Optical characteristic measuring apparatus and optical characteristic measuring method

• US 20090033936A1
• Filed: 06/09/2006
• Published: 02/05/2009
• Est. Priority Date: 06/13/2005
• Status: Abandoned Application

• Current Assignee: Tokyo University of Agriculture and Technology
• Original Assignee: National University Corporation Tokyo University of Agriculture and Technology
• Inventors: Wakayama, Toshitaka, Otani, Yukitoshi
• Application Number:
  US11/922,006
• Publication Number:
  US 20090033936A1
• Time in Patent Office: Days
• US Class Current: 356/364
• CPC Class Codes: G01N 21/23 Bi-refringence

Abstract

An optical characteristic measuring apparatus including a carrier retarder of which the retardation is known and a quarter-wave plate without wavelength dependence, wherein light emitted from a light source (light-emitting device) is incident on a measurement target through a first polarizer (polarizer), the carrier retarder, and the quarter-wave plate, and the light which has passed through the measurement target is incident on a photodetector through a second polarizer (analyzer). A spectral peak is extracted from a frequency spectrum obtained by analyzing a light intensity signal detected by the photodetector. The optical characteristic element of the measurement target is calculated based on the extracted spectral peak and the retardation of the carrier retarder.

Claims

1. An optical characteristic measuring apparatus measuring optical characteristics of a measurement target, the optical characteristic measuring apparatus comprising:

an optical system including first and second carrier retarders of which the retardations are known and differ from each other and first and second quarter-wave plates without wavelength dependence, the optical system causing light emitted from a light source to be incident on the measurement target through a first polarizer, the first carrier retarder, and the first quarter-wave plate and modulated by the measurement target, and causing the modulated light to be incident on light-receiving means through the second quarter-wave plate, the second carrier retarder, and a second polarizer; and

calculation means for performing a spectrum extraction process of extracting a spectral peak from a frequency spectrum obtained by analyzing a light intensity signal detected by the light-receiving means, and an optical characteristic element calculation process of calculating an optical characteristic element representing the optical characteristics of the measurement target based on the extracted spectral peak and the retardations of the first and second carrier retarders.

2. The optical characteristic measuring apparatus as defined in claim 1,

wherein the optical system is set so that:

the principal axis direction of the first carrier retarder is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the first polarizer;

the principal axis direction of the first quarter-wave plate is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the first carrier retarder; and

the principal axis direction of the first quarter-wave plate is rotated by 0°

or 90°

either clockwise or counterclockwise with respect to the principal axis direction of the first polarizer.

3. The optical characteristic measuring apparatus as defined in claim 1,

wherein the optical system is set so that:

the principal axis direction of the second carrier retarder is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the second polarizer;

the principal axis direction of the second quarter-wave plate is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the second carrier retarder; and

the principal axis direction of the second quarter-wave plate is rotated by 0°

or 90°

either clockwise or counterclockwise with respect to the principal axis direction of the second polarizer.

4. The optical characteristic measuring apparatus as defined in claim 1,

wherein, when the retardations of the first and second carrier retarders are α

δ and

β

δ

, the retardations of the first and second carrier retarders are set so that a ratio of (α

+β

) and (α

−

β

) is two or more or ½

or less.

5. The optical characteristic measuring apparatus as defined in claim 1,

wherein the calculation means calculates at least one of the angle of rotation, the retardation, and the principal axis direction of the measurement target.

6. The optical characteristic measuring apparatus as defined in claim 1,

wherein the calculation means subjects the spectral peak extracted by the spectrum extraction process to Fourier analysis to calculate a real number component and an imaginary number component of the spectral peak, and calculates the optical characteristic element of the measurement target based on the real number component and the imaginary number component of the spectral peak and the retardations of the first and second carrier retarders.

17. The optical characteristic measuring apparatus as defined in claim 1,

wherein the light source emits light containing a predetermined band component;

and

wherein the optical system further includes spectroscopic means which disperses the light containing the predetermined band component into a spectrum and causes the light dispersed into a spectrum to be incident on the light-receiving means.

18. The optical characteristic measuring apparatus as defined in claim 1,

wherein the light source sequentially emits first light to Mth light (M is an integer equal to or larger than two) which differ in band.

