Heavy metal-oxide glass optical fibers for use in laser medical surgery

An improved optical fiber for transmitting mid-infrared wavelength laser light in surgical instruments, includes, a heavy-metal oxide component, preferably GeO.sub.2 doped with heavier cations and anions, is capable of delivering of at least three watts of laser power continuously for more than ten minutes, without failure. This glass fiber has an .alpha.(dB/m) at 2.94.mu.m of 10, preferably less, and can transmit at least 27% of the IR through a thickness of one foot.

FIELD OF INVENTION 
The present invention relates to improved IR transmitting fibers and, more 
particularly, to the use of oxide and heavy-metal containing glass fibers 
for coupling with a mid-infrared laser for medical laser surgical 
applications. 
BACKGROUND OF THE INVENTION 
Laser microsurgery and coronary angioplasty require precise removal of 
tissue without thermally damaging the surrounding tissues. Such 
medical/surgical lasers require using a wavelength in the mid-infrared 
wavelength region, i.e. between about 1.0 and 3.0 microns, which is the 
wavelength range most strongly absorbed by animal tissue. The 2.94 micron 
wavelength of the Er:Yag laser is the most well-absorbed by animal tissue 
and thus the Er:Yag laser is preferred for many surgical procedures. 
The tissue absorption coefficient (.alpha.=1000 cm.sup.-1) is the highest 
with the Er:Yag laser. The .alpha. of other existing medical lasers ranges 
from 4 cm.sup.-1 for a He-Ne laser to 600 cm.sup.-1 for a CO.sub.2 laser. 
Thus, the Er:Yag is widely m- 1 for a C02 viewed as the best surgical 
laser (see "Laser Evolution", Nov. 1991). To efficiently use the power 
delivered by the Er:Yag laser, a ruggedized infrared (IR) optical fiber 
which transmits at 2.94 microns must be used. Coupled to the output of the 
laser beam, the IR fiber can deliver the power to ablate tissues. 
Infrared transmitting zirconium fluoride based glasses such as ZrF.sub.4 
--BaF.sub.2 --LaF.sub.3 --AlF.sub.3 --NaF--PbF.sub.2 (see Esterowitz et 
al, "Angioplasty With a Laser and Fiber Optics at 2-94 .mu.m") have 
emerged as the materials of choice for the IR transmitting fiber because 
their optical transmission between 2.5 microns to 5.0 microns exceeds 90 
percent, as shown in FIG. 1. Similarly, fluoride glass fibers exhibit 
optical losses as low as 0.06 dB/m at 2.94 microns. This is equivalent to 
a transmission of over 90 per cent in a one foot long fiber. A flexible 
fiber hand-piece with a minimum length of 6 inches and a desirable length 
of one foot or greater can be made adaptable to many laser delivery 
systems. 
However, the zirconium fluoride based glass fibers have a drawback in that 
they are capable of carrying only very low power. Investigations recently 
carried out at several medical laser companies have shown the following: a 
300 micron core fluoride glass fiber, when coupled to an Er:Yag laser 
operating with an output power of 180 mJ at a repetition rate of 10 Hz, 
could transmit around 135 mJ or 1.35 watts but failed after only two 
minutes. As the laser output power increased, the fiber damage occurred 
much faster. Fiber damage always occurred at the fiber input end face or 
along the fiber length resulting in a localized melt-down of the glass 
followed by power rupture. As a result, zirconium fluoride based glass 
fibers have a very limited use in conjunction with the Er:Yag laser, and 
in effect can only be used for a very short time because fiber damage 
quickly occurs. 
It is known that AlF.sub.3 used as a dopant for ZrF.sub.4 base glass can 
increase the Tg of the glass considerably. However, the quantity of 
AlF.sub.3 which can be incorporated as a dopant is very low, as AlF.sub.3 
tends to destabilize the glass and make it difficult to form into fibers. 
Even when formed, such fibers are not stable, as the resultant AlF.sub.3 
containing glass fibers tend to easily crystallize under localized heating 
which would inevitably occur with laser usage, thus inducing fiber damage 
and failure. Therefore, the addition of AlF.sub.3 to the conventional 
ZrF.sub.4 glass is not a solution to the problem of localized melt-down 
and resultant failure of the fiber. AlF.sub.3 based glass of about 30 mol% 
AlF.sub.3 is also known, but this glass is very unstable and difficult to 
form into fibers. 
SUMMARY OF THE INVENTION 
An object of the present invention is therefore to overcome deficiencies in 
the prior art, such as indicated above. 
Another object of the present invention is to provide improved IR 
transmitting optical fibers, especially useful for laser surgery. 
A further object of this invention is to provide a family of optical fibers 
which are transparent to IR between 1 and 3 microns and which can be used 
with a surgical laser, e.g. an Er:Yag laser, which operates around the 
main absorption band of water and which can deliver at least 1.35 watts of 
laser power continuously for more than ten minutes, and which optical 
fibers can be used to transmit laser light for precise cutting of animal, 
e.g. human, tissues. 
A study of zirconium fluoride based optical glass fiber used with the 
Er:Yag laser has revealed damage induced by localized heating. When the 
Er:Yag laser beam was launched into the fiber, the fiber input end face 
was subjected to the highest power density which resulted in the 
overheating of surface particle defects. Such localized overheating caused 
the fluoride glass to soften and then partially crystallize. It was also 
observed that when intense overheating occurred, the tip of the fiber 
completely melted. The same phenomenon could apply to damage spots, 
especially the submicron defects in the nature of platinum particles 
dissolved in the glass from the melt crucible or microscopic bubbles and 
crystalline impurities, present along the length of the fiber. 
It has thus been determined according to the present invention that in 
order to prevent such localized heating that would eventually damage the 
fiber, high temperature glasses having high glass transition temperature 
(Tg), thus high softening and high crystallization temperatures, and 
capable of transmitting at 2.94 microns, must be used as the fiber 
material. In addition, these glasses must have a high glass forming 
ability, i.e. a low tendency toward devitrification or crystallization. 
High grade and improved laser grade surgical fibers have therefore been 
developed according to the present invention based on three concepts: (1) 
proper choice of fiber material, i.e. high working temperature and stable 
glass, containing proper dopants to provide excellent IR transmission at 
2.94 microns; (2) determining preferred processing techniques to enhance 
the 2.94 micron optical transmission; and (3) determining preferred 
techniques for producing the surgical fiber in large commercial 
quantities. 
