Systems and methods for weighted combination of quadrant photodetector output for beam tracking

1. A system comprising:

an optical element that receives an optical beam;

a wide field-of-view (FOV) quadrant photodetector that receives, from the optical element, first light originating from the optical beam;

a narrow FOV quadrant photodetector that receives, from the optical element, second light originating from the optical beam; and

a controller that controls an orientation of the optical element in a manner that tracks the optical beam during at least a period of time based on a weighted combination of:

output of the wide FOV quadrant photodetector in response to the first light; and

output of the narrow FOV quadrant photodetector in response to the second light.

2. The system of claim 1 , wherein:

the weighted combination comprises a constant ratio of the output of the wide FOV quadrant photodetector to the output of the narrow FOV quadrant photodetector over the period of time.

3. The system of claim 1 , wherein:

the weighted combination comprises a normalized combination ranging, over the period of time,

from 100 percent of the output of the wide FOV quadrant photodetector and 0 percent of the output of the narrow FOV quadrant photodetector,

to 0 percent of the output of the wide FOV quadrant photodetector and 100 percent of the output of the narrow FOV quadrant photodetector.

4. The system of claim 3 , wherein the weighted combination changes linearly over the period of time.

5. The system of claim 1 , wherein:

the controller controls the orientation of the optical element based on the weighted combination when the output of the narrow FOV quadrant photodetector indicates a centroid of the second light is located outside a linear response range of the narrow FOV quadrant photodetector.

6. The system of claim 1 , wherein:

the controller controls the orientation of the optical element based on the weighted combination when:

the output of the narrow FOV quadrant photodetector indicates a centroid of the second light is located outside a linear response range of the narrow FOV quadrant photodetector; and

a sign of the output of the narrow FOV quadrant photodetector and a sign of the output of the wide FOV quadrant photodetector are the same.

7. The system of claim 1 , wherein:

the controller controls the orientation of the optical element without the output of the wide FOV quadrant photodetector when the output of the narrow FOV quadrant photodetector indicates a centroid of the second light is located within a linear response range of the narrow FOV quadrant photodetector.

8. The system of claim 7 , wherein:

the linear response range of the wide FOV quadrant photodetector is less than 20 micro radians.

9. The system of claim 1 , wherein:

the controller controls the orientation of the optical element without the output of the wide FOV quadrant photodetector when:

the output of the narrow FOV quadrant photodetector indicates detection of a centroid of the second light; and

a sign of the output of the narrow FOV quadrant photodetector and a sign of the output of the wide FOV quadrant photodetector are different.

10. The system of claim 1 , wherein:

the controller controls the orientation of the optical element without the output of the narrow FOV quadrant photodetector when the output of the narrow FOV quadrant photodetector indicates no detection of a centroid of the second light.

11. The system of claim 1 , wherein:

the system further comprises a detection circuit that detects a modulation of the optical beam; and

the controller controls the orientation of the optical element without the output of the narrow FOV quadrant photodetector:

while the output of the narrow FOV quadrant photodetector indicates no detection of a centroid of the second light; or

during a synchronization time period in which the detection circuit attempts to synchronize with the modulation of the optical beam.

12. The system of claim 11 , wherein:

the detection circuit comprises a phased-lock loop.

13. The system of claim 11 , wherein:

the system further comprises a telescope that:

receives the optical beam, wherein the optical beam comprises:

an optical data signal; and

a beacon signal for the optical data signal; and

forwards the optical beam to the optical element; and

the controller:

directs the telescope toward an area of interest in free space;

alters the orientation of the optical element to scan the area of interest in free space; and

stabilizes the orientation of the optical element in response to the wide FOV quadrant photodetector receiving the optical beam, as indicated by the wide FOV quadrant photodetector receiving the first light originating from the optical beam, wherein the first light and the second light are derived from the beacon signal.

14. The system of claim 13 , further comprising:

an optical filter that filters the beacon signal from the optical beam; and

a beam splitter that derives the first light and the second light from the beacon signal.

15. The system of claim 1 , wherein:

the optical element comprises a fine steering mirror (FSM).

16. The system of claim 1 , wherein the controller:

detects the output of the narrow FOV quadrant photodetector indicating a centroid of the second light is located at an origin of the narrow FOV quadrant photodetector;

stores the output of the wide FOV quadrant photodetector in response to the output of the narrow FOV quadrant photodetector indicating the centroid of the second light is located at the origin of the narrow FOV quadrant photodetector; and

adjusts future outputs of the wide FOV quadrant photodetector using the stored output.

17. A method comprising:

receiving, by an optical element, an optical beam;

receiving, from the optical element by a wide FOV quadrant photodetector, first light originating from the optical beam;

receiving, from the optical element by a narrow FOV quadrant photodetector, second light originating from the optical beam; and

controlling, by a controller, an orientation of the optical element in a manner that tracks the optical beam during at least a period of time based on a weighted combination of:

output of the wide FOV quadrant photodetector in response to the first light; and

output of the narrow FOV quadrant photodetector in response to the second light.

18. The method of claim 17 , wherein:

controlling the orientation of the optical element based on the weighted combination occurs when:

the output of the narrow FOV quadrant photodetector indicates a centroid of the second light is located outside a linear response range of the narrow FOV quadrant photodetector; and

a sign of the output of the narrow FOV quadrant photodetector and a sign of the output of the wide FOV quadrant photodetector are the same.

19. The method of claim 18 , further comprising:

controlling the orientation of the optical element without the output of the wide FOV quadrant photodetector when the output of the narrow FOV quadrant photodetector indicates a centroid of the second light is located within a linear response range of the narrow FOV quadrant photodetector.

20. A non-transitory computer-readable medium comprising:

computer-readable instructions that, when executed by at least one processor of a computing device, cause the computing device to:

receive an output from a wide FOV quadrant photodetector generated in response to receiving first light originating from an optical beam provided by an optical element;

receive an output from a narrow FOV quadrant photodetector generated in response to receiving second light originating from the optical beam; and

control an orientation of the optical element in a manner that tracks the optical beam during at least a period of time based on a weighted combination of:

the output received from the wide FOV quadrant photodetector; and

the output received from the narrow FOV quadrant photodetector.