A preservative system comprising iodopropynyl butyl carbamate and phenoxyethanol at a weight ratio of iodopropynyl butyl carbamate to phenoxyethanol within the range of about 1:90 to about 1:400 shows a broad anti-microbial effect and can permit use of the preservative system at a low level in end use products such as personal care products. When first and second order gratings are superimposed, input light is partially reflected by the first order component and partially coupled out of the waveguide by the second order component. A tapered ramp extends from the round body to the square head. , after having been cured, is at least 5%.