JP2003035843A - Method for manufacturing metal coated optical fiber, sleeved metal coated optical fiber and optical semiconductor module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a metal coated optical fiber, a sleeved metal coated optical fiber and an optical semiconductor module reducing man hours of core adjusting operation of an LD(laser diode) chip and the optical fiber, preventing the fiber from moving caused by heat of YAG(yttrium-aluminum- garnet) welding, improving the yield and improving the connection efficiency. SOLUTION: The metal coated optical fiber 10 is manufactured by a protective coating layer releasing step f1 to release the protective coating layer of the optical fiber so as to unsheathe the bare fiber, a vertically cutting off step f2 to dissect and cut off an end part of the bare fiber at right angles to the optical axis so as to produce a vertically dissected surface, an AR(antireflection) coating step f3 to impart the AR coating with >=0.1% reflectance to the surface of the vertically dissected surface, a high melting metal oxide layer forming step f4 to form the first chromium oxide layer on the outer periphery of the bare fiber, a high melting metal layer forming step f5 to form the second chromium layer on the outer periphery thereof and a low melting metal layer forming step f6 to form the third metal layer on the outer periphery thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-coated optical fiber, a sleeved optical fiber, and a method for manufacturing an optical semiconductor module. More specifically, a method for manufacturing a metal-coated optical fiber in which a metal coating is applied to the outer periphery of a bare fiber of an optical fiber, and an AR coating is applied to a cut end surface of the bare fiber, a metal-coated optical fiber with a sleeve, and an optical semiconductor module Regarding

[0002]

2. Description of the Related Art As a conventional optical semiconductor module, a pigtail type LD with an optical fiber for optically coupling a laser diode (hereinafter abbreviated as LD) and an optical fiber
There is a module (hereinafter abbreviated as LD module). The LD module performs optical coupling between an LD and an optical fiber via a lens and an isolator, and is used as a signal light source for optical fiber communication, an optical amplifier light source, and the like.
Further, as a technique related to the structure of the optical fiber incorporated in the LD module, there is a structure described in JP-A-12-121886. That is, the ferrule 12
Is composed of a zirconia member (not shown) in which the optical fiber 10 is internally fixed and fixed, and a metal member in which the optical fiber coating 11 is fixed. , And again 0
In the 018 step, "the tip of the optical fiber 10 exposed at the tip of the ferrule 12 is processed obliquely (not shown)."

FIG. 13 shows an example of the structure of a conventional LD module. The LD module 50 mounts the LD chip 41 and the collimating lens 42, which is the first lens, on a single Peltier element-equipped substrate 43.
The collimated light is made into a collimated light by adjusting the optical axis of the LD case, and the LD case 44 is sealed by the collimator lens 42 and hermetically sealed by injecting an inert gas.
And the focal lens 46 are arranged on the optical axis, and the end face of the ferrule 47 with an optical fiber is moved to the focal point of the focal lens 46 and moved forward and backward in the optical axis direction to rotate the optical coupling efficiency to the maximum position. It was manufactured by fixing it to 48 adapters 49 by YAG laser welding or the like.

[0004]

However, the above-mentioned prior art has the following problems. That is, in the LD module, in order to stably drive the LD, the deterioration of the emitting end face and the lens face of the LD is prevented by hermetically sealing with an inert gas or the like, and at the same time, the end face of the optical fiber, the lens face or the optical fiber line. It was necessary to reduce the reflected light reflected from the laser and minimize the deterioration of the S / N ratio due to the amplification of the returned light in the LD. Further, in the above-mentioned conventional technology, many man-hours for assembling and aligning,
The dimensional accuracy of the ferrule with an optical fiber is required to reduce and stabilize the variation in the output power from the optical fiber between pigtail type LDs with an optical fiber, which has been a cause of cost improvement. In particular, both the accuracy of the outer diameter of the ferrule and the eccentricity of the fiber core with respect to the outer diameter of the ferrule require submicron accuracy, and in order to further improve the incidence efficiency on the fiber, the ferrule end surface is mirror-polished and the ferrule outer circumference is improved. On the other hand, it was necessary to align the center of the fiber within 2 μm. In addition, the ferrule and the fiber are bonded and fixed with a polymer resin adhesive.If YAG welding of the adapter and ferrule is performed after the alignment of the assembly, the fiber easily moves due to the temperature rise due to the welding heat and the incidence from the LD This causes an increase in power variation, resulting in poor yield and cost increase. Therefore, in order to provide low-cost products that have long-term stability with little variation between LD modules, in order to improve the accuracy of component parts, the component structure that facilitates alignment work, and fiber fixing and sealing processes It was necessary to have a structure and manufacturing method that prevent the movement of the fiber due to the heat generated in the.

The present invention has been made in order to solve various problems of the above-mentioned prior art, and it is possible to reduce the number of assembling steps and improve the yield by reducing the number of steps for aligning the LD chip and the optical fiber. It is possible to provide inexpensive and high-precision parts that replace ferrules with optical fiber, prevent movement of fiber due to YAG welding heat, reduce variations between LD modules, improve coupling efficiency, and high reliability. Another object of the present invention is to provide a method for manufacturing a metal-coated optical fiber, a metal-coated optical fiber with a protective resin, a metal-coated optical fiber with a sleeve, and an optical semiconductor module, which can be reduced in cost.

