Electro-optic silicon modulator with alternative capacitance-loaded coplanar waveguide structures
Embodiments of the present disclosure provide a high-speed silicon modulator without the microwave mode conversion and provide 50-ohm impedance matching to drivers simultaneously. In one aspect, a device may include an input waveguide region, an optic splitter, two optic phase shifters, an optic splitter, and an output waveguide. The device may include two curved waveguides. Either or both of the curved waveguides may have specially doped regions including PN junctions or MOS capacitors. The PN junctions or MOS capacitors may be alternatively connected to both slots of a coplanar waveguide forming the electrodes.
1. An alternate capacitance-loaded coplanar waveguide (ACLCPW) structure, comprising:
a ground-signal-ground (GSG) coplanar waveguide (CPW) structure, comprising:
a first ground metal;
a signal metal;
a second ground metal;
a first slot located between the first ground metal and the signal metal; and
a second slot located between the second ground metal and the signal metal; and
a phase shifter alternately located in the first slot and the second slot, the phase shifter periodically comprising:
a first active segment located in the first slot, comprising a first contact region of a first type connected to the first ground metal and a second contact region of a second type connected to the signal metal;
a second curved passive segment configured to form a waveguide transition from the first slot to the second slot;
a third active segment located in the second slot, comprising a third contact region of the first type connected to the second ground metal and a fourth contact region of the second type connected to the signal metal; and
a fourth curved passive segment configured to form the waveguide transition from the second slot to the first slot,
wherein the first active segment, the second curved passive segment, the third active segment and the fourth curved passive segment of the phase shifter form a periodically alternating capacitance loading between the first and second slots of the CPW structure.
2. The structure of claim 1 , wherein the phase shifter comprises two to fifty periods of repeating structures comprising the first active segment, the second curved passive segment, the third active segment and the fourth curved passive segments.
3. The structure of claim 1 , wherein a ratio of a total length of the first active segment and the third active segment of the phase shifter to a total length of the first active segment, the second curved passive segment, the third active segment and the fourth curved passive segment of the phase shifter is within a range of 0.1 to 0.9 to provide a coplanar waveguide (CPW) with 20 to 75-ohm equivalent microwave impedance.
4. The structure of claim 1 , wherein a length of the first active segment and the third active segment of the phase shifter is in a range of 10 um to 1.0 mm.
5. The structure of claim 1 , wherein the first active segment and the third active segment of the phase shifter are of a PN junction type or a MOS capacitor type.
6. The structure of claim 1 , wherein a minimum value of curvature radius of the second curved passive segment and the fourth curved passive segment of the phase shifter is greater than 20 um.
7. The structure of claim 1 , wherein a vertical distance between the second and fourth curved passive segments and electrode metal is greater than 1.0 um.
8. The structure of claim 1 , wherein the first active segment and the third active segment of the phase shifter have a same segment length or different segment lengths, and wherein the second curved passive segment and the fourth curved passive segment of the phase shifter have a same segment length or different segment lengths.
9. The structure of claim 1 , wherein the first type is P type and the second type contact is N type, or the first type contact is an N-type contact region and the second type contact is P-type contact region.
10. The structure of claim 1 , wherein the first type is N type and the second type contact is P type.