JPH03167514A - Molded lens with metallic holder and production thereof and optical semiconductor module provided with the lens - Google Patents

Abstract

PURPOSE:To obtain the lens with a metallic mold suitable for an optical semiconductor module having high coupling efficiency by disposing an annular metallic holder around the glass between metallic molds in such a manner that the center line thereof parallels approximately with the pressing direction by the metallic molds. CONSTITUTION:Glass 8 softened by heating is pressed by the metallic molds 2, 4 and the surface shapes of the molds 2, 4 are partly transferred to the glass to obtain the molded lens. The annular metallic holder 6 is disposed around the glass between the molds 2 and 4 in such a manner that the center line thereof parallels approximately with the pressing direction by the molds 2, 4. The glass extruded by the press is so formed as to come into tight contact with the inner periphery of the metallic holder 6. The optical semiconductor module with which the high optical coupling efficiency is obtainable and which can maintain the optical coupling efficiency stably over a long period of time is obtd. in this way.

Description

[Detailed Description of the Invention] Table of Contents Overview Industrial Field of Application Prior Art Problems to be Solved by the Invention Means and Functions for Solving the Problems Examples Summary of Effects of the Invention Molded lens with metal holder and manufacturing method thereof In addition, regarding the optical semiconductor module equipped with the above-mentioned lens, the objective is to provide a lens with a metal mold that is suitable for an optical semiconductor module with a high optical coupling efficiency, for example, by pressing heated and softened glass with a mold. In the method for manufacturing a molded lens in which a part of the surface shape of the mold is transferred to glass, a circular metal holder is placed in the mold so that its center line is approximately parallel to the direction of pressing by the mold. The metal holder is arranged around the glass in between, and the glass extruded by a press is configured to tightly adhere to the inner periphery of the metal holder.

INDUSTRIAL APPLICATION FIELD The present invention relates to a molded lens with a metal holder, a method for manufacturing the same, and an optical semiconductor module equipped with the lens. Here, the optical semiconductor module is used to effectively input light emitted from an optical semiconductor element in a light emitting system such as a semiconductor laser into an optical fiber, or to input light emitted from an optical fiber into a light receiving system such as a photodiode. An optical/electrical optical system in which an optical semiconductor element, an optical fiber, and a lens system for optically coupling these elements are fixedly held in a predetermined positional relationship in order to effectively make the light incident on the light receiving surface of the optical semiconductor element. equipment. Hereinafter, for convenience of explanation, a case where the present invention is applied to a semiconductor laser module (LD module) will be described, but the present invention is not limited to this.

In next-generation optical communication systems, services such as long-distance transmission of high-speed signals of billions of bits per second or more, branching of signal light and distribution to many receivers, etc. are being considered, and services such as high-output ( For example, a semiconductor laser module of 1Qmi or more is required.

Furthermore, in the case of modules equipped with optical amplifiers, which have been attracting attention recently, optical coupling between a semiconductor laser type optical amplifier and an optical fiber, or a rare earth doped fiber (an optical fiber whose core is doped with a rare earth element such as εr) is used. High efficiency is required for optical coupling between a pumping light source and an optical fiber in an optical amplifier that utilizes an optical fiber. In these systems, the optical coupling efficiency directly affects the performance of the communication system, so improving the optical coupling efficiency between the semiconductor laser and the optical fiber has become a major technical issue.

2. Description of the Related Art In conventional semiconductor laser modules, light emitted from a semiconductor laser is focused using a minute ball lens or a gradient index lens, and the light is made to enter an optical fiber. However, the optical coupling efficiency is not necessarily high due to the effects of lens aberrations, etc., and the light that actually enters the optical fiber is 20 to 4 times the light emitted from the semiconductor laser.
This is approximately 0%, which means that more than half of the light is wasted. The resulting optical output was also about 3 to 5 mW, which was not sufficient.

