Low-Loss and Low-Birefringence High-Contrast Silicon-Oxynitride Waveguides for Optical Communication

Silicon-oxynitride waveguides fabricated by plasma-enhanced chemical vapor deposition are very attractive for passive optical components used in optical networks. We use a combination of an high-index contrast and compact core dimensions for the realization of small bending radii. To achieve the high quality requirements with the desired waveguide design the layer deposition and the waveguide fabrication are optimized. Furthermore, we discuss the interface of the high-index optical components to standard single-mode fiber (SSMF) and coupling tolerances, which is more difficult compared to common fiber-mode-matched wave guides. We show results of fabricated Mach-Zehnder interferometer-switches, tunable ring resonators and present a solution to reduce the waveguide birefringence by adjusting the mechanical stress of the cover layer.     

Vertical InP/InGaAsP tapers for low-loss optical fibre-waveguide coupling

The authors have realised vertically tapered and antireflection-coated waveguides in InP/InGaAsP with 1.7 dB coupling loss and relaxed alignment tolerances to lensed single-mode fibres with spot diameters of 3.8 mu m. The waveguide tapers are fabricated by a dip-etch process that is well suited for integration with optical waveguide circuits.<>     

Low-loss, single-mode, organic polymer waveguides utilizingrefractive index tailoring

Low-loss, single-mode optical waveguides have been fabricated from photopolymerizable acrylic monomers. The material system consists of a low-index cladding resin and a high-index core resin. The two resins are miscible so that precise control over the refractive index can be obtained. This allows the fabrication of single-mode waveguides with specific cross-sectional dimensions. One advantage of this is the ability to fabricate waveguides with high coupling efficiencies to other devices such as optical fiber or semiconductor lasers. The materials adhere to a wide variety of substrates and exhibit average waveguide losses of 0.56 dB/cm at 1300 nm for single-mode waveguides. Details of the fabrication procedure, index of refraction tailoring technique, and waveguide loss data are presented     

Design of a nanoelectromechanical high-index-contrast guided-wave optical switch for single-mode operation at 1.55 /spl mu/m

A design is presented for a nanoelectromechanical optical switch based on the horizontal deflection of an input waveguide to align with one of two output waveguides. The use of high-index (GaAs) strip waveguides surrounded by air, designed to be single-mode at 1.55 /spl mu/m, significantly decreases device dimensions as compared to previous designs. Design tradeoffs between optical and mechanical properties of the device are discussed. By means of three-dimensional numerical simulations, optical transmission is optimized for two different design strategies: butt and parallel coupling. High polarization-independent transmission (over 90%) is predicted for realistic design parameters.     

Coupling to high-index waveguides via tapered microstructured optical fibre

A novel method of coupling to high-index, small mode-field diameter, waveguides using free-standing tapered 'grapefruit' microstructured optical fibre pigtails with mode fields down to 1 /spl mu/m is presented. 0.15 dB mode mismatch loss with chalcogenide rib waveguides is demonstrated, a reduction of more than 5 from high NA fibre, and it is shown that they can be used to butt-couple to silicon nanowires.     

Buried annealed/proton-exchanged LiNbO3 waveguides fabricated by direct bonding technique

A new method for fabrication of buried annealed/proton-exchanged LiNbO₃ waveguides using direct bonding technique is demonstrated. The buried waveguides were fabricated and tested at 1.55 m wavelength, and guided modes with excellent symmetry were obtained. The waveguides are suitable for efficient coupling to optical fibres and/or efficient nonlinear-optic wavelength conversion devices.     

Optical-fibre coupling to high-silica channel waveguides with fibre-guiding grooves

A practical coupling technique between high-silica multimode channel waveguides and optical fibres has been demonstrated using guiding grooves formed simultaneously with waveguides on a substrate. The fibre-waveguide (15 mm long)-fibre insertion loss was 1.23 dB.     

Fabrication and characterisation of D-fibres with a range of accurately controlled core/flat distances

The fabrication and evaluation of D-fibres, whose optical properties are compatible with standard single-mode fibre designs, is reported. The high tolerances achieved in the process of drawing a tapered preform are shown to be necessary for predicting the transverse coupling behaviour of the fibres.     

MT-compatible laser-ablated interconnections for optical printed circuit boards

Integration of optical interconnections on a printed circuit board (PCB) is very challenging, since compatibility should be maintained with standard PCB manufacturing technology. This paper describes the use of laser ablation, a technique already used in PCB manufacturing for drilling microvias, as a suitable technique for the fabrication of multimode polymer waveguides, micromirrors, alignment features, and microlenses. A frequency-tripled Nd-YAG laser and a KrF excimer laser are used, both mounted on the same stage, resulting in very high alignment accuracies. This paper demonstrates a parallel optical link over approximately 5-cm-long PCB integrated waveguides, fully connected using a standard MT-based connector. This proves that laser ablation can be a key technology in optical board manufacturing to reach the stringent coupling tolerances.     

Microwave Modeling of Optical Periodic Waveguides

A design procedure and experimental method is presented for modeling optical periodic waveguides by means of more convenient parallel plate microwave configurations. These models are suitable for verifying the beam-coupling properties of dielectric gratings that operate in the fundamental TE/sub 0/ surface-wave mode. In particular, blazed gratings with high coupling efficiencies have been constructed and their characteristics have been measured. The results have shown that previously developed design criteria, which are based on a simple Bragg-scattering approach, can yield highly efficient broad-band beam couplers that are not subject to critical fabrication tolerances.     

