Jianq Cao

In this paper, the development of a high-power continuous wave (CW) fiber laser near 980 nm is reviewed. This review is focused primary on the power evolution resulting from the designation of Yb-doped fibers, which is important in the suppression of the amplified spontaneous emission (ASE) around 1030 nm. Current studies on the in-band ASE as the...

In this paper, a hundred-watt-level near-diffraction-limited step-index Yb-doped fiber (YDF) laser near 980 nm is demonstrated firstly, to the best of our knowledge. By using the 11.7-W 979-nm single-mode seed light, the in-band amplified spontaneous emission (ASE) is well suppressed and the maximum output power of 101.5 W with the beam quality (M²...

Requirements on the double-cladding Yb-doped fiber (DCYF) for power scaling of diffraction-limited fiber amplifiers are studied in this paper. By considering the limitations of thermal lens and transverse mode instability separately, it is found that the power scaling limit can be enlarged to more-than 100 kW and 80 kW, respectively, with the prope...

The comparative study on the continuous-wave double-cladding Yb-doped fiber (DCYF) amplifiers operating around 978 nm and 982 nm is carried out in this paper. By means of numerical and experimental studies, it is revealed that compared with 978-nm amplifiers, the amplified spontaneous emission (ASE) around 1030 nm can be better suppressed in 982-nm...

In this paper, a hundred-watt monolithic fiber laser operating near 980 nm is demonstrated by using a double-cladding Yb-doped fiber (DCYF) with 20-μm core and 125-μm inner-cladding diameter. The fiber laser is fabricated with the master oscillator power amplifier (MOPA) configuration to scale up the output power. In our experiment, it is found tha...

In this paper, the scalability of slope efficiency of a Yb-doped fiber amplifier operating near 980 nm is studied with the core-pumping scheme. By means of numerical prediction, it is found that the theoretical limit of slope efficiency should be about 92.2%. Then, the experiment study is carried out. An 85.3% slope efficiency of emission around 98...

In this paper, we study the temperature characteristic of a gain fiber core in distributed side-coupled cladding-pumped (DSCCP) fiber amplifiers by optical frequency domain reflectometry (OFDR). To the best of our knowledge, this is the first temperature distribution measurement of a fiber core in DSCCP fiber lasers. The temperature distributions a...

The effect of seed power on the inter-modal four-wave mixing (IM-FWM) effect in a distributed side-pumped fiber amplifier is investigated for the first time, to the best of our knowledge. By using a seed source smaller than 70 W, the effect of seed power on the IM-FWM is studied experimentally. Surprisingly, it is found that the IM-FWM effect becom...

In this paper, the in-band amplified spontaneous emission (ASE) in the Yb-doped continuous-wave (CW) fiber amplifier operating near 980 nm is experimentally studied for the first time, to the best of our knowledge. A core-pumped single-mode Yb-doped fiber amplifier is fabricated and the effects of pump power, seed power, and active fiber length on...

A 100-W all-fibre amplifier operating near 980 nm is demonstrated with a double-clad Yb-doped fibre (DCYF) having a 60/125-μm core/cladding diameter. By preliminarily optimising the length of DCYF (about 1.4 m), a total output power of about 113.4 W is obtained with 9-W seed light, the peak-to-peak suppression of 1030-nm ASE being about 21.5 dB. Th...

In this Letter, to the best of our knowledge, the first kilowatt monolithic Yb-doped fiber laser operating near 980 nm is demonstrated. The fiber laser is achieved with the help of an all-fiber amplifier fabricated with a 105/250- $\unicode{x00B5}{\rm m}$ µ m core/cladding-diameter double-cladding Yb-doped fiber. With 11-W seed light, about 1.11-kW...

In this paper, a 500-W-level all-fiber amplifier operating near 980 nm is demonstrated firstly, to the best of our knowledge. The amplifier is fabricated with a 105/250-μm core/cladding-diameter double-cladding Yb-doped fiber (DCYF). By optimizing the length of DCYF, the record 556-W output power and 50.5% slope efficiency are obtained with a 1.85-...

In this paper, a cost-effective 50-W-level all-fiber oscillator operating near 980 nm is demonstrated with the 20-μm core-diameter double-cladding Yb-doped fiber (DCYF) firstly, to the best of our knowledge. By using the 15-degree angle-cleaved output fiber end-facet, the record 54.8-W output power is obtained with the slope efficiency about 15.6%....