Recently, attempts have been made to achieve high optical coupling efficiency by using aspherical glass molded lenses as coupling lenses for optical semiconductor modules. Attempts have been made to put this type of lens into practical use as an objective lens for optical discs. When using glass mold lenses for optical semiconductor modules, there were problems such as large size, long focal length, and small NA (numerical aperture), but recently, mold processing and measurement technology has advanced. Specifications that can be applied to optical communications (for example, diameter 2 [1111
1. It has become possible to obtain a focal length of in and NA=0.55 or more. The manufacturing method of this molded lens basically involves only one step, placing the glass material in a precision mold and pressing it to transfer the shape of the mold onto the glass, making it highly suitable for mass production. There is. In addition, since the lens shape is aspherical, the light receiving angle of the lens can be widened, and aberrations can be kept small, compared to the case of using microsphere lenses or distributed index lenses. It has been demonstrated that optical coupling efficiency of more than twice (70-80%) can be obtained.

Problem 1 to be solved by the invention is that when an optical coupling lens is used for a semiconductor laser module, the relative positional relationship between the semiconductor laser, the lens, and the optical fiber must be adjusted with an accuracy of 1 μm or less during assembly. There is a need. Furthermore, if the positional deviation after fixation is not suppressed to about 0.1 to 0.2 μm, including changes over time, the optical output will fluctuate. The semiconductor storage is installed on a metal carrier that has both the function of a heat sink and the function of grounding electrical signals. Further, the lens is fixed within, for example, a cylindrical metal holder. By welding and fixing the metal carrier and the metal holder, the semiconductor laser and the optical fiber are fixed and held in a predetermined positional relationship. Although the above accuracy can be relatively easily satisfied for the dimensional accuracy of the fixed parts between metals, there are various problems in terms of dimensional accuracy etc. for the fixed parts between dissimilar materials such as the metal holder and the glass lens. Ta. The conventional methods and their problems are shown below.

(a) Method of pressing the lens into the metal holder)
Method of metalizing the side surface of the lens and soldering it to a metal holder (C) Method of fusing and fixing it using a low-melting glass material (
d) Method of fixing using an adhesive In method (a), the inner diameter of the metal holder is set to be the same as or slightly smaller than the outer diameter of the lens, the metal holder is heated to thermally expand, and the lens is pushed into the lens by applying pressure. This is a method of fixing by cooling, which uses stress applied to the side surface of the lens. When this method is used, stress is applied to the lens, so that the refractive index becomes non-uniform due to the photoelastic effect, and the optical characteristics of the lens may deteriorate. When using conventional spherical lenses, etc., the optical coupling efficiency was at a low level, so no significant characteristic deterioration was observed due to press fitting, but when using an aspherical glass molded lens, there was If the stress is large, the optical coupling efficiency will decrease.

The method of et al.) is a method often used when using a distributed index lens. Metallization on the tltlJ plane of a distributed index lens can be performed before cutting the lens base material, but since mold lenses are individually pressed or molded, metallization is applied only to the sides of each mold lens. It is necessary and the productivity is extremely low.

Method (C) involves interposing a fusing material between the lens and the metal holder, leaving them at a high temperature of 400°C or higher for about 10 to 30 minutes to soften the fusing material, and then slowly cooling to fuse them. This is a method of solidifying the material. With this method, it is necessary to keep the lens at a high temperature for a long time, which may cause the lens to be deformed or the refractive index to become non-uniform, resulting in deterioration of the optical properties of the lens.

In the method (d) using an adhesive, since the solidified adhesive has a large linear thermal expansion coefficient, reliability against temperature fluctuations after fixing is low. Furthermore, the output characteristics of the semiconductor laser may deteriorate due to the influence of harmful gases released from the solidified adhesive.

As explained above, no matter which of the conventional fixing methods is applied to a molded lens, it is difficult to provide a stable optical semiconductor module with a high level of optical coupling efficiency.

The present invention was created in view of the above circumstances, and an object of the present invention is to provide a molded lens with a metal holder that is suitable for an optical semiconductor module with high optical coupling efficiency.

