Micromechanical modulator
First Claim
1. A modulator for modulating an optical signal comprising:
- a substrate characterized by a refractive index;
a membrane having an optically transparent portion and comprising at least three layers of material,the first of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the first layer,the second of which layers has a refractive index which is approximately equal to the square root of the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the second layer,the third of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-half of a wavelength of the optical signal, as measured within the third layer;
a flexible support for positioning the membrane in a first position wherein the membrane is oriented in spaced and superposed relation to the substrate defining an air gap, and wherein, of the at least three layers, the first layer is proximal to the substrate and the third layer is distal to the substrate; and
a means for supplying bias to the membrane and substrate;
wherein, under the action of bias, the membrane moves to a second position, changing the air gap, where the change from the first to the second position causes a change in the amount of the optical signal that is reflected from the membrane.
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Accused Products
Abstract
A method and apparatus for modulating an optical signal, and a method for fabricating such an apparatus, are disclosed. The modulator comprises a membrane, which consists of at least three layers, and a substrate, spaced to form an air gap. The layers of the membrane are characterized by a relationship between the refractive indices of the layers and the refractive index of the substrate. The membrane is suspended in a first position over the substrate by a flexible support arrangement. A biasing force is applied to the membrane and the substrate to create an electrostatic force to move the membrane towards the substrate to a second position. The reflectivity of the device to an optical signal changes as the membrane moves from the first position to the second position, thereby modulating the signal.
127 Citations
25 Claims
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1. A modulator for modulating an optical signal comprising:
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a substrate characterized by a refractive index; a membrane having an optically transparent portion and comprising at least three layers of material, the first of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the first layer, the second of which layers has a refractive index which is approximately equal to the square root of the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the second layer, the third of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-half of a wavelength of the optical signal, as measured within the third layer; a flexible support for positioning the membrane in a first position wherein the membrane is oriented in spaced and superposed relation to the substrate defining an air gap, and wherein, of the at least three layers, the first layer is proximal to the substrate and the third layer is distal to the substrate; and a means for supplying bias to the membrane and substrate; wherein, under the action of bias, the membrane moves to a second position, changing the air gap, where the change from the first to the second position causes a change in the amount of the optical signal that is reflected from the membrane. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A modulator for modulating an optical signal comprising:
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a substrate characterized by a refractive index; an optical fiber having a first end in optical communication with an optically transparent portion of a membrane; the membrane comprising at least three layers of material, the first of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the first layer, the second of which layers has a refractive index which is approximately equal to the square root of the product of the refractive indices of the substrate and the optical fiber and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the second layer, the third of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-half of a wavelength of the optical signal, as measured within the third layer, a flexible support for positioning the membrane in a first position wherein the membrane is oriented in spaced and superposed relation to the substrate, defining an air gap, and wherein the first end of the optical fiber is in superposed relation to the membrane and is spaced from the membrane by approximately an integer multiple of one-quarter of a wavelength of the optical signal, as measured in air, and wherein, of the at least three layers, the first layer is proximal to the substrate and distal to the optical fiber and the third layer is distal to the substrate and proximal to the optical fiber; and a means for supplying a biasing force to the membrane and substrate, wherein, under the action of the biasing force, the membrane moves to a second position, where the change from the first to the second position causes a change in the amount of the optical signal that is reflected from the membrane. - View Dependent Claims (15, 16)
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17. A device which, under the action of an applied biasing force, has a variable reflectivity to an incident optical signal received by the device, comprising:
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a substrate; a membrane having an optically transparent portion and comprising at least three layers of material, the first of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the first layer, the second of which layers has a refractive index which is approximately equal to the square root of the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the second layer, the third of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-half of a wavelength of the optical signal, as measured within the third layer; a flexible support for supporting the membrane in spaced and superposed relation to the substrate forming an air gap having a size which varies from a first size in the absence of the biasing force to at least a second size when the biasing force is applied, wherein, of the at least three layers, the first layer is proximal to the substrate and the third layer is distal to the substrate. - View Dependent Claims (18, 19)
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20. A method for varying reflectivity of a device to an optical signal, comprising the steps of:
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providing a device comprising a membrane and a substrate in spaced, superposed relation defining an air gap, the membrane having an optically transparent portion and comprising at least three layers of material, the first of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the first layer, the second of which layers has a refractive index which is approximately equal to the square root of the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the second layer, the third of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-half of a wavelength of the optical signal, as measured within the third layer; exposing the device to an optical signal; and applying a biasing force to the device causing the membrane to move towards the substrate thereby changing the size of the air gap and the reflectivity of the device. - View Dependent Claims (21, 22)
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23. A method for fabricating a device having a low and a high reflectivity state for modulating an optical signal, comprising the steps of:
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providing a substrate; and forming a vertically-movable membrane over the substrate so that an air gap is defined between the membrane and a portion of the substrate, the membrane having an optically transparent portion and comprising at least three layers of material, the first of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the first layer, the second of which layers has a refractive index which is approximately equal to the square root of the refractive index of the substrate and a thickness approximately equal to one-quarter of a wavelength of the optical signal, as measured within the second layer, the third of which layers has a refractive index which is approximately equal to the refractive index of the substrate and a thickness approximately equal to one-half of a wavelength of the optical signal, as measured within the third layer. - View Dependent Claims (24, 25)
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Specification