Rayleigh Backscattering Noise Research Articles

Recent advancement of RB noise alleviation techniques in different communication networks and its lacunae: a review

Abstract Telecommunication networks are forced to be advanced day by day for high data rate transportation over long-reach to fulfil the ever-increasing demand of the subscribers. Different used schemes, modulation techniques are smart enough to support high data rate transmission over long distance but some impairment like Rayleigh backscattering (RB) brings a limitation on data rate or transmission distance. RB noise effect arises and affects the system performance when more than one signal of similar wavelengths are transmitted through a same feeder fiber in full-duplex networks and different researchers have already proposed various schemes to eliminate RB noise effect in different transport networks. The present paper surveys and analyses the techniques which proposed in last 15 years for mitigation of RB noise in communication systems. The origin of RB and the impact of it in different communication systems are also explained. All the proposed networks are aimed to support next generation communication systems by providing high data rate (up to 160 Gbps downstream and 20 Gbps upstream) over long reach (up to 115 km single mode fiber link) with lesser RB noise effect but exact quantification of RB noise mitigation is not reported till now which could be a future scope for the new researchers.

Enriching Capacity and Transmission of Hybrid WDM-FSO Link for 5G Mobility

A dramatic increase in user and capacity demands has been noted after the COVID-19 pandemic. These challenges have damaged the 5G communication system mobility. Therefore, developing mobility and enhancing capacity transmission of 5G advanced services are the focused research gaps in the current era. In this paper, the free space optics (FSO) link is modeled with wavelength division multiplexing (WDM) technology based optical fiber system, purposing to enhance the 5G capabilities in multi-channel, high distance, and bidirectional transmissions. In addition, the presented hybrid FSO-WDM supported optical fiber network is analyzed for 4, 8, and 16 × 10 Gbps downlink and uplink transmission. The paper also includes the mathematical discussion of merged fiber length (SMF = 30 km) and FSO (600 m) with improved mobility management. In another contribution, the tolerance against Rayleigh backscattering (RB) noises is developed through various wavelengths of downlink and uplink channels. Finally, we perform the simulation analysis and reliability of the proposed structure for the 5G advanced communication system.

A long-reach optically powered multi-band radio-over-fiber network by employing PolM-to-IM converter with enhanced fault-protection ability and less Rayleigh backscattering noise effect

A multi-band radio-over-fiber network is established on polarisation-to-intensity converter with upgraded fault protectivity for transportation of information (10 Gbps/15 GHz, 10 Gbps/60 GHz and 10 Gbps) for end-users over ∼[40 + 30] km single-mode fiber (SMF) link with lessen impairments owing to Rayleigh Backscattering (RB) is proposed and demonstrated. Employment of unalike wavelengths for downstream and upstream results RB minimization. Fault protection capability is uplifted by incorporating the integrated SMF/free-space optics (FSO) link which provides the data continuity condition either through SMF or FSO even when anyone link is in non-workable condition due to damage or environmental limitations. Co-existence of power over fiber (PoF) signal with integrated SMF/FSO scheme was also investigated. Power penalty of 0.74 dB, 0.84 dB, low bit error rate (BER) value (∼10-3for OFDM signal, ∼10-9 for pseudo-random bit sequence (PRBS) signal), <32 dB power budget are achieved by this transmission by employing integrated SMF/FSO scheme and 2.6 dB, 2.1 dB power penalty, 34–35 dB power budget are recorded for transportation of signal in absence of integrated SMF/FSO network. The conjunction of PoF and integrated SMF/FSO scheme enhances the application field areas but causes the transmission distance contraction. Comparatively, lower power penalty than earlier (0.6 dB, 1.7 dB), 29–30 dB power budget, low BER value (∼10-3 for OFDM signal, 10-9 for PRBS signal) are measured for the transmission in presence of integrated SMF/FSO network. Larger power budgets (∼33 dB), ∼2 dB power penalty, expectable BER values are obtained without integrated SMF/FSO network for this transmission.

Discriminating Rayleigh backscattering induced false crosstalk in inline interferometric FBG sensor arrays.

