Showing papers on "Mode volume published in 1981"
TL;DR: In this article, the backscattered light amplitude is measured from one end of a fiber as a function of optical frequency by tuning a HeNe laser over its linewidth.
Abstract: The backscattered light amplitude is measured from one end of a fiber as a function of optical frequency by tuning a HeNe laser over its linewidth. Fourier transform by a low‐frequency electronic spectrum analyzer then reveals the spatial distribution of scattering and of the fiber losses.
504 citations
TL;DR: Single-mode fiber couplers produced as fused biconical-taper structures are reported on that exhibit low loss, arbitrary branching ratio, polarization independence, and broadband operation in wavelength.
Abstract: Single-mode fiber couplers produced as fused biconical-taper structures are reported on. The devices exhibit low loss (0.5 dB), arbitrary branching ratio, polarization independence, and broadband operation in wavelength.
231 citations
TL;DR: In this article, a finite element program for the analysis of anisotropic optical waveguides is described and the appearance of spurious numerical modes, due to the fact that the functional is non-positive definite, is discussed and a possible solution to the problem is presented.
Abstract: A finite element program for the analysis of anisotropic optical waveguides is described. The appearance of spurious numerical modes, due to the fact that the functional is nonpositive definite is discussed and a possible solution to the problem is presented. For isotropic waveguides it is shown that both EH- and HE-type modes can be very accurately approximated by two different scalar finite element programs. Finally, a method for calculating the attenuation of leaky modes in a single material integrated optic waveguide using this scalar finite element method is proposed.
192 citations
TL;DR: A new all-fiber gyroscope is described, using a laser-diode source to reduce coherent scattering effects and proper choice of modulation frequency to reduce instabilities.
Abstract: A new all-fiber gyroscope is described. All components are constructed directly on a single continuous optical fiber, removing localized sources of reflection. A laser-diode source is used to reduce coherent scattering effects. Proper choice of modulation frequency is shown to reduce instabilities further. Long-term stability at rest of better than 0.2 masculine/h is observed with 30-sec integration time.
188 citations
TL;DR: The rotational sensitivity of the Fiber resonator gyro is derived and shown to be approximately equal to that of the fiber interferometer gyro for typical fiber and source parameters.
Abstract: The rotational sensitivity of the fiber resonator gyro is derived and shown to be approximately equal to that of the fiber interferometer gyro for typical fiber and source parameters. The fiber resonator, like the fiber interferometer, is susceptible to errors due to thermally induced nonreciprocity; however, by reducing splice and coupler losses, it should be possible to reduce these errors well below those in the fiber interferometer.
109 citations
TL;DR: In this article, three basic types of single-polarization single-mode (SPSM) optical fibers have been developed: elliptical-core fiber, stress-induced birefringent fiber, and side-pit fiber.
Abstract: Strictly speaking, an ordinary axially symmetrical single-mode fiber is a "two-mode" fiber because two orthogonally polarized HE 11 modes can be propagated in it. This fact results in the instability of the polarization state of the propagated mode when geometrical perturbation exists in the fiber, and also the so-called polarization mode dispersion. These are harmful in some applications of single-mode fibers to communication and measurement. To prevent these adverse effects, single-polarization single-mode (SPSM) optical fibers have been developed. Three basic types of the SPSM fiber are elliptical-core fiber, stress-induced birefringent fiber, and side-pit fiber. This paper describes the principles of these three types, performance obtained experimentally, theoretical approaches, and measurement techniques related to the SPSM fibers. Finally, relevant technical tasks in the future are mentioned.
103 citations
TL;DR: A fiber-optic magnetic-field sensor is constructed by bonding a single-mode fiber to a nickel cylinder by means of the magnetostrictive effect, permitting detection of fields as small as 4.4 x 10(-6) Oe/m of fiber.
Abstract: A fiber-optic magnetic-field sensor is constructed by bonding a single-mode fiber to a nickel cylinder The magnetic field, by means of the magnetostrictive effect, alters the state of polarization of light in the fiber A sensitivity of 176 × 10−2 rad/m Oe is demonstrated, permitting detection of fields as small as 44 × 10−6 Oe/m of fiber
98 citations
TL;DR: The local parameters of linear, circular, and elliptical birefringence of backscattered light along a single-mode fiber are analyzed, and the twist-bending-induced ellipticalbireferingence in an extremely low bireFringent single- mode fiber is measured using the backscattering method.
