Abstract:
An optical to RF interface connector has a cellular housing that has a back most portion configured for press fitting into a hole of the housing of an electro-optical apparatus, with the hole and back most portion of the shell being key to one another to insure proper orientation of the connector. The press fitting is further configured for providing both an RF seal, and moisture seal. The frontmost portion of the connector shell is configured for securely coupling to an optical interface male connector that is attached to an end of a fiber optic cable. The innermost portion of a connector shell is further configured for receiving and retaining therein either a auto detector or light detecting device for converting optical signals received from the fiber optic cable into electrical signals for processing, or is light transmitting device for converting electrical signals into optical signals for transmission over the associated fiber optic cable. A light mark is provided between within the connector shell between the light detecting transmitting device and a optical fiber terminating end of the male connector for permitting the passage of optical signals therebetween. The back most portion of the connecter shell is further configured for receiving the light detecting or transmitting device in an augmentation associated with the key position of the back most portion of press fit into the electro optical apparatus housing, for insuring that electrical leads of the light transmitting or light receiving device do not interfere with one another in being connected either to a printed circuit board or other termination within the housing of the associated apparatus.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to electrical and RF connectors, and more specifically relates to both connectors for use at an interface between the end of a fiber optic cable and a photodetector or a light transmitting device, or in the former converting light from the cable into an electrical signal, and for the latter converting an electrical signal into an optical signal for transmission over the fiber optic cable, and also relates to a fiber node including such connectors. 
   BACKGROUND OF THE INVENTION 
   Optical transmission of television and data signals has been rapidly expanded for use in television, and telecommunication systems. In cable television systems, fiber optic cable is now being employed in many systems from the point of transmission of television and data signals to the subscriber&#39;s premises. The use of coaxial cable for television and telecommunication systems is rapidly being replaced by the use of fiber optic cables because optical signals travel greater distances and require less repeater amplification than electrical signals transmitted via coaxial cable. Fiber optic signal distribution systems are also immune to electromagnetic interference either as ingress or egress. 
   As one example of usage of fiber optic cables in cable television systems, such cables consist of numerous single optical fibers, each capable of carrying a full spectrum of television and data information services. It is possible to allocate each fiber in a fiber optic cable at the subscriber end of a distribution system to an individual subscriber. Typically, a male connector is attached to the end of each fiber to enable the fibers to be connected to terminal equipment in a subscriber&#39;s home or business. The terminal equipment permits bi-directional communication between a subscriber and the cable television provider. In this example, the terminal equipment converts optical signals from the provider into electrical radio frequency signals for use by the subscriber, and also converts the electrical signals generated by the subscriber or the subscriber&#39;s equipment into optical signals for transmission over the optical cable to the provider. 
   Known terminal equipment typically employs an optical to RF interface connector configured for direct attachment to a printed circuit board within the housing of the terminal equipment. The fiber optic cable at the subscriber&#39;s end typically has a male connector attached to it, whereby the connector in a portion of the associated fiber optic cable must be passed through a hole in the housing of the terminal equipment, and plugged into the female optical to RF interface connector mounted on the printed circuit board. Interconnecting the terminal end of a fiber optic cable to a subscriber&#39;s terminal equipment is time consuming, and sometimes involves coiling of the fiber optic cable within the housing of the terminal equipment, that may attenuate the optical signal, or in a worse case may interrupt the signal, all of which increases the installation time to insure proper operation. The present inventors recognize that there is a need in the art for improved optical to RF interface connectors and connection systems. 
