Satoshi Mitsugi

Microoptical Two-Dimensional Devices for the Optical Memory Head of an Ultrahigh Data Transfer Rate and Density Sytem Using a Vertical Cavity Surface Emitting Laser (VCSEL) Array

The parallel optical memory system has important advantages for realizing both a fast data transfer rate and high memory capacity since it is based on multibeam recording and a smaller spot size using the vertical cavity surface emitting laser (VCSEL) and a nanoprobe array. The concept, theoretical analysis and fabrication process for the integrated VCSEL nanoprobe array head are discussed with emphasis on the micro-optical issues such as the improvement of optical efficiency by microlens focusing. The flat-tip nanoprobe structure was successfully prepared with the small metal aperture of 150 nm and 1.25% optical throughput using metal aperture Si or GaP semiconductor nano-probes. To realize better optical throughput in the integrated VCSEL, a special nanoprobe array and a microlens array were developed. The microlens array was prepared using a thermal reflow process of the photoresist and lens shape pattern transfering to the semiconductor nanoprobe bottom face by dry etching. Since this two-dimensional array system requires three-dimensional micro-optical adjustment to focus a very small spot on the recording media, this research can provide guidelines for new micro-optical components in future technology.

Fabrication of Micro-Pyramidal Probe Array with Aperture for Near-Field Optical Memory Applications

A new optical memory system is urgently required to realize high memory capacity and fast data transfer rates in the coming multimedia era. To overcome the current capacity barrier of far-field techniques, a novel near-field optical memory of evanescent wave has been proposed using a vertical cavity surface emitting laser (VCSEL) probe array, consisting of the VCSEL array as a light source and the micro-pyramidal probe array as an evanescent wave exit. The design and fabrication for the aperture probe array were developed in this research. An array of up to 10,000 pieces was prepared successfully using microfabrication processes, including photolithography, silicon wet etching, thermal oxidation and thin film deposition. The pyramidal probes in the array show little variation in size and are sufficiently sharp to apply to the near-field recording head. The probe tip has a small size of 100 nm and the aperture has a diameter of around 150 nm. A smaller aperture can be fabricated with more careful control of the experimental procedures, including the etching process and thermal wet oxidation.

Numerical Simulation of Readout Using Optical Feedback in the Integrated Vertical Cavity Surface Emithing Laser Microprobe Head

The vertical cavity surface emitting laser (VCSEL) characteristics of voltage change in the integrated VCSEL microprobe head have been analyzed using the finite difference time domain (FDTD) method and laser rate equations. The reflectance difference of 9.7% from the phase change media was calculated with the GaP microprobe having a 150 nm aperture, resulting in the voltage change of 2.9 mV in the VCSEL. The 30 dB CNR of the readout signal was evaluated with the relative noise of VCSEL and it was found that the CNR could increase with further improvement of the VCSEL structure and the reflectance difference in the media.

Design and Lasing Operation of Micro-Arc-Ring Lasers

A micro-arc-ring cavity (MARC) laser is proposed for microphotonic integrated circuits. This device is based on tightly confined optical waves by a total internal reflection in a lateral microcavity. We present a basic design concept of a MARC laser for low-threshold operation and for transverse mode control. We have fabricated a 0.98 µ m GaInAs/GaAs strained quantum well MARC laser by using direct electron beam lithography and reactive ion beam etching. The reflectivity of the etched reflector was estimated to be ~ 74% from the threshold.

GaInAs/GaAs Micro-Arc Ring Semiconductor Laser

We have proposed a micro-arc-ring-cavity (MARC) laser, which consists of an etched concave reflector and two plane reflectors. The resonant optical wave can be tightly confined by total internal reflection in the lateral microcavity. We present the theoretical basis of a MARC laser, focusing on the design issue for low threshold operation, transverse mode control and light output coupling. We also present some experimental lasing characteristics of 0.98 µ m GaInAs/GaAs strained quantum well MARC lasers fabricated by direct electron beam lithography and reactive ion beam etching.

Fabrication of InP vertical facets by reactive ion etching and sidewall roughness evaluation for semiconductor microcavities

A dry etching technique is important for microfabrication of photonic devices, including semiconductor microcavities. Smooth etched sidewalls are needed to form low loss semiconductor microcavities and optical waveguides, because rough surfaces cause noticeable scattering losses. So far, scattering losses in etched reflectors or waveguides caused by interface roughness have been theoretically studied. Scattering losses should be dependent on not only the amplitude of roughness but also its correlation length; however the spatial frequency of the roughness of etched surfaces has not been discussed yet. In this paper, we present a spatial frequency analysis of the measured sidewall roughness of dry etched InP facets, and the correlation length of the sidewall roughness is estimated from the power spectrum to discuss its effect on reflectivities of the etched facet.

A design of polygonal micro-ring cavities for photonic integrated circuits

Summary form only given. In this paper, we present a model of polygonal shaped ring cavities for reducing a scattering loss as well as for resonant mode control. An optimal cavity design will be discussed to realize a high finesse micro-ring semiconductor cavity.

RIBE micro-fabrication of semiconductor photonic devices for micro-photonic integrated circuits

The authors present the reactive ion beam etching (RIBE) micro fabrication of miniature photonic devices, such as micro ring lasers, corner reflector arrays and star couplers. The key issue is to develop nanometer semiconductor fabrication processes with low induced damages. The proposed concept might be helpful for the size reduction in large scale integrated photonics.