We report on design and lasing characteristics of GaN vertical-cavity surface-emitting lasers (VCSELs) with an
elongated cavity for use in uniform elements of a two-dimensional (2D) laser array. Calculations of VCSELs with the
elongated cavity taking into account the wavelength dispersion of the refractive index show that the transverse mode
spacing can be significantly narrower than the gain spectrum with a small tradeoff of the differential quantum efficiency.
The result clearly shows that the elongated cavity is robust against the thermally induced peakshift of the gain spectrum,
and thus preferable for use in elements of density packed laser array for which uniform operation of each element is
crucial. The VCSEL with the elongated cavity fabricated by the wafer thinning technique operates under current
injection by using highly reflective distributed Bragg reflectors (DBRs) made of transparent ZrO2 and SiO2 film stacks. Together with high reflectivity and wide stop band of the DBR, the elongated cavity of 6 μm (36λ) allows multimode lasing oscillation with a mode spacing of 2.9 nm, which is one order of magnitude narrower than the gain spectrum. In addition, we demonstrate a 5x5 GaN VCSEL array.
A 405 nm LDs crystallization method of a-Si has been applied to the processing of bottom gate (BG) type
microcystalline (μc-) Si TFT for the first time. We have successfully demonstrated superior I-V characteristics of BG μc-
Si TFTs. In order to verify the validity of our process, we performed a heat flow simulation and compared commercially
available lasers having wavelengths of 405, 445 and 532 nm. The simulation explained well the experimental results and
showed that the wavelength is a crucial factor on uniformity, energy efficiency, and process margin and the 405 nm gave
the best results among the three wavelengths.
We successfully demonstrated a multi-striped InGaN-based laser diode (LD) array with an optical output power of 6.3 W
under continuous wave operation. The LD array was operated on a conventional metal package without any cooling
system. The world highest power operation as InGaN LD array is attributed to thermally optimized layout design taking
advantage of highly efficient wide-striped emitters.
We proposed the integrated optical pick-up with a catadioptric system which has a super resolution effect and with ferrofluid cooling structure. All of optical elements such as an objective lens, a laser diode and a photodetector are integrated into the moving part of the actuator to miniaturize the pick-up. Laser beam is double reflected between first reflecting region on top of the objective lens and second reflecting region on a reflecting mirror placed under the objective lens to miniaturize the optical system. The moving part having the laser diode and the photodetector needs high cooling performance to realize the optical system. We developed the cooling structure with ferrofluid held between a magnet and a coil of the actuator. Ferrofluid works as a cooling path to conduct the heat in the moving part towards external parts. We achieved the results as described below. Temperature of the laser diode is approximately equivalent to conventional pick-up against the heat of about 200mW generated in the moving part. Thermal resistance of 120 degree/Watt is available for practical use. The cooling structure leads the results of optical characteristics. As a super resolution effect, spot size of the integrated optical pick-up with wavelength of 660nm and a numerical aperture (NA) of 0.55 is equivalent to spot size of conventional pick-ups with wavelength of 660nm and a NA of 0.65. Focal and tracking error signals for servo control are available for practical use. The cooling performance is enough for realizing the integrated optical pick-up.