We achieved the first 10 Gb/s WDM transmission at 1064 and 1550 nm over 24 km of photonic crystal fiber (PCF). We confirmed an improvement in the bit error rate (BER) performance after the transmission, namely "negative power penalties" of -0.5 and -0.3 dB at 1064 and 1550 nm, respectively. Our experimental result and theoretical estimation revealed that the signal degradation induced by the chromatic dispersion can be effectively suppressed by employing the pre-chirp technique with a conventional Z-cut lithium niobate (LN) modulator. We also show theoretically that we can expect to realize 10 Gb/s transmission over a 24 km PCF with negligible BER degradation in the 1060 to 1600 nm wavelength range by using the pre-chirp technique.

This paper describes a low-loss submarine optical fiber cable for a long-distance submarine repeaterless transmission system that employs remote pumping. The features of this system are that it has an increased signal power budget and is cost effective and easy to maintain. First, we investigated the relationship between the signal and pump losses and the Raman gain efficiency of optical fiber needed to achieve a submarine repeaterless transmission system operating at 2.5 Gbps and over a distance exceeding 370 km. We manufactured a submarine optical fiber cable based on the results and confirmed that it had low-loss characteristics. Second, we evaluated the long-term loss stability of the optical fiber with a high-power continuous wave (CW) laser light as the pump source. We confirmed that the loss remained unchanged after 1900 hours of exposure to 8 W CW laser light at a wavelength of 1.48 µm. This submarine optical fiber cable is being employed in a commercial submarine repeaterless transmission system between Okinawa and Miyakojima.

We examined the characteristics of fiber fuse propagation in hole-assisted fibers (HAF). The fiber fuse propagated in the same way as in conventional single-mode fiber (SMF) when the diameter of an inscribed circle linking the air holes (c) was much larger than the diameter of the melted area (Dmelted). The melted area is caused by fiber fuse propagation and Dmelted is assumed to be almost the same size as the plasma. However, when c was much smaller than Dmelted, the fiber fuse did not propagate in HAF with input powers above 15 W at 1480 and 1550 nm. This result indicates that the threshold power of fiber fuse propagation in HAF can be at least 10 times larger than that in conventional SMF in the optical communication band. We also observed the dynamics of fiber fuse termination at a splice point between HAF and a conventional fiber by using a high-speed camera, when c was much smaller than Dmelted. We consider that the reduction in gas density caused by the air holes results in fiber fuse termination. When c was almost the same as Dmelted, we observed a new propagation mode and its dynamics for a fiber fuse with a damage track whose period was approximately 30 times longer than that in conventional SMF. We also made the first observation of a new threshold power (upper threshold) for a fiber fuse.

Recently, there have been a number of studies on wavelength division multiplexing (WDM) systems designed to increase transmission capacity and flexibility. This has in turn made it necessary to design the optical loss for optical fiber networks over a wide wavelength range. However, there is no general optical loss design method that allows us to employ for an optical fiber network over a wide wavelength range. In this paper, we propose a novel optical loss design and estimation method based on multiple regression analysis and statistical loss design technology for designing new optical fiber networks and for upgrading those that have already been installed. We show that the method can be used for highly accurate optical loss design and estimation from the O- to the L-band (1260 nm to 1625 nm), except for the E-band, by using easily obtainable optical loss values at wavelengths of 1310 and 1550 nm, which are usually used for communication. Moreover, we also show that the accuracy of our proposed method can be improved by selecting proper additional predictor wavelengths.

The polarization dependence of femtosecond soliton-soliton interactions is investigated in detail. When the polarization direction of two solitons is orthogonal, the soliton interaction can be reduced in comparison to that for parallel polarization. The soliton self-frequency shift (SSFS) is still observed even in the orthogonal condition, but the quantity of the SSFS is much smaller than in the parallel condition. A stronger soliton interaction is observed between two solitons in an in-phase condition, than in an out-of-phase condition. The largest SSFS occurs in-phase with parallel polarization. The polarization dependence of femtosecond soliton interaction in a distributed erbium-doped fiber amplifier (DEDFA) is also investigated. It is shown that when the optical gain of the DEDFA is given adiabatically, the input pulse separation at which the first soliton occurs is less with orthogonal polarization. This is because the soliton pulse width is reduced due to the adiabatic soliton narrowing caused by the optical amplification.