JPH01313980A - Second harmonic wave generating device - Google Patents

Abstract

PURPOSE:To increase conversion efficiency, and realize high density integration by arranging a second harmonic wave generating region composed of II-VI compound semiconductor crystal, on a semiconductor laser layer composed of III-V compound semiconductor, and providing a diffraction grating at a position, in the region, where laser light diffracted by a diffraction grating in a semiconductor laser arrives. CONSTITUTION:A second harmonic wave generating region (SHG region) II is constituted of II-VI compound semiconductor crystal. For example, epitaxial growth is enabled on an AlGaAs system semiconductor laser, and the SHG region II can be easily formed in a unified body. Since the fundamental wave from the semiconductor laser I couples with the SHG region II without passing the external space, the intensity of the fundamental wave can be increased. By a diffraction grating GI in the semiconductor laser I, the fundamental wave generated from the semiconductor laser I is diffracted in the direction of the SHG region II and introduced. By diffracting the introduced fundamental wave with a diffraction grating GII in the SHG region II, the fundamental wave is effectively converted into the second harmonic wave. Thereby high density integration is enabled, and the conversion efficiency is increased.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a device for generating second harmonics of semiconductor laser light. This device is useful, for example, in recording and reproducing optical recording media, and in, for example, semiconductor manufacturing processes. [Prior art] Conventionally, wavelength/month/2 (angular frequency is 2
For example, a device schematically shown in FIGS. 6(a) and 6(b) is known as a device for generating a second harmonic wave, that is, a second harmonic wave. This device includes a conversion element 61 for converting the wavelength of a fundamental laser beam and a fundamental wave generation light source 60.
It is a device having the following. Note that the conversion element 61 in FIG. 6(a) is a schematic cross-sectional view taken along the line BB shown in FIG. 6(b), and FIG. 6(b) is a schematic side view of the conversion element 61. . As shown in this figure, the fundamental wave (angular frequency: W, wavelength: λ
0) is introduced into the waveguide 62 of the conversion element 61 from the fundamental wave generation light source 60, a part of the fundamental wave propagates in a region 63 diagonally downward with respect to the waveguide 62 and becomes a second harmonic (angle Frequency = 2W, wavelength: λo/2). Note that the propagation region 63 of the second harmonic is diagonally downward because the second harmonic is phase matched with the fundamental wave in this direction. A LiNbO5 crystal is adopted as the conversion element 61, and LxN
A conversion element in which an optical waveguide 62 is formed by ion-exchanging Li'''' of a bOs crystal with Ho has been developed at the Matsushita Electric Industrial Semiconductor Research Center and has already been announced. According to the above announcement, the wavelength is 0.84 for this conversion element.
When 7L11 semiconductor laser light is introduced as the fundamental wave,
A second harmonic with a wavelength of 0.42μ is generated. If such a second harmonic generator is used for recording or reproducing an optical recording medium such as an optical disk, the area of the light spot can be reduced to 1/2 by reducing the wavelength of the laser beam to 1/2.
4, the optical recording density can be increased four times. Furthermore, pattern density can also be improved when used in semiconductor manufacturing processes that utilize light, such as exposure, etching, and doping.

[Problem to be solved by the invention]

The conventional second harmonic generator as described above is required to be further miniaturized and integrated. Furthermore, there is a need for a compact integrated second harmonic generation device that is not inferior in performance such as conversion efficiency to conventional devices, and preferably has improved performance. The conversion efficiency, which is one of the performances of the second harmonic generator, will be described below as a conventional example. Normally, the conversion efficiency improves in proportion to the intensity of the fundamental wave, but the Li
Nb0. In a device made of a crystal, the light emitted from the fundamental wave generating light source 60 once exits to the outside space, so the coupling efficiency with the conversion element 61 becomes small, and the light emitted from the fundamental wave generation light source 60 is
It is not possible to efficiently increase the strength of the fundamental wave within. Therefore, its conversion efficiency is as low as about 2.5%. The purpose of the present invention is to achieve sufficient performance such as conversion efficiency,
Another object of the present invention is to provide a second harmonic generator device that is small and integrated. [Means for Solving the Problems J] The present invention provides a second semiconductor laser layer made of a ■-■ group compound semiconductor crystal on a semiconductor laser layer made of an m-v group compound semiconductor crystal.
