Linewidth-narrowed, tunable spectrum can be obtained by external cavity feedback laser diode array (LDA). The external cavity is made up of fast axis collimator, collimating optical system and diffraction grating. Due to smile effect, each beam from emitter strikes the grating at a different angle, so the spectrum of each emitter has a different center wavelength and is expanded. All the emitters spectra compose the array spectrum whose width is increased by the smile effect. A spectrum filter is placed in the output branch to further narrow the spectrum. By this, the linewidth of LDA output is reduced from 2 nm to 0.12 nm with a tuning range of 12 nm (806～818 nm).