U.S. patent number 5,881,195 [Application Number 08/725,780] was granted by the patent office on 1999-03-09 for image guide comprising a plurality of gradient-index optical fibers.
This patent grant is currently assigned to Nanoptics, Inc.. Invention is credited to James K. Walker.
United States Patent |
5,881,195 |
Walker |
March 9, 1999 |
**Please see images for:
( Certificate of Correction ) ** |
Image guide comprising a plurality of gradient-index optical
fibers
Abstract
The present invention is an image guide which has applications
in such areas as endoscopy and industrial imaging. This invention
utilizes gradient-index optical fiber in order to produce an image
guide with improved performance characteristics. These improved
performance characteristics include increased brightness, enhanced
resolution, greater flexibility, and smaller diameter. The smaller
diameter of the image guide permits access through smaller
apertures in order to image inaccessible locations.
Inventors: |
Walker; James K. (Gainesville,
FL) |
Assignee: |
Nanoptics, Inc. (Gainesville,
FL)
|
Family
ID: |
27108909 |
Appl.
No.: |
08/725,780 |
Filed: |
October 4, 1996 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
712919 |
Sep 12, 1996 |
|
|
|
|
Current U.S.
Class: |
385/116 |
Current CPC
Class: |
G02B
23/26 (20130101); G02B 6/06 (20130101); G02B
6/02038 (20130101); G02B 6/03633 (20130101) |
Current International
Class: |
G02B
6/02 (20060101); G02B 23/26 (20060101); G02B
6/028 (20060101); G02B 6/06 (20060101); G02B
006/06 () |
Field of
Search: |
;385/115,118,147,33 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0265074 |
|
Apr 1988 |
|
EP |
|
0427232 |
|
May 1991 |
|
EP |
|
0710855 |
|
May 1996 |
|
EP |
|
9115793 |
|
Oct 1991 |
|
WO |
|
Other References
Greengrass, S.M. and M. Cunningham (1993) "Endoscopy" Measurement +
Control 26(4): 109-114. .
Tsumanuma et al. (1988) "Ultra Thin Silica Based Imagefiber For The
Medical Usage" Proc. of SPIE (Jan. 13-16, 1988, Los Angeles, CA,
USA), Optical Fibers in Medicine III 906:9296. .
"Borescope Aids Welding in Confined Spaces" (1990)NTIS Tech Notes,
Springfield, VA, US. .
Emslie, Christopher (1988) "Review Polymer Optical Fibers" Journal
of Materials Science 23:2281-2293. .
Epstein, Max (1982) "Fiber Optics in Medicine" In: CRC Critical
Reviews in Biomedical Engineering 7(2):79-120..
|
Primary Examiner: Ullah; Akm E.
Attorney, Agent or Firm: Saliwanchik, Lloyd &
Saliwanchik
Parent Case Text
CROSS-REFERENCE TO A RELATED APPLICATION
This application is a continuation-in-part of co-pending
application Ser. No. 08/712,919, filed Sept. 12, 1996 now
abandoned.
Claims
I claim:
1. An image guide, comprising a plurality of gradient-index optical
fibers, wherein when an input image is incident on a first end of
said image guide, each of said plurality of gradient-index optical
fibers transmits an amount of light from the first end of said each
fiber to a second end of said each fiber, such that a plurality of
amounts of light are transmitted from the first end of the image
guide to the second end of the image guide, and wherein an output
image is formed at the second end of the image guide by the
plurality of amounts of light output at the second ends of the
plurality of gradient-index optical fibers, such that each output
amount of light is one pixel of the output image.
2. The image guide, according to claim 1, comprising glass optical
fibers.
3. The image guide, according to claim 1, comprising plastic
optical fibers.
4. The image guide, according to claim 3, wherein said
gradient-index plastic optical fibers comprise at least two
miscible polymers with different indices of refraction.
5. The image guide, according to claim 4, wherein said miscible
polymers are selected from the following group: methacrylate family
and acrylate family.
6. The image guide, according to claim 3, wherein said
gradient-index plastic optical fibers comprise a copolymer wherein
the ratio of monomer subunits varies as a function of radius.
7. The image guide, according to claim 3, wherein said
gradient-index plastic optical fibers comprise a polymer with low
molecular weight additives, wherein the concentration of the low
molecular weight additives varies in the radial direction.
8. The image guide, according to claim 1, wherein said image guide
is a fiber optic taper.
9. The image guide, according to claim 1, wherein said image guide
is a fiber optic plate.
10. An imaging scope comprising an image guide, wherein said image
guide comprises a plurality of gradient-index optical fibers,
wherein when an input image is incident on a first end of said
image guide, each of said plurality of gradient-index optical
fibers transmits an amount of light from the first end of said each
fiber to a second end of said each fiber, such that a plurality of
amounts of light are transmitted from the first end of the image
guide to the second end of the image guide, and wherein an output
image is formed at the second end of the image guide by the
plurality of amounts of light output at the second ends of the
plurality of gradient-index optical fibers, such that each output
amount of light is one pixel of the output image.
