Nonlinear Photonic Crystal Research Articles

Photonic crystal lightsail with nonlinear reflectivity for increased stability.

Recent research has studied the feasibility of using laser radiation pressure to propel lightweight spacecraft, such as sails, at relativistic speeds. One major challenge is the effect of laser beam distortion on sail stability. We propose and investigate the use of lightsails based on Kerr nonlinear photonic crystals as a passive method for increasing sail stability. The key concept is to flatten the dependence of reflected intensity on incident intensity at the laser wavelength, using a specially designed, guided-resonance mode of the nonlinear photonic crystal. We use coupled-mode theory to analyze the resonance characteristics that yield the flattest curve. We then design a silicon nitride photonic crystal that supports a resonance with the desired properties. We show that our design simultaneously provides both high stability and high thrust on the sail, unlike designs based on linear materials.

Aberrated moving soliton in nonlinear photonic crystal

ABSTRACTBased on computer simulation, we demonstrate the nonlinear localization of a femtosecond laser pulse energy in 1D- and 2D photonic structures at the inclined incidence of a beam (or several beams) on a face of the photonic structure consisting of layers or rectangular elements. We show that, in 1D photonic crystal (PC), the energy localization is due to the formation of the moving soliton with the aberrated wave front – the aberrated soliton, which moves inside the photonic structure, being reflected many times from the PC faces, and its appearance depends on the photonic structure elements, ambient medium and the incident laser pulse shape. The dependence of the light energy localization on the sizes of the rectangular elements is investigated. We demonstrate controlling the light energy localization due to the incidence of several beams on the photonic structure and discuss the possibility of observing the described phenomena in a physical experiment.

Bistability phenomena based on frequency-sensitive self-collimation in nonlinear photonic crystals

By introducing the change of beam behavior near the frequency sensitive self-collimation point, a new kind of bistability is observed in a finite nonlinear photonic crystal (PhC). The mechanism of such a PhC bistability is from the complex interplay between cavity resonance, nonlinearity and beam behavior. Additionally, it has unique properties, including: high frequency sensitivity, small volume, short switching time, robustness and position flexibility. With the consideration of beam behavior, a new theory based on the coupled-mode equation has been constructed, whose result agrees with the numerical one very well. The new PhC bistability could be widely used to design various optical devices, as a bistable all-optical switch has also been demonstrated.

Quasi-phase-matched second-harmonic generation in nonlinear crystals with harmonic modulation of nonlinearity

We propose a new type of nonlinear photonic crystal with the lattice representing a harmonic function of the propagation coordinate. This type of spatial modulation of the quadratic nonlinearity is implemented to enhance the second-harmonic generation (SHG) efficiency. The process resembles that realized in periodic nonlinear photonic crystals with rectangular nonlinearity modulation under quasi-phase-matching. Residual periodic oscillations of the second-harmonic intensity were found. Comparison of the unipolar and bipolar modulations showed that they are equivalent with regard to the oscillations. The SHG efficiency in the harmonic lattices is 1.6 times lower compared with the efficiency corresponding to the quasi-phase-matching in periodic nonlinear photonic crystals with rectangular lattices.

Solution‐Processed Barium Titanate Nonlinear Woodpile Photonic Structures with Large Surface Areas

Three dimensional (3D) nonlinear photonic crystals are one of the potential candidates for enabling photonic circuits. Most of the current top‐down fabrication approaches for such crystals are time consuming and suffer from small surface areas and limitations to specific substrates. Herein, a bottom‐up fabrication technique (UV‐soft nanoimprint lithography) together with solution processing of barium titanate (BaTiO3) nanoparticles is used to create large‐scale 3D nonlinear woodpile photonic crystals. Opposed to other 3D photonic crystals, the woodpile structure can be fabricated layer by layer. This property makes it suitable for roll‐to‐roll fabrication, which can be easily adapted in industry. The prepared photonic crystals with up to eight layers have surface areas of 1.0 cm2. The linear and nonlinear optical behavior of these 3D woodpile structures is characterized. Their transmission stop band lies around 757 nm and a relative linear minimum transmission of 48.4% for a four‐layer sample is obtained. Images of diffraction patterns together with polarization‐dependent second harmonic generation measurements prove a cubic photonic crystal structure in the linear and nonlinear regime. In addition to second‐order nonlinearity, BaTiO3 exhibits electro‐optic, elasto‐optic, and thermo‐optic effects. Therefore, it is especially suited for future active photonic crystal applications.

