Apparatus using two-mode optical waveguide with non-circular core
First Claim
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1. An apparatus, comprising:
- an optical waveguide having a core with a non circular cross section; and
a source of light for introducing light signals having at least one wavelength into the wavelength for propagation therein, such that a substantial portion of the light is at one or more wavelengths less than a first predetermined cutoff wavelength of said waveguide to cause the waveguide to guide light in both a fundamental spatial propagation mode and a higher order spatial propagation mode;
said waveguide being sized to provide a second predetermined cutoff wavelength for said signals, less than the first predetermined cutoff wavelength, the noncircular cross section of the core having cross-sectional dimensions selected such that light guided by the waveguide in the higher order mode at wavelengths greater than the second predetermined cutoff wavelength propagates in only a single, stable, spatial intensity pattern, substantially all of the light signals introduced into the waveguide by said source of light being at one or more wavelengths greater that the second predetermined cutoff wavelength to cause said light signals to propagate in only one spatial intensity pattern for the higher order mode.
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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.
320 Citations
88 Claims
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1. An apparatus, comprising:
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an optical waveguide having a core with a non circular cross section; and a source of light for introducing light signals having at least one wavelength into the wavelength for propagation therein, such that a substantial portion of the light is at one or more wavelengths less than a first predetermined cutoff wavelength of said waveguide to cause the waveguide to guide light in both a fundamental spatial propagation mode and a higher order spatial propagation mode; said waveguide being sized to provide a second predetermined cutoff wavelength for said signals, less than the first predetermined cutoff wavelength, the noncircular cross section of the core having cross-sectional dimensions selected such that light guided by the waveguide in the higher order mode at wavelengths greater than the second predetermined cutoff wavelength propagates in only a single, stable, spatial intensity pattern, substantially all of the light signals introduced into the waveguide by said source of light being at one or more wavelengths greater that the second predetermined cutoff wavelength to cause said light signals to propagate in only one spatial intensity pattern for the higher order mode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. An apparatus, comprising:
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an optical waveguide having a core with a noncircular cross section; and a source of light for introducing light signals having at least one wavelength into the waveguide for propagation therein, such that a substantial portion of the light is at one or more wavelengths less than a first predetermined cutoff wavelength of said waveguide to cause the waveguide to guide light in both a fundamental spatial propagation mode and a higher order spatial propagation mode; wherein said waveguide is sized to provide a second predetermined cutoff wavelength for said signals, less than the first predetermined cutoff wavelength, the noncircular cross section of the core having cross-sectional dimensions selected such that light guided by the waveguide in the higher order mode at wavelengths greater than the second predetermined cutoff wavelength propagates in only a single, stable, spatial intensity pattern, substantially all of the light signals introduced into the waveguide by said source of light being at one or more wavelengths greater than the second predetermined cutoff wavelength to cause said light signals to propagate in only one spatial intensity pattern for the higher order mode; and wherein the waveguide comprises an optical fiber, the fundamental mode being the LP01 mode of the optical fiber and the higher order mode being the LP11 mode of the optical fiber, the single intensity pattern being the even mode intensity pattern of the LP11 mode. - View Dependent Claims (28, 29, 30, 31)
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32. An apparatus, comprising:
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an optical waveguide having a core with a noncircular cross section; and a source of light for introducing light signals having at least one wavelength into the waveguide for propagation therein, such that a substantial portion of the light is at one or more wavelengths less than a first predetermined cutoff wavelength of said waveguide to cause the waveguide to guide light in both a fundamental spatial propagation mode and a higher order spatial propagation mode; wherein said waveguide is sized to provide a second predetermined cutoff wavelength for said signals, less than the first predetermined cutoff wavelength, the noncircular cross section of the core having cross-sectional dimensions selected such that light guided by the waveguide in the higher order mode at wavelengths greater than the second predetermined cutoff wavelength propagates in only a single, stable, spatial intensity pattern, substantially all of the light signals introduced into the waveguide by said source of light being at one or more wavelengths greater than the second predetermined cutoff wavelength to cause said light signals to propagate in only one spatial intensity pattern for the higher order mode; and wherein the waveguide comprises an optical fiber, said apparatus additionally comprising; a generator for producing a traveling flexural wave which propagates in said optical fiber, the energy of said traveling flexural wave confined to said optical fiber and having a wavelength in the direction of propagation selected in accordance with a beat length for two modes of the fiber to cause light to be cumulatively coupled from one of the modes to the other of the modes and shifted in frequency. - View Dependent Claims (33)
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34. An apparatus, comprising:
