JPH03137605A - Optical waveguide, wavelength changing element and short-wavelength laser light source - Google Patents

Abstract

PURPOSE:To make the distribution of guided light in an electromagnetic field perfectly symmetric with respect to an axis and to attain high efficiency of coupling to an optical fiber by adhering optical waveguides formed in first and second substrates to each other to form an optical waveguide. CONSTITUTION:Proton exchange waveguides are formed on LiNbO3 substrates 1, 2 and annealed at 350 deg.C in the air for 1 hr to form optical waveguides 3, 4 of 5 mum width and 2 mum depth. The waveguides 3, 4 are washed, aligned with a mask aligner and adhered to each other and both ends are polished to form an incidence part 5. When semiconductor laser light having 0.8 mum wavelength is allowed to enter the resulting waveguide, emergent guided light is made nearly circular and the distribution of the guided light in an electromag netic field is made nearly symmetric with respect to the axis of propagation. When an optical fiber is coupled to the waveguide, loss measured at the coupled part is 0.8 dB.

Description

Detailed Description of the Invention Industrial Application Field of the Invention G1 Optical information processing using a coherent light source Related to optical waveguides, wavelength conversion elements, and short wavelength laser light sources used in the optical application measurement and control field. The conventional structure of an optical waveguide is to fabricate a striped Ti film on a LiNbO3 substrate by sputtering and photolithography, heat it at high temperature to form a waveguide, and then thermally diffuse Mg onto the waveguide. By lowering the refractive index of the waveguide on the substrate side, the waveguide is embedded in the substrate.
There is a method to make the electromagnetic field distribution of the propagating waveguide mode symmetrical with respect to the propagation axis.9 Figure 5 shows the configuration of a conventional optical waveguide. Kinou 4'
is the electromagnetic field distribution of the waveguide mode propagating in the waveguide.This allows the electromagnetic field distribution of the waveguide mode propagating in the waveguide to match the electromagnetic field distribution of the waveguide mode propagating in the optical fiber. Conventional wavelength conversion elements that achieve high coupling efficiency include E, Lim, and M.
, M.

Fejer, R.L., Byer, '5econd.
harmonic generation of gre
en light in a periodical
y-poled LiNbO3waveguide,
"Submitted to CLEO '89.
FIG. 6 shows a basic configuration diagram of a conventional wavelength conversion element.

5° is the base K 6' is made of a nonlinear material The waveguide 7' is made of a nonlinear material and the nonlinear polarization is inverted with respect to the nonlinear polarization of the waveguide.The fabrication method thereof is sputtering and photolithography. After forming Ti stripes using the method, Ti was diffused at 1000°C to form a polarization inversion grating layer.Next, to form a proton exchange waveguide, a waveguide mask was formed with aluminum.
After heat treatment in benzoic acid at 300℃, the mask is removed and rare annealing is performed to form the waveguide.The polarization inversion grating formed in this way creates periodic nonlinear polarization within the waveguide made of nonlinear material. By forming different layers and matching the phase of the second harmonic, a highly efficient wavelength conversion element can be constructed.

Problems to be Solved by the Invention The optical waveguide formed by the method described above has one advantage: Because the electromagnetic field distribution of the guided light exists inside the substrate, the efficiency of the surface integrated element formed to control the guided light decreases. Furthermore, it is difficult to control the diffusion of the low refractive index layer formed on the surface, and it is difficult to make the electromagnetic field distribution completely axially symmetrical. Although the method of lowering the refractive index of the waveguide surface by 4Mg thermal diffusion, which is processed at around 1000°C, cannot be used in waveguides, there are problems such as difficulty in forming buried waveguides. In view of the above points, one waveguide is formed by bringing the waveguides formed on two substrates into close contact with each other, and the waveguide is axially symmetrical with respect to the waveguide propagation direction. The purpose is to provide an axially symmetrical waveguide relatively easily.A Also, after forming a surface integrated element on the waveguide for controlling guided light, the waveguides are brought into close contact with each other to integrate the element inside the waveguide. The purpose of this technology is to provide a device with high efficiency in controlling guided light.In the case of ion exchange waveguides, the purpose is also to provide a waveguide that is axially symmetrical with respect to the waveguide propagation direction. In addition, in the wavelength conversion element configured as above, since the polarization inversion layer is formed by Ti diffusion, diffusion occurs in the lateral direction as well as in the depth direction.For this reason, the polarization inversion layer is sufficiently deep with respect to the waveguide. The period of the grating (3
Therefore, it is difficult to increase the conversion efficiency of a wavelength conversion element.In view of the above points, the present invention aims to connect a waveguide having a polarization inversion layer formed on two substrates. The present invention aims to provide a highly efficient wavelength conversion element by making it possible to reduce the depth of the waveguide and the polarization inversion layer formed in the waveguide to half of the conventional one by bringing the waveguides into close contact with the waveguides.

