# US 11,994,718 B2 · Mach-Zehnder interferometer with mirrored facet

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- Number: US 11,994,718 B2
- Document ID: US11994718B2
- Status: Granted
- Kind: B2
- Application number: 17/129,252
- Filed: 2020-12-21
- Published: 2021-11-25
- Granted: 2024-05-28
- Earliest claimed: 2020-05-20
- Assignees: Lumentum Operations LLC
- Applicants: Lumentum Operations LLC
- Inventors: Barthelemy Fondeur; Hiroaki Yamada; Jiamin Zheng
- Web page: https://patentgrep.com/patent/US11994718B2

## CPC

- G02B 6/2935: {Mach-Zehnder configuration, i.e. comprising separate splitting and combining means}
- G02F 1/225: in an optical waveguide structure
- G02F 1/212: {Mach-Zehnder type}
- G02B 2006/12104: {Mirror; Reflectors or the like}
- G02B 2006/12159: {Interferometer}
- G02F 2201/20: delay line
- 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

In some implementations, a Mach-Zehnder interferometer (MZI) includes a delay line arm formed in a chip and a mirrored facet formed in the chip. The delay line arm may be configured to propagate light to the mirrored facet. The mirrored facet may be configured to reflect, to the delay line arm, a percentage of the light propagated to the mirrored facet by the delay line arm.

## Claims

### Claim 1

A Mach-Zehnder interferometer (MZI), comprising:
a delay line arm formed in a chip configured to propagate light to a mirrored facet formed in the chip; and
the mirrored facet configured to reflect, to the delay line arm, a percentage of the light propagated to the mirrored facet by the delay line arm,
wherein the mirrored facet comprises a trench,
wherein a first surface of the trench is configured to reflect the percentage of the light, and
wherein a second surface of the trench, opposite the first surface, is angled non-parallel to the first surface to reflect light that passes through the trench away from the delay line arm.

### Claim 2 (depends on 1)

The MZI of claim 1, wherein the mirrored facet is an etched facet of the chip.

### Claim 3 (depends on 1)

The MZI of claim 1, wherein the mirrored facet is metallized to increase the percentage of the light reflected at the mirrored facet.

### Claim 4 (depends on 1)

The MZI of claim 1, wherein the delay line arm is positioned in a spiral configuration, and
wherein the mirrored facet is positioned within the spiral configuration.

### Claim 5 (depends on 1)

The MZI of claim 1, wherein the delay line arm is positioned in an arc configuration, and
wherein the mirrored facet is positioned at end of the delay line arm.

### Claim 6 (depends on 1)

The MZI of claim 1, wherein:
the mirrored facet has an approximately 90% reflectivity; and
another mirrored facet of a non-delay line arm of the MZI has an approximately 4% reflectivity.

### Claim 7

A Mach-Zehnder interferometer (MZI), comprising:
a first mirrored facet formed in a chip;
a second mirrored facet formed in the chip;
an optical transmission element formed in the chip;
a delay line waveguide formed in the chip that is connected between the optical transmission element and the first mirrored facet; and
a non-delay line waveguide formed in the chip that is connected between the optical transmission element and the second mirrored facet,
wherein the first mirrored facet comprises a first trench,
wherein a first surface of the first trench is configured opposite a second surface of the first trench, and
wherein the second surface is angled non-parallel to the first surface.

### Claim 8 (depends on 7)

The MZI of claim 7, wherein the first trench is through the delay line waveguide and the second mirrored facet comprises a second trench through the non-delay line waveguide.

### Claim 9 (depends on 7)

The MZI of claim 7, wherein the first mirrored facet is metallized to improve reflectivity of the first mirrored facet and the second mirrored facet is non-metallized.

### Claim 10 (depends on 7)

The MZI of claim 7, wherein:
the non-delay line waveguide includes a power balancing splitter configured to reduce a power of light returning from the non-delay line waveguide to substantially match a power of light returning from the delay line.

### Claim 11 (depends on 7)

The MZI of claim 7, wherein at least one of the first mirrored facet or the second mirrored facet is positioned at an edge of the chip.

### Claim 12 (depends on 7)

The MZI of claim 7, wherein at least one of the first mirrored facet or the second mirrored facet is positioned in the chip and within a spiral shape formed by at least one of the delay line waveguide or the non-delay line waveguide.

### Claim 13 (depends on 7)

The MZI of claim 7, wherein:
the first mirrored facet has an approximately 90% reflectivity; and
the second mirrored facet has an approximately 4% reflectivity.

### Claim 14

An optical device comprising:
a substrate;
a first Mach-Zehnder interferometer (MZI) formed on the substrate, comprising:
a first delay line arm, and
a first mirrored facet positioned at an end of the first delay line arm; and
a second MZI formed on the substrate, comprising:
a second delay line arm, and
a second mirrored facet positioned at an end of the second delay line arm,
wherein at least one of the first mirrored facet or the second mirrored facet comprises a trench,
wherein a first surface of the trench is configured opposite a second surface of the trench, and
wherein the second surface is angled non-parallel to the first surface.

### Claim 15 (depends on 14)

The optical device of claim 14, wherein:
the first mirrored facet is positioned at a first internal location on the substrate; and
the second mirrored facet is positioned at a second internal location on the substrate.

### Claim 16 (depends on 14)

The optical device of claim 14, wherein the trench is through the first delay line arm.

### Claim 17 (depends on 14)

The optical device of claim 14, wherein the trench is through the second delay line arm, and
wherein the trench includes a metal layer formed on one or more surfaces of the trench.

### Claim 18 (depends on 14)

The optical device of claim 14, wherein the second delay line arm is positioned in a spiral configuration on the substrate.

### Claim 19 (depends on 14)

The optical device of claim 14, wherein:
the first mirrored facet is configured to reflect a first percentage of light that propagates to the first mirrored facet via the first delay line arm; and
the second mirrored facet is configured to reflect a second percentage of light that propagates to the second mirrored facet via the second delay line arm,
wherein the first percent of light is different than the second percentage of light.

### Claim 20 (depends on 14)

The optical device of claim 14, wherein:
the first mirrored facet has an approximately 90% reflectivity; and
the second mirrored facet has an approximately 4% reflectivity.