An apparatus and method for measuring residual stress and photoelastic effect of an optical fiber is disclosed. The lower unit includes one or more lower unit chips overlying the top surface of the lower unit substrate that are electrically connected to the conductive features of the lower unit substrate. The projection can cooperate with the groove to prevent relative rotation between the annular element and the body. These steps are followed by heating the turbine blade or vane to form an aluminium layer on the external surface and a chromium layer on the internal surface.