Narrow linewidth 650 nm DBR laser diode for quantum applications

Laser systems are utilized in quantum for various applications. Multiple wavelengths and tailored solutions are required depending on the technology that the laser will be applied to. For instance, lasers can be used for controlling particles and molecules, including excitations of the quantum systems. Key performance requirements for lasers used in these applications include narrow linewidth, frequency stability, and single-frequency operation. This performance can be achieved with laser diodes with integrated gratings, such as distributed Bragg reflector (DBR) and distributed feedback (DFB) structures. Laser diodes offer benefits such as low power consumption, compact size, and easy integrability to photonic integrated circuits. In addition, on-chip integrated gratings have advantages over external cavity diode lasers: reduced complexity in systems, smaller size, and better robustness. In this work, we present narrow linewidth DBR laser diode operating in the 650 nm wavelength regime which is required for quantum applications such as repumping in trapped Ba⁺ ion computing. In-house epitaxial design is based on a GaAs/AlInP/AlGaInP structure, including GaInP quantum well. Grating region is implemented as surface grating, requiring electron beam lithography (EBL) and high-aspect ratio etching by inductively coupled plasma reactive ion etching (ICP-RIE). Results for multiple variants are presented to achieve optimal device performance and grating coupling efficiency, targeting narrow linewidth operation required for quantum applications such as trapped ion computing.