One-dimensional spherical photonic crystal

We report on an experimental demonstration of a one-dimensional photonic crystal with a spherical geometry. The photonic crystal is fabricated by atomic layer deposition of bi-layers of aluminum oxide and titanium dioxide at... [ view full abstract ]

We report on an experimental demonstration of a one-dimensional photonic crystal with a spherical geometry. The photonic crystal is fabricated by atomic layer deposition of bi-layers of aluminum oxide and titanium dioxide at the end of a multimode fiber shaped as a ball by fusion (see figure “Concept”). In addition to the simulations providing an optimized design and a theoretical explanation of the behavior of light in such a device, we present an experimental characterization of the structure optical features.

The fabrication of the sphere is done using a fiber splicer. By adapting current and time of the electric arc generated by the device, it is possible to shape the end of a multimode fiber into a ball with desired controllable diameter and position with respect to the fibers axis. The fiber is coated with a multilayered structure. The multilayer, designed by transfer matrix method and finite difference time domain method is fabricated by atomic layer deposition (ALD). This technique allows a high control of the thickness and a conformal coating all around the fiber. The multilayer is optically interrogated at different angles, by using with a supercontinuum as a light source and an optical spectrum analyzer as a detector, in a goniometric arrangement.

The multilayers is designed to open a photonic band gap in the visible region of light. Scanning electron micrograph (SEM) pictures (see figure “SEM pictures”) show that the sphere is conformally coated. The thickness of the high refractive index layers is 80 nm and the thickness of the low refractive index layers is 55 nm. When a white light source is injected in the fiber, transmitted light shows a photonic band gap spectrally centered at 650 nm, as expected from simulations. 

The development of such a structure fabricated at the end of a fiber opens a way to the high integration of sources together with filters, with applications in the field of lab-on-fiber, laser, specialty fibers, and other fiber integrated components.