Three layer waveguide for thin film lens fabrication
First Claim
1. A thin film lens fabricated in a layered optical waveguide comprising:
- a multilayer optical waveguides comprising a first thin flim layer of (X2 O5) on a substrate, an intermediate thin of titanium dioxide (TiO2) thereon, and a second thin film layer of (X2 O5) over the TiO2, wherein X is an element selected from the group consisting of niobium and tantalum, the three layers together defining a waveguide, and the extremities of the first and second layers of (X2 O5) providing a top and bottom boundary of the waveguide whereby a wave is propagated by reflection between said top and bottom boundaries; and
a step-in-thickness lens in said waveguide formed by plasma etching away the desired lens shape in said second (X2 O5) layer, said TiO2 operating as an etch stop during etch to provide a flat bottom for said etching away lens and, therefore, provide a flat top boundary for said lens formed by said remaining first and intermediate layer, whereby in said lens area the wave is propagated by reflection between said lens top boundary and said bottom boundary.
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Abstract
In thin film optical systems including thin film optical waveguides, of such materials as Nb2 O5, it is desirable to fabricate thin film lenses. One of the types of lenses which can be made is the step-in-thickness type. This type of thin-film lens can be fabricated by plasma etching through a photoresist mask in such materials as Nb2 O5 and Ta2 O5. Plasma etching yields an etch wall with smooth steep sides which is important for good quality thin-film lenses; however, the etch rate is too variable for reproducible etch depth based upon etch time, and the bottom of the etch is very rough, causing excessive scattering loss. It has been found that a sandwich-like structure of Nb2 O5, TiO2 and Nb2 O5 provides an improved arrangement in that a good control of the etch depth and a smooth flat bottom in the etch areas have been achieved by introducing the layer of TiO2 as an etch stop.
24 Citations
9 Claims
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1. A thin film lens fabricated in a layered optical waveguide comprising:
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a multilayer optical waveguides comprising a first thin flim layer of (X2 O5) on a substrate, an intermediate thin of titanium dioxide (TiO2) thereon, and a second thin film layer of (X2 O5) over the TiO2, wherein X is an element selected from the group consisting of niobium and tantalum, the three layers together defining a waveguide, and the extremities of the first and second layers of (X2 O5) providing a top and bottom boundary of the waveguide whereby a wave is propagated by reflection between said top and bottom boundaries; and a step-in-thickness lens in said waveguide formed by plasma etching away the desired lens shape in said second (X2 O5) layer, said TiO2 operating as an etch stop during etch to provide a flat bottom for said etching away lens and, therefore, provide a flat top boundary for said lens formed by said remaining first and intermediate layer, whereby in said lens area the wave is propagated by reflection between said lens top boundary and said bottom boundary. - View Dependent Claims (2, 3, 4, 5)
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6. A thin film lens fabricated in a niobium pentoxide thin film waveguide in which waveguide the index of refraction is related to the film thickness, comprising;
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a thin film waveguide on a substrate made up of two thin film layers of niobium pentoxide Nb2 O5 plus a thin film layer of titanium dioxide TiO2 between said two layers, the total thickness of said three layers establishing the effective refractive index of said waveguide; and
,a step-in-thickness lens in said waveguide, said lens formed by having plasma etched away the desired lens shape in said second Nb2 O5 layer, said TiO2 operating as an etch stop during etch to provide a flat bottom for said etched away area and, therefore, provide a flat top boundary for said lens formed by said remaining first and intermediate layer, the total thickness of said first Nb2 O5 layer and the TiO2 layer establishing the effective refractive index of said lens.
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7. A triple layered thin film optical waveguide for thin film lens fabrication comprising:
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a first thin film layer of niobium pentoxide (Nb2 O5) on a substrate, an intermediate thin film layer of titanium dioxide (TiO2) thereon, and a second thin film layer of Nb2 O5 over the TiO2, the three layers together defining a waveguide, the total thickness of said three layers establishing the effective refractive index of said waveguide, the total thickness of said three layers being less than the thickness at which the TE1 mode can propagate so that only the TEo mode can propagate, and the total thickness of said first and intermediate layers being sufficiently great that the effective index of refraction of said first and intermediate layers exceeds the cutoff thickness for the waveguide.
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8. A method for preparing a thin film lens in a thin film optical waveguide comprising:
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providing a first thin film layer of optical X2 O5 on a substrate; providing an intermediate thin film layer of optical titanium dioxide (TiO2) on said first layer; providing a second thin film layer of optical X2 O5 on said intermediate layer, wherein x is an element selected from the group consisting of niobium and tantalum, said three layers comprising an optical waveguide; providing a photoresist mask over the waveguide, the mask including a desired lens shape, etching away by plasma etch in the second X2 O5 layer the masked lens shape, the TiO2 layer beneath providing an etch stop; whereby the remaining first and intermediate layers beneath the etch provide the desired lens. - View Dependent Claims (9)
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Specification