Osamu Hanaizumi

Numerical analysis of eigenmodes and splice losses of thermally diffused expanded core fibers

Field distributions and far-field patterns (FFPs) of the eigenmodes of thermally diffused expanded core (TEC) fibers are clarified by numerical analysis. The spot size of the TEC fiber is estimated by using the FFP that can be measured more easily than the near-field pattern (NFP). Splice losses of two TEC fibers are analyzed numerically considering a single or composite effect of gap, offset, and tilt. The results are useful for estimating isolations of fiber-integrated optical isolators and insertion losses of other fiber-integrated type optical devices. Splice losses considering multiple reflection between two endfaces of the TEC fibers with gaps are also analyzed numerically. This is useful for the design of fiber-integrated tunable wavelength filters.

Wide Y-junctions with low losses in three-dimensional dielectric optical waveguides

This paper proposes a simple structure (antenna coupledY- junction) which reduces radiation losses ofY-junctions in 3-D optical waveguides by decreasing refractive indexes near the branching regions. A principle to reduce radiation losses and a design theory are presented for the newY-junction by using geometrical optics. It is theoretically shown that losses of the properly designed 3-DY-junctions can be reduced by around an order of magnitude compared to those of conventional ones when the branching angles are large.

Low radiation loss Y-junctions in planar dielectric optical waveguides

Abstract A simple structure is proposed to reduce radiation losses of Y-junctions in planar optical waveguides by decreasing refractive indices near the branching regions. The losses of the properly designed Y-junctions can be reduced by around an order of magnitude compared with those of conventional ones when the branching angles are large.

Propagation of light beams along line defects formed in a-Si/SiO2 three-dimensional photonic crystals: Fabrication and observation

We have fabricated optical waveguides in three-dimensional (3D) photonic crystals and observed propagation of light beams. Light beams with wavelengths of 1.15 μm propagate along the line defects formed in the 3D photonic crystals. The 3D photonic crystals consist of a-Si/SiO2 multilayers laminated alternately by rf bias sputtering on a periodically hollowed silica substrate with a triangular lattice. The pit diameter is 0.2 μm and the pitch of the lattice is 0.5 μm. The thickness of each laminated layer is 0.2 μm. Line defects are formed normal to the surface by laminating a-Si/SiO2 multilayers with ten periods on the substrate in which the corrugation patterns have been omitted in a certain area corresponding to the core. The measurements of transmittance normal to the surface show that the wavelength of 1.15 μm used in observation of propagation is in the passband for the one-dimensional periodic region corresponding to the core and in the stop band for the 3D periodic region corresponding to the cladd...

Blue-light emission from sputtered Ti:SiO2 films without annealing

Blue-light emission from Ti:SiO2 sputtered films was observed at room temperature without annealing and it could be seen by the naked eye. The peaks of photoluminescence spectra were located at 3.03–3.05 eV and full width at half maximum ranged from 0.38–0.40 eV, which were almost the same in samples having different energies of absorption edge. SiOx layers may contribute to emission, which are interfacial regions between Ti particles and surrounding SiO2 medium, and the size of Ti particles may affect the efficiency of emission.

Fabrication of an expanded core fiber having MFD of 40 /spl mu/m preserving outer diameter

A thermally-diffused expanded core (TEC) fiber with the mode field diameter (MFD) of 40 /spl mu/m has been fabricated by improving the diffusion process using an electric furnace. The outer diameter of any TEC fiber is preserved and the excess loss (normal-TEC-normal) is as low as 0.1 dB.<<ETX>>

Fabrication of 3D photonic crystals by autocloning and its applications

3D photonic crystals can produce a number of fascinating optical devices utilizing the band gap, the dispersive passband, and unisotropic band structure. We previously proposed a process for fabricating a 3D periodic nanostructure which can behave as photonic crystals. The key technique in the process is the deposition of a multilayer by bias sputtering replicating periodically a corrugated layer pattern, which is named the autocloning effect. This paper reviews our recent works on 3D photonic crystals: the mechanism of the autocloning effect, propagation analysis in the 3D photonic crystal by an FDTD method, and applications such as plane-normal waveguides or wavelength-selective filters.

Observation of gain in an optically pumped surface-normal multiple-quantum-well optical amplifier

An optically pumped surface-normal optical amplifier with a 100-period InGaAs/InGaAlAs multiple quantum well is fabricated, and a signal gain exceeding 2 dB is observed for what we believe to be the first time. A laser diode with the wavelength lambda of 1.45 microm is used for pumping. An optical single-pass gain as high as 2.4 dB is obtained at lambda = 1.585 microm with 65-mW pumping (spot diameter 12 microm).

a-Si:H/SiO2 multilayer films fabricated by radio-frequency magnetron sputtering for optical filters.

We examined the optical properties of a-Si:H/SiO2 multilayer films fabricated by radio-frequency magnetron sputtering for optical bandpass filters (BPFs). Because of the high refractive-index contrast between a-Si:H and SiO2, the total number of layers of an a-Si:H/SiO2 multilayer can be relatively small. We obtained an a-Si:H refractive index of 3.6 at lambda = 1550 nm and its extinction coefficient k < 1 x 10(-4) and confirmed by Fourier-transform infrared spectroscopy that such small k is influenced by the Si-H bonding in the film. We fabricated a-Si:H/SiO2 BPFs by using in situ optical monitoring. Thermal tuning of a-Si:H/SiO2 BPF upon a silica substrate was also performed, and a thermal tunability coefficient of 0.07 nm/degree C was obtained.

Buried ion‐exchanged optical waveguides with refractive index profiles controlled by rediffusion

New buried optical waveguides whose refractive index profiles can be controlled by rediffusion are formed by the ion exchange and rf sputtering technique. A buried waveguide with a nearly symmetric refractive index distribution and a new slowly tapered structure are fabricated.