Showing papers on "Radiation mode published in 2000"

An All-Dielectric Coaxial Waveguide.

Abstract: An all-dielectric coaxial waveguide that can overcome problems of polarization rotation and pulse broadening in the transmission of optical light is presented here. It consists of a coaxial waveguiding region with a low index of refraction, bounded by two cylindrical, dielectric, multilayer, omnidirectional reflecting mirrors. The waveguide can be designed to support a single mode whose properties are very similar to the unique transverse electromagnetic mode of a traditional metallic coaxial cable. The new mode has radial symmetry and a point of zero dispersion. Moreover, because the light is not confined by total internal reflection, the waveguide can guide light around very sharp corners.

Lightwave propagation through a 120° sharply bent single-line-defect photonic crystal waveguide

Abstract: We have demonstrated 1.55 μm wavelength lightwave propagation through a 120° sharply bent waveguide formed in a triangular-lattice two-dimensional photonic crystal (2D PC). Such propagation has not previously been experimentally confirmed. The photonic crystal was fabricated in a silicon-on-insulator (SOI) wafer with the top silicon layer of the wafer used as a core layer. A 877-μm-long single-line-defect waveguide was formed in the PC with a sharp 120° bend near the middle of the waveguide. A tapered-hemispherical-end fiber was coupled to the input end of the waveguide for the light input, and the output from the other end of the waveguide was directly observed by scanning its near-field profile with another tapered-hemispherical-end fiber.

Single-mode waveguide propagation and reshaping of sub-ps terahertz pulses in sapphire fibers

Abstract: Waveguide propagation of sub-ps terahertz pulses in single-crystal sapphire fibers is reported. An incident THz pulse of approximately 0.6 ps duration undergoes considerable reshaping due to the absorptive and dispersive waveguide propagation, resulting in transmitted chirped pulse durations of 10–30 ps. Good agreement between theory and experiment is obtained by analyzing the propagation in terms of the single HE11 waveguide mode. The dominance of the single HE11 mode, despite the fiber dimensions allowing for multimode propagation, is attributed to the free-space to waveguide coupling.

Optical bend sensor based on measurement of resonance mode splitting of long-period fiber grating

Abstract: We report an effective new method of realizing optical bend sensing based on the measurement of bending-curvature encoded resonance mode splitting of long-period fiber grating. The bending induced mode splitting exhibits a near-linear response and the bending sensitivity achieved by this method is nearly four times higher than the previously reported wavelength shift detection method. The evolution of the transmission loss under bending appears dependent on the initial mode coupling strength.

Coupling system to a microsphere cavity

Abstract: A system of coupling optical energy in a waveguide mode, into a resonator that operates in a whispering gallery mode. A first part of the operation uses a fiber in its waveguide mode to couple information into a resonator e.g. a microsphere. The fiber is cleaved at an angle Φ which causes total internal reflection within the fiber. The energy in the fiber then forms an evanescent field and a microsphere is placed in the area of the evanescent field. If the microsphere resonance is resonant with energy in the fiber, then the information in the fiber is effectively transferred to the microsphere.

Single mode optical fiber coupling systems

Abstract: Coupling devices (90, 140) for coupling a lens (8, 30, 72, 96) to a single mode optical fiber (4, 104, 144, 184) are disclosed. The lens assembly is the coupling device and includes a single mode optical fiber (4, 104, 144, 184), a lens (8, 30, 72, 96), and a locating tube (6, 114, 182).

Investigation of mode coupling in step index plastic optical fibers using the power flow equation

Abstract: Using the power flow equation, we have examined the mode coupling caused by intrinsic perturbation effects of the step index plastic optical fiber. A numerical solution has been obtained by the explicit finite difference method. Results show the state of mode coupling along the fiber. They indicate that the equilibrium mode distribution is achieved at much shorter lengths compared to the case with glass fibers.

