CO2 laser polishing of conical shaped optical fiber deflectors

Abstract

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.

Double Ring Firing Single Optical Fiber Deflector

“…Bare fiber optic deflectors deliver the laser light in the same direction with optical fiber axis, where side-firing fiber optic deflectors transmit the laser light perpendicular to optical fiber axis. Radial type optical fiber deflectors are ideally suited for laser tissue ablation, because conically shaped optical fiber end transmit the laser energy radially and the laser energy is homogeneously distributed into a ring-shaped beam [8], [9].…”

“…On the other hand, ring-shaped beams are more ideal compared to the bare optical fiber deflectors for ablation of cylindrical body parts such as veins, since their homogeneous circular beam leads to equivalently homogeneous ablation of vein walls, and they are prone to cause less temperature rise on the tissue [17]. Different radial emitting light fiber deflector fabrication techniques are proposed in the literature [9], [18], [19].…”

Spatial effect of conical angle on optical-thermal distribution for circumferential photocoagulation

“…Thermal injury or incomplete treatment can also lead to complications such as discomfort, pain, and risk of recurrence. For light diffusers, a number of fabrication techniques have been developed, including acid-etching [9,10], melt-drawing [9,11], scattering media [12,13], CO 2 laser polishing [14], long period gating (LPG) [15,16], and UV micro-drilling [10,17]. However, both the acid-etching and melt-drawing techniques are limited to using small core diameters (33-125 µm), and external impact is often employed to roughen the fiber tip surface, causing physical damage to the fiber surface [9,11].…”

“…Depending on the TiO 2 concentration, the addition of scattering media can lead to unpredictable light diffusion from the tip [12,13]. In spite of creating a conical tip for radial emissions, a CO 2 laser was able to fabricate a short range of the active element for the diffusing tip [14]. In the case of the LPG technique using a KrF excimer laser, the fabricated fibers are protected by coating a mixture of clear epoxy and TiO 2 .…”

“…Although the CO 2 laser can provide a simple machining process, the emission profile still yielded an intensity peak at the proximal end of the diffuser [18]. In addition, to minimize the laser light leakage at the distal end of the diffuser, several options have been introduced such as the addition of a reflector at the distal end tip (i.e., micro-gold mirror, right conical end, corner cube retro-reflector, and high diffuse backscattering layer) [12,13,16] and tapered fiber tip (i.e., acid, mechanical polishing, or laser) [9,11,14,18]. Yet, with the proposed options, it is still complex to attain the uniform light emissions from the diffusing tip with minimal energy loss in a forward direction.…”