Amplification of 12 OAM Modes in an air-core erbium doped fiber

We theoretically propose an air-core erbium doped fiber amplifier capable of providing relatively uniform gain for 12 orbital angular momentum (OAM) modes (|L| = 5, 6 and 7, where |L| is the OAM mode order) over the C-band. Amplifier performance under core pumping conditions for a uniformly doped core for each of the supported pump modes (110 in total) was separately assessed. The differential modal gain (DMG) was found to vary significantly depending on the pump mode used, and the minimum DMG was found to be 0.25 dB at 1550 nm provided by the OAM (8,1) pump mode. A tailored confined doping profile can help to reduce the pump mode dependency for core pumped operation and help to increase the number of pump modes that can support a DMG below 1 dB. For the more practical case of cladding-pumped operation, where the pump mode dependency is almost removed, a DMG of 0.25 dB and a small signal gain of >20 dB can be achieved for the 12 OAM modes across the full C-band

High repetition rate, high pulse energy, Raman shifted wavelength selectable fiber laser source in the visible

We have demonstrated a Raman-shifted wavelength-selectable fiber laser source with fundamental spatial-mode output producing ~1µJ pulse-energy at 1MHz repetition-rate with 1.3ns pulse-width using a large-core photonic crystal fiber

Recent progress in SDM amplifiers

Space division multiplexing (SDM) utilizing few-mode fibers or multicore fibers supporting multiple spatial channels, is currently under intense investigation as an efficient approach to overcome the current capacity limit of high-speed long-haul transmission systems based on single mode optical fibers. In order to realize the potential energy and cost savings offered by SDM systems, the individual spatial channels should be simultaneously multiplexed, transmitted, amplified and switched with associated SDM components and subsystems. In this paper, recent progress on the implementation of various SDM amplifiers and its related SDM components is presented

Broadband silica-based thulium doped fiber amplifier employing dual-wavelength pumping

We report a broadband and gain-flattened silica-based thulium-doped fiber amplifier with dual-wavelength pumping (790nm + 1600nm). 15dB gain bandwidth is more than 220nm ranging from 1700 to 1920nm with a maximum gain of 29dB and a noise figure of less than 5dB

Modal gain control in a multimode erbium doped fiber amplifier incorporating ring doping

We theoretically demonstrate the performance of a step index multimode (two mode-group) erbium-doped fiber amplifier with a localized erbium doped ring distribution for Space Division Multiplexed (SDM) transmission

Low-loss 25.3km few-mode ring-core fibre for mode-division multiplexed transmission

We report the design, fabrication and characterisation of a few-mode ring-core fibre supporting 4 mode groups. The low loss (~0.3dB/km) and length (25.3km) are both records for a ring-core fibre

Multimode EDFA performance in mode-division multiplexed transmission systems

We report a detailed study on the system performance of a two-mode group EDFA. In particular we quantify how the gain spectrum and BER performance are affected by input signal and pump power as required in the execution of our ongoing MDM transmission experiments

Modelling of multimode Erbium-doped fibre amplifiers for mode-division multiplexed transmission systems

This PhD thesis, undertaken within the framework of MODEGAP, covers the design and optimization of high-performance in-line Multimode Erbium-Doped Fiber Amplifiers (MM-EDFAs) or Few-mode (FM) EDFA for next-generation SDM transmission systems based on Mode-Division Multiplexing (MDM). In the MM-EDFAs, minimizing the differential modal gain (DMG) is of paramount importance to prevent system outage.By using an experimentally validated commercial amplifier simulator, I proposed a 2-mode-group EDF design incorporating ring doping that allows accurate modal gain control amongst the two-mode groups using a simple and much more practical LP01 pump mode. Subsequently a 2-mode-group ring-doped EDF according to my design was fabricated in-house and a portable 2-mode-group EDFA with low DMG built and tested, confirming my predictions. My 2-mode-group EDFA design lay at the heart of several successful 2-mode-group fiber based transmission experiments, as listed in this thesis.To investigate the vector modes effects in FM-EDFAs, we developed our own MM-EDFA simulator capable of modelling both the Linear Polarized (LP) modes and the full vector solutions. We have concluded that, in practice, the LP amplifier model is valid and sufficient enough to predict the FM-EDFA performance. I proposed a 4-mode-group EDFA design that offered DMG < 1dB across four-mode groups using a customized pump profile. As the number of guided modes increases, the required pump power also increases which means expensive single-mode pump diodes are needed in the core-pumping approach. Cladding pumping is an alternative way to provide pump radiation with the advantages of reducing the costs. Consequently, I upgraded our in-houseamplifier simulator to a cladding-pump-able MM-EDFA design tool incorporating an optimization algorithm (i.e. Genetic Algorithm) that accepts customized criteria and allows a large number of free parameters to be optimized simultaneously. Using this tool, I proposed the designs and optimizations of cladding-pumped 4 and 6-mode-group EDFAs.Apart from the standard step-index MM-EDFAs, I also investigated novel fiber amplifiers with ring-index profiles for SDM applications. The first type of ring-index fiber discussed in this thesis is of solid core and weakly guiding. The solid-core ring core fiber has an advantage of reducing digital signal processing complexity in MDM transmission. I proposed a 6-mode-group ring core multimode erbium doped fiber amplifier (RC-MM-EDFA) capable of providing almost identical gain among the six mode groups within the C band using either core- or cladding-pumped implementations. The second type of ring-index fiber is an air-core fiber that enables the stable transmission of Orbital Angular Momentum (OAM) modes, which can be used as another degree of freedom for information multiplexing. I have created a new variant of my amplifier model targeting OAM modes and have achieved DMG lower than 0.5 dB for 12 OAM modes in an air-core EDF