A strictly single-transverse-mode all-fiber laser is demonstrated with a 10-um core-diameter Yb-doped fiber. 1-kW output power is obtained with the slope efficiency of 78% and no Raman component can be observed in the output spectrum.

The effect of tens-of-Watt seed light on the stimulated Raman scattering (SRS) in a distributed side-pumped Yb-doped fiber amplifier is studied. By using two sorts of seed sources with the power smaller than 70 W, it is observed in experiment that the SRS can be enhanced by lowering the seed power. To the best of our knowledge, this is the first ob...

In this paper, a more-than ten-Watt all-fiber oscillator operating near 980nm is demonstrated with a commercially-available 20/125-μm double-cladding Yb-doped fiber (DCYF) firstly, to the best of our knowledge. The 15-W output power is eventually obtained with the slope efficiency of 13% and central wavelength around 978 nm. Moreover, the power sca...

The inter-modal four-wave mixing (IM-FWM) and transversal mode instabilities (TMI) are experimentally studied in high-power distributed side-pumped fiber amplifiers. To the best of our knowledge, we have made the first demonstration of TMI and IM-FWM which can be suppressed simultaneously by increasing the bending diameter. Besides, the experimenta...

A 20-W all-fiber oscillator operating near 980 nm is demonstrated with a commercially-available double-cladding Yb-doped fiber. 20.1-W output power is eventually obtained with the slope efficiency of 16.1% and the center wavelength around 978 nm.

A simplified model is presented for studying the inter-modal four-wave mixing (IMFWM) effect in high-power Yb-doped fiber amplifiers. Together with IM-FWM, the transverse mode competition is also taken into account in this model.

The high-power 980-nm superfluorescent Yb-doped fiber source (SYFS) fabricated with the distributed side-coupled cladding-pumped (DSCCP) fiber is studied with the purpose of improving its efficiency. In experiment, by strengthening the pump light coupling of DSCCP fiber, more-than 23% slope efficiency with the record value of 23-W 980-nm emission i...

In this paper, the thermal-lens induced mode coupling in step-index large mode area fiber laser is systematically investigated. The pertinent mode coupling coefficient is studied firstly, to the best of our knowledge. It is demonstrated that the mode coupling can be induced by the thermal-lens induced waveguide changing along the active fiber. It i...

In this paper, the stimulated Raman scattering (SRS) threshold of the distributed-pumped fiber amplifier consisting of multiple sub-amplifiers is analytically studied based on the rate-equation model. The SRS threshold formula is presented where the predictions agree well with the numerical results. With the help of the formula, the effect of the p...

In this paper, a generalized numerical model describing the pump light propagating in the distributed side-coupled cladding-pumped (DSCCP) fibers with identical pump cores is present, with which the pump light propagation in the DSCCP fiber is analytically investigated. It is found that the local pump absorption should be smaller than the inner-cla...

A 37-W all-fiber 980-nm superfluorescent fiber source is firstly demonstrated in experiment, to the best of our knowledge. The slope efficiency is about 38.7% with the 3-dB bandwidth about 4.5 nm.

Numerical model describing the thermal-lens induced mode coupling in the fiber amplifier is presented based on which the thermal-lens induced mode coupling in a short-cavity single-frequency fiber amplifier is briefly discussed.

A high-power all-fiber superfluorescent source operating near 980 nm is experimentally studied with the help of a large-core distributed side-coupled cladding-pumped Yb-doped fiber. By optimizing the active fiber length and the angle cleaving of the output fiber facet, a 10 W all-fiber superfluorescent source operating near 980 nm is demonstrated f...

The high-power all-fiber superfluorescent source operating near 980 nm is studied experimentally and numerically. In experiment, an all-fiber superfluorescent source operating near 980 nm is fabricated with the distributed side-coupled cladding-pumping (DSCCP) Yb-doped fiber (YDF). By optimizing the active fiber and angle-cleaving of the output por...

The adiabaticity criterion of the thermally-guided very-large-mode-area (TG VLMA) fiber is presented based on the mode-coupling theory firstly, to the best of our knowledge. The requirement for the adiabatic propagation of fundamental mode is discussed systematically. It is revealed that the pump absorption plays the most important role and the adi...

The characteristics of a single-mode continuous-wave thermally guiding very-large-mode-area fiber amplifier are investigated numerically using the rate-equation model while taking thermal transfer into account. It is revealed that the seed power should play an important role in the fiber amplifier and should be large enough to ensure high output ef...