In general, the glasses of the present invention should be substantially 
water-free (less than 0.1 ppm of water), have a Tg of at least 290.degree. 
C. and preferably at least 315.degree. C., and a coupling efficiency.sup.1 
of at least 20% and preferably at least 35% and most preferably at least 
50% over an optical path length of 1 foot; in this respect, the 
transmission should be at least 40% and preferably at least 50% over an 
optical path length of 1 foot. In addition, the glass should have a 
critical cooling rate, Rc, of less than 5.5.degree. C./min and preferably 
less than 3.0.degree. C./min, where Rc is defined as the slowest cooling 
rate at which a glass melt can be quenched without inducing 
crystallization. In this way the glass fiber will be able to deliver at 
least 1.35 watts of laser power continuously for at least five minutes and 
preferably more than ten minutes, efficiently and without failure. 
FNT .sup.1 "Coupling efficiency" as here used takes into account not only 
attenuation losses through the fiber, i.e. percent transmission through 
the fiber, but also reflection losses at the fibers ends.

DETAILED DESCRIPTION OF THE INVENTION 
The preferred materials in the present invention are glasses based on or 
containing GeO.sub.2, TeO.sub.2, Sb.sub.2 O.sub.3, PbO, Bi.sub.2 O.sub.3, 
Al.sub.2 O.sub.3, P.sub.2 O.sub.5, Al (PO.sub.3).sub.3, M(PO.sub.3).sub.2 
where M is Mg, Ca, Ba or Sr, and NPO.sub.3 where N is Li, Na or K. Most 
preferred are those based on GeO.sub.2. These oxide glasses, hereinafter 
referred to as heavy-metal oxide glasses, generally exhibit a glass 
transition temperature (Tg) and a glass stability much higher than the Tg 
and the glass stability in zirconium fluoride based glasses. As a result, 
localized heating which damages the fiber is prevented. 
However, glasses formed entirely of one of these preferred oxides, 
especially those of lower molecular weight, do have a drawback in that 
their multiphonon absorption edge or infrared cut-off edge is only 
slightly above 2.94 microns. This will undermine transmission at 2.94 
microns especially in a fiber as long as one foot. The absorption of 
infrared energy depends on atomic vibrations and follows Hooke's law which 
may be expressed as: 
##EQU1## 
where .nu.=absorbing frequency (cm-1) 
.lambda.=absorbing wavelength (microns) 
f=force constant or bond strengths 
.mu.=average mass of all ions 
To push the infrared absorption edge toward longer wavelengths, the forces 
of attraction between ions should be low, i.e. the mass of the ions should 
be high. To overcome this problem, the heavy-metal oxide glasses are doped 
with even heavier cations or anions or both to stabilize the heavy-metal 
oxide ions and reduce their vibrations at the atomic level when stimulated 
by IR. While it has been previously known that adding heavy metal ions to 
glass in general will push the infrared cut-off edge toward longer 
wavelengths, this concept has never been previously used, insofar as is 
known, to increase the transmission of IR at 2.94 .mu.m in heavy-metal 
oxide glasses, especially in connection with laser usage. 
The most preferred glass of the present invention is an oxide glass where 
GeO.sub.2 is the glass former. The only GeO.sub.2 fiber known to have been 
developed prior to the present invention originated from the work of H. 
Takahashi and I. Sugimoto, "Decreased Losses in Germanium-Oxide Glass 
Optical Fiber Prepared by VAD Method", Japanese Journal of Applied 
Physics, Vol. 22, No. 3 (Mar. 83) pp L139-L140. This fiber was doped with 
20 mol% antimony (Sb) and was intended for telecommunication applications 
at 2.4 microns. At 2.94 microns, the loss of transmission of light through 
the fiber (i.e. the attenuation) was high, i.e. 10 dB/m, so that it 
transmits only about 44% of the IR through a length of one foot. It also 
has about 12% reflection losses at both ends, thus reducing its coupling 
efficiency to only 32%. Its use with an Er:Yag laser would thus result in 
low power transmission. 
To increase the transmission at 2.94 microns, it is necessary to push the 
infrared cut-off edge of the GeO.sub.2 glass toward longer wavelengths. To 
do so, it is absolutely necessary to substitute part of GeO.sub.2 with 
dopants containing either larger and heavier cations than Ge which has an 
atomic weight of 72.6, or larger and heavier anions than 0 (such as F, Cl, 
Br, I) or a combination of both. As regards the larger and heavier 
cations, it will be understood that a smaller quantity of a larger and 
heavier cation will accomplish the same result as a larger quantity of a 
cation which is not so heavy. Thus, smaller quantities of Pb, Bi, Te, Hf, 
La, Ba, etc., having an atomic weight of about 125 and greater will 
accomplish the same extension of the infrared cut-off edge as will larger 
quantities of cations having an atomic weight above 73 but less than about 
125, such Zr, Sb, As, Sr, Ca, Cd, Y, etc. Thus, for example as noted 
above, the use of 20 mol% of Sb.sub.2 O.sub.3 as a dopant for GeO.sub.2 
(80 mol%), as in the case of the Takahashi et al glass, did not push the 
infrared cut-off edge as far as most desirable. 
Dopants having either or both lighter cations and anions, such as ZnO or 
TiO.sub.2, etc. can be added to the glass in small amounts to modify glass 
properties, such as stability, hardness, etc.; but the addition of lighter 
compounds does not contribute to the transmission of 2.94 micron IR. 
Typical germanate glass compositions of the present invention are shown in 
Table 1. 
TABLE 1 
__________________________________________________________________________ 
TYPICAL GERMANATE GLASSES OF THE INVENTION 
Types Of 
Germanate 
Glass GeO.sub.2 
PbO 
PbF.sub.2 
NaF 
Alf.sub.3 
TeO2 
ZrO.sub.2 
La.sub.2 O.sub.3 
BaO 
Bi.sub.2 O.sub.3 
Sb.sub.2 O.sub.3 
As.sub.2 O.sub.3 
SrF.sub.2 
ZnO.sub.2 
CaF.sub.2 
PbCl.sub.2 
__________________________________________________________________________ 
I 43 57 
II 61 24 15 
III 60 40 
IV 40 56 4 
V 40 56 4 
VI 54 8 38 
VII 38 56 6 
VIII 43 49 8 
IX 73 27 
X 42 5 53 
XI 32 48 20 
XII 25 35 40 
XIII 80 20 
XIV 32 28 40 
XV 20 30 50 
XVI 50 30 20 
XVII 50 25 25 
XVIII 60 20 20 
XIX 18 79 3 
__________________________________________________________________________ 
From Table 1 it will be apparent that the amount of GeO.sub.2 can vary 
considerably, dependent on the co-component dopants. If one or more of 
very heavy compounds such as PbO, PbF.sub.2, PbCl.sub.2, Bi.sub.2 O.sub.3 
are used as the dopants, then the quantity of GeO.sub.2 may even exceed 80 
mol%, whereas if the dopants are of a lighter weight the quantity of 
GeO.sub.2 should preferably not exceed about 75%. The excellent stability 
provided by GeO.sub.2 diminishes when the content of GeO.sub.2 becomes 
less than about 10 mol%. The suitability of various glass compositions can 
be determined by routine experimentation, based on the teachings of the 
present disclosure. 
