Space-time analogy and its application to design schemes borrowed from Fourier optics for processing ultrafast optical signals

Abstract

Square-wave pulse generation with a variable duty ratio can be realized with the help of ideas of Talbot array illuminators formulated for binary phase gratings. A binary temporal phase modulation of CW laser field propagating through a group-delay-dispersion circuit of the fractional Talbot length P/Q results in a well defined sequence of square-wave-form pulses. When P = 1 a duty ratio of the pulses D is 1/2 for Q = 4 and 1/3 for Q = 3 and 6. Maximum intensity of the pulses doubles and triples compared to the CW intensity for D = 1/2 and 1/3, respectively. These pulses can be used for return-to-zero laser field modulation in optical fiber communication. For D = 1/3 extra features between the pulses are found originating from a finite rise and drop time of phase in a binary phase modulation. Similar effect as a benefit of the time-space analogy is predicted for binary phase gratings and interpreted as gleams produced by imperfect edges of the components of the rectangular phase gratings.