Showing papers on "Radiation mode published in 1988"

Apparatus using two-mode optical waveguide with non-circular core

Abstract: An apparatus utilizes a two-mode optical waveguide with a non-circular core to provide stable spatial intensity patterns in both propagation modes for light propagating therein. The light has a wavelength, and the non-circular core has cross-sectional dimensions selected such that (1) the waveguide propagates light at that wavelength in a fundamental mode and a higher order mode, and (2) substantially all of the light in the higher order mode propagates in only a single, stable intensity pattern. Embodiments of the invention include, for example, modal couplers, frequency shifters, mode selectors and interferometers. One of the interferometer embodiments may be used as a strain gauge.

Local normal mode analysis of guided mode interactions with waveguide gratings

Abstract: The reflection of a guided mode obliquely incident to a periodic, shallow, surface corrugation, waveguide grating is analyzed using the local normal mode expansion of coupled-mode theory. The coupling coefficients which give the strength of the TE-TE, TE-TM, TM-TE, and TM-TM mode interactions are evaluated as a function of incidence angle. The results are compared to the coupling coefficients obtained using a number of other analytical techniques. >

Fiber optic inter-mode coupling single-sideband frequency shifter

Abstract: A birefringent single-mode optical fiber (200) which propagates light into orthogonal polarization modes is subjected to a series of second order traveling flexural waves for propagation within the fiber (200). An acoustic wave generator (202) applies a periodic lateral squeezing force to the fiber (200), thus causing a second order flexural wave to propagate within the fiber (200). The wavelength of the second order flexural wave is selected to cause light propagating in one polarization mode to be coupled to the orthogonal polarization mode. The optical signal in the second orthogonal propagation mode has a frequency which is equal to either the sum of or the difference between the frequency of the optical signal in the first propagation mode and the frequency of the traveling flexural wave. The frequency of the optical signal in the second orthogonal propagation mode is shifted upward of or downward from the frequency of the optical signal in the first propagation mode as determined by the direction of propagation of the first optical signal with respect to the direction of propagation of the traveling flexural wave, and as also determined by whether the phase propagation velocity of the optical signal in the first propagation mode is greater or less than the propagation velocity of the optical signal in the second propagation mode. The centripetal couple of squeezing forces is preferably oriented at an angle of substantially 45° with respect to the axes of birefringence of the fiber (200).

Grating-coupled surface emitting laser and method for the modulation thereof

Abstract: Disclosed is a grating-coupled surface emitting laser capable of obtaining a beam with high directivity, structured by forming a light output window in a limited regions with high intensity radiations along the propagation direction. Its intensity distribution of radiation mode along the axis can be controlled by injecting a current independently into the multiply-divided electrodes or by pumping optically these electrodes independently. The control is, in principle, achieved by an equivalent change of the phase-shift of the gratings.

Dynamic coupler using two-mode optical waveguides

Abstract: An optical mode coupling apparatus includes an optical waveguide in which an optical signal at a signal wavelength propagates in a first spatial propagation mode and a second spatial propagation mode of the waveguide. The optical signal propagating in the waveguide has a beat length. The coupling apparatus includes a source of perturbational light signal at a perturbational wavelength that propagates in the waveguide in the first spatial propagation mode. The perturbational signal has a sufficient intensity distribution in the waveguide that it causes a perturbation of the effective refractive index of the first spatial propagation mode of the waveguide in accordance with the optical Kerr effect. The perturbation of the effective refractive index of the first spatial propagation mode of the optical waveguide causes a change in the differential phase delay in the optical signal propagating in the first and second spatial propagation modes. The change in the differential phase delay is detected as a change in the intensity distribution between two lobes of the optical intensity distribution pattern of an output signal. The perturbational light signal can be selectively enabled and disabled to selectively change the intensity distribution in the two lobes of the optical intensity distribution pattern.

Multimode channel waveguide optical coupling devices and methods

Abstract: A waveguide, approximately Y-shaped in plan view, provides coupling between first and second optical fibers, each attached to an end of the waveguide on the branched portion of the Y, and a third fiber attached to the single end of the Y. A fourth fiber, smaller in cross section than the waveguide on the single-ended portion of the Y and placed with its adjacent end therein between the junction of the Y and the third fiber, and bent gradually to one side, extends away from the waveguide before reaching the end to which the third fiber is attached. Typically the first fiber directs light from an emitter into the waveguide, the second fiber directs light away from the waveguide to a detector, the third fiber directs light away from the waveguide to a reference detector, and the fourth fiber directs light away from the waveguide to a sensor and back from the sensor into the waveguide.

