Abstract:
An optical transceiver that reduces the EMI noise leaked therefrom is disclosed. The optical transceiver provides a metal housing, an optical subassembly, and an electronic circuit. The metal housing includes a first space to install the electronic circuit, and a second space to install the optical subassembly. At least the first space has inner surfaces having a corrugated shape to reduce the resonance of the electromagnetic waves.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 12/390,179 filed Feb. 20, 2008, which claims priority of U.S. Provisional Patent Application No. 61/064,225 filed on Feb. 22, 2008; the entire contents of all of which applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical transceiver, in particular, the invention relates to an EMI shielding structure of the optical transceiver. 
     2. Related Background Arts 
     The U.S. Pat. No. 7,195,403, has disclosed an arrangement of the interconnection from the connector plug exposed in the external of the optical transceiver to the electronic circuit set within the transceiver. In this arrangement, the interconnection is buried within the substrate, while the top and the back surfaces of the substrate provide the ground patterns each coming in contact with the shield gasket, which is made of electrically conductive elastic material, to shield the electronic circuit in the transceiver from the external. 
     Another U.S. Pat. No. 7,425,135, has disclosed a mechanism to fix the flexible printed circuit board with the substrate. The flexible printed circuit board electrically connects the optical sub-assembly, such as transmitter optical sub-assembly or receiver optical sub-assembly, with the electronic circuit prepared on the substrate. Further, the multi-source agreement, titled “10 Gigabit Small Form Factor Pluggable Module Rev. 3.1 (Apr. 2, 2003)” defines the specifications of one type of pluggable optical transceivers known as XFP transceiver. 
     As the transmission speed of the optical communication increases, some standard comes up to 10 Gbps and over 10 Gbps is practically designed, the electro-magnetic interference (EMI) noise leaked from the equipment becomes an important subject. As a characteristic wavelength becomes shorter, even a slight gap in the equipment, which conventionally causes no effect for the EMI leakage, results in a large EMI noise with high frequency components. The U.S. Pat. No. 7,195,403 above described has disclosed an effective mechanism to shield between the primary electronic unit within the optical transceiver and the connector plug exposed externally. However, it is inevitable for the optical transceiver to provide an optical path in a side where the optical connector is mated that opens the primary electronic unit to the outside. Thus, it is necessary for the optical transceiver capable of transmitting high-frequency signals to provide some shielding mechanism for the high frequency EMI noise in the side of the optical connector. 
     Moreover, in such equipment that processes the high frequency signals, a resonance frequency, which is roughly determined by the physical dimensions of the space where the electronic circuit is primarily installed therein, may partially overlap with the operational frequency of the optical transceiver. This overlapping of the resonance frequency with the operational frequency degrades the frequency characteristic of the transceiver. As the frequency spectrum of the resonance becomes sharp, the degradation in the frequency characteristic of the transceiver is apparent. 
     One type of the optical transceiver is used in the host system such that the transceiver is inserted into the cage prepared in the host system to mate the connector plug provided in the rear end of the transceiver with the connector installed in the deep end of the cage, which secures the communication between the transceiver and the host system. Such an optical transceiver is called as the pluggable transceiver. Because the transceiver is inserted into the cage, the outer dimensions thereof are regulated in a type of a multi-source agreement (MSA). Therefore, it is practically impossible to adjust the dimensions of the transceiver to escape from the overlapping of the resonance frequency with the operating frequency. It is necessary to shift the resonance frequency from the operating frequency, or to moderate the frequency spectrum of the resonance in the optical transceiver whose dimensions are independently determined. 
     SUMMARY OF THE INVENTION 
     The present invention, which is to provide a solution for subjects described above, has a feature to reduce the electro-magnetic resonance within the metal housing. The optical transceiver according to the present invention has a function for the host system, where the optical transceiver is to be installed therein, to convert an optical signal to an electrical signal mutually. The transceiver comprises an electrically conductive upper housing, an electrically conductive lower housing, an electronic circuit and an optical subassembly. The upper and lower housings form, by assembling with respect each other, a first space and a second space. The first space installs the electronic circuit therein, while, the second space installs the optical subassembly therein. In the present invention, the first space and the second space are electrically shielded each other in addition that both spaces are shielded from an external. 
