Quasiperiodic Optical Superlattice Research Articles

Flexible dual-wavelength second-harmonic generation in nested quasi-periodic optical superlattice

Flexible dual-wavelength second-harmonic generation in nested quasi-periodic optical superlattice

Quasi-Phase-Matching Efficiency Optimization for Coupled Second-Order Nonlinear Processes

It is well known how to tailor the conversion efficiency grid of a single quasi-phase-matching (QPM) grating when the involved processes are uncoupled. However, it becomes much more sophisticated in the presence of coupling between multiple processes. In this case, different processes compete for the same QPM “resources” throughout the grating, and one process can outweigh the others over a certain range of interaction. Here we propose the generalized iterative domino (GID) algorithm to meet these challenges for the first time (to our best knowledge). Instead of tailoring the strength of each “global” Fourier coefficient, GID algorithm can properly adjust the spatially varying “local” Fourier coefficients in favor of the final yield. Three methods, including cascaded single-period (C1P) structure, quasi-periodic optical superlattice (QPOS), and hyperfine aperiodic optical superlattice (HAOS) optimized by GID, are numerically and experimentally investigated under the platform of third-harmonic generation (THG). It shows that the THG efficiency of HAOS + GID can exceed the record achieved by C1P structure by 33%. This method is applicable to general wavelength converters involving with multiple coupled nonlinear processes.

Three-colour entanglement produced by the single-pass quasi-phase-matching fourth harmonic generation

Three-colour continuous-variable entanglement produced by single-pass cascaded quasi-phase-matching fourth harmonic generation is investigated. The fourth harmonic can be generated through cascaded double-frequency processes in a quasiperiodic optical superlattice by using quasi-phase-matching technology. The conversion dynamics of the cascaded double-frequency processes is studied using quantum stochastic methods. The nature of the entanglement is discussed by applying a necessary and sufficient criterion for continuous-variable entanglement. Strong three-colour entanglement among the fundamental, second-, and fourth-harmonic beams with a double frequency interval can be produced without an optical oscillator cavity. This is experimentally feasible and has potential applications in quantum communication and computation networks.

Bright three-color continuous-variable entanglement generated by a cascaded sum-frequency process in an optical cavity

Bright three-color continuous-variable (CV) entanglement generated by a cascaded sum-frequency process in an optical cavity is investigated. The second- and fourth-harmonic beams can be generated by two quasi-phase-matched cascaded sum-frequency processes in a quasi-periodic optical superlattice. Quantum correlations among the fundamental and second- and fourth-harmonic beams are calculated and discussed by applying a sufficient and necessary inseparability criterion for CV three-mode entanglement. Strong three-color CV entanglement beams with a double frequency interval can be produced in this simple system. It is experimentally feasible and may be very useful for applications in quantum communication and computation networks.

Simultaneous harmonic generation and polarization control in an optical superlattice

Simultaneous second-harmonic generation and electric-optic coupling in a periodic or quasi-periodic optical superlattice has been demonstrated experimentally. The output of the second harmonic can be controlled by the DC electric field or the temperature. The results offer us a way to manipulate the nonlinear interactions.

Generation of two-photon entangled states through a cascaded nonlinear optical process in a quasiperiodic optical superlattice

The search for new methods to produce entangled photons is a subject of great interest in quantum optics. We show theoretically that two_photon entangled states may be generated through a cascaded nonlinear optical process in a quasiperiodic optical superlattice. When an idler photon ωi produced from spontaneous parametric down conversion (ωp=ωs+ωi) combines with a pum p photon to produce a sum frequency photon ωb(ωb=ωi+ω p), the latter is entangled with the remaining signal photon ωi. Both a pulsed and a cw 532nm laser have been used to pump a quasi_phase matched LiTaO 3 crystal to generate simultaneously 630nm signal photons through parametric d own conversion and 460nm sum frequency photons. The advantage of this method is that entangled photons of short wavelength may be produced.

Quasi-phase-matched generation of tunable blue light in a quasi-periodic structure.

We present what is to our knowledge a new approach to generating tunable blue light by cascaded nonlinear frequency conversion in a single LiTaO3 crystal. Simultaneous quasi-phase matching of an optical parametric generation process and a sum-frequency mixing process is achieved by means of structuring the crystal with a quasi-periodic optical superlattice. The spectral (wavelength tuning and bandwidth) and power characteristics of the blue-light generation are studied with a fixed-wavelength 532-nm picosecond laser and a wavelength-tunable nanosecond optical parametric oscillator (OPO) as the pump sources. By tuning the OPO wavelength, we could tune the blue output over approximately 20 nm. Temperature tuning of the blue output at a fixed pump wavelength of 532 nm was limited to approximately 1.5 nm. A maximum blue power of 15 microW was generated at a pump power of 0.5 mW, corresponding to an efficiency of 3%.

