# US 5,347,608 A · Optical waveguide and optical waveguide device

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- Number: US 5,347,608 A
- Document ID: US5347608A
- Status: Granted
- Kind: A
- Application number: 08/068,102
- Filed: 1993-05-28
- Granted: 1994-09-13
- Earliest claimed: 1992-06-30
- Assignees: Ibiden Co., Ltd.
- Inventors: Masanori Nakamura; Yoshikazu Sakaguchi
- Web page: https://patentgrep.com/patent/US5347608A

## CPC

- G02B 6/12004: {Combinations of two or more optical elements}
- G02B 6/136: by etching
- G02F 1/225: in an optical waveguide structure
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS

## Abstract

Optical device including an optical waveguide composed of a LiTaO.sub.3 monocrystalline substrate and a LiNbO.sub.3 monocrystalline thin film waveguide formed on the surface of the substrate, with the lattice length of the LiNbO.sub.3 monocrystalline thin film waveguide and the LiTaO.sub.3 monocrystalline substrate being matched with each other, and an electrode provided on at least one of the branched sections of the waveguide extending along the optical axis thereof for changing a refractive index of the waveguide. The optical device having the optical waveguide has excellent electro-optic effects and a resistance to optical damage as well as an advanced modulation efficiency and a stable amplitude modulation.

## Claims

### Claim 1

A single mode optical waveguide comprising:
a LiTaO.sub.3 monocrystalline substrate, and a LiNbO.sub.3 monocrystalline thin film waveguide formed on a surface of said LiTaO.sub.3 monocrystalline substrate, said thin film waveguide having Mach-Zehnder type branched sections on a part of the thin film waveguide, and including at least an Na content in a range of 0.1 to 14.3 mol % and a Mg content in a range of 0.8 to 10.8 mol %, so that lattice lengths of the LiNbO.sub.3 monocrystalline thin film waveguide and the LiTaO.sub.3 monocrystalline substrate are matched with each other with the following relationship being satisfied;
in the case of TM mode,
1.9<(T+0.7)/.lambda.<5.7 (T>0)
in the case of TE mode,
0.29<(T+0.04)/.lambda.<1.19 (T>0)
where T(.mu.m) represents a thickness of the LiNbO.sub.3 monocrystalline thin film waveguide and .lambda.(.mu.m) a wavelength of the guided wave.

### Claim 2 (depends on 1)

The single mode optical waveguide as claimed in claim 1, wherein the shape of the optical waveguide satisfies the following relationship;
in the case of TM mode,
W.ltoreq.(4.lambda.-0.5).times.(.lambda..sup.2 /.DELTA.T+2.0)
in the case of TE mode,
W.ltoreq.(0.04.lambda..sup.3 +0.1.lambda..sup.2)/.DELTA.T+2.5.lambda.
where W(.mu.m) represents a width of the waveguide, .DELTA.T(.mu.m) an etching depth, and .lambda.(.mu.m) a wavelength of the guided wave.

### Claim 3 (depends on 1)

The optical waveguide as claimed in claim 1, wherein the LiNbO.sub.3 monocrystalline thin film waveguide formed on the surface of the LiTaO.sub.3 monocrystalline substrate is an inverted ridge type waveguide.

### Claim 4 (depends on 1)

The optical waveguide as claimed in claim 1, wherein the LiNbO.sub.3 monocrystalline thin film waveguide formed on the surface of the LiTaO.sub.3 monocrystalline substrate is a ridge type waveguide.

### Claim 5 (depends on 1)

The optical waveguide as claimed in claim 1, wherein the branched LiNbO.sub.3 monocrystalline thin film is formed on a (0001) face of the surface of the LiTaO.sub.3 monocrystalline substrate.

### Claim 6 (depends on 1)

The optical waveguide as claimed in claim 1, wherein a lattice length of an axis of the LiTaO.sub.3 monocrystalline substrate is matched with a lattice length of an axis of the LiNbO.sub.3 monocrystalline thin film.

### Claim 7 (depends on 1)

The optical waveguide as claimed in claim 1, wherein a lattice length of the LiNbO.sub.3 monocrystalline thin film is in a range of 99.81 to 100.07% of a lattice length of the LiTaO.sub.3 monocrystalline substrate for matching the lattice lengths with each other.

### Claim 8

A waveguide device comprising an LiTaO.sub.3 monocrystalline substrate, an LiNbO.sub.3 monocrystalline thin film waveguide formed on a surface of said LiTaO.sub.3 monocrystalline substrate, said thin film waveguide having Mach-Zehnder type branched sections on a part of the thin film waveguide, and an electrode for changing a refractive index of the waveguide provided on at least one of the branched sections, and including at least an Na content in a range of 0.1 to 14.3 mol % and a Mg content in a range of 0.8 to 10.8 mol %, so that lattice lengths of the LiNbO.sub.3 monocrystalline thin film waveguide and the LiTaO.sub.3 monocrystalline substrate are matched with each other with the following relationship being satisfied;
in the case of TM mode,
1.9<(T+0.7)/.lambda.<5.7 (T>0)
in the case of TE mode,
0.29<(T+0.04)/.lambda.<1.19 (T>0)
where T(.mu.m) represents a thickness of the LiNbO.sub.3 monocrystalline thin film waveguide and .lambda. (.mu.m) a wavelength of the guided wave.

### Claim 9 (depends on 8)

The waveguide device as claimed in claim 8, wherein said electrode for varying a refractive index of the waveguide comprises a planar electrode.

### Claim 10 (depends on 8)

The waveguide device as claimed in claim 8, wherein the LiNbO.sub.3 monocrystalline thin film waveguide formed on the surface of the LiTaO.sub.3 monocrystalline substrate is an inverted ridge type waveguide.

### Claim 11 (depends on 8)

The waveguide device as claimed in claim 8, wherein the LiNbO.sub.3 monocrystalline thin film waveguide formed on the surface of the LiTaO.sub.3 monocrystalline substrate is a ridge type waveguide.

### Claim 12 (depends on 8)

The waveguide device as claimed in claim 8, wherein the branched LiNbO.sub.3 monocrystalline thin film is formed on a (0001) face of the surface of the LiTaO.sub.3 monocrystalline substrate.

### Claim 13 (depends on 8)

The waveguide device as claimed in claim 8, wherein a lattice length of an axis of the LiTaO.sub.3 monocrystalline substrate is matched with a lattice length of an axis of the LiNbO.sub.3 monocrystalline thin film.

### Claim 14 (depends on 8)

The waveguide device as claimed in claim 8, wherein a lattice length of the LiNbO.sub.3 monocrystalline thin film is in a range of 99.81 to 100.07% of a lattice length of the LiTaO.sub.3 monocrystalline substrate for matching the lattice lengths with each other.