U.S. patent application number 13/666953 was filed with the patent office on 2014-05-01 for multipoint photonic doppler velocimetry using optical lens elements.
This patent application is currently assigned to National Security Technologies, LLC.. The applicant listed for this patent is National Security Technologies, LLC.. Invention is credited to Brent Copely Frogget, Vincent Todd Romero.
Application Number | 20140118719 13/666953 |
Document ID | / |
Family ID | 50514246 |
Filed Date | 2014-05-01 |
United States Patent
Application |
20140118719 |
Kind Code |
A1 |
Frogget; Brent Copely ; et
al. |
May 1, 2014 |
MULTIPOINT PHOTONIC DOPPLER VELOCIMETRY USING OPTICAL LENS
ELEMENTS
Abstract
A probe including a fisheye lens is disclosed to measure the
velocity distribution of a moving surface along many lines of
sight. Laser light, directed to the surface and then reflected back
from the surface, is Doppler shifted by the moving surface,
collected into fisheye lens, and then directed to detection
equipment through optic fibers. The received light is mixed with
reference laser light and using photonic Doppler velocimetry, a
continuous time record of the surface movement is obtained. An
array of single-mode optical fibers provides an optic signal to an
index-matching lens and eventually to a fisheye lens. The fiber
array flat polished and coupled to the index-matching lens using
index-matching gel. Numerous fibers in a fiber array project
numerous rays through the fisheye lens which in turn project many
measurement points at numerous different locations to establish
surface coverage over a hemispherical shape with very little
crosstalk.
Inventors: |
Frogget; Brent Copely; (Los
Alamos, NM) ; Romero; Vincent Todd; (Los Alamos,
NM) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
National Security Technologies, LLC. |
Las Vegas |
NV |
US |
|
|
Assignee: |
National Security Technologies,
LLC.
Las Vegas
NV
|
Family ID: |
50514246 |
Appl. No.: |
13/666953 |
Filed: |
November 1, 2012 |
Current U.S.
Class: |
356/27 ;
385/33 |
Current CPC
Class: |
G02B 13/06 20130101;
G01S 7/4818 20130101; G01S 17/58 20130101; G01S 7/4812 20130101;
G02B 6/32 20130101 |
Class at
Publication: |
356/27 ;
385/33 |
International
Class: |
G02B 6/32 20060101
G02B006/32; G01S 17/58 20060101 G01S017/58 |
Goverment Interests
STATEMENT REGARDING FEDERAL RIGHTS
[0001] This invention was made with government support under
Contract No. DE-AC52-06NA25946 and was awarded by the U.S.
Department of Energy, National Nuclear Security Administration. The
government has certain rights in the invention.
Claims
1. A photonic Doppler velocimetry probe comprising a housing
defining an interior space between a first end and a second end;
one or more optic signal conductors entering the housing through
the second end a terminating end within the interior space of the
housing, the one or more optic signal conductors configured to
provide one or more optic signals to one or more lenses in the
probe, the probe configured for velocimetry measurements; a
ferrule, located within the housing, having one or more passages
configured to receive and secure at least one of the one or more
optic signal conductors to the ferrule; an index-matching lens
having a flat surface adjacent the ferrule to receive the optic
signal, the index-matching lens having an index of refraction
selected to match an index of refraction of the one or more optic
signal conductors; a fish eye lens, mounted at the first end,
configured to receive the optic signal and project the optic signal
outward in a direction controlled by the configuration of the fish
eye lens.
2. The probe of claim 1 wherein the one or more optic signal
conductors are one or more optic fibers.
3. The probe of claim 2 wherein the one or more optic fibers are
single mode optic fibers.
4. The probe of claim 3 wherein the terminating end of the one or
more optic fibers and a side of the ferrule are end polished.
5. The probe of claim 1 further comprising index-matching material
between the index-matching lens and the ferrule, the index-matching
material consisting of index-matching gel or index-matching
epoxy.
6. The probe of claim 1 wherein the optic signal is at 1550 nm
wavelength.
7. The probe of claim 1 further comprising one or more additional
lens elements between the index-matching element and the fish eye
lens.
8. The probe of claim 1 wherein the fisheye lens, index-matching
lens and the one or more optic signal conductors are configured to
receive a reflection of the optic signal and conduct the reflection
back through the optic signal conductor.
9. A photonic Doppler velocimetry probe comprising a housing
defining an interior space; one or more optic signal conductors
having a terminating end configured to provide optic signals; an
index-matching lens, located in the interior space, configured to
receive the optic signals, the index-matching lens having an index
of refraction selected to match an index of refraction of the one
or more optic signal conductors; a fish eye lens configured to
receive the optic signals after the optic signals pass through the
index-matching lens and project the optic signal outward in a
direction controlled by the configuration of the fish eye lens,
onto a curved surface, the curved surface being the subject of
photonic Doppler velocimetry measurement.
