Optical Beat Interference Noise Research Articles

Reduction of optical beat interference noise using statistical adaptive derivative equalizer

In this paper, we propose a statistical adaptive derivative equalizer (SADE) in order to reduce an optical beat interference (OBI) noise in an optical access link. The proposed SADE generates an output signal similar to the shape of the input pulse amplitude modulation (PAM)-4 signal waveform, which is implemented as an adaptive total variation that responds to the shape of the multi-step signal waveform with the weighting function considering the Lorentzian characteristics of the OBI noise. We implement a 20-km optical link and measure the bit error rate (BER) and signal to noise ratio (SNR) to see if the OBI noise was reduced using the proposed technique. A 1.5-dB SNR gain was observed over the overall SNR range of received PAM-4 signal than that without the use. A power penalty in the case of using only SADE was improved by 1.5 dB at 7% forward error correction (FEC) limit compared to that without the SADE. Furthermore, when the proposed SADE and matched filter were applied simultaneously, about 2.5-dB power penalty was observed at the 7% FEC limit.

Novel OBI noise reduction technique by using similar-OBI estimation in optical multiple access uplink

A novel optical beat interference (OBI) noise reduction technique for optical multiple access uplink using the same wavelength is presented. The OBI noise is estimated by similar-OBI and mitigated by subtracting estimated OBI noise using the digital signal processing technique. To derive similar-OBI, an RF clipping tone is transmitted out of signal band. We numerically and experimentally verified the validity of proposed OBI noise reduction method in orthogonal frequency division multiplexing access (OFDMA) passive optical network (PON) uplink where the OBI noise has been reduced and signal to noise ratio (SNR) has been improved from 4.4 dB to 10.6 dB.

Notice of Retraction: Simple colorless long-reach WDM-PON with rayleigh backscattering noise mitigation employing remodulated orthogonal coding

We propose and experimentally demonstrate a novel colorless full-duplex passive optical network architecture with Rayleigh backscattering optical beat interference (OBI) noise mitigation by using orthogonal codes. A pair of orthogonal codes are generated and transmitted from optical line terminal (OLT) to optical network unit (ONU) with the same wavelength, in which, one for downstream signal coding, and the other for the upstream seeding signal. In ONU, the upstream signal is remodulated without erasing the downstream signal. Extra centralized CW light sources and gain-saturation RSOAs are not needed. By using orthogonal codes, the spectral overlap between upstream and downstream signal is reduced, which can mitigate OBI noise significantly. The performance of transmission and power margin are investigated through experiments at different data rates, transmission distances compared with normal on-off keying (OOK) signals. The remodulated upstream signals are correlatively received at OLT with coding gain which is useful in long-reach transmissions. Due to coding gain and OBI noise mitigation, total 4~9dB power margin is achieved for 5Gb/s downstream and 1.25Gb/s upstream with 20km to 70km transmission distances.

Ring-Based Colorless WDM-PON With Rayleigh Backscattering Noise Mitigation

We propose and experimentally demonstrate a novel ring-based wavelength-division-multiplexing passive optical network (WDM-PON). By using an orthogonal coding and correlation technique, the ring-based WDM-PON can efficiently mitigate the optical beat interference noise induced by Rayleigh backscattering. In our proposed orthogonal coding scheme, no extra light sources are required for the upstream (US) transmission, which means the number of light sources can be halved and the saved wavelengths can be used for more optical network units. In addition, compared to previous ring-based WDM-PONs, the proposed ring-based WDM-PON requires fewer fiber Bragg gratings and no blue/red-band filter, which means the proposed orthogonal coding scheme costs less. The performance of the proposed scheme is investigated through an experiment. In the experiment, 2.5 and 5 Gb/s US data rate and 5 Gb/s downstream data rate are investigated in two different ring architectures. According to the experimental results under different situations, it can be concluded that the US orthogonal coding scheme performs better than the normal US on-off keying in a ring-based WDM-PON. The power margin can be up to 1.8 dB when the US data rate is 2.5 Gb/s, and the power margin can be up to 1.69 dB when the US data rate is 5 Gb/s.

