System and method for glint reduction

Abstract

Systems and methods for reducing the deleterious effects of specular reflections (e.g., glint) on active illumination systems are disclosed. An example system includes an illuminator or light source configured to illuminate a scene with electromagnetic radiation having a defined polarization orientation. The system also includes a receiver for receiving portions of the electromagnetic radiation reflected or scatter from the scene. Included in the receiver is a polarizer having a polarization axis crossed with the polarization orientation of the emitted electromagnetic radiation. By crossing the polarizer with the polarization of the emitted electromagnetic radiation, the polarizer may filter out glint or specular reflections in the electromagnetic radiation returned from the scene.

1 . A method of reducing glint from a returned electromagnetic radiation signal, comprising:
 illuminating a scene with an electromagnetic radiation signal having a predetermined first polarization;   receiving, at a receiver, the returned electromagnetic radiation signal that is scatter or reflected from the scene as a result of illuminating the scene with the electromagnetic radiation signal; and   passing the returned electromagnetic radiation signal through a polarizer included in the receiver, the polarizer having a second polarization that differs from the predetermined first polarization of the electromagnetic radiation signal.   
     
     
         2 . The method of  claim 1 , wherein the polarizer is orthogonally crossed with the predetermined first polarization. 
     
     
         3 . The method of  claim 1 , wherein the polarizer is a plastic sheet polarizer. 
     
     
         4 . The method of  claim 1 , wherein the polarizer is a thin film polarizer. 
     
     
         5 . The method of  claim 1 , wherein the polarizer is a crystal polarizer. 
     
     
         6 . The method of  claim 1 , wherein the polarizer is selected from the group consisting of a linear polarizer, a circular polarizer, and elliptical polarizer. 
     
     
         7 . The method of  claim 1 , wherein the electromagnetic radiation signal is a pulse having a duration of 100 nS or less. 
     
     
         8 . The method of  claim 1 , further comprising:
 modulating the returned portion of the electromagnetic radiation signal as a function of time;   converting into one or more electrical signals the modulated returned portion of the electromagnetic radiation signal that has passed through the polarizer; and   determining 3D information regarding the scene based on the electrical signals.   
     
     
         9 . A system, comprising:
 an illuminator configured to illuminate a scene with electromagnetic radiation having a predetermined first polarization; and   a polarizer having a second polarization that differs from the predetermined first polarization of the electromagnetic radiation, the polarizer configured to receive a portion of the electromagnetic radiation returned from the scene.   
     
     
         10 . The system of  claim 9 , wherein the polarizer is orthogonally crossed with the predetermined first polarization. 
     
     
         11 . The system of  claim 9 , wherein the illuminator includes a light source for emitting polarized light. 
     
     
         12 . The system of  claim 9 , the illuminator includes a polarizer configured so that it is crossed with the second polarization. 
     
     
         13 . The system of  claim 9 , wherein the electromagnetic radiation is a pulse having a duration of 100 nS or less. 
     
     
         14 . The system of  claim 9 , further comprising:
 a modulator configured to modulate the returned portion of electromagnetic radiation as a function of time;   an array of optical elements receiving the modulated returned portion of the electromagnetic radiation, wherein at least one of the optical elements has a predetermined first optical transmission state different from a second predetermined optical transmission state of another of the optical elements; and   a sensor having an array of pixels corresponding to the array of optical elements, located to receive output from the array of optical elements.   
     
     
         15 . The system of  claim 14 , wherein the array of optical elements is integrally formed on the array of pixels. 
     
     
         16 . A 3D imaging system, comprising:
 an illuminator configured to illuminate a scene with electromagnetic radiation having a predetermined first polarization;   a sensor subsystem including:
 a polarizer having a second polarization that differs from the predetermined first polarization of the electromagnetic radiation, the polarizer configured to receive a portion of the electromagnetic radiation returned from the scene; 
 a modulator configured to modulate the returned portion of the electromagnetic radiation as a function of time; and 
 a sensor configured to receive the returned portion of the electromagnetic radiation that has passed through the polarizer and modulator; and 
   a processor, operatively coupled to the modulator and sensor, configured to compute 3D information regarding the scene based on one or more signals from the sensor.   
     
     
         17 . The system of  claim 16 , wherein the polarizer is orthogonally crossed with the predetermined first polarization. 
     
     
         18 . The system of  claim 16 , wherein the illuminator is configured to emit one or more electromagnetic radiation pulses each having a duration of 100 nS or less. 
     
     
         19 . The system of  claim 16 , wherein the polarizer has an extinction ratio of about 10 4 :1. 
     
     
         20 . The system of  claim 16 , wherein the polarizer is a thin film polarizing beamsplitter prism.