JP4709864B2 - Thin film substrate for wavelength conversion element and waveguide for wavelength conversion element - Google Patents

Description

  The present invention relates to a wavelength conversion element thin film substrate and a wavelength conversion element waveguide that convert the wavelength of signal light to another wavelength by using a difference frequency generation effect generated in a nonlinear optical medium.

In the production of the wavelength conversion light source module, a quasi-phase matching (QPM: Quasi-Phase Matching) is formed on the thin film substrate for wavelength conversion elements (LiNbO ₃ ) in order to create a converted light having the sum or difference frequency of the signal light wavelength and the control light wavelength. It is necessary to form a periodic domain-inverted region called a pattern. A method for forming the domain-inverted region is described in, for example, Patent Document 1 and Patent Document 2.
Japanese Patent Laid-Open No. 02-187735 JP 2003-140214 A

  FIG. 1 is a diagram for explaining a manufacturing method for forming a domain-inverted structure on a wavelength conversion element thin film substrate by an electric field application method using a resist pattern and a liquid electrode. The electric field application method shown in FIG. 1 is formed by forming a large number of resist patterns 12 in which line segment patterns are arranged in parallel on a wavelength conversion element thin film substrate 11a that is uniformly polarized in advance in the thickness direction of the substrate. Is immersed in a liquid electrode 13 such as an aqueous lithium chloride solution, and an electric field is applied by the charge applying means 16 to forcibly invert the polarization in the region where the resist pattern 12 does not exist. By adjusting the arrangement of the resist pattern 12, the polarization periodicity of the wavelength conversion element thin film substrate 11b can be realized, and the QPM pattern can be formed on the wavelength conversion element thin film substrate 11b. In FIG. 1, an arrow 14 indicates the direction of polarization.

  In order to surely cause the polarization inversion phenomenon over the entire surface of the substrate by the electric field application method of FIG. 1, it is necessary to make the length of the resist pattern 12 shorter than a certain value (for example, a line segment pattern having a length of 1 mm). . The reason is that if both ends of the resist pattern 12 that triggers polarization reversal due to electric field concentration are too far apart, a region where the polarization reversal phenomenon is not completed occurs, and the yield in that region decreases. In order to avoid this, for example, a QPM pattern 20 as shown in FIG. 2 is designed. In the QPM pattern 20, the length of the line segment pattern 23 in the longitudinal direction is 1 mm, and a gap of about 10 to 20 μm is provided between the line segment patterns 23 in the longitudinal direction.

  When the QPM pattern 20 is formed with a resist pattern on the wavelength conversion element thin film substrate 30 and the electrolytic application method is performed, the periodic polarization inversion structure formed on the wavelength conversion element thin film substrate 30 is as shown in FIG. A ridge waveguide (length: 50 mm) serving as a clad portion of the wavelength conversion element is formed by cutting the wavelength conversion element thin film substrate 30 as shown in FIG. 3 with a dicing saw so as to be orthogonal to the line segment pattern. The In FIG. 3, the area | region cut | disconnected with a dicing saw is shown as wavelength formation element waveguide formation area | region A1-A4. However, since the periodic polarization reversal structure of the QPM pattern 20 as shown in FIG. 3 has a gap 31 region, the ridge waveguide includes the gap 31 region and does not have a quasi-phase matching depending on the cutting position in the dicing saw. There was a fear that a conversion element was produced. In FIG. 3, the wavelength conversion element waveguide formation regions A3 and A4 correspond. In order to prevent the gap 31 from being included in the ridge waveguide, the alignment mark 25 for the dicing saw needs to be formed in advance by a photo-etching method. In the conventional periodically poled structure of the QPM pattern, There was a problem of complicated processes and associated high costs. Although the case where the ridge waveguide is cut out from the thin film substrate for the wavelength conversion element has been described, the same problem occurs when the waveguide chip device is cut out from the substrate. In the following description, the ridge waveguide is described as a wavelength conversion element waveguide.

  Accordingly, in order to solve the above-mentioned problems, the present invention eliminates the need for a positioning mark for a dicing saw, and is for a wavelength conversion element having a QPM pattern periodic polarization reversal structure that can be manufactured at a low cost with a simple process. An object of the present invention is to provide a thin film substrate and a waveguide for a wavelength conversion element obtained by cutting the thin film substrate.

  In order to achieve the above object, the wavelength conversion element thin film substrate according to the present invention employs a shift parallel arrangement in which the gaps of the QPM pattern are laid out obliquely.