Simulating Correlations of Structured Spontaneously Down‐Converted Photon Pairs

AbstractIntroducing structure into photon pair generation via spontaneous parametric down‐conversion (SPDC) is shown to be useful for controlling the output state and exploiting new degrees of freedom for quantum technologies. This paper presents a new method for simulating first‐ and second‐order correlations of the down‐converted photons in the presence of structured pump beams and shaped nonlinear photonic crystals. This method is nonperturbative, and thus accounts for high‐order effects, and can be made very efficient using parallel computing. Experimental results of photodetection and coincidence rates in complex spatial configurations are recovered quantitatively by this method. These include SPDC in 2D nonlinear photonic crystals, as well as with structured light beams such as Laguerre Gaussian and Hermite Gaussian beams. This simulation method reveals conservation rules for the down‐converted signal and idler beams that depend on the nonlinear crystal modulation pattern and the pump shape. This scheme can facilitate the design of nonlinear crystals and pumping conditions for generating non‐classical light with pre‐defined properties.

Smart optically induced nonlinear photonic crystals for frequency conversion and control

We extend the functionality of nonlinear photonic crystals by fabricating a structure combining a few individual optical transformations in second harmonic generation. In particular, we employed all-optical spontaneous polarization reversal in ferroelectrics to create nonlinear holograms with curved fork-like spatial modulation of nonlinearity for the generation of second harmonic optical vortices. The curved fork-like structure represents a combination of a standard vortex harmonic generator (fork structure) and an axicon, thereby allowing us to realize the second harmonic “perfect vortices” whose diameter remains constant independently of their topological charge.

Topological photonic crystals: a review.

The field of topological photonic crystals has attracted growing interest since the inception of optical analog of quantum Hall effect proposed in 2008. Photonic band structures embraced topological phases of matter, have spawned a novel platform for studying topological phase transitions and designing topological optical devices. Here, we present a brief review of topological photonic crystals based on different material platforms, including all-dielectric systems, metallic materials, optical resonators, coupled waveguide systems, and other platforms. Furthermore, this review summarizes recent progress on topological photonic crystals, such as higherorder topological photonic crystals, non-Hermitian photonic crystals, and nonlinear photonic crystals. These studies indicate that topological photonic crystals as versatile platforms have enormous potential applications in maneuvering the flow of light.

Multi-resonant optical parametric oscillator without mirrors based on 1D and 2D-PPLT nonlinear photonic crystal

In this work, we demonstrate that it is possible to obtain an optical parametric oscillator with a simultaneous amplification of multiple frequencies using only a nonlinear photonic crystal with highly polished end-faces, preventing the utilization of external cavity mirrors.

High conversion efficiency second-harmonic beam shaping via amplitude-type nonlinear photonic crystals

An efficient two-dimensional arbitrary harmonic wavefront shaping has been demonstrated in amplitude-type nonlinear photonic crystals, where the phase-matching condition is fulfilled through the birefringence and nonlinear Raman–Nath effects in longitudinal and transverse phase matching, respectively. The binary modulated nonlinear photonic crystal was fabricated by femtosecond laser micromachining based on binary computer-generated holograms. Three second-harmonic Hermite–Gaussian beams, H G 10 , H G 11 , and H G 12 , were achieved by pumping a nanosecond pulsed fundamental Gaussian beam, with the measured normalized conversion efficiency of 8.4 % W − 1 c m − 2 in the first diffraction order of the H G 11 structure. The amplitude-type nonlinear photonic crystal opens wide possibilities in the field of efficient harmonic beam shaping and mode conversion.

Laser-written three dimensional nonlinear photonic crystals

Laser-written three dimensional nonlinear photonic crystals

New dynamical nonlinear mechanism, a way to enhance nonlinear efficiency and detect ultrafast electronic processes in photonic crystals.

