Chip-integrated Brillouin Saser Gyroscope

Abstract

On-chip Brillouin laser gyroscopes harnessing opto-acoustic interaction are an emerging approach to detect rotation, due to their small footprint, excellent stability and low power consumption. However, previous implementations rely solely on optical readout, leaving the simultaneously generated saser (sound amplification by stimulated emission) undetected due to the lack of capability to access the acoustic output. Here, we propose a gyroscope based on saser detection using a suspension-free chip platform that supports low-loss confinement of both optical and acoustic modes. With experimental feasible parameter with optical and acoustic quality factors of 10^5 and 5000, respectively, sasers show significantly suppressed thermal and frequency noises, leading to gyroscope performance that outperforms its optical counterparts. We predict an angle random walk ~0.1 deg/sqrt(h) by saser gyroscope, while a conventional Brillouin laser gyroscope requires significantly higher pump power and optical quality factor to achieve comparable performance. Our work establishes the foundation for active phononic integrated circuits with Brillouin gain, opening avenues in inertial sensing, quantum transduction, and RF signal processing.

Figures (3)

• Figure 1: Principle of an on-chip Brillouin saser gyro. (a) Schematic of the on-chip Brillouin saser gyroscope. Two counter-propagating optical beams are injected into the cavity to generate Brillouin sasers. Stokes photons are coupled out to the pumping waveguide, while phonons are extracted via the opposite waveguide and converted into microwave signals using an interdigital transducer (IDT). The insets display the simulated electric field distribution of the photonic mode and the displacement field of the phononic mode, along with an illustration of the Sagnac effect. Under rotation, the clockwise (CW, red arrow) and counter-clockwise (CCW, blue arrow) waves experience different round-trip path lengths, resulting in a resonance frequency splitting. (b) Working regimes corresponding to different modal quality factors ($Q$). The laser and saser exhibit superior performance in regimes (i) and (iii), respectively, with a transition region in regime (ii). Since the acoustic wave vector is approximately twice of the optical wave vector, the acoustic Sagnac frequency shift is approximately twice of the optical wave, as depicted in the inset.
• Figure 2: Noise characteristics of Brillouin saser and laser. The optical quality factor is fixed at $Q_{\mathrm{opt}} = 10^7$, while the acoustic quality factors are $Q_{\mathrm{aco}} = 5 \times 10^1$ for the laser and $Q_{\mathrm{aco}} = 5 \times 10^3$ for the saser, respectively. (a) Dependence of linewidth on pump power ($P$) for the saser (orange curve) and laser (blue curve) under thermal noise. Both linewidths scale inversely to $P$, with the saser demonstrating a narrower linewidth than the laser across the measured range. (b) Temperature dependence of linewidths for both saser and laser under thermal noise. While the relationship is linear over a wide temperature range, nonlinear behavior emerges in the cryogenic regime (inset), consistent with the temperature dependence of thermal phonon populations. (c) Pump transferred noise characteristics showing linewidth dependence on pump noise for saser and laser regimes. The output linewidth scales linearly with the pump linewidth, but is significantly suppressed through the Brillouin scattering process.
• Figure 3: Gyroscope performance characterization. Pump linewidth is fixed at 1 kHz. (a,b) ARW dependence on modal quality factors with (a) fixed optical quality factor $Q_{\mathrm{opt}}=1\times10^7$ and (b) fixed acoustic quality factor $Q_{\mathrm{aco}}=5\times10^3$. Brillouin saser and laser gyroscopes exhibit superior performance in distinct quality factor regimes. Increasing pump power ($P$) reduces ARW in both cases, necessitating higher $Q_{\mathrm{opt}}$ or $Q_{\mathrm{aco}}$ values to establish the absolute advantage of either saser-based or laser-based gyroscopes. (c,d) ARW as a function of modal quality factors with $P$ fixed at (c) 5 mW and (d) 50 mW. The blank regions correspond to parameter spaces where the Brillouin threshold exceeds 5 mW and 50 mW, respectively. Within the working regions, saser and laser regimes are separated by a distinct cross-over band. (e,f) ARW dependence on $Q_{\mathrm{opt}}$ and $P$ with $Q_{\mathrm{aco}}$ fixed at (e) $Q_{\mathrm{aco}}=50$ and (f) $Q_{\mathrm{aco}}=5000$.