CN206848297U - A kind of Michelson interference formula optical fiber acceleration transducer - Google Patents

Abstract

A Michelson interferometric optical fiber acceleration sensor, including a cylinder, an upper limit pin, a first collimator, an optical coupler, a lower limit pin, a quality block, a second collimator, a ring magnet; an optical isolator, and a laser light source , photodetector and phase demodulation circuit. In the utility model, the mass block is designed as a part of the free space optical path of the Michelson interferometer, and the mass block is placed in a suspended state by using the magnetostatic row magnetic flux effect, and the external acceleration change is converted into a small displacement of the mass block, and then through the differential optical fiber The Michelson interferometer detects the phase change caused by mass displacement and demodulates the acceleration change of the sensor in real time. The sensor uses magnetic levitation to avoid the influence of mechanical damping, and introduces a double-reflection Faraday rotation optical structure to eliminate the influence of polarization fading. It has the advantages of high sensitivity, good stability, small size, and simple fabrication, and has a good application prospect.

Description

A Michelson Interferometric Fiber Optic Acceleration Sensor

technical field

The utility model relates to an acceleration sensor, in particular to a Michelson interference optical fiber acceleration sensor.

Background technique

Compared with conventional acceleration sensors, optical fiber acceleration sensors have obvious advantages in sensitivity, dynamic range, reliability, etc., and are widely used in national defense, military and other fields. At present, most fiber optic acceleration sensors use elastic elements and mass blocks to convert external acceleration into displacement or strain, and then transmit the displacement or strain to the sensing fiber to change the optical wavelength, phase and other parameters of the signal in the sensing fiber. , by demodulating the change of optical parameters to obtain the acceleration of the outside world. For example, the patents "A Cantilever Beam Type Fiber Bragg Grating Accelerometer" (Application No.: 200710065321.X), "Fiber Bragg Grating Accelerometer Based on Cantilever Beam Deflection" (Application No.: 200710065322.X) etc. adopt the cantilever beam mechanical structure , the acceleration is converted into the wavelength change of the grating before detection. However, although the patents "A Fiber Optic Accelerometer" (Application No.: 201510519101.4) and "A Vertical Vibration Displacement Sensor Based on Michelson Interferometer" (Application No.: 201310018899.5) use interferometric phase sensing technology to detect acceleration or displacement, but A mechanical structure is still required as a sensitive element, and the sensitivity of the sensor is not high and the repeatability is poor. Therefore, how to give full play to the advantages of the interferometric phase sensor and reduce the influence of the mechanical structure is a problem that needs to be considered in the design of a high-sensitivity acceleration sensor.

Contents of the invention

The technical problem to be solved by the utility model is to provide a Michelson interferometric optical fiber acceleration sensor, which overcomes the influence of the mechanical structure on the sensitivity of the traditional optical fiber acceleration sensor, and designs the mass block as a part of the free space optical path of the Michelson interferometer. The static magnetic levitation technology avoids the influence of mechanical damping, converts the acceleration effect into the differential change of the interferometer arm length, reduces the interference of the external environment, and improves the sensitivity of the sensor.

The technical scheme that the utility model takes is:

A Michelson interference optical fiber acceleration sensor, characterized in that it includes a cylinder, an upper limit pin, a first collimator, an optical coupler, a lower limit pin, a quality block, a second collimator, and a ring magnet.

The first collimator is fixedly installed directly above the cylinder, and the second collimator is fixedly installed directly below. The mass block is suspended inside the cylinder, and has an equal distance from the first collimator and the second collimator. The mass block is used to adjust the sensitivity and resonant frequency of the acceleration sensor, reflect the incident light from the first collimator and the second collimator, and rotate the polarization state of the light by 90° clockwise.

The first collimator and the second collimator are connected to the optical coupler, and the optical coupler, the first collimator, the upper reflective surface of the proof mass and the free space optical path between them constitute the first Michelson interference arm; The optical coupler, the second collimator, the lower reflection surface of the proof mass and the free space optical path between them constitute the second Michelson interference arm.

A ring magnet is arranged in the cylinder, and the ring magnet is used to generate a static magnetic field, and the mass block is in a suspended state by utilizing the magnetic flux removal effect.