The superfluorescent Yb-doped fiber source operating near 980 nm is studied. The design requirement is theoretically discussed aiming to suppress the amplified spontaneous emission around 1030 nm in the 980-nm superfluorescent fiber source. Based on the theoretical study, a multi-Watt, all-fiber, bi-directional, pumped, superfluorescent source oper...

In this paper, the properties of continuous-wave Yb-doped fiber amplifiers operating near 980 nm are investigated numerically. The effects of the seed light, active fiber configuration, pump power, pumping scheme and residual reflectivity of output port on performance of the 980-nm amplifier are revealed. It is found that besides the core-to-claddi...

Thermal-lens induced coupling between the fundamental and higher-order modes in the high-power fiber amplifier is revealed firstly, to the best of our knowledge, and the variation of pertinent coefficient is discussed.

The 4-kW all-fiber distributed side-pumped oscillator are firstly demonstrated with the distributed side-coupled cladding-pumped (DSCCP) fiber, to the best of our knowledge. Using four cascaded gain sections, the 3.96-kW output power with 73.0% slope efficiency is obtained, and the stimulated Raman scattering (SRS) suppression is about 48 dB. The t...

The beam quality variations of transverse modes with thermal load in the thermally-guiding (TG) very-large-mode-area (VLMA) fiber are numerically investigated in this paper. It is found that the beam qualities of transverse modes can be optimized with the production of thermal load. The beam quality variations are not monotonous due to the thermall...

A 2 kW pump-light-stripper-free all-fiber distributed-pumping oscillator fabricated with the distributed side-coupled cladding-pumped Yb-doped fiber is demonstrated for the first time, to the best of our knowledge. An output power of 1969 W with a slope efficiency of 72.2% is obtained. By utilizing the final-section counter-pumping scheme, pure out...

The stimulated Raman scattering (SRS) in high-power continuous-wave (CW) fiber amplifier is investigated with the seeded Raman noise taken into account. It is revealed that the seeded Raman noise, as a portion of seed light, should enhance SRS in high-power CW fiber amplifier even when it is much weaker than the seeded signal light. The analytic fo...

The very-large-mode-area (VLMA) fiber is of great importance for suppressing the nonlinear effects which are considered as main limitations to the power scaling-up of high-power fiber lasers and amplifiers. The thermally guiding (TG) VLMA fiber is a novel VLMA fiber, the waveguide of which is formed by the thermal lens effect. Then, a low numerical...

An 8-W all-fiber bi-directional pumped superfluorescent source operating near 980 nm is demonstrated firstly, to the best of our knowledge. The recorded 8.38W combined output power is obtained with the 3-dB bandwidth about 3.5 nm.

A 1-kW all-fiber distributed-counter-pumping oscillator is demonstrated firstly to the best of our knowledge. The output power of 1.08 kW with a slope efficiency of 66% is obtained.

The beam qualities of transverse modes in the thermally-guiding very-large-mode-area fiber are numerically investigated. Their variations with the thermal load are given.

In this paper, the propagation properties of the 3 × 1 single-mode-to-multimode (SM-MM) fiber combiner with finite cladding, is numerically investigated. It is found that the finite cladding has an indispensable effect on the property of the combiner. Because of the confinement of the finite cladding, both the taper ratio and transfer efficiency ca...

The transverse-mode evolution in thermally guided (TG) index-antiguided-core (IAGc) fibers is numerically studied in this paper. With the finite-element method and thermal conduction equations, the fundamental mode evolution with a thermal load is investigated, and four evolution stages (i.e., the cladding-confined, quasi-cladding-confined, quasi-c...

A high-power all-fiber broadband superfluorescent source is fabricated by using a distributed side-coupled cladding-pumped Yb-doped fiber. It is found experimentally that besides the optical feedback, the active fiber parameters have a significant effect on the power scaling. By optimizing the fiber length, a record amplified spontaneous emission o...

An all-fiber single-stage superfluorescent source with a recorded 186-W combined output power is demonstrated. The efficiency is 78% with the bandwidths larger than 20 nm.

The optical coupling between two strongly-coupled highly multi-mode fibers is studied.The coupling process is measured in experiment. The effects of the differences between two fiber cores on the coupling process are revealed.

A simplified numerical model predicting the output power of thermally guiding index-antiguided-core fiber amplifier is presenteD.The output power variation of the amplifier is discussed with the model.