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an optical waveguide having a core with a noncircular cross section; and a source of light for introducing light signals having at least one wavelength into the waveguide for propagation therein, such that a substantial portion of the light is at one or more wavelengths less than a first predetermined cutoff wavelength of said waveguide to cause the waveguide to guide light in both a fundamental spatial propagation mode and a higher order spatial propagation mode; wherein said waveguide is sized to provide a second predetermined cutoff wavelength for said signals, less than the first predetermined cutoff wavelength, the noncircular cross section of the core having cross-sectional dimensions selected such that light guided by the waveguide in the higher order mode at wavelengths greater than the second predetermined cutoff wavelength propagates in only a single, stable, spatial intensity pattern, substantially all of the light signals introduced into the waveguide by said source of light being at one or more wavelengths greater than the second predetermined cutoff wavelength to cause said light signals to propagate in only one spatial intensity pattern for the higher order mode; and wherein said waveguide comprises a first optical fiber, said apparatus additionally comprising a second optical fiber which is dissimilar to the first fiber, said second fiber having at least one spatial propagation mode, only two of the modes of the fibers having matching propagation velocities, one of the matching modes being in the first fiber and the other being in the second fiber, said fibers juxtaposed to form an interaction region in which light is transferred between their cores, the proximity of the fiber cores at the interaction region selected such that light propagating in one of the matching modes in one of the fibers is coupled to the other of the fibers, the remainder of the modes all having mismatched propagation velocities such that the propagation velocity of each of the mismatched modes differs sufficiently from all of the other modes to prevent substantial optical coupling between any of the mismatched modes. - View Dependent Claims (35, 36, 37, 38)
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39. An apparatus, comprising:
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an optical waveguide having a core with a noncircular cross section; and a source of light for introducing light signals having at least one wavelength into the waveguide for propagation therein, such that a substantial portion of the light is at one or more wavelengths less than a first predetermined cutoff wavelength of said waveguide to cause the waveguide to guide light in both a fundamental spatial propagation mode and a higher order spatial propagation mode; wherein said waveguide is sized to provide a second predetermined cutoff wavelength for said signals, less than the first predetermined cutoff wavelength, the noncircular cross section of the core having cross-sectional dimensions selected such that light guided by the waveguide in the higher order mode at wavelengths greater than the second predetermined cutoff wavelength propagates in only a single, stable, spatial intensity pattern, substantially all of the light signals introduced into the waveguide by said source of light being at one or more wavelengths greater than the second predetermined cutoff wavelength to cause said light signals to propagate in only one spatial intensity pattern for the higher order mode; and wherein said waveguide comprises a first optical fiber, said apparatus additionally comprising a second optical fiber which is dissimilar to said first optical fiber, said fibers juxtaposed to form an interaction region for coupling light exclusively between a selected spatial mode in the first fiber and a selected spatial mode in the second fiber, one of the selected modes being of a higher order than the other of the selected modes, the length of the interaction region being at least an order of magnitude greater than the maximum cross sectional dimension of the core of either of the fibers, and each of the fibers having a cross sectional area which is substantially the same within the interaction region as outside the interaction region.
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40. An apparatus, comprising:
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an optical waveguide having a core with a noncircular cross section; and a source of light for introducing light signals having at least one wavelength into the waveguide for propagation therein, such that a substantial portion of the light is at one or more wavelengths less than a first predetermined cutoff wavelength of said waveguide to cause the waveguide to guide light in both a fundamental spatial propagation mode and a higher order spatial propagation mode; wherein said waveguide is sized to provide a second predetermined cutoff wavelength for said signals, less than the first predetermined cutoff wavelength, the noncircular cross section of the core having cross-sectional dimensions selected such that light guided by the waveguide in the higher order mode at wavelengths greater than the second predetermined cutoff wavelength propagates in only a single, stable, spatial intensity pattern, substantially all of the light signals introduced into the waveguide by said source of light being at one or more wavelengths greater than the second predetermined cutoff wavelength to cause said light signals to propagate in only one spatial intensity pattern for the higher order mode; wherein the fundamental spatial mode includes two polarization modes, the cross-sectional dimensions of the core further selected to cause the polarization modes of the fundamental mode to be non-degenerate; wherein the single intensity pattern of the higher order spatial mode includes two polarization modes, the cross-sectional dimensions of the core further selected to cause these polarization modes to be non-degenerate; and wherein the non-degeneracy between the polarization modes of the fundamental mode and higher order mode produces a beat length between polarization modes on the order of 10 cm or less, for both sides of polarization modes.
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41. An optical apparatus, comprising:
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an optical waveguide comprising first and second propagation modes having first and second propagation constants, respectively, said first propagation constant different from said second propagation constant such that light in said first mode propagates at a different velocity than light in said second mode, said light being comprised of first and second components having first and second characteristics, respectively, a portion of each of said components propagating in each of said propagation modes, said first component in said first propagation mode being in phase with said first component in said second propagation mode at a predetermined location on said fiber, said second component in said first mode being out of phase with said second component in said second mode at said predetermined location; and first and second propagation paths coupled to receive said light from said predetermined location of said waveguide such that (1) said first component of said first mode and said first component of said second mode are combined in one of said first and second paths, and (2) said second component of said first mode and said second component of said second mode are combined into the other of said first and second paths, thereby separating light having said first characteristics from light having said second characteristic. - View Dependent Claims (42, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53)
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43. An apparatus as defined by claim 43, wherein said first and second components have the same polarization.
