JPH0921934A - Optical reception module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relax the accuracy of alignment of an optical fiber with a photodetector without lowering the performance of an optical reception module. SOLUTION: This module is constituted in such a way that a photodetector array 2 and a fiber array 1 are incorporated in supporting substrate 3, and a spacer 4 is aligned in the height of the fiber array 1 with that of a PD, and the fiber array 1 is formed by arranging optical fibers 1a, 1b,... at a pitch 250μm, and the photodetector array 2 is arranged in length longer that that between the optical fibers on both sides of the fiber array by arranging the PDs 2a, 2b,... at a pitch 100μm (light receiving area 60μm, gap 40μm), and one of outgoing light L is made incident on plural PDs, which selects a corresponding PD without performing accurate positioning in advance as a result.

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, and more particularly to an optical receiving module applicable to optical communication, optical information processing, optical interconnection and the like.

[0002]

2. Description of the Related Art "Prototype of multi-channel LD, PD array module" which can be illustrated as a known document describing the prior art of the present invention (Kaoru Moriya, 3 members, 1992 IEICE Spring Conference, C- 269, P4-311)
An optical module is proposed in. The one in this document is
A structure in which a PD (photodiode) is mounted on the side surface of a member for fixing an optical element and is arranged via a fiber and a lens fixed on a silicon V groove and an optical axis is adjusted using an adjustment fixing block and then fixed I have.

FIG. 5 is a diagram showing an optical module (PD array module) described in the above document, in which 1
1 is a carrier, 12 is a lens array, 13 is a tape fiber, 14 is a PD array, 15 is a block for adjusting and fixing,
16 is a SiV groove fiber alignment member. The tape fibers 13 are precisely arranged in V grooves formed at equal intervals by anisotropic etching of silicon. As the lens array 12, a lens array in which microlenses are monolithically integrated is used.

FIG. 6 is a view showing another example of the conventional optical coupling between an optical fiber and a light receiving element (see Japanese Patent Laid-Open No. 5-37004), in which the recess 20 has a buffer layer 21 and a light absorbing layer 22.
And a gap layer 23 is formed so as to accommodate the tip of the optical fiber 26 in a portion of the semiconductor substrate 25 corresponding to the light receiving portion 24.
The recess 20 facilitates and facilitates optical coupling between the optical fiber and the light receiving element.

FIG. 7 is a view showing a back-illuminated type light receiving element with a lens used in still another example of optical coupling between a conventional optical fiber and a light receiving element (see Japanese Patent Application Laid-Open No. 4-340509). 30 is provided on the incident surface on the back side of the light receiving element D so as to collect the signal light L on the light absorption layer 31, and the microlens 30 does not vertically enter the signal light L on the electrode 32. I am trying. In general, a back-illuminated light-receiving element using a microlens has a larger tolerance for optical coupling position deviation than a front-side light-receiving element.

[0006]

In the optical coupling shown in the above-mentioned conventional example, the optical fiber and the light receiving element are mechanically aligned with each other in some form, and then the light emitted from the optical fiber is received by the light receiving element. Although light is received, the optical fiber and the light receiving element have a one-to-one relationship in any of the examples. Therefore, if an error occurs in positioning, not only loss of light but also crosstalk will occur. However, high accuracy was required for positioning. Then, a V-groove fiber fixing member was used, accuracy was ensured by the concave portion of the light receiving element substrate, and a microlens was formed to take a positioning error countermeasure.

However, the formation of the concave portion and the microlens in the V-groove fiber fixing member and the light receiving element substrate causes a cost increase due to a complicated process and a reduced yield. The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the accuracy of alignment between an optical fiber and a light receiving element without degrading the performance of the optical receiving module.

[0008]

In order to solve the above-mentioned problems, the present invention as set forth in claim 1 is as follows.
In an optical receiving module having at least two optical fibers and a light receiving element for receiving light emitted from the optical fibers, a pitch between the light receiving elements is made smaller than a pitch between the optical fibers, The light emitted from one optical fiber is received by a plurality of light receiving elements.

