Single detector receiver for multi-beam LADAR systems

1. An apparatus, comprising:

an optical pickup capable of picking up a split-beam LADAR signal comprising a plurality of optical signals;

a timing synchronization reference;

a time domain multiplexer including:

a delay for each of the optical signals, each delay being staggered and being measured relative to the timing synchronization reference, the delay including:

varying lengths of optical fiber, each optical signal propagating through a unique length of fiber;

a plurality of optical circulators, one for each of the optical signals, positioned at one end of the respective length of optical fiber; and

a plurality of reflectors, one for each of the optical signals, positioned at the opposite end of the respective length of optical fiber; and

a combiner capable of combining the delayed optical signals into the multiplexed signal; and

an optical detector capable of detecting the multiplexed optical signal.

2. The apparatus of claim 1 , wherein the optical pickup comprises a plurality of fibers.

3. The apparatus of claim 1 , wherein the timing synchronization reference comprises a backscatter reference or a laser trigger signal.

4. The apparatus of claim 1 , wherein the combiner comprises one of a tree coupler or a cascade of tap couplers.

5. The apparatus of claim 1 , wherein the combiner comprises:

the active surface of the optical detector; and

a lens focusing the picked-up, delayed optical signals onto the active surface.

6. The apparatus of claim 1 , further comprising a PIN detector tapping the multiplexed optical signal.

7. The apparatus of claim 1 , further comprising:

a second optical detector; and

a switch or a polarization splitter through which the second optical detector receives the multiplexed optical signal.

8. The apparatus of claim 1 , further comprising a variable optical attenuator.

9. The apparatus of claim 8 , wherein the variable optical attenuator comprises a single channel variable optical attenuator capable of attenuating the multiplexed optical signal.

10. The apparatus of claim 8 , wherein the variable optical attenuator comprises a multi-channel variable optical attenuator capable of individually attenuating the plurality of optical signals.

11. The apparatus of claim 1 , wherein the optical detector comprises an avalanche photodiode.

12. An apparatus, comprising:

means for picking up a plurality of optical signals;

means for time domain multiplexing the optical signals, including;

means for synchronizing the multiplexing;

means for delaying each of the optical signals by a staggered amount measured relative to the synchronizing means; and

means for combining the delayed optical signals into the multiplexed signal, including:

varying lengths of optical fiber, each optical signal propagating through a unique length of fiber;

a plurality of optical circulators, one for each of the optical signals, positioned at one end of the respective length of optical fiber; and

a plurality of reflectors, one for each of the optical signals, positioned at the opposite end of the respective length of optical fiber; and

means for detecting the multiplexed optical signal.

13. The apparatus of claim 12 , wherein the combining means comprises one of a tree coupler or a cascade of tap couplers.

14. The apparatus of claim 12 , wherein the combining means comprises:

an active surface of the detecting means; and

a lens focusing the picked-up, delayed optical signals onto the active surface.

15. The apparatus of claim 12 , further comprising a PIN detector tapping the multiplexed optical signal.

16. The apparatus of claim 12 , further comprising:

second means for detecting the multiplexed optical signal; and

means for directing the multiplexed optical signal to the second detecting means.

17. The apparatus of claim 16 , wherein the directing means comprises a switch or a polarization splitter.

18. The apparatus of claim 12 , further comprising a variable optical attenuator.

19. A method, comprising:

receiving a plurality of LADAR signals;

time domain multiplexing the received LADAR signals into a multiplexed LADAR signal, including:

inserting a unique, staggered delay into each of the LADAR signals, including:

inserting the delays includes propagating the received LADAR signals through varied lengths of optical fibers; and

circulating the LADAR fibers through the optical fibers to a respective reflector and back through a lens; and

combining the delayed LADAR signals;

detecting the multiplexed LADAR signal; and

demultiplexing the detected LADAR signal.

20. The method of claim 19 , wherein combining the delayed LADAR signals includes combining them through one of a tree coupler or a cascade of tap couplers.

21. The method of claim 19 , wherein the wherein combining the delayed LADAR signals includes focusing the delayed LADAR signals onto an active surface of an optical detector.

22. The method of claim 19 , further comprising detecting the combined LADAR signals.

23. The method of claim 19 , further comprising:

splitting multiplexed LADAR signal; and

detecting the split multiplexed LADAR signal.

24. The method of claim 9 , further comprising switching the multiplexed LADAR signal between a first and a second detector.

25. The method of claim 19 , further comprising attenuating the multiplexed LADAR signal.

26. A LADAR apparatus, comprising:

means for receiving a plurality of LADAR signals;

means for time domain multiplexing the received LADAR signals into a multiplexed LADAR signal, including:

means for inserting a unique, staggered delay into each of the LADAR signals, including:

means for propagating the received LADAR signals over varied distances; and

means for circulating the LADAR signals to a respective reflector and back through a lens; and

means for combining the delayed LADAR signals;

means for detecting the multiplexed LADAR signal; and

means for demultiplexing the detected LADAR signal.

27. The LADAR apparatus of claim 26 , wherein the combining means includes one of a tree coupler or a cascade of tap couplers.

28. The LADAR apparatus of claim 26 , wherein the wherein the combining means includes means for focusing the delayed LADAR signals onto the active surface of the optical detector.

29. The LADAR apparatus of claim 26 , further comprising means for detecting the combined LADAR signals.

30. The LADAR apparatus of claim 26 , further comprising:

means for splitting multiplexed LADAR signal; and

means for detecting the split multiplexed LADAR signal.

31. The LADAR apparatus of claim 26 , further comprising means for switching the multiplexed LADAR signal between a first and a second detector.

32. The LADAR apparatus of claim 26 , further comprising means for attenuating the multiplexed LADAR signal.

33. The LADAR apparatus of claim 26 , further comprising:

a second optical detector; and

a switch through which the second optical detector receives the multiplexed optical signal; and

a polarization splitter through which the second optical detector receives the multiplexed optical signal.