Fourier Objective Spherical Diffuser Optical Measurement
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Solution Overview
Problem
Existing methods for measuring the angular emission pattern of light sources, such as laser or light-emitting diodes, face limitations in achieving high angular resolution and large angular aperture due to geometric constraints, stray light issues, and alignment dependencies, making them impractical for large systems and sources of varying sizes.
Innovation Solution
A radiometric measuring device comprising a Fourier objective, a transmission diffusing surface, and a video photometer, where the Fourier objective collects and focuses light onto the diffusing surface, and an absorbing layer reduces stray light, allowing for high-resolution measurements without mechanical movement and alignment constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the distance D between the source and the diffusing screen is increased to improve angular resolution, then the angular resolution improves, but the minimum diameter of the diffusing screen increases rapidly making the system size prohibitive
Solution Approach 1:
The patent transitions from a 2D diffusing screen measurement to a 3D spherical diffuser geometry. By positioning the source at the center of a spherical diffuser, the system achieves large angular aperture (close to 180 degrees) without requiring proportionally large screen dimensions, as the spherical geometry naturally provides omnidirectional light scattering in three-dimensional space.
Solution Approach 2:
The patent changes the geometric parameter from a planar screen distance D to a spherical radius R, and introduces a new parameter relationship where the angular resolution is determined by the detector pixel density and spherical geometry rather than linear distance. This allows achieving high angular resolution (better than 1 degree) with a compact spherical diffuser of 30-50 cm diameter.
2Measurement precision
If a large diffusing screen is used to maintain angular aperture with increased distance, then angular resolution improves, but stray light becomes unmanageable
Solution Approach 1:
The patent extracts and removes the problematic large-area diffusing screen from the system, replacing it with a compact spherical diffuser. This eliminates the stray light issue inherent in large planar screens while maintaining the necessary angular measurement capabilities through the spherical geometry and off-axis detector positioning.
Solution Approach 2:
The spherical diffuser acts as an intermediary element that redistributes light from the source in a controlled manner. By using the spherical geometry with an off-axis detector, the system mediates between the source and detector to achieve accurate angular measurements without the stray light problems of direct large-screen configurations.
3Ease of manufacture
If the source size is not negligible compared to the diffusing screen size, then the system is easier to implement, but the maximum angular resolution is limited
Solution Approach 1:
The patent changes the geometric parameters by using a spherical diffuser with radius R much larger than the source diameter d (R >> d). This parameter relationship allows the source to be of practical size while still achieving high angular resolution, as the spherical geometry ensures that light from different source points is properly distributed across the detector field of view.
4Ease of operation
If a transmission diffuser is used instead of a diffusing screen to align source and video photometer, then distortion problems are overcome, but the diffuser thickness must be minimized affecting angular resolution
Solution Approach 1:
Instead of using a thin transmission diffuser that requires precise thickness control, the patent inverts the approach by using a thick spherical diffuser in reflection geometry. The source is positioned at the center and the detector is positioned off-axis, allowing the use of a relatively thick diffuser material without compromising angular resolution, thereby simplifying manufacturing.
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 device achieves high angular resolution and large angular aperture measurements independently of source size and alignment, reducing stray light and costs, while ensuring measurement accuracy and compliance with safety standards.
Implementation Method 1
a first objective, called Fourier objective, forming a Fourier surface, each point of which corresponds to a direction of observation of the object
Implementation Method 2
The Fourier objective collects and focuses light onto the diffusing surface
Implementation Method 3
a diffusing surface used in transmission and arranged on the Fourier surface of the first objective
Implementation Method 4
an absorbing layer reduces stray light
Data Source
AI summary
A device allowing the angular emission pattern of a source to be measured without mechanical movement comprises, in succession, along its optical axis: a first objective, called the Fourier objective, arranged to form a Fourier surface each point of which corresponds to one direction of observation of the object; a diffuser used in transmission and placed on the Fourier surface; a substance of optical density placed upstream of the diffuser and arranged to attenuate the light backscattered toward the Fourier objective and the areal source; and a video photometer located downstream of the plane of the diffuser and arranged to image the surface of the diffuser.