[0006]

As a first aspect, the present invention is a method for manufacturing a metal-coated optical fiber used in an optical semiconductor module for optically coupling a laser diode and an optical fiber, which is a laser diode emission light. A step of peeling off the protective coating layer on the surface of the optical fiber on the side opposite to the axial surface to expose the bare fiber; and cleaving the exposed bare fiber end portion at 90 ° flat with respect to the optical axis. A vertical cutting step of cutting to provide a vertical cleavage surface; and an AR coating step of applying an AR (Anti-reflection) coating having a reflectance of 0.1% or more on the surface of the vertical cleavage surface; A refractory metal oxide layer made of oxide of chromium or titanium having a higher melting point than the solderable low melting point metal layer of the third layer is formed as the first layer on the outer periphery of the exposed bare fiber. A step of forming a melting point metal oxide layer; and, as a second layer on the outer periphery of the high melting point metal oxide layer, a high melting point metal layer made of chromium or titanium having a higher melting point than the solderable low melting point metal layer of the third layer. Forming a high melting point metal layer; and forming a solderable low melting point metal layer made of nickel, gold, a nickel-gold alloy, or a gold-based alloy as a third layer on the outer periphery of the high melting point metal layer. Melting point metal layer forming step; and a method for producing a metal-coated optical fiber, comprising: producing a metal-coated optical fiber.

According to the method of manufacturing a metal-coated optical fiber of the first aspect, a metal-coated optical fiber having excellent characteristics can be efficiently manufactured by using the various steps described above. Further, in the metal-coated optical fiber obtained by the present invention, the refractory metal oxide layer of the first layer contributes to the improvement of the adhesion strength with the inorganic optical fiber, and the good adhesion with the optical fiber (quartz glass). Can be obtained.
Further, the refractory metal oxide layer of the first layer and the refractory metal layer of the second layer contribute as a solder anticorrosion layer. Furthermore, the third layer is a layer that enables soldering at low temperatures. Since the low melting point metal of the third layer has a lower melting point than the high melting point metals of the first and second layers, soldering at low temperature is possible. Becomes For this reason, it is preferable that the metal-coated optical fiber and the metal sleeve for sealing are bonded and fixed, and that the metal-coated optical fiber and the metal-coated optical fiber and the pigtail type LD with an optical fiber are fixed to the mounting substrate so that they are compatible with the solder. Further, by providing the above-mentioned metal layers, the strength of the optical fiber itself is also affected. Although the strength of the optical fiber is extremely reduced when the protective coating is peeled off to expose the bare fiber, the strength of the bare fiber can be increased by forming the metal thin film layer. In addition, a vertical cleavage surface is provided at the end of the exposed bare fiber by cleavage at 90 ° to the optical axis, and an AR having a reflectance of 0.1% or more is provided on the flat surface of the vertical cleavage surface. Coating (hereinafter,
Since it is abbreviated as AR coat), the metal-coated optical fiber can secure a return loss of 30 dB or more. Therefore, the metal-coated optical fiber obtained by the manufacturing method of the present aspect is used as a light source for optical fiber communication, and an optical fiber in which the LD and the optical fiber are optically coupled in space through a lens and an optical isolator. Pigtail type LD with
It is suitable as an optical fiber to be mounted on a module for use.

As a second aspect of the present invention, following the vertical cutting step; the vertical cleavage surface is thermally polished by a flame, an electron beam or a high power laser to remove residual scratches, and the thermally polished vertical cleavage surface is obtained. And a heat-polishing step as described above is added. In the manufacturing method according to the second aspect, residual scratches on the vertical cleavage surface can be removed by adding a thermal polishing step using a flame, an electron beam, etc., and residual scratches on the cut surface due to cleavage of the optical fiber grow. It is possible to prevent cracking.

As a third aspect of the present invention, in the present invention, following the AR coating step, the AR coating vertical cleavage plane or A
In the method for producing a metal-coated optical fiber, an R-coat heat-polishing vertical protective surface is applied with a UV-curable resin to cure and form a protective resin. By using the manufacturing method of the third aspect, the vertical cleavage surface can be protected by the protective resin until necessary. When it is not necessary to protect the vertical cleavage surface by incorporating it into an optical semiconductor module or the like, the protective resin may be removed before use. It is preferable to form the protective resin before forming the refractory metal oxide layer, the refractory metal layer and the like, because the metal oxide layer and the like are not formed on the AR coat vertical cleavage surface.

As a fourth aspect, the present invention provides the step of forming the refractory metal oxide layer; subsequently, at the boundary between the refractory metal oxide layer of the first layer and the refractory metal layer of the second layer, A mixed layer forming step of forming a mixed layer of these refractory metal oxide and refractory metal is added. In the manufacturing method of the fourth aspect, by forming a mixed layer of refractory metal oxide and refractory metal at the boundary between the refractory metal oxide layer of the first layer and the refractory metal layer of the second layer, A solder anticorrosion layer having an increased adhesion strength between the first layer and the second layer can be obtained.