     The optical transceiver of the invention may further include a circuit substrate to install the electronic circuit thereon. The circuit substrate extends from the second space in an end thereof to be connected with the optical subassembly to the external in another end thereof to be mated with the host system through the first space. The circuit substrate may provide a ground pattern at a boundary around the first space. 
     In the optical transceiver according to an embodiment thereof, at least the first space has inner surfaces with a corrugated shape to reduce the resonance of the electromagnetic wave. The corrugated shapes has various pitches to reduce the resonance further. 
     The present invention is better understood upon consideration of the detailed description below and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates an external appearance of the optical transceiver according to the embodiment of the invention; 
         FIG. 2  is an exploded view of the optical transceiver shown in  FIG. 1 ; 
         FIG. 3  illustrates an inside of the optical transceiver; 
         FIG. 4  illustrates a lower housing of the optical transceiver; 
         FIG. 5  illustrates an upper housing of the optical transceiver; 
         FIG. 6  is a cross section of the optical transceiver taken along the longitudinal direction thereof; and 
         FIG. 7  magnifies a portion where the FPC board is connected with the substrate; and 
         FIG. 8  is a side view of the FPC board with the substrate. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is an external appearance of an optical transceiver  10 , which is viewed from the bottom side thereof, according to an embodiment of the present invention. The optical transceiver  10  is a type of, what is called, an XFP transceiver whose outer dimensions and electrical specifications are defined by a multi-source agreement (MSA). The transceiver  10  has a housing with the dimension of 18.3.times.71.1.times.8.5 mm.sup.3 and may perform the optical communication with the full-duplex mode and of the transmission speed of 10 Gbps. The transceiver  10  provides an optical receptacle  11  to receive a duplex optical connector with the LC-type in the front side thereof, while, it provides, in the rear side, a plug connector  12  that is mated with an electrical connector prepared in the host system that installs the optical transceiver  10 . Here, the front side corresponds to a side where the optical connector is mated, while, the rear side corresponds to a side where the electrical connector is mated. The transceiver  10  also provides an actuator  72  with a curled edge  72   c  in a tip end thereof that releases the transceiver  10  from the cage on the host system. The actuator  72  may slide in front and rear by rotating a bail  71  in front of the optical receptacle  11 . This sliding motion of the actuator  72  may release the engagement of the transceiver  10  with the cage and may extract the transceiver  10  from the cage. 
       FIG. 2  is an exploded view of the transceiver  10  and  FIG. 3  illustrates the inside of the transceiver  10  by removing the upper housing  20 . The latch-releasing mechanism  70  includes, as mentioned above, the bail  71  and the actuator  72 . These members,  71  and  72 , are assembled in the side of the optical receptacle  11 . That is, the bail  71  has a reversed U-shape with a pair of leg portions  71   a  each providing a projection  71   b  in an inner side thereof. The leg portion  71   a  further provides another projection  71   c  in a rear of the first projection  71   b . While, the actuator  72  has a normal U-shape set between the leg portions  71   a  of the bail  71  so as to fit the cross section of the bail  71 . The sides  72   d  of the actuator  72  extend an arm portion  72   b  toward the rear side of the transceiver  10 . The end of the arm portion  72   b  provides the curled edge  72   c.    