Other objects of the present invention will become apparent from the above-mentioned technical problem and the following description.

Means and actions to solve the problem FIG. 1 is a diagram explaining the principle of the invention.

The method for manufacturing a molded lens with a metal holder of the present invention includes:
In a method for manufacturing a molded lens, in which heated and softened glass is pressed by molds 2 and 4 to transfer part of the surface shape of the molds 2 and 4 to the glass, an annular metal holder 6 is used. It is arranged around the glass between the molds 2.4 so that its center line is approximately parallel to the pressing direction by the mold 2.4, and the glass extruded by the press is inside the metal holder 6. It is designed to fit closely around the circumference. In FIG. 1, reference numeral 8 indicates glass softened by heating, and reference numeral 10 indicates heating means for the molds 2, 4, and the like.

As described above, the method of the present invention focuses on the fact that when molded lenses are manufactured using a mold press, softened glass is extruded in a direction perpendicular to the pressing direction, and the method focuses on the manufacturing of molded lenses and the metal holder of the molded lenses. This is done at the same time as fixing to. Therefore, there is no need to fix the molded lens to the metal holder again, improving productivity.

In addition, since the glass that makes up the lens itself functions as a fusing material, the fusing material shown in (C) in the conventional method is no longer necessary, and the number of materials whose linear thermal expansion coefficients need to be matched can be reduced. can.

Further, as shown in (C) in the conventional method, there is no need to bring the lens to a high temperature again after forming it, so there is no possibility that the lens will be deformed or the refractive index will become non-uniform.

Further, by forming irregularities on the inner periphery of the metal holder and increasing the area of close contact between the softened glass and the metal holder, the fixing strength can be increased. It is virtually impossible to achieve a fixing structure in which unevenness is formed on the inner periphery of a metal holder using conventional methods, and has only been made possible by the method of the present invention, which utilizes the characteristics of the method for manufacturing molded lenses.

By forming irregularities on the inner periphery of the metal holder, there is no fear that the molded lens will fall off from the metal holder unless the molded lens is damaged.

In addition, solder, adhesive, etc. between the molded lens and the metal holder,
Since there is no adhesive, it is now possible to easily align the optical axis of the molded lens with the geometric center axis of the metal holder, which is effective in eliminating the need for adjustments in the module assembly process. be.

By making the center line of the annular metal holder 6 slightly inclined with respect to the pressing direction by the molds 2 and 4, the optical axis of the manufactured molded lens with the metal holder is aligned with the center line of the metal holder 6. This configuration is effective in preventing the adverse effects of reflected light. In this case, a decrease in optical coupling efficiency can be suppressed by optimally designing the lens surface of the aspherical lens.

In a method for manufacturing a molded lens, in which heated and softened glass is pressed with a mold to transfer a part of the surface shape of the mold to the glass, a depression is formed to be filled with glass extruded by the press. By arranging the metal holder on the side of the glass between the molds, the same effect as described above is produced.

The molded lens with metal holder of the present invention has these two
This is a molded lens with a metal holder manufactured by any one of the methods.

The optical semiconductor module of the present invention includes an optical semiconductor element, an optical fiber, a single or plural lenses that optically couple the optical semiconductor element and the optical fiber, these optical semiconductor elements,
An optical semiconductor module comprising an optical fiber and a frame having a metal part that fixes and holds the lens in a predetermined positional relationship, the lens or a part thereof (if the lens is a single lens, the single lens). When the lens is a plurality of lenses, e [or a part of the plurality of lenses] is the molded lens with a metal holder according to the present invention, and the metal holder of the molded lens with a metal holder is the metal holder of the above-mentioned frame. It is fixed by laser welding to a metal part (a metal carrier to which an optical semiconductor element is fixed, a module frame, etc.).

