EP0145972A1
Expired / Lapsed
EP
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Coherent optical communication system with FSK heterodyne or homodyne detection and little influence by distortion of a modulated optical signal
Assignee: NEC Corp
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Filing: 1984-11-15
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Granted: —
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Expires: 2004-11-15
Abstract
Abstract A laser (21) is frequency modulated by an electrical modulating signal of a bit rate into a modulated signal of a first and a second modulated frequency. A combination of an optical mixer (27) and an optical detector (31) carries out optical heterodyne or homodyne detection on the modulated optical signal to produce a detected signal having a first and a second frequency component. A component separator (32) is for selecting only one of the components from the detected signal. A detector (33) detects the selected component to produce a demodulated electrical signal representative of the modulating signal. The laser is preferably a semiconductor laser. More preferably, the semiconductor laser is frequency modulated after the modulating signal is converted to a current of an mBnB code sequence. When the bit rate is below and above about 10 Mbit/second, either the modulating signal or the mBnB code sequence current is preferably used in frequency modulating the semiconductor laser after caused to pass through a high-pass and a low-pass filter, respectively.
Inventors
- 👤 Katsumi Emura
- 👤 Minoru Shikada
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 06:56
CPC Classifications
H; H04; H04B; H04B10/00; H04B10/60; H04B10/61; H04B10/63; H04B10/64; H04L; H04L27/00; H04L27/10; H04L27/14
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
220 words
In an optical communication system comprising a transmitter, a receiver, and an optical path between said transmitter and said receiver, said transmitter comprising a laser for generating an optical carrier signal of a carrier frequency and modulating means for frequency modulating said carrier signal by an electrical modulating signal into a modulated optical signal for transmission to said optical path, said receiver comprising a local optical source for generating a local optical signal of a local oscillation frequency predetermined in consideration of said carrier frequency, an optical mixer for mixing said local optical signal and the modulated optical signal received through said optical path to produce a mixed optical signal, and demodulating means for demodulating said mixed optical signal into a demodulated electrical signal representative of said modulating signal, the improvement wherein said modulating means is for making said modulated optical signal take a first and a second modulated frequency in compliance with said modulating signal, said mixer being for making said mixed optical signal essentially consist of first and second frequency components corresponding to said first and said second modulated frequencies, respectively, said demodulating means comprising first means for separating said first frequency component from said mixed optical signal and second means for demodulating the first frequency component separated by said first means to produce said demodulated electrical signal.
Claim 2
Dependent Claim
220 words
In an optical communication system comprising a transmitter, a receiver, and an optical path between said transmitter and said receiver, said transmitter comprising a laser for generating an optical carrier signal of a carrier frequency and modulating means for frequency modulating said carrier signal by an electrical modulating signal into a modulated optical signal for transmission to said optical path, said receiver comprising a local optical source for generating a local optical signal of a local oscillation frequency predetermined in consideration of said carrier frequency, an optical mixer for mixing said local optical signal and the modulated optical signal received through said optical path to produce a mixed optical signal, and demodulating means for demodulating said mixed optical signal into a demodulated electrical signal representative of said modulating signal, the improvement wherein said modulating means is for making said modulated optical signal take a first and a second modulated frequency in compliance with said modulating signal, said mixer being for making said mixed optical signal essentially consist of first and second frequency components corresponding to said first and said second modulated frequencies, respectively, said demodulating means comprising first means for separating said first frequency component from said mixed optical signal and second means for demodulating the first frequency component separated by said first means to produce said demodulated electrical signal.
Claim 3
Dependent Claim
43 words
An optical communication system as claimed in Claim 1, said laser being a semiconductor laser, said modulating signal (Claim 2 continued) being a binary modulating signal, wherein said modulating means is for directly frequency modulating said carrier signal by said binary modulating signal.
Claim 4
Dependent Claim
85 words
An optical communication system as claimed in Claim 1, said laser being a semiconductor laser, said modulating signal being a binary modulating current, wherein said modulating means comprises: means responsive to said binary modulating current for superposing a distortion cancelling current on said binary modulating current to produce a compensated modulating current, said distortion cancelling current having a waveform which said binary modulating current has when passed through a low-pass filter; and means for directly frequency modulating said carrier signal by said compensated modulating current.
Claim 5
Dependent Claim
74 words
An optical communication system as claimed in Claim 1, said laser being a semiconductor laser, said modulating signal being a binary modulating signal, wherein said modulating means comprises: code converting means for converting said binary modulating signal to an mBnB code sequence current where each of m and n represent a natural number, m being less than n; and frequency modulating means for frequency modulating said carrier signal by said mBnB code sequence current.
Claim 6
Dependent Claim
21 words
An optical communication system as claimed in Claim 4, wherein 1 ≦ m = 9 and 2 ≦ n ≦ 10.
Claim 7
Dependent Claim
23 words
An optical communication system as claimed in Claim '4 or 5, wherein n is selected from (m + 1) and (m + 2).
Claim 8
Dependent Claim
31 words
An optical communication system as claimed in any of frequency Claims 4 to 6, wherein said/modulating means is for directly frequency modulating said carrier signal by said mBnB code sequence current.
Claim 9
Dependent Claim
79 words
An optical communication system as claimed in any of Claims 4 to 7, wherein said frequency modulating means comprises: means responsive to said mBnB code sequence current for superposing a distortion cancelling current on said mBnB code sequence current to produce a compensated modulating current, said distortion cancelling current having a waveform which said mBnB code sequence current has when passed through a low-pass filter; and means for directly frequency modulating said carrier signal by said compensated modulating current.
Claim 10
Dependent Claim
78 words
An optical communication system an claimed in any of Claims 4 to 7,wherein said frequency modulating means comprises: means responsive to said mBnB code sequence current for superposing a distortion cancelling current on said mBnB code sequence current to produce a compensated modulating current, said distortion cancelling current having a waveform which said mBnB code sequence current has when passed through a high-pass filter; and means for directly frequency modulating said carrier signal by said compensated modulating current.
References Cited (Backward Citations)
US4295226A
Cited
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