Polarization evolution dynamics of dissipative
soliton fiber lasers
LEI GAO,
1,4
YULONG CAO,
1
STEFAN WABNITZ,
2,3
HONGQING RAN,
1
LINGDI KONG,
1
YUJIA LI,
1
WEI HUANG,
1
LIGANG HUANG,
1
DANQI FENG,
1
AND TAO ZHU
1,5
1
Key Laboratory of Optoelectronic Technology and Systems (Ministry of Education), Chongqing University, Chongqing 400044, China
2
Dipartimento di Ingegneria dell’Informazione, Elettronica e Telecomunicazioni, Sapienza Università di Roma, 00184 Rome, Italy
3
Novosibirsk State University, Novosibirsk 630090, Russia
4
e-mail: gaolei@cqu.edu.cn
5
e-mail: zhut@cqu.edu.cn
Received 24 July 2019; revised 12 September 2019; accepted 12 September 2019; posted 13 September 2019 (Doc. ID 373626);
published 1 November 2019
Dissipative solitons emerge as stable pulse solutions of nonintegrable and nonconservative nonlinear physical
systems, owing to a balance of nonlinearity, dispersion, and loss/gain. A considerable research effort has been
dedicated to characterizing amplitude and phase evolutions in the spatiotemporal dynamics of dissipative solitons
emerging from fiber lasers. Yet, the picture of the buildup process of dissipative solitons in fiber lasers is incom-
plete in the absence of corresponding information about the polarization evolution. Here, we characterize prob-
abilistic polarization distributions in the buildup of dissipative solitons in a net-normal dispersion fiber laser
system, mode-locked by single-wall carbon nanotubes. The output optical spectra under different pump powers
are filtered by a tunable filter, and are detected by a polarization state analyzer. The laser system operates from
random amplified spontaneous emission into a stable dissipative soliton state as the cavity gain is progressively
increased. Correspondingly, the state of polarization of each spectral wavelength converges towards a fixed point.
To reveal the invariant polarization relationship among the various wavelength components of the laser output
field, the phase diagram of the ellipticity angle and the spherical orientation angle is introduced. We find that,
within the central spectral region of the dissipative soliton, the state of polarization evolves with frequency by
tracing a uniform arc on the Poincaré sphere, whereas in the edges of the dissipative soliton spectrum, the state of
polarization abruptly changes its path. Increasing cavity gain leads to spectral broadening, accompanied by a
random scattering of the state of polarization of newly generated frequencies. Further increases of pump power
result in dissipative soliton explosions, accompanied by the emergence of a new type of optical polarization rogue
waves. These experimental results provide a deeper insight into the transient dynamics of dissipative soliton
fiber lasers.
© 2019 Chinese Laser Press
https://doi.org/10.1364/PRJ.7.001331
1. INTRODUCTION
Solitons are spatiotemporal localized wave structures, associated
with analytical solutions of conservative and integrable systems,
such as the nonlinear Schrödinger equation (NLSE), where the
interaction of nonlinearity and diffraction/dispersion is bal-
anced [1]. In optics, NLSE-based soliton laser systems possess
a high degree of coherence, due to the well-defined phases
among the various longitudinal laser modes. Solitons propagate
with a transform-limited pulse duration and collide with each
other while maintaining their shapes and velocities. Yet, most
natural systems occur as dissipative and nonintegrable. Various
localized structures, such as self-similar pulses, gain-guided
pulses, dissipative solitons, and even sporadic rogue waves,
proliferate and decay with a diverse range of spatial-temporal
periodic and localized structures [2–4].
Dissipative solitons (DSs) are highly coherent solutions of
nonlinear wave equations, and arise from a balance among non-
linearity, dispersion, and loss/gain [1–4]. At variance with
NLSE solitons in integrable fiber systems operating in the
anomalous dispersion regime, DSs in dissipative fiber laser
systems operating in the normal dispersion regime exhibit
extremely complex and striking dynamics. For example, DSs
have much broader (when compared with solitons) pulse
durations and linear phase chirping, which makes them ideal
for high energy ultrafast fiber lasers and phase-dependent
optical processing. Moreover, their flat and broad optical
Research Article
Vol. 7, No. 11 / November 2019 / Photonics Research 1331
2327-9125/19/111331-09 Journal © 2019 Chinese Laser Press