Showing papers on "Radiation mode published in 1998"

Properties of photonic crystal fiber and the effective index model

Abstract: We report on the waveguiding properties of a new type of low-loss optical waveguide. The photonic crystal fiber can be engineered to support only the fundamental guided mode at every wavelength within the transparency window of silica. Experimentally, a robust single mode has been observed over a wavelength range from 337nm to beyond 1550nm (restricted only by available wavelength sources). By studying the number of guided modes for fibers with different parameters and the use of an effective index model we are able to quantify the requirements for monomode operation. The requirements are independent of the scale of the fiber for sufficiently short wavelengths. Further support for the predictions of the effective index model is given by the variation of the spot size with wavelength,

Single-mode excitation of multimode fibers with ultrashort pulses.

Abstract: Single-mode excitation of step-index multimode fibers with light sources with short temporal coherence lengths is demonstrated. Multimode fiber designs with reduced microbending-induced mode coupling are described that allow the propagation of the fundamental mode over long lengths with negligible mode coupling even in the presence of tight fiber bends. At a wavelength of 1.56microm a fiber with a core diameter of 45microm can preserve the fundamental mode for a propagation length of ~20m . Such fibers allow coiling with a coil diameter as small as 7cm.

Low attenuation optical waveguide

Abstract: Disclosed is a single mode optical waveguide fiber having a core refractive index profile in which the profile parameters are selected to providean attenuation minimum. A set of profiles having the same general shape and dimensions is shown to have a group of profiles contained in a sub-set which exhibit a minimum of attenuation as compared to the remaining members of the set. The members of the sub-set have been found to have the lowest effective group index, n geff, and the lowest change in .beta.2 under waveguide fiber bending.

Integrated optical isolator based on efficient nonreciprocal radiation mode conversion

Abstract: An integrated optical isolator is demonstrated based on efficient nonreciprocal conversion from a fundamental TM mode to a deep TE radiation mode away from the cutoff. The isolator is realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet, which has a very large Faraday rotation. 27 dB isolation is obtained at a wavelength of 1535 nm.

Large mode area photonic crystal fiber

Abstract: formed by a polarization doublet. The transverse inten­ sity distribution of these guided modes for a wavelength of λ = 632.8 nm was also calculated and the result for one of the polarizations is shown in Figure la. Our work proves that electromagnetic propagation in a realistic PCF can support a robust single-mode structure nearly at all wavelengths for certain fiber para­ meters. It is notable that this approach is based on a full-vector method, so that polarization effects are in­ corporated in an exact manner. Our results for both dis­ persion curves and intensity distributions completely agree with those experimentally measured. This method provides a powerful tool for a better understanding of the PCF's properties because it allows us to fully determine the dispersion curves of their guided modes, as well as their electro­ magnetic field and in­ tensity distributions. The flexibility of our approach also permits the simula­ tion of a great variety of fiber designs. By analyzing the disper­ sion curves of these different fibers, we have already discov­ ered a richer modal structure in some of them. In the example shown in Figure lb there exists, besides the fundamental dou­ blet, two other polar­ ization doublets. Sim­ ilarly, we can use this tool to optimize the design of PCFs with unconventional dis­ persion relations, of potential interest for pulse propagation.

Optical waveguide probe and its manufacturing method

Abstract: An optical waveguide probe which is formed into a hook shape by a manufacturing method using a silicon process and which emits a light from its tip for detection, comprising an optical waveguide (1) which is formed into a hook shape, the probe needle part (5) of which is sharpened and which is made of dielectric, and a board (2) supporting the optical waveguide (1) laminated on the board (2). The optical waveguide (1) is composed of a core (8) through which a light is transmitted and a cladding (9) whose refractive index is smaller than that of the core (8).

