Optical systems with solid transparent substrate
A variety of femtoprojector optical systems are described. Each of them can be made small enough to fit in a contact lens using plastic injection molding, diamond turning, photolithography and etching, or other techniques. Most, but not all, of the systems include a solid cylindrical transparent substrate with a curved primary mirror formed on one end and a secondary mirror formed on the other end. Any of the designs may use light blocking, light-redirecting, absorbing coatings or other types of baffle structures as needed to reduce stray light.
1. An optical system comprising:
a solid transparent substrate having a first end and a second opposing end, and further having a third surface also opposing the first end;
a convex mirror on the second end of the substrate, and a concave mirror on the first end of the substrate, the concave mirror having a central opening; wherein light rays propagate between a first aperture in the central opening and a second aperture on the third surface via reflections off the two mirrors; and
a light baffle system comprising:
a first absorbing baffle on the substrate between the first aperture and the concave mirror;
a second absorbing baffle on the substrate between the convex mirror and the second aperture;
a third absorbing baffle on a sidewall of the substrate.
2. An optical system comprising:
a solid transparent substrate having a first end and a second opposing end;
a convex mirror formed on the second end of the substrate, and a concave mirror formed on the first end of the substrate, the concave mirror having a central opening;
an annular exit aperture on a surface of the substrate opposing the first end of the substrate; wherein light rays from an image source positioned outside the first end of the substrate enter the substrate through an entrance aperture in the central opening, are reflected off the convex mirror and then the concave mirror, and exit the substrate through the exit aperture; and
a light baffle system that blocks stray rays from the image source from propagating directly from the entrance aperture to outside the substrate.
3. The optical system of claim 2 wherein the light baffle system includes an absorbing baffle on the substrate between the convex mirror and the exit aperture.
4. The optical system of claim 3 wherein the absorbing baffle comprises a non-flat obscuration.
5. The optical system of claim 3 wherein the absorbing baffle has a maximum lateral dimension “a”; and
a≥b +FOV( h/n fp ),
where n fp is the index of refraction of material into which the image source emits light, h is a height of the optical system, b is a maximum lateral dimension of the image source, and FOV is a field of view occupied by an image projected by the optical system from the image source.
6. The optical system of claim 2 wherein the light baffle system includes an absorbing baffle on the substrate between the entrance aperture and the concave mirror.
7. The optical system of claim 2 wherein the light baffle system includes an absorbing baffle on a sidewall of the substrate.
8. The optical system of claim 2 wherein the light baffle system prevents any stray rays from the image source being projected to an area that overlaps with an image projected from the image source.
9. The optical system of claim 2 wherein the surface of the annular exit aperture is curved.
10. The optical system of claim 2 wherein the convex mirror has a maximum lateral dimension “c”; and
c
≤
(
1
n
f
p
)
(
h
w
b
)
FOV
,
where n fp is the index of refraction of material into which the image source emits light, h is a height of the optical system, w is a maximum lateral dimension of the optical system, b is a maximum lateral dimension of the image source, and FOV is a field of view occupied by an image projected by the optical system from the image source.
11. The optical system of claim 2 wherein the substrate has a length of not more than 2 mm.
12. A method for manufacturing an optical system, comprising:
creating a solid transparent substrate in a shape having a first end and a second opposing end, and further having a third surface also opposing the first end;
forming a concave mirror with a central opening on the first end of the substrate; and
forming a convex mirror on the second end of the substrate; wherein light rays from an image source positioned outside the first end of the substrate enter the substrate through an entrance aperture in the central opening, are reflected off the convex mirror and then the concave mirror, and exit the substrate through an exit aperture on the third surface.
13. The manufacturing method of claim 12 , further comprising:
forming a light baffle system on the substrate, wherein the light baffle system blocks stray rays from the image source from propagating directly from the entrance aperture to outside the substrate.
14. The manufacturing method of claim 13 wherein forming the light baffle system on the substrate comprises:
coating one or more surface regions of the substrate with an absorbing coating.
15. The manufacturing method of claim 13 wherein forming the light baffle system on the substrate comprises:
coating a surface region of the substrate between the convex mirror and the exit aperture with an absorbing coating.
16. The manufacturing method of claim 13 wherein forming the light baffle system on the substrate comprises:
coating a sidewall surface of the substrate with an absorbing coating.
17. The manufacturing method of claim 12 wherein forming the convex mirror on the second end of the substrate comprises coating the second end of the substrate to form the convex mirror, and forming the concave mirror on the first end of the substrate comprises coating the first end of the substrate to form the concave mirror.
18. The manufacturing method of claim 12 wherein creating the substrate in the shape comprises diamond turning the substrate into the shape.
19. The manufacturing method of claim 12 wherein creating the substrate into the shape comprises using wafer scale optics techniques to create a plurality of solid transparent substrates in the shape.
20. The manufacturing method of claim 12 wherein the substrate has a length of not more than 2 mm.