Facile active control of a pulsed erbium-doped
fiber laser using modulation depth tunable
carbon nanotubes
XINTONG XU,
1,2
SHUANGCHEN RUAN,
1,
*JIANPANG ZHAI,
1
LING LI,
1
JIHONG PEI,
2
AND ZIKANG TANG
3
1
Shenzhen Key Laboratory of Laser Engineering, Guangdong Provincial Key Laboratory of Micro/Nano Optomechatronics Engineering,
Shenzhen University, Shenzhen 518060, China
2
College of Information Engineering, ATR National Defence S&T Key Laboratory, Shenzhen University, Shenzhen 518060, China
3
Institute of Applied Physics & Materials Engineering, Faculty of Science and Technology, University of Macau, Macau, China
*Corresponding author: scruan@szu.edu.cn
Received 12 June 2018; revised 31 August 2018; accepted 31 August 2018; posted 5 September 2018 (Doc. ID 335051);
published 12 October 2018
Short pulsed fiber lasers have been widely made using single-walled carbon nanotubes as a saturable absorber
(SA). However, most of the currently used devices can only operate in one determined operation state with an
unchangeable modulation SA depth in the cavity, which significantly limits their application in photonic devices.
In this paper, well-aligned carbon nanotube arrays are synthesized using zeolite AlPO
4
-5 as a template, which
features anisotropic optical absorption. The linear optical absorption of the as-synthesized carbon nanotube ar-
rays can easily be tuned by adjusting a polarization controller, thus providing a tunable modulation depth for the
carbon nanotube SA. By exploiting this SA in an erbium-doped fiber laser cavity, both Q-switched and mode-
locked pulsed lasers are achieved by simply adjusting a polarization controller under a fixed pump power of
330 mW. In addition, the repetition rate of the Q-switching and pulse duration of the mode-locking can be
tuned according to the variation of modulation depth. Moreover, soliton molecules can be obtained when
the modulation depth of the SA is 4.5%.
© 2018 Chinese Laser Press
https://doi.org/10.1364/PRJ.6.000996
1. INTRODUCTION
Single-walled carbon nanotubes (SWCNTs) have extraordinary
optical and electronic properties that make them attractive for
numerous applications [1–4]. Recently, carbon nanotubes have
been widely used as saturable absorbers (SAs) in pulsed fiber
lasers owing to their large saturable absorption, ultrafast recov-
ery time, and broadband operation [ 5–10 ]. To date, SWCNT-
based SAs have been successfully used for mode-locking and
Q-switching in fiber lasers, in which the operating wavelength
ranges from 1.0 to 2.0 μ m. Normally, mode-locked fiber lasers
can generate pulses with ultra-short duration, while Q-switched
fiber lasers can generate pulses with high energy. Therefore,
fiber lasers with different laser operation states in a fixed laser
cavity are urgently needed. Generally, carbon nanotubes are
embedded in polymer matrices to form SWCNT-polymer SAs,
leading to the random orientation of the carbon nanotubes
[11–14]. In this condition, the absorption of the carbon nano-
tubes is fixed when they are inserted into a laser cavity, leading
to a fixed modulation depth of the SA. Thus, the fiber laser
is limited to a single laser-operation state, mode-locking or
Q-switching, which significantly restricts its application. To pro-
mote the application of carbon nanotube SAs, it is important to
develop a facile method to control the modulation depth,
which is the key parameter for the realization of fiber lasers with
several different laser operations [15–17].
The results of previous works have demonstrated that the
modulation depth can be changed by adjusting SA absorption
[15,18,19]. Well-aligned carbon nanotube arrays have an ex-
cellent anisotropic response to optical radiation due to their
constrained electron motion and electron–phonon coupling.
On this basis, pol arization-sensitive optical devices based on
well-aligned carbon nanotube arrays have been developed
[20–22]. Thus, well-aligned carbon nanotube array SAs may
provide a meth od to control the operation state of pulsed lasers
by adjusting the polarization state in the laser cavity based on
their polarized absorption property.
In our previous work, well-aligned carbon nanotube arrays
were fabricated inside the channels of zeolite AlPO
4
-5 (AFI)
single crystals, which exhibited very specific properties such
as one-dimensional superconductivity and anisotropic optical
absorption [23–25]. In this paper, well-aligned carbon nano-
tube arrays fabricated in AFI channels are used as polarization-
sensitive SAs for the manipulation of the operation state of
pulsed lasers. The as-synthesized well-aligned carbon nanotube
996
Vol. 6, No. 11 / November 2018 / Photonics Research
Research Article
2327-9125/18/110996-07 Journal © 2018 Chinese Laser Press