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US 9,752,865 B1Granted
Height measurement using optical interference
AssigneeInternational Business Machines Corporation
InventorsRichard A. Haight, James B. Hannon, Rudolf M. Tromp
Life of this patent
Estimating the term…
Abstract
Methods and systems for measuring a distance include measuring a first interference pattern between a lens and a target surface using a light source at a first wavelength. A second interference pattern is measured between the lens and the target surface using a light source at a second wavelength, different from the first wavelength. An absolute measurement of a distance between the lens and the target surface is determined based on the first interference pattern and the second interference pattern.
Claims16
A method for measuring a distance, comprising:
- measuring a first interference pattern between a lens and a target surface using a light source at a first wavelength;
- measuring a second interference pattern between the lens and the target surface using a light source at a second wavelength, different from the first wavelength;
- and
- determining an absolute measurement of a distance between the lens and the target surface using a processor based on the first interference pattern and the second interference pattern by measuring a radius of a smallest ring in the first interference pattern and a radius of a smallest ring in the second interference pattern and solving:
- λ
- 1
- 2
-
- n
- 0
-
- (
- N
- +
- 1
- 2
- -
- r
- 1
- )
- =
- λ
- 2
- 2
-
- n
- 0
-
- (
- M
- +
- 1
- 2
- -
- r
- 2
- )
- where λ1 is the first wavelength, λ2 is the second wavelength, n0 is the index of refraction of a medium between the lens and the target surface, r1 is a ratio between the radius of the smallest ring in the first interference pattern and the squared spacing between rings in the first interference pattern, r2 is a ratio between the radius of the smallest ring in the second interference pattern and the squared spacing between rings in the second interference pattern, and N and M are integers to be determined.
35 more elements
A system for measuring a distance, comprising:
- a lens positioned a distance above a target surface;
- a camera configured to measure a first interference pattern between the lens and the target surface using a light source at a first wavelength and to measure a second interference pattern between the lens and the target surface using a light source at a second wavelength;
- a processor configured to determine an absolute measurement of the distance between the lens and the target surface based on the first interference pattern and the second interference pattern to measure a radius of a smallest ring in the first interference pattern and a radius of a smallest ring in the second interference pattern, and to solve:
- λ
- 1
- 2
-
- n
- 0
-
- (
- N
- +
- 1
- 2
- -
- r
- 1
- )
- =
- λ
- 2
- 2
-
- n
- 0
-
- (
- M
- +
- 1
- 2
- -
- r
- 2
- )
- where λ1 is the first wavelength, λ2 is the second wavelength, n0 is the index of refraction of a medium between the lens and the target surface, r1 is a ratio between the radius of the smallest ring in the first interference pattern and the squared spacing between rings in the first interference pattern, r2 is a ratio between the radius of the smallest ring in the second interference pattern and the squared spacing between rings in the second interference pattern, and N and M are integers to be determined.
34 more elements
A system for measuring a distance, comprising:
- a lens positioned a distance above a target surface;
- a camera configured to measure a first interference pattern between the lens and the target surface using a light source at a first wavelength and to measure a second interference pattern between the lens and the target surface using a light source at a second wavelength;
- a processor configured to determine an absolute measurement of the distance between the lens and the target surface based on the first interference pattern and the second interference pattern;
- and
- an optical system configured such that a beam of light from the first light source overlaps in space with a beam of light from the second light source and emerges from the lens at a same point as the beam of light from the second light source such that each beam of light measures a same distance between the lens and the target surface.
2 more elements
Dependencies are inferred from the claim text.