Reaching <100 ppm/K output intensity temperature stability with single-color light-emitting diodes.

Optical sources with highly temperature-stable output intensity and low power consumption are desired in portable devices for metrology, and in medical applications, communications, and illumination. This paper introduces and demonstrates an optical stabilization scheme that uses the drift in peak-emission wavelength of light emitted from an LED as a temperature feedback signal to realize output intensity temperature coefficients below 100 ppm/K. The control principle relies on a conventional feedback loop but with a specially designed weakly polarizing optical interference coating that exhibits different transmittivity/reflectivity ratio dependence on wavelength for two different polarizations and by using a weighted sum of two polarizations as the output power correcting signal in a feedback loop. The method does not need a thermometer or temperature control stage, and its calibration can be performed electronically, adding to the simplicity of the design and making it also suitable for portable and battery-operated instruments.