Mode gaps in the refractive index properties of low-dose ion-implanted LiNbO3 waveguides

Abstract: Data are presented for the refractive index profiles for low-dose He+ ion-implanted LiNbO3 waveguides. In the nuclear stopping region, the extraordinary index is increased for low ion doses, by contrast with index reduction normally associated with ion-implanted waveguiding structures. The index increase was confirmed by fabricating a buried waveguide for the extraordinary index by use of multi-energy implants. For single-energy implants, data are shown which map the extraordinary index at the surface together with that in the nuclear collision zone, as a function of angle relative to the z axis of light propagation in surface waveguides for X and Y cut LiNbO3. These indices cross over near 45°, which results in a mode gap for which waveguide modes are not supported. A mechanism for this behavior is discussed based on defect-induced lattice relaxation. The phenomenon of a controlled mode gap may have applicability for optoelectronic and nonlinear materials and devices.

Method of forming a tapered section in a semiconductor device to provide for reproducible mode profile of the output beam

Abstract: A method for fabricating a high power laser diode device with an output emission with a nearly circular mode profile for efficient coupling into an optical fiber. A vertical taper waveguide and a window tolerance region are formed in a base structure of the device employing successive etching steps. Further regrowth completes the device structure. The resultant laser device has a vertical and lateral tapered waveguide that adiabatically transforms the highly elliptical mode profile in an active gain section of the device into a substantially circular mode profile in a passive waveguide section of the device.

Optical waveguide illuminator

Abstract: Methods and apparatus for producing an optical waveguide illuminator are disclosed. By controlling the propagation of light in the core and cladding regions of the waveguide, distributed light emission along a length of an optical fiber or along a planar waveguide surface can be achieved by varying the core/cladding refractive index ratio and introducing light scattering centers in the core.

High order spatial mode optical fiber

Abstract: The invention relates to method and apparatus for transmitting an optical signal having optical energy substantially in a high order spatial mode. The optical waveguide, in one embodiment, includes a few mode fiber designed to have specific transmission characteristics for supporting the single high order spatial mode, and the few mode fiber transmits the single high order spatial mode. The optical waveguide, in one embodiment, has a dispersion and a dispersion slope for a given transmission bandwidth. Another aspect of the invention includes a method for transmitting an optical signal having optical energy substantially in a single high order spatial mode. The method includes the steps of providing a few mode fiber, which supports optical energy in the single high order spatial mode. In one embodiment, the single high order spatial mode is the LP 02 spatial mode In another embodiment, the few mode fiber supports an optical signal having optical energy having less than twenty spatial modes.

Microsphere resonator mode characterization by pedestal anti-resonant reflecting waveguide coupler

Abstract: The stripline pedestal anti-resonant reflecting optical waveguide (SPARROW) is an efficient and robust coupling device for silica microsphere whispering-gallery-mode excitation. The concept incorporates alternating layers of Si and SiO/sub 2/, designed to isolate the mode of the sphere and the waveguide from the dielectric substrate. Experimental characterizations of this coupling technique are presented, including displacement measurements, and whispering-gallery-mode intensity mapping. Power extraction efficiencies of over 98% are reported.

Large diameter optical waveguide, grating, and laser

Abstract: A large diameter optical waveguide, grating, and laser includes a waveguide having at least one core surrounded by a cladding, the core propagating light in substantially a few transverse spatial modes; and having an outer waveguide dimension of said waveguide being greater than about 0.3 mm. At least one Bragg grating may be impressed in the waveguide. The waveguide may be axially compressed which causes the length of the waveguide to decrease without buckling. The waveguide may be used for any application where a waveguide needs to be compression tuned. Also, the waveguide exhibits lower mode coupling from the core to the cladding and allows for higher optical power to be used when writing gratings without damaging the waveguide. The waveguide may resemble a short “block” or a longer “cane” type, depending on the application and dimensions used.

Optical mode structure of the plasma waveguide

Abstract: The quasibound modes of an evolving plasma waveguide were investigated by using variably delayed end-injected and side-injected probe pulses. The use of these different coupling geometries allowed the probing of the waveguide's optical modes during two temporal regimes: early-time plasma channel development, characterized by leaky optical confinement, and later channel hydrodynamic expansion characterized by stronger confinement. The wave equation was solved to determine the available quasiguided optical modes and their confinement for experimentally measured electron density profiles. The guided intensity patterns and spectra measured at the waveguide exit were successfully explained in terms of these mode solutions. The spectrum of broadband end-coupled probe pulses was found to be unaffected by the guiding process, mainly because those modes which survived to the waveguide exit were well-bound, and for strongly bound fields, the transverse mode profiles are wavelength independent. By contrast, side coupling to the quasibound modes of the plasma waveguide was seen to be highly mode and frequency selective.

