JPH11232680A - Short wavelength light source and, optical recording apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stable higher harmonics both at a continuous operation and at a modulation operation by setting a variation of an average output at the modulation operation with a short wavelength light source and a variation for the continuous operation within a specific value. SOLUTION: A wavelength variable DBR semiconductor laser is used at an SHG blue laser comprising an optical waveguide type wavelength conversion device and a semiconductor laser to make an average power at a modulation operation equal to a power at a continuous operation. Modulation is carried out to make an average output of the semiconductor laser constant, thereby setting a variation of the average output within 20%. Since the average outputs of the semiconductor laser as a fundamental harmonic at the continuous operation and modulation operation are made equal, a temperature of a semiconductor laser chip and an average carrier density in an active layer can be made constant and an oscillation wavelength of the wavelength variable DBR semiconductor laser can be maintained constant, whereby stable modulation characteristics for a blue light are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short wavelength light source comprising a semiconductor laser and a wavelength conversion device, and a recording / reproducing apparatus equipped with the short wavelength light source.

[0002]

2. Description of the Related Art In recent years, the commercialization of optical recording media capable of recording, reproducing, and erasing information, and the research and development of high-density rewritable optical recording media capable of recording higher-quality moving images have been actively conducted. It has been done.

[0003] As a rewritable optical recording medium, a disk-shaped substrate is provided with a T-type substrate such as GeSbTe, GeSnTe or InSe.
e, Se based chalcogenide thin film or InS
A phase-change optical recording medium including a semimetal thin film such as b as a recording layer is known. Also, a magneto-optical recording medium including a thin metal film such as TbFeCo as a recording layer is known. There is also a write-once optical recording medium using a dye material.

In a phase-change optical recording medium, a recording laser beam is instantaneously irradiated on a recording thin film layer made of the above-mentioned phase-change material, and the irradiated portion is locally heated to a predetermined temperature. The irradiated portion is converted to a crystalline state when the ultimate temperature is equal to or higher than the crystallization temperature, and is converted to an amorphous state when rapidly cooled after melting beyond the melting point. Either the amorphous state or the crystalline state is defined as a recorded state or an erased state (unrecorded state), and by forming a pattern corresponding to an information signal, reversible information recording or erasing is performed. . Optical characteristics are different between the crystalline state and the amorphous state, and a signal can be reproduced by optically detecting a change in reflectance or a change in transmittance using the difference due to the optical characteristics.

In a magneto-optical recording medium, a focused laser beam is irradiated and locally heated to a predetermined temperature. Information is recorded or erased by applying a magnetic field simultaneously with the heating and inverting the magnetization direction of the magneto-optical recording thin film according to the information.

Next, a modulation method used when information is recorded on a phase change optical recording medium or a magneto-optical recording medium will be described. In a phase change optical recording medium, a modulation strategy as shown in FIG. 13 is used. Four-level modulation of a reproduction level, an erasure level, a recording level, and a cooling level is performed. First, the address signal is reproduced at the reproduction level, and then the laser output is switched to the erase level. The previously recorded information is erased and the laser output is switched to the recording level where the information is recorded.

FIG. 13 shows a 3T signal and a 5T signal as an example. The 3T signal is a 1.5T single pulse
It consists of a cooling pulse of 0.5T. Also,
The 4T signal has a starting pulse of 1.0T and an intermediate pulse of 0.5T.
It is composed of a terminal pulse of 1.0T and a cooling pulse of 0.5T, and a pulse of 4T or more has a configuration in which an intermediate pulse is repeated.

In the magneto-optical recording medium, various recording methods have been proposed by modulating a magnetic field and a laser output. There are (1) pulse magnetic field + DC output, (2) pulse magnetic field + pulse output, and (3) DC magnetic field + pulse output. FIG. 14 illustrates an example of the method of (2) pulse magnetic field + pulse output as an example.

FIG. 14A shows a magnetic field current, and FIG. 14B shows a driving current of the semiconductor laser. When recording a 1T mark, the magnetic field current is inverted at 1T. At this time, the laser drive current is always modulated in a single period T. By changing the period of the magnetic field current, marks such as 2T and 3T can be recorded.

As a technique for realizing a high density optical disc, a short-wavelength light source in the blue / green region has attracted attention. As a technology for shortening the wavelength, a semiconductor laser and a quasi phase matching (hereinafter referred to as QPM) type optical waveguide type wavelength conversion (Yamamoto et al., Optics Letters Vol.16, No.15, 1156)
(1991)) Second harmonic generation using a device (hereinafter referred to as S
HG).

[0011]

When a random signal is recorded on a phase-change optical disk, a pulse signal having a length of 3T to 11T is formed in order to thermally change the crystal state.
When the mark recording of T to 11T is performed, each mark is distorted. Therefore, normally, mark recording is performed by a multi-pulse as shown in FIG.

