Peh Siong Teh

Three mode Er3+ ring-doped fiber amplifier for mode-division multiplexed transmission

We successfully fabricate three-mode erbium doped fiber with a confined Er(3+) doped ring structure and experimentally characterize the amplifier performance with a view to mode-division multiplexed (MDM) transmission. The differential modal gain was effectively mitigated by controlling the relative thickness of the ring-doped layer in the active fiber and pump launch conditions. A detailed study of the modal gain properties, amplifier performance in a MDM transmission system and inter-modal cross-gain modulation and associated transient effects is presented.

200 W Diffraction limited, single-polarization, all-fiber picosecond MOPA

A fully fiberized, single-polarization, gain-switched diode-seeded fiber master oscillator power amplifier (MOPA) system is demonstrated delivering 28 ps pulses at variable repetition frequencies ranging from 53 MHz up to 858 MHz. An average signal output power of 200 W was achieved with good OSNR for all operating frequencies. A maximum pulse energy of 3.23 μJ at a repetition frequency of 53 MHz was achieved, corresponding to a pulse peak power of 107 kW. The extraction of higher pulse energy was limited primarily by the onset of nonlinear effects such as SRS which lead to compromised pulse quality at higher peak powers.

Control of Material Transport Through Pulse Shape Manipulation—A Development Toward Designer Pulses

The variety of laser systems available to industrial laser users is growing and the choice of the correct laser for a material target application is often based on an empirical assessment. Industrial master oscillator power amplifier systems with tuneable temporal pulse shapes have now entered the market, providing enormous pulse parameter flexibility in an already crowded parameter space. In this paper, an approach is developed to design interaction parameters based on observations of material responses. Energy and material transport mechanisms are studied using pulsed digital holography, post process analysis techniques and finite-difference modelling to understand the key response mechanisms for a variety of temporal pulse envelopes incident on a silicon 〈1|1|1〉 substrate. The temporal envelope is shown to be the primary control parameter of the source term that determines the subsequent material response and the resulting surface morphology. A double peak energy-bridged temporal pulse shape designed through direct application of holographic imaging data is shown to substantially improve surface quality.

High-power, high repetition-rate, green-pumped, picosecond LBO optical parametric oscillator

We report on a picosecond, green-pumped, lithium triborate optical parametric oscillator with record-high output power. It was synchronously pumped by a frequency-doubled (530 nm), pulse-compressed (4.4 ps), high-repetition-rate (230 MHz), fiber-amplified gain-switched laser diode. For a pump power of 17 W, a maximum signal and idler power of 3.7 W and 1.8 W was obtained from the optical parametric oscillator. A signal pulse duration of ~3.2 ps was measured and wide tunability from 651 nm to 1040 nm for the signal and from 1081 nm to 2851 nm for the idler was achieved.

Compact, high-pulse-energy, picosecond optical parametric oscillator

We report a high-energy optical parametric oscillator (OPO) synchronously pumped by a 7.19 MHz, Yb:fiber-amplified, picosecond, gain-switched laser diode. The 42-m-long ring cavity maintains a compact design through the use of an intracavity optical fiber. The periodically poled MgO-doped LiNbO(3) OPO provides output pulse energies as high as 0.49 μJ at 1.5 μm (signal) and 0.19 μJ at 3.6 μm (idler). Tunability from 1.5 to 1.7 μm and from 2.9 to 3.6 μm is demonstrated, and typical M(2) values of 1.5 × 1.3 and 2.8 × 1.9 are measured for the signal and idler, respectively, at high power.

1.06

We investigate efficient broadband infrared supercontinuum generation in meter-length single-mode small-core tellurite holey fiber. The fiber is pumped by 1.06 μm picosecond pulses in the normal dispersion region. The high Raman gain coefficient and the broad Raman gain bands of the tellurite glass are exploited to generate a cascade of Raman Stokes orders, which initiate in the highly normal dispersion region and quickly extend to longer wavelengths across the zero dispersion wavelength with increasing pump power. A broadband supercontinuum from 1.06 μm to beyond 1.70 μm is generated. The effects of the pump power and of the fiber length on the spectrum and on the power conversion efficiency from the pump to the supercontinuum are discussed. Power scaling indicates that using this viable normal dispersion pumping scheme, 9.5 W average output power of infrared supercontinuum and more than 60% conversion efficiency can be obtained from a 1 m long tellurite fiber with a large mode area of 500 μm2 .

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We present the first demonstration of nanosecond-pulsed fiber MOPA systems seeded by semiconductor laser diodes at 2 μm incorporating arbitrary pulse shaping capabilities, achieving up to 1.0 mJ (12.5 kHz, 100 ns) pulse energy.

m Picosecond Pulsed, Normal Dispersion Pumping for Generating Efficient Broadband Infrared Supercontinuum in Meter-Length Single-Mode Tellurite Holey Fiber With High Raman Gain Coefficient

We demonstrate a gain-switched diode-seeded, ytterbium-doped fiber based master oscillator power amplifier (MOPA) system, capable of delivering 2.4 μJ, 35 ps pulses at a repetition frequency of 215 MHz in a single-polarization, close to diffraction limited beam. We are aware that the corresponding average power of > 500 W is a record for such a MOPA system. Further pulse energy scaling was limited primarily by the onset of nonlinear effects such as self-phase modulation and stimulated Raman scattering which led to a compromised pulse quality at higher peak powers (> 70 kW).

High-energy diode-seeded nanosecond 2 μm fiber MOPA systems incorporating active pulse shaping

We report a rapidly tunable, wavelength agile fiber laser system capable of the synchronous generation of sequences of pulses with different wavelengths in the visible region of the spectrum using stimulated Raman scattering of multi-step pump pulses in a 250 m length of fiber. The frequency doubled output of a single polarization all-fiber Yb-doped MOPA operating at 1060 nm was used as the pump source. By adjusting the pump power and the pulse profiles we achieved the sequential excitation of green (1st Stokes), yellow (4th Stokes) and red light (6th Stokes) using 3-step pulses, or the combination of any two using 2-step pulses. The wavelength switching time was <5 ns and was limited only by the pulse shaping drive electronics.

Single polarization picosecond fiber MOPA power scaled to beyond 500 W

We report on the first fabrication of a glass fiber based laser-induced crystalline waveguide. The glass and crystal are based on the stoichiometric composition of (La,Yb)BGeO(5). A laser induced waveguide has been fabricated on the surface of a ribbon glass fiber using milliwatt-level continuous wave UV laser radiation at a fast scanning speed. Evidence of crystallinity in the created structure was observed using micro-Raman spectroscopy and scanning electron microscopy. Preliminary investigations on the waveguiding behavior and the nonlinear performance in the crystalline waveguide are reported.