In-band Optical Signal-to-noise Ratio Monitoring Research Articles

Modulation-format-independent in-band OSNR monitoring technique using Gaussian process regression for a Raman amplified multi-span system with a cascaded filtering effect.

We propose and experimentally demonstrate an accurate modulation-format-indepen-dent and cascaded filtering effect (CFE) insensitive in-band optical signal-to-noise ratio (OSNR) monitoring technique enabled by Gaussian process regression (GPR) utilizing a widely tunable optical bandpass filter (OBPF) and optical power measurements. By adjusting the center frequency of a widely tunable OBPF and measuring the corresponding output optical power as the input features of GPR, the proposed OSNR monitoring technique is experimentally proven to be transparent to modulation formats and robust to CFE, chromatic dispersion (CD), polarization mode dispersion (PMD), and nonlinear effect (NLE). Experimental results for 9-channel 32Gbaud PDM-16QAM signals with 50GHz channel spacing demonstrate OSNR monitoring with the root mean squared error (RMSE) of 0.429 dB and the mean absolute error (MAE) of 0.294 dB, in the OSNR range of -1∼30 dB. Even better, our proposed technique has the potential to be employed for link monitoring at the intermediation nodes and can eliminate the necessity to know the transmission information.

A novel in-band OSNR monitoring technique based on fractional Fourier transform of LFM signal

We propose a novel in-band optical signal to noise ratio (OSNR) monitoring technique in digital coherent receiver based on fractional Fourier transform (FrFT), which employs the power aggregation property of linear frequency modulation (LFM) signal in fractional domain. In our method, the LFM signal with extremely low power is added on the data signal. Thus, the received signal exists a peak in fractional domain, which can be used to indirectly differentiate the data signal power from noise thereby calculating the OSNR. Meanwhile, the proposed technique does not occupy additional spectrum resource and avoids any additional hardware on top of the standard digital coherent receiver. Experimental results of a 10 Gbaud quadrature phase-shift keying (QPSK) system show that the proposed technique is highly accurate, with the monitoring error less than 0.55 dB in the OSNR range of 9–29 dB for back-to-back transmission and 0.9 dB in the OSNR range of 11–25 dB for 960 km standard single mode fiber (SSMF) transmission.

Reference Optical Spectrum Based In-Band OSNR Monitoring Method for EDFA Amplified Multispan Optical Fiber Transmission System With Cascaded Filtering Effect

The reference optical spectrum (ROS) based in-band optical signal-to-noise-ratio (OSNR) monitoring methods are accurate and inherently robust to fiber chromatic dispersion and polarization mode dispersion. They are also very simple and suitable to be deployed ubiquitously in the transmission system. In this paper, a ROS-based in-band OSNR monitoring method is proposed for erbium doped fiber amplifier (EDFA) amplified multispan dense wavelength division multiplexing systems with cascaded filtering effect (CFE) caused by cascaded add-drop filters or wavelength selective switches. In such systems, the optical signal as well as the optical noise may experience significant CFE making the ROS-based methods proposed before ineffective. The new method solves this problem and performs very well for OSNR in the range of 10–30 dB when the fiber nonlinear effect and nonideal filtering effect are present. The OSNR monitor based on the new method is also more convenient to use as only one-time calibration is required when used at different monitoring locations along the optical link.

Integrated In-Band OSNR Monitor Based on Asymmetrical Parallel-MZIs for WDM signals

We propose a novel in-band optical signal-to-noise ratio (OSNR) monitor based on asymmetrical parallel Mach–Zehnder interferometers (A-PMZI). By exploiting two different lengths of delay arms in the A-PMZI, the monitor requires no prior knowledge of the noise-free coherence properties of the signal. The A-PMZI is fabricated on a SOI platform and demonstrated for OSNR monitoring of 4 × 28 GBd NRZ-QPSK WDM signals. Experimental results show that OSNR measurements from 7.7 to 24.8 dB within error of ±0.5 dB are achieved for all four channels. Due to the advantages of high fabrication tolerance and broad bandwidth of multimode interferometer couplers in the A-PMZI, the monitor works well in the whole C-band. Moreover, the monitor is insensitive to input optical power and chromatic dispersion.

Guideline of choosing optical delay time to optimize the performance of an interferometry-based in-band OSNR monitor.

We propose and experimentally demonstrate a guideline of choosing optical delay time in an interferometry-based optical signal-to-noise ratio (OSNR) monitor to achieve the optimal monitoring performance by calculating the normalized autocorrelation function of the channel noise. According to the position of the first zero point of the calculated autocorrelation function, the delay time is determined; consequently the OSNR monitoring range up to 29 dB (within an error≤±0.5 dB) is achieved for 112 Gb/s PM-QPSK signal with a channel filter bandwidth of 100 GHz. The experimental results also show that the guideline is applicable to channel filters with different bandwidths and shapes. In simulation, the guideline is proven to be valid in OSNR monitoring for a 28 Gbaud PM-16QAM signal and a 50 Gbaud PM-QPSK signal.

