Polarization output power stabilization of a vertical-cavity surface-emitting laser

Abstract

This paper provides an experimental investigation of the polarization stabilization at the output power of an 850 nm vertical-cavity surface-emitting laser (VCSEL) with optical feedback (OF) and a range of polarization angles, OF strength, and the bias current. The VCSEL’s polarization stabilization is evaluated using the extinction ratio measurements of the optical output power of the polarization modes of the VCSEL. The results clearly show that rotation of the polarization angle and the OF level can radically change the polarization stabilization of the VCSEL. Both the polarization angle and OF introduce polarization switching (PS) and instability in the optical output power of the VCSEL. Consequently, these lead to performance degradation of the VCSEL in terms of the operating point and the modulation bandwidth. At a fixed OF level of −7 dB, polarization destabilization is first observed at 45° with the increasing level of polarization angle, whereas for the fixed polarization angles of 40° and 90°, polarization destabilization is observed at −14.5 dB and −14 dB, respectively, with the increasing level of orthogonal OF. We show that, with parallel OF, no PS is observed over the entire OF level. The results also indicate that the VCSEL with no polarization angle requires higher levels of OF in order to ensure PS compared with the case with the polarization angle.