11. The imaging scope, according to claim 10, wherein said imaging
scope is an endoscope.
12. The imaging scope, according to claim 10, further comprising a
sheath within which said imaging scope is inserted during use.
13. The endoscope, according to claim 11, said endoscope
comprising:
(a) a means for mechanically guiding said endoscope into and within
a body;
(b) a means for angulating the distal tip; and
(c) a means for illuminating an obect to be imaged within the body,
wherein said apparatus has a minimum radius of curvature less than
about 8.0 mm.
14. The imaging scope, according to claim 10, wherein said imaging
scope is an angioscope.
15. The imaging scope, according to claim 10, wherein said imaging
scope is a borescope.
16. The imaging scope, according to claim 10, wherein said imaging
scope is an industrial imaging scope.
17. The image guide, according to claim 1, wherein the spatial
relationship of the fibers comprising the first and second ends of
the image guide are coherently related to each other.
18. The image guide, according to claim 1, wherein each of said
plurality of gradient-index optical fibers have a diameter between
about 1 .mu.m and about 30 m.
19. The image guide, according to claim 1, wherein essentially all
of said plurality of gradient-index optical fibers have
approximately the same length.
20. The image guide, according to claim 1, wherein essentially the
entire cross-sectional area of each of said plurality of
gradient-index optical fibers is available to transmit light.
21. The image guide, according to claim 5, wherein at least one
miscible polymer is fluorinateed.
22. The image guide, according to claim 5, wherein at least one
miscible polymer is chlorinated.
23. The image guide, according to claim 1, wherein said plurality
of gradient-index optical fibers have an index profile which can be
represented as n(r)=n.sub.1 [1-2.DELTA.f(r)].sup.1/2 for r.ltoreq.a
where f(0)=0, f(a)=1, a is the radius of the core and ##EQU5##
24. The image guide, according to claim 23, wherein ##EQU6## where
g is a profile parameter.
25. The image guide, according to claim 24, wherein g=2 such that
the index of refraction profile is parabolic.
Description
BACKGROUND OF THE INVENTION
Image guides are bundles of optical fibers which convey optical
images. Because each optical fiber of an image guide transmits only
a minute discrete portion of the image, it is of course necessary
for each end of the image guide to be coherently related to the
other end such that the image exiting the image guide is identical
to that which enters the multiplicity of fibers. Image guides are
used in a variety of industrial and medical imaging scopes. For
example, endoscopes utilize image guides to convey images of human
and/or animal vessels and internal cavities. Additionally, image
guides are also used in industrial borescopes used for many types
of industrial imaging.
Image quality is critical to the performance of image guides.
Specifically, resolution, brightness, and contrast sensitivity are
a few important performance characteristics which affect image
quality. Resolution can be expressed as the measure of the image
guide's ability to separate images of two neighboring object
points. Improved image resolution can be obtained by having a
larger number of optical fibers, in the bundle, per unit area. The
brightness of an image guide is a measure of the ratio of the
amount of light exiting the output end of the image guide to the
amount of light incident to the input end of the image guide. The
brightness of an image guide can be improved by, for example,
increasing the portion of the image guide end available for light
transmission, increasing the numerical aperture (NA), and/or
decreasing the transmission loss of the image guide. The contrast
sensitivity is a measure of the ratio of the amount of light,
comprising the image, exiting the output end of the image guide to
the total amount light exiting the output end of the image guide.
The light exiting the output end of the image guide, and not
contributing to the image, reduces the contrast sensitivity.
Depending upon the intended use of the image guide, other
characteristics such as flexibility may also be important. For
example, it is often advantageous for image guides to have great
flexibility to reach otherwise inaccessible locations such as
coronary vessels. In other applications, such as laparoscopy, a
more rigid image guide is preferred. The subject invention
concerns, in one aspect, improved image guides which result in
endoscopes and borescopes with highly advantageous
characteristics.
One specific embodiment of the subject invention is the use of
improved image guides in angioscopes. Angioscopy is a specific type
of endoscopy which uses a flexible angioscope to transmit images
from the heart and the coronary tree. Angioscopes are valuable
tools for use in the investigation and treatment of heart and
vascular disease. In various studies, atheromatous plaque rupture
and splitting, endothelial exfoliation, and thin mural thrombi that
could not be detected by angiography were able to be detected by
angioscopy (Ushida, Y. et al. [1989] Am. Heart Jourmal
117(4):769-776). Unfortunately, angioscopes, which are typically
between 1.0 and 1.5 mm in diameter, are not small enough to access
the entire coronary tree.
