Improved beam steering accuracy of a single beam with a ID phase-only spatial light modulator

ArticleinOptics Express 16(22):18275-87 · November 2008with12 Reads
DOI: 10.1364/OE.16.018275 · Source: PubMed
Abstract
The limited number of pixels and their quantized phase modulation values limit the positioning accuracy when a phase-only one dimensional spatial light modulator (SLM) is used for beam steering. Applying the straightforward recipe for finding the optimal setting of the SLM pixels, based on individually optimizing the field contribution from each pixel to the field in the steering position, the inaccuracy can be a significant fraction of the diffraction limited spot size. This is especially true in the vicinity of certain steering angles where precise positioning is particularly difficult. However, by including in the optimization of the SLM setting an extra degree of freedom, we show that the steering accuracy can be drastically improved by a factor proportional to the number of pixels in the SLM. The extra degree of freedom is a global phase offset of all the SLM pixels which takes on a different value for each steering angle. Beam steering experiments were performed with the SLM being set both according to the conventional and the new recipe, and the results were in very good agreement with the theoretical predictions.
    • "The deflection vs. theoretical efficiency curve is shown in Fig. S1D, along with the measured relative SLM power deflection efficiency on the sample (Fig. S1C, D). For pixelated SLMs with quantized phase levels, the theoretical scalar beam redirection efficiency is reduced for deflections with a non-integral number of pixels per phase ramp, but this effect is small (Engstrom et al., 2008). At max r , the maximum possible lateral deflection, the pattern necessarily has only two phase levels, which lowers the maximum diffraction efficiency, and additionally, results in a symmetric phase pattern. "
    Conference Paper · Apr 2016 · Nanoscale Research Letters
    • "In our experiment, a safe working area of 26×26 µm 2 is used for the optical tweezer patterns and the imaging plane. The discrete phase induces a beam steering error [27] but the amount of the error is only 4 nm in our system with 256 gray levels. Thus the resolution is limited by 4 nm, which is much smaller than the long term drift (100 nm) and the LCSLM refresh fluctuation (100 nm). "
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