Showing papers on "Silicon photonics published in 1998"

All-optical wavelength conversion using SOA nonlinearities

Abstract: In this article the increasing use of WDM systems in telecommunications networks is highlighted, and the potential role for wavelength conversion in future upgrades of such systems is reviewed. Techniques for achieving wavelength conversion by all-optical means using nonlinearities in semiconductor optical amplifiers are explained, and experimental results obtained at BT Laboratories are used to illustrate the state of the art.

Near-field optical imaging of light propagation in semiconductor waveguide structures

Abstract: We have investigated light propagation in optical devices by near-field scanning optical microscopy (NSOM) at the telecommunication wavelength of 1.55 μm. NSOM images obtained on the top of channel waveguides measure the mode profile perpendicular to the propagation direction and show a modulation of intensity along this direction. This modulation demonstrates the periodic variation of the mode size predicted for the propagation in small guides and marks the direction of propagation. We show that NSOM analysis can completely assess complex optical devices with subwavelength resolution: determination of the optical path, variation of the light intensity along this path, and measurement of local radiative losses.

4 x 4 digital optical matrix switch using polymeric oversized rib waveguides

Abstract: For the first time the concept of oversized rib waveguides has been employed in a complex integrated optical device. Using commercially available polymers, a strictly nonblocking 4/spl times/4 digital optical matrix switch with full functionality has been realized. The matrix consists of 24 1/spl times/2 switching elements and showed a polarization independent average crosstalk of -28.8 dB.

Semiconductor optical amplification element

Abstract: The invention provides a semiconductor optical amplification element which reduces noise light emission and increases saturation output power. The semiconductor optical amplification element has an optical waveguide which includes a core layer formed from an active layer acting as an optical amplification medium and amplifies and outputs an optical signal without electrically converting. The light reflection factor on an inputting side end of the element for the optical signal is lower than the light reflection factor on another outputting side end of the element.

Fabrication and optical characterization of Pb(Mg1/3Nb2/3)O3-PbTiO3 planar thin film optical waveguides

Abstract: Highly (110)-oriented and (100) nearly epitaxial 0.7PMN-0.3PT thin films were deposited on (1012) sapphire and (100) LaAlO3 substrates, respectively, using a dip-coating method. Optical waveguide characterization and electro-optic effect measurements of the film on sapphire substrate were demonstrated. Low propagation loss of 4.1 dB/cm and high quadratic electro-optic coefficient of 0.75×10−16 (m/V)2 were obtained at wavelength of 632.8 nm. Epitaxial PMN-PT thin films will be suitable for integrated optic devices.

Novel liquid sensor based on porous silicon optical waveguides

Abstract: The introduction of solvents into the pores of optical waveguides formed using porous silicon is shown to dramatically reduce the interfacial scattering loss of the waveguides (by as much as 34-dB cm/sup -1/ in one example), in a reversible manner. The degree of loss reduction is dependent on the type of solvent introduced. These observations, combined with the fact that a substantial portion of the guided-mode field interacts with the solvent introduced into the pores, indicate that an enhanced sensitivity for sensor applications may be achievable across a broad range of operational wavelengths.

Integrated optical circuit

Abstract: The invention relates to an integrated optical circuit comprising a silicon substrate (1) and waveguides (2, 3) arranged thereon. At least one photonic crystal is provided as a waveguide, which is formed by a mesh of needles (6). The needles (6) can be produced by corpuscular radiation deposition.

All-optical set-reset operation in a distributed feedback GaInAsP waveguide

Abstract: An optical bistable device is realized by an optical feedback structure and the optical Kerr effect. We fabricated an optical distributed feedback waveguide in a GaInAsP-InP wafer. All-optical set-reset operation has been observed in the GaInAsP-InP waveguide at a wavelength of 1.56 /spl mu/m.

Noise reduction of 20 Gbit/s pulse train using spectrally filtered optical solitons

Abstract: It is demonstrated that intensity noise in an optical pulse train can be effectively reduced by the spectral filtering of solitons in an optical fibre.

Light controllable defect modes in three-dimensional photonic crystal

Abstract: The authors experimentally demonstrate the controllability of the defect mode in a submillimetre three-dimensional silicon photonic crystal. The resonant mode at 253 GHz is created inside the forbidden gap by inserting interstitial defects. The transmission level of the mode is modulated externally by more than 8 dB with a 330 mW laser illumination. Transmission spectra are confirmed by numerical simulations.

Strip-Loaded High-Confinement Waveguides for Photonic Applications

Abstract: Sol-gel is a promising deposition technique for the fabrication of silica-on-silicon photonic components. Silica-titania compositions provide large index differences, and thus strong mode confinement, and are suitable hosts for Er-doped optical amplifiers. We have developed channel waveguides based on phosphosilicate strip loads over high index titania-doped guiding layers. Here we demonstrate that low propagation loss (0.3 dB/cm) can be obtained in such guides at optical communication wavelengths. Alumina co-doped guiding layers are shown to inhibit OH retention without causing titania segregation, and reduced humidity during spinning is shown to be necessary to achieve low propagation losses.

