that is centered above the cylindrical path 131 fig6 is a diagrammatic view partly in section that is similar to fig5 but shows the substrate 18 with the coating 19 formed thereon and also shows the cutting machine 56 more specifically after the groove 51 has been formed the coating 19 is formed on the top surface of the substrate 18 in fig2 the groove 151 is formed with a depth that is greater than the thickness of the coating 19 thus a portion 19 a of the coating 19 is disposed in the bottom of the groove 151 but is not in contact with the remainder of the coating 19 that is on the top surface of the substrate 18 alternatively however the groove 151 could be shallower such that the portion 19 a of the coating 19 is in contact with the remainder of the coating but still defines a discontinuity in the coating the portion of the coating 19 that is within the diameter 26 has a radially inwardly facing edge surface 158 thereon next the tool 62 of the cutting machine 56 is used to cut the substrate 18 due to the physical width of the tool 62 this cutting operation will remove a portion of the optical component 11 disposed between the cylindrical path 131 and a further cylindrical path 171 that is concentric to and disposed radially inwardly of the path 131 the tool 62 is positioned radially so that as it is moved downwardly.