LIDAR Systems with Multi-faceted Mirrors

Abstract

Example embodiments relate to LIDAR systems with multi-faceted mirrors. An example embodiment includes a LIDAR system. The system includes a multi-faceted mirror that includes a plurality of reflective facets, which rotates about a first rotational axis. The system also includes a light emitter configured to emit a light signal toward one or more regions of a scene. Further, the system includes a light detector configured to detect a reflected light signal. In addition, the system includes an optical window positioned between the multi-faceted mirror and the one or more regions of the scene such that light reflected from one or more of the reflective facets is transmitted through the optical window. The optical window is positioned such that the optical window is non-perpendicular to the direction toward which the light emitted along the optical axis is directed for all angles of the multi-faceted mirror.

What is claimed is: 
     
         1 . A light detection and ranging (LIDAR) system comprising:
 a multi-faceted mirror comprising a plurality of reflective facets, wherein the multi-faceted mirror is configured to rotate about a first rotational axis;   a light emitter configured to emit a light signal along an optical axis, wherein light emitted along the optical axis is reflected from one or more of the reflective facets and is directed toward one or more regions of a scene;   a light detector configured to detect a reflected light signal that is reflected by the one or more regions of the scene, wherein a direction toward which the light emitted along the optical axis is directed is based on a first angle of the multi-faceted mirror about the first rotational axis; and   an optical window positioned between the multi-faceted mirror and the one or more regions of the scene such that light reflected from one or more of the reflective facets and directed toward the one or more regions of the scene is transmitted through the optical window, wherein the optical window has a rotational orientation about an axis that is parallel to the optical axis such that, for all values of the first angle of the multi-faceted mirror about the first rotational axis as the multi-faceted mirror rotates about the first rotational axis, the optical window is non-perpendicular to the direction toward which the light emitted along the optical axis is directed.   
     
     
         2 . The LIDAR system of  claim 1 , further comprising a base, wherein the multi-faceted mirror, the light emitter, and the light detector are coupled to the base, wherein the base is configured to rotate about a second rotational axis, and wherein the direction toward which the light emitted along the optical axis is directed is based on a second angle of the base about the second rotational axis. 
     
     
         3 . The LIDAR system of  claim 1 , further comprising an additional optical window positioned on an opposite side of the multi-faceted mirror from the optical window, wherein the additional optical window is positioned between the multi-faceted mirror and at least one of the one or more regions of the scene such that light reflected from one or more of the reflective facets and directed toward the at least one of the one or more regions of the scene is transmitted through the additional optical window, and wherein the additional optical window has a rotational orientation about an axis that is parallel to the optical axis such that, for all values of the first angle of the multi-faceted mirror about the first rotational axis as the multi-faceted mirror rotates about the first rotational axis, the additional optical window is non-perpendicular to the direction toward which the light emitted along the optical axis is directed. 
     
     
         4 . The LIDAR system of  claim 3 , wherein the optical window and the additional optical window are non-parallel to one another. 
     
     
         5 . The LIDAR system of  claim 3 , wherein the optical window and the additional optical window are substantially parallel to one another. 
     
     
         6 . The LIDAR system of  claim 3 , wherein the optical window and the additional optical window are angled oppositely of one another relative to the multi-faceted mirror. 
     
     
         7 . The LIDAR system of  claim 3 , wherein the optical window and the additional optical window have non-symmetrical angular orientations relative to the multi-faceted mirror. 
     
     
         8 . The LIDAR system of  claim 1 , wherein the optical window is movable, reorientable, or rotatable. 
     
     
         9 . The LIDAR system of  claim 8 , further comprising a stage and a controller, wherein the controller is configured to control the stage to move, reorient, or rotate the optical window. 
     
     
         10 . The LIDAR system of  claim 1 , wherein the optical window is oriented such that, for all values of the first angle of the multi-faceted mirror about the first rotational axis as the multi-faceted mirror rotates about the first rotational axis, an angle of the optical window relative to the direction toward which the light emitted along the optical axis is directed is less than the critical angle of a material used to fabricate the optical window. 
     
     
         11 . The LIDAR system of  claim 1 , wherein the optical window is oriented such that, for all values of the first angle of the multi-faceted mirror about the first rotational axis as the multi-faceted mirror rotates about the first rotational axis, an angle of the optical window relative to the direction toward which the light emitted along the optical axis is directed is equal to the Brewster's angle of an interface between the optical window and an external environment. 
     
     
         12 . The LIDAR system of  claim 1 , wherein the rotational orientation of the optical window about the axis that is parallel to the optical axis results corresponds to an angle of between 5° and 15° relative to a plane of rotation of the multi-faceted mirror. 
     
     
         13 . The LIDAR system of  claim 12 , wherein the angle is between 9.5° and 10.5°. 
     
     
         14 . The LIDAR system of  claim 1 , further comprising a filter covering at least a portion of an exterior side of the optical window, wherein the filter reduces transmission of at least some wavelengths that are not produced by the light emitter. 
     
     
         15 . The LIDAR system of  claim 14 , wherein the filter comprises a neutral-density filter. 
     
     
         16 . The LIDAR system of  claim 14 , wherein the filter comprises a dichroic filter. 
     
     
         17 . The LIDAR system of  claim 14 , wherein the filter reduces transmission of wavelengths in a visible spectrum. 
     
     
         18 . The LIDAR system of  claim 17 , wherein the filter is characterized by an average reflectivity value throughout the visible spectrum. 
     
     
         19 . The LIDAR system of  claim 18 , wherein the average reflectivity value throughout the visible spectrum is at least 25%. 
     
     
         20 . The LIDAR system of  claim 17 , wherein a reflectivity of the filter across the visible spectrum is substantially constant such that the filter acts as an un-tinted mirror for light within the visible spectrum.