Showing papers on "Radiation mode published in 2003"

Nanotaper for compact mode conversion.

Abstract: We propose and demonstrate an efficient coupler for compact mode conversion between a fiber and a submicrometer waveguide. The coupler is composed of high-index-contrast materials and is based on a short taper with a nanometer-sized tip. We show that the micrometer-long silicon-on-insulator-based nanotaper coupler is able to efficiently convert both the mode field profile and the effective index, with a total length as short as 40 microm. We measure an enhancement of the coupling efficiency between an optical fiber and a waveguide by 1 order of magnitude due to the coupler.

Terahertz quantum-cascade laser at λ≈100 μm using metal waveguide for mode confinement

Abstract: We report lasing at ∼3.0 THz (λ≈98–102 μm) in a quantum-cascade structure in which mode confinement is provided by a double-sided metal waveguide. The depopulation mechanism is based on resonant phonon scattering, as in our previous work. Lasing takes place in pulsed mode up to a heat-sink temperature of 77 K. The waveguide consists of metallic films placed above and below the 10-μm-thick multiple-quantum-well gain region, which gives low losses and a modal confinement factor of nearly unity. Fabrication takes place via low-temperature metallic wafer bonding and subsequent substrate removal using selective etching. This type of waveguide is expected to be increasingly advantageous at even longer wavelengths.

Improved large-mode-area endlessly single-mode photonic crystal fibers

Abstract: We numerically study the possibilities for improved large-mode-area endlessly single-mode photonic crystal fibers for use in high-power delivery applications. By carefully choosing the optimal hole diameter, we find that a triangular core formed by three missing neighboring air holes considerably improves the mode area and loss properties compared with the case with a core formed by one missing air hole. In a realized fiber we demonstrate an enhancement of the mode area by ∼30% without a corresponding increase in the attenuation.

RF module and mode converting structure and method

Abstract: The present invention is directed to enable mode conversion between a TEM mode and another mode to be performed among a plurality of waveguides. An RF module comprises: a microstrip line as a first waveguide for propagating electromagnetic waves in a TEM mode; and a waveguide having a multilayer structure as a second waveguide connected to the first waveguide, for propagating electromagnetic waves in another mode different from the TEM mode. An end of the first waveguide is directly or indirectly connected so as to be conductive to one of ground electrodes of the second waveguide from the direction orthogonal to the stacking direction of the ground electrodes. Since magnetic fields are coupled so that the direction of the magnetic field of the first waveguide and that of the magnetic field of the second waveguide match with each other in the E plane, mode conversion between the TEM mode and another mode to be excellently performed between the waveguides.

Properties of a hollow-core photonic bandgap fiber at 850 nm wavelength.

Abstract: We describe a hollow-core photonic bandgap fiber designed for use in the 850 nm wavelength region. The fiber has a minimum attenuation of 180dB/km at 847nm wavelength. The low-loss mode has a quasi- Gaussian intensity profile. The group-velocity dispersion of this mode passes through zero around 830nm, and is anomalous for longer wavelengths. The polarization beat length varies from 4 mm to 13 mm across the band gap. We expect this fiber to be useful for delivery of high-energy ultrashort optical pulses.

RF module using mode converting structure having short-circuiting waveguides and connecting windows

Abstract: The present invention is directed to enable mode conversion between a TEM mode and another mode to be performed among a plurality of waveguides. An RF module comprises: a TEM waveguide as a first waveguide for propagating electromagnetic waves in a TEM mode; and a waveguide having a multilayer structure as a second waveguide connected to the first waveguide, for propagating electromagnetic waves in another mode different from the TEM mode. An end of the first waveguide is directly conductively connected to one of ground electrodes of the second waveguide from the stacking direction side of the ground electrodes. Since magnetic fields are coupled so that the direction of the magnetic field of the first waveguide and that of the magnetic field of the second waveguide match with each other in the H plane, mode conversion between the TEM mode and another mode can be excellently performed between the waveguides.