an element on which a harmonic generation region is mounted, and a diffraction grating within the semiconductor laser at a position where the fundamental laser beam from the active layer of the semiconductor laser reaches, and within the second harmonic generation region. The second harmonic generation device is characterized in that it has a diffraction grating at a position where the laser light diffracted by the diffraction grating in the semiconductor laser reaches. In other words, the apparatus of the present invention is an apparatus in which a fundamental wave generating light source and a conversion element are integrated, and the element is compactly integrated as a monolithic device. Hereinafter, the small integrated elements included in the device of the present invention will be explained in detail. The semiconductor laser in the device of the present invention is made of a ■-■ group compound semiconductor crystal, and examples thereof include AlGaAs-based semiconductors, Ga1nAs-based semiconductors, GaAsSb-based semiconductors, and Ga1nAsP-based semiconductors. The second harmonic of these ■-v group compound semiconductor lasers is
Compared to the second harmonic of TV-Vl group compounds (pb series), it has a shorter wavelength, so it is suitable for use in recording and reproduction of optical recording media, semiconductor manufacturing processes, etc. as mentioned earlier. be. The second harmonic generation region (hereinafter referred to as SH) in the device of the present invention
(referred to as G region) is composed of II-Vl group compound semiconductor crystals, such as Zn5eS-based crystals, Zn5eT
Examples include e-based crystals, Cd)1gTe-based crystals, and the like. Since a ■-■ group compound is used as the SHG region, it can be grown epitaxially on, for example, an AI GaAs semiconductor laser, and the SHG region can be easily integrated. Can not. Furthermore, since the fundamental wave from the semiconductor laser is coupled to the SHG region without passing through the external space, the intensity of the fundamental wave can be increased and high conversion efficiency can be obtained. In the device of the present invention, in order to introduce and optically couple the fundamental wave generated from the semiconductor laser into the SHG region, a diffraction grating in the semiconductor laser at a position where the fundamental wave laser light from the active layer of the semiconductor laser reaches. , and a diffraction grating in the SHG region at a position where the laser light diffracted by the diffraction grating in the semiconductor laser reaches. In other words, the fundamental wave generated from the semiconductor laser is diffracted and introduced in the direction of the SHG region by the diffraction grating in the semiconductor laser, and the introduced fundamental wave is diffracted by the diffraction grating in the SHG region to effectively produce the second harmonic. Can be converted into waves. Note that the term "diffraction grating" as used herein refers to an interface where two layers with different refractive indexes are laminated, and the interface between the eyebrows is formed in a regular uneven surface shape. Regarding the pitch and diffraction angle of the unevenness of this diffraction grating,
This will be explained in Example 1, which will be described later. Further, in the element included in the device of the present invention, the second harmonic and the fundamental wave coexist, but if it is necessary to selectively emit the second harmonic from the element, for example,
The device of the present invention may be provided with an end face that reflects the fundamental laser beam oscillated from the semiconductor laser and transmits the second harmonic of the fundamental laser beam. The device of the present invention is a second harmonic generating device characterized by having at least an element having the configuration as described above, and further includes means for applying a voltage in the forward direction of a semiconductor laser, etc., if necessary. , various components are added as appropriate.

【Example】

Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 FIGS. 1(a) and 1(b) are diagrams showing an example of an element in an apparatus of the present invention, and FIG.
FIG. 1(b) is a cross-sectional view taken along the line A-A shown in FIG. 1(b) in a direction parallel to the resonance plane. The device of this example has Ga on a p''-GaAs substrate 25.
An As/AlGaAs semiconductor laser (I) is formed,
Furthermore, a ZeSeS-based SHG region (II) is added on top of it.
