Showing papers on "Radiation mode published in 1987"

Mode conversion in optical fibers with monotonically increasing core radius

Abstract: In this paper we discuss mode conversion in a straight fiber which maintains its circular cross section but whose radius a(z) increases monotonically with the length coordinate z so that it passes from the single-mode to the multimode regime. Our principal concern is with step-index fibers which are treated in the scalar approximation. We study conversion of power from the incident dominant mode to other core and cladding modes for several functions a(z) . The results of our calculations show clearly that the dominant mode is able to adapt itself to the changing fiber radius provided the change is gradual. For comparison, we also consider a fiber with an infinitely extended radial parabolic-index profile as an approximation to graded index fibers. We show that it too exhibits mode conversion similar to that of the step-index fiber, provided that the comparison is made on the basis of corresponding mode spot sizes instead of actual core radii.

Laser diode pumped fiber lasers with pump cavity

Abstract: A fiber laser having a single mode fiber core of laser material is pumped by a high power coherent laser diode source by providing a multi-mode fiber around the single mode core to define a pump cavity which propagates pump radiation while allowing the pump radiation to couple to the single mode core. Laser diode arrays and extended emitter laser diodes can be used to pump a single mode fiber by inputting the pump radiation into the multi-mode fiber surrounding the single mode fiber core. The milti-mode fiber has a much greater diameter than the single mode core.

Single mode channel optical waveguide with a stress-induced birefringence control region

Abstract: In a single mode optical waveguide having a substrate, a cladding layer formed on the substrate, a core portion embedded in the cladding layer, and an elongated member for applying a stress to the core portion or a stress relief groove for relieving a stress from the core portion in the cladding layer along the core portion. The position, shape and material of the elongated member or the groove are determined in such a way that stress-induced birefringence produced in the core portion in accordance with a difference in thermal expansion coefficient between the substrate and the single mode optical waveguide is a desired value.

Method of accessing optical fiber circuit and connector plug thereof

Abstract: PURPOSE:To efficiently take out signal light to the outside by disposing a waveguide having a prescribed refractive index in tight contact with the clad part of an optical fiber for wave guiding. CONSTITUTION:The waveguide 5 has the refractive index above the refractive index of the clad part of the optical fiber 10 for guiding the in-circuit signal light. This waveguide 5 is disposed in such a manner that the waveguide comes into contact with the clad part by an much as a prescribed length in the same direction as the signal light guiding direction of the optical fiber 20. The waveguide is fixed by a layer 51 of an adhesive agent and a photodetector 30 is provided to the end of the waveguide 5. The radiation mode and clad mode light generated in the optical fiber juncture of this constitution are partly guided through the waveguide 5 to the outside so that the signal light is partly taken out. The conversion efficiency of about -20dB is obtd. according to this method. The excitation of the external signal light of the same level as the level of the in-circuit signal light is possible if a high-output light source is used.

Reducing bend and coupling losses in integrated optical waveguides

Abstract: A groove is disposed in a substrate longitudinally along the outside radius of a bent integrated optical waveguide to constrain the mode of optical energy propagating therein such that the optical energy that would normally be radiated is confined to the waveguide, thereby reducing transmission loss through the bend. Further, to reduce coupling loss between an integrated optical waveguide and an optical fiber, two grooves are disposed longitudinally along either side of the integrated optical waveguide to constrain the mode of optical energy propagating in the waveguide to approximate the mode of the optical energy propagating in the optical fiber. To further reduce both bend and coupling losses, the ends of the grooves bend away from the waveguide.

Multichannel waveguide junctions for guided‐wave optics

Abstract: We propose and analyze a new class of multichannel optical waveguide junctions. These junctions consist of a multimode channel waveguide that branches into several single‐mode channels. We show that such waveguide junctions, when properly designed, can route each of the spatial modes of the multimode waveguide into a different single‐mode channel. These waveguide junctions should be useful in selective mode excitation, routing, switching, modulation, and wavelength multiplexing/demultiplexing of guided waves, as well as for mode control in semiconductor lasers.