10. The probe of claim 9 wherein the one or more optic signal
conductors comprise one or more optic fibers.
11. The probe of claim 10 wherein the one or more optic fibers
comprise single mode optic fibers.
12. The probe of claim 11 wherein the one or more optic signal
conductors are secured by a disk having one or more passages, and
the one or more optic signal conductors pass through the one or
more passages and are end polished to be generally flush in with a
side of the disk.
13. The probe of claim 9 further comprising index-matching gel
material between the index-matching lens and the one or more optic
signal conductors.
14. The probe of claim 9 wherein the optic signal is at 1550 nm
wavelength.
15. The probe of claim 9 further comprising one or more additional
lens elements between the index-matching element and the fish eye
lens.
16. The probe of claim 9 wherein the fisheye lens, index-matching
lens and the one or more one or more optic signal conductors are
configured to receive a reflection of the optic signal and conduct
the reflection back through the optic signal conductor.
17. A method, during photonic Doppler velocimetry, for presenting
an optic signal to a curved surface and receiving a reflection from
the curved surface during movement of the curved surface
comprising: establishing a distal end of a probe facing the curved
surface, the distal end of the probe including a fisheye lens
facing the curved surface; generating an optic signal; presenting
the optic signal to an optic signal conductor; passing the optic
signal through the optic signal conductor to one or more lenses,
the one or more lens including an index matched lens; directing the
optic signal into a fisheye lens, the fisheye lens changing the
path of the optic signal to thereby project the optic signal onto a
position on the curved surface; initiating movement of the curved
surface; receiving a reflection of the optic signal at the fisheye
lens as part of velocimetry measurement of the curved surface, the
reflection being reflected from the curved surface; passing the
reflection through the one or more lenses to the optic signal
conductor.
18. The method of claim 17 wherein the optic signal conductor is a
single mode fiber optic cable.
19. The method of claim 17 wherein the reflection proceeds along
the same path through the fisheye lens, the one or more lenses, and
the optic signal conductor as the optic signal.
20. The method of claim 17 wherein projecting the optic signal onto
a position on the curved surface includes projecting the optic
signal to multiple locations on the curved surface and receiving a
reflection includes receiving multiple reflections from the curved
surface.
Description
FIELD OF THE INVENTION
[0002] This invention relates to photonic Doppler velocimetry and
in particular to a method and apparatus for multipoint photonic
Doppler velocimetry using optical lens elements.
RELATED ART
[0003] Photonic Doppler velocimetry (PDV) can be used to monitor
movement of a curved surface that is moving along multiple points,
such as during an experiment. The movement of the curved surface
may occur due to an implosion, explosion, or any other force or
factor that causes movement of the surface. Such movement often
occurs during dynamic material experiments. These dynamic material
experiments frequently involve complicated geometries and therefore
large numbers of data points are a distinct advantage. Various
solutions have been proposed to record the movement of the surface,
but each of these various solutions suffer from various
drawbacks.
[0004] One proposed prior art solution for measurement of the
moving curved surface is the use of electrical shorting pins. In
such a configuration, electrical shorting pins of various lengths
were used to contact the moving service. An electrical pin provides
a shorting signal between the surface and the pin tip when the tip
of the pin comes into contact with the moving surface. Each
electrical shorting pin gives a single timing point when the
collapsing surface contracts the pin. Each length of a pin records
one distance, so that many different lengths of pins are needed to
follow the movement of an imploding surface. However, longer pins
can interfere with the surface movement and interfere with the
shorter pins. As a result, data may be corrupted by the
interference. In addition, data is only collected by a pin when
that pin contacts the moving surface. Movement prior to contact
with the pin is not recorded. Moreover, a dense array of pins at
many lengths is needed and this density may not be possible to
achieve while also achieving desired data recordation.
[0005] Several different optical designs have been proposed to
measure the behavior of the moving surface. One such proposed
solution involved a ball shaped housing with discrete fibers
pointed outward toward the surface of interest. This solution
provided optic monitoring but it suffered from being size limited.
As the number of optic fiber points is increased, this probe
eventually comes to its limit in how small the entire group can be
made, while still having reasonable optical fiber bending radii.
The bend radius of the optic fibers limit size reductions in the
probe and there is a limit to the number of fibers which may be
packed in the probe.
[0006] Therefore, there is a need in the art for an accurate and
cost effective light delivery and collection system for use as a
collection probe in a PDV system.
