The cost effective and wavelength stability of laser light sources are critical issues for practical implementation of wavelength division multiplexingpassive optical network (WDM-PON) technology. This paper explains the optimized laser structure design and fabrication process to realize the Fabry Perot-Laser Diode (FP-LD) with vertical tapered-waveguide by diffusionlimited etching as a simple and low cost fabrication method. Then, it will be applied to the injection-locking technique to produce the single-mode operation wavelength that finally can be used as a low cost optical network unit (ONU) light source in a WDM-PON system. After injection-locking measurements, the output wavelength of the 500 μm total cavity length with 200 μm taper region which produces 8.566 mW output power and 16% slope efficiency FP-LD is locked to the externally injected light from tunable laser source. The measured of the best side mode suppression ratio (SMSR) is higher than 30 dB. This value is sufficient to be used for WDM-PON applications in “the third window” of optical fiber communication systems.