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PhD project: Enhancing Nonlinear Optics in 2D Materials

Efficient nonlinear optical interactions are essential for many applications in modern photonics. However, they typically require intense laser sources and long interaction lengths, requirements that often render nonlinear optics incompatible with new nanophotonic architectures in integrated optics and metasurface devices. Obtaining materials with stronger nonlinear properties is a crucial step towards applications that require lower powers and smaller footprints. [1]

1. Reshef, O., De Leon, I., Alam, M. Z., & Boyd, R. W. (2019). Nonlinear optical effects in epsilon-near-zero media. Nature Reviews Materials.

Epsilon Near Zero Materials:

Towards All Optical Switching at Telecom Wavelength

A new class of materials with a vanishing permittivity, known as epsilon- near-zero (ENZ) materials, has been reported to exhibit unprecedented ultrafast nonlinear efficiencies within sub-wavelength propagation lengths [1]. It has been shown that a thin ITO film exhibits an extremely large ultrafast third-order nonlinearity at ENZ wavelengths and can further be enhanced by antennas resulting in excitation of ENZ modes [2,3].

In our research we study the wavelength dependent nonlinear physics of thin ENZ layers that show ENZ/plasmonic modes and work towards all optical switching in the telecommunications wavelength range.

1. Reshef, O., De Leon, I., Alam, M. Z., & Boyd, R. W. (2019). Nonlinear optical effects in epsilon-near-zero media. Nature Reviews Materials.
2. Alam, M. Z., De Leon, I., Boyd, R. W., Alam, M. Z., Leon, I. De, Boyd, R. W. (2016). Large optical nonlinearity of indium tin oxide in its epsilon-near-zero region. Science, 352(6287), 795–797.
3. Alam, M. Z., Schulz, S. A., Upham, J., De Leon, I., & Boyd, R. W. (2018). Large optical nonlinearity of nanoantennas coupled to an epsilon-near-zero material. Nature Photonics, 12(2), 79–83.

Graphene:

Enhanced High Harmonic Generation

In past research projects, graphene has shown to generate significant high harmonic (HH) signal spanning from the IR to the VIS wavelength range [1,2]. This effect was proposed to be further enhanced by utilizing the plasmonic resonances of patterned graphene [3].

In our ongoing research project we generate even stronger HH signal with patterned metal-insulator-graphene hybrid samples.

1. Yoshikawa, N., Tamaya, T., & Tanaka, K. (2017). High-harmonic generation in graphene enhanced by elliptically polarized light excitation. Science, 356(6339), 736–738.
2. Baudisch, M., Marini, A., Cox, J. D., Zhu, T., Silva, F., Teichmann, S., … Biegert, J. (2018). Ultrafast nonlinear optical response of Dirac fermions in graphene. Nature Communications, 9(1), 1018.
3. Cox, J. D., Marini, A., & de Abajo, F. J. G. (2017). Plasmon-assisted high-harmonic generation in graphene. Nature Communications, 8, 14380.

All-Optical Generation of Plasmons in Graphene

Recently, independently reported experimental measurements [1,2] of a frequency mixing process, with a difference frequency generation (DFG) in the mid-infrared, implied enhancement due to the presence of plasmons.

In our recent research collaboration we showed, that the perturbative model of graphene nonlinearities does not describe well existing experiments, and propose an alternative non-perturbative mechanism based upon photothermal effects, whose predicted strength is closer to experimental values [3]. Further research and more in-depth modelling will be necessary to understand the complete physical picture.

1. Constant, T. J., Hornett, S. M., Chang, D. E., & Hendry, E. (2016). All-optical generation of surface plasmons in graphene. Nature Physics, 12(2), 124–127.
2. Yao, B., Liu, Y., Huang, S.-W., Choi, C., Xie, Z., Flores, J. F., … Wong, C. W. (2017). Broadband gate-tunable THz plasmons in graphene heterostructures. Nature Photonics, 11(January), 272–278.
3. Tollerton, C. J., Bohn, J., Constant, T. J., Horsley, S. A. R., Chang, D. E., Hendry, E., & Li, D. Z. (2019). Origins of All-Optical Generation of Plasmons in Graphene. Scientific Reports, 9(1), 3267.

Selected previous projects:

[Master] Active Switching of all Dielectric Metasurfaces

All-dielectric resonant nanophotonics is a rapidly developing research field driven by its exceptional application potential for low-loss nanoscale metadevices. The tight confinement of the local electromagnetic fields and interferences in resonant photonic nanostructures can boost many optical effects, thus offering novel opportunities for the subwavelength control of light-matter-interactions. Active, light-emitting nanoscale structures are of particular interest, as they offer unique opportunities for novel types of light sources and nanolasers. [1]

We presented an electrically tunable all-dielectric optical metasurfaces based on liquid crystals [2] and an electrically tunable transparent displays [3]. We also investigated active tuning and directional shaping of spontaneous emission by Mie-Resonant dielectric metasurfaces [4,5].

Future projects could include ultrafast all optical switching of metasurfaces.

1. Staude, I., Pertsch, T., & Kivshar, Y. (2018). All-dielectric resonant meta-optics goes active, 1–14.
2. Komar, A., Fang, Z., Bohn, J., Sautter, J., Decker, M., Miroshnichenko, A., … Neshev, D. N. (2017). Electrically tunable all-dielectric optical metasurfaces based on liquid crystals. Applied Physics Letters, 110(7), 071109.
3. Zou, C., Komar, A., Fasold, S., Bohn, J., Muravsky, A. A., Murauski, A. A., … Staude, I. (2019). Electrically Tunable Transparent Displays for Visible Light Based on Dielectric Metasurfaces. ACS Photonics, 6(6), 1533–1540.
4. Bohn, J., Bucher, T., Chong, K. E., Komar, A., Choi, D.-Y., Neshev, D. N., … Staude, I. (2018). Active Tuning of Spontaneous Emission by Mie-Resonant Dielectric Metasurfaces. Nano Letters, 18(6).
5. Vaskin, A., Bohn, J., Chong, K. E., Bucher, T., Zilk, M., Choi, D.-Y., … Staude, I. (2018). Directional and Spectral Shaping of Light Emission with Mie-Resonant Silicon Nanoantenna Arrays. ACS Photonics, acsphotonics.7b01375.

[5 month research project abroad] Mode Division Multiplexing in Multi-Mode Fibres

Mode-division multiplexing (MDM) is seen by many as a potential means of overcoming the limited capacity of single-mode fibre. In MDM channels are multiplexed onto the orthogonal modes of few- or multi-mode-fibres (FMF/MMF), extending the capacity by a factor equal to the number of modes.

We have characterised laser written photonic lanterns with different core-spacing at the multi-mode output, by measuring their transfer matrix using a SDM- OVNA. We found that a very low MDL of ≈ 1 dB can be achieved [1].

Advanced generations of this technology have now reached the market and are commercially available [2].

1. Bohn, J., Carpenter, J., Gross, S., Withford, M., & Schroder, J. (2015). Characterization of laser inscribed on-chip photonic lanterns with different core distances. In European Conference on Optical Communication, ECOC (Vol. 2015-Novem).
2. Modular Photonics: https://www.modularphotonics.com

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