JP2016177316A - Method for manufacturing wavelength conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wavelength conversion efficiency of a wavelength conversion element in which a ferroelectric crystal substrate having a periodical polarization inversion structure formed by a voltage application method is adhered to a support substrate.SOLUTION: A wavelength conversion element 14 includes: a support substrate 9; a ferroelectric crystal substrate 1A composed of a Z-cut substrate or an off-cut Z-cut substrate of ferroelectric crystal and having a first major surface and a second major surface; a periodical polarization inversion structure 7A provided in the substrate 1A; an optical waveguide provided in the substrate 1A; and an adhesive layer 12 adhering the second major surface 1b of the substrate to the support substrate 9. The periodical polarization inversion structure 7A is formed by applying voltage between a plurality of electrode pieces provided on the first major surface 1a of the substrate and a uniform electrode on an insulating film provided on the second major surface 1b of the substrate 1, and is formed into a thin film by polishing the first major surface 1a of the substrate.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a wavelength conversion element and a method for manufacturing the same.

  Quasi-phase-matching second harmonic generation (Second-Harmonic) in which a periodically poled structure is formed in a ferroelectric single crystal such as lithium niobate single crystal or lithium tantalate single crystal. -Generation) devices can generate light of a relatively arbitrary wavelength from ultraviolet to infrared. This device can be used in a wide range of applications such as optical disk memory, medical use, photochemistry use, and various optical measurement applications.

  The inventor has studied to provide a high-efficiency harmonic generation element by forming a periodically poled structure in a ridge-type optical waveguide (Patent Document 1: Japanese Patent Application Laid-Open No. 2009-222872).

  When forming a periodically poled structure on a ferroelectric single crystal substrate, defects are likely to occur. For this reason, various manufacturing methods have been proposed. In the method described in Patent Document 2 (Japanese Patent Laid-Open No. 2005-70192), a ferroelectric single crystal substrate is laminated with a separate substrate, immersed in an insulating liquid, for example, oil, and a pulsed voltage is applied to apply periodic polarization. An inversion structure is formed.

  In the method described in Patent Document 3 (Japanese Patent Application Laid-Open No. 2009-145560), an insulating film is provided on the surface of a lithium niobate Z substrate, a strip-like elongated gap is provided in the insulating film, and then the insulating film and the gap are formed. A conductive film is provided so as to cover it. Then, by applying a pulse voltage to the conductive film, a periodically poled structure is formed on the substrate.

  In the method described in Patent Document 4 (Japanese Patent Application Laid-Open No. 2010-134425), an insulating film is provided on the surface of a lithium niobate Z substrate, and a striped elongated gap is provided in the insulating film. A conductive film is provided so as to cover it. Then, by applying a pulse voltage to the conductive film, a periodically poled structure is formed on the substrate.

JP2009-222872A JP-A-2005-70192 JP2009-145560 JP2010-134425A

  The present inventor forms a periodically poled structure on a ferroelectric crystal substrate by a voltage application method as described in Patent Documents 3 and 4, and further thins the ferroelectric crystal substrate as described in Patent Document 1. However, it has been studied to mass-produce wavelength conversion elements by forming ridge type optical waveguides.

  Specifically, as described in Patent Documents 3 and 4, a plurality of rows of insulating layers are formed on the first main surface side of the ferroelectric crystal substrate, and electrode pieces made of a conductive material are formed in the gaps between adjacent insulating layers. Part was formed. In addition, a uniform electrode is formed on the second main surface of the ferroelectric crystal substrate, and a voltage corresponding to the period of the electrode piece is applied by applying a voltage between the electrode piece and the uniform electrode. A periodic domain-inverted structure was formed. Then, after removing the uniform electrode and the insulating layer from the ferroelectric crystal substrate, the main surface on the electrode piece side of the ferroelectric crystal substrate is bonded to the support substrate, and the main surface on the uniform electrode side is polished. Thus, the ferroelectric crystal substrate was thinned. This is because the periodic polarization reversal structure can be accurately formed on the electrode piece side, so that the wavelength conversion efficiency is increased, but it is considered that the accuracy of the periodic polarization reversal structure is low on the uniform electrode side without a period. It is. Therefore, the main surface on the electrode piece portion side of the substrate is utilized, and the main surface on the uniform electrode side that is not used is polished so as to reduce the thickness.

