All-Optical Clock and Data Recovery using Self ...

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All-Optical Clock and Data Recovery using Self-Pulsating Lasers for High-Speed Optical Networks Yasmine El-Sayed1 , Amr Wageeh2 , Tawfik Ismail3 , and Hassan Mostafa1,4 1

Department of Electronics and Communications Engineering, Cairo University Department of Electronics and Communications Engineering, Helwan University 3 Department of Engineering Applications of Laser, National Institute of Laser Enhanced Science, Cairo University 4 Center for Nano-electronics & Devices, American University in Cairo & Zewail City for Science and Technology 2

Abstract— All-Optical Clock and Data Recovery (OCDR) is an important function for future optical networks and optical signal processing. The OCDR realizes a long-distance optical data transmission system by restoring the incoming data and then retransmitting. The Self-Pulsating (SP) lasers are the promising technologies to enable fast and high-speed data recovery system in an optical domain. In this paper, we design and implement the OCDR based on two SP laser types, Amplified Feedback Laser (AFL) and Distributed Bragg Reflector Laser (DBRL). A comparative study and measurement of the network performance for the two types have been presented. Index Terms— Optical Clock and Data Recovery, Optical Networks, Self-pulsating Laser, Amplified Feedback Laser, Distributed Bragg Reflector Laser.

I. I NTRODUCTION Optical Clock and Data Recovery (OCDR) solution is considered the most promising technique to increase the optical networks distance and correspondingly, the data rate. OCDR is capable of synchronizing, and reshaping (regenerating) the data along the fiber cable. This will help to significantly expand the transmission distance as well as boost the transmission rate, achieving small Bit Error Rate (BER) at the receiver end [1][2]. Several solutions have been reported for all-optical clock recovery, such as quantum dash lasers [3], self-pulsating lasers [4] and passive filtering techniques [5][6]. As a result of the advantages of self-pulsation (SP) lasers such as attractive due to their compactness, reliability, low power consumption, and low cost. Currently, there are several researches have been focused on four types of SP lasers. They are dual-mode lasers with two different distributed feedback lasers, self-pulsating Distributed Bragg Reflector Laser (DBRL), Quantum Structure FabryPerot Laser, and Amplified Feedback Laser (AFL) [4]. In this work, we successfully implemented two different designs of OCDR based on SP lasers, AFL and DBRL for high-speed optical networks. The implementation of OCDR including performance evaluation with different bitrate and transmission distance, and comparative study between the two methods. This paper is organized as follows. Section II presents the OCDR Implementation using AFL and DBR self-pulsating

laser. The results and comparative study are presented and discussed in Section III. Finally, the conclusions are drawn in Section IV. II. A RCHITECTURE I MPLEMENTATION In this section, we present a complete design and implementation of two different types of of self pulsating, AFL and DFRL, using OptiSystem tools. OptiSystem is a comprehensive software design suite that enables users to plan, test, and simulate optical links in the transmission layer of modern optical networks [7]. A. Basic Concepts and Definitions Amplified Feedback Laser (AFL) AFL is a method of SP which depends on injecting two longitudinal modes. It consists of three parts Distributed Feedback Laser (DFB), phase tuning and amplified section [8]. The schematic diagram for AFL is shown in Fig. 1 phase tuning section is used for controlling the injection current to decide the effective length. The amplification section is used to amplify the produced current and allow the feedback to the DFB section to control the injection current [9].

Fig. 1: Schematic diagram of AFL The relation between input and output electric field of AFL can be described by: Ein (t) = K.ejθ Eout (t − τ )

(1)

Where K, θ are the strength and phase of feedback respectively and τ is the time delay which describes by 2LEC /υg . where LEC is the external cavity length for resonating and phase synchronization as shown in Fig. 2 and υg is the

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group velocity. The feedback strength describes as function of frequency of beating mode f by: K = K0

πf τ sin πf τ

(2)

Fig. 4: The Proposed Architecture for OCDR Self-Pulsating Laser using AFL Fig. 2: AFL with external cavity [9] Distributed Bragg Reflector Laser (DBRL) Distributed Bragg Reflector (DBR) Laser is shown in Fig. 3. It consists of two Fiber Bragging Gratings (FBGs), separated by eribium dopped fiber. The FBG has a periodic structure from multiple layers with varying refractive index to reflect a desired wavelength. The dopped fiber feeds with pump laser and operates as an amplification medium [10].

