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Narrow linewidth non-magnetic VCSEL for quantum sensing

Quantum magnetic detection sensors, or atomic magnetometers, are based on the principle of highly sensitive detection of weak magnetic fields by means of the interaction between lasers and atoms. The light source used in the atomic magnetometer is mainly VCSEL, mainly because VCSEL has the advantages of wide operating temperature range and high beam quality. Using VCSEL as the light source can be integrated with the sensor in a compact package, which greatly reduces the overall cost of the machine. size, cost and power consumption. However, atomic magnetometers have very strict requirements on the performance of VCSELs, including high-temperature operation (≥80°C), single-mode (SMSR>30 dB), narrow linewidth (<100 MHz), and no magnetism, which greatly increases the performance of VCSELs. Difficulty in developing chips and modules.

According to Memes Consulting, the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences (abbreviation: Changchun Institute of Optics and Mechanics) and Changchun Zhongke Changguang Space-Time Optoelectronics Technology Co., Ltd. have focused on the application of chip-level atomic clocks in VCSEL since 2010. A series of research results have been reported in terms of high temperature and low threshold operation, wavelength control, mode stability, and the practical application of VCSELs in chip atomic clock systems.

This paper mainly introduces a new research achievement of the research group of Changchun Institute of Optics and Mechanics on high temperature, narrow linewidth, and nonmagnetic VCSEL. The surface microlens integrated external cavity VCSEL proposed in this research can realize stable single mode operation (SMSR=36.3 dB), the corresponding laser output power is 1.52 mW, and the laser frequency linewidth is 38 MHz; the magnetic field of the light source module made of this VCSEL chip is only 0.03 nT, which can meet the application requirements of quantum sensing . Relevant research results have been published in the journal "Chinese Optics".

In order to develop surface microlens integrated external cavity VCSEL devices, realize narrow linewidth non-magnetic laser output, and meet the application requirements of quantum sensors such as atomic magnetometers, the researchers designed and grown a VCSEL epitaxial structure suitable for surface integrated microlenses, completed The surface micro-lens integrated external cavity VCSEL device is prepared, and non-magnetic materials are selected in terms of electrode materials to meet application requirements. Also we develop the substrate for the chip submount by ceramic components.

Schematic diagram of surface microlens integrated external cavity VCSEL device

The researchers tested the current-power characteristics of the microlens-integrated VCSEL device at room temperature and high temperature environments to evaluate the device's suitability for high-temperature operation. The results show that the output power of VCSEL at room temperature is 2.559 mW at a driving current of 5 mA, the corresponding voltage is 2.79 V, and the electro-optic conversion efficiency is 18.3%. Under the conditions of 4 mA driving current and 90°C, the laser center wavelength of the device is 896.3 nm, and the SMSR is 36.3 dB. The laser can maintain a good single-mode working state, and the test result of the VCSEL laser linewidth is 38 MHz. The cavity mode-gain mismatch and multiple sets of high-gain quantum wells adopted by the device can effectively alleviate its performance degradation at high temperatures.

VCSEL output spectrum test results

VCSEL line width test results

In order to meet the application requirements of the atomic magnetometer, the researchers used the VCSEL chip to make a non-magnetic package VCSEL light source module, and used a magnetometer to test the residual magnetism of the light source module. The results show that the magnetic field strength generated by the module is lower than 0.03 nT (peak-peak value), which can meet the requirements of practical applications.

Non-magnetic package VCSEL light source module

VCSEL module remanence test results

All in all, this research is aimed at the application requirements of quantum sensing for VCSEL high temperature operation, narrow line width, and non-magnetism. Starting from the chip structure, a VCSEL with an integrated microlens structure has been developed. The device has excellent performance, can meet the application requirements of quantum sensing, and has great potential for future development. XINXIN GEM provides TO can for the VCSEL package.

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