Optical detector
An optical detector includes a light emitter having a light emitting window extended in an extension direction to emit a projection beam from the light emitting window toward a measurement area and to detect a return beam from the measurement area. The optical detector includes a scanning mirror that scans by reflecting the projection beam. The scanning mirror swings within a finite angular range around a rotation axis that is along a direction corresponding to the extension direction.
1. An optical detector configured to project a projection beam toward a measurement area and detect a return beam from the measurement area, the optical detector comprising:
a light emitter having a light emitting window extended in an extension direction to emit the projection beam from the light emitting window;
a projecting optical system configured to collect and project the projection beam emitted from the light emitter; and
a scanning mirror configured to receive the projection beam from the projecting optical system and scan by reflecting the projection beam, wherein the scanning mirror is configured to move within a finite angular range around a rotation axis that is along a direction corresponding to the extension direction;
a receiving optical system configured to condense the return beam reflected by the scanning mirror in a detectable manner,
a housing having an optical window to reciprocate the projection beam and the return beam between an inside of the housing and the measurement area, the housing forming an exterior part of the optical detector, wherein
the projecting optical system and the receiving optical system are arranged side by side along the extension direction and parallel to the rotation axis, and
the projection beam and the return beam have an overlap in which footprints are overlapped with each other inside of the housing,
the optical detector further comprising
a projection holding member that holds the projecting optical system, wherein
the projection holding member has a concave portion recessed toward an optical axis of the projecting optical system to avoid interference with the projection beam reflected at an end of the angular range where a reflection angle at the scanning mirror is the minimum.
2. The optical detector according to claim 1 , further comprising
at least one processor to control a swing motion of the scanning mirror.
3. The optical detector according to claim 2 , further comprising
a single photon avalanche photodiode light receiving element that generates an electric pulse as a digital signal in response to a reception of a photon by the return beam, wherein the angular range is divided into a plurality of phase regions in the swing motion of the scanning mirror,
the at least one processor causes the projection beam to emit plural times while passing through at least one phase region of the plurality of phase regions, and
the at least one processor integrates the electric pulses generated by a detection of the projection beam and the return beam corresponding to the emission of the projection beam so as to calculate a flight time of light from the emission to the detection.
4. The optical detector according to claim 2 , wherein
the at least one processor is able to change the angular range.
5. The optical detector according to claim 2 , wherein
the at least one processor is able to change a speed of the swing motion.
6. The optical detector according to claim 2 , wherein
the at least one processor lengthens a retention time per unit angle in the swing motion as the angular range corresponds to a farther region where a distance to a measurement target in the measurement area is farther.
7. The optical detector according to claim 2 for a vehicle, wherein
the measurement area corresponding to the angular range is located front outside or rear outside of the vehicle, and
the at least one processor sets a retention time per unit angle in the swing motion longer in a central part of the angular range than in a side part of the angular range.
8. The optical detector according to claim 2 for a vehicle, wherein
the measurement area corresponding to the angular range is located lateral outside of the vehicle, and
the at least one processor sets a retention time per unit angle in the swing motion longer in a side part of the angular range than in a central part of the angular range.
9. The optical detector according to claim 1 , wherein
the scanning mirror has a reflecting surface that is common for reflecting the projection beam toward the measurement area and for reflecting the return beam from the measurement area.
10. The optical detector according to claim 1 , further comprising:
a detection unit configured to detect the return beam condensed by the receiving optical system, wherein
the light emitter and the detection unit are arranged side by side along the extension direction and parallel to the rotation axis.
11. The optical detector according to claim 10 , wherein
a projection optical axis of the projecting optical system from the light emitter to the scanning mirror is parallel to a receiving optical axis of the receiving optical system from the light emitter to the detection unit.
12. The optical detector according to claim 1 , wherein
the projecting optical system consists of an optical lens.
13. The optical detector according to claim 12 , wherein
the receiving optical system consists of an optical lens, and
a diameter of the optical lens of the receiving optical system is larger than a diameter of the optical lens of the projecting optical system.
14. The optical detector according to claim 1 , wherein
a focal length of the projecting optical system is set such that an image corresponding to the light emitting window is formed at a position outside of the housing.
15. The optical detector according to claim 1 , wherein
the scanning mirror is located at a distance from the light emitting window such that an aspect ratio of a footprint of the projection beam on a reflecting surface of the scanning mirror is compressed in the extension direction.
16. The optical detector according to claim 15 , wherein
the light emitter has a plurality of small windows and a plurality of laser oscillation elements arranged in the extension direction that is parallel to the rotation axis, and
each of the plurality of laser oscillation elements emits laser light as coherent light in a beam state through the respective window of the plurality of small windows to form the projection beam.
17. The optical detector according to claim 16 , wherein
the aspect ratio of the light emitting window is determined by the plurality of laser oscillation elements arranged in the extension direction.