With a short wavelength light source composed of a wavelength conversion device and a DBR semiconductor laser, it is easy to obtain a pulse output at a single frequency, but a pulse width and a peak are required to perform various types of multi-pulses and recording compensation. It was difficult to change the output.

Therefore, the present invention solves the above problems,
It is an object of the present invention to provide an optical recording / reproducing apparatus capable of recording high-density information on a phase-change optical disk or a magneto-optical disk using a short wavelength light source including a wavelength conversion device and a tunable DBR semiconductor laser.

[0014]

In order to solve the above-mentioned problems, a short-wavelength light source according to the present invention comprises: (1) at least a distributed Bragg reflection type semiconductor laser and a wavelength conversion device; When the intensity of a semiconductor laser output is modulated by modulating a current or a voltage and the intensity of a harmonic light output obtained by wavelength conversion is modulated, an average laser output or an average operating current (voltage) of the distributed Bragg reflection type semiconductor laser is used.
Is intensity-modulated so that the variation is within ± 20%.

The optical recording apparatus of the present invention comprises: (2) a short wavelength light source comprising at least a semiconductor laser and a wavelength conversion device, and a magnetic field modulator for performing magnetic field modulation. The short-wavelength light output emitted from the light source is modulated into three values of Pa, Pb and Pc (Pa>Pb> Pc), the short-wavelength light output is set to Pb, and the signal in the address area is reproduced. When the optical output is intensity-modulated by Pa and Pb, magnetic field modulation is performed to erase and record marks.

Further, the optical recording apparatus of the present invention comprises: (3) a semiconductor laser and a wavelength conversion device, wherein an optical modulator is formed on the wavelength conversion device, and the drive current of the semiconductor laser is reduced. The short-wavelength optical outputs Pa and Pb (Pa> Pb) are obtained by modulating, and the short-wavelength optical outputs Pc and Pd (Pa>Pc> Pd) are obtained by modulating the voltage applied to the optical modulator. To reproduce, to erase by Pc, and to record by Pa.

In the short wavelength light source of the present invention, (4) the distributed Bragg reflection type semiconductor laser and the wavelength conversion device are mounted on the submount such that the surfaces on which the junction side and the optical waveguide side are formed are in contact with each other. Things.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION As an optical waveguide type wavelength conversion device, a wavelength conversion device of a quasi-phase matching system is most noticed. Mg-doped used as substrate
LiNbO ₃ has a large nonlinear optical constant and a small change in light-induced refractive index, and is a promising substrate for obtaining high-output short-wavelength light. However, in order to realize wavelength conversion with high efficiency, it is necessary to match the wavelength of the semiconductor laser, which is the fundamental wave, with the phase matching wavelength of the wavelength conversion device, and its allowable wavelength width is as small as 0.1 nm.

On the other hand, a wavelength tunable DBR semiconductor laser used as a semiconductor laser that is a fundamental wave has a DBR region for fixing and changing the wavelength, and a current of approximately 2 nm is obtained by injecting current into the DBR region. A variable range can be realized. However, the oscillation wavelength is the active layer temperature,
Since it changes depending on the temperature of the DBR region, the carrier density in the active layer, and the like, it is difficult to maintain the absolute wavelength in any state. In particular, when the laser output is intensity-modulated, the chip temperature and carrier density of the semiconductor laser greatly change, so that the oscillation wavelength shifts, and as a result, multi-mode oscillation and longitudinal mode shift are likely to occur (there is a case where the DBR region is provided). A Fabry-Perot semiconductor laser that does not have a wavelength spread to about 2 nm, but a wavelength tunable DBR semiconductor laser spreads to about 0.3 nm.)

The multimode or longitudinal mode shift of the oscillation wavelength causes deterioration of the modulation waveform and deterioration of the conversion efficiency. In particular, when the peak current at the time of modulation is multi-level modulated, or when the operation is switched from the continuous operation to the modulation operation, it is difficult to obtain stable modulation characteristics due to large changes in the semiconductor laser chip temperature and carrier density.

In a wavelength tunable DBR semiconductor laser, the oscillation wavelength changes due to a change in semiconductor laser chip temperature, carrier density, and the like. Therefore, when the average output during modulation changes, the DBR current capable of phase matching also changes. I will.

Specifications required for a light source for application to an optical disc are modulation characteristics with rise and fall times of several ns or less (square wave). In the present invention, the oscillation wavelength shift during modulation is suppressed by making the chip temperature and the carrier density of the wavelength-tunable DBR semiconductor laser uniform, or the modulation function formed on the wavelength conversion device by operating the semiconductor laser at a constant output. It is intended to realize modulation characteristics satisfying the specifications of the optical disk by performing intensity modulation or the like.

Hereinafter, description will be made with reference to the drawings. (Embodiment 1) In this embodiment, in an SHG blue laser composed of an optical waveguide type wavelength conversion device and a semiconductor laser, the average power during the modulation operation and the power during the continuous operation are made the same, thereby achieving a stable operation. A method of obtaining a modulated blue light will be described. In this embodiment, a tunable DBR semiconductor laser is used as the semiconductor laser.

