Optical pulse amplitude modulator (PAM) with multiple modulator segments
View Patent ↗Various embodiments of the present disclosure are directed towards an optical module comprising an optical modulator device (OMD) for pulse amplitude modulation (PAM) in which the OMD comprises multiple modulator segments. A first modulator segment and a second modulator segment are spaced from each other along a ring-shaped waveguide. Further, a length of the second modulator segment is twice a length of the first modulator segment. As such, a power factor of the second modulator segment is twice a power factor of the first modulator segment. During use of the OMD, the first and second modulator segments are driven by separate non-return-to-zero (NRZ) electrical signals. The NRZ electrical signals are generated by a driver, which generates the NRZ electrical signals so as to coordinate operation of the first and second modulator segments to generate a PAM optical signal.
1 . A method for forming an optical module, comprising:
patterning a semiconductor layer to form a ring-shaped waveguide in the semiconductor layer;
doping the semiconductor layer to form a first modulator, a second modulator, and a third modulator spaced from each other along the ring-shaped waveguide, wherein the first, second, and third modulators respectively have a first PN junction, a second PN junction, and a third PN junction in the ring-shaped waveguide;
depositing a dielectric layer covering the semiconductor layer, as well as the first and second modulators;
forming contact vias extending through the dielectric layer respectively to the first and second modulators; and
forming a heater covering the second PN junction and laterally offset from the first and third PN junctions;
wherein the second PN junction has a length along the ring-shaped waveguide that is two times a length of the first PN junction, wherein the heater has a length along the ring-shaped waveguide that is greater than the length of the first PN junction and that is less than a length of the third PN junction, and wherein the ring-shaped waveguide is undoped between the first PN junction and the second PN junction.
2 . The method according to claim 1 , further comprising:
patterning the semiconductor layer to further form an input-output waveguide bordering and coupled to the ring-shaped waveguide to form a ring resonator.
3 . The method according to claim 1 , further comprising:
patterning the semiconductor layer to form a pair of protrusions in the semiconductor layer, wherein the ring-shaped waveguide is between and borders the pair of protrusions, wherein an N-type region of the second PN junction extends from the ring-shaped waveguide to one of the protrusions, wherein a P-type region of the second PN junction extends from the ring-shaped waveguide to another one of the protrusions, and wherein the heater completely covers the pair of protrusions.
4 . The method according to claim 1 , further comprising:
forming a complementary metal-oxide-semiconductor (CMOS) driver; and
electrically coupling the CMOS driver to the first modulator and the second modulator, wherein the CMOS driver is configured to electrically drive the first modulator and the second modulator with separate non-return-to-zero (NRZ) signals.
5 . The method according to claim 1 , wherein the length of the third PN junction along the ring-shaped waveguide is two times the length of the second PN junction.
6 . A method for forming an optical module, comprising:
patterning a semiconductor layer to form a ring-shaped waveguide extending laterally in a closed path and in the semiconductor layer, wherein the ring-shaped waveguide has a plurality of outer sidewalls;
doping the semiconductor layer to form a first modulator, a second modulator, and a third modulator spaced from each other along the closed path, wherein the first, second, and third modulators respectively have a first PN junction, a second PN junction, and a third PN junction in the ring-shaped waveguide, and wherein the first, second, and third PN junctions are localized along different sidewalls of the plurality of outer sidewalls;
forming a complementary metal-oxide-semiconductor (CMOS) driver; and
electrically coupling the CMOS driver to the first modulator and the second modulator, wherein the CMOS driver is configured to electrically drive the first modulator and the second modulator with separate non-return-to-zero (NRZ) signals.
7 . The method according to claim 6 , wherein the second modulator has a power factor that is two times a power factor of the first modulator.
8 . The method according to claim 6 , further comprising:
forming a plurality of heaters respectively overlying the first and second modulators, wherein the plurality of heaters have different lengths along the ring-shaped waveguide.
9 . The method according to claim 6 , wherein the CMOS driver, the ring-shaped waveguide, and the first and second modulators are configured to generate an optical pulse amplitude modulation (PAM) signal in an input-output waveguide bordering and coupled to the ring-shaped waveguide.
10 . A method for forming an optical module, comprising:
patterning a semiconductor layer to form a ring-shaped waveguide in the semiconductor layer;
patterning the semiconductor layer to further form an input-output waveguide bordering and coupled to an undoped portion of the ring-shaped waveguide;
doping the semiconductor layer to form a first modulator and a second modulator spaced from each other along the ring-shaped waveguide, wherein the first and the second modulators respectively have a first PN junction and a second PN junction in the ring-shaped waveguide;
depositing a dielectric layer overlying the semiconductor layer;
patterning the dielectric layer to form a first opening and a second opening respectively overlying the first and second modulators and laterally offset from the input-output waveguide when viewed top down;
depositing a heater layer overlying the dielectric layer and filling the first and second openings; and
performing a planarization into the heater layer to form a first heater and a second heater respectively in the first and second openings, wherein the second heater has a length along the ring-shaped waveguide that is about two times a length of the first heater.
11 . The method according to claim 10 , wherein the doping forms a third modulator in the ring-shaped waveguide, spaced from the first and second modulators, and wherein the patterning of the dielectric layer, the depositing of the heater layer, and the planarization form a third heater overlying the third modulator and having a length along the ring-shaped waveguide that is about two times the length of the second heater.
12 . The method according to claim 10 , wherein the ring-shaped waveguide and the input-output waveguide are formed by a common etching process.
13 . The method according to claim 10 , wherein the ring-shaped waveguide is continuous in a closed path and is continuous from the first modulator to the second modulator.
14 . The method according to claim 1 , wherein the heater is separated from the second PN junction by the contact vias.
15 . The method according to claim 1 , further comprising:
forming a first additional heater and a second additional heater completely and respectively covering the first and third modulators, wherein the first and second additional heaters have individual lengths along the ring-shaped waveguide that are respectively greater than the length of the first PN junction and the length of the third PN junction.
16 . The method according to claim 6 , further comprising:
forming a fourth modulator comprising a fourth PN junction in the ring-shaped waveguide and localized along the same sidewall of the plurality of outer sidewalls as the first PN junction.
17 . The method according to claim 6 , wherein the first and third modulators are respectively on opposite sides of the ring-shaped waveguide and have length-wise centers overlapping with an axis extending orthogonal to the closed path.
18 . The method according to claim 6 , further comprising:
forming a heater completely covering the second PN junction and laterally offset from the first and third PN junctions, wherein the heater has a length along the ring-shaped waveguide that is greater than a length of the first PN junction and that is less than a length of the third PN junction.
19 . The method according to claim 11 , wherein the length of the second heater along the ring-shaped waveguide is greater than a length of the first modulator and is less than a length of the third modulator.
20 . The method according to claim 10 , further comprising:
forming a first conductive wire and a second conductive wire overlying the first modulator, wherein the first and second conductive wires partially separate the first heater from the first modulator.