March 10, 2011 / Vol. 9, No. 3 / CHINESE OPTICS LETTERS 031403-1
Wavelength stabilization of a 980-nm semiconductor laser
module stabilized with high-power uncooled dual FBG
Yize Huang (黄黄黄毅毅毅泽泽泽)
1
, Yi Li (李李李 毅毅毅)
1,2∗
, Haifang Wang (王王王海海海方方方)
1
, Xiaojing Yu (俞俞俞晓晓晓静静静)
1
,
Hu Zhang (张张张 虎虎虎)
1
, Wei Zhang (张张张 伟伟伟)
1
, Huiqun Zhu (朱朱朱慧慧慧群群群)
1,3
, Sheng Zhou (周周周 晟晟晟)
1
,
Ruoxi Sun (孙孙孙若若若曦曦曦)
1
, and Yuming Zhang (张张张宇宇宇明明明)
1
1
Scho ol of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology,
Shanghai 200093, China
2
Shanghai Key Lab oratory of Modern Optical Systems, Shanghai 200093, China
3
Institute of Thin Films and Nanomaterials, Wuyi University, Jiangmen 529020, China
∗
Corresp onding author: liyi@usst.edu.cn
Received July 26, 2010; accepted Novemb er 19, 2010; posted online February 21, 2011
An optimized dual fib er Bragg grating (FBG) is proposed for 980-nm semiconductor lasers without ther-
mo electric co olers to restrict temp erature-induced wavelength shift. The mathematical mo del of the
temp erature-induced wavelength shift of the laser with the dual FBG is built using the external cav-
ity feedback rate equations. The external cavity parameters are optimized for achieving the stability
mo de-locking laser output. The spectral characteristics of the dual FBG stabilized laser are measured to
range from 0 to 70
◦
C. The side mode suppression ratio (SMSR) is more than 45 dB, while the full-width
at half-maximum (FWHM) is less than 1 nm. The peak wavelength shift is less than 0.1 nm. The dual
FBG wavelength shift prop ortional coefficient is between 0.1086 and 0.4342.
OCIS co des: 140.3425, 140.3480, 140.3570.
doi: 10.3788/COL201109.031403.
High-power wavelength-stabilized 980-nm semiconductor
lasers comprise the main pump sources for fiber lasers
and erbium-dop ed fiber amplifiers (EDFAs) in current
telecommunications networks
[1−5]
. Dense wavelength di-
vision multiplexing (DWDM) systems with high speed
and capacity have been deployed in long-haul and metro
networks. EDFAs are efficient optical amplifiers for
DWDM systems, and their performance depends on the
characteristics of pump lasers, including frequency spec-
trum, output optical power and polarization state, and
so on. The amplifier gain is sensitive to the pump
wavelength, which drives the market almost exclusively
toward cheap and wavelength-stabilized semiconductor
lasers. Conventionally, thermoelectric coolers (TECs) are
fixed in semiconductor laser modules to eliminate the
output wavelength shift caused by ambient temperature
change and current-induced heating. TECs are removed
in uncooled laser modules based on fiber Bragg grat-
ing (FBG) external cavity stabilization to reduce power
consumption, size, and cost. However, it is impossible
to avoid a large wavelength detuning between the las-
ing peak wavelength and the Bragg wavelength at 0–
70
◦
C ambient temperature. Because the dual FBG form,
an external cavity as frequency-selective component, the
uncooled semiconductor laser can operate within the
range of 0–70
◦
C with an accurate emission wavelength.
Contrary to laser modules with the single FBG external
cavity semiconductor laser, there is no wavelength detun-
ing in a dual FBG stabilized semiconductor laser
[6,7]
. In
general, the dual FBG external cavity is considered as
two filters in series, especially for strong external feed-
back; however, the dual FBG external cavity should be
modeled as a Fabry-Perot (F-P) cavity for weak exter-
nal feedback because semiconductor lasers are sensitive
to the weak external optical feedback. Various dynam-
ics, including instability and chaos, have been reported
and observed in this system. Therefore, the investigation
of the laser module with the low reflectivity dual FBG
based on a F-P external cavity is very important through
analysis of the rate equations. Meanwhile, there is a
contradiction between the side mode suppression ratio
(SMSR) and the output p ower efficiency in the semicon-
ductor laser module. Relatively high external reflectiv-
ity makes the laser achieve high SMSR while decreasing
the output power efficiency of the laser. A high-power
semiconductor laser is vital to further application. How-
ever, suppression of other lasing modes to achieve single
longitudinal mode output must greatly reduce the over-
all output power. When the external length is longer
than the coherent length, in which the laser is under the
coherence collapse, the laser can operate steadily within
the external reflective bandwidth. In this case, the stable
output wavelength is achieved. Although the increase of
high-frequency noise is caused by the beat-frequency phe-
nomenon under the coherence collapse, numerous modes
and their incoherence equalize the low-frequency output
power with jumping modes. Therefore, a high-power un-
cooled dual FBG stabilized 980-nm semiconductor laser
module has been proposed to achieve the high SMSR
with low output power loss
[8−11]
.
In this letter, the wavelength shift of the semiconduc-
tor laser module with dual FBG external cavity is studied
through the FBG coupled mode theory and the external
cavity feedback rate equations. The characteristics of the
F-P external cavity are integrated into the effective ex-
ternal transmittivity (T
eff
), which is substituted into the
rate equations to analyze the wavelength shift through
the relation between the light and carriers. The active
1671-7694/2011/031403(5)
c
° 2011 Chinese Optics Letters