High-spatial-resolution optical microsphere cavity magnetic field sensing system
Technical Field
The invention relates to a magnetic field sensing system with a high spatial resolution optical microsphere cavity, in particular to a magnetic field sensing system constructed by a magnetostrictive medium and an optical microsphere cavity, and belongs to the field of optics.
Background
At present, the means of measuring the biological magnetic field is mainly a superconducting quantum interference device working at low temperature, and the magnetometer of the latest optical means is still limited by spatial resolution. A novel magnetic field detection scheme based on an optical microsphere cavity is provided, the spatial resolution of hundreds of microns can be obtained, and the magnetic field detection scheme has the advantages of low cost and low power consumption and can be directly applied to biological magnetic field measurement or abnormal magnetic field detection in a monitoring area in the future. Furthermore, it can be integrated into fiber optic systems, is not subject to electromagnetic interference, and can be remotely probed. The existing biological magnetic field detection equipment is high in manufacturing cost, the size of the biological magnetic field detection equipment is large due to low-temperature working conditions, the biological magnetic field detection equipment cannot meet the requirements of different patients when detection is carried out, for example, the magnetoencephalography of an infant patient may need to adjust the distance between the detection equipment and the brain of the infant patient so as to ensure the detection precision, and for example, some ICU patients which are not suitable for moving may need to move the detection equipment, so that the equipment which is made into a helmet-type movable equipment is more practical. However, the existing superconducting quantum interference device can not meet the requirements. An optical microsphere cavity magnetic field sensing array system is designed, the spatial resolution of hundred microns is achieved, and the actual detection requirements can be met after the required detection sensitivity is obtained through system optimization.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a high-spatial-resolution optical microsphere cavity magnetic field sensing system which can be used in the field of magnetic field detection requiring high spatial resolution and low-frequency magnetic field detection capability.
A high-spatial-resolution optical microsphere cavity magnetic field sensing system comprises a signal generator, a tunable laser, an isolator, an attenuator, a polarization controller, an optical fiber cone, a magnetostrictive medium, a microsphere cavity, low-refractive-index ultraviolet curing glue, a photoelectric detector, an oscilloscope and a data processing and display system;
one path of two paths of signals output by the signal generator is sent to a voltage tuning port of the tunable laser, and the other path of the two paths of signals is sent to the oscilloscope; the light emergent end of the tunable laser is connected with the input end of the isolator, the output end of the isolator is connected with the input end of the attenuator, and the optical fiber between the output end of the attenuator and the input ends of one or more optical fiber cones is provided with a polarization controller; when a plurality of optical fiber cones are connected, a light splitting device is arranged between the polarization controller and the optical fiber cones; the optical field output by each optical fiber cone enters the microsphere cavity in an evanescent wave coupling mode, the optical field in the cavity is coupled and output to the receiving end of the corresponding photoelectric detector through each optical fiber cone, the signal output by the photoelectric detector enters an oscilloscope, and the signal output by the oscilloscope enters a data processing and display system. The tunable laser, the isolator, the attenuator, the polarization controller, the optical fiber cone and the photoelectric detector in the sensing system are connected by adopting optical fibers; the photoelectric detector is connected with the oscilloscope by using an electrical cable with two universal ports; the microsphere cavity is fixed on the magnetostrictive medium through low-refractive-index ultraviolet curing glue, the positions of the microsphere cavity, the magnetostrictive medium and the optical fiber cone are fixed, and the refractive index value of the low-refractive-index ultraviolet curing glue ensures that an optical field is transmitted in the microsphere cavity; the section diameter of the cone area part of the optical fiber cone is 0.5-0.75 of the wavelength of input light; the microsphere cavity and the optical fiber cone are always in a coupling state.
Preferably, the tuning range of the tunable laser covers the detection range required by the experiment, and the wave band is selected from a communication wave band and matched with the receiving wave band of the detector.
Preferably, the diameter of the microsphere cavity is 80-500 micrometers.
Preferably, the material of the microsphere cavity is silicon dioxide.
Preferably, the microsphere cavity is replaced by a columnar micro-cavity or a bottle-shaped micro-cavity, so that the maximum diameter of the space of the cavity is ensured to be 80-500 microns, the light field output by the light source is transmitted in the cavity with low loss, and meanwhile, evanescent waves exist on the outer surface of the cavity.
Preferably, the magnetostrictive medium is Terfenol-D or other medium capable of stretching under the action of a magnetic field.
Preferably, the magnetostrictive medium is in the shape of a plate, a cylinder or a helmet.
Preferably, the optical fiber is designed to ensure low loss transmission and easy detection of optical signals in the selected wavelength band.
Preferably, the polarization state of the polarization controller is such that the optical quality factor of the optical mode is highest.
Preferably, the attenuator is arranged to ensure that the optical power reaching the detector is within the acceptable power range of the detector.
The sensing system has high spatial resolution when sensing the magnetic field and has the capability of detecting the low-frequency magnetic field. Meanwhile, the system is mainly constructed by optical fibers, has small volume and easy integration, and can be used for remotely detecting magnetic field information.