Besides the germanate glasses, there are other heavy-metal oxide glasses 
that are effective with the Er:Yag laser. The other heavy-metal oxide 
glasses of this invention include tellurate glasses, phosphate and 
fluorophosphate glasses, antinonate glasses, bismuth and lead glasses and 
aluminate glasses. These, however, suffer from one or more difficulties as 
pointed out below. 
The tellurates are glasses which contain TeO.sub.2 as the glass network 
former. TeO.sub.2 glass by itself does not transmit well at 2.94 microns 
but the addition of dopants having larger and heavier cations than Te or 
larger and heavier anions than O, or both, results in a much higher 2.9 
micron transmission. Examples of such a glass are 60TeO.sub.2 
-10PbO-30ZnF.sub.2 and 20TeO.sub.2 -20PbO-20ZnF.sub.2 -40V.sub.2 O.sub.3. 
As noted above, dopants having lighter cations, such as V.sub.2 O.sub.3, 
can be incorporated into the glass to increase its stability against 
devitrification. The tellurate glasses have a drawback in that Te is a 
highly toxic chemical. 
Glasses that contain P.sub.2 O.sub.5 as the glass former are referred to as 
phosphate glasses. Glasses that contain Al(PO.sub.3).sub.3 or 
M(PO.sub.3).sub.2 where M=Mg, Ca, Ba, Sr, or NPO.sub.3 where N=Li, Na, K, 
are referred to as fluorophosphate glasses. Both of these glasses exhibit 
a large absorption band at 4.8 microns as a result of the P-O absorption 
(see FIG. 5). This absorption band will adversely affect the glass 
transmission at 2.94 microns especially in a one foot long fiber. 
Therefore, to optimize the fiber transmission at 2.94 microns, the (P-O) 
concentration in these phosphate and fluorophosphate glasses must be kept 
as small as possible. Examples of phosphate and fluorophosphate with small 
(P-O) contents are 10P.sub.2 O.sub.5 -60CaF.sub.2 -30AlF.sub.3 and 
1.7Al(PO.sub.3).sub.3 -38.3AlF.sub.3 -10NaF-8MgF.sub.2 -27CaF.sub.2 
-7SrF.sub.2 -8BaF2. In general, the (P-O) content should not exceed about 
10 mol%. 
The antinonates are glasses that contain Sb.sub.2 O.sub.3 as the glass 
former. The infrared cut-off edge is at longer wavelengths for antimonate 
glasses than the comparable germanate glass since Sb is much heavier than 
Ge. Sb.sub.2 O.sub.3 glass by itself, however, exhibits a poor glass 
forming ability. To stabilize the Sb.sub.2 O.sub.3 glass, other oxide 
dopants such as Al.sub.2 O.sub.3 and R.sub.2 O where R is Li, Na or K must 
be added. Examples of such glasses are 45Sb.sub.2 O.sub.3 -20Al.sub.2 
O.sub.3 -35Na.sub.2 O and 50Sb.sub.2 O.sub.3 -18Al.sub.2 O.sub.3 
-26K.sub.2 O-6Na.sub.2 O. Note also that GeO.sub.2 can also be 
incorporated into the Sb.sub.2 O.sub.3 glass to enhance its stability. 
Antimonate glass is also receptive to dopants having anions which are 
heavier than O, i.e. F, Br, Cl and I. Such dopants will move the infrared 
edge of the glass toward longer wavelengths and therefore will enhance the 
glass transmission at 2.94 microns. Examples of such glasses are 
80Sb.sub.2 O.sub.3 -20PbCl.sub.2 ; 70Sb.sub.2 O.sub.3 -30PbBr.sub.2 ; 
70Sb.sub.2 O.sub.3 -30PbI.sub.2 ; 80Sb.sub.2 O.sub.3 -20MnF.sub.2 ; 
80Sb.sub.2 O.sub.3 -20ZnF.sub.2 ; 80Sb.sub.2 O.sub.3 -20ZnF.sub.2 and 
80Sb.sub.2 O.sub.3 -20SrCl.sub.2. 
Bismuth and lead glasses contain Bi.sub.2 O.sub.3 and PbO as glass network 
formers. Bi and Pb are large and heavy elements thus contributing to the 
high transparency of these glasses at 2.94 microns. However, bismuth and 
lead glasses have the drawback that they are relatively unstable and have 
high refractive indices which contribute to lower coupling efficiency than 
other heavy-metal oxide glasses. Dopants having lighter cations such as 
Ga.sub.2 O.sub.3, CdO, SiO.sub.2 are added to prevent crystallization. 
Examples of such glasses are 61Bi.sub.2 O.sub.3 -13Ga.sub.2 O.sub.3 
-26CdO; 25Bi.sub.2 O.sub.3 -57.5PbO-17.5Ga.sub.2 O.sub.3 and 
85PbO-15Al.sub.2 O.sub.3. 
Aluminate glasses contain Al.sub.2 O.sub.3 as the primary glass former. 
Secondary glass formers include CaO, Tio.sub.2, Nb.sub.2 O.sub.5 and 
Ta.sub.2 O.sub.5. Al is lighter than Bi, Pb, Sb, Te and Ge thus 
contributing to a lower transmission at 2.94 microns. The incorporation of 
dopants having larger and heavier cation than Al such as BaO, ZrO.sub.2, 
PbO and Bi.sub.2 O.sub.3 or larger and heavier anion than O such as 
PbF.sub.2 and AlF.sub.3, or both, enhances the transmission at 2.94 
microns; and because Al is so relatively light, in general the aluminate 
glasses should not usually contain more than about 60 mol% Al.sub.2 
O.sub.3. Examples of such glasses are: 35.9Al.sub.2 O.sub.3 
-59.4CaO-4.7BaO; 32.5Al.sub.2 O.sub.3 -55.2CaO-7.OBaO-5.3PbO; 27Al.sub.2 
O.sub.3 -64CaO-7Bi.sub.2 O.sub.3 -2AlF.sub.3 ; 20Al.sub.2 O.sub.3 
-40Ta.sub.2 O.sub.5 -40K.sub.2 O; 15Al.sub.2 O.sub.3 -42.5Nb.sub.2 O.sub.5 
-42.5K.sub.2 O; and 25.02Al.sub.2 O.sub.3 -19.83TiO.sub.2 -19.83Ta.sub.2 
O.sub.5 -4.12ZrO.sub.2 -12.46BaO-9.37K.sub.2 O-9.37Na.sub.2 O. 
