Spatially dephasing local oscillator for coherent free-space optical communications

Patent metadata

Field	Value
Publication number	US-10122471-B2
Application number	US-201615204898-A
Country	US
Kind code	B2
Filing date	Jul 7, 2016
Priority date	Jul 7, 2016
Publication date	Nov 6, 2018
Grant date	Nov 6, 2018

Abstract

A coherent transceiver system includes a local oscillator (LO) light source to generate an LO optical signal. An adaptive fiber array is coupled to the LO light source to dephase the LO optical signal. A balanced detector is coupled to the adaptive fiber array to receive a dephased LO signal from the adaptive fiber array and an optical input signal and to generate a heterodyne signal. A controller receives the heterodyne signal and generates one or more control signals. The adaptive fiber array utilizes the control signals to dephase the LO optical signal.

First claim

What is claimed is:

1. A coherent transceiver system, the system comprising:
a local oscillator (LO) light source configured to generate an LO optical signal;
an adaptive fiber array coupled to the LO light source and configured to dephase the LO optical signal;
a balanced detector coupled to the adaptive fiber array and configured to receive a dephased LO signal from the adaptive fiber array and an optical input signal and to generate a heterodyne signal comprising a plurality of channel heterodyne signals, wherein the balanced detector comprises a beam splitter and optical couplers configured to generate a first and a second combined beam to be out of phase by 180 degrees, and the heterodyne signal comprises a difference between the first and the second combined beam; and
a controller configured to receive the heterodyne signal and to generate one or more control signals,
wherein the adaptive fiber array utilizes the one or more control signals to dephase the LO optical signal.

2. The system of claim 1 , wherein the adaptive fiber array comprises a fiber splitter configured to split the LO optical signal into a plurality of optical channel signals, wherein an optical channel signal of the plurality of optical channel signals is associated with a channel wavelength, and wherein the adaptive fiber array is configured to match a phase of the LO optical signal with a phase of the optical input signal based on the one or more control signals.

3. The system of claim 2 , wherein the adaptive fiber array further comprises a plurality of electro-optical (EO) phase modulators, wherein an EO phase modulator of the plurality of EO phase modulators comprises a lithium niobate crystal modulator.

4. The system of claim 3 , wherein the EO phase modulator is configured to receive a control signal of the one or more control signals and to adjust a phase of the optical channel signal based on the control signal to generate a dephased optical channel signal.

5. The system of claim 4 , wherein the adaptive fiber array further comprises a plurality of fiber array collimators, wherein a fiber array collimator of the plurality of fiber array collimators is configured to collimate the dephased optical channel signal.

6. The system of claim 5 , wherein the beam splitter is configured to split the optical input signal and the dephased LO signal into the first and the second combined beam.

7. The system of claim 1 , wherein the controller comprises a hill-climbing controller and is configured to facilitate estimating a desired phase of the dephased optical channel signal using a dither signal for each optical channel.

8. The system of claim 7 , wherein the controller is configured to provide the dither signal to the EO phase modulator, and the EO phase modulator is configured to modulate a phase of the optical channel signal using the dither signal.

9. The system of claim 7 , wherein the controller comprises a demodulator and a filter and is configured to demodulate and filter the channel heterodyne signal of the plurality of channel heterodyne signals using the demodulator and the filter.

10. The system of claim 7 , wherein the controller is configured to use an estimated desired phase of the dephased optical channel signal as an initial phase value and increments the initial phase value in an optimization loop to maximize a power of the heterodyne signal.

11. A method of providing a coherent transceiver system, the method comprising:
providing a local oscillator (LO) light source to generate an LO optical signal;
coupling an adaptive fiber array to the LO light source;
configuring the adaptive fiber array to dephase the LO optical signal and to generate a dephased LO signal;
coupling a balanced detector to the adaptive fiber array, the balanced detector comprising a beam splitter and optical couplers;
configuring the balanced detector to generate a heterodyne signal comprising a plurality of channel heterodyne signals using the dephased LO signal and an optical input signal;
configuring the beam splitter and the optical couplers to generate a first and a second combined beam to be out of phase by 180 degrees, wherein the heterodyne signal comprises a difference between the first and the second combined beam; and
providing a controller to receive the heterodyne signal and to generate one or more control signals,
wherein the adaptive fiber array is configured to utilizes the one or more control signal to dephase the LO optical signal.

12. The method of claim 11 , wherein coupling the adaptive fiber array comprises coupling a fiber splitter, and wherein the method further comprises configuring the fiber splitter to split the LO optical signal into a plurality of optical channel signals, wherein an optical channel signal of the plurality of optical channel signals is associated with a channel wavelength.

13. The method of claim 12 , further comprising configuring an electro-optical (EO) phase modulator of the adaptive fiber array to receive a control signal of the one or more control signals and to adjust a phase of the optical channel signal based on the control signal to generate a dephased optical channel signal.

14. The method of claim 13 , further comprising collimating the dephased optical channel signal using a plurality of fiber array collimators.

15. The method of claim 13 , wherein the beam splitter of the balanced detector is configured to split the optical input signal and the dephased LO signal into the first and the second combined beam.

16. The method of claim 15 , further comprising:
configuring the controller to provide a dither signal to the EO phase modulator, and
configuring the EO phase modulator to modulate a phase of the optical channel signal using the dither signal.

17. The method of claim 15 , further comprising configuring the controller to use an estimated desired phase of the dephased optical channel signal as an initial phase value and increments the initial phase value in an optimization loop to maximize a power of the heterodyne signal.

18. A free-space optical (FSO) communication system comprising:
at least two FSO transceivers:
an FSO transceiver of the at least two FSO transceivers coupled via an FSO modem to a network, wherein the FSO transceiver comprises:
a local oscillator (LO) light source configured to generate an LO optical signal;
an adaptive fiber array coupled to the LO light source and configured to dephase the LO optical signal;
a balanced detector coupled to the adaptive fiber array and configured to receive a dephased LO signal from the adaptive fiber array and an optical input signal and to generate a heterodyne signal comprising a plurality of channel heterodyne signals, wherein the balanced detector comprises a beam splitter and optical couplers configured to generate a first and a second combined beam to be out of phase by 180 degrees, and the heterodyne signal comprises a difference between the first and the second combined beam; and
a controller configured to receive the heterodyne signal and to generate one or more control signals,
wherein the adaptive fiber array utilizes the one or more control signal to dephase the LO optical signal.

19. The FSO communication system of claim 18 , wherein the adaptive fiber array further comprises a plurality of fiber array collimators.

20. The FSO communication system of claim 19 , wherein a fiber array collimator of the plurality of fiber array collimators is configured to collimate the dephased optical channel signal.

Assignees

• Lockheed Corp

Inventors

• Bock Kevin Richard
• PERKINS Patrick Eliott
• Tischhauser Christopher William

Classifications

• H04B10/11

  Arrangements specific to free-space transmission, i.e. transmission through air or vacuum · CPC title

• H04B10/1121 Primary

  One-way transmission · CPC title

• H04B10/40

  Transceivers · CPC title

• H04B10/6165

  Estimation of the phase of the received optical signal, phase error estimation or phase error correction · CPC title

• H04B10/64 Primary

  Heterodyne {, i.e. coherent receivers where, after the opto-electronic conversion, an electrical signal at an intermediate frequency [IF] is obtained} · CPC title