According to a second aspect of the present invention, in the first aspect, the pitch between the light receiving elements is set to be equal to or less than half the pitch between the optical fibers, and the output from a specific optical fiber is reduced. Make sure there is a light-receiving element that responds only to the light emitted.

According to a third aspect of the present invention, in the first or second aspect, the light receiving elements are arranged in two rows and arranged in a zigzag pattern, and the pitch between the light receiving elements is reduced. Without increasing the number of light receiving elements within the desired interval, the function can be performed more effectively.

[0011]

1 (A) and 1 (B) are schematic views of an embodiment of the present invention. FIG. 1 (A) is a diagram showing a relationship between light emitted from an optical fiber and a light receiving element. 1B is a perspective view of the mounting form. In the fiber array 1, the optical fibers 1a, 1b, ... Are formed with a pitch of 250 μm,
In the light receiving element array 2, the light receiving elements (hereinafter referred to as PDs (photodiodes)) 2a, 2b, ... Have a pitch of 100 μm.
(Light receiving region 60 μm, gap 40 μm), and the light emitted from one optical fiber enters a plurality of PDs.

Then, light is sequentially incident on each optical fiber,
The PD corresponding to each optical fiber is determined while monitoring the output of each PD. In FIG. 1A, the optical fiber 1a
PD2a, 2b, 2c for the optical fiber 1b and PD2 for the optical fiber 1b
d, 2e, 2f, the optical fiber 1c has PDs 2g, 2h,
2i corresponds. That is, the corresponding PD is selected as a result without performing accurate positioning in advance.

For concrete mounting, the light receiving element array 2 and the fiber array 1 are assembled on the support substrate 3, and the spacer 4 is used.
Makes the heights of the fiber array 1 and PD match.
In FIG. 1 (B), the fiber array 1 and the light receiving element array 2 are illustrated as separated for the sake of explanation, but they are actually closer to each other.

With the above-described structure, it is not necessary to strictly determine the relative positional relationship between the fiber array 1 and the light receiving element array 2 in the array longitudinal direction in advance, and to arrange the fiber array 1 and the light receiving element array 2. If the parallelism is obtained, the position in the longitudinal direction of the array may be roughly adjusted after that, so that the mounting is very easy. However, some unused PDs may appear at both ends of the light receiving element array 2.

Further, it seems that there is a portion (gap portion) having no photosensitivity between the PDs, but in reality,
The depletion layer of the adjacent PD also extends to this gap portion, and most of the light incident on this gap portion also contributes to the signal generated by the PD. However, at this time, if the magnitude of the reverse bias applied to the PD is not adjusted according to the size of the gap portion, the depletion layer may not be fully extended and the response speed may be lowered, so that caution is required. In this embodiment, the pin PD formed by using the epi substrate of 2E13 [1 / cm ³ ] is used, and the reverse bias is 5 [V].

In the embodiment of FIG. 1, the PD pitch is
1/2 of the pitch of the optical fiber (100 μm / 25
0 μm), but theoretically P for one optical fiber
Unless the configuration is such that two or more Ds are supported (the ratio of the PD pitch to the optical fiber pitch is one-half or less), a large amount of crosstalk occurs, which often does not work well. The smaller the ratio between the PD pitch and the optical fiber pitch, the better.

FIG. 2 is a diagram for explaining an example in which the crosstalk occurs, which is a pitch 250 of the optical fiber.
The relationship between the fiber output light and the PD when the PD pitch is 200 μm with respect to μm is shown. Fiber light L1c
Enters and reacts with PD2c and PD2d.
2c reacts with the fiber light L1b, and PD2d reacts with the fiber light L1d. Therefore, the PD that specifies only the fiber light L1c cannot be determined.

