JP2000278215A - Optical transmission equipment - Google Patents

Abstract

(57) [Problem] To optimize drive data for maintaining constant light output by suppressing quenching failure and light emission delay against characteristic deterioration of laser diode without requiring special rules of thumb. To SOLUTION: A characteristic deterioration of a laser diode (100) is detected as an abnormal modulation current and a control means (170).
Operates the drive data such that the bias current is increased by a predetermined current amount and the modulation current is reduced without changing the overall drive current value flowing through the laser diode that causes a light emission delay in this state. When this process is repeated, the quenching defect that the bias current of the laser diode exceeds the threshold current eventually occurs. When the change point of the extinction failure is detected from the emission delay, the modulation current and the bias current immediately before the change point are currents that are faithful or approximate to the deteriorated characteristics of the laser diode. Use this as the optimal drive current

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission device having a laser diode, and more particularly, to a technique for optimizing a drive current of a laser diode with respect to deterioration of characteristics of the laser diode due to aging. For example, the present invention relates to a technology effective when applied to a digital optical communication system.

[0002]

2. Description of the Related Art A laser diode emits light when a drive current exceeds an oscillation threshold current (hereinafter simply referred to as a threshold current), and the emission intensity is proportional to a modulation current exceeding the threshold current. In order to increase the response speed of the light emitting operation of the laser diode, the threshold current or a current near the threshold current is always supplied as a bias current, and the modulation current is applied to the bias current as a pulse current corresponding to a data signal. An optical pulse can be generated by overlapping and flowing.

In order to stably perform optical communication, it is necessary that the light intensity at the time of light emission is constant. At this time, the light emitting characteristics of the laser diode greatly depend on the temperature. That is, the threshold current is increased as the temperature increases, and the modulation current required to obtain a predetermined light emission intensity is also increased as the temperature increases. In addition, the emission characteristics of the laser diode deteriorate with aging, and as the period of use increases, the threshold current increases, and the modulation current required to obtain a predetermined emission intensity also increases. Moreover,
The characteristic change according to temperature and aging differs between the threshold current and the modulation current.

In response to such a characteristic change, the average level of the emission intensity of the laser diode is detected from the current of the photodiode provided opposite to the laser diode, and the bias current is increased by an amount corresponding to the decrease in the detected level. Conventionally, an auto power control technique capable of obtaining a constant luminous intensity has been employed. An example of a document describing this technique is disclosed in JP-A-8-2
No. 04268.

[0005] However, in the above prior art, only the bias current is changed, and the modulation current is not controlled. As a result of this control, if the bias current exceeds the threshold current, extinction failure occurs, and if the bias current is smaller than the threshold current, light emission delay occurs. In short, the above prior art merely controls only the sum of the bias current and the modulation current with respect to a characteristic change such as a threshold current of the laser diode due to a temperature change or an aging change.

[0006]

SUMMARY OF THE INVENTION Accordingly, the inventor of the present invention has been to maintain a constant light output by minimizing quenching failure and light emission delay with respect to deterioration in characteristics of a laser diode due to changes in ambient temperature and aging. (PCT / JP97 / 03260). According to the technique of this application, drive data for determining a modulation current and a bias current required to obtain a predetermined light emission intensity are prepared in advance in a storage unit for each predetermined temperature, and the storage unit is controlled in accordance with the temperature. And control the bias current and the modulation current of the laser diode based on the obtained drive data. Further, an automatic power control is performed in which the bias current or the modulation current is feedback-controlled so that the emission intensity of the laser diode becomes constant. During operation, the drive current actually flowing through the laser diode whose emission intensity is kept constant by the auto power control is measured, and the difference between the measured drive current and the drive current determined by the drive data corresponding to the detected temperature at that time is allowed. It is detected whether or not the temperature exceeds the range, and when the temperature exceeds the allowable range, the driving data relating to the temperature on the storage means is updated so as to define the difference between the driving currents as the increment of the bias current and the modulation current, respectively. I do. At this time, how to divide the difference between the modulation current and the bias current is determined by using an empirical rule or the like.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical transmission device which can easily and accurately correct drive data in accordance with deterioration in characteristics of a laser diode without depending on empirical rules.

Another object of the present invention is to provide an optical transmission device that can easily maintain a constant optical output by minimizing quenching failure and emission delay with respect to deterioration in characteristics of a laser diode due to aging. It is in.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0010]

The following is a brief description of an outline of a typical invention among the inventions disclosed in the present application.

That is, an optical pulse is generated by applying a bias current (IB) to the laser diode (100) and superimposing a modulation current (Im) as a pulse current corresponding to a data signal on the bias current. The optical transmission device (1) selects drive data corresponding to the ambient temperature from the storage means (173) to initially determine the bias current and the modulation current, and operates the drive data to control the optical output of the laser diode. Control means (17) for performing feedback control of the modulation current so as to keep the modulation current at a constant value.
0). The control means responds to an abnormality of the modulation current that causes the laser diode to emit light, and increases the bias current by a predetermined amount and decreases the modulation current by a predetermined amount that causes the laser diode to have an extinction failure every time a process of reducing the modulation current is performed. It is determined whether the state has been reached, and the bias current and the modulation current immediately before reaching the predetermined state are adopted as the optimum drive current of the laser diode.

