Search

We propose and demonstrate a mode-division-multiplexed transmitter by employing a VCSEL-based 2-D matrix and a multi-plane light converter (MPLC). The triangular matrix light spots from VCSELs are designed with a 250-μ pitch in both x- and y- directions for scalable and low-loss mode multiplexing. The VCSELs are directly modulated by co-packaged BiCMOS drivers on a silicon interposer, fabricated on a wafer level. The MPLC is utilized to form seven phase masks to convert the individual Gaussian beams to multiplex Hermite-Gaussian modes, which can be coupled into a multi-mode fiber. In the demonstration, we packaged ten 10-G class VCSELs with the drivers, and the form factor of the co-packaged optics is 10-mm × 10-mm. With the fan-out evaluation board, the sub-module is characterized for short and long transmissions by multiplexing the ten directly modulated outputs from VCSELs. The testing results indicate 200-Gb/s capacity over 100-m MMF with direct detection and 28-km few-mode fiber with coherent detection.

Few-mode fibers and coupled-core multi-core fibers are attractive transmission media for space-division multiplexed transmission systems as they enable a high spatial channel multiplicity whilst sustaining the current standard cladding diameter. This paper compares space-division multiplexed recirculating loop transmission using either a 3-mode few-mode fiber or a 3-core coupled-core multi-core fiber. After analyzing the spectral attenuation properties of both fibers, we investigate the wavelength and transmission distance dependence of the transmission channel characteristics. We find that the channel memory length is shorter and mode-dependent loss is lower in the coupled-core multi-core fiber, which can be attributed to the fundamental mode-structure differences between the two fiber types. This leads to a higher data rate at similar transmission distance for the coupled-core multi-core fiber.

We experimentally demonstrate an elliptical-aperture multimode diversity receiver to mitigate the impairment from anisotropic turbulence, which is emulated by employing an electrically-controlled heater. The anisotropy gradually decreases as the flow-level of the introduced airflow from fans increases. In contrast to circular-aperture reception, the elliptical-aperture multimode diversity receiver can effectively resist beam wander under anisotropic turbulence, reducing outage probability from 14.63% to 0.38% for detecting a dual-polarization 30-Gbaud QPSK signal. Without the aid of an adaptive optics system, this work demonstrates the feasibility of realizing an anisotropic-turbulence-resistant FSO link using multimode and multi-aperture diversity reception employing digital coherent combining techniques.

We experimentally demonstrate on-chip modal crosstalk mitigation over two mode-division multiplexing (MDM) integrated circuits supporting four and eleven waveguide modes employing low-coherence matched detection. 30-Gbaud 8-PSK mode-multiplexed signal is successfully transmitted over the circuits without using multiple-in-multiple-output (MIMO) processing under a maximum modal crosstalk of 10 dB. Ten-mode-multiplexed on-chip transmission achieves a total capacity of 900 Gbit/s. This work shows the feasibility of using high-order modes in on-chip MDM transmission for future high-capacity optical interconnects.

We introduce recently developed space division multiplexing (SDM)-associated technologies into optical wireless communications (OWC) and propose to use incoherent and low-coherence spatial modes to realize optical broadcasting with reliable performance by mitigating coherent interference. We experimentally demonstrate reconfigurable optical beam steering using a programmable multi-plane light conversion (MPLC)-based mode multiplexer (MMUX) and realize point-to-multi-point optical wireless communications with low-loss up-link optical beam combining and reach extension using multimode fiber (MMF). Both incoherent and low-coherence spatial modes can be generated employing cost-efficient components such as a multimode vertical cavity surface emitting laser (MM-VCSEL) and broadband amplified spontaneous emission (ASE) noise source.

High-capacity, long-haul transmission over a coupled-core three-core multi-core fiber is investigated in a recirculating loop experiment. We report key system characteristics, such as the optimum launch power as well as the wavelength dependence and distance-evolution of mode-dependent loss and the impulse response time spread. We further performed two high data-rate, long-haul transmission demonstrations with more than 75 nm optical bandwidth in C- and L-bands over distances up to 4800 km. The reported data-rate of 172 Tb/s over 2040 km is the highest demonstrated in any multi-span transmission system employing optical fibers with standard cladding diameter of 125 micro-meter to date. Additionally, transmission of 81 Tb/s over 4800 km distance demonstrates the potential of using coupled-core multi-core fibers in combination with wideband optical signals over long-haul distances.