The heavy-metal oxide glasses have another conventional drawback in that 
they invariably contain small amounts of water which are originally bonded 
to the raw oxide starting materials and/or which become incorporated into 
the glass during melting in the atmosphere. Since water absorbs strongest 
at 2.94 microns, trace amounts of it can undermine the ability of the 
glass to transmit at 2.94 microns, especially in a one foot or longer 
fiber, as this problem becomes increasingly severe as the path length 
through the glass increases. 
To eliminate the presence of water and water absorption, the heavy-metal 
oxide glasses must be processed in a water-free atmosphere, e.g. a dry 
glove box atmosphere of argon or nitrogen. The weighing and batching of 
the chemicals, and the melting of the glass must be conducted in a dry 
atmosphere of less than 0.1 ppm water. Prior to the present invention, 
heavy-metal oxide glasses were generally processed in air, thus picking up 
moisture from the atmosphere. 
It is known to use fluoride dopants such as PbF.sub.2 or AlF.sub.3 in heavy 
metal oxide glass to minimize the water content. Thus, in addition to dry 
melting according to the present invention, one or more halide compounds 
such as a fluoride and/or a chloride may be added to enhance the water 
removal. However, the use of a halide alone is not adequate. Another 
technique to enhance water removal and for the drying of the raw materials 
according to the present invention is to use a reactive gas such as 
fluorine or chlorine, at low temperatures of less than 100.degree. C. to 
prevent conversion of oxide to fluoride or chloride. 
Two techniques can be used successfully to fiberize the heavy-metal oxide 
glasses. The rotational casting process described by Tran et al in U.S. 
Pat. No. 5,055,120 (1991) is very efficient in making glass preforms from 
heavy-metal oxide glasses the viscosities of which are less than 50 poises 
at the melt temperature. In this process, the cladding glass melt is 
poured into a metallic mold which is subsequently rotated to form a tube. 
The core melt is then poured into the tube to form a preform. Finally the 
preform is drawn into fibers using an electric furnace. 
The second approach, called the double crucible method, as described in 
"Material Systems, Fabrication and Characteristics of Glass Fiber Optical 
Waveguide" by Merle D. Rigterink, Ceramic Bulletin, Vol. 55, No. 9 (1976), 
is preferred when the cladding glass melt cannot be rotated to form a 
perfect tube, i.e. when the melt viscosity is relatively high at the melt 
temperature. The double crucible technique consists of loading the core 
glass in the inner crucible and the cladding glass in the outer crucible. 
Both crucibles are equipped with a small nozzle at the bottom and are 
concentric to each other. The crucible set-up is heated to the glass 
softening temperature in an electric furnace. Core and cladding glasses 
can then be drawn down from the crucible nozzles. 
The following examples, offered illustratively only, further explain the 
present invention. In the following examples all transmission curves were 
obtained from glass samples which were ground and polished to a thickness 
of 2 mm. 
EXAMPLE 1 
Used as starting chemicals were GeO.sub.2, PbO and PbF.sub.2. Twenty-five 
grams in total of these materials were used to prepare a germanate glass 
the final composition of which was 56GeO.sub.2 -29PbO-15PbF.sub.2. The 
chemical powder wall weighed and mixed in a platinum crucible inside a 
glove box filled with argon. The water content of the glove box was less 
than 0.1 ppm. The crucible was capped with a platinum lid then placed 
inside an electric furnace located within the glove box and was heated to 
1100.degree. C. and soaked for three hours. The resulting molten glass was 
cast into a cylindrical mold, 1.5 cm in diameter, which was maintained at 
an annealing temperature of 330.degree. C. The mold was then cooled slowly 
to room temperature. The glass disc thus obtained was used for 
characterization. 
By way of comparison, (1) a 25 g germanate glass containing 80GeO.sub.2 
-20Sb.sub.2 O.sub.3 according to Takahashi et al was prepared using the 
same procedure described above; and (2) a 25 g zirconium fluoride based 
glass containing 53ZrF.sub.4 -18BaF.sub.2 -3LaF.sub.3 -3AlF.sub.3 
-18NaF-5PbF.sub.2 was melted under the same conditions as above except 
that the temperature at which the components were melted was 875.degree. 
C. and the temperature of the mold into which the mold was cast was 
263.degree. C. 
Using a Perkin-Elmer DSCII differential scanning calorimeter, the glass 
transition temperatures (Tg) and the critical cooling rates of the three 
glasses were determined. As expected, the Tgl's of the germanate glasses, 
600.degree. C. for the GeO.sub.2 -Sb.sub.2 O.sub.3 glass and 330.degree. 
C. for the GeO.sub.2 -PbO-PbF.sub.2 glass, were higher than that of the 
fluoride glass which was only 263.degree. C. The Rc's of the two germanate 
glasses were about 2.5.degree. C./min whereas the Rc of the fluoride glass 
was about 5.degree. C./min. 
The optical transmission curves plotted in FIG. 1 show the infrared edge of 
each of the three glass samples. The infrared cut-off edge is defined as 
the wavelength at which the transmission starts to decrease. The infrared 
cut-off edge of the Takahashi et al GeO.sub.2 -Sb.sub.2 O.sub.3 sample is 
4.1 microns (Curve B), and the closest to 2.94 microns. When heavy 
compounds of PbO and PbF.sub.2 were substituted, the edge shifted toward 
4.7 microns (Curve A) thus enhancing significantly the transmission at 
2.94 microns in a long fiber. The fluoride glass (Curve C) is most 
transparent with an infrared cut-off edge of 5.8 microns, but such 
fluoride glass has too low a Tg. 
It should be noted that dry melting alone did not eliminate water in the 
glass. This is shown by the large water absorption band located at 2.9 
microns in the case of GeO.sub.2 -Sb.sub.2 O.sub.3 glass sample (Curve B). 
