Optical coherence tomography have plural reference beams of differing modulations

• US 6,198,540 B1
• Filed: 09/24/1999
• Issued: 03/06/2001
• Est. Priority Date: 03/26/1997
• Status: Expired due to Fees

• Current Assignee: KOWA Company Limited
• Original Assignee: KOWA Company Limited
• Inventors: Ueda, Mamoru, Ohbayashi, Kohji, Yoshizawa, Itaru, Hirono, Taisuke
• Primary Examiner(s): Turner, Samuel A.
• Application Number:
  US09/402,023
• Time in Patent Office: 529 Days
• Field of Search: 356/479, 356/497, 351/205, 606/4, 606/10
• US Class Current: 356/479
• CPC Class Codes: G01B 2290/35 Mechanical variable delay line
• CPC Class Codes: G01B 9/02002 using two or more frequencies
• CPC Class Codes: G01B 9/02007 Two or more frequencies or sources used for interferometric measurement using only beat G01B9/02003
• CPC Class Codes: G01B 9/02028 Two or more reference or object arms in one interferometer
• CPC Class Codes: G01B 9/02091 Tomographic interferometers, e.g. based on optical coherence
• CPC Class Codes: G01N 21/4795 spatially resolved investigating of object in scattering medium in vivo A61B

Abstract

An optical measuring instrument which enables measurement of necessary data in a short period of time and uses a light with a short coherence length. In this instrument, such a light emitted from a light source is divided into a measurement light and a plurality of reference lights. The plurality of reference lights are processed by different frequency modulations, and then multiplexed with a light reflected from a measurement object irradiated by the measurement light. On the basis of an output of a photoelectric converter for detecting the level of the multiplexed light and the frequency of each reference light, optical characteristic data related to a plurality of measurement points are calculated.

Claims

1. An optical measuring instrument comprising:

optical multiplexing means for multiplexing incident light;

light emitting means for emitting the light having a short coherence length;

optical demultiplexing means for demultiplexing the light emitted by said light emitting means into a measurement light beam and first through N-th reference light beams;

reference light introducing means for modulating the first through N-th reference light beams demultiplexed by said optical demultiplexing means in patterns different from each other and introducing the thus modulated first through N-th reference light beams to the optical multiplexing means;

measurement light introducing means for introducing the measurement light demultiplexed by said optical demultiplexing means to a measurement object sample and introducing the measurement light reflected and scattered within by the measurement object sample to said optical multiplexing means;

photoelectric converting means for outputting an electric signal assuming a level corresponding to an intensity of the light multiplexed by said optical multiplexing means; and

calculating means for calculating optical characteristic data about first through N-th measuring points existing in positions corresponding to lengths of optical paths extending from said optical demultiplexing means of the first through N-th reference light beams to said optical multiplexing means at that point of time within the measurement object sample from the electric signals outputted by said photoelectric converting means on the basis of patterns of modulation effected on the first through N-th reference light beams by the reference light introducing means.

2. An optical measuring instrument as claimed in claim 1, characterized in that said reference light introducing means comprises:

first through N-th reflectors provided in positions upon which the first through N-th reference light beams demultiplexed by said optical demultiplexing means is incident;

introducing means for introducing to said optical multiplexing means the first through N-th reference light beams reflected by said first through N-th reflectors; and

reflector position control means for modulating the first through N-th reference light beams in patterns different from each other by controlling positions of said first through N-th reflectors.

3. An optical measuring instrument as claimed in claim 2, characterized in that

said first through N-th reflectors are reflectors of which side surfaces receive incidences of the reference light beams, each having a rotary shaft and assuming such configuration that a distance of the side surface upon which the reference light beam is incident from the center of the rotary shaft changes corresponding to an angle of rotation of the rotary shaft, and in that

said reflector position control means controls the angle of rotation of the rotary shaft.

4. An optical measuring instrument as claimed in claim 2, characterized in that

said first through N-th reflectors are reflectors, fixed to the same rotary shaft, of which side surfaces receive incidences of the reference light beams, each assuming such a configuration that a distance of the side surface upon which the reference light beam is incident from the center of the rotary shaft changes corresponding to the angle of the rotation of the rotary shaft besides at a rate different from rates of the changes in the distance of other reflectors, and in that

said reflector position control means controls the angle of rotation of the rotary shaft.

