Optical connector, optical element holding structure, and structure of a mount section of an optical connector

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a structure of a mount section of an optical connector to be employed in the field of optical communication such as that used in office automation, factory automation, and vehicle-mounted equipment.

Background Art

An optical connector which is to be fixedly mounted on a mount board while incorporating optical elements has been improved in terms of a noise resistance characteristic of optical elements for withstanding external noise. In order to suppress radiation noise origination from the optical elements, the optical elements are built into a connector housing while being housed in a shielding shell made of highly conductive material, such as metal.

<patcit id="pcit0001" dnum="WO0079856A"><text>WO 00/79856</text></patcit> discusses combined shielding of electromagnetic interferences and thermal control of microelectronic assemblies. According to this document, an electronic component is first mounted on a substrate, then covered with thermally conductive gel and a plastic housing which is coated on the inside with metal. The metal coating is electrically connected to a grounding circuit on the substrate via an electrically conductive gel at the periphery.

<patcit id="pcit0002" dnum="US5259053A"><text>US 5,259,053</text></patcit> shows an optical connector formed of a main section and an end panel section, within which active optical devices are seated. The optical devices are urged into alignment when the end section is inserted in the main section.

<patcit id="pcit0003" dnum="JP02186309A"><text>JP 02 186 309</text></patcit> discloses a plug and a receptable which are fitted in a direction perpendicular to the direction of the optical fibre. The plug contains a light shielding plate which shields the light from the optical fibre even if it is not coupled to the receptable. Therefore, even when the plug is released, irradiation from the fibre into the human eye is prevented.

<patcit id="pcit0004" dnum="JP09061677A"><text>JP 09 061 677</text></patcit> discloses to mount a housing main body of an optical fiber connector including a shield case on a circuit board using a screw to fix and ground the shield case to the circuit board.

<patcit id="pcit0005" dnum="WO0079856A"><text>WO 00/79856</text></patcit> discusses combined shielding of electromagnetic interferences and thermal control of microelectronic assemblies. According to this document, an electronic component is first mounted on a substrate, then covered with thermally conductive gel and a plastic housing which is coated on the inside with metal. The metal coating is electrically connected to a grounding circuit on the substrate via an electrically conductive gel at the periphery.

<patcit id="pcit0006" dnum="JP05003330A"><text>JP 05 003 330 A</text></patcit>, which forms the basis for the preamble of claim 1 of the present invention, discloses a metallic case which comprises a bottom plate extending along a bottom surface thereof. In addition, the case is formed integrally with a heatsink. This heatsink comprises lead terminals connectable to an earth pattern of a substrate.

Figs. 6 and 7 show conceivable constructions for grounding a shielding shell of an optical connector of another type.

In an optical connector 101 shown in Fig. 6, a lead terminal 106 is provided at right angles on a shielding shell 102 for sheathing an optical element D, so as to project downward beyond a connector housing 105. While the optical connector 101 is mounted on a mount board 108, the lead terminal 106 penetrates through the mount board 108 and is soldered to a trace for grounding purpose formed on a lower surface of the mount board 108. As a result, the shielding shell 102 is grounded by way of the lead terminal 106.

The technique described in <patcit id="pcit0007" dnum="JP5003330A"><text>Japanese Patent Publication No. Hei. 5-3330</text></patcit> can be listed as a related-art technology analogous to that mentioned above.

In an optical connector 110 shown in Fig. 7, ground tab pieces 113 are formed on both sides of a shielding shell 112 so as to jut outward from both sides of a main body section of a connector housing 115. The optical connector 110 is fixedly mounted on a mount board 118 such that the tab pieces 113 are brought, in an overlappedmanner, into plane contact with ground traces 119 formed on an upper surface of the mount board 118. As a result, the shielding shell 112 is grounded by way of the tab pieces 113.

However, in the case of the optical connector 101 shown in Fig. 6, the shielding shell 102 is merely grounded by way of the pin-shaped lead terminal 106. Hence, high ground resistance arises, and an insufficient electromagnetic shielding effect is achieved.

