JP3187706B2 - Optical module manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical module in which a lens is welded to a holder by using a low-melting glass. More specifically, the method comprises the steps of: The present invention relates to a method for manufacturing an optical module in which a moisture-resistant protective film is formed on a surface of a glass pool facing a holder opening, and thereafter, a holder and an optical semiconductor element are joined. This optical module is useful as, for example, a light emitting device or a light receiving device in an optical LAN or the like, or a light source in a bar code reader.

[0002]

2. Description of the Related Art An optical module is an optical component incorporating various optical semiconductor elements, such as an optical connector and an optical collimator, and is used in various fields. For example, an optical connector used in the field of optical communication is an optical module that optically couples a semiconductor light emitting element or a semiconductor light receiving element with an optical fiber. 2. Description of the Related Art In a computer system that performs data communication using an optical LAN or the like, a semiconductor light emitting element module and a semiconductor light receiving element module are installed on a circuit board in pairs. Specifically, an optical semiconductor element (for example, a semiconductor light emitting element such as a laser diode or a semiconductor light receiving element such as a photodiode), a lens, and a receptacle core for fitting and holding a ferrule of an optical plug to be connected are provided. At the time of plug connection, the optical semiconductor element and the optical fiber of the ferrule are optically coupled via a lens. In addition, an optical collimator, which is a light source of a bar code reader, has a function of condensing light emitted from a laser diode with a lens so that a specified beam size can be obtained at a position separated by a predetermined distance.

[0003] As lenses used in optical modules, ball lenses and rod lenses are generally used. Of course, lenses of various other shapes may be used. Among them, spherical lenses are inexpensive because high-precision products can be easily manufactured only by machining, and because the lenses have no directionality, azimuth adjustment at the time of lens mounting is unnecessary and easy to assemble. It has many advantages and is often used. To fix the lens to the holder, welding with low melting glass,
Adhesion with a resin adhesive, soldering, mechanical fixing such as fitting a ring-shaped elastic member, and the like are available. Among these, the bonding method requires a liquid adhesive to be poured into a narrow area, and has difficulty in handling before curing. In order to perform the soldering, it is necessary to metallize the lens. Particularly, it is difficult to metallize a spherical lens, and since the metallization generates a direction, the mounting operation is complicated. Mechanical press-fitting and fixing requires other parts such as a ring-shaped elastic member, and the assembling work is complicated and costly. For these reasons, the welding method using low melting point glass is advantageous and widely used.

[0004] Specifically, a low-melting glass ring molded product obtained by compacting a powder of low-melting glass (for example, having a melting point of about 365 ° C) into a ring shape is used. This low-melting glass ring molded body is inserted into the step on the inner wall of the holder supporting the lens, and is placed in a heating furnace to perform heat treatment at a temperature of about 400 ° C. Thereby, the low-melting glass ring molded body is melted, and the lens 50 is welded to the holder 52 as shown in FIG. A glass pool solidified after the low-melting glass ring molded body has melted is indicated by reference numeral 54.

[0005]

When a component having a structure in which an element is incorporated in a hermetically sealed package is used as an optical semiconductor element, it is necessary to particularly hermetically seal the holder holding the lens. Absent. Therefore, outside air containing moisture easily enters and exits inside the holder. By the way, since the low-melting glass ring molded body used for glass welding is formed by compacting the powder of the low-melting glass as described above, when it is dropped into a predetermined position, fine fragments and powder are scattered. It may adhere to the lens surface. If the heating and melting treatment is directly performed to fix the lens, the adhered debris and powder are melted, or the low-melting glass itself is wrapped around to form a local coating of the low-melting glass on the lens surface. However, low-melting glass is particularly vulnerable to moisture, and devitrification (cloudiness) often occurs over time. Therefore, as shown in FIG. 6, a devitrified portion 56 made of a low-melting glass film is formed.
When such a devitrified portion is formed, the light amount of the optical module is reduced.

[0006] In addition, outside air containing moisture easily enters and exits the glass pool (low-melting glass) inside the holder. Due to this moisture, fine cracks are formed on the surface of the glass pool, and a phenomenon that the glass pool becomes brittle occurs. This results in a decrease in the fixing strength of the lens, and in some cases, the lens may fall off.

