Mode-locked dysprosium fiber laser: Picosecond pulse generation from 2.97 to 3.30 μm

Abstract

Mode-locked fiber laser technology to date has been limited to sub-3 µm wavelengths, despite significant application-driven demand for compact picosecond and femtosecond pulse sources at longer wavelengths. Erbium-and holmium-doped fluoride fiber lasers incorporating a saturable absorber are emerging as promising pulse sources for 2.7-2.9 µm, yet it remains a major challenge to extend this coverage. Here, we propose a new approach using dysprosium-doped fiber with frequency shifted feedback (FSF). Using a simple linear cavity with an acousto-optic tunable filter, we generate ∼33 ps pulses with up to 2.7 nJ energy and 330 nm tunability from 2.97 to 3.30 µm (∼3000-3400 cm −1 )-the first mode-locked fiber laser to cover this spectral region and the most broadly tunable pulsed fiber laser to date. Numerical simulations show excellent agreement with experiments and also offer new insights into the underlying dynamics of FSF pulse generation. This highlights the remarkable potential of both dysprosium as a gain material and FSF for versatile pulse generation, opening new opportunities for mid-IR laser development and practical applications outside the laboratory.

Dysprosium Mid‐Infrared Lasers: Current Status and Future Prospects

“…It is Dy 3+ -doped fibers, however, where technological progress has been most rapid, albeit limited exclusively to the 3 µm transition. Notably, in the last few years numerous Dy:ZBLAN fiber lasers performance landmarks have been reported, including picosecond pulse generation beyond 3 µm, [112,113] 10-W output power, [102] 73% slope efficiency [101] and >550-nm tunability. [100] These demonstrations also surpass many performance records of the more established Er 3+ and Ho 3+ MIR fiber laser ions.…”

“…Thus there is significant recent research effort investigating alternative saturable absorber materials, such as 2D nanomaterials. With a slight modification to the cavity in Figure 15a wherein the AOTF section is replaced an SA arrangement consisting of a tight focusing lens and a silver mirror coated with black phosphorous (BP), passive Q-switching [110] Q-switched (passive) 166.8 kHz 795 ns 1.51 µJ 2.71 -3.08 2019 [111] Mode-locked (FSF) 44.5 MHz 33 ps 2.7 nJ 2.97 -3.3 2019 [112] Mode-locked (NPE) 60 MHz 828 fs 4.8 nJ 3.1 2019 [113] Swept-wavelength rapidly varying CW wavelength 2.89 -3.25 2019 [109] has been successfully demonstrated from a Dy:ZBLAN fiber laser. [110] This simple arrangement generates stable single pulse operation with energy up to 1 µJ and duration of 740 ns.…”

“…A novel alternative approach to successful picosecond pulse generation in MIR Dy fiber lasers is frequency shifted feedback. [112] While complete description of the mechanism can be found elsewhere (see ref. [121]), in brief, with a frequency shifting element placed in the cavity, light is continually shifted monotonically each round trip, eventually shifting outside the gain bandwidth and inducing loss.…”

“…For this reason pulse durations from the FSF Dy:ZBLAN setup are lower limited in duration, and despite anomalous dispersion in the ZBLAN fiber in this wavelength range, soliton shaping is not found to influence the pulse properties. [112] Recently a similar demonstration of FSF-pulsed operation in Ho:ZBLAN utilized an AOM in place of a narrowband AOTF. Here the wider effective filter bandwidth enabled an order of magnitude reduction in pulse duration, thus FSF in Dy systems have prospects for ultrafast pulse generation.…”

Gain-switched Dy3+:ZBLAN fiber laser operating around 3 μm

“…Moreover a tunable Dy 3+ :ZBLAN fiber laser operating at wavelengths in the range from 2.8 to 3.4 μm was also presented [13]. Further, mode-locked picosecond and femtosecond dysprosium fiber lasers have been reported [14,15]. Recently, a swept-wavelength (2.8-3.4 μm) Dy 3+ :ZBLAN fiber laser was used for the real time sensing of ammonia gas [16].…”