Lithium Niobate Planar Waveguides Research Articles

Lithium niobate planar and ridge waveguides fabricated by 3 MeV oxygen ion implantation and precise diamond dicing

We report on the fabrication and optimization of lithium niobate planar and ridge waveguides at the wavelength of 633 nm. To obtain a planar waveguide, oxygen ions with an energy of 3.0 MeV and a fluence of 1.5×1015 ions/cm2 are implanted in the polished face of LiNbO3 crystals. For planar waveguides, a loss of 0.5 dB/cm is obtained after annealing at 300°C for 30 min. The ridge waveguide is fabricated by the diamond blade dicing method on optimized planar waveguides. The guiding properties are investigated by prism coupling and end-face coupling methods.

Simulation and Analysis of Single-Mode Microring Resonators in Lithium Niobate Thin Films

The single-mode microring resonators on lithium niobate thin films were designed and simulated using 2.5-D variational finite difference time domain mode simulations from Lumerical mode Solutions. The single-mode conditions and the propagation losses of lithium niobate planar waveguide with different SiO2 cladding layer thicknesses were studied and compared systematically. The optimization of design parameters such as radii of microrings and gap sizes between channel and ring waveguides were determined. The key issues affecting the resonator design such as free spectral range and Quality Factor were discussed. The microring resonators had radius R = 20 μm, and their transmission spectrum had been tuned using the electro-optical effect.

Impact of carbon-ion implantation on the nonlinear optical susceptibility of LiNbO3.

In this work we study the impact of ion implantation on the nonlinear optical properties in MgO:LiNbO3 via confocal second-harmonic microscopy. In detail, we spatially characterize the nonlinear susceptibility in carbon-ion implanted lithium niobate planar waveguides for different implantation energies and fluences, as well as the effect of annealing. In a further step, a computational simulation is used to calculate the implantation range of carbon-ions and the corresponding defect density distribution. A comparison between the simulation and the experimental data indicates that the depth profile of the second-order effective nonlinear coefficient is directly connected to the defect density that is induced by the ion irradiation. Furthermore it can be demonstrated that the annealing treatment partially recovers the second-order optical susceptibility.

UV laser-induced poling inhibition in proton exchanged LiNbO_{3} crystals

The applicability of the UV laser-induced poling inhibition method for ferroelectric domain engineering in proton exchanged lithium niobate planar waveguides is investigated. Our results indicate that intense UV irradiation of proton exchanged lithium niobate samples can, indeed, produce poling inhibited domains in this material under certain irradiation conditions. However, there is strong indication that the temperature gradient that is formed during UV irradiation modifies the local proton concentration leading to changes in the refractive index profile of the original planar waveguide.

Ultralong propagation of a surface plasmon polariton wave within an ultrawide bandwidth via phase-sensitive optical parametric amplification.

The propagation length enhancement of surface plasmon polariton (SPP) waves could lead to practical applications. This Letter proposes the numerically verified phase-sensitive nonlinear χ(2)-based optical parametric amplification (OPA) for ultralong propagation of a SPP wave within an ultrawide bandwidth. The strong nonlinear interaction between the SPP mode and the hybrid guided mode, which limits the length enhancement, is mitigated in a silver-coated linearly chirped periodically poled lithium niobate planar waveguide via slowly phase-matched OPA. Obtained results indicate an ultralong propagation length for a SPP mode of about 4 cm when a 135 MW/cm pump intensity is launched. The acceptance bandwidth of the amplified SPP shows its dependency on the pump intensity; for a pump intensity range between 70 and 135 MW/cm, the acceptance bandwidth is still ultrawide, varying from 28 to 18 nm, respectively.

Supercontinuum Generation in Lithium Niobate Ridge Waveguides Fabricated by Proton Exchange and Ion Beam Enhanced Etching**Supported by the National Natural Science Foundation of China under Grant Nos 61575129 and 11375105, the Postdoctoral Science Foundation of China under Grant No 2016M602511, the Shenzhen Science and Technology Planning under Grant No JCYJ20160422142912923, and the State Key Laboratory of Nuclear Physics and Technology,

We report on the fabrication of the 10-mm-long lithium niobate ridge waveguide and its supercontinuum generation at near-visible wavelengths (around 800 nm). The waveguides are fabricated by a combination of MeV copper ion implantation followed by wet etching in a proton exchanged lithium niobate planar waveguide. Using a mode-locked Ti:sapphire laser with a central wavelength of 800 nm, the generated broadest supercontinuum through the ridge waveguides spans 302 nm (at −30 dB points), from 693 to 995 nm. Temporal coherence properties of the supercontinuum are experimentally studied by a Michelson interferometer and the coherence length of the broadest supercontinuum is measured to be 5.2μm. Our results offer potential for a compact and integrated supercontinuum source for applications including bio-imaging, spectroscopy and optical communication.

