Optical circuit and method of fabricating the same

• US 6,334,008 B2
• Filed: 02/11/1999
• Issued: 12/25/2001
• Est. Priority Date: 02/19/1998
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Nakabayashi, Yukinobu
• Primary Examiner(s): Sanghavi, Hemang
• Assistant Examiner(s): PAK, SUNG H
• Application Number:
  US09/247,907
• Publication Number:
  US 20010046341A1
• Time in Patent Office: 1,048 Days
• Field of Search: 385/14, 385/2, 385/3, 385/4, 385/8, 385/9, 385/10, 385/16, 385/45, 385/129
• US Class Current: 385/14
• CPC Class Codes: G02F 1/225 in an optical waveguide structure
• CPC Class Codes: G02F 1/3558 Poled materials, e.g. with periodic poling; Fabrication of domain inverted structures, e.g. for quasi-phase-matching [QPM]
• CPC Class Codes: G02F 2201/126 push-pull

Abstract

An optical circuit include a plurality of optical wave guides each having an electro-optic crystal such as LiNbO₃ or LiTaO₃ and a domain orientation different from the other waveguide. More specifically, in accordance with the invention, a portion of the circuit is inverted with respect to a domain. For instance, in an optical wave guide having a domain-inverted portion, if electric fields having the same orientation are applied to a plurality of portions which vary an index of refraction thereof, indexes of refraction are caused to vary in opposite polarities. Hence, it is possible to lower a voltage at which an optical device operates. If the present invention is applied to a Mach-Zehnder type phase shifter, it would be possible to accomplish push-pull operation, only if an electric field has one orientation. The invention further lower a voltage at which the phase shifter operates through a difference in an index of refraction between two optical wave guides.

Claims

1. An optical circuit, comprising:

a plurality of optical wave guides each including an electro-optic crystal, said plurality of optical wave guides including a first wave guide and a second wave guide, said first wave guide having a domain orientation different from said second optical wave guide;

a first signal electrode overlapping one of said first wave guide and said second wave guide;

a second signal electrode overlapping the other of said first wave guide and said second wave guide; and

means for applying voltages of a same phase to said first signal electrode and said second signal electrode.

2. The optical circuit of claim 1, wherein said means applies said voltages of a same phase by diverging a single wire connected to said first signal electrode and said second signal electrode into two portions inside or outside of said optical circuit.

3. The optical circuit of claim 2, further comprising:

a ground electrode surrounding at least one of said first signal electrode and said second signal electrode.

4. The optical circuit of claim 3, wherein said ground electrode does not overlap either of said first wave guide and said second wave guide.

6. The optical switch of claim 4, further comprising:

a pair of ground electrodes surrounding a point of diversion of said two output wave guides.

5. A digital type optical switch comprising:

(a) an input optical wave guide including an electro-optic crystal;

(b) at least two output optical wave guides connected to said input optical wave guide in Y-shaped fashion;

(c) a signal electrode overlapping both of said two output optical wave guides, said signal electrode applying a voltage for varying an index of refraction of said output optical wave guides to thereby select one of said output optical wave guides through which an optical output is obtained, and

wherein said output optical wave guides have domain orientations inverted with respect to each other.

7. The optical switch of claim 5, further comprising:

first and second ground electrodes formed adjacent to said output wave guides but not overlapping said wave guides.

8. An optical circuit, comprising:

a first wave guide and a second wave guide, said first wave guide having a domain orientation different from said second optical wave guide;

first and second Y-shaped optical fiber portions, said first Y-shaped optical fiber portion connecting first ends of said first and second optical wave guides and said second Y-shaped optical fiber portion connecting second ends of said first and second optical wave guides; and

a signal electrode located at a non-overlapping center position between said first wave guide and said second wave guide, said signal electrode being the only signal electrode in said circuit.

9. The optical circuit of claim 8, further comprising:

a first ground electrode which overlaps said first wave guide; and

a second ground electrode which overlaps said second wave guide.

10. A method of modulating light, comprising:

providing a light modulator which includes two optical wave guides each having an electro-optic crystal and a domain orientation different from the other wave guide, said light modulator further including a first signal electrode overlapping one of the two optical wave guides and a second signal electrode overlapping the other of the two optical wave guides; and

applying voltages having the same phase to said first signal electrode and said second signal electrode.

11. The method of claim 10, wherein said applying step includes applying said voltages of a same phase by diverging a single wire connected to said first signal electrode and said second signal electrode into two portions inside or outside of said optical circuit.

12. A light modulator, including:

two optical wave guides each including an electro-optic crystal, said two optical wave guides cooperating with each other to constitute a phase shifter and having domain orientations inverted with respect to each other;

first and second Y-shaped optical fiber portions, said first Y-shaped optical fiber portion connecting first ends of said two optical waveguides and said second Y-shaped optical fiber portion connecting second ends of said two optical waveguides; and

a first signal electrode overlapping said two optical wave guides.