阅读说明：本技术 用于分析样本的装置和方法 (Device and method for analyzing a sample ) 是由 史蒂文·詹姆斯·弗里斯肯 格兰特·安德鲁·弗里斯肯 于 2014-06-20 设计创作，主要内容包括：本申请提供了一种用于分析样本的装置和方法,用于使用光谱波前分析仪分析波前以在所述波前的二维采样点阵列提取光学相位和光谱信息,其中,所述采样点之间的相对相位信息得以保持。还提供了用于通过反射眼睛的波前并以多个角度测量所述波前以提供眼睛的离轴相对波前曲率和像差的映射来测量眼睛的方法和系统。通过这些方法和系统提供的波长与光束孔径上的采样点之间的相位精度具有许多眼睛应用,包括角膜和眼前断层扫描术、高分辨率视网膜成像,以及作为探测光束入射角的函数的用于确定近视发展并设计和测试用于校正近视的镜片的波前分析。(An apparatus and method for analyzing a sample is provided for analyzing a wavefront using a spectral wavefront analyzer to extract optical phase and spectral information at a two-dimensional array of sampling points of the wavefront, wherein relative phase information between the sampling points is maintained. Methods and systems for measuring an eye by reflecting a wavefront of the eye and measuring the wavefront at a plurality of angles to provide a map of off-axis relative wavefront curvature and aberrations of the eye are also provided. The phase accuracy between the wavelength and the sampling points on the beam aperture provided by these methods and systems has many ocular applications, including corneal and anterior eye tomography, high resolution retinal imaging, and wavefront analysis as a function of probe beam incident angle for determining myopia progression and for designing and testing lenses for correcting myopia.)

1. An apparatus for analyzing a sample, the apparatus configured to:

forming a plurality of probe beams and one or more reference beams from the multi-wavelength wavefront;

directing the plurality of probe beams simultaneously to a two-dimensional array of spots on the sample;

passing a plurality of signals obtained by reflection of the probe beam from the sample or a plurality of signals obtained by passing the probe beam through the sample through a microlens array or an aperture array;

extracting phase and spectral information from the signal, the phase and spectral information including phase as a function of wavelength with respect to the one or more reference beams; and

processing the extracted phase and spectral information to provide a tomographic profile of the sample at each of the points.

2. The apparatus of claim 1, wherein the apparatus comprises one or more microlens arrays for forming the plurality of probe beams.

3. The apparatus of claim 1, wherein the apparatus is configured to extract the phase and spectral information from the plurality of signals in a single acquisition to reduce artifacts caused by motion of the sample.

4. The apparatus of claim 1, wherein the tomographic profile comprises a profile of two or more interfaces in an anterior segment of the eye.

5. The device of claim 4, wherein the two or more interfaces comprise an anterior surface of a cornea of the eye.

6. The apparatus of claim 1, wherein the apparatus is configured to extract the phase and spectral information using the one or more reference beams to interfere with the plurality of signals.

7. The apparatus of claim 1, wherein the apparatus comprises polarizing optics for orthogonally polarizing the reference beam and the probe beam and analyzing a first polarization state after the signal is recombined with the one or more reference beams.

8. The apparatus of claim 7, wherein the polarizing optics are configured to analyze a plurality of polarization states to provide balanced detection of the signal.

9. The apparatus of claim 1, wherein the apparatus is configured to form a plurality of probe beams and a substantial number of reference beams.

10. The apparatus of claim 1, wherein the apparatus comprises an etalon to enhance coherence length of light in the probe and reference beams.

11. A method for analyzing a sample, the method comprising the steps of:

(a) forming a plurality of probe beams and one or more reference beams from the multi-wavelength wavefront;

(b) directing the plurality of probe beams simultaneously to a two-dimensional array of spots on the sample;

(c) passing a plurality of signals obtained by reflection of the probe beam from the sample or a plurality of signals obtained by passing the probe beam through the sample through a microlens array or an aperture array;

(d) extracting phase and spectral information from the signal, the phase and spectral information including phase as a function of wavelength with respect to the one or more reference beams; and

(e) processing the extracted phase and spectral information to provide a tomographic profile of the sample at each of the points.

12. The method of claim 11, wherein the plurality of probe beams are formed by one or more microlens arrays.

13. The method of claim 11, wherein the phase and spectral information is extracted from the plurality of signals in a single acquisition to reduce artifacts caused by motion of the sample.

14. The method of claim 11, wherein the tomographic profile comprises a profile of two or more interfaces in an anterior segment of the eye.

15. The method of claim 14, wherein the two or more interfaces comprise an anterior surface of a cornea of the eye.

16. The method of claim 11, wherein the phase and spectral information is extracted by interfering the plurality of signals with the one or more reference beams.

17. The method of claim 11, wherein the reference beam and the probe beam are orthogonally polarized, and further comprising the steps of: after the signal is recombined with the one or more reference beams, a first polarization state is analyzed.

18. The method of claim 17, wherein a plurality of polarization states are analyzed to provide balanced detection of the signal.

19. The method of claim 11, wherein step (a) comprises forming a plurality of probe beams and a substantially plurality of reference beams.

