Multimode, Large-Core, and Plastic Clad (PCS) Fibers

This is a continuation from the previous tutorial - Elliptical core and D-shape Fibers

1. INTRODUCTION

After years of playing ensemble roles, large-core multimode fiber has stepped into the spotlight of fiber optic technology and innovation. From the smallest of veins in the human body, to the vastness of the universe, when the need for every photon matters, the advantages of large-core \((>200\) \(\text{micron})\) multimode specialty fibers are taking the lead.

As the name implies, multimode fibers are those types of fibers designed to carry multiple rays of light or modes. There are two types of multimode fibers: step index and graded index. For purposes of this chapter, we discuss the types and applications of large-core step-index multimode optical fibers.

Many industrial and medical applications require a range of geometries, clad– core ratios, and numerical apertures \(\text{(NAs)}\) for step-index multimode fibers depending on whether the end-use is for laser surgery, illumination, or sensing. Fiber core geometries can range from 100 \(\mu\text{m}\) to more than 1000 \(\mu\text{m}\), and the clad–core ratios can range from 1.05 to more than 1.20.

In general, the larger the \(\text{NA}\) available, the smaller the clad–core ratio or the smaller the fiber core can be. Smaller cores and core–clad ratios lead to lesser expense for materials and more flexible fibers.

Smaller dimensioned optical fibers also permit the use of smaller catheters, enabling associated surgery procedures to be less invasive. Small systems also can require broader illumination from optical fibers that may be minimized in number or in size.

For ultraviolet \(\text{(UV)}\) applications, pure silica core all-silica optical fibers are the more reliable and have the best transmission. Generally high-power transmission also requires the excellent chemical stability of all-silica optical fibers. In the past, all-silica fibers were restricted to \(\text{NAs}\) of 0.22 or less.

Early on, pure silica core and doped silica clad fibers of this \(\text{NA}\) were not very thermally stable for large diameter sizes, for example, much above 800-\(\mu\text{m}\) cores.

The thermal problems were related to the interface between the doped and undoped silicas and, over time, were solved so that today 0.22 \(\text{NA}\) fibers with cores much greater than 1 mm are available with suitable thermal stability. An \(\text{NA}\) of 0.22 has an acceptance angle of about 25 degrees.

Medical applications for lasers and optical fibers continue to grow and evolve over the years. Much of this growth is spurred by the development of more minimally invasive procedures, which can benefit from small-diameter fibers to deliver high radiation energy from laser sources in a variety of emission patterns.

These applications also benefit from using the low intrinsic loss character of silica-based core material, as well as the power capability of a silica/silica construction. Pure silica core all-silica optical fibers are now available with an \(\text{NA}\) of \(0.30+0.02\).

Variations include fibers with nonsolarizing \(\text{UV}\) transmission, as well as fibers with transmission through the near-infrared \(\text{(NIR)}\) region of the electromagnetic spectrum.

Additionally ultrahigh NA fibers with silica cores and silica/silica structures are now available for use in the visible and \(\text{NIR}\) regions with effective \(\text{NAs}\) higher than 0.6. Properties of these fibers are presented and the advantages over other fibers and potential medical applications are discussed in the following sections.

To produce a step-index multimode fiber, a core material of silica (either pure or doped) is clad with a lower index material (doped silica, hard plastic, plastic) to form a waveguide, as illustrated in Fig. 1.

These fibers will have a protective jacket beyond the cladding that does not effect the transmission of light through the fiber, although there are additional

coatings and buffer layers that can be added to change the \(\text{NA}\) of a fiber. The \(\text{NA}\) of the fiber is calculated as 

\[\tag{1}\text{NA}=[n^2_\text{core}-n^2_\text{clad}]^{1/2}.\]

Step-index fibers will only propagate light that enters the fiber within its acceptance angle. For certain applications, there are great benefits to either increasing or reducing the \(\text{NA}\) and thereby changing the acceptance angle.

The fiber-pure synthetic fused silica core can be of a high \(\text{OH}\) content for applications in the deep \(\text{UV}\) to visible \(\text{(VIS)}\) wavelengths or a low OH content for use in the VIS to \(\text{NIR}\) wavelengths.

The low \(\text{OH}\) silica core can be doped to produce fibers with very high NAs. Silica is a good material based on its optical and thermal properties. It can be produced synthetically with ultrahigh purity and can operate from less than 200 to more than 2400 nm with little absorption (Fig. 2). 

