Seiichi Kashimura

Loss Reduction of GeO2-Doped Silica Waveguide with High Refractive Index Difference by High-Temperature Annealing

The effect of a GeO2-doped core on high-temperature annealing has been investigated to reduce the propagation loss of a waveguide device with high refractive index difference (Δ). A SiO2–GeO2 waveguide core was prepared on a fused silica substrate by rf magnetron sputtering and reactive ion etching. With increasing the annealing temperature, the roughness of the core side-wall gradually disappears and the rectangular core gradually becomes rounded. The effect of smoothing and rounding the cores was a significant reduction of the scattering loss, and moreover, it enabled the complete embedding of narrow gaps between cores in cladding glass using conventional plasma chemical vapor deposition. The propagation loss of the waveguide with a Δ of 1.5% was 0.07 dB/cm at 1.55 µm wavelength, the effect of which was demonstrated in the fabrication of an arrayed-waveguide grating demultiplexer.

High-silica guided-wave optical devices

A high-silica embedded channel waveguide with low loss and high precision structure has been fabricated using low-temperature glass formation, lithography, reactive ion etching, and a flame hydrolysis glass deposition processes. Fusion splicing of the waveguide and single-mode fiber has also been achieved by CO/sub 2/ laser beam irradiation. Furthermore, this waveguide structure can be applied to many devices such as multi/demultiplexers, star couplers, and hybrid integration of optical active components.<<ETX>>

Dispersion compensator using a compact arrayed-waveguide grating with a dispersion-adjusting structure

A dispersion compensator consisting of a compact arrowhead arrayed-waveguide grating (AWG) with a dispersion-adjusting structure has been proposed. Dispersion parameters can be adjusted by filling lens-shaped deep trenches with refractive index-controlled resin. Dispersion compensators based on an 8ch, 12.5GHz-spacing AWG have been fabricated. The dispersion-adjusting structure consists of three double concave trenches located near the focal plane in a second slab waveguide. Dispersion compensators with total dispersions of 234ps/nm and 1103ps/nm were fabricated by using resins with refractive indices of 1.51 and 1.405, respectively.

Planar lightwave circuit dispersion compensator using a compact arrowhead arrayed-waveguide grating

An ultra-compact chromatic dispersion compensator, based on a compact arrowhead arrayed-waveguide grating (AWG), has been proposed and fabricated. A dispersion compensating mirror, monolithically integrated into the second slab of the AWG, modulates the phase of each spectral component of the input light. The use of the compact arrowhead structure provides a dispersion compensator with a small footprint. The chromatic dispersion, the bandwidth and the insertion loss of the dispersion compensator based on the 8ch, 12.5GHz-spacing high-resolution arrowhead AWG are 123ps/nm, 70GHz and 7.5dB, respectively. Dispersion compensation experiments for 40Gbit/s, NRZ and RZ signals have been successfully demonstrated.

Thermo-optically switchable drop filter with photoinduced Bragg grating on silica-based waveguide

Summary form only given. In summary, a novel switchable drop filter has been proposed and demonstrated with photoinduced Bragg grating on a silica-based waveguide with the heater power consumption of 0.124 W (a driving current is 60 mA). Good switching responses were obtained by 0.4-nm shifts of Bragg wavelength.

Fabrication and investigation of fast response variable optical attenuator on silica substrate

We have developed fast response variable optical attenuator (VOA) on silica substrate by analyzing thermal response using equivalent circuit. The response time and power consumption are 2.5 msec and 100 mW respectively

Fabrication and characterization of non-doped SiO2 cladding layer for polarization-insensitive silica waveguide by using plasma enhanced chemical vapor deposition

We developed a technique for fabricating the cladding layers of silica waveguides and used this technique to fabricate an arrayed waveguide grating (AWG). The technique consists of two deposition process of non-doped SiO2. The first deposition process is a two-step deposition process combining plasma-enhanced chemical vapor deposition (PECVD) using tetraethylorthosilicate (TEOS) gas with an etching-back non-doped SiO2 by RF sputtering, and the second is a deposition process by means of PECVD using SiH4 gas. The non-doped SiO2 cladding layer must meet requirements of a thickness over 10 µm without cracking and a refractive index the same as that of fused silica. By using this fabrication technique, these requirements are satisfied and narrow core-to-core gaps are successfully filled with non-doped SiO2 without producing voids. The developed silica waveguide with non-doped SiO2 cladding has a propagation loss of 0.07 dB/cm and the developed AWG has a polarization sensitivity of 0.001 nm, which is one order of magnitude lower than that of existing AWGs.

Fabrication of waveguide-type add/drop grating filter by radio-frequency magnetron sputtering to insert GeO2-SiO2 cladding layers

We developed a waveguide-type add/drop grating filter that has GeO2–SiO2 cladding layers inserted into the conventional waveguide structure by rf-magnetron sputtering, to suppress cladding mode coupling loss. Optimizing the fabrication conditions for the GeO2–SiO2 core and cladding layers enabled us to fabricate a waveguide-type add/drop grating with low loss and without voids in the narrow core-to-core gaps. Our results showed that this waveguide, having high quality GeO2–SiO2 films and a unique structure, had a propagation loss of 0.18 dB/cm and suppressed the cladding mode coupling loss around 1550 nm to approximately 0.3 dB, compared with the 5.0 dB loss of conventional waveguides.