Composite optical fiber and imaging catheter and method for producing the same

A composite optical fiber for use with a sensor includes an imaging optical fiber which receives information-carrying light that is reflected from a target, and a transparent material that includes the imaging optical fiber in its interior and which transmits an illuminating light from a light source to the target. The light-receiving optical fiber is an integral part of the transparent material, and it has an increased cross-sectional area for transmitting the illuminating light with respect to its overall outside diameter. The optical fiber can be produced by the extrusion technique without arranging a multiplicity of light-transmitting fibers and encasing them within a heat-shrinkable tube.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a composite optical fiber, an imaging 
catheter, and a method for producing the same. 
2. Description of the Prior Art 
An endoscope (hereinafter referred to as an "imaging catheter") is 
conventionally used to examine blood vessels, the heart, and the interior 
of body cavities. A typical imaging catheter is shown in FIG. 1 wherein an 
illuminating light 4 from a light source 1 is guided through an optical 
transmission fiber 2 into a blood vessel 3. The image of the target, which 
is formed by a lens installed at the tip of the catheter, is sent back 
through an image fiber 5 to a direct-vision adapter 6 which enlarges the 
image for direct viewing by an operator. If the target is the wall of the 
blood vessel, and its viewing is obstructed by the blood flowing between 
the catheter and the target, a physiological saline solution 8 is supplied 
from a syringe 7 and squirted from the top of the catheter to flush away 
the blood. 
As shown in FIG. 2, a composite optical fiber 9, which makes up the imaging 
catheter that achieves these functions, comprises the image fiber 5, a 
brine transferring tube 10 and a plurality of small diameter optical 
fibers 2' for transmitting the illuminating light, and all of these 
elements are confined in a casing 11 such as a heat-shrinkable tube. 
However, since the optical fibers 2' are circular in cross section, a gap 
exists between them and also between the image fiber 5 and the brine 
transfer tube 10. As a result, the cross-sectional area, through which the 
illuminating light is transmitted, is relatively small with respect to the 
overall cross section of the imaging catheter. Furthermore, the casing or 
sheath 11 that is used to retain the optical fibers 2' around the image 
fiber 5 unavoidably adds to the outside diameter of the optical fiber 9. 
As a further disadvantage, assembling and arranging a plurality of optical 
illumination transfer fibers 2', an image fiber 5 and a brine transfer 
tube 10 requires considerable time and labor, and, consequently, the cost 
of producing the composite optical fiber 9 is increased. 
SUMMARY OF THE INVENTION 
Therefore, a primary object of the present invention is to provide an 
optical fiber for use with a sensor that is free from the above-described 
disadvantages of the conventional product. This object is achieved by a 
composite optical fiber that comprises an imaging optical fiber which 
receives information-carrying light from the target and a transparent 
material that includes said imaging optical fiber in its interior and 
which transmits an illuminating light from a light source, said imaging 
optical fiber being an integral part of the transparent material. Said 
transparent material further contains an opening for permitting a 
physiological saline solution to flow through it. 
A further object of the present invention is to provide a method of making 
such a composite optical fiber by passing an imaging fiber through a first 
die while extruding a light-absorbing layer from the first die to coat the 
imaging fiber with the light-absorbing layer; passing the coated imaging 
fiber through a second die while extruding a transparent plastic material 
from the second die to coat the imaging fiber further with the transparent 
plastic material; and forming an opening in the transparent material as 
said transparent material is extruded from the second die. 
A yet further object of the present invention is to provide a method of 
making an imaging catheter using the novel, composite optical fiber of the 
present invention by treating a downstream end of the composite optical 
fiber with an acid to remove only the transparent material and leave the 
light-receiving optical fiber exposed; mirror-polishing a part of an 
exposed surface of the transparent material; spreading a film of matching 
oil on the mirror-polished surface; connecting an auxiliary optical fiber 
to the oil-coated, mirror-polished surface; and connecting an exposed end 
of the light-receiving optical fiber to a sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention are described by reference 
to FIGS. 3-9. 
FIG. 3 is a cross section of one embodiment of a composite optical fiber 9 
of the present invention. The composite optical fiber 9 comprises an 
imaging fiber 5 which receives information-carrying light from a target; a 
transparent material 12 that includes said imaging fiber 5 in its interior 
and which transmits an illuminating light from a light source to the 
target; a light-absorbing layer 13 which is formed around the imaging 
fiber 5; and an opening 14 which is cut through the transparent material 
12, parallel to the imaging fiber 5, for permitting the flow of a 
physiological saline solution. 
