On the Comparison Between Low Noise Amplifiers and Photonic Upconverters for Millimeter and Terahertz Radiometry

We analyze the feasibility of upconverting THz radiation to the optical domain for high sensitivity room temperature radiometry, as an alternative to radiometers based on low noise amplifiers (LNAs). Following a semiclassical approach, the noise performance of the upconverters is studied. A similar analysis is followed to model the thermal and quantum sources of noise in low noise amplifiers. A comparison between both schemes is done, showing the potential of the upconversion approach if high efficiencies are accomplished. This is due to the low thermal occupation achievable in whispering-gallery mode upconverters and the fact that the minimum introduced noise is not fundamentally bounded by a quantum limit when direct detection is performed.