1 DMD Diffraction Efficiency Calculator Functionality

The MATLAB code behind the calculator for computing DMD diffraction patterns and the optical design efficiency utilizes non-paraxial scalar diffraction theory as demonstrated by Dr. James Harvey [1]. This method approximates more rigorous Electro Magnetic (EM) methods and has shown good agreement with measurements. For longer wavelengths that approach the mirror size, the accuracy is reduced and more rigorous methods can be required [1]. This model is important to use when designing DMD based optical systems to correctly account for diffractive effects.

The user enters key DMD and optical parameters which are then converted to direction cosines in Fourier transform space. The method iterates through the illumination cone angle and launches plane waves from each discrete sample location. DMD’s behave similarly to a 2D blazed diffraction grating. As the plane waves interact with the DMD, a range of diffraction orders are generated as each wave interaction occurs. The magnitude of the Fourier transform squared is then taken and the resulting diffraction pattern is stored for each incident wave. The model incoherently integrates over wavelength and source extent. The diffraction efficiency is calculated from the fractional power that falls within the projection lens aperture. The ratio of the output versus the input optical power is considered the diffraction efficiency.

Once the application has completed each calculation, a variety of outputs are displayed. The diffraction pattern in 2D and 3D are displayed along with a diffraction efficiency plot. An excel file is created with stored diffraction efficiency values across the wavelength spectrum. The average diffraction efficiency is shown and weighted against the photopic curve where the output is then recorded as the photopic diffraction efficiency. The diffraction pattern energy distribution can be saved to an excel file if the user selects the “Save Diffraction Pattern Data?” checkbox.