FIG. 3 is a view for explaining another embodiment of the invention of the present application, in which the PD row shown in FIG. 2 is vertically divided into two in the array longitudinal direction, and the upper row is shown. And the lower row are shifted by a half pitch, and the PDs are arranged in a staggered pattern. By providing the PDs in a zigzag pattern, the number of PDs in a desired length can be increased without reducing the pitch between the PDs, and the pitch of each PD row is 1 compared to the pitch of the optical fiber. Even if it is larger than / 2, the PD that can specify the fiber light can be determined. In FIG. 3, the PD 2d ′ corresponds to the fiber light L1c that could not be specified in FIG.

The above-mentioned staggered arrangement is theoretically necessary when the adjacent fiber lights are lined up completely without a gap, and the ratio of the PD pitch to the optical fiber pitch is the same. Is larger than 1/2, but in reality, the adjacent fiber lights are not completely aligned without a gap, so the condition of the pitch ratio is slightly relaxed (the pitch ratio becomes larger than 1/2. ).

FIG. 4 is a diagram of an embodiment in which the staggered arrangement is applied to the embodiment shown in FIG. 1, and the staggered arrangement has a structure in which the pitch ratio shown in FIG. 1 is 1/2 or less. However, it is effective, and if the correspondence between the optical fiber and the PD is determined by observing the output of each PD, a configuration with less crosstalk can be realized. Further, in the staggered arrangement, if the first-stage amplifiers are independently connected to the PD rows on the upper row side and the lower row side, it is possible to reduce the parasitic capacitance and improve the frequency characteristic.

[0021]

【The invention's effect】

Effect corresponding to claim 1: Since the plurality of PDs can be associated with one optical fiber by making the pitch of the PD smaller than the pitch of the optical fiber, the result is that after alignment, the optical fiber is accommodated. Since the PD to be used is determined, the required accuracy can be greatly relaxed as compared with the conventional required accuracy of alignment between the PD and the optical fiber. Effect corresponding to claim 2: In addition to the effect corresponding to claim 1, by setting the PD pitch to be less than half the pitch of the optical fiber, it is possible to reliably correspond to only one optical fiber.
It was possible to determine D, and a configuration with less crosstalk was realized. Effect corresponding to claim 3: In addition to the effect corresponding to claims 1 and 2, the PDs are divided into upper and lower parts with respect to the longitudinal direction of the array, and the PDs are arranged in a staggered manner, so that the pitch is not reduced. It was possible to increase the number of PDs between desired distances and reduce crosstalk. In particular, since crosstalk can be avoided even when the PD pitch cannot be half the fiber pitch or less, this case is particularly effective. Further, since the PD row is divided into the upper row and the lower row, it is possible to connect the upper row and the lower row to the first-stage amplifiers respectively, so that the parasitic capacitance can be reduced and the response speed can be improved. .

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention.

FIG. 2 is a diagram for explaining an example in which crosstalk occurs.

FIG. 3 is a diagram for explaining another embodiment of the present invention.

FIG. 4 is a diagram of an embodiment in which the PD array shown in FIG. 1 is arranged in a staggered array.

FIG. 5 is a diagram showing a conventional example of an optical module (PD array module).

FIG. 6 is a diagram showing another example of optical coupling between a conventional optical fiber and a light receiving element.

FIG. 7 is a diagram showing a back-illuminated type light receiving element with a lens used in still another example of optical coupling between a conventional optical fiber and a light receiving element.

[Explanation of symbols]

1 ... Fiber array, 2 ... Light receiving element array, 3 ... Support substrate, 4 ... Spacer.

Claims (3)

[Claims] 1. An optical receiving module having at least two optical fibers and a light receiving element for receiving light emitted from the optical fibers, wherein a pitch between the light receiving elements is equal to a pitch between the optical fibers. Optical receiving module characterized by being smaller than the conventional one. 2. The optical receiving module according to claim 1, wherein the pitch between the light receiving elements is half or less of the pitch between the optical fibers. 3. The light receiving elements are arranged in two rows and arranged in a staggered pattern, or
2. The optical receiver module according to item 2.