Abstract: The local parameters of linear, circular, and elliptical birefringence of backscattered light along a single-mode fiber are analyzed, and the twist–bending-induced elliptical birefringence in an extremely low birefringent single-mode fiber is measured using the backscattering method. The experimental results are in good agreement with the theoretical calculations. For a 130-μm-diameter fiber, twisted by 133°/m and wound around a drum of 15-cm radius, the induced elliptical birefringence is|Ω| = 18°/m at λ = 904 nm.
96 citations
TL;DR: The efficient conversion of 1.06-μm radiation in a graded-index multimode optical fiber oscillator into a small number of spectral components propagating in specific modes of the fiber and falling in the spectral range spanning from the blue to 1.53 μm is reported.
Abstract: The efficient conversion of 1.06-μm radiation in a graded-index multimode optical fiber oscillator into a small number of spectral components propagating in specific modes of the fiber and falling in the spectral range spanning from the blue to 1.53 μm is reported. The effect is shown to result primarily from phase-matched four-photon mixing. The converted light is found to propagate as individual fiber modes which are identified. The wavelengths of the spectral components of the output of the oscillator are governed primarily by fiber geometry. Analysis of the results also indicates the presence and gives a measure of the fiber-core birefringence sensed by low-order modes of propagation of the graded-index multimode fibers we have studied. The efficiency of the oscillator source and the specific characteristic wavelengths available with common graded-index fibers suggest several possible applications, which are discussed.
56 citations
Patent•
08 Apr 1981TL;DR: In this article, the authors describe a sensing device which includes a sensing element in the form of an optical fiber, a device for coupling light into the fiber and a device that measures changes in the specific physical parameters of the light passing through the fiber to determine special physical influences applied to the fiber characterized by the fiber being a multicore fiber having at least two adjacently extending cores surrounded by a common cladding.
Abstract: A sensing device which includes a sensing element in the form of an optical fiber, a device for coupling light into the fiber and a device for measuring changes in the specific physical parameters of the light passing through the fiber to determine special physical influences applied to the fiber characterized by the fiber being a multicore fiber having at least two adjacently extending cores surrounded by a common cladding and the means for measuring the changes in the parameter of the light measuring the alterations in the light passing through each of the cores. To make the device sensitive to bending and deformation in all directions, the fiber may have two cores and be twisted through 90° or the fiber may have three or more cores which are not disposed in the same plane. The measuring of the amount of change may be by measuring the interference pattern from superimposed beams of the output from the two cores or by measuring the intensity of each of the output beams separately.
53 citations
TL;DR: In this paper, the effective cutoff wavelength of the LP 11 mode for nylon-coated step-index type single-mode fibers stranded in a cable was investigated, and it was found from the pulse propagation experiments that the singlemode operation was effectively attained in the two-mode region up to the V -value of 3.0.
Abstract: The effective cutoff wavelength of the LP 11 mode is investigated for nylon-coated step-index type single-mode fibers stranded in a cable. It is found from the pulse propagation experiments that the single-mode operation is effectively attained in the two-mode region up to the V -value of 3.0. It is numerically estimated that splice loss, bending loss, and absorption loss due to the OH-ion in cladding are reduced by choosing the operating V -value as large as 3.0.
Patent•
09 Nov 1981
TL;DR: In this paper, a photodetector is used for power monitoring at a fiberoptic tap, where one fiber, having a certain mode volume is spliced to a second fiber having a relatively lower mode volume.
Abstract: At a fiberoptic tap used for monitoring purposes, one fiber, having a certain mode volume is spliced to a second fiber having a relatively lower mode volume. Consequently, in passing from the first fiber to a second fiber, some light is radiated away from the splice. This radiated light is directed to a photodetector. The tap is particularly advantageous for transmitter power monitoring since the radiated optical power is superfluous to that light which is capable of transmission by the line fiber.
