CN111337060A - Hybrid sensor based on vernier effect of parallel structure and manufacturing method thereof - Google Patents

Abstract

The invention discloses a hybrid sensor based on a vernier effect of a parallel structure and a manufacturing method thereof, and the hybrid sensor comprises a Michelson interferometer and a Fabry-Perot interferometer which are arranged in parallel, wherein the Michelson interferometer comprises a single-mode fiber a, a spherical structure and a special fiber PCF which are sequentially arranged along the fiber transmission direction, one end of the single-mode fiber a is fixedly connected with one side of the spherical structure, the other side of the spherical structure is fixedly connected with one end of the special fiber PCF, the Fabry-Perot interferometer comprises a single-mode fiber b, a silica micro-tube b and a single-mode fiber c which are sequentially arranged along the fiber transmission direction, one end of the single-mode fiber b is fixedly connected with one end of the silica micro-tube b, and the other end of the silica micro-tube b is fixedly connected with one end. The invention has the advantages of simple structure and manufacture, high sensitivity, high stability, low temperature cross sensitivity and the like.

Description

A hybrid sensor based on the vernier effect of a parallel structure and its manufacturing method

technical field

The invention relates to a sensor and a manufacturing method thereof, in particular to a hybrid sensor based on the vernier effect of a parallel structure and a manufacturing method thereof, belonging to the field of optical fiber sensors.

Background technique

Optical fiber sensors have attracted much attention due to their advantages such as low transmission loss, corrosion resistance, large measurement dynamic range, and anti-electromagnetic interference. They have been widely used in bridge health monitoring, metallurgy, aerospace and military, especially in flammable, explosive and strong electromagnetic fields. There are great advantages in the sensing of disturbed environments. Due to their unique advantages, they can measure a variety of physical quantities, such as temperature, refractive index, strain, humidity, and more. Among them, temperature and refractive index play an important role in the sensing field.

Fiber Michelson interferometer sensor is a very classic fiber optic interferometer sensor. It is designed based on the principle of Michelson interferometer. It belongs to double-beam or multi-beam reflection interferometer. Photonic crystal fibers have attracted more and more attention in the field of optical fibers due to their high birefringence, high nonlinearity, and no-cut-off single-mode transmission. Fiber Fabry-Perot interferometer is a multi-beam reflection sensor, which is mainly composed of two parallel reflection surfaces with high reflectivity in the cavity. Compared with the optical fiber transmission interferometer, the optical fiber reflection interferometer structure has the advantage of simpler application. The vernier effect was originally used in the vernier caliper to improve the accuracy of its length measurement, but now the vernier effect is also used more and more in the field of optical fiber sensing to improve the sensitivity of the sensor. By tracking the large envelope signal formed by the two superimposed signals, the sensitivity of the sensor can be greatly improved compared to a single one that does not use the vernier effect. However, most of the vernier effects reported so far are in series structure and have some problems such as temperature cross-sensitivity and complex structure fabrication.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a hybrid sensor based on the vernier effect of a parallel structure and a manufacturing method thereof, which are simple to manufacture and have high sensitivity.

For solving the above-mentioned technical problems, the technical scheme adopted in the present invention is:

A hybrid sensor based on the vernier effect of a parallel structure is characterized in that it includes a Michelson interferometer and a Fabry-Perot interferometer arranged in parallel, and the Michelson interferometer includes a single-mode fiber a, a spherical structure and a special Optical fiber PCF, one end of the single-mode fiber a is fixedly connected to one side of the spherical structure, and the other side of the spherical structure is fixedly connected to one end of the special optical fiber PCF. The Fabry-Perot interferometer includes single-mode fibers b arranged in sequence along the optical fiber transmission direction. , silica microtube b and single-mode optical fiber c, one end of single-mode optical fiber b is fixedly connected to one end of silica microtube b, and the other end of silica microtube b is fixedly connected to one end of single-mode optical fiber c.

Further, the Michelson interferometer and the Fabry-Perot interferometer are connected in parallel through a coupler.

Further, the Michelson interferometer also includes a silica microtube a, one end of which is sleeved outside the other end of the special optical fiber PCF and is fixedly connected to the other end of the special optical fiber PCF.

Further, the Michelson interferometer is the sensing part of the sensor, and its interference intensity is expressed as follows:

where I ₁ and I ₂ are the light intensities of the core and cladding modes, respectively, λ is the wavelength in vacuum, L ₁ =1.8cm is the cavity length of the Michelson interferometer, and Δn _eff is the difference between the core and cladding modes difference in effective refractive index.

