Editorial Feature

Advances in Spatial Light Modulation for Enhanced Holographic Data Processing

For many years, optics has been utilized in computing, primarily for connecting various components of computers for communications. Optical information processing has emerged as a promising approach, efficiently utilizing attributes of light, such as its speed and parallelism, to handle data at high rates.

Advances in Spatial Light Modulation for Enhanced Holographic Data Processing

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The primary function of a Spatial Light Modulator (SLM) in optical systems is to convert electricity into light. The processing plane of these systems typically includes lenses, holograms (either optically recorded or computer-generated), and nonlinear components.

SLMs play a crucial role in creating practical optical processors, and ongoing research aims to enhance their efficiency and performance.1

SLM Technology: An Overview

Spatial modulation of light has been applied in optical communications and information processing for many years.

SLMs can modulate key light attributes, such as amplitude, phase, polarization, or a combination of these parameters, based on the two spatial dimensions of the modulator.2 These electro-optical devices have attracted significant international interest due to their versatile utility in numerous optical imaging applications.

The main platforms used to develop SLMs include mechanical or thermally deformable systems, known as digital micro-mirror devices (DMDs), and widely used magneto-optic devices.

However, the term "SLM" typically refers to non-mechanical components that leverage the electro-optical anisotropy of liquid crystals (LCs). LCs are organic materials with properties that lie between those of solids and liquids.3

The fluid nature of different LC mesophases is ensured by the existence of a liquid order. In the nematic mesophase, for example, molecules lack positional order but are oriented in a preferred direction, defined by a vector known as the director axis.

When an electric field is applied to an LC material, elastic forces are generated, causing the molecules to reorient themselves in a manner that minimizes strain energy. This reorientation can be controlled spatially by manipulating the applied electric field, typically in one or two dimensions.

Such control allows for the modulation of the phase of an incident optical wave,4 known as the "readout beam," which carries the information to be encoded into the phase of the light.

In more recent applications, DMDs are utilized. These devices have micro-mirrors that are used in light modulation.5 This rapid switching between two fixed micro-mirror states enables high-speed amplitude modulation of light, making DMDs suitable for applications requiring fast frame rates, such as video projection.

However, because DMDs operate in a binary fashion (each mirror is either in an "on" or "off" state), they are limited in their ability to provide customized modulation of phase and polarization of light.

Other types of SLMs based on LC technology are often preferred for applications requiring more complex modulation, such as phase and polarization modulation.

Advancements in SLM Holography

Novel systems that enable multi-view holographic 3D display systems have proven to be an effective solution for addressing the limited field of view, a common issue in industrial applications of augmented reality (AR) displays. These systems significantly improve upon traditional shortcomings.

These system breakthroughs are achieved by utilizing phase SLMs to upload synthetic phase holograms, simplifying image splicing, and avoiding bandwidth limitation among separately reconstructed images.6

The phase SLM is crucial in generating high-quality holographic images with real physical depth cues and high resolution.

To further enhance the viewing experience and expand the field of view, a directional controlling element known as a holographic optical element (HOE) is integrated into the system. The HOE redirects the multiview reconstructed images into multiple viewing zones, thereby enabling multiview display and increasing the effective field of view of the holographic display system.

By combining the capabilities of phase SLMs and HOEs, multiview holographic 3D display systems can overcome the limitations of traditional holographic displays and offer immersive viewing experiences with improved field of view, making them suitable for a wide range of AR and other 3D display applications.

The experimental results showed that the system was successfully capable of achieving multi-view holographic AR 3D display with a 4K resolution, surpassing the present systems in efficiency.

The development of a CGH generation algorithm represents another significant advancement in holography technology, particularly in terms of efficiency and real-time performance.

This approach can quickly generate a 3D hologram utilizing a one-step backward computation technique within a unique split Lohmann lens-based diffraction model. The model is based on the Fourier holography system, which involves the interaction between an RGB image and the hologram plane.

In this diffraction model, the propagation of light waves from the RGB image to the hologram is modulated by a pre-designed and depth-dependent virtual split Lohmann lens phase.7

This phase modulation efficiently maps input RGB depth content to hologram patterns that are then displayed on the SLM. This allows for the rapid development of complex holograms, particularly for AR.

