Large-range stretch-tunable flat lens for broadband imaging

Diffractive lenses offer significant weight advantages over refractive lenses, making them well-suited for compact imaging systems. Varifocal diffractive lenses, in particular, hold promise for enhancing flexibility in applications such as microscopy and smartphone cameras. However, developing achromatic varifocal diffractive lenses remains a key challenge. Here, we present a tunable harmonic diffractive lens operating across the visible spectrum with polydimethylsiloxane (PDMS). Its focal length scales proportionally with the fourth power of the applied stretch ratio within a broadband. Fabricated with a 23 μm profile and 100 μm substrate, the lens achieves continuous focal tuning from 40.4 to 79.5 mm under white light through motor-controlled stretching (1-1.2×). Imaging tests confirm its broadband imaging performance.