Optical modes in subwavelength-scale nanostructures are hard to reach from conventional far-field optics because they mainly exist in the form of near-field. Here, we propose an experimental method that can map out the near-field optical modes of any arbitrary nanostructures. We set up a far- to near-field transmission matrix system by using near-field scanning optical microscope and wavefront shaping of incident wave. By applying the singular value decomposition of the measured transmission matrix, we could identify symmetric and antisymmetric modes of a pair of nano-antenna whose width and separation are well below the diffraction limit. Our method will help designing complex functional nanostructures by providing the experimental means of understanding their optical response.
Micro-disk resonators were fabricated using Er doped silicon-rich silicon nitride (SRSN:Er). SRSN:Er thin films are fully CMOS-compatible and show efficient Er3+ luminescence pumped off-resonantly via Si nanoclusters. The high refractive index of SRSN (>2.0 at 1.5 μm) allows freedom in designing compact micro-disk resonators. Micro-disks with two different contents of Er (0.2 at.%, 0.02 at.%) with a diameter of 25 μm were fabricated, and characterized using evanescent coupling using tapered fibers. Whispering gallery modes with Q-factors in excess of 13000 were obtained, and FDTD calculations indicate that much higher values should be possible. Finally, we demonstrate excitation of fundamental whispering gallery mode via off-resonant, top-pumping of the SRSN microdisk.
We propose and demonstrate reconfigurable microfiber-coupled photonic crystal (PhC) lasers. In this generic
configuration, the position of a PhC resonator can be defined (and redefined) repeatedly by simply relocating a curved
microfiber along the linear PhC waveguide. In the proximity of the PhC waveguide in contact with the microfiber, the
cutoff frequency (effective index) of the PhC waveguide becomes smaller (larger) than that of a bare PhC waveguide.
Accordingly, when a curved microfiber is in contact with the PhC waveguide, a linear PhC resonator having Gaussianshaped
potential well is formed. Experimentally we confirm the formation of the reconfigurable resonator by observing
laser operation slightly below three available band edges.
The influence of etching slope on cavity Q-factors in two-dimensional (2D) photonic crystal (PhC) slab is studied. Through FDTD simulation, it is confirmed that the Q-factor decreases with etching slope. The main loss comes from the horizontal coupling into propagating TM-modes. We designed three-lattice-long modified linear cavities having high Q-factors. However, the measured Q-factor was about 250. This small Q-factor is attributed to the non-vertical (13°) side wall.