Prismatic Light Guide Reduces Parallax in TOF Sensors
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Solution Overview
Problem
Time of flight (TOF) sensors face issues with parallax due to the separation distance between the transmit and receive optics, resulting in undetectable areas and poor mode mixing at the extreme edges of the field of view, particularly with multi-modal VCSEL output light pulses.
Innovation Solution
A prismatic light guide with an annular body region and a central opening, featuring a ring-shaped light output surface and internally reflecting surfaces, is used to collimate and direct light, addressing parallax concerns and improving light distribution across the field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transmit optic and receive optic are separated by a distance to enable both to function, then both optics can operate independently, but parallax error occurs and creates undetectable areas between the fields of view
Solution Approach 1:
The patent combines the transmit optic and receive optic into a single integrated optic structure. The transmit portion and receive portion are formed as one piece, eliminating the separation distance between them. This merging eliminates parallax error while maintaining the independent functionality of both transmit and receive operations, as the integrated optic can still direct light for transmission and collect light for reception simultaneously.
2Measurement precision
If a single integrated optic is used for both transmit and receive functions, then parallax error is eliminated, but the extreme edge areas of the field of view suffer from poor mode mixing of multi-modal VCSEL output light pulses
Solution Approach 1:
The patent applies different surface characteristics to different regions of the integrated optic. The extreme edge areas are provided with a textured surface that differs from other portions of the optic. This textured surface specifically addresses the mode mixing problem at the edges by scattering and redistributing the light modes, improving detection reliability in those specific regions without affecting the overall parallax elimination benefit.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the detection range and reduces parallax errors, allowing for more accurate distance measurement and improved light utilization across the entire field of view, particularly at the edges and beyond the nearest detectable distance.
Implementation Method 1
the annular body region including a first reflective surface defining the central opening and further including a ring-shaped light output surface surrounding the central opening and configured to output light in response to light that propagates within the prismatic light guide in response to the received beam of light and which reflects off the first reflective surface
Data Source
AI summary
A transmit integrated circuit includes a light source configured to generate a beam of light. A receive integrated circuit includes a first photosensor. A transmit optic is mounted over the transmit and receive integrated circuits. The transmit optic is formed by a prismatic light guide and is configured to receive the beam of light. An annular body region of the transmit optic surrounds a central opening which is aligned with the first photosensor. The annular body region includes a first reflective surface defining the central opening and further includes a ring-shaped light output surface surrounding the central opening. Light is output from the ring-shaped light output surface in response to light which propagates within the prismatic light guide in response to the received beam of light and which reflects off the first reflective surface.