Fiber with ferrule, and optical module and method of manufacturing the same

The optical module comprises a ferrule, an optical fiber inserted into the ferrule, an optical communication functional unit for making the optical communication with the optical fiber, and a resin molded portion covering a part of the ferrule and the optical communication functional unit. The ferrule is provided with one or more concave grooves in a region exposed from the resin molded portion. Since this concave portion serves as a resin reservoir at the time of molding, the resin is prevented from adhering and covering on the outer surface of ferrule exposing from the resin molded portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fiber with a ferrule used for an optical communication, an optical module using the fiber, and a method for manufacturing the optical module. More particularly, this invention relates to an optical module which can prevent a molding resin from adhering on a top end portion of an outer surface of the ferrule.

2. Description of the Related Art

To reduce the size and cost of an optical transmitter/receiver, it is required to mount a semiconductor laser (LD) and a monitor photodiode (M-PD) on a substrate such as a Si bench by the surface mounting technique.FIGS. 6 and 7show a manufacturing process of an optical module.FIG. 6is a flowchart of the manufacturing process of the optical module, andFIG. 7is an explanatory view of a manufacturing method of the optical module.

First of all, a Si bench21having a V-groove for fixing an optical fiber14and an electrode pattern for soldering a LD22and a M-PD23is prepared.

The LD22and the M-PD23are soldered onto the Si bench21, and the optical fiber14inserted into a ferrule11is fixed to the Si bench21by the resin. An intermediate product in this state is called a sub-module. At fixing the optical fiber14, the optical fiber14is sandwiched between a glass plate40and the Si bench21.

The sub-module is fixed onto a die pad of a lead frame20, wire bonded and sealed with a resin by the transfer molding technique, so as to form a resin molded portion13.

Next, a tie bar27and a frame28of the lead frame20are cut, each lead29is electrically isolated. The lead29exposed from the resin molded portion13is bent at a predetermined angle.

In the above process, a state within a mold at the time of the transfer molding is illustrated inFIGS. 8A-8C.FIG. 8Ashows a state where the sub-module fixed on the lead frame is accommodated within the mold before the resin is filled into the mold. In this state, the resin is filled into the mold30from a resin filler hole32formed at an end face of the mold30, thereby sealing the sub-module fixed on the lead frame20as shown in FIG.8B.

However, with the above technique, the resin is adhered on a portion of the ferrule11exposed from the resin molded portion13, resulting in a problem of increasing the coupling loss as the connector, or increasing an inferior optical module to lower the yield.

That is, when the sub-module is accommodated within the mold, and transfer-molded, as shown inFIGS. 8A and 8B, the resin exudes (or leaks) from a small gap between the mold30and the ferrule11. In extreme cases, an exuded (or leaked) resin16is adhered and covered around a top end side of the ferrule11, as shown in FIG.8C.

This cause is considered as below. At the time of transfer molding, the resin temperature is increased up to about 170° C., for example, to soften the resin, and in this state, the resin is injected through the resin filler hole under a high pressure of about several 10 kg/cm2to about several 100 kg/cm2. The injected resin is filled in a space within the mold, and cured with the elapse of time. Here, the ferrule is made of hard ceramic, and hardly deformed when sandwiched between upper and lower mold parts of the mold. Therefore, a gap as large as several μm to several 10 μm is produced between the surface of ferrule and the mold. From this gap, uncured resin is exuded (or leaked) and then cured at the gap between the ferrule and the mold.

The ferrule has a diameter of 1.25 mm, for example. If there is even a slight irregularity of the resin on the outer surface of the ferrule, it impedes the proper fitting with an optical fiber connector of the other side, leading to the dispersed coupling power and the lower yield. Especially, if the resin is exuded remarkably at the time of molding, the optical fiber end face is covered with the resin, as shown inFIG. 8C, thereby increasing an inferior optical module to lower the yield and increase the cost.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a fiber with a ferrule, an optical module and a method for manufacturing the optical module, in which the resin is prevented from adhering and covering on the top end portion of the outer surface of the ferrule at the time of molding.

It is another object of the present invention to provide a method for manufacturing an optical module in which the ferrule and the resin molded portion can be positioned at high precision.

The present invention can accomplish the above objects by forming a concave portion around an outer circumference of the ferrule.

The fiber with the ferrule, according to the present invention, comprises a ferrule having at least one concave portion and an optical fiber inserted into the ferrule.

