Observation of Wavelength Tuning in a Mode-Locked Figure-9 Fiber Laser

Abstract

We demonstrate an all-PM Er-doped soliton mode-locked fiber oscillator based on the figure-9 configuration with a compact adjustable reflection-type non-reciprocal phase shifter. An analytical model based on the Jones matrix is established to simulate the wavelength tuning phenomenon. Experimentally, it is observed that the increase in pump power results in a significant redshift in the spectrum of output pulses. When the angle of the half-wave plate is rotated in one direction, the output spectrum is redshifted and then blueshifted successively. Good qualitative agreement is presented between the simulations and the experimental results. It is shown that the increase in pump power changes the nonlinear phase shift, which causes the redshift of the transmittance curves at the laser output port. In contrast, the rotation of wave plates not only changes the nonlinear phase shift difference, but also causes variations in linear phase bias and modulation depth. The changes in these parameters lead to the redshift and blueshift of the transmission curves, which enables wavelength tuning.

All-PM Yb-doped mode-locked fiber laser with high single pulse energy and high repetition frequency

“…In addition, the nonlinear phase shift varies with raising pump power causes a redshift in the transmission curve at the output port. The nonlinear phase shift, modulation depth, and linear phase bias will be changed by rotating the waveplate, which ultimately leads to a redshift in the transmission curve [34]. The central wavelength was shifted from 1027.8 nm to 1028.9 nm.…”

Methods of Radiation Wavelength Tuning in Short-Pulsed Fibre Lasers

“…Acousto-optical spectral filters that do not conform to the all-fibre format were also used for wavelength tuning of fibre laser pulses within tens of nanometres [52]. Narrow-range (several nanometres) wavelength tuning is possible in certain fibre laser configurations by adjustment of pump radiation power [53]. Tuning of the pulse wavelength is possible by electronically controlled heating of the reflective long-period Bragg grating [54].…”

“…Without a spectral filter, SOA may shift the wavelength of short pulses to shorter wavelengths by up to 20 nm [122]. Smaller (several nm) wavelength shifts of ~140 fs long optical pulses were observed in a combined (fibre-discrete) cavity with a NALN [123] resulting from pumping radiation power variation [53].…”

“…The structure SMF-MMF-SMF was used in [124] as a spectrally selective element for setting the desirable radiation wavelength. Continuous tuning of the transmission spectrum of such a structure was not demonstrated, but setting a fixed radiation Smaller (several nm) wavelength shifts of ~140 fs long optical pulses were observed in a combined (fibre-discrete) cavity with a NALN [123] resulting from pumping radiation power variation [53].…”

L-band wavelength-tunable fiber laser mode-locked by all polarization-maintaining nonlinear polarization rotation

“…Modifying the pump power of the laser diode (LD) presents a promising tuning method that is neither mechanical nor thermal, and a figure-9 laser achieves this pump power tuning method in 2023 [16]. However, this laser achieves only a 5 nm tuning range and includes free-space components.…”