Abstract:
A cannula can have a ferrule with two interspaced optical fiber passages extending therebetween, each securely housing an optical fiber therein having a first tip exposed at a connection end, and a second tip protruding from an opposite implant end by a penetration distance, and a bore extending into the ferrule from the connection end. The cannula can be removably connected by a patch cord having a ferrule with a guide pin, with a relatively high degree of optical alignment, by inserting both ferrules into corresponding ends of a sleeve and engaging the guide pin within the bore.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS/PRIORITY CLAIM 
       [0001]    This application claims priority of U.S. provisional application No. 61/313,258, filed Mar. 12, 2010 by applicant, the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The field of optogenetics is a very promising sector of health sciences which receives much researching efforts. Essentially, many optogenetic research applications involve emitting light from an optical fiber into body tissue, typically of a mammal such as mice or rats. This typically involves adhering a housing of the optical fiber, referred to as a fiber optic cannula, to the surface of the body with optical fiber extending therefrom into the body tissue. 
       SUMMARY 
       [0003]    Some research applications done on neurons require implanting two or more optical fibers at precise locations in the brain of the animal. Given the small size of the fiber optic components, this was difficult to achieve. 
         [0004]    It was found that a high degree of precision in the distance between two or more fibers could be achieved by housing such fibers in a common ferrule. However, because it is often required to disconnect the animal from the optical source between experiments, there is a specific need for a special connector which would allow connecting-disconnecting the cannula to/from the optical source, while allowing the cannula to have a small size so as to create as little discomfort to the animal between the experiments. This connector should allow for the precise angular alignment of the optical fibers in the cannula with the ones of the patch cord, to reduce power losses. 
         [0005]    Further, it is sometimes required to provide liquids and/or electric wires or the like close to the location of the optical fibers in the tissue. It was found that this can be achieved by providing for a conduit passage extending through the cannula and connector. 
         [0006]    In accordance with one aspect, there is provided a fiber-optic cannula comprising a ferrule with a central axis, a connection end and a implant end opposite the connection end and at least two interspaced optical fiber passages extending therebetween, parallel to said central axis and each securely housing an optical fiber therein having a first tip exposed at said connection end, and a second tip protruding from said implant end by a penetration distance, a guide axis parallel to and spaced from both the optical fiber passages and the central axis, and a bore extending into the ferrule from the connection end along the guide axis. 
         [0007]    In accordance with another aspect, there is provided a fiber-optic connector comprising a first ferrule and a second ferrule, both ferules having a body portion having a straight external surface with a central axis, a connector end and a distal end and at least two interspaced optical fiber passages extending therebetween, parallel to said central axis and each securely housing an optical fiber therein having a tip exposed at said connector end, and a guide axis parallel to and spaced from both the optical fiber passages and the central axis; wherein the first ferrule has a male guide pin protruding from the connector end along the guide axis, and the second ferrule has female bore mating the male guide pin and extending inwardly from the connector end along the guide axis; and a sleeve having two opposite open ends and an internal surface mating with the external surface of both ferrules to slidingly receive each ferrule at a corresponding end with the guide pin received in the bore and the optical fiber tips being aligned with corresponding optical fiber tips of the other ferrule. 
         [0008]    In accordance with another aspect, there is provided a cylindrically shaped fiber-optic cannula comprising: a cylindrical ferrule having a connection end with a mating face for releasable connection to a fiber-optic cord and an implanting end for insertion into tissue, said ferrule having: at least one fiber-optic channel therethrough with an optical fiber tightly mounted therein from said connection end to said implanting end for carrying light from said fiber-optic cord into a biological tissue; a cylindrical outside surface adapted for tight insertion in a cylindrical sleeve for axial alignment of said fiber-optic connector ferrule with a corresponding ferrule with mating faces toward one another, for connection of said optical fiber from said cylindrical ferrule to said fiber-optic cord; and an off-center guiding hole adapted to tightly receive a guiding rod continuously from said cylindrical fiber-optic connector ferrule to said corresponding ferrule for angular alignment thereof. 