SUMMARY
[0007] A new fisheye lens design is disclosed for use in probe
(which may be any size or miniaturized) to measure the velocity
distribution of a moving surface along many lines of sight. An
optic signal is directed to the surface using a launching fiber and
a fisheye lens. The optic signal may be laser light. The optic
signal is scattered back along each beam projected on the surface
and is Doppler shifted by the moving surface before being collected
into the launching fiber. The received light is mixed with
reference laser light in each optical fiber, in a technique called
photonic Doppler velocimetry, providing a continuous time
record.
[0008] An array of single-mode optical fibers sends laser light
through the fisheye lens toward the surface. In one embodiment, the
lens consists of an index-matching positive element, two positive
doublet groups, and two negative singlet elements. The optical
design minimizes beam diameters, physical size, and back
reflections for excellent signal collection. The fiber array
projected through the fisheye lens provides many measurement points
of surface coverage over a hemisphere with very little crosstalk.
The probe measures surface movement with only a small encroachment
into the center of the cavity.
[0009] The fiber array is coupled to the index-matching element
using index-matching gel. The array is bonded and sealed into a
blast tube for ease of assembly and focusing. This configuration
also allows the fiber array to be flat polished at a common object
plane. In areas where increased measurement point density is
desired, the fibers can be close packed. To further increase
surface density coverage, smaller diameter cladding optical fibers
may be used.
[0010] Disclosed herein is a photonic Doppler velocimetry probe
comprising a housing defining an interior space between a first end
and a second end. One or more optic signal conductors enter the
housing through the second end. The optic signal conductors
terminate within the interior space of the housing. The one or more
optic signal conductors provide one or more optic signals to one or
more lenses in the probe. A ferrule, located within the housing, is
configured with one or more passages such that the passages receive
and secure the one or more optic signal conductors to the ferrule.
An index-matching lens is adjacent the ferrule and configured with
a flat surface adjacent the ferrule to receive the optic signal.
The index-matching lens has an index of refraction selected to
match an index of refraction of the optic signal conductors. Also
part of this embodiment is a fish eye lens, mounted at the first
end, configured to receive the optic signal and project the optic
signal outward, in a direction controlled by the configuration of
the fish eye lens.
[0011] In one embodiment, the one or more optic signal conductors
are optic fibers. The optic fibers may be single mode optic fibers.
It is contemplated that the terminating end of the one or more
optic fibers and a side of the ferrule are end-polished. The probe
may further comprise an index-matching material between the
index-matching lens and the ferrule such that the index-matching
material consists of index-matching gel or index-matching epoxy.
The optic signal may be at 1550 nm wavelength. The probe may also
include one or more additional lens elements between the
index-matching element and the fisheye lens. In one embodiment, the
fisheye lens, index-matching lens, and the optic signal conductors
are configured to receive a reflection of the optic signal and
conduct the reflection back through the optic signal conductor.
[0012] The photonic Doppler velocimetry probe may be configured as
a housing defining an interior space and one or more optic signal
conductors having a terminating end configured to provide optic
signals near or within the housing. The optic signal conductors may
be fiber optic cables. Also part of this embodiment is an
index-matching lens, located in the interior space, configured to
receive the optic signals. The index-matching lens may have an
index of refraction selected to match an index of refraction of the
one or more optic signal conductors. A fisheye lens is provided and
configured to receive the optic signals after the optic signals
pass through the index-matching lens. The fisheye lens projects the
optic signal outward, in a direction controlled by the
configuration of the fish eye lens onto a curved surface that is
the subject of photonic Doppler velocimetry measurement.
[0013] In one configuration optic signal conductors are optic
fibers, which may be single mode optic fibers. The optic signal
conductors may be secured by a disk having one or more passages.
The optic signal conductors may pass through the passages and be
end-polished flat with a side of the disk faxing the index-matching
lens. In one embodiment, the probe further comprises an
index-matching gel material between the index-matching lens and the
one or more optic signal conductors. There may be one or more
additional lens elements between the index-matching element and the
fisheye lens. In one configuration, the fisheye lens, the
index-matching lens and the optic signal conductors are configured
to receive a reflection of the optic signal and conduct the
reflection back through the optic signal conductor to measurement
equipment.
[0014] Also disclosed is a method for use during photonic Doppler
velocimetry, for presenting an optic signal to a curved surface and
receiving a reflection from the curved surface during movement of
the curved surface. This method includes establishing a distal end
of a probe facing the curved surface such that the distal end of
the probe includes a fisheye lens facing the curved surface. Then,
generating an optic signal and presenting the optic signal to an
optic signal conductor. This method then passes the optic signal
through the optic signal conductor to one or more lenses. The one
or more lens includes an index matched lens. This method directs
the optic signal into a fisheye lens such that the fisheye lens
changes the path of the optic signal to thereby project the optic
signal onto a position on the curved surface. At this stage,
movement of the curved surface is initiated and the fisheye lens
receives a reflection of the optic signal. The reflection passes
through the lenses to the optic signal conductor.
