Apodized grating coupler
AssigneeFacebook Technologies, LLC
InventorsWanli Chi, Yang Yang, Dominic Meiser, Wai Sze Tiffany Lam
Life of this patent
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Abstract
An optical coupler includes a plurality of volume gratings in a substrate. The gratings include an array of fringes extending along length and thickness dimensions of the substrate. A difference between a refractive index of the fringes and a refractive index of the substrate depends on a depth coordinate along the thickness dimension of the substrate. A dependence of the difference on the depth coordinate has a bell-shaped function which suppresses ghost image formation due to optical crosstalk between gratings of neighboring spatial pitches.
Claims20
An optical coupler comprising:
- a substrate;
- and
- a plurality of volume gratings in the substrate, each volume grating of the plurality of volume gratings comprising an array of fringes at a grating pitch, the fringes extending along length and thickness dimensions of the substrate;
- wherein a difference between a refractive index of the fringes and a refractive index of the substrate depends on a depth coordinate along the thickness dimension of the substrate, wherein a dependence of the difference on the depth coordinate comprises a bell-shaped function.
A lightguide comprising:
- a substrate comprising two opposed surfaces running parallel to one another for propagating a light beam by a series of reflections therefrom;
- a plurality of in-coupling volume gratings in the substrate for in-coupling the light beam into the substrate;
- and
- a plurality of out-coupling volume gratings in the substrate corresponding to the plurality of in-coupling volume gratings, for out-coupling portions of the light beam along the substrate;
- wherein each volume grating of the plurality of in-coupling or out-coupling volume gratings comprises an array of fringes at a grating pitch, the fringes extending along length and thickness dimensions of the substrate;
- wherein a difference between a refractive index of the fringes and a refractive index of the substrate of at least one of the plurality of in-coupling or out-coupling volume gratings depends on a depth coordinate along the thickness dimension of the substrate, wherein a dependence of the difference on the depth coordinate comprises a bell-shaped function.
A method of manufacturing a lightguide, the method comprising:
- forming, in a substrate comprising two opposed surfaces, a plurality of in-coupling volume gratings for in-coupling a light beam into the substrate, and a plurality of out-coupling volume gratings corresponding to the plurality of in-coupling volume gratings, for out-coupling portions of the light beam along the substrate, wherein each volume grating of the plurality of in-coupling or out-coupling volume gratings comprises an array of fringes at a grating pitch, the fringes extending along length and thickness dimensions of the substrate;
- and
- apodizing the volume gratings of at least one of the plurality of in-coupling or out-coupling volume gratings such that a difference between a refractive index of the fringes and a refractive index of the substrate of the at least one of the plurality of in-coupling or out-coupling volume gratings depends on a depth coordinate along the thickness dimension of the substrate, wherein a dependence of the difference on the depth coordinate comprises a bell-shaped function with a maximum at a center of the bell-shaped function.
Dependencies are inferred from the claim text.