Abstract:
A fiber optic cable coupler comprises a housing adapted to receive a first fiber optic cable and a cable connector having a distal end and a proximal end. The distal end of the cable connector is adapted to engage the housing and the proximal end of the cable connector is adapted to receive a second fiber optic cable. The first and second fiber optic cables each have an exposed end. The cable connector retains the second fiber optic cable so that the second fiber optic cable exposed end is opposed to and in longitudinal alignment with the first fiber optic cable exposed end. The cable connector is also adapted to maintain a user selectable distance between the first fiber optic cable exposed end and the second fiber optic cable exposed end.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention pertains to bundled fiber optic cables and more particularly to the coupling of bundled fiber optic cables with different diameters.  
         BACKGROUND OF THE INVENTION  
         [0002]    Optical spectrometers allow the study of a large variety of samples over a wide range of wavelengths. Materials can be studied in the solid, liquid, or gas phase either in a pure form or in mixtures. Various designs allow the study of spectra as a function of temperature, pressure, and external magnetic fields.  
           [0003]    Known optical spectrometers utilize one or more fiber-optic strands to deliver light energy to an internal spectrum analyzer. The spectrum analyzer measures the energy of the light energy at different wavelengths, processes it, and outputs the results to a computer. Often, an assembly of many fiber-optic strands (a fiber optic bundle) is used to deliver light energy to the analyzer. Similarly, a fiber optic bundle will deliver light energy to a series of analyzers, with a specified set of strands connected to one particular analyzer. Frequently, spectrophotometer systems utilize an external sampling fiber optic cable, or bundle, to bring the light energy from a desired sample to the spectrophotometer case, while a second internal fiber optic cable or bundle delivers the collected light energy to the analyzer.  
           [0004]    When utilizing multiple fiber optic bundles to transfer light energy to a spectral analyzer it is essential that all of the collected light energy be delivered equally and evenly from one bundle to the other. Unequal illumination of the fibers may result in both wavelength and amplitude errors in a measured spectrum. In addition, because each of the individual fibers in the sampling bundle may be transmitting slightly different signals, they should equally contribute to the total signal transmitted to the spectrophotometer&#39;s internal fiber optic bundle.  
           [0005]    Often, when external sensing cable bundles are connected to the spectrometer, the profile of the fiber optic cable does not match the connector profile on the spectrometer. This can result in many of the previously mentioned problems.  
           [0006]    In order to connect the sampling cable to the spectrophotometer internal fiber optic cable, known fiber optic couplers position the two cables in contact with one another. This type of coupler works well with single strand fiber optic cables having equal diameters. But they often fail to achieve a satisfactory connection between cable bundles or between a single strand cable and a cable bundle. For example, when the bundle delivering light to the spectrometer is smaller than the instrument&#39;s internal fiber optic bundle, some of the instrument&#39;s fibers may not be illuminated, resulting in potential measurement errors. And, when the external bundle is larger, some of the external bundle&#39;s fibers may not contribute any, or a sufficient amount of, their collected light energy to the instrument&#39;s fiber optic bundle.  
           [0007]    Other approaches, such as the use of collimation optics, also do not address the problem that results from coupling fiber optic bundles having dissimilar sizes. Additionally, the use of collimating optics causes throughput losses due to the presence of additional air/glass interfaces and due to the absorbance of the glass itself.  
           [0008]    An additional problem arises where an incoming fiber optic bundle is split into two or more individual fiber optic bundles within the spectrometer and the smaller bundles are then routed to separate spectrum analyzers. If the initial fiber optic bundle does not receive an even distribution of light energy from the sampling source, the several spectrum analyzers within the spectrophotometer may receive different levels of light energy. Some of the spectra analyzers may not receive any light energy at all.  
           [0009]    Furthermore, known systems for attempting to accommodate the above problems do not provide for an adequate amount of reproducibility in the alignment and positioning of the incoming and internal fiber optic cables bringing into question the accuracy of repeated measurements.  
         SUMMARY OF THE INVENTION  
         [0010]    In one aspect, a fiber optic cable coupler comprises a housing adapted to receive a first fiber optic cable, the first fiber optic cable having an exposed end. The fiber optic cable coupler also comprises a cable connector having a distal end and a proximal end, the distal end adapted to engage the housing, the proximal end adapted to receive a second fiber optic cable having an exposed end. The cable connector retains the second fiber optic cable so that the second fiber optic cable exposed end is opposed to and in longitudinal alignment with the first fiber optic cable exposed end. The cable connector is also adapted to maintain a user selectable distance between the first fiber optic cable exposed end and the second fiber optic cable exposed end.  
