Showing papers on "Radiation mode published in 1980"

Computation of mode properties in optical fiber waveguides by a propagating beam method

Abstract: Propagating beam solutions for optical waveguides can be made to generate such mode-related properties as propagation constants, relative mode powers, and group delays with high precision and considerable flexibility. These quantities are needed in the analysis of optical fiber dispersion. The technique requires the generation of correlation functions from the numerical solutions of a wave equation. These correlation functions are in turn Fourier-transformed with respect to axial distance z. The resulting spectra display sharp resonances corresponding to mode groups, and the positions and heights of these resonances determine the previously mentioned mode properties. The spectral analysis is made highly accurate by the use of line-shape fitting techniques. With this method, mode group delays can be determined to a precision of +/-0.12 psec/km using a computation covering a 5-cm propagation path.

Device for coupling radiation into an optical waveguide

Abstract: An optical device coupling light between a first light waveguide and either a second light waveguide or a radiation source characterized by the first light waveguide having a core of a predetermined cross-sectional area, a reflective layer or mirror of a high reflectance being disposed on an angle to the axis of the waveguide and occupying only a small portion of the total cross-sectional area of the core so that only a small portion of the light traveling in the core of the first waveguide will be blocked by the presence of the mirror. The second waveguide will have a core diameter substantially smaller than that of the first waveguide and the mirror is mounted in the first core adjacent to the connection with the second core. The radiation source may be either a laser diode, semi-conductor laser or a light emitting diode.

An analytic solution for mode coupling in optical waveguide branches

Abstract: Mode coupling between local normal modes in branching and separating optical waveguides is treated. An analytic solution for power transfer is provided for structures whose shape has a particular functional form. Analytic results are compared to numerical calculations for linear branches. Numerical examples for the design of shaped structures fabricated with Ti:LiNbO 3 channel waveguides are given.

Impulse response prediction based on experimental mode coupling coefficient in a 10-km long graded-index fiber

Abstract: Mode coupling coefficients and impulse responses in a multimode graded-index fiber are investigated both experimentally and theoretically. Mode coupling coefficient measurements at 1.27 μm are made for a fiber before and after nylon coating. The fiber is 10 km in length and has no splicing point. The mode coupling coefficient change due to nylon coating is found to be relatively small. In the nylon-coated fiber, the coefficient increases monotonically as increasing a principal mode number, and the tendency is in good agreement with the theoretical prediction considering random bends along the fiber axis. With the increase in mode coupling coefficient and 0.01 dB/km of excess loss by nylon coating, 2.7 percent of increase in 3-dB bandwidth is observed. This increase in 3-dB bandwidth is explained by the theoretical calculation. The length dependence of 3-dB bandwidth exhibits a small mode mixing effect in the fiber. By the theoretical predictions based on the experimental mode coupling coefficients, the coupling length is estimated to be 25 km. It is also clarified that the length dependence of 3-dB bandwidth shows the L-0.5characteristic for L > 200 km.

Normalization of single-mode fibers having an arbitrary index profile

Abstract: A method is proposed whereby the propagation characteristics of a single-mode fiber having an arbitrary refractive-index profile may be expressed in terms of a newly defined equivalent step-index profile. The theory is based on the fact that the field distribution of the HE11 mode of a fiber closely resembles the Gaussian profile. The method makes it possible to characterize a fiber from a simple measurement of the HE11 mode spot size without making difficult index profile and core radius measurements. It is also found that the step-index distribution is suitable for single-mode fibers.

Polarizer and method

Abstract: Apparatus and method for changing the degree of polarization of light in a waveguide such as an optical fiber. A portion of the cladding of a strand of fiber optic material is removed, and a body of birefringent material is mounted in the area in which the material has been removed in close proximity to the core of the fiber. The birefringent material modifies the propagation of two polarization modes within the fiber in such manner that one of the modes is coupled to a bulk wave mode and removed from the guide, while the second mode excites no bulk waves and remains guided.

An optical TE‐TM mode splitter using a LiNbO3 branching waveguide

Abstract: A novel optical TE‐TM mode splitter using a Ti‐diffused branching waveguide in Y‐cut LiNbO3 is proposed and demonstrated. Mode splitting has been confirmed experimentally at an applied voltage V0=−20 V.