The image guide of existing angioscopes typically has a diameter of
about 0.27 mm and is surrounded by fibers arranged
circumferentially to provide uniform illumination of the inner
lumen. FIG. 1 is a schematic structure of an angiofiberscope image
guide. An angioscope image guide is typically a hexagonal array of
about 2000 fibers of the step index type. A step index (SI) optical
fiber is one in which a fiber is composed of a core surrounded by a
cladding where the refractive indices of the core and cladding are
n.sub.1 and n.sub.2 respectively, where n.sub.1 >n.sub.2.
Typically, this SI optical fiber is glass but, as discussed below,
SI polymer optical fiber is also known. Light at less than the
critical angle, which is transmitted down the core experiences
internal reflection with very high efficiency at the core/cladding
interface. Although the light reflects efficiently at the boundary,
a small fraction of the light temporarily penetrates the cladding
in the form of evanescent waves before returning to the core. If
the cladding is not thick enough, these evanescent waves can pass
through the cladding causing some of this light to leak out, or
tunnel, through the cladding into the adjacent fiber. This causes a
reduction in resolution and a reduction in contrast sensitivity. If
the core diameter is reduced, at fixed cladding thickness, less
light is transmitted and the image loses brightness. On the other
hand, if the cladding thickness is reduced, for a fixed core
diameter, more leakage, or tunneling, occurs. Hence, there is an
optimum fiber core diameter and cladding thickness. This
optimization process has been studied experimentally (Tsumanuma, T.
et al. [1988] Proc. SPIE 906:92-96). Tsumanuma et al. determined
that a core diameter of 3 .mu.m and cladding thickness of 1 .mu.m
was optimal.
With a core diameter of 3 .mu.m and a cladding thickness of 1
.mu.m, only 36% of the light which hits the end of the step-index
glass fiber image guide actually strikes the area defined by the
cores of the microfibers. Most of the available light is lost on
the cladding area. Since it is only light striking the core area
which can contribute to image brightness, only a marginal reduction
in microfiber diameter can be made without significant brightness
reduction.
The resolution of an image guide is dependent on the number of
microfibers per unit cross-sectional area. For example, existing
angioscope image guides cannot be increased significantly in
diameter to incorporate more microfibers, due to the dimensions of
the vascular system, and the diameter of the presently employed
microfibers cannot be reduced in size without significant
brightness reduction. Therefore, it is difficult to improve the
resolution of existing angioscopes.
Another important characteristic of flexible image guides is
flexibility as measured by the minimum bend radius of the image
guide. The flexibility of existing angioscopes is typically limited
by the stiffness of the image guide. For example, the typical
minimum bend radius is about 8 mm, which makes procedures difficult
in some regions of the coronary tree. This degree of flexibility
has been achieved by acid leaching of the image guide to divide it
into several separate units, except for its ends where the
nicrofiber spatial coherence is mandatory. Further subdivision of
the glass image guide would increase flexibility, but at the
expense of rapidly increasing the fragility of the microfibers.
There is already a fairly rapid deterioration of image quality due
to microfiber breakage which shows up as black spots on the image.
In addition, coloration of the transmitted image of glass
endoscopes has been observed (Tsumanurna et al, supra) when the
endoscope is subjected to severe bending as occurs in angioscopy.
This can cause loss of spectroscopic information in angioscopic
clinical diagnosis due to wavelength dependent light leakage from
the fiber cores.
Many image guides are made with step index glass optical fiber.
Polymer optical fiber fabricated with a step index (SI) of
refraction is also known to those in this art. A cross section of
such an SI fiber is shown in FIG. 2. Both polymer and glass SI
fibers are constructed with a core and cladding with refractive
indices n.sub.1 and n.sub.2 respectively, where n.sub.1
>n.sub.2. A second type of fiber is known as gradient-index or
graded-index (GRIN) fiber can also be made with polymer or glass.
The GRIN structure is also shown in FIG. 4.
In comparing the SI structure with the GRIN structure, it is noted
that there are different trajectories of light rays in these two
fiber structures. This is shown schematically in FIG. 5. Within SI
fiber, the light travels in straight lines. At angles less than the
critical angle of internal reflection, the light is reflected at
the core cladding interface. At angles greater than the critical
angle, the light is refracted into the cladding from which it
travels into the adjacent fiber in the SI image guide. This large
angle light traverses the various fibers in the image guide until
it reaches the side of the image guide and is absorbed. In
contrast, within GRIN fiber, the light travels in a curved
trajectory, always being refracted back towards the axis of the
fiber. At angles less than the critical angle, light never reaches
the outer edge of the fiber. At angles greater than the critical
angle, the light exits the fiber similar to the case of the SI
image guide.
BRIEF SUMMARY OF THE INVENTION
The subject invention pertains to image guides having highly
advantageous optical and physical characteristics. The excellent
characteristics of the image guides of the subject invention result
from the use of gradient-index (GRIN) optical fiber. A further
aspect of the subject invention concerns novel manufacturing
processes used to produce image guides.
