JPH03278728A - Optical transmitter - Google Patents

Abstract

PURPOSE:To prevent the production of an undesired optical output from a laser diode(LD) by controlling the operating state of a bias current control means and a signal current control means individually so as to permit the production of an optical output from the LD. CONSTITUTION:When a stimulation enable signal ST is set to an L level, a stimulation enable signal identification circuit 14 generates an output controlling turning-on of transistors(TRs) 12, 13. Then a base-emitter of a current control TR 7 is short-circuited by the TR 12 and the base-emitter of an APC TR is short-circuited by the TR 13 and the TRs 12, 10 are kept OFF. Thus, when no input signal is given and an (APC) signal is inputted to the TR 10, no bias current flows to the LD 6. Thus, the production of the optical output from the LD 6 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Fields] The present invention relates to a laser diode (hereinafter referred to as L) as a light emitting element.
It is abbreviated as D. ).

[Prior Art] Recently, optical communication, which uses optical fibers as transmission lines to send information in the form of optical signals, has come into general use.

In such an optical communication system, as shown in FIG. 3, a large number of optical transmission bags Wt21.
2... are connected via optical multiplexers 31, 32... In this case, each optical transmitter that forms a slave station! f2
+22... uses an LD as a light emitting element, and turns on the optical output signal only when transmitting information from its own station, and turns it off in other cases.

FIG. 4 shows an example of a conventional optical transmitter using a commonly used LD. In this case, the emitters of transistors 4.5 are connected in common, the collector of transistor 4 is connected to ground, and the transistor 5.
A differential circuit is constructed by connecting the collector of the transistor 4.5 to the ground via the LD 6, and by inputting an input signal (transmission signal) to the base of the transistor 4.5, the differential circuit performs a switching operation. In addition, a signal current control section is provided in which the power supply -■ is connected to the common connection point of the emitters of the transistors 4 and 5 of such a differential circuit through the current control transistor 7 and the resistor 8 to control the signal current to the LD 6. At the same time, an inductance 9 is connected to the connection point between the collector of the transistor 5 and the LD 6, and an automatic power control (APC)
It is abbreviated as. ) A bias current control section connected to the power supply -■ via a transistor 10 and a resistor 11 is provided to
The bias current for 6 is supplied.

Such an optical transmitter inputs an input signal (transmission signal) to the base of the transistor 4.5 to operate the differential circuit, inputs the APC voltage to the base of the APC transistor 10, and also inputs the APC voltage to the base of the APC transistor 10. By inputting a control voltage to the base of the transistor 7, a bias current and a signal current are applied to the LD6. As a result, as shown in FIG. 5, a bias current a is applied to the LD6 by the APC transistor 10, and modulation is performed by the signal currents from the transistors 4.5 and 7, so that an optical output C is obtained in the LD6. , an optical output signal d corresponding to this optical output C is output.

[Problems to be Solved by the Invention] However, according to such an optical transmitter, the input signal (
Even when no transmission signal (transmission signal) is applied and the differential circuit is not operating, if there is an input to the APD transistor 10, a bias current flows to the LD 6 and continues to output a constant optical output. This means that when used as a slave station in the optical communication system shown in FIG.
... will generate optical output even though there is no transmission signal, so unnecessary superposition of optical components will occur on optical transmission line 1, which will have an adverse effect on the receiving system connected to optical transmission line 1. There was a risk that it would cause

Therefore, a conventional idea has been to provide a switch means that can directly turn on and off the power line related to the LD6, and when there is no transmission signal, the power line is forcibly turned off by the switch means to prevent light output from the LD6. It is being However, when the power line is turned on and off directly in this way, it takes time for the power to start up when the power line is turned on, which causes a delay in the rise of the optical output of the LD6, making it impossible to obtain a stable optical output signal. There is a drawback, and if the power line is directly turned on, LD6
There was also a risk that transient current stress would be applied to the LD6, leading to deterioration of the LD6 itself.

The present invention has been made in view of the above circumstances, and is an optical transmitter that can prevent the generation of unnecessary optical output from the LD, provide stable optical output, and further prevent deterioration of the LD due to current stress. The purpose is to provide

[Means for Solving the Problems] The optical transmitting device of the present invention includes bias current control means for controlling a bias current for an LD and signal current control means for controlling a signal current, and these bias current control means and signal current control means are provided. The operating states of the means are individually controlled to permit the generation of optical output from the LD.

[Function] As a result, according to the present invention, bias current is supplied to the LD only when the LD is instructed to allow optical output, so the LD generates a pre-output only when necessary, and other can block light output from the LD. Furthermore, since the bias current and signal current can be supplied to the LD while the power supply to the LD is turned on, a stable optical output signal is generated without causing any delay in the rise of the optical output of the LD. Further, there is no need to apply transient current stress to the LD, and causes of deterioration of the LD can be avoided.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of the same embodiment, in which the same parts as in FIG. 4 are denoted by the same reference numerals. In this case, a switching transistor 12 is connected between the base of the current control transistor 7 and the power supply -2, and a switching transistor 13 is connected between the base of the APC transistor 10 and the power supply -2.

These transistors 12 and 13 have their bases supplied with the output of the light emission permission signal identification circuit 14.

The light emission permission signal identification circuit 14 receives the light emission permission signal ST as an external signal.
When T is at rLJ level, the above transistor 12.1
3, and the light emission permission signal ST reaches rH.
When the level reaches J, an output is generated to turn off the transistors 12 and 13. In this case, the transistors 12 and 13 have the off-operation time tl of the transistor 12 and the off-operation start time t2 of the transistor 13.
When tl > t2, the relationship is set.

