JPH0575547A - Optical transmitter - Google Patents

Abstract

PURPOSE:To prevent the excessive emission of light and to increase the lifetime of an optical transmitter by inputting the two branched input signals to a laser driving circuit and a mark rate detecting circuit and inhibiting the emission of the laser light when the output of the mark rate detecting circuit is smaller than the prescribed value A or larger than the prescribed value B respectively. CONSTITUTION:The signal inputted to an input terminal 12 is branched into two signals and inputted to a semiconductor laser driving circuit 1 and a mark rate detecting circuit 4. Then the input signal is cut off, and the output value of the circuit 4 serving as an excessive DC signal higher than the high level of a no-input start signal or a prescribed input signal is smaller than the prescribed value A or larger than the prescribed value B. As a result, a cut-off circuit 3 works to cut off the supply of the driving current to a semiconductor laser 6 from the circuit 1. Then the light emission of the laser 6 is stopped. Thus the excessive emission of light is prevented and the lifetime is increased for the laser 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter suitable for use in optical fiber communication and the like.

[0002]

2. Description of the Related Art An optical transmitter for intensity-modulating emitted light from a semiconductor laser by a signal input to the optical transmitter has a circuit configuration represented by FIG. For example, Japanese Patent Laid-Open No. 2-1
Japanese Patent No. 55285 is a prior art based on the circuit configuration of FIG.

In the figure, 1 is a semiconductor laser drive circuit, 2 is
Is a semiconductor laser module having a semiconductor laser 6, a monitor photodiode 7, a temperature detecting element 9 and a thermoelectric cooling element 8 built therein. Reference numeral 5 is an optical output stabilizing circuit which stabilizes the optical output of the semiconductor laser 6 by the current of the monitor photodiode 7 flowing through the resistor 11. Reference numeral 10 is a temperature stabilization circuit that stabilizes the temperature of the semiconductor laser 6 by using the temperature detection element 9 and the thermoelectric cooling element 8. The input signal for modulating the intensity of the emitted light of the semiconductor laser is input to the input terminal 12
Is applied to the semiconductor laser drive circuit 1 and converted into an optical modulation signal current and a DC bias current by the semiconductor laser drive circuit 1 and supplied to the semiconductor laser 6. The DC bias current value is almost equal to the oscillation threshold value of the semiconductor laser 6. The modulation signal current value and the DC bias current value are controlled by the optical output stabilizing circuit 5.

With the above operation, the conventional optical transmitter has a structure in which the light emitted from the semiconductor laser is intensity-modulated and transmitted to the optical fiber.

[0005]

In the prior art, the control of the emitted light of the semiconductor laser when the input signal to the optical transmitter is cut off, no input is opened, or an excessive direct current signal is higher than the specified input signal high level is provided. No consideration is given to the function. Therefore, the semiconductor laser is made to emit excessive light within the above time, and the electro-optical characteristics of the semiconductor laser represented by the increase of the oscillation threshold thereof are deteriorated. When the light emitted from the semiconductor laser is received by the optical receiving station, it is feared that a code error that cannot be investigated by the optical receiving station alone may occur.

A first object of the present invention is to prevent the semiconductor laser from emitting light within the above-mentioned time period and to prolong the life of the semiconductor laser.

A second object of the present invention is to inhibit the light emission of the semiconductor laser within the above time period and to generate an optical input interruption alarm in the optical receiving station.

[0008]

[Means for Solving the Problems] Means for achieving the above-mentioned goal will be described below. The optical transmitter shown in FIG. 3 includes a mark ratio detection circuit having a function of detecting an integrated value of a pulse component of an input signal input to the semiconductor laser drive circuit, and a semiconductor laser drive current (the optical modulation signal current A cutoff circuit for turning on / off the supply of the DC bias current) from the semiconductor laser drive circuit to the semiconductor laser is provided. When the output of the mark ratio detection circuit is equal to or less than the real number specified value A that satisfies A <B or is equal to or more than the real number specified value B, the cutoff circuit is operated to prohibit the emission of the semiconductor laser.

[0009]

The operation of the means for solving the above problems is as follows.

The output voltage characteristic of the mark ratio detection circuit with respect to the input signal mark ratio is shown in FIG. The mark ratio detection circuit
The integrated value of the pulse component of the input signal is output. Therefore, E
When an input signal containing a DC component is input to the mark ratio detection circuit through an interface such as CL or TTL, its output is 0, as indicated by the solid line in FIG.
A characteristic that changes substantially linearly in the range from 100% to 100% is obtained.

As described above, the input signal applied to the optical transmitter is branched into two directions, one is input to the semiconductor laser drive circuit, and the other is input to the mark ratio detection circuit having the characteristics shown in FIG. When the cutoff circuit and the mark rate detection circuit are connected and the input value (mark rate detection circuit output value) of the cutoff circuit is equal to or less than the specified value A and greater than or equal to the specified value B, that is, the mark rate is The cutoff circuit is configured by a comparator or the like so as to operate when the voltage becomes lower than ML and higher than MH.

When an input signal scrambled to a mark ratio of about 50% is applied to the input terminal of the optical transmitter constituted by the circuits having the above-mentioned respective functions, the output value of the mark ratio detection circuit is as shown in FIG. It becomes a value near C of. At this time, the cutoff circuit does not operate, a drive current is supplied from the semiconductor laser drive circuit to the semiconductor laser, and the intensity modulation of the semiconductor laser emission light is performed.

