Self-alignment of optical fibers with optical quality end-polishedsilicon rib waveguides using wet chemical micromachining techniques

This paper presents a new cost-effective method for self-aligning optical fibers on silicon platforms and for achieving optical quality end-polished silicon-on-insulator (SOI) rib waveguide devices using wet chemical micromachining techniques. Through accurate alignment to the (011) plane of the (100) device layer of a SOI wafer, rib waveguide devices with self-alignment features are fabricated with the ends of each waveguide wet etched and concurrently polished providing an optical quality facet or fiber-to-waveguide interface. Eliminating the need to saw cut and then mechanically polish the ends of fabricated devices, the overall fabrication process is simplified whilst also providing an integrated optic fiber alignment capability at the ends of the fabricated waveguide devices with an alignment accuracy limited by fiber size tolerance. Experimental measurements were carried out to verify the optical quality of the waveguide facets formed using this new technique which proved excess facet losses of practically unmeasurable quantities     

Compact evanescent optical switch and attenuator withelectromechanical actuation

We report the design and the realization of an out-of-plane bending structure supporting a waveguide that is used as an optical attenuator and an optical switch. Both devices are based on evanescent field interaction induced by spatial confinement either between two waveguides or between one waveguide and an absorbing medium. The attenuator exhibits typical attenuation of 65 dB/cm. Even if the bad quality of the waveguide has prevented the correct operation of the switch, we show that the attenuation figure establishes the feasibility of a compact evanescent optical coupler with mechanical drive featuring a total length below 1 mm     

Polymer microring resonators for biochemical sensing applications

Polymer microring resonators were demonstrated for sensing biomolecules without using fluorescent labels. The microring devices, fabricated by a direct imprinting technique, possess high Q factors of /spl sim/20000. This feature provides high sensitivity and a low detection limit for biochemical sensing applications. With these properties, the devices were used to detect and quantify the biomolecules present either in a homogeneous solution that surrounds the microring waveguide (homogeneous sensing) or specifically bound on the waveguide surface (surface sensing). In the former sensing mechanism, the current devices can detect an effective index change of 10/sup -7/ refractive index units (RIU); in the latter, they can reach a detection limit of /spl sim/250 pg/mm/sup 2/ of biomolecular coverage on the microring surface. In addition, the experiments show that the devices can detect both small and large biomolecules.     

Novel waveguide structures for enhanced fiber grating devices

An emerging class of fiber waveguide structures is being used to increase the functionality of fiber gratings, enabling new devices critical to the performance of next generation light-wave communications systems. These devices rely on advances in the fabrication of optical fiber waveguides, which go beyond the conventional doped silica design and fall into two general categories: 1) local modifications to the waveguide after fabrication and 2) fibers drawn with modified claddings that include nonsilica regions throughout their length. This paper provides a comprehensive review of emerging fiber waveguide structures that enhance the functionality of optical fiber grating devices. Two examples of technologies that fall into the first category are thin metal films deposited onto the cladding surface, which can be used for thermal tuning and infusion of nonsilica materials into the air regions, which change the waveguide structure and can provide enhanced tunability. The second category is typified by air-silica microstructured optical fibers, which contain air-voids that run along the length of the fiber. These fibers have unique cladding mode properties that can be exploited in fiber grating based devices     

Design and screening of highly reliable 980-nm pump lasers

Presents a design and screening approach that can be adopted to improve reliability of high-power 980-nm semiconductor lasers. Flared-ridge waveguide chips were realized on GRIN-SCH single-quantum-well structures. Without any screening, flared devices, thanks to the reduced peak power and current density, showed a 20% reduction in failure rate with respect to devices with straight waveguide. By adopting extended screening criteria, a more reliable population was selected, showing a reduction by a factor of two in the failure rate extrapolated at standard operating conditions.     

3-D photonic circuit technology

Vertically coupled, wafer-bonded III-V semiconductor waveguide devices provide a means to obtain more powerful, compact photonic integrated circuits and allow for the combination of different materials onto a single chip. Various switching, filtering, multiplexing, and beam splitting devices in the InP-InGaAsP and GaAs-AlGaAs systems for signals in the 1550-nm range have been realized. An investigation of optimal optical add-drop multiplexer waveguide layout shapes has been performed through integration of the coupled-mode Riccati equation, providing potential sidelobe levels of less than -32 dB and filter bandwidths over 20% narrower than those of previous devices. Effects of nonideal processing conditions on filter performance are analyzed as well.     

