A miniature iris diaphragm made from an electrochromic material has been created by two German researchers who are aiming to add aperturing capabilities to the next generation of smartphone cameras.1 The iris has no moving parts.
Traditionally, cameras have contained a mechanical iris diaphragm, a set of overlapping blades that are mechanically moved to change the size of the aperture. However, it has been almost impossible to miniaturize these mechanical systems for use in cell-phone cameras.
The researchers, from the University of Kaiserslautern, have proposed an alternative method using an electrochromic material called PEDOT that transforms from transparent to opaque when a low electrical voltage is applied to it.
In their study, the researchers fabricated a micro-iris using two glass substrates sandwiched together, with each one carrying a thin film of PEDOT on an underlying transparent electrode. The micro-iris is 55 µm thick and can be switched into an opaque state using a current of 20 µA with a voltage of 1.5 V. The device exhibits a memory effect and does not require a continuous current to maintain the opaque state, so its power consumption remains very small.
Multiple settings
The electrochromic iris contains two concentric circles that can be turned on or off, resulting in three different f-stop settings. In addition, the iris has one very unconventional setting—that where the inner ring is opaque and the outer ring transparent, thus simultaneously passing an annular ring and a central spot. Such a setting could be used for novel "bokeh" out-of-focus effects.
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.
"There is currently no technological solution available that meets all the demands of integrated iris apertures in smartphones," says lead author Tobias Deutschmann. "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 optimized 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 smart phone business."
REFERENCE:
1. T. Deutschmann and E. Oesterschulze, Journal of Optics 16 (2014); doi: 10.1088/2040-8978/16/7/075301
