1White Paper

JUN 2020

QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

QuPC® Connectors Optical Interconnect
for Quantum Networks
Dr. Bernard Lee, Dr. Richard Pitwon

2QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS3QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

QuPC® Connectors Optical Interconnect forQuantum Networks
Contents

4Introduction

5

Principles of Quantum Superposition and Entanglement

6Quantum Key Distribution (QKD)

7QuPC Connectors for QKD Applications

8Material

9Manufacturing

11 SENKO QuPC Connectors
12 Summary
13 Reference
13 Biography

4QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

Introduction
Data is an important asset to any organization
across the globe. Investment in Information Technology(IT) security systems is increasing with more organizations
adopting Cloud solutions to manage everyday operations
from data repositories to running virtual desktops. Some of thekey priorities for organizations are protection of intellectual
property, critical infrastructure, customer information, andcapital controls. Cyber-attacks and data breaches are expected
to increase with the expansion of computer networks. Oneof the most difficult GPSms of data security breach todetect is eavesdropping, also known as sniffing orsnooping BUtacks. Eavesdropping occurs when an attacker
intercepts a weakly secured connection between a clientand server and taps into the secure traffic passed between
them. The attacker can then install a network monitoring
software in any device in the network between thetransmitting device and the receiving device. Device
monitoring within a larger network becomes harder todetect. There are many data security approaches such asdata encryption, encryption key management, andtokenization, but as these means of safeguarding
network data become more sophisticated, so too dothe means of intercepting JU *O QBSUJDVMBS  UIFFNFSHFODF PGRVBOUVN DPNQVUFST  XIJDI BSF FYQFDUFE
to be able to solve mathematical problems thatcannot be solved using conventional computers,
inevitably presents a significant threat to cybersecurity and attacks the foundations oftoday’s
cryptography. Quantum Key Distribution (QKD) isanewmethodofsecuring encryption andauthentication by exploiting the quantum effects of“superposition” and “entanglement” to enable theexchange of secret symmetric cryptographic
keys,
which
aresecure,evenagainst
eavesdropping
attempts powered by quantum computing.

As the technology eco-system for QKD, quantum computing
and quantum measurement continues to grow at anaccelerated rate, international standards will soon need to
be introduced to define conditions for quantum networks.
The International Telecommunication Union (ITU) has alreadystarted to address the stringent requirements for future
quantum networks; a new ITU standard, “ITU Y.3800 - Overviewon networks supporting quantum key distribution”, describes
the basic conceptual structures of QKD networks as thefirst in a series of emerging ITU standards on network andsecurity aspects of quantum information technologies. Other
international standards organizations, such as the IEC and ISO,are expected to follow suit over the coming years.

5QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

Principles of Quantum Superposition and Entanglement
Particles (e.g. photons or electrons) have physicalproperties such as position, spin, polarization, and momentum,
which are described by a mathematical construct called a“wave function”. According to quantum mechanics, prior toobservation, a particle may have many different states atthe same time, thus existJOH in a state of “superposition”. It
is only when the particle is observed throughmeasurement, that the particle’s wave function “collapses”
to reveal a single state. For example, an unobserved particle
could have a balanced superposition of both a clockwise
and anti-clockwise spin, that is to say there will be a 50%
chance that the particle will have one state or the otherwhen measured. Once measured, however, subsequent
measurements (in an ideal system without otherdisruptive factors) will always reveal the same state,
therefore the act of observing has caused its wave
function to collapse into one of the states.

Particles can become “entangled” when a pair, or group, ofparticles is generated or share the same special proximity ina way that their quantum states become linked. For example,
if you have a pair of entangled particles that are generated
with the condition that their total spin is zero, and one ofthe particles is later measured to have a clockwise spin, then,from that immediate point, the other entangled particle,
if measured, would always be revealed to have a counterclockwise spin, regardless of how far apart these two particles
may be separated. Therefore the wave function of theentangled particle system would be said to have collapsed
with the measurement of the first particle. This propertyof entanglement can be used to create extremely securecommunication links or form an integral part of a quantum
computer or quantum measurement network.

6QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

Quantum Key Distribution (QKD)
Quantum Key Distribution (QKD) provides pairs (E91 protocol) to derive a random string of numbers
procedures for generating and distributing symmetrical used to form a secure quantum key. The statistical results ofcryptographic keys with information security based on the the measured photons indicate whether the photon has been
quantum CFIBWJPS of photons. QKD is not a standalone intercepted or not.
security feature, but a complementary technology andservice for communication networks. Keys generated by QKD The main challenge of introducing QKD into existing
modules that implement the QKD protocol can be used by communication networks is the requisite change to the
any cryptographic applications that use symmetric keys such network infrastructure and cryptographic protocols. QKD
as One Time Pad (OTP), Hash Based Message Authentication technologies have unique features and restrictions, such as
Mode (HMAC), and Advanced Encryption Standard (AES).QKD the requirement for point-to-point links and ultra-low loss,
can exploit either the measurement of single photons “quantum” channels.
(BB84 protocol) or the measurement of entangled photon

Cipher Text
Plain Text

Plain Text

Encryptor

Decryptor

Application LinkKeyKeyClassic Channel

QKD Module

Quantum Channel

QKD Module

QKD Link
The basic elements of a QKD communication system are the transmitter and receiver (QKD modules), and a QKD link between
them comprising a Classical Channel and a Quantum Channel. The Classical Channel is used for data exchange between theQKD modules, while the Quantum Channel transmits quantum signals such as single or entangled photons, from which thecryptographic keys are derived.

7QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

QuPC Connectors for QKD Applications
Over the 2020’s, QKD, quantum computing and quantum measurement applications are expected to gain
traction. Central to these applications is the requirement to send single or entangled photons over optical networks
without“decoherence”. Decoherence, in this respect, refers to the collapse of the photon wave function, and can be caused bydirect measurement or by disruption to the photon propagation due to aberrations (imperfections) in the optical conduit(optical fibeS and connectors). QKD protocols try and account for decoherence due to environmental factors, such as poor
quality of the optical fibeS and imperfections in the optical connector, however if these are too great, QKD becomes lessuseful. The chances of transmitting a photon from transmitter to receiver without disruption, absorption or decoherence
through other means, go down as the length of the Quantum Channel increases and the quality of the Quantum Channel (i.e.
optical fibeS and connectors) decreases.
The emerging field of quantum communications is therefore expected to fuel demand for a new generation of lower loss
optical cables and connectors, which will allow larger proportions of single or entangled photons to propagate over opticalnetworks without decoherence, thus improving the efficiency of the quantum optical network. Given that the power of asingle photon can be of the order of -100 dBm, transmission over longer Quantum Channel distances represents a
considerable challenge and thus the optical losses in the Quantum Channel must be minimized. To BEESFTT this, SENKO hasdeveloped a new grade of connector that surpasses even the most stringent IEC connector grade. SENKO’s “QuPC” Connector
exhibits insertion and return losses similar to a fusion splice.

Insertion LossReturn Loss

≤ 0.1dB average≤ 0.2dB max
in 97% of splices≥ 60dB

Insertion & Return Loss of Fusion Splices as per IEC Standards IEC 61300-3-6 and IEC 61300-3-7
The two main areas of improvement required to increase connector performance are the material quality andmanufacturing process.

8QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

MaterialThe coherent single or entangled photon
string is transmitted through an optical fiber network. This
makes the optical fiber itself an important factor in
improving the connector quality. Light does notpropagate through the whole optical fiber, but only
through the core, therefore the relative dimensions of thecore and cladding of the optical fiber will have a big impact
on the connector quality. There are three main parametersthat must be tightly controlled: 1) the core-cladding
concentricity, 2) core ovality, and 3) cladding ovality.
The core-cladding concentricity is the measure of how
symmetrically central the position of the core is with respectto the cladding. The deviation of fiber core from the center ofthe cladding is known as the core-cladding concentricity error,
which all fibers exhibit, to some degree. In order to produce
a QuPC Connector, this error must be minimized. Core ovality
and cladding ovality is the degree of deviation of the core andcladding from being a perfect circle. An oval core will cause
imperfect core connections, which will increase insertion loss
and back reflection, while an oval cladding will cause highferrule concentricity error.
The ferrule is the part of an optical connector, which holds
the optical fiber in place and is physically mated to anotherferrule to make a continuous pathway for light to pass fromUIFDPSFPGPOFGJCFSUPUIFDPSFPGBOPUIFS. The concentricityof a ferrule is the measure of how symmetrically central theposition of the ferrule hole (or bore) center is relative to its
circumference. It is also crucial to minimize the size of theferrule hole diameter. A larger hole will cause a highvariability in the position of the optical fiber, which will thenlead to increased fiber core misalignment. The diameter of aSingle Mode optical fiber is 125μm, thus the ferrule hole must
be reduced to a diameter that is as close to the fiber diameteras possible accounting for tolerances and additional space for
epoxy adhesive to secure the optical fiber.

