We present the fabrication of a kind of hexagonal and triangular cavity mold, which can cast Polymethyl Methacrylate
(PMMA) resonators and couplers. The mold is designed on (111) silicon wafer according to its crystal structure and
anisotropic etching properties in the etchant of ethylene diamine, pyrocatechol, and water (EDP/EPW), forming
sidewalls by six {110} crystal surfaces, which are perpendicular to the (111) plane and constitute precise hexagons and
triangles. The RIE-ICP etching is used to define the depth of the triangle and hexagonal cavities, and the following EDP
etching smoothes the sidewalls of cavities. Only high temperature EDP etching is proved to be able to get smooth
sidewalls. Before etching, the wafer is aligned to the right crystal orientation by pre-etched marks. The etched results of
different geometrical cavities are analyzed and discussed based on the crystal structure.
A triangulation distance sensor is constructed bending the wafer with metal hinges. On the Si wafer, elements are pre-aligned at the planer condition using the photolithography. The position sensitive detector (PSD), mirror, and alignment pit for a ball lens are prepared. 3-sensor array is integrated in 20x17x10 mm3 size. Compared with our previous study using polymer, the metal hinge stabilizes the long-term performance and the process. Optical
elements including LD chip are all included on the wafer. The demonstrated measurement range is 18-40 mm.
The triangulation distance sensor is constructed using the originally proposed wafer bending technique. Since the bending process is final in the fabrication sequence, the planer photolighography can be combined. On the Si wafer, the elements are pre-aligned at the unfolded planer condition. The position sensitive detector (PSD), mirror, and alignment pit for the collimation ball lens are prepared. The realized sensor substrate is 1.4mm in depth. Taking the advantage of the batch fabrication, 2x2 sensor array is prepared. The dynamic range of 4mm with ± 1% noise is confirmed.
KEYWORDS: Near field scanning optical microscopy, Silicon, Optical components, Optical storage, Near field optics, Particles, Near field, Waveguides, Actuators, Silica
Data-storage using near-field optical microscopy is a promising technology for the breakthrough of high-density optical disk memory since wavelength limit of conventional lens-optics is not applied. We have proposed a MEMS for the near-field optical data storage, which consists of integrated optical micro-probes and a micro media-translation-table. Three-dimensional lithography based on the bulk micromachining using resist spray coater is applied to the integration of waveguide, micro-pinhole tip, cantilever, and photodiode for the MEMS probes. The media-translation-table consists of the inverted scratch drive actuators (inverted SDAs) fabricated by surface micromachining.
KEYWORDS: Electrodes, Near field, Near field scanning optical microscopy, Photomicroscopy, Data storage, Etching, Near field optics, Head, Silicon, Low pressure chemical vapor deposition
We proposed a micro-translation-table to convey a recording medium to a near-field optical head. The microtranslation- table consisted of inverted scratch-drive-actuators (SDAs) actuated by electrostatic force. The microtranslation- table was fabricated on a silicon substrate with surface micromachining technology. The SDAs were arrayed in the same direction. An object was translated by mounting the object on the inverted SDA array. Each SDA can be operated with the step resolution of 1 nanometer order. Therefore, the SDA array is precise as well as powerful. We observed that a micro object was translated in the designed direction with the fabricated SDAs by applying AC voltage of ±600 V at 100Hz. The size of the SDA plate was 70 µm long, 70 µm wide, 1.3µm thick and with the bushing of 1 .5 µm high. We proposed a novel mechanism releasing the SDAs from the object by retracting them. Therefore, the X-Y translation is possible by placing the inverted SDAs in four different directions. When the SDA was retracted, the vertical displacement of the SDA plate was measured.
Si micromachining is a promising technique for fabricating several optical components. It is also indispensable for the low-cost assembly. We studied the Si micromachining for fabricating optical sensors and components. The Si crystalline etching was studied for generating the mirror surface smooth enough to be used in micro-laser-cavity. The etched Si mirror surface was transferred to the polymer replica by molding. Laser oscillation was demonstrated with the replicated solid-dye-micro-laser. The optical transmission structures were also fabricated by etching through Si wafer with the deep RIE, and used for new optical components. The integrated pinhole filter, position sensor and optical encoder were proposed. Integration of optical components with micro-actuator makes the optical system variable. The three-dimensional structures with actuators were fabricated by the new lithographic technique using spray resist coater. A tunable filter for telecommunication and a laser beam scanner with micro-mirror were fabricated.
Wavelength division multiplexing (WDM) systems can offer large capacity of the optical fiber communication. However, it requires the wavelength selective add-drop filters. A novel tunable wavelength filter, consisting of fiber grating and movable diaphragm, is proposed and fabricated by using a surface micro-machining technology. By moving the diaphragm at near the side polished fiber, the effective refractive index of the fiber core is controlled. This modulation of effective refractive index of the fiber core enables to control the wavelength of the fiber Bragg grating.
Here we demonstrate two fine optical components fabricated by replica-molding from anisotropically etched Si molds. One component is microcavity in micro-scales and the other is grating computer with a pitch of 500 nanometer. We investigated the feasibility of two methods for the microfabrication of the SI molds: one method is for making hundreds of micrometer size Si molds by using conventional photolithography and reactive ion etching technique combined with post anisotropical crystalline etching; and the other is for fabrication of micro periodic structure in optical waveguide was presented. Periodicities in excess of 5000 lines/mm were successfully transferred from silicon mold to polymer layer. The yield, repeatability and efficiency of the original master are very good. This technique can also be used to fabricate other nanometer-scale structures.
