Heterogeneously Integrated C-band p-i-n Type Mach-Zehnder Modulators Utilizing InP Chips on SOI Wafer Bonding Technology

We report an InP/Si heterogeneously integrated C-band p-i-n type Mach-Zehnder modulator (MZM) using InP chips on SOI wafer bonding. This MZM employs Si waveguides for the miniaturization of devices and the quantum confined Stark effect (QCSE) of InP-based quantum-well structures for highly efficient modulation. Thermo-optic (TO) phase adjusters are placed on each Si waveguide arm for changing the refractive index. A two‑storied taper structure enabling a low‑loss optical transition between Si waveguide and InP ridge waveguides is realized through precise alignment (<±100 nm) achieved by stepper lithography after chip bonding. We fabricated two types of MZMs. The first was a single-channel MZM exhibiting a high modulation efficiency of VπL = 0.43 Vcm and a high electrical/optical (EO) 3dB bandwidth of 73 GHz, with a half-wavelength voltage (Vπ) of = 7.2 V (electrode length: 1 mm, filling factor (FF) of electrode: 60%). Subsequently, we fabricated an In-phase and Quadrature (IQ) modulator incorporating four MZMs, achieving a device size of 3.8 mm × 3.3 mm. Each of the four MZMs within the IQ modulator achieved similar performance to the single MZM, attaining an EO 3 dB bandwidth of 60 GHz and Vπ = 6 V (electrode length: 0.9 mm, FF: 80%). These results demonstrate that heterogeneously integrated MZMs using InP chips on SOI wafer bonding are highly promising for achieving both high modulation efficiency and wide bandwidth operation.