There is an upper limit pin on the cylinder to limit the maximum stroke of the upward movement of the mass block, and a lower limit pin on the cylinder to limit the maximum stroke of the downward movement of the mass block;

Preferably, the mass block is composed of a magnetic ring, a first Faraday rotator, and a second Faraday rotator. The two sides of the Faraday rotator are respectively coated with a high-reflection film and an antireflection film. The high-reflection film surface of the first Faraday rotator and the second Faraday The high-reflection film surface of the optical mirror is stacked, and then glue is dispensed and solidified in the magnetic ring. The double-sided reflection structure design of the Faraday magnetic ring is convenient for differential detection of the optical path change of the Michelson interferometer. The state rotates 45° clockwise, and then rotates 45° after reflection, for a total of 90°. Then, the polarization changes of the forward incident light and the reverse reflected light in the coordinate direction are reversed, and the resulting polarization fading cancels each other out, thereby effectively eliminating the influence of the polarization fading and improving the signal-to-noise ratio.

Preferably, the magnetic ring generates a saturated magnetic field to ensure that the Faraday rotator produces a magneto-optical effect, rotates the polarization state of incident and reflected light by 90°, and generates a magnetic flux rejection effect with the ring magnet, so that the mass is in a one-dimensional free suspended state. Since the Faraday rotator needs to be under the action of a magnetic field to produce the magneto-optical effect, and it works in the saturated magnetic field region, a ring magnet is designed on the sensor, and the mass block is suspended by using the magnetic flux removal effect, which will neither affect the optical rotation effect nor The reduction in sensitivity of the proof mass due to mechanical contact is reduced.

Preferably, the optical coupler is connected to the optical isolator, and the optical isolator is connected to the laser light source; the optical coupler is connected to the photodetector, and the photodetector is connected to the phase demodulation circuit. This kind of Michelson interferometer, which constitutes a double arm containing a free optical path, can detect vibration and other parameters more sensitively.

Preferably, a method for measuring the acceleration of a Michelson interference optical fiber acceleration sensor, the continuous optical signal of the laser light source enters the optical coupler after passing through the optical isolator, and is divided into two beams of light with equal power and enters the first Michelson interference arm, The second Michelson interference arm, when the environmental acceleration of the acceleration sensor is constant, the static magnetic force makes the mass block in a magnetic levitation state, the mass block is in a balanced state through flexible adjustment, and the phase difference between the two arms of the interferometer is stable;

When the environmental acceleration changes, the mass block vibrates within the range of the upper limit pin and the lower limit pin, the distance between the mass block and the two collimators changes, the first Michelson interference arm of the interferometer, the second Michaelson arm The reverse differential change of the inferior interference arm is detected by the photodetector, and the phase change of the sensing system is demodulated in real time by using the 3*3 coupler demodulation method or the PGC demodulation method to obtain the acceleration of the mass block.

Preferably, a method for measuring the acceleration of a Michelson interferometric optical fiber acceleration sensor is characterized in that: the acceleration causes the displacement Δx of the mass block (6) to change, and the resulting phase difference Δφ is:

Among them, λ is the central wavelength of the laser light source.

This design increases the change of the optical path caused by the displacement change of the acceleration to four times that of the traditional interferometric sensor, and allows the two arms of the Michelson interferometer to participate in the sensing at the same time, and by adjusting the weight of the mass block, the Michaelson interferometer The two arm lengths of the interferometer are adjusted to be equal. When the acceleration acts, the two arm lengths produce a differential change, which effectively reduces the influence of temperature and laser source noise, and improves the performance of the interferometer.

The utility model is a Michelson interference optical fiber acceleration sensor, and the technical effect is as follows:

(1) High sensitivity and good stability. The static magnetic levitation method is used to make the mass block in the balance state of gravity and magnetic field levitation force, which avoids the influence of mechanical friction on the sensitivity of the traditional acceleration sensor and improves the sensitivity of the sensor; the mass block consists of two Faraday rotators and a collimator The two arms of the fiber optic Michelson interferometer effectively reduce the influence of polarization fading noise; at the same time, the mass block causes the differential change of the interferometer arm length difference, the sensitivity is increased by 2 times, and the temperature and light source noise are also eliminated or reduced And so on, the stability is good. The phase detection can be demodulated by the mature 3*3 coupler method, the technology is mature, and the frequency detection range is wide.

