Showing papers on "Radiation mode published in 1986"

Dielectric-fibre surface waveguides for optical frequencies

Abstract: A dielectric fibre with a refractive index higher than its surrounding region is a form of dielectric waveguide which represents a possible medium for the guided transmission of energy at optical frequencies. The particular type of dielectric-fibre waveguide discussed is one with a circular cross-section. The choice of the mode of propagation for a fibre waveguide used for communication purposes is governed by consideration of loss characteristics and information capacity. Dielectric loss, bending loss and radiation loss are discussed, and mode stability, dispersion and power handling are examined with respect to information capacity. Physicalrealisation aspects are also discussed. Experimental investigations at both optical and microwave wavelengths are included.

Highly selective evanescent modal filter for two-mode optical fibers.

Abstract: Efficient and selective coupling between a single-mode fiber and the LP11 mode of a double-mode fiber is demonstrated in an evanescent directional coupler. With greater than 90% coupling to the LP11 mode, suppression of the coupled power to the lower-order LP01 mode was measured to be at least 24 dB. This device has application as a modal filter for the construction of in-line all-fiber optical components.

Dual band slotted microstrip antenna

Abstract: A dual band microstrip antenna including a slotted microstrip radiating pllel to and spaced from a ground plane with dielectric material therebetween, the slotted microstrip radiating and having a first resonance corresponding to the dominant radiation mode that would occur in an unslotted microstrip and a second resonance created by the slot. The polarizations of the two resonances are perpendicular to each other with the slot resonance being polarized along the centerline of the slot.

High power mode conversion for linearly polarized HE11 hybrid mode output

Abstract: Efficient plasma heating by ECR-wave irradiation requires axisymmetric, narrow, pencil-like millimetre wave beams with well-defined polarization. The linearly polarized gaussian-like HE11, mode satisfies these conditions best. This quasi-optical hybrid mode can be generated from TE0n gyrotron mode compositions by the two multi-step mode conversion processes: (1) ΣTE0n to TE01 to TE11 to HE11 or (2) ΣTE0n to TE01 to TM11 to HE11. The first scheme has the advantage that the converters can all be made without bends, allowing an arbitrary choice and fast change of the polarization plane. The second scheme does not exhibit this advantage, but it is more suitable at very high frequencies (e.g. 140GHz) because efficient TE01-to-TM11 transducers can be made considerably shorter than serpentine TE01-to-TE11 mode converters. This paper presents computations on mode converter systems of the first type at 70GHz and of both types at 140GHz (ID = 27 · 8 mm for 200kW transmission lines). The structure of wall perturbati...

Integrated optical device

Abstract: An integrated optical device for performing optical data processing in an integrated arrangement using an optical waveguide comprises a substrate, a slab optical waveguide provided on the substrate, a channel optical waveguide provided at a portion of the slab optical waveguide, and a grating coupler provided with a grating structure at a portion of the channel optical waveguide to optically couple the slab optical waveguide and the channel optical waveguide.

Waveguide to be used as optical probe in multiple internal reflection spectroscopic analysis

Abstract: Waveguide apparatus for use in substance analysis has a waveguide, with a surface area in contact with the substance, for transmitting electromagnetic radiation along the axis of the waveguide whereby propagation characteristics of the radiation are altered in accordance with properties of the substance adjacent the waveguide. A waveguide entrance prism is positioned at the radiation entrance end of the waveguide, for guiding radiation into the waveguide. The prism has a first face arranged at an angle with the waveguide axis to cause radiation entering the prism to propagate along the waveguide. In one embodiment, a longitudinal partition is arranged adjacent the waveguide substantially parallel to the waveguide axis, for partitioning the waveguide surface area into at least two parts so that multi-substance analysis can be carried out. In another embodiment, the waveguide entrance prism includes a first face perpendicular to the waveguide axis, and second and third faces at an angle to both the waveguide axis and the first face. In effect, two entrance prisms are provided in the second embodiment. The second embodiment also includes a reflector and filter at the distal end of the waveguide to filter and reflect radiation back to the entrance prism.

