Waveguide Parameters Research Articles

A Direct Method for the Simultaneous Estimation of Self-Steepening and the Fractional Raman Contribution in Fiber Optics

We propose an original, simple, and direct method for the simultaneous estimation of the self-steepening parameter and the fractional Raman contribution in fiber optics. Our proposal is based on the dependence of the modulation instability gain on both parameters, as obtained from a linear stability analysis of the newly introduced photon-conserving generalized nonlinear Schrödinger equation (pcGNLSE), and requires only the CW or quasi-CW pumping of the waveguide under test and a few direct spectral measurements. Further, we demonstrate the feasibility of the estimation procedure by means of detailed simulations for typical waveguide parameters in relevant spectral ranges. Last, we discuss the range of applicability of the proposed method and compare its results, advantages, and disadvantages with a recently introduced method based on short-pulse dynamics.

Transfer of information through waveguides near an exceptional point

The propagation of light in a pair of waveguides (WGs) with a complex index of refraction is studied, when the WG parameters are adjusted in such a way as to bring the system extremely close to an exceptional point (EP) while slightly breaking $\mathcal{P}\mathcal{T}$ symmetry. We find that this breaking of $\mathcal{P}\mathcal{T}$ symmetry does not affect the structure of the output signals, although the corresponding propagation constants become slightly complex. Only for sufficiently strong breaking of the $\mathcal{P}\mathcal{T}$ symmetry the signal is enhanced or suppressed in a substantial manner. Moreover, due to the EP it is impossible to tap light into another WG and thus read the transmitted signal without destroying completely the nodal structure and changing dramatically the intensity of the signal.

Ultrabroadband beam splitting in a dissipative system of three waveguides

We show that a system of three parallel waveguides, among which the central one is dissipative, leads to an ultrabroadband power splitting associated with an overall 50% power loss. The present approach is reminiscent of non-Hermitian systems in quantum mechanics and does not require a perfect effective index matching between the external and the central waveguides. The present concept does not need any slow adiabatic evolution of the waveguide parameters and may therefore be realized over very short device lengths, especially in the case where the central waveguide is of the plasmonic type.

Analysis of light coupling in AlxGa1-xAs waveguide arrays.

Light propagation in arrays of AlxGa1-xAs waveguides is studied. The power coupling constant between two adjacent waveguides is precisely measured as waveguide material and structure is varied. Aluminum concentration contrast between waveguide core/cladding layers and waveguide width/height produce an asymmetric effective refractive index between linearly polarized modes, which in turn causes a polarization dependence of the coupling constants. Experimental measurement results agree well with an analytical model. The sensitivity of coupling constant to the waveguide parameters is analyzed. Through a careful geometric design, comparable coupling constants can be achieved in three waveguide arrays with different structure. Similar formation processes of discrete spatial optical solitons are observed respectively, confirming that the parameterization in the discrete nonlinear Schrödinger equation characterizes waveguide arrays.

Adiabatic guided wave optics - a toolbox of generalized design and optimization methods.

Starting from the fully vectorial coupled local-mode theory, a general design rule for adiabatic waveguide design is derived. The design rule guarantees adiabaticity and puts an upper limit on the transmission loss of any guided wave transformation. The rule is applicable to any waveguide geometry, admits multi-dimensional optimization, and accounts for radiative loss to guided and radiation modes. Moreover, the design technique is enhanced with further optimization procedures that eliminate coupling between particular pairs of modes. The utility of this toolbox of design rules and methods is illustrated through the design of a 2×2 coupler and a bilayer waveguide transition. These design procedures can be used to optimize single-mode and multimode photonic devices by varying one or more waveguide parameters.

Measurements of quantum dot level populations using an optical waveguide

A scheme is proposed for measuring electron level populations in a semiconductor quantum dot embedded in a multimode waveguide. The photon transmittance of the waveguide under steady-state pumping is shown to depend on the presence of an electron in the ground state of the quantum dot. The influence of waveguide, quantum dot, and photon source parameters on the electron detection process is examined. It is shown that, even at a moderate mode Q-factor (104 to 105), the measurement contrast and signal-to-noise ratio are rather high (above 104). The feasibility of using the proposed method for probing the state of a charge qubit is discussed.