As a fifth aspect, the present invention provides the step of forming the refractory metal layer; followed by the step of forming the refractory metal layer at the boundary between the second refractory metal layer and the third refractory metal layer. And an alloy layer forming step of forming an alloy layer of a low melting point metal; 5th above
In the method for manufacturing a metal-coated optical fiber according to the aspect, since the alloy layer of these two layers is formed at the boundary between the high melting point metal layer of the second layer and the low melting point metal layer of the third layer, soldering of the low melting point metal layer is performed. It is possible to prevent poor adhesion of the high melting point metal layer to the solder due to cracking. In addition, even if the third layer low melting point metal gets into the solder, the strong bonding force between the alloy layer and the solder layer does not cause the sheath of the fiber to slip out, and it is possible to prevent the movement of the position of the fiber tip. It is possible to improve the yield by eliminating the deterioration of characteristics after YAG welding of the fiber to the case.

As a sixth aspect, the present invention provides first, second,
The metal-coated optical fiber or the metal-coated optical fiber with a protective resin obtained by the manufacturing method according to the third, fourth, or fifth aspect is inserted into a metal sleeve for sealing, and the sleeve and the metal-coated optical fiber are hermetically sealed with solder. And a method for manufacturing a metal-coated optical fiber with a sleeve. In the method for manufacturing a metal-coated optical fiber with a sleeve of the sixth aspect, since the sealing metal sleeve and the metal-coated optical fiber are hermetically sealed with solder,
The obtained metal-coated optical fiber with a sleeve can be preferably used as a component for an optical semiconductor module. The solder may be ordinary solder, but high temperature solder is preferable.

As a seventh aspect, the present invention is a method for manufacturing an optical semiconductor module used in a light source for optical fiber communication, in which a laser diode and an optical fiber are optically coupled in space through a lens, an optical isolator and the like. A metal sleeve for sealing, in which the metal-coated optical fiber portion of the metal-coated optical fiber with a sleeve obtained by the manufacturing method according to the seventh aspect is directly fixed to a substrate by soldering, and the metal-coated optical fiber is internally provided. Is directly fixed to one end of the case by high temperature soldering or YAG laser welding,
When a metal resin coated optical fiber with a protective resin is used, the protective resin is finally removed, which is a method of manufacturing an optical semiconductor module. In the method for manufacturing an optical semiconductor module according to the seventh aspect, the metal-coated optical fiber with a sleeve is used for manufacturing an optical semiconductor module, and an LD case side surface distant from a fixing point on a Peltier element-equipped substrate on the optical fiber end face side. Since the sealing metal sleeve can be directly fixed to the position, an optical semiconductor module having excellent characteristics can be obtained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The contents of the present invention will be described below in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this. FIG. 1 is a chart showing an example of a method for producing a metal-coated optical fiber of the present invention. FIG. 2 is an electron micrograph showing the change in the shape of the fiber cleaved surface before and after thermal polishing. FIG. 2 (a) shows a state after the fiber tip angle of 0 ° cleavage and before thermal polishing, and FIG. 2 (b).
Shows a state where flame thermal polishing was performed as thermal polishing, and FIG. 6C shows a state where electron beam polishing was performed as thermal polishing. 3A and 3B are schematic diagrams showing how to provide various metal layers by sputtering in the method for producing a metal-coated optical fiber of the present invention. FIG. 3A is a conceptual diagram thereof and FIG. 3B is obtained. It is sectional drawing which shows various metal layers. Figure 4
FIG. 3A is a schematic view showing an example of a metal-coated optical fiber obtained by the manufacturing method of the present invention. FIG. 1A is a front view, FIG. 1B is a right side view, and FIG. A in Figure (a)
It is a sectional view of a portion-a. FIG. 5 is a front view showing an example of a metal resin coated optical fiber with a protective resin obtained by the manufacturing method of the present invention. FIG. 6 is a longitudinal sectional view showing an example of an optical fiber with a sleeve obtained by the manufacturing method of the present invention. FIG. 7 is a chart showing the relationship between the fiber tip angle and the return loss. FIG. 8 is a chart showing the return loss on the LD light incident surface. FIG. 9 is a chart comparing adhesion strengths due to differences in material and film thickness of the metal film. Figure 10
FIG. 3 is a graph showing variations in adhesion strength (Example 1: with high melting point oxide layer). FIG. 11 is a graph showing variations in adhesion strength (Comparative Example 1: No refractory oxide layer). FIG. 12 is a configuration diagram of an optical semiconductor module (module for pigtail type LD with optical fiber) obtained by the manufacturing method of the present invention.

In these figures, 1 is a bare fiber, 1
m is a metal-coated bare fiber portion, 2 is a protective coating layer, 3 is an optical fiber element wire, 4 is a refractory metal oxide layer (chromium oxide), 4'is a mixed layer, and 5 is a refractory metal layer (chrome). ,
5'is an alloy layer, 6 is a solderable low-melting metal layer (gold), 7 is an AR-coated vertical cleavage surface (AR-coated thermal polishing vertical cleavage surface), 10 is a metal-coated optical fiber, 10j is a metal coating with a protective resin. Optical fiber, 11 is a metal sleeve for sealing, 12 is a solder sealing portion, 20 is an optical fiber with a sleeve, 21 is an LD chip, 22 is a focal lens, 23 is an optical isolator, and 24 is a substrate (a substrate with a Peltier element). ,
25 is a case, 26 is an adapter, 27 is a high temperature soldering part, 30 is an optical semiconductor module (module for optical fiber pigtail type LD), j is a protective resin, and r
Is an AR coat.

