JP2004165383A - Semiconductor laser device, second harmonic generator, and optical pickup apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device capable of suppressing part of an emission end face of an active layer at a side of a diffraction grating layer from being molten and destroyed, and a second harmonic generator and an optical pickup apparatus employing the same. <P>SOLUTION: The semiconductor laser device is used, which includes the active layer 4, and the diffraction grating layer 8 placed above the active layer 4 as its upper layer. The diffraction grating layer 8 is formed within a range narrower than that of the principal face of the active layer 4. The active layer 4 is formed in a way that a band gap in a DBR region and a phase control region equivalent to regions beneath the diffraction grating layer 8 is greater than a band gap in a gain region. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor laser device, a second harmonic generation device using the same, and an optical pickup device.
[0002]
[Prior art]
As a light source for a high-density optical disk, a laser light source in the blue region has been demanded. The blue region is a short wavelength region in which the condensing spot system on the optical disk can be made smaller than the red region or infrared region light. This is effective for improving the reproduction density.
[0003]
As an effective means for obtaining laser light in the blue region, there is a method of converting light in the infrared region into light having a short wavelength in the blue region using a second harmonic generation (SHG) element having a waveguide. No. At present, LiNbO is widely used as a constituent material of the SHG element. ₃ Is a non-linear optical material represented by
[0004]
Usually LiNbO ₃ A grating is formed on the SHG element constituted by the above by an ion exchange technique in accordance with the wavelength of infrared light which is input light. In addition, the SHG element needs to be configured so that the wavelength of the infrared light that propagates through the waveguide, the wavelength of the blue light that propagates through the waveguide, and the grating pitch have an integer ratio. Therefore, the range of the wavelength of incident infrared light is limited to a narrow range by the SHG element.
[0005]
Therefore, a DBR (Distributed Bragg Reflector) laser having high selectivity of oscillation wavelength, capable of performing single longitudinal mode oscillation, and capable of adjusting a change in oscillation wavelength with temperature is used as an infrared laser serving as a light source. Can be As a conventional DBR laser, for example, a laser disclosed in Patent Document 1 can be mentioned. This conventional DBR laser will be described with reference to FIG.
[0006]
FIG. 24 is a side view schematically showing the structure of a conventional DBR laser. As shown in FIG. 24, a conventional DBR laser has an n-type GaAs buffer layer 52 having a thickness of 0.5 μm and an n-type AlGaAs having a thickness of 1.5 μm (Al composition 0.45) on an n-type GaAs substrate 51. Cladding layer 53, active layer 54, p-type AlGaAs (Al composition 0.4) carrier confinement layer (cladding layer) 55 having a thickness of 400 °, p-type AlGaAs (Al composition 0.15) diffraction grating layer having a thickness of 0.25 μm 56, a 1.5 μm thick p-type AlGaAs (Al composition 0.45) cladding layer 57 and a 0.5 μm thick p-type GaAs contact layer 58 are sequentially provided. The lowermost layer is provided with an electrode 62, and the uppermost layer is provided with electrodes 59 to 61. The electrodes 59 to 62 are used for driving a DBR laser.
[0007]
The n-type GaAs buffer layer 52, the n-type AlGaAs cladding layer 53, the active layer 54, the p-type AlGaAs carrier confinement layer 55, and the p-type AlGaAs optical guide layer 56 are formed by a molecular beam epitaxy (MBE) method.
[0008]
Further, the p-type AlGaAs diffraction grating layer 56 is provided with diffraction gratings 56a and 56b. The diffraction grating 56a is formed by applying a resist on the p-type AlGaAs layer, patterning it into a stripe shape having a width of 300 μm by two-beam interference exposure, and further performing reactive ion beam etching (RIBE). ing. In the example of FIG. 24, the pitch of the diffraction grating 56a is 2440 ° and the depth is 10 °. It is.
[0009]
The diffraction grating 56b is also formed by the same patterning and reactive ion beam etching as the diffraction grating 56a. However, in forming the diffraction grating 56b, patterning is performed using a resist different from the resist used for the diffraction grating 51a. As a result, the diffraction grating 51a and the diffraction grating 52b have the same pitch but different depths.
[0010]
The p-type AlGaAs cladding layer 57 and the p-type GaAs contact layer 58 are formed by a liquid phase epitaxial growth (LPE) method.
[0011]
Incidentally, the conversion efficiency of the SHG element from the infrared region to the blue region is from several% to several tens%, and is generally proportional to the square of the power of light input to the SHG element which is a nonlinear optical element.
[0012]
Therefore, in order to obtain blue light of about 5 mW required for reproduction of a high-density optical disk, the power of infrared light needs to be at least about 50 mW. Further, in order to obtain light in the blue range of about several tens mW required for recording on a high-density optical disk, the power of light in the infrared range needs to be at least 100 mW or more. For this reason, a high output characteristic of 100 mW or more is required for a DBR laser used as a light source for recording and reproduction of a high-density optical disk.
[0013]
[Patent Document 1]
JP-A-6-53619
[0014]
[Problems to be solved by the invention]
However, when the conventional DBR laser shown in FIG. 24 performs a high-output operation of 100 mW or more, the power density of light in the active layer 54 becomes large. The active layer 54 has a relatively large absorption coefficient with respect to the laser light, and further has a characteristic that the end face reflectance of the laser light on the diffraction grating layer 56 side is small.
[0015]
For this reason, when a high output operation of 100 mW or more is performed in the conventional DBR laser shown in FIG. Optical Damage) level is reduced.
[0016]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor laser device capable of suppressing a portion on the diffraction grating layer side of an emission end face of an active layer from being melted and broken, a second harmonic generation device and an optical pickup device using the same. It is in.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor laser device according to the present invention is a semiconductor laser device having an active layer and a diffraction grating layer located above the active layer, wherein the diffraction grating layer is The active layer is formed within a range narrower than the main surface of the first region, and the active region includes a first region including a region directly below the diffraction grating layer and a second region not including a region directly below the diffraction grating layer. And the band gap in the first region is larger than the band gap in the second region.
[0018]
In the semiconductor laser device according to the present invention, a first light guide layer, a second light guide layer, and a ridge-type third light guide layer are sequentially formed on the diffraction grating layer. A current blocking layer having a conductivity type opposite to that of the third light guide layer is formed on the second light guide layer so as to sandwich a side surface of the third light guide layer, and the second light guide layer is formed on the second light guide layer. Assuming that the band gaps of the light guide layer, the third light guide layer, and the current block layer are Eg1, Eg2, and Eb, respectively, the relationship of Eg1>Eb> Eg2 is preferably satisfied.
[0019]
In the semiconductor laser device according to the present invention, a layer formed of a constituent material having an etching rate lower than that of the constituent material of the diffraction layer is provided between the active layer and the diffraction layer. preferable.
[0020]
In the semiconductor laser device according to the present invention, it is preferable that a plurality of layers functioning as electrodes are arranged on the uppermost layer along the laser emission direction. When there are three layers functioning as the electrodes, the gain, phase and oscillation wavelength are controlled by the magnitude of the current injected into each layer.
[0021]
In the semiconductor laser device according to the present invention, it is preferable that the band gap wavelength in the first region is set shorter than the oscillation wavelength of the laser light. Further, it is preferable that the third light guide layer has a portion parallel to an axis perpendicular to the cleavage plane and a portion inclined with respect to an axis perpendicular to the cleavage plane. Further, it is preferable that the third light guide layer is formed such that a cross section perpendicular to the emission direction has a trapezoidal shape.
[0022]
In the semiconductor laser device according to the present invention, the diffraction grating layer, the first light guide layer, the second light guide layer, and the third light guide layer are formed by doping Si. The current blocking layer is preferably formed by doping Se.
[0023]
Next, in order to achieve the above object, a second harmonic generation device according to the present invention includes the semiconductor laser device according to the present invention and a nonlinear optical element having a waveguide, wherein the nonlinear optical element is The laser light emitted from the semiconductor laser device is arranged so as to be coupled to the waveguide. In the second harmonic generation device according to the present invention, it is preferable that the semiconductor laser device and the nonlinear optical element are arranged on the same substrate.
[0024]
According to another aspect of the present invention, there is provided an optical pickup device comprising: a diffraction grating, a condensing lens, and an optical element that extracts only a predetermined deflection component from light including a plurality of deflection components. And at least the second harmonic generator according to the present invention. In the optical pickup device according to the present invention, it is preferable that the second harmonic generation device is disposed on a substrate, and a light receiving element is provided on the substrate.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a semiconductor laser device, a second harmonic generation device, and an optical pickup device of the present invention will be described with reference to FIGS.
[0026]
First, the configuration of the semiconductor laser device of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view showing an example of the semiconductor laser device of the present invention. FIG. 2 is a side view of the semiconductor laser device shown in FIG. FIG. 3 is a top view of the semiconductor laser device shown in FIG.
[0027]
The semiconductor laser device of the present invention shown in FIGS. 1 to 3 is a DBR laser having a diffraction grating inside a waveguide. As shown in FIGS. 1 and 2, a semiconductor laser device according to the present invention includes a buffer layer 2, a first cladding layer 3, an active layer 4, a second cladding layer 5, a first etching prevention layer 6 on a substrate 1. Second etching preventing layer 7, diffraction grating layer 8, first light guide layer 9, second light guide layer 10, ridge-shaped third light guide layer 11, current blocking layer 12, third clad layer 13, contact layer 14a To 14c.
[0028]
1 and 2, the substrate 1 is formed of an n-type GaAs semiconductor crystal. The buffer layer 2 is an n-type GaAs layer having a thickness of 0.2 μm. The first cladding layer 3 is a 3.0 μm thick n-type Ga _0.5 Al _0.5 This is an As layer. The active layer 4 is made of Ga _0.7 Al _0.3 A double quantum well structure composed of an As barrier layer (thickness 50 °) / a GaAs well layer (thickness 42 °) _0.7 Al _0.3 It is formed so as to be sandwiched between As guide layers (thickness: 100 °). The second cladding layer 5 is made of p-type Ga _0.5 Al _0.5 This is an As layer.