The cladding materials can be doped silica, hard plastic, or plastic. The combination of the silica core and various cladding options offers a multitude of fiber products for a wide range of applications. 

The upper limit number of modes that can be carried in a step-index fiber is known as the normalized frequency parameter, or \(V\) number. It is calculated as follows:

\[\tag{2}V=(2\pi a/\lambda)NA\]

2. LARGE-CORE SILICA/SILICA (ALL-SILICA) FIBER

A pure fused silica core with doped silica clad produces an industry-standard fiber with an \(\text{NA}\) of 0.22.

These fibers are available with core diameters from 50 to 2000 microns. Silica/silica fibers can offer excellent transmission from the deep \(\text{UV}\) to the \(\text{NIR}\), along with a good focal ratio degradation, which is important in 

spectroscopy applications, especially in astronomy. Individual silica/silica fibers with polyimide coatings can handle temperatures of \(400^\circ\) and in fused bundle configurations can reach close to \(1500^\circ\) at the fused ends. Applications in medical/pharmaceutical, forensic, sensors, remote detection, or monitoring of hazardous environments all benefit from the use of optical fibers, and all-silica fibers are best suited to provide this mechanism, especially in the \(\text{UV}\) region.

The use of excimer lasers and strong \(\text{UV}\) light sources has grown in medical and industrial fields, as has the number of spectroscopic techniques that use \(\text{UV}\) absorbance and luminescence measurement to characterize material. Although some commercially available fibers can handle transmission of low intensities of laser radiation, there still exist difficulties for high-power radiation transmission.

These standard fibers offer low attenuation and high transmission in the 215- to 254-nm spectral range, but on exposure to unfiltered deuterium lamps sources, the fibers drop to less than 50% transmission within 24 hours of continuous irradiation. Standard \(\text{UV}\) fibers develop color centers when subjected to pulsed excimer laser radiation (193 nm).

This solarization issue has been virtually eliminated by the development of Optran \(\text{UVNS}\) \(\text{UV}\) Non-Solarizing fibers. The \(\text{UVNS}\) fibers exhibit only minor changes in transmission when exposed to unfiltered deuterium lamp sources, and while the standard synthetic silica fibers developed color centers within 10,000 pulses of excimer laser radiation, the \(\text{UVNS}\) fibers remained virtually unchanged, as can be seen in Fig. 3.

Although these fibers are drawn using standard techniques, the preforms are produced using a proprietary procedure for the modified plasma chemical vapor deposition of silica.

Although the first Optran \(\text{UVNS}\) fibers had an \(\text{NA}\) of 0.22, fibers have been developed with \(\text{NAs}\) of 0.26–0.30, allowing sampling of larger areas and greater collection of transmitted or reflected beams from material under test.

The acceptance circle at a fixed distance from the fiber end increases dramatically from the 0.22 to the 0.30 \(\text{NA}\), with the 0.30-\(\text{NA}\) fiber having an acceptance circle that is 86% larger. The long-term stability in \(\text{UV}\) applications 

and larger \(\text{NAs}\) extend the range of usefulness for these fibers in medical and spectroscopic applications. The larger \(\text{NA}\) allows the use of a smaller fiber core, which reduces the cost and increases the flexibility of the fibers, especially for remote detection, sensing, and medical applications requiring high-power densities such as excimer laser angioplasty and the perforation of the heart muscle.

Nonsolarizing silica/silica optical fibers can be fused to form a pattern of fibers slightly deformed into a hexagonal shape that produces a tight-packed structure with minimal dead space. These bundles are excellent replacements for epoxy bundles or liquid-light guides, as they provide higher transmission over the wavelength range and can withstand temperatures up to \(1500^\circ\); the maximum for an epoxy bundle is \(400^\circ\), and the liquid-light guides withstand less than \(50^\circ\).

The bundles can be used with high-power lasers, pump diode lasers, and high-intensity \(\text{UV}\) light sources. Applications include high-temperature sensing, illumination, spot curing, and wafer fabrication.

When these bundles are produced with nonsolarizing fibers, the lifetime for the bundles is greatly improved over that of liquid-light guides and the transmission can be as much as 50% higher (Figs. 4. and 5.).

Because the bundles can be produced in lengths of up to 20 m, they offer an efficient cost-effective solution for remote spectroscopy. The active area for these bundles can be as small as 0.8 mm and as large as 20 mm.

