LETI: Fundamental Research of LETI Scientists Will Help Create New Microwave Devices

In the last decade, the bistability effect, which occurs in various resonant systems before the auto-oscillation threshold, has attracted the increasing attention of scientists. This phenomenon has great potential for applications in optics, spintronics, microwave photonics, and related areas of microelectronics.

The team of the Department of Physical Electronics and Technology of LETI, headed by Associate Professor Vitaly Vitko, conducts fundamental research devoted to the formation of nonlinear properties of active ring resonators made of ferrite and ferroelectric structures.

In the first phase of the project, scientists developed a theory for the formation of nonlinear properties of active ring resonators on ferrite and ferroelectric waveguide structures separately. The theory was tested on an experimental model of a ring resonator on a ferromagnetic film. The researchers recorded nonlinear frequency shifts and bistable property formation and measured the frequency range of bistability depending on different amplitudes of the input signal and amplification coefficients in the ring.

The main hypothesis put forward in the research is that in an active ring resonator on a ferrite-ferroelectric waveguide structure, nonlinear effects can arise due to both the nonlinearity of the ferrite film and the nonlinearity of the ferroelectric. Thus, by controlling the input parameters of the system affecting the nonlinear response of ferrite and ferroelectric, it is possible to control the bistable behavior of the ring resonator. The second hypothesis is the possibility of dual electronic control of the bistable properties of active ring resonators. In other words, the bistable properties of such a ring resonator can be controlled by both electric and magnetic fields.

“Hypotheses appeared because active ring resonators on magnetic films have two features. First, it is possible to control the level of signal propagation loss to obtain different quality factors of such a resonator and greatly increase the amplitude of the signal that circulates in the ring. Second, the spin-wave delay line has different dispersion properties depending on the orientation of the magnetic field with relation to the direction of wave propagation,” says Vitaly Vitko.

“In the course of the research, it turned out that it is possible to put an active ring resonator into a bistable regime not only by increasing the amplitude of the input signal but also by compensating the level of losses in the resonator. In addition, when the magnetic field strength increases, the nonlinear coefficient of spin waves increases, which leads to a broadening of the bistability range.”

Vitaly Vitko, Associate Professor of the Department of Physical Electronics and Technology of LETI
In terms of contribution to fundamental science, this work will provide new knowledge about the processes that precede the auto-oscillation of active ring resonators but directly affect the subsequent regimes of monochromatic signal generation and generation of soliton pulses.

The results will be used to develop new electrically controlled devices based on the bistability effect – keys, triggers, memory cells – which will be used to create new microwave devices with improved characteristics. They will have a major impact on the development of promising telecommunications, navigation, and radar systems.

In 2020, the research team published two articles on the subject, one of them in the Results in Physics journal (Q2).

The researchers are currently engaged in building a theory of the formation of the nonlinear spectrum of an active ring resonator, which includes a ferrite-ferroelectric waveguide structure.