Light coupling to waveguides via angularly tuned photonic nanojet

We conduct a theoretical and experimental study on the generation and control of angularly tuned photonic nanojets (PNJs) using a dielectric microsphere under off-axis Gaussian beam excitation for efficient waveguide coupling. Our results show that under plane wave excitation, the nanojet's photon flux in the shadow region remains aligned with the incident beam, regardless of its angle. However, employing a focused Gaussian beam with off-axis excitation enables precise steering of the nanojet emission by up to 80° relative to the illumination axis. Furthermore, we experimentally demonstrate the application of this technique for coupling light into a waveguide, validating its feasibility for integrated photonic systems. The ability to manipulate PNJ direction through off-axis excitation offers enhanced control over optical signal routing. This method extends across a broad wavelength range, making it suitable for various photonic and plasmonic applications, including optical interconnects, waveguide-based sensing, and signal processing.