System and method for determining range in 3D imaging systems
A system and method of imaging an object. An array of detectors is mounted in an image plane. Each detector in the array of detectors is connected to a timing circuit having an interpolator, wherein the interpolator includes a first circuit which charges a first capacitor at a different rate than it discharges. An optical pulse is transmitted toward an object so that a portion of the optical pulse is reflected from the object as a reflected pulse and a first value representative of when the optical pulse was transmitted toward the object is recorded. The reflected pulse is detected at one or more detectors and a pulse characteristic of the pulse and a second value representative of when the reflected pulse arrived at the detector are recorded. Range to the object is then calculated as a function of the first and second values and the reflected pulse characteristic.
1. A method of imaging an object, comprising:
mounting an array of detectors in an image plane;
connecting each detector to a timing circuit;
generating a correction table, wherein generating a correction table includes connecting a resonator/attenuator to the array of detectors, directing a calibrating optical pulse into the resonator/attenuator such that the resonator/attenuator transmits two or more optical pulses to the array of detectors, and correcting for nonlinearities at each detector;
transmitting a transmit optical pulse toward an object so that a portion of the transmit optical pulse is reflected from the object as a reflected pulse, wherein transmitting the transmit optical pulse includes recording a first value, wherein the first value is representative of when the transmit optical pulse was transmitted toward the object;
detecting arrival of the reflected pulse at one or more detectors within the array of detectors, wherein detecting arrival of the reflected pulse includes:
integrating the reflected pulse over a predetermined interval of time to determine a reflected pulse characteristic; and
recording a second value, wherein the second value is representative of when the reflected pulse arrived at the detector; and
measuring range to the object as a function of the first and second values, the reflected pulse characteristic and the correction table.
2. The method according to claim 1 , wherein recording a second value includes storing a value representative of a capacitor voltage.
3. The method according to claim 1 , wherein transmitting an optical pulse includes directing a portion of the optical pulse to a detector and wherein recording a first value includes storing a value representative of a capacitor voltage.
4. The method according to claim 1 , wherein each timing circuit includes an interpolator, wherein each interpolator includes an interpolator circuit which charges a capacitor at a different rate than it discharges the capacitor, and wherein recording a second value includes triggering the interpolator circuit as a function of when the reflected pulse arrived at the detector.
5. The method according to claim 4 , wherein triggering the interpolator circuit includes discharging the capacitor at a first rate until a subsequent transition of the master clock.
6. The method according to claim 4 , wherein triggering the interpolator includes:
discharging the capacitor at a first rate until a subsequent transition of the master clock; and
capturing voltage across the capacitor.
7. The method according to claim 1 , wherein the resonator attenuator includes a variable attenuator, a fiber coupler, a fiber resonator and a fiber collimator and wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the variable attenuator and the fiber coupler.
8. The method according to claim 7 , wherein the variable attenuator can be set to prevent optical pulses from reaching the detector array through the resonator/attenuator.
9. The method according to claim 1 , wherein the resonator attenuator includes a variable attenuator and a fiber bundle and wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the variable attenuator and the fiber bundle.
10. The method according to claim 1 , wherein the resonator attenuator includes one or more optical fibers, wherein each end of each optical fiber is coated so that they are partially reflective and wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the one or more optical fibers.
11. A method of imaging an object, comprising:
mounting one or more detectors in an image plane;
connecting each detector to a timing circuit;
connecting a resonator/attenuator to the one or more detectors, wherein the resonator attenuator includes a variable attenuator, a fiber coupler, a fiber resonator and a fiber collimator;
generating a correction table, wherein generating a correction table includes directing a calibrating optical pulse into the resonator/attenuator such that two or more optical pulses are projected on the one or more detectors, and correcting for nonlinearities at each detector, wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the variable attenuator and the fiber coupler;
transmitting a transmit optical pulse toward an object so that a portion of the transmit optical pulse is reflected from the object as a reflected pulse, wherein transmitting the transmit optical pulse includes recording a first value, wherein the first value is representative of when the transmit optical pulse was transmitted toward the object;
detecting arrival of the reflected pulse at one or more detectors within the array of detectors, wherein detecting arrival of the reflected pulse includes:
integrating the reflected pulse over a predetermined interval of time to determine a reflected pulse characteristic; and
recording a second value, wherein the second value is representative of when the reflected pulse arrived at the detector; and
measuring range to the object as a function of the first and second values, the reflected pulse characteristic and the correction table.
12. The method according to claim 11 , wherein the variable attenuator can be set to prevent optical pulses from reaching the detector array through the resonator/attenuator.
13. A method of imaging an object, comprising:
mounting one or more detectors in an image plane;
connecting each detector to a timing circuit;
connecting a resonator/attenuator to the one or more detectors, wherein the resonator/attenuator includes a variable attenuator and a fiber bundle;
generating a correction table, wherein generating a correction table includes directing a calibrating optical pulse into the resonator/attenuator such that two or more optical pulses are projected on the one or more detectors, and correcting for nonlinearities at each detector, wherein directing a calibrating optical pulse into the resonator/attenuator includes passing the calibrating optical pulse through the variable attenuator and the fiber bundle;
transmitting a transmit optical pulse toward an object so that a portion of the transmit optical pulse is reflected from the object as a reflected pulse, wherein transmitting the transmit optical pulse includes recording a first value, wherein the first value is representative of when the transmit optical pulse was transmitted toward the object;
detecting arrival of the reflected pulse at one or more detectors within the array of detectors, wherein detecting arrival of the reflected pulse includes:
integrating the reflected pulse over a predetermined interval of time to determine a reflected pulse characteristic; and
recording a second value, wherein the second value is representative of when the reflected pulse arrived at the detector; and
measuring range to the object as a function of the first and second values, the reflected pulse characteristic and the correction table.
14. The method according to claim 13 , wherein the variable attenuator can be set to prevent optical pulses from reaching the detector array through the resonator/attenuator.