Ultrashort all-fiber Fabry-Perot interferometer fabricated by a CO₂ laser

We proposed and demonstrated a method to fabricate ultrashort all-fiber Fabry-Perot interferometers by splicing a standard single-mode fiber and another single-mode fiber with a concave surface constructed by a CO₂ laser pulse. The geometric parameters of the concave surface could be controlled flexibly by adjusting the laser pulse and the relative position between the laser beam and the optical fiber. In our experiments, the minimum depth of the concave surfaces is 0.12 µm, which offers a means of fabricating an all-fiber Fabry-Perot interferometer with submicrometer cavity length. Moreover, the ultralow-roughness concave surface fabricated by a CO₂ laser pulse is beneficial to improve the fringe visibility of the interferometer. These advantages make it attractive for practical applications.