A liner stop for retaining a flow sleeve relative to a combustion liner in a combustor is disclosed. In particular the invention teaches an apparatus and method that allows cost effective co-directional operation of an optical amplifier to support full duplex traffic on a single fiber, and the design of an optical fiber transmission system based on this optical amplifier technology. A weighting value is assigned to a difference value between sensing signals obtained from mutually adjacent sensing electrodes, based on which the coordinates, or the like, of a touch input are determined, thus significantly reducing the influence of noise and accurately determining a touch input. Cement is then circulated into the annulus between the expanded first tubular and the bore wall. , and more particularly, for rendering a vector texture to touch-based, free-form drawing, writing, etc.