Substrate-type optical waveguide element

Patent metadata

Field	Value
Publication number	US-9851505-B2
Application number	US-201715447693-A
Country	US
Kind code	B2
Filing date	Mar 2, 2017
Priority date	Sep 30, 2014
Publication date	Dec 26, 2017
Grant date	Dec 26, 2017

Abstract

Provided is a substrate-type optical waveguide element in which when (i) effective refractive indexes of a TE polarized wave and a TM polarized wave in the first core are N TE @WG1 and N TM @WG1, respectively, and (ii) effective refractive indexes of a TE polarized wave and a TM polarized wave in the second core are N TE @WG2 and N TM @WG2, respectively, a magnitude relation of the effective refractive indexes N TM @WG1 and N TM @WG2 at a start position of a parallel-core section is opposite to a magnitude relation of the effective refractive indexes N TM @WG1 and N TM @WG2 at an end position of the parallel-core section, and at least one of the cores includes (a) a main part having a quadrilateral cross section and (b) a protruding part protruding from one of side surfaces of the main part in a direction parallel to a boundary surface between a lower cladding and a upper cladding.

First claim

The invention claimed is:

1. A substrate-type optical waveguide element comprising:
a lower cladding whose refractive index is N c11 ;
a first core and a second core, refractive indexes of which are N co (N co >N c11 ), the first core and the second core each being formed on the lower cladding; and
an upper cladding whose refractive index is N c12 (N co >N c12 ), the upper cladding being provided on the lower cladding so as to bury the first core and the second core, wherein:
when (i) effective refractive indexes of a TE polarized wave and a TM polarized wave in the first core are N TE @WG1 and N TM @WG1, respectively, in a case where the second core is absent, and (ii) effective refractive indexes of a TE polarized wave and a TM polarized wave in the second core are N TE @WG2 and N TM @WG2, respectively, in a case where the first core is absent,
(A) each of the effective refractive indexes N TE @WG1, N TM @WG1, N TE @WG2, and N TM @WG2 is continuous as a function of distance from a start position of a parallel-core section in which the first core and the second core extend in parallel to each other,
(B) the effective refractive indexes N TE @WG1 and N TM @WG1 satisfy a relation of N TE @WG1>N TM @WG1 all along the parallel-core section, while the effective refractive indexes N TE @WG2 and N TM @WG2 satisfy a relation of N TE @WG2>N TM @WG2 all along the parallel-core section,
(C) a magnitude relation of the effective refractive indexes N TM @WG1 and N TM @WG2 at the start position of the parallel-core section is opposite to a magnitude relation of the effective refractive indexes N TM @WG1 and N TM @WG2 at an end position of the parallel-core section, and
(D) at least one of the first core and the second core includes (a) a main part having a quadrilateral cross section orthogonal to a light traveling direction and (b) a protruding part protruding from one of side surfaces of the main part in a direction parallel to a boundary surface between the lower cladding and the upper cladding, the protruding part having a quadrilateral cross section orthogonal to the light traveling direction.

2. The substrate-type optical waveguide element as set forth in claim 1 , wherein:
when Wm1 is a width of the main part of the first core, Wp1 is a width of the protruding part of the first core, W1 is a sum of Wm1 and Wp1, Wm2 is a width of the main part of the second core, Wp2 is a width of the protruding part of the second core, and W2 is a sum of Wm2 and Wp2, the widths Wm1, W1, Wm2, and W2 are each continuous as a function of distance from the start position of the parallel-core section,
the widths Wm1, W1, Wm2, and W2 satisfy Wm1≧Wm2 and W1>W2 or satisfy Wm1>Wm2 and W1≧W2, at the start position of the parallel-core section, and
the widths Wm1, W1, Wm2, and W2 satisfy Wm1≦Wm2 and W1<W2 or satisfy Wm1<Wm2 and W1≦W2, at the end position of the parallel-core section.

3. The substrate-type optical waveguide element as set forth in claim 2 , wherein:
a height of the main part of the first core is equal to or substantially equal to a height of the main part of the second core, and
a height of the protruding part of the first core is equal to or substantially equal to a height of the protruding part of the second core.

4. The substrate-type optical waveguide element as set forth in claim 2 , wherein:
the protruding part of the first core protrudes in a direction away from the second core, and
the protruding part of the second core protrudes in a direction away from the first core.

5. The substrate-type optical waveguide element as set forth in claim 2 , wherein:
the widths Wm1 and Wp1 are larger than the height of the main part of the first core, and
the widths Wm2 and Wp2 are larger than the height of the main part of the second core.

6. The substrate-type optical waveguide element as set forth in claim 1 , wherein:
when N c1 is a larger one of the refractive index N c11 of the lower cladding and the refractive index N c12 of the upper cladding, a relative refractive index difference defined by the following Formula (a) is 0.25 or higher:

[

Math
.

⁢
1

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RELATIVE

REFRACTIVE
⁢

⁢
INDEX

DIFFERENCE

=

1
2

⁡

[

1
-

(

N
cl

N
co

)

2

]

.

(
a
)

7. The substrate-type optical waveguide element as set forth in claim 6 , wherein:
the first core and the second core are each made of silicon; and
the lower cladding and the upper cladding are each made of silica.

8. The substrate-type optical waveguide element as set forth in claim 2 , wherein:
when W upper is a value defined by the following Formula (b):

[

Math
.

⁢
6

]

W

Assignees

• Fujikura Ltd

Inventors

• Oka Akira

Classifications

• G02B6/125

  Bends, branchings or intersections · CPC title

• G02B6/126 Primary

  using polarisation effects {(G02B6/1226 takes precedence)} · CPC title

• G02B6/2773

  Polarisation splitting or combining · CPC title

• H04J14/06

  Polarisation multiplex systems · CPC title

• G02F2203/07

  Polarisation dependent · CPC title