Zero dispersion single mode optical fiber with center core and side core in the 1.5 μm wavelength region

Abstract: A 15 μm zero dispersion single mode optical fiber comprising a center core, a side core disposed on an outer side of the center core and having a refractive index lower than that of the center core, and a cladding portion disposed on an outer side of the side core Each of the refractive indices of the center core and the side core has a step-like profile in the direction of the radius of the optical fiber The bending loss is low The mode field diameter can be increased without deteriorating the bending loss, and the splice loss can be reduced The chromatic dispersion varies only to a small extent with respect to changes in the core diameter, so that the zero dispersion wavelength can be well controlled

Photon and atomic statistics in generalized Jaynes-Cummings models

Abstract: The interaction between a single two-level atom and a single mode is studied in some Jaynes-Cummings models. The coupling is supposed to depend on a function of the photon number operator. The evolution operator is calculated; then the probability distribution is obtained. Different statistical quantities are computed for the two states of the atom and different initial distributions for the radiation mode. Three modes are taken and studied, namely thermal, coherent and squeezed coherent light.

Non-reactive radial line power divider/combiner with integral mode filters

Abstract: A parallel plate radial transmission line (14) having parallel plate spacing of less than lambda/2 and which utilizes a specific higher order mode, preferably the first higher order circumferential mode. Undesired modes are suppressed by mode suppression slots (66) formed in one or both of the parallel plates and which are oriented parallel to the current flow lines (68) of the particular mode that is used. These slots (66) have a negligible effect on the mode being used but they couple out other modes that are generated by means such as by imperfections and imbalances in any active devices (36) coupled to the radial line. A centrally located feed is used to launch circularly polarized energy of the TE11 mode in the particular circumferential mode in the radial line (14). The feed may also receive circularly polarized energy of the particular circumferential mode in the radial line, linearly polarize that received energy and conduct it in the TE11 mode.

Longitudinal mode fiber acoustic waveguide with solid core and solid cladding

Abstract: An elastic waveguide, for propagating acoustic waves, consists of an elongated solid core region and an elongated solid outer cladding region. The acoustic waves propagate in a mode where the principle particle displacement is substantially parallel to the longitudinal axis of the waveguide, this mode is called longitudinal mode. The material densities and the bulk shear wave velocities of the core and cladding region are substantially the same but the bulk longitudinal wave velocity of the cladding region is larger than that of the core region.

Frequency and phase locking method for laser array

Abstract: A system and method are described for establishing a common operating frequency and phase for the lasers in a two-dimensional array, each of which has an actual frequency which deviates from a common nominal frequency. A waveguide structure is placed in the path of the beams emitted from the various lasers, and a plurality of optical gratings are provided in the waveguide in alignment with the laser beams to deflect portions of the beams into propagation along the waveguide and into cross-coupling with the other lasers in the array. The periodic gratings are characterized by grating periods substantially equal to λ/n 1 , and the thickness of the waveguide core is at least equal to approximately λ/(4√n 2 2 -n 3 2 ), where λ is the wavelength of the guided mode, n 1 is the effective refractive index for the guided mode, and n 2 and n 3 are the refractive indices for the waveguide core and substrate, respectively. Two-dimensional coupling is achieved either by waveguide coupling in one direction and evanescent coupling in the other direction, or by a pair of gratings for each laser beam at angles to each other to produce waveguide coupling in both directions.

Optical filter and optical device using same

Abstract: An optical filter is formed by providing a plurality of gaps, which have a desired width and such a depth that is larger than the thickness of the waveguide layer, in a slab or a waveguide layer in a three-dimensional optical waveguide so as to extend in the light propagating direction at desired period intervals. These gaps are filled with a film of a material, the refractive index of which is different from that of the waveguide layer, to complete the optical filter. A multiplex wavelength transmission device is formed monolithically by providing at least one optical filter, which is formed in the above-mentioned manner, in an optical waveguide, and arranging one or both of a light-emitting semiconductor element and a photodetector on the side of an optical signal which has passed through the optical filter, and on the side of an optical signal which has been reflected on the same optical filter.