Core and Cladding Concentricity and Ovality

Perfect Ferrule Concentricity

Ferrule Concentricity Error

Large ferrule holediameter

Minimized ferrule holediameter9QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

Manufacturing
Even with high quality optical fiber and ferrule components with tight tolerances, the connector manufacturing
processes must also be tightly controlled to produce high quality connectors.
One of the connector manufacturing processes is the mixing of epoxy and curing process. There are multiple controlled steps toensure proper management, application, and curing.

STORAGE

Epoxy has a shelf life and must be stored in a specific temperature range depending on the type of epoxy
used.

MIXING

Most epoxy used is a two-part mixture where the correct ratio must be used. The mixing process must be
controlled to eliminate any air bubbles because they will expand during the curing process, which cause
imperfect fiber to ferrule adhesion.

APPLICATION

Once the epoxy is mixed, it has a short pot life where it must be used as it will start to crystalize. Using epoxy
that has started to crystalize can cause fiber microbends inside the ferrule. The right amount of epoxy must
be inserted into the ferrule hole. Too little will cause imperfect fiber to ferrule adhesion, while too much willcause an overspill onto the connector ferrule.

CURINGThe temperature range and duration of the curing process must be suitable for the type of epoxy used. A
curing temperature that is too low will result in incomplete curing while a temperature that is too high cancause air bubbles to form, both of which will lead to imperfect fiber to ferrule adhesion.

*NQSPWFNFOUTUPUIFGFSSVMFQPMJTIJOHQSPDFTTBSFEFUFSNJOFECZUIFDBSFGVMBEKVTUNFOUPGUIFQPMJTIJOHQBE MFWFMPGBQQMJFEQSFTTVSF UIFUZQFPGQPMJTIJOHGJMN BDDVSBDZPGUIFQPMJTIJOHBOHMFBOEUIFQPMJTIJOHBQFYPGDVSWBUVSF5IFTFGBDUPSTDPOUSPMUIFHSBOVMBSJUZBOETNPPUIOFTTPGUIFDPOOFDUPSFOEGBDF SFEVDFUIFBQFYPGGTFU BOEDFOUSBMJ[FUIFBQFYPGDVSWBUVSF BMMPG
XIJDITFSWFTUPSFEVDFUIFBJSHBQCFUXFFOUIFPQUJDBMGJCFSDPSFTCFJOHDPOOFDUFE
Connector end-face parameters
Apex of curvature

Axis of fiber

Apex Offset

Perfect Endface

Endface withApex Offset

Fiber undercut

Endface with
Fiber undercut

Fiber protrusion

Endface with
Fiber protrusion

As it is impossible to perfectly center the fiber core in the ferrule due to manufacturing tolerances, a connector tuning process isused to correct concentricity errors caused from using ferrules with larger hole diameters. Although the quality control measures
to improve the optical performance of SENKO’s QuPC Connector include reduction of the ferrule hole diameter, tuning canstill further improve the connector’s performance. The tuning process involves assembling the optical fiber connector whilemeasuring the signal characteristics through the connector and examining its physical properties to determine the optimal
position of the fiber and ferrule in the connector.

10QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

Grade-Q Connector

Material

FerruleFerruleconcentricity

Ferrule holediameter

Manufacturing

Polishing

FibeS

Cladding
to Coreconcentricity

Core
Ovality

FibeS toFerruleattachment

Cladding
Ovality

Polishing
Film

Polishing
Angle

Polishing
Apex ofCurvature

Epoxy&Curing

Tuning

11

QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKSSENKO QuPC Connectors
With the improvements in optical fiber, connector ferrules, and manufacturing processes, SENKO has developed
the QuPC connector, which has a DPOOFDUPSMPTTQFSGPSNBODFUIBUJTTVQFSJPSUPUIBUPGBGVTJPOTQMJDF. The connectors feature apremium super low insertion loss of less than 0.1dB, and an optical return loss of more than 80dB. This far exceeds theITU specified performance for a fusion splice. Aligned with future development of higher density connectivity, the QuPC
connectors are also available in CS and SN connector form factors.