The addition of fluoride such PbF.sub.2, as in the case of the GeO.sub.2 
-PbO-PbF.sub.2 glass sample, combined with dry melting, resulted in 
elimination of the water. In the later case, F reacted with OH from the 
water to form HF. 
EXAMPLE 2 
Used as starting materials were GeO.sub.2 and Sb.sub.2 O.sub.3. Twenty-five 
grams in total of these oxides were used to prepare a heavy-metal oxide 
glass containing the Takahashi et al composition of 80GeO.sub.2 
-20Sb.sub.2 O.sub.3. Inside a glove box with an argon atmosphere of less 
than 0.1 ppm water, the chemical powder was weighed, mixed and then placed 
in a Teflon beaker. A reactive gas, fluorine in this case although other 
water-reactive gases can be used, was passed slowly through the powder via 
a small Teflon tube, about 5mm inside diameter. The beaker was heated to 
around 70.degree. C. After eight hours, the powder was transferred to a 
capped platinum crucible and melted using the same procedure of Example 1. 
The transmission curve for the glass sample is plotted in FIG. 2. When 
compared with the transmission curve for the same compositional glass but 
without fluorine treatment (Curve B shown in FIG. 1), it is clear that 
fluorine treatment combined with dry melting enhances the water removal 
from the glass. 
EXAMPLE 3 
A 25 g germanate glass containing 30GeO.sub.2 -50PbO-18AlF.sub.3 
-2PbF.sub.2 was melted under the same conditions as in Example 1. Its 
transmission characteristics shown in FIG. 3 and its Rc value are very 
similar to those of the 56GeO.sub.2 -29PbO-15PbF.sub.2 glass of Example 1, 
except that its Tg of 380.degree. C. is higher. 
EXAMPLE 4 
Used as starting materials were Sb.sub.2 O.sub.3, PbO, PbF.sub.2 and 
GeO.sub.2 - Twenty-five grams in total of these chemicals were used to 
prepare a germanate glass containing 25Sb.sub.2 O.sub.3 -25PbF.sub.2 
-50GeO.sub.2. The batching and melting procedures were similar to the ones 
used in Example 1. The transmission curve obtained for the glass is 
plotted in FIG. 4. The Tg and Rc of the glass obtained by differential 
scanning calorimetry was 310.degree. C. and 2.5.degree. C./min, 
respectively. 
EXAMPLE 5 
A 25 g tellurate glass containing 57TeO.sub.2 -13PbO-28ZnF.sub.2 
-2PbF.sub.2 was melted under the same conditions as in Example 1. The 
transmission curve obtained from the glass sample plotted in FIG. 5 shows 
an extended infrared cut-off edge as compared to that of the glasses of 
Examples 1 and 3, which was attributed to the heavier Te cation. Using 
differential scanning calorimetry, a Tg value of 350.degree. C. and an Rc 
value of 3.degree. C./min were obtained. 
EXAMPLE 6 
Used as starting materials were P.sub.2 O.sub.5, CaF.sub.2, and AlF.sub.3. 
Twenty-five grams in total of these materials were used to prepare a 
phosphate glass containing 60CaF.sub.2 -26.5AlF.sub.3 -3.5PbF.sub.2 
-10P.sub.2 O.sub.5. The batching and melting procedures were similar to 
the ones used in Example 1. The transmission curve for the glass plotted 
in FIG. 6 shows an absorption band at 4.8 microns due to P-O and an 
infrared cut-off edge at about 4 microns, making this glass barely 
suitable, i.e. suitable only for short length fibers of 6 inches or 
shorter. The Tg and Rc of the glass obtained by differential scanning 
calorimetry were 448.degree. C. and 3.degree. C./min respectively. 
EXAMPLE 7 
Used as starting materials were Al(PO.sub.3).sub.3, AlF.sub.3, ZrF.sub.4, 
BaF.sub.2, CaF.sub.2, SrF.sub.2, YF.sub.3, MgF.sub.2, NaF and PbF.sub.2. 
Twenty-five grams in total of these chemicals were used to prepare a 
fluorophosphate glass containing 0.2Al(PO.sub.3).sub.3 -29AlF.sub.3 
-10.2ZrF.sub.4 -9.8BaF.sub.2 -18.3CaF.sub.2 -12SrF.sub.2 -8.3YF.sub.3 
-3.5MgF.sub.2 -3.8NaF-5PbF.sub.2. The batching and melting procedures were 
similar to the ones used in Example 1. The transmission curve for the 
glass plotted in FIG. 7 shows an absorption band at 4.8 microns due to 
P-O. This absorption band is smaller than the one obtained for the 
phosphate glass of Example 5 because of a smaller (P-O) concentration. The 
Tg and Rc of the glass obtained by differential scanning calorimetry were 
390.degree. C. and 4.5.degree. C./min, respectively. The presence of so 
much AlF.sub.3, needed in this glass to increase the Tg to an acceptable 
level, tends to severely de-stabilize the glass, and the phosphate is 
needed to permit stable fiber manufacture. 
EXAMPLE 8 
Used as starting oxides were Bi.sub.2 O.sub.3, PbO, CdO and Ga.sub.2 
O.sub.3. Twenty-five grams in total of the oxides were used to prepare a 
bismuth glass containing 61Bi.sub.2 O.sub.3 -26CdO-13Ga.sub.2 O.sub.3, and 
25 g in total of the oxides were used to prepare a lead-bismuth glass 
containing 25Bi.sub.2 O.sub.3 -57.5PbO-17.5Ga.sub.2 O.sub.3. The batching 
and melting procedures are similar to the ones described in Example 2. The 
transmission curves for both glass samples are plotted in FIG. 8. The Tg's 
of the bismuth and lead-bismuth glasses, obtained by differential scanning 
calorimetry, were 375.degree. C. and 350.degree. C., respectively. The 
Rc's of both glasses were about 3.5.degree. C./min. 
EXAMPLE 9 
Used as starting oxides were Al.sub.2 O.sub.3, Ta.sub.2 O.sub.5 and K.sub.2 
O. Twenty-five grams in total of these materials were used to prepare an 
aluminate glass containing 20Al.sub.2 O.sub.3 -40Ta.sub.2 O.sub.5 
-40K.sub.2 O. The batching and melting procedures were similar to the ones 
used in Example 2, except that the melt temperature was raised to 
1500.degree. C. The transmission curve obtained for the glass sample is 
plotted in FIG. 9. The Tg and Rc of the glass, obtained by differential 
scanning calorimetry, were 525.degree. C. and about 5.degree. C./min, 
respectively. 
