Calibrate a Spatial Light Modulator (SLM) for Phase Delay (Viewer Inspired) | Thorlabs Insights

The phase delay (phase modulation) provided by a reflective liquid crystal on silicon spatial light modulator (SLM) depends on a number of things, including the applied control voltage, ambient conditions, and the characteristics of the incident light. When a manufacturer calibrates the SLM’s phase delay as a function of the applied voltage, the calibration is typically performed under specific operating conditions and for collimated light with a particular wavelength and angle of incidence. Since an application’s setup and operating conditions can differ significantly from the manufacturer's, it is often beneficial to recalibrate the SLM’s phase delay for each application.

This Video Insight demonstrates an interferometric method for calibrating the phase delay of reflective SLMs that are designed to modulate the phase without affecting the linear polarization state of the incident light. The calibration setup requires only a collimated, linearly polarized input beam and a camera, in addition to the SLM.

It is common to represent phase delay patterns using grayscale values, in which each shade of gray represents a specific phase delay. Calibration determines the specific phase delay provided for each grayscale value, under the current operating conditions. The calibration approach applies a uniform phase delay to one half of the SLM's panel. This side provides a reflected beam, as a mirror would. A binary phase grating is applied to the other half, which provides a diffracted beam. The reflected and negative first order diffracted beams overlap and create interference fringes, which are monitored during the calibration procedure. The voltage applied to the mirror side of the SLM is varied across the full range, and the fringes shift each time the applied voltage changes. The fringe shift is directly related to the change in phase delay.

00:00 Introduction
01:30 Phase Delays & Grayscale Values
04:28 SLM Calibration Approach
06:22 Linearly Polarize & Align Input
07:48 Placing the Camera
08:27 Applying Calibration Pattern
08:50 Half-Wave Plate Purpose & Use
09:34 Optimize Fringe Properties
11:25 Measurement & Analysis

Components used in this Demonstration Include:

[zyzzrespector]

I don't have the background to understand half of this but the Stud on screen really helped me out!

[danieldahl]

Incredible work, very clear and concise. Another video idea could be to show people how to measure a flatness profile for an SLM.
Keep these amazing videos coming people in the optics community really appreciate them.

[TheWaffleburglar]

Very helpful, Jack’s a great teacher!

[BingOuyang-nx]

Would you also provide the link to the camera lens you used to capture the fringe? Thank you!

[ShashankJoshi-mn]

how did you calculate the distance of the camera from slm, can you explain this? What is 6.25 mm term in Y= 6.25 mm/tan phi = 29 cm come from? Is that slm panel width? or beam diameter? Can you explain this please. Also can you explain the grating period calculation, how did you get 25.6 microns?

[giammi]

7:55 is tan(phi), not tan-1(phi). Great video!

[lavleshpensia]

Dear Sir/Mam.
Can you make a video on all resolution targets, like Sector Star Targets, 1951 USAF Targets, and NBS 1963A Targets? It will be helpful for us and as well as publicity your company products.

[kaushikgupta]

So slow this video is!! but great explanation.