We demonstrate a Brillouin OTDR sensing range of 250 km on a telecommunication fiber. Including a normal dispersion fiber at a selected position helps to reduce the nonlinear noise arising from modulation instability at the remote end.

Using intermodal four-wave mixing in an optical step-index fiber, we demonstrate tunable low-noise frequency conversion of single photons emitted from a InAs/GaAs quantum dot with peak conversion efficiency of -0.6 dB.

The controlled excitation of higher-order modes in multimoded optical fibers enables order-of-magnitude power scalings of elementary nonlinear processes such as soliton propagation, dispersive-wave generation and four-wave mixing without losing the benefit of an essentially single-moded spatial output profile. In addition, intermodal nonlinear couplings add new opportunities compared to single-moded fibers. This contribution reviews our numerical and experimental work exploring these opportunities, highlighting some of our most recent results.

We demonstrate efficient Bragg-scattering four-wave mixing frequency conversion in a few-mode fiber with two pumps spectrally separated from the signal and idler by 600 nm. The wideband frequency conversion is made possible by propagating the frequency components in two different spatial modes, the pumps are excited in the LP11 mode, while the signal is excited in the LP01 mode, and the Bragg scattering (BS) idler is generated in the LP01 mode. For these processes, we experimentally characterize their conversion efficiency and bandwidth. The dependency of conversion efficiency on peak pump power and the separation between BS components are measured, demonstrating a peak conversion efficiency of up to 79%.

We introduce a versatile, easy-to-implement Gaussian process model that provides a flexible framework for modeling core-radius fluctuations of an optical fiber. The flexibility of the model allows for easy modification of the fiber profile to fit known characteristics, such as forcing the profile through carefully measured radii at specific points. The model is then used to show the drastic impact that fluctuations have on the efficiency of wide-spanning four-wave mixing systems. Furthermore, by optimizing the fiber design of a simple step-index fiber, we show that the efficiency of the four-wave mixing can be drastically improved even in the presence of large core-radius fluctuations.

We demonstrate an experimental method to characterize the transfer function for quantum frequency conversion via Bragg scattering four-wave mixing by performing measurements in the classical regime.

We demonstrate propagation of higher order modes in fiber tapers with negligible intermodal coupling, enabling wavelength control of dispersive wave generation in a single LP0,m mode around 800nm.

We model and measure the Brillouin power spectrum of Brillouin OTDR assisted by Raman amplification. We show how Raman pump depletion leads to measurement errors due to spectral translation of the Brillouin spectrum.

The generation of light in a laser system is constrained by the gain medium, limiting the available wavelengths. We demonstrate in-fiber generation of ultrafast pulses between ∼550 and 800 nm via dispersive wave generation (DWG), in higher-order modes (HOMs). Using higher-order modes enables power scaling, due to their large effective area compared to the fundamental modes of single-mode fibers and dispersion engineering, even in simple step-index fibers. The process occurs in a single higher-order mode, which we excite using passive glass components (an axicon and two telescopes). The output pulses have energies up to 12 nJ at the biologically relevant wavelength of 705 nm.

Four wave mixing (FWM) holds great promise as a tool to perform signal processing of classical light as well as of quantum states. However, typically FWM require use of high power pumps and as a consequence, the FWM process is accompanied by spontaneous Raman scattering as well as spontaneous FWM. In addition, FWM is also very sensitive to changes in the phase matching along propagation, caused by fluctuations in the core geometry of the fiber. In this work, we review recent progress in predicting and measuring the conversion efficiency and noise figure of wavelength conversion using FWM and we show consequences due fluctuations in the core geometry.

We demonstrate a numerical model for investigating the impact of core -radius fluctuations on four-wave mixing efficiency in optical fibers. The model is validated against experiments and used to suggest effective mitigation methods. (c) 2024 The Author(s)

We demonstrate frequency conversion between waves spanning over 600 nm using intermodal Bragg scattering driven by two high-power pumps separated by up to 49 nm while achieving above -10 dB conversion efficiency.

We demonstrate a Brillouin OTDR sensing range of 251 km using two sections of remotely pumped Erbium doped fiber amplifiers. The temperature shift is measured with an accuracy of 3.3 ◦ C at 251 km.

Uncoupled-core multicore fibers are becoming popular tools for many fields including optical fiber sensing. We analyze for the first time the polarization effects that take place when these fibers are bent.

Strain and temperature sensing based on mode interference in a few-mode fiber is analyzed theoretically and experimentally. The effect of using different mode combinations is explored. A fiber guiding four LP modes is investigated as an example. Good agreement between modeling and experimental results is found for strain sensor. We demonstrate the sensors feasibility by measuring strain ranging from 0 mm to 16 mm with a sensi-tivity of 3.43 nm/mm and measuring temperature ranging from 30 degrees C to 100 degrees C with a sensitivity of 4.8 pm/degrees C.

We report the numerical and experimental study of probe pulse deformation in a forward-pumped distributed Raman amplifier on a 40-km standard single mode fiber. Distributed Raman amplification can improve the range of OTDR-based sensing systems, but it could result in pulse deformation. A smaller Raman gain coefficient can be used to mitigate pulse deformation. The sensing performance can still be maintained by compensating for the decrease in the Raman gain coefficient by increasing the pump power. The tunability of the Raman gain coefficient and pump power levels are predicted while keeping the probe power below the modulation instability limit.

We demonstrate dispersive wave generation at visible wavelengths from a 1030nm pump in a single LP 0,m mode (m = 9,10) of a commercial 50um core fiber, obtaining pulses of 14nJ at 710nm and approximately 50fs.

We consider the potential for generating photon pars with high-dimensional entanglement in their orbital angular momentum through multiple simultaneous four-wave-mixing processes. We study a realistic fiber design and show that states with high entanglement negativity may be obtained.

We demonstrate generation of highly correlated photon pairs via spontaneous four-wave mixing driven by continuous-wave pumping in a hydrogenated amorphous silicon waveguide and obtain a coincidence-to-accidental ratio of 106.2±1.3.

We demonstrate power-scaling of nonlinear frequency conversion in fibres via dispersive wave generation using higher order modes. By pumping in the LP0, m modes at 1030 nm we show wavelength selectability between 550 and 800 nm with pulse energies up to tens of nJ.