Theoretical and Experimental Investigation of a Ka-band Gyro-TWT with Lossy Interaction Structure

The stability analysis of a Ka-band gyrotron traveling-wave tube amplifier (gyro-TWT) operating in the circular TE₀₁ mode at the fundamental cyclotron harmonic is presented. The small signal linear theory is used to analyze the amplification of operation mode and oscillation of parasitic modes. The optimum dielectric parameters including loss layer thickness and permittivity are given. Propagation loss of operation mode is 3 dB/cm with the thickness of loss layer d = 0.7 mm and relative permittivity ξ″ = 11−6j, and propagation loss per unit length of parasitic modes TE₁₁, TE₂₁, TE₀₂ at each oscillation frequency (24.85 GHz, 27.85 GHz, 61.2 GHz) is 2.5 dB/cm, 6 dB/cm, 7.5 dB/cm, respectively, sufficient to suppress oscillations of operation and parasitic modes. Taking advantage of the optimized parameters of loaded dielectric, a high gain scheme has been demonstrated in a 34-GHz, TE₀₁-mode gyro-TWT, producing 160 kW saturated output power at 40 dB stable gain and 22.8% efficiency with a 3-dB bandwidth of 5%.     

Numerical analysis of InP/InGaAsP ARROW waveguides using transfermatrix approach

The transfer matrix method is employed to analyze the modal propagation within planar InP/InGaAsP antiresonant reflecting optical waveguides (ARROW) at the operational wavelength of 1.55 μm. The numerical results provide an accurate picture of dispersion and attenuation of both TE and TM polarized waves. Spatial properties of the modes are also investigated and detailed plots of the variation of electric field amplitude with layer thickness are given     

Optical waveguides in SIMOX structures

Propagation characteristics determined experimentally and theoretically for planar optical waveguides formed in separation by implantation of oxygen (SIMOX) structures are discussed. All samples were found to support both TE and TM modes at both 1.15 μm and 1.523 μm with a lowest propagation loss of 8 dB/cm. This loss was measured at a wavelength of 1.15 μm for the TE₀ mode of a planar waveguide with a 2.0-μm-thick Si guiding layer     

Study and Design of Spiral Bent Waveguide Configuration

A new version of the scalar transverse electric（TE） wave equation in the bent waveguide is introduced. Then. TE polarized field in curved single-mode waveguides is analyzed by using the finite- difference beam propagation method（FD-BPM）. The bending loss in bent waveguides is gotten for the optical fields obtained from BPM and comparisons are made among losses of the waveguides with various curvature radiuses, refractive index differences and cross sections. Based on the results, the design of spiral bent waveguide configuration is proposed as follows： refractive index difference being of 0. 007, both width and thickness of waveguides being of 6 μm, the curvature radius in the spiral centre being of 4 mm, and the bending loss coefficient of the designed spiral bent waveguide being of 0. 302 3 dB/cm.     

Dispersion characteristics of cylindrical metal-clad opticalwaveguides

A study of the dispersion characteristics of cylindrical metal-clad optical waveguides indicates that: (1) the propagation of electromagnetic energy in metal-clad optical waveguides differs in principal from that of dielectric step-index waveguides and ideal metallic waveguides; (2) hybrid modes exist in this structure, and the cutoff frequency of the HE₁₁ mode does not equal zero; (3) TM and HE(EH) modes have attenuation higher at least by an order of magnitude than that of TE modes; and (4) the surface plasma wave can propagate in this structure. Thus, the lowest order mode is TE₀₁      

Design of optical strip-loaded waveguides with zero modalbirefringence

Integrated optic devices are usually sensitive to the polarization state of light, because the two polarized modes of the waveguides that form the devices in general have different propagation constants and may also suffer from different losses. The performance of such devices becomes unstable when they are connected to single-mode fibers, as the polarization state of the output light from a practical fiber link usually fluctuates in an unpredictable manner. A simple solution could be provided by using waveguides in which the two polarized modes are degenerate, i.e., have equal propagation constants. In this paper, it is shown theoretically with the spectral index method that the quasi-transverse electric (TE) and quasi-transverse magnetic (TM) modes of a properly designed optical strip-loaded waveguide can have equal propagation constants. The conditions for achieving mode degeneracy, or zero modal birefringence, are presented and discussed. Strip-loaded waveguides with degenerate polarized modes can be used potentially for forming polarization-insensitive optoelectronic devices     

Impedance boundary method of moments for accurate and efficientanalysis of planar graded-index optical waveguides

An impedance boundary method of moments (IBMOM) is proposed to accurately and efficiently compute the propagation characteristics including the number of guided modes of general graded-index dielectric slab waveguide structures. The method is based on Galerkin's procedure in the method of moments and employs the exact impedance boundary condition at the interfaces between the graded-index region and constant-index cladding. Legendre polynomials are utilized in the field expansion. Computational results are shown for waveguides with various inhomogeneous refractive index profiles. The results indicate that typically five Legendre polynomials are sufficient for accurate solutions of the dominant TE and TM modes in optical waveguides having a finite region of inhomogeneous refractive index. Diffused optical waveguides with untruncated index profiles as well as coupled dielectric waveguides can be accurately analyzed using ten Legendre polynomials     