20. The method of claim 11, wherein the method further comprises the steps of: passing the multi-wavelength wavefront through an etalon to enhance the coherence length of light in the probe beam and the reference beam.

Technical Field

The present invention relates to the metrology of optically reflective and scattering media and to the fields of hyperspectral imaging and wavefront analysis. The invention has been developed primarily for use in eye metrology and will be described hereinafter with reference to this application. It is to be understood, however, that the invention is not limited to this particular field of use.

Background

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

The measurement of optical components, in particular the human eye, has been solved by a series of different instruments capable of providing information about different aspects of the morphology and function of the eye and identifying various anomalies. Measuring the profile of the surface of the eye is of particular interest in applications requiring the fitting of contact lenses, and as the range and functionality of contact lenses increases, the need to accurately measure surface topography (topographies) over larger areas becomes increasingly important. Other measurements that may be made include wavefront analysis, which is a phase-based measurement of an optical characteristic of the eye (i.e., eye function). Measurement of various features of the anterior segment of the eye can be of great value in surgical applications. Significant progress has been made in imaging the retina of the eye, and Optical Coherence Tomography (OCT) has enabled three-dimensional analysis of various eye structures by scanning methods using information contained in the intensity and phase of reflected light.

Fig. 1 schematically shows a Placido disc (Placido disc) topographer capable of calculating the degree of elevation (elevation) and curvature of the cornea of a living human eye. A series of illuminated concentric rings 100 are specularly reflected from a target cornea 101, and the reflected image is projected by a lens system 102 onto an imaging sensor 103. The captured image is processed using software to identify the ring reflections and the corresponding physical rings. Using the known geometry of the ring 100 and the lens system 102, a reverse ray tracing 104 is performed between each ring image and the corresponding physical ring to determine the slope of the corneal surface at each reflection point from the corneal vertex 105. The slope, curvature and axial depth of the next ring reflection point along each ray is calculated using an "arc step" algorithm.

Fig. 2 schematically shows a "push-broom" hyperspectral imager ('push broom' hyperspectral imager) capable of spectrally analyzing the intensity of light at many points along the slit aperture 222. The slit aperture 222 is used to analyze a linear portion of the sample 221 (e.g., an image formed by a distance vision imaging system or other imaging system). The collimating lens 223 directs the light collected through the slit aperture to a dispersive element (e.g., a grating 225) that angularly disperses the wavelength components of the light, and the focusing lens 224 focuses each wavelength component onto a separate location along the wavelength axis of the focal plane array 226 where the information is collected and analyzed. A complete hyperspectral image can be obtained by scanning the sample 221 relative to the slit aperture 222. Hyperspectral imaging also extends to two-dimensional "single shot" applications, where light intensities of different wavelengths across a region are measured "single shot" rather than in a scanning fashion.

Hyperspectral imaging only collects information about intensity and therefore loses any phase information. Its value for eye metrology is limited and biological applications are generally limited to understanding spectral features, such as oxidation of blood, which are manifested by absorbance or fluorescence.

Figure 3b schematically shows a wavefront analyser for determining the wavefront aberration (aberration) of an eye. An input known beam or wavefront 321 (typically but not necessarily monochromatic) propagates through a beam splitter 322 to the eye 324 to be measured, where it is desired that the beam be focused on the retina 325, or near the retina 325, due to the optical power 323 of the eye. A small portion of the reflected component is then collimated by the optical power of the eye and separated from the input beam 321 by the beam splitter 322 to form an output wavefront 326 containing information about the remaining power and aberrations of the eye 324.

The output wavefront 326 is analysed using a Shack-Hartmann analyser 327, shown in magnified form in figure 3b, the analyser 327 consisting of a lenslet array 331 which samples and focuses a predetermined grid of wavefronts onto a focal plane array 333. The position of the image spot 334 formed by each microlens can be used to estimate the slope 335 of the wavefront 326 at each sampling point, and if the slope can be determined accurately enough and if the variation between sampling points is not large, it is possible to reconstruct the actual phase 328 of the wavefront at the sampling points. It has been proposed to use a multi-spectral wavefront analyzer to determine the dispersive properties of optical components, such as the longitudinal chromatic aberration of the eye, for example as discussed in "RGB Shack-Hartmann wavefront sensor" from p. jane and j. schweingelin, modern Optics journal 2008, volume 55, page 737- & lt 748 (p. yin and j. schwiegerling 'RGB Shack-Hartmann wave front sensor', j. model Optics 55(2008)737 748) and "wavelength tunable wavefront sensor for the human eye" from s. manlaza bundle et al, Optics Express 2008, volume 16, page 7748- & lt 7755 (s. manzanera 'Awavelength tunable navave front sensor for the human eye', Optics Express, 7748- & lt 7755). However, relative phase information between different wavelengths is not obtained.