Further, the Fabry-Perot interferometer is the reference part of the sensor, and its interference intensity is expressed as follows:

where I ₃ and I ₄ are the light intensity reflected at the interface between the two ends of the silica microtube b and the single-mode fiber b and the single-mode fiber c, respectively, λ is the wavelength in vacuum, and L ₂ =120 μm is the Fabry- The cavity length of the Perot interferometer, n is the refractive index of the air in the microtubule.

Further, the light intensity output by the Michelson interferometer and the Fabry-Perot interferometer in parallel is:

I = I _S + I _R (3)

Therefore, the free spectral range FSR of the interference lines of the two interferometers can be expressed as:

The generation of the vernier effect requires a small difference in the free spectral range between the two parallel sensors; it can be known from equations (4) and (5) that the change of FSR can be achieved by changing the cavity length of the two interferometer sensors;

The total output spectrum of two sensors with similar FSR in parallel is the result of the combined action of two single sensors. The output spectrum obtained after this parallel connection will generate a large envelope, and the free spectral range of the large envelope can be expressed as follows:

Sensitivity amplification can be achieved by tracking the trough data of this large envelope rather than the trough data of a single sensing line, and the amplification factor is:

A method for making a hybrid sensor based on a parallel structure vernier effect, which is characterized by comprising the following steps:

Step 1: Make a Michelson interferometer, make a spherical structure, and then splicing the special optical fiber PCF and silica microtubes on both sides of the spherical structure in turn;

Step 2: Make a Fabry-Perot interferometer, splicing one end of the single-mode fiber b and the silica microtube b, and then find the splicing point with the help of an industrial microscope, and turn the horizontal axis of the optical fiber adjustment frame to cut the required length of the microtube , and finally splicing the other end of the silica microtube b with the single-mode fiber c;

Step 3: Set up the Michelson interferometer and the Fabry-Perot interferometer in parallel.

Further, in the step 1, the manufacturing process of the spherical structure is to first peel off the coating layer at 2 cm of the end face of a single-mode optical fiber with an optical fiber clamp, wipe it with cotton dipped in alcohol, and then use a fiber cleaver to cut the end face. Cut it flat and put it into one end of the fusion splicer to set appropriate parameters and then discharge. After several discharges, a spherical structure is completed.

Further, the second step is to first put one end of the cut single-mode optical fiber b and one end of the silica microtube b into the two ends of the fusion splicer, set appropriate parameters, and then use the automatic mode for fusion splicing, and then use the industrial microscope to perform fusion splicing. With the help of finding the fusion splicing point, turn the horizontal axis of the optical fiber adjustment frame to cut the required microtube length, and finally put one end of the cut single-mode fiber c and the other end of the silica microtube b into the two ends of the fusion splicer. After parameters, the automatic mode is used for welding.

Compared with the prior art, the present invention has the following advantages and effects: the sensor of the present invention has the advantages of simple structure, high sensitivity, high stability and low temperature cross-sensitivity. By introducing a new structure and vernier effect into the optical fiber sensing system, the sensitivity and stability of the sensing system can be greatly improved. In this patent, the vernier effect is achieved by connecting the Michelson interferometer and the Fabry-Perot interferometer in parallel, thereby obtaining the amplification of the sensor sensitivity. The invention can well improve the stability of the sensing system through the parallel structure, and the sensor based on the photonic crystal fiber Michelson interferometer can well perform liquid refractive index sensing and protect the fiber end face from external environment interference. The envelope can greatly improve the sensitivity of the sensing system.

Description of drawings

FIG. 1 is a schematic diagram of the Michelson interferometer of the hybrid sensor based on the parallel structure Vernier effect of the present invention.

FIG. 2 is a schematic diagram of the Fabry-Perot interferometer of the hybrid sensor based on the parallel structure Vernier effect of the present invention.

FIG. 3 is a schematic diagram of a hybrid sensor based on the Vernier effect of the parallel structure of the present invention.

Detailed ways

The present invention will be further described in detail by the following examples. The following examples are to explain the present invention and the present invention is not limited to the following examples.