To solve such a problem, several methods can be considered. In order to prevent devitrification due to the low-melting glass on the lens surface, it is conceivable to remove fine powder and debris adhering to the lens surface before the heating and melting treatment. The task of completely removing the powder is very difficult in practice. Even if it can be removed, it is inevitable that the low-melting glass wraparound generated during heating and melting is inevitable, and it is impossible to prevent cracks generated on the surface of the glass pool. Although it is conceivable that the inside of the holder holding the lens has an airtight structure, it is costly and structurally complicated. As another means, it is conceivable to use glass that is relatively resistant to devitrification. However, glass having excellent moisture resistance has a high melting point, and is difficult to use as a lens welding material.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to devitrify despite the fact that fine fragments or powder of the low melting point glass adhere to the lens surface due to welding with the low melting point glass. Accordingly, it is an object of the present invention to provide a method of manufacturing an optical module capable of obtaining a highly reliable product without reducing the amount of light of the optical module and without reducing the lens fixing strength.

[0009]

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing an optical module in which a holder having a built-in lens and an optical semiconductor element hermetically sealed are coupled such that the lens and the optical semiconductor element are located coaxially. It is. The holder holds the lens on the inner wall.
Substantially cylindrical with ring-shaped steps for mounting
Of the lens, drop the lens into the holder
Low melting point glass placed between the lens and holder on the step
Hold the lens by heating and melting the sling
It is a structure that is welded inside. Here, the feature of the present invention is that after welding the lens inside the holder using low melting point glass,
The present invention is characterized in that a moisture-resistant protective film is formed by a physical vapor deposition method on a surface of both the lens and the formed glass pool facing the holder opening. The lens used here is preferably a spherical lens. The ratio a / b between the diameter a of the opening and the depth b from the opening to the spherical lens is used as the holder.
There that is desirable to so as to be 1 or more. The moisture-resistant protective film to be formed is, for example, SiO ₂ having a thickness of 30 to 200 nm.
There is a film, and this film can be formed by an evaporation method.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A lens is welded to a holder using low melting point glass. This welding is performed by molding a low-melting glass ring compact obtained by compacting a low-melting glass powder into a ring shape.
This is carried out by dropping into the holder inner wall step between the lens and the holder, and heating and melting. When dropping the low-melting glass ring compact, fine glass fragments and powder are scattered and adhere to the lens surface, which melts and spreads to form a local coating. The thin deposits may become devitrified (cloudy) by absorbing moisture in the surrounding air during long-term use. However, in the present invention, even if such a local film of the low-melting glass is formed, a moisture-resistant protective film is formed on the surface of the lens surface and the surface of the glass pool facing the holder opening immediately after welding in this state. Would. Then, since the low melting point glass is covered with this moisture resistant protective film,
Moisture does not penetrate into the low melting glass, so that no devitrification phenomenon occurs. Fine cracks can also be prevented from entering the surface of the glass pool. Thereby, a highly reliable optical module can be obtained for a long period of time.

The formation of the moisture-resistant protective film can be achieved by arranging a large number of holders each having a built-in lens inside the film forming chamber and performing a vapor deposition process or the like. In particular, if the shape of the holder is configured to have a wide and shallow opening, the vapor deposition material can be sufficiently supplied to the surface of the lens and the surface of the glass chamber.
Efficient and favorable moisture-resistant protective film can be formed to a desired thickness.

[0012]

1 and 2 are process explanatory views showing one embodiment of a method for manufacturing an optical module according to the present invention. FIG. 1 shows a manufacturing process up to completion of the lens built-in holder, and FIG. 2 shows a joining process of the completed lens built-in holder and the optical semiconductor element. In this embodiment, a spherical lens is used as a lens.

First, as shown in FIG. 1A, a spherical lens 12 is mounted inside a holder 10. The holder 10 is a substantially cylindrical member made of, for example, stainless steel, and has a first step portion 10a for mounting the spherical lens 12 on the inner wall, and a hermetically sealed optical semiconductor element (not shown). Having a second stepped portion 10b. When the spherical lens 12 is dropped into the holder 10, the spherical lens 12 is supported by the edge of the first step 10a because the lens diameter is larger than the diameter of the circular through hole 10c at the tip of the holder. As a result, the center of the spherical lens 12 automatically coincides with the center axis of the through hole 10c. Next, the low-melting glass ring molded body 14 is dropped between the spherical lens 12 and the holder 10 on the first step portion 10a. The low-melting glass ring molded body 14 is a member obtained by compacting a powder of low-melting glass (for example, having a melting point of about 365 ° C.) into a ring shape. Conversely, in this order, after the low-melting glass ring molded body 14 is loaded, the spherical lens 12 may be dropped.

