High Power Laser Science and Engineering, (2019), Vol. 7, e31, 7 pages.
© The Author(s) 2019. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1017/hpl.2019.18
Fabrication of kW-level chirped and tilted fiber Bragg
gratings and filtering of stimulated Raman scattering in
high-power CW oscillators
Kerong Jiao
1
, Jian Shu
2
, Hua Shen
1,2
, Zhiwen Guan
1
, Feiyan Yang
1
, and Rihong Zhu
1,2
1
MIIT Key Laboratory of Advanced Solid Laser, Nanjing University of Science and Technology, Nanjing 210094, China
2
School of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology, Nanjing 210094,
China
(Received 18 February 2019; revised 27 March 2019; accepted 4 April 2019)
Abstract
Suppression of stimulated Raman scattering (SRS) by means of chirped and tilted fiber Bragg gratings (CTFBGs) has
become a key topic. However, research on high-power systems is still lacking due to two problems. Firstly, after the
inscription, there are a large number of hydroxyl compounds and hydrogen molecules in CTFBGs that cause significant
heating due to their strong infrared absorption. Secondly, CTFBGs can couple Stokes light from the core to the cladding
and the coating, which causes serious heating in the coating of the CTFBG. Aimed at overcoming these bottlenecks, a
process that combines constant-low-temperature and variable-high-temperature annealing is used to reduce the thermal
slope of the CTFBG. Also, a segmented-corrosion cladding power stripping technology is used on the CTFBG to remove
the Stokes light which is coupled to the cladding, which solves the problem of overheating in the coating of the CTFBG.
Thereby, a CTFBG with both a kilowatt-level power-carrying load and the ability to suppress SRS in a fiber laser has
been developed. Further, we establish a kW-level CW oscillator to test the CTFBG. Experimental results demonstrate
that the power-carrying load of the CTFBG is close to 1 kW, the thermal slope is lower than 0.015
◦
C/W, and the SRS
suppression ratio is nearly 23 dB.
Keywords: chirped and tilted fiber Bragg gratings; fiber optics components; high-power fiber laser; stimulated Raman scattering
1. Introduction
Fiber lasers have been widely used in many fields, in-
cluding industrial processing
[1, 2]
, biomedicine
[3, 4]
and
communication
[5]
, due to their compact structure, high
efficiency and high spatial beam quality
[6]
. With increasing
demand for high power, stimulated Raman scattering (SRS)
has become one of the main factors limiting the development
of fiber lasers
[7]
. To solve this problem in recent years,
an increasing number of researchers have focused their
attention on using specially structured fiber gratings to
suppress the SRS in fiber lasers.
One such method is to use long-period fiber gratings
(LPGs). LPGs, usually used in the sensing field
[8, 9]
, can
couple the forward-propagating core modes to the forward-
propagating cladding modes. Therefore, a specific wave-
length of light can be coupled from the core to the cladding
by controlling the period of the LPG. In 2010, Nodop
Correspondence to: H. Shen, MIIT Key Laboratory of Advanced Solid
Laser, Nanjing University of Science and Technology, Nanjing 210094,
China. Email: edward bayun@163.com
et al.
[10, 11]
used this characteristic of LPGs to suppress SRS
in pulsed fiber lasers with an average power of 70 µW and
a suppression ratio exceeding 20 dB (99%). However, LPGs
are sensitive to temperature, strain and bending, which leads
to a drift in the cladding-mode resonances and a reduction of
the suppression ratio. Another approach is to use CTFBGs.
Unlike LPGs, CTFBGs can couple the forward-propagating
core modes to the backward-propagating cladding modes.
Furthermore, compared with LPGs, the period of a CTFBG
is much smaller, which means the cladding-mode resonances
of CTFBGs change only slightly under the influence of
temperature, strain and bending. This makes CTFBGs the
preferred method of suppressing SRS by fiber gratings. In
2014, Liu et al.
[12]
introduced chirp into a TFBG and real-
ized the design and inscription of a CTFBG with broadband
filtering for the first time. Moreover, potential applications
of CTFBGs in the field of sensing and communication were
also proposed. Wang et al.
[13]
first applied a CTFBG to
a 22 W low-power CW fiber laser to suppress the SRS in
2017, and reported a 25 dB (99.68%) SRS suppression ratio.
Further, they achieved inscription of a CTFBG in PS-GDF-
1
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