This is an element formed by epitaxial growth using the E method. Furthermore, inside this semiconductor laser (1), there is a diffraction grating G.
(I) is formed, and a diffraction grating G (II) is formed inside the SHG region (II). In addition, in order to apply a voltage in the forward direction (perpendicular to the laminated film) to this element, a p-type electrode 26 made of Au is formed on the underside of the substrate 25, and an n-type electrode made of Au! 1 is formed on the SHG region (II) via an insulating layer 12 such as 5isN< or SiO□, which constitutes a current injection window. The configurations of the semiconductor laser (I) and the SHG region (II) of this example will be explained in more detail below. The QaAs/AlGaAs semiconductor laser (I) has a thickness of 0. The p-GaAs active layer 22 of tu is p-A
lo, a Gao, sAs p-clad layer 23 and n-Alo, t Gao, a As n-clad layer 1
Consists of a double heterostructure sandwiched between 9 and 21,
A configuration is included in which a diffraction grating G (I) is formed between the n-Ale, 4 Gao, 8 As layer 20 and the n-cladding layer 19. In addition, i-AI is used for the purpose of confining the current.
o, 2 Gao, s As layer 18 as low cladding layer 19
After the film is formed, it is etched, regrown, and buried. Furthermore, there is a p'' between the substrate 25 and the p-clad l1f23.
- A GaAs buffer layer 24 is formed. The pitch of the diffraction grating G(1) will be explained below. In this example, the semiconductor laser (I) and the SHG region (ir) are joined so that their respective waveguides are parallel, and the diffraction gratings G(I) and G(II) are also parallel to it. Therefore, the pitch Δ(I) of the diffraction grating G(I)
can be determined by the following formula (1). Δ(I)−J2・(λO/2π) ・・・・・・(
1) °C: degree, that is, an integer of 1 or more. Furthermore, it is necessary that °C≧2. Further, in this embodiment, the pitch in the case of β=3 was adopted. Although the coupling efficiency improves as β becomes smaller, it is easier to form a diffraction grating when β is larger, so β=3 is considered to be the most appropriate value. In this example, since the fundamental laser beam oscillated from the active layer 22 has a wavelength of λ6 = 900 nm and π = 3.385, the pitch Δ(I) = 3 according to the above formula (1).
It becomes 99 nm. The structure of the Zn5eS-based SHG region (II) is that an n-Zn5eo, eSo, r layer 15 is formed between Ga-doped n-Zn5e SHG layers 14 and 16, and the layer 15 and the layer The interface with 16 is the diffraction grating G(II)
It is formed as. That is, the diffraction grating G(I
The formation of I) was carried out by adding n-Zn5ea, eSo, r near the center of the Ga-doped +rZnSe layer. In addition, 5HGJif 14 and 16 are no.
-Zn5eo, 9 So, sandwiched between r layers 13 and 17. Further, 5HGJi 13 and 17 have a high carrier concentration for the purpose of improving ohmic contact. The grating pitch of the diffraction grating G(II) is such that the diffracted light from the diffraction grating G(1) in the semiconductor laser is
In the case of this embodiment, the diffraction grating G (I) and the same order CI) are set in accordance with the above formula (1) so that the input coupling can be made into ! =3. ! = 3, λ, ) = 900 nm, π = 2.485, and the pitch is determined from the above equation (1), the pitch Δ(I
I)=543 nm. Further, the rear end surface (b) of the element of this example is made of, for example, Ti.
It is coated with a dielectric multilayer film such as O2 or 5iOa, and has a reflectance of 90 for both the fundamental wave and the second harmonic.
