Patent Application
20050135769
The present invention relates to optical connectors and, in particular, relates to optical connector assemblies for the placement of the same within modules and rack cards.
It is well known that, in many electrical and electronic systems, due regard must be given to the shielding of components from electromagnetic interference (EMI). In opto-electronic systems, despite the apparent ruggedness of optical signals with respect to an EMI, EMI considerations need to be taken into account because of the electronics associated with the transmission and detection of light signals. For example, high speed synchronous optical network transport nodes are made up of many high speed electro-optical modules having electronic components operating at frequencies between 2.5 and 10 GHz or more. Each module will contain at least one printed circuit board (PCB). Each PCB is individually housed in a sealed enclosure thereby forming an EMI containment module. An electrically conductive bulkhead will extend from the front of each module and provide a shield for the module at the front, an enable the module to be secured to the shelf. Furthermore, third order, non-linear effects can affect the performance of not only the active components but also on the passive components. These considerations apply to other optical communications schemes.
Network equipment building system (NEBs) criteria levels have been drafted by Bellcore and other interested industrial bodies to provide a voluntary standard for industry players to determine the minimum EMI criteria and physical properties of components and systems for networks. In particular NEBS3 specifies certain electromagnetic compatibility levels and fire resistant requirements.
As another example, NEBS3 electromagnetic compliance requires telecommunications equipment to pass an open door emissions test with stringent limits. Most systems radiate sufficient electromagnetic energy to fail this test unless steps are taken to shield and ground the radiated energy. The level of required shielding will vary greatly depending on many variables of which aperture size (unshielded areas) and radiated frequency are two of the most significant. The ability of the design to minimize aperture size for plastic optical connectors is not easily accomplished especially when consideration is given to providing other features such as modularity, multiple choices for connector types and maintaining dense packaging and the like. Different systems have been designed according to NEBS3 requirements but none provide for a sufficiently protective enclosure at the circuit pack level. Accordingly, NEBS3 open door electromagnetic compatibility testing has not addressed such requirements. Hence, relatively large unshielded areas that reduce EMI shielding effectiveness have not been constructed to enable modularity and readily allow a variety of connector choices or allow easy access for servicing and maintenance of the optical fibre elements.
In electronic fields, printed circuit boards—each carrying electronic components and sometimes referred to as circuit packs, are mounted within shelves for connection at rear edges of the boards to other larger, interconnective circuit boards called backplanes. For this purpose, the backs are slideable into and out of fronts of the shelves in this manner.
As a general design consideration, circuit packs must also be shielded from external EMI as well as provide EMI protection generated by the circuit packs themselves. Accordingly, circuit packs are conventionally housed within EMI shields which may include a form of shielded housing surrounding the packs such that an EMI contained module is formed. It has also been found convenient, where EMI conditions allow, for two or more circuit packs to be retained within the same shielded housing. This shielded housing is then inserted into a receiving station within an electrical connection of the one or more circuit packs to the backplane.
In view of the trend for miniaturization of components, there is a need for compact enclosures into which optical fibre connectors fit securely and which prevent stray electronic EMI emissions.
In accordance with a first aspect of the invention there is provided the fibre optic connector arrangement to an electromagnetic interference (EMI) shielded enclosure, wherein the EMI shielded enclosure has a front cover, wherein the fibre optic connector comprises at least one fibre optic terminal, wherein the fibre optic terminal has an axis to accept an input fibre optic cable along such axis, wherein the axis of these fibre optic terminals is approximately between 15° and 75° to a normal with the front cover, and wherein the EMI enclosure provides an output port through which fibre optic pigtails can exit the enclosure.
Where there are a number of terminals, each terminal is preferably arranged such that the terminal connectors arranged closely spaced together to maximize the use of internal space within the EMI shielded enclosure. Conveniently, the front cover of the enclosure has apertures adapted to accept standard fibre optic terminals with or without specific adaptors. Conveniently, the EMI shielded enclosure comprises a general rhomboid configuration whereby the optical connectors have an axis which is generally parallel with the sides of the rhomboid configuration. Conveniently, the rhomboid may be truncated whereby to provide an output passage for optic fibre without causing fibres therein to bend beyond specified limits. A generally cylindrical piece surrounding the fibres beyond the output aperture may be attached to this truncated section whereby to afford greater electromagnetic emission control.
A faceplate of the enclosure may be integrally fabricated with the faceplate of a module the enclosure of a generally rectilinear or rhomboid shape with sides of the enclosure being cut by side front and rear side plates. Alternatively, the enclosure may be provided by two clam-like shells. In this case any particular components will be of conductive material and a conductive gasket will be applied between any two components.
