Invited column-‘Ultra-fast fiber laser technology (I)’
2018, 47(8): 803001.
doi: 10.3788/IRLA201847.0803001
New research method and laser performance had been achieved in ultrafast fiber lasers when computing technique was introduced in. In this paper, the research progress on ultrafast fiber lasers based on computing technique was briefly summarized and analyzed, the enabling property of computing technique for ultrafast fiber lasers was revealed. The further combination of ultrafast fiber laser and computing technique may open a new avenue for research and application.
2018, 47(8): 803002.
doi: 10.3788/IRLA201847.0803002
Ultrafast fiber lasers have become the ideal candidate for ultrafast light source and been applied in practice. Due to the small beam diameter and the long interaction distance between light and fibers, the nonlinear effect is unavoidable. Before the appearance of multiple pulses resulted from the excessive nonlinear effect, the phenomenon of period doubling bifurcation(PDB) can be observed in ultrafast fiber lasers under appropriate operation conditions. The PDB refers to the recurrence of pulse parameters at the rate of times of cavity transmission time. The PDB is the intrinsic features of nonlinear systems. It is universal among different nonlinear systems. The latest research progress of the PDB in ultrafast fiber lasers was summarized. The characteristics of the PDB in different dispersion regimes were analyzed. In addition, the features of the PDB of vector solitons, and that of multiple pulses were discussed.
2018, 47(8): 803003.
doi: 10.3788/IRLA201847.0803003
Pulsed fiber lasers have raised extensive attentions for their great application prospects in material processing and fabrication, optical communications, biomedical fields and research of nonlinearity. Saturable absorbers(SA) are used to obtain pulsed laser, two-dimensional materials have unique optical and electrical properties, which have many applications in the fields of optical and optoelectronic devices. In particular, they are widely used in pulsed fiber lasers, due to the features including saturable absorption, simple preparation process, easy integration with optical fiber systems, wide operating wavelength. This article reviews the pulsed fiber laser applications based on the integration of two-dimensional materials and optical fibers, and dicusses the external field controls of such pulsed fiber lasers.
2018, 47(8): 803004.
doi: 10.3788/IRLA201847.0803004
High power all-fiber mid-infrared(MIR) supercontinuum(SC) light sources have attracted much attention for their wide applications in fundamental research, environments, medicine, and national defense security. Currently, such SC light sources are mainly based on fluoride glass fibers. While the relative low damage threshold and poor chemical durability of the fluoride glass fibers influenced their applications in practical high power MIR SC light sources. For further improving the performances of the MIR SC light sources and developing practical high power MIR SC light source, a fluorotellurite glass(TeO2-BaF2-Y2O3, TBY) with good thermal and chemical stabilities was developed, and fluorotellurite glass fibers was fabricated based on it. By using the fluorotellurite glass fibers as the nonlinear media, coherent SC generation from 1.4-4 m and broadband SC generation from 0.4-5.14 m were obtained in our experiments. Moreover, SC light source with an average power of 10 W was also obtained, and the spectral range covered 947-3 934 nm.
2018, 47(8): 803005.
doi: 10.3788/IRLA201847.0803005
Ultra-short pulse lasers at 1.0 m waveband have important applications in many fields such as laser processing, optical precision measurement, biomedicine etc. However, because the Yb-doped fiber laser operates in the all-normal dispersion regime, the pulse width of the laser output is usually large. Because the microfiber could provide anomalous dispersion at 1.0 m waveband by changing its size, in order to achieve ultra-short pulse the microfiber was employed as dispersion compensation device to compress the Yb-doped fiber laser pulse. In this work, the diameter and length of taper waist of the home-made microfiber were 3 m and 5 cm, respectively. The pulse width of the Yb-doped fiber laser was 37.6 ps, while it was compressed to be 8.5 ps by the microfiber. These results offer a more simple and inexpensive method for pulse compression.
2018, 47(8): 803006.
doi: 10.3788/IRLA201847.0803006
The mode-locking mechanism of an all-polarization-maintaining fiber laser based on a nonlinear polarization loop mirror was demonstrated. Instead of a fiber coupler in the traditional nonlinear amplifying loop mirror based mode-locked fiber laser, a polarization beam splitter (PBS) was implied in the nonlinear polarization loop mirror. The combination of the PBS, non-reciprocal components and a piece of gain fiber acted as the core elements in nonlinear polarization loop mirror to achieve stable mode-locking in an all-polarization-maintaining fiber laser. A passively mode-locked erbium-doped fiber laser based on this mode-locking mechanism was also presented. The laser directly emited an optical pulse train of 141 fs duration (75 MHz) with 30 mW total output power. The laser had bidirectional outputs, and the power from two outputs was adjustable by adjusting the waveplate in the cavity. Moreover, the environment stability of the free-running laser was characterized, yielding an average output power fluctuation of 0.05% in 1 h and the relative repetition rate stability of 2.010-8 in 1 s. The configuration enables self-start mode-locking, generating optical pulse trains with high environmental stability, high repetition rate and short pulse duration and fully meets the requirements of ultra-short pulse laser sources in femtosecond based ranging, laser machining, spectroscopy and other applications in spaceflight technologies.
