JP5754456B2 - Laser light source device - Google Patents

Description

  The present invention relates to a wavelength conversion type laser light source device using a nonlinear optical crystal. More specifically, the present invention relates to a laser light source device having a means for controlling temperature so that the conversion efficiency of the nonlinear optical crystal is maximized in a wavelength conversion type laser light source using the nonlinear optical crystal.

Development of an apparatus using a laser beam as a light source of a projection type projector used for movies, home theaters, and the like is underway. These laser light sources are known to use light emitted directly from a semiconductor laser element and to convert light emitted from the semiconductor laser element into another wavelength using a nonlinear optical crystal. It has been.
Recently, as a blue or green laser light source, a periodically poled lithium niobate (PPLN) or a periodically poled lithium tantalate (PPLT) or the like is applied to the nonlinear optical crystal. The laser light source used has been developed.

As such a technique, for example, one described in Patent Document 1 is known. According to the publication, a light source composed of a semiconductor laser, a wavelength conversion element that enters laser light emitted from the light source and converts it into a second harmonic (when using, for example, PPLN as a nonlinear optical crystal), A laser light source device including an external resonator (for example, volume Bragg grating: VBG) that selects and reflects light of a predetermined wavelength emitted from a wavelength conversion element toward the light source is described.
Further, it is described that a temperature adjustment unit is provided between the sub-base to which the wavelength conversion element is attached. Furthermore, by adjusting the temperature of the wavelength conversion element using the temperature adjustment unit, the pitch of the polarization inversion period of the wavelength conversion element can be adjusted, so that the light conversion efficiency can be improved. It is described.

FIG. 11 is a block diagram showing a schematic configuration of the laser light source device.
The wavelength conversion element (for example, PPLN) 5 mounted on the laser light source unit LH shortens the wavelength of light emitted from the laser light source element (for example, a semiconductor laser, which will be described below as a semiconductor laser) 2 as compared with the incident light. For example, infrared light can be converted into green light.
The lighting circuit 20 includes a power supply circuit U1 and a pulse circuit U2 that supplies pulsed power, and supplies a voltage / current for lighting the semiconductor laser 2.
This wavelength conversion element 5 has a feature that it is quasi-phase-matched by raising the temperature to a predetermined temperature to increase the efficiency of light conversion, and requires highly accurate temperature control. Therefore, a heating means 7 for heating the wavelength conversion element 5 (hereinafter referred to as the heater 7) is provided, and a temperature detection means Th1, for example, a thermistor for detecting the temperature of the heater 7, is provided.

The control unit 21 includes a control unit 21a, a temperature control unit 21b, and a drive circuit U3. The drive circuit U3 that drives the heater 7 is driven by the temperature control unit 21b.
The power feeding circuit U1 is controlled by the control means 21a of the control unit 21 so that the voltage applied to the semiconductor laser 2 and the current to flow become a preset value or a value set from the outside. In addition, the start and stop of the power supply is controlled. The control means 21a and temperature control means 21b of the control unit 21 are constituted by, for example, an arithmetic processing unit (CPU or microprocessor).
The pulse circuit U2 is controlled by the control unit 21. The control unit 21 turns on / off the switching element of the pulse circuit U <b> 2 and generates a pulse output for driving the semiconductor laser 2.
The temperature control unit 21b provided in the control unit 21 controls the amount of power supplied to the heater 7 based on the difference between the temperature detected by the temperature detection unit Th1 and the set temperature that is the target temperature, and the temperature of the wavelength conversion element. Is feedback controlled so that becomes the above set temperature.
The wavelength conversion element 5 (for example, PPLN) has an optimum temperature at which the conversion efficiency of the laser light changes depending on the temperature of the wavelength conversion element, and the light conversion efficiency can be maximized.
For this reason, the temperature control means 21b controls the heater 7 by controlling the heater 7 so that the temperature of the wavelength conversion element 5 detected by the temperature detection means Th1 becomes the temperature at which the light conversion efficiency is maximized. It is common.

JP 2009-54446 A

As described above, in the laser light source device using the wavelength conversion element 5 (for example, PPLN), the conversion efficiency of the laser light changes depending on the temperature of the PPLN. The optimal temperature must be set.
FIG. 12 is a diagram illustrating the relationship between the set temperature of the wavelength conversion element and the amount of heat applied to the wavelength conversion element. The horizontal axis of the figure shows the set temperature when the temperature of the wavelength conversion element is feedback controlled, and the line A is the heating amount of the wavelength conversion element (also referred to as IR radiant heat amount) by the radiant heat from the laser light source, and the line B Indicates the amount of heating by the heater 7 (the amount of power supplied to the heater 7), and the line C indicates the total amount of heat that is the sum of these.
FIG. 4A shows a case where a high-temperature hang-up state is not described, and FIG. 5B shows a case where a high-temperature hang-up state is entered.

As shown in FIG. 12A, when the set temperature of the wavelength conversion element is increased, a phenomenon occurs in which the heater power supply amount becomes maximum at a certain temperature Tc.
In general, when the temperature of the wavelength conversion element 5 is increased, the temperature of the wavelength conversion element should increase if the amount of power supplied to the heater simply increases. However, in practice, as shown in FIG. 12A, the amount of power supplied to the heater 7 becomes a maximum at a certain set temperature.
The set temperature of the wavelength conversion element that maximizes the amount of power supply coincides with the set temperature at which the light output of the laser light source is maximized (that is, the conversion efficiency of the wavelength conversion element is the highest).

This phenomenon can be explained as follows.
In the vicinity of the temperature (Tc) at which the amount of power supplied to the heater 7 is maximized, most of the infrared light output from the semiconductor laser 2 is converted to visible light, but the temperature region in which the rate of conversion of infrared light into visible light is low. Then, most of them are confined as infrared rays and used for so-called radiant heating (heating by IR radiation) for heating the wavelength conversion element 5.
As described above, in the laser light source device shown in FIG. 11, the temperature of the wavelength conversion element 5 is feedback-controlled to control the set target temperature. Therefore, the heater 7 depends on the increase / decrease in the disturbance of the infrared rays. The amount of electric power supplied to is also controlled to increase or decrease. Therefore, in a region where the wavelength conversion element 5 receives a large amount of radiant heat, the temperature is sufficiently set even if the amount of power supplied to the heater 7 is small. Conversely, at the point where the conversion efficiency to visible light is high (near the temperature Tc), since the radiant heat is reduced, the temperature control means 21b controls the power supply amount to the heater 7 to be increased. For this reason, it is considered that the point where the amount of power supply is the highest is the temperature region where the conversion efficiency of the wavelength conversion element is the highest.

By the way, in general, in a projector light source, the amount of light needs to be adjusted depending on the use environment and lighting conditions. For example, the amount of light required differs between when projecting images outdoors on a sunny day and when projecting indoors such as in a movie theater dark. Further, the power supplied to the light source differs greatly between when the projector is lit in the power saving mode and when the projector is lit with normal power. As described above, increase / decrease control of the laser lighting current is required for the laser light source device as the light source.
However, when the laser lighting current is increased in accordance with the laser light quantity increase command, the wavelength conversion element 5 temperature is kept at a temperature higher than the wavelength conversion optimum temperature as described below, and a desired converted light output is obtained. It was found that the amount of light could be significantly reduced.

Hereinafter, the high-temperature hang-up will be described.
In the laser light source device described above, when the laser lighting current is increased according to the laser light quantity increase command, the heating amount of the wavelength conversion element 5 by the laser light also increases. For this reason, the temperature of the wavelength conversion element 5 rises temporarily.
When the heating amount of the wavelength conversion element 5 by the laser light increases, the IR radiation heat amount A and the total heat amount C shown in FIG. 12 increase. For this reason, the temperature control means 21b controls to reduce the amount of power supplied to the heater 7, but when the temperature of the wavelength conversion element 5 does not decrease even if the output to the heater circuit is cut off, FIG. As shown, the temperature of the wavelength conversion element 5 cannot be controlled. As a result, the temperature of the wavelength conversion element 5 rises, and the temperature of the wavelength conversion element 5 enters the region of the high-temperature hang-up state shown in FIG.
That is, in FIG. 12B, when the temperature of the wavelength conversion element is raised, the heating amount of the wavelength conversion element 5 by the fundamental wave light at the temperature of the high temperature hang-up 1 becomes larger than the energy necessary for maintaining the temperature. In this case, the temperature of the wavelength conversion element 5 continues to rise even when the power supply to the heater 7 is stopped, and rises to the temperature of the high temperature hangup 2 and stops. If this high temperature hang-up occurs, the temperature of the wavelength conversion element cannot be lowered even if the power supply to the heater 7 is stopped.

The operation when there is a command to increase the laser light quantity (light control command) will be described with reference to the time chart of FIG. In FIG. 13, (a) is the timing of the dimming trigger (laser current increase command), (b) is the change in laser current, (c) is the amount of power supplied to the heater, and (d) is the temperature of the wavelength conversion element. Show.
As shown in FIG. 13 (a), when there is a command to increase the amount of laser light (dimming command), the feed circuit U1 shown in FIG. 11 immediately increases the laser current as shown in FIG. The current level changes from IL1 to IL2 (increase A). As a result, the temperature of the wavelength conversion element 5 rises as shown in FIG.

  Here, the temperature of the wavelength conversion element 5 does not increase so much because the increase amount of the laser current due to the command to increase the amount of laser light is small, and the temperature of the wavelength conversion element is indicated by a broken line in FIG. If it rises to a high temperature, it will not be in a hot hang-up state. That is, the amount of power supplied from the drive circuit U3 to the heater 7 temporarily decreases as shown in FIG. 5C, but then the temperature at which the wavelength conversion element 5 reaches the maximum conversion efficiency (in FIG. 13). When the power supply amount reaches a maximum temperature (Tc), the heater power supply amount changes at a value larger than 0 level, as indicated by the broken line in FIG. This is the controllable state of FIG.

On the other hand, when the increase amount of the laser current due to the command to increase the amount of laser light is large, the temperature of the wavelength conversion element 5 is greatly increased, and the temperature of the wavelength conversion element increases as shown by the solid line in FIG. The amount of heating by the fundamental light becomes larger than the amount of heat necessary to maintain the temperature of the conversion element. For this reason, the temperature of the wavelength conversion element cannot be controlled by increasing or decreasing the amount of power supplied to the heating means such as a heater.
That is, the heating amount of the wavelength conversion element 5 by the fundamental light at the temperature of the high temperature hang-up 1 becomes larger than the energy necessary for maintaining the temperature, and the temperature of the wavelength conversion element 5 continues to rise even when the power supply to the heater 7 is stopped. Then, the temperature rises to the temperature of the high temperature hangup 2 and stops.
Since the temperature of the wavelength conversion element is controlled by the temperature control means 21b, when the high temperature hang-up state is established, the amount of power supplied to the heater 7 becomes 0 level as shown in FIG. That is, in this state, the temperature of the wavelength conversion element 5 cannot be lowered even if the power supply to the heater is stopped.

As described above, when the laser lighting current is increased in accordance with the laser light quantity increase command, the amount of heating of the wavelength conversion element 5 by the laser light also increases, and the temperature of the wavelength conversion element 5 does not drop to the optimum temperature and control is not possible ( High temperature hang-up).
In this high-temperature hang-up state, the temperature of the wavelength conversion element 5 is held at a temperature higher than the temperature at which the wavelength conversion efficiency is maximized, the desired converted light output cannot be obtained, the light amount is greatly reduced, and the laser light amount increase command The state in which the amount of light is reduced compared to before will be maintained.

  The present invention solves the above-mentioned problems, and the problem of the present invention is that a high-temperature hang-up state occurs, and even when the temperature control of the wavelength conversion element becomes uncontrollable, the controllable state is quickly brought about. It is to provide a laser light source device capable of recovering and recovering a high light output.

As described above, in a laser light source device that performs wavelength conversion using a wavelength conversion element in which the conversion efficiency varies with temperature and an optimum temperature that maximizes the light conversion efficiency exists, the temperature control of the wavelength conversion element is performed in the Peltier mode. A part of the fundamental wave light that is not wavelength-converted and has a structure that does not leak the fundamental wave light out of the package without using a device that can also cool the element, such as a heater, contributes to the heating of the wavelength conversion element. In a laser light source device, a high temperature hang-up state may occur.
This high-temperature hang-up state means that the amount of heating by the fundamental wave light (IR radiation heat) is higher than the amount of heat necessary to maintain the temperature in the laser light source device at a temperature higher than the temperature at which the conversion efficiency of the wavelength conversion element is maximum. The temperature of the wavelength conversion element cannot be controlled by increasing or decreasing the amount of power supplied to the heating means such as a heater, and the temperature can be lowered even if power supply to the heating means such as a heater is stopped. It is in a state where it cannot be done.
In the present invention, in order to suppress the high temperature hang-up state, the laser light source device is provided with high-temperature hang-up suppression means.
The high temperature hang-up suppression means temporarily stops power supply to the heater circuit (or decreases the power supply amount), and increases the laser light amount after a certain period from the laser light amount increase command. As a result, it is possible to suppress an excessive increase in temperature of the wavelength conversion element, and as a result, it is possible to provide a laser light source device that prevents high-temperature hang-up and can stably control the temperature of the wavelength conversion element. That is, in the present invention, the above-described problem is solved as follows.

(1) A semiconductor laser, a wavelength conversion element that converts the wavelength of laser light emitted from the laser, a heater for heating the wavelength conversion element, a power supply circuit for supplying power to the semiconductor laser, and the heater And a temperature control means for detecting the temperature of the wavelength conversion element and controlling the amount of power supplied to the heater to control the temperature of the wavelength conversion element to a desired temperature. In a laser light source device having a power supply circuit for supplying power to a laser and a control means for controlling the heater power supply circuit, the control means is provided with the heater in a temperature region higher than a temperature at which the conversion efficiency of the wavelength conversion element is maximized. provided hot hang suppression means for suppressing the hot hung state can not be controlled results in a temperature of the wavelength conversion element also reduces the power supply amount to .
The high temperature hang-up suppression means stops the power supply to the heater or sets the power supply amount to a predetermined value until the first period T2 elapses from the increase command in response to the power supply amount increase command to the semiconductor laser. After the second period T1 (T1 <T2) has elapsed from the increase command, and the temperature of the heater is lowered to a temperature at which the high-temperature hang-up state does not occur even when the power supply amount to the laser is increased , The amount of power supplied to the semiconductor laser is increased.
(2) In the above (1), the high temperature hang-up suppressing means changes the length of the first period T2 in accordance with the amount of increase in the amount of power supplied to the semiconductor laser in the increase command.
(3) In the above (1) and (2), the high-temperature hang-up suppressing means changes the length of the second period T1 in accordance with the amount of increase in the amount of power supplied to the semiconductor laser in the increase command.
(4) In the above (1), (2) and (3), a periodically poled lithium niobate is used as the wavelength conversion element.

In the present invention, the following effects can be obtained.
(1) Although the fundamental light incident on the wavelength conversion element increases due to the increase in the laser light amount (increase in the lighting current), the first period T2 from the increase command to the increase command for the power supply amount to the semiconductor laser increases. The power supply to the heater is stopped or the power supply amount is reduced to a predetermined value until a lapse of time, and the power supply amount to the semiconductor laser is increased after the second period T1 has elapsed from the increase command. It is possible to suppress the wavelength conversion element from becoming higher than the desired temperature due to an increase in the fundamental wave light due to an increase in the amount of laser light. For this reason, it is possible to prevent an uncontrollable state (high temperature hang-up state) in which the temperature does not decrease even when heating is stopped in a temperature range higher than the temperature at which the conversion efficiency of the wavelength conversion element is maximized.
(2) The length of the first period T2 is changed or the length of the second period T1 is changed in accordance with the amount of increase in the amount of power supplied to the semiconductor laser by the laser light quantity increase command. If
When the laser light amount increase amount is small, the time during which the heater temperature is not controlled can be shortened, or the delay time from the laser light amount increase command to the increase of the laser light amount can be shortened.

It is a figure which shows the structure of the laser light source apparatus of the Example of this invention. It is a block diagram which shows the structure of the control part and lighting circuit in the laser light source apparatus of 1st Example of this invention. It is a figure which shows the example of a structure which actualized the electric power feeding circuit. It is a figure which shows the example of a simplified structure of a pulse circuit. It is a figure which shows the connection relationship of a structure of a drive circuit, a control part, a heater, etc. It is a timing chart which shows an example of the current waveform supplied to a heater from a drive circuit. It is a flowchart which shows an example of the control processing in the temperature control means of a control part. It is a time chart which shows changes, such as a laser current and the amount of electric power supplied to a heater, when there is a laser light quantity increase command (dimming command) when a hang-up suppression means is provided. It is a flowchart which shows an example of the control processing in a hangup suppression means. It is a time chart which shows changes (a heater power supply amount is reduced), such as a laser current and a power supply amount to a heater, when there is a laser light quantity increase command (dimming command). It is a block diagram which shows schematic structure of a laser light source device. It is a figure which shows the relationship between the preset temperature of a wavelength conversion element, and the calorie | heat amount added to a wavelength conversion element. It is a time chart which shows changes, such as a laser current and a power supply amount to a heater, when there is a laser light quantity increase command (dimming command).

FIG. 1 is a diagram showing a configuration of a laser light source apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the laser light source device includes a laser light source unit LH, a lighting circuit 20 for lighting a semiconductor laser, and a control unit 21.
In the laser light source unit LH, the substrate 1 serving as a base plate (heat sink) formed of a material having high thermal conductivity, for example, copper (Cu), prevents leakage of laser light, and the members housed inside are exposed to the outside air. A shut-off container (for example, made of aluminum) 3 that shields and insulates from dust is attached.
A semiconductor laser 2 that emits infrared light as fundamental wave light is provided on the substrate 1 in the shielding container 3. The semiconductor laser 2 is, for example, an external cavity surface emitting laser array that emits 1064 nm.

A fundamental wave light reflecting element 4 (for example, the VBG) that reflects light in a specific narrow band wavelength region of the fundamental wave light with a high reflectance (for example, 99.5%) is disposed at a position facing the semiconductor laser 2. Thus, an external resonator is configured for the semiconductor laser 2. The fundamental wave light reflecting element 4 transmits the converted light.
Further, between the semiconductor laser 2 and the fundamental wave light reflecting element 4, a part of the wavelength of the fundamental wave light (phase matched wavelength light, phase matching temperature is 80 C ° to 100 C °, for example) is converted. Then, a wavelength conversion element (for example, the PPLN) 5 to be wavelength converted light (second harmonic: SHG) is disposed. The wavelength conversion element 5 converts infrared light, which is fundamental light output from the semiconductor laser 2, into visible light or ultraviolet light.
A heat transfer plate 6 is disposed in thermal contact with the wavelength conversion element 5, and a heating means (for example, a heater) 7 that heats the wavelength conversion element 5 is provided on the heat transfer plate 6, and wavelength conversion. Temperature detection means Th1 (for example, a thermistor) for detecting the temperature of the element 5 is provided.
The semiconductor laser 2, the wavelength conversion element 5, and the fundamental wave reflection element 4 constitute an external cavity type vertical surface emitting laser. Here, the semiconductor laser 2, the wavelength conversion element 5, and the fundamental wave reflection element 4 are used. The part to be configured is called a light source unit 12.

A dichroic output mirror 10 is provided on the surface of the shut-off container 3 facing the substrate 1, and wavelength-converted light that is transmitted through the fundamental light reflection element 4 is output from the dichroic output mirror 10.
The dichroic output mirror 10 reflects the fundamental wave light that is transmitted without being reflected by the fundamental wave light reflecting element 4 without being transmitted. The fundamental light reflected by the dichroic output mirror 10 is incident on and absorbed by a beam dump 11 (for example, a black anodized aluminum plate). The beam dump 11 is in thermal contact with the shielding container 3.
Further, a dichroic mirror 8 that transmits the fundamental wave light, reflects the wavelength converted light, and extracts it in the lateral direction is provided between the semiconductor laser 2 and the wavelength conversion element 5, and is reflected by the dichroic mirror 8. The wavelength-converted light is reflected by the reflection mirror 9 in the same direction as the wavelength-converted light transmitted through the fundamental wave light reflecting element 4, and is transmitted through the dichroic output mirror 10 and emitted.
That is, the light source unit 12 of the laser light source device targeted by the present invention is disposed on the wavelength conversion element 5 that converts the wavelength of the fundamental wave light emitted from the semiconductor laser 2 and on the emission side of the wavelength conversion element 5, and the wavelength Of the light emitted from the conversion element 5, the fundamental wave light reflecting element 4 (for example, VBG) constituting an external resonator with respect to the semiconductor laser 2 that reflects the light of a specific narrow band wavelength region of the fundamental wave light with high reflectance. It has.
In addition, although a holding member for holding each member is provided, it is not shown in the drawing.

In FIG. 1, the fundamental wave light emitted from the semiconductor laser 2 enters the wavelength conversion element 5 via the dichroic mirror 8 as indicated by an arrow in the figure.
A part of the light incident on the wavelength conversion element 5 is wavelength-converted, and the wavelength-converted light is transmitted through the fundamental wave light reflection element 4 and emitted through the dichroic output mirror 10. The fundamental wave light that has not been wavelength-converted by the wavelength conversion element 5 is reflected by the fundamental wave light reflection element 4, enters the wavelength conversion element 5, and is wavelength-converted by the wavelength conversion element 5. The wavelength-converted light is reflected by the dichroic mirror 8 and emitted through the reflection mirror 9 and the dichroic output mirror 10.
Further, the fundamental wave light incident on the dichroic mirror 8 without being wavelength-converted by the wavelength conversion element 5 passes through the dichroic mirror 8 and enters the semiconductor laser 2.
On the other hand, the fundamental wave light that has not been reflected by the fundamental wave light reflecting element 4 and transmitted through the element, and the fundamental wave light that has been reflected without passing through the dichroic mirror 8 and reflected by the reflection mirror 9 are indicated by arrows in FIG. As described above, the light is reflected by the dichroic output mirror 10 and is incident on the beam dump 11 and absorbed.

As the wavelength converter 5, lithium niobate having a periodic polarization inversion structure (LiNbO3), lithium niobate doped with magnesium (MgO: LiNbO _3), lithium tantalate niobate (LiTaNbO _3), lithium tantalate ( LiTaO ₃ ) or potassium titanate phosphate (KTiOPO ₄ ) can be used, and in general, periodically poled lithium niobate (PPLN), periodically poled Mg-doped lithium niobate (PPMgLN), periodically A quasi phase matching type wavelength conversion element called polarization inversion lithium tantalate (PPLT) or periodic polarization inversion potassium titanate phosphate (PPKTP) can be used.

As shown in FIG. 1, the light source device of the present embodiment is provided with a control unit 21 and a lighting circuit 20.
The lighting circuit 20 supplies pulsed power to the semiconductor laser 2 to light the semiconductor laser 2. The control unit 21 controls the operation of the laser light source device, such as controlling the lighting circuit 20, and controls the temperature of the wavelength conversion element 5 so that the wavelength conversion element 5 has an optimum wavelength conversion efficiency. Control to be.
That is, the temperature of the wavelength conversion element 5 detected by the temperature detection unit Th1 is input to the control unit 21, and the control unit 21 determines the temperature of the wavelength conversion element when the conversion efficiency of the wavelength conversion element is maximum as the wavelength. The temperature of the wavelength conversion element 5 is feedback-controlled so that the temperature of the wavelength conversion element 5 becomes the optimum set temperature by controlling the amount of heating by the heating means 7 as the optimum setting temperature of the conversion element.

FIG. 2 is a block diagram illustrating a configuration of a control unit and a lighting circuit in the laser light source device according to the embodiment of the present invention.
As shown in the figure, the lighting circuit 20 includes, for example, a power supply circuit U1 represented by a step-down chopper, a step-up chopper, or other type of switching circuit, and a pulse circuit U2 that supplies pulsed power. Then, a suitable voltage / current is output to the semiconductor laser 2 in accordance with the state of the semiconductor laser 2 or the lighting sequence.
Depending on the laser type, a method of applying a rectangular wave pulse voltage of approximately several hundred kHz to the laser is well known. In this embodiment, the pulse circuit U2 is arranged at the output stage of the power feeding circuit U1, generates a pulse at a desired frequency, and outputs the pulse to the semiconductor laser 2.
Depending on the laser type different from the above, the pulse circuit U2 may be omitted and the output voltage from the power supply circuit U1 may be directly applied to the laser light source corresponding to the semiconductor laser 2.

The semiconductor laser 2 shown in this embodiment emits infrared rays, and has a wavelength conversion element 5 (for example, PPLN) that is an element that converts a wavelength for conversion into visible light.
This wavelength conversion element 5 has a feature that it is pseudo-phase matched to raise the efficiency of light conversion by raising the temperature to a predetermined temperature, and requires highly accurate temperature control. Therefore, the laser light source unit LH also includes the wavelength conversion element 5 and heating means 7 (hereinafter, described as the heater 7) for raising the temperature thereof, and the temperature of the heater 7 (that is, the temperature of the wavelength conversion element 5). An element temperature detecting means Th1 for detecting, for example, a thermistor is arranged.

The control unit 21 includes a control unit 21a, a temperature control unit 21b, and a drive circuit U3. The drive circuit U3 that drives the heater 7 is driven by the output of the temperature control unit 21b.
The power supply circuit U1 is controlled by the control unit 21 so that the voltage applied to the semiconductor laser 2 and the current to flow are set to a preset value or a value set from the outside. In addition, the start and stop of the power supply is controlled. The control means 21a and the temperature control means 21b of the control unit 21 are constituted by, for example, an arithmetic processing unit (CPU or microprocessor).
The pulse circuit U2 is controlled by the temperature control means 21b of the control unit 21. The temperature control means 21b determines the optimum pulse frequency and duty cycle ratio for obtaining high light output efficiency, and turns on / off the switching element of the pulse circuit U2 according to the value, and outputs a pulse for driving the semiconductor laser 2. Is generated.

The control means 21a of the control unit 21 includes a high-temperature hangup suppression means 21c, and the high-temperature hangup suppression means 21c heats the wavelength conversion element 5 when there is a command to increase the amount of laser light, as will be described later. The power supply to 7 is temporarily stopped, and after a certain period, the power supply amount to the laser 2 is increased by the power supply circuit U1 to increase the laser light quantity. Thereby, the excessive temperature rise of the wavelength conversion element can be suppressed, and high-temperature hang-up can be suppressed.
The temperature control means 21b controls the amount of power supplied to the heater 7 based on the difference between the temperature detected by the element temperature detection means Th1 and the set temperature at which the conversion efficiency of the wavelength conversion element is maximized. Control is performed so that the temperature of the element 5 becomes the set temperature.
That is, the temperature control unit 21b drives the drive circuit U3 to control the amount of power supplied to the heater 7, and performs feedback control so that the temperature of the wavelength conversion element 5 detected by the element temperature detection unit Th1 becomes the set temperature. To do.
Specifically, the temperature control unit 21b sends a signal indicating the power supply amount for controlling the power supply amount to the heater 7 to the drive circuit U3, and the drive circuit U3 drives the heater 7 so that the wavelength conversion element 5 is driven. The feedback control is performed so that the temperature of the above becomes the above set temperature.
The output form of the drive circuit U3 may be one that outputs a voltage level, or one that controls the amount of power supply using the PWM method.

FIG. 3 is a diagram showing a specific configuration example of the feeding circuit U1 that can be used in the lighting circuit 20 in the laser light source device of the present invention.
The power supply circuit U1 based on a step-down chopper circuit operates by receiving a voltage supplied from a DC power source M1, and adjusts the amount of power supplied to the semiconductor laser 2.
In the power feeding circuit U1, the control unit 21 drives the switching element Q1 such as an FET to turn on / off the current from the DC power source M1, charge the smoothing capacitor C1 through the choke coil L1, and A current is supplied to the semiconductor laser 2. During the period in which the switching element Q1 is in the on state, the current flowing through the switching element Q1 directly charges the smoothing capacitor C1 and supplies current to the semiconductor laser 2 as a load. Energy is stored in the form of magnetic flux in the coil L1, and during the period when the switching element Q1 is in the OFF state, the energy stored in the form of magnetic flux in the choke coil L1 is supplied to the smoothing capacitor C1 via the flywheel diode D1. Charging and current supply to the semiconductor laser 2 are performed.
The stop state of the power feeding circuit U1 described above with reference to FIG. 2 refers to a state where the switching element Q1 is stopped in the off state.

In the step-down chopper type power supply circuit U1, the amount of power supplied to the semiconductor laser 2 can be adjusted according to the period during which the switching element Q1 is on, that is, the duty cycle ratio, with respect to the operation cycle of the switching element Q1. it can. Here, a gate drive signal having a certain duty cycle is generated by the control unit 21, and the gate terminal of the switching element Q1 is controlled via the gate drive circuit G1, thereby turning on / off the current from the DC power source. Off is controlled.
The current and voltage to the semiconductor laser 2 can be detected by the feeding current detection means I1 and the feeding voltage detection means V1. The supply current detection means I1 can be easily realized using a shunt resistor, and the supply voltage detection means V1 can be easily realized using a voltage dividing resistor.

  The feed current detection signal from the feed current detection means I1 and the feed voltage detection signal from the feed voltage detection means V1 are input to the control unit 21, and the control unit 21 outputs the gate drive signal. The switching element Q1 is turned on / off, and feedback control is performed so that the target current is output. This makes it possible to supply appropriate power or current to the laser.

FIG. 4 is a diagram showing a simplified configuration example of the pulse circuit U2 that can be used in the lighting circuit 20 in the laser light source device of the present invention.
The pulse circuit U2 is configured by a circuit using a switching element Q2 such as an FET.
The switching element Q2 is driven according to a signal generated by the control unit 21 via the gate drive circuit G2. The switching element Q2 repeats on / off operations at high speed, and each time the switching element Q2 is turned on, power is supplied to the semiconductor laser 2 from the capacitor group C2 charged by the output of the power feeding circuit U1 via the switching element Q2. Is called.

For example, in a system in which a pulse voltage of a rectangular wave of about several hundred kHz is applied to a laser, a pulse driving system is more suitable for a junction temperature (junction temperature) in a semiconductor element, such as a laser diode, than a simple DC driving. As a result, the light output efficiency can be increased. Generally speaking, when the laser diode is DC driven, the forward voltage is reduced as compared with the pulse drive. Therefore, when the same amount of power is supplied to the laser diode, it is necessary to increase the supply current. This is because the loss due to the increase in current increases and the temperature of the junction increases.
In any case, the control unit 21 can determine the optimum pulse frequency and duty cycle ratio for obtaining higher light output efficiency, and can drive the semiconductor laser 2 in accordance with the values. However, from the viewpoint of cost, the pulse circuit U2 may be deleted on the assumption that the light output efficiency is somewhat deteriorated, and the semiconductor laser 2 or the like may be directly driven by DC.

FIG. 5 is a diagram showing a simplified configuration example showing a connection relationship between the drive circuit U3, the temperature control means 21b of the control unit 21, the wavelength conversion element 5 and the like in the laser light source device of the present invention.
The laser light source unit LH is equipped with the wavelength conversion element 5, and there is a condition that maximizes the optical output, that is, maximizes the efficiency of optical wavelength conversion. The condition is the temperature of the wavelength conversion element 5, and high conversion efficiency can be obtained by giving an appropriate temperature condition. Therefore, a mechanism for adjusting the wavelength conversion element 5 to an optimum temperature by raising the temperature of the wavelength conversion element 5 from the outside is required. Therefore, it is important to provide a heater 7 in the vicinity of the wavelength conversion element 5 and to control the heater 7 so that the temperature of the wavelength conversion element 5 becomes an optimum temperature.

When supplementing about the appropriate temperature conditions of the wavelength conversion element 5 here, the optimum value differs for each individual due to manufacturing factors or the configuration of the wavelength conversion element 5 and manufacturing reasons. The temperature is about 100 ° C., and there is “variation” in the same range.
The arithmetic processing unit (CPU or microprocessor) constituting the control unit 21 needs to perform control so as to satisfy the optimum temperature condition of the wavelength conversion element 5 as described above.
This is realized by controlling the temperature of the heater 7 indirectly in order to keep the temperature of the wavelength conversion element 5 constant at a desired temperature. Therefore, the temperature detecting means Th1 is arranged on the heat transfer plate 6 (see FIG. 1) in the vicinity of the heater 7.

As described above, the control unit 21 includes the temperature control unit 21b, and the temperature control unit 21b acquires temperature information of the wavelength conversion element 5 by the temperature detection unit Th1. Then, the set temperature and the temperature detected by the temperature detecting means Th1 are compared, and the amount of power supplied to the heater 7 is feedback controlled.
As a form of power supply to the heater 7 here, a pulse signal of the PWM signal from the temperature control means 21b of the control unit 21 is applied to the gate terminal of the switching element Q3 via the gate drive circuit G3 of the drive circuit U3. The switching element Q3 is turned on / off.
As a result, a predetermined pulse voltage is supplied to the heater 7 with a predetermined cycle from a DC power source of, for example, DC 24V. In this way, the control unit 21 controls the amount of power supplied to the heater 7 and, as a result, stably controls the wavelength conversion element 5 to have an optimum temperature.

FIG. 6 is a timing chart in which the current waveform supplied to the heater 7 from the drive circuit U3 in the lighting circuit of the laser light source device according to the embodiment of the present invention is simplified.
In order to feedback control the amount of power supplied to the heater 7, the temperature control means 21b of the control unit 21 determines the PWM1 period and the PWM ON width shown in the figure, and generates a PWM signal.
Instead of the PWM signal, a signal representing an analog amount similar to the PWM signal such as a frequency modulation signal may be generated.
The amount of power supplied to the heater 7 is adjusted by increasing or decreasing the ON width, and the temperature of the wavelength conversion element 5 is controlled.
As the feedback control method, a control method generally known as “on / off-PID control” can be used. PID control is a method of controlling a target temperature by combining a proportional element, an integral element, and a derivative element. For example, a value of about several kHz is applied to the PWM output frequency used in this embodiment.

FIG. 7 is a flowchart showing an example of control processing in the temperature control means 21b of the control unit 21. The flowchart of FIG. 7 can be realized by software processing in the microcomputer mounted in the control unit 21 described above, and the temperature control unit 21b of the control unit 21 executes, for example, the processing shown in the following flowchart. The temperature of the wavelength conversion element 5 is controlled to the set temperature.
The temperature control means 21b of the control unit 21 controls the temperature of the wavelength conversion element 5 (the temperature of the heat transfer plate 6 heated by the heater 7 in FIG. 1) in order to control the temperature of the wavelength conversion element 5 to the target temperature. The output operation amount to the heater 7 is periodically executed and controlled by detecting the temperature detection means Th1 and comparing the detected temperature with the set temperature as the target temperature.
This will be described by taking as an example PI control that combines a proportional element and an integral element, which is a typical technique.

In FIG. 7, heater control is started in step (B01). First, in step (B02), the current temperature of the heat transfer plate 6 heated by the heater 7 correlated with the temperature of the wavelength conversion element 5, that is, wavelength conversion. The temperature measurement value (PPLN temperature measurement value) of the element 5 is measured by the temperature detection means Th1, and the temperature measurement value (Tm_PPLN) is obtained.
Next, in step (B03), the target temperature of the wavelength conversion element 5, that is, the temperature setting value (PPLN temperature setting value) of the wavelength conversion element 5 is read to obtain the optimum temperature setting value (Ts_PPLN).
Then, in step (B04), the optimum temperature set value (Ts_PPLN) is compared with the actually measured temperature value (Tm_PPLN) measured by the temperature detecting means Th1, and the difference (en) is obtained. Using this difference (en), PI calculation is performed in step (B05). In this PI calculation, the amount of power supplied to the heater 7, that is, the operation amount to the heater 7 is obtained from Equation (1).
MVn = MVn−1 + Kp × en + Ki × en−1 (1)
Here, MVn is the operation amount of this time, MVn-1 is the operation amount of the previous period, en is the difference value of the temperature calculated this time, en-1 is the temperature difference value of the previous period, and Kp and Ki are constants.

The manipulated variable (MVn) calculated by the PI calculation is updated as the ON width of the PWM signal sent from the control unit 21, but the manipulated variable (MVn) is the maximum in step (B06) and step (B07). When the value (MVn upper limit value) is exceeded, the maximum value is set, and when the value (MVn lower limit value) is less than the minimum value (MVn lower limit value), the upper limit is set with the minimum value as the manipulated variable (MVn) (step (B08)). ), Step (B09)).
In step (B06 to B9), the finally determined operation amount is updated as the ON width (Duty (n)) of the PWM signal sent from the control unit 21, and the heater control in that cycle is finished (step). (B10, B11)).
A series of operations from step (B01) to step (B11) is repeated at a predetermined cycle. By periodically executing this flowchart and performing feedback control, the wavelength conversion element 5 is stably controlled to reach an optimum temperature.
The control algorithm described here uses a PI control method composed of proportional control and an integral element, but uses other feedback control methods including control with a differential element such as PID control. It doesn't matter.

Next, the high temperature hang-up suppressing means 21c according to the present invention will be described.
As described above, the high-temperature hang-up suppressing unit 21c does not immediately increase the laser light amount when there is a command to increase the laser light amount, and supplies power to the heater 7 that heats the wavelength conversion element 5 from the increase command. Until the first period T2 elapses, the stop or the power supply amount is reduced to a predetermined value. Then, after the second period T1 has elapsed from the increase command, the amount of power supplied to the semiconductor laser is increased.

The operation of the high-temperature hang-up inhibiting means 21c will be described with reference to the time chart of FIG. FIG. 8 is an operation time chart when there is a command (a dimming command) for increasing the amount of laser light when the high temperature hang-up suppression means is provided, and FIG. 8 (a) is a dimming trigger (laser current). (B) indicates the change in laser current, (c) indicates the amount of power supplied to the heater, and (d) indicates the temperature of the wavelength conversion element (heater temperature).
When there is a command (dimming command) for increasing the amount of laser light shown in FIG. 11A, the hang-up suppression means 21c, as shown in FIG. A command to turn off the power supply to 7 is issued, and the power supply amount to the heater is set to 0 level. At the same time, the laser current increase command is delayed for the period T1, and the laser current is held at the value of IL1, as shown in FIG.
As a result, the temperature of the heater 7 decreases as shown in FIG. When the period T1 elapses after the heater 7 is turned off and the temperature of the heater 7 decreases to a temperature at which the high-temperature hang-up state does not occur even if the laser current is increased, the laser current is reduced to IL2 as shown in FIG. increase.

  As the laser current increases, the temperature of the heater 7 (wavelength conversion element 5) increases as shown in FIG. Then, after the heater T is turned off, the heater 7 is turned on again after the period T2 has elapsed. Since the temperature of the heater 7 (wavelength conversion element 5) decreases while the heater 7 is turned off, the heater 7 (wavelength conversion) does not enter a high-temperature hang-up state even when the heater 7 is turned on. The temperature of the element 5) is controlled by the temperature control means 21b and maintained at the set temperature described above.

The time periods T1 and T2 may be determined in advance by, for example, obtaining a time during which high-temperature hang-up can be suppressed by experiments or the like, but depending on the current change amount (increase amount) of the laser current. May be changed.
Table 1 shows an example of values of T1 and T2 with respect to the laser current change amount. As shown in the table, when the laser current change amount is small, the values of T1 and T2 are set to be small, and when the laser current change amount is large, the values of T1 and T2 are set accordingly. Enlarge. That is, when the amount of change in the laser current is large, the amount of heating of the wavelength conversion element also increases, and accordingly, the time for turning off the heater is increased and the time for increasing the laser current is delayed accordingly. With this configuration, when there is a dimming command, the amount of laser light can be increased with a short delay time when the increase amount of the laser current is small .

FIG. 9 is a flowchart illustrating an example of a control process in the hang-up suppression unit of the control unit 21. The flowchart in FIG. 9 can be realized by software processing in a microcomputer mounted in the control unit 21.
In FIG. 9, when a dimming command (laser current increase amount A) for increasing the laser current from IL1 to IL2 is given, in step S1, T _n = 0, the laser current ILn = IL1, and the heater are set to OFF. Then, in step S2, while increasing the _{T n} by _{ΔT (T n = T n-} 1 + ΔT), at step S3, to wait until the _{T n} ≧ T1. When T _n ≧ T1, the laser current ILn is set to IL2 in step S4, while T _n is increased by ΔT in step S5 (T _n = T _n−1 + ΔT), and in step S6, T _n ≧ T2 Wait until When T _n ≧ T2, the heater is turned on in step S7 and the process is terminated.

In the example shown in FIG. 8, the case where the heater 7 is turned off when there is a dimming command (laser current increase command) has been described. However, as shown in FIG. 10, without turning off the heater 7, The amount of power supplied to the heater 7 may be reduced.
FIG. 10 is an operation time chart when there is a command to increase the laser light quantity (dimming command), as in FIG. 8, and FIG. 10 (a) shows the timing of the dimming trigger (laser current increase command). (B) shows the change in laser current, (c) shows the amount of power supplied to the heater, and (d) shows the temperature of the wavelength conversion element (heater temperature).
The time chart of FIG. 10 is the same as that of FIG. 8, but the amount of power supplied to the heater shown in (c) is reduced without being zero.
In this case, it is considered that the temperature of the wavelength conversion element (heater temperature) rises compared to the case of FIG. 8, but the temperature rise of the wavelength conversion element (heater) is small and the high-temperature hang-up shown by the dotted line in FIG. If the temperature does not rise to 1, the high-temperature hang-up state can be suppressed as in the case of FIG.

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Semiconductor laser 3 Blocking container 4 Fundamental wave light reflection element (VBG)
5 Wavelength conversion element (PPLN)
6 Heat transfer plate 7 Heating means (heater)
8 Dichroic mirror 9 Reflecting mirror 10 Dichroic output mirror 11 Beam dump 20 Lighting circuit 21 Control unit 21a Control unit 21b Temperature control unit 21c High temperature hangup suppression unit Th1 Temperature detection unit LH Laser light source unit U1 Feed circuit U2 Pulse circuit U3 Drive circuit M1 DC power supply Q1, Q2, Q3 Switching element L1 Choke coil C1 Smoothing capacitor C2 Capacitor group D1 Flywheel diodes G1, G2, G3 Gate drive circuit I1 Feed current detection means V1 Feed voltage detection means

Claims (4)

A semiconductor laser, and a wavelength conversion element that converts the wavelength of laser light emitted from the laser;
A heater for heating the wavelength conversion element, a power supply circuit for supplying power to the semiconductor laser, a heater power supply circuit for supplying power to the heater,
A temperature control means for detecting the temperature of the wavelength conversion element and controlling the amount of power supplied to the heater to control the temperature of the wavelength conversion element to a desired temperature; a power supply circuit for supplying power to the semiconductor laser; and A laser light source device having a controller for controlling the heater power supply circuit,
The controller may, from hot hung state can not be controlled the temperature of the conversion efficiency wavelength conversion element also reduces the amount of power supplied to the heater in the high temperature region above the temperature of maximum of the wavelength conversion device arising comprising a high temperature hang inhibiting means for deter,
The high temperature hang-up suppression means is
In response to the command to increase the power supply amount to the semiconductor laser, the power supply to the heater is stopped or the power supply amount is reduced to a predetermined value until the first period T2 has elapsed from the increase command. After the second period T1 (T1 <T2) has elapsed and the power supply amount to the laser is increased, the temperature of the heater is lowered to a temperature at which the high temperature hang-up state does not occur. A laser light source device characterized by being increased. 2. The laser light source according to claim 1, wherein the high-temperature hang-up suppressing unit changes the length of the first period T <b> 2 in accordance with an increase in the amount of power supplied to the semiconductor laser in the increase command. apparatus.   3. The high-temperature hang-up suppressing means changes the length of the second period T1 in accordance with an increase in the amount of power supplied to the semiconductor laser in the increase command. The laser light source device described.   4. The laser light source device according to claim 1, wherein the wavelength conversion element is a periodically poled lithium niobate.

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