Moreover, in this related-art and the similar related-art thereof, an optical element is fittingly inserted into a housing recess formed in a metal case; an opening of the housing recess is formed so as to become slightly larger than the element main body so that the element main body of the optical element can be fitted into the recess.

Accordingly, there is a chance of slight clearance arising between an interior surface of the housing recess of the metal case and an exterior surface of the element main body. Such a clearance may, in turn, cause a drop in heat transfer efficiency.

In the case of the optical connector 110 shown in Fig. 7, the tab pieces 113 are brought into plane contact with the ground traces 119. Hence, low ground resistance arises, and a sufficient electromagnetic shielding effect is achieved. However, the ground tab pieces 113 significantly jut outward from both sides of the main body section of the connector housing 115. Hence, there arises a problem of a necessity for using a large area for fixedly mounting the connector 101.

SUMMARY OF THE INVENTION

The present invention has been conceived in light of the problem and is aimed at providing an optical element holding structure which is superior in countermeasures against heat as well as against noise. Another aim of the present invention is to provide a structure to be used for mounting an optical connector which enables minimizing of ground resistance of a shielding shell and minimizing of an area required for mounting an optical connector.

The first aspect of this invention is a structure of a mount section of an optical connector according to claim 1. <ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 is a cross-sectional view showing the construction of a mount section of an optical connector according to an embodiment of the invention;</li><li>Fig. 2 is a perspective view showing a metal shielding shell according to the optical connector;</li><li>Fig. 3 is a cross-sectional view showing the construction of a mount section of an optical connector according to a first modification;</li><li>Fig. 4 is a cross-sectional view showing the construction of a mount section of an optical connector according to an example;</li><li>Fig. 5 is a plot showing results of an immunity test;</li><li>Fig. 6 is an exploded perspective view showing a first background art; and</li><li>Fig. 7 is an exploded perspective view showing a second background art.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT;

The construction of amount sectionof an optical connector according to an embodiment of the invention will be described hereinbelow.

As shown in Fig. 1, the mount section of an optical connector has a construction to be used for mounting, on a mount board 430, an optical connector 401 having incorporated therein optical elements D, such as a light-emitting element and a light-receiving element.

The optical connector 401 comprises a connector housing 402 formed from insulation material, such as resin, and a metal shielding shell 410 made of metal material.

A housing recess section 404 which is open at a bottom thereof is formed in the connector housing 402.

More specifically, the housing recess section 404 is formed in a housing main body section 403 located in the rear part of the connector housing 402, and guide sleeve sections 406 are formed in the connector housing 402 so as to protrude forward from the forward part of the main body section 403.

The housing recess section 4 04 is open in the bottom surface of the main body section 403. An element housing case section 411 (to be described later) of the metal shielding shell 410 is to be housed in the housing recess section 404 by way of the opening formed in the bottom.

Of the housing main body section 403, a bottom surface of a rear wall section 403a of the housing recess section 404 recedes from the remaining bottom surface of the connector housing 402. While the connector housing 402 is mounted on the mount board 430, a ground piece 418 (to be described later) can be interposed between the bottom surface of a rear wall section 403a and an upper surface of the mount board 430.

Each of the guide sleeve sections 406 is formed in a substantially-cylindrical member projecting forward of the main body section 403. Formed in the guide sleeve section 406 is a guide hole 406h which enables insertion of a ferule 450 of a mating optical connector. The guide hole 406h is in communication with the housing recess 404. When the ferrule 450 is inserted into any of the guide sleeve sections 406, an end face of an optical fiber held in the ferrule 450 is positioned so as to oppose an optical coupling section Db of the optical element D housed in the housing recess 404 (i.e., an optical light-emitting plane or an optical light-receiving plane) . As a result, optical coupling is established between the optical fiber and the optical element D.

The guide sleeve sections 406 are enclosed by a substantially-angularly-cylindrical protective wall section 407 while being spaced a given interval away from each other.

As shown in Figs. 1 and 2, the metal shielding shell 410 is formed by means of punching and bending, e.g., a metal plate, as required. The element housing case 411 capable of housing the optical element D, a heatsink section 415, and a grounding piece 418 are formed into a single piece.

