1.6 Tbit/s OFDM WDM-PON system employing RSOA as a colorless transmitter

doi:10.21203/rs.3.rs-1859091/v1

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1.6 Tbit/s OFDM WDM-PON system employing RSOA as a colorless transmitter

https://doi.org/10.21203/rs.3.rs-1859091/v1

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In this paper, we have evaluated a bidirectional Wavelength Division Multiplexing Passive Optical Network (WDM-PON) employing Intensity Modulated/Direct Detection Optical Orthogonal Frequency Division Multiplexing (IM/DD-OFDM). The proposed system employs 100 Gbps 16 Quadrature Amplitude Modulation (16-QAM) downstream and 5 Gbps On-Off keying (OOK) upstream wavelengths, respectively. The proposed system is considered low-cost as non-coherent IM/DD OFDM technology and a simple Reflective Semiconductor Optical Amplifier (RSOA) colorless transmitter are employed and no Dispersion Compensating Fiber (DCF) is needed. Based on the BER results of WDM signals, the proposed WDM-PON system can achieve up to 1.6 Tbit/s (100 Gbit/s/λ × 16 wavelengths) downstream transmission over a 30 km single mode fiber (SMF).

Passive Optical Network (PON)

Orthogonal Frequency Division Multiplexing (OFDM)

Reflective Semiconductor Optical Amplifier (RSOA).

WDM-PON (wavelength division multiplexing passive optical network) is considered a cost-effective solution in broadband optical access networks due to its capabilities of higher capacity, superior performance, and longer range [1–2]. WDM-PON can be enhanced by using optical orthogonal-frequency-division-multiplexing (OFDM). OFDM is a high-efficiency modulation technique that can be utilized in WDM-PON to increase bandwidth usage and extend transmission distance. With OFDM, you can overcome the limitations of optical fiber, such as chromatic and polarization dispersion, as well as inter-symbol interference [3]. While coherent OFDM systems offer higher receiver sensitivity. Direct Detection OFDM is an attractive solution for PONs because it reduces phase noise and frequency offset while reducing system complexity [4,5].

The operation cost of PONs can be reduced by employing colorless optical sources at ONUs. These colorless sources, such as the Reflective Semiconductor Optical Amplifier (RSOA) and injection-locked Fabry–Perot laser diode (FP-LD), are used to re-modulate the downstream signal with the upstream data [6,7]. Spectrally efficient modulation techniques such as M-ary quadrature amplitude modulation (M-QAM) can be employed for IM/DD optical OFDM systems to increase both the capacity and efficiency of these systems. Recently, IM/DD optical OFDM systems have been investigated as a cost-effective solution for PONs [8–13]. A bidirectional WDM-PON system employing RSOA was demonstrated in [14], where a 40 Gbps downstream OFDM signal and a 10 Gbps upstream OFDM signal were utilized. In [15], Bidirectional long reach WDM-PON system based on RSOA was investigated, where 20 Gbps downstream data and 10 Gbps upstream data were transmitted over 45 km Single Mode Fiber (SMF). In [16], a novel cost-effective RSOA based bidirectional WDM Radio over Free Space Optics (Ro-FSO) PON was established for next-generation free space optics network. 10 Gbps downstream, 1.25 Gbps upstream signal, and 1.49 Gbps video signal were sent over 500 m FSO channel. In [17], a 10 Gbps bidirectional RSOA based WDM-PON was investigated over a 25-kilometer fiber cable, where Differential Phase Shift Keying (DPSK) downstream signals and OFDM modulated upstream signals were used. WDM-PON architecture based on incoherent unpolarized light was demonstrated using a RSOA as a colorless optical source in [18]. In [19], a bidirectional RSOA based WDM-PON using 10 Gbps DPSK downstream signal and 5 Gbps OOK upstream signal with high extinction-ratio in both directions was demonstrated over 20 km SMF. In [20], Remotely Pumped Erbium Doped Fiber Amplifier (EDFA) based long-haul WDM-PON scheme was investigated, where 40 Gbps Quadrature Phase Shift Keying (QPSK) downstream and 10 Gbps OOK RSOA based upstream transmission were employed over 40 km SMF. In [21], a WDM OFDM-PON architecture was demonstrated, where 10 Gbps data was transmitted in both downstream and upstream directions up to 50 km SMF. IM/DD OFDM and simple OOK data were used for downstream and upstream transmission, respectively. In [22], a long-haul OFDM WDM–PON that provided 100 Gbps downstream data and 2 Gbps upstream data on a single wavelength was evaluated. In [23], for long haul transmission distances, a 100 Gbps IM/DD OFDM system with high order modulation techniques (4-QAM) was investigated. This paper investigates OFDM WDM–PON system providing up to 100 Gbps 16-QAM OFDM downstream and 5 Gbps OOK upstream signals using a single wavelength. The wavelength reuse system uses a colorless ONU based on wavelength-seeded RSOA to reduce WDM-PON costs.

The OFDM technique is a multicarrier high data rate transmission technique used in communication systems. The OFDM system uses a large number of lower-rate subcarriers to transmit the overall high data rate. The different sub-carriers are orthogonal to each other, which means they are completely independent of one another. This is achieved by positioning the carrier at the nulls in the modulation spectra of each other. An OFDM signal is produced as a sum of orthogonal subcarriers that are modulated using different digital coding schemes such as PSK and QAM. The purpose of this format is to reduce intercarrier and inter-symbol interference (ICI and ISI) significantly.

The transmitted data is a stream of coded symbols in various formats, including PSK and QAM. Firstly, the input serial data stream is converted into a parallel stream of OFDM symbols. OFDM symbols are then allocated to subcarriers that correspond to orthogonal frequencies. For data to be sent over an optical carrier, each OFDM symbol must be converted from the frequency domain into the time domain. This is done by applying an inverse Fourier transform (IFFT) to each OFDM symbol. Since optical channels such as fibers are dispersive, it is required for each OFDM time-domain symbol to have a guard extension (a cyclic prefix (CP)) to reduce the ISI and ICI. Next, each time-domain OFDM symbol is placed into a serial stream. Signals are then converted from digital to analog using digital-to-analog converters (DACs) utilizing interpolation techniques such as step, linear, and cubic. Finally, an internal smoothing filter may be applied.

The block diagram of the proposed WDM–PON system is shown in Fig. 1. At the central office (CO), there are N continuous-wave (CW) laser sources, where a data rate of 100 Gbps is generated for each one using a pseudo random binary sequence (PRBS) generator. The generated bits are converted into symbols using a 16-QAM sequence generator (4 bits per symbol). The QAM signals are then modulated into multiple orthogonal sub-carriers using an OFDM modulator. With a Fast Fourier transform (FFT) size of 1024 and a CP of 100, 512 OFDM subcarriers in the 16-QAM format are employed. After IFFT, CP is added to each OFDM symbol to prevent inter-symbol interference (ISI) between OFDM symbols. As the number of OFDM subcarriers (512) is half that of FFT points (1024), the generated bit rate is 50 Gbps.

Subcarrier tones with a lower rate will have a frequency range of 0 to 2.5 GHz. Using an analog mixer and a radio frequency (RF) source, a quadrature electrical modulator is utilized to increase the frequency of OFDM downstream signals up to 20 GHz. The Mach-Zehnder Modulator (MZM) modulates the RF electrical signal into the optical domain by utilizing a continuous-wave laser source with a linewidth of 0.01 MHz and an output power of 10 dB to reduce the effect of fiber nonlinearity. Following the MZM, the optical signal passes to a N×1 WDM multiplexer (MUX) that multiplexes N downstream wavelength signals before being amplified by an erbium doped fiber amplifier (EDFA) that has 10 dB gain and 4 dB noise figure (NF), respectively.

The resulting aggregate optical signal is then sent over a SMF with an attenuation of 0.2 dB/Km and a dispersion of 16 ps/nm/km. A WDM demultiplexer (DeMUX) at the remote node (RN) is used to separate the WDM OFDM signals, which are then routed to different ONUs. A 3-dB optical splitter is used at each ONU to receive half of each WDM signal, which is then converted to an electrical signal by a PIN photo-detector (PD). The PIN has a thermal power density of 15x10^-24 W/Hz and a dark current of 10 nA. The received electrical signal is then amplified using an electrical amplifier. The electrical amplifier has a gain of 10 dB and a noise power spectral density of -60 dBm/Hz. The amplified signal is down-converted and recovered to the baseband band between 0 and 2.5 GHz using a quadrature demodulator. The transmitted QAM signals are then successfully recovered using an OFDM demodulator. The QAM sequence detector converts incoming symbols (QAM signals) to bits based on the number of bits per symbol. The remaining optical signal is injected into an RSOA for re-demodulation with the 5 Gbps OOK upstream data. Table 1 lists the parameters of the RSOA. The parameters of the RSOA have been carefully optimized to increase the bandwidth and support higher data rates. The RSOA operates in the gain saturation region, so the downstream data is eliminated, and the upstream data is directly carried by the downstream signal. The re-modulated signals of these RSOAs are then combined again by a WDM MUX at the RN. Then the combined signal is sent back upstream to the central office (CO) over a SMF. At the CO, upstream signals are demultiplexed by an 1×N DeMUX and then every wavelength signal is detected by a PIN PD.