[0029]
The first etching prevention layer 6 and the second etching prevention layer 7 are formed of the diffraction grating layer 8 in order to prevent a part of the second cladding layer 5 from being removed by etching when forming the diffraction grating layer 8. It is formed of a material having a lower etching rate than the constituent material. Further, between the first etching prevention layer 6 and the second etching prevention layer, the first etching prevention layer 6 is formed of a material having a lower etching rate.
[0030]
Specifically, the first etching prevention layer 6 is a p-type GaAlAs layer having a thickness of 100 °. The AlAs mixed crystal ratio of the first etching prevention layer 6 is defined as Xs. The second etching prevention layer 7 is made of p-type Ga _0.4 Al _0.6 This is an As layer, and is formed only on a partial region of the first etching prevention layer 6.
[0031]
Further, the diffraction grating layer 8 is made of p-type Ga _0.8 Al _0.2 The As layer is formed by patterning and etching, and has a distributed Bragg reflection effect on guided light. The first light guide layer 9 is made of p-type Ga _0.5 Al _0.5 An As layer, which is formed on the first etching prevention layer 6 where the second etching prevention layer 7 is not provided and the diffraction grating layer 8. It is preferable that the thickness of the first light guide layer 9 is as small as possible so as not to significantly affect the light distribution. The second light guide layer 10 is a p-type GaAlAs layer having a thickness of 100 °. The mixed crystal ratio of AlAs of the second light guide layer 10 is Xg.
[0032]
The third light guide layer 11 is a p-type Ga layer having a thickness of 2 μm. _0.5 Al _0.5 The As layer is formed in a ridge shape, and forms a waveguide. Further, the upper surface of the third light guide layer 11 functions as a window through which current flows. In the following, the upper surface of the third light guide layer 11 functioning as the window is also referred to as a “striped window”.
[0033]
The current blocking layer 12 is made of n-type Ga _0.4 Al _0.6 An As layer, whose conductivity type is opposite to that of the third light guide layer 11. The current blocking layer 12 is formed so as to sandwich the side surface of the third light guide layer 11 in a region on the second light guide layer 10 where the third light guide layer 11 is not formed. For this reason, the upper surface of the third light guide layer 11 functions as a window for flowing the current injected from the contact layer 14a.
[0034]
If the thickness of the current block layer 12 is small, the lateral mode becomes unstable due to insufficient light confinement in the lateral direction, so that the maximum thickness of the current block layer 12 is desirably 0.4 μm or more. In the examples of FIGS. 1 and 2, the maximum thickness of the current blocking layer is 0.7 μm.
[0035]
The third cladding layer 13 is made of p-type Ga having a thickness of 1 μm. _0.5 Al _0.5 This is an As layer. The contact layers 14a to 14c are electrodes for injecting current, and are formed by dividing a 2 μm-thick p-type GaAs layer into three sections perpendicular to the emission direction.
[0036]
As shown in FIGS. 1 and 2, in the semiconductor laser device of the present invention, the diffraction grating layer 8 is provided in a range narrower than the main surface of the active layer 4. For this reason, as shown in FIG. 2, a portion of the active layer 4 immediately below the diffraction grating layer 8 becomes a DBR region. Further, the active layer 4 is adjacent to the DBR region as a phase control region, and adjacent to the phase control region is a gain region.
[0037]
Further, the contact layer 14c is provided immediately above the DBR region, the contact layer 14b is provided immediately above the phase control region, and the contact layer 14a is provided immediately above the gain region. Therefore, as described later, the gain, phase, and oscillation wavelength can be controlled by the magnitude of the current injected into each contact layer.
[0038]
With such a configuration, the current injected from the contact layer 14a is confined inside the third light guide layer 11 by the current blocking layer 12, and generates light in the active layer 4 below the contact layer 14a. The light generated at this time is subjected to distributed Bragg reflection by the diffraction grating layer 8, and the wavelength is selected. As a result, a single longitudinal mode oscillation occurs.
[0039]
As shown in FIG. 3, the third light guide layer 11 is formed so as to be bent at a portion located immediately below the contact layer 14c, and has a portion 11a parallel to an axis perpendicular to the cleavage plane and a cleavage surface. And a portion 11b inclined with respect to a vertical axis. Therefore, the striped window also has a bent shape. In the example of FIG. 3, the inclination angle θ is 5 °, and the length of the inclined portion 11b in the direction perpendicular to the cleavage plane is 300 μm.
[0040]
For this reason, light having a wavelength that is not strongly affected by distributed Bragg reflection reaches the inclined portion 11b and is reflected by the cleavage surface, but light reflected by the cleavage surface is reflected in a direction different from that of the inclined portion 11b. Will be. That is, single longitudinal mode oscillation can be easily performed by using the semiconductor laser device shown in FIGS.
[0041]
FIG. 4 is a diagram illustrating a relationship between the effective reflectance and the inclination angle θ. The effective reflectivity shown in FIG. 4 is a rate at which the light reflected on the cleavage plane is returned to the inclined portion 11b of the second light guide layer 11 again. As can be seen from FIG. 4, by setting the inclination angle θ appropriately, the effective reflectance can be reduced to 10%. ^-6 It can be suppressed to the following levels. In this case, only light having a wavelength that is strongly subjected to distributed Bragg reflection by the diffraction grating layer 8 can be laser-oscillated with good reproducibility.
[0042]
Further, as shown in FIGS. 1 and 2, in the semiconductor laser device of the present invention, the active layer 4 has a first region including a region directly below the diffraction grating layer 8 (hatching is applied in the active layer 4). Portion) and a second region not including a region directly below the diffraction grating layer 8 (a portion of the active layer 4 that is not hatched), and the band gap in the first region is the second region. It is larger than the band gap in the region.
[0043]
In the examples of FIGS. 1 and 2, the phase matching region and the DBR region immediately below the diffraction grating layer 8 are disordered by ion implantation or impurity diffusion. It is larger than the band gap in the region.
[0044]
By the way, the power density of the laser light propagating through the waveguide of the semiconductor laser device is several MW / cm. ² Heat generated by light absorption in the waveguide leads to deterioration of the semiconductor laser device. In general, when heat is generated in a semiconductor laser, the band gap is reduced, and light absorption of laser oscillation light is increased. In addition, an increase in light absorption leads to a further increase in heat generation, a further reduction in the band gap, and as a result, an increase in light absorption. In this case, the temperature eventually rises to the melting point of the constituent material of the semiconductor laser element, and the semiconductor laser element itself is melted and destroyed (COD).
[0045]
In addition, in order to greatly change the oscillation wavelength and the phase, it is necessary to inject as much current as possible into the DBR region and the phase matching region, and to greatly change the refractive index in this region. Is more remarkable.
[0046]
On the other hand, in the semiconductor laser device of the present invention, as described above, the band gaps in the phase control region and the DBR region are larger than the band gaps in the gain region. For this reason, it is possible to suppress the laser light generated in the gain region from being absorbed in the DBR region and the phase matching region, and to suppress heat generation due to light absorption in these two regions. Therefore, it is possible to suppress the positive feedback increase in the heat generated by the light absorption in the phase matching region and the DBR region.
[0047]
From this, according to the semiconductor laser device of the present invention, even if heat is generated in the DBR region and the phase matching region by performing current injection for phase control and wavelength control, light absorption in the phase matching region and the DBR region occurs. Is suppressed, it is possible to suppress the occurrence of COD due to a rapid increase in heat generation due to light absorption.
[0048]
Further, in the semiconductor laser device of the present invention, in order to prevent light emission when current is injected into the DBR region or the phase control region from affecting the light emission characteristics of the gain region, the DBR region and the phase control region Is preferably as short as possible. However, if the band gap wavelength is made too short, the waveguide loss in the DBR region and the phase matching region becomes large, so it is necessary to take care not to make the wavelength too short.
[0049]
Specifically, it is preferable that the bandgap wavelength in the DBR region and the phase control region be shorter than the bandgap wavelength in the gain region in the range of 10 nm to 80 nm. 1 and 2, the band gap wavelengths in the DBR region and the phase control region are shorter by 15 nm than the band gap wavelengths in the gain region. At this time, the waveguide loss in the DBR region and the phase control region is 20 cm. ^-1 It is as follows.
[0050]
Here, the bandgap wavelength is a value obtained by converting the bandgap into a wavelength. When the bandgap wavelength is λg [μm] and the bandgap is Eg [eV], the bandgap wavelength is obtained by the following equation (1). Can be.
λg = 1.24 / Eg (1)
[0051]
Furthermore, Al _X Ga _1-X The relationship between the Al composition X of As (0 ≦ X ≦ 1) and the band gap Eg (X) [eV] can be obtained by the following equation (2). Also, Al _X Ga _1-X As has a property that as the band gap increases, the refractive index of the laser beam emitted from the active layer 4 decreases.
Eg (X) = 1.42 (1-X) + 2.26X-0.67X ² ・ ・ ・ ・ ・ (2)
[0052]
Next, a case where the semiconductor laser device of the present invention is used as an excitation light source for an SHG element will be described below with reference to FIGS. When the semiconductor laser device of the present invention shown in FIGS. 1 to 3 is used as an excitation light source for an SHG element, an oscillation wavelength, that is, an oscillation wavelength, that is, a high second harmonic conversion efficiency is obtained in a nonlinear optical element used as an SHG element. , It is necessary to control the wavelength that is distributed Bragg reflected. The wavelength of the distributed Bragg reflection can be controlled by controlling the value of the current injected into the contact layer 14c. This is because, when a current is mainly injected into the contact layer 14c, heat is generated below the contact layer 14c, thereby changing the refractive index of the region where the diffraction grating layer 7 is formed.
[0053]
That is, if the value of the current injected into the contact layer 14c is increased and the amount of heat generated under the contact layer 14c is increased, the effective refractive index with respect to the laser light propagating through the waveguide increases, so that the oscillation wavelength changes to the longer wavelength side. Can be done. Conversely, if the value of the current injected into the contact layer 14c is reduced and the amount of heat generated below the contact layer 14c is reduced, the oscillation wavelength can be changed to a shorter wavelength.