Transmission characteristics of a curved hollow silica waveguide at 10.6 µm

Abstract: Experimental measurements of the transmission and mode output of a 2 mm bore hollow silica waveguide have been made as a function of its radius of curvature. Even a small amount of bending is observed to have a significantly detrimental effect on both transmission and mode output. The results are presented and compared to theoretical predictions. One interesting conclusion of the work is that as the waveguide is bent, coupling of optical energy occurs from the fundamental waveguide mode into higher order modes which have lower attenuation in the curved waveguide. The result is that higher transmission is measured than would have been predicted based on the sole existence of the fundamental mode.

Birefringence calculations in side-tunnel optical fibers: a rectangular-core waveguide model.

Abstract: A side-tunnel optical fiber is approximated by a rectangular-core waveguide, the polarization characteristics of which can be obtained by a simple perturbation analysis. It is shown that birefringence properties of a side-tunnel fiber match well those of the corresponding rectangular-core waveguide.

Coupling device for single mode optical fiber and communications system comprising same

Abstract: Optical radiation can be efficiently removed from, or injected into, single mode optical fiber at an intermediate point along the fiber, by causing quasi-resonant coupling of the guided mode LP01 to an appropriate tunneling leaky (TL) mode, e.g., LP11. Such coupling is caused by means of a "grating" in the fiber, with the grating being formed by impressing a periodic (or pseudo-periodic) modulation on the fiber, or by causing a periodic (or pseudo-periodic) variation of the refractive index of the fiber by means of the photoelastic or the photorefractive effect. The nominal grating spacing ^(z) is chosen such that Oo = (2π/ ) > β01-2πncl^o, where w is the average grating spacing, β01, is the propagation constant of the LP01 mode, ncl is the refractive index of the fiber cladding, and o is the wavelength of the radiation to be coupled from or into the fiber. Furthermore, ^(z) is to be chosen such that Oo β01, - βrs, where βrs is the propagation constant of the selected TL mode. In order for the coupling to be quasi-resonant, it is necessary that αrs, the attenuation constant of the selected TL mode, be relatively small, typically < 1 dB/cm. By appropriately choosing ^(z) and/or the amplitude function of the grating, it is possible to increase the coupling efficiency above what is possible with a constant spacing, constant amplitude grating. Devices according to the invention can be advantageously used not only as radiation couplers but also as filters and, if they are of the photorefractive type, as amplitude modulators.

Refractive optical waveguide interface and lens

Abstract: An integrated optical waveguide structure which provides for efficient, single-mode propagation of light across an interface between two contiguous waveguide layers of differing effective refractive index. The waveguides are formed by layers of increased index of refraction formed at the surface of a substrate and serve to support propagation of optical electromagnetic radiation along the surface of the substrate. A refractive interface is provided at the interface of two such surface layers supporting modes of differing effective indexes of refraction. By underlying one of the surface layers with an additional layer having a particular, but different, index of refraction, a single mode of propagation is supported throughout both of the surface waveguides. General applications in the formation of optical waveguide components as well as a more extensive treatment with the formation of a lens is also disclosed using proton exchange in crystalline LiNbO3.

Threshold current analysis of InGaAsP-InP ridge-waveguide lasers

Abstract: The marked depression of the refractive index by injected carriers in the InGaAsP-lnP material system essentially influences the performances of laterally inhomogeneously pumped laser diodes such as the usual ridge-waveguide structures. This is because, together with the built-in index guiding, an M-shaped waveguide is formed that may become leaky even for the fundamental waveguide mode. The characteristics of these waveguides are calculated and compared with previous results. Hence, the waveguide structure is studied for a wide range of device parameters showing that optical losses can be kept within acceptable limits by applying effective index steps in excess of 0.02. Furthermore, the mode gain is calculated for the corresponding carrier profiles and the threshold current is estimated. According to experiment, the results show that threshold currents around 20 mA can be achieved with appropriate waveguide structures at wavelengths of 1.3 μm and 1.55 μm

Differential mode loss and mode conversion in passive fiber components measured using the chromatic launching and the central spot far field techniques

Abstract: Mode spectra launched conventionally and using the chromatic launching (CL) method are analyzed using the central spot far field (CSFF) method. This is applied to study the differential mode loss and mode conversion properties of passive optical fiber components manufactured using the fused-head-end (FHE) technique.