The crosstalk between channels is a main factor restricting the performance of interferometric fiber Bragg grating (FBG) time-division and wavelength-division hybrid multiplexing arrays. The time-division crosstalk caused by multiple reflections and the wavelength-division crosstalk due to insufficient isolation are the main crosstalk problems in the Fabry-Perot (F-P) structure, seriously limiting the number of multiplexing devices and the system's applications. Many theoretical research and suppression scheme designs have been done to solve these problems. We have previously found a new crosstalk phenomenon called the false crosstalk in hybrid multiplexing arrays. This paper focuses on this phenomenon and constructs a theoretical model to analyze its causes and influencing factors. The model demonstrates the influences of Rayleigh backscattering (RB) noise and sensor position on the false crosstalk. Both theoretical and experimental results show that the false crosstalk is induced by parasitic interference in the leading fiber and changes with the leading fiber length. This study quantitatively reveals the crosstalk performance degradation with the change of sensor position in the hybrid multiplexing array and provides key support for optimizing the system array design and expanding the large-scale multiplexing capacity.

A Hollow-Core Photonic-Crystal Fiber-Optic Gyroscope Based on a Parallel Double-Ring Resonator.

A novel system structure of resonant fiber optical gyroscope using a parallel double hollow-core photonic crystal fiber ring resonator is proposed, which employs the double closed loop and reciprocal modulation–demodulation technique to solve the problem of the length mismatch between rings. This structure can suppress the residual amplitude modulation noise and laser frequency noise, essentially eliminating the influence of the Rayleigh backscattering noise and dramatically reduce the Kerr-effect-induced drift by three orders of magnitude. Thanks to its excellent noise suppression effect, the sensitivity of this novel system can approach the shot-noise-limited theoretical value of 8.94 × 10−7 rad/s assuming the length of the fiber ring resonator is 10 m.

Hybrid WDM-FSO-PON with integrated SMF/FSO link for transportation of Rayleigh backscattering noise mitigated wired/wireless information in long-reach

This paper presents a hybrid Wavelength division multiplexing-free space optics-passive optical network for bidirectional transmission with 4×10 Gbps downlink and 2×10 Gbps uplink to provide information to the wired and wireless users simultaneously over total 60 km SMF and 650 m FSO or 62 km SMF link with enhanced fault protection capability. Noise tolerance against Rayleigh backscattering (RB) also enhanced by employing two different ports of interleavers and by allowing different wavelengths of light as carrier signals for uplink and downlink transmission through a single feeder fiber. Integrated single mode fiber (SMF)/free space optics (FSO) link increase the reliability against failure of any one channel between SMF and FSO link, besides that it maintains the continuity of data transfer even where fiber link installation is restricted due to environmental boundary such as between two mountains, wide river etc. Low bit error rate (10−9), <1 dB power penalties (0.7 dB, 0.85 dB, 0.9 dB) are obtained between B2B and over total transmission link. A comparison between our proposed network and the network when the signal transmitted over total transmission link (60 km SMF+ 650 m FSO, or 62 km SMF) at a time also verified with their power budgets. Divergence losses at different FSO lengths (17 m to 680 m) are also calculated to determine the maximum possible FSO length for this proposed set up. Therefore, the proposed architecture proofs its feasibility, reliability and the capacity to continue transfer of high data rate over long distance even in the unfair environmental situation, which makes it an attractive platform to the next generation communication system (5G) to fulfill the thirst of end users.

Hybrid WDM free space optical system using CSRZ and Rayleigh backscattering noise mitigation

Abstract Hybrid wavelength-division-multiplexing (WDM) and free space optical (FSO) access networks are getting great attention due to numerous advantages. In this work, hybrid WDM-FSO system is demonstrated for 55 km at capacity of 5 × 10 Gbit/s using compressed spectrum return to zero (CSRZ) WDM-FSO in downstream and nonreturn to zero (NRZ) in upstream for demonstrating transmitter diversity which inturn decrease the interchannel interference. For the suppression of Rayleigh backscattering (RB) interferometric beat noise, bidirectional cyclic multiplexer is employed. Cyclic multiplexer provide λ 1 to λ 5 wavelengths for optical line terminal (OLT) to ONU transmission and λ 2 to λ 6 for ONU to OLT transmission. Insertion losses of each component are considered and in the end, power budget is also calculated. Results revealed that FSO length of 780–1050 m are obtained using various WDM-FSO downstream signals and their power budget, redundant budget, maximum distance, and insertion losses also calculated.