Simultaneous high-efficiency and equal-level second- and third-harmonic generation achieved by controllable linear gratings in a quasiperiodic optical superlattice

We report a theoretical study of the simultaneous high-efficiency, equal-level outputs of second and third harmonics in a quasiperiodic optical superlattice at any given fundamental intensity. The principle is that nonlinear coupling is effectively controlled by introducing proper quasiphase mismatches, by use of the tunability of linear refractive index gratings induced by applying a dc electric field based on the electro-optic effect. The theoretical results verify that this approach is feasible and very efficient. In addition, we also make a comparison with temperature tuning control, demonstrating that the performance of electro-optic control is much better than that of temperature tuning control.

Parametric and cascaded parametric interactions in a quasiperiodic optical superlattice

Quasi-phase-matching optical parametric and cascaded parametric processes in a two-component quasiperiodic superlattice were studied in theory and experiment. This letter demonstrates how to obtain red at 666 nm and blue at 443 nm simultaneously from the superlattice using a 532 nm laser as a pump through these two processes mentioned above. The result confirms that some nonlinear frequency conversion processes occurring in a high-dimension χ(2) nonlinear photonic crystal may be efficiently achieved in such a one-dimension quasiperiodic optical superlattice.

Analytical Expression for the Fourier Spectrum of a Quasiperiodic Fibonacci Superlattice with k Components (k ? 3)

The two-component quasiperiodic optical superlattice has been proved useful to some coupled parametric processes such as the direct third-harmonic generation. In this paper a three-component quasiperiodic superlattice has been studied theoretically. Using the projection method, the analytical expression of its Fourier spectrum has been deduced. The results might be conducive to the design of nonlinear optical devices related to the coupled parametric processes, such as the fifth-harmonic generation.

Third-harmonic generation in a general two-component quasi-periodic optical superlattice

The quasi-periodic optical superlattice is a promising material for use in optical frequency conversion. We propose a method for designing a quasi-periodic structure for efficient third-harmonic generation (THG) at any given wavelength. With this method we have made a LiTaO(3) sample in which 27% THG at 0.48microm was achieved, together with a series of highly efficient multiwavelength second-harmonic generation outputs. The result is in good agreement with the theoretical prediction.

Quasiperiodic optical superlattice in KTiOPO4 by electric poling technique

We demonstrate electrical polarization reversal and fabrication of quasi-periodic optical superlattice in c-cut KTiOPO4 by applying pulsed electric field to a sample. Domain switching process was monitored by recording the transient current during switching. The spontaneous polarization was measured to be 19.0 μC cm−2. The quasi-periodic domain reversal was confirmed by selective etching method.

Quasi-phase-matched harmonic generation through coupled parametric processes in a quasiperiodic optical superlattice

We have investigated and fabricated an optical superlattice of LiTaO3, in which two building blocks, each containing a pair of antiparallel 180° ferroelectric domains, were arranged as a Fibonacci sequence. The second- and third-harmonic generation in this structure have been studied and measured. The results verifies that the second-harmonic spectrum and the third harmonic may be generated in a quadric nonlinear medium by a series of quasi-phase-matching processes. The experimental results are in good agreement with theory.

Characterization of harmonic generation in an intergrowth optical superlattice

In this paper we obtain an analytical solution to the harmonic generation processes in a quasiperiodic optical superlattice. The derived theory was applied to an intergrowth optical superlattice made from a single crystal with laminar domain reversal to realize third-harmonic generation processes. The quasiperiodic structure can provide more reciprocal vectors to compensate for the phase mismatches of the optical parametric processes, which make most of the intense harmonic peaks labelled by the corresponding reciprocal vector indices. The dependence of the harmonic intensity spectrum on structure parameters is presented. Conditions for efficient third-harmonic generation are also discussed in detail.

Quasi-Phase-Matched Third-Harmonic Generation in a Quasi-Periodic Optical Superlattice

Quasi-periodic structure can be introduced into nonlinear optical materials such as LiTaO 3 crystals. Such structures were used for quasi–phase-matching second-harmonic generation. These materials are now shown to be able to couple second-harmonic generation and sum-frequency generation through quasi–phase-matching. The approach led to a direct third-harmonic generation with high efficiency through a coupled parametric process. The result verifies that high-order harmonics may be generated in a quadric nonlinear medium by a number of quasi–phase-matching processes, and therefore, exhibits a possible important application of quasi-periodic structure materials in nonlinear optics.