Showing papers on "Radiation mode published in 1983"

Quasi-optical waveguide filter

Abstract: A waveguide filter particularly well suited for use in the millimeter and submillimeter wavelength range of the spectrum. The filter includes a number of uniformly spaced gratings installed in a waveguide section and having grating strip patterns contoured to conform with a selected waveguide mode, such as the circular TE11 mode. The gratings are angularly oriented in the manner of a free-space plane-wave quasi-optical filter and provide similar desired frequency characteristics, but without the disadvantages of large size and the need for planewave launchers.

Rayleigh backscattering theory for single-mode optical fibers

Abstract: The theory of backscattering in single-mode optical fibers is described through use of a correlation function for the refractive-index fluctuation in the fiber. A simple formula for the backscattered power is derived using two correlation functions for the Booker–Gordon and Gaussian models. The zeroth-order approximation of the formula, in which the correlation length is much smaller than the spot size of the waveguide mode, coincides with Brinkmeyer’s model. The backscattered power at the input end of single-mode fiber is compared with that for multimode fiber. It is also shown that the backscattered power level at the input end is lower by approximately 55 dB than the input power level.

Influence of temperature and initial titanium dimensions of fiber-Ti:LiNbO 3 waveguide insertion loss at λ = 1.3 µm

Abstract: This paper describes the influence of fabrication parameters on fiber-Ti:LiNbO 3 waveguide-fiber insertion loss measured at \lambda = 1.32 \mu m in c -cut LiNbO 3 . We present a systematic study of the influence of titanium thickness on insertion loss. Within the range examined, diffusion of 950 A thick 6 μm wide strip of Ti at 1050°C for 6 h produced the minimum loss of 2.0 dB in a 2 cm long waveguide for both TE and TM modes. An analysis of fiber-waveguide coupling for the particular case of an asymmetric diffused waveguide is presented. In general, we find that coupling loss due to modal mismatch between the fiber and waveguide and propagation loss in the waveguide contribute approximately equally to total insertion loss.

Refractive index and attenuation characteristics of SiO 2 –Ta 2 O 5 optical waveguide film

Abstract: The refractive index and optical attenuation of sputtered SiO2–Ta2O5 waveguide film were measured in the 0.633–1.32-μm wavelength region. The waveguide film had a large refractive-index range of 1.46–2.08, which can be adjusted by suitable selection of the composition ratio of the SiO2–Ta2O5 target. Substrate heating, up to 270°C, during the sputtering process was effective for obtaining low attenuation. The waveguide films showed low attenuations, <0.41 dB/cm for the TE0 mode. The best fits of the form λγ to the measured attenuation have γ between 0 and −1, where λ is the wavelength. This wavelength dependence of the attenuation can be interpreted based on mode conversions due to the film surface roughness.

Polarization characteristics of LiNbO3 channel waveguide directional couplers

Abstract: Measurements are described on Z-LiNbO 3 , single-mode, channel waveguide directional couplers for the TE- and TM-mode polarizations at 0.83- and 1.3-μm wavelengths. The coupling characteristics for each polarization are strongly dependent on the mode confinement, and, hence, on the mode dispersion, and also vary differently with changes in mode dispersion. With particular waveguide fabrication parameters, the TE- and TM-mode coupling coefficients are equal for any waveguide spacing; for other fabrication conditions, the coupling coefficients are always unequal or equal at only one spacing. Theoretical calculations, based on experimentally determined diffusion parameters, follow the trend of measured values in most cases and correctly predict the effect on the coupling characteristics of changes in waveguide fabrication.

Integrated optical transducers

Abstract: An integrated optical transducer includes a single mode input optical waveguide, two single mode optical waveguide branches having different physical lengths, and a single mode output optical waveguide. When used as a transducer, the optical path lengths of the waveguide branches are dependent on the physical quantity measured. A plurality of such transducer elements may be used jointly to provide a binary output of high sensitivity and wide range of measurement. The waveguide element may also be used as an optical pulse source.

Wavelength tunable TE to TM mode converter

Abstract: An improved wavelength tunable TE to TM optical mode converter is provided by confining the electric fields for mode conversion and wavelength tuning to non-overlapping regions of a bi-refringent waveguide. Several electrode configurations for providing this spatial separation are disclosed.

