A new type of Optical Switch using a quantum dot

Posted on by FS.COM

An optical switch developed at the Joint Quantum Institute (JQI) spurs the mark integration of photonics and electronics.

What, isn’t electronics adequate? Well, nothing travels faster than light, as well as in your time and effort to hurry in the processing andtransmission of knowledge, the combined use of photons along with electrons is desirable for developing a workable opto-electronic protocol. The JQI switch can steer a beam of light from one direction toanother in only 120 picoseconds, requiring hardly any power, no more than 90 atto joules. At the wavelength used, in the near infrared,this amounts to about 140 photons. This is actually the setup of a waveguide made from a photonic crystal, a great device put into the fiber optic transmission area.

A quantum dot is placed inside a tiny zone free from holes. Light is distributed into and from the waveguide via endcaps. If properly timed, a pump laser pulse allows probe pulse to exit the side. When the probe and pump beams are not aligned, the probe beam will exit the farend of the waveguide. The center piece of most electronic gear is the transistor, a solid-state component where a gate signal is used to a nearby tiny conducting pathway, thus switching on and off the passage of the information signal.

The analogous process in photonics would be a solid-state component which provides a gate, enabling or disabling the passage of light through a nearby waveguide, or as a router,for switching beams in different directions. Within the JQI experiment, prepared and conducted in the University of Maryland and at the National Institute for Standards and Technology (NIST) by Edo Waks and his colleagues, an all-optical switch has been created utilizing a quantum dot placed in the resonant cavity. The dot, consisting of a nm-sized sandwich of the elements indium and arsenic, is so tiny that electrons moving inside can emit light at only discrete wavelengths, as though the dot were an atom. The quantum dot sits inside a photonic crystal, a material that has been tired of many tiny holes.

The holes preclude the passage of sunshine with the crystal except for a narrow wavelength range. Actually, the dot sits in the small hole-free arcade which acts just like a resonant cavity. When light travels on the nearby waveguide a lot of it gets into the cavity, where it interacts using the quantum dot. And it is this interaction which could transform the waveguide’s transmission properties. Although 140 photons are needed in the waveguide to create switching action,only about 6 photons actually are required to bring about modulationof the quantum dot, thus throwing the switch.

Previous optical switches happen to be able to work only by utilizing bulky nonlinear-crystals and high input power. The JQI switch, by comparison, achieves high-nonlinear interactions using a single quantum dot and very low power input. Switching required only 90 atto joules of power, some five times less than the very best previous reported device made at labs in Japan, which itself used 100 times less power than other all-optical switches. Japan switch, however, has the advantage of operating at room temperature, as the JQI switch needs a temperature close to 40 K.

Continuing our analogy with electronics: light traveling on the waveguide by means of an information-carrying beam could be switched from one direction to another using the presence of asecond pulse, a control beam. To steer the probe beam the side from the device, the slightly detuned pump beam needs toarrive simultaneously with the probe beam, that is on resonance with the dot. The dot lies just off the middle tabs on the waveguide, inside the cavity. The temperature from the quantum dot is tuned to become resonant using the cavity, leading to strong coupling. If the pump beam doesn’t reach the same time as the probe, the probe beam will exit in another direction.

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