A systematic approach to quantifying the impact of stray diffractive orders in zoom systems with multiple diffractive surfaces

In optical systems utilizing multiple diffractive surfaces, the number of potential non-design order combinations grows combinatorically. To meet stringent 'as-built' MTF performance, a predictive understanding of how the PSF contributions from the stray order combinations coherently interfere with the design order PSF and an idea on the potential contrast degradation is essential early-on in the design phase. The challenge is exacerbated in zoom objectives, particularly when a diffractive surface is used in a moving group. This paper presents a continuous zoom objective as a design example with multiple diffractive surfaces, and an approach utilizing the sum over orders (SOO) method to analyze the cumulative impact of all possible stray order combinations. The methodology involves sorting combinations by their normalized irradiance to identify the most significant contributors. An approach to determine appropriate weighting for these combinations based on their energy distribution and on the spectral range is also discussed in this paper.