Solution of the Helmholtz equation for electromagnetic waves in an annular (segmented-annular) rectangular waveguide

Formulation of the problem. When designing waveguides, spatial solutions are often in demand. However, from a methodological (including educational) point of view, mostly linear-extended structures with various sectional shapes are considered. The aim of this work is to consider a waveguide as a structure composed of segments bent in a plane with a certain radius. On the other hand, this solution is common for a plane-oriented waveguide path and, in the case of an infinitely large radius, converges to a solution for a straight waveguide. Practical significance. The presented solution of the Helmholtz equation for electromagnetic waves in an annular (segmentedannular) waveguide can be considered as a methodological basis for calculating a spatially oriented rectangular waveguide path. A step-by-step solution of the Helmholtz equation for a bent rectangular waveguide is presented; a methodology for determining the parameters of the electromagnetic field in a bent homogeneous waveguide is given. Expressions are derived for determining the parameters of the electromagnetic field components for waves of type E and H. General solutions are obtained that converge at an infinitely large bending radius to harmonic functions characteristic of solutions as applied to rectilinear waveguides. This technique can be applied both for analytical evaluation or numerical calculation and spatial modeling of waveguide parameters, and for designing the waveguide path as a whole. The presence of relatively simple analytical expressions greatly facilitates the task of analyzing and optimizing the waveguide path and building software and computing systems for their assessment, modeling and development.

Radial density profile and stability of capillary discharge plasma waveguides of lengths up to 40 cm

Abstract We measured the parameter reproducibility and radial electron density profile of capillary discharge waveguides with diameters of 650 $\mathrm{\mu} \mathrm{m}$ to 2 mm and lengths of 9 to 40 cm. To the best of the authors’ knowledge, 40 cm is the longest discharge capillary plasma waveguide to date. This length is important for $\ge$ 10 GeV electron energy gain in a single laser-driven plasma wakefield acceleration stage. Evaluation of waveguide parameter variations showed that their focusing strength was stable and reproducible to $<0.2$ % and their average on-axis plasma electron density to $<1$ %. These variations explain only a small fraction of laser-driven plasma wakefield acceleration electron bunch variations observed in experiments to date. Measurements of laser pulse centroid oscillations revealed that the radial channel profile rises faster than parabolic and is in excellent agreement with magnetohydrodynamic simulation results. We show that the effects of non-parabolic contributions on Gaussian pulse propagation were negligible when the pulse was approximately matched to the channel. However, they affected pulse propagation for a non-matched configuration in which the waveguide was used as a plasma telescope to change the focused laser pulse spot size.

Sensitivity analysis of rectangular waveguides with different anisotropic surface impedance boundaries using modal extended theory

This article presents a sensitivity analysis of rectangular waveguides loaded with anisotropic surface impedance boundaries on their vertical walls, by using modal extended theory (MET). Using this method, several dispersion diagrams are computed for various anisotropic impedance boundary conditions of the surface walls of the waveguides in order to assess how the slight changes on the surface impedance can affect on the bandwidth and the fundamental cutoff frequency of the waveguide. The results obtained with MET were validated by comparison with the commercial software ANSYS HFSS. The results show that small anisotropic variations of the surface wall impedances lead to variation on the fundamental cutoff frequency and the bandwidth of the waveguide. Most significantly, and compared to an isotropic metasurface case, the variation of the transverse impedance of the metasurface is the one that have more significant effect over the waveguide parameters. This is an useful information for the metasurface design in order to take into account the fabrication tolerance of these structures and how they can have an influence over the final constructed device.

Application of Spectral Pyrometry Under Conditions of Intense Microwave Electromagnetic Fields

The paper discusses practical application of spectral pyrometry for controlling the temperature of a dielectric object subjected to heating in a high-intensity microwave electromagnetic field. The authors describe the advantages of using spectral versus color and brightness pyrometry when measuring high temperatures (500°C and above). To eliminate a negative impact of the electromagnetic field on a fiber-optic cable, which is exposed to thermal radiation from a microwave field-heated object and may fail in case of overheating, it is proposed to place a below-cutoff waveguide inside instead of outside of the microwave heating chamber. It is shown that such solution completely eliminates the negative impact of the electromagnetic field on the fiber-optic cable and allows positioning the receiving end of the cable in close proximity to the heated object. A calculation of geometric parameters of the below-cutoff waveguide is provided given the operating frequency of the electromagnetic field of 2450 MHz.

Multi-Parameter Optimization of an InP Electro-Optic Modulator

In this article, a method for indium phosphide (InP) electro-optic modulator (EOM) optimization is introduced. The method can be used for the design and analysis of an EOM based on the Mach-Zehnder interferometer (MZI) design. This design is based on the division of the input optical signal into two optical paths and then, after processing, it combines the light into a single waveguide. The symmetry of the structure can provide state-of-the-art EOM characteristics with a push-pull control signal. Using a traveling wave electrode (TWE) design as a starting point, the authors varied the heterostructure design and optical waveguide parameters to obtain the optimal values of initial optical loss, evenness of the initial optical loss in the operating wavelength range, and the extinction ratio and length of the modulator arm. The key features of the proposed optimization method include the following: all independent input parameters are linked into a single system, where the relationship between the electrical and optical parameters of the modulator is realized; all physically realizable combinations of the input parameters are available for analysis; and EOM optimization is possible for one target parameter or for a group of target parameters. The results of the EOM optimization using the described method are presented.

