Patent EP0534644A2 successfully refreshed from Google Patents.
EP0534644A2
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EP
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Optical communications systems
Assignee: Nortel Networks Ltd
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Filing: 1992-09-10
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Granted: —
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Expires: 2012-09-10
Abstract
Abstract In an optical communications system including a transmitter (laser 1) and a receiver, with an optical amplifier (3) and an optical filter (4) therebetween, the position of the passband of the optical filter (4) is adjusted automatically in dependence on a received pilot carrier signal frequency transmitted with the data. This facilitates initial selection of transmitter laser (1) and avoids the need for transmitter laser frequency stabilisation. The optical filter acquires and tracks the optical carrier used by the transmitter
Inventors
- 👤 Anagnostis Hadjifotiou
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-10 01:26
CPC Classifications
H; H04; H04B; H04B10/00; H04B10/60; H04B10/66; H04B10/67; H04B10/671; H04B10/675
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
98 words
An optical communications system comprising an optical transmitter (1) and an optical receiver (5) and including an optical amplifier (3) and an optical filter (4) arranged in series therebetween, data being transmitted by the transmitter to the receiver, characterised by including means whereby an optical pilot carrier signal is added to the data to be transmitted and means (AM1, 7, FL1, 6) whereby the position of the passband of the optical filter (4) is adjusted in dependence on the received optical pilot carrier signal frequency such that the position of the passband tracks variations in the transmitted frequency.
Claim 2
Dependent Claim
94 words
A system as claimed in claim 1 characterised in that the optical amplifier (3) is a preamplifier of the receiver and including means whereby the received pilot carrier signal is detected differentially at the receiver (5) from the output of the optical filter (4), amplified, filtered to remove high frequency signal components generated by said detection and applied to a controller (6) for the optical filter, the controller serving to change the frequency of the maximum response of the optical filter so that it coincides with that of the transmitted optical pilot carrier signal.
Claim 3
Dependent Claim
92 words
A system as claimed in claim 1 characterised in that the optical amplifier is an optical line repeater amplifier (13) and including means whereby the pilot carrier signal at the output of the optical filter (14) is detected (16), amplified (18), filtered (19) to remove high frequency signal components generated by said detection and applied to a controller (20) for the optical filter, the controller serving to change the frequency of the maximum response of the optical filter (14) so that it coincides with that of the transmitted optical pilot carrier signal.
Claim 4
Dependent Claim
24 words
A system as claimed in claim 2 or claim 3 wherein the detected pilot carrier signal is filtered and rectified prior to said filtering.
Claim 5
Dependent Claim
27 words
A system as claimed in claim 2 or claim 3 wherein the detected pilot carrier signal is mixed with a local reference frequency prior to said filtering.
Claim 6
Independent Claim
19 words
A system as claimed in any one of the preceding claims wherein the optical amplifier is a semiconductor device.
Claim 7
Independent Claim
21 words
A system as claimed in any one of the preceding claims wherein the optical amplifier is an erbium doped silica fibre.
Claim 8
Independent Claim
30 words
A system as claimed in any one of the preceding claims wherein the optical filter is a multilayer interference filter or another filter whose band pass position can be adjusted.
Claim 9
Dependent Claim
41 words
A system as claimed in claim 2 or claim 3 wherein the optical filter, detection means, amplifying means, filtering means and said controller comprise a tracking filter which serves automatically initially to acquire the carrier signal and then to track it.
References Cited (Backward Citations)
No citation records indexed.
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