JPS63300206A - Optical coupling structure between optical fiber and light receiving element - Google Patents

Abstract

PURPOSE:To increase coupling efficiency and to improve package performance even when SMF and a light receiving element with a small light receiving diameter are coupled with each other by converging reflected light from the mirror surface of an optical fiber end part on the light receiving element through a lens provided integrally with the optical fiber. CONSTITUTION:The end part of the optical fiber 14 is cut slantingly and the cut surface is made into the mirror surface 15. The lens 16 which converges propagated light reflected by the mirror surface 15 is provided integrally with the optical fiber 14. Then the light receiving surface of the light receiving element 17 is arranged opposite the lens 16. Thus, the lens 16 is provided integrally with the optical fiber 14 to suppress the divergence of a projection beam and improve tolerance. Further, the side face functions as a cylindrical lens because of the relation between the numerical aperture and diameter of the optical fiber 14 and when a projection beam is made elliptic, the integration of the lens 16 and optical fiber 14 prevents the side face of the optical fiber 14 from functioning as the cylindrical lens.

Description

[Detailed Description of the Invention] Overview When optically coupling an optical fiber and a light receiving element, the end of the optical fiber is cut diagonally, the cut surface is made into a mirror surface, and a lens is used to condense the propagating light reflected by the mirror surface. , is provided integrally with the optical fiber, and has a structure in which the light-receiving surface of the light-receiving element is arranged opposite to the lens.

According to this optical coupling structure, it is possible to obtain high coupling efficiency and good mounting performance.

INDUSTRIAL APPLICATION FIELD The present invention relates to an optical coupling structure between an optical fiber and a light receiving element in an optical receiving module.

In recent years, in the field of optical communications, research has been actively conducted on high-speed systems having transmission speeds of several Gbit/s or higher, and as a result, demands for higher speeds in individual system components are increasing. Specifically, as a transmission line,
A single mode optical fiber (hereinafter also referred to as SMF) with good wavelength dispersion characteristics is used, and as a light receiving element, a single mode optical fiber with a small light receiving diameter (30 μm or less) and a small element capacitance (1 pF) is used.
(below) are used. In this way, when optical fibers and light-receiving elements are being increasingly miniaturized, when optically coupling them together, it is important to (a) have high coupling efficiency to increase reception sensitivity, and (b) to modularize the device. Good mountability is required.

2. Description of the Related Art Conventionally, as an optical coupling structure between an optical fiber and a light receiving element, a structure in which light emitted from an optical fiber is focused onto a light receiving surface of a light receiving element using a lens has been widely adopted.

This specific example will be explained with reference to FIGS. 4(a) and 4(b). (
In a), an optical fiber 6 having a spherical lens 6a formed at its tip and a light-receiving element 4 fixed on a mounting table 2 are sealed with a mold 8 while facing each other. The signal light propagating through the optical fiber 6 is focused onto the light receiving surface of the light receiving element 4 by the spherical lens 6a, and undergoes optical-to-electrical conversion.
The signal can be taken out as an electrical signal via the electrode terminal 10 protruding from the mold 8.

(b) is an example in which, in addition to the above structure, an electric circuit element 12 is integrally built into the mold 8'.

The signal photo-electrically converted in the light receiving element 4 is amplified by the electric circuit element 12 and taken out from the electrode terminal 10', thereby improving noise characteristics.

Problems to be Solved by the Invention The module structure shown in FIGS. 4(a) and 4(b) focuses the light emitted from the optical fiber 6 by the spherical lens 6a, so the problem of (a) can be solved. However, in (a), the light-receiving surface of the light-receiving element 4 and the optical fiber 6 are arranged perpendicularly, so the module form is vertical, and it is difficult to attach to the wiring board, etc. There was a problem in that it required space to implement. In addition, in the structure of (b), although the mountability of the module itself on the wiring board etc. is improved, only the light receiving element 4 is connected to the optical fiber 6.
, the electrical circuit element 12 and the unillustrated arrangement a
Since it is arranged perpendicularly to the substrate, the electrical interface between the light receiving element 4 and the electric circuit element 12 must be three-dimensional, which poses a problem in that there is a limit to high-density packaging. As described above, the conventional coupling structure could not satisfy the requirement (b).

In contrast, a coupling structure shown in FIG. 5 has been proposed as one with improved mounting performance. For example, the end of the Gl multimode optical fiber 6 is polished diagonally to form a mirror surface 6b, and the propagating light reflected by the mirror surface 6b and emitted mainly from the side surface of the optical fiber 6 is transferred to the light receiving element 4. The light is made to directly enter the light receiving surface. According to this structure, the optical axis of the optical fiber 6 and the light-receiving surface of the light-receiving element 4 can be arranged in parallel, so that high-density packaging is possible.

However, if the diameter of the optical fiber 6 is relatively large and the light-receiving diameter of the light-receiving element 4 is not relatively large, the tolerance (allowable error regarding relative positional relationship) will be small, and therefore, in high-speed optical communication systems. , small diameter SM
When coupling F to a light-receiving element having a small light-receiving diameter, such as an APD, there is a problem in that the requirement (a) may not be satisfied.