The segmented waveguide program for long wavelength propagation calculations

Abstract: : A computer which obtains waveguide mode solutions for very low frequencies and low frequencies (VLF/LF) is described. The program allows for multiple homogeneous segments to be specified, allowing for consideration of variations in the earth-ionosphere waveguide. Path geometry and geophysical parameters can be computed by the program. Ionospheric disturbances due to man-made or naturally events can also be modeled using the program. Keywords include: Longwave propagation, Wavelength mode, and Propagation path.

Fiber optic apparatus and method for spectrum analysis and filtering

Abstract: An acousto-optic frequency shifter having a long interaction region is used as an optical analyzer. A variable frequency signal generator is used to drive an acoustic transducer to launch an acoustic wave in contact with an optical fiber. The acoustic frequency is varied over a known range to generate acoustic waves having known wavelengths. An optical signal having an unknown optical wavelength is introduced into one end of the optical fiber in a first polarization mode. The effect of the acoustic wave on the optical signal is to cause coupling of the optical signal from the first polarization mode to a second orthogonal polarization mode. The amount of the coupling is dependent upon the phase-matching between the acoustic wavelength and the optical beat length. The coupling between the polarization modes is maximum when the acoustic wavelength is equal to the optical beat length. The intensity of the optical signal coupled to the second polarization mode can be measured to determine the optical wavelength corresponding to the acoustic wavelength when the maximum intensity occurs.

Propagation properties of single-mode dielectric waveguide structures: a path integral approach

Abstract: A simple and efficient numerical method for the calculation of the fundamental and first-order mode propagation properties of single-mode waveguide structures with arbitrarily graded refractive-index profiles is presented. The method is based on a path integral treatment of the propagation equation of paraxial optics. The accuracy of the method and its potential for use in waveguide-structure design and characterization are illustrated by calculating the propagation constant for the fundamental and first-order modes of a graded-index slab waveguide, the intensity distribution of the fundamental mode of a graded-index slab waveguide, and by calculating the coupling length of a graded-index slab directional coupler as a function of fabrication-related variables.

Radiation Characteristics of a Dielectric Slab Waveguide Periodically Loaded with Thick Metal Strips

Abstract: A theoretical analysis is presented for the radiation characteristics of a dielectric slab waveguide periodically loaded with thick metal strips. A boundary-integral-equation formulation is employed to describe the fieIds in the grating layer. Through numerical calculations, we show that the leakage constant of the fundamental TM mode is much larger than that of the fundamental TE mode. This property will find application in mode filters for millimeter- and submillimeter-wave integrated circuits.

Optical fiber sensors

Abstract: A distributed optical fiber sensor cable, for sensing perturbations such as pressure, comprises a length of optical fiber (10) and means adapted, in response to the perturbation to be sensed, to mechanically deform separate portions of the length of the fiber at sensing elements (11,12,13) periodically along their length in order to cause optical power launched into a mode of propagation in the core (14) and guided thereby to be coupled to an unguided mode, for example a cladding (15) mode. The coupling is optical wavelength selective and the separate sensing elements are each addressed with a different wavelength (λ11, λ12, λ13) for spatial resolution along the length of the cable.

Theoretical study off silicon-clad planar diffused optical waveguides

Abstract: A silicon-clad planar diffused optical waveguide structure is proposed and propagation characteristics for a wavelength of 0.6328 ?m are investigated. The refractive index profile of the substrate is assumed to be a Gaussian profile and a maximum index change of 0.01 is also assumed. Computer modelling studies indicate that silicon-clad diffused optical waveguides exhibit a damped periodic oscillation in the attenuation and mode index curves. The attenuations of these waveguide structures are relatively small compared with those of the four-layer planar homogeneous waveguide structures reported by Batchman and McWright. The attenuation may be reduced with a low-index buffer layer. Furthermore, the attenuation and mode index are significantly altered by the conductivity changes of silicon.