We quantitatively investigate the energy efficiency and the possibility of detecting the electronic ultrafast processes of a new dynamical nonlinear mechanism suitable for the nonlinear photonic crystal switching effect with femtosecond pumping. It is found that the energy efficiency of the new dynamical nonlinear mechanism is considerably higher than traditional band-gap shift mechanism, and the characteristics of the transmission curve are related to the parameters of the electronic ultrafast processes. Thus, the dynamical nonlinear mechanism is a new way to enhance the nonlinear efficiency and to indirectly detect the electronic femtosecond or even attosecond processes. Besides that, the totally new patterns of transmission and reflection spectra revealed in this work also imply the deep differences between two mechanisms. Wide potential usages could be expected for the properties found by this work.

Research development on fabrication and optical properties of nonlinear photonic crystals.

Since the lasers at fixed wavelengths are unable to meet the requirements of the development of modern science and technology, nonlinear optics is significant for overcoming the obstacle. Investigation on frequency conversion in ferroelectric nonlinear photonic crystals with different superlattices has been being one of the popular research directions in this field. In this paper, some mature fabrication methods of nonlinear photonic crystals are concluded, for example, the electric poling method at room temperature and the femtosecond direct laser writing technique. Then the development of nonlinear photonic crystals with one-dimensional, two-dimensional and three-dimensional superlattices which are used in quasi-phase matching and nonlinear diffraction harmonic generation is introduced. In the meantime, several creative applications of nonlinear photonic crystals are summarized, showing the great value of them in an extensive practical area, such as communication, detection, imaging, and so on.

All optical NOR and NAND gates using four circular cavities created in 2D nonlinear photonic crystal

The paper presents novel 2D photonic crystal (PhC) structures comprising of four circular cavities (CCs) that mimic NOR and NAND gates. 2D Finite difference time domain (2DFDTD) method is used for simulation and analysis of optical behavior of the proposed structures considering perfectly matched layers (PML) around the simulation region. Photonic band gap (PBG) and projected band diagram are obtained using plane wave expansion (PWE) method. It is shown that both the structures function with optical inputs of same wavelength and intensity. The proposed NOR and NAND gates are having low operating powers and good contrast ratio. Being universal gates, NOR and NAND allows for Boolean completeness.Implementation of bypass waveguides is a unique feature of the structures proposed in this paper. When the output is LOW, most of the optical power channelizes out of the structure through bypass waveguides, which otherwise, would go into the input ports affecting the input devices or would remain trapped inside the structure resulting in heating. This issue is not touched in the previous literature and in our opinion, being addressed for the first time.

Efficient parametric generation in a nonlinear photonic crystal pumped by a dual beam.

We investigate parametric down-conversion in a hexagonally poled nonlinear photonic crystal, pumped by a dual pump with a transverse modulation that matches the periodicity of the χ (2) nonlinear grating. A peculiar feature of this resonant configuration is that the two pumps simultaneously generate photon pairs over an entire branch of modes, via quasi-phase matching with both fundamental vectors of the reciprocal lattice of the nonlinearity. The parametric gain of these modes depends thus coherently on the sum of the two pump amplitudes and can be controlled by varying their relative intensities and phases. We find that a significant enhancement of the source conversion efficiency, comparable to that of one-dimensionally poled crystals, can be achieved by a dual symmetric pump. We also show how the four-mode coupling arising among shared modes at resonance can be tailored by changing the dual pump parameters.

Efficient nonlinear beam shaping in three-dimensional lithium niobate nonlinear photonic crystals

Nonlinear beam shaping refers to spatial reconfiguration of a light beam at a new frequency, which can be achieved by using nonlinear photonic crystals (NPCs). Direct nonlinear beam shaping has been achieved to convert second-harmonic waves into focusing spots, vortex beams, and diffraction-free beams. However, previous nonlinear beam shaping configurations in one-dimensional and two-dimensional (2D) NPCs generally suffer from low efficiency because of unfulfilled phase-matching condition. Here, we present efficient generations of second-harmonic vortex and Hermite-Gaussian beams in the recently-developed three-dimensional (3D) lithium niobate NPCs fabricated by using a femtosecond-laser-engineering technique. Since 3D χ(2) modulations can be designed to simultaneously fulfill the requirements of nonlinear wave-front shaping and quasi-phase-matching, the conversion efficiency is enhanced up to two orders of magnitude in a tens-of-microns-long 3D NPC in comparison to the 2D case. Efficient nonlinear beam shaping paves a way for its applications in optical communication, super-resolution imaging, high-dimensional entangled source, etc.