Strain free planar optical waveguides

Abstract: The present invention is directed to a planar optical waveguide comprising a waveguide core layer interposed between upper and lower cladding layers, characterized in that a so-called “effective” coefficient of thermal expansion of the layer containing the waveguide core is approximately the same as that of the substrate supporting the optical waveguide.

Planar waveguides with high refractive index

Abstract: A planar optical component having a relatively high refractive index waveguide that is capable of being coupled to a standard optical fiber or other standard optical waveguide having a relatively low refractive index waveguide exhibits reduced loss of signal as compared with conventional planar optical components having a high refractive index waveguides. The component includes a waveguide which includes a first waveguide segment having a core material with a first refractive index, a second waveguide segment having a core material with a second refractive index, and a transition waveguide segment between the first and second waveguide segments. The transition waveguide segment includes a core material with the first refractive index and a core material with the second refractive index. The first and second core materials have an interface that is sloped or tapered at an acute angle relative to the direction that the light is propagated through the waveguide to reduce reflective losses between the core materials having different refractive indices. The first waveguide segment can be fabricated to have geometric and optical properties that closely match those of a standard optical fiber, thereby reducing loss of signal at the interface between an optical fiber and the component.

An optical switch having a planar waveguide and a shutter actuator

Abstract: An optical switch having an input waveguide and two output waveguides separated by and disposed around a trench. The input waveguide and a first output waveguide have respective optical paths defined by their respective cores; those optical paths (and cores) being coaxial with each other. Those waveguides are also separated by a trench having a medium provided therein that has a refractive index different from that of the waveguides. The input waveguide and first output waveguide are separated by a distance defined by the trench and that is insufficient to affect the transmission characteristics of an optical signal propagating from the input waveguide to the first output waveguide, even though the optical signal experiences different refractive indices as it propagates across the trench from the input waveguide to the first output waveguide. The input waveguide and a second output waveguide are arranged generally on the same side of the trench such that an optical signal passing from the input waveguide to the second output waveguide does not completely traverse the trench. Thus, even though an optical signal passing from the input waveguide to either of the first or second output waveguide encounters different refractive indices, the distance over which the optical signal must travel between the waveguides is small enough so as to not affect the optical transmission characteristics of that signal.

Dispersion compensating module and mode converter, coupler and dispersion compensating optical waveguide therein

Abstract: A dispersion compensating module, mode converter, coupler and dispersion compensated optical fiber therein. The dispersion compensating fiber has a plurality of core segments, the refractive index profile being selected to exhibit properties such that an LP02 mode at 1550 nm may be propagated a distance (generally 0.5-3.0 km), upon conversion to LP02, to compensate for dispersion of a length of transmission waveguide preferably greater than 25 km propagating in an LP01 mode. In another embodiment, the dispersion compensating module has a mode converter having a reflective fiber grating for converting a first to a second mode interconnected to a dispersion compensated fiber propagating in the second mode. The mode converter has a coupler adapted to operatively couple light propagating in a first mode from a first fiber into a second, and a reflective fiber grating operatively coupled to the second fiber; the grating being capable of converting light from the first into the second mode. According to another embodiment, an optical fiber coupler is provided having a first fiber with a first propagation constant in a first mode, and a second fiber within the coupler having a second propagation constant, the second fiber including a necked-down portion which is formed prior to fusion of the fibers, the necked-down portion being formed such that the local propagation constant of the second fiber substantially matches the first propagation constant thereby enhancing first mode coupling.

Optical waveguide wavelength filter with ring resonator and 1xn optical waveguide wavelength filter

Abstract: A novel optical waveguide wavelength filter with a ring resonator (3) in which an ADD/DROP operation between an input-side optical waveguide (1) and an output-side optical waveguide (2) through the ring resonator (3) is performed, wherein the input-side optical waveguide (1) intersects the output-side optical waveguide (2), and the ring resonator (3) is superposed on the input- and output-side optical waveguides (1, 2), whereby a 1xN optical waveguide wavelength filter is easily realized. A 1xN optical waveguide wavelength filter composed of such an optical waveguide wavelength filter, having a small size, and having an excellent filter response is also disclosed.