The fiber with the ferrule of the present invention can be effectively used for an optical module. The resin exuded from a gap between the mold and the ferrule is stored in the concave portion, whereby the outer circumference of the ferrule and the optical fiber end face are prevented from being covered with the resin. The concave portion is provided at the position of the ferrule that is exposed from the resin molded portion when the optical module is made.

Further, an optical module, according to the present invention, comprises a ferrule, an optical fiber inserted into the ferrule, an optical communication functional unit for making the optical communication with the optical fiber, and a resin molded portion covering a part of the ferrule and the optical communication functional unit, wherein the ferrule has at least one concave portion in a region exposed from the resin molded portion.

By providing the concave portion, the resin exuded from the gap between the mold and the ferrule is stored in the concave portion, thereby preventing the outer circumference of ferrule and the optical fiber end face from being covered with the resin. The concave portion may be formed in width, length and depth sufficient to store the resin exuded from the gap between the mold and the ferrule. The shape of concave portion is not specifically limited, but a groove formed around the entire outer circumference of the ferrule is suitable. Since the groove is formed around the entire circumference of the ferrule, the resin exuded from any position in the gap between the mold and the ferrule can be surely stored within the groove.

The optical communication functional unit comprises at least one of a light emitting element and a light receiving element, and an electronic circuit component. For example, an optical transmission module may employ a LD as the light emitting element and a driver IC for the LD as the electric circuit component. Further, the optical transmission module may use a M-PD for sensing the light intensity of the LD. An optical receiving module may employ a PD as the light receiving element and an amplifier for amplifying the signal of PD as the electric circuit component. The optical transmitting/receiving module may comprise at least one pair of light emitting element and driver IC, and at least one pair of light receiving element and amplifier.

Moreover, a method for manufacturing an optical module, according to the present invention, having a ferrule with at least one concave portion, an optical fiber inserted into the ferrule, an optical communication functional unit, a substrate and a lead frame, the method comprising mounting the optical fiber, the ferrule and the optical communication functional unit on the substrate to form a sub-module, mounting the sub-module on the lead frame, and making a molding for the lead frame where the sub-module is mounted within a mold having an upper mold part and a lower mold part in a state where the concave portion of the ferrule is in contact with mating faces of the upper and lower mold parts which are mated with each other.

By making the molding in a state where the concave portion is in contact with the mating faces of the upper and lower mold parts of the mold, the resin exuded from the gap between the mold and the ferrule can be led into the concave portion. Therefore, the outer circumference of ferrule and the optical fiber end face are prevented from being covered with the resin. The transfer molding is suitably employed.

It is preferable that the mold has a projection formed on at least one of the upper mold part and the lower mold part, and the transfer molding is performed in a state where the projection is fitted into the concave portion. The outside shape of the ferrule and the resin molded portion, especially, the distance between the top end of ferrule and the end surface of the resin molded portion is required to have the high positional precision. If the projection is formed in the mold and the molding is made in a state where the projection is fitted into the concave portion, the optical module can be formed in a state that the distance between the top end of ferrule and the end surface of the resin molded portion is defined at high precision.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the present invention will be described below by way of example.

FIG. 1Ais a perspective view of a sub-module for an optical module according to the present invention.FIG. 1Bis a perspective view showing a state after molding the sub-module and shows an optical module that is ideally molded without any gap between a mold and a ferrule.

As shown inFIG. 1A, a sub-module comprises a fiber with a ferrule10where an optical fiber14is inserted into a ferrule11′, an optical communication functional unit15and an Si bench21for mounting the fiber with ferrule10and the optical communication functional unit15thereon. The ferrule11′ has a concave groove12provided around the entire outer circumference of the ferrule11′. The concave groove12is provided on the ferrule11′ so that it is placed outside the outer shape of a resin molded portion13formed by molding the sub-module with the resin as shown in FIG.1B. The optical communication functional unit15makes the optical communication with the optical fiber14, and it is enclosed inside the resin molded portion13. For example, the optical communication functional unit15has an LD and a driver IC.

FIG. 2shows a specific manufacturing process of the optical module according to the present invention. The sub-module is mounted on a lead frame20in the same manner as shown in FIG.7. That is, an LD22and an M-PD23are soldered onto a Si bench21, and a fiber with a ferrule10is fixed by the resin onto the Si bench21to form the sub-module as an intermediate product. The sub-module is fixed, and connected by a wire bonding24to a die pad of the lead frame20. Then, an obtained component is placed within a mold30having an upper mold part30aand a lower mold part30b.

