Integrated design of pi/2 converter and its experimental performance

Abstract

Transverse modes of light have been widely exploited in both classical and quantum optics in recent years. Among the devices to manipulate the transverse modes of light, a π/2 converter is a fundamental and important one that analogs to the quarter-wave plate in the polarization degree of freedom. While a π/2 converter is typically achieved by a pair of well-adjusted cylindrical lenses, it suffers from complexity in its installation and adjustment, which strongly limits its practical applications. In this paper an integrated design of a π/2 converter is reported. We compute the necessary parameters for manufacturing according to refractive theory of a cylindrical surface. Based on the change of refractive indices, we simulate the response of Gouy phase versus wavelengths. We also implement an experiment to verify the conversion between Laguerre-Gaussian modes and Hermite-Gaussian modes by using our compact π/2 converter to confirm its simple adjustment and reliable performance in practice.

Mode Conversion and Transfer of Orbital Angular Momentum Between Hermite-Gaussian and Laguerre-Gaussian Beams

“…( 15) that the conjugate phase element is also a CP lens. Moreover, this type of mode converter can be processed into an integrated device with DOE technique [29], and the converter's front surface and back surface are both CP lenses but with a different strength coefficient of CP and with the same focal length of the lens. The length of this converter is f , the focal length of lens in the front surface.…”

“…In other words, one can use this robust mode converter to generate OAM beams or measure the OAM of optical field [28]. Moreover, such a converter can also be integrated into an optical device with diffractive optical elements (DOE) technique, and the device has simple adjustment and reliable performance [29].…”

Security analysis method for practical quantum key distribution with arbitrary encoding schemes

“…Hence, we analyze the high-dimensional spatial modes encoding scheme in free-space link with unknown misalignment. The MPUB protocol extremely simplifies the implementation [44,45] and enhances the robustness to turbulence by using non-MUBs encoded with multiple degrees of freedom. The security analysis in Ref.…”

High-dimensional quantum key distribution based on mutually partially unbiased bases

“…For a practical realization of high-dimensional QKD, using the proposed MPUBs leads to a stable propagation by overcoming the mode-dependent diffraction. By using a passive π/2 mode converter [44], both Laguerre-Gaussian and Hermite-Gaussian modes can be easily generated and measured [45]. A security proof based on an asymptotic scenario is given in this work to confirm the security of the MPUB-based QKD protocol.…”