US-12619108-B2 - High bandwidth travelling wave electro absorption modulator (EAM) chip

Abstract

High bandwidth (e.g., >100 GHz) modulators and methods of fabricating such are provided. An EAM comprises a waveguide mesa comprising a continuous multi-quantum well (MQW) layer; a plurality of electrode segments disposed on the waveguide mesa; and a microstrip transmission line disposed on an insulating material layer and in electrical communication with the plurality of electrode segments via conducting bridges. The waveguide mesa comprises alternating active sections and passive sections. An electrode segment of the plurality of electrodes is disposed on a respective one of the active sections. Portions of the continuous MQW layer disposed in each of the active sections having an energy gap defining an active energy gap value. Portions of the continuous MQW layer disposed in each of the passive sections having an energy gap defining an passive energy gap value. The active energy gap value is less than the passive energy gap value.

Inventors

• Moshe B. Oron
• Elad Mentovich
• Tali Septon
• Oren Steinberg
• Isabelle Cestier

Assignees

• MELLANOX TECHNOLOGIES, LTD.

Dates

Publication Date

20260505

Application Date

20220630

Claims (20)

1. 1 . An electro-absorption modulator (EAM) device comprising: a waveguide mesa comprising a continuous multi-quantum well (MQW) layer; a segmented travelling wave electrode (TWE) structure comprising a plurality of electrode segments disposed on the waveguide mesa; and a microstrip transmission line disposed on an insulating spacer layer and in electrical communication with the segmented TWE structure via conducting bridges, wherein: the waveguide mesa comprises alternating active sections and passive sections, each electrode segment of the plurality of electrode segments is disposed on a respective one of the active sections, portions of the continuous MQW layer disposed in respective longitudinal portions of each of the active sections have an energy gap defining an active energy gap value, portions of the continuous MQW layer disposed in respective longitudinal portions of each of the passive sections have an energy gap defining a passive energy gap value, and each active energy gap value is less than each passive energy gap value.
2. 2 . The EAM device of claim 1 , wherein the continuous MQW layer is formed using a single epitaxial growth process.
3. 3 . The EAM device of claim 2 , wherein a quantum well intermixing process and rapid thermal annealing process are performed after the single epitaxial growth process to cause the active energy gap value to be different from the passive energy gap value.
4. 4 . The EAM device of claim 2 , wherein a selective area growth method is used to form the continuous MQW layer using the single epitaxial growth process.
5. 5 . The EAM device of claim 1 , wherein each of the plurality of electrode segments has a length in a propagation direction defined by the waveguide mesa that is less than 65 microns.
6. 6 . The EAM device of claim 1 , wherein the EAM device has an electrode filling factor of less than 0.5.
7. 7 . The EAM device of claim 6 , wherein the EAM device has an electrode filling factor substantially equal to 0.3.
8. 8 . The EAM device of claim 1 , wherein the EAM device has a mesa waist of less than 2.3 um.
9. 9 . An integrated electro-absorption modulator (EAM)-laser device comprising: a semiconductor laser comprising a laser part of a continuous multi-quantum well (MQW) layer; a waveguide mesa comprising a waveguide part of the continuous MQW layer; a segmented travelling wave electrode (TWE) comprising a plurality of electrode segments disposed on the waveguide mesa; and a microstrip transmission line disposed on an insulating spacer layer and in electrical communication with the segmented TWE structure via conducting bridges, wherein: the waveguide mesa comprises alternating active sections and passive sections, an electrode segment of the plurality of electrode segments is disposed on a respective one of the active sections, portions of the waveguide section the continuous MQW layer disposed in respective longitudinal portions of each of the active sections have an energy gap defining an active energy gap value, portions of the continuous MQW layer disposed in respective longitudinal portions of each of the passive sections have an energy gap defining a passive energy gap value, and each active energy gap value is less than each passive energy gap value.
10. 10 . The integrated EAM-laser device of claim 9 , wherein the laser part of the continuous MQW layer defines an energy gap having a laser energy gap value and the laser energy gap value is less than the active energy gap value.
11. 11 . The integrated EAM-laser device of claim 9 , wherein the continuous MQW layer is formed using a single epitaxial growth process.
12. 12 . The integrated EAM-laser device of claim 11 , wherein a quantum well intermixing process and rapid thermal annealing process are performed after the single epitaxial growth process to cause the active energy gap value to be different from the passive energy gap value.
13. 13 . The integrated EAM-laser device of claim 12 , wherein the quantum well intermixing process and the rapid thermal annealing process cause the laser energy gap value to be less than the active energy gap value.
14. 14 . The integrated EAM-laser device of claim 11 , wherein a selective area growth (SAG) method is used to form the continuous MQW layer using the single epitaxial growth process.
15. 15 . The integrated EAM-laser device of claim 14 , wherein an SAG mask of a first width is used to form the laser part of the continuous MQW layer, SAG masks of a second width are used to form the portions of the continuous MQW layer disposed in the active sections of the waveguide mesa, and SAG masks of a third width are used to form the portions of the continuous MQW layer disposed in the passive sections of the waveguide mesa, wherein the first width is larger than the second width and the second width is larger than the third width.
16. 16 . The integrated EAM-laser device of claim 15 , wherein the third width is zero.
17. 17 . The integrated EAM-laser device of claim 9 , wherein each of the plurality of electrode segments has a length in a propagation direction defined by the waveguide mesa that is less than 65 microns.
