Intensity modulated direct detection broad optical-spectrum source communication

• US 10,038,499 B2
• Filed: 12/30/2015
• Issued: 07/31/2018
• Est. Priority Date: 12/30/2015
• Status: Active Grant

• Current Assignee: Meta Platforms, Inc. (f/k/a Facebook, Inc.)
• Original Assignee: Meta Platforms, Inc. (f/k/a Facebook, Inc.)
• Inventors: Birnbaum, Kevin Michael
• Primary Examiner(s): Payne, David
• Assistant Examiner(s): KRETZER, CASEY L
• Application Number:
  US14/984,093
• Publication Number:
  US 20170195057A1
• Time in Patent Office: 944 Days
• CPC Class Codes: H04B 10/112 Line-of-sight transmission over an extended range
• CPC Class Codes: H04B 10/118 specially adapted for satellite communication
• CPC Class Codes: H04B 10/501 Structural aspects
• CPC Class Codes: H04B 10/516 Details of coding or modulation
• CPC Class Codes: H04B 10/541 Digital intensity or amplitude modulation

Abstract

Optical systems and methods for transmission of multiple beams and direct detection of those beams are described. One transmitter for use in a free space optical communication system includes a broad spectrum light source and an optical component including a plurality of sections positioned to receive an optical beam produced by the broad spectrum light source. The sections of the optical component are formed to introduce optical path differences into portions of the optical beam that impinge on the optical component such that each section introduces a delay into a corresponding portion of the optical beam. The introduced delays cause each portion of the optical beam to lack coherence with other portions of the optical beam. A direct detection receiver detects the intensity of the aggregate beams and produces a signal with improved signal-to-noise ratio. The disclosed technology can be used with modulated optical beams such as intensity modulated beams.

Claims

1. An optical transmitter for transmitting light in a free space optical communication system, comprising:

a broad spectrum light source; and

an optical component including a plurality of sections and positioned to receive an optical beam produced by the broad spectrum light source, wherein;

the plurality of sections are formed to introduce optical path differences into portions of the optical beam that impinge on the optical component such that each section introduces a delay into a corresponding portion of the optical beam that is different from a delay introduced into other portions of the optical beam by other sections of the optical component,

the delays introduced by the plurality of sections cause each portion of the optical beam that impinges on a corresponding section of the optical component to lack coherence with other portions of the optical beam that impinge on other sections of the optical component, and

the optical beam received by the optical component is a modulated optical beam having a modulation rate, r, the light source has a spectral bandwidth, Δ

f, that is larger than r, each of the plurality of the sections of the optical component is formed to introduce a particular optical path difference that is larger than c/Δ

f and is also smaller than c/r, where c is the speed of light in vacuum.

2. The optical transmitter of claim 1, wherein the optical beam received by the optical component is one of an intensity modulated optical beam.

3. The optical transmitter of claim 1, wherein the broad spectrum light source is one of:

a broad-band laser diode (LD), a super-luminescent diode (SLD), a light-emitting diode (LED), or an amplified spontaneous emission (ASE) source.

4. The optical transmitter of claim 1, wherein:

the optical component is a Fresnel lens with a plurality of circular zones, and

each of the plurality of sections corresponds to one circular zone of the Fresnel lens.

5. The optical transmitter of claim 1, wherein:

the optical component is a plate with a step-like spatial profile including a plurality of segments, and

each of the plurality of sections corresponds to one segment of the plurality of segments of the plate.

6. The optical transmitter of claim 1, wherein the broad spectrum light source and the optical component are located inside one or both of (a) an unmanned flying vehicle or (b) a ground-based station, and the optical component is positioned to provide a plurality of the portions of optical beam, after propagation through the multiple sections of the optical component, for transmission onto atmosphere.

7. The optical transmitter of claim 1, wherein the optical component is positioned at the exit aperture of the optical transmitter.

8. A method for producing multiple beams for transmission at a free space optical communication system, comprising:

receiving a modulated light beam at an optical component that comprises a plurality of sections; and

allowing the modulated light beam to propagate through the optical component,

wherein;

each section of the optical component that is illuminated by the light beam introduces a particular delay into a portion of the light beam that propagates through such section,

each particular delay introduced by a corresponding section of the optical component causes the portion of the light beam that exits the corresponding section to lack coherence with other portions of the light beam that exits other sections of the optical component, and

the optical beam received by the optical component has a modulation rate, r, and is produced by a light source having a spectral bandwidth, Δ

f, that is larger than r, each of the plurality of the sections of the optical component is formed to introduce a particular optical path difference that is larger than c/Δ

f and is also smaller than c/r, where c is the speed of light in vacuum.

9. The method of claim 8, wherein the modulated light beam is one of an intensity modulated light beam.

10. The method of claim 8, wherein the optical component is a Fresnel lens with a plurality of circular zones, and each of the plurality of sections corresponds to one circular zone of the Fresnel lens.

11. The method of claim 8, wherein the optical component is a plate with a step-like spatial profile including a plurality of segments, and each of the plurality of sections corresponds to one segment of the plurality of segments of the plate.

12. The method of claim 8, further comprising transmitting a plurality of the portions of optical beam, subsequent to propagation through the multiple sections of the optical component, through atmosphere.

13. A free space optical communication system, comprising:

a transmitter, comprising;

a broad spectrum light source; and

an optical component including a plurality of sections and positioned to receive an optical beam produced by the broad spectrum light source, wherein;

the plurality of sections are formed to introduce optical path differences into portions of the optical beam that impinge on the optical component such that each section introduces a delay into a corresponding portion of the optical beam that is different from a delay introduced into other portions of the optical beam by other sections of the optical component,

the delays introduced by the plurality of sections cause each portion of the optical beam that impinges on a corresponding section of the optical component to lack coherence with other portions of the optical beam that impinge on other sections of the optical component,

the optical beam received by the optical component is a modulated optical beam having a modulation rate, r, the light source has a spectral bandwidth, Δ

f, that is larger than r, each of the plurality of the sections of the optical component is formed to introduce a particular optical path difference that is larger than c/Δ

f and is also smaller than c/r, where c is the speed of light in vacuum; and

a receiver positioned to receive a plurality of the portions of the optical beam that exits the optical component and propagates through atmosphere, the receiver including a photodetector to sense an intensity of the received portions of the optical beam.

14. The free space optical communication system of claim 13, wherein the broad spectrum light source is one of:

a broad-band laser diode (LD), a super-luminescent diode (SLD), a light-emitting diode (LED), or an amplified spontaneous emission (ASE) source.