[0015] In one embodiment, the optic signal conductor is a single
mode fiber optic cable. It is contemplated that the reflection will
proceed along the same path through the fisheye lens, through the
one or more lenses, and into the optic signal conductor as the
optic signal. The step of projecting may comprise projecting the
optic signal onto a position on the curved surface.
[0016] Other systems, methods, features and advantages of the
invention will be or will become apparent to one with skill in the
art upon examination of the following figures and detailed
description. It is intended that all such additional systems,
methods, features and advantages be included within this
description, be within the scope of the invention, and be protected
by the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The components in the figures are not necessarily to scale,
emphasis instead being placed upon illustrating the principles of
the invention. In the figures, like reference numerals designate
corresponding parts throughout the different views.
[0018] FIG. 1 illustrates a side view of an exemplary environment
of use of the probe disclosed herein.
[0019] FIG. 2 illustrates a perspective view of the probe assembly
104 and the interior surface.
[0020] FIG. 3A is a cut away side view of the probe assembly.
[0021] FIG. 3B illustrates a perspective view of the probe assembly
shown in FIG. 3A.
[0022] FIG. 4 illustrates a detailed view of a ferrule as shown in
element in FIG. 3A.
[0023] FIG. 5 illustrates an enlarged view of the junction between
the index-matching lens and the ferrule.
[0024] FIG. 6 illustrates an example passage layout within the
ferrule.
[0025] FIG. 7 illustrates on exemplary lens arrangement with
resulting ray traces through the lenses.
[0026] FIG. 8 illustrates an example arrangement of an alternative
lens arrangement with resulting ray traces.
[0027] FIG. 9 illustrates a plot of distortion improvement realized
in the embodiment of FIG. 8 over the embodiment of FIG. 7.
DETAILED DESCRIPTION
[0028] Photonic Doppler velocimetry (PDV) with a novel light signal
path is utilized to measure movement of a curved surface. PDV uses
light scattered and reflected from a moving surface to continuously
measure the movement of that surface. This method takes advantages
of the Doppler principles. Namely, the Doppler-shifted light from
the moving surface is compared to unshifted light to create fringes
in a Michelson interferometer made up of fiber-optic components.
Then, a fiber-optic circulator is used as the beam splitter of the
interferometer. Reference (unshifted) light is provided through
mixing with an external reference laser source or from back
reflections in the probe itself. Surface velocities of between a
few millimeters per second up to 14 km/s have been measured and it
is expected that further development will allow operation at higher
velocities. A PDV probe lens or bare fiber can both transmit and
receive the laser light. In the embodiment disclosed herein a 1550
nm telecommunications wavelength, continuous-wave (CW) fiber laser
is used with matching fiber, fiber related devices, optic
detectors, and signal digitizers.
[0029] As discussed above, drawbacks exist in the prior art with
the probe that is used to present the light signal to the moving
surface and collect the light signal from the moving surface. The
probe structure and associated light path disclosed herein
overcomes those drawbacks. FIG. 1 illustrates a side view of an
exemplary environment of use of the probe disclosed herein. This is
but one possible environment of use and as such it is contemplated
that other uses for the disclosed system may be arrived at by one
of ordinary skill in the art.
[0030] As shown in FIG. 1, the probe assembly 104 is provided in
the interior space 108 that is bounded by a curved interior surface
112 of a structure 116. The structure 116 is surrounded on an
exterior surface 120 by a material 124. The material 124 may
comprise any material that exerts a force on the surface 120 to
thereby move the material 116 inward toward the probe assembly 104.
In one embodiment, the material 124 comprises an explosive material
that when detonated, implodes the interior surface 112 inward
toward the probe assembly 104.
[0031] In other embodiments, it is contemplated that a material 124
other than explosives may be utilized such as, but not limited to
heat, air pressure, liquid pressure, radiation, or any other type
of force. The material 116 may comprise any type material or
barrier. The interior area 108 may comprise any type material or
void including but not limited to, a vacuum, air or other gas, or
even other material, such as gel or liquid, or a solid compressible
material.
[0032] It is also contemplated that the interior surface 112 may
move outward, away from the probe assembly 104 instead of inward
toward the probe assembly. In other embodiments, the surface may
move in a non-uniform manner with a first portion of the surface
116 moving toward the probe assembly 104 and a second part of the
surface moving away from the probe assembly.
[0033] On the exterior of the probe assembly 104 is an exterior
lens 130 which rests in a support 134. Below the exterior lens 130
are one or more lens, discussed below in greater detail, which are
contained in a housing 138. In one embodiment, the exterior lens is
a fisheye lens. A fisheye lens provides an ability to image over a
very wide range of angles using optic signals which enter the lens
from a single direction, such as through a planar surface.
