Abstract:
An optical device module includes a stub ferrule for guiding a laser light to an optical fiber to be connected, a sleeve for holding an optical-connector ferrule of the optical fiber to be connected and the stub ferrule, a holder for fixing the stub ferrule and the sleeve, and an adapter for connecting the holder and an optical module, in which the sleeve is formed by a nonmetallic material, reducing the structure of metal portion and restraining the antenna effect when electromagnetic noise enters.

Description:
INCORPORATION BY REFERENCE  
       [0001]     The present application claims priorities from Japanese applications JP 2005-184250 filed on Jun. 24, 2005, JP 2004-263189 filed on Sep. 10, 2004, the contents of which are hereby incorporated by reference into this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to an optical device module used in an optical receptacle type optical transceiver, such as a light-emitting device module or a light-receiving device module, and also to an optical transceiver of light receptacle structure in which the above-mentioned optical device module is mounted.  
         [0003]     With the increase in the amount of transmission in recent years due to the diffusion of the Internet, for example, optical transceivers have come to be used as articles of everyday use. As for the mode of using optical transceivers in this case, it is most effective to use optical receptacle type optical transceivers, which can be directly detached and connected to the panel of a router or a switch, for example, to which the optical connector can be directly connected. In other words, the optical transceivers of this type are superior in maintainability and expandability. Moreover, there is strong requirement that optical transceivers should provide characteristics as general-purpose devices, which include better EMC characteristics and desirable optical connection characteristics in handling the optical connector.  
         [0004]      FIG. 4  shows the structure of a light-emitting device module or light-receiving device module for a conventional optical receptacle. A stub ferrule  403  is contacted to an optical-connector ferrule by the spring force of the optical connector part in the receptacle, not shown, and guides a laser beam into an optical fiber. As the leading end portion of the stub ferrule  403  is aligned to the optical-connector ferrule by a sleeve  402 , light is coupled into a single mode fiber about 10 μm in diameter.  
         [0005]     After the stub ferrule  403  is press-fit into a metal-made holder  404  and a sleeve  402  is mounted, a metal-made sleeve cover  401  is fixed by being press-fit to the metal-made holder  404  from the outside. The parts  401 ,  402 ,  403  and  404 , which have been put together and which have been centered with respect to a light-emitting device or a light-receiving device  406 , are connected together by YAG welding.  
         [0006]     In order that the stub ferrule  403  and the sleeve  402  can attain a high connection characteristic of an optical connector which requires a μm-level accuracy, they are often made of a ceramic superior in hardness and machining accuracy.  
         [0007]     In the structure of a light-emitting device module or light-receiving device module for a conventional optical receptacle, in an optical transceiver which adopts this kind of module, problems described below are likely to occur.  
         [0008]     (1) In a light-emitting device module or a light-receiving device module, a light-emitting device or a light-receiving device  408  which operates at high speed is mounted, and the light-emitting device is driven by a modulated relatively large current (several tens of mA, for example) and the light-receiving device deals with a minute modulated current signal (several tens of μA, for example) obtained as a result of photoelectric conversion. If the sleeve cover  401  at the leading end portion of the light-emitting device module or the light-receiving device is made of metal, this metal portion may act as a radiating antenna or receiving antenna. As a result, EMI and EMS characteristics deteriorate.  
         [0009]     (2) When a statically charged person touches an optical connector connected to an optical transceiver, if the sleeve cover  401  at the leading end portion of the light-emitting device module or light-receiving device module is a metal piece, the static electricity released from the human body conducts through a metal spring in the optical connector and the optical ferrule metal-made retainer and is discharged to the metal sleeve cover  401  at the leading end portion of the light-emitting device module or the light-receiving device module which comes close to the optical connector when optical connector is connected. This discharged static electricity flows through the metal-made holder  404  and the metal-made adapter  405 , causing a malfunction to occur in an internal circuit, including the light-emitting device or the light-receiving device  408 .  
         [0010]     To improve those problems, in a technology disclosed in JP-A-2001-66468, a method of using a resin material for the sleeve cover is adopted. However, because the resin material is inferior in hardness than a metal material, when a stress, which corresponds to a transversal tensile force to the optical fiber, is applied to the optical connector under the condition that the optical connector is connected to an optical receptacle type optical transceiver, that resin portion itself is deformed by the stress, thus increasing the optical connection loss.  
         [0011]     In recent years, besides maintenance personnel skilled in this special field, an increasing number of general users handle optical fibers, and there has been higher demand for optical connection characteristics and resistance characteristics in handling optical fibers, which is undesirable.  