The ferrule11′ is sandwiched between the upper and lower mold parts30aand30bof the mold30in a state that the concave groove12of the ferrule11′ is in contact with mating faces of the upper and lower mold parts30aand30bwhich are mated with each other, as shown in FIG.2A. If the resin is injected from a resin filler hole32of the mold30, the resin molded portion13is formed except for a portion including the concave groove12of the ferrule11′, as shown in FIG.2B.FIG. 2Cshows the enlarged ferrule portion ofFIG. 2Bwith the elapse of the time, in which a resin16is exuded (or leaked) from a gap between the mold30and the ferrule11′. The exuded rein16is flowed into the concave groove12. As the concave groove12is under the almost atmospheric pressure, the exuded resin16is subjected to a lower pressure in the concave groove12, and filled in the concave groove12while being cured with the elapse of the time. Meanwhile, the resin molded portion13of the optical module is also cured.

When the resin molded portion13is completely cured, the exuded resin16is cured with in the concave groove12without reaching the top end of ferrule11′, that is, does not leak in a direction toward the top end of ferrule11′ from the concave grove12, as shown in FIG.2D. Thus, the resin molding process is completed.

FIGS. 3A,3B and3C show three embodiments of the fiber with the ferrule10according to the present invention.

FIG. 3Ais a first embodiment of the fiber with the ferrule in which the concave groove12is formed around the entire outer circumference of the ferrule11′. For example, the ferrule11′ is made of zirconia, and has an outer diameter of about 1 mm to 3 mm, and a length of about 3 mm to 10 mm. The concave groove12has a width (in the longitudinal direction of the ferrule11′) of about 1 μm to 500 μm and a depth (in the radial direction of the ferrule11′) of about 10 μm to 200 μm. The concave groove12may be formed by using a mold having a convex portion corresponding to the groove of ferrule when producing the ferrule, or formed by cutting after producing the ferrule. If the width or depth of the concave groove is too narrow or shallow, the exuded resin can not be dammed, that is, the concave groove can not store all of exuded resin. On the contrary, if the width or depth of the concave groove is too wide or deep, the strength of the ferrule or its connection strength with the connector is not sufficient, and the groove working is troublesome.

A fiber portion protruding from the ferrule11′ is as long as about 0 mm to 6 mm. The outer diameter of the optical fiber14is typically 125 μm in the clad portion in a single mode fiber (SMF) or a multi mode fiber (MMF). Of course, these dimensions depend on the sizes of other components, for example, the size of the Si bench, and the arrangement of the semiconductor laser (LD) or the photodiode (PD) that is optically coupled to the optical fiber14.

FIG. 3Bis a second embodiment of the fiber with the ferrule in which two concave grooves12′ are formed around the entire outer circumference of the ferrule11′. In this case, as the two concave grooves are formed as the resin reservoir for storing the exuded resin, the fiber with the ferrule is useful for the injection of resin for a longer time. Therefore, the resin is more securely prevented from exuding and adhering around the top end of ferrule. Of two concave grooves12′, one concave groove provided in proximity to the resin molded portion may be used as the resin reservoir, and the other concave groove provided apart from the resin molded portion may be used as a fitting hole with the mold at the time of molding, as shown in example 2.

The concave groove12may not be formed like a ring as shown inFIGS. 3A and 3B. For instance, the concave groove12″ may have a semi-circular shape, as shown in FIG.3C. The shape of the concave groove12is not limited to the above embodiments, but the exuded resin must not be filled in the concave groove before the resin molded portion is cured.

Practically, the optical module of the present invention was fabricated. First of all, a V-groove25for the ferrule11′ and a V-groove26for the optical fiber14were formed on the Si bench21having 10 mm long, 6 mm wide and 1.5 mm thick, by anisotropic etching, as shown in FIG.4A. Further, a metallization pattern for bonding and a wiring pattern (both not shown) are formed on the Si bench21so that the LD22and the monitor PD23can be disposed on the extension from the top end of the optical fiber14. Then, the LD22and the monitor PD23are bonded on the Si bench21by a solder material such as AuSn. For example, the LD22is a LD composed of a light emitting layer of InGaAsP having a light emitting wavelength of 1.3 μm, and has a dimension of 300 μm wide×300 μm long×120 μm thick. The monitor PD23is, for example, a PD of the end face incidence type composed of a light receiving layer of InGaAs and has a dimension of 400 μm wide×500 μm long×200 μm thick.

