# US 12,032,200 B2 · Trench assisted multi-core optical fiber with reduced crosstalk

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- Number: US 12,032,200 B2
- Document ID: US12032200B2
- Status: Granted
- Kind: B2
- Application number: 17/698,832
- Filed: 2022-03-18
- Published: 2023-06-29
- Granted: 2024-07-09
- Earliest claimed: 2021-12-28
- Assignees: Sterlite Technologies Limited
- Applicants: Sterlite Technologies Limited
- Inventors: Apeksha Malviya; Srinivas Reddy Munige; Janarthanan Balakrishnan; Shubham; Ranjith Balakrishnan; Anand Pandey
- Web page: https://patentgrep.com/patent/US12032200B2

## CPC

- G02B 6/02009: {Large effective area or mode field radius, e.g. to reduce nonlinear effects in single mode fibres}
- G02B 6/02042: {Multicore optical fibres}
- G02B 6/0365: {arranged - - +}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

Disclosed is a multi-core optical fiber having a plurality of cores extending parallelly along a central axis of the multi-core optical fiber. Each core of the plurality of cores is up-doped with an up-dopant. The multi-core optical fiber further has a plurality of buffer layers such that each buffer layer of the plurality of buffer layers envelop a corresponding core of the plurality of cores. Each buffer layer of the plurality of buffer layers has a predefined buffer layer thickness. The multi-core optical fiber further has a plurality of trench layers such that each trench layer of the plurality of trench layers envelops a corresponding buffer layer of the plurality of buffer layers. Each trench layer of the plurality of trench layers is down-doped with a down-dopant. The multi-core optical fiber has an inter-core crosstalk of less than −30 decibel/kilometres (dB/km) at a wavelength of 1550 nanometres (nm).

## Claims

### Claim 1

A multi-core optical fiber, comprising:
a plurality of cores extending parallelly along a central axis of the multicore optical fiber, wherein each core of the plurality of cores is up-doped with an up-dopant, wherein each core of the plurality of cores has an associated core relative refractive index RRI, wherein the core RRI of the plurality of cores is equal;
a plurality of buffer layers, wherein each buffer layer of the plurality of buffer layers envelops a corresponding core of the plurality of cores; and
a plurality of trench layers, wherein each trench layer of the plurality of trench layers envelops a corresponding buffer layer of the plurality of buffer layers,
wherein each trench layer of the plurality of trench layers is down-doped with a down-dopant
wherein each trench layer of the plurality of trench layers has a trench relative refractive index (RRI) in a range of −0.1% to −0.25%, wherein the multicore optical fiber has a cable cut-off of less than or equal to 1260 nm.

### Claim 2 (depends on 1)

The multi-core optical fiber of claim 1, wherein the plurality of cores is an even number of cores.

### Claim 3 (depends on 1)

The multi-core optical fiber of claim 1, wherein each buffer layer of the plurality of buffer layers has a predefined buffer layer radius in a range of 4 micrometers (μm) to 7 μm.

### Claim 4 (depends on 1)

The multi-core optical fiber of claim 1, wherein a core pitch between a pair of adjacent cores of the plurality of cores is in a range of 35 μm to 45 μm.

### Claim 5 (depends on 1)

The multi-core optical fiber of claim 1, wherein each buffer layer of the plurality of buffer layers and each trench layer of the plurality of trench layers has an associated a buffer RRI and a trench RRI, respectively, wherein the core RRI is greater than the buffer RRI and the buffer RRI is greater than the trench RRI.

### Claim 6 (depends on 1)

The multi-core optical fiber of claim 1, further comprising a cladding and a coating such that the cladding envelopes each trench layer of the plurality of trench layers and the coating envelops the cladding.

### Claim 7 (depends on 1)

The multi-core optical fiber of claim 1, wherein each core of the plurality of cores has a shape selected from at least one of, a circular shape, an oval shape, a hexagonal shape, and a triangular shape.

### Claim 8 (depends on 1)

The multi-core optical fiber of claim 1, wherein each buffer layer of the plurality of buffer layers has traces of an up-dopant and a down-dopant, wherein the up-dopant is associated with the plurality of cores and the down-dopant is associated with the plurality of trench layers.

### Claim 9 (depends on 1)

The multi-core optical fiber of claim 1, wherein the up-dopant is germanium and the down-dopant is fluorine.

### Claim 10 (depends on 1)

The multi-core optical fiber of claim 1, wherein an inter-core crosstalk between the plurality of cores at a wavelength of 1550 nanometres (nm) is less than −30 decibel/kilometres (dB/km).