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We present a method for joint optimization of transmitter in-phase, quadrature and inter-polarization time skew, amplitude mismatch, and bias voltages. The method is based on a cooperative coevolutionary genetic algorithm with fitness functions extracted from a directly detected reference QAM signal generated at the transmitter. As a calibration method, it is able to find the values that will statically generate the best possible constellation. To the extent of the simulation investigations conducted, the algorithm is capable to calibrate time skews, bias voltages, IQ phase imbalances, and relative amplitude imbalances with standard deviation of residual error as low as 0.24 ps, 0.019 V, 0.56°, and 0.003, respectively, for a dual polarization IQ modulator with Vπ = 4V and a 16QAM reference signal operating at 16 GBd. An experimental demonstration is also reported.

To accommodate the demand of exponentially increased global wireless data traffic, the prospective data rates for wireless communication in the market place will soon reach 100 Gb/s and beyond. In the lab environment, wireless transmission throughput has been elevated to the level of over 100 Gb/s attributed to the development of photonic-assisted millimeter wave and terahertz (THz) technologies. However, most of recent demonstrations with over 100 Gb/s data rates are based on spatial or frequency division multiplexing techniques, resulting in increased system's complexity and energy consumption. Here, we experimentally demonstrate a single channel 0.4 THz photonic-wireless link achieving a net data rate of beyond 100 Gb/s by using a single pair of THz emitter and receiver, without employing any spatial/frequency division multiplexing techniques. The high throughput up to 106 Gb/s within a single THz channel is enabled by combining spectrally efficient modulation format, ultrabroadband THz transceiver and advanced digital signal processing routine. Besides that, our demonstration from system-wide implementation viewpoint also features high transmission stability, and hence shows its great potential to not only decrease the system's complexity, butalsomeet the requirements of prospective data rates for bandwidth-hungryshort-range wireless applications., QC 20180307

Optical phase conjugation is a well-known technique to provide dispersion and nonlinearity compensation directly in the optical domain. The link properties play an important role in the achievable improvements in transmission reach/rate. Here, we review our recent investigations on the impact of sub-optimum transmission links as well as our effort on the implementation of the optical phase conjugator itself looking beyond using highly nonlinear fibers as nonlinear medium and focusing on integrated silicon waveguides. Preliminary results on combining optical phase conjugation with digital techniques such as probabilistic shaping will also be discussed.

In-line optical phase conjugation is a well-known technique to enhance the received signal quality through nonlinearity compensation. Being able to implement the conjugation in cm-scale highly nonlinear devices, which can be integrated on a silicon chip could potentially lead to several benefits in terms of small footprint and co-integration with linear signal processing functionalities, as well as lower power consumption. Here, we focus on silicon waveguides to implement the optical phase conjugation through four-wave mixing. The challenges in terms of conversion efficiency imposed by the presence of nonlinear loss are tackled by using a lateral p-i-n diode along the waveguide. When the diode is reverse biased, the conversion efficiency can be effectively enhanced by the decrease in free-carrier absorption. Low-penalty conversion can therefore be achieved for WDM signals and the high quality of the generated idlers is critical in demonstrating a 1-dB Q-factor improvement through optical phase conjugation in a 5 WDM channel 16-QAM transmission system after 644-km of dispersion compensated transmission. The performance improvement enables a performance better than the HD-FEC threshold for all the transmitted channels.

Improvements in signal-to-noise ratio (1.2 dB) and transmission reach (16 %) are demonstrated for dual-polarization WDM 16-QAM signals through nonlinearity compensation by optical phase conjugation in a silicon waveguide with a lateral p-i-n diode

Gains offered by mid-link OPC and probabilistic shaping are compared in a dispersion-managed link with 64QAM input. Probabilistic shaping is optimized online and tailored to the specific channel and transceiver conditions, including the OPC stage.

A perturbation-based nonlinear compensation scheme assisted by a feedback from the forward error correction (FEC) decoder is numerically and experimentally investigated. It is shown by numerical simulations and transmission experiments that a feedback from the FEC decoder enables improved compensation performance, allowing the receiver to operate very close to the full data-aided performance bounds. The experimental analysis considers the dispersion uncompensated transmission of a 532 GBd WDM system with DP-16QAM and DP-64QAM after 4200 km and 1120 km, respectively. The experimental results show that the proposed scheme outperforms single-channel digital backpropagation.

