Nonreciprocal transmission in a cavity-magnon system by rotational Sagnac effect

TL;DR

The paper proposes a rotating cavity-magnon system to realize ultrahigh nonreciprocal optical transmission via the Sagnac effect, exploiting opposite Fize shifts for CW and CCW WGMs in a YIG sphere. By deriving a theoretical model that includes two WGMs, magnon coupling, and magnon squeezing, the authors show that the isolation can exceed 40 dB under experimentally accessible parameters and can be further enhanced with squeezing. A key feature is that reversing the WGM rotation direction switches the nonreciprocity without tuning other parameters, offering a practical path to tunable, on-chip optical isolators with high isolation and robustness to dissipation. The work highlights the potential for compact, high-performance nonreciprocal devices in quantum and classical photonics, with implications for integrated photonic circuits and signal integrity.

Abstract

Ultrahigh nonreciprocal transmission has been achieved in a cavity-magnon system, which consists of two whispering gallery modes (WGMs) and a single magnon mode within a magnetic insulator yttrium iron garnet sphere. The nonreciprocal frequency shift induced by the Sagnac effect enables unidirectional transmission of an input field, while suppressing propagation in the opposite direction, thereby facilitating nonreciprocal optical transmission. Within experimentally accessible parameter regimes, the optical isolation ratio can exceed 40 dB, representing the highest isolation ratio reported to date. Furthermore, applying squeezing to the magnon mode further enhances this isolation performance. Additionally, the directionality of light isolation can be reversed simply by modifying the rotation of the WGM cavity. These findings offer promising prospects for developing high-performance, tunable, and compact optical nonreciprocal devices.

Figures (7)

• Figure 1: Sketch of the system. A WGM cavity rotates CW with an angular velocity $\Omega$. This cavity supports two optical modes propagating in CW and CCW directions, along with a magnetostatic mode within a YIG sphere.
• Figure 2: (a) Transmission coefficients as a function of $\Delta_F/\gamma_m$. (b) The isolation ratio as a function of $\Delta_F/\gamma_m$. The parameters are $\Delta=0$, $g_0/2\pi$=41 MHz, $G=0.5$, $\kappa /2\pi$ = 1.1 MHz, $\gamma_m/2\pi$=4 MHz, $\eta=0.5$, $P_1=P_2=P_3=100$ mW, $\omega_m/2\pi$=10.1 GHz, which are typical experimentally utilized parameters ZARERAMESHTI20221Maayani2018PhysRevResearch.1.023021righini2011whispering.
• Figure 3: The isolation ratio $I$ vs $\Delta_F/\kappa$ and $\gamma_m$. $\Delta/\kappa=0$ in panel (a) and 20 in panel (b). $\kappa /2\pi$ = 1.1 MHz. The other parameters are the same as in Fig. \ref{['fig:fig2']}. The plot is symmetric with respect to the line $\Delta_F/\kappa=0$. The maximum values of $I$ are 45.890 dB (when $\gamma_m=1.5$ MHz) in panel (a) and 41.352 dB (when $\gamma_m=1.503$MHz) in panel (b).
• Figure 4: The isolation ratio $I$ vs $\Delta_F/\gamma_m$ and $\kappa$. $\Delta/\gamma_m=0$ in panel (a) and 5 in panel (b). $\gamma_m/2\pi=4$ MHz. The other parameters are the same as in Fig. \ref{['fig:fig2']}. The maximum values of $I$ are 51.437 dB (when $\kappa=0.114$MHz) in panel (a) and 50.542 dB (when $\kappa=0.112$MHz) in panel (b).
• Figure 5: Under optimal parameter $\Delta_F$ conditions, the isolation ratio $I$ varies with (a) $\gamma_m$ and (b) $\kappa$. $\kappa/2\pi=1.1$ MHz in panel (a) and $\gamma_m/2\pi=4$ MHz in panel (b). The other parameters are the same as in Fig. \ref{['fig:fig2']}. The red dots represent the reciprocal points $\gamma_0$ and $\kappa_0$. Indeed, this functional plot corresponds to Eq. (\ref{['eq18']}).