Disclosed is a unit substrate for an optical device, the unit substrate including: an optical device-mounting region provided on an upper surface of the unit substrate; and first and second metal substrates bonded to each other with a vertical insulating layer interposed therebetween. A lower surface of the unit substrate is electrically connected to the mounting region, and side and upper surfaces of the unit substrate are electrically isolated from the mounting region such that an optical device is capable of operating in an environment with low electrical resistance.