JPH04152582A - Optical transmitter - Google Patents

Abstract

PURPOSE:To achieve a required optical output by generating a pulse current value and a bias current value based on the temperature indicated by a temperature signal from a heat-sensitive device and send the pulse current and bias current to a laser diode. CONSTITUTION:A laser current control circuit 26 is equipped with a digital memory device, such as ROM, in which detailed data on a temperature feature curve comparing current and optical output calculated for both bias current and current changes between 1-3 deg.C is stored. When the temperature changes, the heat-sensitive device 25 detects the temperature, the bias current value and the pulse current value for that temperature are read from the laser current control circuit 26, and the actual values of the bias circuit 24 and the pulse current drive circuit 23 are controlled. In this way, a steady optical output that follows temperature changes can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical transmitter for optical communication equipment that converts the strength and weakness of an electrical signal into the strength and weakness of an optical signal and connects it to an optical fiber cable to perform optical communication. It is something.

[Prior Art] Fig. 4 shows an example of an optical transmitter using a conventional laser diode as shown in the manufacturer's manual, and Fig. 3 shows an example of an optical transmitter using a conventional laser diode.
This is a temperature characteristic diagram of the current vs. optical output of a laser diode.
In the figure, (1) is a laser diode that converts an input pulse voltage signal into a light pulse, (2) is a photodiode that receives the backlight of this laser diode (1) and converts the light pulse into a current pulse, and (3) is a photodiode that converts the light pulse into a current pulse. A first operational amplifier converts the current pulse of this photodiode (2) into an averaged voltage, (4) is a first resistor that determines the voltage gain of this first operational amplifier, and (5) is The photodiode (2
) a first capacitor that integrates the current pulses.

(6) is a second amplifier that amplifies the output of the first amplifier (3).
(7) and (8) are a second resistor and a third resistor that determine the voltage gain of the second operational amplifier.

(9) is a second capacitor that integrates the voltage signal of the second operational amplifier (6); (10) and (11) are a fourth capacitor for bias voltage applied to the second operational amplifier (6); and a fifth resistor, (12) is a variable resistor for setting the bias voltage, and (13) is a resistor for flowing DC current to the laser diode (1) in accordance with the output voltage of the second operational amplifier. 1 transistor, (14) is the sixth resistor of the current load of this first transistor, (15) is a coil that blocks the alternating current flowing to the first transistor (14), (1
6) is a second transistor that drives the laser diode (1) in response to an input pulse voltage signal; (17)
) is the seventh current load of this second transistor (16).
resistance, (18) is the input terminal of the input pulse voltage signal,
(19) is a power supply (20a) that supplies negative power
(21a) and (22a) show curves in which the current versus optical output of a laser diode is plotted at each temperature.

High temperature (22a), medium temperature (21a), low temperature (20a)
), (20c) consists of bias current and pulse current at low temperature shown in curve (20a) (20b)
This is the optical output when the laser diode current shown in is applied. Similarly, (22c) consists of bias current and pulse current at high temperature shown in curve (22a) ((22
(b) is the optical output when a laser diode current is applied.

Next, the operation will be explained.

As shown in FIG. 3, the current vs. light output of a laser diode does not have a linear characteristic, and almost no light is emitted unless a bias current is applied until a threshold current determined by the temperature flows. Therefore, when driving a laser diode, (
A laser diode current shown in 20b) (a current obtained by receiving a large-power pulse voltage signal on a DC bias current at the input terminal (18) and superimposing a pulse current corresponding to the input pulse voltage signal in the second transistor (16)) is applied. Obtain the required light output.

Moreover, the temperature characteristic curve (20a) (21, a) (22
As shown in a), the characteristics differ at each temperature, and it is necessary to increase the bias current as the temperature increases (20C). Moreover, since the slope of the characteristics becomes gentler, the optical output decreases when the pulse current is constant.

A conventional optical transmitter receives the rear output light of a laser diode with a photodiode (2), converts the optical pulse into a current pulse, and converts the current into a first operational amplifier (3) and a first resistor (4). ) and the first capacitor (5) to amplify the averaged voltage signal. Furthermore, this averaged voltage signal is applied to the negative input terminal of the second operational amplifier (6) through a second resistor (7).

A fourth resistor (10), a fifth resistor (11), and a variable resistor (12) are connected to the positive input terminal of the second operational amplifier (6).
I set it with . The bias voltage of the bias current of one norther diode is set. This bias voltage and the averaged voltage are compared by the second operational amplifier (6), and if the required optical output is not obtained, the bias voltage increases and the laser diode is activated through the first transistor (13). A large bias current is applied to increase the optical output and maintain the required value (automatic optical output adjustment APC).