Means for Solving the Problems The present invention (companies) includes a first substrate, an optical waveguide formed on the surface of the substrate, a second substrate, and an optical waveguide formed on the surface of the second substrate. provision and said first
An optical waveguide characterized in that an optical waveguide formed on the surface of the substrate and an optical waveguide formed on the surface of the second substrate are brought into close contact with each other. an optical waveguide made of a nonlinear material which is made of a nonlinear material; an optical waveguide made of a nonlinear material formed on the surface of the second substrate; and a part made of a nonlinear material in which the nonlinear polarization formed in the optical waveguide is inverted with respect to the nonlinear polarization of the optical waveguide, and has a periodic structure. The wavelength conversion element according to the present invention is further characterized in that the optical waveguide formed on the surface of the Ml substrate, the optical waveguide formed on the surface of the second substrate, and the portion where the nonlinear polarization is reversed are brought into close contact with each other. a first substrate, an optical waveguide made of a nonlinear material formed on the surface of the substrate, a portion made of a linear material periodically formed in the optical waveguide, a second substrate and a nonlinear material formed on the surface of the second substrate. An optical waveguide made of a material and a portion made of a linear material formed periodically within the optical waveguide, and the optical waveguide and the portion made of the linear material formed on the surfaces of the first and second substrates are brought into close contact with each other. A wavelength conversion element according to the present invention is further characterized by a first substrate made of a nonlinear material, an optical waveguide layer formed on the surface of the substrate, a second substrate made of a nonlinear material, and an optical waveguide layer formed on the surface of the substrate. The present invention is also applicable to a wavelength conversion element characterized in that an optical waveguide layer formed in a round shape and an optical waveguide formed on the surfaces of the first and second substrates are brought into close contact with each other. This allows the electromagnetic field distribution of the waveguide mode propagating through the waveguide to be symmetrical with respect to the waveguide propagation axis, enabling highly efficient coupling with optical fibers. Since surface-integrated elements for controlling waveguide light can be formed inside the waveguide, elements that control waveguide light with high efficiency can be constructed. A symmetrical waveguide can be fabricated, and a waveguide with a symmetrical structure can also be constructed by the configuration of the wavelength conversion element described above. The distribution is symmetrical with respect to the propagation axis, making it possible to couple with the optical fiber with high efficiency.Also, the polarization inversion part can be formed in the center of the waveguide, where the electromagnetic field density within the waveguide is highest. Furthermore, after forming a polarization inversion layer in the waveguide, the two waveguides are bonded together.The depth of the polarization inversion layer formed in the waveguide can be doubled compared to conventional An example of efficient wavelength conversion (Example 1) Figure 1 shows the configuration of an optical waveguide in the first example, which includes a first substrate, an optical waveguide formed on the surface of the substrate, and a second substrate. and an optical waveguide formed on the surface of the second substrate, and the optical waveguide formed on the surface of the first substrate and the optical waveguide formed on the surface of the second substrate are brought into close contact with each other. In figure 1, l is LiNbO5 substrate 2
is a LiNbO5 substrate, 3 is a proton exchange waveguide method formed on a LiNbO5 substrate 1, 4 is a proton exchange waveguide method formed on a LiNbO5 substrate 2, and 5 is an entrance part prepared by polishing. LiNbO5 substrate 1. A Ta5ks stripe mask was fabricated by photolithography and dry etching.
