Higher Order Propagation Modes Research Articles

Design and Performance Analysis of Strip Photonic Waveguide with Coating Layer for Multimode Propagation

Introduction: Photonic devices play a pivotal role in the realm of high-speed data communication due to their inherent capability to expedite the transfer of information. Historically, research efforts in this domain have predominantly concentrated on investigating the fundamental mode propagation within photonic waveguides. Methods: This study diverges from the conventional approach by delving into the untapped potential of higher-order modes in addition to the fundamental mode of propagation. The exploration of these higher-order modes opens up new possibilities for optimizing and enhancing the performance of photonic devices in high-speed data communication scenarios. As a distinctive aspect of this study, various coating materials were scrutinized for their impact on both fundamental and higher-order mode propagation. The materials under examination included AlN (aluminum nitride), Germanium, and Silicon. These materials were chosen based on their unique optical properties and suitability for influencing different modes of light propagation. The findings from the study reveal that applying a coating of germanium demonstrates advantageous characteristics, particularly in terms of reduced signal loss, even when considering higher-order modes of propagation within photonic devices. Results: In this context, the results indicate that germanium-coated waveguides exhibit notably low propagation losses, with measurements as minimal as 0.25 dB/cm. This low level of loss is particularly noteworthy, especially when the waveguide has a width of 550 nm and is coated with a thickness of 50 nm. The dimensions and coating specifications play a crucial role in determining the efficiency of light transmission within the waveguide. Conclusion: The fact that the propagation loss is substantially low under these conditions suggests that the germanium-coated waveguide, even when considering higher-order modes of light propagation, can effectively maintain the integrity of the optical signal.

Bragg Gratings and Fabry-Perot Cavities in Low-Loss Multimode CYTOP Polymer Fiber

We report the inscription of fiber Bragg gratings (FBGs) and Fabry-Perot (FP) cavities in a gradient index cyclized transparent optical polymer (CYTOP) polymer optical fiber (POF) using a femtosecond laser. Through careful control of the inscription parameters, the coupling between the grating and the fiber’s higher order propagation modes is reduced, allowing for single peak grating spectra. Furthermore, we inscribe a 10-nm chirped grating and an FBG FP cavity with a free spectral range of 240 pm. We measure the group delay of the chirped grating and characterize the fiber FP cavity for strain and temperature.

Single-Mode Operation in Flat Fibers Slab Waveguide via Modal Leakage

An approach to obtain single-mode operation on a semirectangular large core area Flat Fiber (FF) slab waveguide is proposed. A new design of FF with two defect eye holes is presented, and its single-mode guiding is analyzed by simulation. To validate the simulation results, a proof of concept FF with a core area $ > 1200{\rm{ \mu }}{{\rm{m}}^2}$ was fabricated, and its modal behavior was examined. It was found that higher order propagation modes could be discriminated from the large core area by introducing a high-refractive index region in the FF eye holes. Experimental results confirmed a single Gaussian mode profile (mode field diameter of $ \approx745{\rm{ \mu m}})$ output of this large core FF, thus validating the simulation results.

Relativistic-ponderomotive effects on cross-focusing of hollow Gaussian laser beams in plasma

AbstractThe present work aims to study the influence of relativistic–ponderomotive effects on cross-focusing of two co-propagating high-power hollow Gaussian laser beams [high-power laser beams (HGLBs)] in collisionless plasma. The effective dielectric constant has been derived on account of relativistic–ponderomotive nonlinearity. The phenomenon of cross-focusing for higher-order modes of HGLB is compared for the case when only relativistic nonlinearity is operative in the system and it is seen that the relativistic–ponderomotive effects make the focusing much stronger and relatively faster. The critical curves for various order of HGLB is discussed and compared with the case when only ponderomotive nonlinearity is present and it reveals that in the case of relativistic–ponderomotive case the spot size reduces effectively. The higher-order modes of propagation of HGLB are also found to be governed by the parameter of another propagating HGLB. The present study is useful in determining the propagation dynamics of HGLB.

