Light interference in waveguides containing periodic one-dimensional air rod arrays

Eliane Flück, L. (Kobus) Kuipers, Niek van Hulst
Applied Optics Group, Dept. of Applied Physics and MESA+ Research Institute,
University of Twente, P.O.Box 217, 7500 AE Enschede, The Netherlands
e-mail: e.flueck@tn.utwente.nl

Using Photon Scanning Tunneling Microscopy (PSTM) we are able to take a direct look inside tailor-made photonic structures. Focused ion beam is used to mill air rods and slits of dimensions on nanometer scale into Si3N4 ridge waveguides. Investigations on first structures consisting out of 1 slit in a waveguide showed the excitation of high loss modes close to the slit and affirmed that PSTM is a powerful investigation tool.

Here, recently obtained PSTM measurements on new structures with 15 air rods in a 1.4 mm wide Si3N4 waveguide ridge are shown (figure 1). The diameter of the rods is 110 nm as well as the spacing between them. Simultaneously with the topography, the optical field distribution has been imaged (1b). The wavelength of the light coupled into the waveguide was 632.8 nm (cw) and its propagation direction was from top of the image to the bottom. At present, field distributions resulting from impinging femtosecond pulses are being investigated. Preliminary results with laser pulses with a central frequency of 630 nm show no great discrepancies with the cw HeNe measurements. In a next study, PSTM will be used to map the phase of the light in this structure simultaneously with the topography and the optical field distribution.

Figure 1: PSTM measurements on a waveguide containing 15 slits of 110 nm diameter fabricated with focused ion beam. Image size: 4.5 mm (vertical) x 6.0 mm (horizontal)
(a) Topographical information
(b) Optical field distribution for light of 632.8 nm (cw) propagating
from the top of the image to the bottom.