Electromagnetic Modeling of NanoLED Arrays

University of Rome Tor Vergata has continued electromagnetic modeling of nanoLED arrays. Using finite difference time domain (FDTD) method implemented in CST software, we have calculated the optical near field of single emitters, of a nanoLED array and of small metallic pin/holes on planar LED structures. From these simulations, we extracted the full-width half maximum (FWHM) of the electromagnetic field strength at different distances from the LEDs, as shown in Fig. 1. It has been found, that the FWHM increases linearly with distance, as for an isolated dipole in a homogeneous medium, with proportionality constant larger than one. This means, that the emitter zone of the LED should not be more distant than half a wavelength from the object to be studied. Similar results have been obtained for pin-hole structures, where in addition the optical power transmitted to the region of interest is largely reduced due to absorption in the metal.

Figure 1: Light emission from a single emitter: structure (left), electric field strength (middle) and power density along a horizontal line at different distances.

For the nanoLED arrays, we have observed substantial optical crosstalk between neighboring pixels. First steps towards an optimization of the array structure in order to suppress crosstalk have been taken, following different approaches including the use of absorbing filler materials.

In order to move towards detection of small objects between the emitter and the detector, simulations of the optical field disturbed by gold spheres on top of the nanoLED arrays have also been performed (see Fig. 2). These simulations allow to define the image reconstruction algorithms necessary to reach the goals of ChipScope.

Figure 2: Simulation model including an object above the nanoLED array (left). On the right the predicted intensity emitted towards the detector for the different pixels is shown for two different positions of the gold sphere (indicated by a white circle).

Contact and further information:

Dr Matthias Auf der Maur, Università di Roma Tor Vergata, auf.der.maur@ing.uniroma2.it