We demonstrate a wafer-level integration of a distributed feedback laser diode (DFB LD) and high-efficiency Mach-Zehnder modulator (MZM) using InGaAsP phase shifters on Si waveguide circuits. The key to integrating materials with different bandgaps is to combine direct wafer bonding of a multiple quantum well layer for the DFB LD and regrowth of a bulk layer for the phase shifter. Buried regrowth of an InP layer is also employed to define the waveguide cores for the LD and phase shifters on a Si substrate. Both the LD and phase shifters have 230-nm-thick lateral diodes, whose thickness is less than the critical thickness of the III-V compound semiconductor layers on the Si substrate. The fabricated device has a 500-µm-long DFB LD and 500-µm-long carrier-depletion InGaAsP-bulk phase shifters, which provide a total footprint of only 1.9 × 0.31 mm2. Thanks to the low losses of the silica-based fiber couplers, InP/Si narrow tapers, and the phase shifters, the fiber-coupled output power of 3.2 mW is achieved with the LD current of 80 mA. The MZM has a VπL of around 0.4 Vcm, which overcomes the VπL limit of typical carrier-depletion Si MZMs. Thanks to the high modulation efficiency, the device shows an extinction ratio of 5 dB for 50-Gbit/s NRZ signal with a low peak-to-peak voltage of 2.5 V, despite the short phase shifters and single-arm driving.
Ultrashort-distance optical interconnects are becoming increasingly important due to continuous improvements in servers and high-performance computers. As light sources in such interconnects, directly modulated semiconductor lasers with an ultrasmall active region are promising. In addition, using Si waveguides is important to provide low loss optical links with functions such as wavelength filtering and switching. In this paper, we demonstrate a wafer-scale heterogeneous integration of lambda-scale embedded active-region photonic-crystal (LEAP) lasers and Si waveguides, achieved through precise alignment. We numerically and experimentally demonstrated the coupling design between the LEAP lasers and Si waveguides; it is important to match propagation constants of Si waveguides and wavenumber of the optical cavity modes. The LEAP lasers exhibit an ultralow threshold current of 13.2-μA and 10-Gbit/s direct modulation. We also achieved the first data transmission using an optical link consisting of a LEAP laser, Si waveguide, and photodetector and obtained an averaged eye diagram at a bit rate of 10 Gbit/s with a bias current of 150 μA.
We fabricate a membrane InP-based electroabsorption modulator (EAM), in which an InGaAsP-based multiple-quantum-well (MQW) absorption region is buried with an InP layer, on Si-waveguide circuits. By optical coupling between the MQW absorption region and Si core, a low-loss and large-absorption-length (300-m-long) supermode waveguide is designed to suppress electric-field screening at high optical input power. The EAM is fabricated by combining direct bonding of the MQW layer and regrowth of the InP layer on a thin InP template bonded on a silicon-on-insulator wafer. The fabricated membrane EAM shows an on-chip loss of less than 4 dB at wavelengths over 1590 nm and temperatures from 25 to 50°C. Since the membrane lateral p-i-n diode structure is beneficial for reducing the RC time constant of a lumped-electrode InP-based EAM, the EO bandwidth of the EAM is around 50 GHz without a 50-ohm termination up to fiber-input power of 10 dBm. Using the device, we demonstrate clear eye openings for 56-Gbit/s NRZ and 112-Gbit/s PAM4 signals at temperatures from 25 to 50°C.
A membrane InGaAlAs electro-absorption modulator with an over 67-GHz bandwidth is integrated with a DFB laser on a Si platform. The integrated device shows a dynamic extinction ratio of 3.8 dB for 100-Gbit/s non-return-to-zero signals.
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