Plasmonics for On-Chip Photodetectors and Light Sources

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2023

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Abstract

Quantum emitters and thermal photodetectors serve as key building blocks for future quantum information and sensing systems. Their properties can be significantly enhanced by integrating them with nanostructured elements, tailoring their interactions with incident optical fields. Quantum emitters integrated into nanophotonic cavities exhibit increased brightness and faster emission due to the Purcell effect, improving their maximum repetition rates as single photon sources, as well as decreasing saturation power leading to less pump induced noise. Further, the significant reduction in fluorescence lifetimes observed for quantum emitters coupled to nanophotonic cavities enhances their viability for use in quantum memory schemes. Many solid-state quantum memories suffer from short coherence times; however, if the fluorescence lifetime is much shorter than the decoherence time of the stored qubit, then it becomes far more likely that the output photon successfully carries the stored qubit. A popular solid-state defect for quantum memory type applications is the silicon vacancy center in diamond. Presented in this dissertation are results showing ensemble silicon vacancy containing diamond membranes integrated with ultrasmall mode volume plasmonic nanocavities. The cavity integrated silicon vacancies exhibit record instrument-limited 8 ps fluorescence lifetimes, corresponding to >135-fold lifetime enhancement factors, as well as 19-fold photoluminescence (PL) intensity enhancement. These results indicate promise of the approach for future fabrication of an ultrafast source of single photons. v Similar nanophotonic cavities can also be used as low heat capacity photothermal converters which, when codesigned with a thermally sensitive layer, act as a photodetector. Metallic metasurfaces have previously been considered less than ideal for polarization sensing, where they are usually operated in a reflection mode and require an external detector. Arrays of subwavelength plasmonic cavities, comprising a metasurface, are designed with spectral and polarization selectivity. Loss in the cavities converts light to heat, which then diffuses into an underlying pyroelectric sensing layer. The structures presented herein exhibit high extinction ratios of up to 19 for orthogonal linear polarization states, with extraction of stokes parameters coming within 12% of the theoretical value. These sensing structures are ultrathin, with active layer thicknesses of 290 nm, and fast with rise times of 2 ns. Preliminary results from smaller devices exhibit sub-nanosecond rise times with responsivity showing good agreement with absorbance. Smaller devices are also characterized for their bandwidth in the frequency domain and show -3dB bandwidths in excess of 1 GHz. These results are extremely fast for pyroelectric detectors and clear paths towards achieving higher responsivity and faster response are laid out. The metasurface absorber elements, or plasmonic cavities, used in these projects exhibit extremely small mode volumes showing promise for future highly integrated devices.

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Wilson, Nathaniel (2023). Plasmonics for On-Chip Photodetectors and Light Sources. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/29183.

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