Illumination system having an aspherical lens

• US 5,285,318 A
• Filed: 06/22/1992
• Issued: 02/08/1994
• Est. Priority Date: 06/22/1992
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: Nioptics Corporation
• Inventors: Gleckman, Philip
• Primary Examiner(s): ROBBINS, THOMAS
• Application Number:
  US07/901,896
• Time in Patent Office: 596 Days
• Field of Search: 359/708, 359/709, 359/869
• US Class Current: 359/709
• CPC Class Codes: F21V 5/048 the lens being a simple lens adapted to cooperate with a point-like source for emitting mainly in one direction and having an axis coincident with the main light transmission direction, e.g. convergent or divergent lenses, plano-concave or plano-convex lenses
• CPC Class Codes: G02B 3/04 with continuous faces that are rotationally symmetrical but deviate from a true sphere , e.g. so called "aspheric" lenses

Abstract

A lens system containing an aspherical portion enabling minimization of spherical aberration as well as the lens length. The lens system includes a conical lens portion providing total internal reflection of light within the lens system and an integrally attached aspherical lens portion. For light rays within a defined angular range of less than about ±24°, the light rays are focused on the exit aperture (for a concentrator) at a minimum lens length, l.

Claims

1. A lens system, comprising:

a conical lens portion providing internal reflection of light rays present therein; and

an aspherical containing lens portion integrally coupled to said conical lens portion and said lens portions having a central longitudinal optical axis and said conical lens portion having an entrance and exit aperture with radii r and r'"'"', respectively, and said aspherical lens portion further having a surface shape causing light rays incident thereon with an angle of incidence θ

less than about 24°

to the central longitudinal optical axis to be imaged after reflection from said conical lens portion on said exit aperture at a minimum distance l in accordance with the expression,

space="preserve" listing-type="equation">l=(r+r'"'"')/(tan θ

'"'"') (1)

rsinθ

=(r'"'"'sin θ

'"'"''"'"')(n)

θ

"=output angle in medium ##EQU2## n=index of refraction described above and edge rays defining ray intercepts at said exit aperture plane such that the derivative of said ray intercept is a positive value.

2. The lens system as defined in claim 1 wherein said aspherical containing lens portion includes at least one of ellipsoidal, parabolic and hyperbolic surfaces.

3. The lens system as defined in claim 1 wherein said aspherical lens portion has no spherical elements thereby providing spherical aberration free imaging.

4. The lens system as defined in claim I wherein said aspherical lens portion comprises on ellipsoid of eccentricity equal to the inverse of the index of refraction.

5. A lens system having a minimum length, comprising:

a conical lens portion providing internal reflection or metallic reflection of light rays present therein; and

an aspherical lens portion integrally coupled to said conical lens portion and said lens portions having a central longitudinal optical axis and said conical lens portion having a characteristic index n and an entrance and exit aperture with radii r and r'"'"', respectively, and said minimum length determined as a function of the angle θ

of light rays relative to the central longitudinal axis and said index n with said aspherical lens portion further having a surface shape causing light rays off-axis from said central optical axis and at each extreme of said aspherical lens portion to pass through s id exit aperture with the light ray incident at a glancing angle at one extreme edge defining an angle θ

'"'"' relative to said central optical axis inside said conical lens portion and said minimum length defined as a function of tan θ

'"'"'.

6. The lens system as defined in claim 5 wherein the angle of acceptance θ

for providing spherical aberration free performance in less than about ±

24°

off said central longitudinal optical axis.

7. The lens system as defined in claim 5 wherein said surface shape of said aspherical lens portion comprises an ellipsoidal shape.

8. The lens system as defined in claim 5 wherein said system comprises a light concentrator.

9. The lens system as defined in claim 5 further including a light source disposed at the distal end of said conical lens portion, said lens system operable to provide spherical aberration free illumination.

10. The lens system as defined in claim 5 further including a light source disposed at a large distance relative to the length of said lens system on the aspherical lens portion side of said lens system, said lens system operable to provide a concentrated image of said light source free of spherical aberration.

11. A method of manufacturing a lens system wherein light rays are optically manipulated using a minimum length lens system, comprising the steps of:

(a) forming a conical lens portion providing reflection of light rays present therein; and

(b) constructing an aspherical lens portion having a surface shape causing light rays off-axis from a central longitudinal optical axis to trace extreme edge rays with a first extreme edge ray tangent to one end of said aspherical lens portion and tracing a path forming an angle θ

to said central optical axis with said minimum length l of said conical lens portion defined by the expression,

space="preserve" listing-type="equation">l=(r+r'"'"')/(tan θ

'"'"') (1)

rsinθ

=(r'"'"'sin θ

")(n)

θ

"=output angle in medium ##EQU3## n=index of refraction described above

12. A method of spherical aberration free manipulation by a user of light rays incident on a lens system off-axis from a central optical longitudinal axis, comprising the steps of:

(a) providing a lens system comprising;

(i) a solid conical lens portion providing total internal reflection of light rays present therein; and

(ii) a solid aspherical lens portion integrally coupled to said solid conical lens portion and said lens portion having a central longitudinal optical axis with said solid aspherical lens portion further having a surface shape causing light rays off-axis from said central optical axis to trace extreme rays with a first extreme edge ray tangent to one end of said aspherical lens portion and tracing a path forming an angle θ

to said central optical axis with said minimum length l of said conical lens portion defined by the expression,

space="preserve" listing-type="equation">l=(r+r'"'"')/(tan θ

'"'"') (1)

rsinθ

=(r'"'"'sin θ

")(n)

θ

"=output angle in medium ##EQU4## n=index of refraction described above (b) interposing said lens system at a selected location relative to a light source, said selected location causing the light from said light source to be incident at an acceptance angle off axis from said central optical longitudinal axis; and

(c) applying the light without spherical aberration in the user desired manner.

13. The method as defined in claim 12 wherein said acceptance angle is less than about ±

24° and

having an absolute value greater than 0°

relative to said central optical longitudinal axis.

14. The method as defined in claim 12 wherein the light source is disposed a large distance from said lens system and the light is concentrated by said lens system forming a spherical aberration free image.

15. The method as defined in claim 12 wherein the light source is disposed adjacent the distal end of said conical lens portion and the light is output from said surface of said aspherical lens portion providing aberration free illumination.