Direct computation of higher-order propagation modes using the imaginary-distance beam propagation method

In this paper we present an extension to the standard method of eigenmode-extraction using the imaginary-distance beam propagation method. We show that it is possible to directly extract higher-order propagation modes of arbitrary shaped waveguide structures by propagating the field along the imaginary axis when the parameters are chosen in an appropriate manner. This method requires an assumption of the propagation constant of the eigenmode. In many cases this value can be determined using fast approximate techniques like the effective index method. Additionally, the approximate mode shape may be introduced as a starting condition and can further accelerate the extraction of the eigenmode. The overall number of propagation steps needed to extract multiple eigenmodes is then significantly smaller than in the case when extracting the modes sequentially with the former method.

Sound attenuation in ducts lined on two opposite walls with porous material, with some applications to splitters

A theory is given for acoustic attenuation in ducts lined on two opposite sides with porous sound-absorbing material incorporating perforated facings, in the presence of uniform flow. Theoretical calculations are compared to measurements by the author, and to experimental data in the literature. Some emphasis in the discussion is placed on three-dimensional higher order modes of propagation. The application of the model to splitter type silencers is discussed, and design curves for duct linings are given.

Nonorthogonal Optical Waveguides and Resonators

The modes of propagation in optical systems which do not possess meridional planes of symmetry (nonorthogonal systems) are investigated in the case where the effect of apertures and losses can be neglected. The fundamental mode of propagation is obtained with the help of a complex ray pencil concept. An integral transformation of the field, based on a quasi-geometrical optics approximation and a first-order expansion of the point characteristic of the optical system, is given; it shows that the complex (three-dimensional) wavefront of the fundamental mode is transformed according to a generalized “ABCD law.” A simple expression is also obtained for the phase-shift experienced by the beam. The higher order modes of propagation are obtained from a power series expansion of the fundamental mode. These higher order modes are expressed, in oblique coordinates, as the product of the fundamental solution and finite series of Hermite polynomials with real arguments. In the special case of systems with rotational symmetry, these series reduce to the well-known generalized Laguerre polynomials. The theory is applicable to media such as helical gas lenses and optical waveguides suffering from slowly varying deformations in three dimensions. Nonorthogonal resonant systems are also investigated. An expression for the resonant frequencies, applicable to any three-dimensional resonator, is derived. Numerical results are given for the resonant frequencies and the resonant field of a twisted path cavity which exhibits interesting properties: the usual polarization degeneracy is lifted and the intensity pattern of all of the modes possesses a rotational symmetry.

Fundamental and Higher-Order Mode Surface Wave Propagation on Layered Anisotropic Substrates—Gold on Lithium Niobate

Calculations for the phase velocity of acoustic surface waves on lithium niobate with a contiguous gold layer have been carried out for the fundamental and higher-order modes of propagation. The anisotropy of the substrate leads to a prediction that the first higher-order mode has a low-frequency cutoff. In some cases the phase velocity dispersion curves for various modes have crossing points. Theoretical calculations and experimental evidence of the position of the crossing points for the first two modes and the phase velocity characteristics of the dominant mode above and below the crossing points as a function of the frequency-film thickness product are given.

Boundary Layer Attenuation of Higher Order Modes in Rectangular and Circular Tubes

The boundary layer attenuation caused by viscous and thermal losses of all higher order modes of propagation in rigid walled rectangular and circular tubes has been calculated using the concept of boundary layer admittance introduced by Cremer. In the case of the rectangular tube Cremer's admittance formula for obliquely incident waves is applied directly in conjunction with Morse's duct formulas to obtain the attenuation of (ny, 0) and (ny, n2) modes. The boundary layer admittance of higher order modes in circular tubes is obtained from an extension of Cremer's method for plane waves. An electromagnetic wave-guide technique for calculating “skin” losses is applied to determine the attenuation of the asymmetric (m, n) circular tube modes. It is shown that the symmetric (0, n) circular tube modes are the least attenuated of all higher order modes in both rectangular and circular tubes; above a certain frequency the attenuation is less than the plane wave attenuation.