optical control beams, one for the first four and one for the second four crystals. In the right-hand column of page 476, lines 10-12, the authors wish that it might be possible for this time-to-space converter to constitute the input stage of an all-optical optic signal processor in free space, but do not indicate what means could be used to construct such a processor.
The present invention is designed for creation of such means and such a processor.
A first object of the present invention is therefore an optical device for processing a digital optical signal in parallel and in free space, the said device comprising:
a) means of input in guided propagation of a digital optical signal comprising at least one temporal series of n bits;
b) means capable of converting the said digital optical signal to a beam of n signals in guided propagation, each of the same comprising at least one temporal series of n bits;
c) means capable of converting the said beam of n digital optical signals in guided propagation, each of the same comprising at least one temporal series of n bits, to a beam of n digital optical signals in free space;
d) means capable of selecting, in parallel and in free space, a bit pre-selected from the said at least one temporal series of n bits of each of the said n digital optical signals, so as to transform the said at least one temporal series of n bits into a spatial figure of the said n bits carrying the same information as that previously contained in the said at least one temporal series,
characterised in that the said device also comprises
e) optical means capable of modifying, in parallel and in free space, at least one bit of the said spatial figure of the said n bits, the said means being selected by the group consisting of means capable of eliminating at least one bit, means capable of inserting at least one bit and means capable of modifying the form of at least one bit, and
f) means of output of the said at least one bit of the said spatial figure of n bits.
Throughout the present description and of the following claims, the expression “propagation in free space” is used to indicate all the modes of propagation of an optical signal which, in a device according to the present invention, are not guided by an optical fibre.
Typically, the said means capable of converting the said digital optical signal to a beam of n digital optical signals in guided propagation, each of the same comprising at least one temporal series of n bits, comprise:
a) means of cloning the said digital optical signal in the said n digital optical signals in guided propagation;
b) first n lines capable of interval-timing the said digital optical signals in guided propagation according to predetermined time intervals;
c) means of controlling and, if necessary, changing the state of polarization of the said n digital optical signals in guided propagation.
Preferably, the said means capable of converting the said beam of n digital optical signals in guided propagation to a beam of n digital optical signals in free space comprise means of collimation capable of guiding the said n digital optical signals in free space in a predetermined direction and maintaining them within predetermined transverse dimensions.
Typically, the said means capable of selecting, in parallel and in free space, a bit pre-selected from the said at least one temporal series of n bits of each of the said n digital optical signals, so as to transform the said at least one temporal series of n bits into a spatial figure of the said n bits carrying the same information as that previously contained in the said at least one temporal series comprises:
a) a first optical switching module;
b) a second optical switching module arranged in series in relation to the said first optical switching module;
c) means of supplying to the said first and, respectively, to the said second optical switching modules a pair of a first and a second beam of optical control pulses having a predetermined time interval between each other.
d) a dichroic mirror capable of guiding the said at least one pair of a first and a second beam of optical control pulses in collinear form in relation to the propagation direction of the said n digital optical signals.
e) means of collimation to guide the said at least one pair of a first and second beam of optical control pulses in free space in such a way that they are incident upon the said dichroic mirror at a pre-fixed angle.
Preferably the said first and second optical switching modules comprise, respectively, a first and second element, capable of causing the plane of polarization of the said n digital optical signals in free space to rotate by a predetermined angle under the action of the said at least one pair of a first and a second beam of optical control pulses, and they also comprise, respectively, a first and a second polarization analyzer capable of filtering, along a predetermined plane of polarization, the said n digital optical signals output from the said first and, respectively, second elements.
The said first and second elements preferably consist of a first and a second indium-doped cadmium tellurium monocry
Boffi Pierpaolo
Martinelli Mario
Mottarella Diego
Piccinin Davide
Boutsikaris Leo
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Pirelli Cavi E Sistemi S.p.A.
Spyrou Cassandra
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