JPH0918412A - Laser diode deterioration detection circuit and burst type optical communication circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To reliably detect the deterioration state of the radar diode before the radar diode becomes unable to oscillate. The present invention relates to a device for detecting a deteriorated state of a laser diode (LD21) used in a burst type optical communication circuit, in which a voltage e6 corresponding to a pre-bias current value just before the LD21 is brought into a laser oscillation region. The deterioration determination voltage e5 is compared with the comparator 33, and e6
An event of> e5 is determined as an LD deterioration state, an LD deterioration detection signal is output to the flip-flop 35 as a start signal, and L is used for warning display of the deterioration state of the LD 21.
The ED 36 is set to the lighting state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode deterioration detecting circuit and a burst type optical communication circuit for detecting a deterioration state of a laser diode used in an optical communication device.

[0002]

2. Description of the Related Art Optical communication circuits using a laser diode (hereinafter referred to as an LD) as a light emitting body are classified into a continuous light emitting type and a burst type.

FIG. 5 shows the configuration of a conventional burst type optical communication circuit. In FIG. 1, reference numeral 1 denotes an LD main body 1a which is an optical signal generating source and P for detecting an optical output level of the LD main body 1a.
This is an LD in which an IN photodiode (hereinafter referred to as PD) 1b is built in the same package. LD body 1a
The voltage Vcc is applied to the anode of and the cathode is connected to the collector of the transistor 2. Transistor 2
A bias voltage e1 is applied from the terminal 4a of the pre-bias circuit 4 to the base of the. The voltage Vcc is applied to the cathode of the PD 1b, and the assault is connected to the terminal 4b of the pre-bias circuit 4 and grounded via the resistor 5. The voltage e of the power source 6 is applied to the terminal 4c of the pre-bias circuit 4.
2 is applied, and a pre-bias request signal (hereinafter referred to as PB_ON signal) is input to the terminal 4d.

When the PB_ON signal is input, the pre-bias circuit 4 outputs the bias voltage e1 from the terminal 4a to the base of the transistor 2 while gradually increasing it from zero.
As a result, the emitter current i1 of the transistor 2 is gradually increased, and the LD body 1a emits light by the input current i, while the received light current i0 is received by the PD 1b and the resistance 5
Through the flow gradually increasing. Pre-bias circuit 4
Compares the voltage drop e3 of the resistor 5 due to the received light current i0 with the power supply voltage e2, and stops the increase of the bias voltage e1 and fixes the bias voltage e1 when the two values match. In this state, the value of the current flowing through the LD body 1a is at the boundary line below the TH current Ith shown in FIG. 6, that is, just before the laser oscillation region (pre-bias state),
The D body 1a is in a region where it operates as a light emitting diode.

On the other hand, the transistor 7, the transistor 8 and the inverting amplifier 9 form a switching circuit which operates by the modulation signal TXD. The collector of the transistor 7 is connected to the cathode of the LD body 1a, and the base is connected to the input side of the inverting amplifier 9. The emitter of the transistor 7 is connected to the emitter of the transistor 8. The voltage Vcc is applied to the collector of the transistor 8 and the base is connected to the output side of the inverting amplifier 9.
The emitters of the transistors 7 and 8 are connected to the collector of the transistor 10,
The emitter of 0 is grounded via the resistor 11. The voltage e4 of the power supply 12 is applied to the base of the transistor 10.

In this switching circuit, the inverting amplifier 9
When the logical level of the modulation signal TXD input to the input terminal is "L", the inverting amplifier 9 inputs the inverted signal to the base of the transistor 8 and the transistor 8 is turned on. As a result, the transistor 10 is biased by the power supply voltage e4 and the current i2 flows through the resistor 11. On the contrary, when the logic level of the modulation signal TXD is "H", the transistor 7 is turned on and the current i2 flows through the transistor 10.

Therefore, when the transistor 7 is in the ON state, the input current i of the LD body 1a increases and the TH current It
As a result, laser amplification occurs and enters the laser oscillation region. In this way, the LD main body 1a outputs an optical modulation signal.

[0008]

By the way, the light emission intensity of the LD gradually decreases as the LD deteriorates, and finally the LD cannot oscillate. Therefore, in order to detect the deterioration of the LD before the oscillation becomes impossible, it is necessary to detect the decrease in the emission intensity of the LD as early as possible. However, in the above burst type optical communication circuit, since the bias voltage e1 is increased to a certain range so that the output of the PD1b becomes constant even if the LD deteriorates, the decrease in the emission intensity of the LD occurs early. Cannot be detected.