-First Embodiment- (Method of Manufacturing Metal-Coated Optical Fiber) An example of the method of manufacturing the metal-coated optical fiber of the present invention will be described with reference to the chart of FIG. In the manufacturing process of the metal-coated optical fiber, first, the protective coating layer peeling step f1 in which the protective coating layer on the surface of the optical fiber opposite to the laser diode emission optical axis surface is peeled to expose the bare fiber;
And a vertical cutting step f2 in which the exposed end portion of the bare fiber is cut by cleavage at a flat angle of 90 ° with respect to the optical axis to provide a vertical cleavage plane; and a reflectance of 0.
AR coating step f3 of applying an AR (Anti-reflection) coating of 1% or more; and a melting point from a solderable low melting point metal layer of a third layer as a first layer on the outer periphery of the exposed bare fiber. High-melting-point metal oxide layer forming step f4 for forming a high-melting-point metal oxide layer made of a high-melting-point chromium oxide or titanium oxide; and as a second layer on the outer periphery of the high-melting point metal oxide layer. Refractory metal layer forming step f5 for forming a refractory metal layer of chromium or titanium having a melting point higher than that of the three solderable low melting point metal layers;
A low melting point metal layer forming step f6 for forming a solderable low melting point metal layer made of nickel, gold, a nickel-gold alloy or a gold-based alloy as a third layer on the outer periphery of the high melting point metal layer; To produce a metal-coated optical fiber. Subsequent to the oblique cutting step f2; a thermal polishing step g1; in which the oblique cleavage surface is thermally polished by a flame, an electron beam, or a high power laser to remove residual scratches, and a thermal polishing oblique cleavage surface is formed. Good. Also, vertical cutting step f
2; or the thermal polishing step g1; a protective resin forming step g2 of applying and curing an ultraviolet curable resin on the vertical cleavage surface or the thermal polishing vertical cleavage surface to form a protective resin may be added. (In this case, it becomes a metal-coated optical fiber with a protective resin) Further, at the boundary between the refractory metal oxide layer of the first layer and the refractory metal layer of the second layer, these refractory metal oxide and refractory metal The mixed layer forming step g3; for forming the mixed layer may be added. Further, an alloy layer forming step g4 for forming an alloy layer of the high melting point metal and the low melting point metal may be added to the boundary between the high melting point metal layer of the second layer and the low melting point metal layer of the third layer.

-Second Embodiment- (Specific Example of Manufacturing Method of Metal Coated Optical Fiber) Specific Example of Manufacturing Method of Metal Coated Optical Fiber FIG.
~ It demonstrates using FIG. First, the bare optical fiber 1 was exposed by peeling the protective coating layer 2 on the surface of the optical fiber on the side facing the LD emission optical axis surface using the optical fiber strand 3. (Protective coating layer peeling step f1) Next, the surface of the bare fiber 1 at the tip portion facing the LD output optical axis surface of the bare fiber exposed portion is scratched with a diamond cutter, and the exposed end portion of the bare fiber 2 is a mirror surface. The flat vertical cleavage plane was formed. (Vertical cutting step f2) As a cutting method for obtaining a vertical cleavage plane in an optical fiber (bare fiber), a very hard blade, for example, a diamond cutter blade is linearly driven in a direction perpendicular to the optical fiber axis to form a side surface of the optical fiber. After making a small initial scratch on one end of the fiber, bending stress is applied to the optical fiber so that this scratch is outside the bend, and the fiber is cleaved from the initial scratch to obtain a vertical end face. In this cutting method, the mirror surface state of the cut end surface can be easily obtained by scratching and cleaving one end of the side surface of the fiber, so the conventional processes such as ferrule insertion / bonding / end surface polishing of the optical fiber strand are reduced. it can. Next, the edge portion of the vertical cleavage plane 7 was subjected to thermal polishing with a flame, an electron beam, a high power laser or the like to remove scratches on the end face of the fiber to form a thermal polishing vertical cleavage plane (thermal polishing step g1). The reason for this thermal polishing is that scratches (cleavage scratches) on the edge during cleavage made with a diamond cutter may remain on the edge of the end face even after cleavage, and cracks may grow from these scratches. This is because the scratches can be removed by polishing and long-term reliability can be obtained. FIG. 2 shows electron microscope photographs of the cleaved surface of the fiber tip before and after thermal polishing. As is clear from this photograph, it can be seen that the thermal cleavage cleanly removes the cleavage scratches. Next, an AR coat r was formed on the heat-polished vertical cleavage surface to form an AR coat vertical cleavage surface 7 (AR coating step f3). The AR coat r was formed by alternately stacking two kinds of substances (SiO ₂ and TiO ₂ ) on the flat vertical cleavage plane at a thickness of ¼ wavelength to form a four-layer film. Next, only on the side surface of the bare fiber 1, the first-layer high-melting-point metal oxide layer 4, the second-layer high-melting-point metal layer 5, the third-layer low-melting-point metal layer 6, the mixed layer 4 ′, and the alloy. Layers 5'are sequentially formed. At this time, in order to prevent these metal thin film layers from being formed on the AR-coated vertical cleavage surface 7 at the tip of the bare fiber 1, an ultraviolet curing resin is applied and cured in advance on this portion to form a protective resin. j was formed (protective resin forming step g2). Then, a refractory metal oxide layer 4 was formed as a first layer on the exposed outer circumference of the bare fiber 1 by sputtering (refractory metal oxide layer forming step f4).
As the oxide layer 4, chromium oxide (CrO2) was used. Next, a refractory metal layer 5 was formed as a second layer on the outer periphery of the oxide layer 4 by sputtering (refractory metal layer forming step f5). As the refractory metal layer 5,
Chromium (Cr) was used. Next, the refractory metal layer 5
A solderable low-melting point metal layer 6 was formed as a third layer on the outer periphery of by sputtering (low-melting point metal layer forming step f6). As the low melting point metal layer 6, gold (Au) which can be soldered at a low temperature was used. As shown in the conceptual diagram of FIG.
A mixed layer 4'of these metals is formed at the boundary between the oxide layer 4 and the refractory metal layer 5 by sputtering chromium 5 and gold 6 successively for a predetermined time and by a predetermined amount. At the boundary between the layer 5 and the low melting point metal layer 6, an alloy layer 5 ′ of these metals is formed. In addition, instead of sputtering, electroplating may be used to form each of the metal layers. As described above, the metal-coated optical fiber 10j with a protective resin shown in FIG. 5 is obtained. Further, by removing the protective resin j from the metal-coated optical fiber 10j with the protective resin, the metal-coated optical fiber 10 shown in FIG. 4 can be manufactured.

