Controlling a Spatial Light Modulator remotely using a Raspberry Pi

Standard phase spatial light modulators (SLMs) have the advantage of being controlled as a secondary display. It saves money on dedicated control interfaces and simplifies the usage. However, when trying to control an experiment remotely, which is especially needed these days, It adds some complexity when using remote desktop software or ssh. I will detail here how to use a Raspberry Pi to control an SLM and send images from a computer on the same local network. The computer that controls the experiment can now easily be controlled from the comfort of your home.

Easy characterization of SLMs' phase deformation

[D. Marco et al., Opt. Lett., 45 (2020)]

Technical papers are important for the scientific community, it helps in particular to reproduce experimental setups. They are unfortunately not valued enough by scientific journals. I want today to highlight such a paper. Liquid crystals phase modulators - and indeed any kind of spatial light modulator (SLM) - are not free of imperfections. One effect that appears is a phase distortion of the reflected field due to spatial non-uniformities that occur during the fabrications. In practice, if you illuminate an SLM with a plane wave and you display a uniform mask, one does not end up with a plane wave, but an aberrated wavefront. In the present paper, the authors use a quite easy to implement technique to retrieve the phase distortion introduced by the SLM.

About mechanical stability using Vialux DMDs

We have been using DMDs from Vialux for a few years now, and I already published few posts about different effects that need to be taken into account when working with such devices (in particular aberrations and diffraction effects). One more trivial, but potentially troublesome, effect is due to vibrations, that come from the FPGA board and transmitted through the rigid flat cables. In this quick post, I show the damaging effect of vibrations and how to easily get rid of them, at least partially.

How to generate macropixel patterns for SLMs/DMDs with the Layout module

In many wavefront shaping experiments, such as for optimization experiments, like the seminal work by I. Vellkoop and A. Mosk, or for measuring the transmission matrix, one needs to control the amplitude and/or the phase of the field on a given number of macropixels (i.e. groups of pixels). Using DMDs, amplitude, and phase modulation can be achieved using the Lee hologram method and then sending the binary images to the device using the for ALP4lib in Python for Vialux DMDs. I released here a module written by M. W. Matthès and myself to easily and efficiently generate such patterns. The code can be found on my Github account here as well as an amplitude and phase modulation example: layout_amplitude_phase_modulation.ipynb.