# US 12,007,605 B2 · Monolithically-integrated, polarization-independent circulator

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- Number: US 12,007,605 B2
- Document ID: US12007605B2
- Status: Granted
- Kind: B2
- Application number: 17/314,991
- Filed: 2021-05-07
- Published: 2021-12-30
- Granted: 2024-06-11
- Earliest claimed: 2011-06-08
- Assignees: Skorpios Technologies, Inc.
- Applicants: Skorpios Technologies, Inc.
- Inventors: Majid Sodagar; Wenyi Wang; Changyi Li; Guoliang Li; Murtaza Askari; Yi Wang; John Dallesasse; Stephen B. Krasulick
- Web page: https://patentgrep.com/patent/US12007605B2

## CPC

- G02B 6/2746: {comprising non-reciprocal devices, e.g. isolators, FRM, circulators, quasi-isolators (magneto-optic non-reciprocal devices G02F1/093)}
- G02B 6/1228: {Tapered waveguides, e.g. integrated spot-size transformers (for coupling with fibres G02B6/305)}
- G02B 6/126: using polarisation effects {(G02B6/1226 takes precedence)}
- G02F 1/093: {used as non-reciprocal devices, e.g. optical isolators, circulators (G02F1/0955 takes precedence)}
- G02B 2006/1215: {Splitter}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS

## Abstract

A polarization-independent, optical circulator is formed in silicon photonics. The polarization-independent, optical circulator uses an optical splitter having two couplers and two waveguides joining the two couplers. One of the two waveguides is thinner than the other to create a large effective index difference between TE and TM modes transmitted through the one waveguide. Polarization rotators, including reciprocal and/or non-reciprocal rotators, are further used to create the optical circulator.

## Claims

### Claim 1

A device comprising:
a laser configured to emit light;
a first splitter comprising:
a first coupler configured to receive light from the laser at a first port and split light received at the first port into a first waveguide and a second waveguide;
a second coupler configured to:
receive light from the first waveguide and from the second waveguide; and
transmit light received from the first coupler by the first waveguide and
the second waveguide to propagate along a first path and along a second path;
the first waveguide; and
the second waveguide;
a second splitter configured to:
receive light from the first path and from the second path; and
combine light received from the first path and from the second path to exit a second port;
a first non-reciprocal polarization rotator in the first path between the first splitter and the second splitter;
a first reciprocal polarization rotator in the first path between the first splitter and the second splitter;
a second non-reciprocal polarization rotator in the second path between the first splitter and the second splitter;
a second reciprocal polarization rotator in the second path between the first splitter and the second splitter; and
a semiconductor substrate, wherein the laser, the first coupler, the second coupler, the first waveguide, the second waveguide, the second splitter, the first non-reciprocal polarization rotator, the first reciprocal polarization rotator, the second non-reciprocal polarization rotator, and the second reciprocal polarization rotator are integrated on the semiconductor substrate, wherein:
the first waveguide has a maximum cross-sectional width that is less than a maximum cross-sectional width of the second waveguide;
the maximum cross-sectional width of the first waveguide and the maximum cross-sectional width of the second waveguide are measured in a direction orthogonal to a direction of beam propagation and halfway between the first coupler and the second coupler; and
the maximum cross-sectional width of the first waveguide is less than a height of the first waveguide.

### Claim 2 (depends on 1)

The device of claim 1, further comprising a third port, wherein:
the third port is part of the first coupler; and
light entering the second port, during operation, is transmitted to the third port.

### Claim 3 (depends on 1)

The device of claim 1, wherein:
a height of the second waveguide and the height of the first waveguide are between 1.3 and 3 microns;
the device further comprises a third port, wherein the third port is part of the first coupler, and light entering the second port, during operation, is transmitted to the third port;
the first path comprises a crystalline semiconductor waveguide;
the first coupler and the second coupler are multi-mode interference couplers; and
the first non-reciprocal polarization rotator comprises garnet.

### Claim 4 (depends on 1)

The device of claim 1, wherein the first path comprises a crystalline semiconductor waveguide.

### Claim 5 (depends on 1)

The device of claim 1, wherein the first coupler and the second coupler are multi-mode interference couplers.

