Integrated Optical Link on Si Wafer Using Low Energy Membrane InP-based Photonic Devices

In this study, we propose an optical link on a silicon (Si) wafer that integrates a membrane laser, membrane electro-absorption modulator (EAM), and membrane photodiode (PD) connected via a low-loss silica-based (SiOx) waveguide for chip-chip optical interconnects. The membrane structure incorporates a lateral p-i-n diode encased in a low-refractive-index SiO2 layer, which facilitates strong optical confinement, reduces the active layer volume in the laser, and lowers the capacitance in the EAM. The laser features a compact 100-μm-long cavity utilizing detuned distributed feedback (DFB) gratings in which the rear grating is designed to select one of the side modes in the stop band of the front grating. This design achieves a low threshold current of 1.7 mA and asymmetric output, reducing the driving current. The EAM utilizes a Franz-Keldysh-effect-based modulator with an absorption length of 100 μm, featuring a low capacitance of 14.5 fF and a 3-dB bandwidth exceeding 67 GHz. The PD is fabricated with an absorption length of 120 μm to ensure high internal responsivity, providing a 3-dB bandwidth of 48 GHz. These membrane photonic devices are integrated onto a Si wafer using a combination of a wafer bonding method and epitaxial regrowth on the bonded InP layer formed on the Si wafer. Static measurements from the fabricated optical link, which connects the DFB laser, EAM, and PD via a 7.6-mm silica-based waveguide, show an output amplitude of 104 μA at the PD, achieved with a low laser input current of 10 mA and an EAM voltage swing of 1.5 V. Dynamic evaluations at laser currents of 5 and 10 mA revealed eye openings for 50- and 64-Gbit/s NRZ signals, achieving low energy costs of 0.14 and 0.26 pJ/bit, respectively. Eye diagrams for high-speed NRZ signals at data rates up to 96 Gbit/s were also observed.