Abstract:
An over molded reflective optical fiber terminal ( 100 ) generally includes an end portion of an optical fiber ( 102 ) that has been stripped of its buffer ( 104 ), a terminal block ( 106 ), an integral mirror ( 108 ) formed on the terminal block ( 106 ), and an optical element such as a window ( 112 ). The terminal block ( 106 ) is preferably formed from transparent injection molded plastic. The block can be molded so as to define a profile for the mirror ( 108 ). By virtue of this design, construction and alignment of the terminal/mirror system is simplified and costs are reduced. In addition, the reflective surface of the mirror ( 108 ) may be protected against dust or other optical interference. Moreover, a compact reliable terminal system for off axis application is provided.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to terminals for optical fibers and, in particular, to an over-molded terminal with an integral reflector for non-axial signal communication applications. The invention has particular advantages for certain photoplethysmography applications. 
     BACKGROUND OF THE INVENTION 
     Optical fibers are used to transmit optical signals in a variety of applications including communications, spot or area illumination and photoplethysmography, e.g., pulse oximetry. The associated optical systems typically include one or more fiber terminals where signals are transmitted to and/or from an end of an optical fiber. In this regard, such terminals are often associated with optics such as lenses or mirrors, for example, for focusing an incoming signal onto the fiber end, for forming an outgoing signal into a beam, for diffusing an outgoing signal as may be desired or for various other functions. One important function of such optics is to receive or transmit non-axial signals, i.e., signals not aligned with the optical axis extending from the fiber end. It may be desired to transmit or receive non-axial signals, for example, in order to reduce optical system dimensions, to couple the optical fiber with other optical components that are constrained to being located off-axis, or to facilitate selective coupling of the fiber relative to multiple optical devices which cannot all be disposed on-axis. 
     Accordingly, it is often desired to provide a reflector or mirror in connection with a fiber terminal. Depending on the intended use of the mirror, many different optical, construction and maintenance issues may need to be considered in connection with the terminal/mirror interface. One of these issues relates to the relative positioning of the fiber end and the mirror. The fiber end generally must be securely anchored and the mirror must be carefully positioned on the fiber axis in order to allow for proper optical coupling of the mirror to the optical fiber. The angular orientation of the mirror generally must also be controlled in relation to the overall optical system for proper alignment so as to reduce optical losses. Additionally, the distance between the fiber end and the mirror may need to be selected in conjunction with the mirror shape such that incoming signals are focused or contrasted on the fiber end, or outgoing signals from the fiber end are focused, collimated or diffused as desired, etc. Moreover, for maintenance purposes, the mirror may need to be sealed or be accessible for cleaning in order to maintain acceptable optical performance. It will thus be appreciated that the design, construction and maintenance of fiber terminals and associated optics can be complicated and expensive. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an integrated fiber terminal and reflector system for use in a variety of off-axis signal transmission applications including transmitting and/or receiving signals that are off-axis relative to a terminated fiber. The invention substantially simplifies construction, alignment and maintenance, and allows for reduced production costs as well as improved optical performance. As set forth below, the invention has particular advantages for certain photoplethysmography applications such as pulse oximetry due to its compactness of design, ease of construction and alignment, and low production costs for probes that may be disposed of after a single use or few uses. 
     According to one aspect of the present invention, a reflective surface is integrally formed on a signal transmissive terminal structure in which a fiber is anchored. The corresponding terminal includes a terminal structure for fixedly retaining an end portion of the optical fiber such that the fiber end portion defines a fiber axis extending axially from the end portion, and a reflective surface integrally formed on the terminal structure and extending across the fiber axis. The terminal structure includes an optically transmissive portion extending across the fiber axis. Preferably, the optically transmissive material is substantially transparent to at least one wavelength of interest. For example, the terminal structure or a portion thereof may be formed from transparent plastic that is molded over the end portion of the fiber. The reflective surface is operative for reflecting signals relative to the fiber axis and a reflection axis, i.e., reflecting signals from the fiber axis to the reflection axis or vice versa. Preferably, the reflective surface is integrally formed on the terminal structure by applying a reflective film or other reflective material to an external surface of the terminal structure. In this regard, the exterior surface of the terminal structure may be shaped to impart the desired optical properties to the reflective surface, e.g., concentrating/focusing, collimating, or diffusing optical signals incident thereon. By virtue of the present invention, construction and alignment of the terminal/mirror system is simplified and costs are reduced. In addition, the reflective surface may be protected against dust or other optical interference. Moreover, a compact and reliable terminal system for off-axis applications is provided. 
