JPH09171127A - Optical communication module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical communication module having an excellent receiving characteristic without affecting the receiving side by a transmitting noise. SOLUTION: A light receiving element 1 and a receiving circuit 6 are mounted on one side of a multilayered circuit board 5, a light emitting element 3 and a transmitting circuit 7 are mounted on the other side of the multilayered circuit board 5 and a shielding layer having more than two layers is arranged in a part located between the light receiving element 1 and the light emitting element 3 of the multilayered circuit board 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication module which performs mutual conversion between an optical signal and an electric signal in digital optical communication.

[0002]

2. Description of the Related Art In digital optical communication, an electric signal of binary logic is converted into light by an optical transmitter, light is transmitted through an optical fiber, and then converted into a binary electric signal by an optical receiver. This enables high-speed long-distance communication, which is difficult with direct transmission of electric signals.

An optical communication module usually includes both an optical transmitter and an optical receiver, and the transmitting side of one optical communication module and the receiving side of the other module are coupled to each other by an optical fiber. Therefore, a pair of two optical fibers is used, and a connector that can be inserted and removed is provided.

A conventional optical communication module will be described below. FIG. 3 shows the structure of a conventional optical communication module,
3A is a top view and FIG. 3B is a side view.

In FIG. 3, 1 is a light receiving element, 2 is a light receiving element holder for holding the light receiving element 1 at an end, 3 is a light emitting element, and 4 is light emitting for holding the light emitting element 3 at an end. Element holder, 14 is the light receiving element 1 and the light emitting element 3
A circuit board in which the terminal pins of are connected to the same end, 6 is a receiving circuit provided on the surface of the circuit board 14, 7 is a transmitting circuit also provided on the surface of the circuit board 14, and 15 is the circuit board 14 Is an electrical connector that is provided in the optical communication module and connects the optical communication module and a mother board (not shown). Reference numeral 9 is an optical fiber connector mounted on the optical communication module, and the ends of two optical fibers are inserted into the light receiving element holder 2 and the light emitting element holder 4, respectively.

Hereinafter, the relationship and operation of each of the above-mentioned components will be described. The digital electric signal sent from the circuit on the mother board to the optical communication module is sent to the transmission circuit 7, and the transmission circuit 7 causes a current to flow through the light emitting element 3 to emit light according to the digital electric signal. This light is collected by the lens fixed inside the light emitting element holder 4 and sent to the inserted optical fiber for transmission. On the other hand, the light emitted from the optical fiber inserted in the light receiving element holder 2 is converted into an electric signal by the light receiving element 1 and amplified by the receiving circuit 6.
It is binarized and transmitted to the mother board as a digital electric signal. As described above, the optical communication module can transmit and receive information by light at the same time.

[0007]

However, since the transmission circuit 7 handles a relatively large current, it affects the reception circuit 6 mounted on the same circuit board 14 as electromagnetic noise.
Since the light receiving element 1 and the receiving circuit 6 handle a weak signal having an extremely high frequency, the light receiving element 1 and the receiving circuit 6 are easily affected by noise, and an error is likely to occur in the received signal.

Further, the light receiving element 1 and the light emitting element 3 are mounted so as to project from the same end of the circuit board 14, and the positions where the respective terminal pins are fixed to the circuit board 14 by soldering are outside the plane of the shield layer. It is burned out and the shielding effect is lost. Although the length of the terminal pin protruding from the shield layer is small, the terminal pin of the light emitting element 3 is a portion where a high-speed large current flows and electromagnetic radiation is easily generated, and the terminal pin of the light receiving element 1 is before amplification. Since it is a portion where a weak current flows, the fact that both are close to each other in parallel is likely to cause electromagnetic interference. Therefore, there is a problem that a reception error due to noise is always likely to occur, and particularly when the level of the received light is low, the noise is relatively increased and the reception error frequently occurs.

Further, the light-receiving element holder 2 and the light-emitting element holder 4 are grounded only by one terminal of the light-receiving element 1 and the light-emitting element 3, respectively, and the potential fluctuation easily occurs due to the inductance component of the terminal pin.
In particular, the light receiving element holder 2 changes its potential due to the induction of ambient electromagnetic field noise, and induces noise in the signal line of the light receiving element 1 to deteriorate the signal quality.

