Single mode fiber optic single sideband modulator and method of frequency
First Claim
1. A fiber optic frequency shifter comprising:
- a single optical fiber for guiding light having a wavelength, said fiber having two predetermined modes of propagation, each of said modes having a different propagation velocity, said fiber having a beat length for said two predetermined modes at said wavelength of said light; and
means for generating a travelling stress wave having a predetermined wavelength for propagation longitudinally along a continuous length of said single fiber, said continuous length comprising plural beat lengths of said fiber, the predetermined wavelength of said travelling stress wave selected in accordance with the beat length for said two predetermined modes of said fiber to cause cumulative coupling of light from one of said modes to the other of said modes through said plural beat lengths, said travelling stress wave interacting with the light to cause the coupled light to be shifted in frequency.
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Accused Products
Abstract
A fiber optic frequency shifter comprising two waveguides having different indices of refraction. In some embodiments the waveguides are two modes of propagation in one fiber. Plural distributed coupling ridges, or electrodes mounted adjacent piezoelectric materials, are independently driven to apply sinusoidally varying forces to the fiber. In some embodiments, the phase relationship of the driving signals for the electrodes or ridges is such that a travelling acoustic wave is launched in the fiber. In other embodiments, regions of stress in the fiber are created by an acoustic wave coupled into the fiber from a transducer coupled to an acoustic medium surrounding the fiber. The input carrier light is shifted in frequency by the frequency of the acoustic wave.
59 Citations
37 Claims
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1. A fiber optic frequency shifter comprising:
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a single optical fiber for guiding light having a wavelength, said fiber having two predetermined modes of propagation, each of said modes having a different propagation velocity, said fiber having a beat length for said two predetermined modes at said wavelength of said light; and means for generating a travelling stress wave having a predetermined wavelength for propagation longitudinally along a continuous length of said single fiber, said continuous length comprising plural beat lengths of said fiber, the predetermined wavelength of said travelling stress wave selected in accordance with the beat length for said two predetermined modes of said fiber to cause cumulative coupling of light from one of said modes to the other of said modes through said plural beat lengths, said travelling stress wave interacting with the light to cause the coupled light to be shifted in frequency. - View Dependent Claims (2, 3, 5, 6, 7, 8)
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4. A fiber optic frequency shifter comprising:
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a first optical fiber for guiding light having two modes of propagation, each of said modes having a different propagation velocity; and a second optical fiber acoustically coupled to said first fiber so as to couple an acoustic wave propagating in said second fiber into said first fiber, said acoustic wave having a wavelength selected in accordance with the beat length of said first fiber to cause coupling of light between said modes of said first fiber, without causing coupling of light between said fibers, said acoustic wave interacting with said light to cause said coupled light to be frequency shifted.
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9. A fiber optic frequency shifter comprising:
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a single optical fiber having two modes of propagation, each mode having a different propagation velocity, thereby providing a beat length between said modes; an acoustic medium having a surface for bearing against said fiber along a continuous length of said fiber; and a transducer for producing an acoustic wave in said acoustic medium to cause said surface of said acoustic medium to undulate with a surface acoustic wave, the wavelength of said surface acoustic wave selected in accordance with the beat length of said fiber to cause coupling of light from one of said modes to the other of said modes, said surface acoustic wave producing stresses on said fiber which propagate along said length of fiber and interact with the light along said continuous length of fiber to cause the light to be shifted in frequency. - View Dependent Claims (10)
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11. A fiber optic frequency shifter comprising:
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a fiber for guiding light within two modes of propagation, each of said modes having a different propagation velocity, said fiber having a beat length for said two modes; and acoustic waveguide means coupled to said fiber, for (i) guiding acoustic energy of an acoustic wave propagating in said waveguide means and (ii) coupling said acoustic energy to said fiber for propagation longitudinally along said fiber, the wavelength of said acoustic wave selected in accordance with said beat length of said fiber to cause coupling of light from one of said modes of said fiber to the other of said modes of said fiber without coupling of light out of said fiber, said acoustic energy interacting with the light to cause the coupled light to be shifted in frequency. - View Dependent Claims (35)
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12. A fiber optic frequency shifter, comprising:
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a single optical fiber having two preselected propagation modes, said fiber having a beat length for said two preselected modes; a member comprising plural coupling elements, each of said coupling elements having a rigid surface for applying force to said fiber at a preselected discrete static spaced location on said fiber; means for individually driving said plural coupling elements in a predetermined phase relationship to individually drive each of said surfaces against said fiber to apply said force to said fiber only at said discrete static spaced locations along said fiber, said phase relationship selected in accordance with said beat length to generate time varying stresses in said fiber so as to simulate an acoustic wave in said fiber without applying an acoustic wave to said fiber, to thereby cause coupling of light between said modes, said phase relationship selected to cause said coupled light to be frequency shifted. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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36. A fiber optic frequency shifter, comprising:
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an optical fiber for propagating an optical signal; means for propagating a travelling stress axially along a continuous length of said fiber, said propagating means including means for causing said stress to interact with said optical signal to frequency shift said optical signal without coupling said optical signal out of said fiber.
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37. A method of frequency shifting, comprising:
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introducing an optical signal into an optical fiber; propagating a travelling stress axially along a continuous length of said fiber, said stress interacting with said optical signal along said length of said fiber to cause said frequency shifting; guiding said optical signal within said fiber during said interacting of said stress and said optical signal to prevent said optical signal from escaping said fiber.
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Specification