Note that the light emission permission signal ST input to the light emission permission (ST) signal identification circuit 14 is not specified in particular, but is ECL (E
g+1tLer Coupled Logic) or TTL (Transistor Transistor
Logic) is easy to use.

The rest is the same as that in FIG. 4, and the explanation here will be omitted.

Next, the operation of the embodiment configured as described above will be explained.

Now, when the light emission permission signal ST is set to the rLJ level, the light emission permission signal identification circuit 14 generates an output that turns on the transistors 12 and 13. Then, the base and emitter of the current control transistor 7 are short-circuited by the transistor 12, and the APC transistor 10 is
The base and emitter are short-circuited by the transistor 13, and each is maintained in an off state.

As a result, even if an APC signal is input to the APC transistor 10 in a state where no input signal (transmission signal) is given, a bias current will not flow through the LD6, so that the optical output from the LD6 is generated. can be prevented. This means that when used as a slave station in the optical communication system shown in Figure 3, the optical transmitters 21, 22, etc. do not generate any optical output while there is no transmission signal. This makes it possible to avoid a situation that would have an adverse effect on the receiving system connected to path 1.

In addition, when the power supply to LD6 is stable, the transistors 12 and 13 are
The operation of the LD6 can be controlled to block the bias current flowing unnecessarily to the LD6, so this method is similar to the conventional method of inserting a switching means directly into the power supply line of the LD6 to block the bias current flowing unnecessarily to the LD6. This eliminates the inconvenience that occurs when the power supply line is turned on and the power supply takes time to rise, causing a delay in the rise of the optical output of the LD6 and making the optical output signal unstable.
A stable optical output signal can be generated without any delay in the rise of the optical output of D6. Moreover, since the disadvantage of applying transient current stress to the LD 6 by directly turning on the power supply line can be eliminated, causes of deterioration of the LD 6 can also be avoided, and the life of the LD 6 can be extended.

On the other hand, when the light emission permission signal ST is switched to the rHJ level,
This time, the light emission enable (ST) signal identification circuit 14 generates an output that controls transistors 12, 13 to turn off. Then, the base-emitter short circuit caused by the transistor 12 in the current control transistor 7 is released, and the base-emitter short circuit caused by the transistor 13 in the APC transistor 10 is also released. Therefore, in this state, the input signal (transmission signal) is applied to the base of transistor 4.5.
When A is given to the base of the APC transistor 10,
When the PC signal is given, APC is sent to LD6 as usual.
When a rebiasing current is applied from the signal current control transistor 10 and a control voltage is input to the base of the signal current control transistor 7, the LD6 is modulated by the signal current at this time, and the LD6 emits light according to the signal current. Output will now be generated.

In this case, the relationship between the light output of the LD 6 and the rHJ level output of the light emission permission signal ST is as shown in FIG.

Now, as shown in the same figure (a), the light emission permission signal ST is rH.
When the level is switched to J level and the light emission permission signal identification circuit 14 generates an output that turns off the transistors 12 and 13, the transistor 13 turns off first and then the transistor 12 turns off due to the difference in operating time. . As a result, first, the bias current applied to the LD6 from the APC transistor 10 after this time t2 is stabilized to be equal to or higher than the threshold value due to the OFF operation time t2 of the transistor 13, and then, due to the OFF operation time t1 of the transistor 12, the bias current applied to the LD 6 is stabilized after this time t2. After time tl, modulation by the signal current applied from transistor 7 starts. As a result, the optical output of the LD6 shows a constant rising pattern as shown in FIG.
Due to the transient response of the transistor 10, no overcurrent flows to the LD 6, and the rise characteristics of the optical output of the LD 6 can be made stable.

Note that the present invention is not limited to the above-mentioned embodiments, but can be implemented with appropriate modifications within the scope without changing the gist.

For example, in the embodiment described above, the light emission permission signal ST is r
Although the generation of optical output from the LD6 is permitted when the light emission permission signal ST is at the HJ level, the generation of optical output from the LD6 may be permitted when the light emission permission signal ST is at the rLJ level. Further, in the above embodiment, the operation of the current control transistor 7 and the APC transistor 10 is controlled by the switch transistor 12.13, but in place of these transistors 12.13, other switch means such as a relay contact may be used. You can also use

[Effects of the Invention] The optical transmitter of the present invention is provided with a bias current control means for controlling the bias current for the LD and a signal current control means for controlling the signal current, and the operating state of the bias current control means and the signal current control means is Since the above-mentioned LDs are individually controlled to allow the generation of optical output, the L
A bias current is now supplied to D, allowing the LD to generate light output only when necessary, and blocking light output from the LD at other times. Furthermore, since the bias current and signal current can be supplied to the LD while the power supply to the LD is stable, a stable optical output signal can be generated without causing any delay in the rise of the optical output of the LD. In addition, transient current stress is not applied to the LD, and deterioration of the LD can also be avoided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a circuit configuration of an embodiment of the present invention;
Fig. 2 is a diagram for explaining the operation of the same embodiment, Fig. 3 is a system diagram showing an example of a system used for optical communication, and Fig. 4 is a circuit configuration diagram showing an example of a conventional optical transmitter. , FIG. 5 is a diagram for explaining the conventional optical transmitter. 1... Optical transmission line, 21 22,... Optical transmitter, 4
．． 5... Transistor, 6... LD, 7... Current control transistor, 10... APC transistor, 12.13... Switch transistor, 14...
・Light emission permission (ST) signal identification circuit.

Claims (1)

[Claims] A laser diode, a bias current control means for controlling a bias current for the laser diode, a signal current control means for controlling a signal current for the laser diode, and the operating states of the bias current control means and the signal current control means are individually controlled. 1. An optical transmitter comprising: light emission permission means for controlling the laser diode to permit the generation of optical output to the laser diode.