As described above, in the optical semiconductor module having the molded lens with a metal holder as a constituent element according to the present invention, it is possible to increase the optical coupling efficiency and increase the optical output through the above-mentioned effect, and furthermore, it is possible to increase the optical coupling efficiency and increase the optical output. , it becomes possible to stably maintain this optical coupling efficiency or optical output at a high level.

Example Examples of the present invention will be described below.

FIG. 2 is a front view (a) of a molded lens with a metal holder showing the first embodiment, and a sectional view (b) taken along the line (b)-(b). In this embodiment, two annular protrusions 12 are formed on the inner periphery of the cylindrical metal holder 6 at the part where the softened glass material comes into close contact, giving it an uneven shape, increasing the area of contact with the glass and increasing the fixing strength. At the same time, the molded lens l4 is prevented from falling off from the metal holder 6. Molded lens 1 integrated with metal holder 6
In No. 4, l6 and 18 are aspherical lens surfaces transferred from a mold.

The structure and material of the mold can be determined depending on the glass material, shape, required precision, etc. of the lens to be pressed.

Specifically, the materials for the mold include platinum-gold alloy, tungsten carbide (WC), and silicon carbide (WC).
SiC), silicon nitride (S13N4), etc. can be used, but in order to ensure the releasability of the lens surface of the molded lens, a thin film made of electroless nickel or other metal is formed on the mold surface. It is desirable. The structure of the press part of the mold is also shown in FIG. 1, but it is desirable that its outer periphery be in circumscribed contact with the inner periphery of the metal holder 6. on the other hand,
The material of the metal holder 6 is selected from the viewpoints of high-temperature fusion properties with the glass material, welding characteristics with the metal carrier, and coefficient of linear thermal expansion. By using an iron-nickel alloy as the material of the metal holder 6, good high-temperature fusion properties can be obtained. In this case, since the coefficient of linear thermal expansion can be adjusted by changing the nickel content, the coefficient of the metal holder can be made to match the coefficient of the molded lens. Select a material for the metal holder 6 that has a linear thermal expansion coefficient equivalent to that of the solidified glass material, or select a glass material that has a linear thermal expansion coefficient equivalent to that of the material for the metal holder 6. By doing so, the stress remaining in the lens after manufacturing can be kept to a low level, and,
The usable temperature range of this molded lens with a metal holder is expanded. When the stress remaining in the molded lens is reduced, non-uniformity in the refractive index due to the photoelastic effect is less likely to occur, and the optical properties of this lens can be maintained at high levels.

FIG. 3 shows a modification of the first embodiment. By forming the structure 20 in the circumferential direction of the inner circumference of the metal holder 6 to make it uneven, the fixing strength can be increased and the molded lens 1
4 from falling off from the metal holder 6.

Although not shown in the drawings, the protrusion 12 and the groove 20 have a U-shaped cross-section, so that the degree of stress concentration can be reduced, thereby reducing the risk of damage to the molded lens 14.

FIG. 4 is a front view (al, sectional view taken along the line (b)-(b)) of a molded lens with a metal holder showing the second embodiment. In this embodiment, three depressions 22 are formed at equal intervals on the inner periphery of the metal holder 6 as irregularities for increasing the contact area between the metal holder and the softened glass. A step is formed on the bottom surface of the depression 22. The glass material is brought into close contact with the metal holder 6 only within the structure 22. To do this, for example, when pressing with a mold, a2 of the inner circumference of the metal holder 6 is
It is preferable to arrange a smoother having excellent mold releasability from the glass material in a portion other than the portion corresponding to No. 2.

According to this structure, when the linear thermal expansion coefficient of the metal holder 6 and the coefficient of the molded lens l4 are different, the thermal stress generated during manufacturing or due to other causes can be absorbed by elastic deformation of the metal holder 6, etc. It can be relaxed. As a result, undesirable distortion is less likely to occur in the molded lens 14, making it possible to maintain good optical characteristics. Even if there is no unevenness formed on the inner circumference of the metal holder 6,
A similar effect can be produced by making the softened glass adhere to the metal holder only in the vicinity of the positions where the inner periphery of the metal holder is divided approximately equally in the circumferential direction.

