Kazuhide Nakajima

Dispersion-flattened photonic crystal fiber with large effective area and low confinement loss

A photonic crystal fiber (PCF) can realize a flat dispersion over a wide wavelength range that cannot be realized with a conventional single-mode fiber. However, the confinement loss tends to increase in a conventional dispersion-flattened PCF (DF-PCF) that has uniform air holes. In this paper, a novel PCF that has two cladding layers with different effective indices is proposed. The authors numerically show that the proposed PCF can achieve an ultralow dispersion variation of less than 0.8 ps/nm/spl middot/km in all telecommunication bands, with both a large effective area greater than 100 /spl mu/m/sup 2/ and a low confinement loss less than 0.01 dB/km.

Ultra low loss and long length photonic crystal fiber

We have succeeded in fabricating a low-loss (0.37dB/km at 1550nm) and long length (10km) photonic crystal fiber by improvement of fabrication process. Using this fiber, we performed the first DWDM transmission experiment. DWDM signal of 8/spl times/l0Gbit/s is successfully transmitted through the PCF.

Dopant dependence of effective nonlinear refractive index in GeO 2 - and F-doped core single-mode fibers

We describe the dopant dependence of the effective nonlinear refractive index n/sub 2eff/ in GeO/sub 2/- or F-doped core fibers theoretically and experimentally. We show that the dopant dependence of the nonlinear refractive index n/sub 2/ of F-doped bulk glass is the inverse of that of GeO/sub 2/-doped bulk glass. We also show that the effective nonlinear refractive index n/sub 2eff/ in F-doped core fibers, estimated by using the dopant content dependence of n/sub 2/, is in good agreement with our experimental results. Moreover, we confirm that n/sub 2eff/ in an optical fiber strongly depends on the refractive index profile of its core.

Dispersion Compensation Over All the Telecommunication Bands With Double-Cladding Photonic-Crystal Fiber

This paper numerically describes the design of double-cladding photonic-crystal fiber (DC-PCF) for ultrabroadband compensation over all telecommunication bands (O to L), i.e., ranging from 1260 to 1625 nm. We show that an ultrabroadband compensating DC-PCF can be designed simply by considering the zero-dispersion wavelength and the relative dispersion to the slope at a particular wavelength of a conventional single-mode fiber (SMF). As a result, we reveal that the proposed DC-PCF can successfully compensate for the dispersion of a conventional SMF with an effective dispersion range of plusmn0.4 ps/nmmiddotkm over all telecommunication bands as well as provide an effective area comparable to that of conventional dispersion-compensating fiber

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.

Suppression of Fiber Fuse Propagation in Hole Assisted Fiber and Photonic Crystal Fiber

We suppressed fiber fuse propagation in hole-assisted fiber (HAF) and photonic crystal fiber (PCF) with input powers above 14 W at 1480 and 1550 nm. This result indicates that the threshold power of fiber fuse propagation in HAF and PCF can be at least 10 times larger than that in conventional single-mode fiber (SMF) in the optical communication band. We also observed the dynamics of fiber fuse termination at a splice point between a test fiber (HAF or PCF) and a conventional fiber (SMF or dispersion-shifted fiber (DSF)). Our experimental results show that air holes in HAF and PCF play an important role in suppressing fiber fuse propagation.

Chromatic dispersion distribution measurement along a single-mode optical fiber

A nondestructive measurement technique, which uses a four-wavelength bidirectional optical time domain reflectometer (OTDR) to measure the chromatic dispersion distribution along a single-mode fiber, is compared with the destructive interferometric technique. The experimental results obtained by this technique are in good agreement with those obtained by the interferometric technique. In addition, a measurement procedure is proposed for a transmission line composed of different types of single-mode fiber. These results show that this technique is extremely useful for the design of wavelength division multiplexer (WDM) and finite difference multiplexer (FDM) 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.

New SBS suppression fiber with uniform chromatic dispersion to enhance four-wave mixing

A new type of stimulated Brillouin scattering (SBS) suppression fiber has been developed whose dopant concentration and core radius are nonuniform along its length. The chromatic dispersion distribution is kept uniform along its length by varying the core radius in accordance with the /spl Delta/ value to enhance four-wave mixing (FWM) intentionally. The output power of the FWM signal with this fiber was about 15 dB higher than that with a conventional disperion-shifted fiber when the input power was 15 dBm, which is just above the SBS threshold power.