Dynamic range expansion of spatial light modulators based on a module-nπ method

Abstract

It is known that the cumbersome 2 π correction is needed in the traditional module- 2 π method (i.e., the phase wrapping method) due to the 2 π deviation of the phase modulation depth of spatial light modulators (SLMs). To avoid the cumbersome 2 π correction in the module- 2 π method, this paper proposes a module- n π method, and it can directly utilize any full-field phase modulation depth. First, for a Gaussian phase with a phase depth of 30 rad, wrapped by the module- 3.6 π , it is reconstructed with the root-mean-square (RMS) values of its phase response are 0.1006 λ (for the Twyman–Green interferometer) and 0.1101 λ (for the Shack–Hartmann wavefront sensor method), respectively, which proves that the monitoring accuracy is relatively consistent. Subsequently, some comparative experiments based on the traditional module- 2 π are performed. The experimental results show that the RMS values of its phase response are 0.8886 λ (for a modulation depth of 11.3 rad) and 0.2261 λ (for a modulation depth of 6.28 rad), respectively. All the results have proved that the SLM with a phase modulation depth exceeding 2 π (e.g., 11.3 rad) has more prominent advantages. More specifically, increasing the SLM’s phase modulation depth can effectively reduce the fringe orders of the wrapped patterns generated by the module- n π method. With the further reduction of the fringe orders, the influence of the fly-back zone error on the wavefront phase modulation is reduced, that is, the modulation accuracy is improved (the RMS values are reduced from 0.2261 λ to 0.1006 λ ). Different from the traditional module- 2 π method, there is no need to consider the problems of the SLMs’ over modulation or the insufficient modulation in the module- n π method. Furthermore, it avoids the cumbersome 2 π correction process, which will make the use of the SLM more convenient.