Optical XOR gate
View Patent ↗An optical XOR gate is formed as a photonic integrated circuit (PIC) from two sets of optical waveguide devices on a substrate, with each set of the optical waveguide devices including an electroabsorption modulator electrically connected in series with a waveguide photodetector. The optical XOR gate utilizes two digital optical inputs to generate an XOR function digital optical output. The optical XOR gate can be formed from III-V compound semiconductor layers which are epitaxially deposited on a III-V compound semiconductor substrate, and operates at a wavelength in the range of 0.8-2.0 μm.
1. A photonic integrated circuit (PIC) which generates an XOR function digital optical output from a pair of digital optical inputs, comprising:
a substrate;
a first set of optical waveguide devices on the substrate, with the first set of optical waveguide devices comprising a first electroabsorption modulator and a first photodetector which are electrically connected in series, with the first electroabsorption modulator receiving a first light portion split out from a first digital optical input of the pair of digital optical inputs by a first optical waveguide splitter on the substrate, and with the first photodetector receiving a second light portion split out from a second digital optical input of the pair of digital optical inputs by a second optical waveguide splitter on the substrate, and with the first photodetector generating from the second light portion a photocurrent signal which changes a reverse-bias voltage on the first electroabsorption modulator to generate a first inverted AND function output from the first light portion;
a second set of optical waveguide devices on the substrate, with the second set of optical waveguide devices comprising a second electroabsorption modulator and a second photodetector which are electrically connected in series, with the second electroabsorption modulator receiving a third light portion split out from the second digital optical input by the second optical waveguide splitter, and with the second photodetector receiving a fourth light portion split out from the first digital optical input by the first optical waveguide splitter, and with the second photodetector generating from the fourth light portion another photodetector signal which changes the reverse-bias voltage on the second electroabsorption modulator to generate a second inverted AND function output from the third light portion; and
an optical combiner to combine the first and second inverted AND function outputs to form the XOR function digital optical output.
2. The apparatus of claim 1 further comprising a first resistor which is electrically connected from an anode side of the first electroabsorption modulator to ground, and a second resistor which is electrically connected from the anode side of the second electroabsorption modulator to ground.
3. The apparatus of claim 1 further comprising at least one semiconductor optical amplifier on the substrate to amplify at least one optical signal selected from the group consisting of the first digital optical input, the second digital optical input, the first light portion, the second light portion, the third light portion, the fourth light portion, and the XOR function digital optical output.
4. The apparatus of claim 1 further comprising a plurality of optical waveguides on the substrate to guide the first light portion from the first optical waveguide splitter to the first electroabsorption modulator, to guide the second light portion from the second optical waveguide splitter to the first photodetector, to guide the third light portion from the first optical waveguide splitter to the second electroabsorption modulator, and to guide the fourth light portion from the first optical waveguide splitter to the second photodetector.
5. The apparatus of claim 1 wherein the optical combiner is located on the substrate.
6. The apparatus of claim 1 wherein the substrate comprises a III-V compound semiconductor substrate, and each electroabsorption modulator and each photodetector comprises a plurality of III-V compound semiconductor layers which are epitaxially grown on the III-V compound semiconductor substrate.
7. The apparatus of claim 6 wherein the III-V compound semiconductor substrate comprises indium phosphide (InP), and the plurality of III-V compound semiconductor layers are selected from the group consisting of indium gallium arsenide phosphide (InGaAsP) layers, indium gallium arsenide (InGaAs) layers, indium aluminum gallium arsenide (InAlGaAs) layers, and combinations thereof.
8. The apparatus of claim 6 wherein the III-V compound semiconductor substrate comprises gallium arsenide (GaAs), and the plurality of III-V compound semiconductor layers are selected from the group consisting of GaAs layers, aluminum gallium arsenide (AlGaAs) layers, indium gallium arsenide phosphide (InGaAsP) layers, indium gallium arsenide (InGaAs) layers, and combinations thereof.