Many methods of analyzing the eye rely on various variations of what is known as Optical Coherence Tomography (OCT) which can provide tomographic data about the structure of the eye and be incorporated into many ocular instruments. There are two main methods available, time domain OCT and spectral domain OCT. In time-domain OCT, the coherence properties of a partially coherent source with a coherence length of a few microns (e.g., a Superluminescent Light Emitting Diode (SLED)) can be exploited by imaging light reflected from a sample and interfering with the image or a single point within the image with a reference beam provided by the same source but with a time-varying path length. At a particular depth in the sample, corresponding to the path length delay, an interference fringe envelope will be detected in the combined reflected back signal, allowing the reconstruction of the reflection profile in the depth dimension. Typically, only a single sample point is processed at a time, and the corresponding depth scan is referred to as an "a-scan". A variation of this technique (known as linear OCT) captures an a-scan in a single beat by appropriately angling the reference and sample beams and detecting fringes along a focal plane array. In each case, the sample points may be scanned in orthogonal dimensions to provide a two-dimensional "B-scan" or even a complete three-dimensional scan.

Spectral domain OCT techniques no longer scan the delay line, but analyze the reflected light by interfering it with a reference beam, as a time-varying function of wavelength (swept source OCT), or by dispersing different wavelengths and detecting them simultaneously along a detector array using a grating or other spectral multiplexer (spectral multiplexer). The spectral domain information is the fourier transform of the spatial (depth) reflection profile, so the spatial profile can be recovered by the fast fourier transform (within the limits of the technology). Modern computing technology enables a-scans scannable in two axes to be performed quickly using, for example, a resonant scanning mirror, to give high resolution full scans at refresh rates that are tradeoffs between clinically allowable optical power, resolution, and signal-to-noise requirements. It is well known that in scanning systems using OCT it is difficult to achieve high precision relative measurements between different sampling points, since the living human eye can move on the order of microns (typically on the order of one second) during scanning.

Raney (Nguyen) et al (optical Express 2013 volume 21, pages 13758 & 13772 (Optics Express 21 (2013)) have proposed OCT systems based on combining an interferometer with a modified hyperspectral imaging system capable of measuring multiple a-scans at the image plane. However, this system does not appear to maintain relative phase information between sampling points or wavelengths, since there is no calibration or method specified to ensure the phase relationship.

Disclosure of Invention

It is an object of the present invention to overcome at least one limitation of the prior art. It is an object of a preferred form of the present invention to provide a system and method for accurate measurement of optical phase in a living biological sample, particularly a sample that may be prone to motion artifacts, such as an eye.

According to a first aspect of the present invention there is provided an optical system for analysing a wavefront, the system comprising a spectral wavefront analyser adapted to extract optical phase and spectral information at a plurality of sampling points of the wavefront, wherein relative phase information between the plurality of sampling points is maintained, and wherein the plurality of sampling points form a two-dimensional sampling array.

The two-dimensional sampling array preferably includes a plurality of beamlets formed by a microlens array.

In a preferred embodiment, the wavefront is obtained by reflection or projection of a probe beam from or through the sample.

The system is preferably adapted to extract optical phase and spectral information from a plurality of sampling points in a single acquisition to reduce artifacts caused by sample motion.

In a preferred embodiment, the system includes a processor adapted to process the optical phase and spectral information to provide a tomographic profile of the sample, or to provide a measurement of corneal topography of the eye, or to determine a profile of one or more interfaces of the anterior segment of the eye.

The system preferably includes an interferometer and extracts optical phase and spectral information by interfering the wavefront with the reference beam. The interferometer preferably comprises one or more dispersive elements for dispersing the reference beam. Preferably, at least one of the one or more dispersive elements comprises a grating. The system preferably comprises polarizing optics adapted to orthogonally polarize the reference and probe beams and to analyse the resulting polarization state after interference of the wavefront with the reference beam. In a preferred embodiment, the polarizing optics are adapted to analyze a plurality of polarization states to provide a balanced detection system.

According to a second aspect of the present invention there is provided a method for analysing a wavefront, the method comprising the step of extracting optical phase and spectral information at a plurality of sampling points of the wavefront, wherein relative phase information between the plurality of sampling points is maintained, and wherein the plurality of sampling points form a two-dimensional sampling array.

In a preferred embodiment, the two-dimensional sampling array preferably comprises a plurality of beamlets formed by a microlens array.

The wavefront is preferably obtained by reflection of a probe beam from or transmission through the sample.

Optical phase and spectral information is preferably extracted from multiple sample points in a single acquisition to reduce artifacts caused by sample motion.

Preferably, the method further comprises the step of processing the optical phase and spectral information to provide a tomographic profile of the sample, or to provide a measurement of corneal topography of the eye, or to determine a profile of one or more interfaces of the anterior segment of the eye.

In a preferred embodiment, the optical phase and spectral information is extracted by interfering the wavefront with a reference beam. The reference beam is preferably dispersed by one or more dispersive elements. Preferably, at least one of the one or more dispersive elements comprises a grating. In a preferred embodiment, the method further comprises the step of orthogonally polarizing the reference beam and the probe beam, and analysing the resulting polarization state after the wavefront has been interfered with the reference beam. Preferably, the plurality of polarization states are analyzed to balance the detection of the wavefront.

According to a third aspect of the present invention, there is provided a method for measuring an eye, the method comprising the steps of:

obtaining a wavefront by reflecting a probe beam from an eye; and is

The wavefront is measured at a plurality of angles to provide a map of the off-axis relative wavefront curvature and aberrations of the eye.

In some embodiments, multiple angles are provided by the dispersive element and the wavefront is measured at multiple wavelengths. Alternatively, multiple angles are provided by reflecting the wavefront off a scanning mirror.

