Title of Invention	WAVEFRONT ABERRATION AND DISTANCE MEASUREMENT PHASE CAMERA
Abstract	A system consisting of a phase camera with micrnlcnses placed in the focal point of a converging lens, wherein the camera data is processed using a combined Fourier "Slice" and Fast Fourier Transform edge detection technique providing both a three-dimensional wavefront map and a real scene depth map within a broad range of volumes, the invention is suitable for use in any field where wave-fronts need to be determined, such as earth-based astronomical observation, ophthalmology, etc., as well as in fields requiring metrology, e.g. real scenes, CCD polishing, automobile mechanics, etc. The invention is particularly suitable for atmospheric tomography using ELTs (large-diameter telescopes: 50 or I(X) metres).

Title of Invention

WAVEFRONT ABERRATION AND DISTANCE MEASUREMENT PHASE CAMERA

Abstract

A system consisting of a phase camera with micrnlcnses placed in the focal point of a converging lens, wherein the camera data is processed using a combined Fourier "Slice" and Fast Fourier Transform edge detection technique providing both a three-dimensional wavefront map and a real scene depth map within a broad range of volumes, the invention is suitable for use in any field where wave-fronts need to be determined, such as earth-based astronomical observation, ophthalmology, etc., as well as in fields requiring metrology, e.g. real scenes, CCD polishing, automobile mechanics, etc. The invention is particularly suitable for atmospheric tomography using ELTs (large-diameter telescopes: 50 or I(X) metres).

