CN210689670U

CN210689670U - Cavity suspension channel type Mach-Zehnder interferometer on optical fiber line

Info

Publication number: CN210689670U
Application number: CN201921690574.0U
Authority: CN
Inventors: 崔鑫磊; 王东宁
Original assignee: China Jiliang University
Current assignee: China Jiliang University
Priority date: 2019-10-10
Filing date: 2019-10-10
Publication date: 2020-06-05
Anticipated expiration: 2029-10-10

Abstract

The utility model provides a Mach-Zehnder interferometer on cavity suspension channel type optic fibre line, including broadband light source, sensing head, spectral analyser. The sensing head is formed by writing micro-rings on the end faces of single-mode optical fibers at two ends by femtosecond laser and melting and butting the micro-rings. The method is characterized in that: the femtosecond laser writes a micro-ring structure, and the high temperature generated by welding discharge expands the air in the ring structure, so as to extrude the fiber core to form a suspension channel in the cavity. Since the channel size is very fine, about 3 μm, a portion of the light travels along the channel, a portion travels from the air cavity, and finally the two beams are coupled back into the single mode core. The light of the broadband light source is transmitted to the optical spectrum analyzer through the sensing head to form a Mach-Zehnder interferometer, the wavelength or the intensity drift of the characteristic peak of the transmission spectrum is measured, and the measured environmental parameters can be calculated. The utility model has the characteristics of the device is firm, preparation is simple etc, can be used to temperature, meet an emergency, atmospheric pressure, humidity, refracting index measurement.

Description

Cavity suspension channel type Mach-Zehnder interferometer on optical fiber line

Technical Field

The utility model provides a Mach-Zehnder interferometer on cavity suspension channel type optic fibre line belongs to the optical fiber sensing technology.

Background

Compared with the traditional sensor, the optical fiber sensor has the advantages of extremely high sensitivity and resolution, wide frequency band range, large dynamic range, no electromagnetic field interference and the like, and is practically applied in the scientific research fields of national defense and military departments, scientific research departments, manufacturing industries, energy industries, medical treatment and the like in recent years. The development trend of the sensor is sensitivity, accuracy, strong applicability, small size and intellectualization. Among a plurality of optical fiber sensors, the optical fiber sensor based on Mach-Zehnder develops rapidly, becomes an important branch in the research field of the optical fiber sensor, is widely applied to continuous real-time safety detection of physical quantities such as strain, stress, temperature, pressure, deformation, vibration, displacement and the like in a structure, and can also be used for monitoring the curing state of a composite material and the like. The method has important significance for safe use and integrity detection of airplanes, ships, buildings and the like. At present, various novel mach-zehnder interferometers and manufacturing methods thereof are diversified, such as a micro-tapered optical fiber based on an internal cavity, a staggered fusion-spliced optical fiber, an optical fiber grating, a special optical fiber and the like. All the above methods have great defects, and the built-in air cavity equipment is very fragile and poor in firmness; the repeatability of the dislocation fusion of the fiber core is difficult to realize, and a large amount of time is needed for manual assembly; the fiber grating writing process is complex, the cost is high, and the instability of the structure limits the application of the fiber grating to a certain extent; special optical fibers are expensive. Furthermore, their Free Spectral Range (FSR) is difficult to control accurately. To overcome these disadvantages, new techniques are needed to fabricate fiber optic sensing devices.

Fiber-on-line interferometers are an attractive miniature and multifunctional fiber sensing device with high sensitivity, and various types of fiber-on-line interferometer configurations have been developed, such as fabry-perot interferometers (FPI), Michelson Interferometers (MI), and mach-zehnder interferometers (MZI). MZI is relatively easy to make, and the structure is flexible, and sensitivity is high. The fiber in-line MZI is mainly constructed by using LPFG pairs, fiber tapers, mismatched cores and a sandwich structure consisting of SMF and hollow fibers. In this configuration, the fiber core mode and cladding mode interfere and propagate along nearly the same path length. Because the Refractive Index (RI) difference between the fiber core and cladding modes is small, the size of the interferometer is quite large, especially when a small Free Spectral Range (FSR) is required to improve device sensitivity. An effective way to achieve a compact device size while maintaining its high sensitivity is to utilize open air cavity based MZIs due to the large RI difference between the fiber core and air. However, the difficulty with this type of MZI device is poor robustness because part of the fiber material is removed by laser micromachining.

SUMMERY OF THE UTILITY MODEL

The utility model discloses it is not enough to prior art, provides a cavity suspension channel type optical fiber goes up mach-Zehnder interferometer, and the device is firm, prepare simple, with low costs, small characteristics, can be applied to the measurement of temperature, meeting an emergency, atmospheric pressure, humidity, refracting index.

The utility model provides a technical scheme that technical problem took does: a cavity suspension channel type Mach-Zehnder interferometer on an optical fiber line comprises a broadband light source, a sensing head and a spectrum analyzer, and the connection mode is as follows: one end of the sensing head is connected with the broadband light source, and the other end of the sensing head is connected with the spectrum analyzer; the method is characterized in that: the femtosecond laser writes a micro-ring structure on the end face of the single-mode fiber, and the high temperature generated by fusion discharge after the two micro-ring structures are butted enables the air in the ring structure to expand, so as to extrude the fiber core to form a suspended channel in the cavity. Because the channel size is extremely fine, the residual size of the channel is 3 mu m and is far smaller than the diameter of the fiber core of the original single-mode optical fiber by 9 mu m, one part of light is transmitted along the channel, one part of light is transmitted from the air cavity, and finally two beams of light are coupled back to the single-mode fiber core to form a transmission spectrum required by the Mach-Zehnder interferometer.

