Optical waveguide modulator
A multi-section optical modulator and related method wherein two waveguide arms traverse a plurality of successive modulating sections. A differential drive signal is applied separately to each waveguide arm of each modulating sections in synchronism with the transmission of light along the waveguide arms, effecting a dual differential driving of each section. By suitably selecting the number of modulating sections and the section length, a high modulation bandwidth and a high modulation efficiency may be achieved simultaneously for a given peak-to-peak voltage swing of the drive signal.
1. An optical waveguide modulator comprising:
a waveguide Mach-Zehnder interferometer comprising a first waveguide arm and a second waveguide arm connected optically in parallel;
a first phase modulator comprising: a first p/n junction located in the first waveguide arm, a first cathode electrode extending along a length of the first waveguide arm in electrical communication with an n-side of the first p/n junction, and a first anode electrode extending along the length of the first waveguide arm in electrical communication with a p-side of the first p/n junction;
a second phase modulator comprising: a second p/n junction located in the second waveguide arm, a second cathode electrode extending along a length of the second waveguide arm in electrical communication with an n-side of the second p/n junction, and a second anode electrode extending along the length of the second waveguide arm in electrical communication with a p-side of the second p/n junction; and,
a drive circuit comprising a first differential driver DC-coupled to the first and second cathode electrodes, and a second differential driver DC-coupled to the first and second anode electrodes;
wherein the drive circuit includes a common pre-equalization circuit configured to convert an input differential data signal into two output differential signals having different common-mode voltage levels, and to feed the two output differential signals to the first and second differential drivers.
2. The optical waveguide modulator of claim 1 wherein the common pre-equalization circuit comprises a unit-gain transistor pair.
3. The optical waveguide modulator of claim 1 wherein the common pre-equalization circuit is configured to boost high-frequency components of the input differential data signal.
4. The optical waveguide modulator of claim 1 wherein each of the first and second differential drivers is configured to operate as an emitter follower or as a collector follower.
5. The optical waveguide modulator of claim 1 comprising an electrical circuit configured to provide one of: a positive DC bias voltage to the first and second cathode electrodes, or a negative DC bias voltage to the first and second anode electrodes.
6. The optical waveguide modulator of claim 1 wherein each of the first and second differential drivers are configured to operate as a current-steering circuit.
7. An optical waveguide modulator comprising:
a waveguide Mach-Zehnder interferometer comprising a first waveguide arm and a second waveguide arm connected optically in parallel;
a first phase modulator comprising: a first p/n junction located in the first waveguide arm, a first cathode electrode extending along a length of the first waveguide arm in electrical communication with an n-side of the first p/n junction, and a first anode electrode extending along the length of the first waveguide arm in electrical communication with a p-side of the first p/n junction;
a second phase modulator comprising: a second p/n junction located in the second waveguide arm, a second cathode electrode extending along a length of the second waveguide arm in electrical communication with an n-side of the second p/n junction, and a second anode electrode extending along the length of the second waveguide arm in electrical communication with a p-side of the second p/n junction; and,
a drive circuit comprising a first differential driver DC-coupled to the first and second cathode electrodes, and a second differential driver DC-coupled to the first and second anode electrodes;
wherein each of the cathode and anode electrodes comprises a first end and a second end, wherein the first and second differential drivers are DC coupled to the first ends of respective cathode or anode electrodes, and wherein:
either the second ends of the anode electrodes are grounded and the second ends of the cathode electrodes are connected to a source of DC voltage, or
the second ends of the cathode electrodes are grounded and the second ends of the anode electrodes are connected to a source of DC voltage.
8. The optical waveguide modulator of claim 7 , wherein the first differential driver and the second differential driver are configured to provide differential drive signals with a common-mode DC offset therebetween.
9. The optical waveguide modulator of claim 7 further comprising an input electrical port for receiving an input data signal, wherein each of the first and second differential drivers is configured to linearly convert the input data signal into the differential drive signals.
10. The optical waveguide modulator of claim 7 wherein each of the first and second differential drivers are configured to operate as a current-steering circuit.
11. The optical waveguide modulator of claim 7 wherein each of the first and second differential drivers is configured to operate as an emitter follower or as a collector follower.