Drawings
FIG. 1 is a schematic structural diagram of a high spatial resolution optical microsphere cavity magnetic field sensing system of the present invention;
FIG. 2 is a schematic diagram of a high spatial resolution optical microsphere cavity magnetic field sensing array expanded based on FIG. 1.
Detailed Description
The essential features and the remarkable advantages of the present invention will be further clarified by the following embodiments, but the contents of the present invention are not limited to the following embodiments:
the first embodiment is as follows: as shown in fig. 1, the high spatial resolution optical microsphere cavity magnetic field sensing system according to this embodiment includes a signal generator 1, a tunable laser 2, an isolator 3, an attenuator 4, a polarization controller 5, an optical fiber taper 6, a magnetostrictive medium 7, a microsphere cavity 8, a low refractive index ultraviolet curing adhesive 9, a photodetector 10, an oscilloscope 11, and a data processing and display system 12. One path of two paths of signals output by the signal generator 1 is sent to a voltage tuning port of the tunable laser 2, and the other path of the two paths of signals is sent to the oscilloscope 11. The light emergent end of the tunable laser 2 is connected with the input end of the isolator 3, the output end of the isolator 3 is connected with the input end of the attenuator 4, and the optical fiber between the output end of the attenuator 4 and the input end of the optical fiber cone 6 is provided with a polarization controller 5. An optical field output by the optical fiber cone 6 enters the microsphere cavity 8 in an evanescent wave coupling mode, the optical field in the cavity can also be coupled and output to a receiving end of the photoelectric detector 10 through the optical fiber cone 6, a signal output by the photoelectric detector 10 enters the oscilloscope 11, and a signal output by the oscilloscope 11 enters the data processing and display system 12. The tunable laser 2, the isolator 3, the attenuator 4, the polarization controller 5, the optical fiber cone 6 and the photoelectric detector 10 in the sensing system are connected by optical fibers; the photodetector 10 and the oscilloscope 11 are connected by a two-port common electrical cable. Data processing system 12 will process the magnetic field signal detected on oscilloscope 11 and display its value on the screen. The change of the external magnetic field causes the magnetostrictive medium 7 to deform, and further causes the cavity length of the microsphere cavity 8 to change, so that the transmission spectrum of the cavity measured on the oscilloscope 11 contains magnetic field information, and the strength and frequency information of the magnetic field can be demodulated through data processing.
The second embodiment is as follows: the embodiment will be described with reference to fig. 2, which is a supplement to the high spatial resolution optical microsphere cavity magnetic field sensing system of the first embodiment, and the sensing system can be expanded to a sensing array for multi-point magnetic field detection as well as single-point magnetic field detection. A plurality of microsphere cavities and the optical fiber cone coupling system are bonded on the magnetostrictive medium, so that a magnetic field sensing array can be obtained, and multi-point magnetic field detection can be carried out. In practice, a device 13 capable of splitting light, such as a fiber coupler, is added after the polarization controller. Meanwhile, the corresponding number of photodetectors 14 and 15 are correspondingly added at the output ends of the fiber cones of the multiple sensing units for receiving. The optical splitting device 13 in fig. 2 may be not only one optical fiber coupler, but also an optical splitting system formed by a plurality of couplers, and splits the optical fiber into multiple paths of light as needed. The magnetic field detection array in fig. 2 may not be limited to three microspheres, and a required magnetic field detection unit may be constructed, and the positions of the microspheres may be selected as required. If necessary, a polarization controller can be added before the light output by the fiber coupler is sent into the fiber cone. In addition, the oscilloscope 11 for data acquisition can also be replaced by a multi-channel data acquisition card.
The third concrete implementation mode: this embodiment is described in conjunction with fig. 1 and 2, and is further defined by the high spatial resolution optical microsphere cavity magnetic field sensing system described in the first and second embodiments. Firstly, placing a microsphere cavity 8 on a magnetostrictive medium 7, coupling a light field into the microsphere cavity 8 by using an optical fiber cone 6, dripping low-refractive-index ultraviolet curing glue 9 into a contact area of the microsphere cavity and the optical fiber cone, continuously adjusting the position of the optical fiber cone 6 to an optimal coupling state, curing the glue by using ultraviolet lamp irradiation, and further fixing the positions of the microsphere cavity and the optical fiber cone on the magnetostrictive medium. Before the ultraviolet lamp irradiates, the coupling state of the optical fiber cone and the microsphere cavity can be adjusted according to requirements. The microsphere cavity 8 can be replaced by a columnar micro-cavity, a bottle-shaped micro-cavity or a micro-cavity with other shapes, as long as the dimension is ensured to be close to each other, the light field output by the light source can be transmitted with low loss in the micro-cavity, and meanwhile, evanescent waves exist on the outer surface of the cavity. The magnetostrictive medium 7 can be in the shape of a flat plate, a cylinder, a helmet or the like, and is designed according to specific application scenes and the arrangement requirements of an actual sensing array, as long as deformation can be ensured under the action of a magnetic field and the cavity length of the resonant cavity is changed.