The bulky nature of optical components has long hindered their convenient integration into our daily lives. Digital single-lens reflex (DSLR) cameras, for example, require multiple sets of bulky lenses that must be interchanged depending on the desired imaging parameters. Analogous to the miniaturization of silicon chips that has revolutionized electronic devices over the past few decades, lightweight and planar optical components are key factors for enabling the development of easy-to-carry or wearable devices.