FIBER OPTIC DIFFUSER AND METHOD OF MANUFACTURE
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to fiber optic diffusers and methods of manufacturing
fiber optic diffusers.
2. Description of the Prior Art
The use of energy delivered from a light source, such as a laser, for medical
applications is well documented. In certain biomedical applications, such as, for example,
photodynamic therapy ("PDT"), optical waveguides (referred to herein as "optical fibers") are
used to deliver light energy to internal areas of the human body not readily accessed directly
by the light source and also to monitor the level of light in such areas. At the treatment site
within the body the light may be used for photoablation, photocoagulation, to activate a
photochemical drug, or to otherwise effectuate optically related treatments.
Optical fibers used in such therapies typically consist of an inner core having
one index of refraction, surrounded by a cladding having a slightly lower index of refraction.
Both the core and cladding may be comprised of either an optical glass or polymer (such as
plastic). Light propagates down the optical fiber by means of total internal reflection at the
interface between the inner core and the cladding. The optical fiber is terminated at its distal
end with a diffuser having an irradiance distribution appropriate to the particular treatment
protocol. An outer protective jacket often covers the optical fiber.
Alternatively, light can be delivered into the body using an optical waveguide
that consists of a core region only and the waveguiding effect is provided by the interface
between the core and the surrounding medium. This type of optical waveguide will also be
referred to herein as an optical fiber.
One current approach to diffuser construction is to diffuse scattering elements
in a clear material such as epoxy, often with a density gradient of scattering elements to
achieve an irradiance pattern that is uniform along the length of the diffuser. One drawback
of this approach is that the diffuser is constructed separately and then attached to the end of
the fiber resulting in a difficult manufacturing process and decreased reliability. Another
drawback is that it is difficult to shape the irradiance pattern significantly because it is
difficult to arrange the scattering elements in a systematic manner. An additional drawback is
that the attachment technique often results in a fiber optic diffuser with a maximum diameter
that is greater than the diameter of the fiber.
Another current approach to diffuser construction is to modify the fiber itself
to prevent the total internal reflection of light at the core-cladding interface. There are several
ways this is accomplished. One way is to choose a ratio of the indices of refraction between
the outer cladding and the core region of the optical fiber so that internal reflection within the
core region is substantially less than total. This causes light to radiate outward through the
side of the core region and to emerge through (a preferably transparent) cladding. Another
way is to alter the interface between the fiber optic core and cladding to increase side
radiation. Texturing the outer surface of the core region to provide a ground glass effect is
one method commonly used. Another is to position or embed light scattering elements such
as tiny particles at the surface of the fiber optic core near the interface with the cladding.
Light scattering particles can also be imbedded throughout the cladding to enhance the side
delivery of radiation. Yet another approach is to melt or otherwise deform the distal end of
the fiber to reduce the waveguiding effect and thereby allow light to be emitted along the
deformed region.
Current approaches that modify the fiber itself have only a limited capability
to tailor the irradiance distribution. Diffusers which rely on mechanical alteration of the core-
to-cladding interface or use a deformed distal end also have the drawback of potentially
weakening the fiber mechanically. Moreover, removal of the cladding can also leave the core
of the fiber exposed to chemical degradation.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide improved optical fiber
diffusers for use in biomedical applications requiring light delivery, the diffusers having
irradiance distributions tailored to particular treatment protocols, thus maximizing the
therapeutic benefits of treatment, allowing the delivery of light to be better controlled, and
reducing the unwanted side effects of treatment. The light diffusion mechanism of the
present invention comprises scattering elements "written" directly into the core of an optical
fiber using pulsed lasers with pulses that have relatively high peak powers (referred to herein
as high power lasers).
It is a further object of the invention to provide optical fiber diffusers having
diameters as small as the optical fiber diameter to reduce the overall profile, which is
advantageous for catheter applications.