   SUMMARY OF THE INVENTION 
   One embodiment of the invention is an optical to RF interface connector that includes a housing or shell having a back portion configured for retaining a light detector device or light/laser transmitter device, and a front portion configured for receiving and securing to a terminating connector mounted on an end of a fiber optic cable, for permitting optical signals to pass between the fiber optic cable and the light detector or light/laser transmitter. The housing or shell is further configured for pressing a back portion into the housing of an associated electrical device. The electrical leads of the light detecting or light transmitting device protrude from the back portion of the shell in a manner facilitating connection of the leads to a printed circuit board located within the housing of the associated electrical device. In another embodiment of the invention, at least two of the inventive optical to RF interface connectors are press fit into the housing of a fiber node or optical to RF media conversion unit, whereby one of the connectors retains a light transmitter for optically transmitting broadband signals back to the optical cable system of a cable television provider, whereas the other connector retains a light detecting device for the reception of broadband signals from the fiber optic cable as transmitted from the cable system provider. In yet another embodiment of the invention, the fiber node or bi-directional RF/optical converter includes means for electrically operating the light transmitting device to convert electrical signals to optical signals for transmission through the fiber optic cable connected to the optical to RF interface output connector, and means for operating the light detecting device to convert optical signals from a fiber optic cable connected to the optical to RF interface input connector into electrical signals, whereby a diplex filter is used to bi-directionally couple electrical output and input signals between a bi-directional RF connector of the converter, and the means for operating the light transmitting device, and means for operating the light detecting or receiving device, respectively. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of the present invention are described below with reference to the drawings, in which like items are identified by the same reference designation, wherein: 
       FIG. 1  is a pictorial view looking toward a front portion of an optical to RF interface connector for one embodiment of the invention; 
       FIG. 2  is a front elevational view of the connector of  FIG. 1 ; 
       FIG. 3  is a back elevational view of the connector of  FIG. 1 ; 
       FIG. 4  is a bottom plan view of the connector of  FIG. 1 ; 
       FIG. 5  is a top plan view of the connector of  FIG. 1 ; 
       FIG. 6A  is a pictorial view looking toward a back portion of the connector of  FIG. 1 , for a first embodiment of the invention; 
       FIG. 6B  is a pictorial view looking toward a back portion of the connector of  FIG. 1 , for a second embodiment of the invention; 
       FIG. 6C  is a pictorial view looking toward a back portion of the connector of  FIG. 1 , for a third embodiment of the invention; 
       FIG. 7  shows a pictorial view looking toward the front of a known optical receiving or electrical transmitting device packaged in either one of the TO-18, TO-46, or TO-52 “top hat” packaging configuration; 
       FIG. 8A  shows a pictorial view looking toward the front or “top hat” end of TO-56 packaging configuration for a known optical transmitting or receiving device; 
       FIG. 8B  shows a bottom view (absent the electrical leads) of the packaging configuration of  FIG. 8A ; 
       FIG. 9  shows a longitudinal cross-sectional view taken along  9 - 9  of  FIG. 1 , for one embodiment of the invention; 
       FIG. 10  shows a top view of a fiber node or optical to RF media conversion device incorporating at least two of the connectors of  FIG. 1 , for another embodiment of the invention; 
       FIG. 11  shows a pictorial view looking toward the back of the device of  FIG. 10 , showing the mounting of the optical to RF interface connectors; 
       FIG. 12  shows a pictorial view looking toward the front of the device of  FIG. 10 ; 
       FIG. 13  shows a bottom plan view of the device of  FIG. 10 ; 
       FIG. 14  shows a block schematic diagram of the electronic circuitry for the device of  FIG. 10 ; 
       FIG. 15  shows a pictorial view looking toward a front portion of an optical to RF interface connector for a second embodiment of the invention; 
       FIG. 16  is a pictorial view looking toward a back portion of the connector of  FIG. 15 ; 
       FIG. 17  is a pictorial view looking toward a front portion of an optical to RF interface connector for a third embodiment of the invention; and 
       FIG. 18  is a pictorial view looking toward a back portion of the connector of  FIG. 17  for the third embodiment of the invention; 
       FIG. 19  is a pictorial view looking toward a front portion of a female optical to RF interface connector for mating with a male ST fiber optical cable termination connector for an alternative embodiment of the present invention; and 
