Katsusuke Tajima

Optical loss property of silica-based single-mode fibers

The optical loss property of silica fibers has been investigated theoretically and experimentally based on their Rayleigh scattering and absorption losses. The Rayleigh scattering loss for fibers has been estimated using Rayleigh scattering coefficients and power distribution in the fiber. The Rayleigh scattering coefficients are measured for preforms prepared for fiber fabrication and are discussed for GeO/sub 2/-doped and F-doped glasses. The relationship between the optical loss and fiber parameters is clarified. Moreover, the loss increase due to residual stress which occurs during the drawing process is simulated. The optical loss limitations for GeO/sub 2/-doped and pure silica core fibers are shown. >

Low-loss photonic crystal fibers

The lowest loss has been achieved in two types of photonic crystal fibre (PCF) due to an improvement of fabrication process. Optical loss at 1.55 /spl mu/m wavelength was 1 dB/km and the Rayleigh scattering coefficient was 2 dB/km /spl mu/m/sup 4/ in the type 2 PCF. These results suggest a possibility of low-loss PCF comparable to that of conventional single-mode fibers.A low-loss photonic crystal fiber (PCF) is an important transmission media for future transmission systems. We describe an optical attenuation of a PCF and discuss a possibility of a low-loss PCF comparable to that of a conventional single-mode fiber

A new single-polarization optical fiber

In the single-polarization optical fiber, two isolated stress-applying parts contribute to radiate one of the two orthogonal polarization modes due to the asymmetrical geometric-index effect in addition to a stress-induced birefringence effect without bending the fiber. The loss spectra for x- and y-polarizations and the length dependence of the crosstalk show that the present fiber exhibits single-polarization characteristics. >

Low Rayleigh scattering P/sub 2/O/sub 5/-F-SiO/sub 2/ glasses

The Rayleigh scattering and infrared absorption losses of P/sub 2/O/sub 5/-F-doped silica glass, which is a candidate material for ultra-low-loss optical fiber, were investigated experimentally. The Rayleigh scattering loss of 8.5 wt.% P/sub 2/O/sub 5/ and 0.3 wt.% F-doped SiO/sub 2/ glass is found to be 0.8 times that of pure silica glass. It is also found that the infrared absorption property of P/sub 2/O/sub 5/-F-SiO/sub 2/ glass is almost the same as that of pure silica glass. The minimum loss for the proposed composition is estimated to be 0.11 dB/km at 1.55 mu m wavelength, and 0.21 dB/km at 1.3 mu m wavelength. >

Design of viscosity-matched optical fibers

An optical fiber with a homogeneously viscous cross section can be designed for an arbitrary index profile by utilizing two kinds of dopant which have different effects on host material viscosity. Examples of designs are shown for silica-based fibers when GeO/sub 2/ and F are used as the dopants.<<ETX>>

Imperfection loss reduction in viscosity-matched optical fibers

An optical fiber with a homogeneously viscous cross section is fabricated by utilizing two kinds of dopant which have different effects on host material viscosity. It is confirmed experimentally that matching the viscosity between the core and cladding greatly reduces imperfection loss.<<ETX>>

Viscosity of GeO/sub 2/-doped silica glasses

The viscosity of GeO/sub 2/-doped silica glasses is experimentally evaluated and found to be expressed as a function of the monoexponential form /spl eta//sub 0/ exp(/spl minus/A/spl Delta/e), where /spl eta//sub 0/ is the viscosity of pure silica glass, A is a positive constant, and /spl Delta/e is an equivalent relative-index difference that is introduced for a silica glass with nonuniform dopant distribution in its cross section. The constant A for GeO/sub 2/-doped silica glasses is found to be about 0.5, which is much smaller than that for fluorine-doped silica glasses and has almost no temperature dependence between 1400/spl deg/C and 2200/spl deg/C. >

Transmission loss of a 125- mu m diameter PANDA fiber with circular stress-applying parts

The transmission loss of a 125- mu m diameter polarization-maintaining and absorption-reducing optical fiber (the PANDA fiber) with circular stress-applying parts (SAPs) has been investigated. The loss is calculated at a 1.55- mu m wavelength for SAPs consisting of B/sub 2/O/sub 3/ doped silica glasses. The experimental measurements show the validity of the analysis. It is shown that, when the half distance between SAPs is more than 2.2 times the core radius, the additional transmission loss due to B/sub 2/O/sub 3/ absorption is less than 0.05 dB/km with normalized frequency of 2.2 to 2.4 and a B/sub 2/O/sub 3/ dopant concentration of 20 mol.%. As a result, it has been confirmed that transmission losses of 125- mu m diameter PANDA fibers can be comparable to those of commercially available single-mode optical fibers. >

Cutoff wavelength measurement in a fiber with improved bending loss

In this letter, we describe a novel method for evaluating the cutoff wavelength in a single-mode fiber based on far-field pattern (FFP) measurement under different launch conditions. We show that the proposed method can be applied not only to conventional fiber but also to a special fiber with superior bending loss performance. We also discuss the relationship between the FFP measurement conditions and the measurement accuracy of the proposed method.

Low-loss optical fibers realized by reduction of Rayleigh scattering loss

Summary form only given. The Rayleigh scattering coefficient of GeO/sub 2/-SiO/sub 2/ core single-mode fiber drawn at low temperature and without increasing the drawing tension was reduced. The minimum loss of 0.16 dB/km was obtained in the GeO/sub 2/-SiO/sub 2/ core fiber at a drawing temperature of 1800 C.