CN100461559C - A laser drive circuit - Google Patents

Abstract

The invention discloses a high-speed and high-reliability modulation laser driving circuit, which includes a digital-to-analog conversion control circuit, a comparison amplifier circuit and a driving laser circuit; The terminals are respectively connected with one input terminal of the comparison amplifier circuit and the input terminal of the driving laser circuit; the other input terminal of the comparison amplifier circuit receives an external modulation signal, and the output terminal is connected with an input terminal of the driving laser circuit connected. The advantages of the present invention are: (1) The laser bias current level, the laser modulation current level and the modulation duty cycle are completely electronically controlled, without replacing electronic components; the adjustment speed is fast and the precision is high; (2) The hysteresis comparator structure is adopted The system reliability and anti-interference ability are enhanced; (3) Compared with the laser external modulation and analog internal modulation, the structure is simple, the integration is high, and the modulation speed is from continuous wave (CW) to 200MHz.

Description

A laser drive circuit

technical field

The invention relates to a laser drive circuit, in particular to a high-speed and high-reliability modulated laser drive circuit.

Background technique

Laser has excellent temporal coherence and spatial coherence. It is similar to radio waves, easy to modulate, and the frequency of light waves is extremely high, and the capacity to transmit information is large. In addition, the divergence angle of the laser beam is small, and the light energy is highly concentrated, which can not only transmit a long distance, but also be easy to keep secret. Therefore, it provides an ideal light source for optical information transmission.

Laser modulation is the loading of the signal to be transmitted onto the laser beam. At present, laser modulation methods can be divided into two types: external modulation and internal modulation.

External modulation means that after the laser is formed, a modulator is placed on the optical path outside the laser, and the physical characteristics of the modulator are changed with a modulation signal. When the laser passes through the modulator, the light wave will be modulated. There are three types of external modulation methods, namely electro-optic modulation, acousto-optic modulation and magneto-optic modulation. When this method is implemented, an external modulator is required, which makes the entire system mechanism more complicated, which is not conducive to system integration and miniaturization.

Internal modulation is to convert the information to be transmitted into a current signal and inject it into the semiconductor laser to obtain an excitation optical signal. Because this modulation method is simple, can work at high frequency, and can ensure a good linear working area and bandwidth, it has been widely used in providing coherent light sources, optical fiber communications, optical discs and optical copying. At present, the internal modulation is mainly realized by the method of analog circuit, and its mechanism is complicated. Moreover, due to the influence of discrete components, the modulation frequency is difficult to reach mega-level; if you want to change the laser bias current level, laser modulation current level and modulation duty cycle, you must manually replace the corresponding electronic components, which is difficult to adjust. Poor adaptability, slow modulation speed, poor anti-interference performance, and low automation level.

When performing internal modulation, due to external interference, the input modulation signal will jitter, or even produce violent pulses. Such a signal input into the laser will also cause errors in the excitation optical signal, and the reliability will be reduced. What is more serious is , The sharp pulse signal will greatly shorten the life of the semiconductor laser.

Contents of the invention

The technical problem to be solved by the present invention is: In order to overcome the disadvantages of complex laser modulator mechanism, difficult adjustment of electrical parameters, slow modulation speed, low reliability and poor anti-interference performance in the prior art, the present invention provides a high-speed and high-reliability Modulated laser drive circuit, the high-speed and high-reliability modulated laser drive circuit is completely controlled by electrical signals, and can precisely adjust the laser bias current level, laser modulation current level and modulation duty cycle without replacing any electronic components; high reliability, anti-corrosion Strong interference ability; simple system structure and high modulation speed.

The technical scheme adopted by the present invention to solve its technical problems is: comprising a digital-to-analog conversion control circuit, a comparison amplifier circuit and a driving laser circuit; respectively connected to one input end of the comparison amplifier circuit and the input end of the driving laser circuit; the other input end of the comparison amplifier circuit receives an external modulation signal, and the output end is connected to an input end of the driving laser circuit .

The digital-to-analog conversion control circuit has two output terminals respectively connected to the two input terminals of the driving laser circuit, and outputs a bias current level and a modulation current level to the driving laser circuit respectively.

The comparison and amplification circuit adopts a hysteresis comparator structure.

The comparative amplifier circuit includes a comparative amplifier and a feedback resistor, the non-inverting input terminal of the comparative amplifier is connected to an output terminal of the digital-to-analog conversion control circuit, and is used to receive the duty cycle modulation voltage output by the digital-to-analog conversion control circuit; The inverting input terminal of the comparative amplifier receives an external modulation signal; the output terminal of the comparative amplifier is connected to an input terminal of the driving laser circuit, and is used to output a modulation square wave signal to the driving laser circuit; the feedback resistor Connected between the non-inverting input terminal and the output terminal of the comparative amplifier.

A current-limiting resistor is also connected between the non-inverting input terminal of the comparison amplifier and the output terminal of the digital-to-analog conversion control circuit.

There is also an impedance matching resistor between the inverting input terminal of the comparative amplifier and the ground.

The driving laser circuit includes a laser driving chip and a laser diode; one input end of the laser driving chip is connected to the output end of the comparison amplifier circuit, and the other two input ends are connected to the two output ends of the digital-to-analog conversion control circuit. The terminals are respectively connected; the output terminal of the laser driver chip is connected with the laser diode.

The input terminal of the digital-to-analog conversion control circuit is connected with the parallel port of the computer.

The working principle of the present invention is: change the output of the digital module to the control circuit through the computer, thereby setting the laser bias current level, the laser modulation current level and the modulation duty cycle; the comparison amplifier circuit adjusts the input modulation signal to a predetermined duty cycle The square wave modulation signal; the drive laser circuit receives the square wave modulation signal output by the comparison amplifier circuit to generate laser modulation current that meets the requirements.

Compared with the prior art, the present invention has the following advantages:

(1) The laser bias current level, laser modulation current level and modulation duty cycle are completely electronically controlled, no need to replace electronic components; the adjustment speed is fast and the accuracy is high;

(2) Adopt hysteresis comparator structure to enhance system reliability and anti-interference ability;

(3) Compared with laser external modulation and analog internal modulation, the structure is simple, the integration is high, and the modulation speed is from continuous wave (CW) to 200MHz.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is the schematic diagram of the high-speed and high-reliability laser drive circuit of the present invention;

Fig. 2 is the structural schematic diagram of the hysteresis comparator of the high-speed and high-reliability laser drive circuit of the invention;

Fig. 3 is the voltage transfer characteristic curve of the hysteresis comparator shown in Fig. 2;

Fig. 4 is the laser modulation characteristic curve by the modulation of the high-speed high-reliability laser drive circuit of the present invention;

Fig. 5 is a flow chart of the computer control software of the high-speed and high-reliability laser drive circuit of the present invention.

Detailed ways

The schematic diagram of the high-speed and high-reliability laser drive circuit shown in Figure 1. The high-speed and high-reliability laser drive circuit includes a digital-to-analog conversion control circuit 1 , a comparison amplifier circuit 2 , and a laser drive circuit 3 . The input terminal of the digital-to-analog conversion control circuit 1 is connected with the parallel port of the computer, and the three output terminals of the digital-to-analog conversion control circuit 1 are respectively connected with an input terminal of the comparative amplifier circuit 2 and two input terminals of the driving laser circuit 3; the comparative amplifier circuit The other input end of 2 receives an external modulation signal, and the output end is connected with an input end of the driving laser circuit 3 .

The digital-to-analog conversion control circuit 1 drives the three output channels of the digital-to-analog conversion control circuit 1 to output the duty cycle modulation voltage to the comparison amplifier circuit 2 and output the bias current level to the driving laser circuit 3 according to the control signal 5 obtained from the parallel port of the computer. and modulation current levels.

The comparative amplifier circuit 2 includes a comparative amplifier 6, a current limiting resistor R1, a feedback resistor R2 and a matching resistor R3. The non-inverting input terminal of the comparative amplifier 6 receives the duty ratio modulation voltage from the digital-to-analog conversion control circuit 1 through the current-limiting resistor R1, and the inverting input terminal receives the external modulation signal 8, and the modulation signal 8 realizes the high-frequency signal through the matching resistor R3 match. The output terminal of the comparison amplifier 6 is connected to the non-inverting input terminal through the feedback resistor R2 to form a hysteresis comparator, and outputs a modulated square wave signal 9 with a predetermined duty cycle.

The driving laser circuit 3 includes a laser driving chip IC10 and a laser diode D11. The laser driving chip IC10 outputs a modulation current signal 12 with the input modulation square wave signal 9 according to the set bias current level and modulation current level. The laser diode D11 can modulate an optical signal 13 in the optical transmission medium in response to the modulating current signal 12 .

Principle and method of hysteresis comparator. Figure 2 shows the schematic diagram of the structure of the hysteresis comparator. The inverting input terminal of the comparator is connected to the input signal V _I , the non-inverting input terminal is connected to the duty cycle modulation voltage V _CL through the current limiting resistor R1 , and the output terminal is connected to the non-inverting input terminal through the feedback resistor R2 to form a hysteresis structure.

The voltage transfer characteristics of the hysteresis comparator shown in Figure 3, the calculation shows that:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; LO</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; CL</span>}}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="C200710065048E00071.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="C200710065048E00071.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}$

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; HI</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="C200710065048E00071.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="C200710065048E00071.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; CL</span>}}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="C200710065048E00071.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="C200710065048E00071.png"\; state="\{\{state\}\}">R</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}}$

Where _V0 is the comparator output voltage. When the input signal V _I is higher than V _HI , the comparator output is zero, and when the input signal is lower than V _L0 , the comparator output is V ₀ . Therefore, the hysteresis characteristic of the hysteresis comparator makes the system have certain anti-interference ability.

As shown in the laser modulation characteristic curve in Figure 4, when the driving current is greater than It, the intensity of the laser increases linearly with the increase of the current, and the strength of the emitted laser is directly related to the size of the driving current. If the modulation signal is added to the laser, that is The intensity of the laser output optical signal can be directly changed. In order to obtain linear modulation, so that the operating point is in the straight line part of the characteristic curve, an appropriate bias current must be added while the modulation signal current is applied, so that the output optical signal can not be distorted.

As shown in Fig. 5, the computer control software part of the present invention mainly includes the control of the laser bias current level, the laser modulation current level and the modulation duty cycle. When the control software of the present invention is started, firstly, the system hardware is detected to ensure the normal connection of the system; secondly, the voltage control words are respectively input to the three channels of the digital-to-analog conversion control circuit, and the laser bias current level, laser modulation current level and modulation Duty cycle size; finally, end and save the setting to the storage medium of the digital-to-analog conversion control circuit.

Claims (8)

1. A laser drive circuit, characterized in that, comprises a digital-to-analog conversion control circuit, a comparative amplifier circuit and a driving laser circuit; the input end of the digital-to-analog conversion control circuit is connected with a computer, and the output ends of the digital-to-analog conversion control circuit are respectively It is connected with one input end of the comparison amplifier circuit and the input end of the driving laser circuit; the other input end of the comparison amplifier circuit receives an external modulation signal, and the output end is connected with an input end of the driving laser circuit. 2. The laser drive circuit according to claim 1, wherein the digital-to-analog conversion control circuit has two output terminals connected to two input terminals of the drive laser circuit respectively, and output to the drive laser circuit respectively Bias current level and modulation current level. 3. The laser drive circuit according to claim 1, characterized in that the comparison amplifier circuit adopts a hysteresis comparator structure. 4. The laser drive circuit according to claim 3, wherein the comparison amplifier circuit includes a comparison amplifier and a feedback resistor, and the non-inverting input terminal of the comparison amplifier is connected to an output terminal of the digital-to-analog conversion control circuit , for receiving the duty ratio modulation voltage output by the digital-to-analog conversion control circuit; the inverting input terminal of the comparative amplifier receives an external modulation signal; the output terminal of the comparative amplifier is connected to an input terminal of the driving laser circuit, and is used outputting a modulated square wave signal to the driving laser circuit; the feedback resistor is connected between the non-inverting input terminal and the output terminal of the comparative amplifier. 5 . The laser drive circuit according to claim 4 , wherein a current-limiting resistor is further connected between the non-inverting input terminal of the comparison amplifier and the output terminal of the digital-to-analog conversion control circuit. 6 . The laser drive circuit according to claim 4 , wherein there is an impedance matching resistor between the inverting input terminal of the comparative amplifier and the ground. 7. The laser drive circuit according to claim 1, wherein the drive laser circuit comprises a laser drive chip and a laser diode; an input end of the laser drive chip is connected to the output end of the comparison amplifier circuit, The other two input ends are respectively connected to the two output ends of the digital-to-analog conversion control circuit; the output end of the laser driver chip is connected to the laser diode. 8. The laser drive circuit according to any one of claims 1-6, characterized in that the input end of the digital-to-analog conversion control circuit is connected to a parallel port of a computer.

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