Lasers Can Now Emit Microwaves And Receive External Radio Frequency Signals

  • Scientists send and receive information via semiconductor laser. 
  • This research could help in the development of hybrid electronic-phonic equipment as well as ultrahigh-speed Wi-Fi. 

Coherent light sources such as semiconductors lasers can create a spectrum containing equally spaced, discrete frequency of lines. Many frequency comb applications, including metrology and spectroscopy, directly use these lasers’ output. In microwave photonics, the output of the frequency comb is transmitted to a fast photodetector and used to generate microwaves.

In 2017, a research team at Harvard University found that terahertz frequencies can be generated via an infrared frequency comb in a quantum cascade laser. In 2018, they discovered that these frequency combs can also act as integrated receivers or transmitter to efficiency encode data.

Now, they have found a method that can extract and send wireless signals from quantum cascade laser frequency combs. In this work, they were able to demonstrate a laser that can wirelessly emit and modulate microwaves, and receive signals at radio frequencies. The findings could help in the development of hybrid electronic-phonic equipment as well as ultrahigh-speed Wi-Fi.

How Does It Work?

Traditional lasers emit the same frequency light, whereas, laser frequency combs are capable of ejecting multiple frequencies at the same time. These frequencies are equally spaced, resembling the teeth of a comb.

Within the laser, different frequencies beat together to generate microwave radiation. The light within the laser cavity causes electrons to oscillate at frequencies that lie within the communication spectrum.

Reference: PNAS | DOI:10.1073/pnas.1903534116 | Harvard SEAS

The team developed a new device that can put data in the microwave signals and transmit them wirelessly. To do this, they created a dipole antenna by etching a gap into the top electrode of the device.

Lasers Emit MicrowavesThe device emits and modulates microwaves wirelessly, using a frequency comb. The ‘beats’ ejected from the laser resemble a painting (right). | Courtesy Marco Piccardo / Harvard SEAS

To encode data on the microwave radiation, researchers modulated the frequency comb. The radiation is sent out from the device through the dipole antenna. A horn antenna then received the radio signal, which is finally filtered and transmitted to the computer.

The laser radio can also receive signals. To demonstrate this, researchers wirelessly controlled the laser behavior using signals from a different device. They sent a song wirelessly to a receiver.

Reference: Under What Conditions Nanolasers Qualify As True Lasers?

Overall, the technology could be extremely useful for future wireless communications. Although we are far still far away from achieving terahertz wireless communication, this work offers a great roadmap explaining how to get there.

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