Analysis of mode structure in hollow dielectric waveguide fibers

Abstract: In this paper, we analyze the electromagnetic mode structure of an OmniGuide fiber\char22{}a hollow dielectric waveguide in which light is confined by a large index-contrast omnidirectional dielectric mirror. In particular, we find that the modes in an OmniGuide fiber are similar to those in a hollow metallic waveguide in their symmetries, cutoff frequencies, and dispersion relations. We show that the differences can be predicted by a model based on a single parameter\char22{}the phase shift upon reflection from the dielectric mirror. The analogy to the metal waveguide extends to the transmission properties, resulting in the identification of the ${\mathrm{TE}}_{01}$ mode as the lowest-loss mode of the OmniGuide fiber.

Photonic crystal fiber design based on the V-parameter.

Abstract: Based on a recent formulation of the V–parameter of a photonic crystal fiber we provide numerically based empirical expressions for this quantity only dependent on the two structural parameters—the air hole diameter and the hole-to-hole center spacing. Based on the unique relation between the V–parameter and the equivalent mode field radius we identify how the parameter space for these fibers is restricted in order for the fibers to remain single mode while still having a guided mode confined to the core region.

Mode-order converter in a multimode waveguide.

Abstract: A novel device that converts the order of modes in an integrated-optic multimode waveguide was proposed and fabricated. The device consists of two mode splitters and tapered waveguides. Its operation at a wavelength of 1.55 μm was confirmed by observation of the output mode profiles. The cross talk measured by an indirect method was >10.2 dB . The excess loss with reference to a straight multimode waveguide was 1.5 dB, compared with the propagation loss of a straight multimode waveguide.

Multiband vector lattice solitons.

Abstract: We predict multiband vector solitons in nonlinear periodic systems, using photonic lattices as a prime example. The solitons consist of two optical fields arising from different bands of the transmission spectrum, which involve both bound state and radiation mode components.

Optical waveguide structure

Abstract: There is provided a planar waveguide structure (700) having a first core layer (708), a second core layer (704) and a cladding layer (706), wherein the cladding layer (706) is disposed between the first core layer (708) and the second core layer (704) to form an inter-core cladding layer (706). The inter-core cladding layer (706) comprises a first region (722) having a first refractive index and an array of sub-regions (724) formed therein having a second refractive index. The subregions (724) do not extend into either the first or the second core layer, and they give rise to a photonic band structure region, which is effective to perturb an evanescent field of an optical signal propagating through the core layers.

Mode converter including tapered waveguide for optically coupling photonic devices

Abstract: A mode converter including a silicon waveguide core deposited over a first silicon dioxide cladding layer. The silicon waveguide core is formed such that a first end of the silicon waveguide core has a larger cross-sectional area than a second end of the silicon waveguide core. The silicon waveguide core may include a vertical taper and/or a lateral taper.

The physical limit for the waveguide enhancement of nonlinear-optical processes

Abstract: The waveguide enhancement of nonlinear-optical processes is shown to be physically limited because of the competition of diffraction and refractive-index-step radiation confinement. In the case of the limiting refractive-index step values for fused silica fibers, the maximum waveguide enhancement of nonlinear-optical processes is achieved with submicron fiber core diameters. Microstructure fibers with high air-filling fractions of the cladding are shown to enhance nonlinear-optical processes with waveguide enhancement factors close to the physical limit. Approximate asymptotic expressions derived for several important particular cases provide an adequate qualitative description of the waveguide enhancement of nonlinear-optical processes and allow the optimal fiber core diameters for the maximum enhancement of nonlinear-optical interactions to be estimated with a satisfactory accuracy.

Mode field patterns and preferential mode coupling in planar waveguide-coupled square microcavities.

Abstract: We report a numerical and analytical study of mode field patterns and mode coupling in planar waveguide-coupled square microcavities, using two-dimensional (2-D) finite-difference time-domain (FDTD) method and k-space representation. Simulated mode field patterns can be identified by k-space modes. We observe that different mode number parities permit distinctly different mode field patterns and spectral characteristics. Simulation results suggest that k-space modes that nearly match the waveguide propagation mode have a relatively high coupling efficiency. Such preferential mode coupling can be modified by the mode number parity.

