# US 11,451,308 B1 · Quantum communications system having pulses divided into time bins and associated methods

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- Number: US 11,451,308 B1
- Document ID: US11451308B1
- Status: Granted
- Kind: B1
- Application number: 17/453,657
- Filed: 2021-11-05
- Granted: 2022-09-20
- Earliest claimed: 2021-11-05
- Assignees: Eagle Technology, LLC
- Applicants: Eagle Technology, LLC
- Inventors: Victor G. Bucklew; Samuel H. Knarr; Samuel Nunez; Cypryan T. Klish; James Drakes
- Web page: https://patentgrep.com/patent/US11451308B1

## CPC

- H04B 10/70: Photonic quantum communication
- H04B 10/524: Pulse modulation
- H04B 10/60: Receivers
- H04L 9/0852: {Quantum cryptography (transmission systems employing electromagnetic waves other than radio waves, e.g. light, infrared H04B10/00; wavelength-division multiplex systems H04J14/02; WDM arrangements H04J14/03)}
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A quantum communications system may include a transmitter node, a receiver node, and a quantum communications channel coupling the transmitter node and receiver node. The transmitter node may include a pulse transmitter and a pulse divider downstream therefrom. The pulse divider may be configured to divide each pulse having a plurality of X photons into a plurality of Y time bins with Y>X. The receiver node may include a pulse recombiner and a pulse receiver downstream from the pulse recombiner.

## Claims

### Claim 1

A quantum communications system comprising:
a transmitter node, a receiver node, and a quantum communications channel coupling the transmitter node and receiver node;
the transmitter node comprising a pulse transmitter and a pulse divider downstream therefrom, the pulse divider configured to divide each pulse having a plurality of X photons into a plurality of Y time bins with Y>X, wherein the pulse divider comprises a plurality of staged birefringent crystals; and
the receiver node comprising a pulse recombiner and a pulse receiver downstream from the pulse recombiner.

### Claim 2 (depends on 1)

The quantum communications system of claim 1 wherein the pulse receiver comprises a detector configured to detect a number of photons greater than 100 photons.

### Claim 3 (depends on 1)

The quantum communications system of claim 1 wherein the pulse receiver comprises a detector configured to detect a number of photons less than 10,000 photons.

### Claim 4 (depends on 1)

The quantum communications system of claim 1 wherein the pulse recombiner comprises a plurality of staged birefringent crystals.

### Claim 5 (depends on 1)

The quantum communications system of claim 1 wherein the pulse transmitter is configured to generate temporally modulated photons.

### Claim 6 (depends on 1)

The quantum communications system of claim 1 wherein the quantum communications channel comprises at least one of a fiber optic communications channel, a free space optic communications channel, and an underwater optic communications channel.

### Claim 7 (depends on 1)

The quantum communications system of claim 1 wherein the pulse transmitter is configured to generate orthogonally modulated photons.

### Claim 8 (depends on 1)

The quantum communications system of claim 1 wherein the pulse transmitter is configured to generate a bit stream of quantum pulses in a quantum key distribution (QKD) protocol.

### Claim 9

A quantum communications system comprising:
a communications system; and
a quantum key distribution (QKD) system operable with the communications system and comprising
a transmitter node, a receiver node, and a quantum communications channel coupling the transmitter node and receiver node,
the transmitter node comprising a pulse transmitter and a pulse divider downstream therefrom, the pulse divider configured to divide each pulse having a plurality of X photons into a plurality of Y time bins with Y>X, and
the receiver node comprising a pulse recombiner and a pulse receiver downstream therefrom, wherein the pulse divider comprises a first plurality of staged birefringent crystals; and wherein the pulse recombiner comprises a second plurality of staged birefringent crystals.

### Claim 10 (depends on 9)

The quantum communications system of claim 9 wherein the pulse receiver comprises a detector configured to detect a number of photons greater than 100 photons.

### Claim 11 (depends on 9)

The quantum communications system of claim 9 wherein the pulse receiver comprises a detector configured to detect a number of photons less than 10,000 photons.

### Claim 12 (depends on 9)

The quantum communications system of claim 9 wherein the pulse transmitter is configured to generate temporally modulated photons.

### Claim 13 (depends on 9)

The quantum communications system of claim 9 wherein the quantum communications channel comprises at least one of a fiber optic communications channel, a free space optic communications channel, and an underwater optic communications channel.

### Claim 14 (depends on 9)

The quantum communications system of claim 9 wherein the pulse transmitter is configured to generate orthogonally modulated photons.

### Claim 15 (depends on 9)

The quantum communications system of claim 9 wherein the pulse transmitter is configured to generate a bit stream of quantum pulses in a quantum key distribution (QKD) protocol.

### Claim 16

A method of operating a quantum communications system comprising a transmitter node, a receiver node, and a quantum communications channel coupling the transmitter node and receiver node, the method comprising:
operating the transmitter node to generate quantum pulses at a pulse transmitter and dividing the quantum pulses at a pulse divider to divide each pulse having a plurality of X photons into a plurality of Y time bins with Y>X; and
operating the receiver node to recombine the divided quantum pulses at a pulse recombiner, and receiving the recombined pulses at a pulse receiver, wherein the pulse divider comprises a first plurality of staged birefringent crystals, and wherein the pulse recombiner comprises a second plurality of staged birefringent crystals.

### Claim 17 (depends on 16)

The method of claim 16 wherein the pulse receiver comprises a detector configured to detect a number of photons greater than 100 photons.

### Claim 18 (depends on 16)

The method of claim 16 wherein the pulse receiver comprises a detector configured to detect a number of photons less than 10,000 photons.

### Claim 19 (depends on 16)

The method of claim 16 wherein the quantum communications channel comprises at least one of a fiber optic communications channel, a free space optic communications channel, and an underwater optic communications channel.

### Claim 20 (depends on 16)

The method of claim 16 wherein the pulse transmitter is configured to generate orthogonally modulated photons.

### Claim 21 (depends on 16)

The method of claim 16 wherein the pulse transmitter is configured to generate a bit stream of quantum pulses in a quantum key distribution (QKD) protocol.