Vertically tapered polymer waveguide mode size transformer for improved fiber coupling

Abstract: We describe a novel vertical taper structure fabricated at the ends of polymer optical waveguide devices to improve the coupling be- tween channel waveguides and single mode fibers. The taper smoothly converts a highly elliptical waveguide mode into a large and more circu- lar mode for low loss coupling and relaxed fiber alignment tolerances. A vertical taper 0.5 to 2 mm in length is made in the upper cladding to reduce its thickness from a few micrometers to zero. The taper is sub- sequently covered by an upper cladding. The new upper cladding has an index higher than that of the previous upper cladding but slightly lower than that of waveguide core. In the taper, the channel waveguide mode gradually loses confinement by the upper cladding so that the mode size grows larger as light propagates toward the end of the device, whereas the confinement by the lower cladding and the lateral confinement are not significantly affected. The waveguide mode grows upward away from the lossy ground electrode and substrate commonly found in many poly- mer devices; therefore, no trade-off between mode size and propagation loss is involved. Two special but simple reactive ion etching techniques, shadow masked etching and etching with a tapered photoresist mask, are developed to make the vertical taper. Mode expansion and a 1.8 dB reduction in coupling loss per tapered end are demonstrated experimen- tally. The performance of the mode size transformer is found to be in- sensitive to both waveguide width and polarization. © 2000 Society of Photo- Optical Instrumentation Engineers. (S0091-3286(00)01206-X)

Optical waveguide having a weakly-confining waveguide section and a strongly-confining waveguide section optically coupled by a tapered neck

Abstract: An optical waveguide includes a first waveguide section (5) providing weak confinement of an optical signal in a direction generally transverse to its propagation direction, a second waveguide section (7) providing strong confinement of the optical signal in all directions relative to the propagation direction, a tapered neck (3) between the first and second waveguide sections to optically couple those waveguide sections, and a core defined through the first and second waveguide sections and tapered neck, and through which the optical signal may propagate in the propagation direction. A method for making such an optical waveguide.

OPTICAL WAVEGUIDE HAVING NEGATIVE DISPERSION AND LARGE A eff

Abstract: The invention is directed to a single mode optical waveguide fiber profile (18, 20, 22, 24) that provides relatively large effective area while limiting macrobend loss. The large effective area results from configuring the core of the waveguide fiber to shift propagated light power away from the waveguide center. Macrobend loss, as measured by pin array or 20 mm mandrel testing, is maintained low by means of a power-limiting index depression (24) surrounding the central core region of the waveguide. In addition, low attenuation is achieved and cut off wavelength is controlled to provide a telecommunications operating window in the wavelength range of about 1250 nm to 1700 nm.

Multimode optical fiber having function to remove higher order mode

Abstract: PROBLEM TO BE SOLVED: To obtain an optical fiber having a large effective core area, low loss, small absolute value of dispersion and small bending loss susceptibility by controlling the difference in the propagation constant between the lowest mode and the second-order mode to be twice or more of the difference in the propagation constant between adjacent modes of higher-order modes. SOLUTION: The distribution structure of the refractive index is designed in such a manner that when light signal enters, three or more modes of linearly polarized waves are present as the propagation modes. In this state, the difference in the propagation constant between LP01 mode and LP11 mode is specified to be twice or more, preferably three times or more, of the difference in the propagation constant of the LP11 mode or higher-order mode and the adjacent higher mode. As a result, this structure enables such an arrangement of modes that only the LP11 mode or higher-order modes are coupled to the crack mode and that only the LP01 mode substantially propagates after the light propagates at a proper distance. If the difference is less than twice, proper attenuation for only the higher-order modes is impossible and a single mode transmission is made difficult.

Waveguide grating device and method of controlling Bragg wavelength of waveguide grating

Abstract: A waveguide grating device controlling Bragg wavelength after manufacture of the device includes an optical waveguide on a substrate. A variable stress is applied to a waveguide grating in part of the waveguide to bend at least the portion of the substrate including the waveguide grating, changing the Bragg wavelength.

