Collimated Phase Deflectometry With Telecentric Depth Decoupling
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Solution Overview
Problem
Traditional Phase Measuring Deflectometry (PMD) systems face challenges in accurate calibration, sensitivity to depth information, and low-frequency shape measurement, limiting their application in optical metrology due to geometric calibration errors and sample positioning difficulties.
Innovation Solution
The Collimated Phase Measuring Deflectometry (CPMD) system employs an on-axis optical geometry with a telecentric lens and collimation optics to decouple lateral coordinates from depth information, using a beam splitter and Fourier lens to measure surface slopes independently of depth, enabling accurate low-frequency shape measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional Phase Measuring Deflectometry (PMD) systems are used, then measurement of surface slopes is possible, but the system is sensitive to depth information and suffers from geometric calibration errors
Solution Approach 1:
A telecentric lens is introduced as an intermediary optical element between the camera and the surface under test. This lens acts as a mediator that decouples the measurement of surface slopes from depth information, allowing accurate slope measurement without sensitivity to axial position variations and reducing geometric calibration errors.
Solution Approach 2:
The optical system parameters are changed by switching from a conventional lens to a telecentric lens, which fundamentally alters the relationship between image coordinates and surface slopes. This parameter change makes the measurement independent of depth information and reduces sensitivity to calibration errors.
2Measurement precision
If traditional PMD systems are used, then surface slope measurement is achieved, but low-frequency shape measurement is limited
Solution Approach 1:
The telecentric lens-based optical system provides universal measurement capability that works effectively for both high-frequency and low-frequency surface features. The system can measure surface slopes across a wide range of spatial frequencies without the limitations that plague traditional PMD systems, making it versatile for various optical metrology applications.
3Ease of operation
If conventional optical geometry is used, then sample positioning is required, but axial depth tolerance is tight
Solution Approach 1:
The telecentric lens serves as an intermediary that creates a decoupling between lateral coordinate measurement and depth information. This allows the system to measure surface slopes accurately regardless of the sample's axial position, providing tight axial depth tolerance while maintaining ease of operation.
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
CPMD enhances measurement capabilities by reducing low-frequency errors and relaxing axial depth tolerance, making it suitable for precise optical metrology and facilitating automatic metrology procedures.
Implementation Method 1
a collimation optical system comprising a Fourier lens... collimating, by the collimation optical system comprising the Fourier lens, the light emitted by the screen
Implementation Method 2
a beam splitter that is disposed adjacent to the second side of the collimation optical system opposite the screen such that the structured light pattern passing through the collimation optical system is redirected by the beam splitter to illuminate a surface of a specimen under test
Implementation Method 3
a camera that has a telecentric lens and is disposed beyond the beam splitter opposite the SUT such that a deflected pattern produced by illuminating the SUT surface is captured by the camera
Data Source
AI summary
Various examples relate to collimated phase measuring deflectometry. In one example, is a collimated phase measuring deflectometer system with a screen that emits a structured light pattern; a collimation optical system comprising a Fourier lens positioned such that the structured light pattern passes through the collimation optical system; a beam splitter positioned such that the structured light pattern is redirected to illuminate a surface of a specimen under test (SUT); and a camera having a telecentric lens positioned such that a deflected pattern produced by illuminating the surface of the SUT is captured by the camera. The deflection pattern is insensitive to the distance from the collimated phase measuring deflectometer to the SUT surface. In another example, a method includes emitting a structured light pattern; collimating the emitted light pattern; reflecting collimated light to illuminate a SUT surface; and acquiring an image of a deflected pattern produced by the illumination.