Abstract
As the use of Digital Micro Mirror Devices (DMDs) becomes more prevalent in optics research, the ability to precisely locate the Fourier “footprint” of an image beam at the Fourier plane becomes a pressing need. In this approach, Bayesian adaptive exploration techniques were employed to characterize the size and position of the beam on a DMD located at the Fourier plane. It couples a Bayesian inference engine with an inquiry engine to implement the search. The inquiry engine explores the DMD by engaging mirrors and recording light intensity values based on the maximization of the expected information gain. Using the data collected from this exploration, the Bayesian inference engine updates the posterior probability describing the beam’s characteristics. The process is iterated until the beam is located to within the desired precision. This methodology not only locates the center and radius of the beam with remarkable precision but accomplishes the task in far less time than a brute force search. The employed approach has applications to system alignment for both Fourier processing and coded aperture design.
Highlights
Spatial light modulators (SLMs) are widely used in optical research to modulate light in a precise and controllable manner
These parallel rays will converge to a bright point at the center of the Fourier plane, rays scattered away from parallel will arrive at the Fourier plane some distance from this central point
The search was facilitated by measuring the power of the light reflected off of individual mirrors of the Digital Micro Mirror Devices (DMDs) which were selected for measurement by the algorithm
Summary
Spatial light modulators (SLMs) are widely used in optical research to modulate light in a precise and controllable manner. With the appropriate polarizing filters, such SLMs can allow modification of phase and/or amplitude of the light These methods are dynamic and useful, the extinction ratio (contrast) is not 100 percent, frame rates in high resolution commercial SLMs are limited (often to 60 Hz) and it can be difficult to precisely control only the. One challenge when using SLMs as dynamic Fourier filters is precisely locating the position of the projected pattern precisely with respect to the center of the beam’s Fourier transform. This could be accomplished by other methods, Bayesian adaptive exploration offers an approach that is well suited to this type of task. The algorithm works through an iterative process switching DMD pixels on and off while taking power measurements in order to determine the size and location of the beam with high precision using the least amount of data possible
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