The EC-iris in the four individual states possible [Credit:�Journal of Optics]

'Smart glass' iris to inspire next gen camera phones

A low-power, lightweight camera iris made using ‘smart glass’ could inspire the next generation of smartphone cameras.

The component is an electro-chemical equivalent to the bulky, overlapping mechanical blades known as iris diaphragms that cameras use to alter the size of the hole – or aperture – through which light enters the device, allowing them to control the amount of light that reaches their sensors, which consequently affects the focus of the resulting image.

The micro-iris invented by researchers from the University of Kaiserslautern in Germany, instead uses an electrochromic material often referred to as smart glass, which transforms from a transparent material into an opaque material when a small electrical voltage is applied to it.

With the rising popularity of small, compact and lightweight consumer devices that are integrated with cameras, it has been almost impossible to miniaturise the traditional mechanical systems, but the researchers’ smart glass approach can be made very small and has very low power consumption.

Tobias Deutschmann, lead author of the research published today in the Journal of Optics, said: “There is currently no technological solution available that meets all the demands of integrated iris apertures in smartphones.

“Many of the proposed devices require the motion of a strong absorbing material to block the path of light. Electrochromic materials, as used in this study, remain stationary whilst they change their absorption, so there is no need for any actuation. This allows for much smaller casings to fit around the devices and thus enables the integration into tiny camera systems.

“We will now further investigate the potential of optimised electrochromic materials, with a particular focus on improving the optical contrast and, in particular, the control of the depth of focus – this is the decisive hardware parameter which determines the success of next-generation models in the smartphone business.”

In their study, the researchers fabricated a micro-iris using two glass substrates sandwiched together, and with each one carrying a thin film of electrochromic material, called PEDOT, on an underlying transparent electrode.

The micro-iris was 55µm thick and could be switched into an opaque state using a current of 20µA with a voltage of 1.5V.

The micro-iris exhibited a memory effect and did not require a continuous current to maintain the opaque state, so its power consumption remained very small.

In addition to testing the intensity of light that passed through the micro-iris, as well as the amount of time it took to switch between different states, the researchers also examined the depth of focus that the micro-iris was able to impart in comparison to a traditional blade-based iris.

In the conclusion of their paper, the researchers admit their results indicated that the light absorption properties of the electrochromic material, as well as the switching time between clear and opaque states, would have to be improved to make the technology viable in consumer products.

But they also note that the synthesis of such materials is under rapid development, making them a promising avenue for future low-power and miniaturised camera irises.

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