(2) Small size and simple structure. The diameter of the sensor can be several mm, and the tubular structure with a length of about 20mm is small in size and easy to install; the ring magnet, Faraday rotator, and magnetic ring can be selected from industrial products, which is easy to assemble.

(3) Passive, convenient for remote detection. The sensor does not need power supply, and the sensitivity of the sensor has little correlation with the length of the transmission fiber, which is convenient for remote detection.

Description of drawings

Fig. 1 is the structural representation of the utility model.

Fig. 2 is a structural schematic diagram of the mass block of the present invention.

detailed description

As shown in Figure 1 and Figure 2, a Michelson interference optical fiber acceleration sensor includes a cylinder 1, an upper limit pin 2, a first collimator 3, an optical coupler 4, a lower limit pin 5, a mass block 6, Second collimator 7, ring magnet 8.

The first collimator 3 is fixedly installed directly above the cylinder 1, and the second collimator 7 is fixedly installed directly below. have equal distances. The proof mass 6 is used to adjust the sensitivity and resonance frequency of the acceleration sensor, reflect the incident light from the first collimator 3 and the second collimator 7, and rotate the polarization state of the light by 90° clockwise.

The first collimator 3 and the second collimator 7 are connected to the optical coupler 4, and the optical coupler 4, the first collimator 3, the upper reflection surface of the proof mass 6 and the free space optical path between the two constitute the first A Michelson interference arm; the optical coupler 4 , the second collimator 7 , the lower reflection surface of the proof mass 6 and the free space optical path between them constitute the second Michelson interference arm.

A ring magnet 8 is arranged inside the cylinder body 1, and the ring magnet is used to generate a static magnetic field, and the mass block is in a suspended state by utilizing the magnetic flux removal effect.

The cylinder body 1 is provided with an upper limit pin 2, which is used to limit the maximum stroke of the mass block 6 moving upward, and the cylinder body 1 is provided with a lower limit pin 5, which is used to limit the maximum stroke of the mass block 6 moving downward;

The proof mass 6 is composed of a magnetic ring 601, a first Faraday rotator 602, and a second Faraday rotator 603. As shown in FIG. The high-reflection film surface of the mirror 602 is stacked with the high-reflection film surface of the second Faraday rotation mirror 603 , and then glue is dispensed and solidified in the magnetic ring 601 . The Faraday rotator is made of yttrium iron garnet single crystal. Under the action of a saturated magnetic field, when the light passes through the Faraday rotator, the polarization state changes by 45°. In the utility model, the optical signal is incident through the transmission surface (anti-reflection film) of the Faraday rotator, returns along the original optical path after passing through the Faraday rotator, and rotates 45° again to ensure that the polarization state of the optical fiber reflected by the Faraday rotator rotates 90°. The magnetic ring generates the saturation magnetic field required by the Faraday rotator, and generates a magnetic flux rejection effect with the ring magnet, so that the mass block 6 as a whole is in a one-dimensional free suspension state. The working wavelength of the Faraday rotator is 1550nm, and the two sides are coated with high-reflection coating and anti-reflection coating. The reflectivity of the high-reflection coating is greater than 99%, and the transmittance of the anti-reflection coating is greater than 99.9%. The high-reflection film surface of the first Faraday rotator 602 and the high-reflection film surface of the second Faraday rotator 603 are stacked, and then glue is dispensed and solidified in the magnetic ring. In actual production, when the natural frequency and sensitivity of the acceleration sensor need to be modulated, it can be Metal is nested on the quality block 6 for counterweight, so as to meet the design requirements of different sensors.

The splitting ratio of the optical coupler is 1:1, the working wavelength is 1550nm, and the insertion loss is less than 3.3dB.

The acceleration sensor uses the magnetostatic row flux effect to keep the mass 6 in a suspended state. When the acceleration of the environment where the sensor is located changes, the spatial position of the mass 6 will change. The first Faraday rotator 602 and the first collimator 3 , The distance between the second Faraday rotator 603 and the second collimator 7 will reversely change, causing the arm length of the Michelson interferometer to change, thereby causing a change in the phase of the sensing light signal. By real-time demodulation of the phase change, the Acceleration is available. The relationship between the displacement Δx of the mass block 6 and the phase difference Δφ is:

Among them, λ is the central wavelength of the laser light source.

