Hiroki Kaneshige

Low-voltage quantum well microring-enhanced Mach-Zehnder modulator

Modulation characteristics of a novel InGaAs/InAlAs multiple quantum well (MQW) microring-enhanced Mach-Zehnder modulator (MRE-MZM) is investigated in detail and its low-voltage operation with high extinction ratio is demonstrated. The MZM has a single microring resonator in one arm and is driven by the change in electrorefractive index induced by the quantum-confined Stark effect in the MQW core layer. As the MQW, a multiple five-layer asymmetric coupled quantum well (FACQW) is used to obtain a large electrorefractive index change. The driving voltage of the proposed MZM is significantly reduced owing to the enhanced phase shift in the microring resonator. High-mesa waveguide structures are grown by solid-source molecular beam epitaxy and fabricated by inductively coupled plasma etching. A directional coupler with an asymmetric branching ratio is used as an input coupler to prevent the degradation of the extinction ratio of the MZM. The extinction ratio of the fabricated MRE-MZM is approximately 27 dB. The product of the half-wave voltage and phase shifter length, V(π) · L, is 1.7 Vmm in static modulation. This value is one-quarter that of a conventional MZM with the same waveguide structure.

InGaAs/InAlAs Multiple Quantum Well Mach–Zehnder Modulator with Single Microring Resonator

We propose and a novel InGaAs/InAlAs multiple quantum well (MQW) Mach–Zehnder (MZ) modulator with a single microring resonator, and a significant reduction of driving voltage is demonstrated for the first time. The modulator is driven by the quantum-confined Stark effect (QCSE) in the MQW and the driving voltage of the proposed modulator is expected to be significantly reduced by the phase-shift-enhancement effect in the microring. A waveguide structure was grown by solid-source molecular beam epitaxy and fabricated by inductively coupled plasma etching. A directional coupler with a shallow gap is employed to control the coupling parameters between a busline and the microring waveguide. An asymmetrical splitter was used as an input coupler to prevent the degradation of the extinction ratio of the MZ modulator. The extinction ratio of the fabricated microring MZ modulator was approximately 17.5 dB. The product of half-wave voltage and phase shifter length VπL was 2.0 Vmm in static modulation. This value was one-third that of a conventional MZ modulator with the same waveguide structure.

Thermo-optically driven silicon microring-resonator-loaded Mach-Zehnder modulator for low-power consumption and multiple-wavelength modulation

Low-power-consumption thermo-optically controlled silicon-microring-resonator loaded Mach–Zehnder modulators (MRR-loaded MZMs) are demonstrated. We experimentally characterized a single microring and cascaded-multiple-microring resonators coupled to one arm of a Mach–Zehnder interferometer (MZI). The driving power consumption of the proposed MZM is significantly reduced owing to the enhanced phase shift in the MRR. The device was fabricated on a silicon-on-insulator (SOI) waveguide structure, and each microring is equipped with TiN microheater for thermo-optic tuning. The coupling efficiency between the microring and a busline waveguide was regulated by varying the gap between two waveguides at a directional coupler. The power consumption of single microring and cascaded MRR-loaded MZMs was approximately 0.4 and 1 mW, respectively. The phase-shift enhancement factor of up to 19 with a maximum extinction ratio of 18 dB was obtained experimentally. Multiple-wavelength operation was also demonstrated in the cascaded MRR-loaded MZM.