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In recent years, space-division multiplexing (SDM) has been proposed and investigated as a technique to increase the per-fiber capacity in order to cope with the ever-increasing demand for capacity in optical transmission networks. Considering the various SDM architectures proposed, multi-mode fibers potentially allow for the highest spatial channel density, but current demonstrations have been limited to mostly short-distance high-mode count or long-distance low-mode count transmission. In this work, we transmit 15 modes × 184 wavelength channels × $24.5 \,\mathrm{GBd}$ PDM-16-QAM signals, spanning the full C-band, over $1001 \,\mathrm{km}$ of 15-mode multi-mode fiber. The resulting net data rate of $273.6 \,\mathrm{Tb}/\mathrm{s}$ is the highest reported data rate in long-distance multi-mode fiber transmission and results in a record capacity-distance product of 273.9 Pb/s$\cdot$km for multi-mode transmission. This was achieved by using mode multiplexers with low mode-dependent loss (MDL) and insertion loss, as well as a 15-mode fiber optimized for a low differential mode delay (DMD) transmission regime.

We experimentally investigate transmitting high-order quadrature amplitude modulation (QAM) signals with carrierless and intensity-only measurements with phase retrieval (PR) receiving techniques. The intensity errors during measurement, including noise and distortions, are found to be a limiting factor for the precise convergence of the PR algorithm. To improve the PR reconstruction accuracy, we propose a distortion-aware PR scheme comprising both training and reconstruction stages. By estimating and emulating the distortion caused by various channel impairments, the proposed scheme enables enhanced agreement between the estimated and measured amplitudes throughout the PR iteration, thus resulting in improved reconstruction performance to support high-order QAM transmission. With the aid of the proposed techniques, we experimentally demonstrate 50-GBaud 16QAM and 32QAM signals transmitting through a standard single-mode optical fiber (SSMF) span of 40 and 80 km, and achieve bit error rates (BERs) below the 6.25% hard decision (HD)-forward error correction (FEC) and 25% soft decision (SD)-FEC thresholds for the two modulation formats, respectively. We also demonstrate that, by adjusting the pilot symbol ratio and using concatenated coding, a post-FEC data rate of up to 140 Gb/s is achievable for both distances, with the optimal pilot symbol ratio being 20%.

As the capacity of optical transport networks undergoes significant growth, there is an ongoing discussion on how to effectively leverage both spectral and spatial degrees of freedom to scale future network capacity. This paper presents an artificial intelligence (AI)-powered multi-task robot comprising a collaborative robotic arm and a mobile robotic base designed for optical network automation. The robot demonstrates the capability of direct fiber switching, establishing static fiber links that consume zero power and have minimal insertion loss from fiber connectors. As a precautionary measure before physically switching fiber cables, the robot performs path verification by detecting robot-driven events using real-time coherent receivers, aiming to avoid accidental unplugging. Additionally, the robot showcases its mobility by efficiently navigating between different network racks and rooms while executing various tasks. Implementing the automation of network operations using robots has the potential to reduce both capital and operational expenditures.

Using a newly developed bismuth doped fiber amplifier and a multi-port optical processor, operating across the E-band, we investigate wideband E/S/C/L-band transmission with signal bandwidths up to 27.8 THz and distances up to 200 km. Dense wavelength-division multiplexed (D-WDM) transmission is enabled by using a combination of thulium, erbium and bismuth doped-fiber amplifiers in combination with distributed Raman amplification. For 50 km transmission, we transmit a wideband DWDM signal comprising 1097 channels covering 212.3 nm (27.8 THz) from 1410.8 nm to 1623.1 nm for a record single-mode fiber (SMF) data-rate of 321 Tb/s (301 Tb/s after decoding), an increase of 25% on the previous record data-rate. We further show single span transmission at 100 km and 150 km before recording 270.9 Tb/s (258.1 Tb/s after decoding) for 200 km transmission over 2 amplified spans. These results show the potential of E-band transmission, to increase the information carrying capability of optical fibers and open the door to multi-band fiber networks built on already deployed fibers.

