LAUSR

An optically tunable in-core Mach-Zehnder interferometer (MZI) based on the photoexcitation dynamics of nitrogen-doped graphene quantum dots (NGQDs) is demonstrated. The tunable MZI is fabricated by depositing NGQDs into a femtosecond laser ablated microgroove in the core. Combining both the high sensitivity to the external refractive index change of the MZI itself and the quantum confinement effect in quantum dots, a tuning range of ~90 nm is achieved as the pump power density of an ultraviolet (UV) LED varies from 0 to 41.1 mW/cm2, which accounts for 85% of the free spectrum range (FSR) of the MZI with a length of $205~\mu \text{m}$ . Such an optically tunable MZI with high integration, tuning efficiency and wide FSR can be suitably used in edge filter demodulation and tunable laser.