Sub-volt drive 100 GHz bandwidth electro-optic modulator
Electro-optical modulators and methods of fabrication are disclosed. An electro-optical modulator includes a Mach-Zehnder interferometer formed in a substrate removed semiconductor layer and a coplanar waveguide. Signals from the coplanar waveguide are capacitively coupled to the Mach-Zehnder interferometer through first and second dielectric layers.
1. An electro-optical modulator comprising:
a Mach-Zehnder interferometer formed in a substrate removed semiconductor layer; and
a coplanar waveguide, wherein
signals from the coplanar waveguide are capacitively coupled to the Mach-Zehnder interferometer through first and second dielectric layers.
2. The electro-optical modulator of claim 1 , wherein the Mach-Zehnder interferometer further comprises:
an input waveguide, a waveguide splitter, two branch waveguides, a waveguide combiner, and an output waveguide, wherein
each of the two branch waveguides comprises an intrinsic structure sandwiched between n-doped and p-doped semiconductor layers.
3. The electro-optical modulator of claim 2 , wherein the intrinsic structure and the n-doped and p-doped semiconductor layers form a staircase waveguide.
4. The electro-optical modulator of claim 2 , wherein
the first dielectric layer is disposed adjacent to the n-doped semiconductor layer along at least a portion of at least one of the branch waveguides, and
the second dielectric layer is disposed adjacent to the p-doped semiconductor layer along the portion of the at least one of the branch waveguides.
5. The electro-optical modulator of claim 4 , further comprising:
a first metal layer connected to a ground conductor of the coplanar waveguide, wherein the first dielectric layer is sandwiched between the n-doped semiconductor layer and the first metal layer along the portion of the at least one of the branch waveguides; and
a second metal layer connected to a signal conductor of the coplanar waveguide, wherein the second dielectric layer is sandwiched between the p-doped semiconductor layer and the second metal layer along the portion of the at least one of the branch waveguides.
6. The electro-optical modulator of claim 5 , wherein
a thickness of the first dielectric layer and a thickness of the second dielectric layer are sufficient to prevent an optical mode propagating in a branch waveguide from overlapping the first metal layer and the second metal layer, respectively.
7. The electro-optical modulator of claim 5 , further comprising:
a first ohmic contact connecting the first metal layer to the n-doped semiconductor layer; and
a second ohmic contact connecting the second metal layer to the p-doped semiconductor layer.
8. The electro-optical modulator of claim 2 , wherein
the intrinsic structure comprises an InGaAlAs multiple quantum well (MQW) structure, and
the n-doped and p-doped semiconductor layers comprise n-InP and p-InP, respectively.
9. The electro-optical modulator of claim 8 , wherein the first and second dielectric layers have an index of refraction less than or equal to 3.1 at a predetermined wavelength of operation of the Mach-Zehnder interferometer.
10. The electro-optical modulator of claim 8 , wherein the first and second dielectric layers comprise one of LiNbO 3 , Ta 2 O 5 , and BaTiO 3 .
11. The electro-optical modulator of claim 1 , where the first and second dielectric layers comprise a material satisfying the equation:
∈ rμ >5 n o 2 ,
where ∈ rμ is a dialectic constant of the material at a microwave frequency of operation the electro-optical modulator and n o is an index of refraction of the material at an optical wavelength of operation of the electro-optical modulator.
12. A method of fabricating an electro-optical modulator comprising:
forming a Mach-Zehnder interferometer in a substrate removed semiconductor layer; and
forming a coplanar waveguide overlaying the Mach-Zehnder interferometer, wherein
signals from the coplanar waveguide are capacitively coupled to the Mach-Zehnder interferometer through first and second dielectric layers.
13. The method of fabricating an electro-optical modulator of claim 12 , wherein forming a Mach-Zehnder interferometer further comprises:
forming an input waveguide, a waveguide splitter, two branch waveguides, a waveguide combiner, and an output waveguide, wherein
each of the two branch waveguides comprises an intrinsic structure sandwiched between n-doped and p-doped semiconductor layers.
14. The method of fabricating an electro-optical modulator of claim 13 , wherein the intrinsic structure and the n-doped and p-doped semiconductor layers form a staircase waveguide.
15. The method of fabricating an electro-optical modulator of claim 13 , wherein
the first dielectric layer is disposed adjacent to the n-doped semiconductor layer along at least a portion of at least one of the branch waveguides, and
the second dielectric layer is disposed adjacent to the p-doped semiconductor layer along the portion of the at least one of the branch waveguides.
16. The method of fabricating an electro-optical modulator of claim 15 , further comprising:
forming a first metal layer connected to a ground conductor of the coplanar waveguide, wherein the first dielectric layer is sandwiched between the n-doped semiconductor layer and the first metal layer along the portion of the at least one of the branch waveguides; and
forming a second metal layer connected to a signal conductor of the coplanar waveguide, wherein the second dielectric layer is sandwiched between the p-doped semiconductor layer and the second metal layer along the portion of the at least one of the branch waveguides.
17. The method of fabricating an electro-optical modulator of claim 16 , wherein
a thickness of the first dielectric layer and a thickness of the second dielectric layer are sufficient to prevent an optical mode propagating in a branch waveguide from overlapping the first metal layer and the second metal layer, respectively.
18. The method of fabricating an electro-optical modulator of claim 16 , further comprising:
forming a first ohmic contact connecting the first metal layer to the n-doped semiconductor layer; and
forming a second ohmic contact connecting the second metal layer to the p-doped semiconductor layer.
19. The method of fabricating an electro-optical modulator of claim 13 , wherein
the intrinsic structure comprises an InGaAlAs multiple quantum well (MQW) structure, and
the n-doped and p-doped semiconductor layers comprise n-InP and p-InP, respectively.
20. The method of fabricating an electro-optical modulator of claim 19 , wherein the dielectric layers have an index of refraction less than or equal to 3.1 at a predetermined wavelength of operation of the Mach-Zehnder interferometer.
21. The method of fabricating an electro-optical modulator of claim 19 , wherein the first and second dielectric layers comprise one of LiNbO 3 , Ta 2 O 5 , and BaTiO 3 .
22. The method of fabricating an electro-optical modulator of claim 12 , where the first and second dielectric layers comprise a material satisfying the equation:
∈ rμ >5 n o 2 ,
where ∈ rμ is the dialectic constant of the material at a microwave frequency of operation the electro-optical modulator and n o is the index of refraction of the material at an optical wavelength of operation of the electro-optical modulator.