Full Text	WAVEFRONT ABERRATION AND DISTANCE MEASUREMENT PHASE CAMERA Object of the Invention The system of the invention consists of a phase camera with microlenses placed in the focal point of a converging lens, wherein the camera data, processed using a combined Fourier "Slice" and fast Fourier transform edge detection technique, provide both a three-dimensional wavefront map and a real scene depth map within a broad range of volumes. This invention is suitable for use in any field where wavefronts need to be determined, such as earth-based astronomical observation, ophthalmology, etc., as well as in fields requiring metrology, e.g. real scenes, CCD polishing, automobile mechanics, etc. The invention is applied to the particular case of atmospheric tomography using ELTs (large- diameter telescopes: 50 or 100 metres). Field of the Art The invention is comprised in the field of optics and image processing. Background of the Invention The present invention relates to both the need for obtaining a three-dimensional wavefront measurement associated to any optical problem in which image quality is essential (e.g. for diagnosis) and to the need for obtaining a sufficiently reliable and precise depth map within a broad range of volumes, from a few microns up to several kilometers. Though the general approach can be applied to other fields, the analyses conducted focus on large aperture telescopes and on scene depth measurement. State of the Art Atmospheric tomography For present large-diameter telescopes (GRANTECAN, Keck,...) and future giant telescopes (50 or 100 metres in diameter) , the adaptive optics system has taken the course of measuring the three-dimensional distribution of the atmospheric phase by using a form of tomography called multiconjugate adaptive optics. The absence of a sufficient number of natural point sources in the sky, such that there is always one present within the field of vision of the object observed by the telescope, makes it necessary to use artificial point sources, e.g. Na stars (90 km high). In order to correct the entire atmosphere which affects the light beam coming from the object in the sky (avoiding focal anisoplanatism), it is necessary to use several of these artificial stars (at least 5) . In order to be generated, each of them requires a very high resolution and high powered pulsed laser, which translates into an incredibly expensive technology. Furthermore, after such a high cost, the multiconjugate adaptive optics can only measure the atmospheric phase associaited to at most three horizontal turbulence layers (with three phase sensors measuring simultaneously), i.e., it scans a minute proportion of the three-dimensional cylinder affecting the image. They also recover an estimation of the phase with calculations that are so complicated that they seriously compromise the adaptive correction of the optical beam within the stability time of the atmosphere in the visible spectrum (10 ms). The technique proposed herein will however allow: -being limited to a single measurement and to a single sensor, within each atmospheric stability time. -a recovery of the phase associated to each turbulent horizontal layer, i.e., tomography of the entire atmosphere, by means of an algorithm based on Fourier transform, which in and of itself is fast but can be accelerated with an intelligent adaptation thereof to graphics processing units (GPU) or to electronic hardware units, such as FPGA (Field Programmable Gate Arrays). -preventing the need to use artificial laser stars, as it will recover in real time the image of the object upon its arrival to the Earth' s atmosphere, since this new technique does not require calibration with a point signal to then be deconvoluted. Human eye tomography The main interest in performing human eye tomography is essentially based on obtaining and having available for medical specialists a clear image of the retinal fundus of the pacient, in order to make more reliable diagnoses. The aqueous humor, the vitreous humor and the lens behave in the eye as means which aberrate the image that can be obtained from the retinal fundus. In fact, it does not require taking measurements as frequently as in the Earth' s atmosphere (one every 10 ms) , because it is a stable deformation; however it does require sufficient three-dimensional resolution to not only obtain a good image of the retinal fundus, but also to detect the spatial location of possible ocular lesions. The few authors who, within the mentioned fields, have placed microlenses in the focal point do not use the Fourier "Slice" technique to take the measurement of the optical aberration, or to correct the image, or to obtain distances. In addition, the Fourier "Slice" technique associated to microlenses in the focal point has only been used to obtain focused photographs of real scenes within ranges of a few cubic metres of volume, with a quality that apparently exceeds the common depth of field technique. In summary, these contributions of other authors have nothing to do with the patent herein described. Description of the Invention A single array of microlenses, forming an image on a CCD with sufficient resolution and placed in the focal point position of a converging lens allows taking tomographic measurements of target three-dimensional space. The measurements are taken once only, i.e., a single image contains sufficient information to recover the three- dimensional environment. Such image can be understood as being made up of 4 dimensions: two coordinates on the CCD associated to the inside of each microlens and two other coordinates associated to the array of microlenses. The proposed technique is based on the Generalized Fourier "Slice" Theorem. The image taken by the CCD is Fourier transform in four dimensions, then a rotation and "slice" operator is applied to it, which decides the depth at which the object will be recovered and reduces the problem of 4 dimensions to just 2. The objective of this invention is to find out the depths at which the objects are located; to that end, by working in the transformed domain and identifying the objects with the edge detection algorithm (high spatial frequencies), it is possible to identify the components of the scene of which it is previously known at what distance they are located. In addition, a Shack-Hartmann sensor consists of an assembly of lenses placed in