Analysis of the effect of coupling coefficients on the slope of PDH-locked frequency discriminator

The effects of the coupling coefficients on the reflected field and the error signal under various misalignments and near-axis conditions are analyzed, and some basic features of the error signal are investigated. According to the definition of traditional coupling efficiency, the relationship between the discriminator slope and the coupling efficiency under the condition of misalignment of waist radius and waist position is derived. The experimental results are in good agreement with the theoretical simulations, the error of the results measured by transmission is within 2%, and the error of the results measured by reflection is within 4%. It shows that the discriminator slope has different expressions under different approximation conditions. On this basis, a fast and simple method for measuring the discriminator slope is found.