JPH11160747A - Short wavelength light source, optical wavelength conversion element and method for inspecting optical wavelength conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an effect due to dispersion in a basic oscillated wavelength of a semiconductor laser by forming plural optical waveguides on an optical wavelength conversion element, changing the widths, the polarization inversion periods of the optical waveguides and changing a phase matching wavelength. SOLUTION: Plural optical waveguides 10 are formed on a sheet of optical wavelength conversion element 11, and the widths, polarization inversion periods of respective optical waveguides 10 are changed, and the phase matching wavelength is changed. By changing the width of the optical waveguide 10, an effective refractive index in the optical waveguide 10 is changed, and the phase matching wavelength of the optical waveguide 10 is changed delicately. When the width of the optical waveguide 10 is enlarged by 0.5 μm. the phase matching wavelength becomes short by 0.5 nm. In such a manner, by changing the width of the optical waveguide 10, the phase matching wavelength is adjusted continuously (a). Further, by gradually changing the optical waveguide width, polarization inversion period, the phase matching wavelength is adjusted continuously and extensively (b).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short wavelength light source using a semiconductor laser and a nonlinear optical crystal, a light wavelength conversion element, and a method for inspecting a light wavelength conversion element.

[0002]

2. Description of the Related Art An optical disk system using a near-infrared semiconductor laser having a wavelength of 780 nm or a red semiconductor laser having a wavelength of 650 nm has been actively developed. In order to realize a high density optical disc, it is desired to reproduce a small spot shape. To achieve this, the high NA (high numerical aperture) of the condenser lens
It is necessary to shorten the wavelength of the light source. As a technology for shortening the wavelength, a near-infrared semiconductor laser and quasi-phase matching (hereinafter, QP)
M) polarization-inverted optical waveguide (Yamamoto et al., Optics
Letters Vol. 16, No. 15, 1156 (1991)) There is a second harmonic generation (hereinafter referred to as SHG) using a device.

FIG. 13 shows a schematic configuration diagram of a short wavelength light source using a domain-inverted waveguide device. 42 in the schematic diagram
Is a 100 mW-class AlGaAs-based DBR (distributed Bragg reflection type) semiconductor laser in the 0.85 μm band, 43 is a collimating lens with NA = 0.5, and 44 is a focusing lens with NA = 0.5. The DBR semiconductor laser 42 is provided with a DBR section for fixing the oscillation wavelength and an internal heater for changing the oscillation wavelength in the DBR section. A polarization-inverted optical waveguide device, which is an optical wavelength conversion element, is made of
It is composed of an optical waveguide 46 formed on _three substrates 45 and a periodically poled region 47. The laser light collimated by the collimator lens 43 is condensed on the end face of the optical waveguide 46 of the domain-inverted optical waveguide device by the focus lens 44, and propagates through the optical waveguide 46 having the domain-inverted region 47. A fundamental wave that has not been converted into a harmonic is emitted from the emission end face. The domain-inverted optical waveguide device has a small allowable phase matching wavelength of about 0.1 nm for performing wavelength conversion with high efficiency.
Therefore, the amount of current injected into the DBR portion of the DBR semiconductor laser 42 is controlled, and the oscillation wavelength is fixed within the allowable phase matching wavelength of the domain-inverted optical waveguide device. Blue light having a wavelength of 425 nm is obtained at about 8 mW with respect to an incident light intensity of 70 mW into the optical waveguide 46.

[0004]

SUMMARY OF THE INVENTION In a short wavelength light source including a semiconductor laser having a DBR region (hereinafter referred to as DBR-LD) and an optical wavelength conversion element, the oscillation wavelength of the semiconductor laser is set to the phase of the optical wavelength conversion element. It is necessary to match the matching wavelength. In practical use and mass production of short-wavelength light sources utilizing harmonic generation by domain-inverted waveguide devices using quasi-phase matching, variations in the oscillation wavelength of DBR-LDs become a problem. Although the DBR-LD can change the wavelength of the fundamental oscillation wavelength +2 nm (hereinafter referred to as the oscillation wavelength range), the fundamental oscillation wavelength actually varies between 847 and 858 nm, which poses a problem.

