In order to improve the slop efficiency of the twins fiber, the coating process of the twins fiber was studied. Two kinds of twins fiber with different coating diameters were fabricated by using different coating molds. By building a 1080 nm laser amplification system, the slop efficiency of the twins fiber with different coating diameters was tested. Slop efficiency of the twins fiber with larger coating diameter was 61.2%. Compared to the twins fiber with small diameter, of which the slop efficiency was 58.6%, it increased by 2.6%. That meant appropriate coating process of the twins fiber could effectively increase the slop efficiency. When the slop efficiency was increased, the heat generated by the twins fiber as the pump changed into signal laser would decrease. This would reduce heat management pressure of twins fiber when it was used in optical fiber laser, and make the application of twins fiber have more broad prospect in high power fiber laser.
In recent years, the power level of laser outputting from twins fiber, being of pump unit fiber and gain unit fiber, is continuing rising. However, little report is focused on the pump coupling efficiency and thermal management on account of the distinctive waveguide of twins fiber. In this paper, the experiment study was launched on pump coupling efficiency and thermal management based on our previous work. To facilitate observing, two waveguides were designed as “cycle pump unit + octagonal gain unit” and “cycle pump unit + cycle gain unit”, while both gain units contained no doping core and the claddings were all 125 um approximately. It indicated that the pump power proportion between pump unit and gain unit was gradually changing with increasing of fiber length when the fiber was pumped from only one side of pump unit. The dynamic balance of pump power proportion could be obtained as the length of “cycle pump unit + octagonal gain unit” twins fiber is more than 4 m. By contrast, the balance point appeared earlier for “cycle pump unit + cycle gain unit” twins fiber before the length was up to 4 m. Further, the laser experiment was executed by using typical twins fiber that was consisted of one octagonal gain unit, containing Ytterbium (Yb) doped fiber core, and cycle pump unit. When the power was pumped into the fiber from the pump unit, the temperature of pumping point was obviously lower than conventional double cladding active fiber.
Most of irradiation resistant fibers are designed to contain pure quartz fiber core to ensure good irradiation resistant performance. However, multimode (MM) fiber containing pure quartz core owns lower bandwidth because of the step index (SI) distribution. Thereby the application of it will be limited though the irradiation resistance is fine attributing to pure quartz core. To combine better irradiation resistance and higher bandwidth, a novel irradiation resistant and high bandwidth MM fiber (RMM-fiber) being of special waveguide was designed and experimental investigated via testing attenuation, bandwidth and mechanical strength before and after 60Co radiation (up to 25 Mrad(Si), 10 Mrad(Si)/s). It is indicated that the RMM-fiber owns lower irradiation induced attenuation comparing with normal MM fiber, and the bandwidth after irradiation is 403.1 MHz km @1300 nm that is much higher than SI type MM fiber. The RMM-fiber shows no reduction but a little rising on mechanical strength. Additionally, it has outstanding environmental suitability in -100°C~+125°C temperature cycling test.
A novel kind of domestic twins fiber that consisted of active unit and passive unit was researched in this paper. The slop efficiency of the twins fiber was observed via various laser amplification testing systems, which were respectively established with two different pump wavelengths and two different numerical apertures of pump output fiber. The effect of both pump wavelength and numerical aperture on the slop efficiency of the twins fiber was analyzed during the experiment. After the laser amplification testing system was optimized, the slop efficiency of the twin fiber increased from 72.1% to 82.1%. The numerical aperture of the pump output fiber would exert a distinct influence on the slop efficiency of the twins fiber. Simultaneously, the method to improve the slop efficiency of the twins fiber and decrease heat generating in high power fiber laser system was suggested.
The process of preparing fluorine-doped multimode gradient optical fiber preform by MCVD is studied in this paper. Different core reactants are doped to form different core refractive index distributions. It is found that the core with more germanic chloride and phosphorus has better refractive index distribution. But it is not conducive to the radiation resistance of the fiber.
Polarization maintenance fiber with high birefringence is an important goal for the development of high power fiber lasers. There are different ways to achieve high birefringence, such as change shape of a fiber’s core and apply stress to a fiber’s core. In this paper, fibers with different ovality of elliptical core are fabricated and tested. On the other hand, stress type PM fibers are also made, including PANDA type fibers and bowtie type fibers. Their test results are compared and analyzed together with their structures. Generally, the bowtie type fibers has highest birefringence, while the PANDA fibers are with high birefringence and high production efficiency. Different application can choose different type of PM Laser fibers.
Protective fiber coating decides the mechanical strength of an optical fiber as well as its resistance against the influence of environment, especially in some special areas like irradiation atmospheres. According to the experiment in this paper, it was found that the tensile force and peeling force of resistant radiation optical fiber was improved because of the special optical fiber coating.
A novel well weathering resistant power delivery fiber which is of double cladding and high optical energy transmitting ability is developed via fluoroplastic out sheath extruding process. The fiber has been comprehensively evaluated including optical performance, mechanical performance, environmental suitability and laser transmitting property. It is shown that the fiber has not only low attenuation, high numerical aperture and better mechanical bending performance, but also outstanding weathering resistance and high power laser transmitting performance, which implies the qualification of the fiber for various kinds of applying situations, such as laser ignition, laser induced expanding sound underwater, ship-based and airborne laser weapon.
Absorption coefficient is a very useful feature for active fiber. In fiber laser system, the length of active fiber is chosen according to absorption coefficient. And the length of fiber can directly influence the feature of fiber laser. Therefore, how to obtain an accurate absorption coefficient is very important. Because fiber exists re-emission in typical absorption band pumped by power. It is difficult to accurately measure absorption coefficient. The absorption coefficients of Yb-doped double cladding fiber at 975 nm measured by several methods were compared. In conclusion, for the fibers with same length pumped by white light, the absorption coefficient is the highest when cutback only once. Meanwhile, when fibers with different length were measured by the same method, the absorption coefficient is inversely proportional to optical fiber length.
KEYWORDS: Optical fibers, Nonlinear optics, Optical testing, Signal attenuation, Single mode fibers, Cladding, Lithium, Electronics, Ions, High power lasers
The power output of 2km and 8km 80μm selected cut-off wavelength single mode optical fiber was measured by 2.4W ASE fiber source at 1550nm waveband. The results show that obvious nonlinearity in 2km fiber does not occur by way of output power and spectrum. Slight nonlinearity is seen in 8km fiber. The power variation is small during the test of power stability with 1.28W input in 8km fiber.
2.0μm emission properties of Ho3+-Yb3+ co-doped tellurite oxy-halide glass exited by 980nm LD is
reported. Mid-infrared transmittance property of glass was investigated by Fouriertransform infrared (FTIR)
spectrometer. The Judd-Ofelt intensity parameters Ωt)t=2,4,6) , spontaneous radiative transition probabilities, branching ratios and radiative lifetime of Ho3+ were calculated according to the absorption spectra by using Judd-Ofelt theory. The absorption, emission cross-sections and gain coefficient of Ho3+:5I7→5I8 are calculated based on the McCumber and Reciprocity theories. Results indicate that the maximum 2.0μm emission intensity of Ho3+ was achieved
at 0.15mol% Ho2O3 and 1.5mol% Yb2O3 concentrations in tellurite oxy-halide glass. The maximum absorption and
stimulated emission cross-section of Ho3+ near 1944nm are 6.37 x 10-210cm2 at 2.0μm and 10.94 x 10-21cm2 respectively. The results suggest Ho3+-Yb3+ co-doped tellurite oxy-halide glass is a good candidate for efficient 2.0μm
laser.
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