JP2003302545A - Optical transmission module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand positional deviation tolerance between the optical waveguide and the optical fiber of an optical transmission module, in other words, to prevent optical coupling efficiency of the module from being degraded even if the optical fiber is deviated from the mounting position. <P>SOLUTION: The optical transmission module is provided with an optical waveguide having a core and a clad layer, an optical fiber, and a substrate on which the optical waveguide and the optical fiber are mounted, in the manner aligned so that the optical fiber and the core are optically coupled. In this module, the core thickness at its end on the optical fiber side is made thinner than the core thickness in other areas. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission module mainly used in an optical transmission system or an optical switching system (both of which are called an optical communication system).

[0002]

2. Description of the Related Art An optical component mounting process is one of the factors that hinder the cost reduction of optical transmission modules.

In the case of an optical transmission module that transmits and receives a light emitting element such as a semiconductor laser to an optical fiber through an optical waveguide,
In order to secure the light coupling efficiency between the optical waveguide and the optical fiber, a so-called active centering method is adopted in which the semiconductor laser is actually emitted and the optical fiber is aligned and fixed at a position where the optical coupling efficiency is maximized. .

However, since this method requires a long time for the process, it has been a stumbling block for reducing the assembly cost.

Various studies have been conducted to solve the above problems and to shorten the assembly process.
As disclosed in Japanese Patent No. 168038, a V groove having high positional accuracy is formed on a silicon substrate by anisotropic etching, and an optical fiber is mounted on the V groove, so that the optical fiber is mounted without active alignment. Have been devised to shorten the.

[0006]

FIG. 9 shows a schematic diagram of the prior art. When such a configuration is used, the coupling efficiency between the optical waveguide and the optical fiber is V-groove or optical waveguide. It is determined by the position accuracy, the mounting accuracy of the optical fiber, and the dimensional accuracy of the optical fiber.

FIG. 10 shows an optical waveguide having a section of 6.5 μm square, a core / clad refractive index difference of 0.45% and a mode radius of 4.7 μm.
7 is a graph showing the correlation between the amount of positional deviation with respect to the optical fiber and the coupling efficiency. The gap between the optical waveguide and the optical fiber is 20
μm.

If the positional variation between the core of the optical fiber and the core of the optical waveguide is ± 3 μm, the maximum coupling efficiency decrease due to the positional deviation is estimated to be 2.2 dB from this figure. In order to facilitate the manufacturability of the module, it is necessary to reduce this decrease in coupling efficiency, and there is a method of improving the mounting accuracy of the optical fiber as a means for that, but there are many technical problems, and Even if the high precision can be achieved, the process time may be increased.

Further, in the case where the tip of the optical fiber is projected from the V groove as shown in FIG. 9, there is a possibility that the end of the optical fiber moves due to temperature change after the module is manufactured, and if the positional deviation tolerance is small, This fluctuation of the optical fiber may cause a defect such as a tracking error.

An object of the present invention is to increase the positional deviation tolerance between the optical waveguide and the optical fiber, that is, not to reduce the optical coupling efficiency of the optical transmission module even if the mounting position of the optical fiber is deviated.

[0011]

The present application includes the following means capable of solving the above problems.

The structure of the optical transmission module includes an optical waveguide having a core made of a polymer organic film and a clad layer,
An optical transmission module comprising an optical fiber, an optical waveguide, and a substrate on which the optical fiber is mounted, and the optical transmission module mounted so that the optical fiber and the core are aligned so as to be optically coupled to each other,
In some of the cores, the thickness of the end portion on the optical fiber side is smaller than the thickness of other regions.

As described above, since the mode diameter of the optical waveguide is expanded by reducing the film thickness of the end portion of the core on the optical fiber side, it is possible to expand the positional deviation tolerance between the optical waveguide and the optical fiber. Is made. That is, it is possible to prevent the optical coupling efficiency of the optical transmission module from being lowered even when the mounting position of the optical fiber is displaced.

The core material is preferably one of fluorinated polyimide, silicone resin, and a member containing these as the main components.

Further, by gradually thinning the end portion, it is possible to prevent unnecessary reflection between the core and the glad layer, so that the optical transmission efficiency of the optical waveguide can be improved. ,preferable.

