Hiroyuki Ikeda

Real-time fingerprint sensor using a hologram

A holographic fingerprint sensor has been developed for a system that identifies a person by his or her fingerprints. The sensor uses a laser as its light source and consists of a light-conducting plate, which is a transparent glass plate with a plain grating-type hologram, and a focusing lens system just under the hologram. Since the sensor uses a plane-parallel plate, all the optical paths from each point of a fingerprint to the hologram are equal, and a bright fingerprint can be created without the trapezoidal distortion that is inherent in conventional prism-type sensors.

Wavelength independent grating lens system.

Grating lenses are small, light, and easily mass-produced. However, wavelength variation in the light source causes aberration and changes the focal length of the grating lens. Therefore, it has been difficult to use grating lenses in high-precision focusing optical systems that use a light source with wavelength variations (e.g., a diode laser). To solve this problem, we designed a grating lens system of two grating lenses, which substantially suppresses aberration and keeps the focal length constant at several tens of nanometers of variation. Each grating is made as a concentric circle. These lenses are arranged so that their centers are collinear. Diffraction angle changes due to wavlength variations are compensated for by the second grating. Our calculations confirmed that the allowable wavelength range was +/-15 nm or more for a numerical aperture (N.A.) of 0.5. We made a prototype of this grating lens system by electron beam lithography and confirmed that this lens system was not affected by limited wavelength variations.

Holographic Fingerprint Sensor

The fingerprint sensor that we developed uses a hologram. Two requirements are important for actual use; laser safety and high-contrast images. The illumination method we developed uses total reflection and a new type of detection. For safety, total-reflection lighting ensures that laser beams cannot enter an operators eyes. To obtain high-contrast images, signal and noise light were separated.

Aberration corrections for a POS hologram scanner

Use of an optically generated IZP (interferometric zone plate) hologram scanner enables highly accurate reading in a supermarket point-of-sale (POS) label reader with a simple optical arrangement. The laser beam spots on the scanning plane which construct the lattice scan pattern designed for the POS label reader cause severe aberrations when a conventional IZP hologram is used. A simple and effective method for removing the aberration is discussed from both the theoretical and experimental aspects, and the feasibility of the method is demonstrated. This method employs oblique-angle coherent plane-wave illumination in the IZP hologram recording process.

New holographic technology for a compact POS scanner.

A new holographic technique has been used to make a compact, accurate, and reliable point-of-sale scanner. Our holo-window technique is capable of changing the scan direction, collecting the signal light, and equalizing the scan velocity. At present, compact scanners tend to sacrifice read operation accuracy, speed, and reliability for size. Our technique permits the miniaturization of the optical system of a scanner while preserving performance. Using the holo-window, we have developed a new scanner that has a letter-size footprint and is only 8 cm high.

Straight-line scanning analysis of an all holographic scanner.

The all holographic straight-line scanner we developed for laser diode printers consists of only a holographic disk and a holographic lens. This simple scanner meets all scanning requirements for printers such as straight-line scanning, low scan line placement error, and beam focusing. It also overcomes the deterioration in scanning characteristics caused by the individual wavelength variations among laser diodes. We extensively analyzed how to obtain straight-line scanning based on different wavelengths and the generalized concept of virtual wavelength ratio enabling flexible scanner design.

Wavefront aberration correction analysis of an all-holographic straight-line scanner

This paper describes an all-holographic straight-line scanner consisting only of a holographic disk and a holographic lens. Scanning beam aberration correction was extensively analyzed using diffraction theory. A new technique for simultaneously optimizing the phase transfer functions of these two holograms is proposed, and a method to construct these two holograms using holographic recording is discussed. This technique led to a compact, high resolution holographic line scanner with a 1/e(2) scanning beam spot size of 100-120 microm for a scanning width of 252 mm. The radius of the disk at the center of illumination is only 28 mm.

Lensless Holographic Line Scanner

A new lensless holographic line scanner has been developed. The scanner consists of two holographic elements, a holographic disk with a flat-field focusing function and a newly devised holographic lens. The holographic lens was designed to circularize the laser diode beam, correct scanning beam aberrations, and reduce positioning error caused by mode hopping of a laser diode. In fabricating the holographic lens, chromatic aberration caused by the difference between the wavelength used for fabrication and that used for operation was successfully corrected by the use of plano-convex and plano-concave lenses. The lensless holographic scanner was found to have a scanning beam diameter of 170 um for a scanning width of 220 mm.

Compact Holographic Disk In All Holographic Line Scanner For Diode Laser Printers

We have developed a compact holographic disk for an all holographic line scanner for diode laser printers. The scanner consists of only a holographic disk and a holographic lens for laser scanning and focusing. No other optics are necessary. The holographic disk performs straight line scanning. The optical power is achieved by a holographic disk and lens. To make the disk more compact, while retaining a required scanning width and scanning beam, the increasing of deviation from a straight line and scanning beam aberration need be overcome. In this paper, we investigate the required phase transfer functions of the holograms to realize the compact holographic disk.

All Holographic Line Scanner For Use In Diode Laser Printers

We have developed an all holographic line scanner for use in diode laser printers. The scanner consists of only a holographic disk and a holographic lens for laser scanning and focusing. No other optics such as a collimating lens and f- θ lens are necessary. The holographic disk performs high precision straight line scanning. The focusing function is achieved by the compound optical power of a holographic disk and lens. To make the disk more compact, while retaining a required scanning width and scanning beam, the increasing deviation from a straight line and scanning beam aberration need be overcome. In this paper, we devised the method to obtain the required phase transfer functions of the holograms and discussed the holographic recording method to fabricate the holograms.