Visualization of 50 MHz Surface Acoustic Wave Propagation Using Stroboscopic Phase-Shift Interferometry

A Stroboscopic phase-shift interferometry has been developed to visualize surface acoustic wave (SAW) propagation on SAW devices quantitatively. The developed interferometry is a Fizeau-type one with a multi-mode semiconductor laser diode and an optical isolator. With the laser light illuminating stroboscopically, observed interference intensity gives information about average displacements of the vibrations. Fifty MHz SAW propagation on the surface of the SAW device has been measured with the interferometry. Distribution of the SAW along the propagation path has been observed, whose amplitude is 3 nm (p-p). Repetition accuracy evaluated with the root mean square method is 1/2500 of the laser wavelength. The system is useful for estimating and improving performances of micro-devices.Presented at 1996 International Workshop on Interferometry (IWI ‘96), August 27-29, Saitama, Japan.     

Automatic Alignment of Optical System Using Shape Memory Alloy

Properties of the shape memory alloy of 29 μm thick Ni-Ti foil are investigated as an actuator to align optical elements. Since the intrinsic properties of the Ni-Ti foil are not satisfactory in reproducibility and hysteresis, a simple feedback control is used. A pinhole integrated with a surrounding position sensor is proposed to realize a confocal optical system having an automatic alignment function. Large displacement (mm) and precision at the level of the optical wavelength are found to be possible.Present at 1996 International Workshop on Interferometry (IWI ‘96), August 27-29, Saitama, Japan.     

Pitch-variable transmission-type bulk gratings driven by shape memory alloy actuator

This paper describes a novel pitch-variable transmission-type bulk grating fabricated by silicon micromachining technology driven by a shape memory alloy (SMA) actuator. The grating is specially designed to change the pitch easily with a small force and assured moderate stress by finite element method. Using deep reactive ion etching (deep-RIE) technology, the grating has a high aspect ratio more than 10. In the diffraction experiment, more than 10% extension ratio has been obtained. The SMA actuator has been installed to the grating. Due to the two-way shape memory effect, the translation mechanism is simple and is easily controlled.     

Micro-optical components based on silicon mold technology

Two micro-optical components fabricated by silicon molds are described. One component is micro-cavity in micro-scales and the other is sub-micron grating with a pitch of 200 nm. The feasibility of two methods for the micro-fabrication of the silicon molds is investigated: one method is for making hundreds of micrometer size silicon molds by using conventional photolithography and deep reactive ion etching (Deep-RIE) technique combined with wet etching; and the other is for fabricating sub-micron grating molds by using electron beam lithography and fast atom beam etching (FAB). Sub-wavelength structure is successfully transferred from silicon mold to poly-methyl methacrylate (PMMA) material. The yield and repeatability of the original master are quite good. This technique can also be used to fabricate other micro-scale structures.     

Si Micromachined Pinhole and Surrounding Photodiode for Incident Beam Position Sensing and Automatic Alignment

The spatial filter of a Si micromachined pinhole integrated with photodiodes is fabricated. The photodiode cells placed around the center pinhole can detect the relative position between the incident beam spot and the pinhole. The position signal obtained from a two or four cell type photodiode and position sensitive detector show the sensitivity even when the beam spot is near the center pinhole. Combined with the feedback control of the shape memory alloy actuator based on the obtained position signal, the pinhole is aligned automatically.     

Moiré signals in reflection

One of the recent applications of the moiré interferometric technique is in mask alignment for lithography. Usually it is necessary to use reflection moiré systems for alignment. We have analysed theoretically and experimentally the behaviour of moiré signals in reflection, as well as in transmission, with the gap as parameter. A periodic variation of the contrast of the moiré signals was observed when the gap was varied within the Fresnel region. The moiré signals were found to be superimposed on a background which varies with the gap. This variation of background was different for reflection and transmission. However, in both cases the alignment signal itself in the alignment method we are proposing, is independent of small variations in the gap between the two gratings.     