When the characteristics of the laser diode deteriorate, the bias current must be increased together with the modulation current in order to obtain the same optical output as before the deterioration. Such characteristic deterioration is detected as abnormal modulation current. When the abnormality of the modulation current occurs, the bias current is smaller than the threshold current of the laser diode, and the laser diode does not emit light for a while after the modulation current flows. That is, the light emission is delayed. In this state, the drive data is manipulated so that the bias current is increased by a predetermined amount and the modulation current is decreased without changing the overall current value flowing through the laser diode. When this process is repeated, the bias current of the laser diode will eventually exceed the threshold current. In this state, the laser diode does not completely extinguish even if the modulation current is cut. That is, extinction failure occurs. As described above, even if the sum of the bias current and the modulation current is kept constant, if the quenching failure occurs, the light emission amount (light emission intensity) of the pulse light emitted from the laser diode in a pulsed manner for each fixed period increases. I do. By paying attention to the increase in the light emission amount, the change point of the extinction failure can be detected from the light emission delay. The modulation current and the bias current immediately before this change point are currents that are faithful or approximate to the deteriorated characteristics of the laser diode. If this is adopted as the optimum drive current, it is possible to keep the light output constant by minimizing the quenching failure and the light emission delay against the characteristic deterioration of the laser diode. No empirical rules are required for this process. In addition, since the drive data is optimized while keeping the sum of the modulation current and the bias current constant, the optimization process can be performed while the optical transmission device can transmit the data.

In order to easily determine whether the modulation current is abnormal, the control means may be configured to obtain a light output from the laser diode that is larger than the light output of the laser diode when the modulation current is abnormal. Is detected, it may be determined whether or not a predetermined state in which the extinction failure occurs is reached.

The control means may update drive data on the storage means in correspondence with the optimum drive current.
Thereby, it is possible to save the trouble of performing the drive data optimizing process on the same drive data repeatedly. After the update of the drive data, the bias current and the modulation current for driving the laser diode are initially determined based on the updated drive data, and the feedback control is performed in this state.

The drive data is, for example, data in which bias current drive data for determining a bias current and modulation current drive data for determining a modulation current are associated with each temperature.
Non-volatile memory (173) in which the storage means for storing the drive data is electrically rewritable by the control means
Then, the control means can easily update both the bias current drive data and the modulation current drive data at the corresponding temperature on the storage means in correspondence with the optimum drive current.

The update target of the drive data on the storage means may be at least the bias current drive data. Since the modulation current can be dealt with only by feedback control of the modulation current by operating the driving data, updating of the modulation current driving data may be omitted. Conversely, bias current drive data and modulation current drive data at other temperatures may be updated. For example, the bias current drive data and the modulation current drive data for another temperature on the storage unit are further updated according to the change rates of the bias current drive data and the modulation current drive data at the updated corresponding temperature. This eliminates the need to perform the drive data optimization process every time at another temperature.

An optical transmission device according to a more detailed embodiment of the present invention comprises a laser diode (10) and a first driving transistor (Tr) for supplying a bias current to the laser diode.
1) and a second drive transistor (Tr) that passes a modulation current to the laser diode in a manner superimposed on the bias current.
2), a monitor means (101) for forming a monitor signal corresponding to the optical output of the laser diode, bias current drive data for defining a bias current flowing through the first drive transistor, and the second drive transistor Storage means (173) for holding modulation current drive data for each temperature for defining a modulation current to flow through the memory; and reading the bias current drive data and the modulation current drive data from the storage means in accordance with the temperature, and A bias current flowing through the first driving transistor and a modulation current flowing through the second driving transistor are initially determined based on the bias current driving data and the modulation current driving data, and the light output of the laser diode is kept at a predetermined value. By manipulating the modulated current drive data based on the monitor signal, Current and a feedback control for controlling means (170) a. The control means operates the bias current drive data and the modulation current drive data to increase the bias current by a predetermined amount and decrease the modulation current when detecting an abnormality related to the modulation current causing an emission delay in the laser diode. While referring to the monitor signal, it is determined whether the laser diode has reached a state where an extinction failure occurs from the referenced monitor signal, and a bias current and a modulation current immediately before the extinction failure are determined as an optimal drive current of the laser diode. To adopt.
As described above, the control unit may update the bias current drive data at the corresponding temperature on the storage unit with data defining the bias current that is the optimum drive current. Further, the control means may update the modulation current driving data of the corresponding temperature on the storage means with data defining the modulation current which is the optimum driving current.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS << Optical Transmission Apparatus >> FIG. 1 shows an embodiment of an optical transmission apparatus, mainly an optical transceiver.
The optical transmission device 1 shown in FIG.
And the optical receiver 1R are representatively shown. Although the optical transceiver 1T is not particularly limited, each of the laser diode modules 10 individually formed into a semiconductor integrated circuit,
An LD driver 110, an input circuit 12, and a microcomputer 17 are provided. The optical receiver 1R includes a pin photodiode 13 individually formed as a semiconductor integrated circuit,
Preamplifier 14, main amplifier 15, and output circuit 16
Is provided.

The laser diode module 10 has a laser diode (also referred to as LD) 100 and a monitoring photodiode (also referred to as PD) 101, and the light output of the laser diode 100 is outputted to an optical output terminal OPOUT. The pin photodiode 13 receives an optical signal from an optical input terminal OPIN. The input circuit 12 is coupled to a data input terminal DTIN and a clock input terminal CLIN, and the output circuit 16 is connected to a data output terminal DTOUT and a clock output terminal CLOUT.