The present invention is intended to solve such a problem, and a laser diode deterioration detecting circuit and burst type optical communication capable of surely detecting the deterioration state of the radar diode before the radar diode becomes unable to oscillate. It is intended to provide a circuit.

[0010]

In order to achieve the above-mentioned object, the laser diode deterioration detecting circuit of the present invention comprises a bias current value detecting means for detecting a bias current value just before the laser diode is brought into the laser oscillation region. ,
Deterioration detection means for comparing the bias current value detected by the bias current value detection means with a predetermined deterioration determination value and detecting the presence or absence of deterioration of the laser diode from the comparison result, and the deterioration detection means for the deterioration detection means. And means for outputting the result.

Further, there is provided means for variably setting the deterioration determination value according to the temperature so as to compensate for the variation of the pre-bias current value due to the temperature.

In order to achieve the above-mentioned object, the burst type optical communication circuit of the present invention has a bias current value detecting means for detecting a bias current value just before the laser diode is brought into the laser oscillation region, and this bias current value detection. Deterioration detection means for comparing the bias current value detected by the means with a predetermined deterioration determination value and detecting the presence or absence of deterioration of the laser diode from the comparison result, and the deterioration detection means for detecting the deterioration of the laser diode. And a notification means for notifying that fact. Further, the burst type optical communication circuit of the present invention includes a bias current value detecting means for detecting a bias current value just before the laser diode is brought into the laser oscillation region, and a bias current value detected by the bias current value detecting means and a predetermined value. The deterioration detection value is compared with the deterioration determination value of No. 1 to detect the presence or absence of deterioration of the laser diode based on the comparison result, and the emission of the laser diode is prohibited when the deterioration of the laser diode is detected by this deterioration detection unit. And a light emission prohibition unit set to.

[0013]

That is, in the present invention, the bias current value just before the laser diode is brought into the laser oscillation region is compared with a predetermined deterioration determination value, and the presence or absence of deterioration of the laser diode is detected from the comparison result. That is, the bias current value on the verge of bringing the laser diode into the laser oscillation region increases as the deterioration progresses, reflecting the degree of deterioration of the laser diode. Therefore, it is possible to catch an event in which the bias current value exceeds a certain value. It is possible to accurately and early detect the occurrence of deterioration of the laser diode.

Further, the deterioration determination value is optimally variably set according to the temperature so as to compensate the fluctuation of the pre-bias current value due to the temperature, so that the deterioration can be detected more accurately in consideration of the influence of the temperature.

In the burst type optical communication circuit of the present invention, when the deterioration of the laser diode is detected, the fact is visually informed or the emission of the laser diode is set to the prohibited state. , It is possible to prevent the occurrence of communication abnormality due to the deterioration of the laser diode.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a burst type optical communication circuit including a laser diode deterioration detecting circuit according to a first embodiment of the present invention.

In the figure, reference numeral 21 denotes an LD main body 21a which is an optical signal generating source and a PIN photodiode (hereinafter referred to as PD) for detecting the optical output level of the LD main body 21a.
21b and 21b are integrated in the same package.
A voltage Vcc is applied to the anode of the LD body 21a, and the cathode is connected to the collector of the transistor 22. The pre-bias circuit 2 is provided at the base of the transistor 22.
The bias voltage e1 is applied from the No. 4 pre-bias terminal 24a. A voltage Vcc is applied to the cathode of the PD 21b, and the assault is connected to the terminal 24b of the pre-bias circuit 24 and grounded via the resistor 25. The voltage e2 of the power supply 26 is applied to the terminal 24c of the pre-bias circuit 24.
And a pre-bias request signal (hereinafter referred to as PB_ON signal) is input to the terminal 24d.

When the PB_ON signal is input from the terminal 24d, the pre-bias circuit 24 outputs the bias voltage e1 from the terminal 24a to the transistor 22 while gradually increasing it from zero. As a result, the emitter current i1 of the transistor 22 gradually increases, and the LD body 21a emits light by the input current i, while the light receiving current i0 flows through the resistor 25 while gradually increasing through the resistor 25.
The pre-bias circuit 24 compares the voltage drop e3 of the resistor 25 due to the received light current i0 with the power supply voltage e2, and when the two values match, stops the increase of the bias voltage e1 and fixes the bias voltage e1. To do. In this state, the value of the current flowing through the LD body 1a is TH shown in FIG.
It is on the borderline of the current Ith or less, that is, just before the laser oscillation region (pre-biased state).

