Ladar receiver range measurement using distinct optical path for reference light
Disclosed herein are various embodiment of an adaptive ladar receiver and associated method whereby the active pixels in a photodetector array used for reception of ladar pulse returns can be adaptively controlled based at least in part on where the ladar pulses were targeted. Additional embodiments disclose improved imaging optics for use by the receiver and further adaptive control techniques for selecting which pixels of the photodetector array are used for sensing incident light.
1. An apparatus comprising:
a light sensor configured to sense incident light, wherein the sensed light includes (1) light corresponding to a reflection of a ladar pulse and (2) light corresponding to an optical pulse that is distinct from the reflection of the ladar pulse; and
a circuit configured to (1) convert a signal corresponding to the sensed light over time into a plurality of digital samples, (2) apply a delay to the samples to generate a plurality of delayed samples, (3) correlate the samples against the delayed samples to find an alignment between the samples and the delayed samples that produces a maximal output, and (4) determine a timing relationship between the optical pulse and the ladar pulse based on the correlation.
2. The apparatus of claim 1 wherein the circuit is further configured to compute range information with respect to a range point targeted by the ladar pulse based on the determined timing relationship.
3. The apparatus of claim 1 wherein the light corresponding to ladar pulse reflection and the light corresponding to the optical pulse are separated by a time delay during their reception by the light sensor; and
wherein the circuit is further configured to perform the correlation by shifting, sample-by-sample, the samples against the delayed samples such that the maximal output corresponds to a number of sample shifts, wherein the number of sample shifts is indicative of the time delay.
4. The apparatus of claim 1 wherein the light sensor comprises a photodetector array, the photodetector array comprising a plurality of addressable pixels.
5. The method of claim 4 wherein the circuit is further configured to select which of the pixels are activated for sensing the light based on a location, in a scan area for a ladar transmitter that transmits the ladar pulse, of a range point targeted by the ladar pulse.
6. The apparatus of claim 1 wherein the circuit is further configured to (1) interpolate the delayed samples, and (2) perform the correlation by correlating the samples against the interpolated delayed samples to find the alignment that produces the maximal output.
7. The apparatus of claim 1 further comprising:
a ladar transmitter, wherein the ladar transmitter is configured to (1) transmit the ladar pulse toward a targeted range point, and (2) transmit the optical pulse toward the light sensor.
8. The apparatus of claim 7 wherein the ladar transmitter is further configured to target a plurality of range points with transmitted ladar pulses via compressive sensing.
9. The apparatus of claim 7 wherein the ladar transmitter is further configured to transmit the optical pulse to the light sensor via a first optical path that is distinct from a second optical path traveled by the ladar pulse to the range point and back to the light sensor as the ladar pulse reflection.
10. The apparatus of claim 7 wherein the ladar pulse and the optical pulse exhibit the same pulse shape.
11. The apparatus of 7 wherein the ladar transmitter is further configured to spawn the ladar pulse and the optical pulse at the same time.
12. The apparatus of claim 7 wherein the light sensor is part of a ladar receiver, and wherein the ladar transmitter and the ladar receiver are in a side-by-side arrangement.
13. The apparatus of claim 12 wherein the ladar receiver includes a pinhole through which the optical pulse is received from the ladar transmitter for reception by the light sensor.
14. The apparatus of claim 12 further comprising a fiber optic feed that connects the ladar transmitter with the ladar receiver for passing the optical pulse for reception by the light sensor.
15. The apparatus of claim 9 wherein the digital samples that represent the light corresponding to the transmitted optical pulse that travels to the light sensor via the first optical path do not include interference from the reflection of the ladar pulse.
16. The apparatus of claim 1 wherein the ladar pulse and the optical pulse each have a known pulse length.
17. The apparatus of claim 1 wherein the circuit comprises a field programmable gate array (FPGA).
18. The apparatus of claim 1 wherein the light sensor comprises a first light sensor for sensing the reflection of the ladar pulse and a second light sensor for sensing the optical pulse.