FIG. 1 is a schematic configuration diagram of an SHG blue laser composed of a wavelength tunable DBR semiconductor laser and an optical waveguide type wavelength conversion device. In the optical waveguide type wavelength conversion device 1, a periodically domain-inverted region 3 and a proton exchange optical waveguide 4 are formed on a Mg-doped LiNbO ₃ substrate 2. The periodically poled region 3 was formed by a two-dimensional electric field application method. A comb-shaped electrode and a parallel electrode with a period of 3.2 μm were formed on the + X substrate surface, and Ta was deposited as a bottom electrode on the −X substrate surface. While applying a voltage of 4 V between the front and back of the substrate, a pulse voltage of 0.4 V and a pulse width of 100 mS was applied to the + X surface to form a domain-inverted region.

Next, after the electrodes were removed by etching, a striped mask was formed, and proton exchange was performed in pyrophosphoric acid to form an optical waveguide 4. The optical waveguide 4 has a width of 4 μm,
It is 2 μm deep and 10 mm long. The end face of the optical waveguide 4 is coated with a non-reflection coating.

The wavelength conversion characteristics and the modulation characteristics were evaluated.
The tunable DBR semiconductor laser 5 includes an active region 6 and a DBR.
Al consisting of region 7 with a wavelength of 851 nm and a laser output of 100 mW
It is a GaAs semiconductor laser. By injecting current into the DBR region 7, a change in the refractive index of the DBR region 7 occurs, and the oscillation wavelength can be varied. For 100mW laser output,
70 mW laser light was coupled to the optical waveguide 4 using the lens 8. By controlling the amount of current injected into the DBR region 6 of the wavelength tunable DBR semiconductor laser 5 and fixing the oscillation wavelength within the tolerance of the phase matching wavelength of the optical waveguide type wavelength conversion device 1, blue light having a wavelength of 426 nm is about 10 mW. Obtained.

The blue output modulation characteristic when directly modulating the wavelength tunable DBR semiconductor laser will be described. In general, the life of a semiconductor laser is related to the average output, so that a high peak output can be obtained by performing a modulation operation (pulse drive). Further, since the wavelength conversion by SHG uses the second-order nonlinear effect, the obtained harmonic output (blue output) is proportional to the square of the output of the semiconductor laser which is the fundamental wave. Therefore, the effect of obtaining a high output by pulse driving the semiconductor laser is particularly great in the case of the SHG blue laser. The tunable DBR semiconductor laser used in the present embodiment has a threshold of 20 mA and an operating current of 150 mW at 100 mW. The peak output at a peak current of 300 mW is 200 mW.

FIG. 2A shows that the average output (130 mW) of the semiconductor laser at the time of modulation is the bias output (Pb = 130 mW, Ib
= 200 mA) and when the drive current is modulated so that (b) the average output (130 mW) of the semiconductor laser during modulation is larger than the bias output (Pb = 70 mW, Ib = 110 mA) It is a blue output waveform obtained when the current is modulated.

The intensity modulation of the semiconductor laser is Pa = 200 mW (Ia =
300 mA) and Pc = 60 mW (Ic = 100 mA). The blue output obtained at this time was 30 mW for Pa and 3 mW for Pc
And the modulation frequency is 10 MHz.

In FIG. 2B, a vertical mode shift occurs in the rising characteristic from the continuous operation (Pb) to the modulation operation, so that the blue output fluctuates. It is considered that the cause of the output fluctuation is that the average output of the semiconductor laser is different between the continuous operation (bias current) and the modulation driving, and the carrier density and the chip temperature in the active layer are greatly changed at the time of rising.

FIG. 3A shows the relationship between the peak current and the oscillation wavelength of the wavelength tunable DBR semiconductor laser when a modulation operation is performed at a modulation frequency of 10 MHz and a duty of 50%. As the peak current increases, the oscillation wavelength causes a longitudinal mode shift toward the longer wavelength side. The oscillation wavelength of the semiconductor laser is 0 for Ip = 300 mA.
This value is shifted by 2 nm, which is a value larger than the allowable width of the phase matching wavelength of the optical waveguide type wavelength conversion device. This phenomenon is also caused by the semiconductor laser chip temperature and the carrier density in the active layer. Therefore, the DBR current for achieving phase matching differs between the continuous operation and the modulation operation, and peak conversion efficiency cannot be obtained.

On the other hand, in FIG. 2A, the longitudinal mode shift does not occur because the average output during the continuous operation (bias current) and the modulation operation are constant, and the DB with respect to the phase matching wavelength does not occur.
Since the R current does not change, no output fluctuation was observed even at the time of rising from the continuous operation to the modulation operation, and stable output characteristics were obtained.