As shown in FIG. 1 and FIG. 2 , a hybrid sensor based on the vernier effect of a parallel structure of the present invention includes a Michelson interferometer and a Fabry-Perot interferometer arranged in parallel. Mode optical fiber a1, spherical structure 2, special optical fiber PCF3 and silica microtube a4, one end of single-mode optical fiber a1 is fixedly connected to one side of spherical structure 2, and the other side of spherical structure 2 is fixed to one end of special optical fiber PCF3 For connection, one end of the silica microtube a4 is sleeved outside the other end of the special optical fiber PCF3 and is fixedly connected with the other end of the special optical fiber PCF3. The working principle of the Fabry-Perot interferometer is: when the incident light propagates along the core of the single-mode fiber a1 and encounters the spherical structure 2, due to the mismatch of the mode field, a part of the light in the core will be coupled into the cladding for transmission, Because of the existence of Fresnel reflection, the light in the core and the cladding will be reflected back at the end of the special fiber PCF3. Due to the different refractive indices of the two light transmission paths, when the two light beams meet again, there is a certain phase difference to cause interference. .

The Fabry-Perot interferometer includes a single-mode optical fiber b5, a silica microtube b6, and a single-mode optical fiber c7 arranged in sequence along the optical fiber transmission direction. One end of the single-mode optical fiber b5 is fixedly connected to one end of the silica microtube b6, and two The other end of the silicon oxide microtube b6 is fixedly connected to one end of the single-mode optical fiber c7. The working principle of the Fabry-Perot interferometer is: when the incident light propagates along the core of the single-mode fiber b5, at the interface between the two ends of the silica microtube b6, the single-mode fiber b5 and the single-mode fiber c7, due to the medium The difference in refractive index produces Fresnel reflection, which interferes when the reflected beam converges again at the single-mode fiber b5.

The Michelson interferometer 8 and the Fabry-Perot interferometer 9 are connected in parallel through the coupler 10. As shown in FIG. 3, both the Michelson interferometer 8 and the Fabry-Perot interferometer 9 are reflective sensors, so only one port is working. We call this port the worker side. The working ends of the Michelson interferometer 8 and the Fabry-Perot interferometer 9 are connected to one end of the same coupler 10 through an optical fiber, and the other end of the coupler 10 is connected to the light source 11 and the spectrum analyzer 12 respectively. After passing through the coupler 10, the light emitted by the light source 11 will be respectively transmitted to the Michelson interferometer 8 and the Fabry-Perot interferometer 9. These two sensors are both reflective types, and their reflection spectra will be analyzed by the spectroscopic analysis through the coupler 10. Instrument 12 accepted. The sensing part is separated from the reference part. In the actual application of the sensor, the sensing part is placed in the sensing environment, while the reference part is not placed in the sensing environment. Compared with the series structure, the parallel structure reduces the influence of external interference on the sensing performance, improves the stability of the system and is easy to manage.

The Michelson interferometer is the sensing part of the sensor, and its interference intensity is expressed as follows:

where I ₁ and I ₂ are the light intensities of the core and cladding modes, respectively, λ is the wavelength in vacuum, L ₁ =1.8cm is the cavity length of the Michelson interferometer, and Δn _eff is the difference between the core and cladding modes difference in effective refractive index.

The Fabry-Perot interferometer is the reference part of the sensor, and its interference intensity is expressed as:

where I ₃ and I ₄ are the light intensity reflected at the interface between the two ends of the silica microtube b and the single-mode fiber b and the single-mode fiber c, respectively, λ is the wavelength in vacuum, and L ₂ =120 μm is the Fabry- The cavity length of the Perot interferometer, n is the refractive index of the air in the microtubule.

The output light intensity of the Michelson interferometer and the Fabry-Perot interferometer in parallel is

I = I _S + I _R (3)

Therefore, the free spectral range FSR of the interference lines of the two interferometers can be expressed as:

The generation of the vernier effect requires a small difference in the free spectral range between the two parallel sensors; it can be known from equations (4) and (5) that the change of FSR can be achieved by changing the cavity length of the two interferometer sensors;

The total output spectrum of two sensors with similar FSR in parallel is the result of the combined action of two single sensors. The output spectrum obtained after this parallel connection will generate a large envelope, and the free spectral range of the large envelope can be expressed as follows:

Sensitivity amplification can be achieved by tracking the trough data of this large envelope rather than the trough data of a single sensing line, and the amplification factor is:

When the phase difference satisfies the condition of △φ=(2m+1)π(m=0,1,2…), the interference spectrum will appear a minimum value, and the wave trough wavelengths of the sensing and reference parts can be expressed as:

In the patent of the present invention, the wavelength demodulation method is used to solve the sensitivity of the sensor. The basic principle is that changes in external physical quantities such as temperature, refractive index, etc. will cause the shift of the trough wavelength. Then, by detecting the shift of the trough wavelength, the measured Changes in physical quantities to achieve the purpose of sensing. The greater the variation trend of the trough wavelength with the external physical quantity, the higher the sensitivity. Based on this principle, a vernier effect is proposed to increase its sensitivity. The sensor based on the vernier effect does not detect the trough movement of a single sensor, but the envelope movement after the vernier is superimposed. A small movement of the trough wavelength of a single sensor will cause a huge movement of the trough wavelength of its superimposed envelope, thus compared with a single sensor. In other words, the shift amount of the superimposed trough wavelength is increased, and its sensitivity is improved by detecting the shift amount of the superimposed trough wavelength. Specifically in this patent, the sensing cavity cavity length and the reference cavity cavity length are 1.8 cm and 120 μm, respectively. According to formulas (4) and (5), its free spectral range can be calculated as: FSR _S =12.6 nm, FSR _R =10 nm. According to formulas (6) and (7), the envelope free spectral range FSR _C =48.5 nm after superposition can be calculated, and the amplification factor is 3.8 times. That is to say, compared with the sensitivity obtained by measuring the trough wavelength of a single MI interferometer, the sensitivity coefficient can be increased by 3.8 times after being amplified by the vernier effect.

The invention innovatively proposes a hybrid structure of the Michelson/Fabry-Perot interferometer based on the vernier effect of the parallel structure. Stable encapsulation of the end of the all-fiber Michelson interferometer is achieved by splicing silica microtubes. This end encapsulation method can well protect the end of the all-fiber Michelson interferometer. It is not easily disturbed by the external environment during sensing and can realize liquid Sensing of refractive index. Compared with traditional single-mode fibers, photonic crystal fibers have lower temperature sensitivity and can solve the problem of temperature cross-sensitivity well in sensing applications. Because the reference part is isolated from the sensing part, the introduction of the vernier effect of the parallel structure makes the system more stable in sensing applications.

A manufacturing method of a hybrid sensor based on the vernier effect of a parallel structure, comprising the following steps:

Step 1: To make a Michelson interferometer, first use a fiber clamp to strip the coating layer about 2cm from the end face of a single-mode optical fiber, wipe it with cotton dipped in alcohol, and then use a fiber cleaver to cut the end face flat and put it into fusion splicing. One end of the machine is set with appropriate parameters and then discharged. After several discharges, a spherical structure is completed. Then, the special optical fiber PCF and the silica microtubes a are spliced sequentially on both sides of the spherical structure.

Step 2: To make a Fabry-Perot interferometer, firstly put one end of the cut single-mode fiber b and one end of the silica microtube b into the two ends of the fusion splicer, set appropriate parameters, and then use the automatic mode to splicing, and then use the industrial With the help of a microscope, find the fusion splicing point and rotate the horizontal axis of the optical fiber adjustment frame to cut the required microtube length. Finally, put one end of the cut single-mode fiber c and the other end of the silica microtube b into the two ends of the fusion splicer and set them appropriately. After the parameters are set, the automatic mode is used for welding.

Step 3: Set up the Michelson interferometer and the Fabry-Perot interferometer in parallel.

The sensor of the invention has the advantages of simple structure, high sensitivity, high stability and low temperature cross-sensitivity. By introducing a new structure and vernier effect into the optical fiber sensing system, the sensitivity and stability of the sensing system can be greatly improved. In this patent, the vernier effect is achieved by connecting the Michelson interferometer and the Fabry-Perot interferometer in parallel, thereby obtaining the amplification of the sensor sensitivity. The invention can well improve the stability of the sensing system through the parallel structure, and the sensor based on the photonic crystal fiber Michelson interferometer can well perform liquid refractive index sensing and protect the fiber end face from external environment interference. The envelope can greatly improve the sensitivity of the sensing system.

The above content described in this specification is merely an illustration of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or substitute in similar ways, as long as they do not deviate from the content of the description of the present invention or go beyond the scope defined by the claims, all It belongs to the protection scope of the present invention.