Surface mode at isotropic–uniaxial and isotropic–biaxial interfaces

Abstract: The surface mode that propagates along the interface between isotropic and uniaxial materials, as first suggested by M. I. D’Yakonov [Sov. Phys. JETP67, 714 (1988)], is quantitatively characterized in terms of (1) the range of crystallographic orientations for which the mode propagates, (2) its propagation constant β, and (3) its field profiles. Previous studies have considered only uniaxial materials whose optic axis is in the plane of the interface. We show that a surface mode can also propagate along the interface between isotropic and arbitrarily oriented uniaxial or biaxial materials. This mode is also quantitatively characterized. For the biaxial material oriented so that its optic axes lie in the plane of the interface, it is shown that this surface mode is guided over a greater range of propagation directions and that the light is confined more tightly than for any isotropic–uniaxial interface of comparable birefringence. In addition, it is shown that the surface modes that occur at isotropic–uniaxial interfaces combine to form a new type of hybrid mode in uniaxial slab waveguides (two interfaces). The resulting modes differ from conventional slab waveguide modes in that (1) they are composed entirely of inhomogeneous waves and (2) at most two of these modes can exist regardless of the waveguide thickness.

Optical waveguide circuit, its manufacturing method and optical waveguide module having the optical waveguide circuit

Abstract: An optical waveguide circuit includes a plurality of waveguides with different lengths. Grooves (12) are formed in the waveguide by removing the upper cladding and the core of the waveguide (4) or by removing the upper cladding, the core and the lower cladding of the waveguide (4), and filled with a material (10) which have a refractive index temperature coefficient whose sign is different from the temperature coefficient of the effective refractive index of the waveguide. The difference between the lengths of the removed parts of the adjacent waveguides is proportional to the difference between the lengths of the remaining parts of the adjacent waveguides.

Laser-pumped compound waveguide lasers and amplifiers

Abstract: A compound planar waveguide comprising multiple confinement structures that provides independent containment of pump and laser radiation. The waveguide may be formed of multiple layers of laser-active and laser-inactive materials to provide step changes in refractive index. The planar waveguide may include a central laserable core layer substantially sandwiched by at least two non-laserable cladding layers to provide an interface between the inner surfaces of the cladding layers and the gain medium core to define a first waveguide by virtue of an index of refraction discontinuity for containing developed laser radiation, and wherein the outer surfaces of the cladding layers define a second waveguide by virtue of an index of refraction discontinuity for containing pump radiation within the waveguide. The second waveguide may be also defined by an interface formed between the cladding layers and additional non-laserable external layers which sandwich the cladding layers. The laser waveguide provides confinement of developed laser radiation which may be independently configured from the waveguide structure that confines the pump radiation. The planar waveguide layers may be also optically bonded together and consist of different optical quality crystals or glass.

Optical pulse compressor for optical communications systems

Abstract: In accordance with the invention, an optical pulse compressor comprises a pulse source (10), a section of nonlinear optical waveguide (11) including a periodic structure such as Bragg grating (12), for providing positive dispersion and a section of linear optical waveguide (13) including a negative dispersion component (14). The nonlinear waveguide should have a second order index N 2 at least ten times the second order index N 2 ' of the linear waveguide. The nonlinear waveguide is preferably chalcogenide fiber, with a Bragg grating photoinduced into the core. Because the grating is 4-5 orders of magnitude more dispersive than standard optical fiber, the length of the nonlinear waveguide section can be scaled down to a few centimeters with accompanying reduction of deleterious processes. Modeling suggests that compression factors of 5 with an initial 60 ps pulse are achievable with grating lengths of about 20 cm.

Polarisation asymmetric active optical waveguide, method of its production, and its uses

