|We study several opto-mechanical systems. Optical sensors for monitoring the
mechanical motions (linear displacement and rotational angle etc.) are
fabricated by silicon micro machining. In addition, micro optical components and
micro-actuators are also studied for the devices and systems used in optical
telecommunication and optical information processing. Optical scanner, optical
switch, optical attenuator are studied.
Moreover, new optical phenomena in micro/nanometer regions are also studied. Micro lasers, sub-wavelength gratings, variable photonic crystals are investigated. New optical materials such as GaN are also studied.
Micro-optics and sensors
We are working on several researches on optical sensors for monitoring mechanical motions. Laser interferometer, optical encoder, optical position sensors are investigated. In the interferometer study, we propose a new micro interferometer using thin film photodiode to detect standing wave interference.
Optical linear and angular encoders are studied for industrial applications. Photo sensors for the encoders are specially designed and fabricated based on semiconductor micro-fabrication processes. In principles, "Moire effect" and "Grating imaging effect" are used in the displacement sensing.
Optical MEMS and integration
Optical MEMS are studied for the applications of optical telecommunication and information interface. In the optical telecommunication, several optical components such as micro-lens, beam-splitters and micro-mirrors are integrated to realize special optical functions. Advantageously using silicon micro-machining, optical components can be integrated with micro-actuators. The micro actuators are used to realize tunable functions. Optical systems are not only miniaturized but also stabilized. We fabricated several types of fiber-optic switches, variable optical attenuators, and tunable filters. We developed a new three-dimensional photolithography using resist spray for the integration of optical components. In order to integrate the components in several optical systems, we propose a bulk-micromachined optical bench fabricated by the three- dimensional photolithography. Bar-code reader and optical data storage system are developed.
In addition to the industrial applications, we carry out some basic studies in the research field of nano-optics. Using electron beam lithography, subwavelength gratings (moth eye structure) are fabricated on photo detectors and light emitting diodes. The detection and emission efficiencies are improved. The reflectance of silicon surface decreases to one hundredth of the original surface. The emission efficiency increases by more than 30%. Photonic crystal devices with tunable function by micro actuator are also studied. Micro dye laser is developed using silicon-molding technique. Near field optics are also studied. An integrated scanning near field optical microscope probe is fabricated for high-density optical data storage.
New materials for optics
GaN semiconductor is studied for a light source of opto-mechatornic systems. Combining GaN light source with Si MEMS, all the components necessary for micro optical systems can be integrated on one chip. Using molecular beam epitaxy, GaN crystals are grown on Si substrate for monolithically integrating the light source on Si-MEMS. We propose some integrated optical systems such as light source with beam steering mechanism.