Bragg Cladding Waveguides Demonstrated

In the Oct. 4 issue of Optics Express and in the Oct. 11 issue of Applied Physics Letters, scientists at Massachusetts Institute of Technology in Cambridge describe silicon-based, on-chip Bragg cladding waveguides that are compatible with CMOS fabrication processes. Potential applications include integrated photonics for telecommunications and biosensing.

The waveguides comprise a low-refractive-index oxide core and layers of paired higher-index dielectrics. To demonstrate the structures, the researchers employed SiO₂, Si and Si₃N₄, grown by the low-temperature oxide method and low-pressure chemical vapor deposition, respectively, but they note that there is a large degree of freedom in the selection of the core material. One may opt for a hollow core for applications with high-intensity radiation sources, for example, or for optically active materials for applications in which one desires to modify the rate of emission.

In tests of a waveguide with a 5-µm oxide core designed for operation at telecom wavelengths, the researchers found that it displayed low losses for both fundamental transverse electric (TE) and transverse magnetic (TM) modes. For 1307-nm radiation, the loss was measured to be 0.42 and 0.47 dB/cm for the TE and TM modes, respectively. For 1550-nm radiation, the respective losses were 0.24 and 0.69 dB/cm.