APC also acts when the temperature rises as shown in (22a) of the temperature characteristic curve, and the bias current becomes (22a).
Increase as shown in b). In this case, as shown in (22c), the pulse current corresponding to the input pulse voltage does not have the function of increasing, so the optical output decreases when the pulse voltage is 1, and conversely, the optical output increases when the pulse voltage is O, and the extinction ratio (light output value of 1, light output value of 10) becomes worse.

As this extinction ratio deteriorates, it becomes increasingly difficult for the receiving side receiving this light to reproduce 1's and 0's.

[Problems to be Solved by the Invention] Conventional laser diode drives in optical transmitters involve a method in which the backlight of the laser diode is received by a photodiode, the electrical output is averaged, and the bias current is controlled. In the temperature characteristics of the diode, the slope of the current vs. output at high temperatures becomes gentler, and the optical output of the input pulse voltage signal 1 decreases. Since this compensation is not provided, there is a problem in that the extinction ratio deteriorates at high temperatures.

This invention was made to solve the above problems.

(1) The objective is to obtain an optical transmitter that can output the bias current value and pulse current value of the laser diode by setting the temperature characteristic curve of the laser diode in advance and detecting the temperature of the laser diode.

(2) Setting the bias current value temperature characteristics of the laser diode in advance, obtaining the bias current value of the laser diode by detecting the temperature of the laser diode, and changing the ratio of 1 and O of the input pulse voltage signal. The purpose of this invention is to obtain an optical transmitter that can calculate the ratio and output a pulse current value from the laser diode backside light output.

[Means for Solving the Problems] (1) The optical transmitter according to the present invention includes a temperature sensing element that detects the temperature of a laser diode, and a laser that is preset by a laser current control circuit in response to the temperature signal. The device reads the bias current value and pulse current value of the diode and instructs the bias current circuit and pulse current drive circuit to obtain the required optical output by flowing each of the bias current and pulse current to the laser diode. be.

(2) The optical transmitter according to the present invention includes a clock extraction circuit that extracts a clock from a pulse train of an input pulse voltage signal;
A first counter circuit that counts 1 of the input pulse voltage signal, a second counter circuit that counts 0, a comparison circuit that calculates a moving average ratio of the count values, and a temperature sensing element that detects the temperature of the laser diode. In response to the temperature signal, the bias current value of the laser diode preset in the bias current control circuit is read out and outputted to the bias current circuit, and the integrated output and moving average ratio of the photodiode that receives the backlight of the laser diode are read out. is input, the magnitude of the pulse current is calculated by the pulse current control circuit, and the required optical output is obtained by flowing the pulse current through the pulse current drive circuit.

[Effect] (1) The laser current control circuit in this invention.

The temperature characteristic curve of the laser diode to be used is digitally set in advance in a storage element such as ROM, and upon receiving the temperature signal from the temperature sensing element, the pulse current value and bias current value for that temperature are read out and the pulse current is calculated. This functions to flow a bias current to the laser diode to obtain the required optical output.

(2) The bias current control circuit in this invention digitally sets the bias current temperature characteristics of the laser diode to be used in advance in a storage element such as a ROM, and adjusts the temperature by receiving a temperature signal from a temperature sensing element. Read out the corresponding bias current, convert the value into an analog signal, send the bias current value to the laser diode, find the moving average ratio of 1 and O of the input pulse voltage, and calculate the average value of the laser diode optical output and its moving average. The ratio is compared, a pulse current value corresponding to the number of pulses is determined, and the pulse current is passed to obtain the required optical output.

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

In Figure 1, (23) is 1 of the input pulse voltage signal.
A pulse current drive circuit that drives the laser diode (1) with a pulse current corresponding to and O.

(24) is a bias circuit that flows a DC bias current corresponding to the threshold value of the laser diode (1); (25)
is a temperature sensing element installed near the laser diode (1) to detect the temperature of the laser diode, and (26) is the temperature characteristic curve of current versus optical output of the laser diode (1) used (for example, (22a) (21a) ) (22a) etc. further subdivided by temperature) are digitally set in advance in memory elements such as R, OM, etc., and the laser In Fig. 2, (27) extracts the clock from the pulse train of the input pulse voltage signal. (28) is a first counter circuit that counts pulses 1 of the input pulse voltage signal; (29) is a second counter circuit that counts 0 of the pulse train of the input pulse voltage signal;
The counter circuit (30) is a pulse train of 1 counted by the first counter circuit (28), a pulse train of 0 counted by the second counter circuit (29), and a pulse train of 0 counted by the clock extraction circuit (27). (31) is a comparison circuit that inputs a clock, counts the total number of pulses, and calculates the moving average ratio of 1 pulse to the total number of pulses; (31) is a photovoltaic circuit that receives the optical output of the laser diode (1) and converts it into current; Pulse current control that calculates the magnitude of the pulse current by inputting the output of the first operational amplifier that averages the output of the diode (2) and the output of the moving average ratio calculated by the comparison circuit (30). The circuit (32) is a bias current control circuit that receives an electrical signal from the temperature sensing element (25), reads out a bias current value corresponding to a preset temperature, and commands the bias circuit (24) to apply a bias current.

