Rapid photo-goniometric technique for LED emission characterization

The emission characteristics of different LEDs are measured using an optical Fourier transform instrument originally designed for flat panel display characterization. In this approach all the light coming from the device is collected by a dedicated optics and imaged on a CCD sensor. The angular aperture of the instrument extends up to ±88° and all the azimuths for 0 to 360° are collected at the same time. The angular resolution is better than 0.5°. The luminous intensity and the color are measured rapidly and accurately. A large measurement spot size (∼2mm) ensures to get all the emission of the device at the same time. It avoids any error and alignment requirements are reduced. In addition to get the luminous intensity distribution very accurately, we have noticed in some cases a dependence of the spectral emission with the angles. This dependence depends on the working conditions of the devices and in particular of the current injected in the LED. Polarization analysis of light emitted by different laser diodes is also presented.