JP2003344723A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module which permits use of a flat isolator of a low cost. <P>SOLUTION: The optical module consists in mounting an optical element on a silicon substrate, mounting graded index fibers on V-grooves disposed in the positions facing the light incident and exit surfaces of the optical element and making signal light incident and emitting the light through the graded index fibers. <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 module in which an optical element is mounted on a silicon substrate used for a long distance transmission module for optical communication.

[0002]

2. Description of the Related Art A transmission module incorporating a laser diode, a lens, and an isolator is used for optical communication, especially for long-distance transmission. In recent years, the cost reduction has been demanded, and the reduction of the process has been rapidly developed. However, as a result, reduction of material costs has emerged as a major issue.

The structure of a conventional isolator is shown in FIG.
This isolator is called a flat isolator 11, and the first polarizer 6, the Faraday rotator 7, the second polarizer 8 and the magnet 9 are attached to the substrate 10 to form the flat isolator 11. A feature of the flat isolator 11 is that it has a structure suitable for mounting on a flat surface such as a package.

As shown in FIG. 5, an optical element 2 such as a laser diode is mounted on a silicon substrate 1 by bumps (not shown), and a deep V groove 3 is formed to collect the light beam. It is formed on the silicon substrate 1, and the ball lens 4 is mounted on it. The optical module 5 and the flat isolator 11 shown in FIG. 4 are mounted in the same package (not shown) to form a transmission module.

In order to reduce the materials used, an isolator structure built in a ferrule as shown in FIG. 6 has been proposed. As shown in FIG. 6 (a), a graded index fiber (hereinafter referred to as GIF) 15, a single mode fiber 14, and a coreless fiber 16 are fused, and this series of fibers is attached to a ferrule 12.
By cutting the portion of the coreless fiber 16 to make a cut portion 13 and mounting the isolator 11 on the cut portion 13,
It constitutes an isolator with a lens.

[0006]

By the way, in order to downsize these modules and reduce the cost of the isolator, it is required to reduce the size of the isolator. This isolator is provided at the part where the light of the laser diode is coupled to the core of the optical fiber by the optical lens system. Therefore, in order to make the isolator small, the optical position with the lens for focusing the laser diode on the core of the optical fiber is used. It is indispensable to have a configuration that keeps the above and easily attaches them.

However, in the structure shown in FIG. 5, since the optical module 5 and the flat type isolator 11 are separated from each other, the distance of the optical system becomes longer, and the deviation of the light beam from the optical axis becomes larger accordingly, and the isolator becomes larger. On the other hand, since a large effective area is required, the size of the isolator cannot be reduced.

Analyzing the factors causing the deviation from the optical axis, one of them is the deviation of the optical axis of the ball lens 4 itself.
This is because an ideal spherical surface cannot be constructed, and its accuracy is limited to ± 5 μm. Also,
Since the deep V groove 3 must be formed on the silicon substrate 1, there is a problem that the accuracy of the groove width and the depth is deteriorated, and the accuracy is ± 3 to 4 μm. Further, since the ball lens 4 is used, astigmatism is large, and high coupling efficiency cannot be obtained, which is a drawback of the optical module 5 shown in FIG.

On the other hand, in the case of the ferrule built-in isolator shown in FIG. 6, the major drawback is that the GIF 15, the single mode fiber 14 and the coreless fiber 16 are cut,
Since the short GIF 15 and the coreless fiber 16 have to be fused because they have to be fused, at least three fusion steps are required, which complicates the manufacturing process. In addition, after putting a series of finished optical fibers into the ferrule 12 and cutting the ferrule 12,
There is a step of attaching the isolator 11 to the cutting portion 13, and an extra step is added as a step.

These mounting errors include the eccentricity of the core of a series of optical fibers (0.5 μm in range), the concentricity of the ferrule 12 (1 μm in range), the ferrule 1
The processing accuracy (± 3 to 4 μm) of the V groove for mounting 2 can be increased.

As a result, in the case of the ferrule built-in isolator shown in FIG. 6, although the size of the isolator can be reduced, the cost cannot be reduced due to the additional process, and the mounting error is large. There was the inconvenience that the focus had to be dropped so that it could be absorbed before it was used.

[0012]

In view of the above, the present invention provides:
An optical element is mounted on a silicon substrate, a graded index fiber is mounted on a V groove provided at a position facing the light input / output surface of the optical element, and an optical signal is input / output through the graded index fiber. The optical module is configured by using

Further, in the present invention, when the length of the graded index fiber is L and the pitch P of the standing wave of the optical signal passing therethrough is L = (n ± 1/4) P, where n = 0, It is characterized by satisfying 1, 2, 3 ...

