Granted Patent B2

US 7,421,204 · App. 10/934,610 · Granted Sep 2, 2008

Abstract

Claims (38)

1. A method for increasing the spectral efficiency of binary coded digital signals, comprising:

encoding a binary bit sequence to convert said binary bit sequence into a series of rectangular pulses having varying repetition rates;

modulating a continuous wave carrier signal via a control signal representative of said encoded binary bit sequence to produce a modulated carrier signal; and

performing single side band filtering of said modulated carrier signal to produce a resulting modulated carrier signal having a normalized frequency deviation about a central frequency of the resulting modulated carrier signal.

2. The method of claim 1 , further comprising:

demodulating said resulting modulated carrier signal to recover therefrom said binary bit sequence.

3. The method of claim 2 , where said resulting modulated carrier signal is demodulated via a Mach-Zehnder Interferometer comprising two optical paths, wherein a first of said two optical paths includes an optical delay device and a second of said two optical paths includes an adjustable phase shifter.

4. The method of claim 1 , wherein said resulting modulated carrier signal comprises a minimum shift keying (MSK) modulation format.

5. A transmission system having increased spectral efficiency of transmitted binary coded signals, comprising:

at least one coding circuit for encoding a binary bit sequence to convert said binary bit sequence into a series of rectangular pulses having varying repetition rates and for providing a control signal representative of said encoding;

at least one continuous wave source for providing a continuous wave carrier signal;

at least one optical modulator for receiving said control signal and modulating said a continuous wave carrier signal according to said control signal; and

at least one narrow band optical filter for filtering said modulated carrier signal to produce a resulting modulated carrier signal having a normalized frequency deviation about a central frequency of the resulting modulated carrier signal.

6. The transmission system of claim 5 , further comprising:

at least one demodulator for demodulating said resulting modulated carrier signal.

7. The transmission system of claim 6 , wherein said demodulator comprises a Mach-Zehnder Interferometer (MZI) and a feedback path.

8. The transmission system of claim 7 , wherein said MZI comprises two optical paths, wherein a first of said two optical paths includes an optical delay device and a second of said two optical paths includes an adjustable phase shifter.

9. The transmission system of claim 8 , wherein said transmission system further comprises a receiver for receiving said demodulated carrier signal.

10. The transmission system of claim 9 , wherein at least a portion of an output of said receiver is fed back to said adjustable phase shifter via said feedback path to accomplish phase locking between said two optical paths of the MZI with respect to a center frequency of said resulting modulated carrier signal.

11. The transmission system of claim 9 , wherein said receiver comprises a photodiode.

12. The transmission system of claim 9 , wherein said receiver comprises a balanced detector.

13. The transmission system of claim 5 , wherein said continuous wave source comprises a distributed feedback laser.

14. The transmission system of claim 5 , wherein said narrow band optical filter performs single side band filtering.

15. The transmission system of claim 5 , wherein said narrow band optical filter comprises a wavelength division multiplexed (WDM) multiplexer.

16. A wavelength division multiplexed (WDM) transmission system having increased spectral efficiency of transmitted binary coded signals, comprising:

a plurality of optical paths, each of said plurality of optical paths including:

at least one coding circuit for encoding a binary bit sequence to convert said binary bit sequence into a series of rectangular pulses having varying repetition rates and for providing a control signal representative of said encoding;

at least one continuous wave source for providing a continuous wave carrier signal;

at least one optical modulator for receiving said control signal and modulating said carrier signal according to said control signal; and

at least one narrow band optical filter for filtering said modulated carrier signal to produce a resulting modulated carrier signal having a normalized frequency deviation about a central frequency of the resulting modulated carrier signal;

a WDM multiplexer for receiving a resulting modulated carrier signal from each of said plurality of optical paths and multiplexing them into a combined signal;

an optical link for propagating said combined signal;

a WDM demultiplexer for separating said combined signal into respective optical channels;

at least one demodulator for demodulating the demultiplexed optical channels; and

at least one receiver for receiving said demodulated optical channels and recovering therefrom said input binary bit sequences.

17. The WDM transmission system of claim 16 , wherein each of said plurality of optical paths comprises a respective demodulator and receiver.

18. The WDM transmission system of claim 16 , wherein said resulting modulated carrier signals comprise a minimum shift keying (MSK) modulation format.

19. The WDM transmission system of claim 16 , wherein said at least one continuous wave source comprises a distributed feedback laser.

Assignments (9)