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Title: Laser inscribed optical waveguides in emerging photonic material platforms
Authors: María, Ramos Vázquez
Keywords: Science::Physics
Issue Date: 11-Jul-2019
Source: María, R. V. (2019). Laser inscribed optical waveguides in emerging photonic material platforms. Doctoral thesis, Nanyang Technological University, Singapore.
Abstract: Indisputably, software run in conventional Von-Neumann architectures has provided solutions to most of the needs met until now. However, an efficient solving method for the solution of hard computational problems remains still a challenge due to the large amount of power and execution times required. In this context, alternative solutions to brute force electronic computing are incessantly searched. The integration of photonic hardware as a replacement of some small blocks of the main software could speed up execution times, providing faster solutions to non-polynomial complete problems, cognitive systems or quantum computations. The thesis titled “laser inscribed optical waveguides in emerging photonic material platforms” portrays the potential of the ultrafast laser writing technique employed on three different materials for the fabrication of optical waveguides as the main building block of advanced optical circuits. The optical waveguides have been explored as a photonic element for future applications in cognitive and quantum computing systems. An alumino-borosilicate glass (Corning EAGLE2000) has enabled low-loss optical waveguides at the convenient wavelength of 800 nm, offering solutions to optical circuits compatible with current Ti:Sapphire technologies and spontaneous-parametric down conversion sources. The well-known travelling salesman problem has been laser inscribed into one of the glass substrates and its solution has been optically found. This has been the first realization of a photonic “oracle” fabricated via femtosecond laser machining of waveguides, providing an enhanced integration by reduction of the physical problem size and, thus, allowing faster execution times compared to other optical approaches developed in fibers. The second material of interest is gallium lanthanum sulfide glass, a chalcogenide which is useful for its non-volatile phase change transitions and highly nonlinear characteristics. An optimum processing window for low-loss single mode waveguides, operating at 800 nm wavelength has been reported for the first time by using a multiscan writing approach, opening the path towards integration of nonlinear optical circuits compatible with Ti:Sapphire technologies. The high Kerr nonlinearity displayed in the glass has been exploited to characterize laser inscribed optical directional couplers acting as ultrafast all-optical switches and an estimation of the nonlinear refractive index of the laser inscribed waveguides has been reported. As a feasible application, gallium lanthanum sulfide waveguides have been explored as an integrated neuromorphic photonic platform, which includes a series of neural biological features. Diamond has been the third material used due to its capability of hosting nitrogen-vacancy (NV) color centers, whose long spin coherence times at room temperature are promising for applications in quantum information and magnetic sensing. Here, femtosecond laser writing has provided integration of optical waveguides aligned with the NV color centers within the bulk of diamond with a submicrometer resolution, allowing efficient optical excitation and collection of the luminescence signal of these defects. In future, such a platform could be applied to quantum sensing devices with record high sensitivity of electric fields, and quantum information systems. Overall, this work shows the potential of ultrafast laser writing as a flexible fabrication tool for the implementation of cognitive and quantum computational problems into compact and scalable chips which are desirable for the study of new optical computing schemes and algorithm optimization.
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