19. The optical characteristic measuring apparatus as defined in claim 1,

wherein the light-receiving means includes two-dimensionally arranged light-receiving sections;

wherein the optical system includes a light guide causing the light to be incident on the two-dimensionally arranged light-receiving sections of the light-receiving means; and

wherein the calculation means calculates the optical characteristics of the measurement target by performing the spectrum extraction process and the optical characteristic calculation process in units of the light-receiving sections of the light-receiving means.

7. An optical characteristic measuring apparatus measuring optical characteristics of a measurement target, the optical characteristic measuring apparatus comprising:

an optical system including a carrier retarder of which the retardation is known and a quarter-wave plate without wavelength dependence, the optical system causing light emitted from a light source to be incident on the measurement target through a first polarizer, the carrier retarder, and the quarter-wave plate and modulated by the measurement target, and causing the modulated light to be incident on light-receiving means through a second polarizer; and

calculation means performing a spectrum extraction process of extracting a spectral peak from a frequency spectrum obtained by analyzing a light intensity signal detected by the light-receiving means, and an optical characteristic element calculation process of calculating an optical characteristic element representing the optical characteristics of the measurement target based on the extracted spectral peak and the retardation of the carrier retarder.

8. The optical characteristic measuring apparatus as defined in claim 7,

wherein the optical system is set so that:

the principal axis direction of the carrier retarder is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the first polarizer;

the principal axis direction of the quarter-wave plate is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the carrier retarder; and

the principal axis direction of the quarter-wave plate is rotated by 0°

or 90°

either clockwise or counterclockwise with respect to the principal axis direction of the first polarizer.

9. The optical characteristic measuring apparatus as defined in claim 7,

wherein the calculation means calculates at least the angle of rotation of the measurement target.

16. The optical characteristic measuring apparatus as defined in claim 7,

wherein the calculation means subjects the spectral peak extracted by the spectrum extraction process to Fourier analysis to calculate a real number component and an imaginary number component of the spectral peak, and calculates the optical characteristic element of the measurement target based on the real number component and the imaginary number component of the spectral peak and the retardation of the carrier retarder.

10. An optical characteristic measuring apparatus measuring optical characteristics of a measurement target, the optical characteristic measuring apparatus comprising:

an optical system including a carrier retarder of which the retardation is known and a quarter-wave plate without wavelength dependence, the optical system causing light emitted from a light source to be incident on the measurement target through a first polarizer and modulated by the measurement target, and causing the modulated light to be incident on light-receiving means through the quarter-wave plate, the carrier retarder, and a second polarizer; and

calculation means performing a spectrum extraction process of extracting a spectral peak from a frequency spectrum obtained by analyzing a light intensity signal detected by the light-receiving means, and an optical characteristic element calculation process of calculating an optical characteristic element representing the optical characteristics of the measurement target based on the extracted spectral peak and the retardation of the carrier retarder.

11. The optical characteristic measuring apparatus as defined in claim 10,

wherein the optical system is set so that:

the principal axis direction of the carrier retarder is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the second polarizer;

the principal axis direction of the quarter-wave plate is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the carrier retarder; and

the principal axis direction of the quarter-wave plate is rotated by 0°

or 90°

either clockwise or counterclockwise with respect to the principal axis direction of the second polarizer.

12. The optical characteristic measuring apparatus as defined in claim 10,

wherein the calculation means calculates at least the angle of rotation of the measurement target.

13. An optical characteristic measuring apparatus measuring optical characteristics of a measurement target, the optical characteristic measuring apparatus comprising:

an optical system including a carrier retarder of which the retardation is known and a quarter-wave plate without wavelength dependence, the optical system causing light emitted from a light source to be incident on the measurement target through a polarizer, the carrier retarder, and the quarter-wave plate and modulated by the measurement target, and causing the modulated light to be incident on light-receiving means; and

calculation means performing a spectrum extraction process of extracting a spectral peak from a frequency spectrum obtained by analyzing a light intensity signal detected by the light-receiving means, and an optical characteristic element calculation process of calculating an optical characteristic element representing the optical characteristics of the measurement target based on the extracted spectral peak and the retardation of the carrier retarder.