The image guides of the subject invention are highly advantageous
because of their small diameter, greater flexibility, and excellent
image quality. These image guides are useful in a wide variety of
industrial and medical applications. Specifically exemplified
herein are endoscopes for use in medical diagnostic procedures such
as angioscopy. Also exemplified are borescopes for use in
industrial imaging. In general, the image guides of the subject
invention can be used in virtually any imaging scope used to
examine locations which are inaccessible to the human eye. Such
scopes may be used to visualize locations ranging from blood
vessels to jet engine blades or high pressure pipes. Such scopes
are also used in non-destructive testing procedures.
The image guides of the subject invention achieve substantial
improvements in performance compared to existing image guides.
Specific advantages that can be achieved utilizing the subject
invention include: (1) a brighter image; (2) improved resolution;
(3) a smaller diameter so as to be able to pass through narrower
openings; (4) greater flexibility; and (5) less expense. By
adjusting the dimensions and materials of the image guides of the
subject invention, these performance characteristics can be
optimized for a particular application. The image guides of the
subject invention are particularly advantageous for applications
which necessitate the use of a guide having a very small diameter
or an image guide which requires a very high resolution for a fixed
diameter.
In a specific embodiment, the subject invention pertains to an
approximately 0.5 mm diameter angiofiberscope with enhanced
flexibility and improved image quality. In the specific application
of angioscopy, the subject invention provides access to essentially
100% of the vascular tree with unprecedented image quality.
Scopes of a variety of sizes can be manufactured with this new
technology. In one embodiment, these scopes can be plug-in
compatible with the already-installed base of electronic cameras,
illumination systems, and monitors. In addition to the small
diameter endoscope for angioscopy, the subject invention can also
be utilized for other applications in medical endoscopy and
industrial imaging.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a schematic structure of an angiofiberscope image
guide.
FIG. 1B is an enlarged view of a cross-section of the image fiber
which shows the pixel arrangement of the fibers.
FIG. 2 shows the structures of the two basic types of optical
fibers.
FIG. 3 shows the trajectories of typical light rays in SI and GRIN
fibers.
FIG. 4 shows brightness of state of the art glass image guide
versus a GRIN guide with the same size microfibers (5.0 .mu.m).
FIG. 5 illustrates, schematically, a specific embodiment of the
subject method for continuous production of GRIN fibers made by
using two miscible optical polymers with different refractive
indices whose relative concentrations vary radially to produce the
required refractive index profile.
FIG. 6A and 6B are is a schematic of the GRIN die block (GDB).
FIG. 7 is a schematic of the flow pattern in the feed chamber.
FIGS. 8A and 8D illustrate a longitudinal cross section and a
transverse cross section, respectively, of the distal end of a
sheath designed to fit over a plastic optical fiber image
guide.
FIGS. 8B and 8E illustrate a longitudinal cross section and a
transverse cross section, respectively, of the distal end of a
sheath designed to fit over a plastic optical fiber image guide,
wherein the sheath comprises an illumination fiber.
FIGS. 8C and 8F illustrate a longitudinal cross section and a
transverse cross section, respectively, of the distal end of a
sheath designed to fit over a guiding means incorporated with a
plastic optical fiber image guide, wherein the sheath comprises an
illumination fiber.
DETAILED DISCLOSURE OF THE INVENTION
The subject invention utilizes gradient-index (GRIN) optical fiber
to produce image guides for use in angioscopes, endoscopes,
borescopes, and other imaging scopes. The subject invention
achieves substantial improvements in performance compared to
existing image guides, including: (1) a brighter image; (2)
improved resolution; (3) a smaller diameter to pass through
narrower openings; (4) greater flexibility; and (5) less expense.
By adjusting the dimensions and materials of the image guides
utilizing the teachings of the subject invention, these
characteristics can be optimized, to facilitate the use of the
image guides for a wide variety of applications. Thus, the image
guides of the subject invention can be used in medical endoscopy as
well as in industrial imaging. With respect to medical endoscopy,
the subject endoscope can be utilized to image internal body
structures, for example vessels, internal cavities, and lumens. In
a specific embodiment, the subject invention utilizes GRIN plastic
optical fiber (POF), to make a major advance in angioscopy. The
subject invention further pertains to new manufacturing processes
useful in the production of the improved image guides described
herein.
The refractive index of a GRIN optical fiber can be generally
represented by the axi-symmetric index profile
where f(0)=0, f(a)=1, a is the radius of the core, and ##EQU1## In
a specific embodiment, ##EQU2## where g is the profile parameter
which, for g=2, yields a parabolic profile.
There are substantial advantages of the GRIN imaging guide of the
subject invention compared to the SI image guide. One of the
advantages pertains to the brightness of the images which can be
obtained. The brightness, B, of the image transmitted by a guide is
defined by the equation: ##EQU3## where S is the ratio of the total
cross-sectional area of the cores of SI fibers (or the total
cross-sectional area of GRIN fibers) to the total cross-sectional
area of the image guide. NA is the numerical aperture of the
fibers, defined ##EQU4## where NA.sub.SI and NA.sub.GRIN are the
numerical apertures for SI and GRIN optical fiber,
respectively.