array form to form the same number of images in a two-dimensional detector. The displacement of each of them in relation to the position corresponding to a planar wavefront measures the local gradient of the wavefront. It is possible to recover the original wavefront through numerical processes. The proposed phase camera contains a Shack-Hartmann in the focal point of a converging lens, which is why the design is also a wavefront phase camera, but placed in the focal point of a lens, with a completely different data processing than what has been associated up until now to the Shack-Hartmann sensor. It is then possible to recover both depths and wavefront phases. Description of the Drawings Figure 1: Diagram of the arrangement of the aperture lens (1), of the lenses (2), and of the CCD (3) forming the phase camera. (5) is the focal point of the converging lens. (6) is the focal of each microlens of the array of lenses. (7) is the local tilt angle of the wavefront. (4) is the optical path displacement experienced by the turbulent wavefront in relation to another one without aberration. Figure 2: Conceptual diagram of the invention applied to a telescope with a large main mirror (1) . Performing atmospheric tomography in the astrophysical observation of a star (8) with adaptive optics. The individual turbulence layers within the atmosphere correspond to (9) and (10) . The phase camera allows scanning the complete cylinder of atmospheric turbulence (13) which affects the final image of the telescope. Figure 3: Conceptual diagram of a classic astrophysical observation of a star (8) using the adaptive optics multiconjugated to two turbulence layers in the atmosphere (9) and (10). It can only recover a very small number of individual turbulence layers (three layers at most). (11) and (12) indicate the wavefront sensors conjugately associated to each turbulent layer. (1) corresponds to the telescope. Preferred Embodiment of the Invention The particular case of an astrophysical observation with a telescope having a diameter exceeding the diameter of coherence r0 of the atmosphere (approximately 20 cm in the visible spectrum) is considered. The turbulence of the atmosphere causes a loss of resolution in the image obtained with the telescope, i.e., loss of high spatial frequencies information. To prevent this loss, it is necessary to know the manner in which the atmospheric turbulence degrades the wavefront of the light coming from the star under study. Natural or artificial point starts which allow characterizing the deformation that the atmosphere introduces in the wavefront can be used to that end. With classic multiconjugate adaptive optics (Figure 3), a wavefront phase sensor must be used for each deformable mirror conjugated to an individual turbulence layer, i.e. two different phase sensors (WFS) which must be aligned and placed in operation in parallel and in different positions of the optical axis. The complexity of the calculations and the need for velocity since the atmosphere changes every 10 milliseconds in the visible spectrum, makes it impossible to overcome the correction today at only three atmospheric turbulence layers. With the phase camera having the design shown in Figure 1, and whose operation in this case is shown in Figure 2, only one sensor is used, which sensor is placed in a single position of the optical axis, and a single measurement, subsequently processed by means of the Fourier Slice technique, will allow obtaining the three-dimensional map of turbulences (wavefront phases) associated to the entire column of atmosphere which affects the observation with the telescope of the invention, as well as the altitude at which these turbulence layers are located. WE CLAIM: 1. A phase camera for obtaining in real time the three-dimensional map of a wavefront and the depth map of a three-dimensional space, comprising a converging lens, an array of microlenses placed in the focal point of the converging lens, a CCD device, and real time processing means adapted to obtain the focal stack of the three-dimensional space by applying a Fourier Slice algorithm, and - identify the components for each depth of the focal stack of such three-dimensional space by means of a fast Fourier transform edge detection algorithm. 2. The phase camera for obtaining in real time the three-dimensional map of a wavefront and the depth map of a three-dimensional space according to claim 1, characterized in that the processing means comprise a GPU unit. 3. The phase camera for obtaining in real time the three-dimensional map of a wavefront and the depth map of a three-dimensional space according to claim 1, characterized in that the processing means comprise an FPGA device. 4. A process for obtaining in real time the three- dimensional map of a wavefront and the depth map of a three- dimensional space, comprising the following steps: obtaining an image of the three-dimensional space with a phase camera; obtaining the focal stack of the three-dimensional space by applying a Fourier Slice algorithm; and identifying the components for each depth of the focal stack of such three-dimensional space by means of a fast Fourier transform edge detection algorithm. 5. A process for obtaining in real time the three- dimensional map of a wavefront and the depth map of a three- dimensional space according to claim 4, wherein the three- dimensional map of a wavefront and the depth map of a three- dimensional space is applied to an observation selected from the group of an astronomical observation, an ophthalmological observation, a real scene observation, an observation of a surface of a CCD and an observation of a surface of a mechanical part. A system consisting of a phase camera with micrnlcnses placed in the focal point of a converging lens, wherein the camera data is processed using a combined Fourier "Slice" and Fast Fourier Transform edge detection technique providing both a three-dimensional wavefront map and a real scene depth map within a broad range of volumes, the invention is suitable for use in any field where wave-fronts need to be determined, such as earth-based astronomical observation, ophthalmology, etc., as well as in fields requiring metrology, e.g. real scenes, CCD polishing, automobile mechanics, etc. The invention is particularly suitable for atmospheric tomography using ELTs (large-diameter telescopes: 50 or I(X) metres).

