Interferometric, self-homodyne optical receiver and method and optical transmission system incorporating same

Claim 2

A self-homodyne optical receiver comprising: a delay channel and a reference channel optically coupled to the delay channel, wherein said delay channel is capable of receiving a phase-modulated optical input signal; a phase delaying loop optically coupled to said delay channel for producing a phase delayed optical signal in quadrature phase with the input signal; an optical-to-electrical photodetector coupled to the delay channel; a differential amplifier coupled to an output of the photodetector; and a phase modulator optically coupled to the reference channel and indirectly controlled by an electrical output signal from the differential amplifier.

Claim 3

The self-homodyne optical receiver as recited in claim 1, wherein said reference channel is optically coupled to said delay channel at two locations along said delay channel with said phase modulator optically coupled to the reference channel between said two locations.

Claim 4

The self-homodyne optical receiver as recited in claim 1, further comprising a second optical-to-electrical photodetector coupled to the reference channel.

Claim 5

The self-homodyne optical receiver as recited in claim 1, wherein said photodetector includes at least one photodiode coupled to the delay channel.

Claim 6

An interferometric, self-homodyne optical receiver comprising: an interferometer including a delay channel and a reference channel optically coupled to the delay channel, wherein said delay channel is capable of receiving a phase modulated optical input signal; an electrically controllable phase modulator optically coupled to said reference channel for phase adjusting said phase modulated optical signal; a phase delaying loop optically coupled to said delay channel for producing a phase delayed optical signal in quadrature phase with said input signal; at least one photodiode coupled to receive said phase adjusted optical input signal optically combined with said phase delayed optical signal; a differential amplifier electrically coupled to an output of said photodiode for producing an electrical output signal which changes corresponding to changes in the phase difference between the phase of the phase adjusted signal and the phase delayed optical signal; and said electrical output signal coupled to said phase modulator for passively controlling the phase of the phase modulated optical input signal in response to changes in the electrical output signal.

Claim 7

An interferometric, self-homodyne optical receiver comprising: an interferometer including a delay channel and a reference channel optically coupled to the delay channel, wherein said delay channel is capable of receiving a phase modulated optical input signal; an electrically controllable phase modulator optically coupled to said reference channel for phase adjusting said phase modulated optical signal; a phase delaying loop optically coupled to said delay channel for producing a phase delayed optical signal in quadrature phase with said input signal; at least one photodiode coupled to receive said phase adjusted optical input signal optically combined with said phase delayed optical signal; a differential amplifier electrically coupled to an output of said photodiode for producing an electrical output signal which changes corresponding to changes in the phase difference between the phase of the phase adjusted signal and the phase delayed optical signal; and said electrical output signal coupled to said phase modulator for passively controlling the phase of the phase modulated optical input signal in response to changes in the electrical output signal.

Claim 8

The interferometric, self-homodyne optical receiver as recited in claim 5, wherein said interferometer comprises a pair of evanescent couplers for optically coupling the delay channel and the reference channel at two locations separated at a controllable distance.

Claim 9

The interferometric, self-homodyne optical receiver as recited in claim 6, wherein said evanescent couplers comprise single mode 3 dB couplers.

Claim 10

The interferometric, self-homodyne optical receiver as recited in claim 5, wherein said differential amplifier compares changes in electrical signals corresponding to changes in the phase of the phase modulated optical input signal combined with the phase delayed optical input signal.

Claim 11

An optical transmission system, comprising: an optical source for generating a phase modulated optical input signal; a self-homodyne optical receiver comprising: a delay channel coupled to a first end of the delay channel to receive the optical input signal; a reference channel coupled to the delay channel to receive the optical input signal therein; a phase delay loop coupled to the delay channel to form a phase delayed optical signal within the delay channel wherein said phase delayed signal is in quadrature phase with said input signal; a phase modulator optically coupled to the reference channel to phase adjust said input signal within the reference channel; a photodetector coupled to a second end of the delay channel opposite the first end to convert the phase delayed signal combined with the phase adjusted optical input signal therein to a corresponding electrical signal; a differential amplifier coupled to receive the electrical signal; and a feedback electrical signal sent from the amplifier to the phase modulator for passively tracking the phase of the optical input signal in proportion to a phase difference output from the differential amplifier.