Unidirectional Ultra-Long Distributed Optical Fiber Sensor

In this paper, we propose and experimentally demonstrate an ultra-long distributed fiber vibration sensing system using unidirectional forward transmission of a continuous-wave signal and coherent detection with digital signal processing. Two optical fibers, which are close to each other, are deployed for sensing. A loop-back configuration is formed by splicing these two optical fibers at the far end of these two fibers. The location of the vibration event is identified by analyzing the null points in the frequency spectrum of the extracted phase signal. Thanks to the nature of unidirectional forward transmission, the Rayleigh backscattering noise can be avoided. Meanwhile, forward transmission enables optical amplifiers to compensate for the signal loss and hence fundamentally overcome the sensing range limit. We successfully demonstrate the localization of single point and multi-point vibrations with measurement errors of less than ±100 m and ±200 m, respectively, over a 500-km sensing range. The proposed scheme opens new possibilities in ultra-long haul distributed optical sensing applications.

Enabling long range distributed vibration sensing using multicore fiber interferometers.

We report a novel long range distributed fiber optic vibration sensor using two counter-propagating interferometers, which are space-division multiplexed in different cores of a seven-core fiber. The proposed system requires only one laser source. Thanks to the spatially separated structure of the two interferometers, it no longer suffers from the coherent Rayleigh backscattering noise, and, since forward transmitting CW light instead of weak backscattering light is used, as a result, the sensing range can be significantly extended. On the other hand, because the two interferometers are implemented in one single compact multicore fiber, the output temporal waveforms have good correlation; therefore, the sampled waveforms can be used directly to determine the vibration location through cross correlation, and no additional complicated data processing (e.g., time-frequency analysis methods) is required. For proof of concept, we achieved distributed vibration detection with 38.5 km sensing range, and the root mean square error of positioning is estimated to be about 54.9 m with 120 measurements. The proposed system has the unique advantages of simple setup, high sensitivity, large dynamic range, ultra-long sensing range, etc.

A bidirectional hybrid WDM-OFDM network for multiservice communication employing self-injection locked Qdash laser source based on elimination of Rayleigh backscattering noise technique

A scheme for transportation of information with minimum Rayleigh backscattering (RB) noise to the multi-users by employing Qdash laser diode as a source is designed and evaluated. In this paper, employing digital phase shift keying, millimeter wave, 16-quadrature amplitude modulation orthogonal frequency division multiplexing (16-QAM OFDM), and 32-QAM OFDM techniques, the data rates of 4 × 10 Gbps are transmitted simultaneously over 50 km single mode fiber, plus 15 m wireless link, 50 m free space optical (FSO) link, 10 m wireless respectively. Four selective self-injection locked modes of Qdash laser are utilized as optical carriers for downstream and upstream transmission. To ensure the matter of mitigation of RB noise, which mainly arises due to the transmission of light-wave of same wavelengths in bidirectional transportation, the carrier signals of different wavelength are used for modulation and remodulation in optical line terminal and optical network unit. Besides being a strong support to increase the tolerance level against RB noise, this architecture is capable to transmit less noisy information wirelessly in radio frequency sensitive areas too. The constancy of the proposed architecture is evaluated by very low power penalty (~ 1.5–1.7 dB, ~ 2.4–2.6 dB, ~ 1.4–1.6 dB, ~ 1.7–1.8 dB for four channels respectively), clear constellation, prominent eye opening, low bit-error-rate (< 10–9 for pseudo random bit sequence data stream and < 3.8 × 10–3 for OFDM signal) and low error vector magnitude (< 12.4% for 16 QAM, < 10% for 32 QAM). Therefore, the proposed architecture could be promising alternative not only due to the scheme for mitigation of RB noise but also be a potent in the field of applications of the communication world to provide less noisy information to the multi-users (wired/wireless/FSO).

Studying the Double Rayleigh Backscattering Noise Effect on Fiber-Optic Radio Frequency Transfer

We report the effect of the double Rayleigh backscattering (DRB) noise, in which the interference of the signal light with the double Rayleigh backscattered light, on the fiber-optic radio-frequency (RF) transfer system. Here, we theoretically analyze and experimentally demonstrate that the DRB noise within the fiber link will become the dominative noise on the fiber-optic RF transfer system once narrow linewidth lasers are used. The strong DRB noise is experimentally confirmed through the measurement of the effect of the coherent interference term of the signal light and the double Rayleigh backscattered light on the 100 km RF transfer system. Our results provide evidence that the conventional RF transfer technique with the telecommunications-grade lasers, in which the chromatic dispersion effect in the single-mode fiber is compensated by dispersion compensation fibers (DCFs), could be the better choice for high-performance RF transfer.