EXAMPLE 10 
Used as starting oxides were Sb.sub.2 O.sub.3, Al.sub.2 O.sub.3, KNO.sub.3 
and Na.sub.2 CO.sub.3. Twenty-five grams in total of these materials were 
used to prepare an antimonate glass containing 50Sb.sub.2 O.sub.3 
-18Al.sub.2 O.sub.3 -26K.sub.2 O-3Na.sub.2 O-3Li.sub.2 O. The batching and 
melting procedures were similar to the ones used in Example 2. The 
transmission curve for the glass is plotted in FIG. 10. The Tg and Rc 
value obtained by differential scanning calorimetry was 403.degree. C. and 
4.degree. C./min, respectively. 
EXAMPLE 11 
The germanate glass of Example 1, 56GeO.sub.2 -29PbO-15PbF.sub.2 (Fiber No. 
1); the germanate glass of Example 2 (Fiber No. 2) 80GeO.sub.2 -20Sb.sub.2 
O.sub.3 ; the germanate glass of Example 3 (Fiber No. 3), 30GeO.sub.2 
-50PbO-18Alf.sub.3 -2PbF.sub.2 ; the germanate glass of Example 4 (Fiber 
No. 4), 25Sb.sub.2 O.sub.3 -25PbF.sub.2 -50GeO.sub.2 ; the tellurate glass 
of Example 5 (Fiber No. 5), 57TeO.sub.2 -13PbO-28ZnF.sub.2 -2PbF.sub.2 ; 
the phosphate glass of Example 6 (Fiber No. 6), 60CaF.sub.2 -26.5AlF.sub.3 
-3.5PbF2-10P.sub.2 O.sub.5 ; the fluorophosphate glass of Example 7 (Fiber 
No. 7), 0.2Al(PO.sub.3).sub.3 -29AlF.sub.3 -10.2ZrF.sub.4 -9.8BaF.sub.2 
-18.3CaF.sub.2 -12 SrF.sub.2 -8.3YF.sub.3 -3.5MgF.sub.2 -3.8NaF-5PbF.sub.2 
; the bismuth glass of Example 8 (Fiber No. 9), 61B1.sub.2 O.sub.3 
-26CdO-13Ga.sub.2 O.sub.3 ; the lead-bismuth glass of Example 8 (Fiber No. 
9), 25Bi.sub.2 O.sub.3 -51.5PbO-17.5Ga.sub.2 O.sub.3 ; the aluminate glass 
of Example 9 (Fiber No. 10), 20Al.sub.2 O.sub.3 - 40Ta.sub.2 O.sub.5 
-40K.sub.2 O; and the antinonate glass of Example 10 (Fiber No. 11) 
50Sb.sub.2 O.sub.3 -18Al.sub.2 O.sub.3 -26K.sub.2 O-3Na.sub.2 O-3Li.sub.2 
O were used as the core material for the making of optical fiber for laser 
surgery. By way of comparison, the fluoride glass of Example 1 (Fiber No. 
12), 53ZrF.sub.4 -18BaF.sub.2 -3LaF.sub.3 -3AlF.sub.3 -18NaF-5PbF.sub.2, 
was also used as a core material for the making of a fluoride glass 
optical fiber. 
The cladding material for each fiber was the same type of glass as the core 
glass except the concentration of one or two components in each respective 
glass was altered to lower the glass refractive index. The core and 
cladding glass compositions of each type of fiber and its respective 
numerical aperture (NA) are given in Table 2. Twenty-five grams of each of 
the cladding glass were made using the same batching and melting 
procedures used for the core glass. 
TABLE 2 
__________________________________________________________________________ 
Core and cladding glass compositions used in the fabrication of 
heavy-metal oride glass fibers. 
Fiber 
Glass 
No. Type (Core)/(Clad) Composition (mol %) NA 
__________________________________________________________________________ 
1 Germanate 
(56GeO.sub.2 --29PbO--15PbF.sub.2)/(61GeO.sub.2 --24PbO--15Pb 
F.sub.2) 0.20 
2 Germanate 
(80GeO.sub.2 --20SB.sub.2 O.sub.3)/(100GeO.sub.2) 
0.48 
3 Germanate 
(32GeO.sub.2 --50PbO--18AlF.sub.3 --2PbF.sub.2)/(32GeO.sub.2 
--48PbO--20AlF.sub.3) 0.19 
4 Germanate 
(25Sb.sub.2 O.sub.3 --25PbF.sub.2 --50GeO.sub.2)/(25Sb.sub.2 
O.sub.3 --21.5PbF.sub.2 --53.5GeO.sub.2) 
0.20 
5 Tellurate 
(57TeO.sub.2 --13PbO--28ZnF.sub.4 --2PbF.sub.2)/(60TeO.sub.2 
--10PbO--30ZnF.sub.2) 0.20 
6 Phosphate 
(60CaF.sub.2 --26.5AlF.sub.3 --3.5PbF.sub.2 --10P.sub.2 
O.sub.5)/(60CaF.sub.2 --30AlF.sub.3 --10P.sub.2 O.sub.5) 
0.19 
7 Fluorophosphate 
[0.2Al(PO.sub.3).sub.3 --29AlF.sub.3 --10.2ZrF.sub.4 
--9.8BaF.sub.2 --18.3CaF.sub.2 -- 0.20 
12SrF.sub.2 --8.3YF.sub.3 --3.5MgF.sub.2 --3.8NaF--5PbF.sub.2 
]/[0.2Al(PO.sub.3).sub.3 -- 
10ZrF.sub.4 --10BaF.sub.2 --18CaF.sub.2 --13SrF.sub.2 
--8YF.sub.3 --3.3MgF.sub.2 --3.5NaF] 
8 Bismuth (61Bi.sub.2 O.sub.3 --26CdO--13Ga.sub.2 O.sub.3)/(55Bi.sub.2 
O.sub.3 --28CdO--13Ga.sub.2 O.sub.3 --4PbO) 
0.19 
9 Lead-Bismuth 
(25Bi.sub.2 O.sub.3 --57.5PbO--17.5Ga.sub.2 O.sub.3)/(28Bi.su 
b.2 O.sub.3 --56PbO--16Ga.sub.2 O.sub.3) 
0.21 
10 Aluminate 
(20Al.sub.2 O.sub.3 --40Ta.sub.2 O.sub.5 --40K.sub.2 
O)/(30Al.sub.2 O.sub.3 --35Ta.sub.2 O--17.5K.sub.2 O--17.5Na. 
