A monolithic four-stage low-noise amplifier (LNA) was successfully demonstrated for direct broadcast satellite (DBS) down-converters using 0.3 µm gate pulse-doped GaAs MESFET's This paper presents the design and test results of the LNA. The key feature of the research is a detailed demonstration of the difference between a noise figure of the four-stage LNA and an optimal noise figure of an employed FET with simulation and experiments. This LNA shows VSWR's of below 1.5: 1 as well as a noise figure of 1.1 dB and a gain of 28 dB at 12 GHz. To the best of our knowledge, it is the lowest noise figure reported so far in 12 GHz-band MMIC amplifiers. In the power characteristics, a 1 dB compression point (P1dB) of 10 dBm and a third order intercept point (IP3) of 19 dBm were shown.

An optical-layer adaptive restoration scheme is validated by a real-time experiment and numerical analyses. In this paper, it is assumed that this scheme can adaptively optimize the bitrate (up to 600Gb/s) and an optical reach with 100Gb/s granularity to maintain high-capacity optical signal transmission. The practicality of 600-Gb/s/carrier optical signal transmission over 101.6-km field-installed fiber is confirmed prior to the adaptive restoration experiment. After modifying the field setup, a real-time experiment on network recovery is demonstrated with bitrate adaptation for 600-Gb/s to 400-Gb/s signals. The results indicate that this scheme can restore failed connections with recovery times comparable to those of conventional restoration scheme; thus 99.9999% system availability can be easily attained even under double-link failures. Numerical analysis clarifies that adaptive restoration can recover >80% of double-link failures on several realistic topologies and improvement amount against conventional scheme is semi-statistically characterized by restoration path length.

The wavelength switching performance of a super-structure-grating DBR laser (SSG-DBR-LD) has been investigated. The lasing wavelength could be selected by directly modulating the wavelength tuning region with the switching time of less than a few nanoseconds. We observed that the pulse width of the output signal in each lasing wavelength monotonically changed with increasing the injection current amplitude when the low level of injection current was fixed. This is considered to be due to the increase of transient time from high level to low level of injection current when the amplitude increases and time duration for carrier density to satisfy the lasing mode at the low level of injection current decreases. For improving the stability of the pulse width of the output signal, a novel method of the mean level of injection current pulse fixed is proposed. Almost the same pulse width for wavelength switching from one supermode to another has been realized because the low level of injection current becomes lower than the conventional method and the time duration for carrier density to satisfy the lasing mode at the low level of injection current increases.

We demonstrated 1-Tb/s-class transmissions of field-deployed large-core low-loss fiber links, which is compliant with ITU-T G.654.E, using our newly developed real-time transponder consisting of a state-of-the-art 16-nm complementary metal-oxide-semiconductor (CMOS) based digital signal processing application-specific integrated circuit (DSP-ASIC) and an indium phosphide (InP) based high-bandwidth coherent driver modulator (HB-CDM). In this field experiment, we have achieved record transmission distances of 1122km for net data-rate 1-Tb/s transmission with dual polarization-division multiplexed (PDM) 32 quadrature amplitude modulation (QAM) signals, and of 336.6 km for net data-rate 1.2-Tb/s transmission with dual PDM-64QAM signals. This is the first demonstration of applying hybrid erbium-doped fiber amplifier (EDFA) and backward-distributed Raman amplifier were applied to terrestrial G.654.E fiber links. We also confirmed the stability of signal performance over field fiber transmission in wavelength division multiplexed (WDM) condition. The Q-factor fluctuations respectively were only less than or equal to 0.052dB and 0.07dB for PDM-32QAM and PDM-64QAM signals within continuous measurements for 60 minutes.

Multi-band transmission technologies promise to cost-effectively expand the capacity of optical networks by exploiting low-loss spectrum windows beyond the conventional band used in already-deployed fibers. While such technologies offer a high potential for capacity upgrades, available capacity is seriously restricted not only by the wavelength-continuity constraint but also by the signal-to-noise ratio (SNR) constraint. In fact, exploiting more bands can cause higher SNR imbalance over multiple bands, which is mainly due to stimulated Raman scattering. To relax these constraints, we propose wavelength-selective band switching-enabled networks (BSNs), where each wavelength channel can be freely switched to any band and in any direction at any optical node on the route. We also present two typical optical node configurations utilizing all-optical wavelength converters, which can realize the switching proposal. Moreover, numerical analyses clarify that our BSN can reduce the fiber resource requirements by more than 20% compared to a conventional multi-band network under realistic conditions. We also discuss the impact of physical-layer performance of band switching operations on available benefits to investigate the feasibility of BSNs. In addition, we report on a proof-of-concept demonstration of a BSN with a prototype node, where C+L-band wavelength-division-multiplexed 112-Gb/s dual-polarization quadrature phase-shift keying signals are successfully transmitted while the bands of individual channels are switched node-by-node for up to 4 cascaded nodes.