In a preferred embodiment, the method further comprises the step of determining the optical depth of the eye by identifying predetermined optical frequencies using the respective reflection points and determining a corresponding relative optical depth associated with each optical frequency.

According to a fourth aspect of the present invention there is provided an optical system for measuring an eye, the system comprising:

means for obtaining a wavefront by reflecting a probe beam from the eye; and

means for measuring the wavefront at a plurality of angles to provide a map of the off-axis relative wavefront curvature and aberrations of the eye.

In some embodiments, the apparatus for measuring a wavefront comprises a dispersive element for providing a plurality of angles and is adapted to measure a wavefront at a plurality of wavelengths. Alternatively, the means for measuring the wavefront comprises a scanning mirror for reflecting the wavefront at a plurality of angles.

Preferably, the system is adapted to determine the optical depth of the eye by identifying predetermined optical frequencies using the respective reflection points and to determine a respective relative optical depth associated with each optical frequency.

According to a fifth aspect of the present invention there is provided a method of designing a lens for correcting myopia, the method comprising the steps of:

obtaining a wavefront by reflecting a probe beam from an eye;

measuring the wavefront at a plurality of angles to provide a map of the relative wavefront curvature of the eye; and designing the lens using the on-axis and peripheral wavefront data such that, in use, the lens corrects for the on-axis wavefront for myopia of the eye and focuses the peripheral wavefront on or behind the retina of the eye.

According to a sixth aspect of the present invention there is provided a system for designing a lens for correcting myopia, the system comprising:

means for obtaining a wavefront by reflecting a probe beam from the eye;

means for measuring the wavefront at a plurality of angles to provide a map of the relative wavefront curvature of the eye; and

means for designing the lens with on-axis and peripheral wavefront data such that, in use, the lens corrects myopia of the eye for the on-axis wavefront and focuses the peripheral wavefront on or behind the retina of the eye.

According to a seventh aspect of the present invention there is provided a method of designing a lens for correcting myopia, the method comprising the steps of:

obtaining a wavefront by reflecting the probe beam from the eye when the optic is in position so that the probe beam passes through the optic;

measuring the wavefront at a plurality of angles to provide a map of wavefront curvature of the eye and lens combination; and

the on-axis and peripheral wavefront data is used to determine whether the lens is correcting the eye for myopia for the on-axis wavefront and to focus the peripheral wavefront on or behind the retina of the eye.

According to an eighth aspect of the present invention there is provided a system for testing a lens for correcting myopia, the system comprising:

means for obtaining a wavefront by reflecting the probe beam from the eye when the optic is in position so that the probe beam passes through the optic;

measuring the wavefront at a plurality of angles to provide a map of wavefront curvature of the eye and lens combination; and

means for using the on-axis and peripheral wavefront data to determine whether the lens is correcting myopia of the eye for the on-axis wavefront and focusing the peripheral wavefront on or behind the retina of the eye.

According to a ninth aspect of the present invention there is provided a lens for correcting myopia, wherein the lens is designed using the method of the fifth aspect or the system of the sixth aspect or tested using the method of the seventh aspect or the system of the eighth aspect.

According to a tenth aspect of the present invention there is provided an article of manufacture comprising a computer usable medium having computer readable program code configured to operate an optical system according to the first or fourth aspects, or to operate a system according to the sixth or eighth aspects, or to implement the method according to the second, third, fifth or seventh aspects.

Drawings

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

fig. 1 schematically illustrates a plectrum topographer capable of calculating the degree of swelling and curvature of the cornea of a living human eye.

FIG. 2 schematically illustrates a "push-and-scan" hyperspectral imager capable of spectral analysis of the intensity of light at many points along the slit aperture.

Figure 3a schematically illustrates a wavefront analyzer for determining wavefront aberrations of an eye.

Fig. 3b shows an enlarged view of a part of fig. 3 a.

FIG. 4a is a conceptual diagram of a high spectral resolution high spectral wavefront analysis system according to an embodiment of the present invention.

Figure 4b illustrates a technique for measuring the spectral phase and amplitude response of the reflected light.

Fig. 5 schematically illustrates an optical train (optical system) of an embodiment of the present invention that interferometrically measures the phase of light at many grid points and wavelengths using a reference beam.

Fig. 6 schematically illustrates an optical train of another embodiment of the present invention that includes a reference arm at which a wavelength-dependent optical wavefront curvature is introduced into a reference beam.

FIG. 7 illustrates how an input wavefront may be divided into a two-dimensional array of beamlets.

Fig. 8 illustrates the use of a reference wavefront, where the spatial profile at some wavelengths is designed to be that of the eye model to reduce the range of phase changes that need to be tracked through the measurement aperture.

FIG. 9 illustrates how a series of off-axis wavefronts can be collected using a single beat wavefront analyzer, according to another embodiment of the present invention.

Fig. 10 illustrates a technique for enhancing path length coherence in low coherence interferometry.

FIG. 11 illustrates an optical relay system adapted to adjust the spatial position of a two-dimensional beamlet array on a sample.

