The present invention relates to a semiconductor based parabolic waveguide-type collimating lens and a monolithically integrated type tunable external cavity laser diode light source. The monolithically integrated type tunable external cavity laser diode light source includes a gain medium for generating a gain of an optical signal, a collimating lens for correcting an divergent light beam to a parallel light beam, a passive waveguide through which the parallel light beam travels, an optical deflector to change a traveling direction of the parallel light beam changing a refractive index of medium on a traveling path of the parallel light beam traveling through the slab waveguide in response to an external electric signal and a diffraction grating to diffract the parallel light beam passing through the optical deflector, wherein these are integrate into one substrate made of an InP-based semiconductor as well as a material such as a GaAs-based semiconductor, a Si-based semiconductor, LiNbO.sub.3-based semiconductor or the like.