Design and optimization of terahertz directional coupler based on hybrid-cladding hollow waveguide with low confinement loss

We propose a design and optimization for directional coupling in terahertz hybrid-cladding hollow waveguide. It is composed of two square hollow waveguides which touch each other and are surrounded by a metallic layer. By employing the finite element method, the coupling performance and loss property are numerically investigated. Numerical results indi- cate that this directional coupler with hybrid-cladding can realize ultra-narrow-band coupling; it provides a low confinement loss performance： the confinement loss can reach as low as 6.27 × 10-5 cm- 1. Moreover, the further analyses of configura- tion and performance show that confinement loss and frequency range shift for the low-confinement-loss frequency regime can be realized and optimized by appropriately tuning the thickness values of the metallic and dielectric layer. In addition, through the further analysis of coupling performance, the possibilities of realizing ultra-narrow-band couplings in different frequency ranges are demonstrated. It is a powerful candidate for high precision optical fiber sensing, and communication in terahertz splitting fields.

STUDY ON Na_2O-GeO_2-SiO_2-PbO GLASSES USED AS THE CLADDING MATERIALS OF HOLLOW WAVEGUIDES FOR TRANSMITTING CO_2 LASER

In this paper a new kind of mid - infrared fiber material is reported. The reflective coefficients (R) of glasses in the system Na2O - ZnO - GeO2-SiO2-PbO have been measured-the refractive index becomes less than unity at 1180 - 900cm-1 range because of the existence of anomalous dispersion. The optical losses of hollow waveguides were calculated,the predicted losses at 940cm-1are 0. 65 and 0. 081B/ m as the inner diameter of fiber is 0. 5 and 1. 0mm respectively. The glasses can be used as the cladding materials of hol-low waveguides for transmitting CO2 laser from the measurements of characteristic temperatures, coefficient of expansion and chemical durability.

CALCULATION OF INFRARED OPTICAL CONSTANTS FOR CO_2 LASER HOLLOW WAVEGUIDE MATERIALS

A simple method was deduced for calculat-ing optical constant, optical loss and transmittance per meter of hollow-core optical fiber using data analysis method, ge-ometerical optical and electromagnetic theory. The method was used to study the Na2O-ZnO-GeO2-SiO2-PbO and Sb2O3 sysem. The glasses have nr<1 region. When the core diameter ao is 0. 5mm, the hollow waveguides of the Sb2O3-containing . glass is predicted with minimum loss of 0. 8 dB/m at 940cm-1

IR Spectra Analysis of SiO_2-TiO_2-GeO_2 Gel Glass of CO_2 Laser Transmitting Hollow Waveguide

Both titanium and germanium were introduced into silicon dioxide system by sol-gel method to move its region of anomalous dispersion caused by IR resonance absorption towards the wavelength of CO 2 laser.It is indicated by IR absorption spectra that as the content of SiO 2 decreases in this glass system TiO 2 and GeO 2 tends to exist in their own phases.As for the gel glass with a composition of 40SiO 2·30TiO 2·30GeO 2,when the temperature is below 600℃,germanium atoms exist mainly in Ge-O-Ge bonds.With the temperature increasing from 800℃ to 1000℃, titanium atoms in Si-O-Ti bonds almost transform into Ti-O-Ti bonds.Furthermore,a large number of Si-O-Ti and Si-O-Ge bonds formed when the temperature approaches 800℃,which makes a notable IR absorption band round the wavelength of CO 2 laser.Therefore, sol-gel based SiO 2-TiO 2-GeO 2 gel glass is a candidate material for CO 2 laser hollow waveguide.

INFLUENCE OF Sb_2O_3 AND PbO CONTENT ON GLASS PROPERTIES OF SiO_2-BASED FOR HOLLOW WAVEGUIDES

The reflective spectra of two glass systems of Na2O-ZnO-GeO2-SiO2-PbO(Sb2O3) were measured to study the effects of PbO and Sb2O3 on properties in SiO2-based glasses. The infrared reflective coefficients and anomalous dispersion regions change with the content of PbO and Sb2O3 respectively, furthermore the refractive indices (nr) of glasses are 0. 81 and 0. 84 at the wavelength of CO2 laser (940cm-1). The glasses of two systems can be used as the cladding materials of hollow waveguides for transmitting CO2 laser.

Ag/PMMA hollow waveguide for solar energy transmission

This paper describes an elaborate study on obtaining Ag/PMMA(polymethyl methacrylate)leaky hollow waveguide which has a large aperture and low loss in transmitting solar energy.Through analyses and comparison,a quartz capillary with the inner diameter of 2 mm was chosen as hollow waveguide.We used the xenon light source,which has the similar spectrum as the sunlight to test and analyze the performance of the Ag/PMMA leakage hollow waveguide.The results are consistent with the transmitted theory of the dielectric/metal leaky type well.Meanwhile,the Ag/PMMA leaky-type hollow waveguide in this work had good qualities.Therefore,it will be a satisfactory medium for solar energy transmission.

Fabrication and Characterization of Novel 3-D Hollow Waveguide for Widely Tunable Devices

We propose a novel 3-dimensional hollow waveguide with a variable air core for widely tunable devices.We observed a wavelength shift of 1.8 nm in a hollow waveguide resonator with a displacement of 6μm in an air core.

Fabrication Silver Film inside Silica Capillary

To study hollow waveguides for CO 2 laser transmission,a liquid-phase depositi on technique is applied to form a silver film inside silica capillary based on t he method of silver mirror reaction.Using this fabrication method,the optimum co mbination of different parameters is gained and hollow waveguides have been made successfully with a bore size of 1mm and a guide with length of as long as 2m o n self-producing apparatus.To meet quality silver film,a relative high temperat ure,low flowing speed and long time are adopted on the basis of low reactant con centration.The maximum transmission efficiency of hollow-core fiber without die lectric coating can be up to 85 percent and loss can be low to 0.5dB/m,maximum o utput power is 53W for stable 20mintues.