  However, when an element as described in Patent Document 1 was actually created and a test for generating a second harmonic by wavelength conversion was repeated, the wavelength conversion efficiency was lower than the theoretical value, and periodic polarization in the optical waveguide was reduced. It was found that the quality of the inverted structure was degraded microscopically.

  An object of the present invention is to further improve the wavelength conversion efficiency in a wavelength conversion element in which a ferroelectric crystal substrate having a periodically poled structure formed by a voltage application method is bonded to a support substrate.

The present invention
Support substrate,
A ferroelectric crystal substrate comprising a ferroelectric crystal Z-cut substrate or an off-cut Z-cut substrate and having a first main surface and a second main surface;
Periodic polarization inversion structure provided on a ferroelectric crystal substrate,
An optical waveguide provided on a ferroelectric crystal substrate, and a wavelength conversion element comprising an adhesive layer that adheres the second main surface of the ferroelectric crystal substrate and a support substrate,
A plurality of electrode pieces provided on the first main surface of the ferroelectric crystal substrate, and a uniform electrode on the insulating film provided on the second main surface of the ferroelectric crystal substrate, with the periodically poled structure The ferroelectric crystal substrate is thinned by polishing the first main surface of the ferroelectric crystal substrate.

The present invention provides a support substrate,
A ferroelectric crystal substrate comprising a ferroelectric crystal Z-cut substrate or an off-cut Z-cut substrate and having a first main surface and a second main surface;
A periodically poled structure provided on the ferroelectric crystal substrate;
An optical waveguide provided on the ferroelectric crystal substrate, and a wavelength conversion element comprising an adhesive layer that bonds the second main surface of the ferroelectric crystal substrate and the support substrate,
The periodic polarization reversal structure includes a plurality of electrode pieces provided on the first main surface of the ferroelectric crystal substrate, and an insulating film provided on the second main surface of the ferroelectric crystal substrate. It is formed by applying a voltage between the upper uniform electrode and the diffusion concentration of the electrode piece portion and the uniform electrode material on the ferroelectric crystal substrate is less than 0.1 ppm.

Further, the present invention is a method for manufacturing the element,
A plurality of electrode pieces are provided on a first main surface of a ferroelectric crystal substrate comprising a Z-cut substrate or an off-cut Z-cut substrate of a ferroelectric crystal, and the second main surface of the ferroelectric crystal substrate is provided. Sequentially providing an insulating film and a uniform electrode;
Forming a periodically poled structure by applying a voltage between the electrode piece and the uniform electrode;
Bonding the second principal surface of the ferroelectric crystal substrate to the support substrate;
The method includes a step of thinning the first main surface of the ferroelectric crystal substrate by polishing, and a step of forming an optical waveguide on the ferroelectric crystal substrate.

  In order to search for the cause of the decrease in wavelength conversion efficiency, the inventor cut a sample from the surface on the electrode piece side of the substrate and analyzed the element by dynamic SIMS (Cameca IMS-6f). As a result, it was found that in addition to the main elements niobium and lithium, for example, molybdenum used as an electrode material exists in a region having a depth of 30 to 40 nm from the surface. This indicates that the material of the electrode piece, for example, molybdenum, diffuses from the main surface of the substrate toward the inside and remains. It was considered that the diffused electrode material lowered the crystal quality and the wavelength conversion efficiency.

  Based on this hypothesis, the present inventor adheres the main surface on the side where the uniform electrode is provided to the support substrate and grinds the main surface on the side where the electrode piece is provided, contrary to conventional common sense. It became thin layer. It was confirmed that no component derived from the electrode material was detected on such a substrate. And when the optical waveguide was formed in the obtained board | substrate, it discovered that wavelength conversion efficiency improved unexpectedly and reached | attained this invention.

