Showing papers on "Radiation mode published in 1994"

Design of a single-mode tapered waveguide for low-loss chip-to-fiber coupling

Abstract: The novel waveguide structures described in this paper have nonlinearly tapered shapes that result in low radiation losses despite their relatively short lengths. The core at the waveguide endface connected with the fiber has a very small cross section and an expanded mode field with a non-Gaussian shape. The taper structures are analyzed by using an improved step-transition method. This method is a based on the theory of enclosing a waveguide within electrical walls and that can therefore treat the radiation modes in a tapered waveguide as discrete mode spectra. Analyzing the relationships between the lengths and shapes of the tapers and the radiation loss due to the tapers show that appropriately tapered semiconductor waveguides operating at an optical wavelength of 1.55 /spl mu/m and having a taper length of less than 0.7 mm can have a radiation loss of only 0.1 dB and a coupling loss with a conventional single-mode fiber of less than 0.5 dB. >

Article comprising a dispersion-compensating optical waveguide

Abstract: Disclosed is optical fiber that can advantageously be used to compensate chromatic dispersion in an optical fiber communication system, typically a system that is upgraded from 1.3 μm to 1.55 μm operating wavelength (λ op ). The fiber typically has a power law core refractive index profile, a refractive index "trench" surrounding the core, and a refractive index "ridge" surrounding the trench. The refractive index profile of the fiber preferably is designed such that the fiber supports the fundamental mode (LP 01 ), does not support the LP 11 mode but does support the LP 02 mode, all at λ op . At λ op , LP 01 has dispersion more negative than -150 ps/nm·km and, in a preferred embodiment, LP 01 also has negative dispersion slope at λ op . In a further embodiment of the invention the refractive index profile is designed such that the cut-off wavelength of the LP 11 mode is less than that of the higher order mode, typically LP 02 , and less than λ op , such that the fiber does not support propagation of the LP 11 mode. In some preferred embodiments the fiber is designed to have dispersion more negative than about -90 ps/nm·km and loss less than about 0.5 dB/km at λ op ˜1.55 μm.

Integrated laser and coupled waveguide

Abstract: A grating (461) coupling the output of a semiconductor laser (410) in a semiconductor waveguide to a dielectric waveguide (451) having a core (458) which may be efficiently butt-coupled to the core of an optical fiber (470); the laser and semiconductor waveguide, coupling grating, and dielectric waveguide are integrated on a single substrate. Further, multiple lasers (410, 420, 430, 440) with differing lasing frequencies may be integrated and their outputs grating coupled into a single dielectric waveguide (450) for wavelength division multiplexing.

Method and apparatus for determination of refractive index

Abstract: In a method of determining the refractive index of a gaseous, liquid or solid sample, preferably a gaseous or liquid sample, there is used a waveguide resonator (1) which includes an open waveguide (4) and a closed waveguide (5) located adjacent the open waveguide The sample is brought to the vicinity of the closed waveguide (5) so as to influence the proximal surroundings of the waveguide and therewith its effective refractive index Light derived from a light source (9) is coupled to one end of the open waveguide (4) and transmitted light is measured at the other end of the open waveguide to establish the influence of the sample on the resonance wavelength and therewith determine the refractive index of the sample or a sample-related refractive index difference A device for carrying out the method includes a waveguide resonator having a sample contact area (12) adjacent the closed waveguide (5) of the waveguide resonator

The radiation modes of baffled finite plates

Abstract: The modal‐style approach for representing the exterior radiation characteristics of structures generally seeks to find a set of orthogonal functions, or radiation modes, that diagonalize a discretized radiation operator in the exterior domain of the structure. The choice of basis functions for the modal representation is arbitrary, though use of the structural modes of vibration tends to provide some physical insight. The radiation modes are found through an eigenanalysis or singular‐value decomposition analysis of the radiation operator. The eigenvalue or singular value associated with a given radiation mode is directly proportional to the radiation efficiency of that radiation mode. In this paper, the dependency of the radiation efficiencies and radiation mode shapes on the number of degrees of freedom permitted in the derivation of the radiation operator is investigated for a baffled finite rectangular plate. The accuracy of the acoustic modal representation depends on the number of degrees of freedom in the radiation operator, with the least efficient radiation modes converging slowest. Further, the rate of convergence is dependent on the particular basis function selection. The convergence behavior has significant impact on those applications of the exterior acoustic modal approach that seek to exploit the least efficient radiation modes.