In the metal-coated optical fiber 10 obtained by the manufacturing method of the present invention, metal oxide having a melting point higher than that of the low melting point metal 6 of the third layer is formed on the outer peripheral surface of the bare fiber 1 from which the protective coating 2 of the optical fiber is removed. After forming a first layer of chromium oxide or titanium oxide as the material layer 4 to strengthen the binding force between the surface of the bare fiber 1 and the metal oxide layer 4, a refractory metal layer 5 of chromium or titanium is formed as the second layer. Has been formed. Furthermore, by forming a mixed layer 4 ′ of the refractory metal oxide 4 and the refractory metal 5 at the boundary between the first layer and the second layer, the bonding force between the two layers can be increased, which allows soldering. Prevent me. Further, as the third layer, a solderable low melting point metal layer 6 of nickel, gold, nickel-gold alloy or gold alloy having good solder wettability and having a lower melting point than the high melting point metals of the first and second layers is formed. To be done. Further, by forming an alloy layer 5'in which the metals of both layers are mixed at the boundary between the second layer and the third layer, the low melting point metal 6 of the third layer is soldered at the time of manufacturing an optical semiconductor module. Even if it is broken, since the binding force between the alloy layer 5 ′ and the low melting point metal layer 6 is strong, the sheath of the fiber does not come off, the movement of the position of the fiber tip can be prevented, and the characteristic deterioration after soldering or welding. Will be eliminated and the yield can be improved. The various metal layers formed on the surface of the bare fiber enable the optical fiber to be fixed and sealed to the mounting board of the pigtail type LD with the optical fiber by high temperature soldering, and to improve the strength of the bare fiber. It is formed for this purpose. If a single metal layer with a thickness of 1 μm or less is formed on the bare fiber, the metal layer will be broken by the solder during solder welding, and the fiber and solder will come into contact with each other at the interface, resulting in a weak bonding force at the interface and a sheath. It is easy to get out,
The fiber tip becomes easy to move.

-Regarding the reason why the AR-coated vertical cleavage surface is used-When the end surface of the optical fiber facing the LD emission surface is perpendicular to the optical axis, the reflected return light becomes large. Figure 7
Shows a table of the angle of the inclined surface of the optical fiber tip with respect to the optical axis (optical fiber tip angle) and the return loss when laser light is incident on the optical fiber. It can be seen that when the tip angle of the optical fiber with respect to the optical axis is small, the reflected return light becomes large, and when the tip angle is large, the incidence efficiency becomes poor. In addition,
In a transmission system of the gigabit order, the return loss is
It should be 50 dB or more.

FIG. 8 shows a chart of the return loss on the LD light incident surface. FIG. 7A is a diagram showing a state of noise generated on a signal of 150 Mbps generated by the reflected return light to the LD. When the return loss is 35 dB, noise of gigahertz order is generated in each case. In addition, FIG.
It shows the noise generation state of the same signal when the return loss is 50 dB or more, and the gigahertz order noise disappears. When an isolator is inserted in the middle, if the return loss from the fiber passes through the isolator and the return loss of 40 dB or more is secured, a pulse with small noise as shown in FIG. The combined return loss of is 55 dB. In addition, the performance of the isolator is 25
In dB, the return loss from the fiber should be 25 dB or more. As shown in the above chart 7, when the end face of the optical fiber facing the LD emission face is perpendicular to the optical axis (fiber tip angle 0 °), the specified return loss cannot be obtained. Therefore, the AR coat r having a reflectance of 0.1% or more is formed on the tip of the optical fiber (vertical cleavage plane) to form the AR coat vertical cleavage plane 7. As a result, the return loss becomes 30 dB or more, and the specified return loss can be secured.

