JPS6360579A - Alarm circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To detect the abnormality of a laser diode with high precision by setting reference voltage coinciding with temperature characteristics on the high temperature side and the low temperature side having different temperature characteristics of bias currents at the time of automatic power regulating drive and comparing each reference voltage and bias currents. CONSTITUTION:When output voltage from a temperature-voltage conversion section 11 is made larger than that from a changeover temperature input section 13, a diode D2 is turned ON, an output from a high temperature side reference output section 14 is elevated, and an output from a low temperature side reference output section 15 is kept constant. On the other hand, D2 is turned OFF, the output from the output section 14 is kept constant, and the output from the output section 15 is reduced. Outputs from the output sections 14, 15 are inputted to an adding section 16 and the adding section 16 conducts addition operation, a voltage conversion output from a bias current-voltage conversion section 17 is inputted to a comparison circuit 18 together with an output from the adding section 16, and reaches an L level when bias currents are made higher than a predetermined level, and an alarm output section 19 is driven. Accordingly, the abnormality of a laser diode LD can be detected without depending upon a temperature by the abnormal bias currents of the laser diode LD.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser alarm circuit used in a communication system using semiconductor lasers (diodes) to warn of abnormalities in the semiconductor lasers.

2. Description of the Related Art Conventionally, a circuit using a (semiconductor) laser diode (hereinafter abbreviated as LD) is used.As shown in FIG. The temperature coefficient differs at a certain temperature.As shown in Figure 7, when the bias current is fixed, the optical output decreases as the temperature rises.APC (
An automatic power adjustment circuit increases the bias current to keep this light output constant. Furthermore, since the bias current vs. optical output characteristics differ depending on the temperature (2), the bias current characteristics with respect to the temperature (2) during APC driving are as shown in Figure 8.On the other hand, as the LD deteriorates, the bias current vs. The temperature characteristic moves to the right in Figure 7. Therefore, A
If deterioration occurs during PC drive, the bias current increases. The LD deterioration alarm circuit detects deterioration by this rise in bias current. Conventionally, a temperature special voltage as shown in FIG. 8 of the bias current was used.

FIG. 6 shows the configuration of a conventional LD alarm circuit. 6th
In the figure, 1 is a temperature/voltage converter that converts the ambient temperature in which the LD is installed into voltage. 2 is APC (L
This is a bias current/voltage converter that converts the bias current of the LD driven by the circuit (which controls the optical output of the D to a constant level against temperature fluctuations, power supply voltage fluctuations, and deterioration of the LD itself) into a voltage. 3 is a comparison unit that compares the output value of the bias current/voltage converter 2 with a value that is approximated by a straight line to the temperature coefficient of the bias current/voltage conversion value of the output of the temperature/voltage converter, and as a result of the comparison, the bias When the current value reaches a predetermined level, the alarm output section 4 is activated to issue an alarm for an abnormality.

In this way, even in the conventional semiconductor laser alarm circuit described above, the LD
deterioration can be detected.

Problems to be Solved by the Invention However, in the conventional alarm circuit described above, since the reference voltage is a linear approximation, there is a problem in that an abnormality in the LD cannot be detected with high accuracy.

The present invention solves these conventional problems,
The purpose of this invention is to provide an excellent alarm circuit that can detect LD abnormalities with high accuracy.

Means for Solving the Problems In order to achieve the above object, the present invention sets a reference voltage that matches the temperature characteristics of the bias current on the high temperature side and the low temperature side, which have different temperature characteristics when driving the APC. The reference voltage and bias current are compared on the low-temperature side and the low-temperature side (two configurations).

Therefore, according to the present invention, L is reduced due to deterioration regardless of temperature.
When the bias current of D reaches a predetermined level, the abnormality can be detected.

Embodiment FIG. 1 shows the configuration of an embodiment of the present invention. In the first factor, 11 is a temperature/voltage conversion section, and its output is determined by a high temperature/low temperature switching section 12 which receives a signal from a switching temperature input section 13 as to whether the temperature is higher or lower than the switching temperature.

The switching temperature of the switching temperature input section 13 is matched to the switching temperature specific to the LD. 14 is a reference voltage output section on the side higher than the switching temperature having the characteristics shown in FIG. 2, and 15 is a reference voltage output section on the side lower than the switching temperature having the characteristics shown in FIG. Reference numeral 16 denotes an adding section that adds the output voltages of the high temperature side and low temperature side reference temperature output sections 14 and 15, and its characteristics are as shown in FIG. 17 is a bias current/voltage conversion section that converts bias current into voltage. 18 is a bias current using the output voltage of the adder 16 as a reference.
This is a comparison section that compares voltage conversion values.