The all-fiberized continuous-wave 980-nm amplifier with an Yb-doped double-cladding fiber (YDCF) is experimentally investigated first, to the best of our knowledge. It is revealed that besides the core-to-cladding ratio of YDCF, the filling of the seed light in the active core is also of great importance for the 980-nm signal amplification. By impr...

A kilowatt all-fiber cascaded amplifier is demonstrated with a distributed side-coupled cladding-pumped Yb-doped fiber for the first time, to the best of our knowledge. Two-stage cascaded amplification is realized in the amplifier, with a total output power of 1.009 kW and an optical-to-optical efficiency of 76.8% with respect to launched pump powe...

The side-coupled cladding-pumped fiber has many advantages in terms of system design, ease of pump injection, signal extraction and power scalability over traditional double cladding fiber. We demonstrate a 290-W all home-made side-coupled cladding-pumped fiber laser with the slope efficiency of 67.8%. To the best of our knowledge, the slope effici...

An all-fiberized broadband superfluorescent source based on a distributed side-coupled cladding-pumped Yb-doped fiber is demonstrated. A recorded 102 W combined output power is obtained with the angle-cleaved output ends. The bandwidth is larger than 10 nm. The power scalability of the superfluorescent source is analyzed numerically. It is found th...

An all-fiberized broadband superfluorescent source based on a distributed side-coupled cladding-pumped Yb-doped fiber is demonstrated. A recorded 102-W combined output power is obtained by the excellently angle-cleaved termination. The bandwidth is larger than 10 nm.

An all-fiberized continuous-wave double-cladding Yb-doped fiber amplifier operating near 980 nm is presented. More-than-6-W signal power is obtained with the slope efficiency of 32%.

The power scalability of diffraction-limited Yb-doped fiber lasers is investigated with a new model which takes into consideration the spectrums of absorption and emission cross sections of active ions. It is found that the maximum output power of a fiber laser is not only dependent on the pump wavelength, but also depends on the core size and clad...

We compare both analytically and numerically the distributed side-coupled cladding-pumped (DSCCP) fiber lasers and double cladding fiber (DCF) lasers. We show that, through optimization of the coupling and absorbing coefficients, the optical-to-optical efficiency of DSCCP fiber lasers can be made as high as that of DCF lasers. At the same time, DSC...

All-fiberized continuous-wave Yb-doped fiber lasers operating near 980 nm are fabricated, and 1.73 W, 980 nm lasing is obtained. Moreover, the output properties of the 980 nm fiber laser are studied by experiment. It is demonstrated, for the first time to the best of our knowledge, that the output power curve versus the active fiber length experien...

The effects of phase errors on phase locking of the all-fiber laser array are discussed. By analyzing the 5-fiber laser array, it is found that the phase properties of the array depend on the order of the magnitude of the inevitable random phase errors in the fiber lasers. The dynamics of maximum phase deviations are also traced to seek the conditi...

The output performance of large mode area (LMA) all-fiber laser are affected by the stripping ability of cladding light, which is consisting of the residual pump light and cladding mode signal light. The common method of stripping cladding light is to recoat the DCF (double clad fiber) with a high index gel, but it strips the cladding light quickly...

In this paper, the output properties of fiber lasers operating near 980 nm are investigated. It is found that the pump threshold increases exponentially with the length and dopant concentration of the active fiber. It is also revealed that the output properties of the 980 nm fiber lasers are more sensitive to the inner cladding diameter of the acti...

The phase-locked states of the array of two mutually-injected fiber lasers are studied in experiment. Controlling of these phase-locked states is realized with a self-feedback loop.

An all-fiberized normal double-clad ytterbium-doped fiber laser operating at 977 nm with mode field mismatch is set up. The effect of splicing loss and refection in the laser cavity on the output performance is discussed.

The model of the distributed side-coupled cladding-pumped fiber laser is established. The analytical solutions of the model are given. The propagations of the pump and signal light are investigated.

In this paper, the effects of the gain property (i.e., the absorption and emission cross sections) on the efficiency of the strongly forward-pumped Yb-doped fiber laser are studied. By means of the analytical study, it is found that the output efficiency increases monotonically with the absorption cross section sigma(a)(lambda(p)). Nevertheless, th...

In this paper, the array of fiber lasers coupled by bi-dimensional mutual injection is firstly, to our knowledge, investigated. Phase locking of the array is theoretically studied and the phase-locked states of the array are given. It is found that the array with bi-dimensional mutual injection can export the same amount of the phase-locked states...

