Advances in silicon photonics have resulted in rapidly increasing complexityof integrated circuits. New methods are desirable that allow directcharacterization of individual optical components in-situ, without the need foradditional fabrication steps or test structures. Here, we present a newdevice-level method for characterization of photonic chips based on a highlylocalized modulation in the device using pulsed laser excitation. Opticalpumping perturbs the refractive index of silicon, providing a spatially andtemporally localized modulation in the transmitted light enabling time- andfrequency-resolved imaging. We demonstrate the versatility of this all-opticalmodulation technique in imaging and in quantitative characterization of avariety of properties of silicon photonic devices, ranging from group indicesin waveguides, quality factors of a ring resonator to the mode structure of amultimode interference device. Ultrafast photomodulation spectroscopy providesimportant information on devices of complex design, and is easily applicablefor testing on the device-level.
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