Optical Planar Waveguides in KTiOPO4 Crystals by MeV Oxygen Ion Implantation

We report on the optical planar waveguide formation in KTiOPO4 crystals by single or double oxygen ion implantation at energies of 2.4-3.0 MeV and doses of 1015 ions/cm^2. The dark-line spectroscopy properties are investigated by a prism-coupling method. With an effective refractive index method, the refractive index profiles of the waveguides are reconstructed. The program code TRIM＇98 （transport of ions in matter） is used to simulate the implantation process of oxygen ions into the KTiOPO4 crystal. It is found that an inherent relationship exists between the nuclear damage and the refractive index changes induced by the ion-beam implantation.     

Optical Waveguide Formed in RbTiOPO4 Crystal by 6.0 MeV O^3＋ Implantation

A planar optical waveguide was formed in RbTiOP04 crystal by 6.0-MeV oxygen ion implantation with the dose of 2 × 10^15 ions/cm2 at room temperature. Annealing at 200℃ for 30min in air is performed to improve the thermal stability of the waveguide. The dark modes of the waveguide are measured at wavelengths 633 and 1539 nm, respectively. The refractive index profiles in the guiding layer are reconstructed by using the reflectivity calculation method. TRIM＇98 code was carried out to simulate the damage profiles caused by the implantation process to obtain a better understanding of the waveguide formation.     

Planar waveguides in neodymium-doped calcium niobium gallium garnet crystals produced by proton implantation

In this work, the fabrication and optical properties of a planar waveguide in a neodymium-doped calcium niobium gallium garnet(Nd:CNGG) crystal are reported. The waveguide is produced by proton(H~+) implantation at 480 ke V and a fluence of 1.0×10~(17) ions/cm~2. The prism-coupling measurement is performed to obtain the dark mode of the waveguide at a wavelength of 632.8nm. The reflectivity calculation method(RCM) is used to reconstruct the refractive index profile. The finite-difference beam propagation method(FD-BPM) is employed to calculate the guided mode profile of the waveguide.The stopping and range of ions in matter 2010(SRIM 2010) code is used to simulate the damage profile induced by the ion implantation. The experimental and theoretical results indicate that the waveguide can confine the light propagation.     

Analysis and Determination of Refractive Index Profiles of O^2＋ Ion-Implanted LiNbO3 Planar Waveguide Using Etching and Ellipsometry Techniques

The refractive index profiles of 3 MeV O^2＋ 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.     

Guiding properties of proton-implanted Nd~(3+)-doped phosphate glass waveguides

We report on the fabrication and properties of an optical waveguide in Nd~(3+)-doped phosphate glass. The planar waveguide was obtained by 550-ke V proton implantation with a dose of 8.0×10~(16) ions/cm~2. The proton–glass interaction was simulated by the stopping and range of ions in matter(SRIM software). The characteristics of the waveguide including the refractive index profile and the near-field intensity distribution were studied by the reflectivity calculation method and the end-face coupling technique. The optical waveguide demonstrated multi-mode behavior at the wavelength of 632.8 nm.The propagation features of the proton-implanted Nd~(3+)-doped phosphate glass waveguide shows its potential to operate as an integrated photonic device.     

Polarized Emission of an Eu^3＋ Doped Azo-Polymer Waveguide

We investigate the polarized emission behaviour of an Eu^3 doped azo-polymer waveguide. Affected by the azobenzene groups in the photoinduced orientation process by the 532nm linearly polarized laser, the ligands were realigned orderly perpendicular to the direction of the orientation direction. This leads to the polarized absorption and emission of the waveguide in the orientation direction. By an m-line apparatus based on the prism coupling technique, two guided propagation modes were observed in the waveguide, and the refractive index at 650hm in TE polarizations is 1. 7505.     

Modal Characterization of a Planar Waveguide in Bismuth Borate Crystal

We report on the fabrication and modal property studies of planar waveguide structure in x-cut bismuth borate biaxial crystal formed by He ion implantation with triple energies. The prism coupling method is used to measure the effective refractive indices of this waveguide. We reconstruct the refractive index distribution of this waveguide by the reflectivity calculation method. Our results indicate that a broadened optical barrier is produced by the multiple He ion implantations. The so-called tunneling effect of the non-stationary mode in this type of barrier waveguide is presented by the well-known finite difference beam propagation method.     

Optical waveguide in Nd:Bi_(12)SiO_(20) crystal produced by multi-energy C ion implantation

We report the fabrication of a planar waveguide in the Nd:Bi_(12)SiO_(20) crystal by multi-energy C ions at room temperature. The waveguide is annealed at 200℃, 260℃, and 300℃ in succession each for 30 min in an open oven. The effective refractive index profiles at transverse electric(TE) polarization are stable after the annealing treatments. Damage distribution for multi-energy C ion implanted in Nd:Bi_(12)SiO_(20) crystal is calculated by SRIM 2010. The Raman and fluorescence spectra of the Nd:Bi_(12)SiO_(20) crystal are collected by an excitation beam at 633 nm and 473 nm, respectively. The results indicate the stabilization of the optical waveguide in Nd:Bi_(12)SiO_(20) crystal.     