(A) schematically shows a state in which a patterned insulating layer 2A and an unpatterned insulating layer 2B are formed on the ferroelectric crystal substrate 1, and (b) further shows a conductive film 3A (electrode piece part). 4) shows a state where the uniform electrode 3B is formed, and (c) is a schematic view showing a state where a voltage is applied to the assembly of FIG. 1 (b). (A) shows a state where the conductive film and the uniform electrode are removed from the substrate of FIG. 1 (c), (b) shows a state where the insulating layer is further removed, and (c) shows a periodically poled structure. 7 shows a state in which the second main surface (main electrode-side main surface) 1b of the substrate 1 on which the substrate 7 is formed is bonded to the support substrate 9, and (d) shows one main surface (electrode piece) of the substrate 1 next. The element 14 obtained by polishing and thinning the main surface 1a on the part side is shown. (A) shows a state in which the first main surface (main surface on the electrode piece portion side) 1a of the substrate 1 on which the periodically poled structure is formed is bonded to the support substrate 9, and (b) shows the substrate 1 next. An element obtained by thinning the second main surface (main surface on the uniform electrode side) 1b is shown. It is a perspective view showing an example of wavelength conversion element 14A. It is typical sectional drawing which shows the principal part of 14 A of elements of FIG. It is a schematic diagram which shows the lens system in an Example. It is the photograph of the 1st main surface side of the board | substrate with which the periodic polarization inversion structure was formed. It is the photograph of the 2nd main surface side of the board | substrate with which the periodic polarization inversion structure was formed. It is a chart which shows the elemental-analysis result by dynamic SIMS (Cameca IMS-6f) of the surface of the electrode piece part side of a board | substrate.

Hereinafter, the present invention will be described in detail with appropriate reference to the drawings.
First, as shown in FIG. 1, a patterned insulating film 2A is formed on the first main surface 1a of the ferroelectric crystal substrate 1, and an insulating film 2B is formed on the entire surface of the second main surface 1b. To do. The insulating film 2A is patterned to form gaps between the adjacent insulating films 2A.

Here, the ferroelectric crystal substrate 1 is composed of a Z-cut substrate or an off-cut Z substrate.
The type of the ferroelectric crystal that constitutes the substrate on which the periodically poled structure is to be formed is not limited. However, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), lithium niobate-lithium tantalate solid solution, K ₃ Li ₂ Nb ₅ O ₁₅ , La ₃ Ga ₅ SiO ₁₄ can be exemplified. Single crystals are particularly preferred.

  In the ferroelectric crystal, in order to further improve the optical damage resistance of the optical waveguide, at least one selected from the group consisting of magnesium (Mg), zinc (Zn), scandium (Sc), and indium (In). Metal elements can be contained, and magnesium is particularly preferred.

  The ferroelectric crystal can contain a rare earth element as a doping component. This rare earth element acts as an additive element for laser oscillation. As this rare earth element, Nd, Er, Tm, Ho, Dy, and Pr are particularly preferable.

  A Z-cut substrate or an off-cut Z substrate is used as the ferroelectric crystal substrate. This off-cut angle is preferably 10 ° or less, and more preferably 5 ° or less. If the off-cut angle of the off-cut Z substrate is 10 ° or less, the deterioration of the wavelength conversion efficiency can be ignored without adjusting the optical axis with the semiconductor laser or correcting the tilt, and a highly efficient wavelength conversion element should be realized. Can do.

The material of the insulating films 2A and 2B is not limited, but may be an oxide such as SiO ₂ or Ta ₂ O ₅ or a nitride such as silicon nitride. As a method for forming the insulating film, an evaporation method, a sputtering method, or a spin coating method may be used.
The thickness of the patterned insulating film 2A is not particularly limited, but is preferably 500 angstroms or more and 4000 angstroms or less. When the thickness of the insulating film is small, the insulating property is low and polarization inversion is difficult to be formed. When the insulating film is too thick, the patterning accuracy is deteriorated.

  The thickness of the insulating layer 1b on the second main surface side is preferably 3000 angstroms or less, and most preferably 2000 angstroms or less. Further, it is preferably 100 angstroms or more, more preferably 1000 angstroms or more.