Optical Waveguide Isolator Based on Nonreciprocal Radiation

Abstract: A new waveguide isolator which has a simple structure is proposed and experimentally demonstrated. The isolator operates on the basis of nonreciprocal guided‐radiation mode conversion in a channel magneto‐optic waveguide. The isolator was realized using a single‐mode rib channel waveguide in Ce‐substituted yttrium iron garnet which has a very large Faraday rotation. 13.3 dB isolation was obtained at a wavelength near 1.55 μm.

Method for achromatically coupling a beam of light into a waveguide

Abstract: A device for achromatic input coupling of an optical beam into a waveguide is disclosed. The device includes a waveguide formed of a material having an effective index of refraction and having first and second surfaces, such waveguide defining a guided mode of propagation. A first grating is provided at the interface at the first surface of the waveguide, such first grating being selected so as to diffract an optical beam at an appropriate angle selected so that the beam is coupled into the guided mode of the waveguide. A second waveguide is provided at the interface at the second surface of the waveguide, such second grating selected so as to diffract a beam to provide an appropriate angle of incidence onto the first grating at the first surface waveguide. An important aspect of the present invention is the use of linear dispersion of the gratings to cancel the linear portion of the sum of the intrinsic waveguide dispersion and the material dispersions of the waveguide and the prism.

Optical waveguide including singlemode waveguide channels coupled to a multimode fiber

Abstract: An intrusion-alarmed optical fiber communication system, where light from two or more sources are launched with a planar channel waveguide launcher into two or more modes of a multimode graded-index transmission fiber, is disclosed. Input fibers containing the source light waves and the output fibers are in direct contact with the waveguide channels. Waveguide channels redistribute the light from input channels to output channels by rerouting, crossing, merging, or splitting channels. Waveguide launcher precisely launches data light into the fundamental mode and intrusion monitor light into high order modes of a multimode graded-index fiber. Fiber intrusion attenuates light in high order modes, but much less of the data in the fundamental mode, thereby forming a basis for the intrusion-alarmed system. Waveguide launcher permits light from a plurality of sources to be launched selectively into several types of fibers: singlemode fibers, multimode fibers, multicore fibers, multimode fibers having high refractive-index ring profile within the fiber core boundary. Waveguide channel configuration permit other versatile functions to be performed; these include optical time domain reflectometry, channel feedback stabilization of the diodes, launching light from more than one light source into the fundamental mode of a multimode graded-index fiber, and other functions. Means for launching and propagating the fundamental mode in multimode graded-index fiber in order to increase bandwidth capacity of said fiber are disclosed. Optical-electronic intrusion-alarmed systems with synchronous phase sensitive detection of intrusion are described, including reference recovery means. In order to decrease false alarm rates, information on transmitter light source variations are transmitted to the receiver via digital bit stream. A precise fiber optic sensor system based on the waveguide launcher is disclosed.

Improved formulation of the film mode matching method for mode field calculations in dielectric waveguides

Abstract: Some numerical problems encountered with the mode matching method for calculating mode fields in dielectric waveguides are discussed. A description is given of how the dimension of the eigenvalue problem for the mode indices can be minimized in a numerically well behaved manner.

Vertical cavity devices as wavelength selective waveguides

Abstract: We show that novel wavelength-sensitive devices can be fabricated by coupling a semiconductor vertical cavity resonator to a low index waveguide. The optical mode in the resonator propagates at an angle, and the resonator resembles a high index waveguide. A taper in the thickness of the resonator allows different parts of the waveguide to operate at different wavelengths. These structures are analyzed using both thin film equations and waveguide normalism. Concentrating on a waveguide demultiplexer, simple design equations are derived, and a demonstration device is fabricated for TE mode at 0.75 /spl mu/m operation. Using AlGaAs/AlAs multilayers and a polymer top waveguide, the spectrometer exhibited a dispersion of 29 nm/cm, a wavelength resolution of better than 1 nm, and an intrinsic device efficiency of about 90%. A similar structure containing a light-emitting quantum well operated as a multiwavelength light source by modifying the spontaneous emission into the polymer waveguide. >

Single-mode, optical-fiber sensors and tunable wavelength filters based on the resonant excitation of metal-clad modes.

