Fiber optic intermode coupling single sideband frequency shifter
First Claim
1. An apparatus for coupling optical energy between optical propagation modes in an optical fiber, comprising:
- an optical fiber having a longitudinal axis, said optical fiber supporting a first optical propagation mode and a second optical propagation mode for an optical signal propagating therein; and
a generator connected to said fiber such that said generator produces a flexural wave which propagates in said optical fiber, the energy of said flexural wave confined to said optical fiber, said flexural wave having a frequency, a propagation velocity and a wavelength, said wavelength of said flexural wave being a function of said frequency and said propagation velocity, and being selected to cause coupling of light from one of said modes to the other of said modes, said generator of said flexural wave having a longitudinal axis substantially coaxial with the longitudinal axis of said optical fiber.
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Accused Products
Abstract
An optical fiber is subjected to a series of traveling flexural waves propagating along a length of the fiber. At least a portion of an optical signal propagating within the optical fiber in a first propagation mode is coupled to a second propagation mode. The optical signal in the second propagation mode has a frequency which is equal to either the sum of or the difference between the frequency of the optical signal in the first propagation mode and the frequency of the traveling flexural waves. The frequency of the optical signal in the second propagation mode is shifted upward or downward from the frequency of the optical signal in the first propagation mode as determined by the direction of propagation of the first optical signal with respect to the direction of propagation of the traveling flexural waves, and as also determined by whether the phase propagation velocity of the optical signal in the first propagation mode is greater than or less than the propagation velocity of the optical signal in the second propagation mode. An acoustic wave is induced in a generator having a gradual tapered cross-section. The generator preferably has the shape of a horn and is coaxially mounted with said optical fiber, so as to suppress the acoustic wave induced in the optical fiber in the reverse direction.
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Citations
34 Claims
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1. An apparatus for coupling optical energy between optical propagation modes in an optical fiber, comprising:
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an optical fiber having a longitudinal axis, said optical fiber supporting a first optical propagation mode and a second optical propagation mode for an optical signal propagating therein; and a generator connected to said fiber such that said generator produces a flexural wave which propagates in said optical fiber, the energy of said flexural wave confined to said optical fiber, said flexural wave having a frequency, a propagation velocity and a wavelength, said wavelength of said flexural wave being a function of said frequency and said propagation velocity, and being selected to cause coupling of light from one of said modes to the other of said modes, said generator of said flexural wave having a longitudinal axis substantially coaxial with the longitudinal axis of said optical fiber. - 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, 27, 28, 29, 30)
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31. A method of coupling optical energy between optical propagation modes in an optical fiber, comprising the steps of:
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inputting an optical signal into an optical fiber having first and second optical propagation modes for signals propagating therein, said optical signal having a longitudinal axis; propagating a flexural wave within said optical fiber, said flexural wave having a frequency, propagation velocity and wavelength within said fiber, said wavelength within said fiber being determined by said frequency and said propagation velocity, said wavelength being selected so that a portion of said optical energy propagating in one of said propagation modes is coupled to said other propagation mode; and exciting said flexural wave by propagating acoustic energy in a direction substantially parallel to the longitudinal axis of said fiber. - View Dependent Claims (32, 33)
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34. A method of manufacturing a fiber optic frequency shifter comprising the steps of:
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providing an optical fiber; surrounding a portion of said optical fiber with an acoustic medium; mounting and orienting acoustic transducers on said acoustic medium to generate an acoustic wave in said acoustic medium; and driving said transducers on said acoustic medium so as to cause said acoustic wave to propagate in a direction substantially parallel to the longitudinal axis of said fiber, to thereby produce a flexural wave in said optical fiber.
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Specification