JP3304879B2 - SHG laser stabilization control device, SHG laser stabilization control method, and optical disk recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to SHG (Second H
The present invention relates to an SHG laser stabilization control device for stabilizing the intensity of emitted light of a laser.

[0002]

2. Description of the Related Art As is well known, a short-wavelength coherent light source is required to increase the recording capacity of an optical disk. In other words, as the areal recording density on the disk increases, the size of the focused spot on the disk must be reduced. From the simple principle that the focused spot size is proportional to the wavelength, it is essential to shorten the wavelength of the light source. Therefore, the emergence of a small and practical short-wavelength light source is expected.

As a technique for shortening the wavelength, a near-infrared semiconductor laser and a quasi phase matching (hereinafter referred to as QPM) type domain-inverted waveguide (Document: Yamamoto et al., Optics)
Letters Vol. 16, No. 15, 1156 (1991)), there is second harmonic generation (hereinafter, referred to as SHG) using a device.

FIG. 20 shows a schematic configuration diagram of a blue light source using a domain-inverted waveguide device. In FIG. 20, 1
Reference numeral 019 denotes a 0.85 μm band 100 mW-class AlGaAs-based distributed black reflection (hereinafter referred to as DBR) laser, 1020 denotes a collimating lens with NA = 0.5,
1021 is a half-wavelength (λ / 2) plate, 1022 is a focusing lens with NA = 0.5, and 1023 is a polarization inversion type waveguide device of a wavelength conversion element.

[0005] The DBR semiconductor laser 19 has a DBR section for fixing the oscillation wavelength, and an internal heater for varying the oscillation wavelength is formed inside the DBR.

The domain-inverted waveguide device 1023 is made of Li
An optical waveguide 1025 formed on a TaO3 substrate 1024;
It is composed of a periodically poled region 1026.

The laser beam collimated by the collimator lens 1020 is rotated in the direction of deflection by the λ / 2 plate 1021 and then focused by the focusing lens 1022 on the end face of the optical waveguide 1025 of the domain-inverted waveguide device 1023. You. Further, the laser light propagates through the optical waveguide 1025 including the domain-inverted region 1026, and the component of the laser light is converted into a harmonic. The harmonic and the unconverted fundamental wave are output from the output end face of the optical waveguide 1025. Is emitted.

[0008] In order to increase the efficiency of wavelength conversion, the polarization inversion waveguide device 1023 has a small allowable phase matching wavelength of about 0.1 nm. Therefore, the injection current into the DBR portion of the DBR semiconductor laser 1019 is controlled to set and fix the oscillation wavelength within the allowable range of the phase matching wavelength of the domain-inverted waveguide device 1023. Thus, about 3 mW of blue light having a wavelength of 425 nm is obtained with respect to the incident light intensity of 70 mW into the optical waveguide 1025.

A DBR semiconductor laser is composed of an active region for providing a gain and a DBR region for controlling an oscillation wavelength. A diffraction grating is formed in the active region so that the DBR region is transparent to a laser beam having a wavelength of 850 nm. In the case of this structure, the oscillation wavelength is controlled to the wavelength of light reflected by the DBR region. Also, the oscillation wavelength can be varied by changing the refractive index of the DBR region. As a method of changing the refractive index of the DBR region, there is a method of changing the wavelength variable current injected into the DBR region, a method of changing the temperature by an electronic cooling element (such as a Peltier element), and the like.

FIG. 3 shows the relationship between the tunable current injected into the DBR region and the oscillation wavelength of the DBR semiconductor laser. As shown in FIG. 3, when the oscillation wavelength is changed by changing the wavelength variable current, the oscillation wavelength shifts toward the longer wavelength side as the wavelength variable current increases while repeating mode hops. In addition, when raising and lowering the wavelength variable current, even if the current amount is the same,
The oscillation wavelength is different. That is, it shows a hysteresis characteristic.
Therefore, when the oscillation wavelength is changed by the wavelength variable current, the wavelength variable current having a desired wavelength is set to a predetermined small wavelength variable current or a predetermined large wavelength variable current value. It is necessary to take measures against hysteresis such as gradually increasing or decreasing the wavelength variable current.

[0011]

A conventional SHG laser using such a DBR semiconductor laser as a fundamental light source has the following problems.

When the oscillation wavelength is changed by the variable wavelength current, it is necessary to obtain a variable wavelength current supplied to the DBR semiconductor laser so that the second harmonic power of the emitted light of the SHG laser is close to the maximum. .

However, as described above, the oscillation wavelength of the DBR semiconductor laser shifts its wavelength while repeating mode hopping with respect to the variable wavelength current, so that the second harmonic power of the output light of the SHG laser becomes maximum. When the tunable current is fixed as described above, if the fixed tunable current is in the vicinity of a current amount that can cause a mode hop,
The second harmonic power of the SHG output became unstable.

After the wavelength variable current is set to a stable point, the temperature of the SHG laser is changed by a Peltier element or the like to search for a temperature at which the second harmonic power of the emitted light of the SHG laser becomes maximum. I do. To search for this temperature, an inflection point (= maximum value) of the second harmonic power is searched for while changing the temperature in a predetermined step, and the temperature corresponding to this inflection point is determined.

[0015] However, with respect to temperature change, SHG
There may be a plurality of maxima in the second harmonic power of the emitted light of the laser. This occurs due to variations in the characteristics of the domain-inverted waveguide device due to the uneven width of the waveguide. If there are multiple maxima,
It is difficult to accurately recognize the maximum second harmonic power, and the temperature of the SHG laser corresponding to the maximum second harmonic power cannot be determined.

Further, as a method of changing the temperature of the SHG laser, a method of changing the temperature of the SHG laser so that
A method of setting the temperature of the SHG laser to the target temperature while performing the temperature servo may be considered.

However, since there is a temperature offset value due to a control error or a circuit offset between the temperature target value and the actual detected temperature, even if the temperature of the SHG laser is adjusted to the temperature target value, the actual temperature of the SHG laser does not change. Temperature did not always coincide with the target temperature, or it took time to settle around the target temperature.

Further, when controlling the wavelength variable current so that the second harmonic power of the output light of the SHG laser is stabilized near the maximum, it is necessary to keep the output characteristics of the semiconductor laser constant without changing it. .

However, when the current to be injected into the active region of the semiconductor laser is controlled by constant voltage driving, SHG
Despite performing temperature control to keep the temperature of the laser constant, the wavelength variable current is changed at a high speed so that the temperature of the DBR region of the semiconductor laser deviates from the temperature control;
And the influence of temperature change in the DBR region is transmitted to the active region due to the proximity of the DBR region and the active region,
The output characteristics of the semiconductor laser fluctuated.

Further, by changing the temperature of the SHG laser,
Even when searching for a temperature at which the second harmonic power of the emitted light of the SHG laser is maximized, as described above, the current injected into the active region is controlled by the constant voltage drive. As a result, a temperature change occurred in the DBR region, and the output characteristics of the semiconductor laser fluctuated.

Therefore, a first object of the present invention is to automatically set a wavelength variable current within a range where the oscillation wavelength of a DBR semiconductor laser cannot cause a mode hop, thereby stabilizing the second harmonic power of the SHG output. An object of the present invention is to provide an SHG laser stabilization control device that can be made stable.

A second object of the present invention is to accurately recognize the maximum second harmonic power even when a plurality of local maxima exist in the second harmonic power of the output light of the SHG laser, and to determine the maximum second harmonic power. An object of the present invention is to provide an SHG laser stabilization control device capable of determining the temperature of the SHG laser corresponding to the second harmonic power.

A third object of the present invention is to provide an SHG laser stabilization control device capable of accurately and promptly controlling the temperature of an SHG laser.

A fourth object of the present invention is to provide an SHG capable of maintaining a constant output characteristic of a semiconductor laser while controlling a current injected into an active region of the semiconductor laser by constant voltage driving.
An object of the present invention is to provide a laser stabilization control device.

A fifth object of the present invention is to provide an optical disk recording / reproducing apparatus to which the above-mentioned SHG laser stabilization control apparatus is applied.

[0026]

In order to solve the above-mentioned problems, a stabilization control device for an SHG laser according to the present invention comprises a semiconductor laser whose wavelength changes stepwise in response to a change in a wavelength variable current; An SHG laser including a wavelength conversion element for converting the wavelength of the emitted light of the semiconductor laser into a short wavelength,
Light detecting means for detecting a stepwise change in the wavelength of the emitted light of the SHG laser; current variable means for changing a wavelength variable current supplied to the semiconductor laser in order to change the wavelength of the semiconductor laser; The wavelength variable current is changed by the current variable means, a gap current value of the wavelength variable current when the stepwise change in the wavelength is detected by the light detection means is determined, and a predetermined current value is added to the gap current value and Wavelength variable current control means for performing one of the subtractions to set the wavelength variable current value.

In one embodiment, the light detecting means detects the intensity of the emitted light of the SHG laser.

In one embodiment, the tunable current control means controls the current variability means to perform either a gradual increase or a gradual decrease of the tunable current, so that the output of the light detection means changes stepwise. The gap current value of the wavelength variable current at which the maximum is obtained, and one of addition and subtraction of a predetermined current value with respect to this gap current value is performed,
Set the wavelength variable current value.

In one embodiment, the variable wavelength current control means controls the current variable means to increase or decrease the variable wavelength current so that the detected SHG laser output is stepwise. The first gap current value of the wavelength variable current that has changed and the next second gap current value adjacent to the first gap current value are obtained, and the first and second gap current values are determined.
A predetermined current value to be added to or subtracted from the gap current value is determined based on the difference current between the gap current values.

In one embodiment, the tunable current source means comprises:
By controlling the current variable means, the wavelength variable current is gradually increased or decreased, and the detected S
A first gap current value of the wavelength-variable current in which the intensity of the emitted light of the HG laser changes stepwise and a next second gap current value adjacent to the first gap current value are obtained, and the first and second gap current values are calculated. 20 to 80% of the difference current is determined as a predetermined current value to be added or subtracted from the gap current value.

In one embodiment, the wavelength variable current control means changes the wavelength variable current by controlling the current variable means to obtain a wavelength variable current ILDpmax at which the output of the light detection means is maximized. , By gradually increasing the wavelength-variable current, the gap current value ILD corresponding to the wavelength-variable current at which the stepwise change in the output of the light detection means is maximized.
When the gap current value ILDspmax is equal to or smaller than the maximum wavelength variable current ILDpmax, the gap current value ILDsp is calculated.
A predetermined current value is added to max. If the gap current value ILDspmax exceeds the maximum wavelength variable current ILDpmax, a predetermined current value is subtracted from the gap current value ILDspmax to set a wavelength variable current value.