Coherent acousto-optic mode coupling in dispersion- compensating fiber by two acoustic gratings with orthogonal vibration directions

Abstract: The acousto-optic mode coupling from core to LP11cl mode of a dispersion-compensating fiber excited by two acoustic waves with orthogonal perturbations is studied by use of a novel composite piezoelectric transducer. Highly polarization-dependent mode-selective spectra are observed that are due to coherent acousto-optic coupling between the core and various constituent cladding modes. Potential applications for implementing an all-fiber wavelength-tunable polarization analyzer are also discussed.

Erbium-doped fiber laser simultaneously mode locked on more than 24 wavelengths at room temperature

Abstract: We demonstrate simultaneous mode locking of more than 24 wavelengths at 3 GHz in an actively mode-locked erbium-doped fiber laser operating at room temperature. The multiwavelength operation is achieved when a frequency shifter and an all-fiber 50-GHz periodic filter are inserted into a ring cavity. Active mode locking is performed with an amplitude modulator, and pulses with a FWHM of 30 ps are obtained.

Interferometric analog optical modulator for single mode fibers

Abstract: A device for simultaneously coupling and modulating incident radiation to a single mode optical fiber based on a solid state truncated integrated Mach-Zehnder interferometer having a back end formed by two converging radiation channels converging at an angle θ and terminating prior to overlapping. The angle θ is calculated to produce in an interference zone formed by the exiting radiation a primary constructive interference fringe that provides an optimum match to an input fiber mode of a fiber positioned within the interference zone. Phase shifting elements in the radiation propagation paths provide a linear shift of the constructive interference fringe across the input of the fiber optic in response to an analog signal.

High density integrated optical chip

Abstract: A high density integrated optical chip (20). The optical chip features an optical function (26) connected to a low minimum bending radius dielectric waveguide (24), and a large mode field size dielectric waveguide (22) to interface with an external optical device (28), such as an optical fiber. The large mode field size dielectric waveguide is optically connected to the low minimum bending radius dielectric waveguide on the optical chip.

Optical waveguide device, optical waveguide laser using same and optical apparatus having same

Abstract: An optical waveguide device comprises a waveguide layer for converting an incident light and emitting the converted light. The waveguide layer is provided with a ridge waveguide and slab waveguides formed on both sides of the ridge waveguide with recess portions intervening therebetween. The waveguide layer satisfies multimode conditions with respect to the incident light, and the light transmitted in the ridge waveguide is in single mode.

Optical waveguide device and optical modulator

Abstract: An optical waveguide device includes a substrate having an electro-optical effect, an optical waveguide formed on the substrate, an electrode provided for the optical waveguide, a monitoring optical waveguide for guiding part of light outputted from the optical waveguide as monitor light, an attenuation section provided for the monitoring optical waveguide for attenuating the monitor light, and a light detection section for detecting the intensity of the monitor light guided by the monitoring optical waveguide and attenuated by the attenuation section

Optical coupling device

Abstract: An optical mode converter comprises a coupling waveguide (4) and a receiving waveguide (3). The coupling waveguide has at an input end a first effective refractive index n1eff and includes a tapered core (41) of a substantially constant refractive index n1 with a substantially square cross section at the input end (5), having a size that tapers down moving away from the input end. The coupling waveguide has also a cladding (42) at least partially surrounding the tapered core. The receiving waveguide has a second effective refractive index n2eff at an output end and comprises a core (31) of a substantially constant refractive index n2, greater than the refractive index n1 of the tapered core (41) of the coupling waveguide, and a cladding (32) at least partially surrounding the core. A side surface (43) of the tapered core of the coupling waveguide (4) is optically in contact, in a coupling portion, with the receiving waveguide (3) so as to allow optical coupling between the coupling waveguide (4) and the receiving waveguide (3). The refractive index n1 of the tapered core of the coupling waveguide (4) is selected so that the first effective refractive index n1eff and the second effective refractive index n2eff differ from each other in absolute value less than 30% of the difference (n2 - n2eff) between the core refractive index and the effective refractive index of the receiving waveguide (3). A method for fabricating an optical tapered waveguide is also disclosed.

