CN211785115U - Optical fiber end surface micro-cantilever sensor - Google Patents

Abstract

The utility model discloses an optical fiber end-face micro-cantilever beam sensor. The optical-fiber end-face micro-cantilever beam sensor comprises: an optical fiber; Being a polymer structure, the cantilever structure includes struts and micro-cantilevers; the micro-cantilever is parallel to the end face of the optical fiber. The optical end-face micro-cantilever beam prepared by the femtosecond laser two-photon polymerization technology of the utility model is a polymer material, the elasticity is larger than that of the silicon-based material, and the detection sensitivity can be greatly increased; the preparation method belongs to the additive manufacturing, and realizes the optical fiber and the cantilever beam. The integrated structure is compact; it does not cause any damage or damage to the optical fiber itself; at the same time, it saves processing time and makes the manufacturing method more flexible. The micro-cantilever beam on the end face of the optical fiber, which is cured by the femtosecond laser two-photon polymerization technology proposed by the utility model, has the characteristics of small size and high elasticity, and can be applied to many fields.

Description

An optical fiber end-face micro-cantilever sensor

technical field

The utility model relates to an optical fiber end face micro-cantilever beam sensor, which belongs to the technical field of sensors.

Background technique

Optical fiber sensors can have outstanding advantages such as high sensitivity, high precision, strong anti-interference ability, large dynamic response range, high pressure resistance, and corrosion resistance.

Existing fiber optic sensors are generally fabricated by the following methods:

Femtosecond laser ablation uses ultra-short pulses of femtosecond laser to directly reduce the material of the fiber end face. When the laser pulse is incident, the energy generated by the absorption of photons by the fiber material will rapidly accumulate in the absorption layer with a thickness of only a few nanometers. The temperature value of the electrons generated in an instant will be much higher than the melting point of the material, and the designated area of the fiber will eventually reach a high-density, ultra-hot, high-pressure plasma state to achieve non-thermal ablation of the fiber. In the hydrogen sensor fabricated by this method, the cantilever beam structure is formed by the material of the optical fiber itself, which has high rigidity and is not conducive to the deformation of the cantilever beam; in addition, the workload of this method is large, and the surface of the processed structure is rough, which makes the resolution of the sensor. lower.

Focused ion beam milling uses the accelerated and focused ion beam emitted by the ion source as the incident beam, and the fiber material is sputtered and stripped in the process of high-energy ions colliding with the atoms on the surface of the fiber, thereby realizing the specified area of the fiber end face. Subtractive manufacturing. In the hydrogen sensor fabricated by this method, the cantilever beam structure is also formed by the material of the optical fiber itself, and the rigidity is large, which is not conducive to the deformation of the cantilever beam; and the production method is time-consuming and inefficient.

Silicon cantilever sticking method, use UV curing glue to directly stick commercial silicon cantilever beam on the end face of optical fiber, or stick silicon cantilever beam to the end face of the encapsulation tube, and then encapsulate the optical fiber. This kind of sticking method requires high precision The micro-manipulator is easy to fall off, the straightness of the cantilever beam is difficult to control, and the rigidity of the silicon-based material is large, which is not conducive to the deformation of the cantilever beam.

Utility model content

In order to overcome the problems existing in the prior art, the utility model provides an optical fiber end face micro-cantilever beam sensor, including:

Optical fibers, including core and cladding;

The cantilever beam structure is polymerized on one end face of the optical fiber by femtosecond laser two-photon polymerization technology;

The cantilever beam structure is a polymer structure, and the cantilever beam structure includes pillars and micro-cantilever beams;

The first end of the strut is combined with the cladding of the fiber end face; one end of the micro-cantilever beam is fixed on the second end of the strut, and the other end of the micro-cantilever beam is suspended above the fiber core to form a cantilever, the micro-cantilever beam The beam is parallel to the end face of the fiber.

Further, along the direction perpendicular to the end face of the optical fiber, the projection of the cantilever on the end face of the optical fiber covers the fiber core.

Further, the thickness of the micro-cantilever beam of the sensor is not more than 10 μm, the width is not more than 100 μm; the height of the pillar is not more than 200 μm.

Further, the optical fiber end-face micro-cantilever beam sensor is a hydrogen sensor, and the surface of the micro-cantilever beam is coated with a hydrogen-sensitive film.

Further, the hydrogen sensitive membrane is a palladium membrane.

Further, the thickness of the palladium film is less than 1 μm.

Further, the thickness of the palladium film is 50-150 nm.