Optical wavelength converting element

Abstract: PURPOSE:To obtain an optical wavelength converting device having a good temperature stability and high efficiency by forming an optical waveguide which has increased its refractive index partially, on the surface of a non-linear single crystal substrate, and providing a thin film having an intermediate refractive index of the substrate and the waveguide, on this waveguide. CONSTITUTION:For instance, an optical waveguide 6 which has increased a refractive index partially is formed on the surface of a non-linear single crystal substrate 5 of LiNbO3, etc., and a thin film 7 whose refractive index has an intermediate value of the substrate 5 and the waveguide 6 is provided on this waveguide 6. It is not always necessary that such a thin film 7 is made of a material having a non-linear optical effect, and an amorphous film of TiO2, etc. is also available. In this way, by providing the thin film 7 having an intemediate refractive index of the substrate 5 and the optical waveguide 6, the conversion efficiency can be raised more than 30 times as high as that of a conventional one. Also, by providing electrodes 8, 8', connecting the Z surface of the substrate 5, and short-circuiting it electrically, the influence of a pyroelectric effect of the substrate 5 can be reduced. In this way, this element is combined with an infrared semiconductor laser, etc. and used as a small-sized visible laser light source for various optical displays, optical information apparatuses, etc.

Radio-frequency-excited carbon dioxide metal waveguide laser.

Abstract: A new type of waveguide laser is described in which a single-surface concave metal waveguide also doubles as the grounded electrode in a radio-frequency-excited gaseous discharge. The laser’s output modes and spectrum have been studied theoretically and experimentally for cw CO2 operation of the laser. Overall operating efficiency and mode stability are comparable with those of conventional dielectric waveguide CO2 lasers, and advantages of the metal waveguide laser include convection cooling, intracavity mode control, and partial self-alignment.

A note on gyrotron traveling-wave amplifiers using rectangular waveguides

Abstract: The coupling constant e between a relativistic electron beam and the TE 10 rectangular waveguide mode is calculated. By reducing the height of the waveguide, this coupling constant may exceed the corresponding value for the operation with the TE 11 circular polarized mode, under identical conditions of the electron beam. The calculation is followed by a discussion on optimum mode choice in gyro-TWA's.

Effect of mode coupling on the total pulse response of perturbed optical fibers.

Abstract: A computer program has been developed to study the total pulse response of optical fibers with profile ripple and central index depressions in the presence of arbitrary mode coupling. We have found that the magnitude of the compression of the total pulse response generated by mode coupling depends significantly on the details of the refractive-index profile of the test fiber.

Zero dispersion in attenuation optimized doubly clad fibers

Abstract: In a weakly guiding single-mode fiber, there exists an optimum value for the HE 11 mode spot size, which minimizes splicing and microbending losses. Zero dispersion and this optimum spot size for the mode can simultaneously be achieved with any inner-cladding depth; increasing the inner-cladding depth, however, allows smaller dopant concentrations in the core and thus lower intrinsic losses, but this induces an enhanced sensitivity to curvatures and to parameter fluctuations. When the inner-cladding depth is sufficiently high, on the other hand, the fundamental mode has a nonzero cutoff and dispersion can be minimized over a wide spectral range. At \lambda = 1.55\mu m, we determine the optimum value for the inner-cladding depth from criteria of both sensitivity to bending and fabrication tolerances or by requiring a given mode dispersion behavior over a wide spectral range.

Mode coupling loss in single-mode fibers with depressed inner cladding

Abstract: Single-mode fibers with depressed inner cladding show sharp resonant loss peaks near the fundamental mode cutoff wavelength where the core-guided mode starts to become a leaky mode. The magnitude of the loss peak exceeds 200 dB/km and was found to be extremely sensitive to fiber curvature. The phenomenon is attritubed to mode coupling between the core-guided mode and the discrete modes guided in the outer cladding.

Use of far-field radiation pattern to characterise single-mode symmetric slab waveguides

Abstract: The far-field intensity pattern is used for determining the core dimensions and refractive-index difference between core and cladding, of a single-mode (TE) symmetric dielectric slab waveguide. Similarities with the same technique in cylindrical co-ordinates are pointed out.

