Showing papers on "Radiation mode published in 2002"

Silicon waveguide two-photon absorption detector at 1.5 μm wavelength for autocorrelation measurements

Abstract: We describe the use of a silicon waveguide for two-photon absorption measurements in an autocorrelator which achieved a peak-power average-power sensitivity of 1 (mW)2 at 1.56 μm wavelength and which was used to measure optical pulses generated by a mode-locked fiber ring laser. The experimental results agreed with a theoretical model of the two-photon-induced photocurrent generation inside the waveguide.

Electromagnetic mode conversion in photonic crystal multimode waveguides

Abstract: A method for converting electromagnetic (EM) energy between guided modes of a photonic crystal waveguide (800) having a waveguide axis (810), the method including: (i) providing the photonic crystal waveguide (800) with a mode coupling segment (820) comprising at least one bend (830) in the waveguide axis (810), wherein during operation the mode coupling segment (820) converts EM energy in a first guided mode to a second guided mode; (ii) providing EM energy in the first guided mode of the photonic crystal waveguide (800); and (iii) allowing the EM energy in the first guided mode to encounter the mode coupling segment to convert at least some of the EM energy in the first guided mode to EM energy in the second guided mode.

Bandwidth control of long-period grating-based mode converters in few-mode fibers.

Abstract: Control of the group-velocity differences between two distinct modes in a few-mode fiber can be used to define the spectral characteristics of long-period gratings written in them. Using this effect, we report the demonstration of strong mode conversion (>99%) with long-period fiber gratings over what is believed to be a record bandwidth of 63 nm. These novel spectra are obtained from gratings written in specially designed few-mode fibers in which the grating phase-matching condition is satisfied over a large spectral range. We show that the bandwidths of such mode converters can be tailored by suitably altering the design of the few-mode fibers. The polarization-dependent coupling for the mode converters varies by less than 0.004% over the entire spectrum.

Optical junction apparatus and methods employing optical power transverse-transfer

Abstract: An optical apparatus comprises an optical device fabricated on a substrate, an external-transfer optical waveguide fabricated on the substrate and/or on the optical device, and a transmission optical waveguide. The optical device and/or the external-transfer waveguide are adapted for and positioned for transfer of optical power therebetween (end-transfer or transverse-transfer). The external-transfer waveguide and/or the transmission waveguide are adapted for transverse-transfer of optical power therebetween (mode-interference-coupled or adiabatic). The transmission waveguide is initially provided as a component mechanically separate from the substrate, device, and external-transfer waveguide. Assembly of the transmission waveguide with the substrate, device, and/or external-transfer waveguide results in relative positioning of the external-transfer waveguide and the transmission waveguide for enabling transverse-transfer of optical power therebetween. Optical power transfer between the device and the transmission waveguide through the external-transfer waveguide is thereby enabled. The transmission waveguide may preferably comprise a planar waveguide on a waveguide substrate.

Microstructured optical fibers: where's the edge?

Abstract: We establish that Microstructured Optical Fibers (MOFs) have a fundamental mode cutoff, marking the transition between modal confinement and non-confinement, and give insight into the nature of this transition through two asymptotic models that provide a mapping to conventional fibers. A small parameter space region where neither of these asymptotic models holds exists for the fundamental mode but not for the second mode; we show that designs exploiting unique MOF characteristics tend to concentrate in this preferred region.

High performance fused-type mode-selective coupler using elliptical core two-mode fiber at 1550 nm

Abstract: In this letter, we demonstrate a high performance fused-type mode selective coupler that couples the LP/sub 11/ mode in one fiber and the LP/sub 01/ mode in another using highly elliptical core two-mode fibers. The phase-matching condition was achieved by etching and prepulling portions of two-mode fibers. The coupling efficiency and the mode extinction ratio of 56% to 80% and 22-32 dB, respectively, were achieved with high temperature stability over 1515- to 1595-nm wavelength range.

Photonic crystal optical waveguides having tailored dispersion profiles

Abstract: An optical waveguide having a workign mode with a tailored dispersion profile, the waveguide indlucing: (i) a dielectric confinement region surrounding a waveguide axis, the confinement region comprising a photonic crystal having at least one photomic bandgap, wherein during operation the confinement region guides EM radiation in a first range of frequencies to propagate along the waveguide axis; (ii) a dielectric core region extending along the waveguide awis and surrounded by the confinement region about the waveguide axis, wherein the core supports at least one guided mode in the first frequency range; and (iii) a dielectric dispersion tailoring region surrounded bz the confinement region about the waveguide axis, wherein the dispersion tailoring region introduces one or more additional modes in the first range of frequencies that interact with the guided mode to produce the working mode.

