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.     

Silicon oxynitride planar waveguiding structures for application inoptical communication

The refractive index of silicon oxynitride (SiON), a widely used material for integrated optics devices, can be chosen in a wide range between 1.45-2.0. We describe how the consequent large design freedom can be exploited on the one hand for a “standard” polarization independent optical channel waveguide having a favorable tradeoff between efficient fiberchip coupling and small bend radii (compact devices) and on the other hand for special-purpose and hybrid components where the refractive index should be finely adjusted for obtaining the desired functionality. We illustrate the applicability of SiON by describing a few devices for optical filtering in a new architecture for wavelength multiplexing, modulation, polarization splitting and second-harmonic generation     

The SHG-response of different phases in proton exchanged lithiumniobate waveguides

Reflection second-harmonic generation from the polished waveguide end face is used to investigate the second-order nonlinear optical properties of as-exchanged and annealed proton-exchanged (PE) waveguides in different H_xLi_1-xNbO₃ phases. A detailed correlation is done between the nonlinear properties, the processing conditions, the refractive index changes, and the optical losses of the waveguides. It is found that for the direct PE samples, where the β₄, β₃, and β₁ phases are generated at the surface, the nonlinearity in the guide is strongly reduced by more than 85% of its bulk value, while for waveguides prepared in the β₂ phase, the nonlinear coefficient is about 55% of the bulk one. A consequence is that the step-like β_i-phase PE LiNbO₃ waveguides with large refractive index increase are advantageous for efficient SHG in Cherenkov configuration. The nonlinearity, strongly reduced after the initial proton exchange, is found to be restored and even increased after annealing. However, this apparent increase of the nonlinearity is accompanied by a strong degradation of the quality of the second-harmonic generation reflected beam in the region of initial waveguides due to beam scattering. The graded proton exchange technique and dilute melt proton exchange have been shown to produce high-quality waveguides with essentially undergraded nonlinear optical properties. It has been also shown that the nonlinear properties of annealed proton exchanged LiNbO₃ waveguides can be effectively recovered by the reverse proton exchange technique. The results obtained are important for the design, fabrication, and optimizing of guided-wave nonlinear optical devices in LiNbO₃     

Wavelength demultiplexer using GaInAs-InP MQW-based variable refractive-index arrayed waveguides fabricated by selective MOVPE

A GaInAs-InP multiple quantum well (MQW)-based wavelength demultiplexer composed of an arrayed waveguide in which the refractive index varies across the array was fabricated. Since optical path length differences between waveguides in the array are achieved through refractive-index differences that are controlled by SiO/sub 2/ mask design in selective metal-organic vapor phase epitaxy (MOVPE), straight waveguide gratings having reduced optical propagation losses can be achieved. Furthermore, by employing MQW waveguides, variations in the refractive index may be induced through an applied electric field, allowing the device to manipulate wavelengths dynamically. A straight arrayed waveguide device having a 1.4% difference in refractive index was fabricated using an asymmetric side mask via a single selective MOVPE growth. The achievement of a diffraction angle difference of 4.40/spl deg/ between wavelengths of 1520 and 1580 nm was confirmed experimentally. In addition, a preliminary wavelength demultiplexer with a wavelength separation of approximately 25 nm and a free spectral range (FSR) of approximately 100 nm was also fabricated.     

The application of porous silicon to optical waveguiding technology

The porosification of silicon can be achieved by the partial electrochemical dissolution (anodization) of the surface of a silicon wafer. The degree of porosity is dependent on the anodization parameters and can generally be controlled within the constraints imposed by substrate dopant type and concentration. Control of porosity leads to control of refractive index, and therein lies the concept of using porous silicon as an optical waveguide. We discuss porous silicon wavegides, for the visible to the infrared, produced by a number of approaches: 1) epitaxial growth onto porous silicon (where the porous layer acts as a substrate for a higher refractive index waveguide epilayer); 2) ion implantation (where either selective areas of high electrical resistivity can be produced, which act as a barrier against porosification, or where the surface of a porosified layer is amorphised to form a waveguide; 3) porous silicon multilayers (where the anodization parameters are periodically varied to produce alternate layers of different porosity and thus refractive index); and 4) oxidation of porous silicon (where a porosified layer is oxidized to form a graded-index, dense or porous, oxide waveguide)     

