Linearly distributed optical modulator with active photonic integrated circuit adjustment
Aspects of the present disclosure provide an optical modulator with linearly distributed active circuitry coupled to a signal electrode to compensate for loss or attenuation of a high frequency modulation signal in the signal electrode. In one embodiment, negative resistance cells are attached to the signal electrode at various points, and have tunable negative resistances to compensate for the loss. In another embodiment, a segmented bias electrode is provided along the length of the optical waveguide in the optical modulator. Each segmented bias electrode may have a pre-determined bias voltage that can reduce impedance mismatches along the length of the signal electrode to reduce echoes and ripples in the modulation signal.
1. An optical modulator, comprising:
a signal input configured to receive a modulation signal;
an optical waveguide extending along a first direction and configured to support a light signal;
a negative resistance cell;
a compensation driver coupled to the negative resistance cell and configured to supply power to active components within the negative resistance cell; and
a signal electrode coupled to the optical waveguide and elongated along the first direction, wherein
a first point along a length of the signal electrode is directly coupled to the signal input,
a second point along the length of the signal electrode is coupled to the negative resistance cell,
wherein the negative resistance cell has a negative resistance tunable by the compensation driver based on a monitored characteristic of a modulated light signal.
2. The optical modulator of claim 1 , wherein the signal electrode is coupled to the optical waveguide at a plurality of contact points arranged along the first direction, and wherein
a negative resistance of the negative resistance cell is selected such that an attenuation of a signal amplitude at a first contact point and a last contact point of the plurality of contact points is no more than 50% when the modulation signal has a frequency of between 30 and 100 GHz.
3. The optical modulator of claim 1 , wherein:
the negative resistance cell is separated from the signal input by at least a portion of the signal electrode.
4. The optical modulator of claim 1 , wherein the signal input is a first differential signal input, the modulation signal is a first differential signal, the optical waveguide is a first waveguide, the signal electrode is a first differential signal electrode, and wherein the optical modulator further comprises:
a second differential signal input configured to receive a second differential signal;
a second optical waveguide extending along the first direction and configured to support a light signal transmitted along the first direction;
a second differential signal electrode coupled to the second optical waveguide and elongated along the first direction, wherein:
a first point along a length of the second differential signal electrode is directly coupled to the second differential signal input,
a second point along the length of the second differential signal electrode is coupled to the negative resistance cell, and wherein
the first and second differential signals are differential representations of an input signal.
5. The optical modulator of claim 1 , further comprising a substrate, wherein:
the optical waveguide is disposed in a first plane in the substrate, and wherein
the negative resistance cell is disposed in a second plane parallel to and offset from the first plane.
6. The optical modulator of claim 5 , wherein the substrate is a first substrate, and wherein:
the negative resistance cell is disposed in a second substrate bonded to the first substrate.
7. The optical modulator of claim 1 , further comprising:
a bias electrode coupled to the optical waveguide and configured to provide a constant voltage.
8. The optical modulator of claim 7 , wherein:
the optical waveguide is a semiconductor carrier-depletion modulator, the signal electrode is a transmission line.
9. The optical modulator of claim 8 , wherein:
the optical waveguide comprises a silicon slab waveguide.
10. The optical modulator of claim 8 , wherein:
the optical waveguide comprises a first doped portion having a dopant of a first type, an intrinsic portion, and a second doped portion having a dopant of a second type, wherein
the first doped portion, the intrinsic portion and the second doped portion are elongated along the first direction and arranged along a second direction different from the first direction, and wherein
the signal electrode is coupled to the first doped portion at one or more points along a length of the first doped portion, and
the bias electrode is coupled to the second doped portion at one or more points along a length of the second doped portion.
11. A method for operating an optical modulator having an optical waveguide and a signal electrode both elongated along a first direction, the signal electrode coupled to the optical waveguide at a plurality of contact points arranged along the first direction, to a signal input at a first point along a length of the signal electrode, and to a negative resistance cell at a second point along the length of the signal electrode, the method comprising:
transmitting a light signal along the first direction in the optical waveguide;
applying a modulation signal at the signal input;
monitoring a characteristic of a modulated light signal transmitted through the optical waveguide;
supplying power to active components within the negative resistance cell via a compensation driver coupled to the negative resistance cell based on the monitored characteristic of the modulated light signal;
selecting a negative resistance of the negative resistance cell such that an attenuation of a voltage at a first contact point and a last contact point of the plurality of contact points is no more than 50% when the modulation signal has a frequency of between 30 and 100 GHz.
12. The method of claim 11 , wherein the optical modulator comprises a plurality of negative resistance cells coupled to a plurality of points along the length of the signal electrode, and the method further comprises:
for each of the plurality of negative resistance cells, selecting a negative resistance of the negative resistance cell such that an attenuation of a voltage at a first contact point and a last contact point of the plurality of contact points is no more than 50% when the modulation signal has a frequency of between 30 and 100 GHz.
13. The method of claim 11 , further comprising:
providing a constant voltage to the optical waveguide via a bias electrode that is coupled to the optical waveguide, the bias electrode elongated along the first direction.
14. A silicon carrier-depletion modulator, comprising:
a signal electrode;
a negative resistance cell;
a compensation driver coupled to the negative resistance cell, the compensation driver configured to supply power to active components within the negative resistance cell based on a monitored characteristic of a modulated light signal;
a modulation driver configured to provide a modulation signal at a signal input; and
a silicon waveguide extending along a first direction and configured to support a light signal, the silicon waveguide coupled between the signal electrode and a bias electrode, wherein the signal electrode is elongated along the first direction, and wherein
a first point along a length of the signal electrode is directly coupled to the signal input,
a second point along the length of the signal electrode is coupled to the negative resistance cell, and
the negative resistance cell has a negative resistance tunable by the compensation driver based on the monitored characteristic of the modulated light signal.
15. The silicon carrier-depletion modulator of claim 14 , further comprising a plurality of negative resistance cells coupled to a plurality of points along the length of the signal electrode.
16. The silicon carrier-depletion modulator of claim 14 , wherein the signal input is a first differential signal input, the modulation signal is a first differential signal, the silicon waveguide is a first silicon waveguide, the signal electrode is a first differential signal electrode, and wherein the silicon carrier-depletion modulator further comprises:
a second differential signal input configured to receive a second differential signal;
a second silicon waveguide extending along the first direction and configured to support a light signal transmitted along the first direction;
a second differential signal electrode coupled to the second silicon waveguide and elongated along the first direction, wherein:
a first point along a length of the second differential signal electrode is directly coupled to the second differential signal input,
a second point along the length of the second differential signal electrode is coupled to the negative resistance cell, and wherein
the first and second differential signals are differential representations of an input signal.