-Third Embodiment- (Example of Comparison of Adhesion Strength Due to Difference in Material and Thickness of Metal Film) (with Comparative Example) FIG. 9 shows adhesion strength due to difference in material and thickness of metal film. 2 is a table comparing the adhesion strengths when the metal layers are provided on the outer circumference of the optical fiber (bare fiber) with different metal materials and film thicknesses of Example 1 and Comparative Examples 1 to 3 by sputtering. . The adhesion strength is obtained by measuring the adhesion strength (N) after soldering the metal-coated optical fibers of Example 1 and Comparative Examples 1 to 3 to the wiring pattern using high temperature solder. Further, FIG. 10 shows the adhesion strength distribution of the metal-coated optical fiber of Example 1. Further, FIG. 11 shows a graph of the adhesion strength distribution of the metal-coated optical fiber of Comparative Example 1. From these charts and graphs, it can be said that the conditions under which good adhesion strength can be stably obtained are the material and film thickness of the metal film of Example 1. Further comparison results are as follows. Example 1: Due to the chromium oxide layer, the average adhesion strength of 24.5 N was stably obtained. Comparative Example 1: Since there was no chromium oxide layer in the first layer, the adhesive strength varied. Comparative Example 2: A little inferior to Comparative Example 1 due to the absence of 1.2 layers. Comparative Example 3: The average adhesion strength was as low as 10.0 N, and the sheath of the fiber was removed.

-Fourth Embodiment- (Method for Manufacturing Optical Fiber with Sleeve) An example of a method for manufacturing the optical fiber with sleeve according to the present invention will be described with reference to FIG. The metal sleeve 1 for sealing the metal-coated optical fiber 10 obtained in Example 1 above.
1 and the end of the sleeve was sealed with high temperature solder, and a solder sealing portion 12 was provided to manufacture a sleeved optical fiber 20. This optical fiber with a sleeve can be preferably used for an optical semiconductor module. Usually, the core eccentricity with respect to the outer diameter of the optical fiber is about 0.2 μm, and even if the metal layer is provided with a thickness of 1 μm, the core eccentricity is 0.
Since it is within 5 μm, the core eccentricity of the optical fiber itself is maintained, the optical axis alignment is completed in a short time, and the cost can be reduced. The conventionally used ferrule with an optical fiber is a composite component, and the core eccentricity increases due to the eccentricity of the fiber and the ferrule, so a highly accurate and expensive ferrule is required.

-Fifth Embodiment- (Method for Manufacturing Optical Semiconductor Module) A method for manufacturing an optical semiconductor module (module for pigtail type LD with optical fiber) of the present invention will be described with reference to FIG. In the optical semiconductor module 30 of the present invention, the LD chip 21 and the metal-coated optical fiber 10 which is optically coupled to the LD chip 21 and internally transmits the laser light.
And a substrate (substrate with Peltier element) 24 on which the LD chip 21 is mounted, and a solder sealing portion 12 of the optical fiber 20 with a sleeve shown in FIG. 6 mounted on the substrate 24 together with the LD chip 21 and sealed. , A focusing lens 22 for optically coupling the metal-coated optical fiber 10 inserted in the metal sleeve 11, an optical isolator 23 installed between the lens 22 and the metal-coated optical fiber 10, and a substrate 24.
And a case 25 for storing the. In the manufacture of the optical semiconductor module, the metal sleeve 11 is welded to the adapter 26 installed on the wall surface of the case 25. Also
The metal-coated bare fiber portion of the tip portion of the metal-coated optical fiber 10 facing the emission optical axis surface of the LD chip 21 is aligned at a position where the optical coupling rate is maximum, and high-temperature solder is used.
It was directly fixed to the substrate 24 by the high temperature soldering portion 27. Further, the sealing metal sleeve 11 is provided at a position of the fiber which is separated from the high temperature soldering portion 27 of the metal coated optical fiber 10 to the substrate 24. Furthermore, the end surface of the sleeve on the LD side and the surface of the fiber provided with the metal layer were fixed with high temperature solder.
As the high temperature solder, gold-20% tin, or 10%
Tin-90% lead solder was used. As a result, the fixing position of the fiber does not shift due to heat generated during welding between the sealing metal sleeve 11 and the adapter 26 installed on the wall surface of the case 25, and the same characteristics as those at the time of alignment can be obtained.
The variation between pigtail type LDs was reduced and the yield was improved. More specifically, the LD chip 21
Since various metal layers are formed on the surface of the bare fiber 1 at the tip portion of the metal-coated optical fiber 10 which faces the emission optical axis surface of, the substrate with the Peltier element is aligned at the position where the optical coupling rate is maximum. It was possible to fix directly to No. 24 with high temperature solder. As a result, since the sealing metal sleeve 11 can be provided at the position of the fiber away from the high temperature soldering portion 27, by fixing between the LD chip 21 side sleeve end surface and the fiber surface provided with the metal layer with high temperature solder, Due to the heat generated during welding between the metal sleeve 11 and the adapter 26 installed on the wall surface of the case 25, the fixed position of the fiber does not shift, and the same characteristics as at the time of alignment can be obtained, and variations between pigtail type LDs can be obtained. It was reduced and the yield was improved. In addition, the core eccentricity to the outer diameter of the optical fiber is about 0.2 μm, and even if the metal layer is provided with a thickness of 1 μm, the core eccentricity is less than 0.5 μm, so the optical axis alignment can be done in a short time, and the cost is low. Down is now possible. When a single metal layer with a thickness of 1 μm or less is formed on the bare fiber, the metal layer gets stuck in the solder during soldering, and the fiber and solder come into contact with each other at the interface. And the position of the fiber tip becomes easy to move. In the above embodiment, in the method of manufacturing a pigtail type LD with an optical fiber that optically couples the LD and the optical fiber with a lens and an optical isolator, an example in which the metal-coated optical fiber of the present invention is used as the optical fiber is described. However, the usage of the metal-coated optical fiber is not limited to this. That is, a pigtail type LD with an optical fiber that has both an LD and a photodiode as a semiconductor element.
Also, since the same manufacturing method as that of the above-described embodiment can be applied to the manufacturing method of the coupling optical system having the different number of lenses, the same effect can be obtained in these cases.

