have been proposed and several types are currently used for tissue ablation. The types of deflector shapes are bare, sidefiring and radial. Bare fiber optic deflectors (basic deflector geometry) transmit the laser energy in the same direction along the fiber. Side-firing optical fiber optical deflectors transmit laser light perpendicular to the fiber axis through specific direction and they are widely used in many medical applications, especially in the prostate tumor ablation [1]. One of the most popular deflector types is radial design. Radial fiber optic deflectors with conically shaped optical fiber end transmit the laser energy radially and the laser energy is homogeneously distributed into a ring-shaped beam. These deflectors are especially used in endovenous laser ablation (EVLA) [2]. Unlike other cone-shaped fiber optical probes [3][4][5][6][7] used for various applications, EVLA operation needs μm-scale, multimode (MM) optical fibers and specific cone-angle values to fulfill the EVLA operation requirements. Thus, multi-mode, larger NA and μm-scale optical fibers are preferred in the operations. The homogeneous, ring-shaped laser energy distribution can be achieved with large cone angles which are detailed in this study. It allows a perfect irradiation of vein walls and their ablation. Among existent fiber processing methods such as chemical, FIB [3][4][5], mechanical polishing method is the best candidate to obtain such desired cone-angles. Furthermore, mechanical polishing process is applicable for mass-production of conical shaped optical fibers used in EVLA operation. In the mechanical polishing process, the deflector geometry is first formed with rough lapping film, then, the surface roughness of the deflector is gradually smoothed by polishing with smoother lapping films [8]. This process is composed of several steps to obtain high quality surface structures and a well-prepared fiber deflector surface eliminates the optical losses such as scattering and back reflection. However, the mechanical fining Abstract A novel method for polishing conical shaped optical fiber deflectors by modulated CO 2 laser exposure is reported. The conical shaped fiber deflector geometry was first formed with rough mechanical polishing, then it was exposed to modulated CO 2 laser operating with wavelength at 10.6 µm to achieve fine polish surfaces. The motivation of this work is to demonstrate that the modulated CO 2 laser exposure approach allows a fiber surface roughness at a nanometer scale without modifying the conical shape of the fiber deflector. The average surface roughness of mechanically polished fiber deflectors with 30 and 9 µm lapping films was smoothed down to 20.4 and 4.07 nm, respectively, after CO 2 laser polishing process. By combining mechanical and laser polishing techniques, fabrication of conical shaped optical fiber deflectors takes less time and it becomes laborer independent and easy to apply.
We demonstrate a 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources operating in the broad absorption spectrum around 915 nm. In the experiment, two different pump diodes were tested to pump over a wide spectrum ranging from 904 to 924 nm by altering the cooling temperature of the pump diodes. Across this so-called pump wavelength regime having a 20 nm wavelength span, the amplified stimulated emission (ASE) suppression of the resulting laser was generally around 35 dB, showing good suppression ratio. Comparisons to the conventional 976 nm-pumped 1018 nm ytterbium-doped fiber laser were also addressed in this study. Finally, we have tested this system for high power experimentation and obtained 67% maximum optical-to-optical efficiency at an approximately 110 W output power level. To the best of our knowledge, this is the first 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources around 915 nm reported in detail.
Applications of high power lasers and amplifiers have been increasing because of its superior properties such as high wall-plug efficiency, excellent beam quality, and reliability [1]. Despite advances in high power fiber components, there is still component reliability based challenges on extraction process of unwanted cladding light [2]. There are several techniques to extract the cladding light from the fiber laser system such as high index polymer coating that of working principle is violating the total internal reflection [2], roughened cladding surface which uses the scattering to eliminate the cladding light [3], soft metal coating to absorb the cladding light [4] and CO2 laser processing of cladding to disturb the light path with the structural manipulations and strip the unwanted light from these structures. There are some limitations for each case. The high index polymer CLS are limited by the thermal degradation of recoated polymer [4]. For the roughened or etching CLS, even though very high attenuations levels were achieved, the roughing or etching process decrease the fiber strength. This could create undesired problems such as heat localization and microcrack formation on cladding wall. Here, we present novel method for practical, robust, compact, and all glass cladding light stripper fabrication on Ytterbium (Yb) doped octagonally shaped double clad fiber (DCF). In the experiment, carbon dioxide (CO2) laser heated Yb-doped octagonal shaped DCF fiber is twisted by using AFL's LAZERMaster (USA-Japan) laser splicing machine. The surface of the DCG gets a twisted pattern since one of the fiber holder was rotating and the other one was fixed and the SEM image of this pattern is shown in Fig.1a. In this component, using 24 times 850μm-long twisted segment, 20mm-long CLS is fabricated. The performance of the twisted CLS was analyzed at the experimental setup shown in Fig.1.b. The output fiber of the diode laser (Dilas) having 200/240µm core/clad diameter is integrated to the cladding of 30cm DCF with 3x1 pump combiner. As a result of power analysis, 95% of the 119W input power was stripped with twisted CLS. The attenuation values and the CLS output power versus launched power are shown in the Figure 1.c. Also, the inset image at Figure 1.c represents the light distribution of the twisted CLS. It is obvious that light extracted from the CLS is homogenous and the attenuation is also stable with increasing launched power.
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