Optical Summation of RF Signals

We present two concepts dedicated to the optical summation of RF signals for radar applications. The first technique relies on a photodiode simultaneously illuminated on its top and back sides. We experimentally demonstrate the summation of two signals covering the whole 25-GHz photodiode bandwidth with amplitude and phase errors below ${\pm}{\hbox {1 dB}}$ and ${\pm {\hbox {4}}}^{\circ}$, respectively. The heterodyne beating noise, which occurs in this type of summation device, is also discussed. The second technique is based on a traveling-wave detector array. We experimentally demonstrates the summation of four signals in the whole 25-GHz photodiodes bandwidth. However, the “summation bandwidth” is limited to 10 GHz due to amplitude and phase errors.