Slab-coupled 1.3-μm semiconductor laser with single-spatial large-diameter mode

Abstract: A high brightness semiconductor diode laser structure, which utilizes a slab-coupled optical waveguide region to achieve several potentially important advances in performance, is proposed and experimentally demonstrated using a simple rib waveguide in an InGaAsP-InP quantum-well structure operating at 1.3-/spl mu/m wavelength. These lasers operate in a large low-aspect-ratio lowest-order spatial mode, which can be butt coupled to a single-mode fiber with high coupling efficiency.

Waveguide shape control and loss properties of light-induced self-written (LISW) optical waveguides

Abstract: We show the feasibility of automatic waveguide formation by means of the self-trapping effect of multimode optical fiber irradiation into a photopolymerizing resin. By using a graded-index multimode optical fiber, we experimentally obtained a straight waveguide of over 20 mm in length. It is shown that its growth properties, such as waveguide shape and diameter, depend on the propagation modal distribution along the optical fiber used for the waveguide formation. Moreover, an all-solid polymer optical waveguide that relies on the selective photopolymerization proceeding into the photopolymerizing resin mixture is also demonstrated. We call this type of waveguide a light-induced self-written optical waveguide. The measured propagation loss in the waveguide is 1.0 dB/cm or less for the wavelength range 0.8/spl sim/1.0 /spl mu/m. The proposed technology is capable of eliminating both costly lenses and the need for an alignment system from optical waveguide devices.

Optical waveguide termination with vertical and horizontal mode shaping

Abstract: An optical device is disclosed which includes a single-mode waveguide (700) which supports a first optical mode in a first region and a second optical mode in a second region. The waveguide includes a guiding layer (703) having at least one wing (750) extended outwardly from the guiding layer (703). The guiding layer (703) may desirably have a rib waveguide (706, 707) cross sectional shape at the wings. The wings (750) decrease in width along the length of the guiding layer to convert a rib waveguide mode at the wings to a channel waveguide mode.

Optical coupling structure

Abstract: An object of this invention is to improve coupling efficiency of a silica optical waveguide having a high relative refractive index difference and a single mode optical fiber. A silica optical waveguide (l0) consists of a single mode optical waveguide, and its core (12) is originally a rectangle. A width of the core (12) of the silica optical waveguide (10) is tapered at a predetermined length part (16) connecting to an optical fiber (20). A thickness of the core (12) in the tapered part (16) is constant.

Minimum length of a single-mode fiber spatial filter.

Abstract: Using the concept of leaky modes, we derive the minimum length of a single-mode fiber required to act as a spatial-mode filter of given quality. The degree of filter action is defined by the ratio of power carried by the fundamental mode to that carried by the leaky modes.

Asymmetric waveguide electroabsorption-modulated laser

Abstract: A modulated laser device (110) comprising two or more vertically stacked asymmetric waveguides (114,116) is provided The laser device (110) comprises a first waveguide (114) having a gain region formed therein for amplifying at least a first mode of light, and a second waveguide (116) vertically coupled to the first waveguide (114) and having a modulator (106) formed therein for modulating a second mode of light having an effective index of refraction different from the first mode Light propagating in the first waveguide (114) is transferred into the second waveguide (116) via a lateral taper in the first waveguide (114) The laser device (110) may further comprise a third waveguide positioned between the first (114) and second waveguide (116) for providing isolation between the gain region (104) and modulator (106) Distributed bragg reflector (DBR) and distributed feedback (DFB) laser designs may be employed in the device

Geometric variations in high index-contrast waveguides, coupled mode theory in curvilinear coordinates.

