High-capacity optical transmitters with reduced size, cost, and power consumption are required to meet growing bandwidth requirements of network systems. A high-modulation-efficiency Mach-Zehnder modulator (MZM) on an Si platform is a key piece of equipment for these transmitters. Si-MZMs have been widely reported; however their performance is limited by the material properties of Si. To overcome the performance limitations of Si MZMs, we have integrated III-V materials on Si substrate and developed a heterogeneously integrated III-V/Si metal oxide semiconductor (MOS) capacitor phase shifter for constructing ultra-high efficient MZM, in which the n-InGaAsP, p-Si, and SiO<sub>2</sub> film are used for constructing the MOS capacitor. The fabricated MZM with the MOS capacitor exhibited a V<sub>π</sub>L of 0.09 Vcm and insertion loss of ~2 dB. 32-Gbps modulation of the MZM was also demonstrated.
A high-efficiency and low-loss Mach-Zehnder modulator on a Si platform is a key component for meeting the demand for high-capacity, low-cost and low-power optical transceivers in future optical fiber links. We report a III-V/Si MOS capacitor Mach-Zehnder modulator with an ultrahigh-efficiency phase shifter, which consists of n-type InGaAsP and ptype Si. The main advantage of this structure is a large electron-induced refractive index change and low free-carrier absorption loss of the n-type InGaAsP. The heterogeneously integrated InGaAsP/Si MOS capacitor structure is fabricated by using the oxygen plasma assisted bonding method. The fabricated device shows V<sub>π</sub>L of 0.09 Vcm, a value over three-times smaller than that of the conventional Si MOS capacitor Mach-Zehnder modulator, without an increase in the insertion loss. This clearly indicates that the proposed III-V/Si MOS capacitor Mach-Zehnder modulator overcomes the performance limit of the Si Mach-Zehnder modulator.
Optical interconnects are expected to reduce the power consumption of ICT instruments. To realize chip-to-chip or chip-scale
optical interconnects, it is essential to fabricate semiconductor lasers with a smaller energy cost. In this context, we
are developing lambda-scale embedded active-region photonic-crystal (LEAP) lasers as light sources for chip-scale
We demonstrated the first continuous-wave (CW) operation of LEAP lasers in 2012 and reported a record low threshold
current and energy cost of 4.8 μA and 4.4 fJ/bit at 10 Gbit/s in 2013. We have also integrated photonic crystal
photodetectors on the same InP chip and demonstrated waveform transfer along 500-μm-long waveguides. Although
LEAP lasers exhibit excellent performance, they have to be integrated on Si wafers for use as light sources for chip-scale
In this paper, we give a brief overview of our LEAP lasers on InP and report our recent progress in fabricating them on
Si. We bonded the InP wafers with quantum-well gain layers directly on thermally oxidized Si wafers and performed all
process steps on the Si wafer, including high-temperature regrowth. After this process modification, we again achieved
CW operation and obtained a threshold current of 57 μA with a maximum output power of more than 3.5 μW at the
output waveguides. An output light was successfully guided through 500 × 250-nm InP waveguides.