Therefore, the present invention solves the above-mentioned conventional problems, and provides an optical communication module having a good reception characteristic without electromagnetically separating the transmission section and the reception section so that transmission noise does not affect the reception side. The purpose is to do.

[0011]

In order to achieve the above object, the present invention comprises a multilayer circuit board having a shield layer inside, a light receiving element for converting received light into an electric signal, and a light receiving element connected to the light receiving element. A light receiving element, a light emitting element that generates transmitted light, and a transmitting circuit that drives the light emitting element, wherein the light receiving element and the receiving circuit are mounted on one surface of the multilayer circuit board, and the light emitting element and the transmitting circuit are provided. Is mounted on the other surface of the multilayer circuit board.

According to the present invention, the transmitting section and the receiving section are electromagnetically separated, and the transmission noise does not affect the receiving side.
An optical communication module having good reception characteristics is provided.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention includes a multilayer circuit board having a shield layer, a light receiving element for converting received light into an electric signal, and a receiving circuit connected to the light receiving element. A light emitting element for generating transmission light, and a transmitting circuit for driving the light emitting element, wherein the light receiving element and the receiving circuit are mounted on one surface of the multilayer circuit board, and the light emitting element and the transmitting circuit are the multilayer. This is a configuration of the optical communication module mounted on the other surface of the circuit board.Since the planar shield layer electromagnetically separates the light receiving element and the light emitting element, they are generated on the transmitting side. The electromagnetic noise is not transmitted to the receiving side, and the receiving characteristics are good.

According to a second aspect of the present invention, in the optical communication module according to the first aspect, the multilayer circuit board has at least two layers arranged in a portion located between the light receiving element and the light emitting element. In the configuration having the shield layers described above, the two or more shield layers electromagnetically separate the light receiving element and the light emitting element from each other, so that electromagnetic noise generated on the transmitting side is received. It is not transmitted to the side, and the reception characteristics are good.

According to a third aspect of the present invention, a multilayer circuit board having a shield layer, a light receiving element for converting received light into an electric signal, an optical fiber for sending the received light to the light receiving element, and the light receiving element. And a light receiving element holder that supports both of the light receiving element, a receiving circuit connected to the light receiving element, a light emitting element that generates transmission light, an optical fiber that receives the transmission light from the light emitting element, and the light emitting element. A light emitting element holder for supporting, and a transmission circuit for driving the light emitting element,
The light receiving element and the receiving circuit are mounted on one surface of the multilayer circuit board, the light receiving element holder is directly connected to the shield layer of the multilayer circuit board, and the light emitting element and the transmitting circuit are on the other side of the multilayer circuit board. The light emitting element holder is mounted on a surface, and the light emitting element holder is configured as an optical communication module directly connected to the shield layer of the multilayer circuit board, and the shield layer electromagnetically acts between the light receiving element and the light emitting element. In order to separate the two, the electromagnetic noise generated on the transmitting side will not be transmitted to the receiving side, and the impedance to the ground potential of the light receiving element holder and the package of the light receiving element will be reduced, and external electromagnetic noise Induction is prevented and the signal-to-noise ratio of the signal current flowing through the light receiving element is improved. In addition, the impedance of the light emitting device package and the light emitting device holder is reduced, the potential fluctuation due to the drive current is prevented, the radiation of electromagnetic induction noise to the outside is prevented, the noise generation amount itself is reduced, and the reception characteristics are improved. It will be good.

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 shows a configuration of an optical communication module according to an embodiment of the present invention, and FIG. 1 (a) is a side view.
FIG. 1B is a top view.