Transmission systems based on the nonlinear Fourier transform (NFT) can potentially address the limitations in transmission reach and throughput set forth by the onset of Kerr-induced nonlinear distortion. Whereas this technique is at a preliminary research stage, a rapid progress has been shown over the past few years leading to experimental demonstrations of dual-polarization systems carrying advanced modulation formats. The lossless transmission required by the NFT to ensure the theoretical validity of the scheme is a fairly strong requirement considering practical transmission links. Here, we address it by using optimized distributed Raman amplification to minimize the power variations to approx. 3 dB over 200 km, thus approaching the lossless transmission requirement. Additionally we experimentally evaluate the improvement provided by equalization schemes applied to the signals in the nonlinear Fourier domain. By combining distributed Raman amplification and nonlinear-Fourier-domain equalization we show transmission reaches for dual-polarization nonlinear frequency division multiplexing (NFDM) systems transmitting both two eigenvalues (8 bit/symbol) up to 2200 km and three eigenvalues (12 bit/symbol) up to more than 600 km at hard-decision (HD) and soft-decision (SD) forward error correction (FEC) threshold, respectively.

We demonstrate Kramers-Kronig detection of a 909.5-Tbit/s DSDM/WDM signal with adaptive rates through a single-mode 37-core fiber. All 3663 channels ( 37 SDM×99 WDM), derived from one source, exhibit error-free performance, achieving an aggregated spectral efficiency of 184.42 bit/s/Hz.

We overcome the low secret key rates of current quantum communication systems using space division multiplexing in a heterogeneous 37-core fiber. We demonstrate record-high rates of 107 Mb/s for the quantum channel alone and of 65 Mb/s when co-propagating with 370 Gb/s classical data.

We demonstrate wavelength-division-multiplexed (WDM) and space-division-multiplexed (SDM) transmission of probabilistically shaped polarization-division-multiplexed (PDM) 1024-state quadrature amplitude modulation (QAM) channels over a 9.7-km single-mode 30-core fiber, achieving aggregated spectral efficiency of 297.82 bit/s/Hz on a 12.5-GHz grid and 7.01-Tbit/s spatial-super-channel on a 25-GHz grid without multiple-input multiple-output (MIMO) processing. Actual soft-decision forward error correction (SD-FEC) decoding was employed to obtain error-free performance, and adaptive rates and spectral efficiencies for individualWDM/SDM channels have been applied according to their channel conditions, by adjusting the SD-FEC overhead without changing the modulation format. Probabilistically shaped PDM-1024-QAM has been used to further increase the aggregated achievable rate due to the added performance improvement through shaping gain.

A method is presented for online probabilistic shaping parameter optimization for channels, which are nontrivial to model and are thus difficult to optimize offline. An example is provided for a mid-link optical phase conjugation based nonlinearity compensation channel with inline dispersion compensation.

We present an analysis of clock recovery algorithms in both polarization division multiplexing systems and mode division multiplexing systems. The impact of inter-polarization time skew and polarization mode dispersion in single-mode fibers, as well as the combined impact of mode mixing and mode group delay spread in multi-mode fibers under different coupling regimes are investigated. Results show that although the clock tone vanishing has a known solution for single-mode systems, in multi-mode systems even for low group delay spread, strong coupling will cause clock tone extinction, making it harder to implement an effective clock recovery scheme.

Simultaneous MIMO-free transmission of 12 orbital angular momentum (OAM) modes over a 1.2 km air-core fiber is demonstrated. WDM compatibility of the system is shown by using 60, 25 GHz spaced WDM channels with 10 GBaud QPSK signals. System performance is evaluated by measuring bit error rates, which are found to be below the soft FEC limit, and limited by inter-modal crosstalk. The crosstalk in the system is analyzed, and it is concluded that it can be significantly reduced with an improved multiplexer and de-multiplexer.

Optical data regeneration is attractive, due to its potential to increase transmission reach and data throughput in communication systems, and several interesting proposals have been made. However, efficient and scalable solutions for regeneration of multiple parallel wavelength channels have been elusive, constituting a key challenge, which must be overcome for optical regeneration to have any prospect of being adapted in actual communication systems. Here we report a scalable wavelength-division multiplexing (WDM) regeneration scheme for phase only regeneration, which satisfies the multichannel requirement, using a set of optical time-lens-based Fourier processors combined with a single phase-sensitive amplifier (PSA). We describe the concept theoretically, and experimentally demonstrate simultaneous regeneration of 16 WDM channels with 50-GHz spacing, each carrying 10-Gbit/s DPSK phase-modulated data. The proposed scheme relies on ultrafast broadband optical processing and is inherently scalable in modulation speed and channel number.