Alternatively, the tip of the graded index fiber has a tip spherical shape, a cleave end, a wedge shape, and the like, and the length of the graded index fiber is L, and the pitch of the standing wave of the optical signal passing therethrough. When P is set, L = (n ± 1/4) P However, the length L is set to a value deviating from n = 0, 1, 2, 3, ..., And the focus of the graded index fiber is adjusted. It is characterized by doing so.

Further, a flat type isolator is mounted on the silicon substrate, and the flat type isolator has a first polarizer, a Faraday rotator and a second polarizer laminated, and the bottom surface thereof is directly attached to the silicon substrate. It is characterized by being joined to.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show the structure of an optical module 20 of the present invention. An optical element 2 such as a laser diode is mounted on a silicon substrate 1 by bumps (not shown), and a shallow V groove 22 is formed in a portion of the silicon substrate 1 facing the light incident / exiting surface of the optical element 2. A graded index fiber (hereinafter referred to as GIF) 21 in the V groove 22
Is mounted so that the light entering and exiting the optical element 2 passes through the GIF 21.

When the length of the GIF 21 is L and the pitch of the standing wave of the optical signal passing therethrough is P, L = (n ± 1/4) P where n = 0, 1, 2, 3 By making the length L satisfying ..., it is possible to make the length L easy to handle while having a light condensing effect.

A deep V groove 3 is formed on the side of the GIGF 21 opposite to the optical element 2 and an isolator 11 is mounted.

On the isolator 11 side of the GIF 21, a cut portion 23 is formed in the silicon substrate 1, and along the cut portion 23, a unit of the first polarizer 6, the Faraday rotator 7, and the second polarizer 8 is formed. Are arranged, and these are attached using the metallization 24 provided at the bottom of the V groove 3. Similarly, the magnet 9 also has a metallization 2 profitable from the bottom of the V groove 3.
4 is attached and is a flat type isolator 11
Are configured.

If a collimator fiber (not shown) is introduced with the side of the isolator 11 opposite to the optical element 2 as a ferrule introducing section, an optical signal can be input / output.

According to the optical module of the present invention, since the GIF 21 is used as the lens, the eccentricity of the fiber is as small as 1 μm or less in the range. Further, since the V groove 22 may be formed shallow, the dimensional accuracy thereof can be improved and the range can be suppressed to about 1 μm.

For example, 1.25 m as in the conventional example of FIG.
In contrast to having to etch half of the ferrule 12 of 625 μm, the present invention only needs to etch half of the fiber 125 μm of the GIF 21, which is 62.5 μm, and does not include the concentricity of the ferrule 12. Therefore, a very small eccentricity shift is realized.

Further, since the GIF 21 is directly attached to the shallow V groove 22, it is sufficient to cut the GIF 21 to a specified length, and the GIF 21 is fused or attached to the ferrule 12 like the ferrule-containing isolator shown in FIG. Since the step of cutting the ferrule 12 is omitted, the structure can be made very simple.

Although the dimensional error of the GIF 21 at the time of cutting causes the deviation of the focal length, if the error is about ± 10 μm, the focal length necessary for forming the optical module can be sufficiently obtained. Also, if you have a tolerance of this level,
Can be cut sufficiently.

Further, the flat type isolator 11 is used.
Can be attached so as to abut against the cut portion 23 on the V groove 3, and the attachment is very easy. Further, since the mounting position error of the isolator portion is not strictly required, there are few restrictions on the mounting.

Further, since the beam diameter of the GIF 21 is about 100 μm as described later, the effective diameter required for the flat type isolator 11 can be set to about 150 μm, and the size can be greatly reduced. Therefore, it is possible to reduce the material cost.

FIG. 3 shows the structure of the GIF 21.
The GIF 21 is composed of a core 21a and a clad 21b, and the size of the core is 100 μm, for example.

When the length of the GIF 21 is L and the pitch of the standing wave of the optical signal passing therethrough is P, it is necessary to set L = P / 4 in order to perform a condensing action on the GIF 21. The length L becomes as short as 125 μm, which makes it difficult to handle.

Therefore, in the present invention, L = (n ± 1/4) P, where n = 0, 1, 2, 3, ... The length L can be set to 625 μm, and its handling can be facilitated.