  Specifically, the thin film substrate for a wavelength conversion element according to the present invention has a quasi phase matching pattern in which a polarization region polarized in the thickness direction and a polarization inversion region polarized in a direction opposite to the polarization direction of the surrounding polarization region. A thin film substrate for a wavelength conversion element having a periodically poled structure periodically arranged, wherein the quasi-phase matching pattern is a line segment pattern having a length in which a longitudinal direction can be accommodated in the polarization region and a predetermined width. Are arranged so that they are on the same straight line in the row direction, which is the direction, and at equal intervals through a predetermined gap, and are arranged so as to be parallel and equally spaced in the column direction, which is the width direction, and The gaps are periodically arranged so as to shift by a certain length in one direction for each row, and the periodic polarization structure uses the line segment pattern of the quasi-phase matching pattern as the domain-inverted region. And

  The edge of the line segment pattern that serves as a trigger for polarization reversal is distributed uniformly in the wafer surface, and a domain-inverted structure having a long line segment pattern can be fabricated on the thin film substrate for a wavelength conversion element. Therefore, when the wavelength conversion element waveguide is formed by cutting the wavelength conversion element thin film substrate, it can be continuously cut by simply aligning the dicing saw with an orientation flat or the like. For this reason, the yield which is the number of the waveguides for wavelength conversion elements obtained from one thin film substrate for wavelength conversion elements can be improved. Further, the same effect can be obtained when the waveguide chip device is cut out after the waveguide chip device is formed on the substrate.

  Accordingly, the present invention provides a thin film substrate for a wavelength conversion element having a QPM pattern periodic polarization reversal structure that eliminates the need for a positioning mark for a dicing saw, can be used to manufacture a wavelength conversion element with a simple process and at low cost. it can.

  The waveguide for wavelength conversion elements according to the present invention is produced by cutting the thin film substrate for wavelength conversion elements. Specifically, the wavelength conversion element waveguide according to the present invention is uniformly polarized in a direction perpendicular to the light propagation direction, and has a polarization section having a certain length in the light propagation direction, A wavelength including a periodically poled structure including polarization inversion regions that are polarized in a direction opposite to the polarization direction of the polarization interval, and polarization inversion intervals having a certain width in the light propagation direction. A waveguide for a conversion element, wherein the domain-inverted sections are all the domain-inverted regions of the first type, the domain-inverted regions are at one end in a direction perpendicular to the light propagation direction and the polarization direction, and other regions Is polarized in the same direction as the polarization direction of the polarization section, the polarization inversion region is at both ends of the light propagation direction and the direction perpendicular to the polarization direction, and the other region is the polarization direction of the polarization section A third type polarized in the same direction as There is a fourth type in which the inversion region is at the other end of the direction perpendicular to the propagation direction and polarization direction of light, and the other region is polarized in the same direction as the polarization direction of the polarization section. , At least one of the first types, at least one of the second types, at least one of the third types, and at least one of the fourth types.

  When the wavelength conversion element waveguide is cut out from the wavelength conversion element thin film substrate, it can be continuously cut by simply aligning the dicing saw with an orientation flat or the like. Therefore, the present invention can provide a waveguide for a wavelength conversion element that does not require an alignment mark for a dicing saw, can be manufactured with a simple process, and can be manufactured at low cost.

  The manufactured wavelength conversion element waveguide may include a plurality of gaps between QPM patterns. However, this part is a minute part of the optical path length of the wavelength conversion element waveguide, and a shift in the conversion wavelength occurs. In addition, the decrease in optical power after conversion can be ignored.

  According to the present invention, a thin film substrate for a wavelength conversion element having a QPM pattern periodic polarization reversal structure that eliminates the need for an alignment mark for a dicing saw, is simple in process, and can be manufactured at low cost, and the same are cut. A waveguide for a wavelength conversion element can be provided.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 4 is a diagram showing a QPM pattern 40 formed on the wavelength conversion element thin film substrate of the present embodiment. The QPM pattern 40 is a pattern in which a plurality of line segment patterns 53 having a predetermined length and a length that can be accommodated in the wavelength conversion element thin film substrate 50 in FIG. 5 are arranged. The QPM patterns 40 are arranged so as to be on the same straight line in the row direction which is the longitudinal direction, and are periodically arranged in parallel and at equal intervals in the column direction which is the width direction. Further, in the QPM pattern 40, there is a gap 31 between line segment patterns 53 adjacent in the row direction, and the line segment patterns 53 are arranged so that the gap 31 is shifted by a certain length in one direction for each row. That is, the area of the gap 31 is arranged obliquely with respect to the line segment pattern 53.