FIG. 5 is a front view (a), (b) of a molded lens with a metal holder showing a third embodiment, and a sectional view taken along the line (b)-(b). In this embodiment, a metal holder 26 is shaped like a rectangular parallelepiped with a depression 28 formed on the l side (top surface in the figure).
The flange 24 formed on a part of the outer periphery of the molded lens l4 is brought into close contact with the metal holder 26 within the recess 28. 28a is a protrusion formed within the recess 28 to increase the area of contact with the glass material.

When manufacturing a molded lens with a metal holder having such a structure, the metal holder 26 is placed on the side of the glass material between the molds during pressing, and the method described in the previous examples etc. is used. This can be done in accordance with the above.

According to this structure, even if the coefficient of linear thermal expansion of the metal holder 26 and the coefficient of glass are significantly different, thermal stress mainly occurs in the portion of the flange 24 near the metal holder 26, resulting in adverse effects such as birefringence. There is no fear. Therefore, this structure or manufacturing method is suitable when the metal holder is made of a material that has good weldability but has a linear thermal expansion coefficient significantly different from that of glass.

FIG. 6 shows a cross-sectional structure of a semiconductor laser module to which the third embodiment is applied. This module includes a third laser beam that focuses the light emitted from the semiconductor laser 30 and its emission end.
A first lens l4 according to the embodiment is fixedly held in a predetermined positional relationship to form an LD assembly 32, a second lens 34 that focuses light from the first lens 14, and an optical fiber 36 into which the focused light enters. are fixedly held in a predetermined positional relationship to form a fiber assembly 38, and these LD assemblies 32
and the fiber assembly 38 is fixedly held in a predetermined positional relationship. In the LD assembly 32,
40 is a metal carrier, and the semiconductor laser 30 and the circuit board 42 are bonded onto the metal carrier 40 using an AuSn bonding material or the like. Further, the metal holder 26 of the molded lens 14 is fixed onto the metal carrier 40 by laser welding after alignment in the optical axis direction and the direction perpendicular to the optical axis. The semiconductor laser assembly 32 is fixed onto a substrate 46 via a temperature stabilizer 44 and the like.

In this embodiment, since the second lens 34, which has a relatively large diameter, does not require as high positioning accuracy as the first lens, the second lens is fixed to the inner hole of the holder 48 with a bonding material, and A ferrule 50, into which the optical fiber 36 is inserted and fixed, is inserted and fixed into this inner hole. The end face of the optical fiber 36 and the end face of the ferrule 50 are polished obliquely to the optical fiber axis to prevent end face reflection.

Reference numeral 52 denotes a casing for maintaining the relative positional relationship between both assemblies and hermetically sealing the LD assembly 32. The casing 52 has a substrate 46 on the bottom surface and a holder 38 on the side surface. are each fixed by laser welding. An optical isolator 5 that allows light from the semiconductor laser 30 to pass through only in one direction is provided in the light transmitting portion of the housing 52.
6 is provided with a spacer 54 in between. 58 is the lth
This is an airtight window with an antireflection film provided between the lens l4 and the optical isolator 56.

According to this structure, the metal holder 26 and the metal carrier 40
are fixed by laser welding, and other parts that may deteriorate over time are also fixed by laser welding, so the optical coupling efficiency can be maintained stably over a long period of time. Furthermore, since a molded aspherical lens is used as the first lens, high coupling efficiency can be achieved from the beginning of module assembly.