Colorless Long-Reach Duplex WDM-PON With Rayleigh Backscattering Noise Mitigation Using Orthogonal Codes

We propose and experimentally demonstrate a novel colorless full-duplex passive optical network (PON) access architecture. Utilizing orthogonal codes and correlation receiving methods, the novel PON can mitigate the optical beat interference (OBI) noise induced by Rayleigh backscattering (RB). A pair of electrical orthogonal codes is generated and modulated at the same wavelength in the optical line terminal (OLT). Then, modulated optical signals are transmitted from the OLT to the optical network units (ONUs). One of the codes is for downstream signal coding, and the other is used as the upstream seed. In the ONU, the upstream signal is remodulated without erasing the downstream signal. Neither extra centralized continuous wave (CW) light sources nor gain-saturated reflective semiconductor optical amplifier is required. By using these orthogonal codes, the spectral overlap between upstream signal and downstream signal in the full-duplex system is reduced, which can mitigate the OBI noise significantly. The performance of transmission and power margin is investigated through the experiments with different transmission distances. The remodulated upstream signals are recovered by correlation algorithm in the OLT. By correlation algorithm, we can get coding gain, which is important in long-reach transmissions. Because of coding gain and the OBI noise mitigation, a link power margin of 4-10 dB can be achieved for 5 Gb/s downstream and 1.25 Gb/s upstream, when the transmission distance is from 20 to 70 km.

Impacts of backscattering noises on upstream signals in full-duplex bidirectional PONs.

The backscattering noises introduced by Rayleigh and stimulated Brillouin scattering have been experimentally studied by means of their spectrum broadening, the scattering power variation and their impacts on upstream signals with different transmission fiber lengths and incident powers in a single-fiber bidirectional passive optical network (PON) communication system. The results show that both spontaneous scattering and simulated scattering can take place. The power and spectrum of backscattering noises are determined by the downstream launch power, laser linewidth and transmission fiber length. With the transmission length increasing, the power of backscattering noises gets higher, the spectrum of the backscattering noise broadens and the simulated threshold power decreases. The backscattering noise can beat with uplink light to modulate envelop of upstream signal resulting in degradation of BER greatly. Under the condition of one single channel for the second next generation PON (NG-PON2), the fiber length is 40km and downstream launch power is up to 11dBm. At this time, the backscattering noises are easy to be stimulated and the scattering power rises up from -20dBm to 10dBm, which can overwhelm the US signal. The spectrum of the optical beat interference noise also rises up with fiber length, which causes the uplink's BER degradation. The experimental results are significant for mitigation of backscattering noises under the condition of bidirectional PONs.

Electrical code divided multiplexing orthogonal frequency division multiplexing-based 60-GHz radio-over-fiber system with extended wireless transmission and optical beating interference noise mitigation in upstream link

This paper proposes an electrical code divided multiplexing orthogonal frequency division multiplexing (ECDM-OFDM) modulation-based radio-over-fiber (ROF) system at the 60-GHz band. Compared with conventional OFDM ROF system, it can increase the distance of wireless links as well as suppressing the optical beating interference noise in the upstream link. The 4.68 Gb/s ECDM-OFDM signal at 60 GHz with a 25-km fiber and 8-m air transmission is experimentally demonstrated. The wireless distance of the ECDM-OFDM signal has been extended 3 m with the same transmitted power. For the upstream signal, no significant receiver power penalties are observed after transmission.

Analysis of optical beat interference noise suppression using RF‐clipping tone in OFDMA‐PON uplink transmission

ABSTRACTIn orthogonal frequency division multiple access‐passive optical network (OFDMA‐PON) uplink transmission with a direct detection system, the optical beat interference (OBI) noise is a very critical issue in regard to channel performance degradation. We have proposed a novel technique to suppress the OBI noise in intensity modulation and direct detection OFDMA‐PON links by using an optical spectrum broadening method using the RF‐clipping tone to improve the SNR of the discrete multitone modulation (DMT) signal with OBI noise suppression. We also experimentally analyzed the dependency of the RF clipping tone on the OBI noise suppression and dither effect. The results show that the received DMT signal in the optical line terminal can achieve 3 Gb/s over a 23 km SSMF with a BER of 2.3×10−4. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2706–2711, 2014

Optical beat interference noise reduction by using out-of-band RF clipping tone signal in remotely fed OFDMA-PON link.

A novel technique for mitigating the optical beat interference (OBI) noise in an optical orthogonal frequency division multiple access passive optical network (OFDMA-PON) uplink transmission is presented. By using an out of signal band RF clipping tone to the optical seed carrier, the OBI noise has been reduced and the resulting throughput and spectral efficiency has been improved. As an experimental verification, we demonstrate that the spectral efficiency of 23 km and 50 km have been doubled in the OFDMA-PON uplink transmission.

Suppression of optical beat interference-noise in orthogonal frequency division multiple access-passive optical network link using self-homodyne balanced detection

A new technique, which reduces optical beat interference (OBI) noise in orthogonal frequency division multiple access-passive optical network (OFDMA-PON) links, is proposed. A self-homodyne balanced detection, which uses a single laser for the optical line terminal (OLT) as well as for the optical network unit (ONU), reduces OBI noise and also improves the signal to noise ratio (SNR) of the discrete multi-tone (DMT) signal. The proposed scheme is verified by transmitting quadrature phase shift keying (QPSK)-modulated DMT signal over a 20-km single mode fiber. The optical signal to noise ratio (OSNR), that is required for BER of 10−5, is reduced by 2dB in the balanced detection compared with a single channel due to the cancellation of OBI noise in conjunction with the local laser.

