Implementation of Mach-Zehnder Modulation OTDM System

Implementation of Mach-Zehnder Modulation OTDM System

D Dhanush

Student, Dept. of ECE

N I E Institute of Technology Mysuru, Karnataka, India

Harish S V

Assistant Professor, Dept. of ECE N I E Institute of Technology Mysuru, Karnataka, India

Karthik S

Student, Dept. of ECE

N I E Institute of Technology Mysuru, Karnataka, India

Abstract Optical fiber communications increase the rate of electronic communication. And the OTDM is one of the best schemes to achieve highspeed transmission of data over optical fiber. OTDM (Optical TimeDivision Multiplexing) is a technique to overcome the electronic bottleneck and achieve a single channel system. In this paper, we simulate and design a point to point OTDM system with MachZehnder modulation by using OptiSystem, and use DPSK (Differential PhaseShift Keying) modulation format in this system.

Keywords Optical Fiber; MachZehnder; Optical Time Division Multiplexing (OTDM); Differential Phase Shift Keying (DPSK);

1. DESIGN FLOW

   In this project, there are two major blocks A. Transmission block and B. Receiver block. In this project, we consider four input channels. Digital Signals from these channels are transmitted through a main channel that is Optical Fiber. These signals are recovered at the receiving end. The figure 1 show the complete block diagram of the DPSK Modulation OTDM System.

   I. INTRODUCTION

   In computer networks and telecommunication, multiplexing of signals is process by which several signals are combined into a signal over shared medium. The reverse process is done to recover the multiplexed signal called De Multiplexing.

   TimeDivision Multiplexing (TDM) is related to each signal appearing for each time in a alternating pattern by the means of synchronized switches. The time domain is divided into several time slots of fixed length, each foe a channel [1][5]. In this project, we use Optical TimeDivision Multiplexing (OTDM). In OTDM, the optical signal from each channel are multiplexed over time domain and so multiplexed signal will be multiplexed optical signal.

   MachZehnder modulator is a special kind of electro optical modulator which is used in the project for optical modulation. A signal controlled element exhibiting electro optical effect is used to modulate the light beam in waveguide. The Modulation is imposed on Amplitude and Frequency of the beam [2][4].

   In this paper, we design and simulate a point to point OTDM (Optical TimeDivision Modulation) system by using OptiSystem, and use DPSK (Differential PhaseShift Keying) modulation format in this system. It achieves efficient and reliable transmission of data which satisfies highspeed optical fiber communications.

   Figure 1 Block Diagram of OTDM System.

   1. Transmitter Block

      As said earlier, in this paper we consider four channels which are modulated and multiplexed. These are done in transmitter block. Transmission block contains five sub blocks. Namely 1. UDBSG, 2. Differential Modulator, 3. Laser Source, 4. Mach Zehnder Modulator and 5. Optical TimeDivision Multiplexing. These five blocks are described as follows.

      1. UDBSG

         User Defined Bit Sequence Generator (UDBSG) which generates some predefined bit sequence at the rate of 30Mb/s. This is a bit sequence generator in which the user can define the sequence. The sequence length is defined by N, if the userdefined sequence is shorter than the N, the sequence will be repeated until the length is equal to N. The figure 2 Shows the layout diagram of User Defined Bit Sequence Generator.

         Figure 2 UDBSG

      2. DIFFERENTIAL MODULATOR

         Differential Phase Shift Keying is a kind of highspeed transmission modulation format. DPSK modulation block consists of duo binary precoder and phase modulator. The coding rule of differential coder is as below.

         bn=an bn1

         DPSK encodes two distinct signals that is the carrier and the modulating signal with 1800 phase shift each. The serial data input is given to the XOR gate and output is again fed back to the other input through 1bit delay. The output of the XOR gate along with the carrier signal is given to the balance modulation, to produce the DPSK modulated signal. Figure 3 shows the layout of DPSK Modulation.

         Figure 3 DPSK Modulation

         The figure 4 shows the waveform of binary input to the DPSK Modulation. And figure 5 shows the output of the DPSK Modulated signal.

         Figure 4 Input Binary Signal

         Figure 5 DPSK Modulated output signal

      3. MACH ZEHNDER MODULATOR

         The MachZehnder modulator is a special kind of electrooptical modulator. The Modulation is imposed on Amplitude and Frequency of the beam. Waveguide LiNbO3 or MachZehnder modulator which accepts optical carrier and electrical modulation signal and gives modulated optical signal. The output so produced is an optical signal with

         varying intensity which is in accordance with input electrical signal.

