Using optical waveguides and ring resonators as examples, they are demonstrating how atomic layer processing (ALP) can be used to significantly improve the optical properties of photonic devices made of SiC.
MPL and Fraunhofer applying SiC to PICs
Cross-section of a photonic structure in silicon carbide (SiC on Insulator, SiCOI).
SiC is of interest due to nonlinear optical effects that can be exploited to modify the colour of laser light. For instance, it can be used to convert infrared light into visible light very efficiently.
The possibility of integrating point defects in the form of colour centres that function at room temperature means SiC may allow the direct integration of quantum functionality in the future.
SiC could therefore be used to produce all the elements required for the construction of powerful, miniaturised quantum systems. It is compatible with microelectronics and microphotonics, and offers new quantum electronic functions.
Since it is compatible with CMOS processes of classic silicon technology, SiC would be ideal for the industrial mass production of quantum PICs.
To build PICs, standardised microphotonics devices with minimal optical losses are needed. Optical waveguides and ring resonators that can efficiently guide or store light in tiny structures are essential for this.
While waveguides perform the function of loss-free optical lines, resonators consist of tiny rings in which the input light completes up to a million cycles. The photon storage times achieved in this way allow these devices to be charged with high circulating optical power, enabling a variety of nonlinear optical effects.
For example, micro-resonators can convert laser light of a specific wavelength into an optical frequency comb, i.e., a light source consisting of several discrete frequencies, which can be used, for example, for very fast parallel data transmission in telecommunications networks.
Another useful effect is the interaction of counter-propagating light. The nonlinear optical coupling of counter-propagating light in ring resonators leads to spontaneous symmetry breaking that allows light to circulate in only one direction, i.e., clockwise or counterclockwise.
This can be used, for example, to implement chip-integrated optical diodes, photonic switches, or optical sensors, which enable the construction of more complex photonic systems.
However, the quality of the photonic devices manufactured on SiC substrates is not yet optimal, and the relatively high surface roughness causes optical losses in the waveguides and resonators.
Flawless surfaces are essential to ensure that photons can move quickly and do not tunnel outwards. A promising solution is to smooth the component surfaces using atomic layer etching (ALE) to create well-defined interfaces and minimize loss and scattering centres.