[0054]
In the semiconductor laser device of the present invention, if the length of the region where the diffraction grating layer 8 is formed on the DBR region in the laser emission direction is large, the distance at which the diffraction grating layer 8 and the guided light act on each other increases. In this case, the diffraction grating layer 8 can obtain a high reflectance with respect to light having a wavelength that is subjected to distributed Bragg reflection. Obtaining a high reflectance by the diffraction grating layer 8 is effective in lowering the operating current value and the threshold value of the oscillation current. In general, the reflectance for light having a wavelength that is subjected to distributed Bragg reflection reflects the strength of coupling between the diffraction grating layer 8 and the laser oscillation light (hereinafter, referred to as a “coupling coefficient κ”), and the refractive index of the diffraction grating layer 8. Length L formed in the wave path (length of diffraction grating layer 8 in the laser emission direction) L _dbr Can be estimated by
[0055]
FIG. 5 shows the reflectance of the diffraction grating layer and the length L in the laser emission direction of the diffraction grating layer when the coupling coefficient κ is changed. _dbr FIG. In FIG. 5, the coupling coefficient κ is 10 cm. ^-1 From 140cm ^-1 Has changed to In the calculation of the graph shown in FIG. 5, the waveguide loss was 20 cm. ^-1 Is set to
[0056]
As can be seen from FIG. ^-1 From 100cm ^-1 In order to obtain a reflectivity at the emission end face that can be obtained by cleavage, that is, a reflectivity higher than the so-called end face uncoating time (32%), it is necessary to use L _dbr Is required to be 200 μm or more.
[0057]
However, as shown in FIG. _dbr Is excessively increased, further improvement of the reflectance cannot be expected, and the reflectance is saturated. For example, κ is 40cm ^-1 In the case of L _dbr Is about 600 μm, the reflectance is saturated. Further, in this case, the heat dissipation in the region where the diffraction grating layer 8 is formed is improved, and the variable width of the oscillation wavelength due to heat generation is reduced. From this, within the range where the reflectance at the emission end face that can be obtained by cleavage can be obtained, L _dbr Is preferably as small as possible.
[0058]
Therefore, in order to obtain the reflectance at the emission end face that can be obtained by cleavage without impairing the variable width of the oscillation wavelength, it is necessary to use L _dbr Is preferably set to 200 μm to 600 μm. In the examples of FIGS. 1 and 2, L _dbr Is set to 300 μm, in which case κ is 40 cm ^-1 ~ 100cm ^-1 When the diffraction grating layer 8 is formed so as to fall within the range, the reflectance of 45% to 80% can be obtained by the diffraction grating layer 8. In the examples of FIGS. 1 and 2, the length of the DBR region in the laser emission direction is 600 μm. Further, in the examples of FIGS. 1 and 2, when the current was changed from 0 mA to 100 mA and the current was injected into the contact layer 14c, the change in the oscillation wavelength was 3 nm.
[0059]
When changing the wavelength for distributed Bragg reflection, there may be two or more wavelengths at which a high reflectance can be obtained near a desired oscillation wavelength. At this time, the oscillation wavelength may mode-hop to a wavelength having a high gain, and may deviate from a desired wavelength.
[0060]
In order to prevent this, in the examples of FIGS. 1 and 2, a current is injected into the contact layer 14b to change the amount of heat generated below the contact layer 14b, thereby controlling the refractive index of the waveguide below the contact layer 14b. are doing. That is, by changing the current injected into the contact layer 14b, control is performed such that the phase condition for laser oscillation of only a desired oscillation wavelength is always satisfied.
[0061]
By the way, when the length of the phase control region in the laser emission direction is large, heat radiation is improved, and the variability of the oscillation wavelength due to heat generation is impaired. Conversely, when the length of the phase control region in the laser emission direction is small, the change in the effective resonator length due to heat generation becomes small. The length of the phase control region in the laser emission direction affects the wavelength difference between adjacent longitudinal modes. That is, when the phase control region is long, the wavelength difference between adjacent longitudinal modes becomes small, and two or more longitudinal modes can exist in a wavelength range where a high reflectance can be obtained by the diffraction grating layer 8. As a result, the longitudinal mode becomes a multi-mode oscillation. In the SHG element, the wavelength range in which high conversion efficiency can be obtained is usually a very narrow wavelength range of 0.1 nm.
[0062]
Therefore, when the semiconductor laser device of the present invention is used as a light source of an SHG element, the semiconductor laser device needs to always oscillate in a single longitudinal mode at a wavelength at which high conversion efficiency can be obtained. For this reason, guaranteeing single longitudinal mode oscillation is very important. In order to guarantee the single longitudinal mode, it is necessary to widen the longitudinal mode interval so that it is not possible to obtain a high reflectance at which two or more longitudinal modes can simultaneously oscillate.
[0063]
Here, assuming that the longitudinal mode interval is Δλ, the wavelength is λo, the effective refractive index is Nr, and the resonator length is L, △ λ is given by the following equation (3). From the following equation (3), it can be seen that the resonator length should be as short as possible in order to increase the longitudinal mode interval Δλ. Δλ = λo ² / (2NrL) (3)
[0064]
In general, it has been found that if Δλ is 0.08 nm or more, single longitudinal mode oscillation occurs even during high-speed modulation in order to obtain single longitudinal mode oscillation. For example, if λo is 820 nm and Nr is 3.3, the resonator length L needs to be 1270 μm or less in order to make Δλ 0.08 nm or more.
[0065]
Assuming that the length of the gain region in the laser emission direction is La, the length of the phase region in the laser emission direction is Lph, and the effective length of the DBR region in the laser emission direction is Ldbrefff, L is given by the following equation (4). Can be
L = La + Lph + Ldrefff (4)
[0066]
Ldbref depends on the magnitude of the coupling coefficient κ. When the coupling coefficient κ is large, the reflectance of the laser beam by the diffraction grating layer becomes large, and the light intensity is attenuated at a short distance, so that Ldbref becomes small. Conversely, when the coupling coefficient is small, the reflection of the laser beam becomes small, and the laser beam exudes throughout the DBR region, so that Ldbref becomes small.
[0067]
For example, the coupling coefficient κ is 80 cm ^-1 When the diffraction grating layer is designed so as to satisfy the following condition, Ldbref is 62.4 μm. Further, when the length of the gain region in the laser emission direction is set to 700 μm, in order to reduce the cavity length L to 1270 μm or less, ie, to generate single longitudinal mode oscillation, the laser emission direction of the phase region Must be set to 507.6 μm or less.
[0068]
By the way, when the length Lph of the phase region in the laser emission direction is too short, the change in the effective resonator length due to heat generation becomes small. Therefore, the length Lph of the phase region in the laser emission direction needs to be 100 μm or more. Therefore, in the examples of FIGS. 1 and 2, the length Lph of the phase region in the laser emission direction is set to 250 μm.
[0069]
Generally, when a current is injected from the contact layer 14c into the active layer 4, a light-emitting component on a longer wavelength side than the band gap of the active layer 4 can be obtained due to the effects of carrier multi-body effect and heat generation. For example, if the bandgap wavelength in the phase control region and the DBR region of the active layer 4 is 795 nm, the wavelength of the spontaneous emission light before laser oscillation spreads to about 830 nm.
[0070]
Therefore, for example, if the band gap wavelength in the phase control region and the DBR region of the active layer 4 is set to 795 nm, and the wavelength distributed Bragg reflection by the diffraction grating layer 8 is set to 820 nm, the level near the band edge becomes Since it is easily absorbed and saturated, the absorption loss of the 820 nm laser oscillation light in the phase control region and the DBR region can be reduced.
[0071]
For this reason, in the semiconductor laser device of the present invention, it is preferable to form the diffraction grating layer 8 so that the wavelength subjected to distributed Bragg reflection is at least 20 nm longer than the band gap wavelength of the active layer 4.
[0072]
Further, in the semiconductor laser device shown in the examples of FIGS. 1 and 2, even when an excessive current is injected into the phase control region and the gain region, the oscillation wavelength selected in the DBR region can be obtained. . This is because in the examples of FIGS. 1 and 2, the maximum gain peak is obtained at around 805 nm, which is slightly longer than the bandgap wavelength of 795 nm of the active layer 4, but as shown in FIG. Since the inclination angle θ of the inclined portion 11b in the third light guide layer 11 to be formed is set to 5 °, the effective reflectance shown in FIG. ^-6 This is because the level becomes very small, which is about the same level or less, and ordinary Fabry-Perot mode oscillation is suppressed.
[0073]
As described above, in the examples of FIGS. 1 and 2, three contact layers 14 a to 14 c are provided in the laser emission direction, and each area of the active layer 4 immediately below each contact layer is replaced with a gain area for causing laser oscillation. , A phase control region for controlling the phase, and a DBR region for generating distributed Bragg reflection. Further, the diffraction grating layer 8 is formed such that the wavelength for distributed Bragg reflection is at least 20 nm longer than the band gap wavelength. For this reason, the phase control region and the DBR region correspond to the band gap wavelength in the gain region by disordering the well layer and the barrier layer of the phase control region and the DBR region using techniques such as impurity diffusion and ion implantation. Therefore, a DBR laser with low loss and variable wavelength can be obtained.
[0074]
1 and 2, the current blocking layer 12 is formed such that its band gap is larger than the band gap of the active layer 4, and the absorption of laser light by the current blocking layer 12 is suppressed. . Therefore, the loss in the waveguide can be significantly reduced, and the lower limit of the operating current can be reduced.
[0075]
Furthermore, due to the suppression of the absorption of the laser light by the current blocking layer 12, the light distribution of the laser light is not limited to the inside of the third light guiding layer 11, but the second light guiding layer 10 below the current blocking layer 12, It extends to one light guide layer 9 and the diffraction grating layer 8. Therefore, the ratio of the laser light propagated by the diffraction grating layer 8 increases, so that the coupling coefficient κ in the diffraction grating layer 8 that determines the wavelength selectivity can be set high. From this, if the semiconductor laser device shown in FIGS. 1 and 2 is used, the wavelength selectivity can be improved by the diffraction grating layer 8, and the single longitudinal mode can be maintained even when a temperature change, a light output change, or the like occurs. can do.
[0076]
In the examples of FIGS. 1 and 2, when the band gaps of the second light guide layer 10, the third light guide layer 11, and the current block layer 12 are Eg1, Eg2, and Eb, respectively, these layers have the following formulas. It is formed so that (5) is satisfied.