Abstract: A method of producing an active optical waveguide having asymmetric polarisation, said method comprising the steps of (a) providin g an active optical waveguide (10) comprising: (i) a transverse refractive index profile (21) comprising a guiding region (11), an intermediate region (13), and a non-guiding region (12); (ii) a transverse photorefractive dopant profile (31) comprising a constant or graded photorefractive dopant concentration within at least one of the guiding, non-guiding and intermediate regions, except that the photorefractive dopant is not located solely in the guiding region; and (iii) exhibiting in said guiding region, intermediate region, or both, light guiding modes having different polarisations; and (b) exposing at least a part (10a, 10b) of the active optical waveguide to an effective transverse illumination of light (20) reacting with the photorefractive dopant and modifying said transverse refractive index profile; said part of the active optical waveguide being exposed to a fluence selectively suppressing the propagation of the light guiding modes having different polarisations so that the propagation of one mode is less suppressed than the propagation of the other mode(s). Such an active optical waveguide, single polarisation mode optical waveguide lasers and multi-wavelength single polarisation mode optical waveguide lasers comprising such an active optical waveguide, methods of their production, and their uses in telecommunications, in spectroscopy, in sensors and in absolute calibrated laser light sources.

Optical coupler optically coupling a light beam of a semiconductor laser source with a single mode optical waveguide or fiber

Abstract: A semiconductor laser and an optical waveguide of an optical coupler, formed on a substrate are optically coupled with each other by aligning their positions horizontally by using a plurality of laser elements and cores for the laser and the waveguide respectively and arranging them in an array respectively so that a difference between their pitches is less than double of tolerance tolerated for optically coupling with each other, the waveguide having partially a composite core composed of: a main core; a sub core surrounding the main core and having a refractive index lower than that of the main core; and a cladding layer surrounding the sub core and having a refractive index lower than that of the sub core.

Optical amplifier and process for amplifying an optical signal propagating in a fiber optic employing an overlay waveguide and stimulated emission

Abstract: A side-polished fiber/overlay waveguide architecture and process for non-invasively implementing an optical amplifier are provided for an optical communications system. A "channel" overlay waveguide is employed to constrain for amplification optical energy evanescently coupled to the overlay waveguide from the side-polished optical fiber. One of two amplification methods can be employed. The first involves inducing stimulated emission with the overlay waveguide and the second uses a second order, non-linear frequency conversion to down-convert a high-power, short-wavelength pump signal into the waveguide to amplify the optical energy coupled thereto. Amplification of optical energy in the channel overlay waveguide can be established within a single beat length of evanescent removal to evanescent return of the optical energy to the side-polished fiber optic.

Integrated optical intensity modulator and method for fabricating the same

Abstract: An integrated optical intensity modulator and a method for fabricating the same are provided. The integrated optical intensity modulator includes a substrate having spontaneous polarization, cut in a predetermined direction, an optical waveguide formed on the substrate, a plurality of domain-inversion areas having domains in the reverse direction of the spontaneous polarization, arranged in a staggered pattern around the optical waveguide, and a first electrode formed on the optical waveguide and second and third electordes formed on the substrates on the right and left of the optical waveguide, wherein if a predetermined voltage is applied to the electrode, a light wave is deflected and scattered in a domain-inversion area in accordance with a change of the refractive index of thedomain-inversion area in the optical waveguide and the refractive index of the spontaneous polarization area. According to the optical intensity modulator of the present invention, the domain-inversion structure of a ferroelectric material isformed in a staggered pattern around the optical waveguide, and an optical guided mode is deflected by an applied voltage, to thereby half driving voltage of the optical waveguide, and an area for deflecting the optical guided mode to the right and left can be formed in multiple stages, to thereby increase the extinction ratio.

Compound optical waveguide and filter applications thereof

Abstract: A compound waveguide device (10) having a channel waveguide (60) in optical proximity to an elongate waveguide (30) propagating an optical signal therein is disclosed. The channel waveguide (60) includes a coupling surface through which optical energy is evanescently coupled to or from the optical signal propagating in the elongate waveguide (30). The channel waveguide (60) is shaped to confine distribution of the optical energy therein along axes transverse to the axis of propagation of the optical energy. Transverse diffraction of the optical energy within the channel waveguide (60) is thereby limited. In one embodiment, the elongate waveguide (30) is a side-polished fiber optic waveguide. Electro-optic control of the compound waveguide is disclosed, as are bandstop, bandpass and detection configurations thereof.

