Slow-light silicon optical modulator
An optical modulator is described. This optical modulator may be implemented using silicon-on-insulator (SOI) technology. In particular, a semiconductor layer in an SOI platform may include a photonic crystal having a group velocity of light that is less than that of the semiconductor layer. Moreover, an optical modulator (such as a Mach-Zehnder interferometer) may be implemented in the photonic crystal with a vertical junction in the semiconductor layer. During operation of the optical modulator, an input optical signal may be split into two different optical signals that feed two optical waveguides, and then subsequently combined into an output optical signal. Furthermore, during operation, time-varying bias voltages may be applied across the vertical junction in the optical modulator using contacts defined along a lateral direction of the optical modulator.
1. An integrated circuit, comprising:
a substrate;
a buried-oxide (BOX) layer disposed on the substrate; and
a semiconductor layer disposed on the buried-oxide layer, wherein the semiconductor layer includes an array of holes, defined by edges, that implement a photonic crystal having a group velocity of light that is less than that of the semiconductor layer,
wherein an optical modulator, having an input optical waveguide, a first optical waveguide, a second optical waveguide and an output optical waveguide, is defined, and the first optical waveguide and the second optical waveguide are defined in the photonic crystal;
wherein, during operation of the optical modulator, an input optical signal received from the input optical waveguide is split into optical signals that, respectively, feed into the first optical waveguide and the second optical waveguide, and the optical signals from the first optical waveguide and the second optical waveguide are combined into an output optical signal that feeds into the output optical waveguide;
wherein the first optical waveguide and the second optical waveguide include a vertical junction defined by n-type doping of a lower portion of the semiconductor layer and p-type doping of an upper portion of the semiconductor layer, wherein the lower portion of the semiconductor layer is connected through a center n-type island, to form a single contact, and wherein the upper portion of the semiconductor layer is connected to two separate p-type contacts; and
wherein, during operation, time-varying bias voltages are applied across the vertical junction in the optical modulator using contacts defined along a lateral direction of the optical modulator.
2. The integrated circuit of claim 1 , wherein the optical modulator has a push-pull configuration, so that, during operation, the first optical waveguide is driven with first time-varying bias voltages corresponding to data, and the second optical waveguide is driven with second time-varying bias voltages corresponding to inverted data.
3. The integrated circuit of claim 1 , wherein polarities of the time-varying bias voltages alternate in different regions along lengths of the first optical waveguide and the second optical waveguide.
4. The integrated circuit of claim 1 , wherein the holes have a cylindrical shape and are filled with a different material than the semiconductor layer.
5. The integrated circuit of claim 4 , wherein the material includes silicon dioxide.
6. The integrated circuit of claim 1 , wherein the photonic crystal has an approximately flat dispersion region and an increased index of refraction relative to that for the semiconductor layer for a range of wavelengths corresponding to an optical signal conveyed during operation of the optical modulator.
7. The integrated circuit of claim 1 , wherein the substrate, the BOX layer and the semiconductor layer constitute a silicon-on-insulator technology.
8. The integrated circuit of claim 1 , wherein the optical modulator includes a Mach-Zehnder interferometer (MZI).
9. The integrated circuit of claim 1 , wherein at least a portion of the photonic crystal has a negative index of refraction.
10. The integrated circuit of claim 1 , wherein the first optical waveguide and the second optical waveguide include tapers.
11. A system, comprising:
a processor;
a memory, coupled to the processor, that stores a program module, which, during operation, is executed by the processor; and
an integrated circuit, comprising:
a substrate;
a buried-oxide (BOX) layer disposed on the substrate; and
a semiconductor layer disposed on the buried-oxide layer, wherein the semiconductor layer includes an array of holes, defined by edges, that implement a photonic crystal having a group velocity of light that is less than that of the semiconductor layer,
wherein an optical modulator, having an input optical waveguide, a first optical waveguide, a second optical waveguide and an output optical waveguide, is defined, and the first optical waveguide and the second optical waveguide are defined in the photonic crystal;
wherein, during operation of the optical modulator, an input optical signal received from the input optical waveguide is split into optical signals that, respectively, feed into the first optical waveguide and the second optical waveguide, and the optical signals from the first optical waveguide and the second optical waveguide are combined into an output optical signal that feeds into the output optical waveguide;
wherein the first optical waveguide and the second optical waveguide include a vertical junction defined by n-type doping of a lower portion of the semiconductor layer and p-type doping of an upper portion of the semiconductor layer, wherein the lower portion of the semiconductor layer is connected through a center n-type island, to form a single contact, and wherein the upper portion of the semiconductor layer is connected to two separate p-type contacts; and
wherein, during operation, time-varying bias voltages are applied across the vertical junction in the optical modulator using contacts defined along a lateral direction of the optical modulator.
12. The system of claim 11 , wherein the optical modulator has a push-pull configuration, so that, during operation, the first optical waveguide is driven with first time-varying bias voltages corresponding to data, and the second optical waveguide is driven with second time-varying bias voltages corresponding to inverted data.
13. The system of claim 11 , wherein polarities of the time-varying bias voltages alternate in different regions along lengths of the first optical waveguide and the second optical waveguide.
14. The system of claim 11 , wherein the holes have a cylindrical shape and are filled with a different material than the semiconductor layer.
15. The system of claim 11 , wherein the photonic crystal has an approximately flat dispersion region and an increased index of refraction relative to that for the semiconductor layer for a range of wavelengths corresponding to an optical signal conveyed during operation of the optical modulator.
16. The system of claim 11 , wherein the substrate, the BOX layer and the semiconductor layer constitute a silicon-on-insulator technology.
17. The system of claim 11 , wherein the first optical waveguide and the second optical waveguide include tapers.