We fabricated a high-density, large-scale magneto-optical (MO) light modulator array to investigate its performance for holographic display applications. The modulator comprised a magnetic nanowire for light modulation using MO Kerr effect and two hard magnets (HMs) to control the switching property of the nanowire. The magnetization direction of the designated pixels in the array was controlled by the external magnetic field, unlike a spatial light modulator, which drives arbitrary pixels with cell selection backplane transistors. Magnetization of the light modulators with HMs can be reversed using a smaller magnetic field compared with those without HMs; this enables the formation of magnetic patterns by switching only the magnetization direction of the nanowire with smaller switching field; the pattern thus obtained is predetermined and not arbitrary. A diffracted beam in a magnetic stripe pattern displayed on the array was observed as spot patterns, and their spot position was consistent with a diffraction angle of the stripe period. We fabricated a magnetic hologram using a 10 k × 10 k pixel array calculated by computer-generated holography and successfully reproduced a holographic three-dimensional image with a wide viewing angle.
We present a phase compensation method for an optical phased array (OPA) to manipulate a sharply defined optical beam. Undesirable initial phase distribution caused by non-uniformity of fabrication processes and variation in the characteristics of phase shifters is measured by utilizing phase-shifting digital holography, where a light wave from a waveguide in arrayed waveguides is used as a reference wave and light waves from the other waveguides are used as object waves. The initial phases can be compensated by using the measured result without falling into local optimal solutions. A numerical simulation showed that the initial phases were correctly measured and compensated by using the proposed method. Applications of the proposed compensation method to a fabricated OPA with 16-channel electro-optic polymer waveguides results in obtaining a sharply defined optical beam.
We have been developing a magneto-optical (MO) spatial light modulator (SLM) with a narrow pixel pitch which enables reproducing holographic three-dimensional (3D) images with wide-viewing angle. In this study, we investigated a light modulation performance for reproducing holographic 3D image of an MO light modulation device array. The light modulation device array can easily realize a magnetic interference fringe pattern by applying an external magnetic field without a transistor (i.e. without fabricating the real MO-SLM). The pattern, however, is not rewritable. The array was designed with a pitch of 1 × 2 μm. When a reproducing illumination light was incident to the device, a holographic 3D image with wide-viewing angle of 36° in the horizontal direction and 18° in the vertical direction was reproduced. A clear holographic image was observed through an analyzer because the phase of the unnecessary diffracted light, generated by the pixel structure, shifts by 90° from that of the magnetically diffracted component by the MO effect. If the light modulation device array is fabricated on the transistor backplane, any magnetization pattern can be realized by injecting a current. The MO-SLM was shown as an effective device for realizing a holographic display with a wide-viewing angle.