Described herein are optical devices including resonant cavity structures. In one embodiment, an optical fiber includes: (1) an elongated core including an outer surface; (2) an inner reflector disposed adjacent to the outer surface of the core and extending substantially along a length of the core; (3) an outer reflector spaced apart from the inner reflector and extending substantially along the length of the core; and (4) an emission layer disposed between the outer reflector and the inner reflector and extending substantially along the length of the core, the emission layer configured to emit radiation that is guided within the optical fiber.