The input circuit 12 includes a buffer memory 120
And input buffer 1 such as D-type flip-flop (F / F)
21. The buffer memory 120 sequentially stores the data signal from the data input terminal DTIN in synchronization with the clock signal from the terminal CLIN. Buffer memory 120
Is stored in the input buffer 121 in synchronization with the clock signal supplied from the clock input terminal CLIN.
And the waveform is shaped and supplied to the driver circuit 11.

The LD driver 110 supplies a bias current corresponding to the threshold current to the LD 100, and responds to a data signal supplied from the input buffer 120 to the LD 100.
The modulation current for on / off control of LD
Flow to 00. The PD 101 photoelectrically converts the light output from the LD 100, and forms a current corresponding to the emission intensity of the LD 100. The optical output of the LD 100 is an optical output terminal OPOUT
To a transmission line such as an optical fiber.

The pin photodiode 13 detects an optical signal supplied from the transmission line to the optical input terminal OPIN and converts it into a received signal current. This received signal current is converted into a voltage signal by the preamplifier 14. The converted voltage signal is provided to main amplifier 15. The main amplifier 15
The input voltage signal is amplified to the ECL level. The output circuit 16 that receives the output of the main amplifier 15 has a timing extraction unit 160, an identification unit 161, and an output buffer 162 such as a flip-flop. The timing extractor 160 divides the input signal into two systems, delays one of the signals, takes the logical product of the delayed signal and the other, and generates a pulse including a clock component of, for example, 155.52 MHz. From this pulse, only a clock component of 155.52 MHz is extracted by a SAW (Surface Acoustic Wave) filter (not shown), which is subjected to limit amplification to generate a clock signal. The identification unit 161 sufficiently amplifies the input signal from the main amplifier 15 and shapes the upper and lower waveforms into a sliced signal. The output buffer 162 performs waveform shaping (suppression of pulse width distortion) on the sliced signal using the clock signal. The output of the output buffer 162 is provided to a data output terminal DTOUT, and the clock signal generated by the timing extraction unit 160 is provided to a clock output terminal CLOUT.

The microcomputer 17 is not particularly limited, but includes a CPU (Central Processing Unit) 170 and a RAM (Random Access Memory).
Random access memory) 171, ROM (Read Only)
Memory: a read-only memory 172, a flash memory 173, which is an example of an electrically erasable and writable nonvolatile storage device, and an input / output circuit (I / O) 174, which are coupled to an internal bus 175. ing. Although not particularly limited, the ROM 172 is a mask ROM holding constant data and the like, and the RAM 171 is
And the flash memory 173 has a CPU
An operation program 170, drive data, and the like are rewritably held.

The microcomputer 17 is a circuit for controlling the entire optical transmission device 1. The drive data of the LD 100 is stored in the flash memory 173. CPU1
70 drives the LD 100 to perform optical transmission, reads drive data corresponding to a temperature detected by a temperature sensor 112 described later from the flash memory 173, and controls the LD driver 110 to drive the LD 100 based on the read data. Do. That is, a data table (drive data table) created based on the temperature characteristics of the LD 100
Are previously prepared in the flash memory 173, and the CP
The U 170 selects drive data corresponding to the optical output, temperature, and the like required by the LD 100 from the flash memory 173 to initially determine the bias current and the modulation current, and further determines the modulation current in the selected drive data. By manipulating the data to be determined, the modulation current is feedback controlled so as to keep the light output of the LD 100 at a constant value. This feedback control can be positioned as software-based automatic power control (also referred to as software APC). In simple terms, the microcomputer 100 drives the LD 100 in such a manner that the bias current is uniquely determined by the drive data, the modulation current is initially determined by the drive data, and the software A
That is, it is controlled by a PC. Therefore, if the characteristics of the LD 100 deteriorate, it is necessary to optimize at least the bias current that is not targeted by the software APC. In consideration of this point, the microcomputer 17 optimizes the driving data by a method described later.

The microcomputer 17 is connected to a protocol controller (not shown) in the optical transmission device via a microcomputer interface terminal (also referred to as a microcomputer interface terminal) MCIF, and receives instructions for transmission / reception control and the like. The microcomputer interface terminal MCIF is connected to the microcomputer 17
Mode terminal and a predetermined port of the input / output circuit.

The microcomputer 17 has, for example, a boot mode in addition to the user program mode. When the user program mode is set in the microcomputer 17, the CPU 170 executes the operation program stored in the flash memory 173. The boot mode stores the flash memory 173 in the microcomputer 1
7 is an operation mode in which rewriting can be performed directly from the outside. When the boot mode is set in the microcomputer 17, the input / output circuit 174 sets the flash memory 173 to a signal input / output state in which external flash memory can be directly rewritten.
That is, when the boot mode is set, a high voltage for rewriting, a program signal, an address and data can be exchanged with the flash memory 173 via the microcomputer interface terminal MCIF. Using this boot mode, the drive data can be initially written in the flash memory 173, and the operation program of the CPU 170 can be written. Flash memory 1
Rewriting of 73 is also possible. Flash memory 173
Can be written or rewritten in the user program mode of the microcomputer 17,
The CPU 170 executes the rewriting control program of the flash memory 173 to
3 can be rewritten.