When a high optical coupling efficiency (for example, about 80%) is achieved as in this embodiment, the reduction in optical coupling efficiency due to obliquely polishing the end face of the optical fiber 36 cannot be ignored. In such a case, as shown in FIG. 7, the first and second lenses 1 are
4. Make the optical fiber 36 oblique to the optical axis ○A in 34. That is, the optical axis of incidence on the optical fiber 36 is made to coincide with the optical axis OA. The angle θ2 between the optical fiber 36 and the light l+110A is determined according to the inclination angle θ1 of the fiber end face. For example, θ1 =6
In the case of θ2, by setting θ2 = 3°, θ2
The optical coupling efficiency can be improved by about 0.4 dB compared to -0°. In order to arrange the optical fiber 36 obliquely in this manner, for example, a part of the inner hole of the holder 48 into which the ferrule 50 is inserted and fixed may be formed obliquely.

Effects of the Invention As stated above, according to the present invention, it is possible to provide an optical semiconductor module that can obtain high first coupling efficiency and maintain stable optical coupling efficiency for a long period of time. This effect is achieved.

Further, it is possible to provide a molded lens with a metal holder and a method for manufacturing the same suitable for this type of optical semiconductor module.

According to the present invention, it becomes possible to provide a large quantity of molded lenses with metal holders whose optical axes are positioned with high accuracy with respect to the outer shape of the metal holder at low cost, thereby reducing costs for subscribers. This greatly contributes to the mass production of inexpensive modules.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the invention, Fig. 2 is a front view of a molded lens with a metal holder showing the first embodiment (a) and a cross-sectional view taken along line Cb
), FIG. 3 is a sectional view of a molded lens with a metal holder showing a modification of the first embodiment, and FIG. 4 is a front view (a) and (b) of a molded lens with a metal holder showing a second embodiment. (Cross-sectional view (b) taken along line bJ, Figure 5 is a front view (a) of a molded lens with a metal holder showing the third embodiment, and cross-sectional view taken along line (b)-(b)). FIG. 6 is a sectional view of a semiconductor laser module to which the third embodiment is applied, and FIG. 7 is an explanatory diagram of a modification of the semiconductor laser module. 2, 4...Mold, 6, 2 6...Metal holder.

Claims (1)

[Claims] 1. A molded lens in which heated and softened glass is pressed by molds (2, 4) so that part of the surface shape of the molds (2, 4) is transferred to the glass. In the manufacturing method of the above-mentioned mold (2),
, 4) are placed around the glass between the molds (2, 4) so that the glass is pushed out by the press into the metal holder (6).
) A method for manufacturing a molded lens with a metal holder, characterized in that the molded lens is brought into close contact with the inner periphery of the metal holder. 2. The method for manufacturing a molded lens with a metal holder according to claim 1, characterized in that the inner periphery of the metal holder (6) is formed with unevenness for increasing the area of close contact with the softened glass. . 3. Claim 1, characterized in that the softened glass is brought into close contact with the metal holder (6) only in portions near positions where the inner periphery of the metal holder (6) is divided approximately equally in the circumferential direction. Or the method for manufacturing a molded lens with a metal holder according to 2. 4. A method for manufacturing a molded lens in which heated and softened glass is pressed with a mold to transfer a part of the surface shape of the mold to the glass, in which a depression is filled with glass extruded by the press. (2
8) A method for manufacturing a molded lens with a metal holder, characterized in that the metal holder (26) formed with the above-mentioned metal holder (26) is placed on the side of the glass between the molds. 5. A molded lens with a metal holder manufactured by the method according to any one of claims 1 to 4. 6. An optical semiconductor element, an optical fiber, a single or plural lenses that optically couple the optical semiconductor element and the optical fiber, and fixing and holding the optical semiconductor element, optical fiber, and lens in a predetermined positional relationship. , and a frame having a metal part, wherein the lens or a part thereof is a molded lens with a metal holder according to claim 5, and the molded lens with a metal holder has a metal holder attached to the frame. An optical semiconductor module characterized in that the optical semiconductor module is fixed to a metal part by laser welding. 7. In the optical semiconductor module according to claim 6, the end face of the optical fiber is formed obliquely with respect to the center line of the optical fiber, and the input optical axis or the output optical axis of the optical fiber is the optical semiconductor module. An optical semiconductor module characterized in that the optical axis of an element and a lens coincide with each other.