2018, 47(8): 803007.
doi: 10.3788/IRLA201847.0803007
A passively harmonic mode-locked erbium-doped fiber laser was built up based on nonlinear polarization rotation(NPR) technique with switchable repetition rates. A 45 tilted fiber grating(45TFG) integrated in the cavity was considered as an ideal polarizer, which was combined with two polarization controllers to realize NPR mechanism. Under fixed pump power of 673 mW, a group of harmonic mode-locked pulses from 1st to 37th could be obtained only through adjusting the two polarization controllers carefully. The laser can produce stable pulses with the maximum repetition rate of 783 MHz which corresponds to 37th harmonic order, and the sidemode suppression ratio (SSR) of 37th harmonic mode is 41 dB. High repetition rate and stable pulses can be used in applications, such as modern optical communication system and optical sensors.
2018, 47(8): 803008.
doi: 10.3788/IRLA201847.0803008
As optical solitons propagate along the fiber, stable bound state solitons can be formed due to complex nonlinear interactions, and phase variation of bound state solitons reveals abundant dynamics in the nonlinear system. Based on the Ginzburg-Landau equation governing the evolution of solitons along the fiber, the dynamics of soliton phase variation induced by the system parameters was numerically studied. It was found that there exist different bound state solitons, and initial conditions finally converge to bound state solitons with different phase difference. The results also indicate that the change of pump strength influences the pulse separation of solution as well as phase difference of bound state, which is of importance for in-depth understanding of the underlying nonlinear interaction mechanism.
2018, 47(8): 803009.
doi: 10.3788/IRLA201847.0803009
The Q-switched mode-locking(QML) rectangular pulses in the L-band erbium-doped passively mode-locked fiber laser based on nonlinear polarization rotation technique was researched experimentally. The Q-switched envelope of this type of pulses contained the rectangular pulse with fundamental repetition rate,which was confirmed as noise-like pulse by an autocorrelator. A 250 m long section of single mode fiber was inserted into the cavity to ensure the noise-like rectangular pulses easy to be obtained. By carefully adjusting polarization controllers and pump power in the cavity, both the continuous-wave mode-locking noise-like rectangular pulses with fundamental repetition rate of 778.21 kHz and the QML noise-like rectangular pulses with tunable repetition rate from 3.81 kHz to 9.01 kHz and the highest energy of Q-switched pulse envelop 1.06 J were achieved. The research results further reveal the fundamental physics of noise-like pulses and QML operation in the passively mode-locked fiber lasers.
2018, 47(8): 803010.
doi: 10.3788/IRLA201847.0803010
With the rapid development of high power ultrafast fiber lasers, divided-pulse amplification (DPA) technology has attracted extensive concerns. DPA can be implemented through birefringent crystals or freespace delay lines. By combining with the techniques of chirped pulse amplification, spatial beam splitting and photonic crystal fiber amplification, DPA can be applied to coherent beam combining and nonlinear compression in order to increase both the pulse energy and peak power of ultrafast fiber lasers. The research progress of DPA in ultrafast fiber lasers was reviewed. Different system structures of DPA in the applications of coherent beam combining were analyzed. The optimization and further development of DPA was also prospected.
2018, 47(8): 803011.
doi: 10.3788/IRLA201847.0803011
With the rapid development of modern digital manufacturing technology, in the field of industrial product measurement, the measurement of the geometric dimensions of objects need some requirements, such as non-contact, high-precision, multiple sizes, high-volume, etc. The existing measurement technologies cannot meet these requirements. In order to achieve multiple sizes, high-efficiency, rapid, and non-contact precise measurement, fiber-coupled lasers with the advantages of good beam quality, ultra-fine line width, high precision, good monochromaticity, small size, convenient using, no adjustment, maintenance-free and high stability were used to develop a precision non-contact measurment system based on fiber lasers. A high-precision measurement method based on fiber-coupled lasers was proposed, which mainly included object imaging based on fiber-optic line laser, bilateral filtering and extraction of laser line, mathematical relationship establishment of measurement model, geometric parameter calibration, data conversion and 3D reconstruction and other key technologies. The fiber laser continuously emitted laser line to the object, adopted a high-resolution camera, and photographed the laser line image of the object through two imaging techniques of illumination/non-illumination to acquire 2D plane size and height information of the object. The laser line image was filtered and corrected, the laser line was quickly extracted, the geometric parameters were calibrated and the coordinate transformation was performed, and then the processing data was processed to obtain the measurement value of the measurement parts of the object. A large number of object measurements and comparative experiments were carried out to verify the validity and accuracy of the measurement system and measurement method. The measurement accuracy can reach micron level. It provides an efficient method and measurement equipment for the three-dimensional high-precision non-contact measurement of industrial products.
