Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-04-27
2001-10-23
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06307658
ABSTRACT:
The invention relates to communications systems using optical networks.
BACKGROUND OF THE INVENTION
Generally, the information conveyed in such systems is binary data in the form of pulses clocked at a determined clock frequency. The amplitude levels of such pulses are representative of the binary data. Initially, the pulses are in electrical form, and they are then converted into an optical signal obtained by modulating the power (or the amplitude) of an optical carrier wave.
The advantage of optical systems is that the optical fibers that constitute the transmission links make it possible for much higher data rates to be achieved than those that can be achieved with electrical lines.
Similarly, there is a difference of about the same order of magnitude between the data-rate capacities of optical-domain systems and those of electrical-domain circuits. One problem is therefore to design electrical-to-optical conversion interfaces at the transmission end and optical-to-electrical conversion interfaces at the reception end that are capable of matching the data rates.
One solution consists in providing time-division multiplexing whereby a plurality of electrical signals to be transmitted are taken synchronously in parallel and are then transmitted serially through the network in the form of an optical time-division multiplex. On reception, the optical signals making up the multiplex are extracted by serial-to-parallel conversion. In addition, in order to make better use of the passband of the optical network, the pulses forming the transmitted data are advantageously compressed.
The conversion interfaces must also be suitable for accommodating the capabilities of electronics. Furthermore, the compression and decompression operations, and the parallel-to-serial and serial-to-parallel conversion operations must be cheap to perform.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the invention is to solve the particular problem of decompression, and, for this purpose, the invention proposes a method of performing such decompression in all-optical manner.
To this end, the invention provides a method of decompressing pulses making up a received binary optical signal, said pulses being contained in successive bit times of duration T, and having a duration &Dgr; not greater than T/q, where q is an integer number not less than 2, said method consisting, in particular, in:
forming q auxiliary signals respectively obtained by amplitude modulating each of q optical carrier waves having different wavelengths as a function of the amplitude of said received signal; and
forming a decompressed signal constituted by superposing q delayed auxiliary signals obtained by applying delays to said auxiliary signals such that any two consecutive delayed auxiliary signals are offset in time substantially by said duration &Dgr;.
Thus, the invention makes use of the spectrum dimension of the optical domain to prevent interferometric noise from being created.
In a first possibility, said auxiliary signals are superposed before said delays are applied to them, by making use of their different wavelengths.
In an another possibility, said delays are applied to said auxiliary signals before they are superposed.
Although both of these possibilities operate in equivalent manner in principle, the first possibility makes implementation cheaper as explained below.
The invention further provides apparatus for implementing the above defined method. The apparatus comprising:
first means for amplitude modulating q optical carrier waves having different wavelengths, the amplitude modulation being performed as a function of the amplitude of said received signal; and
second means for forming a decompressed signal constituted by superposing q delayed auxiliary signals obtained by applying delays to said auxiliary signals such that any two consecutive delayed auxiliary signals are offset in time substantially by said duration &Dgr;.
Finally, the invention further provides a communications system comprising an optical network, at least one transmitter terminal provided with time-division multiplexing apparatus, and at least one receiver terminal provided with time-division demultiplexing apparatus, wherein said time-division demultiplexing apparatus includes decompression apparatus as defined above.
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K. Nonaka et al. “Simultaneous Time-and Wavelength Domain Optical Demultiplexing of NRZ Signals by Using a Side-Injection-Light-Controlled Bistable Laser Diode”, Electronics Letters, vol. 31, No. 21, Oct. 12, 1995, p. 1865/1866.
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Chauzat Corinne
Chiaroni Dominique
De Bouard Dominique
Sotom Michel
Alcatel
Pascal Leslie
Phan Hanh
Sughrue Mion Zinn Macpeak & Seas, PLLC
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