GaN-based nitride semiconductor films deposited on nitrified HfO2/Si substrate by molecular beam epitaxy

Nitrified HfO₂/Si substrate was used to grow GaN-based film with molecular beam epitaxy. Four-period InGaN/GaN layered structure and p/n junction were deposited on the nitrified HfO₂/Si. X-ray photoelectron spectroscopy (XPS) result shows that N was effectively incorporated into the HfO₂. The crystallographic relationship of the GaN/HfO₂/Si is GaN(0 0 0 2)∥HfO₂(1 1 1)∥Si(1 1 1). Temperature-dependent photoluminescence (PL), PL peak wavelength, PL peak intensity, and PL full-width at half-maximum of the p/n junction were investigated. Light-emitting diode was fabricated from the p/n junction. Red light was emitted at low voltage and yellow light was emitted when increasing the voltage.     

Broadband Antireflection Subwavelength Gratings for Polymethyl Methacrylate Fabricated with Molding Technique

We fabricated a two-dimensional subwavelength grating (SWG) on a polymethyl methacrylate (PMMA) film using a molding technique. A method of fabricating SWGs with high accuracy using a replica technique in an atmospheric environment was proposed. The SWG consisted of tapered gratings with a 200 nm period and a 200 nm deep groove. The reflectivity at wavelengths from 400 nm to 800 nm was measured and compared with the results calculated on the basis of rigorous coupled-wave analysis. At these wavelengths, the reflectivity decreased to approximately half that of the PMMA film.     

Bach Fabrication of Microlens at the end of Optical Fiber using Self-photolithgraphy and Etching Techniques

This paper describes a simple batch process for fabrication of microlens and microlens array at the end of an optical fiber or an optical fiber bundle using self-photolithography and etching techniques. A photoresist micro-cylinder was exactly formed at the core of the fiber end by exposing an UV light from the other end of the fiber and conventional development, rinse processes. A photoresist microlens was formed by thermal reflowing of the fiber at 170°C for 1 h. A measurement of transmissivity showed that the fabricated photoresist microlens is applicable for a wavelength that is longer than 450 nm. Alternatively, a glass microlens was fabricated at the core of the fiber by dry etching with an SF₆ gas using the photoresist microlens as a mask. The focusing of the lensed fiber was confirmed and simulation work showed that the lensed fiber could focus the light with a beam spot of 2 μm, numerical aperture (NA) of 0.285 and a depth of focus of 16 μm.     

Micro fluorescent analysis system integrating GaN-light-emitting-diode on a silicon platform

A micro fluorescent analysis system is proposed using silicon micromachining. GaN blue light-emitting diode (LED) monolithically integrated on a silicon substrate is used as a light source for the fluorescent analysis system. The blue light suits the excitation of several dyes used commonly in fluorescent analysis. Silicon photodiode (Si-PD) that matches the visible and near infrared fluorescent wavelengths of dyes is integrated on a silicon substrate. Polydimethylsiloxane (PDMS) micro-channels are also stacked for flowing dye-sensitized liquid. Therefore, the proposed system is an integrated system that can be composed on a silicon platform, i.e. a bottom layer of Si-PD, a middle layer of GaN-LED on silicon substrate and a top layer of micro PDMS channel. An aperture is opened into the GaN-LED layer by deep reactive ion etching to create a ring-shaped GaN-LED and a through-hole for detection. The light from the ring-shaped GaN-LED in the middle layer excites the dye-sensitized liquid in the top micro-channel layer. The fluorescence emitted from dye is detected by the Si-PD on the bottom layer at an angle larger than 90 degrees from the direction of excitation. Therefore, the detection optics consist basically of a dark-field illumination optical system. In order to evaluate the performance of the integrated system, fluorescence of fluorescein isothiocyanate (FITC) solution flowing in the micro channel is measured. From the measurement, the noise, sensitivity and limit of detection in the fabricated system are evaluated for FITC dye to be 0.57 pA, 1.21 pA μM(-1) and 469 nM, respectively. From these results, a compact fluorescence analysis system is demonstrated.