Abstract: Perturbation theory formulation of Maxwell’s equations gives a theoretically elegant and computationally efficient way of describing small imperfections and weak interactions in electro-magnetic systems. It is generally appreciated that due to the discontinuous field boundary conditions in the systems employing high dielectric contrast profiles standard perturbation formulations fail when applied to the problem of shifted material boundaries. In this paper we developed a novel coupled mode and perturbation theory formulations for treating generic non-uniform (varying along the direction of propagation) perturbations of a waveguide cross-section based on Hamiltonian formulation of Maxwell equations in curvilinear coordinates. We show that our formulation is accurate and rapidly converges to an exact result when used in a coupled mode theory framework even for the high index-contrast discontinuous dielectric profiles. Among others, our formulation allows for an efficient numerical evaluation of induced PMD due to a generic distortion of a waveguide profile, analysis of mode filters, mode converters and other optical elements such as strong Bragg gratings, tapers, bends etc., and arbitrary combinations of thereof. To our knowledge, this is the first time perturbation and coupled mode theories are developed to deal with arbitrary non-uniform profile variations in high index-contrast waveguides.

Dispersion shifted optical waveguide fiber

Abstract: A single mode optical waveguide fiber designed for high data rate, or WDM systems or systems incorporating optical amplifiers. The optical waveguide has a compound core having a central region and at least one annular region surrounding the central region. A distinguishing feature of the waveguide core is that the minimum refractive index of the central core region is less than the minimum index of the adjacent annular region. A relatively simple profile design has the characteristics of ease in manufacturing together with, flexibility in tailoring D w to yield a preselected zero dispersion wavelength, dispersion magnitude over a target wavelength range, and dispersion slope. The simplicity of profile gives reduced polarization mode dispersion.

Optical waveguide element and method of fabrication thereof

Abstract: A ridge type channel optical waveguide is formed in an optical waveguide layer. A cladding layer having a refractive index smaller than that of the optical waveguide layer and having a width substantially the same as that of the channel optical waveguide and having a thickness which increases in a tapered manner toward an end surface, is formed above both of a light entering end portion and a light exiting end portion of the channel optical waveguide. By the cladding layer, a mode field diameter in a direction orthogonal to a substrate surface can be enlarged, and a coupling loss with an optical fiber can be greatly reduced. Further, loss due to mode mismatching can be prevented by a light confining effect.

Optical waveguide circuit including multiple passive optical waveguide devices, and method of making same

Abstract: An optical waveguide device includes a first passive optical waveguide device and a second passive optical waveguide device. The first passive optical waveguide device is etched, at least in part, in a semiconductor layer of a wafer. The value and position of an effective mode index within the first passive optical waveguide device remains substantially unchanged over time. The second passive optical waveguide device is formed at least in part from a polysilicon layer deposited above an unetched portion of the semiconductor layer. The effective mode index of a region of static effective mode index within the optical waveguide is created by the polysilicon layer of the second passive optical waveguide device. The value and position of the effective mode index within the region of static effective mode index remains substantially unchanged over time. The optical waveguide forms at least a part of both the first passive optical waveguide device and the second passive optical waveguide device. The optical waveguide couples the first passive optical waveguide device and the second passive optical waveguide device, and the optical waveguide is formed at least in part using the semiconductor layer.

Integration of electro-optic polymer modulators with low-loss fluorinated polymer waveguides.

Abstract: We have demonstrated a hybrid Mach–Zehnder optical modulator consisting of a large-core, low-loss fluorinated passive polymer waveguide and an electro-optic (EO) polymer waveguide. The combination exhibits low fiber coupling loss to the passive waveguide and reduced transmission loss because the EO polymer waveguide is used only in the active region. The two waveguides are connected by vertical tapers that permit low-loss adiabatic coupling between the two modes. The half-wave voltage and the insertion loss of the fabricated modulator are 3.6 V and 6 dB, respectively, at a wavelength of 1.55 µm. The estimated coupling loss with the standard single-mode fiber is ∼0.5 dB.

High efficiency optical mode transformer for matching a single mode fiber to a high index contrast planar waveguide

Abstract: The present invention includes a device and a method for fabricating a device that is an optical power mode transformer that accepts light in a mode transformation direction where the transformer is attached to or embedded in a semiconductor microchip and includes a first single or multimode optical input (SM) waveguide including a first core surrounded by a cladding, and, a second high contrast index grade (HC) waveguide including a second core having a tapered region and surrounded by said cladding, a portion of the tapered region of the core being embedded within the first optical input waveguide region with an embedded length sufficient for efficient light transfer from the first input waveguide to the said second waveguide wherein the embedded portion of the tapered region is fully surrounded by the first input waveguide along an axial and radial cross-section of the second waveguide in the mode transformation direction. In this manner, it is possible that the long (SM) waveguide eventually actually acts as a cladding for the (HC) waveguide.