         [0012]     In the case where the sleeve or the sleeve holder is made of a resin, when the optical connector is disconnected or connected, it sometimes occurs that the optical-connector ferrule, which is generally made of a hard substance, at the end of the optical connector contacts the resin sleeve or sleeve holder and scrapes the surface, with the result that scraping chips of the resin material are produced. The scraping chips enter between the contact surfaces of the optical-connector ferrule and the stub ferrule of the light-emitting device module or light-receiving device module, involved in coupling of light, giving rise to an increase in optical connection loss at the contact surfaces and deteriorations in optical connection characteristics, such as an increase in reflected light.  
         [0013]     Furthermore, in the connection between an optical fiber cable and an optical transceiver or an optical transmitter or an optical receiver, light is coupled by contact between an optical connector on the optical fiber cable side and an optical receptacle with which the optical connector is connected on the optical transmitter/receiver side.  
         [0014]     The structure of a conventional optical receptacle is such that the stub ferrule is split and enclosed by a sleeve and those parts are fixed with two parts, a sleeve cover and a holder, by YAG welding, and the stub ferrule is engaged with the ferrule of the optical connector. The stub ferrule and the split sleeve are made of ceramic and the sleeve cover and the holder are made of steel.  
         [0015]     In the above-mentioned structure, however, problems will arise as follows: (1) Because a large proportion of the structure is accounted for by metal parts, the optical transmitter or receiver tends to work as a radiation transmission antenna or a reception antenna and, as a result, the EMC characteristics deteriorate, and (2) Because a metal and a ceramic are used at the leading end portion of the receptacle where the connector is connected, on account of electrical noise entering from the connector side, the characteristics of the other component parts deteriorate.  
         [0016]     On the other hand, in a technology disclosed in JP-A-5-249344, an attempt is made to improve static electricity discharge resistance by forming the receptacle main body by a high insulation material, but no consideration is given to means for solving the problem of electrostatic discharge through the optical connector, nor is any concrete method disclosed for use with a light-emitting device module or light-receiving device module for a receptacle as opposed to the present invention.  
       SUMMARY OF THE INVENTION  
       [0017]     The present invention has as its object to provide an optical receptacle structure excellent in the EMI and EMS characteristics and superior in the optical connection characteristics under a transversal tensile stress to the optical fiber when connecting the optical connector, and higher in economic advantages and improved in ease of assembly.  
         [0018]     A ceramic material is used to form the leading end portion of the light-emitting device module or light-receiving device module, which is a part of the optical receptacle structure.  
         [0019]     By using a ceramic material for the leading end portion where the connector of the optical receptacle is connected, a high level of insulating property can be maintained, making it possible to increase the resistance to external electrical noise, such as electrostatic discharge. Because the proportion of metal component parts is reduced, it is possible to minimize the radiation of noise generated in the light-emitting device module or light-receiving device module. Because a ceramic material has high hardness and good machinability with high accuracy, it is possible to minimize deterioration in the optical connection characteristics under a transversal tensile stress to the optical fiber when connecting the optical connector.  
         [0020]     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a diagram showing a first embodiment of the present invention;  
         [0022]      FIG. 2  is a diagram showing a second embodiment of the present invention;  
         [0023]      FIG. 3A  is a diagram showing a third embodiment of the present invention;  
         [0024]      FIG. 3B  is a diagram showing the third embodiment of the present invention; and  
         [0025]      FIG. 4  is a diagram showing related art. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0026]     As shown in  FIG. 1 , a nonmetallic sleeve  101  as a single unified body of a sleeve and a sleeve cover is fixed to the stub ferrule  102  and the holder  103 . The holder is fixed to the light-emitting device module or light-receiving device module directly or through the intermediary of some other part.  
       Embodiment 1  
       [0027]      FIG. 1  is a diagram showing a first embodiment of the present invention. Incidentally, the basic function of each portion is the same as the corresponding portion in the related art shown in  FIG. 4  unless otherwise described. The nonmetallic sleeve  101  holds the optical-connector ferrule and the stub ferrule  102  to be connected, and is in a unified structure of the sleeve cover  401  and the sleeve  402  in  FIG. 4  described above. The sleeve  101  connects two cores about 10 μm in diameter, which serve as waveguides located along the central axes of the optical-connector ferrule and the stub ferrule  102 , with accuracy of the external dimensions of the two ferrules. On the other hand, with regard to the accuracy of the internal diameter of the ferrules, machining work with μm-level accuracy is required. The stub ferrule  102  and the holder  103  are press-fit and fixed in such a way as to obtain stable positional accuracy.  
