Ultrafast laser-written 3D nano-antenna for flux extraction and vertical focusing above near-infrared waveguides

Ultrafast laser photoinscription of transparent materials has a unique capacity to generate tunable positive and negative multiscale index structures in flexible 3D designs. Combined with the employment of engineered non-diffractive beams, this enables the generation at the same time of micrometric size waveguides for efficient transport of optical signals and high aspect ratio nanostructures capable of nonperturbatively sampling the optical field propagating nearby in the waveguides, enabling therefore the implementation of signal extraction or antenna functions. We present results for the development of 3D nanoscaled grating arrangements in nonplanar circular geometry working as antennas with focusing properties, capable therefore not only to extract a part of the flux from a waveguide but also to focalize it at a given image plane above the sample, as a function of wavelength. Different geometries were studied, all with equal focusing radius, but different spacing between the nanostructures, in order to understand the sampling and grating efficiency as a function of the number of emitters and their relative distance to the waveguides. The goal of this work is to demonstrate how the high flexibility and the 3D aspect of ultrafast laser photo-inscription of bulk transparent materials can be used for developing efficient optical antennas that could direct flux from a waveguide to a detector, without the need of any relay optics, by fabricating a grating-lens inside the chip, with potential applications in the field of integrated optics spectrometry.