           [0011]    In another aspect, a device for transmitting light energy from an exposed end of a first fiber optic cable bundle to an exposed end of a second fiber optic cable bundle comprises a first housing adapted to retain the first fiber optic cable bundle, the first housing having a longitudinal axis and a passage extending along the longitudinal axis. The device also comprises a second housing adapted to engage the first housing and retain the second fiber optic cable bundle, the second housing adapted to maintain a user selected distance between the first and second fiber optic cable bundle exposed ends.  
           [0012]    In a further aspect, a method of coupling fiber optic cables having different diameters comprises retaining a first fiber optic cable in a first position, the first fiber optic cable having an exposed end, retaining a second fiber optic cable in a second position, the second fiber optic cable having an exposed end, longitudinally aligning the first and second fiber optic cable exposed ends, and adjusting the distance between the first and second fiber optic cable exposed ends so that light energy emitted by the first fiber optic cable exposed end evenly illuminates the second fiber optic cable exposed end.  
           [0013]    As will become apparent to those skilled in the art, numerous other embodiments and aspects of the invention will become evident hereinafter from the following descriptions and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The drawings illustrate both the design and utility of the preferred embodiments of the present invention, wherein:  
         [0015]    [0015]FIG. 1 is a diagram showing a spectrophotometer system utilizing a fiber optic bundle matching connector constructed in accordance with the present invention;  
         [0016]    [0016]FIG. 2 is a diagram showing selected internal fiber optic components and connections of the spectrophotometer system of FIG. 1;  
         [0017]    [0017]FIG. 3 is an exploded perspective view of a typical connection between a spectrophotometer housing and an external fiber optic connector;  
         [0018]    [0018]FIGS. 3A and 3B are cross sectional views of a contact-type alignment of differently sized fiber optic cable bundles;  
         [0019]    [0019]FIGS. 4A and 4B are cross sectional views of the alignment of differently sized fiber optic cable bundles in accordance with the present invention  
         [0020]    [0020]FIG. 5 is an exploded perspective view of a fiber optic bundle matching connector constructed in accordance with the present invention;  
         [0021]    [0021]FIGS. 6A and 6B are side and front cross sectional views of a fiber optic bundle matching connector constructed in accordance with the present invention;  
         [0022]    [0022]FIGS. 7A and 7B are side and front cross sectional views of a fiber optic bundle matching connector housing constructed in accordance with the present invention;  
         [0023]    FIGS.  8 A- 8 C are side, front and rotated side cross sectional views of a fiber optic bundle matching connector jam nut constructed in accordance with the present invention;  
         [0024]    FIGS.  9 - 12  are various views of a fiber optic bundle matching connector cable connector constructed in accordance with the present invention; and  
         [0025]    [0025]FIGS. 13A and 13B are views of how a fiber optic bundle matching connector constructed in accordance with the present invention varies the distance between a pair of fiber optic cable bundles. 
     
    
     DETAILED DESCRIPTION  
       [0026]    [0026]FIG. 1 shows a spectrophotometer system  100 . The spectrophotometer system  100  generally includes a spectrophotometer  110  and a general purpose computer  140 . Preferably the general purpose computer  140  is a personal computer or other known system capable of organizing and analyzing data gathered by the spectrophotometer  1110 . The computer  140  is preferably programmed to analyze spectrophotometric data in accordance with known industry applications.  
         [0027]    The spectrophotometer  110  includes a light output terminal  112  that transmits a white light source from inside the spectrophotometer  110 , an input terminal  114  that brings reflected light energy from a sample  130  back into the spectrophotometer  110 , a data port  122  that couples to a data cable  134  so that data obtained by the spectrophotometer  110  can be readily transferred to the computer  140 . A sampling cable  120  has a proximal end  121  that includes a light source cable  116  coupled to the light output terminal  112  and an input cable  118  coupled to the input terminal  114 . The light source cable  116  and the input cable  118  are preferably fiber optic bundles that each include one or more individual fiber optic strands. The light source cable  116  and the input cable  118  preferably merge together as a single cable bundle  126  and extend to a distal end  123  of the sampling cable  120 , although it is readily apparent that merging the two bundles is not necessary. The distal end  123  of the sampling cable  120  includes a sampling tip  124  with a sampling element  128 . The sampling element  128  is preferably the exposed end of the fiber optic strands. The sampling element  128  both illuminates the sample  130  and sends the reflected light energy back to the spectrophotometer  110 . Mated with the input terminal  114  is a fiber optic bundle matching connector  200  constructed in accordance with the present invention. Generally, the fiber optic bundle matching connector  200  provides an adjustable junction between the input cable  118  and the input terminal  114 .  