FIG. 3B shows the relationship between the average output and the oscillation wavelength during semiconductor laser modulation. When the variation of the average output is within 20%, the variation of the oscillation wavelength is 0.05 nm or less. The allowable width of the phase matching wavelength of the optical waveguide type quasi phase matching type wavelength conversion device having a length of 10 mm is 0.1 nm, and this value is a width at which the blue output becomes a half value of the peak. It is not permissible for the output to fluctuate by half when trying to use it in various fields. Therefore, the fluctuation of the oscillation wavelength is 0.05
It is necessary to control the average output to less than nm, and it is essential that the fluctuation of the average output be within the range of 20% or less. In the present embodiment, the modulation is performed so that the average output of the semiconductor laser is constant. However, by setting the fluctuation of the average output within a range of 20% or less, as shown in FIG. An output waveform can be realized.

In addition, the element length can be shortened, or the periodically poled region can be divided (Mizuchi et al., IEEE Journal of Quantum
Electronics, vol. 30. No. 7, (1994)), although the conversion efficiency is reduced, it is possible to increase the allowable wavelength range for the phase matching wavelength. Thus, by making the average output fluctuation of the semiconductor laser during modulation within 20%, more stable output waveforms and rising characteristics can be realized.

Further, the wavelength tunable DBR semiconductor laser according to the present embodiment is fixed to the submount so that the surface opposite to the junction-down portion is in contact (junction-up). Since the heat radiation state of the layer portion is improved, the longitudinal mode shift during modulation is reduced. Therefore, by setting the fluctuation of the average output of the semiconductor laser at the time of modulation to within 20%, more stable output waveform and rising characteristics can be realized.

As in the present embodiment, by making the average output of the semiconductor laser, which is the fundamental wave in the continuous operation and the modulation operation, the same, the temperature of the semiconductor laser chip and the average carrier density in the active layer are kept constant. Tunable D
Since the oscillation wavelength of the BR semiconductor laser can be kept constant,
A stable blue light modulation characteristic can be realized. Particularly, stable start-up characteristics can be realized.

In this embodiment, the modulation operation is performed at Ia = 300 mA and Ic = 100 mA. However, as shown in FIG. 4A, Pa = 250 mW (Ia = 40 mA).
0 mA) and Pc = 10 mW (Ic = 25 mA), the modulation was performed with the average semiconductor laser output kept constant, so that stable blue output modulation characteristics could be realized. As a result, two levels of peak blue output of 30 mW and 45 mW can be obtained, and multi-level modulation can be performed.

Further, as shown in FIG.
, Pa and Pc can be made asymmetric with respect to Pb, and the average output can be kept constant. For example, Pb = 1
When 30 mW, Pc = 60 mW, and duty = 33%, Pa = 270 mW can be set, and a higher peak blue output can be realized.

In this embodiment, the modulation is performed so that the average output of the semiconductor laser is constant. However, even if the modulation is performed so that the average operating current or voltage is constant, almost the same effect can be obtained, and the stable operation can be achieved. A blue modulation waveform is obtained.

As described above, by making the average output at the time of modulation constant and changing only the peak output, multi-level modulation becomes possible, and it can be applied to various fields as a light source for optical disks and laser printers. .

(Second Embodiment) Recording on a magneto-optical disk using the modulation method of the first embodiment will be described. In the magneto-optical disk system, the recorded marks are not erased when the magnetic field modulation is not performed. Therefore, in the present embodiment, mark recording is performed using a modulation strategy as shown in FIG. 5 (pulse output / pulse magnetic field method). FIG.
(a) is the formed mark shape, (b) magnetic field current,
(c) Blue output is shown.

As described in the first embodiment, in the SHG blue laser composed of the wavelength tunable DBR semiconductor laser and the optical waveguide type wavelength conversion device, the modulated output of blue light does not follow a large change in operating current. Therefore, in the first embodiment, the oscillation wavelength is stabilized by making the average output during the modulation operation of the semiconductor laser, which is the fundamental wave, the same as the output during the continuous operation, and the blue light that is stably modulated is emitted. It has been realized.

In the method of FIG. 5, Ia = 300 mA, Ib = 200 mA, Ic
= 100 mA and is modulated between Ia and Ic around Ib. The blue output obtained at this time is Pa = 30 mW, Pb = 15 mW, Pc = 3 mW
Met. The transmission efficiency of the optical pickup is about 40%, and the peak blue output obtained after the objective lens is about
It was 12 mW. Blue output after objective lens in Ib is 6mW
Met.

The configuration of an optical pickup for a magneto-optical disk equipped with an SHG blue laser will be described. FIG.
FIG. 2 is a schematic configuration diagram of an optical pickup. The blue light emitted from the SHG blue laser 9 is collimated by a collimating lens 10, shaped by a shaping prism 11,
12. The light passes through the reflection mirror 13 and is condensed on the optical disk 15 by the objective lens 14.

