Electro-optic devices having engineered electrodes
An optical device including a waveguide and an electrode is described. The waveguide includes at least one optical material having an electro-optic effect. The electrode includes a channel region and extensions protruding from the channel region. The extensions are closer to a portion of the waveguide than the channel region is.
1 . An optical device, comprising:
a waveguide including at least one optical material having an electro-optic effect, including lithium, and being configured to carry an optical signal, the waveguide residing on a substrate structure including a substrate; and
an electrode including a channel region and a plurality of extensions protruding from the channel region, the plurality of extensions being closer to a portion of the waveguide than the channel region is, the electrode for carrying an electrode signal that modulates the optical signal in the waveguide in a frequency window, wherein the waveguide has a waveguide loss for the optical signal being modulated using the electrode signal of not more than 1 dB/cm and wherein the electrode has a frequency dependent electrode loss for the frequency window in a frequency range from DC to not more than five hundred GHz, the frequency dependent electrode loss being less than 0.8 dB per square root of an electrode signal frequency per centimeter, the electrode signal frequency being measured in GHz, the frequency window being at least 10 GHz;
an additional electrode having an additional channel region and an additional plurality of extensions protruding from the additional channel region;
wherein the electrode signal generates an electric field at the waveguide, the electric field modulating the optical signal in the frequency window of at least 10 GHz via the electro-optic effect, the plurality of extensions being configured to increase the electric field proximate to the waveguide for modulating the optical signal,
wherein at least a first extension of the plurality of extensions and at least a second extension of the additional plurality of extensions each includes a top portion and a bottom portion, a first portion of the waveguide being closer to the substrate than the top portion, the bottom portion being closer to the substrate than a second portion of the waveguide is;
wherein the first extension and the second extension configure a portion of the electric field between the first extension and the second extension for the waveguide having a particular cut of the at least one optical material.
2 . The optical device of claim 1 , wherein the waveguide has a sidewall surface roughness of not more than ten nanometers, the sidewall surface roughness being defined by at least one mask patterned using photolithography and at least one physical etch.
3 . The optical device of claim 2 , wherein the waveguide includes a ridge portion and a thin film portion, the ridge portion having the sidewall surface roughness.
4 . The optical device of claim 2 , wherein a total height of the waveguide is less than one micrometer.
5 . The optical device of claim 1 , wherein the waveguide and the electrode reside on the substrate structure, the waveguide having a waveguide microwave dielectric constant, the electrode having an electrode microwave dielectric constant, and the substrate structure having a substrate microwave dielectric constant, a microwave mode for the electrode signal intersecting a portion of the substrate structure and having a substrate microwave velocity in the portion of the substrate structure not less than a waveguide microwave velocity of the microwave mode for the waveguide.
6 . The optical device of claim 5 , wherein the substrate structure is either a first substrate structure or a second substrate structure, the first substrate structure including a first substrate and a first underlayer, the first substrate having a low substrate microwave dielectric constant less than the waveguide microwave dielectric constant, the first underlayer being between the first substrate and the waveguide, the second substrate structure including a second substrate having a high microwave dielectric constant greater than the waveguide microwave dielectric constant in combination with a second underlayer, the second underlayer having a low underlayer microwave dielectric constant of less than the waveguide microwave dielectric constant, the second underlayer being between the first substrate and the waveguide, the first substrate and the second substrate corresponding to the substrate.
7 . The optical device of claim 1 , further comprising:
cladding adjacent to at least a portion of the waveguide and at least a portion of the electrode, the cladding having a cladding microwave dielectric constant, the waveguide having a waveguide microwave dielectric constant, and the electrode having an electrode microwave dielectric constant, the waveguide microwave dielectric constant being greater than the cladding microwave dielectric constant, a microwave mode for the electrode signal intersecting a portion of the cladding and having a cladding microwave velocity in the portion of the cladding not less than a waveguide microwave velocity of the microwave mode for the waveguide.
8 . The optical device of claim 1 , wherein the plurality of extensions have a pitch along the channel region, the pitch being less than a microwave wavelength in the electrode divided by π.
9 . The optical device of claim 1 wherein the waveguide carries the optical signal, the electrode carries the electrode signal, and wherein the plurality of extensions are configured to reduce a velocity mismatch between the optical signal and the electrode signal.
10 . The optical device of claim 1 , wherein the waveguide and the electrode reside on the substrate structure and wherein the plurality of extensions have a location, the location being selected from a first location and a second location, the first location being between the substrate structure and the channel region and the second location being such that the channel region is between the substrate structure and the plurality of extensions.
11 . The optical device of claim 1 , wherein each of the plurality of extensions includes a connecting portion coupled to the channel region and a retrograde portion, the connecting portion being between the retrograde portion and the channel region.
12 . The optical device of claim 1 , wherein the electrode has an absorption electrode loss for the frequency window in the electrode signal frequency to not more than five hundred GHz, the absorption electrode loss being less than 0.005 dB per GHz per centimeter, the frequency window being at least 10 GHz.
13 . The optical device of claim 1 , wherein the electrode includes an electrode bending section, wherein the waveguide includes a waveguide bending section, and wherein the electrode bending section and the waveguide bending section are configured to provide a path difference between the optical signal for the waveguide and the electrode signal for the electrode.
