COL 9(9), 090604(2011) CHINESE OPTICS LETTERS Septemb er 10, 2011
Eye-safe, single-frequency pulsed all-fiber laser for
Doppler wind lidar
Yuan Liu (刘刘刘 源源源), Jiqiao Liu (刘刘刘继继继桥桥桥), and Weibiao Chen (陈陈陈卫卫卫标标标)
∗
Shanghai Key Laboratory of All Solid-State Laser and Applied Techniques, Shanghai Institute of Optics and Fine Mechanics,
Chinese Academy of Sciences, Shanghai 201800, China
∗
Corresp onding author: wbchen@mail.shcnc.ac.cn
Received February 17, 2011; accepted April 14, 2011; posted online July 12, 2011
A single-frequency pulsed erbium-doped fiber (EDF) laser with master-oscillator power-amplifier
configuration at 1 533 nm is developed. A short-cavity, erbium-doped phosphate glass fiber laser is utilized
as a seeder laser with a linewidth of 5 kHz and power of 40 mW. The seeder laser is modulated to be a
pulse laser with a repetition rate of 10 kHz and pulse duration of 500 ns. The amplifier consists of two
pre-amplifiers and one main amplifier. The detailed characteristics of the spectrum and linewidth of the
amplifiers are presented. A pulse energy of 116 µJ and a linewidth of 1.1 MHz are obtained. This laser
can be a candidate transmitter for an all-fiber Doppler wind lidar in the boundary layer.
OCIS codes: 060.2320, 060.2420.
doi: 10.3788/COL201109.090604.
A coherent Doppler lidar has been proven to be a power-
ful tool to measure wind in low troposphere with high al-
titude resolution and high speed accuracy. Conventional
ground-based Doppler lidar uses high-energy pulsed laser,
such as 1.06-µm Nd:YAG or 2.02-µm Tm, Ho:YAG laser,
a large aperture telescope, and a separate transceiver op-
tical component. For a portable, mobile, and airborne
application, a compact, eye-safe, and rugged coherent
Doppler wind lidar is required. The all-fiber pulsed
Doppler wind lidar has attracted attention because of its
maintenance-free, lightweight, high efficiency, and goo d
beam qualities
[1,2]
. An eye-safe, narrow-linewidth local
oscillator and a single-frequency pulsed fiber amplifier
with a high repetition rate are necessary for an all-fiber
Doppler wind lidar
[3]
. An all-fiber Doppler lidar to mea-
sure wind field up to a 1-km altitude is currently being
developed by our group. Therefore, a single-frequency,
polarization-maintaining, pulsed fiber laser with an en-
ergy of higher than 100 µJ and a narrow linewidth of less
than 1.3 MHz is required to develop an all-fiber Doppler
wind lidar.
Philippov et al. reported an erbium-ytterbium co-
doped fiber (EYDF) master-oscillator-power-amplifier
(MOPA) system with a space-coupling power am-
plifier stage; 0.29-mJ and 100-ns pulses with a rep-
etition rate of 4 kHz were obtained
[4]
. Shi et al.
presented a single-frequency fiber laser at 1 550 nm with
an output energy of 52 µJ and a linewidth of 5 MHz us-
ing a Q-switched seeder and the MOPA
[5]
. Canat et al.
introduced a narrow linewidth erbium-ytterbium fiber
MOPA for coherent detection lidars; the seeder laser
was a distributed feed back (DFB) diode laser with a
linewidth of 500 kHz, and the fiber is a pedestal and
multifilament core erbium-ytterbium large mode area
(LMA) fiber
[6]
. Another single-frequency fiber laser
with the MOPA configuration was also presented
[7,8]
.
In a previously reported result, most all-fiber single-
frequency lasers use the commercial DFB laser as seeder
with a linewidth of greater than 500 kHz and an energy
of less than 100 µJ. Thus, both the linewidth of the lo-
cal oscillator and the pulse energy are not optimized in
the all-fiber Doppler lidar. In this letter, we develop a
narrow-linewidth, polarized, pulsed fiber laser with an
energy of greater than 100 µJ and a local laser linewidth
of less than of 10 kHz at an eye-safe wavelength.
The experimental setup of the polarization maintain-
ing (PM) all-fiber MOPA laser system is shown in Fig.
1. The seeder laser is split into two beams. One beam is
taken as the local oscillator, and the other seeder beam
is modulated as a pulsed laser and amplified by two pre-
amplifiers and one main amplifier.
The seeder laser was developed in our laboratory. It
was made of a high concentration of doped erbium, yt-
terbium, and phosphate glass fiber laser with a gain
coefficient of 4.2 dB/cm. The cavity consisted of a
half reflective (HR) mirror and a fiber Bragg grating
(FBG) output coupler. The output laser was polarized
by a polarizer controller. The PM output power was 30
mW with a linewidth of less than 5 kHz at 1 533 nm,
and the detailed characteristics of the seeder laser were
published
[9]
. An isolator was inserted b etween the seeder
and the beam split coupler. The seeder beam was split
into two beams by a 10/90 fiber coupler. One beam with
10% of the seeder power was taken as the local oscillator
of the developing coherent lidar. Another beam with 90%
of the seeder power was directly modulated to a square-
shaped waveform with a high-pulse repetition rate by an
acousto-optic modulator (AOM) (AMF-55-1550-2FP(+),
Fig. 1. Exp erimental setup of the MOPA fiber laser system.
LD: laser diode; MFA: mode field adaptor; 1. acousto-optic
mo dulator (AOM); 2. PM double-clad EYDF; 3. LMA PM
double-clad EYDF.
1671-7694/2011/090604(4) 090604-1
c
° 2011 Chinese Optics Letters