Improved diamond-like carbon coating deposition uniformity on cylindrical sample by its suspension in RF PECVD chamber

The paper discusses the uniformity of diamond-like carbon (DLC) thin overlays deposited with radio frequency plasma-enhanced chemical vapor deposition (RF PECVD) method on optical fibers with induced long-period gratings (LPGs). When refractive index around the LPG increases, a spectral response of the LPG strongly depends on properties of the overlay. Using LPG suspended in the RF PECVD chamber, we have found that DLC thickness distribution around the fiber highly depend on a distance between the LPG and the electrode. More asymmetrical deposition, which takes place when the LPG is located closer to the electrode, induces appearance of a series of additional resonances in LPG transmission spectrum. It has been found that for the fiber suspended 7.2 mm over the electrode the coating has the highest uniformity. Higher uniformity obtained by fiber suspension in the chamber has been compared with the effect resulting from fiber rotation between two consecutive processes. It is shown that more symmetrical deposition is obtained for the suspended samples than for the rotated ones. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim