JPH07294776A - Optical receiving module - Google Patents

Abstract

PURPOSE:To assure a high light reflection attenuation quantity without deterioration of electric signals and optical coupling by rotating a substrate mounted with a photodetector and IC around a coaxial connector at a specific angle and making light incident inclinatorily on this photodetector. CONSTITUTION:An orthogonal coordinate system having its X-axis at a direction where the signals are transmitted through a coaxial connector 3 on the high-frequency substrate 1 mounted with the photodetector 6 and the IC for amplifying its output on the same plane and having its Y-axis at an incident direction of light is taken. The axis rotating 6 from the the Z-axis around the X-axis as a center of rotation is taken as a ZI-axis. The substrate 1 is arranged on the plane created by the X-axis and the ZI-axis. The rotating angle theta is determined by a trade off relation between the optical coupling and the light reflection attenuation quantity. The rotating angle thetais made small when the photodetector is directed to the direction where the absolute value of the Z-axis component of the axial vector perpendicular to the side face of the ferrule 4 is maximized. As a result, the contact relation between the high-frequency signal line on the substrate and the coaxial connector does not change and, therefore, the inclining of the photodetector relative to the optical axis is possible without deteriorating the transmission characteristic of the electric signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency optical receiver module used in optical communication, which requires a high optical return loss.

[0002]

2. Description of the Related Art As the transmission speed becomes higher than Gb / s, in order to reduce the parasitic capacitance and the parasitic inductance component due to the mounting of the device, the light receiving device and the IC are arranged as close as possible, and the same including the bypass capacitor and the power supply line. It has a structure to be mounted on a substrate. As an example of this implementation, Japanese Patent Laid-Open No. 5-0
No. 74935. An example of incorporating this substrate into a module is shown in FIG. In order to increase the mounting efficiency of the module, it is desirable that light is incident parallel to the surface 7 on which the module is mounted and that an electric signal is output parallel to the surface 7 on which the module is mounted. In order to reinforce the ground, the board 1 is mounted so that the ground surface is in close contact with the metal surface, and is hermetically sealed in the case 2. The light emitted from the ferrule 4 at the end of the optical fiber is condensed by the lens 5 and optically coupled with the light receiving element 6 on the lens 1. For the end surface of No. 4, there is a means of oblique polishing of about 8 degrees or non-reflection coating in order to prevent deterioration of the light reflection attenuation amount due to end surface reflection. Considering the ferrule cost, diagonal polishing is cheaper. Further, since the light from the ferrule is emitted with an inclination, the light is incident on the light receiving element with an inclination, and the light reflection attenuation amount due to the reflected light from the light receiving surface is also reduced. Therefore, an obliquely-polished ferrule of about 8 degrees is used. The substrate 1 was arranged perpendicular to the Y axis so that the optical coupling was maximized when the direction of light incident on the module was the Y axis.

[0003]

In the mounting method described above, light is obliquely incident on the light receiving element, but the light reflected by the light receiving element is re-focused by the lens, and the light reflection attenuation amount deteriorates.

[0004]

A rectangular coordinate system having a direction in which a signal is transmitted through a coaxial connector 3 on a substrate as an X axis and a direction in which light is incident as a Y axis is taken, and the X axis is the center of rotation. The axis rotated by θ from the axis is the Z1 axis, and the substrate 1 is arranged on the plane formed by the X axis and the Z1 axis. The rotation angle θ is determined by the trade-off relationship between optical coupling and light reflection attenuation. The rotation angle θ can be made smaller in the direction in which the absolute value of the Z-axis component of the axis vector perpendicular to the end face of the ferrule is maximized.

[0005]

With the above structure, the contact relationship between the high-frequency signal line on the substrate and the coaxial connector does not change, so that the optical element can be tilted with respect to the optical axis without deteriorating the transmission characteristics of the electric signal. When the distance between the optical element and the ferrule is l, the light reflected by the optical element hits l tan θ above the lens and reduces the return light to the ferrule when compared with the case where the optical element is not tilted with respect to the optical axis. it can.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining an embodiment of the present invention. The light passes through a single mode fiber having a core diameter of 10 μmφ and is emitted from the end face of the ferrule that is obliquely polished by 8 degrees. If the refractive index of the core glass is 1.5, the light rays emitted from the end face of the ferrule are inclined by about 5 degrees. When the end face of the ferrule is oriented so that the case upper component (Z component) of the axis vector perpendicular to the end face of the ferrule is maximized, the light rays are refracted downward and emitted. The light receiving element for high frequency needs to have a small light receiving diameter in order to reduce the capacitance. In order to support high frequencies of 5 Gb / s or more, elements with a light receiving diameter of 30 μmφ or less are used.
Furthermore, in order to support high frequencies of 10 Gb / s or more, 2
An element having a light receiving diameter of 5 to 20 μmφ or less is used. In order to achieve optical coupling with this light receiving element, the beam waist diameter of the Gaussian beam must be narrowed down to 15 μmφ. When a quarter pitch SELFOC lens is used, this can be achieved when the distance from the ferrule to the SELFOC lens is 1.5 mm and the distance from the SELFOC lens to the light receiving element is 1.5 mm. In this optical system, when the substrate is not tilted, the target of the light reflection attenuation amount is -27.
In dB, about 50% of the modules cannot reach the goal. Here, the substrate surface is tilted so that the axis vector perpendicular to the substrate surface on which the light receiving element is located faces the case 6 to 8 degrees with respect to the Y axis. The tilting of the substrate surface can be achieved by obliquely processing the metal surface 8 on which the substrate is mounted. With the above improvement, 99% or more of the modules can achieve the target of the optical return loss. For optical coupling, the light receiving diameter is
It is sθ times and equalization. If θ is 7 degrees, it is considered that the Z component of the light receiving diameter is reduced by 0.99.
Since the light receiving diameter is larger than the beam waist, there is no deterioration in optical coupling. FIG. 2 shows an embodiment in which a back illuminated light receiving element is used. The end face of the ferrule is rotated 180 degrees from the above example, and the direction of tilting the substrate is also the opposite side to the above example.

[0007]

As described above in detail, a large amount of light reflection attenuation can be obtained without deterioration of electric signals and optical coupling, and the yield can be improved. Further, regarding the manufacturing, it is possible to take measures by making a small change in the conventional module, and it is possible to manufacture at the same cost as the conventional.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an embodiment of the present invention when a back-illuminated light receiving element is used.

FIG. 3 is a diagram showing a structural example of a conventional optical receiver module.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... High-frequency board on which light-receiving element, IC is mounted, 2 ... Case, 3 ... High-frequency coaxial connector, 4 ... Ferrule, 5 ... Selfoc lens, 6 ... Light-receiving element, 7 ... Module mounting surface, 8 ... Board mounted Metal to do.

Claims (1)

[Claims] 1. A light receiving element and I for amplifying an output of the light receiving element.
C is mounted on the same plane, and a substrate A mounted so as to be parallel to the light receiving surface of the light receiving element is hermetically sealed in a case, and a signal on the substrate is output by a coaxial connector. In the optical receiving module, a direction in which a signal on the substrate is transmitted is an X axis, a direction in which light is incident on the module is a Y axis, and a direction perpendicular to the X axis and the Y axis is a Z axis. The Cartesian coordinate system is used, and the axis tilted from the Z axis by 4 to 10 degrees about the X axis is the Z1 axis,
An optical receiver module in which a substrate A is arranged on a plane formed by the Z axis and the Z1 axis.