Yukako Takizawa

Imaging Characteristics of Transmission-Type Volume Holographic Imaging Elements

The imaging characteristics of volume holographic imaging elements (VHIEs) are evaluated numerically and experimentally. To evaluate the imaging characteristics of a VHIE, a volume holographic imaging simulator between one-dimensional regions is fabricated. In the simulator, the propagated light in free space and the diffracted light at the VHIE are calculated by numerical Fresnel propagation and Kogelniks coupled wave theory, respectively. The imaging characteristics of VHIEs for imaging between point sources and between one-dimensional regions are evaluated. Furthermore, we numerically and experimentally investigate the influences of Bragg-mismatched light on imaging characteristics along the direction of the optical axis of a VHIE.

Fabrication of an integrated holographic imaging element for a three-dimensional eye-gaze detection system

We evaluate the imaging characteristics of an integrated optical imaging element that is used to obtain images from opposite directions in one imaging sensor for a three-dimensional eye-gaze detection system. The element consists of a transmission-type holographic imaging element, a reflection-type holographic imaging element, and a noise reduction filter. In the evaluation of the imaging characteristics, modulation transfer functions of both the reflection-type and the transmission-type holographic imaging elements are evaluated. Results indicate that both holographic imaging elements have enough resolution, even under white-light illumination conditions, for eye-gaze detection. We also demonstrate the simultaneous detection of images by an artificial eye and objects by using the integrated element under white light or sunlight.

Background Noise Reduction in an Integrated Volume Holographic Imaging Element for Eye-Gaze Detection

In a three-dimensional (3D) eye-gaze detection system with an integrated volume holographic imaging element (VHIE) and two image sensors, human eye gaze is detected by analyzing both the reflected images of two eyes of a human and the transmitted images that the human is watching. To make the detection of the reflected images of the eyes more effective, a noise filter for removing the background noise is fabricated and is then attached to the integrated VHIE. The results obtained by the noise reduction technique are presented.

Vibration measurement in non-rigid test environment with speckle interferometry

We propose a new method for vibration measurement in non-rigid test environment with electronic speckle pattern interferometry (ESPI). The ESPI is useful for non-contact, real-time analysis of vibration. This method needs rigid test environment, however. When the interferometer and a vibration surface are on a non-rigid table or their environments are separated, especially at manufacturing areas, high-amplitude, low-frequency noise fluctuation overwhelms a vibration signal and the amplitude fringes disappear. We use electronic shutter function of a TV camera and reduce exposure time of an image sensor. With the time reduction, we may extract an image from many input images, during whose acquisition time noise fluctuation turns back and its magnitude is so small that the vibration signal goes to be included in the image. We accumulate the images and increase the contrast of the amplitude fringe map. We evaluated usefulness of this method with circular saw vibration. The interferometer and the saw are fixed on a rigid board and the noise fluctuation is electronically superposed on the vibration signal with sine wave. This method is successful for a fluctuation amplitude of 60μm.

Optimized integrated volume holographic imaging element for 3D eye-gaze detection

Optimization of integrated volume holographic optical imaging element (IVHIE) is investigated. IVHIE can image eye and the scene to be gazed on an image sensor. A filter is attached to the IVHIE to remove the transmitted background scene and then is optimized.

Optical Switching Elements Using Controllable Defect Modes in One-Dimensional Photonic Crystals

Optical switching elements using controllable defect modes in one-dimensional photonic crystals are proposed. The transmittance in a defect mode is markedly changed by modifying the local structure of the photonic crystals. Such modification is implemented by micro electro mechanical systems (MEMS) or optical manipulation. We present two methods of changing the transmittance in the defect mode. The spectral transmittance and peak wavelength in the defect mode, and the extinction ratio between on and off states are numerically analyzed using plane waves and Gaussian beams. Numerical results show that the extinction ratio is about 40 dB in 43 layers of SiO2 and air with a thickness of 6.8 µm.

Imaging characteristics of holographic imaging element for eye-gaze detection

A holographic imaging element (HIE) by use of a transmission-type holographic optical element is evaluated by a numerical simulator. To design HIE and evaluate its imaging characteristics, we fabricate a holographic imaging simulator between one-dimensional arbitrary spaces. In the simulator, two calculation methods that are free space propagation and diffraction at the holographic element are used. The propagated light between the input plane and a transmission-type HIE, or between the HIE and the observation plane is calculated by numerical Fresnel propagation. The diffracted light at the HIE is calculated by Kogelniks coupled wave theory. By using the simulator, imaging characteristics of a pair of point sources and one- dimensional regions are evaluated.