Fiber optic bundles with epoxy ends have almost limitless room for design. From a common end of bundled fibers (virtually no limit to the size of the active area), almost any number of legs can be broken out for either the distribution of light to or the collection of light from a source.

These bundles can be produced with fibers with core diameters from \(50\mu\text m\) to 1.5 mm in randomized or mapped distribution. The design of the bundle depends on its intended use and can be configured with the fibers in a spot, rectangular, linear, circular, or almost any other geometry.

The available options allow for applications from spectroscopy to instrumentation to industrial monitoring and sensing. Rugged jacketing materials are available for field applications including mining and downhole

sensing. Bundles of small fibers are very flexible, with the bend radius being based on the diameter of a single fiber, not the entire bundle.

This allows instrumentation designers the flexibility of locating equipment out of harms way and routing only the fibers. Industrial, spectroscopic, aircraft, military, space, tactical, and hazardous sensing applications all benefit from the limitless design potential available. 

3. HIGH NA AND LOW NA SILICA/SILICA FIBERS

Many medical and sensing applications have need of ‘‘broad’’ irradiation patterns but benefit from small-diameter fibers to provide minimal invasive surgery. These applications also benefit from using the low intrinsic loss character of silica-based core material and the power capability of a silica/silica construction.

Pure silica core all-silica optical fibers are now available up to an \(\text{NA}\) of \(0.30\pm 0.02\). Variations include fibers with nonsolarizing \(\text{UV}\) transmission and fibers with transmission through the \(\text{NIR}\) region of the electromagnetic spectrum.

Additionally ultrahigh \(\text{NA}\) fibers with silica cores and silica/silica structures are now available for use in the \(\text{VIS}\) and \(\text{NIR}\) regions, with effective \(\text{NAs}\) higher than 0.6.

Medical applications require a range of geometries, clad– core ratios, and \(\text{NAs}\) for step-index multimode fiber depending on whether the end-use is for laser surgery, illumination, or sensing.

Fiber core geometries can range from \(100\;\mu\text{m}\) to more than \(1000\;\mu\text{m}\), and the clad–core ratios can range from 1.05 to more than 1.20. In general, the larger the \(\text{NA}\) available, the smaller the clad–core ratio or the smaller the fiber core can be. Smaller cores and core– clad ratios lead to lesser incurred materials expense and more flexible fibers. Smaller dimensioned optical fibers also permit the use of smaller catheters, enabling associated surgery procedures to be less invasive.

Small systems also can require broader illumination from optical fibers, which may be minimized in number or in size. For \(\text{UV}\) applications, pure silica core all-silica optical fibers are the most reliable and have the best transmission. Generally high-power transmission also requires the excellent chemical stability of all-silica optical fibers. In the past, all-silica fibers were restricted to \(\text{NAs}\) of 0.22 or below.

Early on, pure silica core and doped silica clad fibers of this \(\text{NA}\) were not very thermally stable for large-diameter sizes (e.g., much above 800-\(\mu\text{m}\) cores). The thermal problems were related to the interface between the doped and undoped silicas and over time were solved, so today 0.22-\(\text{NA}\) fibers with cores much greater than 1 mm are available with suitable thermal stability. An \(\text{NA}\) of 0.22 has an acceptance angle of about 25 degrees.

Medical applications for lasers and for optical fibers continue to grow through time. Much of this growth is spurred by the development of more minimally invasive procedures, which puts greater demands on using the smallest feasible optical fibers and systems.

At the other end of the spectrum of uses are the new medical applications/procedures that use short pulsed radiation at very high power levels and power densities. Large-diameter fibers are often used because of the power densities. Even here, the ability to lower core sizes is welcomed because of their improved handling characteristics.

All-silica fibers for use in the \(\text{VIS}\) to \(\text{NIR}\) wavelengths can now be produced with \(\text{NAs}\) as high as 0.53. For \(\text{NAs}\) up to 0.30, the fiber construction employs a pure silica core with doped silica clad.

For \(\text{NAs}\) of 0.37 and higher (up to 0.53), the silica core is doped. High-power laser diodes typically operate in the \(\text{VIS}\) to \(\text{NIR}\) ranges of the spectrum, and as a result, fibers with doped cores can be used for most applications.

