Morphology-Controllable Ultrafast Fiber Lasers Based on Intracavity Manipulation of Transverse Modes

The performances of mode-locked fiber lasers rest with the design and configuration of the cavity, and their temporal morphologies are rarely linked with the modulation of transverse modes. Here, we demonstrate a morphology-controllable ultrafast fiber laser based on the intracavity manipulation of transverse modes, capable of producing dual-color pulses, narrowband picosecond pulses, and broadband femtosecond pulses. Unlike traditional multicolor pulses with unequal group velocities, the dual-color pulse operates in a synchronous state, displaying a multipeak structure where the modulation period relies on the group-delay difference of two modes in the fiber. Simulation results fully reproduce the experimental observations and show that the laser follows the minimum-loss principle with pulse morphologies depending on the mode-interference-induced filtering effect. This work connects transverse-mode modulation with pulse morphology, providing a stable and cost-effective laser source for terahertz-wave generation and nonlinear spectroscopy.

Figure 1

Principle and experimental setup of morphology-controllable ultrafast fiber lasers. (a) Configuration of the fiber laser. (b) Principle of the MIIF. (c) Effective refractive indices of LP₀₁ and LP₁₁ modes in TMF. (d) Performance of MIIF without (black curve) and with (red curve) pressure on TMF.

Figure 2

Performance of dual-color synchronized pulses. (a) Spectrum; (b) radio-frequency spectrum; (c) pulse train; (d) AC trace; (e) retrieved pulse profile from FROG trace; (f) subpulse separation and wavelength difference versus TMF length.

Figure 3

Properties of narrowband pulses and broadband stretched pulses. (a),(c) Typical output spectrum; (b),(d) AC trace of output pulse.

Figure 4

Simulation results of optical spectra, pulse profiles, and AC traces. (a),(b) Dual-color synchronized pulses; (c),(d) narrowband picosecond pulses; (e),(f) broadband stretched pulses.

Figure 5

Intracavity evolution of normalized dual-color synchronized pulses, narrowband pulses, and broadband stretched pulses. (a₁)–(a₃) Spectra; (b₁)–(b₃) pulses. Upper panel shows dispersion parameters and components versus cavity position.

Figure 6

Energy evolution of dual-color synchronized pulse, narrowband pulse, and broadband stretched pulse versus roundtrips.