An Optical Circulator That Directs Light Without Using Magnets

  • Researchers develop a microscale vibrating glass ring that works as a circulator. 
  • This small glass ring resonator interacts with light and directs it on an optical chip, without using magnets. 

Circulators are crucial modules in communication technology. They transmit information from one node to another without any data loss in a network.

Similarly an optical circulator is designed in a way that light entering from one port exits from the next. A beam of light is allowed to travel only in one direction between ports. Because of low insertion loss and high isolation of input and reflected optical powers, these circulators are extensively used in fiber optic sensor applications and advanced communication systems.

However, all circulators require small magnets (centimeter-sized) to uniquely direct light, which is quite hard to manufacture for use on optical chips.

To deal with this problem, researchers at the University of Texas and AMOLF in Netherlands, have developed a vibrating glass ring that works as a microscale circulator. It interacts with light and directionally routes it on a photonic chip, without using any magnetic component.

How Does It Work?

Light propagates symmetrically – If it can travel from point 1 to point 2, it can follow the exact reverse route to travel back to point 2. Generally, a small magnetic circulator is used to break this symmetry, but such hardware are difficult to build for use on optical chips.

This small glass ring resonator, on the other hand, uses a different mechanism to route light. The ring has some sort of mechanical vibration, which enables one-way optical transmission when a beam of light interacts with it.

A controlled-laser is used to project light on a microscale ring. If the light of a different wavelength propagates in the same direction as the control light, it could excite ring-vibration through radiation pressure.

Because light doesn’t propagate symmetrically in a vibrating component, the optical force behaves similar to what magnetic field does in a conventional circulator.

Credits: Henk-Jan Boluijt | AMOLF

As you can see in the image, a light (yellow) enters the vibrating ring from top left port and leaves at the bottom left port. At the same time another light (red) enters from bottom left port and is forced to propagate to the bottom right exit. It can’t take the reverse route of the yellow light.

Reference: Nature Communications | doi:10.1038/s41467-018-04202-y | AMOLF

Challenges Involved

Using a non-magnetic structure (ring, in this case) for one-way optical transmission is not as easy as it sounds. One of the most challenging part is to decide the specific exit to which a beam of light can be directed, in such a way that it always takes the next port.

To do this, they precisely controlled the optical paths in the microscale ring so that light from every input constructively interferes in the target output. Researchers have shown this circulation in their experiment and demonstrated that it could be actively configured. The laser’s power and wavelength enable the circulation to be switched off and on and alter handedness.

More specifically, researchers have demonstrated a nonreciprocal circulation of light through radiation pressure interaction in a 3-mode system, which can be reconfigured via the phase, strength and detuning control fields.

The theoretical model and experiment recognize numerous different regimes of circulating response, unveiling destructive intra-cavity interference between direct and mode conversion paths on the component properties. This is extremely useful for optical routing and signal processing on optical devices.

Read: Speed Of Light Could Be Reduced To Zero At “Exceptional Points”

Applications

This is the first nonmagnetic optical circulator with numerous practical applications. One can use it to create building blocks for electronic chips that use photons to transfer data, rather than electrons. It could also be used for future communication networks and quantum machines.

Written by
Varun Kumar

Varun Kumar is an experienced science and technology journalist interested in machines, AI, and space exploration. He received a Master's degree in computer science from Indraprastha University. To find out what his latest project is, feel free to directly email him at [email protected] 

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