Next, it is difficult to identify an optical waveguide, and it is also difficult to find a desired optical waveguide. Further, in the measurement of the phase matching wavelength, since laser light has conventionally been coupled to the optical waveguide using a focus lens, very high-precision alignment was required, and much time was spent.
In addition, only one sample could be measured. This also becomes a problem when mass-producing.

The present invention provides a semiconductor laser (DBR-
The objective of the present invention is to overcome the problems of the inspection process of a short wavelength light source and a harmonic generation device using an LD) and an optical wavelength conversion element, and realize mass production and practical use of the short wavelength light source.

[0007]

In order to solve the above-mentioned problems, the present invention provides (1) forming a plurality of optical waveguides on one optical wavelength conversion element, and determining the width of each optical waveguide and the polarization inversion period. And changing the phase matching wavelength.

Further, the present invention is characterized in that (2) a marker is formed near the optical waveguide as a mark so that the phase matching wavelength of each optical waveguide can be known, and the shape, position and number of the marker are changed. .

Further, the present invention is characterized in that (3) when measuring the phase matching wavelength of each optical waveguide, the emitted light of the high-output tunable laser is irradiated over a wide range on the end face of the optical wavelength conversion element.

[0010]

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

(Embodiment 1) The semiconductor laser used in this embodiment has a wavelength tunable region (DBR section),
It is manufactured by epitaxial growth using a VD apparatus. After growing n-AlGaAs on the n-GaAs substrate, AlGaA
A waveguide region and an active region of s are formed, and p as a cladding layer
-AlGaAs is laminated. Next, a waveguide is formed by photolithography. After a resist is coated on the wafer and a grating pattern is formed by interference exposure, a grating (DBR) is formed by etching only the waveguide region. In the second MOCVD growth, p-GaAs is formed on the wafer to reduce contact resistance. Electrodes for current injection are formed on the DBR region and the active region.

The obtained DBR semiconductor laser had a threshold value of 30 mA and an operating current of 150 mA at an output of 100 mW. The fundamental oscillation wavelength (oscillation wavelength when the current supplied to the DBR section is 0 mA) is 850 nm, and the wavelength variable range (wavelength change width when the current supplied to the DBR section is 0 to 100 mA) is 2 nm, and 850 to 852 nm.
m was available.

The DBR-LD can change the oscillation wavelength only by adjusting the operating current, and is very easy to handle. However, the wavelength variable range is about 2 nm, and the wavelength can be changed only in the direction in which the oscillation wavelength increases. Therefore, the DBR-LD used in this embodiment cannot output blue light in an optical waveguide having a phase matching wavelength of 849 nm.

The method of changing the oscillation wavelength with a semiconductor laser other than the DBR-LD includes (1) changing the temperature of the semiconductor laser, (2) using a grating externally (see FIG. 1A), and (3) band. There is a method of using a pass filter (see FIG. 1B).

A semiconductor laser can change the oscillation wavelength at 0.3 nm / ° C. by changing the temperature. However, fine adjustment is difficult, it is difficult to keep the temperature constant, and it is difficult to lock the wavelength to a desired value.

When a grating is used, the wavelength is variable within a range of ± 10 nm. That is, the laser light emitted from the semiconductor laser 1 can be resonated between the end face of the light wavelength conversion element 2 and the grating 3 to change the wavelength and lock. However, when the wavelength is changed, mechanical adjustment is required, and the use of an external grating is not suitable for downsizing a short-wavelength light source.

Even when a bandpass filter is used, ±
The wavelength is variable in the range of 10 nm. However, when the wavelength is changed also in this method, mechanical adjustment is required when changing the angle of the bandpass filter 8, and is not suitable for miniaturization.

As described above, the mechanical adjustment is not required when changing the wavelength, the oscillation wavelength is variable only by the operating current, and the DB is suitable for miniaturization of the short wavelength light source.
R-LD has a great advantage.

