Superpixel-based spatial amplitude and phase modulation using a digital micromirror device.

Sebastianus A Goorden,Jacopo Bertolotti,Allard P Mosk

doi:10.1364/oe.22.017999

Abstract

We present a superpixel method for full spatial phase and amplitude control of a light beam using a digital micromirror device (DMD) combined with a spatial filter. We combine square regions of nearby micromirrors into superpixels by low pass filtering in a Fourier plane of the DMD. At each superpixel we are able to independently modulate the phase and the amplitude of light, while retaining a high resolution and the very high speed of a DMD. The method achieves a measured fidelity F = 0.98 for a target field with fully independent phase and amplitude at a resolution of 8 × 8 pixels per diffraction limited spot. For the LG10 orbital angular momentum mode the calculated fidelity is F = 0.99993, using 768 × 768 DMD pixels. The superpixel method reduces the errors when compared to the state of the art Lee holography method for these test fields by 50% and 18%, with a comparable light efficiency of around 5%. Our control software is publicly available.

Highlights

Full control over light allows many exciting applications
The digital micromirror device (DMD) [23] is an excellent candidate for controlling light fields, as it has a very high number of spatial degrees of freedom, a very high framerate, it operates in a broad wavelength range and it is relatively cheap
Lee holography with pixel dithering has been demonstrated and the obtained errors are at the 5% level for low resolution fields [34]

Summary

Introduction

Full control over light allows many exciting applications. By tailoring light fields we can use optics to obtain a great level of control over particles [1]. Wavefront shaping allows compensation for and exploitation of scattering due to spatial inhomogenieties in the refractive index of a material [7]. The most common technique to obtain phase modulation with a DMD is Lee holography [31] and has been shown to allow for efficient and fast wavefront shaping [32]. We propose and demonstrate a superpixel-based [36] phase and amplitude modulation method, which is highly robust and easy to use while offering full spatial control over the phase and amplitude of a light field. Our setup is designed to obtain full spatial control over the phase and amplitude of light in one specific plane, which we call the target plane. The lenses are placed slightly off-axis with respect to each other, resulting in an extra phase factor in the target plane. The lenses are placed in such a way that the phase prefactors of the micromirrors within each superpixel are distributed (a)

E2 E3 E4

Test field 1

Test field 2

Origin of residual errors

Findings

Conclusions