P.C. Shardlow

100 kW peak power picosecond thulium-doped fiber amplifier system seeded by a gain-switched diode laser at 2 μm

We report on the generation of picosecond pulses at 2 μm directly from a gain-switched discrete-mode diode laser and their amplification in a multistage thulium-doped fiber amplifier chain. The system is capable of operating at repetition rates in the range of 2 MHz-1.5 GHz without change of configuration, delivering high-quality 33 ps pulses with up to 3.5 μJ energy and 100 kW peak power, as well as up to 18 W of average power. These results represent a major technological advance and a 1 order of magnitude increase in peak power and pulse energy compared to existing picosecond sources at 2 μm.

Exploiting the short wavelength gain of silica-based thulium-doped fiber amplifiers

Short wavelength operation (1650-1800 nm) of silica-based thulium-doped fiber amplifiers (TDFAs) is investigated. We report the first demonstration of in-band diode-pumped silica-based TDFAs working in the 1700-1800 nm waveband. Up to 29 dB of small-signal gain is achieved in this spectral region, with an operation wavelength accessible by diode pumping as short as 1710 nm. Further gain extension toward shorter wavelengths is realized in a fiber laser pumped configuration. A silica-based TDFA working in the 1650-1700 nm range with up to 29 dB small-signal gain and noise figure as low as 6.5 dB is presented.

90nm gain extension towards 1.7µm for diode-pumped silica-based thulium-doped fiber amplifiers

We report the first demonstration of in-band diode-pumped silica-based thulium-doped fiber amplifiers working in the 1.7-1.8 μm waveband. Compared to previously reported results, 90 nm gain extension has been achieved by exploiting novel amplifier designs.

First demonstration of a 2μm few-mode TDFA for mode division multiplexing

We report the first demonstration of an inline few-mode thulium doped fiber amplifier (TDFA) operating at 2μm for mode division multiplexed transmission. Similar gain and noise figure performance for both the LP(01) and LP(11) modes are obtained in a cladding pumped 2-mode group TDFA. A maximum gain of 18.3dB was measured at 1970nm with a 3dB gain bandwidth of 75nm while the average noise figure was measured to be between 7 and 8dB for wavelengths longer than 1970nm.

Laser pulse control of a Q-switched Nd:YVO 4 bounce geometry laser using a secondary cavity

A novel technique for obtaining enhanced control of pulsing parameters in a laser is described and implemented for the first time in a 1.1%Nd:YVO4 bounce geometry laser. The method uses a secondary laser cavity to control the gain in a Q-switched primary laser cavity and has enabled clean single-pulse Q-switched operation to be obtained across a repetition rate range of 1-800 kHz, where previously laser breakthrough had occurred below 150 kHz. Control of the pulse energy from the Q-switched laser is also demonstrated at a fixed repetition rate of 100 kHz by this technique.

High gain holmium-doped fibre amplifiers

We investigate the operation of holmium-doped fibre amplifiers (HDFAs) in the 2.1 µm spectral region. For the first time we demonstrate a diode-pumped HDFA. This amplifier provides a peak gain of 25 dB at 2040 nm with a 15 dB gain window spanning the wavelength range 2030 - 2100 nm with an external noise figure (NF) of 4-6 dB. We also compare the operation of HDFAs when pumped at 1950 nm and 2008 nm. The 1950 nm pumped HDFA provides 41 dB peak gain at 2060 nm with 15 dB of gain spanning the wavelength range 2050 - 2120 nm and an external NF of 7-10 dB. By pumping at the longer wavelength of 2008 nm the gain bandwidth of the amplifier is shifted to longer wavelengths and using this architecture a HDFA was demonstrated with a peak gain of 39 dB at 2090 nm and 15 dB of gain spanning the wavelength range 2050 - 2150 nm. The external NF over this wavelength range was 8-14 dB.

High power fiber lasers with radially polarized output beams

A scheme for directly exciting the radially-polarized TM01 mode in a fiber laser is reported. Preliminary results for cladding-pumped ytterbium-doped and thulium-doped fiber lasers are discussed along with prospects for scaling to high power levels.

Silica-based thulium doped fiber amplifiers for wavelengths beyond the L-band

We present a suite of silica-based thulium-doped fiber amplifiers (TDFAs) operating across the 1650-2050nm waveband. High gain and low NF are achieved by combining several TDFA designs optimized for short, central and long wavelength operation.

Few-Mode TDFA for Mode Division Multiplexing at 2µm

We report the first demonstration of an inline two mode group thulium-doped fiber amplifier (TMG-TDFA) operating at 2μm for mode-division multiplexed transmission. Similar gain and noise figure performance are obtained for both spatial modes under cladding-pumped operation.

Holmium doped fibre optimised for resonant cladding pumping

Two-micron lasers are of great interest in a range of applications, from spectroscopy and free space communications, to polymer machining and laser surgery. They also provide an important stepping-stone for wavelength generation further into the mid-infrared via nonlinear frequency conversion. Holmium doped fibre laser systems offer particularly attractive properties as they allow access to the atmospheric transmission window between 2.1 and 2.25 μm. Recently, operational efficiencies for resonantly pumped Ho:silica fibre close to the quantum limit have been demonstrated for core pumped lasers [1]. To further power scale Ho:fibre lasers, development of cladding-pumped fibre configuration is necessary and indeed has enabled scaling of such fibres to >400 W cw average power [2]. Conventional polymer-coated double-clad fibres have high inner-cladding propagation loss at the ∼1.95 μm pump wavelength, resulting from the presence of OH− contamination and absorption in the polymer outer-cladding [3]. Here we report on optimisation of holmium all glass double-clad optical fibre in order to provide efficient operation for cladding pumping at 1.95μm.