Mode conversion due to discontinuities in modified grounded coplanar waveguide

Abstract: Modified grounded coplanar waveguide (CPW) is the same as conventional grounded coplanar waveguide except that the side planes are not of infinite extent. This structure is overmoded, but is still used in monolithic circuits since it does not require via holes. Conversion from the desired CPW mode to an undesirable microstrip-like mode is calculated using a full-wave analysis. The results indicate that mode conversion occurs at discontinuities, but that it is a small effect. In very-high-Q circuits, resonances may occur due to this coupling, but this conversion can be made small for reasonable structural dimensions. >

Slot antenna in circular waveguide.

Abstract: Disclosed is a circular waveguide in which a slots are formed which are shaped and disposed such that they interrupt either the right hand or left hand circulating mode (RC and LC respectively) residing in the waveguide. Locating the slots in the waveguide wall is accomplished in accordance with the theory that for TE modes in circular waveguide with circumferential variation of e.sup.±jmφ, current flow lines are produced that are helical. The slots are located so as to interrupt the helical current of the desired mode. In one embodiment, an ortho-polarization mode transducer and a circular polarizer are used to feed the slotted waveguide. By control of the amplitude and phase of the energy propagating in the waveguide, aximuthal pattern control can be effected. By dielectric loading the waveguide to make λ g in the loaded waveguide equal to λ-free space, endfire radiation can be achieved.

Optical waveguide element, method of making the same and optical coupler employing optical waveguide element

Abstract: An optical waveguide element includes an optical waveguide formed on a light-transmissive dielectric substrate and having a higher refractive index than the refraction index of the substrate, the optical waveguide including a region having an effective refractive index which varies nonlinearly in a direction in which a light wave is propagated through the optical waveguide. The light wave guided through the optical waveguide enters the region, in which the angles of incidence and reflection of the guided wave at the boundary between the region and the substrate is gradually reduced due to the variation in the effective refractive index. When the angles of incidence and reflection of the guided wave becomes smaller than a critical angle, the guided wave is emitted out of the waveguide. Since the effective refractive index changes nonlinearly with respect to the distance the guided wave is propagated, the light emitted into the substrate tends to converge at a point, and the beam pattern of the emitted light is spread less.

Fiber optic sensor for detecting mechanicl quantities

Abstract: A fiber optic sensor for the detection of mechanical quantities comprising a light source, a first fiber optic waveguide coupled to the light source, the front face of the first waveguide being ground at a 45° angle to the axis of the fiber and mirrored, a second fiber optic waveguide arranged parallel to the first waveguide, the front face of the second waveguide being ground at a 45° angle to the axis of the fiber and mirrored, the two mirrored faces being held opposite to one another, and a photoelement receiver coupled to the other end of the second waveguide. At least one of the waveguides can move either along the fiber axis or around the fiber axis relative to the other waveguide, the motion varying the light received by the receiver and thereby indicating the magnitude of the mechanical quantity.

Covered optical waveguide having an inlet opening

Abstract: An optical waveguide device includes an optical waveguide extending straight over a predetermined length, a metal cover layer formed on the optical waveguide at least partly and formed with an opening extending therethrough, and a prism fixedly attached to the metal cover film covering the opening. The prism has an index of refraction higher than that of the optical waveguide and the prism receives an incoming light beam and causes the light beam thus received to be coupled into the optical waveguide through the opening. The device may include a substrate on which the optical waveguide is formed with or without a buffer layer therebetween. A photodetector may also be formed integrally with the optical waveguide at one end thereof for detecting light coupled into and propagating along the optical waveguide. Such a device including a photodetector may be used as an optical component of an optical pick-up for use in an optical information recording and reproducing system.

Ribbon beam free electron laser

Abstract: An FEL array is comprised of adjacent FEL modules. Each module preferably uses a ribbon beam plasma-anode E-gun (PAG) or another plasma-assisted E-gun to produce a planar E-beam that interacts with a planar wiggler magnetic field. The modules may share a common electron gun. A control signal is input through a phase priming array to preselect the radiation mode. A planar, distributed Bragg resonator/reflector is used to set up a high-Q cavity, enabling the low gain module to produce high power radiation. The FEL modules are arranged in an array to reduce the output radiation flux density while achieving high output power density in the far-field, and to permit beam steering by phase control of individual modules. The relatively low current density of the individual E-guns lessens the size of the guiding magnetic field in each module to the extent that the wiggler magnetic field alone is sufficient to perform this guiding function.