% or more. In addition, the front end surface (a) is coated with a dielectric multilayer film with a different configuration, and the reflectance for the fundamental wave is 90% or more, but the reflectance for the second harmonic is l
It is as low as 0%. The device of this embodiment is a second harmonic generation device having the elements configured as described above. Next, an example of a process in which the second harmonic is generated in the apparatus of this embodiment will be described. First, as shown in FIG. 1(b), a current is injected in the forward direction of the element. In other words, carriers are transferred to the n-type electrode 11 and the p-type electrode 11.
injection from the shaped electrode 26. Note that carriers from the n-type electrode 11 are first injected into the SHG region (II) from the current injection window (that is, the part where the insulating layer 12 is not formed), and since the SHG region (II) is n-type, The carriers will be injected into the semiconductor laser (I). Then, the fundamental laser beam (wavelength λ6 = 900 nm, effective refractive index π = 3.385 in the laser) becomes the first
It oscillates with a light intensity distribution of mode w(I) as shown in Figure (a). As shown in mode w(1), the oscillated fundamental wave laser light is also sufficiently present in the diffraction grating G(I) part, and the fundamental wave laser light in that part is shown in c and d in the figure. ,
It is diffracted in the directions of e and f. Each diffraction angle (the angle that the diffracted light forms with the normal to the diffraction grating surface) can be calculated using the following equation (2). sinθ=(2m/jri -1...(2)θ:
Diffraction angle m: 0.1.2 or 3 f2: Order in the above equation (1) In this example, β=3, so the above equation (2) becomes the following equation (3). sin θ = (2m/3)-1 (3) θ: diffraction angle m: Oll, 2 or 3 Therefore, from the above formula (3), the diffraction angle θ is
O", 70.5@, 109.5°, 180". Among these four types of diffracted light, the diffraction angles are 70.5° and 1
The diffracted light at 09.5° (e and f directions) enters the SHG region (II) and is injected into the diffraction grating G (II). The fundamental wave diffracted light incident on the diffraction grating G(II) is diffracted in directions g, h, i, and j in the figure. As mentioned earlier, the diffraction grating G(II) has the same order as the diffraction grating G(I)<t=s), so from the above formula (3), the diffraction angle is
It can be seen that the diffraction angles are O", 70.5", 109.5", and 180°, respectively. Among these four types of diffracted lights, the diffraction angles are Oo and 180°.
The diffracted light (j and g directions) of 5HGN14 and 1
6, there is a fundamental laser beam with a light intensity distribution of mode w(II) shown in FIG. 1(a). A part of the fundamental wave of this mode w(II) is 5HGIJ14
Due to the second-order nonlinear effect at 16 and 16, the light is converted into a second-order harmonic of the light intensity distribution of mode 2w (II) as shown in FIG. 1(a). This second harmonic is phase matched while propagating in the SHG region,
The light is emitted from the front end surface (a). As mentioned earlier, the reflectance of the front end face (a) for the second harmonic is lO
%, but the reflectance for the fundamental wave is 90% or more, so the fundamental waves of mode w(I) and mode w(II) are hardly emitted. As explained above, diffraction gratings G(I) and G(II
), the semiconductor laser (I) and the SHG region (II)
will be optically coupled. Note that in the semiconductor laser (1), due to the nonlinearity of AlGaAs, a part of the fundamental laser light is converted into second harmonics, but most of it is absorbed in the semiconductor laser (I). , for some of the second harmonics that are not absorbed, the diffraction gratings G(I) and G(II) act as 6th-order (71=6) diffraction gratings, so they are in the SHG region (II) along with the fundamental wave. The light is coupled into the front end face (a), and is emitted from the front end face (a). Embodiment 2 FIG. 2 shows another embodiment of the element in the device of the present invention, and is a sectional view in a direction parallel to the resonance plane. The device of this example has almost the same configuration as the device of Example 1, except that the SHG region (IT) has a ridge shape. By making the SHG region (II) into a ridge shape, the lateral confinement of the second harmonic becomes good, and therefore, the i-Alo for confining the current in Example 1,
