Planar optical waveguides formed in β-BBO by MeV O+ implantation

The planar waveguides have been fabricated in z-cut β-BaB₂O₄ crystal by 2.8 MeV O⁺ ion implantation with the doses of 8×10¹⁴ and 2×10¹⁵ ions/cm² at room temperature. The waveguides were characterized by the prism-coupling method. The dark modes are measured before and after the annealing at 300°C for 20 and 40 min in air. The refractive index profile is reconstructed using the reflectivity calculation method. It is found that relatively large positive changes of extraordinary refractive indices happen in the guiding regions, and a slight change increases with the doses, which are different from most of the observed ion-implanted waveguides.     

Study of UV-bleached channel-waveguide performance in nonlinear optical polymer films

We report studies on UV-photobleached optical channel waveguides in nonlinear optical polymer films. The nonlinear optical polymer used is poly(methyl methacrylate)/DR1 side-chain polymer. The effective indices of the channel waveguides are measured with the prism-coupling technique, along with the effective indices of bleached and unbleached polymer films. The effective-index method was used to predict the effective indices of the channel waveguides from measurements of the slab waveguides, without detailed knowledge of the index distributions in the polymer films. Some local stress-related effects on the boundaries of the channel waveguides caused by the UV-bleaching process are identified by comparison between direct channel measurement and prediction. It is found that the technique used in this study can be employed to predict the performance of channel waveguides processed such that they have no excessive internal stress distributions.     

Synthesis of symmetric and asymmetric planar optical waveguides

A novel and accurate refractive index profile synthesis method for planar optical waveguides is presented and demonstrated using the transmitted near-electric-field-data. This method is based on the inverse transmission-line (TL) technique. From Maxwell's equations, a TL equivalent circuit (electric T-circuit) for the refractive index profile of a planar optical waveguide is derived. The authors demonstrate how to use this model to carry out the inverse problem and synthesise the exact refractive index profile numerically from near-field-data. The TL method can reconstruct arbitrary refractive index profiles for planar optical waveguides that support singlemode or multi- modes. The cases of both symmetric and asymmetric arbitrary refractive index profile planar waveguides are discussed. The accuracy of the reconstructed waveguides is examined numerically.     

Refractive indices and thicknesses of optical waveguides fabricated by silicon ion implantation into silica glass

Planar optical waveguides formed by Si ion implantation into PECVD SiO₂ have been characterized by the dark mode spectroscopy method at a wavelength of 0.6328 μm. The measured effective index values of the guided modes have been used to investigate the optical properties of the core layers of the waveguides after different pre-implantation treatments. It was found that annealing the specimens before implantation, affected both the refractive index and thickness of the core layers. In the annealed specimens a thicker core layer and a larger relative refractive index difference between the core and the buffer layer resulted.     

Lithium iodate planar waveguides by proton implantation

Permanent optical waveguides have been produced by proton implantation in LiIO₃ single crystals by using a Van De Graaff accelerator. The effects of the crystal cut and of the implantation paramaters on the optical waveguides properties, investigated by dark line mode spectroscopy, are presented. The profiles of the ordinary and extraordinary refractive indices are reconstructed by an inverse WKB method. Optical barriers with depths of few hundredths (Δn < 0) are currently obtained and their location can be accurately adjusted from 4 to 17 μm.     

Systematic modeling study of channel waveguide fabrication by thermal silver ion exchange

A systematic study of thermal silver ion exchange used for the fabrication of optical channel waveguides is reported in a single-alkali glass. The diffusion equilibrium and diffusion dynamics are experimentally studied, and the concentration-dependent diffusion coefficients are determined. The relationship between the fabrication conditions, i.e., time, temperature, and melt concentration, and the induced waveguide refractive index profile is established. It is demonstrated that the diffusion equation can be solved, without use of any free parameters, to predict the refractive index profiles of both planar and channel waveguides. A 1.6 cm diameter integrated optic ring resonator, with a propagation loss of 0.1 dB/cm, is fabricated in a glass by thermal silver ion exchange. The induced refractive index profile is related to the optical characteristics of the functional device.     

