A novel design and analysis of low loss abrupt bends of dielectricslab waveguides

On the basis of the well-known laws of reflection and refraction of the plane electromagnetic waves, a concept for designing very low loss nonadiabatic junctions between tilted straight sections of dielectric waveguides is investigated. Combining the ray representation of the propagating modes with the equivalent source formulation of the dielectric waveguide excitation problem, a simple and accurate 2-D theory for treating such bends in slab waveguides is developed. Numerical results for typical cases are explained along with some new junctions for achieving large angle redirection of guided waves with very low bending loss     

A new low-loss wide-angle Y-branch configuration for opticaldielectric slab waveguides

A new Y-branch configuration for dielectric slab waveguides is proposed, based on the natural refraction of optical field at the dielectric interfaces and analysed by BPM. It has been shown that the radiation loss of the structure is very small with relatively wide branching angle and fairly insensitive to the fabrication errors     

A new low-loss high-k temperature-compensated dielectric for microwave applications

A new dielectric material has been developed with a temperature-stable dielectric constant of 38. The low loss exhibited at microwave frequencies, the excellent reproducibility, and the good mechanical properties of this dielectric make it an attractive substrate for microstrip circuits. The dielectric is also suitable for the resonant elements of dielectric filters and stabilizing cavities for hybrid solid-state sources.     

Numerical optimization procedure for low-loss sharp bends in MgOCo-doped Ti:LiNbO3 waveguides

Recent results provided experimental evidence that losses in bent Ti:LiNbO₃ waveguides can be drastically reduced by using additional titanium and magnesium oxide. We determine an optimization procedure for the index profile in curved sections. The beam propagation method indicates that in optimized bends, losses are orders of magnitude below those of conventional bends. Tolerances in mask alignment and in deposited film thickness are estimated to be well compatible with present technology     

Design of low-loss tapered waveguides using the telescope structure compensation

A low-loss tapered waveguide is achieved by telescope structure compensation. The configuration of this design is similar to the Galilean telescope based on bulk geometrical optics. We numerically calculate the transmission efficiency in the use of the beam propagation method (BPM) and the finite-difference time-domain method. The BPM simulation results reveal that the normalized transmission efficiency is more than 95%, even if the tapered angle is as large as 10/spl deg/.     

A new approach for analysis of closed dielectric waveguides

The dispersion characteristics of a class of closed dielectric waveguides are investigated by the method which combines the building-block approach of mul timode network theory with rigorous mode matching procedure. Several numerical examples for different guiding structures have been given by the approach. The same structures are also analyzed with the finite element method and the EDC method for comparison. The calculations show that the present approach yields as highly accurate results as the finite element method while almost retaining the simplicity of the EDC method, and justify the utility of the present method     

Low-loss bends in planar optical ridge waveguides

Bending losses lower than 0.7 dB for 90° bend sections with radii of curvature as small as 75 μm were measured on silicon-based Al₂O₃ ridge waveguides with SiO₂ cladding layers at a wavelength of 632.8 nm. These values, which are close to the calculated values, are the lowest thus far reported     

Electromagnetic fields in circular bends of slab waveguides

A rigorous theory for analysis of radiation and transmission of electromagnetic waves in uniformly curved sections of slab waveguides is presented. Eigenmodes with continuous eigenvalues are defined for the sectorial region, which includes the circularly bent section of slab waveguides. General fields in the sectorial region can be expanded in terms of these eigenmodes. The theory is applied to the analysis of transient fields in the circularly bent section of a slab waveguide connected to a straight section. Numerical examples of radiation patterns and field distributions are presented for the TE₀-mode incident from the straight section     

A novel wide-angle low-loss dielectric slab waveguide Y-branch

A new Y-branch structure for dielectric waveguides is proposed and analysed using simple geometrical optics and beam propagation methods. It is shown both qualitatively and quantitatively that the proposed structure has larger branching angles but lower radiation loss than those associated with either conventional Y-branches or structures with antenna coupled and phase front accelerators. The optimal design parameters calculated by numerical simulations are in very good agreement with those found from the geometrical optics. The simulations also reveal that the performance is fairly insensitive to fabrication errors     

A new equivalent network method for analyzing discontinuityproperties of open dielectric waveguides

A novel network approach is proposed for analyzing interacting discontinuities on open planar dielectric waveguides by accurately taking account of both surface modes and waves with continuous spectra. In this approach, a continuum of the radiation wave is recomposed into a set of the newly defined spectral composite modes, each of which carries a finite magnitude of radiation power. These new modes, in conjunction with surface modes, construct the complete orthonormal set for expressing an arbitrary local field on a dielectric slab waveguide. This leads to an equivalent network approach effective for solving discontinuity problems, even on an open waveguide using the conventional method for closed-waveguide problems. A number of numerical results are shown to demonstrate the usefulness of the proposed approach     

Low-cost and low-loss multimode waveguides of photodefinable epoxy

To satisfy the urgent need for low-cost multimode planar waveguides, we developed photodefined, multimode-fiber compatible waveguides with low-cost commercially available epoxies showing low losses from 550 to 1100 nm and around 1300nm.     

