Optical waveguides and optical devices with optical waveguides

• US 20030202764A1
• Filed: 12/18/2002
• Published: 10/30/2003
• Est. Priority Date: 04/24/2002
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Lee, Youngkun, Tomaru, Tatsuya, Hosomi, Kazuhiko, Katsuyama, Toshio
• Granted Patent: US 6,931,189 B2
• Time in Patent Office: Days
• US Class Current: 385/129
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 6/1225 comprising photonic band-gap structures or photonic lattices
• CPC Class Codes: G02B 6/1228 Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: G02B 6/14 Mode converters
• CPC Class Codes: G02B 6/30 for use between fibre and thin-film device

Abstract

The invention provides an optical waveguide for enabling the reduction of a coupling loss caused by difference in the size of a mode field diameter between optical waveguide modes different in the mode field diameter and a coupling loss caused by reflection on a boundary caused by the difference of media and an optical device using it. Structure provided with a mode field diameter converter provided with an antireflection part required to reduce a coupling loss between a microoptical circuit and a single mode optical fiber is integrally produced using effective refractive index control based upon photonic crystal structure.

Claims

1. An optical waveguide, comprising:

a core; and

a clad provided with a photonic crystal member, wherein;

the effective refractive index of the clad is spatially varied and a mode field diameter which is electric field strength distribution in a plane perpendicular to a traveling direction in an optical waveguide mode is spatially varied respectively by changing the structure of the photonic crystal member.

2. An optical waveguide according to claim 1, wherein:

for the optical waveguide mode, a fundamental guided mode exists; and

the mode field diameter of the fundamental guided mode is spatially varied.

3. An optical waveguide according to claim 1, wherein:

the photonic crystal structure is made of one-, two- or three-dimensional photonic crystals.

4. An optical waveguide according to claim 1, wherein:

the cross sections of the core spatially vary in a tapered shape or in a reversely tapered shape in a traveling direction in the optical waveguide mode.

5. An optical waveguide according to claim 1, wherein:

one-, two- or three-dimensional photonic crystal structure and a region for preventing light from being reflected are provided on the input side and on the output side of the optical waveguide.

6. An optical device, comprising:

a first transmission member in which a fundamental guided mode exists;

a second transmission member in which a fundamental guided mode of size different from that of the first transmission member exists; and

an intermediate member provided for transmitting light from the first transmission member to the second transmission member and composed of a core and a clad having photonic crystal structure, wherein;

the intermediate member changes the photonic crystal structure so that the effective refractive index of the clad is spatially varied and spatially changes a mode field diameter which is electric field strength distribution in a plane perpendicular to a traveling direction in an optical waveguide mode.

7. An optical device according to claim 6, wherein:

the fundamental guided mode of the first transmission member is converted to the fundamental guided mode of the second transmission member or the fundamental guided mode of the second transmission member is converted to the fundamental guided mode of the first transmission member by changing the photonic crystal structure of the intermediate member.

8. An optical device according to claim 6, wherein:

in the intermediate member, the photonic crystal structure of the clad is changed so that difference in a refractive index between the core and the clad is increased as light advances from a region having a large mode field diameter to a region having a small mode field diameter.

9. An optical device according to claim 6, wherein:

photonic crystal structure is provided on the input side and on the output side of the intermediate member; and

a region for preventing the reflection of light on an interface between the first transmission member and the second transmission member is provided on the input side and on the output side of the intermediate member.

10. An optical device according to claim 6, wherein:

the intermediate member is provided with a line-defect waveguide or a coupled-defect waveguide.