WO1999023041A1

WO1999023041A1 - Fiber optic diffuser and method of manufacture

Info

Publication number: WO1999023041A1
Application number: PCT/US1998/023003
Authority: WO
Inventors: Steven J. Rychnovsky; Michael G. Shinn
Original assignee: Miravant Systems, Inc.
Priority date: 1997-10-30
Filing date: 1998-10-30
Publication date: 1999-05-14
Also published as: AU1288899A

Abstract

A fiber optic diffuser is disclosed in which the scattering elements are generated by an optical damage process to the core of an optical fiber. This eliminates the need to manufacture, and attach, a separate diffusing element. The location of the individual scattering elements can be selected arbitrarily, which allows diffusers with arbitrary irradiance distributions to be fabricated. A method of manufacturing the diffuser using a high power laser source is also disclosed.

Description

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.

Claims

CLAIMSWhat is claimed is:

1. A method of diffusing light from a glass body, comprising the steps of:

a) focusing a relatively strong laser beam to a point within the glass body so as to

heat a small region within the glass body and thereby permanently modify the small region's

microscopic structure; b) allowing the small region within the glass body to cool; and

c) applying a light source to the glass body so that the modified microscopic

structure of the glass body will cause at least some of the applied light to be scattered.

2. The method of claim 1 wherein the glass body comprises a core surrounded by

a cladding, the glass body having a proximal and a distal end.

3. The method of claim 2 wherein the laser beam is focused to a point within the

core through the cladding.

4. The method of claim 2 wherein the laser beam is focused to a point within the

core from the distal end of the glass body.

5. The method of claim 1 wherein the glass body has an outer surface having an

index of refraction, the method further comprising the step of immersing the glass body in a liquid having an index of refraction substantially matching the index of refraction of the outer

surface prior to focusing the laser beam to a point within the glass body.

6. The method of claim 5 wherein the outer surface comprises either a core, a

cladding surrounding the core, or a protective jacket surrounding the cladding.

7. A method of diffusing light from an optical waveguide having a guiding core

comprising the steps of:

a) focusing a relatively strong laser beam to a point within the core of the

waveguide to heat a focal region within the waveguide and thereby permanently modify the

focal region's optical properties;

b) allowing the focal region to cool; and

c) applying a light source to the optical waveguide so that the modified structure

of the waveguide will cause at least some of the applied light to be scattered.

8. The method of claim 7 wherein the guiding core is comprised of a transparent

glass.

9. The method of claim 7 wherein the guiding core is comprised of a polymer.

10. The method of claim 7 wherein the optical waveguide further comprises a

cladding surrounding the guiding core, and wherein the guiding core comprises a proximal

and a distal end.

11. The method of claim 10 wherein the laser beam is focused to a point within

the guiding core through the cladding.

12. The method of claim 10 wherein the laser beam is focused to a point within

the guiding core from the distal end of the optical waveguide.

13. The method of claim 7 wherein the optical waveguide has an outer surface

having an index of refraction, the method further comprising the step of immersing the

optical waveguide in a liquid having an index of refraction substantially matching the index

of refraction of the outer surface prior to focusing the laser beam to a point within the optical

waveguide.

14. The method of claim 13 wherein the outer surface comprises either the guiding

core, a cladding surrounding the guiding core, or a protective jacket surrounding the cladding.

15. A method of forming a fiber optic diffuser, the diffuser comprising an optical

fiber having a core and a cladding, and having a proximal and a distal end, the method

comprising the steps of:

a) arranging a writing laser with high peak power capable of emitting a laser

beam;

b) arranging an optical lens for focusing the writing laser beam on a focal point

within the core of the optical fiber; c) emitting laser energy from the writing laser sufficient to heat a small region

within the core near the focal point and thereby permanently modify the small region's

microscopic structure; and

d) allowing the small region within the core to cool.

16. The method of claim 15 wherein the writing laser is capable of emitting a

beam of relatively strong pulses or an externally modulated, relatively high power beam.

17. The method of claim 15 wherein the laser beam is focused to the focal point

within the core through the cladding.

18. The method of claim 15 wherein the laser beam is focused to the focal point

within the core from the distal end of the optical fiber.

19. The method of claim 15 wherein the optical fiber has an outer surface having

an index of refraction, the method further comprising the step of immersing the optical fiber

in a liquid having an index of refraction substantially matching the index of refraction of the

outer surface prior to emitting the laser energy.

20. The method of claim 19 wherein the outer surface comprises either the core,

the cladding, or a protective jacket surrounding the cladding.

21. The method of claim 15 further comprising the step of modifying the focal

point of the focused writing laser beam to heat a subsequent small region within the core and

thereby permanently modifying the subsequent small region's microscopic structure.

22. The method of claim 21 wherein the focal point of the focused writing laser

beam is modified by moving the optical fiber along its optical axis.

23. The method of claim 21 wherein the focal point of the focused writing laser

beam is modified by changing the relative position of the optical fiber and the focal point by

moving either the optical fiber or the focal point along the optical axis of the optical fiber.

24. The method of claim 21 wherein the focal point of the focused writing laser

moving either the optical fiber or the focal point in a direction transverse to the optical axis of

the optical fiber.

25. The method of claim 21 wherein the focal point of the focused writing laser

beam is modified by rotating the optical fiber along its optical axis.