FIG. 2 is an overall block diagram of the optical transmission device. Although not particularly limited, the optical transmission device shown in FIG. 1 constitutes one interface board out of a number of interface boards constituting an ATM switch or the like. The optical transceiver 1T and the optical receiver 1R are connected to an optical trunk network by an optical fiber. Optical transceiver 1
After the T and the optical receiver 1R, a SUNI (Serial U
ser Network Interface) 3 and SUN
At the connection with the optical transceiver 1T at I3, serial / parallel conversion of data is performed, and at the connection with the optical receiver 1R at SUNI3, parallel / serial conversion of data is performed. The protocol controller 4 is an ATM
(Asynchronous Transfer Mode), assemble / disassemble data cells and multiplex / demultiplex data cells. The transmission signal is provided to the protocol controller 4 via the parallel input circuit 6 and the transmission buffer 5. The reception signal is provided from the protocol controller 4 to the parallel output circuit 8 via the reception buffer 7. The parallel input circuit 6 and the parallel output circuit 8 are connected to another exchange via, for example, an interface cable (not shown).

<< Optical Transceiver >> FIG. 3 shows a detailed example of the optical transceiver 1T. The LD driver 110 includes a transistor (first driving transistor) Tr1 for determining a bias current flowing through the LD 100;
A transistor (second drive transistor) Tr2 for determining a modulation current to be supplied to the LD 100 is provided as a current source transistor. The transistors Tr3 and Tr4 are L
It is a switching transistor for controlling on / off of a modulation current flowing through D100. The transistors Tr1 to Tr4 are npn-type bipolar transistors.

The transistors Tr3 and Tr4 are connected in parallel, the common emitter is connected to the collector of the transistor Tr2, and the emitter of the transistor Tr2 is connected to the ground voltage GND via the resistor R2. LD100 is connected to the collector of the transistor Tr3.
Are connected, and the anode of the LD 100 and the collector of the transistor Tr4 are commonly connected to the power supply voltage Vcc.

As shown in a detailed example in FIG. 4, the switching control circuit 114 for the transistors Tr3 and Tr4 includes a series circuit of the transistors Tr5 and Tr6 and a series circuit of the transistors Tr7 and Tr8 each having the power supply voltage Vcc. It is arranged between the ground voltages GND. The transistors Tr5 to Tr8 are npn-type bipolar transistors. The bases of the transistors Tr6 and Tr8 are biased at a predetermined voltage,
7 functions as a load resistance. In other words, the series circuit of the transistors Tr5 and Tr6 and the transistor Tr7
The series circuit of the transistor Tr8 and the transistor Tr8 form an emitter follower circuit. The emitter of the transistor Tr5 is connected to the base of the transistor Tr3, and the emitter of the transistor Tr7 is connected to the base of the transistor Tr4.

The bases of the transistors Tr5 and Tr7 are supplied with the differential output of the differential output amplifier AMP, and when their inputs are inverted, the states of the base potentials of the transistors Tr3 and Tr4 are inverted. . Amplifier A
The output of the selector 121 is supplied to MP.

When the base potential of the transistor Tr3 is set to a high level, the transistor Tr3 is shifted to a saturation state, and when the base of the transistor Tr4 is set to a high level, the transistor Tr4 is shifted to a saturation state. The transition of the transistors Tr3 and Tr4 to the saturated state is performed in a complementary manner, whereby the switching operation of the transistors Tr3 and Tr4 is performed in a complementary manner, so that a pulse-shaped modulation current is supplied to the LD 100 via the current source transistor Tr2. Will be washed away.

As shown in FIG. 3, the transistor Tr1 has a collector connected to the collector of the transistor Tr3 and an emitter connected to the ground voltage GND via the resistor R1. This transistor Tr1
Supplies a bias current to the LD 100 according to the base voltage applied thereto. Needless to say, this bias current is preferably a current near the threshold current of the LD 100 from the viewpoint of preventing quenching failure and emission delay of the LD 100.

The PD 101 is connected in series to the resistor R3, and is arranged between the power supply voltage Vcc and the ground voltage GND in a reverse connection state. The PD 101 supplies a current according to the light emission intensity output from the LD 100.

In FIG. 3, the microcomputer 1
7 is a digital / analog conversion circuit (D / A) for converting a digital signal into an analog signal.
176, an analog / digital conversion circuit (A / D) 177 for converting an analog signal to a digital signal, timer 1
79 and other input / output circuits 178. The D / A 176 has two D / A conversion channels DA.
A / D 177 has four A / D conversion channels ADC1 to ADC4.

D / A conversion channels DAC1, DAC2
Has a unique register accessed by the CPU 170, D / A converts the value of the corresponding register, and outputs the base bias voltage of the transistors Tr1 and Tr2. Although not particularly limited, the D / A conversion channels DAC1, DAC2, and DAC3 convert an 8-bit digital signal into an analog signal in 256 gradations.

The LD10 is connected via the transistor Tr3.
The modulation current flowing to 0 is determined by the drive data set in the D / A conversion channel DAC2 by the CPU 170. The bias current flowing through the LD 100 is
70 is determined by the drive data set in the D / A conversion channel DAC1. The CPU 170 selects drive data corresponding to a desired light emission intensity and an ambient temperature from the drive data table according to the operation program and sets the data in the D / A conversion channels DAC1 and DAC2, so that the bias current of the LD 100 is reduced. The modulation current is initially determined.

