- Researchers develop a high-capacity integrated circuit that efficiently operates in the terahertz frequency band.
- It minimizes the leakage of unnecessary signal between ports of integrated circuits and enhances signal-to-noise ratio.
Terahertz waves begin at a wavelength of 1 millimeter and proceed into smaller wavelengths. Since these waves are non-ionizing, they are safe to use. They can pass through a paper, skin, wood and plastic, but can’t penetrate water, metal or concrete.
Although terahertz waves have tons of useful applications, their adoption has been slow. The reason is we don’t have hardware/source that can provide enough power to transmit these waves over longer distances. But this is going to change soon.
Recently, researchers at Tokyo Institute of Technology built a new high-speed IC (integrated circuit) for wireless data transmission that functions in terahertz wavelengths.
The broadband network is spreading at an enormous rate, and high-speed wireless transmission system of 100 Gbps (gigabits per seconds) has already made a lot of buzz worldwide. However, the capacity of transmitting data wirelessly can be further extended. This could be done in 3 ways –
- Increasing the bandwidth of transmission
- Expanding the modulation multilevel number
- Expanding the spatial multiplexing number
To realize next generation high-speed wireless transmission technology from 400 gigabits per second to even 1 terabits per second, it’s important to concurrently increase both the bandwidth and modulation multilevel number in one carrier, while also extending the spatial multiplexing number by superimposing them several times.
The bandwidth of transmission is limited in carrier frequencies ranging from 28 to 110 GHz. Therefore, scientists are trying to utilize frequency from 300 GHz to terahertz wave. Frequency band at such level makes it easier to increase and secure a wide transmission bandwidth.
However, high carrier frequencies often results in leakage of signals between the ports within integrated circuits. So far, scientists haven’t discovered any efficient solution to achieve high signal-to-noise ratio.
That’s the reason current wireless transmission technology is limited to a few Gbps. It cannot be increased even if we use a 300 GHz frequency band because a high modulation multilevel value and a wide transmission bandwidth won’t be possible at the same time.
Researchers devised a new isolation chip and integrated it with a mixer circuit, which has 3 ports: radio frequency port (RF), local oscillation frequency port (LO), and intermediate frequency port (IF). Also, they built an integrated circuit with Inp-HEMT (stands for indium phosphide high electron mobility transistor).
Mixer IC and module
After implementing this high isolation design setup, they found that the leakage of unnecessary signals dropped to a minimal level between all ports in ICs. They also managed to enhance signal to noise ratio, which was limiting the use of 300 GHz frequency band in wireless transmission systems up to now.
Reference: Tokyo Institute of Technology | International Microwave Symposium
With this new setup, they realized wireless front-end module of 300 GHz frequency band, and established a reception of 16 Quadrature Amplitude Modulation signal in back-to-back transmission, over a distance of 2.22 meters with a 50 dBi antenna. Moreover, they demonstrated 100 Gbps of transmission speed on 300 GHz band.
Transmission experiment | Courtesy of researchers
So far, researchers have established transmission rate of 100 Gbps using one carrier. For their next study, they plan to utilize spatial multiplexing systems (multiple carriers), like multiple-input and multiple-output (MIMO) and orbital angular momentum (OAM), along with high isolation design technology.
Researchers believe that this combination could yield over 400 Gbps of wireless transmission rate. If successful, the technique could be applied in numerous fields, including sensing and imaging in which tremendously high frequencies are supposed to be used.