JPH01200734A - Optical communication transmission equipment - Google Patents

Abstract

PURPOSE:To make an optical attenuator unnecessary even when the present equipment is used as a transmitting device for a short distance and to attain high reliability and a long life by switching the bias electric current of a semi- conductor laser diode(LD) by a switch. CONSTITUTION:An input signal is inputted to a pulse driving circuit 1, and a semi-conductor laser diode(LD) 2 is driven. Then, the optical output of the LD 2 is detected by an optical detector 3 and a level detecting circuit 4, and a DC bias is generated from a bias circuit 6 in comparing with a reference voltage in a comparing circuit 5. A DC bias is connected to the LD 2 by a switch circuit 7 corresponding to a switching signal when it is used at a high output, and in case of a low output, it is cut off. Thus, the title device can be used as a transmission equipment for a short distance without using an optical attenuator. Consequently, the trouble of the multipath reflection and so on of the optical attenuator does not exist, and high reliability and a long life can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical communication transmitter used in an optical communication system.

Problems to be solved by conventional techniques and inventions under DI] Conventionally,
In optical communication systems, in consideration of equipment commonality and future relocation, even when the transmission distance is short, a semiconductor laser diode (hereinafter referred to as LD) is used instead of a light emitting diode (hereinafter referred to as LED) as a light source even when the transmission distance is short. is often used. In this case, in order to prevent the optical receiving device from exceeding the AGC range of the receiving circuit due to its high optical input level, an optical attenuator (hereinafter abbreviated as ATT) is installed for the receiving circuit.
The light level had to be adjusted to be within the GC range.

As described above, in conventional optical communication systems, when the transmission distance is short, it is necessary to insert an optical ATT into the receiving device. Moreover, for this reason, multiple reflections at the optical ATT may become a problem.

In view of the above problems, it is an object of the present invention to provide an optical communication transmitter that can be used for both short-distance and long-distance applications.

[Failure to solve the problem]

The optical communication transmitter of the present invention includes means for switching the bias current of the LD using a switch.

This allows the LD to be easily switched between a state in which the LD is used in laser oscillation and a state in which the laser oscillation is stopped and used in a natural light emitting state, and has the function of greatly changing the optical transmission output level.

[Hara Osamu]

The present invention will be described in detail with reference to FIGS. 3 and 4.

FIG. 3 shows the current-output characteristics of the LD under normal usage. When the drive current exceeds the threshold value Ith, the LD starts laser oscillation and the optical output level increases rapidly. Therefore, L.D.
For driving, a method is generally used in which the value of the DC bias current is set to a value close to Ith, and in addition to this bias current, a pulse current is supplied in order to obtain a predetermined optical output.

In order to keep the optical output constant, the optical output level is detected by a photodetector, and the DC bias current is controlled according to this detected value so that it remains at a constant value.

In the present invention, we focus on the fact that the optical output has an output level equivalent to that of an LED even with a DC bias current of less than Ith.
As shown in FIG. 4, the DC bias current is switched so as not to be supplied, and the optical output level is lowered when the LD is in a state where it is barely capable of laser oscillation.

〔Example〕

Embodiments of the present invention are shown in FIGS. 1 and 2.

In FIG. 1, an input signal is input to a pulse drive circuit 1 and drives an LD (semiconductor laser diode) 2. The level of the optical output of the LD 2 is detected by a photodetector 3 and a level detection circuit 4.

The comparison circuit 5 compares the voltage with a reference voltage, and the DC bias circuit 6 generates a DC bias based on the comparison result.

In this embodiment, with this configuration, the DC bias is turned on,
A switch circuit 7 for turning off is added. DC bias is set to L when using at high output by switch circuit 7.
Connected to D2.

In the case of low output, the switch circuit 7 disconnects the signal. In FIG. 1, switching of the switch circuit 7 is performed by a switching signal, but this switching signal may also be generated by, for example, the optical input level. However, the switching of the switch circuit 7 may be performed manually.

For example, when using it as a short-distance transmitting device, the switch circuit 7 may be turned off in advance to provide a low optical output.

FIG. 2 shows another embodiment in which a switch circuit 8 is inserted and connected to the output of the level detection circuit 4. in this case,
By switching the switch circuit 8 to the reference voltage side, it is possible to set the output power for short distances, that is, at low output.

FIG. 5 shows an example of the effects of the present invention. Assuming that the output during laser oscillation of the LD is a (Q dBm), the optical output level when laser oscillation is stopped is b (-25 dBm), and the transmission line loss is 0.5 dB/km, the optical reception level characteristics with respect to the transmission distance are as follows: show. This means that the receiver's AG
If the C range is equal to or higher than the output level when the laser oscillation is stopped, and the dynamic range C is C>a-b, then by using the optical communication transmitter of the present invention, no optical ATT is required. High reliability and long life are often achieved.

〔Effect of the invention〕

As is clear from the above explanation, in the present invention, by providing a switch means for switching the bias current of the LD,
Not only can it be used for long distances, but it can also be used as a short distance transmitter without using an optical ATT. Furthermore, by eliminating the need for an optical ATT, it is possible to provide an optical communication transmitting device that is free from problems such as multiple reflections, has high reliability, and has a long service life.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing embodiments of the present invention, FIGS. 3 and 4 are diagrams showing current-optical output characteristics of a semiconductor laser diode for detailed explanation of the present invention, and FIGS. FIG. 5 is a characteristic diagram showing the relationship between transmission distance and optical reception level, which does not provide a detailed explanation of the present invention. 1...Pulse drive circuit, 2...Semiconductor laser diode, 3...Photodetector, 4...Level detection circuit. 5... Comparison circuit, 6... DC bias circuit, 7, 8
...Switch circuit. Figure 1 Figure 3 Figure 4 Figure 5 Light receiver during laser oscillation
Arc range Ruin, sending side * [kml

Claims (1)

[Claims] 1. An optical communication device using a semiconductor laser diode as a light source, which is equipped with a means for switching a bias current to the semiconductor laser diode, and a state in which the semiconductor laser diode is caused to oscillate by the switching means and a spontaneous emission in which the laser oscillation is stopped. An optical communication transmitting device characterized in that the state of the optical communication transmitting device can be easily switched and used.