Full Text

WAVEFRONT ABERRATION AND DISTANCE MEASUREMENT PHASE CAMERA
Object of the Invention
The system of the invention consists of a phase camera
with microlenses placed in the focal point of a converging
lens, wherein the camera data, processed using a combined
Fourier "Slice" and fast Fourier transform edge detection
technique, provide both a three-dimensional wavefront map and
a real scene depth map within a broad range of volumes.
This invention is suitable for use in any field where
wavefronts need to be determined, such as earth-based
astronomical observation, ophthalmology, etc., as well as in
fields requiring metrology, e.g. real scenes, CCD polishing,
automobile mechanics, etc. The invention is applied to the
particular case of atmospheric tomography using ELTs (large-
diameter telescopes: 50 or 100 metres).
Field of the Art
The invention is comprised in the field of optics and
image processing.
Background of the Invention
The present invention relates to both the need for
obtaining a three-dimensional wavefront measurement associated
to any optical problem in which image quality is essential
(e.g. for diagnosis) and to the need for obtaining a
sufficiently reliable and precise depth map within a broad
range of volumes, from a few microns up to several kilometers.
Though the general approach can be applied to other
fields, the analyses conducted focus on large aperture
telescopes and on scene depth measurement.
State of the Art
Atmospheric tomography
For present large-diameter telescopes (GRANTECAN,
Keck,...) and future giant telescopes (50 or 100 metres in
diameter) , the adaptive optics system has taken the course of
measuring the three-dimensional distribution of the

atmospheric phase by using a form of tomography called
multiconjugate adaptive optics. The absence of a sufficient
number of natural point sources in the sky, such that there is
always one present within the field of vision of the object
observed by the telescope, makes it necessary to use
artificial point sources, e.g. Na stars (90 km high).
In order to correct the entire atmosphere which affects
the light beam coming from the object in the sky (avoiding
focal anisoplanatism), it is necessary to use several of these
artificial stars (at least 5) . In order to be generated, each
of them requires a very high resolution and high powered
pulsed laser, which translates into an incredibly expensive
technology. Furthermore, after such a high cost, the
multiconjugate adaptive optics can only measure the
atmospheric phase associaited to at most three horizontal
turbulence layers (with three phase sensors measuring
simultaneously), i.e., it scans a minute proportion of the
three-dimensional cylinder affecting the image. They also
recover an estimation of the phase with calculations that are
so complicated that they seriously compromise the adaptive
correction of the optical beam within the stability time of
the atmosphere in the visible spectrum (10 ms).
The technique proposed herein will however allow:
-being limited to a single measurement and to a single
sensor, within each atmospheric stability time.
-a recovery of the phase associated to each turbulent
horizontal layer, i.e., tomography of the entire atmosphere,
by means of an algorithm based on Fourier transform, which in
and of itself is fast but can be accelerated with an
intelligent adaptation thereof to graphics processing units
(GPU) or to electronic hardware units, such as FPGA (Field
Programmable Gate Arrays).
-preventing the need to use artificial laser stars, as
it will recover in real time the image of the object upon its
arrival to the Earth' s atmosphere, since this new technique

does not require calibration with a point signal to then be
deconvoluted.
Human eye tomography
The main interest in performing human eye tomography is
essentially based on obtaining and having available for
medical specialists a clear image of the retinal fundus of the
pacient, in order to make more reliable diagnoses. The aqueous
humor, the vitreous humor and the lens behave in the eye as
means which aberrate the image that can be obtained from the
retinal fundus.
In fact, it does not require taking measurements as
frequently as in the Earth' s atmosphere (one every 10 ms) ,
because it is a stable deformation; however it does require
sufficient three-dimensional resolution to not only obtain a
good image of the retinal fundus, but also to detect the
spatial location of possible ocular lesions.
The few authors who, within the mentioned fields, have
placed microlenses in the focal point do not use the Fourier
"Slice" technique to take the measurement of the optical
aberration, or to correct the image, or to obtain distances.
In addition, the Fourier "Slice" technique associated to
microlenses in the focal point has only been used to obtain
focused photographs of real scenes within ranges of a few
cubic metres of volume, with a quality that apparently exceeds
the common depth of field technique. In summary, these
contributions of other authors have nothing to do with the
patent herein described.
Description of the Invention
A single array of microlenses, forming an image on a CCD
with sufficient resolution and placed in the focal point
position of a converging lens allows taking tomographic
measurements of target three-dimensional space.
The measurements are taken once only, i.e., a single
image contains sufficient information to recover the three-
dimensional environment. Such image can be understood as being

