US-12620773-B2 - Performance heterogeneous lasers and active components

US12620773B2US 12620773 B2US12620773 B2US 12620773B2US-12620773-B2

Abstract

A device comprises first, second and third elements fabricated on a common substrate. The first element comprises an active waveguide structure supporting a first optical mode and at least one of the modal gain control structures. The second element comprises a passive waveguide structure supporting a second optical mode. The third element, at least partly butt-coupled to the first element, comprises an intermediate waveguide structure supporting intermediate optical modes. If the first optical mode differs from the second optical mode by more than a predetermined amount, a tapered waveguide structure in at least one of the second and third elements facilitate efficient adiabatic transformation between the second optical mode and one of the intermediate optical modes. No adiabatic transformation occurs between any of the intermediate optical modes and the first optical mode. Mutual alignments of the first, second and third elements are defined using lithographic alignment marks.

Inventors

Tin Komljenovic
Chong Zhang
Minh Tran

Assignees

Nexus Photonics, Inc.

Dates

Publication Date: 20260505
Application Date: 20220428

Claims (15)

1 . A device comprising: first, second and third element fabricated on a common substrate; wherein the first element comprises an active waveguide structure supporting a first fundamental optical mode and first higher-order optical mode, the second element comprises a passive waveguide structure supporting a second optical mode, and the third element, at least partly butt-coupled to the first element, comprises an intermediate waveguide structure supporting intermediate optical modes; wherein first element comprises at least three sublayers ( 401 a , 401 b , 401 c ) and a modal gain control structure; wherein one of the sublayers, the active region sublayer ( 401 b ), of the first element is positioned between two other sub-layers and comprises an active region comprising at least one of quantum wells and quantum dots; wherein the modal gain control structure including at least one of pad structures comprising metal or having bandgap below a photon energy of the modes in active waveguide structure is placed directly on top of the active region sublayer without a contact sublayer between the modal gain control structure and the active region sublayer; wherein an overlap between the first higher-order optical mode and at least one of the modal gain control structures is larger than the overlap between the first fundamental optical mode and the same modal gain control structure; wherein a tapered waveguide structure in at least one of the second and third elements facilitate efficient adiabatic transformation between the second optical mode and one of the intermediate optical modes; wherein no adiabatic transformation occurs between any of the intermediate optical modes and the first optical mode; and wherein mutual alignments of the first, the second and the third element are defined using lithographic alignment marks that facilitate precise alignment between layers formed during processing steps of fabricating the first, the second and the third element.
2 . The device of claim 1 , wherein a lower surface of the third element is planar.
3 . The device of claim 1 , wherein an interface between the first and the third element is angled at an angle optimized to minimize reflections.
4 . The device of claim 3 , further comprising: an anti-reflective coating layer deposited on at least one angled interface.
5 . The device of claim 1 , wherein the first element comprises at least three sub-layers, where in at least one of the sub-layers in the active waveguide structure comprises a n-contact layer, at least one of the sub-layers in the active waveguide structure comprises a p-contact layer, and at least one of the sub-layers in the active waveguide structure comprises an active region.
6 . The device of claim 5 , wherein the active region comprises quantum wells.
7 . The device of claim 5 , wherein the active region comprises quantum dots.
8 . The device of claim 5 , wherein the active region comprises a pin-junction.
9 . The device of claim 5 , wherein the active region comprises a pn-junction.
10 . The device of claim 1 , wherein the active waveguide structure and the intermediate waveguide structure at butt-coupled interface have a wall region which is widened near the butt-coupled interface.
11 . The device of claim 10 , wherein cross-sections of structures defining mode guiding in the active waveguide structure and the intermediate waveguide structure are enlarged at the wall region using a gradual taper.
12 . The device of claim 10 , wherein cross-sections of structures defining mode guiding in the active waveguide structure and the intermediate waveguide structure are enlarged at wall region using an abrupt transition.
13 . The device of claim 1 , wherein the second element comprises silicon nitride.
14 . The device of claim 1 , wherein the second element comprises lithium niobate.
15 . The device of claim 1 , wherein the second element comprises tantalum pentoxide.

