Calibration of spatial light modulators suffering from spatially varying phase response
Artikel i vetenskaplig tidskrift, 2013
We present a method for converting the desired phase values of a hologram to the correct pixel addressing values of a spatial light modulator (SLM), taking into account detailed spatial variations in the phase response of the SLM. In addition to thickness variations in the liquid crystal layer
of the SLM, we also show that these variations in phase response can be caused by a non-uniform electric drive scheme in the SLM or by local heating caused by the incident laser beam. We demonstrate that the use of a global look-up table (LUT), even in combination with a spatially varying
scale factor, generally does not yield sufficiently accurate conversion for
applications requiring highly controllable output fields, such as holographic
optical trapping (HOT). We therefore propose a method where the pixel
addressing values are given by a three-dimensional polynomial, with two
of the variables being the (x;y)-positions of the pixels, and the third their
desired phase values. The coefficients of the polynomial are determined by
measuring the phase response in 8×8 sub-sections of the SLM surface; the
degree of the polynomial is optimized so that the polynomial expression
nearly replicates the measurement in the measurement points, while still
showing a good interpolation behavior in between. The polynomial evaluation
increases the total computation time for hologram generation by only
a few percent. Compared to conventional phase conversion methods, for an SLM with varying phase response, we found that the proposed method
increases the control of the trap intensities in HOT, and efficiently prevents
the appearance of strong unwanted 0th order diffraction that commonly
occurs in SLM systems.
Computer holography
Phase modulation
Holographic optical element
Digital holography
Spatial light modulators
Diffractive optics
Optical tweezers
Laser trapping
Optical manipulation