(Embodiment 2) FIGS. 2A and 2B are configuration diagrams of an optical wavelength conversion element using a quasi-phase matching method. The light wavelength conversion element is formed using a semiconductor process. Specifically, as shown in FIG. 3, first, the wafer 12 of MgO the implanted LiNbO ₃ crystal Ta13 or S
TiO ₂ is deposited by sputtering, and a photomask 15 is applied to the wafer by applying a resist 14 thereon, and is brought into close contact with the wafer. Only the portion where the mask was present remains due to the development processing. Thereafter, Ta13 other than the portion having the mask is etched by dry etching. The resist 14 is removed by dipping in acetone. Thereafter, the wafer 12 is cut into a predetermined size, immersed in pyrophosphoric acid heated to about 200 ° C. for about 7 to 10 minutes, and subjected to proton exchange, whereby the optical waveguide 10 is formed. After the proton exchange, a thermal diffusion process is performed to expand the optical waveguide 10, and the cut end face of the element is optically polished, and then a non-reflective coating is deposited to complete it. Optical waveguide 10
The conditions vary from 3 to 6 μm in the width direction and from 1.5 to 2.5 μm in the depth direction. This condition can be adjusted by the design of the photomask, the proton exchange time, and the heat diffusion processing time. Further, the domain-inverted structure 11 is formed by the electric field application method, and the second harmonic (SHG) is generated. The domain inversion period is 2.9 to 3.1 μm. The size of the light wavelength conversion element 9 produced this time is 10 × 5 × 0.7 mm,
30μ so that the optical waveguide 10 is not affected by the adjacent optical waveguide
They are formed at m intervals.

By changing the width of the optical waveguide, the effective refractive index in the optical waveguide changes, and the phase matching wavelength of the optical waveguide can be slightly changed. In the present embodiment, when the width of the optical waveguide is increased by 0.5 μm, the phase matching wavelength is reduced by 0.5 nm. By changing the width of the optical waveguide in this way, the phase matching wavelength can be continuously adjusted. Also, by changing the width of the optical waveguide, it is possible to optimize the coupling efficiency for laser beams having different beam spots.

As described above, it is possible to change the phase matching wavelength by changing the width of the optical waveguide. However, if the width of the optical waveguide is too large, light confinement in the optical waveguide will be reduced. , Or the propagation mode is not single, so that blue light, which is a harmonic, is not much emitted. Therefore, when the phase matching wavelength is largely changed, it is preferable to change the polarization inversion period.
In the present embodiment, the phase matching wavelength can be shifted by about 3 nm by changing the period of the polarization inversion by 0.05 μm.

By gradually changing the width of the optical waveguide and the period of polarization reversal, the phase matching wavelength can be continuously and widely adjusted. The optical wavelength conversion device produced in the present embodiment can select a phase matching wavelength within a range of 845 to 860 nm within one device (see FIG. 2B). This allows
The disadvantage that the DBR-LD can change the oscillation wavelength by only 2 nm in the plus direction can be covered.

Further, as an application of the present invention, the fundamental oscillation wavelength is substantially the same in each lot in the manufacturing process of the semiconductor laser.
When a large number of semiconductor lasers are manufactured, it is also possible to prepare many optical waveguides having a phase matching wavelength near 852 nm as shown in FIG. 4 and select an optimal optical waveguide from the optical waveguides and combine them. .

As described above, according to the present invention, even if the fundamental oscillation wavelength of the semiconductor laser varies, the width of the optical waveguide and / or the polarization reversal period is changed, and the phase matching wavelength is shifted little by little, so that the variation of the fundamental oscillation wavelength is obtained. Can negate the effects of This produces tremendous effects such as yield improvement in the mass production process.

(Embodiment 3) For practical use of a short wavelength light source, a direct coupling module using a direct coupling method shown in FIG. More specifically, an optical wavelength conversion element 18 is arranged on the submount 16 just before the end face of the semiconductor laser chip 17 and coupled to the optical waveguide 19 to obtain a harmonic. As shown in FIG. 6, differently shaped markers 22 to 24 are
It was formed 10 μm lateral to the optical waveguide 21 formed on 20. Each marker is designed in a shape corresponding to the phase matching wavelength of each optical waveguide.

