400mW ultrashort cavity low-noise single-frequency Yb3 -doped phosphate fiber laser
蒸发残渣
Shanhui Xu,Zhongmin Yang,*Weinan Zhang,Xiaoming Wei,Qi Qian,Dongdan Chen,magma
铸造模拟软件
Qinyuan Zhang,Shaoxiong Shen,Mingying Peng,and Jianrong Qiu
State Key Laboratory of Luminescent Materials and Devices and Institute of Optical纸片胎
Communication Materials,South China University of Technology,Guangzhou510640,China
*Corresponding author:yangzm@scut.edu
Received June23,2011;revised August22,2011;accepted August22,2011;
posted August24,2011(Doc.ID149805);published September15,2011
A compact,low-noise,single-frequency fiber laser by using a newly developed Yb3þheavily doped single-mode
phosphate glass fiber has been demonstrated.Over400mW stable continuous wave single transverse and longitu-dinal mode laser at1:06μm was achieved from a0:8cm long active fiber.The measured slop
e efficiency and esti-mated quantum efficiency of laser emission are72.7%and93%,respectively.The signal-to-noise ratio is higher than72dB,and the linewidth of the fiber laser is less than7kHz,while the measured relative intensity noise is less than−130dB=Hz at frequencies of over1:5MHz.©2011Optical Society of America
OCIS codes:140.3510,060.2280,140.3615.
A single-frequency fiber laser at1:06μm has experienced intense research in the past few years for applications, such as laser interferometric gravitational-wave observa-tory,advanced remote sensing,coherent beam com-bining,kilowatt-class high power laser with a master oscillator power amplifier technique,and laser LIDAR [1–4].Especially in the application of multiple paths co-herent beam combining,a low-noise single-frequency la-ser with hundreds of milliwatt output power is required. Although optical amplifiers can boost the single-frequency output power,it is still preferable to obtain the hundreds milliwatt level,high signal-to-noise ratio la-ser directly from fiber oscillators.A short linear reso-nance cavity configuration,such as a distributed Bragg reflector(DBR),is beneficial to single-frequency laser emission for mode-hop-free,narrower linewidth,lower noise,and all in a compact all-fiber design[5–7].
Y.Kaneda et al.have reported a DBR laser at1:06μm with>200mW output power in a Yb3þ-doped phosphate glass fiber for first time[8].A single-frequency laser with the linewidth of<3kHz has been achieved from a1:5cm length phosphate glass fiber.However,the effective length of the resonator is designed to be4–5cm,which easily leads to multi-longitude mode emissions and needs extremely strict temperature control for the cavity.To ensure the laser operating on the single longitude mode, further shortening the resonance cavity is required,but it would limit the laser output power.In order to increase the laser output power,a higher concentration of Yb3þions is necessary to be doped into the glass fiber core. However,higher Yb3þconcentration can easily cause the blue cooperative upconversion emission due to the ions-cluster effects and decrease the quantum efficiency of Yb3þat1:06μm.In addition,during laser operation a significant gradient heat distribution along the fiber length deteriorates the laser performance[9,10].
In our previous works,a3D short-cavity heat flow management technique was proposed and an efficient 300mW low-noise single-frequency fiber laser at1:5μm
was achieved from a2cm long Er3þ=Yb3þ-codoped phos-phate glass fiber[10].In this paper,we report an over 400mW low-noise single-frequency fiber laser at 1:06μm from a1:4cm effective resonator cavity constructed by a0:8cm long Yb3þ-doped phosphate glass fiber.