Low drive voltage electro-optic Bragg deflector using a periodically poled lithium niobate planar waveguide.

An electro-optic Bragg light deflector is demonstrated in a thinned, periodically poled lithium niobate planar waveguide confined between two silica layers on a silicon substrate. More than 97% of diffraction efficiency is obtained with an operating wavelength of 633 nm for the two orthogonal light polarizations with a drive voltage of about 5 V. The temporal electric drift and the response time of the component are also studied.

Time and Temperature Dependent Study of Zn and Ni Codiffused LiNbO<sub>3</sub> Waveguides

Zn and Ni codiffused lithium niobate planar and channel waveguides are fabricated at various temperatures for different times. Compositional and optical properties of the waveguides are studied. Single-mode channel waveguides are measured for 2-D refractive index profiling using a modified end-fire coupling method at excitation wavelengths of both 633 and 1550 nm. Planar waveguides with the same metallic thicknesses as those of channel waveguides are analyzed using secondary-ion-mass-spectrometry to obtain the diffused metal ion concentration profiles. The relationship between the diffusion depths and index depths is discussed based on the completeness of the diffusion process.

Photovoltaic laser beam degradation in lithium niobate planar waveguides: two-center model approach

Photovoltaic laser beam degradation in lithium niobate (LiNbO3) has been investigated through a finite-differences beam propagation method for nonlinear media. The simulations use a two-center model (Fe2+↔Fe3+, NbLi4+↔NbLi5+) that has been recently proved to be necessary to successfully describe the photorefractive effect in nominally pure LiNbO3. Refractive index profiles and intensity and phase beam profiles have been calculated for a wide intensity range and several material distances. A good agreement is obtained on comparing simulations and experimental data. This includes self-defocusing for moderate intensities and the complex beam profile structures appearing for high intensities, providing a complete description of this nonlinear optical phenomenon.

Efficient high-power frequency doubling of distributed Bragg reflector tapered laser radiation in a periodically poled MgO-doped lithium niobate planar waveguide

We report on efficient single-pass, high-power second-harmonic generation in a periodically poled MgO-doped LiNbO3 planar waveguide using a distributed Bragg reflector tapered diode laser as a pump source. A coupling efficiency into the planar waveguide of 73% was realized, and 1.07 W of visible laser light at 532 nm was generated. Corresponding optical and electro-optical conversion efficiencies of 26% and 8.4%, respectively, were achieved. Good agreement between the experimental data and the theoretical predictions was observed.

Planar and ridge waveguides formed in LiNbO_3 by proton exchange combined with oxygen ion implantation

We report on the fabrication of planar and ridge waveguides in lithium niobate by proton exchange combined with oxygen ion implantation. The implanted energy ranges from 600 to 1400 keV with a dose of 1 x 10(15) ions/cm(2). The modes in proton exchanged waveguide can be modulated by O ion implantation. There are different damage profiles in proton-exchanged and ion-implanted waveguides in Rutherford backscattering/channeling spectra. The refractive index profile in single-mode waveguide in lithium niobate has been obtained based on Intensity Calculation Method. Also ridge waveguide was fabricated on the basis of planar waveguide by Ar ion beam etching. The measured near-field intensity distributions of the ridge waveguide modes show a reasonable agreement with the simulated ones. The estimated propagation loss was approximately 2.2 dB/cm.

Bi-directional spatial soliton emission at engineered nonlinear waveguide interfaces

We observed tunable bi-directional emission of spatial solitons at a quadratically nonlinear interface in periodically poled lithium niobate planar waveguides. The interface consists of the boundary between two quasi-phase-matched regions with a different poling period. We show the intensity and phase-mismatch (temperature or wavelength) dependence of the phenomena.