Polishing-induced birefringence in single-mode fibers.

Abstract: Polishing a flat surface on a fiber changes the birefringence at the core or introduces birefringence in a circular fiber. In this paper, a circularly symmetric fiber is studied both experimentally and by a simple model in which the birefringence arises from the application of forces along the polished surface. The polishing-induced birefringence first rises to a maximum and then falls off as the polished surface approaches the core.

Waveguide type optical multiplexer/demultiplexer

Abstract: PURPOSE:To improve the transmission characteristic by using a single mode optical waveguide as one of optical waveguides which are coupled by reflection with a wavelength selecting element between them and using a multimode optical waveguide wider than the single mode optical waveguide as the other. CONSTITUTION:The optical wave from a light emitting element 7 is propagated in a single mode optical waveguide 2 including an interference film filter 4 and is coupled to a single mode optical fiber 6. Meanwhile, the optical wave from the single mode optical fiber 6 is reflected on the interference film filter 4 and is propagated in a multimode optical waveguide 5 placed in the reflection optical path and is coupled to a light receiving element 8. The interference film filter 4 is stably fixed with a good perpendicularity because a groove part 3 for interference film filter insertion has a depth to reach the inside of a silicon substrate 1, and the optical waveguides 5 in the reflection optical path to which the emitted light from the optical fiber 6 is reflected on the interference film filter 4 is constituted with a multimode optical waveguide wider than the single mode optical waveguide 2. Thus, the work precision of the groove part for interference film filter insertion is considerably reduced, and economization and characteristics of a multiple wavelength transmission system are improved.

Mode coupler for monopulse antennas and the like

Abstract: A coupler for extracting energy in the TE 21 mode from a circular waveguide propagating energy in both the TE 11 and TE 21 modes, characterized in that an annular iris on the inner circumference of the waveguide and a longitudinally stepped transition portion of the waveguide define therebetween a TE 21 mode resonant cavity which is coupled via a narrow axially extending rectangular slot contained in the wall portion of the waveguide which defines the cavity. At least one external resonant chamber may be provided on the waveguide through which the TE 21 mode energy is extracted and transmitted to a detector thereof via the slot, which chamber cooperates with the resonant cavity to define a multiple resonant filter for improving the matching to the TE 21 mode while reducing the perturbation to the TE 11 mode.

The influence of mode partition fluctuations in nearly single longitudinal mode lasers

Abstract: A simple relationship between the mode ratio of a two-mode laser and an empirical mode partition coefficient is derived. The effects of the mode ratio of a two-mode laser on the bit-error-rate floor of an optical fiber system are calculated, and the power penalties due to mode partitioning in the presence of Gaussian receiver noise are evaluated. The analysis provides a simple way to calculate the effects of mode ratio on the sensitivity of optical receivers.

Spectral polarization method for the determination of birefringence and polarization dispersion in strongly birefringent single-mode waveguides

Abstract: It is shown that a spectral polarization method can be used to determine directly the spectral dependence of the polarization dispersion of radiation propagating along a single-mode fiber waveguide, and of the "group" birefringence proportional to this dispersion. The interpretation of the results is confirmed experimentally by a study of a model sample of a birefringent crystal and of a single-mode fiber waveguide using other methods. It is also shown that this method can be used to determine highly accurately the cutoff wavelength of a single-mode fiber waveguide.

Single Mode Fibre Characteristics

Abstract: Single mode fibres (having circular symmetry) are now being extensively used in fibre-optic communication systems. In this paper, starting from the definition of a mode, we have discussed the important characteristics of these fibres such as the material and waveguide dispersion, attenuation, near and far-field radiation patterns, splicing and microbending losses, various spot sizes, etc. We have also discussed the commonly-used Gaussian approximation and its limitations.

High-efficiency light modulator using guided-to-radiation mode coupling in a graded-index waveguide.