The A / D conversion channels ADC1 to ADC1
ADC4 is an emitter voltage of the transistor Tr1 sequentially,
A / D conversion is performed for the input of the monitor voltage stored in the capacitor CA and the output voltage of the temperature sensor 112 in accordance with the emitter voltage of the transistor Tr2 and the anode voltage of the PD 101, and the A / D conversion is performed on the allocated input voltage.
Each of them has its own register for holding the conversion result accessible by the CPU 170. Although not particularly limited, the A / D conversion channels ADC1 to ADC4 are 1
It has a conversion accuracy of 0 bits.

Thus, based on the conversion results of the A / D conversion channels ADC1 to ADC4, the CPU 170 adjusts the bias current flowing through the transistor Tr1, the modulation current flowing through the transistor Tr2, and the L received by the PD 101.
The emission intensity of D100 and the temperature detected by the temperature sensor 10 can be obtained as needed. CPU 170
The operation of calculating the above information by accessing the registers of the A / D conversion channels ADC1 to ADC4 is not particularly limited, but is instructed by a timer interrupt from the timer 179.

The CPU 170 monitors the accumulated voltage of the capacitor CA via the A / D conversion channel ADC3, and can detect the light emission intensity (degree of light output) of the LD 100 based on the monitored voltage. For example, if the LD 100 forms a light emission waveform as shown in FIG. 5B with respect to the waveform (A) of the signal supplied to the base of the transistor Tr3 as illustrated in FIG. The voltage stored in the capacitor CA is converted to an A / D conversion channel ADC.
Sampled at 3 and A / D converted. The result of the A / D conversion is a value proportional to the area of the hatched portion for each fixed section of the emission waveform shown in FIG. CPU 170
Is compared to a reference value to obtain the LD100
Can be recognized.

The CPU 170 controls the A / D conversion channel A
The emission intensity of the LD 100 detected using the DC3 is used for the software APC. That is, the CPU 170 detects the LD detected via the A / D conversion channel ADC3.
When the emission intensity of 100 is higher than the target value, D / A
The modulation current drive data set in the conversion channel DAC2 is increased by one step, and conversely, if the detected light emission intensity is smaller than the target value, the modulation current drive data set in the D / A conversion channel DAC2 is reduced by one step to detect and emit light. Feedback control is performed until the intensity converges to the target value. The one stage means, for example, one bit of the least significant bit of the data to be D / A converted. In the case of an 8-bit D / A converter, data whose size is determined in 256 steps is 1
It will change in steps.

The CPU 170 can detect the transition to the extinction failure state based on the light emission intensity of the LD 100 detected via the A / D conversion channel ADC3. For example, the waveform (B) in FIG. 5 is a light emission waveform of the LD 100 in a state where there is no extinction failure or a state where a light emission delay occurs. In this state, if the bias current is increased without changing the total current of the bias current and the modulation current flowing to the LD 100, and the modulation current is reduced by that amount to bring about the extinction failure state, as shown in the waveform (C) of FIG. Transistor Tr
Even in the off period of No. 3, the LD 100 emits light due to the bias current, and the light-emitting area indicated by oblique lines increases. The transition to this state, that is, the transition to the extinction failure state, can be identified by detecting a state in which a light emission intensity higher than the light emission intensity detected in the state of waveform (B) is obtained.

The CPU 170 monitors the emitter voltage of the transistor Tr1 via the A / D conversion channel ADC1, converts the monitored voltage into a current, and converts the converted current value and the transistor Tr1 via the D / A conversion channel DAC1. Is compared with a bias current that is to be supplied to the controller, and an abnormality in the bias current can be detected based on the difference. Similarly, the CPU 170 monitors the emitter voltage of the transistor Tr2 via the A / D conversion channel ADC2, converts the monitored emitter voltage into a current, and supplies the converted current to the transistor Tr2 via the D / A conversion channel DAC2. The modulation current is compared with the modulation current to be determined, and based on the difference, an abnormality in the modulation current can be detected.

<< Update of Drive Data >> Drive data for determining a modulation current and a bias current to be supplied to the LD 100 is stored in a drive data table. The drive data table includes drive data (modulation current drive data and bias current drive data) to be set in the D / A conversion channels DAC1 and DAC2 in order to obtain a predetermined target optical output for each use environment temperature. 170 are formed in the flash memory 173.

FIG. 6 shows the drive current (I
The relationship between d) and the light emission intensity (P0) is illustrated. In the figure, the bias currents Ib (T1), Ib (T2), Ib at the temperatures T1, T2, T3 shown representatively are shown.
(T3) and threshold currents Ith (T1), Ith (T
2), Ith (T3) and modulation currents Im (T1), Im
(T2) and Im (T3). The bias current is set to, for example, approximately 90% of the threshold current. As is clear from FIG. 6, when trying to obtain a constant luminous intensity, as the temperature increases, both the threshold current and the modulation current must be increased accordingly. on the other hand,
FIG. 7 shows a temperature characteristic of the LD 100. As is clear from the figure, since the threshold current Ith and the drive current Id show nonlinear characteristics with respect to the temperature (T), the bias current Ith
Similarly, b and the modulation current Im also need to be nonlinearly controlled with respect to the temperature (T).

When the characteristics of the LD 100 deteriorate, the bias current must be increased together with the modulation current in order to obtain the same optical output as before the deterioration. In this state, the characteristic waveform LD (i) of the LD 100 in the normal state shown in FIG.
It is clear from comparison with the characteristic waveform LD (k) of D100.

The optical transceiver 1T performs the process of optimizing the driving data while maintaining the optically transmittable state with respect to the characteristic deterioration of the LD 100.

FIG. 9 shows C including the driving data update process.
An example of a drive control procedure of the LD 100 by the PU 170 is shown.

The optical transceiver 1T is made optically operable by power-on reset of the microcomputer 17 and the like, and normal drive control of the LD 100 is started (S1). Microcomputer 17
The normal drive control by the software AP includes: an operation of initially determining a bias current and a modulation current;
C operation. The former detects the ambient temperature via the temperature sensor 112, selects bias current drive data and modulation current drive data necessary for obtaining a required light emission intensity at that temperature from the flash memory 173, and selects the selected drive. This is an operation of setting data in the registers of the D / A conversion channels DAC1 and DAC2 and thereby initially determining a bias current and a modulation current. The software APC operation detects the light emission intensity of the LD 100 via the A / D conversion channel ADC3, and controls the D / A conversion channel 2 so that the light emission intensity converges to the target light emission intensity.
In this operation, the modulation current drive data is manipulated to feedback-control the modulation current. Assuming that the characteristics at the beginning of using the LD 100 are waveform LD (i) in FIG. 8, the initially set bias current is Ib (i), and the modulation current is Im.
(I). Thereafter, when the characteristics of the LD 100 gradually deteriorate, the modulation current is gradually increased by the software APC. For example, as illustrated in FIG. 8, the modulation current is increased to Im ′ (i).

The microcomputer 17 periodically samples the modulation current using a timer interrupt or the like (S2). The sampling method is as described above. Assuming that the sampled modulation current is Im, it is determined whether Im> α (S3). Although α is not particularly limited, α is an integer multiple of the initial value Im (i) of the modulation current. The processing in step S3 is performed when the LD 10
This means that the characteristic deterioration of 0 has been determined. When the characteristics of the LD 100 deteriorate as shown by the waveform LD (k) in FIG. 8, the modulation current is changed to Im ′ (i) by the software APC.
In this state, if Im ′ (i)> α, it is determined in step S3 that the modulation current is abnormal. In the abnormal state of the modulation current, the bias current of the LD 100 is smaller than the threshold current, and the LD 100 is in a state of causing a light emission delay.

When detecting an abnormality in the modulation current, the microcomputer 17 holds the monitor value Sm of the light emission intensity by the PD 101, the modulation current Im, and the bias current Ib at that time in a work area such as the RAM 171 (S17).
4). According to FIG. 8, the value of the bias current Ib (i) and the value of the modulation current Im ′ (i) are held. The monitor value S
m is stored in, for example, the register Sm1 (S5).

Then, the D / A conversion channels DAC1 and DAC1 are arranged so that the bias current is increased by the unit current amount and the modulation current is reduced without changing the overall current value flowing through the LD 100.
The drive data in the DASC 2 is operated (S6). Assuming that the increasing / decreasing unit current amount is Δn, the modulation current is Im−Δ
n, the bias current is set to Ib + Δn, and set to the D / A conversion channels DAC1 and DASC2. After operating the drive data, a new emission intensity monitor value Sm is obtained (S7) and stored in the register Sm2 (S8).
Then, it is determined whether the value of the register Sm2 is larger than the value of the register Sm1 (S9). That is, the amount of increase in bias current due to Δn and the amount of decrease in modulation current are equal, and LD1
00 does not change, so long as the increased bias current does not exceed the threshold current of LD 100 (L
(As long as D100 maintains the emission delay)
The Sm sampled in step 7 maintains the Sm sampled in step S4. As described with reference to FIG. 5, the emission intensity monitor value Sm is
Increases only after the quenching failure. Until then, the value of the register Sm2 is substituted into the register Sm1, n is updated to n + 1 (S10), and the processing of steps S6 to S9 is repeated.

The state of Sm2> Sm1 is detected immediately after the light emission delay state changes to the extinction failure state.
That is, the bias current at that time depends on the LD whose characteristics have deteriorated.
100 corresponds to the current value near the change point of the extinction failure from the light emission delay at 100, in other words, it means that the value is slightly over the threshold current of the LD 100 whose characteristics have been degraded,
The values are faithful or approximate to the deteriorated characteristics of the LD 100. Since the driving current at this time is a current that causes a slight extinction failure, the modulation current and the bias current immediately before that are adopted as the optimum driving current for driving the LD 100 (S11). That is, Im-Δ (n−1) is used as the modulation current, and Ib + Δ (n−1) is used as the bias current.