Wavelength dispersion characteristics of single-mode fibers in low-loss region

Abstract: Wavelength dispersion characteristics of single-mode silica fibers in a very low-loss region, including zero dispersion wavelengths, are studied in detail using a "difference method." Wavelength dispersion of single-mode fibers is compared for fibers with same material dispersion but with different waveguide structure. Material dispersion is evaluated by extracting waveguide dispersion from experimental results. Effects of waveguide dispersion on the zero dispersion wavelength of the single-mode fiber in a longer wavelength region are clearly analyzed. Single-mode fiber design consideration is given from the wavelength dispersion point of view.

Slab waveguide demultiplexer for multimode optical transmission in the 1.0–1.4-μm wavelength region

Abstract: Optical fiber transmission technology has developed rap­ idly due to improvements in fabrication of optical fibers, light sources, and other optical devices. Wavelength-divisionmultiplexing (WDM) transmission, by which different wavelength signals are transmitted via a single optical fiber, is considered to be a promising technology for future systems, especially for subscriber loops and large-capacity transmission systems. In a WDM system, a multi/demultiplexer is an essential part of the optical sender and receiver. Many types of multi/demultiplexer having good performances have al­ ready been developed. A demultiplexer using a plane

I Graded Index Optical Waveguides: A Review*

Abstract: Publisher Summary This chapter discusses the waveguiding characteristics of graded index fibers with emphasis on near parabolic profiles that play a major role in the future optical communication system. For a study of the important characteristics of a waveguide (like pulse dispersion and attenuation), it is necessary to know the way a monochromatic beam would propagate along the perfect guide; by a perfect guide, it imply that the refractive index variation does not change along the z-direction. A rigorous study of the propagation of a beam would imply the solution of Maxwell's equations that, in most cases, would involve considerable mathematical complexity. The chapter also discusses the geometrical optics method to study the propagation characteristics of graded index optical fibers with circular cross-section. As the most important application of an optical fiber is in the field of communication, extensive studies have been made on the distortion of an optical pulse as it propagates through the fiber and in the determination of optimum profiles, which lead to small dispersions The calculation of power attenuation is of great importance in determining the performance of a waveguide. This arises primarily because of (1) the excitation of leaky rays, (2) material absorption, (3) bending, and (4) imperfections in the waveguide.

Measurements of mode conversion coefficients in graded-index fibers

Abstract: A new method of measuring mode conversion coefficients in multimode fibers is proposed. The principle is based on the phenomenon that modal power propagating along a fiber undergoes a gradual change due to mode coupling and mode-dependent losses. Application of the principle has made it possible to measure mode conversion coefficients of a graded-index fiber that, to the authors' belief, had not been reported before. In the experiment, it was found that the mode conversion coefficient is roughly independent of the mode order. A resolution limit of the mode analyzing technique is also discussed for graded-index fibers.

Superluminescent led with efficient coupling to optical waveguide

Abstract: Optical power is coupled into an optical waveguide system such as an optical fiber with maximum efficiency by a superluminescent light-emitting diode having lateral confinement of the light in the junction plane. The waveguide developed in the light-emitting diode is constructed to have an effective numerical aperture equal to the numerical aperture of the optical waveguide, and the refractive index n, the length L and width D of the waveguide in the diode is constructed such that the parameter nD/2L is much less than the numerical aperture. As a result, the inverted population of electrons within the active region are utilized with maximum efficiency to develop rays that are coupled into, and can be guided by, the optical waveguide system.

Simplified parameter-based analysis of single-mode optical guides

Abstract: An approach to single- (and low-) mode waveguides is described that enables the important mode characteristics to be derived from much reduced profile data. Uniformity with generalised parameters for multimode guides is demonstrated, and experimental determination discussed.

Optical fiber waveguide for measuring magnetic fields

Abstract: An optical fiber waveguide for detecting magnetic fields. The optical fiber waveguide includes therein an array of discrete elongate magnetized particles, all polarized in the same direction with their axes generally parallel with the longitudinal axis of the waveguide, which in the presence of a time-varying magnetic field are subjected to magnetostrictive effects and undergo linear dimension changes to cause a related longitudinal dimension change of the optical fiber waveguide whereby a laser beam passing longitudinally through the waveguide is subject to phase shifts detectable by interferometry.

Radiation losses of step-tapered channel waveguides.

Abstract: We compute the radiation losses of a rectangular dielectric waveguide (integrated optics channel waveguide) that is tapered so that its wider cross-sectional dimension increases by roughly a factor of three while its narrow dimension remains constant. As the waveguide widens its refractive index decreases to ensure that the waveguide supports only one guided mode. The taper is approximated by a discontinuous staircase curve. A rectangular waveguide taper of 2-microm thickness, tapering from 3- to 10-microm width through fourteen steps of 0.25-microm height, has a minimum loss (at 0.6328-microm wavelength) of 0.13 dB for a 200-microm taper length.

Refracted power technique for cutoff wavelength measurement in single-mode waveguides

Abstract: A technique to measure the local (2?3 mm) values of cutoff wavelength ?c in single-mode waveguides is described. The technique, insensitive to the length of waveguide used, involves the spectral measurement of refracted power. The feasibility of using the cutoff wavelength determined by this technique to predict the zero dispersion wavelength is also studied.

Optical surface wave mode converters and modulators utilizing static strain-optic effects

Abstract: Periodic perturbations of dielectric waveguides can be obtained by an evaporated SiO 2 thin film grating through the static strain-optic effect. These waveguides are applied to TE-TM mode converters and modulators in Ti-diffused LiNbO 3 waveguides. Using a coupling length of 3 mm in an optical surface waveguide, we have demonstrated a TE-TM mode conversion efficiency of 80 percent and a TE-TM mode modulator with 100 percent modulation with an applied field of 2 V/μm. A theoretical analysis of a reflector for a semiconductor laser waveguide is also described.

Scattering and Mode Conversion of Guided Modes by a Spherical Object in an Optical Fiber

Abstract: The scattering and the mode conversion of the guided modes due to a spherical object in a step-index optical fiber is analyzed theoretically. The incident fiber mode is expanded in terms of the spherical vector wave functions, and the scattered fields are obtained by applying the boundary conditions on the surface of the object with the aid of these expansions. The expression for the total scattered power and the mode conversion coefficients are given. As an example, the scattering and mode conversion caused by a spherical air bubble are evaluated numerically.

An analysis of the coupling of an injection laser diode to a planar LiNbO 3 waveguide

Abstract: Calculated butt coupling efficiency between a GaAlAs double heterostructure laser and a single-mode LiNbO 3 Ti-diffused optical waveguide is presented in this paper as a function of the transverse displacement, the angular alignment, the longitudinal separation between the laser and the waveguide end surfaces, the radiation field of the laser diode and its dependence on the laser diode structure, and the mode profile of the waveguide and its dependence on experimental diffusion parameters The maximum efficiency is less than 40 percent because of the mismatch between the waveguide mode and the laser radiation, caused primarily by the experimental limitations in their structures The effect of the reflection of the waveguide end surface on the laser oscillation has also been estimated

Holography with guided optical waves

Abstract: Waveguide holograms are recorded in a storage material layer covering a planar dielectric waveguide with a guided mode as reference wave. They are also read-out with a guided mode. In the storage material, assumed to have a lower refractive index than the waveguiding film, the fields of the reference and of the read-out wave are evanescent waves.

Waveguide mode coupler for use with gyrotron traveling-wave amplifiers

Abstract: A rectangular waveguide to circular waveguide coupler and vice versa. The upler includes a first section of circular waveguide spaced by a gap from a reflective-plane conducting wall, the latter having a hole for passage of an electron beam if the coupler is used in a traveling wave tube, and a second section of circular waveguide disposed external to, and coaxial with, at least a portion of the first waveguide section and extending to the wall to provide a conductive boundary surrounding the gap. The region between the first and second waveguide sections forms an input port of the coupler; the first waveguide section forms the output port of the coupler. Electromagnetic waves in a TE 01 coaxial waveguide mode are applied to the input port from a rectangular waveguide supporting the dominant TE 10 mode. The second waveguide section has a cut-off determining dimension r e proportioned to support both the TE 01 and TE 02 circular electric modes in the region of the gap at the frequency of the applied waves. The first waveguide section has cut-off determining dimensions r 1 proportioned to support the circular electric TE 01 mode to the exclusion of all higher-numbered circular electric modes at the frequency of the applied waves.