Mitigation of Rayleigh backscattering in RoF-WDM-PON employing self coherent detection and bi-directional cross wavelength technique

A scheme for mitigation of Rayleigh backscattering in RoF-WDM-PON with self-coherent detection by using bi-directional crossed network has been projected and investigated. In this paper, 10 Gbps 16-QAM signal transmits via two different carrier frequencies for downstream and upstream transmission, such that impairment due to re-modulation noise can be mitigated effectively in upstream transmission. This architecture increases the tolerance limit against Rayleigh backscattering noise as it does not allow the signals of same wavelength to propagate through a same feeder fiber. Less noisy information for wired link and 15 m wireless link are detected by homodyne and heterodyne detection respectively in coherent detector. Reliability of the proposed scheme is evaluated by low bit-error-rate, low error vector magnitude, low power penalty, clear constellations and open eye diagrams. Therefore, acceptable performance of the proposed system proves the potential to be a prominent solution for optimising noise and also it has application even in platform of multiservice network in communication field.

A Bidirectional Hybrid WDM-PON with High Data Rate Transmission for Wired and Wireless Users in Long-Reach with Enriched Noise Tolerance Capacity against Rayleigh Backscattering

Transportation of 10 Gbps, 10 Gbps/40 GHz, 10 Gbps/200 MHz data for downlink (DL) and 6 Gbps data for uplink (UL) transmission with Rayleigh backscattering (RB) noise mitigation for wired and wireless users even in radio-frequency sensitive areas have been proposed and investigated. A 2×2 wavelength-division-multiplexing mux/demux is employed to separate DL and UL to avoid RB noise. Power penalty of &lt; 1 dB at Bit error rate value of 10−9 and clear eye-diagrams express the reliability and fruitfulness of the proposed network.

A Bidirectional Hybrid WDM-PON with High Data Rate Transmission for Wired and Wireless Users in Long-Reach with Enriched Noise Tolerance Capacity against Rayleigh Backscattering

Transportation of 10 Gbps, 10 Gbps/40 GHz, 10 Gbps/200 MHz data for downlink (DL) and 6 Gbps data for uplink (UL) transmission with Rayleigh backscattering (RB) noise mitigation for wired and wireless users even in radio-frequency sensitive areas have been proposed and investigated. A 2 × 2 wavelength-division-multiplexing mux/demux is employed to separate DL and UL to avoid RB noise. Power penalty of &lt; 1 dB at Bit error rate value of 10−9 and clear eye-diagrams express the reliability and fruitfulness of the proposed network.

Highly Reliable Metro-Access Network Based on a Dual-Fiber Ring Architecture and Optimized Protection Mechanisms

Network reliability is very important for the next generation of optical networks. In this paper, a highly reliable protection mechanism, which integrates the approaches of optical protection and microwave protection, is proposed for metro-access optical networks based on the wavelength division multiplexing (WDM) technique. By designing a scheme for the convergence of optical and wireless access and cooperating with designed remote nodes (RNs), not only can access for both wired and wireless service be provided simultaneously in each optical network unit (ONU) but also microwave protection can be realized when a failure occurs in a distribution segment. By developing a novel optical switch module (OSM) to cooperate with the dual-fiber ring structure, flexible switching can be achieved to protect against multiple types of failures in the feeder segment, including single-fiber faults, dual-fiber faults and multifiber faults. Based on the above structure, the influence of Rayleigh backscattering (RB) noise can be mitigated when the network is operating under all operating scenarios except for an inner-fiber fault. To further mitigate the influence of noise, optimization for upstream transmission performance is implemented by configuring a reflective semiconductor optical amplifier (RSOA). Furthermore, the feasibility of the overall scheme is verified through experiments and simulations under different operating conditions. The results show that the proposed mechanisms can achieve acceptable bit error rate performance and quality of service (QoS) metrics while also offering various advantages, including high reliability, large scale, and a relatively low cost.