x Gao, a Since AsN 13 is not needed, it does not have that layer 18. Further, in the semiconductor laser (I) of this embodiment, since the equal low refractive index of the lower part of the ridge is increased, the oscillation light is confined in the lower part of the ridge due to the difference in the equal refractive index. In other words, the semiconductor laser (I) of this example is a refractive index guided laser with high efficiency. The device of this embodiment is a second harmonic generation device having the elements configured as described above. That is, the second harmonic generation device has a refractive index waveguide type element that can generate the second harmonic well as in Example 1 and has good lateral confinement of the second harmonic. Embodiment 3 FIG. 3 shows another embodiment of the element in the device of the present invention, and is a sectional view in a direction parallel to the resonance plane. In the device of this example, the current injection window formed by the insulating layer 12 extends not over the top surface of the ridge but on both sides of the bottom of the ridge! This device has almost the same configuration as the device of Example 2, except that it is formed in the following manner. In addition, in order to maintain good ohmic contact, a low resistance n''-GaAs cap layer 27 is newly provided. No current flows directly through (II). Therefore, for example, when driving a laser, S
When a current is passed directly to the HG region (II), the SHG region (
II) will no longer become a high voltage of several tens of volts. Furthermore, in this embodiment, since no current is directly passed through the SHG region (II), the I constituting the SHG region (II)
There is no need to dope the I-Vll group ring conductor crystal with impurities, the laser drive voltage can be reduced, and the SHG region (II
) The absorption of harmonics due to the lowering of the energy gap also decreases. Furthermore, when a current is directly passed through the SHG region (II), since the SHG region (II) is n-type, the substrate 26 needs to be p-type; however, in this embodiment, p-type and n-type Both substrates are available. Furthermore, in this embodiment, since the current is injected to both sides of the lower part of the ridge and from l, the stability of the transverse mode of the fundamental laser beam oscillated from the semiconductor laser (1) is excellent. This is due to the following reasons. - That is, in a normal semiconductor laser, a plasma effect occurs in which the refractive index decreases in proportion to the concentration in a portion where the carrier concentration has increased. Therefore, for example, when current is injected from the top of the ridge, the refractive index near the peak of the carrier distribution (gain distribution) decreases, and laser light leaks laterally by the amount of the decrease.
However, in this embodiment, since current is injected from both sides of the lower part of the ridge and from l, the carrier distribution in the active N22 becomes broad Gaussian or bimodal. Further, below k and 1, the equipolar refractive index decreases due to the plasma effect. In the element of this example, as in Example 2, the equipolarized refractive index of the lower part of the ridge is increased, so carriers are confined to the lower part of the ridge, but k and ! By lowering the equipolar refractive index on the lower side of , the difference in the equipolar refractive index becomes even larger, and its confinement is performed better. The device of this embodiment is a second harmonic generation device having the elements configured as described above. That is, this is a second harmonic generation device that can generate the second harmonic well as in Example 2 and has elements that exhibit the advantages described above. Embodiment 4 FIG. 4 shows another embodiment of the element in the device of the present invention, and is a sectional view in a direction parallel to the resonance plane. The device of this example has almost the same structure as that of Example 3 except that the semiconductor laser (I) has a lateral injection type (TJS) structure. The structure of the semiconductor laser (I) portion of the device of this example will be described in detail below. In the semiconductor laser (I), an n-type AlGaAs type semiconductor crystal is epitaxially grown on an insulating 1-GaAs substrate 30, and the active layer 28 has a double heterostructure. After forming the n-type AlGaAs film, a low concentration Zn diffusion region (p) and a high concentration Zn diffusion region (o) are created by diffusion of Zn, and the n-GaAs active layer 28 is laterally p-p”.