Further, the thickness of the micro-cantilever beam of the hydrogen sensor is not more than 5 μm, the width is in the range of 5-30 μm; the height of the pillar is 20-80 μm.

Further, the sensor is any one of a temperature sensor, a refractive index sensor, a humidity sensor, a vibration signal sensor, a magnetic field sensor, and a biological sensor.

In the optical fiber end-face micro-cantilever beam sensor of the utility model, the optical end-face micro-cantilever beam prepared by the femtosecond laser two-photon polymerization technology is a polymer material, and its elasticity is larger than that of a silicon-based material, which can greatly improve the response time without increasing the reaction time. Increase the detection sensitivity; the preparation method belongs to additive manufacturing, which realizes the integration of the optical fiber and the cantilever beam, and has a compact structure; does not cause any damage or damage to the optical fiber itself, thereby protecting the integrity of the optical fiber; at the same time, the processing time is greatly saved , and the structural design is more flexible, making the manufacturing method more flexible, and providing a great guarantee for meeting the needs of different environments.

The micro-cantilever beam on the end face of the optical fiber, which is cured by the femtosecond laser two-photon polymerization technology proposed by the utility model, has the characteristics of small size and high elasticity, and can be applied to many fields.

Description of drawings

1 is a schematic structural diagram of an optical fiber end-face micro-cantilever hydrogen sensor according to an embodiment of the present invention;

Fig. 2 is the scanning electron microscope diagram 1 of the optical fiber end face micro-cantilever hydrogen sensor according to the embodiment of the present utility model;

Fig. 3 is the scanning electron microscope diagram 2 of the optical fiber end face micro-cantilever hydrogen sensor according to the embodiment of the present utility model;

Fig. 4 is the processing optical path system of utilizing femtosecond laser two-photon polymerization technology to prepare optical fiber end face micro-cantilever hydrogen sensor in the embodiment of the present utility model;

5 is the reflection spectrum of the micro-cantilever Fabry-Perot interferometer of the optical fiber end face of the hydrogen sensor according to the embodiment of the utility model;

6 is the spectral drift of the reflection spectrum with the change of hydrogen concentration during the hydrogen test of the embodiment of the present utility model;

7 is an exponential relationship curve of a certain interference valley wavelength with the hydrogen concentration drift during the hydrogen test according to the embodiment of the present invention.

Reference number:

10-fiber, 12-core, 11-cladding, 20-pillar, 30-microcantilever.

Detailed ways:

The technical solutions of the present utility model will be described in further detail below through the accompanying drawings and embodiments.

FIG. 1 is a schematic structural diagram of an optical fiber end face micro-cantilever beam sensor according to an embodiment of the present invention.

The optical fiber end-face micro-cantilever sensor includes an optical fiber 10 and a cantilever structure. The optical fiber 10 includes an inner core 12 and a cladding 11 for covering the core 12 . The cantilever beam structure of the present application is formed on the end face of the optical fiber 10 by femtosecond laser two-photon polymerization technology.

The cantilever beam structure includes struts 20 and micro-cantilever beams 30 . Wherein, the first end of the strut 20 is combined with the end face of the optical fiber 10 . One end of the micro-cantilever beam 30 is fixedly formed on the second end of the pillar 20 , and the other end of the micro-cantilever beam 30 is suspended to form a cantilever. Wherein, the micro-cantilever is parallel to the end face of the optical fiber. An air gap is formed between the fiber end face and the cantilever of the micro-cantilever beam 30 , and the distance of the air gap is the height of the pillar 20 .

By using femtosecond laser two-photon polymerization technology, the surface of the fabricated microcantilever is relatively smooth and has good parallelism with the fiber end face, forming an extrinsic Fabry-Perot interferometer. The cantilever formed by the femtosecond laser two-photon polymerization technology is a polymer material, and the polymer is more elastic than the silicon-based material, which can greatly increase the detection sensitivity without increasing the reaction time.

Through the scanning electron microscope images shown in FIG. 2 and FIG. 3 , the polymer micro-cantilever beam 30 can be clearly distinguished, and the cantilever beam structure is closely combined with the end face of the optical fiber 10 . In the SEM image of FIG. 2 , in order to clearly indicate the position of the fiber core 12 , the position of the fiber core 12 is circled by a dotted line in the figure.

