Switching light on and off - with photons

Nov 09, 2011 By Vivek Venkataraman
Rubidium atoms will absorb photons only if two photons of specific wavelengths arrive at the same time. This allows one stream of photons to turn another on or off. (Gaeta Group)

(PhysOrg.com) -- Cornell researchers have demonstrated that the passage of a light beam through an optical fiber can be controlled by just a few photons of another light beam.

Such all-optical control is the idea behind photonics, where replace in circuits, yielding higher speed and lower power consumption. Just as a transistor can switch an electric current on or off, need a way for one light beam to switch another. One of the holy grails is single-photon switching, where just one photon controls the passage of another.

Researchers in the Quantum and Nonlinear Optics group of Alexander Gaeta, professor of applied and , have come close to that goal. They report their new approach in the Nov. 4 issue of the journal Physical Review Letters.

Light consists of small packets of energy called photons. Under the right conditions, a photon can be absorbed by an atom. Gaeta's group exploited the unusual property of the element rubidium, which can absorb photons only if two photons of certain wavelengths arrive at the same time. They filled a hollow-core optical fiber with rubidium vapor and fired a continuous infrared at a wavelength of 776 nanometers (nm) in one end and an intermittent "control" signal at 780.2 nm in the other.

In the narrow tube, light interacts strongly with the . When the control beam is on, rubidium atoms absorb both wavelengths, and the signal is cut off; when the control is off the signal passes through.

The effect is observed with less than 20 control photons at timescales as fast as five-billionths of a second, allowing modulation at frequencies up to 50MHz, the researchers said, referring to the rate of transmission of on and off pulses of light representing digital ones and zeroes in fiber-optic communication. The technique also may have applications in quantum computing, where single photons can act as "qubits," the quantum equivalent of ones and zeroes.

The research was funded by the National Science Foundation and the Defense Advanced Research Projects Agency.

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not rated yet Nov 09, 2011
This may indeed be a path to the long sought "optical transistor". If so then this is huge because it opens up the area of photonic computing based on traditional TTL designs. (and also the easy integration of the two technologies)
5 / 5 (1) Nov 09, 2011
These would be like optical logic gates ?
not rated yet Nov 09, 2011
You could couple several of these to make logic gates. Quantum dots for emission of laser light and microcavities (e.g. from graphene) for confining a few rubidium atoms could make this type of 'transistor' very small.
2 / 5 (1) Nov 09, 2011
This is perfect and long overdue. No electrons are needed no more. You just need a source of light to run a computer. The light could very well be ambient light or solar light.
Digital processing could all be done with light but cell phones and plenty of other devices will still need some electrons to radiate electromagnetic fields or power the speaker.
5 / 5 (1) Nov 10, 2011
This is an invertor 0=1 or 1=0 it is good for data switching but to make logical decisions you need two inputs to control one output ie AND gate, OR gate so no optical computer yet but someday soon.
not rated yet Nov 10, 2011
This is perfect, but it means that we can say about new photonic field or not?