Claims (9)

1. a hybrid sensor based on parallel structure vernier effect, it is characterized in that: comprise the Michelson interferometer and the Fabry-Perot interferometer that are arranged in parallel, the Michelson interferometer comprises the single-mode fiber a, spherical structure that are arranged successively along the optical fiber transmission direction And the special fiber PCF, one end of the single-mode fiber a is fixedly connected to one side of the spherical structure, and the other side of the spherical structure is fixedly connected to one end of the special fiber PCF. Optical fiber b, silica microtube b, and single-mode optical fiber c, one end of single-mode optical fiber b is fixedly connected to one end of silica microtube b, and the other end of silica microtube b is fixed to one end of single-mode optical fiber c connect. 2 . The hybrid sensor based on the vernier effect of a parallel structure according to claim 1 , wherein the Michelson interferometer and the Fabry-Perot interferometer are connected in parallel through a coupler. 3 . 3. The hybrid sensor based on the vernier effect of a parallel structure according to claim 1, wherein the Michelson interferometer further comprises a silicon dioxide micropipe a, and one end of the silicon dioxide micropipe a is sleeved It is outside the other end of the special optical fiber PCF and is fixedly connected with the other end of the special optical fiber PCF. 4. The hybrid sensor based on the vernier effect of a parallel structure according to claim 3, wherein the Michelson interferometer is the sensing part of the sensor, and its interference intensity is expressed as follows:

where I ₁ and I ₂ are the light intensities of the core and cladding modes, respectively, λ is the wavelength in vacuum, L ₁ =1.8cm is the cavity length of the Michelson interferometer, and Δn _eff is the difference between the core and cladding modes difference in effective refractive index. 5. The hybrid sensor based on the vernier effect of a parallel structure according to claim 4, wherein the Fabry-Perot interferometer is the reference part of the sensor, and its interference intensity is expressed as follows:

where I ₃ and I ₄ are the light intensity reflected at the interface between the two ends of the silica microtube b and the single-mode fiber b and the single-mode fiber c, respectively, λ is the wavelength in vacuum, and L ₂ =120 μm is the Fabry- The cavity length of the Perot interferometer, n is the refractive index of the air in the microtubule. 6. The hybrid sensor based on the vernier effect of a parallel structure according to claim 5, wherein the output light intensity after the parallel connection of the Michelson interferometer and the Fabry-Perot interferometer is I = I _S + I _R (3) Therefore, the free spectral range FSR of the interference lines of the two interferometers can be expressed as:

The generation of the vernier effect requires a small difference in the free spectral range between the two parallel sensors; it can be known from equations (4) and (5) that the change of FSR can be achieved by changing the cavity length of the two interferometer sensors; The total output spectrum of two sensors with similar FSR in parallel is the result of the combined action of two single sensors. The output spectrum obtained after this parallel connection will generate a large envelope, and the free spectral range of the large envelope can be expressed as follows:

Sensitivity amplification can be achieved by tracking the trough data of this large envelope rather than the trough data of a single sensing line, and the amplification factor is:

7. The manufacturing method of the hybrid sensor based on the vernier effect of a parallel structure according to any one of claims 1-6, characterized in that it comprises the following steps: Step 1: Make a Michelson interferometer, make a spherical structure, and then splicing the special optical fiber PCF and silica microtubes on both sides of the spherical structure in turn; Step 2: Make a Fabry-Perot interferometer, splicing one end of the single-mode fiber b and the silica microtube b, and then find the splicing point with the help of an industrial microscope, and turn the horizontal axis of the optical fiber adjustment frame to cut the required length of the microtube , and finally splicing the other end of the silica microtube b with the single-mode fiber c; Step 3: Set up the Michelson interferometer and the Fabry-Perot interferometer in parallel. 8 . The method for manufacturing a hybrid sensor based on a parallel structure vernier effect according to claim 7 , wherein: in the step 1, the manufacturing process of the spherical structure is to first clamp an optical fiber on a single-mode optical fiber. 9 . Peel off the coating layer at 2cm of the end face, wipe it with cotton dipped in alcohol, then use a fiber cutter to cut the end face flat and put it into one end of the fusion splicer. Set the appropriate parameters and discharge it. After several discharges, a spherical structure is produced. Finish. 9 . The method for making a hybrid sensor based on a parallel structure vernier effect according to claim 7 , wherein the step 2 is to first sequentially connect one end of the cut single-mode optical fiber b and the silica microtube. 10 . b put one end into the fusion splicer and set the appropriate parameters at both ends to perform fusion splicing in automatic mode, and then find the fusion splicing point with the help of an industrial microscope and rotate the horizontal axis of the optical fiber adjustment frame to cut the required microtube length, and finally cut the cut One end of the single-mode optical fiber c and the other end of the silica microtube b are put into the fusion splicer. After setting appropriate parameters, the automatic mode is used for fusion splicing.

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