Magneto-optic Spatial Light Modulator Research Articles

High performance electrically-derived single-pixel magnetophotonic spatial light modulator

Spatial light modulators (SLMs) utilize components such as magnetophotonic crystals (MPCs) to alter specific characteristics of a light beam in space. In magneto-optical (MO) spatial light modulators, MPCs play a crucial role in spatially modulating light by manipulating local light intensity and polarization rotation. This study explores how the refractive indices of birefringent electro-optical materials within MPCs influence MO rotation and reflection. In this order, using a transfer matrix method, we designed thin MPCs with a MO rotation around 90° and almost full reflection, for having SLMs with high contrast. The direction of applied voltage to the structure was found to be a critical factor, leading to significant reduction in power consumption for SLMs incorporating the MPCs. These characteristics render the designed MO spatial light modulator well-suited for applications in projectors and displays.

Holographic Image Reconstruction Using a Magneto-Optical Spatial Light Modulator with Its Pixel Pitch of 1 μm and its Layout of 10k × 5k

Holographic Image Reconstruction Using a Magneto-Optical Spatial Light Modulator with Its Pixel Pitch of 1 μm and its Layout of 10k × 5k

Magneto-optical spatial light modulator driven by current-induced domain wall motion for holographic display applications.

We have developed a magneto-optical spatial light modulator (MO-SLM) with a 10 k × 5 k pixel layout and with a pixel pitch horizontally of 1 µm and vertically of 4 µm. An MO-SLM device pixel has a magnetic nanowire made of Gd-Fe magneto-optical material whose magnetization was reversed by current-induced magnetic domain wall motion. We successfully demonstrated the reconstruction of holographic images, showing large viewing zone angles as wide as 30 degrees and visualizing different depths of the objects. These characteristics are unique to holographic images, providing physiological depth cues which may play a vital role in three-dimensional (3D) perception.

High-performance blue-green-red magneto-optical spatial light modulators based on thin film multilayers

Herein, we report high-performance thin film multilayer structures with the capability of operating as high-contrast magneto-optical spatial light modulators (MOSLMs) for simultaneously operating at blue-green-red (BGR) wavelengths. The adjustment is carried out by tuning the applied magnetic field to use the high potential of CeF3 as a new and transparent visible Faraday rotator. For practical purposes, to avoid instabilities due to the wavelength fluctuations, we showed that achieving a suitable tunable MOLSM with flat-top responses is possible by offering appropriate approach in designing of multilayers.

Interface-Driven Multiferroicity in Cubic BaTiO3-SrTiO3 Nanocomposites.

Perovskite multiferroics have drawn significant attention in the development of next-generation multifunctional electronic devices. However, the majority of existing multiferroics exhibit ferroelectric and ferromagnetic orderings only at low temperatures. Although interface engineering in complex oxide thin films has triggered many exotic room-temperature functionalities, the desired coupling of charge, spin, orbital and lattice degrees of freedom often imposes stringent requirements on deposition conditions, layer thickness and crystal orientation, greatly hindering their cost-effective large-scale applications. Herein, we report an interface-driven multiferroicity in low-cost and environmentally friendly bulk polycrystalline material, namely cubic BaTiO3-SrTiO3 nanocomposites which were fabricated through a simple, high-throughput solid-state reaction route. Interface reconstruction in the nanocomposites can be readily controlled by the processing conditions. Coexistence of room-temperature ferromagnetism and ferroelectricity, accompanying a robust magnetoelectric coupling in the nanocomposites, was confirmed both experimentally and theoretically. Our study explores the 'hidden treasure at the interface' by creating a playground in bulk perovskite oxides, enabling a broad range of applications that are challenging with thin films, such as low-power-consumption large-volume memory and magneto-optic spatial light modulator.

Advanced Materials and Device Architectures for Magnetooptical Spatial Light Modulators

AbstractFaraday and Kerr rotations are magnetooptical (MO) effects used for rotating the polarization of light in transmission and reflection from a magnetized medium, respectively. MO effects combined with intrinsically fast magnetization reversal, which can go down to a few tens of femtoseconds or less, can be applied in magnetooptical spatial light modulators (MOSLMs) promising for nonvolatile, ultrafast, and high‐resolution spatial modulation of light. With the recent progress in low‐power switching of magnetic and MO materials, MOSLMs may lead to major breakthroughs and benefit beyond state‐of‐the‐art holography, data storage, optical communications, heads‐up displays, virtual and augmented reality devices, and solid‐state light detection and ranging (LIDAR). In this study, the recent developments in the growth, processing, and engineering of advanced materials with high MO figures of merit for practical MOSLM devices are reviewed. The challenges with MOSLM functionalities including the intrinsic weakness of MO effect and large power requirement for switching are assessed. The suggested solutions are evaluated, different driving systems are investigated, and resulting device architectures are benchmarked. Finally, the research opportunities on MOSLMs for achieving integrated, high‐contrast, and low‐power devices are presented.