The light attenuation .alpha., is given in units of dB/meter, and L
is the length of the image guide in units of meters. The
approximate values of these parameters for 5 .mu.m outer diameter
fibers are given in Table 1.
TABLE 1 ______________________________________ Values of parameters
describing optimized SI angioscope image guide, and the GRIN guide
Image guide S NA .alpha. (dB/m)
______________________________________ SI (glass) 0.36 0.43 1.0
GRIN (plastic) 1.0 0.46 0.2
______________________________________
Because the GRIN fiber has no cladding, 100% of the GRIN image
guide cross-sectioned surface area is available to transmit light
compared to 36% for the optimized SI glass image guide. The
numerical aperture of the two types of optical fiber are
comparable. In the case of glass (Tsumanuma et a., supra), the high
value of NA=0.43 is achieved by appropriate ionic doping at the
expense of deteriorating the transmission to a value of .alpha.=1.0
dB/m. A 5.0 .mu.m diameter GRIN-POF has been measured (Koike, Y. et
al. [1993] In Design Manual and Handbook and Buyers Guide,
Information Gatekeepers, Inc., Boston, p.19) to have an attenuation
of 0.2 dB/m. There are at least three ways to produce GRIN-POF,
namely, using two or more miscible polymers, using a copolymer with
monomer subunits, or by doping a polymer with a low molecular
weight additive. For GRIN-POF, a value of NA =0.46 can be achieved
with available polymers by making the GRIN-POF by using two or more
miscible polymers with different refractive indices. The relative
concentrations of the two or more miscible polymers vary radially
to produce the required GRIN profile. Alternatively, a copolymer
can be used in which the ratio of monomer subunits change as a
function of radius in a manner such as to produce the required GRIN
profile. Most available GRIN-POF, which is produced by radial
dependently doping a given polymer with a low molecular weight
additive, has NA in the range 0.1 to 0.22. This NA is adequate for
the 100 m lengths used in digital transmission for local area
networks. By changing the ratio of the polymer components in the
fiber, instead of doping with an additive, the NA can be increased
to 0.46 or more.
The brightness, B, of the transmitted image has been evaluated
using the parameters given in Table 1, and is plotted in FIG. 4. It
can be seen that the GRIN-POF image guide is about twice as bright
as the existing state of the art SI glass optical fiber (GOF) image
guides. We shall assume that the working length of the angioscope
is about 1.3 m, and the total length is 3.3 m.
The resolution of an image guide can be improved if a larger number
of microfibers is used per unit area. An image guide made of
GRIN-POF has 100% of the cross-sectional area of each fiber end
available to transmit light. For fundamental physical reasons, the
diameter of an optical fiber can only be reduced to about 1.0 .mu.m
without losing the ability to transmit light. Therefore, there is
much potential improvement in resolution from the existing state of
the art of a 5 .mu.m microfiber diameter down to the fundamental
limit of 1.0 .mu.m.
Thus, while the brightness of the GRIN-POF guide is about double
that of the SI-GOF guide, the improvement in resolution using the
GRIN-POF guide is up to a factor of five. These improvements in
image quality are substantial and demonstrate the advantages of the
GRIN-POF technology of the subject invention.
The flexibility of glass guides is limited to about 8 mm minimum
bending radius. This is not adequate for some branches of the
coronary tree. In addition, coloration of the transmitted image of
glass endoscopes has been observed (Tsumanuma et al., supra) when
an endoscope is subjected to severe bending as occurs in
angioscopy. The endoscopes of the subject invention can have a
factor of about five or more greater flexibility, which can provide
important advantages particularly in angioscopic applications. If
flexibility is not an important criterion in a specific
application, then a glass image guide made of GRIN fiber can be
used and would offer higher resolution than the existing glass
image guides made of SI fibers.
The enhanced flexibility of the subject plastic GRIN fibers is due
to the mechanical properties of polymers, which depend upon their
processing history. Molecular orientation, such that the polymer
chains are aligned along the axial direction of the image guide,
produces macroscopic anisotropy. An excellent modern review of this
subject is provided by Struik, L.C.E. [1990] Intemal Stresses,
Dimensional Instabilities, and Molecular Orientations in Plastics,
John Wiley & Sons Ltd., Chichester, England. The properties of
the chain segments measured in the direction of the polymer chains
(and image guide) are determined by strong covalent chemical bonds,
whereas weak Van der Waals forces are operating in the transverse
direction of the image guide. As a direct result of molecular
orientation, there is: (a) increased axial strength of the guide
and (b) increased axial strain to break of the guide; and,
therefore, enhanced flexibility.
