Refractive Index Profile Of Waveguide Research Articles

Analysis of metal-clad optical waveguide polarizers by the vector beam propagation method

The attenuation characteristics of a metal-clad planar optical waveguide polarizer are computed by a modified finite-difference beam propagation method, taking into consideration the complex refractive indices of the metals used and the vector characteristics of the guided mode. Numerical results for practical optical waveguide refractive-index profiles such as the step and Gaussian distributions are presented. The method should find applications in the design of metal-clad optical waveguide polarizers and other lossy waveguide devices with arbitrary refractive-index profiles and can be easily expanded to three-dimensional cases.

Proton-exchanged LiNbO_3 waveguides: relevance of atmospheric environment during annealing

The relevance of the type of atmosphere used during the annealing of proton-exchanged LiNbO(3) planar waveguides is discussed. The experimental evidence, based on a comparison of the refractive-index profiles of waveguides annealed under wet O(2), dry O(2), or ambient atmospheres, with various gas flow rates, suggests that the atmosphere type does not influence the properties of the resulting waveguide.

Characterization of an AlGaAs rib waveguide using a grating in a Fabry–Perot étalon configuration

We characterize an AlGaAs rib waveguide using a structure based on a third-order Bragg reflector fabricated by electron-beam lithography. The grating forms a resonant cavity with the sample's uncoated output facet, and we observe a Fabry-Perot étalon behavior superimposed on the Bragg reflector characteristics. We present transmitted intensity measurements as a function of wavelength and temperature. We derive results for waveguide refractive-index profile, loss coefficient, group effective index, effective-index wavelength dispersion, and effective-index temperature dispersion. An auxiliary prism on top of the grating allows us to couple light out of the waveguide into the air. Angular measurements of the outcoupled orders at different wavelengths confirm the wavelength dispersion measurements made on the Fabry-Perot étalon formed by the grating and the cleaved mirror.

Optical characterisation of Z-cut proton-exchanged LiNbO3 waveguides fabricated using orthophosphoric and pyrophosphoric acid

We carry out a systematic study of proton-exchange waveguides fabricated using orthophosphoric and pyrophosphoric acid. Proton-exchange is carried out using three different processes: surface-coating, spin-coating, and immersion. Waveguide refractive index profiles and effective diffusion coefficients (210°C to 235°C), as determined from optical waveguide prism coupling measurements, have been compared to those of waveguides fabricated by immersion in benzoic acid. In addition to there being no apparent differences in the optical quality and properties of waveguides fabricated using phosphoric and benzoic acids, contrary to previous reports, we do not find any major advantages in using the surface coating or spin coating techniques for waveguide fabrication. The only situation in which we have obtained as high a value of Δne as has been claimed by other workers, e.g. Δne = 0.145, λ = 0.6328 μm, is where the waveguide refractive index profile is calculated using the inverse WKB method for waveguides which support only three or four modes. Under such conditions, the IWKB method is inaccurate.

Refractive-index profile measurement of highly multimode planar waveguides by guided-beam tracking

A novel method of measuring the refractive-index profile of deep multimode planar waveguides is described. Unlike in mode spectroscopy, several modes are excited simultaneously by a prism coupler. Superposition of the modes forms a guided beam that refracts continuously inside the graded-index waveguide and reflects periodically from the waveguide surface. Measurement of the periodicity as a function of the excitation angle enables one to calculate the refractive-index profile of the waveguide.

Application of the WKB method in determination of the refractive-index profile of planar diffused waveguides

An analysis is made of the potentialities of the quasiclassical approximation and a method is proposed for the determination of the refractive index profile directly from experimental values of the effective refractive indices of multimode planar waveguides formed by diffusion. The method proposed is used to determine the refractive index profile of waveguides formed by the diffusion of titanium into a lithium niobate substrate.

Automatic analysis of interferograms: optical waveguide refractive index profiles

Compensation of mode velocities in optical waveguides can be achieved by fabricating fibers having graded refractive index cores. One technique for measuring these index profiles is interference microscopy. We have developed a machine aided method for analysis of interference micrographs for the rapid determination of optical waveguide refractive index profiles. Our method consists of digitizing the interference micrograph with a scanning microdensitometer, followed by computer determination of the position of the center line of each fringe. The data obtained are then converted into refractive index and fiber radius information, which is used to calculate a best fit power law function.

Optical waveguide refractive index profiles determined from measurement of mode indices: a simple analysis

The WKB approximation is used to derive simple equations that predict the shape of the index profile from measured mode indices of a planar optical waveguide. This nondestructive test is a useful tool in the study of diffused guides. The index profile is assumed either to decrease monotonically from the surface or to be symmetrical in the case of a buried guide. The approximation uses straight line segments to connect the measured points. Results are compared with mathematical solutions for exponential, Fermi, and step distributions and with other independent experimental observations of the profile in a nickel-diffused LiNbO(3) guide.