sub.2 O) 0.12 
11 Antimonate 
(50Sb.sub.2 O.sub.3 --18Al.sub.2 O.sub.3 --26K.sub.2 
O--3Na.sub.2 O--3Li.sub.2 O/(48Sb.sub.2 O.sub.3 --18Al.sub.2 
O.sub.3 --26K.sub.2 O--6Na.sub.2 O) 0.18 
12 Fluoride (53ZrF.sub.4 --18BaF.sub.2 --3CaF.sub.3 --3AlF.sub.3 
--18NaF--5PbF.sub.2)/(53ZrF.sub.4 -- 0.20 
20BaF.sub.2 --4LaF.sub.3 --3AlF.sub.3 --20NaF) 
__________________________________________________________________________ 
EXAMPLE 12 
The rotational casting technique was used to prepare Fibers 1, 3 through 7 
and 12 of the Table 2 because of their low melt viscosities. In each case, 
23 g of cladding glass and 25 g core glass were used to make a preform 6.5 
cm long and 1 cm in diameter. The pre-melts for cladding and core glasses 
were remelted for two hours at a temperature T.sub.melt. The cladding melt 
wall cast into a mold pre-heated a temperature T.sub.mold which was about 
the glass transition temperature. The mold was then spun and the melt 
solidified to form a cladding tube. The rotational casting process 
parameters T.sub.melt, are given in Table 3 for each of the Fibers from 1, 
3 through 7 and 12. 
TABLE 3 
______________________________________ 
Preform processing and draw parameters used in the 
fabrication of the heavy-metal oxide glass fibers. 
Fiber Preform T.sub.melt 
T.sub.mold 
T.sub.draw 
No. Type (.degree.C.) 
(.degree.C.) 
(.degree.C.) 
______________________________________ 
1 Germanate 950 330 420 
3 Germanate 950 380 450 
4 Germanate 950 310 400 
5 Tellurate 1050 350 510 
6 Phosphate 1000 445 625 
7 Fluorophosphate 
1000 390 535 
12 Fluoride 800 263 330 
______________________________________ 
The core melt was subsequently poured into the tube to form a preform 
having a waveguide structure. The preform was then drawn into fiber at a 
temperature T.sub.draw in an electric furnace flushed with a dry argon 
atmosphere. The fiber was coated with UV-acrylate buffer to preserve its 
mechanical strength. All fibers obtained had a core diameter of 325 
microns and a clad diameter of 525 microns, .+-.8 microns. 
The double crucible technique was applied in the fabrication of Fibers 2 
and 8 through 11 because of their high melt viscosities. The double 
crucible set up consisted of a small platinum crucible concentrically 
placed inside a larger crucible. The inside diameters of the inner and 
outer crucibles were 2 cm and 4 cm, respectively. The bottoms of the inner 
and outer crucibles were tapered to form a nozzle measuring 1.9 mm and 2.2 
mm, respectively. The double crucible set-up was placed inside an electric 
furnace flushed with dry argon gas and was pre-heated at a temperature 
T.sub.draw which was the softening or working temperature of the glass. 
The pre-melts for cladding and core glasses were remelted for two hours at 
a temperature T.sub.melt. The cladding melt and core melt were cast into 
the outer crucible and inner crucible, respectively. The melts rapidly 
cooled down to the working point and were drawn down into fibers having a 
325 micron core and a 525 micron clad, .+-.15 microns. The fiber was 
coated in-line with a UV acrylate buffer to preserve its mechanical 
strength. 
The double crucible draw parameters are given in Table 4 for each of the 
Fibers 2 and 8 through 11. 
TABLE 4 
______________________________________ 
Double crucible draw parameters used in the 
fabrication of the heavy-metal oxide glass fibers. 
Fiber Glass T.sub.melt 
T.sub.draw 
No. Type (.degree.C.) 
(.degree.C.) 
______________________________________ 
2 Germanate 1150 825 
8 Bismuth 1000 475 
9 Lead-Bismuth 1000 435 
10 Aluminate 1100 750 
11 Antimonate 1100 615 
______________________________________ 
EXAMPLE 13 
The fibers prepared using the methods of Example 11 were characterized in 
terms of their optical transmission. Using a Nerst glower, a 
monochromater, infrared filters and an InSb detector, the fiber loss 
measurements were carried out at 2.06 microns and 2.94 microns, using the 
conventional fiber cut-back technique. In the cut-back technique, the 
light transmission through a long fiber, T.sub.long, was first measured. 
The fiber was then cut into a shorter length, and the light transmission 
through the short fiber, T.sub.short, was recorded. The fiber 
attentuation, .alpha., expressed in dB/m was obtained as follows: 
##EQU2## 
when L.sub.2 =length of the long fiber 
L.sub.1 =length of the short fiber 
The measured attenutation for each of the fibers of Example 11 is set forth 
in Table 5. 
TABLE 5 
______________________________________ 
Measured attenuation for each of the surgical fibers. 
Fiber Glass .alpha.(dB/m) at 
.alpha.(dB/m) at 
No. Type 2 microns 2.94 microns 
______________________________________ 
1 Germanate 1.1 2.9 
2 Germanate 0.8 10 
3 Germanate 0.9 2.7 
4 Germanate 1.0 2.9 
5 Tellurate 1.5 2.2 
6 Phosphate 2.3 7.6 
7 Fluorophosphate 
0.2 0.5 
8 Bismuth 3.2 5.1 
9 Lead-Bismuth 4.6 6.9 
10 Aluminate 4.8 8.3 
11 Antimonate 1.9 3.7 
12 Fluoride 0.1 0.06 
______________________________________ 
As can be seen from Table 5 above, the attenuation .alpha. for Germanate 
Fiber No. 2 at 2.94 microns was 10 dB/m. According to an article by 
Drexhage and Moynihan entitled "Infrared Optical Fibers" appearing in 
SCIENTIFIC AMERICAN, November 1988, at page 116, one part per million (1 
ppm) of hydroxyl ion causes an attenuation of 10 dB/m at 2.9 microns. 
Therefore, in view of Fiber No. 2, the amount of water in the fibers of 
the present invention must be less than 1 ppm. 
