Multiple Wavelength-division-multiplexing Channels Research Articles

Multi-Wavelength Photonic Neuromorphic Computing for Intra and Inter-Channel Distortion Compensations in WDM Optical Communication Systems

Digital signal processing (DSP) has been widely applied in optical communication systems to mitigate various signal distortions and has become one of the key technologies that have sustained data traffic growth over the past decade. However, the strict energy budget of application-specific integrated circuit-based DSP chips has prevented the deployment of some powerful but computationally costly DSP algorithms in real applications. As a result, fiber nonlinearity-induced signal distortions impede fiber communication systems, especially in wavelength-division multiplexed (WDM) transmission systems. To solve these challenges in DSP, there has been a surge of interest in implementing neural networks-based signal processing using photonics hardware (i.e., photonic neural networks). Photonic neural networks promise to break performance limitations in electronics and gain advantages in bandwidth, latency, and power consumption in solving intellectual tasks that are unreachable by conventional digital electronic platforms. This work proposes a photonic recurrent neural network (RNN) capable of simultaneously resolving dispersion and both intra and inter-channel fiber nonlinearities in multiple WDM channels in the photonic domain, for the first time to our best knowledge. Furthermore, our photonic RNN can directly process optical WDM signals in the photonic domain, avoiding prohibitive energy consumption and speed overhead in analog to digital converters (ADCs). Our proposed photonic RNN is fully compatible with mature silicon photonic fabrications. We demonstrate in simulation that our photonic RNN can process multiple WDM channels simultaneously and achieve a reduced bit error rate compared to typical DSP algorithms for all WDM channels in a pulse-amplitude modulation 4-level (PAM4) transmission system, thanks to its unique capability to address inter-channel fiber nonlinearities. In addition to signal quality performance, the proposed system also promises to significantly reduce the power consumption and the latency compared to the state-of-the-art DSP chips, according to our power and latency analysis.

WDM photon pair source stabilized in a wide temperature range with cascaded optical nonlinearities and DFG monitoring.

In this paper, we report a multi-channel wavelength division multiplexed (WDM) photon pair source operating in a wide temperature range. The photon pair generation rates in multiple WDM channels were stabilized against changes in the operation temperature by combining the spectral flatness of cascaded optical nonlinearities (cascaded sum frequency generation/spontaneous parametric downconversion) with a differential frequency generation monitoring feedback system. The proposed method was experimentally validated using a type-I periodically poled LiNbO3 ridge waveguide device as the photon pair source. We successfully generated 16 WDM photon pairs at almost the same rate (0.024358 ± 0.000631 pairs/s/Hz), even when the operating temperature was varied from 27.01 °C to 60.16 °C.

Optical Equalizers for Bandwidth-Limited Transmitters and PAM-Based Fiber Optic Links

Optical feed-forward equalization (FFE) of a single-mode fiber link has been studied theoretically. It is demonstrated that a simple short optical FFE having three to five taps can provide significant performance improvement of bandwidth-limited transmitters for both short and long reach links compared with the nonequalized scenario. Since optical FFEs can simultaneously operate on multiple wavelength division multiplexing channels, they can provide a simple, low power, and cost-effective solution for high-speed optical communication links.

SOA Based Photonic Integrated WDM Cross-Connects for Optical Metro-Access Networks

We present a novel optical metro node architecture that exploits the Wavelength Division Multiplexing (WDM) optical cross-connect nodes for interconnecting network elements, as well as computing and storage resources. The photonic WDM cross-connect node based on semiconductor optical amplifiers (SOA) allows switching data signals in wavelength, space, and time for fully exploiting statistical multiplexing. The advantages of using an SOA to realize the WDM cross-connect switch in terms of transparency, switching speed, photonic integrated amplification for loss-less operation, and gain equalization are verified experimentally. The experimental assessment of a 4 × 4 photonic integrated WDM cross-connect confirmed the capability of the cross-connect chip to switch the WDM signal in space and wavelength. Experimental results show lossless operation, low cross-talk <−30 dB, and dynamically switch within few nanoseconds. Moreover, the operation of the cross-connect switch with multiple WDM channels and diverse modulation formats is also investigated and reported. Error-free operation with less than a 2 dB power penalty for a single channel, as well as WDM input operation, has been measured for multiple 10/20/40 Gb/s NRZ-OOK, 20 Gb/s PAM4, and data-rate adaptive DMT traffic. Compensation of the losses indicates that the modular architecture could scale to a larger number of ports.