  A method for forming the gap by patterning the insulating film is not particularly limited. For example, a gap can be formed by spin-coating a photoresist on an insulating film, forming a resist pattern through mask exposure and development, and performing an etching process using the resist pattern as a mask. The etching process may be wet etching or dry etching, but ideally wet etching is preferable because it hardly damages the substrate surface.

  Next, as shown in FIG. 1B, a conductive film 3A is formed on the plurality of rows of insulating films 2A. The conductive film 3A includes an insulating film covering portion 20 that covers the insulating film 2A and an electrode piece portion 4 that directly covers the main surface 1a. Therefore, a large number of elongated electrode pieces 4 in a plurality of rows are arranged, and the insulating film 2 </ b> A is interposed between the adjacent electrode parts 4.

  On the second main surface 1b side of the substrate 1, a uniform electrode 3B is formed on the insulating layer 2B.

  The material of the conductive film and the uniform electrode is not limited, but a laminated film of Al, Au, Ag, Cr, Cu, Ni, Ni—Cr 2, Pd, Ta 2 Mo, W, Ta, AuCr or the like is preferable.

  The method for forming the conductive film and the uniform electrode is not particularly limited, and may be an evaporation method or a sputtering method. The film thickness of the electrode can be, for example, 500 to 3000 angstroms.

  Next, a voltage is applied between the electrode piece and the uniform electrode by a voltage application method to form a periodically poled structure on the substrate. Preferably, as shown in FIG. 1C, the conductive film or the electrode piece is connected to the power source 6 and a capacitor is interposed between the uniform electrode 3B and the power source. This capacitor may be a circuit component.

Or the capacitor | condenser may be the dielectric substrate 5 in which electrode 33A, 33B was formed in both main surfaces.
In this case, the uniform electrode 3B and the first electrode on the dielectric substrate 5 are electrically connected, and preferably the temperature of the ferroelectric crystal substrate 1 is higher than the temperature of the dielectric substrate 5. By applying a voltage between the second electrode on the dielectric substrate and the electrode piece part 4, a periodic polarization inversion part is formed.

  The dielectric substrate can also be immersed in an insulating liquid. In addition, the ferroelectric crystal substrate and the dielectric substrate can be immersed in an insulating liquid in another container.

In the present embodiment, the temperature of the ferroelectric crystal substrate during voltage application is preferably 80 ° C. or higher, and more preferably 140 ° C. or higher, from the viewpoint of promoting the formation of the domain-inverted structure. Further, the temperature of the ferroelectric crystal substrate at the time of voltage application is preferably 250 ° C. or less, and more preferably 200 ° C. or less, from the viewpoint of preventing cracking of the ferroelectric crystal substrate and pyroelectricity.
Further, the temperature of the dielectric substrate at the time of voltage application is preferably 130 ° C. or less, and more preferably 80 ° C. or less, from the viewpoint of preventing the substrate from cracking or pyroelectricity. This lower limit is not particularly limited, and may be room temperature.

  From the above viewpoint, the temperature difference between the temperature of the ferroelectric crystal substrate and the temperature of the dielectric substrate when a voltage is applied is preferably 60 ° C. or higher, and more preferably 100 ° C. or higher.

  The ferroelectric crystal substrate and the dielectric substrate can be placed in an atmosphere, but are preferably immersed in an insulating liquid. In this case, a temperature difference is provided between the temperatures of the insulating liquids. Examples of the insulating liquid include insulating oil (for example, silicon oil) and fluorine-based inert liquid.

The material of the dielectric substrate 5 is required to have a high insulation property, a uniform volume resistivity within the material, and a predetermined structural strength. Examples of this material include silicon, sapphire, crystal, and glass. In addition, ferroelectric single crystals such as lithium niobate, lithium tantalate, lithium niobate-lithium tantalate solid solution, and K ₃ Li ₂ Nb ₅ O ₁₅ are particularly preferable.

  The voltage application method is not particularly limited. For example, a substrate may be placed in an inert atmosphere and a voltage may be applied, or a substrate may be placed in an insulating liquid and a voltage may be applied. When a voltage application probe pin is used when applying a voltage, the contact position of the pin with respect to the electrode is preferably in the middle.

