Grating based phase control optical delay line

• US 6,111,645 A
• Filed: 05/15/1998
• Issued: 08/29/2000
• Est. Priority Date: 04/29/1991
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Bouma, Brett E., Fujimoto, James G., Tearney, Guillermo
• Primary Examiner(s): Kim, Robert H.
• Application Number:
  US09/079,687
• Time in Patent Office: 837 Days
• Field of Search: 356/345, 356/351, 356/349, 356/356, 356/354
• US Class Current: 356/499
• CPC Class Codes: A61B 1/00096 Optical elements
• CPC Class Codes: A61B 1/00172 with means for scanning
• CPC Class Codes: A61B 1/00183 for variable viewing angles
• CPC Class Codes: A61B 2562/0242 for varying or adjusting the optical path length in the tissue
• CPC Class Codes: A61B 3/1005 for measuring distances inside the eye, e.g. thickness of the cornea A61B3/11 takes precedence
• CPC Class Codes: A61B 3/102 for optical coherence tomography [OCT]
• CPC Class Codes: A61B 3/1225 using coherent radiation
• CPC Class Codes: A61B 5/0064 Body surface scanning
• CPC Class Codes: A61B 5/0066 Optical coherence imaging
• CPC Class Codes: A61B 5/0084 for introduction into the body, e.g. by catheters A61B5/1459 takes precedence
• CPC Class Codes: A61B 5/441 Skin evaluation, e.g. for skin disorder diagnosis
• CPC Class Codes: A61B 5/6852 Catheters
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: G01B 11/00 Measuring arrangements characterised by the use of optical techniques
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01B 11/026 by measuring distance between sensor and object G01B11/0608 takes precedence
• CPC Class Codes: G01B 11/12 internal diameters
• CPC Class Codes: G01B 11/2441 using interferometry
• CPC Class Codes: G01B 2290/20 Dispersive element for generating dispersion
• 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 9/02091 : Tomographic interferometers, e.g. based on optical coherence
• CPC Class Codes: G01J 1/00 : Photometry, e.g. photographic exposure meter spectrophotometry G01J3/00; specially adapted for radiation pyrometry G01J5/00 ; exposure meters built in cameras G03B17/06
• CPC Class Codes: G01N 21/4795 : spatially resolved investigating of object in scattering medium in vivo A61B
• CPC Class Codes: G02B 26/06 : for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00
• CPC Class Codes: G02B 27/4233 : having a diffractive element [DOE] contributing to a non-imaging application diffusers having a diffractive element G02B5/0252; filters having a diffractive element G02B5/203; systems for controlling the direction of light having diffractive elements G02B26/0808; scanning systems having diffractive elements G02B26/106; beam shaping systems using diffractive optical elements G02B27/0944; beam splitting or combining systems operating by diffraction G02B27/1086
• CPC Class Codes: G02B 27/4244 : in wavelength selecting devices spectrometry G01J
• CPC Class Codes: G02B 27/4255 : for alignment or positioning purposes optical displacement encoding scales G01D5/347
• CPC Class Codes: G02B 5/1828 : having means for producing variable diffraction controlling the direction of light by means of one or more diffracting elements G02B26/0808; acousto-optical elements G02F1/11, G02F1/33; electro- or magneto-optical diffraction G02F1/292, G02F1/2955
• CPC Class Codes: G11B 2007/0013 : for carriers having multiple discrete layers
• CPC Class Codes: G11B 7/005 : Reproducing G11B7/0065 takes precedence
• CPC Class Codes: G11B 7/08564 : using galvanomirrors
• CPC Class Codes: G11B 7/127 : Lasers; Multiple laser arrays lasers per se H01S
• CPC Class Codes: G11B 7/1353 : Diffractive elements, e.g. holograms or gratings diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44
• CPC Class Codes: G11B 7/24 : Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the arrangement of information on the carrier G11B7/007
• CPC Class Codes: H01S 5/141 : using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence

Abstract

An apparatus for performing high speed scanning of an optical delay and its application for performing optical interferometry, ranging, and imaging, including cross sectional imaging using optical coherence tomography, is disclosed. The apparatus achieves optical delay scanning by using diffractive optical elements in conjunction with imaging optics. In one embodiment a diffraction grating disperses an optical beam into different spectral frequency or wavelength components which are collimated by a lens. A mirror is placed one focal length away from the lens and the alteration of the grating groove density, the grating input angle, the grating output angle, and/or the mirror tilt produce a change in optical group and phase delay. This apparatus permits the optical group and phase delay to be scanned by scanning the angle of the mirror. In other embodiments, this device permits optical delay scanning without the use of moving parts.

Claims

1. An optical interferometric imaging system for imaging a sample comprising:

an optical source capable of producing an optical signal having an optical spectrum;

an interferometer in communication with said optical source;

a detector in optical communication with said interferometer; and

an optical delay line apparatus in optical communication with said interferometer comprising;

a plurality of optical elements in optical communication with other,

wherein at least one of said plurality of optical elements is used to spatially disperse the optical spectrum of the optical signal to provide a spatially dispersed optical signal,

wherein at least one of said plurality of optical elements is adjustable to affect the phase delay and the group delay of the optical signal.

