Showing papers on "Radiation mode published in 1985"

Passive harmonic source ranging in waveguides by using mode filter

Abstract: The conventional beam‐forming technique cannot be used for source location in a waveguide because of the modal interference structure of the field. In this paper a new method of passive source ranging in a layered waveguide is proposed. The mode filtering processor was used to process the field data of a vertical array to obtain individual modes. The source range information can be extracted by measurement of three individual mode phases. The source range was expressed in terms of the ‘‘mode interference distance’’ as follows: r=Li j*Di j+Δri j; Δri j=Di j ×(δφi j/2π), where Li j is a certain integer, δφi j is the phase difference of the ith and jth modes, Di j is the ‘‘mode interference distance’’ defined by Di j=2π/(ki−k j), and ki is the wavenumber of the ith mode given by a numerical mode code. The information of Li j can be estimated by means of comparison with the phase of the jth mode with another mode, say the mth mode, and then Li j would be estimated by solving the following equation: (δφ jm/2π)...

Device for tapping radiation from, or injecting radiation into, single made optical fiber, and communication 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 LP 01 to an appropriate tunneling leaky (TL) mode, e.g., LP 11 . 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 Λ(z) is chosen such that Ω o =(2π/Λ)>β 01 -2πn cl /λ o , where Λ is the average grating spacing, β 01 is the propagation constant of the LP 01 mode, n cl is the refractive index of the fiber cladding, and λ o is the wavelength of the radiation to be coupled from or into the fiber. Furthermore, Λ(z) is to be chosen such that Ω o ˜β 01 -β rs , where β rs is the propagation constant of the selected TL mode. In order for the coupling to be quasi-resonant, it is necessary that α rs , the attenuation constant of the selected TL mode, be relatively small, typically <1 dB/cm. By appropriately choosing Λ(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.

Integrated structure for bi-directional optical fiber transmission

Abstract: An integrated structure for bi-directional optical fiber transmission has a laser diode, a photodetector, and a bi-directional optical waveguide integrated on a common substrate, the waveguide guiding radiation from the laser diode out of the structure and directing incoming radiation of a different wavelength through the structure to the photodetector. The structure also includes a passive optical component cooperating with the strip waveguide for substantially isolating the radiation propagated in one direction in the waveguide from the laser diode, and substantially isolating the radiation propagated in the opposite direction in the waveguide from the photodetector. A method for manufacturing this structure includes essentially growing two epitaxial multi-layer structures spaced from each other and covering selected portions of the substrate constituting the laser diode and the photodetector, with the strip waveguide extending therebetween.

Generation of the Gaussian-like HE11 mode from gyrotron TEOn mode mixtures at 70 GHz

Abstract: This work reports calculations and measurements on mode converters for the transformation of TEOn gyrotron mode mixtures (primarily TEO2) into the linearly polarized HE11 hybrid mode at 70 GHz. This mode is ideal for quasi-optical launching systems for ECRH of plasmas. Mode transducers with axisymmetric radius perturbations convert the gyrotron TEOn mode composition into the TEO1 mode. Proper matching of the phase differences between the various modes and of the perturbation amplitudes of the several converter sections is required. The TEO1 wave is used for long-distance transmission through smooth-walled overmoded waveguides. A mode converter with constant diameter and periodically perturbed curvature transfers the unpolarized TEO1 mode into the polarized TE11 wave. The experimentally determined ΣTEOn-to-TEO1 conversion efficiency is (98.5±1)% (99% predicted) while the TEO1-to-TE11 transformer has a (94±2)% efficiency (93% theoretically); ohmic losses are included. The “Gaussian-like” HE11 mode with axisymmetric power distribution and almost no cross polarization is produced in a circumferentially corrugated TE11-to-HE11 mode transducer with a measured conversion efficiency of (98.3±1.5)% (98.5% predicted). The overall efficiency of the complete mode converter system in the desired mode was determined to be (91±2.5)%. High-power operation (200kW, 100ms) has been successfully demonstrated.

