JPH03120884A - Semiconductor laser module - Google Patents

Abstract

PURPOSE:To reduce generation of heat stress and to hold stable optical coupling efficiency by forming heat expansion coefficient difference of a holding member and a converging means at a specified value or below. CONSTITUTION:A stem 8 has a copper tungsten alloy property which is equivalent to a holding member. A semiconductor laser 1 to project laser light is mounted on a submount 2. A plate 6 of copper tungsten alloy (or ceramic) property to bond and fix a spherical lens 5 to collect laser light from the laser 1 by a low melting point glass 7, a monitoring photodiode 3 to monitor laser light projection, and a temperature detecting element 4 to detect a temperature of the stem 8 are mounted on one side of the stem 8 and a cooling side of a heat electron cooling element 9 is connected to the other thereof. The spherical lens 5 and the plate 6 are coupled by using a low melting point glass whose thermal expansion coefficient is approximately equal to them. A heat expansion coefficient difference is restrained not more than 1X10<-4>/ deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor laser module suitable for an optical transceiver for an optical communication system, and particularly to a semiconductor laser module that can maintain stable optical coupling efficiency.

[Prior art] A semiconductor laser module according to the conventional technology is disclosed in Japanese Patent Application Laid-open No. 1983
As described in Publication No. 10686, a semiconductor laser that generates laser light by applying an electric current and a spherical lens are bonded and fixed to a stem made of copper tung stem, etc., and the laser light emitted from the semiconductor laser is transmitted through the spherical lens. The light beam is configured to be outputted to a focusing lens coupled to an optical fiber via a condenser lens.

Generally, the thermal expansion coefficients of the spherical lens and the copper-tungsten alloy stem are approximately the same, but there is a difference of 104 times between these and the solder.

[Problems to be Solved by the Invention] The semiconductor laser module according to the above-mentioned prior art has a large difference in coefficient of thermal expansion between the spherical lens, the copper-tungsten alloy stem, and the solder that fixes them. In this case, repeated thermal stress is generated, which leads to strength deterioration and slight positional deviation in the soldered parts, resulting in fluctuations in the optical coupling ratio.

An object of the present invention is to eliminate the problems caused by the prior art, and to provide a semiconductor laser module that can maintain stable optical coupling efficiency.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a semiconductor laser that irradiates laser light and a condensing means that condenses the laser light from the semiconductor laser and outputs it to the outside. In the semiconductor laser module, the difference in thermal expansion coefficient between the holding member for holding the semiconductor laser and the light focusing means and the adhesive means for bonding the holding member and the light focusing means is set to 1×10−' or less. The characteristics of

The present invention also provides a stem on which a semiconductor laser is mounted, a ball lens for condensing laser light from the semiconductor laser, a flat plate for mounting the ball lens on the stem, and an adhesive for adhesively fixing the flat plate and the ball lens. A second feature of the semiconductor laser module having a fixing means is that the difference in coefficient of thermal expansion between the stem, the ball lens, the flat plate, and the adhesive fixing means is approximately 1×10 −′ or less.

Furthermore, the present invention provides a semiconductor laser module comprising a tipped optical fiber for condensing and outputting laser light from a semiconductor laser, and a stem on which the semiconductor laser is mounted and the tipped optical fiber is adhesively fixed by adhesive fixing means.
The third aspect is that the difference in coefficient of thermal expansion between the stem, the tip optical fiber, and the adhesive fixing means is approximately 1×10−' or less.
The characteristics of

In the semiconductor laser module according to the second or third aspect of the present invention, the stem is formed of a copper-tungsten alloy, the flat plate is formed of ceramic or a copper-tungsten alloy, and the adhesive fixing means is formed of low-melting glass. The fourth feature is that

[Function] The semiconductor laser module having the first feature forms an optical coupling path by forming a difference in coefficient of thermal expansion between the holding member, the light condensing means, and the adhesive fixing means to approximately 1×10−' or less. The optical coupling efficiency can be kept stable by reducing the occurrence of thermal stress caused by the difference in the coefficient of thermal expansion of each component.

