Optical cross-correlation of millimeter wave signals applied to interferometric radiometry

This paper presents a method to perform in the optical domain the correlations required when processing millimeter wave interferometric radiometer signals. The main problem when addressing the design of an interferometric radiometer working at W-band resides on the distribution and correlation of large bandwidth signals acquired by each radiometer receiver. In order to avoid the necessity of baseband processing of signals with large relative bandwidths, the signals coming from the radiometric receivers are up-converted to the optical domain using LiNbO₃ optical phase modulators. The modulated signals from each receiver pairs are added and and detected by a photodiode. The correlation is obtained from the resulting photocurrent.