The impact of the OPC offset on the nonlinearity compensation is experimentally investigated, achieving gains up to 0.6-dB SNR and 0.17-bit/symbol mutual information with optimal mid-link OPC for dispersion-compensated transmission up to 966 km

A 1-dB Q-factor improvement through optical phase conjugation in a silicon waveguide with a lateral p-i-n diode enables BER

A polarization-diversity loop with a silicon waveguide with a lateral p-i-n diode as a nonlinear medium is used to realize polarization insensitive four-wave mixing. Wavelength conversion of seven dual-polarization 16-quadrature amplitude modulation (QAM) signals at 16 GBd is demonstrated with an optical signal-to-noise ratio penalty below 0.7 dB. High-quality converted signals are generated thanks to the low polarization dependence (≤0.5 dB) and the high conversion efficiency (CE) achievable. The strong Kerr nonlinearity in silicon and the decrease of detrimental free-carrier absorption due to the reverse-biased p-i-n diode are key in ensuring high CE levels.

A wavelength converter based on AlGaAsOI waveguide is characterized by varying the input signal quality. Signal-to-idler conversion penalty is measured in terms of effective received SNR, and trade-offs between penalty and converted signal quality are outlined.

The use of a micro-ring resonator (MRR) to enhance the modulation extinction ratio and dispersion tolerance of a directly modulated laser (DML) is experimentally investigated with a bit rate of 25 Gb/s as proposed for the next generation data center communications. The investigated system combines a 11-GHz 1.55-μm directly modulated hybrid III-V/SOI DFB laser realized by bonding III-V materials (InGaAlAs) on a silicon-on-insulator (SOI) wafer and a silicon MRR also fabricated on SOI. Such a transmitter enables error-free transmission (BER< 10−9) at 25 Gb/s data rate over 2.5-km SSMF without dispersion compensation nor forward error correction (FEC). As both laser and MRR are fabricated on the SOI platform, they could be combined into a single device with enhanced performance, thus providing a cost-effective transmitter for short reach applications.

A hybrid III-V/SOI directly modulated DFB laser operating at 1.5 μο is fabricated, showing a side mode suppression ratio above 50 dB and a 3-dB bandwidth of 12 GHz. Error-free transmission (BER<10−9) at 10 Gb/s over 66-km SSMF is demonstrated without dispersion compensation and FEC.

The tremendous traffic growth in intra/inter-datacenters requires low-cost high-speed integrated solutions [1]. To enable a significantly reduced footprint directly modulated lasers (DMLs) have been proposed instead of large external modulators. However, it is challenging to use DMLs due to their low dispersion tolerance and limited achievable extinction ratio (ER). A promising solution to this problem is optical spectral reshaping (OSR) since it is possible to increase the dispersion tolerance as well as to enhance the achievable ER for both on-of-keying [2] and 4-pulse amplitude modulation (PAM) [3] signals. However, moving to 4-PAM,many of the impressive demonstrations reported so far rely heavily on off-line digital signal processing (DSP), which increases latency, power consumption and cost. In this talk, we report on (i) a detailed numerical analysis on the complex transfer function of the optical filter for optical spectral reshaping in case of pulse amplitude modulation and(ii) an experimental demonstration of real-time dispersion-uncompensated transmission of 10-GBd and 14-GBd 4-PAM signals up to 10- and 26-km SSMF. This is achieved by combining a commercial 10-Gb/s DML with optical spectral shaping, thus removing the need for any complex off-line DSP and improving dispersion tolerance. These achievements are enabled by OSR based on a passive microring resonator fabricated on the SOI platform [4]. Significant improvement in receiver sensitivities was observed for both a 10-GBd signal after 10-km SSMF transmission and 14-GBd with no penalty after 26-km SSMF transmission., QC 20171109

