1. Introduction

Fiber-to-the-home (FTTH) networks, also known as last mile broadband segment, have the required potential to match the huge capacity of data networks with the next-generation connectivity demands. Major telecommunication investments in FTTH infrastructure are expected for the next decade, with many initiatives already launched around the globe, driven by the new bandwidth hungry services and the necessity by the operators to deploy a future-proof

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

infrastructure to maintain the quality of service (QoS). The FTTH world is taking shape and, as it does so, researchers are emphasizing much more on the network design and proposing the specific applications [1, 2]. Next-generation (NG) services to deploy a smart city concept, such as cloud computing, machine-to-machine (M2M) communications, Drone-of-Things (DoT) and Internet-of-things (IoT), require high-capacity optical fiber infrastructure as a backbone. According to the statistics, high-speed data traffic is increasing at a rate of 30–40% every year [3], around the globe. For this very reason, the M2M/IoT applications will not only benefit from fiber-optic broadband, they will require proper security and privacy in these networks. Both M2M and IoT are using the Internet to transpose the physical world onto the networked one, with many interconnected devices communicating autonomously. This bandwidth demand forces the network providers to adopt fiber-based last-mile connections and raising the challenge of moving access-network capacity to the next level, 1–10 Gbits/s data traffic to the home [4]. The researchers believe that FTTH is the key to develop a sustainable future in terms of smart city infrastructures, as a matter of fact, it is the only available state-of-the-art technology, when it comes to providing unprecedented bandwidth, multiuser data capacity, high-speed data transfer, consistency, secure communications and expendability.

involve the generation and detection of very weakly powered optical signals, ideally at the single photon level. A range of successful technologies has been implemented via the DV-QKD protocol, but typically these are quite different in terms of the equipment required from the technologies that are used in classical communications [18]. CV-QKD protocols have therefore been of attention as these protocols can make use of conventional telecommunication equipment and additional resources are not required at all. Moreover, the secure keys are randomly encoded on the quadrature of the coherent state of a light signal [19]. Such technique has the potential advantages because of its capability of attaining high secure key rate with modest

Recent Progress in the Quantum-to-the-Home Networks http://dx.doi.org/10.5772/intechopen.80396 23

During the last few years, there is an increasing trend to use CV-QKD to send encrypted data over public communication channels, as listed in Table 1. The main purpose is to adopt the classical equipment, that is coherent receiver that can be installed for dedicated photon counting [20]. The quadrature of the calibrated received signals is observed by implementing a balanced optical coherent receiver either using the homodyne or heterodyne method. The nonavailability of much advanced reconciliation signal processing techniques at low SNR values implies the restrictions on the transmission distance of CV-QKD networks to 60 km, which is lower than that of DV-QKD [21]. The resultant secure key rates of CV-QKD network are restricted by the bandwidth of the coherent receiver, electronic circuitry for analogue-todigital conversion (ADC) and the performance of reconciliation schemes as signal postprocessing algorithms. The net performance of the system is degraded by the excess noise that

In this chapter, we discuss the design challenges and the initial results, based on experimental and numerical analysis, to characterize and evaluate the distribution of secure data to the subscribers by implementing the quantum-to-the-home (QTTH) concept. We have systematically studied the design challenges and the analysis of using: (1) phase-encoded data, that is,

technological resources and advancements in the network infrastructure.

affects the optical signals at the high data rates [22, 23].

Table 1. Overview of recent CV-QKD demonstrations.

With progressively more people using the smart IoT electronic devices and multiple-sensors, data security and privacy are the areas of exploration, concerned with shielding the inter and intra-connected electronic devices and networks in the infrastructure. Data encryption on the signals in transit, either it is from the devices to the base station or from the base station to the cloud, is the vital component of cybersecurity in the next-generation networks. It provides a physical layer of defense that shields confidential and private data from the external hackers. The most secure and widely used algorithms to protect the confidentiality and integrity are developed on symmetric cryptography methods. Much amended security is delivered with a mathematically indestructible form of encryption known as one-time pad [5]. In this method, the information is secured by using accurately random sequence of the identical length as the original transmitted data. In both classical and new algorithms for data encryption, the main functional challenge is to securely share the generated keys between the two parties, namely, sender (Alice) and receiver (Bob). Quantum key distribution (QKD) methods address these challenges by using quantum properties to exchange the secret information, that is, cryptographic key, which can then be used to encrypt messages that are being transmitted over an insecure public channel.