Polyimide/Ta2O5/polyimide antiresonantreflecting optical waveguides

A novel antiresonant reflecting optical waveguide (ARROW) fabricated using both the organic and dielectric thin film technologies is presented for the first time. The ARROW consisted of the fluorinated polyimide and tantalum pentoxide (Ta₂O₅) hybrid layers deposited on a Si substrate. For TE polarized light, the propagation loss of the waveguide as low as 0.8 dB/cm is obtained at 632.8 nm. The propagation loss for TM polarized light is 2.7 dB/cm. Some design considerations of the hybrid ARROW are also discussed in this work     

Stress-induced polymer waveguides operating at both 1.31 and 1.55 /spl mu/m wavelengths

Metal-defined polymer optical waveguides have been demonstrated for the first time. A metal strip patterned on top of a polymer slab waveguide causes a stress-induced refractive index change, providing lateral optical mode confinement within the core layer. Fabricated waveguides exhibit low propagation loss values of 1.1 dB/cm at 1.31 /spl mu/m and 1.3 dB/cm at 1.55 /spl mu/m for both TE and TM polarisations.     

Application of Generalized Characteristic Vectors to Problems of Propagation in Clad Inhomogeneous Dielectric Waveguides

A transformation matrix that uses generalized characteristic vectors is used to convert Maxwell's equations into a set of loosely coupled equations for the wave amplitudes. This transformation is suitable for permittivity profiles with turning points. In earlier full-wave solutions to these equations, several special functions that account for the local features of the permittivity profile, especially near the turning points, were used to obtain appropriate expansions of the fields. The transverse field components, the propagation coefficients, as well as the phase and group velocities, are computed for both horizontally polarized (TE) and vertically polarized (TM) modes of the dielectric waveguides using the full-wave approach. These solutions are compared with analytic solutions for waveguides with special permittivity profiles. They are also compared with recently published results based on a perturbational approach.     

Full vectorial finite-element solution of nonlinear bistable optical waveguides

The accurate computation of the propagation constants and field distributions of different modes in nonlinear optical dielectric waveguides is addressed in this paper. Using the vector finite-element formulation of the beam propagation method, combined with the imaginary distance propagation technique, both linear and nonlinear modes can be accurately calculated. The proposed technique is applied to obtain the fundamental TE nonlinear mode of a strip-loaded waveguide, and the excellent agreement seen with published results shows its high numerical precision.     

Optical transmission losses in polycrystalline silicon strip waveguides: Effects of waveguide dimensions, thermal treatment, hydrogen passivation, and wavelength

Signal propagation delays dominate over gate delays in the ever-shrinking ultra large scale integrated (ULSI) circuits. Consequently, silicon-based monolithic optoelectronic circuits (SMOE) with their light speed signal propagation can provide unique advantages for future generations of microprocessors. For such SMOE circuits, we need optical interconnects compatible with silicon technology. Strip waveguides consisting of polycrystalline silicon (polySi) clad with SiO₂ offer excellent optical confinement and ease of fabrication that are ideal for such interconnect applications. One major challenge with using this material system, however, is its insertion loss. In this paper we provide techniques for minimizing optical transmission losses in polySi strip waveguides. Our previous work using polySi strip waveguides, showed an optical transmission loss of 15 dB/cm at λ=1.55 μm, which is a communication wavelength of choice in optical fibers because it represents an absorption minimum. Similar measurements in crystalline silicon strip waveguides¹ yielded transmission losses of less than 1 dB/cm. Hitherto, in decreasing loss from 77 dB/cm to 15 dB/cm, we had minimized loss from surface scattering by improving the film surface morphology, and decreased bulk absorption with hydrogen passivation. In this paper we report a further reduction in the residual bulk loss from 15 dB/cm to 9 dB/cm. By experimenting with different waveguide core dimensions, we find that the contribution of bulk loss towards net transmission loss decreases with waveguide core thickness. Additionally, high temperature treatment provides strain relief in the polySi, decreasing transmission loss. Annealing in an oxygen ambient is not recommended because it always increases transmission loss. Hydrogen passivation improves transmission, attributable to passivation of light-absorbing dangling bond defect sites present at polySi grain boundaries. Together, these methods have resulted in the lowest measured loss value of 9 dB/cm at λ=1.55 μm. Since integrated SiGe and Ge photodetectors are more efficient at shorter wavelengths like λ=1.32 μm, transmission loss is also measured at λ=1.32 μm. Losses at the two wavelengths (1.32 μm and 1.55 μm) are similar when defects and stress in the waveguides are minimized.     

Coupling between gaussian and guided modes at the input and output of oversized circular waveguides

The coupling between a gaussian TEMoo bearn with HE 1m modes for dielectric waveguides and TE1m and TM1m modes for metallic waveguides is analytically studied. An optimization method allows to know HE11 or TE11 modes create gaussian TEMmm bearns at the output of the waveguide.     

