Fundamental TE Mode Research Articles

170 Gbit/s transmission in an erbium-doped waveguide amplifier on silicon

Signal transmission experiments were performed at 170 Gbit/s in an integrated Al(2)O(3):Er(3+) waveguide amplifier to investigate its potential application in high-speed photonic integrated circuits. Net internal gain of up to 11 dB was measured for a continuous-wave 1532 nm signal under 1480 nm pumping, with a threshold pump power of 4 mW. A differential group delay of 2 ps between the TE and TM fundamental modes of the 5.7-cm-long amplifier was measured. When selecting a single polarization open eye diagrams and bit error rates equal to those of the transmission system without the amplifier were observed for a 1550 nm signal encoded with a 170 Gbit/s return-to-zero pseudo-random 2(7)-1 bit sequence.

Hybrid integration of Ca_028Ba_072Nb_2O_6 thin film electro-optic waveguides with silica/silicon substrates

Ca(0.28)Ba(0.72)Nb(2)O(6) (CBN-28) waveguides based on thin film technology were fabricated on SiO(2)/(100) Si substrates. By using X-ray diffraction, we confirmed the preferential c-axis orientation of the CBN structures. An effective unclamped electro-optic r33 coefficient of 12 pm/V was measured in CBN thin films by using an ellipsometric technique in reflection geometry. In addition, by means of a Fabry-Perot technique, the propagation losses of our strip loaded waveguides were estimated to be as low as 4.8 dB/cm and 6.5 dB/cm at telecommunication wavelengths for the fundamental TE and TM modes, respectively.

Radiation Suppressing Metallo–Dielectric Optical Waveguides

In this paper, a theoretical study of the optical performance of the parallel-plate waveguide, the nonradiative dielectric (NRD) waveguide, and a recently proposed metallo-dielectric waveguide (MDW) [Buckley and Berini, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Optics</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Letters</i> , vol. 34, no. 2, pp. 223-225, 2009] is reported. One-dimensional analysis is used to gain insight into their operation, followed by full-wave 2-D simulations of the waveguides in their straight and curved form. The modes supported by the NRD waveguide are perturbed by the excitation of surface plasmon polaritons (SPPs) along the metal surfaces causing high propagation loss for the straight waveguide and mode deformation along radial bends, as r <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> rarr 0. In contrast the recently proposed MDW shows promise due to its ability to guide the fundamental TE mode over long-range ( ~ 1.2 dB/mm) and through aggressive bends with low loss while retaining its mode character. The waveguide also has potential use in optoelectronic/electrooptic components due to the presence of the metal plates.

Compact dual-mode rectangular waveguide filters using square ridge resonators

A new class of compact rectangular waveguide filters is proposed in this paper. The key element is a square ridge resonator realized within a rectangular waveguide supporting the fundamental TE10 mode. The square ridge can support two modes resonating along orthogonal directions in the gap between the ridge and the opposite waveguide wall. This structure enables dual-mode degeneracy without the need of oversized cavities, thus allowing for considerable size reduction with respect to the conventional dual-mode implementations. Different filter structures employing one or more ridges within short waveguide sections are proposed as attractive solutions for pseudo-elliptic band-pass or dual-band filters. The experimental results of a manufactured fourth-order pseudo-elliptic pass-band filter validate the feasibility of the proposed class of filters.

Phase-Shifted Traveling-Wave-Tube Circuit for Ultrawideband High-Power Submillimeter-Wave Generation

A novel slow-wave vacuum electron device circuit, consisting of a half-period-staggered double-vane array and a high-aspect ratio sheet electron beam, has been conceived for a high-power wideband submillimeter-wave generation. A particle-in-cell simulation, which is based on a finite-difference time-domain algorithm, has shown that this circuit has a very wide intrinsic bandwidth (in excess of 50 GHz around the operating frequency of 220 GHz) with a moderate gain of 13 dB/cm. Moreover, the saturated conversion efficiency is predicted to be 3%-5.5% over the operating band corresponding to an output power of 150-275 W, assuming a beam power of 5 kW. Of particular importance, this structure is based on the TE-fundamental mode interaction, thereby avoiding the complex over moding instabilities that usually cause spurious signal oscillation in conventional high-aspect-ratio structures. This planar circuit has simple 2-D geometry that is thermally and mechanically robust as well as being compatible with conventional microfabrication techniques. This concept is expected to open numerous opportunities in potential applications of versatile electronic devices in the low-millimeter- and submillimeter-wave regions.

