JPH10321953A - Second higher harmonics generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a high output in a second higher harmonics generating device. SOLUTION: Adjacent to an outgoing end face of a phase synchronous semiconductor laser 3, a nonlinear waveguide type wavelength conversion array element 4 is arranged on the same substrate where a quasi-phase matching domain inversion array waveguide 6 and a diffraction grating 7 are also formed. By the return light from the differaction grating 7, the fundamental wave oscillated from the phase synchronous semiconductor laser 3 is incident on a domain inversion array waveguide 6 and is converted into second harmonics in the domain inversion array waveguide 6, and the second harmonics are output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a second harmonic generator, and more particularly, to a second harmonic generator having a semiconductor laser and a wavelength conversion element having a periodic domain inversion structure. It is.

[0002]

2. Description of the Related Art A method of converting a fundamental wave into a second harmonic using an optical wavelength conversion element provided with a region where a spontaneous polarization (domain) of a ferroelectric material having a nonlinear optical effect is periodically inverted. Has already been proposed by Bleombergen et al. (See Phys. Rev., vol. 127, No. 6, 1918 (1962)). In this method, the period ド メ イ ン of the domain inversion unit is set to {c = 2π / {β (2ω) -2β (ω)} where β (2ω) is the propagation constant of the second harmonic and 2β (ω) is the propagation constant of the fundamental wave. By setting so as to be an integral multiple of the coherent length Λc given by a constant, the fundamental wave and the second harmonic can be phase-matched (so-called quasi-phase matching).

As shown in, for example, Japanese Patent Application Laid-Open No. 6-69582, an optical waveguide type optical conversion wavelength element having an optical waveguide made of a nonlinear optical material and converting the wavelength of a fundamental wave guided therethrough is used. Attempts have been made to form a periodic domain inversion structure as described above to achieve efficient phase matching.

Further, a semiconductor laser in which a semiconductor laser and a waveguide wavelength conversion element for generating a second harmonic by quasi-phase matching using a periodic domain inversion structure are efficiently coupled to each other, and a non-reflection coating is applied to an emission surface side The laser is fed back by a distributed reflection type diffraction grating formed on the second harmonic generation element, and the oscillation wavelength of the semiconductor laser is controlled to twice the wavelength of the second harmonic generation element to generate the second harmonic. The generating element is disclosed in U.S. Pat. No. 5,185,752.

[0005]

However, in the above configuration, the optical output of the semiconductor laser used practically is 150 m.
It is limited to about W and there is a drawback that a high-power second harmonic cannot be obtained.

The present invention has been made in view of the above circumstances, and has as its object to provide a second harmonic generator capable of generating a high-power second harmonic.

[0007]

According to the present invention, there is provided a second harmonic generation apparatus comprising: a phase-locked semiconductor laser array having a plurality of waveguides for oscillating a fundamental wave; And a wavelength conversion array element having a plurality of waveguides for converting the fundamental wave emitted from each of the waveguides into a second harmonic.

The wavelength conversion array element is a nonlinear waveguide array element including a quasi phase matching domain inversion array waveguide and a diffraction grating arranged on the phase-locked semiconductor laser array side, and feedback from the diffraction grating is provided. The fundamental wave is oscillated from the phase-locked semiconductor laser array by light, the fundamental wave incident on the domain inversion array waveguide is converted into a second harmonic, and the second harmonic is output. Is desirable.

It is preferable that the domain inversion array waveguide and the diffraction grating are formed on the same substrate, and the period of the diffraction grating and the period of the domain inversion are the periods for phase matching with the fundamental wave.

Further, it is desirable that the diffraction grating is a distributed black reflection type diffraction grating.

[0011]

According to the second harmonic generation device of the present invention, a fundamental wave is generated using a phase-locked semiconductor laser array, and the fundamental wave oscillated from each of the plurality of waveguides is applied to each of the wavelength conversion array elements. Since the fundamental wave is incident on the domain inversion waveguide and converted into the second harmonic in each domain inversion waveguide and output, the total output is obtained by integrating the output from each waveguide, and the high output second harmonic is obtained. You can get the waves.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic top view of a second harmonic generator according to a first embodiment of the present invention. 2, 3 and 4 are sectional views taken along line II-II in FIG.
It is the III-III line sectional view and the IV-IV line sectional view.

The second harmonic generator is a phase-locked semiconductor laser array 3 having a plurality of waveguides 10 coupled in a Y-branch.
And a non-linear waveguide type wavelength conversion array element 4 disposed on the emission end face (front surface) side of the semiconductor laser array 3 and having a diffraction grating 7 and a periodic domain inversion array waveguide 6.

First, the fabrication of the phase-locked semiconductor laser array 3 will be described.