Nonreciprocal Magnetooptic Waveguides

The longitudinal magnetooptic effect can be used in a unique way to mix TE and TM modes of a planar dielectric waveguide where the strength of mixing is dependent upon propagation direction (forwards or reverse). A detailed study of Faraday effect circulators in optical dielectric waveguides is presented and accurate design data for a practical version are offered. At this writing, experimental confirmation has been hampered by lack of success optically contacting two dissimilar materials.     

Theory Of Optically Controlled Millimeter-wave Phase Shifters

In this paper we analyze the millimeter-wave propagation characteristics of a dielectric wavegaide containing a plasma-dominated region. Such a device presents a new method for controlfirrg millimeter-wave propagation in semiconductor waveguides via either optical or electronic means resulting in ultrafast switching and gating. We have calculated the phase shift and attenuation resulting from the presence of the plasma. Higher order modes, both TE and TM, as well as millimeter-wave frequency variation, are studied in both Si and GaAs dielectric wavegnides. We have also formulated a surface plasma model that is a good approximation to the more elaborate volume plasma model. Phase shifts are predicted to he as high as 1400°/cm for modes operating near cutoff. These modes suffer very little attenuation when the plasma region contains a sufficiently high carrier density.     

Measurement of depolarization ratio and ultimate limit ofpolarization crosstalk in silica-based waveguides by using a POLCR

A polarization optical low coherence reflectometer (POLCR) is described that enables us to excite only the transverse electric (TE) mode of a test waveguide and to measure its Rayleigh backscatter signal distributions in the TE and transverse magnetic (TM) modes at a spatial resolution of 0.3 mm. The depolarization ratios of silica-based waveguides with relative refractive index differences of Δ=0.45 and 0.75% are obtained as 0.14 and 0.10, respectively, by measuring the bias in the ratio between the distributions in the TM and TE modes of each waveguide. By using the depolarization ratios and the Rayleigh backscatter signal levels, we calculate the ultimate polarization crosstalks to be -53 and -51 dB over 1 km, respectively. The actual polarization crosstalks of previously fabricated waveguides are about 50 dB higher than their ultimate limits for the same length of fiber     

Spectral Domain Analysis of Frequency Dependent Propagation Characteristics of Planar Structures on Uniaxial Medium

The propagation characteristics of single and multilayered uniaxial dielectric waveguides and planar structures on uniaxial medium can be determined by utilizing Hertzian potentials along the optical axis. The electric and magnetic Hertzian potentials, having components along the optical axis only, lead to TM and TE modes, respectively, with respect to that axis. The dyadic Green's function in Fourier transform domain (immittance matrix) required to solve for the propagation characteristics of planar structures on uniaxial medium are derived for all three orientations of the optical axis. The immittance matrix for all three cases is in the same form as that for the isotropic medium and hence the known Galerkin's method can be used to solve for the propagation characteristics of the structure.     

Low-loss polymeric optical waveguides fabricated with deuteratedpolyfluoromethacrylate

Deuterated polyfluoromethacrylate which has high transparency, low birefringence and good processability was newly synthesized for use as optical waveguide materials, and both single-mode and multimode optical waveguides were fabricated using the polymer. The propagation loss and waveguide birefringence of the single-mode waveguides were as low as 0.10 dB/cm and -5.5×10^-6 at 1.31 μm, respectively. The propagation losses of the multimode waveguides were less than 0.02 dB/cm at both 0.68 and 0.83 μm, and 0.07 dB/cm at 1.31 μm     

Disorder-induced buried-stripe optical waveguides in GaAs/AlGaAs MQW material

Buried-stripe optical waveguides have been fabricated in GaAs/AlGaAs multiquantum-well material by masked Si/sup +/ implantation followed by annealing at 750 degrees C to produce selective-area quantum well mixing. The waveguides were found to support both TE and TM modes with propagation losses of 33 and 56 dBcm/sup -1/, respectively, at a wavelength of 1.15 mu m.<>     

Design and Simulation of Broadband IR integrated Waveguide Amplifiers with Long - Period Waveguide Grating Filter

A novel broadband IR integrated Er-Yb codoped phosphate glass waveguide amplifier with a long-period waveguide grating is proposed. The long-period waveguide grating, which is used as a gain equalizer, is directly fabricated in the waveguide. The amplifier model is based on propagation and population-rate equations and includes both uniform and pair-induced up-conversion mechanisms. It is solved numerically by combining overlapping integral and Runge-Kutta(RK) algorithm. The intrinsical gain spectrum of the proposed amplifier is obtained by solving a set of rate and power propagation equations and, the deleterious gain peaking is reduced by the long-period waveguide grating filter. The effects of transmission spectrum of the proposed long-period grating on flattening gain are discussed. An average gain  ~ 20dB between 1532 nm and 1565 nm with gain difference of  < 3dB is achieved.