Eg1>Eb> Eg2 (5)
[0077]
Furthermore, in general, in semiconductor materials, the magnitude of the band gap and the refractive index are in an inversely proportional relationship. Therefore, when the refractive indexes of the second light guide layer 10, the third light guide layer 11, and the current blocking layer 12 are N1, N2, and Nb, the following equation (6) is derived from the above equation (5).
N1 <Nb <N2 (6)
[0078]
In this case, according to the above equation (6), a layer having a lower refractive index than the third light guide layer 11, that is, the second light guide layer 10 is present below the third light guide layer 11, so that the third light guide layer 11 is present. Inside 11, it is possible to spread the light distribution more vertically. Therefore, according to the examples shown in FIGS. 1 and 2, the beam radiation angle in the vertical direction can be reduced, and the coupling efficiency with the SHG element can be increased.
[0079]
In the same mixed crystal material such as AlGaAs and InGaP, the relationship between the dielectric constant and the band gap is inversely proportional to the refractive index. Therefore, the refractive index can be reduced by decreasing the dielectric constant. Further, when the dielectric constant of the second light guide layer 10 is reduced, the capacity of the depletion layer formed between the current blocking layer 12 and the third light guide layer 11 can be reduced. As a result, the oscillation wavelength, Deterioration of high-speed response of phase and optical output can be suppressed. Therefore, in a preferred embodiment, the Al composition of the second light guide layer 10 is increased to reduce the dielectric constant of the second light guide layer 10.
[0080]
Further, it is preferable that the AlAs mixed crystal ratio of the third light guide layer is made as small as possible. 1 and 2, the AlAs mixed crystal ratio of the third light guide layer is set to be smaller than the mixed crystal ratio of the current blocking layer 12.
[0081]
As described above, in the examples shown in FIGS. 1 and 2, by forming the semiconductor laser device so as to satisfy the above equations (5) and (6), it is possible to simultaneously improve the high-speed response characteristics and reduce the beam radiation angle. ing.
[0082]
Here, the AlAs mixed crystal ratio Xs of the first etching prevention layer 6 and the AlAs mixed crystal ratio Xg of the second optical guide layer 10 will be described. First, the AlAs mixed crystal ratio Xs of the first etching prevention layer 6 will be described.
[0083]
In the present invention, the value of the AlAs mixed crystal ratio Xs of the first etching prevention layer 6 is preferably as small as possible. This is because, when a layer having a large AlAs mixed crystal ratio becomes a regrowth interface during regrowth, the regrowth interface becomes a high-resistance layer by oxidation, so that the operating voltage and the operating current value increase, and the temperature characteristics of the element deteriorate. This is because reliability decreases.
[0084]
From experiments conducted by the inventors of the present invention, in order to reduce the influence of oxidation at the regrowth interface, the AlAs mixed crystal ratio of the layer (first etching prevention layer 6) serving as the regrowth interface is set to 0.3 or less. I know I need to. If the AlAs mixed crystal ratio of the layer serving as the regrowth interface (first etching prevention layer 6) is too small, the band gap of this layer becomes too small to absorb laser oscillation light, and as a result, the waveguide It is also known that the loss increases and the threshold value of the oscillation current and the operating current value increase.
[0085]
Therefore, in the examples of FIGS. 1 and 2, the value of Xs is set to 0.2. Therefore, if the semiconductor laser device shown in FIGS. 1 and 2 is used, the influence of oxidation caused by exposing the first etching prevention layer 6 to the atmosphere before regrowth can be reduced. Further, the first etching prevention layer 6 becomes transparent to the laser oscillation light in the 820 nm band, and furthermore, it is possible to form a low-resistance regrowth interface and prevent an increase in waveguide loss.
[0086]
In the examples of FIGS. 1 and 2, the thickness of the first etching prevention layer 6 is set to 10 nm. The reason why the thickness of the first etching prevention layer 6 is set so thin is that the controllability of the effective refractive index difference Δn between the inside and the outside of the ridge-shaped third optical guide layer 11 is not impaired. That's why.
[0087]
As described above, in the examples of FIGS. 1 and 2, the AlAs mixed crystal ratio Xs of the first etching prevention layer 6 is set to 0.2, and the first etching prevention layer 6 is a layer having a small AlAs mixed crystal ratio. It is. In general, the refractive index tends to increase as the AlAs mixed crystal ratio decreases. Further, the light distribution of the laser light propagating through the waveguide tends to concentrate on the layer having the highest refractive index.
[0088]
Therefore, as shown in FIGS. 1 and 2, when the first etching prevention layer 6 having a small AlAs mixed crystal ratio is provided in the vicinity of the active layer 4, the vertical light distribution of the laser light propagating through the waveguide is improved. It will be concentrated on the active layer 4. As a result, the light density of the active layer increases, the light output level that causes COD can be reduced, and the decrease in COD level can be suppressed.
[0089]
By the way, as the confinement of the light distribution in the vertical direction in the active layer 4 increases, the divergence angle in the vertical direction of the far-field image of the laser light emitted from the emission end face also increases. Therefore, the magnitude of the vertical spread angle is an index of the COD level. In order to obtain a high output operation of 100 mW or more, it can be said that it is preferable to minimize vertical light confinement in the active layer and minimize the vertical divergence angle.
[0090]
However, if the light confinement in the vertical direction in the active layer 4 is too small, the mode gain generated in the light distribution propagating through the waveguide also becomes small, so that the threshold value of the oscillation current and the operating current value increase. Therefore, in order to obtain a high COD level while suppressing an increase in the threshold value of the oscillation current and the operating current value, it is necessary to design the waveguide so that the vertical divergence angle is in the range of 15 ° to 19 °. There is.
[0091]
Controlling the lateral confinement of the light distribution inside the ridge-type third light guide layer 11 is important for obtaining a stable fundamental transverse mode oscillation up to a high output. The lateral confinement of the light distribution can be controlled by the magnitude of the effective refractive index difference Δn between the inside and the outside of the ridge-shaped third light guide layer 11.
[0092]
When the effective refractive index difference Δn is large, the confinement of the light distribution in the lateral direction becomes strong, so that the light density at the center of the waveguide becomes large, and strong stimulated emission occurs. As a result, in the active layer 4 located immediately below the central portion of the waveguide, spatial hole burning of carriers whose operating carrier concentration is reduced occurs. For this reason, the effective refractive index difference Δn is further increased due to the plasma effect, and confinement of the light distribution in the horizontal direction is further increased. As a result, the COD level is reduced. On the other hand, when the effective refractive index difference Δn is small, light confinement in the lateral direction becomes weak, and stable fundamental transverse mode oscillation cannot be obtained.
[0093]
From these points, in order to obtain stable fundamental transverse mode oscillation up to a high output, the value of Δn must be 3 × 10 ^-3 ~ 4 × 10 ^-3 It is necessary to design the waveguide so as to fall within the range.
[0094]
Next, the AlAs mixed crystal ratio Xg of the second light guide layer 10 will be described. The second light guide layer 10 also functions as an etching prevention layer when the third light guide layer 11 is formed into a ridge shape by etching. Therefore, Xg is preferably different from the AlAs mixed crystal ratio of the third light guide layer 11. Since the magnitude of Xg greatly affects the light distribution in the vertical and horizontal directions, care must be taken in setting its value.
[0095]
FIG. 6 is a diagram showing the relationship between the AlAs mixed crystal ratio Xg of the second light guide layer and the effective refractive index difference Δn of the third light guide layer.
[0096]
In FIG. 6, the effective refractive index difference Δn is obtained from the effective refractive index of the third light guide layer 11 and the effective refractive index of the active layer 4. Here, Δn1 is obtained from the effective refractive index of a region not located immediately below the diffraction grating layer 8, and Δn2 is obtained from the effective refractive index of a region located immediately below the diffraction grating layer 8.
[0097]
Since the diffraction grating layer 8 is formed of a material having a high refractive index, the light distribution in the vertical direction tends to concentrate on the active layer 4 immediately below the region where the diffraction grating layer 8 is formed. Therefore, as shown in FIG. 6, Δn1 is a value larger than Δn2.
[0098]
Further, as described above, in order to obtain high output and stable fundamental transverse mode oscillation, the value of Δn must be 3 × 10 ^-3 ~ 4 × 10 ^-3 Is required to be within the range. From FIG. 6, Xg needs to be about 0.5 or more in order to make both Δn1 and Δn2 within this range.
[0099]
FIG. 7 is a diagram showing the relationship between the AlAs mixed crystal ratio Xg of the second light guide layer and the vertical divergence angle. As described above, the vertical divergence angle needs to be within the range of 15 ° to 19 ° in order to obtain a high COD level while suppressing an increase in the threshold value of the oscillation current and the operating current value. Therefore, from FIG. 7, Xg needs to be about 0.55 or more.
[0100]
6 and 7, the AlAs mixed crystal ratio Xg of the second light guide layer is preferably 0.55 or more. In this case, stable fundamental transverse mode oscillation can be obtained without being affected by the presence or absence of the diffractive optical grating layer 8, and furthermore, a high COD level can be reduced while suppressing an increase in the threshold value and operating current value of the oscillation current. Obtainable.
[0101]
In the examples of FIGS. 1 and 2, the AlAs mixed crystal ratio Xg of the second light guide layer is set to 0.7, which is 0.2 larger than the AlAs mixed crystal ratio 0.5 of the third light guide layer 11. . This value is set such that the larger the difference in the AlAs mixed crystal ratio between the third light guide layer 11 and the second light guide layer is, the more the third light guide layer 11 is formed into a ridge shape by etching. This is because the selective etching property in that case can be improved.
[0102]
In the examples of FIGS. 1 and 2, the AlAs mixed crystal ratio of the current blocking layer 12 is set to 0.6, which is 0.1 larger than the AlAs mixed crystal ratio of the third light guide layer 11. . This is because if the AlAs mixed crystal ratio of the current blocking layer 12 is the same as the AlAs mixed crystal ratio of the third light guide layer 11, the refractive index inside the third light guide layer 11 decreases due to the plasma effect during current injection. This is because the third optical guide layer 11 becomes an anti-waveguide type waveguide and a single transverse mode oscillation cannot be obtained.