The voltage is preferably a pulse voltage, and a DC bias voltage may be further applied. Preferred conditions for the pulse voltage are as follows.
Pulse voltage: 2.0kV ~ 8.0kV (/ mm)
Pulse width: 0.1ms to 10ms
DC bias voltage: 1.0 kV to 5.0 kV (/ mm)

  Next, as shown in FIG. 2A, the conductive film and the uniform electrode are removed, and then the insulating film is removed as shown in FIG. 2B, whereby the substrate on which the periodically poled structure 7 is formed. Get one. The periodic polarization reversal structure 7 is composed of polarization reversal portions 7a and non-reversal portions 7b that are alternately arranged in the light traveling direction.

  Next, according to the present invention, as shown in FIG. 2C, the second main surface (main electrode-side main surface) 1 b of the substrate 1 is bonded to the main surface 9 a of the support substrate 9. Reference numeral 12 denotes an adhesive layer.

As this adhesive, Aron ceramics having a thermal expansion coefficient that is relatively close to materials having an electro-optic effect, such as an epoxy adhesive, an acrylic adhesive, a thermosetting adhesive, an ultraviolet curable adhesive, and lithium niobate C (trade name, manufactured by Toa Gosei Co., Ltd.) (thermal expansion coefficient 13 × 10 ⁻⁶ / K) can be exemplified.

  Next, the first main surface (main surface on the electrode piece portion side) 1a of the substrate 1 is polished to obtain a thin layer, thereby obtaining the element 14 provided with the wavelength conversion substrate 1A (FIG. 2D). Reference numeral 7A denotes a periodically poled structure.

  As this polishing method, a method using both lapping and CMP can be exemplified. Specifically, in order to shorten the polishing time, first lapping is performed with 3 to 5 um abrasive grains, and then lapping is performed with 1 um abrasive grains, and then the work-affected layer generated by lapping is removed. The thickness of 3 μm is polished and removed by CMP processing to reduce the thickness.

  From the viewpoint of wavelength conversion efficiency, the thickness of the thinned substrate 1A is preferably 6 μm or less, and more preferably 4 μm or less. Similarly, from the viewpoint of wavelength conversion efficiency and mechanical strength, 1.5 μm or more is preferable.

  On the other hand, in the comparative example, as shown in FIG. 3A, the first main surface (main surface on the electrode piece portion side) 1 a of the substrate 1 is bonded to the main surface 9 a of the support substrate 9. Then, as shown in FIG. 3B, the second main surface (main electrode-side main surface) 1b of the substrate 1 is polished to form a polished surface 1d.

  In this method, since it is considered that the periodically poled structure is satisfactorily formed on the electrode piece side, it is predicted that the best wavelength conversion efficiency can be obtained by polishing the main surface side of the uniform electrode. . However, in practice, the present invention has a higher wavelength conversion efficiency. This is because the electrode material diffused into the substrate over a depth of several tens of nm from the electrode piece on the main surface 1a, and the crystal quality was locally degraded.

  On the other hand, in the present invention, since there is an insulating layer between the uniform electrode and the substrate main surface 1b, it is possible to prevent the diffusion of the electrode material and the periodic polarization inversion structure is provided on the side where the uniform electrode is provided. It was found that the film was well formed, and higher wavelength conversion efficiency was obtained as a whole. This is the discovery of the inventor.

  The element of the present invention can be applied to a harmonic generation element such as a second harmonic generation element. When used as a second harmonic generation element, the wavelength of the harmonic is preferably 330-1600 nm.

  4 and 5 show an example of a more detailed configuration of the wavelength conversion element.

  A pair of elongated grooves 15 is provided in the ferroelectric crystal substrate 1A. The grooves 15 are parallel to each other, and a ridge portion 16 is formed by these grooves. A channel-type optical waveguide 20 is formed by the ridge portion 16 and the groove 15. An extending portion 17 is formed on each outer side of each groove 15. Further, the periodic domain-inverted structure 7A is formed on the entire substrate 1A, for example, as described above.