         The MachZehnder structure has an input branch, which splits the incoming optical signal into two arms. These two optical arms subsequently recombined by the output optical branch. Application of an electrical signal to one or both of the optical arms through electrodes controls the degree of interference of optical signals from two arms at the output optical branch the different paths can lead to constructive and destructive interference of signals at the output depending on the applied electric signal's voltage. Then the output intensity can be modulated according to the voltage.

         In the above figure 6 shows the MachZehnder Modulation technique. The laser source which acts as a carrier in the Optical System which is fed to waveguide. The signal is converted into Return to Zero (RZ) format. Then this signal is fed to electrode. The modulated signal will be optical wave.

         Figure 6 MachZehnder Modulation

         The input Binary Signal fed to MachZehnder is shown in figure 7 and the output Optical waveform of MachZehnder modulation is shown in figure 8

         Figure 7. Input Electrical Waveform

         Figure 8. Output Optical Waveform

      4. OPTICAL TIMEDIVISION MULTIPLEXER

      The optical signal from each channel are multiplexed over time domain and so multiplexed signal will be multiplexed optical signal. Optical TimeDivision multiplexer combines basic data stream from four channels as a highspeed data stream. Optical TimeDivision multiplexer consists of time delayer and power combiner. Finally, the multiplexed data stream propagates in fiber link.

      The Optical TimeDivision Multiplexing is made up of power combiner and delayer. Each channel has a calculated

      delay. If there are N channels to be multiplexed, then the delay of nth channel () is given by below formula.

      = 1/ ((Bit rate)) × (nth channel 1)/ N

      The Power combiner will sum up the power of the input optical signal. The figure 9. shows the layout diagram of 4 channel Optical TimeDivision Multiplexing. Here in this paper we considered only four channels. So Optical signal from each channel is multiplexed using below setup. Each channel is applied with respective delay and the signals are added up in power combiner.

      For example, in our project we consider only four channel. Lets consider the bit rate of the system is 1Gbps. So for first channel there will be no time delay, that is 0 seconds. For second channel there will be delay of 0.25ns. For third channel there will be delay of 0.5ns. For fourth channel there will be delay of 0.75ns.

      Figure 9 Optical TimeDivision Multiplexr

      The four input optical signals from different channels of MachZehnder are fed to Optical TimeDivision Multiplexing are shown in figure 10 to figure 13. And the output Optical waveform of Optical TimeDivision Multiplexing is shown in figure 14.

      Figure 10 Optical Signal of channel 1

      Figure 11 Optical Signal of channel 2

      Figure 12 Optical Signal of channel 3

      Figure 13 Optical Signal of channel 4

      Figure 14 Optical Signal of of Multiplexed channel

   2. RECEIVER BLOCK

      Receiver block contains four subblocks. Namely

      1. Optical TimeDivision Demultiplexing, 2. DPSK De modulator, 3. Photo Diode, 4. Filters and BER Analyzer. These five blocks are described as follows.

   1. OPTICAL TIMEDIVISION DEMULTIPLEXER

      The Optical TimeDivision DeMultiplexer consists of Power Splitter cascaded with MachZehnder Modulator. The Optical TimeDivision DeMultiplexer takes single optical signal and routes it to several data streams. In this paper we have considered four channel Optical TimeDivision Multiplexer, so in the receiver part Optical TimeDivision DeMultiplexer splits into four channels.

      Power Splitter cascaded with Optical Time Delayer and MachZehnder Modulator forms Optical TimeDivision Multiplexer. Power splitter splits data stream into identical data stream. These data streams are added with respective optical delay. Delay() for each arm is calculated by the below formula.

      = 1/ ((Bit rate)) × (N nth channel 1) / N

      Power Splitter splits the signal to four identical arms. This arms are added with calculated delay from the above formula for different channels. These optical signals are fed to input optical branch of MachZehnder Modulator. The electrodes are fed with high logic (1 or +Vcc). In the modulation process we have used RZ format and high logic LASER, so in the receiver part we use high logic Return to Zero format signal and the same is fed to electrodes of MachZehnder Modulator. The below Figure 15 and 16 shows the Optical TimeDivision DeMultiplexer used to recover the optical signal sent by transmitter.

      Figure 15 Optical TimeDivision DeMultiplexer

      Figure 16 MZM sub block

      The input multiplexed optical signal is shown in the figure

      17. and the Demultiplexed and recovered optical signals of four channels from the MachZehnder Modulators are shown in the figure 18 to 21.