The optical disk 15 is used as a recording layer on a substrate.
This is a magneto-optical disk on which TbFeCo is laminated, and its film is designed to be recorded by magnetic field modulation.

The reflected light from the optical disk 15 is
, And is divided into a servo detector and a signal reproduction detector.
The servo detector includes a four-part PIN photodiode 25, and focus and tracking are detected by an astigmatism method and a push-pull method. In the signal reproduction, the deflection direction is rotated 45 degrees by the λ / 2 plate 18, and the PBS2
The signal is guided to the two PIN photodiodes 21 and 22 by 0, and the Kerr rotation angle on the optical disk is detected by taking the difference.

An address area and a recording area are formed on the magneto-optical disk. After reproducing the address signal, the optical output is made higher than the recording output, and the mark is recorded by modulating the magnetic head on the opposite side of the substrate. . In the present embodiment, the laser output during recording is set to 12 mW, and the output during address signal reproduction is set to 6 mW. As shown in the first embodiment, since the average output of the semiconductor laser at the time of address reproduction and at the time of recording is constant, a stable blue light modulation waveform was obtained, and high-density recording with a mark length of 0.1 μm was realized. .

In the phase change optical disk system, Pb
If the level exceeds the melting point, the recording mark will be erased,
If an attempt is made to reproduce an address signal at the Pb level, recording marks other than the address area will be erased. However, in the magneto-optical disk system, even if the recording area is reproduced with a relatively high output, signal deterioration does not occur if the temperature of the recording film is equal to or lower than the Curie point temperature (in the present embodiment,
The power to reach the Curie point temperature of the recording film is designed to be 8 mW). Therefore, the recording method using the modulation method of the present embodiment is suitable for a magneto-optical disk system, and the effect is large.

(Embodiment 3) In this embodiment, an SHG composed of a wavelength conversion device in which a planar electrode for modulation is formed on an optical waveguide and a wavelength tunable DBR semiconductor laser.
An example in which a blue laser performs direct modulation of an operating current and multilevel modulation using a modulator on an optical waveguide will be described.

FIG. 7 shows the configuration of an optical waveguide type wavelength conversion device to which a planar electrode according to the present invention is added. As in the first embodiment, a periodically poled region 27 and a proton exchange optical waveguide 28 are formed on a Mg-doped LiNbO ₃ substrate 26. Unlike the first embodiment, the mask used to form the optical waveguide 28 is not removed and the modulation electrode 2
9 was used. The optical waveguide 28 has a width of 4 μm and a depth of 2 μm.
m, length 10 mm. The end face of the optical waveguide 28 is provided with an anti-reflection coating. Using a tunable DBR semiconductor laser, wavelength conversion characteristics and modulation characteristics were evaluated. 100mW
The laser light of 70 mW with respect to the laser output was coupled to the optical waveguide 28.

The amount of current injected into the DBR region of the tunable DBR semiconductor laser is controlled, and the oscillation wavelength is fixed within the allowable range of the phase matching wavelength of the optical waveguide type wavelength conversion device, so that blue light of 426 nm wavelength is about 10 mW. Obtained.

Next, the modulation characteristics when an electric field is applied to the modulation electrode 29 will be described. When a voltage is applied to the modulation electrode 29, an electric field is applied in the Z direction (the direction of the arrow), so that the refractive index in the optical waveguide 28 changes due to the electro-optic effect, and as a result, the phase matching wavelength changes. The blue output obtained by the conversion can be intensity-modulated.

FIG. 8 shows the relationship between the applied voltage and the obtained blue output. When the applied voltage is 0 V, a blue output of 10 mW is obtained. When the applied voltage is 5 V, the blue output is 5 m.
Reduced to W. The response speed was 5 ns, depending on the power supply.

Next, by making the average output of the semiconductor laser described in the first embodiment the same during the modulation operation and during the continuous operation,
Directly modulate the drive current of the wavelength tunable DBR semiconductor laser,
A multi-level blue output level is realized by a combination of the method of modulating the blue output of the SHG blue laser and the blue output modulation by the modulator on the optical waveguide type wavelength conversion device described above.

FIG. 9 shows an example of a modulation strategy when random recording is performed on a phase change optical disk. It is modulated by four values of a reproducing level Pr, an erasing level Pb, a recording level Pw, and a cooling level Pc. In this case, at the time of erasing and at the time of recording, it is possible to perform modulation with a constant average output as described in the first embodiment.
By using the modulation method of the first embodiment, a stable modulation waveform can be obtained. However, the average output changes when trying to get the regeneration level or cooling level,
The carrier density and temperature in the active layer change, a longitudinal mode shift occurs, and an output fluctuation occurs in the rising characteristics.

