Yuzo Ono

Antireflection effect in ultrahigh spatial-frequency holographic relief gratings

An interpretation model for low reflectivity in ultrahigh spatial-frequency holographic relief gratings is proposed. The model is based on the concept that the grating effective index, caused by grating ultrahigh spatial frequency, is graded in the depth direction and forms an antireflective constitution similar to the multilayer coating. Numerical results show that a sinusoidal grating is antireflective over wide groove depth, wavelength and incident angle ranges, and a grating with nearly triangular section, having a circle arc index distribution, has a very low reflectivity, >10(-4)%. Reflectivity vs groove depth, obtained experimentally for a holographically recorded photoresist grating, agrees fairly well with the numerical results.

Dual wavelength optical head for 0.6 mm and 1.2 mm substrate thicknesses

A dual wavelength optical head for 0.6 mm and 1.2 mm substrate thicknesses, containing 635 nm and 785 nm laser diodes, has been developed. Holographic optical element (HOE) type optics and variable magnification type optics are described. For both types of optics, high light power efficiency is obtained, which is suitable for random access memory (RAM) applications. Moreover, the use of 785 nm light makes it possible to read compact disc-recordable (CD-R). A readout operation for a quadruple density CD and a conventional CD has been successfully demonstrated.

Compact optical head using a holographic optical element for CD players

A small-size lightweight optical head using a holographic optical element (HOE) for optical disk systems has been developed. This optical head consists of only four optical elements. The HOE has the three optical functions required for an optical head: splitting the reflected beam; focusing error detection; and tracking error detection. A new optical configuration has been designed for this optical head to remove the influence of wavelength variation in the light source. The offset signal in the tracking error signal, which causes unstable operation, has been reduced by introduction of the holograms which are used only for detecting tracking error.

Multi-Beam Optical Disk Drive for High Data Transfer Rate Systems

A multi-beam optical disk drive, which improves the data transfer rate for magneto-optical disk systems, has been developed. The optical head employs an image rotator for tracing several tracks simultaneously. Four-channel parallel read/write operation has been achieved, and a digital video recording system with a data transfer rate of 22 Mbps has been realized. Real-time data verification at a linear velocity of 33 m/s has been demonstrated. Double track density recording, using a crosstalk canceler, has also been accomplished, and a 5.1×10-5 bit error rate has been obtained.

Holographic laser scanners using generalized zone plates

Aberration properties in holographic zone plates for use in laser scanners are investigated. A generalized holographic zone plate is proposed. To generate the zone plate hologram, holographic optical product operations between plural coherent spherical waves, are applied. When spherical waves, N in number, are applied, aberration can be corrected in a scan length magnification equal to or less than N(2). Experimentally, a remarkable aberration correction effect for this hologram generation method is demonstrated for over 50-cm scan length. The configuration and features are described for the developed point-of-sale (POS) scanner employing generalized zone plate holograms.

Holographic Optical Element with Analyzer Function for Magneto-Optical Disk Head

A new holographic optical element, made of a birefringent LiNbO3 substrate, has been developed for magneto-optical, disk heads. The element includes the analyzer function required for magneto-optical signal detection, in addition to focusing and tracking error signal detection functions. The analyzer function was realized by introducing a birefringent grating structure, using proton exchange method. More than 15dB extinction ratios were obtained for the fabricated element.

Holographic disk with high data transfer rate: its application to an audio response memory

This paper describes a memory realized with a high data transfer rate using the holographic parallel-processing function and its application to an audio response system that supplies many audio messages to many terminals simultaneously. Digitalized audio messages are recorded as tiny 1-D Fourier transform holograms on a holographic disk. A hologram recorder and a hologram reader were constructed to test and demonstrate the holographic audio response memory feasibility. Experimental results indicate the potentiality of an audio response system with a 2000-word vocabulary and 250-Mbit/sec bit transfer rate.

Free-space optical bus using cascaded vertical-to-surface transmission electrophotonic devices

A free-space optical bus, which consists of cascaded optical switch devices, is proposed. The switch devices have multiple functions, such as data transmission, data detection, and data repetition. Basic interconnection characteristics were measured with vertical-to-surface transmission electrophotonic devices. Optical switching energy as low as 150 FJ and up to 4 MHz and a relatively high datatransmission rate, i.e., more than 20 MHz, were obtained. Connection cascadability and extendibility were confirmed.

Holographic disk scanners for bow-free scanning.

Scan loci of holographic disk scanners are investigated. Bow-free scanning conditions are derived for holographic disk scanners employing generalized holographic zone plates. Hologram disk design and a holographic technique to generate the generalized holographic zone plates are described. Experimentally, scanning with less than ±100-μm bow deviation is demonstrated for a 40-cm scan length by using this disk design method.

Reflection polarizing holographic optical element for compact magnetooptical disk heads

A reflection polarizing holographic optical element with sinusoidal surface-relief has been developed for compact magnetooptical (MO) disk heads. The element has the polarizing beam splitter function as well as the focusing and tracking error signal detection functions. To produce the sinusoidal surface-relief structure with photolithography, a new fabrication process, which includes procedures for converting a rectangular profile into a sinusoidal profile, is introduced. Replicas were also fabricated with high replication fidelity using the photopolymerization method. The developed element was used in an MO disk head. A 57-dB C/N ratio, which is sufficient value for practical use was achieved for a 1-MHz readout signal.