Tech Briefs Magazine - June 2022 - 34

Communications
Optical De-Multiplexing Method for QKD Encryption
Space-and-wave division for quantum key distribution photon detection.
Glenn Research Center, Cleveland, OH
C
lassical laser communication gimbals
are coupled to 105um multimodal receiving
fibers for the high-power transmission
of data, fine pointing, and tracking.
These fibers cannot be used in free space
optical communication applications using
Quantum Key Distribution (QKD) since
polarization state information encoded by
QKD photons is not retained.
NASA inventors have developed a
space-and-wave (SAW) division method
to de-multiplex low energy QKD photons
from high energy free space optical transmissions.
The method exploits available
double-clad fiber optic cable with 9um
core fiber diameter and 105um 1st cladding
outer diameter.
By optimizing wavelengths used for QKD
photon and data transmission (wave division),
a focusing lens can be used to create
a diffraction pattern that focuses QKD photons
on the core and the higher energy signal
onto the 1st cladding (spatial division).
The SAW method enables de-multiplexing
of simultaneously transmitted optical
data and built-in photonic QKD encryption
keys. The method was developed
by NASA to send and receive encryptionkeys
using weak coherent pulsed light
rather than entangled photons; it can be
applied to the encryption of any free
space optical communications.
The SAW division method uses a double
clad fiber with a 9um core and a
105um 1st cladding. This arrangement
captures 1590nm wavelength QKD photons
in the core channel and a 1555.75nm
wavelength data channel in the 1st cladding.
By defining wavelength separation
between 30-40nm, a single focusing lens
can be used to focus only one wavelength
to a diffraction limited spot.
Using this method, a QKD channel is
focused to a diffraction limited spot on the
9um core of the double clad fiber. The
chosen wavelength separation generates a
defocused diffraction pattern with a hollow
center, and with remaining optical
power in concentric rings outside of the
9um core, yet inside the 105um core.
The QKD signal is directed into the
9um core, and the data channel is coupled
into the 105um secondary core for traditional
data demodulation.
There are several applications of this
technology
in
telecommunications,
aircraft-to-ground, etc.).
mercialize
including
QKD-encrypted optical data links
(satellite-to-ground,
satellite-to-satellite,
NASA is actively seeking licensees to comthis
technology. Please contact
NASA inventors have developed a space-and-wave (SAW) division method to de-multiplex low energy
QKD photons from high energy free space optical transmissions. (Image: NASA)
NASA's Licensing Concierge at Agency-PatentLicensing@mail.nasa.gov
or call at 202-3587432
to initiate licensing discussions. For
more information, visit https://technology.
nasa.gov/patent/LEW-TOPS-163.
High-Speed Communication Vouchsafed by the Laws of
Quantum Physics
A new protocol provides for much higher secure communication rates with longer distances.
Massachusetts Institute of Technology, Cambridge, MA
S
34
ecurity in encrypted communication
is a top priority because of our highly
connected and mobile society's increasing
reliance on the internet. Engineers
at Department of Electrical Engineering
and Computer Science and the Research
Laboratory of Electronics, MIT, have developed
a new protocol for high-speed
communication between two parties
with security vouchsafed by the laws of
quantum physics. The protocol can also
be used to distribute cryptographic keys,
as in quantum key distribution (QKD) at
much higher secure key rates than existing
QKD methods.
Quantum illumination (QI) is a common
encryption technique that uses
multimode entangled light beams to sewww.techbriefs.com
cure
communication against a passive
eavesdropper, who is allowed to collect
all light that is lost in propagation between
the two communicating parties.
QI faces issues that keep it from being
applicable, namely: (1) it is not secure
against an active attack in which an
eavesdropper injects their own light into
the sender to learn about the message;
Tech Briefs, June 2022
TB Communications 0622_1.indd 34
Cov
ToC
5/19/22 12:48 PM
https://technology.nasa.gov/patent/LEW-TOPS-163 http://www.techbriefs.com http://info.hotims.com/82322-850

Tech Briefs Magazine - June 2022

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