# US 2019/0170941 A1 · Adiabatically coupled photonic systems with vertically tapered waveguides

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- Number: US 2019/0170941 A1
- Document ID: US20190170941A1
- Status: Published application
- Kind: A1
- Application number: 16/212,355
- Filed: 2018-12-06
- Published: 2019-06-06
- Earliest claimed: 2017-12-06
- Assignees: Finisar Corporation
- Applicants: Finisar Corporation
- Inventors: Daniel Mahgerefteh; Jin-Hyoung Lee; Bernd Huebner
- Web page: https://patentgrep.com/patent/US20190170941A1

## CPC

- G02B 6/1228: {Tapered waveguides, e.g. integrated spot-size transformers (for coupling with fibres G02B6/305)}
- G02B 6/12002: {Three-dimensional structures}
- G02B 6/12004: {Combinations of two or more optical elements}
- G02B 6/305: {and having an integrated mode-size expanding section, e.g. tapered waveguide}
- G02B 6/1223: {high refractive index type, i.e. high-contrast waveguides}
- G02B 2006/12061: {Silicon}
- G02B 2006/12147: {Coupler}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

In an example, a photonic system and method include a photonic integrated circuit (PIC) including a silicon (Si) waveguide and a first silicon nitride (SiN) waveguide. The system also includes an interposer including a second SiN waveguide including vertical tapers on the second SiN waveguide by increasing a thickness of the second SiN waveguide in a direction toward the first SiN waveguide to allow an adiabatic optical mode transfer and decreasing the thickness of the second SiN waveguide in a direction away from the first SiN waveguide to inhibit the optical mode transfer.

## Claims

### Claim 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.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 1)

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

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 1)

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.

### Claim 6 (depends on 5)

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.

### Claim 7 (depends on 6)

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.

### Claim 8 (depends on 1)

The photonic system of claim 1, wherein,
the first SiN waveguide includes a tapered end having a first effective refractive index n1; and
the second and third SiN waveguides together form first and second low-index contrast portions of effective index n2 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 n3 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,
wherein n3 approaches n1, and n3>n2, and the tapered end of the first SiN waveguide is optically coupled to the third high-index contrast portion of the interposer.

### Claim 9

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.

### Claim 10 (depends on 9)

The photonic system of claim 9, further comprising:
a third SiN waveguide, 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.

### Claim 11 (depends on 10)

The photonic system of claim 10, 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.

### Claim 12 (depends on 10)

The photonic system of claim 10, 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.

### Claim 13 (depends on 10)

The photonic system of claim 10, wherein the second SiN waveguide vertically tapers between a thickness of about 20 nm to about 250 nm.

### Claim 14 (depends on 10)

The photonic system of claim 10, wherein the second SiN waveguide and the third SiN waveguide are separated by a distance of about 1 μm.

### Claim 15

A method, comprising:
propagating an optical signal in a silicon (Si) waveguide including a first laterally tapered end;
firstly optically coupling the optical signal from the first laterally tapered end of the Si waveguide to a first silicon nitride (SiN) waveguide including a second laterally tapered end; and
secondly optically coupling the optical signal from the second laterally tapered end of the first SiN waveguide to a second SiN waveguide in response to the second SiN waveguide being vertically tapered to an increased thickness near the second laterally tapered end of the first SiN waveguide.

### Claim 16 (depends on 15)

The method of claim 15, further comprising thirdly optically coupling the optical signal from the second SiN waveguide to a third SiN waveguide in response to the second SiN waveguide being vertically tapered to a decreased thickness away from the first SiN waveguide.

### Claim 17 (depends on 16)

The method of claim 16, wherein the second SiN waveguide and the third SiN waveguide are configured as high-contrast waveguides for optical mode transfer with the second SiN waveguide having a thickness of about 250 nm and the third SiN waveguide having a thickness of about 20 nm and separated by a distance of about 1 μm.

### Claim 18 (depends on 16)

The method of claim 16, further comprising fiber mode coupling the optical signal from the second SiN waveguide and the third SiN waveguide to a fiber.

### Claim 19 (depends on 18)

The method of claim 18, wherein the second SiN waveguide and the third SiN waveguide are configured as low-contrast waveguides for inhibiting optical mode transfer, the second and third SiN waveguides each having a thickness of about 20 nm, and spaced apart by about 1 μm.

### Claim 20 (depends on 19)

The method of claim 19, further comprising overlapping the fiber with the second SiN waveguide and the third SiN waveguide by a distance of about 3 μm.