  In the channel-type optical waveguide 20, polarization is performed in the Z direction perpendicular to the light propagation direction, and the polarization direction is periodically reversed. As a result, the fundamental wave incident from the incident surface of the optical waveguide 20 undergoes wavelength conversion in the optical waveguide 20, and the harmonics are emitted from the emission surface.

  An underclad 11B is formed on the second main surface 1b side of the ferroelectric crystal substrate 1A, and an overclad 11A is formed on the first main surface. The second main surface of the substrate 1A is bonded to the support substrate 9 via the underclad 11B and the lower adhesive layer 12B. The first main surface of the substrate 1A is bonded to the upper substrate 13 by the upper adhesive layer 12A through the over clad 11A. The base adhesive layer 12B is formed along a substantially flat second main surface. The upper adhesive layer 12A is also filled in the ridge groove 15 to form a groove filling portion. Thereby, the element 14A is formed.

  The channel type optical waveguide formed on the substrate is not limited, and may be a ridge type optical waveguide or a diffusion type optical waveguide. The diffusion optical waveguide can be formed by metal diffusion (for example, titanium diffusion) or proton exchange. The processing method for forming the ridge structure is not limited, and methods such as machining, ion milling, dry etching, and laser ablation can be used.

  Moreover, the sheet | seat of an organic resin adhesive can be interposed between a wavelength conversion layer, a support substrate, and an upper side board | substrate, respectively, and it can join. Preferably, a sheet made of a thermosetting, photocurable or photothickening resin adhesive is interposed between the substrate 1A, the support substrate 9, and the upper substrate 13 to cure the sheet. A film resin is appropriate as such a sheet.

  Moreover, it is preferable that the thickness of an upper side adhesive layer is 0.5-3.0 micrometers from a viewpoint of this invention.

  The specific material of the upper substrate is not particularly limited, and examples thereof include glass such as lithium niobate, lithium tantalate, and quartz glass, quartz, and Si. In this case, from the viewpoint of the difference in thermal expansion, the substrate 1A, the support substrate, and the upper substrate are preferably made of the same material, and lithium niobate single crystal is particularly preferable. Although the thickness of the upper substrate and the thickness of the support substrate are not particularly limited, 100 μm or more is preferable from the above viewpoint. Moreover, although there is no upper limit in particular of the thickness of a support substrate and the thickness of an upper board | substrate, 2 mm or less is preferable practically.

  The detection limit of the electrode material by dynamic SIMS is 0.1 ppm.

(Comparative example)
In accordance with the method described with reference to FIGS. 1, 2A, 2B, 3, 4, and 5, a wavelength conversion element 14A was manufactured.
Specifically, as the substrate 1, a MgN-added LiNbO ₃ (MgOLN) Z-cut substrate was used. A SiO ₂ film was formed as an insulating film on the + z plane (first main surface) 1 a of the substrate 1. Further, an SiO ₂ film was formed as the insulating film 2B on the −z plane (second main surface) 1b. The thickness of each insulating film was about 2000 angstroms.

  Subsequently, a photoresist was spin-coated on the insulating film, and a resist pattern was formed through mask exposure and development. Using this resist pattern as a mask, a wet etching process is performed to form a patterned insulating film 2A as shown in FIG.

  Subsequently, conductive films 3A and 3B were formed by sputtering. These film thicknesses were 2000 angstroms and the material was molybdenum.

The substrate 1 thus produced was immersed in insulating oil, and a pulse voltage was applied at 170 ° C. The voltage application condition was set to about 6 kV / mm, and a rectangular pulse having a width of about 1 msec was applied. The number of times of pulse application depends on the pattern area. For example, when it is 20 mm ² , 20000 pulses are suitable.

The dielectric substrate 5 was a non-doped LiNbO ₃ Z-cut substrate. Molybdenum films were formed on the + z plane and the −z plane of the dielectric substrate 5 by sputtering as electrodes 33A and 33B, respectively. The film thickness of each conductive film was 1000 angstroms.

  After voltage application, in order to confirm whether polarization inversion was formed, wet etching was performed with a hydrofluoric acid mixed solution (hydrofluoric acid: nitric acid = 1: 2). As a result, a periodically poled structure corresponding to a period of about 7 μm was obtained uniformly.

