ABSTRACT Atomic magnetometers (AMs) are among the most sensitive magnetic field sensors, with uses in magnetic anomaly detection, geosciences, and fundamental physics research. Despite notable progress, developing highly integrated, miniaturized components with high resolution, sensitivity, and efficiency for chip‐scale AMs remains a significant challenge. Here, we present a novel integrated polarization detection scheme based on a bifocal liquid‐crystal polarization metalens (LCPM) for chip‐scale AMs. By leveraging geometric phase and holographic synthesis principles, the LCPM efficiently separates and focuses left‐ and right‐handed circularly polarized light at the rubidium D1 transition wavelength (795 nm), achieving a high focusing efficiency of up to 80% and extinction ratios of 104 and 134 for the two channels. We demonstrate a prototype AM operating in the spin‐exchange relaxation‐free regime, achieving a high magnetic‐field sensitivity of 17 fT/Hz 1/2 and a dynamic range of ±4.8 nT. The proposed LCPM‐based scheme reduces the optical‐path volume by 94% compared to traditional polarization detection systems. Importantly, our method is compatible with large‐scale, cost‐effective production through established liquid‐crystal manufacturing lines, paving the way for high‐throughput fabrication of chip‐scale AMs. This innovation enables compact, affordable polarization detection with enhanced sensitivity of atomic sensors, opening new opportunities for high‐resolution biomagnetic imaging and quantum precision measurements.
ABSTRACT Atomic magnetometers (AMs) are among the most sensitive magnetic field sensors, with uses in magnetic anomaly detection, geosciences, and fundamental physics research. Despite notable progress, developing highly integrated, miniaturized components with high resolution, sensitivity, and efficiency for chip‐scale AMs remains a significant challenge. Here, we present a novel integrated polarization detection scheme based on a bifocal liquid‐crystal polarization metalens (LCPM) for chip‐scale AMs. By leveraging geometric phase and holographic synthesis principles, the LCPM efficiently separates and focuses left‐ and right‐handed circularly polarized light at the rubidium D1 transition wavelength (795 nm), achieving a high focusing efficiency of up to 80% and extinction ratios of 104 and 134 for the two channels. We demonstrate a prototype AM operating in the spin‐exchange relaxation‐free regime, achieving a high magnetic‐field sensitivity of 17 fT/Hz 1/2 and a dynamic range of ±4.8 nT. The proposed LCPM‐based scheme reduces the optical‐path volume by 94% compared to traditional polarization detection systems. Importantly, our method is compatible with large‐scale, cost‐effective production through established liquid‐crystal manufacturing lines, paving the way for high‐throughput fabrication of chip‐scale AMs. This innovation enables compact, affordable polarization detection with enhanced sensitivity of atomic sensors, opening new opportunities for high‐resolution biomagnetic imaging and quantum precision measurements.
Abstract Atomic magnetometers (AMs) that use alkali vapors, such as rubidium, are among the most sensitive sensors for magnetic field measurement. They commonly use polarization differential detection to mitigate common‐mode noise. Nevertheless, traditional differential detection optics, including polarization beam splitters (PBS) and half‐wave plates, are typically bulky and large, which restricts further reductions in sensor dimensions. In this study, a combination of liquid crystal polarization grating (LCPG) and liquid crystal quarter‐wave plate is used for differential detection in AMs, with magnetic field strength determined by measuring the intensity of two diffracted beams from the LCPG. The experimental findings indicate that the fabricated LCPG exhibits a circularly polarized extinction ratio of 3,656 and achieves an average diffraction efficiency of 99 %. In addition, the differential detection method based on LCPG can achieve an angular resolution of 1.48 × 10 −7 rad. Subsequently, the method is employed in an AM to achieve an average magnetic sensitivity of 13.8 fT/Hz 1/2 . Compared to the PBS‐based differential detection method, this method enhances the magnetometer response coefficient by 13 % and achieves co‐side distribution of the two diffracted beams, thereby avoiding the need for additional vertical optical paths. The effective thickness of the detection optics is reduced to the micrometer scale, allowing for future integration as thin films onto microfabricated vapor cells. This study offers a practical solution for miniaturized AMs with exceptionally high sensitivity.
High-performance atomic magnetometers (AMs) rely on the measurement of optical rotation, which requires a set of bulky polarization optics that limit their applications in scenarios where portability and compactness are necessary. In this study, a miniaturized AM is constructed based on a cubic 87 Rb vapor cell and monolithic metalens, which provides an integrated scheme to achieve optical rotation detection induced by the circular birefringence of polarized atoms. The designed metalens achieves polarization splitting with deflection angles of ±10 ∘ and focusing with efficiencies of approximately 30% for orthogonal linear polarizations. The sensitivity of our compact device is ∼30 fT/Hz 1/2 with a dynamic range of around ±1.45 nT. We envision that the presented approach paves the way for the chip integration of emerging atomic devices, which are in demand for applications such as biomagnetic imaging and portable atomic gyroscopes.
