Optical Summation of RF Signals

We present two concepts dedicated to the optical summation of RF signals for radar applications. The first technique is based on a traveling wave detector array. We experimentally demonstrate the summation of four signals in the whole 25 GHz photodiodes bandwidth. However, a deeper study reveals that amplitude and phase errors increase dramatically at high frequency, limiting the practical application to 10 GHz. The second 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 plusmn1dB and plusmn4deg, respectively. The heterodyne beating noise which occurs in this type of summation remains below -40 dB