The imaging fiber 5 is prepared by arranging a plurality of optical fibers 
in a quartz tube, in a side-by-side assembly, and drawing the assembly to 
form finer filaments. The light-absorbing layer 13 prevents the leakage of 
light from the imaging fiber 5 and is made of a material that has a low 
light transmittance and a higher refractive index than quartz. A suitable 
example is a hard silicone resin mixed with a fine carbon powder. The 
transparent material 12 is made of a material which has a high light 
transmittance such as polymethyl methacrylate, polystyrene or 
polycarbonate, and it may contain a cladding to eliminate surface flaws, 
dirt or other factors which may reduce the transmission efficiency of the 
illuminating light. A suitable cladding may be formed by coating the inner 
surface of the transparent material 12 and the outer surface of the brine 
conduit 14 with a plastic which has a lower index of refraction than the 
transparent material. The cladding on the transparent material 12 may be 
further coated with a fluorinated resin, such as Teflon.RTM., to provide 
better slip and more effective protection from surface flaws and dirt. 
The imaging fiber 5 is formed as an integral part of the plastic 
transparent material 12, and this can be achieved by extrusion using an 
apparatus of the type illustrated in FIGS. 4 and 5. As the imaging fiber 5 
is passed through a die 15, it is coated with a light-absorbing layer 13 
which is also extruded from the die 15. Then, the imaging fiber 5, with 
the light-absorbing layer 13 coated onto it, is passed through a lower die 
16 to form a transparent plastic material 12. At the same time, an opening 
14, which forms the passage for the physiological saline, is formed in the 
transparent material 12 by means of an element 16a which is installed in 
the die 16. The resulting composite optical fiber 9 emerges from the 
bottom of the die 5 and is continuously wound on a capstan take-up roller 
(not shown) in the direction indicated by the arrow. 
An imaging catheter is prepared from the composite optical fiber 9 by the 
following method. As shown in FIG. 6, the downstream part of the composite 
optical fiber, which is to be equipped with a branching mount 17, is 
treated with sulfuric acid or the like to remove the transparent material 
12 and leave only the image fiber 5 behind. A tube 18, which is connected 
to a syringe (not shown), is inserted into the exposed brine conduit 14 
and fixed by a suitable adhesive. Part of the exposed surface 19 of the 
transparent material 12 is mirror-polished to provide a mirror-smooth 
surface 20, and one end of an auxiliary optical fiber 21 for transmitting 
illuminating light is connected to a light source (not shown) and also 
attached to the mirror-smooth surface 20 with a film of matching oil which 
is spread on that surface. The illuminating light is then fed to the 
transparent plastic material 12 after it has been guided through this 
auxiliary optical fiber 21. The downstream end of the image fiber 5 is 
connected to a direct-vision adapter (not shown), and the branching 
section of the optical fiber 9 is covered with the branching mount 17 to 
protect the joint. 
FIG. 7 shows the structure of another branching mount 17 that can be used 
with the imaging fiber of the present invention. In this embodiment, the 
part of the optical fiber which is to be equipped with the branching mount 
17 and the downstream portion of the optical fiber are split into two 
portions in the longitudinal direction, and the image fiber 5 is then 
separated from the transparent material 12. As in the embodiment shown in 
FIG. 6, a tube 18 is inserted into the exposed brine conduit 14 and fixed 
by an adhesive. The split portions of the transparent material 12 which 
extend from the branching mount 17 are joined by heating or another 
suitable means, and the downstream end of the so-joined transparent 
material 12 is connected to the light source (not shown). 
FIGS. 8 and 9 show an embodiment in which the optical fiber of the present 
invention is used as a dental imaging fiber for examining the interior of 
a tooth 21 for the gingiva 22. In practice, a small hole is cut down to 
the gingiva 22 in the tooth 21, and the tip of the optical fiber 9', 
including the light-transmitting fiber and light-receiving fiber, is 
inserted into that hole. The outside diameter of the optical fiber 9', 
when used as a dental imaging fiber, must not exceed 0.7 mm, and this has 
been impossible when the conventional fiber arrangement has been used. 
However, the optical fiber 9' of the present invention satisfies this 
rigorous dimensional requirement by forming the transparent, 
light-transmitting plastic material 12 concentric around, and as an 
integral part of, the imaging fiber 5 with the light-absorbing layer 13, 
as shown in FIG. 9. 
The optical fiber of the present invention can be used as an imaging 
catheter with an endoscope for examining blood vessels or the heart, and 
it can also be used as an imaging catheter with an endoscope in dentistry, 
ophthalmology, otolarynglogy or urology. By replacing the imaging fiber 
with an ordinary light-receiving optical fiber, the product of the present 
invention can be used with SO.sub.2 sensors, heart rate and output 
sensors, and medical and industrial spectroscopic analyzers. 
As described above, the optical fiber of the present invention does not 
have a gap formed between the transparent, light-receiving material, the 
imaging optical fiber, or the brine conduit; therefore, it has an 
increased cross-sectional area for transmitting the illuminating light 
with respect to the overall outside diameter of the optical fiber. 
Moreover, the optical fiber of the present invention can be continuously 
and efficiently produced by the extrusion technique at low cost, without 
arranging a multiplicity of light-transmitting fibers and encasing them 
with a heat-shrinkable tube. As a further advantage, the absence of a gap 
between the transparent, light-transmitting material and the imaging 
optical fiber, and the elimination of a heat-shrinkable tube as an outer 
sheath, provides a fine optical fiber that can be easily assembled into or 
branched from an imaging fiber system.