In-band OSNR monitoring based on low-bandwidth coherent receiver and tunable laser

An in-band optical signal-to-noise ratio (OSNR) monitoring technique with high resolution and large measurement range is demonstrated based on lowbandwidth coherent receiver and a tunable laser. The measurement range of OSNR is from 10 to 25 dB and the resolution can be controlled about ± 1 dB.

Toward Terabit Autonomic Optical Networks Based on a Software Defined Adaptive/Cognitive Approach [Invited

Terabit elastic optical networking (EON) is foreseen as a viable solution to extend the lifetime of a network exploiting the available bandwidth in previously deployed optical fibers. EON is based on bandwidth-variable transponders capable of supporting multiple bit rates and/or modulation formats according to traffic requirements and node architectures that route arbitrary channel bandwidths. Thus, EON increases the heterogeneity of the network, which may create the need for autonomic adaptive and/or cognitive techniques. In this context, the software-defined networking (SDN) paradigm emerges as an opportunity to enable such techniques thanks to the centralized view of the network by decoupling the control plane and the data plane. This paper surveys different activities carried out at the Optical Technologies Division in Centro de Pesquisa e Desenvolvimento em Telecomunicações, Brazil. We review an optical transport SDN controller for virtual optical networks that supports two adaptive algorithms. First, the autonomic flexible transponder reconfigures the transmission modulation format according to a threshold level. Second, the adaptive global spectrum equalization reconfigures the wavelengths’ attenuation profiles applied at the optical nodes to improve the signals’ optical signal-to-noise ratio (OSNR) at reception. Finally, we report experimental results of an in-band OSNR monitor for advanced modulation formats.

Periodic Training Sequence Aided In-Band OSNR Monitoring in Digital Coherent Receiver

We propose and demonstrate a new data-aided in-band optical-signal-to-noise ratio (OSNR) monitoring method, which employs the periodic property of a specially de- signed short training sequence to differentiate the signal power from noise and is proved to be insensitive to the first-order polarization mode dispersion (PMD). This method is verified in a typical 112-Gb/s polarization multiplexed-quadrature phase shift keying and a 224-Gb/s polarization multiplexed-16 quadrature amplitude modulation coherent optical transmission system. The results show that the method is highly accurate, with the moni- toring error less than 1 dB in the OSNR range of 7-30 dB under different linewidths and has good robustness to a large amount of residual accumulated CD and first-order PMD.

High-Sensitivity In-Band OSNR Monitoring System Integrated on a Silicon Photonics Chip

We report on a compact ( footprint) silicon photonics integrated system performing high-sensitivity monitoring of in-band optical signal-to-noise ratio (OSNR). The system, including a thermally tunable racetrack resonator filter and an unbalanced Mach-Zehnder interferometer, performs the autocorrelation measurement of a filtered fraction of the noisy signal spectrum. Monitor performance is evaluated on a 10 Gb/s ON/OFF keying nonreturn to zero signal, demonstrating an accuracy of 0.4 dB over a wide OSNR range from 8 to 28 dB. We also demonstrate that the proposed system induces a tiny distortion of the optical signal, making it suitable for in-line monitoring of signal quality.

Enhancing the Sensitivity of Interferometer Based In-Band OSNR Monitoring by Narrow Band Filtering

We present a method to enhance the sensitivity of interferometer based techniques employed for the in-band measurement of optical signal-to-noise ratio (OSNR) in wavelength division multiplexed (WDM) optical transmission systems. With respect to conventional schemes, a narrow band filter (NBF) is added before the variable delay interferometer performing the autocorrelation measurement. The NBF is used to select within the signal spectrum only those frequencies where the signal power spectral density (PSD) is locally lower and more sensitive to noise effects. Performance monitoring of a 10 Gb/s on-off keying (OOK) non-return to zero (NRZ) signal is numerically and experimentally investigated for an OSNR level ranging from 5 dB to 25 dB. Design criteria are pointed out for the bandwidth and the detuning of the NBF with respect to the signal carrier wavelength, as well as for the delay of the interferometer, in order to maximize the system sensitivity to OSNR variations. Experimental results, achieved by using an integrated ring-resonator NBF, demonstrate that presented technique enables to effectively detect small noise variations at high OSNR levels (> 15 dB), where conventional interferometer based techniques exhibit a poor sensitivity. Moreover we demonstrate that the NBF can operate directly on the transmitted optical signal without introducing any significant perturbation, this making the presented technique suitable for in-line OSNR measurements.