made up of 4 dimensions: two coordinates on the CCD associated
to the inside of each microlens and two other coordinates
associated to the array of microlenses.
The proposed technique is based on the Generalized
Fourier "Slice" Theorem. The image taken by the CCD is Fourier
transform in four dimensions, then a rotation and "slice"
operator is applied to it, which decides the depth at which
the object will be recovered and reduces the problem of 4
dimensions to just 2. The objective of this invention is to
find out the depths at which the objects are located; to that
end, by working in the transformed domain and identifying the
objects with the edge detection algorithm (high spatial
frequencies), it is possible to identify the components of the
scene of which it is previously known at what distance they
are located.
In addition, a Shack-Hartmann sensor consists of an
assembly of lenses placed in array form to form the same
number of images in a two-dimensional detector. The
displacement of each of them in relation to the position
corresponding to a planar wavefront measures the local
gradient of the wavefront. It is possible to recover the
original wavefront through numerical processes. The proposed
phase camera contains a Shack-Hartmann in the focal point of a
converging lens, which is why the design is also a wavefront
phase camera, but placed in the focal point of a lens, with a
completely different data processing than what has been
associated up until now to the Shack-Hartmann sensor. It is
then possible to recover both depths and wavefront phases.
Description of the Drawings
Figure 1: Diagram of the arrangement of the aperture
lens (1), of the lenses (2), and of the CCD (3) forming the
phase camera. (5) is the focal point of the converging lens.
(6) is the focal of each microlens of the array of lenses. (7)
is the local tilt angle of the wavefront. (4) is the optical
path displacement experienced by the turbulent wavefront in

relation to another one without aberration.
Figure 2: Conceptual diagram of the invention applied to
a telescope with a large main mirror (1) . Performing
atmospheric tomography in the astrophysical observation of a
star (8) with adaptive optics. The individual turbulence
layers within the atmosphere correspond to (9) and (10) . The
phase camera allows scanning the complete cylinder of
atmospheric turbulence (13) which affects the final image of
the telescope.
Figure 3: Conceptual diagram of a classic astrophysical
observation of a star (8) using the adaptive optics
multiconjugated to two turbulence layers in the atmosphere (9)
and (10). It can only recover a very small number of
individual turbulence layers (three layers at most). (11) and
(12) indicate the wavefront sensors conjugately associated to
each turbulent layer. (1) corresponds to the telescope.
Preferred Embodiment of the Invention
The particular case of an astrophysical observation with
a telescope having a diameter exceeding the diameter of
coherence r0 of the atmosphere (approximately 20 cm in the
visible spectrum) is considered. The turbulence of the
atmosphere causes a loss of resolution in the image obtained
with the telescope, i.e., loss of high spatial frequencies
information. To prevent this loss, it is necessary to know the
manner in which the atmospheric turbulence degrades the
wavefront of the light coming from the star under study.
Natural or artificial point starts which allow characterizing
the deformation that the atmosphere introduces in the
wavefront can be used to that end.
With classic multiconjugate adaptive optics (Figure 3),
a wavefront phase sensor must be used for each deformable
mirror conjugated to an individual turbulence layer, i.e. two
different phase sensors (WFS) which must be aligned and placed
in operation in parallel and in different positions of the
optical axis. The complexity of the calculations and the need

for velocity since the atmosphere changes every 10
milliseconds in the visible spectrum, makes it impossible to
overcome the correction today at only three atmospheric
turbulence layers.
With the phase camera having the design shown in Figure
1, and whose operation in this case is shown in Figure 2, only
one sensor is used, which sensor is placed in a single
position of the optical axis, and a single measurement,
subsequently processed by means of the Fourier Slice
technique, will allow obtaining the three-dimensional map of
turbulences (wavefront phases) associated to the entire column
of atmosphere which affects the observation with the telescope
of the invention, as well as the altitude at which these
turbulence layers are located.