FIG. 10 shows a modulation method according to the present invention for realizing the modulation strategy shown in FIG. FIG. 10A is a time chart of the operating current of the tunable DBR semiconductor laser, FIG. 10B is a time chart of the voltage applied to the optical waveguide type wavelength conversion device, and FIG. 10C is a time chart of the blue output. The output of the reproduction level Pr, the erasure level Pb, and the cooling level Pc is switched by changing the voltage applied to the modulator on the optical waveguide type wavelength conversion device. The multi-pulse modulation at the recording level Pw is performed by operating current modulation of the wavelength tunable DBR semiconductor laser.

First, the reproduction level (Pr = 3 mW) depends on the operating current.
Driving was performed at 200 mA (laser output: 130 mW). At this time, the voltage applied to the modulator on the optical waveguide type wavelength conversion device was 8 V. Next, the applied voltage is switched to 0 V, and the blue output changes to the erase level (Pb = 15 mW). Next, the operating current is modulated between 300 mA and 100 mA while the voltage applied to the electrodes on the optical waveguide type wavelength conversion device is kept constant at 0 V. At this time, the peak blue output, that is, the recording level
(Pw = 30 mW) is obtained. The cooling level (Pc = 0 mW) can be obtained by returning the operating current to 200 mA and changing the voltage applied to the modulator on the optical waveguide type wavelength conversion device.
In the present embodiment, the voltage was obtained by changing the applied voltage from 0 V to 10 V. By changing the modulation pulse of the operating current,
Modulation waveform composed of multi-pulses (3T to 11T)
Could be obtained.

As a result, a recording level of 30 mW and an erasing level were obtained.
15mW, playback level 3mW, cooling level 0mW blue output (P
w>Pb> Pr).

The SHG blue laser was mounted on an optical pickup, and a recording experiment on a phase change optical disk was performed. The transmission efficiency of the optical pickup was about 40%, and the blue output during recording obtained after the objective lens was about 12 mW. The blue output at the erasing level, the reproducing level, and the cooling level were 6 mW, 1.2 mW, and 0 mW, respectively.

In this embodiment, a reproducing level is realized by applying a voltage to the upper electrode of the optical waveguide device. However, since it is necessary to drive the semiconductor laser at an operating current of 200 mA and a laser output of 130 mA, it is not desirable in terms of the reliability of the semiconductor laser for performing long-time reproduction. Therefore, the reproduction level obtained by applying a voltage to the electrode is used only when reproducing the address signal at the time of recording, and when performing normal data reproduction, the operation current is set to 100 mA to obtain the reproduction level. Is practically preferable.

The recording / reproducing method will be described with reference to FIG. Blue light emitted from the SHG blue laser 30 is collimated by a collimating lens 31 and beam-shaped by a shaping prism. The beam-shaped blue light passes through a polarizing beam splitter (PBS) 33 and is guided to a λ / 4 plate 34 and an objective lens 35 having a numerical aperture (NA) of 0.6. The objective lens 35 has a numerical aperture of 0.6 for a substrate thickness of 0.6 mm.
Aspherical lens.

The beam reflected by the phase change optical disk 39 is reflected by the PBS 33, passes through the lens 36 and the cylindrical lens 37, and is guided onto the PIN photo detector 38. An anti-reflection coating optimized for the blue region is formed on the surface of the PIN photodetector, and is divided into four parts.

The focus servo signal was detected by the astigmatism method, and the tracking servo signal was detected by the push-pull method.

As the substrate of the phase change optical disk 39 used in the experiment, a polycarbonate substrate having the same thickness as that of the DVD and having a thickness of 0.6 mm was used, and land / grooves having a space interval of 0.35 μm were formed on the substrate. Further, a recording layer (GeSbTe) sandwiched between dielectric layers (ZnS) was formed on a substrate, and Au was used as a reflective layer. The composition ratio of the recording layer was designed so that the absorption characteristics and the reflectance difference between the crystal and the amorphous layer were optimized in the blue region.

When random marks were recorded on the phase-change optical disk by the modulation strategy shown in FIG. 10, random marks with sharp edges could be formed. Same SH
When a random signal was reproduced with an optical pickup of a G blue laser, about 8% of jitter was obtained in data to clock.

As described above, when a modulator on an optical waveguide is used, a multilevel output level can be easily realized.
Even if a wavelength tunable DBR semiconductor laser of W is used as a continuous wave, it operates as continuous light, so that only a peak blue output of about 10 mW can be obtained. In order to apply to various fields (especially optical disk systems that can record and play back)
A peak output of 20mW or more is required. As in the present embodiment, by combining with direct modulation of a semiconductor laser, a stable multi-level modulation waveform with good rising characteristics can be realized, and it can be applied to fields such as optical disks.