  FIG. 5 is a view for explaining the wavelength conversion element thin film substrate 50 of this embodiment having the periodic polarization structure of the QPM pattern 40 of FIG. The thin film substrate for wavelength conversion element 50 is a periodic polarization in which a polarization region polarized in the thickness direction and a polarization inversion region polarized in a direction opposite to the polarization direction of the surrounding polarization region are periodically arranged in a QPM pattern 40. Provide structure. In the periodic polarization structure, the line segment pattern 53 of the QPM pattern 40 is a polarization inversion region, and the periphery of the line segment pattern 53 is a polarization region 55. Specifically, the polarization region 55 is a region other than the line segment pattern 53 in the wavelength conversion element thin film substrate 50.

  In the wavelength conversion element thin film substrate 50, for example, the periodic polarization structure of the QPM pattern 40 is formed by the electric field application method described in FIG. By cutting out the wavelength conversion element waveguide formation regions A1 to A4 from the wavelength conversion element thin film substrate 50, a wavelength conversion element waveguide described below can be obtained. The same applies to the case where the waveguide chip device is cut out after the waveguide chip device is formed on the wavelength conversion element thin film substrate 50.

(Embodiment 2)
FIG. 6 is a diagram showing the wavelength conversion element waveguide 60 of the present embodiment. The wavelength conversion element waveguide 60 of the present embodiment is uniformly polarized in a direction E perpendicular to the light propagation direction L, and has a polarization section 62 having a certain length in the light propagation direction L, and polarization. Periodic polarization in which polarization inversion sections 63 having polarization inversion regions 63a polarized in the direction opposite to the polarization direction of the sections 62 and having a constant width in the light propagation direction L exist alternately in the light propagation direction L A wavelength conversion element waveguide 60 having a structure, wherein the polarization inversion section 63 is a first type 63-1, which is a polarization inversion region 63a, and the polarization inversion region 63a is perpendicular to the light propagation direction L and the polarization direction E. The second type 63-2 in which the other region is polarized in the same direction as the polarization direction of the polarization section 62, and the polarization inversion region 63a is perpendicular to the light propagation direction L and the polarization direction E. At both ends of the direction T, the other region is the part of the polarization section 62 The third type 63-3 polarized in the same direction as the direction and the polarization inversion region 63a are at the other end in the direction L perpendicular to the light propagation direction L and the polarization direction E, and the other region is the polarization section 62. There is a fourth type 63-4 polarized in the same direction as the polarization direction of at least one first type 63-1, at least one second type 63-2, at least 1 in the light propagation direction L. Two third types 63-3 and at least one fourth type 63-4 are arranged in this order.

  The wavelength conversion element waveguide 60 is a waveguide in which the polarization sections 62 and the polarization inversion sections 63 exist alternately in the light propagation direction L. The polarization section 62 of the wavelength conversion element waveguide 60 is uniformly polarized in the vertical direction E. The polarization inversion section 63 of the wavelength conversion element waveguide 60 has a polarization inversion area 63 a that is polarized in the direction opposite to the polarization direction of the polarization section 62. Moreover, the polarization inversion section 63 is divided into four types. The first type 63-1 is a type in which the entire domain inversion section 63 is the domain inversion region 63a. The second type 63-2 is a type in which the domain-inverted region 63a is only on one side of the direction T perpendicular to the light propagation direction and the polarization direction E when viewed from the light propagation direction L. The third type 63-3 is a type in which the domain-inverted regions 63a are on both sides of the direction T perpendicular to the light propagation direction and the polarization direction E when viewed from the light propagation direction L. The fourth type 63-4 is a type in which the domain-inverted region 63a is only on the opposite side to the second type 63-2. In the second type 63-2 to the fourth type 63-4, the region other than the polarization inversion region 63a is polarized in the same direction as the polarization direction of the polarization section 62.

  The polarization section 62 is the polarization region 55 of FIG. 5, and the polarization inversion section 63 is the line segment pattern 53 of FIG. The domain-inverted region 63a in the domain-inverted section 63 is the line segment pattern 53 in FIG. 5, and the other region in the domain-inverted section 63 is the gap 31 in FIG. That is, the first type 63-1 of the polarization inversion section 63 is a portion near the center of the line segment pattern 53 of FIG. The second type 63-2 to the fourth type 63-4 of the polarization inversion section 63 are portions including the gap 31 in FIG.