Single mode transmission and acoustic backscattering measurements in a laboratory waveguide

Abstract: Our purpose was to make ’’farfield’’ sound scattering measurements in a limited space. We used a thick waveguide, about 35 acoustic wavelengths deep, and excited it in the first mode. The waveguide had pressure release surfaces on the top and bottom. To excite and receive in the first mode, we used a vertical array that was amplitude shaded to match the eigenfunction of the first mode. Experimental measurements verified that 90% of the energy was in the first mode. A pair of omnidirectional transducers were used as a probe transmitter and receiver to calibrate the system for scattering measurements. At 220 kHz, 24‐cm depth, and 100‐cm range, the cross section of the scattering region was about 6 cm high. At this range the first Fresnel zone was 10 cm wide. Scattering measurements of the target strength of a steel sphere, diameter 0.8 cm, gave −54±1 dB compared to −54 dB theoretical target strength.

Mode conversion at splices in multimode graded-index fibers

Abstract: Mode conversions occurring at a splice in multimode graded-index fibers are investigated theoretically, and their effects on impulse responses are verified experimentally. The relation describing the mode behavior at a splice in existence of a geometrical offset and fiber parameter mismatches is derived by taking a skew ray as well as meridional ray into consideration. Then the mode transfer matrix is obtained to determine the variations in mode power distribution and impulse response due to the mode conversions occuring at a splice. The measured mean delay time difference between lower and higher mode pulse responses and baseband frequency response for spliced graded-index fibers are compared with the theory obtained from the transfer functions of individual fibers and the mode transfer matrix which describes the mode conversions at a splice due to a transverse displacement and fiber parameter mismatches.

Hydrogen atoms interacting with a quantised radiation mode

Abstract: A model consisting of a hydrogen atom coupled to a single quantised radiation mode in the long-wavelength approximation is studied mathematically. It is shown that the Hamiltonian H for this model is dilatation analytic. This result makes it possible to describe various resonance phenomena associated with atoms in radiation fields by means of analytic continuation techniques. Furthermore, it is shown that H possesses an infinite number of bound states with negative energy. Nevertheless the photoionisation probability tends to one with increasing field strength.

Optical waveguide and method of propagating waves therein

Abstract: Conventional optical waveguides are of very small diameter making handling and coupling difficult. Also the HE 11 mode is used and this can give rise to contamination where inhomogeneities arise in the waveguide. The waveguide of the present invention has a tube of higher permittivity optical material, with a core of lower permittivity optical material and cladding again of lower permittivity material. The critical dimension is the thickness of the tube and the tube diameter can therefore be made very much larger than that of the conventional optical waveguide. Such a waveguide when properly excited will support the HE 11 wave as a single mode or alternatively the TE 01 mode as a pure wave. Methods of launching and propagating these modes are described.

A Coupled-Waveguide TE/TM Mode Splitter

Abstract: A novel channel waveguided TE/TM mode splitter is presented. This splitter can spatially separate the TE and TM mode components and is compatible with single mode fiber systems. The operation principle is as follows. Two straight waveguides are formed closely parallel to each other on c-plate LiNbO3 by preferential Ti diffusion. An Al strip loaded on waveguide 2 induces a large change in the propagation constant for the TM mode, so that the TM mode component, fed into waveguide 1, cannot couple to waveguide 2 ("straight-through state"). By applying external voltages V1 and V2 to the two planar electrodes, formed on waveguide 1 with an Al2O3 buffer layer in-between, a complete power transfer from waveguide 1 to waveguide 2 takes place for the TE mode ("crossover state"). Less than -20 dB crosstalk was realized at 1.15 µm wavelength for V1=20 V and V2=-15 V. The insertion loss was 1.7 dB.

Reconstruction of the refractive index profile in diffused waveguides

Abstract: A simple method is proposed for measuring the refractive index n(x) at the surface of a diffused waveguide whereby the profile n(x) can be reconstructed uniquely from the mode spectrum of the waveguide. A description is given of a method of measuring effective refractive indices of the waveguide modes using a grating element for coupling radiation into the waveguide. The profile n(x) in single-mode waveguides is discussed.

Optical waveguide filters for the visible spectrum

Abstract: A study has been made of wavelength selective devices which use a grating structure superimposed on a thin film optical waveguide. Good agreement was found between the theoretical and experimental wavelength response of filters in three forms of optical waveguide: with the grating ion-beem etched into a single homogeneous guiding layer, with the grating in a photoresist film on a homogeneous layer and with the grating in a photoresist film on a silver ion-exchanged waveguide. Details of the method of fabrication of the gratings and waveguides are given. Filters made with gratings ion-beanm etched into waveguide had bandwidths of 0.2 to 0.5 nm at 600 nm while the filters with superimposed gratings in photoresist had somewhat wider bandwidths.