Topological Photodetectors

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Photodetectors are devices which detect the presence of light and are very important components for applications in spectroscopy, imaging, diagnostics and for driving our information technology infrastructure. Conventional photodetectors detect optical power, i.e., convert the total number of photons impinging on the active area into a corresponding current. Therefore, most applications involving light utilize intensity to encrypt or decrypt information, i.e., by modulating the intensity of light at different wavelengths to encode information and counting the total number of photons at the detector end. However, light can also be engineered to carry much more information encoded in its phase and the direction of the oscillation of electric field. Vortex light is an example of a complex type of light which can be used to carry much more information that conventional light beams. However, it is not easy to detect and distinguish different types of vortex beams for on-chip applications. In this project, new types of quantum materials will be explored along with specially designed devices to assemble on-chip photodetectors that will produce different currents depending on the nature and type of light vortices. These new types of photodetectors can increase the information carrying capacity of our optical systems by utilizing more degrees of freedom of light than conventional systems that can enable us to continue to meet the ever-increasing demands on our devices to process more information. Research and educational activities will be integrated by the involvement of undergraduates in the research program, incorporating latest research results in the teaching modules, and training high school and college teachers from the Philadelphia district with student population from minority and underrepresented sections.On-chip topological photodetectors working at room temperature that are sensitive to different spin (SAM) and orbital angular momentum (OAM) states of topological (vortex) light will be developed. These topological photodetectors can enable a nonlinear scaling of information carrying capacity of optical systems that still mostly rely on optical power. At a fundamental level, the proposed studies will pave the way to understanding and engineering novel optoelectronic response in quantum topological materials via symmetry and geometry concepts. The project will extend these ideas to design the next generation of photodetectors with enhanced functionalities to replace bulky table-top optics currently used for sensing OAM modes of light. To develop on-chip topological photodetectors, materials that have a photoresponse sensitive to complex phase and intensity distribution of the OAM modes along with sensitivity to photon spin (polarization) will be explored. Most materials are neither sensitive to optical polarization nor the spatial or phase gradients of the optical beam, which makes this task challenging. For this purpose, topological Weyl semimetals will be studied due to their unique symmetry that can support OAM-SAM sensitive and strong nonlocal photoresponse at room temperature. By utilizing artificial neural network algorithms, these devices will then be trained to read out the OAM-SAM modes with high fidelity for applications in imaging, spectroscopy, and integrated systems for processing much larger bandwidth information.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.