Fiber-compatible K+-Na+ ion-exchanged channelwaveguides: fabrication and characterization

A systematic study of waveguides fabricated by K⁺-Na ⁺ exchange in soda-lime silicate and BK7 glasses is presented. The measured K⁺ concentration profile, the refractive index profile, and the diffusion profile obtained by solving the one-dimensional diffusion equation are correlated to explain the differences in the index profiles in the two glasses. The mobility of the potassium ions was measured by fabricating waveguides using electromigration. Surface waveguides formed by diffusion from a molten KNO₃ salt bath were buried by applying an electric field. Single-mode channel waveguides for operation at a wavelength of 1.3 μm that exhibit excellent mode matching with conventional optical fibers, achieving a fiber-waveguide insertion loss of less than 1 dB for a 20-mm-long waveguide, have been obtained     

Influence of Ag+-Na+ ion-exchange equilibriumon waveguide index profiles

The Ag⁺-Na⁺ ion-exchange process in a soda-lime silicate glass was studied at 330° as a function of composition of AgNO₃-NaNO₃ melt, mixing condition, and exchange time. The concentration profile of silver in glass was measured by atomic absorption spectroscopy and SEM technique. The surface index change and the index profile were determined from mode index measurement. Ion-exchange was modeled by an ion-diffusion limited process in the glass with an equilibrium chemical reaction at the melt-glass interface. A large value of 75 for the equilibrium constant at low-silver melt concentrations (<10^-2 mole fractions) shows that uptake of silver in glass varies in highly nonlinear fashion with the melt concentration. The results provide boundary conditions necessary for solution of the diffusion equation and design of single-mode waveguides     

Proton-exchanged optical waveguides in Z-cut LiNbO3 using phosphoric acid

Proton-exchanged Z-cut LiNbO₃ planar waveguides formed using phosphoric acid were characterized optically. The refractive index profile and the diffusion parameters were studied systematically. These waveguides have propagation losses of less than 1 dB/cm and exhibit properties that are different from those obtained using benzoic acid. The index profile is not a simple step function and can be modeled accurately by a polynomial expression. A maximum surface index increase of 0.145 was measured at a 0.633-μm wavelength. The diffusion constant D₀ and the activation energy Q for the proton-exchange process using this acid were found to be 6.43×10⁸ μm²/h and 82.91 kJ/mol, respectively. The annealing properties of these waveguides were also established, and the effects of annealing on surface index change and waveguide depth increase were found to follow a power-law relationship     

He~＋离子注入KTiOPO_4晶体波导的制备及其性能研究

报道了液氮温度Ｈｅ＋离子不同的注入能量和剂量条件下ＫＴｉＯＰＯ４晶体波导的制备，利用Ｍ线光谱法测量了退火后波导各导模的有效折射率，计算了波导层折射率的分布和晶体中离子的射程分布与损伤分布，二者吻合得较好。     

Characterization of asymmetric graded-index planar optical waveguides from the knowledge of TE/sub 0/-TE/sub 1/ mode cutoff wavelengths

The authors have proposed (1991) a simple method for predicting the index profile parameter (the profile exponent q in case of a power law profile or the aspect ratio S in case of trapezoidal index profile) of a graded-index optical fiber which is single moded in the 1.3-1.55 mu m wavelength range from a measurement of the LP/sub 11/ and LP/sub 02/ cutoff wavelengths. They extend the method with appropriate modification to determine the asymmetry parameter sigma , the maximum refractive index n/sub f/ and the characteristic thickness d of the guiding layer of a few-moded graded-index asymmetric planar optical waveguide from a measurement of the TE/sub 0/ and TE/sub 1/ cutoff wavelengths. The method is simple and can give firsthand information about these parameters with reasonably good accuracy.<>     

Theoretical modeling and characterization of annealedproton-exchanged planar waveguides in z-cut LiNbO3

Planar optical waveguides in z-cut LiNbO₃ fabricated by the annealed proton-exchange technique using pure pyrophosphoric acid as the initial proton source have been investigated. A generalized Gaussian function was used to accurately model the refractive-index profile, resulting in considerable improvements over previous work. The nonlinear dependence of the index on the proton concentration was verified by directly calculating the change in the area under the index versus depth curves. Annealing was found to allow for flexibility in the tailoring of the waveguide parameters. An empirical correlation of the changes in these parameters with the fabrication conditions was achieved through the use of a general power law     

