KR100819275B1 - Method of Driving Current for Pumping Green Laser - Google Patents

Abstract

The present invention relates to a current driving method for pumping a green laser, the driving current of the threshold current level before the modulation signal of the green laser by the switching operation according to the operation control signal LD_En input from the outside in the green laser driving circuit To generate fundamental wave laser light in the laser medium of the green laser by 808 nm laser light, and to supply the fundamental wave laser light generated from the laser medium through the nonlinear crystal in advance for a time until resonance of the laser light is formed. By doing so, there is an effect of reducing the light output delay time (Turn-on delay).

Light source, drive circuit, green laser, laser medium, nonlinear crystal, automatic light output control, turn-on delay, pumping

Description

Current driving method for pumping green lasers {Method of Driving Current for Pumping Green Laser}

1 is a block diagram of a light source driving circuit according to an embodiment of the present invention

2 is a green laser driving circuit diagram according to an embodiment of the present invention;

3 is an operation waveform diagram of a green laser driving circuit according to an embodiment of the present invention;

4 is a flowchart illustrating a threshold current driving method for pumping a green laser according to an exemplary embodiment of the present invention.

5 is an exemplary diagram showing pumping in a Nd: YVO 4 + KTP crystal according to an embodiment of the present invention.

* Description of the main drawing codes *

300: light source driving circuit 310: resistor (Rmpd)

320: automatic light output control unit 330: constant current source

340: switching unit 350: modulated signal input unit

360: operation control signal input unit 370: current mirror unit

380: error amplifier 390: current source

400: resistive element (Rmod) 410: pumping area

420: resonance region

The present invention provides a driving current of about the threshold current before the modulation signal of the green laser by the switching operation according to the operation control signal LD_En input from the outside in the green laser driving circuit, and the laser medium of the green laser by the 808nm laser light. The present invention relates to a current driving method for pumping a green laser which generates a fundamental wave laser light in advance and supplies a fundamental wave laser light generated from a laser medium through a nonlinear crystal and passes in advance for a resonance of the laser light. .

Display devices using laser light sources disclosed to date have been proposed to use red, blue, and green laser light sources as light sources for reasons of easy modulation of image signals, improved color reproduction, and improved brightness. In particular, when the semiconductor laser is used as the display light source, the light output power is changed by the influence of the ambient temperature or the deterioration of the light source, which causes a decrease in color quality and brightness of the display device. Therefore, a device for keeping the light output power of the light source constant, that is, an automatic light output control circuit is essentially required.

Such display devices require red (RED, 640 nm), green (GREEN, 532 nm), and blue (BLUE, 450 nm) laser light sources, respectively. Currently, high power lasers emitting wavelengths of 640 nm red and 450 nm blue are commercially available. High power lasers that emit a wavelength of 532 nm, which is green, include a diode pumped solid state (DPSS) laser. Here, a diode pump solid-state (DPSS) laser is a laser that excites and oscillates a solid laser medium, which is commonly used, using a diode laser having a short wavelength line width. It is a laser that can be obtained. Diode pumped solid-state (DPSS) lasers are increasingly used for marking and cutting industries, and are being developed as light sources for displays due to their small size, high efficiency, and high output characteristics.

On the other hand, since the output power of a semiconductor laser varies greatly with temperature, in order to stabilize the light output power, the light output must be kept constant based on the detection current detected by the photodiode. A photodiode is installed at the rear of the diode chip to detect the light output power emitted to the rear of the laser diode chip. That is, a driving circuit having an automatic power output control (APC) function is used to keep the light output constant.

Korean Patent Publication No. 2005-54792 (name: laser diode driving circuit using a photodiode), which is one of the related arts, uses an automatic optical output control circuit (APC) that requires rapid raging of current. One of the characteristics in driving a semiconductor laser is a so-called 'turn-on delay' of light output.

When such turn-on delay occurs, data may appear wrongly on the medium due to a delay in data recording in an optical storage system that records data on an optical storage medium. In addition, in an image display system using a laser, a delay may occur between a frame signal and a laser light output, thereby causing a phenomenon such as distortion of an image or some omission. In addition, in the case of employing a green laser in a light pumping method using a conventional automatic light output control circuit, the diode pump solid-state laser (DPSS), which is a green laser, has a complicated lasing step. Not only the characteristics such as thermal lens formation time, second harmonic wavelength conversion, etc. are unstable, but also cause a turn-on delay of the light output.

Therefore, an object of the present invention is to control the driving current of the green laser corresponding to the modulation signal by adjusting the timing of the switching operation according to the operation control signal LD_En input from the outside, thereby turning-on delay of the light output. To minimize.

Another object of the present invention is to minimize the turn-on delay, while minimizing the power consumed by the light source to be used in a portable laser device.

According to an aspect of the present invention, there is provided a green laser driving circuit comprising: inputting an operation control signal from an external source; supplying a power supply voltage to the green laser driving circuit when the operation control signal is at a low level; Supplying a threshold current from the constant current source of the green laser driving circuit to the green laser according to the operation control signal, absorbing 808 nm laser light from the green laser, and detecting the green laser by the 808 nm laser light. Generating a fundamental wave laser light in a laser medium and supplying a threshold current until the fundamental wave laser light generated from the laser medium passes through a nonlinear crystal to form a resonance of the laser light.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a configuration diagram of a light source driving circuit according to an exemplary embodiment of the present invention.

As shown in FIG. 1, the light source driving circuit 300 according to an exemplary embodiment of the present invention receives a part of light output from a light source and modulates a current signal detected by a light receiving unit and an external image control unit (not shown). (Modulation) Control to maintain a constant light output of the light source in response to the signal input. At this time, the externally input modulation signal is for color reproduction and screen brightness improvement. It is not a simple pulse ON / OFF modulation signal but an analog modulated input signal.

The light source is an element that outputs light toward the front and the rear, and is arranged in units of a plurality of light sources. For example, for improved color reproduction of image signals, red, blue, and green lasers are arranged to emit laser light proportional to the magnitude of the driving current applied to each laser. Done. As the light source, a semiconductor laser that emits light of a constant wavelength or a semiconductor laser having a variable wavelength can be provided.

Among these, the green laser absorbs 808 nm laser light by injecting a current into a GaAs-based semiconductor laser and generates fundamental wave laser light (1064 nm) from a region pumped by the 808 nm laser light. A pumped solid state laser is used that includes a laser medium and a nonlinear crystal that passes through the fundamental wave laser light (1064 nm) excited in such a laser medium and converts it into a second harmonic laser light (532 nm) and outputs it. .

In a preferred form of the invention, the laser medium may be selected from the group consisting of Nd: YAG, Nd: YLF, Nd: YVO 4 and Yb: YAG, wherein the nonlinear crystals are also tertiary to generate a third harmonic laser ball. It can be made of nonlinear crystalline materials with nonlinear coefficients.

The light receiving unit is configured of a monitor photodiode (MPD) which is located behind the laser diode chip and detects a part of light. The green laser module driven by the light source driving circuit 300 of the present invention has a structure in which an anode of a laser diode LD and a cathode of a monitor photodiode MPD are connected to each other, and a monitor photodiode MPD. Is connected to the resistors 310 and Rmpd. The feedback voltage generated in the resistance element 310 (Rmpd) is provided to the automatic light output controller 320 by the detection current supplied from the anode of the monitor photodiode MPD.

The light source driving circuit 300 includes an automatic light output control unit 320 that controls a driving current to maintain a constant light output in the laser diode LD in response to a modulation signal provided from an external image control unit (not shown). Include. Here, the light source driving circuit 300 is different in the type of light output according to the RGB modulation signal input from the outside, the driving current of each light source is the resistance value of the resistor elements (310, Rmpd) provided in each of the modulation signal It works differently depending on the size.

On the other hand, the light source driving circuit 300 is a switching unit 340 composed of a pMOS type field effect transistor (FET) as a switching element to control the supply of the power supply voltage (Vcc) according to the operation control signal LD_En input from the outside. And a constant current source 330 for supplying a constant current to the green laser by the switching operation (ON / OFF) of the switching unit 340. The constant current source 330 is additionally connected to the automatic light output controller 320 in order to shorten the light output turn-on delay of the green laser, and the ON / OFF operation is performed by the control of the switching unit 340. You lose.

2 is a green laser driving circuit diagram according to an embodiment of the present invention.

As shown in FIG. 2, the automatic light output controller 320 of the green laser driving circuit 300 according to an exemplary embodiment of the present invention receives a portion of light output from the green laser and converts it into a current signal. The feedback voltage Vb is generated by the detection current Impd output from the photodiode MPD and is connected to the resistors 310 and Rmpd. In addition, the current mirror unit 370 outputs a modulation current corresponding to the external modulation signal input (GREEN Modulation). The current mirror 370 is a pMOS type in which a resistance element 400 (Rmod) is connected to a modulation signal input unit 350 to which a modulation signal is input, and a gate connected to a resistance device 400 (Rmod) and a drain in common. It is composed of a field effect input transistor (Q3) and an output transistor (Q4), the source of each transistor (Q3, Q4) according to the operation control signal (LD_En) input to the operation control signal input unit 360, the power supply voltage ( It is connected to the switching unit 340 that controls the supply of Vcc is supplied with a power supply voltage (Vcc).

In the green laser driving circuit 300, the supply of the power voltage Vcc is controlled by the switching unit 340 according to the operation control signal LD_En input to the operation control signal input unit 360, and green in the constant current source 330. The driving current I1 is supplied in advance for a predetermined time to the threshold current level of the laser. At this time, when the modulation signal (GREEN, the amplitude voltage of Va) is input to the modulation signal input unit 350, the current mirror unit 370 in the switching unit 340 connected to the source of each transistor (Q3, Q4) The power supply voltage Vcc is supplied by the switching operation On / Off to output the modulation current Imod from the drain of the output transistor Q4 as shown in Equation 1 below.

Imod = (Vm-Va) / Rmod

At this time, the maximum value of the output modulation current (Imod) may increase until the output current (Impd) of the monitor photodiode (MPD), the light generated in this case is not output. Meanwhile, the operation of the current mirror unit 370 will be described in detail as follows. If Va = 0, the input transistor Q3 is turned on so that a current of (Vm-Va) / Rmod flows and the same amount of current flows through the output transistor Q4 into the resistor element 310 (Rmpd). Normally, Imod is set higher than the detection current Impd. When Va = 0, the feedback current is only supplied from Imod and Impd = 0. Therefore, there is no light output in this case. When Va becomes equal to Vcc, the input transistor Q3 is turned off, and since Imod = 0, a detection voltage generated only by Impd is generated in the resistor elements 310 and Rmpd. At this time, the light output becomes the maximum value. When Va is about half of Vcc, the magnitudes of Impd and Imod are similar, and the light output is reduced by half of the maximum value. This principle allows analog optical output for analog modulated input signals.

The detection current Impd of the monitor photodiode MPD, which receives a portion of the light output from the green laser and converts the light into a current signal, is determined by the direct current characteristic of the green laser. That is, the driving current of the laser to obtain the desired light output is determined by the direct current characteristic of the laser diode, and the output current of the monitor photodiode (MPD) corresponding to a part of the light output generated when the driving current flows through the laser ( Impd) is determined.

The current Impd output from the monitor photodiode MPD determined as described above generates a feedback voltage through the resistor elements 310 and Rmpd, and the feedback voltage is output by the error amplifier 380 of the automatic optical output controller 320. It is compared with a preset reference voltage Vref. When the feedback is normally performed and the automatic light output control is operated, the feedback voltage becomes equal to the reference voltage of the error amplifier 380. The resistance of the resistors 310 and Rmpd for the feedback circuit operation is determined as shown in Equation 2, and the light output of the green laser can be adjusted according to the resistance of the resistors 310 and Rmpd.

Rmpd = Vref / Impd

In the present invention, the maximum value is set to the light output by the resistance value of the resistance element 310 (Rmpd), and the light output is adjusted by changing the input modulation voltage within this maximum value.

The modulation current Imod output from the current mirror unit 370 and the detection current Impd output from the monitor photodiode MPD are added to generate a voltage drop in the resistance elements 310 and Rmpd. The feedback voltage can be obtained from this voltage drop, and the driving current I2 supplied from the current source 390 to the green laser is adjusted from the current source 390 so that the intensity of light is kept constant in the green laser according to the feedback voltage. That is, the automatic light output control unit 320 changes the driving current applied to the green laser according to the magnitude of the feedback current provided from the laser, as in the widely used APC (Automatic Power Control) method. Control the laser light output of Green Laser to remain constant.

3 is an operation waveform diagram of a green laser driving circuit according to an exemplary embodiment of the present invention.

As shown in FIG. 3, the green laser driving circuit 300 has an optical output P ′ when the light output of the green laser is performed with respect to the input modulation signal of the green laser among the RGB (RED, GREEN, BLUE) sequential driving signals. The LD waveform repeats Ton and Toff at regular intervals (a).

At this time, the power supply voltage Vcc is supplied from the switching unit 340 according to the operation control signal LD_En input from the outside to the operation control signal input unit 360 (b), and the constant current is controlled according to the control of the switching unit 340. In the circle 330, the driving current I1 is constantly supplied to the threshold current level of the green laser (c). Thereafter, according to the modulation signal GREEN input, the current source 390 supplies the operating current I2 to the green laser for automatic light output control (d). The current flowing through the green laser can be represented by the sum of I1 and I2, as shown in (e) of FIG.

The time difference between the operation control signal LD_En and the modulation signal GREEN may be changed by adjusting the timing of the operation control signal LD_En input from the outside. During this time difference (set time), green current flows as much as the threshold current, and the turn-on delay factors can be eliminated by the stepped pre-supply threshold current so that when the modulation signal is input, the green laser immediately In response, a light output waveform having a reduced turn-on delay can be obtained (f).

4 is a flowchart illustrating a threshold current driving method for pumping a green laser according to an exemplary embodiment of the present invention, and FIG. 5 is an exemplary diagram illustrating pumping in a Nd: YVO 4 + KTP crystal according to an exemplary embodiment of the present invention.

As shown in FIG. 4, when the operation control signal LD_En input to the operation control signal input unit 360 from outside is inputted with a "LOW" level (S400), the switching unit 340 supplies the power supply voltage Vcc. In operation S410, the constant current source 330 starts supplying a threshold current (about 200 mA) of the green laser to the green laser (S420). In addition, the modulation signal of the green laser maintains the "LOW" level until the predetermined set time (about 1 mS), and the light output should be 0.

In this case, as shown in FIG. 5, the green laser receives a threshold current from the constant current source 330 and absorbs 808 nm laser light from the Nd: YVO 4 laser (S430) (a), 808nm laser light. Excitation in the pumping region 410 of the Nd: YVO 4 laser medium coated with a film that does not reflect light to produce fundamental wave laser light (1064 nm) (S440) (b) substantially with respect to the fundamental wave laser light (1064 nm). The thermal lens is formed so as to completely transmit.

Then the fundamental wave laser light (1064) excited from the Nd: YVO4 laser medium in the KTP crystal coated with a film that does not reflect the fundamental wave laser light (1064 nm) and a high reflectivity film for the second harmonic laser light (532 nm). nm) and is optically coupled and pre-supplied for a set time until resonance of the laser occurs by the emission of the excited laser (S450). (c) That is, the resonance of the light is pumped fundamental wave laser light (1064 nm). The resonance region 420 is formed by reflecting at a reflection angle corresponding to the incident angle of.

In addition, after a predetermined set time has passed from the start of supply of the power supply voltage Vcc, when the modulation signal starts, the green laser passes the fundamental wave laser light (1064 nm) excited in the laser medium in response to the external input modulation signal. From the resonant region, it converts to the second harmonic laser light (532 nm) and starts to output.

 On the other hand, the monitor photodiode MPD receives a part of the green laser light output and converts it into a current signal to output the monitor detection current Impd. The detection current Impd is summed with the modulation current Imod output from the current mirror unit 370 and flows through the resistance element 310 (Rmpd) to generate a voltage drop. Vref).

According to the result of comparison, the driving current I2 supplied from the current source 390 to the green laser is controlled, and the green laser is added to the threshold current I1 flowing for a predetermined time (about 1 mS). By driving the light output delay time (Turn-on delay) is reduced, the green laser light is constantly output in response to the external input modulation signal (Turn-on, S460). In addition, when the operation control signal LD_En input to the operation control signal input unit 360 enters the "HIGH" level (S470), the transistor Q5 is turned off (OFF), so that the power supply voltage Vcc is supplied to the driving circuit. The supply of is cut off, so that the driving current ILD is not supplied to the green laser, and therefore the laser light is not output (Turn-off, S480).

As a result, the green laser driving circuit 300 receives the green laser from the constant current source 330 during the operation time of the switching unit 340 according to the operation control signal LD_En input from the outside to the operation control signal input unit 360. By supplying a current to the threshold current level of () and controlling the driving current of the green laser corresponding to the modulation signal, the turn-on delay of the light output is reduced.

Therefore, the operation control signal input LD_En is input to the switching unit 340 to turn on / off the power supply voltage Vcc, thereby supplying a threshold current to the green laser only during the set time, thereby delaying the turn-on delay. The additional power consumption required to reduce the turn-on delay can be minimized.

As described above, a current driving method for pumping a green laser according to an embodiment of the present invention can be made. Meanwhile, the above description of the present invention has been described with reference to specific embodiments, but various modifications can be made without departing from the gist of the present invention. There may be various embodiments. Therefore, the scope of the present invention should not be defined by the described embodiments, but by the claims and equivalents of the claims.

The present invention made as described above can not only reduce the turn-on delay of the green laser by supplying the threshold current of the green laser before the modulation signal of the green laser for a predetermined time, but also by using the laser. In the image display system used, a delay between the frame signal and the laser light output can be prevented to obtain a stable light source.

Claims (10)

In the green laser drive circuit, Inputting an operation control signal from the outside; Supplying a power voltage to the green laser driving circuit when the operation control signal is at a low level; Supplying a threshold current from the constant current source of the green laser driving circuit to the green laser according to the operation control signal; Absorbing 808 nm laser light in the green laser; Generating fundamental wave laser light in the laser medium of the green laser by the 808 nm laser light; And supplying a threshold current until the fundamental wave laser light generated from the laser medium passes through a nonlinear crystal to form a resonance of the laser light. The current driving method of claim 1, wherein the constant current source supplies a driving current to the green laser in accordance with the operation control signal. 3. The method of claim 2, wherein the threshold current is supplied for a predetermined time period when performing the process of passing the fundamental wave laser light generated from the laser medium through a nonlinear crystal to form a resonance of the laser light. , After supplying the threshold current, the green laser further comprises the step of converting the fundamental wave laser light from the non-linear crystal to the second harmonic laser light and outputs the current driving method for pumping the green laser. The current driving method of claim 3, wherein the light output of the green laser is adjustable according to a resistance value of the resistance element of the green laser driving circuit. The current driving method of claim 1, wherein the threshold current and the driving current are not supplied from the constant current source to the green laser for a predetermined time when the operation control signal is at a high level. The current driving method of claim 1, wherein the green laser is a semiconductor laser or a solid-state laser of which wavelength is emitted. 5. The method of claim 4, wherein the solid state laser is a material consisting of a laser medium of any one of Nd: YAG, Nd: YLF, Nd: YVO4, and Yb: YAG. The method of claim 3, wherein the nonlinear crystal is a nonlinear material made of any one of KTP, PPLN, LBO, BBO, and KN. 2. The method of claim 1, wherein the nonlinear crystal is a nonlinear material that converts and outputs a third harmonic laser light. The green laser driving circuit of claim 1, wherein the green laser driving circuit includes an automatic light output control circuit configured to change a driving current applied to the green laser to control the laser light output of the green laser to be constant. Current drive method for

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