The sensor also includes an optical isolator 9 , a laser light source 10 , a photodetector 11 and a phase demodulation circuit 12 . The continuous optical signal of the laser light source 10 enters the optical coupler 4 after passing through the optical isolator 9, and is divided into two beams of light with equal power and enters the optical path of the first Michelson interference arm and the second Michelson interference arm respectively.

When the environmental acceleration of the acceleration sensor is constant, the magnetostatic force makes the mass block 6 in a state of magnetic levitation. At this time, the mass block 6 is in a balanced state, and the phase difference between the two arms of the interferometer is stable. When the environmental acceleration changes, the mass block 6 vibrates within the range of the upper limit pin 2 and the lower limit pin 5, the distance between the mass block 6 and the two collimators changes, and the first Michelson interference arm of the interferometer , The reverse differential change of the second Michelson interference arm, that is, the length of one arm increases, the length of the other arm decreases, and the size is the same, the change of the optical path difference is 4 times of the displacement change of the mass block 6, which is more than the classic Michaelson The sensitivity of the inferior interferometric accelerometer is doubled. The change of the optical path difference will cause the change of the light intensity signal. After being detected by the photoelectric detection 11, the phase change of the sensing system can be demodulated in real time by using the 3*3 coupler demodulation method or the PGC demodulation method, and the phase change of the mass block 6 can be obtained. acceleration.

It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should belong to the protection scope of the appended claims of the present utility model.

Claims (3)

1. A Michelson interferometric fiber optic acceleration sensor, characterized in that it includes a cylinder (1), an upper limit pin (2), a first collimator (3), an optical coupler (4), a lower limit pin ( 5), mass block (6), second collimator (7), ring magnet (8); the first collimator (3) is fixedly installed directly above the cylinder (1), and the second collimator is fixedly installed directly below device (7), the mass block (6) is suspended inside the cylinder (1), and has an equal distance from the first collimator (3) and the second collimator (7); the mass block (6) is used for Adjust the sensitivity and resonant frequency of the acceleration sensor, reflect the incident light from the first collimator (3) and the second collimator (7), and rotate the polarization state of the light by 90° clockwise; The first collimator (3), the second collimator (7) are connected to the optical coupler (4), the upper reflective surface of the optical coupler (4), the first collimator (3), and the proof mass (6) And the free-space optical path between the two constitutes the first Michelson interference arm; the optical coupler (4), the second collimator (7), the lower reflection surface of the proof mass (6) and the free The spatial optical path constitutes the second Michelson interference arm; A ring magnet (8) is arranged inside the cylinder (1), and the ring magnet (8) is used to generate a static magnetic field, and the mass block (6) is in a suspended state by utilizing the magnetic flux removal effect; The cylinder body (1) is provided with an upper limit pin (2), which is used to limit the maximum stroke of the mass block (6), and the cylinder body (1) is provided with a lower limit pin (5), which is used to limit the mass block (6). 6) The maximum stroke of downward movement; The optical coupler (4) is connected to the optical isolator (9), and the optical isolator (9) is connected to the laser light source (10); the optical coupler (4) is connected to the photodetector (11), and the photodetector (11) is connected to Phase demodulation circuit (12). 2. A Michelson interferometric optical fiber acceleration sensor according to claim 1, characterized in that: the mass (6) is composed of a magnetic ring (601), a first Faraday rotator (602), a second Faraday rotator (603), one side of the Faraday rotator is coated with a high-reflection film, and the other side is coated with an anti-reflection film; the first Faraday rotator (602) has a high-reflection film surface and the second Faraday rotator (603) has a high-reflection film Then glue is dispensed and solidified in the magnetic ring (601). 3. A Michelson interferometric optical fiber acceleration sensor according to claim 2, characterized in that: the magnetic ring (601) generates a saturated magnetic field to ensure that the Faraday rotator produces a magneto-optical effect, and the polarization state of the incident and reflected light Rotate by 90°, and generate a magnetic flux rejection effect with the ring magnet (8), so that the mass block (6) is in a one-dimensional free suspension state.