Detailed Description

The present invention relates to systems and methods for obtaining detailed optical metrology data of a sample by acquiring precise relative phase information of a multi-wavelength optical wavefront formed between wavelengths and spatially by reflection or transmission of a light beam of known intensity and phase profile incident on the sample to be measured, where optical and/or reflection terms can be determined. The ability to extract optical phase and spectral information at multiple sampling points can be exploited to provide a measurement system that can be configured to measure human eye parameter ranges using techniques such as high accuracy corneal topography, grid-based anterior eye tomography, line-based anterior eye tomography, high resolution retinal imaging, wavefront analysis as a function of probe beam incidence angle for determining myopia progression, and single-shot acquisition of ps resolved (ps resolved) images for monitoring retinal ablation (retinal ablation).

FIG. 4a is a conceptual diagram of a high spectral resolution high spectral wavefront analysis system according to an embodiment of the present invention. An input known multi-wavelength wavefront 421 (which may be, for example, planar or spherical) passes through a polarization-or power-splitting type beam splitter 422 and reflects from a sample 423 to be tested, which may be composed of a plurality of distributed or discrete reflective layers or interfaces 424 (e.g., as may be found in the anterior segment of the eye). Information about the morphology and reflectivity of the sample is encoded into the shape and spectral response of the reflected wavefront 425, which is separated from the input wavefront 421 by the beam splitter 422. Similar to the shack-hartmann analysis, the wavefront 425 is sampled by a two-dimensional grid 427, however in this case the sampling is performed by a spectral wavefront analyzer 426 to produce optical phase and spectral information in the form of a phase 428 and amplitude 429 of the sample as a function of wavelength λ for each point in the grid 427 for subsequent analysis by a processor equipped with suitable computer readable program code. Preferably, the sampling is selected to ensure continuity and accurate calibration of the relative phase and amplitude profile 430 in both spatial dimensions and wavelengths, so that the phase and amplitude data of the sampling can be determined even in the event of motion of the test sample (which would otherwise move when a clinical in vivo measurement is taken).

Fig. 4b illustrates a technique for measuring the spectral phase and amplitude response of light reflected from the sample 423 at a single point to clearly explain the working principles that will be used in the following embodiments. A portion of the planar multi-wavelength wavefront 421 is directed via the beam splitter 422 through the focusing lens 459 to the sample 423 and a second portion (the reference wavefront) of the planar multi-wavelength wavefront 421 is directed to the grating 460. Light from the reference wavefront is dispersed 461 and 462 according to wavelength and combined with the multi-wavelength wavefront 463 reflected from the sample 423 to form a fringe pattern 464 whose period Ω (λ) corresponds to the wavelength λ due to the angular change associated with the dispersion of the grating 460. The optical frequency of the light reflected from the sample is converted to a spatial frequency, which can be analyzed by fourier analysis of the resulting interference fringes using a processor equipped with suitable computer readable program code. In this particular embodiment, grating 460 plays a role in reflection near the Littrow reflection angle (Littrow reflection angle), although these options may not be as important as several other configurations.

Fig. 5 schematically illustrates an optical train of a spectral wavefront analyzer that interferometrically measures the phase of light at multiple wavelengths on a two-dimensional sampling point grid (i.e., a two-dimensional sampling array) using a reference beam, according to an embodiment of the present invention.

A Polarizing Beam Splitter (PBS)521 splits a known multi-wavelength input wavefront 520, e.g., from a SLED or swept wavelength source, into a reference beam 542 and a probe beam 543 depending on the polarization state of the input wavefront (e.g., elliptical). Reference beam 542 passes through the quadrantOne waveplate 522 and reflects from the mirror 523, and the probe beam 543 passes through another quarter waveplate 525 and reflects from the sample 524, which can also be composed of a plurality of distributed or discrete reflective layers or interfaces 545 (e.g., a reflective layer or interface found in the anterior segment of the eye). The reference and probe beams are recombined at PBS 521 by polarization multiplexing and directed to microlens array 526 and selective aperture array 527 to form a two-dimensional sampling array (effectively part of the beam waist (waist) of beamlets 544). Aperture array 527 is optional, but it improves the spatial resolution of the system and improves isolation between adjacent beamlet measurements. The multi-wavelength beamlets are collimated by lens 528 (for a transmissive configuration, as shown) and directed to a second PBS 529 that separates the beamlets into reference and probe components. The two components are directed through respective polarization waveplates 540 and 541 onto respective diffraction gratings 530 and 531, which may be arranged to have dispersion directions of the same or opposite sign depending on the orientation of the diffraction gratings. Alternatively, for applications where less dispersion is desired, conventional prisms or other dispersion techniques may be used. Dispersed reference and probe beamlets are recombined by PBS 529, and an optical train of cylindrical lenses 532 and 533 or spherical lens passes through one or more polarization analyzing elements 534 (e.g., YVO) before the recombined image is detected at focal plane array 535₄A discrete plate (as shown), or another PBS, relays the recombined image. Each beamlet forms an image 536 that is tightly focused to be orthogonal to and spread over the dispersion axis. If the dispersions of gratings 530 and 531 are arranged in opposition, the optical train is configured to form far-field images of the reference and probe beamlets that would interfere once the polarization of the reference and probe beamlets is analyzed. If a single wavelength of light is considered, the spatial oscillation frequency within each beamlet will correspond to the wavelength of light, and the phase relative to the reference beam can be obtained by the location of the zero-valued maximum corresponding to that frequency. It will be appreciated by those skilled in the art that since each wavelength corresponds to a particular spatial oscillation, a configuration may be utilizedA processor provided with suitable computer readable program code analyzes the superposition of the plurality of wavelength fringe patterns by fourier transform techniques. An example of a fourier transform technique is described in co-pending patent co-pending treaty patent application entitled "Wavefront Analyser" filed on even date herewith, the contents of which are incorporated herein by reference. Furthermore, if the far field image has curvature or aberrations, corrections can be made in the mathematical analysis, which reduces the requirements for precise optical components and tolerances, thus significantly reducing the cost of the instruments widely used in clinical applications. In the particular case where there is a linear correlation between the optical and spatial frequencies, the sum of the spatial frequencies may form a correspondence between the depth of the sample reflection point and the spatial interference envelope.

