[en] The domain inversion in LiNbO₃ is fabricated by proton exchange and rapid heat treatment. The proton concentration is measured by secondary-ion mass spectroscopy. A modified diffusion model is proposed, the result of which agrees well with the measured data. Comparisons with the existing models are made, which suggests that our model may be more extensively applicable. (authors)

[en] Domain-inverted structures in LiNbO₃ are fabricated by proton exchange followed by rapid heat treatment. The domain inversion mechanism is discussed in relationship to the pyroelectric field and to the concentration gradient of protons. (author)

[en] We demonstrate quasi-phase-matched Cerenkov second-harmonic and sum-frequency generation in a two-dimensional optical superlattice waveguide. Multiple radiation spots with different azimuth angles are simultaneously exhibited from such a hexagonally poled waveguide. The fundamental understanding and potential applications of such Cerenkov effects are presented and discussed. (authors)

[en] Exploring and understanding the nature of gravity has always been a human endeavour. In particular, two recent achievements in astronomy, the laser interferometer gravitational-wave observatory (LIGO), which has detected gravitational-wave signals, and the event horizon telescope (EHT), which has captured black hole shadows, have further stimulated broad interest in ancient and mysterious gravity. Despite the tremendous advances in experimental astronomy techniques for detecting gravity, the study of some gravitational phenomena still faces challenges, especially the quantum effects related to gravity. On the other hand, analogical gravity systems provide a new experimental platform for studying gravitational effects; they can be used to study in a laboratory environment those gravitational phenomena that still present challenges for current astronomical observation, for example the quantum gravitational effect near black holes. This paper introduces the simulation of various phenomena in curved space-time realized by photonic chips, which portray a good analogical gravitational system. (authors)

[en] In this paper, we experimentally demonstrate reversible wavefront shaping through mimicking gravitational field. A gradient-index micro-structured optical waveguide with special refractive index profile was constructed whose effective index satisfying a gravitational field profile. Inside the waveguide, an incident broad Gaussian beam is firstly transformed into an accelerating beam, and the generated accelerating beam is gradually changed back to a Gaussian beam afterwards. To validate our experiment, we performed full-wave continuum simulations that agree with the experimental results. Furthermore, a theoretical model was established to describe the evolution of the laser beam based on Landau’s method, showing that the accelerating beam behaves like the Airy beam in the small range in which the linear potential approaches zero. To our knowledge, such a reversible wavefront shaping technique has not been reported before. (paper)

[en] (Mn, Co)-codoped ZnO films have been synthesized on c-sapphire (0001) by a radio-frequency magnetron sputtering system in which two targets were sputtered together. X-ray-diffraction measurements indicate that the films are highly c-axis oriented. X-ray photon spectra show that the doped Mn and Co ions in (Mn, Co) ZnO films are both in the divalent states. The films show ferromagnetic behavior with a coercivity of about 90 Oe and a saturation moment of 0.11μ_B/(0.3Mn²⁺+0.7Co²⁺) at 300 K. In the lower temperatures between 5 and 20 K, a relatively large positive magnetoresistance over 10% was observed for (Mn_0.03, Co_0.07)Zn_0.90O film. The number of carrier concentration is experimentally established to be 1.5613x10¹⁸ cm^-3 and the mobility to be 2.815 cm² V^-1 s^-1 for (Mn_0.03, Co_0.07)Zn_0.90O film by Hall measurements at 300 K. The origins of the room-temperature magnetism and the large positive magnetoresistance are also discussed

[en] Zn_0.99Mn_0.01O and Zn_0.985(Mn_0.01,Sb_0.005)O thin films were prepared on sapphire(0001) by reactive radio-frequency (rf) magnetron sputtering. Zn_0.99Mn_0.01O showed no obvious ferromagnetic behavior while Zn_0.985(Mn_0.01, Sb_0.005)O exhibited robust ferromagnetic signals with a saturation magnetization of 0.92 μ_B/Mn²⁺, and Zn_0.985(Mn_0.01, Sb_0.005)O film grown in an oxygen rich condition exhibited a larger saturation magnetization of 1.76 μ_B/Mn²⁺. The results are most consistent with the bound magnetic polaron model, in which localized p-type defects mediate the ferromagnetic ordering.

[en] We propose a scheme for generating three primary colours with a 1064 nm pump wave. Three quasi-phase-matched parametric processes, i.e., second-harmonic generation, optical parametric generation, and sum-frequency generation, are coupled in a single optical superlattice. On the basis of the plane-wave approximation, the coupling process is investigated theoretically. And a special design for a quasiperiodic structure is presented

[en] To improve the light extraction efficiency of a GaN-based light-emitting diode (LED), a new complex periodic photonic crystal structure containing two kinds of hemispheres was designed. This complex photonic crystal structure is arrayed on the surface of the planar LED, and a finite-difference time-domain method was used to optimize the hemisphere materials (ZnO, GaN, and SiC) and the structural parameters of the complex photonic crystal (the size of the hemisphere radius and the lattice constant of complex structure). A high improvement of light extraction efficiency is achieved in complex photonic crystal LED, translated into an 8.3-fold enhancement for the case of a planar LED. (paper)

[en] We propose two schemes for realizing quantum secure direct communication (QSDC) by using a set of ordered two-photon three-dimensional hyperentangled states entangled in two degrees of freedom (DOFs) as quantum information channels. In the first scheme, the photons from Bob to Alice are transmitted only once. After insuring the security of the quantum channels, Bob encodes the secret message on his photons. Then Alice performs single-photon two-DOF Bell bases measurements on her photons. This scheme has better security than former QSDC protocols. In the second scheme, Bob transmits photons to Alice twice. After insuring the security of the quantum channels, Bob encodes the secret message on his photons. Then Alice performs two-photon Bell bases measurements on each DOF. The scheme has more information capacity than former QSDC protocols. (general)