624-628In this paper, a Differential Quadrature Amplitude Modulation (DQAM) technique for 200 x100 Gbps Super Dense Wavelength Division Multiplexing (SD-WDM) system is proposed. Optimized rating outcome in terms of the quality factor, bit error rate, crosstalk, and acceptable minor effect of the channel spacing with the support of RAMAN-EDFA-RAMAN Hybrid Optical Amplifier (HOA) is reported

Goyal, Rakesh

Kumar, Chakresh

NOPR

  Indian Journal of Pure & Applied Physics Vol. 58, August 2020, pp. 624-628     Impact of High Speed Differential Quadrature Amplitude Modulation using Hybrid Optical Amplifier for Super Dense Wavelength Division  Multiplexing System Chakresh Kumara,b* & Rakesh Goyala aDepartment of Electronics & Communication Engineering, I K Gujral, Punjab Technical University, Kapurthala -144 601, India bUniversity School of Information, Communication & Technology, Guru Gobind Singh Indraprastha University,  New Delhi-110 078, India Received 7 July 2019; accepted 18 June 2020 In this paper, a Differential Quadrature Amplitude Modulation (DQAM) technique for 200 x100 Gbps Super Dense Wavelength Division Multiplexing (SD-WDM) system is proposed. Optimized rating outcome in terms of the quality factor, bit error rate, crosstalk, and acceptable minor effect of the channel spacing with the support of RAMAN-EDFA-RAMAN Hybrid Optical Amplifier (HOA) is reported.  Keywords: Differential Quadrature Amplitude Modulation, Hybrid Optical Amplifier, quality factor, bit error rate (BER), crosstalk, output power 1 Introduction Transmission of high spectral efficiency optical signal from one place to another place with less loss and good rating of quality factor is also an interesting challenge for a researcher. Many researchers have proposed the different modulation techniques such as Amplitude Modulation (AM), Frequent Modulation (FM), Phase Modulation (PM) and much more. But these are the basic modulation technologies which have some limitations in term of optical signal transmission. In fact, low power signal is converted into a high power signal with the help of the carrier signal. Moreover, the optical carrier signal is generated from the CW laser and boost up the level of the optical signal in terms of the modulation signal for long haul distance. Many researchers are focusing to raise the transmission speed up to 100 Gbps or more with the support of different advanced modulation technology for optical communication such as M-ary Differential Phase Shift Keying (DPSK)1, Optical Differential Quadrature Phase Shift Key (ODQPSK)2, Differential Quadrature Phase Shifting Keying (DQPSK)3 and Symmetrical Differential Phase Shift Keying (SDPSDK)4 etc. Unfortunately, the effect of the hybrid optical amplifier is not considered in the literatures, which is an important consideration for long haul optical communication. Super dense wavelength division multiplexing system is the advanced technology to transmit the higher capacity optical signal5-7. In the multiple play services, a number of channels are packed to provide the services such as high-quality video and communication8. But the effect of the fiber nonlinearity and amplified spontaneous (ASE) emission can be dismissed  with the help of different Hybrid Optical Amplifiers (HOAs)9. High spectral efficiency is the hot demand for the optical network. Chung et al.10. have explored the new technology for 16 x 10 Gbps for the transmission distance of 1040 km with the help of RAMAN amplifier, but this model only highlighted the data transmission speed up to 10 Gbps which does not fulfill the demand of high capacity transmission. Downie et al.11 have evaluated the error free data transmission of 43Gbps for the transmission distance of 1200 km with 50 GHz channel spacing, but the effect of the hybrid amplifier is not shown in this literature which is an important effect in terms of low bit error and good rating quality factor for single span optical communication system. In this paper, we have used a very advanced modulation (DQAM) technology for optical transmission. Transmission of 100 Gbps is shown by the support of RAMAN-EDFA-RAMAN hybrid optical amplifier (HOA). Moreover, the layout of the —————— *Corresponding author: (E-mail:chakreshk@gmail.com) KUMAR et al.: IMPACT OF HIGH SPEED DIFFERENTIAL QUADRATURE AMPLITUDE   625paper is represented in the five sections. Literature review and evaluation of existing technology are shown in section one, description of proposed modulation transmitter and receiver are given in section two, description of simulation setup is given in section three, results and discussion are given in section four and paper is ceased with the analysis in section five respectively.   