A compact (13.38.05.6 mm) 40 Gbit/s 1.55-µm electroabsorption (EA) modulator monolithically integrated distributed feedback (DFB) laser diode (EML) [1] module integrated with a driver IC has been developed. Its compactness was realized by employing a broadband feed-through and a bias tee which were accurately designed by 3-dimensional (3D) electromagnetic simulation. It was confirmed that the simulation results of the frequency response and the actual measurement results are corresponding well. Clear eye opening of the 40 Gbit/s optical output waveform of the fabricated EML module was observed. Degradation was not observed even when the 40 Gbit/s electrical signal was launched into the module via the flexible printed circuit (FPC).

We investigate the impact of electrical band-limitation on the transmission performance of both carrier suppressed return-to-zero (CSRZ) and CSRZ differential phase shift keying (CSRZ-DPSK) format for high spectral efficiency DWDM systems. Results show that electrical band-limitation improves signal spectral compactness, leading to reduced linear crosstalk and improved tolerance against chromatic dispersion in optical fiber link without causing any degradation to fiber nonlinearity tolerance. In addition, it is shown that the electrical band-limitation is more efficient to CSRZ-DPSK signal than CSRZ signal in reducing signal degradation caused by linear crosstalk and fiber chromatic dispersion.

We numerically and experimentally investigated the upgradability of the longest and the typical segments of the JIH system. Through these studies, we confirmed that a 100 GHz-spaced 25 42.7 Gbit/s transmission with the total capacity of 1 Tbit/s can be attainable even by using NRZ signal and standard FEC for the typical segments. We also found that RZ signal format was desirable for the longest segment and a further wide system margin could be expected by using adjacent channel polarization control and advanced FEC technologies.

Channel bit rates of 40 Gbit/s are the next step after 2.5 and 10 Gbit/s in the SONET/SDH hierarchy. They enable multi Tbit/s transmission of live traffic over a single fiber. All recent optical transmission records concerning aggregate capacitiy per fiber were achieved using this technology. Comparing the limiting effects of 2.5, 10 and 40 Gbit/s system configurations reveals that 40 Gbit/s allows for the longest regenerator free distance on NZDSF. In this paper we describe transmitter and receiver designs as well as results from field trials. The first trial demonstrated a transmission of live traffic with a record aggregate capacity of 3.2 Tbit/s, whereas the second successfully demonstrated a doubling of the channel capacity to 80 Gbit/s using polarization multiplexing with automated polarization control.

Methodologies for more efficient Raman amplification and a more suitable modulation format for 40 Gbit/s WDM unrepeatered transmission are investigated. Management of the fiber effective area is proposed to realize low noise distributed Raman amplification. An Aeff management technique in which low-Aeff fiber is located in a median section instead of the last section, was confirmed numerically and experimentally to improve the OSNR and Q-factor. Carrier-suppressed-return-to-zero (CS-RZ) modulation has the advantage of reducing fiber-nonlinearity effects and permitting denser multiplexing of the wavelengths. 40 Gbit/s 32-channel unrepeatered WDM transmission over 202 km was demonstrated employing the proposed methodologies.

The effectiveness of Aeff enlarged positive dispersion fiber (EE-PDF) and hybrid amplification configuration with erbium-doped fiber amplifier (EDFA) and fiber Raman amplifier for reducing the fiber nonlinearity and improving the transmission performance in long distance 40 Gbit/s-based WDM transmission was investigated. We have confirmed that the use of EE-PDF in modified dispersion map for 40 Gbit/s transmission is quite effective to increase the transmissible distance and have successfully demonstrated 16 40 Gbit/s WDM transmission over 2000 km with proper dispersion management. We have also confirmed that the use of distributed Raman amplification is quite effective to extend the repeater spacing. By adding the optimum Raman amplification, almost the same transmission performance was obtained with a doubled repeater spacing in long distance 40 Gbit/s-based WDM transmission.

Today, an ultra-high capacity transmission system based on N40 Gb/s channel rate is the most promising approach to achieve multi-terabit/s of capacity over a single fiber. We have demonstrated 5.12 Tbit/s transmission of 128 channels at 40 Gbit/s over 3100 km and 10.24 Tbit/s transmission of 256 channels at 42.6 Gbit/s (using FEC) over 100 km, based on four main technologies: 40 Gbit/s electrical time-division multiplexing (ETDM), vestigial sideband demultiplexing (VSB), advanced amplifier technology including Raman amplification and TeraLightTM fiber. A record spectral efficiency of 1.28 bit/s/Hz is applied to achieve 10.24 Tbit/s transmission within the C- and L-band.

This paper describes the impact of novel Return-to-Zero (RZ) formas for dense wavelength-division-multiplexing (DWDM) transport systems using 40-Gbit/s channels. The introduction of phase modulation using phase reversal in RZ-signal encoding process dramatically reduces its optical modulation bandwidth and enhances its tolerance against fiber nonlinearities. By using proposed RZ formats, DWDM transmission performance in 40-Gbit/s channels can be enhanced with high spectral efficiency compared with conventional Non-Return-to-Zero (NRZ) and Return-to-Zero (RZ) formats.

In this paper, we address the key enabling technologies for long-span WDM transmissions at 40 Gbit/s. Experimental results of 1.28 Tbit/s (32 40 Gbit/s) unrepeatered transmission over 240 km of conventional 80-µm2 NDSF will be reported. Bi-directional pumped distributed Raman amplification has allowed a record unrepeatered WDM transmission distance over this fibre type, without using effective-area-enlarged fibres or remotely pumped EDFAs.

This paper describes the design, fabrication, and performance of a novel Ti:LiNbO3 optical modulator with a two-stage coplanar waveguide electrode for 40 Gbit/s optical transmission systems. The structure consists of a thin lower electrode and a thick upper electrode in conjunction with a ridge structure. The lower electrode ensures low voltage and the upper layer provides good microwave characteristics. Based on simulation results, a fully-packaged module was fabricated. The measured 3-dB electrical bandwidth is 30 GHz with a half-wave voltage of 2. 9 V.

The effectiveness of periodic dispersion compensation on single-channel 40 Gbit/s soliton transmission system was experimentally investigated. This technique requires just the dispersion compensation fibers and wideband optical filters in the transmission line, which has no difficulty to be used in the practical system. By using polarization-division-multiplexing together with periodic dispersion compensation, single-channel 40 Gbit/s transmission over 4700 km was demonstrated. Single-polarization 40 Gbit/s transmission experiments, which are more suitable for system implementation and compatible with WDM were also conducted. We investigated the transmission characteristics and pulse dynamics in different dispersion maps and in the optimized dispersion map, single-channel, single-polarization 40 Gbit/s transmission over 6300 km was successfully demonstrated.