Modal cutoffs in single- and few-mode fiber couplers

Abstract: Optical coupling, or crosstalk, between two parallel, identical single- or few-mode fibers is describable as a superposition of the modes of the composite waveguide. Like the modes of a single-fiber waveguide, the modes of the two-fiber waveguide are cut off. Exact and simple accurate asymptotic formulae are derived giving the cutoff value as a function of separation. For single-mode couplers, perturbation theory gives the fundamental and second modes \Psi+ and \Psi- as the sum and difference of the fundamental modes \Psi_{1} and \Psi_{2} of each fiber. In reality \Psi+ is the fundamental mode of the composite waveguide, whereas \Psi- is the second mode and has a finite cutoff. This limits the smallest V -value for which low-loss coupling is possible. The limitation is least severe for step-profile fibers.

Laterally coupled optical amplifier

Abstract: A method and apparatus for amplifying bandwidths of light energy propagated in an optical transmission waveguide in which a length of gain medium optical waveguide is coupled between spaced waveguide end sections defining amplifier input and output ports. The gain medium optical waveguide is preferably defined by an optical fiber core and cladding in which portions are formed of neodymium doped glass. The gain medium fiber is pumped by light energy in a spectrum absorbed by neodymium to provide light energy in wavelength regions including the bandwidth of interest. Noise resulting from the pumping light energy source, as well as spontaneous emission outside of the bandwidth of interest are filtered by dispersive lateral coupling of the gain medium optical fiber to the transmission waveguide.

Intrinsic mode theory of tapered optical waveguides

Abstract: The concept of an ‘intrinsic’ mode has recently been devised as the basis for a systematic theory of wave propagation in slowly varying waveguides. An intrinsic mode is a self-consistent plane-wave spectrum which is approximated, to lowest order in the slow scale, by a more conventional adiabatic mode. However, where the adiabatic mode breaks down (at its transition from bound to cutoff behaviour) the intrinsic mode is uniform, and correctly predicts the radiation which occurs into the substrate or cladding. The object of this paper is to summarise the relevant theory and to present numerical computations of the intrinsic modes for a model problem consisting of a dielectric wedge with plane boundaries.

Integrated optical waveguide polarizer

Abstract: A single-mode optical waveguide polarizer for use in conjunction with electrooptical devices that operate best when presented with only a single polarization mode. The polarizer is fabricated on a conventional substrate, such as lithium niobate, using a waveguide strip of indiffused material, such as titanium. To achieve polarization discrimination, a polarizer section of the waveguide strip is made small enough in width to support only a single polarization mode, specifically the TM mode, but not the orthogonal TE mode. Losses are minimized by the use of tapered waveguide sections adjacent to the polarizer section.

The Determination of Mode Coupling Coefficients

Abstract: Analytical expressions for coupling coefficients for oblique incidence on a grating with an arbitrary groove profile on a planar waveguide with an arbitrary refractive index profile are obtained in the form of mode eigenfunctions values on the waveguide surface.

Measurement of wavelength dependence of the far-field pattern of single-mode optical fibers.

Abstract: A new method of measuring the far-field pattern of single-mode optical fibers is presented. The method involves measuring the total power passed by a linear aperture in the far field and can be used with a white-light source. The measured far fields can then be used to determine the wavelength variance of characteristics such as the rms spot size (near or far field) and Gaussian-overlap spot size. The Gaussian-overlap spot size measured agrees well with results from both the transverse-offset and the direct far-field methods.

Optical waveguide, particularly optical fiber

Abstract: Light (19) propagated by optical waveguide or fiber (10) is reflected by a reflecting plane (17) thereof onto an exit surface (20) of the waveguide to leave it. Reflections of light by the exit surface, the reflecting plane and/or other surface (22) of the waveguide which propagate back therethrough are avoided by selection of the angle (13) between the reflecting plane and the light incident thereon from the waveguide. The waveguide may comprise a core (11) and a cladding (12), particularly in coaxial arrangement, with the reflecting plane at an end thereof. A photodetector (14) may be located to detect light exiting the waveguide with no reflections off the photodetector propagating backwards down the waveguide.

