Coherent LADAR using intra-pixel quadrature detection
A frequency modulated (coherent) laser detection and ranging system includes a read-out integrated circuit formed with a two-dimensional array of detector elements each including a photosensitive region receiving both return light reflected from a target and light from a local oscillator, and local processing circuitry sampling the output of the photosensitive region four times during each sample period clock cycle to obtain quadrature components. A data bus coupled to one or more outputs of each of the detector elements receives the quadrature components from each of the detector elements for each sample period and serializes the received quadrature components. A processor coupled to the data bus receives the serialized quadrature components and determines an amplitude and a phase for at least one interfering frequency corresponding to interference between the return light and the local oscillator light using the quadrature components.
1. A laser detection and ranging (LADAR) system, comprising:
an array of detector elements, each detector element within the array including a photosensitive material configured to receive return light reflected from a target and oscillating local light and to generate a signal to be sampled during each sample period clock cycle;
a data bus coupled to the detector elements, the data bus configured to receive multiple samples of each signal generated by the detector elements for each sample period clock cycle; and
a processor coupled to the data bus and configured to receive, from the data bus, the samples from the detector elements and to determine an amplitude and a phase for an interfering frequency corresponding to interference between the return light and the oscillating local light using the samples.
2. The system according to claim 1 , wherein the array of detector elements is a two-dimensional array and comprises a large format array.
3. The system according to claim 1 , wherein:
the samples are quadrature components for each sample period clock cycle; and
the processor is configured to employ the quadrature components to determine an amplitude and a phase for each of a plurality of interfering frequencies corresponding to interference between the return light and the oscillating local light.
4. The system according to claim 1 , wherein each detector element within the array includes sample component signal line connections to the data bus.
5. The system according to claim 1 , wherein each detector element within the array is configured to receive a clock signal from the data bus.
6. The system according to claim 1 , wherein the data bus is configured to serialize the samples from the detector elements for each sample period clock cycle for transmission to the processor.
7. The system according to claim 1 , wherein the array of detector elements and the data bus are contained within a read-out integrated circuit (ROTC).
8. The system according to claim 1 , further comprising:
a laser source configured to emit both light illuminating the target and the oscillating local light; and
an imaging telescope configured to be positioned between the target and the array of detector elements and configured to focus the return light reflected from the target onto the array of detector elements.
9. The system according to claim 8 , wherein the laser source comprises:
a master oscillator;
a first frequency modulator configured to modulate a frequency of a signal output by the master oscillator to generate a first signal, the emitted light based on the first signal; and
a second frequency modulator configured to modulate the frequency of the signal output by the master oscillator to generate a second signal, the oscillating local light based on the second signal.
10. A laser detection and ranging (LADAR) system, comprising:
an array of detector elements, each detector element within the array including a photosensitive material configured to receive return light reflected from a target and oscillating local light and to generate a signal to be sampled during each sample period clock cycle;
a data bus coupled to the detector elements and configured to receive samples from the detector elements for each sample period clock cycle;
a processor coupled to the data bus and configured to receive, from the data bus, the samples from the detector elements and to determine an amplitude and a phase for an interfering frequency corresponding to interference between the return light and the oscillating local light using the samples; and
a laser source configured to emit both light illuminating the target and the oscillating local light, wherein the laser source comprises:
a master oscillator;
a first frequency modulator configured to modulate a frequency of a signal output by the master oscillator to generate a first signal;
a second frequency modulator configured to modulate the frequency of the signal output by the master oscillator to generate a second signal;
an amplifier configured to amplify the first signal and generate the light illuminating the target; and
a local oscillator configured to respond to the second signal and generate the oscillating local light.
11. A laser detection and ranging (LADAR) method, comprising:
receiving, at an array of detector elements, return light reflected from a target, each detector element within the array including a photosensitive material configured to receive the return light reflected from the target and oscillating local light and to generate a signal to be sampled during each sample period clock cycle;
receiving, on a data bus coupled to the detector elements, multiple samples of each signal generated by the detector elements for each sample period clock cycle;
transmitting, to a processor coupled to the data bus, the samples from the detector elements for each sample period clock cycle; and
determining, with the processor, an amplitude and a phase for an interfering frequency corresponding to interference between the return light and the oscillating local light using the samples.
12. The method according to claim 11 , wherein the array of detector elements is a two-dimensional array and comprises a large format array.
13. The method according to claim 11 , wherein the samples comprise quadrature components for each sample period clock cycle, the method further comprising:
employing the quadrature components to determine an amplitude and a phase for each of a plurality of interfering frequencies corresponding to interference between the return light and the oscillating local light.
14. The method according to claim 11 , wherein each detector element within the array includes sample component signal line connections to the data bus.
15. The method according to claim 11 , wherein each detector element within the array is configured to receive a clock signal from the data bus.
16. The method according to claim 11 , further comprising:
serializing, in the data bus, the samples from each of the detector elements for each sample period clock cycle for transmission to the processor.
17. The method according to claim 11 , wherein the array of detector elements and the data bus are contained within a read-out integrated circuit (ROTC).
18. The method according to claim 11 , further comprising:
emitting both light illuminating the target and the oscillating local light from a laser source; and
positioning an imaging telescope between the target and the array of detector elements to focus the return light reflected from the target onto the array of detector elements.
19. The method according to claim 18 , further comprising:
employing a first frequency modulator to modulate a frequency of a signal output by a master oscillator and generate a first signal, the emitted light based on the first signal; and
employing a second frequency modulator to modulate the frequency of the signal output by the master oscillator and generate a second signal, the oscillating local light based on the second signal.
20. A laser detection and ranging (LADAR) method, comprising:
emitting both light illuminating a target and oscillating local light from a laser source, which comprises:
employing a first frequency modulator to modulate a frequency of a signal output by a master oscillator and generate a first signal;
employing a second frequency modulator to modulate the frequency of the signal output by the master oscillator and generate a second signal;
amplifying the first signal to generate the light illuminating the target; and
receiving the second signal at a local oscillator that generates the oscillating local light;
receiving, at an array of detector elements, return light reflected from the target, each detector element within the array including a photosensitive material configured to receive the return light reflected from the target and the oscillating local light and to generate a signal to be sampled during each sample period clock cycle;
receiving, on a data bus coupled to the detector elements, samples from the detector elements for each sample period clock cycle;
transmitting, to a processor coupled to the data bus, the samples from the detector elements for each sample period clock cycle; and
determining, with the processor, an amplitude and a phase for an interfering frequency corresponding to interference between the return light and the oscillating local light using the samples.