Farhan Qamar*, Muhammad Khawar Islam, Romana Farhan, Mudassar Ali and Syed Zafar Ali Shah Secure Optical QAM Transmission Using Chaos Message Masking https://doi.org/10.1515/joc-2018-0225 Received December 12, 2018; accepted January 22, 2019 Abstract: This work presents the joint use of advance mod- ulation scheme i. e. m-QAM and optical chaos to combine the best of the two advantages i. e. higher data rates and security. A semiconductor laser diode is driven into chaotic region using direct modulation scheme and 4-QAM signal is added by Chaos message masking (CMS). The chaotically masked data stream is transmitted over an optical commu- nication link to investigate the propagation issues and syn- chronization of chaos at the receiver. The transmitted chaos is synchronized at the receiver to unmask the QAM stream and binary data by using subtraction rule and conventional QAM demodulator, respectively. The deterioration of con- stellation diagrams and bit error rate found dependent upon transmitter/receiver synchronization and link para- meters. The use of 4-QAM chaotic scheme is extendable to m-QAM and is applicable to long haul, short haul point to point and for passive optical networks. Keywords: secure optical communication, chaos message masking, QAM modulation format, network security, semi-conductor lasers 1 Introduction The demand of high data rates and bandwidth hungry appli- cations in the field of optical communication has led to the interest in implementation of advance modulation formats in optical networks. Next Generation Networks (NGN), High Definition (HD) videos, video-on demand and wireless high-speed file transfer are some bandwidth hungry applications that are made possible by using advance mod- ulation formats [1–5]. Although using advance modulation formats is the key to obtain highest possible data rates [1, 2] however the security issues still need to be addressed in these formats [6]. Optical chaos being the important discov- ery of this century finds its application in secure communica- tion [7–14], chaotic lidar [15], ultra-fast random number generators (RNG) [16–20], optical time domain reflectometer (OTDR) [21] and photonic ultra-wideband signal generator [22]. Optical chaos for secure optical communication has been explored with basic modulation formats successfully [23]. However, higher data rates and security can be achieved simultaneously by combining the strength of QAM modula- tion formats and chaotic optical communication [2, 14]. The optical chaos can be generated by using semicon- ductor lasers and fiber lasers [7, 9]. The issues related to generation and control of chaos, effect of fiber transmission, Effect of amplifier noise on optical chaos synchronization and DWDM applications are discussed in our previously reported work [24]. The optical QAM message can be made secure by using Additive Chaos Modulation (ACM), Chaos Shift Keying (CSK) or CMS [25, 26]. However, chaos masking is selected in this work due to its simplicity of implementation [27]. In chaos masking technique, the message is mixed with the chaotic waveform and is transmitted over the communi- cation link [11, 28]. Chaos control being an important aspect of secure communication [29] is successfully done to achieve the desired result. The message is recovered by synchronizing the transmitter and receiver and using subtraction [30, 31]. The objective of this work is to demonstrate secure 4-QAM signal transmission over an optical channel by using CMS scheme and chaos generated through Semiconductor lasers. This is also the extension of our previous work [32]. 2 Mathematical model The chaotic communication system requires generation of identical chaos both at transmitter and receiver. Optical chaotic waveforms reported so far in existing literature are of two types: (i) the ‘non-pulsed’ chaos is continuous oscil- lation generated by semiconductor laser diodes or nonli- nearity based Erbium doped fiber ring laser (EDFRL) *Corresponding author: Farhan Qamar, Department of Telecommunication & Information Engineering, UET Taxila, 47050, Taxila, Pakistan, E-mail: farhanqamar83@hotmail.com https://orcid.org/0000-0003-4406-4308 Muhammad Khawar Islam, Department of Electrical Engineering, Taibah University, Madinah, K.S.A Romana Farhan, Mudassar Ali, Department of Telecommunication & Information Engineering, UET Taxila, 47050, Taxila, Pakistan Syed Zafar Ali Shah, Department of Electrical Engineering, Air University, Islamabad, Pakistan J. Opt. Commun. 2019; aop Brought to you by | Göteborg University - University of Gothenburg Authenticated Download Date | 11/24/19 3:42 AM