         [0028]    Turning to FIG. 2, portions of the spectrophotometer  1   10  and the spectrophotometer system  100  are shown in greater detail. In a preferred embodiment, the input terminal  114  leads through the wall of the spectrophotometer  110  to an internal fiber optic cable bundle  150 . As an example, both the internal fiber optic cable bundle  150  and the input cable  118  include  57  separate fiber optic strands. (See exploded cross section  132 ). Each of the individual fiber optic strands within the cable bundle  150  is coupled to a spectrum analyzer  160 . An adapter  164  mates the fiber optic strands in the cable bundle  150  with the spectrometer  160 .  
         [0029]    As described in conjunction with FIG. 2, the input cable  118  and the internal fiber optic cable bundle  150  both carry  57  individual fiber optic strands. This format creates a one-to-one relationship between the diameter of the input cable  118  and the internal cable  150 , making mating the two cables at the input terminal  114  relatively straightforward, i.e. the input cable  118  fully illuminates the internal bundle  150 .  
         [0030]    [0030]FIG. 3 shows an arrangement where an input cable  360  contains a different number of individual fiber optic strands than its corresponding internal cable bundle  150 . In FIG. 3, the input cable  360  has  10  individual fiber optic strands (as shown in the enlarged cross section  362 ). The input terminal  114  on the spectrophotometer  110  is fixed and couples with the internal cable bundle  150 . As described above in conjunction with FIG. 2, the internal cable bundle  150  has a fixed number of fiber optic cables. Since in this example there are just over half as many fiber optic strands in the input cable  360  as in the internal cable bundle  150 , the diameters of the input cable  360  and the internal cable bundle  150  are different. In such situations, the internal cable bundle typically cannot be physically joined through a direct connection without sacrificing or compromising the quality of the light energy that is collected at the sample  130 .  
         [0031]    For example, if the input cable  360  contains fewer individual fiber optic strands than the internal cable bundle  150  and therefore has a smaller diameter, some of the individual fiber optic strands in the internal cable bundle  150  may not receive any light energy from the input cable  360 . (See FIG. 3A for illustration). When the input cable  360  is directly abutting the internal cable bundle  150 , individual fiber optic strands  151  and  156  may not receive any of the light energy transmitted through the input cable  360 . This uneven illumination of the internal fiber optic bundle compromises the quality of the spectrometer measurement.  
         [0032]    Similarly, if the input cable  360  contains more individual fiber optic strands than the internal cable bundle  150  and therefore has a larger diameter than the internal cable bundle  150 , some of the individual fiber optic strands in the input cable  360  will not align with the cross section of the internal cable bundle  150  and some of the collected light energy will be lost. (See FIG. 3B for illustration). When the input cable  360  is directly connected to the internal cable bundle  150 , individual fiber optic cables  361  and  365  may not transmit any of the light energy they carry into the input cable  360 . This exclusion of the light from some of the collecting fiber optic strands from that transferred to the internal fiber optic bundle may compromise the quality of the spectrometer measurement.  
         [0033]    In either of the situations described in conjunction with FIGS. 3A and 3B, there is a strong likelihood that the results generated by the spectrum analyzer  160  will be incorrect. FIGS. 3A and 3B are meant to be illustrative and do not necessarily represent an accurate scale of the cable bundles in relation to the individual fiber optic strands. In practice, the fiber optic strands are more closely packed within the cable and the non light transmitting protective jacket around the individual strands are usually no more than 10-15% of the diameter of the actual strand.  
         [0034]    In order to ensure accurate and reproducible results when using input cables and internal cable bundles with different diameters and/or a different number of individual fiber optic strands, the fiber optic cable matching connector  200  constructed in accordance with the present invention is utilized.  
         [0035]    [0035]FIGS. 4A and 4B illustrate how the fiber optic cable matching connector  200  provides a non-contact coupling between the two fiber optic cable bundles and ensures that the fiber optic strands in the input cable bundle provide equal and even illumination to the internal fiber optic bundle  150  and that the spectrum analyzer&#39;s entrance slit is uniformly illuminated regardless of the diameter of each cable bundle and regardless of the number of individual strands in each bundle. In both FIGS. 4A and 4B the light energy from a sample evenly illuminates the spectrum analyzer&#39;s entrance slit. Thus, the accuracy of the measured spectrum is ensured.  