RGB Magnetophotonic Crystals for High-contrast Magnetooptical Spatial Light Modulators

Magnetooptical spatial light modulators (MOSLMs) are photonic devices that encode information in photonic waveforms by changing their amplitude and phase using magnetooptical Faraday or Kerr rotation. Despite the progress on both MO materials and switching methods, significant improvements on materials engineering and SLM design are needed for demonstrating low-power, multicolor, analog and high-contrast MOSLM devices. In this study, we present design rules and example designs for a high-contrast and large figure-of-merit MOSLM using three-color magnetophotonic crystals (MPC). We demonstrate for the first time, a three-defect MPC capable of simultaneously enhancing Faraday rotation, and high-contrast modulation at three fundamental wavelengths of red, green and blue (RGB) within the same pixel. We show using 2D finite-difference time-domain simulations that bismuth-substituted yttrium iron garnet films are promising for low-loss and high Faraday rotation MOSLM device in the visible band. Faraday rotation and loss spectra as well as figure-of-merit values are calculated for different magnetophotonic crystals of the form (H/L)p/(D/L)q/(H/L)p. After an optimization of layer thicknesses and MPC configuration, Faraday rotation values were found to be between 20–55° for losses below 20 dB in an overall thickness less than 1.5 µm including three submicron garnet defect layers. The experimental demonstration of our proposed 3-color MOSLM devices can enable bistable photonic projectors, holographic displays, indoor visible light communication devices, photonic beamforming for 5 G telecommunications and beyond.

Two Micron Pixel Pitch Active Matrix Spatial Light Modulator Driven by Spin Transfer Switching

We have developed an active matrix-addressed magneto-optical spatial light modulator driven by spin-transfer switching (spin-SLM) which has a 100 × 100 array pixel layout with a 2 µm pixel pitch. It has pixel-selection-transistors and logic circuits which convert serial data into parallel data to reduce input terminals. We have confirmed successful magnetization switching of each pixel by injecting a pulse current generated from the logic circuit, and its optical display capability by showing digital characters.

Active Matrix Magneto-Optical Spatial Light Modulator Driven by Spin-Transfer-Switching

We have developed a magneto-optical spatial light modulator (SLM) driven by spin-transfer-switching (STS), called spin-SLM, using a field-effect-transistor array active-matrix backplane, which plays an important role for developing large scale spin-SLM display devices. The fabricated spin-SLM device has 10 × 5 array pixel layout using magnetic tunneling junctions with sizes of 0.5 μm × 0.5 μm that are driven by a mosfet backplane. We have successfully demonstrated its electrical operation with current densities as low as 0.6 MA/cm2, one of the lowest levels ever achieved with STS devices, and confirmed changes in optical contrast by magnetization switching of the light modulation elements. We have demonstrated the potential for large-scale active-matrix spin-SLM technology as a potential enabler in the realization of electro-holographic displays.

Improvement of diffraction efficiency of three-dimensional magneto-optic spatial light modulator with magnetophotonic crystal

We have developed three-dimensional magneto-optic spatial light modulators (3D-MOSLMs) that use magnetic domains as submicron scale pixels to represent holograms. Our display system uses a submicron-scale magnetic pixel array on an amorphous TbFe film to create a wide viewing angle hologram. However, in previous work the reconstructed images had a low intensity and a low optical contrast; brightness of the reconstructed image was 4.4 × 10−2 cd/m2 with 532 nm illumination light at 10.8 mW/cm2, while display standard ISO13406 recommends 100 cd/m2 or more. In this paper, we describe our development of a 3D-MOSLM composed of an artificial magnetic lattice structure of magnetophotonic crystals (MPCs). The MPCs enhance the diffraction efficiency of reconstructed 3D images and reduce the power consumption for controlling the magnetic pixels by a light localization effect. We demonstrate reconstructed 3D images using the MPC and show significant brightness improvement.

A Magneto-Optical Spatial Light Modulator Driven by Spin Transfer Switching for 3D Holography Applications

