Single-frequency, polarization-stable, Fabry-Perot fiber laser using a nonpolarization-maintaining fiber and an intracavity etalon

Summary form only given. We propose and experiment with a novel configuration of the single-mode, polarization-stable fiber laser using a nonpolarization-maintaining active fiber. Key features of the laser are twofold: two 45° Faraday rotators are set on both ends of the active fiber. The frequency-selective element is newly designed so as to suppress the reflection from the etalon. We first consider the polarization property of the laser. Note that the state of polarization of the light reflected from a Faraday mirror is orthogonal to that of the incoming light at any position on the return pass. Therefore, the eigenstate of polarization is determined uniquely by the frequency-selective element acting as a polarizer even if any birefringence exists in the active fiber. To achieve single longitudinal-mode oscillation, a narrow-bandwidth filter such as an etalon must be inserted in the cavity. In the case of the FP laser, the intracavity etalon should be tilted from the optical axis; otherwise the reflection from the etalon causes spurious oscillation. However, such tilt of the etalon degrades finesse, resulting in poor mode selectivity. To overcome this problem, we employ a novel configuration for the frequency-selective element. The light reflected from the etalon, whose frequency is outside the passband of the etalon, experiences Faraday rotation by 90°, and is blocked by the polarizer at the incident port. On the other hand, the light whose frequency is within the passband can pass through the etalon without being blocked by the polarizer at the output port. In this way the etalon can be used without tilting, and the mode selectivity of the etalon is maximized.