Chip-integrated Brillouin Saser Gyroscope (2511.16525v1)

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.

• The paper demonstrates that direct saser detection via integrated phononic circuitry doubles the Sagnac frequency shift compared to optical methods.
• It employs microring resonators with co-confined optical and acoustic modes to leverage backward Brillouin interaction for effective noise suppression.
• Numerical simulations reveal that high acoustic Q factors (>5000) on LNOS platforms enable significant reduction of thermal and pump noise at practical pump powers.

Chip-Integrated Brillouin Saser Gyroscope: Architecture, Noise Suppression, and Performance Advancements

Introduction and Motivation

The "Chip-integrated Brillouin Saser Gyroscope" (2511.16525) presents a comprehensive theoretical analysis and design proposal for an inertial rotation sensor based upon direct saser (sound amplification by stimulated emission of radiation) detection on a photonic-phononic integrated platform. Historically, chip-scale Brillouin laser gyroscopes have exploited the Sagnac effect via optical readout, utilizing ultranarrow linewidth Brillouin lasing; however, the inherent symmetry of the underlying opto-acoustic Brillouin process generates both optical and acoustic outputs, with the latter being largely ignored due to the lack of phononic collection and readout capabilities in conventional photonic chips.

Leveraging advances in phononic integrated circuitry, especially thin-film lithium niobate on sapphire (LNOS) platforms, the authors demonstrate theoretically that a high acoustic quality factor ($Q_{\mathrm{aco}}$) enables direct saser detection with drastically enhanced noise immunity and doubled Sagnac sensitivity, outperforming purely optical detection schemes while requiring more relaxed fabrication and pump specifications.

System Architecture and On-Chip Sagnac Enhancement

The chip-scale architecture employs microring resonators supporting co-confined optical and acoustic modes, utilizing the phase-matched backward Brillouin interaction to generate coherent photon-phonon pairs upon pump excitation. As shown schematically, counter-propagating optical beams generate both Stokes photons and gigahertz phonons, with Stokes outputs coupled optically and phonons extracted electrically via interdigital transducers (IDTs).

Figure 1: Principle and functional regimes of the on-chip Brillouin saser gyroscope, illustrating photon and phonon confinement, dual extraction, and doubled acoustic Sagnac frequency shift relative to optical.

Both the photonic and phononic modes exhibit Sagnac frequency splitting upon rotation, manifesting as beatnotes in both optical and acoustic output. The acoustic wavevector being approximately twice that of the optical mode directly yields an acoustic Sagnac frequency shift that is double the optical counterpart for identical propagation paths, a key factor in sensitivity enhancement.

Regimes of operation are determined by the modal quality factors, separating laser-preferred (high optical $Q$), saser-preferred (high acoustic $Q$), and a crossover region. Notably, the LNOS platform facilitates unsuspended, high-$Q$ phononic confinement synergistically with high-$Q$ optical modes, unlike standard silicon photonic or silica devices.

Noise Analysis: Thermal, Pump Frequency, and Mode Pulling Effects

A central result is the quantitative comparison of noise contributions in both optical (laser) and acoustic (saser) beatnote readout, analyzed through linearized Langevin equations for the coupled three-mode system. The linewidths of each output scale inversely with intracavity population and strongly depend on the modal dissipation rates and the transfer of pump frequency noise via mode pulling effects.

Figure 2: Output linewidth dependence on pump power, temperature, and transferred pump noise, contrasting laser and saser regimes for fixed and varying modal $Q$.

Numerical simulations demonstrate that for acoustic quality factors $Q_{\mathrm{aco}} \gtrsim 5000$, the saser output exhibits marked suppression of both thermal and frequency noise at practical pump powers—a regime made possible by low-loss phononic confinement in LNOS. In this case, saser linewidths are substantially narrower than laser linewidths under equivalent conditions. While increased pump power narrows both outputs, optimal noise suppression for saser detection occurs at modest optical $Q$ values, thus alleviating requirements for ultrahigh-$Q$ photonic fabrication.

Further, temperature dependence analysis reveals saturation toward minimum intrinsic linewidth at cryogenic temperatures, but even at room temperature ($n_{\mathrm{th}} \sim 700$), high-$Q$ phononic confinement yields quantum-limited performance.

Angle Random Walk and Sensitivity Performance

Angle random walk (ARW) is a critical figure of merit in gyroscopic devices, reflective of the minimum resolvable rotation rate over time. The authors define ARW as

$$\zeta = \sqrt{\frac{4\pi\times \min\{\Delta\nu_{\mathrm{laser}}, \Delta\nu_{\mathrm{saser}}\}}{S_{\mathrm{eff}}^2}}$$

where $S_{\mathrm{eff}}$ is the effective system sensitivity.

Figure 3: ARW dependence on modal $Q$ factors and pump power, with operational boundaries for laser and saser regimes. Saser regime is advantageous at moderate pump and acoustic $Q$ values, circumventing ultrahigh photonic $Q$ requirements.

Performance phase diagrams delineate two salient operating regions: (1) the conventional laser regime, requiring optical $Q > 10^{10}$ for subdegree ARW at 200 mW pump power; (2) the saser regime, achieving $\zeta \sim 0.085\,\mathrm{deg}/\sqrt{\mathrm{h}}$ with acoustic $Q = 5000$, optical $Q = 10^5\!\!-\!\!10^6$, and pump power as low as 5–200 mW. Such operating points are readily accessible in phononic LNOS platforms, rendering saser detection a practical route for chip-scale angular sensing in navigation, robotics, and quantum devices.

Implications and Future Perspectives

The theoretical framework presented substantiates direct saser-based gyroscope operation as a superior alternative to conventional optical-only approaches when high acoustic $Q$ is attainable. Key practical advantages include:

• Significant suppression of pump frequency and thermal noise in output beatnotes compared to solely optical detection.
• Requisite ARW sensitivity at orders-of-magnitude lower pump power and with more manufacturable optical $Q$.
• Enablement of integrated, active phononic circuit architectures for RF and quantum signal transduction, inertial navigation, and sensing.

The work lays foundational principles for Brillouin gain-enabled phononic circuits on LNOS, facilitating high-$Q$, piezoelectrically accessible gigahertz-frequency phonons. Future directions will likely involve experimental demonstration of saser gyroscopes, further integration with programmable phononic circuits, and generalization to hybrid opto-acoustic quantum sensors.

Conclusion

This paper establishes that chip-integrated Brillouin saser gyroscopes on modern photonic-phononic platforms substantially outperform prior laser-based devices under realistic modal $Q$ and pump power constraints. The doubly sensitive Sagnac response, explicit suppression of pump and thermal noise, and electrical readout capability combine to yield practical, low-footprint, high-resolution rotation sensors. The architectural shift toward direct phonon detection opens new routes for precision inertial sensing and hybrid signal processing applications in integrated quantum systems.