of fig2 a is 12 u00d7 w 1 u00d7 w 2 w 1 u00d7 w 2 this ratio can be increased by reducing k 1 and or k 2 i e the frame 31 area surrounding the micro tunnels 32 the ratio of transmitted light 34 to incident light 33 defines the transmission ratio of the micro tunnel array 30 the transmission ratio increases as the micro tunnel density increases and both can be equal when the received light 33 and or the micro tunnels 32 are uniformly distributed over the array area w 1 u00d7 w 2 the length l preferably several microns to several hundreds of microns of the straight micro tunnels 32 can be smaller than the frame 35 thickness t preferably several hundreds of microns to several millimeters as shown in fig2 d in this case portions of the frame 35 can be made thick enough to provide extra support to the whole micro tunnel array 30 a perspective view of this straight micro tunnel is similar to that shown in fig2 c except with a micro tunnel length l less than the frame 35 thickness t micro tunnels 32 of array 30 can be tapered rather than straight as shown in fig2 e and 2g the entrance aperture a 1 of the tapered micro tunnel 32 of fig2 f is smaller than the exit aperture a 2 in fig2 e the micro tunnel length l is shown smaller than t but can.