Steerable surface emitting laser design based on a line of bound states in the continuum (Invited Paper)

Traditional photonic crystal surface-emitting lasers (PCSELs) rely on isolated quasi-bound states in the continuum (q-BIC) that are generally at the center of the Brillouin zone and which offer high directionality and quality factors. However, due to the isolated nature of the q-BICs they rely on, PCSELs are fundamentally limited in applications that demand continuous tunability, requiring the construction of many different PCSELs that are switched on and off to achieve such tunability. Here, we introduce a new cavity geometry that uses a novel polarization- and angle-selective Bragg reflector to develop a surface emitting laser that features a continuous line of bound states in the continuum. The resulting dispersion allows for high-Q lasing states across a broad wavevector range, with the potential for twin-beam emission whose angular separation can be tuned by adjusting the temperature and injection current into the quantum well gain medium. Numerical simulations confirm that this configuration yields a high-quality factor and supports single-mode operation over large areas due to its reduced density of resonances. The approach will not only enable continuous angular beam control but also offers compatibility with existing fabrication methods. Our study represents a significant step toward overcoming the limitations of isolated-q-BIC-based devices and opens new possibilities for dynamic and tunable beam-steering in integrated photonics. Acknowledgement: SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.