[0024]

According to the manufacturing method of the present invention, in the LD module for optically coupling the LD and the optical fiber, the protective coating layer on the surface of the optical fiber on the side facing the LD emission optical axis surface is peeled off and By forming the oxide layer of the high melting point metal of the first layer as the bare fiber outer peripheral surface contact layer, forming the high melting point metal layer as the second layer, and then forming the solderable low melting point metal as the third layer. The strength of the optical fiber strand can be increased, the adhesion is excellent, and soldering can be performed. As the refractory metal of the first layer and the second layer, since chromium or titanium having a higher melting point than the soldering metal layer of the third layer is used, the refractory metal oxide layer of the first layer is an inorganic material The adhesion strength with the fiber was improved, and the second refractory metal layer had an effect as a solder anticorrosion layer. In the refractory metal oxide layer of the first layer and the refractory metal layer of the second layer, the boundary between the first layer and the second layer is formed by mixing refractory metal oxide and refractory metal. It has become possible to increase the adhesion strength between layers. The low melting point metal of the third layer, nickel having a lower melting point than the high melting point metal of the first layer and the second layer,
It became possible to solder at low temperature by using gold or the like. Further, the boundary between the low melting point metal layer of the third layer and the high melting point metal layer of the second layer is formed by forming an alloy layer of these two layers so that There was an effect of preventing poor adhesion of the two high melting point metal layers to the solder. Therefore, by forming the above-mentioned various metal layers, it is possible to prevent the occurrence of the sheath omission phenomenon due to the metal layer being entangled in the solder during soldering and the fiber and the solder contacting each other at the interface. It was Further, the exposed bare fiber end can be cleaved by 90 ° flat with respect to the optical axis to obtain a mirror state of the end face, and by further applying an AR coat having a reflectance of 0.1% or more to the vertical cleaved face, Since it is possible to achieve a good return loss of 30 dB or more, it is not necessary to insert the ferrule of the optical fiber strand, adhere to it, and form the tip by polishing the end face, which reduces the number of processing steps and reduces the cost of parts. It has become possible. Further, by removing residual scratches on the cut surface due to the cleavage of the optical fiber by thermal polishing, for example, flame, electron beam, etc., it is possible to prevent crack generation due to the growth of residual scratches, and a long-term reliable LD module can be obtained. It became so. Further, by inserting the metal-coated optical fiber into a sealing metal sleeve and hermetically sealing the sleeve and the metal-coated optical fiber with solder, a sleeved optical fiber having excellent characteristics can be obtained.
In addition, in the LD module, the metal sleeve for sealing can be welded and fixed at the position of the LD case away from the fixing point to the substrate with Peltier element on the end face side of the optical fiber. The sleeve can be hermetically sealed by high-temperature solder between the end surface of the LD side sleeve and the fiber surface provided with the metal layer. Therefore, in the method of manufacturing an LD module, by using the metal-coated optical fiber as an optical fiber to be mounted on the LD module, it is possible to reduce the processing man-hours and the number of parts of the entire device, thereby reducing the cost of the LD module. And improved reliability can now be achieved. Therefore, the present invention is extremely effective in contributing to the industry.

[Brief description of drawings]

FIG. 1 is a chart showing an example of a method for producing a metal-coated optical fiber of the present invention.

FIG. 2 is an electron micrograph showing a change in the shape of the cleaved surface of the fiber before and after thermal polishing, where FIG. 2 (a) shows the state after the fiber tip angle 0 ° cleavage and before thermal polishing, and FIG. Flame thermal polishing is performed as polishing, and FIG. 6C shows an electron beam polishing as thermal polishing.

FIG. 3 is a schematic view showing how to provide various metal layers by sputtering in the method for producing a metal-coated optical fiber according to the present invention. FIG. 3 (a) is a conceptual diagram and FIG. 3 (b).
FIG. 4 is a cross-sectional view of various obtained metal layers.

FIG. 4 is a schematic view showing an example of a metal-coated optical fiber obtained by the manufacturing method of the present invention, where FIG. 4 (a) is a front view, FIG. 4 (b) is a right side view, and FIG. FIG. 4B is a sectional view of a portion aa in FIG.

FIG. 5 is a front view showing an example of a metal resin coated optical fiber with a protective resin obtained by the manufacturing method of the present invention.

FIG. 6 is a vertical cross-sectional view showing an example of a metal-coated optical fiber with a sleeve obtained by the manufacturing method of the present invention.

FIG. 7 is a chart showing the relationship between the fiber tip angle and the return loss.

FIG. 8 is a chart showing the return loss on the LD light incident surface.

FIG. 9 is a chart comparing adhesion strengths due to differences in metal film material and film thickness.

FIG. 10 is a graph showing variations in adhesion strength (Example 1: with refractory oxide layer).

FIG. 11 is a graph showing variations in adhesion strength (Comparative Example 1: no refractory oxide layer).

