Repetition rate optimized 2 µm gain-switched diode pumped MIR supercontinuum

Abstract

Mid-infrared supercontinuum (SC) sources can benefit from low-cost pumps with center wavelength longer than the zero-dispersion wavelength of fluoride fibers (∼1600nm). This makes thulium-doped lasers an attractive technology, but their relative intensity noise (RIN) is typically not characterized. Furthermore, is low pump noise even a requirement for SC applications? With focus on low cost, we have developed a three-stage amplified 1946 nm gain-switched diode (GSD) demonstrating 12% RIN and flexible repetition rate control, which crucially allows the user to optimize SC performance specific to the application. We demonstrate a maximum −10dB bandwidth of 1873–3986 nm at 2 MHz and a minimum RIN of 6.1% at 1900 nm, 10.4% at 2300 nm, and 16.6% at 3250 nm at 1 MHz. We define a figure of merit for operation between the 3000 and 3500 nm region and demonstrate that it is maximized at 3 MHz, showcasing the power of this control in optimizing specific performance metrics. This performance is compared with a SC spanning 1900–3796 nm, pumped by an amplified thulium-doped mode-locked fiber laser operating at 5.8 MHz with <0.11% RIN. Despite the vastly superior pump noise, comparative SC RIN values of 2.0% at 1900 nm, 9.5% at 2300 nm, and 8.5% at 3250 nm were obtained, indicating that the modulational instability driven SC generation process dominates noise performance, thereby reducing the need for low pump noise.