WE CLAIM:
1. A phase camera for obtaining in real time the
three-dimensional map of a wavefront and the depth map of a
three-dimensional space, comprising
a converging lens,
an array of microlenses placed in the focal point of the
converging lens,
a CCD device, and
real time processing means adapted to
obtain the focal stack of the three-dimensional
space by applying a Fourier Slice algorithm, and
- identify the components for each depth of the
focal stack of such three-dimensional space by
means of a fast Fourier transform edge detection
algorithm.
2. The phase camera for obtaining in real time the
three-dimensional map of a wavefront and the depth map of a
three-dimensional space according to claim 1, characterized in
that the processing means comprise a GPU unit.
3. The phase camera for obtaining in real time the
three-dimensional map of a wavefront and the depth map of a
three-dimensional space according to claim 1, characterized in
that the processing means comprise an FPGA device.
4. A process for obtaining in real time the three-
dimensional map of a wavefront and the depth map of a three-
dimensional space, comprising the following steps:
obtaining an image of the three-dimensional space with a
phase camera;
obtaining the focal stack of the three-dimensional space
by applying a Fourier Slice algorithm; and
identifying the components for each depth of the focal

stack of such three-dimensional space by means of a fast
Fourier transform edge detection algorithm.
5. A process for obtaining in real time the three-
dimensional map of a wavefront and the depth map of a three-
dimensional space according to claim 4, wherein the three-
dimensional map of a wavefront and the depth map of a three-
dimensional space is applied to an observation selected from
the group of an astronomical observation, an ophthalmological
observation, a real scene observation, an observation of a
surface of a CCD and an observation of a surface of a
mechanical part.

A system consisting of a phase camera with micrnlcnses placed in the focal point of a converging lens, wherein the camera data is processed using a combined Fourier "Slice" and Fast Fourier Transform edge detection technique providing both a three-dimensional wavefront map and a real scene depth map within a broad range of volumes, the invention is suitable for use in
any field where wave-fronts need to be determined, such as earth-based astronomical observation, ophthalmology, etc., as well as in
fields requiring metrology, e.g. real scenes, CCD polishing, automobile mechanics, etc. The invention is particularly suitable for
atmospheric tomography using ELTs (large-diameter telescopes: 50 or I(X) metres).

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Patent Number

270085

Indian Patent Application Number

3322/KOLNP/2008

PG Journal Number

49/2015

Publication Date

04-Dec-2015

Grant Date

27-Nov-2015

Date of Filing

13-Aug-2008

Name of Patentee

UNIVERSIDAD DE LA LAGUNA

Applicant Address

MOLINOS DE AGUA, S/N E-38207 LA LAGUNA, TENERIFE

Inventors:

#	Inventor's Name	Inventor's Address
1	ROSA GONZALEZ, FERNANDO	C/LOS POLLITOS, 48, SAN MIGUEL DE GENETO E-38296 LA LAGUNA, TENERIFE
2	RODRIGUEZ, RAMOS, JOSE MANUEL	URBANIZACION PARQUE LA VEGA, 11 CAMINO LAS PERAS, E-38203 LA LAGUNA TENERIFE
3	MARICHAL-HERNANDEZ, JOSE GIL	C/PEGASO, 2, EL MAYORAZGO, E-38108 S/C DE TENERIFE, TENERIFE

PCT International Classification Number

G01J 9/00

PCT International Application Number

PCT/ES2007/000046

PCT International Filing date

2007-01-18

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	P200600210	2006-01-20	Spain