The element housing case 411 is formed so as to be able to be housed in the connector housing 402 while housing the optical element.D therein.

More specifically, the element housing case section 411 is formed into substantially the shape of a box capable of housing the entirety of an element main body Da of the optical element D. The bottom surface of the element housing case section 411 is open. The element main body sectionDa is inserted and housed in the element housing case section 411 by way of the opening formed in the bottom thereof. A window section 411h is formed in a front surface of the element housing case section 411. The optical coupling section Db of the element main body section Da (i.e., the light-emitting plane of the light-emitting element or the light-receiving plane of the light-receiving element) faces outside by way of the window section 411h.

The grounding piece 418 is formed into the shape of a plate extending along the bottom surface of the connector housing 402.

In the embodiment, the grounding piece 418 is provided so as to extend along the bottom surface of the rear wall section 403a of the housing recess section 404. While the connector housing 402 is mounted on the mount board 430, the grounding piece 418 is interposed between the bottom surface of the rear wall section 403a and the mount board 430. Further, a lower surface of the grounding piece 418 is formed so as to be able to come into plane contact with a predetermined ground trace 431e formed on the upper surface of the mount board 430.

More specifically, the heatsink section 415 is formed such that at least a part of the heatsink section 415 is exposed outside of the connector housing 402.

Specifically, the heatsink section 415 is formed into the shape of a substantially-square plate corresponding to the back of the connector housing 402. The heatsink section 415 is spaced a predetermined interval from and in parallel with the back of the element housing case 411. A lower edge of the heatsink section 415 and a lower edge of the back of the element housing case 411 are joined together at the bottom surface of the rear wall section 403a by means of the grounding piece 418.

Lead terminals 419 project downward at right angles from the four corners of the metal shielding shell 410. While the metal shielding shell 410 is attached to the connector housing 402, the lead terminals 419 project downward from the connector housing 402 and can be soldered to the mount board 430.

The mount board 430 is a well-known board on which predetermined traces are formed from copper foil. As shown in Fig. 1, a ground trace 431e is formed in an area assigned to the grounding piece 418 on one surface of the mount board 430 (i.e., an upper surface side of the mount board 430 shown in Fig. 1) within the area in which the optical connector 401 is to be mounted. Formed in the area in which the optical connector 401 is to be mounted are through holes 430h which enable insertion of a lead terminal Dc of the optical element D and the lead terminals 419 of the metal shielding shell 410. Another predetermined ground trace 432e and a signal trace 433 are formed on the other surface side of the mount board 430 (i.e., a lower surface of the mount board 430 shown in Fig. 26).

The optical connector 401 is assembled in the manner set forth and mounted on the mount board 430.

First, while the optical element D is housed in the element housing case section 411 of the metal shielding shell 410, the element housing case section 411 is inserted into the housing recess 404, and the heatsink section 415 is provided along the back of the connector housing 402. The metal shielding shell 410 is inserted into the connector housing 402 from below until the grounding piece 418 contacts the bottom surface of the rear wall section 403a, thus completing assembly of the connector housing 402.

Next, the lead terminals 419 of the metal shielding shell 410 and the lead terminal Dc of the optical element D are inserted into the corresponding through holes 430h. When the optical connector 401 is mounted within a predetermined mount area on the mount board 430, the grounding piece 418 comes into plane contact with the ground trace 431e provided on the mount board 430. In this state, the lead terminals 419 projecting beyond the lower surface of the mount board 430 are soldered to the ground trace 432e, and the lead terminal Dc is soldered to the signal trace 433, whereby the optical connector 401 is fixedly mounted on the mount board 430.

By means of the construction of the mount section of the optical connector 401, the metal shielding shell 410 is grounded by way of the plane contact existing between the grounding piece 418 and the ground trace 431e, as well as by way of the soldered portion existing between the lead terminals 419 and the ground trace 432e.

