An analytical study on the presence of inter-modal cross-talk in a modal wavefront sensor

A modal wavefront sensor is known for its quick detection, flexibility and simplicity in the measurement of the various aberration modes (in the form of an orthogonal basis set such as the Zernike modes) present in the wavefront of an incident beam. But the output of these type of sensor suffers from inter-modal crosstalk that may arise due to the coexistence of a large number of aberration modes in the incident beam. This leads to degradation of the quality of the sensor output, resulting in inaccuracy in the measurement of aberration modes. Booth et al. provided an optimized expression of the sensor output that reduced the inter-modal cross-talk and improved the linear response of the sensor to a great extent. However, the issue of cross-talk still persists and the sensor for a particular mode is still vulnerable to the presence of other modes. In the present work, we present an analytical study of the influence of inter-modal cross-talk on the output of a holographic modal wavefront sensor for various aberration modes. Theoretical, simulation and experimental results are presented for better visualization of the cross-talk effect.