Next, the fiber with ferrule10is positioned and fixed in the V-groove25and the V-groove26by the resin. The ferrule11′ has a diameter of 1.25 mm and a length of 6 mm, and the concave groove12has a width of 200 μm and a depth of 100 μm. The distance from the groove-side end surface of the module resin molded portion13formed by the molding to the concave groove12is 500 μm. The protruding length of the optical fiber14(SMF) from the ferrule11′ is 3 mm. The V-grooves25and26and the bonding pattern can be formed at high precision in respect of the relative position by the photolithography technique, whereby the high coupling efficiency is obtained without taking the conventional troublesome procedure of making the alignment by emitting the light from the LD22.

Then, the transfer molding process is performed to cover the sub-module with the mold resin, except for a part of the lead29and the top end portion of the ferrule11′ including the concave groove12, as shown in a perspective view of FIG.4B.

The transfer mold resin was the epoxy type, in which the resin temperature was 170° C., the injection pressure was 150 atm, and the pressure of upper and lower mold parts was 17 tons. It took three minutes in total to make the injection of resin, curing, and extraction of the produced optical module.

As shown inFIG. 2, the resin was filled in the concave groove, immediately after extracting the optical module from the mold. The resin stored on the concave groove12in the ferrule11′ and the resin adhered between the concave groove12and the resin molded portion13in the ferrule11′ were removed. Thus an excellent module was obtained, as shown in FIG.1B and FIG.4B. Thereafter, the tie bar and the frame of the lead frame are cut, each lead is electrically isolated, and the lead29exposed from the package is bent at a predetermined angle. The obtained optical module has no resin adhered on the ferrule11′ exposing from the resin molded portion13.

In the above description, the concave portion of the ferrule was employed as the resin reservoir at the time of transfer molding, but may be employed to fit a projection31of the mold30at the time of molding into it.

The mold30has a projection31formed on an inner face of the mold30. In this embodiment, the projection31is formed on an inner face of the lower mold part30b. The projection31is fitted into the concave groove12of the ferrule11′ when the optical module is set within the mold30, as shown in FIG.5. The top end of the ferrule11′ (or the top end of the optical fiber) is required to be closely contact with the top end portion of the ferrule of the other connector to be fitted with. If the exposing amount of ferrule11′ from the resin molded portion13is 2.5 mm, for example, the positional precision from the groove-side end portion of the resin molded portion13to the top end portion of ferrule11′ is required to be as large as about ±20 μm to assure the close contact with the other connector. For this purpose, it is required to provide a distance between the groove-side end portion of the resin molded portion and the top end of the ferrule at high precision. In this embodiment, the projection31is previously formed in the mold30. The molding is performed in a state that the projection31is fitted into the concave groove12of the ferrule11′. Therefore, the outer shape of the resin molded portion13and the top end position of the ferrule11′ can be defined by the shape of the mold. As a result, the positions of the top end of the ferrule11′ and the groove-side end surface of the resin molded portion13can be obtained at the high precision. Of course, another concave portion may be formed for positioning the projection31, but not for reserving the resin, while the concave portion12is used as the resin reservoir.

The shape or arrangement of the groove according to the present invention is not limited to the above example, but it is required to be exposed outside the resin molded portion13.

TEST EXAMPLE

A coupling test was conducted using a connector for the optical fiber having an optical power meter connected at the terminal end. In the coupling test, the connector for the optical fiber was coupled into or decoupled from the ferrule of optical module in a state where the LD module ofFIG. 4Bis in an illuminant state. For each of 100 samples of the optical module, the coupling test was conducted 100 times. As a result, the variation in the coupling efficiency was small, and all the 100 samples were excellent.

The present invention is not limited to the above constitution. In the above description, the LD module was exemplified, but the optical receiving module may employ the light receiving element such as the PD and the amplifier. Also, the fiber with ferrule of the present invention may be coupled with the module having the optical components such as a waveguide and a filter mounted. Moreover, the bench may be made of ceramic.

As described above, according to the present invention, the concave portion is formed in a region of the ferrule exposed from the resin molded portion, so that the resin is prevented from adhering and covering on the top end side of ferrule by the leakage of resin at the time of molding, whereby the yield is improved, the cost is lowered and the mass production is enabled.