The tip surface of the GIF 21 has a tip spherical shape,
It can be cleaved, wedge-shaped or the like. With the spherical shape as shown in FIG. 3, the numerical aperture at the tip can be increased to bring the coupling efficiency close to that of an aspherical lens. As a result, the light emitted from the optical element 2 is converted into collimated light like the light ray 30.

As the shape of the tip surface, the cleave end is a state in which it is cut by a fiber cutter, and a technique has been established in which connection loss is not caused even by such processing. If the laser diode forming the optical element 2 has a large aspect ratio, the tip of the GIF 21 can be formed into a wedge shape to convert the shape of the emitted light from an ellipse to a circle, thereby improving the coupling efficiency. Can be connected to.

Of course, if a high numerical aperture is not required, a tip spherical structure is not required. Further, if the collimated light design is not performed, the single focus design is also possible. In that case, the pitch setting may be changed.

Further, in the GIF 21, L = (n ± 1/4) P, where n = 0,1,2,3 ... It can also be adjusted.

Further, the isolator 11 does not necessarily have to be mounted on the silicon substrate 1, and can be joined to the side surface of the silicon substrate 1 as a separate body.

[0036]

EXAMPLE An optical module shown in FIG. 1 was produced as an example of the present invention.

The GIF 21 has a core size of 100 μm, a clad of 12.5 μm, and a length L of 625 μm. The flat type isolator 11 uses a magnet and other parts separated, and the size of the isolator 11 is 200 μm in the opening.
The size was mφ, the outer shape was 250 μm square, and the length direction was 0.7 mm. The magnet 9 has a metallization formed of Ti / P / Au on the bottom surface, and is attached separately here. Therefore,
The depth of the V groove 3 is 125 μm. The silicon substrate 1 has a size of 2.5 mm square, and the optical element 2 of the laser diode is mounted thereon by bumps.

This optical module is mounted in a package,
After inserting the collimator fiber into the ferrule introduction part, optically adjusting and attaching the collimator fiber with YAG, the characteristics were evaluated, and it was found that the coupling efficiency was 50% and the isolation was 35 dB.

[0039]

As described above, according to the present invention, the size of the flat isolator can be greatly reduced and the GIF lens can be easily attached, so that an optical module suitable for long-distance transmission can be provided. , Can achieve technological innovation of high-speed transmission module.

[Brief description of drawings]

FIG. 1 is a perspective view showing an optical module of the present invention.

FIG. 2 is a plan view showing an optical module of the present invention.

FIG. 3 is a cross-sectional view of a GIF used in the optical module of the present invention.

FIG. 4 is a perspective view of a conventional flat type isolator.

FIG. 5 is a perspective view showing a conventional optical module.

FIG. 6 shows a conventional ferrule-containing isolator, in which (a) is a configuration diagram of a series of optical fibers and (b) is a perspective view.

[Explanation of symbols]

1 Silicon substrate 2 optical elements 3 V groove 4 ball lens 5 Optical module 6 First polarizer 7 Faraday rotator 8 Second polarizer 9 magnets 10 substrates 11 Isolator 12 ferrules 13 cutting part 14 Single mode fiber 16 coreless fiber 21 GIF 22 V groove 23 cutting part 24 Metallization 30 rays

Claims (5)

[Claims] 1. An optical element is mounted on a silicon substrate, and a graded index fiber is mounted on a V groove provided at a position facing a light input / output surface of the optical element, and an optical signal is transmitted through the graded index fiber. An optical module characterized in that it is made to enter and exit. 2. When the length of the graded index fiber is L and the pitch P of standing waves of an optical signal passing therethrough, L = (n ± 1/4) P, where n = 0, 1, 2 , 3 ..., The optical module according to claim 1, wherein 3. The graded index fiber has a tip-shaped structure, a cleaved end structure, a wedge-shaped structure, etc., the length of the graded index fiber is L, and the pitch of a standing wave of an optical signal passing therethrough. When P is set, L = (n ± 1/4) P However, the length L is set to a value deviating from n = 0, 1, 2, 3, ..., And the focus of the graded index fiber is adjusted. The optical module according to claim 1, wherein 4. The optical module according to claim 1, further comprising a flat isolator mounted on the silicon substrate. 5. The flat isolator according to claim 4, wherein a first polarizer, a Faraday rotator and a second polarizer are laminated, and the bottom surface thereof is directly bonded to a silicon substrate. Optical module.