     Inserting the first projection  71   b  of the bail  71  into the hole  31   a  formed in the front side wall  31   b  of the lower housing  30 , and setting the second projection  71   c  in the arched groove  31   c  also formed in the side wall  31   b  of the lower housing  30  by passing through the arched slit  72   e  formed in the side  72   d  of the actuator  72 , the latch-releasing mechanism  70  is assembled with the lower housing  30 . Rotating the bail  71  by the first projection  71   b  as an axis so as to traverse the optical receptacle  11 , it causes the sliding motion of the second projection  71   c  in the arched groove  31   c  to slide the actuator  72  toward the front side of the transceiver  10 . Then, the curled edge  72   c  in the tip end of the arm portion  72   b  pushes out the hook of the cage outwardly, which is not illustrated in the figure, to release the engagement between the transceiver  10  and the cage. Thus, the transceiver  10  may be extracted from the cage. 
     The optical transceiver  10  roughly comprises the upper housing  20 , the lower housing  30 , the substrate  40  that installs an electronic circuit thereon, the receiver optical transmitter sub-assembly (hereafter denoted as ROSA)  50 , the transmitter optical sub-assembly (hereafter denoted as TOSA)  60 , and the latch-releasing mechanism  70 . The upper and lower housings,  20  and  30 , both made of metal die-casting, are assembled to each other as putting the gasket  80  therebetween to electrically shield the circuit on the substrate  40  from the external. The gasket  80  comprises a first gasket  80   a  that shields a first space  10   a  where the primary portion of the electronic circuit is installed therein, and a second gasket  80   b  that shields a second space  10   b  where the ROSA  50  and the TOSA  60  are installed therein. Assembling the upper housing  20  with the lower housing  30 , the optical receptacle  11  is formed in the front side. 
     The substrate  40 , which may be a multi-layered substrate, roughly includes three portions. The first portion  40   d  installs the primary circuit thereon, is set within the first space  10   a  and is shielded with the gasket  80   a . The second portion  40   e  includes a plurality of pads connected with the FPC substrates,  91  and  92 , each extended from the ROSA  50  and the TOSA  60 , and shielded with the second gasket  80   b . The third portion  40   f  includes the connector plug  12  and is exposed in the external. Interconnecting patterns, which connect the connector plug  12  in the third portion  40   f  with the primary circuit in the first portion  40   d , run in the inner layer of the multi-layered substrate  40 ; while, in the top and back surfaces of the substrate  40  at the boundary between the first  40   d  and third portions  40   f  provide the ground patterns  40   g  that comes in contact with the gasket  80   a . This ground pattern  40   g  in the top surface of the substrate  40  extends into the first portion  40   d  so as to surround the primary circuit in the first portion  40   d . The ground pattern  40   g  further extends in the boundary between the first  40   d  and the second  40   e  portions of the substrate  40  and comes in contact with the gasket  80   a  thereat again. Thus, the first space  10   a  may be fully shielded by gasket  80   a , the ground pattern  40   g  and the upper  20  and lower  30  housings. 
     A conventional optical transceiver often shields the electronic circuit and the optical components as unifying the first space  10   a  for the electronic circuit with the second space  10   b  for the optical components. However, such an arrangement is hard to prevent the leakage of the EMI noise thorough the optical path inevitably existing between each sub-assembly, the ROSA  50  or the TOSA  60 , and the optical receptacle  11 . The optical transceiver  10  according to an embodiment of the present invention provides an additional shielding mechanism in the boundary between the first space  10   a  for the electronic circuit and the second space  10   b  for the optical components; accordingly, even the EMI leakage through the optical path is remained, the magnitude of the leakage may effectively reduced. 
     In order to secure a heat dissipating path from the electronic circuit, in particular, from the ICs  40   a  on the substrate  40  to the outside, the heat sink  40   b  is put between the IC  40   a  and the upper housing  20 . The height of the heat sink  40   b  is adjusted so as to fill a gap between the IC  40   a  and the upper housing  20 . The top of the side wall  30   a  of the lower housing  30  forms a step  30   c  with a height of 0.75 mm. Setting the substrate  40  in a peripheral portions thereof on this step  30   c , and sandwiched by the upper and the lower housings,  20  and  30 , the substrate  40  is assembled with the housings,  20  and  30 . A plurality of screws  30   e , three screws are illustrated in the figure, fix the lower housing  30  to the upper housing  20  as putting the substrate  40  therebetween. The substrate  40  provides cut portion  40   c  to run off the rear screw holes  30   d  in both sides thereof. Fitting this cut portion with the wall of the screw holes  30   d , the sliding motion of the substrate  40  in front and rear when the connector plug  12  is mated with the connector on the host system may be prevented in addition that the upper and the lower housings,  20  and  30 , put the substrate  40  therebetween. 
