Nonlinear refractive index of carbon nanotubes

Materials with strong optical nonlinearities are essential for applications in optical signal processing, quantum technologies, and optical machine learning. Low-dimensional materials such as carbon nanotubes are promising due to their tunability, large nonlinear response, and compatibility with the CMOS process flow used in integrated photonics. This project investigates the nonlinear optical properties of high-density monochiral semiconducting carbon nanotube (CNT) thin films for use in next-generation photonic devices.

We perform Z-Scan measurements at different wavelengths on a film of highly pure (6,5) semiconducting carbon nanotubes to study the nonlinear properties of the film near an excitonic resonance. Using a theoretical approach based on the many-body semiconductor Bloch equations (SBEs), we identified that many-body effects, such as Coulomb scattering and excitation-induced dephasing, drive the strong nonlinearities observed in the material. The film achieved a nonlinear refractive index ($n_2$) of approximately 10 cm²/GW, five orders of magnitude greater than that of silicon.

This work highlights the untapped potential of excitonic materials in photonic device design. Indeed, these materials offer a balance between strong nonlinearities and manageable losses and could, thus, be suitable for applications in all-optical signal processing.

This project is in collaboration with the University of Wisconsin & the University of Michigan @ Ann Arbor. Paper is in progress