Likewise, reflections into the outer surface of a fisheye lens are
directed though a single plane on the interior side of the fisheye
lens. The `fisheye` term refers to simulating a large angular view.
In one configuration, this lens type produces a whole-sky or
whole-view image as a finite circle. Some fisheye lenses `see`
beyond 180 degrees with darkness beyond it lens limit. In general,
a fisheye lens is a wide angle lens that produces strong visual
distortion intended to create a wide panoramic or hemispherical
image. Fisheye lenses achieve extremely wide angles of view by
forgoing producing images with straight lines of perspective
(rectilinear images), opting instead for a special mapping (for
example: equisolid angle), which gives images a characteristic
convex non-rectilinear appearance. In various different embodiments
the term fisheye lens includes a circular fisheye lens, a full
frame fisheye lens, a zoom fisheye lens, a miniature fisheye lens,
or any other configuration.
[0034] FIG. 2 illustrates a perspective view of the probe assembly
104 and the interior surface 112. As compared to FIG. 1, similar
elements are identified with identical reference numbers. As shown,
the housing 138 of probe assembly extends near or into the interior
of the structure 116. The exterior lens is at the distal end of the
probe structure which faces the interior surface 112. The structure
116 has an interior surface 112 and an outer surface 120 which form
a dome or spherical shape. As discussed below in greater detail,
the exterior lens (not shown in FIG. 2) projects one or more optic
signals on the interior of the inner surface 112. These points of
projection are shown by reflection points 150. These projections
points 150 may be arranged at any point on the interior surface
subject to the monitoring preferences. As discussed below in
greater detail, the location of the reflection points is determined
by the location of the fiber optic cables and the lenses within the
housing 138. This is but one configuration for the surface 112.
[0035] Turning to FIG. 3A, a cut away side view of the probe
assembly 104 is shown. This is but one possible configuration for
the probe assembly and it is contemplated that one of ordinary
skill in the art, after reading this disclosure, may arrive at
different configurations which do not depart from the claims that
follow. In general, the probe assembly 104 includes an outer
housing 344 which defines an interior area as shown. While the
housing 344 may be of any shape, in this embodiment the housing is
cylindrical on its interior surface. As shown, at a distal end 302
of the housing 344 is an exterior lens mount 300 configured to hold
or otherwise support an exterior lens 304 which may comprise a
fisheye lens. Below the exterior lens 304 are one or more
additional lens and open spaces or voids. Although shown in a
particular configuration it is contemplated that other arrangements
of lens may be arrived at without departing from the scope of the
claims that follow. The lens arrangement is configured to convey
optic signals from the exterior lens 304 to the interior of the
housing 344. The lens disclosed herein may have one or more
coatings on the lens which contacts air or the void. These coatings
decrease optical reflection, dispersion, and scattering and thereby
increase optic signal transmission into and out of the lens.
Anti-reflection coatings for glass-to-air interfaces and the use of
a minimum of lens elements are important for the operation of the
external reference light.
[0036] In this example embodiment, opposing the exterior lens 304
is a plano-concave lens 308. Below the plano-concave lens 308 is a
space 312 and then a doublet lens 316. Below the doublet lens 316
is an aperture spacer 320 and then another doublet lens 324. Below
the doublet lens 324 is a space 328 and below the space 328 is an
index matched lens 340. These lenses operate in combination to
conduct light signals through the interior of the housing.
[0037] Below the index-matching lens 340 is a ferrule 332
configured as a cylindrical disk having a top surface and bottom
surface contained by an outer circumferential surface. The ferrule
may also be a disk, washer, plate or any other element configured
to function as disclosed herein. The ferrule 332 is discussed below
in greater detail in connection with FIGS. 4, 5, and 6. The top
surface is configured to fit flush with or nearly flush with a
bottom surface of the index-matching lens 340. Within the ferrule
332 are one or more cylindrical holes, referred to herein as
passages, which pass from the first side to the second side to form
a passage. Within the passages are optic signal conductors 350,
such as fiber optic cables, optic channels, vacuum, gas, lenses, or
any other medium capable of carrying an optic signal. The optic
signal conductors 350 have a first end which is adjacent the
index-matching lens 340 and second opposing end which interfaces or
connects to an optic signal generator and an optic signal detector
(not shown).
[0038] As an advantage of this configuration over prior art
devices, the optic fibers 350 are established and maintained in
linear alignment to the planar bottom surface of the index-matching
element 340. This alignment maximizes optic signal transmission. In
addition, by maintaining a generally linear configuration for the
optic fibers, unwanted bending of the optic fibers is avoided. This
allows use of thinner optic fibers and a high density of optic
fibers as compared to prior art configurations which in turn
increases measurement point density.
