An Accurate Experimental Investigation of an Optical Sensing Microwave Amplifier

This paper deals with an accurate experimental investigation of the optical sensing behavior of a microwave low-noise amplifier (LNA). The tested amplifier, employing a commercial InGaAs pHEMT has been analyzed in terms of the scattering parameters and the noise figure. The analysis has been carried out by observing how the device behavior is influenced by a continuous wave laser illumination for different optical wavelengths, power levels, and bias conditions. It has been assessed that the LNA performance is significantly influenced by the light exposure with optical effects more pronounced at higher wavelengths for a fixed incident power. Upon applying the recommended bias conditions of the sensing amplifier, the main changes consist of a degradation of the noise figure and gain. As opposite to this, an overall performance enhancement is clearly recognizable with the amplifier biased at the transistor pinch-off. The results obtained in the present work fully confirm a theoretical analysis previously carried out by employing different devices and LNA design.