DMD-MOS

Overview

A multi-object spectrograph (MOS) is an instrument that can acquire the spectra of hundreds of astrophysical objects simultaneously, saving much on observing time. In the recent years, the digital micromirror device (DMD) has shown potential in becoming the central component of the MOS, being used as a programmable slit mask. A DMD-based multi-object spectrograph is being developed at the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto. I am currently working on a wavelength calibration fit to correct hyperspectral imaging distortion in this DMD-MOS. For some wavelength λ, a point on the DMD given by (x,y) can be mapped to a point on the image plane, (x_d,y_d), and the goal is to find this mapping. For more information about the fit, see the Reports folder.

In September 2020, I submitted a poster for the Royal Astronomical Society (RAS) Early Career Poster Competition which shows some of my earlier work in this project, for the case of y=0.

Brief Summary of Steps

1. Generate IMA files for use as masks in Geometric Image Analysis (GIA) in Zemax OpticStudio, on the plane of the DMD surface; each "opening" in the mask represents a micromirror on the DMD
2. Launch 1,000 to 1,000,000 rays in the DMD-MOS system using GIA; determine where the rays land on the detector
3. Use k-means to cluster points together corresponding to rays from the same micromirror
4. For each λ, use the equation y_d = a_sx_d²+c_s to fit smile distortion, where (x_d,y_d) are centroids obtained from k-means
5. Determine a_s and c_s as functions of x, y, and λ
6. Fit keystone distortion

Smile fit for minimum wavelength λ=0.400µm:

Fit for c_s as a function of y and λ (c_s has no dependency on x):

Key Milestones and Current Progress

• December 2020 - Fit determined for the c_s coefficient in smile distortion fit (case of x=0) with a maximum fit error of 17.6µm on the detector, which is less than 2× the pitch of a pixel (fit error is shown in the figure below)
• August 2020 - Fit determined for the case of y=0 with a maximum fit error of around 22µm on the detector

Repository Folders

• Smile_Fit contains the code for the smile fit
• RAS_Poster contains the code used to generate the results in the poster I submitted for the RAS Early Career Poster Competition
• Paraxial_Sim_Convolution contains code used in a preliminary simulation of the DMD-MOS system using paraxial approximation and by convolving the input signal
• ima_gen contains the code used to generate IMA files for GIA in Zemax-OpticStudio
• Reports contains some PDF progress reports of the project
• MATLAB contains the MATLAB standalone application used with ZOS-API