JPH06324232A - Light signal receiver and light transmission system - Google Patents

Abstract

PURPOSE:To stabilize the transmission characteristics of the light signal receiver for optical communication. CONSTITUTION:This light signal receiver is so constituted that signal light 16 is made incident on an optical fiber 13 via an optical connector 14 and that the signal light 16 emitted from a ferrule 15 is condensed by a lens 12 and is made incident on a photodiode 11. This signal light is made incident on the photodiode 11 through a diaphragm 17 having an aperture diameter below the photodetecting diameter at the photodetecting surface of the photodiode 11. The signal light 16 exclusive of the photodetecting diameter of the photodiode 11 is removed by the diaphragm 17 fixed to the photodetecting surface of the photodiode 11 in the case the signal light 16 having the spot diameter larger than the photodetecting diameter of the photodiode 11 is made incident on the photodiode 11. The irregular reflection at the photodetecting surface end of the photodiode 11 and on the outer side thereof is thus prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver for optical communication.

[0002]

2. Description of the Related Art In an optical communication system using a semiconductor laser as a light source, when a photodiode is used as a receiver, the photodiode is modularized in order to easily obtain the signal light transmitted through an optical fiber. An optical fiber called a pigtail and a lens can be efficiently coupled to the photodiode.

A conventional optical receiving module will be described below. FIG. 4 shows an optical system of a conventional optical receiver. In FIG. 4, 31 is a photodiode, 32 is a lens, 33 is an optical fiber, 34 is an optical connector, 35 is a ferrule, and 36 is signal light. Ferrule 35 here
The end surface of is obliquely polished to prevent the signal light 36 from being reflected by the end surface and returning to the semiconductor laser which is the light source.
Similarly, the photodiode 31 is also mounted obliquely with respect to the optical axis of the lens 32, and the end face of the ferrule 35, the lens 32,
The photodiodes 31 are fixed so as not to be parallel to each other. In the above configuration, the signal light 36 enters the optical fiber 33 via the optical connector 34, and the signal light 36 emitted from the ferrule 35 is condensed by the lens 32 and enters the photodiode 31.

[0004]

In the conventional optical receiver configured as above, the photodiode 31 is used.
If the signal light 36 incident on is partially out of the light receiving portion of the photodiode 31 or if the spot diameter is larger than the light receiving diameter, the signal light 36 is emitted from the photodiode 31.
There is a problem in that the light is impinged on the edge of the light-receiving surface or the outside thereof and is diffusely reflected, and the reflected light becomes a noise component to deteriorate the transmission characteristics or make it unstable. Even if the signal light 36 is collected by the lens 32 and its spot diameter is adjusted to be smaller than the light receiving diameter of the photodiode 31, an unnecessary signal component clad mode that propagates while totally reflecting the clad is obtained. Is signal light 36
, The spot diameter of the cladding mode is larger than that of the propagation mode when the signal light 36 enters the photodiode 31. Therefore, similarly, the signal light 36 impinges on the light-receiving surface end of the photodiode 31 or the outside thereof and is diffusely reflected, and the reflected light becomes a noise component to deteriorate the transmission characteristics or make the transmission unstable. It was

In view of the above points, the present invention provides a stable transmission characteristic when the spot diameter of the incident signal light is larger than the light receiving diameter of the photodiode or when the unnecessary signal component cladding mode is included in the signal light. It is an object of the present invention to provide an obtained optical receiving device.

[0006]

In order to achieve the above object, the present invention provides an optical fiber for receiving light, a photodiode, and an optical axis between the optical fiber for receiving light and the photodiode. And comprising at least one lens that collects incident light from the optical fiber for light reception,
The light receiving device has a structure in which a diaphragm is provided on the light receiving surface of the photodiode.

[0007]

According to the present invention, when the signal light having a spot diameter larger than the light receiving diameter of the photodiode is incident on the photodiode, the present invention has a diaphragm fixed on the light receiving surface of the photodiode to provide a signal outside the light receiving diameter of the photodiode. Light is removed, and diffused reflection at the light-receiving surface end of the photodiode or outside thereof is prevented, and stable transmission characteristics are obtained.

[0008]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an optical system diagram of an optical receiver in a first embodiment of the present invention. In FIG. 1, 1
1 is a photodiode, 12 is a lens, 13 is an optical fiber, 14 is an optical connector, 15 is a ferrule, 16 is a signal light, and 17 is a diaphragm. Here, the end surface of the ferrule 15 is obliquely polished. Similarly, the photodiode 11 is also mounted obliquely with respect to the optical axis of the lens 12. The configuration of these components is the same as the above-mentioned conventional example.

A characteristic feature of this embodiment is that a diaphragm 17 is provided on the light receiving surface of the photodiode 11. The diaphragm 17 is fixed to the light receiving surface of the photodiode 11, and the diameter of the aperture is equal to or smaller than the light receiving diameter of the photodiode 11. The opening is a knife edge to prevent light diffraction.