A method of manufacturing an optical transmission module which can solve the above-mentioned problems includes an optical waveguide having a core and a clad layer, an optical fiber, and a substrate on which the optical waveguide and the optical fiber are mounted. In a method of manufacturing an optical transmission module in which the optical fiber and the core are aligned and mounted so as to optically couple with each other, an inclination is provided on the substrate, a core material is formed on the inclination, and There is a method of forming a core by cutting the core material on the way.

As a method of manufacturing an optical transmission module, an optical waveguide having a core and a clad layer, an optical fiber, and a silicon substrate on which the optical waveguide and the optical fiber are mounted are provided. In a method for manufacturing an optical transmission module that is mounted so that the core and the core are optically aligned, an inclination is provided on the silicon substrate, a core material is formed on the inclination, and silicon is formed in the middle of the inclination. There is a method of forming a groove by anisotropic etching.

The core material in these manufacturing methods is preferably formed by spin coating a varnish.

Further, as the core material, it is preferable to use one of fluorinated polyimide, silicone resin, and a member containing these as main components.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present invention will be described below with reference to the schematic diagram shown in FIG.

When the thickness of the core of the optical waveguide is made thin, the light confinement becomes strong to some extent, and the mode diameter becomes small. When the thickness is further reduced, light leaks from the core and the mode diameter widens, as shown in the figure. The change in the mode diameter of the light beam due to the change in the thickness of the end of the optical waveguide
FIG. 6 shows the result calculated by the eam Propagation Method) simulation. (A) is the shape of the optical waveguide,
It has a structure in which the thickness is reduced from 6.5 μm to 2.5 μm at 200 μm. Further, (b) is a simulation result showing a mode spread state of the optical waveguide having the structure of (a). Further, (c) is a graph showing the correlation between the thickness of the optical waveguide end portion and the mode diameter obtained from the simulation result.
As can be seen from these, the mode shape can be controlled by adjusting the width of the optical waveguide.

Here, a method of calculating the coupling efficiency of the light beam between the optical waveguide and the optical fiber will be described. First, it is assumed that the light beam is a Gaussian beam, and the coupling of 0th-order Gaussian beams is considered. The beam spot diameters (radius where the amplitude of the Gaussian beam is 1 / e of the center value) at the beam waists of the optical waveguide and the optical fiber (where the radius of curvature of the Gaussian beam wavefront becomes infinite = each end) are W1, respectively. The coupling efficiency η is expressed by the following equation, where W2, Z is the distance between the beam waists, X is the amount of vertical deviation in the optical axis, and λ is the wavelength of the propagating light beam.

[0023]

[Equation 1]

Where κ is

[0025]

[Equation 2]

[0026] According to the above equation, (1) W1 = W
2, (2) It can be seen that when these values are as large as possible, the coupling efficiency and the tolerance for the optical axis shift are improved.

Since the mode diameter of the conventional optical waveguide, that is, the beam spot diameter W1 of the incident system is 3.8 μm, which is a smaller value than that of the optical fiber, W1 = W2 does not hold and the coupling efficiency and the positional deviation tolerance are optimal. It can not be said.

Therefore, the thickness of the end portion of the optical waveguide is reduced,
The optical coupling characteristics can be improved by increasing the mode diameter of the light beam propagating through the optical waveguide. For example, if W1 = W2 is set, the maximum optical coupling efficiency can be obtained as shown in FIG. This allows
Even if the displacement of 3 μm occurs, it is possible to obtain the same coupling efficiency as in the case of the displacement of about 2 μm in the conventional technique. Further, if the mode diameter can be increased, the positional deviation tolerance can be increased.

Next, a means for forming an optical waveguide having a shape as shown in FIG. 5 will be considered. In the case of using a thin film process, a technique of gradually changing the thickness in the film thickness direction is generally very difficult, and a complicated process is required. In the present invention, the above-mentioned shape is realized without complicating the manufacturing process by using a polymer material that spin-coats an optical waveguide in a varnish state and then heat-cures it so that it has desired properties. You can When a groove is formed on the surface of the substrate and varnish is spin-coated on the groove, the varnish near the edge of the groove on the surface of the substrate has a smaller film thickness than other portions on the surface of the substrate. This phenomenon becomes more remarkable as the solid content concentration of the varnish decreases. FIG. 8 shows a graph showing the correlation between the solid content concentration of the varnish and the film thickness at the groove end. It can be seen that even if the substrate surface is kept constant at 6.5 μm, the degree of decrease in film thickness at the groove edge varies depending on the solid content concentration. This phenomenon is caused by the fluidity of the varnish, and utilizes the effect that the varnish tends to flatten when coated on a substrate with irregularities. Further, the decrease in the film thickness at the groove end becomes more remarkable as the film thickness of the coating film becomes smaller and the groove becomes deeper. [First Example] Next, a first embodiment of the present invention will be described with reference to FIG.

In FIG. 1, (a) is an enlarged overhead view of the optical coupling portion between the optical waveguide and the optical fiber of the optical transmission module according to the present invention. Further, (b) is a sectional view perpendicular to the substrate surface on the optical axis. Although not shown in the figure, an optical element such as a semiconductor laser exists at the end of the optical waveguide to transmit or receive a light beam. On the other hand, the end of the optical fiber is connected to the station, and an optical signal is transmitted.

First, the manufacturing process of the first embodiment of the present invention shown in FIG. 1 will be described with reference to FIG.

As the substrate 11, a silicon substrate having a surface crystal orientation (100) is used. The specifications required for the substrate 11 are firstly that a groove with high dimensional accuracy can be formed on the surface of the substrate. In this respect, the silicon substrate is very advantageous, and by using anisotropic etching, it is possible to form a V-shaped groove with very high dimensional accuracy.
Other requirements include that the surface is flat and smooth, that it does not affect the waveguiding characteristics of light (a structure can be adopted), and that it is easy to cut out into individual elements. However, a member other than a silicon wafer may be used as long as these conditions are satisfied.

A V groove 41 is formed on the surface of the silicon substrate 11 (a). As an etching method, a known technique using a normal photolithography process using an aqueous potassium hydroxide solution as an etching solution was used. The V groove 41 is 2 in this embodiment.
It has a stepped structure. The shallow groove 411 on the one-step surface is a portion where the optical fiber is mounted, and is dimensioned such that the core of the optical fiber is at the same height as the core of the optical waveguide. Second deep V groove 41
Reference numeral 2 denotes a groove provided for controlling the film thickness at the core end portion of the optical waveguide. In this embodiment, the V groove 412 has a depth of 200 μm.
And

After forming the V groove, a thermal oxide film is formed on the silicon substrate by using a known technique. Next, an insulating thin film as the lower clad layer 12 is formed on the surface of the substrate 11 (b). In this example, fluorinated polyimide was used as the lower cladding layer 12. First, a varnish-shaped polyimide precursor having a solid content concentration of 25% was dropped on the substrate surface,
By spin-rotating the substrate, the varnish is uniformly coated on the entire surface of the substrate. Then, the substrate is heat-treated to imidize the varnish. As for the lower clad layer 12, when the thickness of the V-groove end portion becomes thin, there is a possibility that the propagation direction of the light beam is not horizontal with respect to the substrate surface. It prevents the film thickness from becoming thin.

Next, an insulating thin film as the core layer 13 is formed on the substrate (c). In this example, fluorinated polyimide having a refractive index difference of 0.45% was used for the cladding layer. The solid content concentration was 7.5%. The coating method is the same as that of the lower clad layer 12, and a varnished polyimide precursor is spin-coated and thermally cured. For the core layer 14, a member having a low solid content concentration is used in order to positively reduce the thickness of the V groove end portion.

Thereafter, the core layer 13 is patterned by using a known fine processing technique (d). Next, the upper clad layer 14 is formed on the upper layer of the substrate (e). The same member and film forming method as those of the lower clad layer 12 were used. Further, the polymer formed on the portion of the silicon substrate 11 where the V groove 41 is formed is removed by a known processing technique (f). Then, the dicing groove 15 is formed on the end faces of the V groove 41 and the optical waveguide (g).

Finally, the module substrate is completed by cutting the substrate 11 into chips. Needless to say, the wiring forming step and the solder forming step are inserted in any of the above steps, if necessary.

In the optical transmission module manufactured by the above manufacturing process, the mode diameter is enlarged in the coupling portion with the optical fiber of the optical waveguide, the maximum coupling efficiency is improved, and the positional deviation tolerance due to the positional deviation of the optical fiber is expanded. It
This eases the mounting accuracy of the optical fiber, and
It is possible to suppress a tracking error due to a minute movement of the optical fiber after the module is manufactured. [Second Example] Next, a second embodiment of the present invention will be described with reference to FIG.

The feature of the present invention is that the optical fiber is used as the active alignment. As described above, the active alignment is a factor that hinders the reduction of the assembly cost, but there are cases where the optical fiber cannot be mounted in the V groove as in the first example due to various restrictions. At that time, an active alignment system is used, but the present invention is also effective for an active alignment optical transmission module.

The manufacturing process of the second embodiment will be described with reference to FIG.

Regarding the method of manufacturing the module shown in FIG.
It is the same up to the upper clad forming step (e) of the first example. The difference from the first example is that the end portion where the V groove of the waveguide is close is completely cut by dicing (f). As a result, the V groove for mounting the fiber does not exist, but the film thickness becomes thin at the end of the optical waveguide.
The mode diameter is enlarged. When active alignment is performed on this optical waveguide, since the mode diameter is larger than that of a normal optical waveguide, the alignment process is greatly facilitated and the process time can be shortened.

[0042]

According to the optical transmission module of the present invention, the positional deviation tolerance between the optical waveguide and the optical fiber can be increased, so that the mounting accuracy of the optical fiber can be relaxed.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of an optical transmission module according to the present invention.

FIG. 2 is a diagram showing a second embodiment of the optical transmission module according to the present invention.

FIG. 3 is a cross-sectional view showing the manufacturing process of the first embodiment of the optical transmission module according to the present invention.

FIG. 4 is a cross-sectional view showing the manufacturing process of the second embodiment of the optical transmission module according to the present invention.

FIG. 5 is a schematic view showing an optical transmission module according to the present invention.

FIG. 6 is a diagram illustrating a simulation result of a light propagation mode of an optical waveguide.

FIG. 7 is a diagram showing a correlation between a varnish solid content concentration and a film thickness at a groove end portion.

FIG. 8 is a diagram showing a change in optical coupling efficiency with an optical fiber depending on a mode diameter of an optical waveguide.

FIG. 9 is a diagram showing a form of a conventional optical transmission module.

FIG. 10 is a diagram showing an optical coupling characteristic between an optical waveguide and an optical fiber according to a conventional technique. .

[Explanation of symbols]

1 ... Optical waveguide (core), 2 ... Clad, 3 ... Optical fiber, 4 ... Light beam, 11 ... Substrate (silicon substrate), 12
... lower clad layer, 13 ... core layer, 14 ... upper clad layer, 15 ... dicing groove, 21 ... lower clad, 22 ...
Upper clad, 41 ... V groove (V groove), 411 ... Optical fiber mounting V groove (shallow V groove), 412 ... Optical waveguide core film thickness control V groove (deep V groove)

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Claims (6)

[Claims] 1. An optical waveguide including a core and a clad layer, an optical fiber, and a substrate on which the optical waveguide and the optical fiber are mounted. The optical fiber and the core are aligned so as to perform optical coupling. In the optical transmission module thus mounted, the thickness of the end portion of the core on the optical fiber side is thinner than the thickness of the core in other regions. 2. The optical transmission module according to claim 1, wherein the end portion is gradually thinned. 3. An optical waveguide including a core and a clad layer, an optical fiber, and a substrate on which the optical waveguide and the optical fiber are mounted, and the optical fiber and the core are aligned so as to perform optical coupling. In the method for manufacturing an optical transmission module that is mounted on the substrate, an inclination is provided on the substrate, a core material is formed on the inclination, and the core is formed by cutting the core material in the middle of the inclination. And a method for manufacturing an optical transmission module. 4. An optical waveguide having a core and a clad layer, an optical fiber, and a silicon substrate on which the optical waveguide and the optical fiber are mounted, and the optical fiber and the core are adjusted so as to be optically coupled. In a method of manufacturing an optical transmission module mounted as a core, an inclination is provided on the silicon substrate, a core material is formed on the inclination, and a groove is formed by anisotropic etching of silicon in the middle of the inclination. And a method for manufacturing an optical transmission module. 5. The method of manufacturing an optical transmission module according to claim 3, wherein the core material is formed by spin coating a varnish. 6. The core material according to claim 3, wherein the core material is fluorinated polyimide, silicone resin,
And a method of manufacturing an optical transmission module, characterized in that any one of the members containing these as main components is used.