外腔反馈的激光二极管阵列(LDA)可获得窄线宽、可调谐的光谱输出。外腔由快轴准直镜、准直光学系统和闪耀光栅组成。由于阵列中各发光单元的排列弯曲导致不同波长的光原路返回,引起谱线展宽,在输出光路中加入光谱滤波器,使激光二极管阵列的线宽进一步窄化。这样,激光二极管阵列的输出光谱由自由运转时的2 nm压缩到0.12 nm,在恒定温度23 ℃时,实现了激光在806～818 nm的调谐,调谐范围达12 nm。

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).