Polymeric optical waveguide films for short-distance opticalinterconnects

We describe three different applications of polymeric waveguide films as short-distance optical interconnects. We fabricated the waveguide films, which were 6.5 cm long and mounted in MT-compatible (MTC) connectors by passive alignment, for MM fiber systems with a 50-μm diameter graded index (GI) core. The average insertion loss of these devices was approximately 0.6 dB at 0.85-μm wavelength. We also fabricated waveguide films with a 350 mirror and an MTC connector for use as 90° out-of-plane optical deflectors, and they exhibited an insertion loss of 1 dB. Two silica planar waveguides for single-mode (SM) fiber systems were also connected by a polymeric waveguide film. Low insertion losses were obtained in both MM and SM films designed to be employed as bending waveguides. This reveals their good potential for use as practical short-distance optical interconnects     

Rare-earth-doped GaN: growth, properties, and fabrication of electroluminescent devices

A review is presented of the fabrication, operation, and applications of rare-earth-doped GaN electroluminescent devices (ELDs). GaN:RE ELDs emit light due to impact excitation of the rare earth (RE) ions by hot carriers followed by radiative RE relaxation. By appropriately choosing the RE dopant, narrow linewidth emission can be obtained at selected wavelengths from the ultraviolet to the infrared. The deposition of GaN:RE layers is carried out by solid-source molecular beam epitaxy, and a plasma N/sub 2/ source. Growth mechanisms and optimization of the GaN layers for RE emission are discussed based on RE concentration, growth temperature, and V/III ratio. The fabrication processes and electrical models for both dc- and ac-biased devices are discussed, along with techniques for multicolor integration. Visible emission at red, green, and blue wavelengths from GaN doped with Eu, Er, and Tm has led to the development of flat-panel display (FPD) devices. The brightness characteristics of thick dielectric EL (TDEL) display devices are reviewed as a function of bias, frequency, and time. High contrast TDEL devices using a black dielectric are presented. The fabrication and operation of FPD prototypes are described. Infrared emission at 1.5 /spl mu/m from GaN:Er ELDs has been applied to optical telecommunications devices. The fabrication of GaN channel waveguides by inductively coupled plasma etching is also reviewed, along with waveguide optical characterization.     

Phase-dithered waveguide grating with flat passband and sharp transitions

A new passband flattening technique for waveguide grating devices is proposed and experimentally demonstrated. It uses phase dithering of grating elements to obtain a flat passband with sharp transitions while maintaining single-mode input and output waveguides. The chromatic dispersion characteristics of the device can be improved simultaneously over the passband. The theory and design method based on an iterative Fourier transform algorithm are presented in detail with simulation and experimental results. The technique can be used in both arrayed waveguide grating and echelle grating-based devices.     

Integrated optic-devices characterization with the Wigner transform

The characterization of integrated optic devices with the Wigner transform is presented. The Wigner transform of planar waveguides, waveguide couplers and optical modulators is computed. It allows the determination of various parameters of the integrated optic devices such as the parity and shape of waveguide modes, the effective numerical aperture, the distance between coupled waveguides, the coupling efficiency, etc. Also presented are the set-ups for the Wigner transform measurement in different phase space coordinates as space-angle and time-frequency     

Monolithic integration via a universal damage enhanced quantum-wellintermixing technique

