Optical Signal-to-noise Ratio Monitor Research Articles

A Novel Cost-Effective and Distributed in-Band OSNR Monitoring Method Using Gaussian Process Regression

We propose and experimentally demonstrate a novel cost-effective and distributed in-band optical signal-to-noise ratio (OSNR) monitoring method using a widely tunable optical bandpass filter and optical power measurements, which employs the Gaussian process regression and is proved to be insensitive to fiber nonlinearity, chromatic dispersion, and optical amplifier type. This method is verified in a 9-channel 10 Gbaud NRZ-QPSK coherent optical transmission system with 50-GHz channel intervals. When there are no add–drop filters or wavelength selective switches in the transmission link, the maximum OSNR deviation, the root-mean-squared error (RMSE), and the mean absolute error (MAE) are less than 0.21 dB, 0.041 dB, and 0.021 dB, respectively, in the OSNR range of 1–29 dB. Instead, when there exist the above optical filtering elements in the transmission link, the maximum OSNR deviation, the RSME, and the MAE are less than 0.24 dB, 0.041 dB, and 0.021 dB, respectively, in the OSNR range of 4–31 dB. Besides, the OSNR monitor based on the novel method can eliminate the necessity to know the transmission information and is more convenient to use because no calibration is required.

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.

Accurate model to predict performance of coherent optical transponder for high baud rate and advanced modulation format.

Bit error rate (BER) versus optical signal to noise ratio (OSNR) characteristics determines the transmission performance for coherent optical transponder. We have developed a model to predict BER versus OSNR at various receiver optical power (ROP). The model has three parameters, which are related to BER noise floor, filter mismatching, and OSNR value without noise loading. The model is applied to high baud rate and quadrature amplitude modulation (QAM) transponders. By considering the influence of baud rate on the fitting parameters, accurate prediction of performance for coherent transponder can be achieved over various baud rates. Novel applications enabled by this model include in-field measurement of BER versus OSNR, simple abstraction of coherent transponder, accurate OSNR monitor and coherent optical channel monitor.

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.

Modulation-format-independent OSNR monitoring insensitive to cascaded filtering effects by low-cost coherent receptions and RF power measurements.

Optical signal-to-noise ratio (OSNR) monitoring is indispensable for ensuring robust and flexible optical networks that provide failure diagnosis, dynamic lightpath provisioning and modulation format adaptation. We propose and experimentally demonstrate a low-cost, modulation-format-independent OSNR monitoring scheme utilizing reduced-complexity coherent receptions, electrical filtering and radio frequency (RF) power measurements. By measuring the RF power of the coherently received baseband signals at three different frequency components, the proposed OSNR monitor is also insensitive to spectral narrowing induced by cascaded wavelength selective switches (WSSs). We experimentally demonstrate accurate data-format-transparent and filtering-effect-insensitive OSNR monitoring for 25-Gbaud dual-polarization (DP-) transmissions with QPSK, 16-QAM and 64-QAM signals over various distances with different amount of filtering effects by cascaded WSSs. We further characterize the influence of different system parameters, such as the bandwidth of the electrical low-pass filter, the laser frequency offset and laser linewidth on the accuracy of the proposed OSNR monitor. The robustness of the proposed OSNR monitoring scheme to fiber nonlinearities, calibration parameter mismatches and variations of WSS parameters are also investigated.

Experimental demonstration of robustness and accuracy of a DLI-based OSNR monitor under changes in the transmitter and link for different modulation formats and baud rates.

We experimentally studied the performance of a delay-line interferometer-based optical signal-to-noise ratio (OSNR) monitor that is pre-calibrated in optimal conditions for 25-Gbaud pol-muxed quadrature-amplitude-modulation (QAM) signals, when unpredicted changes outside the monitor occurred either in the transmitter or the link.

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.

Demonstration of in-service wavelength division multiplexing optical-signal-to-noise ratio performance monitoring and operating guidelines for coherent data channels with different modulation formats and various baud rates

We demonstrated a delay-line interferometer (DLI)-based, optical-signal-to-noise ratio (OSNR) monitoring scheme of 100 Gbit/s polarization multiplexed quadrature-phase-shift-keying (PM-QPSK) four-channel WDM at 50-GHz International Telecommunication Union (ITU) grid with <0.5 dB error for signals with up to 26dB of actual OSNR. We also demonstrated data format transparency and baud rate tunability of the OSNR monitor by measuring the OSNR for a 200 Gbit/s PM-16-QAM (25-Gbaud) signal and a 200 Gbit/s PM-QPSK (50-Gbaud) signal. We also explored and studied different monitor parameters, including the shape of the filter spectrum, the bandwidth of the filter, DLI delay, and DLI phase-detuning to determine the design guidelines for a desired level of accuracy for the OSNR monitor in an optical network.

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.

OSNR Monitoring for NRZ-PSK Signals Using Silicon Waveguide Two-Photon Absorption

We study the use of two-photon absorption (TPA) in a silicon optical waveguide for measuring the optical signal-to-noise ratio (OSNR) of a nonreturn to zero phase-shift keying (NRZ-PSK) signal. The average photocurrent generated in the silicon waveguide increased by 70 nA (from 375 to 445 nA) for a change in OSNR from 28 to 6 dB and a constant total input power of 10 dBm. The nonresonant nature of the silicon waveguide TPA detector enables the simple measurement of OSNR over a continuous wide (>; 10 nm) wavelength range. For a 10-Gb/s NRZ-PSK signal, we show that when the residual dispersion in the optical signal exceeds 425 ps/nm, further increases in dispersion have little effect on the photocurrent. Thus, this TPA-based OSNR monitor can be used in practical systems with large dispersion.

An OSNR monitor for optical packet switched networks

Optical packet switched networks bring about new challenges to the research in optical performance monitoring. We present the first experimental demonstration of an optical signal-to-noise ratio (OSNR) monitor capable of direct OSNR monitoring on the packet basis. By measuring the radio frequency noise from optical packets with a special performance monitoring segment, the OSNR monitoring error is found to be less than 0.6dB for consecutive packets with varying OSNR of 16 to 27 dB. The response time of the OSNR monitor can be around 10 ns

In-band OSNR monitoring using fibre optical parametric amplifier

An in-band optical signal-to-noise ratio (OSNR) monitor based on an optical parametric amplifier is presented. This is achieved using the nonlinear relationship between the input signal power and the power in a new wave generated by cascaded four-wave mixing. The average output power of the new wave is dependent on the OSNR of the input signal. Experiments on the OSNR monitor show a good match to simulations.

Performance of an OSNR monitor based on the polarization-nulling technique

Feature Issue on Optical Performance Monitoring (OPM). We report on the performance of an optical signal-to-noise ratio (OSNR) monitor with the polarization-nulling technique. The results show that this monitor was robust to polarization-mode dispersion and in-band cross talk. For a demonstration, we monitored the OSNR of the optical signal transmitted through a 2×60 km long aerial fiber link for one week and confirmed that the OSNR could be measured with accuracy better than ±0.3 dB (when the OSNR is lower than 26 dB).