The use of a micro-ring resonator (MRR) to enhance the modulation extinction ratio and dispersion tolerance of a directly modulated laser (DML) is experimentally investigated with a bit rate of 25 Gb/s as proposed for the next generation data center communications. The investigated system combines a 11-GHz 1.55-mu m directly modulated hybrid III-V/SOI DFB laser realized by bonding III-V materials (InGaAIAs) on a silicon on-insulator (SOI) wafer and a silicon MRR also fabricated on SOL Such a transmitter enables error-free transmission (BER< 10(-9)) at 25 Gb/s data rate over 2.5-km SSMF without dispersion compensation nor forward error correction (FEC). As both laser and MRR are fabricated on the SOI platform, they could be combined into a single device with enhanced performance, thus providing a cost-effective transmitter for short reach applications., QC 20180322

We experimentally demonstrate a single channel 32-GBd 16QAM THz wireless link operating in the 0.4 THz band. Post-FEC net data rate of 106 Gbit/s is successfully achieved without any spatial/frequency multiplexing., QC 20170713Non-duplicate with diva 1164969

Multi-eigenvalues transmission with information encoded simultaneously in both orthogonal polarizations is experimentally demonstrated. Performance below the HD-FEC limit is demonstrated for 8-bits/symbol 1-GBd signals after transmission up to 207 km of SSMF.

This paper studies the impact of probabilistic shaping on effective signal-to-noise ratios (SNRs) and achievable information rates (AIRs) in a back-to-back configuration and in unrepeated nonlinear fiber transmissions. For back-to-back, various shaped quadrature amplitude modulation (QAM) distributions are found to have the same implementation penalty as uniform input. By demonstrating in transmission experiments that shaped QAM input leads to lower effective SNR than uniform input at a fixed average launch power, we experimentally confirm that shaping enhances the fiber nonlinearities. However, shaping is ultimately found to increase the AIR, which is the most relevant figure of merit as it is directly related to spectral efficiency. In a detailed study of these shaping gains for the nonlinear fiber channel, four strategies for optimizing QAM input distributions are evaluated and experimentally compared in wavelength division multiplexing (WDM) systems. The first shaping scheme generates a Maxwell-Boltzmann (MB) distribution based on a linear additive white Gaussian noise channel. The second strategy uses the Blahut-Arimoto algorithm to optimize an unconstrained QAM distribution for a split-step Fourier method based channel model. In the third and fourth approach, MB-shaped QAM and unconstrained QAM are optimized via the enhanced Gaussian noise (EGN) model. Although the absolute shaping gains are found to be relatively small, the relative improvements by EGN-optimized unconstrained distributions over linear AWGN optimized MB distributions are up to 59%. This general behavior is observed in 9-channel and fully loaded WDM experiments., Comment: 9 pages, 7 figures, 7 tables

A simple method for joint estimation of transmitter’s in-phase/quadrature and inter-polarization time skew is proposed and experimentally demonstrated. The method is based on clock tone extraction of a photodetected signal and genetic algorithm. The maximum estimation error was 0.5 ps.

Aluminum Gallium Arsenide on insulator (AlGaAs-OI) has recently been developed into a very attractive platform for optical signal processing. This paper reviews key results of broadband optical signal processing using this platform.

Pilot based equalization is studied in a 5x10 Gbaud WDM transmission experiment. The equalization is independent of the modulation format and is demonstrated for 256/1024QAM with uniform and probabilistically optimized distribution using an optimized pilot insertion rate of 2-5%.

Real-time transmission of 14-GBd 4-PAM signal is demonstrated by combining a commercial 1.55-µm DML with a silicon MRR. BER below the HD-FEC threshold is measured after 26-km SSMF transmission without offline digital signal processing.

Simultaneous MIMO-free transmission of a record number (12) of orbital angular momentum modes over 1.2 km is demonstrated. WDM compatibility of the system is shown by using 60 WDM channels with 25 GHz spacing and 10 GBaud QPSK.

We propose a novel and strikingly simple design for all-optical bit-rate-transparent RZ-to-NRZ conversion based on optical phase filtering. The proposed concept is experimentally validated through format conversion of a 640 Gbit/s coherent RZ signal to NRZ signal.

The impact of signal-conjugate wavelength shift on nonlinearity compensation through optical phase conjugation is investigated for 64- and 256-QAM. Wavelength-shift independent achievable rate improvements between 0.2 and 0.3 bit/symbol are reported for shifts up to 30 nm in 500-km transmission.