Generation of structured light beams by dual phase modulation with a single spatial light modulator

Abstract

Precise control of amplitude and wavefront of optical fields are prerequisites for many applications, especially in singular optics. This has led to the increasing efforts for developing efficient techniques to control the shape of the light in different dimensions. A spatial light modulator (SLM) can be efficiently used for phase-only or amplitude-only modulation; but offers limitation in complex light field modulation. Hence, shaping the complex amplitude of optical beams is challenging mainly because there are no complex modulators. While there is ongoing research to develop complex amplitude modulating SLMs, a solution is still non-existent. In this study, to achieve complex light modulations, a simple experimental set-up employing single phase-only SLM has been proposed. The SLM has been used as operating in a split-screen-mode. The non-iterative approach of dual-pass modulation has been applied where two cascaded phase value distributions (PVD) are encoded side-by-side onto the SLM. The first PVD is designed to enable amplitude modulation in the second PVD plane which finally helps achieve wavefront shaping. Hence, both amplitude and phase modulation of light beam are possible in this configuration. Commonly known singular beams such as Laguerre-Gaussian and Bessel-Gaussian modes have been generated theoretically as well as experimentally to verify the feasibility of the proposed technique. The method used helps to achieve arbitrary shaped beams as well.

A conceptual review on Bessel beams

“…The intensity of the laser beam passes through this liquid crystal display modulated by the computer-generated hologram. Thus, by projecting holograms of LG, HG, and BBs on SLM, we can transform the conventional Gaussian beam from the laser cavity to LG, HG, and BBs respectively [64][65][66][67][68][69][70].…”

Determining Topological Charge of Bessel-Gaussian Beams Using Modified Mach-Zehnder Interferometer

“…The schematic diagram for the generation of BG beams is shown in Figure 1. Here, the desired BG beam is produced using dual-pass modulations from the phase-only holograms encoded side-by-side on a single liquid crystal SLM [30]. The SLM screen is divided into two parts, where each half is displayed with a computer-generated hologram (CGH).…”

“…Also, BG beams contribute significantly to optical tweezers [17] and high-resolution imaging [18]. For the progress of potential applications, various efficient methods for BG beam generation have been reported [19][20][21][22][23][24][25][26][27][28][29][30][31].…”

“…BG beams produced through fiber-based technology deliver a compact and flexible implementation compared to diffractive optical elements. However, it is challenging to design fiber with a special diffractive structure to generate BG beams [30].…”

“…In this case, both the holograms were designed to precisely modulate the desired amplitude as well as phase within the incoming beam. The generated BG beams with this approach are beneficial in achieving the desired beam in zeroth order with sufficiently high energy as compared to beams produced in first order using grating [30]. Also, there is no limitation on the range of BG beams produced as compared to the case of axicons, which may be an essential requirement in various practical applications.…”