Femtoprojector optical systems
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. A femtoprojector optical system for projecting an image produced by an image source to a retina of a user's eye, the femtoprojector optical system comprising:
a convex secondary mirror facing the image source, where image-forming rays from the image source are incident on and reflected by the secondary mirror;
a concave primary mirror facing the secondary mirror and further reflecting the image-forming rays from the secondary mirror, the secondary mirror and primary mirror cooperating to project the image from the image source;
a light baffle system that includes an obscuration, the obscuration blocking stray rays from the image source that are not reflected by the secondary mirror; and
a solid transparent substrate with the primary mirror on one end of the substrate and with the secondary mirror on an opposite end of the substrate;
where the femtoprojector optical system is small enough to mount in a contact lens wearable by a human user.
2. The femtoprojector optical system of claim 1 where the light baffle system prevents any stray rays from being projected to an area that overlaps with the projected image.
3. The femtoprojector optical system of claim 1 where the obscuration blocks all axially-propagating rays from the image source that are not reflected by the secondary mirror.
4. The femtoprojector optical system of claim 1 where the obscuration is annular in shape, and an inner edge of the annular obscuration is adjacent to an outer edge of the secondary mirror.
5. The femtoprojector optical system of claim 1 where the obscuration is annular in shape, and a maximum lateral dimension a of the annular obscuration complies with
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 femtoprojector optical system, b is a maximum lateral dimension of the image source, and FOV is a field of view occupied by the image produced by the image source.
6. The femtoprojector optical system of claim 1 where the obscuration is axially offset from the secondary mirror.
7. The femtoprojector optical system of claim 1 where the obscuration is sloped towards the image source.
8. The femtoprojector optical system of claim 1 where the light baffle system further includes a sidewall that is external to the primary mirror and blocks stray rays emitted from the image source at oblique angles.
9. The femtoprojector optical system of claim 8 where the sidewall is an absorbing coating that is an integral part of the femtoprojector optical system.
10. The femtoprojector optical system of claim 8 where the substrate is inserted into a hole with an absorbing sidewall.
11. The femtoprojector optical system of claim 1 where a maximum lateral dimension of the secondary mirror is smaller than a maximum lateral dimension of the image source.
12. The femtoprojector optical system of claim 11 where a maximum lateral dimension of the obscuration is larger than the maximum lateral dimension of the image source.
13. The femtoprojector optical system of claim 1 where the femtoprojector optical system has an exit aperture with a maximum lateral dimension of not more than 1 mm.
14. The femtoprojector optical system of claim 1 where the primary mirror is a reflective material coating the end of the substrate.
15. The femtoprojector optical system of claim 14 where the end of the substrate coated by the primary mirror is formed by one of injection-molding, compression molding, diamond-turning, etching, embossing, or curing a photosensitive polymer.
16. The femtoprojector optical system of claim 1 where the substrate includes a clear, non-reflective mounting area for the image source.
17. The femtoprojector optical system of claim 1 where the primary mirror and the secondary mirror are both aspheric.
18. The femtoprojector optical system of claim 1 where the femtoprojector optical system has a height h as measured from the image source to the secondary mirror of less than 2 mm and an aspect ratio of (height h):(width w) of not more than 2:1 where the width w is a width of the primary mirror.
19. The femtoprojector optical system of claim 18 where the aspect ratio of (height h):(width w) is not more than 1:1.
20. The femtoprojector optical system of claim 18 where the height his 1 mm or less.
21. The femtoprojector optical system of claim 1 where a ratio of the contact lens diameter to the width w is in a range of 15:1 to 30:1.
22. The femtoprojector optical system of claim 1 where the image source is Lambertian.
23. The femtoprojector optical system of claim 1 where the femtoprojector optical system provides a magnification in a range of 3×-5×.