High-speed electro-optic modulator
First Claim
1. A variable optical attenuator modulator comprising:
- an input optical fiber;
a polarization separator that separates incident light from the input optical fiber into two polarization components along separate paths within the modulator;
a solid-state electro-optic phase retarder that receives the two polarization components from the polarization separator, the retarder having electrodes that provide an electric field across the retarder, said electric field in said phase retarder producing relative phase retardation with respect to the two polarization components, said retarder comprising a crystalline ceramic material;
a voltage control circuit that is connected to the electrodes such that an adjustable electric field can be applied across the retarder;
a polarization recombiner that combines the polarization components from the retarder to form a modulated optical signal; and
an output fiber optically coupled to the recombiner and that receives the modulated optical signal.
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Accused Products
Abstract
An optical modulator is provided to control the intensity of a transmitted or reflected light. In a transmission mode, a separator splits arbitrarily polarized light into two polarization rays and one is made to travel a separate path from the other. A recombiner causes the two rays to recombine at an output unless an electro-optic phase retarder changes the polarization of the two rays, in which case, both of them miss the output by an amount which is a function of the voltage on the retarder. A normally-off version with low polarization mode dispersion is obtained by changing the orientation of the recombiner. A normally-on version with low polarization mode dispersion is obtained with a passive polarization direction rotator. Similar results can be obtained in a reflection mode where the input and output are on the same side of the modulator. Versions using a GRIN lens are particularly suited to modulation of light out of and back into fiber-optic cables. The device can be operated as a variable optical attenuator, an optical switch, or a high speed modulator and is insensitive to polarization of the input light. A preferred material for the phase retarder is a hot-pressed ceramic lead lanthanum zirconate titanate composition.
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Citations
37 Claims
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1. A variable optical attenuator modulator comprising:
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an input optical fiber;
a polarization separator that separates incident light from the input optical fiber into two polarization components along separate paths within the modulator;
a solid-state electro-optic phase retarder that receives the two polarization components from the polarization separator, the retarder having electrodes that provide an electric field across the retarder, said electric field in said phase retarder producing relative phase retardation with respect to the two polarization components, said retarder comprising a crystalline ceramic material;
a voltage control circuit that is connected to the electrodes such that an adjustable electric field can be applied across the retarder;
a polarization recombiner that combines the polarization components from the retarder to form a modulated optical signal; and
an output fiber optically coupled to the recombiner and that receives the modulated optical signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
a first fixed 45°
polarizer direction rotator disposed between said separator and phase retarder;
a second fixed 45°
polarizer direction rotator disposed between said phase retarder and said recombiner,so that said phase retarder electrodes provide a transverse electric field at 90°
to said separator plane.
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10. The attenuator of claim 9 wherein said first and second fixed 45°
- polarizer direction rotators comprise half-wave plates with their c-axes oriented perpendicular to the direction of the optical paths and at 22.5°
+N×
45°
(N an integer) with respect to said separator plane.
- polarizer direction rotators comprise half-wave plates with their c-axes oriented perpendicular to the direction of the optical paths and at 22.5°
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11. The attenuator of claim 1 such that the modulator operates at a voltage of 500 volts or less.
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12. A light intensity modulator comprising:
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a polarization separator receiving light at an input area and that separates the light into two polarization components that transit the modulator along separate paths;
a PLZT phase retarder having electrodes that provide a transverse electric field that produces relative phase retardation with respect to components of each of the two polarization components produced by the polarization separator; and
a polarization recombiner from said polarization separator and receiving the light at an output area with an orientation with respect to said polarization separator; and
a reflector oriented to direct light transiting said separator and said retarder in the forward direction back through said retarder and said recombiner in the reverse direction to the output area. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A method of modulating an optical signal comprising:
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coupling light from an input optical fiber to a polarization separator to separate the light into a plurality of polarization components;
providing a solid state electro-optic phase retarder including a crystalline ceramic material;
applying an electric field in a direction across an optical path of the polarization components with the solid state electro-optic phase retarder to provide relative phase retardation between the components; and
combining the polarization components to form a modulated output signal. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37)
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Specification