2. The imaging system of claim 1, wherein at least one adjustable optical element repeatedly scans to produce a substantially uniform rate of change of optical group delay and a time varying optical phase delay, and wherein said processor compensates for the time varying optical phase delay.

3. The optical interferometric imaging system of claim 1, wherein said interferometer further comprises:

a sample arm for receiving a sample optical signal;

a reference arm in optical communication with said optical delay line apparatus;

an optical imaging module positioned to receive the spatially dispersed, delayed optical signal from said optical delay line apparatus and sample optical signal from said sample arm; and

a reflective element in optical communication with said optical imaging module;

said reflective element placed away from the Fourier plane of the dispersed optical spectrum so as to balance first order group velocity dispersion between said sample arm and said reference arm.

4. The optical imaging system of claim 3, further comprising a signal processing unit in electrical communication with said detector and wherein the adjustable optical element is repetitively scanned and said signal processing unit compensates any non-uniform rate of change of phase delay.

5. The optical interferometric imaging system of claim 3, wherein said spatially dispersive element comprises a diffractive element.

6. The optical interferometric imaging system of claim 3, further comprising an acousto-optic modulator in optical communication with said optical delay line.

7. The optical interferometric imaging system of claim 3, further comprising an electro-optic beam deflector in optical communication with said optical delay line.

8. The optical interferometric imaging system of claim 3, wherein the adjustable optical element comprises a polygon scanning mirror.

9. The optical interferometric imaging system of claim 3, wherein said spatially dispersive element has a periodic optical structure with an adjustable period, said spatially dispersive element angularly dispersing the optical signal.

10. The optical interferometric imaging system of claim 3, wherein said spatially dispersive element comprises a holographic optical element.

11. The optical interferometric imaging system of claim 3, wherein said reflective element is a rotating polygonal mirror.

12. The optical interferometric imaging system of claim 1 or 3 wherein at least one of said plurality of optical elements is a double-pass mirror.

13. A scanning OCT imaging system comprising:

an optical source capable of producing an optical signal having an optical

spectrum;

an interferometer in communication with said optical source;

a detector in optical communication with said interferometer;

a signal processor in electrical communication with said detector;

an optical delay in optical communication with said interferometer,

wherein said optical delay comprises adjustable optical elements capable of spatially dispersing said optical signal and affecting an optical group delay of said optical signal;

a scanning device capable of adjusting said adjustable optical elements thereby controlling said optical group delay;

wherein said interferometer interferometrically combines the delayed optical signal with a portion of the optical signal not transmitted through the apparatus and wherein said detector detects said interferometrically combined signal, producing a substantially zero frequency heterodyne or homodyne signal in response thereto, and

wherein said signal processor produces images of the sample in response to said heterodyne or homodyne signal.

17. The scanning OCT imaging system of claim 3 or 13, further comprising a double-pass mirror.

14. A method for producing an image of a sample comprising:

providing an optical source;

providing a detector in optical communication with said optical source;

providing an interferometer in communication with said optical source and said detector;

providing an interferometer in communication with said optical source and said detector;

providing an optical delay line, said optical delay line comprising adjustable optical elements capable of spatially dispersing an optical signal from said optical source and adjusting at least one of the phase delay and optical group delay of said spatially dispersed optical signal, in optical communication with said interferometer;

providing a sample in proximity with said interferometer;

transmitting a signal from said optical source to said sample and said optical delay line;

adjusting said adjustable elements thereby affecting at least one of the phase delay and group delay of optical signal received by said optical delay line;

combining signal from the sample and the spatially dispersed, delayed optical signal;

detecting the combined signal and producing an image in response to said detection.

15. The method of claim 14, further comprising repetitively scanning at least one adjustable element to produce a substantially uniform rate of change of optical group delay and a time varying optical phase delay, and compensating for said time varying optical phase using said processor.

16. The method of claim 14, further comprising providing a double-pass mirror to guide the optical signal.

18. A scanning OCT imaging system comprising:

an optical source capable of producing an optical signal having an optical spectrum;

an interferometer in communication with said optical source;

a detector in optical communication with said interferometer;

a signal processor in electrical communication with said detector;

an optical delay in optical communication with said interferometer,

wherein said optical delay comprises adjustable optical elements capable of spatially dispersing said optical signal and affecting an optical group delay of said optical signal;

a scanning device capable of adjusting said adjustable optical elements thereby controlling a scan of said optical group delay;

wherein said interferometer interferometrically combines the delayed optical signal with a portion of the optical signal not transmitted through the apparatus,

wherein said detector detects said interferometrically combined signal, thereby producing a substantially non-zero frequency heterodyne signal during at least a portion of said scan,

and wherein said signal processor produces images of the sample in response to said non-zero frequency heterodyne signal.