       FIGS. 4 and 5  illustrate the lower housing  30  and the upper housing  20 , respectively. The lower housing  30  provides the primary structure of the optical receptacle  11  in the front end thereof. Assembling the lower housing  30  with the upper housing  20 , the optical receptacle  11  with the specification of the LC-type connector is formed. A portion in the rear of the optical receptacle  11  forms the second space  10   b  for installing the ROSA  50  and the TOSA  60  so as to be surrounded with the side walls  31   d  and the bottom  30   i  and the ceiling  20   i . The second space  10   b  provides saddle portions  30   g  whose shapes fit with the cylindrical outer shape of the ROSA  50  and the TOSA  60 . The ribs  30   h  perform the optical alignment of the ROSA  50  and the TOSA  60 , in particular, the sleeve portions  50   b  and  60   b  thereof, with respect to the optical receptacle  11 . That is, a pair of flanges provided in the sleeve portion,  50   b  and  60   b , puts the rib  30   h  therebetween, which determines the position of the OSAs,  50  and  60 , along respective optical axes. The upper housing  20  provides structures,  20   g  and  20   h , similar to those prepared in the lower housing  30 . 
     The first space  10   a  is partitioned from the second space  10   b  by the walls,  21   e  and  31   e , while, it is isolated from the external by the walls,  21   f  and  31   f , in the rear side of the transceiver  10 . That is, the first space  10   a  is surrounded by the side walls,  20   c  and  30   c , in sides thereof, partition walls,  21   e  and  31   e , in the front while other partition walls,  21   f  and  31   f , in the rear and the bottom  30   j  and the ceiling  20   j . Moreover, the first space  10   a  of the present embodiment has a feature that the inner surfaces,  22   a ,  22   b ,  32   a  and  32   b , of respective walls are formed in corrugated. The height of the corrugation is about 0.25 mm in this embodiment, while the pitch thereof is about 3.2 mm in the first sides,  22   a  and  32   a , while, it is about 2.9 mm in the second sides,  22   b  and  32   b , which is different from the first sides. 
     The transmission speed of the optical communication has continuously increased and it has come to 10 Gbps for the present optical transceiver  10 . When an electrical signal with such high frequency components is processed within a closed space, the resonance or the resonance frequency determined by the dimensions of the closed space influences the frequency characteristic of the circuit. The resonance frequency of the transceiver with the dimensions of the XFP type according to the present embodiment becomes a several giga-hertz to several tens of giga-hertz, which just includes or overlaps with the transmission speed of the transceiver  10 . When the closed space is determined by the parallel plate, the resonance determined by the inner distance between the walls facing to each other becomes conspicuous and the high frequency characteristic of the circuit within the closed space degrades. The optical transceiver  10  according to the present embodiment has the inner walls with the corrugated shape to moderate the resonance. Moreover, the present transceiver may further reduce the resonance above mentioned by setting the pitches of the respective corrugation different from each other. 
     Although the upper and lower housings,  20  and  30 , illustrated in  FIGS. 2 to 5  do not provide any groove to set the gaskets,  80   a  and  80   b , therein in the top of the side walls, an arrangement where the gaskets  80  in such a groove may facilitate the assembly of the transceiver  10 . 
