Characterisation and Light Manipulation in Photonic Integrated Circuits

Lead Research Organisation: University of Southampton
Department Name: Optoelectronics Research Centre


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.

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509747/1 01/10/2016 30/09/2021
1921224 Studentship EP/N509747/1 29/09/2016 31/03/2020 Nicholas Dinsdale
Description During the course of this award, the technique of Ultrafast Photomodulation Spectroscopy (UPMS) has been developed and significantly improved upon as a new novel tool for the characterisation of photonic integrated circuits. The technique allows the mapping of light fields inside devices using only far-field optical pulses, even in the presence of protective cladding layers. The approach is non-destructive and can be applied at the wafer scale. Scan times have been improved from the order of tens of minutes for a typical device to just a couple of minutes, with the potential to go significantly faster, and the spatial resolution has also be improved from around 1.5 micrometres to 500 nanometers; revealing a great deal more detail in the light fields. A new analytical model was developed, which allows the direct quantitative comparison of an ideal design structure to a real-world fabricated device. We also investigated several approaches for multiple refractive index perturbation pattern optimisation, including deep learning, opening up new avenues for all-optical enhanced functionalities of photonic components.
Exploitation Route If there is significant interest in the technique the experiment could be incorporated onto a wafer-scale testbed as a diagnostic tool for silicon photonics manufacturing.
Sectors Digital/Communication/Information Technologies (including Software)

Description Light shaping on a chip with nanophotonics and complexity 
Organisation Institute of Optics Bordeaux
Country France 
Sector Academic/University 
PI Contribution Fabricated samples, developed the experimental method/setup and carried out the experiments.
Collaborator Contribution Developed the theory and in-house numerical code for modelling the perturbation mapping technique. Their custom code provides a substantial speed advantage compared propriety software, such as Lumerical FDTD.
Impact - New and novel research published in a peer-reviewed high impact factor journal. - Professional development - specifically enhanced my programming skills and understanding of the fundamental theory behind my research. - Networking - multiple trips to Bordeaux have allowed me to spend time with other research group and develop further contacts.
Start Year 2017