The present work shows the characterization of a transmissive spatial light modulator (SLM) trademark CRL-Opto and model XGA2L11. This modulator will be used as a variable retarder to generate different polarization states which are produced when the different gray levels from 0 to 250 are displayed in the SLM. So, it is important to determine its response and linear range of work, these parameters were determined experimentally. For this, the SLM was tested with four different wavelengths: red (633 nm), orange (612 nm), violet (405 nm), and green (550 nm). For doing this, the SLM was placed between two linear polarizers aligned first in parallel and then in perpendicular form. The gray levels were varying uniformly from 0 to 250 with increments of 10 in gray levels, and the gray levels were displayed over all the pixels of the SLM. The different intensities for each gray level were measured with a Thorlabs detector model PM100A. Finally, we show the results obtained for each wavelength where we found out that the best linear response was for the green laser with a wavelength of 550 nm.