     If desired, a further optical device may be mounted on the terminal structure. For example, the optical device may be mounted on an exterior surface of the terminal structure extending across the reflection axis in order to operate on signals transmitted along the reflection axis, e.g., incoming or outgoing signals. Depending on the application, the optical device may perform any of various functions. For example, the optical device may diffuse signals transmitted from the optical fiber in order to illuminate a desired area. Alternatively, the optical device may collimate, concentrate or focus signals transmitted from the optical fiber onto a further optical element such as another optical fiber, a lens, or an optical detector. Conversely, the optical device may operate on incoming signals, for example, to focus or assist in focusing the incoming signal onto the end of the terminated optical fiber. 
     According to another aspect of the present invention, a method is provided for forming an optical fiber terminal. The method includes the steps of providing an optical fiber having an exterior buffer material, removing the buffer material from an end portion of the fiber, molding an optically transmissive material over the end portion of the fiber, and applying a reflective material to an exterior surface of the molded, optically transmissive material such that the reflective material extends across an axis of the fiber. The buffer material may be a liner material such as is commonly provided in connection with optical fibers to prevent accidental breakage or shield ambient light. Such buffer material can be removed from the end portion by way of a conventional stripping operation. The optically transmissive material may then be molded over the end portion of the fiber, for example, by way of injection molding transparent plastic on the optical fiber end. As part of this molding process, and exterior surface of the plastic may be shaped to impart desired optical properties to the reflective material subsequently applied to the exterior surface. Depending on the nature of the optically transmissive material and the reflective material, the reflective material may be applied by direct deposition onto the optically transmissive material adhesive bonding, or other processes. In the case of adhesive bonding, the adhesive may be applied outside of the area of the reflective surface or an index matched adhesive may be employed. In all such cases, it is an advantage of the present invention that the reflective material is integrally formed on the terminal structure such that proper optical performance is insured. 
     In one embodiment, the optical terminal of the present invention is implemented in connection with a pulse oximeter probe. Pulse oximetry generally involves transmission of optical signals of a predetermined wavelength or wavelengths through a portion of a patient&#39;s body such as a finger, ear lobe or the like. The optical signal transmitted through the patient&#39;s tissue is then detected and can be analyzed to determine oxygen saturation, perfusion or the like as is well known. It is desirable to provide the portion of the oximeter instrument which engages the patient in the form of a detachable probe. Such a probe may be disposed of after a single use or a small number of uses. Accordingly, it is desirable to reduce the cost of the probe by locating relatively few components in the probe but, rather, locating most of the active and expensive components in an oximeter housing to which the probe is coupled. Thus, for example, the use of fiber optics can allow a signal source and/or a signal detector to be located in the housing. 
     Accordingly, the probe may include a transmitting fiber and associated optics and/or receiving fiber and associated optics. Alternatively, the receiving fiber and associated optics may be replaced by a detector and electrical leads. The probe also includes a housing structure for engaging the patient. For example, the housing may be shaped and dimensioned for engaging a patient&#39;s finger. In accordance with the present invention, the terminal of the present invention may be engaged within the probe housing structure for transmitting and/or receiving pulse oximetry signals. In this regard, the terminal structure may be bonded to the probe housing structure or may be removably inserted into the housing structure with appropriate mechanisms to insure proper registration of the transmitting and receiving elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and further advantages thereof, reference is now made to the following detailed description taken in conjunction with the drawings in which, 
     FIG. 1 is a perspective view showing a fiber optic terminal in accordance with the present invention; 
     FIG. 2 is a side cross sectional view of the terminal of FIG. 1; 
     FIG. 3 is a ray diagram illustrating the optical performance of the terminal of FIG. 1; and 
     FIG. 4 is a side cross sectional view, partially schematic, showing the terminal of FIG. 1 incorporated into a pulse oximetry housing. 
