Teruhiro Shiono

Rectangular-apertured micro-Fresnel lens arrays fabricated by electron-beam lithography.

Rectangular-apertured micro-Fresnel lens arrays are proposed. These lens arrays have been fabricated by an electron-beam writing system specially developed for the fabrication of microoptical devices. It is experimentally demonstrated that the lens arrays showed uniform focusing characteristics, and that each lens exhibited a diffraction-limited focusing characteristic with efficiency of 74%.

Reflection micro-Fresnel lenses and their use in an integrated focus sensor.

Blazed reflection micro-Fresnel lenses and their use in an integrated focus sensor are proposed. Theoretical analysis indicates that the optical characteristics of reflection Fresnel lenses can be improved compared with a conventional transmission micro-Fresnel lens. These reflection Fresnel lenses were fabricated using electron-beam lithography and exhibited the diffraction-limited focusing characteristics with 71% high efficiency. The focus sensor has a folded optical path and includes a beam splitter integrated with thin film components, such as a reflection elliptical Fresnel lens and a quadrant photodetector. The reflection elliptical Fresnel lens in the focus sensor exhibiting excellent astigmatic characteristics agreed with the theoretical results, and the focus error signal was detected. This sensor can be developed as the optical head of an optical disk system.

Two-photon absorption recording in photochromic diarylethenes using laser diode for three-dimensional optical memory

We have studied two-photon absorption (TPA) recording in photochromic diarylethenes for a three-dimensional (3D) optical memory, and demonstrated the TPA recording for the first time using a laser diode with a pulse width of 2 ns without a thermal influence. In comparison with the recording sensitivity by a femtosecond fiber laser, it was found that the peak power can be greatly reduced and the TPA sensitivity has squared characteristics depending on the pulse width range from 94 fs to 2 ns. Finite difference time domain (FDTD) analysis of optical intensity through refractive pits suggests that 3D recording in multilayered medium is more suitable, because optical aberrations induced by the lens effect of refractive pits are greatly reduced and the reflectance from a pit is improved, in comparison with that in a bulk medium.

High-efficiency blazed diffractive optical elements for the violet wavelength fabricated by electron-beam lithography

Blazed diffractive optical elements (DOEs) were studied for the violet wavelength by electron-beam lithography. By optimizing electron-beam writing parameters and electron-dose distributions, we fabricated eight kinds of grating (period A = 10-0.54 microgm) with excellent blazed structure. It has been demonstrated that the measured diffraction efficiency values agreed well with the rigorous theoretical ones. For the fine period of 0.54 microm, we confirmed a peak appearance of 75.6% (TE) experimentally. A wave aberration as small as approximately 0.01 lambda (rms) was obtained for the first-order diffracted wave from the fabricated DOEs. Blazed DOEs for the violet wavelength could be used as key devices in a high-density optical disk pickup of the next generation.

Planar-optic-disk pickup with diffractive micro-optics

An integrated optical-disk pickup with a diffractive planar micro-optic system is proposed. In this device, the beam follows a zigzag optical path inside a glass substrate that is used as a light guide. To fabricate off-axis diffractive optical elements, we have recently developed an electron-beam writing system with a curve-pattern generator. It is demonstrated that a transmission off-axis objective microlens, a reflection twin-focusing beam splitter, and reflection layers were integrated on a glass substrate, and such a diffractive planar micro-optic system exhibited an excellent focusing performance and operated forfocus-error signal detection, as designed.

Diffraction-limited blazed reflection diffractive microlenses for oblique incidence fabricated by electron-beam lithography

Blazed reflection diffractive microlenses potentially have many uses. The fabrication accuracy and the optical characteristics of these microlenses can be greatly improved compared with transmission diffractive microlenses. The reflection microlenses for oblique incidence can be flexibly used without a beam splitter. The functions of the electron-beam writing system that we developed have been expanded so that the diffraction-limited microlenses for oblique incidence can be fabricated. It is demonstrated that the fabricated microlens exhibits diffraction-limited focusing characteristics with 78% high efficiency at a large oblique angle of 30 degrees . These microlenses could be used as key devices in planar optics and optical interconnections.

Blazed reflection micro-Fresnel lenses fabricated by electron-beam writing and dry development

The microfabrication of a blazed reflection micro-Fresnel lens (RMFL) using electron-beam writing and dry development is proposed and demonstrated. The electron-beam-written resist film made of polymethyl isopropenyl ketone and an aromatic azido compound achieved the blazed structure by O(2) plasma development. The surface roughness of the RMFL was improved without the bridge and scum. The fabricated RMFL exhibited the diffraction-limited characteristics. A high efficiency of 71% was obtained at a period of 10 microm. The margin for the electron-beam writing condition to achieve high efficiency was much broader than in the conventional process. This process would be effective for the fabrication of blazed RMFLs and other grating components.

Computer‐controlled electron‐beam writing system for thin film micro‐optics

A computer‐controlled electron‐beam writing system has been developed. The system has various functions for fabricating thin film micro‐optical devices. The ability of 0.1‐μm patterning, smooth circular and elliptic scanning of an electron beam, and excellent blazing characteristics have been demonstrated. The system has been confirmed to be an efficient means for fabricating micro‐optical devices.

Microexplosion recording in spin-coated polymer films including ZnO nanoparticles for three-dimensional optical memory

As a microexplosion recording material, we propose polymer films including ZnO nanoparticles (ZnO polyester composite) for write-once multilayered recording media. These media with the ZnO composite material can be fabricated by a spin-coating method and can be read at the violet wavelength of 0.405 µm. By the electromagnetic analysis of diffraction loss, we clarified the pit design and the optical performance for void formation recording. From the results of experiments performed using three kinds of mode-locked pulsed lasers (pulse widths of 150 fs, 16 ps and 6 ns), with a clear reflection microscope image of submicrometer pits, the microexplosion sensitivity was confirmed to be greatly improved by 14, 38 and 50 times, respectively.

High-efficiency diffractive micromachined chopper for infrared wavelength and its application to a pyroelectric infrared sensor

We have developed a diffractive micromachined chopper (DMC) for an IR wavelength of ~10 mum. This device operates mechanically by movable reflection grating beams. It modulates the diffraction efficiency by controlling the displacement of grating beams by an electrostatic force. For a CO(2) laser beam, a high modulation efficiency of 84% with an -0.8-dB small insertion loss was obtained by detecting 0th-order diffracted light. A novel pyroelectric IR microsensor with a DMC and a diffractive multilevel Si microlens was proposed and it demonstrated the detection of human existence.