Resonant phase modulator
First Claim
1. Light beam modulation apparatus for varying the optical phases of a light beam output signal relative to the optical phase of a light beam input signal, the apparatus comprising:
- an optically resonant electro-optical crystal, having a first partially transmissive crystal face to receive a light beam having a frequency-stabilized single frequency and to cause a portion of the light beam to propagate internally within the crystal, and having at least second and third crystal faces positioned to reflect this internally propagating portion of the beam so that this portion follows a closed path within the crystal with a phase shift φ
that varies around a resonant value φ
r =2Nπ
, where N is a non-zero integer, along this closed path, where a portion of this internally propagating portion of the light beam that arrives at the first crystal face combines with an externally reflected portion of the light beam to form an output beam propagating in a selected direction; and
a voltage source positioned adjacent to the crystal to impress a controllable, time-varying voltage deference across the crystal in a second selected direction to controllably vary the phase shift φ
about the resonant value φ
r =2Nπ
.
1 Assignment
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Accused Products
Abstract
Apparatus and method for modulating the phase or the amplitude of a monochromatic light beam, the apparatus including in one embodiment a Mach-Zehnder interferometer that consists of two beam splitters or beam combiners, a fully reflective mirror and an electro-optical crystal for modulation of one of two beam components. The electro-optical crystal serves as an optical resonator for the portion of the light beam admitted into the crystal material, using total internal reflection of the light beam from two or more of the crystal surfaces. The crystal has a high finesse so that a relatively small change in voltage applied across the crystal produces a large (≈180°) change in the external phase shift associated with the modulated component of the light beam. The modulated and unmodulated light beam components may be recombined for purposes of communication of information, using the mutual extinction of the two beam components when the optical phase shift between the two beam components is approximately 180°. Transverse or longitudinal electro-optical materials can be used for the crystal, and the driving voltages required are less than 50 volts in some configurations. Communications at frequency up to and beyond 1 GHz. are possible.
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Citations
25 Claims
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1. Light beam modulation apparatus for varying the optical phases of a light beam output signal relative to the optical phase of a light beam input signal, the apparatus comprising:
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an optically resonant electro-optical crystal, having a first partially transmissive crystal face to receive a light beam having a frequency-stabilized single frequency and to cause a portion of the light beam to propagate internally within the crystal, and having at least second and third crystal faces positioned to reflect this internally propagating portion of the beam so that this portion follows a closed path within the crystal with a phase shift φ
that varies around a resonant value φ
r =2Nπ
, where N is a non-zero integer, along this closed path, where a portion of this internally propagating portion of the light beam that arrives at the first crystal face combines with an externally reflected portion of the light beam to form an output beam propagating in a selected direction; anda voltage source positioned adjacent to the crystal to impress a controllable, time-varying voltage deference across the crystal in a second selected direction to controllably vary the phase shift φ
about the resonant value φ
r =2Nπ
. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17)
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18. Light beam modulation apparatus comprising:
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a light beam source that produces a single frequency, frequency-stabilized light beam with a selected polarization direction; beam splitter means for receiving the light beam and for producing first component and second component light beams that issue therefrom in different directions; phase shift means for receiving the first component light beam from the splitter means, for splitting off a portion of this light beam and shifting the phase of this portion, relative to the remainder portion of the first component light beam, by a time-variable, controllable phase shift φ
about a resonant phase shift value φ
r =2Nπ
, where N is a non-zero integer, and for combining the split-off portion of the beam with the remainder portion of the beam as a first composite light beam that propagates in a selected direction; andbeam combiner means for combining the first composite light beam with the second component light beam as an overall composite light beam, whereby the amplitude of the overall composite light beam may be controllably modulated. - View Dependent Claims (15, 19, 20, 21, 22, 23)
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24. Light beam modulation apparatus for varying the optical phases of a light beam output signal relative to the optical phase of a light beam input signal, the apparatus comprising:
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an optically resonant electro-optical crystal, having a first partially transmissive crystal face with optical reflectivity at least 50 percent to receive a light beam having a frequency-stabilized single frequency and to cause a portion of the light beam to propagate internally within the crystal, and having at least second and third crystal faces positioned to reflect this internally propagating portion of the beam so that this portion follows a closed path within the crystal with a phase shift φ
that varies around a resonant value φ
r =2Nπ
, where N is a non-zero integer, along this closed path, where a portion of this internally propagating portion of the light beam that arrives at the first crystal face combines with an externally reflected portion of the light beam to form an output beam propagating in a selected direction; anda voltage source positioned adjacent to the crystal to impress a controllable, time-varying voltage difference across the crystal in a second selected direction to controllably vary the phase shift φ
about the resonant value φ
r =2Nπ
.
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25. Light beam modulation apparatus for varying the optical phases of a light beam output signal relative to the optical phase of a light beam input signal, the apparatus comprising:
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an optically resonant electro-optical crystal, having a first partially transmissive crystal face to receive a light beam having a frequency-stabilized single frequency and to cause a portion of the light beam to propagate internally within the crystal, and having at least second and third crystal faces positioned to reflect this internally propagating portion of the beam so that this portion follows a closed path within the crystal with a phase shift φ
that varies around a resonant value φ
r =2Nπ
, where N is a non-zero integer, along this closed path, where a portion of this internally propagating portion of the light beam that arrives at the first crystal face combines with an externally reflected portion of the light beam to form an output beam propagating in a selected direction, and where the round trip optical path within the crystal has a length L and one of the first, second and third crystal faces is curvilinear and has a radius R satisfying the relation R>
L/2; anda voltage source positioned adjacent to the crystal to impress a controllable, time-varying voltage difference across the crystal in a second selected direction to controllably vary the phase shift φ
about the resonant value φ
r =2Nπ
.
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Specification