The increased \(\text{NAs}\) of these fibers correspond to an acceptance area that is up to 550% larger (comparing 0.22–0.56; see Fig. 6.). The ability to provide a smaller fiber that is able to capture all of the lasers’ output power without the use of lenses or additional optical components allows for a more reliable system (fewer components) within a smaller package.

The higher \(\text{NA}\) of these fibers offers a benefit in photodynamic therapy \(\text{(PDT)}\) and diagnostic applications. The diffusers used to distribute light to the diseased tissue take light from the higher order modes traveling in a fiber, and the higher the \(\text{NA}\), the greater the potential for harvesting these modes near the cladding– core interface. On the diagnostic side, the broader acceptance angle of the fibers allows for the most efficient collection of the luminescence.

The ultrahigh \(\text{NA}\) fibers described can be used as delivery fibers, especially for high-power diode laser systems. The benefits arise because of requirements of

phase space to allow reduction in size from the dimension of a bundle of coupling fibers to a delivery fiber size. In other words, the product of \(\text{NA}\) and fiber bundle size is equal to the product of the delivery fiber size and its \(\text{NA}\) 

Other uses of the large \(\text{NA}\) fibers are in illumination applications, especially in cases in which the fiber end is not in air. For example, fewer illumination fibers might be used in an ophthalmology application if the \(\text{NA}\) of the fiber can be more than 0.50. Hands-free helmet-type illuminators are another area that benefits from being able to use these ultrahigh \(\text{NA}\) optical fibers. 

Medical applications that generally need to treat larger areas and whose light sources are not in the \(\text{UV}\) can be more efficiently performed with larger \(\text{NA}\) fibers, as more area is covered by the fiber output.

Examples might be \(\text{PDT}\), wound healing, and general interstitial radiation therapy. Whether the medical action is by photons directly or indirectly as converted to thermal phonons, these applications benefit greatly from large \(\text{NA}\) optical fibers. Some aspects of tissue welding that are shared with wound healing such as a need to treat areas much larger than the output of a standard optical fiber can easily be seen to benefit from fibers with larger \(\text{NA}\) values.

A special point with reference to the ultralow \(\text{OH}\) grades of these fibers is that they can be used in medical applications with lasers or other sources operating at wavelengths above 2 \(\mu\text{m}\).

Figure 7. depicts the mid-IR transmission spectrum for one such fiber. Some variations have also been used to transmit radiation at wavelengths as high as 2.4 \(\mu\text{m}\). They provide good transmission in a very desirable wavelength and with the ability to maintain high-power densities.

Photons are available from sources other than lasers. Coupling photonic energy in many cases using lamps, high-brilliance \(\text{LEDs}\), or other high, power \(\text{LEDs}\) can be a challenge, because the sources often have broad beams and are projected in highly divergent beams from the source.

Rather obviously, optical fibers with large to ultralarge \(\text{NAs}\) would be a benefit in capturing the photons and transmitting them to some remote application area, such as inside a patient or to several patients in adjacent stations, rooms, or beds.

In summary, optical fibers are now available for use or in the design of photonic treatment systems that have the following properties: \(\text{NA}\) values up to 0.30 for pure silica core, fluorosilica-doped cladding, high or low \(\text{OH}\), in nonsolarizing \(\text{UV}\) grades; \(\text{NA}\) values up to 0.56 for germanium-doped core, fluorosilica-doped cladding, low to ultralow \(\text{OH}\) grades. These open up more efficient uses of fiber optics and photonics in a wide range of medical applications and treatments.

There are all-silica fibers available with very low \(\text{NAs}\) (down to 0.11), which allows for the coupling of narrow active area devices. These have applications in delivery of power from laser diodes and narrow band devices. The advantages of silica coupled with the options of very low to very high \(\text{NA}\) allow for the development of an ever-expanding list of applications never considered.

Figure 7. \(\text{Mid}\)-\(\text{IR}\) spectral loss for a 0.28 numerical aperture low-\(\text{OH}\) silica/silica fiber.

4. PLASTIC AND HARD POLYMER CLAD SILICA FIBERS

Plastic Clad Silica Fibers 

Plastic clad silica \(\text{(PCS)}\) fibers have structures with a silica glass core surrounded by a thin plastic (silicone) cladding material (Fig. 8.). Oftentimes, a protective jacket made from polymeric materials such as Tefzel is also applied.