-n homozygous and serves as a recombination region. Carriers are injected into the semiconductor laser (I) through the p-side electrode 26 and the n-side electrode 11. The device of this embodiment is a second harmonic generation device having the elements configured as described above. That is, the second harmonic can be generated well as in Example 2, and furthermore, since an insulating substrate is used, it is suitable for integration, which is an advantage due to the TJS structure. Although Examples 1 to 4 of the present invention have been described above, the present invention is not limited to these. For example, in Examples 1 to 4, the SHG region is Zn
Although it has a double heterostructure of 5e, it has a superlattice structure,
For example, Zn5e 50 A/Zn5eo, *So
, +5OA multi-periodic structure. For example, although the pitch of the diffraction grating G(II) in the SHG region in Examples 1 to 4 was constant, as shown in FIG. By changing the settings, harmonics can be emitted vertically from the end face. Hereinafter, a description will be given of how to change the grating pitch so that the second harmonic is phase matched. In Examples 1 to 4, the diffraction grating pitch Δ1 on the semiconductor laser side and the diffraction grating pitch Δ2 on the SHG side are the wavelength λ of the fundamental wave. It is calculated by the above formula (1) based on the effective refractive index π and the effective refractive index π. Therefore, in order to phase match the second harmonic, calculation cannot be made directly from the above equation (1). Because, 5
) (The second harmonic generated in the G region (II) has a wavelength of λ
o/2, the effective refractive index is naturally different from that of the fundamental wave. That is, the grating pitch Δ3 for phase matching of the second harmonic
can be determined by the following equation (4). Δ3 = β' ・ (λo / 2) / 2π'
......(4) λ0: Wavelength of the fundamental laser beam in vacuum π': Effective refractive index of the second harmonic in the SHG region β' = An integer greater than or equal to 1 Therefore, for example, as shown in FIG. As such, the diffraction grating G(
It is sufficient to optically couple the laser beams in a part of II) (the part with a pitch Δ2), and perform phase matching of harmonics in a part (the part with a pitch Δ3). In Examples 1 to 4, the wavelength of the fundamental laser beam is λ6
= 900 nm, below the effective refractive index of the second harmonic'
is 2.60. Therefore, the above formula (4) is expressed as Δ3
=86.5412'. In order to set the pitch Δ3 to a value similar to the pitch Δ2 (=543 nm), c'=6 may be used, and in that case, Δ3 = 519 nm. (Effects of the Invention) As explained above, the second harmonic generator device of the present invention is a highly integrated device in which the fundamental wave generation light source and the conversion element are integrated, and the element is small and integrated as a monolithic device. It is a highly standardized device and has sufficient performance such as conversion efficiency.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are cross-sectional views showing the device of Example 1, FIGS. 2-4 are cross-sectional views showing the devices of Examples 2-4, respectively, and FIG. A schematic diagram showing an aspect of a diffraction grating of an element of the invention. FIGS. 6(a) and 6(b) are schematic diagrams showing an example of a conventional second harmonic generator. 11.27... N-type electrode 12... Insulating layer 13, 17 ・=n"-ZnSeo, e So,
r layer 14, 16 ・S HGN n-Zn5e15・=
-n-Zn5eo, *So, r layer 18=-i-
Ala, z Gao, a As layer 19.21...n-
Cladding layer 20 -- n-Alo, 4 Gao, s As layer 2
1- ++jl-Alo, a Gao, s Asf
f1F22, 28...active layer 23...
・P-cladding layer 24...Buffer layer 2
5,3θ...Substrate 26...P-type capacitor 28...
... Active layer 29 ... Cladding layer G (I), G (II) ... Diffraction grating (a) ...
・Front end face (b)...Rear end face 60...
... Fundamental wave generation light source 61 ... Conversion element 62 ...
... Waveguide 63 ... Second harmonic propagation region Patent applicant Canon Corporation

Claims (3)

[Claims] (1) It has an element in which a second harmonic generation region made of a group II-VI compound semiconductor crystal is mounted on a semiconductor laser layer made of a group III-V compound semiconductor crystal, and A diffraction grating is provided at a position where the fundamental laser beam from the active layer of the semiconductor laser reaches, and a diffraction grating is provided at a position where the laser beam diffracted by the diffraction grating in the semiconductor laser reaches within the second harmonic generation region. A second harmonic generator characterized by having a grating. (2) The second harmonic generation device according to claim 1, wherein the element has an end face that reflects the fundamental laser beam oscillated from the semiconductor laser and transmits the second harmonic of the fundamental laser beam. (3) The second harmonic generation device according to claim 1 or 2, further comprising means for applying a voltage in the forward direction of the semiconductor laser.