It is a further object of the invention to provide methods of manufacturing the
improved diffusers that permit tailoring of the irradiance distributions during manufacture.
It is a further object of the invention to provide methods of manufacture
wherein
diffusers are formed internally within optical fibers, thus eliminating the need for separate
mechanical attachment of the diffusers to the optical fibers, reducing the number of
manufacturing steps required, and thereby reducing expense and improving reliability.
These and other objects are met by the present invention which includes a
method of diffusing light from an optical waveguide (such as, for example, a glass body, a
polymer, or other medium capable of transmitting light) by first focusing a relatively strong
laser beam to a point within the waveguide so as to heat a small region within the waveguide
and thereby permanently modify the small region's microscopic structure. After the small
region within the waveguide is allowed to cool, a light source may then be applied to the
waveguide so that the modified microscopic structure of the waveguide will cause at least
some of the applied light to be scattered. The laser beam may preferably be focused to a
point within the core through the cladding surrounding the core.
In one embodiment of the present invention, the light is focused into the
optical waveguide's core from the distal end when the waveguide is surrounded by air.
Alternatively, in a preferred embodiment, the waveguide is immersed in a liquid having an
index of refraction substantially matching the index of refraction of the waveguide at its
surface. This reduces the reflection of light at the surface of the waveguide and allows light
to be more properly focused within the waveguide. This allows for more well-defined
scattering centers to be formed within the waveguide.
The method of the present invention may be used to form a fiber optic diffuser
comprising an optical fiber having a core, a cladding, and, if required, a protective jacket.
The distal end of the core preferably has at least one internal scattering element comprising a
small region having optically induced changes to the microscopic structure of the region. The
proximal end of the optical fiber is preferably adapted for coupling to a source of optical
radiation and at least one internal scattering element directs a portion of the coupled optical
radiation outwardly from the diffuser. The internal scattering elements may preferably be
dispersed along the axial length of the diffuser, and the distribution may generally increase in
a direction from the proximal end of the diffuser to the distal end of the diffuser.
Alternatively, the distribution of scattering elements may be selected to provide a
substantially uniform axial distribution of optical radiation over the length of the fiber optic
diffuser. Alternatively, the location of the scattering centers can be such that arbitrary
diffuser output profiles can be achieved. The diffused optical radiation may preferably be
used to activate a photochemical drug and the distribution of scattering elements is preferably
tailored to a particular treatment protocol.
The present invention also includes an automated process for manufacturing a
fiber optic diffuser within an optical fiber, wherein the optical fiber has a core surrounded by
a cladding. Preferably, the automated process includes the steps of focusing light from a
writing laser having a first wavelength to a small region within the core of the distal end of
the fiber so as to heat the small region, causing the microscopic structure of the small region
to be permanently modified; applying a light emission source having a second wavelength to
the proximal end of the optical fiber so as to cause light to be scattered by the small region;
testing the light of the second wavelength that is diffused from the optical fiber core with a
test means that selectively measures light of the second wavelength; and concurrently
adjusting the operation of the writing laser so that light of the second wavelength that is
diffused from the optical fiber core meets a desired standard.
In another embodiment, the presently preferred invention includes an
apparatus for producing a fiber optic diffuser formed from an optical fiber having a core and a
cladding. The apparatus preferably includes a high power writing laser capable of emitting a
relatively strong laser beam and an optical lens for focusing the emitted laser beam on a focal
point within the core of the optical fiber such that the focused laser beam is capable of heating
a small region within the core near the focal point and thereby permanently modify the small
region's microscopic structure. The focal point within the core of the optical fiber may be
adjusted to any arbitrary position along the length of the optical fiber. Preferably, the
apparatus may also include a holding tank for holding a liquid having an index of refraction
substantially matching index of refraction of the optical fiber at its surface. Using this
holding tank, the emitted laser beam is preferably focused on a focal point within the core of
the optical fiber within the holding tank.
