The impact of optical feedback on the emission properties of edge-emitting diode lasers is crucial for their use in various applications with unavoidable optical feedback. A hybrid master oscillator power amplifier (MOPA) concept based on a low-power laser (MO) and a tapered amplifier (TPA) is well suited for those applications. The MOPA offers the ability to mechanically separate the MO from the TPA, which allows to shield the MO against possible optical feedback from the TPA by using an optical isolator. However, the feedback emitted from the TPA towards the MO has not been investigated in detail yet. In addition to the feedback from the TPA the MOPA as a whole can be subject to external feedback. Depending on the beam path in the respective application, feedback ratios in the range from 10−4 to 10−2 to the TPA may occur. The optical feedback coupled to the TPA is expected to be also amplified in the TPA which increases the feedback towards the MO dramatically. Therefore, the propagation of feedback light through the TPA and its emission characteristics towards the MO have to be studied in detail. A beam propagation method including a model for the charge carriers and a fast thermal solver utilizing a Green’s function approach is used to simulate feedback propagation inside the TPA. A description of the model, with focus on the thermal solver, will be presented as well as a comparison to measurements. The results allow to optimize MOPAs with respect to feedback more accurately.
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