We achieved 50-Gb/s operation of a ring-resonator-based silicon modulator for the first time. The pin-diode phase shifter, which consists of a side-wall-grating waveguide, was loaded into the ring resonator. The forward-biased operation mode was applied, which exhibited a V(π)L as small as 0.28 V · cm at 25 GHz. The driving voltage and optical insertion loss at 50-Gb/s were 1.96 V(pp) and 5.2 dB, respectively.

Engineers are currently facing some technical issues in support of the exponential performance growths in information industries. One of the most serious issues is a bottleneck of inter-chip interconnects. We propose a new "Photonics-Electronics Convergence System" concept. High density optical interconnects integrated with a 13-channel arrayed laser diode, silicon optical modulators, germanium photodetectors, and silicon optical waveguides on single silicon substrate were demonstrated for the first time using this system. A 5-Gbps error free data transmission and a 3.5-Tbps/cm(2) transmission density were achieved. We believe that this technology will solve the bandwidth bottleneck problem among LSI chips in the future.

We present high-speed operation of pin-diode-based silicon Mach-Zehnder modulators that have side-wall gratings on both sides of the waveguide core. The use of pre-emphasis signals generated with a finite impulse response digital filter was examined in the frequency domain to show how the filter works for different filter parameter sets. In large signal modulation experiments, V(π)L as low as 0.29 V·cm was obtained at 12.5 Gb/s using a fabricated modulator and the pre-emphasis technique. Operation of up to 25-Gb/s is possible using basically the same driving configurations.

A precise flip-chip bonding (FCB) technology for indium phosphide semiconductor optical amplifiers (InP-SOAs) on a silicon photonics platform within less than ±1-µm alignment accuracy was developed. For efficient optical coupling and a relaxed alignment tolerance, the mode field on both the InP-SOAs and the Si waveguides was expanded by spot-size converters (SSCs). On the InP-SOAs, width-tapered SSCs were used to obtain an isotropic mode-field having an approximately a 3-µm diameter. On the silicon photonics platform, dual-core SSCs were used to expand the same mode-field size of 3 µm as for the SSCs on SOAs. Using the FCB technology and the SSCs, an in-line optical amplification of 15 dB was achieved by in-line integrated SOAs with angled waveguides. The optical coupling losses were 7.7 dB, which included 5.1-dB excess losses by misalignment and a gap between InP-SOA and Si waveguides. A 4 × 4 Si switch with a hybrid-integrated 4-ch SOA array was fabricated, and achieved the first demonstration of a lossless Si switch.

Slow-light Mach–Zehnder modulators on a silicon-on-insulator substrate are examined in this paper. The phase shifter on each arm consists of ten cascaded ring resonators in an all-pass filter configuration, and this acts as a slow-light structure. Fabricated devices show seven-fold enhancement in modulation efficiency compared with that of a conventional modulator; this enhancement was due to the slow light. Large signal modulations of 10 Gbps have been obtained using a driving signal of only 1 V peak-to-peak.

We developed PIN-diode-based silicon Mach-Zehnder modulators, which have side-wall-gratings in the phaseshifter sections. Such passive waveguides with gratings were fabricated using ArF immersion lithography, which showed a small scattering loss of 0.4 dB/mm. We extensively investigated the forwardbiased operation of the modulators by using equivalent circuit analysis and the measurement of the fabricated devices. We argue carrier recombination time only plays a minor role for the overall performance of the modulator. Dependences of the modulation efficiency on other various critical parameters are discussed. In particular, if we use relatively short phase shifter, the forwardbiased operation provides smaller V π L than reversed one even at high frequency of 20 GHz, at the expense of the narrow bandwidth. Our approach enables high-speed operation up to 50 Gb/s, by using phase shifter as short as 250 μm and preemphasis signals. For 12.5-Gb/s operation, the modulator cell size was only 300 μm × 50 μm, which was suitable for the applications of high-density optical interconnects.

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We experimentally demonstrate the lossless transmission of wavelength division multiplexing (WDM) signals through a silicon-photonics 4 × 4 switch with a flip-chip bonded 4-channel semiconductor optical amplifier (SOA). We first optimized the input power and gain of the SOA-integrated switch to obtain the optimum operation point in terms of the transmitted signal quality. We then performed simultaneous transmission of 8-ch, 32-Gbaud, SP 16-QAM WDM (800 Gb/s) signals through all the four paths of the switch. The effect of crosstalk on the switch was very small, and thus could not be observed. We also examined multistage (up to four stages) transmission of the signals with circulating configurations. We show that even for a 4-stage transmission, the bit error rate of the transmitted signal is below the 20% forward-error-correction limit. Finally, we discuss approaches to improve the optical signalto-noise ratio of the transmitted signals to enlarge the signal quality margin and increase the possible number of the cascading stages and/or WDM channels for wide applications.