Heat treated in pyrophosphoric acid at 230°C for 5 minutes to form a proton exchange waveguide.The produced proton exchange waveguide was annealed in air at 350°C for 1 hour to form a width of 5 μm and a depth of 2 μm.
After cleaning these two waveguides, align them with a mask aligner to bring the waveguides 3 and 4 into close contact with each other, and then polish both end faces to form an incident part.
When we excited the semiconductor laser light with a wavelength of 0.8 μm into the tightly formed waveguide and observed the near-field pattern of the guided light emitted from the end face of the waveguide, we found that it was approximately circular, indicating that the electromagnetic field distribution of the guided light was propagating. Even though it shows that it is symmetrical about the axis, it is next coupled with a single mode fiber with a core diameter of 6 μm and the fiber and waveguide are aligned under a microscope. When we measured the loss at the junction of the L fiber waveguide using a semiconductor laser beam with a wavelength of 0.8 μm, it was 0.8 dB. The refractive index is 2.2 between the two substrates that are brought into close contact with each other.
When using gel-like LiNbO5, the waveguide loss is reduced by ld.
The loss in the waveguide can be reduced from 0.5 dB/cm to 0.5 dB/cm.By using a material with a refractive index similar to that of the substrate, such as wind-free gel glass, as a mating material, it is possible to reduce waveguide loss. In this example, if a substrate made of a nonlinear material is used, it is impossible to construct a wavelength conversion element.In this example, a proton exchange waveguide on a LiNbO5 substrate is used as an optical waveguide. Ion-exchange waveguide method Ti-diffusion waveguide on LiNbO5 substrate A similar effect can be obtained with a thin film waveguide (Example 2). This figure shows the structure of the optical waveguide in the example shown in FIG. 4, which shows the structure of the optical waveguide equipped with a reflective grating. 41 is the LiNbO5 substrate 2 is a LiNbO5 group K, and 3 is the proton exchange waveguide formed on the LiNbO5 substrate 1. iil & 4 is a proton exchange waveguide formed on the LiNbO5 substrate 2; 5 is an incident waveguide fabricated by polishing; and 6 is a reflection type grading formed on the waveguide 3; on the proton exchange waveguide fabricated in Example 1. 5id2 to 50
After depositing by OA sputtering method, a grating with a period of 0.4 μm and a width of 0.1 μm was formed by photolithography, and the grating period was made 0.1 μm by bringing two waveguides into close contact.Finally, the end face was polished and the incident By forming the gratings formed on the two waveguides and pasting them together, we were able to reduce the period of the grating to 1/2 of the fabricated period.Also, by forming the grating inside the waveguide, Since the perturbation caused by the grating exists inside the waveguide, it is possible to increase the efficiency of the grating.
100.200.500.1000) and measured the reflection efficiency: 98% at a grating length of 200 μm
This is compared to the conventional grating length of 50
The control of guided light by electrodes can also be performed with high efficiency (Example 3) since the electro-optic effect can be exerted inside the waveguide. shows the configuration of a wavelength conversion element in a third embodiment; a first substrate, an optical waveguide made of a nonlinear material formed on the surface of the substrate, and a nonlinear polarization formed in the optical waveguide; A part made of a nonlinear material that is inverted with respect to
an optical waveguide made of a nonlinear material formed on the surface of the second substrate; and an optical waveguide made of a nonlinear material in which the nonlinear polarization formed in the optical waveguide is inverted with respect to the nonlinear polarization of the optical waveguide, and has a periodic structure. In FIG. 11 is L
iNb can base Kaede 12 is LiNbO5 base K 13 is 11
14 is a polarization inversion layer formed on the substrate of 12. 15 is a proton exchange waveguide region formed on the substrate of 12. 16 is a polarization inversion layer formed by Ti diffusion. The manufacturing method will be described. Ti stripes with a period of 2 μm, a width of 0.4 μm, and a grating length of 1 mm are formed on LiNbO5 substrates 11 and 12, which are nonlinear materials, by sputtering and photolithography, and then Ti is diffused at 1000° C. for 1 hour to have a width of 1 μm. A Ti diffused layer with a depth of 0.4 μm was fabricated, and even though the polarization of the Ti diffused layer was reversed with respect to the nonlinear polarization of the LINbOs substrate, a waveguide mask was made of aluminum to form a proton exchange waveguide. After heat treatment in benzoic acid at 300℃, the mask was removed and rare annealing was performed.
A waveguide 13.15 with a width of 4 μm and a depth of 0.5 μm is formed. Even though the waveguide maintains the nonlinear polarization of the substrate, the waveguide is made of a nonlinear material. Polarization inversion layer 14.1 consisting of
Although it is possible to form a grating consisting of 6 parts, the end faces can be formed by aligning the two fabricated waveguides with a mask analizer and closely contacting them. 4Ti diffusion depth is 17
2, a grating with a period of 2 μm can be formed.9 The fabricated element is excited with light from a semiconductor laser with a wavelength of 0.8 μm and 10 m 1 F, and the second harmonic of the excitation light is generated with a wavelength of 0.8 μm.
The second harmonic generated is 5nW.
The conversion efficiency is 10%/W-cm2, but the conversion efficiency of a conventional wavelength conversion element with a polarization inversion grating formed on a waveguide is 2.4X/W-cm2, which is a very high conversion efficiency. In this example, Li is used as the substrate made of nonlinear material.
Strength using NbO5 L doped with MgO
Highly nonlinear materials such as ferroelectric materials such as iNbO5, LiTaO5, and KNbOs, organic materials such as MNA, and compound semiconductors such as ZnS cannot be used as the substrate. By using a metal mask such as Ti instead of a polarization inversion layer and injecting ions such as SL into the waveguide, a layer of linear material is periodically formed in the waveguide to form a wavelength conversion element. Although a wavelength conversion element having a conversion efficiency of about half of that of the wavelength conversion element of this example can be manufactured even if the wavelength conversion element of this example is manufactured (Example 4), FIG. 4 shows the configuration of a short wavelength laser light source in the fourth example. a coherent light source; a first substrate; an optical waveguide made of a nonlinear material formed on the surface of the substrate; an optical waveguide made of a nonlinear material having a structure, a second substrate formed on the surface of the second substrate, and a nonlinear polarization formed in the optical waveguide that is inverted with respect to the nonlinear polarization of the optical waveguide. The optical waveguide formed on the surface of the first substrate and the optical waveguide formed on the surface of the second substrate are brought into close contact with each other, and the optical waveguide formed on the surface of the second substrate is brought into close contact with the part made of a substance and has a periodic structure, and the optical waveguide formed on the surface of the second substrate is brought into close contact with A short wavelength laser light source comprising a wavelength conversion element having an entrance part made by polishing a surface perpendicular to the wave path, and a condensing optical system that excites light from the coherent light source to the entrance part of the wavelength conversion element. In Figure 4, 11 is a LiNbO5 substrate and 12 is Li
13 is a proton exchange waveguide m formed on a substrate 11 of NbO5 groups, 14 is a polarization inversion layer formed by Ti diffusion, 15 is a proton exchange waveguide region formed on the substrate 12, and 16 is a polarization inversion layer formed by Ti diffusion. Layer 17 is made by polishing the end face. Incidence part 18 is a condensing optical device. 19 is a semiconductor laser with a wavelength of 0.8 μm. In the wavelength conversion element made in Example 3, the grating length is 1 cm and U