For a better understanding of the invention, there will now be described, by way of example only, specific embodiments according to the present invention with reference to the accompanying figures as shown in the accompanying drawing sheets, wherein:
a and 6b show a second embodiment of the invention.
There will now be described, by way of example, the best mode contemplated by the inventor for carrying out the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced by various other methods and apparatus. In other instances, well known methods and structures have not been described in detail so as not to obscure the central concepts of the present invention.
Referring now to
Referring now to
The optical connector housing 30 is also arranged to prevent emissions from inside the module radiating to the exterior of the module through the use of conductive gaskets 49 between the contacting edges of the connector housing and the front face of the faceplate, indicated in outline format by reference numeral 31. Conveniently, the side plates 40, 42 have depressions positioned to accommodate gasket 49 and to assist with both the seating of the gasket 49 and the addition of overall strength to the optical connection housing. With reference to
In one particular embodiment of the invention, the optical housing connector 30 is mounted to a module faceplate and has connector adaptors that are mounted to the fibre optic connector housing. Examples of appropriate adaptors include types such as LC, SL, FC, DIN or E2000, the appropriate selection of which is dependent upon the particular design needs and/or applicable standard to be followed. Note that the faceplate of the module could be an integral cast portion of the faceplate of the enclosure. The fibre optic connectors for the circuit pack (referred to as an optical fibre pigtails) are subsequently plugged into the body of the connector adaptors. The generally rhomboid enclosure is then fixed to the faceplate with the side plates fastened thereto. The fully assembled enclosure, including the conductive gaskets and the extension of the pigtail through aperture 48, provides an enclosure with a high level of both EMI shielding and fire resistance. The conductive gaskets are compressed after fastening the side plates to the rhomboid section and effectively form an aperture free, low resistance ground path. Preferably, there is an overlap of at least 5 mm. between each of the component parts of the module to help ensure such EMC control and, further to provide appropriate structural strength. Dimpling (not shown) formed in the side shields can assist in maintenance of the fastening hardware within the width of the faceplate. It will be appreciated that the assembly of the housing in this fashion enables the fibre to be inspected before enclosing the same.
Referring to
a and 6b show a further embodiment of the optical connector according to the present invention. As shown in
The assembly process may be reversed if there is a need to service or upgrade the optical fibres. The side plates are removed by unfastening the screws, after which, any selected parts may be detached.
The present invention thus provides a configurable modularity. For example, the housing may be constructed to be half the thickness of a single module such that multiples may be placed side-by-side as well as atop one another. The modules of the present invention also allows for a more efficient use of the limited space available within a module through the use of fibre optic terminals disposed at an angle between approximately 15° and 75° to the normal of the faceplate, thereby permitting the connectors to be placed more closely together. However, the determination of an optimal angle is often a matter of various physical design considerations, possibly including ergodynamic factors. In particular, if a front cabinet cover is used to enclose the entire rack system and modules, then there will be a clearance distance between the module face plates and that front cabinet cover. In this scenario, the maximum acceptable bend radius of the externally attached fiber optic cables may dictate a minimum angle of the inclination of the fiber optic terminals. Similarly, a technician's finger size and/or access angle to the fiber optic connectors (either from the outside or inside of the module) may dictate a particularly advantageous angle for positioning the fiber optic terminals.
It is anticipated that a 45° angle will most likely be employed for typical situations, but reasonable variations will be employed to enable the most efficient use of space within any particular configuration. Using the chosen arrangements, the depth of the housings may be significantly reduced relative to what is known in the art, thereby permitting a closer packing of the optical terminal bodies (where a plurality of optical terminals are involved). Thus, high density, thin, tightly pitched circuit packs may be constructed to be not significant larger than a normal space occupied by connectors and fibre. The invention of the present invention has been designed to accommodate 57 and 27.5 mm pitch circuit packs, although in practice, smaller pitch circuit packs are possible. Similarly, angle of approximately 35° has been used to accommodate a 25 mm clearance between a front cabinet cover and the module face plates. Due to its modular construction and attachment, the present invention is compatible with a wide variety of faceplate manufacturing methods, including extrusion machining, welding, etc. Of course, the fibre optic terminators may include male or female receptacles so as to be coordinatively coupled to any fibre optic cable input to the module. The integration of optical connector mounting with custom modular metal enclosure provides a high degree of electromagnetic shielding effectiveness, fire resistance, and optional fibre routing control, while maintaining a flexible and an easy accessed optical interface.
While the present invention has been described in the context of a specific example, it shall be appreciated that the invention is not so limited to a single example, but that similar embodiments and variations are within the scope of the invention. For example, the invention encompasses not only optical connectors, but any connectors within a circuit module.
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/498,526, filed Aug. 28, 2003, the entire contents of which are incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60498526 | Aug 2003 | US |
