Silicon-Integrated 850-nm Hybrid-Cavity VCSEL

Conference poster, 2015

Silicon photonics is a promising energy-efficient and cost-effective platform for optical integrated circuits. However, due to its indirect bandgap silicon cannot be used to produce effective light sources. An attractive solution to this is heterogeneous integration of the GaAs-based vertical-cavity surface-emitting laser (VCSEL) on silicon. The GaAs-based VCSEL has proven to be both high-speed and energy efficient, with data rates above 70 Gb/s and less than 100 fJ/bit dissipated power up to 50 Gb/s. By employing ultra-thin divinylsiloxane-is-benzocyclobutene (DVS-BCB) adhesive bonding a GaAs-based “half-VCSEL” with a gain region and a top distributed Bragg Reflector (DBR) has been attached to a dielectric DBR on silicon. This creates a hybrid cavity where the standing-wave optical field is extending into both the silicon and GaAs-based parts of the cavity. The hybrid-cavity may eventually enable light to be tapped off to an in-plane waveguide, e.g. using a high contrast grating (HCG) instead of the bottom DBR. Replacing the whole bottom DBR with an HCG also gives the possibility to set the wavelength according to the grating parameters, enabling fabrication of multi-wavelength VCSEL arrays that together with integrated wavelength multiplexers could form 850-nm wavelength division multiplexed (WDM) transmitters. A 9 µm oxide aperture diameter VCSEL has a threshold current of 1.2 mA and a maximum output power of 1.6 mW at ~845 nm. The performance is currently limited by the too small gain-to-resonance detuning and the high thermal impedance.