Next, the operation will be explained.

(1) In the laser current control circuit (26), the temperature characteristic curve of current versus optical output of the laser diode used is divided into two types: bias current and optical output slope with respect to current change. Detailed data is digitally set in advance in a storage element such as a ROM. A bias circuit (2) receives an input pulse voltage signal that repeats 1 and 0, and according to the instructions of the bias current value and pulse current value at a certain temperature of the laser diode detected by the temperature sensing element (25).
4) and a pulse current drive circuit (23) respectively apply current and set the required optical output corresponding to each pulse of the input pulse voltage. When the temperature changes, the temperature sensing element (25) detects the temperature, and the bias current value and pulse current value for that temperature are read out from the laser current control circuit (26), and the bias circuit (24) and the pulse current value are read out from the laser current control circuit (26). Since the drive circuit (23) drives each value, a constant optical output that follows the temperature can be obtained.

(2) In the bias current control circuit (32), temperature-corresponding bias values of the laser diode to be used are digitally set in advance in a storage element such as a ROM at intervals of 1 to 3°C. With the bias current set for the temperature of the laser diode detected by the temperature sensing element (25),
The count value of 1 and 0 of the pulse train of the input pulse voltage is calculated by the comparator circuit (30) as a pulse moving average ratio of 1 to the total number of pulses. The calculated value and the average value obtained from the output of the first operational amplifier (3) of the photodiode that detects the laser diode light output are used as feedback inputs, and the pulse current control circuit (31) is operated to control one pulse train of the input pulse voltage. It has the function of controlling the magnitude of the optical output corresponding to 0 and 0, and is designed to obtain a constant optical output with this authority.

[Advantageous Effect] As described above, according to the present invention, the temperature characteristics of the current versus optical output of the laser diode are controlled separately into the bias current and the optical output change with respect to the current change. This has the effect of obtaining a highly accurate optical transmitter with a large extinction ratio.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams showing one embodiment of the present invention, Figure 3 is a diagram showing the temperature characteristics of the current versus optical output of a laser diode, and Figure 4 is a diagram showing a conventional optical transmitter. FIG. (1) is a laser diode, (2) is a photodiode, (3) is a first arithmetic unit, and (4) is a first resistor. (5) is the first capacitor, (6) is the second operational amplifier, (7) is the second resistor, (8) is the third resistor, (9) is the second capacitor, (10) ) is the fourth resistance, (11
) is the fifth resistor, (12) is the variable resistor, (13) is the first transistor, (14) is the sixth resistor, (1
5) is a coil. (16) is the second transistor, and (17) is the seventh resistor. (18) is an input terminal, (19) is a power supply, (23) is a pulse current drive circuit, (24) is a drive circuit,
(25) is the temperature sensing element, (26) is the laser current side circuit, (27) is the clock extraction circuit, (28) is the first
(29) is the second counter circuit,
(30) is a comparison circuit, (31) is a pulse current control circuit, and (32) is a bias current control circuit. In addition, in FIG. 1, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] (1) In an optical transmitter that converts an input pulse voltage signal into an optical pulse signal using a laser diode, a pulse current drive circuit that drives a pulse current flowing through the laser diode in response to the pulse voltage signal; A bias circuit that flows a bias current, a temperature sensing element that detects the temperature of the laser diode, and receiving an electric signal from this temperature sensing element, reads out a preset bias current value and a pulse current value, and reads out a preset bias current value and a pulse current value. An optical transmitter comprising a laser current control circuit that outputs a command to a bias circuit. (2) a clock extraction circuit that extracts a clock from a pulse train of an input pulse voltage signal; a first counter circuit that counts 1s in the pulse train of the input pulse voltage signal; and a second counter circuit that counts 0s in the pulse train; Said first
a comparison circuit that calculates a moving average ratio of the number of 1 counts of the counter circuit and the number of 0 counts of the second counter circuit;
the pulse current drive circuit; the bias circuit;
the temperature sensing element; a bias current control circuit that receives an electrical signal from the temperature sensing element to read a preset bias current value and outputs a command to the bias circuit; and a photodiode that receives backlight from a laser diode; It is characterized by comprising an amplifier that integrates the output of the photodiode, and a pulse current control circuit that has terminals for inputting the output of the comparison circuit and the voltage of the amplifier and calculates the magnitude of the pulse current. optical transmitter.