Phase-modulated fiber optic telecommunications system

• US 6,476,952 B1
• Filed: 11/26/2001
• Issued: 11/05/2002
• Est. Priority Date: 01/17/2001
• Status: Expired due to Term

• Current Assignee: Oyster Optics, LLC
• Original Assignee: Oyster Optics, Inc. (Oyster Optics, LLC)
• Inventors: Snawerdt, Peter
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): PAYNE, DAVID C
• Application Number:
  US09/994,248
• Time in Patent Office: 344 Days
• Field of Search: 359/173, 359/183, 359/154, 359/156, 359/158, 359/161, 380/21
• US Class Current: 398/141
• CPC Class Codes: H04B 10/548 Phase or frequency modulation
• CPC Class Codes: H04B 10/85 Protection from unauthorised access, e.g. eavesdrop protection

Abstract

A fiber optic data transmission system includes a transmitter having a laser emitting a continuous wave light, the transmitter including a phase modulator phase modulating the continuous wave light and a control circuit controlling the phase modulator as a function of an electronic input data stream having a time delay, so as to create a phase-modulated optical signal. An optical fiber transmits the phase-modulated optical signal. A receiver includes an interferometer for receiving the phase-modulated optical signal, the interferometer having a first arm and a second arm, the second arm being longer than the first arm, the interferometer having an interferometric delay corresponding to the time delay and a phase difference imparted by the first and second arms, the control circuit imparting a phase to represent a binary zero or one as a function of the phase difference.

Claims

1. A fiber optic data transmission system comprising:

a transmitter having a laser emitting a continuous wave light, the transmitter including a phase modulator phase modulating the continuous wave light and a control circuit controlling the phase modulator as a function of an electronic input data stream having a time delay, so as to create a phase-modulated optical signal;

an optical fiber transmitting the phase-modulated optical signal; and

a receiver, the receiver including an interferometer for receiving the phase-modulated optical signal, the interferometer having a first arm and a second arm, the second arm being longer than the first arm, the interferometer having an interferometric delay corresponding to the time delay and a phase difference imparted by the first and second arms, the control circuit imparting a phase to represent a binary zero or one as a function of the phase difference, the control circuit including a digital-to-analog converter having an output for altering the phase of the phase modulator.

2. The system as recited in claim 1 wherein the control circuit includes an exclusive-or or an exclusive-nor gate with the time delay being in a feedback loop.

3. The system as recited in claim 1 wherein the receiver imparts a 180-degree phase difference.

4. The system as recited in claim 3 wherein at least one of the first arm and the second arms includes an additional phase modulator.

5. The system as recited in claim 1 wherein the control circuit includes a phase-compensation circuit for rotating a phase imparted by the phase modulator by a predetermined amount.

6. The system as recited in claim 5 wherein the predetermined amount is a function of the phase difference imparted by the interferometer.

7. The system as recited in claim 6 wherein phase compensation circuit includes an N-bit register storing the predetermined amount.

8. The system as recited in claim 7 wherein the phase compensation circuit includes an ALU for summing without carry the predetermined amount.

9. The system as recited in claim 8 wherein the control circuit includes a delayed feedback exclusive-or gate having a gate output and receives the input data stream as an input, and wherein a most significant bit of an ALU output of the ALU is fed together with the gate output through an other exclusive-or gate.

10. The system as recited in claim 9 wherein the digital-to-analog converter has an input, the input of the digital-to-analog converter being an output of the other exclusive-or gate and least significant bits of the ALU output.

11. The system as recited in claim 5 wherein the phase compensation circuit rotates the phase by an amount equal to [(PD−

180)/max(Z,1)] mod 360, where PD is the phase difference and Z is the number of bits of delay imposed by the second arm of the interferometer relative to the first arm.

12. An optical data transmitter comprising:

a laser for producing light;

a phase modulator phase modulating the light; and

an electronic control circuit for receiving an electronic input data stream and controlling the phase-modulator, the electronic control circuit including an input data circuit having an electronic delay and a phase compensation circuit for altering an output of the input data circuit, the phase compensation circuit including an N-bit register for storing a desired phase compensation amount, an ALU for summing without carry the desired phase compensation amount, and a delayed feedback exclusive-or gate having a gate output and receiving the input data stream as an input, and wherein a most significant bit of an ALU output of the ALU is fed together with the gate output through another exclusive-or gate.

13. A fiber optic data transmission system comprising:

a transmitter having a laser emitting a continuous wave light, the transmitter including a phase modulator phase modulating the continuous wave light and a control circuit controlling the phase modulator as a function of an electronic input data stream having a time delay, so as to create a phase-modulated optical signal;

an optical fiber transmitting the phase-modulated optical signal; and

a receiver, the receiver including an interferometer for receiving the phase-modulated optical signal, the interferometer having a first arm and a second arm, the second arm being longer than the first arm, the interferometer having an interferometric delay corresponding to the time delay and a phase difference imparted by the first and second arms, the control circuit imparting a phase to represent a binary zero or one as a function of the phase difference,

the control circuit including a phase-compensation circuit for rotating a phase imparted by the phase modulator by a predetermined amount wherein the predetermined amount is a function of the phase difference imparted by the interferometer, the phase compensation circuit including an N-bit register storing the predetermined amount, an ALU for summing without carry the predetermined amount, and a delayed feedback exclusive or gate having a gate output and receiving the input data steam as an input, and a most significant bit of an ALU output of the ALU being fed together with the gate output through an other exclusive-or gate.

14. The system as recited in claim 13 wherein the control circuit includes a digital-to-analog converter having an output for altering a phase of the phase modulator, and the input of the converter is an output of the other exclusive-or gate and least significant bits of the ALU output.