In an alternative embodiment, the sample and reference arms are dispersed and focused in the dispersion axis after PBS 529 is recombined. The effect is to associate a linear array of pixels with each beamlet, wherein each pixel of the array corresponds to a particular wavelength, thereby forming a two-dimensional sample matrix, wherein each sample beamlet is measured with the linear array corresponding to each sample beamlet. In some cases, this approach, similar to a spectrometer, may provide better signal-to-noise ratio, but it is more difficult to correct for aberrations of the optics because it requires focusing each wavelength as tightly as possible (which is difficult to achieve if the imaging optics do not have considerable complexity).

In yet another embodiment, the one or more polarization analyzing elements 534 are adapted to analyze more than one polarization state of the recombined image to provide a balanced detection system.

Fig. 6 schematically illustrates an alternative embodiment in which the reference arm of the optical train in fig. 5 is modified to introduce wavelength-dependent optical wavefront curvature into reference beam 542. In this embodiment, the reference beam polarization component of the input beam 520 passes through a compound lens 621 that includes a positive refractive power element 624 and a negative refractive power element 625 composed of glass with different dispersions. The compound lens 621 introduces wavefront curvature 622 (which is a continuous function of wavelength λ)Varied) and designed to be at a predetermined wavelength λ₀With effectively zero diopters.

FIG. 7 schematically illustrates another variation of the spectral wavefront analyzer illustrated in FIG. 5, wherein the input wavefront is divided into a two-dimensional array of beamlets. The input known multi-wavelength beam 520 passes through a spherical microlens array 721 or a pair of cylindrical microlens arrays to form an appropriate divergence grid, i.e., an array of sampling/reference points 722 corresponding to the waist of the beamlet. These beamlet waists are relayed through the appropriate optical train of lenses 723, 726 in the reference arm and a similar optical train including lenses 723, 727 in the probe arm of the sample 524 to be measured. A respective wavefront (724 and 725) forming a thin beam near the waist in each arm is relayed through PBS 521 and lens 728 to microlens array 526, which serves to increase the numerical aperture (and thus reduce the spot size) of each spot, before traveling through the remainder of the spectral wavefront analysis system depicted in fig. 5. In this manner, each detection beamlet corresponds to processing through a single microlens and prevents scattering due to aperture array 527, avoiding unwanted scattering.

It should be emphasized that the use of a two-dimensional array of sampling points provides the advantage of being able to detect the relative phase and amplitude of the entire spectrum of light beams reflected from the eye or other sample in a single beat (and hence with minimal motion artifacts), thereby allowing tomographic features to be reconstructed, and/or the wavefront of the light beam to be measured, with high accuracy. If the exposure is too long so that there is relative sample motion during the acquisition time, the detected fringes will be reduced, but their corresponding positions will not be affected. The fringe-decaying effect can be ameliorated by using a single short light pulse during the acquisition period.

In the spectral wavefront analysis techniques described above, maintaining phase accuracy between the wavelengths produced by the relative phase information and the sampling points on the beam aperture can be used to develop instruments having a variety of applications including digital holographic reconstruction of high resolution two and three dimensional microscopy, accurate topography of surfaces and layers, and new techniques for wavefront analysis of the eye as will be described below.

FIG. 8 illustrates a technique for a wavefront reflected from an anterior surface of an eye model in a reference arm of an interferometer according to one aspect of the invention. The input nominal plane wavefront 821 is split by the polarizing beam splitter 521 into a probe beam 822 and a reference beam 823. The reference beam 823 passes through the quarter wave plate 522 and is focused by the lens 824 through the aperture 825. Due to the use of refractive optical element 824, the optical path lengths of all beam paths are substantially equal at the aperture. The light diverges spherically from the aperture 825, but is reflected back by a reflective member 826 (e.g., a planar diffractive optics component). This creates a spherically varying optical path length difference that can be approximated by the path length difference of light moving to the first specular reflection point of the eye or other sample 524 on the probe beam path 822. This results in a significant reduction in the phase change of the recombined wavefront 827, which can be more easily tracked in the remainder of the wavefront analysis system without phase ambiguity. More than one diffractive optic component 826 may be used, and the diffractive optic component may also use a non-planar substrate, which allows for more complex depth profiles to be approximated. Further, for a multi-wavelength wavefront 821, the apparatus of FIG. 8 can be used to form wavelength-dependent wavefront curvature, as described in connection with FIG. 6.

