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.
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.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.