Adiabatically coupled photonic systems with vertically tapered waveguides

1. A photonic system, comprising:

a photonic integrated circuit (PIC) including a first silicon nitride (SiN) waveguide; and

an interposer including a second SiN waveguide that vertically tapers with an increasing thickness in a direction toward the first SiN waveguide to allow an adiabatic optical mode transfer between the first SiN waveguide and vertically tapers with a decreasing thickness in a direction away from the first SiN waveguide to allow an adiabatic optical mode transfer between the second SiN waveguide and a third SiN waveguide, wherein:

the first SiN waveguide includes a tapered end having a first effective refractive index n 1 ; and

the second and third SiN waveguides together form first and second low-index contrast portions of effective index n 2 at two ends, a third high-index contrast portion section between the first and second low-index contrast portions, the third high-index contrast portion having a third effective index n 3 and vertical tapers adiabatically coupling the first and second low-index contrast portions to the third high-index contrast portion between the first and second low-index contrast portions,

n 3 approaches n 1 , and n 3 >n 2 , and the tapered end of the first SiN waveguide is optically coupled to the third high-index contrast portion of the interposer.

2. The photonic system of claim 1 , further including an Si waveguide including a taper at one end to adiabatically couple light between the Si waveguide and the first SiN waveguide.

3. The photonic system of claim 1 , wherein the second SiN waveguide of the interposer terminates after decreasing in thickness.

4. The photonic system of claim 1 , wherein the first SiN waveguide includes a first lateral taper to allow an optical mode transfer between the first SiN waveguide to the second SiN waveguide.

5. The photonic system of claim 1 , wherein the third SiN waveguide is adjacent to the second SiN waveguide, the third SiN waveguide configured to allow an optical mode transfer between the second SiN waveguide and the third SiN waveguide.

6. The photonic system of claim 5 , wherein the second SiN waveguide and the third SiN waveguide are configured to facilitate optical mode transfer with the first SiN waveguide when the second SiN waveguide and the third SiN waveguide are configured as high-contrast waveguides with the second and third SiN waveguides having thicknesses of about 250 nm and 20 nm respectively, and spaced apart by about 1 μm.

7. The photonic system of claim 6 , wherein the second SiN waveguide and the third SiN waveguide are configured to inhibit optical mode transfer with the first SiN waveguide when the second SiN waveguide and the third SiN waveguide are configured as low-contrast waveguides with the second and third SiN waveguides each having a thickness of about 20 nm, and spaced apart by about 1 μm.

8. A photonic system, comprising:

a silicon (Si) waveguide including a first lateral taper on a terminal end, the Si waveguide configured to propagate an optical signal in an optical mode;

a first silicon nitride (SiN) waveguide including a non-tapered portion configured to adiabatically optically couple the optical signal from the first lateral taper of the Si waveguide, the first SiN waveguide further including a second lateral taper on a terminal end; and

a second SiN waveguide including a first vertical taper to increase a thickness of the second SiN waveguide to adiabatically couple the optical signal between the first SiN waveguide and the second SiN waveguide, the first SiN waveguide terminating before the second lateral taper, the second SiN waveguide further including a second vertical taper to decrease the thickness of the second SiN waveguide and

a third SiN waveguide, wherein:

the first SiN waveguide includes a tapered end having a first effective refractive index n 1 ; and

the second and third SiN waveguides together form first and second low-index contrast portions of effective index n 2 at two ends, a third high-index contrast portion section between the first and second low-index contrast portions, the third high-index contrast portion having a third effective index n 3 and vertical tapers adiabatically coupling the first and second low-index contrast portions to the third high-index contrast portion between the first and second low-index contrast portions,

n 3 approaches n 1 , and n 3 >n 2 , and the tapered end of the first SiN waveguide is optically coupled to the third high-index contrast portion.

9. The photonic system of claim 8 ,

wherein the second SiN waveguide and the third SiN waveguide are configured to facilitate optical mode transfer with the first SiN waveguide when the second SiN waveguide and the third SiN waveguide are configured as high-contrast waveguides.

10. The photonic system of claim 9 , wherein the second SiN waveguide and the third SiN waveguide are configured to inhibit optical mode transfer with the first SiN waveguide when the second SiN waveguide and the third SiN waveguide are configured as low-contrast waveguides.

11. The photonic system of claim 9 , wherein the Si waveguide and the first SiN waveguide are configured as part of a photonic integrated circuit (PIC) and the second SiN waveguide and the third SiN waveguide are configured as part of an interposer for coupling with the PIC.

12. The photonic system of claim 9 , wherein the second SiN waveguide vertically tapers between a thickness of about 20 nm to about 250 nm.

13. The photonic system of claim 9 , wherein the second SiN waveguide and the third SiN waveguide are separated by a distance of about 1 μm.