REDUCTION OF SUBSTRATE OPTICAL LEAKAGE IN INTEGRATED PHOTONIC CIRCUITS THROUGH LOCALIZED SUBSTRATE REMOVAL

• US 20090274418A1
• Filed: 05/01/2008
• Published: 11/05/2009
• Est. Priority Date: 05/01/2008
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Hoyt, Judy L., Popovic, Milos, Ram, Rajeev, Holzwarth, Charles, Orcutt, Jason S.
• Granted Patent: US 7,920,770 B2
• Time in Patent Office: Days
• US Class Current: 385/30
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 6/122 Basic optical elements, e.g. light-guiding paths
• CPC Class Codes: G02B 6/1223 high refractive index type, i.e. high-contrast waveguides

Abstract

Structures including optical waveguides disposed over substrates having a chamber or trench defined therein, and methods for formation thereof.

Claims

1. A structure comprising:

a substrate having a recess defined therein;

a layer disposed over the recess, (i) the layer comprising a first cladding material and a second cladding material, and (ii) the recess and a bottom surface of the layer defining a chamber; and

a first optical waveguide disposed in the layer, the first optical waveguide having a first core including a first core material and (ii) a first guided mode,

wherein (i) the first cladding material contacts the first core, the second cladding material contacts the substrate, and the first and second cladding materials are rigidly connected, (ii) the first core and at least one of the first and second cladding materials have an index contrast of greater than 10%, and (iii) a majority of the first guided mode is contained in the core and in at least one of the first cladding material and the second cladding material.

2. The structure of claim 1, wherein (i) the first guided mode has a first field evanescent decay length, (ii) a bottom portion of the first optical waveguide is disposed a first distance from the bottom surface of the layer, and (iii) the first distance is less than 5 first evanescent decay lengths.

3. The structure of claim 1, wherein (i) the layer defines an access port, (ii) a cross-section of the access port is defined by an area of intersection of the access port and the chamber, (iii) a surface area of the chamber is the sum of a surface area of the recess and an area of a portion of the bottom surface of the layer disposed over the recess minus an area of the cross-section of the access port, and (iv) the area of the cross-section of the access port is smaller than the surface area of the chamber.

4. The structure of claim 1, wherein the chamber comprises a low-index material.

5. The structure of claim 1, wherein the chamber is sized to contain a remaining portion of the first guided mode.

6. The structure of claim 1, further comprising

an optical ring resonator;

wherein the optical ring resonator comprises the first optical waveguide.

7. The structure of claim 1, wherein the first guided mode comprises an associated operating wavelength range having a center free-space wavelength, and each cross-sectional dimension of said first optical waveguide is smaller than the center free-space wavelength.

8. The structure of claim 1, further comprising:

a second optical waveguide having a second core including a second core material and a second guided mode, the second guided mode having an associated second field evanescent decay length,

wherein (i) a bottom portion of the second optical waveguide is disposed at a second distance from the bottom surface of the layer, the second distance being smaller than 5 second evanescent decay lengths, and (ii) the first and second optical waveguides are optically coupled.

9. The structure of claim 1, wherein the first and second cladding material are the same material.

10. A structure comprising:

a substrate having a trench defined in a backside thereof, the trench having a cross-section defined by (i) a trench width defined by a distance between two opposing sidewall portions of the trench, and (ii) a trench height equal to at least 5 times the trench width;

a first optical waveguide disposed over a top surface of the substrate and having (i) a first core comprising a first core material, and (ii) a first guided mode;

a first cladding material in contact with the first core; and

a second cladding material in contact with the substrate,

wherein (i) the first core and at least one of the first and second cladding materials have an index contrast of greater than 10%, and (ii) a majority of the first guided mode is contained in the first core and in at least one of the first cladding material and the second cladding material.

11. The structure of claim 10, wherein (i) the first guided mode has an associated field evanescent decay length, and (ii) the trench is disposed at a distance of less than 5 evanescent decay lengths from a bottom portion of the first core.

12. A method for forming a structure, the method comprising:

defining an optical waveguide in a layer disposed over a substrate, the optical waveguide having a core material and a guided mode;

defining an access port through the layer; and

removing a portion of the substrate underneath the optical waveguide to form a recess in the substrate.

13. The method of claim 12, wherein (i) the layer comprises a first cladding material and a second cladding material, (ii) the first core material and at least one of the first and second cladding materials have an index contrast of greater than 10%, and (iii) a majority of the first guided mode is contained in the first core material and in at least one of the first cladding material and the second cladding material.

14. The method of claim 12, wherein the substrate comprises at least one of a group IV element or compound, a III-V compound, or a II-VI compound.

15. The method of claim 12, wherein defining said access port comprises reactive ion etching.

16. The method of claim 12, wherein defining said access port comprises performing a wet chemical etch.

17. The method of claim 12, wherein removing the portion of the substrate comprises a dry etch.

18. The method of claim 12, wherein removing the portion of the substrate comprises performing a wet chemical etch to form the recess.

19. The method of claim 12, further comprising filling the access port after the formation of the recess.

20. A method for forming a structure, the method comprising;

defining an optical waveguide in a layer disposed over a top surface of a substrate, the optical waveguide having a core material and a guided mode, the layer comprising a first cladding material and a second cladding material; and

forming a trench in a backside of the substrate, the trench (i) having a cross-section defined by a width separating two sidewalls of the trench and a height, and (ii) terminating at a bottom surface of the layer beneath the optical waveguide.