However, when the input signal is cut off, no input is opened, or an excessive DC signal is higher than the specified input signal high level, the output value of the mark ratio detection circuit is the specified value A in FIG.
Below or above the specified value B, the cutoff circuit operates,
The supply of the drive current from the semiconductor laser drive circuit to the semiconductor laser is cut off, and the emission of the semiconductor laser emission light is prohibited.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment will be described with reference to FIGS.

FIG. 1 is a block diagram showing a circuit configuration example of an optical transmitter of the present invention. The input signal applied to the input terminal 12 is scrambled to have a mark ratio of about 50% and is branched in two directions. One is input to the semiconductor laser drive circuit 1 and the other is input to the mark ratio detection circuit 4. In the configuration of FIG.
The output characteristic with respect to the input signal mark rate of the black ratio detection circuit 4 shows the characteristic of the solid line in FIG. When the input signal is applied to the input terminal 13, the output of the mark ratio detection circuit 4 is
It becomes a value near C in FIG. 4, and this value is input to the cutoff circuit 3. When the cutoff circuit 3 is configured by a comparator or the like so that the input level operates at a specified value A or lower and a specified value B or higher,
Under the above input conditions, the cutoff circuit 3 is in a non-operating state, the drive current is supplied from the semiconductor laser drive circuit 1 to the semiconductor laser 6, and the intensity modulation of the semiconductor laser emission light is performed. The unmodulated light enters the optical fiber connected to the semiconductor laser module 2 and the monitor photodiode 7 built in the semiconductor laser module 2. A monitor current, which is substantially proportional to the intensity of light emitted from the semiconductor laser 6 from the monitor photodiode 7, is converted into a monitor voltage by the flow resistor 11. This monitor voltage is input to the optical output stabilizing circuit 5, and the semiconductor laser drive current is adjusted so that the monitor voltage becomes constant.

The semiconductor laser module 2 also contains a temperature detecting element 9 for detecting the temperature of the semiconductor laser 6 and a thermoelectric cooling element 8, and the temperature of the semiconductor laser 6 is kept constant via a temperature stabilizing circuit 10. Control to temperature.

When the input signal is cut off, no input is opened, or an excessive direct current signal is higher than the specified input signal high level,
The output value of the mark ratio detection circuit 4 becomes equal to or less than the specified value A or the specified value B in FIG. 4, the cutoff circuit 3 operates, and the supply of the drive current from the semiconductor laser drive circuit 4 to the semiconductor laser 6 is cut off. Emission of light emitted from the semiconductor laser is prohibited.

FIG. 2 is a circuit diagram of a semiconductor laser module 2 corresponding to the first embodiment using a semiconductor laser module which does not include the temperature detecting element 9 and the thermoelectric cooling element 8. The second embodiment can also realize the same function as that of the first embodiment.

Further, even if the output characteristic of the mark rate detection circuit 4 with respect to the input signal mark rate has the characteristic shown in FIG. 5, the function equivalent to that of the first and second embodiments can be realized.

[0020]

According to the present invention, when the input signal is cut off, no input is opened, or an excessive direct current signal is above the specified input signal high level, the output value of the mark ratio detection circuit is below the specified value A or When the value becomes equal to or more than the specified value B, the cutoff circuit operates, the supply of the drive current from the semiconductor laser drive circuit to the semiconductor laser 6 is cut off, the emission of the semiconductor laser emission light is prohibited, and the semiconductor laser emits excessive light within this time. Without increasing the life of the semiconductor laser.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical transmission circuit according to an embodiment of the present invention,

FIG. 2 is a block diagram of an optical transmission circuit according to a second embodiment of the present invention,

FIG. 3 is a block diagram of a conventional optical transmission circuit,

FIG. 4 is a first output characteristic with respect to an input signal mark rate of a mark rate detection circuit,

FIG. 5 is a second output characteristic diagram with respect to an input signal mark rate of the mark rate detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser drive circuit, 2 ... Semiconductor laser module, 3 ... Cutoff circuit, 4 ... Mark ratio detection circuit, 5 ... Optical output stabilization circuit, 6 ... Semiconductor laser, 7 ... Monitor photo diode, 8 ... Heat Electronic cooling element, 9 ... Temperature detecting element, 10 ... Temperature stabilizing circuit, 11 ... Resistor, 12 ... Input terminal.

Claims (1)

[Claims] 1. A semiconductor laser, and a semiconductor laser drive circuit for supplying to the semiconductor laser a semiconductor laser drive current composed of an optical modulation signal current for intensity-modulating emitted light of the semiconductor laser according to an input signal and a DC bias current. In an optical transmitter including a mark ratio detection circuit for detecting an integrated value of a pulse component of an input signal and a cutoff circuit for turning on / off the supply of the semiconductor laser drive current, an input signal is bifurcated and one of them is driven by the semiconductor laser. When inputting to the circuit and inputting the other to the mark rate detecting circuit, and the output of the mark rate detecting circuit becomes a real number specified value A or less satisfying A <B or a real number specified value B or more, the cutoff circuit is operated. And an optical transmitter provided with a function of inhibiting light emission of the semiconductor laser.