Abstract: The resonant excitation of metal-clad modes, including fundamental and higher-order modes, in a multilayer structure deposited on the polished cladding of a single-mode optical fiber is theoretically analyzed and experimentally demonstrated. The excitation of metal-clad modes is shown as a resonant power transfer from the fiber to the metal-clad mode that takes place for an external refractive-index value such that the effective index of the metal-clad mode reaches the cladding level. The observed attenuation on the TM polarization provides a suitable transducing mechanism for refractive-index sensor devices as well as the principle for developing tunable wavelength-polarized filters with a wide range of optical performance characteristics.

Observation of mode selection in a radially anisotropic cylindrical waveguide with liquid‐crystal cladding

Abstract: Observation of mode selection in an optical fiber with nematic liquid‐crystal cladding is reported. The TE01 mode is guided, while the TM01 mode leaks out. This behavior is achieved by radially oriented liquid‐crystal directors in the cladding of an optical fiber with isotropic core. A theory which quantitatively accounts for the results is given.

Optical waveguide intensity modulator using electro-optic polymer

Abstract: An optical waveguide intensity modulator of a polymer waveguide utilizes and electro-optic effect and optical birefringence induced from a poling process of a nonlinear polymer thin-film. The optical waveguide intensity modulator is constructed by a series combination of a TE/TM mode selector, a TE or TM mode converter and another TE or TM mode selector. In the polymer waveguide, the mode selectors and mode converter can be easily obtained by making the direction of a poling field to be horizontal (or vertical) and approximately 45° direction. According to the present invention, the optical waveguide intensity modulator is formed by integrating the TE or TM mode selectors and the TE or TM mode converter onto a single substrate. Further, because no element, is required which results in optical loses for example an optical isolator, an optical coupler or a curved portion of the waveguide, the efficiency of the device can be improved.

Mode selective loss penalties in VCSEL optical fiber transmission links

Abstract: The system performance with respect to modal noise of both single mode and multi-transverse mode vertical cavity surface emitting lasers is reported. A bit error ratio floor is observed with only 1 dB of mode selective loss for the single mode device but no such floor is observed using the multimode device with up to 7.8 dB of mode selective loss. The modal noise penalty for the single mode device is attributed to its higher coherence and spectral fluctuations during modulation. >

Distributed coupling between a single-mode fiber and a planar waveguide

Abstract: Light transfer between a curved single-mode fiber and a two-mode planar waveguide is investigated experimentally with respect to its dependence on the refractive index and the thickness of the planar waveguide and for different polishing depths. The behavior of this distributed coupler is treated theoretically with a coupled-mode model, which takes into account the two dimensions of the waveguide configuration, as well as the even or the odd symmetry of the planar waveguide mode field. Coupling of a fiber to a multimode planar waveguide is also considered.

Optical waveguide chemical and biological sensor

Abstract: An optical waveguide sensor particularly useful as a chemical or biological sensor is described which comprises a single mode fibre optic waveguide including a core surrounded by a cladding and having a tapered portion which tapers adiabatically inwardly to a waist of diameter typically about that of the original core, and then adiabatically outwardly by variation of the cladding whereby under operating conditions the evanescent electromagnetic field associated with the guided mode of the waveguide is externally accessible in the region of the tapered portion; an optical source, such as a laser, optically coupled to one end of the waveguide; and a detector coupled to the other end of the waveguide for detecting optical radiation modulated or coupled into the waveguide at the tapered portion. The tapered portion is preferably in the form of a loop to facilitate construction of the sensor as a probe, and includes a binder for binding a chemical or biological compound, for example, a silane for use in conjunction with a recognition entity.