       FIG. 20  is a pictorial view looking toward a rear portion of the connector of  FIG. 19 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 1 , a pictorial view looking toward the front left side of the present connector  2  is shown for a first embodiment of the invention. In this embodiment, the female connector is configured for receiving an ST style male connector, the latter being a male fiber optic cable connector that is known in the art. The protrusions  4  and an open slot  6  provide for the bayonet interlocking configuration with the male ST connector at the end of a fiber optic cable (not shown). The protrusions  4  and open slot  6  are formed in a frontmost cylindrical segment  8 , having a front face  3  with a beveled inside edge  5 , and a hole  18 , as shown. The inside diameter of hole  18  of the initial portion of the cylindrical segment  8  is dimensioned for snugly receiving the outermost portion of the male ST connector (not shown) to be received by the connector  2 . As will be described in greater detail below, a ferrule located at the frontmost portion of the standard ST male optical fiber connector is received in hole  18  of connector  2 . The hole  18  has a back face  10 , that has a centrally located hole  20 . The cylindrical segment  8  terminates to a back cylindrical segment  12  that includes a flat portion  14  for providing a D-configuration. In the preferred embodiment, segment  12 , is knurled on its cylindrical portion, as shown. The back cylindrical segment  12  has a larger outside diameter than a frontmost cylindrical segment  8  of connector  2 , as shown. The back circumferential edge  16  is beveled, with the back cylindrical segment  12  being otherwise configured for press fitting into a D-hole (not shown) of the housing of an electrical optical device. Use of the D-hole configuration, along with the flattened portion  14  of segment  12 , insures that the connector  2  is properly oriented when press fit into the housing, to insure that the leads of an electrical optical device retained in the segment  12  are optimally aligned to facilitate connection of the leads from the device (not shown) to a printed circuit board or other electrical termination within the housing (not shown) of the electro-optical device (not shown). This configuration will be discussed in greater detail below. 
   A front elevational view of the present connector  2  is shown in  FIG. 2 . As previously explained, the hole  18  in the frontmost segment  8  receives a portion of the male ST connector, and the hole  20  of the reduced inside diameter segment  10  is sized to receive the center ferrule of the male ST connector (not shown). Note that the front edge of the hole  20  includes a beveled surface  21  proximate its interface with the backwall  10  of hole  18 . 
   In  FIG. 3 , a back elevational view of the connector  2  is shown. A beveled edge  22  is provided on a back portion or edge of the cylindrical segment  12 , as previously mentioned. Proceeding inward from the beveled edge  22 , a flat band like circular face or portion  24  is shown, followed by a hole  26 , followed by a flat ring-like portion  28  (back face of hole  26 ), followed by countersunk hole  30  having a cylindrical sidewall  27  defining the sides thereof, and a backwall  29 , terminating to the center hole  20  which extends through to the reduced inside segment  10  in the frontmost portion or segment  8 . As will be shown in greater detail below, the countersunk hole  30 , and its backwall  28  are configured for receiving and press fitting therein an electro-optical device having a top-hat configuration, as will be described in greater detail below. Bottom and top plan views of the connector  2  are shown in  FIGS. 4 and 5 , respectively. 
   A pictorial view looking toward the back of the connector  2  is shown in  FIG. 6A , for one embodiment of the invention. In another embodiment of the invention, as shown in  FIG. 6B , a slotway  32  is included in a portion of a sidewall  23  of the countersunk hole  26  for insuring proper alignment of an optical device to be press fitted therein to, such as TO-18, TO-46, and TO-52 top-hat shells as known in the art. A pictorial view looking toward the front of such a top-hat electrical optical device  33  is shown in  FIG. 7 . The shell includes a tab  34  protruding from a collar-like portion  36 , and a frontmost cylindrical portion  38  extending from the top  36 . A circular window  40  is included at the top of a stub-like cylindrical portion  38 , for providing for the passage of a lightbeam either from the device in the case of a light transmitting device, or to the device in the case of a light receiving device, for example. Three electrical leads  42  are shown in this example protruding from the bottom of the device, which as previously explained, are typically electrically connected to a printed circuit board, or some other component within the housing of the electro-optical device to which the present connector  2  is press fit. 
   In another embodiment of the invention, as  FIG. 6C , three elongated semicircular protrusions  44  are axially aligned and spaced apart on the sidewall  23  of the hole  26  for ensuring proper alignment of an electro-optical receiving or transmitting device that is housed within a TO-56 shell. A pictorial view looking toward the front of a optical device  35  housed in TO-56 shell is shown in  FIG. 8A  to include a pair of electrical leads  46 , a collar-like portion  48 , a cylindrical stud-like portion  50  extending from the collar  48 , the latter having an optical window  52  in the top center portion thereof for permitting the passage of light. The collar  48  includes three semicircular grooves  54  spaced apart about its circumference, as shown in the back view of  FIG. 8B . When the device  35  of  FIGS. 8A and 8B , as housed in a TO-56 top-hat shell, in this example, is press fit into the connector  2 , the grooves  54  align with the semicircular protrusions  44  (see  FIG. 6C ), for ensuring that the associated optical device  35  is properly aligned, thereby ensuring that electrical leads  46  can be connected within the housing without interference with one another. The optical device alignment mechanisms shown in the embodiments of the invention of  FIGS. 6B and 6C  are not meant to be limiting, and the back portion of the connector  2  can be configured for receiving optical electrical devices contained within other housing or shell configurations. 