Optical waveguide sensor, device, system and method for glucose measurement

Abstract: An optical waveguide sensor for glucose measurement comprises a substrate, a first optical waveguide layer formed on a surface of the substrate, an entrance grating and an exit grating which are formed contacting with the first optical waveguide layer and being spaced from each other, a second optical waveguide layer located between the entrance grating and the exit grating while being in contact with the first optical waveguide layer, the second optical waveguide layer having a higher refractive index that that of the first optical waveguide layer, and a functioning layer containing an enzyme and a coloring reagent which is formed on the second optical waveguide layer.

Dynamic wavelength-selective grating modulator

Abstract: Techniques and devices for modulating an optical signal transmitting through an optical waveguide such as a fiber and a planar waveguide by dynamically controlling an adjustable grating formed in a cladding layer of the waveguide.

Improved transmission characteristics of moderate refractive index contrast photonic crystal slabs

Abstract: Finite two-dimensional (2D)-photonic crystal slab waveguide structures from moderate refractive index materials have been investigated theoretically and results were compared with experimental data. 3D-finite difference time domain (3D-FDTD) simulations reveal a strong dependence of the transmission on the etching depth. For structures with etching depths less than the waveguide core thickness, both a substantial leakage of optical power to the substrate and a spatial mismatch of the transmitted field to the waveguide mode were found, leading to unsatisfactory transmissions. These losses occur mainly on the airband side of the spectrum where the optical field is concentrated in the holes. However, hole depths extending into the substrate by only 0.5 μm lead to an almost perfect mode match at transmission values exceeding 90%.

Large diameter D-shaped optical waveguide and coupler

Abstract: A large diameter D-shaped optical waveguide device 9 , includes an optional circular waveguide portion 11 and a D-shaped waveguide portion 10 having at least one core 12 surrounded by a cladding 14 . A portion of the waveguide device 9 has a generally D-shaped cross-section and has transverse waveguide dimension d 2 greater than about 0.3 mm. At least one Bragg grating 16 may be impressed in the waveguide 10 and/or more than one grating or pair of gratings may be used and more than one core may be used. The device 9 provides a sturdy waveguide platform for coupling light into and out of waveguides and for attachment and alignment to other waveguides, for single and multi-core applications. The core and/or cladding 12,14 may be doped with a rare-earth dopant and/or may be photosensitive. At least a portion of the core 12 may be doped between a pair of gratings 50,52 to form a fiber laser or the grating 16 or may be constructed as a tunable DFB fiber laser or an interactive fiber laser within the waveguide 10. The waveguide may resemble a short “block” or a longer “cane” type, depending on the application and dimensions used.

Analysis of general geometric scaling perturbations in a transmitting waveguide: fundamental connection between polarization-mode dispersion and group-velocity dispersion

Abstract: We develop a novel perturbation theory formulation to evaluate polarization-mode dispersion (PMD) for a general class of scaling perturbations of a waveguide profile based on generalized Hermitian Hamiltonian formulation of Maxwell’s equations. Such perturbations include elipticity and uniform scaling of a fiber cross section, as well as changes in the horizontal or vertical sizes of a planar waveguide. Our theory is valid even for discontinuous high-index contrast variations of the refractive index across a waveguide cross section. We establish that, if at some frequencies a particular mode behaves like pure TE or TM polarized mode (polarization is judged by the relative amounts of the electric and magnetic longitudinal energies in the waveguide cross section), then at such frequencies for fibers under elliptical deformation its PMD as defined by an intermode dispersion parameter t becomes proportional to group-velocity dispersion D such that t 5 lduDu, where d is a measure of the fiber elipticity and l is a wavelength of operation. As an example, we investigate a relation between PMD and group-velocity dispersion of a multiple-core step-index fiber as a function of the core‐clad index contrast. We establish that in this case the positions of the maximum PMD and maximum absolute value of group-velocity dispersion are strongly correlated, with the ratio of PMD to group-velocity dispersion being proportional to the core‐clad dielectric contrast. © 2002 Optical Society of America OCIS codes: 060.2310, 060.2400, 060.2280, 060.0060.