This article presents a statistical analysis of modal dispersion of a 69-km-long field-deployed coupled-core four-core fiber link. The link is characterized over a band of approximately 5 THz at 1550 nm, in terms of complex modal dispersion vector, eigenvalues of its modal dispersion matrix, and intensity impulse response. Experimental statistical results are in very good agreement with the theoretical models based on the assumption of strong mode mixing. We also show that a careful analysis of the modal dispersion vector enables the accurate assessment of the skew between channels, distinguishing the contribution of the input patch cords from that of the output ones. Notably, we show that the Stokes-space representation of modal dispersion allows to compensate for the delays introduced at the fiber input and output by the optical vector network analyzer used for measurements. In addition, we provide evidence and theoretical justification of spectral persistence of the principal states in fibers with strong mode mixing. That is, although the modal content and the group delays of the principal modes change from frequency to frequency, the sorting of the principal modes with respect to their group delays is largely frequency independent.

We discuss the use of the fiber channel transfer matrix extracted from a digital coherent receiver for environmental sensing. We show that the polarization rotation vector describing the unitary part of the matrix is highly sensitive to perturbations affecting the optical fiber link. This vector can be readily extracted from the time-dependent transfer matrix reconstructed by the coherent receiver during system operation and may serve as an effective observable to monitor environmental changes.

Comb sources and multi-wavelength lasers can be used as central sources of light in many communication systems using high channel count wavelength division multiplexing. Here, we demonstrate a 16 wavelengths comb source built through large scale hybrid integration of 16 active gain chips with a passive silica chip that incorporates a 16 channel arrayed waveguide grating. Optical coupling between the 16 gain chips and the silica chip is achieved through 32 ball lenses (two per channel), that are aligned and attached in place with an automated process that we developed. The 16 channels have 100 GHz spacing and are centered in the C-band. We show monomode lasing, both in single-channel and multi-channel operation, with side mode suppression ratio as high as, respectively, 67 dB and 55 dB. The total output power of our comb source is about 17.9 dBm when all the 16 channels are activated simultaneously. The channels of our multi-wavelength laser have very narrow Lorentzian linewidths, with best value as narrow as 880 Hz and worst value of about 3.6 kHz. Our comb source integrates hybridly a large number of optical components, however thanks to the parallel architecture and the possibility of packaging the lenses with an automated process, our integration approach can be scaled to an even higher number of channels.

Much efforts have been put to elaborate and improve different high precision measurement schemes for characterization of advanced photonic devices and optical fibers with increasing bandwidth requirements. In light of this, swept-wavelength interferometry and dual-comb spectroscopy have been extensively applied in characterization procedures. In this paper we present in detail an experimental scheme that combines these two techniques and overcomes their limitations by using a tunable laser source in order to sweep over the frequency comb spacing and capture all intermediate frequencies. We demonstrate full-field broadband measurements over 1.25 THz comb bandwidth with increased frequency resolution, which can be performed in only 5 ms sweep. We also show that the nonlinearity of the laser sweep can be removed without an auxiliary interferometer in the setup.

The local variations of group and phase propagation delays induced by bending and twisting a coupled core three-core fiber are experimentally characterized, for the first time, to the best of our knowledge, along the fiber length, with millimeter-scale spatial resolution. The measurements are performed by means of spectral correlation analysis on the fiber’s Rayleigh backscattered signal, enabling for a distributed measurement of the perturbation effects along the fiber length. A mathematical model validating the experimental results is also reported.

Optical vector network analyzers (OVNAs) based on swept-wavelength interferometry are applied widely in optical metrology and sensing to measure the complex transfer functions of optical components, devices, and fibers. Phase noise from laser sweep nonlinearities degrades the measurement quality as the distance increases and limits the usage of the OVNA in characterizing systems with long impulse responses as required in space-division multiplexing links with a high mode count or in the presence of large modal differential group delay (DGD). In this Letter, we use a densely distributed broadband ultra-weak fiber Bragg grating array to directly measure the distortion due to phase noise at a 5-m increment up to 400 m and use this measured data to directly eliminate the distortion. We experimentally extend the measurement range of the swept-wavelength OVNA over 400 m and successfully characterize a 2-km six-mode multimode fiber link with an accumulated impulse response as wide as 20 ns.