On the other hand, the transistor 27 and the transistor 2
8 and the inverting amplifier 29 form a switching circuit which operates according to the modulation signal TXD. The collector of the transistor 27 is connected to the cathode of the LD body 21a, and the base is connected to the input side of the inverting amplifier 29. The emitter of the transistor 27 is connected to the emitter of the transistor 28. The voltage Vcc is applied to the collector of the transistor 28, and the base is connected to the output side of the inverting amplifier 29. The emitters of the transistors 27 and 28 are connected to the collector of the transistor 30, and the emitter of the transistor 30 is grounded via the resistor 31. The voltage e4 of the power supply 32 is applied to the base of the transistor 30.

In this switching circuit, the inverting amplifier 2
When the modulation signal TXD is not input to 9, the inverting amplifier 29
By inputting the inverted signal to the base of the transistor 28, the transistor 28 is turned on. As a result, the transistor 30 is biased by the voltage e4 of the power supply 32, and the current i2 flows through the resistor 31. On the contrary, when the modulation signal TXD is input to the inverting amplifier 29, the transistor 27 is turned on.
The N state is established, which causes the transistor 30 to have a current i.
2 flows. Thus, when the transistor 27 is in the ON state, the input current i of the LD body 21a increases and the TH current I
As a result, laser amplification occurs and enters the laser oscillation region. In this way, the LD main body 21a outputs an optical modulation signal.

Further, at 33, a voltage e6 corresponding to a pre-bias current value which is a current flowing through the LD body 21a in the pre-biased state is compared with a predetermined deterioration determination voltage e5 obtained from the power source 34, and e6> e5 is satisfied. At this time, it is a comparator that outputs a start signal to the flip-flop 35. Reference numeral 35 is a flip-flop that sets the LED 36 for lighting the deterioration state of the LD 21 to a lighting state when a start signal is input from the comparator 33.

Since the pre-bias current value just before the LD 21 is brought into the laser oscillation region increases as the deterioration of the LD 21 progresses, the LD 21 is detected by catching an event in which the pre-bias current value rises above a certain value. The deterioration state of can be detected.

Therefore, in this embodiment, the comparator 33 compares the voltage e6 corresponding to the pre-bias current value with the deterioration determination voltage e5, and the event of e6> e5 is L
By determining the D deterioration state, the LD deterioration detection signal can be derived from the comparator 33 as a start signal to the flip-flop 35. Then, the LED 3 is turned on by the flip-flop 35 that receives the start signal.
6 is set to the lighting state, and the LD deterioration state is notified.

Therefore, according to this embodiment, it is possible to detect the deterioration state of the LD 21 accurately and early.

Next, a second embodiment of the present invention will be described.

FIG. 2 is a diagram showing the configuration of a burst type optical communication circuit including a laser diode deterioration detection circuit according to the second embodiment. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

In the present embodiment, 35 'is a light emission prohibiting signal (L level) to the AND gate 37 when the start signal which is the LD deterioration detection signal from the comparator 33 is inputted.
Is output. Further, in the present embodiment, the inverting amplifier 29 for inverting and amplifying the modulation signal TXD.
The AND gate 37 is connected to the input side of the modulation signal TX.
A light emission prohibiting signal (L level) from D and the flip-flop 35 'is inputted.

Therefore, when the LD deterioration state is detected by the comparator 33, the output logic level of the AND gate 36 is "L" regardless of the logic level of the modulation signal TXD.
, The transistor 27 is fixed in the OFF state, and L
Emission of D21 is prohibited. As a result, unstable optical signal output due to LD deterioration can be prevented.

FIG. 3 shows a third embodiment of the present invention.

This embodiment is a combination of the main components of the first and second embodiments. That is, in this embodiment, the first comparator 33 and the second comparator 33
When the LD deterioration state is detected by each of the comparators 33 ', the LED 36 is set to the lighting state, and at the same time, the output of the AND gate 37 is fixed to the L level and the light emission of the LD 21 is prohibited.

Next, a fourth embodiment of the present invention will be described.

In order to detect the LD deterioration state more accurately based on the pre-bias current value, it is necessary to consider the variation in the pre-bias current value due to the temperature. Therefore, a means for optimally variably setting the deterioration determination voltage applied to the comparator so as to compensate for the variation in the pre-bias current value due to this temperature will be described.