Fig. 9 schematically illustrates an optical train of a spectral wavefront analyzer in accordance with another embodiment of the present invention, in which a series of off-axis wavefronts from a sample can be collected using a single beat wavefront analyzer. In this system, each wavelength represents a different angle of incidence of the input beam 910 on the eye 915 under test, and thus represents a different point on the retina 916 from which the sample wavefront to be analyzed emanates.

Similar to the embodiment of fig. 5, a multi-wavelength input wavefront 910 of known characteristics is split into two components by a beam splitter 912 (which may be a polarizing beam splitter or a conventional power beam splitter). One component (probe beam) is relayed through relay lenses 911 and 913 to a dispersion element (e.g., a transmission diffraction grating 914) that disperses the component angularly according to wavelength into a plurality of tracks. The light in these trajectories is substantially focused by the refractive elements of the eye 915 to be measured to form a plurality of discrete spots 917, 918 on the retina 916 of the eye. A small portion of the light from each spot is reflected back through the system and recombined by the diffraction grating 914 before being focused into an aperture 919, which may be, for example, a slit oriented orthogonal to the direction of the dispersion axis. The aperture 919 is positioned at the focal length of the lens 924 that collimates the recombined light 926, the recombined light 926 at least on an axis orthogonal to the slit 919 before impinging the focal plane array 925.

The second component of the input wavefront 910 (i.e., the reference beam) is relayed through relay lenses 911 and 920 to a diffraction grating 921, which angularly disperses the second component along different trajectories 922 and 923 according to wavelength. The angularly multiplexed wavefronts are relayed through beam splitter 912 and lenses 920 and 924 to interfere with the combined wavefront reflected from the eye under test 915 to form a plurality of interference patterns on the focal plane array 925, where the number of interference patterns is determined by the number of wavelength components in the input wavefront 910.

In embodiments where beam splitter 912 is a polarizing beam splitter, the combination of the two beams may be achieved by polarization operations (e.g., by inserting a quarter wave plate and polarization analyzing element as described above with reference to FIG. 5) to analyze the relative phases of the two beams at each point in space.

As described in more detail in the above-mentioned co-pending PCT patent application entitled Wavefront Analyser, the interference pattern derived at each wavelength corresponds to a spatial frequency in the direction of the dispersion axis, and the phase of each wavelength component can be reconstructed from the phase of the corresponding spatial frequency. The provision of dispersive elements in the reference and probe beam paths means that a larger spatial frequency range can be used, from two pixels and above, and advantageously the phase of each wavelength can be unambiguously resolved. Although this single-shot technique can provide greater accuracy by capturing the entire wavefront at all off-axis trajectories of the eye 915 simultaneously as compared to the scanning technique, it is important to note that since the single-shot technique is an interferometric technique, a short capture time is still important in order to reduce any fringe attenuation due to relative motion of the eye under test. Also, in addition to rapidly blocking the focal plane array, this can be facilitated by using short pulse illumination.

The use of the above-described off-axis wavefront analysis to diagnose myopia and monitor the progression or treatment of myopia is now being considered. Recent studies have shown that in some cases there may be a causal relationship between the off-axis focusing performance of the eye and the development of myopia. It is important to consider methods of quantifying this development to help understand the occurrence of myopia and to develop successful treatments. The apparatus disclosed in figure 9 allows a beam reflected from the retina of the eye under test around a predetermined axis to capture a wide range of off-axis wavefronts. By measuring the reflected wavefront at multiple angles, a map of the off-axis relative wavefront curvature and aberrations of the eye can be obtained. Since a set of discrete beam angles at the eye is obtained by the dispersive element, it is possible to accurately track the phase from one wavelength to the next and thus deal with large changes in focus that occur without requiring the measurement apparatus to make multiple mechanical adjustments. Alternatively, instead of using a grating or other dispersive element to disperse the wavelengths, the wavelengths can be directed at varying angles by reflecting all the wavelengths off a scanning mirror positioned relative to the optical train to effect rotation of the beam about a point approximately one focal length from the effective optical center of the ocular lens. Again, this is described in more detail in co-pending PCT patent application entitled Wavefront Analyzer.

The scanning mirror may also be advantageous in an optical relay system to extend the flexibility of the apparatus shown in FIG. 7 to project a grid of beam waists 725 onto the sample 524. As shown in fig. 11, a suitable relay system 1120 includes a scanning mirror 1121 and two refractive elements 1122 and 1123, which may be, for example, lenses or mirrors. The scan mirror 1121 is positioned at approximately the focal length from at least one of the two refractive elements, preferably element 1122 closer to the sample 524. Angular adjustment of the scan mirror 1121 on either axis 1124 results in a lateral displacement of the re-imaged beam waist 1125 on the respective axis. The scan mirror 1121 can be positioned at the focal point of two refractive elements 1122 and 1123 (as shown in FIG. 11), in which case the relay system 1120 forms a 4F optical system, although the spacing of the refractive elements can be varied if necessary to adjust the trajectory of beamlets 1125. Scanning the pixelated sample probe (i.e., the grid of beam waists) across the sample 524 in two or more exposures enables denser spatial sampling of the reflected sample wavefront without requiring large scanning mirrors or large angles to give full imaging coverage of the 3D structure. Since the mirror 1121 is located at the focal point of the relay system 1120, a small MEMS type mirror that can be fast stable, compact, and lightweight can be utilized to miniaturize the system. This provides considerable advantages to improve metrology of the reflective surface to be measured and allows reconstruction of arbitrary scans across or through the sample.