By means of the construction of the mount section of the optical connector 401 configured in the manner mentioned above, the plate-like grounding piece 418 that is provided so as to extend along the bottom surface of the connector housing 402 is formed integrally in the element housing case section 411. The metal shielding shell 410 is grounded by way of the grounding piece 418. As compared with the related-art example shown in Fig. 6 in which an optical connector is grounded by way of only a pin-shaped lead terminal, the optical connector of the invention can minimize ground resistance.

In pursuant to the embodiment, the grounding piece 418 is brought into plane contact with the ground trace 431e formed on one surface of the mount board 430. By means of a configuration of plane contact, contact resistance developing between the grounding piece 418 and the ground trace 431e can be reduced, thus minimizing ground resistance.

In the embodiment, the lead terminals 419 of the metal shielding shell 410 are formed and soldered to the ground trace 432e. However, the lead terminals 419 may be omitted.

In the metal shielding shell 410, the heat developing in the optical element D is in principle transferred from the element housing case section 411 to the heatsink section 415 by way of the grounding piece 418. The heat is then dissipated outside from the heatsink section 415. In the embodiment, the grounding piece 418 remains in plane contact with the ground trace 431e, and hence the heat developing in the optical element D is also transferred from the element housing case section 411 to the trace 431e by way of the grounding piece 418. The heat is then dissipated outside from the trace 431e. Hence, the optical element D is also superior in a heatsink characteristic.

Since the grounding piece 418 is provided so as to extend along the bottom surface of the connector housing 402, the grounding piece 418 does not jut outward of the connector housing 402. Hence, the area required for mounting the optical connector 401 can be minimized. Further, the construction of the connector housing 402 can be simplified. Hence, a die employed for manufacturing the connector housing 402 can also be simplified.

In the embodiment, the heatsink section 415maybe omitted.

In the embodiment, the grounding piece 418 is a member to be used for coupling the element housing case section 411 with the heatsink section 415 at the bottom surface of the connector housing 402. By utilization of the grounding piece 418 by way of which the element housing case section 411 and the heatsink section 415 are coupled together, the metal shielding shell 410 can be grounded efficiently.

Like the construction of a mount section of an optical connector 401B according to a first modification shown in Fig. 3, a screw through hole 418Bh is formed in the grounding piece 418, and a screw through hole 430Bh is formed in the mount board 430. A screw hole 403aBh is formed in the bottom of the rear wall section 403a of the housing recess 404 of the connector housing 402. A screw S is inserted into the screw insertion holes 430Bh, 418Bh from below the lower surface of the mount board 430. The thus-inserted screw S is screw-engaged with a screwhole 403aBh and may be fastened so as to bring the grounding piece 418 into pressing contact with the ground trace 431e. In this case, the screw S is to be used for bringing the grounding piece 418 into pressing contact with the ground trace 431e. Hence, the screw S may be made of metal or resin.

Although the first modification omits the lead terminals 419 and the corresponding through holes 430h, they may be retained.

In the first modification, the grounding piece 418 and the ground trace 431e are forcibly brought into pressing contact with each other by means of fastening force of the screw S. For this reason, ground resistance can be made much lower.

Like a mount section of an optical connector 401C according to an example shown in Fig. 4, a metal screw Sm is brought into electrical contact with the grounding piece 418, as well as with a ground trace 434e formed on the lower surface of the mount board 430. In this case, the screw Sm may be inserted into the mount board 430 and the grounding piece 418 from the lower surface of the mount board 430 and fastened to the connector housing 402.

More specifically, a screw insertion hole 430Ch is formed in the mount board 430, and a screw hole 418Ch is formed in the groundingpiece 418. Further, a screw hole 403aCh is formed in the bottom of the rear wall section 403a of the housing recess 404 in the connector housing 402. The ground trace 434e is formed in the area surrounding the screw hole 403aCh on the lower surface of the mount board 430. The metal screw Sm is screwed and fastened, from the lower surface of the mount board 430, to the screw hole 418Ch and the screw hole 403aCh by way of the screw insertion hole 430Ch.

