SLM-FAQ
Is it necessary to calibrate my SLM? / How do I calibrate my SLM?
For an optimal usage of the SLM, it needs to be calibrated for the used wavelength. The SLM comes with a set of calibration files for different wavelengths depending on the SLM version.
If the supplied configurations differ slightly from your wavelength used (e.g. you use 530 nm instead of 520 nm mentioned in the calibration file) you can still use it and fine tune the result by slightly changing the voltage settings.
Use the HOLOEYE SLM Configuration Manger software to load the according calibrations to the SLM. The exact procedure is explained in the Configuration Manager manual or in the videos you find at the website for each Spatial Light Modulator model.
If you use a wavelength, we do not supply configuration files for or if you require a different phase shift, the Configuration Manager allows you to create a custom CLUT for your SLM model if you provide it with a gray value vs phase response measurement. For details, please check the Configuration Manager manual.
If you require assistance during the calibration process or you would like to know about best ways to measure the phase, please contact us!
Can I do amplitude modulation with my phase-only SLM?
You can do amplitude modulation with your phase-only SLM. For amplitude modulation you need to rotate the incident polarization by 45º and use an analyzer after the SLM.
As our SLMs are optimized for phase modulation at first, the contrast might not be as good as for our amplitude devices. Also dependent on the used SLM the output might get slightly “blurry” due to the higher thickness of the LC layer.
As the phase SLMs are typically calibrated for a linear phase response, the calibration needs to be adjusted for optimal amplitude contrast. Please contact us if you need support on this!
Which incident polarization do I need for phase-only modulation?
Our SLMs are based on liquid crystals, which are anisotropic materials. Therefore, for phase-only modulation you need linear polarization parallel to the director vector of the liquid crystal molecules.
For most of HOLOEYE LCOS SLMs the required incident polarization is parallel to the long axis of the display. For few SLM versions it is parallel to the short axis. Please refer to the SLM manual at the section of the SLM version you use.
How can I clean the LCOS display of my SLM?
To clean the LCOS display of a HOLOEYE SLM, first remove the aperture from the top of the display. Make sure to work under antistatic conditions / use ESD protection measures.
Use Isopropanol or pure Ethanol and a lab quality cotton swab. Gently wipe of the dirt using low force. Reattach the display aperture afterwords.
If an intense contamination can not be romoved this way, please get in contact with HOLOEYE!
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How do I illuminate the SLM? Which incident angles are acceptable?
Basically there are 3 different options to illuminate the SLM:
Option A – Using a polarizing beam splitter:
This is the preferred setup for optimal usage of the SLM. Our calibration files are created using normal incidence on the SLM. They have been tested also to maintain a linear phase response for the given phase shift up to an incident angle of 10º.
Drawback: You will loose some light due to the beam splitter.
Option B – Near perpendicular incidence:
If you need high light efficiency we recommend option (B). The incident angle should not exceed +/-10
Option C – Higher incident angles / 45°
For larger incident angles the SLM performance changes:
- the AR coating will not work as intended => strong front reflection and undesired interference effects between front and back reflection can occur.
- the optical path length within the LCOS display is larger => different phase response
- the birefringence of the LC molecules change => different phase response
- geometric distortions will happen, even though this could be compensated on addressed image level.
Some of the effects can in principle be compensated on SLM calibration level. If greater angles of incidence are required for your application, please contact us at slm@holoeye.com with the serial number of your SLM to support you in the process and inform you about the expected maximum phase response at your required angle.