In a preferred method for inducing molecular orientation in a
polymeric GRIN image guide, the image guide fiber is stretched, at
an appropriate temperature, at low strain rate. This gives the
required enhancement in mechanical properties without reduction in
optical transmission.
In the subject invention, by using the technique of molecular
alignment, a 270 .mu.m diameter polymethylmethacrylate based POF
image guide has exhibited unlimited 180.degree. flexing cycles with
a bending radius of 1.5 mm. This is to be compared with an 8 mm
bending radius limit for the SI glass guide.
The enhanced image quality and flexibility of the angioscopic image
guide of the subject invention represents an additional major
advance in this type of instrumentation. The subject GRIN-POF image
guide is brighter, higher resolution, more flexible, and lower cost
than the existing image guides. The GRIN-POF scopes of the subject
invention are improved over existing SI-GOF scopes by, for
example:
1. For fixed microfiber diameter of about 5 .mu.m and an image
guide width of about 270 .mu.m, the GRIN-POF scopes are at least
about 50% brighter than SI-GOF scopes.
2. The resolution of the subject GRIN-POF scopes for a fixed guide
width of 270 .mu.m are at least 50% higher than SI-GOF scopes.
3. The flexibility of the subject GRIN-POF scopes are at least
about three times higher than the existing SI-GOF guide.
In a specific embodiment, the imaging scopes of the subject
invention can be inserted into a plastic tube (sheath), which can
have a transparent end plate. This combination can then be used for
imaging internal body structures. The image viewed through the end
plate is unimpaired by the sheath or end plate. The advantage of
this sheath is that it is disposable and allows the imaging scopes
to be reused with minimal sterilization.
In a preferred embodiment, the sheath can have at least one
internal, or external, illuminating optical fiber(s) which
transmits light to illuminate the internal body structure to be
imaged. Additionally, it is preferred but not essential, that there
be no transparent end plate at the distal end of the illuminating
optical fiber(s) to avoid the illuminating light reflecting at such
a plate and impairing the quality of the image. A longitudinal
cross section and a transverse cross section of a sheath comprising
an external illumination fiber are shown in FIGS. 8B and 8E,
respectively.
When performing, for example, endoscopy or angioscopy, a flexible
guiding means, typically made of metal, is often incorporated to
facilitate guiding the endoscope or angioscope within the body. A
longitudinal cross section and a transverse cross section of a
sheath comprising an external illumination fiber, where the sheath
is designed to fit over a guiding means incorporated with a plastic
optical fiber image guide, are shown in FIGS. 8C and 8E,
respectively. In this case, the sheath and illuminating fiber could
be regarded as disposable after a single use.
Accordingly, the intubation scope and/or sheath of the subject
invention can comprise such a flexible guiding means, such that
many combinations of imaging scope, guiding means, illuminating
fiber(s), and sheath are possible.
Following are examples which illustrate procedures for practicing
the invention. These examples should not be construed as
limiting.
EXAMPLE 1
Production of GRIN Fiber
General processes for fabricating a plastic GRIN optical fiber are
known to those skilled in this art. These processes can produce
plastic GRIN fiber wherein the refractive index varies in a
controlled way as a function of radius. Typically, the refractive
index varies parabolically as a function of the radius. The varying
refractive index can be achieved by, for example, radial
dependently doping a given polymer with a low molecular weight
additive. Alternatively, in a preferred embodiment of the present
invention, plastic GRIN fiber is made by using two miscible
polymers with different refractive indices whose relative
concentrations vary radially to produce the required refractive
index profile.
FIG. 5 illustrates, schematically, a specific embodiment of the
subject method for continuous production of GRIN fibers made by
using two miscible optical polymers with different refractive
indices whose relative concentrations vary radially to produce the
required refractive index profile. Two optical polymers (materials
M.sub.a and M.sub.b) with different refractive indices are
introduced to the GRIN die block (GDB) through separate feed
channels, A and B, by two extruders, X1 and X2. The GDB is shown,
schematically, in more detail in FIG. 6. Material M.sub.a, which is
fed to the channel A, flows into the mixing chamber D through the
channel C1, whereas the material M.sub.b flows from channel B to a
mixing chamber D through the channel C2. By varying the gap, G, or
length, L, of the channels C1 and C2, the flow rate of each
material can be varied in the axial, or z-direction (see FIG. 7).
Consequently, a blend with a gradually varying composition in the
z-direction can be prepared in the mixing chamber D.
Since the refractive index of the polymer blend depends on the
ratio of component polymers in the blend composition, the blended
material in the mixing chamber D can have a gradually varying
refractive index along the z-direction. While the rotating mixer
blade D located in the middle of the mixing chamber D provides
uniform mixing of the two materials M.sub.a and M.sub.b at each
location of z, axial mixing in the z-direction does not occur since
there is essentially no pressure gradient in the z-direction.
