Kazuyuki Shiraki

SBS threshold of a fiber with a Brillouin frequency shift distribution

The SBS threshold of a fiber with Brillouin frequency shift distribution along its length is investigated theoretically and experimentally. We obtain a simple equation for estimating the SBS threshold from the effective gain coefficient, which is calculated by using the Brillouin frequency distribution along its length. The dopant concentration dependence of the Brillouin frequency shift are measured for fibers with an F and GeO/sub 2/ codoped silica core. The evaluated frequency shift per unit of dopant concentration is 277 MHz/wt% and 45 MHz/wt% for F and GeO/sub 2/, respectively, at 1.55 /spl mu/m. The SBS threshold of a fiber with a nonuniform Brillouin frequency shift distribution prepared by the VAD method is investigated experimentally. The fiber exhibits 7 dB improvement in its SBS threshold. This value is in good agreement with one estimated by calculating the effective gain coefficient. This simple equation will be useful for estimating the SBS threshold of various fibers.

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 distortion slow light in flat Brillouin gain spectrum by using optical frequency comb.

We present a novel method for realizing a slow light with a broadband flat Brillouin gain and low distortion by using an optical frequency comb. We obtained a pump light consisting of 20 discrete line spectra using an optical frequency comb generation technique and a flat SBS gain with a 200 MHz bandwidth. We have realized a large relative pulse delay of 2.46 while suppressing the broadening factor to less than 1.19 for a pulse with a duration of 5.44 ns.

Performance of strain-free stimulated Brillouin scattering suppression fiber

We have investigated experimentally the performance of an SBS suppression fiber with a nonuniform dopant concentration along its length fabricated by the VAD method. We have achieved an SBS threshold of 15 dBm against a continuous wave at 1.55 /spl mu/m. This is 7 dB larger than that of conventional fiber. We have confirmed experimentally that the increase in the SBS threshold can be estimated from the ratio of the Brillouin frequency shift change over the effective interaction length to the intrinsic Brillouin gain bandwidth. Moreover, we have confirmed that there is no BER degradation after a transmission of 138 km through a 2.5 Gb/s intensity modulation direct detection system when the SBS suppression fiber is used with an input power of 16 dBm.

Four-wave mixing suppression effect of dispersion distributed fibers

The four-wave mixing (FWM) suppression effect of dispersion distributed fibers (DDFs), which have a nonuniform chromatic dispersion along their length, has been investigated experimentally and theoretically. We fabricated two different kinds of DDF by the vapor-phase axial deposition (VAD) method to clarify the FWM suppression effect. Moreover, we investigated experimentally the effect of our fabricated DDFs on the transmission characteristics of 4/spl times/10 Gb/s wavelength division multiplexing (WDM) systems. We confirmed that the proposed DDFs can not only suppress PWM but also improve the input power limitation for WDM systems.

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>>

Optical properties of sodium alminosilicate glass

Abstract Optical properties of sodium alminosilicate (NAS) glasses are investigated theoretically and experimentally. Rayleigh ratio and infrared absorption loss are measured for various compositions of NAS glasses prepared by melting. These measurements show that Rayleigh scattering loss of SiO 2 glass is greatly reduced when Na 2 O and Al 2 O 3 are added to it, which results in reduction of the glass fixation temperature and the photoelastic constant. The multiphonon edge absorption in the 2.5–6 μm region is also measured and the infrared edge wavelength is found to be the same as that of pure silica. The total loss of a NAS glass is found to be 0.055 dB/km at a wavelength of 1.56 μm. This value is about one-third that of pure silica core fiber and it indicates the potential of NAS glasses as a low loss fiber material.

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>>

Ultra-Broadband Mode Conversion With Acousto-Optic Coupling in Hole-Assisted Fiber

This paper describes the acousto-optic properties of hole-assisted fibers (HAFs) numerically and experimentally. We show that the HAF beat length between the guided and first higher-order modes has small wavelength dependence compared with that of the single mode fiber and so we can achieve broadband acousto-optic coupling. Ultra-broadband acousto-optic coupling is realized by using a HAF with flattened beat length characteristics. The coupling bandwidth reaches 120 nm, and can be controlled by designing the air hole structure.