In this embodiment, an example using a modulator constituted by plane electrodes has been described.
The same effect can be obtained by using the directional coupler type modulator shown in FIG. In the configuration of FIG. 7, the blue light output is modulated by giving a change in the refractive index to the optical waveguide and shifting the phase matching wavelength. The directional coupler modulator modulates the semiconductor laser light output itself and obtains blue light by wavelength conversion. In the directional coupler modulator, the semiconductor laser light coupled into the optical waveguide 40 is split into two. When a voltage is applied to the electrode 41, the refractive index in the optical waveguide changes and a phase difference occurs. 0 phase difference
In the case of (1), the output of the combined semiconductor laser light is the maximum output, but if the phase difference is shifted by π, they cancel each other and become the minimum output. The light that has passed through the directional coupler modulator is
The light propagates through the wavelength converter where the periodically poled regions 42 are formed, and is converted into blue light. As described above, the modulation strategy of FIG. 9 can be realized by combining the direct modulation of the semiconductor laser with the directional coupler modulator.

In the first to third embodiments, a tunable DBR semiconductor laser is used as a semiconductor laser constituting a short-wavelength light source, but a short-wavelength semiconductor laser having a reflection type grating outside is used. Similarly, in a light source or a short wavelength light source having a DBR portion formed on an optical waveguide type wavelength conversion device, a longitudinal mode shift during modulation is also observed, and the modulation method described in Embodiments 1 to 3 is used. Thereby, a stable modulation waveform can be realized.

In the first to third embodiments, the quasi-phase matching type optical waveguide type wavelength conversion device is used as the wavelength conversion device. A stable modulation waveform can be realized by the modulation schemes of the first to third embodiments even for a short wavelength light source using the wavelength conversion device.

[0070]

As described above, according to the present invention, in a short wavelength light source composed of a semiconductor laser and a wavelength conversion device, the fluctuation of the average output during the modulation operation is within 20%, or the fluctuation during the continuous operation. Is set within 20%, stable harmonics can be obtained in both the continuous operation and the modulation operation. In particular, instantaneous stabilization can be realized at the rising portion during the modulation operation, so that good recording characteristics of an optical disc or the like can be realized. Can be realized. By applying a short wavelength light source using this modulation method to a magneto-optical disk system,
A stable recording / reproducing system is realized. Further, by using an optical waveguide type wavelength conversion device having an integrated modulation function, a multi-level modulation characteristic can be realized and applied to various fields, so that the effect is large.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an SHG blue laser including a wavelength tunable DBR semiconductor laser of the present invention and an optical waveguide type wavelength conversion device.

2A is a diagram showing a blue output waveform when a drive current is modulated so that the average output of the semiconductor laser at the time of modulation of the present invention is equal to the bias current at the time of continuous operation; FIG. Diagram showing a blue output waveform when the drive current is modulated in a state where the average output of the semiconductor laser is larger than the bias output

3A is a diagram illustrating a relationship between a peak current and an oscillation wavelength of a tunable DBR semiconductor laser. FIG. 3B is a diagram illustrating a relationship between an average output and an oscillation wavelength of the tunable DBR semiconductor laser.

FIG. 4 is a diagram showing a blue output waveform when the drive current is modulated so that the average output of the semiconductor laser during modulation according to the present invention becomes the same as the bias current during continuous operation.

FIG. 5 is a diagram showing a modulation strategy of the present invention. (A) A diagram showing a mark shape. (B) A diagram showing a magnetic field current of a magnetic head. (C) A diagram showing an obtained blue output.

FIG. 6 is a schematic configuration diagram of a recording / reproducing apparatus for a magneto-optical disk.

FIG. 7 is a schematic configuration diagram of an optical waveguide type wavelength conversion device in which the modulator of the present invention is integrated.

FIG. 8 is a diagram showing a relationship between an applied voltage and an obtained blue light output of an optical waveguide type wavelength conversion device in which the modulator of the present invention is integrated.

FIG. 9 is a diagram showing a modulation strategy when random recording is performed on a phase change optical disk.

10A is a time chart of the operating current of the wavelength tunable DBR semiconductor laser, FIG. 10B is a time chart of the voltage applied to the optical waveguide type wavelength conversion device, and FIG. 10C is a diagram showing the obtained blue output.

FIG. 11 is a schematic configuration diagram of a recording / reproducing apparatus for a phase change optical disk.

FIG. 12 is a schematic configuration diagram of an optical waveguide type wavelength conversion device in which the directional coupler type modulator of the present invention is integrated.

FIG. 13 is a diagram showing a modulation strategy when recording on a phase change optical disk.