         [0036]    Referring to FIG. 4A the cable bundles  360  and  150  are separated from each other by a distance d. When the cable bundle  360  is smaller than the internal bundle  150 , the two bundles are positioned such that the diverging beam exiting the external bundle  360  illuminates the full diameter of the exposed end of the internal bundle  150 . The angular spread of light leaving a fiber optic cable is defined by the fiber&#39;s numerical aperture (NA). In the case of many of the fibers commonly used in the spectrometer industry, the fiber has a NA of 0.22. This translates to a beam angle of about 25°. In this example the fibers have a numerical aperture (NA) of 0.22 and thus the light exits the external bundle  360  in an approximately 25° cone. The exiting light enters the internal bundle  150  any time it falls within this 25° cone. Since all of this light falls within the 25° field-of-view of the internal bundle  150 , a maximum amount of the light is transferred from the bundle  360  to the internal bundle  150  and the individual fibers comprising the internal bundle  150  receive an equal amount of illumination.  
         [0037]    Referring to FIG. 4B the cable bundles  360  and  150  are now separated from each other by a distance d′. When the external bundle  360  is larger than the internal bundle  150 , the two bundles are positioned such that the field-of-view (or collection aperture) of the internal bundle  150  views the entire face of the external fiber optic bundle  360 . Even though some of the light delivered by the input cable  360  is lost (i.e. it falls outside the field of view of the internal bundle  150 ), this spacing ensures that each strand of the input cable  360  contributes illumination to the internal fiber optic bundle  150 . The optical efficiency of the connection may be improved by increasing the reflectance of the internal surfaces of the matching connector (e.g. a selection of high reflectance materials and/or polishing such as electro-polishing or nickel plating).  
         [0038]    FIGS.  5 - 12  show the fiber optic bundle matching connector  200  and its various components in further detail. Turning first to FIG. 5, an exploded perspective view showing the main components of the fiber optic bundle matching connector  200  is presented. The fiber optic bundle matching connector  200  includes a housing  210 , a spring washer  211 , a jam nut  216 , and a cable connector  218 . The housing  210  has a threaded external surface  213  and includes an aperture  228  adapted to receive a set screw. The threaded external surface  213  of the housing  210  allows the housing to securely engage through the wall of the spectrophotometer  110  or through another solid surface. The housing  210  is generally tubular in shape. Extending along the longitudinal axis of the housing  210  is a passage  212 . The passage  212  is also threaded for receipt of the cable connector  218 . The jam nut  216  has a threaded aperture  215  along its longitudinal axis that is adapted to engage the cable connector  218 . The cable connector  218  has a threaded distal end  219 , a threaded proximal end  223  and a hex nut  221 . As used herein, the term distal refers to the portions of a component that are further away from the spectrophotometer  110  and the term proximal refers to those portions of a component that are closer to the spectrophotometer  110 . The threaded distal end  219  is adapted to engage both the j am nut  216  and the housing  210  through each of their respective apertures. The jam nut  216  further includes opposing extensions  217  that allow a user to easily tighten the jam nut  216  around the cable connector  218  and into the housing  210 . Tightening the jam nut  216  secures the cable connector  218  in place. Preferably the threaded ends  219  and  223  of the cable connector  218  are SMA type fittings designed to engage with a standard SMA connector. For example, as shown in FIG. 5, the input cable  118  includes an SMA connector  220  that engages with the threaded proximal end  223  of the cable connector  218 .  
         [0039]    In FIGS. 6A and 6B, the fiber optic bundle matching connector  200  is shown engaged through the wall of the spectrophotometer  110 . The fiber optic bundle matching connector  200  engages the input cable  118  at a proximal end  204  and engages the internal cable bundle  150  at a distal end  202 . The input cable  118  includes an SMA connector  220  that threads onto the threaded proximal end  223  of the cable connector  218 . An aperture  114  through the wall of the spectrophotometer  110  provides a mounting location for the fiber optic bundle matching connector  200 . An internal casing wall  214  of the spectrometer  110  also includes an aperture  114   a  for the fiber optic bundle matching connector  200  to pass through. A lockwasher  224 , and a nut  226  secure the fiber optic cable matching connector  200  in the aperture  114  of the spectrophotometer  110 . The housing internal chamber  212  receives the threaded end  219  of the cable connector  218 .  