In this embodiment, as in the second embodiment, an optical wavelength conversion element whose phase matching wavelength is shifted by changing the width of the optical waveguide and the polarization inversion period is used. A square marker 22 corresponds to an optical waveguide having a wavelength of 850 nm, and a round marker 23 corresponds to an optical waveguide having a phase matching wavelength of 851 nm. Similarly, markers having different shapes corresponding to the phase matching wavelengths of the respective optical waveguides are formed adjacent to the optical waveguides.

FIG. 7 shows the fabrication of the direct coupling module.
Was used. The bonding machine is a Y-axis stage 31, XZθ stage 33, upper CCD
A camera 27, a lower CCD turtle 30 (light source: coaxial incident white light source), a stage calibration marker 29 for calibrating a relative position of the two stages,
It comprises a tool 32 for fixing the semiconductor laser device and the light wavelength conversion device. Since the fundamental oscillation wavelength of the semiconductor laser chip 26 was 850.8 nm, while observing the image from the CCD camera 27 on the bonding machine, the round marker 23 having a phase matching wavelength of 851 nm was attached to the optical wavelength conversion element 20. The image was recognized while sliding in the Z direction, and the light wavelength conversion element was bonded onto the Si submount 28.

The positioning adjustment of the bonding was performed using the positioning marker 25. First, the stage calibration marker 29 is moved to the upper CCD camera 2.
7. Observe simultaneously with the lower CCD camera 30, and recognize the relative position between the stages. Next, the lower CCD camera 30 recognizes the image of the positioning marker 25 on the light wavelength conversion element 20, and obtains information such as the XZ position of the light wavelength conversion element and the θ deviation of the optical axis. Next, while the upper CCD camera 27 recognizes the image of the positioning marker 29 on the Si submount 28 and recognizes the XZ position of the Si submount 28, the θ deviation of the optical axis coincides with the deviation of the light wavelength conversion element 20. As Si submount 28
Θ deviation of the optical axis.

Next, the XZθ-axis stage 33 is moved to the X-axis position so that the position of the optical wavelength conversion element 20 and the position of the Si submount 28 coincide.
Moved in the Z direction, the Y-axis stage was moved, the light wavelength conversion element 20 was placed on the light wavelength conversion element mounting portion of the Si submount 28, an ultraviolet curing agent was injected, and ultraviolet light was applied to fix it (FIG. 8). reference). The semiconductor laser chip 26 was also bonded using solder in the same process. The lateral accuracy of the bonding apparatus is about 0.5 μm, and the direct-coupling short-wavelength light source module manufactured in the present embodiment has a harmonic (blue light) of about 5 mW with respect to the input of the infrared semiconductor laser 100 mW.
Was output.

It is conceivable to use markers of different shapes formed in the present embodiment as markers for positioning. For example, as shown in FIG. 9, when the calibration marker 35 is made hexagonal and three types of markers for phase matching wavelength recognition are formed: triangular, quadrangular, and hexagonal, hexagonal calibration is performed. By matching the vertex of the marker 35 with the vertex of the triangular marker 34 at three points, the operation of positioning and recognizing the phase matching wavelength can be achieved by one operation. Similarly, in the case of a quadrangle and a hexagon, four points and six points may be similarly matched.

Further, it is also possible to identify the phase matching wavelength using only markers having the same shape. For example, as shown in FIG. 10, the number of the circular markers 36 can identify the phase matching wavelength.

Further, it can be used for purposes other than the identification of the phase matching wavelength. As a first example, when the conditions of the optical waveguide 21 are the same in FIG. 6, it can be used for inspection of the optical waveguide. Optical waveguides with round markers are available. It is preferable to use an optical waveguide having a triangular marker so that it cannot be used as an optical waveguide.

As a second example, similarly, it can be used for selection such that an optical waveguide from which blue light is emitted most among optical waveguides under the same condition is an optical waveguide of a square marker.

As described above, various conditions can be identified by combining markers having different shapes and / or the number of markers.

As described above, according to the present invention, the phase matching wavelength of the optical waveguide and the inspection and selection of the optical waveguide can be easily performed, so that the characteristics of the optical waveguide can be quickly and accurately recognized, and a great effect is achieved in mass production. I do.

The nonlinear optical crystals used in the first, second and _third embodiments are LiTaO ₃ , KTP
Or the like may be used.