As the cladding material is not \(\text{UV}\) cured in these fibers, they will have better transmission in the \(\text{UV}\)-wavelength range while offering the advantage of being less expensive than all-silica fiber designs. \(\text{PCS}\) fibers can be more difficult to terminate, as the fiber core can piston from within the cladding. The \(\text{NA}\) of this fiber is 0.40 in short lengths. 

Hard Polymer Clad Silica

Hard polymer clad silica \(\text{(HPCS)}\) fibers have emerged over the last few decades as an option for many applications in the medical, industrial, scientific, and military markets.

The fiber structure is generally a pure fused silica core with a cladding of a thin hard polymer material and an outer jacket. 

The \(\text{HPCS}\) optical fibers function well over a wide range of temperatures. Samples of fiber exposed to liquid nitrogen temperatures (-\(196^\circ\)) and below were used to carry spectroscopic information from materials held at these

temperatures. On the other end, the fibers are usable up to \(125^\circ C\) almost continuously. Of more interest in medical applications is that the static fatigue behavior of these fibers remains predictable and unchanged even in moist (steam) environments. 

The fibers are available in both high and low \(\text{OH}\) for operation in the \(\text{UV}\), \(\text{VIS}\), and \(\text{NIR}\) regions. The \(\text{HPCS}\) fibers will transmit \(\text{UV}\) wavelengths but use at less than 400 nm is hampered by the absorption of the hard cladding, as depicted in Figs. 9. and 10.

However, developments have led to HPCS fibers with attenuations less than 1 \(\text{dB}\)/\(\text{m}\) even at 300 nm and less than 1.5 \(\text{dB}/\text{m}\) at 275 nm.

The properties of this fiber design offer advantages in a variety of applications. The ease of termination and high strength make the fiber suitable for short data links, especially in harsh environments including those with exposure to radiation.

Because the fibers have a high core-to-clad ratio and the cladding remains on during termination, it is possible to do terminations on the fiber with very little loss due to fiber core mismatches. Fibers can be cut and connectorized in field environments, allowing for great flexibility in military, mining, and oilfield sensing applications.

In the medical market, the mechanical, optical, and structural properties of the fiber are especially useful in the design of laser delivery, endoscopic, and biosensing systems. High core-to-clad ratio provides better coupling, ability to accept higher energy density, and reduced losses due to bending or flexing.

In the competitive world of medical disposables, \(\text{HPCS}\) fibers offer an advantage in cost as well. Industrial applications for the fibers include sensors for indicating distance, temperature, proximity, liquid levels, and

short-haul data links, often to areas with hazardous or extremely harsh environments. Use of \(\text{HPCS}\) fiber in the military includes the initiation of explosives, tactical short-link communications, and vehicular systems.

The initiation of explosives with fiber optics was one of the earliest applications for \(\text{HPCS}\) fibers and remains in use in both mining and military applications. The automotive industry has investigated the use of \(\text{HPCS}\) fibers for applications that require higher temperature and strength than is available in all-plastic fiber designs. 

The \(\text{HPCS}\) fibers are available with \(\text{NAs}\) of 0.37–0.48, and there is ongoing research for increasing these numbers. Constant investigation of new cladding materials offers the opportunity for even higher reliability fibers in terms of strength and fatigue.

The unique properties of \(\text{HPCS}\) fibers will continue to offer benefits to an ever-increasing number of innovative new applications.

5. SILICA FIBERS WITH NANO-POROUS CLADDING/COATING

Unlike all-silica fibers, which require a jacket or buffer material to protect the outer layer from potential damage due to environmental exposure to moisture, fibers are being produced with a nano-porous cladding that requires no additional jacket.

Using modified sol-gel technology, the cladding is produced on line from an oligimeric organo-silicate. ‘‘Sol-gel’’ technologies transition a liquid ‘‘sol’’ into solid ‘‘gel’’ form and allows for great flexibility in design.

The objectives of this research are the development of radiation-resistant multimode fibers for space applications, fiber optic lines that could have signal taken off without creating a break in the main line, and biomedical/technological applications in which the fibers could be used as a tip for \(\text{PDT}\). Placement of sensing materials, even high toxic or active ones, could be achieved by including them in the nano-porous cladding.

They could be placed in an inactive form and then remotely activated by a photonic signal. Some specific applications could include direct treatment of body tissues and fluids, sensing the delivery dosages of radiation procedures, and locating specific tissues, such as cancerous tissue with minimally invasive techniques. Tests have indicated that complexes such as rhodamine can be activated by signals traveling in the fiber core after incorporation of the complex in a section of the modified sol-gel clad fiber.