     The second space  10   b  is formed by the partition walls,  21   e  and  31   e , in the rear end thereof, the saddle portions,  20   g  and  30   g , in the front side thereof, and a double structure of sloped walls,  21   g  and  31   g , and outer walls  31   d . Between the partition walls,  21   e  and  31   e , is put with the first gasket  80   a , while, between the sloped walls,  21   g  and  31   g , is set with the second gasket  80   b . Although the second gasket has a smaller diameter than that of the first gasket  80   a , the shielding function is not reduced because there is the double structure of the sloped walls,  21   g  and  31   g , and the outer wall  31   d . Because of the existence of the sloped side walls,  21   g  and  31   g , whose top surface smoothly continues from the front partition walls,  21   e  and  31   e , the second gasket  80   b  may be continuously extended from the partition wall,  21   e  and  31   e , to the saddle portions,  20   g  and  30   g.    
       FIG. 6  is a cross section of the transceiver  10  taken along the longitudinal direction thereof.  FIG. 6  explicitly illustrates the first and second spaces,  10   a  and  10   b , formed by the upper and lower housings,  20  and  30 , with the gasket  80   a  put between the front side walls,  21   e  and  31   e , and between the rear side walls,  21   f  and  31   f . Moreover, the second space  10   b  is also surrounded by the other gasket  80   b  in the front side thereof to electrically shield the second space  10   b . Thus, the metal housings,  20  and  30 , and two gaskets,  80   a  and  80   b , may effectively shield the first space  10   a  for the electronic devices, and the second space  10   b  for the optical components such as the ROSA  50  and the TOSA  60 . Moreover, between the IC  40   a  and the upper housing  20  is inserted with the heat sinks  40   b  to conduct heat generated by the IC  40   a  to the cage thorough the housing  20 . 
       FIGS. 7 and 8  magnify the portion where the ROSA  50  and the TOSA  60  are electrically connected with the substrate  40 . The present transceiver  10  connects the OSAs,  50  and  60  with the substrate  40  by respective flexible printed circuits (hereafter denoted as FPC),  91  and  92 . That is, the OSAs,  50  and  60 , provide the device portion,  50   a  and  60   a , and the sleeve portion,  50   b  and  60   b . The device portion,  50   a  and  60   a , extends a plurality of lead pins,  50   c  and  60   c . The FPC,  91  and  92 , is soldered with the lead pin,  50   c  and  60   c , in one end thereof; while, connected with the pads,  40   i  and  40   j , on the substrate  40  in the other end. The FPC,  91  and  92 , has a shape that it is extended upward from the point connected with the lead pin, bent downward at the hairpin portion,  91   a  and  92   a , and bent again with substantially right angle toward the rear of the transceiver  10  to be connected with the pad,  40   i  and  40   j , on the substrate  40 . 
     The transceiver  10  of the present embodiment provides a beam lead devices,  95  and  96 , on the substrate  40  to bend the FPCS,  91  and  92 , at right angle. These lead devices,  95  and  96 , are not electrically connected with any circuit components at all. They are prepared only to support to bend the FPCS,  91  and  92 . That is, the FPC boards,  91  and  92 , whose end,  91   e  and  92   e , is connected with the pads,  40   i  and  40   j , in the top surface of the substrate  40 , is bent upwardly at substantially right angle so as to be wound around the outer surface of the lead device,  95  and  96 , as being put between the device,  95  and  96 , and the substrate  40 , folded back at the hair pin portion,  91   a  and  92   a , and is connected at the other end thereof,  91   c  and  92   c , with the lead pins,  50   c  and  60   c , extending from the device portion of the OSAs,  50   a  and  60   a . The lead devices,  95  and  96 , used herein may be a type of rectifying diode or a general purposed diode for a small signal application whose diameter is about 1 mil or less. The optical transceiver  10  shown in the figures of the present application has the type of the XFP transceiver whose height is determined by the MSA standard to be 8.5 mm. In a case where the FPC board,  91  and  92 , is bent within such a small space, the curvature of the bend inevitably becomes small, which causes a large stress on the connected portion with the substrate  40 , namely, the pad,  40   i  and  40   j , soldered with the FPC boards,  91  and  92 . This may degrade the electrical reliability of the soldered pad. The optical transceiver  10  of the present embodiment, to relief the stress caused in the pad,  40   i  and  40   j , on the substrate  40 , presses the FPC boards,  91  and  92  against the substrate  40  with the lead devices,  95  and  96 . Because the lead devices,  95  and  96 , are not electrically connected with anywhere, this arrangement for the FPC boards,  91  and  92 , does not cause any influence on the electrical performance of the transceiver  10 . 