The present invention also includes a method of phototherapy by placing a
fiber optic diffuser in proximity to a treatment site, the diffuser comprising a core surrounded
by a cladding and having a proximal end adapted for coupling to a source of therapeutic
optical radiation and a distal end for diffusing the optical radiation outwardly, the distal end
containing a plurality of light scattering elements distributed therein, with each scattering
element comprising a small region of material having optically induced changes to the local
structure of the material. At least one source of therapeutic optical radiation is then applied to
the proximal end of the fiber optic diffuser to effect treatment with the radiation diffused from
the distal end of the diffuser.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further described in connection with the accompanying
drawings, in which:
Figure la is a partial cutaway view of the optical fiber diffuser;
Figure lb is a detail view showing the diffusion elements within the core of the
optical fiber;
Figure 2 illustrates how diffusion elements within the optical fiber core are created
using a high-power writing laser and focusing optics, focusing through the optical fiber
cladding;
Figure 3 illustrates how diffusion elements within the optical fiber core are created
using a high-power writing laser and focusing optics, focusing from the distal end of the
optical fiber;
Figure 4 illustrates how the level of diffusion resulting from the diffusion zones
within the optical fiber core can be tested using a test laser and light measurement apparatus;
Figure 5 illustrates how an arbitrary irradiance distribution can be created, with the
light intensity varying along the length of the diffuser, allowing diffusers to be tailored to
particular treatment protocols;
Figure 6 illustrates the manufacturing method of the present invention as incorporated
into an automated system;
Figure 7 is a partial cutaway view of an alternative embodiment of the optical fiber
diffuser of the present invention;
Figure 8 is a graphical representation of light radiation as a function of axial position
along an optical fiber diffuser manufactured in accordance with one embodiment of the
present invention;
Figure 9 is a graphical representation of light radiation as a function of axial position
along an optical fiber diffuser manufactured in accordance with another embodiment of the
present invention;
Figure 10a illustrates an optical fiber showing light reflecting off the outer surface of
the fiber;
Figure 10b illustrates an alternative embodiment of the present invention in which the
scattering centers are formed within the core of an optical fiber as the optical fiber is
immersed in a liquid;
Figure 1 la illustrates the length of an optical fiber diffuser that may be formed using
one embodiment of the present invention;
Figure 1 lb illustrates another embodiment of the present invention in which a hole is
formed in the focusing lens, thus increasing the length of the fiber optic diffuser that may be
produced in accordance with the present invention; and
Figure 12 illustrates one preferred manufacturing assembly for producing optical fiber
diffusers in accordance with the present invention.
These drawings are provided for illustrative purposes only and should not be
used to unduly limit the scope of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in Figures la and lb, the optical fiber diffuser 10 of the present
invention is fabricated from a standard optical fiber, which typically includes a core 12,
surrounded by a cladding 14, which may be surrounded by a jacket 16. An optical fiber
diffuser 10 may be used, for example, in photodynamic therapies or other therapies involving
the application of light. The core 12 of the optical fiber diffuser 10 may be formed from
glass, polymers (such as plastic), or any other suitable medium capable of transmitting light.
Although the optical fiber diffuser 10 illustrated in Figure 1 has had the jacket 16 of the
optical fiber removed from the distal end 20 of the fiber, the present invention may be used
with optical fibers without first removing their associated jackets 16, provided that the jacket
16 sufficiently allows light to penetrate and pass through to the core 12. The core 12 of the
fiber has been modified with the creation of multiple small scattering centers 28 in the
structure of the core 12 of the optical fiber. The scattering centers 28 (i.e., elements) consist
of small regions of optically-damaged core 12 (i.e., glass or plastic for polymer fibers), which
result in a permanent modification to the microscopic structure of the small regions of the
core 12.
In the fabrication method of the present invention (Figures 2 and 3), the
diffuser is formed within the distal end 20 of the optical fiber itself. As can be appreciated by
those skilled in the art, the diffuser may be formed in any arbitrary region of the optical fiber.