14 . A subassembly, comprising:
an optical modulator, the optical modulator including a waveguide, an electrode, and an additional electrode on a substrate structure including a substrate, the waveguide including at least a portion of at least one optical material having an electro-optic effect and including lithium, the waveguide being configured to carry an optical signal, the electrode including a channel region and plurality of extensions, the plurality of extensions residing between the channel region and the waveguide, the plurality of extensions being closer to a portion of the waveguide than the channel region is and being configured to increase an electric field proximate to the waveguide for modulating the optical signal via the electro-optic effect, the electrode for carrying an electrode signal that modulates the optical signal in the waveguide in a frequency window, wherein the waveguide has a waveguide loss for the optical signal being modulated using the electrode signal of not more than 1 dB/cm and wherein the electrode has a frequency dependent electrode loss for the frequency window in a frequency range from DC to not more than five hundred GHz, the frequency dependent electrode loss being less than 0.8 dB per square root of an electrode signal frequency per centimeter, the electrode signal frequency being measured in GHz, the frequency window being at least 10 GHz, the additional electrode having an additional channel region and an additional plurality of extensions protruding from the additional channel region; and
wherein at least one of the subassembly includes a driver coupled to the optical modulator and configured to electrically drive the electrode or the electrode signal is provided to the optical modulator by an electrical data signal for the optical modulator;
wherein at least a first extension of the plurality of extensions and at least a second extension of the additional plurality of extensions each includes a top portion and a bottom portion, a first portion of the waveguide being closer to the substrate than the top portion, the bottom portion being closer to the substrate than a second portion of the waveguide is;
wherein the first extension and the second extension configure a portion of the electric field between the first extension and the second extension for the waveguide having a particular cut of the at least one optical material.
15 . A method, comprising:
providing a waveguide on a substrate structure including a substrate, the waveguide including at least one optical material having an electro-optic effect, the at least one optical material including lithium, the waveguide being configured to carry an optical signal; and
providing an electrode and an additional electrode, the providing the electrode and the additional electrode including:
providing a channel region for the electrode and an additional channel region for the additional electrode; and
providing a plurality of extensions protruding from the channel region and an additional plurality of extensions protruding from the additional channel region, the plurality of extensions being closer to a portion of the waveguide than the channel region is, the electrode carrying an electrode signal that modulates the optical signal in the waveguide in a frequency window, the plurality of extensions being configured to increase an electric field proximate to the waveguide for modulating the optical signal via the electro-optic effect; wherein the waveguide has a waveguide loss for the optical signal modulated using the electrode signal of not more than 1 dB/cm and wherein the electrode has a frequency dependent electrode loss for the frequency window in a frequency range from DC to not more than five hundred GHz, the frequency dependent electrode loss being less than 0.8 dB per square root of an electrode signal frequency per centimeter, the electrode signal frequency being measured in GHz, the frequency window being at least 10 GHz;
wherein at least a first extension of the plurality of extensions and at least a second extension of the additional plurality of extensions each includes a top portion and a bottom portion, a first portion of the waveguide being closer to the substrate than the top portion, the bottom portion being closer to the substrate than a second portion of the waveguide is;
wherein the first extension and the second extension configure a portion of the electric field between the first extension and the second extension for the waveguide having a particular cut of the at least one optical material.
16 . The method of claim 15 , wherein the waveguide has a sidewall surface roughness of not more than ten nanometers and wherein the providing the waveguide further includes:
defining at least one mask patterned using photolithography; and
performing at least one physical etch that provides the sidewall surface roughness.
17 . The method of claim 15 , wherein the waveguide and the electrode reside on the substrate structure, the waveguide having a waveguide microwave dielectric constant, the electrode having an electrode microwave dielectric constant, and the substrate structure having a substrate microwave dielectric constant, a microwave mode for the electrode signal intersecting a portion of the substrate structure and having a substrate microwave velocity in the portion of the substrate structure not less than a waveguide microwave velocity of the microwave mode for the waveguide.
18 . The method of claim 17 , wherein the substrate structure is either a first substrate structure or a second substrate structure, the first substrate structure including a first substrate and a first underlayer, the first substrate having a low substrate microwave dielectric constant less than the waveguide microwave dielectric constant, the first underlayer being between the first substrate and the waveguide, the second substrate structure including a second substrate having a high microwave dielectric constant greater than the waveguide microwave dielectric constant in combination with a second underlayer, the second underlayer having a low underlayer microwave dielectric constant of less than the waveguide microwave dielectric constant, the second underlayer being between the first substrate and the waveguide, the first substrate and the second substrate corresponding to the substrate.
19 . The method of claim 15 , further comprising:
providing cladding adjacent to at least a portion of the waveguide and at least a portion of the electrode, the cladding having a cladding microwave dielectric constant, the waveguide having a waveguide microwave dielectric constant, and the electrode having an electrode microwave dielectric constant, the waveguide microwave dielectric constant being greater than the cladding microwave dielectric constant, a microwave mode for the electrode signal intersecting a portion of the cladding and having a cladding microwave velocity in the portion of the cladding not less than a waveguide microwave velocity of the microwave mode for the waveguide.
20 . The method of claim 15 wherein the waveguide carries the optical signal, the electrode carries the electrode signal, and wherein the providing the plurality of extensions further includes:
configuring the plurality of extensions to reduce a velocity mismatch between the optical signal and the electrode signal.
21 . The optical device of claim 1 , wherein the optical signal is modulated in a portion of the waveguide in proximity to a portion of the electrode, the portion of the waveguide and the portion of the electrode each being at least five millimeters long.
22 . The optical device of claim 1 , the electrode signal has a voltage amplitude of not more than one volt.
23 . The optical device of claim 1 , wherein the optical device is driver-less.
24 . The optical device of claim 23 , wherein the electrode signal is provided by an electrical data signal for the optical device.
25 . The optical device of claim 1 , wherein the waveguide includes a ridge, first portion of the waveguide including a first portion of the ridge, and the second portion of the waveguide including a second portion of the ridge.
26 . The optical device of claim 25 , wherein the first portion of the waveguide is between the top portion and the substrate.
27 . The optical device of claim 25 , wherein the bottom portion is between the second portion of the waveguide and the substrate.