Patent Description:
In many applications, one requires imaging hard to reach places. For accessibility, optical fibers are often used to reach the imaging area. At the end of the fiber, at the imaging site, it is necessary to have a lens to form an image on the end of the fiber that may then be transmitted to the rest of the imaging system.

An example of such an application is the imaging of tissue in the brain of a live, freely moving mammal. In this example, the lens is located in the brain tissue, and an imaging optical fiber must be coupled to the lens to allow the transfer of a focused image away from the imaging site to where the rest of the imaging system resides. In such experiments, it may be necessary to image the brain many times over an extended time period. However, the process of connecting the fiber to the lens, performing the imaging session and disconnecting the fiber from the lens can be clumsy and time-consuming.

In many existing fiber-lens connectors, there are various problems that limit the functionality of the connector. It is often difficult to maintain the focusing properties of the imaging device, as the focus may change from one imaging session to another. It is also frequently difficult to manipulate the connector relative to brain tissue which can sometimes lead to the tissue being damaged. The size and weight of conventional connectors can also be a problem, particularly when trying to image a small mammal, such a mouse and, if they are too big, they can interfere with natural animal movement and behavior. In addition, the coupling of existing connectors is not always completely stable or easily manipulatable by a user. <CIT> discloses a fiber-lens connector with adjustable focus.

In accordance with the present invention, an optical imaging connector is provided that has a fiber assembly that is removably attachable to a lens assembly. The lens assembly has a lens, such as a graded refractive index (GRIN) lens, that may be fixed in position adjacent to an imaging target, such as the brain tissue of a laboratory animal. The fiber assembly may be easily connected and disconnected from the lens assembly such that, when the two assemblies are connected, an image collected by the lens is coupled into an optical fiber of the fiber assembly. Quick detachment and reattachment of the fiber assembly from the lens assembly allows for repeated measurements to be easily taken from an imaging target.

The fiber assembly has an optical fiber ferrule in which is located an optical fiber for transporting an optical image. A ferrule adapter is fixed to the ferrule and has a radial extension with a first coupling portion. The lens assembly has a lens with a distal end configured to be fixed adjacent to an imaging target. The lens is mounted in a lens holder with its proximal end adjacent to a ferrule receptacle of the lens holder that receives the ferrule and maintains it in a substantially co-axial relationship with the lens. The lens holder also has a radial extension with a second coupling portion that engages with the first coupling portion of the ferrule adapter to removably couple the fiber assembly to the lens assembly. In an exemplary embodiment, the first and second coupling portions comprise at least one magnetic element that provides a magnetic attraction between the first and second coupling portions.

The connector also has a focus adjustment mechanism that is part of the lens assembly. The mechanism is manually adjustable by a user to change the longitudinal position of the second coupling portion relative to the lens holder. This, in turn, changes an axial position of the ferrule when it is located in the ferrule receptacle, and thereby changes the focusing, as the distance between the lens and the fiber is also changed. In an exemplary embodiment, the radial extension of the lens holder includes a threaded aperture, and the focus adjustment mechanism makes use of a screw that has an external thread that meshes with the internal thread of the threaded aperture. Rotation of the screw changes a longitudinal position of the second coupling portion, thereby axially moving the ferrule adapter and the ferrule relative to the lens holder.

The first coupling portion and the second coupling portion may also be configured to maintain a constant relative angular orientation between them when the two coupling portions are engaged with each other. A top of the screw used to adjust the focus may act as a detent and extend into a space of the first coupling portion in which it prevents relative rotation between the two coupling portions. Maintaining this common angular orientation between the fiber assembly and the lens assembly ensures that the image transported by the fiber will always have the same orientation relative to the imaging target.

In an alternative embodiment, an optical imaging connector has an optical fiber ferrule in which is located an optical fiber, as well as a ferrule adapter fixed to the ferrule that has an external screw thread and an axially-extending detent on a distal side of the adapter. A lens is configured to have its distal end fixed adjacent to an imaging target, while its proximal end is mounted in a lens holder adjacent to a ferrule receptacle that receives the fiber ferrule and maintains it in a substantially coaxial relationship with the lens. The lens holder has an external screw thread and receives the detent when the ferrule adapter and the lens holder are axially adjacent to each other so as to prevent a relative rotation therebetween. The lens holder may have, for example, a slot into which the detent, which may be an axially-extending tab, is inserted.