Optical waveguide switch

Abstract: An optical waveguide switch is disclosed in which at least two optical waveguides intersect at a predetermined angle to each other to provide, on both sides of the intersection region, input side optical waveguide regions for receiving incident light and output side optical waveguide regions for outputting guided light, and in which the incident light is input into one of the input side optical waveguide regions and is output from a desired one of the output side optical waveguide regions. In accordance with the present invention, an optically nonlinear material whose refractive index undergoes a substantial variation, depending on the intensity of incident light, is disposed in the intersection region. A loop is provided in association with a corresponding one of the input side optical waveguide regions for essentially branching the guided light in the corresponding waveguide output side optical waveguide region for feedback to the corresponding input side optical waveguide region.

Non-reciprocal optical waveguide device, particularly for use as an isolator or circulator

Abstract: The invention relates to a non-reciprocal optical element, particularly for use an an isolator or circulator, which is connected to at least two monomode optical waveguides and which has a magneto-optical waveguide structure which is subjected to a transversal magnetic field directed perpendicularly to the direction of propagation of the optical wave. This arrangement is simplified by combining the functions of the coupler and the phase shifter, which is achieved by means of the following features: the magneto-optical waveguide structure (1,11) is formed as a multimode waveguide which can propagate at least one fundamental mode (5) and the first-order mode (6), the optical waveguides (A,B,C,D,9,10) are off-centered with respect to the waveguide structure (1,11), the dimensions and/or the cross-sectional distribution of the refractive index of the optical waveguide structure (1,11) are chosen to be such that the two modes (5,6) have a reciprocal phase difference of (π2)+pb 2nπ the magnetic field strength and/or the structural build-up of the magneto-optical waveguide structure (1,11) are chosen to be such that the two modes (5,6) have a non-reciprocal phase difference of (π2)+2mπ in which n and m may be integers including 0.

Shortened dual-mode horn antenna

Abstract: A hollow waveguide includes a conductive peripheral wall arrangement centered on a longitudinal axis. The waveguide is short-circuited at a first transverse plane. A center conductor is connected to the short-circuit and extends along the longitudinal axis to an abrupt open circuit termination at a second transverse plane. The arrangement is fed at a location between the first and second transverse planes to produce both a fundamental waveguide mode and a center-conductor coupled mode. The fundamental mode has an amplitude taper in the horizontal direction but not in the vertical direction. At the abrupt termination, a higher-order waveguide mode is generated which, when phase-shifted by 180°, provides an amplitude taper in a vertical direction. A radiating aperture located near the 180° phase shift point produces a radiation pattern which is similar in both the verticla and horizontal planes.

Radiation mode composition of open resonators in the form of axisymmetric, weakly irregular waveguides

Abstract: Reduction of spurious wave conversion in irregular sections of an opencylindrical resonator is studied. The relative power level of extraneous waves at the output of a resonator with a sinusoidally varying radius is considered. It is shown that improvement in radiation purity is possible through optimization of the output waveguide junction profile.

Optical waveguide coupling device

Abstract: An optical coupling device for use as a wavelength division multiplexer or demultiplexer comprises an array of first optical waveguides 2-5 for carrying respective optical channels comprising optical signals with different wavelengths lambda 1- lambda 4; and a second optical waveguide 1 for carrying a wavelength division multiplex of the optical channels. A diffraction grating 8 may be provided to couple each channel between the respective first waveguide 2-5 and the second waveguide 1. Each first waveguide 2-5 has a tapered optical field spot size to assist in reducing the channel spacing of the device. The increase in spot size may be achieved by physically tapering the fibre or by changing the core region by diffusion.

