Showing papers on "Radiation mode published in 2004"

Polarization maintaining large mode area photonic crystal fiber

Abstract: We report on a polarization maintaining large mode area photonic crystal fiber Unlike, previous work on polarization maintaining photonic crystal fibers, birefringence is introduced using stress applying parts This has allowed us to realize fibers, which are both single mode at any wavelength and have a practically constant birefringence for any wavelength The fibers presented in this work have mode field diameters from about 4 to 65 micron, and exhibit a typical birefringence of 15·10-4

Efficient input and output fiber coupling to a photonic crystal waveguide

Abstract: The efficiency of evanescent coupling between a silica optical fiber taper and a silicon photonic crystal waveguide is studied. A high-reflectivity mirror on the end of the photonic crystal waveguide is used to recollect, in the backward-propagating fiber mode, the optical power that is initially coupled into the photonic crystal waveguide. An outcoupled power in the backward-propagating fiber mode of 88% of the input power is measured, corresponding to a lower bound on the coupler efficiency of 94%.

Fundamental mode operation of a 19-core phase-locked Yb-doped fiber amplifier.

Abstract: We demonstrate, theoretically and experimentally, a high power/energy 19-core Yb-doped fiber amplifier that operates in its fundamental in-phase mode. The calculated result using an improved coupled mode theory with gain shows that, with a Gaussian beam as seed, the in-phase supermode dominates. Experimentally, we use a Q-switched single-core fiber laser with single transverse mode as seed, and amplify it with a 5.8 m 19-core fiber. The measured near and far fields are close to the in-phase supermode. The measured M2 factor of the amplified beam is 1.5, which is close to the theoretical value. A pulse energy gain of 20 dB is obtained with the amplified pulse energy up to 0.65 mJ at a repetition frequency of 5 kHz. No appreciable stimulated Brillouin scattering is observed at this power level.

Slow-light enhancement of radiation pressure in an omnidirectional-reflector waveguide

Abstract: We study the radiation pressure on the surface of a waveguide formed by omnidirectionally reflecting mirrors. In the absence of losses, the pressure goes to infinity as the distance between the mirrors is reduced to the cutoff separation of the waveguide mode. This divergence at constant power input is due to the reduction of the modal group velocity to zero, which results in the magnification of the electromagnetic field. Our structure suggests a promising alternative, microscale system for observing the variety of classical and quantum-optical effects associated with radiation pressure in Fabry–Perot cavities.

Coupling of small, low-loss hexapole mode with photonic crystal slab waveguide mode

Abstract: Coupling characteristics between the single-cell hexapole mode and the triangular-lattice photonic crystal slab waveguide mode is studied by the finite-difference time-domain method The single-cell hexapole mode has a high quality factor (Q) of 33Chi106 and a small modal volume of 118(lambda/n)3 Based on the symmetry, three representative types of coupling geometries (shoulder-couple, butt-couple and side-couple structures) are selected and tested The coupling efficiency shows strong dependence on the transverse overlap of the cavity mode and the waveguide mode over the region of the waveguide The shoulder-couple structure shows best coupling characteristics among three tested structures For example, two shouldercouple waveguides and a hexapole cavity result in a high performance resonant-tunneling-filter with Q of 97Chi105 and transmittance of 048 In the side-couple structure, the coupling strength is much weaker than that of the shoulder-couple structure because of the poor spatial overlap between the mode profiles In the direct-couple structure, the energy transfer from the cavity to the waveguide is prohibited because of the symmetry mismatch and no coupling is observed

Characteristics of a stick waveguide resonator in a two-dimensional photonic crystal slab

Abstract: Optical loss and polarization characteristics of the photonic crystal stick waveguide resonator modes were investigated using both theory and experiment. A stick waveguide resonator with 12 missing air holes was found to have a very high Q(>3 800 000) mode originating from the lossless guided mode below the light line. Photoluminescence spectra show sharp resonance peaks at regular intervals in k space, satisfying the resonant condition. Linear polarizations parallel or perpendicular to the waveguide were observed, depending on the mode symmetry. This polarization selection is explained in terms of the far-field cancellation effect of the in-plane field components.

Large flattened-mode optical fiber for reduction of nonlinear effects in optical fiber lasers

Abstract: We have developed and demonstrated a large flattened mode (LFM) optical fiber, which raises the threshold for non-linear interactions in the fiber core by a factor of 2.5 over conventional large mode area fiber amplifiers. The LFM fiber works by incorporating a raised index ring around the outer edge of the fiber core, which serves to flatten the fundamental fiber mode from a Bessel function to a top hat function. This increases the effective area of the core intersected by the mode by a factor of 2.5 without increasing the physical size of the core. This is because the core is uniformly illuminated by the LFM mode rather than having most of the light confined to the center of the core. We present experimental and theoretical results relating to this fiber and its design.