An intense light from a high-power writing laser 40 is focused with focusing optics 50 to a
small point within the core 12 of the optical fiber, creating a small area of optically induced
damage. A short pulse of light from the high-power writing laser 40 imparts sufficient energy
to the focal point within the fiber core that the core material at the small region near the focal
point is changed (i.e., optically induced damage). These changes are generally thought to be
a result of initial melting followed by rapid cooling after the pulse has passed. With this
rapid cooling the material returns to its solid state leaving a local discontinuity between the
melted volume and the surrounding material. These local discontinuities between the bulk
core material and the optically damaged regions have the useful characteristic of scattering
light, thus functioning as scattering centers 28 within the optical fiber core 12.
A diffuser having a specifically tailored irradiance distribution is
manufactured by forming numerous scattering centers 28 within the optical fiber core 12. For
each scattering center the relative positions of the fiber and the focusing optics are changed,
moving the focal region to a different point in the fiber, where another scattering center is to
be created. This process is repeated until all individual scattering centers have been created,
thereby forming the diffuser within the fiber.
The light from the high-power writing laser 40 and focusing optics 50 can be
focused on a point within the core 12 either through the cladding 14 from the side, as shown
in Figure 2, or from the distal end 20 of the fiber, as shown in Figure 3. Although one writing
laser is shown, multiple lasers (not shown) may also be used, operating either at the same or
different wavelengths, to achieve the required effect; the focusing optics thus may comprise
multiple sets of optics (not shown). The writing laser 40 is preferably capable of emitting a
beam of relatively strong pulses or an externally modulated, relatively high power beam.
- 11 - During manufacture of the diffuser, the irradiance distribution being created
may be measured using an emission source 60 attached to the proximal end of the optical
fiber (Figure 4). In this invention the distal end is used to refer to the end of the optical fiber
at which the diffuser is located and the proximal end refers to the opposite end of the fiber.
The emission source transmits light down the fiber which is diffused by the scattering centers
28, and which is then detected and quantified by an optical output detector 70.
A similar technique can be used to monitor the formation of scattering centers.
Once a scattering center is formed, it scatters light from the pump laser along the direction of
the optical axis. The result is a significant change in the amount of pump light that is
detected at either end of the optical fiber. Monitoring changes in the amount of this light that
is coupled into the fiber core modes allows one to detect when a scattering center is formed.
It is envisaged that diffuser emission profiles can be tailored to provide non-
uniform or customized output profiles. Figure 5 shows a diffuser that has been formed by
creating a relatively high population of scattering centers 28 (or scattering centers 28 of
relatively large size) near the distal end of the fiber, a region having a lower density of
scattering centers 28 (or scattering centers 28 of relatively small size) proximal to this region,
and then high density region of scattering centers 28 (or scattering centers 28 of relatively
large size) proximal to this region. The effect of such a population of damage sites on the
diffuser optical output profile is illustrated in Figure 5b, which illustrates the diffuser' s output
power as a function of the distance along the diffusing element. The scattered intensity will
be high near the regions with high densities of scattering centers 28 (or scattering centers 28
of relatively large size), then lower near the region of fewer scattering centers 28, then higher
near the region of high densities of scattering centers 28.
In order to achieve a uniform output intensity along the length of the diffuser,
it is necessary to have the amount of scattering increase from the proximal toward the distal
end of the fiber, because there is less light available at the distal end and, therefore, more
scattering is necessary as the light travels to distal end of the fiber. To achieve non-uniform
light output will require similar considerations in locating the scattering centers or the
distribution of scattering. The current technique is especially suited for addressing these
concerns as it allows the scattering centers and their size to be located in an arbitrary,
predefined manner.