         [0009]    Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0010]    In the figures, 
           [0011]      FIG. 1  is a schematic view showing an optogenetic system for delivering light into an organism; 
           [0012]      FIG. 2  is a view showing the fiber optic connector between a patch cord and cannula of the system shown in  FIG. 1 ; 
           [0013]      FIG. 3  is a front elevation of the cannula of  FIG. 2 ; 
           [0014]      FIGS. 4 and 5  are cross sectional views taken along cross-section lines  4 - 4  and  5 - 5  of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows an example of an optogenetic system  10 . In this example, the optogenetic system  10  includes a light source  12  which can be a LED source, laser source, white light source for instance. At the other end, a fiber optic cannula  14  is shown adhered to a body surface  16  of a mammal, with optical fiber  18  penetrating into body tissue  20  of the mammal to provide light thereto. A patch cord  22  connects the light source to the cannula  14 . The connector  24  between the patch cord  22  and the cannula  14  includes a ferrule  26  provided at the end of the patch cord  22 , a ferrule  28  forming part of the cannula  14 , and a sleeve  30  which can receive both ferrules  26 ,  28 . 
         [0016]    The components of the cannula  14  and connector  24  are shown in greater detail on  FIG. 2 . The patch cord  22  is shown on the left hand side and the cannula  14  is shown on the right hand side. In this particular example, the cannula  14  is a two-fiber cannula which houses two optical fibers  18   a ,  18   b  which can be interspaced from one another by a very precise distance (d, shown in  FIG. 5 ). More precisely, the ferrule  28  has two optical fiber passages, which can be made by high precision machining of the ferrule  28  for instance. The optical fiber passages  32  can be seen to be parallel to a central axis  34  of the ferrule  28 , and extend from a connection end  36  thereof (which is typically precisely polished flat) to a distal end, or implant end, adapted to attachment to a body surface. During use, the distal end  38  is adhered to the surface of the body. In this particular example, the ferrule  28  has an elongated body portion  42  having an external surface forming a sleeve engagement path and extending from the connection end  36 , and a flange portion  46  at the distal end  38 . Optical fibers  18   a ,  18   b , better seen on  FIG. 5 , are housed in the optical fiber passages  32  and extend from the connection end to protrude outwardly from the distal end  38  by a penetration distance D. 
         [0017]    Referring back to  FIG. 2 , it will be noted that the flange portion  46  is optional, and is used in this example with longitudinal grooves  48 . The cannula  14  can be adhered to a surface of a body such as the skull of a mouse with the optical fibers  18   a ,  18   b  extending into body tissue, such as the brain, to stimulate neurons with light signals. The adhesion can be done with a thick adhesive substance. When longitudinal grooves  48  are used in the flange, the adhesive can set into the grooves  48  and the grooves  48  thus contribute to provide further rotation resistance to the adhered cannula  14 . 
         [0018]    As also shown in  FIG. 5 , the cannula  14  also has a bore  50  to act as a socket, i.e. delimiting a pin reception path, to receive a guide pin  52  of the patch cord  22  and contribute to maintain alignment of the optical fibers in the connection between the two ferrules  26 ,  28 . In this specific embodiment, the cannula  14  also has an optional hollow needle  54 , the use of which will be detailed below. In alternate embodiment, there can be more than two optical fiber passages, or just one, for instance. 
         [0019]    For the cannula  14  not to be too cumbersome for the animal on which it is adhered, the ferrule  28  is preferably kept small. In this specific example, the ferrule  28  has an elongated body portion  42  having a circular cross-section (shown in  FIG. 3 ). For exemplary purposes, it will be mentioned here that in this particular case the circular cross-section has a diameter of 2.5 mm and the length of the ferrule  28  can be between 6 an 10 mm, for example. Other dimensions are possible as well, and in alternate embodiments, the cross-section can be oval or elliptical for instance. Further in this example, optical fibers having a core diameter of 200 μm and a cladding diameter of 240 μm can be used for instance, and the optical fiber passages can be spaced apart from one another by a distance d such as between 0.5 and 2 mm. Other dimensions of optical fibers can be used as well, such as single mode having 9-10 μm core or multi-mode having a 500 μm core diameter, for instance. 
         [0020]    In this example, the patch cord  22  has a ferrule  26  quite similar to the one used in the cannula  14 . This ferrule  26  also has two interspaced optical fiber passages ( 54   a ,  54   b  in  FIG. 5 ) interspaced from one another, and two associated optical fibers  56   a ,  56   b  precisely reaching the connection end  58  and having buffer  60  and jacket  62  shown extending out from the distal end  64 . An optional tube  66  or jacket can also be used, the use of which will be discussed below. The elements extending out the distal end  64  can be covered by a sheathing, which is not shown in  FIG. 2 . Of course, the position of the optical fiber passages  54   a ,  54   b  in the cross-section of the body portion will be made to correspond closely to the position of the optical fiber passages  32  in the cross-section in the cannula (as shown in  FIG. 3 ). Otherwise, the misalignment of at least one of the two optical fiber connections may be inevitable, and generate undesired power losses. One difference of the patch cord ferrule  26  is the absence of a flange portion  46 , which was not required in this case. Another difference resides in the fact that this ferrule  26  has a guide pin  52  providing a male portion protruding from the connection end  58 . 