In this study, three novel optical sensors are described. They are the pinhole integrated with the surrounding photodiode, the transmission type position sensor fabricated on the Si mesh structure, and the photodiode thinner than the optical wave length in the active layer. These sensors have unique optical functions as well as photodetection. These devices offer new concepts and easy construction of the optical systems to realize applications, which have been complicated or laborious in the conventional way. They are automatic alignment of the pinhole, detecting many points along a straight line, and detecting the intensity profile of the interference of the standing wave respectively. Each sensor absorbs only a part of the incident light beam and the rest passes through the sensor and enables to detect the information of the incident light beam not disturbing the optical field very much. The almost light beam continues to propagate to the down stream, and the transmitted beam can be used for the further function.
A novel optical interferometer based on detecting the standing wave is described. The key device is a newly developed ultra- thin Si photodetector. The active layer of the ultra-thin photodetector is thinner than a half of wavelength of the incident light. Only a small part of the incident light is detected and the rest passes through the ultra-thin photodetector before being absorbed. Being inserted in the optical field, this ultra-thin photodetector can detect the thin intensity profile formed along the propagating direction of the laser beam. Taking advantage of this function, we have realized the vertical construction of a new interferometer detecting standing wave and the waveguide is not used, leading to the possibilities to achieve the integration of the interferometer by stacking planar components layer by layer and to array many interferometers together. The design, fabrication, and operation of this displacement sensor are discussed. The measured interference signal confirms the feasibility of the new sensor system. For one example of the arrayed interferometer, the dual ultra-thin Si photodetector is also fabricated with a phase shifter, and the displacement direction can be detected by comparing the phase of the two signals.
We fabricated 2D subwavelength structured (SWS) surface on crystal silicon and SiO2 substrates. The SWS surface patterns were generated by electron beam lithography and etched by SF6 fast atom beam. In the case of the silicon SWS surface with the period of 150nm, the grating had conical profile and the groove was approximately 350nm deep. The reflectivity was examined at the wavelengths between 200nm and 2500nm. At 400nm, the reflectivity decreased to 0.5 percent from 54.7 percent of the silicon substrate. The reflectivity was also examined for the incident angel with He-Ne laser light. Thus, it was shown that the silicon SWS surface prevented the reflection in the wide ranges of wavelength and incident angle. We also fabricated the hole type SWS surface and the column type SWS surface on silicon substrates. In both types, the grating period was 200nm and the grooves were approximately 275nm deep. Moreover, the SiO2 SWS surface with the period of 150nm was fabricated and the reflectivity was examined at the wavelengths between 200nm and 2500nm.
Subwavelength structured (SWS) surface directly patterned on a substrate performs as antireflection surface. We fabricated the two-dimensional SWS surfaces on crystal silicon substrates and tested the reflection properties for visible and infrared wavelengths. The SWS surfaces were patterned by electron beam lithography and etched by SF6 fast atom beam (FAB). In this work, the FAB process was first applied to fabricate the SWS surface. We fabricated the hole type SWS surface and the column type SWS surface. In both types, the grating period was 200 nm and the grooves were approximately 275 nm deep. The dependence of the reflectivity on the free-space wavelength between 200 nm and 2500 nm was examined. In addition, dependence of the reflectivity on the incident angle was examined with He-Ne laser light. From those experimental results, it was shown that the fabricated SWS surfaces, especially column type SWS surface, prevented the reflection in the wide ranges of wavelength (200 nm less than (lambda) 0 less than 2500 nm) and incident angle (5 degrees less than (theta) less than 60 degrees).
Novel thin film photodiode is proposed. The active layer is thinner than the wavelength of the incident light. A part of the incident light beam is detected and the rest passes through the thin film photodiode without the absorption. Being inserted in the optical field, this sensor can detect the intensity profile formed along the propagating direction of the laser beam. This function is applied to construct the new interferometer detecting the intensity profile of the standing wave produced by the incoming and the reflected laser beams.
KEYWORDS: Silicon, Photodiodes, Optical components, Beam splitters, Deep reactive ion etching, 3D applications, Position sensors, Spatial filters, Fabrication
Recent progress of the deep reactive ion etching explores several new applications of 3D structures of silicon devices. We have developed new optical and electrical devices having the penetrating holes to transmit the optical beam to the down stream. The transmission silicon position sensor having the divided cell type photodiode on the Si mesh structure is fabricated. The beam splitter is considered to be integrated in this device and a part of the incident light beam is detected by the photodiode. Using nearly same technique, the pinhole of the spatial filter surrounded by the divided cell type photodiode is fabricated to detect the relative position between the incident beam spot and the center pinhole.
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. In our previous study, the automatic alignment of the pinhole realized the accuracy of 1 micrometers using the feedback control based on the obtained position signal. To increase the alignment accuracy, the suitable design of the pinhole and the photodiode cell is necessary, since it decides the sensitivity to the laser spot position. The sensitivity is examined changing the separation length between the photodiode cells.
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