The operation of the optical receiving apparatus of this embodiment having the above-mentioned structure will be described below. Signal light 16
Enters the optical fiber 13 via the optical connector 14, and the signal light 16 emitted from the ferrule 15 is condensed by the lens 12 and passes through the diaphragm 17 to enter the photodiode 11. Here, when the signal light 16 incident on the photodiode 11 is partly out of the light receiving portion of the photodiode 11 or when the spot diameter is larger than the light receiving diameter, the unnecessary signal component cladding mode is the signal light 16.
, The signal light 16 outside the light receiving diameter of the photodiode 11 is removed by the lens 12 and the diaphragm fixed to the light receiving surface of the photodiode 11, and the signal light 16 is received at the end of the light receiving surface of the photodiode 11. Prevents diffuse reflection on the outside. Therefore, stable transmission characteristics can be obtained.

As described above, according to this embodiment, by fixing the diaphragm 17 having an opening diameter smaller than the light receiving diameter to the light receiving surface of the photodiode 11, a spot diameter larger than the light receiving diameter of the photodiode is obtained. Even when the signal light is incident on the photodiode, the signal light outside the light receiving diameter of the photodiode 11 is removed, and diffused reflection at the end of the light receiving surface of the photodiode or the outside thereof can be prevented and stable transmission characteristics can be obtained.

Needless to say, the same effect can be obtained even if the diaphragm 17 is not fixed to the light receiving surface of the photodiode 11 but is fixed between the lens 12 and the photodiode 11 by another method.

When the signal light 16 contains a cladding mode, the length of the optical fiber 13 is made long enough to sufficiently attenuate the cladding mode, so that the cladding mode is prevented from entering the photodiode 11. It can be avoided. (Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a diaphragm according to the second embodiment of the present invention. In FIG. 2, 21 is a diaphragm,
22 is an optical absorber. The diaphragm 21 is configured by coating the optical absorbers 22 on both surfaces thereof.

The effect of the diaphragm 21 of this embodiment constructed as described above will be described below. If the signal light incident on the photodiode is partly out of the light receiving portion of the photodiode, or if the spot diameter is larger than the light receiving diameter, or if the signal light contains an unnecessary signal component cladding mode, The signal light outside the light receiving diameter of the photodiode is removed by the diaphragm 21 provided on the light receiving surface of the photodiode, and the signal light is not received outside the light receiving surface. At this time, since the optical absorber 22 does not reflect the light outside the aperture of the diaphragm 21, no return light is generated at the end surface of the diaphragm 21. Further, multiple reflection between the photodiode light receiving surface and the end surface of the diaphragm 21 does not occur. The optical absorber 22 may be black alumite.

As described above, according to this embodiment, the diaphragm 2
By coating the optical absorbers 22 on both end surfaces of 1, the return light at the end surface of the diaphragm 21 and the multiple reflection between the photodiode light receiving surface and the end surface of the diaphragm 21 can be prevented, and stable transmission characteristics can be obtained. (Embodiment 3) A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram of an optical transmission system according to a third embodiment of the present invention. In FIG.
31 is an electric signal, 32 is an optical transmitter, 33 is a drive circuit,
34 is an optical signal, 35 is an optical fiber, 36 is an optical receiver,
37 is an amplifier circuit. The optical receiving device 36 is defined by claim 1.
Alternatively, it has an aperture according to claim 2.

The operation of the optical transmission system of this embodiment constructed as above will be described below. The digital or analog electric signal 31 is input to the optical transmitter 32 and converted into an optical signal 34. Then, the optical signal 34 is transmitted to the optical receiving device 36 using the optical fiber 35 as a transmission medium. At this time, the optical signal 34 is converted into the electric signal 31, amplified by the amplifier circuit 37, and output.

As described above, according to this embodiment, by using the optical receiving device 36 according to claim 1 or 2, it is possible to prevent the deterioration of the transmission characteristic newly generated in the optical receiving section and to perform stable transmission. An optical transmission system having characteristics can be obtained.

[0021]

As described above, according to the present invention,
By providing a diaphragm with an aperture diameter equal to or smaller than the light receiving diameter on the photodiode light receiving surface, if the signal light incident on the photodiode is partly off the light receiving portion of the photodiode or the spot diameter is If greater than
Furthermore, the signal light with a spot diameter larger than the light receiving diameter of the photodiode, which occurs when unnecessary signal component cladding mode is included in the signal light, is removed to prevent irregular reflection at the light receiving surface edge of the photodiode or outside thereof. Therefore, the transmission characteristics of the optical receiver can be stabilized, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is an optical system diagram of an optical receiving device according to a first embodiment of the present invention.

FIG. 2A is a plan view of a diaphragm according to a second embodiment of the present invention, and FIG. 2B is a side view of the diaphragm.

FIG. 3 is a configuration diagram of an optical transmission system according to a third embodiment of the present invention.

FIG. 4 is an optical system diagram of a conventional optical receiver.

[Explanation of symbols]

 11 Photodiode 12 Lens 13 Optical Fiber 14 Optical Connector 15 Ferrule 16 Signal Light 17 Aperture

Claims (3)

[Claims] 1. An optical fiber for light reception, a photodiode, and an optical fiber arranged between the optical fiber for light reception and the photodiode on the optical axis to collect incident light from the optical fiber for light reception. An optical receiving device comprising at least one lens, wherein a light-receiving surface of the photodiode is provided with a diaphragm. 2. The optical receiver according to claim 1, wherein the diaphragm has an optical absorber formed by coating on both sides. 3. An optical transmission system having the optical receiving device according to claim 1.