FIG. 8 shows a concrete change process of the modulation current and the bias current when the processes of steps S6 to S11 are repeated. In the first stage shown by S6 (1), the bias current is Ib (i) + ΔI, and the modulation current is Ib (i) + ΔI.
m ′ (i) −ΔI, and from the second stage S6 (2) to the n-th
Step S6 (n), and (n + 1) th step S6 (n +
Each time 1) is followed, the bias current is increased by ΔI and the modulation current is decreased. In the example of FIG. 8, the n-th stage S6 (n)
From (n + 1) th step S6 (n + 1) to LD1
00 changes from the light emission delay state to the extinction failure state. When this state is detected, the bias current and the modulation current are returned to the state of the immediately preceding n-th stage, whereby the waveform LD
The drive current of the LD 100 degraded to the characteristic shown by (k) is such that the bias current is Ib (k) = Ib (i) + nΔ
I, the modulation current is optimized to Im (k) = Im ′ (i) = nΔI. Note that the current step ΔI is not limited to being the same at each stage, and the step may be gradually reduced later or vice versa.

After optimizing the drive current, the drive data table is updated based on the bias current drive data and the modulation current drive data (S12). If you update it,
It is not necessary to repeat the same optimization processing. The update target can be limited to only the drive data related to the temperature that has been optimized this time. In this case, if there is no update processing time,
At least only the bias current drive data needs to be updated. This is because the modulation current can be handled by software APC. Further, the bias current drive data and the modulation current drive data relating to another temperature on the drive data table may be updated together. For example, the drive data can be updated according to a change rate substantially equal to a change rate of the bias current drive data and the modulation current drive data at the updated corresponding temperature.

After the update of the drive data, the bias current and the modulation current for driving the laser diode are initially determined by the updated drive data, and the feedback control is performed in this state.

According to the optical transmission device, the following operations and effects can be obtained.

(1) Deterioration of the characteristics of the LD 100 is detected as abnormal modulation current. In this state, the bias current is increased by a predetermined amount by increasing the bias current without changing the overall drive current flowing through the laser diode that causes light emission delay. Manipulate drive data to reduce current. By repeating this process,
The bias current of the laser diode will eventually cause extinction failure exceeding the threshold current. As described above, even if the sum of the bias current and the modulation current is kept constant, if the quenching failure occurs, the light emission amount (light emission intensity) of the pulse light emitted from the laser diode in a pulsed manner for each fixed period increases. I do. By paying attention to the increase in the light emission amount, the change point of the extinction failure can be detected from the light emission delay. The modulation current and the bias current immediately before this change point are currents that are faithful or approximate to the deteriorated characteristics of the laser diode. Since this is adopted as the optimum drive current, it is possible to keep the light output constant while minimizing the quenching failure and the light emission delay with respect to the characteristic deterioration of the laser diode. No empirical rules are required for this process.

(2) In the above-described optimization processing, the entire current value of the drive current flowing through the laser diode is not changed.
The drive data optimizing process can be performed while the optical transmission device is capable of optical transmission.

(3) The update target of the drive data on the storage means may be at least the bias current drive data. Since the modulation current can be dealt with only by feedback control of the modulation current by operating the driving data, updating of the modulation current driving data may be omitted. vice versa,
The bias current drive data and the modulation current drive data at other temperatures may be updated. This eliminates the need to perform the drive data optimization process every time at another temperature.

Although the invention made by the present inventors has been specifically described above, the present invention is not limited thereto, and various changes can be made without departing from the gist of the invention.

For example, the light emission output to be output by the optical transmission device 1 is of a nature physically determined according to the communication environment in which the light transmission device 1 is placed. For example, an operation program of the CPU 170 or an external instruction, Alternatively, the CPU 170 can be notified by a signal from a circuit such as a dip switch. If the emission intensity corresponding to the drive data held by the drive data table is different from the specified emission intensity, the drive data in the drive data table is
It can be used by multiplying the ratio according to the ratio of both data.

The optical transmission device is not limited to the interface board described with reference to FIG. For example, a form as an optical transceiver module or an optical transmission module in which an optical transceiver is built in a casing can be adopted.

The present invention relates to a PDS (Passive Double Star) in which an optical fiber is introduced into a telephone or ISDN subscriber system.
Optical transmission systems such as ATM-LAN (Asynchro
nousTransfer Mode-Local Area Network).

[0065]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

That is, the drive data optimization process for keeping the light output constant by minimizing the quenching failure and the light emission delay against the characteristic deterioration of the laser diode is realized without requiring any special rule of thumb. be able to.

In the optimizing process, since the entire current value of the driving current flowing through the laser diode is not changed, the optimizing process of the driving data can be performed while the optical transmission device can transmit light.

Since the drive data on the storage means is updated with the optimized drive data, it is not necessary to repeat the same optimization process every time. By updating the drive data of another temperature on the storage unit based on the data optimized for one temperature, it is not necessary to optimize the drive data every time at another temperature.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of an optical transmission device according to the present invention, focusing on an optical transceiver.

FIG. 2 is a block diagram schematically showing an entire optical transmission device configured as an interface board.

FIG. 3 is a circuit diagram showing a detailed example of an optical transceiver.

FIG. 4 is a circuit diagram showing an example of a switching control circuit for causing a modulation current to flow in a diode in a pulse shape.

FIG. 5 is an explanatory diagram showing a transmission signal waveform, a light emission waveform of an LD in a light emission delay state, and a light emission waveform of an LD in an extinction failure state;

FIG. 6 is an explanatory diagram showing a relationship between a drive current of a LD and a light emission intensity.

FIG. 7 is an explanatory diagram showing temperature characteristics of an LD.

FIG. 8 is an explanatory diagram showing a drive current optimization process in relation to a characteristic diagram of an LD.