Bragg reflection waveguides with a matching layer

Abstract: It is demonstrated that Bragg reflection waveguides, either planar or cylindrical, can be designed to support a symmetric mode with a specified core field distribution, by adjusting the first layer width. Analytic expressions are given for this matching layer, which matches between the electromagnetic field in the core, and a Bragg mirror optimally designed for the mode. This adjustment may change significantly the characteristics of the waveguide. At the particular wavelength for which the waveguide is designed, the electromagnetic field is identical to that of a partially dielectric loaded metallic or perfect magnetic waveguide, rather than a pure metallic waveguide. Either a planar or coaxial Bragg waveguide is shown to support a mode that has a TEM field distribution in the hollow region.

Optical waveguide having specular surface formed by laser beam machining

Abstract: An optical waveguide having means for performing optical coupling with high efficiency at a predetermined position in an optical circuit substrate and which optionally includes an optical-electrical circuit board. Also provided are an optical waveguide, an optical path thereof being changed in an optical circuit at a steep angle and the optical waveguide for performing coupling and splitting of light being decreased in size in the optical circuit. The optical waveguide has a core and a cladding layer, and a wall surface, which is formed by cutting out at least a part of the core in a thickness direction of the core through irradiation of a laser beam and crosses at least a part of the core, which is a specular surface.

Multiple-core planar optical waveguides and methods of fabrication and use thereof

Abstract: A multiple-core optical waveguide comprises: a substrate; lower and upper waveguide core layers; a waveguide core between the upper and lower waveguide core layers; upper and lower cladding; and middle cladding between the upper and lower waveguide core layers substantially surrounding the waveguide core. Each of the lower, middle, and upper claddings has a refractive index less than refractive indices of the lower waveguide core layer, the upper waveguide core layer, and the waveguide core. Along at least a given portion of the optical waveguide, the upper and lower waveguide core layers extend bilaterally substantially beyond the lateral extent of a propagating optical mode supported by the optical waveguide, the lateral extent of the supported optical mode being determined at least in part by the width of the waveguide core along the given portion of the optical waveguide.

Two-mode operation in highly birefringent photonic Crystal fiber

Abstract: A photonic crystal fiber with different air-hole diameters along the orthogonal axes is found to support only the first two modes over a very broad wavelength range (>650 nm). The second-order mode is approximately linearly polarized and has stable-intensity lope positions that do not change in response to environmental disturbances. Strain sensitivity as a function of operating wavelength of a two-mode interferometric sensor made from such a fiber is also investigated.

Integrated optics spot size converter and manufacturing method

Abstract: The invention relates to an optical component (1) comprising a combination of optical waveguide elements for modifying the spot size of a mode of an electromagnetic field propagated by an optical waveguide element, the optical waveguide elements being formed on a substrate The object of the present invention is to provide a mode coupler with low coupling loss that is easy to manufacture and process tolerant The problem is solved in that the optical component further comprises a first section (10), comprising a first optical waveguide element (11) adapted to sustain at least one mode of the electromagnetic field, a second section (20) comprising at least two cooperating optical waveguide elements (21, 22), each of said at least two cooperating optical waveguide elements comprising at least one waveguide segment, said at least two cooperating optical waveguide elements being optically connected to said first optical waveguide element of said first section; wherein said cooperating optical waveguide elements (21, 22) of said second section (20) are adapted to maintain optical coupling between said optical waveguide elements to ensure that said at least one mode of the electromagnetic field is sustained by said at least two cooperating optical waveguide elements in cooperation Preferably, the waveguides of the first and/or second sections are tapered according to a cosine function or to a 5th or 7th order polynomial

Vectorial eigenmode solver for bent waveguides based on mode matching

Abstract: Vectorial eigenmode solver for circularly bent dielectric waveguides is described. The approach is strictly analogous to the well-known film mode-matching method for straight waveguides. Accurate calculation of radiation loss is enabled by leaving the calculation window open in the radial direction. In order to increase numerical stability and accuracy, a new computer code was written for cylindrical functions of complex order and argument. A high-contrast bent rib guide is used for comparison of results with a commercial mode solver.

Simulations of the effect of the core ring on surface and air-core modes in photonic bandgap fibers.

Abstract: We show through computer simulations that the thin silica ring that surrounds the air core of a photonic-bandgap fiber introduces surface modes. The intensity profile and dispersion of these modes indicate that they are the modes of the waveguide formed by the ring surrounded by air on one side and the photonic crystal cladding on the other. The ring also induces small perturbations of the fundamental core mode. Coupling to those surface modes, which have propagation constants close to that of the core mode, are likely to induce substantial loss to the core mode. By reducing the thickness of the ring and/or by suitably selecting its radius the propagation constants of the surface modes can be moved farther from that of the core mode and the loss reduced.