Simple technologies for fabrication of low-loss silica waveguides

A simple and reproducible technology is developed for the fabrication of low-loss silica waveguides on silicon substrates. The guiding layer is formed by changing the Si-O ratio composition of the SiO/sub 2/ layer. The waveguides can be made to have a good match to either optical fibres or guided-wave devices in III-V compound semiconductors.<>     

Time-delay measurement in singlemode, low-loss photonic crystal waveguides

The group delay in low-loss, singlemode, 1 mm-long photonic crystal slab waveguides is measured using the phase shift technique for the first time. Low group velocities (相似文献   

A new low-loss mode in semiconductor magnetoplasmas

A new semiconductor plasma wave mode that can propagate with very little attenuation at frequencies smaller than the plasma collision frequency is described. The wave propagates at right angles to a dc magnetic field and may be used for modulation of lasers or for tunable filters in the microwave /millimeter wave region.     

Radiation losses from sinusoidal serpentine bends in optical waveguides

Radiation losses due to curvature in optical waveguides with sinusoidal bends are found in terms of the amplitude and period of the fluctuation. For tolerable loss, the critical factor is the minimum radius of curvature, i.e. the radius of curvature at a point of maximum deviation.     

A rigorous analytical solution to abrupt dielectric waveguidediscontinuities

A simple analytical method is proposed for analyzing transmitted, reflected, and radiated fields in abrupt discontinuities of dielectric waveguides, such as step discontinuities and sharp bends. Approximate transmitted fields, both guided mode fields and radiated fields, are first calculated by assuming the incident field to be the source field on the discontinuity interface. Next, the approximate reflected fields are calculated by assuming the difference field of the incident and approximate transmitted fields to be the source field on the discontinuity interface. Then, the improvements for these approximate transmitted fields and approximated reflected fields are calculated successively. Only a few successive steps are suffice for obtaining rigorous solutions. Numerical examples are presented for step discontinuities and sharp bends of dielectric slab waveguides     

Study and design of step-index channel waveguide bends withlarge-angle and low-loss characteristics

By using micro-prisms, improved three-dimensional (3-D) bends of the embedded and buried waveguides of step-index profile are proposed. A simple phase compensation rule for the optimal design of the micro-prism is also presented. Through the simulation of 3-D semivectorial finite-difference beam propagation method, the transmission characteristics of the improved bends are shown to have been enhanced dramatically as compared with those of the conventional ones. Even for a bend angle of as large as 10°, the normalized transmitted power can still be greater than 95%. These results of 3-D bends are then compared with those of the two-dimensional (2-D) ones which are simplified from 3-D structures by the effective index method, and physical explanation of the discrepancy between the 3-D and 2-D results is introduced. The influences of waveguide structures and prism parameters on the transmission characteristics are discussed in detail. Some criteria for the design of large-angle low-loss 3-D improved bends are also accessed     

Design of strip-loaded optical waveguides for low-loss coupling tooptical fibers

Mismatch between the fundamental mode of a waveguide and that of an attached optical fiber may cause a significant loss of power in a guided-wave structure. These losses can be minimized, however, by proper shaping of the waveguide mode through judicious choice of dimensions and refractive indexes. It is shown by computer modeling and qualitative arguments that coupling losses between standard optical fibers (5-10-μm modal diameter) and strip-loaded waveguides constructed of GaAs/AlGaAs may be reduced to less than 10% at each facet. A wavelength of 0.85 μm is used as a specific example, with modal shapes explored systematically for a series of different waveguide structures     

Nondegenerate four-wave mixing wavelength conversion in low-loss passive InGaAsP-InP quantum-well waveguides

Results on wavelength shifters based on four-wave mixing that operate in the 1.5-/spl mu/m regime are reported. These devices utilize the near-bandedge resonant enhancement in the third-order nonlinearity in passive InGaAsP-InP quantum-well waveguides. Over the erbium-doped fiber-amplifier gain band approximately -20 dB conversion efficiency was obtained with /spl ap/18-dBm CW pump power. The conversion efficiency was nearly constant for wavelength shifts up to /spl ap/26 nm (3.3 THz), limited by the phase-matching bandwidth of the 8.5-mm-long device.