Single-mode operation of coplanar waveguides

A grounded coplanar waveguide structure with finite-size ground planes is analysed as three coupled microstrip lines. The three normal propagation modes of this structure are examined for various geometries, and some physical layout guidelines are established.     

Single-mode condition for silicon rib waveguides

The geometrical conditions required for single-mode propagation in large cross-section silicon-on-insulator (SOI) waveguides were investigated using the beam propagation method (BPM). The cases of both vertical-walled and sloping-walled (trapezoidal) rib structures were considered. In the trapezoidal case some approximate methods were compared with the simulated results. Expressions for the single-mode condition for both types of waveguide were defined.     

Hollow-core silica waveguides

Measurements have been made of the transmission at 10.6 μm of the HE11mode in hollow silica waveguides of 1.04 and 2 mm bore diameters in both straight and bent configurations. Transmission losses of the straight waveguides were found to be 1.91 and 0.69 dB/ m, respectively. The experimental results have been compared to the predictions of the theoretical treatments available. Experimental bend losses show a linear rather than square-law dependence on curvature for all but the smallest curvatures studied.     

Second-order optical nonlinearity in thermally poled phosphorus-doped silicon dioxide thin-film waveguides

A phosphorus-doped silicon dioxide nonlinear planar waveguide on a GE124 fused silica substrate using plasma-enhanced chemical vapour deposition and thermal poling technique is implemented. The stable second-order nonlinear susceptibility induced in the waveguide is estimated to be around 0.58 pm/V by means of hydrofluoric acid etching, Maker?s fringe measurement and grid search curve fitting using a double-step nonlinear profile. This nonlinear planar waveguide may be applied to fabricate an electrooptic device on the silicon photonic chip.     

Single-mode lightwave transmission in SOI-type photonic-crystalline-defect waveguides with phase-shifted holes

Single-mode lightwave transmission was observed in novel line-defect photonic-crystal (PC) waveguides. The waveguide structure is constructed by adding phase-shifted holes in an ordinary missing-hole line defect. This device permits a fine single-mode lightwave transmission even though the waveguide structure is fabricated on silicon-on-insulator (SOI) substrate, which seriously promotes off-plane leakage of waveguiding modes     

Single-mode stripe optical waveguides formed by silver ion exchange

We report on the fabrication and mode structure of narrow stripe optical waveguides formed by silver ion exchange. Single-mode propagation at 0.633 ?m wavelength has been obtained in guides whose width exceeds 7 ?m.     

Single-mode and polarization-independent silicon-on-insulator waveguides with small cross section

The fabrication restrictions that must be imposed on the geometry of optical waveguides to make them behave as single-mode devices are well known for relatively large waveguides, with shallow etch depth. However, the restrictions for small waveguides (/spl sim/1 /spl mu/m or less in cross section) are not well understood. Furthermore, it is usually a requirement that these waveguides are polarization independent, which further complicates the issues. This paper reports on the simulations of the conditions for both single-mode behavior and polarization independence, for small and deeply etched silicon-on-insulator (SOI) waveguides. The aim is to satisfy both conditions simultaneously. The results show that at larger waveguide widths, waveguide etch depth has little effect on the mode birefringence because the transverse-electric (TE) mode (horizontal-polarized mode) is well confined under the rib region. However, at smaller rib widths, the etch depth has a large influence on birefringence. An approximate equation relating the rib-waveguide width and etch depth to obtain polarization-independent operation is derived. It is possible to achieve single-mode operation at both polarizations while maintaining polarization independence for each of the waveguide heights used in this paper but may be difficult for other dimensions. For example, a 1-/spl mu/m SOI rib waveguide with an etch depth of 0.64 /spl mu/m and rib width of 0.52 /spl mu/m is predicted to exhibit such characteristics.     

Single-mode optical waveguides and phase modulators in the InP material system

The characteristics of several different single-mode optical waveguides in the InP material system are discussed. Slab-coupled rib waveguides in GaInAsP (lambda_{gap} approx 1 mum) epitaxial layers grown on InP have shown propagation losses as low as 1.7 cm^-1at 1.3 μm and 2.7 cm^-1at 1.15 μm. Oxide-confined InP rib guides fabricated using a lateral overgrowth technique have losses of about 1.5 cm^-1at 1.15 μm. Three-guide couplers have been made by fabricating three parallel oxide-confined guides in close proximity. InP p+-n-n+ guides capable of modulating TE-polarized radiation have been fabricated using epitaxial techniques and Be-ion implantation. By measuring the phase difference between the TE-like and TM-like modes as a function of applied voltage, an estimate of the r41electrooptic coefficient in InP at 1.3 μm that is in good agreement with a previously reported value was obtained. Guides of this type should find use as the active components in InP switches and interferometers.     

