Quantum confined stark effect electroabsorption modulator on a SOI platform
An electroabsorption modulator. The modulator comprising an SOI waveguide; an active region, the active region comprising a multiple quantum well (MQW) region; and a coupler for coupling the SOI waveguide to the active region. The coupler comprising: a transit waveguide coupling region; a buffer waveguide coupling region; and a taper region; wherein, the transit waveguide coupling region couples light between the SOI waveguide and the buffer waveguide coupling region; and the buffer waveguide coupling region couples light between the transit waveguide region and the active region via the taper region.
1. An electroabsorption modulator comprising:
an SOI waveguide;
an active region, the active region comprising a multiple quantum well (MQW) region; and
a coupler for coupling the SOI waveguide to the active region,
the coupler comprising:
a transit waveguide coupling region;
a buffer waveguide coupling region; and
a taper region,
wherein:
the transit waveguide coupling region is configured to couple light between the SOI waveguide and the buffer waveguide coupling region,
the buffer waveguide coupling region is configured to couple light between the transit waveguide coupling region and the taper region, and
the taper region is configured to couple light between the buffer waveguide coupling region and the active region.
2. The electroabsorption modulator of claim 1 , wherein the taper region comprises a multi-segment mode expander.
3. The electroabsorption modulator of claim 1 , wherein the multiple quantum well region is a Ge/SiGe multiple quantum well region.
4. The electroabsorption modulator of claim 1 , wherein:
the transit waveguide coupling region comprises a first portion of a transit waveguide; and
the buffer waveguide coupling region comprises a buffer waveguide located on top of a second portion of the transit waveguide.
5. The electroabsorption modulator of claim 4 , wherein:
the transit waveguide has a refractive index bigger than that of the SOI waveguide but smaller than that of the buffer waveguide.
6. The electroabsorption modulator of claim 4 , wherein:
the SOI waveguide is a 3 um waveguide;
the transit waveguide has a thickness of no more than 400 nm; and
the buffer waveguide has a thickness of no more than 400 nm.
7. The electroabsorption modulator of claim 6 , wherein the transit waveguide has a thickness of no more than 600 nm.
8. The electroabsorption modulator of claim 6 , wherein the transit waveguide has a thickness of no more than 800 nm.
9. The electroabsorption modulator of claim 4 , wherein each of the buffer waveguide and transit waveguide are SiGe waveguides.
10. The electroabsorption modulator of claim 4 , wherein the active region comprises:
a P-doped region between a buffer layer and a lower surface of a spacer layer underneath the multiple quantum well region; and
an N-doped region located at an upper surface of a spacer layer on top of the multiple quantum well region.
11. The electroabsorption modulator of claim 10 , further comprising multiple N-type doped layers with different germanium compositions and doping concentrations.
12. The electroabsorption modulator of claim 1 , wherein a waveguide slab of a P-doped region in the active region is P-doped with ion implantation followed by an RTA process.
13. The electroabsorption modulator of claim 1 , further comprising electrodes arranged in a ground-signal (GS) configuration, wherein a ground electrode is located at an opposite side of the active region from a signal electrode.
14. The electroabsorption modulator of claim 1 , further comprising electrodes arranged in a ground-signal-ground (GSG) configuration, where a first ground electrode and a second ground electrode are located at the same side of the active region as a signal electrode.
15. The electroabsorption modulator of claim 1 , wherein the multiple quantum well region includes at least 5 quantum wells.
16. The electroabsorption modulator of claim 1 , wherein a spacing between respective pairs of the quantum wells is in the range of 10 nm to 20 nm.
17. The electroabsorption modulator of claim 1 , wherein each quantum well in the multiple quantum well region has a thickness in the range of 5 nm to 15 nm.
18. The electroabsorption modulator of claim 1 , further comprising a metal electrode in contact with a surface of the active region opposite to the coupler, wherein the MQW region includes at least one tapered portion of MQW material which extends into the taper region; and wherein the metal electrode extends as far as the tapered portion of MQW material.
19. The electroabsorption modulator of claim 18 , wherein the electrode has a length in a direction towards the taper region which is greater than 2.5 μm.
20. The electroabsorption modulator of claim 1 , wherein the active region includes an N-doped region located above an upper surface of a spacer layer on top of the multiple quantum well region, and wherein the N-doped region comprises Si 0.9 Ge 0.1 .
21. The electroabsorption modulator of claim 1 , wherein:
the transit waveguide coupling region comprises a first portion of a transit buffer layer on the SOI waveguide; and
the buffer waveguide coupling region comprises a second portion of the transit buffer layer on the SOI waveguide and a first portion of a buffer layer on the second portion of the transit buffer layer, the second portion of the transit buffer layer being between the SOI waveguide and the first portion of the buffer layer.
22. The electroabsorption modulator of claim 21 , wherein:
an index of refraction of the transit buffer layer is greater than an index of refraction of the SOI waveguide; and
an index of refraction of the buffer layer is greater than the index of refraction of the transit buffer layer.
23. The electroabsorption modulator of claim 1 , wherein:
the taper region comprises a first mode expander region and a second mode expander region;
the first mode expander region is configured to couple light between the buffer waveguide coupling region and the second mode expander region;
a first end of the first mode expander region abuts against the buffer waveguide coupling region;
the first mode expander region comprises a first portion of a buffer layer having a first width at the first end of first mode expander region, the width of the first portion of the buffer layer expanding, according to a first taper angle, to a second width at a second end, opposite the first end, of the first mode expander region;
a first end of the second mode expander region abuts against the second end of the first mode expander region; and
the second mode expander region comprises a second portion of the buffer layer having the second width at the first end of the second mode expander region, the width of the second portion of the buffer layer expanding, according to a second taper angle, greater than the first taper angle, to a third width at a second end, opposite the first end, of the second mode expander region.