We designed, fabricated, and tested a 90° optical hybrid using multiplane light conversion. The device supports an octave of bandwidth (900–1800 nm) in simulations. The measured phase errors are below 3° for free space output, and below 8° with a fiber array output, across a measurement bandwidth of 390 nm. The fully-packaged device (with input and output fiber arrays) has a measured insertion loss of 5.52 dB at 1550 nm. A high-speed transmission experiment with QPSK format was conducted to verify the performance of the fully-packaged device.

Cladding-pumped optical fiber amplifiers are of increased interest in the context of space-division multiplexing but are known to suffer from low power efficiency. In this context, ytterbium (Yb) co-doping can be an attractive solution to improve the performance of erbium (Er) doped fiber amplifiers. We present a detailed direct comparison between Er/Yb-co-doping and Er-doping using numerical simulations validated by experimental results. Two double-cladding fibers, one doped with Er only and the other one co-doped with Er and Yb, are designed, fabricated and characterized. Using the experimentally extracted parameters, we simulate multi-core fiber amplifiers and investigate the interest of Er/Yb-co-doping. We calculate the minimum gain of the amplifiers over a 35-nm spectral window considering various scenarios.

Signal propagation in Space-Division Multiplexed (SDM) systems in the linear regime is dominated by the effects of modal dispersion (MD) and mode-dependent loss (MDL). While multiple models have been proposed for characterizing these phenomena separately or to study the effect of MD on MDL, the effect of MDL on the system MD has never been analyzed. In this article, we report such an analysis, where the inclusion of MDL is accounted for by introducing a complex MD vector $\vec{\tau }$ . We show that the signal delay spread, quantified by the duration of the intensity impulse response function, is not affected by the presence of MDL, and its functional dependence on $\vec{\tau }$ remains the same as in the absence of MDL (in which case $\vec{\tau }$ is a real-valued vector). The model, which represents SDM systems operating in the regime of strong coupling between modes, is validated by comparison with experimental data.

We report on the ultra-wideband (UWB) transmission of a 103 nm signal over 3 × 100 km of standard single mode fiber (SSMF), a widely-deployed fiber in terrestrial transmission networks. In such UWB systems, nonlinear effects such as stimulated Raman scattering (SRS) must be taken into account in the system design. We characterize the SRS impact in high power regime for this UWB spectrum. We study the evolution of SRS over the bandwidth when tilting the input spectrum to counter the inter-band power transition. We transmit 254 probabilistically constellation shaped (PCS)-64QAM channels over 300 km of SSMF and demonstrate a 107-Tb/s transmission throughput over a continuous 103 nm optical bandwidth using backward Raman pumping and SOA technology.

We experimentally investigate high-capacity few-mode fiber transmission for short and medium-haul optical links. In separate experiments, we demonstrate C + L band transmission of 283 Tbit/s over a single 30 km span and recirculating loop transmission of 159 Tbit/s over 1045 km graded-index three mode fiber. The first experiment reached a data-rate per fiber mode within 90% of the record data-rates reported in the same transmission bands for single-mode fibers. The second experiment demonstrated the feasibility of reaching high data-rates over long distance few-mode fiber transmission, despite strong impairments due to mode-dependent loss and differential mode delay.

We report on the multiplexing of 12 spatial and polarization channels and 120 wavelength channels in the C -band, each carrying 16 quadratic-amplitude modulation symbols at 30 GBd over graded-index few-mode fiber. A combination of multiple fiber spools with positive and negative modal dispersion values is exploited to form a 59-km link with 0.35-ns differential mode group delay. The link is placed inside a sixfold synchronized recirculating loop transmission setup. Photonic lanterns with low insertion and mode-dependent loss are employed to excite the six spatial modes in the few-mode fiber. A net transmission rate of 138 Tb/s at a spectral efficiency of 34.91 b/s/Hz over 590 km is demonstrated.

We demonstrate the full bandwidth measurement of the intermodal four-wave mixing efficiency for a 4.7-km three-spatial-mode few-mode fiber. Large fluctuations of intermodal four-wave mixing between the LP $_{01}$ and LP $_{11}$ modes are experimentally observed. These fluctuations exhibit a strong wavelength dependence that can be persistent in time. The fluctuations are also shown to display some polarization dependence.

We directly measure the spatially and spectrally resolved gain of erbium doped multicore and few mode fiber amplifiers using a coherent swept wavelength interferometer operated in the reflection mode. It greatly simplifies the characterization of multispatial mode amplifiers because it enables characterization of the mode-dependent gain with only a single mode-selective multiplexer at the input. The gains for both multicore fiber amplifier and three spatial modes (LP01 and ${\rm{LP}}_{{11}}$ ) amplifier are measured. Measurements for multicore fiber amplifier are conducted using two pump schemes, core pump and cladding pump. Also, the comparison with the cutback experiments shows the validity of this technique.