Photosensitivity and application with 157-nm F/sub 2/ laser radiation in planar lightwave circuits

Photosensitivity studies of germanosilica planar waveguides were carried out with short-wavelength 157-nm light from an F/sub 2/ laser. More than a 5/spl times/10/sup -3/ refractive-index change was induced in a nonuniform index profile concentrated near the cladding-core interface and confirmed by an atomic force microscopy in 157-nm radiated fiber. This profile geometry narrows with the laser exposure to offer practical application in trimming phase errors and controlling birefringence in frequency domain modulators where a 1.7/spl times/10/sup -3/ effective index change and a 5/spl times/10/sup -4/ birefringence change were induced, respectively. The 157-nm photosensitivity response is more than 15 times stronger than that by a 248-nm KrF laser and more than twofold stronger than that by a 193-nm ArF laser.     

InGaAsP/GaAs单量子阱半导体激光器光学特性的研究

用改进的液相外延方法 L PE 生长了无铝的 In Ga As P/Ga As分别限制单量子阱半导体激光器 ,测量其远场分布近似为高斯分布 .用缓变波导理论分析了产生这种分布所对应的光波导结构的折射率分布模型 ,并简单解释了其生成原因 ,为改善光束质量提供了参考     

Suppression of cladding-mode coupling loss in fiber Bragg gratings by independent control of refractive index and photosensitive profiles in a single-mode optical fiber

A new method to suppress the cladding-mode coupling loss in fiber Bragg gratings, by independent control of the core refractive index profile and the photosensitive profile, is proposed and experimentally demonstrated. Across the core and the inner cladding, a uniform step photosensitive profile was introduced by co-doping GeO/sub 2/ and B/sub 2/O/sub 3/. The core refractive index was selectively raised by further doping Al/sub 2/O/sub 3/ in the core that has negligible photosensitivity at 244 nm. For strong Bragg gratings inscribed on the fiber, the cladding-mode coupling loss was suppressed below 0.3 dB.     

Proton-exchange optical waveguides in Z-cut LiNbO/sub 3/ using toluic acid

Proton-exchanged planar waveguides were demonstrated in Z-cut LiNBO/sub 3/ using toluic acid as a new organic proton source. These waveguides exhibit a propagation loss of around 1 dB/cm, and a step refractive index profile with an index increase of 0.124 measured at 0.663 mu m. The diffusion rate was found to be lower than those obtained using the popular benzoic and phosphoric acids.<>     

Correlation study between VAD preform deposition surface and Germanium doping profiles

The refractive index profile of germanium doped preforms for optical fibers is determined by the radial distribution of germanium concentration. Knowing that there is a correlation between the germanium doping profile and the deposition surface profile of vapor-phase axial deposition (VAD) preforms, the study of this correlation has been carried out in order to estimate, indirectly, the refractive index profile of VAD preforms for optical fibers during the deposition stage. This correlation was studied through the parameterization of the preform deposition surface using two parameters: the power law index profile that best fits the preform bottom profile (/spl alpha/) and the axial distance from the bottom tip to a reference height (h). A range of values of these parameters to produce VAD preforms with standard and special doping profiles has been presented. Preforms with triangular index profile can be fabricated with /spl alpha/ and h values of about 2.0 and 5.0 mm, respectively, and preforms with parabolic index profiles can be produced with /spl alpha/ and h values of about 2.0 and 4.0 mm, respectively.     

Optical Channel Waveguides in $hbox {KTiOPO}_{4}$ Crystal Produced by Proton Implantation

We reported on, to our knowledge the first time, the channel waveguide formation in KTiOPO₄ crystal by the implantation of protons with a special designed photoresist mask. The 2-D refractive index profile was constructed according to the measured dark-mode spectroscopy (for longitudinally planar configuration) as well as the shape of the channel waveguide cross section. Based on this index distribution, the modal profile was calculated through a numerical simulation, which showed reasonable agreement with the near-field light intensity distribution of the guided mode that was obtained by an end-coupling method. After annealing at 200deg C for 30 min in air, propagation loss of the channel waveguides was determined to be as low as ~2.9 dB/cm at wavelength of 632.8 nm.     

