Grating coupled laser for Si photonics

Patent metadata

Field	Value
Publication number	US-11435522-B2
Application number	US-201916569486-A
Country	US
Kind code	B2
Filing date	Sep 12, 2019
Priority date	Sep 12, 2018
Publication date	Sep 6, 2022
Grant date	Sep 6, 2022

Abstract

A grating coupled laser (GCL) includes an active section and a passive section. The passive section is butt coupled to the active section to form a butt joint with the active section. The active section includes an active waveguide. The passive section includes a passive waveguide, a transmit grating coupler, and a top cladding. The passive waveguide is optically coupled end to end with the active waveguide and includes a first portion and a second portion. The first portion of the passive waveguide is positioned between the second portion of the passive waveguide and the active waveguide. The transmit grating coupler is optically coupled to the passive waveguide and includes grating teeth that extend upward from the second portion of the passive waveguide. The top cladding is positioned directly above the first portion of the passive waveguide and is absent directly above at least some of the transmit grating coupler.

First claim

What is claimed is:

1. A system comprising:
a grating coupled laser (GCL), the GCL comprising:
a substrate that has a bottom and a top;
an active section positioned above the top of the substrate and being configured to generate light; and
a passive section positioned above the top of the substrate and coupled to the active section to form an interface with the active section,
wherein the active section includes an active waveguide, the active waveguide having a first cross-sectional area orthogonal to a first length of the active waveguide, wherein the passive section includes:
(i) a passive waveguide optically coupled end to end with the active waveguide and being configured to transmit the light from the active waveguide in a first horizontal direction, the passive waveguide including a first portion and a second portion, the first portion of the passive waveguide positioned between the second portion of the passive waveguide and the active waveguide, the passive waveguide having a second cross-sectional area orthogonal to a second length of the passive waveguide, the second cross-sectional area of the first portion being greater at the interface than the second cross-sectional area of the second portion, the second cross-sectional area of the first portion at the interface being greater than the first cross-sectional area of the active waveguide;
(ii) a transmit grating coupler optically coupled to the passive waveguide, the transmit grating coupler including a plurality of grating teeth that extend upward from the second portion of the passive waveguide, the transmit grating coupler being configured to transmit the light from the passive waveguide in a direction having a vertical component, the passive waveguide comprising a tapered region that tapers inward in a vertical direction moving from the interface at the first portion toward the transmit grating coupler at the second portion such that the second cross-sectional area of the passive waveguide decreases moving from the interface at the first portion toward the transmit grating coupler at the second portion in the tapered region; and
(iii) a top cladding that is positioned directly above the first portion of the passive waveguide, the top cladding terminating at a termination within the tapered region such that the top cladding is positioned directly above a part of the tapered region of the passive waveguide and is completely absent above the second portion of the tapered region of the passive waveguide;

a photonic integrated circuit (PIC) comprising a PIC waveguide and a receive grating coupler, the receive grating coupler optically coupled to the PIC waveguide, the PIC waveguide disposed underneath the grating coupled laser, the receive grating coupler being configured to receive the light from the transmit grating coupler and being configured to transmit the light in a second horizontal direction opposite to the first horizontal direction;
a sub-mount mounted on the PIC, the sub-mount having a portion of the bottom of the substrate of the GCL mounted thereon such that the GCL is configured to be individually tested and burned in before assembly on the PIC, the transmit grating coupler of the GCL extending beyond the sub-mount; and
an optical isolator mounted on the PIC adjacent the sub-mount and having a portion of the GCL mounted thereon, the optical isolator positioned between the transmit grating coupler of the GCL and the receive grating coupler of the PIC, the receive grating coupler being optically coupled to the transmit grating coupler through the optical isolator.

2. The system of claim 1 , wherein the passive waveguide comprises a quantum well intermixing (QWI) waveguide.

3. The system of claim 1 , wherein the passive waveguide comprises a same quantum well layer as the active waveguide, wherein the quantum well layer in the passive waveguide has a shifted bandgap relative to the quantum well layer in the active waveguide such that the passive waveguide is transparent to a lasing wavelength of the active waveguide.

