A thin-film narrowband retroreflector is proposed for a diverging free-space wave. The retroreflector consists of a focusing grating coupler in a waveguide resonator on a reflective substrate. The retroreflector is designed and fabricated for an incident wave diverging from a 5.25μm diameter spot. The retroreflector gives a reflection towards the divergence point of the incident wave at the resonance wavelength determined by the waveguide resonator, but otherwise a specular reflection. The retroreflection spectrum of a 4nm bandwidth with the peak of 75% is demonstrated. This configuration will provide a lens-less external-cavity-mirror diode laser of a lasing wavelength fixed to the resonance wavelength.

提出了一种用于发散自由空间波的薄膜窄带回射器。回射器由位于反射基板上的波导谐振器中的聚焦光栅耦合器组成。后向反射器的设计和用于入射波从5.25发散制造μ米直径光斑。回射器以波导谐振器确定的谐振波长向入射波的发散点进行反射，否则为镜面反射。演示了 4nm 带宽的回射光谱，峰值为 75%。这种配置将提供激光波长固定为谐振波长的无透镜外腔镜二极管激光器。