CN106482765A - A kind of F P microcavity Fibre Optical Sensor and preparation method thereof - Google Patents

Abstract

The invention discloses a novel F-P microcavity optical fiber sensor and a manufacturing method thereof. In the optical fiber sensor involved in the present invention, a reflective surface is made in the optical fiber, and two reflective surfaces of the F-P microcavity sensor are formed with the end face of the optical fiber. The reflective surface is obtained by changing the refractive index of the fiber core through laser action. By controlling the pulse energy and focus position of the laser, the present invention only causes changes in the refractive index in the set part of the core area without damaging the optical fiber, thereby ensuring the integrity of the optical fiber and overcoming the existence of existing F-P cavity manufacturing methods. It has the characteristics of strong stability, small size, simple structure, easy production, good robustness, anti-interference from harsh environments, and short processing cycle, and achieves higher sensitivity, ultra-high resolution and a wide range of Refractive index sensing has broad application prospects in health detection and biochemical sensing.

Description

A kind of F-P microcavity optical fiber sensor and its manufacturing method

technical field

The invention relates to a novel F-P microcavity optical fiber sensor and a manufacturing method thereof, belonging to the field of optical fiber sensing.

Background technique

The all-fiber F-P (Fabry-Perot) interferometer sensor has a series of features such as simple structure, small size, light weight, anti-electromagnetic interference, chemical corrosion resistance, high sensitivity, suitable for long-distance measurement, and easy to form a large-scale sensor network. Advantages, has become a research hotspot at home and abroad, and has broad application prospects in aerospace, food safety, air quality monitoring, fire early warning, biomedicine and other industries. As the application field of FP interferometer expands day by day, there are many ways of making it. At present, the main production methods of all-fiber FP interferometers are:

(1) Fusion splicing of ordinary single-mode optical fiber and other different types of optical fiber, such as multi-mode optical fiber, photonic crystal optical fiber, hollow-core optical fiber, etc. However, the method of fusion splicing will lead to problems such as mismatch of light generation modes in different fibers, easy breakage of fusion splices, and poor repeatability of manual operation. At the same time, the use of special optical fibers increases the cost of the sensor.

(2) Perform pretreatment on the end face of the optical fiber, such as HF (hydrofluoric acid) chemical corrosion, multiple welding discharges, and coating on the end face of the optical fiber. This method needs to pre-process the end face of the optical fiber into some specific shapes, which increases the experimental procedures. More importantly, these methods cannot accurately control the cavity length and require a series of complicated manufacturing processes to assemble the separated optical fibers. , and these devices themselves are also very fragile.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of existing F-P cavity manufacturing methods, and provide a method for manufacturing optical fiber F-P microsensors, which is used to solve the problems of poor repeatability of existing F-P cavity manufacturing methods, difficulty in accurately controlling cavity length, complex assembly process, and device failure. Vulnerability, high cost and other issues.

In order to achieve the above object, the implementation of the present invention adopts the following technical solutions:

A kind of F-P microcavity optical fiber sensor, it is characterized in that, two reflecting mirrors are made in the optical fiber, constitute two reflective surfaces of F-P microsensor; Wherein a reflective mirror surface is formed by laser modulation optical fiber refractive index; Another reflective surface is Fiber end face.

Correspondingly, the present invention proposes a kind of optical fiber F-P microsensor manufacturing method, it is characterized in that, comprises the following steps:

(1) Process an end face at one end of the optical fiber as a reflector of the F-P microcavity;

(2) Place the optical fiber on a three-dimensional mobile platform so that the axis of the optical fiber is perpendicular to the incident direction of the laser;

(3) According to the F-P microcavity design parameter requirements, adjust the three-dimensional mobile platform to determine the cavity length;

(4) Focus the laser on the fiber core at a certain distance from the fiber end face to feed laser energy, so that the energy at this point exceeds the damage threshold of the fiber core material to form a modulation point with a refractive index different from that of the fiber core, forming an F-P microcavity another reflective surface.

Further, the end face of the optical fiber in the step (1) is cut into a flat surface on the optical fiber with a cleaver, or processed into a tapered surface.

Further, a layer of biochemically sensitive film is added on the end face of the optical fiber to form a film structure.

Further, the end face of the optical fiber in the step (1) is coated with a reflective film.

Further, the laser used is a femtosecond laser.

Further, the optical fiber is a single-mode optical fiber.

Furthermore, the manufacturing method of the optical fiber sensor of the present invention can be used for the microcavity fiber optic microsensor of the present invention.