Next, after periodic polarization reversal was formed, a SiO ₂ underclad 11B having a thickness of 0.4 μm was formed by sputtering. After the adhesive 12B is applied to the support substrate 9 made of a non-doped lithium niobate substrate having a thickness of 0.5 mm, the first main surface 1a (main surface on which the electrode piece portion is formed) of the substrate 1 is applied to the support substrate 9. The second main surface (main surface on which the uniform electrode was formed) 1b of the substrate 1 was ground and polished to a thickness of 3.7 μm (FIGS. 3A and 3B).

Next, the ridge portion 16 was formed by laser ablation processing. After forming the ridge portion, a SiO ₂ overclad 11A having a thickness of 0.5 μm was formed by sputtering. After the adhesive 12A was applied on the over clad 11A, the upper substrate 13 made of non-doped lithium niobate single crystal having a thickness of 0.5 mm was adhered. The device was cut into a length of 9 mm and a width of 1.0 mm with a dicer to obtain a chip.

The dimensions of each part of the obtained chip are shown below (see FIG. 4).
Chip length L: 8mm
Chip width Cw: 0.7mm
Tip height Ch: 1 mm
Ridge width Rw: 5.8um
Ridge depth Rd: 2.4um
Slab height Sh: 3.75um
Polarization inversion period Λ: 6.56um

As shown in FIG. 6, the basic light oscillated from the light source 22 was condensed by the lens systems 23A and 23B and made incident on the element 14A. The fundamental wave is wavelength-converted in the element 14 </ b> A and emitted as the second harmonic 25. In this waveguide, optical properties were measured using a Yb-doped fiber laser. As a result of adjusting the oscillation wavelength of the fundamental wave from the laser to 1061 nm, adjusting the oscillation output to 350 mW, and condensing the fundamental light on the waveguide end face with a lens, 280 mW could be coupled to the waveguide. When phase matching was performed by adjusting the waveguide temperature, a maximum SHG output of 72 mW was obtained. The wavelength of the harmonic at that time was 530.5 nm.
Furthermore, as a result of measurement by dynamic SIMS (IMS-6f manufactured by Cameca), molybdenum was diffused at a diffusion concentration of 10 ppm on the outermost surface of the substrate.

  Further, the first main surface (the main surface on which the electrode piece portion was formed) of the substrate on which the periodically poled structure was formed was measured by dynamic SIMS (Cameca IMS-6f). The measurement results are shown in FIG. It can be seen that in addition to niobium and lithium, molybdenum diffuses to a depth of nearly 40 nm.

(Example)
A wavelength conversion element was manufactured in the same manner as in the comparative example. However, unlike the comparative example, as shown in FIGS. 2 (c) and 2 (d), the second main surface of the substrate (the main surface 1 b on the uniform electrode side) is bonded to the support substrate 9, and the first The main surface (main surface on the electrode piece portion side) 1a was polished, and other elements were manufactured in the same procedure as in Comparative Example 1, and the same evaluation was performed.

  As a result, 280 mW could be coupled to the waveguide as a result of condensing the basic light onto the waveguide end face with a lens. When phase matching was performed by adjusting the waveguide temperature, a maximum SHG output of 98 mW was obtained. The wavelength of the harmonic at that time was 530.5 nm.

  Further, the obtained substrate surface was wet-etched with fluoric acid and then observed with a microscope. FIG. 7 shows the first main surface (main surface on the electrode piece portion side) of the substrate, and FIG. 8 shows the second main surface (main surface on the uniform electrode side) of the substrate. In all cases, the domain-inverted portion was well formed throughout, and no defect or domain-inversion defect was found. As a result of measurement by dynamic SIMS (IMS-6f manufactured by Cameca), the diffusion concentration of molybdenum as the electrode material was less than the detection limit (0.1 ppm) at the outermost surface of the second main surface of the substrate.

The present invention relates to a method for manufacturing a wavelength conversion element.

The present invention provides a method for manufacturing a wavelength conversion element.