The connector includes a focus adjustment mechanism with an internal screw thread that engages both the screw thread of the ferrule adapter and the screw thread of the lens holder. The focus adjustment mechanism is manually rotatable by a user to change a relative longitudinal position between the ferrule adapter and the lens holder, thereby changing an axial position of the ferrule in the ferrule receptacle. In particular, the focus adjustment mechanism may include a nut with screw threads having different thread directions, i.e., right-handed and left-handed, at the two openings of the nut. Thus, rotation of the nut causes the ferrule adapter and the lens holder to move either toward or away from each other. When engaged, the focus adjustment mechanism maintains the ferrule adapter and the lens holder in a substantially coaxial position relative to each other, while rotation of the mechanism to an extreme position provides disengagement of the internal screw thread from the screw threads of the ferrule adapter and the lens holder, allowing detachment of the ferrule from the lens holder.

In order that the subject matter may be readily understood, embodiments are illustrated by way of examples in the accompanying drawings, in which:.

Depicted in <FIG> is a first embodiment of a lens-fiber connector shown in exploded form. The connector includes two main assemblies, a lens assembly and a fiber assembly, each of which consists of components that are fixed to one another. The two assemblies can, however, be removably coupled together, with the fiber assembly being connected or disconnected from the lens assembly. The fiber assembly includes an optical fiber located in a ferrule <NUM>, to which is attached a ferrule adapter <NUM>. Mounted in the ferrule adapter <NUM> is a cylindrical magnet 16a, which has a mutual attraction to a cylindrical magnet of the lens assembly, as discussed in more detail below. The lens assembly includes a lens <NUM> that is located at an imaging site, and resides in a first aperture of a collet <NUM>, the opposite side of which receives the fiber ferrule <NUM> of the fiber assembly. Also located in the collet <NUM> is a threaded aperture that receives a focusing screw <NUM> having threads that mesh with the threads of the collet aperture. Surrounding a portion of the top <NUM> of the screw <NUM> is the cylindrical magnet 16b of the lens assembly.

<FIG> is a front view, showing the components of each of the lens assembly and the fiber assembly in an assembled configuration. The two assemblies are shown side-by-side relative to an axis along which they may be connected together during an imaging operation. A section line indicates the perspective of the cross-sectional side view shown in <FIG>, which is instructive for an understanding of the system operation.

As shown in <FIG>, the connector is asymmetrical relative to a longitudinal axis of the connector. The lens <NUM> is a lens that can have different diameters or lengths and, as mentioned above, in the present embodiment, it is a graded refractive index (GRIN) lens. In this embodiment, the lens has a diameter of <NUM> and a length of about <NUM>, although other sizes are possible. The miniature size of the lens makes it well suited for connection to an anatomical region of interest, such as the brain tissue, of a small mammal, such as a mouse. In a typical imaging situation, the lens is fixed to the brain tissue of the subject using a strong biocompatible glue, such as meta-bond or dental cement. As experiments of this nature require imaging of the brain tissue multiple times over a long period of time (often several months), the lens assembly remains in place during this period, while the fiber assembly is disconnected during periods when imaging is not required.

The lens <NUM> has a cylindrical exterior and is inserted into a mating cylindrical extension of the collet <NUM>, and is glued to the collet at a precise location within the collet, the glue being applied, for example, at interface <NUM> shown in <FIG>. In the present embodiment, the lens is located in the collet at a position that will provide a minimum distance of about <NUM> or <NUM> microns between the proximal end of the lens and the distal end of a fiber of the fiber assembly when the fiber assembly and the lens assembly are connected together. A receiving aperture 13a of the collet <NUM> into which the fiber is inserted has a tapered surface 13c adjacent to the lens <NUM> that ensures this minimum distance, and prevents contact between the fiber and the lens, which might otherwise damage the lens or scratch the tip of the fiber.

Another aperture 13b of the collet <NUM> lies adjacent to the aperture 13a and has an internal screw thread that mates with an exterior thread of screw <NUM>. In this embodiment, longitudinal axes of the apertures 13a and 13b are parallel. As shown in <FIG>, the screw <NUM> has an upper portion that is not threaded and that has a narrower diameter than the threads on the lower portion of the screw. Annular magnet 16b is located around this upper screw portion, the diameter of which is sufficiently small to receive it, while the larger diameter of the screw threads prevents further movement of the magnet down the body of the screw. The height of magnet 16b is such that the top <NUM> of the screw <NUM> protrudes out of the magnet by a small amount when the magnet 16b is resting adjacent to the screw threads. This provides access to the screw to allow it to be adjusted by a user either by hand or by an appropriate tool, such as a screwdriver.