[0103]
In the semiconductor laser device of the present invention, as described above, the value of the effective refractive index difference Δn is set to 3 × 10 ^-3 ~ 4 × 10 ^-3 Within this range, stable fundamental transverse mode oscillation with high output can be obtained. Therefore, in order to stably produce a high-output semiconductor laser device with a high yield, the effective refractive index difference Δn should be 3 to 4 × 10 ^-3 You need to precisely control the range.
[0104]
Incidentally, the effective refractive index difference Δn obtained from the effective refractive index inside the third light guide layer 11 and the effective refractive index in the gain region that is not directly below the diffraction grating layer 8 is the distance between the current blocking layer 12 and the active layer 4. That is, the total (total film thickness) td of the film thicknesses of the second clad layer 5, the second etching prevention layer 7, the first light guide layer 9, and the second light guide layer 10, and the third light guide layer 11 It can be controlled by the difference Δx in the AlAs mixed crystal ratio with the current block layer 12.
[0105]
The current injected from the third light guide layer 11 spreads out of the third light guide layer 11 through the layers existing between the current blocking layer 12 and the active layer 4. At this time, if the total film thickness td is large, the reactive current not contributing to laser oscillation increases. Therefore, it is better that the total film thickness td is not too thick, and specifically, it is preferably 0.2 μm or less.
[0106]
On the other hand, if the total film thickness td is less than 0.05 μm, the reactive current not contributing to laser oscillation is reduced, but Δn is 10 μm. ^-2 The above value is large, and Zn, which is an impurity for making the third light guide layer 11 p-type, diffuses into the active layer 4 and the temperature characteristics of the active layer 4 deteriorate. Therefore, the total thickness td is preferably set to 0.05 μm or more. From these points, in the examples of FIGS. 1 and 2, the total film thickness td is set to 0.18 μm.
[0107]
In the present invention, the difference Δx in AlAs mixed crystal ratio, which is another important parameter for controlling the effective refractive index difference Δn, is preferably set to 0.05 to 0.15 or less. This is because if the difference Δx in the AlAs mixed crystal ratio is larger than 0.15, the reproducibility in production of the difference Δx in the AlAs mixed crystal ratio has a greater effect on Δn. If the difference Δx in the AlAs mixed crystal ratio is less than 0.05, the light distribution cannot be stably confined inside the third light guide layer 11, and stable fundamental transverse mode oscillation cannot be obtained. Because. 1 and 2, the difference Δx in the AlAs mixed crystal ratio is set to 0.1.
[0108]
As described above, when the semiconductor laser device is manufactured by setting the total film thickness td and the difference Δx between the AlAs mixed crystal ratios in the above-described range, the reactive current can be reduced. ^-3 The control of the effective refractive index Δn can be performed with the precision of the table.
[0109]
In the examples of FIGS. 1 and 2, the value of the effective refractive index difference Δn is 3 × 10 so that stable fundamental transverse mode oscillation with high output can be obtained. ^-3 ~ 4 × 10 ^-3 3.7 × 10 which is within the range ^-3 Is set to
[0110]
On the other hand, in the conventional semiconductor laser device shown in FIG. 24, a p-type AlGaAs (Al composition 0.15) diffraction grating layer 56 having a thickness of 0.25 μm is formed on the gain region of the active layer. When such a thick layer is formed on the gain region of the active layer, the light distribution of the laser light greatly spreads to the diffraction grating layer 56 having a low Al mixed crystal ratio, and the controllability of the light distribution in the lateral direction is impaired. For this reason, the semiconductor laser device shown in FIG. 24 needs to have a buried heterostructure in order to confine the light distribution in the lateral direction and provide an effective refractive index difference inside and outside the waveguide.
[0111]
However, when such a buried heterostructure is employed, the effective refractive index difference in the lateral direction becomes 10%. ^-2 The light distribution becomes extremely large as described above, and the light distribution is strongly confined in the horizontal direction. For this reason, when the semiconductor laser device is operated at a high output, spatial hole burning of carriers in the active layer occurs. This not only causes kink which causes non-linearity in current-light output characteristics, but also causes melting and destruction of the emission end face. From this, it can be said that it is difficult to realize a high-output DBR laser with the conventional semiconductor laser device shown in FIG.
[0112]
In the present invention, the difference Δxg between the AlAs mixed crystal ratio of the second etching prevention layer 7 and the AlAs mixed crystal ratio of the diffraction grating layer 8 is set as large as possible if the diffraction grating layer 8 is formed by wet etching. It is preferable to keep it. This is because, when the diffraction grating layer 8 is manufactured by wet etching, if Δxg is small, it becomes difficult to selectively etch only the diffraction grating layer 8.
[0113]
When the diffraction grating layer 8 is formed by wet etching, the control of the shape of the diffraction grating layer 8 is very important because it greatly affects the coupling coefficient κ between the guided light and the diffraction grating. Therefore, it can be said that the shape of the diffraction grating layer 8 is preferably controlled by selective etching, rather than by etching time.
[0114]
In order to improve the selective etching property, it is preferable that Δxg is large to some extent, specifically, it is preferable to set it to 0.05 or more. In the examples of FIGS. 1 and 2, ΔXg is set to 0.1. Note that the selective etching is an etching method in which the etching is stopped when the diffraction grating layer 8 is etched to expose the second etching prevention film 7 serving as a base.
[0115]
In the present invention, the thickness (maximum value) of the diffraction grating layer 8 is preferably set to 5 nm to 60 nm. 1 and 2, the thickness of the diffraction grating layer 8 is set to 20 nm. When operating at high output, ± 10 of Δn ^-3 Since it is necessary to control Δn in the DBR region with the precision of the stage, it is preferable that the film thickness of the diffraction grating layer 8 is as thin as possible so as not to significantly affect the light distribution. However, when the thickness is less than 5 nm, the coupling coefficient κ between the guided light and the diffraction grating decreases, and the reflectance of the laser beam in the DBR region decreases. On the other hand, if the thickness exceeds 60 nm, the coupling coefficient κ becomes large and a large reflectance can be obtained. However, the wavelength range in which a large reflectance can be obtained becomes large, and the selectivity of the oscillation wavelength is impaired.
[0116]
As described above, in the semiconductor laser device shown in the examples of FIGS. 1 and 2, the effective refractive index difference Δn is set to ± 10 in all of the gain region, the phase control region, and the DBR region. ^-3 It can be controlled with the precision of the table, and stable single transverse mode oscillation can be obtained even at high output.
[0117]
In the present invention, the band gap of the second cladding layer 5 needs to be sufficiently larger than the band gap of the active layer 4 in order to effectively confine carriers in the active layer 4 and obtain laser oscillation in the 820 nm band. is there. Therefore, the AlAs mixed crystal ratio of the second cladding layer 5 is preferably set to about 0.45 to 0.55. In the examples of FIGS. 1 and 2, the AlAs mixed crystal ratio of the second cladding layer 5 is set to 0.5.
[0118]
Further, in the present invention, the width W1 of the striped window (see FIGS. 1 and 2) is adjusted to the basic transverse mode in order to greatly widen the light distribution in the horizontal direction and reduce the maximum light density at the end face. It is good to make it as large as possible within the range. However, if it is too large, a higher-order transverse mode can be oscillated. Therefore, it is preferable that the width W1 of the striped window is set in the range of 2 μm to 5 μm. In the examples of FIGS. 1 and 2, the width W1 of the striped window is set to 3.5 μm. W2 is preferably set in the range of 2.5 μm to 5.5 μm in consideration of the relationship with W1 so as to easily obtain the fundamental transverse mode oscillation.
[0119]
In this case, it is preferable that the surface (lower surface) of the third light guide layer 11 on the side of the diffraction grating layer 8 is formed larger than the stripe-shaped window (upper surface). That is, it is preferable that the transverse section (the section perpendicular to the emission direction) of the third light guide layer 11 has a trapezoidal shape with the upper base being W1 and the lower base being W2 as shown in FIG. This is because, if the third light guide layer 11 has such a shape, the current block layer 12 can be easily regrown on the side surface (slope) of the third light guide layer 11.
[0120]
In the present invention, the period of the diffraction grating 8g (see FIG. 2) constituting the diffraction grating layer 8 is preferably set to a period that is an integral multiple of the wavelength in the medium. The wavelength of the laser light guided through the optical resonator is selected by the Bragg reflection by the diffraction grating 8g.
[0121]
The AlAs mixed crystal ratio of the diffraction grating layer 8 is preferable because it realizes good wavelength selectivity and facilitates regrowth on the diffraction grating layer 8. From the viewpoint of preventing absorption, it is preferably set to 0.3 or less. In the example of FIG. 1 and FIG. 2, it is set to 0.2.
[0122]
The wavelength selectivity of the diffraction grating 8g is determined by the difference in the refractive index between the diffraction grating layer 8 and the first optical guide layer 9 in which the diffraction grating 8g is embedded. Therefore, in the present invention, the AlAs mixed crystal ratio of the first light guide layer 9 is set to 0.5 or more in order to realize a sufficient refractive index difference from the diffraction grating layer 8 required for the single longitudinal mode. Is preferred. In the example of FIG. 1 and FIG. 2, it is set to 0.5.
[0123]
Here, the current injected into the gain region, the phase control region, and the DBR region will be described. FIG. 8 is a diagram showing the relationship between the current value and the optical output when the current is injected only into the gain region of the semiconductor laser device shown in FIG. FIG. 8 shows a case where the threshold value of the oscillation current is 25 mA. As shown in FIG. 8, in the semiconductor laser device shown in FIG. 1, a high optical output of 250 mW or more can be obtained by setting the current value of the injected current to 290 mA or more.
[0124]
Also, as can be seen from FIG. 8, the light output increases discontinuously as the current value of the injected current is increased by about 30 mA. This is because the longitudinal mode in which the laser oscillates hops to the adjacent longitudinal mode by current injection into the gain region. Further, in the case of a DBR laser such as the semiconductor laser device shown in FIG. This is because only the wavelength in the “DBR reflection window”).
[0125]
In the present invention, the diffraction grating 8g of the diffraction grating layer 8 has a DBR reflection window having a wavelength width of 0.2 nm or less and a mode gain difference between adjacent longitudinal modes existing in the DBR reflection window of 2 cm. ^-1 Preferably, it is formed as described above. In this case, the single longitudinal mode can be oscillated even during pulse modulation.
