Hajime Hiraga

Lensed-taper launching coupler for small-bore, infrared hollow fibers

A new type of launching coupler for small-bore, hollow fibers, consisting of a lens and a tapered hollow waveguide, is proposed to increase the alignment tolerance between an input laser beam and small bore fibers. First, we designed the structural dimensions of the coupler by using a ray-tracing method. Then, a series of experiments employing tapered hollow waveguides made of Pyrex glass was performed to investigate the effectiveness of the new coupler. It is shown that the coupler has a high efficiency with attenuation of around 0.5 dB, especially when the inside of the taper section is coated with a polymer and silver film. In addition, we also show that the coupler has great tolerance for the transverse displacement of a waveguide axis, which gives a 0.1-dB loss increase for a 300-mum displacement.

Fabrication of silver hollow nickel waveguides with multiple inner dielectric layers by the outer-coating method

Silver hollow nickel waveguides have been fabricated based on the outer-coating method with multiple inner dielectric layers composed of germanium and zinc sulfide. By choosing the sputtering conditions for germanium and zinc sulfide properly, we have fabricated, for the first time to our knowledge, a low-loss waveguide with multiple inner dielectric layers for Er:YAG laser light transmission.

Lensed-taper launching coupler for high-energy Er:YAG laser

To achieve efficient launching from the Er:YAG laser light to hollow fibers, we have developed a lensed-taper coupler, which is composed of a lens and a tapered hollow section with an inner coating of a cyclic olefin polymer and a silver. Transmission properties of the coupler have been experimentally investigated for the high-energy Er:YAG laser.

Simplified technique of fabricating dielectric-coated silver hollow nickel waveguides by the outer-coating method of the liquid phase process

Abstract Considerable simplification has been made in the fabrication of rugged dielectric-coated silver hollow nickel waveguides. The new method is based on the outer-coating method and does not use any expensive equipment; such as RF-sputtering apparatus. In order to show its effectiveness; polyimide-coated silver hollow nickel-waveguides have been successfully fabricated with small attenuation.

Transmission properties of fluorocarbon polymer-coated silver hollow glass waveguide with tapered section for Er:YAG laser light

We have succeeded in fabricating low-loss fluorocarbon polymer (FCP)-coated silver hollow glass waveguides by using a liquid-flow coating method. The thickness of a FCP film is strongly dependent on the flow speed and the concentration of FCP solution. It is shown that the optimum condition exists for depositing the polymer to reduce the roughness of layer. The transmission loss of the fabricated waveguide with inner diameter of 700 micrometers is about 0.2 dB/m for Er:YAG laser light. An efficient tapered coupler with a lens is also investigated to couple the laser beam with large diameter to small-bore waveguides.

Characterization of copper waveguides for mid-IR radiation with applications in medicine

Copper hollow waveguides with an inner dielectric layer have been developed by using simple techniques of chemical etching and oxidation for the inner wall of the copper tubes. Transmission properties of hollow waveguides have been measured. It is shown, for the first time that a thin Cu2O layer is obtained by using chemical oxidation techniques. It is also shown that the thickness of a Cu2O layer can be controlled by the oxidation time.

Fabrication of robust hollow waveguide devices for Er:YAG laser light

We report transmission properties of two kinds of robust bent hollow stainless steel (St) waveguides whose inner surface is coated by the thin silver (Ag) and fluorocarbon- polymer (FCP) layers. The bore size of the waveguides is 700 micrometer and all types of waveguides have been fabricated based on the liquid phase process, i.e., the process of silver mirror reaction for the silver layer and liquid flow- coating method for the fluorocarbon polymer layer. Measurements have been conducted for the fixed bent FCP- coated Ag hollow St waveguides with the length of 3 cm and the bending angles of 20 and 70 degrees, respectively for Er:YAG laser light. It turned out that the losses of 0.8 dB and 0.7 dB have been attained for the above 20 degree and 70 degree structures, respectively. As the St tube itself has the very robust structure and high heat conductivity compared with the corresponding glass hollow waveguide, the waveguide devices proposed in this paper will open a new application in medicine.

Lensed taper coupler for hollow waveguides

A launching coupler for hollow fibers consisting of a convex lens and a tapered hollow-guide piece is proposed. We fabricated the coupler which has a conical-tapered, Pyrex glass tube as the tapered section. The bore size of the taper-guides input end is 3 mm and the output end is 0.7 mm which is the same as the size of coupled hollow fibers. The results of preliminary experiments show that the launching system has a large tolerance for the coupling condition between laser light and hollow fibers.

Fabrication of dielectric-coated silver hollow nickel waveguide with multiple inner dielectric layers for Er:YAG laser light transmission

Design and fabrication of silver hollow nickel waveguides have been conducted based on the outer-coating method with three inner dielectric layers composed of two zinc sulfide layers and a germanium layer. The sputtering conditions are optimized experimentally for depositing silver, germanium, and zinc sulfide layers and a low-loss waveguide with multiple inner dielectric layers has been fabricated, for the fist time, for Er:YAG laser light transmission.