Analysis of core-mode to radiation-mode coupling in fiber Bragg gratings with finite cladding radius

Abstract: Fiber Bragg gratings (FBGs) are often surrounded with dielectric material whose refractive index is higher than that of cladding. The purpose is to prevent cladding modes because coupling to cladding modes may cause undesirable dips on the short wavelength side of the main Bragg band in the core-mode transmission spectrum. In such FBGs, core-mode to radiation-mode coupling can cause a loss band continuum. Until now, however, reported analyses of this core-mode to radiation-mode coupling have been limited to hypothetical FBGs with an infinite cladding radius. This paper presents, to the best of our knowledge, the first analysis of core-mode to radiation-mode coupling in real FBGs with a finite cladding radius. We derive a formula to calculate the core-mode transmission loss caused by the radiation-mode coupling. We show calculated core-mode transmission spectra that exhibit such fringes as have already been observed experimentally but not yet theoretically estimated.

Distributed resonant ring fiber filter

Abstract: Disclosed is a fiber optic filter that includes a central core (19), a ring core (20) concentric with the central core (19), an inner cladding region (21) of refractive index ni, and a cladding layer (22) of refractive index nc surrounding the ring core (20). The maximum refractive index n1 of the central core (19) and the maximum refractive index n2 of the ring core (20), are greater than nc and n1. At least at one wavelengths, power transfers between the two cores at (19 and 20). At least a portion of the filter (10) is wound around a reel (18) which determines the attenuation.

Single transverse mode selectively oxidized vertical cavity lasers

Abstract: Vertical cavity surface emitting lasers (VCSELs) which operate in multiple transverse optical modes have been rapidly adopted into present data communication applications which rely on multi-mode optical fiber. However, operation only in the fundamental mode is required for free space interconnects and numerous other emerging VCSEL applications. Two device design strategies for obtaining single mode lasing in VCSELs based on mode selective loss or mode selective gain are reviewed and compared. Mode discrimination is attained with the use of a thick tapered oxide aperture positioned at a longitudinal field null. Mode selective gain is achieved by defining a gain aperture within the VCSEL active region to preferentially support the fundamental mode. VCSELs which exhibit greater than 3 mW of single mode output power at 850 nm with mode suppression ratio greater than 30 dB are reported.

High order spatial mode transmission system

Abstract: The invention relates to methods and apparatus for transmitting an optical signal having optical energy. The system, in one embodiment, includes at least one transmission span including an optical waveguide. The transmission span transmits substantially all of the optical energy in a single high order spatial mode. The optical waveguide, in one embodiment, has a dispersion and a dispersion slope for a given transmission bandwidth. In another embodiment, the invention further relates to an optical transmission system which includes a spatial mode transformer positioned to receive an optical signal. The spatial mode transformer transform the optical energy of the optical signal from a low order spatial mode to a high order spatial mode. The system further includes an optical transmission waveguide in optical communication with a spatial mode transformer, and the optical transmission waveguide transmits substantially all of the optical energy in the high order spatial mode. Another aspect of the invention relates to a method for transmitting an optical signal having optical energy substantially in a single high order spatial mode. The method includes the steps of receiving the optical signal having optical energy in the single high order spatial mode, and transmitting the optical signal having optical energy in the single high order spatial mode through a transmission span. The transmission span includes an optical waveguide.

Structure for connecting optical waveguide

Abstract: PROBLEM TO BE SOLVED: To provide an optical waveguide connection structure that enables reduction in connection loss between optical waveguides of a different spot size in the waveguide mode, as well as reduction in reflection attenuation, that requires no high accuracy in a connecting device or operation, and that is easily manufactured by manufacturing process technology of an integrated circuit. SOLUTION: The optical waveguide connecting structure is for optically connecting, a first optical waveguide (a) having a first core 3 guiding/ transmitting light and a clad 2, whose refractive index is smaller than that of the first core, with a second optical waveguide (b), having a second core 4 that has a refractive index larger than that of the first core of the first optical waveguide. In the second core of the second optical waveguide, a tapered part 7 is formed, of which the dimension in the width direction diminishes toward the end of the second waveguide, while the cross sectional height is maintained in the longitudinal direction, and the first core of the first optical waveguide and the tapered part in the second core of the second optical waveguide are arranged so as to be optically closed to each other in a state with them being contacted or parallel with each other longitudinally.