>That issue of scalability in optical systems is “quite fundamental,” Lu says; this new approach offers a way to circumvent it. “We have other applications in mind,” he says, to take advantage of the device’s “optical selectivity in a 3-D bulk object.” For example, a block of material could allow only one precise angle and color of light to pass through, while all others would be blocked.<p>Putting my science fiction hat on, if that meant you could build a light-absorbing material you could potentially have (for instance) camouflage that reflected on a certain wavelength only known to your friendly forces. Or hidden assets that require a filter to see - hidden keypads, hidden instructions, that kind of thing.