Losses in optical waveguide formed by silver-sodium ion exchange

Abstract: Propagation losses of optical waveguides formed by ion exchange from molten salts of silver nitrate are discussed The refractive index in pyrex glass substrates is shown to obey an exponential profile and the resultant mode functions are also examined for the graded-index surface waveguide in order to understand the mechanism of a scattering loss The attenuation of the sample waveguides is found to range from 20 to 25 dB/cm for TE 0 mode excitation and to be decreasing with increasing both the mode number of the guided beam and the waveguide thickness that is proportional to a square root of diffusion time These results indicate that the predominant loss origin is silver ion concentration diffused in the glass

Selective waveguide mode converter

Abstract: A mode converter is disclosed which selectively generates a predetermined higher order mode(s) from an incident fundamental mode. This mode converter comprises a dielectric region having an effective-dielectric-constant/thickness profile which is the same as the amplitude profile of the desired higher order mode(s).

Optical fiber fabrication process comprising determining mode field radius and cut-off wavelength of single mode optical fibers

Abstract: A single mode optical fiber manufacturing process can be monitored and/or controlled determining the mode field radius and/or the cut-off wavelength of fiber produced by the process, comparing these measured fiber parameter values to predetermined target values, and setting a process step in accordance with the result of the comparison. Both fiber parameters are determined by a procedure comprising measuring, as a function of angle, the far-field power emitted by a test fiber segment, and determining the parameters of a Gaussian function G(θ), typically by maximizing the value of an overlap integral.

Determination of Single-Mode Fiber Refractive Index Profiles by a Propagation Mode Near-Field Scanning Technique

Abstract: The characteristics of an optical fiber, such as spot size, single-mode condition, and dispersion characteristics, are principally determined by its refractive index profile It is important to establish an efficient and accurate method for measuring the refractive index profile For a single-mode fiber, however, the measurement of the profile is very difficult because of its small core diameter and low refractive index difference Several methods were proposed for the measurement of the refractive index profile of single-mode fibers, such as the far-field radiation pattern technique [1],[2], the scattering pattern method [3], the reflection method [4], the focusing method [5], the refracted near-field technique [6], and the interferometric slab method [7]

Coherent optical measurement of surface roughness and its application in the paper industry.

Abstract: A coherent optical method to measure the surface characteristics of rolling material e.g. paper on line without mechanical contact in industrial enviroument is presented. This method is based on the optical heterodyne detection of light scattered into a single radiation mode by the rough surface. The detection is followed by an appropriate signal processing that makes characterization of the surface smoothness by parameters called "correlation lengths" indicating the average size of uniform surface elements. These parameters show good correlation with other, widely used static surface roughness measurement methods. Furthermore they gi're the possibility of deeper insight into the surface structure of different types of paper.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Comparison of cutoff wavelength measurements for single-mode waveguides.

Abstract: The intrinsic cutoff wavelength of the LP11 mode is investigated using three different types of measurement for an ITT single-mode fiber. Characterization of the far-field pattern of the LP01 mode gives a cutoff value ~660 nm, a near-field transmission experiment gives ~690 nm, and a refracted power measurement gives ~830 nm. We conclude that the refracted power technique is the best experimental method for the determination of the intrinsic cutoff wavelength of a fiber sample. The effect of the loss of coupling efficiency into the LP11 mode as cutoff is approached on the transmission and refracted power experiments is noted.

Mode matching for a passive resonant ring laser gyroscope

Abstract: An analytical method of matching the mode of an input laser to the lowest-order mode of a passive resonant ring laser gyro is described, as are the steps in determining the location and focal length of cylindrical mode matching lenses. Results were obtained with no mode matching, with a compromise spherical lens, with horizontal mode matching only, and with the proper cylindrical mode matching lenses. Compared with no mode matching, the latter case shows that the amplitude of the lowest-order mode is increased ∼2.5 times. In addition, the number and intensity of higher-order modes are reduced to near zero, and the relative intensity of the lowest-order mode to the higher-order mode increased from ∼5 to ∼60 times greater.

An analysis of an abrupt transition from a uniform empty waveguide to a periodically loaded waveguide

Abstract: A ‘ quasi-Green's function ’ for a uniform periodic waveguide of rectangular cross-section has been constructed by examining the modal and space-harmonic behaviour of waveguide slow-wave structures using a mode-matching technique. It has been successfully used to generate a moment method solution for a typical discontinuity problem comprising an end-junction between standard empty waveguide and a uniform periodic waveguide.