It is envisaged that diffuser emission profiles can also be tailored to specific
treatment sites. For example, diffusers can be manufactured in such a way that their
emissions will possess an inverted triangle profile appropriate to treating the uterus; in other
applications where body cavities possess complex shapes requiring a sculptured emission
profile, the diffuser can be fabricated to match the required profile. Customized emission
profiles could also be created by scanning a tumor prior to treatment and then sculpting the
diffuser to emit a profile which fills the tumor completely while emitting little light into non-
tumor tissue. A similar approach would allow custom fibers to be used to fill the prostate or
other glands while avoiding spilling light into adjacent tissue and thus again containing the
PDT effect within the target tissue.
Although described in the context of conventional optical fibers, the present
invention can also be applied to non-conventional waveguides, such as a solid glass or plastic
rod of a diameter significantly larger than is typical of conventional optical fibers. Such a
light diffusing wand could also be used to deliver diffusive light to areas of the body that
have sufficiently large openings to be easily accessed. Examples would include
gynecological applications, adjunctive treatment associated with brain tumor surgery, light
treatment of lesions in the oral cavity, and light treatment of the colon.
In an automated manufacturing process, the fabrication of the diffuser may be
computer controlled for improved manufacturability using techniques well-known in the art.
As illustrated in Figure 6, the optical fiber is connected at its proximal end to the emission
source 60 throughout the process of creating the scattering centers. The writing laser operates
at a different wavelength (λ,) than the emission source (λ2). Optical filters 80 which
selectively block light at λ, but transmit light at λ2 protect the emission source 60 and the
optical output detector 70 from the power of the writing laser. The writing laser, optical
output detector, and the positioning system (not shown) for controlling relative positions of
the writing laser, optical fiber, and optical output detector may all be under the control of a
computer (not shown). Feedback within the control software permits precise tailoring of the
irradiance distribution. Variations well-known in the art to the manufacturing process are
possible; for example, the optical filters 80 may be omitted and mechanical or optical
blockers (not shown) used to protect the emission source 60 and the optical output detector 70
during firing of the writing laser, in which case the writing laser and emission source may
operate at the same wavelength.
An alternative form of the optical fiber diffuser of the present invention is
shown in Figure 7. In this alternative form, the outer jacket 16 of the optical fiber is left
intact over the entire optical fiber. The outer jacket comprises an optically transparent
material such as a transparent plastic. During fabrication of the diffuser, light from the
writing laser 40 and focusing optics 50 may be focused through both the transparent outer
jacket 16 and the cladding 14 to the core of the fiber 12. The light from the writing laser is
unfocused as it passes through the outer jacket, thus allowing fabrication of scattering centers
within the core of the fiber without damage to the outer jacket. Alternatively, scattering
centers may be created within the core of the fiber from the distal end 20 of the fiber. In
testing and use of the diffuser of the alternate embodiment, light from an emission source at
the proximal end of the optical fiber is diffused by the scattering centers and passes
unimpeded through the transparent outer jacket. The intact outer jacket of the alternate
embodiment provides both mechanical and chemical protection to the optical fiber.
An experimental demonstration of one preferred embodiment of the present
invention was performed using a pulsed laser operated in both single shot mode and at low
repetition rate (5 Hz). The writing beam used a wavelength of 532 nanometers with 30
picosecond pulses having energies ranging from 60 microjoules to 175 microjoules. This
beam was focused into an optical fiber from the side as illustrated in Figure 6. In this
demonstration the jacket 16 was stripped from the fiber and the fiber was mounted on a three-
axis translation stage having the additional capability to adjust pitch and yaw. Using these
mechanical adjustments, the fiber was aligned such that it could be translated along its optical
axis, always keeping the focused spot located at the fiber core. Using this technique, several
diffusers were fabricated.