         [0028]     The nonmetallic sleeve  101  is fixed to the holder  103  with an adhesive. As a material for the nonmetallic sleeve, a Zirconia ceramic material is used. With Zirconia often used for the stub ferrule, it is possible to secure μm-level accuracy when it is ground into a desired shape. It is difficult to realize machining with such accuracy when a resin material is used. To secure firm fixation while maintaining specified accuracy, the holder  103  is joined to the adapter  104  by YAG welding and the adapter  104  is further joined to the light-emitting module or light-receiving module  105  by YAG welding.  
         [0029]     According to this embodiment, the sleeve portion  101  is made of a ceramic and the holder portion and the adapter portion are made of a metal. Under the condition that the light-emitting device module or light-receiving device module is mounted in the housing of an optical transceiver, the metal portions of the holder  103  and the adapter  104  are fixed to the metal housing by using an insulation retaining material in the metal housing.  
         [0030]     In a light-emitting device module or light-receiving device module operating at high speed of 10 Gbits/s, for example, the holder  103  and the adapter  104  are often reduced to a circuit ground potential to realize high-frequency characteristics. Even in this case, it is possible to separate the circuit ground potential necessary for a receptacle type optical transceiver from the potential of the metal housing. Moreover, because the sleeve  101  is a unified body of the sleeve and the sleeve cover, which helps reduce the number of parts and decrease production cost.  
       Embodiment 2  
       [0031]      FIG. 2  is a diagram showing a second embodiment of the present invention. As shown in  FIG. 2 , a stub ferrule  203  is press-fit and fixed to the holder  204  to realize stable positional accuracy. Note that in this embodiment, the sleeve  202  may be a slot sleeve or a precision sleeve without an ordinary slot structure.  
         [0032]     In this embodiment, a sleeve cover  201  is press-fit and fixed to the holder to protect the sleeve  202 . The holder  204  is joined to the adapter  205  by YAG welding, and the adapter  205  is further joined to further joined to the light-emitting device or light-receiving device  206  by YAG welding.  
         [0033]     Incidentally, the sleeve  202 , the sleeve cover  201 , and the stub ferrule  203  are made of a ceramic, and the holder  204  and the adapter  205  are made of a metal. In other words, the structure in  FIG. 2  is similar to the structure shown in  FIG. 4 , except that a ceramic sleeve cover  201  is used in place of the metal sleeve cover  401 .  
         [0034]     In this embodiment, Zirconia, a ceramic, is used for the sleeve cover  201  which corresponds to the metal sleeve cover  401  in  FIG. 4 . The thermal expansion coefficient of the sleeve cover  201  is 10.4 ppm/K. An SUS steel with a thermal expansion coefficient α=10.4 ppm/K is used for the metal-made holder  204 . By selecting materials with relatively close thermal expansion coefficients for the parts involved in the press-fitting process, it is possible to meet mechanical connection strength requirements of the press-fit parts and also prevent temperature-stress-induced destruction of the Zirconia ceramic parts over the entire temperature range from low temperatures to high temperatures.  
         [0035]     According to this embodiment, the sleeve cover  201  is made of a ceramic, and the holder  204  and the adapter  205  are made of metal. Under the condition that a light-emitting device module or light-receiving device module is mounted in the housing of an optical transceiver, the metal-made holder  204  and the metal-made adapter  205  are held by using an insulation retaining material in the metal-made housing.  
         [0036]     In a light-emitting device module or light-receiving device module which operates at high speed of 10 Gbits/s, for example, the holder  204  and the adapter  205  are often reduced to a circuit ground potential to realize specified high-frequency characteristics. Also in this case, it is possible to separate the circuit ground potential necessary for the receptacle type optical transceiver from the potential of the metal housing.  
         [0037]     The sleeve cover  201  is press-fit and fixed to the holder  204 , which is considered more advantageous in terms of connection strength of the fixture portion of the holder  204  than in a case where the sleeve  101  is connected by an adhesive in the first embodiment and also in terms of suppressing the irregularity in the fixing strength caused by an uneven coating amount of adhesive.  