5. An optical measuring instrument as claimed in claim 1, characterized in that said reference light introducing means comprises:

first through N-th reflectors fixed to a fixing member having the rotary shaft so that the distances thereof from the rotary shaft are different from each other;

introducing means for introducing to said optical multiplexing means the first through N-th reference light beams reflected by said first through N-th reflectors; and

reflector position control means for modulating the first through N-th reference light beams in the patterns different from each other by controlling the angle of rotation of the rotary shaft.

6. An optical measuring instrument as claimed in claim 5, characterized in that said first through N-th reflectors are cylindrical mirrors.

7. An optical measuring instrument as claimed in claim 5, characterized in that

said first through N-th reflectors are rotatably fitted to said fixing member, and in that

said reflector position control means controls a position of the fixing member and controls angles of said first through N-th reflectors to said fixing member so that reflecting surfaces of said first through N-th reflectors are directed in a direction corresponding to a tilt of said fixing member.

8. An optical measuring instrument as claimed in claim 1, characterized in that said reference light introducing means comprises:

first through N-th optical fibers for introducing to said optical multiplexing means the first through N-th reference light beams demultiplexed by said optical demultiplexing means, said optical fibers being partially wound on first through N-th electrostrictive elements; and

electrostrictive element control means for controlling said first through N-th electrostrictive elements so as to modulate the first through N-th reference light beams in the patterns different from each other.

9. An optical measuring instrument as claimed in claim 1, characterized in that said reference light introducing means includes an acousto-optic element for modulating the reference light beam.

10. An optical measuring instrument as claimed in claim 1, characterized in that said reference light introducing means comprises:

optical media exhibiting a distribution of refractive indexes and provided on optical paths of the first through N-th reference light beams; and

optical medium position control means for modulating the first through N-th reference light beams in the patterns different from each other by changing relative positions of the optical media with respect to the optical paths of the first through N-th reference light beams.

12. An optical measuring instrument as claimed in claim 1, characterized in that said reference light introducing means maintains, when said calculating means obtains the electric signals for calculating the optical characteristic data, a state where a variation width of each of the optical paths of the first through N-th reference light beams which extend from said optical demultiplexing means of the first through N-th reference light beams to said optical multiplexing means becomes approximately a coherent light length, or under, of the light emitted by said light emitting means.

13. An optical measuring instrument as claimed in claim 12, characterized by further comprising reference light optical path length changing means for changing the lengths of the optical paths of the first through N-th reference light beams.

14. An optical measuring instrument as claimed in claim 12, characterized in that said reference light introducing means performs on the first through N-th reference light beams a frequency modulation in a configuration of sine wave with an amplitude being set so that a DC component contained in the electric signal outputted by said photoelectric converting means becomes “

0”

.

15. An optical measuring instrument as claimed in claim 1, further comprising detecting means for detecting a modulation pattern given to each of the reference light beams by said reference light introducing means, characterized in that

said calculating means calculates the optical characteristic data about the first through N-th measuring points by use of the electric signals outputted by said photoelectric converting means and a result of the detection by said detecting means.

16. An optical measuring instrument as claimed in claim 1, further comprising:

measurement light introducing position changing means for changing a position to which said measurement light introducing means introduce the measurement light; and

storing means for storing introducing position information defined as information indicating the introducing position in such a form that a use order is recognizable, characterized in that

said calculating means calculates the optical characteristic data about the respective measuring points on which the introducing position information is stored in said storing means by controlling said measurement light introducing position changing means on the basis of the position information stored in said storing means.

17. An optical measuring instrument as claimed in claim 16, characterized in that

said storing means stores the introducing position information and measuring time information in such a form that the use order is recognizable, and in that

said calculating means calculates the optical characteristic data by using the electric signals outputted by said photoelectric converting means for a time corresponding to the measuring time information corresponding to each of the measuring points with respect to the measuring points on which the introducing position information is stored in said storing means.