In one of these cases, the pulse energy of the writing laser 40 was set at 125
microjoules and the laser was operating at a 5 Hz repetition rate. The output of a low-power
helium-neon laser operating at 633 nm was directed into the proximal end of the fiber such
that the buildup of scattering centers could be monitored at the distal end. In this case, rather
than using the detector shown in Figure 6, the development of scattering centers was
monitored by viewing the distal end through a pair of laser safety glasses that blocked the 532
nm beam. With the relative positions of the fiber and writing laser 40 held fixed, the distal
end of the fiber was observed and as soon as a scattering center began to develop, i.e., as soon
as a red spot began to develop within the fiber, the fiber was translated such that the writing
laser 40 was then focused on a fresh spot within the fiber and the process repeated. In
practice, the result was a nearly continuous back and forth translation of the fiber along its
optical axis while the writing laser was running continuously at 5 Hz.
As is known, the focused spot of a laser beam is elliptical rather than spherical,
with the major axis of the ellipse parallel to the optical axis of the beam. For the above
experiment, this results in elliptical scattering centers that are aligned along the optical axis of
the writing laser beam, and are peφendicular to the optical axis of the fiber. To increase the
amount of scattering, the fiber was rotated 90 degrees around its optical axis, with the above
procedure repeated with the fiber in this orientation. Using this technique, elliptical
scattering centers with their optical axes oriented at 90 degrees to each other within the core
of the fiber may be created.
To quantify the nature of the diffuser created in the above procedure, the
diffusing portion of the optical fiber was placed in front of a Spiricon® laser beam analyzer
oriented such that the diffuser was viewed from the side. With the fiber oriented in this
position, the proximal (opposite) end of the fiber was connected to a Miravant™ laser (DD2
Model). The resulting intensity profile is illustrated in Figure 8. As shown by the figure, this
type of scattering center density and size results in a diffuser with an output light distribution
that is strongest near the proximal end of the diffuser.
The present invention may also be used to create optical fiber diffusers having
arbitrary non-uniform diffuser outputs. As an illustration of this embodiment, another fiber
was mounted as above, except in this case the laser pulse energy was increased to
approximately 175 microjoules. At this energy, a sufficient amount of damage is induced
with a single pulse to result in significant scattering of light from the writing laser 60.
Multiple shots from the writing laser 60 on a single focus spot resulted in increasing the
amount of scattering from that spot, as a result of increasing the size of the damage spot. To
take advantage of this, the focus spot of the writing beam was situated near the distal end of
the fiber and that spot was irradiated with 20 pulses from the writing laser 60. The optical
fiber was then moved 0.0125 inches along its optical axis so that the beam of the writing laser
60 would be focused at a new spot located 0.0125 inches proximal to the previous spot. The
laser 60 was then turned on for 20 shots and a new damage spot was created. This process
was repeated until damage spots had been written along the distal 2 cm length of the optical
fiber. At that point, this same process was continued except the scattering centers were
spaced 0.025 inches apart. The result is a 2 cm section at the distal end containing scattering
centers spaced 0.0125 inches apart. Proximal to that is similar diffuser section, also 2 cm
long, only with scattering centers spaced 0.025 inches apart. This results in a very simple
non-uniform population of scattering centers. The diffuser' s optical output measured using
the above Spiricon® assembly is illustrated in Figure 9. As illustrated in Figure 9, this simple
non-uniform distribution of scattering centers results in a more uniform light output of the
diffuser as would be expected. The strong output peak at the distal end of the diffuser is most
likely due to scattering from the end of the fiber and is an indication that only a fraction of the
total light is scattered out of the optical fiber by the diffusing centers.
The above experiments demonstrate the fundamental feasibility of this
concept. Although these demonstrations use a side-firing arrangement for the writing fiber,
an unjacketed fiber, a specific pulse energy, a specific wavelength, a specific optical focusing
scheme, and a specific scheme for monitoring the formation of the scattering centers, these
may all be varied and the resulting technique will still be within the spirit and scope of the
present invention.
