Increased optical data transmission speed

Pulsed lasers emit light repeatedly for a short time as if blinking. They have the advantage of focusing more energy than a continuous wave laser, the intensity of which remains unchanged over time. If digital signals are loaded into a pulsed laser, each pulse can encode one bit of data. In this regard, the higher the repetition rate, the greater the amount of data that can be transmitted. However, conventional fiber optic based pulsed lasers have generally had a limitation in increasing the number of pulses per second above the MHz level.

The Korea Institute of Science and Technology (KIST) announced that the research team led by principal investigator Dr. Yong-Won Song at the Center for Opto-Electronic Materials and Devices was able to generate laser pulses at a rate at least 10,000 times higher than the state of the art. This achievement was accomplished by inserting an additional resonator containing graphene into a fiber optic pulsed laser oscillator that operates in the femtosecond domain (10^-15 seconds). Data transmission and processing speeds are expected to increase dramatically by applying this method to data communications.

The KIST research team noted that the characteristics of the wavelength and intensity of laser light that change over time are correlated (Fourier transform). If a resonator is inserted into the laser oscillator, the wavelength of the pulsed laser is periodically filtered, thereby changing the pattern of change in laser intensity. Based on this basic research, lead researcher Song synthesized graphene, which has the characteristics of absorbing and eliminating weak light and amplifying the intensity by passing only strong light through the resonator. This makes it possible to precisely control the change in intensity of the laser at a high rate, and thus the pulse repetition rate could be increased to a higher level.

In addition, graphene is generally synthesized on the surface of a catalytic metal, then the product is separated from the catalyst and transferred to the surface of a desired substrate. In this process, there has usually been the problem that the graphene is damaged or that impurities are introduced. The aforementioned KIST research team solved the problem of reduced efficiency occurring during the manufacturing process by forming graphene directly on the surface of a copper wire, which is easily obtained, and coating the wire with an optical fiber for its use as a resonator.

As a result, it has been possible to obtain a repetition rate of 57.8 GHz, thus overcoming the limitations of pulsed lasers in terms of repetition rate, typically constrained to MHz. Additionally, the characteristic of graphene such that heat is generated locally when the laser is absorbed has been exploited to tune the characteristics of the graphene resonator by applying an additional laser to the device.

KIST researcher Seong-Jae Lee said, “In the current scenario, where the demand for data traffic increases exponentially, ultra-fast pulsed lasers operating at ultra-high speed and admitting tuning characteristics are expected to provide a new approach to adapt to this rapidly evolving computational scenario. “Principal investigator Song, who led this research, added,” We anticipate that the development of ultra-fast pulsed lasers based on resonators and graphene will bring our advance in technological development and the related market in the field of optical information devices based on nanomaterials. ”

Provided by the National Science and Technology Research Council