The axially varying blend prepared in the mixing chamber D is then
fed through the channel E to the feed chamber F which houses a
rotating cone F1. As used herein, reference to a cone refers to any
tapering cylindrical form. The taper can be, but does not have to
be, at a constant angle. While the material is flowing from D
toward the die exit H through E and F, the axial variation of the
blend composition in the mixing chamber D is converted to a radial
variation, thus creating the gradient-index fiber.
In FIG. 7, the flow pattern of the polymer blend is shown
schematically. Since the material fed to the feed chamber F at a
downstream location near the die exit H is swept by the upstream
material, it is positioned away from the rotating cone F1. The flow
patterns 1, 2, and 3 of FIG. 7 show such positioning of materials
schematically. Due to the rotating cone F1, the materials in the
feed chamber F follow a helical stream line pattern. For
simplicity, however, only the axial and radial components of the
flow pattern are depicted in FIG. 7. The rotating cone is for the
uniform positioning of the material in the circumferential
direction so that the axisymmetry of refractive index can be
ensured while creating radially varying refractive index. The
rotation speed of F1 should be sufficiently high to ensure the
axisymmetry of refractive index, preferably taking into account the
residence time of the material in the feed chamber F.
When the material leaves the die exit H, the circular strand has a
refractive index decreasing with the radial position and a
gradient-index optical fiber is formed when the strand is pulled
off.
EXAMPLE 2
Production of Small Diameter GRIN Fiber Image Guide
The subject plastic GRIN image guide can be produced by thermal
processing of the original GRIN fiber. Examples of thermal
processing include fusing, drawing, and stretching. Many original
GRIN fiber sections can be fused together to produce a multifiber
image guide. This multifiber image guide can be drawn to reduce the
diameter of the image guide and each individual fiber contained
therein. Finally, the image guide can be stretched to increase the
flexibility.
At elevated temperature, low molecular weight additives have
enhanced diffusivity. As a result, plastic GRIN fiber made with
additives may end up with a degraded refractive index profile.
Therefore, in a preferred embodiment, the plastic GRIN image guide
should be made with fiber composed entirely of at least two
miscible polymers where there will be no degradation of the
profile.
In one embodiment, approximately 0.5 mm diameter GRIN fiber is cut
into 1.0 m length sections, and approximately 10,000 fiber sections
are bundled together in a 100.times.100 square. This bundle is set
within a 50 mm.times.50 mm cross-section stainless steel square
tube. The tube is placed in a heated oven and the fibers are
subjected to pressure at an appropriate temperature to make a fused
boule of solid polymeric fibers. A square tube is preferred because
it is easier to apply pressure to the bundle of fibers, although a
round tube can also be used. The solid square boule may be machined
into a round boule if a round image guide, rather than a square
image guide, is desired. The solid boule is then placed in the
heating chamber of a drawing tower, in which the lower part of the
boule is continuously heated and drawn down to a uniform diameter
multi-microfiber image guide. As those skilled in the art would
readily appreciate, it is important when manufacturing image guides
that the ends of the image guide be coherently related to each
other.
Image guides can be produced with outer diameters as small as
approximately 0.5 mm down to approximately 0.1 mm containing
microfibers of approximately 5 .mu.m down to approximately 1 .mu.m,
respectively. This range of microfiber diameters extends from the
existing glass microfiber diameter (5 .mu.m) of small diameter
fiberscopes down to the fundamental limit (approx. 1.0 .mu.m).
The image guide may have an outer protective cladding of polymer
extruded upon it in the conventional cross-head die method, or by
solution cladding if desired. The image guide is cut to length, the
ends are polished and a gradient-index rod lens is attached,
preferably glued, onto one end. The resulting fiberscope can be
sterilized with solution, or ETO prior to use and thereafter, to
facilitate reuse, if desired.
EXAMPLE 3
Production of Large Diameter GRIN Fiber Image Guide
A GRIN fiber image guide can be made with either GRIN-GOF or
GRIN-POF. If made with glass, the image guide will be more rigid
and can have application where a more rigid image guide is
preferred. If made with polymer, the image guide will be flexible
and can be used in applications where flexibility is desired. A 3
mm diameter GRIN POF image guide can be made with the high
resolution of 1000.times.1000 corresponding to the high definition
television (HDTV) standard. Image guide with a 100.times.100 array
of 3 .mu.m diameter microfibers is produced as described in Example
2. This square image guide, 0.3 mm diameter, fiber bundles are
arranged in a 10.times.10 array with dimensions of 3 mm.times.3 mm
of the desired length of say 1 m. Low viscosity epoxy is used at
each end (within 1 cm of the end) of the array to secure the
positions of the fibers. When the epoxy is cured the ends are cut
and polished. The guide is given a GRIN lens at one end, and
protective cladding as described in Example 2. The resulting image
guide has a higher resolution than heretofore achieved.
