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US 5,319,438 AGranted
Interferometric, self-homodyne optical receiver and method and optical transmission system incorporating same
AssigneeBoard of Regents, The University of Texas System
InventorKamran Kiasaleh
Life of this patent
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Abstract
An interferometric, self-homodyne optical receiver is disclosed for detecting and demodulating phase modulated optical signals without requiring a local oscillator normally associated with coherent optical receivers. The self-homodyne receiver includes an interferometer having a phase modulator optically coupled to one channel of the interferometer and a phase-locked arrangement providing electrical signals which control the phase modulator and phase of one channel of the interferometer with respect to the other channel.
Claims23
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.
3 more elements
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.
4 more elements
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.
7 more elements
A method for detecting phase modulated optical signals and recovering data modulated about said signal, comprising:
- receiving a phase modulated optical input signal into a delay channel;
- coupling the input signal into a reference channel;
- phase delaying the input signal within the delay channel so that said phase delayed input signal is in quadrature phase with said input signal;
- phase adjusting the input signal within the reference channel to produce a phase adjusted input signal;
- producing an electrical output signal proportional to the phase difference between the phase delayed input signal and the phase adjusted input signal, wherein said electrical output signal has a delay component;
- and
- detecting the input signal within said delay channel in accordance with changes in the electrical output signal.
4 more elements
A method of detecting information from a phase-modulated optical signal, comprising:
- receiving a phase-modulated optical input signal into a delay channel having a delay loop;
- coupling the input signal into a reference channel;
- phase delaying the input signal within the delay channel so that said phase delayed input signal is in quadrature phase with said input signal;
- phase adjusting the input signal within the reference channel to produce a phase adjusted input signal;
- comparing the phase delayed input signal with the phase adjusted input signal;
- producing an electrical error signal proportional to the phase difference between the phase delayed input signal and the phase adjusted input signal, wherein said electrical output signal has a delay component;
- cancelling said delay component from said electrical error signal;
- and
- detecting the modulation term of the phase-modulated input optical signal from said electrical error signal.
6 more elements
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.
7 more elements
Dependencies are inferred from the claim text.