TL;DR: In this paper, the interaction of surface guided modes with scatterers inside a fiber dielectric waveguide is investigated analytically using a volume integral equation technique based on Green's function theory for fiber boundaries.
Abstract: The interaction of surface guided modes with scatterers inside a fiber dielectric waveguide is investigated analytically. A volume integral equation technique, based on Green’s function theory for fiber boundaries, is used to formulate the problem. For the case of spherical scatterers, an analytical solution is developed by using an expansion in spherical vector wave functions, when b(k1 − k2) < 1, where (k1 − k2) is the difference between the wave numbers of the fiber and the spherical scatterer whose radius is b. Expressions are obtained for the reflection, transmission, and radiated-field quantities up to the order of [b(k1 − k2)]5. Numerical results are computed and presented for several cases. Coupling between even–odd HE11 modes is treated also.
TL;DR: In-line fiber-optic spectral-bandpass filters with one, two, three, and four elements are designed in analogy to the Sole filters of bulk optics by bending the fiber into the form of small coils, which are rotated to suitable angles and arranged between polarizers.
Abstract: In-line fiber-optic spectral-bandpass filters with one, two, three, and four elements are designed in analogy to the Solc filters of bulk optics by bending the fiber into the form of small coils, which are rotated to suitable angles and arranged between polarizers. One four-element filter has a bandwidth of 3.5% at a center wavelength of 704 nm and a free spectral range of 17%.
TL;DR: It is pointed out that fiber bundles instead of single fibers can be used to transmit high power laser light for object illumination to prevent the light path break induced by the high power density of concentrated laser light.
Abstract: Basic and practical problems on the formation of fringes in endoscopic hologram interferometry using fiber optics have been studied in connection with medical diagnosis of living body cavities, nondestructive testing of inner parts of machines, etc. It is pointed out that fiber bundles instead of single fibers can be used to transmit high power laser light for object illumination to prevent the light path break induced by the high power density of concentrated laser light. The effects of extended source illumination by the fiber bundle, image transmission through the ordered fiber bundle, and fiber bundle movement on the fringe visibility were investigated.
Patent•
05 Mar 1981TL;DR: In this article, a spatial filter in the lens assembly enables the lens or lenses therein to couple the separated modes to two different output fibers with high efficiency and low coupling loss, while the two signals in the output fibers are processed so that the common components which constitute noise are cancelled.
Abstract: When a multimode optical fiber is deformed in accordance with an input signal to be sensed, light from lower order core modes is coupled to higher order core modes. A lens assembly is provided which separates the light in the higher order core modes from the light remaining in the lower order core modes. A spatial filter in the lens assembly enables the lens or lenses therein to couple the separated modes to two different output fibers with high efficiency and low coupling loss. The two signals in the output fibers are processed so that the common components which constitute noise are cancelled, while the signal components are additively combined and appear at the system's output so as to provide a highly sensitive, low noise fiber optic sensor system.
TL;DR: Changes in transverse refractive index induced by the photoelastic effect are calculated when an optical fiber is subjected to a uniformly applied diametral stress and it is found that regions of comparable or higherRefractive index than the core may be induced in the outer region of the fiber.
Abstract: Changes in transverse refractive index induced by the photoelastic effect are calculated when an optical fiber is subjected to a uniformly applied diametral stress. For moderate values of the force per unit length applied to the fiber, we find that regions of comparable or higher refractive index than the core may be induced in the outer region of the fiber. Thus the stressed region is capable of acting as a mode converter that affects the transmission characteristics of the fiber and may enable coupling of energy in or out of the fiber.
TL;DR: When an optical fiber is pressed into a V groove, the stress-induced birefringence in the fiber depends on the groove angle 2gamma, and in practice, friction is dominant, precluding the possibility of bireFringence-free holding of the fiber by clamping it into aV groove.
Abstract: When an optical fiber is pressed into a V groove, the stress-induced birefringence in the fiber depends on the groove angle 2γ. Ignoring friction, this birefringence should vanish at 2γ = 60°. In practice, friction is dominant, precluding the possibility of birefringence-free holding of the fiber by clamping it into a V groove.