Multiwavelength upconversion waveguide laser

Abstract: A multiwavelength upconversion waveguide laser producing visible or ultraviolet wavelength radiation comprising a semiconductor laser diode producing relatively long wavelength radiation, a channel waveguide having a thin film material which converts the relatively long wavelength radiation into visible or ultraviolet wavelength radiation, and a optical resonator which recirculates the visible or ultraviolet wavelength radiation. The optical resonator may use an output optical coating or one or more Bragg grating reflectors as an output coupler. One or more optical resonators may be used to produce one or more visible or ultraviolet radiation wavelengths. One or more independently controllable lightwave modulators are used to modulate the visible or ultraviolet wavelength radiation.

Integrated optical circuit having a waveguide end of lens geometry, and method for making same

Abstract: A method and apparatus are disclosed whereby integrated optical circuits having waveguide ends of lens geometry are formed which improve the waveguide's optical coupling to light sources and detectors. A channel waveguide is formed on a substrate and the waveguide ends are shaped into lens form by etching to form a protrusion and heating the waveguide to or above the softening temperature of core material of the waveguide resulting in surface tension in the core material that functions to shape the protrusion into a substantially cone-shaped lens end having a smooth surface.

Article comprising optical fiber having low polarization mode dispersion, due to permanent spin

Abstract: The presence of (typically unintended) birefringence in single mode optical fiber can severely limit the usefulness of the fiber for, e.g., high bit rate or analog optical fiber communication systems, due to the resulting polarization mode dispersion (PMD). It has now been discovered that PMD can be substantially reduced if, during drawing of the fiber, a torque is applied to the fiber such that a "spin" is impressed on the fiber. Desirably the torque is applied such that the spin impressed on the fiber does not have constant spatial frequency, e.g., has alternately clockwise and counterclockwise helicity. At least a portion of optical fiber according to the invention has spin alternately clockwise and counterclockwise.

Optical waveguide device and optical microscope using the same

Abstract: An optical waveguide device formed by a material showing anisotropy for refraction index and an optical instrument using the same device. The device comprises an electro-optic single crystal substrate on which are formed a first core portion higher in refractive index than the substrate with respect to both ordinary and extraordinary rays and a second core portion higher in refractive index than the substrate with respect to extraordinary rays pnly whereby the first core portion forms a single-moded waveguide for ordinary rays, and the overlapping region of the first and second core portions forms a double-moded waveguide for extraordinary rays. This optical waveguide device is used in place of a pinhole elementin an optical system of a confocal scanning optical microscopeso as to guide illuminating light to an object to be detected and to guide the reflected light from the object into a detector. This microscope includes a polarization conversion element for converting the polarizing direction of the illuminating light to one different from that of reflected light. The optical waveguide device functions as a single-moded waveguide for the illuminating light and as a double-moded waveguide for the reflected light.

Optical non-reciprocal circuit of waveguide type

Abstract: An optical non-reciprocal circuit is constituted by a channel waveguide, a planar waveguide, and a diffraction lattice or grating. The channel waveguide is disposed in a planar substrate that is transmissive to optical waves. The planar waveguide is disposed on only one side of a substrate plane divided by the channel waveguide in the substrate plane and having an equivalent refractive index lower than that in the channel waveguide. The diffraction grating provides a spatial periodic change of the refractive index to a guided optical wave of the channel waveguide. The periodicity of the lattice direction, that is, the direction of the wavenumber vector is neither parallel nor perpendicular to the optical transmission direction of the channel waveguide but is given a finite angle. The optical non-reciprocal circuit can be realized by using only an ordinary dielectric material with the circuit being highly productive and low priced and having high performance.

Analysis of metal-clad optical waveguide polarizers by the vector beam propagation method

Abstract: The attenuation characteristics of a metal-clad planar optical waveguide polarizer are computed by a modified finite-difference beam propagation method, taking into consideration the complex refractive indices of the metals used and the vector characteristics of the guided mode. Numerical results for practical optical waveguide refractive-index profiles such as the step and Gaussian distributions are presented. The method should find applications in the design of metal-clad optical waveguide polarizers and other lossy waveguide devices with arbitrary refractive-index profiles and can be easily expanded to three-dimensional cases.