     FIG. 9  is a partial cross-sectional view of the connector  2  of  FIG. 1  taken along  9 - 9 . In this example, an optical device  56  having electrical leads  58  protruding from the bottom thereof is shown installed within the connector  2 , wherein the retention is via press fit in the preferred embodiment, as previously described. In other embodiments of the invention, the optical device  56  can be secured by other than press fitting, such as the use of appropriate epoxies, and other adhesive materials, for example. Note that in the example given, the connector  2  is press fit into a D-hole of the enclosure or housing  60  of the electro-optical apparatus. 
   With further reference to the cross section of connector  2  shown in  FIG. 9 , various important dimensional features are shown. Dimension “A” determines the depth of an electro-optical transmitting or receiving device  56  that is predetermined for the top-hat shell thereof. The dimension “B” is predetermined for controlling the depth of the electro-optical device  56  within connector  2 . Dimension “C” is the inside diameter of the hole  30 , which is predetermined for permitting press fitting of the collar or flange portion  62  of device  56  into hole  30 . Dimension “D” represents the innermost and minimum diameter of the inward hole  26  of connector  2  for receiving the flange or collar portion  62  of electro-optical transmitting or receiving device  56 . Dimension “E” represents the length of the hole  20  necessary for receiving the optical fiber ferrule sleeve of the male ST connector (not shown) to be mated to the connector  2  of the present invention. Dimension “F” is the inside diameter of hole  20  necessary for snugly but slidingly receiving the ferrule of the mating ST male connector. Note that dimensions “A,” “B,” and “E” determine the distance required such that the receiving or transmitting end of the optical fiber within the ferrule sleeve of the mating male connector, and the light receiving or transmitting electro-optical device  56  are in physical contact. 
   The above-described embodiments of the invention are not meant to be limiting. The dimensions “A” through “F,” and the length and configuration of the frontmost cylindrical segment  8  of connector  2  can all be modified for accommodating different types of electro-optical transmitting and receiving devices  56 , and for mating with many other male terminating connectors at the ends of fiber optic cables, other than ST male connectors. As will be described below, other known optical cable terminating connectors that can be mated with by changing the configuration of a connector  2  include MT/RJ, SC, SC/APC, E-2000, O-C, FC, FC/APC, LC, and LC/APC all of which are known in the art. Note that the acronym “APC” stands for Angle-polished Physical Contact. 