Gain-forming effect on optical signal-to-noise ratio in Raman fiber amplifier

Abstract We have introduced the comprehensive optical-to-noise ratio (OSNR) to investigate simultaneously the effects of all three major linear noise sources in distributed Raman fiber amplifier (DRFA). The total noise power contains double Rayleigh backscattering (DRB) noise, amplified spontaneous emission (ASE) noise, and relative intensity noise (RIN). Also, we have introduced an approximated gain profile approach, which helps in evaluating the OSNR for higher-order pumping (HOP) configuration for backward, forward, and bidirectional DRFA schemes. Finally, by applying the dynamic and static full-numerical computations on a system of eight wavelength division multiplexing (WDM) channels (for amplifier lengths of 70, 140, and 210 km), we demonstrated that for RIN frequencies greater than 100 kHz, the higher-order bidirectional pumping scheme exceeds the backward schemes by 12 dB.

Bidirectional coherent optical communication system combining unidirectional optical signal amplification

A new type of bidirectional coherent optical communication system is proposed combining unidirectional optical signal amplification. We analyze the application of discrete Raman amplifier (DRA) on the basis of dispersion compensating fiber in this system, and optimize the amplifier configuration considering the influence factors such as Rayleigh backscattering noise and amplified spontaneous emission noise. In addition, the gain and pump efficiency improvement in a novel design of double-pass DRA. The feasibility of the single-fiber bidirectional coherent optical communication system is ensured by the theoretical analyses and MATLAB coding. The system greatly decreases the phase shift problem caused by the frequency offset between the transmitter and local oscillator as well as the laser linewidth. It has practical value for secure communication systems.

Utilizing single-wavelength for OFDM wireless downstream and remodulated OOK upstream in colorless access network to mitigate Rayleigh backscattering noise

Abstract To avoid the Rayleigh backscattering (RB) beat noise in colorless wavelength division multiplexing (WDM) access architecture, the dual-band modulation diagram is proposed for demonstration. In the study, 11.25 Gbit/s orthogonal frequency division multiplexing (OFDM) wireless downstream and 2.5 Gbit/s remodulated on–off keying (OOK) upstream traffic are achieved by using same wavelength. Moreover, the bit error rate (BER) measurements of wireless downstream and wired upstream wavelengths are also executed and discussed after 20 km fiber connection.

Leak monitoring and localization in baghouse filtration system using a distributed optical fiber dynamic air pressure sensor

• Distributed optical fiber dynamic air pressure sensor is proposed to identify and locate broken bags in baghouse filtration systems in cement industry. • Detection of broken bags with hole diameters of 0.3 cm is achieved using ADA-SVM algorithm without the interference of electromagnetic field. • The technique can be potentially used for dust emission control in environment protection field. Coherent Rayleigh backscattering noise produced by the detection of the dynamic airflow applied to a standard optical fiber is proposed to monitor and locate the potential broken fabric bags within a baghouse filtration system with a sensing distance of 2 km. The optical fiber cable hangs freely inside the fabric bags with small leak holes. Experimental results demonstrated that the proposed distributed optical air pressure sensor is capable of identifying broken bags via the measurement of airflow perturbation applied onto the optical fiber cable. Field test at a baghouse filtration test platform was conducted and results showed that the location accuracy of the system is less than ±5 m with a detectable hole diameter of 0.3 cm and a recognition rate of ~87.6% measured by Adaboost-Support Vector Machine (ADA-SVM) method. A false alarm rate of 9% for this particular leak diameter is achieved.

Stable RF transmission in dynamic phase correction with Rayleigh backscattering noise suppression

Abstract We propose a dynamic phase correction scheme for stable radio frequency (RF) transmission over fiber based on the phase-locked loop (PLL). Rayleigh backscattering noise is suppressed by separating the frequency of counter-propagating RF signals. We apply the optical carriers of the same central wavelength to the system. In this way, the effect of temperature induced group velocity dispersion (TIGVD) is effectively reduced and the symmetry of the round-trip transmission is improved. To eliminate fiber-induced phase variations during the round-trip transfer, the error signal drives the PLL structure to dynamically pre-compensate the phase of the outgoing 2.4 GHz signal. The stable frequency distribution over 80 km optical fiber with a relative frequency stability of 3.4E−17 at 10000 s is achieved, which is close to the noise floor.