Optical Beat Noise Reduction Using FM to AM Conversion of Injection-Locked FP-Laser Diode in Reflective SOA Based WDM/SCM-Passive Optical Networks

A new scheme for reducing optical beat interference noise in a reflective semiconductor optical amplifier based wavelength division multiplexed/subcarrier multiplexing - passive optical network is proposed. This method uses an Fabry Perot laser locked by modulated lights from optical network units in a central office. As an experimental verification, it is reported that carrier to noise ratio is enhanced by 10 dB and power penalty is improved by 16 dB.

Reduction of optical beat interference using gain-saturated RSOA in upstream WDM/SCM optical links

A new scheme for reducing optical beat interference (OBI) noise in optical network units is proposed for subcarrier multiplexing-based access network applications. The optical spectrum of the transmit lasers is broadened by using a radio frequency (RF) clipping tone with a modulation depth greater than one. This reduces the impact of the OBI noise. The distortions caused by an RF clipping tone are also suppressed by introducing a gain-saturated reflective optical amplifier, which shows the characteristics of high-pass filter. The proposed scheme has been verified by measuring the error vector magnitude of 16QAM signal with 20 Mbps. Error-free transmission has been achieved even when the light of OBI-noise-causing lasers is stronger than that of the signal laser by 7 dB

Hybrid WDM/SCMA-PON using wavelength-locked fabry-Pe/spl acute/rot laser diodes

We propose a large-capacity hybrid passive optical network (PON) with a wavelength-sharing technique achieved by applying subcarrier multiple access on each single channel of a wavelength-division-multiplexed (WDM) PON. We also use forward-error correction to reduce the effect of optical beat interference noise. We demonstrate three-subchannel sharing in a 100-GHz-spaced WDM-PON to accommodate three times more subscribers simultaneously at a fully dedicated connection rate of 125 Mb/s

OBI noise reduction using gain saturated SOA in reflective SOA based WDM/SCM-PON optical links

A new method for suppressing optical beat interference (OBI) noise in a reflective semiconductor optical amplifier (SOA) based WDM/SCM-PON is proposed. This method uses the SOA operated in gain saturation range in the central office, which acts as a highpass filter. As experimental verification, it was found that carrier-to-noise ratio increased up to 10 dB and error vector magnitude after 10 km transmission reduced from 16 to 6% compared with those without an SOA with received optical power of −13 dBm.

Optical beat noise reduction in WDM-SCM access networks using modulated optical pulse train

We proposed a new method to suppress the optical beat interference (OBI) in wavelength-division-multiplexing/subcarrier-multiple-access network. The proposed scheme uses the modulated optical pulse train that has broad bandwidth in frequency domain. Since the OBI noise is inversely proportional to the optical bandwidth of beating optical signals, the generated OBI noise by beating of optical pulse train signals from several optical network units (ONUs) spreads over wide frequency range. In addition, the chance of optical beating is low because optical pulse trains from different ONU have different pulse timing. We have demonstrated the proposed idea experimentally. In beating experiment, the carrier-to-noise ratio was obtained over 30 dBc regardless of optical beating. In addition, 6-Ms/s 16 quadrature amplitude modulator data at 0.7 GHz was successfully transmitted up to 20 km with an average error-vector-magnitude of 4.5% in presence of optical beating.

Operation of an LED with a single-mode semiconductor amplifier as a broad-band 1.3-μm transmitter source

A semiconductor amplifier and an edge-emitting LED are operated in a single-mode-fiber connected configuration to demonstrate a broad-linewidth 1.3-/spl mu/m transmitter. The output from the LED is increased by a 13.5-dB chip gain through the amplifier to 2.3-mW while maintaining a broad 3-dB spectral width of 600 /spl Aring/ from the LED. A 600-Mb/s modulation speed was demonstrated, with open eye-patterns from the amplifier, with direct current modulation applied to the LED. A theoretical analysis shows that the LED-amplifier gain is about 7 dB less than the peak amplifier gain for a narrow-line signal due to the broad spectrum and wavelength offset of the LED. The 1.3-/spl mu/m LED-amplifier may be useful as a transmitter for fiber access networks to avoid optical beat interference noise, or as a broadband source for wavelength sliced WDM networks. The device has the potential to be monolithically integrated for wavelengths at 1.3 and 1.5 /spl mu/m. >