In the embodiment of the present invention, the post 20 avoids the position of the fiber core 12 , and the post 20 is combined at the cladding of the end face of the optical fiber and is staggered from the fiber core 12 . The cantilever of the micro-cantilever beam 30 is suspended above the fiber core 12 (see Figure 2), and the cantilever covers the fiber core in a direction parallel to the end face: along the direction perpendicular to the fiber end face, the projection of the cantilever on the fiber end face can cover fiber core.

In the embodiment of the present invention, as a preferred solution, the thickness range of the micro-cantilever beam 30 is less than 10 μm, and the width range is not more than 100 μm. The thickness and width of the micro-cantilever beam 30 affect the performance and reliability of the optical fiber end-face micro-cantilever beam sensor.

The cavity length of the extrinsic Fabry-Perot interferometer is the air gap between the fiber core 12 and the cantilever of the micro-cantilever beam 30 , and the distance of the air gap is the height of the strut 20 . Preferably, the height of the pillar 20 is not greater than 200 μm.

The thickness and width dimensions of the micro-cantilever beam 30 and the height dimensions of the pillar 20 are determined according to the specific application field of the optical fiber end-face micro-cantilever beam sensor.

The pillars are used as supports. In a specific embodiment, the pillars 20 have a length of 5-50 μm and a width of 5-100 μm. It can be understood that the length and width of the pillar are not limited thereto.

When the optical fiber end face micro-cantilever sensor of this embodiment is applied to a hydrogen sensor, the thickness of the micro-cantilever beam 30 is not more than 5 μm, the width is in the range of 5-30 μm; the height of the pillar 20 is 20-80 μm. As a preferred solution, the thickness of the micro-cantilever beam 30 is 3 μm, the width is 20 μm, and the height of the pillar 20 is 60 μm. The dimensions of the first end of the pillar 20 tightly coupled with the end face of the optical fiber 10 are 30 μm in length and 30 μm in width.

In this embodiment of the present invention, the optical fiber 10 may be a single-mode or multi-mode optical fiber, which is not specifically limited. In a specific embodiment, the diameter of the optical fiber 10 is 125 μm, and the cantilever length of the micro-cantilever beam 30 is 30 μm.

When the optical fiber end-face micro-cantilever beam sensor of this embodiment is applied to a hydrogen sensor, a hydrogen-sensitive film is also plated on the surface of the micro-cantilever beam 30 .

Preferably, the hydrogen-sensitive membrane is a palladium membrane.

The thickness of the palladium film layer is not more than 1 μm. As a solution for further improvement, the thickness of the palladium film is 50-150 nm.

The embodiment of the present utility model also provides a preparation method of an optical fiber end face micro-cantilever beam sensor, comprising the following steps:

Step S1 , cut one end of the optical fiber 10 flat, lay the optical fiber 10 flat on a glass slide, and drip photoresist on the end face of the optical fiber 10 , so that the end face of the optical fiber 10 is immersed in the photoresist, and covered with a cover glass.

Specifically, in this step, an optical fiber cleaver can be used to cut the single-mode optical fiber 10 flat; after the optical fiber 10 is flat and fixed on the glass slide, support parts are arranged on the glass slides on both sides of the optical fiber 10, and the support parts support the Cover glass to prevent the coverslip from squeezing the fiber 10.

By laying the fiber 10 flat is meant that the axis of the fiber 10 is parallel to the glass slide.

The support portion can be in various forms, for example, tapes can be attached or padded on the carrier sheets on both sides of the optical fiber 10, and in order to meet the thickness requirements of the support portion, multiple layers (two or more) of tapes can be attached; or, it is also possible to set Glass sheets or plastic blocks are used as supports. It can be understood that the specific form of the support portion is not limited to this. Preferably, the thickness of the support portion is 150-300 μm, and this setting can achieve better molding effect during femtosecond laser two-photon polymerization.

In step S2, a 3D lithography machine is used to form a polymer cantilever beam structure on the end face of the optical fiber 10 by using a femtosecond laser two-photon polymerization technology, and a sample of the optical fiber 10 having the cantilever beam structure is obtained.

In this step, the step of "using femtosecond laser two-photon polymerization technology to form a polymer cantilever beam structure on the end face of the optical fiber 10" includes: fixing the glass slide so that the sample is fixed on the three-dimensional precision displacement platform; controlling the three-dimensional precision displacement platform through the computer The movement of the displacement platform in the three directions of X, Y and Z enables the femtosecond laser beam to write the photoresist after passing through the processing optical path system.

