Bursts with shape-alterable pulses in a compact
Tm-doped fiber laser with simultaneous active
intracavity phase and intensity modulations
Xiong Wang, Pu Zhou,* Xiaolin Wang, Hu Xiao, and Zejin Liu
College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
*Corresponding author: zhoupu203@163.com
Received August 25, 2014; revised October 6, 2014; accepted October 7, 2014;
posted October 8, 2014 (Doc. ID 221631); published October 27, 2014
We present a compact Tm-doped fiber laser (TDFL) to generate pulse bursts at 1.92 μm based on phase and in-
tensity modulations. A phase modulator (PM) and an intensity modulator (IM) were included in the linear TDFL
cavity to perform the simultaneous active intracavity phase and intensity modulation. Stable pulse bursts have
been achieved with tunable repetition rate in the range of 36–44 kHz (modulated by the PM) and duration of about
9.6 μs. The repetition rate of the individual pulse in a burst is about 9 MHz (modulated by the IM), and the pulse
width is about 6 ns. By changing the IM signal’s repetition rate and duty cycle, different individual pulse shapes
are obtained with pulse durations between 6 and 34 ns. © 2014 Chinese Laser Press
OCIS codes: (140.3510) Lasers, fiber; (140.3070) Infrared and far-infrared lasers; (140.4050) Mode-locked
lasers; (060.2390) Fiber optics, infrared.
http://dx.doi.org/10.1364/PRJ.2.000172
1. INTRODUCTION
Pulse bursts are normally bundles of pulses at relatively low
repetition rate and wide duration, composed of plentiful indi-
vidual pulses with higher repetition rate and narrower pulse
width [
1–4]. Compared with conventional pulse trains, pulse
bursts with clusters of subpulses have the advantages of ablat-
ing material at a faster speed while minimizing the thermal
effects [
3,4]. Moreover, pulse bursts almost enable the free
handling of pulse trains to optimize the special work quality
anticipated in a variety of applications [
2–7], including
material micromachining, laser acceleration, and environment
measurements. Thus pulse burst fiber lasers have been widely
investigated in recent years, mostly at the 1 μm band [
8–15].
Kalaycioglu et al. reported the pulse bursts with 1 kHz repeti-
tion rate and 20 μJ individual pulse energy in 2011 [
13], and
they subsequently presented the 1 mJ pulse bursts in an
Yb-doped fiber amplifier in 2012 [
14]. Later in 2012, Breitkopf
et al. pushed the energy power of pulse bursts at 1 μmto58mJ
with burst repetition rates of 20 Hz [15]. The excellent inves-
tigations above actually make the 1 μm pulse bursts available
for most of the current practical applications.
Different from Yb-doped fiber lasers, Tm-doped fiber lasers
(TDFLs) have a broader emission band covering from
∼1.7 μmto∼2.2 μm, which corresponds to various absorption
bands of material, such as water and greenhouse gases
[
16,17]. The absorption at spectral lines of greenhouse gases
enables TDFLs to be employed in environment monitoring
and gas sensing [
16,17]. Furthermore, high absorption by
water makes TDFLs outstanding eye-safe laser sources in a
variety of applications, including material micromachining, LI-
DAR, free-space communications, and medical procedures
[
17–19]. Thus TDFLs near 2 μm have attracted intense atten-
tion and have the potential to open a whole exotic area in laser
industries [
20,21]. Therefore pulse bursts generated by TDFLs
are also in great demand and should be well investigated. Up
to now, there have been no reports on pulse-burst generation
in TDFLs, to the best of our knowledge.
The conventional method to generate pulse bursts is to tailor
the pulse trains from an ultra-fast oscillator with an acousto-
optic modulator (AOM), and the reported pulse bursts are
mainly composed of picosecond or femtosecond individual
pulses [
13–15]. Actually, pulse bursts with nanosecond individ-
ual pulses and pulse spacing of tens of nanoseconds also have
significant applications [
22–26]. Furthermore, an individual
pulse’s shape in the pulse bursts plays an important role when
applying the pulse in practical applications [
6,7]. For example,
a step-flat top pulse in a material process has the advantage of
initiating the process by a high-intensity pulse part and contin-
uing the procedure with a lower intensity pulse part [
27].
Actually, it has been demonstrated that simultaneous Q
switching and mode locking can generate a burst-like pulse
train from a fiber cavity with two AOMs based on intensity/
amplitude modulations [
28]. In addition, multiple pulses in
gain-switched TDFLs have also been investigated [
29,30]. But
generation of bursts with shape-alterable pulses in TDFLs
based on simultaneous active intracavity phase and intensity
modulation has not been investigated yet.
In this paper, we propose and present a compact TDFL with
monolithic configuration to generate pulse bursts with shape-
alterable nanosecond individual pulses. A phase modulator
(PM) and an intensity modulator (IM) are employed in the la-
ser to perform the simultaneous active intracavity phase and
intensity modulation. The repetition rate of the bursts can be
tuned in the range of 36–44 kHz with a duration of about
9.6 μs, which is modulated by the PM. The repetition rate
of the individual pulse is about 9 MHz with duration of
172 Photon. Res. / Vol. 2, No. 6 / December 2014 Wang et al.
2327-9125/14/060172-05 © 2014 Chinese Laser Press