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Optics Letters

Closed-loop atomic spin gyroscope via injection current modulation and magnetic feedback

Xiaoping Li, Wenfeng Fan, Shimiao Fan, Wei Quan

Published Apr 30, 2026• 0 citations
Publisher

Abstract

In traditional spin-exchange relaxation-free (SERF) gyroscopes, open-loop detection leaves the scale factor vulnerable to fluctuations in probe laser intensity and environmental temperature. To address this, an external-modulator-free closed-loop atomic spin gyroscope (ASG) is demonstrated using direct probe laser injection current modulation. A magnetic feedback loop maintains the total optical rotation at a zero point, decoupling the inertial signal from intensity and optical depth variations. Experimental results demonstrate a closed-loop rotation sensitivity of 2.8×10 −6 °/s/Hz 1/2 at 1 Hz. Compared to open-loop measurements under identical conditions (1×10 −5 ∘ /s/Hz 1/2 ), low-frequency noise is significantly suppressed. By eliminating bulky external modulators and effectively suppressing low-frequency noise, this design offers a highly competitive architecture for miniaturized atomic inertial sensors.

DOI
10.1364/ol.600447

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In traditional spin-exchange relaxation-free (SERF) gyroscopes, open-loop detection leaves the scale factor vulnerable to fluctuations in probe laser intensity and environmental temperature. To address this, an external-modulator-free closed-loop atomic spin gyroscope (ASG) is demonstrated using direct probe laser injection current modulation. A magnetic feedback loop maintains the total optical rotation at a zero point, decoupling the inertial signal from intensity and optical depth variations. Experimental results demonstrate a closed-loop rotation sensitivity of 2.8×10 −6 °/s/Hz 1/2 at 1 Hz. Compared to open-loop measurements under identical conditions (1×10 −5 ∘ /s/Hz 1/2 ), low-frequency noise is significantly suppressed. By eliminating bulky external modulators and effectively suppressing low-frequency noise, this design offers a highly competitive architecture for miniaturized atomic inertial sensors.
The atomic spin gyroscope (ASG), based on spin-exchange relaxation-free (SERF) co-magnetometers, is poised to become the next generation of high-precision inertial sensors. However, the long-term stability of the gyro can be limited by electron spin polarization. In this study, we investigate a novel real-time, in situ quantum feedback control technique for electron spin polarization in ASGs. By varying the pumping rates, we analyze the gyroscope’s response to the modulation magnetic field, finding that electron polarization dramatically affects the magnetic field response properties of ASGs. It’s demonstrated that the amplitude or phase of the electron spin resonance can be locked for in situ control of electron spin polarization in real-time. A K-Rb-21Ne co-magnetometer is established to implement the proposed method, where a transverse modulating magnetic field is applied to resonate with the electron spin. The lock-in amplification (LIA) technique is used to obtain the amplitude or phase of the electron spin resonance, and the electron spin polarization is closed-loop controlled by locking the second harmonic resonance amplitude or phase. The gyro signal is extracted from the first harmonic of the electron spin resonance. Our experimental results show that real-time in situ feedback control of electron spin significantly improves ASG’s long-term stability and suppresses low-frequency noise. This proposed method has broad application prospects, including optically pumped magnetometers (OPMs), nuclear magnetic resonance gyroscopes (NMRGs), and co-magnetometers.
Spin-exchange relaxation-free (SERF) atomic magnetometers usually adopt Faraday modulation to achieve better performance but suffer from laser intensity noise, thermal noise generated by the Faraday modulator, and nonmagnetic technical noise. These noises limit the sensitivity of the SERF magnetometer. We demonstrate a SERF magnetic gradiometer with dual-beam and closed-loop Faraday modulation. Operating in the SERF regime, the gradiometer utilizes an additional Faraday modulator rotation feedback to suppress probe laser intensity noise and thermal noise associated with the Faraday modulator, and it simultaneously uses dual-beam difference to cancel common-mode nonmagnetic technical noises. A gradient sensitivity of 14 fT/Hz1/2 per 1 cm gradiometer base length was achieved using Cs atoms.
A nuclear spin gyroscope based on an alkali-metal–noble-gas co-magnetometer operated in spin-exchange relaxation-free (SERF) regime is a promising atomic rotation sensor for its ultra-high fundamental sensitivity. However, the fluctuation of probe light intensity is one of the main technical error sources that limits the bias stability of the gyroscope. Here we propose a novel method to suppress the bias error induced by probe light intensity fluctuations. This method is based on the inherent magnetic field response characteristics of the gyroscope. By the application of a bias magnetic field, the gyroscope can be tuned to a working point where the output signal is insensitive to probe light intensity variation, referred to herein as ‘zero point’, thus the bias error induced by intensity fluctuations can be completely suppressed. The superiority of the method was verified on a K–Rb–21Ne co-magnetometer, and a bias stability of approximately 0.01 °/h was obtained. In addition, the method proposed here can remove the requirement of the closed-loop control of probe light intensity, thereby facilitating miniaturization of the gyroscope volume and improvement of reliability.
We report a novel Cs-(129)Xe atomic spin gyroscope (ASG) with closed-loop Faraday modulation method. This ASG requires approximately 30 min to start-up and 110 °C to operate. A closed-loop Faraday modulation method for measurement of the optical rotation was used in this ASG. This method uses an additional Faraday modulator to suppress the laser intensity fluctuation and Faraday modulator thermal induced fluctuation. We theoretically and experimentally validate this method in the Cs-(129)Xe ASG and achieved a bias stability of approximately 3.25 °∕h.
We propose a high-sensitivity spin polarization detection scheme based on optical amplitude modulation in atomic co-magnetometers, which is different from the traditional configuration.A linearly polarized laser with intensity modulation interacts with electron spins, generating optical rotation angles.Through differential amplification and demodulation, atomic spin polarization information is extracted with high precision.The effectiveness of the proposed method is verified by applying external perturbations during testing.Compared to traditional detection methods, the proposed approach effectively enhances inertial measurement sensitivity.Specifically, at 1 Hz, the measurement sensitivity has improved from 9.7 × 10 -6 to 3.25 × 10 -6 deg/(s Hz 1/2 ).Furthermore, the proposed scheme is easily integrable and conducive to future research on miniaturizing co-magnetometers and can also be applied to many other related fields.
Spin-exchange relaxation-free atomic spin gyroscope (SERF gyro) has ultrahigh theoretical sensitivity and is regarded as one of the most potential atomic gyroscopes. To investigate its rotation response, a high linear atomic spin precession detection module was developed firstly by modifying the fiber reflective Sagnac interferometer for atomic spin precession detection and operating it in closed-loop mode. The SERF gyro based on K-Rb-21Ne comagnetometer was built and tested and appeared obvious nonlinear response feature. The nonlinear rotation response model was deduced by assuming the rotation-induced nuclei spin procession detecting as an in-situ magnetometer inside the SERF gyro and the fitting curves are in good agreement with the experimental results. The optimized pump power for maximum sensitivity and measurable dynamic range were analyzed theoretically and demonstrated experimentally. The investigation results show that the nonlinear rotation response is an intrinsic property of SERF gyro and its measurable dynamic range is limited due to the saturation characteristic of the sum of pumping and relaxation rate. This indicates that SERF gyro is propitious to a position gyroscope with high sensitivity.