Diamond-like carbon films deposited onto optical fibres and waveguides: application in chemical sensing

Abstract

The paper presents the diamond-like carbon (DLC) film as a coating for multimode optical fibre, single-mode optical fibre with long-period grating (LPG) and planar optical waveguides. Thin DLC coatings significantly change sensing elements' properties. Constructed systems can be very sensitive to concentration changes of several chemical solutions (e.g. sodium chloride, calcium chloride and ethylene glycol) due to changes of refractive index of the solutions. The influence of Radio Frequency Plasma Chemical Vapour Deposition (RF PCVD) process parameters on sensitivity is discussed. A novel integrated planar waveguide sensing system with DLC film is presented. The films were analysed morphologically and optically.

Optical effect of diamond‐like carbon film coating of long‐period optical fiber gratings

“…The LPG wavelength shift seems to depend more on the thickness of the DLC coating than on its refractive index. The DLC film can further act to stimulate the sensitivity of LPG structures to variations in the external refractive index [1]. To our knowledge, we have for the first time successfully deposited DLC coatings on tapered LPGs which can increase their application areas as fiber optic sensors.…”

“…Previous works [1][2][3][4] have shown that DLC meets the requirements for smooth and hermetic coatings for optical fibers and can also significantly improve the sensitivity of optical fiber sensors. LPG has a wide range of applications, including band-rejection filters, gain flattening filters and sensors [1,[5][6][7][8][9][10][11][12][13]. During the last decade, various coatings for LPG have been presented [8][9][10][11][12][13].…”

“…Using the Radio Frequency Plasma Chemical Vapor Deposition (RF PCVD) method, it is possible to deposit DLC films onto various substrates without inflicting significant damage to the substrates [2]. DLC films deposited in this manner are 50÷300 nm thin and very smooth (4 nm roughness), have a high refractive index (n = 1.8÷2.1) and adhere well to glass and silicon plates [1,3,4]. In most cases, it is virtually impossible to measure the refractive index and the thickness of coatings on optical fibers.…”

“…Thin coatings significantly change the properties of sensing elements. Constructed LPG systems can be very sensitive to changes in the concentration of various chemical solutions (e.g., ethylene glycol) due to changes in the refractive index of the solutions [1]. Often applied non-plasma coating deposition methods (e.g., the Langmuir-Blodgett technique [9]) give coatings with well-defined thickness and refractive index in contradistinction to plasma deposition methods.…”

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

“…Typically, dip-coating methods are applied for obtaining thin overlays around the fiber [5,6]. In our previous works, we have shown various nano-overlays deposited with radio-frequency plasma-enhanced CVD (RF PECVD) method on the LPGs [4,[7][8][9][10]. We have found that position of the sample in the plasma chamber has significant influence on thickness of the deposited overlay [9].…”