Development and applications of
gain-switched fiber lasers [Invited]
Jianlong Yang, Yulong Tang, and Jianqiu Xu*
Key Laboratory for Laser Plasmas (Ministry of Education) and the Department of Physics, Shanghai Jiao Tong University,
Shanghai 200240, China
*Corresponding author: jqxu09@sjtu.edu.cn
Received February 27, 2013; revised April 19, 2013; accepted April 19, 2013;
posted April 19, 2013 (Doc. ID 186120); published June 11, 2013
We briefly review the development of gain-switched rare-earth-doped fiber lasers and their applications in wave-
length conversion to mid-IR, supercontinuum generation, and medicine in recent years. We illustrate the simi-
larities between gain-switching and Q-switching techniques that will provide tools for the design and optimization
of the gain-switched fiber lasers. From the nature of the gain-switched fiber lasers, benefits of this kind of lasers to
2-μm region and in-band-pumped (two-level system) laser systems are obvious. Advantages of in-band-pumped
2-μm lasers are discussed and analyzed with a simple numerical simulation in terms of Tm-doped fiber lasers. We
also propose the key factors in the development of the gain-switched fiber lasers and predict the future
tendency. © 2013 Chinese Laser Press
OCIS codes: (060.2390) Fiber optics, infrared; (140.3430) Laser theory; (140.3510) Lasers, fiber; (140.3538)
Lasers, pulsed.
http://dx.doi.org/10.1364/PRJ.1.000052
1. INTRODUCTION
In the pulsed fiber laser regime, gain-switching is an alternative
technique to generate a high-repetition-rate pulse train with
nanosecond pulse duration besides Q-switching and external
modulation of a continuous-wave (CW) laser. Compared to
conventional solid-state bulk lasers, realization of the gain-
switched operation is convenient in the regime of rare-earth-
doped fiber lasers due to their high optical gain. Consequently,
the gain-switched fiber lasers have drawn extensive interest
and been well developed in recent years [1–3]. Especially
for fiber lasers operating at wavelengths around 2 μm, gain-
switching rather than direct modulation of a laser diode
(LD) (which has low efficiencies at wavelengths longer than
1.8 μm because of Auger recombination [4]) is the preference
for pulsed lasers or the seeder to master oscillator power am-
plifier (MOPA) fiber lasers. As a kind of fiber lasers, gain-
switched fiber lasers have all the general advantages of fiber
lasers, such as single-mode operation, high efficiency, and
being maintenance-free [5]. Furthermore, several other fea-
tures establish an important role of gain-switched fiber lasers
in the fields of laser research, application, and commercializa-
tion, as summarized below:
• Simple geometry. Unlike Q-switching and CW laser modu-
lation, gain-switchingdoesnot needadditional in-cavity compo-
nents, which is convenient for realizing all-fiber configurations
of gain-switched fiber lasers and compact system designs.
• High pulse energy. Without restrictions of the damage
thresholds of the in-cavity components, the pulse energy is
only limited by the core area of the doped fiber. As a result,
it can be scaled to a much higher level than that of other pulse
generation techniques. For Tm-doped fiber lasers without
further amplifier stages, pulse energy up to 14.7 mJ has been
reported [6].
• Wide spectral coverage. Gain-switching has been applied
to almost every rare-earth cation used in fiber lasers: Nd
3
[1],
Tm
3
[2,3,6,7], Er
3
[8–10], Yb
3
[10–12], Ho
3
[13,14]. The
corresponding wavelengths vary from near-IR (845 nm) to
mid-IR (2.7 μm).
• Narrow bandwidth. Using fiber Bragg gratings (FBGs),
gain-switched fiber lasers can acquire laser pulses with spec-
tral bandwidths of less than one nanometer [12,14,15]. The
chirp-free operation of the gain-switched fiber lasers makes
them suitable for applications, such as Doppler lidar [14]
and nonlinear frequency conversion [12].
In this paper, we briefly review and summarize the develop-
ment and progress made to date toward gain-switched
fiber lasers and their applications in wavelength conversion
to mid-IR, supercontinuum generation, and medicine. In
Section 2, we introduce the gain-switched fiber lasers and
illustrate their physical processes, which are compared to
Q-switching for more explicit understanding. We summarize
and discuss the state-of-the-art results in Section 3. In
Section 4, we illustrate the applications of gain-switched fiber
lasers and discuss the key factors that will influence their
future uses. Finally, we draw our conclusions in Section 5.
2. BASIC PRINCIPLE
Figure 1 shows the typical configuration of an all-fiber gain-
switched fiber laser, in which it is evident that gain-switched
fiber lasers generally have an extremely simple geometry.
Usually, a pulsed pump source has a pigtail output and the
pump light couples into the core of gain fiber directly for bet-
ter absorption. (Because the rare-earth-doped fibers have
large absorption cross sections at pump wavelengths and
available high-power LDs, such as Tm-doped silica fiber at
∼793 nm, a cladding-pumped scheme can also be employed
52 Photon. Res. / Vol. 1, No. 1 / June 2013 Yang et al.
2327-9125/13/010052-06$15.00/0 © 2013 Chinese Laser Press