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Cascaded frequency conversion of orbital angular momentum states in periodically poled LiTaO3 crystal

Xinyuan Fang, Guang Hui Yang, Dunzhao Wei, Dan Wei, Rui Ni, Xiaopeng Hu, Yong Zhang, Shining N. Zhu, Min Xiao

Published Dec 13, 2015• 0 citations
OpenAlex

Abstract

We report that the optical orbital angular momentum (OAM) is conserved in the two-step cascaded nonlinear processes through quasi-phase-matched (QPM) in a dual-structure periodically poled LiTaO!(PPLT) crystal. Because of the different reciprocal vectors provided by the different structures in the crystal, collinear second harmonic (SH) beam with an OAM of l2 and third harmonic (TH) beam with an OAM of l3 are simultaneously generated by the input fundamental beam with an OAM of l1. The OAM conversion law (l2 = 2l1, l3 = 3l1) holds well in this nonlinear process. Our results provide an effective way to obtain three beams (fundamental beam, SH beam, TH beam) with different OAMs at the same time, which can be used to enhance the capacity of optical communication.

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•Jan 1, 2015•0 citations
We report that the optical orbital angular momentum (OAM) is conserved in the two-step cascaded nonlinear processes through quasi-phase-matched (QPM) in a dual-structure periodically poled LiTaO!(PPLT) crystal. Because of the different reciprocal vectors provided by the different structures in the crystal, collinear second harmonic (SH) beam with an OAM of l2 and third harmonic (TH) beam with an OAM of l3 are simultaneously generated by the input fundamental beam with an OAM of l1. The OAM conversion law (l2 = 2l1, l3 = 3l1) holds well in this nonlinear process. Our results provide an effective way to obtain three beams (fundamental beam, SH beam, TH beam) with different OAMs at the same time, which can be used to enhance the capacity of optical communication.
We experimentally demonstrate multiple copies of optical orbital angular momentum (OAM) states through quasi-phase-matched (QPM) second-harmonic (SH) generation in a 2D periodically poled LiTaO3 (PPLT) crystal. Since the QPM condition is satisfied by involving different reciprocal vectors in the 2D PPLT crystal, collinear and noncollinear SH beams carrying OAMs of l2 are simultaneously generated by the input fundamental beam with an OAM of l1. The OAM conservation law (i.e., l2 = 2l1) holds well in the experiment, which can tolerate certain phase-mismatch between the interacting waves. Our results provide an efficient way to obtain multiple copies of the wavelength-converted OAM states, which can be used to enhance the capacity in optical communications.
Nonlinear interaction between orbital angular momentum (OAM) modes has interesting effects and tremendous applications in both classical and quantum realms. Here we propose a strategy of using perfect vortices, which not only overcomes the spatial mode matching problem of nondegenerate OAM modes, but also reveals the OAM-only influence on the momentum matching by tuning the OAMs of the fundamental wave. We use perfect vortices of degenerate and nondegenerate OAM modes to clearly demonstrate the flexible control of OAM modes on nonlinear interaction by carefully exploring second-harmonic generation (SHG) in periodically poled crystal. We generate second-harmonic perfect vortices with the OAM order up to 40. Based on the observed phase-matching temperature shift caused by OAMs, we also use the SHG nonlinear process to distinctly confirm the OAM-only-induced subluminal effect. Our results pave the way toward unveiling the underlying physics behind nonlinear process of OAM modes and building high-capacity quantum links between systems operating at various wavelengths. The inverse process of SHG we developed, perfect-vortex-based spontaneous parametric down-conversion, may provide a promising solution for high-dimensional OAM entangled source.
Orbital-angular-momentum- (OAM) based photonic nonlinear interfaces, such as the nonlinear manipulation of a single-photon OAM state between the communication wavelength for entanglement distribution and the near-visible wavelength for quantum memories. Here, we experimentally demonstrate this kind of quantum state transformation for simultaneously adjusting the weight of the spatial OAM modes and operating the wavelength of single photons by effectively cascading the frequency conversion and electro-optical (EO) polarization coupling in a periodically poled lithium niobate crystal. The fidelity of the OAM state is measured to be higher than 95% before and after the frequency conversion. The results show that the OAM state of single photons can be modulated on demand by applying a transverse electric field across the nonlinear crystal. Our work demonstrates the integration and high performance of our proposed transformation interface, and paves a route toward connecting different remote nodes based on quantum memories in a large-scale OAM-encoded quantum network.
We propose an adiabatic scheme for cascaded fourth-harmonic generation (FHG) in chirped dual-period quasi-phase-matched (QPM) crystals, where adiabatic evolution is introduced into the multi-step frequency conversion process. By engineering two chirped QPM gratings for the fundamental-to-second-harmonic ( FF → SH ) and second-to-fourth-harmonic ( SH → FH ) interactions, efficient harmonic generation is achieved through a continuous adiabatic passage in phase-mismatch space, rather than discrete phase-matching conditions in conventional QPM schemes. This approach enables robust and tunable energy transfer among harmonics, allowing controllable generation of second- and fourth-harmonic signals. Numerical results show a maximum FHG efficiency of 94% and a tunable bandwidth of ∼13 nm under realistic conditions. The tunability originates from the controlled shift of QPM resonances along the propagation direction.
We review recent experimental and theoretical progress in the study of optical parametric generation and cascaded frequency up conversion in two-dimensional purely nonlinear lattices, relying on acoherent coupling of multiple resonances in the quadratic lattice. Since their original proposal (1), two dimensional (2D) nonlinear photonic crystals in periodically poled materials have been the subject of a number of experimental and theoretical investigations, exploring the enhanced possibilities to engineer the nonlinear dynamics of quadratic interactions afiorded in such structures (2,3). Most of the studies have concerned frequency up-conversion, until the recent demonstration of twin-beam optical parametric generation (TB-OPG) in 2D hexagonally poled crystals (4,5). TB-OPG experiments in hexagonally poled MgO:LiTaO3 lattices demonstrated enhanced para- metric gains as well as a rich spectral and angular response underpinned bythe coherent coupling of concurrent nonlinear processes throughshared signal or idlermodes. They provided evidence forrich interaction scenarios, generating multiple outputs in the infrared as well in the visible and encompassing also self-phase modulation and cascaded upconversion processes arising from the interplay of multiple lattice resonances.A good agreement was found with a simple model in- volving the cross-seeding of two non-collinear OPG processes via a common signal (idler), while the development of advanced ad-hoc simulation tools enabled to fully account for the complex nonlinear dynamics in the 2D lattices and faithfully reproduce the rich spectral-angular response seen in the experiments (6).