QKD is a method used to assign encryption keys between two nodes, that is, Alice and Bob. The unconditional security of QKD is established on the intrinsic laws of quantum mechanics [6, 7]. Any eavesdropper (i.e., commonly known as Eve or hacker) on the public communication channel attempting to obtain the information between Alice and Bob will interpose the quantum state of the encrypted data and thus can be noticed by the users as defined by the noncloning theorem [8] by monitoring the disruption in terms of quantum bit error rate (QBER) or excess noise. The exploration for long distance and equally high bit-rate quantum encrypted data transmission using optical fibers [9] has led researchers to evaluate the range of methods [10, 11]. Two classical methods were developed and implemented for encrypted transmission over a standard single mode fiber (SSMF), that is, DV-QKD [12, 13] and CV-QKD [14–16]. DV-QKD protocols, such as the famous BB84 or coherent one-way (COW) [17], involve the generation and detection of very weakly powered optical signals, ideally at the single photon level. A range of successful technologies has been implemented via the DV-QKD protocol, but typically these are quite different in terms of the equipment required from the technologies that are used in classical communications [18]. CV-QKD protocols have therefore been of attention as these protocols can make use of conventional telecommunication equipment and additional resources are not required at all. Moreover, the secure keys are randomly encoded on the quadrature of the coherent state of a light signal [19]. Such technique has the potential advantages because of its capability of attaining high secure key rate with modest technological resources and advancements in the network infrastructure.

During the last few years, there is an increasing trend to use CV-QKD to send encrypted data over public communication channels, as listed in Table 1. The main purpose is to adopt the classical equipment, that is coherent receiver that can be installed for dedicated photon counting [20]. The quadrature of the calibrated received signals is observed by implementing a balanced optical coherent receiver either using the homodyne or heterodyne method. The nonavailability of much advanced reconciliation signal processing techniques at low SNR values implies the restrictions on the transmission distance of CV-QKD networks to 60 km, which is lower than that of DV-QKD [21]. The resultant secure key rates of CV-QKD network are restricted by the bandwidth of the coherent receiver, electronic circuitry for analogue-todigital conversion (ADC) and the performance of reconciliation schemes as signal postprocessing algorithms. The net performance of the system is degraded by the excess noise that affects the optical signals at the high data rates [22, 23].

In this chapter, we discuss the design challenges and the initial results, based on experimental and numerical analysis, to characterize and evaluate the distribution of secure data to the subscribers by implementing the quantum-to-the-home (QTTH) concept. We have systematically studied the design challenges and the analysis of using: (1) phase-encoded data, that is,


infrastructure to maintain the quality of service (QoS). The FTTH world is taking shape and, as it does so, researchers are emphasizing much more on the network design and proposing the specific applications [1, 2]. Next-generation (NG) services to deploy a smart city concept, such as cloud computing, machine-to-machine (M2M) communications, Drone-of-Things (DoT) and Internet-of-things (IoT), require high-capacity optical fiber infrastructure as a backbone. According to the statistics, high-speed data traffic is increasing at a rate of 30–40% every year [3], around the globe. For this very reason, the M2M/IoT applications will not only benefit from fiber-optic broadband, they will require proper security and privacy in these networks. Both M2M and IoT are using the Internet to transpose the physical world onto the networked one, with many interconnected devices communicating autonomously. This bandwidth demand forces the network providers to adopt fiber-based last-mile connections and raising the challenge of moving access-network capacity to the next level, 1–10 Gbits/s data traffic to the home [4]. The researchers believe that FTTH is the key to develop a sustainable future in terms of smart city infrastructures, as a matter of fact, it is the only available state-of-the-art technology, when it comes to providing unprecedented bandwidth, multiuser data capacity, high-speed

With progressively more people using the smart IoT electronic devices and multiple-sensors, data security and privacy are the areas of exploration, concerned with shielding the inter and intra-connected electronic devices and networks in the infrastructure. Data encryption on the signals in transit, either it is from the devices to the base station or from the base station to the cloud, is the vital component of cybersecurity in the next-generation networks. It provides a physical layer of defense that shields confidential and private data from the external hackers. The most secure and widely used algorithms to protect the confidentiality and integrity are developed on symmetric cryptography methods. Much amended security is delivered with a mathematically indestructible form of encryption known as one-time pad [5]. In this method, the information is secured by using accurately random sequence of the identical length as the original transmitted data. In both classical and new algorithms for data encryption, the main functional challenge is to securely share the generated keys between the two parties, namely, sender (Alice) and receiver (Bob). Quantum key distribution (QKD) methods address these challenges by using quantum properties to exchange the secret information, that is, cryptographic key, which can then be used to encrypt messages that are being transmitted over an

QKD is a method used to assign encryption keys between two nodes, that is, Alice and Bob. The unconditional security of QKD is established on the intrinsic laws of quantum mechanics [6, 7]. Any eavesdropper (i.e., commonly known as Eve or hacker) on the public communication channel attempting to obtain the information between Alice and Bob will interpose the quantum state of the encrypted data and thus can be noticed by the users as defined by the noncloning theorem [8] by monitoring the disruption in terms of quantum bit error rate (QBER) or excess noise. The exploration for long distance and equally high bit-rate quantum encrypted data transmission using optical fibers [9] has led researchers to evaluate the range of methods [10, 11]. Two classical methods were developed and implemented for encrypted transmission over a standard single mode fiber (SSMF), that is, DV-QKD [12, 13] and CV-QKD [14–16]. DV-QKD protocols, such as the famous BB84 or coherent one-way (COW) [17],

data transfer, consistency, secure communications and expendability.

