We present advancements in erbium-doped fiber (EDF) technology, that addresses the growing demand for increased capacity in long-haul optical communication systems. Bandwidth requirements have expanded beyond the traditional C-band to use the super C-band, L-band and super L-bands-covering a total bandwidth of up to 12 THz. EDF designs have evolved to deliver broader gain spectra and higher output power, supporting these new requirements.

Extended L-band amplification in erbium-doped fibers is inherently inefficient as it utilizes the tail of the gain spectrum. This work demonstrates, via experiments and simulations, a significant gain improve-ment of 3.28 dB by reflecting only 1 % of the out-of-band amplified spontaneous emission.

We demonstrate a TMI-free 5.2 kW single-mode output from a fiber amplifier using Yb 20/400 fibers with reduced core thermo-optic coefficient. The TMI threshold is increased by 50% compared to that of commercial Yb-doped fibers.

We report the performance of an LMA Yb-doped fiber, designed for increasing the transverse mode instability threshold and minimizing nonlinear effects in multi-kilowatt class fiber lasers, by reducing the thermo-optic coefficient of the fiber core, compared with that of standard aluminophosphosilicate Yb-doped fibers. A TMI-free 5.2 kW single-mode output power from a Yb 20/400 fiber with a 17.5 mu m mode-field diameter was achieved in a broad bandwidth, co-pumped amplifier with 78% optical-to-optical efficiency, while a 4 kW signal output was attained in a 26 GHz linewidth amplifier. Negligible photodarkening loss was observed during 150 hour laser operation at 2 kW.

We report the performance of new LMA Yb fibers with increased cladding absorption for pumping in the 915 nm absorption band. A 0.5 dB/m cladding-absorption Yb20/400 fiber showed negligible photodarkening loss in 400-hour laser operation at 3 kW, with 77% optical-to-optical efficiency. Low-SRS and TMI-free operation at 3.5 kW signal power was achieved with a 0.65 dB/m cladding-absorption and 20.2 μm mode-field diameter Yb fiber, tested in a co-pumped amplifier. The Raman peak was 31 dB below the signal peak at the maximum power.

We report a new Yb-doped gain fiber with 20 µm core and 400 µm cladding, designed for improving the long-term operation of commercial fiber lasers powered by cost-effective pump diodes, centered near 976 nm wavelength. The fiber was tested in a co-pumped amplifier, reaching 3.8 kW signal power with 89% optical-to-optical efficiency. Negligible photodarkening loss was observed in over 200-hour laser operation at 2 kW. The signal power was limited to 3.8 kW by TMI and can be further increased by optimizing the pumping configuration. The fiber is compatible with available 20/400 commercial fibers and components allowing fast system integration.

We developed a few-mode receiver potentially independent of the number of modes. The receiver is supported by Kramers-Kronig coherent detection and demonstrated on a 55km few-mode link with 16-WDM spatial-super-channels and total throughput >8 Tbit/s.

Quantum communication (QC) represents a key enabler for many quantum applications. However, low information rates and short propagation distances, limit the development of this field and its practical applications. High-dimensional (Hi-D) QC can address these challenges enhancing the information rate and the systems error tolerance. We report our recent results on Hi-D quantum communication where we prove the capability of preparing, manipulating, transmitting and measuring Hi-D quantum states through multi-core and multimode fiber.

Orbital angular momentum (OAM) modes in fibres are modes that potentially can be used for mode-division multiplexing systems. OAM modes possess a helical phase front which can be written as exp(iLφ), with L being the topological charge and φ being the azimuthal coordinate. Here, we present a chip capable of multiplexing waveguide modes to OAM modes in a fibre in the C-band.

Quantum networks are the ultimate target in quantum communication, where many connected users can share information carried by quantum systems. The keystones of such structures are the reliable generation, transmission and manipulation of quantum states. Two-dimensional quantum states, qubits, are steadily adopted as information units. However, high-dimensional quantum states, qudits, constitute a richer resource for future quantum networks, exceeding the limitations imposed by the ubiquitous qubits. The generation and manipulation of such $D$-level systems have been improved over the last ten years, but their reliable transmission between remote locations remains the main challenge. Here, we show how a recent air-core fiber supporting orbital angular momentum (OAM) modes can be exploited to faithfully transmit $D$-dimensional states. Four OAM quantum states and their superpositions are created, propagated in a 1.2 km long fiber and detected with high fidelities. In addition, three quantum key distribution (QKD) protocols are implemented as concrete applications to assert the practicality of our results. This experiment enhances the distribution of high-dimensional quantum states, attesting the orbital angular momentum as vessel for the future quantum network.

