COL 10(12), 121401(2012) CHINESE OPTICS LETTERS December 10, 2012
Realization of a low threshol d multiwaveleng th
brillouin/erbium fiber laser by optimizing
the reflecte d power
A. W. Al-Alimi
1,2∗
, A. F. Abas
1,2
, M. A. Mahdi
1,2
, M. H. Al-Mansoori
3
, and M. Mokhtar
1,2
1
Wireless and Photonic Networks Research Centre, Engineering and Technology Complex,
Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
2
Photonics and Fiber Optic Systems Laboratory, Department of Computer and Communication Systems Engineering,
Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
3
Faculty of Engineering, Sohar University, P. O Box 44, Sohar P. C. 311, Oman
∗
Corresponding author: mogni 66@yahoo.com
Received April 30, 2012; accepted July 10, 2012; posted online October 16, 2012
A multiwavelength Brillouin/erbium fiber laser (BEFL) with low threshold power is realized. A low
threshold power of 3 mW and a wide tuning range of 18 nm can be achieved by controlling the reflected
power in the nonlinear optical loop mirror (NOLM). Up to 24 lines with a wavelength spacing of 0.086 nm
are generated at the Brillouin pump and at the 1 480-nm pump with −0.5 dBm (0.9 mW) and 25 mW of
power, respectively.
OCIS codes: 140.3510, 290.5900, 060.2410.
doi: 10.3788/COL201210.121401.
The multi-wavelength laser s ources have been used in
many applications, such as in dense wavelength division
multiplexing (DWDM) systems, optical fiber sensors,
and microwave photo nics
[1,2]
. By offering co st-saving
solutions, the erbium-doped fiber laser (EDFL) has at-
tracted much interest in its use as a multi-wavelength
laser source. However, the homogeneous linewidth of
the gain medium in EDFLs should be reduced, and the
mode competition between adjacent laser signa ls should
be suppressed. Several techniques have be en proposed
to solve this problem, such as cooling down the EDF to
liquid nitrog e n temperature
[3]
, using frequency-shifted
feedback
[4]
, and optimizing the cavity loss
[5,6]
. Other
multiwavelength sources that utilize different nonlinear
effects, such as four-wave mixing (FWM)
[7,8]
, nonlin-
ear polarizatio n rotation (NPR)
[9]
, stimulated Brillouin
scattering (SBS)
[10]
, and stimulated Raman scattering
(SRS)
[11]
were previously reported. The inadequate Bril-
louin gain in the single mode fiber requires another gain
medium to compensate the cavity loss and to improve the
laser operation efficiency. This co nce pt was successfully
demonstrated by C owle a nd Stepanov
[12]
. The combi-
nation of the SBS effect and the EDF in the same laser
cavity creates a Brillouin/ e rbium fiber laser (BEFL).
Different BEFL structures have been proposed to gener-
ate multiple waveleng ths when achieving low threshold
values and low pump power per channel are both very
impo rtant. The pre-amplification technique in a linear
cavity
[13−18]
is widely used to reduce the SBS thresh-
old and to enha nce the performance of the BEFL. The
reverse-S-shaped section was used as another method
to reduce the threshold power, in which the Brillouin
Stokes (BS) signals couple back into the laser cavity
[19]
.
However, in this structure, the use of many optical com-
ponents requires a high thr e shold power. When the
reverse-S-shaped fiber section was replaced by a broad-
band, partially reflec ting fiber Bragg grating (FBG), the
threshold power was improved
[20]
. The tr ansmission and
the r eflection power intensity o f the no nlinear optical
loop mirr or (NOLM) have b een investigated by Doran
et al.
[21]
. The rapid auto-switching ability of the NOLM
makes it a valuable technique in optical signal processing
applications, which include pulse shaping
[22]
, amplitude
equalizing
[23]
, and self-switching
[24]
. More studies
[25,26]
have recently exploited the effect of the NOLM as an
effective component to improve the BEFL performance.
In this letter, multiwavelength BEFL was experimen-
tally demonstrated. Beside the double pass amplification
method, the power intensity levels in the NOLM was op-
timized by the proper adjustment of the output coupling
ratio of the varia ble optical coupler (VOC) to achieve
low threshold powe r. A low threshold powe r of a bout
3 mW at a Brillouin pump (BP) power of 0 dBm was
reported.
The experimental s etup of the proposed tunable
BEFL is shown in Fig. 1. The linear cavity struc-
ture simply consists of two circulators (C1 a nd C2), one
VOC, a 1 480-nm wavelength selective coupler (WSC),
and 10-m-lo ng EDF with an absor ption coefficient of
5.6 dB/m at 1 531 nm. The wavelength selective cou-
pler (WSC) was used to combine the 1 480-nm pump
power and the oscillating signals. C1 was used as input
and output port, whereas C2 was used to form a fiber
loop mirror (FLM) in which the lase r guided back to
the cavity. The BP power and wavelength were provided
by an external-cavity tunable laser source (TLS) with a
maximum power of 8 dBm and 200-kHz line width. The
TLS ca n be tuned over a tuning range of 10 0 nm (from
1 520 to 1 620 nm). An optical spectrum analyzer (OSA)
with 0.01-nm resolution was connected to port 3 of C1
to monitor the BEFL o utput.
The NOLM was formed by splicing a 3-km standard
1671-7694/2012/121401(4) 121401-1
c
2012 Chinese Optics Letters