A new large-diameter optical fibre waveguide for operation in the TE01 mode

Abstract: It is shown that by using an optical fibre of 'tubular' structure, comprising a thin layer of higher refractive index sandwiched between a core and a cladding of lower refractive index, it is possible to transmit the TE01 mode in isolation with the HE11 mode virtually cut off. Possible advantages of this arrangement are discussed.

Correlation between Mode Fluctuations in a Semiconductor Laser

Abstract: The correlation between fluctuations of different modes of a single mode semiconductor laser has been measured at several temperatures. The lasing mode is found to have a strong coupling with its adjacent nonlasing modes, but the coupling is exceptionally weak if the adjacent mode does not become a lasing mode when the temperature is changed.

Device for light transmission

Abstract: A light transmission device for transmitting light from a stationary light source to a movable recording element of an electronic reproduction device composed of at least one fiber optical light waveguide and one guide element for the fiber optical waveguide. Due to the motion of a fiber optical waveguide, inhomogeneous light distributions arise at its exit face, this leading to disturbing streaked exposures of the recording medium. In the present invention to avoid such streak-like exposures, it is proposed that the guide element be a metal band which is mounted in a U-shape with the fiber optical waveguide being connected to one side of the metal band. Thus, as the recording element shifts, the curvature of the fiber optical waveguide remains constant to prevent shifting of the light distribution exiting the fiber optical waveguide.

Method of and apparatus for measuring the cut-off wavelength of the first higher order mode in optical fibers

Abstract: The cut-off wavelength of the first higher order mode in optical fibers for telecommunication is measured based on the fact that the introduction of perturbations in an optical fiber can generate greater losses on higher order modes than on the lower order modes A spectral scanning of the fiber output power is effected under a certain number of different perturbations conditions and the values obtained are combined so as to determine the fraction of power guided in the fundamental mode The cut-off wavelength is that where this fraction exceeds a certain value

A new large-diameter optical fibre waveguide for operation in

Abstract: It is shown that by using an optical fibre of 'tubular' structure, comprising a thin layer of higher refractive index sandwiched between a core and a cladding of lower refractive index, it is possible to transmit the TE~~ mode in isolation with the HE^^ mode virtually cut off. Possible advantages of this arrangement are discussed.

Electro-Optically Induced Optical Waveguide in KNbO3

Abstract: Electro-optically induced optical waveguiding in the wavelength range 0.5 μm – 1.3 μm and cut-off modulation in a structure based on KNbO3 (electro-optic coefficient r33 = 64 pm/V) single crystals are reported.

Single Mode Channel Waveguide Polarizer on LiNbO3

Abstract: Single mode stripe waveguides with a dielectric/metal overlay operate as absorption polarizers. For Ti:LiNbO3 TM/TE differential losses of 100 dB/cm are measured.

Influence of surface polaritons on mode attenuation in a middle-infrared irregular dielectric cavity waveguide

Abstract: Geometric-optics methods supplemented by phenomenological results on wave reflection from a randomly rough surface of a dielectric, for which the real part of the permittivity function is negative and the imaginary part is small, are used to study the influence of the excitation of surface polaritons induced by roughness of the walls of a cavity waveguide channel on the propagation constants of the modes in this waveguide. It is found that the coupling of the waveguide mode field to surface polaritons as a result of the random irregularity of the walls of the guiding channel is responsible for a considerable increase in the mode attenuation in the waveguide.