Detection of a Single 40 Gb/s Polarization-Multiplexed QPSK Channel With a Real-Time Intradyne Receiver in the Presence of Multiple Coincident WDM Channels

We have characterized the performance of a single-ended intradyne receiver when multiple wavelength-division multiplexed (WDM) channels are incident. Detection of a single 40 Gb/s dual-polarization QPSK channel is achieved within a band of up to 17 WDM channels using a receiver with real-time digital signal processing and without optical demultiplexing. Measurements are presented of the performance in a back-to-back configuration as well as after transmission over 400 km of standard single-mode fiber. The dependence of the coincident channels' interference on various parameters, such as the net chromatic dispersion and the orientation of the coincident channels' polarization tributaries relative to the receiver polarizer, is explored. We also investigate using a single interfering channel with its power appropriately scaled to represent multiple interfering channels as an alternative configuration for evaluating receiver performance. The single-interferer approach has significant disadvantages including increased polarization sensitivity and different scaling of the interference term arising from the channel-channel beating compared to true multi-channel interference.

Simultaneous all-optical 3R regeneration scheme with improved scalability using TOAD

A novel re-timing, re-amplifying, and re-shaping (3R) regeneration system is proposed to process multiple WDM (wavelengthdivision-multiplexing) channels simultaneously. Its re-timing capability is investigated by both simulation and experiment with polarizationscrambling method at 10 Gb/s bit rate. Jitter tolerance up to 0.8 UIpp is demonstrated with BER improvement and floor breaking ability.

Fractional Lambda Switching Principles of Operation and Performance Issues

This article introduces fractional lambda (λ) switching (FλS) and studies its blocking issues. FλS uses a global common time reference (CTR) for implementing pipeline forwarding (PF) inside the network. A global CTR is conveniently realized with the UTC (coordinated universal time) standard. Resource reservation over an FλS network requires a schedule. As in other scheduling cases, a call may not be accepted, even though there is enough capacity, because the schedule is not available—the call is then considered blocked. This work studies the probability of call blocking as a function of link utilization. The results show that (especially if multiple-wavelength division multiplexing channels are deployed on optical links between fractional λ switches) high-link utilization can be achieved with negligible call blocking, even when the switching fabric is a Banyan network.

Simultaneous label swapping and wavelength conversion of multiple independent WDM channels in an all-optical MPLS network using PPLN waveguides as wavelength converters

This paper presents the demonstration of all-optical simultaneous label swapping and wavelength conversion of multiple independent wavelength-division multiplexed (WDM) channels using periodically poled lithium niobate (PPLN) waveguides as wavelength converters. Label swapping is one of the required functions in the physical layer for efficient data flow control in the proposed multiprotocol label switching (MPLS) networks. The technique operates directly on the optical signal without optoelectronic (O/E) conversion; therefore, it is bit-rate, label length, and protocol/format independent. Experimental results are presented for the label swapping of distinct 8-b-long labels in a system with 2 WDM data channels at 10 Gb/s. There is a guard time of 400 ps between the payload and the label. The power penalty introduced by the method is less than 3 dB. This method can potentially accommodate 10 WDM channels simultaneously over the PPLN waveguide's ∼40 nm /spl lambda/-shifting bandwidth.

Perfectly synchronized bit-parallel WDM data transmission over a single optical fiber

We demonstrate a bit-level synchronization technique by conducting a bit-parallel wavelength-division-multiplexed (WDM) data transmission over 27.5 km of optical fiber. Multiple WDM channels, which may represent individual bits in a byte or a word in parallel computer input-output, are transmitted in the optical fiber in non-return-to-zero format. These bits experience time skew due to group velocity dispersion. By sampling with an all-optical switch in the range where all these bits overlap, we obtained perfectly synchronized WDM signals. The synchronized WDM channels are demultiplexed with an array waveguide grating. Bit error rates below 10/sup -10/ are measured for each channel. The spectral range of the experimental demonstration covers about 24 nm with the smallest wavelength separation of 1.4 mm, enough to pack 16 bits into the span. More bits are available if smaller channel-separation and wider spectral span are employed.

All-fibre periodic spectral filter for simultaneous generation of multiple WDM channels from broad bandwidth pulsed sources

An all-fibre spectral filter is demonstrated for the simultaneous generation of several wavelength division multiplexed (WDM) pulsed sources using the spectral slicing technique. More than 10 WDM channels, each with a base rate of 10 GHz, are generated from a single 190 fs pulse train.