Highly directional grating outcouplers with tailorable radiation characteristics

We describe the design, fabrication, and evaluation of highly directional grating outcouplers, incorporated in grating-coupled surface-emitting semiconductor lasers. In particular, we demonstrate the use of grating-duty cycle variations to control the radiation factor into air, with maintained directionality of the outcoupling. This is accomplished by using rectangular gratings in combination with a multilayer-substrate reflector. The performance of the outcouplers is compared with numerical calculations based on a perturbation method. Controlled variations of the radiation factor enable advanced holographic-wavefront conversion, making grating-coupled surface emitters equipped with such outcouplers attractive in a large number of applications, both as single-element devices and in optical-integration schemes.