We have proposed a germanium doped core fiber design for large mode area single-mode applications. The designed fiber effective index, dispersion and bend loss of the fundamental mode and next higher order modes have been calculated using the numerical method. The fiber exhibits a high differential loss between the fundamental mode and higher order modes. Therefore, the designed fiber structure effectively suppresses the higher order modes and retains only the first mode (or fundamental mode) in the core region. Our simulation results demonstrate that, a low loss of 0.1dB/m is achieved for fundamental mode at 1060nm wavelength with 10cm bend radius, along with it also exhibits a high loss of 4.8 dB/m to first higher order mode. The fiber shows a large mode area of 831.4 μm2 at 1060nm wavelength. The proposed paper further explores the fiber properties such as dispersion and fabrication tolerances. Our design shows a dispersion of 39 ps/km-nm at 1060nm, and also the structure shows a less dispersion variation over a wavelength band of 400nm. The fiber reduces the fabrication difficulties as compared to the other designed fibers. We fabricated the present fiber using the renowned vapor axial deposition technique. In this method, we can achieve the large diameter preforms and also the method decreases the tolerances when dealing with glasses.
The treatment using photodynamic therapy (PDT) among cancer treatment methods shows remedial value in various cancers. The optical fiber probe infiltrates into affected parts of the tissues that are difficult to access, such as pancreatic cancer, carcinoma of extrahepatic bile duct, prostate cancer, and bladder cancer by using endoscopic retrograde cholangiopancreatography (ERCP) and endoscopic ultrasonography (EUS) with various types of diffusing tips.
In this study, we developed cylindrical diffusing optical fiber probe (CDOFP) for PDT, manufactured ball-shaped end which is easily infiltrated into tissues with diffusing length ranging from 10mm to 40mm through precision laser processing, and conducted beam profile characterization of manufactured CDOFP. Also, chemical reaction between photo-sensitizer and laser in PDT is important, and hence the thermal effect in tissues as per diffusing length of probe was also studied as it was used in a recent study.