2 Description of proposed transmitter and receiver The transmitter of proposed DQAM is shown  in Fig. 1. The differential quadrature amplitude modulator delivers the transmission of two data streams of 50 Gbps from the data sources and provides the best outcome in terms of spectral efficiency and enhanced dispersion tolerance12. In this way, the resultant bit rate is coming out with the rate of 100 Gbps. Modulation is accomplished with the help of two MZM (Mach-Zehnder) modulators. Each of the MZM is fed with the data (generated from the data source and NRZ electrical drive) and further modulated with the carrier signal. The carrier signal is generated from CW laser, which is further applied to MZMs with the help of an optical splitter (OS). The resultant signals in phase and quadrature arms are combined with the phase difference of π/2 to generate the DQAM modulated signal. Further, this modulated signal is transmitted through the optical fiber with the help of the HOA.  To detect such a high capacity signals, we required a very advanced receiver which is shown in Fig. 2. The received optical signal is applied to two parallel Mach-Zehnder demodulator with the help of an optical splitter. The optical delay is set with the period of 2/B. To remove the intersymbol interference (ISI), the phase difference of π/4 and –π/4 are set to upper and lower arms respectively. Each MZM demodulator received the balanced bit rate of 50 Gbps. Two PIN photodiodes with low pass filters are placed after the MZM demodulator for optical-to-electrical (O-E) conversion. The input signal is in the form of E0 [cos(w0tδ1) + j sin(w0tδ2) ] and output after the PIN photodiodes are in the form of cos(δ1) + sin(δ2)  and cos(δ1) - sin(δ2) respectively. In this way,  high rating signal of 100 Gbps is received at the receiver side.  3 Simulation setup Our complete proposed simulation setup including high spectral efficiency transmitter and receiver for 200 x 100 Gbps are shown in Fig. 3.  Simulation is going to establish with the help of 200 CW laser sources. The beam of laser sources is generated at 180.9 to 193.4 THz. 200 channels are placed with 12.5 GHz channel spacing and input signal spectrum occupies the bandwidth of 6.4 THz.   Fig. 1 — Schematic representation of DQAM transmitter   Fig. 2 — Schematic representation of DQAM receiver   Fig. 3 — DQAM simulation setup with hybrid amplifier  INDIAN J PURE APPL PHYS, VOL. 58, AUGUST 2020   626RAMAN amplifiers are pumped by 1480 nm at 760 mW. EDFA is set to fix output power of 32mW and noise figure of 4.5 dB to amplify the signal. The total gain of cascade amplifier is given by equation (1)13  GRER = GRaman1GEDFAGRaman2  … (1)  PIN photodiodes with the quantum efficiency of 0.875 and dark current of 0.1 nA are used on the receiver section. Parameters of RAMAN amplifier are given as 12 km of Raman fiber length, 0.2 dB/km of Raman loss, 1453 nm of pump wavelength, 600 mW of pump power, 0.2 dB/km of pump attenuation, 2.15 ps/nm/km is set for reference frequency of dispersion, and 300 K of operating temperature respectively. In a similar manner, the parameters of EDFA amplifier are already explained in this paper. The evaluated rating of the received signal in terms of eye diagram is given as eye closure of 0.11570 dB and eye opening of.0106989 (a.u.) for channel 1, eye closure of 0.104414 dB and eye opening of 47.5934 (a.u) for channel 200 respectively. It is observed that insertion of data bits from the data source (which means more number of users or data bits induce more eye closure).  4 Result and discussion The impact of channel spacing of 50 GHz and 100 GHz on the hybrid optical amplifier in terms of power variations is shown in fig. 4 (a) & 4 (b). The recorded values for the 50 GHz channel spacing lies between 7 dBm to 7.1 dBm for 0 dBm power, and -0.4 dBm to -0.6 dBm for -7 dBm power. In a similar way, the recorded values for 100 GHz channel spacing lies between 5 dBm to 5.3 dBm for 0 dBm power, and -0.3 to -0.02 dBm for -7 dBm power respectively. It is analyzed that the variation in power for 50 GHz channel spacing is greater than 100 GHz channel spacing due to degradation in power level. So it can be concluded that RAMAN-EDFA-RAMAN hybrid optical amplifier provides the best accepted rating outcome for 100 GHz channel spacing.  