We propose a continuous wave dual-wavelength-pumped scheme for visible supercontinuum (SC) generation. The scheme is numerically studied in this paper. In the scheme, the dual-wavelength pump source is produced through a four-wave mixing process in a photonic crystal fiber. SC generation is numerically investigated by solving the generalized nonlin...

Passive coherent beam combining, which uses optical feedback from the fibers to force all to lock in phase, seems to be a promising way for high power output. Fused-taper fiber laser array is one of the passive methods, in which phase locking is realized by mutual energy coupling, without any active phase control. In this paper, we use a dynamical...

The chaotic dynamics in the array of two coupled solid-state lasers with one laser frequency-modulated is numerically studied. By analyzing the spectrum of the cosine of the phase difference between two lasers, the chaotic dynamics of the array are discussed in detail. It is found that the spectrum component, with the frequency smaller than but clo...

In this paper, the long-exposure far-field properties of the array of mutually-injected fiber lasers are studied to understand the effect of the multiple phase-locked states on coherent beam combining of the array. It is found that the long-exposure far-field will degenerate into the superposition of the intensities of the elementary lasers when al...

Phase locking of arrays of mutually-injected fiber lasers is investigated theoretically. The phase-locked states of this array are analytically discussed. It is revealed that phase locking of this array is affected by the transfer characteristic of the coupler used for mutual injection. Arrays fabricated with two kinds of couplers (i.e., 1 × 3 cou...

The effect of mutual-injection ways on phase locking of arrays of two mutually injected fiber lasers is studied theoretically. The phase-locked states of arrays with different ways of mutual injection are given analytically. Itis found that different ways of mutual injection will result in different phase-locked states. The relationships between ph...

In this paper, coherent beam combining of N-laser interferometric array fabricated with 2×2 couplers is theoretically studied. By investigating phase locking of the interferometric array, the conditions needed to get high-efficiency beam combining of this array are given. It is found that the gains of the array do not only provide the mechanism of...

The interference of two beams from a multi-longitudinal-mode fiber laser is investigated. An interesting phenomenon is reported that interference fringes, with the visibility much higher than the value estimated from laser spectrum, emerge in experiment.

Phase-locked states of linear arrays of mutually-injected fiber lasers are theoretically investigated. It is found that the number of phase-locked states of N-laser linear array is the same as that of N-laser ring array.

The array of two mutually-injected fiber lasers is theoretically studied. It is found that the self-organization mechanism of this array is virtually the longitudinal-mode competition in the compound laser cavity. Two phase-locked states of this array are predicted. The performance of this array is also investigated, and the theoretical result agre...

A dynamics model of self-organized fiber laser arrays is presented in this paper. The model does not only break the limitation of the standard slowly varying wave approximation, but also be built on the basis of Maxwell-Bloch equations which make this model more suitable to study the dynamics (especially phase dynamics) of fiber laser arrays. In th...

The effect of polarization controlling on coherent beam combining of two-fiber laser arrays of interferometric configuration is researched. Three kinds of arrays, built on the basis of Michelson and Mach-Zehnder interferometers, are investigated experimentally. It is found that polarization controlling is not necessary for coherent beam combining o...

The dynamics of the array consisting of two coupled solid-state lasers with frequency modulations was researched numerically. Array intensity’s chaotic behavior is predicted when the modulation frequency is low. The physical mechanism of the chaos is discussed here qualitatively. It was found that not only a harmonic resonance itself but also the d...

Coherent combination of fiber lasers through mutual injection locking is demonstrated experimentally in this paper. By moving the mutual injection couplers from the output port to the high reflection feedback port of the lasers, a modified combining configuration is constructed with obviously enhanced slope efficiency as compared with the conventio...

Self-organized coherent fiber laser arrays of interferometer configuration are researched numerically with circulating field theory. The numerical results agree well with the experimental observations. The self-organization mechanism of the array is verified to be longitudinal mode selection in an interferometer resonator. Influences of the arm len...

Coupled laser array, which realizes phase locking of elementary lasers with evanescent waves coupling, is a promising scheme to realize coherent beam combination. To reveal the stability of the phase-locked state in the array, the influence of the frequency drift on the phase dynamics of the two-coupled-laser array is researched. It is demonstrated...

A promising approach to overcome the output power limitation of a single fiber laser was combining of fiber laser, which was attractive and developing very fast. This technology could be divided into the coherent combination and the incoherent combination. More optical field intensity on the axes and energy distribution concentrated of the coherent...