### Claim 6 (depends on 1)

The device of claim 1, wherein the second splitter comprises two couplers and two waveguides optically connecting the two couplers.

### Claim 7 (depends on 1)

The device of claim 1, wherein the first coupler is a 1×2 coupler.

### Claim 8 (depends on 1)

The device of claim 1, wherein the first non-reciprocal polarization rotator comprises garnet.

### Claim 9 (depends on 8)

The device of claim 8, wherein the garnet is integrated on the semiconductor substrate by being in a pit of a silicon-on-insulator (SOI) wafer.

### Claim 10 (depends on 1)

The device of claim 1, wherein the semiconductor substrate is silicon.

### Claim 11

A method for an optical isolator and/or circulator, the method comprising:
receiving light at a first port from a laser, wherein the first port is part of a first coupler, wherein:
the first coupler is part of a first splitter; and
the first splitter comprises the first coupler, a second coupler, a first waveguide between the first coupler and the second coupler, and a second waveguide between the first coupler and the second coupler, wherein:
the first waveguide has a maximum cross-sectional width that is less than a maximum cross-sectional width of the second waveguide;
the maximum cross-sectional width of the first waveguide and the maximum cross-sectional width of the second waveguide are measured in a direction orthogonal to a direction of beam propagation and halfway between the first coupler and the second coupler; and
the maximum cross-sectional width of the first waveguide is less than a height of the first waveguide;
splitting, using the first coupler, received light from the first port into the first waveguide and the second waveguide;
receiving, at the second coupler, light from the first waveguide and the second waveguide;
transmitting light, received by the second coupler, into a first path and a second path, wherein:
a first non-reciprocal polarization rotator is in the first path between the first splitter and a second splitter;
a first reciprocal polarization rotator is in the first path between the first splitter and the second splitter;
a second non-reciprocal polarization rotator is in the second path between the first splitter and the second splitter;
a second reciprocal polarization rotator is in the second path between the first splitter and the second splitter;
receiving light from the first path and the second path, at the second splitter, wherein the laser, the first coupler, the second coupler, the first waveguide, the second waveguide, the second splitter, the first non-reciprocal polarization rotator, the first reciprocal polarization rotator, the second non-reciprocal polarization rotator, and the second reciprocal polarization rotator are integrated on a semiconductor substrate; and
combining, at the second splitter, light received from the first path and from the second path to exit a second port.

### Claim 12 (depends on 11)

The method of claim 11, wherein:
a height of the second waveguide and the height of the first waveguide are between 1.3 and 3 microns.

### Claim 13 (depends on 11)

The method of claim 11, wherein:
the first non-reciprocal polarization rotator comprises garnet; and
the garnet is integrated on the semiconductor substrate in a pit of a silicon-on-insulator (SOI) wafer.

### Claim 14 (depends on 11)

The method of claim 11, further comprising a third port, wherein:
the third port is part of the first coupler; and
the method further comprises transmitting light received at the second port to the third port.

### Claim 15

A device for an optical isolator and/or circulator, the device comprising:
a laser;
a first splitter comprising:
a first coupler configured to receive light from the laser at a first port and split light received at the first port into a first waveguide and a second waveguide;
a second coupler configured to:
receive light from the first waveguide and from the second waveguide; and
transmit light received from the first coupler by the first waveguide and the second waveguide to propagate along a first path and along a second path;
the first waveguide; and
the second waveguide; and
a second splitter configured to:
receive light from the first path and from the second path; and
combine light received from the first path and from the second path to exit a second port, wherein:
the first waveguide has a maximum cross-sectional width that is less than a maximum cross-sectional width of the second waveguide;
the maximum cross-sectional width of the first waveguide and the maximum cross-sectional width of the second waveguide are measured in a direction orthogonal to a direction of beam propagation and halfway between the first coupler and the second coupler; and
the maximum cross-sectional width of the first waveguide is less than a height of the first waveguide.

### Claim 16 (depends on 15)

The device of claim 15, wherein the laser, the first coupler, the second coupler, the first waveguide, the second waveguide, and the second splitter are integrated on a semiconductor substrate.

### Claim 17 (depends on 15)

The device of claim 15, wherein the first waveguide is crystalline silicon and the second waveguide is crystalline silicon.