In one embodiment, the wavelength variable current control means changes the wavelength variable current by controlling the current variable means to obtain a wavelength variable current ILDpmax at which the output of the light detection means is maximized. , The wavelength variable current is gradually reduced, and the gap current value ILD corresponding to the wavelength variable current at which the stepwise change in the output of the light detection means is maximized.
After calculating spmax, if the gap current value ILDspmax is equal to or less than the maximum wavelength variable current ILDpmax, the gap current value ILDspm
The predetermined current value is subtracted from ax to obtain the gap current value ILDspmax.
Exceeds the maximum wavelength variable current ILDpmax, a predetermined current value is added to the gap current value ILDspmax to set the wavelength variable current value.

In one embodiment, the wavelength variable current control means controls the current variable means to increase or decrease the wavelength variable current in a stepwise manner, thereby changing the output of the light detection means in a stepwise manner. Is determined, the gap current value ILDspmax of the wavelength variable current is obtained, and either the wavelength variable current is gradually increased or gradually decreased, and the gap current value of the wavelength variable current when the output of the photodetector changes stepwise is obtained. Is calculated, and a difference current between the obtained gap current values is obtained, and one of addition and subtraction of a predetermined current value smaller than the difference current to the gap current value ILDspmax is performed to set a wavelength variable current value.

In one embodiment, the wavelength variable current control means controls the current variable means to increase or decrease the wavelength variable current in a stepwise manner to change the output of the light detection means. Is determined, the gap current value ILDspmax of the wavelength variable current is obtained, and either the wavelength variable current is gradually increased or gradually decreased, and the gap current value of the wavelength variable current when the output of the photodetector changes stepwise is obtained. Is calculated, and a difference current between the calculated gap current values is calculated, and either one of addition and subtraction of a predetermined current value that is 20% to 80% of the difference current with respect to the gap current value ILDspmax is performed, and the wavelength-variable current is calculated. Set the value.

In one embodiment, the SHG laser has a configuration in which the semiconductor laser and the wavelength conversion element are integrated on the same substrate.

In one embodiment, a temperature varying means for changing the temperature of the SHG laser, a temperature detector for detecting the temperature of the SHG laser, and a temperature of the SHG laser determined based on an output of the temperature detector. Temperature control means for controlling the temperature variable means so as to be at a temperature.

In one embodiment, the wavelength variable current for changing the wavelength of the semiconductor laser is controlled while the power variable current for changing the intensity of the emitted light of the semiconductor laser is kept constant.

In one embodiment, a filter is provided for cutting the infrared light of the SHG laser emission light, and the emission light of the SHG laser is detected via the infrared light cut filter.

According to the present invention, there is provided an SHG laser stabilization control device comprising: a semiconductor laser whose wavelength changes stepwise in response to a change in a wavelength variable current; and a wavelength converter for converting the wavelength of light emitted from the semiconductor laser to a shorter wavelength. An SHG laser including an element, light detection means for detecting the emission light intensity of the SHG laser, and current variable means for changing a wavelength variable current supplied to the semiconductor laser to change the wavelength of the semiconductor laser; By controlling the current variable means, the wavelength variable current is changed to obtain the maximum output of the light detection means, the wavelength variable current is gradually increased, and a first threshold smaller than the maximum output by a predetermined value is obtained. The output Pth1 of the photodetector when the output exceeds Pth1 is obtained, and the wavelength variable current is gradually increased so that the output of the photodetector exceeds a second threshold smaller than Pth1 by a predetermined value. It asked the wavelength variable current at the time,
Wavelength variable current control means for setting a wavelength variable current value by adding a predetermined current value to the obtained wavelength variable current.

In one embodiment, the first threshold value is a stepwise change in the output of the light detection means closest to the maximum output on the side less than the wavelength variable current corresponding to the maximum output of the light detection means. Is set to be equal to or less than the maximum value of the output range of the photodetector, which continuously changes with the change of the wavelength variable current, from the wavelength variable current at which the maximum output is generated to the wavelength variable current corresponding to the maximum output. .

In one embodiment, the second threshold value is smaller than the wavelength variable current corresponding to the maximum output of the light detection means, and the step change of the output of the light detection means closest to the maximum output is performed. At this point, it is set between a larger value and a smaller value of the light detection means output.

A stabilization control device for an SHG laser according to the present invention is a semiconductor laser in which the wavelength changes stepwise with respect to a change in the wavelength variable current, and a wavelength converter for converting the wavelength of light emitted from the semiconductor laser to a shorter wavelength. An SHG laser including an element, light detection means for detecting the emission light intensity of the SHG laser, and current variable means for changing a wavelength variable current supplied to the semiconductor laser to change the wavelength of the semiconductor laser; By controlling the current variable means, the wavelength variable current is changed to determine the maximum output of the light detection means, and the wavelength variable current is gradually reduced, and a first threshold smaller than the maximum output by a predetermined value is obtained. The output Pth1 of the photodetector when the output exceeds the threshold value is obtained, and the wavelength variable current is gradually reduced so that the output of the photodetector exceeds a second threshold value smaller than Pth1 by a predetermined value. It asked the wavelength variable current at the time,
Wavelength variable current control means for setting a wavelength variable current value by subtracting a predetermined current value from the obtained wavelength variable current.

In one embodiment, the first threshold is:
On the side exceeding the wavelength variable current corresponding to the maximum output of the light detection means, the wavelength corresponding to the maximum output is obtained from the wavelength variable current in which the step change of the light detection means output closest to the maximum output has occurred. It is set to be equal to or less than the maximum value of the output range of the photodetector which continuously changes with the change of the wavelength variable current until the variable current is reached.

In one embodiment, the second threshold value is a step-like value of the light detection means output closest to the maximum output on the side exceeding the wavelength variable current corresponding to the maximum output of the light detection means. At the changing point, the output is set between the larger value and the smaller value of the output of the light detecting means.

A stabilization control device for an SHG laser according to the present invention is a semiconductor laser in which the wavelength changes stepwise in response to a change in the wavelength variable current, and a wavelength converter for converting the wavelength of the light emitted from the semiconductor laser to a shorter wavelength. An SHG laser including an element, light detection means for detecting the emission light intensity of the SHG laser, and current variable means for changing a wavelength variable current supplied to the semiconductor laser to change the wavelength of the semiconductor laser; By changing the wavelength variable current by the current variable means, a gap current value of the wavelength variable current in which the output of the light detection means changes stepwise is determined. A wavelength-variable current control means for setting a wavelength-variable current value by performing either of them, and a temperature-variable means for changing the temperature of the SHG laser. A temperature detector for detecting the temperature of the SHG laser; and controlling the temperature variable means based on an output of the temperature detector so that the temperature of the SHG laser becomes a predetermined temperature. A temperature control means for controlling the temperature variable means so that the output of the light detection means becomes a predetermined value after the wavelength variable current is set to a predetermined current value by the variable current control means.

In one embodiment, the temperature control means controls the temperature variable means based on the output of the temperature detector so that the temperature of the SHG laser becomes a predetermined temperature. After the wavelength variable current is set to a predetermined current value by the current control means, the temperature of the SHG laser is changed within a predetermined range by the temperature variable means, and a temperature at which the output of the light detection means becomes a predetermined value is obtained.
Next, the temperature is changed again by a predetermined change width around the obtained temperature center, and the output of the light detection means is controlled to be a predetermined value.

[0047] In one embodiment, the temperature control means controls the temperature variable means based on the output of the temperature detector so that the temperature of the SHG laser becomes a predetermined temperature. After the wavelength variable current is set to a predetermined current value by the current control means, the temperature of the SHG laser is changed to a temperature lower than a target lower limit temperature by the temperature variable means, so that the temperature of the SHG laser is reduced to the predetermined value. After reaching the lower limit temperature, the temperature of the SHG laser is changed toward a temperature higher than the target upper limit temperature, and when the temperature of the SHG laser is changing from the lower limit temperature to the upper limit temperature, The temperature at which the output of the light detection means reaches a predetermined value is obtained, and the temperature of the SHG laser is changed again by a predetermined change width around the obtained temperature, Serial light detection means output is controlled to be a predetermined value.

The SHG laser stabilization control device of the present invention
A semiconductor laser in which the wavelength changes stepwise in response to a wavelength variable current and the emission light intensity changes in response to a power variable current, and a wavelength conversion element that converts the wavelength of the emission light of the semiconductor laser to a shorter wavelength An SHG laser including: a first light detecting means for detecting a harmonic light beam of the light emitted from the SHG laser; a second light detecting means for detecting a fundamental light beam of the light emitted from the SHG laser; Current variable means for changing a wavelength variable current supplied to the semiconductor laser to change a wavelength; and a wavelength variable current changed by the current variable means, whereby the output of the first light detection means changes stepwise. The gap current value of the wavelength variable current is obtained, and one of addition and subtraction of a predetermined current value from the gap current value is performed, and the wavelength variable current value is calculated. The variable wavelength current control means, and the control by the wavelength variable current control, the power variable current is controlled so that the output of the second light detection means is constant, and after the control by the wavelength variable current control, Power variable current control means for controlling the power variable current so that the output of the first light detection means is constant.

The SHG laser stabilization control device of the present invention
A semiconductor laser in which the wavelength changes stepwise in response to a wavelength variable current and the emission light intensity changes in response to a power variable current, and a wavelength conversion element that converts the wavelength of the emission light of the semiconductor laser to a shorter wavelength An SHG laser including: a first light detecting means for detecting a harmonic light beam of the light emitted from the SHG laser; a second light detecting means for detecting a fundamental light beam of the light emitted from the SHG laser; Current variable means for changing a wavelength variable current supplied to the semiconductor laser to change a wavelength; and a wavelength variable current changed by the current variable means, whereby the output of the first light detection means changes stepwise. The gap current value of the wavelength variable current is obtained, and one of addition and subtraction of a predetermined current value from the gap current value is performed, and the wavelength variable current value is calculated. A wavelength tunable current control means for a constant, the temperature varying means for varying a temperature of the SHG laser, a temperature detector for detecting the temperature of the SHG laser,
Controlling the temperature variable means so that the temperature of the SHG laser becomes a predetermined temperature based on the output of the temperature detector, and in this state, after the wavelength variable current is set to a predetermined current value by the wavelength variable current control means, A temperature control unit for controlling the temperature variable unit so that the output of the first light detection unit becomes a predetermined value; and a second unit for controlling by the wavelength variable current control and changing the temperature of the SHG laser. The power variable current is controlled so that the output of the light detection means is constant, and when the control by the wavelength variable current control and the temperature change of the SHG laser are not performed,
Power variable current control means for controlling the power variable current so that the output of the first light detection means is constant.

The optical disk recording / reproducing apparatus of the present invention comprises the above-described SHG laser stabilization control device, and optical means for condensing the emitted light of the SHG laser on the optical disk in the SHG laser stabilization control device.

[0051]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) In the first embodiment, the wavelength variable current is automatically set within a range where the oscillation wavelength of the DBR semiconductor laser does not cause mode hop, and the second harmonic power of the SHG output is stabilized. Is being converted.

FIG. 1 is a block diagram showing a schematic configuration of an SHG laser stabilization control device according to a first embodiment of the present invention.

In FIG. 1, the semiconductor laser 1 includes an active region 1-1 for providing a gain and a DBR region 1-2 for controlling an oscillation wavelength. The SHG laser 3 is an SHG laser comprising the semiconductor laser 1 and a nonlinear optical element.
(Second Harmonic Generation) The device 2 and the device 2 are integrated on the same base material 4.

The SHG laser 3 has a collimating lens, a λ / 2 plate, and a focusing lens between the semiconductor laser 1 and the SHG device 2 as in the SHG laser of FIG. 20. In FIG. Omitted. The light beam from the semiconductor laser 1 is (not shown)
After being collimated by a collimating lens, λ (not shown)
The deflection direction is rotated by a half plate, and the light is focused on the end face of the optical waveguide of the SHG device 2 by a focusing lens (not shown).

The control of the wavelength variable current in the present invention is preferably performed in a state where the temperature of the SHG laser 3 is stabilized at a predetermined value by performing the temperature control described later. In this state, the constant current control means 8 injects a constant amount of current into the active region 1-1 of the semiconductor laser 1. Further, the wavelength variable current control means 12 controls the wavelength variable current injected into the DBR region 1-2 of the semiconductor laser 1 to adjust the oscillation wavelength of the semiconductor laser 1 to the phase of the SHG device 2 as described later in detail. Set and fix within the allowable range of matching wavelength. The SHG device 2 emits a laser beam including a fundamental wave (850 nm) and a second harmonic (425 nm).

The laser light emitted from the SHG device 2 preferably passes through an infrared light cut filter 9. As a result, the fundamental wave is cut, and only the second harmonic enters the photodetector 10 as laser light. SHG
In order to focus the output of device 2 on photodetector 10, a condensing lens (not shown) is placed immediately after SHG device 2 so that a light spot is formed on photodetector 10. What should I do?

The photodetector 10 detects the intensity of the second harmonic from the SHG laser 3. The detection output of the photodetector 10 is input to the wavelength variable current control means 12. The wavelength variable current control means 12 outputs the output of the photodetector 10,
While measuring the output of the G laser 3, the current variable means 11 is adjusted to control the wavelength variable current injected into the DBR region 1-2.

Below the substrate 4 on which the SHG laser 3 is integrated, a temperature variable means (for example, a Peltier element) 5 capable of electronically varying the temperature is provided. SHG laser 3
Is provided with a temperature detector 6 for detecting the temperature. The temperature control means 7 adjusts the current supplied to the temperature variable means 5 so that the temperature detected by the temperature detector 6 becomes the target temperature (for example, 25 ° C.), and the temperature of the SHG laser 3 becomes the target temperature. Control so that

Next, the control of the wavelength variable current will be described in more detail with reference to FIGS. 1, 2, 3 and 4.

FIG. 2 is a graph showing the characteristics of the SHG device 2 and showing the relationship between the second harmonic wavelength and the output power. FIG. 3 is a graph showing the relationship between the wavelength variable current injected into the DBR region of the semiconductor laser 1 and the output wavelength of the semiconductor laser 1. FIG. 4 is a graph showing the relationship between the tunable current and the second harmonic power output from the SHG laser 3. When the phase matching condition between the semiconductor laser 1 and the SHG device 2 is not constant due to the variation in the characteristics of the SHG device 2 or the like, FIGS. b), the characteristics as shown in FIGS. 4 (c) and 4 (d) are obtained.

As shown in FIG. 2, the half value width of the second harmonic of the SHG device 2 is 0.13 nm. FIG.
As shown in (1), the output of the semiconductor laser 1 shifts to the longer wavelength side as the wavelength tunable current increases while repeating mode hopping at every wavelength tunable current of 5 mA. And
The output wavelength of the semiconductor laser 1 is
It changes by about 0.1 nm. For this reason, as shown in FIG. 4, in the wavelength variable current range of 15 to 35 mA, the second harmonic power output from the SHG laser 3 largely changes at a mode hop boundary (hereinafter, referred to as a mode boundary). The waveform becomes such that it continuously increases or decreases between the boundary and the adjacent mode boundary (hereinafter referred to as "between modes"). Furthermore,
The slope of the increase or decrease of the output power of the SHG laser 3 between modes differs depending on the phase matching state.

Now, if the wavelength current is controlled so that the second harmonic power from the SHG laser 3 is maximized, the tunable current will be as shown in FIGS. 4 (a), (b), (c),
In any of the cases (d), the mode boundary is set. Alternatively, the tunable current may be maximum between modes not shown. The probability that the wavelength variable current is set at the mode boundary is very high, and in this case, the second harmonic power from the SHG laser 3 becomes extremely unstable.

Here, focusing on the variation ΔP of the second harmonic power P from the SHG laser 3 at the mode boundary, the gap current value ILDspmax of the wavelength-variable current at which the variation ΔP is the maximum is represented by the second harmonic power The gap current value at the mode boundary closest to the wavelength variable current ILDpmax where P is the maximum or the gap current value at the mode boundary closest to the wavelength variable current ILDpmax or more.

Next, an algorithm in the SHG laser stabilization control device of the first embodiment will be described with reference to FIGS.

FIGS. 5A and 5B show the relationship between the tunable current and the second harmonic power output from the SHG laser 3 for each different phase matching condition between the semiconductor laser 1 and the SHG device 2. It is a graph shown. FIG. 6 shows a flowchart of the wavelength variable current control in the first embodiment.

First, the wavelength variable current control means 12 controls the current variable means 11 in response to the command to start the wavelength variable current control, and the wavelength variable current ILD is increased by 0.5 m per step.
The wavelength-variable current ILD of A is added to change the wavelength-variable current ILD step by step within a range of about 0 to 112 mA, and the wavelength at which the output of the photodetector 10, that is, the output P of the SHG laser 3, becomes maximum. The variable current ILDpmax is obtained (steps 101 and 102).

Next, in order to avoid the influence of the hysteresis characteristic of the semiconductor laser 1 on the variable wavelength current, the variable wavelength current control means 12 sets the variable wavelength current to a sufficiently small value (for example, a value approximately 20 mA smaller than ILDpmax). After the setting, the wavelength variable current is increased again to a predetermined value (for example, a value about 20 mA larger than ILDpmax) by 0.5 mA for one step, and the output of the photodetector 10 is changed in response to one step change of the wavelength variable current. The change amount, that is, the gap current value ILDspmax of the wavelength variable current at which the change amount ΔP of the output of the SHG laser 3 becomes maximum is obtained (steps 103 and 10).
4).

Then, the wavelength variable current control means 12 determines whether ILDspmax is larger or smaller than the obtained ILDpmax (step 105). As a result, if it is smaller or equal (step 105, YES), the wavelength variable current return amount corresponding to an integer n times the wavelength variable current change amount δILD of one step is added to ILDspmax, and the in-mode wavelength variable current between the modes is added. ILDmc is obtained (step 106). If it is larger (step 105, NO), 1 from ILDspmax
The wavelength variable current return amount corresponding to an integer n times the wavelength variable current change amount δILD in the step is subtracted to obtain the in-mode wavelength variable current ILDmc between the modes (step 107).

The wavelength variable current return amount is such that the width between modes is 5
mA, preferably, n is set to 5 and 2.5 mA
It should just be set to about. Thereby, the in-mode wavelength variable current ILDmc is set to a wavelength variable current corresponding to substantially the center between modes. Alternatively, preferably, an integer value m obtained by dividing a change amount of the wavelength variable current when changing from the mode boundary to the next mode boundary by the wavelength variable current change amount δILD is obtained, and a value between 2 and m-2 is obtained. The value of n may be determined as appropriate.

After obtaining the in-mode wavelength variable current ILDmc in this way, the wavelength variable current control means 12
In order to avoid the influence of the hysteresis characteristic of the semiconductor laser 1,
The tunable current injected into the DBR region 1-2 is gradually increased and set as the in-mode tunable current ILDmc (step 108).

The above control algorithm ILDspmax and IL
When the Dpmax comparison process is expressed by if..., Then.

If ILDspmax ≦ ILDpmax then ILDmc = ILDspmax + δILD × n if ILDspmax> ILDpmax then IDBRmc = IBDRspmax−δIDBR × n It is configured using a digital signal processor (DSP) provided with an A / D converter for inputting the output from the D / A 10 and a D / A converter for controlling the current variable means 11, and performs software processing.

When the tunable current injected into the DBR region 1-2 of the semiconductor laser 1 is set to the in-mode tunable current ILDmc in this manner, the in-mode tunable current ILDmc is set.
Since the LDmc can be set sufficiently away from the gap current value at the mode boundary, the second harmonic power from the SHG laser 3 can be stabilized near the maximum.

Next, a modification of the first embodiment will be described with reference to a wavelength variable current control flowchart shown in FIG.

A comparison between the processing of the flowchart of FIG. 6 and the processing of the flowchart of FIG. 7 shows that the wavelength variable current is gradually increased in the processing of the flowchart of FIG. The difference is that the variable current is gradually reduced.

First, the wavelength variable current control means 12 controls the current variable means 11 in response to the command to start the wavelength variable current control, and the wavelength variable current
The wavelength-variable current ILDpmax at which the output P of the SHG laser 3 detected by the photodetector 10 is maximized by subtracting the wavelength-variable current change amount δILD of A to change the wavelength-variable current ILD in the range of about 0 to 112 mA. (Step 20)
1,202).

Next, the wavelength variable current control means 12 sets the wavelength variable current to a sufficiently large value (for example, a value about 20 mA larger than ILDpmax) in order to avoid the influence of the hysteresis characteristic of the semiconductor laser 1 on the wavelength variable current. After the setting, the wavelength variable current is reduced again to a predetermined value (for example, a value smaller by 20 mA than ILDpmax) in steps of 0.5 mA, and the photodetector 10 detects the change of the wavelength variable current in one step. The gap current value ILDspmax of the wavelength-variable current at which the change amount ΔP of the output of the SHG laser 3 becomes maximum is obtained (steps 203 and 204).

Then, the variable wavelength current control means 12 determines whether ILDspmax is larger or smaller than ILDpmax (step 205). As a result, if smaller or equal (step 205, YES), the tunable current return amount corresponding to an integer (n) times the tunable current change amount δILD of one step is subtracted from ILDspmax, and the intra-mode wavelength between modes is subtracted. The variable current ILDmc is obtained (step 206). If it is larger (step 205, NO), ILDspmax
Then, a wavelength variable current return amount corresponding to an integer n times the wavelength variable current change amount δILD of one step is added to obtain an in-mode wavelength variable current ILDmc between modes (step 207).

After obtaining the in-mode wavelength variable current ILDmc in this way, the wavelength variable current control means 12
In order to avoid the influence of the hysteresis characteristic of the semiconductor laser 1, set the wavelength tunable current to a sufficiently large value.
The variable wavelength current injected into the DBR region 1-2 is gradually reduced and set as the in-mode variable wavelength current ILDmc (step 208).

ILDspmax and IL of the above control algorithm
When the Dpmax comparison process is expressed by if..., Then.

If ILDspmax ≦ ILDpmax then ILDmc = ILDspmax−δILD × n if ILDspmax> ILDpmax then IDBRmc = ILDspmax + δILD × n

(Second Embodiment) In the first embodiment,
By adjusting the amount of return of the wavelength variable current to the maximum gap current value ILDspmax, the in-mode wavelength variable current I
Seeking LDmc.

On the other hand, in the second embodiment, the first and second thresholds are sequentially obtained and set, and the gap current value is determined from the second threshold value. The mode variable wavelength current between the modes is obtained by adjusting the variable current return amount.

Accordingly, in the second embodiment, although the procedure for obtaining the in-mode wavelength variable current is different from that of the first embodiment, the wavelength variable current is automatically set and the second harmonic power of the SHG output is adjusted. It is similar to the first embodiment in that it is stabilized.

The configuration of the SHG laser stabilization control device of this embodiment is completely the same as that of the device shown in FIG. 1, and only the control algorithm of the wavelength variable current by the wavelength variable current control means 12 is different. Therefore, the description of the configuration of the device of the present embodiment will be omitted, and only the control algorithm of the wavelength variable current will be described.

FIGS. 8A, 8B and 8C show the tunable current and the second output from the SHG laser 3 for each different phase matching condition between the semiconductor laser 1 and the SHG device 2. FIG.
It is a graph which shows the relationship of a harmonic power. FIG. 9 shows the second
4 shows a wavelength variable current control flowchart in the embodiment.

First, the wavelength variable current control means 12 responds to the wavelength variable current control start command,
1 to control the wavelength variable current ILD to 0.5 mA per step.
Of the wavelength variable current change .delta.ILD, and changes the wavelength variable current ILD one step at a time in the range of about 0 to 112 mA to obtain the maximum output Pmax of the SHG laser 3 and the wavelength variable current ILDpmax at this time (step 301, 30
2).

Next, the wavelength variable current control means 12
AA% (preferably about 70%) of x is set to the first threshold value Pt
h1 and after performing a process of avoiding the influence of the hysteresis characteristic of the semiconductor laser 1, a predetermined range (for example, I
In the range of LDpmax ± 20 mA), the wavelength variable current is increased by 0.5 mA per step (step 303). Then, the wavelength variable current control means 12 outputs the first threshold value Pth1
Then, the output P1 of the SHG laser 3 when it exceeds the threshold is obtained (step 304).

Thereafter, the wavelength variable current control means 12 sets the BB% (preferably 70%) of the output P1 to the second threshold value P
After setting the threshold value th2 and performing the processing for avoiding the influence of the hysteresis characteristic of the semiconductor laser 1 again, a predetermined range (for example, a range of ILDpmax ± 20 mA) is used for one step.
The wavelength variable current is increased by mA (step 30).
5). Then, a wavelength variable current when the output P of the SHG laser 3 exceeds the second threshold value Pth2 is obtained, and this wavelength variable current is set as a gap current value ILDmb at the mode boundary (step 306).

Subsequently, the wavelength variable current control means 12
Adds the wavelength variable current return amount corresponding to an integer n times the wavelength variable current change amount δILD in one step to the obtained gap current value ILDmb at the mode boundary to obtain the in-mode wavelength variable current ILDmc between the modes (step 307).

The wavelength variable current return amount is such that the width between modes is 5
mA, preferably, n is set to 5 and 2.5 mA
It should just be set to about. Thereby, the in-mode wavelength variable current ILDmc is set to a wavelength variable current corresponding to substantially the center between modes. Further, the wavelength variable current return amount may be obtained based on a difference current between the first wavelength variable current at the mode boundary and the second wavelength variable current at the next mode boundary. in this case,
The wavelength variable current return amount is appropriately set in the range of 20 to 80% of the difference current.

After obtaining the in-mode wavelength variable current ILDmc in this way, the wavelength variable current control means 12
After the processing for avoiding the influence of the hysteresis characteristic of the semiconductor laser 1 is performed, the tunable current injected into the DBR region 1-2 of the semiconductor laser 1 is gradually increased to increase the in-mode tunable current ILD.
mc is set (step 308).

In the above algorithm, the following conditions must be satisfied in order to set an accurate in-mode wavelength variable current ILDmc.

(Condition 1) The first threshold value Pth1 is SHG
The wavelength variable current ILDp corresponding to the maximum output Pmax of the laser 3
On the side less than max, the maximum value Pmi of the output of the SHG laser 3 between the modes from the mode boundary closest to the maximum output Pmax to the mode boundary of the wavelength variable current ILDpmax.
Must be set below max.

This condition is expressed by the following equation (1).

Pmimax ≧ Pth1 = Pmax × AA% (1) (Condition 2) The second threshold value Pth2 is smaller than the wavelength variable current ILDpmax corresponding to the maximum output Pmax of the SHG laser 3 and is smaller than the maximum output Pmax. At the mode boundary closest to
It must be set between the larger output Pmbup and the smaller output Pmbdn of the SHG laser 3 changing stepwise.

This condition is expressed by the following equation (2).

Pmbdn <P1 × BB% <Pmbup (2) (Condition 3) AA% in the above equation (1) and the above equation (2)
Must satisfy the following equation (3).

AA% ≦ BB% (3) Here, ignoring the above conditions 1 to 3, for example, AA = B
When the processing of the flowchart of FIG. 9 is performed with B = 50 (%), the in-mode wavelength variable current ILDmc can be set accurately in FIGS. 8 (a) and 8 (b). However, in FIG. 8C, the gap current value ILDmb cannot be obtained accurately, and accordingly, it is not possible to set an accurate in-mode wavelength variable current ILDmc.

When the above conditions 1 to 3 are satisfied, FIG.
Also in (c), the gap current value ILDmb can be accurately obtained and the accurate in-mode wavelength variable current ILDmc can be set.

That is, in the present embodiment, when the first threshold value Pth1 is set at the mode boundary, the output P1 of the SHG laser 3 when exceeding the first threshold value Pth1
Increases stepwise to the maximum output Pmax, so that a second threshold Pth2 slightly smaller than the first threshold Pth1 is obtained from the output P1.
The gap current value ILDmb at the mode boundary can be determined based on the threshold value Pth2. Also, the first threshold value P
When th1 deviates from the mode boundary, that is, is set between modes, the SHG when the first threshold value Pth1 is exceeded
The output P1 of the laser 3 becomes substantially the same as the first threshold value Pth1, and a second threshold value Pth2 sufficiently smaller than the first threshold value Pth1 is obtained from the output P1.
Since the threshold value Pth2 is set at the mode boundary, the gap current value ILDmb at the mode boundary can be obtained based on the second threshold value Pth2. As a result, the gap current value ILDmb can be accurately obtained, and the accurate in-mode wavelength variable current ILDmc can be set.

As in the first embodiment, the wavelength variable current control means 12 for realizing the control algorithm as described above preferably includes an A / D converter for inputting an output from the photodetector 10 and a current D / for controlling the variable means 11
Digital signal processor with DS converter (DS
P) or the like, and perform software processing.

By setting the tunable current to be injected into the DBR region 1-2 of the semiconductor laser 1 in this way as the in-mode tunable current ILDmc, the in-mode tunable current ILDmc is set.
Since the LDmc can be set sufficiently away from the gap current value at the mode boundary, the second harmonic power from the SHG laser 3 can be stabilized near the maximum.

Next, a modification of the second embodiment will be described with reference to a wavelength variable current control flowchart shown in FIG.

When comparing the processing of the flowchart of FIG. 10 with the processing of the flowchart of FIG. 9, the wavelength variable current is gradually increased in the processing of the flowchart of FIG. The difference is that the variable current is gradually reduced.

First, the wavelength variable current control means 12 responds to the wavelength variable current control start command,
1 to control the wavelength variable current ILD to 0.5 mA per step.
Is subtracted from the wavelength variable current change .delta.ILD to change the wavelength variable current ILD one step at a time in the range of about 0 to 112 mA to obtain the maximum output Pmax of the SHG laser 3 and the wavelength variable current ILDpmax at this time (step 401, 40
2).

Next, the wavelength variable current control means 12 sets Pma
AA% (preferably about 70%) of x is set to the first threshold value Pt
h1 and after performing a process of avoiding the influence of the hysteresis characteristic of the semiconductor laser 1, a predetermined range (for example, I
In the range of LDpmax ± 20 mA), the wavelength variable current is reduced by 0.5 mA per step (step 403). Then, the wavelength variable current control means 12 outputs the first threshold value Pth1
Then, the output P1 of the SHG laser 3 when it exceeds the threshold is obtained (step 404).

Thereafter, the wavelength variable current control means 12 sets the BB% (preferably 70%) of the output P1 to the second threshold value P.
After setting the threshold value th2 and performing the processing for avoiding the influence of the hysteresis characteristic of the semiconductor laser 1 again, a predetermined range (for example, a range of ILDpmax ± 20 mA) is used for one step.
The wavelength variable current is decreased by mA (step 40).
5). Then, a variable wavelength current when the output P of the SHG laser 3 exceeds the second threshold value Pth2 is obtained, and this variable wavelength current is set as a gap current value ILDmb at the mode boundary (step 406).

Subsequently, the wavelength variable current control means 12
Subtracts the tunable current return amount corresponding to an integer n times the tunable current change amount δILD in one step from the determined gap current value ILDmb at the mode boundary to obtain the intra-mode tunable current ILDmc between the modes (step 407).

The wavelength-variable current return amount is such that the width between modes is 5
mA, preferably, n is set to 5 and 2.5 mA
It should just be set to about. Thereby, the in-mode wavelength variable current ILDmc is set to a wavelength variable current corresponding to substantially the center between modes. Further, the wavelength variable current return amount may be obtained based on a difference current between the first wavelength variable current at the mode boundary and the second wavelength variable current at the next mode boundary. in this case,
The wavelength variable current return amount is appropriately set in the range of 20 to 80% of the difference current.

After obtaining the in-mode wavelength variable current ILDmc in this way, the wavelength variable current control means 12
After the processing for avoiding the effect of the hysteresis characteristic of the semiconductor laser 1 is performed, the tunable current injected into the DBR region 1-2 of the semiconductor laser 1 is gradually reduced so that the in-mode tunable current ILD is reduced.
mc is set (step 408).

In the above algorithm, in order to set an accurate in-mode wavelength variable current ILDmc, the following conditions must be satisfied.

(Condition 1) The first threshold value Pth1 is SHG
The wavelength variable current ILDp corresponding to the maximum output Pmax of the laser 3
On the side exceeding max, the maximum value P of the output of the SHG laser 3 between modes from the mode boundary closest to the maximum output Pmax to the mode boundary of the tunable current ILDpmax.
Must be set below mimax.

This condition is expressed by the following expression (4).

Pmimax ≦ Pth1 = Pmax × AA% (4) (Condition 2), on the side exceeding the wavelength variable current ILDpmax corresponding to the maximum output Pmax of the SHG laser 3, the maximum output Pmax
Must be set between the larger output Pmbup and the smaller output Pmbdn of the SHG laser 3 which changes stepwise at the mode boundary closest to.

This condition is expressed by the following equation (5).

Pmbdn <P1 × BB% <Pmbup (5) (Condition 3) AA% in the above equation (4) and the above equation (5)
Must satisfy the following expression (6).

AA% <BB% (6) The wavelength variable current control means 12 for realizing the above-described control algorithm is preferably an output from the photodetector 10, as in the first embodiment. And a digital signal processor (DSP) provided with a D / A converter for controlling the current variable means 11 and an A / D converter for inputting.

When the tunable current injected into the DBR region 1-2 of the semiconductor laser 1 is set as the in-mode tunable current ILDmc in this manner, the in-mode tunable current ILDmc is set.
Since the LDmc can be set sufficiently away from the gap current value at the mode boundary, the second harmonic power from the SHG laser 3 can be stabilized near the maximum.

(Third Embodiment) In this embodiment, similarly to the first and second embodiments, the tunable current is automatically set. However, not only this, but also the temperature of the SHG laser 3 is automatically set. , The second harmonic power of the SHG output is set near the maximum and stabilized.

FIG. 11 shows an SHG according to a third embodiment of the present invention.
FIG. 2 is a block diagram illustrating a schematic configuration of a laser stabilization control device. In FIG. 11, the same reference numerals are given to the portions that perform the same operations as in FIG. 1, and the description will be omitted.

In this embodiment, the temperature control means 7A
Is used to input not only the temperature of the semiconductor laser 1 detected by the temperature detector 6 but also the second temperature of the SHG laser 3 detected by the photodetector 10 in order to enable the temperature control of the SHG laser 3. Input harmonic power.

The temperature control means 7A adjusts the current flowing through the temperature variable means 5 so that the difference between the temperature detected by the temperature detector 6 and the target temperature becomes zero. Further, the temperature control means 7A controls the target temperature such that the output of the SHG laser 3 detected by the photodetector 10 becomes a predetermined value.

The SHG laser stabilizing device of this embodiment is
Preferably, similarly to the first and second embodiments, the wavelength variable current control is performed so that the output of the SHG laser 3 is stabilized near the maximum, and then the temperature target is controlled by the temperature control unit 7A. By changing the value, the temperature at which the output of the SHG laser 3 is maximized is searched.

Here, the temperature characteristics of the SHG laser 3, particularly the semiconductor laser 1, will be described with reference to FIG.

FIG. 12A is a graph showing the relationship between the temperature of the semiconductor laser 1 and the oscillation wavelength. As shown in FIG. 12A, when the temperature of the semiconductor laser 1 changes by 1 ° C.
The oscillation wavelength of the semiconductor laser 1 changes by 0.06 nm. In the case of the present embodiment, at 20 ° C., the oscillation wavelength of the semiconductor laser 1 is 850 nm.

FIG. 12B is a graph showing the relationship between the temperature of the semiconductor laser 1 and the gap current value at the mode boundary. In the present embodiment, the temperature of the semiconductor laser 1 is 25 ° C.
When the wavelength variable current is 25 mA, the output of the semiconductor laser 1 makes a mode hop. The graph in FIG. 12B shows the characteristic that the wavelength variable current (gap current value) changes according to the temperature of the semiconductor laser 1. In the present embodiment, when the temperature of the semiconductor laser 1 is changed from 25 ° C. to 20 ° C., the gap current value changes from 25 mA to 23.5 mA. Conversely, the temperature of the semiconductor laser 1 is changed from 25 ° C. to 3
When the temperature changes to 0 ° C., the gap current value changes from 25 mA to 26
mA.

FIG. 12C is a graph showing the characteristics of the output power of the semiconductor laser 1 including the wavelength characteristics of the DBR region 1-2 with respect to the temperature of the semiconductor laser 1. In this embodiment, the characteristics are such that the output power of the semiconductor laser 1 is maximized when the temperature of the semiconductor laser 1 is 20 ° C.

Next, SH with respect to the temperature of the SHG laser 3
The output power characteristic of the G laser 3 will be described with reference to FIG.

FIG. 13A is a graph showing wavelength characteristics of the SHG device 2 with respect to temperature. In the present embodiment, the wavelength characteristic of the SHG device 2 is 0.035 nm /
When a wavelength of 850 nm is input at 20 ° C., a second harmonic of 425 nm is output.

FIG. 13B is a graph showing wavelength characteristics of the SHG laser 3 with respect to temperature. Here, the wavelength characteristics of the SHG laser 3 when viewed from the semiconductor laser 1 side are shown. In this case, the result obtained by subtracting the above wavelength characteristic of 0.035 nm / ° C. of the SHG device 2 from the above wavelength characteristic of 0.06 nm / ° C. of the semiconductor laser 1 is the SHG laser 3.
Wavelength characteristic. Therefore, the wavelength characteristic of the SHG laser 3 with respect to the temperature is 0.025 nm / ° C.

FIG. 13C is a graph showing the second harmonic power characteristic from the SHG laser 3 with respect to the temperature of the SHG laser 3 on the assumption that the SHG device 2 has ideal characteristics. As shown in the graph of FIG. 13C, in the present embodiment, when the SHG device 2 has ideal characteristics, it is possible to obtain the second harmonic output of up to 3 mW at 20 ° C. . Then, the second harmonic power characteristic with respect to temperature is a characteristic symmetrical with respect to 20 ° C.

FIG. 13D is a graph showing the characteristic of the second harmonic power from the SHG laser 3 with respect to the output wavelength of the SHG laser 3 on the assumption that the characteristic of the SHG device 2 varies.

When there is a variation in the SHG device 2 such that the waveguide of the SHG device 2 is not uniform, for example, as shown in the graph of FIG. 13D, the second harmonic of the SHG laser 3 with respect to the wavelength of the SHG laser 3 The characteristics of the wave power are asymmetric around 20 ° C. and have two inflection points. The asymmetry, the number of inflection points and their positions vary depending on the characteristics of the device.

FIG. 13E is a graph showing the characteristic of the second harmonic power from the SHG laser 3 with respect to the temperature of the SHG laser 3 on the assumption that the characteristic of the SHG device 2 varies.

Since the wavelength characteristic of the SHG laser 3 with respect to the temperature is linear, when the temperature of the SHG laser 3 is applied to the horizontal axis in FIG. 13D instead of the wavelength, FIG. Is obtained.

As described above, if there is a characteristic variation such as an uneven waveguide of the SHG device 2,
The second harmonic power from the SHG laser 3 has a characteristic having a plurality of inflection points. Therefore, the maximum value of the output of the SHG laser 3 is searched for by changing the temperature of the SHG laser 3 (for example, by changing the temperature in a predetermined step to search for an inflection point (= maximum value),
In the case of controlling the harmonic power to the maximum), it is necessary to accurately select the maximum inflection point from the inflection points.

In this embodiment, the temperature control means 7A
Thus, the maximum inflection point is accurately selected from the inflection points, and the temperature of the SHG laser 3 is set to the temperature of the maximum inflection point.

The outline of the algorithm in this embodiment is as follows. First, as in the first and second embodiments, the tunable current is controlled so that the second harmonic power from the SHG laser 3 is stabilized near the maximum. Later, the temperature of the SHG laser 3 at which the second harmonic power is further increased is searched by the temperature control means 7A. At this time, as a countermeasure when a plurality of inflection points exist as described above, first, the SHG laser 3 is used.
While the target temperature is largely changed in a temperature range from a predetermined value lower temperature to a predetermined value higher temperature with respect to the initial temperature of
The output of the SHG laser 3 and the output of the temperature detector 6 are measured to search for the temperature of the SHG laser 3 at which the second harmonic power from the SHG laser 3 becomes maximum. This is called rough temperature exploration. Thereafter, in the vicinity of the temperature determined by the rough temperature search, a step of a predetermined temperature width, for example, 0.1 step per step.
By changing the temperature of the SHG laser 3 within a temperature range of
The temperature at which the output of the HG laser 3 is maximized is searched. This is called fine temperature search.

Next, the algorithm in the SHG laser stabilization control device of the third embodiment will be described in detail with reference to FIGS.

FIG. 14 is a control flowchart of the rough temperature search.

First, in response to the rough temperature search start command, the temperature control means 7A sets the temperature target value to 5 ° C. with respect to the initial temperature (for example, 22 ° C.) of the SHG laser 3 detected by the temperature detecting means 6. Set the lower minimum temperature to 17 ° C,
While monitoring the temperature of the SHG laser 3 detected by the temperature detecting means 6, the temperature varying means 5 is controlled to adjust the temperature of the SHG laser 3 to the target temperature (step 50).
1).

Next, the temperature control means 7A confirms that the temperature of the SHG laser 3 has become stable around the target temperature of 17 ° C. (step 502). Subsequently, the temperature control unit 7A sets the target temperature to the upper limit temperature 27 ° C., which is 5 ° C. higher than the initial temperature, and monitors the temperature of the SHG laser 3 while
The temperature of the SHG laser 3 is raised to the target temperature by controlling the temperature varying means 5. Thereby, the SHG laser 3
Changes from 17 ° C to 27 ° C. At this time, the temperature control means 7A outputs the output of the photodetector 10, ie, SHG
The output P of the laser 3 is monitored, and the output P becomes maximum S
The temperature Tpmax1 of the HG laser 3 is obtained. Thereafter, the temperature control means 7A determines that the temperature of the SHG laser 3 has reached the target temperature of 27 ° C.
Confirm that it has become stable in the vicinity (step 50)
3).

When the temperature Tpmax1 of the SHG laser 3 at which the output P of the SHG laser 3 is maximized is obtained, the temperature control means 7A controls the temperature variable means 5 while monitoring the temperature of the SHG laser 3, and The temperature of the laser 3 is set to the temperature Tpmax1 (step 504).

FIG. 15 is a control flowchart of the fine temperature search.

First, in response to the fine search start command, the temperature control means 7A outputs the output (Pn-1) of the SHG laser 3 detected by the photodetector 10 at the temperature Tpmax1 set by the rough temperature search. Is sampled (step 601). Thereafter, the temperature control means 7A
The target temperature is set to a predetermined step width, for example, 1 from the temperature Tpmax1.
The temperature of the SHG laser 3 is set higher by 0.1 ° C. and the temperature of the SHG laser 3 is increased by controlling the temperature varying means 5 while monitoring the temperature of the SHG laser 3 detected by the temperature detecting means 6 (step 602). It is determined whether or not the output Pn of the SHG laser 3 has become larger than the value before the change in the target temperature (step 603). When the output Pn of the SHG laser 3 has become larger than the value before the target temperature change (step 60).
3, YES), and set the target temperature higher by 0.1 ° C.
The temperature of the SHG laser 3 is increased (step 602),
It is determined whether or not the output Pn of the SHG laser 3 has become larger than the value before the change in the target temperature (step 603).

If the output Pn of the SHG laser 3 has become smaller than the value before the target temperature change (step 603, N
O), the temperature control means 7A sets the target temperature to 0.
The temperature of the SHG laser 3 detected by the temperature detecting means 6 is set to be lower by 1 ° C.
Is controlled to lower the temperature of the SHG laser 3 (step 604), and it is determined whether or not the output Pn of the SHG laser 3 has become larger than the value before the target temperature change (step 6).
05). If the output Pn of the SHG laser 3 has become larger than the value before the target temperature change (step 605, YES),
Further, the target temperature is set lower by 0.1 ° C., the temperature of the SHG laser 3 is lowered (step 604), and it is determined whether or not the output Pn of the SHG laser 3 has become larger than the value before the change of the target temperature (step 604). 605).

If the output Pn of the SHG laser 3 has become smaller than the value before the target temperature change (step 605, N
O), the temperature control means 7A raises the target temperature by 0.1 ° C. for one step and raises this target temperature to the temperature Tpmax2.
Then, the temperature of the SHG laser 3 is raised by 0.1 ° C. for one step, and the temperature of the SHG laser 3 is set to the temperature Tpmax2 and stabilized (step 606).

As described above, the target temperature is changed in increments of 0.1 ° C. in the direction in which the output of the SHG laser 3 increases, and the temperature when the output of the SHG laser 3 changes from increase to decrease, ie, the photodetector 10 The temperature Tpmax2 at which the inflection point (= maximum value) of the output is obtained. Then, the target temperature is set to the inflection point temperature Tpmax2, and the fine temperature search ends.

As described above, it is assumed that there are a plurality of inflection points in the second harmonic power from the SHG laser 3 due to a characteristic variation such as an uneven waveguide of the SHG device 2. Also, the temperature of the SHG laser 3 can be set to a temperature at which the second harmonic power is maximized.

Next, another example of the rough temperature search will be described with reference to the wavelength variable current control flowchart shown in FIG.

First, in response to the rough temperature search start command, the temperature control means 7A sets the lower limit temperature 17 ° C. lower by 5 ° C. than the initial temperature (for example, 22 ° C.) of the SHG laser 3 detected by the temperature detecting means 6. Set, and lower limit temperature 17
A target temperature of 15 ° C. lower than the temperature is set (step 70).
1). Then, the temperature control means 7A controls the temperature variable means 5 so that the temperature of the SHG laser 3 reaches the target temperature of 15 ° C.

In the course of lowering the temperature of the SHG laser 3 in this way, the temperature control means 7A determines that the temperature of the SHG laser 3 has reached the lower limit temperature of 17 ° C. before the temperature of the SHG laser 3 reaches the target temperature of 15 ° C. Is confirmed (step 702). In response, the temperature control means 7A
The upper limit temperature 27 ° C. is set 5 ° C. higher than the initial temperature 22 ° C. of the HG laser 3, and the target temperature 29 ° C. higher than the upper limit temperature 27 ° C. is set. Then, the temperature control means 7A
The temperature varying means 5 is controlled so that the temperature of the HG laser 3 reaches the target temperature of 29 ° C. At this time, the temperature control means 7
Monitors the output P of the SHG laser 3 and obtains the temperature Tpmax1 of the SHG laser 3 at which the output P becomes maximum. Thereafter, the temperature control means 7A confirms that the temperature of the SHG laser 3 has reached a target temperature of about 27 ° C. (step 70).
3).

When the temperature Tpmax1 of the SHG laser 3 at which the output P of the SHG laser 3 is maximized is obtained, the temperature control means 7A controls the temperature variable means 5 while monitoring the temperature of the SHG laser 3, and The temperature of the laser 3 is set to the temperature Tpmax1 (step 704).

When the temperature lower than the lower limit temperature is set as the target temperature and the temperature higher than the upper limit temperature is set as the target temperature, the temperature of the SHG laser 3 is quickly changed to the lower limit temperature and the upper limit temperature. Therefore, the control time of the rough temperature search can be shortened.

To realize the above control algorithm, the temperature control means 7A is preferably provided with a photodetector 10A.
Digital signal processor including an A / D converter for inputting an output from the A / D converter, an A / D converter for inputting an output from the temperature detector 6, and a D / A converter for controlling the temperature varying means 5. (DSP), etc., and perform software processing.

(Fourth Embodiment) In this embodiment, similarly to the first and second embodiments, the wavelength variable current is automatically set. However, not only this, but also the active region 1 of the semiconductor laser 1 is set. The output of the SHG laser 3 is stabilized by controlling the power variable current injected to −1.

FIG. 17 shows an SHG according to the fourth embodiment of the present invention.
FIG. 2 is a block diagram illustrating a schematic configuration of a laser stabilization control device. In FIG. 17, portions that perform the same operations as those in the apparatus in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

In FIG. 17, reference numeral 14 denotes an SHG laser 3
Is a beam splitter that splits a light beam from the light source.
Reference numeral 16 denotes a second photodetector that detects one of the beams split by the beam splitter 14. Reference numeral 15 denotes a first photodetector that detects the second harmonic laser light from the SHG laser by inputting the other beam split by the beam splitter 14 through the infrared light cut filter 9. Reference numeral 17 denotes current varying means for injecting a power variable current into the active region 1-1 of the semiconductor laser 1. Reference numeral 18 denotes a power variable current control unit that controls the current variable unit 17 to control a power variable current injected into the active region 1-1 of the semiconductor laser 1.

In the first embodiment, the current injected into the active region 1-1 of the semiconductor laser 1 is made constant by the constant current control means 8. On the other hand, in the present embodiment, the power variable current is changed. By the control means 18, the first
The difference is that the power variable current injected from the current variable means 17 into the active region 1-1 of the semiconductor laser 1 is controlled so that the output of the photodetector 15 or the second photodetector 16 becomes constant.

In this embodiment, prior to the control of the wavelength variable current, the power variable current control means 18 controls the second photodetector 1.
The power variable current injected into the active region 1-1 of the semiconductor laser 1 is controlled so that the output of the semiconductor laser 6 becomes constant. That is, the power variable current control unit 18
The power variable current injected into the active region 1-1 of the semiconductor laser 1 is controlled such that the fundamental wave power from the semiconductor laser 1 becomes constant.

In the state where the power variable current is controlled so that the fundamental wave power is constant, preferably, the temperature of the SHG laser 3 is kept constant, as in the first embodiment. While performing the control, the tunable current is controlled so that the second harmonic power from the SHG laser 3 detected by the first photodetector 15 is near the maximum and stable.

When the wavelength variable current control is completed, the power variable current control means 18 controls the power variable current injected into the active region 1-1 of the semiconductor laser 1 so that the output of the first photodetector 15 becomes constant. Control. That is, the power variable current control means 18 controls the power variable current injected into the active region 1-1 of the semiconductor laser 1 so that the second harmonic power from the SHG device 2 becomes constant.

Here, as a result of changing the wavelength variable current,
As the output of the first photodetector 15 increases, the component of the fundamental power decreases. In the present embodiment, since the power variable current is controlled so that the fundamental wave power is kept constant in the wavelength variable current control, the second variable power control for the change in the wavelength variable current is performed.
The rate of change of the harmonic power is larger than in the first embodiment in which a constant current is injected into the active region 1-1. Therefore, in the wavelength variable current control for stabilizing the second harmonic power from the SHG laser 3 near its maximum, the detection sensitivity of the second harmonic power from the SHG laser 3 to a change in the wavelength variable current is improved. Can be.

Further, in this embodiment, after the wavelength variable current control, the power variable current is controlled so that the second harmonic power from the SHG laser 3 becomes constant. Wave power can be obtained.

(Fifth Embodiment) In this embodiment, similarly to the first and second embodiments, the tunable current is automatically set. However, not only this, but also the temperature of the SHG laser 3 is automatically set. By controlling the current injected into the active region 1-1 of the semiconductor laser 1,
The output of the HG laser 3 is stabilized.

FIG. 18 shows an SHG according to a fifth embodiment of the present invention.
FIG. 2 is a block diagram illustrating a schematic configuration of a laser stabilization control device. In FIG. 18, the same reference numerals are given to the portions that perform the same operations as those of the device in FIG. 17, and the description is omitted.

In the apparatus of this embodiment, the temperature control means 7 is replaced with the temperature control means 7 in the apparatus of FIG.
A is mainly different in that A is applied, and similarly to the third embodiment, the temperature of the SHG laser 3 is searched such that the second harmonic power from the SHG laser 3 is maximized (hereinafter referred to as the temperature search). Name).

In the present embodiment, when performing the wavelength variable current control and the temperature search, the power variable current control means 18 controls the active region 1- of the semiconductor laser 1 so that the output of the second photodetector 16 becomes constant. The power variable current to be injected into the device 1 is controlled. That is, the power variable current control means 18
The power variable current injected into the active region 1-1 of the semiconductor laser 1 is controlled so that the fundamental wave power from the laser 3 becomes constant.

In the state where the power variable current is controlled so that the fundamental wave power is constant, preferably, the wavelength variable current control is performed similarly to the first embodiment.
After controlling the wavelength tunable current so that the output of the SHG laser 3 is stabilized near the maximum, the temperature target is changed by the temperature control means 7A and the SH is controlled in the same manner as in the third embodiment.
The temperature at which the output of the G laser 3 is maximized is searched.

When the wavelength variable current control and the temperature search are completed, the power variable current control means 18 controls the active region 1 of the semiconductor laser 1 so that the output of the first photodetector 15 becomes constant.
The power variable current injected to -1 is controlled. That is, S
The power variable current injected into the active region 1-1 of the semiconductor laser 1 is controlled so that the second harmonic power of the output of the HG device 2 becomes constant.

Here, when the output of the first photodetector 15 increases as a result of changing the wavelength variable current or as a result of temperature search, the power component of the fundamental wave decreases. In the present embodiment, in the wavelength variable current control, the power variable current is controlled so that the fundamental wave power is constant. Therefore, the rate of change of the second harmonic power with respect to the change of the wavelength variable current is the active region 1−. 1 is larger than in the first embodiment in which a constant current is injected. Therefore, the second from the SHG laser 3
In the wavelength variable current control and the temperature search for stabilizing the harmonic power near the maximum, the detection sensitivity of the second harmonic power from the SHG laser 3 to the change in the wavelength variable current can be improved.

Further, in this embodiment, after the wavelength variable current control, the power variable current is controlled so that the second harmonic power from the SHG laser 3 becomes constant. Wave power can be obtained.

(Sixth Embodiment) This embodiment shows an optical disk recording / reproducing apparatus to which the SHG laser stabilization control apparatus of the fifth embodiment is applied.

FIG. 19 shows an optical disk recording / reproducing apparatus according to a sixth embodiment of the present invention. In FIG. 19, parts that perform the same operations as those in the apparatus in FIG. 18 are denoted by the same reference numerals.

The optical disk recording / reproducing apparatus of the present embodiment comprises:
As is clear from FIG. 19, not only is the stabilization control device for the SHG laser shown in FIG.
9, focusing lens 20, mirror 21, objective lens 22, lens holder 23, permanent magnet 24a, permanent magnet 24b, leaf spring 25a, leaf spring 25b, coil 26a,
A coil 26b and a disk 27 are provided.

The function of the SHG laser stabilization control device shown in FIG. 19 is different from that of the device shown in FIG.

In FIG. 19, the light emitted from the SHG laser 3 is made substantially collimated by the collimator lens 19 before being incident on the infrared light cut filter 9. The infrared light cut filter 9 cuts out the fundamental wave component of the incident light and outputs a laser light of only the second harmonic. The laser light of only the second harmonic is input to the beam splitter 14A. The beam splitter 14 </ b> A reflects a part of the second harmonic laser light, and the reflected light is input to the first photodetector 15. The wavelength variable current control, the temperature search, and the power variable current are controlled in substantially the same manner as in the fifth embodiment so that the second harmonic detected by the first photodetector 15 is stabilized near the maximum value. ing. However, since the fundamental wave from the SHG laser 3 is not detected, control slightly different from that in the fifth embodiment is performed.

The difference between the power variable current control means 18A of this embodiment shown in FIG. 19 and the stabilization control of the SHG laser by the power variable current control means 18 shown in FIG. 18 of the eighth embodiment is as follows. It is.

In FIG. 18, before passing through the infrared light cut filter 9, a part of the light emitted from the SHG laser 3 is reflected by the beam splitter 14, and the reflected light, that is, the fundamental wave is converted to a second photodetector. The detection output of the second photodetector 16 is input to the power variable current control means 18. At the time of the wavelength variable current control, the power variable current control means 18 controls the SH based on the output of the second photodetector 16.
The control is performed so that the fundamental wave power from the G laser 3 becomes constant.

On the other hand, in FIG. 19 of the present embodiment, the second harmonic is detected by the first photodetector 15 from the SHG laser 3 via the infrared light cut filter 9, and the first photodetection is performed. Only the detection output of the detector 15 is input to the power variable current control means 18A. Therefore, the power variable current control unit 18A cannot recognize the fundamental wave power from the SHG laser 3, and therefore, in controlling the wavelength variable current, a constant current is applied to the active region 1-1 of the semiconductor laser 1. Injecting.

However, the power variable current control means 1
8A, like the power variable current control means 18, can control the power variable current so that the second harmonic power from the SHG laser 3 becomes constant after the wavelength variable current control, so that more stable Second harmonic power can be obtained.

In FIG. 19, the laser beam of the second harmonic transmitted through the beam splitter 14A is
The reflected light is input to the objective lens 22. The objective lens 22 converges the input second harmonic laser light and irradiates it onto the disk 27. Disk 27
The second harmonic laser light reflected by the objective lens 22
Is reflected by the mirror 21 and input to the beam splitter 14A. The second harmonic laser light from the disk is reflected by the beam splitter 14A and input to the focusing lens 20. The focusing lens 20 converges the second harmonic laser light from the disk and inputs the laser light to the third photodetector 28.

The third photodetector 28 includes a plurality of divided photodetectors in order to generate a servo error signal in an optical disk described later. Third photodetector 28
Is preferably divided into four, and based on the output of each divided photodetector, a focus error is detected by a known astigmatism method or the like, and a tracking error is detected by a known push-pull method or the like. Can be. Also,
Based on the sum of the outputs of the respective photodetectors, information recorded on the disc can be reproduced to obtain a reproduced signal.

The optical disk device configured as above is
When the apparatus is started, the stabilization control of the SHG laser is performed in a state where the disk mounted on a spindle motor (not shown) is rotating.

In the state where a stable and desired output can be obtained as the output of the SHG laser 3, the second harmonic laser beam irradiated on the disk 27 based on the output of the third photodetector 28 Is generated, and a coil 26a, a coil 26b, a leaf spring 25a, and a leaf spring 25a are generated based on the focus error signal.
b, a permanent magnet 24a, and a focus actuator schematically constituted by a permanent magnet 24b.
3 and the objective lens 22 are moved in a direction substantially perpendicular to the disk 27, and the convergence state of the second harmonic laser light irradiated on the disk 27 is controlled. This is called a focus servo.

Also, after operating the focus servo,
Based on the output of the third photodetector 28, a tracking error signal indicating the deviation of the irradiation position of the second harmonic laser beam with respect to the track of the disk 27 is generated, and based on the tracking error signal, a tracking error signal of the second harmonic is generated. The laser beam is controlled so as to follow the track on the disk 27. This is called a tracking servo.

With the focus servo, tracking servo, etc., the information on the disk 27 can be reproduced from the sum of the output signals of the divided photodetectors of the third photodetector.

Further, by controlling the wavelength variable current, SH
In a state where the output of the G laser 3 is stabilized, the power variable current injected into the active region 1-1 of the semiconductor laser 1 is adjusted by the power variable current means 18, and the second harmonic laser light from the SHG laser 3 is adjusted. Is appropriately changed. As a result, the intensity of the second harmonic laser light required for recording information on the disk 27, the intensity of the second harmonic laser light required for erasing the information on the disk 27, and the information on the disk 27 are reduced. The intensity of the second harmonic laser light required for reproduction can be selectively set.

As described above, in the optical disk recording / reproducing apparatus to which the SHG laser stabilization control device of the fifth embodiment is applied, the areal recording density on the optical disk is improved and stable recording / reproducing characteristics are obtained. be able to.

In each of the above embodiments, the intensity of the emitted light of the SHG laser is detected, and the time when the intensity of the emitted light changes stepwise is regarded as the mode boundary.
However, the present invention is not limited to this. When the wavelength of the emitted light of the SHG laser changes stepwise, it is regarded as a mode boundary, and the intensity of the emitted light of the SHG laser and its change at this time may be obtained. Absent.

[0192]

As described above, according to the SHG laser stabilization control device of the present invention, the wavelength variable current is automatically set within a range where the oscillation wavelength of the DBR semiconductor laser cannot cause a mode hop. Thus, the second harmonic power of the SHG output can be stabilized.

Further, even when a plurality of local maxima exist in the second harmonic power of the output light of the SHG laser, the maximum
By accurately recognizing the harmonic power, the temperature of the SHG laser corresponding to the maximum second harmonic power can be determined.

Further, temperature control of the SHG laser can be performed accurately and promptly.

The output characteristics of the semiconductor laser can be kept constant while controlling the current injected into the active region of the semiconductor laser by constant voltage driving.

In the optical disk recording / reproducing device of the present invention, since the above-described SHG laser stabilization control device is applied, the surface recording density on the optical disk can be improved and stable recording / reproducing characteristics can be obtained. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an SHG laser stabilization control device according to a first embodiment of the present invention.

FIG. 2 is a graph showing characteristics of an SHG device.

FIG. 3 is a graph showing a relationship between a wavelength variable current injected into a DBR region of a semiconductor laser and an output wavelength of the semiconductor laser.

FIG. 4 is a graph showing a relationship between a wavelength variable current of a semiconductor laser and a second harmonic power of an SHG laser.

FIG. 5 is a graph used for explaining a wavelength variable current control algorithm according to the first embodiment of the present invention.

FIG. 6 is a flowchart illustrating wavelength variable current control according to the first embodiment of the present invention.

FIG. 7 is a flowchart illustrating a wavelength variable current control according to a modification of the first embodiment of the present invention.

FIG. 8 is a graph used to explain a wavelength variable current control algorithm according to the second embodiment of the present invention.

FIG. 9 is a flowchart illustrating wavelength variable current control according to the second embodiment of the present invention.

FIG. 10 is a flowchart illustrating a wavelength variable current control according to a modification of the second embodiment of the present invention.

FIG. 11 is a block diagram illustrating a schematic configuration of an SHG laser stabilization control device according to a third embodiment of the present invention.

12A is a graph showing the relationship between the temperature of the semiconductor laser and the oscillation wavelength, FIG. 12B is a graph showing the relationship between the temperature of the semiconductor laser and the gap current value at the mode boundary, and FIG. 12C is the temperature of the semiconductor laser. 6 is a graph showing output power characteristics of a semiconductor laser including wavelength characteristics of a DBR region with respect to FIG.

13A is a graph showing the wavelength characteristic of the SHG device with respect to temperature, FIG. 13B is a graph showing the wavelength characteristic of the SHG laser with respect to temperature, and FIG. 13C is based on the assumption that the SHG device has ideal characteristics. , A graph showing the second harmonic power characteristics with respect to the temperature of the SHG laser, and (d) shows the SHG device having a variation characteristic.
A graph showing the characteristics of the second harmonic power with respect to the output wavelength of the HG laser.
6 is a graph showing a characteristic of a second harmonic power with respect to a temperature of an SHG laser on the assumption that a G device is used.

FIG. 14 is a flowchart illustrating control of rough temperature search according to the third embodiment of the present invention.

FIG. 15 is a flowchart illustrating control of fine temperature search according to the third embodiment of the present invention.

FIG. 16 is a flowchart showing another control of the rough temperature search according to the third embodiment of the present invention.

FIG. 17 is a block diagram illustrating a schematic configuration of an SHG laser stabilization control device according to a fourth embodiment of the present invention.

FIG. 18 is a block diagram illustrating a schematic configuration of an SHG laser stabilization control device according to a fifth embodiment of the present invention.

FIG. 19 is a block diagram showing an optical disc recording / reproducing apparatus according to a sixth embodiment of the present invention.

FIG. 20 is a schematic configuration diagram of a conventional blue light source using a domain-inverted waveguide device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 SHG device 3 SHG laser 4 Substrate 5 Temperature variable means 6 Temperature detector 7, 7A Temperature control means 8 Constant current control means 9 Infrared light cut filter 10 Photodetector 11 Current variable means 12 Wavelength variable current control Means 14 Beam splitter 15 First photodetector 16 Second photodetector 17 Current variable means 18 Power variable current control means 21 Mirror 22 Objective lens 23 Lens holder 24a, 24b Permanent magnet 25a, 25b Leaf spring 26a, 26b Coil 27 Disk 28 Third photodetector

Continuation of front page (56) References JP-A-8-181390 (JP, A) IEEE Proceedings-J, 138 [2], p. 171-177 (58) Field surveyed (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 G02F 1/37

Claims (19)

(57) [Claims] 1. A semiconductor laser having a scan <br/> step varying makes DBR portion wavelength in response to a change in the wavelength variable current,
An SHG laser including a wavelength conversion element for converting the wavelength of the emitted light of the semiconductor laser into a short wavelength; a light detecting unit for detecting a stepwise change in the wavelength of the emitted light of the SHG laser; A current variable means for changing a wavelength variable current supplied to the DBR unit to change the current , and a wavelength variable current by controlling the current variable means.
Of the light detection means.
Gap of the tunable current that maximizes the step change in force
Output current at which the peak current value and the output of the photodetector become maximum.
Find the large current value and determine the relationship between the gap current value and the maximum output current value.
A predetermined current value to the gap current value.
Or an SHG laser stabilization control device comprising a wavelength variable current control means for setting a wavelength variable current value by subtraction . 2. The SHG laser stabilization control device according to claim 1, wherein said light detecting means detects an output light intensity of said SHG laser. 3. The tunable current control means changes the tunable current at least once after the apparatus is started, in a range from a sufficiently small value to a range including a tunable current at which the emission light intensity of the SHG laser is maximized. 2. The SHG laser stabilization control device according to claim 1, wherein the control of the wavelength variable current is performed thereafter. 4. The variable wavelength current control means controls the current variable means to increase or decrease the wavelength variable current, and the detected SHG laser output changes stepwise. A first gap current value of the wavelength variable current and a next second gap current value adjacent to the first gap current value are obtained, and based on a difference current between the first and second gap current values, the gap current value is calculated. 3. The SHG laser stabilization control device according to claim 2, wherein a predetermined current value to be added or subtracted is obtained. 5. The variable wavelength current control means controls the current variable means to perform either a gradual increase or a gradual decrease of the wavelength variable current, and the detected light intensity of the SHG laser is stepwise changed. First of changed wavelength tunable current
A gap current value and a next second gap current value adjacent to the first gap current value are obtained, and 20 to 80% of a difference current between the first and second gap current values is added to and subtracted from the gap current value. 3. The SHG laser stabilization control device according to claim 2, wherein any one of them is obtained as a predetermined current value. 6. The variable wavelength current control means changes the variable wavelength current by controlling the variable current means, and controls the variable wavelength current I to maximize the output of the light detection means.
While determining LDpmax, the wavelength-variable current is gradually increased, and a gap current value ILDspmax corresponding to the wavelength-variable current at which the stepwise change in the output of the photodetector is maximized is determined. Current IL
If not more than Dpmax, a predetermined current value is added to the gap current value ILDspmax. If the gap current value ILDspmax exceeds the maximum wavelength variable current ILDpmax, the gap current value ILDspma
3. The SHG laser stabilization control device according to claim 2, wherein a wavelength variable current value is set by subtracting a predetermined current value from x. 7. The variable wavelength current control means controls the current variable means to change the variable wavelength current so that the output of the light detection means is maximized.
While determining LDpmax, the wavelength-variable current is gradually reduced, and a gap current value ILDspmax corresponding to the wavelength-variable current at which the stepwise change in the output of the photodetector is maximized is determined. Current IL
If Dpmax or less, a predetermined current value is subtracted from the gap current value ILDspmax, and if the gap current value ILDspmax exceeds the maximum wavelength variable current ILDpmax, the gap current value ILDsp
The SHG laser stabilization control device according to claim 2, wherein a wavelength variable current value is set by adding a predetermined current value to max. 8. The variable wavelength current control means controls the current variable means to increase or decrease the wavelength variable current so that the stepwise change in the output of the light detection means is maximized. Determine the gap current value ILDspmax of the wavelength variable current, and further perform either the gradual increase or the gradual decrease of the wavelength variable current to determine the gap current value of the wavelength variable current when the photodetector output changes stepwise, The wavelength variable current value is set by calculating a difference current between the determined gap current values and adding or subtracting a predetermined current value less than the difference current to the gap current value ILDspmax. SHG laser stabilization control device. 9. The tunable current control means controls the current variability means to perform either a gradual increase or a gradual decrease of the tunable current, so that the stepwise change in the output of the light detection means is maximized. Determine the gap current value ILDspmax of the wavelength variable current, and further perform either the gradual increase or the gradual decrease of the wavelength variable current to determine the gap current value of the wavelength variable current when the photodetector output changes stepwise, A difference current between the determined gap current values is determined, and 20% of the difference current with respect to the gap current value ILDspmax.
3. The S according to claim 2, wherein the wavelength variable current value is set by performing either addition or subtraction of a predetermined current value that is 〜80%. 4.
HG laser stabilization controller. 10. The SHG laser stabilization control device according to claim 2, wherein the SHG laser has a configuration in which the semiconductor laser and the wavelength conversion element are integrated on the same base material. 11. A temperature varying means for changing a temperature of the SHG laser, a temperature detector for detecting a temperature of the SHG laser, and a temperature of the SHG laser becoming a predetermined temperature based on an output of the temperature detector. 3. The SHG laser stabilization control device according to claim 2, further comprising a temperature control means for controlling the temperature variable means. 12. The SHG laser stabilization according to claim 2, wherein the wavelength variable current for changing the wavelength of the semiconductor laser is controlled while the power variable current for changing the intensity of the emitted light of the semiconductor laser is controlled to be constant. Control device. 13. The SHG laser stabilization control according to claim 2, further comprising a filter that cuts infrared light of the SHG laser emission light, and detecting the emission light of the SHG laser through the infrared light cut filter. apparatus. 14. The SHG laser stabilization control device according to claim 1, wherein the light detection means detects a light intensity of a second harmonic of the SHG laser output. 15. The SHG laser, wherein a condenser lens for condensing light emitted from the wavelength conversion element on the photodetector is arranged on an output side of the wavelength conversion element. The SHG laser stabilization control device according to claim 1. 16. A method for adjusting a wavelength in response to a change in a wavelength variable current.
Semiconductor laser having a DBR portion that changes stepwise
The wavelength of the emitted light of the semiconductor laser to a shorter wavelength.
Wave of emitted light of SHG laser including wavelength conversion element for conversion
A light detection step of detecting a stepwise change in length , and the DBR section for changing the wavelength of the semiconductor laser.
Variable step for changing the wavelength variable current supplied to the
And whether the wavelength variable current gradually increases or decreases in the current variable step.
By doing this, the stepwise change in the light detection step
Gap current value of wavelength tunable current to be maximum and the light detection
Find the maximum output current value that maximizes the output in the process, and
The gap is determined by the relationship between the gap current value and the maximum output current value.
By adding or subtracting a predetermined current value from the current value
Variable current control step for setting a variable wavelength current value
And a method for controlling the stabilization of the SHG laser. 17. The method according to claim 17, wherein the tunable current control step comprises:
In the flow variable step, the wavelength variable current is changed to
The wavelength tunable current ILDpmax that maximizes the output in the process
Together with gradually increasing the wavelength variable current, in the light detection step
Tunable current that maximizes the step change in
Find the corresponding gap current value ILDspmax
When the current value ILDspmax is less than the maximum tunable current ILDpmax
If there is, add a predetermined current value to the gap current value ILDspmax
And the wavelength variable current IL having the maximum gap current value ILDspmax.
If Dpmax is exceeded, the predetermined current is deducted from the gap current value ILDspmax.
17. The variable wavelength current value is set by subtracting the flow value.
3. The method for controlling stabilization of an SHG laser according to item 1. 18. The variable-wavelength current control step includes the step of:
In the flow variable step, the wavelength variable current is changed to
The wavelength tunable current ILDpmax that maximizes the output in the process
Along with this, the wavelength variable current is gradually reduced, and
Tunable current that maximizes the step change in
Find the corresponding gap current value ILDspmax
When the current value ILDspmax is less than the maximum tunable current ILDpmax
If there is, the specified current value is subtracted from the gap current value ILDspmax.
Tunable current with the maximum gap current value ILDspmax
If ILDpmax is exceeded, a predetermined gap current value ILDspmax
2. The wavelength variable current value is set by adding current values.
7. The method for controlling stabilization of an SHG laser according to item 6. 19. An optical disk recording / reproducing apparatus comprising: the SHG laser stabilization control device according to claim 1; and optical means for condensing the emitted light of the SHG laser on the optical disk in the SHG laser stabilization control device.