The construction of large-scale integrated photonic circuit cannot be separated from the important role played by silicon-based optoelectronic devices. As a basic and important link in on-chip photon propagation, beam splitting is of great significance for the efficient utilization of sources and the compact integration of optoelectronic devices. It is widely used in power splitting, polarization separation, wavelength division multiplexing and other scenarios. This paper reviews the on-chip beam splitting methods in recent years, which are mainly divided into the following categories: y-branch, multimode interference coupling, directional coupling, and inverse design. This paper introduces their research status, including optimization design methods, functions and applications in large-scale quantum chips and optoelectronic hybrid integration, looking forward to providing a reference for the further research of beam splitting methods and the wide application of beam splitters in the frontier field in the future.

The large volumes induced by complex free‐space optical paths pose a challenge to quantum precision measurement and optical communication in traditional optics. Meanwhile, on‐chip integration is an important requirement for quantum technology. To simplify complicated optical systems, the development of miniaturized and integrated devices with a variety of structures, such as optical waveguide, microcavity, photonic crystal, and metasurface, has attracted increasing attention. Herein, on‐chip light–atom interactions affected by these nanostructures from the aspects of recent advancement in their physics and applications are reviewed. In recent years, different nanostructures are used to realize the functions of macro‐optical systems. The structural characteristics, interaction mechanisms, and main achievements in terms of the applications of the corresponding devices are demonstrated and compared. Finally, the research trends and challenges as well as the scope for future work are discussed.

Using spin‐exchange relaxation‐free (SERF) atomic magnetometer array (AMA) in magnetocardiography and magnetoencephalography has presented a challenge in reducing its packing volume for integrated instrumentation and convenient maintenance. This study presents a novel, space‐saving SERF AMA based on an 8‐channel planar lightwave circuit (PLC) waveguide splitter with a compact footprint of 26 × 2.5 mm2. The PLC splitting configuration allows the synchronization of the pump for a multisensor array, resulting in highly consistent performance among the sensors, with an impressive ultrahigh sensitivity of 34 fT Hz−1/2 within a measurement bandwidth of 105 Hz. The PLC splitting method shows great promise in expanding the channel capacity of small‐scale SERF AMAs, offering a cost‐effective method for high‐resolution medical diagnoses through functional magnetic imaging of humans. In addition, this method is expected to find applications in fields such as electromagnetic induction imaging, biological magnetism, and geomagnetic observation.

Nanophotonics There have been numerous studies of on‐chip different nano‐structures such as waveguides, microcavities, photonic crystals, and metasurfaces, used for realizing the functions of macro‐optical systems involving light‐atom interactions in recent years. The structural characteristics, interaction mechanisms, and main achievements in terms of the applications of the corresponding devices are demonstrated, summarized and compared. More information can be found in article number http://doi.wiley.com/10.1002/adpr.202200153 by Weiyi Wang, Zhen Chai, and co‐workers.

The current polarization differential detection method used for atomic co‐magnetometers and other atomic sensors usually depends on the beam splitting plane at 45° from the incident light, so the beam splitter needs a certain thickness and a second optical path perpendicular to the original optical axis for detection, which restricts the integration degree of the beam splitter and photodetectors on the probe optical path. To address this issue, a new spin‐selective beam‐splitting metasurface‐based technique for atomic spin detection is proposed in this study, which utilizes a silicon nitride (SiN) metasurface for chiral beam‐splitting detection. The experimental results show that the 2.8 × 2.8 mm fabricated metasurface supports the beam splitting focusing of the left and right circular partial incident light with a distance up to 1.340 mm. It has a remarkable ability to detect optical rotation angles, achieving an angular measurement sensitivity of 3.0526 × 10−5 rad at 70 kHz. Compared with the traditional beam splitter, the probe's optical path volume can be reduced by at least 80%. This method can enhance the integration of atomic sensors and provide a novel approach for the development of atom sensors on chips.