   The present connector  2 , through the use of press fit into the housing of an electro-optical apparatus or device, is suitable for radio frequency interference (RFI) sealing of the housing, and moisture sealing, where the housing is used for an outdoor environment. The present inventors have developed an engineering prototype for a “fiber node”  64  (also known as an “optical to RF media conversion unit,” or “a bi-directional RF/optical converter”) that utilizes the present connectors  20  for facilitating the connection of fiber optic cables thereto. More specifically, the present inventors have designed a fiber node  64  to have many unique features, including the use of the subject inventive connectors  2  for eliminating the requirement of passing a fiber optic cable with its connector through a hole in the housing of the device  64  to mate with a female connector mounted upon a PC board, or otherwise within the employer of the housing  60  of the fiber node  64  apparatus. As shown in  FIG. 10 , a top view of the fiber node  64  includes at one end a leftmost one of the present connectors  2  for providing a “REV Fiber Out” port  66  fiber interface with a laser transmitting device representing electro-optical device  56  of  FIG. 9 , for transmission of the optically modulated reverse CATV spectrum along a fiber optic cable connected to the associated connector  2 , as previously described. The rightmost connector  2  represents a fiber optic port “FWD Fiber In” port  68  for providing a fiber optic interface for the reception of the optically modulated forward CATV spectrum from a fiber optic cable terminated to the port  68  for coupling optical signals to a light receiving device representing electro-optical device  56  of  FIG. 9 . Four F-type coaxial connectors are associated with ports  72 ,  74 ,  76 , and  78 , respectively. Port  72  provides a reverse spectrum test point (Rev TP). Port  74  provides a DC power termination, for in this example receiving 12 volts. Also in this example, the reverse spectrum frequency ranges from 5 to 42 MHZ. Port  76  provides a termination for a forward spectrum test point (Fwd TP) for a spectrum signal frequency range of 52-870 MHZ. Lastly, port  78  provides a “DC/RF” termination for both interfacing bi-directional RF signals to a user, and receiving DC power from a known adapter device that combines DC power and RF signals on a single coaxial cable. Also shown as provided on the top of the fiber node  64 , are a light emitting diode (LED)  80  that is activated to emit light to indicate that the light transmitting optical device  56  is active at port  66 , and another LED  82  activated to indicate that optical signals are being received at port  68  by an optical or light receiving device employed for the electro-optical device  56 . Test points  84 ,  86 , and  88  are included in this example between LEDS  80  and  82 , as shown. One volt per milliwatt of optical power is provided at test point  84  for checking the power level of the signals being transmitted, which is proportional to the optical signal strength thereof. Test point  86  provides a common ground for the test points  84  and  88 . Test point  88  provides for a measure of the DC bias level, which is proportional to the optical signal strength of the optical signals being received at port  68 . Note also that the housing  60  includes left side and right side mounting flanges  90 , and  92 , respectively, each having open elevated slots  94 ,  96 , respectively, for facilitating the positioning of the housing  60  on a flat mounting surface (not shown). 
   In  FIG. 11 , a back view of the fiber node  64  is shown. Note that the housing is formed from appropriate metal material, in this example. A ground termination device  89  is provided along a side portion of the housing proximate port  72 , as shown in this example. A front view of the fiber node  64  is shown in  FIG. 12 . A bottom view thereof is shown in  FIG. 13 . A bottom cover plate  98  is secured to the bottom of fiber node  64  in a manner hermetically sealing the components contained within the housing from the elements, via a known sealing technique such as using appropriate gasket material and adhesives or solder. 
   A block schematic diagram is shown in  FIG. 14  for the fiber node  64  in this embodiment of the invention. The fiber node  64  provides a bi-directional RF and optical converter device or apparatus that includes a printed circuit board  103  mounted within the fiber node housing  60 , in this example, via four grounding screws  120  located at each corner of the printed circuit board  103 , as shown and at other locations where grounding of the circuit to the housing is necessary. A laser diode  100  is secured within a connector  2  at port  66 , whereas a photodiode  102  is secured within the associated connector  2  at port  68 . The photodiode  102  converts optical input signals into electrical signals which are connected to input terminals of a receive control circuit  114 , and an amplifier  118 . The receive control circuit  114  provides power to LED  82  for indicating that signals are being received, and also delivers a voltage proportional to the optical power to the test point  88 . The output of amplifier  118  is connected to the input of a directional coupler  116 . The directional coupler couples electrical input signals to the forward receive test point port  76 , and also to a diplex filter  112 . Electrical signals are also bi-directionally coupled between the diplex filter  112  and port  78 , the latter providing bi-directional RF signal flow between a subscriber and the cable system provider. The diplex filter  112  also has an output connected to a directional coupler  106  for delivering electrical RF output signals from directional coupler  106  to port  72  providing a reverse transmit test point, and also to the input of a laser driver  104 . The laser driver  104  is connected to a transmit control circuit  108 , and also to laser diode  100 ; in this example, for converting the reverse RF output signals to optical signals, for transmission to the cable provider. The transmit control  108  also provides an output to LED  80  for indicating times that reverse RF output signals are being transmitted. The transmit control  108  also delivers a voltage proportional to the transmitted optical power to test point  84 . 