Each exposure captures a set of two-dimensional depth scans across the sample. In each exposure, depth scans are acquired simultaneously, eliminating the problem of relative movement of the sample between scans. The exact location and angle of each beamlet in grid 1125 relative to the other beamlets does not change, and the exact location and angle can be calibrated very precisely when the instrument has been fabricated. This provides a significant advantage for scanning systems that use a rotating mirror that is not at the focus of the relay system to acquire a single scan, in which a degree of uncertainty is introduced between any two measurements due to the inability to accurately measure the exact position of the mirror at any point.

The set of depth scans acquired in each exposure may be segmented using standard image processing techniques to locate surfaces within the sample, which for ocular applications may include the anterior and posterior surfaces of the cornea. A mathematical surface model (e.g., Zernike polynomials) may be fitted to the segmented surface data using standard surface fitting methods. Typically, the time between exposures means that there will be some relative displacement or rotation between each set of data due to the motion of the scanning mirror or the sample. For this motion, data from subsequent exposures may be corrected by registering the mathematical model from the initial exposure with the surface data. The segmented data points are rotated and/or shifted about all three axes and the distance from the shifted/rotated surface points to the initial mathematical surface is minimized using standard optimization techniques to determine the best alignment between the surfaces. The mathematical surface model may then be updated to include the initial data points as well as data points from subsequent exposures to gradually increase the accuracy of the surface model.

The ability to analyze the off-axis wavefront data from the sample can also be used to design or customize a contact lens or lens that will correct the refractive power of a myopic patient in the on-axis wavefront, while ensuring that the peripheral wavefront is focused on or behind the retina, thereby preventing or reducing myopia progression. In addition, the patient's eyes may be imaged again with the corrective eyeglasses in place to confirm that the eyeglasses are functioning as desired, or to monitor the progression of myopia.

The technique described above with reference to fig. 9 can also be used to measure the optical depth of the eye (i.e. the length, in terms of the number of optical cycles of the central wavelength, from the first reflection point of the eye to be measured to the retinal reflection) if the coherence length of the source (determined by the length of the detectable interference effect) is suitably long. One method of increasing the coherence length in low coherence interferometry is discussed with reference to fig. 10. A light source 1003 (e.g., an LED or semiconductor optical amplifier with an inherent spectral width 1010 of a few tens of nanometers) is first filtered using a device comprising a collimating lens 1004, etalon 1005 and mirror 1006, the collimating lens 1004, etalon 1005 and mirror 1006 being in the collimated portion of the beam with a path length related to the desired wavelength separation of the spectral sampling points. The coherence length of the resulting output beam 1007 is inversely proportional to the spectral width of each wavelength component 1011 of the output beam. In the specific example shown in fig. 10, a reduction in spectral width from 40 nm to 0.02 nm would increase the coherence length by 200 x. In this way, even an etalon with an appropriately low degree of precision can significantly increase the range in which a measurable fringe can be detected.

Instead of using etalons, optical delay devices including, for example, beam splitters and combiners, may be utilized to provide different path lengths, with the optical delay being selected to provide coherence at the front surface of the eye and the retina, for example, simultaneously. Different positions of the sample or reference beam in the instrument may also include this delay.

Surface registration techniques (surface registration techniques) described with reference to the optical relay system in fig. 10 may also be used to register data from acquired multiple exposures with different delay path lengths, provided that the two sets of data include a common reference surface. The method can be used, for example, to register one set of data comprising the anterior and posterior surfaces of the cornea and lens with another set of data comprising the anterior corneal surface and the retina. Accurate measurement of all optically important surfaces of the eye (relative to a common reference) means that it is possible to reconstruct the wavefront of the eye along an arbitrary axis by performing an analogue ray tracing technique using the average population value of the refractive indices of the cornea, lens, aqueous humor and vitreous humor. For ocular applications that focus on sparse reflections from various interfaces within the eye, this may allow simultaneous measurements to be taken of, for example, the anterior surface and the retina. However, undersampling the spectrum can lead to ghosting and artifacts.

In the above embodiments, the analyzed wavefront is obtained by reflection from the sample (e.g., eye) to be measured. It should be understood, however, that the wavefront may also be obtained by transmission through the sample under test. In either case, information about the sample is encoded in the shape and spectral composition of the wavefront. It will be appreciated that the illustrated embodiment enables the extraction of optical phase and spectral information, such as phase and amplitude data, as a function of wavelength at a plurality of sample points of a wavefront reflected from a sample. Relative phase information between sampling points is maintained and the resulting phase accuracy can be used to provide systems and methods that rely on optical phase in the eye and other live biological samples that may be prone to motion artifacts for accurate measurement.

The present invention claims priority from australian provisional patent application no 2013902254 filed on 2013, month 6 and 20, the contents of which are incorporated herein by reference.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.