People seem very quick to proclaim Quantum Computing as the solution to faster computers, however the development of Optical Computers rarely rate a mention. The motivation behind this thread is to give some awareness as to what optical computing is and what it is capable of and hopefully invite some discussion. The first widely used photonic waveguides were optic fibres which were developed around 1980. Optic fibres are an excellent means of data transfer over long distances. Optic fibres have also been used to construct some very clever photonic devices (splitters, multiplexers and circulators for example), however there is a fundamental limitation in using optic fibres in minaturised circuits. This limitation is due to the way optic fibres guide light. Fibres guide light through total internal reflection (devices such as these are often termed 'index guided'). If one bends a fibre too much (as is necessary when minaturising photonic circuitry), the fibre will no longer guide light efficiently. A solution to this problem emerged in the form of photonic crystals, that guide light using the phenomenon of photonic bandgaps (which are not unlike electronic bandgaps). If light of a particular frequency that falls within a photonic band gap, is incident on a photonic crystal, the photon will be reflected (the photon effectively satisfies Bragg's condition). If one creates a defect through the crystal, the photon will be guided. This method of guiding light does not suffer from the same drawbacks as index guided devices, however there is the issue of fabricating such crystals. In order for a band gap to be present at a particular wavelength, the dielectric constant of the crystal must be modulated in dimensions of the order of half that wavelength. Thus to guide wavelengths commonly used in optical devices (1.55 microns), the modulations must be of the order of hundreds of nanometers. In addition to guiding light on a small scale, there needs to be some sort of way to store data optically (i.e. the optical equivalent of a transistor). One such proposed method is holographic storage, however it suffers from the drawbacks of being short-lived (about a day or so) and must be kept very cool (around 100 K) to work properly. Nonlinear Fabry-Perot cavities are another proposed solution, however they are expensive to make and difficult to align and operate. The difficulty is in that most optically bistable materials are only bistable under very specific conditions and usually at a low temperature. Despite these experimental obstacles, optical computing, in my opinion, is closer to being a reality than quantum computing. Okay, I'm running out of time, so I will wrap up discussion here for now. Please feel free to discuss anything mentioned in this post, or if you have an opinion regarding optical vs quantum computing, I would be interested to know. Regards, Claude.