[Paper Review] Yb-doped all fiber picosecond laser based on grade-index multimode fiber with microcavity

Zhipeng Dong, Shujie Li+5 more|arXiv (Cornell University)|Sep 13, 2018

Advanced Fiber Laser Technologies20 references3 citations

TL;DR

This paper presents a compact, all-fiber Yb-doped picosecond laser using a grade-index multimode fiber with an embedded microcavity as a nonlinear saturable absorber. The device achieves 17.05 ps pulses at 1035 nm with 1.26 mW average power and 37.098 MHz repetition rate, demonstrating low cost, high stability, and high damage threshold for applications in optical sensing and material processing.

ABSTRACT

We demonstrate an all-fiber mode-locked laser at all-normal dispersion with a saturable absorber, which is based on a section of grade-index multimode fiber with inner microcavity embedded in the splice points. The absorption modulation depth of this nonlinear saturable absorber is 2.2% in the suitable bent state. The fiber laser operates at central wavelength of 1035nm with average power of ~1.26mW, pulse-duration of 17.05 ps, repetition rate of 37.098MHz. This kind of saturable absorber has superiorities of low cost, high stability and high damage threshold, which may facilitate applications in optical sensing, material processing and light detection.

Motivation & Objective

• To develop a low-cost, all-fiber mode-locked laser operating in all-normal dispersion.
• To address the need for stable, high-damage-threshold saturable absorbers in compact fiber lasers.
• To utilize a grade-index multimode fiber with an embedded microcavity to enable passive mode locking.
• To achieve sub-20 ps pulse generation with high stability and scalability for practical applications.

Proposed method

• A section of grade-index multimode fiber with an inner microcavity is spliced into the laser cavity to form a nonlinear saturable absorber.
• The microcavity structure induces controlled bending-induced nonlinear loss modulation, enabling saturable absorption behavior.
• The laser operates in all-normal dispersion regime, relying on self-phase modulation and nonlinear polarization evolution for pulse formation.
• The saturable absorber exhibits a modulation depth of 2.2% when optimally bent, enabling stable mode locking.
• The laser cavity is constructed entirely from optical fibers, ensuring alignment-free operation and high environmental stability.
• The system is pumped with a Yb-doped fiber amplifier to achieve lasing at 1035 nm with a repetition rate of 37.098 MHz.

Experimental results

Research questions

• RQ1 Can a grade-index multimode fiber with an embedded microcavity function as an effective saturable absorber in a mode-locked fiber laser?
• RQ2 What is the optimal bending condition for achieving maximum modulation depth in the microcavity-based saturable absorber?
• RQ3 Can an all-fiber, all-normal dispersion Yb-doped laser generate sub-20 ps pulses using this novel absorber design?
• RQ4 How does the damage threshold and stability of the microcavity-based absorber compare to conventional saturable absorbers?
• RQ5 What are the achievable pulse duration, average power, and repetition rate in such a compact, all-fiber configuration?

Key findings

• The laser generates 17.05 ps pulses at a central wavelength of 1035 nm with an average output power of 1.26 mW.
• The repetition rate of the mode-locked pulse train is 37.098 MHz, consistent with the cavity round-trip time.
• The saturable absorber based on the microcavity-embedded grade-index multimode fiber achieves a modulation depth of 2.2% under optimal bending conditions.
• The all-fiber design ensures high stability and low sensitivity to environmental perturbations.
• The laser system exhibits a high damage threshold due to the robust fiber-based structure of the saturable absorber.
• The proposed saturable absorber is low-cost and compatible with standard fiber fusion splicing techniques, enabling scalable fabrication.