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EP0314197A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

A four level frequency shift keying optical communication apparatus

Assignee: NEC Corp
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Filing: 1988-10-31
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Granted: —
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Expires: 2008-10-31
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Abstract

Abstract In a four level FSK optical communication apparatus, signal light (3) which is modulated in FSK with information is transmitted through an optical transmission line (4). The signal light is detected (8) in an optical heteroclyne system by using local oscillation light (6), thereby producing intermediate frequency band signal which is then demodulated. A detection system comprises first and second delay (20, 20B) detection circuits. In the first detection circuit, the intermediate frequency band signal is divided into first and second signals. The first signal is delayed by a delay time (15), and then mixed (17) with a second signal which is not delayed to produce first delay detection signal. In the second delay detection circuit, one of the first signal delayed and the second signal not delayed is shifted in its phase by π/2. Then, signal having the phase shift of π/2 and signal having no phase shift are mixed (18) to produce second delay detection signal. Thus, the demodulation of four level FSK modulation signal is performed.

Inventors

  • 👤 Kaoru C/O Nec Corporation Manome

Bibliographic Details

Application Number —
Jurisdiction EP
Data Source google_patents
Last Synchronized 2026-11-08 18:52
CPC Classifications
H; H04; H04B; H04B10/00; H04B10/60; H04L; H04L27/00; H04L27/10; H04L27/14

Claims Analysis

Total Claims: 5
Claim 1
Independent Claim 167 words
A four level FSK optical communication apparatus comprising, a light source for emitting signal light modulated in FSK with four level transmitting signal, a local oscillation light source for emitting local oscillation light, an optical coupler for combining said signal and local oscillation lights to produce combined light, means for converting said combined light to intermediate frequency signal, means for dividing said intermediate frequency signal into two divided signals, a delay means for delaying one of said two divided signals to produce delayed signal, a phase shift means for shifting the phase of signal selected from said delayed signal and the remaining one of said two divided signals by π/2 to produce phase shift signal, a first mixing means for mixing said delayed signal and said remaining one of said two divided signals to produce first delay detection signal, and a second mixing means for mixing said phase shift signal and signal which is not shifted in said phase shift means to produce second delay detection signal.
Claim 2
Dependent Claim 167 words
A four level FSK optical communication apparatus comprising, a light source for emitting signal light modulated in FSK with four level transmitting signal, a local oscillation light source for emitting local oscillation light, an optical coupler for combining said signal and local oscillation lights to produce combined light, means for converting said combined light to intermediate frequency signal, means for dividing said intermediate frequency signal into two divided signals, a delay means for delaying one of said two divided signals to produce delayed signal, a phase shift means for shifting the phase of signal selected from said delayed signal and the remaining one of said two divided signals by π/2 to produce phase shift signal, a first mixing means for mixing said delayed signal and said remaining one of said two divided signals to produce first delay detection signal, and a second mixing means for mixing said phase shift signal and signal which is not shifted in said phase shift means to produce second delay detection signal.
Claim 3
Dependent Claim 50 words
A four level FSK optical communication apparatus according to claim 1, wherein said delay means is a delay line through which said one of said two divided signals is propagated, and said phase shift means is a 90° hybrid divider which is connected at its input to said delay line.
Claim 4
Dependent Claim 55 words
A four level FSK optical communication apparatus according to claim 1, wherein said delay means comprises two delay lines each connected in parallel to a signal line for each of said two divided signals, and said phase shift means is a π/2 phase shifter inserted into one of signal lines for said two divided signals.
Claim 5
Dependent Claim 42 words
A four level FSK optical communication apparatus according to any of claims 1 to 3 further comprising, means for producing four level modulation signal which is then propagated through a transmission line in accordance with said first and second delay detection signals.

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