This is placed in a heating furnace and subjected to a heat treatment at about 400 ° C. As a result, the low-melting glass ring molded body 14 is melted, and the spherical lens 12 can be glass-welded to the holder 10 as shown in FIG. 1B. Symbol 1 for the glass pool
Indicated by 5. After the spherical lens is welded inside the holder in this way, as shown in FIG. 1C, a moisture-resistant protective film 16 is formed on the surface of the spherical lens 12 and the glass reservoir 15 facing the holder opening by a vacuum evaporation method. Specifically, a vapor deposition material (for example, SiO ₂ or MgF) 22 necessary for film formation is put in the crucible 20 and heated by an electron beam method or a resistance heating method to evaporate the vapor deposition material to form the spherical lens 12 and It is attached to the surface of the glass pool 15. Thereby, the moisture-resistant protective film 16 is formed on the surface of the spherical lens 12 and the glass pool 15 facing the holder opening (see D in FIG. 1). In order to efficiently form a film on the surfaces of the spherical lens 12 and the glass reservoir 15, the shape of the holder 10 must be the diameter a of the holder opening.
It is preferable that the ratio a / b of the depth b from the opening to the spherical lens be 1 or more. Preferred moisture-resistant protective film 16
For example, there is a SiO ₂ film having a thickness of about 30 to ₂₀₀ nm.

Next, as shown in FIG. 2, the optical semiconductor element 18 housed in a package and hermetically sealed is connected to the holder 10 containing the spherical lens 12. A moisture-resistant protective film 16 is formed on the surfaces of the spherical lens 12 and the glass pool 15 by the procedure shown in FIG. Positioning is performed by fitting the base portion 18a of the package of the optical semiconductor element 18 to the second step portion 10b of the holder 10 so as to be pressed against the second step portion 10b, and is fixed by an adhesive or YAG laser welding. The mounting position of the optical semiconductor element 18 is determined by the processing size of the holder 10, and the alignment in the optical axis direction is not performed. In this way, an optical module as shown in FIG. 2B is obtained. Needless to say, a coupling structure that can perform alignment in the optical axis direction as necessary may be used.

FIG. 3 shows an example in which a rod lens is used instead of a spherical lens. Since the basic manufacturing procedure is the same as that shown in FIGS. 1 and 2, corresponding parts are denoted by the same reference numerals and detailed description thereof will be omitted.
The rod lens 13 is fitted into the holder 10, and the low-melting glass is fused by heating. The portion of the glass pool is indicated by reference numeral 15. Then, the moisture-resistant protective film 1 is formed on one end surface of the rod lens 12 and the surface of the glass pool 15.
6 is formed.

When a laser diode is incorporated as an optical semiconductor element, an optical collimator serving as a light source for a bar code reader can be obtained by combining an optical semiconductor element and a lens as shown in FIG. 2B.

FIG. 4 shows another example in which an optical connector is formed. This has a receptacle core 30 into which a ferrule (not shown) of an optical plug to be connected is fitted, in addition to the optical module as shown in FIG. 2B. Here, the receptacle core 30 is made of stainless steel (for example, SUS).
304), and is formed on at least the inner peripheral surface of the bore by CVD (chemical vapor deposition).
In this case, a high hardness film 31 such as iC is formed. A ferrule stopper 32 is mounted on the base end side of the bore of the receptacle core 30. Of course, instead of forming a high hardness film, a structure in which a ceramic sleeve is fitted in a receptacle core may be used. Such a receptacle core 30 is YAG-welded to the holder 10 in a centered state (weld portions are indicated by reference characters W). The ferrule of an optical plug is inserted into the receptacle core 30 to monitor the amount of light emitted from the optical fiber or the amount of light detected by the semiconductor light-receiving element, perform precise alignment in the mating direction, and irradiate the YAG laser beam at the peak coupling position. And spot welding.
Then, a plastic connector housing 34 is mounted on the outer peripheral side. When such an optical connector is used, a mating optical ferrule is fitted into the bore of the receptacle core 30, and a plug frame of the optical plug is fitted and mechanically coupled to the connector housing.
In this state, optical alignment and coupling between the optical semiconductor element and the optical fiber of the ferrule are simultaneously achieved.

By incorporating a semiconductor light emitting element such as a laser diode as an optical semiconductor element, a light emitting device for an optical LAN in which light emitted from the laser diode is condensed by a spherical lens and enters an optical fiber of a ferrule is provided. Can be configured. If a semiconductor light receiving element such as a photodiode is incorporated in place of the semiconductor light emitting element, a light receiving element for an optical LAN can be configured.

