Optical module and optical reflecting member

Details Optical module and optical reflecting member Optical module and optical reflecting member

1999-02-18

2001-07-10

Kim, Robert H. (Department: 2877)

Optical waveguides

With disengagable mechanical connector

Optical fiber to a nonfiber optical device connector

C385S094000

Reexamination Certificate

active

06257773

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module, used in optical communications, incorporating therein a semiconductor device such as light-receiving device or light-emitting device; and an optical reflecting member for optically coupling an optical fiber and the semiconductor device to each other with high accuracy.
2. Related Background Art
A conventional optical module in which an optical fiber acting as a transmission medium for signal light and a semiconductor device such as light-receiving device or light-emitting device are optically coupled to each other such modules employs a structure for maintaining the optically coupled state between the optical fiber and semiconductor device by integrally encapsulating a condenser lens and a plane reflecting surface located in the optical path between an end face of the optical fiber and the semiconductor device. As the conventional optical module, for example, Japanese Patent Application Laid-Open No. 63-090866 discloses an optical receiver module configured such that light emitted from an end face of an optical fiber and then passed through a condenser lens is reflected by a plane reflecting surface to be incident on the light-receiving surface of a light-receiving device.
SUMMARY OF THE INVENTION
Having studied the conventional optical module, the inventors have found the following problems. While the conventional optical module employs a configuration in which a condenser lens and a plane reflecting mirror are integrally encapsulated with a transparent resin together with a semiconductor device, it is necessary to establish optical axis alignment between the condenser lens and the plane reflecting mirror and semiconductor device, and encapsulate them with a resin after the position of the semiconductor device is set with a sufficiently high accuracy. However, it has been quite difficult to improve the positioning accuracy of such a semiconductor device, whereby this technique has been unsuitable for making an optical module employed in the field of optical communications.
Although the conventional optical module is applicable to fields which do not require a relatively high accuracy, e.g., a field which allows a relatively broad luminous flux incident on a light-receiving device having a large light-receiving area, it can not be used a field in which a very high alignment accuracy is required such as optical communications because the core diameter of the optical fiber is only about a few &mgr;m and the light-receiving area of the light-receiving device only about several hundred square &mgr;m. When an optical module for optical communications is manufactured by employing a conventional technique, there has been a possibility to occur detrimental effects such as the lowering of the optical coupling efficiency between the optical fiber and the semiconductor device.
In recent years, as the transmission speed in optical fiber communications has been reaching a GHz band, there has been a demand for developing an optical module which can attain a higher aligning accuracy.
The optical module according to the present invention comprises a configuration in which alignment can be adjusted much more easily than conventional module and which is less likely to be influenced by ambient temperature while maintaining a high optical coupling efficiency between an optical fiber and a semiconductor device.
The optical module according to the present invention comprises a housing, having a mounting surface for mounting a semiconductor device; a sleeve, extending along a predetermined direction from a side wall of the housing, for supporting a ferrule attached to a font end of an optical fiber; and an optical reflecting member, for optically coupling the optical fiber and the semiconductor device to each other, having a curved reflecting surface, put in the housing. Here, the semiconductor device encompasses, at least, a light-emitting device and a light-receiving device. The optical module encompasses an optical transmitter module in which a light-emitting device is mounted, while the light-emitting surface of the light-emitting device and the end face of an optical fiber are optically coupled to the light-emitting device; and an optical receiver module in which a light-receiving device is mounted, while the light-receiving surface of the light-receiving device and the end face of an optical fiber are optically coupled to the light-receiving device.
In particular, the reflecting surface of the optical reflecting member preferably has a concave form coinciding with a portion of a virtually defined rotational ellipsoid. In order to attain a high aligning accuracy, the optical reflecting member having such a form is installed at a predetermined position within the housing such that the core of the exit end face of the optical fiber coincides with the first focal point of the rotational ellipsoid, whereas the surface of the semiconductor device (the light-emitting surface in the light-emitting device or the light-receiving surface in the light-receiving device) coincides with the second focal point of the rotational ellipsoid.
In the optical receiver module, even if a signal luminous flux is emitted from the end face of the optical fiber with an angle, it will be reflected by a certain portion of the reflecting surface and reach the light-receiving surface of the light-receiving device as long as the end face coincides with the first focal point. On the other hand, in the case of an optical transmitter module, the light emitted from the light-emitting surface of the light-emitting device with an angle also reaches the end face of the optical fiber due to the action of the reflecting surface mentioned above.
In general, a resin material is utilized as the material for the optical reflecting member due to its productivity, whereas, as shown in
FIG. 1
, feet of a resin-molded optical reflecting member
12
(lower end portions
12
a
to
12
d
) are directly attached with an adhesive onto the mounting surface, on which the semiconductor device (e.g., photo diode PD) is mounted. In this specification, the mounting surface in the housing means not only the upper face of a main plate
31
on which the PD is directly mounted, but also the upper faces of spacers
310
.
The resin material employed in the optical reflecting member
12
has a high thermal expansion coefficient. When the heat generated from the semiconductor device during the operation of the optical module or the heat generated by circuit components is directly transmitted to the optical reflecting member
12
via the lower end portions
12
a
to
12
d
, unexpected stress will be applied to the optical reflecting member
12
. When the optical reflecting member
12
itself is deformed by thermal expansion, the position of the reflecting surface
14
may change or the curvature thereof may fluctuate, thereby remarkably lowering the optical coupling efficiency between the semiconductor device and the optical fiber as shown in FIG.
2
. In
FIG. 2
, a broken line
120
indicates a thermally expanded optical reflecting member, whereas a broken line
140
indicates the reflecting surface of the thermally expanded optical reflecting member.
In an optical module using a resin-molded reflecting member, stress may remain through a thermal process in its assembling step. When stress remains in the resin-molded optical reflecting member, a difference in temperature between its manufacture environment and operation environment (change of the ambient temperature) causes the installed position of the reflecting surface to be displaced or its curvature to fluctuate (the shape of the optical reflecting member as a whole would change due to thermal expansion). Therefore, the light-collecting position on the light-receiving surface of the semiconductor device would shift and the sensitivity of PD would fluctuate. In the case where a laser diode LD or laser emitting device LED is mounted as the semiconductor device, the optical coupling efficiency between t

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