Characterisation and Light Manipulation in Photonic Integrated Circuits

超快光调制光谱（UPMS）是一种远场技术，用于在晶圆级对单个集成光子器件进行无损表征。在UPMS中，外部入射的飞秒光泵浦脉冲通过等离子体色散效应在绝缘体上硅（SOI）波导的折射率分布中产生高度局部化的扰动。由于泵浦光的超快性质，可以获得远远超过通过电效应可实现的自由载流子浓度，这可以用来调制器件的传输。UPMS是用于光子芯片表征的多样化工具，允许在时间域或空间域中进行泵浦探测测量。探测和泵浦脉冲之间的延迟时间的精细控制允许观察到超快响应，以及设备内的直接飞行时间测量。而通过记录作为扰动位置的函数的透射变化，可以建立二维空间光调制图。这样的地图提供了光通过设备的传播的直接可视化，并且在低损耗设备的情况下，可以用于恢复关于电场的信息，而不需要直接访问近场。此外，由多个扰动组成的图案可以用于对光的波前进行整形，从而允许具有复杂和可重构功能的光子结构，例如可变调制器/开关、多路复用器（解多路复用器）和模式转换器。

Ultrafast photomodulation spectroscopy (UPMS) is a far-field technique for non-destructive characterisation of individual integrated photonic components at the wafer scale. In UPMS, externally incident femtosecond optical pump pulses create highly localised perturbations in the refractive index profile of a silicon-on-insulator (SOI) waveguide via the plasma dispersion effect. Due to the ultrafast nature of the pump light, free-carrier concentrations far exceeding those achievable by electrical effects can be obtained, which can be exploited to modulate the transmission of the device. UPMS is a diverse tool for photonic chip characterisation, allowing for pump-probe measurements in either the temporal or spatial domain. Fine control of the delay time between probing and pumping pulses allow for ultrafast responses to be observed, as well as direct time of flight measurements within the device. While through the recording of the change in transmission as a function of the perturbation position it is possible to build up a two-dimensional spatial photomodulation map. Such maps provide a direct visualisation of the propagation of light through a device, and in the case of low loss devices can be used to recover information on the electric field without requiring direct access to the near-field. Furthermore, patterns made up of multiple perturbations can be used to shape the wavefront of light, allowing for photonic structures with complex and reconfigurable functionalities, such as variable modulators/switches, (de)multiplexers and mode converters.