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Recent theoretical work suggested upper bounds on the operating bandwidths offlat lenses. Here, we show how these bounds can be circumvented via amulti-level diffractive lens (MDL) of diameter = 100 mm, focal length = 200 mm,device thickness = 2.4{\mu} m and operating bandwidth from ? = 400 nm to 800nm. We further combine the MDL with a refractive lens to demonstrate a hybridtelescope. By appealing to coherence theory, we show that the upper bound onrelative bandwidth is surprisingly independent of lens diameter or numericalaperture, but is only limited by the bandwidth of the image sensor. Sincelarge-area achromatic flat lenses produce significant reductions in weight overtheir refractive counterparts, these calculations and experiments open upopportunities for very large scale diffractive and diffractive-refractivetelescopes.

Circumventing size-bandwidth limits in imaging with flat lenses