Image copyright Other Image caption The iris uses concentric chemical rings to open and close the aperture

A new type of chemical iris designed for smartphone cameras has been created by researchers in Germany.

Traditional cameras use mechanical blades to change the size of the aperture through which light enters.

The new micro-iris features transparent chemical rings which turn opaque when a small voltage is applied.

The ultrathin device could inspire a new generation of tiny cameras for phones and tablets according to a study in the Journal of Optics.

Our results prove that the electrochromic iris can be utilised in principle to control the transmitted light and depth of focus Tobias Deutschmann, University of Kaiserslautern

As in the human eye, the iris in a camera controls the amount of light that reaches a sensor, affecting the overall focus of the image.

Typical mechanical irises feature overlapping blades which open and close around a central aperture.

But attempts to miniaturise these have reached a physical limit, according to researchers at the University of Kaiserslautern.

Battery powered

Instead, they propose an alternative, chemical design - just 55 micrometres thick.

It features concentric rings which can be darkened and lightened to adjust the size of the aperture and thus, the depth of focus.

The device consists of two glass substrates sandwiched together, each one carrying a thin film of the electrochromic polymer PEDOT (poly 3,4-ethylenedioxythiophene) on an underlying transparent electrode.

The chemical can be switched into an opaque state with a low voltage (1.5V) and does not require a continuous current to maintain its state - making it highly suitable for battery-powered devices.

"Our results prove that the electrochromic [EC] iris can be utilised in principle to control the transmitted light and the depth of focus," said lead author Tobias Deutschmann.

"The potential of the iris in its current state is mostly restricted by the insufficient absorption contrast and relatively long switching time of the commercially available PEDOT material.

"However, the synthesis of optimised EC materials is under rapid development.

"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."