About optical computers

Optical computers do all or much of their work by using light instead of electron currents. These could be made to work with low energy use and with high speed. Every time electrons get converted to photons or reverse some energy will be lost and these conversion should be ideally as few as possible.

I tried to explain how interference could be used for computer logic. Boolean logic is simplistic enough to make calculator with vacuum tubes, capacitors or just water flowing through pipes and other physical behaviors can probably be used for computer logic as well.

Illustration above shows polarization with arrows which also shows where would photon push electrons in case these arrows point negative charge of photon. This polarization can be considered useful for filtering light as some filters only let certainly polarized light through. Liquid crystal screen can be used to change which polarization is needed to pass but those adjustable filters tend to need intense electric fields which could be in form of intense enough photons.

If different photon beams overlap then they combine their effects. If they overlap in space (0 or 360 degree phase difference) (constructive interference left) then they can amplify each others electric fields increasing how much they work on electrons and other charged particles or photons. If they are skewed by half a wavelength (180 degree phase difference) then they can cancel (destructive interference) each other out as electrons would be pushed in opposite directions at same place.
Further electric field amplification can be created by slowing as it compresses electric and magnetic fields by about as many times as light got slowed. In case of photonic crystals light could be slowed by repeating transparent materials that have layers with thickness of half the wavelength intended for slowing.

Data processing

Some Boolean logic gates and their symbols. Zero usually shows lack of signal and 1 that strong enough signal comes out from logic gate.

AND gate could require constructive interference to build up energy to get signal going (charge maybe phosphorus atom with more light or get electron moving farther). But phosphorus would glow for long time and it could leave background noise that could need to be blocked until that area can be used again. If this AND gate needed electrons it could use detector material from digital cameras to create electrons with another light source and get them moving in wire until they get absorbed. If it gets stronger light signal to push it in one direction with more intensity then it could reach to some far enough detector that reads output and only gets electron if enough photons amplify each other. Another way would be to push electrons in front of other light channels before electrons lose energy by creating light. AND gates could possibly be just weakly transparent filters that need enough photons to be bright enough for next part.

OR gate could be any example where 2 beams can reach one output light channel or detector where one or both or more beams working make output 1. This one can look like Y shaped fiber optic cable that combines inputs from 2 input branches and combines them to one output fiber. If this "logic gate" was entirely plastic like that Y then they could work with speed of light in there with near zero energy and cooling requirements. 

XOR gate could work with use of destructive interference with 2 lasers that are apart by half a wavelength. If only 1 of those laser worked then it could transmit out of output fiber but if they both happen to work then they cancel each others light.

NOR also with destructive interference if 1 baseline beam works anyway and if any input light switched on they could weaken main beam with interference. Input beams at maybe 50% baseline beam intensity so they wouldn't have enough constructive interference to overcome baseline beam too much and reactivate it.

XNOR gate could work almost like NOR gate but with such beams that input beams are as strong baseline beam. If one input works then it cancels baseline beam but if both work then they could get beam with close to baseline beam electric field activity.

NAND destructive interference if both inputs are on but otherwise signal gets through. Could use strong baseline beam and weak input beams that can cancel baseline beam together. 

NOT (inverter) gate that use of 2 beams that would cancel each other out if both were working at same time. One baseline beam that always works and 1 input beam that could cancel it.


Interference type can be regulated by moving mirrors within fraction of wavelength to switch between constructive and destructive interference leaving room to "reprogram" logic gate into other logic gate types or for redirecting beam towards other directions. Adjustable mirrors also help with testing if interference works with any mirror alignment or if something is broken. These movable mirrors could possibly also help with heat expansion if device changes temperature and size.

Possible example of optical logic in calculation:

Full adder for adding together numbers in binary made of 2 XOR, 2 AND and 1 OR gate. S is for smaller number and C for larger one to be carried over. In case of 1+0=1 XOR gate would receive 1 and 0 getting output of 1 and if there was no number to carry over then Cin was 0 allowing second XOR gate to transmit light signal to output S with almost speed of light that got altered with interference on the way. In this case AND gates don't get enough input to output signal on their own.
In binary 1+1=2 is 1+1=10. In this case XOR gates leave 0 as their lights could destructively interfere but these signals combining in AND gate create signal "1" for output channel Cout which could show up as light in fiber for Cout and lack of light in fiber S.

Data storage

Sort of light storage for up to minutes can happen with phosphorus when it absorbs light but that loses signal through few minutes. Phosphorus can also be used to create photons by hitting them with electrons. In case data is stored with electrons then phosphorus could be simpler way of converting it to light.  

Fast volatile type of RAM with light could work if it had many parallel light beams creating patterns that could be read with light detectors but that obviously doesn't work if light is switched off.

Storage for years can work like in current non-volatile RAM type memories where strong electric field forces electron into floating gate type area where it can't leave without strong outside field (including from intense photon) switching on again.  

Possible future applications 

Optical computer could be chemical detector that detects and analyses substances with only light without contacting substances. It saves electricity by not needing electrons plus it can analyze large 3d volume at same time looking for certain frequencies to know substance with possibly no need to contact sensors in case terahertz detectors are good and local heat doesn't confuse too much. Analyzer could be "library" on light beams each lighting up more if light for it's frequency shows up due to constructive interference.Terahertz detectors for chemicals could have many parallel beams with slight distance difference (for phase difference) so molecules could move in relation to detector and at least some channel should be able to notice certain wavelength radiate.


Another weirder and more distant use for optical computers could be creating artificial sentience in case sentience requires suitable electromagnetic radiation patterns in any environment even if it was in air or vacuum.  Slowed light could carry signal slowly enough to imitate neural signal speed but that need some solid or very controlled environment (like Bose-Einstein condensate).
As another part in that interference patterns could be used to measure brain activity without contact by measuring phase of reflecting light fast enough. Maybe researchers during some brain surgery with volunteers could find out exact light type that would give patient sense of widened sentience or sense of acceptable added sensory input.

Optical lattice type unmoving or slowly moving interference patterns could possibly create hovering invisible processors that detect at least metal and like radio waves could go through concrete. These could not go through electric conductors but nonconductors like air, water, vacuum, clothing and glass could be passable. These could be improved like a refined wall penetrating radar but which could maybe have more complex "behavior". As conductors absorb EM radiation they could one day be usable to control or disrupt machinery. Control of organic life is less likely as cells can create strong electricity of their own and radio waves go through animals with little absorption. In warfare they could possibly be used to create zones that are uncomfortable to people (maybe stimulating nerves that cause vomiting etc) and confusing to machines. In case they work it's almost certain that military commanders would want to use devices that create sort of "ghosts" that move with speed of life, can pass many walls and cause damage to opposing side. If beams  are concentrated enough then like visible lasers they can reach far with very low energy use and possibly override what people and cameras could see or sense otherwise.