         [0021]    A sleeve  30  is provided which receives the body portions of both ferrules  26 ,  28  to maintain the connection. The tighter the fit between the sleeve  30  and the ferrules  26  and  28 , and between the guide pin  52  and the bore  50 , the firmer the connection will be held together. In this particular case, it will be noted that to achieve a very tight fit, the sleeve  30  is provided with a slit  68  along its entire length, and can be made of a material which is at least slightly elastic, such as zirconia, and is manufactured with an interference fit with the diameter of the body portion  42  of the ferrules  26 ,  28  it receives. Henceforth, when the ferrules  26 ,  28  which can have a bevelled connection end are pushed into a corresponding end of the sleeve  30 , the ferrules  26 ,  28  push the slit  68  open, and the elasticity of the sleeve material thereafter biases the slit  68  to close it. The internal surface  70  of the sleeve thus exerts a force against the external surface  42  of the ferrules, which increases the amount of frictional resistance to disconnection. The amount of frictional resistance to disconnection is also affected by the area of contact between the sleeve  30  and ferrules  26 ,  28 , and thus by the length and diameter of the ferrules  26 ,  28  and sleeve  30 . 
         [0022]    It is understood from the above that the tightness of the fit between the sleeve  30  and the ferrules  26 ,  28  is directly related to the precision obtainable with the alignment of the optical fiber connection. Another important factor is the position of the guide pin  52  and mating bore  50  in the cross section and the tightness of the fit between the guide pin  52  and bore  50 . In fact, the guide pin  52  and bore  50  provide an angular alignment feature, and contribute to maintain the angular alignment when the connector  24  is subjected to torsion stress. To achieve good precision, both the guide pin position and bore position should precisely correspond to an axis referred to herein as the guiding axis  72 , relative to the parallel central axis  34  and optical fiber passages. Further, it will be understood that positioning the guiding axis  72  further away from the central axis  34  will typically increase angular alignment precision because it increases the lever arm  1  with the central axis  34 , or rotation axis. In this particular example, the guiding axis  72  is spaced by about 0.5 mm from the outer surface  42  of the ferrules  26 ,  28  which come into contact with the sleeve  30 . 
         [0023]    Turning now to  FIG. 4 , it will be seen that in this particular case, openings in both ferrules  26 ,  28  can be machined in exactly the same manner in a molded or machined body of material such as zirconia, metal or plastic for instance, and the guide pin  52  can be inserted into a bore  74  of one of the ferrules  26  and adhered into place for instance. In an alternate embodiment, the guide pin  52  can be provided in the cannula portion  14  of the connector  24  rather than in the patch cord portion  22  of the connector  24 , though positioning it in the patch cord portion  22  can be preferred to reduce the weight and cumbersomeness of the cannula  14  for the animal when it is disconnected from the patch cord  22 . 
         [0024]    A further optional feature of the cannula  14  and connector  24  provided in this embodiment is also shown in  FIG. 4 . The optional feature is a conduit passage which can extend across and through both ferrules  26 ,  28  to deliver a fluid, electrical wires or the like through the cannula  14  and into the body tissue. The conduit passage  76  can include a passage portion  78 ,  80  extending further from the bottom of the bore  50 ,  74  of both ferrules  26 ,  28 , and entirely across, and the guide pin  52  can hollow, so as to allow continuing the passage across it. If fluid is to be delivered, it can be provided into the patch cord ferrule  26  from a flexible tube  66  inserted securely into the conduit passage at the distal end  64 . A hollow needle  54  can be provided at the implant end  38  of the cannula  14  to prolong the conduit passage  76  into the body tissue. Providing the conduit passage  76  through the guide pin  52  is particularly practical to deliver fluid. In this case, the guide pin  52  can serve both as a portion of the conduit passage  76  and an angular alignment feature for the optical connection. 
         [0025]    It will be noted that alternate embodiments can have more than one guide pin and more than one conduit passage if desired. 
         [0026]    As can be seen from the above, the examples described and illustrated are intended to be exemplary only. The scope is indicated by the appended claims.