[0039] To maximize transmission of the optic signal between the
index matched lens 340 and the optic signal conductors 350, the
index matched lens is indexed matched to the optic signal
conductor. For example, if the optic signal conductor 304 is an
optic fiber then the material of the lens 340 is selected to have
the same index of refraction as the fiber optic cable. This
minimizes back reflections at the interface between optical fiber
ends and the index matched lens. This design may use an
index-matching, fused silica lens element in contact with the
fibers. The index-matching lens element performs the multiple
duties of keeping back reflections low, bending the light to be
telecentric out of and into the optical fibers from the rest of the
fisheye lens, and flattening the image plane. The index-matching
element and optical fiber array can also be adjusted as a unit for
fine focusing.
[0040] An index-matching gel may be utilized between the index
matched lens 340 and the optic signal conductors 350 to further
improve index-matching. Other substances may also be utilized at
the junction such as index-matching epoxy.
[0041] It is contemplated that the lens and ferrule are sized to
fit snuggly within the interior of the housing to maintain optical
and special alignment between elements. The interior of the housing
may also be lined or coated with a material to minimize reflection
or light scattering.
[0042] FIG. 3B illustrates a perspective view of the probe assembly
shown in FIG. 3A. As compared to FIG. 3A, common elements are
identified with identical reference numbers. As shown, probe
assembly 302 includes the housing 344 having a distal end 312. At
the distal end 312 is the exterior lens 304 configured as a fisheye
lens or any other lens shape capable of carrying two or more optic
signals out of the lens and receiving two or more reflections.
Supporting the exterior lens 304 is the lens mount 300.
[0043] FIG. 4 illustrates a detailed view of a ferrule as shown in
element 332 in FIG. 3A. This is but on possible configuration
provided for purposes of discussion. As shown, the ferrule 332
includes a top surface 404 on one or more cylindrical passages 408
between the top surface 404 and the opposing bottom surface (not
shown). Any number and arrangement of passages 408 may be
established in the ferrule 332. It is also contemplated that the
passages 408 may be of various different sizes and shapes as shown
to accommodate various different arrangements of optic signal
conductors 350 which reside within the passages 408.
[0044] In one embodiment, the optic fibers are spatially positioned
by being mounted into passages or holes in the optical fiber
ferrule 332. The optic fibers are bonded into the ferrule and then
the ferrule and optic fibers are polished together. To compensate
for imperfections in contact across the fiber ferrule,
index-matching gel is added for better coupling at the
fiber-to-lens surface. Commercial optical fiber ferrules for MT
connectors are made of glass-filled polyphenylene sulfide (PPS)
based thermoplastic. Other ferrule material may include PPS, Macor,
Vespel, Torlon and Photoveel II. Photoveel II performs well for the
micro-hole drilling used to spatially position our single-mode
optical fibers. It enables clean, burr-free holes at 125-micron
diameter. It also polishes well with the optical fibers. Flat
polishing is performed to ensure good coupling with the
index-matching element. Photoveel II is a fine-grain, machinable
nitride ceramic that is used in the probe card industry. The
arrangement of the passages 408 within the ferrule 332 is discussed
below in greater detail in connection with FIG. 6.
[0045] FIG. 5 illustrates an enlarged view of the junction between
the index-matching lens and the ferrule. As shown, the
index-matching lens 340 is adjacent the ferrule 332, both of which
are contained within the housing 344. The ferrule 332 has one or
more passages 408 through which an optic signal conductor 350, such
as a fiber optic cable, passes. The index-matching lens 340 has a
top surface that is opposite a bottom surface which defines the
junction or interface 516 between the index-matching lens 340 and
the ferrule 332. At this junction, the index-matching gel or
index-matching epoxy may be utilized to reduce refraction, back
reflection, and any other index of refraction mismatches. The ends
of the optic signal conductor 350 may be flat polished.
[0046] FIG. 6 illustrates an example passage layout within the
ferrule. This lay out also controls the position that the optic
signal impacts and exits the fisheye lens. Due to the optic
behavior of a fisheye lens, where the optic signal enters the
fisheye lens controls where the optics signal exists from the
fisheye lens, and consequently where the optic signal will strike
the interior surface under measurement. This is but one possible
layout arrangement for passages this layout may be modified based
on the optic system, the surface to be monitored as part of the PDV
process and the desired location of the reflection points on the
surface which is being monitored. Referring back to FIG. 2, the
reflection points 150 (FIG. 2) are controlled by the location of
the passages 408 in the ferrule 332 (and the optic system, which
control projection of the optic signals on to the inner surface 112
of FIG. 2).