9. The apparatus of claim 1 wherein the first digital optical input and the second digital optical input have a wavelength in the range of 0.8-2.0 microns.
10. An optical XOR gate which receives a first digital optical input and a second digital optical input and generates therefrom an XOR function digital optical output, comprising:
a III-V compound semiconductor substrate having a plurality of III-V compound semiconductor layers epitaxially grown thereon;
a first electroabsorption modulator formed from the plurality of III-V compound semiconductor layers, with the first electroabsorption modulator receiving a first light portion of the first digital optical input;
a first waveguide photodetector formed from the plurality of III-V compound semiconductor layers to receive a second light portion of the second digital optical input and to generate therefrom a first photocurrent signal which changes an absorption of light in the first electroabsorption modulator, thereby modulating the first light portion being transmitted through the first electroabsorption modulator to provide a first digitally-modulated output from the first electroabsorption modulator;
a second electroabsorption modulator formed from the plurality of III-V compound semiconductor layers, with the second electroabsorption modulator receiving a third light portion of the second digital optical input;
a second waveguide photodetector formed from the plurality of III-V compound semiconductor layers to receive a fourth light portion of the first digital optical input and to generate therefrom a second photocurrent signal which changes the absorption of light in the second electroabsorption modulator, thereby modulating the third light portion being transmitted through the second electroabsorption modulator to provide a second digitally-modulated output from the second electroabsorption modulator; and
an optical waveguide combiner to combine the first and second digitally-modulated outputs to generate the XOR function digital optical output.
11. The apparatus of claim 10 wherein the first electroabsorption modulator and the first waveguide photodetector are electrically connected in series, and the second electroabsorption modulator and the second waveguide photodetector are electrically connected in series.
12. The apparatus of claim 10 further comprising a first resistor which is electrically connected from an anode side of the first electroabsorption modulator to ground, and a second resistor which is electrically connected from the anode side of the second electroabsorption modulator to ground.
13. The apparatus of claim 10 wherein the first and third light portions of the first digital optical input are provided by a first optical waveguide splitter which is formed from the plurality of III-V compound semiconductor layers, and the second and fourth light portions of the second digital optical input are provided by a second optical waveguide splitter which is formed from the plurality of III-V compound semiconductor layers.
14. The apparatus of claim 10 wherein the optical waveguide combiner is formed from the plurality of III-V compound semiconductor layers.
15. The apparatus of claim 10 wherein the III-V compound semiconductor substrate comprises indium phosphide (InP), and the plurality of III-V compound semiconductor layers are selected from the group consisting of indium gallium arsenide phosphide (InGaAsP) layers, indium gallium arsenide (InGaAs) layers, indium aluminum gallium arsenide (InAlGaAs) layers, and combinations thereof.
16. The apparatus of claim 10 wherein the III-V compound semiconductor substrate comprises gallium arsenide (GaAs), and the plurality of III-V compound semiconductor layers are selected from the group consisting of GaAs layers, aluminum gallium arsenide (AlGaAs) layers, indium gallium arsenide phosphide (InGaAsP) layers, indium gallium arsenide (InGaAs) layers, and combinations thereof.
17. The apparatus of claim 10 wherein a plurality of passive optical waveguides are formed from the plurality of III-V compound semiconductor layers to guide the first light portion to the first electroabsorption modulator, to guide the second light portion to the first waveguide photodetector, to guide the third light portion to the second electroabsorption modulator, and to guide the fourth light portion to the second waveguide photodetector.
18. The apparatus of claim 10 wherein the first digital optical input and the second digital optical input have a wavelength in the range of 0.8-2.0 microns.
19. The apparatus of claim 10 further comprising at least one semiconductor optical amplifier formed from the plurality of III-V compound semiconductor layers to amplify at least one optical signal selected from the group consisting of the first digital optical input, the second digital optical input, the first light portion, the second light portion, the third light portion, the fourth light portion and the XOR function digital optical output.