FIG. 14 is a diagram showing (a) a magnetic field current and (b) a driving current of a semiconductor laser when recording on a magneto-optical disk with a pulse output and a pulse magnetic field.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical waveguide type wavelength conversion device 2 LiNbO3 substrate 3 Periodically poled area 4 Optical waveguide 5 Wavelength tunable DBR semiconductor laser 6 Active area 7 DBR area 8 Lens 9 SHG blue laser 10 Collimating lens 11 Shaping prism 12 PBS 13 Reflecting mirror 14 Objective Lens 15 Optical disk 16 Magnetic head 17 PBS 18 λ / 2 plate 19 Lens 20 PBS 21 PIN photo timer 22 PIN Photo timer Auto 23 Lens 24 Cylindrical lens 25 PIN Photo timer Auto 26 LiNbO3 substrate 27 Polarized area 28 Optical waveguide 29 Modulating electrode 30S Blue laser 31 Collimating lens 32 Shaping prism 33 PBS 34 λ / 4 plate 35 Objective lens 36 Lens 37 Cylindrical lens 38 PIN photo diode 39 Phase change Optical disc 40 the optical waveguide 41 electrode 42 domain-inverted regions

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masahiro Odomegawa 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (13)

[Claims] 1. A semiconductor laser comprising a semiconductor laser and a wavelength conversion device, wherein the semiconductor laser output is intensity-modulated by modulating a driving current or voltage of the semiconductor laser, and at the same time, the harmonic light output obtained by wavelength conversion is intensity-modulated. In this case, the short-wavelength light source is characterized in that the intensity is modulated so that the average laser output of the semiconductor laser fluctuates within ± 20%. 2. A semiconductor laser comprising a semiconductor laser and a wavelength conversion device, wherein the semiconductor laser output is intensity-modulated by modulating a driving current or a voltage of the semiconductor laser, and at the same time, the harmonic light output obtained by the wavelength conversion is intensity-modulated. When the average value of the current or voltage of the semiconductor laser is ±
A short-wavelength light source characterized in that the intensity is modulated so that the fluctuation is within 20%. 3. A semiconductor laser and a wavelength conversion device, wherein the semiconductor laser output is intensity-modulated by modulating a drive current or voltage of the semiconductor laser, and at the same time, the harmonic light output obtained by the wavelength conversion is intensity-modulated. In this case, the harmonic light output is intensity-modulated while switching between continuous operation and modulation operation such that the average laser output of the semiconductor laser is within ± 20% of the laser output during continuous operation. light source. 4. A semiconductor laser and a wavelength conversion device, wherein the intensity of the output of the semiconductor laser is modulated by modulating the drive current or voltage of the semiconductor laser, and the intensity of the harmonic light output obtained by the wavelength conversion is simultaneously modulated. In this case, the intensity of the harmonic light output is modulated while switching between continuous operation and modulation operation such that the average operating current or voltage of the semiconductor laser is within ± 20% of the operating current or voltage during continuous operation. Short wavelength light source. 5. A short-wavelength light source comprising at least a semiconductor laser and a wavelength conversion device, and a magnetic-field modulator for performing magnetic field modulation, wherein short-wavelength light outputs emitted from the short-wavelength light source are Pa and Pb. And Pc are modulated into three values, and Pa> P
b> Pc, the short-wavelength light output is set to Pb to reproduce a signal in the address area, and when the short-wavelength light output is intensity-modulated by Pa and Pc, magnetic field modulation is performed. An optical recording apparatus for erasing and recording a recording mark on a recording layer. 6. When the short-wavelength light output is intensity-modulated by Pa and Pc, the average laser output of the semiconductor laser during the modulation is within ± 20% of the laser output during continuous operation (Pb). The optical recording apparatus according to claim 5, wherein: 7. An optical modulator comprising at least a semiconductor laser and a wavelength conversion device, an optical modulator formed on the wavelength conversion device, multi-level modulation of a driving current of the semiconductor laser, and application to the optical modulator. A short-wavelength light source characterized in that a short-wavelength light output emitted from the short-wavelength light source is multi-level modulated by multi-level modulation of a voltage. 8. A short wavelength light source comprising at least a semiconductor laser and a wavelength conversion device, wherein an optical modulator is formed on the wavelength conversion device, and a short wavelength light is generated by modulating a driving current of the semiconductor laser. Optical outputs Pa and Pb (Pa>Pc> Pb) are obtained, and short-wavelength optical outputs Pc and Pd (Pa>Pc> Pd) are obtained by modulating the voltage applied to the optical modulator. An optical recording apparatus for reproducing a recording mark of the recording layer, erasing the recording mark of the recording layer by Pc, and recording on the recording layer by Pa. 9. The short wavelength light source according to claim 1, wherein said wavelength conversion device is an optical waveguide type wavelength conversion device. 10. The semiconductor laser according to claim 1, wherein said semiconductor laser is a distributed Bragg reflection semiconductor laser.
Or the short-wavelength light source according to any of 6. 11. The wavelength conversion device according to claim 5, wherein the wavelength conversion device is an optical waveguide type wavelength conversion device.
The short-wavelength light source according to any one of the above. 12. The optical recording apparatus according to claim 5, wherein said semiconductor laser is a distributed Bragg reflection type semiconductor laser. 13. A short-wavelength light source characterized in that a distributed Bragg reflection semiconductor laser and a wavelength conversion device are mounted on a submount such that surfaces on which a junction side and an optical waveguide side are formed are in contact with each other.