CN103268000B - By corroding the interferometer that expanded core fiber is realized - Google Patents

Abstract

The interferometer realized by corroding the expanded core fiber is especially suitable for the field of optical fiber sensing. It solves the problems of large size, poor sensitivity and high manufacturing cost faced by the current interferometer based on the fiber structure. The interferometer includes a core expansion area (2) and an erosion area (3) fabricated on an optical fiber (1). Production method: remove the coating from the optical fiber (1), push the two ends of the optical fiber (1) to the middle while heating the optical fiber (1) to make the core expansion area (2), and then corrode the core expansion in the radial direction with HF solution In the middle of zone (2), corrosion zone (3) is formed. Heating methods include: spark discharge, _CO2 laser focusing or flame heating. The diameter of the optical fiber (1) is D ₁ , the maximum diameter of the expanded core area (2) is D ₂ , the length is 2L ₁ +L ₂ , the length of the corrosion area (3) is L ₂ , and the depth is H. The laser signal is divided into two or more paths during propagation, and interference fringes are generated at the output end of the interferometer.

Description

Interferometer realized by corroding expanded core fiber

technical field

The invention relates to an interferometer, which is especially suitable for the field of optical fiber sensing.

Background technique

With the advancement of optical fiber sensing technology, various sensing devices with different principles and structures are emerging. One of the more important passive optical devices based on optical fiber structure has been widely used. This is the MZ interferometer. Its working principle It is the optical splitter that divides the original optical signal into two or more channels, so that the optical signals of different channels pass through the unreasonable path, resulting in an optical path difference, and the beam combiner at the end of the interferometer combines the optical signals of different channels. Interference occurs.

Since the width of the interference fringes of the MZ interferometer is directly related to the length of the fiber between the beam splitter and the beam combiner, the longer the fiber, the denser the interference fringes will be, and the stress or temperature parameters can be applied to this fiber to achieve stress or is a temperature sensor. The traditional MZ interferometer based on optical fiber structure generally pulls out two cones on the optical fiber at a certain distance. The first cone is equivalent to a beam splitter, which divides the optical signal in the fiber core into the cladding for transmission, and the second cone It is equivalent to a beam combiner, which can recombine the optical signals in the cladding to the core, and finally interfere. The MZ interferometer of this structure is simple to manufacture, but because the optical fiber between the two cones needs to be removed from the coating and keep the outer surface clean, and the length of this section of optical fiber is usually long, the sensitivity is low when used in the sensor field, making limited in practical applications. The other is to replace the two cones with long-period fiber gratings, in which the long-period fiber grating plays the role of coupling the optical signal from the core to the cladding and from the cladding back to the core. This MZ interferometer requires a fiber grating writing device, which is very expensive. There are other optical fiber MZ interferometers with other structures that need to use special optical fibers, and their production costs are greatly increased.

To sum up, the current problems faced by interferometers based on optical fiber structures are: large size, poor sensitivity, and high manufacturing cost.

Contents of the invention

The technical problem to be solved by this invention is:

The problems faced by the interferometer based on fiber optic structure at present are: large size, poor sensitivity, and high manufacturing cost.

Technical scheme of the present invention is:

An interferometer realized by corroding a core-expanded optical fiber, the interferometer includes a core-expanded area 2 and an etched area 3 fabricated on an optical fiber 1 .

Production method: remove the coating from the optical fiber 1, push the two ends of the optical fiber 1 toward the middle while heating the optical fiber 1 to make the core expansion area 2, and then corrode the middle of the core expansion area 2 in the radial direction with HF solution to form the corrosion area 3 . Heating methods include: spark discharge, _CO2 laser focusing or flame heating.

The diameter of the optical fiber 1 is D ₁ , the maximum diameter of the expanded core area 2 is D ₂ , the length is 2L ₁ +L ₂ , the length of the corrosion area 3 is L ₂ , and the depth is H.

D ₁ =50-500 μm.

D ₂ =1.1D ₁ to 10D ₁ .

L ₁ =0.5D ₁ to 10D ₁ .

L ₂ =0.5L ₁ ~5L ₁ .

0.1D ₂ ≤ H<0.5D ₂ .