FIG. 12 is a configuration diagram of an optical semiconductor module (module for pigtail type LD with optical fiber) obtained by the manufacturing method of the present invention.

FIG. 13 is a structural example of an LD module obtained by a conventional manufacturing method.

[Explanation of symbols]

1 Bare fiber 1 m Metal coat Bare fiber part 2 Protective coating layer 3 Optical fiber element wire 4 Refractory metal oxide layer (chromium oxide) 4'Mixed layer 5 Refractory metal layer (chromium) 5'Alloy layer 6 Solderable Low melting point metal layer (gold) 7 AR coating vertical cleavage surface (vertical cleavage surface) 10 metal coating optical fiber 10j metal coating optical fiber with protective resin 11 sealing metal sleeve 12 solder sealing portion 20 sleeve optical fiber 21 LD chip 22 Focusing Lens 23 Optical Isolator 24 Substrate (Substrate with Peltier Element) 25 Case 26 Adapter 27 High Temperature Solder Section 30 Optical Semiconductor Module (Module for Pigtail Type LD with Optical Fiber) j Protective Resin r AR Coating (Coat)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 6/36 G02B 6/36 5F073 H01S 5/022 H01S 5/022 (72) Inventor Hidenori Harada Ueda Nagano Prefecture City Oita 300 Oya Tokyo Special Electric Wire Co., Ltd. Ueda factory (72) Inventor Takashi Izawa 300 Ueda, Nagano Prefecture Udai factory (72) Tokyo Special Electric Wire Co., Ltd. Ueda factory (72) Inoue Minase 300 Ueda, Ueda, Nagano Prefecture 300 Address F-Term in Ueda Factory of Tokyo Special Electric Wire Co., Ltd. 5F073 AB27 AB28 AB30 BA01 EA29 FA25 FA30

Claims (7)

[Claims] 1. A method of manufacturing a metal-coated optical fiber used in an optical semiconductor module for optically coupling a laser diode and an optical fiber, comprising: a protective coating on the surface of the optical fiber facing the laser diode emission optical axis surface. A protective coating layer peeling step of peeling the layer to expose the bare fiber; and a vertical cutting step of cutting the exposed end portion of the bare fiber into a 90 ° flat with respect to the optical axis by cleavage to provide a vertical cleaved surface; , AR (Anti-reflection) with a reflectance of 0.1% or more on the surface of the vertical cleavage surface
An AR coating step of applying a (non-reflective) coating; and a high layer consisting of an oxide of chromium or titanium having a higher melting point than the solderable low melting point metal layer of the third layer as the first layer on the outer periphery of the exposed bare fiber. A refractory metal oxide layer forming step of forming a refractory metal oxide layer; and chromium having a higher melting point than the solderable low melting point metal layer of the third layer as a second layer on the outer periphery of the refractory metal oxide layer. Or a refractory metal layer forming step of forming a refractory metal layer made of titanium; and nickel, gold as a third layer on the outer periphery of the refractory metal layer,
A low melting point metal layer forming step of forming a solderable low melting point metal layer made of a nickel-gold alloy or a gold alloy;
And a method for producing a metal-coated optical fiber, comprising: 2. A vertical polishing step; followed by a thermal polishing step of thermally polishing the vertical cleaved surface with a flame, an electron beam or a high power laser to remove residual scratches to form a thermally polished vertical cleaved surface. The method for producing a metal-coated optical fiber according to claim 1, wherein the metal-coated optical fiber is added. 3. Following the AR coating step;
The metal coating according to claim 1 or 2, wherein a protective resin forming step of applying and curing an ultraviolet curable resin to form a protective resin on the R-coated vertical cleavage surface or the AR-coated heat-polished vertical cleavage surface is added. Optical fiber manufacturing method. 4. A step of forming the refractory metal oxide layer; and subsequent to the step of forming the refractory metal oxide layer, the refractory metal oxide layer and the refractory metal oxide layer at the boundary between the refractory metal oxide layer of the first layer and the refractory metal layer of the second layer. The method for producing a metal-coated optical fiber according to claim 1, 2 or 3, wherein a mixed layer forming step of forming a mixed layer of refractory metal is added. 5. Following the step of forming a refractory metal layer;
An alloy layer forming step of forming an alloy layer of these high melting point metal and low melting point metal at the boundary between the second layer high melting point metal layer and the third layer low melting point metal layer; Item 5. A method for producing a metal-coated optical fiber according to item 1, 2, 3 or 4. 6. The metal-coated optical fiber obtained by the manufacturing method according to claim 1, 2, 3, 4 or 5, is inserted into a metal sleeve for sealing, and the sleeve and the metal-coated optical fiber are vaporized by soldering. A method for manufacturing a metal-coated optical fiber with a sleeve, which comprises tightly sealing. 7. A method of manufacturing an optical semiconductor module used as a light source for optical fiber communication, wherein a laser diode and an optical fiber are optically coupled in space through a lens, an optical isolator, and the like. The metal-coated optical fiber portion of the metal-coated optical fiber with a sleeve obtained by the manufacturing method described above is directly fixed to the substrate by soldering, and a metal sleeve for encapsulation in which the metal-coated optical fiber is installed is provided at one end of the case and high-temperature solder. Alternatively, a method for manufacturing an optical semiconductor module, which comprises directly fixing the resin by YAG laser welding and finally removing the protective resin when a metal-coated optical fiber with a protective resin is used.