Birefringence compensation of silica waveguides

A novel method of compensating stress-induced birefringence in silica waveguides by incorporating a layered structure is introduced and analyzed by using a numerically efficient, vectorial H-field finite element-based modal solution approach.     

Pulse delay measurements in the zero-material-dispersion region for germanium- and phosphorus-doped silica fibres

Wavelength-dependent pulse dispersion in germanium- and phosphorus-doped silica fibres of different concentrations was measured using mode-locked subnanosecond pulses in the 1.064?1.55 ?m wavelength range. Zero dispersion for GeO2-SiO2 fibres was observed in the 1.3?1.33 ?m region depending on the concentration. P2O5-doped silica fibres showed zero dispersion near 1.28 ?m, independent of doping concentration.     

Single-mode vertical integration of p-i-n photodetectors with optical waveguides for monitoring in WDM transmission systems

A new InP-based waveguide photodetector utilizing single-mode vertical integration of a p-i-n structure atop of a low-loss optical waveguide is reported. Over all states of polarization, in a spectral range across the C-band, the device exhibits high on-chip responsivities of /spl sim/1.1 A/W, which remains nearly constant at a reverse bias above 5 V and optical powers up to 1 mW. If integrated within the output channels of a planar demultiplexer, it enables a very compact optical spectral analyzer to be realized.     

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.<>     

Broad-band array multiplexers made with silica waveguides onsilicon

A waveguide array multiplexer design that is particularly suitable for making broadband low-order devices is presented. Two-channel multiplexers at 1.0-1.55 μm, 1.31-1.53 μm, and 1.47-1.55 μm are demonstrated. Compared to conventional waveguide multiplexers, these devices have wide spectral ranges of low crosstalk. The devices are polarization independent. The crosstalk and fiber-to-fiber insertion loss for the 1.31-1.53 μm multiplexer were about -35 and -2 dB, respectively     

Sputtered silica waveguides with an embedded three-dimensional structure

Single-mode sputtered silica waveguides (SS guides) are fabricated by filling channels of 8-μm width in a silica substrate with core silica material and embedding with a cladding layer. Silica deposition process is carried out by bias sputtering. The measured waveguide loss was 1.2 dB/cm. The change of cross-sectional profile in the sputtering process on the channel is analyzed with the result in good agreement with experiments. The optimum sputtering condition for filling the channel is elucidated. The method is applied to embedding gratings fabricated on the silica substrate.     

Liquid core modal interferometer integrated with silica waveguides

An integrated structure is demonstrated as a refractive index sensor. The structure consists of a liquid-filled elliptical microchannel embedded in silica glass and integrated with waveguides. The microchannel features entry points that are open to the top surface of the device and distinct from the optical input. The structure allows light to couple from a solid-core input waveguide to the liquid-core waveguide formed by the microchannel, and back to a solid-core output waveguide. Bimodal interference allows the structure to be sensitive to the refractive index of the liquid, with a full beat corresponding to a refractive index change of /spl sim/10/sup -4/. The structure allows the direct integration of optical fluids with silica waveguides for sensing and optical processing applications.     

Single-mode optical Y-branching circuit using deposited silica guides (DS guides)

A new optical Y-branching circuit using embedded single-mode glass waveguides is presented. The glass waveguides were made by depositing core glass on a silica substrate after forming grooves to contain the core (DS guides). Waveguide transmission loss is 0.6 dB/cm. The loss caused at a branching point is 0.13 dB when the branching angle is 0.3°.     

Low loss channel waveguides fabricated in fused silica by germaniumion implantation

The authors report the first low loss channel waveguides (0.10 0.15 dB/cm) formed in fused silica by the implantation of MeV Ge ions. The loss coefficient α was measured as a function of ion dose (8×10¹³-8×10¹⁶ ion/cm²) and annealing temperature (250 to 600°C) at 1300 nm. The as-implanted waveguides exhibited a minimum value of α=0.9 dB/cm at an intermediate range of dose with a reduction to 0.10-0.15 dB/cm after annealing at 500°C     

SiO2平面光波导的PECVD制备和膜层特性研究

研究了等离子体增强化学汽相沉积（PECVD）的光波导膜层的光学特性,论述了沉积工艺参量和退火处理对膜层性能的影响,优化工艺获得了高质量的波导膜层,成功设计制作了在1 550nm中心波长损耗低于0.1db/cm的平面光波导和阵列波导光栅（AWG）器件。     

Polarization crosstalk in high index contrast planar silica waveguides with slanted sidewalls

Numerically simulated results, by using rigorous full vectorial approaches, indicate the possibility of significant polarization crosstalk in a high index contrast planar silica waveguide, particularly when the sidewalls are not exactly vertical.