A dynamic impedance matching algorithm of three-stub tuners based on equivalent circuit analysis

Three-stub waveguides are common impedance matching devices which are essential for a wide range of high-power microwave applications. Based on equivalent circuit analysis method, this article presents a novel matching algorithm which can be applied for three-stub tuners to implement continuous, automatic and real-time impedance matching. Equivalent model of a stub waveguide is firstly established by using transmission lines in series and capacitors in parallel. Then, according to the proposed model, the mathematical expression of reflection coefficient at different stub depth is derived by using currently detected reflection coefficient and stub depth. Later, based on the derived expression, an algorithm is developed to determine the optimum insertion depths of the stubs when VSWR is minimum. The S 11 parameters of the stub waveguide which are calculated by the method agree well with those measured by vector network analyser. Meanwhile, the algorithm is able to limit reflection coefficient under –10 dB and can easily be redesigned for waveguides of different sizes. Thus, it shows a promising future in industrial impedance matching applications.

Dynamical Characteristics of Twin-Microring Lasers With Mutual Optical Injection

Nonlinear dynamics of mutually injected twin-microring semiconductor lasers are studied numerically and experimentally. For the twin-microring laser, a bridge waveguide directly connecting two identical microrings is utilized to realize mutual optical injection or mode coupling. The coupling coefficient is related to the waveguide parameter and influences the mutual injection process dramatically. By adjusting the frequency offset between two microrings, four-wave mixing, injection locking, periodic, and multi-period oscillation states are observed from the experimental lasing spectra. The plentiful nonlinear dynamical states are induced by the mode interaction between the two microrings and can be well explained by the rate equations with mutual optical injection.

Features of ultrasonic non-destructive testing models of rectangular anisotropic elastic waveguides with a membrane coating

A numerical-analytical fuzzy-set method for synthesizing estimates of the influence of uncertainty factors in the form of scatter of the initial physical-mechanical and geometric parameters of a long waveguide of prismatic geometry from anisotropic single-crystal material of a cubic system on the phase velocities of traveling normal elastic waves for applying in ultrasonic nondestructive evaluation are presented. Waveguide has absolutely flexible inextensible thin coatings of a faces. The technique is based on the description of parameters with scatter errors in the form of fuzzy-intervals quantities and on the transition to fuzzy-set arguments in the analytical representations of wave numbers for various branches of the dispersion spectrum. The alpha-level form of the heuristic generalization principle is used. Examples of a fuzzy-set description of a series of frequency distributions characteristics of phase velocities of traveling normal waves for a waveguide from a silicon single crystal are given.

Easy-hard phase transition in parameter estimation for optical waveguides

The determination of the parameters of cylindrical optical waveguides, e.g. the diameters vec {d}=(d_1,ldots ,d_r) of r layers of (semi-) transparent optical fibres, can be executed by inverse evaluation of the scattering intensities that emerge under monochromatic illumination. The inverse problem can be solved by optimising the mismatch R(vec {d}) between the measured and simulated scattering patterns. The global optimum corresponds to the correct parameter values. The mismatch R(vec {d}) can be seen as an energy landscape as a function of the diameters. In this work, we study the structure of the energy landscape for different values of the complex refractive indices vec {n}, for r=1 and r=2 layers. We find that for both values of r, depending on the values of vec {n}, two very different types of energy landscapes exist, respectively. One type is dominated by one global minimum and the other type exhibits a multitude of local minima. From an algorithmic viewpoint, this corresponds to easy and hard phases, respectively. Our results indicate that the two phases are separated by sharp phase-transition lines and that the shape of these lines can be described by one “critical” exponent b, which depends slightly on r. Interestingly, the same exponent also describes the dependence of the number of local minima on the diameters. Thus, our findings are comparable to previous theoretical studies on easy-hard transitions in basic combinatorial optimisation or decision problems like Travelling Salesperson and Satisfiability. To our knowledge our results are the first indicating the existence of easy-hard transitions for a real-world optimisation problem of technological relevance.

Optimization of parameters of binary phase axicons for the generation of terahertz vortex surface plasmon polaritons on cylindrical conductors

The feasibility of generating surface plasmon polaritons carrying orbital angular momentum ("vortex plasmons") on cylindrical conductors by an end-fire coupling technique in the spectral range from 8.5 to 141 μm (~ 2-40 THz) is considered. The front face of the cylinder is illuminated by Bessel beams formed using binary spiral phase axicons, or annual vortex beams formed in the focal plane of an additional lens. Graphs are constructed that reveal the relationship between the waveguide parameters (conductor diameter, which is equal to the diameter of the illuminating beam, and the “twist” angle of the plasmon) and the axicon parameters (the ratio of the axicon period to the radiation wavelength) for the above wavelengths and topological charges of the beams ranging from 1 to 9. The results obtained indicate the possibility of conducting experiments in the long-wavelength range for modeling a plasmon multiplex communication channel.