Planar optical waveguides in Bi4Ge3O12 crystal fabricated by swift heavy-ion irradiation

We report on the fabrication of the planar waveguides in Bi4Ge3O12 crystal by using 17 MeV C5+ or O5+ ions at a fluence of 2×10(14) ions/cm2. The reconstructed refractive index profiles of the waveguides produced by either C5+ or O5+ irradiation are the "well" + "barrier" pattern distribution. The two-dimensional modal profiles of the planar waveguides, measured by using the end-coupling arrangement, are in good agreement with the simulated modal distributions. After thermal annealing treatment at 260 °C for 30 min, the propagation loss for C5+ and O5+ irradiated waveguides could be reduced down to ~1.1 and ~4.8 dB/cm, respectively, which exhibit acceptable guiding qualities for potential applications in integrated optics.     

Modal behavior in single-mode slab waveguides consisting of inhomogeneous cores

We present an analytical method for TE and TM modes in weakly guiding inhomogeneous single-mode slab waveguides. Based on our results, the modal behavior or propagation constants depend on index profiles of the waveguides. It is important to know how the modal behavior depends on the index profile in single-mode waveguides, because it determines wave-front characteristics of propagating modes.     

Planar optical waveguides formed in β-BBO by MeV O+ implantation

The planar waveguides have been fabricated in z-cut β-BaB₂O₄ crystal by 2.8 MeV O⁺ ion implantation with the doses of 8 × 10¹⁴ and 2 × 10¹⁵ ions/cm² at room temperature. The waveguides were characterized by the prism-coupling method. The dark modes are measured before and after the annealing at 300°C for 20 and 40 min in air. The refractive index profile is reconstructed using the reflectivity calculation method. It is found that relatively large positive changes of extraordinary refractive indices happen in the guiding regions, and a slight change increases with the doses, which are different from most of the observed ion-implanted waveguides.     

Analysis of mode scattering from an abruptly ended dielectric slab waveguide by an accelerated iteration technique

A new modification of the integral equation method using an iteration technique with "accelerating" parameters is presented to solve the problem of guided-mode scattering from an abruptly ended asymmetrical slab waveguide. The optimal choice of the parameters is shown to be closely connected with the variational principle. The electric-field distribution at the terminal plane, the reflection coefficient of the guided mode, and the far-field radiation pattern are computed. Numerical results are presented for several cases of abruptly ended waveguides, including the systems with constant and variable profiles of the refractive indices. The phenomenon of the radiation pattern rotation is examined in detail.     

Direct integration of nanoscale conventional and slot waveguides

Slot waveguides can provide high optical confinement in a nanoscale low-index layer. While a conventional waveguide has a Gaussian-like Eigenmode profile, the Eigenmode profile of a slot waveguide is quite non-Gaussian type, due to the large discontinuity of refractive indices and thus the transverse electric field component between the high and low index layers of a slot waveguide. Although the field profiles of the two types of waveguides seem different, here we show that direct integration of conventional and slot waveguides yields efficient coupling of light into and out of slot waveguides using the rigorous finite-difference time domain method. The proposed direct coupling method has comparable performance to recently proposed taper based coupling methods, while having advantages in easier integration with conventional waveguide optics and higher integration density. We also show that coupling efficiency is not sensitive to the symmetricity of the slot waveguide, resulting in good manufacturing tolerance. The proposed direct coupler may have a number of applications in lightwave interconnects, sensing and data storage.     

Reflectivity properties of an abruptly ended asymmetrical slab waveguide for the case of transverse magnetic modes

We deal with the scattering phenomenon from an abruptly terminated asymmetrical slab waveguide for the case of transverse magnetic (TM) modes. The analysis uses both the integral equation method and the variational technique. The reflection coefficient of the dominant TM guided mode and the far-field radiation pattern are computed, and the discontinuity of the electric field distribution on the core-clad interface is exhibited. Numerical results are presented for several cases of abruptly ended waveguides, including the three-layer slab guide and the structure with variable profile of the refractive index.     

Experimental study of Cu(+)-Na(+) exchanged glass waveguides

Optical waveguides have been obtained by field-assisted Cu(+)-Na(+) exchanged on glass. The refractive index profiles of the waveguides are determined by means of the prism-coupling technique and Chiang's method [J. Lightwave Technol. LT-3, 385 (1985)], and they correlate with the index profile calculated as a function of the glass composition. The composition profile is examined with the aid of a scanning electron microscopy with energy-dispersive x-ray analysis, and the diffusion process is explained by the one-dimensional diffusion equation.     

