Aiming at wideband and flat supercontinuum generation (SC) from optical fibers in the 1.55-µm wavelength region, we study both experimentally and theoretically how SC spectra are influenced by group-velocity dispersion (GVD) of fibers. In the anomalous GVD region, since the peak power of pump pulses is kept high during propagation through the fiber by the higher-order soliton effect, the Raman effect has an adverse effect to flat and wideband SC generation. In the zero GVD region, the interplay of the third-order dispersion (TOD) and the self-phase modulation splits the SC spectrum into two main components. On the other hand, in the normal GVD region, nevertheless the SC spectrum broadens wider and smoother than those in anomalous and zero GVD regions, it is still asymmetric when TOD of the fiber can not be ignored. From these results, we find that a dispersion-flattened fiber with normal GVD is the most suitable for flat and wideband SC generation. A 280-nm wide SC spectrum with the spectral-density fluctuation less than 10 dB is actually generated from such a fiber.

Aiming at wideband and flat supercontinuum generation (SC) from optical fibers in the 1.55-µm wavelength region, we study both experimentally and theoretically how SC spectra are influenced by group-velocity dispersion (GVD) of fibers. In the anomalous GVD region, since the peak power of pump pulses is kept high during propagation through the fiber by the higher-order soliton effect, the Raman effect has an adverse effect to flat and wideband SC generation. In the zero GVD region, the interplay of the third-order dispersion (TOD) and the self-phase modulation splits the SC spectrum into two main components. On the other hand, in the normal GVD region, nevertheless the SC spectrum broadens wider and smoother than those in anomalous and zero GVD regions, it is still asymmetric when TOD of the fiber can not be ignored. From these results, we find that a dispersion-flattened fiber with normal GVD is the most suitable for flat and wideband SC generation. A 280-nm wide SC spectrum with the spectral-density fluctuation less than 10 dB is actually generated from such a fiber.

We analyze the dispersion-managed optical transmission system for the non-return-to-zero (NRZ) pulse format. First, we investigate the physical image of dispersion management by computing small-signal-based transfer functions, and summarize the dependence of transmission performance on system parameters. Next, the Q-map is computed numerically to design long-distance large-capacity dispersion-managed transmission systems for a single channel in a more detailed manner. It is shown that the third-order dispersion of fibers negatively influences transmission performance, and third-order dispersion compensation is proved to be an effective method for extending the transmission distance of high bit-rate systems. Utilizing these results, guidelines can be derived for the optimal design of long-distance large-capacity NRZ transmission systems.

We design and demonstrate a high repetition-rate similariton generation system using normal dispersion fiber amplifiers (NDFA's). We numerically calculate the pulse evolution in NDFA's and clarify the condition to generate similariton pulses in a finite-length NDFA. Then we design the similariton generation system in consideration of the use of Erbium-doped fibers (EDF's) and show that a km-long fiber amplifier with low normal dispersion can generate a high repetition-rate similariton train from practical pico-second pulse sources. In the experiment, we demonstrate a 10-GHz similariton source using a 1.2-km-long EDF. For application to multi-wavelength light sources, we measure the bit-error rate of the spectrally sliced similariton, and show that it exhibits low-noise performance, which is attributed to the spectral flatness.

We analyze the dispersion-managed optical transmission system for the non-return-to-zero (NRZ) pulse format. First, we investigate the physical image of dispersion management by computing small-signal-based transfer functions, and summarize the dependence of transmission performance on system parameters. Next, the Q-map is computed numerically to design long-distance large-capacity dispersion-managed transmission systems for a single channel in a more detailed manner. It is shown that the third-order dispersion of fibers negatively influences transmission performance, and third-order dispersion compensation is proved to be an effective method for extending the transmission distance of high bit-rate systems. Utilizing these results, guidelines can be derived for the optimal design of long-distance large-capacity NRZ transmission systems.