[0126]
Generally, when a current is injected into the gain region, the wavelength at which laser oscillation is possible changes to a longer wavelength side due to a change in the refractive index. Accordingly, the wavelength of the longitudinal mode is changed from the wavelength of the central region having a high reflectance in the DBR reflection window to the wavelength of an end region having a low reflectance. Therefore, when a current is injected into the gain region, the reflectance in the longitudinal mode (N-order mode) during laser oscillation decreases. Therefore, with the injection of current into the gain region, mode hop occurs when the wavelength of the adjacent longitudinal mode (N + 1 order mode) having a high order becomes a region where the reflectance from the diffraction grating 8g is high.
[0127]
FIG. 9 is a diagram illustrating the relationship between the value of the current injected into the phase control region and the oscillation wavelength. In general, when a current is injected into the phase control region, the effective resonator length changes due to a change in the refractive index of the phase control region while the wavelength at which a high reflectivity can be obtained by the DBR reflection window is constant. A mode hop will occur in the vertical mode.
[0128]
As can be seen from FIG. 9, every time the value of the current injected into the phase control region (phase control region injection current value) is increased by about 10 mA, a mode hop to the adjacent longitudinal mode existing in the DBR reflection window occurs. You can see that.
[0129]
Also, as the magnitude of the injection current value in the phase control region is increased, the oscillation wavelength changes to a slightly longer wavelength as a whole. This is because the heat generated in the phase control region is transmitted to the DBR region, and the DBR reflection window changes to the longer wavelength side as described later.
[0130]
FIG. 10 is a diagram showing the relationship between the value of the current injected into the DBR region and the oscillation wavelength. As can be seen from FIG. 10, when the value of the current injected into the DBR region (DBR region injection current value) is increased, the DBR reflection window undergoes a change in the refractive index due to heat generation, and the oscillation wavelength changes to the longer wavelength side.
[0131]
Further, since the laser oscillation wavelength is constant until the mode hops to the adjacent longitudinal mode, as shown in FIG. 10, the laser oscillation wavelength when current is injected into the DBR region changes stepwise. In the example of FIG. 10, when the DBR region injection current value changes from 0 mA to 100 mA, the laser oscillation wavelength changes from 820.2 nm to 823.1 nm by about 3 nm.
[0132]
From the characteristics shown in FIGS. 9 and 10, if current is injected into the phase control region and the DBR region at the same time, it is possible to continuously change the oscillation wavelength while keeping the order of a certain longitudinal mode constant. You can see that it is possible.
[0133]
Next, a manufacturing process of the semiconductor laser device of the present invention will be described with reference to FIGS. FIGS. 11, 12 and 13 are perspective views showing steps of manufacturing the semiconductor laser device shown in FIG. 11 (a) to 11 (d), 12 (e) to 12 (h), and 13 (i) to 13 (k) show one process in the manufacturing process of the semiconductor laser device shown in FIG. These are a continuous series of steps.
[0134]
First, as shown in FIG. 11A, an n-type GaAs buffer layer 2 and an n-type GaAs buffer layer 2 are formed on a substrate 1 formed of n-type GaAs by MOCVD or MBE. _0.5 Al _0.5 As first cladding layer 3, active layer 4, p-type Ga _0.5 Al _0.5 As clad layer 5 of As, first etching prevention layer 6 of p-type GaAlAs, p-type Ga _0.4 Al _0.6 As second etching prevention layer 7 of As, p-type Ga to be a diffraction grating layer _0.8 Al _0.2 An As layer 8 'is formed.
[0135]
In the example of FIG. 11A, Se is used as the n-type dopant. This is for improving the single longitudinal mode property at the time of pulse modulation by the saturable absorption effect of Se. Si is used as a p-type dopan.
[0136]
In the example of FIG. 11A, the active layer 4 has an unstrained multiple quantum well structure, as already described in the description of FIGS. However, the present invention is not limited to this, and the active layer 4 may have a strained quantum well structure or may be a bulk made of a single material. Also, the conductivity type of the active layer is not particularly limited, and may be p-type or n-type, or may be undoped.
[0137]
Next, as shown in FIG. 11B, a diffraction grating layer 8 having a diffraction grating 8g periodically arranged along the laser emission direction is formed. In the example of FIG. 11B, the diffraction grating layer 8 is formed by p-type Ga. _0.8 Al _0.2 This is performed by applying a resist on the As layer 8 ', forming a resist pattern using an interference exposure method, an electron beam exposure method, or the like, and further performing wet etching or dry etching.
[0138]
Next, as shown in FIG. 11C, a part of the diffraction grating layer 8 and a part of the second etching prevention layer 7 located immediately above the gain region and the phase control region are wet-etched or dry-etched. To remove.
[0139]
Next, as shown in FIG. 11D, a resist and SiO 2 are formed in a region on the gain region of the first etching prevention layer 6. ₂ Film or SiN _x A protective film 15 such as a film is formed, and ion implantation or impurity diffusion is performed on the entire upper surface of the stacked body shown in FIG. As a result, the portion of the active layer 4 (a) where the protective film 15 is not formed is disordered, and the size of the band gap increases.
[0140]
Next, as shown in FIG. 12E, the MOCVD method or the MBE method is used to cover the diffraction grating layer 7 and the exposed portions of the first and second etching prevention layers 6 and 7. , P-type Ga _0.5 Al _0.5 First optical guide layer 9 of As, p-type Ga _0.3 Al _0.7 A second light guide layer 10 of As is formed, and a 2 μm-thick p-type Ga _0.5 Al _0.5 An As layer 11 'is formed.
[0141]
Next, as shown in FIG. _0.5 Al _0.5 A stripe-shaped resist pattern is formed on the As layer 11 'by photolithography, and wet etching is performed to form the ridge-shaped third light guide layer 11 shown in FIG. This etching is performed until the second light guide layer 10 is exposed.
[0142]
In this etching, an etchant that selectively etches a layer having an AlAs mixed crystal ratio of about 0.5 is used. Therefore, Ga _0.3 Al _0.7 Etching stops at the second light guide layer 10 of As. Therefore, variation in characteristics due to variation in etching can be suppressed, and a semiconductor laser device suitable for mass production with high yield can be obtained.
[0143]
Next, as shown in FIG. 12 (g), SiO 3 is formed on the upper surface of the third light guide layer 11 serving as a stripe-shaped window. ₂ Film and SiN _x A protective film 16 such as a film that enables selective growth is formed. Thereafter, as shown in FIG. 12 (h), the n-type Ga is applied so that the side surface of the third light guide layer 11 and the exposed portion of the second light guide layer 10 are covered. _0.4 Al _0.6 The current blocking layer 12 is formed by selectively growing the As layer.
[0144]
Subsequently, as shown in FIG. 13I, the protective film 16 is removed by etching. Next, as shown in FIG. 13J, a p-type Ga layer is formed on the current block layer 12 and the third light guide layer 11. _0.5 Al _0.5 A third cladding layer 13 of As and a p-type GaAs layer 14 are formed.
[0145]
Thereafter, as shown in FIG. 13 (k), the p-type GaAs layer 14 is subjected to wet etching or dry etching, and is divided into three to form contact layers 14a, 14b and 14c. In order to increase the output, a low reflection coating having a reflectance of 3% is applied to the front end face from which the laser light is emitted, and a non-reflection coating having a reflectance of 1% or less is applied to the rear end face.
[0146]
As shown in FIG. 3, since the rear end face of the third light guide layer 11 serving as a waveguide is bent, the reflectance of the rear end face is 10%. ^-6 The following are very small values. However, by applying the above-described anti-reflection coating to the rear end face, reflection from the rear end face that does not depend on the diffraction grating can be suppressed, so that the longitudinal mode control by the diffraction grating can be further ensured.
[0147]
Next, another example of the semiconductor device of the present invention will be described with reference to FIGS. 14 to 16 are perspective views showing other examples of the semiconductor laser device of the present invention.
[0148]
In the semiconductor laser device shown in FIG. 14, the second light guide layer 10 is formed only in a region directly below the third light guide layer 11, and the side surface of the second light guide layer 10 and the third light guide layer 11 It differs from the semiconductor laser device shown in FIGS. 1 to 3 in that the side face is sandwiched by the current block layer 12. Except for the points described above, the semiconductor laser device shown in FIG. 14 has the same configuration as the semiconductor laser device shown in FIGS.
[0149]
The semiconductor laser device shown in FIG. 14 is manufactured by the manufacturing process shown in FIGS. 11 to 13, similarly to the semiconductor laser device shown in FIGS. 1 to 3. However, in the semiconductor laser device shown in FIG. 14, in the step of FIG. 12F, etching is performed until the first light guide layer 9 is exposed. Is different.
[0150]
Thus, in the semiconductor laser device shown in FIG. 14, p-type Ga having a high AlAs mixed crystal ratio is used. _0.3 Al _0.7 The current blocking layer 12 is formed on the exposed first light guide layer 9 by removing the As second light guide layer 10 except for a part thereof. Therefore, when the current blocking layer 12 is formed by regrowth, oxidation of the regrowth interface can be suppressed. As a result, the deterioration of the crystallinity of the current block layer 12 can be reduced, and the threshold value of the oscillation current and the operating current value can be reduced.
[0151]
In the semiconductor laser device shown in FIG. 15, the thickness of the second light guide layer 10 that is not in the region directly below the third light guide layer 11 is reduced, and the current is applied on the thinned second light guide layer 10. The difference from the semiconductor laser device shown in FIGS. 1 to 3 is that a block layer 12 is formed. Except for the above, the semiconductor laser device shown in FIG. 15 has the same configuration as the semiconductor laser device shown in FIGS. Note that the thickness of the second light guide layer 10 is 100 ° in a portion that is not thinned, and is 50 ° in a portion that is thinned.
[0152]
The semiconductor laser device shown in FIG. 15 is also manufactured by the manufacturing steps shown in FIGS. 11 to 13, similarly to the semiconductor laser device shown in FIGS. However, in the semiconductor laser device shown in FIG. 15, in the step of FIG. 12F, the second light guide layer 10 is also etched to reduce its thickness. Is different from the semiconductor laser device shown in FIG.