  The wavelength conversion element waveguide 60 may include the gap 31 as shown in FIG. 6 depending on the inclination of the gap 31 of the QPM pattern 40 and the method of cutting out the wavelength conversion element waveguide formation region from the wavelength conversion element thin film substrate 50. is there. However, since there are few portions including the gap 31 with respect to the entire wavelength conversion element waveguide 60, the shift of the conversion wavelength does not occur, and the decrease in the optical power after conversion can be ignored.

The structures of the thin film substrate for wavelength conversion element and the waveguide for wavelength conversion element of the present invention are not limited to the LiNbO ₃ substrate described in this specification, and KNbO ₃ , LiTaO ₃ , LiNb _(x) Ta having a nonlinear optical effect. _(1-x) O ₃ (0 ≦ x ≦ 1) or KTiOPO ₄ , or a compound substrate containing at least one selected from the group consisting of Mg, Zn, Sc, and In as an additive Is also applicable.

It is a figure explaining the electric field application method using a resist pattern and a liquid electrode. (A) is the figure which showed the cross section after forming many resist patterns which arranged the line segment pattern in parallel on the thin film substrate for wavelength conversion elements as a mask. (B) is the figure which showed the cross section after applying a voltage to a liquid electrode and forcibly inverting the polarization of the area | region where a resist pattern does not exist. It is a figure explaining the pattern of the periodic polarization inversion structure formed in the conventional thin film substrate for wavelength conversion elements. It is a figure explaining the conventional thin film substrate for wavelength conversion elements. It is a figure explaining the pattern of the periodic polarization inversion structure formed in the thin film substrate for wavelength conversion elements which concerns on this invention. It is a figure explaining the thin film substrate for wavelength conversion elements concerning the present invention. It is a figure explaining the waveguide for wavelength conversion elements concerning the present invention.

Explanation of symbols

11a: Wavelength converting element thin film substrate 11b: Wavelength converting element thin film substrate 12: Resist pattern 13: Liquid electrode 14: Arrow 15: Back electrode 16: Electric field applying means 20, 40: Quasi-phase matching (QPM) pattern 23, 53 : Line segment pattern 25: alignment mark 30, 50: wavelength conversion element thin film substrate 31: gap 55: polarization region 60: wavelength conversion element waveguide 62: polarization section 63: polarization inversion section 63a: polarization inversion area 63- 1: First type 63-2 of polarization inversion section: Second type of polarization inversion section 63-3: Third type of polarization inversion section 63-4: Fourth type of polarization inversion section A1 to A4: For wavelength conversion element Waveguide formation region L: light propagation direction E: direction T: direction perpendicular to light propagation direction and polarization direction

Claims (2)

A polarization region polarized in the thickness direction;
A domain-inverted region that polarizes in a direction opposite to the polarization direction of the surrounding polarized region;
Is a thin film substrate for a wavelength conversion element comprising a periodic polarization structure periodically arranged in a quasi-phase matching pattern,
The pseudo phase matching pattern is:
A line segment pattern having a length and a predetermined width that fits in the polarization region in the longitudinal direction is arranged so as to be on the same straight line in the row direction that is the longitudinal direction and at equal intervals through a predetermined gap. Are arranged so as to be parallel and equally spaced in the column direction which is the width direction, and further, the gaps are periodically arranged so as to shift by a certain length in one direction for each row,
The periodic polarization structure is:
A thin film substrate for a wavelength conversion element, wherein the line segment pattern of the quasi phase matching pattern is used as the domain-inverted region. A polarization section that is uniformly polarized in a direction perpendicular to the light propagation direction and has a certain length in the light propagation direction;
A domain-inverted region including a domain-inverted region that is polarized in a direction opposite to the direction of polarization of the domain-polarized section, and having a certain width in the light propagation direction;
Is a waveguide for a wavelength conversion element having a periodic polarization structure that alternately exists in the light propagation direction,
The polarization inversion interval is
The first type, which is all the domain-inverted region,
A second type in which the domain-inverted region is at one end of a direction perpendicular to the light propagation direction and the polarization direction, and the other region is polarized in the same direction as the polarization direction of the polarization section;
A third type in which the domain-inverted regions are at both ends of a light propagation direction and a direction perpendicular to the polarization direction, and the other regions are polarized in the same direction as the polarization direction of the polarization section;
as well as,
A fourth type in which the domain-inverted region is at the other end of the light propagation direction and the direction perpendicular to the polarization direction, and the other region is polarized in the same direction as the polarization direction of the polarization section;
There is
Wavelengths arranged in the light propagation direction in the order of at least one of the first type, at least one of the second types, at least one of the third types, and at least one of the fourth types. Waveguide for conversion element.

Images