Advanced Overmoded Waveguide Components for High-Power Millimetre Wave Applications at 28, 70 and 140 GHz

Abstract: Improved oversized waveguide components of transmission lines developed for high-power (200 kW) millimetre wave applications at 28, 70 and 140 GHz, as e.g. electron cyclotron resonance heating (ECRH) of plasmas for thermonuclear fusion research with gyrotrons, are described. Axisymmetric narrow pencil beams with well-defined polarization (HE11 mode) are used at openended corrugated waveguide antennas. The HE11 mode can be generated from TE0n output modes of gyrotrons by the multi-step mode conversion processes: (1) TE0n?TE01?HE11?HE11 or (2) TE0n?TE01?TM11?HE11. This paper reprts computations and measurements on mode transducer systems of the first type at 28, 70 and 140 GHz and of the second type at 70 and 140 GHz. In all cases the overall efficiency of the complete mode converter sequence in the desired mode is approximately (91-94)%. The mode purity in the transmission lines is conserved by using optimimized corrugated waveguide bends and diameter tapers with non-linear contours. Highly efficient corrugated mode filters decouple the different waveguide sections.

Waveguide type optical modulator

Abstract: PURPOSE:To reduce insertion loss and to eliminate optical damage to a waveguide and liquid crystal and to improve the reliability by combining the electrooptic effect of a quartz single-mode optical waveguide on an Si substrate with the electrooptic effect of the liquid crystal charged in the gap of the waveguide complementarily. CONSTITUTION:A liquid crystal layer 4 is charged in the gap 3 of the quartz single-mode optical waveguide 2 formed on the top surface of the Si substrate to combine the electrooptic effect of the waveguide 2 with that of the liquid crystal layer 4 complementarily. This combination reduces the connection loss between single-mode optical fibers 7a and 7b and the waveguide 2 to 0.8dB, the propagation loss of the waveguide 2 to 0.1dB with 1.3mum wavelength, and the radiation loss due to the gap 3 to 0.3dB, so the insertion loss of the whole element is 0.5-1dB and neither the waveguide 2 nor the liquid crystal 4 have optical loss, so that the reliability is improved.

Photodetecting element module

Abstract: PURPOSE:To suppress deterioration in transmission characteristic by polishing diagonally the end face of an optical fiber facing a focusing type lens and forming a photodetecting element at the angle reciprocal with the polished surface of the optical fiber surface. CONSTITUTION:An optical fiber 3, a rod lens 6, an APD chip 7, an APD package 8, the locus 10 of the exit light from the fiber 3 and the locus 10 of the reflected light from the chip 7 or the package 8 are illustrated. The end 3b of the fiber 3 is polished or cut diagonal with the optical axis and therefore the Fresnel reflected light at the end face 3b of the optical fiber cannot have backward propagating mode and is radiated as a radiation mode to the outside of the fiber 3. The exit light from the fiber 3 is emitted with inclination by theta/2 of the polishing angle theta with respect to the optical axis. When an imaging magnification is assumed to be one in this embodiment, the exit light from the lens 6 is made incident with inclination by theta/2 to the chip 7 and the reflected light thereof is not made incident again to the fiber 3 as shown by the locus 11 of the reflected light. The angle phi of inclination of the package 8 is highly effected for reflection if said angle is large but if the angle is excessively large, the quantum efficiency decreases.

Interaction of optical waveguide modes with spin waves in an yttrium iron garnet film

Abstract: Experiments have been carried out in order to investigate the interaction of optical waveguide modes with spin waves in yttrium-iron-garnet films. The waves were excited using an array of copper wire antennas placed 4 mm apart. The light source for the experiments was a He + Ne laser operating at a wavelength of 1.15. In order to study the mode conversion of the optical waveguide, the excitation antenna was fed a microwave signal which was modulated in amplitude by a meander of 1 kHz. The output signal from the photodiode was measured as a function of the microwave input power for mode conversions TM(0) and TE(0). Over the range of microwave input powers investigated, the mode conversion behavior was found to be linear. The maximum conversion coefficient was 0.04 percent. The applications of iron-garnet films in integrated optics and spin-wave electronic devices are discussed. 5 references.