The illustration to show, the effect of crosstalk induced by RAMAN-EDFA-RAMAN HOA with respect to applied input power is shown in Fig. 5. The variations in crosstalk are given as -22 dB to -11 dB for the 50 GHz channel frequency, and -24 to -13 dB for 100 GHz channel spacing respectively. It is evaluated that variation in crosstalk is increasing with respect to increasing input power just because of internal gain saturation. Further, the recorded results have shown that the accepted rating outcome are better than the results obtained by Oberg et al.14 To illustrate the performance of the proposed model in term of quality factor with respect to bit rate is shown in Fig. 6. It is observed that proposed HOA delivers the best outcome for 50GHz channel spacing   Fig. 4 — Output power versus channel spacing for DQAM, SD-WDM system (a) Power variations for 50 GHz channel spacing(b) Power variations for 100 GHz    Fig. 5 — Crosstalk versus applied input power  KUMAR et al.: IMPACT OF HIGH SPEED DIFFERENTIAL QUADRATURE AMPLITUDE   627in terms of 50 Gbps bit rate. Moreover, the performance of the system is degraded with 100 GHz channel spacing at 45 Gbps due to non usage of any dispersion compensation techniques. Variations of bit error rate with respect to bit rate for different channel spacing is shown in Fig. 7. The observed values lies between 1.3e-13 to 3.1e-1 for  50 GHz channel spacing, and 1.4e-14 to 2.5e-1 for 100 channel spacing. So it is observed that the performance of proposed modulation shows the accepted BER  (> 50) Gbps with the quality factor (> 30) dB. The variation in gain and quality factor for different channel spacing and input power are shown in Table 1. It is observed that the quality factor of received signal is affected by increasing the channel spacing. It occurs due to the addition of its own nonlinearity and crosstalk by each amplifier in the arrangement of HOA. But it can also be resolved by placing the isolator in the middle of two optical amplifiers.  5 Conclusion We have evaluated the impact of DQAM modulation technology for the 200 x 100 Gbps SD-Table 1 — Variations of gain and quality factor with respect to channel spacing Random number of channel Variations of Gain Variations of Quality Factor 50 GHz Channel Spacing 100 GHz Channel Spacing 50 GHz Channel Spacing 100GHz ChannelSpacing 0 dBm -7 dBm 0 dBm -7 dBm 0 dBm -7 dBm 0 dBm -7 dBm 1.0000 16.2000 15.5000 11.2000 9.2000 30.2000 25.5000 23.5500 24.3900 11.4737 16.1791 15.4843 11.1843 9.1843 29.8806 25.0601 23.0551 23.9035 21.9474 16.1581 15.4686 11.1686 9.1686 29.5611 24.6202 22.5602 23.4170 32.4211 16.1372 15.4529 11.1529 9.1529 29.2417 24.1803 22.0654 22.9305 42.8947 16.1162 15.4372 11.1372 9.1372 28.9222 23.7404 21.5705 22.4440 53.3684 16.0953 15.4214 11.1214 9.1214 28.6028 23.3005 21.0756 21.9575 63.8421 16.0743 15.4057 11.1057 9.1057 28.2833 22.8606 20.5807 21.4710 74.3158 16.0534 15.3900 11.0900 9.0900 27.9639 22.4207 20.0858 20.9845 84.7895 16.0324 15.3743 11.0743 9.0743 27.6444 21.9808 19.5910 20.4980 95.2632 16.0115 15.3586 11.0586 9.0586 27.3250 21.5409 19.0961 20.0115 105.7368 15.9905 15.3429 11.0429 9.0429 27.0055 21.1011 18.6012 19.5250 116.2105 15.9696 15.3272 11.0272 9.0272 26.6861 20.6612 18.1063 19.0385 126.6842 15.9486 15.3115 11.0115 9.0115 26.3666 20.2213 17.6115 18.5520 137.1579 15.9277 15.2958 10.9958 8.9958 26.0472 19.7814 17.1166 18.0655 147.6316 15.9067 15.2801 10.9801 8.9801 25.7277 19.3415 16.6217 17.5790 158.1053 15.8858 15.2643 10.9643 8.9643 25.4083 18.9016 16.1268 17.0925 168.5789 15.8648 15.2486 10.9486 8.9486 25.0888 18.4617 15.6319 16.6060 179.0526 15.8439 15.2329 10.9329 8.9329 24.7694 18.0218 15.1371 16.1195 189.5263 15.8229 15.2172 10.9172 8.9172 24.4499 17.5819 14.6422 15.6330 200.0000 15.8020 15.2015 10.9015 8.9015 24.1305 17.1420 14.1473 15.1465    Fig. 6 — Quality factor versus bit rate    Fig. 7 — Variations of BER with respect to bit rate  INDIAN J PURE APPL PHYS, VOL. 58, AUGUST 2020   628WDM system with the help of RAMAN-EDFA-RAMAN HOA in term of varying channel spacing, the influence of crosstalk, quality factor, and bit error rate respectively. The accepted rating outcome is reported with the comparison of references15-20 in the scenario of reduction in crosstalk, improvement in quality factor, channel spacing, gain ripple, cost, and speed, etc. Moreover, it has also observed that proposed model has shown the better outcome in terms of higher spectral efficiency (> 100 Gbps) with fiber (>200 km) for the commercial research.  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Impact of High Speed Differential Quadrature Amplitude Modulation using Hybrid Optical Amplifier for Super Dense Wavelength Division  Multiplexing System

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Impact of High Speed Differential Quadrature Amplitude Modulation using Hybrid Optical Amplifier for Super Dense Wavelength Division Multiplexing System

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