An optical chopper includes an optical loop having first and second terminals and includes first and second nonlinear elements. The optical loop is arranged to receive, at the first and the second terminals, a pulse-modulated signal and a continuous beam, respectively. The optical loop is arranged to cause the pulse-modulated signal and the continuous beam to counter-propagate in the loop and to produce in the first nonlinear element an inverted pulse-modulated signal having modulation which is inverted with respect to the pulse modulation of the pulse-modulated signal and to cause the inverted pulse-modulated signal to chop the pulse-modulated signal in the second nonlinear element.