As shown in FIG. 4 , a processing optical path system for preparing the micro-cantilever beam 30 on the end face of the optical fiber 10 by the femtosecond laser two-photon polymerization technology proposed by the present invention. The femtosecond laser beam is expanded by the beam expander to expand the laser spot by 2-3 times, and then passes through the attenuator and power meter in turn; the attenuator is used to adjust the laser power value, and the power meter is used to detect the laser power value; After the sub-reflection, the beam reaches the dichroic mirror. The near-infrared band beam in the beam is reflected by the dichroic mirror and enters the objective lens and then focused into the glue for processing. The visible light part of the beam passes through the dichroic mirror and then passes through the filter to enter the CCD imaging for real-time observation and curing. Phenomenon.

In this step, the glass slide can be fixed by the vacuum adsorption of the piezoelectric mobile platform, and after the sample is fixed on the three-dimensional precision displacement platform, the three-dimensional precision displacement platform is moved to make the sample at the initial processing point position of the initial processing plane, so that the femtosecond The spot convergence point of the laser beam is located at the initial processing point; the switch of the shutter diaphragm is controlled and the three-dimensional precision moving platform is driven to move, so that the laser beam starts from the end face of the optical fiber 10 and laterally aggregates the micro-cantilever beam 30;

In this step, a suitable cantilever beam structure can be designed through CAD software programming, and a reasonable moving path can be adjusted, and the interlayer spacing and line spacing can be optimized to a suitable spacing, and polymerization processing can be performed according to the designed path.

During the polymerization process, if the precision moving platform is used as the reference, then the laser beam is relatively scanning. The moving path can be designed according to the shape of the cantilever beam structure, so that the laser beam starts from the end face of the optical fiber 10 to perform plane layered scanning from bottom to top, and raster scanning is performed on each layer; in order to reduce the processing time, the line scanning in the layer adopts back and forth scanning. According to the focal depth of the selected objective lens, set the appropriate interlayer spacing to 0.25~1 μm, and the line spacing to 0.25~1 μm.

In this step, a high-power objective lens is selected as the processing objective lens, for example, a 50x air objective lens is selected; the femtosecond laser power with a wavelength of 1026 nm is set to an appropriate power, and the femtosecond laser power and displacement speed matching the selected objective lens are set. For example, in this specific embodiment, the femtosecond laser power is 0.5-4 mw, and the displacement speed is 0.05-1 mm/s.

Step S3, developing: after curing is completed, remove the cover glass on the sample, remove the tapes on both sides, and immerse the sample together with the slide glass in the developing solution, the unexposed photoresist is dissolved in the solution, and the cured The polymer cantilever structure is retained, and the polymer micro-cantilever 30 on the end face of the optical fiber 10 is obtained after curing.

In this step, the developing solution is a mixed solution of acetone and isopropanol mixed in a certain proportion (proportion), and is immersed in the mixed solution for several minutes.

Through the above method, the optical fiber end-face micro-cantilever sensor can be prepared.

The photoresist is polymerized by a femtosecond laser beam, and the cantilever beam formed is a polymer material, and the polymer is more elastic than a silicon-based material, which can greatly increase the detection sensitivity.

If the fiber end-face micro-cantilever sensor is a hydrogen sensor, the following steps need to be performed after step S3:

Step S4, sputtering palladium film: placing the sample in a magnetron sputtering coater, and using the magnetron sputtering coater to coat a hydrogen-sensitive film on the surface of the micro-cantilever beam 30 to prepare a hydrogen sensor.

In this step, the hydrogen-sensitive membrane is a palladium membrane. During coating, the end face of the optical fiber 10 can be made to face the palladium target, and the rotating substrate can be rotated to make the film sputter more uniform. By controlling the sputtering time, a palladium film layer with a thickness of not more than 1 μm can be obtained on the surface of the micro-cantilever beam 30 .

Figure 5 is the reflection spectrum of the micro-cantilever Fabry-Perot interferometer on the fiber end face. Near the wavelength of 1550nm, the free spectral range is about 20nm, and the cavity length of the interferometer is 60μm, which conforms to the relationship between the free spectrum and the cavity length: FSR=λ ² /2nL.

After preparing the optical fiber end-face micro-cantilever hydrogen sensor, the hydrogen test is carried out. The hydrogen test method includes:

Insert the optical fiber end-face micro-cantilever sensor into the microchannel containing hydrogen-nitrogen mixed gas, and connect the broadband light source and the spectrometer through a 3dB coupler to measure the reflection spectrum; adjust the concentration of hydrogen in the hydrogen-nitrogen mixed gas, and use the spectrometer to track and monitor the reflection spectrum with the hydrogen gas. Concentration drift.