Floquet Chern insulators of light

Achieving topologically-protected robust transport in optical systems has recently been of great interest. Most studied topological photonic structures can be understood by solving the eigenvalue problem of Maxwell’s equations for static linear systems. Here, we extend topological phases into dynamically driven systems and achieve a Floquet Chern insulator of light in nonlinear photonic crystals (PhCs). Specifically, we start by presenting the Floquet eigenvalue problem in driven two-dimensional PhCs. We then define topological invariant associated with Floquet bands, and show that topological band gaps with non-zero Chern number can be opened by breaking time-reversal symmetry through the driving field. Finally, we numerically demonstrate the existence of chiral edge states at the interfaces between a Floquet Chern insulator and normal insulators, where the transport is non-reciprocal and uni-directional. Our work paves the way to further exploring topological phases in driven optical systems and their optoelectronic applications.

Enhancement of ABCs efficiency at computer simulation of optical pulse interaction with inhomogeneous nonlinear medium

We focus our attention on enhancing of computation performance at numerical simulation of a laser pulse interaction with inhomogeneous nonlinear medium (optical periodic structure or photonic crystal) which is described in the framework of 1D Schrödinger equation without using slowly varying envelope in spatial coordinate. It allows taking into account the optical pulse reflection from medium inhomogeneous. In practice, as a rule at computer simulation the domain size before photonic crystal is many times greater than the photonic crystal size. Decreasing this domain one can essentially increase a computation performance. This aim is achieved by re-statement of the problem: instead of initial distribution of complex amplitude along spatial coordinate before the photonic crystal we consider its specifying as a boundary condition (BC), which results in the pulse propagation in both directions of the propagation axis. Taking this into account and that a part of a laser pulse reflects from faces of photonic crystal layers, we use the artificial boundary conditions (ABCs). To avoid an influence of waves propagated in negative direction of spatial coordinate on the laser pulse interaction in photonic crystal (this influence appears due to imperfection of ABC). We introduce in consideration some number of artificial waves related with the equation under consideration. With this aim, firstly, we provide a computation of the laser pulse propagation in a linear medium and storage the complex amplitude values at chosen section of a coordinate, along which a laser light propagates. Then we use this complex amplitude values as a left boundary condition for 1D nonlinear Schrödinger equation in domain containing a nonlinear photonic crystal. To decrease amplitude of the wave reflected from artificial boundaries. We demonstrate also that instead of a complex amplitude values storage one can use the corresponding analytical expression for the linear Schrödinger equation solution, corresponding to a laser pulse propagation in a linear domain before the photonic crystal. We discuss also various ways for full transform of the optical pulse energy for reflected wave into artificial waves. This results essentially increasing of computation efficiency.

Nonlinear wavefront shaping with optically\xa0induced three-dimensional nonlinear photonic crystals

Generation of coherent light with desirable amplitude and phase profiles throughout the optical spectrum is a key issue in optical technologies. Nonlinear wavefront shaping offers an exceptional way to achieve this goal by converting an incident light beam into the beam (or beams) of different frequency with spatially modulated amplitude and phase. The realization of such frequency conversion and shaping processes critically depends on the matching of phase velocities of interacting waves, for which nonlinear photonic crystals (NPCs) with spatially modulated quadratic nonlinearity have shown great potential. Here, we present the first experimental demonstration of nonlinear wavefront shaping with three-dimensional (3D) NPCs formed by ultrafast-light-induced ferroelectric domain inversion approach. Compared with those previously used low-dimensional structures, 3D NPCs provide all spatial degrees of freedom for the compensation of phase mismatch in nonlinear interactions and thereby constitute an unprecedented system for the generation and control of coherent light at new frequencies.

Frequency Doubling Of Femtosecond Laser Pulses In Nonlinear Photonic Crystals With Account Of High-Order Dispersion

We studied numerically the frequency doubling of femtosecond laser pulses (up to ∼5 fs) in nonlinear photonic crystals. We investigated the impact of a number of factors (phase modulation of the primary emission pulse and spatial modulation of nonlinear susceptibility, up to the third order dispersion of a nonlinear photonic crystal) on the efficiency of nonlinear conversion and the duration of the secondharmonic pulse. We show that the efficiency of second-harmonic generation reaches η2ω∼ 45% when ultrashort (down to 5 fs) laser pulses are used.