Table 1

Main RSOA parameters
Parameters	Values
Input Facet Reflectivity	50×10^− 6
Output Facet Reflectivity	50×10^− 6
Active Length	0.0006 m
Taper Length	0.0001 m
Width	0.4×10^− 6
Height	0.4×10^− 6
Optical Confinement Factor	0.45
Nonlinear gain parameter	112×10^− 6 m³

The OFDM WDM–PON system was investigated using the OptiSystem simulation tool [24]. The simulated WDM-OFDM-PON system comprises N = 16 wavelengths. Each OLT/ONU path, which is identified by an individual wavelength (λ), can handle data rates up to 100 Gbps downstream and 5 Gbps upstream, respectively. The 16 wavelengths were allocated from 193.1 THz (λ₁ = 1552.52 nm) to (λ₁₆ = 1546.52 nm) with 50 GHz channel spacing.

Figure 2 shows the spectrum of the OFDM signal before the quadrature modulator (Q-Mod) and after the quadrature demodulator (Q-DeMod) at the CO and ONU, respectively. Figure 3 shows the spectrum of the OFDM signal after the Q-Mod and the detected signal after the PIN PD at the CO and ONU, respectively. It is clear from Fig. 3 that the spectrum of the baseband OFDM signal has been shifted by 20 GHz using the Q-Mod. Additionally, the results indicate the high gain that is introduced by the quadrature demodulator. These results were obtained at λ₁.

Bit-error-rate (BER) versus optical signal-to-noise ratio (OSNR) measurements are used to examine the performance of downstream OFDM and upstream OOK signals. Figures 4 and 5 show the BER values after 20 km SMF as well as the related constellation and eye diagrams for downstream and upstream signals, respectively. λ₁, λ8 and λ₁₆ were chosen to be viewed in the figure to show the results of the first, middle, and last wavelengths of the spectrum. The results show that for the downlink, as the OSNR increases, the BER decreases. However, the Uplink results indicate that there is little variation in the BER with the increase of the OSNR. This can be explained by the fact that the RSOA is operating in the saturation region. Additionally, the perfect constellation diagram and eye-opening show that chromatic dispersion, channel noise, and ISI have no significant effect on OFDM or OOK modulated signals. The BER results are clearly above the FEC limit. For example, the downstream WDM signals λ₁, λ8 and λ₁₆ can achieve a BER of 1.6×10^− 4, 2×10^− 4 and 5.2×10^− 4 (at OSNR = 30 dB) respectively. Figures 6 and 7 show the variations in BER with link range for downstream OFDM and upstream OOK signals, respectively. The results demonstrate that the system can achieve a transmission distance of 30km SMF as indicated by the intersection of the BER curves with the FEC limit.

A cost-effective high speed OFDM WDM-PON system utilizing a centralized light-wave source and direct detection has been proposed and investigated. An RSOA is utilized as a colorless optical source to remodulate OFDM downstream signals for upstream transmission. The RSOA's parameters were optimized to increase its bandwidth and support higher data rates. The results show that a data rate of up to 100 Gbps for downlink transmission and 5 Gbps for uplink transmission can be realized without dispersion compensation. The acquired BER results suggest that the proposed WDM-PON system can achieve up to 1.6 Tbit/s (100 Gbit/s/λ × 16 wavelengths) downstream transmission over 30 km single mode fiber (SMF). As a result, this system offers a promising solution for next-generation wavelength reuse WDM-PONs, which might deliver a variety of broadband services, including high-speed Internet, cloud data centers, and mobile backhaul.

Funding Erciyes University Scientific Research Projects Coordination Unit funded this research (Project No: FDK-2019-8750).

Data Availability Data sharing not applicable to this article as no datasets were generated during the current study.

Code Availability Software application.

Conflict of interests The authors declare that they have no conflict of interest.

Kani, J. I., Bourgart, F., Cui, A., Rafel, A., Campbell, M., Davey, & Rodrigues, R. (2009). Next-generation PON Part I: technology roadmap and general requirements. Journal of Electrical Engineering IEEE Commun Mag, 47, 43–49
Fady El-Nahal and, & Hanik, N. (2020). Technologies for Future Wavelength Division Multiplexing Passive Optical Networks. IET Optoelectronics, 14(2), 53–57
Djordjevic, I., & Vasic, B. (2006). Orthogonal frequency division multiplexing for high-speed optical transmission. Opt Exp Vol, 14(9), 3767–3775
Kabil, A. E., & Faqihi, M. (2018). “Optical OFDM (O-OFDM) for Intensity Modulated/Direct Detection Optical Systems,” IEEE International Conference on Communication, Networks and Satellite (Comnetsat)
Feng, N., & Li, Y. (2021). A novel adaptive QAM coder /decoder for bit and power loading in IM/DD OFDM-PON transmission system. Optik, 238, 166766
Chow, C., Yeh, C., Wang, C., Shih, F., & Chi, S. (2009). Signal remodulation of OFD16-QAM for long reach carrier distributed passive optical networks. IEEE Photon Technol Lett, 21, 715–717
Das, A. S., & Patra, A. S. (2014). Bidirectional transmission of 10 Gb/s using RSOA based WDMPON and optical carrier suppression scheme. Journal Of Optical Communication, 35, 239–243
Dang, J., Wu, L., & Zhang, Z. (2017). "OFDM systems for optical communication with intensity modulation and direct detection”, Optical Fiber and Wireless Communications, pp. 85–104,
Nguyen, T., Mhatli, S., Giacoumidis, E., Compernolle, L., Wuilpart, M., & Mégret, P. (2016). “Fiber nonlinearity equalizer based on support vector classification for coherent optical OFDM”,IEEE Photon. J., vol. 8, no. 2,
Selvendran, S., Raja, A. S., Esakki Muthu, K., & Lakshmi, A. (2019). Certain investigation on visible light communication with OFDM modulated white LED using optisystem simulation. Wirel Pers Commun, 109, 1377–1394
Oubei, H., Shen, C., Kammoun, A., & Zedini, E. (2018). Light based underwater wireless communications. Japanese Journal Of Applied Physics, 57, 1–18
Dang, J., Wu, L., & Zhang, Z. (2017). “Optical Fiber and Wireless Communications,”
Fady El-Nahal, “Bidirectional OFDM-WDM-PON system employing 16-QAM intensity modulated OFDM downstream and OOK modulated upstream”,Photonics Letters of Poland, Vol. 8, No. 2, pp:60–62,
Dong, T., Bao, Y., Ji, Y., Pak Tao Lau, A., Li, Z., & Lu, C. (November 2012). “Bidirectional Hybrid OFDM-WDM-PON System for 40-Gb/s Downlink and 10-Gb/s Uplink Transmission Using RSOA Remodulation,”IEEE Photon. Technol. Lett., Vol. 24, No. 22,
Tawade, L., Mhatli, S., & Attia, R. (2014). Bidirectional long reach WDM-PON delivering downstream data 20 Gbps and upstream data 10 Gbps using mode locked laser and RSOA. Optical And Quantum Electronics, 47, 779–789
Mandal, G., Mukherjee, R., Das, B., & Sekhar Patra, A. (2018). Next-generation bidirectional Triple-play services using RSOA based WDM Radio on Free-Space Optics PON. Optics Communication, 411, 138–142
Choudhury, P., & Khan, T. (2016). Symmetric 10 Gb/s wavelength reused bidirectional RSOA based WDM-PON with DPSK modulated downstream and OFDM modulated upstream signals. Optics Communication, 372, 180–184
Sperm, M., & Babic, D. (2019). Wavelength reuse WDM-PON using RSOA and modulation averaging. Optics Communication, 451, 1–5
Zhang, J. 1, Yuan1, X., Gu, Y. 2, & Huang, Y. (2009). “A Novel Bidirectional RSOA Based WDM-PON with Downstream DPSK and Upstream Re-Modulated OOK Data,” ICTON
Zhang, Z., Chen, X., Wang, L., & Zhang, M. (2013). “40-Gb/s QPSK Downstream and 10-Gb/s RSOA based Upstream Transmission in Long-Reach WDM PON Employing Remotely Pumped EDFA and FBG Optical Equalizer,” 8th International Conference on Communications and Networking in China (CHINACOM)
Pandey, G., & Goel, A. (2014). “Long reach colorless WDM OFDM-PON using direct detection OFDM transmission for downstream and OOK for upstream,”Opt Quant Electron,
Mhatli, S., Ghanbarisabagh, M., & Tawade, L. (2014). “Long-reach OFDM WDM–PON delivering 100 Gb/s of data downstream and 2 Gb/s of data upstream using a continuous-wave laser and a reflective semiconductor optical amplifier,”Opt. Lett., Vol. 39, No. 23,
Taspınar, N., & Alhalabi, M. (2021). Performance investigation of long-haul high data rate optical OFDM IM/DD system with different QAM modulations. J Electr Eng, 72(3), 192–197
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1.6 Tbit/s OFDM WDM-PON system employing RSOA as a colorless transmitter

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Abstract

Figures

I. Introduction

Ii. Ofdm Technology

Iii. System Architecture

Iv. Results And Analysis

V. Conclusion

Declarations

References

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