In the hydrogen test, two flow controllers can be used to control the flow of pure hydrogen produced by the hydrogen generator and pure nitrogen released by the nitrogen bottle, and then the gas is mixed through a three-port connector, and finally the mixed gas passes through the plastic micro For channel output, the size of the plastic microchannel is, for example, about 500 μm. During the test, the concentration of hydrogen in the hydrogen-nitrogen mixed gas can be adjusted by adjusting the flow controller. Figure 6 shows the spectral shift of the reflectance spectrum of the device as a function of hydrogen concentration. With the increase of hydrogen concentration, the spectrum shows a clear blue shift. Figure 7 summarizes the exponential relationship of the wavelength of an interference valley as a function of hydrogen concentration.

In the optical fiber end-face micro-cantilever beam sensor of the utility model, the optical end-face micro-cantilever beam prepared by the femtosecond laser two-photon polymerization technology is a polymer material, and its elasticity is larger than that of a silicon-based material, which can greatly improve the response time without increasing the reaction time. Increase the detection sensitivity; the preparation method belongs to additive manufacturing, which realizes the integration of the optical fiber and the cantilever beam, and has a compact structure; does not cause any damage or damage to the optical fiber itself, thus protecting the integrity of the optical fiber; at the same time, the processing time is greatly saved , and the structural design is more flexible, making the manufacturing method more flexible, and providing a great guarantee for meeting the needs of different environments.

The fiber end-face micro-cantilever beam solidified by the femtosecond laser two-photon polymerization technology proposed by the utility model has the characteristics of small size and high elasticity, and can be applied in many fields: the micro-cantilever beam can be used as a hydrogen sensor after palladium plating; It has high thermo-optic coefficient and can be used as temperature sensor, which is a kind of temperature sensor with high sensitivity; because the cavity between the microcantilever beam and the end face of the fiber is open, it can be used for refractive index sensing; because the polymer absorbs water Expansion, it can be used for humidity measurement; according to the vibration characteristics of the micro-cantilever, it can also be used for the measurement of vibration signals such as sound waves and vibration; by replacing the magnetic photoresist, it can be used as a magnetic field sensor; by biologically modifying the micro-cantilever, it can be used for biosensors .

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention In the protection scope of the present invention, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. A fiber-optic end-face micro-cantilever sensor, comprising:

an optical fiber including a core and a cladding;

the cantilever beam structure is polymerized on one end face of the optical fiber through a femtosecond laser two-photon polymerization technology;

the cantilever beam structure is a polymer structure and comprises a support and a micro-cantilever beam;

the first ends of the legs are coupled to the cladding of the fiber end face; one end of the micro-cantilever beam is fixed at the second end of the pillar, the other end of the micro-cantilever beam is suspended above the fiber core to form a cantilever, and the micro-cantilever beam is parallel to the end face of the optical fiber.

2. The fiber-optic end-face micro-cantilever sensor of claim 1, wherein the projection of the cantilever onto the fiber-optic end-face covers the fiber core in a direction perpendicular to the fiber-optic end-face.

3. The fiber-optic end-face micro-cantilever sensor of claim 1, wherein the micro-cantilever of the sensor has a thickness of no more than 10 μm and a width of no more than 100 μm; the height of the pillars is not more than 200 μm.

4. The fiber-optic end-face micro-cantilever sensor according to claim 1, wherein the fiber-optic end-face micro-cantilever sensor is a hydrogen sensor, and the surface of the micro-cantilever is plated with a hydrogen sensitive film.

5. The fiber-optic end-face micro-cantilever sensor according to claim 4, wherein the hydrogen-sensitive membrane is a palladium membrane.

6. The fiber-optic end-face micro-cantilever sensor of claim 5, wherein the palladium membrane has a thickness of less than 1 μm.

7. The fiber-optic end-face micro-cantilever sensor according to claim 6, wherein the palladium membrane has a thickness of 50 to 150 nm.

8. The fiber-optic end-face micro-cantilever sensor according to claim 4, wherein the micro-cantilever of the hydrogen sensor has a thickness of no more than 5 μm and a width in the range of 5-30 μm; the height of the support is 20-80 μm.

9. The fiber-optic end-face micro-cantilever sensor according to claim 1, wherein the sensor is any one of a temperature sensor, a refractive index sensor, a humidity sensor, a vibration signal sensor, a magnetic field sensor, and a biosensor.

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