Insertion Loss≤ 0.1dB
Return Loss≥ 80dB

SENKO’s QuPC connector range

Connector .BJOUFOBODF
As the connector end-face must be protectedagainst scratches or pitting to maintain its low-loss
performance, the recommendation is to use SENKO’s nonabrasive gel based cleaner. The use of regular connector
hygiene products such as cassette cleaners and click cleaners
require the connector end-face to be pressed against acleaning tape, which then wipes away any contamination.
However, if there are any solid contaminants present on theend-face, such as dust, the act of wiping can cause microscratches on the connector end-face.

12QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

Summary
Optical interconnect is entering a “Third Age”, in which optical links are replacing copper interconnect over evenshorter distances, due to increasing bandwidths and decreasing loss margins, now even moving into the system enclosure itself
and up to the chip. Further to that, the ICT community is now recognizing the need for Quantum Networks for QKD, quantum
computer and quantum measurement interconnect, and international standards organizations are preparing to support this.
With its QuPC optical connector range, Senko has produced an optical connector that is able to exceed the performance of an
optical fusion splice and is virtually undetectable by an OTDR. Over the next ten years, hyperscale data centers and exascale
supercomputers will increasingly incorporate quantum communication and quantum computer nodes to complement theirvalue proposition, for example through quantum computing as a service (QaaS) or hyper-secure inter-data centre interconnect.
SENKO is leading the international connector community into the era of quantum connectivity.

Hyperscale data center and supercomputer with quantum computer, communicationand sensor nodes interconnected by QuPC links

13QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS

References
1. Bub, Jeffrey, “Quantum Entanglement and Information”, The Stanford Encyclopedia of Philosophy (Spring 2019
Edition), Edward N. Zalta (ed.)
2. Ludmil Hadjiivanov and Ivan Todorov, “Quantum entanglement”, Institute for Nuclear Research and Nuclear
Energy, 13 June 2015
3. Quantum Networks, https://en.wikipedia.org/wiki/Quantum_network

Biography
Dr. Bernard HL Lee is currently the Director of Technology & Innovation at SENKO Advanced Components. He started his career in
optical communications when he was appointed as a Senior Research Office for the European Union IST project known as DAVID in
2000. In 2003, he joined Telekom Malaysia R&D where he has held various technical and management positions there including theHead of Photonic Network Research and also Head of Innovation and Communications. Bernard then joined the parent company,
Telekom Malaysia (TM) in 2010 as the Assistant General Manager of the Group Business Strategy Division where he oversees thecompany’s business direction. Bernard obtained his BICSI RCDD accreditation in 2016 and currently serve as the MalaysianCountry Chair for BICSI Southeast Asia. Bernard is also a member of the International Electrotechnical Commission (IEC)
standards subcommittee on fibeS optic interconnecting devices and passive components (SC86B) and a Chartered Engineer (CEng)
Dr. Richard Pitwon is the CEO of Resolute Photonics with more than 20 years transformational expertise in optical and photonic
system interconnect, integration and architectures for hyperscale data centre, HPC, 5G and IoT data-communications applications.
At Xyratex (2002) and then Seagate (2014), he managed internal and international, multi-million-dollar collaborative research anddevelopment programmes, skilled in building multi-disciplinary teams to deliver advanced system solutions and coordinating acrossmultiple geographies. He holds 54 patents in diverse fields, has authored over 50 peer-reviewed publications including 4
international standards and given over 70 public talks. He is the current chair of the IEC international standards subcommittee
on fibeS optic interconnecting devices and passive components (IEC SC86B) and principal UK standards expert (BSI) for opticalinterconnect, optical circuit boards, photonic integrated circuits and electronic assembly. He is a Chartered Engineer (CEng), Fellowof the IET (FIET), Fellow of the Institute of Physics (FInstP) and Senior Member of the IEEE (SIEEE).

14QUPC® CONNECTORS - OPTICAL INTERCONNECT FOR QUANTUM NETWORKS