# US 2019/0171029 A1 · Integrated optical circulator enabling polarization diversity

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- Number: US 2019/0171029 A1
- Document ID: US20190171029A1
- Status: Published application
- Kind: A1
- Application number: 15/975,268
- Filed: 2018-05-09
- Published: 2019-06-06
- Earliest claimed: 2017-12-06
- Assignees: Google Inc.
- Applicants: Google LLC
- Inventors: Ryohei Urata; Lieven Verslegers; Hong Liu; Daoyi Wang
- Web page: https://patentgrep.com/patent/US20190171029A1

## CPC

- G02B 27/283: {used for beam splitting or combining}
- G02B 5/3083: {Birefringent or phase retarding elements (G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001)}
- G02B 6/105: {having optical polarisation effects}
- G02B 6/126: using polarisation effects {(G02B6/1226 takes precedence)}
- G02B 6/272: {comprising polarisation means for beam splitting and combining}
- G02B 6/2773: {Polarisation splitting or combining}
- G02B 27/0977: {Reflective elements}
- G02F 1/093: {used as non-reciprocal devices, e.g. optical isolators, circulators (G02F1/0955 takes precedence)}
- G02B 6/27: with polarisation selective and adjusting means
- G02B 6/2746: {comprising non-reciprocal devices, e.g. isolators, FRM, circulators, quasi-isolators (magneto-optic non-reciprocal devices G02F1/093)}
- G02B 6/2766: {Manipulating the plane of polarisation from one input polarisation to another output polarisation, e.g. polarisation rotators, linear to circular polarisation converters}
- G02B 6/4213: {the intermediate optical elements being polarisation selective optical elements (G02B6/27 takes precedence)}
- G02B 6/4246: {Bidirectionally operating package structures}
- 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 photonic integrated circulator can be fabricated by including a plurality of polarizing beam splitters and optical polarization rotators such that two copies of the optical signal are output at a receiver in substantially aligned polarization states. The circulator can be used for facilitating bi-directional communications between photonic integrated circuit devices, which are inherently polarization sensitive, while reducing signal loss.

## Claims

### Claim 1

An integrated optical circulator enabling polarization diversity, the integrated optical circulator comprising:
a first port configured to receive a first optical signal;
a second port configured to transmit the first optical signal received at the first port and also configured to receive a second optical signal;
a first polarization beam splitter configured to:
receive the second optical signal;
split the second optical signal into a first optical signal component and a second optical signal component;
direct the first optical signal component towards a first reflective surface wherein the first reflective surface is configured to further direct the first optical signal component to pass through a first optical polarization rotator; and
direct the second optical signal component through a second optical polarization rotator;
a second polarization beam splitter configured to receive the second optical signal component after the second optical signal component passes through the second optical polarization rotator, and direct the second optical signal component towards a second reflective surface, the second reflective surface directing the second optical signal component towards a third optical polarization rotator;
a third port configured to transmit the first optical signal component of the second optical signal after it passes through the first optical polarization rotator, the third port transmitting the first optical signal component at a first polarization state; and
a fourth port configured to transmit the second optical signal component of the second optical signal after it passes through the third optical polarization rotator, the fourth port transmitting the second optical signal component at a second polarization state substantially aligned with the first polarization state.

### Claim 2 (depends on 1)

The integrated optical circulator of claim 1 wherein at least one optical polarization rotator is a half-wave plate.

### Claim 3 (depends on 1)

The integrated optical circulator of claim 1, wherein the first optical polarization rotator and the second optical polarization rotator are different portions of a continuous optical polarization rotator.

### Claim 4 (depends on 1)

The integrated optical circulator of claim 1, wherein:
a fifth port is configured to receive a third optical signal;
a sixth port is configured to transmit the third optical signal received at the fifth port and also configured to receive a fourth optical signal;
the first polarization beam splitter is further configured to:
receive the fourth optical signal;
split the fourth optical signal into a third optical signal component and a fourth optical signal component;
direct the third optical signal component towards the first reflective surface wherein the first reflective surface is configured to further direct the third optical signal component to pass through the first optical polarization rotator; and
direct the fourth optical signal component through the second optical polarization rotator;
the third polarization beam splitter is configured to receive the fourth optical signal component after the fourth optical signal component passes through the second optical polarization rotator, and direct the fourth optical signal component towards the second reflective surface, the second reflective surface directing the fourth optical signal component towards a third optical polarization rotator;
a seventh port configured to transmit the third optical signal component after it passes through the first optical polarization rotator, the seventh port transmitting the third optical signal component at the first polarization state; and
an eighth port configured to transmit the fourth optical signal component after it passes through the third optical polarization rotator, the eighth port transmitting the fourth optical signal component at the second polarization state.

### Claim 5 (depends on 1)

The integrated optical circulator of claim 1, wherein at least one additional optical polarization rotator is optically coupled to either the first optical polarization rotator, the second optical polarization rotator, or both.

### Claim 6 (depends on 5)

The integrated optical circulator of claim 5, wherein the at least one additional optical polarization rotator is a Faraday rotator.

### Claim 7 (depends on 1)

The integrated optical circulator of claim 1, wherein the third reflective surface is a polarizing beam splitter.

### Claim 8 (depends on 1)

The integrated optical circulator of claim 1, wherein the fourth reflective surface is a polarizing beam splitter

### Claim 9 (depends on 1)

The integrated optical circulator of claim 1, wherein the first polarization state and second polarization state are p-polarizations.

### Claim 10 (depends on 1)

The integrated optical circulator of claim 1, wherein the first transmitted signal is p-polarized.

### Claim 11 (depends on 1)

The integrated optical circulator of claim 1, wherein the first polarizing beam splitter splits the second optical signal into a first optical signal component and a second optical signal component carrying orthogonal polarizations.