[0047] In this example embodiment, the passages are defined by two
generally straight lines 604 of individual passages 408. In the
center of the ferrule is an offset linear opening 608 in which
numerous adjacent optic signal conductors may be placed as shown
within passages 408. Extending outward from the offset linear
opening 608 are groups of individual passages 612 and two large
openings 616 into which multiple optic signal conductors are
placed. The optic signal conductors may be grouped or packed into
the larger openings 616.
[0048] FIG. 7 illustrates one exemplary lens arrangement with
resulting ray traces through the lenses. This is but one possible
arrangement of lenses and it is contemplated that one of ordinary
skill in the art or those familiar with optics may arrive at
different lens arrangements. In this configuration, working from
the right hand side of the figure, the index-matching lens 340
receives optic signals from one or more optic signal conductors or
generators, such as optic fibers, lasers, optic channels, lenses,
or any other optic signal source.
[0049] A curved image plane is very inconvenient for mounting an
array of optical fibers. Just like the eyepiece lens and reflective
lens designs, the panoramic type lens also has the problem of
wrapping around near 90 degrees from the lens center axis as
angular coverage is increased. This design uses more elements to
image onto a flat plane.
[0050] However, off-axis field points for those designs come into
the image plane at a significant angle, as shown in FIG. 4. To get
maximum light signal coupled both out of and back into the optical
fibers, the optical fibers would have to be mounted at different
angles across the image plane. That would make fabrication and
assembly more time consuming. Therefore, preference for this design
was to make the image light telecentric so that off-axis field
points (or optical fibers) are normal to the image surface, such as
the index matched lens 430
[0051] In this embodiment, the index-matching lens 340 has a flat
surface 704 which receives the optic signal from the light
source(s). By making the surface 704 flat, maximum signal
transmission into the lens 340 may occur. This configuration also
provides the benefit of reducing the complexity of the interface
between optic fibers (not shown) and the flat surface 704 of the
lens 340. As a result, angled end polishing may be eliminated.
Index-matching gel (not shown) reduces any index mismatch between
optic fibers and the lens 340.
[0052] Opposing the index-matching lens is a first doublet lens
group 324. A focusing gap 708 is provided between lens 324 and lens
340. This focusing gap 708 may increase or decrease in length to
obtain optimal focus of the optic signal through the lenses onto
the inner surface shown in FIGS. 1 and 2.
[0053] Opposing the first doublet lens group 324 is a second
doublet lens group 316, and then a single lens element 308,
followed by the external lens element 304. In this embodiment, the
external lens element 304 is a fisheye lens. Use of a fisheye lens
provides the benefit of a single external lens element and an
ability to project optic signals onto all locations of the internal
surface of the object subject to movement measurement. For example,
light signal input at point 720A passes through the shown lens
elements to generate light output location 720B. The optic signal
projected by the lens 304 from point 720B is projected onto the
inner surface. Concurrently, with the single external lens element
and using the same lens arrangement, an optic signal reflection
from the inner surface is received by the fisheye lens 304 at point
720B and optically directed back into the same point 720A in the
index-matching lens 340. This reflection is conveyed into the same
optic signal conductor (fiber optic cable) which presented the
optic signal to the lens for processing.
[0054] Likewise, an optic signal presented by a fiber optic cable
to position 724A, which is at or near the edge of the
index-matching lens 340, is directed through the lenses 340, 324,
316, 308, 304 to point 724B. From point 724B, the optic signal is
projected onto the inner surface as shown in FIGS. 1 and 2. As can
be appreciated, although the optic signals are input into the flat
surface 704 at points 720A and 724B, which are only a small
distance away and in the same flat plane, the projection of these
optic signals occurs at vastly different angles from the lens 304.
By adjusting the location that the input signal is provided on the
surface 704 (see FIG. 6), the optic signal may thus be projected to
any location on the inner surface of the material that is having
its motion tracked due to the behavior of the fisheye lens.
[0055] FIG. 8 illustrates an example arrangement of an alternative
lens arrangement with resulting ray traces. The functionality of
the embodiment of FIG. 8 is generally similar to the functionality
of FIG. 7. As shown, an index-matching lens 804 receives the optic
signals. Opposing the index-matching element are one or more lens
808, 812, 816 followed by an external lens 820, such as a fisheye
lens.
[0056] As compared to the embodiment of FIG. 7, the angle 824 which
the optic signals are or can be projected from the external lens
820 is greater than the embodiment of FIG. 7. This provides the
benefit of greater coverage and capability to project the optic
signals beyond 180 degree range and likewise, receive reflections
from a greater area of the inner surface.