Characterization of annealed proton exchanged LiNbO3waveguides for nonlinear frequency conversion

A thorough and detailed characterization of annealed proton-exchanged (APE) waveguides in Z-cut LiNbO₃ is described. The mode index measurements in planar waveguides as a function of wavelength and annealing time are reported, including useful analytical relations for the refractive index change, its dispersion, and the depth profile as a function of annealing parameters. Analytical expressions for the mode propagation characteristics are presented and experimentally verified with reasonable accuracy. It is shown that the planar waveguide characterization results can be used to model the channel waveguide characteristics accurately. The model provides closed-form expressions for the mode index and the mode field profile, and the theoretical results are in excellent agreement with the measured data. The technique is used to accurately predict the phase mismatch between the fundamental and second harmonic modes in frequency-doubling experiments using APE channel waveguides. An optimum waveguide geometry for which the phase mismatch is relatively insensitive to the waveguide nonuniformity was predicted and verified experimentally     

用Tl_2SO_4制造玻璃光波导

本文报道了用TI盐(TI_2SO_4)离子交换法制备玻璃光波导的实验结果。与用AgNO_3离子交换制备的光波导相比,波导损耗较低,折射率分布呈准阶跃型,拟合确定其折射率分布函数为费米函数,折射率增量Δn>0.13。     

Fabrication of planar optical waveguides by K+-ion exchange in BK7 and Pyrex glass

Planar graded index optical waveguides have been formed by K+ ion exchange in BK7 optical glass and Pyrex glass. Measurements of the mode indexes have been made and are well described by the WKB dispersion relation with a complementary error function refractive index profile for both glass types with refractive index changes (Delta n) of 0.0094 and 0.0073 for BK7 and Pyrex, respectively. A linear relation was found between the diffusion depth and the square root of the diffusion time for both materials, and effective diffusion coefficients were calculated. Diffusion times necessary to achieve a desired number of modes and diffusion depths have also been established.     

Neodymium-doped cladding-pumped aluminosilicate fiber laser tunable in the 0.9-/spl mu/m wavelength range

A tunable high-power cladding-pumped neodymium-doped aluminosilicate fiber laser is demonstrated. The maximum power reached was 2.4 W with a slope efficiency of 41% and a threshold pump power of 1.68 W, both with respect to launched pump power, when cladding pumped by two 808-nm diode pump sources at both fiber ends. The dependence of the tuning range on the fiber length is investigated. The tuning range changed from 922 to 942 nm for a 25-m-long fiber to 908-938 nm with a 14-m-long fiber, because of reabsorption effects. The output linewidth was 0.26 nm in a diffraction-limited beam. Operation on the challenging 0.9-/spl mu/m three-level transition in neodymium-doped double-clad fiber laser was facilitated by a W-type core refractive index profile. This filtered out the unwanted and competing strong transition at 1.06 /spl mu/m while guidance of 0.9 /spl mu/m remained intact.     

Buried optical waveguide polarizer by titanium indiffusion andproton-exchange in LiNbO3

Buried optical waveguide polarizers on LiNbO₃ have been realized by titanium indiffusion, followed by proton-exchange and annealing. The proton-exchange process decreases the ordinary refractive index and so modifies the index profile of the titanium indiffused waveguide. The measured intensity profile is in good agreement with calculation. An aluminum film absorbs the surface TM mode on z-cut LiNbO₃, leaving a buried nearly symmetric TE mode with lower optical loss than surface-guided TE modes. The extinction ratio obtained is estimated to be greater than 50 dB/cm at 0.633 μm     

Crosstalk characteristics of Ti-LiNbO3intersecting waveguides and their application as TE/TM mode splitters

Crosstalk characteristics of an intersecting waveguide are presented. Two straight channel waveguides which intersect at an angle of a few degrees ony-cut LiNbO3were fabricated by in-diffusion of Ti. Experimental results show that the crosstalk characteristics are determined by the refractive index change profile and the geometry of intersection associated with guided wave modes. In a special case, a TE/TM mode splitter was obtained by using the intersecting waveguide which provides adequate anisotropy by the change in refractive indices. Splitting ratio was 17 and 14 dB for the TE and TM modes, respectively.     

Proton-exchanged optical waveguides in LiNbO/sub 3/ using octanoic acid

Low-loss proton-exchanged planar waveguides in z-cut LiNbO/sub 3/ were fabricated and characterized optically using octanoic acid as a proton source. The waveguide exhibited a step-index profile with an index change of 0.118 measured at 0.633 mu m. The lowest waveguide propagation loss measured was 1.2 dB/cm, and it was reduced further to 0.4 dB/cm after annealing. The diffusion rate and the activation energy using this acid were found to be lower than those reported using other acids.<>