18. 18 . The integrated EAM-laser device of claim 9 , wherein the EAM device has an electrode filling factor of less than 0.5.
19. 19 . The integrated EAM-laser device of claim 9 , wherein the EAM device has a mesa waist of less than 2.3 um.
20. 20 . A method of fabricating an electro-absorption modulator (EAM) device, the method comprising: forming a continuous multi-quantum well (MQW) layer of a waveguide mesa; and forming a plurality of electrode segments on the waveguide mesa, wherein: the waveguide mesa comprises alternating active sections and passive sections, portions of the waveguide mesa having an electrode segment of the plurality of electrode segments disposed thereon are active sections of the waveguide mesa, portions of the continuous MQW layer disposed in respective longitudinal portions of each of the active sections have an energy gap defining an active energy gap value, portions of the continuous MQW layer disposed in respective longitudinal portions of each of the passive sections have an energy gap defining a passive energy gap value, and each active energy gap value is less than each passive energy gap value; and forming a microstrip transmission line on an insulating spacer layer and in electrical communication with each of the plurality of electrode segments via conducting bridges.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Application No. 63/266,527, filed Jan. 7, 2022, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD Embodiments relate to high bandwidth (e.g., bandwidth ≥100 GHz) electro-absorption modulators (EAMs) and methods of fabrication of high bandwidth EAMS. BACKGROUND As data communication demands increase in both volume and speed, fiber optics have become an increasingly popular communication medium. As a part of the utilization of fiber optics for communicating data, the communicated data stream may be generated by electro-optic modulators, such as Mach-Zehnder modulators (MZMs) and electro-absorption modulators (EAMs), that modulate an optical beam to encode data into the data stream. However, the 3 dB modulation bandwidth of conventional electro-absorption modulators is in the range of a gigahertz (GHz) to a few tens of GHz (˜30 GHz). This is significantly less than the approximately 120 GHz bandwidth required by next generation optics-based telecommunications systems and next generation optical links. BRIEF SUMMARY Various embodiments provide electro-absorption modulators (EAMs) having high bandwidth. Various embodiments provide modulators having 3 dB modulation bandwidth of at least 100 GHz. Various embodiments provide methods for fabricating EAMs having 3 dB modulation bandwidth of at least 100 GHz. In various embodiments, the EAM is a traveling wave EAM comprising a waveguide mesa that includes a continuous multi-quantum well (MQW) layer and a travelling wave electrode (TWE) structure that includes a plurality of electrode segments disposed on the waveguide. The plurality of electrode segments cover no more than half of the surface of the waveguide mesa on which the electrode segments are disposed. In an example embodiment, the continuous MQW layer of the waveguide mesa is formed to have different bandgap energies (e.g., the energy between the conduction band and the valence band within the MQW layer material) at different points along the continuous MQW layer. For example, sections of the MQW layer on which an electrode segment is disposed is referred to as an active section of the MQW layer and sections of the MQW layer on which an electrode segment is not disposed is referred to as a passive section. In an example embodiment, the bandgap energy in the active sections is less than the bandgap energy in the passive sections. According to aspects of the present disclosure, a high bandwidth EAM device is provided. In an example embodiment, the EAM device includes a waveguide mesa including a continuous MQW layer and a segmented TWE structure. The TWE includes a plurality of electrode segments disposed on the waveguide mesa. The EAM device further comprises a microstrip transmission line disposed on an insulating material and in electrical communication with each of the plurality of electrode segments via conducting bridges. The waveguide mesa includes alternating active sections and passive sections. An electrode segment of the plurality of electrode segments is disposed on a respective one of the active sections. The portions of the MQW layer disposed in an active section have an energy gap (e.g., between the conduction band and the valence band of the MQW layer material) defining an active energy gap value. The portions of the MQW layer disposed in a passive section have an energy gap (e.g., between the conduction band and the valence band of the MQW layer material) defining a passive energy gap value. The active energy gap value is less than the passive energy gap value. In an example embodiment, the EAM has a filling factor (FF) of less than 0.5, meaning that the plurality of electrode segments cover less than half of the surface of the waveguide mesa on which the plurality of electrode segments are disposed. In an example embodiment, the continuous MQW layer is referred to as continuous because it is a continuous layer of material and does not include any butt joints along its length (in the direction of propagation of the EAM). According to another aspect, an integrated EAM-laser device is provided. In an example embodiment, the integrated EAM-laser device comprises a semiconductor laser including a laser part of a continuous MQW layer, a waveguide mesa comprising a waveguide part of the continuous MQW layer, a segmented TWE structure including a plurality of electrode segments disposed on the waveguide mesa, and a microstrip transmission line disposed on an insulating material and in electrical communication with each of the plurality of electrode segments disposed on the waveguide mesa via conducting bridges. The waveguide mesa includes alternating active sections and passive sections. An electrode segment of the plurality of electrode segments is disposed on a respective one of the active sections. The portions of the MQW layer disposed in an active section have an energy gap (e.g