Optical planar waveguides in yb3＋-doped phosphate glasses produced by He＋ ion implantation

Optical planar waveguides in Yb 3+-doped phosphate glasses are fabricated by implanting triple-energy helium ions. The guiding modes and the near-field intensity distribution are measured by using the prism-coupling method and the end-face coupling setup with a He-Ne laser at 633 nm The intensity calculation method (ICM) is used to reconstruct the refractive index profile of the waveguide. The absorption and the fluorescence investigations reveal that the glass bulk features are well preserved in the active volumes of the waveguides, suggesting the fabricated structures for possible applications as waveguide lasers.     

Optical planar waveguides in Yb³⁺-doped phosphate glasses produced by He⁺ ion implantation

Optical planar waveguides in Yb 3+-doped phosphate glasses are fabricated by implanting triple-energy helium ions. The guiding modes and the near-field intensity distribution are measured by using the prism-coupling method and the end-face coupling setup with a He-Ne laser at 633 nm The intensity calculation method (ICM) is used to reconstruct the refractive index profile of the waveguide. The absorption and the fluorescence investigations reveal that the glass bulk features are well preserved in the active volumes of the waveguides, suggesting the fabricated structures for possible applications as waveguide lasers.     

Visible and near-infrared optical properties of Nd:CLNGG crystal waveguides formed by proton implantation

A Nd:CLNGG waveguide structure operated at wavelengths of both 632.8 nm and 1539 nm was demonstrated for the first time to our knowledge, which was produced by the 480-keV H~+ion implantation with a dose of 1.0×10~(17)protons/cm~2.Its propagating modes at 632.8 nm and 1539 nm were measured by the well-known prism coupling technique. The refractive index profile at either 632.8-nm wavelength or 1539-nm wavelength was optical barrier type in the proton-implanted Nd:CLNGG crystal optical waveguide, which was calculated by using the reflectivity calculation method. The near-field light intensity distributions were also simulated by the finite-difference beam propagation method in the visible and nearinfrared bands.     

Laser-induced damage of high reflectors for Ti:sapphire laser system

A broadband(～176nm,R>98%,λo=800nm)and high laser-induced damage threshold(LIDT= 2.4J/cm~2)TiO_2/HfO_2/SiO_2 high reflector(HR)for Ti:sapphire chirped-pulse amplification(CPA)laser system is fabricated by the electron beam evaporation.The refractive index and extinction coefficient of TiO_2 and HfOu films are calculated from single-layer films' transmittance spectra.The properties of HR are mainly determined by the high refractive index material.The high refractive index leads to wide bandwidth.A low extinction coefficient indicates low absorption and high LIDT.The possible damage mechanism of HR is discussed.     

Reduction of insertion loss after annealing of silicon oxynitride optical waveguides

The insertion losses of silicon oxynitride (SiON) waveguides have been measured in the 1550 nm wavelength region. The waveguide structure consisted of a 2.0μm SiON waveguide core with a refractive index of 1.50, a 0.5μm SiO₂ upper cladding and a 5.0μm SiO₂ lower cladding with a refractive index of 1.45. It was found that the wavelength-dependent insertion losses of the waveguide were greatly reduced by annealing, and the loss was decreased more than 5.7 dB/cm at 1550 nm after annealing at optimum conditions. The former was attributed to the reduction of the absorption caused by N-H and Si-H vibration modes, and the latter was due to the improvement of the interface roughness and homogeneity in the waveguides after annealing.     

Refractive index of ionic liquids under electric field:Methyl propyl imidazole iodide and several derivatives

Ionic liquids have received wide attention due to their novel optoelectronic structures and devices as an optical means of regulating electricity.However,the quantitative testing and analysis of refractive index of ionic liquids under electric field are rarely carried out.In the present study,an experimental apparatus including a hollow prism is designed to measure the refractive indices of ionic liquids under different electric fields.Five groups of imidazole ionic liquids are experimentally investigated and an inversion is performed to determine the refractive indices under electric fields.The error propagation analysis of the apex angle and the minimum deflection angle are conducted,and the machining accuracy requirements of the hollow prism are determined.The results show that the refractive indices of imidazole ionic liquids change with the light wavelength,following a downward convex parabola.Furthermore,the refractive index decreases with the carbon chain length of ionic liquid at a given wavelength,presenting an order of C3MImI>C4MImI>C5MImI>C3MImBr>C3MImBF4.Notably,the refractive index of imidazole ionic liquid exhibits a nonlinear change with the applied voltage at 546 nm and a monotonical decrease at 1529 nm.Besides,the variation of refractive index at 1529 nm with the applied voltage is larger than that at 546 nm and 1013 nm.Importantly,the variation of refractive index is contrary to that of absorption coefficient under electric field.This study illustrates that the theory of electrode and carrier transport can be used to explain the law of variation of n–k value of ionic liquid under the electric field,and provides the support for the evaluation of physical properties of ionic liquids,the measurement of optical functional parameters and the regulation of electric–optic performances of optical devices.     