Analytical model of spatial four-waveguide coupler

Analytical model of spatial four-guide coupler is presented by utilizing Marcatili's principle, where the spatial four-guide coupler can be described by two perpendicular five-layer slab waveguides. The common expressions to calculate the effective indices and the mode field distributions are shown in this paper. Introducing perturbation corrections to take the effect of the distinct regions into account, more accurate results can be obtained. The effective refractive indices and coupling lengths of specific examples are investigated to verify the feasibility of the analytical model by comparing with the numerical approaches such as finite difference (FD) numerical calculation and beam propagation method (BPM).     

Full vectorial modal analysis of specialty fibers and their Bragg grating characterization

Optical fibers and specialty waveguides are the bases of the majority of today's telecommunication, biomedical, sensing, and light-delivery applications. Modal analysis plays an important role in optimizing the optical performance of these fibers when they are integrated with optical systems. We present a full vectorial modal theoretical analysis of specialty cylindrical symmetric fibers with arbitrary index profiles, using a staircase approximation and scattering matrix approach with no constraints on the refractive index profile. We demonstrate the generality of this method by investigating the modal characteristics of two specialty fibers: graded-index fiber and concentric-shell multicore fiber. The calculated modal effective indices for the graded-index fiber are compared with those calculated by the WKB method, stressing the main differences between the scalar and vectorial approaches. Using the same approach, we calculate the Bragg grating response of a holographic grating written in the guiding regions of a concentric-shell fiber and compared them with experimental measurements.     

Annealing behavior of barriers in ion-implanted LiNbO3 and LiTaO3 planar waveguides

We formed planar waveguides in LiNbO(3) and LiTaO(3) crystals by megaelectron volt He-ion implantation. The dark modes of both waveguides are measured and their refractive-index profiles are described according to the parameterized index profile reconstruction method. The extraordinary indices of both ion-implanted waveguides exhibit quite different profiles. We compare the thermal stability of barriers in ion-implanted LiNbO(3) and LiTaO(3) waveguides by annealing at different temperatures. The results show that the barrier in a LiTaO(3) planar waveguide has higher thermal stability than that in a LiNbO(3) waveguide. The experiments also show that annealing at a temperature higher than 400 degrees C results in recrystallization of the barrier.     

Refractive index profiles of planar optical waveguides in β-BBO produced by silicon ion implantation

The planar waveguides have been fabricated in z-cut beta barium metaborate crystals by 2.8 MeV Si⁺ ion implantation with doses of 1 × 10¹⁵ and 3 × 10¹⁵ ions/cm² at room temperature. The waveguides were characterized by the prism-coupling method. The refractive index profiles were reconstructed using reflectivity calculation method. It is found that relatively large positive changes of extraordinary refractive indices happen in the guiding regions, and the negative changes of ordinary refractive indices happen at the end of the track. TRIM’98 (transport of ions in matter) code was used to simulate the damage profile in β-BBO by 2.8 MeV Si⁺ ion implantation.     

Direct measurement of substrate refractive indices and determination of layer indices in slab-guiding structures

We present a new method for accurate and nondestructive measurement of the refractive indices of substrates and guiding layers in slab waveguides. This method is based on the excitation of leaky waves in substrates and guided waves in guiding layers owing to the etching of grating couplers on the top of structures. It is particularly applicable to high refractive-index materials and to in situ measurements near the energy band gap of semiconductor waveguides. We present results that were obtained for an InP substrate with an InGaAsP epitaxial layer with regard to their refractive indices and temperature coefficients.     

Potassium-and silver-double-ion-exchanged slab glass waveguides: characterization and modeling

Double-ion-exchanged glass waveguides are made first by a potassium-ion exchange followed by a silver-ion exchange. The inverse WKB method is used to determine the index profile. It is shown that a combination of a truncated quadratic function and a complementary error function represents the refractive index best. A direct WKB method is employed to find the maximum index change and the diffusion coefficient of the second exchange process. The concentration of silver, potassium, and sodium ions are measured by an x-ray photoelectron spectroscopy technique. The results agree well with the index profile when a quadratic function is used.