EXAMPLE 4
Production of a 3 mm Diameter Fiber Optic Taper
When an image is presented at one end of existing fiber optic
tapers, the output face of the taper displays an image which is
larger or smaller than the input image. The ratio of image sizes is
equal to the ratio of the dimensions of the input and output faces
of the taper (called the taper ratio). Existing tapers are based on
glass SI fiber and have typical taper ratios of 2:1 or 3:1. At the
small end of the taper, the microfiber is usually no less than 5
.mu.m, for the important reasons discussed earlier. Therefore, the
microfiber dimension at the large end of the taper will be 15
.mu.m, for a taper ratio of 3:1. The spatial resolution of existing
taper is, thus, severely limited.
This example describes a fiber optic taper which has about twice
the resolution of the existing tapers. An image guide is made in
the manner described in Example 2 with dimensions 0.75
mm.times.0.75 mm, and containing 7.5 .mu.m microfiber. A
20.times.20 array of sections of this image guide, 20 cm long, is
packed into a square cross section stainless steel tube. The
assembly is placed into a vacuum oven. After a vacuum is
established, the temperature is increased. At a temperature, about
20.degree.-60.degree. C. above the polymer glass transition
temperature, the fibers fuse into a solid mass. The oven is allowed
to cool to room temperature, and the fused boule is removed from
the fixture. The boule is placed in a stretching machine, whose
design is identical to the machines used for producing glass fiber
optic tapers. Each end of the boule is held by a rotating chuck.
The center of the boule is heated by a cylindrical heater. When the
boule has reached the appropriate temperature, the chucks are both
retracted in unison. The boule is stretched and forms an hour glass
shape. Heat is turned off and the boule is permitted to cool while
still rotating. The boule is removed from the fixture, and cut at
the locations required for the desired taper ratio of 3:1. Two
symmetric tapers are produced from each stretched boule. The
microfiber dimensions at the large and small ends are 7.5 .mu.m and
2.5 .mu.m respectively. This GRIN based fiber optic taper has twice
the resolution of existing glass tapers.
EXAMPLE 5
Production of a Fiber Optic Plate
Fiber optic plates are frequently used to attach to the surface of
an opto-electronic device such as a charge coupled device (CCD). As
dimensions of the structures of these semiconducting devices
continue to decrease, it is increasingly important to use a fiber
optic plate with microfibers less than 5 .mu.m in size. In this
way, the resolution of the system will be improved.
This example concerns the production of a fiber optic plate
containing 2.5 .mu.m microfibers. Image guide fiber was produced,
as in Example 2, with dimensions 250 .mu.m.times.250 .mu.m. One
meter lengths of this fiber are packed into a 25 mm.times.25 mm
fixture to form an array of 1000.times.1000 fibers. The fibers are
fused as before to form a solid boule.
Next, this solid boule is cut into sections and a 25 by 25 bundle
of these solid boule sections is placed within a 1 inch.times.1
inch stainless steel square tube. The tube is placed in a heated
oven and the solid boule sections are subjected to pressure at an
appropriate temperature to make a second fused boule of solid
polymeric fibers, said second boule being approximately 1 inch by 1
inch. Finally, a section is cut off the end of the boule and the
ends of the boule section are polished to make a fiber optic
plate.
EXAMPLE 6
Referring to FIGS. 8A-8F, this example provides three illustrative
combinations of image guide, illuminating fiber, guiding means,
and/or sheath. FIGS. 8A and 8D illustrate a longitudinal cross
section and a transverse cross section, respectively, of the distal
end of a sheath designed to fit over a plastic optical fiber image
guide. The sheath covers the distal tip of the image guide with a
transparent end plate. In this case, any illuminating fibers and/or
guiding means would not be enclosed within this sheath, although
they could have their own sheaths.
FIGS. 8B and 8E illustrate a longitudinal cross section and a
transverse cross section, respectively, of the distal end of a
sheath designed to fit over a plastic optical fiber image guide,
wherein the sheath comprises an illumination fiber. The distal end
of the illumination fiber is not covered by the sheath, in this
example, so as to not impair the image. Accordingly, the
illuminating fiber can be disposed of with the sheath. In this
embodiment, the sheath acts to attach and position the illumination
fiber with respect to the image guide.
FIGS. 8C and 8F illustrate a longitudinal cross section and a
transverse cross section, respectively, of the distal end of a
sheath designed to fit over a guiding means incorporated with a
plastic optical fiber image guide, wherein the sheath comprises an
illumination fiber. The distal end of the illumination fiber is not
covered by the sheath, but the distal end of the image guide plus
guiding means is covered. In this embodiment, the guiding means can
be reused along with the image guide. Other geometrical
arrangements of the guiding means, image guide, and illumination
fiber are obviously possible.
It should be understood that the examples and embodiments described
herein are for illustrative purposes only and that various
modifications or changes in light thereof will be suggested to
persons skilled in the art and are to be included within the spirit
and purview of this application and the scope of the appended
claims.
* * * * *