METHOD FOR DEPTH RESOLVED WAVEFRONT SENSING, DEPTH RESOLVED WAVEFRONT SENSORS AND METHOD AND APPARATUS FOR OPTICAL IMAGING

• US 20110134436A1
• Filed: 04/21/2010
• Published: 06/09/2011
• Est. Priority Date: 04/29/2009
• Status: Active Grant

• Current Assignee: Adrian Podoleanu, Simon Tuohy
• Original Assignee: Adrian Podoleanu, Simon Tuohy
• Inventors: Tuohy, Simon, Podoleanu, Adrian
• Granted Patent: US 8,451,452 B2
• Time in Patent Office: Days
• US Class Current: 356/512
• CPC Class Codes: A61B 3/1015 for wavefront analysis
• CPC Class Codes: A61B 3/102 for optical coherence tomography [OCT]
• CPC Class Codes: A61B 3/156 for blocking
• CPC Class Codes: G01B 2290/45 Multiple detectors for detecting interferometer signals
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02002 using two or more frequencies
• CPC Class Codes: G01B 9/02004 using frequency scans
• CPC Class Codes: G01B 9/0201 using temporal phase variation
• CPC Class Codes: G01B 9/02027 Two or more interferometric channels or interferometers
• CPC Class Codes: G01B 9/02038 Shaping the wavefront, e.g. generating a spherical wavefront
• CPC Class Codes: G01B 9/02063 by particular alignment of focus position, e.g. dynamic focussing in optical coherence tomography
• CPC Class Codes: G01B 9/02068 Auto-alignment of optical elements
• CPC Class Codes: G01B 9/0209 Low-coherence interferometers
• CPC Class Codes: G01B 9/02091 Tomographic interferometers, e.g. based on optical coherence

Abstract

Methods and devices are disclosed for acquiring depth resolved aberration information using principles of low coherence interferometry and perform coherence gated wavefront sensing (CG-WFS). The wavefront aberrations is collected using spectral domain low coherence interferometry (SD-LCI) or time domain low coherence interferometry (TD-LCI) principles. When using SD-LCI, chromatic aberrations can also be evaluated. Methods and devices are disclosed in using a wavefront corrector to compensate for the aberration information provided by CG-WFS, in a combined imaging system, that can use one or more channels from the class of (i) optical coherence tomography (OCT), (ii) scanning laser ophthalmoscopy, (iii) microscopy, such as confocal or phase microscopy, (iv) multiphoton microscopy, such as harmonic generation and multiphoton absorption. In particular, a swept source (SS) is used that drives both an OCT channel and a coherence gated wavefront sensor, where:

• • a) both channels operate according to SS-OCT principles;
  • b) OCT channel integrates over at least one tuning scan of the swept source to provide a TD-OCT image of the object;
  • c) CG-WFS integrates over at least one tuning scan of the swept source to provide an en-face TD-OCT mapping of the wavefront.
    For some implementations, simultaneous and dynamic aberration measurements/correction with the imaging process is achieved. The methods and devices for depth resolved aberrations disclosed, will find applications in wavefront sensing and adaptive optics imaging systems that are more tolerant to stray reflections from optical interfaces, such as reflections from the microscope objectives and cover slip in microscopy and when imaging the eye, the reflection from the cornea.

Claims

1. A method for depth resolved wavefront sensing of an optical beam reflected or transmitted by an object, the method comprising

using a wavefront sensing principle to sense aberration information from a plurality of depths defining a depth interval range of the wavefront sensing principle within the object;

and

using a low coherence interferometry method with a coherence gate to reduce the plurality of depths and narrow the depth interval range of the wavefront sensing principle to the depth interval defined by the coherence gate.

2. A method according to claim 1 where the said aberration information is the local tilt of the wavefront in points across the optical beam section from a direction perpendicular to the beam propagation direction.

3. A method according to claim 1 wherein the said low coherence interferometry method employs balance detection to reduce the strength of non interference signals.

4. A method for depth resolved wavefront sensing according to claim 1 wherein the wavefront sensing principle to sense uses laser ray tracing.

5. A method for depth resolved wavefront sensing according to claim 1, 2 or 3 wherein the wavefront sensing principle to sense uses Shack-Hartmann wavefront sensing.

6. A method for depth resolved wavefront sensing according to claim 1 wherein the wavefront sensing principle to sense uses pyramid wavefront sensing.

