Actively mode-locked all fiber laser with cylindrical vector beam output

Area of Science:

• Optics and Photonics
• Laser Physics
• Fiber Optics

Background:

• Cylindrical vector beams (CVBs) offer unique polarization properties valuable in various optical applications.
• Achieving stable and pure CVBs from fiber lasers presents significant challenges in mode selection and control.

Purpose of the Study:

• To demonstrate an all-fiber actively mode-locked laser capable of emitting cylindrical vector beams.
• To investigate the use of intra-cavity few-mode fiber Bragg gratings for mode selection and spectrum filtering.
• To achieve active mode-locking using a Mach-Zehnder modulator.

Main Methods:

• An intra-cavity few-mode fiber Bragg grating (FMFBG) inscribed in a four-mode fiber (4MF) was utilized for mode selection and spectral filtering.
• Mode coupling was induced via offset splicing between single-mode fiber (SMF) and the 4MF within the laser cavity.
• Active mode-locking was implemented using a Lithium Niobate (LiNbO3) Mach-Zehnder modulator (MZM).

Main Results:

• The laser successfully emitted a cylindrical vector beam at a wavelength of 1547 nm.
• The laser produced mode-locked pulses with a duration of 2 ns and a repetition rate of 12.06 MHz.
• Both radially and azimuthally polarized beams were obtained with high mode purity by adjusting the intra-cavity polarization state.

Conclusions:

• The developed all-fiber actively mode-locked laser is a viable platform for generating high-purity cylindrical vector beams.
• The integration of FMFBG and offset splicing offers an effective approach for mode control in fiber lasers.
• This technology holds potential for applications requiring tailored polarization states, such as advanced microscopy and optical trapping.