Influence of Different Substrates on Laser Induced Damage Thresholds at 1064nm of Ta2O5 Films

Ta2O5 films are prepared on Si, BK7, fused silica, antireflection （AR） and high reflector （HR） substrates by electron beam evaporation method, respectively. Both the optical property and laser induced damage thresholds （LIDTs） at 1064 nm of Ta2O5 films on different substrates are investigated before and after annealing at 673 K for 12 h. It is shown that annealing increases the refractive index and decreases the extinction index, and improves the O/Ta ratio of the Ta2O5 films from 2.42 to 2.50. Moreover, the results show that the LIDTs of the Ta2O5 films are mainly correlated with three parameters： substrate property, substoichiometry defect in the films and impurity defect at the interface between the substrate and the films. Details of the laser induced damage models in different cases are discussed.     

Spectral broadening induced by intense ultra-short pulse in 4H–SiC crystals

We report the observation of spectral broadening induced by 200 femtosecond laser pulses with the repetition rate of 1 kHz at the wavelength of 532 nm in semi-insulating 4H–SiC single crystals.It is demonstrated that the full width at half maximum of output spectrum increases linearly with the light propagation length and the peak power density,reaching a maximum 870 cm~(-1)on a crystal of 19 mm long under an incident laser with a peak power density of 60.1 GW/cm~2.Such spectral broadening can be well explained by the self-phase modulation model which correlates time-dependent phase change of pulses to intensity-dependent refractive index.The nonlinear refractive index n_2 is estimated to be1.88×10~(-15)cm~2/W.The intensity-dependent refractive index is probably due to both the nonlinear optical polarizability of the bound electrons and the increase of free electrons induced by the two-photon absorption process.Super continuum spectra could arise as crystals are long enough to induce the self-focusing effect.The results show that SiC crystals may find applications in spectral broadening of high power lasers.     

Effect of Fe concentration on the nonlinear refraction and reverse saturable absorption in ferroelectric X-cut LiNbO_3 crystal

In this Letter, the effects of the iron(Fe) dopant concentration on the nonlinear optical properties of iron-doped ferroelectric X-cut Li Nb O3 crystals plates are studied by using the Z-scan technique with a cw laser at the wavelength of 532 nm. The amount of iron in the compound is varied from 0 to 0.15 mol%. Measurements of nonlinear refractive index n2 and the nonlinear absorption coefficient β are determined. The sign of the nonlinear refractive index is found to be negative and the magnitude is on the order of 10-8cm2∕W. This nonlinear effect increases as the concentration increases from 0 to 0.15 mol%. A good linear relationship is obtained between nonlinear refractive index, nonlinear absorption coefficient, and concentration.     

Effect of crystalline lens surfaces and refractive index on image quality by model simulation analysis

The surfaces and refractive index of crystalline lens play an important role in the optical performance of human eye.On the basis of two eye models,which are widely applied at present,the effect of lens surfaces and its refractive index distribution on optical imaging is analyzed with the optical design software ZEMAX (Zemax Development Co.,San Diego,USA).The result shows that good image quality can be provided by the aspheric lens surfaces or (and) the gradient-index (GRIN) distribution.It has great potential in the design of intraocular lens (IOL).The eye models with an intraocular implantation are presented.     

Preparation of broadband antireflective coating by sol-gel method

A sol-gel method for the preparation of silica coating that varied in refractive index is developed. Silicon dioxide sol is obtained by hydrolysis and co-condensation reactions occurred in acid-catalyzed system. Surface morphology, refractive index, and transmission spectrum of the samples are studied. The results of transmission spectra of single-sided coatings show that the average transmittance of the samples increases about 4% compared with the uncoated one in the spectra range from 400 to 1 200 nm in the case of vertical incidence. For the double-sided coating the maximum transmittance is 99% at the wavelength of 840 nm.     

High sensitivity refractive index gas sensing enhanced by surface plasmon resonance with nano-cavity antenna array

The surface plasmon resonance gas sensor is presented for refractive index detection using nano-cavity antenna array.The gas sensor monitors the changes of the refractive index by measuring the spectral shift of the resonance dip,for modulating the wavelength of incident light.It is demonstrated that minute changes in the refractive index of a medium close to the surface of a metal film,owing to a shift in the resonance dip of the wavelength,can be detected.The average detection sensitivity is about 3200 nm/RIU(refractive index units),which is more than twice that of a metal grating-based gas sensor.The reflectivity of the surface plasmon resonance dip is only ～ 0.03%,and the full widths at half maximum(FWHMs) of bandwidth of the angle and wavelength are ～ 0.20° and 4.71nm,respectively.