22 Telecommunication Networks - Trends and Developments

insecure public channel.

m-PSK (where m = 2, 4, 8, 16 ….) to produce secure quantum keys and (2) limitations of using fast optical receivers in-terms of electronic and shot noise for commercially available coherent receiver to detect the CV-QKD signals. Furthermore, the transceivers, noise equivalent power (NEP) from ADCs and transimpedance amplifier (TIA) are emulated according to the physical parameters of the available off-the-shelf modules. Both single channel (suitable for high-speed point-to-point links) and especially wavelength division multiplexed (WDM) transmissions (suitable for multicasting) are investigated. We have also implemented: (1) local local oscillator (LLO) method to avoid possible eavesdropping or hacking on the reference laser signal and (2) a phase noise cancelation (PNC) algorithm for digital post-processing of the received signals. Moreover, we have depicted the trade-off between the secure key rates achieved and the splitratio of the access network considering the hybrid classical-quantum traffic. The proposed setup is further studied by incorporating different fiber types, for example, pure silica core fiber (PSCF) and low loss switch based on microelectromechanical systems (MEMS) for multiuser configurations. These detailed discussions will help the people from academics and industry to implement the QTTH concept in real-time networks. Furthermore, the designed system is energy efficient and cost-effective.

where ω1 is the RF angular frequency of the signal. The output is used as the input of I/Q modulator, Mach-Zehnder modulator (MZM). The equivalent optical field can be expressed as

n o h i ffiffiffiffiffi

<sup>j</sup> <sup>ω</sup>tþj<sup>π</sup> ð Þ<sup>4</sup> ½ � � AI t ½ � ð Þþ Q tð Þ ffiffiffiffiffiffiffi

where A refers to the modulation index; ω, PS, and φ1t represent the angular frequency of the carrier, power and phase noise of the received signal. For investigating, the modulation variance VA of the optical received signal, evaluated as the shot-noise-units (SNUs), the parameter A and variable optical attenuator have been optimized at the input of the public communication. To further simplify the numerical model of the QTTH network, the quantum channel loss is expressed as the attenuation of the optical communication channel. Mathematically, noise

π 2

2Ps p e

Ps p e

Recent Progress in the Quantum-to-the-Home Networks http://dx.doi.org/10.5772/intechopen.80396

<sup>T</sup> <sup>þ</sup> <sup>E</sup> � <sup>1</sup> (5)

<sup>j</sup> <sup>ω</sup>LLOtþφ<sup>2</sup> ½ �<sup>t</sup> (6)

<sup>η</sup> (7)

<sup>T</sup> (8)

<sup>j</sup> <sup>ω</sup>tþφ<sup>1</sup> ½ � ð Þ<sup>t</sup> (3)

25

<sup>j</sup> ð Þ <sup>ω</sup>þω<sup>1</sup> <sup>t</sup>þφ<sup>1</sup> ½ � ð Þtd (4)

π 2 h i <sup>þ</sup> jcos ASQð Þþ <sup>t</sup>

variance produced by the communication channel is given as in Eq. (5).

<sup>χ</sup>line <sup>¼</sup> <sup>1</sup>

the incoming signal. The electric field of the LLO can be expressed as in Eq. (6).

ELLOt <sup>¼</sup> ffiffiffiffiffiffiffiffiffiffi PLLO <sup>p</sup> <sup>e</sup>

where T is the relationship between transmission distance and E is the excess noise. Realistically, excess noise measurements, expressed as SNUs [18, 32], may come from the laser phase noise, laser line width, imperfect modulation and coherent receiver imbalance [33]. In this chapter, we have implemented a local local oscillator (LLO) concept, which is considered as the vital configuration to keep the laser at the receiver side, that is, Bob, in order to stay away from any hacking attempt on the quantum channel to get the reference phase information of

where PLLO, ωLLO and φ2t represents the power, angular frequency and phase noise of the LLO, respectively. The structure of the Bob, that is, coherent receiver, consists of a 90� optical hybrid and two balanced photodetectors. The coherent receiver has an efficiency of η and electrical noise of Vel. Practically, Vel comprises electrical noise from transimpedance amplifiers (TIA) as well as the major contribution from the ADC. For this reason, the receiver added noise

<sup>χ</sup>det <sup>¼</sup> <sup>2</sup> <sup>þ</sup> <sup>2</sup>Vvl � <sup>η</sup>

Furthermore, the aggregate noise variance of the quantum network, including Alice and Bob,

<sup>χ</sup>system <sup>¼</sup> <sup>χ</sup>line <sup>þ</sup> <sup>χ</sup>det

in Eq. (3) and further be simplified as in Eq. (4).

E tð Þ<sup>≃</sup> ffiffiffiffiffiffiffi 2Ps p e

variance can be expressed as in Eq. (7).

can be expressed as in Eq. (8).

E tðÞ¼ cos AS1ð Þþ t