4. The system of claim 1 , further comprising a passivation layer formed on the transmit grating coupler.

5. The system of claim 4 , wherein the top cladding comprises a p-doped top cladding and wherein the passivation layer comprises silicon dioxide (SiO 2 ) or silicon nitride (SiN).

6. The system of claim 1 , wherein:
a core of the active waveguide has the first cross-sectional area orthogonal to the first length of the active waveguide at the interface;
a core of the passive waveguide has the second cross-sectional area orthogonal to the second length of the passive waveguide at the interface; and
the first cross-sectional area of the core of the active waveguide is greater than the second cross-sectional area of the core of the passive waveguide.

7. The system of claim 6 , wherein:
the system further comprises a mirror positioned beneath the receive grating coupler; the mirror comprises a layer of silicon positioned beneath the receive grating coupler; the PIC waveguide comprises a silicon nitride waveguide;
the PIC further comprises a silicon waveguide have an input portion positioned directly beneath an output portion of the silicon nitride waveguide, the input portion of the silicon waveguide and the output portion of the silicon nitride waveguide forming an adiabatic coupler;
an optical mode size of each of the transmit grating coupler and the receive grating coupler is between 20 to 40 micrometers;
the system further comprises the submount coupled between the GCL and the PIC, the GCL coupled to a top surface of the submount and the submount coupled to a top surface of the PIC;
a portion of the GCL extends beyond the submount; and
the optical isolator is positioned adjacent to the submount and between the GCL and the PIC.

8. The system of claim 1 , further comprising a mirror positioned beneath the receive grating coupler.

9. The system of claim 8 , wherein the mirror comprises a layer of silicon positioned beneath the receive grating coupler.

10. The system of claim 1 , wherein the PIC waveguide comprises a silicon nitride waveguide, the PIC further comprising a silicon waveguide having an input portion positioned directly beneath an output portion of the silicon nitride waveguide, the input portion of the silicon waveguide and the output portion of the silicon nitride waveguide forming an adiabatic coupler.

11. The system of claim 10 , further comprising a passivation layer formed on the transmit grating coupler, wherein the top cladding comprises a p-doped top cladding and wherein the passivation layer comprises silicon dioxide (SiO2) or silicon nitride (SiN).

12. The system of claim 1 , wherein an optical mode size of each of the transmit grating coupler and the receive grating coupler is between 20 to 40 micrometers.

13. The system of claim 1 , wherein the submount is coupled between the GCL and the PIC, the GCL coupled to a top surface of the submount and the submount coupled to a top surface of the PIC.

14. The system of claim 13 , wherein a portion of the GCL extends beyond the submount; and wherein the optical isolator is positioned adjacent to the submount and between the GCL and the PIC.

15. The system of claim 1 , wherein the passive waveguide comprises a same quantum well layer as the active waveguide, wherein the quantum well layer in the passive waveguide has a shifted bandgap relative to the quantum well layer in the active waveguide such that the passive waveguide is transparent to a lasing wavelength of the active waveguide.

16. The system of claim 15 , further comprising

Assignees

• Finisar Corp
• Ii Vi Delaware Inc

Inventors

• Mahgerefteh Daniel
• Lin Shiyun
• Matsui Yasuhiro
• Wang Ding
• Young David Bruce

Classifications

• G02B2006/12121

  Laser · CPC title

• G02B6/12007

  forming wavelength selective elements, e.g. multiplexer, demultiplexer · CPC title

• G02B6/4208

  using non-reciprocal elements or birefringent plates, i.e. quasi-isolators (optical isolators per se G02F1/093, G02F1/0955) · CPC title

• H01S5/021

  Silicon based substrates · CPC title

• G02B6/34

  utilising prism or grating {(G02B6/293 takes precedence)} · CPC title