There has been a rapid advance in wavelength-division multiplexing (WDM) and high bit-rate time-division multiplexing (TDM) as techniques for coping with burgeoning demand for transmission capacity. In the past this expansion of capacity has been achieved by 2.5-Gbit/s and 10-Gbit/s WDM using the C-band (around 1550 nm), but research on the 1600-nm L-band (around 1600 nm) is being stepped up to obtain further expansion. With the achievement of 40-Gbit/s speeds, which mark the limit of electrical signal processing, optical TDM, with speeds of 100 Gbit/s, is coming into use. In this kind of high-density, high bit-rate WDM transmission, the occurrence of non-linear phenomena within optical fibers reduces transmission quality, and this raises the importance of technology for suppressing non-linearity and specifically, in the case of WDM transmission systems, of four-wave mixing (FWM). Obviously there is also the problem of signal distortion due to dispersion, so that technology for suppressing cumulative dispersion is also essential. There is also a need for transmission lines with sophisticated dispersion management over a wide band of wavelengths, and it may be consisted of novel fibers.

Fiber four-wave mixing (FWM) based parametric wavelength conversion experiment is demonstrated. Over 91nm multi-channel simultaneous conversion is achieved. The bandwidth is to our knowledge, the broadest value of the published results. We shall argue that the method to realize the broadband wavelength conversion. Efficiency and/or bandwidth of the wavelength conversion is degraded mainly by the following obstacles, (a) inhomogeneity of the chromatic dispersion distribution along the fiber, (b) mismatch of the states of polarization (SOP) between pump and signals and (c) bandwidth limitation from coherence length. We discuss that an extremely short high-nonlinear fiber should overcome the above three obstacles. Furthermore we comment on the higher-order dispersion and also the influence of the stimulated Brillouin scattering (SBS). High-nonlinearity dispersion-shifted fiber (HNL-DSF) is a promising solution to generate the FWM efficiently in spite of the short length usage. We develop and fabricate HNL-DSF by the vapor-phase axial deposition method. Nonlinear coefficient of the fiber is 13.8 W-1km-1. We measure the conversion efficiency spectra of the four HNL-DSFs with different lengths. Length of each fiber is 24.5 km, 1.2 km, 200 m and 100 m respectively. It is shown that conversion bandwidth increases monotonically as the fiber length decreases. The result apparently proves the advantage of the extremely short fiber.

Industrial products usually involve initial failure type components. It is most important to remove initial failure products by screening after aging. Considering constant delivery products with a long average life time, both initial failure type and the repair system, we shall find that soon after initial delivery the number repaired exceeds the number produced. We call this point the maintenance deffect point". To solve this problem, it is effective to remove initial failure products by screening after aging. The aging effect is calculated under the assumption that failure occurs according to the Weibull distribution. In the case where aging time is normalized by using time, the effect becomes similar to the effect calculated under the assumption of the non-repair system. In this case, the total cost consists of failure cost and aging cost. By using the aging effect to calculate failure cost, we find that the aging time for minimum total cost in a macroscopic view is almost independent of both the shape parameter m and the accelerating factor α. It does depend, however, on the cost ratio, which is the ratio of the aging cost limit to the repair cost limit at no aging. This result is useful in programming both aging space and electric power for aging at the time of plant construction. This programming results in highly reliable products.