In FIG. 1, 1 is a light receiving element, 2 is a light receiving element holder, 3 is a light emitting element, and 4 is a light emitting element holder. 5
Is a multi-layer circuit board, 6 is a receiving circuit, 7 is a transmitting circuit, 8 is a connector for connecting the optical communication module and the mother board, and the above are the main elements constituting the optical communication module. 9
Is an optical fiber connector attached to the optical communication module, and the ends of two optical fibers are inserted into the light receiving element holder 2 and the light emitting element holder 4, respectively. Items designated by the same reference numerals in FIGS. 1 and 3 are the same elements.

FIG. 2 shows a schematic view of the copper foil pattern of the multilayer circuit board 5. The multilayer circuit board 5 has a four-layer structure and is composed of a first layer, a second layer, a third layer, and a fourth layer from the side on which the receiving circuit 6 is mounted. 2A is a schematic view showing a copper foil pattern of a first layer of a circuit board in the optical communication module, and FIG. 2B is a schematic diagram of a copper foil pattern of a fourth layer of the circuit board in the optical communication module. It is a schematic diagram shown, and each has a pattern viewed from the side on which the receiving circuit 6 is mounted. In FIG. 2, a wiring pattern between terminals is omitted for the sake of explanation. The second layer is a solid shield layer connected to the ground potential of the receiver circuit 6, and the third layer is a solid shield layer connected to the ground potential of the transmitter circuit 7. Regarding the second layer and the third layer Is omitted.

In the pattern of the first layer, the light receiving element holder 2
A shield surface 10 having an area sufficiently larger than the size of the light receiving element holder 2 is provided at a position facing each other, and the conductive surface is exposed in order to establish electrical conduction with the light receiving element holder 2. Similarly, the pattern of the fourth layer includes the light emitting element holder 4
A shield surface 11 having an area that is sufficiently larger than the size of the light emitting element holder is provided at a position facing each other, and the conductive surface is exposed in order to establish electrical conduction with the light emitting element holder 4.

The structure of the optical communication module according to the first embodiment will be described below. The optical communication module is shown in FIG.
It is connected to a mother board (not shown) through the connector 8 in the direction of the arrow shown in (a). The optical fiber connector 9 is shown in FIG.
It is inserted into the optical communication module in the direction of the arrow shown in (b). The multilayer circuit board 5 is arranged perpendicularly to the connecting direction with the mother board and the inserting direction of the optical fiber connector 9. The receiving circuit 6, the connector 8 and the light receiving element 1 are mounted on the first layer of the multilayer circuit board 5, and the transmitting circuit 7 is mounted on the opposite fourth layer.
And the light emitting element 3 is mounted.

The light-receiving element 1 has three terminal pins, which are a signal terminal, a bias voltage terminal, and a terminal directly connected to the package. All of them are surface-mounted by soldering on the first surface of the multilayer circuit board 5. There is. The ground terminal pin directly connected to the package is connected to the ground terminal of the receiving circuit 6 at point A. The metal light-receiving element holder 2 is also connected to the light-receiving element 1 by welding, and thus is also connected to the ground terminal of the receiving circuit 6. First of the multilayer circuit board 5
A shield surface 10 connected to the ground potential of the receiving circuit 6 is provided in a region of the layer facing the light receiving element holder 2, and the side surface of the light receiving element holder 2 is soldered at a point B of the shield surface 10 to maintain electrical continuity. ing.

Since the light receiving element holder 2, the package of the light receiving element 1 and the ground terminal pin of the light receiving element 1 are connected to the ground potential of the receiving circuit 6 at the points A and B, the light receiving element holder 2 and the light receiving element are connected. The impedance of the package No. 1 with respect to the ground potential is reduced, the induction of external electromagnetic field noise is prevented, and the signal-to-noise ratio of the signal current flowing through the light receiving element is improved.

The light emitting element 3 has three terminal pins, namely, a drive terminal for supplying a drive current, a monitor terminal for monitoring the amount of light emission, and a ground terminal directly connected to the package. These three terminal pins are mounted on the second surface of the multilayer circuit board 5 by soldering, and the ground terminal pin directly connected to the package is connected to the ground potential of the transmitter circuit 7 at the point C. Since the light emitting element holder 4 made of metal is connected to the light emitting element 3 by welding, it is connected to the ground potential of the transmission circuit 7. A shield surface 11 connected to the ground potential of the transmitter circuit 7 is provided in a region of the multilayer circuit board 5 facing the light emitting element holder 4 of the fourth layer, and the side surface of the light emitting element holder 4 is soldered at a point D of the shield surface 11. They are joined and maintain electrical continuity.