11. An optical measuring instrument comprising:

optical multiplexing means for multiplexing incident light;

light emitting means for emitting first through N-th light beams having a short coherence length and wavelengths different from each other;

optical demultiplexing means for generating first through N-th reference light beams and first through N-th measurement light beams by demultiplexing the first through N-th light beams emitted by said light emitting means into reference light beams and measurement light beams;

reference light introducing means for modulating the first through N-th reference light beams generated by said optical demultiplexing means and introducing these reference light beams to said optical multiplexing means;

measurement light introducing means for introducing the first through N-th measurement light beams demultiplexed by said optical demultiplexing means to one point of a measurement object sample and introducing to said optical multiplexing means the first through N-th measurement light beams reflected and scattered within by the measurement object sample;

photoelectric converting means for outputting an electric signal assuming a level corresponding to an intensity of the light multiplexed by said optical multiplexing means; and

calculating means for calculating optical characteristic data about first through N-th measuring points existing in positions corresponding to lengths of optical paths extending from said optical demultiplexing means of the first through N-th reference light beams to said optical multiplexing means at that point of time within the measurement object sample from the electric signals outputted by said photoelectric converting means by use of patterns of modulation effected on the first through N-th reference light beams by said reference light introducing means and information on wavelength of the first through N-th reference light beams.

18. An optical measuring instrument comprising:

optical multiplexing means for multiplexing incident light;

light emitting means for emitting the light having a short coherence length;

optical demultiplexing means for demultiplexing the light emitted by said light emitting means into a measurement light beam and reference light beams;

reference light modulating means for generating modulation reference light beams, by utilizing multi-reflections of the reference light, containing a plurality of light components of which frequencies and optical path lengths to positions of being introduced by said optical multiplexing means are different from each other on the basis of the reference light beams demultiplexed by said optical demultiplexing means, and for introducing the modulation reference light beams to said optical multiplexing means;

measurement light introducing means for introducing the measurement light beams demultiplexed by said optical demultiplexing means into the measurement object sample and for introducing the measurement light beams reflected and scattered within by the measurement object sample to said optical multiplexing means;

photoelectric converting means for outputting an electric signal assuming a level corresponding to an intensity of the light multiplexed by said optical multiplexing means; and

calculating means for calculating optical characteristic data about a plurality of measuring points within the measurement object sample from the electric signals outputted by said photoelectric converting means on the basis of frequencies and lengths of the optical path extending from the light emitting means to the optical multiplexing means of a plurality of optical components contained in the modulation reference light beams.

19. An optical measuring instrument as claimed in claim 18, characterized in that said reference light modulating means comprise:

a half-mirror upon which the reference light is incident;

a total reflection mirror for reflecting the light penetrating said half-mirror to make this beam of light travel back to said half-mirror;

moving means for moving said half-mirror or said total reflection mirror in a direction of its normal line; and

modulation reference light introducing means for introducing the light returned by said total reflection mirror and penetrating said half-mirror as modulation reference light to said optical multiplexing means.

20. An optical measuring instrument as claimed in claim 18, characterized in that said reference light modulating means comprise:

a half-mirror upon which the reference light is incident;

a first total reflection mirror for reflecting the light penetrating said half-mirror to make this beam of light travel back to said half-mirror;

a second total reflection mirror for returning to said half-mirror the reflected light, by said half-mirror, of the light coming from said first total reflection;

moving means for moving said first total reflection mirror in a direction of its normal line; and

modulation reference light introducing means for introducing the light returned to said half-mirror by said first total reflection mirror and penetrating said half-mirror as modulation reference light to said optical multiplexing means.

21. An optical measuring instrument as claimed in claim 18, characterized in that said reference light modulating means comprise:

a half-mirror upon which the reference light is incident;

a first total reflection mirror for reflecting the light penetrating said half-mirror to make this beam of light travel back to said half-mirror;

a second total reflection mirror for returning to said half-mirror the reflected light, by said half-mirror, of the light coming from said first total reflection;

moving means for moving said second total reflection mirror in a direction of its normal line;

and modulation reference light introducing means for introducing the light returned to said half-mirror by said first total reflection mirror and penetrating said half-mirror as modulation reference light to said optical multiplexing means.