Asymmetrical single-mode silica waveguide deposited by PECVD

Silicon oxynitride (SiON) layer and SiO₂ buffer layer were deposited on silicon wafers by PECVD technique using SiH₄, N₂O and N₂. The refractive index of SiON films measured at a wavelength of 1552 nm using a prism coupler, could be continuously varied from 1.4480 to 1.4508. Optical planar waveguides with a thickness of 6 μm and a refractive index contrast (Δn) of 0.36% have been obtained. In addition, etching experiments were performed using ICP dry etching equipment on thick SiON films grown on Si substrates covered with a thick SiO₂ buffer layer. In order to measure optical properties, a polarization maintaining single-mode fiber was used for the input and a microscope objective for the output at 1.55 μ m. A low-loss and low propagation SiON-based waveguide was fabricated with easily adjustable refractive index of core layer.     

Scaling the modulation bandwidth and phase efficiency of a silicon optical modulator

We present an optimized design and detailed simulation of an all-silicon optical modulator based on a silicon waveguide phase shifter containing a metal-oxide-semiconductor (MOS) capacitor. Based on a fully vectorial Maxwell mode solver, we analyze the modal characteristics of the silicon waveguide. We show that shrinking the waveguide size and reducing gate oxide thickness significantly enhances the phase modulation efficiency because of the optical field enhancement in the voltage induced charge layers of the MOS capacitor, which, in turn, induce refractive index modulation in silicon due to free carrier dispersion effects. We also analyze the device speed by transient semiconductor device modeling. As both optical absorption and modulation bandwidth increase with increasing doping concentration, we show that, with a nonuniform doping profile in the waveguide, balance between the device operation speed and optical loss can be realized. Our simulation suggests that a TE-polarized optical phase modulator with a bandwidth of 10 GHz and an on-chip optical loss less than 2 dB is achievable in silicon.     

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     

Preparation of Textured Growth Pb(Zr,Ti)O3 Thin Films on Si Substrate Using SrTiO3 as Buffer Layers

PZT thin films are deposited on SiO₂/Si substrate by metallo-organic decomposition (MOD) process, using SrTiO₃ (STO) as buffer layer for textured growth. The STO layers deposited on SiO₂/Si substrate by pulsed laser deposition process show (100)/(200) preferred orientation, whereas the STO buffer layer deposited on silica substrate using spin-coating technique show random orientation behavior. The use of STO as buffer layers enhanced the crystallization and the preferred orientations of the PZT films. The PZT on STO buffered SiO₂/Si substrates thus obtained possess high refractive index, (n)_PZT/STO = 2.1159, and are of good enough quality for optical waveguide applications.     

Guiding of dynamically modulated signals in arrays of photorefractive spatial solitons

As the formation of spatial optical solitons in photorefractive mediad is governed by modification of the refractive index, every single solitons in complex configurations of solitons can act as a single waveguide for other light beams. In this article, we demonstrate guiding of amplitude-modulated beams in complex configurations of photorefractive solitons carrying information; we analyze the received signal in the kilohertz frequency range. The possibility of data transmission combined with waveguide couplers opens the route to all-optical networks.     

Applications of Highly-Nonlinear Chalcogenide Glass Devices Tailored for High-Speed All-Optical Signal Processing