         [0040]    As mentioned previously, the SMA connector  220  is preferably a fiber optic fitting that receives the input cable  118  and feeds collected light energy from the sample  130 , through a passage in the cable connector  218  to the spectrophotometer  110 . The individual strands of optical fiber are loosely threaded through the fiber optic cable&#39;s housing. At the ends of the cable, the fibers pass into the terminating connectors (e.g. a SMA connector) and are fixed in place. When the connector is viewed from the end of a fiber optic cable assembly the ends of the individual strands of optical fiber arrayed in a circular bundle are visible.  
         [0041]    Other types of connectors, both standard and proprietary, may also be utilized. In most cases, the connectors provide a means to hold the polished ends of the optic fiber strands in a fixed geometry relative to the mating connector.  
         [0042]    The cable connector  218  preferably comprises a tubular housing that can transmit fiber optic energy from one end to the other. The cable connector  218  also includes a hex nut  221  that allows the cable connector  218  to be rotated, either manually or with a bolt driver, and thereby longitudinally positioned within the housing  210 . By positioning the cable connector  218  within the housing  210 , the distance between two opposing fiber optic cable tips retained within the fiber optic bundle matching connector  200  can be adjusted. Markings on the surface of the hex nut  221  allow the distance between the exposed end of the input cable  118  and exposed end of the internal cable  150  to be determined with more precision.  
         [0043]    [0043]FIGS. 7A and 7B show the housing  210  in greater detail. The housing  210  has an inner bushing  238  that carries the threads that engage the cable connector  218 . Variously sized bushings  238  can be inserted into the chamber  212  in order to accommodate differently sized cable connectors. The fiber optic bundle matching connector  200  can therefore be easily adapted for use with many different makes and models of spectrophotometers having variously sized internal fiber optic cable bundles  150 . The housing  210  also includes a flanged end  236  that is shaped to receive the jam nut  216  and externally engage with the aperture  114  through the wall of the spectrophotometer  110 . FIGS. 8A and 8B show a preferred embodiment of the jam nut  216 .  
         [0044]    Turning to FIGS.  9 - 12  the cable connector  218  receives an input tip  232  and an output tip  234 . The input tip  232  is coupled to the input cable  118  and the output tip  234  is coupled to the fiber optic cable bundle  150 . The input tip  232  and the output tip  234  provide a uniform connection between the respective fiber optic cable bundles and the cable connector  218 . When both the input tip  232  and the output tip  234  are fully inserted into the cable connector  218 , they are in contact with each other. The housing aperture  228  receives a set screw that when tightened through the aperture  228 , secures the output tip  234  and cable bundle  150  in place within the housing  210  and cable connector  218 .  
         [0045]    When the cable connector  218  is rotated clockwise via the hex nut  221 , the input tip  232  will move toward the output tip  234  (i.e. to the right in FIG. 6A). Conversely, when the cable connector  218  is rotated counter-clockwise via the hex nut  221 , the input tip  232  will move away from the output tip  234  (i.e. to the left in FIG. 6A). The jam nut  216  is preferably a compression-type fitting and when tightened will secure the cable connector  218  in position. The spring washer  211  ensures a secure fit between the jam nut  216  and the housing  210  and also minimizes movement of the cable connector  218 .  
         [0046]    [0046]FIGS. 13A and 13B illustrate how the distance between the input tip  232  and the output tip  234  varies when the hex nut  218  is turned counter-clockwise (FIG. 13A), and clockwise (FIG. 13B), as well as the varying spacing (d and d′) that can be achieved by utilizing a fiber optic cable matching connector constructed in accordance with the present invention.  
         [0047]    It is noted that the dimensional information contained in FIGS.  7 - 12  are associated with a preferred design of the fiber optic bundle matching connector  200 . However, these dimensions are in no way meant to be limiting and it is contemplated that variously sized fiber optic bundle matching connectors may be constructed to accommodate a wide variety of spectrophotometers applications. Similarly, each of the individual dimensions shown in FIGS.  7 - 12  may be altered in order to accommodate any number of specialized situations.  
         [0048]    Although the present invention has been described and illustrated in the above description and drawings, it is understood that this description is by example only and that numerous changes and modifications can be made by those skilled in the art without departing from the true spirit and scope of the invention. The invention, therefore, is not to be restricted, except by the following claims and their equivalents.