The wavelength conversion element is a support substrate,
A ferroelectric crystal substrate comprising a ferroelectric crystal Z-cut substrate or an off-cut Z-cut substrate and having a first main surface and a second main surface;
A periodically poled structure provided on the ferroelectric crystal substrate;
An optical waveguide provided on the ferroelectric crystal substrate, and an adhesive layer that adheres the second main surface of the ferroelectric crystal substrate and the support substrate.

In the manufacturing method of the present invention , a conductive film and a plurality of rows of insulating films are provided on a first main surface of a ferroelectric crystal substrate comprising a ferroelectric crystal Z-cut substrate or an off-cut Z-cut substrate , film, wherein an insulating film covering portion that covers the insulating film, said insulating comprises a plurality of electrodes piece provided between the film and the insulating film on the second main surface of the ferroelectric crystal substrate And sequentially providing uniform electrodes;
Forming the periodically poled structure by applying a voltage between the electrode piece and the uniform electrode;
Bonding the second main surface of the ferroelectric crystal substrate to a support substrate;
Thinning the first main surface of the ferroelectric crystal substrate by polishing to remove the material of the conductive film diffused from the first main surface ; and the ferroelectric crystal substrate And a step of forming an optical waveguide.

Claims (6)

Support substrate,
A ferroelectric crystal substrate comprising a ferroelectric crystal Z-cut substrate or an off-cut Z-cut substrate and having a first main surface and a second main surface;
A periodically poled structure provided on the ferroelectric crystal substrate;
An optical waveguide provided on the ferroelectric crystal substrate, and a wavelength conversion element comprising an adhesive layer that bonds the second main surface of the ferroelectric crystal substrate and the support substrate,
The periodic polarization reversal structure includes a plurality of electrode pieces provided on the first main surface of the ferroelectric crystal substrate, and an insulating film provided on the second main surface of the ferroelectric crystal substrate. The ferroelectric crystal substrate is formed by applying a voltage to the upper uniform electrode, and the ferroelectric crystal substrate is thinned by polishing the first main surface of the ferroelectric crystal substrate. The wavelength conversion element characterized by the above-mentioned.   2. The element according to claim 1, wherein the optical waveguide is a ridge type optical waveguide, and ridge grooves are formed on both sides of the ridge type optical waveguide.   An upper substrate provided on the first main surface side of the ferroelectric crystal substrate; and an adhesive layer for bonding the first main surface of the ferroelectric crystal substrate and the upper substrate. The device according to claim 1, wherein the device is a device.   The wavelength conversion according to any one of claims 1 to 3, wherein a diffusion concentration of the electrode piece portion and the uniform electrode material in the ferroelectric crystal substrate is less than 0.1 ppm. element. Support substrate,
A ferroelectric crystal substrate comprising a ferroelectric crystal Z-cut substrate or an off-cut Z-cut substrate and having a first main surface and a second main surface;
A periodically poled structure provided on the ferroelectric crystal substrate;
An optical waveguide provided on the ferroelectric crystal substrate, and a wavelength conversion element comprising an adhesive layer that bonds the second main surface of the ferroelectric crystal substrate and the support substrate,
The periodic polarization reversal structure includes a plurality of electrode pieces provided on the first main surface of the ferroelectric crystal substrate, and an insulating film provided on the second main surface of the ferroelectric crystal substrate. It is formed by applying a voltage between the upper uniform electrode, and the diffusion concentration of the electrode piece portion and the uniform electrode material in the ferroelectric crystal substrate is less than 0.1 ppm A wavelength conversion element. A method for manufacturing the device according to any one of claims 1 to 5,
A plurality of electrode pieces are provided on a first main surface of a ferroelectric crystal substrate comprising a Z-cut substrate or an off-cut Z-cut substrate of a ferroelectric crystal, and the second main surface of the ferroelectric crystal substrate is provided. Sequentially providing an insulating film and a uniform electrode;
Forming the periodically poled structure by applying a voltage between the electrode piece and the uniform electrode;
Bonding the second main surface of the ferroelectric crystal substrate to a support substrate;
A wavelength conversion element comprising: a step of thinning the first main surface of the ferroelectric crystal substrate by polishing; and a step of forming an optical waveguide on the ferroelectric crystal substrate. Manufacturing method.

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