[0057] FIG. 9 illustrates a plot of distortion improvement realized
in the embodiment of FIG. 8 over the embodiment of FIG. 7. This
figure shows plots of the optic fiber position versus angular
position in a hemisphere. In this plot, the vertical axis 904
represents fiber R value in millimeters while the horizontal axis
908 represents angle, in degrees, of distortion. The distortion is
the difference between the linear fiber position and the model
fiber position. The plot shows how further optimization has
decreased the distortion in the improved design.
[0058] As shown, plot 920 represents current while plot 924
represents linear R for the lens arrangement of FIG. 7. The plots
920, 924 represent performance of the lens arrangement of FIG. 7.
Plot 930 represents improved current. Plot 934 represents linear R
for the improved lens arrangement of FIG. 8. The plots 930, 934
represent performance of the lens arrangement of FIG. 8. As can be
appreciated, significant improvements are realized by the improved
lens arrangement.
EXAMPLE EMBODIMENT
[0059] A series of live dynamic PDV tests within hemispherical
shells were fielded using a discrete collimator multipoint ball
probe, a multiple lens array probe, and a fisheye probe design
(described in the next section). All three gave high-quality data
during testing. The fisheye lens' performance stood out over prior
art probes in several ways.
[0060] First, the fisheye element does not encroach into the center
of the imploding hemisphere. This is important because
experimentalists ideally want the measurement to record data until
the shock wave impacts the probe. Therefore, the smaller the probe
the better it will record late-time information. Second, the
physical size of the waist near the center of the cavity is
smaller. This helps to fit the probe through a small opening for
blast mitigation. Third, angular coverage can be more complete.
Fourth, the fisheye probe is easier to assemble than prior art
multipoint probes.
[0061] During these tests to minimize costs, the PDV recording
system was implemented using components that were obtained from the
telecommunications industry. Components use light in the 1550 nm
band, including CW fiber lasers, amplifiers, detectors, optical
isolators, splitters, combiners, and optical fiber attenuators were
selected for use. Therefore, the fisheye lens for PDV was designed
for operation at the 1550 nm wavelength. Glass, such as lenses, for
high transmission in this wavelength region were chosen. Some
effort to reduce chromatic aberration and extend the band to
visible red light was also made, but was not emphasized.
Optimization
[0062] During optimization the lens was modeled by tracing from a
spherical surface through the lens to the fiber plane with all
field points weighted equally. This method optimized imaging at
1550 nm from the large to the small conjugate side. Analysis was
later performed with the lens model flipped to trace from the
fibers to the spherical surface. An example fisheye lens was used
as a starting point. Due to inherent fisheye lens barrel
distortion, magnification is not constant across the field.
Therefore, the numerical aperture of the outer field points was
larger than that of the center field points. To address this,
vignetting factors were employed so that the outer field points
would not make a light cone excessively large for a standard
single-mode optical fiber. As optimization progressed, and during
testing, adjustments were made to the vignetting factors of these
outer field points.
[0063] During optimization merit function weighting was high for
the 1550 nm wavelength. Weight was also entered to make each field
point normal to the image surface. A small weight was set to
minimize the incident angle of light on the first surface. Glasses
were initially allowed to vary, but were later fit to the model. A
short lens effective focal length helped for small beam diameter
channels and reduced physical size. A trade-off in the overall
magnification or size of the optical fiber plane versus
point-to-point resolution on the surface is made.
[0064] During assembly, the fiber ferrule and index-matching
element with index-matching gel are bonded together. Index-matching
epoxy did not yield as good of results as index-matching gel. After
the other lenses were glued into the housing, the index-matched
lens/fiber-array unit is moved to the proper distance for fine
focusing of the fiber beams using an infrared camera.
Fisheye Probe Improvements
[0065] Inherently, fisheye lens images are distorted. The
distortion manifests itself as pincushion distortion when going
from the optic fiber plane to the curved surface and as barrel
distortion when going from the curved surface to the optical fiber
plane. The points at higher angles in FIGS. 7 and 8 are spread out
more than those at lower angles. This change in magnification
versus field angle causes elliptical optical fiber spots on the
concave inner surface of FIG. 2 at high angles. It also manifests
itself as a loss of efficiency for PDV signals at the higher
angles. High incidence angles on lens elements at high angles may
also have less effective anti-reflection coatings.
[0066] It is contemplated that further work was done to improve the
fisheye lens probe's design performance. For example, global
optimizations with merit functions that emphasize telecentric light
at the optical fiber plane, good imaging, and minimizing
magnification differences across the image field were performed to
increase efficiency at the higher angles. Again, a small weight to
minimize the outer surface incident angle was set.
[0067] While various embodiments of the invention have been
described, it will be apparent to those of ordinary skill in the
art that many more embodiments and implementations are possible
that are within the scope of this invention. In addition, the
various features, elements, and embodiments described herein may be
claimed or combined in any combination or arrangement.
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