OPTICAL MODULATOR

• US 20180210242A1
• Filed: 01/22/2018
• Published: 07/26/2018
• Est. Priority Date: 05/14/2013
• Status: Active Grant

• Current Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Original Assignee: Elenion Technologies, LLC (Nokia Corporation)
• Inventors: Baehr-Jones, Thomas, Liu, Yang
• Granted Patent: US 10,120,212 B2
• Time in Patent Office: Days
• CPC Class Codes: G02F 1/011 in optical waveguides, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/0113 Glass-based, e.g. silica-based, optical waveguides
• CPC Class Codes: G02F 1/015 based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction G02F1/03 takes precedence
• CPC Class Codes: G02F 1/0152 using free carrier effects, e.g. plasma effect
• CPC Class Codes: G02F 1/025 in an optical waveguide structure G02F1/017, G02F1/2257 take precedence
• CPC Class Codes: G02F 1/035 in an optical waveguide structure
• CPC Class Codes: G02F 1/0353 involving an electro-optic TE-TM mode conversion
• CPC Class Codes: G02F 1/0356 controlled by a high-frequency electromagnetic wave component in an electric waveguide structure
• CPC Class Codes: G02F 1/2257 the optical waveguides being made of semiconducting material

Abstract

A novel phase shifter design for carrier depletion based silicon modulators, based on an experimentally validated model, is described. It is believed that the heretofore neglected effect of incomplete ionization will have a significant impact on ultra-responsive phase shifters. A low VπL product of 0.3 V·cm associated with a low propagation loss of 20 dB/cm is expected to be observed. The phase shifter is based on overlapping implantation steps, where the doses and energies are carefully chosen to utilize counter-doping to produce an S-shaped junction. This junction has a particularly attractive VπL figure of merit, while simultaneously achieving attractively low capacitance and optical loss. This improvement will enable significantly smaller Mach-Zehnder modulators to be constructed that nonetheless would have low drive voltages, with substantial decreases in insertion loss. The described fabrication process is of minimal complexity; in particular, no high-resolution lithographic step is required.

Claims

1. An optical modulator comprising:

a substrate;

an optical waveguide disposed upon the substrate and characterized by a width dimension, a length dimension, and a height dimension, the height dimension being perpendicular to the substrate;

a p-type region of semiconductor material disposed within the optical waveguide;

an n-type region of semiconductor material disposed within the optical waveguide;

wherein the n-type region and the p-type region share a non-planar junction interface that is shaped so as to enhance an overlap between an optical mode in the optical waveguide and the junction interface when the optical modulator semiconductor device is operational; and

wherein at least one of the p-type region and the n-type region comprises a protrusion interposed in the height dimension between portions of the other of the p-type region and the n-type region.

2. The optical modulator of claim 1 wherein the optical waveguide includes an N and P implantation overlap region comprising at least a portion of the non-planar junction interface defined by the protrusion region.

3. The optical modulator of claim 1, wherein the non-planar junction interface comprises a convex side and a concave side as viewed in a cross-section taken perpendicular to a light propagation direction in the optical waveguide, wherein the p-type region is on the concave side of the non-planar junction interface and the n-type region is on the convex side of the non-planar junction interface.

4. The optical modulator of claim 1, wherein the non-planar junction interface comprises a convex side and a concave side as viewed in a cross-section taken perpendicular to a light propagation direction in the optical waveguide, wherein the n-type region is on the concave side of the non-planar junction interface and the p-type region is on the convex side of the non-planar junction interface.

5. The optical modulator of claim 1 including a p-type contact region extending along the optical waveguide in electrical communication with the p-type region and an n-type contact region extending along the optical waveguide across from the p-type region in electrical communication with the n-type region.

6. The optical modulator of claim 1, wherein in a first cross-section of the optical waveguide the p-type region is on a concave side of the non-planar junction interface and the n-type region is on a convex side of the non-planar junction interface, and wherein in a second cross-section the n-type region is on a concave side of the non-planar junction interface and the p-type region is on a convex side of the non-planar junction interface, wherein the first and second cross-sections are perpendicular to a light propagation direction in the optical waveguide at two different locations in the optical waveguide along the direction of light propagation.

