Gain-switched CW fiber laser for improved supercontinuum generation in a PCF

Abstract

Abstract:We demonstrate supercontinuum generation in a PCF pumped by a gain-switched high-power continuous wave (CW) fiber laser. The pulses generated by gain-switching have a peak power of more than 700 W, a duration around 200 ns, and a repetition rate of 200 kHz giving a high average power of almost 30 W. By coupling such a pulse train into a commercial nonlinear photonic crystal fiber, a supercontinuum is generated with a spectrum spanning from 500 to 2250 nm, a total output power of 12 W, and an infrared flatness of 6 dB over a bandwidth of more than 1000 nm with a power density above 5 dBm/nm (3 mW/nm). This is considerably broader than when operating the same system under CW conditions. The presented approach is attractive due to the high power, power scalability, and reduced system complexity compared to picosecond-pumped supercontinuum sources.

Gain-switched all-fiber laser with narrow bandwidth

“…The pump is turned off before the generated spike is emitted to avoid the following smaller spikes. The generated pulse duration, energy, and build-up time depend on pump energy, cavity design, and repetition rate [11,17]. The output pulses of the gain-switched fiber laser are shown in Fig.…”

“…3(a) the temporal traces of the pump and the emitted spikes are shown for a fixed absorbed pump energy of 150 µJ and at repetition rates from 1 kHz to 5 kHz. The lowest repetition rates imply that the delay between the pump pulses are on the order of the lifetime of the excited Yb-ions ( f −1 ∼ τ Y b ) of around 1 ms [11]. The amount of residual excited Ybions still present when a new pump pulse arrives is therefore dependent on the repetition rate.…”

“…In terms of optical components a gain-switched fiber laser only requires the same components as an all-fiber CW laser, which makes it simple and cost-effective. Output pulse energies are typically in the tens to hundreds of microjoule range and with nanosecond pulse duration [9][10][11]. An example of an application is within supercontinuum generation [11], where the increased peak power reduces the dependence on the zero dispersion wavelength [12].…”

“…Output pulse energies are typically in the tens to hundreds of microjoule range and with nanosecond pulse duration [9][10][11]. An example of an application is within supercontinuum generation [11], where the increased peak power reduces the dependence on the zero dispersion wavelength [12]. One downside of gain-switching is that the full capacity of the pump lasers is not utilized due to the pulsed pumping.…”

“…One downside of gain-switching is that the full capacity of the pump lasers is not utilized due to the pulsed pumping. Gain-switching is studied the most in Tmdoped lasers [9,10,13] but it has also been demonstrated in Nd-doped [14], Ho-doped [15], and Yb-doped fiber lasers [11,[16][17][18].…”