      Figure 17 Multiplexed Optical Input Signal

      Figure 18 Optical Signal of channel 1

      Figure 19 Optical Signal of channel 2

      Figure 20 Optical Signal of channel 3

      Figure 21 Optical Signal of channel 4

   2. PHOTODETECTOR

      The PIN Photodiode component is used to convert an optical signal into an electrical current based on the devices Responsivity. When an optical signal strikes the diode, it generates electrical current corresponds to optical intensity by the electronhole pair formation. This current is called photocurrent. By the means of this device we convert optical signal into corresponding electrical signal. The layout diagram of Photodetector is show in the Figure 22.

      Figure 22 Photodetector

   3. DPSK DEMODULATOR

      Received electrical signals are demodulated to get the binary data sent by the transmitter. The carrier signal which is used in transmitter block is multiplied with input electrical signal in quadrature phase modulator. The carrier is shifted by 900. The input electrical signal is split into two and this are multiplied with carrier and phase shifted carrier. These signals are compressed and change to Mary format. These signals are compared and coded using DPSK Decoder. The output signal is a demodulated Binary Data. The layout diagram of DPSK demodulator is shown in figure 23.

      Figure 23 DPSK DeModulation

      The figure 24 shows the waveform of input DPSK signal to the DPSK Demodulator. And figure 25 shows the Binary output of the DPSK Demodulated signal.

      create user defined subsystems and scripting [6]. Optiwave provides a design tool structures leads to hightechnology business.

      IV. CONCLUSION

      Figure 24 Input DPSK Signal

      Figure 25 Output Binary Signal

   4. FILTERS AND BER ANALYSER

   Filter is used for signal processing functions such as to attenuate or to reduce noise or for selectively filtering some frequencies. To get so we use low power filters, amplifiers and Bessel filters of order 4.

   BER visualizer allows us to calculate and display the bit error rate (BER) of an electrical signal automatically. It can estimate the BER using different algorithms. It can also plot BER patterns and estimate this system penalties and margins. Using this we estimate the output correctness of received signal.

2. SOFTWARE USED

We simulate this project using OptiSystem 15.0.0. The OptiSystem is software designed by Optiwave.

OptiSystem is a software from Optiwave Systems Inc. OptiSystem is a comprehensive design tool that enables us to plan, test, and simulate optical links in the layers of Optical System. Optiwave built a complete solution with an extensive component library that is fully capable of designing the complete transmission layer for the creation of next generation networks. OptiSystem 15.0.0 supports External Software like MatLab, Scilab, EDA and so on. It allows to

In this paper we propose a DPSK Modulation OTDM system and verify that the system is feasible. Accuracy of Optical TimeDivision Multiplexing and Demultiplexing is analyzed. As Optical signals from individual channels are multiplexed, the efficiency and Data recovery is high. This system is more useful because it improves bit rate of transmission and bandwidth of the system.

ACKNOWLEDGMENT

The authors would like to express sincere gratitude to Harish S V, Assistant Professor, Dept. of ECE, N I E Institute of Technology, Mysuru for their guidance and constant encouragement. I take this opportunity to record my sincere thanks to all the faculties of the Dept. of ECE, N I E Institute of Technology, Mysuru for their help and encouragement.

REFERENCES

1. K. Merzouk*, Y. Le Guennec, B. Cabon Low Cost 10 Gb/s OTDM System IEEE 2007.

2. D.T. Neilson, C. R. Doerr, L. Zhang, and L. L. Buhl EAMbased InP MZ modulator for 40Gb/s PSBT using 20Gb/s tributaries ECOC 2008, 2125 September 2008, Brussels, Belgium.

3. Luo Wen, Guan Yalin A DPSK Modulation OTDM System at 40Gbps at 2016 IEEE International Conference on Electronic Information and Communication Technology (ICEICT 2016).

4. Giuseppe Scotti, Pasquale Tommasino, AlessandroTrifiletti, and Antonello Vannucci A MachZehnder ModulationModel for the Digen of OpticalFiber Anolog Transmission IEEE 2011.

5. Arpana Mishra and Priyesh Mishra – Optical Communication with TimeDivision Multiplexing (OTDM) and Hybrid WDM/OTDM PON International Journal of Science and Research (IJSR 2016).

6. Optiwaves Optisystem 15.0. evaluation about the software website : https://optiwave.com/optisystem1500install/about