Kerr-stabilized super-resonant modes in coupled-resonator optical waveguides.

Abstract: We investigate the effects of the optical Kerr nonlinearity in a coupled-resonator optical waveguide (CROW). Under certain conditions, there exists a stationary spatial distribution of the field whose envelope does not change with time-a super-resonant mode. The analysis does not indicate the existence of traveling hyperbolic-secant solitons of the Schrodinger type.

Propagation losses of the fundamental mode in a single line-defect photonic crystal waveguide on an InP membrane

Abstract: We have investigated light propagation through a single line-defect photonic crystal waveguide on a InP membrane. Modal analysis was performed using the finite-difference time-domain method. The fundamental mode has been found to be very close to the fundamental mode in a “refractive” waveguide but, in this case, it is inherently leaky. The propagation losses of this mode in the complete three-dimensional structure have been computed and measured to determine if its use could be of interest for practical applications. Propagation losses in the range of 0.1 dB/μm have been found numerically and experimentally for the fundamental mode whereas stronger out-of-plane losses have been observed for the other leaky mode within the band gap. The origins of the out-of-plane losses were then investigated and have clarified the inherent lower leakage of the fundamental mode.

Selective guided mode coupling via bridging mode by integrated gratings for intraboard optical interconnects

Abstract: Growing attention is paid to intraboard optical interconnects among multichip modules because of its potential to solve so-called pin bottleneck problem in constructing ultrahigh speed information processing unit. Vertical integration of waveguides and their coupling as well as input/output coupling of guided waves from/to free- space waves are key issues. Three types of high performance coupling via bridging modes by integrated gratings are reviewed. Use of radiation mode as bridging mode is discussed with advantage of selective coupling between two waveguides among multistory structure. Three waveguides were integrated with grating couplers, and wavelength-division demultiplexing with 5 nm separation and 0.5 nm selectivity from one waveguide to two other waveguides was demonstrated. Utilization of supermode as bridging mode is shown for optical add/drop multiplexing (OADM) function between two waveguides. Device was designed to have high power transfer efficiency of almost 100% with high wavelength selectivity of 2 nm, while preliminary experimental results were 40% efficiency with 1 nm selectivity. OADM between guided wave and free-space wave is also discussed with utilization of supermode. Power transfer efficiency of 25% with wavelength selectivity of 4 nm was obtained in coupling of guided wave to free-space wave, while theoretically predicted efficiency was 70% with 2 nm selectivity.

Polarization-engineered transverse-optical-coupling apparatus and methods

Abstract: An optical signal may be received into orthogonal linearly polarized modes of a transmission optical waveguide, the transmission waveguide including first and second transverse-coupling segments thereof. Optical signal polarized along one polarization direction may be substantially completely transferred from the transmission waveguide into a first transverse-coupled waveguide, the first transverse-coupled waveguide being optically transverse-coupled to the first transverse-coupling segment of the transmission waveguide. Optical signal polarized along the other polarization direction may be substantially completely transferred from the transmission waveguide into a second transverse-coupled waveguide, the second transverse-coupled waveguide being optically transverse-coupled to the second transverse-coupling segment of the transmission waveguide. The optical signals carried by the first and second transverse-coupled waveguides may be combined into a single waveguide. The polarization directions of the transmission waveguide may be rotated about 90° between the first and second transverse-coupling segments.

Wavelength monitoring optical fibers using detection in the near field

Abstract: The specification describes a wavelength monitoring system for multiple wavelength communications systems, such as WDM systems, based on the recognition that the mechanism for spatially separating the individual wavelength bands can be achieved within the optical fiber itself. Individual wavelength bands are separated using a series of discrete gratings spaced longitudinally along the fiber core. The wavelength bands are extracted from the fiber core by converting the energy in the selected band from a core-guided mode to a radiation mode. By using a tilted grating, the light in the radiation mode is directed through the cladding and out of the fiber. Spatial resolution of the selected bands can be any desired physical length. An important implication of this is that detection can be made in the near field using inexpensive detecting apparatus. Near field is defined for convenience in this case as the optical field of the radiated energy without any optically modifying elements (collimating devices, diffraction elements, mirrors, etc.). This eliminates nearly all of the optics, and the attendant expense, in prior art monitoring systems.