14. The optical characteristic measuring apparatus as defined in claim 13,

wherein the optical system is set so that:

the principal axis direction of the carrier retarder is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the polarizer;

the principal axis direction of the quarter-wave plate is rotated by 45°

either clockwise or counterclockwise with respect to the principal axis direction of the carrier retarder; and

the principal axis direction of the quarter-wave plate is rotated by 0°

or 90°

either clockwise or counterclockwise with respect to the principal axis direction of the polarizer.

15. The optical characteristic measuring apparatus as defined in claim 13,

wherein the calculation means calculates at least the dichroism of the measurement target.

20. An optical characteristic measuring method for measuring optical characteristics of a measurement target, the optical characteristic measuring method comprising:

a process of providing first and second carrier retarders of which the retardations are known and differ from each other and first and second quarter-wave plates without wavelength dependence, causing light emitted from a light source to be incident on the measurement target through a first polarizer, the first carrier retarder, and the first quarter-wave plate and modulated by the measurement target, and causing the modulated light to be incident on light-receiving means through the second quarter-wave plate, the second carrier retarder, and a second polarizer;

a spectrum extraction process of extracting a spectral peak from a frequency spectrum obtained by analyzing a light intensity signal detected by the light-receiving means; and

an optical characteristic element calculation process of calculating an optical characteristic element representing the optical characteristics of the measurement target based on the extracted spectral peak and the retardations of the first and second carrier retarders.

24. The optical characteristic measuring method as defined in claim 20,

wherein the light source emits light containing a predetermined band component;

and

wherein the light modulation process includes dispersing the light containing the predetermined band component into a spectrum and causing the light dispersed into a spectrum to be incident on the light-receiving means.

25. The optical characteristic measuring method as defined in claim 20,

wherein the light source sequentially emits first light to Mth light (M is an integer equal to or larger than two) which differ in band.

21. An optical characteristic measuring method for measuring optical characteristics of a measurement target, the optical characteristic measuring method comprising:

a process of providing a carrier retarder of which the retardation is known and a quarter-wave plate without wavelength dependence, causing light emitted from a light source to be incident on the measurement target through a first polarizer, the carrier retarder, and the quarter-wave plate and modulated by the measurement target, and causing the modulated light to be incident on light-receiving means through a second polarizer;

a spectrum extraction process of extracting a spectral peak from a frequency spectrum obtained by analyzing a light intensity signal detected by the light-receiving means; and

an optical characteristic element calculation process of calculating an optical characteristic element representing the optical characteristics of the measurement target based on the extracted spectral peak and the retardation of the carrier retarder.

22. An optical characteristic measuring method for measuring optical characteristics of a measurement target, the optical characteristic measuring method comprising:

a process of providing a carrier retarder of which the retardation is known and a quarter-wave plate without wavelength dependence, causing light emitted from a light source to be incident on the measurement target through a first polarizer and modulated by the measurement target, and causing the modulated light to be incident on light-receiving means through the quarter-wave plate, the carrier retarder, and a second polarizer;

a spectrum extraction process of extracting a spectral peak from a frequency spectrum obtained by analyzing a light intensity signal detected by the light-receiving means; and

an optical characteristic element calculation process of calculating an optical characteristic element representing the optical characteristics of the measurement target based on the extracted spectral peak and the retardation of the carrier retarder.

23. An optical characteristic measuring method for measuring optical characteristics of a measurement target, the optical characteristic measuring method comprising:

a process of providing a carrier retarder of which the retardation is known and a quarter-wave plate without wavelength dependence, causing light emitted from a light source to be incident on the measurement target through a polarizer, the carrier retarder, and the quarter-wave plate and modulated by the measurement target, and causing the modulated light to be incident on light-receiving means;

a spectrum extraction process of extracting a spectral peak from a frequency spectrum obtained by analyzing a light intensity signal detected by the light-receiving means; and

an optical characteristic element calculation process of calculating an optical characteristic element representing the optical characteristics of the measurement target based on the extracted spectral peak and the retardation of the carrier retarder.