The present invention was created in view of these circumstances, and its purpose is to provide an optical coupling structure between an optical fiber and a light receiving element that can simultaneously satisfy the requirements (a) and (b). It is in.

Means for Solving the Problems FIG. 1 is a basic structural diagram of the present invention, which was made to solve the problems of the prior art.

The end of the optical fiber 14 is cut diagonally, and the cut surface is made into a mirror surface 15.

A lens 16 that condenses the propagating light reflected by the mirror surface 15 is provided integrally with the optical fiber 14.

The light-receiving surface of the light-receiving cable 17 is arranged to face the lens 16.

Function In FIG. 1, if there is no lens 16, the mirror surface 15
When the reflected light is emitted from the side surface of the optical fiber 14, the beam spreads, and the tolerance in the distance direction (direction) between the optical fiber 14 and the light receiving element 17 is particularly small. By providing the lens 16 integrally with the optical fiber 14, the spread of the output beam is suppressed,
1 - Tolerance is improved.

Furthermore, if the side surface functions as a cylindrical lens and the output beam becomes elliptical due to the relationship between the numerical aperture and the diameter of the optical fiber 14, the integration of the lens 16 and the optical fiber 14 is difficult. It has the effect of preventing the side surface from functioning as a cylindrical lens.

Embodiment Hereinafter, specific means for realizing the coupling structure shown in FIG. 1 will be explained based on the embodiment shown in FIGS. 2 and 3.

FIG. 2 is a manufacturing process diagram when a lens is formed by fixing an optical adhesive. Reference numeral 18 denotes an SMF, and first, a liquid or fluid optical adhesive is applied near the end of the SMF to form a lens 20. At this time, due to the surface tension of the optical adhesive before solidification, the exposed surface of the lens 20 becomes approximately spherical (a). Next, the SMF 18 or the SMF 18 and the lens 20 are arranged so that the center of the cut surface 22 is approximately located on the normal line of the tangential plane at the apex of the lens 20.
Cut diagonally (b). Finally, a mirror surface 22' is formed by polishing the cut surface 22 so that it satisfies the total reflection condition, or by depositing a reflective film of metal or the like after polishing the cut surface 22.

By processing the ends of the SMF 18 in this way, the SMF 18
After being reflected by the mirror surface 22', the propagating light of the MF 18 is emitted from the lens 20 without causing beam spread, and can be coupled with high efficiency to a light receiving element (not shown) having a small receiving diameter.

FIG. 3 is a diagram showing another embodiment of the present invention, in which the SM "18 itself is melted at high temperature, then allowed to cool and solidify, and a lens is formed by the surface tension during melting. First, either heat the end of the SMF 18 or
A portion that is to become an end portion of the MF 18 is cut by, for example, discharge heating, and a substantially spherical lens 24 is formed in this portion (a).

Next, the lens 24 portion is cut at a cutting surface 26 so as to be inclined, for example, at 45 degrees with respect to the optical axis of the SMF 18 (b).

By forming a mirror surface 26' on the cut surface 26 as in the previous embodiment, the joint structure shown in FIG. 1 can be obtained.

In the above embodiment, the lenses 20.24 are made of optical adhesive and the SMF 18 itself because the refractive index of the lenses 20.24 is approximately matched to the core and cladding of the SMF 18, so that the emitted light can be condensed well. This is to obtain an effect.

Effects of the Invention As detailed above, according to the present invention, the reflected light from the mirror surface formed at the end of the optical fiber is focused onto the light-receiving surface of the light-receiving element by the lens provided integrally with the optical fiber. Therefore, even when coupling the SMF to a light-receiving element having a small light-receiving diameter, it is possible to achieve optical coupling with high coupling efficiency and good mounting performance.

[Brief explanation of the drawing]

Fig. 1 is a basic structural diagram of the present invention. Fig. 2 is a processing process diagram of an SMF end showing an embodiment of the present invention. Fig. 3 is a processing process diagram of an SMF end showing another embodiment of the present invention. 4 is a cross-sectional configuration diagram of an optical receiving module showing a conventional optical coupling structure between an optical fiber and a light receiving element, and FIG. 5 is a diagram for explaining another conventional optical coupling structure. 4.17... Light receiving element, 6.14... Optical fiber, 6a... Spherical lens, 10.10'... Electrode terminal, 12... Electric circuit element, 15.22', 26 '...Mirror surface, 16.20.24...Lens, 18...SMF, 22.26...Cut surface. Agent: Patent attorney Tei Iga-7 [:,-,・, 1\
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Claims (1)

[Claims] The end of the optical fiber (14) is cut diagonally to make the cut surface a mirror surface (15), and a lens (16) is used to condense the propagating light reflected by the mirror surface (15).
) is provided integrally with the optical fiber (14), and the light-receiving surface of the light-receiving element (17) is disposed opposite to the lens (16).