EXAMPLE 14 
The 325 micron core and 525 micron clad optical fibers prepared using the 
methods of Example 11 were tested for their power handling capability 
using an Er:Yag laser and an Ho:Yag laser. The Er:Yag and Ho:Yag lasers 
emit 250 micro-second pulses of radiation at 2.94 microns and at 2.06 
microns, respectively, and deliver a maximum of 500 NJ per pulse in 
multimode operation. Each fiber under test was carefully cleaned until two 
good ends were obtained. The laser radiation I.sub.i was coupled to the 
fiber via a CaF.sub.2 lens combination having a 22 mm focal length. The 
output energy, I.sub.o, was measured with a radiometer set to measure ten 
consecutive pulses. A repetition rate of 10 Hz was used. The duration of 
the laser operation was stretched to a maximum of twenty minutes to avoid 
damaging the laser cavity. The resulting values of I.sub.i, I.sub.o, the 
fiber length under test, the power coupling efficiency and the condition 
of each fiber after the test are given in Table 6 for the Er:Yag laser and 
in Table 7 for the Ho:Yag laser. 
TABLE 6 
__________________________________________________________________________ 
Power handling characteristics of heavy-metal oxide glass 
fibers as compared to fluoride glass fiber using an Er:Yag laser. 
coupling 
Fiber 
Glass I.sub.o (mJ) 
efficiency 
No. Type I.sub.i (mJ) 
(1 ft length) 
(1 ft length) 
Fiber Conditions 
__________________________________________________________________________ 
1 Germanate 
500 340 68% No damage observed after maximum 
duration of test of twenty minutes. 
2 Germanate 
500 160 32% No damage observed after maximum 
duration of fifteen minutes. 
3 Germanate 
500 360 72% No damage observed after maximum 
duration of test of twenty minutes. 
4 Germanate 
500 350 70% No damage observed after maximum 
duration of test of twenty minutes. 
5 Tellurate 
500 345 68% No damage observed after maximum 
duration of test of twenty minutes. 
6 Phosphate 
500 260 52% No damage observed after maximum 
duration of test of twenty minutes. 
7 Fluorophosphate 
500 440 88% No damage observed after maximum 
duration of test of twenty minutes. 
8 Bismuth 500 175 35% No damage observed after maximum 
duration of test of twenty minutes. 
9 Lead-Bismuth 
500 135 27% No damage observed after maximum 
duration of test of twenty minutes. 
10 Aluminate 
500 200 40% No damage observed after maximum 
duration of test of twenty minutes. 
11 Antimonate 
500 300 60% No damage observed after maximum 
duration of test of twenty minutes. 
12 Fluoride 500 450 90% Input ends melted, fiber 
fractured after 1 min 05 
__________________________________________________________________________ 
sec. 
TABLE 7 
__________________________________________________________________________ 
coupling 
Fiber 
Glass I.sub.o (mJ) 
efficiency 
Fiber 
No. Type I.sub.i (mJ) 
(1 ft length) 
(1 ft length) 
Conditions 
__________________________________________________________________________ 
1 Germanate 
500 390 78% No damage observed after 
maximum duration of test 
of twenty minutes. 
2 Germanate 
500 412 82% No damage observed after 
maximum duration of fifteen 
minutes 
3 Germanate 
500 410 82% No damage observed after 
maximum duration of test 
of twenty minutes. 
4 Germanate 
500 410 82% No damage observed after 
maximum duration of test 
of twenty minutes. 
5 Tellurate 
500 365 73% No damage observed after 
maximum duration of test 
of twenty minutes. 
6 Phosphate 
500 385 77% No damage observed after 
maximum duration of test 
of twenty minutes. 
7 Fluorophosphate 
500 447 89.5% No damage observed after 
maximum duration of test 
of twenty minutes. 
8 Bismuth 500 225 45% No damage observed after 
maximum duration of test 
of twenty minutes. 
9 Lead-Bismuth 
500 180 36% No damage observed after 
maximum duration of test 
of twenty minutes. 
10 Aluminate 
500 280 56% No damage observed after 
maximum duration of test 
of twenty minutes. 
11 Antimonate 
500 350 70% No damage observed after 
maximum duration of test 
of twenty minutes. 
12 Fluoride 500 450 90% Both input and output 
ends developed craters 
after 1 min. 33 sec. 
power quickly dropped 
to zero. 
__________________________________________________________________________ 
The results from these tests indicate that all heavy metal oxide glass 
fibers of this invention exhibit power handling much longer than the 
fluoride glass fiber which is absolutely required in laser surgery, 
although their power transmission efficiency is lower due to their higher 
attenuation at 2.94 microns and 2.06 microns. The fluoride glass fiber on 
the other hand could deliver 90% of the laser output power but was 
considered useless because of its almost instantaneous degradation. The 
fluoride glass fiber breaks down after only 1-1.5 minutes when coupled to 
an Er:Yag laser at an output power of about 3 watts, required for many 
surgical procedures. The power handling ability of the present heavy metal 
oxide glass fibers is a first time result in this field, insofar as known. 
The test results of Table 6 also show that the power transmission of Fibers 
2, 8 and 9 was among the lowest because fiber 2 had a high attenuation of 
10 dB/m at 2.94 microns. Fibers 8 and 9 on the other hand had lower 
attenuation but very high refractive indices of 2.43 and 2.46, 
respectively. These high refractive indices contributed a total of about 
35% reflection loss at the two ends of fibers 8 and 9. To increase the 
coupling efficiencies, the ends of fibers 8 and 9 can be coated with a 
standard anti-reflection coating that will reduce the total reflection 
loss of the two fibers to about 10%. 
All the heavy-metal oxide glasses of the present invention exhibited 
transmission in the 90% range between 1 to 3 microns over a 2mm optical 
path length and at least 27% over 1 foot optical path length. The optical 
attenuation of the heavy-metal oxide glass fibers increases as the 
operational wavelength decreases toward 1 micron, since the infrared 
absorption cut-off edge becomes weaker at shorter wavelengths. This 
behavior is apparent from the test results of Tables 6 and 7 which show 
that the fiber coupling efficiency was higher at 2.06 microns than at 2.94 
micron. As a result the heavy-metal oxide glass fibers can be efficiently 
used in conjunction with any surgical lasers covering the 1 to 3 microns 
operational wavelength region. 
The foregoing description of the specific embodiments reveal the general 
nature of the invention so that others can, by applying current knowledge, 
readily modify and/or adapt for various applications such specific 
embodiments without departing from the generic concept, and, therefore, 
such adaptations and modifications should and are intended to be 
comprehended within the meaning and range of equivalents of the disclosed 
embodiments. It is to be understood that the phraseology or terminology 
employed herein is for the purpose of description and not of limitation.