A phase-only spatial light modulator (SLM) is a device that is commonly used in various optical applications. Generally, SLM offers great advantages such as low power consumption and compact design. However, due to the manufacturing process, the main drawbacks of the SLM are surface non-uniformity and cross-talk between adjacent pixels, which add undesirable phase modulation. As a result, the SLM’s functionality is impacted, leading to image quality degradation, in terms of the signal-to-noise ratio (SNR), of optical reconstruction in holographic projection, for instance. Therefore, the aim of the current study is to measure and compensate for the surface non-uniformities of the SLM and improve its phase modulation. To achieve this, Shack-Hartmann wavefront sensor (SHWFS) is utilized. At first, a flat constant phase pattern is displayed on the SLM, and its surface phase shape is measured using a plane wave illumination. The reflected wavefront from the SLM is measured using SHWFS and then its phase information has been calculated. Hence, the calculated phase values are converted into a phase-only computer-generated hologram (CGH). The calculated CGH is displayed on the phase-only SLM to compensate for the phase errors of the SLM. The reflected wavefront has been measured after displaying the CGH to evaluate the compensation process. The experimental results reveal that the SHWFS provides high accuracy in the measurement of the phase distortion introduced by the surface of SLM. The SHWFS method is simple, robust, offers real-time performance, and is vibration-insensitive when compared with interferometric approaches.
The adaptive Shack-Hartmann wavefront sensor (SHWFS), which integrates deformable mirror (DM) with SHWFS, is effectively used for measuring and characterizing optical elements such as thick lenses, contact lenses, and intraocular lenses (IOLs). The major advantage of combining the DM with SHWFS is the ability of the DM to implement dynamic corrections of any existing wavefront aberrations. However, the measurement dynamic range of the system is limited by the active area of the DM which has a relatively small bandwidth product. This issue can be physically overcome using compound-lens methodology that uses an additional lens or lens system along with the lens under test. The selection criterion of the compound-lens system is based on the focal length of the tested lens, the effective focal length of the tested lens with the compound lens, and the distance between them. Thus, the optimal selection of the compound-lens system and the setup parameters significantly contribute to readjusting the laser beam diameter to properly fit the DM’s active area. Hence, the measurement dynamic range could be successfully extended. To prove the concept, the dynamic range of the used adaptive SHWFS system is first determined. Then, a group of lenses beyond the dynamic range of the system was measured using the compound-lens methodology. The experimental results reveal that the proposed compound-lens methodology can effectively extend the dynamic range of the measurements while keeping the root-mean-square error minimal.
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