A novel technique for quantum-well intermixing is demonstrated, which has proven a reliable means for obtaining postgrowth shifts in the band edge of a wide range of III-V material systems. The technique relies upon the generation of point defects via plasma induced damage during the deposition of sputtered SiO₂, and provides a simple and reliable process for the fabrication of both wavelength tuned lasers and monolithically integrated devices. Wavelength tuned broad area oxide stripe lasers are demonstrated in InGaAs-InAlGaAs, InGaAs-InGaAsP, and GaInP-AlGaInP quantum well systems, and it is shown that low absorption losses are obtained after intermixing. Oxide stripe lasers with integrated slab waveguides have also enabled the production of a narrow single lobed far field (3°) pattern in both InGaAs-InAlGaAs, and GaInP-AlGaInP devices. Extended cavity ridge waveguide lasers operating at 1.5 μm are demonstrated with low loss (α=4.1 cm^-1) waveguides, and it is shown that this loss is limited only by free carrier absorption in waveguide cladding layers. In addition, the operation of intermixed multimode interference couplers is demonstrated, where four GaAs-AlGaAs laser amplifiers are monolithically integrated to produce high output powers of 180 mW in a single fundamental mode. The results illustrate that the technique can routinely be used to fabricate low-loss optical interconnects and offers a very promising route toward photonic integration     

Focused ion-beam implantation induced thermal quantum-wellintermixing for monolithic optoelectronic device integration

By focused ion beam implantation induced thermal intermixing the bandgap of quantum-well layer structures can be selectively changed. This allows lateral bandgap engineering and gives a new degree of freedom for lateral structuring. The principle technological aspects like the dependence of the bandgap shift on implantation parameters and the spatial resolution are investigated and applied to the fabrication of photonic and optoelectronic devices. Lateral waveguiding in InP-based materials, the possibility of monolithic integration of bandgap shifted waveguide areas into active devices and the improvement of the lateral carrier confinement in ridge waveguide lasers are demonstrated. Due to the high spatial resolution, modulated bandgap gratings could be realized with periods down to 90 mn. These bandgap gratings were used to create gain-coupled distributed-feedback lasers in different material systems with well controlled single-mode emission     

Interferometric near-field imaging technique for phase andrefractive index profiling in large-area planar-waveguide optoelectronicdevices

A versatile, interferometric optical technique is described for nondestructively imaging the near-field output phase uniformity and refractive index profile in broad-area optoelectronic waveguide devices or heterostructure materials. In active traveling-wave optical power amplifier devices, measurements are presented for thermal lensing, solder bond inhomogeneities, heatsink impedance, and carrier-lensing effects due to nonuniform gain saturation by the amplifier input beam, transverse amplified spontaneous emission, or intensity filaments. The thermal performance of diamond and copper heatsinks for high-power optical amplifiers is compared. In passive devices, the technique is used to observe heteroepitaxial material compositional uniformity, defects, photoelastic stress, and intentional structural waveguide index modifications. The technique has a phase and spatial resolution as low as λ/100 and 1 μm. The corresponding refractive index and temperature resolutions (dependent on device length) are as low as Δn=10^-5 and ΔT=0.025°C for 1000-μm-long devices     

Tapered rib adiabatic following fiber couplers in etched GaAsmaterials for monolithic spot-size transformation

Design details and demonstration data are presented for an (Al,Ga)As monolithic tapered rib waveguide achieving modal spot-size transformation. The tapered rib adiabatic following fiber coupler structure (TRAFFIC) achieves two-dimensional (2-D) expansion of the output optical mode of single-transverse-mode semiconductor waveguide modulators and lasers using a one-dimensional (1-D) taper between noncritical initial and final taper widths which are compatible with optical lithographic techniques. Measurements are presented of total mode expansion losses between ~1.5-2.0 dB and semiconductor to single-mode-fiber waveguide coupling losses of ~0.5-1.0 dB for doped pin optical-modulator-type waveguides using the TRAFFIC waveguide. A semiconductor laser with a TRAFFIC tapered-rib mode-expansion section and measured coupling loss between the laser output and single-mode fiber of only 0.9 dB is described. Finally, a TRAFFIC Spot-size transformer for undoped waveguide modulators with total mode expansion losses of 1.84 dB and excellent modal behavior at 1.32-μm wavelength is presented. The TRAFFiC structure is particularly well suited for integration with both active and passive etched rib waveguide devices. Fabrication is relatively simple, requiring only patterning and etching of the tapered waveguide and uniform-width outer mesa waveguide without any epitaxial regrowth     

Body fitted grid generation with moving boundary and its application for dielectric waveguides