26. The method of claim 15 further comprising the step of applying a light source

to the optical fiber so that the modified microscopic structure of the core will cause at least

some of the applied light to be scattered.

27. The method of claim 26 further comprising the step of coupling an optical

detector to the optical fiber to detect and quantify the amount of applied light scattered by the

fiber optic diffuser.

28. A fiber optic diffuser comprising an optical fiber having a core and a cladding

surrounding the core, and having a proximal end and a distal end, and in which the core at the

distal end has at least one internal scattering element comprising a small region of the core

having optically induced changes to the microscopic structure of the small region.

29. The fiber optic diffuser of claim 28 wherein the proximal end is adapted for

coupling to a source of optical radiation and the at least one internal scattering element directs

a portion of the coupled optical radiation outwardly from the diffuser.

30. The fiber optic diffuser of claim 29 wherein the at least one scattering element

comprises a distribution of scattering elements along the axial length of the diffuser, and

wherein the distribution of scattering elements generally increases in a direction from the

proximal end of the diffuser to the distal end of the diffuser.

31. The fiber optic diffuser of claim 30 wherein the distribution of scattering

elements is selected to provide a substantially uniform axial distribution of optical radiation

over the length of the fiber optic diffuser.

32. The fiber optic diffuser of claim 30 wherein the distribution of scattering

elements is arranged to provide an arbitrary, non-uniform optical output from the diffuser.

33. The fiber optic diffuser of claim 30 wherein the optical radiation is used to

activate a photochemical drug and wherein the distribution of scattering elements is tailored

to a particular treatment protocol.

34. The fiber optic diffuser of claim 30 wherein the optical radiation is used to

deliver optical radiation for optically-based therapy.

35. The fiber optic diffuser of claim 28 wherein the diameter of the diffuser

remains substantially constant over the length of the diffuser.

36. An optical transmission and diffusion device comprising a core surrounded by

a cladding and having a proximal end adapted for coupling to a source of optical radiation

and a distal end for directing optical radiation outwardly, the distal end comprising a plurality

of light scattering elements distributed therein, each scattering element comprising a small

region having optically induced changes to the microscopic structure of the region.

37. The optical transmission and diffusion device of claim 36 where each

scattering element directs optical radiation entering the proximal end outward from the distal

end of the device.

38. The optical transmission and diffusion device of claim 36 wherein the

distribution of scattering elements is selected to provide a substantially uniform axial

distribution of optical radiation over the distal end of the optical transmission and diffusion

device.

39. The optical transmission and diffusion device of claim 36 wherein the

distribution of scattering elements generally increases along the distal end of the optical

transmission and diffusion device.

40. The fiber optic diffuser of claim 36 wherein the distribution of scattering

41. The optical transmission and diffusion device of claim 36 wherein the optical

radiation is used to activate a photochemical drug and wherein the distribution of scattering

elements is tailored to a particular treatment protocol.

42. The fiber optic diffuser of claim 36 wherein the optical radiation is used to

deliver optical radiation for optically-based therapy.

43. The optical transmission and diffusion device of claim 36 wherein the

diameter of the device remains substantially constant over the length of the optical

transmission and diffusion device.

44. An automated process for manufacturing a fiber optic diffuser within an

optical fiber, the optical fiber having a core and a cladding, and having a proximal end and a

distal end, the process comprising the steps of:

a) 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;

b) 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;

c) 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

d) 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.

45. An automated process for manufacturing a fiber optic diffuser within an

distal end, the process comprising the steps of:

microscopic structure of the small region to be permanently modified;

b) repeating step a) at different small regions within the core to provide a

predetermined spatial population of scattering centers within the core.

46. An apparatus for forming a fiber optic diffuser, the diffuser comprising an

optical fiber having a core and a cladding, and having a proximal and a distal end, the

apparatus comprising:

a high power writing laser capable of emitting a relatively strong laser beam;

an optical means 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

microscopic structure.

47. The apparatus of claim 46 wherein the optical means comprises a lens, the lens

comprising means for allowing the optical fiber to pass through the lens such that the focal

point within the core of the optical fiber may be adjusted to any arbitrary position along the

length of the optical fiber.

48. The apparatus of claim 46 wherein the optical fiber has an outer surface having

an index of refraction, the apparatus further comprising a means for holding a liquid having

an index of refraction substantially matching the index of refraction of the outer surface, and

wherein the emitted laser beam is focused on a focal point within the core of the optical fiber

within the means for holding a liquid.

49. The apparatus of claim 48 wherein the outer surface comprises either the core,

the cladding, or a protective jacket surrounding the cladding.

50. A method of phototherapy comprising the steps of:

a) placing a fiber optic diffuser in proximity to a treatment site, the diffuser

comprising a core and having a proximal end adapted for coupling to a source of therapeutic

comprising a plurality of light scattering elements distributed therein, each scattering element

comprising a small region of material having optically induced changes to the local structure

of the material;

b) providing at least one source of therapeutic optical radiation to the proximal

end of the fiber optic diffuser; and

c) activating the source of therapeutic optical radiation to effect treatment with

diffused radiation.

51. The method of claim 50 wherein the diffuser further comprises a cladding

surrounding the core.

52. The method of claim 51 wherein the diffuser further comprises a protective

jacket surrounding the cladding.