7. The optical modulator of claim 1 wherein the p-type region comprises a plurality of p-type protrusions spaced along the length dimension, each of the p-type protrusions interposed in the height dimension between portions of the n-type region, and wherein the n-type region comprises a plurality of n-type protrusions interleaved with the p-type protrusions along the length dimension, each of the n-type protrusions interposed in the height dimension between portions of the p-type region.

8. The optical modulator of claim 7 including a p-type contact region extending along the optical waveguide in electrical communication with the p-type protrusions and an n-type contact region extending along the optical waveguide in electrical communication with the n-type protrusions.

9. The optical modulator of claim 7 wherein the optical waveguide comprises a rib defined by a first side wall and a second side wall, wherein the p-type region comprises at least a portion of the first side wall extending contiguously along a length of the rib, wherein the n-type region comprises at least a portion of the second side wall extending contiguously along the length of the rib, wherein the p-type protrusions extend in a direction from the first side wall towards the second side wall, and wherein the n-type protrusions extend in a direction from the second wall towards the first side wall.

10. The optical modulator of claim 7 wherein the optical waveguide includes a plurality of first implantation overlap regions spaced along the length dimension and comprising the p-type protrusion and a plurality of second implantation overlap regions interleaved with the first implantation overlap regions and comprising the n-type protrusion.

11. The optical modulator of claim 1 wherein the semiconductor material comprises silicon.

12. The optical modulator of claim 11 wherein the p-type region is doped with boron and the n-type region is doped with at least one of phosphorous or arsenic.

13. A method of fabricating an optical modulator comprising:

a) providing a semiconductor material upon a planar substrate; and

,

b) forming an optical waveguide with the semiconductor material, the optical waveguide comprising a p-type region and an n-type region defined therein so that at least one of the p-type region and the n-type region comprises a protrusion region interposed between portions of the other of the p-type region and the n-type region in a height dimension normal to the substrate, said protrusion region defining a non-planar junction interface between the n-type and p-type regions for enhancing an overlap between an optical mode of the optical waveguide and the non-planar junction interface.

14. The method of claim 13 further comprising providing a p-type contact region in electrical communication with the p-type region and an n-type contact region in electrical communication with the n-type region.

15. The method of claim 13 wherein b) comprises defining a slab waveguide structure in the semiconductor material.

16. The method of claim 15 wherein b) includes implanting n-type and p-type dopants into the slab waveguide structure in multiple implantation steps to produce the n-type and p-type regions, respectively.

17. The method of claim 16 wherein b) comprises defining an implantation overlap region in the slab waveguide structure, and wherein the step of implanting comprises implanting the n-type dopants and the p-type dopants into the implantation overlap region at different energies so at to form a first dopant distribution within the implantation overlap region with two peaks in a direction normal to the substrate, and implanting the other of the n-type dopants and p-type dopants at a third energy so at to form a second dopant distribution in the implantation overlap region, the second dopant distribution having a peak that is located between the two peaks of the first dopant distribution in the direction normal to the substrate.

18. The method of claim 16 wherein b) comprises:

b1) defining, in the slab waveguide structure, a plurality of first implantation overlap regions spaced along a length thereof and a plurality of second implantation overlap regions interleaved with the first implantation overlap regions;

b2) implanting the n-type dopants into the first implantation overlap regions at two different energies so at to form, in each of the first implantation overlap regions, an n-type dopant distribution with two peaks in a direction normal to the substrate, and implanting the p-type dopants into the first implantation overlap regions so at to form a p-type dopant distribution having a peak that is located between the two peaks of the n-type dopant distribution in the direction normal to the substrate; and

,

b3) implanting the p-type dopants into the second implantation overlap regions at two different energies so at to form, in each of the second implantation overlap regions a p-type dopant distribution with two peaks in the direction normal to the substrate, and implanting the n-type dopants into the second implantation overlap regions so at to form an n-type dopant distribution having a peak that is located between the two peaks of the p-type dopant distribution in the direction normal to the substrate.

19. The method of claim 18 comprising shielding the plurality of second implantation regions from implantation prior to b2), and shielding the plurality of second implantation regions from implantation prior to b3).