Emerging atomic magnetometers (AMs) are among the most advanced sensors for detecting and characterizing magnetic fields. Recently, there has been growing interest in the miniaturization and integration of AMs due to the urgent demand for portability and compactness in various fields such as biomagnetism imaging. While conventional AMs require a bulky setup of optical devices for the pumping and optical readout of atomic spin, here, a novel chip-scale single-beam AM scheme is proposed by leveraging extreme transmissive circular polarization dichroism (TCPD) and geometric phase manipulation of spin-selective interference meta-optics. This is achieved through silicon-based metasurfaces that enable the realization of arbitrary-to-circular polarization conversion and wavefront modulation within a monolithic chip at Rb D1 transition wavelength (λ = 795 nm). Two spin-selective interference metasurfaces, i.e., meta-circular-polarizer (MCP) and meta-circular-polarizer-lens (MCPL), are fabricated and characterized, with a measured TCPD of 0.68 for the MCP as well as focusing efficiency and TCPD of around 70.67% and 0.69 for the MCPL, respectively. As a proof of concept, a 4 × 4 × 4 mm 3 Rb vapor cell is combined with our metasurface to construct a miniaturized single-beam AM. The sensitivity of our compact metasurface-based system is about 15 fT/Hz 1/2, with a dynamic range near zero-field of ± 2.2 nT. We envision that this work could facilitate the development of burgeoning chip-scale quantum sensors, which hold great potential for high-spatial-resolution biomagnetic imaging, on-chip nuclear magnetic resonance, and so forth.
Abstract Emerging miniaturized atomic sensors such as optically pumped magnetometers (OPMs) have attracted widespread interest due to their application in high‐spatial‐resolution biomagnetism imaging. While optical probing systems in conventional OPMs require bulk optical devices including linear polarizers and lenses for polarization conversion and wavefront shaping, which are challenging for chip‐scale integration. In this study, an integrated optical probing scheme based on localized‐interference metasurface for chip‐scale OPM is developed. Our monolithic metasurface allows tailorable linear polarization conversion and wavefront manipulation. Two silicon‐based metasurfaces namely meta‐polarizer and meta‐polarizer‐lens are fabricated and characterized, with maximum transmission efficiency and extinction ratio (ER) of 86.29 % and 14.2 dB for the meta‐polarizer as well as focusing efficiency and ER of 72.79 % and 6.4 dB for the meta‐polarizer‐lens, respectively. A miniaturized vapor cell with 4 × 4 × 4 mm 3 dimension containing 87 Rb and N 2 is combined with the meta‐polarizer to construct a compact zero‐field resonance OPM for proof of concept. The sensitivity of this sensor reaches approximately 9 fT/Hz 1/2 with a dynamic range near zero magnetic field of about ±2.3 nT. This study provides a promising solution for chip‐scale optical probing, which holds potential for the development of chip‐integrated OPMs as well as other advanced atomic devices where the integration of optical probing system is expected.
ABSTRACT Optically pumped atomic magnetometers (AMs) have become powerful tools for biomagnetic sensing owing to their ultrahigh sensitivity. However, their broader deployment increasingly requires compact, scalable, and low‐cost free‐space photonic interfaces capable of delivering high quality beams for light‐atom interaction. Here, we present a photonic chip based on a silicon nitride (SiN) optical phased array (OPA) that serves as a free‐space optical interface for AMs, combining high radiation efficiency, low divergence, and compatibility with batch fabrication. The device generates a stable linearly polarized beam with long propagation capability, a polarization extinction ratio of 26.1 dB, and a degree of linear polarization of 99.5%, with a maximum overall radiation efficiency of 26.5%. In a dual beam atomic magnetometer, the chip emitted beam serves as the probe beam and enables differential detection with a sensitivity of 8 fT/Hz 1/2 . To assess fabrication reliability and reproducibility, we performed a statistical analysis of 168 devices fabricated by deep‐ultraviolet (DUV) lithography, with more than 50% exhibiting radiation efficiencies above 15%. These results demonstrate a low‐cost, scalable photonic interface for chip integrated AMs and highlight its potential for large scale implementation.
Optically pumped magnetometers (OPMs) enable high-resolution biomagnetic imaging, yet conventional single-beam designs are constrained by bulky, alignment-intensive polarization optics and susceptibility to laser-power noise. Here, we propose and demonstrate a compact, noise-suppressed OPM that uses a single planar liquid-crystal polarization grating (LCPG) functioning simultaneously as a high-efficiency polarization converter and a beam splitter. At the component level, the LCPG replaces multiple bulk elements, converts 795 nm light with 95% first-order diffraction efficiency and an ellipticity of ~44.6°, and exhibits robust performance against variations in incident-light polarization direction, ambient temperature, and angle of incidence. At the sensor level, a power-differential configuration effectively suppresses noise originating from pump-power fluctuations. We fabricated a probe with a total volume of 4 cm 3 and benchmarked it against a conventional OPM: the LCPG-enabled differential mode achieves a sensitivity of 8.6 fT/Hz 1/2 , representing an ~28% improvement over the conventional configuration. Importantly, the approach is compatible with mature, high-throughput, and cost-effective liquid-crystal manufacturing. These results demonstrate a scalable design strategy for OPMs that unites component-level efficiency, robustness, and cost-effectiveness with sensor-level compactness and noise suppression, paving the way for next-generation chip-scale quantum sensors.