Fourier-Filtered Wavefront Sensor for Low-Light Aberration Sensing
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Solution Overview
Problem
Existing wave front sensors, such as Shack-Hartmann wavefront sensors, are susceptible to noise for low-order aberrations like tip, tilt, and focus, particularly in low light applications, necessitating the development of improved sensors for enhanced precision and accuracy.
Innovation Solution
Employing optical systems with Fourier transform capabilities, utilizing a lenslet array, a mask at the focal plane, and a sensor array to measure both phase and intensity of the wave front, with configurations like 4-f systems, spatial light modulators, and polarization-sensitive detectors to enhance precision and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional wave front sensors (e.g., Shack-Hartmann) are used, then the device structure is simple, but measurement precision deteriorates for low-order aberrations in low light conditions
Solution Approach 1:
The wave front sensor divides the incoming wave front into multiple sub-wave fronts using an array of sub-apertures. Each sub-aperture captures a localized portion of the wave front, allowing independent phase measurement that is less susceptible to noise. This segmentation enables precise measurement of low-order aberrations by analyzing phase differences across multiple discrete regions.
Solution Approach 2:
The patent introduces an intermediary optical system comprising a first lenslet array, a mask at the focal plane, and a second lenslet array. This intermediary system transforms the wave front information through Fourier optics, creating an intensity distribution that encodes phase information in a noise-resistant manner. The mask acts as a mediator that selectively transmits or blocks light to enhance the signal-to-noise ratio for low-order aberration measurements.
2Reliability
If Fourier transform optical systems are used to improve measurement precision, then noise resistance improves, but device complexity increases
Solution Approach 1:
The patent merges multiple optical functions into a unified Fourier transform optical system. The first lenslet array performs spatial Fourier transformation, the mask at the focal plane performs spectral filtering, and the second lenslet array performs inverse Fourier transformation. By combining these functions in sequence, the system achieves noise-resistant measurement without requiring separate independent subsystems, thereby managing complexity while improving reliability.
Solution Approach 2:
The system changes the parameter domain from direct phase measurement to intensity measurement in the Fourier domain. By transforming the wave front into the frequency domain through Fourier optics, low-order aberrations appear as distinct low-frequency components that can be measured with higher signal-to-noise ratio. This parameter transformation fundamentally improves noise resistance while the modular optical design keeps complexity manageable.
3Measurement precision
If phase-shifting interferometry is employed to enhance accuracy, then measurement accuracy improves, but measurement time increases
Solution Approach 1:
The patent employs periodic phase shifting in the interferometry process, where the phase of the reference wave is systematically varied through discrete steps. This periodic modulation of the reference wave phase creates a series of interferograms that can be processed to extract precise wave front information. The periodic nature allows for robust noise rejection while maintaining relatively fast acquisition through efficient phase-stepping algorithms.
Solution Approach 2:
The system performs preliminary Fourier transformation and filtering of the wave front before the final phase measurement step. By pre-processing the wave front information through the Fourier optics system and mask filtering, the subsequent phase-shifting interferometry operates on already-enhanced data with reduced noise content. This preliminary action reduces the number of phase steps needed and accelerates the overall measurement process while maintaining high accuracy.
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 proposed solution provides improved wave front sensing with higher precision, dynamic range, and insensitivity to environmental vibrations, enabling better aberration correction and image quality enhancement in optical systems.
Implementation Method 1
a mask positioned at a focal plane of the first lenslet array to receive and filter a Fourier transformed wave front that is produced by the first lenslet array at the focal plane
Implementation Method 2
Each section of the mask is configured to (a) produce a reference wave front from the Fourier transformed wave front incident thereon
Implementation Method 3
a sensor array that includes a plurality of light sensitive detectors and is positioned to receive the reference wave front produced in (a) and the wavefront in (b), and to detect an intensity value representative of a phase of the incoming wave front
Data Source
AI summary
Systems, devices and methods with improved wave front sensing and detection capabilities are described. One example wave front sensor includes a lenslet array that receives an incoming wave front, and a mask that is positioned at a focal plane of the lenslet array to receive and filter a Fourier transformed wave front that is produced by the first lenslet array at the focal plane. Each section of the mask receives light from a corresponding lens of the lenslet array and is configured to produce a reference wave front and to allow a portion of the Fourier transformed wave front to be transmitted or reflected. The wave front sensor also includes a sensor array having a plurality of light sensitive detectors that is positioned to receive the two wave fronts and to detect an intensity value representative of a phase of the incoming wave front.