Impulse response of single-mode fibers with polarization-mode coupling

Abstract: The transmission properties of a two-mode system with uniform mode coupling are analyzed in detail in the time domain. The impulse response of the system is found analytically taking mode dispersion and frequency-dependent mode coupling into account. By calculating the pulse response when the system is excited with a Gaussian pulse, the effective mode dispersion and energy coupling are determined. Through this analysis it is shown that the coupling will introduce an oscillating tail on the excited mode with a duration equal to the polarization-mode dispersion and a magnitude determined by the ratio between the birefringence and the mode-coupling coefficient. For polarization-preserving fibers this tail may be several nanoseconds long, but the magnitude is likely to be small. The presence of mode coupling reduces the effective mode dispersion but causes the state of polarization to be unstable. Finally it is shown that material dispersion will not affect the polarization-handling properties of the system but leads to oscillating responses from the individual modes.

Experimental study of submillimeter radiation patterns produced by HCN waveguide laser and HCN laser-excitated oversized hollow dielectric waveguide

Abstract: The near and far field patterns that the EH11 waveguide mode produces upon being launched from the end of an oversized hollow dielectric waveguide have been studied in the submillimeter region for a HCN waveguide laser and waveguide excitated by it. Experimental results agree, in general, with the calculation of Degnan using the Fresnel approximation to scalar diffraction theory.

Phase matched optical dielectric waveguide using the artificial anisotropic structure

Abstract: Birefringent material in a thin film dielectric waveguide is used to realize phase matching of the waves with different polarizations. However, this method cannot be used exclusively due to lattice mismatch as happens in a mode conversion type isolator. This paper proposes an artificial anisotropic waveguide realizing phase matching with isotropic dielectric materials only. the structure is a slab waveguide loaded with dielectric strips parallel to the wave propagation direction. This structure can equalize the phase velocities of the Ex and Ey modes. A numerical analysis based on the mode matching technique is used to obtain the phase match condition. the effect of an artificial anisotropy is confirmed in a waveguide fabricated in experiments. A waveguide is realized in which difference of the propagation constants of the Ex and Ey modes is extremely small. It is believed possible that a thin film optical isolator can be reproduced with this waveguide.

Optical branching and coupling fiber

Abstract: PURPOSE:To obtain an ideal fiber-shaped optical branching and coupling fiber by connecting a two-waveguide path fiber and a three-waveguide path fiber. CONSTITUTION:The three-waveguide path fiber 20 has two waveguide paths 21, 22 placed at the same position with waveguide paths 11, 12 that do not cause combination in two waveguide path fiber 10, and a waveguide path 23 placed combinably with above-mentioned waveguide paths. When light (signal) projects on the waveguide path 11 of a fiber 10A of the optical branching and coupling fiber, it is branched to the waveguide path 22 through waveguide path 23 of the fiber 20, and goes out from waveguide paths 11 and 12 of a fiber 10B. When light is projected on wavguide paths 11 and 12 of the fiber 10A, the light is coupled through the waveguide path 23 of the fiber 20 and goes out from waveguide paths 11 and 12 of the fiber 10B. The degree of coupling is determined by constants (thickness, specific difference of refraction etc.), distance and length of waveguide path fiber 20 are connected by heat melting or butted in some cases.

Mode energy transformation between two connected multimode general square-law-index optical waveguides

Abstract: A coherent states method is used to investigate the mode coupling coefficients in the most general buttjoint problem for two multimode general square-law-index optical waveguides, when two different waveguides with elliptical cross-sections are to be butt-jointed with axis displacement, tilt and some turning of symmetry axes with respect to each other. The explicit expressions for the mode coupling coefficients and recurrence relations for the mode overlap integrals are obtained; the sum rules for the mode coupling coefficients are formulated and a method of experimental data analysis is proposed for this general problem. The method of calculating mode coupling coefficients is proposed for the case of the butt-joint problem when the waveguide cross-sections are only partially overlapping and then it is used to investigate the influence of misalignment on mode power distribution and pulse dispersion in the second waveguide. The experimental data are compared and it is shown that the coupling coefficients obtained in square-law-index model can be used in dispersion calculations forα-profile fibres in the case when the valueα is not far from the valueα=2.