Terahertz bandwidth integrated radio frequency spectrum analyzer via   nonlinear optics
  We report an integrated all-optical radio frequency spectrum analyzer based on a ~ 4cm long doped silica glass waveguide, with a bandwidth greater than 2.5 THz. We use this device to characterize the intensity power spectrum of ultrahigh repetition rate mode-locked lasers at repetition rates up to 400 GHz, and observe dynamic noise related behavior not observable with other techniques. 
Marcello Ferrera, Christian Reimer, Alessia Pasquazi, Marco Peccianti,   Matteo Clerici, Lucia Caspani, Sai T. Chu, Brent E....
physics.optics