The Yb3þ-doped phosphate glass fiber was drawn using a fiber-drawing tower through a phosphate glass preform fabricated by the rod-in-tube technique[11]. More details of processing the glass preform can be found in our previous work on the Er3þ=Yb3þ-codoped phosphate glass fiber[12,13].15:2wt%Yb3þions were doped uniformly in the core region.The measured fluor-escence lifetime of a Yb3þion is1:84ms,which is higher than that of Yb3þion concentration at12:0wt%in other reports[14].The designed phosphate glass fiber has a core diameter of5:0μm with an NA of0.14at1:06μm. The cutoff wavelength was calculated to be900nm.The core-to-cladding offset is less than1:0μm.The propaga-tion loss at1300nm of the Yb3þ-doped phosphate glass fiber is lower than0:06dB=cm.A peak absorption coeffi-cient of the fiber core glass is10:7cm−1at976nm,and a net gain coefficient of the phosphate glass fiber was mea-sured to be5:7dB=cm.Such strong absorption coeffi-cient allows efficient absorption of the pump light within a few centimeters,and generates hundreds of milliwatts of output power without the need of an exter-nal optical amplifier.
The laser cavity is composed of one narrowband fiber Bragg grating(NB-FBG)and one dielectric mirror,which is butt-coupled to the one end facet of a short piece of Yb3þ-doped phosphate fiber,as shown in Fig.1.The NB-FBG was irradiated with a3dB linewidth of0:05nm and a reflectivity of55.0%at1063:90nm,and it was fused splicing with the0:8cm long phosphate fiber.The reflec-tivity of
the dielectric mirror is larger than99.0%at 1:06μm and smaller than2%at976nm.Two high-power 976nm FBG-stabilized pump laser diodes(976nm LD1 and976nm LD2)with orthogonal polarization output were combined through a polarization beam combiner. The pump lasers were coupled into the laser cavity through a980=1064nm WDM,and the emission spectrum and the optical power of fiber laser were measured by an optical spectrum analyzer(OSA)and a power meter, respectively.
3708OPTICS LETTERS/Vol.36,No.18/September15,2011
0146-9592/11/183708-03$15.00/0©2011Optical Society of America
As shown in Fig.1,the effective length of the resonator includes the 0:8cm active fiber and a half of the 1:0cm NB-FBG.It is only less than 1:4cm,giving a longitudinal mode spacing of 7:4GHz.The NB-FBG has a reflection bandwidth of less than 13:3GHz.It is clear that only one longitudinal mode is supported within the laser cav-ity.Figure 2(a)illustrates the output spectrum of the Yb 3þ-doped phosphate fiber laser.The fiber laser spec-trum centered at 1063:90nm is recorded with a spectrum resolution of 0:1nm by OSA.The signal-to-noise ratio (SNR)of more than 72dB is obtained.The laser cavity was assembled into a copper tube,which was tempera-ture-controlled by a cooling system with a resolution of 0:05°C.The single-frequency characteristics were con-firmed by the scanning Fa
bry –Perot interferometer (SA210-9A),as shown in Fig.2(b).With the proper tem-perature control,the laser operated stably in a single fre-quency without mode hop and mode competition.As shown in Fig.2(c),the output power of the Yb 3þ-doped phosphate fiber laser at 1:06μm versus the launched pump power.The lasing threshold is around 25mW.When the pump power is above the threshold,the laser output power is approximately linearly increased with the pump power.An output power of 408mW is obtained from the 0:8cmYb 3þ-doped phosphate fiber at the pump
power of 570mW,which is the highest output power from this kind of fiber lasers reported to date [8,15–17].The slope efficiency against the launched pump power is measured to be 72.7%,and the experimental quantum ef-ficiency of the laser emission related to the absorbed pump power is estimated to be 93%,since only 85%of the pump power was coupled into the phosphate fiber core due to the coupling loss,scattering,and pump leak-age.From our understanding,these are also the highest slope efficiency and quantum efficiency from this kind of single-frequency fiber laser [8,15–17].The stabilities of the output power at 300mW in an hour were investigated and the result is shown in Fig.2(d).The power instability of <0:25%of the average power was observed,which is caused by the small fluctuations in the pump laser power and the small changes of ambient temperature.After the fiber laser worked for half an hour,the output power of the laser obviously beca
me very stable.As shown in Fig.2(c),the output power was saturated at the pump power larger than 570mW.When the pump power was set to be more than 740mW,the output power of the laser became unstable due to the backscatter light inducing the instability of the two pump LDs.
