1

All-Optical Clock and Data Recovery usingSelf-Pulsating Lasers for High-Speed Optical

NetworksYasmine El-Sayed1, Amr Wageeh2, Tawfik Ismail3, and Hassan Mostafa1,4

1Department of Electronics and Communications Engineering, Cairo University2Department of Electronics and Communications Engineering, Helwan University

3Department of Engineering Applications of Laser, National Institute of Laser Enhanced Science, Cairo University4Center for Nano-electronics & Devices, American University in Cairo & Zewail City for Science and Technology

Abstract— All-Optical Clock and Data Recovery (OCDR) isan important function for future optical networks and opticalsignal processing. The OCDR realizes a long-distance optical datatransmission system by restoring the incoming data and then re-transmitting. The Self-Pulsating (SP) lasers are the promisingtechnologies to enable fast and high-speed data recovery systemin an optical domain. In this paper, we design and implementthe OCDR based on two SP laser types, Amplified FeedbackLaser (AFL) and Distributed Bragg Reflector Laser (DBRL). Acomparative study and measurement of the network performancefor the two types have been presented.

Index Terms— Optical Clock and Data Recovery, OpticalNetworks, Self-pulsating Laser, Amplified Feedback Laser, Dis-tributed Bragg Reflector Laser.

I. INTRODUCTION

Optical Clock and Data Recovery (OCDR) solution is con-sidered the most promising technique to increase the opticalnetworks distance and correspondingly, the data rate. OCDRis capable of synchronizing, and reshaping (regenerating) thedata along the fiber cable. This will help to significantlyexpand the transmission distance as well as boost the transmis-sion rate, achieving small Bit Error Rate (BER) at the receiverend [1][2]. Several solutions have been reported for all-opticalclock recovery, such as quantum dash lasers [3], self-pulsatinglasers [4] and passive filtering techniques [5][6].

As a result of the advantages of self-pulsation (SP) laserssuch as attractive due to their compactness, reliability, lowpower consumption, and low cost. Currently, there are severalresearches have been focused on four types of SP lasers.They are dual-mode lasers with two different distributed feed-back lasers, self-pulsating Distributed Bragg Reflector Laser(DBRL), Quantum Structure FabryPerot Laser, and AmplifiedFeedback Laser (AFL) [4].

In this work, we successfully implemented two differentdesigns of OCDR based on SP lasers, AFL and DBRL forhigh-speed optical networks. The implementation of OCDRincluding performance evaluation with different bitrate andtransmission distance, and comparative study between the twomethods.

This paper is organized as follows. Section II presents theOCDR Implementation using AFL and DBR self-pulsating

laser. The results and comparative study are presented anddiscussed in Section III. Finally, the conclusions are drawn inSection IV.

II. ARCHITECTURE IMPLEMENTATION

In this section, we present a complete design and imple-mentation of two different types of of self pulsating, AFLand DFRL, using OptiSystem tools. OptiSystem is a compre-hensive software design suite that enables users to plan, test,and simulate optical links in the transmission layer of modernoptical 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 DistributedFeedback Laser (DFB), phase tuning and amplified section[8]. The schematic diagram for AFL is shown in Fig. 1 phasetuning section is used for controlling the injection current todecide the effective length. The amplification section is usedto amplify the produced current and allow the feedback to theDFB section to control the injection current [9].

Fig. 1: Schematic diagram of AFL

The relation between input and output electric field of AFLcan be described by:

Ein(t) = K.ejθEout(t− τ) (1)

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

2

group velocity. The feedback strength describes as functionof frequency of beating mode f by:

K = K0πfτ

sinπfτ(2)

Fig. 2: AFL with external cavity [9]

Distributed Bragg Reflector Laser (DBRL) DistributedBragg Reflector (DBR) Laser is shown in Fig. 3. It consistsof two Fiber Bragging Gratings (FBGs), separated by eribiumdopped fiber. The FBG has a periodic structure from multiplelayers with varying refractive index to reflect a desired wave-length. The dopped fiber feeds with pump laser and operatesas an amplification medium [10].

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 withan electric signal generated by the random bit generator whichgenerates a data with bitrates from 10 Gb/s to 40 Gb/s. Themodulated output is directed to an optical fiber with variablelength from 500 m to 50 km. At the receiving end, theincoming optical signal is split by using a 50:50 splitter. Onepart sends to Photo Detector (PD) which converts the opticalsignal to corresponding electrical signal. The converted signalis filtered by using Low Path Filter (LPF) has a band widthequal to 0.75 bitrate and then forwards to the oscilloscope(OSC1). The other part forwards to the OCDR which consistsof 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 basedon AFL, while replacing the AFL with DBRL. In the DBRL,we adjust the two FBG with the wavelength of the transmitter.

Fig. 4: The Proposed Architecture for OCDR Self-PulsatingLaser using AFL

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

III. RESULTS AND COMPARISONS

In this section, we show the results have been achieved fromthe simulation based on Optisystem. In this simulation, we arechanged the distance from 1km to 50km, and the bitrate from1Gb/s to 40Gb/s.

Fig. 6 presents the BER versus the transmission distancewhile keeping the bitrate at 10Gb/s. As we can seen for theBER less than 10−2 the distance is increased from 16km to35km. So, this architecture is increased the distance to doubleits value while keeping the BER on the same level.

Fig 7 plots the BER versus the transmission distance atbitrate 10Gb/s. We can observe that for BER equals 10−2 thetransmission distance is increased to 46km. Thus, the proposedOCDR architecture using DBRL is improved the transmissiondistance comparing to the architecture is used the AFL. Acomparative study between the two architecture with differentbitrates and transmission distance is summarized in Table I.

As presented in the table I for BER equals 10−2 thetransmission distance is doubled in the AFL and tripled inDBRL at bitrate equals 10Gb/s. If the bitrate is increased to25 Gb/sec or 40 Gb/sec the transmitted distance by using theAFL is not improved well while the DBRL gives a betterperformance.

TABLE I: The transmission distance at BER 10−2 for bitrate10, 25 and 40 Gb/s

Bitrate AFL DBRL without OCDR10 Gb/sec 35 km 46 km 16 km25 Gb/sec 4 km 8 km 3 km40 Gb/sec 2 km 5 km 1 km

3

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

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

IV. CONCLUSIONS

In this paper, AFL and DBR lasers have been used inimplementing two types of OCDR for optical access network.The results from this work are shown that the performanceachieved by the proposed architecture which uses the DBRLis improved the system performance while increasing eitherthe transmission bitrate or the distance.

ACKNOWLEDGEMENT

This research was funded by NTRA, ITIDA, Cairo Univer-sity, Zewail City of Science and Technology, AUC, the STDF,Intel, Mentor Graphics, MCIT.

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