Also shown in <FIG> are the fiber ferrule <NUM> and ferrule adapter <NUM>. In this embodiment, the ferrule <NUM> has a diameter of <NUM> and length of approximately <NUM>. As shown in the cross-section of the adapter <NUM>, it is fixed to the exterior of the ferrule <NUM>, and has a laterally-extending magnet holder <NUM>. Located within the magnet holder <NUM> is cylindrical magnet 16a, which preferably has the same diameter and bore as magnet 16b. Magnet 16a is fixed within the magnet holder <NUM>, which is located to align with the magnet 16b when the fiber assembly and lens assembly are connected together. That is, when the ferrule <NUM> is inserted in the collet <NUM>, it may be rotated so that the magnets 16a and 16b are adjacent to each other, such that further insertion of the ferrule <NUM> in the collet results in insertion of the top <NUM> of screw <NUM> into the bore of the magnet 16a. The magnets 16a and 16b are mutually attractive, and hold the two assemblies together in this position.

As will be recognized by those skilled in the art, the position of the screw <NUM> and magnet 16b will affect the relative positioning of the fiber assembly and the lens assembly. The ferrule adapter <NUM> is fixed to the ferrule <NUM>, such as by gluing, at a position that results in the fiber being adjacent to the tapered surface 13c of the collet <NUM> when the screw <NUM> is fully screwed into the threaded aperture of the collet. As the screw <NUM> is unscrewed from the threaded aperture, the point of contact between the magnets 16a and 16b moves further from collet <NUM>, and the distal end of the ferrule <NUM> moves away from the tapered surface 13c, while remaining in the receiving aperture 13a. Thus, the distance between the tip of the fiber and the lens, and thereby the focusing of the lens on the fiber, can be changed by adjusting the screw from the top.

When the fiber assembly and lens assembly are connected together, the magnets keep the assemblies, and therefore the fiber and lens, firmly in place. In addition, the location of the top <NUM> of screw <NUM> in the bore of the magnet 16a prevents a relative rotational movement between the ferrule <NUM> and the collet <NUM>, and therefore between the fiber and the lens. This prevents relative rotation of an image from the lens at a detector (not shown) to which the fiber is connected, allowing for easy comparison of images taken at different times.

An opening on the top of the magnet-holding portion <NUM> of the ferrule adapter <NUM> provides access to the top of the screw when the fiber assembly and the lens assembly are connected together. Thus, a user can adjust the focus while the fiber and lens are properly positioned relative to each other by turning the screw to change the relative distance between them. In this way, the user can observe the image while changing the fiber-lens distance so as to achieve the best possible focus. Moreover, the frictional resistance of the screw in the threaded aperture of the collet is sufficiently high that there is no slippage of the screw position without it being manually adjusted. Thus, once a desired adjustment is made, the proper focusing position remains for this lens, regardless of how many times the user disconnects and reconnects the fiber assembly. Furthermore, if multiple ferrules with different fibers are used with the system, and all have the same positioning of the fiber relative to the ferrule and the ferrule adapter, the correct focusing position will be maintained for each of the fiber ferrules used with a given lens assembly.

In an embodiment like that of <FIG>, the components of the connector may be assembled in a particular order to ensure a proper optical alignment. First, the screw <NUM> is located in the threaded aperture of the collet <NUM> and screwed all the way down. Magnet 16a is glued to the ferrule adapter <NUM>, which is then located on the ferrule, but not yet glued. Magnet 16b is located on the screw head with an orientation that provides mutual attraction between the magnets 16a, 16b, and the GRIN lens <NUM> is inserted into collet <NUM>. The fiber ferrule is then inserted into the receiving aperture 13a of the collet <NUM> until it reaches the tapered surface 13c. The fiber ferrule adapter is then positioned on the ferrule <NUM> so that the magnets 16a, 16b are adjacent to each other. With the connector components in this position, the lens <NUM> is glued to the collet <NUM> and the ferrule adapter <NUM> is glued to the fiber ferrule <NUM>. The magnet 16b is also glued to the top of screw <NUM>. Once the glue sets, the connector components have correct relative positions that allow proper optical alignment that is repeatable when the fiber assembly is disconnected and reconnected to the lens assembly.

The focusing between the lens <NUM> and the fiber of ferrule <NUM> is adjustable by rotating the screw to change the distance between a tip of the ferrule <NUM> and the lens <NUM>. This focusing adjustment allows the connector to compensate for differences in how the lens <NUM> may be positioned relative to the imaging target, such as the brain tissue of a mammal being examined. Different positioning of the lens may result in different necessary focusing adjustments, but since the grin lens may be fixed in position, and the focusing adjustment remains with the collet <NUM> and lens <NUM>, the adjustment does not need to be repeated each time the fiber assembly is reconnected to the lens assembly. Moreover, there may be multiple lens assemblies to which one fiber assembly is connected, and since the focusing adjustment for each resides on the lens assembly, there is no need for readjustment once the proper focusing adjustment is made for each lens assembly. Thus, the connector allows for simple, repeatable connections between the fiber assembly and one or more lens assemblies.

