All-optical RF spectrum analysis of ultra-high speed optical signals

We experimentally demonstrate an all-optical technique for monitoring the radio-frequency (RF) spectrum of ultra-high bit-rate signals, with bandwidths exceeding 1 THz. This monitoring scheme exploits the ultra-fast response time of the optical Kerr nonlinear effect, such that the instantaneous intensity of the signal is translated to a phase modulation of a co-propagating probe, which can be measured as a frequency modulation on a standard optical spectrum analyzer, without the need for high-speed electronics. This scheme is applied to measure the optical RF spectrum of ultra-high bit-rate 160 and 320 Gb/s optical signals, and shows that impairments caused by either chromatic dispersion or amplitude modulation can be effectively monitored, thereby providing a useful diagnostic tool. The advantages of ultra-high bandwidth (up to terahertz), very fast response time and simple setup are highlighted.