The second feature of the semiconductor laser module is that the difference in thermal expansion coefficient between the stem, the ball lens, the flat plate, and the adhesive fixing means is approximately 1×10−' or less, so that the ball lens that forms the optical coupling path, It is possible to reduce the occurrence of thermal stress due to the difference in thermal expansion coefficient between the stem, the flat plate, or the adhesive fixing means, and thereby maintain stable optical coupling efficiency.

The third feature of the semiconductor laser module is that the difference in coefficient of thermal expansion between the stem, the tip optical fiber, and the adhesive fixing means is approximately 1×10−' or less, so that the stem and the tip beam are attached to the stem. The optical coupling efficiency can be maintained stably by reducing the occurrence of thermal stress with the adhesive fixing means for adhesively fixing the fiber.

The fourth feature of the semiconductor laser module is that the second
Alternatively, in the semiconductor laser module according to the third feature, the stem is made of a copper-tungsten alloy, the flat plate is made of ceramic or a copper-tungsten alloy, and the adhesive fixing means is made of a low-melting point glass, thereby providing an optical coupling path with an extremely small difference in thermal expansion coefficient. The optical coupling efficiency can be kept stable by reducing the occurrence of thermal stress.

[Example 1] Hereinafter, an example of a semiconductor laser module according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a semiconductor laser module according to this embodiment, and this module is roughly divided into two parts: a semiconductor laser 1 that irradiates laser light is mounted on one end, and a thermionic cooling system that cools the laser 1 is mounted on the other end. a stem 8 connected to the element 9; holding parts 14 and 15 equipped with a focusing rod lens 12 for condensing the emitted light from the semiconductor laser 1;
It is composed of a package 11 that hermetically covers the stem 8 and the holding parts 14 and 15.

The stem 8 is made of a copper-tungsten alloy corresponding to a holding member, and is mounted on a submount 2 made of SiC with high thermal conductivity, and includes a semiconductor laser 1 that emits laser light by applying a current, and a semiconductor laser 1 that emits laser light by applying current. A ball lens 5 for concentrating laser light, a copper-tungsten alloy (or ceramic) flat plate 6 to which the lens 5 is adhesively fixed with a low melting point glass 7, and a monitoring photodiode 3 for monitoring laser light emission. and a temperature detection element 4 for detecting the temperature of the stem 8 are mounted on one side, and the cooling side of a thermionic cooling element 9 is connected to the other side.

Further, this thermionic cooling element 9 has a flange 10 attached to the heat radiation side for attachment to an external heat sink (not shown).

The thermal expansion coefficient of the low melting point glass 7 to which the ball lens 5 is adhesively fixed is 7.0XIO-'10C, and the thermal expansion coefficient of the flat plate 6 is 6.5X10-'/ in the case of copper-tungsten alloy.
''C, in the case of ceramic, it is 6.7xl (r'/'C).The thermal expansion coefficient of the ball lens 5 is 8.7X10-'10C, when the material is BK-7, and when the material is TaF-3. ,7
, 9X10~610C.

The holding parts 14 and 15 also hold a focusing rod lens 12 whose outer peripheral surface is metallized so as to focus the laser beam from the ball lens 5, and input the laser beam from the Wooden lens 12 through the ferrule 15. optical fiber 13
and are laser welded or brazed to the package 11 so as to hold them coaxially.

The positional relationship of the optically coupled optical components is as shown in FIG. 2, with the semiconductor laser 1 and the ball lens 5 disposed on the stem 8. Focusing rod lens 12. The optical fibers 13 are optically coupled in a straight line, and the amount of coupling loss deterioration due to the amount of positional deviation of these optical components on the coupling path differs depending on each component.

As shown in FIG. 3, the relationship between the amount of positional deviation and the amount of deterioration in coupling loss is as follows. Characteristic B due to misalignment of the focusing rod lens 12 with respect to the large semiconductor laser 1; Characteristic C due to misalignment of the optical fiber 13 with respect to the semiconductor laser 1 which has the second largest amount of deterioration; characteristic C due to misalignment of the optical fiber 13 with respect to the semiconductor laser 1; This characteristic has a large tolerance for positional deviation between the semiconductor laser 1 and the ball lens 5 with respect to the focusing rod lens 12.

