Visible wavelength external cavity diode lasers in photonic integrated circuits for atomic technologies

Atoms can be controlled by manipulating their internal states using agile, quiet and reliable laser sources. An external-cavity diode laser (ECDL) is a crucial enabling technology to realize such laser sources since it allows for the narrowing of the linewidth of a laser diode and precise tuning of the laser frequency. This project aims to miniaturize the external cavity using a photonic integrated circuit (PIC) (i.e., a single chip), which will increase the reliability and functionality of the optical frequency source for quantum experiments. A PIC ECDL will be designed and fabricated using aluminum nitride (AlN). Since several atomic transitions of interest in quantum applications are in the visible spectrum, AlN is an ideal material due to its large bandgap that allows for low-loss waveguide propagation. AlN also enables key functionality for preparing narrow linewidth and agile optical frequencies. Thus, an AlN waveguide will be fabricated and tested to ensure low waveguide losses at visible wavelengths. An external cavity feedback laser will be fabricated by coupling a laser diode directly into the AlN waveguide. A micro-ring resonator feedback circuit will be used to select and narrow the laser output. The light will be further coupled into fibre optics for delivery to atoms in a vacuum chamber, demonstrating the viability of using PIC ECDLs to interact with atomic energy levels. This AlN PIC ECDL would be a compact optical frequency source that could help enhance existing quantum experiments, enable experiments currently unviable with bulk optical setups and allow for the translation of quantum atomic technologies out of the laboratory (i.e., large-scale quantum computation, high-precision gravimeters for resource mapping and portable optical atomic clocks).

Figure 1. A conceptual render of an external cavity diode laser in an aluminum nitride integrated photonic circuit.