Patent EP0241039A2 successfully refreshed from Google Patents.
EP0241039A2
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EP
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Optical-fibre transmission system with polarization modulation and heterodyne coherent detection
Assignee: OTC Optical Technologies Center SRL
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Filing: 1987-04-09
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Granted: —
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Expires: 2007-04-09
Abstract
Abstract Optical-fibre transmission system with heterodyne coherent detection, in which at the transmitting side the polarization of an optical carrier is modulated, and at the receiving side the beam resulting from the combination of the modulated beam and the beam emitted from a local oscillator (12) is split into two orthogonally-polarized components. The two optical signals are detected and sent to an electronic mixer (19a, 19b) which receives the two components and carries out a synchronous demodulation eliminating the effects of the linewidth of the source (1) and of the local oscillator (12).
Inventors
- 👤 Riccardo Calvani
- 👤 Renato Caponi
- 👤 Francesco Cisternino
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-10 00:55
CPC Classifications
H; H04; H04B; H04B10/00; H04B10/50; H04B10/516; H04B10/532
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
197 words
L. Coherent optical-fibre transmission system, comprising a source (1) of a light radiation at a first frequency, a modulator (4), receiving an information signal, modulating by such a signal the radiation emitted by the source and sending the modulated signal onto the fibre (8), a device (11) combining the modulated signal outgoing from the fibre (8) with a second light radiation, emitted by a local oscillator (12) and having a frequency slightly different from that of the first radiation, and means (14,15) demodulating the signal resulting from said combination, characterized in that the source (1) and the local oscillator (12) are longitudinal monomode lasers which generate linearly-polarized light radiations; in that the modulator (4) is a modulator wherein the birefringence state is modified by the modulating signal, so that the modulated signal is a polarization-modulated signal; and in that the demodulating means comprise at least a polarization separating device (14) which separates the signal resulting from the combination into two orthogonally-polarized components, which are separately converted into electrical signals and are supplied to a mixer (19), performing a synchronous demodulation cancelling phase noise due to the linewidth of the source (1) and of the local oscillator (12).
Claim 2
Dependent Claim
59 words
System according to claim 1, characterized in that it also comprises a compensator (10) associated with an automatic control system with feedback, inserted between the fibre (8) and the combining device (11), to compensate variations in the polarization states of the modulated signal introduced by the fibre (8) and variations in time of the birefringence of the fibre (8).
Claim 3
Dependent Claim
53 words
System according to claim 1 or 2, wherein the combining device (11) generates two basically equal output beams, characterized in that the demodulation means comprises a polarization separating device (14), a pair of detectors (15, 16) and a mixer (19) for each outgoing beam, the output signals of the mixers being added together.
Claim 4
Dependent Claim
45 words
System according to any one of the previous claims, characterized in that it comprises a device (22, 23) for automatic control of the frequency of the local oscillator (12), driven by the electrical signal resulting from the conversion of one of said combined- signal components.
References Cited (Backward Citations)
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