A wafer-level optical package solution for chip-scale atomic magnetometers is presented, which is based on microelectronic fabrication process on a 4 inch wafer. A module is fabricated following the process. By measuring the intensity of the light, it is indicated that the quality of parallelism and polarizability of the laser beam from a Vertical Cavity Surface Emitting Laser (VCSEL) in the module are acceptable. The frequency of the VCSEL is locked to D1 line of Rubidium through proper adjustment of temperature and driving current. The module is employed in an atomic magnetometer which operates in Mz configuration for the detection the strength of magnetic fields. Results show the feasibility of the package in a magnetometer system.
A wafer-level optical package solution for chip-scale atomic magnetometers is presented, which is based on microelectronic fabrication process on a 4 inch wafer. A module is fabricated following the process. By measuring the intensity of the light, it is indicated that the quality of parallelism and polarizability of the laser beam from a Vertical Cavity Surface Emitting Laser (VCSEL) in the module are acceptable. The frequency of the VCSEL is locked to D1 line of Rubidium through proper adjustment of temperature and driving current. The module is employed in an atomic magnetometer which operates in Mz configuration for the detection the strength of magnetic fields. Results show the feasibility of the package in a magnetometer system.
An optically pumped magnetometer was drastically miniaturized, by taking advantage of MEMS techniques, producing the chip-scale atomic magnetometers (CSAM) physics package. The key component of the package is an alkali vapor cell. To probe the magnetic field experienced by the atoms, the injection current to the VCSEL was modulated at 3.4 GHz near half the hyperfine frequency of87Rb. Lock-in detection is used to determine the center of the resonance, and the magnetic field is determined by counting the modulation frequency, which is related to the Larmor precession frequency under these locked conditions. The ITO heaters create a large magnetic field gradient, which broadens the resonance and reduces the sensitivity.
This paper presents a novel scheme on the integration of chip-scale SERF magnetometer using a vertical-cavity surface-emitting laser(VCSEL) as pumping and detecting laser. The fabrication and integration process of the whole system based on stacking PCB boards consist of VCSEL, optical components, rubidium vapor cell, photo-detector, three axis Helmholtz coils. By calculation and measurement, it was found that the module is designed with a minimum output power of 0.15mW and a competitive volume of 1.4×1.4×2.5cm3. Experiments show that the sensitivity of chip-scale SERF magnetometer based on VCSEL is around 1.87pT/Hz1/2in magnetic shield environment, the integration and miniaturization design process of the magnetometer can be empolyed for magnetoencephalography(MEG) measurement.
Highly sensitive optical magnetometers present high performance in detection of biological magnetic fields from the heart or the brain and have impact on other areas as diverse as magnetic resonance imaging, space science and remote monitoring. A chip-scale SERF-regime optical magnetometer based on a MEMS process is fabricated instead of a large-chamber one and the optical module and the vapor cell are fabricated based on the MEMS process. Industrialization, low cost and high systematic integration level of magnetic sensors can also be achieved based on the wafer-level packaging. Besides, a 200KHz AC electronic current was applied to the heaters for reducing magnetic noises generated by DC currents from heating resistors. The experimental setup based on a SERF-regime magnetometer to test magnetic fields is shown and results indicate that magnetic fields are tested successfully.
A new generation of small low-power atomic sensors, including clocks, magnetometers, and gyroscopes, is being developed based on recently available MEMS and VCSEL technologies.These sensors rely on spectroscopic interrogation of alkali atoms, typically rubidium or cesium, contained in small vapor cells.The relevant spectroscopic wavelengths (in vacuum) are 894.6 nm (D1) and 852.3 nm (D2) for cesium, and 795.0 nm (D1) and 780.2 nm (D2) for rubidium.The D1 wavelengths are either preferred or required, depending on the application, and vertical-cavity surface-emitting lasers (VCSELs) are preferred optical sources because of their low power consumption and circular output beam.This paper describes the required VCSEL characteristics for atomic clocks and magnetometers.The fundamental VCSEL requirement is single-frequency output with tunability to the particular spectroscopic line of interest.Singlepolarization and single-transverse-mode operation are implicit requirements.VCSEL amplitude noise and frequency noise are also important because they contribute significantly to the sensor signal-to-noise ratio.Additional desired VCSEL attributes are low cost, low power consumption, and several years of continuous operating lifetime.This paper also describes the 894-nm VCSELs that we have developed for cesium-based atomic sensors.In particular, we discuss VCSEL noise measurements and accelerated lifetime testing.Finally, we report the performance of prototype atomic clocks employing VCSELs.
We are developing a new detection scheme for magnetometers based on atomic vapor confined in millimeter-scale micromachined enclosures and atomic Zeeman transitions. By adding three micro-reflective mirrors and modifying the light path arrangement, the new detection scheme effectively hurdles the main obstacle which prevents SERF from being applied in chip scale sensors, i.e. the difficulty to implement the transverse laser fields using MEMS fabrication methods. Instead of guiding the pumping laser beam parallel to the wafer plates that is not compatible with MEMS fabrication, such scheme rotates both pumping and probing laser beams, and maintains the orthogonal relationship between them. Finally, several fabrication process suited for this scheme are discussed.
The physics package of a chip-scale atomic clock (CSAC) has been successfully realized by integrating vertical cavity surface emitting laser (VCSEL), neutral density (ND) filter, λ/4 wave plate, 87 Rb vapor cell, photodiode (PD), and magnetic coil into a cuboid metal package with a volume of about 2.8 cm 3 . In this physics package, the critical component, 87 Rb vapor cell, is batch-fabricated based on MEMS technology and in-situ chemical reaction method. Pt heater and thermistors are integrated in the physics package. A PTFE pillar is used to support the optical elements in the physics package, in order to reduce the power dissipation. The optical absorption spectrum of 87 Rb D1 line and the microwave frequency correction signal are successfully observed while connecting the package with the servo circuit system. Using the above mentioned packaging solution, a CSAC with short-term frequency stability of about 7 × 10 −10 τ −1/2 has been successfully achieved, which demonstrates that this physics package would become one promising solution for the CSAC.