High-contrast waveguides in sputtered pure TeO,_2 glass thin films

We present a technological approach to the realization of channeled optical waveguides, starting from reactively sputtered tellurite glass thin films, grown on silica-coated 4" Si wafers. In particular, optical lithographic process and etching recipes have been developed to overcome the solubility of TeO(2) films in aqueous solutions, and to process them into high-index contrast structures with minimized post-etch roughness. Optical tests on preliminary rib waveguide geometries feature 6.3 dB/cm propagation loss for fundamental TE mode at lambda = 1.5 microm.

Effect of a backward wave on the stability of an ultrahigh gain gyrotron traveling-wave amplifier

A systematic stability analysis method using theoretical tools combining linear and self-consistent nonlinear theory is presented to analyze an ultrahigh gain gyrotron traveling-wave (gyro-TWT) amplifier operated in the fundamental TE11 mode in the Ka-band. It characterizes the role that the backward-wave component plays in the internal feedback physical processes of two major kinds of self-induced oscillations associated with TE11(1) absolute instability and TE21(2) gyrobackward-wave oscillation. For the first time, self-induced constriction in TE11(1) absolute instability caused by a strong backward-wave component is revealed through simulation. Both the thickness and resistivity of the distributed wall loss loaded on the inside of the interaction waveguide have obvious effects on stabilizing both kinds of oscillations. Following the stability analysis, a multistage interaction circuit is proposed by nonlinear analysis which shortens the length of the entire structure and enables the ultrahigh gain gyro-TWT to operate with high stability and wide bandwidth.

Waveguide Pseudoelliptic Filters Using Slant and Transverse Rectangular Ridge Resonators

This paper presents a novel class of resonators suitable for the design of waveguide pseudoelliptic filters. The basic structure is a rectangular ridge arbitrarily located and oriented within a rectangular waveguide sized to allow the propagation of the fundamental TE10 mode. The ridge has the capability to provide both a reflection and a transmission zero, thus behaving as a singlet. The coupling coefficients of the resonator can be controlled by varying the position and orientation of the ridge, or by additional elements such as irises or ridge taps. Compact pseudoelliptic filters can be designed by cascading multiple ridges and half a wavelength waveguide sections. A practical design procedure is presented. The experimental results of a fifth-order filter with three resonant ridges validate the proposed approach.

Anisotropy adjustment and thickness of thin layer doped by nanoparticules magnetic for the realization of phase matching between fundamental modes in monomode waveguides

Recently, research has been concentrated on the study of the magnetic nanoparticules for their use in the design of magneto-optical devices. The magneto-optical waveguides for example exploit the Faraday effect to obtain a rotation of polarization TE and TM independent of the propagation direction. In this work, we study isolating component whose operating principle is based on the minimization of the phase mismatch between TE and TM fundamental propagation modes. It appeared promising to use as a guiding film the thin layers doped by magnetic nanoparticules γ -Fe 2 O 3 in order to carry out an adequate phase mismatch. This last can be adjusted by permanent linear birefringence resulting from the application of an external magnetic field during the gelation of the solution which constitutes the guiding film. Many studies were undertaken primarily to minimize the birefringence between TE and TM modes, for that this work represents a new potential means to reach the phase matching by acting on the anisotropy and the thin layer thickness. This condition can be realized in the waveguides with SiO 2 /TiO 2 guiding thin layer doped by nanoparticules of maghemite γ -Fe 2 O 3 . The simulations carried out by the FMM method and MATLAB allowed to deduce the conditions to decrease the phase mismatch and increase the conversion ratio of TE/TM modes in order to ameliorate the isolation.

Birefringence in magneto-optical rib waveguides made by SiO2/TiO2 doped with γ-Fe2O3

Magneto-optic waveguides are the basic elements for nonreciprocal integrated optics; the phase matching between the fundamental TE and TM modes is an essential condition in magneto-optic waveguides. This condition can be satisfied with selected geometries planar or rib waveguides. We simulated the performance of such devices and determined the waveguide dimensions (height, width, and etching depth) that would allow the same propagation constants for both polarizations TE and TM.

