Optical path difference measurement techniques for SLMs

Phase calibration of spatial light modulators by means of Fresnel images

“…Strictly speaking, a lateral derivative of this error is added to the observed pattern. Taking into account that the typical errors due to the curvature are of the order of λ over the area of a typical SLM [9][10][11][12], and also that a typical aperture can contain approximately 1000 elementary cells in one direction, the magnitude of this error over one elementary cell can be evaluated as being of order of λ/1000. As an important practical consideration, the observation should be performed in the first Fresnel plane, where the shear value is the smallest and thereby this residual phase error is also minimum.…”

“…It is apparent that the phase modulation curve of a SLM can be directly measured with the aid of an interferometer. Moreover, it is also possible to study spatial phase distortions along the device aperture with interferometric methods, as those based on the analysis of Fizeau-type fringes [12], or on the use of a Twyman-Green 3 interferometer [11] or a Mach-Zehnder interferometer [13] with a four-phase step shift equipment added [10]. The main drawback of this kind of systems is its high sensitivity to mechanical vibrations, as well as the large number of optical components that are required.…”

Multipoint phase calibration for improved compensation of inherent wavefront distortion in parallel aligned liquid crystal on silicon displays

“…Transmissive LCDs have commonly been assumed to have a spatially uniform response except for the work described in Ref. [32]. However, in the case of a reflective liquid crystal on silicon (LCoS) SLM, inherent curvatures of the device surface, mainly because of limitations in the polishing process of the silicon backplane, cause reflective wavefront distortion in the optical system [20,28,30].…”