High power, high energy, all-fiber Mamyshev oscillator

A team at the National University of Defense Technology is working on a high-power, high-energy, all-fiber Mamyshev oscillator, His research was published in Ultrafast under the title "All-PM Fiber Mamyshev Oscillator Delivers Hundred-Nanojoule and Multi-Watt Sub-100 fs Pulses" Science.

High power/energy ultrafast fiber laser has been widely used in material processing, medicine, advanced manufacturing and other fields. Compared with solid state laser, fiber laser has the advantages of compact system, good flexibility, good heat dissipation and high beam quality.

However, the monopulse energy and average power of ultrafast fiber lasers, especially those with all-fiber structure, still lag behind solid-state lasers due to the serious nonlinear effects in the fiber. In recent years, Mamyshev oscillators have attracted a lot of attention due to their potential to produce high-energy ultrafast pulses.

As shown in FIG. 1: The experimental device ISO and isolator for all fiber MO and LD laser diode at the Perna Joule level.

A Mamyshev oscillator based on all-polarization-maintaining fiber with a core/cladding diameter of 10/125 μm has been reported by National University of Defense Technology. It achieves a monopulse energy of 153nj and a compressed pulse width of 73fs. In addition, by adjusting the resonator parameters, the maximum 5th order harmonic mode-locking is realized, the average output power is 3.4 W, and the compression pulse width is 100 fs.

FIG. 2 shows the pulse characteristics of high energy MO.

FIG. 3: Pulse characteristics at maximum output power.

In recent years, the pulse energy and average power of ultrafast fiber lasers have been greatly improved by using Mamyshev oscillators with cascade spectral broadening and bias spectral filtering effects. Continuous light and weak pulses will be blocked in the Mamyshev oscillator. Because the spectrum is broadened enough, the strong pulse can be retained in the cavity after the two filters with different central wavelengths, so as to obtain the ultra-fast laser with high pulse energy.

FIG. 4 shows pulse characteristics at a pump power of 5w.

FIG. 5 shows the long-term stability of MO at high energy within 5 h.

However, most of the previous results adopt spatial structure, and introduce a large number of free space elements for signal collimation and coupling, which makes the system cumbersome and easy to be interfered.

The goal is to achieve a high power/energy ultrafast fiber laser with an all-fiber structure, the researchers said. In this paper, a fully polarization-maintaining fiber Mamyshev oscillator with a core/cladding diameter of 10/125 μm is reported.

Whereas conventional Mamyshev oscillators typically consist of a two-stage gain fiber amplifier, this laser has only one amplifier arm. A passive optical fiber is used to widen the spectrum of the other arm, reduce the accumulation of nonlinear phase in the cavity, and make the system more compact.

This class group respectively achieved a high-performance ultrafast fiber laser with a single pulse energy of 153 nJ and an average power of 3.4 W, which is the highest pulse energy and average power recorded in an all-fiber ultrafast laser oscillator with a pulse duration of picosecond/femtosecond.

An all-fiber ultrafast laser with higher power/pulse energy is expected to be realized by using a novel pulse evolution mechanism with larger core diameter and higher fault tolerance for nonlinear phase accumulation.

Links to relevant papers:

https://spj.science.org/doi/10.34133/ultrafastscience.0016

Source: Sohu-Yangtze River Delta laser Alliance