By modularizing the focusing optical system and semiconductor laser,
It consists of a short wavelength laser light source of 14 x 14 x 28 mm.
The output of the semiconductor laser is 40m9j, and the second
Harmonic output was obtained. This enabled the construction of a compact, short-wavelength laser light source with optical output. If a nine-resistance semiconductor laser was connected directly to the waveguide input section, the module could be further miniaturized, but as described in the detailed explanation of the invention. a first substrate, an optical waveguide formed on the surface of the substrate, a second substrate, and an optical waveguide formed on the surface of the second substrate, and the optical waveguide formed on the surface of the first substrate and the second substrate. A waveguide with a symmetrical structure can be constructed by closely contacting the optical waveguide formed on the surface of the substrate. This allows for highly efficient coupling with optical fibers, and it is relatively easy to fabricate by aligning the waveguide with a mask aligner. Since integrated elements can be formed, it is possible to construct elements that control guided light with high efficiency.Furthermore, even in ion exchange waveguides fabricated at low temperatures, it is possible to fabricate waveguides that are axially symmetrical with respect to the waveguide propagation direction. The effect is great~ Also, the first substrate and the optical waveguide are made of a nonlinear material formed on the surface of the substrate, and the optical waveguide is made of a nonlinear material in which the nonlinear polarization formed in the optical waveguide is inverted with respect to the nonlinear polarization of the optical waveguide. , and an optical waveguide including a portion having a periodic structure, a second substrate, and a nonlinear material formed on the surface of the second substrate, and a nonlinear polarization formed in the optical waveguide is inverted with respect to the nonlinear polarization of the optical waveguide. an optical waveguide formed on the surface of the first substrate, an optical waveguide formed on the surface of the second substrate, and a portion in which the nonlinear polarization is reversed; By using the wavelength conversion element, we were able to construct a waveguide with a symmetrical structure, making the electromagnetic distribution of the waveguide mode propagating in the waveguide symmetrical with respect to the waveguide propagation axis, which enabled highly efficient coupling with optical fibers. In addition, it is possible to form a polarization inversion grating in the center of the waveguide, where the electromagnetic field density is highest within the waveguide. The depth of the waveguide and polarized grating is 1
The polarization inversion layer can be manufactured easily.Also, if the manufactured gratings are shifted by half a period and brought into close contact with each other, the period of the gratings can be halved, which makes manufacturing easier. Also, a coherent light source, a first substrate, a waveguide made of a nonlinear material formed on the surface of the substrate, and a nonlinear material whose nonlinear polarization formed in the optical waveguide is inverted with respect to the nonlinear polarization of the optical waveguide. an optical waveguide made of a nonlinear material formed on a second substrate and a surface of the second substrate; and a nonlinear polarization formed in the optical waveguide is inverted with respect to the nonlinear polarization of the optical waveguide. an optical waveguide formed on the surface of the first substrate, an optical waveguide formed on the surface of the second substrate, and a portion in which the nonlinear polarization is reversed; and a short-wavelength laser comprising a wavelength conversion element having an entrance part made by polishing a surface perpendicular to the waveguide, and a condensing optical system that excites light from the coherent light source to the entrance part of the wavelength conversion element. The light source can form a compact, high-output, short-wavelength laser light source, and its practical effects are enormous.