(Embodiment 4) In the inspection of the phase matching wavelength of each optical waveguide of the optical wavelength conversion element, conventionally, parallel light emitted from a high output wavelength tunable titanium-sapphire laser is focused using a focus lens. After coupling the laser beam to the optical waveguide, the inspection was performed by changing the wavelength of the titanium-sapphire laser. However, this method can measure only one laser at a time, and the likelihood (up to the maximum coupling efficiency) Moving distance when the value becomes half: Fig. 11
(Refer to FIG. 2), there is a problem that very high precision alignment of 0.5 μm is required.

In the inspection method of the present invention, the phase matching wavelength of a plurality of optical waveguides was measured using a beam emitted from a laser or a beam narrowed down to some extent using a lens. That is, in the present embodiment, the spot size was set to about 0.5 × 0.5 mm.

Specifically, as shown in FIG. 12, first, the output of the titanium-sapphire laser 37 was set to 1 W, and the beam was applied to the incident end face of the light wavelength conversion element 39. On the emission end face of the light wavelength conversion element 39, an optical filter 40 that allows only blue light to pass and a CCD camera 41 are provided. The light wavelength conversion element 39 used was the same as that described in the first embodiment. As the oscillation wavelength of the titanium-sapphire laser 37 was gradually increased from a low wavelength to a high wavelength, harmonics generated at the phase matching wavelength of each optical waveguide could be sequentially observed by the CCD camera 41. In the present embodiment, the spot size at the end face of the light wavelength conversion element is set to about 0.5 × 0.5 mm. However, the measurement may be performed with a cylindrical lens as the focus lens 38 and an elliptical beam spot shape. . In the case where the beam emitted from the titanium-sapphire laser is directly applied to the end face of the optical wavelength conversion element, the output of the laser may be further increased.

When the phase matching wavelength of the optical waveguide was measured one by one, the spot size at the end face of the light wavelength conversion element of the laser was measured at about 10 × 10 μm. The spot size of the optical waveguide is
Since it was 5 × 2 μm, the phase matching wavelength could be measured without fine adjustment. If the spot size is 10 μm or less, the likelihood becomes small and adjustment becomes difficult.

As a result, the time required for the phase matching wavelength inspection process in the related art is about 10 minutes, which is about 1 minute, and the phase matching wavelengths of a plurality of optical waveguides can be measured. The shortening of this time and the elimination of the need for fine alignment have great effects in mass production.

In the above embodiment, a dye laser may be used instead of the titanium-sapphire laser.

[0043]

As described above, according to the present invention, a plurality of optical waveguides are formed on a single optical wavelength conversion element, and the optical waveguides are formed by changing the phase matching wavelength of each optical waveguide. Even if the oscillation wavelength varies, a short-wavelength light source using a nonlinear optical crystal can be constructed by configuring the phase matching wavelength of any one of the optical waveguides on the optical wavelength conversion element to match the oscillation wavelength of the semiconductor laser. In practical use and mass production, it is possible to eliminate the influence of the variation of the fundamental oscillation wavelength of the semiconductor laser, thereby improving the yield.

Further, according to the present invention, a marker is provided near the optical waveguide as a mark so that the phase matching wavelength of each optical waveguide can be determined, and the phase matching wavelength of each waveguide is determined by the shape, position and number of markers. You can easily check it.

Further, according to the present invention, when measuring the phase matching wavelength of each optical waveguide, it is necessary to irradiate the output light of the wavelength tunable laser over a wide area on the end face of the optical wavelength conversion element, so that high precision alignment is required. Without this, the phase matching wavelengths of a plurality of optical waveguides can be measured at a time, and the inspection process of the phase matching wavelength of the optical wavelength conversion element can be simplified and rationalized.

[Brief description of the drawings]

FIG. 1 shows a method of changing the oscillation wavelength of a semiconductor laser. FIG. 1 (a) shows a method using an external grating. FIG. 1 (b) shows a method using a bandpass filter.

FIGS. 2A and 2B are schematic diagrams of a light wavelength conversion element, and FIG. 2B is a schematic view of the light wavelength conversion element as viewed from above.