Fig. 5: The Proposed Architecture for OCDR Self-Pulsating Laser using DBRL

III. R ESULTS AND C OMPARISONS

Fig. 3: Structure of Distributed Bragg Reflector (DBR) Laser

B. OCDR using Amplified-Feedback Laser (AFL) The block diagram of OCDR using AFL is shown in Fig. 4. In this architecture, the Mach-Zehnder Modulator (MZM) modulates the received optical beam from laser source with an electric signal generated by the random bit generator which generates a data with bitrates from 10 Gb/s to 40 Gb/s. The modulated output is directed to an optical fiber with variable length from 500 m to 50 km. At the receiving end, the incoming optical signal is split by using a 50:50 splitter. One part sends to Photo Detector (PD) which converts the optical signal to corresponding electrical signal. The converted signal is filtered by using Low Path Filter (LPF) has a band width equal to 0.75 bitrate and then forwards to the oscilloscope (OSC1). The other part forwards to the OCDR which consists of Dispersion Compensator (CD), SP-AFL, EDFA and OBPF. The recovered optical signal directs to the second oscilloscope (OSC2) after it passes through PD and LPF. C. OCDR using Distributed Bragg Reflector Laser (DBRL) The block diagram of OCDR using DBRL is shown in Fig. 5. We kept the architecture similar to the in the OCDR based on AFL, while replacing the AFL with DBRL. In the DBRL, we adjust the two FBG with the wavelength of the transmitter.

In this section, we show the results have been achieved from the simulation based on Optisystem. In this simulation, we are changed the distance from 1km to 50km, and the bitrate from 1Gb/s to 40Gb/s. Fig. 6 presents the BER versus the transmission distance while keeping the bitrate at 10Gb/s. As we can seen for the BER less than 10−2 the distance is increased from 16km to 35km. So, this architecture is increased the distance to double its value while keeping the BER on the same level. Fig 7 plots the BER versus the transmission distance at bitrate 10Gb/s. We can observe that for BER equals 10−2 the transmission distance is increased to 46km. Thus, the proposed OCDR architecture using DBRL is improved the transmission distance comparing to the architecture is used the AFL. A comparative study between the two architecture with different bitrates and transmission distance is summarized in Table I. As presented in the table I for BER equals 10−2 the transmission distance is doubled in the AFL and tripled in DBRL at bitrate equals 10Gb/s. If the bitrate is increased to 25 Gb/sec or 40 Gb/sec the transmitted distance by using the AFL is not improved well while the DBRL gives a better performance. TABLE I: The transmission distance at BER 10−2 for bitrate 10, 25 and 40 Gb/s Bitrate 10 Gb/sec 25 Gb/sec 40 Gb/sec

AFL 35 km 4 km 2 km

DBRL 46 km 8 km 5 km

without OCDR 16 km 3 km 1 km

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Fig. 8: BER versus bitrate at transmission distance = 10km

Fig. 6: BER versus transmission distance for OCDR using AFL at 10Gb/s

Fig. 7: BER versus transmission distance for OCDR using DBRL at 10Gb/s

IV. C ONCLUSIONS In this paper, AFL and DBR lasers have been used in implementing two types of OCDR for optical access network. The results from this work are shown that the performance achieved by the proposed architecture which uses the DBRL is improved the system performance while increasing either the transmission bitrate or the distance. ACKNOWLEDGEMENT This research was funded by NTRA, ITIDA, Cairo University, Zewail City of Science and Technology, AUC, the STDF, Intel, Mentor Graphics, MCIT. R EFERENCES [1] K. Kim, J. Lee, S. Lee, J. Lee, and Y. Jang, Low-Cost, Low-Power, HighCapacity 3R OEO-Type Reach Extender for a Long-Reach TDMA-PON, ETRI Journal vol.34, no.3, 2011. [2] T. von Lerber, S. Honkanen, A. Tervonen, H. Ludvigsen and F. Kppers, Optical clock recovery methods: Review, Optical Fiber Technol., vol. 15, no. 4, pp.363 -372, 2009

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