Ladar Transmitter with Induced Phase Drift for Improved Gaze on Scan Area Portions
Disclosed herein is a scanning ladar transmitter that employs an optical field splitter/inverter to improve the gaze characteristics of the ladar transmitter on desirable portions of a scan area. Also disclosed is the use of scan patterns such as Lissajous scan patterns for a scanning ladar transmitter where a phase drift is induced into the scanning to improve the gaze characteristics of the ladar transmitter on desirable portions of the scan area.
1 . A method comprising:
scanning a first mirror and a second mirror at different sinusoidal frequencies to define a Lissajous scan pattern within a scan area; and
inducing a periodic phase drift in the scanning of at least one of the first and second scannable mirrors.
2 . The method of claim 1 wherein the different sinusoidal frequencies comprise different resonant frequencies.
3 . The method of claim 2 wherein the first resonant frequency is a frequency of f, and wherein the second resonant frequency is a frequency of f+1.
4 . The method of claim 1 wherein the inducing step comprises:
varying a command signal to a driver for the at least one of the first and second scannable mirrors such that the scanning includes the periodic phase drift over time.
5 . The method of claim 1 wherein the inducing step comprises:
inducing the periodic phase drift in the scanning of at least one of the first and second scannable mirrors without altering the fundamental period.
6 . The method of claim 1 further comprising:
computing the induced periodic phase drift according to a total least squares method using time as an independent variable.
7 . The method of claim 1 wherein the first scannable mirror comprises a MEMS mirror.
8 . The method of claim 1 wherein the second scannable mirror comprises a MEMS mirror.
9 . The method of claim 1 wherein the inducing step comprises inducing the periodic phase drift in the scanning of only one of the first and second scannable mirrors.
10 . The method of claim 1 wherein the inducing step comprises inducing the periodic phase drift in the scanning of both the first and second scannable mirrors such that the periodic phase drift is spread across the first and second scannable mirrors.
11 . The method of claim 1 further comprising:
transmitting a plurality of light pulses to the scan area via the scanning first and second mirrors.
12 . The method of claim 11 wherein the light pulses include light at a first and second wavelength, the method further comprising:
selectably reflecting light within the light pulses at the second wavelength toward a position sensor via a dichroic mirror; and
the position sensor sensing the reflected light at the second wavelength, the sensed light being indicative of a position of the scanning first or second scannable mirrors.
13 . The method of claim 12 further comprising:
adjusting the scanning of the first or second scannable mirrors based on the sensed reflected light to compensate for unintended nonlinear time warping in the scanning.
14 . A beam scanner apparatus for a ladar transmitter, the apparatus comprising:
a first scannable mirror configured to scan to a plurality of scan positions;
a second scannable mirror positioned optically downstream from the first scannable mirror, the second scannable mirror configured to scan to a plurality of scan positions, wherein the scan positions of the first and second scannable mirrors define where the ladar transmitter is targeted within a scan area; and
a beam scanner controller configured to drive the first scannable mirror and the second scannable mirror to scan at sinusoidal frequencies such that the first scannable mirror is driven at a first sinusoidal frequency while the second scannable mirror is driven at a second sinusoidal frequency, the first and second sinusoidal frequencies cooperating together to so that the ladar transmitter targets within the scan area according to a Lissajous scan pattern; and
wherein the beam scanner controller comprises:
a first driver for controllably scanning the first scannable mirror;
a second driver for controllably scanning the second scannable mirror; and
a processor configured to compute a periodic phase drift and provide a control signal to at least one of the first and second drivers that induces the computed periodic phase drift in the scanning of at least one of the first and second scannable mirrors.
15 . The apparatus of claim 14 wherein the first and second sinusoidal frequencies comprise first and second resonant frequencies.
16 . The apparatus of claim 15 wherein the first resonant frequency is a frequency off, and wherein the second resonant frequency is a frequency of f+1.
17 . The apparatus of claim 14 wherein the processor is further configured to:
vary the command signal such that the scanning includes the periodic phase drift over time.
18 . The apparatus of claim 14 wherein the processor is further configured to generate the control signal such that the control signal induces the periodic phase drift without altering the fundamental period.
19 . The apparatus of claim 14 wherein the processor is further configured to compute the induced periodic phase drift according to a total least squares method using time as an independent variable.
20 . The apparatus of claim 14 further comprising:
a dichroic mirror positioned optically downstream from the second scannable mirror, wherein the dichroic mirror is configured to selectively reflect received light of a specified frequency; and
a position sensor positioned and configured to sense light reflected by the dichroic mirror, the sensed light being indicative of a position of the first or second scannable mirrors.
21 . The apparatus of claim 14 wherein the first scannable mirror comprises a MEMS mirror.
22 . The apparatus of claim 14 wherein the second scannable mirror comprises a MEMS mirror.
23 . The apparatus of claim 14 wherein the processor is further configured to provide the control signal that induces the computed periodic phase drift to only one of the first and second drivers.
24 . The apparatus of claim 14 wherein the processor is further configured to provide a control signal to the first driver and a second control signal to the second driver, wherein the first and second control signals induce the periodic phase drift in both the first and second scannable mirrors such that the periodic phase drift is spread across the first and second scannable mirrors.
25 . The apparatus of claim 14 further comprising:
the ladar transmitter, wherein the ladar transmitter comprises a light source, the ladar transmitter configured to transmit a plurality of light pulses from the light source via the beam scanner apparatus.
26 . The apparatus of claim 25 wherein the ladar transmitter further comprises a processor in cooperation with the light source and the beam scanner apparatus, the processor configured to intelligently select a subset of range points within a scan area for targeting via compressive sensing.
27 . A method comprising:
scanning a first mirror and a second mirror to define a spiral scan pattern within a scan area, wherein the scanning comprises scanning the first mirror at a dampened transient resonant frequency; and
inducing a periodic phase drift in the scanning of the first mirror.
28 . The method of claim 27 further comprising:
transmitting a plurality of light pulses to the scan area via the scanning first and second mirrors.