The availability of three-dimensional photonic crystals with a band gap makes it possible to accurately control and even capture photons. The high reflection of the structures can be used to produce a 'cage for light' in a photonic crystal. Inside such a cage the light continues to ‘bounce’ backwards and forwards between the walls of the cage until it can once again escape from it, preferably after a 'push on the button'. This makes it possible to control optical bits instead of electronic bits, so the optical computer has now come a step closer. An optical computer can process far more data simultaneously than a conventional computer. As optical computers contain electronic components as well, it is important that the new manufacturing method is entirely compatible with the methods in the chip industry so that electronic and photonic components can be simply manufactured on a single chip.
More details about the process
The researchers made the three-dimensional nanostructures in two steps using an innovative process. First of all they made use of ASML's advanced deep-UV lithography: with the help of UV light, a gigantic camera projected the orthogonal pore structure on a layer of photoresist. This provided a mask with millions of minute pores. Then using a plasma etching process from the chip industry they etched very deep nano pores in a silicon wafer.
The second step is crucial: on the thin side of the wafer the researchers applied a second mask with extreme accuracy and they then used a very unconventional method to produce the same pattern of holes in the mask as in the first step. The challenge lay in the requirement that the pattern on the mask could deviate by no more than 30 millionths of a millimetre (30 nanometres) and 0.5º from the optimum position and angle. This was necessary to ensure that the required diamond structure arose after etching. The pattern was applied using standard equipment from the chip industry. The second set of pores was etched in the same manner as the first set. By using standard equipment the electronics and the three-dimensional structures made in this new method can be integrated onto silicon chips.
The pores in the new three-dimensional structure form a diamond structure which is the same as the carbon atoms in the well-known gemstone diamond or the silicon atoms in crystalline silicon.
The new structure has been magnified about 2000 times compared to a diamond crystal. To be certain of their success, the researchers sacrificed a number of their structures by carefully opening these up so that the diamond structure could be accurately analysed for pore depth, pore diameter, pore shape and alignment. This confirmed that the structure formed in the wafer is indeed as shown by the dotted lines in Figure 1.
Optical reflecting measurements like those shown in Figure 4 confirmed that the new diamond structures behave as very good photonic crystals. The roughness of the surface and the thickness of the crystal currently limit the maximum reflectivity. The broad forbidden bands are found at infrared wavelengths which are used in the telecommunication industry (1330 and 1550 nm).
 J.M. van den Broek, L.A. Woldering, R.W. Tjerkstra, F.B. Segerink, I.D. Setija, and W.L. Vos, Inverse woodpile photonic band gap crystals with a cubic diamond-like structure made from single crystalline silicon, Advanced Functional Materials http://onlinelibrary.wiley.com/doi/10.1002/adfm.201101101/abstract