Description

FIELD OF THE INVENTION The present invention relates to semiconductor lasers, amplifiers, modulators, and photodetectors. More specifically, certain embodiments of the invention relate to improved performance of heterogeneously integrated lasers, amplifiers, modulators and photodetectors using dissimilar materials that are optically coupled. BACKGROUND OF THE INVENTION A photonic integrated circuit (PIC) or integrated optical circuit is a device that integrates multiple photonic functions and as such is analogous to an electronic integrated circuit. The major difference between the two is that a photonic integrated circuit provides functions for information signals imposed on optical carrier waves. The material platform most commercially utilized for photonic integrated circuits is indium phosphide (InP), which allows for the integration of various optically active and passive functions on the same chip. Although many current PICs are realized in InP platforms, there has been significant research in the past decade in using silicon rather than InP for the realization of PICs, due to some superior characteristics as well as superior processing capabilities for the former material, that leverage the investment already made for electronic integrated circuits. The biggest drawback in using silicon for PICs is that it is an indirect bandgap material which makes it hard to provide electrically pumped optical sources. This problem is generally solved by assembling PICs comprising two or more chips made from dissimilar materials in separate processes. Such an approach is challenging due to a need for very fine alignment, which increases packaging costs and introduces scaling limitations. Another approach to solving the bandgap problem is to bond two dissimilar materials and process them together, removing the need for precise alignment during the bonding of larger pieces or complete wafers of the dissimilar materials, and allowing for mass fabrication. In this disclosure, we use the term “hybrid” to describe the first approach that includes precise assembly of separately processed parts, and we use the term “heterogeneous” to describe the latter approach of bonding two materials and then processing the bonded structure to define the waveguides and other components of interest. To transfer the optical signal between dissimilar materials, the heterogeneous approach utilizes tapers whose dimensions are gradually changed until the effective mode refractive indices of dissimilar materials match and there is efficient power transfer. This approach generally works well when materials have similar refractive indices as is the case with silicon and InP. In cases where there is larger difference in effective indices, such as between e.g. SiN and GaAs, the requirements on taper tip dimensions become prohibitive limiting efficient power transfer. Specifically, extremely small taper tip widths (of the order of nanometers) may be necessary to provide good coupling. Achieving such dimensions is complex and may not be cost-effective. Although InP and silicon-based PICs address many current needs, they have some limitations; among them are the fact that the operating wavelength range is limited by material absorption increasing the losses, and the fact that there is a limit on the maximum optical intensities and consequently optical powers that a PIC can handle. To address these limitations, alternate waveguide materials have been considered, such as SiN, TiO2, Ta2O5, AlN or others. In general, such dielectric waveguides have higher bandgap energies which provides better high-power handling and transparency at shorter wavelength, but, in general such materials also have lower refractive indices. E.g. SiN with bandgap of ˜5 eV has refractive index of ˜2, AlN has bandgap of ˜6 eV and refractive index of around ˜2, and SiO2 with bandgap of ˜8.9 eV has refractive index of ˜1.44. For comparison, the refractive index of both InP and GaAs is >3. This makes the tapered approach challenging. The alternative hybrid approach suffers from the drawbacks already mentioned above, namely the need for precise alignment, and correspondingly complex packaging and scaling limitations. A recent approach to the problems discussed above was presented in U.S. Pat. No. 10,859,764 B2, employing butt-coupling in combination with a mode-converter to allow the heterogenous process to be used without the need for extremely small taper widths. The present invention is directed towards PICs employing butt-coupling in this way, and that include an active device such as a laser, amplifiers, modulators and photodetectors with improved performance. In particular, embodiments described below are concerned with the detailed design of the optical coupling structure and mode control in the active components necessary for creating of high-performance lasers, amplifiers, modulators and photodetectors. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a device according