The connector provides a number of different advantages, particularly for doing brain imaging of small mammals. As discussed above, the distance between the fiber and the lens <NUM> remains the same for all imaging sessions, so the user can be confident that the changes they see in the biological tissue result from changes in the tissue, not from the focusing properties of the imaging device. The user can also be confident that the same object plane is being imaged in all imaging sessions, as once the focal distance between lens and fiber is set during the first imaging session, it remains the same for all subsequent imaging sessions. The system also allows the change of focus to be done in a gradual, continuous manner without pushing and pulling on the lens, which prevents injury to brain tissue. Because the same rotational orientation between the fiber assembly and the lens assembly is maintained when the assemblies are disconnected and reconnected, the orientation of the imaging field will also remain the same between different imaging sessions.

The configuration of the connector is also particularly suitable for miniaturized applications like imaging of the brain of a small rodent, such as a mouse. In an exemplary embodiment, the size of the connector is small enough that a number of connectors (e.g., four) can fit on the head of a mouse. For example, in the embodiment shown in <FIG>, the lens <NUM> may have a diameter of <NUM>, and a length of about <NUM>. With the screw <NUM> fully inserted into the threaded aperture of the collet <NUM>, the collet has an overall length of about <NUM>, and a maximum width of about <NUM>. The ferrule of this embodiment has a diameter of about <NUM> and a length of approximately <NUM>. Thus, it can be seen that the connector is particularly suited for miniaturized applications. The weight of the connector is also minimized, e.g., about <NUM>, so that a small rodent can support multiple connectors in a way that the weight does not interfere with natural animal movement and behavior.

The connector is also well suited to use by a single user. In particular, the design allows a user to change the focus when the lens is implanted in the head of an animal, such as a mouse, while the animal is awake and minimally restrained, by allowing, for example, the user to hold the animal with one hand and change the focus with the other hand. A user can do this for a number of implants, e. four, very quickly, as the focusing mechanism for each of the lens assembly implants is easily accessible, accurate and fast. Finally, as the subject, e.g. a mouse, moves around with the lens and fiber on its head, the image remains completely stable, as there is no relative movement between the lens and fiber once it is fixed in place.

Shown in <FIG> is an alternative embodiment of the invention that has a more slender profile than the embodiment of <FIG>. In the exploded perspective view of <FIG>, a grin lens <NUM> is shown adjacent to a collet <NUM> having an aperture that receives the lens <NUM>. The collet <NUM> has a slot <NUM> that receives a key <NUM> that extends from a fiber ferrule adapter <NUM> that is fixed on fiber ferrule <NUM>. The collet <NUM> has a threaded exterior that meshes with an internal thread at a distal end of nut <NUM>, while the ferrule adapter <NUM> has a threaded exterior that meshes with an internal thread at a proximal end of nut <NUM>.

The internal threads of the proximal and distal end of nut <NUM> are, respectively, in opposite thread directions. That is, one of these internal threads is a left-handed thread, while the other is a right-handed thread. Thus, when the collet <NUM>, nut <NUM> and ferrule adapter <NUM> are assembled together, a rotation of the nut in one direction will cause both the collet <NUM> and the ferrule adapter <NUM> to be drawn toward each other, while a rotation in the opposite direction will cause them to move further apart. The focusing of the connector can therefore be controlled by a user simply by rotating the nut <NUM>, which may be adjustable by hand, so as to move the lens and fiber relative to each other in an axial direction. When these components are assembled together, tab <NUM> of the ferrule adapter <NUM> is located in the slot <NUM> of the collet <NUM>, thereby maintaining a constant relative rotational orientation of the ferrule adapter and the lens <NUM>. This relative orientation remains regardless of how many times the user disconnects and reconnects the fiber to the lens.

Claim 1:
An optical imaging connector comprising:
a fiber assembly comprising:
an optical fiber ferrule (<NUM>) in which is located an optical fiber for transporting an optical image; and
a ferrule adapter (<NUM>) fixed to the ferrule (<NUM>); and
a lens assembly comprising:
a lens (<NUM>) with a distal end configured to be fixed adjacent to an imaging target; and
a lens holder (<NUM>) in which the lens (<NUM>) is mounted with its proximal end adjacent to a ferrule receptacle that receives the ferrule (<NUM>) and maintains it in a substantially co-axial relationship with the lens (<NUM>), characterized in that
the ferrule adapter (<NUM>) has a radial extension with a first coupling portion and the lens holder (<NUM>) has a radial extension with a second coupling portion that engages the first coupling portion to removably couple the fiber assembly to the lens assembly; and
the lens assembly further comprises a focus adjustment mechanism that is manually adjustable by a user to change a longitudinal position of the second coupling portion relative to the lens holder (<NUM>) and thereby change an axial position of the ferrule in the ferrule receptacle.