Investigation of the mutual repelling and attraction of dark spatial solitons in a proton-implanted planar waveguide in lithium niobate

Results of the experimental study of the formation and interaction of dark photovoltaic spatial solitons in a proton-implanted planar lithium niobate waveguide for microwatt-level forming and read out beams are presented.

Growth and characterization of lithium niobate planar waveguides by liquid phase epitaxy

Single crystal thin films of Yb, Zn: LiNbO 3 have been grown on LiNbO 3 substrates using liquid phase epitaxy with K 2 O flux. The segregation coefficients decrease abruptly at high doping concentrations, indicating a doping threshold. The surface roughness of the thin film increased with doping concentration. The propagation loss of the as-grown lithium niobate thin film sample was 0.154 ± 0.002 dB / mm at a wavelength of 1 μ m measured by the cutback method.

Low-threshold, narrow-line THz-wave parametric oscillator with an intra-cavity grazing-incidence grating

We report a low-threshold, narrow-line THz-wave parametric oscillator with an intra-cavity grazing-incidence grating and a 1-mm thick, 45-mm long lithium-niobate planar waveguide. When pumped by an actively Q-switched Nd:YAG laser, the threshold energy and intensity of the parametric oscillator were about 2.2 mJ and 70 MW/cm(2), respectively. The linewidths of the output THz wave were 12 and 134 GHz with and without the intra-cavity grating, respectively.

Parametric Solitons in Two-Dimensional Lattices of Purely Nonlinear Origin

We demonstrate spatial solitons via twin-beam second-harmonic generation in hexagonal lattices realized by poling lithium niobate planar waveguides. These simultons can be steered by acting on power, direction, and wavelength of the fundamental frequency input.

Analysis and Determination of Refractive Index Profiles of O2+ Ion-Implanted LiNbO3 Planar Waveguide Using Etching and Ellipsometry Techniques

The refractive index profiles of 3MeV O2+ ion-implanted planar waveguides in lithium niobate are reconstructed based on etching and ellipsometry techniques. SRIM2003 code is used to simulate the damage distribution in waveguide. It is demonstrated that the index profile of this kind of waveguide, extending to several micrometres in depth, can be determined by etching in combination with following ellipsometric measurements. A good agreement is found between the simulated damage distributions in waveguide and the index profiles based on experimental data, and the width of refractive index barrier is wider than the result of SRIM2003.

Photonic band-gap enhanced second-harmonic generation in a planar lithium niobate waveguide

Enhanced second-harmonic generation (SHG) conversion efficiency was theoretically predicted in waveguide geometry with coupling to a one-dimensional grating photonic band gap (PBG). We report a series of experiments using samples made with lithium niobate. A waveguide was fabricated near the surface by applying the proton-exchange technique. The characteristics of waveguide modes were determined by several techniques: prism coupling, diffraction, and Cherenkov radiation. The WKB method was used to analyze the results. Ultraviolet laser lithography was applied to make PBG gratings on the sample. We further investigated Cherenkov second-harmonic generation (CSHG), i.e., SHG radiated into the substrate, under the condition of a band-edge PBG resonance in the waveguides. The SHG inside planar waveguides was also experimentally investigated. We fabricated waveguides with multiple pump modes and found that the second mode was more efficient in enhancing the second harmonic signal. This result is explained by our model. Several samples were investigated in detail; the highest conversion efficiency of CSHG with a PBG was enhanced around 50 times above the CSHG signal without a PBG. A numerical model was constructed with parameters calculated from our sample characterization data to interpret the experimental results.

Second harmonic generation in helium-implanted periodically poled lithium niobate planar waveguides

Second harmonic generation in the visible has been successfully performed in helium implanted planar waveguides in 10 μm-periodically poled lithium niobate (PPLN) by using second order quasi-phase matching. The conversion efficiency was found to be 40% higher than that of the PPLN bulk crystal.

Tunable Lithium Niobate Waveguide Loop

A novel, compact, and tunable lithium niobate (LN) planar waveguide loop structure composed of two Y junction reflectors is proposed for optical and radio frequency signal processing applications. The preliminary device shows a high quality factor of 6.5/spl times/10/sup 4/, due to the low propagation loss of the titanium-diffused LN waveguide. The tunability of the loop by electric field is estimated.