An n-Alx1Ga1-x1As cladding layer 12, an Alx2Ga1-x2As optical waveguide layer 13, and an Alx3Ga1-x are formed on an n-GaAs substrate 11 by metal organic chemical vapor deposition (MOCVD).
3As active layer 14, Alx2Ga1-x2As optical waveguide layer 15, p-Alx
A 1Ga1-x1As cladding layer 16 and a p-GaAs cap layer 17 are sequentially laminated. The composition satisfies x3 <x2 <x1, which is a value that can confine light and carriers.

Further, after an insulating film is formed on the cap layer 17, a plurality of stripes 10a having a width of about 3 μm and Y-branch coupling to the stripes 10a which are continuous with the stripes 10a and adjacent to each other are performed by ordinary lithography. A plurality of Y-branch stripes 10b are patterned on an insulating film,
Using this insulating film as a mask, the p-Alx1Ga1-x1As cladding layer 16 is partially removed by dry or wet etching to form Y-coupled ridge stripes.
After that, p-Inx4 (Ga1-z
4Alz4) 1-x4As1-y4Py4 The layer 18 is selectively buried. p-Inx4 (Ga1-z4Alz4) 1-x4As1-
The refractive index of the y4Py4 layer 18 (0 ≦ z4 ≦ 1, x4 to 0.49y4) is p−
A composition that is smaller than the refractive index of the Alx1Ga1-x1As cladding layer 16 is used. The remaining thickness of the p-Alx1Ga1-x1As cladding layer 16 is in a range from zero to about 300 nm, and the thickness is such that the waveguide 10 having a narrow stripe structure composed of a ridge structure achieves a single transverse mode refractive index waveguide. Is a value (approximately 1 μm) that couples so that the phases of the light oscillated from each stripe can be synchronized with each other. Subsequently, the insulating film is removed, the p-GaAs contact layer 19 is grown, the n-side electrode 20 and the p-side electrode 21 are formed, and further cut into bars by cleavage, and the front surface from which light is emitted is coated with an antireflection film. 1, and a high reflectivity coat 2 is applied to the rear surface. Then cut into chips.

Next, the nonlinear waveguide type wavelength conversion array element 4
Will be described.

For example, Applied Physics Letters, Vol. 69
No. 18, (1996) pp. 2629-2631, or JP-A-6-242479.
It is manufactured by using the method for manufacturing a periodic domain inversion structure described in No. The material is MgO- cut out in the direction perpendicular to the Z axis.
Using LiNbO 3, a domain that electrically polarizes in the Z-axis direction is periodically inverted in the X-axis direction by a corona discharge method to form a periodic domain inversion structure 5. The cycle of domain inversion is
The period is set to a period in which the fundamental wave oscillated by the semiconductor laser array 3 is quasi-phase matched. Thereafter, the wafer is cut out in a direction perpendicular to the Y-axis, the Y-plane is polished, and the array is guided from above the Y-plane by ordinary lithography and the proton exchange method described in, for example, the aforementioned US Pat. No. 5,185,752. A wave path 6 is formed. The width and the spacing of the waveguides are set to the same size as the waveguide 10 of the semiconductor laser array 3. The distributed Bragg reflection (DBR) diffraction grating 7 is a primary diffraction grating having a period in the X-axis direction, and is formed by ordinary holographic exposure, selective removal of a mask, and dry or wet etching. The period is a period for locking the wavelength of the fundamental wave. Then, the cut surface is polished by cutting in the direction perpendicular to the X axis, and a non-reflection coating 8 is applied to the incident surface side with respect to the wavelength of the phase-locked semiconductor laser. A non-reflection coating 9 is applied to the emission surface for the second harmonic.

The waveguide 10b on the emission side of the phase-locked semiconductor laser array 3 manufactured as described above and the waveguide 6 on the diffraction grating 7 side of the nonlinear waveguide type wavelength conversion array element 4 are directly coupled.

The principle of laser oscillation is as follows. The phase-locked semiconductor laser array 3 oscillates in TE fundamental single mode by feedback light from the diffraction grating 7 formed in the MgO-LiNbO3 nonlinear waveguide type wavelength conversion array element 4, and the fundamental wave oscillated in fundamental single mode has a wavelength. The light enters the periodic domain inversion array waveguide 6 formed in the conversion array element 4 and is converted into a second harmonic. The second harmonic is emitted from the emission end face on which the non-reflection coating 9 is applied. A plurality of waveguides 10b are provided by a phase-locked semiconductor laser array 3 having a Y-branch coupling waveguide 10.
Phase-locked fundamental wave is oscillated (Applied Physic
s Letter, Vol. 49 (1986) pp. 1632-1634), since each fundamental wave is converted to a second harmonic and output, the total output is higher than that of the conventional device. Can be obtained.

