Asymmetric Refractive Index Profile Research Articles

A fundamental mode converter based on tapered LiNbO3-on-insulator photonic wire with a laterally asymmetric structure

We report a mode converter based on a tapered X-cut/Y-propagation ridge-type LiNbO 3 -on-Insulator (LNOI) photonic wire (PW) with a laterally asymmetric refractive index profile realized by introducing a semi-infinite dielectric cover layer on one side of the LNOI PW. The interplay of material and waveguide birefringence enables to realize mode hybridization, which is a prerequisite for realizing mode conversion. The introduction of the semi-infinite cover layer and the use of a taper structure modify mode index and electric field distribution, enabling to realize mode conversion. Aiming at 1.55 μm wavelength, we have simulated mode hybridization and conversion characteristics of the tapered, laterally asymmetric ridge-type LNOI PW. The results show that a conversion between fundamental TM 00 and TE 00 modes can be realized. The conversion efficiency can be optimized by choosing an appropriate cover layer material and/or adjusting its thickness. An ultra-compact device with a taper length <100 μm is expected. • A mode converter based on a tapered LNOI photonic wire (PW) is proposed. • The device has a laterally asymmetric refractive index profile. • Asymmetric index profile and taper structure enable to realize mode conversion. • A conversion between fundamental TM 00 and TE 00 modes is realized. • An ultra-compact device with a taper length <100 μm is expected.

Analysis of Bloch Surface Waves at the Interface Between Two Semi-infinite Rugate Filters with Symmetric Refractive Index Profiles

Surface electromagnetic waves are representation of Maxwell’s frequency domain equations at the interface of two dissimilar materials. In this article, two canonical boundary value problems have been formulated to analyze the multiplicity of electromagnetic surface waves at the interface between two dissimilar materials. In the first problem, interface between two semi-infinite rugate filters having symmetric refractive index profiles is considered and in the second problem, to enhance the multiplicity of surface electromagnetic waves, a homogeneous dielectric slab is included between two semi-infinite symmetric rugate filters. Multiplicity has been observed by varying the size of dielectric material from 0 to 1000 nm. Numerical results show that the number of Tamm waves of different phase speeds, different polarization states, different degrees of localization, and different field profiles that are being propagated at interface between two semi-infinite rugate filters having symmetric refractive profile is almost twice as when asymmetric refractive index profile is used. Having two interfaces when a homogeneous dielectric layer is placed between two semi-infinite rugate filters has increased the multiplicity of electromagnetic surface waves.

Specific features of chitosan waveguides optical response formation to changes in the values of relative humidity

In this paper we report about numerical simulation of optical response of chitosan waveguide to the change in the relative humidity value. It is shown that optical response occurs by changing of waveguide propagation conditions. Herein, at a lower humidity value (less than 30%) chitosan waveguide has an asymmetric refractive index profile. The humidity level increasing leads to appearing a gradient profile of refractive index. Obtained numerical data has good agreement with experimental results.

Femtosecond laser writing of optical edge filters in fused silica optical waveguides

The positional alignment of femtosecond laser written Bragg grating waveguides within standard and coreless optical fiber has been exploited to vary symmetry and open strong optical coupling to a high density of asymmetric cladding modes. This coupling was further intensified with tight focusing of the laser pulses through an oil-immersion lens to control mode size against an asymmetric refractive index profile. By extending this Bragg grating waveguide writing into bulk fused silica glass, strong coupling to a continuum of radiation-like modes facilitated a significant broadening to over hundreds of nanometers bandwidth that blended into the narrow Bragg resonance to form into a strongly isolating (43 dB) optical edge filter. This Bragg resonance defined exceptionally steep edge slopes of 136 dB/nm and 185 dB/nm for unpolarized and linearly polarized light, respectively, that were tunable through the 1450 nm to 1550 nm telecommunication band.

New design for a variable optical attenuator based on a bent channel waveguide

We present a new method for bend loss control in a curved channel optical waveguide and employ it in a novel design of a thermo-optic variable optical attenuator. We show that the introduced asymmetric refractive index profile of the waveguide structure, combined with the optimal placement of the heating electrodes, leads to a significant increase of the dynamic range of the attenuator.

Effect of Asymmetric Refractive-index Profile on Skew in Single-mode Fiber Ribbons

Low cost fiber ribbons with small skew value must be realized for high bitrate parallel optical transmission systems. The influence of asymmetric refractive-index profile is precisely investigated for this purpose. The previously proposed variational analysis can deal with the asymmetric profile. The accuracy of this analysis is checked theoretically and experimentally. The calculated skew values by the variational analysis are compared with ones by vector analysis using a multilayer approximation for symmetric profiles. The calculated values by the variational analysis are compared with the experimental data for asymmetric profiles. Considering the clarified accuracy of the analysis, skews of several asymmetric profiles are calculated. By measuring skew values of commercially available fiber ribbons, realization of low cost, small skew fiber ribbons is discussed.