Claim 12

An optical transmission system, comprising: an optical source for generating a phase modulated optical input signal; a self-homodyne optical receiver comprising: a delay channel coupled to a first end of the delay channel to receive the optical input signal; a reference channel coupled to the delay channel to receive the optical input signal therein; a phase delay loop coupled to the delay channel to form a phase delayed optical signal within the delay channel wherein said phase delayed signal is in quadrature phase with said input signal; a phase modulator optically coupled to the reference channel to phase adjust said input signal within the reference channel; a photodetector coupled to a second end of the delay channel opposite the first end to convert the phase delayed signal combined with the phase adjusted optical input signal therein to a corresponding electrical signal; a differential amplifier coupled to receive the electrical signal; and a feedback electrical signal sent from the amplifier to the phase modulator for passively tracking the phase of the optical input signal in proportion to a phase difference output from the differential amplifier.

Claim 13

The transmission system as recited in claim 9, wherein said optical source includes a remote laser.

Claim 14

The transmission system as recited in claim 9, further comprising an optical path coupled between the optical source and the receiver.

Claim 15

The transmission system as recited in claim 9, wherein said photodetector includes at least one photodiode coupled to the second end of the delay channel.

Claim 18

The method as recited in claim 13, wherein said phase modulating comprises passive phase modulating the input signal within said reference channel with respect to said input signal.

Claim 19

The method as recited in claim 14, wherein said passive phase modulating comprises phase adjusting the input signal absent a local oscillator.

Claim 20

The method as recited in claim 13, wherein said phase delaying comprises providing a delaying loop within the delay channel.

Claim 21

The self-homodyne optical receiver as recited in claim 1, wherein said electrical output signal has a delay component.

Claim 22

The self-homodyne optical receiver as recited in claim 17, further comprising an echo canceller coupled to said differential amplifier for removing said delay component from said electrical output signal.

Claim 23

The optical transmission system of claim 9, wherein said feedback electrical signal has a delay component.

Claim 24

The optical transmission system of claim 19, further comprising an echo canceller coupled to said differential amplifier for removing said delay component from said electrical output signal.

Claim 25

The method as recited in claim 16, said detecting step further comprising cancelling the delay component from said electrical output signal.

Claim 28

Apparatus for detecting information from a phase-modulated optical input signal, comprising: an interferometer including a delay channel and a reference channel optically coupled to the delay channel, wherein said delay channel is capable of receiving a phase modulated optical input signal; an electrically controllable phase modulator optically coupled to said reference channel for phase adjusting said phase modulated optical signal; a phase delaying loop optically coupled to said delay channel for producing a phase delayed optical signal in quadrature phase with said input signal; at least one evanescent coupler for optically coupling the delay channel to the reference channel; a photodiode coupled to the delay channel to receive said phase adjusted optical input signal optically combined with said phase delayed optical signal; a photodiode coupled to the reference channel to receive said phase adjusted optical input signal optically combined with said phase delayed optical signal; a differential amplifier electrically coupled to an output of each of said photodiodes for producing an electrical error signal which changes corresponding to changes in the phase difference between the phase of the phase adjusted signal and the phase delayed optical signal, wherein said error signal carries the modulation information of the optical input signal and also contains a delay component; said electrical error signal coupled to said phase modulator for passively controlling the phase of the phase modulated optical input signal in response to changes in the electrical error signal; and means for cancelling the delay component of said electrical error signal.

Claim 29

Apparatus for detecting information from a phase-modulated optical input signal, comprising: an interferometer including a delay channel and a reference channel optically coupled to the delay channel, wherein said delay channel is capable of receiving a phase modulated optical input signal; an electrically controllable phase modulator optically coupled to said reference channel for phase adjusting said phase modulated optical signal; a phase delaying loop optically coupled to said delay channel for producing a phase delayed optical signal in quadrature phase with said input signal; at least one evanescent coupler for optically coupling the delay channel to the reference channel; a photodiode coupled to the delay channel to receive said phase adjusted optical input signal optically combined with said phase delayed optical signal; a photodiode coupled to the reference channel to receive said phase adjusted optical input signal optically combined with said phase delayed optical signal; a differential amplifier electrically coupled to an output of each of said photodiodes for producing an electrical error signal which changes corresponding to changes in the phase difference between the phase of the phase adjusted signal and the phase delayed optical signal, wherein said error signal carries the modulation information of the optical input signal and also contains a delay component; said electrical error signal coupled to said phase modulator for passively controlling the phase of the phase modulated optical input signal in response to changes in the electrical error signal; and means for cancelling the delay component of said electrical error signal.