Fumio Koyama

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We demonstrate a metal nano-aperture GaAs vertical cavity surface emitting laser (VCSEL) for sub-wavelength optical near-filed probing, which exhibits the strong plasmon enhancement of both optical near-fields and voltage signals with forming a metal nano-particle in the nano-aperture. The threshold current is as low as 300microA, which shows a potential of(More)
We demonstrate single-mode fiber transmission distance enhancement up to 120 km of a directly-modulated injection-locked VCSEL modulated by a 10Gb/s NRZ signal. Injection locking induced data pattern inversion of the VCSEL causes adjustable chirp, which greatly extends reach. Both experiments and simulations are shown to explain this phenomenon.
A tunable Bragg reflector based on a 3D hollow waveguide (HWG) has been proposed. Ultrawide tuning ranges of 152 nm and 164 nm, respectively, in Bragg wavelengths of TE and TM modes of the Bragg reflector have been presented experimentally. With a 3D hat-shaped HWG, a giant birefringence of 0.012 has been demonstrated that can be varied with a variable air(More)
We propose a novel design for multi-wavelength arrays of vertical cavity surface-emitting lasers (VCSELs) using high-contrast gratings (HCGs) as top mirrors. A range of VCSEL cavity wavelengths in excess of 100 nm is predicted by modifying only the period and duty-cycle of the high-contrast gratings, while leaving the epitaxial layer thickness unchanged.(More)
Robust and tolerant single-transverse-mode photonic crystal GaInAs vertical-cavity surface-emitting lasers are fabricated and investigated. Triangular lattice patterns of rectangular air holes of various etch-depths are introduced in the top mirror. The stable single-transversemode operation is observed with a large margin of allowance in the etch depth (t(More)
A hollow optical waveguide is proposed in which light can be confined in an air gap between a distributed Bragg reflecting (DBR) mirror and a high-index-contrast grating (HCG) mirror. Because of the combined effect of vertical (DBR) and lateral (HCG) periodicity, the proposed hollow waveguide shows a small modal birefringence on the order of 10 À4. In(More)
We propose a novel hollow-core slow light waveguide using high contrast grating (HCG). Light propagates in air along a path bounded by two HCG layers. A strong interaction between the light and the HCG leads to a large group index, and thus the slow light effect. Waveguide loss and group index can be optimized separately by tuning the HCG and waveguide(More)
We demonstrate a novel hollow waveguide optical switch composed of an multi-mode interference (MMI) coupler with a variable air core. The numerical simulation and experiment of the proposed optical switch is carried out for investigating the operation of the switch. Switching operation can be obtained by the mechanical displacement of the air core of an MMI(More)
—A tunable bandpass filter is constructed using pat-terned mirrors and a diffraction grating to serve as an optical equalizer. The frequency response of an intensity-modulated light source can be tailored by the passband profile of the equalizer to achieve a larger 3-dB bandwidth. We demonstrate that the 3-dB bandwidth of two LiNO 3 modulators is increased(More)