The working principle of the present invention is as follows: focus the laser light on the fiber core of the fiber, and change the refractive index of the fiber core at the laser focus. The refractive index change area is used as a mirror surface 1 of an optical fiber microsensor based on an F-P microcavity; the end face with a certain distance from it in the axial direction is used as a mirror surface 2 of an F-P microcavity fiber sensor; The two mirrors of the micro-cavity fiber sensor; when the optical path difference between the two mirrors of the F-P micro-cavity fiber sensor or the reflectivity of the mirror changes, it will cause changes in the interference fringes, thereby realizing the measurement of physical quantities;

Compared with prior art, a kind of optical fiber sensor device based on F-P microcavity of the present invention has the following advantages:

(1) By controlling the pulse energy and focus position of the laser, the change of the refractive index is only caused in the set part of the core area without damaging the fiber, which ensures the integrity of the fiber and improves the resistance of the F-P microcavity fiber microsensor to the outside world Capability and robustness to harsh environment interference;

(2) The processing cycle is extremely short, and the time used for the experiment is extremely short, no more than 0.1 second, which greatly improves the production efficiency of the device;

(3) The preparation method has a wide range of applications, and can make microsensors based on F-P microcavity fiber optics on various optical fibers;

(4) The fabricated device has simple and compact structure, stable performance and high flexibility;

(5) Laser processing technology has good repeatability, high precision, low cost and good controllability;

(6) In terms of refractive index measurement, the microsensor structure of the present invention has at least an order of magnitude improvement in sensitivity compared to the same type of intensity-modulated optical fiber sensor that has been reported.

Description of drawings

Fig. 1 is the structural diagram of the optical fiber microsensor that the end face that the present invention makes flat;

Fig. 2 is the structural diagram of the tapered optical fiber microsensor that the present invention makes;

Fig. 3 is the schematic diagram that the present invention utilizes laser to make fiber optic microsensor;

Fig. 4 is the device schematic diagram of test device signal among the present invention;

Figure 5 shows the variation of the reflection spectrum of the F-P fiber optic microsensor with a cavity length of 50um and the end surface cut flat with the external refractive index;

Figure 6 shows the change of the bottom of the reflection spectrum at a certain wavelength of the F-P fiber optic microsensor with a cavity length of 50um and a flattened end face;

Fig. 7 is the structural diagram of coated optical fiber microsensor of the present invention;

In all the drawings, the same reference numerals are used to represent the same components or structures, wherein: 11—optical fiber, 12—three-dimensional displacement platform, 13—laser beam, 14—microscopic objective lens, 15—laser, 22—plane Cavity mirror 1, 23—plane cavity mirror 2, 31—tapered cavity mirror 1, 32—tapered cavity mirror 2, 33—partial enlarged view of mirror 2, 41—broadband light source, 42—optical fiber circulator , 43—spectrometer, 44—the cavity length described in Embodiment 1 is a 50um optical fiber microsensor; 73—film structure.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

The microsensor processing of the present invention is specifically as follows.

Embodiment 1: A reflective surface is a flat processing method

(1) Use a cleaver to cut an end face of the optical fiber as a mirror of the F-P microcavity;

(2) Place the optical fiber on a three-dimensional mobile platform so that the axis of the optical fiber is perpendicular to the incident direction of the laser;

(3) According to the F-P microcavity parameter requirements, adjust the three-dimensional mobile platform to determine the cavity length;

(4) Make the laser focus on the core of the fiber through the objective lens of the microscope, feed the laser energy, and form a modulation point of the refractive index at the laser focusing part in the fiber to form another mirror of the F-P microcavity.

As shown in Fig. 1, the characteristic of the optical fiber microsensor of making is, comprise a single-mode optical fiber (11), the end reflective mirror surface two (13) of single-mode optical fiber cut flat and the reflective mirror surface one (12) apart from the end face certain distance . Described reflection mirror surface one (12) and reflection mirror surface two (13) have constituted F-P microcavity; Described reflection mirror surface one (12) is that the optical fiber core refractive index changes because laser action; Described reflection mirror surface two (13) is composed of Fresnel reflection on the end face of the optical fiber; the distance between the first mirror surface (12) and the second mirror surface (13) is determined according to actual needs.

Embodiment 2: A reflective surface is a tapered processing method

(1) Use a fusion splicer to extend the optical fiber into a tapered shape as a mirror of the F-P microcavity;

(2) Place the optical fiber on a three-dimensional mobile platform so that the axis of the optical fiber is perpendicular to the incident direction of the laser;

(3) According to the F-P microcavity parameter requirements, adjust the three-dimensional mobile platform to determine the cavity length;

(4) Make the laser focus on the core of the fiber through the objective lens of the microscope, feed the laser energy, and form a modulation point of the refractive index at the laser focusing part in the fiber to form another mirror of the F-P microcavity.

As shown in FIG. 2 , this embodiment is basically the same as Embodiment 1, and the special feature is that the second reflecting mirror ( 22 ) is a tapered microsensor, and a smaller optical fiber microsensor can be obtained.

Embodiment 3: Fabrication of a fiber optic microsensor based on an F-P microcavity

(1) Place the optical fiber with the end face cut flat on the three-dimensional mobile platform;

(2) Adjust the three-dimensional mobile platform so that the axis of the optical fiber is perpendicular to the incident direction of the laser;

(3) Adjust the three-dimensional mobile platform to determine the cavity length;

(4) Make the laser focus on the core of the fiber through the objective lens of the microscope, feed the laser energy, and form a modulation point of the refractive index at the laser focusing part in the fiber to form another mirror of the F-P microcavity.

