Tapered rib waveguides

• US 5,078,516 A
• Filed: 11/06/1990
• Issued: 01/07/1992
• Est. Priority Date: 11/06/1990
• Status: Expired due to Term

• Current Assignee: Stanford University
• Original Assignee: Bell Communications Research, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Shahar, Arie, Thurston, Robert N., Kapon, Elyahou
• Primary Examiner(s): Lee, John D.
• Assistant Examiner(s): BARNS, STEPHEN
• Application Number:
  US07/609,907
• Time in Patent Office: 427 Days
• Field of Search: 350/96.12, 350/96.15, 350/96.17, 350/96.11
• US Class Current: 385/129
• CPC Class Codes: G02B 2006/12097 Ridge, rib or the like
• CPC Class Codes: G02B 2006/12116 Polariser; Birefringent
• CPC Class Codes: G02B 6/1228 Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: G02B 6/125 Bends, branchings or intersections

Abstract

A tapered single-mode rib waveguide for which only laterally patterning is required. A sublayer is disposed between the low-index substrate and the high-index rib and has an intermediate index. Preferably a thin buffer layer of very low refractive index is disposed between the rib and the sublayer. The widths of the rib are chosen so that in a wide portion the optical power of the single-mode is concentrated in the rib or buffer layer but in a narrow portion the optical power is concentrated in the sublayer or substrate and additionally has a wide lateral distribution. A similar effect can be obtained by tapering an upper rib disposed on top of an untapered lower rib.

Claims

1. A tapered single-mode rib waveguide, comprising:

a substrate having a first refractive index;

a sublayer formed on said substrate and having a second refractive index greater than said first refractive index;

a buffer layer formed on said sublayer and having a third refractive index less than or equal to said second refractive index; and

a tapered rib formed on said buffer layer and having a fourth refractive index greater than or equal to said second refractive index, wherein said tapered rib comprises a first longitudinally untapered portion of a first cross-section and a longitudinally tapered portion smoothly connected to said first portion and flaring laterally outward therefrom.

2. A rib waveguide as recited in claim 1, wherein said tapered rib further comprises a second longitudinally untapered portion of a second-section larger than said first cross-section.

3. A rib waveguide as recited in claim 2, wherein at a predetermined wavelength a single optical mode is supported partially within both said first and second portions.

4. A rib waveguide as recited in claim 3, wherein said rib has a substantially constant height in said first, second, and tapered portions.

5. A tapered single-mode rib waveguide, comprising:

a substrate of a first refractive index;

a first rib of a second refractive index greater than said first refractive index formed on said substrate and longitudinally extending along a surface thereof; and

a second rib of a third refractive index greater than said second refractive index formed on said first rib and longitudinally extending along a medial surface portion thereof, said second rib having a varying width in a first portion and a substantially constant width in a second portion.

6. A tapered single-mode rib waveguide, comprising:

a substrate of a first refractive index;

a layer formed on said substrate and having a second refractive index greater than said first refractive index;

a first rib of said second refractive index formed on said layer and longitudinally extending along a surface thereof; and

a second rib of a third refractive index greater than said second refractive index formed on said first rib and longitudinally extending along a medial surface portion thereof, said second rib having a varying width in a first portion and a substantially constant width in a second portion.

7. A rib waveguide as recited in claim 6, wherein said second rib has a terminating point on said surface of said first rib.

8. A tapered single-mode rib waveguide, comprising:

a substrate of a first refractive index;

a first rib of a second refractive index greater than said first refractive index formed on said substrate and longitudinally extending along a surface thereof; and

a second rib of a third refractive index formed on said first rib and longitudinally extending along a medial surface portion thereof, said second rib having a varying width in a first portion and a substantially constant width in a second portion;

wherein said first rib has a varying width in a portion adjacent said first portion of said second rib.

9. A rib waveguide as recited in claim 8, wherein said third refractive index is greater than said second refractive index.