Optical waveguide device and second harmonic generator using the same

Abstract: An optical waveguide device for use as a second harmonic generator includes a nonlinear optical crystalline substrate of KTiOPO4 and an optical waveguide core of a dielectric material, such as Ta2 O5, disposed on the nonlinear optical crystalline substrate. The optical waveguide converts a fundamental wave having a wavelength λ which is guided through the optical waveguide into a second harmonic wave having a wavelength λ/2, the second harmonic wave having the same polarization as the fundamental wave which is guided through the optical waveguide. The optical waveguide has a thickness of 190 nm or greater. The optical waveguide device also has a dielectric loaded strip disposed on the optical waveguide core. The dielectric loaded strip may be made of SiO2 or SiO2 doped with Ta2 O5. Alternatively, the optical waveguide may be a ridge-type optical waveguide, and the optical waveguide device may also has a cladding layer disposed on the nonlinear optical crystalline substrate and the optical waveguide core.

Polarization properties of a fiber-to-asymmetric planar waveguide coupler

Abstract: A coupled mode model describing the light transfer between a single-mode fiber and a planar asymmetric waveguide, which takes into account the two dimensions of the waveguide cross sections, as well as the TE or TM polarization of the planar waveguide modes, is presented. This model is applied to the practical case of a distributed (curved fiber) coupler, and the possibility of light modulation by changing the refractive index: of the cover medium is pointed out. The action of such a coupler as a polarizer, which could be externally driven, is also considered. >

Limitations of two‐dimensional passive waveguide model for λ=980 nm Al‐free ridge waveguide lasers

Abstract: The performance characteristics of ridge waveguide InGaAs/InGaAsP/GaAs strained quantum well lasers emitting at 980 nm are reported. Factors limiting the validity of a passive waveguide two‐dimensional approximation model are investigated. In particular, is was found that a gain‐guiding effect is responsible for the fundamental mode stabilization and lateral far‐field broadening. Ridge waveguide laser parameters which influence the stability of lateral single mode operation are discussed. An output power of 180 mW in spatial single mode operation was attained, and it was limited by catastrophic optical damage of the mirror facet.

Optical device and method of making the same

Abstract: An optical device includes an optical waveguide with a block that is fusion spliced to one end. The block has a refractive index approximately equal to the effective refractive index of the waveguide and is of such a length that substantially all the light exiting the waveguide propagates directly to the end of the block remote from the waveguide.

Explicit formulas of normalized radiation modes in multilayer waveguides

Abstract: A new formulation for the normalization of radiation modes in one-dimensional lossless multilayer waveguide structures is derived using the transmission matrix method. In this formulation, an individual radiation mode is excited by two sources located at opposite ends of the two outermost regions of the waveguide. Proper choice of the absolute phase of one of the sources results in simple expressions for the normalized radiation modes. Calculation of radiation loss of grating-assisted directional couplers is used as an example to show the simplicity and usefulness of this method. >

Te-Me mode converter on polymer waveguide

Abstract: A TE-TM mode converter of a polymer electro-optic polarization waveguide type uses the electro-optic birefringence and the electro-optic effect as a non-linear optical waveguide medium, in which an optical director formed during the poling of a polymer thin film is determined by the direction of the poling electrical field. The poling electrode design enables the optical director having the angle of 45° to the electrical direction of the TE and TM modes to be formed in the polymer thin film. When the waveguide receives the incident light of the TE mode or TM mode, the TE (or TM) mode is switched into the TM (or TE) mode by an effective refraction factor between the optical director and the director perpendicular thereto. If a length of the poling electrode and the birefringence of the waveguide is adjusted, the changes of various electo-optic polarization states are possible. The poled thin film has an electro-optic effect. If a voltage is applied to the thin film, the size of the birefringence derived by the poling is changeable. The use of the electro-optic effect enables the outputting state of the waveguide to be maintained at the TE or TM mode by a bias electrode, and if the switching voltage is applied to the waveguide, the TE-TM mode switching can be accomplished.