    
    
     DETAILED DESCRIPTION 
     In the following description, the invention is set forth in the context of a specific overmolded reflective optical fiber terminal and embodiments where the terminal is incorporated into a pulse oximetry housing. It should be appreciated however that various aspects of the invention may be implemented in other types of fiber terminals and in other applications. 
     Referring to FIGS. 1-3, an overmolded reflective optical fiber terminal is generally identified by the reference numeral  100 . The terminal  100  generally includes an end portion of an optical fiber  102  that has been stripped of its buffer  104 , a terminal block  106 , an integral mirror  108  formed on the terminal block  106 , and an optical element such as a window  112 . Each of these components will be described in turn below. 
     The optical fiber  102  may be any of various optical fibers that are known or may hereafter be developed. Typically, such optical fibers include an optical fiber core surrounded by coaxial cladding. The cladding generally operates to reflect radiation at the core/cladding interface so that optical signals can be transmitted through the core with minimal optical losses. The illustrated fiber also includes a coaxial buffer  104  surrounding the fiber. Such buffer materials are typically provided to strengthen the optical fiber so as to avoid accidental breakage. In addition, the buffer may further insulate the fiber core from ambient light which could increase noise levels. For the purposes of pulse oximetry applications such as discussed below, the optical fiber  102  is preferably suitable for transmitting near infrared optical signals. As shown, the fiber  102  is stripped of the buffer  104  at an end portion thereof where the fiber extends into the terminal block  106 . 
     The illustrated terminal block performs a number of functions. First, the terminal block anchors the fiber end  220  of fiber  102 . In this regard, it will be appreciated that, for certain applications, it is important to fix the position of the fiber end relative to the mirror  108  and other optical components of an optical system. For example, if the fiber  102  is intended to receive optical signals via the window  112  and mirror  108 , it may be important for the fiber end  220  to be located in a focal plane of the mirror  108  or otherwise positioned such that incoming signals are concentrated on the fiber end  220 . Relatedly, it may be important for the relative positioning of the fiber end  220  and mirror  108  to be maintained such that the mirror  108  is located on the fiber axis  214  whereby the fiber axis  214  is coupled with reflection axis  216  via the mirror  108 . Such relative positioning can be controlled by appropriately forming the terminal block  106 . 
     The terminal block  106  also supports the mirror  108  and window  112 . As will be described in more detail below, external surface  113  of terminal block  106  may be formed to impart the desired optical qualities to the mirror  108 . For example, external surface  113  may have a convex profile so as to concentrate or focus an incoming beam transmitted through window  112  onto the fiber end  220 . Alternatively, as shown, the mirror  108  may have a concave profile so as to diffuse the signal transmitted from fiber  102 . In the illustrated embodiment, it will be appreciated that the concave mirror  108  is also reversibly operative for concentrating an incoming signal onto the fiber end  220  as generally shown in the ray diagram of FIG.  3 . External surface  105  may be used for mounting an optical component such as window  112 . Thus, the position, shape and angular orientation of the external surface can be selected in relation to the window  112 , mirror  108 , and fiber end  220  so as to provide the desired optical performance. 
     The illustrated terminal block  106  also includes a flange  110 . As shown, the flange  110  provides a widened mounting surface  115  for window  112 . The flange  110  may also be useful, as described below, for mating with complementary structure of a pulse oximetry probe housing (or other structure for other applications), so as to insure proper registration of the terminal  100  with other optical components. 
     The mirror  108  couples the fiber axis  214  with the reflection axis  216 . Accordingly, the mirror may operate to reflect signals transmitted from the fiber  102  onto the reflection axis  216  and/or reflect incoming signals from reflection axis  216  into the fiber  102  via fiber axis  214 . As noted above, external surface  113  may be formed to define the mirror  108 . The mirror  108  can then be completed by applying a reflective material onto the formed surface  113 . The reflective material may be applied in various ways depending on the nature of the terminal block and the reflective material. For example, if the terminal block was formed from glass, the reflective material may be directly deposited onto the terminal block  106  such as via sputtering. In the illustrated embodiment, the terminal block  106  is formed of injection molded plastic and the reflective material is bonded thereto. In this regard, the reflective material may be applied by spraying, by providing a separate film that is adhered to the terminal block  106  via heating, or via an adhesive applied across or outside of the reflective surface. Where the adhesive is applied across the reflective surface, a transparent, index matched adhesive is preferably employed. Regarding optical performance, the reflective material is preferably highly reflective at least with regard to the wavelengths of interest. In the illustrated embodiment, the reflective material is a spray coating of infrared reflective film. 
