Optical element and manufacturing method thereof

Patent metadata

Field	Value
Publication number	US-11852953-B2
Application number	US-201917779958-A
Country	US
Kind code	B2
Filing date	Dec 3, 2019
Priority date	Dec 3, 2019
Publication date	Dec 26, 2023
Grant date	Dec 26, 2023

Abstract

A highly-efficient ridge waveguide includes a base substrate of a single-crystal and a core substrate made of a nonlinear optical medium, the base substrate and the core substrate being directly bonded, and includes a thin film layer formed on a surface of the core substrate on the upper side of a periodically polarization-reversed structure, and becomes a wavelength conversion element. A direct bonding method through thermal diffusion is applied to bonding. The core substrate has a ridge structure formed in a light propagating direction and a reversed structure formed by processing this. A surface of the core substrate is ground and a thin film layer is formed on the ground surface. A core formed by digging a core layer of the core substrate in an unbonded state is provided on an upper surface of an undercladding layer of the base substrate in a bonded state. Two side surfaces of the core are in contact with an air layer.

First claim

The invention claimed is:

1. An optical element comprising:
a first substrate of a single-crystal; and
a second substrate made of a nonlinear optical medium or an electro-optic medium, the first substrate and the second substrate being bonded, wherein
the second substrate has a ridge structure formed in a light propagating direction and a periodically polarization-reversed structure formed by processing the ridge structure,
a surface of the first substrate and a surface of the periodically polarization-reversed structure on the second substrate are directly bonded, and
the optical element further includes a thin film layer formed on a surface of the second substrate on an upper side of the periodically polarization-reversed structure, and
a third substrate having a first side contacting the thin film layer, a second side contacting the first substrate, and third and fourth sides that contact an air layer that is between the second and third substrates.

2. The optical element according to claim 1 , wherein a groove structure for thickness control is formed in part of the thin film layer.

3. The optical element according to claim 2 , including a protection layer formed to embed the groove structure in an upper surface of the thin film layer and achieve planarization, the protection layer being made of an oxide having a refractive index close to a refractive index of a core of the second substrate.

4. The optical element according to claim 3 , wherein the nonlinear optical medium or the electro-optic medium of the second substrate is any one of LiNbO 3 , LiTaO 3 , and LiNb x Ta 1-x O 3 (0≤x≤1), or a material obtained by doping them with at least one or more kinds selected from the group consisting of Mg, Zn, Sc, and In as an additive.

5. The optical element according to claim 2 , wherein the nonlinear optical medium or the electro-optic medium of the second substrate is any one of LiNbO 3 , LiTaO 3 , and LiNb x Ta 1-x O 3 (0≤x≤1), or a material obtained by doping them with at least one or more kinds selected from the group consisting of Mg, Zn, Sc, and In as an additive.

6. The optical element according to claim 1 , wherein the nonlinear optical medium or the electro-optic medium of the second substrate is any one of LiNbO 3 , LiTaO 3 , and LiNb x Ta 1-x O 3 (0≤x≤1), or a material obtained by doping them with at least one or more kinds selected from the group consisting of Mg, Zn, Sc, and In as an additive.

7. A method of manufacturing an optical element including a first substrate of a single-crystal and a second substrate made of a nonlinear optical medium or an electro-optic medium, the first substrate and the second substrate being bonded, the method comprising:
a ridge structure forming step of forming a ridge structure on the second substrate in a light propagating direction;
a periodically polarization-reversed structure forming step of processing the ridge structure to form a periodically polarization-reversed structure;
a bonding step of bonding a surface of the first substrate and a surface of the periodically polarization-reversed structure on the second substrate by carrying out a direct bonding method through thermal diffusion;
a grinding step of processing, by grinding, a surface of the second substrate, bonded in the bonding step, on an upper side of the periodically polarization-reversed structure into a desired thickness;
a thin film layer forming step of forming a thin film layer on a ground surface of the second substrate on the upper side of the periodically polarization-reversed structures; and
a groove structure forming step of forming a mask pattern in advance at a place corresponding to part of the thin film layer on the ground surface of the second substrate after the grinding step, and then etching a surface of the ground surface to form a groove structure for thickness control, wherein
in the thin film layer forming step, the thin film layer is formed such that the groove structure is formed in the part.

8. The method of manufacturing an optical element according to claim 7 , including a protection layer forming step of forming a protection layer made of an oxide having a refractive index close to a refractive index of a core of the second substrate so as to embed the groove structure in an upper surface of the thin film layer and achieve planarization.

9. The method of manufacturing an optical element according to claim 8 , wherein the nonlinear optical medium or the electro-optic medium of the second substrate is any one of LiNbO 3 , LiTaO 3 , and LiNb x Ta 1-x O 3 (0≤x≤1), or a material obtained by doping them with at least one or more kinds selected from the group consisting of Mg, Zn, Sc, and In as an additive.

10. The method of manufacturing an optical element according to claim 7 , wherein the nonlinear optical medium or the electro-optic medium of the second substrate is any one of LiNbO 3 , LiTaO 3 , and LiNb x Ta 1-x O 3 (0≤x≤1), or a material obtained by doping them with at least one or more kinds selected from the group consisting of Mg, Zn, Sc, and In as an additive.

11. An optical element comprising:
a first substrate of a single-crystal; and
a second substrate made of a nonlinear optical medium or an electro-optic medium, the first substrate and the second substrate being bonded, wherein
the second substrate has a ridge structure formed in a light propagating direction and a periodically polarization-reversed structure formed by processing the ridge structure,
a surface of the first substrate and a surface of the periodically polarization-reversed structure on the second substrate are directly bonded, and
the optical element further includes a thin film layer formed on a surface of the second substrate on an upper side of the periodically polarization-reversed structure,
wherein a groove structure for thickness control is formed in part of the thin film layer, and
wherein a protection layer is formed to embed the groove structure in an upper surface of the thin film layer and achieve planarization, the protection layer being made of an oxide having a refractive index close to a refractive index of a core of the second substrate.

12. The optical element according to claim 11 , wherein the nonlinear optical medium or the electro-optic medium of the second substrate is any one of LiNbO 3 , LiTaO 3 , and LiNb x Ta 1-x O 3 (0≤x≤1), or a material obtained by doping them with at least one or more kinds selected from the group consisting of Mg, Zn, Sc, and In as an additive.

Assignees

• Nippon Telegraph & Telephone

Inventors

• Umeki Takeshi
• Kazama Takushi
• Kashiwazaki Takahiro
• Embutsu Koji
• Tadanaga Osamu
• Inoue Asuka
• Kasahara Ryoichi

Classifications

• G02F1/3775 Primary

  with a periodic structure, e.g. domain inversion, for quasi-phase-matching [QPM] (G02F1/383 takes precedence) · CPC title

• G02B6/1223

  high refractive index type, i.e. high-contrast waveguides · CPC title

• G02B6/1342

  using diffusion (diffusion in single crystals C30B31/00; diffusion in glass C03C23/00) · CPC title

• G02F1/3551 Primary

  Crystals · CPC title

• G02B2006/1204

  Lithium niobate (LiNbO3) · CPC title