The Role of Holography in 3D Printing

The introduction of Tomographic Volumetric Additive Manufacturing (VAM) has revolutionized the fabrication of mesoscale objects by enabling rapid printing within tens of seconds. This method leverages holographic phase modulation to enhance printing capabilities significantly.

Recently, researchers have used holographic phase modulation to increase the efficiency of VAM. Employing holographic phase modulation with an SLM in VAM printing offers several key advantages. 8

It improves light projection efficiency and allows resolutions to reach the light diffraction limit, enabling the fabrication of highly detailed structures.

The novel process involves using CGH to convert phase, encoded on a 2D modulator, into the desired intensity projections by propagating light through a photosensitive resin container.

This approach has been validated through simulations and experiments, with the latter involving the implementation of a volumetric printer using a DMD as the 2D phase modulator in a Fourier configuration.

Combining tiled holograms with point-spread-function shaping mitigates speckle noise, resulting in high-quality printed objects. The holographic projections have been utilized to fabricate millimetric 3D objects in less than a minute, achieving resolutions down to 164 µm. This advancement opens new possibilities for rapid and precise manufacturing in various fields.

The development of novel materials for SLMs is essential for advancing optical processing capabilities. Materials with faster response times, higher resolution, and improved efficiency are crucial for enabling real-time processing of complex holographic data and enhancing the performance of SLM-based systems.

Researchers are engineering novel materials and phase-modulation techniques that significantly increase the efficiency of SLM-based holographic data processing systems. The implementation of Artificial Intelligence (AI)- based algorithms also ensures a promising future for SLM systems in various advanced applications.

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References and Further Reading

[1] Kazanskiy N. et. al. (2022). Optical Computing: Status and Perspectives. Nanomaterials. 12(13). 2171. Available at: https://doi.org/10.3390/nano12132171

[2] Jullien A. (2020). Spatial Light Modulators. Photonics. 101. 59 – 64. Available at: https://doi.org/10.1051/photon/202010159

[3] Tiwari, V. et. al. (2022). Spatial Light Modulators and Their Applications in Polarization Holography. In Holography-Recent Advances and Applications. IntechOpen. Available at: https://doi.org/10.5772/intechopen.107110

[4] Guzman C. et. al. (2017). How to Shape Light with Spatial Light Modulators. Chapter 1. 1-58. Available at: https://doi.org/10.1117/3.2281295.ch1

[5] Tahara, T. (2024). Incoherent digital holography with two polarization-sensitive phase-only spatial light modulators and reduced number of exposures. Applied Optics, 63(7), B24-B31. Available at: https://doi.org/10.1117/1.jmm.14.4.041307

[6] Qin, X. et. al. (2023). "High Resolution Multiview Holographic Display Based on the Holographic Optical Element" Micromachines. 14(1). 147. Available at: https://doi.org/10.3390/mi14010147

[7] Chang, C. et. al. (2024). Split Lohmann computer holography: fast generation of 3D hologram in single-step diffraction calculation. Advanced Photonics Nexus, 3(3), 036001-036001. Available at: https://doi.org/10.1117/1.APN.3.3.036001

[8] Álvarez-Castaño, I. et. al. (2024). Holographic Volumetric Additive Manufacturing. arXiv preprint arXiv:2401.13755. Available at: https://doi.org/10.48550/arXiv.2401.13755

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

Ibtisam Abbasi

Written by

Ibtisam Abbasi

Ibtisam graduated from the Institute of Space Technology, Islamabad with a B.S. in Aerospace Engineering. During his academic career, he has worked on several research projects and has successfully managed several co-curricular events such as the International World Space Week and the International Conference on Aerospace Engineering. Having won an English prose competition during his undergraduate degree, Ibtisam has always been keenly interested in research, writing, and editing. Soon after his graduation, he joined AzoNetwork as a freelancer to sharpen his skills. Ibtisam loves to travel, especially visiting the countryside. He has always been a sports fan and loves to watch tennis, soccer, and cricket. Born in Pakistan, Ibtisam one day hopes to travel all over the world.


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