Modulation Of Millimeter Waves By Optically Illuminating n-i-p-i Structures

Semiconductor n-i-p-i structures have been used as all-optical spatial light modulators in devices where one optical beam controls another.l Here we demonstrate that a n-i-p-i can also be used as an optically controlled microwave modulator. The basis for the device is the change in free carrier density of several orders of magnitude caused by illumination with low intensity light.2 In our measurements, light from an argon ion laser with an intensity of about 800 mW/cm2 illuminates the n-i-pi to produce free carriers that attenuate the transmitted signal through a combination of reflection and absorption.