FIG. 5 is a schematic top view of a second harmonic generator according to a second embodiment of the present invention. 6, 7, and 8
6 is a sectional view taken along line II-II, a sectional view taken along line III-III, and a sectional view taken along line IV-IV in FIG. 5, respectively.

The second harmonic generation device comprises a phase-locked semiconductor laser array 33 having a plurality of waveguides 40 coupled in a Y-branch.
And a nonlinear waveguide type wavelength conversion array element 34 disposed on the emission end face (front surface) side of the semiconductor laser array 33 and having a diffraction grating 37 and a periodic domain inversion array waveguide 36.

First, the fabrication of the phase-locked semiconductor laser array 33 will be described.

An n-Inx1 (Alx2Ga1-x2) 1- is formed on an n-GaAs substrate 41 by metal organic chemical vapor deposition (MOCVD).
x1P cladding layer 42 (x1 = 0.49), Inx1 (Alx3Ga1-
x3) 1-x1P optical waveguide layer 43, Inx4Ga1-x4P tensile strain active layer 44, Inx1 (Alx3Ga1-x3) 1-x1P optical waveguide layer 45, p-Inx1 (Alx2Ga1-x2) 1-x1P cladding layer 46, p- GaAs cap layers 47 are sequentially stacked. Composition is x3 <x
2 <x1, which is a value that can confine light and carriers.

Further, after an insulating film is formed on the cap layer 47, a plurality of stripes 40a having a width of about 3 μm and continuous with the stripes 40a are formed by ordinary lithography.
A plurality of Y-branch stripes 40b, which are Y-branch-coupled to adjacent stripes 40a, are patterned into an insulating film, and the insulating film is used as a mask to dry or wet etch the p-Inx1 (Alx2Ga1-x2) 1-x1P cladding layer 46. To form a ridge stripe for Y-coupling. After that, using the insulating film as a mask, p-Inx
1Al1-x1P layer 48 is selectively buried. p-Inx1 (A
The remaining thickness of the lx2Ga1-x2) 1-x1P cladding layer 46 is in the range of about 0 to 300 nm, and is a thickness that achieves single transverse mode refractive index guiding in the narrow-striped waveguide 40 having a ridge structure. The distance between the stripes is set to a value (about 1 μm) that couples the phases of the light emitted from the stripes so that they can be synchronized with each other. Subsequently, the insulating film is removed, a p-GaAs contact layer 49 is grown, an n-side electrode 50 and a p-side electrode 51 are formed, and the bar is cut out by cleavage, and the front surface from which light is emitted is coated with an antireflection film. 31
Then, a high reflectance coat 32 is applied to the rear surface. Then cut into chips.

Next, the nonlinear waveguide type wavelength conversion array element 34
Will be described.

For example, Applied Physics Letters, Vol. 69
No. 18, (1996) pp. 2629-2631, or JP-A-6-242479.
It is manufactured by using the method for manufacturing a periodic domain inversion structure described in No. The material is MgO- cut out in the direction perpendicular to the Z axis.
Using LiNbO3, a domain that electrically polarizes in the Z-axis direction is periodically inverted in the X-axis direction by a corona discharge method to form a periodic domain inversion structure 35. The cycle of domain inversion is
The period is set to a period in which the fundamental wave oscillated by the semiconductor laser array 33 is quasi-phase matched. Thereafter, the sample is cut out in a direction perpendicular to the Z-axis, and the Z-plane is polished. Then, the array is guided from above the Z-plane by ordinary lithography and the proton exchange method described in, for example, the aforementioned US Pat. No. 5,185,752. The wave path 36 is formed. The width and the interval of the waveguide are set to the same size as the waveguide 40 of the semiconductor laser array 33. The distributed Bragg reflection (DBR) diffraction grating 37 is a first-order diffraction grating having a period in the X-axis direction, and is formed by ordinary holographic exposure, selective removal of a mask, and dry or wet etching. The period is a period for locking the wavelength of the fundamental wave. Thereafter, cutting in the direction perpendicular to the X-axis and polishing of the cut surface are performed, and a non-reflection coating 38 is applied on the incident surface side with respect to the wavelength of the phase-locked semiconductor laser. An anti-reflection coating 39 is applied to the output surface for the second harmonic.

The waveguide 40b on the emission side of the phase-locked semiconductor laser array 33 manufactured as described above and the waveguide 36 on the diffraction grating 37 side of the nonlinear waveguide type wavelength conversion array element 34 are directly coupled.

The principle of laser oscillation is as follows. The phase-locked semiconductor laser array 33 oscillates in the TM fundamental single mode by feedback light from the diffraction grating 37 formed in the MgO-LiNbO3 nonlinear waveguide type wavelength conversion array element 34, and the fundamental wave oscillated by the fundamental single mode has a wavelength. The light enters the periodic domain inversion array waveguide 36 formed in the conversion array element 34 and is converted into a second harmonic. The second harmonic is emitted from the emission end face on which the non-reflection coating 39 is applied. A plurality of waveguides 40b are provided by a phase-locked semiconductor laser array 33 having a Y-branch coupling waveguide 40.
Phase-locked fundamental wave is oscillated (Applied Physic
s Letter, Vol. 49 (1986) pp. 1632-1634), since each fundamental wave is converted to a second harmonic and output, the total output is higher than that of the conventional device. Can be obtained.

