Researchers from the University of Southampton have presented a device-level method for the characterisation of photonic chips based on a highly localised modulation in the device using pulsed laser excitation. Optical pumping perturbs the refractive index of silicon, providing a spatially and temporally localised modulation in the transmitted light, enabling time- and frequency-resolved imaging.

They have demonstrated the versatility of this all-optical modulation technique in imaging and in the quantitative characterisation of a range of properties of silicon photonic devices, from group indices in waveguides, to quality factors of a ring resonator, and to the mode structure of a multimode interference device. Ultrafast photomodulation spectroscopy provides important information on devices of complex design, and is easily applicable for testing at the device level. Press release

The paper is available here.