Thulium-doped fiber sources for novel applications

Abstract

Very recently, the 2µm wavelength region is attracting growing attention as a potential new transmission window for optical communications to accommodate the everincreasing internet traffic. This is underpinned by the emerging technology of hollowcore photonic bandgap fibers (HC-PBGFs), which holds great promise as a transmission medium with predicted ultra-low loss window around 2µm. In order to realize optical communications at 2µm, high quality optical amplifiers are indispensable.
The first part of this thesis focuses on the development of thulium doped fiber amplifiers (TDFAs) for 2µm optical communications. To start with, a fiber laser pumped TDFA is developed. It provides high gain (>35dB), noise figure (NF) as low as 5dB, and over 100nm wide bandwidth around 2µm. As a crucial step forward, diode-pumping scheme of TDFAs is investigated. Amplification in the range 1810-2050nm with up to 36dB gain and NF as low as 4.5dB is achieved using in-band diode-pumping scheme. Moreover, by exploiting proven amplifier design and newly developed passive device, TDFAs operating in the 1.7-1.8µm waveband are presented. The TDFA gain is extended to as short as 1720nm with 20dB gain achieved. In total, TDFAs so far have covered a remarkable gain bandwidth of 28.6THz. As an ideal platform for testing the TDFA performance, 2µm data transmission experiments are conducted and show that the TDFAs developed well meet the requirements of optical communication systems.
The second part of this thesis describes the development of high power 2µm fiber sources. Fiber master oscillator power amplifier (MOPA) systems directly seeded by 2µm semiconductor diode laser are developed, showing remarkable flexibility and versatility in terms of pulse control. MOPA systems working in the nanosecond regime feature arbitrary pulse shaping capabilities with pulse energy up to 1.0mJ (12.5kHz, 100ns ). When working in the picosecond regime by gain-switching the seed diode laser, the system is capable of operating at repetition rates in the range 2MHz - 1.5GHz without change of configuration, delivering high quality 33ps pulses with up to >3.5µJ energy and over 100 kW peak power, as well as up to 18W of average power.

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ORCID for David J. Richardson: orcid.org/0000-0002-7751-1058

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