A light source includes a base, a first bonding layer, at least two laser diodes, a second bonding layer, a substrate, and a planar waveguide. The laser diodes are fixed to and are electrically connected to the base using the first bonding layer, and each of the laser diodes includes a side surface for emitting light. The substrate is fixed to the base using the second bonding layer. The waveguide is formed on the substrate and includes an output section including an output end and at least two input branches branching off from an end of the output section opposite to the output end. Each of the input branches includes an input end opposite to the output section and aligning with a respective one of the side surfaces of the at least two laser diodes.