Side detection of strong radiation-mode out-coupling from blazed FBGs in single-mode and multimode fibers

Abstract: We report on the effective side detection of radiation-mode out-coupling from blazed fiber Bragg gratings (BFBGs) fabricated in single-mode fiber (SMF) and multimode fiber (MMF). The far-field radiation power distribution from BFBGs have been measured achieving a high spatial-spectral resolution (0.17 mm/nm). We have also investigated comparatively the transmission-loss characteristics of BFBGs in both fiber types, fabricated using phase-mask and holographic inscription techniques. Our results reveal clearly that the radiation out-coupling from BFBGs is significantly stronger and spectrally more confined in MMF than in SMF.

Planar optical waveguide amplifier with mode size converter

Abstract: Planar wave guide devices deposited by reactive pulsed dc sputtering processes are presented. Devices according to the present invention include a waveguide with a core sputter deposited onto a substrate and a cladding sputter deposited onto the core. In some embodiments, second waveguide can be deposited in close proximity to the first waveguide to form a direction coupler. In some embodiments, light traveling through the waveguide can be amplified or attenuated in response to signals applied to the waveguide. In some embodiments, a DWDM device is formed in the waveguide. In other devices, a mode-locked laser is formed.

Integrated optical waveguide structure with low coupling losses to an external optical field

Abstract: An integrated optical waveguide structure having a waveguide core for guiding an optical field, formed on a lower cladding layer. The waveguide core has a waveguide core layer substantially coextensive to the lower cladding layer and having a substantially uniform thickness, and a waveguide core rib of a substantially uniform height protruding from a surface of the waveguide core layer opposite to a surface thereof facing the lower cladding layer. A layout of the waveguide core rib defines a path for the guided optical field. The integrated optical waveguide structure has a circuit waveguide portion in which the waveguide core layer has a first width, adapted for guiding the optical field through an optical circuit, and at least one coupling waveguide portion adapted for coupling the circuit waveguide portion to an external optical field. The coupling portion has a terminal waveguide core rib portion having a second width lower than the first width and terminating in a facet, and a transition waveguide core rib portion optically joining to each other the circuit waveguide portion and the terminal waveguide portion, the transition waveguide core rib portion being laterally tapered so that a width thereof decreases from the first width to the second width. The waveguide structure allows an integrated optical device designer satisfying optical circuits needs and, at the same time, ensuring a satisfactory coupling efficiency with an external field.

Arrayed waveguide grating, arrayed waveguide grating module, arrayed waveguide grating module waveguide compensation method, optical communication system

Abstract: An arrayed waveguide grating 101 is shown, which comprises at least one input waveguide 103, a plurality of output waveguides 104, at least one wavelength compensation output waveguide 105 disposed adjacent to the output waveguide 104, a channel waveguide array 107, an input side slab-waveguide 108, and an output side slab-waveguide 109. The wavelength compensation output waveguide 105 has a tapering connecting portion connected to the output side slab-waveguide 105. Thus, the outputted light has a sharp spectrum, thus permitting ready wavelength compensation.

High power low-loss fiber waveguide

Abstract: In general, in one aspect, the invention features an article including a high-power, low-loss fiber waveguide (100) that includes alternating layers of different dielectric materials (130, 140) surrounding a core (120) extending along a waveguide axis (199), the different dielectric materials including a polymer (130) and glass (140).

Planar optical component for coupling light to a high index waveguide, and method of its manufacture

Abstract: A planar optical component (30) is presented that defines an optical path for light propagation in between a first waveguide (103) and an optical fiber. The optical component (30) comprises a waveguide structure defining a transition region between the first waveguide (103) and the optical fiber. The transition region is formed by first and second cladding layers and first and second core segments (C1, C2). The first core segment (C1) is formed by a core of said first waveguide (103) having a refractive index n1, and the second core segment (C2) is formed by a core of a second connecting waveguide (102) having a refractive index n2

Optical waveguide, method of its production, and its use

Abstract: An optical waveguide with a longitudinal direction and a cross-section perpendicular thereto for propagating optical radiation at a free-space wavelength λ, the optical waveguide comprising: a core region (103), a cladding region (100,101,102) surrounding the core region, and a substantially one-dimensional (1D) periodic structure of structural elements with a period Λ; wherein said structural elements comprises cross-sectionally extended continuous elements; use of such an optical waveguide in optical amplifier, a tunable optical amplifier, an optical laser, and a tunable optical laser; a preform for its production; and a method of its production.