Tapered polymer single-mode waveguides for mode transformation

This paper presents a tapered polymer waveguide structure for coupling light between optical waveguides with differing geometries. Optical fibers, lasers, and other photonic integrated circuit components can be coupled with tapered waveguides. The polymer waveguide performs a mode transformation between different mode shapes and sizes. For example, the mode transformation can be from an elliptical laser diode mode to that of a circular optical fiber mode. The input and output of a tapered waveguide structure are analyzed, for the case of laser to fiber coupling, in order to determine the effect of misalignments on the coupling efficiency. Adiabaticity in waveguide propagation is discussed. The fabrication of our polymer waveguides is also described     

Multimode Fiber Devices for Optical Fiber Links, Printing, and Display

It is generally agreed that multimode graded index fiber has become the main fiber technology for optical communication applications. Multimode graded index fibers provide sufficient bandwidth for most applications without the critical tolerances of single mode fibers. In this paper, multimode fiber devices and components based on packaging miniaturized optical components for a GaAs laser array source package, and multichannel waveguides will be discussed. Experimental results, fabrication process and technology limitation for some of the multimode devices will be included. One major drawback of using multimode fibers is the difficulty to obtain simple and efficient switches and taps which are essential for data bus or other optical links. Some possible solutions for multimode fiber switches with miniaturized bulk wave devices will be presented.     

Retention grooves for optical-fibre connectors

Optical-fibre aligning grooves with lands of fungiform cross-section cramp inserted fibres and hold them accurately in place. Such grooves have been realised by a combination of photolithographic, etching and electrodeposition techniques. Experiments have shown that linear arrays of optical fibres can be positioned to close tolerances, while the mounting operation of the fibres is facilitated. The technique requires no adhesive. Measuring results are presented, showing that the lateral misalignment of fibres between to separately fabricated connector halves is within 5% of the outside fibre diameter. That entails a geometric coupling loss within 0.4 dB with a mean loss at 0.26 dB.     

Neodymium-doped tantalum pentoxide waveguide lasers

The fabrication, spectroscopic properties, and laser performance of Nd/sup 3+/-doped Ta/sub 2/O/sub 5/ channel waveguide lasers are described. Lasing is obtained at both 1.066 and 1.375 /spl mu/m with threshold pump powers as low as 2.7 mW. The rib waveguides are reactive-ion-etched into Nd:Ta/sub 2/O/sub 5/ layers formed by reactive magnetron sputtering. These high-index low-loss rare-earth-doped waveguides are fabricated on silicon substrates and offer the potential for integration with photonic crystal structures for compact optical circuits.     

Amorphous silicon rich silicon nitride optical waveguides for high density integrated optics

Amorphous silicon rich silicon nitride optical waveguides clad in silica are presented as a high-index contrast platform for high-density integrated optics. Performance of different cross-sectional geometries have been measured and are presented with regards to bending loss and insertion loss. A sample double ring add-drop filter is presented.     

Spot-size conversion using uniform waveguide sections for efficientlaser-fiber coupling

Using numerically simulated results, it is shown that an efficient laser-to-fiber coupling is possible by incorporating a uniform spot-size converter (SSC) with two nonidentical but phase matched optical waveguides. Using a “diluted” waveguide with a low index contrast, the power coupling loss can be significantly reduced from 10.4 dB to only 1.15 dB and at the same time 1.0 dB alignment tolerances can also be improved to achieve ±1.8 μm. Besides the improved coupling, the beam divergence of the far-field is also reduced considerably to 9°, accompanied by a significant lowering of the reflected power from the fiber interface     

Efficient coupling of laser diodes to tapered monomode fibres with high-index end

The coupling efficiency between monomode fibres and laser diodes can be significantly increased by means of a high-index microlens which is attached on the cleaved end of a tapered monomode fibre. Coupling efficiencies of more than 50% can be attained.     

Design and Application of Compact and Highly Tolerant Polarization-Independent Waveguides

In this paper, the design, fabrication, and application of a highly tolerant polarization-independent optical-waveguide structure suited for operation in the third communication window is presented. The waveguide structure has been optimized toward minimized sensitivity to technological tolerances and low fabrication complexity. The tolerance analysis has been based on the typical processing tolerances of the widely applied silicon-oxynitride technology, being plusmn3times10 ^-4 in refractive index, plusmn1% in thickness, and plusmn0.1 mum in channel width. The optimized waveguide design fulfills the criterion of a channel birefringence within 5times10^-5, including processing tolerance. It also enables a fiber-to-chip coupling loss below 1 dB/facet and is suited for the realization of low-loss bends with a radius down to 600 mum. Based on this waveguide design, a passband-flattened optical wavelength filter with 50-GHz free spectral range has been realized and tested. The measured TE-TM shift of 0.03 nm confirms the polarization dependence of the optical waveguides being as low as 3times10^-5     

Effects of fibre propagation loss on diode-laser?fibre coupling

Throughput efficiences and alignment tolerances for coupling lasers to long (? 1 km) fibres are strongly dependent on the fibre modal excitation. It is found that, for accurately predicting system performance and for determining packaging tolerance requirements, laser-fibre coupling measurements should be made with long fibres.     

Non-evanescent adiabatic directional coupler

A directional coupling mechanism based on an adiabatic coupling between three optical modes is suggested. The optical power transfer between two waveguides which are far apart is mediated by adiabatic coupling between zero-order optical modes of the individual waveguides and a high-order intermediate mode. The analytical model for an adiabatic three-mode coupling based on a scalar wave equation is presented. The directional coupling via the adiabatic mode coupling between copropagating modes is described and compared with a nonadiabatic directional coupling assisted by periodic perturbation. It is shown that adiabatic directional coupling has much less sensitivity to the mode parameters and to the wavelength