M. Caterina Netti(a), Martin D. B. Charlton(b), Greg J. Parker(b) and Jeremy
J. Baumberg(a,b)
(a) Department of Physics and Astronomy, University of Southampton
(b) Department of Electronics and Computer Science, University of
Southampton, Southampton

Two-dimensional photonic crystal (2D PC) waveguides encompass several interesting properties for designing nanoscale optoelectronic devices. The confinement of radiation in the planar waveguideand the control of the propagation of guided and lossy modes can be powerfully engineered by choosing core material and structural parameters of the etched lattice pattern.In this work we present a complete and systematic investigation of waveguide transmittance andreflectance experiments on 2D PC waveguides. The crystals consisted of a triangular lattice of airpores etched in a silicon nitride (Si3N4) planar waveguide structure. The measurements we have developed use a `white-light laser' source, essential for producing detailed and calibratedmeasurements over an extremely wide spectral range. We observe strong photonic bandgaps in both TE and TM modes within the same frequency range, and demonstrate their tuning with the structural design parameters [1]. The complete transformation from Bragg scattering to photonic bandgaps is resolved by varying the number of patterning periods [2]. Through angle-tuning we are able toreconstruct the dispersions and compare the photonic density of states with calculation. In contrast, a complete map of the dispersion of leaky air modes is resolved instead by free-space reflectance experiments. Complex dependencies as a function of polarization and crystal orientation are obtained for symmetric PC slabs, showing how TE and TM electromagnatic fields interact in a 2D periodic air/ Si3N4 structure. This Fabry-Perot cavity filled with a photonic crystal medium is a new type of resonator. Through such measurements we are now able to compare the actual structureswith ideal structures and to tie up in detail the calculation and design of these structures.

[1] M.C. Netti, M.B.D. Charlton, G.J. Parker and J.J. Baumberg, "Visible
Photonic Bandgap
Engineering in Silicon Nitride Waveguides", to appear in Appl. Phys. Lett.
76, (2000).
[2] M.C. Netti, M.B.D. Charlton, G.J. Parker and J.J. Baumberg, "Photonic
Band Gaps vs Patterning
Periods for Triangular Lattice Photonic Crystals" to be submitted for
publication to Appl. Phys. Lett.