That is, the relationship between the amount of positional deviation on the coupling path of the optical components in this semiconductor laser module and the amount of deterioration is such that the positional deviation between the semiconductor laser 1 and the ball lens 5, that is, the laser beam condensing means shown in the characteristic A, is the most coupled. It can be seen that this leads to loss deterioration.

The semiconductor laser module according to the prior art described above has a thermal expansion coefficient of 2.65X10-'' for coupling the ball lens and flat plate.
/'C (solder with a Pb to Sn ratio of 60:40) to 2,87xlO-''/'C (solder with a Pb to Sn ratio of 90:10) and a solder that is significantly different from that of the ball lens and flat plate were used. In this case, there is a difference of about 10' in the thermal expansion coefficient, so when a temperature cycle test is performed between -400°C and +85°C, which is the upper and lower storage temperature limit of the semiconductor laser module, due to the difference in the thermal expansion coefficient. Thermal stress is applied to the solder joint, causing strength deterioration and microcracks due to stress fatigue, and the positional shift increases joint loss.

In the semiconductor laser module according to this embodiment, the ball lens 5 and the flat plate 6 are bonded to each other using a low melting point glass (having a thermal expansion coefficient of 7.9X10-'/'
C to 8.7xlO-6/'C), the difference in thermal expansion coefficient is suppressed to 1 x 10-'/'C or less, and the thermal stress is reduced to 1/10-' or less. can do. Therefore, the semiconductor laser module according to this embodiment can reduce the positional deviation between the ball lens 5 and the flat plate 6, and reduce the amount of coupling loss deterioration. Note that the low melting point glass 7 corresponds to an adhesive fixing means for adhesively fixing the ball lens 5 to the flat plate 6.

FIG. 4 is a diagram showing a semiconductor laser module according to another embodiment of the present invention, and is an example in which a tipped optical fiber 17 is used for optical coupling with the semiconductor laser 1. The spherical tip of the spherical optical fiber 17 functions as a condensing means similar to the spherical lens of the embodiment described above to introduce laser light into the interior.

That is, the semiconductor laser module according to this embodiment is roughly divided into a semiconductor laser 1 that emits laser light, as shown in FIG.
．． A stem 8' is equipped with a temperature detection element 4 and a monitoring photodiode 3, and has the tip optical fiber 17 adhesively fixed in a through hole 18 with molded lead glass powder 7'.
Then, the heat dissipation side of the thermionic cooling element 9 in contact with the rear end of the stem 8' is adhesively fixed so as to be connected to an external heat sink (not shown), and the tip optical fiber 17 is inserted into the through hole 19 using molded lead glass. It consists of a package 11 that is adhesively fixed with powder 7'.

The stem 8 is made of copper-tungsten alloy as in the previous embodiment, and the submount 2 is also made of SiC having high thermal conductivity. The package 11 is made of Kovar having a thermal expansion coefficient of 6.2×10-'/'C.

This semiconductor laser module has a tip optical fiber 17.
By passing through the through hole 19 of the package 11 and the through hole 18 of the stem 8' to ensure an optical coupling path with the semiconductor laser 1, the molded lead glass powder 7' is irradiated with YAG laser light and melted. , the fiber 17 is adhesively fixed and the semiconductor laser 1 is hermetically sealed.

Therefore, the semiconductor laser module according to this embodiment has optical fibers 17. Molded lead glass powder 7° and stem 8
Since the difference in coefficient of thermal expansion is suppressed to less than I x 10-'/'C, strength deterioration and minute cracks due to thermal stress fatigue due to the difference in coefficient of thermal expansion are prevented, and increase in coupling loss due to positional deviation is prevented. I can do it. The low melting point glass 7' corresponds to an adhesive fixing means for adhesively fixing the tip optical fiber 17 to the stem 8.