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54. An apparatus comprising:
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an optical waveguide having a non-circular core, said core being sized to have dimensions that are selected so that said waveguide propagates light in a predetermined wavelength range such that the light having a wavelength within said predetermined wavelength range propagates in a fundamental spatial propagation mode and in a second order spatial propagation mode, each of said fundamental spatial propagation mode and said second order spatial propagation mode supporting the propagation of light in first and second orthogonal polarization modes; a light source that introduces light into said optical waveguide at a waveguide within said predetermined wavelength range to propagate in said waveguide in both of said fundamental and second order spatial propagation modes and in both of said two polarization modes within each of said spatial propagation modes; means optically coupled to said waveguide for separating said light after passing through said optical waveguide into a first portion having said first polarization and a second portion having said second polarization, each of said first and second portions including light in said first and second spatial propagation modes; and a detection system that detects the intensity of the light in said first and second portions, the intensity of the light in said first and second portions varying in response to a perturbation of said waveguide, said detection system providing a first output signal responsive to the intensity of the light in said first portion and a second output signal responsive to the intensity of the light in said second portion. - View Dependent Claims (55, 56, 57, 58, 59)
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60. An apparatus comprising:
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a light source coupled to a single core optical waveguide such that light from said light source propagates in said optical waveguide in first, second, third and fourth propagation paths as first, second, third and fourth light signals; and a detection system that (1) detects the phase difference between said first and second light signals propagating in said first and second propagation paths and (2) detects the phase difference between said third and fourth light signals propagating in said third and fourth propagation paths, said detection system utilizing (1) said detected phase difference between said first and second light signals and (2) said detected phase difference between said third and fourth light signals to provide an output signal responsive to perturbation of at least one of said first, second, third and fourth propagation paths of said optical waveguide. - View Dependent Claims (61)
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62. A method of propagating light from a source of light through an optical waveguide having a core with a non-circular cross-section, comprising the steps of:
selecting the wavelength of the light and the cross-sectional dimensions of the non-circular core such that (1) the waveguide propagates light in a fundamental spatial propagation mode and a higher order spatial propagation mode, and (2) substantially all of the light in the higher order mode propagates in only a single, stable intensity pattern. - View Dependent Claims (63, 64, 65, 66, 67, 68)
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69. A method of propagating light from a source of light through an optical waveguide having a core with a non-circular cross section, comprising the steps of:
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selecting the wavelength of the light and the cross-sectional dimensions of the non-circular core such that (1) the waveguide propagates light in a fundamental spatial propagation mode and a higher order spatial propagation mode, and (2) substantially all of the light in the higher order mode propagates in only a single, stable intensity pattern, wherein the fundamental spatial mode includes two polarization modes, the method additionally comprising further selecting the cross-sectional dimensions of the core to cause the polarization modes of the fundamental mode to be nondegenerate; wherein the waveguide comprises a first optical fiber, said method additionally comprising the step of coupling the light from a selected one of the fundamental and higher order modes of the first fiber to a selected mode of a second fiber, without coupling light from the other of the fundamental and higher order modes to the selected mode of the second fiber.
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70. A method of propagating light from a source of light through an optical waveguide having a core with a non-circular cross section, comprising the steps of:
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selecting the wavelength of the light and the cross-sectional dimensions of the non-circular core such that (1) the waveguide propagates light in a fundamental spatial propagation mode and a higher order spatial propagation mode, and (2) substantially all of the light in the higher order mode propagates in only a single, stable intensity pattern, wherein the fundamental spatial mode includes two polarization modes, the method additionally comprising further selecting the cross-sectional dimensions of the core to cause the polarization modes of the fundamental mode to be nondegenerate; said method additionally comprising the step of introducing light into the waveguide such that the light propagates in two spatial modes of the waveguide, and such that the light propagates through a sensing section of the waveguide for exposure to an ambient effect, and detecting only a selected portion of the spatial intensity pattern defined by a superposition of the spatial intensity patterns of the two modes, said selected portion of the spatial intensity pattern including substantial portions of light from both of the two spatial modes. - View Dependent Claims (71, 72, 73, 74, 75, 76)
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77. A method of separating light having a first wavelength from light having a second wavelength, comprising:
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propagating said light in a waveguide comprising first and second propagation modes having first and second propagation constants, respectively, said first propagation constant different from said second propagation constant such that light in said first mode propagates at a different velocity than light in said second propagation mode; propagating a component of said light at said first wavelength in each of said first and second modes; propagating a component of said light at said second wavelength in each of said first and second modes; coupling both of said components at said first wavelength to a first propagation path; and coupling both of said components at said second wavelength to a second propagation path. - View Dependent Claims (78, 79, 80, 81, 82)
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83. A method of separating light having a first polarization from light having a second polarization, comprising:
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propagating said light in a waveguide comprising first and second propagation modes having first and second propagation constants, respectively, said first propagation constant different from said second propagation constant such that light in said first mode propagates at a different velocity than light in said second mode; propagating a component of said light having said first polarization in each of said first and second modes; propagating a component of said light having said second polarization in each of said first and second modes; coupling both of said components having said first polarization to a first propagation path; and coupling both of said components having said second polarization to a second propagation path. - View Dependent Claims (84, 85, 86, 87, 88)
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Specification