Electrode configuration for electro-optic modulators
An electro-optic modulator for high voltage applications exhibits reduced corona and arcing by utilizing dielectric-coated electrodes in conjunction with a non-centrosymmetric crystal. The inclusion of an insulative coating (i.e., a dielectric material) on at least a portion of the electrodes reduces the possibility of arcing or corona, without requiring the application of any type of coating material directly on the crystal itself. Thus, the birefringent response of the crystal is not impacted by this coated electrode configuration of the present invention. In one configuration, the exposed surfaces of the electrodes are coated with an insulative material, while maintaining a direct contact between the electrodes and the surface of the crystal.
1. An electro-optic modulator comprising:
a non-centrosymmetric crystal that exhibits changes in internal birefringence in response to an applied voltage, the non-centrosymmetric crystal having opposing major surfaces; and
electrodes coupled to the opposing major surfaces of the non-centrosymmetric crystal with at least one electrode including a dielectric coating over at least a portion of its external surface, the coating of a thickness sufficient to reduce arcing in the presence of voltages in excess of 1000 volts.
2. The electro-optic modulator as defined in claim 1 wherein the electrodes include a first electrode covering a first major surface of the non-centrosymmetric crystal and a second electrode covering a second, opposing major surface of the non-centrosymmetric crystal.
3. The electro-optic modulator as defined in claim 2 wherein exposed surfaces of the first and second electrodes are covered with the dielectric coating.
4. The electro-optic modulator as defined in claim 1 wherein the electrodes include at least one electrode disposed in a spaced-apart relationship with a first major surface of the non-centrosymmetric crystal, the at least one electrode encapsulated within the dielectric coating, creating a capacitive connection between the at least one electrode and the first major surface of the non-centrosymmetric crystal.
5. The electro-optic modulator as defined in claim 1 wherein the electrodes comprise a pair of electrodes disposed in a spaced-apart relationship with the opposing major surfaces of the non-centrosymmetric crystal, each electrode encapsulated with the dielectric coating.
6. The electro-optic modulator as defined in claim 1 wherein the electrodes are configured as partially encapsulated, with a first electrode including a first section in contact with a major surface of the non-centrosymmetric crystal and an adjacent second section spaced-apart from the non-centrosymmetric crystal with a portion of the dielectric coating disposed therebetween.
7. The electro-optic modulator as defined in claim 1 wherein the electrodes are configured as partially encapsulated, with a first electrode including a first section in contact with a first major surface of the non-centrosymmetric crystal and an adjacent second section spaced-apart from the first major surface of the non-centrosymmetric crystal with a portion of the dielectric coating disposed therebetween, and a second electrode including a first section in contact with a second, opposing major surface of the non-centrosymmetric crystal and an adjacent second section spaced apart from the second major surface of the non-centrosymmetric crystal with a portion of the dielectric coating disposed therebetween.
8. The electro-optic modulator as defined in claim 1 wherein the non-centrosymmetric crystal comprises CdTe.
9. The electro-optic modulator as defined in claim 1 wherein the dielectric coating exhibits a breakdown voltage of less than about 0.003V/mm.
10. The electro-optic modulator as defined in claim 1 wherein the dielectric coating is formed to exhibit a thickness in the range of about 0.020 mm to 0.040 mm.
11. The electro-optic modulator as defined in claim 10 wherein the dielectric coating is formed to exhibit a thickness on the order of about 0.025 mm.
12. The electro-optic modulator as defined in claim 1 wherein the dielectric coating is selected from the group consisting of resins and polymers that prevent corona and arcing.
13. The electro-optic modulator as defined in claim 1 wherein the dielectric coating is selected from the group consisting of: an organic polymer; an oxygen-containing, nitrogen-containing, sulfur-containing, or phosphorus-containing hydrocarbon polymer; a halogenated hydrocarbon polymer; inorganic polymers; ceramics and glasses.
14. The electro-optic modulator as defined in claim 1 wherein the electrodes are formed of a material selected from the group consisting of: carbon-based materials, transitional metal-based materials (i.e., Group IB, Group IIB, Group IVB, Group VB, Group VIB, Group VIIB, and Group III), Group IVA metals, and any alloy thereof.