Investigation of all-optical analog-to-digital quantization using a chalcogenide waveguide: A step towards on-chip analog-to-digital conversion

We have investigated all-optical analog-to-digital quantization by broadening the pulse spectrum in a chalcogenide (As₂S₃) waveguide and subsequently slicing the measured spectrum using an array of filters. Pulse spectral broadening was measured for 8 different power levels in a 6 cm long As₂S₃ waveguide and used to analyze an 8-level all-optical quantization scheme employing filters with full-width at half-maximum (FWHM) bandwidth of 2 nm. A supercontinuum spectrum with -15 dB spectral width up to 324 nm was observed experimentally at large powers. This large spectral broadening, combined with filtering using a 128 channel arrayed waveguide grating (AWG) with 2 nm filter spacing, has the potential for all-optical quantization with 7-bit resolution. In order to encode the quantized signal we propose an encoder scheme which can be implemented using optical Exclusive-OR gates. Demonstrating all-optical quantization using a planar waveguide is an important step towards realizing all-optical A/D conversion on a chip.