Low-loss twists in oversized rectangular waveguide

Abstract: The unwanted mode conversion from twists in overmoded waveguides is calculated from numerical integration of the coupled-mode equations, considering simultaneous coupling of the five lowest-order modes coupled in a twist. Twists with tapered or linearly varying rates of twist are shown to be superior in medium- or broad-band applications to those with uniform twist rate. Measurements consistent with these theoretical calculations are discussed for uniform twists in WR90 waveguide at 60 GHz and for an electroformed twist having a linearly tapered rate of twist in WR187 waveguide from 15.7 to 17.7 GHz. The coupling coefficients needed in the calculations are derived and are compared with the results of other work, including a modal expansion of the dominant mode in twisted waveguide. The work also considers the transmission through an oversized waveguide with a mode converter generating a trapped unwanted mode, and the result for the dependence of the resonance depth on the mode conversion and the attenuation of the trapped mode is found. >

Nonlinear optical waveguide device including grating for changing of the wavelength of light

Abstract: A device for the changing of the wavelength of light comprising a non-linear optical crystal, first and second optical waveguides that are formed in the non-linear optical crystal, and an introducing means that is positioned adjacent to the second optical waveguide, the light being incident upon the first optical waveguide and propagated within the first optical waveguide, resulting in harmonic light that satisfies the phase-matching conditions, and the harmonic light being introduced, by the introducing means, into the second optical waveguide from which the harmonic light is output.

Optical demultiplex element

Abstract: PURPOSE:To divide optical signals having narrow wavelength intervals with a small extinction ratio, by installing a means which gives an optical loss to at least one of two optical waveguides. CONSTITUTION:When multiplexed optical signals lambda1 and lambda2, whose wavelengths are about 1.55mum and wavelength intervals are about 0.1nm, are inputted, the optical signal lambda1 and lambda2 are branched at a ratio of about 1:1 by means of an optical coupler 3 and propagated to two optical waveguides 2a and 2b having different optical paths. Since the optical waveguides 2a and 2b have different optical paths, radii of curvature, etc., their propagation losses are different from each other and, as the waveguide 2b has a longer optical path and smaller radius of curvature as compared with the other waveguide 2a, the propagation loss of the wavelength 2b is larger than that of the other waveguide 2a by about 1dB. Therefore, the optical signals lambda1 and lambda2 propagated through the optical waveguide 2b become smaller in power than those propagated through the other waveguide 2 by about 1dB. Accordingly, a voltage of about 10V is impressed across electrodes 4 and sothat the specific refractive index of the optical waveguide 2a' can be made smaller and the radiation mode can be made larger. Thus the powers of the optical signals lambda1 and lambda2 propagated through the optical waveguides 2a are made smaller by about 0.5dB so as to make the difference in propagation loss between the two optical waveguides 2a and 2b smaller by about 0.5dB.

Method of measuring polarization and birefringence in single-mode optical fibers

Abstract: A constant force perpendicular to the fiber axis is applied to the fiber so as to cause a power coupling from the fundamental mode, which is guided, to a secondary mode which is irradiated, and the intensity of the scattered radiation associated with that secondary mode is measured. Such intensity depends on the local state of polarization. By dispacing the force application point step by step along the fiber axis and by measuring for each point the intensity of the scattered radiation, beat length is obtained as the distance between two consecutive points where the scattered radiation has the same intensity.

Channel waveguide modulator

Abstract: An optical modulator comprises a crystal whose top surface includes an channel waveguide (12, 22) whose axis makes an angle with the crystal optic axis larger than the critical angle for TE-polarized leaky mode propagation. An electrode structure (13, 23, 24) overlies the top surface of the crystal for inducing mode conversion of TM-polarized waves propagating in the waveguide to lossy radiation modes.

Index guided semiconductor laser device

Abstract: An index guided semiconductor laser device comprising a striped optical waveguide in the active layer, at least a part of the wavegide having continuous indentations at the interface between the waveguide and the outside of the waveguide, whereby only laser light of a high-order transverse mode is radiated from the waveguide to the outside of the waveguide and only laser light of the fundamental transverse mode is propagated within the waveguide.

Optical fiber tap

Abstract: PURPOSE:To obtain branched light with excellent transmission characteristics while suppressing the mode conversion loss of transmission light by optically coupling a main line with a tap fiber without reducing the radius of curvature of a main line optical fiber too small CONSTITUTION:The main line optical fiber 1 consists of a multi-mode optical fiber having a core 3 and a clad 5 and a part of light in a waveguide mode is converted into clad mode light at a mode conversion area 8 in a bent part 1a Since a gap between the area 8 and the one end part 2a of the tap fiber 2 is filled with a light translucent material 7 having >=1 diffractive index, the clad mode light in the area 8 can be lead into the material 7 and made incident on the fiber 2 Since only a part of the waveguide mode light is converted into the clad mode light in the area 8 without converting the clad mode light up to radiation mode light and it is unnecessary to reduce the radius R of curvature of the bend part 1a too small, the mode conversion loss of the transmission light can be suppressed