       Embodiment 3  
       [0038]      FIGS. 3A and 3B  are diagrams showing a third embodiment of the present invention.  FIG. 3  shows an optical transceiver including a light-emitting device module or a light-receiving device module for an optical receptacle, which has been described in the above-described embodiment.  FIG. 3B  shows the structure of the optical receptacle block when the optical-fiber-side optical connector is connected to the optical transceiver in  FIG. 3A . The light-emitting device module or the light-receiving device module  303  with a ceramic sleeve  301  having the features of the sleeve shown in the first embodiment is fixed to the optical transceiver  304  by using an insulation retaining material  305 . Numeral  302  denotes a light-emitting device or a light-receiving device.  
         [0039]     As shown in  FIG. 3B , when connecting an optical connector, the optical-fiber-side optical connector  307  is inserted into the optical receptacle portion of the optical transceiver, and the optical-connector ferrule  310  is pressed against the stub ferrule  306  of the light-emitting device module or light-receiving device module  303  is pressed against and connected to the stub ferrule  306  of the light-emitting device module or light-receiving device module by the spring force of a metal spring  309  in the optical connector. The optical connector  307  has a metal-made optical fiber holder  308  in it to hold the optical-connector ferrule  310  firmly in contact with the optical fiber. If the sleeve cover  401  ( FIG. 4 ) corresponding to the sleeve  301  was used and it was made of metal, because of its being close in distance to the metal-made optical fiber holder  308  in the optical connector  307 , unwanted high-frequency noise is electrically coupled to the optical fiber holder  308  and propagates on it, and is radiated through the metal spring  309  into a free space.  
         [0040]     Moreover, unwanted electromagnetic noise and static electricity coming from outside may propagate through the metal spring  309  in the optical connector  307  to the metal-made optical fiber holder  308 . In other words, if there was a sleeve cover  401  corresponding to the sleeve  301  and it was made of metal, the above-mentioned unwanted electromagnetic noise and static electricity may propagate inside the module. In such a case, this may give rise to malfunction not only in the light-emitting device module or light-receiving device module  303  but also in the internal circuit to which the module is connected.  
         [0041]     In contrast to the above case, in the present invention, the sleeve  301  is made of a ceramic, a nonmetallic substance. There is a considerable space between the light-emitting module or light-receiving module  305  and the metal-made optical fiber holder  308  in the optical connector  307 , so that it is possible to prevent propagation of unwanted electromagnetic noise and static electricity.  
         [0042]     In the present invention, the connection portion between the optical connector  307  and the light-emitting device module or light-receiving device module  303  is structured such that the optical-connector ferrule  310  of the optical connector  307  is inserted about 4.0 mm into the sleeve  301 . Therefore, when the sleeve  301  or a sleeve cover corresponding to the sleeve  301  is made of a resin or a soft material, if an external stress acts on the optical connector  307  in a direction different from the direction of its pressing against the stub ferrule  306 , it becomes difficult to maintain the connected position of the optical-connector ferrule  310  and the stub ferrule  306 .  
         [0043]     In contrast, in the present invention, by using a nonmetallic hard material (ceramic Zirconia material) which is strong against external stress and less likely to be deformed, it becomes possible to prevent the connected position of the optical-connector ferrule  310  and the stub ferrule  306  as described above.  
         [0044]     Additional description will be made with reference to  FIGS. 1 and 2 .  
         [0045]      FIG. 1  shows an embodiment of the present invention. As shown in  FIG. 1 , the sleeve  101  is fixed to the stub ferrule  102  and the holder  103  by using an adhesive. The holder  103  is joined to the adapter  104  by YAG welding, and the adapter  104  is joined to the light-emitting module or the light-receiving module  105  by YAG welding. The sleeve  101  and the stub ferrule  102  are made of a ceramic, and the holder  103  and the adapter  104  are made of a metal.  
         [0046]      FIG. 2  shows another embodiment of the present invention. As shown in  FIG. 2 , the sleeve  202  and the stub ferrule  203  are press-fit and fixed to the holder  204 . The sleeve  202  is a slot sleeve. To protect the sleeve, a sleeve cover  201  is press-fit and fixed to the holder or fixed to the holder by using an adhesive. A unified sleeve is fixed to the stub ferrule  203  and the holder  204  by using an adhesive.  
         [0047]     The holder  204  is joined to the adapter  205  by YAG welding, and the adapter  205  is further joined to the light-emitting module or light-receiving module  206  by YAG welding. The sleeve  202 , the sleeve cover  201 , and the stub ferrule  203  are made of ceramic. The holder  204  and the adapter  205  are made of metal.  
         [0048]     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.