Graded-index antiresonant reflecting optical waveguides

This paper is devoted to the theoretical analysis of planar antiresonant reflecting optical waveguides (ARROW’s) with graded-index core layers. It presents results of numerical calculations involving relevant iteration procedure aimed at proper design of antiresonant claddings and illustrates modal properties of graded-index ARROWs for various waveguide parameters.

Polarization-Insensitive Hybrid Plasmonic Waveguide Design for Evanescent Field Absorption Gas Sensor

We propose a polarization-insensitive design of a hybrid plasmonic waveguide (HPWG) optimized at the 3.392 µm wavelength which corresponds to the absorption line of methane gas. The waveguide design is capable of providing high mode sensitivity (Smode) and evanescent field ratio (EFR) for both transverse electric (TE) and transverse magnetic (TM) hybrid modes. The modal analysis of the waveguide is performed via 2-dimension (2D) and 3-dimension (3D) finite element methods (FEMs). At optimized waveguide parameters, Smode and EFR of 0.94 and 0.704, can be obtained for the TE hybrid mode, respectively, whereas the TM hybrid mode can offer Smode and EFR of 0.86 and 0.67, respectively. The TE and TM hybrid modes power dissipation of ~3 dB can be obtained for a 20-µm-long hybrid plasmonic waveguide at the 60% gas concentration. We believe that the highly sensitive waveguide scheme proposed in this work overcomes the limitation of the polarization controlled light and can be utilized in gas sensing applications.

Silicon Waveguide Integrated with Germanium Photodetector for a Photonic-Integrated FBG Interrogator.

We report a vertically coupled germanium (Ge) waveguide detector integrated on silicon-on-insulator waveguides and an optimized device structure through the analysis of the optical field distribution and absorption efficiency of the device. The photodetector we designed is manufactured by IMEC, and the tests show that the device has good performance. This study theoretically and experimentally explains the structure of Ge PIN and the effect of the photodetector (PD) waveguide parameters on the performance of the device. Simulation and optimization of waveguide detectors with different structures are carried out. The device’s structure, quantum efficiency, spectral response, response current, changes with incident light strength, and dark current of PIN-type Ge waveguide detector are calculated. The test results show that approximately 90% of the light is absorbed by a Ge waveguide with 20 μm Ge length and 500 nm Ge thickness. The quantum efficiency of the PD can reach 90.63%. Under the reverse bias of 1 V, 2 V and 3 V, the detector’s average responsiveness in C-band reached 1.02 A/W, 1.09 A/W and 1.16 A/W and the response time is 200 ns. The dark current is only 3.7 nA at the reverse bias voltage of −1 V. The proposed silicon-based Ge PIN PD is beneficial to the integration of the detector array for photonic integrated arrayed waveguide grating (AWG)-based fiber Bragg grating (FBG) interrogators.

Exploring new chaotic synchronization properties in the master-slave configuration based on three laterally coupled semiconductor lasers with self-feedback

We have developed a theory model for a three-element laser array where three lasers are laterally coupled using the coupled mode theory and Maxwell equations. New chaotic synchronization properties have been observed systematically in the master-slave configuration, consisting of the driving three-element laser array with self-feedback and the response three-element laser array subjected to the parallel injection or cross injection. Under the parallel injection, the dynamic evolutions of high-quality complete chaotic synchronization between laser elements in different parameter spaces seriously depend on the self-feedback mode of the driving laser elements, such as one, two and all of them with self-feedback. It is found that when only the driving middle one or all of the driving laser elements are subject to self-feedback, high-quality complete chaotic synchronization of all laser elements can be achieved in the same large region of the most of the parameter spaces. In addition, we report here for the first time (to our knowledge) the interestingly symmetrical properties of leader/ laggard chaotic synchronization in the configuration under the cross-injection. Namely, the leader/ laggard chaotic synchronization with high quality between laser elements periodically varies with the delay differences, under the key parameters limited to a certain range. The varying traces of these synchronizations are like sine wave. The mirror symmetry between the laggard chaotic synchronization with in-phase (anti-phase) and the leader one with in-phase (anti-phase) can be achieved by the optimization of the structural parameters of laser waveguides. With the optimization of the related operating parameters, for one of the side-lasers, its leader/ laggard chaotic synchronization can be achieved the anti-symmetry between in-phase and anti-phase. On the other hand, for two symmetrical side-lasers, their leader/ laggard chaotic synchronization with in-phase and anti-phase can reach the anti-symmetry.