7. A method for depth resolved wavefront sensing according to claim 1 wherein the said low coherence interferometry method is full field time domain optical coherence tomography using phase shifting interferometry.

8. A method for depth resolved wavefront sensing according to claim 1 wherein the said low coherence interferometry method is full field time domain optical coherence tomography using a smart array.

9. A method for depth resolved wavefront sensing according to claim 1 wherein the said low coherence interferometry method is spectral domain optical coherence tomography using a swept narrow band optical source.

10. A method for optical imaging of an object comprising acquiring an image from the object while carrying out a method according to any preceding claim to acquire depth resolved wavefront sensing.

11. Depth resolved coherence gated wavefront sensor (CG-WFS) comprising:

an optical source to provide an optical beam to be sent to an object to collect wavefront information from that object; and

a wavefront sensor, WFS, which collects an average of the wavefront information from that object from within a WFS depth range in which a reference beam diverted from the optical source is added to that from the object to implement low coherence axial gating and provide depth resolved aberration information from a subinterval of the WFS depth range, restricted to a coherence gate depth range.

12. A depth resolved coherence gated wavefront sensor according to claim 11, where the wavefront information is collected either in reflection from, or transmission through the said object.

13. A depth resolved coherence gated wavefront sensor according to claim 11, where the optical source is a low coherent source, with a sufficient broad bandwidth to achieve the desired depth resolution of the coherence gate to reduce the depth interval of the wavefront information.

14. A depth resolved coherence gated wavefront sensor according to claim 11, where the optical source is a swept narrow band optical source, with a sufficient broad tuning band to achieve the desired depth resolution of the coherence gate to reduce the depth interval of the wavefront information.

15. Apparatus for optical imaging comprising:

an imaging instrument;

a depth resolved coherence gated wavefront sensor (CG-WFS);

an optical source to provide an optical beam to be sent to an object to collect wavefront information from that object as well as to image the object;

a wavefront corrector under the control of the CG-WFS, that is used to compensate for the aberrations in the imaging instrument and the object

and where the CG-WFS comprises a wavefront sensor, WFS, to which a reference beam diverted from the optical source is added to the beam from the object to implement low coherence axial gating and provide depth resolved aberration information from inside the object within a subinterval of the WFS depth range, restricted to a low coherence axial gate determined by the low coherence axial gating.

16. Apparatus for optical imaging according to claim 15, where the depth resolved coherence gated wavefront sensor can be configured to work either in regime (i) as a standard non interferometric wavefront sensor or in regime (ii) as a coherence gated wavefront sensor, to collect single path aberrations in regime (i) from the object towards the apparatus and double path aberrations in regime (ii), to the object from the apparatus and from the object to the apparatus, where the two sets of aberrations are processed by the apparatus to provide aberrations in the single path from the apparatus towards the sample, to optimise the excitation of the object.

17. Apparatus for optical imaging according to claim 15 where the said imaging instrument consists in an OCT channel, a scanning laser opthalmoscope (SLO), a confocal microscope (CM) or a multi-photon microscopy (MM) channel or several of such channels operating simultaneously.

18. Apparatus for optical imaging according to claim 17 where the said OCT channel operates according to time domain principle and the optical source is a swept source.

19. Apparatus for optical imaging according to claim 15 where the wavefront sensing integrates over the whole tuning range of the said narrow band optical source to provide time domain (TD)-OCT coherence gate selection of an en-face distribution of aberrations at a given depth within the object.

20. Apparatus for optical imaging according to claim 15 that uses the same narrow band swept optical source for both the imaging instrument and the coherence gated depth resolved wavefront sensor (CG-WFS), where the CG-WFS uses a parallel array of photodetectors, each driving a SS-OCT channel, and where the OCT channel in the said imaging instrument operates according to TD-OCT principle by integrating over the whole tuning range of the said optical source to provide TD-OCT coherence gate selection of an en-face image from a given depth within the object.

21. Coherence gated depth resolved wavefront sensor according to claim 15, where the swept narrow band optical source consists in a supercontinuum source providing a short pulse and large bandwidth which drives a dispersing element, where such dispersing element is a dispersion shifted fiber or a dispersion compensating fiber.

22. Apparatus for optical imaging according to claim 15, where the focus is changed to compensate for chromatic aberration in synchronism with tuning the frequency of the said swept optical source.