     Next, a method to assemble the optical transceiver described above will be explained. Firstly, the substrate  40  mounts the electronic components including the ICs  40   a  thereon by the soldering to make the electronic unit. Concurrently with and independent on the assembly of this electronic unit, the semiconductor optical devices such as a laser diode and a photodiode are assembled in the device portions,  50   a  and  60   a , and optically aligned with the sleeve portions,  50   b  and  60   b , to make the ROSA  50  and the TOSA  60 , respectively. The optical alignment of the device portion  50   a  with the sleeve portion  50   b  thereof is carried out such that the photodiode in the device portion  50   a  practically detects an optical signal by a preset magnitude from the test fiber set within the sleeve portion  50   b . While, the alignment of the device portion  60   a  with the sleeve portion  60   b  in the TOSA  60  is performed such that the laser diode in the device portion  60   b  emits signal light to the test fiber set in the sleeve portion  60   b  by being practically provided with the driving current to the laser diode and the signal light is detected from the other end of the testing fiber. Thus, the ROSA  50  and the TOSA  60  are completed. 
     Secondly, the device portion of respective OSAs,  50   a  and  60   a , are assembled with the FPC boards,  91  and  92 . The FPC boards,  91  and  92 , provide in one end thereof a plurality of through-holes whose positions correspond to the arrangement of the lead pins extending from the device portion,  50   a  and  60   a . Passing the lead pins into these through-holes and soldering the lead pins with the land around respective through-holes, the FPC boards,  91  and  92 , are assembled with respective OSAs,  50  and  60 . Subsequently, the other end of the FPC boards,  91   e  and  92   e , are soldered with pads,  40   i  and  40   j , on the substrate  40 . Leveling the substrate  40 , the sleeve portion of respective OSA,  91   c  and  92   c , heads their tip end upward. 
     Next, the lead devices,  95  and  96 , are set in positions closer to the edge of the substrate  40  compared to the position where the FPC boards is soldered with the pad,  40   i  and  40   j , on the substrate  40 . In this process, the lead devices,  95  and  96 , press the FPC boards,  91  and  92 , against the substrate  40  such that, even when the ROSA  50  and the TOSA  60  are forced to bend the FPC boards,  91  and  92 , the pads in the edge of the FPC boards,  91   e  and  92   e , may be free from the stress. Subsequently, the FPC boards,  91  and  92 , are bent upward as tracing the outer surface of the lead devices,  95  and  96 , and folded back so as to form the hairpin portion,  91   a  and  92   a , and head the tip end of the sleeve portions of the ROSA  50  and the TOSA  60  forward. 
     Setting the substrate  40  with the ROSA  50  and the TOSA  60  in respective positions  30   g  of the lower housing  30  and the gaskets,  80   a  and  80   b , on top of the side walls of the lower housing  30 , the process puts the upper housing  20  on the lower housing  30 . Fixing the housings with the screws, the optical transceiver  10  according to the present embodiment is completed. Here, where the side walls of the lower housing  30  or the upper housing  20  provides the groove in the top thereof and the gasket is set within the sleeve, the assembly of the upper housing  20  with the lower housing  30  may be facilitated. 
     While the preferred embodiments of the present invention have been described in detail above, many changes to these embodiments may be made without departing from the true scope and teachings of the present invention. The present invention, therefore, is limited only as claimed below and the equivalents thereof.