FIG. 9 is a CPU including a process of optimizing drive data of an LD;
6 is a flowchart showing an example of an LD drive control procedure according to the first embodiment.

[Explanation of symbols]

 Reference Signs List 1 optical transmission device 1T optical transceiver 17 microcomputer 100 laser diode 101 photodiode 110 laser driver 112 temperature sensor 170 CPU 173 flash memory 176 D / A DAC1, DAC2 D / A conversion channel 177 A / D ADC1 to ADC4 A / D conversion Channel Tr1 Driving transistor for bias current Tr2 Driving transistor for modulation current

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H04B 10/28 10/26 (72) Inventor Makoto Haneda 5-2-1, Josuihoncho, Kodaira-shi, Tokyo F-term (Reference) 5F073 EA13 GA03 GA04 GA12 GA14 GA24 5K002 AA05 BA13 CA09 CA11 DA05

Claims (12)

[Claims] An optical transmission device for generating an optical pulse by applying a bias current to a laser diode and superimposing a modulation current as a pulse current corresponding to a data signal on the bias current to cause the laser diode to emit an optical pulse. The bias data and the modulation current are initially determined by selecting drive data corresponding to the temperature from the storage means, and the modulation current is feedback-controlled so that the light output of the laser diode is maintained at a constant value by operating the drive data. The control means increases the bias current by a predetermined amount and decreases the modulation current by a predetermined amount in response to an abnormality of the modulation current causing an emission delay in the laser diode. Is determined to have reached a predetermined state where extinction failure occurs, and the bias current and the modulation current immediately before reaching the predetermined state are determined. The optical transmission apparatus, characterized in that the one in which is employed as the optimum driving current of the laser diode. 2. The control means detects a state in which a light output larger than a light output of the laser diode when the modulation current is abnormal is obtained from the laser diode, thereby setting a predetermined state in which the quenching failure occurs. 2. The optical transmission device according to claim 1, wherein the optical transmission device determines whether or not the optical transmission has been reached. 3. The optical transmission device according to claim 1, wherein said control means updates drive data on said storage means in correspondence with said optimum drive current. 4. The drive data is data in which bias current drive data for determining a bias current and modulation current drive data for determining a modulation current correspond to each temperature. A nonvolatile memory electrically rewritable by a means, wherein the control means updates the bias current drive data and the modulation current drive data at a corresponding temperature on the storage means in accordance with the optimum drive current. The optical transmission device according to claim 3, wherein: 5. The controller according to claim 1, wherein the controller is configured to control the bias current drive data and the modulation current for another temperature on the storage unit in accordance with a change rate of the bias current drive data and the modulation current drive data at the updated corresponding temperature. The optical transmission device according to claim 4, wherein the driving data is further updated. 6. A laser diode, a first drive transistor for flowing a bias current to the laser diode, a second drive transistor for flowing a modulation current to the laser diode in a manner superimposed on the bias current, and Monitoring means for forming a monitor signal corresponding to an optical output; bias current drive data for defining a bias current flowing through the first driving transistor; and a modulation current for defining a modulation current flowing through the second driving transistor. Storage means for holding drive data for each temperature; reading out the bias current drive data and modulation current drive data from the storage means in accordance with the temperature; and reading the bias current drive data and modulation current drive data based on the read bias current drive data and modulation current drive data. Bias current flowing through one drive transistor and second drive A control means for initially determining a modulation current flowing through a transistor and performing feedback control of the modulation current by manipulating the modulation current drive data based on the monitor signal so as to keep an optical output of the laser diode at a predetermined value. When the control means detects an abnormality related to a modulation current that causes an emission delay in the laser diode, the control means operates the bias current drive data and the modulation current drive data to increase the bias current by a predetermined amount. Further, referring to the monitor signal while reducing the modulation current, it is determined whether the laser diode has reached a state where an extinction failure occurs from the referenced monitor signal, and the bias current and modulation current immediately before the extinction failure are detected by the laser diode. An optical transmission device characterized in that the optical transmission device is adopted as an optimum drive current for the optical transmission device. 7. The storage means is a non-volatile memory electrically rewritable by the control means, and the control means stores a response in the storage means by data defining a bias current which is the optimum drive current. 7. The optical transmission apparatus according to claim 6, wherein the bias current driving data of the temperature to be updated is updated. 8. The apparatus according to claim 1, wherein the control means updates the modulation current driving data of the corresponding temperature in the storage means with data defining the modulation current which is the optimum driving current. 8. The optical transmission device according to 7. 9. The control means according to claim 1, wherein said bias current drive data and said modulation current drive data at said updated corresponding temperature have a change rate substantially the same as said change rate. 9. The optical transmission device according to claim 8, wherein the driving data and the modulation current driving data are further updated. 10. The control means detects a state in which the laser diode obtains an optical output larger than the optical output of the laser diode when the modulation current is abnormal. The optical transmission device according to claim 6, wherein the optical transmission device determines the value. 11. The control means has means for detecting a modulation current flowing through a second drive transistor, and the modulation means initially obtained by the modulation current drive data read from the storage means in accordance with the temperature. 11. The optical transmission device according to claim 10, wherein when the difference between the magnitude of the current and the magnitude of the modulation current actually flowing by the feedback control exceeds a specified value, it is determined that the modulation current is abnormal. 12. The optical transmission device according to claim 11, further comprising a temperature measuring means for measuring a temperature near the laser diode.