Light-emitting device and organic electroluminescent light-emitting device

Abstract: PROBLEM TO BE SOLVED: To achieve improved light-extraction efficiency from an organic EL light-emitting device or the like by using a mode transforming means, to solve the problem with of the low light-extraction efficiency of a conventional organic EL light-emitting device and or the like. SOLUTION: A light-emitting diode has at least a light-emitting layer on a substrate, and there is provided a mode conversion means for converting a guided mode to a radiation mode in the interior of the substrate, in the interior of the light-emitting layer or the like, or in interfaces of these interiors. COPYRIGHT: (C)2005,JPO&NCIPI

Mode multiplexing in optical frequency mixers

Abstract: Asymmetric Y junctions allow the development of a new class of optical frequency mixers that utilize higher-order waveguide modes for signal processing. We measure high-contrast (>30 dB) mode sorting in asymmetric Y junctions by use of a novel technique: efficient TM00, TM10, and TM20 mode mixing in a periodically poled lithium niobate waveguide. We also demonstrate an odd-to-even mode wavelength converter capable of spectral inversion without offset or bidirectional wavelength conversion.

External gain element with mode converter and high index contrast waveguide

Abstract: An external gain system includes a gain source (100), a laser coupler, one or more mode converters (102, 107), a high index contrast waveguide (105), and a filter structure (104) fabricated on either high or low index contrast waveguides. The filter structure defines the external. cavity with the front facet of the laser diode. An external cavity laser is farther integrated with one or more functional blocks (150) to perform a specific function. A multiplexer is integrated with the external cavity laser array, where the waveguide ends of the external cavity serve as an input to the multiplexer, to form an integrated WDM transmitter. The output of the transmitter, if fabricated on high index contrast waveguide, is then coupled to a low index waveguide or fiber matched waveguide by using a mode converter. The gain system can be configured to become a linear optical amplifier and can also be configured as a low cost wavelength converter.

Mode transformation and loss reduction in silicon waveguide structures utilizing tapered transition regions

Abstract: A low loss coupling arrangement between a slab/strip waveguide and a rib waveguide in an optical waveguiding structure formed on a silicon-on-insulator (SOI) platform utilizes tapered sections at the input and/or output of the rib waveguide to reduce loss. Optical reflections are reduced by using silicon tapers (either vertical tapers, horizontal tapers, or two-dimensional tapers) that gradually transition the effective index seen by an optical signal propagating along the slab/strip waveguide and subsequently into and out of the rib waveguide. Loss can be further reduced by using adiabatically contoured silicon regions at the input and output of the rib waveguide to reduce mode mismatch between the slab/strip waveguide and rib waveguide. In a preferred embodiment, concatenated tapered and adiabatic sections can be used to provide for reduced optical reflection loss and reduced optical mode mismatch.

Experimental demonstration of Bloch mode parity change in photonic crystal waveguide

Abstract: We experimentally show coupling between two photonic crystal waveguide Bloch modes having a different parity. A monomode ridge waveguide etched in a silicon-on-insulator substrate and connecting to the photonic crystal waveguide allows us to excite the even Bloch mode. Transmission measurements, performed on a broad spectral range, show the even mode propagation along the defect line. Then, spectrally resolved near-field patterns obtained by using a scanning near-field optical microscope in collection mode for wavelengths, inside and outside the multimode region of the photonic crystal waveguide, clearly demonstrate coupling phenomenon between even and odd modes.

Design of trapezoidal-ridge waveguide by finite-element method

Abstract: Transmission characteristics of single and double trapezoidal-ridge waveguides, are analysed by the finite-element method. Design data of cutoff wavelength and single-mode bandwidth for different ridge dimensions are presented in tabulated forms. Field patterns of dominant mode and the first higher-order TE mode in both waveguides are also illustrated. Numerical results provide an extension to the existing design data of rectangular-ridge waveguides and are considered to be helpful in practical applications.

Optical fiber with improved bending behavior

Abstract: An optical fiber with improved bending behavior is disclosed. The optical fiber, a single mode optical fiber having core and clad, satisfies α-profile wherein a refractive index in the core is increased toward its center, and has a specific refractive index difference Δ1 in the central region of the core and Δ2 at a radius rcore of the core. The optical fiber also satisfies a mode field diameter of 8.6~9.5µm at 1310nm wavelength, a zero dispersion wavelength of 1300~1324nm, a dispersion of 18 ps/nm-km or less at a 1550nm, a cable cutoff wavelength of 1260nm or less, a bending loss of 0.1dB or less at 1625nm when wound 100 times with a bending radius of 25mm. Thus, the optical fiber may satisfy every optical characteristic such as zero dispersion wavelength and dispersion at 1500nm, suggested by the general and common signal mode optical fiber, though the bending loss is decreased.