Light modulator comprising an optical fibre

Abstract: A fibre optic modulator comprises an optical fibre 2 and a waveguide 10 of active material. The waveguide 10 is dimen­ sioned such that any mode of the waveguide has a propoga­ tion constant which is separated from the propogation con­ stant of the optical fibre mode by an amount equal to or greater than λ/L where λ is the wavelength of transmitted electromag­ netic radiation in the mode of the optical fibre and L is the length of the effective portion of the waveguide of active mate­ rial.

Measurement of cut-off wavelength in monomode fibres by a polarization method

Abstract: A method for the measurement of cut-off wavelength of higher order mode in monomode fibres, based on the different polarization properties of the modes, is discussed It permits one to derive the fraction of power guided in the fundamental mode, at each wavelength Experimental results that prove the reliability and the accuracy of the method are provided Criteria for the choice of the sample length for the measurement are also discussed Finally a very simplified, yet precise, measurement procedure is suggested

Photodetecting optical element module

Abstract: PURPOSE:To suppress influence of reflection at the far end by polishing or cutting an optical fiber diagonally with the optical axis and disposing a photodetecting optical element roughly in parallel with the end face of the optical fiber CONSTITUTION:The end face 3b of an optical fiber 3 is polished or cut diagonally with the optical axis Fresnel reflected light is therefore unable to attain backward propagation mode and is radiated as radiation mode to the outside of the fiber 3 On the other hand, the ray emitted from the fiber 3 is subjected to reflection by the window of an avalanche photodiode APD package 7 and an APD chip 6, but the APD package is disposed roughly in parallel with the end face 3b of the optical fiber and therefore the reincidence of the reflected light to the fiber 3 is obviated The influence of the reflection at the far end is thus suppressed

Length dependence of cutoff wavelength for single‐mode fiber

Abstract: The effective cutoff wavelength of single-mode fiber cable cannot be completely determined because the bending loss, which prevents propagation of the second-order mode, depends upon the bending distribution of the fiber as well as on the length and index profile of the fiber. By measuring the bending loss of the LPn mode of step-index single-mode fiber, it is found that the effective cutoff wavelength of reel-wound fiber shifts to lower wavelengths along the distance. The length dependence is proved by experiment and agrees well with the theory. The length dependence of the cutoff wavelength of optical cable is estimated by experiment and it is established that the effective cutoff wavelength can be prescribed by the microbending profile and, compared with the value given by the conventional bend method of a 2-m sample, the decrease in effective cutoff wavelength for 1-m cable is estimated as 0.1 um. If this length dependence is used, it can be applied in long-distance systems provided a fiber having longer cutoff wavelength and favorable.bending loss characteristics or low dispersion is used.

A method of providing an optical fibre mode scrambler

Abstract: The present invention relates to a mode scrambling arrangement for a multimode or graded-index optical fiber and, more particularly, to an optical fiber mode scrambler achieved by forming a deformation (13) as, for example, a groove or notch on one side of the multimode or graded-index optical fiber (10, 11, 12) orthogonal to the longitudinal axis (14) thereof. The groove or notch can be produced by any suitable etching or machining process to extend through the cladding layer (11) and at least very slightly into the outer surface of the core (10) of the multimode or graded-index optical fiber. The depth of the groove or notch into the core can be controlled by monitoring the mode pattern in the multimode fiber during the etching or machining process to provide maximum mode scrambling with minimal loss.

Determining Spectral Parameters of Waveguide Devices by Investigation of Mode Polarization Distribution

Abstract: In this paper waveguide devices consisting of a number of wavelength-dependent channels are studied. The determined and random mode couplings that produce the characteristic polarization states of signals are analysed by statistical dependences. The entropy of the polarization distribution is introduced and is applied to determine the spectral separation of the wavelength channels. The results are used to examine a stripe waveguide on LiNbO3 :Ti as an example.