The core diameter and the fiber diameter of the (single-mode) fiber are 9 μm and 125 μm, respectively.

Compared with the prior art, the utility model beneficial effect be:

1. the sensing head adopts the common single-mode optical fiber with low price, and has the advantages of simple manufacture and low cost.

2. The sensor head has different sensitivities to temperature, stress, refractive index, air pressure and humidity, and can be used for simultaneously measuring environmental parameters.

3. The sensing head is firmer, the smoothness and the uniformity of the surface of the optical fiber are kept after welding, and the sensing head has good symmetry.

4. The manufacture of the sensing head is easy to control, the size of the cavity and the internal channel can be controlled by controlling the radius and the depth of the femtosecond writing ring structure and the electric quantity and the time of welding of a welding machine, and further the Free Spectral Range (FSR) of the sensing head can be controlled.

Drawings

In order to more clearly illustrate the embodiments or technical solutions of the present invention, the present invention will be further described with reference to the accompanying drawings and embodiments.

Fig. 1 is a schematic diagram of an application system of the present invention.

Fig. 2 is a schematic view of the structure of the femtosecond writing part on the surface of the single-mode fiber according to the present invention.

Fig. 3 is a final structural integrity diagram of the present invention.

In the figure, 1 is a broadband light source, 2 is a sensing head, 3 is a spectrum analyzer, 4 is a single-mode optical fiber, 4(a) is a single-mode optical fiber core, 4(b) is a single-mode optical fiber cladding, 5 is an annular groove, 6 is an air cavity, and 7 is a micro-channel in the air cavity.

Detailed Description

The invention is further described below with reference to the accompanying drawings and examples:

fig. 1 is a schematic diagram of an application system of the present invention, which includes a broadband light source 1, a sensing head 2, and a spectrum analyzer 3. The connection mode is as follows: broadband light source 1 is connected with the one end of sensing head 2, and the other end of sensing head 2 is connected with spectral analysis appearance 3.

Fig. 2 shows a schematic structural diagram of the sensing head 2 of the present invention during the femtosecond processing and preparation process, specifically, an annular groove with a width of 3 μm and a depth of 6 μm is engraved at a distance of 15 μm from the fiber core on the flattened end face of the single-mode fiber. The structure is formed by a single-mode optical fiber 4 comprising a single-mode optical fiber cladding 4(b), a single-mode optical fiber core 4(a) and an annular groove 5.

Fig. 3 shows the final structure diagram of the sensor head 2 of the present invention, which is the final structure formed by the fusion splicer after fusion splicing, and is composed of a single-mode fiber 4 including a single-mode fiber cladding 4(b) and a single-mode fiber core 4(a), an air cavity 6, and an air cavity inner micro-channel 7

The manufacturing method and the steps of the sensing head 2 are as follows: the first step is as follows: placing the cut-flat single-mode optical fiber on a femtosecond processing platform, and finding out the midpoint of the optical fiber to determine a focal plane; secondly, writing a ring structure by taking the middle point of the optical fiber as the center of a circle, wherein the width of the ring structure is 3 mu m, and the depth of the ring structure is 3 mu m, so that the structure shown in FIG. 2 is obtained; thirdly, ultrasonically cleaning the annular structure in the figure 2 to ensure that no residue exists in the annular structure; the fourth step: two identical structures of figure 2 were fused.

With reference to fig. 1, 2 and 3, a specific working principle is described: the sensing head 2 is of a cavity suspension channel structure formed by combining femtosecond writing and melting, the sensing head 2 receives a light beam emitted from the broadband light source 1, one part of the light beam is guided into a fiber core by a micro channel, and the other part of the light beam is propagated into the fiber core from an air cavity to form an output spectrum of the Mach-Zehnder interferometer.

The above-mentioned embodiments, further detailed description of the objects, technical solutions and advantages of the present invention, it should be understood that the above description is only the embodiments of the present invention, and is not intended to limit the present invention, and any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A cavity suspension channel type Mach-Zehnder interferometer on an optical fiber line comprises a broadband light source, a sensing head and a spectrum analyzer, and the connection mode is as follows: one end of the sensing head is connected with the broadband light source, and the other end of the sensing head is connected with the spectrum analyzer; the method is characterized in that: the femtosecond laser writes a micro-ring structure on the end face of the single-mode fiber, and the high temperature generated by fusion discharge after the two micro-ring structures are butted enables the air in the ring structure to expand, so as to extrude the fiber core to form a suspended channel in the cavity.

2. A cavity suspended channel type mach-zehnder interferometer as defined in claim 1 wherein: the femtosecond laser writes the micro-ring structure, two micro-ring structures are in fusion butt joint, the high temperature generated by fusion discharge enables the air in the ring structure to expand, and then the fiber core is extruded to form a suspension channel in the cavity, because the channel size is extremely fine, one part of light is transmitted along the channel, one part of light is transmitted from the air cavity, and finally two bundles of light are coupled back to the single-mode fiber core.

3. The cavity-suspended channel type mach-zehnder interferometer for an optical fiber line as claimed in claim 1, wherein: the fiber core diameter and the fiber diameter of the single-mode fiber are respectively 9 micrometers and 125 micrometers; core index 1.4682; the length of the cavity is about 50 μm consistent with the length of the suspension channel; the diameter of the suspension channel in the cavity is about 3 μm.