In recent years,passively Q-switched fiber laser are widely used in material processing,optical communications,biomedicine and laser spectroscope [
Acta Photonica Sinica, Volume. 50, Issue 10, 1014004(2021)
Passively Q-switched Erbium-doped Fiber Laser with Maleic Acid-doped Polyaniline Saturable Absorber(Invited)
Based on an organic nonlinear optical material, Maleic Acid-Doped Polyaniline (MADP) Saturable Absorber (SA), a stable Q-switched pulse operation was realized in an erbium-doped all-fiber laser for the first time. In this experiment, the modulation depth and saturable absorption intensity of the MADP-SA were measured at 13.9% and 0.336 MW/cm2 using the twin detector technique, respectively. The MADP-SA is inserted into the fiber resonator in the form of a thin film sandwich. The stable Q-switched pulse operation are achieved with the repetition rate range from 33.78 kHz to 87.01 kHz, the narrowest pulse width of 2.29 μs and the maximum single pulse energy of 54.64 nJ. MADP can be considered as a good candidate for pulsed fiber laser applications and other optoelectronic devices.
Introduction
In recent years,passively Q-switched fiber laser are widely used in material processing,optical communications,biomedicine and laser spectroscope [
Organic nonlinear optical materials have the advantages of mechanical flexibility and low cost [
MADP is an organic conductive compound formed after chemical doping with acid. It exhibits excellent electrical conductivity and environmental stability. In addition,after strong light irradiation,MADP shows short response time and high nonlinear optical properties. Therefore it can be used as a SA in the laser for short pulse generation. This kind of short-pulse fiber laser is widely used in industrial cutting,material processing,laser spectroscopy and biomedicine[
In this work,we demonstrated a Q-switched fiber laser at 1 560 nm based on MADP-SA at the first time. By inserting MADP into laser cavity,a stable Q-switched pulse with maximum output power of 3.6 mW and a minimum pulse width of 2.29 μs can be achieved,which corresponding to the maximum pulse energy of 54.64 nJ. The experimental results depicted that MADP can be considered as a good candidate for pulse laser generation in optoelectronic devices.
Preparation and characterization of MADP
MADP is an organic conductive compound formed by chemically doping acid,which exhibits excellent electrical conductivity,optical properties and environmental stability. Therefore,it is considered to be the most promising polymer material. The MADP film used in this experiment was prepared by chemical oxidation polymerization. The production method is relatively simple. At a constant temperature,the analysis of pure aniline is added to a certain amount of water. The acid was added while stirring to form aniline salt,and then poured into the acid solution of the oxidant. After the reaction lasted for half an hour,it is filtered,washed and dried several times to obtain a powdered eigenstate polyaniline. A certain amount of N-Methyl Pyrucketone(NMP)is then added to the powdered eigenstate polyaniline,dripping the formed dark blue ink liquid on the cover glass and spin coating at a speed of 5 000 r/min. Then the glass slides loaded with materials are stored in the vacuum drying box and exposed to malic acid vapor. Over time,the color of the film changes from dark blue to green and then transferred to deionized water to remove the MADP film from the cover glass. In this way,a MADP film is formed.
In order to understand the basic properties of the material,a corresponding characterization study was carried out. In this experiment,surface and side features of MADP films were obtained using Scanning Electron Microscopy(SEM). Therefore,the surface and side morphology details of the sample can be carefully observed.
Figure 1.SEM image and FTIR spectra of the MADP film
The saturable absorption properties,which indispensable characterize the optical properties of materials,is an important parameter for evaluating a SA[
Figure 2.Experimental setup for measuring nonlinear absorption characteristics and the transmission curve of MADP-SA
where T is transmission,∆T is modulation depth,I is input intensity of the laser,Isat is saturable power intensity and Ans is non-saturable absorbance.
Experiment setup and results
Expriment setup
Taking advantage of the saturable absorption properties of MADP,we further constructed a passively Q-switched all-fiber Er-doped laser with the MADP as a SA. The experimental setup of the compact MADP SA based EDF fiber laser is depicted in
Figure 3.Schematic of the all-fiber Q-switched EDF laser cavity
To measure the output states of laser in the intra-cavity. A real-time sampling oscilloscope(Tektronix DPO3052,500 MHz,2.5 GS/S,Shanghai,China)and a photodetector(Harmoniclaser UltraPD-1550,Yancheng,China)was employed to monitor the temporal evolution and output power of the output pulse train. Meanwhile,an optical spectrum analyser(HORIBA IHR550,Shanghai,China)with a resolution of 0.02 nm was utilized to record the optical spectrum.
Results
In our experiment,through adjusting the PC cautiously,a stable Q-switched phenomenon emerges when pump power is increased to 160 mW.
Figure 4.Q-switched pulse trains under different pump power
Figure 5.Repetition rate and pulse width and output power and single pulse energy versus pump power of the Q-switched operation
Figure 6.The Q-switched pulse width and the wavelength spectrum of the Q-switched EDF laser at the pump power of 380 mW
We compare previously reported results with our work about Er-doped Q-switching fiber laser based on different organic materials. As
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Conclusion
In summary,a stable passively Q-switched Er-doped all-fiber laser has been demonstrated using the organic material as SA. The modulation depth and saturable intensity of the MADP-SA are 13.9% and 0.336 MW/cm2. Based on the MADP-SA,Q-switched pulse exhibited the maximum pulse energy of 54.64 nJ and minimum pulse width of 2.29 μs at the pump power of 380 mW. To our best knowledge,this is the first report on a Q-switched Er-doped fiber laser based on MADP SA. We believe that it will have excellent application prospects in ultrafast photonics.
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Xiaoli WANG, Yingying JIAN, Jingjing LEI, Zihao ZHANG, Junli WANG, Weiwei WU. Passively Q-switched Erbium-doped Fiber Laser with Maleic Acid-doped Polyaniline Saturable Absorber(Invited)[J]. Acta Photonica Sinica, 2021, 50(10): 1014004
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Received: Jul. 20, 2021
Accepted: Aug. 27, 2021
Published Online: Nov. 3, 2021
The Author Email: WANG Junli (dispersion@126.com)