An elastically stretchable composite sheet includes an elastically stretchable first web and an inelastically stretchable second web of thermoplastic synthetic resin fiber which is intermittently bonded to the first web in a y-direction. A device can establish a near field communication link with a verified device on a network, wherein the near field communication link can be a secure andor encrypted link to provision the device without comprising security constraints within the network. The invention provides a method whereby adding probe substances usually not present in blood offers standardized substrates for measuring the enzymatic activity. The flexible optical waveguide can be produced by subjecting a surface of the substrate, on which surface the lower cladding layer is to be formed, to physical treatment with a whetstone or chemical treatment with a corona discharge and then successively forming the lower cladding layer, the core layer, and the upper cladding layer on the surface of the substrate.