Dissipative soliton resonance in a mode-locked Nd-fiber laser operating at 927 nm

Cavity-birefringence-based manipulation of long-duration optical pulses in a passively mode-locked fiber laser with large normal dispersion

Optical pulse manipulation in the large normal dispersion regime through intracavity birefringence management is demonstrated experimentally in an erbium-doped fiber (EDF) laser, for the first time to the best of our knowledge. The EDF laser is passively mode-locked based on a nonlinear amplifying loop mirror (NALM) in a figure-of-eight (f-8) configuration. Different lengths of the same type of polarization-maintaining fiber (PMF) are incorporated into the NALM to vary the net cavity birefringence. For each length of PMF, various polarization states and pump powers were tested and compared to achieve a pulse duration tuning range as large as possible. For comparison, these polarization states and pump powers were also studied by incorporating the PMF into the unidirectional loop of the f-8 cavity. Our results reveal some new features for the management of cavity birefringence that can enable long-duration pulse manipulation in the large normal dispersion regime.

Efficient three-level continuous-wave and GHz passively mode-locked laser by a Nd3+-doped silicate glass single mode fiber

Nd³⁺-doped three-level (⁴F_3/2-⁴I_9/2) fiber lasers with wavelengths in the range of 850-950 nm are of considerable interest in applications such as bio-medical imaging and blue and ultraviolet laser generation. Although the design of a suitable fiber geometry has enhanced the laser performance by suppressing the competitive four-level (⁴F_3/2-⁴I_11/2) transition at ∼1 µm, efficient operation of Nd³⁺-doped three-level fiber lasers still remains a challenge. In this study, taking a developed Nd³⁺-doped silicate glass single-mode fiber as gain medium, we demonstrate efficient three-level continuous-wave lasers and passively mode-locked lasers with a gigahertz (GHz) fundamental repetition rate. The fiber is designed using the rod-in-tube method and has a core diameter of 4 µm with a numerical aperture of 0.14. In a short 4.5-cm-long Nd³⁺-doped silicate fiber, all-fiber CW lasing in the range of 890 to 915 nm with a signal-to-noise ratio (SNR) greater than 49 dB is achieved. Especially, the laser slope efficiency reaches 31.7% at 910 nm. Furthermore, a centimeter-scale ultrashort passively mode-locked laser cavity is constructed and ultrashort pulse at 920 nm with a highest GHz fundamental repetition is successfully demonstrated. Our results confirm that Nd³⁺-doped silicate fiber could be an alternative gain medium for efficient three-level laser operation.

Ultrafast fiber laser at 0.9 µm with a gigahertz fundamental repetition rate by a high gain Nd3+-doped phosphate glass fiber

Fiber lasers, owing to the advantages of excellent beam quality and unique robustness, play a crucial role in lots of fields in modern society. Developing optical glass fibers with superior performance is of fundamental importance for wide applications of fiber lasers. Here, a new Nd³⁺-doped phosphate single-mode fiber that enables a high gain at 0.9 µm is designed and fabricated. Compared to previous Nd³⁺-doped silica fibers, the developed phosphate fiber exhibits a significant gain promotion, up to 2.7 dB cm^-1 at 915 nm. Configuring in a continuous-wave fiber laser, this phosphate fiber can provide a slope efficiency of 11.2% in a length of only 4.5 cm, about 6 times higher than that of Nd³⁺-doped silica fiber. To showcase its uniqueness, an ultrafast fiber laser with ultrashort cavity is constructed, such that an ultrashort pulse train with a fundamental repetition rate of up to 1.2 GHz is successfully generated. To the best of our knowledge, this is the highest fundamental repetition rate for mode-locked fiber lasers at this wavelength range - two orders of magnitude higher than that of prior works. These results indicate that this Nd³⁺-doped phosphate fiber is an effective gain medium for fiber amplifiers and lasers at 0.9 µm, and it is promising for two-photon biophotonics that requires long-term operation with low phototoxicity.

Noise-like pulse generation in an Nd-doped single-mode all-fiber mode-locked Raman laser operating at 0.93 µm

Based on the Nd-doped single-mode fiber (SMF) as the gain medium and SMF as the Raman medium, an all-fiber mode-locked Raman laser operating at 0.93 µm waveband was demonstrated for the first time. A mandrel with a diameter of 10 mm was employed to introduce bending losses to suppress the dominant emission of Nd-doped fiber at 1.06 µm. A noise-like pulse with a pulse width of 194.70 fs, a repetition rate of 1.73 MHz and a single pulse energy of 2.03 nJ was obtained in the mode-locked Raman laser with a Stokes wavelength of 932.59 nm. Such an ultrafast all-fiber Raman laser operating at 0.93 µm has the advantages of low cost, simple structure and compactness, and can be used as an ideal light source for the two-photon microscopy.

Mode-locked all-PM Nd-doped fiber laser near 910 nm

We present a compact passively mode-locked fiber laser emitting near 910 nm with an all-polarization-maintaining fiber laser architecture. The ring-cavity laser configuration includes a core-pumped neodymium-doped fiber as a gain medium and a semiconductor saturable absorber mirror as a passive mode-locking element. A bandpass filter is used to suppress parasitic emission near 1.06 µm and allows wavelength tuning between 903 and 912 nm. The laser operates in a highly stable and self-starting all-normal-dispersion regime with a minimum pulse duration of 8 ps at 28.2 MHz pulse repetition rate and 0.2 nJ maximum pulse energy. A single-pass amplifier stage increases the pulse energy up to 1.5 nJ, and pulse compression with a pair of gratings is demonstrated with nearly Fourier transform limited pulses.

Towards visible-wavelength passively mode-locked lasers in all-fibre format

Mode-locked fibre lasers (MLFLs) are fundamental building blocks of many photonic systems used in industrial, scientific and biomedical applications. To date, 1-2 μm MLFLs have been well developed; however, passively mode-locked fibre lasers in the visible region (380-760 nm) have never been reported. Here, we address this challenge by demonstrating an all-fibre visible-wavelength passively mode-locked picosecond laser at 635 nm. The 635 nm mode-locked laser with an all-fibre figure-eight cavity uses a Pr/Yb codoped ZBLAN fibre as the visible gain medium and a nonlinear amplifying loop mirror as the mode-locking element. First, we theoretically predict and analyse the formation and evolution of 635 nm mode-locked pulses in the dissipative soliton resonance (DSR) regime by solving the Ginzburg-Landau equation. Then, we experimentally demonstrate the stable generation of 635 nm DSR mode-locked pulses with a pulse duration as short as ~96 ps, a radio-frequency signal-to-noise ratio of 67 dB and a narrow spectral bandwidth of <0.1 nm. The experimental results are in excellent agreement with our numerical simulations. In addition, we also observe 635 nm noise-like pulse operation with a wide (>1 nm) and modulated optical spectrum. This work represents an important step towards miniaturized ultrafast fibre lasers in the visible spectral region.