Laser noise is an important parameter of the single-frequency fiber laser.The relative intensity noise (RIN)was measured using bandwidth resolution 3:1kHz of the electrical spectrum and the results are shown in Fig.3.As shown by the left inset of Fig.3,at the low frequencies of <230kHz there are noise peaks at −100dB =Hz,due to environmental influences,such as acoustics or vibration.With increasing the frequency to 500kHz,the RIN de-creases from −100dB =Hz to −120dB =Hz.A relaxation os-cillation frequency peak of −112dB =Hz was observed at the frequencies of 970kHz.The RIN is stabilized less than −130dB =Hz for frequencies above 1:5MHz.
In order to further investigate the phase noise charac-teristics of the fiber laser,the linewidth of the fiber laser was measured by a self-heterodyne method using a 10km fiber delay.It is 60kHz with −20dB from the peak,which indicates the measured laser linewidth is approximately 3:0kHz FWHM,as shown in the right inset of Fig.3.The linewidth resolution of the self-heterodyne measurement with a 10km fiber delay is about 6:6kHz,so the laser line-width is affirmed to be less than 7kHz.
橙书包公益
项目In conclusion,an over 400mW single longitude mode laser at 1:06μm from a 0:8cm long Yb 3þ-dopedDielectric Mirror
0.8-cm Yb 3+-doped Phosphate Fiber
NB-FBG
Laser Output
980/1060nm WDM
976 nm LD1
1060nm Isolator
976 nm LD2
PBC
广东中烟办公协同Fig.1.(Color online)Experimental setup of the short linear cavity Yb 3þ-doped phosphate fiber laser. P o w e r L e v e l (d B m )
Wavelength (nm)
P Z T V o l t a g e (V )
Time (s)
L a s e r O u t p u t P o w e r (m W )
Pump Power (mW)280
290
300
310
P o w e r (m W )
Time (min)
< 0.25 %
(d)
Fig.2.(Color online)(a)Laser spectrum of the Yb 3þ-doped phosphate fiber laser.(b)The longitudinal modes characteris-tics of the fiber laser measured by the scanning Fabry –Perot interferometer.(c)The output power of the fiber laser at 1064nm versus the pump power.(d)The power stabilities of the fiber laser for an
hour.
Fig.3.(Color online)Noise characteristics of the Yb 3þ-doped phosphate fiber laser.Inset (left):the magnified RIN at the low frequencies of <2:0MHz.Inset (right):the self-heterodyne line-width of the fiber laser.
September 15,2011/Vol.36,No.18/OPTICS LETTERS
3709
phosphate fiber has been demonstrated.The slope effi-
ciency is72.7%and the quantum efficiency of laser emis-
sion has been estimated to be93%.The SNR is more
than72dB,and the RIN of the fiber laser is less than −130dB=Hz at the frequency higher than1:5MHz.The laser linewidth is less than7kHz.These results show that
the short linear cavity based on the Yb3þ-doped phos-
phate single-mode glass fiber is a very promising candi-
date as an efficient and compact single-frequency fiber laser at1:0μm region.
This research was supported by the China State863
Hi-tech Program(2011AA030203),the National Natural
Science Foundation of China(NSFC)(U0934001and
60977060),the Guangdong Province and Hong Kong In-
vite Public Bidding Program(TC10BH07-1),the Science
and Technology Project of Guangdong(2009A090100044,
2009B091300127,cgzhzd0903,and2010B2101230),the
Project of Education Department of Guangdong Province
(2009N9100200),the Fundamental Research Funds for
the Central Universities(2009ZM0219,2011ZZ0001,and
中档轿车2009ZZ0054),the Open Research Fund of State Key La-
boratory of Precision Spectroscopy,and the Young Nat-
ural Science Foundation of South China University of
Technology(E5090880).
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3710OPTICS LETTERS/Vol.36,No.18/September15,2011
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