Fumio Yamagishi

Optical MEMS for photonic switching-compact and stable optical crossconnect switches for simple, fast, and flexible wavelength applications in recent photonic networks

We review the development trends and state-of-the-art technologies of large-port-count optical switches over the past decade. Practical implementation of optical switch fabrics is discussed in terms of optical switch architectures, optical configurations, port counts, switch elements, and so on. We describe compact and stable optical crossconnect three-dimensional microelectromechanical systems (3-D-MEMS) switches that are a key technology in recent photonic networks. To show how these enable simple, fast, and flexible wavelength applications in the photonic layer, we discuss the fast and stable MEMS switching by novel comb actuator and V-shaped torsion bar, compact optical configuration with roof-type mirror, stable switch housing with cubic structure, packaging techniques by tolerance expansion and simple procedures of the component assembly, MEMS mirror controller with fast and low power digital notch circuit, reliability by shock absorption, and field trials. In addition, we discuss the impact of these switches on system integration for recent metropolitan area networks and enterprise networks.

A rotational comb-driven micromirror with a large deflection angle and low drive voltage

We have designed, fabricated, and tested a V-shaped torsion bar for use with a comb-driven micromirror. This torsion bar suppressed undesired sticking of the comb teeth, and enabled a large rotational angle and a low drive voltage. We observed 5-degree rotation of a comb-driven micromirror with a drive voltage of 90 V.

Multichannel optical switch that uses holograms.

We propose a compact multichannel optical switch that uses holographic polarizing beam splitters and polarization switching devices and show its advantages and performance in an 8 x 8 nonblocking Banyan network.

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.

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.

Compact holographic head-up display

We have developed a head-up display (HUD) using a holographic combiner. A HUD superimposes information in front of the driver. The HUD must be unaffected by sunlight and should be small. A holographic combiner eliminates the VFD wash-out, and compensates for the distortion of concave mirror. The size of unit is reduced by folding the optical path. The image distance is extended to 1.2 m by using a powered element. The dimensions of the HUD unit is 155 X 135 X 77 mm, and the thickness of the optical unit is 40 mm.

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.