The guided waves within the fiber core extend into the cladding for some distance— where the complex is incorporated into the cladding—thus, interacting with it and activating it. Further studies on these effects will allow for the design of sensors for various chemical and biochemical moieties.

Development of high-strength fibers with the potential of having modified sections interact with the surrounding environment is an exciting advancement for sensing and biomedical applications.

6. UNLIMITED APPLICATION POTENTIAL

In this chapter, we have indicated the construction of specialty, large-core, step-index multimode fibers and the variations of manufacture that make possible fibers with choices for wavelength performance and lifetime, \(\text{NA}\), strength and fatigue, and high coupling efficiency in everything from a single strand to a bundle of thousands of fibers.

Much like an artist choosing a palette, designers now have options to use fibers for applications never considered. On the most basic level, a fiber optic moves light, for a reason as simple as illumination to as complex as the composition of a star. 

In the same way, every human has a fingerprint unique to him or her, every element has a signature that can be defined spectrally as belonging only to that element. A spectrometer can identify the elements present in an object by studying the makeup of the light emitted. Fiber can be the bridge between the mystery of an object’s composition and the key to unlocking that mystery, the spectrometer.

By deciphering the spectral response, whether it be the emission of light from a star, a sample of groundwater, or human cells, we can begin to identify the physical properties of the material. The study of these spectra (spectroscopy) is used in physical and analytical chemistry to identify a substance by the spectra emitted. In astronomy, a telescope can use a spectrograph to measure the chemical composition and physical properties or to measure the speed of astronomical objects.

The various disciplines of spectroscopy \(\text{(UV, VIS, IR, Raman,etc.)}\) all benefit from the availability of specialty optical fibers and assemblies. The advancements in specialty optical fibers make it possible to engineer probes capable of delivering and collecting light in completely new and innovative ways.

Regardless of the end-use, delivery of light from a source is the first application of optical fibers. Specialty step-index multimode fibers offer the means of coupling very wide or very narrow beams of light over a wide spectrum for delivery to the other side.

Individual fibers or bundles of fibers can be coupled to light sources for the illumination of materials or samples or the delivery of a laser beam. The use of fiber optics in the medical world is explosive and the most widely known use of the specialty fiber to the general public.

Specialty fiber optics coupled with laser technology now allow for minimally invasive surgical procedures that would have required open surgeries. Urology (soft tissue and lithotripsy), dentistry, ear, nose, and throat, ophthalmic, orthopedic, gynecology, and vascular applications all benefit from the use of specialty fibers. Shorter recovery times with less pain, better wound healing and blood coagulation, and less chance of infection are all byproducts of the development of these fibers.

\(\text{PDT}\) is generally used to treat hyperproliferative tissue diseases, including dysplasia. Such diseases commonly affect extended volumes of tissue but from a patient standpoint are relatively localized. In the normal application of \(\text{PDT}\) to these diseases, the light, with appropriate wavelength for the photosensitizer being used, is transmitted to the treatment site through optical fibers that are terminated at their distal end with diffusers.

Diffusers may be lenses, elongated sections used to scatter light sideways or special tips that deflect energy primarily around the fiber tip rather than forward. In normal operation, the diffusers used to distribute light from the optical fiber transmission medium to the diseased tissue take light from the higher order modes traveling in the fiber and disperse them into the surrounding tissue.

The higher the \(\text{NA}\) of the optical fiber, the greater the potential for having most of the light in higher order modes near the cladding–core interface, where they can be more easily harvested for treating the diseased tissue. Overlaunching treatment light into the fibers helps to populate the higher order modes. The number of modes in the fibers grows much faster than linearly as the \(\text{NA}\) increases for a fixed core size and operating wavelength( s). Small gains \(\text{NA}\), thus, can have great benefits.

\(\text{PDTs}\) will offer the world a better standard of care for many types of cancer. Photosensitive drugs delivered to a site in the body and activated by a laser delivered through a fiber will revolutionize the way we view the treatment of disease.

Specialty fiber optic products are a means to many ends. From the scientific investigation of everything from groundwater to the makeup of the universe to the opportunity to initiate explosives without the loss of human life to the health concerns of our world, specialty fiber plays a leading role, a role that will continue to expand to meet the ever-changing requirements of the future.