Koichi Imanaka

Low-wavefront aberration and high-temperature stability molded micro Fresnel lens

A high-diffraction efficiency (>50%), small lens diameter (0.5 mm phi ), short focal length (1 mm), and thin (0.25 mm) molded micro Fresnel lens suitable for compact optical devices is discussed. The device is fabricated by means of a photopolymerization process using a UV-curable resin. By adopting glass as the substrate, low-wavefront aberration (<0.04 lambda , RMS value) and diffraction-limited focusing characteristics have been obtained at ambient temperatures between 20 degrees C and 100 degrees C. These characteristics are superior to those in a conventional aspherical plastic lens.<<ETX>>

Hybrid normal-reverse prism coupler for light-emitting diode backlight systems

For the first time to our knowledge, a hybrid normal-reverse prism coupler was formed on the bottom surface of a light guide in a LED backlight system to achieve a thin, lightweight, LED backlight system. The hybrid prism coupler (HPC) simultaneously exhibits two functions: extraction of guided light from the light guide and focusing the radiated light from the light guide, corresponding to the optical functions of the prism and diffusive sheets used in conventional LED backlight systems. Therefore, using a HPC eliminates the prism and diffusive sheets that have been indispensable optical elements in conventional LED backlight systems, which consequently reduces the thickness of the LED backlight system by 40% compared with conventional systems.

Super-compact dual-axis optical scanning unit applying a tortional spring resonator driven by a piezoelectric actuator

A novel super compact dual axis optical scanner composed of a miniature resonator driven by a piezoelectric actuator and a micro-collimated light source using a micro Fresnel lens has been developed. The scanner is able to scan an optical beam in two directions with a scanning angle of more than 20 degrees, and its dimensions are 30 mm X 20 mm X 20 mm.

Migration‐enhanced epitaxy on a (111)B oriented GaAs substrate

AlGaAs layers with a featureless specular surface morphology were grown successfully on an exactly (111)B oriented GaAs substrate by migration‐enhanced epitaxy (MEE) even at growth temperatures below 500 °C. We have also observed reflection high‐energy electron diffraction (RHEED) intensity oscillation of AlGaAs on a (111)B oriented substrate by MEE. The single quantum well (SQW) is prepared by MEE on a (111)B and a (100) substrate simultaneously, and the photoluminescence intensity from (111) SQW is shown to be about 50 times higher than that from (100) SQW.

Low-loss RF MEMS metal-to-metal contact switch with CSP structure

We reported a novel RF-MEMS switch with an extremely low insertion loss of-0.5 dB and a high isolation of-30 dB up to 10 GHz. The switch was fabricated ultra compact size of 1.8/spl times/1.8/spl times/1.0 mm/sup 3/ with Chip Scale Packaging (CSP) structure utilizing wafer level packaging technology. The wafer level packaging with frit glass makes it possible to mount the device directly on the circuit board without any extra outer package and bonding of wires, which deteriorate the RF characteristics. The package is made from cavitied glass wafer as cap-material and frit glass as seal-material. The device wafer consists of single crystal silicon actuators, a base glass substrate and a cap glass.

Low‐temperature (350 °C) growth of AlGaAs/GaAs laser diode by migration enhanced epitaxy

Migration enhanced epitaxy, in which group III and group V elements are deposited onto the substrate alternately under ultrahigh vacuum, has been employed to reduce AlGaAs growth temperature. By optimizing growth conditions of AlGaAs, molecular‐beam intensities, and substrate temperatures between 600 and 250 °C, an AlGaAs/GaAs single‐quantum‐well laser diode has been fabricated successfully at very low temperature of 350 °C for the first time. A broad area laser diode emitting at 780 nm shows the threshold current density of 2.5 kA/cm2 at room temperature under the pulsed operation.

Low thermal expansion polymide buried ridge waveguide AlGaAs/GaAs single‐quantum‐well laser diode

A novel ridge waveguide laser diode has been developed in which the ridge is buried in a newly developed polyimide with a low thermal expansion coefficient close to that of AlGaAs which reduces the thermal stress to the junction and simplifies the wafer processing. A planar configuration, which is suitable for optoelectronic integration and an episide down mount for high‐power operation, has been achieved by an etch‐back process. Under cw operation, a low threshold current of 15 mA at 25 °C, a characteristic temperature T0 of 145 K, and maximum power output higher than 30 mW/facet have been obtained in a molecular‐beam‐epitaxial‐grown graded‐index separate confinement heterostructure single‐quantum‐well laser emitting at 780 nm.

Microcollimated laser diode with low wavefront aberration

A microcollimated laser diode (MCLD) utilizing a 1-mm short focal length, phi 0.5-mm small diameter micro Fresnel lens (MFL) as the collimating lens is discussed. The MCLD is assembled with a 780-nm quantum-well laser diode dice and an MFL in the smallest commercially available laser package. The radiated laser beam from the MCLD has a power of higher than 2 mW at 50 mA driving current, a phi 2 mm beam diameter with a nearly Gaussian intensity profile, and a low wavefront aberration of less than lambda /14 (RMS value) measured at a 1-m distance.<<ETX>>

GaAs double quantum well laser diode with short-period (AlGaAs)m(GaAs)n superlattice barriers

A short‐period (AlGaAs)m(GaAs)n superlattice has been applied to the barrier layers in a single and a multiple quantum well structure prepared by molecular beam epitaxy in order to improve the interface quality. With a 38 A thin GaAs quantum well without employing aluminum, a low threshold current density of 260 A/cm2, a high characteristic temperature (T0) of 205 K, and a high differential quantum efficiency of 75% have been achieved in a double quantum well ridge waveguide laser diode emitting at 780 nm.

Two-dimensional silicon micromachined optical scanner integrated with a photodetector

A highly miniaturized optical scanner integrated with a photo detector has been developed for miniaturization of scanning type of optical sensors. The scanner is fabricated by silicon micromachining technologies and is driven by a piezoelectric actuator. It is capable of two dimensional scanning and photo detection. The scanning angle is over 40 deg X 30 deg and the photo detecting sensitivity is 0.49 A/W for 680 nm wavelength light.