Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-08-17
2003-06-10
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S239000, C250S214100
Reexamination Certificate
active
06576888
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light receiving module.
2. Related Background Art
The conventional light receiving modules are generally classified into the following two types. The first type embraces light receiving modules containing a waveguide type semiconductor photodetector, and the second type embraces light receiving modules containing a surface receiving type semiconductor photodetector.
SUMMARY OF THE INVENTION
In the technical field of optical communications, there are demands for light receiving modules capable of operating at high speeds. For example, these light receiving modules are recently required to perform transmission at about 10 Gbps. However, according to the inventor's technical knowledge, it is not easy to develop a structure of an optical communication module capable of providing electric signals from the light receiving element at the foregoing fast transmission rate while maintaining sufficient coupling efficiency between an optical fiber and the light receiving element even with variation in alignment between the optical fiber and the light receiving element in manufacturing process. Namely, there are needs for an optical communication module capable of processing electric signals including transmission information at about 10 Gbps while maintaining the optical coupling efficiency.
In the optical communication modules of the former type, an optical fiber and a waveguide semiconductor photodetector are arranged on a straight line. In this configuration, the propagation direction of optical signals coincides with the transmission direction of electric signals. An end face of the optical fiber is optically coupled with one end face of the waveguide semiconductor photodetector. In the former type, since the optical characteristics of the optical communication modules are sensitive to the alignment between the optical fiber and the waveguide light receiving element, it is necessary to carry out the positioning of the two members with high accuracy.
In the latter type, the end face of the optical fiber is optically coupled with a light-receiving surface of the surface receiving type semiconductor photodetector. In this type, however, one end of the optical fiber faces the light receiving surface of the surface receiving type semiconductor photodetector. On the other hand, generally, the light receiving element and an electron device are placed on a common plane so as to be connected with each other, such that the light receiving element is connected through bonding wires to the electron device. In this configuration, the traveling direction of optical signals does not coincide with the traveling direction of electric signals. According to the inventor's technical experiences, it can be hardly said that this structure is applicable to the light receiving modules.
Without using the above configuration, there is another candidate for the structure as shown below. This light receiving module has a configuration in which the surface receiving type semiconductor photodetector is mounted on one side face of a submount of rectangular parallelepiped and an electron device is mounted on an upper surface of the submount. The two devices are connected to each other through an conductive layer extending from the upper surface to the side face of the submount. In this structure, the optical fiber, surface receiving semiconductor photodetector, and electron device are arranged in a line, but the structure is complicated.
Another known module is an light receiving module in which the surface receiving type semiconductor photodetector and the electron device are mounted on an upper surface of a submount and in which light from one end of the optical fiber is guided via a concave mirror to the light-receiving surface of the surface receiving type photodetector. In this structure, the optical fiber, surface receiving type semiconductor photodetector, and electron device are also arranged in a line. However, an additional optical component such as the concave mirror is required for the optical coupling between the optical fiber and the surface receiving type semiconductor photodetector.
In both configurations above, the structures of the light receiving modules are complex and require their tolerance to be close for the alignment between the optical fiber and the photodetector. This means that a plateau region in the coupling efficiency between the optical fiber and the photodetector, i.e. the range in which the optical coupling efficiency is substantially invariable with variation in their alignment, is small.
It is an object of the present invention to provide an light receiving module capable of achieving satisfactory coupling efficiency between the optical fiber and the semiconductor photodetector and capable of increasing data transmission rates.
One aspect of the present invention is a light receiving module. The light receiving module comprises a mounting member, an optical fiber, a semiconductor photodetector, a mount substrate, and a signal processing semiconductor element.
The mounting member has a pair of arm portions and a connecting portion. Each of the arm portions extends in a first direction. The connecting portion extends in a direction intersecting with the first direction to connect the pair of arm portions. The optical fiber has a first end and a second end. The semiconductor photodetector has a light incidence surface optically coupled to the first end of the optical fiber, and a light receiving element portion. The mounting substrate is arranged between the pair of arm portions of the mounting member and is mounted with the optical fiber and the semiconductor photodetector. The signal processing semiconductor element is placed on the mounting member and processes a signal from the semiconductor photodetector.
By the mounting substrate, the optical fiber is enabled to be optically coupled to the semiconductor photodetector. The mounting substrate is placed between the pair of arm portions of the mounting member. This arrangement permits the placement of the signal processing semiconductor element in the proximity of the semiconductor photodetector. This placement ensures the satisfactory optical coupling between the optical fiber and the semiconductor photodetector and permits reduction in the length of electrical connection between the semiconductor photodetector and the signal processing semiconductor element in the light receiving module.
The light receiving module may also be configured to further comprise a housing capable of accommodating the mounting substrate and the mounting member. The housing has a plurality of wall portions and terminals. The mounting member is placed so as to be located between the mounting substrate and the wall portions. The semiconductor photodetector is electrically connected to the terminals via a wiring member placed on the mount member. The wiring member on the mounting member enables the reduction of a connection path between the semiconductor photodetector and the terminals of the housing.
In the light receiving module, the semiconductor photodetector has an electrode surface on which electrode pads are provided, and the semiconductor signal processor has a pad surface on which electrode pads are provided. The pad surface and the electrode surface are arranged to be positioned relative to a reference surface within manufacturing positional variations. This arrangement of the pad surface and the electrode surface makes a reduction feasible in the wire length between the semiconductor photodetector and the signal processing semiconductor element.
The light receiving module may also be configured to further comprise a housing that accommodates the mounting member and the mounting substrate and contains therein a wiring surface having a wiring layer. In this light receiving module, the signal processing semiconductor element has a pad surface on which electrode pads are provided. The wiring surface and the pad surface are arranged so as to be position
Fujimura Yasushi
Kida Yuuji
Le Que T.
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
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