Fig. 7: 3D GRIN waveguides coupled to ring resonators.
From: Direct laser writing of volumetric gradient index lenses and waveguides
a 3D multiphoton imaging of a subsurface U-shaped waveguide printed in PSiO2 coupled to a microring resonator, with coupling ports displaced by 250 μm. b Top-view multiphoton image of a 60-μm diameter all-pass microring resonator coupled to a bus waveguide. The inset shows the submicron gap between the microring and the bus waveguide. c Measured microring resonator spectrum for a 600 nm gap device operating in TE mode (inset: resonance near 1539.5 nm shows a 0.36 nm FWHM). d Microring spectrum for a 400 and 800 nm gap device operating in TE mode