Next, the method for forming a moisture-resistant protective film according to the present invention will be described in more detail. First, a large number of samples 40 (the state shown in FIG. 1B) in which spherical lenses are welded to the inside of the holder using low-melting glass are prepared. At the time of its manufacture, there is no particular problem even if fine powder of low melting point glass adheres to the surface of the spherical lens. These are aligned and fixed by a jig 42 or the like such that the surface of the spherical lens facing the opening of the holder faces downward, and is installed inside a film forming chamber 44 for vacuum evaporation.
Then, a crucible 46 is provided below, and a vapor deposition material 48 (for example, SiO ₂ or MgF) required in the crucible 46 is provided.
Insert Then, the air is evacuated to a necessary high vacuum state by a vacuum pump (not shown) and heated by an electron beam (EB) method, a resistance heating method, or the like. By heating and evaporating the thin film material in a high vacuum, the evaporated particles are deposited on the surface of the spherical lens and the surface of the glass pool to form a thin film. The thickness of the thin film is controlled to about 30 to 200 nm. by this,
The surface of the lens (the surface of the lens that covers low-melting glass if it adheres) and the surface of the glass pool
A film of O ₂ or the like is formed, so that it is possible to prevent moisture in the outside air from entering the low-melting glass and devitrifying the low-melting glass. The film can be formed by a sputtering method instead of the vacuum evaporation method.

In some cases, an optical filter film such as an ND (neutral density) filter film for adjusting light transmittance is formed on the surface of the lens. This is used for adjusting the amount of emitted light and the slope efficiency in order to satisfy safety standards for laser products. That is, the light transmittance is controlled by the ND filter film, and the amount of light emitted from the laser diode is apparently adjusted. A film forming material such as metal chromium or metal titanium is formed on the ND filter film for adjusting the light transmittance so as to have a film thickness of about several tens nm. Such a metal film may be oxidized by being exposed to the outside air as it is. Even in such a case, the moisture-resistant protective film of the present invention is effective. That is, in the state shown in FIG. 1C, after forming a necessary optical filter film, a moisture-resistant protective film may be formed thereon in a similar manner.
The metal film is protected by this moisture-resistant protective film, and long-term reliability is ensured.

[0022]

As described above, the present invention is a method for forming a moisture-resistant protective film on a surface of a lens and a glass pool facing a holder opening after a lens is welded to the inside of a holder with low-melting glass. Even if fine particles or powder of the low-melting glass adhere to the surface, they are finally covered with the moisture-resistant protective film, so that the devitrification phenomenon of the low-melting glass does not occur, and when used for a long time, There is no possibility that the light amount will decrease. Further, since the surface of the glass pool is also covered with the moisture-resistant protective film, it is possible to prevent the generation of minute cracks due to moisture absorption, and it is possible to securely and firmly hold the lens. In this respect, the reliability over a long period is significantly improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a manufacturing process of an optical module according to the present invention.

FIG. 2 is an explanatory view showing a coupling structure between the holder and the optical semiconductor element.

FIG. 3 is an explanatory view showing another example of the optical module manufactured according to the present invention.

FIG. 4 is an explanatory view showing another example of use of the optical module manufactured according to the present invention.

FIG. 5 is an explanatory view of a step of forming a moisture-resistant protective film on a spherical lens welded to a holder.

FIG. 6 is an explanatory diagram showing a problem of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Holder 12 Spherical lens 14 Low-melting glass ring molded object 15 Glass pool 16 Moisture-resistant protective film 18 Optical semiconductor element

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 14/00-14/58 G02B 1/10 G02B 6/00-6/54 G02B 7/00-7 / twenty four

Claims (3)

(57) [Claims] 1. A method for manufacturing an optical module, wherein an optical semiconductor element hermetically sealed with a holder having a built-in lens is coupled so that the lens and the optical semiconductor element are positioned coaxially. Ring for attaching a lens to
A substantially cylindrical member having a step-like shape,
Lens and holder on the step
Heating and melting the low melting glass ring placed between
Manufacture of an optical module and forming a moisture-resistant protective film by after welding the lens inside the holder, physical vapor deposition on a surface facing both of the holder opening of reservoir the lens and glass is formed by Method. 2. A substantially cylindrical member having a ratio of a / b between the diameter a of the opening and the depth b from the opening to the ball lens of 1 or more is used as the holder. A method for manufacturing an optical module according to claim 1. 3. The moisture-resistant protective film has a thickness of 30 to 200 nm.
The method for manufacturing an optical module according to claim 1, wherein the optical module is an iO ₂ film and is formed by a vapor deposition method.