Projection lens with four glass elements having spherical surfaces

Patent metadata

Field	Value
Publication number	US-11378786-B2
Application number	US-201916678496-A
Country	US
Kind code	B2
Filing date	Nov 8, 2019
Priority date	Nov 9, 2018
Publication date	Jul 5, 2022
Grant date	Jul 5, 2022

Abstract

A projection lens can include four lens elements, each lens element being formed from glass and including spherical or planar incident and exiting surfaces. Compared to a projection lens that uses three lens elements, the four-element projection lens has relaxed manufactured and alignment tolerances. Unlike a projection lens that uses one or more plastic elements or uses aspherical surfaces, the all-glass projection lens can be manufactured using relatively fast and inexpensive grinding and polishing techniques. One or two of the glass lens elements can optionally be formed symmetrically, so as to be reversible. One glass element can optionally be piano-convex. A right-angle prism can direct light from a video display into the four glass elements. An achromatic prism can angularly divert the optical axis by about eight degrees and can direct light out of the four glass elements into a near-eye waveguide.

First claim

What is claimed is:

1. An optical system, comprising:
a projection lens having a positive total refractive power and configured to direct light in a light ray bundle from a display into a near-eye waveguide, the projection lens having an optical axis that corresponds to a center of the light ray bundle, the projection lens comprising:
a first lens element positioned along the optical axis, the first lens element having a convex spherical first incident surface facing the display and a convex spherical first exiting surface facing away from the display;
a second lens element positioned along the optical axis, the second lens element having a convex spherical second incident surface facing the first lens element and a concave spherical second exiting surface facing away from the first lens element;
a third lens element positioned along the optical axis, the third lens element having a concave spherical third incident surface facing the second lens element and a concave spherical third exiting surface facing away from the second lens element; and
a fourth lens element positioned along the optical axis, the fourth lens element having a convex spherical or planar fourth incident surface facing the third lens element and a convex spherical fourth exiting surface facing away from the third lens element,
wherein:
the first lens element is formed from a first glass having a refractive index between 1.72 and 1.85 at a wavelength of 587.6 nm and an Abbe number between 40 and 55:
the second lens element is formed from second glass having a refractive index between 1.72 and 1.85 at a wavelength of 587.6 nm and an Abbe number between 38 and 55;
the third lens element is formed from a third glass having a refractive index greater than 1.8 at a wavelength of 587.6 nm and an Abbe number between 20 and 24; and
the fourth lens element is formed from a fourth glass having a refractive index greater than 1.85 at a wavelength of 587.6 nm and an Abbe number between 28 and 35.

2. The optical system of claim 1 , wherein:
the first incident surface, the first exiting surface, and the first glass define a refractive power of the first lens element to be positive and between 88% and 128% of the total refractive power;
the second incident surface, the second exiting surface, and the second glass define a refractive power of the second lens element to be positive and between 35% and 68% of the total refractive power;
the third incident surface, the third exiting surface, and the third glass define a refractive power of the third lens element to be negative and between 165% and 216% of the total refractive power; and
the fourth incident surface, the fourth exiting surface, and the fourth glass define a refractive power of the fourth lens element to be positive and between 87% and 125% of the total refractive power.

3. The optical system of claim 2 , wherein:
the refractive power of the second lens element, divided by the refractive power of the first lens element, is between 0.28 and 0.71; and
the refractive power of the fourth lens element, divided by the refractive power of the third lens element, is between −0.64 and −0.49.

4. The optical system of claim 1 , wherein:
the first incident surface, the first exiting surface, and the first glass define a refractive power of the first lens element to be positive and between 112% and 128% of the total refractive power;
the second incident surface, the second exiting surface, and the second glass define a refractive power of the second lens element to be positive and between 35% and 54% of the total refractive power;
the third incident surface, the third exiting surface, and the third glass define a refractive power of the third lens element to be negative and between 183% and 216% of the total refractive power; and
the fourth incident surface, the fourth exiting surface, and the fourth glass define a refractive power of the fourth lens element to be positive and between 91% and 125% of the total refractive power.

5. The optical system of claim 4 , wherein:
the refractive power of the second lens element, divided by the refractive power of the first lens element, is between 0.28 and 0.46; and
the refractive power of the fourth lens element, divided by the refractive power of the third lens element, is between −0.60 and −0.49.

6. The optical system of claim 1 , wherein the first incident surface and the first exiting surface have a same radius of curvature.

7. The optical system of claim 1 , wherein the third incident surface and the third exiting surface have a same radius of curvature.

8. The optical system of claim 1 , wherein the fourth incident surface is planar.

9. An optical system comprising:
a projection lens having a positive total refractive power and configured to direct light in a light ray bundle from a display into a near-eye waveguide, the projection lens having an optical axis that corresponds to a center of the light ray bundle, the projection lens comprising:
a first lens element positioned along the optical axis, the first lens element having a convex spherical first incident surface facing the display and a convex spherical first exiting surface facing away from the display;
a second lens element positioned along the optical axis, the second lens element having a convex spherical second incident surface facing the first lens element and a concave spherical second exiting surface facing away from the first lens element;
a third lens element positioned along the optical axis, the third lens element having a concave spherical third incident surface facing the second lens element and a concave spherical third exiting surface facing away from the second lens element;
a fourth lens element positioned along the optical axis, the fourth lens element having a convex spherical or planar fourth incident surface facing the third lens element and a convex spherical fourth exiting surface facing away from the third lens element;
a display configured to display video and direct light from the displayed video into the projection lens;
a controller configured to direct a video signal to the display to be displayed on the display; and
a near-eye waveguide configured to receive light from the projection lens and operably guide the received light toward a human eye,
wherein:
the projection lens further comprises an achromatic prism positioned along the optical axis between the near-eye waveguide and the fourth lens element and configured to angularly divert the optical axis by an angle between seven degrees and nine degrees;
the achromatic prism is formed from a first prism element, facing the fourth lens element, in contact with a second prism element, facing the near-eye waveguide;
the first prism is formed from a flint glass having a refractive index between 1.85 and 2.01 at a wavelength of 587.6 nm and an Abbe number between 18.0 and 23.8; and
the second prism is formed from a crown glass having a refractive index of 1.73 at a wavelength of 587.6 nm and an Abbe number of 54.7.

10. The optical system of claim 9 , wherein the projection lens further comprises a right-angle prism positioned along the optical axis between the display and the first lens element, the right-angle prism configured to angularly divert the optical axis by ninety degrees, the right-angle prism being formed from a crown glass having a refractive index greater than or equal to 1.728 at a wavelength of 587.6 nm and an Abbe number greater than 50.

11. An optical system, comprising:
a projection lens having a positive total refractive power and configured to direct light in a light ray bundle from a display into a near-eye waveguide, the projection lens having an optic

Assignees

• Snap Inc

Inventors

• Bates Robert Matthew
• Greengard Adam Douglas

Classifications

• G02B13/16 Primary

  for use in conjunction with image converters or intensifiers {, or for use with projectors, e.g. objectives for projection TV} · CPC title

• G02B9/34 Primary

  having four components only · CPC title

• G02B2027/0116

  comprising devices for correcting chromatic aberration · CPC title

• G02B27/0025

  for optical correction, e.g. distorsion, aberration · CPC title

• G06F3/14

  Digital output to display device {; Cooperation and interconnection of the display device with other functional units} · CPC title