Practical upper limits to cutoff wavelength for different single-mode fiber designs

Abstract: A practical upper limit to cutoff wavelength in single-mode fiber is investigated. Based on the relationship between the attenuation of the LP 11 mode and the length dependence of cutoff wavelength, a formula is developed to predict this limit for four fiber designs commonly seen in commercially available fibers. It is found that, depending on fiber design, the upper limit of factory-measured fiber cutoff wavelength is anywhere from 20 to 60 nm above the system operating wavelength, even for a worst case "straight fiber" layout. Under actual field layout conditions, however, the limits converge to approximately 65 nm above the system wavelength for all four fiber designs. The practical upper limit predicted here is confirmed through an experimental evaluation of modal noise effects in a 1.2-Gbit/s single-mode fiber system.

Integrated optics spectrum analyzer

Abstract: An optical waveguide comprises two out-diffused optical waveguide sections, an in-diffused optical waveguide section, and two narrow transition regions intimately connecting the out-diffused waveguide sections and the in-diffused waveguide section. This waveguide structure can decrease the level of in-plane scattering caused by surface irregularities and reduce the difficulty of coupling light into and out or the waveguide. The structure can be made to perform as a transverse magnetic mode filter and increase the intensity of light focussed into the guide beyond the limits imposed by the optical damage resistance of a strictly in-diffused waveguide.

Non-transform limited pulse locked radiation mode radiation generator with external cavity having non-linear transmission characteristic improving mode locking

Abstract: A radiation generator in which substantially all the radiation modes are locked with respect to one another comprises a radiation generating cavity defined by mirrors and a crystal for generating a continuous train of non-transform limited pulses of coherent radiation. An external cavity is positioned in association with the radiation generating cavity whereby radiation may pass in use in both directions between the two cavities. The external cavity is defined by a medium having a non-linear transmission characteristic which may be substantially non-dispersive for radiation from the generating cavity, and/or which has a negative group delay dispersion. The radiation path length is such that pulses fed into the external cavity are fed back to the radiation generating cavity in synchronism with a later pulse from the generating cavity.

Structure of waveguide type optical device

Abstract: PURPOSE:To widen a working temp. range by fixing only the waveguide element directly on a housing and supporting a fiber array to be coupled to the waveguide element by an elastic body fixed on the housing. CONSTITUTION:Only the waveguide element 2 is directly fixed on the housing 3 at the time of fixing the coupling body of the fiber array and the waveguide element 2 on the housing 3. The fiber array 1 is supported by the elastic body 4 fixed on the housing 3 or the coupling part of the fiber array 1 and the waveguide element 2 is reinforced if the strength is insufficient with only the support at one point. The reason for fixing only the waveguide element 2 directly on the housing 3 is to prevent the difference in the thermal expansion or thermal shrinkage of the waveguide element 2 as well as the fiber array 1 and the housing 3 from acting as a thermal strain and stress on the coupling part of the waveguide element 2 and the fiber array 1. The reason for supporting the fiber array 1 by the elastic body 4 is to absorb the thermal strain in the elastic body 4. The service temp. range of the optical device is thereby widened.

Periodic type optical filter

Abstract: PURPOSE:To multiplex and demultiplex an optical signal whose frequency interval is a GHz order by executing an adjustment of optical waveguide length by a wavelength order of light, and also, enlarging a specific refractive index difference of a ring-like optical waveguide, and forming small a cross section shape of its optical waveguide. CONSTITUTION:On first and the second optical waveguides 13, 14 and a ring-like optical waveguide 17 for constituting a Mach-Zehnder interferometer, phase adjustment use electrodes 21, 22 in a phase adjusting means 24 are loaded and a control of the optical waveguide lengths 13, 14 is executed by an order of the optical wavelength. Also, as for a bending loss, comparing with input use optical waveguides 11, 12 and output use optical waveguides 15, 16, a specific refractive index difference of the ring-like optical waveguide 17 is made larger, and also, a cross section shape of the optical waveguide 17 is made smaller, by which the influence of the bending loss can be nearly disregarded. In such a way, an optical signal whose frequency interval is a GHz order can be multiplexed and demultiplexed at a low loss.