FIG. 4 is a diagram showing the configuration of the deterioration determining voltage variable setting means. In the figure, reference numeral 51 is a comparator for comparing the voltage e6 corresponding to the pre-bias current value with the deterioration determination voltage e5 'to detect the presence or absence of deterioration of the LD. Reference numeral 52 is a power supply that generates a reference deterioration determination voltage e5, 53 is a resistor, and 54 is a thermistor resistor. That is, the deterioration determining voltage variably setting means is the power source voltage e5.
Is divided by a resistor 53 and a thermistor resistor 54, and is input to the comparator 51 as a deterioration determination voltage 5 '. As a result, an optimum deterioration determination voltage e5 'that follows the temperature characteristics of the pre-bias current value is obtained,
It is possible to accurately detect LD deterioration in consideration of the influence of temperature.

[0035]

As described above, according to the laser diode deterioration detection circuit and the burst type optical communication circuit of the present invention, the bias current value just before the laser diode is brought into the laser oscillation region and the predetermined deterioration judgment value are set. Compare
By catching an event in which the bias current value exceeds the deterioration determination value, it is possible to accurately and early detect the occurrence of deterioration of the laser diode.

Further, the deterioration judgment value is optimally variably set according to the temperature so as to compensate for the variation of the pre-bias current value due to the temperature, so that the deterioration can be detected more accurately in consideration of the influence of the temperature.

Further, in the burst type optical communication circuit of the present invention, when the deterioration of the laser diode is detected, the fact is visually informed or the emission of the laser diode is prohibited. , It is possible to prevent the occurrence of communication abnormality due to the deterioration of the laser diode.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a burst type optical communication circuit including a laser diode deterioration detection circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a second embodiment of the present invention.

FIG. 3 is a diagram for explaining a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a deterioration determination voltage variable setting means that is a fourth embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional burst type optical communication circuit.

FIG. 6 is a diagram showing a relationship between an input current and a light output of a laser diode.

[Explanation of symbols]

 21 ... LD (laser diode) 21a ... LD body 21b ... PD (PIN photodiode) 22 ... Transistor 24 ... Pre-bias circuit 33 ... Comparator (first comparator) 33 '... Comparator (second comparator) 34 ...... Power supply for deterioration determination voltage e5 35 ...... Flip-flop (first flip-flop) 35 '... Flip-flop (second flip-flop) 36 ... LED 37 ... AND gate 51 ... Comparator 52 ... Reference Power supply for deterioration determination voltage e5 53 ... Resistor 54 ... Thermistor resistance

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04B 10/06

Claims (5)

[Claims] 1. A bias current value detecting means for detecting a bias current value on the verge of bringing a laser diode into a laser oscillation region, and a bias current value detected by the bias current value detecting means and a predetermined deterioration determination value. A laser diode deterioration detecting circuit comprising: a deterioration detecting means for comparing and detecting the presence or absence of deterioration of the laser diode based on the comparison result; and a means for outputting a deterioration detection result of the deterioration detecting means. 2. The laser diode deterioration detection circuit according to claim 1, further comprising means for variably setting the deterioration determination value according to temperature so as to compensate for a change in the pre-bias current value due to temperature. Laser diode deterioration detection circuit. 3. A burst type optical communication circuit using a laser diode as an optical signal generating source, a bias current value detecting means for detecting a bias current value just before the laser diode is brought into a laser oscillation region, and the bias current. Deterioration detection means for comparing the bias current value detected by the value detection means with a predetermined deterioration determination value and detecting the presence or absence of deterioration of the laser diode from the comparison result, and the deterioration detection means A burst type optical communication circuit comprising: a notifying unit for notifying that deterioration is detected. 4. A burst type optical communication circuit using a laser diode as an optical signal generating source, a bias current value detecting means for detecting a bias current value just before the laser diode is brought into a laser oscillation region, and the bias current. Deterioration detection means for comparing the bias current value detected by the value detection means with a predetermined deterioration determination value and detecting the presence or absence of deterioration of the laser diode from the comparison result, and the deterioration detection means A burst type optical communication circuit, comprising: a light emission prohibiting unit that sets light emission of the laser diode to a prohibited state when deterioration is detected. 5. The burst type optical communication circuit according to claim 3 or 4, further comprising means for variably setting the deterioration determination value according to temperature so as to compensate for variations in the pre-bias current value due to temperature. Burst type optical communication circuit.