Introduction
In this work we propose and simulate a novel CMOS-compatible platform based on Silicon Carbide (SiC), in-air-suspended waveguides (Fig. 1) operating at 1550nm. The proposed design can be realized with a single lithography process, simplifying fabrication with respect to previous SiC photonic realization [1].
Although its refractive index of 2.6 is lower than that of other common photonic materials like Silicon, SiC is interesting because its transparency window extends to visible wavelengths and it does not suffer from two-photon-absorption at 1550 nm. Moreover, the presence of χ(2) nonlinearity and of optically active defects in the near infrared makes SiC a promising candidate to realize sources of quantum states of light and fast integrated modulators.
Methods
We utilize a subwavelength structure that allows guiding and removal of the bottom substrate analogous to the scheme realized for midIR SOI photonics [2]. The simulation of the optical structure was performed with FDTD methods and MPB software from which the waveguide’s band structure and bandgap were obtained (Fig. 2). The dimensions of the suspended waveguide (Fig. 1A) results from a trade-off between having as few modes as possible, and a field which is well confined to minimize roughness losses on the lateral structures (Fig. 1B). While the structure is essentially a Bragg grating, the longitudinal periodicity is chosen to be much smaller than the wavelength of operation, thus the energy of the photons is much below the bandgap (dashed line in Fig. 2) and diffraction losses are completely avoided. Slow light regime can be achieved by increasing the periodicity, as the quasi-momentum approaches the edge of the first Brillouin zone.
Results
The waveguides we propose are 600 nm wide, 300 nm high and they have 300 nm periodicity for normal operation. The minimum width of the suspending arms is 100 nm, well above the capabilities of e-beam lithography, and it is limited by the mechanical strength required to suspend the SiC waveguide. If the periodicity is increased to 420 nm, we expect the waveguide to possess group indexes higher than 10, offering the opportunity to control the light-matter interaction strength.
Discussion
Our platform enables the realization of scalable, SiC CMOS-compatible photonic devices at 1550 nm with tunable properties that can be used for linear and quantum operation.
[1] Martini, F., and Politi, A., Optics express, 25 (10), 10735-10742 (2017)
[2] Penadés, J. S. et al., Optics express, 24 (20), 22908-22916 (2016)