Single-mode fiber polished into the core as a sensor element

Abstract: The light transmittance of a single-mode fiber, polished into the core, at different polishing depths is investigated experimentally. New results concerning amplitude, polarization and wavelength characteristics of such waveguide structure are presented, revealing the feasibility of this structure to act as a simple fiber-optic sensing element.

Article comprising an optional waveguide tap

Abstract: A dispersive optical waveguide tap comprises a blazed refractive index grating in the core of the waveguide, coupling means, focusing means and utilization means. The grating is selected such that guided mode light of predetermined wavelength will, in the absence of the coupling means, be directed into one or more cladding modes of the waveguide. The presence of the coupling means, in optical co-operation with the waveguide, changes the guiding conditions such that the cladding modes are substantially eliminated from a portion of the waveguide that includes the cladding, whereby the grating directs the guided mode light into one or more radiation modes. The blaze angle typically is ≦15°. The focusing means serve to bring the radiation mode light substantially to a focus in at least one dimension, the focal point (or line) depending on the wavelength of the light. The utilization means exemplarily comprise an array of photodetectors, and the coupling means exemplarily comprise an appropriately shaped glass member and index matching means. Dispersive waveguide taps are advantageously used in WDM optical communication systems, e.g., to provide status information (e.g., channel wavelength, channel power, including presence or absence of a channel) to, e.g., a system maintenance unit. The status information facilitates maintenance of operating conditions by conventional feedback control. Any optical element that can bring the tapped radiation to a focus on the utilization means can serve as a focusing element. Exemplary focusing elements are optical lenses (cylindrical or non-cylindrical), diffraction gratings, volume gratings (holograms), and combinations thereof.

Method for making optical device with composite passive and tapered active waveguide regions

Abstract: A semiconductor optical device, for example a laser, has a composite optical waveguide including a tapered, MQW active waveguide in optical contact with a substantially planar, passive waveguide. The fundamental optical mode supported by the composite waveguide varies along the length of the composite waveguide so that, in a laser, the laser mode is enlarged and is a better match to single mode optical fibre. A method for making such semiconductor optical devices is also disclosed.

Guided wave methods and apparatus for nonlinear frequency generation

Abstract: Methods and apparatus are disclosed for the nonlinear generation of sum and difference frequencies of electromagnetic radiation propagating in a nonlinear material. A waveguide having a waveguide cavity contains the nonlinear material. Phase matching of the nonlinear generation is obtained by adjusting a waveguide propagation constant, the refractive index of the nonlinear material, or the waveguide mode in which the radiation propagates. Phase matching can be achieved even in isotropic nonlinear materials. A short-wavelength radiation source uses phase-matched nonlinear generation in a waveguide to produce high harmonics of a pulsed laser.

Efficient propagation algorithm for 3D optical waveguides

Abstract: The well established free space radiation mode (FSRM) method is extended to the analysis of dielectric waveguide discontinuities and propagation in fully three dimensional structures. Unlike beam propagation methods (BPM) the method intrinsically incorporates continuous reflections and is inherently wide angled in nature. Results are given for a representative selection of practical structures, such as single and double step discontinuities and tapers, for both TE and TM polarisations. The method is computationally efficient with minimal memory requirements.

Waveguide type grating device

Abstract: A waveguide type grating device according to the invention includes a quartz substrate, a cladding and two waveguides. Waveguides are arranged to provide an input port, an Add port, an output port, a Drop port, directional 3 dB couplers, core width-changing portions, and grating portions each interposed between core width-changing portions. The width of core is changed between each non-grating portion and each grating portion in an adiabatic structure, for example, a parabolic structure. For this structure, a waveguide type grating device is structured to suppress the increase in wavelength loss due to coupling from progressive propagation mode to regressive radiation mode, with less cost and smaller dimension.