Measurement of phase and coupling parameters in magneto-optic coupled mode waveguides

Abstract: A method for measuring the phase constant difference between the orthogonally polarized modes and the coupling coefficient in a magneto‐optic coupled mode waveguide is described and demonstrated. It is based on measurements of polarization of the output light of the resulting ellipse due to the waveguide dispersion without the perturbation, the external magnetic field, and the variation of the mode conversion efficiency with the alternating perturbation. A reasonable Faraday rotation angle, which corresponds to the saturated coupling coefficient for a waveguide far from cutoff, has been obtained.

Optical circuit device

Abstract: PURPOSE:To realize efficient optical coupling by providing a hole, which piercing a substrate, between an optical waveguide and a groove. CONSTITUTION:A hole 6 piercing a substrate 1 is provided between an optical waveguide 2 and an optical fiber supporting groove 3 by a simple and high- precision fine working method. Si having crystal face azimuth (100) is used as the substrate 1 and the optical waveguide 2 is a quartz single mode optical waveguide. The material of the core of the optical waveguide 2 is SiO2+TiO2, and the material of the clad around the core is SiO2+P2O5+B2O3, and a quartz single mode optical fiber is used as an optical fiber 4. Since a V groove 3 is formed by crystal face (111), the angle of the V groove 3 is crystal-graphically determined; and the width of the V groove 3 is so designated that the optical waveguide 2 and the optical axis of the optical fiber 4 coincide with each other at the time of arranging the optical fiber 4 in the V groove 3, and the crystal face azimuth of the side face of a hole 5 is (110) and the width of its sectional shape is made equal to that of the V groove 3. Thus, efficient optical coupling is realized.

Self stabilisation of the fundamental lateral mode in index-guided semiconductor lasers

Abstract: Lateral mode stability in index guided semiconductor lasers is discussed. As is well known, the fundamental mode self-focuses at high power due to perturbations in the refractive index profile produced by spatial hole burning. However, the lateral waveguide is not strengthened for all modes. The first order mode, for example, is actually slightly defocused. In strong waveguides the gain profile perturbation due to hole burning is the dominant cause of the first-order mode reaching threshold. In weak wave-guides, however, the defocusing effect can compete with the gain profile perturbation effect leading to stable fundamental mode operation at high output powers.

High-density optical waveguide and its manufacture

Abstract: PURPOSE:To form the high-density optical waveguide by coupling two optical waveguide plates which are made of photosensitive resin setting bodies with high refractive indexes and have plural linear optical waveguides in a specific configuration and isolating them by a clad layer made of resin which has a lower refractive index then the optical waveguides. CONSTITUTION:The two optical waveguide plates are formed which have the linear optical waveguides 2 formed of the photosensitive resin setting bodies having the higher refractive index than the surface of the substrates 1 on the surfaces of the substrates 1 at intervals. Those optical waveguide plates are coupled on the entire surfaces of the optical waveguide plates with the optical waveguides in, and core arrays of the linear optical waveguides 2 of both optical waveguide plates fill small gaps of optical waveguide absent spaces 3 of the opposite plates. Then the core arrays of both optical waveguide plates are all isolated by the clad layer 4 which is made of resin having the lower refractive index than the optical waveguides 2 and fill the small gaps. Consequently, the high-density optical waveguides are obtained.

Effect of carrier diffusion on the nonlinear response of optical waveguides

Abstract: Using a self-consistent numerical method, we calculate the carrier-density-dependent changes in the propagation constant of a TE mode in a symmetric slab semiconductor waveguide. By modeling the nonlinearity with the plasma theory, the effect of transverse carrier diffusion on the nonlinear response of a waveguide is investigated for typical waveguide parameters.