As shown in Figure 1, the characteristic of the optical fiber microsensor of making is that the optical fiber (11) is placed on the three-dimensional mobile platform (32), so that the axial direction of the optical fiber (11) is perpendicular to the incident direction of the laser beam (33); Observe and adjust the position of the optical fiber (11), so that the laser beam output by the laser (35) is gathered at the center of the optical fiber (11) through the microscope objective lens (34); the laser energy is fed into the optical fiber (11) The internally written F-P interferometer, different cavity lengths correspond to different free spectral ranges (FSR), and in practical applications, cavity lengths of different lengths can be conveniently made according to requirements;

In this embodiment, the first reflective mirror surface is formed by changing the refractive index due to the action of the laser, and the second reflective mirror surface is an end face of an optical fiber; the wavelength of the femtosecond pulsed laser is 520nm; the optical fiber is Ordinary single-mode fiber, the core diameter is about 8.3um.

Refractive index sensing experiment of the sensor of the present invention:

Embodiment four:

(1) This F-P Refractive Index Sensing Device

Light source (41) is connected the input port of a fiber optic circulator (42), the output of fiber optic circulator (42) is connected the F-P fiber microsensor (44) that the femtosecond pulse laser described in embodiment one prepares, and reflection port connects Spectrum analyzer (43); the light that light source (41) sends is first imported into optical fiber micro-refractive index sensor (44) through described optical fiber circulator (42), then the external refractive index signal that optical fiber micro-sensor (44) collects Through the optical fiber circulator (42), it is finally displayed on the spectrum analyzer (43).

(2) The F-P Refractive Index Sensing Results

Figure 5 shows the change of the spectrum of the optical fiber microsensor with a cavity length of 50um in different refractive index solutions. It can be seen from the figure that in the solution, the intensity at the bottom of the interference spectrum changes rapidly, and Figure 6 shows that at a certain wavelength The light intensity at the bottom of the interference spectrum varies with the refractive index. Experiments show that when the refractive index is 1.44, the sensitivity can reach 1902.8dB/RIU, which is the highest known optical fiber refractive index sensitivity based on intensity modulation so far. This is at least an order of magnitude improvement over reported sensitivities.

Embodiment 5: Laser modulation F-P cavity combined with optical fiber coating structure

(1) Feed in laser energy, form a modulation point of refractive index at the laser focusing part in the fiber, and form another mirror of the F-P microcavity;

(2) Coating on the end face of the optical fiber;

As shown in Figure 7, a laser modulation F-P cavity combined with an optical fiber coating structure, the embodiment of the F-P cavity is basically the same as the first embodiment, and its feature is that the coating or adsorption film (73) on the end surface of the optical fiber, such as metal, biochemical sensitive material Membranes can be made into various basic physical quantities and biochemical microsensors.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (9)

1. a kind of F-P microcavity Fibre Optical Sensor has two reflecting mirrors it is characterised in that making in optical fiber, constitutes F-P microcavity and passes Two reflectings surface of sensor；One of mirror surface is formed by Laser Modulation optical fibre refractivity；Another reflecting surface is light Fine end face.

2. F-P microcavity Fibre Optical Sensor according to claim 1 is it is characterised in that light path between described two reflecting mirrors During the reflectivity change of difference or mirror surface, the change of interference fringe can be caused, to realize the measurement of physical quantity.

3. a kind of F-P microcavity Fibre Optical Sensor manufacture method is it is characterised in that comprise the steps：

(1) process an end face in optical fiber one end, this end face is as a reflecting mirror of F-P microcavity；

(2) optical fiber is placed in three-dimensional mobile platform, make optical fiber is axially perpendicular to laser light incident direction；

(3) required according to F-P microcavity design parameter, adjust three-dimensional mobile platform, determine that chamber is long；

(4) make laser focusing fibre core position feed-in laser energy apart from fiber end face certain distance in fiber core, make this Place's energy exceedes core material damage threshold and forms the refractive index modulation point different from fibre core, and another of composition F-P microcavity is anti- Penetrate face.

4. Fibre Optical Sensor manufacture method according to claim 1 is it is characterised in that optical fiber end in described step (1) Face, is in one plane of fiber cut with cutter, or is processed into a conical surface.

5. Fibre Optical Sensor manufacture method according to claim 1 is it is characterised in that addition of one on described fiber end face The biochemical sensitive membrane of layer, forms membrane structure.

6. Fibre Optical Sensor manufacture method according to claim 1 is it is characterised in that optical fiber end in described step (1) Reflectance coating is coated with face.

7. Fibre Optical Sensor manufacture method according to claim 1 is it is characterised in that the laser using is femtosecond laser.

8. Fibre Optical Sensor manufacture method according to claim 1 is it is characterised in that described optical fiber is single-mode fiber.

9. a kind of Fibre Optical Sensor based on F-P microcavity is it is characterised in that it is made using any one of claim 3-8.