We investigate the data-rate increase of 256-QAM over 64-QAM signals in few-mode fiber transmission. Simulations and experimental validation indicate an increased total data throughput by applying 256-QAM, achieving 146 Tbit/s total data-rate at an average spectral efficiency of 10.67 bit/s/Hz/mode over the entire C-band.

Raman scattering among conventional linearly polarized (LP) modes in single mode optical fibers is generally accepted as a promising way to achieve distributed amplification due to the fact that Raman amplification may provide gain at any wavelength, determined by the used pump wavelength, and excellent noise performance. Here, we show that Raman scattering among orbital angular momentum (OAM) modes in optical fibers have similar properties. We show theoretically that the Raman gain among OAM modes is independent on the topological charge of the OAM modes and that the gain efficiency when the pump and signal are parallel (orthogonally) polarized is similar to the Raman scattering among LP modes in parallel (orthogonal) states of polarization. In addition, we experimentally characterize Raman gain among OAM modes in a fiber supporting multiple OAM modes for both the pump and signal. Finally, we discuss the impact of polarization mode dispersion.

The Internet today transmits hundreds of terabits per second, consumes 9% of all electricity worldwide and grows by 20–30% per year1,2. To support capacity demand, massively parallel communication links are installed, not scaling favourably concerning energy consumption. A single frequency comb source may substitute many parallel lasers and improve system energy-efficiency3,4. We present a frequency comb realized by a non-resonant aluminium-gallium-arsenide-on-insulator (AlGaAsOI) nanowaveguide with 66% pump-to-comb conversion efficiency, which is significantly higher than state-of-the-art resonant comb sources. This enables unprecedented high data-rate transmission for chip-based sources, demonstrated using a single-mode 30-core fibre. We show that our frequency comb can carry 661 Tbit s–1 of data, equivalent to more than the total Internet traffic today. The comb is obtained by seeding the AlGaAsOI chip with 10-GHz picosecond pulses at a low pump power (85 mW), and this scheme is robust to temperature changes, is energy efficient and facilitates future integration with on-chip lasers or amplifiers5,6. By seeding a non-resonant aluminium-gallium-arsenide-on-insulator nanowaveguide with 10-GHz picosecond pulses at a low pump power of 85 mW, a single energy-efficient frequency comb source carrying 661 Tbit s–1 of data, equivalent to more than the total Internet traffic today, is achieved.

Quantum communication (QC) concerns the faithful transmission of quantum states between separated parties, and represents a key enabler for many quantum applications, ranging from quantum key distribution (QKD) to distributed quantum computing. However, low information rates and short propagation distances, due to high channel losses and perturbations of the quantum states, limit the development of this field and its practical applications. High-dimensional (Hi-D) quantum communication can address these challenges by adding more information per photon, directly enhancing the information rate and the systemu0027s error tolerance. We transmit Hi-D quantum states using photons prepared in four orbital angular momentum (OAM) modes in a 1.2 km long OAM-carrying fiber. This is the first experimental demonstration of Hi-D quantum states transmission using the OAM basis over an optical fiber. Furthermore, we successfully implement a real-time decoy-state Hi-D QKD protocol, and demonstrate the highest secret key rate and longest transmission distance of OAM-QKD presented to date.

Quantum communication (QC) concerns the faithful transmission of quantum states between separated parties, and represents a key enabler for many quantum applications, ranging from quantum key distribution (QKD) to distributed quantum computing. However, low information rates and short propagation distances, due to high channel losses and perturbations of the quantum states, limit the development of this field and its practical applications. High-dimensional (Hi-D) quantum communication can address these challenges by adding more information per photon, directly enhancing the information rate and the system's error tolerance. We transmit Hi-D quantum states using photons prepared in four orbital angular momentum (OAM) modes in a 1.2 km long OAM-carrying fiber. This is the first experimental demonstration of Hi-D quantum states transmission using the OAM basis over an optical fiber. Furthermore, we successfully implement a real-time decoy-state Hi-D QKD protocol, and demonstrate the highest secret key rate and longest transmission distance of OAM-QKD presented to date.

We implement the first fiber-based orbital angular momentum (OAM) state high-dimensional quantum key distribution protocol using four OAM modes, and demonstrate the hightest secret key rate and longest transmission distance for OAM presented to date.

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.

We demonstrate a free-space Kramers-Kronig receiver specifically designed for few-mode operation. This is achieved by combining the local oscillator and signal as fewmode signals, prior to demultiplexing.

On-chip multiplexing of the spatial modes of few-moded fibers can dramatically expand the communications bandwidth of single optical fibers.

The set of fibre modes carrying orbital angular momentum (OAM) is a possible basis for mode division multiplexing. In this regard, fibres supporting OAM modes have been fabricated [1], and optical communication using these fibres, has been demonstrated [2]. A vital part of any long range communication system is an optical amplifier. Here we demonstrate, for the first time, Raman amplification of OAM modes.