The present invention also includes a method to overcome the difficulty in
focusing the writing beam into the optical fiber to create scattering centers. This is primarily
a result of the fact that light is reflected off the outer surface of the fiber as illustrated in
Figure 10a. This outer surface could be the core of the optical fiber, the cladding surrounding
the core, or even the protective jacket. This reflection is due to the relatively large difference
in refractive index between the outer surface and the air surrounding it. To minimize this
problem, as shown in Figure 10b, the fiber can be placed in a liquid 80 (e.g., water) such that
the refractive index difference is reduced and the resulting reflection of the writing beam light
at the outer surface of the fiber is substantially reduced. Preferably, the index of refraction of
the liquid 80 is selected to substantially match the index of refraction at the surface of the
optical fiber.
The present invention further includes a method and apparatus to produce
optical fiber diffusers of arbitrary length having scattering centers located in any arbitrary
position along the core of the optical fiber. The basic arrangement illustrated in Figure 3
shows that the length of the diffuser that can be constructed is generally limited to the focal
length of the lens 50. For diffusers longer than this, the distal end of the fiber runs into the
surface of the lens 50 as illustrated in Figure 11a. To eliminate this problem, a hole 52 may
preferably be placed through the lens 50 to allow the fiber to pass through as illustrated in
Figure l ib, thus allowing the fiber to pass through the lens 50 such that the focal point within
the core of the fiber may be adjusted to any arbitrary position along the length of the optical
fiber.
Figure 12 illustrates one preferred diffuser fabrication assembly 90.
Preferably, the fabrication assembly includes a writing laser 40 that emits a laser beam 92.
The laser beam 92 is expanded and collimated through a set of lenses, 94a and 94b. The laser
beam 92 is then re-positioned so that it is parallel to the axis of the optical fiber 120 using, for
example, a set of mirrors 102 and 104. The laser beam 92 then passes through an iris 98,
which attenuates the amount of light directed at the optical fiber 120 and modulates the
diameter of the focused spot of the laser beam 92. The laser beam 92 then passes through a
focusing lens 110 and is focused into the core of the optical fiber 120. Preferably, the optical
fiber 120 is retained and translated along its optical axis using, for example, an independent
linear stage 109 that positions the focused spot of the laser beam 92 relative to the distal end
of the optical fiber 120. The optical fiber 120 is held to this linear stage 109 using a holding
fixture 108. In order to keep the fiber aligned relative to the optical axis of the lens 110, it is
preferably passed through a fiber guide 111 that is held fixed to the optical mount that holds
the lens 110. In the configuration shown in Figure 12, the optical fiber 120 also passes
through a hole in the mirror 104 to allow the linear stage 109 to be situated well outside the
optical beam path. To reduce reflection of the writing laser beam at the fiber's surface, the
fiber and is immersed into a liquid bath 100, which contains liquid having an index of
refraction substantially matching the index of refraction of the surface of the optical fiber 120.
Using this assembly, the laser beam 92 is focused into the liquid bath 100 and into a focal
point within the core of the optical fiber 120. The position of the focused spot in the plane
transverse to the optical axis is controlled by adjusting the linear translation stages (not
shown). These translate the beam relative to the optical axis of the lens, thereby causing the
focus spot to move within the transverse plane but not move substantially relative to the distal
end of the fiber.
While the present invention is characterized as an optical fiber diffuser, it may
also be used to detect light in treatment protocols using multiple optical fibers or separate
sources of illumination. Further, the field of use of the present invention is not limited to
biomedical applications, but includes all applications in which remote delivery or sensing of
light is necessary or desirable. The method of creating light scattering centers within an
optical fiber by optical damage is specifically not limited to conventional optical fibers, but
may be applied to any optically transparent material where the inclusion of scattering centers
is desired for light diffusion or detection.
The above is a detailed description of particular embodiments of the invention.
It is recognized that departures from the disclosed embodiments may be within the scope of
this invention and that obvious modifications will occur to a person skilled in the art. This
specification should not be construed to unduly narrow the full scope of protection to which
the invention is entitled.