FIG. 3 is a diagram showing a method for manufacturing an optical wavelength conversion element.

FIG. 4 is a configuration diagram of an optical wavelength conversion element.

FIG. 5 is a block diagram of a module using a direct coupling method.

FIG. 6 is an explanatory view of a marker.

FIG. 7 is a configuration diagram of a bonding machine.

8A and 8B are diagrams showing a method of alignment, FIG. 8A is a diagram before alignment, and FIG. 8B is a diagram after alignment.

FIGS. 9A and 9B show the application of the phase matching wavelength identification marker to alignment. FIG. 9A is a diagram before alignment, and FIG. 9B is a diagram after alignment.

FIG. 10 shows identification with a single marker.

FIG. 11 is a diagram showing likelihood.

FIG. 12 is a configuration diagram of a measurement system when measuring a phase matching wavelength of an optical wavelength conversion element.

FIG. 13 is a schematic diagram of a short wavelength light source.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 grating 2 semiconductor laser 3 active layer 4 collimating lens 5 focus lens 6 optical wavelength conversion element 7 optical waveguide 8 bandpass filter 9 MgO: LiNbO ₃ substrate 10 optical waveguide 11 periodic polarization inversion section 12 MgO: LiNbO ₃ substrate 13 Ta film Reference Signs List 14 resist film 15 photomask 16 Si submount 17 semiconductor laser chip 18 optical wavelength conversion element 19 optical waveguide 20 optical wavelength conversion element 21 optical waveguide 22 marker 23 marker 24 marker 25 positioning marker 26 semiconductor laser chip 27 upper CCD camera 28 Si Submount 29 Calibration marker 30 Lower CCD camera 31 Y-axis stage 32 Tool 33 XZθ-axis stage 34 Marker 35 Calibration marker 36 Round marker 7 Titanium - Sapphire laser 38 focusing lens 39 the light wavelength conversion device 40 an optical filter 41 CCD camera 42 semiconductor laser 43 collimator lens 44 the focus lens 45 MgO: LiNbO ₃ substrate 46 an optical waveguide 47 periodically poled regions

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuo Kitaoka 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (11)

[Claims] 1. A quasi-phase matching type optical wavelength conversion element having a periodically poled region comprising a semiconductor laser and a nonlinear optical crystal, wherein the optical wavelength conversion element includes at least two or more optical waveguides. A short-wavelength light source, wherein the light emitted from the light source is coupled to any one of the optical waveguides to output a harmonic. 2. The short wavelength light source according to claim 1, wherein the optical waveguides have different phase matching wavelengths. 3. The short-wavelength light source according to claim 1, wherein at least one of the width of the optical waveguide and the polarization inversion period is different. 4. The semiconductor laser according to claim 1, wherein said semiconductor laser has an active region for providing a gain and a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength.
4. The short-wavelength light source according to any one of claims 1 to 3. 5. An optical wavelength conversion device comprising a periodically poled region made of a nonlinear optical crystal and an optical waveguide, comprising a marker corresponding to the optical waveguide. 6. The optical wavelength conversion device according to claim 5, wherein said markers have different shapes. 7. The optical wavelength conversion device according to claim 6, wherein the optical waveguides have different phase matching wavelengths. 8. The optical wavelength conversion device according to claim 5, wherein at least one of the width of the optical waveguide and the polarization inversion period is different. 9. An optical wavelength conversion element having an optical waveguide made of a nonlinear optical crystal and a wavelength tunable laser,
By irradiating outgoing light output from the wavelength tunable laser to the optical waveguide to the end face of the optical wavelength conversion element, changing the oscillation wavelength of the wavelength tunable laser, and observing a harmonic output from the optical waveguide. An inspection method of an optical wavelength conversion element for measuring a phase matching wavelength of the optical waveguide. 10. The method for inspecting an optical wavelength conversion device according to claim 9, wherein a spot size at an end face of said optical wavelength conversion device is 10 μm or more. 11. The method for inspecting an optical wavelength conversion device according to claim 9, wherein the phase matching wavelengths of at least two or more optical waveguides of the optical wavelength conversion device are simultaneously measured.