The cost and power consumption of optical transmitters are now hampering further increases in total transmission capacity within and between data centers. Photonic integrated circuits (PICs) based on silicon (Si) photonics with wavelength-division multiplexing (WDM) technologies are promising solutions. However, due to the inefficient light emission characteristics of Si, incorporating III-V compound semiconductor lasers into PICs via a heterogeneous integration scheme is desirable. In addition, optimizing the bandgap of the III-V material used for each laser in a WDM transmitter becomes important because of recent strict requirements for optical transmitters in terms of data speed and operating temperature. Given these circumstances, applying a direct-bonding scheme is very difficult because it requires multiple bonding steps to bond different-bandgap III-V materials that are individually grown on different wafers. Here, to achieve widebandWDMoperation with a single wafer, we employ a selective area growth technique that allows us to control the bandgap of multi-quantum wells (MQWs) on a thin InP layer directly bonded to silicon (InP-on-insulator). The InP-on-insulator platform allows for epitaxial growth without the fundamental difficulties associated with lattice mismatch or antiphase boundaries. High crystal quality is achieved by keeping the total III-V layer thickness less than the critical thickness (430 nm) and compensating for the thermally induced strain in the MQWs. By carrying out one selective MQW growth, we successfully fabricated an eight-channel directly modulated membrane laser array with lasing wavelengths ranging from 1272.3 to 1310.5 nm. The fabricated lasers were directly modulated at 56-Gbit/s with pulse amplitude modulation with four-amplitude-level signal. This heterogeneous integration approach paves the way to establishing III-V/Si WDM-PICs for future data-center networks.
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