Fabrication of 780 nm DBR laser diodes for quantum applications

Lasers have multiple applications in the field of quantum. A few examples are cooling and repumping lasers for atoms and ions used in constructing qubits, frequency combs and atomic clocks. The performance required from a laser solution varies between the applications, however, single-mode operation, narrow spectral linewidth, and extreme frequency stability over operation lifetime are demanded for any of the applications. Use of semiconductor laser diode as a laser source offers multiple advantages, such as tunability by current and temperature, small size, and low energy consumption. Narrow spectral linewidths from semiconductor lasers can be achieved by the means of external cavities, or monolithic approaches such as distributed Bragg reflector (DBR) and distributed feedback (DFB) lasers. The selection of the most suitable solution depends on the required output power, linewidth, and mode-hop free tuning range requirements. The use of monolithic on-chip gratings for wavelength stabilization decreases system complexity and increases overall rigidity compared to external cavity solutions. In this work, we present device-level results for our 780 nm DBR laser design and compare them to the simulations. The 780 nm wavelength range is of particular interest for quantum computing due to the Rb atom D2 line. For optimization purposes, devices with varied grating designs, ridge geometries and gain area lengths were fabricated and measured. Future improvements related to device processing, design, and extending to other wavelengths are discussed.