Single mode optical fiber having multi-step core structure and method of fabricating the same

Abstract: An optical fiber having a multi-step core structure, and a method of fabricating the same, are provided. The optical fiber includes a central core having a predetermined diameter a1 from an central axis and a refractive index n1, a first outer core having a diameter a2 and a refractive index n2 smaller than the refractive index n1 and surrounding the central core, a second outer core having a diameter a3 and a refractive index n3 smaller than the refractive indexn2 and surrounding the first outer core, and a cladding having a diameter a4 anda refractive index n0 smaller than the refractive index n3 and surrounding the second outer core. The diameter of the core is increased by making the refractive index distribution of the core multi-stepped, thus providing easy fabrication. The optical fiber has a low dispersion value in a 1550nm wavelength, thus making superspeed long distance transmission possible.

Optical waveguide plate for display

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

Athermal integrated optical waveguide device

Abstract: An athermalized integrated optical waveguide device in which thermal spectral shifts are inhibited is provided and in which the light transmitting properties are insensitive to temperature variations and fluctuations. The athermnalized integrated optical waveguide device has at least two waveguide core arms, preferably comprised of a silica glass, with the core arms cladded with a waveguide cladding composition, preferably a silica glass that has a boron concentration different than the cores. The first waveguide arm and the second waveguide arm have a difference in an effective index thermal slope in order to provide an athermalized device such as an intereferometer on a substantially planar substrate. In addition the at least two waveguide core arms are comprised of path segments having different waveguide core dimensions.

Optical waveguide fabrication method

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

Self-tuning optical waveguide filter

Abstract: A self-tuning optical waveguide filter for attenuating a lower power light signal at λ1 more than a higher power signal at λ2 comprises a length of single core waveguide and a light injector for applying λ1, λ2 into the waveguide in two propagating modes subject to mode beating. The mode beating produces high intensity regions of λ1 physically displaced from high intensity regions of λ2. A portion of the waveguide is doped with a saturable absorber for disproportionately attenuating wavelengths at lower power levels. Advantageously the waveguide is a single-core fiber having its central core doped with rare-earth saturable absorber. In a preferred embodiment, the fiber is dimensioned to propagate λ1, λ2 in the LP01 and LP02 modes, and the saturable absorber is Erbium.

Frustration of Bragg reflection by cooperative dual-mode interference: a new mode of optical propagation.

Abstract: A new optical mode of propagation is described, which is the natural eigenmode (supermode) of a fiber (or any optical waveguide) with two cospatial periodic gratings. The mode frustrates the backward Bragg scattering from the grating by destructive interference of its two constituent submodes (which are eigenmodes of a uniform waveguide). It can be used in a new type of spatial mode conversion in optical guides.

Large volume manufacturing of dispersion compensating fibers

Abstract: Summary form only given. We report results of large volume production of more than 10000 km of dispersion-compensating fibers (DCF). This is equivalent to more than 1000 modules, which each can compensate 60 km of standard fiber. Reproducible large volume production of DCF is a difficult task. The design is very sensitive towards small variations in the index profile. For example, we find for our design that a 1% variation of either the core diameter or core index results in a change in dispersion of 5 and 2.5% respectively. Another challenge is to obtain low polarization-mode dispersion (PMD). DCF is more than one order of magnitude more sensitive to core ovalities than conventional telecommunication fibers due to the high core index used. Therefore extreme care has been taken to avoid core ovalities. At the same time we stimulate the mode coupling by introducing oscillatory twist into the fiber during draw. Enhanced mode coupling not only reduces the PMD, but also gives a more stable PMD value, for example during temperature cycling of DCF modules.

Compact mode expanders using resonant coupling between a tapered active region and an underlying coupling waveguide

Abstract: A novel technique for enhanced laser-fiber coupling, based on resonant power coupling between a tapered active waveguide and an underlying coupling waveguide, is presented. Spot-sizes are transformed from 2.0/spl times/1.1 /spl mu/m in the active region to 6.0/spl times/3.1 /spl mu/m in the coupling waveguide, over a length of 200 /spl mu/m, with a mode transformation loss of only 0.36 dB. Butt-coupling efficiencies of 55% (2.6 dB loss) are estimated to standard cleaved single-mode fibers at 1.55 /spl mu/m. The proposed device requires a single epitaxial growth and conventional processing techniques, making it amenable for low-cost manufacturing.