Gradient-index antireflective subwavelength structures for planar waveguide facets

We demonstrate the use of subwavelength gratings etched into the facets of silicon-on-insulator ridge waveguides as a means of reducing facet reflectivity by the gradient-index effect. Reflectivities as low as 2.0% and 2.4% for the fundamental TE and TM modes, respectively, are demonstrated experimentally for light of 1.55 microm wavelength, in agreement with both effective medium theory and finite-difference time domain calculations. Simulations show that facet reflectivites can be further reduced to less than 1% by increasing the grating modulation depth.

Mapping the broadband polarization properties of linear 2D SOI photonic crystal waveguides

Both quasi-TE and TM polarisation spectra for a silicon-on-insulator (SOI) waveguide are recorded over (1100-1700)nm using a broadband supercontinuum source. By studying both the input and output polarisation eigenstates we observe narrowband resonant cross coupling near the lowest quasi-TE mode cut-off. We also observe relatively broadband mixing between the two eigenstates to generate a complete photonic bandgap. By careful analysis of the output polarisation state we report on an inherent non-reciprocity between quasi TE and TM fundamental mode cross coupling. The nature of polarisation distinction in such bandgap structures is discussed in the context of polarisation scattering at an interface.

Continuous-wave operation of a 460-GHz second harmonic gyrotron oscillator

We report the regulated continuous-wave (CW) operation of a second harmonic gyrotron oscillator at output power levels of over 8 W (12.4 kV and 135 mA beam voltage and current) in the TE(0,6,1) mode near 460 GHz. The gyrotron also operates in the second harmonic TE(2,6,1) mode at 456 GHz and in the TE(2,3,1) fundamental mode at 233 GHz. CW operation was demonstrated for a one-hour period in the TE(0,6,1) mode with better than 1% power stability, where the power was regulated using feedback control. Nonlinear simulations of the gyrotron operation agree with the experimentally measured output power and radio-frequency (RF) efficiency when cavity ohmic losses are included in the analysis. The output radiation pattern was measured using a pyroelectric camera and is highly Gaussian, with an ellipticity of 4%. The 460-GHz gyrotron will serve as a millimeter-wave source for sensitivity-enhanced nuclear magnetic resonance (dynamic nuclear polarization) experiments at a magnetic field of 16.4 T.

Quasi-vectorial analysis of the optical characteristics of rib waveguides and directional couplers based on InGaAs/InAlAs multiple quantum wells

A new three-dimensional quasi-vectorial beam propagation method based on the series expansion (SE-QV-BPM) is proposed for simulating the optical rib waveguide and directional coupler based on InGaAs/InAlAs multiple quantum wells. For the same etched-depth, the confinement of TM mode in horizontal direction is shown to be stronger than that of TE mode, and the singular behaviors for TM modes at the corners are clearly observed. For the same gap width, the coupling length of TM mode for directional coupler is larger than that of TE mode. The effective indices and modal profiles of the quasi-vectorial fundamental TE and TM modes for shallow- and deep-etched rib waveguides and directional couplers are obtained. Besides, the evolution of the injected field with propagation distance through the directional coupler is demonstrated. The calculation has good efficiency due to the small size of the resulting matrix, and the rib structures can be conveniently dealt with since the sinusoidal functions are selected as the basis functions. Moreover, the variable transformation is introduced to avoid the boundary truncation.

Design of dispersion-compensating Bragg fiber with an ultrahigh figure of merit

We report a novel idea for achieving highly efficient dispersion-compensating Bragg fiber by exploiting a modified quarter-wave stack condition. Our Bragg fiber yielded an average dispersion of approximately -1800 ps/(nm km) across the C band for the fundamental TE mode and an ultrahigh figure of merit of approximately 180,000 ps/(nm dB), which is at least 2 orders of magnitude higher than that of conventional dispersion-compensating fibers. The proposed methodology could be adopted for the design of a dispersion compensator across any desired wavelength range.