In this example, the metal shielding shell 410 is electrically connected as a result of the metal screw Sm being screw-engaged with the screw hole 418Ch. Further, a portion of a screw head Sma of the metal screw Sm close to a screw shaft Smb is brought into plane contact with and electrically connected to the ground trace 434e. Hence, the grounding piece 418 is connected to the trace 434e and grounded by way of the metal screw Sm having a comparatively large diameter.

As compared with the related-art example in which the optical connector is grounded by way of only the pin-shaped lead terminal, this example also enables minimization of ground resistance.

In place of the construction which has been described in connection with the embodiment and in which the grounding piece 418 is brought into plane contact with and grounded by way of the ground trace 431e provided on the mount board 430, this example employs a construction in which the grounding piece 418 is connected to the ground trace 434e by way of the metal screw Sm and is thus grounded.

In the embodiment, an optical connector mounted on a mount board was actually manufactured. The optical connector was subjected to an immunity test.

Objects of the test were an optical connector grounded (plane-grounded type) by means of bringing the grounding piece 418 into plane contact with the ground trace 431e in the manner as described in connection with the embodiment, and an optical grounded (screw-grounded type) by way of the metal screw Sm in the manner as mentioned in connection with the example. For the purpose of comparison, an optical connector similar to that described in connection with the embodiment but not grounded (non-grounded type) and an optical connector grounded (lead-terminal-grounded type) by way of only one lead terminal 419 were also subjected to an immunity test.

The tests were conducted in accordance with the TEM cell method under specified conditions; namely, a frequency range of 430 through 350 MHz, an applied electro-magnetic field of 200 V/m, and 80% AM modulation.

As shown in Fig. 5, the optical connector of screw-grounded type was improved in degradation of receiving level as compared with the optical connector of lead-terminal-grounded type corresponding to the related-art optical connector and the optical connector of non-grounded type. The optical connector of plane-grounded type was improved as compared with the optical connector of screw-grounded type. The test results show that sufficient electromagnetic shielding effect was achieved by virtue of a reduction in ground resistance.

By means of the structure of the mount section of the optical connector according to this embodiment constructed in the manner mentioned previously, a plate-like grounding piece which is provided so as to extend along a bottom surface of a connector housing is formed integrally in an element housing case. A metal shield shell is grounded by way of the grounding piece. Hence, as compared with a related-art example in which an optical connector is grounded by way of only a pin-shaped lead terminal, the optical connector can minimize ground resistance.

The grounding piece is provided so as to extend along the bottom surface of the connector housing. Hence, the grounding piece does not jut out from the connector housing. Further, an area required for fixedly mounting the optical connector can also be minimized.

By means of the construction of the mount section of the optical connector according to this embodiment, the metal shielding shell is grounded efficiently by means of utilization of the element housing case section and the heatsink section.

As described in this embodiment, the grounding piece is brought into plane contact with a ground trace formed on one side of a mount board, thereby diminishing resistance existing between the grounding piece and the ground trace and minimizing ground resistance.

In this case, as described in this embodiment, a screw is inserted into the mount board and the grounding piece from the other side of the mount board and screw-engaged with the connector housing by means of fastening. By means of the fastening force of the screw, the grounding piece and the ground trace are forcibly brought into contact with each other, thereby diminishing ground resistance to a much greater extent.

As described in this embodiment, a metal screw is brought into electrical contact with the ground trace formed on the other side of the mount board and into electrical contact with the grounding piece. In this state, the metal screw is inserted into the mount board and the ground piece from the other side of the mount board and screw-engaged with the connector housing by means of fastening. By way of the metal screw, the metal shielding shell can be electrically connected to the ground trace while involving much lower ground resistance.

By means of the optical connector according to the invention, a plate-like grounding piece which is provided so as to extend along the bottom surface of the connector housing formed on the mount board and which is electrically connectable to the ground trace is formed integrally in an element housing case section. As compared with the related-art optical connector which is grounded by means of only a pin-shaped lead terminal, the optical connector can minimize ground resistance.

The grounding piece is provided so as to extend along the bottom surface of the connector housing. Hence, the grounding piece does not jut out from the connector housing, and the area required for fixedly mounting the optical connector can be minimized.