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.

Atomic magnetometers are widely acknowledged as one of the most sensitive devices for magnetic field measurement. Our study presents a novel method that enables bandwidth expansion of single-beam magnetometers in the spin-exchange relaxation-free regime. This method bases on increasing the modulation amplitude of magnetic field combining with negative feedback with proportional gain. Through our method, the magnetometer’s total relaxation rate is moderately increased by elevating modulation amplitude and frequency, and correspondingly, the detection bandwidth experiences dramatic improvement from 230 Hz to 1380 Hz. The application of negative feedback with proportional gain further increases this bandwidth to higher than 4 kHz, which is over 17 times of its original value. The sensitivity of the magnetometer under this condition is measured as 25 fT/ $\text {Hz}^{\text {1/2}}$ for open-loop scheme and 35 fT/ $\text {Hz}^{\text {1/2}}$ for closed-loop scheme. Comparatively, the sensitivity measured on conventional conditions in our experiment is 12 fT/ $\text {Hz}^{\text {1/2}}$ . This approach offers a profitable trade-off that extraordinary expansion of detection bandwidth can be acquired with the price of a little sensitivity loss. Our method is advantageous for miniaturization of atomic magnetometers as no extra hardware is added, which is of special interest for applications including biomagnetic measurement where large detection bandwidth is sometimes in need.

In this article, we found an appropriate operating frequency of pump light for stabilizing the light frequency based on the atomic absorption of the vapor cell in the minimized atomic magnetometer. The traditional way to apply this stabilizing method is to stabilize the laser frequency at the absorption peak because its derivative is always zero and not affected by the cell temperature if the pressure shift is suppressed. However, it is observed experimentally that the response amplitude has a drop of up to 40% from the maximum at the absorption peak. It is due to the hyperfine optical pumping, and we explored the applicable condition to obtain the maximum response amplitude by solving the Liouville equation and proved it experimentally as well. Furthermore, we found that under the appropriate pressure, the frequency to obtain maximum response is close to the zero points of the second-order derivative which are not affected by cell temperature as well. Therefore, it is purposed to stabilize the pump laser frequency at these points. It is demonstrated experimentally that the frequency stabilization is the same, while the response amplitude is increased by more than 40% compared to stabilizing at the absorption peak. These results are instructive in improving the performance of minimized atomic magnetometers.