In the first and second embodiments, an n-type substrate is used, but the same can be achieved by using a p-type substrate. Further, in the above embodiment, a structure called a SQW-SCH having a single quantum well and a constant optical waveguide layer composition has been described. However, instead of the SQW, an MQW having a plurality of quantum wells is used.
It may be.

In the first embodiment, the material for oscillating the TE mode is AlGaA, which is lattice-matched to the GaAs substrate.
s, InAlGaAsP-based, or I lattice-matched to InP substrate
nAlGaAsP may be used. Further, an InGaAsP-based material that forms a compressive strain in the active layer with respect to the GaAs substrate and the InP substrate may be used.

In the second embodiment, the material that causes tensile strain in the active layer that oscillates in TM mode may be a GaAsP-based material that causes tensile strain on the GaAs substrate.

In order to control the etching depth when the optical waveguide has a ridge structure, an etching stop layer may be provided. Alternatively, the ridge may be formed by penetrating the active layer, and the optical waveguide stripe may be formed by a pnp buried structure. In the above configuration, the structure in which the p-cladding layer is buried is described. However, the buried growth may not be performed, and a groove for guiding the refractive index may be formed on the side surface.

As a growth method, a molecular beam epitaxial growth method using a solid or gas as a raw material may be used. Further, although the case where MgO-LiNbO3 is used as the material of the wavelength conversion element has been described, LiTaO3 may be used.

It should be noted that the second harmonic generator according to the present invention provides an ultra-high-speed information / image processing, communication, measurement, medical,
Further, it can be applied as a light source in fields such as printing.

[Brief description of the drawings]

FIG. 1 is a schematic top view of a second harmonic generator according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the second harmonic generator shown in FIG. 1, taken along the line II-II.

FIG. 3 is a III-III of the second harmonic generator in FIG.
Line cross section

FIG. 4 is a sectional view taken along the line IV-IV of the second harmonic generator in FIG.

FIG. 5 is a schematic top view of a second harmonic generation device according to a second embodiment of the present invention.

6 is a cross-sectional view of the second harmonic generator shown in FIG. 5, taken along the line II-II.

FIG. 7 is a III-III of the second harmonic generator in FIG.
Line cross section

8 is a cross-sectional view of the second harmonic generator shown in FIG. 5, taken along the line IV-IV.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 antireflection coating 2 high reflection coating 3 phase-locked semiconductor laser array 4 MgO-LiNbO3 nonlinear waveguide type wavelength conversion array element 5 periodic domain inversion structure 6 periodic domain inversion array waveguide 7 diffraction grating 8 non-reflection coating for fundamental wave 9 Non-reflection coating for second harmonic 10 Y-branch coupling waveguide 11 n-GaAs substrate 12 n-Alx1Ga1-x1As cladding layer 13 Alx2Ga1-x2As optical waveguide layer 14 Alx3Ga1-x3As active layer 15 Alx2Ga1-x2As optical waveguide layer 16 p -Alx1Ga1-z1As cladding layer 17 p-GaAs cap layer 18 p-Inx4 (Ga1-z4Alz4) 1-x4As1-y4
Py4 embedded layer 19 p-GaAs contact layer 20 n-side electrode 21 p-side electrode

Claims (4)

[Claims] 1. A phase-locked semiconductor laser array having a plurality of waveguides each of which oscillates a fundamental wave, and said phase-locked semiconductor laser array is disposed close to an output end face of said phase-locked semiconductor laser array and emitted from each of said waveguides. A second harmonic generation device, comprising: a wavelength conversion array element having a plurality of waveguides for converting a fundamental wave into a second harmonic. 2. The wavelength conversion array element is a nonlinear waveguide array element including a quasi phase matching domain inversion array waveguide and a diffraction grating arranged on the phase-locked semiconductor laser array side. The fundamental wave is oscillated from the phase-locked semiconductor laser array by the feedback light of the above, the fundamental wave incident on the domain inversion array waveguide is converted into a second harmonic, and the second harmonic is output. The second harmonic generator according to claim 1, wherein: 3. The domain-inverted array waveguide and the diffraction grating are formed on the same substrate, and a period of the diffraction grating and a period of the domain inversion are periods for phase matching with the fundamental wave. The second harmonic generator according to claim 2. 4. The second harmonic generator according to claim 2, wherein said diffraction grating is a distributed black reflection type diffraction grating.