Time-space-conversion optical signal processing using arrayed-waveguide grating

Ultrafast optical signal processing over 100 Gbit/s data rate, which is difficult to do by traditional electronic means, has been achieved using time-spaceanversion technology. Such processing enables many operations such as the formation, reshaping, pattern recognition and even routing of an ultrafast bit stream. This technology has been widely demonstrated by using free-space optics with diffraction grating pairs and lenses at visible wavelengths[ 11. We have proposed time-space-conversion optical signal processing using an arrayed-waveguide grating (AWG) [2]. Figure 1 shows schematics of time-space-conversion processing systems using (a) diffraction gratings (DGs) and (b) arrayed-waveguide gratings (AWGs). In both systems, a temporal waveform is converted to a frequency spectrum in the focal plane by the dispersive element. The frequency spectrum is then modulated in parallel by a spatial filter and reconverted to a reshaped temporal waveform. When the waveform u(t) with the carrier lightwave frequency vo is incident on the dispersive elements, such as a DG and an AWG, it is transformed into u(t-npx/c) on the x axis lying along the exit surface of the dispersive element, where @ is a dispersion parameter, c is the speed of light, and n is the refractive index of the media through which the light propagates. The maximum time window To is determined by npx/c, hence, T₀=nβ/c Nd=mN/v0