Reference numeral 19 denotes an alarm output section that sends out an alarm signal in response to the signal from the comparison section 18. In this way, since the above-mentioned embodiment (the deviation can be matched to the temperature characteristic of the LD bias current during APC driving, which is the temperature characteristic of the reference voltage), highly accurate abnormality detection can be performed.

FIG. 5 shows a specific circuit configuration of this embodiment.

In the figure, a temperature/voltage converter 11 performs temperature/voltage conversion using the temperature dependence of the forward voltage of the diode D1. The high-temperature/low-temperature switching section 12 utilizes the switching characteristics of the operational amplifier A5 and the combination diode D2 to set the voltage corresponding to the temperature from the temperature/voltage conversion ELL and the output voltage from the switching temperature input section 13, respectively. The hot side consists of an error amplifier with operational amplifiers A2 and A4,
Controls the input voltage to the inverting and non-inverting inputs to the low temperature side reference voltage output section 14.15. Here, when the output voltage of the temperature/voltage conversion 911 becomes larger than the output voltage of the switching temperature input section 13, the diode D2 is turned on, and the output of the high temperature side reference output section 14 increases, while the low temperature side reference The output of the output section 15 remains constant. Further, the output voltage of the temperature-voltage converter 11 is switched to the temperature input unit 13.
When the output voltage becomes smaller than the output voltage, diode D2 turns OFF.
Therefore, the output of the high temperature side reference voltage output section 14 becomes constant, and the output of the low temperature side reference voltage output section 15 decreases. That is, the characteristics of the high temperature side and low temperature side reference voltage output sections 14 and 15 correspond to the characteristics shown in FIGS. 2 and 3, respectively. Adder 'B16 is equipped with an operational amplifier A5,
The outputs of the high-temperature side and low-temperature side couch output sections 14 and 15 are input and addition operations are performed to show the characteristics shown in FIG. 4. The bias current/voltage converter 17 includes a laser diode LD as an APC circuit of a semiconductor laser, a photodiode PD for receiving light emitted from the laser diode, an operational amplifier A6, and a transistor T.
The voltage conversion output is inputted together with the output of the adder 16 to a comparator 18 provided with a comparator C, and when the bias current becomes higher than a predetermined level, it becomes a LOW level (active level). The alarm output unit 19 is composed of an output buffer 1A7 using TTL or the like.

Effects of the Invention As is clear from the above embodiments, the present invention provides a reference voltage for detecting an abnormality in the bias current of an LD whose temperature characteristics match those of the bias current. This has the advantage that abnormalities can be detected regardless of temperature.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a semiconductor laser alarm circuit according to an embodiment of the present invention (Fig. 2 is an explanatory diagram showing the relationship between the temperature of the circuit and the reference voltage on the high temperature side, and Fig. 3 is a diagram showing the relationship between the temperature of the same circuit and the high temperature side reference voltage. Characteristic diagram showing the relationship between low temperature side reference voltage, No. 4
The figure is a characteristic diagram showing the relationship between the temperature of the circuit and the output voltage of the adder, FIG. 5 is a circuit diagram showing a specific example of the structure of the circuit, and FIG. 6 is a block diagram showing the structure of a conventional semiconductor laser alarm circuit.
Figure 7 is a characteristic diagram showing the relationship between the bias current and optical output of the same circuit, Figure 8 is a characteristic diagram showing the relationship between the temperature of the same circuit and bias current/voltage conversion value, and Figure 9 is a characteristic diagram showing the relationship between the temperature and the bias current/voltage conversion value of the same circuit. temperature·
FIG. 3 is a characteristic diagram showing the relationship between voltage conversion values. 11... Temperature/voltage conversion section, 12... High temperature/low temperature switching section, 13. ... switching temperature input section, 14... high temperature side reference voltage output section, 15... low temperature side reference voltage output section, 16... adding section, 17... bias current/voltage conversion section, 18. ... Comparison section, 19... Alarm output section. Name of agent: Patent attorney Toshio Nakao
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Claims (1)

[Claims] A high temperature side reference voltage output section which has a temperature coefficient similar to the bias current of a laser diode which has a different temperature coefficient on the high temperature side and low temperature side of the ambient temperature, and also switches between the high temperature side and the low temperature side, and a low temperature side reference voltage. Two types of reference voltages consisting of an output section are provided, and an abnormality in the laser diode is detected and notified by comparing the two types of reference voltages with a voltage conversion value of the bias current of the laser diode in a comparison section. Semiconductor laser alarm circuit.