The stress birefringence and mode coupling effects in polarization-preserving fibres are most important problems which need to be improved. For a realization of some optical devices, the dielectric waveguide with sinusoidally varying circular cross-section has been investigated. It becomes very important to analyse the electromagnetic field distribution in a dielectric waveguide with a time-dependent moving boundary. This paper shows that numerical methods can simulate the effect of the external disturbance on the dielectric waveguide from time to time. The author has discussed body fitted grid generation with moving boundary for the Poisson and Laplace equations.^1,2 We have extended this technique for Maxwell's equation. The technique employs a kind of an expanded numerical grid generation. As the author adds the time component to grid generation, the time dependent co-ordinate system which coincides with a contour of moving boundary can be transformed into a fixed rectangular co-ordinate system. We could show the electric distribution in the waveguide time by time to verify the possibility of an application for an optical fibre. This technique makes it possible not only to analyse the effect of the external disturbance in a coherent optical communication system but also to fabricate optical devices.     

Efficient optical coupling between a polymeric waveguide and anultrafast silicon MSM photodiode

One task of the integration of optoelectronic functions with silicon devices is the construction of an optical waveguide on Si and the optical coupling of this waveguide to a silicon photodetector. We have fabricated polymeric strip waveguides on Si and demonstrate a very efficient design for the optical coupling between the polymeric waveguide and an ultrafast Si-based metal-semiconductor-metal (MSM) mesa-type photodetector. This detector uses high-quality epitaxial Si as the sensitive layer, which is sandwiched between two metallic contacts. If these MSM detectors are excited by a vertically incident free beam of λ=840 nm and pulses of 100-fs full-width at half-maximum (FWHM), they respond with electrical pulses of 3, 5-ps length (FWHM, T=300 K)     

一种新型对称宽边耦合共面波导巴仑的分析

本文介绍了一种新型对称宽边耦合共面波导巴仑。它是基于一般耦合传输的网络模型结合对称宽边耦合共面波导理论导出的。作为一个例子，我们设计了中心频率12GHz巴仑，其输出辐相特性优于文献[1]对称宽边耦合微带巴仑。所研究的巴仑可地微波单片集成电路（MMIC）和多层介质微波集成电路（MuMIC）的混频器、调制器和倍频器等诸多微波器件中。     

Dielectric Solid-State Planar Waveguide Lasers: A Review

This review takes a look at the historical development of the dielectric planar waveguide laser leading to key state-of-the-art technologies that fall within this broad subject area. Discussed herein are many of the advantages offered by the waveguide geometry such as high optical gain, and thus, low threshold-power requirements, suitability for quasi-three-level laser transitions, integration with functional devices on single substrates, guided spatial-mode control, and its considerable immunity to thermal effects and external environmental conditions. A detailed snapshot is made of many active host media for which there has been reported laser action in the planar waveguide geometry, covering many of the major rare-earth-ion transitions. Several fabrication techniques are highlighted and appraised for their applicability to different host media, touching on their benefits and drawbacks. Challenges and future prospects for these lasers are considered.     

O/E Integration of Polymer Waveguide Devices by Using Replication Technology

The simple optoelectronic integration of polymer-based optical waveguide devices and the development of the realization processes have been critical issues for cost-effective, high-volume manufacturing of a next-generation optoelectronic integrated circuit (OEIC). We demonstrated the replication technology as a means of implementing the polymer microoptoelectromechanical system (MOEMS)-based packaging structure providing the optical/electrical (O/E) integration of the functional polymer waveguide device. To achieve this, a micromechanical packaging structure consisting of an electric-circuit-embedded polymer optical bench and planar-lightwave-circuit (PLC)-type waveguide chip with alignment microstructure was designed, and the realization process incorporating the UV imprint technique was investigated. To improve optical coupling efficiency, the electric circuit was embedded under the optical bench and the contact pads were opened at the bottom of the alignment pits. In addition, a conductive adhesive-fill space was created at the alignment pits to accommodate the surplus conductive adhesive. Efficient fiber-chip coupling and good electrical contact of upside-down mounted single-mode waveguide chip was accomplished by the simple joining of the electric-circuit patterned micropedestals on the waveguide chip and the alignment pits on the bench. A coupling loss of 0.9 dB per coupling face was measured with a single-mode fiber at a wavelength of 1.5 mum. It was concluded that the replication technology has versatile application capabilities in manufacturing next generation optical interconnect systems