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AssigneeThe Regents of the University of California
InventorsRobert J. Deri, Frank Patterson
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The polarization dependence of optical wavelength filters is eliminated by using waveguide directional couplers. Material birefringence is used to compensate for the waveguide (electromagnetic) birefringence which is the original cause of the polarization dependence. Material birefringence is introduced in a controllable fashion by replacing bulk waveguide layers by finely layered composites, such as multiple quantum wells using III-V semiconductor materials. The filter has use in wavelength-division-multiplexed fiber optic communication systems. This filter has broad application for wavelength-tunable receivers in fiber optic communication links, which may be used for telecommunications, optical computer interconnect links, or fiber optic sensor systems. Since multiple-wavelength systems are increasingly being used for all of these applications, the filter is useable whenever a rapidly tunable, wavelength-filtering receiver is required.
A polarization-independent optical wavelength filter, comprising a directional coupler channel dropping filter comprising at least two waveguides of differing core refractive indices, birefringences and thicknesses brought into proximity such that light can couple from a thicker first waveguide of said at least two waveguides into a thinner second waveguide of said at least two waveguides, wherein said first waveguide comprises birefringent material with birefringence greater than the birefringence of said second waveguide by an amount adjusted so that the effective modal indices of said two waveguides exhibit about the same change with changing polarizations, wherein the birefringence of said second waveguide may be zero, wherein said optical wavelength filter is polarization-independent.
A polarization-independent optical wavelength filter, comprising a directional coupler channel dropping filter comprising at least two waveguides of differing core refractive indices, birefringences and thicknesses brought into proximity such that light can couple from a thicker first waveguide of said at least two waveguides into a thinner second waveguide of said at left two waveguides, wherein said first waveguide comprises birefringent material with birefringence greater than the birefringence of said second waveguide, wherein the birefringence of said second waveguide may be zero, wherein said optical wavelength filter is polarization-independent, wherein said birefringent material in the core of said thicker first waveguide comprises a layered composite of at least three layers, wherein said layered composite comprises a multiple quantum well.
A polarization-independent optical wavelength filter, comprising a directional coupler channel dropping filter comprising at least two waveguides of differing core refractive indices, birefringences and thicknesses brought into proximity such that light can couple from a thicker first waveguide of said at least two waveguides into a thinner second waveguide of said at least two waveguides, wherein said first waveguide comprises birefringent material with birefringence greater than the birefringence of said second waveguide, wherein the birefringence of said second waveguide may be zero wherein said optical wavelength filter is polarization-independent, further comprising a grating located between said first waveguide and said second waveguide.
A polarization-independent optical wavelength filter, comprising a directional coupler channel dropping filter comprising at least two waveguides of differing core refractive indices, birefringences and thicknesses brought into proximity such that light can couple from a thicker first Waveguide of said at least two waveguides into a thinner second waveguide of said at least two waveguides, wherein said first waveguide comprises birefringent material with birefringence greater than the birefringence of said second waveguide, wherein the birefringence of said second waveguide may be zero, wherein said optical wavelength filter is polarization-independent, wherein said birefringent material comprises a multilayer comprised of several periods, wherein each period of said periods comprises two layers, wherein each period has a thickness less than the optical wavelength of said filter.
A polarization-independent optical wavelength filter, comprising a directional coupler channel dropping filter comprising at least two waveguides of differing core refractive indices, birefringence and thicknesses brought into proximity such that light can couple from a thicker first waveguide of said at least two waveguides into a thinner second waveguide of said at least two waveguides, wherein said first waveguide comprises birefringent material with birefringence greater than the birefringence of said second waveguide, wherein the birefringence of said second waveguide may be zero, wherein said optical wavelength filter is polarization-independent, wherein said first waveguide comprises a multiple quantum well.
A polarization-independent optical wavelength filter, comprising a directional coupler channel dropping filter comprising at least two waveguides of differing core refractive indices, birefringences and thicknesses brought into proximity such that light can couple from a thicker first waveguide of said at least two waveguides into a thinner second waveguide of said at least two waveguides, wherein said first waveguide comprises birefringent material with birefringence greater than the birefringence of said second waveguide, wherein the birefringence of said second waveguide may be zero, wherein said optical wavelength filter is polarization-independent, further comprising a substrate, wherein said first waveguide comprises a first layer and a second layer and a multiplicity of layers located therebetween, wherein said second waveguide is located adjacent to said first waveguide, and wherein said second waveguide further comprises an outer cladding layer, further comprising an outer layer located adjacent to said outer cladding layer of said second waveguide.
A polarization-independent optical wavelength filter, comprising a directional coupler channel dropping filter comprising at least two waveguides of differing core refractive indices, birefringences and thicknesses brought into proximity such that light can couple from a thicker first waveguide of said at least two waveguides into a thinner second waveguide of said at least two waveguides, wherein said first waveguide comprises birefringent material with birefringence greater than the birefringence of said second waveguide, wherein the birefringence of said second waveguide may be zero, wherein said optical wavelength filter is polarization-independent, further comprising a substrate, wherein said first waveguide comprises a first layer and a second layer and a multiplicity of layers located therebetween, wherein said second waveguide is located adjacent to said first waveguide, and wherein said second waveguide further comprises an outer cladding layer, wherein said substrate comprises n.sup.+ GaAs, said first layer of said first waveguide comprising Al.sub.0.5 Ga.sub.0.5 As having a thickness of 0.65 .mu.m, said multiplicity of layers comprising 17 layers, wherein each layer comprises Al.sub.0.6 Ga.sub.0.4 As having a thickness of 11.5 nm and Al.sub.0.2 Ga.sub.0.8 As having a thickness of 38.5 nm, said final layer comprising Al.sub.0.5 Ga.sub.0.5 As having a thickness of 0.75 .mu.m, said second waveguide comprising Al.sub.0.2 Ga.sub.0.8 As having a thickness of 0.34 .mu.m, and said outer cladding layer comprising Al.sub.0.5 Ga.sub.0.5 As having a thickness of 0.17 .mu.m.
Dependencies are inferred from the claim text.