TL;DR: In this paper, a low-loss two-mode test fiber designed for operating in the 1.3 μm wavelength region is prepared: the core diameter is 21μm with \alpha = 2.65 and \Delta = 0.31 percent.
Abstract: Structural design of two-mode optical fiber is investigated. It is clarified theoretically that the operating V -value V 0 with zero group delay time difference \Delta\tau between the LP 01 and LP 11 modes is extended to the quasi-two-mode region above the cutoff V -value of the next higher order LP 21 mode. The optimum operating V -value V_{0m} is numerically determined to be 6.45 with the optimum index profile parameter \alpha_{opt} = 2.24 for \Delta = 0.3 percent. It is also shown theoretically that an index depression at the core center increases \Delta\tau due to the V -value deviation from V 0 , and that V 0 becomes smaller than that with no central index depression for the same α. A low-loss two-mode test fiber designed for operating in the 1.3 μm wavelength region is prepared: the core diameter is 21μm with \alpha = 2.65 and \Delta = 0.31 percent, and the test fiber has a precisely controlled graded-index profile with a small central index depression. Experimental results show that the two-mode propagation is maintained in the quasi-two-mode spectral region. Furthermore, small \Delta\tau characteristics against V -value deviation \DeltaV from V 0 are verified experimentally. It is also shown that the two-mode test fiber has about two times larger tolerance for the misalignment at a splice than a step-index single-mode fiber.
TL;DR: In this paper, a closed-form integral and an algorithm for an approximate integral that allow loss coefficients to be computed for high-order modes are presented. But the authors do not consider the power distribution among the modes of a fiber.
Abstract: An extension is derived of a bending-loss-coefficient equation derived by Marcuse [ J. Opt. Soc. Am.66, 216 ( 1976)]. The original derivation employed approximations that limited the loss formula to low-order modes. We develop a closed-form integral and an algorithm for an approximate integral that allow loss coefficients to be computed for high-order modes. The overall loss of a multimode fiber is then analyzed by making simple assumptions about the power distribution among the modes of a fiber.
TL;DR: The analytically predicted reduction in fiber sensitivity that is due to the balancing of pressure-induced length changes with strain-induced index changes is demonstrated experimentally.
Abstract: The pressure sensitivity of the phase of light propagating in aluminum-coated fibers is studied both analytically and experimentally. The analytically predicted reduction in fiber sensitivity that is due to the balancing of pressure-induced length changes with strain-induced index changes is demonstrated experimentally.
TL;DR: A new nondestructive and noncontacting method to measure accurately the refractive-index profile of single-mode optical fiber preforms is presented, providing a simple yet powerful alternative to those techniques.
Abstract: A new nondestructive and noncontacting method to measure accurately the refractive-index profile of single-mode optical fiber preforms is presented. The method is based on the fact that a Ge-doped preform core fluoresces strongly when excited by UV radiation. The preform, which need not be index matched, is excited transversely to its axis by a He–Cd laser emitting at a wavelength of 325 nm. The intensity of the resulting fluorescence radiation is detected by a video camera and plotted giving the index distribution directly. The profiles so obtained in <1 min are in excellent agreement with those measured by interferometry and by the focusing method, thus providing a simple yet powerful alternative to those techniques.
Patent•
10 Aug 1981TL;DR: Optical fibers having enhanced mode coupling produced by an asymmetric refractive index profile that varies periodically along the length of the fiber are described in this paper, where the prescribed variations are obtained by means of a fabrication process that includes periodically varying the source of at least one of the fibre materials in a direction transverse to the fiber drawing direction.
Abstract: Optical fibers having enhanced mode coupling produced by an asymmetric refractive index profile that varies periodically along the length of the fiber are described. The prescribed variations are obtained by means of a fabrication process that includes periodically varying the source of at least one of the fiber materials in a direction transverse to the fiber-drawing direction. This transverse periodicity is translated into the desired longitudinal periodicity along the fiber by the fiber-drawing process.
TL;DR: In this article, two methods for measuring the parameters expressing birefringence and elastooptically induced optical activity (twist-induced rotation of polarization plane) are proposed.