Abstract: Analysis and experiment were done on a light intensity modulator using guided-to-radiation mode coupling in a graded-index waveguide; high-efficiency modulation was demonstrated in the Nb-diffused Z-cut LiTaO3 waveguide. In the analysis, we developed a numerical integration method for modal analysis of a graded-index waveguide and showed that more than 50-dB/cm modulation efficiency is obtainable in a Nb-diffused Z-cut LiTaO3 waveguide by choosing an appropriate amount and depth of Nb diffusion. After studying the characteristics of Nb diffusion into Z-cut LiTaO3 we fabricated slab and channel waveguide modulators. The measured modulation depth was 28 dB/5 mm at 400 V across 50-μm spaced electrodes in the slab modulator and was 19 dB/5 mm at 70 V across 10-μm spaced electrodes in the channel modulator.

Accurate numerical analysis of an elliptically cored optical fiber for polarization preservation, using mode-matching method

Abstract: The Mode-Matching Method has been known as an accurate and reliable method for numerical analysis not only on the diffraction problem in the electromagnetic field, but also on the elastic waveguide and the optical thin-film waveguide. This method is applied for the rigorous analysis of an elliptically-cored optical fiber with large ellipticity whose accurate analysis in the wide range of frequency including the cutoff has so far been difficult. Moreover, a very high degree of accuracy of five figures is achieved for the normalized propagation constant. Both the dispersion relation and the field distribution in the hybrid modes are clarified and it is also confirmed that the hybrid mode analysis is not always necessary in the case of larger ellipticity. The properties of the higher-order mode cutoff and the polarization preservation whose rigorous discussion has not been always sufficient, are analyzed more accurately. The results are compared with the results obtained by other methods, and more exact design data for the single mode, polarization-preserved optical fiber with elliptical core are presented. Through these analyses, it is also confirmed that the Mode-Matching Method is still a useful and reliable method for rigorous analysis of the rod-type dielectric waveguide with arbitrarily shaped cross section.

Comparison between pseudomode and radiation mode methods for deriving microbending losses

Abstract: With a curvature power spectrum proportional, for example, to ??(4+2?) the agreement between Gambling's and Peter-to ??(4 + 2?) theories was found to deteriorate dramatically for large values of ?. Gambling's method always leads to a higher loss than Petermann's; the ratio of both results can reach 10 or more in realistic cases.

Dual core single mode optical fiber with refractive index groove

Abstract: PURPOSE:To suppress an increase in transmission loss due to bending and microbend loss by using dual cores with a refractive index groove, making the refractive index of the 2nd core larger than that of a clad, and making the refractive index of the 1st core at the center part larger than that of the 2nd core. CONSTITUTION:An optical fiber is constituted by arranging the 1st core, the 2nd core 2, an intermediate layer 3, and the clad 4 concentricaly in order from the center and the refractive indexes of the respective layers are denoted as n1, n2, n3, and n4 respectively. The refractive index n1 of the 1st core 1 is largest and the refractive index n3 of the intermediate layer 3 is smallest. The refractive index n2 of the 2nd core 2 is an intermediate value between the refractive index n4 of the clad 4 and the refractive index n1 of the 1st core 1. Consequent ly, the optical fiber has a wide wavelength band of 1.5mum in wavelength where the smallest loss is expected, and the dual core single core optical fiber which is tolerant to bending loss and microbend loss is obtained.

Waveguide-containing communication and sensing systems

Abstract: An optical system, including a waveguide (e.g., 50) such as an optical fiber, in which optical signals are noninvasively coupled into the waveguide at any point along the length of the waveguide, is disclosed. This is achieved by coupling substantially constant intensity electromagnetic radiation (e.g., 65) into the waveguide, and then impinging upon the waveguide a directed beam of energy (e.g., 851, from an energy source. Alternatively, the waveguide is impinged upon by a combination of an energy beam and a stimulus, e.g., a temperature change. The energy beam, or energy beam and stimulus, induce at least partial absorption of the guided, substantially constant intensity electromagnetic radiation by radiation-absorbing material in the waveguide, to produce the desired optical signal.