Novel in-band OSNR monitoring method based on polarization interference

We propose a novel in-band optical signal-to-noise ratio (OSNR) monitoring method based on polarization interference. The method realizes a monitoring accuracy of ±0.5 dB within the range of 9-34 dB. Our results indicate that the proposed method is transparent to bitrate and modulation format, as well as independent of polarization mode dispersion and chromatic dispersion.

In-band OSNR monitor with high-speed integrated Stokes polarimeter for polarization division multiplexed signal

An in-band optical signal-to-noise ratio (OSNR) monitor is proposed, based on an instantaneous polarization state distribution analysis. The proposed monitor is simple, and is applicable to polarization division multiplexed signals. We fabricate a high-speed Stokes polarimeter that integrates a planar lightwave circuit (PLC) based polarization filter, high-speed InP/InGaAs photodiodes and InP hetero-junction bipolar transistor (HBT) trans-impedance amplifiers (TIA). We carry out proof-of-concept experiments with the fabricated polarimeter, and successfully measure the OSNR dependent polarization distribution with 100-Gb/s dual polarization quadrature phase shift keying (DP-QPSK) signals.

An Ultracompact OSNR Monitor Based on an Integrated Silicon Microdisk Resonator

Optical signal-to-noise ratio (OSNR) monitoring is essential for control and management of dynamic optical networks. Small footprint, low cost, and less power consumption are always desirable for such monitoring system. In this paper, we demonstrate an integrated dispersion-insensitive in-band OSNR monitor based on a compact silicon microdisk resonator (MDR) with only 5-μm radius. The MDR (Q ~ 54 000) functions as an ultranarrow bandpass filter in the measurement of the OSNR. The monitoring performance is evaluated in a 10-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) system and is shown to be insensitive to chromatic dispersion from 0 to 850 ps/nm. The input power requirement of the monitor is also studied, which is consistent with the desire for low-power operation. Finally, we analyze the sensitivity of this technique for various Q factors of the MDRs. The results indicate that the sensitivity of this scheme can be improved with higher Q factors.

Multi-channel in-band OSNR monitoring using Stimulated Brillouin Scattering

We investigate an optical performance monitor based on Stimulated Brillouin scattering (SBS), for enabling the measurement of the in-band optical signal to noise ratio (OSNR) for multiple channels of a wavelength-division multiplexed (WDM) signal simultaneously. The principle relies on propagating the signal in a nonlinear waveguide so that each channel pumps SBS to produce a back-scattered Stokes wave of unique carrier wavelength, and with a power that depends on the in-band OSNR of the channel itself. We experimentally demonstrate a highly sensitive OSNR measurement for a 3 x 40 Gb/s signal, with a small sensitivity to the input state of polarization, and a large dynamic range (25 dB) in the Stokes power. Our results also reveal the insensitivity of SBS to both chromatic and polarization-mode dispersions, and the indirect role these effects can play in mitigating the suppression of SBS from the nonlinear Kerr effect.

In-Band OSNR Monitoring Technique Based on Link-by-Link Estimation for Dynamic Transparent Optical Networks

A cost-effective optical performance monitoring system, based on link-by-link optical signal-to-noise ratio (OSNR) estimation, is proposed for a dynamic transparent optical network. The proposed technique estimates the OSNR by monitoring the channel powers at the input and output of each optical link and the total input power to the inline EDFAs. In-band OSNR monitoring was successfully demonstrated at 42.7 Gb/s RZ-DQPSK signals, reflecting the transmission performance.

All-optical in-band OSNR monitoring at 40 Gb/s using a nonlinear optical loop mirror

We present an all-optical in-band optical signal-to-noise ratio (OSNR) monitor using a nonlinear optical loop mirror. Monitoring is enabled from the nonlinear power transfer function of the loop mirror. Experimental results are provided at 40 Gb/s for three modulation formats: nonreturn-to-zero, carrier-suppressed return-to-zero, and return-to-zero. The monitor discriminates the various OSNR levels over a dynamic range of more than 25 dB with every modulation format.

Precise in-band OSNR and spectrum monitoring using high-resolution swept coherent detection

We propose and demonstrate a novel in-band optical signal-to-noise-ratio (OSNR) and spectrum monitoring technique based on swept coherent detection. This technique measures the signal and the in-band amplified spontaneous emission spectra by properly adjusting the polarization states of the signal and the local oscillator. A high resolution of 0.002 nm is achieved. By integrating the detected spectra of the signal and the noise, the in-band OSNR can be obtained in a very precise manner. We monitor the OSNR values with high accuracy in the range of 10-30 dB.