Guided Mode Characteristics of Metal-Clad Planar Optical Waveguides Produced by Diffusion (Short Paper)

Abstract: Analytical and numerical results for the guided mode characteristics of metal-clad planar waveguides produced by diffusion are developed. Values of the complex propagation constants are obtained numerically and are shown to be in good agreement with the analytical results. These give insight into how waveguide and material parameters determine the loss. Since the profile of the waveguide represents the variation of the refractive index of the diffused-channel waveguide with the depth dimension, the results obtained can be used to reduce the dimensionality of the diffused-channel waveguide and facilitate the application of the effective-index method.

Stable power‐combining mode operation of a cylindrical cavity multiple‐device oscillator

Abstract: Presented in this paper is a discussion of the output power combining capability and the stable operation of the desired mode in a cylindrical cavity multiple-device oscillator, in which several devices are placed inside a cylindrical cavity to combine the output of all devices by way of coupling with the TM020 mode of the cavity. A lumped element equivalent circuit is first derived that has the fundamental characteristic of the oscillator structure. From the modal analysis based on this equivalent circuit, it is found that the oscillation output as the sum of the available powers of individual devices can be obtained in principle at TM010 and TM020 modes. It is also noted that the TM020 mode cannot be a stable mode when it is chosen as the desired mode and the TMm10 mode (m ≧ 1) is generated as a stable rotational or standing wave mode. Then we discuss the method of loading the resistor for suppressing unwanted modes in which only the desired output combining mode is stable. Finally, an eight-device oscillator with a simple structure fabricated for trial is used in experiments of power combining and unwanted mode suppression and the results of the analysis of the modal analysis are qualitatively confirmed.

A novel technique for laser diode to single mode fiber coupling

Abstract: An optical fiber coupler based on the semi-linear passive phase conjugate mirror is analyzed. The threshold coupling strength is determined from theoretical considerations. An estimate of 50% for the overall coupling efficiency is made, assuming there is good mode matching between the light incident on the fiber and the propagating mode. The coupler exhibits a high degree of alignment insensitivity allowing for simple manufacture.

Integrated-optics polarizer based on a buried waveguide in glass

Abstract: An integrated-optics polarizer based on a waveguide buried in glass was proposed and constructed. This polarizer had a rigid contact with a single-mode fiber waveguide; its extinction coefficient was 44 dB and the losses of the transmitted polarization were 4.5 dB at the wavelength of 0.63 µ.

Characteristics of an He?Ne laser with a transverse microwave discharge in a longitudinal magnetic field

Abstract: An experimental investigation was made of the influence of a longitudinal magnetic field on the power and noise of He–Ne laser radiation utilizing a transverse microwave (λ = 0.63 µ) discharge. The laser radiation power increased in the presence of the magnetic field. The maximum increase in the output power produced by a field of H = 34.3 Oe reached 35% for the TEM00q radiation mode and 20% for the TEM33q mode. The field increased also the laser radiation noise in the range 1–20 kHz.

Milled-groove method for fiber-to-waveguide couplers

Abstract: We report a simple milled-groove process integrated with a two-step ion-diffused waveguide fabrication for efficient coupling between single-mode fibers and integrated optical waveguides and Y - branches. We demonstrate such a coupling technique using a) a multimode transition to single-mode waveguide coupler, and b) an integrated optical 3-dB branching waveguide coupler from a single-mode fiber to silver/sodium ion-enchanged waveguide components. The coupling loss was about 1-2 dB over a propagation length of 2 cm at an operating wavelength of 633 nm.

Determination and calculation of chromatic dispersion in two-layer single-mode fiber waveguides

Abstract: A comparison of the measured and calculated chromatic dispersion was made using a rigorous electrodynamic formulation of the problem of a single-mode fiber waveguide and the model of an equivalent step refractive index profile. An analysis is made of various methods of constructing the equivalent step profile from the refractive index profile of a blank of a waveguide and the spectral dependence of the size of the mode spot. It is shown that the parameter of the equivalent step profile is best obtained from the higher-order moments of the refractive index profile. It is suggested that the radius of the core of a single-mode fiber waveguide be determined from the condition of equality of the experimental and calculated cutoff wavelengths of the first higher-order mode.