We demonstrate cladding-pumped six-core Erbium-doped fiber amplifiers (EDFAs) using two different pump coupling schemes: edge-coupled and side-coupled pumping, where a single multimode laser diode can be applied to pump all cores. Using two in-line cladding-pumped EDFAs at the input and output of a 31-km coupled-six-core fiber, we realized 465-km space-division multiplexing and wavelength division multiplexing transmission in a recirculating loop and achieved a spectral efficiency of 18 bits/s/Hz. Through side-coupled pumping, the cladding-pumped six-core EDFA produced >18-dBm output power per core and had

We characterize the distributed Raman amplification in a 70-km three spatial-mode few-mode fiber with different pump configurations and demonstrate bidirectional pumped Raman amplification and 1050 km combined wavelength-division and spatial-division multiplexed transmission in the same fiber with a zero net gain fiber span.

This paper presents a single-carrier optical coherent transmitter that synthesizes high-fidelity waveforms from N spectral slices with the state-of-the-art electrical drivers. The synthesis technique overcomes the electronic speed bottlenecks and produces an optical waveform bandwidth that is N times the electrical bandwidths. Using two 32 GHz slices, we synthesized and transmitted a 60-GBd polarization-division multiplexed, quadrature phase-shift keying (PDM-QPSK) waveform over 4480 km with a Q2-factor of 8.71 dB. To demonstrate high-fidelity waveform synthesis, we generated a 60-GBd PDM 16-QAM and observed a 2.5-dB implementation penalty at BER of 1×10–2. To address scalability, we also developed the phase mismatch compensation algorithm for the transmitter that uses photonic integrated circuits.

Signal transmission with capacity of 41.6 Tbit/s (net data rate 16.8 Tbit/s) over 12 spatial and polarization modes is demonstrated. Dense optical orthogonal frequency division multiplexing signals with a channel spacing of 16.7 GHz across the full C band is generated. The resulting 12 tributaries are (de-)multiplexed using a novel fully packaged photonic lantern based 3-D-waveguide spatial-multiplexer. The spatially multiplexed signals are transmitted over 74.17-km weakly coupled six-mode few mode fiber enabling inline differential mode delay compensation. All 12 tributaries are detected using three oscilloscopes via coherent heterodyne receiver. The bit error rate of the 255 channel in each mode is evaluated to be below the forward error correction limit 2.4 $\,\times\,$ 10 ${\bf ^{-2}}$ assuming 20% overhead.

Presents corrections to the paper, “High capacity transmission with few-mode fibers,” (Rademacher, G.), Lightw. Technol., vol. 37, no. 2, pp. 425–432, Jan. 2019.

We demonstrate two 160-Gb/s modulation formats that posses the same intensity pulse profile but differ regarding their phase coding. We analyze the nonlinear transmission properties of both coherent modulation formats by experimental and analytical investigations. The results show that the pairwise alternating phase coded carrier suppressed return-to-zero (PAP-CSRZ) signal outperforms the conventional CSRZ format. Our modulation technique is even applicable at higher speed as demonstrated with the generation of the first CSRZ signal at a record rate of 320 Gb/s.

A red-shift optical filter all-optical wavelength converter compatible to all-optical WDM networks is introduced and demonstrated at 40 and 10 Gb/s. The wavelength converter provides reshaping and can act as a power equalizer. We use the device to overcome wavelength blocking in a looped-fiber network demonstration equivalent to 42 cross-connect switches and a 16800 km transmission distance.

This paper analytically and experimentally examines node architectures for wavelength-routing networks, with emphasis on the degree of wavelength conversion provided. Wavelength flexibility simplifies network management and increases network capacity but requires large cross-connects and deployment of wavelength converters (WCs). A simple probabilistic model is used to upper-bound the number of WCs required at a network node, under dynamic traffic load. When provisioned in a shareable pool, with a fixed number of wavelength channels per fiber, the number of WCs required remains low as overall network capacity is scaled up. Motivated by this analysis, experiments demonstrate the feasibility of implementing wavelength-flexible network nodes using large microelectromechanical (MEMS)-based cross-connects and all-optical WCs. In one design, WCs were attached directly to cross-connect output ports, and in another, they were attached in a loop-back fashion to allow sharing. Error-free transmission at 10 Gb/s was demonstrated in both cases.