Abstract: New methods for measuring the parameters expressing birefringence and elastooptically induced optical activity (twist-induced rotation of polarization plane) are proposed. In these methods, the fiber being tested (typically l m long) is twisted, and the variation of the state of polarization at the output end is measured. Parameters Δ β (expressing the birefringence) and α (expressing the optical activity) can be determined from these data upon least squares principle. The proposed methods can be applied effectively to those fibers which have Δ β of 3 ~ 100 rad/m. The obtained values of α agree well with the material data. have been reported. In the first method, we launch a linearly polarized light at 45° to the principal axis of the fiber and view the fiber from the side [4]. Thus the wavelength of the beat between the two modes, hence Δ β, is measured. In the second method, we cut the fiber little by little and measure the change of the polarization state at the fiber output to know the beat length [5]. In the third \"twisting\" method, Δ β and α are measured indirectly from the twist-induced variation of the ellipticity of the output light from a short twisted fiber, by the curve fitting technique [3, 6, 7].
TL;DR: In this paper, the cutoff characteristics of the first higher-order mode and phase coefficient, group velocity and power distribution characteristics of dominant modes are presented over a wide range of parameters and a two-layer step index elliptical fiber waveguide is presented as a special case.
Abstract: Single mode propagation in three-layer step index elliptical fiber waveguides is investigated theoretically. Previous analysis of the elliptical dielectric tube waveguide is extended to include cladded, W-type and tube-type fibers. Numerical results on cutoff characteristics of the first higher-order mode and phase coefficient, group velocity and power distribution characteristics of the dominant modes are presented over a wide range of parameters. A two-layer step index elliptical fiber waveguide is presented as a special case. High eccentricity single mode fibers have small modal beat lengths but have small core size and greater power distribution in the claddings. W-type fiber in the middle range of eccentricities is suggested for single mode single polarization applications.
TL;DR: In this paper, a general and efficient model for optical fibers with a few modes and arbitrary index profiles is established, which yields a solution of the vectorial wave equation and analytical expressions for the group delay and the far field.
Abstract: A general and efficient model for optical fibers with a few modes and arbitrary index profiles is established. The model yields a solution of the vectorial wave equation and analytical expressions for the group delay and the far field. Convergence tests have shown that the dispersion can be calculated with an accuracy better than 0.2 ps/(km . nm).
TL;DR: This paper describes the fabrication process and coupling principle of a single-mode fiber coupler, and Precise etching properties of the fibers used are presented.
Abstract: This paper describes the fabrication process and coupling principle of a single-mode fiber coupler. Precise etching properties of the fibers used are presented. Fiber etching is shown to result in smooth surfaces. Coupling is seen to vary with the refractive index of the material separating the fiber cores. Coupling efficiency is shown to be variable in a controlled and reversible manner after coupler fabrication. For a 3-dB coupling efficiency, <1-dB insertion loss has been obtained.
Patent•
22 Jan 1981TL;DR: In this paper, a high efficiency gas laser which utilizes transverse electrical excitationf a laser gas medium confined in a circular cylindrical volume is presented. But the design is comprised of a new design making possible the higher efficiencies through use of dielectric coupling between concave electrodes.
Abstract: A high efficiency gas laser which utilizes transverse electrical excitationf a laser gas medium confined in a circular cylindrical volume. Limitation of the excitation energy to only the optical mode volume of the laser eliminates the inefficiency associated with conventional TEA laser technology in which a much larger gas volume is excited for a given optical mode volume. The present invention is comprised of a new design making possible the higher efficiencies through use of dielectric coupling between concave electrodes.
TL;DR: Dynamic measurements of optical phase modulation in a single-mode fiber subjected to controlled mechanical vibrations are reported and an accurate analysis of the fiber strain state explains the observed phase vs frequency characteristic behavior.
Abstract: Dynamic measurements of optical phase modulation in a single-mode fiber subjected to controlled mechanical vibrations are reported. An accurate analysis of the fiber strain state explains the observed phase vs frequency characteristic behavior. The integration properties of the single-mode fiber are evaluated quantitatively for the vibrations applied. The experimental results emphasize the excellent capabilities of optical fibers to sense mechanical vibrations.