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 having strong dielectric constant dispersion.
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 having strong dielectric constant dispersion.
2. The electro-optical modulator of claim 1 , 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.
3. The electro-optical modulator of claim 1 , wherein the dielectric layers have relative dielectric constant greater than or equal to 100 at a predetermined modulation frequency.
4. 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 waveguide element comprises an intrinsic bulk or multi quantum well structure (i-MQW) sandwiched between n-doped and p-doped semiconductor layers.
5. The electro-optical modulator of claim 4 , wherein
the first dielectric layer is disposed on 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 on the p-doped semiconductor layer along the portion of the at least one of the branch waveguides.
6. The electro-optical modulator of claim 5 , further comprising:
a first conductor overlaying the first dielectric layer along the portion of the at least one of the branch waveguides, the first metal layer connected to a ground conductor of the coplanar waveguide; and
a second conductor overlaying the second dielectric layer along the portion of the at least one of the branch waveguides, the second metal layer connected to a signal conductor of the coplanar waveguide.
7. The electro-optical modulator of claim 6 , wherein
a thickness of the first dielectric layer and the second dielectric layer is sufficient to prevent an optical mode propagating in a branch waveguide from overlapping the first metal layer and the second metal layer, respectively.
8. The electro-optical modulator of claim 6 , further comprising:
a first ohmic contact connecting the first metal layer to the n-doped semiconductor layer along the portion of the at least one of the branch waveguides; and
a second ohmic contact connecting the second metal layer to the p-doped semiconductor layer along the portion of the at least one of the branch waveguides.
9. The electro-optical modulator of claim 4 , wherein
the i-MQW comprises InGaAlAs, and
the n-doped and p-doped semiconductor layers comprise n-InP and p-InP, respectively.
10. The electro-optical modulator of claim 1 , wherein the first and second dielectric layers comprise one of LiNbO 3 , Ta 2 O 5 , and BaTiO 3 .
11. 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 having strong dielectric constant dispersion.
12. The method of fabricating an electro-optical modulator of claim 11 , 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.
13. The method of fabricating an electro-optical modulator of claim 11 , wherein the dielectric layers have relative dielectric constant greater than or equal to 35 at a predetermined modulation frequency.
14. The method of fabricating an electro-optical modulator of claim 11 , wherein forming the Mach-Zehnder interferometer further comprises:
forming an input waveguide, a waveguide splitter, two branch waveguides, a waveguide combiner, and an output waveguide, wherein
each waveguide element comprises an intrinsic bulk or multi quantum well structure (i-MQW) sandwiched between n-doped and p-doped semiconductor layers.
15. The method of fabricating an electro-optical modulator of claim 14 , further comprising:
depositing the first dielectric layer on the n-doped semiconductor layer along at least a portion of at least one of the branch waveguides, and
depositing the second dielectric layer on 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:
depositing a first conductor overlaying the first dielectric layer along the portion of the at least one of the branch waveguides, the first metal layer connected to a ground conductor of the coplanar waveguide; and
depositing a second conductor overlaying the second dielectric layer along the portion of the at least one of the branch waveguides, the second metal layer connected to a signal conductor of the coplanar waveguide.
17. The method of fabricating an electro-optical modulator of claim 16 , wherein
a thickness of the first dielectric layer and the second dielectric layer is 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 to connect the first metal layer to the n-doped semiconductor layer along the portion of the at least one of the branch waveguides; and
forming a second ohmic contact to connect the second metal layer to the p-doped semiconductor layer along the portion of the at least one of the branch waveguides.
19. The method of fabricating an electro-optical modulator of claim 14 , wherein
the i-MQW comprises InGaAlAs, 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 11 , wherein the first and second dielectric layers comprise one of LiNbO 3 , Ta 2 O 5 , and BaTiO 3 .