[Brief explanation of the drawing]

FIG. 1 shows a strabismus configuration of an optical waveguide according to an embodiment of the present invention. FIG. 2 shows a strabismus configuration of a reflective optical waveguide using a waveguide according to another embodiment of the invention. Figure 4 is a perspective view of the configuration of a wavelength conversion element in another embodiment of the present invention. Figure 5 is a perspective view of the configuration of a short wavelength laser light source in another embodiment of the present invention. Figure 5 is the basic configuration of a conventional optical waveguide. FIG. 2 is a basic configuration diagram of a wavelength conversion element. 1, 2...Substrate 3,4...Waveguiding method 5...Incidence part

Claims (11)

[Claims] (1) A first substrate, an optical waveguide formed on the surface of the substrate, a second substrate, and an optical waveguide formed on the surface of the second substrate, the optical waveguide formed on the surface of the first substrate and the optical waveguide formed on the surface of the second substrate. An optical waveguide characterized in that an optical waveguide formed on the surface of a second substrate is brought into close contact with the optical waveguide. (2) The optical waveguide according to claim 1, further comprising a matching layer between the first and second substrates. (3) The optical waveguide according to claim 1, wherein portions having different refractive indexes are periodically formed on the surfaces of the waveguides formed on the surfaces of the first and second substrates. (4) The optical waveguide according to claim 1, characterized in that an electrode is provided on the waveguide formed on the second substrate. (5) a first substrate, an optical waveguide made of a nonlinear material formed on the surface of the substrate, and a nonlinear material formed in the optical waveguide, the nonlinear polarization of which is inverted with respect to the nonlinear polarization of the optical waveguide, and a periodicity of the nonlinear material; an optical waveguide consisting of a structured portion, a second substrate, and a nonlinear material formed on the surface of the second substrate; and a nonlinear polarization in which the nonlinear polarization formed in the optical waveguide is inverted with respect to the nonlinear polarization of the optical waveguide. an optical waveguide formed on the surface of the first substrate, an optical waveguide formed on the surface of the second substrate, and a portion in which the nonlinear polarization is inverted, which are made of a substance and have a periodic structure, and are brought into close contact with each other; A wavelength conversion element characterized by: (6) a first substrate, an optical waveguide made of a nonlinear material formed on the surface of the substrate, a portion made of a linear material periodically formed in the optical waveguide, a second substrate, and a portion made of a linear material formed on the surface of the second substrate; comprising an optical waveguide made of a nonlinear material formed and a part made of a linear material formed periodically in the optical waveguide, and an optical waveguide and a part made of a linear material formed on the surfaces of the first and second substrates. A wavelength conversion element characterized by being brought into close contact with each other. (7) A first substrate made of a nonlinear material, an optical waveguide layer formed on the surface of the substrate, a second substrate made of a nonlinear material, and an optical waveguide layer formed on the surface of the substrate, A wavelength conversion element characterized by having an optical waveguide formed on the surface of the substrate No. 2 in close contact with each other. (8) A coherent light source, a first substrate, a waveguide made of a nonlinear material formed on the surface of the substrate, and a nonlinear material made of a nonlinear material whose nonlinear polarization formed in the optical waveguide is inverted with respect to the nonlinear polarization of the optical waveguide. and an optical waveguide including a portion having a periodic structure, a second substrate, and a nonlinear material formed on the surface of the second substrate, and a nonlinear polarization formed in the optical waveguide is inverted with respect to the nonlinear polarization of the optical waveguide. an optical waveguide formed on the surface of the first substrate, an optical waveguide formed on the surface of the second substrate, and a portion in which the nonlinear polarization is inverted; and a wavelength conversion element having an entrance part made by polishing a surface perpendicular to the waveguide, and a condensing optical system that excites the light from the coherent light source to the entrance part of the wavelength conversion element. Short wavelength laser light source. (9) a coherent light source, a first substrate, an optical waveguide made of a nonlinear material formed on the surface of the substrate, a portion made of a linear material periodically formed in the optical waveguide, a second substrate and the second substrate; comprising an optical waveguide made of a nonlinear material formed on the surface of a substrate and a portion made of a linear material formed periodically within the optical waveguide, and made of the optical waveguide and the linear material formed on the surfaces of the first and second substrates. a wavelength conversion element including an entrance part made by bringing the parts into close contact with each other and polishing a surface perpendicular to the waveguide layer; and a condensing optical system that excites light from the coherent light source to the entrance part of the wavelength conversion element. A short wavelength laser light source characterized by comprising: (10) A coherent light source, a first substrate made of a nonlinear material, an optical waveguide layer formed on the surface of the substrate, a second substrate made of a nonlinear material, and an optical waveguide layer formed on the surface of the substrate, A wavelength conversion element is provided with an incident part made by bringing the optical waveguides formed on the surfaces of the first and second substrates into close contact with each other and polishing a surface perpendicular to the waveguides. A short wavelength laser light source characterized by having a focusing optical system for excitation at an incident part. (11) A short wavelength laser light source according to claim 8, 9, or 10, characterized in that a semiconductor laser, a light emitting part of the semiconductor laser, and an input part of a wavelength conversion element are directly connected.