  Mode purity is an important reference for the quality of the optical vortex.
In this work, we propose a self-interference method to directly measure single
component in superposed optical vortices based on phase-shifting technology.
This method has excellent flexibility and robustness, which can be applied to a
variety of occasions and harsh conditions. Careful alignment and optimized
error analysis allow us to generate and measure single component with mode
purity as high as 99.997%.