     Various types of optical components may be mounted on surface  115 . For example, a collimating lens may be employed to form an output collimated beam and/or to concentrate an incoming beam on the fiber end in conjunction with the mirror  108 . Alternatively, a concentrating or focusing lens may be employed, for example, to focus a transmitted signal onto a detector surface or the end of an optically coupled fiber or optics associated with a coupled fiber. In the illustrated embodiment, a diffusive window  112  is mounted on surface  115 . Such a diffusive window may be desirable in connection with various applications such as pulse oximetry, in order to provide a broadened beam  218 . In pulse oximetry, such a broadened beam may be preferable to reduce errors resulting from bone, veins or other artifact. Optionally, an optical band pass filter may be implemented in conjunction with the window  112  to minimize the admittance of ambient light or other optical noise. 
     The illustrated terminal  100  can be formed as follows. First, a fiber  102  is obtained and the buffer  104  is stripped from an end portion of the fiber  102  in conventional fashion. The terminal block  106  can then be injection molded onto the fiber end  220  by inserting the fiber end  220  into a mold and injecting transparent plastic so as to form the terminal block  106 . The mirror  108  can then be completed by spray coating reflective material onto surface  113  or otherwise applying a reflective film to the surface  113  such as via heating or an adhesive. The window  112  or other optics can then be applied to surface  115  using an adhesive such as an index matched transparent adhesive applied between the window  112  and the surface  115 . The placement of the mirror  108  is controlled by the design of the mold. Similarly, the placement of the window  112  can be controlled by molding an appropriate indentation into surface  115 . Alternatively, placement of the window  112  may be selected by transmitting an optical signal through the fiber  102  and then moving the window  112  until the desired output effect is achieved. 
     FIG. 4 shows a side cross sectional view, partially schematic, of a pulse oximetry housing  400  incorporating the terminal  100 . As is well known, pulse oximetry relates to transmitting optical signals through tissue in order to determine oxygen saturation, perfusion or the like. Generally, the transmitted optical signal includes one or more wavelengths where oxygen related analytes of interest have an absorption peak or other spectral characteristic that can be quantified. Accordingly, pulse oximetry generally involves transmitting a radiation signal through tissue and detecting the radiation signal transmitted through the tissue. In the illustrated embodiment, the probe housing  400  is of a type commonly used to engage a patient&#39;s finger  402  and is generally shaped and dimensioned to extend over the end of the patients finger. A spring or the like is typically provided in conjunction with the housing so that the housing securely clamps onto the patient&#39;s finger. The illustrated terminal  100  is used to transmit an optical signal  406  through the finger  402 . The transmitted signal is then received by a detector element  408  on the opposite side of the patient&#39;s finger  402 . Although only shown schematically, it will be appreciated that the detector element  408  may include detectors such as photo diodes that are located in the probe housing  400 . Alternatively, the detector element  408  may include a further fiber optic terminal for capturing the transmitted signal and transmitting the signal via an optical fiber to a detector unit located in a remote housing. 
     In the illustrated embodiment, the terminal  100  is located within a complementary shaped portion  404  of the probe housing  400 . Such complementary shaping holds the terminal  100  securely in place and assures proper registration relative to the detector structure  408 . In this regard, the probe housing  400  may be hinged to allow insertion of the terminal. Alternative designs may allow the terminal  100  to be engaged within the housing  400  by way of adaptors that engage with a snapping action. Additionally, although not shown, the terminal  100  may be secured in place using an adhesive if desired. 
     While various embodiments of the present invention have been described in detail, it is apparent that further modifications and adaptations of the invention will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.