[Effects of the Invention] As described above, in the semiconductor laser module according to the first feature of the present invention, the difference in coefficient of thermal expansion between the holding member, the condensing means, the flat plate, and the adhesive fixing means is approximately 1×10′″4 or less. By forming such a structure, it is possible to reduce the occurrence of thermal stress caused by the difference in the coefficient of thermal expansion of each component and to keep the optical coupling efficiency stable.

The semiconductor laser module according to the second feature includes a stem,
The difference in thermal expansion coefficient between the flat plate and adhesive fixing means is approximately 1×1.
0'' or less, it is possible to reduce the occurrence of thermal stress due to the difference in thermal expansion coefficient of the ball lens, stem, flat plate, or adhesive fixing means that constitute the optical coupling path, and to keep the optical coupling efficiency stable. .

In the semiconductor laser module according to the third feature, the difference in coefficient of thermal expansion between the stem, the optical fiber and the adhesive fixing means is approximately 1×10 −' or less, so that the stem and the optical fiber can be connected to the stem. It is possible to maintain stable optical coupling efficiency by reducing the occurrence of thermal stress with the adhesive fixing means.

Further, in a semiconductor laser module according to a fourth feature, in the semiconductor laser module according to the second or third feature, the stem is made of a copper-tungsten alloy.

The flat plate is made of ceramic or copper-tungsten alloy.

By forming the adhesive fixing means from low-melting glass, it is possible to construct an optical coupling path with an extremely small difference in thermal expansion coefficient, reduce the occurrence of thermal stress, and keep the optical coupling efficiency stable.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a semiconductor laser module according to an embodiment of the present invention, FIG. 2 is a diagram showing the positional relationship of optical coupling paths of the semiconductor laser module, and FIG. 3 is a diagram showing coupling loss due to the amount of deviation in this positional relationship. FIG. 4, which is a diagram for explaining the amount of deterioration, is a diagram showing a semiconductor laser module according to another embodiment of the present invention. 1: Semiconductor laser, 2: Submount, 3. Monitor photodiode, 4: Temperature detection element, 5: Ball lens, 6: Flat plate, 7: Low melting point glass, 8: Stem, 9: Thermionic cooling element, 10 :Flange, 11:Package, 12:
Focusing rod lens, 13: Optical fiber, 14: Holding component, 15; Ferrule, 16; Holding component, 17. Tip optical fiber, 18 and 19: Through hole, 20.
Hole, 7゛: Molded lead glass powder, 8゛ stem.

Claims (4)

[Claims] (1) A holder for holding the semiconductor laser and the focusing means in a semiconductor laser module comprising a semiconductor laser that irradiates laser light and a focusing means that collects the laser light from the semiconductor laser and outputs it to the outside. The difference in thermal expansion coefficient between the member and the adhesive means for bonding the holding member and the light condensing means is 1×
A semiconductor laser module characterized in that the semiconductor laser module is formed to have a diameter of 10^-^4 or less. (2) A stem equipped with a semiconductor laser that irradiates laser light, a ball lens that focuses the laser light from the semiconductor laser, a flat plate on which the ball lens is mounted on the stem, and the flat plate and the ball lens are bonded together. In a semiconductor laser module comprising an adhesive fixing means for fixing the semiconductor laser, the laser beam from the semiconductor laser is focused by a ball lens and outputted to the outside, wherein a difference in thermal expansion coefficient between the stem, the ball lens, the flat plate, and the adhesive fixing means is provided. A semiconductor laser module characterized in that a semiconductor laser module is formed to have a size of approximately 1×10^-^4 or less. (3) A semiconductor laser that emits laser light, a tipped optical fiber that collects the laser beam from the semiconductor laser and outputs it to the outside, and the semiconductor laser is mounted and the tipped optical fiber is adhesively fixed by adhesive fixing means. 1. A semiconductor laser module comprising a stem, wherein the difference in coefficient of thermal expansion between the stem, the tip optical fiber, and the adhesive fixing means is approximately 1×10^-^4 or less. (4) In the semiconductor laser module according to claim 2 or 3, the stem is formed of a copper-tungsten alloy, the flat plate is formed of ceramic or a copper-tungsten alloy, and the adhesive fixing means is formed of low-melting glass. A semiconductor laser module characterized by: