JPH09189930A - Wavelength converting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the output power of SHG laser light outputted from an SHG element. SOLUTION: This converting device uses a dynamic longitudinal single-mode laser such as a DBR laser element 2 as a basic wave light source and makes basic wave laser light L0 , generated by the dynamic longitudinal single-mode laser, incident on the SHG element 3, which outputs SHG laser light L1 of short wavelength. At this time, the device is provided with a driving current modulating means 6 which imposes high-frequency modulation on a driving current I supplied to the dynamic longitudinal single-mode laser with current width including at least one of the maximum and minimum values of the output of the SHG laser light, and the dynamic longitudinal single-mode laser is driven with the high-frequency modulated driving current (i).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light wavelength converter, and more particularly, to an SHG laser using a dynamic longitudinal single mode laser and an SHG (Second Harmonic Generation) element. The present invention relates to a wavelength conversion device that generates light.

[0002]

2. Description of the Related Art As one of the next-generation optical discs, a DVD (digital video disc) in which the recording information density is increased is about to be provided. In order to increase the recording density of optical discs including this DVD,
It is necessary to shorten the wavelength of laser light used for optical pickups. This is because the shorter the wavelength of the laser light, the more the beam spot diameter can be narrowed down, and the higher the density can be made.

For such a purpose, research and development of a blue / green small-sized semiconductor laser having a short wavelength has been carried out, but it is still at a laboratory level and has not been put into practical use. Therefore, the SHG laser is used as one method for obtaining a blue / green laser beam having a short wavelength. This SHG laser allows the fundamental laser light to pass through the SHG element which is a non-linear optical element.
It is intended to obtain a laser beam of a short wavelength consisting of a half wavelength of the fundamental wave.

By the way, the SHG element has a very narrow fundamental wave width, for example, a quasi phase matching (QPM) type S
In the HG element, the full width at half maximum of SHG is about 0.2 nm
Only about. In order to satisfy this severe operating condition,
As a fundamental wave light source, a wavelength converter using a dynamic vertical single mode laser with a small wavelength change, for example, a DBR (distributed Bragg reflection type) laser element or a DFB (distributed feedback type) laser element is used.

FIG. 8 shows the DBR laser device and SHG.
The structure of the conventional wavelength converter using an element is shown. In the figure, 1 is a laser drive power source, 2 is a DB for generating a fundamental wave
R laser element, 3 is SHG for generating SHG laser light
Elements 4 are temperature control elements, and 5 is a temperature controller.

When a driving current is supplied from the laser driving power source 1 to the DBR laser element 2, the DBR laser element 2 outputs a laser beam L ₀ as a fundamental wave. By inputting this fundamental wave laser light L ₀ into the SHG element 3, the SHG laser light L having a half wavelength of the fundamental wave is emitted from the SHG element 3 based on the nonlinear optical characteristics.
₁ is output. In order to prevent temperature change, D
The BR laser element 2 and the SHG element 3 are temperature-controlled by a temperature control element 4 and a temperature controller 5.

[0007]

However, the above conventional wavelength converter also has the following problems.
That is, the wavelength of the fundamental wave laser light L ₀ output from the DBR laser element 2 is not a completely constant value, and as shown in FIG. fluctuate. Due to this periodic wavelength fluctuation, for example, the wavelength of the DBR laser light has a maximum value λ.
When SHG output power when the ₁ is temperature-controlled wavelength conversion device by the temperature control element 4 and the temperature controller 5 so as to maximize the output power of the SHG laser light L ₁ output from the SHG element 3 in FIG. 10 As shown, it exhibits a non-monotonically increasing characteristic that it oscillates with a change in the drive current and increases while cyclically changing in a sawtooth shape.

By the way, when this kind of laser light source is used for an optical pickup of an optical disk or the like, the APC (Automatic Powe) is used so that the output power of the laser light becomes constant.
r Control) is required. The laser light source is shown in Figure 10.
In the case where the SH optical power characteristic is as described above, if the APC occurs at a position where the output power sharply changes in the vertical direction, the output power changes abruptly even with a slight change in the drive current, and the APC operation becomes unstable. I will end up. When such a phenomenon occurs, for example, in the case of an optical disc, the focus servo and the tracking servo become out of order, which causes a problem that reproduction becomes impossible.

The present invention has been made to solve the above-mentioned problems, and an SHG output from an SHG element is provided.
It is an object of the present invention to provide a wavelength conversion device that stabilizes the output power of laser light.

[0010]

In order to solve the above problems, the present invention employs the following means. That is,
The invention according to claim 1 uses a dynamic longitudinal single-mode laser as a fundamental wave light source, and the fundamental wave laser light generated by the dynamic longitudinal single-mode laser is incident on the SHG element to thereby cause a short wavelength from the SHG element. In the wavelength conversion device configured to output the SHG laser light, the driving current supplied to the dynamic longitudinal single-mode laser has at least one of the maximum value and the minimum value of the oscillation of the output of the SHG laser light. It is characterized in that drive current modulating means for high frequency modulation with a current width including one or more is provided, and the dynamic longitudinal single mode laser is driven by the high frequency modulated drive current.

With such a configuration, when the output power of the SHG laser light output from the SHG element is detected as the average value of the oscillation outputs corresponding to the maximum value and the minimum value,
The SH optical power characteristic of the wavelength conversion device can be a monotonically increasing curve. Therefore, even if the drive current slightly fluctuates up and down from the set position, the output power of the SHG laser light output from the SHG element can be prevented from abruptly changing, and the output power can be stabilized.

The invention according to claim 2 uses a dynamic longitudinal single-mode laser as a fundamental wave light source, and
A quasi-phase matching type element is used as the HG element, and a fundamental wavelength laser beam generated by the dynamic longitudinal single mode laser is incident on the SHG element so that the SHG element outputs a short wavelength SHG laser beam. In the above wavelength converter, the SHG element is phase-matched with a first polarization inversion layer having a polarization inversion pitch that is phase-matched with the maximum value of the oscillation wavelength of the dynamic longitudinal single-mode laser, and with a minimum value of the oscillation wavelength. The SHG element is provided with a second polarization inversion layer having a polarization inversion pitch.

With such a configuration, the output power of the SHG laser light output from the SHG element is the SHG wave generated in the first polarization inversion layer and the SHG wave generated in the second polarization inversion layer. And the SH optical power characteristic of the wavelength conversion device can be a monotonically increasing curve. Therefore, even if the drive current slightly fluctuates up and down from the set position, the output power of the SHG laser light output from the SHG element can be prevented from abruptly changing, and the output power can be stabilized.

Further, the invention according to claim 3 uses a dynamic longitudinal single mode laser as a fundamental wave light source,
A quasi-phase matching type element is used as an SHG element, and a fundamental wavelength laser beam generated by the dynamic longitudinal single mode laser is incident on the SHG element so that the SHG element outputs a short wavelength SHG laser beam. In the wavelength converter, the SHG element is provided with a polarization inversion layer having a polarization inversion pitch modulated so as to continuously perform phase matching from the minimum value to the maximum value of the oscillation wavelength of the dynamic longitudinal single mode laser. It is characterized by using an SHG element.

With such a configuration, even if the oscillation wavelength of the dynamic longitudinal single-mode laser fluctuates between the minimum value and the maximum value, the SHG laser light output from the SHG element is output from the SHG element. Output power does not change, and the SH optical power characteristic of the wavelength conversion device can be a monotonically increasing curve. Therefore, even if the drive current slightly fluctuates up and down from the set position, the output power of the SHG laser light output from the SHG element can be prevented from abruptly changing, and the output power can be stabilized.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a first example of the wavelength conversion device according to the present invention. FIG. 1 is a diagram showing the configuration of a wavelength conversion device, and FIG. 2 is its output power characteristic diagram. In FIG. 1, 1 is a laser drive power source, 2 is a DBR laser element for generating a fundamental wave, 3 is an SHG element for generating an SHG laser beam, 4 is a temperature control element, 5 is a temperature controller, and 6 is a drive current modulator. is there. In addition,
The same or corresponding parts as those of the conventional device shown in FIG. 8 are designated by the same reference numerals.

In this first example, as shown in FIG.
The drive current I supplied to the R laser element 2 is high-frequency modulated with a current width including at least one of a maximum value and a minimum value of oscillation of the oscillation output of the SHG laser light centered on the current value. The DBR laser element 2 is driven by the high-frequency modulated drive current i.

The drive current modulator 6 performs the modulation operation of the drive current I described above, and supplies the DBR laser element 2 with the high-frequency modulated drive current i to drive the DBR laser element 2. Thus, the drive current I
Is high-frequency-modulated with a predetermined current width using drive current i
When the BR laser element 2 is driven and the output power of the SHG laser light output from the SHG element 3 is detected as the average value of the periodic fluctuations thereof, as shown by the solid line in FIG. It becomes a monotonically increasing curve.

Therefore, no matter where the drive current is set, the output power detected as the average value of the SHG laser light L ₁ output from the SHG element 3 smoothly increases and decreases by a monotonous increase. As a result, even if the drive current value slightly fluctuates up and down around the set value, the SHG laser light L
_The output power detected as the average value of ₁ does not suddenly change, and the output power can be apparently stabilized.

In order to detect the SHG laser light L ₁ as an average value, for example, the frequency component of the periodic fluctuation of the output power of the SHG laser light generated by the modulation of the DBR laser drive current is detected by the laser light detector. The modulation frequency of the drive current of the DBR laser may be increased so that the frequency becomes too high. A frequency filter that cuts the frequency component of the periodic fluctuation of the output power of the SHG laser light detected by the laser light detector may be used.

As the frequency of the high frequency signal for modulating the drive current, a high frequency which does not adversely affect the intended information signal is used. For example, in the case of an optical disc, the signal frequency band of recorded information is about several tens of MHz, so that it is sufficient to perform modulation using a frequency sufficiently higher than this frequency, for example, a high frequency of about 100 MHz.

FIGS. 3 to 5 show a second example of the wavelength conversion device according to the present invention. 3 is a diagram showing a configuration of a wavelength conversion device according to a second example, FIG. 4 is an enlarged perspective view showing a structural example of an SHG element used in the second example, and FIG. 5 is an SH optical output power characteristic diagram. .

In the second example, the circuit configuration itself is the same as that of the conventional device (FIG. 8), but the SHG element 3A used has special characteristics. That is, as shown in the structure in FIG. 4, for example, a QPM (quasi phase matching) SHG element is used, and the polarization inversion pitch P1 for phase matching at the maximum wavelength λ ₁ in FIG. The first polarization inversion layer 8 and the second polarization inversion layer 8 having the polarization inversion pitch P2 phase-matched at the minimum wavelength λ ₂ in FIG. 9 are formed.

As described above, when the first domain-inverted layer 8 having the domain-inverted pitch P1 and the second domain-inverted layer 9 having the domain-inverted pitch P2 are formed in series, the SHG element 3 outputs the SHG. As shown in FIG. 5, the output power of the laser light L ₁ is a combination of the SHG wave generated by the polarization inversion pitch P1 and the SHG wave generated by the polarization inversion pitch P2. At this time, the SHG wave generated by the polarization inversion pitch P1 and the SHG wave generated by the polarization inversion pitch P2 are inverted waveforms in which the maximum and minimum positions are shifted by 180 degrees. As shown in FIG. 5, the wave L ₁ has a monotonically increasing curve without unevenness.

Therefore, even if the drive current value slightly fluctuates up and down around the set value, the output power of the SHG laser beam L ₁ does not suddenly fluctuate, and the output power is stabilized. You can

In FIG. 4, the first polarization inversion layer 8
Then, the position of the second domain-inverted layer 9 may be reversed in the front-back direction. In addition, the first polarization inversion layer 8 and the second polarization inversion layer 9
Need not be integrally formed on the substrate 7, but the same effect can be obtained by separately forming SHG elements having the respective polarization inversion layers and optically coupling them.

FIGS. 6 and 7 show a third example of the wavelength conversion device according to the present invention. FIG. 6 shows S used in the third example.
FIG. 7 is an enlarged perspective view showing a configuration example of the HG element, and FIG. 7 is an SH optical output power characteristic diagram thereof. Since the circuit configuration itself is the same as that of the conventional device (FIG. 8), its illustration is omitted.

This third example also gives the SHG element 3B to be used special characteristics. That is, as shown in the structure of FIG. 6, the SH of the QPM (quasi phase matching) method is used.
A G element is used, and the minimum wavelength λ _{2 in} FIG.
To the maximum wavelength λ ₁ of the domain-inverted layer 10 having a domain-inverted pitch modulated so as to be continuously phase-matched.

As described above, when the polarization inversion layer 10 having the polarization inversion pitch modulated so that the phase is continuously matched from the minimum wavelength to the maximum wavelength is formed, the SHG laser light L ₁ output from the SHG element has a wavelength of The output power fluctuation due to the fluctuation disappears, and a monotonically increasing curve is obtained as shown in FIG.

Therefore, even if the drive current value slightly fluctuates up and down around the set value, the output power of the SHG laser light L ₁ does not suddenly fluctuate, and the output power can be stabilized.

The wavelength of the DBR laser light is a minimum value λ.
When the temperature is controlled so that the SHG output power becomes maximum at the time of ₂ (Fig. 9), the SH optical power characteristic curve is shown in Fig. 1.
However, this case can be implemented in exactly the same manner.

[0032]

As described above, according to the first aspect of the invention, a dynamic longitudinal single mode laser is used as a fundamental wave light source, and a fundamental wave laser beam generated by the dynamic longitudinal single mode laser is used. Incident on the SHG element
In a wavelength conversion device configured to output a short wavelength SHG laser light from an HG element, a driving current supplied to the dynamic longitudinal single mode laser is set to a maximum value and a minimum value of oscillation of the output of the SHG laser light. Since a driving current modulating means for high-frequency modulating with a current width including at least one of each of the above is provided, and the dynamic longitudinal single mode laser is driven by the high-frequency modulated driving current, the SH of the wavelength conversion device is provided. The optical power characteristic can be a monotonically increasing curve. Therefore, even if the drive current slightly fluctuates up and down from the set position, the output power of the SHG laser light output from the SHG element does not suddenly fluctuate,
It is possible to stabilize the output power.

According to the second aspect of the present invention,
A dynamic longitudinal single mode laser is used as a fundamental wave light source and a quasi phase matching type element is used as an SHG element, and the fundamental wave laser light generated by the dynamic longitudinal single mode laser is incident on the SHG element. By SHG
In a wavelength conversion device configured to output a short wavelength SHG laser light from an element, the first SHG element has a polarization inversion pitch that is phase-matched at a maximum value of an oscillation wavelength of the dynamic longitudinal single mode laser. A polarization inversion layer,
Since the SHG element including the second polarization inversion layer having the polarization inversion pitch that is phase-matched with the minimum value of the oscillation wavelength is used, the SH optical power characteristic of the wavelength conversion device can be a monotonically increasing curve. Therefore, even if the drive current slightly fluctuates up and down from the set position, the output power of the SHG laser light output from the SHG element does not suddenly fluctuate, and the output power can be stabilized.

Further, according to the invention of claim 3, the dynamic longitudinal single mode laser is used as the fundamental wave light source and the quasi phase matching type element is used as the SHG element. Of the fundamental wave laser beam generated by the SHG element
In a wavelength conversion device configured to output a short wavelength SHG laser light from an HG element, the SHG element is configured to continuously perform phase matching from a minimum value to a maximum value of an oscillation wavelength of the dynamic longitudinal single mode laser. Since the SHG element provided with the domain-inverted layer having the domain-inverted pitch modulated in the above is used, the SH optical power characteristic of the wavelength conversion device can be a monotonically increasing curve. Therefore, even if the drive current slightly fluctuates up and down from the set position, the output power of the SHG laser light output from the SHG element does not suddenly fluctuate, and the output power can be stabilized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first example of a wavelength conversion device according to the present invention.

FIG. 2 is a SH optical power characteristic diagram of the first example.

FIG. 3 is a diagram showing a second example of the wavelength conversion device according to the present invention.

FIG. 4 is an enlarged perspective view showing a structural example of an SHG element used in a second example.

FIG. 5 is a SH optical power characteristic diagram of a second example.

FIG. 6 is an enlarged perspective view showing a structural example of an SHG element used in a third example.

FIG. 7 is a SH optical power characteristic diagram of the second example.

FIG. 8 is a diagram showing a configuration of a conventional wavelength conversion device.

FIG. 9 is a wavelength characteristic diagram of a DBR laser device.

FIG. 10 is an SH optical power characteristic diagram of the DBR laser device when the temperature is controlled so that the SHG output power becomes maximum when the wavelength is the maximum value.

FIG. 11 is an SH optical power characteristic diagram of the DBR laser device when the temperature is controlled so that the SHG output power is maximized when the wavelength is the minimum value.

[Explanation of symbols]

1 Laser Driving Power Supply 2 DBR Laser Element 3 SHG Element 3A SHG Element 3B SHG Element 4 Temperature Control Element 5 Temperature Controller 6 Drive Current Modulator 7 SHG Element Substrate 8 First Polarization Inversion Layer 9 Second Polarization Inversion Layer 10 Modulation Polarization inversion layer consisting of the defined polarization inversion pitch L ₀ fundamental wave laser light L ₁ SHG laser light λ ₁ DBR laser element oscillation wavelength maximum value λ ₂ DBR laser element oscillation wavelength minimum value

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Teruichi Watanabe 6-1, 1-1 Fujimi, Tsurugashima City, Saitama Pioneer Research Institute

Claims (3)

[Claims] 1. A dynamic longitudinal single-mode laser is used as a fundamental wave light source, and the fundamental wave laser light generated by the dynamic longitudinal single-mode laser is incident on an SHG element.
In a wavelength conversion device adapted to output a short wavelength SHG laser light from a G element, a driving current supplied to the dynamic longitudinal single mode laser is set to a maximum value and a minimum value of oscillation of the output of the SHG laser light. A wavelength conversion device for driving the dynamic longitudinal single-mode laser by means of the high-frequency-modulated drive current. 2. A dynamic longitudinal single mode laser is used as a fundamental wave light source, and a quasi phase matching type element is used as an SHG element, and the fundamental wave laser light generated by the dynamic longitudinal single mode laser is used as the SHG element. A wavelength conversion device configured to output an SHG laser beam of a short wavelength from an SHG element by entering the element, wherein the SHG element is a polarization that performs phase matching at a maximum value of an oscillation wavelength of the dynamic longitudinal single mode laser. A wavelength conversion device comprising a first polarization inversion layer having an inversion pitch and an SHG element having a second polarization inversion layer having a polarization inversion pitch that is phase-matched with a minimum value of an oscillation wavelength. 3. A dynamic longitudinal single mode laser is used as a fundamental wave light source, and a quasi phase matching type element is used as an SHG element, and the fundamental wave laser light generated by the dynamic longitudinal single mode laser is used as the SHG element. A wavelength conversion device configured to output an SHG laser beam of a short wavelength from an SHG element by entering the element, wherein the SHG element is a continuous oscillation from a minimum value to a maximum value of the oscillation wavelength of the dynamic longitudinal single mode laser. A wavelength conversion device using an SHG element provided with a domain-inverted layer having a domain-inverted pitch modulated so as to be phase-matched.