Waveguide polaritons: interaction of a quantum well exciton with an electromagnetic mode of a planar waveguide

A transfer matrix method has been used to calculate the dispersion relations of planar dielectric waveguides containing quantum well excitons. It is found that waveguide polaritons are formed, whose dispersion displays the classic anti-crossing behaviour at the exciton resonance frequency. For a quantum well placed at the anti-node of the fundamental TE mode of the waveguide considered, the Rabi-splitting is calculated to be 6.55 meV, with waveguide polaritons of lifetimes of ∼7 ps, corresponding to a displacement along the waveguide axis of ∼0.3 mm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Coupling a coherently emitting twin laser to a fiber by a Y waveguide: modeling results

When a twin laser emits the mode fields in coherent form, a Y waveguide can be used to mix and focus the twin signals in the longitudinal axis of a fiber core. In best conditions of coupling, both modal fields are assumed to mix coherently in the waveguide junction. A general expression is derived for the coupling coefficient as a function of the longitudinal displacement between components and misalignments of vertical and angular errors. We show how the Y waveguide avoids the drop in coupling efficiency caused by the separation between main emitters and the longitudinal axis of the fiber, and calculate the coupling factors between each main signal and the signal transmitted through the furthest Y waveguide branch to estimate the order of magnitude of possible losses. The coupling efficiency between the TE fundamental mode field and one branch is compared with the expression obtained using the Gaussian approximation. The intensity transmitted by the whole system using a coupled twin-mode solution is analyzed, taking into account the general coupling coefficients between main stripe outputs and branches.

Propagation characteristics and guiding of a high-power microwave in plasma waveguide.

The propagation characteristics of a high-power microwave [electromagnetic (em) wave] in a plasma waveguide are reported. The plasma waveguide is formed by expanding plasmas via the ponderomotive force of the high-power microwave and the microwave pulse remains trapped within the plasma waveguide and is guided in it. With the increase of the incident microwave power, the width of the plasma waveguide increases and the half width of the radial electric field distribution decreases. This shows that the em wave modifies the refractive index of the plasma waveguide area. For a plasma waveguide with narrower width, the microwave propagates along the plasma waveguide at the fundamental TE mode, while as the waveguide width increases the higher mode component starts appearing. Analytical treatment to the propagation of the electromagnetic wave in a dielectric waveguide having a step-index profile and the numerical calculations for the radial distribution of the electric field show fairly good agreement with the results observed in the present experiments.

Finitte-Difference Time-Domain Studies on Optical Transmission through Planar Nano-Apertures in a Metal Film

The finite-difference time-domain (FDTD) method is employed to numerically study the transmission characteristics of an H-shaped nano-aperture in a metal film in the optical frequency range. It is demonstrated that the fundamental TE10 mode concentrated in the gap between the two ridges of the H-shaped aperture provides a high transmission efficiency above unity and the size of the gap determines the sub-wavelength resolution. Fabry–Perot-like resonance is observed. Localized surface plasmon (LSP) is excited on the edges of the aperture in a silver film but has a negative effect on the signal contrast and field concentration, while aluminum acts similar to an ideal conductor if the film thickness is several times larger than the finite skin depth. In addition, it is shown that two other ridged apertures, C-shaped and bowtie-shaped apertures, can also be used to achieve a sub-wavelength resolution in the near field with a transmission efficiency above unity and a high contrast.

Numerical analysis of a modified rooftop mirror using mode interference

AbstractIn this paper, an improved rooftop mirror is proposed and its characteristics are evaluated by numerical analysis. First, it is shown by FDTD analysis that it is not easy to obtain a high reflection characteristic with fundamental mode incidence in the conventional structure. Next, the reflection characteristics are analyzed for an improved structure in which the incident single‐mode waveguide is connected to a multimode interference waveguide inside the rooftop. In such a process, comparison with the results obtained by FDTD analysis demonstrates that the simple guided mode propagation method neglecting the radiation mode is effective for design of a mode interference section. A reflectivity of 96% is attained by introduction of the mode interference section for both fundamental TE and TM mode incidence. Further, the wavelength characteristics of the reflection coefficient are studied. The effects of misalignment of the waveguide axis and shift of the apex angle of the rooftop on the reflection characteristics are discussed. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(1): 1–8, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10172