   With reference to  FIGS. 15 and 16 , a second embodiment of the invention is for providing in this example a rectangular configured optical to RF interface connector  104  for mating with SC, LC E2000, MTRJ, and MU male fiber optic cable termination connectors. The frontmost segment of the connector  104  for this second embodiment of the invention is a substantially rectangular shell or enclosure  106  including an interface keyway or slot  108  cut through the shell from the open front face  110  toward the rear portion of the shell  106 , as shown. The shell  106  has a hollow cavity  112 , and a back wall  114  that has a cylindrical optical fiber ferrule guide  116  protruding therefrom into the interior of the cavity  112 , as shown. The through hole  118  of the optical ferrule guide  116 , similar to the hole  20  shown in  FIG. 9  for the connector of the first embodiment of the invention, passes through to the back cylindrical segment  118  to permit light to travel between the electro-optical device  56  mounted within the back cylindrical segment  118 , in substantially the same manner as shown in  FIG. 9  for the first embodiment of the invention. As in the previous embodiment, the flat portion  120  in the back cylindrical segment  118  serves as a press-fit orientation key. The remaining round outside portion of cylindrical segment of  118  is narrowed in the preferred embodiment of invention. An O-ring seal  122  is provided around the innermost portion of the back cylindrical segment  118 , as shown. Otherwise, the back cylindrical segment  118  of this alternative embodiment is substantially similar to the back cylindrical segment  12  of the first embodiment of the invention, as shown in  FIG. 9 . 
   A third embodiment of the invention is shown in  FIGS. 17 and 18  for an optical to RF interface connector configured for mating with male FC, and SMA Optical fiber termination connectors. More particularly, the connector includes a threaded frontmost cylindrical segment  124  that is provided with a connector interface keyway  126  cut into its front edge, as shown. A cylindrical optical fiber ferrule guide  128  is centrally located within the cylindrical segment  124 , as shown, and serves the same purpose as the ferrule guide of the second embodiment of the invention (see  FIG. 15 ). A back cylindrical segment  130  is included as shown, with the rounded portion narrowed to provide better press-fit retention, and also configured with a flat portion  132  serving as a press-fit orientation key. The back cylindrical portion  130  has a greater outside diameter than the frontmost threaded cylindrical segment  124 , in this example. A circular flange  134  is located between the frontmost threaded cylindrical segment  124  and the back cylindrical portion  130 , as shown. The flange  134  has a greater outside diameter than the back cylindrical portion  130 . The configuration of the back portion  130  is substantially the same as that of the back portion  118  of the second embodiment of the invention shown in  FIG. 16 , which each include inner ring seal  122 . 
   With reference to  FIGS. 19 and 20 , an alternative embodiment of the invention for providing a female optical to RF interface connector for mating with a male ST fiber optical cable termination connector includes a frontmost cylindrical portion  8  that is configured in substantially the same manner as shown in  FIGS. 1 through 6A . The back cylindrical portion  130  is configured in substantially the same manner as that shown for the embodiments of  FIGS. 17 and 18 . 
   The various embodiments of the present invention provide a connector that relative to the prior art increases the interface reliability for the fiber optic cable connection, and reduces insertion loss by eliminating the necessity to loop a portion of fiber optic cable around the inside perimeter of the housing of a device, and by providing a direct electrical connection from the connector to the printed circuit board or other electrical components housed within the enclosure of the particular fiber optic device. Also, the alternative connector embodiments of the invention all permit the use of smaller enclosures or housings for the associated electro-optical devices, and further insure an RF seal to meet the requirements of Electromagnetic Interference suppression greater than 120 dB. Also particularly the press-fit connector embodiments insure a pressure tight seal between the connector and the housing of the associated device for preventing moisture migration into the interior of the housing. A yet further another advantage of the present invention in its various embodiments is that the alternative connector embodiments provide for optimum heat sinking of the active optical component mounted within the connector, whereby heat can pass from the optical component to the connector, and therefrom to the housing or enclosure of the associated device, thereby temperature stabilizing the optical component. 
   Although various embodiments of the invention have been shown and described, they are not meant to be limiting. Those of skill in the art may recognize certain modifications to these embodiments, which modifications are meant to be covered by the spirit of the appended claims. For example, the press fit configuration of connectors of the various embodiments of the invention can alternatively be screw-in type mounting by configuring the back portion to be externally threaded. Also, said connector embodiments can be made from any suitable metallic material such as nickel or tin plated brass, for example.