Chisato Fukai

Ultrawide-band single-mode transmission performance in a low-loss photonic crystal fiber

We describe the ultrawide-band single-mode transmission performance of a photonic crystal fiber (PCF) in the 850 to 1550 nm wavelength range. We confirmed that the fabricated PCF achieves a single-mode operation over the 850 to 1550 nm wavelength range by measuring the mode-field diameter (MFD) and modal delay characteristics. The 10-Gb/s-based wavelength-division multiplexing (WDM) signals with a total capacity of 190 Gb/s were successfully transmitted over a 5.2-km low-loss PCF utilizing the 850, 1310, and 1550 nm regions simultaneously. Our experimental results show that an endlessly single-mode PCF provides an ultrawide-band of more than 160 THz for future optical communication systems.

Applicability of Photonic Crystal Fiber With Uniform Air-Hole Structure to High-Speed and Wide-Band Transmission Over Conventional Telecommunication Bands

We discuss the applicability of photonic crystal fiber (PCF) with a uniform air-hole structure to high-speed and wide-band transmission over conventional telecommunication bands. We design the PCF to maximize the effective area by utilizing the macro-bending losses of the fundamental and first higher order modes (HOM) and clarify that a single-mode and low bending loss PCF can realize the largest effective areas of 133 and 157 mum2 for transmission over the 1260-1625 nm (O ~ L bands) and 1460-1625 nm (S ~ L bands) wavelength ranges, respectively. We then investigate the impact of the designed PCF on nonlinearity reduction over a wide wavelength range and show that the PCF helps to increase the maximum channel power in a wavelength division multiplexing system. We also discuss the distributed Raman amplification (DRA) characteristics of PCF with a large effective area. Our results show that we can expect to improve the signal to noise ratio with DRA in spite of the low nonlinearity of the designed PCF. Dispersion compensating fiber (DCF) with a conventional W-shaped index profile is designed to compensate for the relatively large dispersion of the PCF, and we show that the designed DCF can extend the dispersion compensation bandwidth from 1340 nm to 1650 nm for a 40 Gbit/s transmission. Finally, we clarify the applicability of the large effective area PCF with the uniform air-hole structure as a high-speed and wide-band transmission medium.

Effective Raman gain characteristics in germanium- and fluorine-doped optical fibers.

We describe the dopant dependence of Raman gain in germanium- and fluorine-doped optical fibers. We clarify, both theoretically and experimentally, the effective Raman gain characteristic in an optical fiber, which is closely related to the fibers refractive-index profile and electromagnetic field profile. We also show that this experimentally determined relationship can be used to evaluate the effective Raman gain characteristic in a germaninum- or a fluorine-doped optical fiber with an arbitrary index profile.

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.

Relationship between optical wiring conditions and MPI degradation

Optical wiring conditions are investigated numerically and experimentally with a viewpoint of MPI induced transmission performance degradation. We reveal the impact of the interval of the bending portion on MPI degradation for the first time.

Raman amplification characteristics at 850 nm in a silica-based photonic crystal fiber

We achieve a 2.5-dB improvement in the power penalty in a 10-Gb/s-based distributed Raman amplification transmission at 850 nm using a silica-based low-loss photonic crystal fiber (PCF). The experimental results agree well with a signal-to-noise ratio improvement model. The model indicates the negligible influence of double Rayleigh backscattering in the fabricated PCF

Long-term reliability of pure silica core single-mode fiber when exposed to high-power laser light

The reliability of a pure silica core single-mode fiber with long-term exposure to continuous wave (CW) high-power laser light is reported. It is found that the optical loss in the 0.6-1.6-/spl mu/m region and the Raman spectrum remain unchanged after 1900 h of exposure to 8-W CW laser light at 1.48 /spl mu/m. The nonbridging oxygen hole center concentration generated by 1900 h of exposure is estimated to be below our detection limit of 2/spl times/10/sup 12/ cm/sup -3/.

Optimum optical fiber design for a DRA-based DWDM transmission system

This paper describes the distributed Raman amplification (DRA) transmission characteristic in an optical fiber both numerically and experimentally. The paper clarifies the relationship between optical fiber parameters and DRA transmission performance with regard to the signal-to-noise ratio (SNR) characteristics and nonlinear impairments. These relationships can be successfully discussed, taking account of various fiber parameters, including Raman gain efficiency, the attenuation coefficient at signal and pump wavelengths, the Rayleigh scattering coefficient, and the nonlinear refractive index, as a function of the relative index difference in an optical fiber. An example of an optimum fiber design for a DRA-based dense-wavelength-division-multiplexing (DWDM) transmission system is also discussed.

Study of few-mode fiber based SMS sensor for simultaneous measurement of temperature and strain

The applicability of few-mode fiber (FMF) as a single-multi-single (SMS) sensor is investigated. We examine experimentally the wavelength shift and/or visibility characteristics in an FMF based SMS sensor by changing the external temperature and longitudinal strain individually. We investigate numerically the temperature sensitivity of the fabricated sensor by considering the temperature dependence of the effective refractive index difference. Our results show that an FMF based SMS sensor can be used to measure the relative variation in temperature and strain simultaneously, and whose sensitivity can be tailored easily by designing two LP modes in an FMF.

PMD suppression method for photonic crystal fiber

We have succeeded in reducing the PMD of PCF to 10% of its initial value by periodic bidirectional twisting without loss increasing and structural deformation. A PCF with PMD of 0.03 ps/rkm has been obtained.