[0153]
As described above, in the semiconductor laser device shown in FIG. 15, the current blocking layer 12 is formed with the etched surface of the etched second optical guide layer 10 as a regrowth interface. Therefore, also in the semiconductor laser device shown in FIG. 15, the oxidation of the regrowth interface can be suppressed, so that the crystallinity degradation in the current block layer 12 can be reduced, and the threshold value of the oscillation current and the operating current value can be reduced. .
[0154]
In the semiconductor laser device shown in FIG. 16, the second light guide layer 10 is formed only in a region directly below the third light guide layer 11, and the first light that is not in a region directly below the third light guide layer 11. The difference from the semiconductor laser device shown in FIGS. 1 to 3 is that the thickness of the guide layer 9 is reduced and the current blocking layer 12 is formed on the first optical guide layer 9 having the reduced thickness. Except for the points described above, the semiconductor laser device shown in FIG. 16 has the same configuration as the semiconductor laser device shown in FIGS.
[0155]
The semiconductor laser device shown in FIG. 16 is also manufactured by the manufacturing steps shown in FIGS. 11 to 13, similarly to the semiconductor laser device shown in FIGS. However, in the semiconductor laser device shown in FIG. 16, in the step of FIG. 12F, the first light guide layer 9 is exposed and the first light guide layer 9 is also etched. 3 is different from the semiconductor laser device shown in FIGS.
[0156]
Thus, in the semiconductor laser device shown in FIG. 16, p-type Ga having a high AlAs mixed crystal ratio is used. _0.3 Al _0.7 The second light guide layer 10 of As is removed except for a part thereof, and a current block 12 layer is formed with the etched surface of the first light guide layer 9 etched as a regrowth interface.
[0157]
Therefore, in the semiconductor laser device shown in FIG. 16, similarly to the semiconductor laser device shown in FIG. 14, when the current blocking layer 12 is formed by regrowth, oxidation of the regrowth interface can be suppressed. . As a result, the deterioration of the crystallinity of the current block layer 12 can be reduced, and the threshold value of the oscillation current and the operating current value can be reduced.
[0158]
The semiconductor laser device of the present invention is not limited to the semiconductor laser device using the above-described GaAlAs-based material. In the present invention, other materials, for example, include at least one of B, In, Al, and Ga as Group V atoms, include at least nitrogen as Group V atoms, and further include As, P, As as Group V atoms. Containing at least one of B, In, Al, and Ga as a group V atom represented by a group V nitride-based semiconductor material that may also include, and an InGaAlP-based material and an InGaAsP-based material; As a V-V semiconductor material containing at least one of As, P and As, and at least one of Zn and Cd as a V-group atom represented by a ZnSMgSe-based material, A V-V group semiconductor material containing at least one of S, Se, and Mg can also be used.
[0159]
Further, in the above-described semiconductor laser device of the present invention, the current blocking layer 12 having a larger band gap than the active layer 4 is formed on the side surface of the third optical guide layer 11 serving as a waveguide, and the real refractive index waveguide is formed. Although it has a mechanism, the present invention is not limited to this. In the semiconductor laser device of the present invention, for example, a part as a current blocking layer may be provided by performing ion implantation or impurity diffusion on a part of the third light guide layer 11. Further, the semiconductor laser device of the present invention may have a ridge waveguide structure having a complex refractive index waveguide mechanism. The complex refractive index waveguide mechanism refers to a structure in which a layer formed of a material that absorbs laser oscillation light is formed on the side surface of the ridge-shaped third light guide layer 11 in order to confine light in the lateral direction.
[0160]
Further, in the above-described semiconductor laser device of the present invention, the third optical guide layer 11 serving as a waveguide has a real refractive index waveguide mechanism in which the waveguide has a forward mesa shape. The layer 11 may have a real refractive index waveguide mechanism in an inverted mesa shape. Further, the current block layer 12 can be formed in an inverted mesa shape, and the material of the current block layer 12 is SiN, SiO ₂ Any material having a band gap larger than that of the active layer such as an insulating material such as AlGaInP may be used.
[0161]
In the above-described semiconductor laser device of the present invention, the third cladding layer 13 is formed so as to cover the upper surface of the current blocking layer 12 and the upper surface (striped window) of the third light guide layer 11. It can also be formed in a ridge shape so as to cover only the window of the shape. In this case, the same effect can be obtained.
[0162]
The semiconductor laser device of the present invention can also be applied to lasers other than DBR lasers, for example, to distributed feedback (DFB) semiconductor lasers, surface emitting lasers, buried heterostructure (BH) lasers, and the like. It is possible. Further, the semiconductor is divided into other electrodes in the direction of the resonator so that the optical output, the bias power, the phase, the wavelength, and the time waveform of the optical output can be individually controlled, thereby enabling further precise control of the operation characteristics. It is also applicable to lasers.
[0163]
Next, a second harmonic generator according to the present invention will be described with reference to FIGS. FIG. 17 is a side view showing an example of the second harmonic generation device of the present invention. As shown in FIG. 17, the second harmonic generation device of the present invention includes a semiconductor laser device 21 of the present invention shown in FIG. 1, FIG. 14, FIG. An SHG element (nonlinear optical element) 22 for generating two harmonics is provided.
[0164]
The SHG element 22 includes a waveguide (not shown) and a diffraction grating 24. The SHG element 22 is arranged so that the excitation light 25 emitted from the semiconductor laser device 21 is coupled to the waveguide of the SHG element.
[0165]
Therefore, when the excitation light 25 is coupled to the waveguide of the SHG element 22, it is diffracted by the diffraction grating 45, and its phase is matched with the phase of the second harmonic. As a result, the excitation light 25 is converted into a second harmonic by the SHG element 22 and emitted from the SHG element 22 as a second harmonic 26.
[0166]
At this time, in order to prevent the far field pattern of the second harmonic wave 26 from being reflected and disturbed by the substrate 23, the end face of the substrate 23 and the end face of the SHG element 22 are brought as close as possible, and the distance between these end faces in the emission direction is set. Is preferably within 10 μm. It is also preferable that the end face of the SHG element 22 projects from the end face of the substrate 23 in the emission direction. In a preferred embodiment, the distance between the semiconductor laser device 21 and the SHG element 22 is made as close as possible in order to increase the coupling between the excitation light and the waveguide formed in the SHG element.
[0167]
By the way, in the semiconductor laser device 21 of the present invention, the diffraction grating layer is not provided above the gain region of the active layer as described above, and therefore, the diffraction grating layer hardly affects the light distribution. Therefore, in the semiconductor laser device 21 of the present invention, the light distribution can be precisely controlled, and the vertical spread angle of the excitation light 25 can be set to 20 ° or less.
[0168]
For this reason, in the second harmonic generation device of the present invention, high coupling efficiency can be obtained even when the distance between the semiconductor laser device 21 and the SHG element 22 is 2 μm or more. Further, since the setting range of the distance between the semiconductor laser device 21 and the SHG element 22 is widened, it is possible to obtain the second harmonic 26 with high reproducibility and high efficiency.
[0169]
In the second harmonic generation device of the present invention, as a constituent material of the substrate 23, any material can be used without particular limitation as long as it can form a flat surface and can form an electrode pattern. Specific examples include semiconductors such as Si, SiC, and AlN, and insulating materials such as glass and resin.
[0170]
Further, as a constituent material of the SHG element 22, a material capable of generating the second harmonic wave 26, for example, LiNbO ₃ , KTP and the like. When the oscillation wavelength of the semiconductor laser device 21 is 820 nm, LiNbO ₃ By using the SHG element formed by the method described above, it is possible to obtain a high-output laser beam in a blue-violet region having a wavelength of 410 nm.
[0171]
FIG. 18 is a diagram illustrating an example in which the second harmonic generation device illustrated in FIG. 17 is used as a light source of an optical pickup. In the example of FIG. 18, a diffraction grating 27 is arranged on the emission side of the second harmonic generator 20. For this reason, the second harmonic 26 emitted from the second harmonic generator 20 is branched into a plurality of emission directions. In FIG. 18, reference numerals 28, 29 and 30 denote branched second harmonics. In particular, reference numeral 29 denotes a 0th-order diffracted light, 28 denotes a -1st-order diffracted light, and 30 denotes a + 1st-order diffracted light.
[0172]
When the second harmonic generator having the diffraction grating 27 is used as a light source of an optical pickup, the zero-order diffracted light 29 is used for reading and writing bit information recorded on an optical disc. The -1st-order diffracted light 28 and the + 1st-order diffracted light 30 are used for detecting the position of a track formed on the optical disc.
[0173]
Further, as described in FIG. 17, the oscillation wavelength of the semiconductor laser device 21 is set to 820 nm, and the SHG element is set to LiNbO 2. ₃ Since a high-output laser beam having a wavelength of 410 nm in the blue-violet region can be obtained, the present invention can be applied to a light source for a high-density optical disk system capable of reading and writing.
[0174]
FIG. 19 is a diagram showing another example in which the second harmonic generator shown in FIG. 17 is used as a light source of an optical pickup. In the example of FIG. 19, a lens 31 is disposed on the emission side of the second harmonic generator 20. Therefore, the second harmonic 26 emitted from the second harmonic generator 20 is collected by the lens 31.
[0175]
When the second harmonic generator including the lens 31 is used as a light source of an optical pickup, the second harmonic 26 is focused to the diffraction limit of the lens 51. Therefore, even when the bits formed on the optical disk are small, reading and writing of bit information can be performed. Also, as in the example of FIG. 18, the present invention can be applied to a light source for a high-density optical disk system capable of reading and writing.
[0176]
FIG. 20 is a diagram illustrating another example in which the second harmonic generation device illustrated in FIG. 17 is used as a light source of an optical pickup. In the example of FIG. 20, an optical element 32 is disposed on the emission side of the second harmonic generator 20. The optical element 32 has a birefringent characteristic, and by using the optical element 32, only a predetermined deflection component can be extracted from light including a plurality of deflection components. Thus, the second harmonic 26 emitted from the second harmonic generator 20 is separated into TE mode light and TM mode light having different polarization directions.