We have successfully fabricated a basic magneto -optical spatial light modulator (MO-SLM) device driven by spin-transfer-switching (STS), which we call Spin-SLM technology. The SLM device is comprised of a one dimensional ten-pixel light modulation array (1 $\times$ 10 pixels) with a fine pitch of 1 $\mu{\hbox{m}}$ . The light modulation pixels were composed of Gd-Fe based giant magneto resistance (GMR) devices, with a free layer of Gd-Fe, an Ag spacer and a Co-Fe/Tb-Fe-Co pinned layer. The GMR devices were sandwiched by a Cu bottom and Indium zinc oxide top electrodes in order to inject current perpendicular to the film plane for switching. Incident light penetrating the transparent top electrode can be modulated due to its magneto-optic Kerr effect with the Gd-Fe free layer. The fabricated device cell size is ${\hbox{220}}\times {\hbox{300}} {\hbox{nm}}^{2}$ . We confirmed successful switching of the individual free layers, which was controlled by STS. We have also fabricated magnetic hologram patterns with the same magnetic materials used in the light modulation layer of the Spin-SLM device in order to determine its feasibility in display applications. The pixel pitch of the pattern was one micron and a reconstructed image by laser light was successfully observed with a wide viewing zone angle as 38 deg, which is nearly the same value expected from calculations. Although these patterns do not have an electrode to switch the magnetization direction, we confirmed the potential of Spin-SLM technology as a display device for 3D holography applications.

Strain-controlled MO Effect on Highly Bi-substituted Neodymium Iron Gallium Garnet Thin Films

Controlling magnetization of magneto-optical materials by voltage instead of electric current is expected to reduce power consumption and miniaturize functional elements in magneto-optical devices such as magneto-optical spatial light modulator. In this study, highly Bi-substituted neodymium iron gallium garnet, Nd0.5Bi2.5Fe4.5Ga0.5O12, thin film on gadolinium gallium garnet substrate prepared by metal organic decomposition method, which has excellent magneto-optical properties in visible wavelength region, was investigated as one of candidates for such devices. The thin film was cemented on a lead zirconate titanate polycrystal chip to apply external stress to the thin film. When the stress was applied, increase of coercivity has been observed by magneto-optical Kerr microscope due to reverse magnetostrictive effect. The result suggested the possibility of the Nd0.5Bi2.5Fe4.5Ga0.5O12 thin film as strain-mediated voltage controlled magneto-optical devices.

Colorization of Magnetic Hologram Images With Optical Space Division Method

We have developed magneto-optic spatial light modulators (MOSLMs) with submicrometer-size magnetic pixels for wide-viewing-angle holographic displays (3-D-MOSLM) that are driven by the thermomagnetic recording. The holographic images were reconstructed by the magnetic hologram pattern on the MOSLM. In this paper, we have studied colorization of reconstruction images of the MOSLMs using optical space division method. This method used some 3-D-MOSLMs to represent intermediate colors. The magnetic films were polycrystalline bismuth, dysprosium, and aluminum substituted yttrium iron garnet (BiDyYFeAlG) films with perpendicular magnetization. The thickness of BiDyYFeAlG films was designed for each wavelength. The MOSLM represented (3-D) images with intermediate colors that were synthesized 3-D images with red and green colors. In addition, tones of intermediate colors were represented by controlling intensity of each reference light. These results demonstrated that 3-D-MOSLMs have promise for full-colorized holographic 3-D displays.

Magneto-optic spatial light modulator with submicron-size magnetic pixels for wide-viewing-angle holographic displays.

Spatial light modulators (SLMs) with submicron-size pixels are promising devices for use in wide-viewing-angle glasses-free holographic 3D displays. In accordance with estimations, an SLM with 1μm pitch pixels can display holographic images over viewing angles of 30deg. In the present work, we have studied magneto-optic SLMs (MOSLMs) with submicron-size pixels for wide-viewing-angle holographic displays that are driven by thermomagnetic recording. Amorphous TbFe films were used as a magneto-optic material. The MOSLM with an 800nm diameter pixels array displayed wide-viewing-angle holographic images. These results demonstrated that MOSLMs with submicron-size pixels have promise for glasses-free holographic 3D displays.

Holographic images reconstructed from GMR-based fringe pattern

We have developed a magneto-optical spatial light modulator (MOSLM) using giant magneto-resistance (GMR) structures for realizing a holographic three-dimensional (3D) display. For practical applications, reconstructed image of hologram consisting of GMR structures should be investigated in order to study the feasibility of the MOSLM. In this study, we fabricated a hologram with GMR based fringe-pattern and demonstrated a reconstructed image. A fringe-pattern convolving a crossshaped image was calculated by a conventional binary computer generated hologram (CGH) technique. The CGH-pattern has 2,048 × 2,048 with 5 μm pixel pitch. The GMR stack consists of a Tb-Fe-Co/CoFe pinned layer, a Ag spacer, a Gd-Fe free layer for light modulation, and a Ru capping layer, was deposited by dc-magnetron sputtering. The GMR hologram was formed using photo-lithography and Krion milling processes, followed by the deposition of a Tb-Fe-Co reference layer with large coercivity and the same Kerr-rotation angle compared to the free layer, and a lift-off process. The reconstructed image of the ON-state was clearly observed and successfully distinguished from the OFF-state by switching the magnetization direction of the free-layer with an external magnetic field. These results indicate the possibility of realizing a holographic 3D display by the MOSLM using the GMR structures.

