Polarization switching mechanism in a single-mode He-Ne laser caused by injection locking

Abstract

Polarization switching in an internal mirror 633 nm He Ne laser caused by injection locking has been reported [1]. In the present paper, the switching characteristics in single mode operation is theoretically analyzed using vectrial injection locking theory [2]. Due to an intracavity birefringence, the slave laser (SL) has two natural polarization states which are orthogonally polarized with each other and there is slight frequency difference between these polarization states for the same longitudinal mode. The frequency of the master laser (ML) is scanned uni directionally (lower to higher for example) in the following description. When the injection locking frequency range (ILER) which is proportionally depends on injection intensity is greater than twice of the above birefringent caused frequency difference (BCFD), the polarization state of SI. switches alternatively by scanning the frequency of ML as shown in Fig. 1. If the ILER is less than the BCED, ILFRs of both polarization states do not overlap and the polarization switching does not occur. In the case of BCED < ILFR < 2 × BCFD, the polarization state of lower frequency switches to that of higher frequency, however polarization switching of reverse direction does not occur as shown in Figs. 2 (a) and (b). The calculated results are well agreed with the experimental results.