Strong polarization conversion in periodically loaded strip waveguides

Abstract: We give a comprehensive explanation for an unexpected strong polarization conversion effect in periodically loaded strip waveguides, which was detected experimentally some years ago. The effect can be put down to the occurrence of hybrid supermodes. Based on this knowledge, design proposals for new, highly efficient polarization converters can be given.

Integrated multistack waveguide polarizer

Abstract: Waveguide polarizers based on embedded thin metallic stacks are proposed. Highly efficient TM polarization is obtained for metal thicknesses smaller than the optical skin depth. The optimal single-metal-layer waveguide is found to yield an extinction ratio better than 12.2 dB/mm and a linear loss below 0.075 dB/mm. Experimental confirmation for this structure is also obtained in polymeric waveguides. Polarization efficiencies better than 100 dB/mm with linear losses below 2 dB/mm are calculated for multi-stack waveguides. This high performance is found to hold even if oxidation at metal-core boundaries is considered.

Efficient optical coupling between a polymeric waveguide and an ultrafast silicon MSM photodiode

Abstract: 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 /spl lambda/=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).

Broadband variable optical attenuator in silica waveguide technology

Abstract: A broad-band variable optical attenuator, with 1 dB flatness over the 1530-1560 range and with variable attenuation up to 20 dB, is described. It is based on cascaded Mach-Zehnders and fabricated in silica waveguide technology.

Waveguides induced by photorefractive screening solitons

Abstract: Summary form only given. Photorefractive spatial solitons form when the optically induced space-charge field modifies the refractive index via electro-optic effect and forms a waveguide that confines the optical beam that has induced the waveguide. Since the photorefractive response is wavelength dependent, one can generate a soliton with a weak beam and guide in it a more intense beam of a less photosensitive wavelength. Here we present theoretical and experimental studies of the waveguides induced by photorefractive screening solitons. We show that the number of guided modes in a waveguide induced by a bright screening soliton increases monotonically with increasing intensity ratio (the ratio between the peak soliton intensity and the background or dark irradiance), whereas the waveguides induced by dark screening solitons are always single-mode waveguides.

Optical waveguide plate for display

Abstract: An optical waveguide plate for a display including a main optical waveguide plate body for introducing light from a light source thereinto, and surface-smoothing materials formed on both surfaces of the main optical waveguide plate body and having approximately the same optical refractive index as that of an optical waveguide plate. The main optical waveguide plate body is composed of a transparent material such as glass and acrylic resin, because it is necessary to totally reflect the introduced light. The surface-smoothing material is composed of, for example, a liquid having good wettability with respect to the main optical waveguide plate body. The range, in which the optical refractive index of the surface-smoothing material is approximately the same as the optical refractive index of the main optical waveguide plate body, lies in 0.8n≦m≦1.2n provided that the optical refractive index of the surface-smoothing material is m, and the optical refractive index of the main optical waveguide plate body is n. It is possible to decrease the plane roughness on the surface of the main optical waveguide plate body, substantially eliminate scratches, dirt and the like, and improve the contrast and brightness of the display.

Optical waveguide fabrication method

Abstract: A method for fabricating an optical waveguide, comprising the following steps. That is, forming an optical waveguide on surface of a substrate via an atmospheric pressure chemical vapor deposition (AP-CVD) method using a silica raw material containing an organic material, and irradiating ultraviolet light on at least a portion of that optical waveguide. The refractive index of the portion of the optical waveguide irradiated with ultraviolet light increases. Since changing the refractive index in this way enables the formation of a diffraction grating, it is possible to manufacture optical filters and wavelength dispersion devices.

Tunable optical add/drop components in silicon-oxynitride waveguide structures

Abstract: Ultra-compact tunable add/drop components, based on the resonant coupler concept, are realized in high index-contrast silicon-oxynitride waveguides. Thermo-optic heaters are used to tailor and tune the filter characteristic.

Experimental demonstration of a raman effect-based optical transistor

Abstract: We demonstrate optical pulse switching and amplification based on simultaneous Raman and Kerr effects in a fiber-loop mirror. Stimulated Raman scattering is shown to play a dominant role in the transfer function of the loop with highly germania-doped fibers, in agreement with theoretical predictions. Optical switching of a 100-ps signal pulse with an amplification factor of 10 was demonstrated in a 20-mol.% GeO2-doped fiber.

Monolithic integration of light emitting diodes, detectors and optical fibers on a silicon wafer: a CMOS compatible optical sensor

Abstract: Silicon light emitting diodes, detectors and optical fibers are monolithically integrated on a Silicon wafer for sensor applications. The Silicon LEDs are avalanche diodes reverse biased beyond the breakdown voltage. The fiber is a Silicon Nitride waveguide which is self aligned to the light emitter and the detector junctions through proper TEOS spacers for efficient optical coupling. The potential of the device as a CMOS compatible monolithic optical sensor is demonstrated.