Ultrahigh nonlinear tapered fiber and planar rib Chalcogenide waveguides have been developed to enable highspeed all-optical signal processing in compact, low-loss optical devices through the use of four-wave mixing (FWM) and cross-phase modulation (XPM) via the ultra fast Kerr effect. Tapering a commercial As₂Se₃ fiber is shown to reduce its effective core area and enhance the Kerr nonlinearity thereby enabling XPM wavelength conversion of a 40 Gb/s signal in a shorter 16-cm length device that allows a broader wavelength tuning range due to its smaller net chromatic dispersion. Progress toward photonic chip-scale devices is shown by fabricating As₂S₃ planar rib waveguides exhibiting nonlinearity up to 2080 W^-1ldr km^-1 and losses as low as 0.05 dB/cm. The material's high refractive index, ensuring more robust confinement of the optical mode, permits a more compact serpentine-shaped rib waveguide of 22.5 cm length on a 7-cm- size chip, which is successfully applied to broadband wavelength conversion of 40-80 Gb/s signals by XPM. A shorter 5-cm length planar waveguide proves most effective for all-optical time-division demultiplexing of a 160 Gb/s signal by FWM and analysis shows its length is near optimum for maximizing FWM in consideration of its dispersion and loss.     

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     

Self-Aligned Single-Mode Polymer Waveguide Interconnections for Efficient Chip-to-Chip Optical Coupling

Single-mode (SM) ultrashort optical interconnections between the fibers and waveguides using self-forming polymeric waveguides with low optical losses at 1300 and 1550 nm were demonstrated. The localized refractive index in the SM regime is estimated by measuring the surface topography induced by monomer diffusion during the waveguide formation. A loss less than$-1$dB can be obtained from self-aligning SM-to-multimode (MM) fibers and SM-to-SM fibers interconnections, respectively. A self-formed waveguide-to-fiber interconnection is fabricated and measured with loss less than 0.2 dB at 1550 nm. The polymer waveguide relaxes the positioning requirements for single-mode chip-to-chip optical interconnections, showing great potential to improve the short-term yield and long-term reliability.     

Novel geometry for an integrated channel selector

A new reflective configuration for a monolithically integrated channel selector with power monitor is proposed. One star coupler, one arrayed waveguide grating, and a minimum number of semiconductor optical amplifier (SOA) gates are used to achieve loss-free transmission. A 32-channel device controlled by only 12 SOA gates is realized in InP. Low on-chip losses result in strongly reduced bias currents and an improved signal to noise ratio compared to previously demonstrated devices. The use of SOAs allows for switching on a nanosecond time scale.     

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     

Analysis and design equations for phase matching using Bragg reflector waveguides

In this paper, we introduce and analyze a novel wave-guide design to provide phase matching for nonlinear optical processes. Phase matching is achieved by designing the structure to guide the fundamental frequency by total internal reflection and the second harmonic (SH) frequency by transverse Bragg reflection. By forcing the SH mode to operate in the middle of the Bragg stopband, we solve for the waveguide dimensions for arbitrary waveguide materials, given the material dispersion between the fundamental and SH frequencies. Using GaAs-AlGaAs as an example, we analytically investigate and quantify properties such as nonlinear coupling efficiency, bandwidth, tunability, and limitations due to dispersion. The technique shows tremendous promise when compared to alternate technologies, where it is particularly attractive as an effective means to obtain ultralow-loss nonlinear optical elements for monolithic integration with coherent light sources and other active devices.     

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.     

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     

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.     

Infrared microscopy studies on high-power InGaAs-GaAs-InGaP laserswith Ga2O3 facet coatings

InGaAs-GaAs separate confinement, heterostructure single quantum-well (SCH-SQW) lasers (λ=0.98 μm) with lattice-matched InGaP cladding layers, using a new Ga₂O₃ low reflectivity (LR) front-facet coating, are reported. The CW peak power density (17 MW/cm²) of 6 μm×750 μm ridge-waveguide lasers is limited by thermal rollover, and repeated cycling beyond thermal rollover produced no change in operating characteristics. The high-power temperature distribution along the active stripe has been measured by high-resolution infrared (3-5 μm) imaging microscopy. The temperature profile acquired for a very high optical power density P_D=11 MW/cm³ was found to be uniform along the inner active laser stripe, and revealed a local temperature increase at the LR front facet ΔT_f of only 9 K above the average stripe temperature ΔT_s=24 K. An excellent front-facet interface recombination velocity <10⁵ cm/s has been inferred from the measured low local temperature rise in the front facet