An LED array on a sapphire substrate may be mounted on a silicon interconnect chip, with LEDs of the array inserted into holes of waveguides on the silicon interconnect chip. The sapphire substrate and the silicon interconnect chip may both have microbumps for carrying electrical signals to or from the LEDs, and the sapphire substrate and silicon interconnect chip may be bonded together using the microbumps. The LEDs may be configured to preferentially emit light in a lateral direction, for increased coupling of light into the waveguides.