Polycrystalline magnetic garnet films comprising weakly coupled crystallites for piezoelectrically-driven magneto-optic spatial light modulators

We have investigated the magnetization process of the polycrystalline magnetic garnet films in order to determine the most suitable composition of garnet films for piezoelectrically-driven magneto-optic spatial light modulators (MOSLMs). For experiment, the bismuth–dysprosium–aluminum-substituted yttrium iron (Bi1.3Dy0.7Y1.0Fe3.1Al1.9O12) garnet films were deposited by an RF magnetron sputter and annealed at 700 °C in air. The annealing time was varied in a range of several minutes to control the grain size. The saturation magnetization, the remanent magnetization and the composition of the fabricated garnet films slightly changed versus the annealing time. Experiments showed that the coercivity and the grain size increased at longer annealing; the coercivity was larger for films with bigger grains. This work shows that garnet films with smaller coercivity are most suitable for controlling the magnetization of garnet and, correspondingly, the magneto-optical rotation of MOSLM pixels driven by piezoelectrics.

磁気光学材料と電気光学材料とを挟んだマイクロキャビティ膜の形成

We fabricated a microcavity -a magneto-optical (MO) film and an electro-optical (EO) film are sandwiched between two Bragg mirrors (BMs)- for development of magneto-optical spatial light modulators driven by electric field (e-MOSLMs). We used (Bi0.5Dy0.7Y1.8)3(Fe3.3Al1.7)5O12 as a MO film and (Pb91La9)1(Zr65Ti35)1O3 (PLZT) as an EO film. The samples showed enhanced Faraday rotation loops and electrical polarization loops, simultaneously. The X-ray diffraction patterns, MO and EO characteristics were measured. Experimental results showed that EO and MO films were successfully formed between BMs.

Magneto-optical and optical properties of Pt/Co GMR films with capping layer

As a light modulating device used in high resolution magneto-optical spatial light modulator (MO-SLM), giant magneto resistance (GMR) devises driven by spin-injection is promising. In this paper, we report on optical and magneto-optical (MO) properties of GMR films, Si/SiO2/bottom electrode/TbFeCo (9 nm)/Cu (4 nm)/(Pt/Co (6 nm))/X (X = Ta, Au, Pt (3 nm)). Kerr rotation spectra of those films with Ta, Au, Pt capping layer ranging between 260 – 700 nm have features similar to those of Pt/Co multilayers reported previously. However, peak positions and rotation angles are slightly different; peak positions of Ta, Au, and Pt are 4.1, 4.3 and 3.8 eV, respectively, and maximum Kerr rotations are 0.35, 0.25 and 0.23°, respectively. Optical constants measured by ellipsometry revealed that those values were changed due to the capping layers with a thickness of 3 nm. These results indicate that the non-magnetic layers should be mentioned as well as the magnetic layers to design MO properties of the light modulating devices for MO-SLM.

Novel magnetophotonic crystals controlled by the electro-optic effect for non-reciprocal high-speed modulators

We present a new type of electro- and magneto-optical spatial light modulators (e-MOSLMs) utilizing the concept of photonic crystals (PCs) – such e-MOSLMs have a microcavity structure. They comprise a magneto-optical (MO) and electro-optical (EO) constituents that can control the direction of the polarization plane, when applying voltage and/or external magnetic fields. Optical spectra of e-MOSLMs were analyzed by using the matrix approach. Calculations showed that e-MOSLMs can change the direction of polarization over a considerably large range of angles at relatively low power consumption and with no significant change of the light intensity.

Fabrication of Magnetophotonic Crystals with Paramagnetic Garnet Films

We fabricated magnetophotonic crystals (MPCs) used in electric field driven magneto-optical spatial light modulators (e-MOSLMs) with a paramagnetic garnet, which is transparent in the blue wavelength region and has a sufficient Faraday rotation angle for several applications including hologram data storage, three-dimensional displays, and optical correlators. The e-MOSLM is composed of two dielectric mirrors and one defect layer comprising magneto-optic (MO) material and electro-optic (EO) material, which controls the localized wavelength due to the change in the refractive index. The e-MOSLM utilizing MPCs allows us to use thin film paramagnetic materials, i.e., a terbium gallium garnet (TGG) and a terbium aluminum garnet (TAG), instead of a rare-earth iron garnet (RIG) because the direction of magnetization does not need to be controlled in the MO layer. We fabricated TGG thin films and MPCs with the structure of a SGGG substrate/(Ta2O5/SiO2)6/TGG/(SiO2/Ta2O5)6 by rf-magnetron sputtering. The sample produced localized peaks in the photonic band gap of the transmission spectra and an enhanced Faraday rotation angle. These results indicate that e-MOSLMs comprising an MPC with a TGG defect layer can be useful devices at the blue wavelength.