Optical fiber with numerical aperture compression

#The present invention is related to the field of catheter tips. More specifically, the present invention is a catheter tip that redirects coherent laser illumination to generally a 90-degree direction from the source direction.

#In the fields of spectroscopy and surgery, optical fibers employing laser inputs are increasingly being used. For surgery, optical fibers are often used in illumination of body cavities, imaging those cavities and in delivering laser energy for incision/excision, coagulation, homeostasis, and vaporization of tissue. Typically, the optical fibers that are used requires a relatively high Numerical Aperture (NA) in order to capture as high a percentage as possible of the optical energy available from the laser source. High NA fibers, however, result in relatively wide divergence of the light spots at a relatively short distance from the ends of the fibers. Such divergence is not permissible for many applications; so that relatively expensive and cumbersome lens systems have been attached to the output ends of such fibers in order to focus or collimate (or nearly collimate) the light exiting from the output end of the fiber. Such lenses must be added to the fiber end as a separate manufacturing step, and tend to cause the endoscope (or spectroscopic probe tip) to be larger and more invasive than would be the case if such lens systems were not required.

#Surgical fibers for energy delivery often are damaged in use, due to inadvertent contact with the target tissues. Contamination of the fiber output with tissue causes localized heating and consequent damage to the fiber, reducing the output beam quality. The wide-angle divergence of energy from high NA fibers contributes to this failure, in that the surgeon, in his search for the energy density he desires from the sought tissue effects, often inadvertently overshoots. This results from the fact that the high energy densities are found only very close to the fiber output; so unintended fiber/tissue contact is likely.

#FIG. 1 is a diagrammatic representation of a spectroscopy system using fiber optic components;

#FIG. 2 is a representation of a typical fiber optic probe of the type used in the system shown in FIG. 1;

#FIGS. 3 and 4 are cross-sectional side views and cross-sectional end views, respectively, of prior art devices used in the systems and probed of FIG. 2;

#Reference now should be made to the drawings, in which the same reference numbers are used throughout the different figures to designate the same components. FIG. 1 is a diagrammatic representation of a typical light-scattering spectroscopy probe system using a bifurcated fiber probe of the type illustrated in FIG. 2. Systems of this type are employed in various types of spectroscopy, such as absorption/transmission spectroscopy, fluorescence spectroscopy and light scattering spectroscopy. An optical source, such as a laser 10, supplies a beam of light to a beam splitter 12, with a portion of the light beam then being applied through a focusing lens 14 to the end of a fiber optic coupler 16. The coupler 16 is connected to the input end of an optical fiber 18, which preferably is a silica-clad silica core (Si/Si) fiber. Although other optical fibers are available, such as polymer-clad silica fibers (PCS), such fibers typically have an unacceptably high intrinsic fluorescence that precludes their use in light-scattering spectroscopy probes. The excitation energy carried by the fiber 18 is supplied to a probe 20, which is immersed in a sample 22. Often, the probe 20 is provided with a mirrored cap to space a mirror pre-established distances from the end of the optical fiber 18. Such caps (not shown in FIG. 1) have apertures in them to allow the fluid of the sample 22 to pass into the cap; so that the energy exiting the end of the optical fiber 18 is reflected back from the mirror. A single fiber may be used in the system of FIG. 1 to also conduct reflected energy from the end cap or other reflective surfaces in the sample 22 into a collection fiber 24 (shown in FIG. 1 as common with the excitation or illumination fiber 18). The reflected energy or scattered fluorescence then applied back to an optical splitter and into a coupler 25 connected to a monochrometer 26. The output of the monochrometer 26 is supplied to a computer and comparator 30, as one of two inputs. The other input to the comparator 30 is supplied from the beam splitter 12 through an optical fiber 28. Comparison of the energy launched by the laser 10 as applied to the computer and comparator 30 by way of the optical fiber 28, with the reflected energy supplied through the monochrometer 26 then permits the desired spectroscopic analysis.

#Systems of the type shown in FIG. 1 typically uses a bifurcated probe of the type shown in FIG. 2, which illustrates in greater detail the different components of the portion of the system shown in FIG. 2 at the point where the excitation or illumination fiber 18 and the collection or detection fiber 24 separate. The system of FIGS. 1 and 2 is very inefficient. Generally, in fluorescence spectroscopy, the low Numerical Aperture (NA) of Si/Si fiber and the solid sphere emission of fluorescence from the sample 22 are incompatible. A very small portion of the emitted light is collected for transmission to the monochrometer 26. In addition, as the probe-to-target distance is increased, the divergence of the excitation radiation (12.7 degrees half-angle for common 0.22 NA fiber) is high enough that energy density sufficient to stimulate fluorescence rapidly drops away. Additional complications also can arise in probes of the type depicted in FIGS. 1 and 2 in that contamination and damage to the fiber assembly is possible, due to the direct contact of the fibers with the analyte.

#In an effort to improve the performance of the system shown in FIGS. 1 and 2, prior art systems have been designed as illustrated in FIGS. 3 and 4, with a separate excitation fiber 18 and a number of collection fibers 24 located in a ring or circle around the exterior of the collection fiber 18. Typically, these fibers are housed in a steel tube 23. As shown in FIG. 3, the excitation fiber 18 and the collection fibers 24 may be set back from the end of the tube 23. The space that is shown in FIG. 3 then may be filled with a suitable optical plug (or quartz window) to prevent contamination from the sample 22 on the ends of the excitation optical fiber 18 and the ends of the collection fibers 24. The bundle of FIGS. 3 and 4 is utilized in the sample of the spectroscopy system of FIG. 1 in the same manner described previously. While the device of FIG. 3 does exhibit an improved ability to collect more of the scattered light, due to numerous fibers for collection surrounding the central excitation fiber, it is still highly inefficient because the NA of the fibers used is incompatible with the efficient delivery of excitation energy and collection of highly scattered fluorescence.