The light emitting element holder 4, the package of the light emitting element 3, and one of the terminal pins of the light emitting element 3 are connected to the ground potential of the transmitter circuit 7 at two points, so that the package of the light emitting element 3 and the light emitting element. The impedance of the holder 4 is reduced, the potential fluctuation due to the driving current is prevented, the electromagnetic induction noise is prevented from being radiated to the outside, and the noise generation amount itself is reduced.

Further, the light-receiving element 1 and the light-emitting element 3 are prevented from interfering with each other by electromagnetic fields by the shield surfaces of four layers from the first layer to the fourth layer of the multilayer circuit board 5. The receiving circuit 6 and the transmitting circuit 7 are shielded by the second layer and the third layer of the multilayer circuit board 5 to prevent noise generated by the transmitting circuit 7 from reaching the receiving circuit 6.

As described above, according to the first embodiment, the electromagnetic noise due to the driving current of the light emitting element 3 is generated by the light receiving element 1 by the four-layered shield provided on the multilayer circuit board 5.
Of the light emitting element 3 and the light emitting element holder 4 to suppress the potential fluctuations of the light emitting element 3 and the light emitting element holder 4, and suppress the potential fluctuations of the package of the light receiving element 1 and the light receiving element holder 2 to reduce the noise. It is possible to prevent external electromagnetic noise from entering the signal line.

[0027]

As is apparent from the above description, according to the present invention, the planar shield layer electromagnetically separates the light-receiving element and the light-emitting element from each other, so that they are generated on the transmitting side. It is possible to realize an optical communication module having good reception characteristics because electromagnetic noise is not transmitted to the receiving side, noise generation to the outside and noise entering from the outside are eliminated.

[Brief description of the drawings]

FIG. 1A is a side view of an optical communication module according to a first embodiment of the present invention, and FIG. 1B is a top view of the optical communication module.

FIG. 2A is a schematic diagram showing a first layer copper foil pattern of a circuit board in the same optical communication module, and FIG. 2B is a schematic diagram showing a fourth layer copper foil pattern of a circuit board in the same optical communication module.

FIG. 3A is a top view of a conventional optical communication module, and FIG. 3B is a side view of the same optical communication module.

[Explanation of symbols]

 1 light receiving element 2 light receiving element holder 3 light emitting element 4 light emitting element holder 5 multi-layer circuit board 6 receiving circuit 7 transmitting circuit 8 connector 9 optical fiber connector

Claims (3)

[Claims] 1. A multi-layer circuit board having a shield layer, a light receiving element for converting received light into an electric signal, a receiving circuit connected to the light receiving element, a light emitting element for generating transmitted light, and the light emitting element. A transmitting circuit for driving, wherein the light receiving element and the receiving circuit are mounted on one surface of the multilayer circuit board,
The optical communication module, wherein the light emitting element and the transmission circuit are mounted on the other surface of the multilayer circuit board. 2. The optical communication module according to claim 1, wherein the multilayer circuit board has at least two shield layers disposed in a portion located between the light receiving element and the light emitting element. 3. A multilayer circuit board having a shield layer, a light receiving element for converting received light into an electric signal, and a light receiving element holder for supporting both the optical fiber for sending the received light to the light receiving element and the light receiving element. A receiving circuit connected to the light receiving element, a light emitting element for generating transmission light, a light emitting element holder for supporting both the optical fiber for receiving the transmission light from the light emitting element and the light emitting element, and the light emitting element A light receiving element and a receiving circuit are mounted on one surface of the multilayer circuit board, the light receiving element holder is directly connected to a shield layer of the multilayer circuit board, and transmits light to the light emitting element. An optical communication module, wherein a circuit is mounted on the other surface of the multilayer circuit board, and the light emitting element holder is directly connected to a shield layer of the multilayer circuit board.