A partial H‐plane waveguide as a new type of compact waveguide

Abstract: A new type of compact waveguide, called a partial H-plane waveguide, is proposed. Analytic expressions of its proper fields and modes are derived and defined. The cutoff frequencies for each mode are calculated by both analytical and numerical methods. The results show that the dispersion characteristics of the first two dominant modes are the same as those of the conventional rectangular waveguide, while the proposed waveguide's cross section is one-quarter that of the conventional one. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 426–428, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20490

Propagation characteristics and guiding of a high-power microwave in plasma waveguide.

Abstract: The propagation characteristics of a high-power microwave [electromagnetic (em) wave] in a plasma waveguide are reported. The plasma waveguide is formed by expanding plasmas via the ponderomotive force of the high-power microwave and the microwave pulse remains trapped within the plasma waveguide and is guided in it. With the increase of the incident microwave power, the width of the plasma waveguide increases and the half width of the radial electric field distribution decreases. This shows that the em wave modifies the refractive index of the plasma waveguide area. For a plasma waveguide with narrower width, the microwave propagates along the plasma waveguide at the fundamental TE mode, while as the waveguide width increases the higher mode component starts appearing. Analytical treatment to the propagation of the electromagnetic wave in a dielectric waveguide having a step-index profile and the numerical calculations for the radial distribution of the electric field show fairly good agreement with the results observed in the present experiments.

Distributed optical structures exhibiting reduced optical loss

Abstract: An optical waveguide includes a set of diffractive elements. The diffractive element set routes within the waveguide a diffracted portion of an input optical signal between input and output optical ports. The input optical signal is successively incident on the diffractive elements. The optical signal propagates in the waveguide in a corresponding signal optical transverse mode substantially confined in at least one transverse dimension. A modal index of the signal optical mode or a modal index of a loss optical mode spatially varies along a signal propagation direction within the optical waveguide, or the loss optical mode is optically damped as it propagates along the optical waveguide. Said signal modal index variation, said loss modal index variation, or said loss mode damping yields a level of optical coupling between the signal optical mode and the loss optical mode at or below an operationally acceptable level.

Semiconductor micro-resonator for monitoring an optical device

Abstract: An optical device includes an optical waveguide through which light propagates and a micro-resonator structure including an optical sensor. The micro-resonator is configured to resonate at a wavelength of light that may be transmitted through the optical waveguide. When light at that wavelength is transmitted through the optical waveguide, it resonates in the resonator and is detected by the optical sensor to produce an electrical signal. The optical resonator may be a micro-cylinder, disc or ring resonator and may be coupled to the waveguide via evanescent coupling or leaky-mode coupling. Multiple resonators may be implemented proximate to the waveguide to allow multiple wavelengths to be detected. When the waveguide is coupled to a tunable laser, signals provided by the optical sensor may be used to tune the wavelength of the laser.

All-fiber narrowband polarization controller based on coherent acousto-optic mode coupling in single-mode fiber.

Abstract: An all-fiber, narrowband, tunable polarization controller is proposed and demonstrated. The device is based on coherent acousto-optic mode coupling induced by two orthogonal acoustic waves on a dispersion-compensating fiber. The cooperative coupling between the two polarizations of the core mode and the TE01 cladding mode through the two gratings permits indirect coupling between the two polarizations of the core mode with nearly 100% efficiency, which makes the polarization-controlling function possible. Experimental results verify the operation of the polarization controller with an insertion loss of <1 dB.

810-W single transverse mode Yb-doped fiber laser

Abstract: We demonstrate 810-W fundamental mode beam from Yb-doped fiber laser operating at 1092 nm. Single-transverse-mode operation is achieved through distributed mode filtering in a coiled 20-µm diameter and 0.06 NA core fiber.

1.3 μm ingaas vertical-cavity surface-emitting lasers with mode filter for single mode operation

Abstract: We report on the performance and analysis of 1.3μm range InGaAs∕GaAs vertical-cavity surface-emitting lasers (VCSELs) with an integrated mode filter consisting of a patterned silicon layer on the top distributer Bragg reflector. In this way, 1mW of single mode power is obtained from a device with a wavelength of 1265nm and a threshold current of 2.6mA at room temperature. An effective index model is used to extract the internal and external losses of the VCSEL structure and to predict the modal losses with and without mode filter, thereby providing a useful design tool for single mode VCSELs.