Dip-coated thin-film polycarbonate optical waveguides.

Abstract: We report on our systematic and detailed study of fabrication and characterization of polycarbonate thin-film optical waveguides. Various waveguide properties, such as refractive index, optical loss, waveguide thickness, dispersion as a function of temperature of waveguides and substrates, and the effect of thickness gradient on optical guiding losses, have been reported. A comparative study of the properties of waveguides fabricated with dioxane and tetrahydrofuran as solvents is also presented.

Optical waveguide circuit, optical branched waveguide circuit, and optical modulator

Abstract: An optical branched waveguide and an optical waveguide circuit which are easily fabricated, have a small size, and are low in cost. A linear first optical waveguide and second optical waveguide are crossed at a predetermined angle with respect to the substrate, a groove forming a predetermined angle relative to the optical waveguides and having a depth set to not less than the depth of the first and second optical waveguides is formed so as to include the intersecting region of the first optical waveguide and the second optical waveguide, and an optical element having a partial reflection and partial transmission function passing part of an incident light guided through the first optical waveguide therethrough and guiding this to the first optical waveguide and, at the same time, reflecting part of the incident light and guiding the same to the second optical waveguide is inserted into the groove so as to include the intersecting region of the first optical waveguide and the second optical waveguide.

Self-alignment with optical microconnectors for free-space optical interconnections.

Abstract: A self-alignment technique that uses optical microconnectors for three-dimensional optics in optical computing systems and optical interconnections is proposed. The optical microconnector consists of an optical plug and a socket. On the output plane of an optical system, optical plugs are made of a photosensitive resin exposed to light through the optical system. Because the corresponding positions of the optical plugs are critical to the image formed by the optical system, a detecting device can be aligned and mounted by the connection of the optical plugs to sockets formed on the surface of the device. Optical microconnectors were experimentally fabricated in a reflective block optical system. An alignment accuracy of ∼20 μm was attained in the experiment.

Multi-channel optical coupling between VCSEL arrays and multimode optical fibers for a 40-channel parallel optical interconnection module

Abstract: We have successfully developed some new assembly techniques for the prototype ParaBIT module to provide the efficient and uniform multi-channel optical coupling between VCSEL/photodiode arrays and multimode optical fibers. The modules which were assembled by using these techniques satisfied the restriction on the optical coupling variation of 1.5 dB.

Buried Optical Waveguides of Porous Silicon

Abstract: It is demonstrated that the refractive-index-controllable nature of luminescent porous silicon (PS) is directly applicable to the development of a three-dimensionally buried optical waveguide. The PS waveguide is fabricated on a p-type silicon wafer by monolithic processes such as photolithography, ion implantation, anodization, and thermal oxidation. An induced high contrast of refractive indices leads to efficient confinement and propagation of visible light. When the active core layer is partially excited by a He-Cd (325 nm) laser, blue emission is observed from a cleaved facet. The PS waveguide is potentially useful as a component of silicon-based photonic integration.

Applications of semiconductor optical amplifiers

Abstract: An overview is given of applications of semiconductor optical amplifiers in optical communication systems. Feasibility is demonstrated for optical pre-amplifier and in-line applications. Experiments on WDM transmission are presented as well as the use of gain-clamping to achieve linear or analog-grade amplification.

Optoelectronic integration in silicon-on-insulator technologies

Abstract: Established silicon microelectronics fabrication techniques can be largely exploited to fabricate low-loss, low-cost and high volume optical integrated devices. Because of the availability of a buried insulator layer underneath a thin monocrystalline silicon film, Silicon-On-Insulator substrates are currently shown to be a natural candidate for the integration of guided-wave optics components working at the fiber-optical communications wavelengths of 1.33 and 1.55 /spl mu/m. In this paper, the authors review the basic principles of optical waveguides on SOI materials and describe some recent realizations based on optoelectronic system integration in SOI technologies (waveguides, switches, phase modulator or shifter, etc.).

Nonlinear Optical Interactions in Optical Fibers

Abstract: We report on our research program aimed at clarifying the physical processes leading to the nonlinear optical response of silica optical fibers and at studying the implications of optical nonlinearities on optical pulse propagation and optical switching devices. The dominant physical processes leading to the nonlinear optical response of an optical fiber are nonresonant electronic polarization, with essentially instantaneous response, the Raman interaction, with sub-picosecond response, and electrostriction, with nanosecond response. We present experimental results that show the consequence of each of these processes on the propagation of a light pulse through an optical fiber. We have also performed one of the first direct measurements of the electrostrictive contribution to the nonlinear refractive index of optical fibers. We measure values ranging from 1.5 × 10-16 to 5.8 × 10-16cm2/W, depending on fiber type. These values are comparable to that of the fast, Kerr nonlinearity (i.e., sum of electronic and Raman contributions) of 2.5 × 10-16cm2/W. The measured electrostrictive nonlinearities are significantly larger than those predicted by simple models, and the possible explanations of this difference are discussed.