Patent EP0131818A2 successfully refreshed from Google Patents.
EP0131818A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Optical FDM system
Assignee: International Standard Electric Corp
•
Filing: 1984-06-29
•
Granted: —
•
Expires: 2004-06-29
Abstract
Abstract In an optical fibre FDM system, the carriers are derived from the output of a high quality Master Oscillator, which output at frequency fo is applied to a Raman Nath modulator (RNM1) whose other input is a frequency f this gives as its outputs (assuming a five channel system) fo-2f, fo-f, fo, fo + f and fo + 2f. These are modulated by modulators (CM1 to CM5) with the signals to be sent, and the modulation results combined in a combiner (CB) for transmission to a remote station. The oscillator output is also sent to the remote stations where it is frequency-shifted by a Bragg modulator (BM) and the resultant similarly dealt with by a Raman Nath device (RNM2) to give five frequencies which are used to demodulate the channels. In an alternative the channel frequencies are switchable.
Inventors
- 👤 Robert Walter Alister Scarr
- 👤 John Bingham
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 13:48
CPC Classifications
H; H04; H04Q; H04Q11/00; H04Q11/0001; H04B; H04B10/00; H04B10/50; H04B10/501; H04B10/506; H04B10/572
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
170 words
A frequency division multiplex (FDM) system in which the transmission medium is an optical fibre cable, which system provides a number of channels whose frequencies are widely and uniformly separated across the available frequency spectrum, characterized in that a single oscillator is associated with all of the channels and provides a single output frequency (f ) at or near to a central point of the frequency spectrum, that the single output frequency (f ) is applied to a modulation arrangement (RNM1) which generates therefrom a number of outputs each providing a carrier frequency for one of the channels, wherein the outputs are derived form the oscillator's output by the subtraction therefrom of a second frequency (f) one or more times to give one or more further frequencies and by the addition of the second frequency (f) to the oscillator's output to give one or more further frequencies, and that the further frequencies, or the further frequencies plus the orginal oscillator frequency are used as the carriers for the FDM channels.
Claim 2
Dependent Claim
170 words
A frequency division multiplex (FDM) system in which the transmission medium is an optical fibre cable, which system provides a number of channels whose frequencies are widely and uniformly separated across the available frequency spectrum, characterized in that a single oscillator is associated with all of the channels and provides a single output frequency (f ) at or near to a central point of the frequency spectrum, that the single output frequency (f ) is applied to a modulation arrangement (RNM1) which generates therefrom a number of outputs each providing a carrier frequency for one of the channels, wherein the outputs are derived form the oscillator's output by the subtraction therefrom of a second frequency (f) one or more times to give one or more further frequencies and by the addition of the second frequency (f) to the oscillator's output to give one or more further frequencies, and that the further frequencies, or the further frequencies plus the orginal oscillator frequency are used as the carriers for the FDM channels.
Claim 3
Dependent Claim
60 words
2 . The system as claimed in claim 1 characterized in that the modulation arrangement (RNM1) is a Raman-Nath device to which the oscillator frequence (f ) and the further frequency (f) are both applied, and in which the Raman-Nath device provides 2N-1 outputs at frequencies N of which are below f and N of which are above f .
Claim 4
Dependent Claim
39 words
The system as claimed in claim 2, characterized in that the Raman Nath device provides outputs at frequencies (f o - 2f), (f o - f), f o , (f o + f) and (f o + 2f ).
Claim 5
Dependent Claim
63 words
The system as claimed in claim 2 or 3, characterized in that each of the outputs of the Raman Nath device is applied to the respective one of 2N+1 channel modulators (CM1 to CM5), one per channel served, and in which the outputs of the channel modulators are combined in a combiner (CB) for application for an optical fibre to a remote station.
Claim 6
Independent Claim
43 words
The system as claimed in any of the claims 1 to 4, characterized in that the output of the oscillator is applied via a further optical fibre to the remote station when it is used to detect the signals on the various channels.
Claim 7
Dependent Claim
93 words
The system as claimed in claim 5, characterized in that at the remote station the received oscillator output is frequency shifted by a third frequency (f IF ), that the shifted frequency (f o + f IF ) is applied to another Raman Nath device (RNM2) to produce five local outputs each of which differs by the third frequency from one of the channel frequencies of the channel modulators (CM1 to CM5), and that the 2N+1 local output frequencies are combined with respective ones of the received channels from which detection is effected.
Claim 8
Dependent Claim
123 words
The system as claimed in claim 5, characterized in that the FDM channels are switchable, in that at the remote stations the received oscillator output is shifted by a third frequency (f IF ) and the shifted output is split by an optical splitter (OS) to give 2N+1 similar outputs which are applied to a set of 2N+1 Bragg modulators (BM1 to BM5), one per channel, that each said Bragg modulator has local oscillator inputs so that it can be used for any one of the channels, that the input modulated signals are split by a further optical splitter to give 2N+1 outputs, and that the outputs from the Bragg modulators and from the further optical splitter are respectively combined to effect detection.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.