Suguru Akiyama

50-Gb/s ring-resonator-based silicon modulator.

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.

First demonstration of high density optical interconnects integrated with lasers, optical modulators, and photodetectors on single silicon substrate

Optical interconnects integrated with lasers, silicon optical modulators and germanium photodetectors on a single silicon substrate were demonstrated for the first time. A 5 Gbps line bit rate and 3.5 Tbps/cm2 transmission density were achieved.

12.5-Gb/s operation with 0.29-V·cm V π L using silicon Mach-Zehnder modulator based-on forward-biased pin diode

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.

Compact PIN-Diode-Based Silicon Modulator Using Side-Wall-Grating Waveguide

We developed PIN-diode-based silicon Mach-Zehnder modulators, which have side-wall-gratings in the phase-shifter 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 forward-biased 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 forward-biased operation provides smaller VπL 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.

A 1 V Peak-to-Peak Driven 10-Gbps Slow-Light Silicon Mach–Zehnder Modulator Using Cascaded Ring Resonators

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.

Wide-wavelength-band (30 nm) 10-Gb/s operation of InP-based Mach-Zehnder modulator with constant driving voltage of 2 V/sub pp/

Wide-wavelength-band operation of InP-based Mach-Zehnder modulators is investigated. From the measured dependences of the half-wavelength voltage on operating wavelength and applied-bias voltage, it is shown that wide-wavelength operation with a constant driving voltage can be realized by adjusting the bias voltage for each operating wavelength. Ten-gigabits/second clear eye openings are demonstrated over a 30-nm wavelength range with a constant driving voltage of 2 V/sub pp/.

Novel InP-based Mach-Zehnder modulator for 40 Gb/s integrated lightwave source

A novel InP-based Mach-Zehnder modulator, which provides impedance matching to 50 ohm, is proposed for 40 Gb/s integrated lightwave source. Its 40 Gb/s operation is successfully demonstrated.

InP-Based Mach–Zehnder Modulator With Capacitively Loaded Traveling-Wave Electrodes

InP-based Mach-Zehnder modulators with capacitively loaded traveling-wave electrodes (CL-TWEs), which have segmented structures along the optical waveguides, are presented. Devices with various structural parameters for gap length (the length between adjacent segmented phase modulators) and total active length were fabricated and investigated both optically and electrically. Excellent characteristics such as characteristic impedance matching to 50 Omega and low electrical propagation losses were obtained. Using the optimum structures, 40- and 10-Gb/s large signal operations were successfully performed with peak-to-peak driving voltages of 3.0 and 1.2 V, respectively. The effects of structural parameters, such as gap length and total active length on electrical and optical modulation properties, are discussed.

40 Gb/s InP-based Mach-Zehnder modulator with a driving voltage of 3 V/sub pp/

A 40 Gb/s InP-based Mach-Zehnder modulator has been developed that has capacitively loaded traveling-wave electrodes and operates in a simple push-pull configuration. It uses pin phase modulators to concentrate the electrical field at the core of the waveguide and thereby reduce the driving voltage. A semi-insulating upper cladding layer is used in the region of the passive optical waveguides to reduce the electrical loss caused by the p-doped cladding layer and thus increase the modulation bandwidth. A fabricated modulator had a bandwidth of 28 GHz and showed a clear eye opening at 40 Gb/s in a push-pull configuration using one electrical driver with a low driving voltage (3.0 V/sub pp/ ).

High-speed and efficient silicon modulator based on forward-biased pin diodes

Silicon modulators, which use the free-carrier-plasma effect, were studied, both analytically and experimentally. It was demonstrated that the loss-efficiency product, a-VpL, was a suitable figure of merit for silicon modulators that enabled their intrinsic properties to be compared. Subsequently, the dependence of VpL on frequency was expressed by using the electrical parameters of a phase shifter when the modulator was operated by assuming a simple driving configuration. A diode-based modulator operated in forward biased mode was expected from analyses to provide more efficient operation than that in reversed mode at high frequencies due to its large capacitance. We obtained an a-VpL of 9.5 dB-V at 12.5 GHz in experiments by using the fabricated phase shifter with pin diodes operated in forward biased mode. This a-VpL was comparable to the best modulators operated in depletion mode. The modulator exhibited a clear eye opening at 56 Gb/s operated by 2 V peak-to-peak signals that was achieved by incorporating such a phase shifter into a ring resonator.