[0177]
In an optical disk system in which information is recorded on an optical disk according to the direction of magnetization, a light source having a high polarization ratio is required as a light source. However, the second harmonic generator 20 including the optical element 32 can efficiently use one of the polarized light sources. Since only light in the wave direction, for example, TE mode light can be extracted, it can be suitably used for such an optical disk system.
[0178]
Next, an optical pickup device of the present invention will be described with reference to FIGS. FIG. 21 is a side view showing an example of the optical pickup device of the present invention. In the example of FIG. 21, the optical pickup device of the present invention includes the second harmonic generator 20, the diffraction grating 27, and the substrate 41 shown in FIG.
[0179]
The substrate 41 has a light receiving element 43 and a mirror 42. The light 44 reflected on the recording surface of the optical disc is received by the light receiving element 43. Further, the second harmonic 26 emitted from the second harmonic generator 20 is reflected by the mirror 42 in the normal direction of the substrate 41 and enters the diffraction grating 27.
[0180]
With this configuration, the light receiving section and the light emitting section required for signal detection of the optical pickup can be integrated on the same substrate. Therefore, the optical pickup device can be reduced in size and thickness.
[0181]
In the optical pickup device of the present invention, as a constituent material of the substrate 41, it is preferable to use a material capable of forming the light receiving element 43 by pn control. Specifically, a V-group semiconductor material such as Si or SiC, or at least one of B, In, Al, and Ga as a V-group atom, at least nitrogen as a V-group atom, and further as a V-group atom Group V atoms represented by at least one of B, In, Al, and Ga as a group V atom represented by a group V nitride-based semiconductor material that may contain As, P, and As, and an InGaAlP-based material and an InGaAsP-based material. V-V semiconductor material including at least one of As, P, and As as V-group atoms, and at least one of Zn and Cd as V-group atoms represented by ZnSMgSe-based material. And V-V semiconductor materials containing at least one of S, Se, and Mg as V-group atoms.
[0182]
Note that the substrate 41 can be made of a material that cannot form a light receiving element by pn control. In this case, the light receiving element 43 may be formed of, for example, a resin material such as glass or plastic.
[0183]
FIG. 22 is a side view showing another example of the optical pickup device of the present invention. In the example of FIG. 22, the optical pickup device of the present invention includes the second harmonic generator 20, the lens 31, and the substrate 41 shown in FIG. The optical pickup device shown in FIG. 22 has the same configuration as the optical pickup device shown in FIG. 21 except that a lens 31 is provided. Therefore, also with this configuration, the light receiving unit and the light emitting unit required for signal detection of the optical pickup can be integrated on the same substrate, so that the optical pickup device can be reduced in size and thickness.
[0184]
FIG. 23 is a side view showing another example of the optical pickup device of the present invention. In the example of FIG. 23, the optical pickup device of the present invention includes the second harmonic generator 20, the optical element 32, and the substrate 41 shown in FIG. The optical pickup device shown in FIG. 23 has the same configuration as the optical pickup device shown in FIG. 21 except that the optical element 32 is provided. Therefore, also with this configuration, the light receiving unit and the light emitting unit required for signal detection of the optical pickup can be integrated on the same substrate, so that the optical pickup device can be reduced in size and thickness.
[0185]
In the examples shown in FIGS. 21 to 23, the diffraction grating 27, the lens 31, and the optical element 32 are separated from the substrate 41. However, in the present invention, they can be directly integrated on the substrate 41. In this case, the size and thickness of the optical pickup device can be further reduced.
[0186]
【The invention's effect】
As described above, according to the semiconductor laser device of the present invention, it is possible to suppress the portion of the active layer on the emission end face on the side of the diffraction grating layer from being melted and destroyed, and to suppress a decrease in the COD level. Further, since the semiconductor laser device of the present invention can have a real refractive index waveguide structure, it is possible to realize high output while lowering the threshold value of the oscillation current and the operating current value.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of a semiconductor laser device of the present invention.
FIG. 2 is a side view of the semiconductor laser device shown in FIG.
FIG. 3 is a top view of the semiconductor laser device shown in FIG. 1;
FIG. 4 is a diagram showing a relationship between an effective reflectance and a tilt angle θ.
FIG. 5 shows the reflectance of the diffraction grating layer and the length L in the laser emission direction of the diffraction grating layer when the coupling coefficient κ is changed. _dbr FIG.
FIG. 6 is a diagram showing a relationship between an AlAs mixed crystal ratio Xg of a second light guide layer and an effective refractive index difference Δn of a third light guide layer.
FIG. 7 is a diagram showing the relationship between the AlAs mixed crystal ratio Xg of the second light guide layer and the vertical divergence angle.
FIG. 8 is a diagram showing a relationship between a current value and an optical output when a current is injected only into a gain region of the semiconductor laser device shown in FIG. 1;
FIG. 9 is a diagram illustrating a relationship between a value of a current injected into a phase control region and an oscillation wavelength.
FIG. 10 is a diagram showing a relationship between a value of a current injected into a DBR region and an oscillation wavelength.
FIG. 11 is a perspective view showing a manufacturing process of the semiconductor laser device shown in FIG. 1;
FIG. 12 is a perspective view illustrating a manufacturing process of the semiconductor laser device illustrated in FIG. 1;
FIG. 13 is a perspective view showing a manufacturing process of the semiconductor laser device shown in FIG. 1;
FIG. 14 is a perspective view showing another example of the semiconductor laser device of the present invention.
FIG. 15 is a perspective view showing another example of the semiconductor laser device of the present invention.
FIG. 16 is a perspective view showing another example of the semiconductor laser device of the present invention.
FIG. 17 is a side view showing an example of the second harmonic generation device of the present invention.
18 is a diagram illustrating an example in which the second harmonic generation device illustrated in FIG. 17 is used as a light source of an optical pickup.
19 is a diagram illustrating another example in which the second harmonic generation device illustrated in FIG. 17 is used as a light source of an optical pickup.
20 is a diagram showing another example in which the second harmonic generation device shown in FIG. 17 is used as a light source of an optical pickup.
FIG. 21 is a side view showing an example of the optical pickup device of the present invention.
FIG. 22 is a side view showing another example of the optical pickup device of the present invention.
FIG. 23 is a side view showing another example of the optical pickup device of the present invention.
FIG. 24 is a side view schematically showing a structure of a conventional DBR laser.
[Explanation of symbols]
1 substrate
2 Buffer layer
3 First cladding layer
4 Active layer
5 Second cladding layer
6 First etching prevention layer
7 Second etching prevention layer
8 Diffraction grating layer
8g Diffraction grating constituting diffraction grating layer
8 'p-type Ga serving as diffraction grating layer _0.8 Al _0.2 As layer
9 First light guide layer
10 Second light guide layer
11 Third light guide layer
11a Part parallel to the axis perpendicular to the cleavage plane of the third light guide layer
11b A portion inclined with respect to an axis perpendicular to the cleavage plane of the third light guide layer
12 Current block layer
13 Third cladding layer
14 p-type GaAs layer
14a, 14b, 14c Contact layer
15, 16 protective film
21 Semiconductor laser device
22 SHG element
23 Substrate Constituting Second Harmonic Generator
24 SHG element diffraction grating
25 Excitation light
26 Second harmonic
27 diffraction grating
28 -1st order diffracted light
290th order diffracted light
30 + 1st order diffracted light
31 lenses
32 optical elements
41 Substrate Constituting Optical Pickup Device
42 mirror
43 Light receiving element

Claims (13)

An active layer, a semiconductor laser device having a diffraction grating layer located above the active layer,
The diffraction grating layer is formed in a range narrower than the main surface of the active layer,
The active layer has a first region including a region directly below the diffraction grating layer, and a second region not including a region directly below the diffraction grating layer, and includes a band in the first region. The semiconductor laser device, wherein the gap is larger than the band gap in the second region. A first light guide layer, a second light guide layer, and a ridge-type third light guide layer are sequentially formed on the diffraction grating layer,
A current blocking layer of a conductivity type opposite to that of the third light guide layer is formed on the second light guide layer so as to sandwich a side surface of the third light guide layer,
2. The relationship of Eg1>Eb> Eg2 is satisfied when the band gaps of the second light guide layer, the third light guide layer, and the current block layer are Eg1, Eg2, and Eb, respectively. Semiconductor laser device. 2. The semiconductor laser device according to claim 1, wherein a layer formed of a constituent material having a lower etching rate than a constituent material of the diffraction layer is provided between the active layer and the diffraction layer. 3. 2. The semiconductor laser device according to claim 1, wherein a plurality of layers functioning as electrodes are arranged on the uppermost layer along the laser emission direction. 5. The semiconductor laser device according to claim 4, wherein there are three layers functioning as said electrodes, and a gain, a phase and an oscillation wavelength are controlled by the magnitude of a current injected into each of said layers. 2. The semiconductor laser device according to claim 1, wherein a band gap wavelength in the first region is set shorter than an oscillation wavelength of the laser light. 3. The semiconductor laser device according to claim 2, wherein the third light guide layer has a portion parallel to an axis perpendicular to the cleavage plane and a portion inclined with respect to an axis perpendicular to the cleavage plane. 3. The semiconductor laser device according to claim 2, wherein the third light guide layer has a trapezoidal cross section perpendicular to the emission direction. The diffraction grating layer, the first light guide layer, the second light guide layer, and the third light guide layer are formed by doping Si, and the current blocking layer is formed by doping Se. The semiconductor laser device according to claim 2, wherein: The semiconductor laser device according to any one of claims 1 to 11, and a nonlinear optical element having a waveguide, wherein the nonlinear optical element transmits laser light emitted from the semiconductor laser device to the waveguide. A second harmonic generator, wherein the second harmonic generator is arranged to be coupled. The second harmonic generator according to claim 10, wherein the semiconductor laser device and the nonlinear optical element are arranged on the same substrate. 12. A diffraction grating, a condenser lens, and one of optical elements for extracting only a predetermined deflection component from light including a plurality of deflection components, and the second harmonic generator according to claim 10 or 11. An optical pickup device comprising at least: 13. The optical pickup device according to claim 12, wherein the second harmonic generator according to claim 10 or 11 is disposed on a substrate, and a light receiving element is provided on the substrate.

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