Photonic-chip-based radio-frequency spectrum analyser with terahertz bandwidth

Signal processing at terahertz speeds calls for an enormous leap in bandwidth beyond the current capabilities of electronics, for which practical operation is currently limited to tens of gigahertz 1 . This can be achieved through all-optical schemes making use of the ultrafast response of χ (3) nonlinear waveguides 2 . Towards this objective, we have developed compact planar rib waveguides based on As 2 S 3 glass, providing a virtual ‘lumped’ high nonlinearity in a monolithic platform capable of integrating multiple functions. Here, we apply it to demonstrate, for the first time, a photonic-chip-based, all-optical, radio-frequency spectrum analyser with the performance advantages of distortion-free, broad measurement bandwidth (>2.5 THz) and flexible wavelength operation (that is, colourless). The key to this is the waveguide's high optical nonlinearity and dispersion-shifted design. Using the device, we characterize high-bit-rate (320 Gb s −1 ) optical signals impaired by various distortions. The demonstrated ultrafast, broadband capability highlights the potential for integrated chip-based signal processing at bit rates approaching and beyond Tb s −1 . A system based on a highly nonlinear planar chalcogenide waveguide is demonstrated to be able to perform radio-frequency spectral measurements with a terahertz bandwidth. High bit-rate tests show that the chip-based system is potentially useful for ultrafast signal processing.