Wavelength tuning and switching of a coupled distributed feedback and Fabry--Perot cavity laser

Abstract: We present a theoretical analysis of a newly demonstrated semiconductor laser with coupled distributed feedback and Fabry–Perot (DFB‐FP) cavities and show that three modes of operation are possible for such a laser. In mode‐switched DFB mode, the wavelength can be switched between longitudinal modes on either side of the stopband. In coupled‐cavity laser mode, there are successive mode hops inside the stopband. Finally, in continuously tunable distributed Bragg reflector mode, a wide wavelength tuning range (4.8 A) without mode hopping can be obtained. The analysis is general enough to be applied to any laser with a periodic waveguide section, and provides an understanding of the mechanisms and the limits of wavelength tuning in such lasers. This type of laser has very important applications in coherent optical communications.

Electro-optical waveguide device

Abstract: PROBLEM TO BE SOLVED: To provide an electro-optical waveguide device which is made extremely smaller in size as compared with the prior art and is improved in performance. SOLUTION: This waveguide device has a device 10 formed of a multilayered structure and includes a waveguide core layer 18 sandwiched between two light confinement layers 16, 32 having a low refractive index. This waveguide core layer 18 is part of diode structures 16, 18, 32 and turns to a charge carrier depletion layer under the reverse bias impressed by the light confinement layers 16, 32. Grooves 20 forming the individual waveguides 30 of the array extend to at least part of the waveguide core layer 18. These grooves 20 house media having the refractive index lower by at least 1.5 than the refractive index of the waveguide core layer 18 in order to prohibit the optical coupling between the adjacent waveguides 30. The waveguides 30 consist of an electro-optical material designed to prohibit the output of unnecessary space modes. The device includes the array of such waveguides 30 with which the electrical biasing is possible.

Optical-fiber reference-value transmitter

Abstract: The optical-fiber reference-value transmitter comprises an optical waveguide coil with at least one winding layer, within which the sections of the optical waveguide fiber between adjacent turns are of equal length. A pressure finger which is connected to a mechanical distance pickup is guided over the layer of the winding and in the process exerts a mechanical pressure on a comparatively narrow zone of the optical waveguide fiber of a turn, whereby a so-called microbending effect is generated in the waveguide fiber. An opto-electronic transmitting and receiving apparatus which is connected to the optical waveguide fiber determines the location of the pressure point caused by the pressure finger and thereby, the position of the pressure finger.

Towards the optimization of dielectric branching waveguides: the effect of longitudinal variations in the branching angle

Abstract: Mathematical models that describe mode propagation in planar Y-branch waveguides indicate there is a region in the branch where mode conversion occurs, provided asymmetry exists in the waveguide geometry or refractive index profile. Since the mode conversion is influenced by the degree of asymmetry and by the branching angle, the Y-branch can be designed to act as a power divider or as a mode splitter. The problem of identifying constant width Y-branch structures where longitudinal variations in the branching angle are introduced to optimize the power division or mode-splitting properties of a branching waveguide is considered. This constrained optimization is performed using forward dynamic programming and a compatible method of mode propagation analysis, the step approximation technique. The propagation characteristics of the optimized waveguide structure are compared to those of conventional constant-slope waveguides. >

Wide wavelength band/low dispersion single mode optical fiber

Abstract: PURPOSE: To obtain strong bending characteristics in a wide mode field diameter without losing wide wavelength and low dispersion characteristics by specifying the diameter of a 1st core and a specific refractive index difference between the 1st core and an outermost clad. CONSTITUTION: The title optical fiber has the distribution of refractive indexes so that the refractive index of the 1st core 1 is larger than that of the outermost layer clad 5, the refractive index of a 2nd core is almost equal to that of the clad 5, the refractive index of a 1st clad 3 is smaller than that of the clad 5, and the refractive index of a 2nd clad 4 is larger than that of the clad 5 and smaller than that of the 1st core 1. The diameter of the 1st core 1 is 4W6μm and the specific refractive index difference between the 1st core 1 and the outermost layer clad 5 is 0.45W0.7%. Consequently, the single mode optical fiber provided with high bending loss characteristics in a large mode field diameter can be obtained without losing the wide wavelength band and low dispersion characteristics. COPYRIGHT: (C)1989,JPO&Japio