Compared with the prior art, the present invention has the following beneficial effects:

The interferometer manufactured by fabricating the expanded core region on the fiber and then corroding it is small enough in both radial and axial dimensions, so that only a small dose is required for the measurement of the refractive index of gaseous or liquid substances. Compared with the traditional sensing structure, which ranges from a few centimeters to tens of centimeters, the size is greatly reduced. In addition, due to the small radial size of the corroded corrosion area, the fiber cladding is very thin or there is no fiber cladding at all, so that the transmission state of the laser is very sensitive to the change of the refractive index of the surrounding object to be measured, which increases the sensitivity. Moreover, the manufacturing process is simple and the cost is low.

Description of drawings

Figure 1 shows the structure of an interferometer with a part of the cladding etched away.

Fig. 2 Schematic diagram of propagation of the interferometer signal with a portion of the cladding etched away.

Figure 3 shows the structure of the interferometer with the entire cladding removed.

Figure 4. Schematic diagram of propagation of the interferometer signal with the entire cladding removed.

Figure 5 shows the structure of the interferometer with a part of the core etched away.

Fig. 6 is a schematic diagram of the propagation of the interferometer signal with a part of the core etched away.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

Implementation

An interferometer realized by corroding a core-expanded optical fiber, as shown in FIG. 1 , is characterized in that the interferometer includes a core-expanded area 2 and an etched area 3 fabricated on an optical fiber 1 .

Production method: remove the coating from the optical fiber 1, push the two ends of the optical fiber 1 toward the middle while heating the optical fiber 1 to make the core expansion area 2, and then corrode the middle of the core expansion area 2 in the radial direction with HF solution to form the corrosion area 3 . Heating methods include: spark discharge, _CO2 laser focusing or flame heating.

The diameter of the optical fiber 1 is D ₁ , the maximum diameter of the expanded core area 2 is D ₂ , the length is 2L ₁ +L ₂ , the length of the corrosion area 3 is L ₂ , and the depth is H.

D ₁ =50-500 μm.

D ₂ =1.1D ₁ to 10D ₁ .

L ₁ =0.5D ₁ to 10D ₁ .

L ₂ =0.5L ₁ ~5L ₁ .

0.1D ₂ ≤ H<0.5D ₂ .

When the depth of corrosion is less than the cladding thickness of the expanded core area 2, as shown in Figure 1, the propagation path of the light in the interferometer is shown in Figure 2. After the laser signal enters the expanded core area 2, it is divided into two paths, one of which is Keep propagating in the fiber core, and the other path propagates in the cladding layer. After continuing to propagate, the optical signal in the cladding layer is divided into two paths, one path continues to propagate in the cladding layer, and the other path is coupled to the corrosion area outside the fiber 3 . As the light continues to propagate, it goes through the opposite process of entering the interferometer, and finally interferes at the other end of the interferometer, producing interference fringes.

When the depth of corrosion is equal to the cladding thickness of the expanded core area 2, as shown in Figure 3, the propagation path of the light in the interferometer is shown in Figure 4. After the laser signal enters the expanded core area 2, it is divided into two paths, one of which is Keep propagating in the core, and the other path propagates in the cladding. After continuing to propagate, the optical signal in the cladding is coupled to the corrosion area 3 . As the light continues to propagate, it goes through the opposite process of entering the interferometer, and finally interferes at the other end of the interferometer, producing interference fringes.

When the depth of corrosion is greater than the cladding thickness of the expanded core area 2, as shown in Figure 5, the light propagation path in the interferometer is shown in Figure 6, and the laser signal is divided into two paths after entering the expanded core area 2, one of which is Keep propagating in the fiber core, and the other path propagates in the cladding. After continuing to propagate, the optical signal in the cladding is coupled to the corrosion area 3, and the optical signal in the fiber core is divided into two paths, and one path is coupled to the corrosion area 3. The other way continues to propagate in the fiber core. As the light continues to propagate, it goes through the opposite process of entering the interferometer, and finally interferes at the other end of the interferometer, producing interference fringes.

Claims (1)

1. The interferometer realized by corroding the core-expanding optical fiber is characterized in that: the interferometer includes a core-expanding area (2) and an etching area (3) made on the optical fiber (1); Production method: remove the coating from the optical fiber (1), push the two ends of the optical fiber (1) to the middle while heating the optical fiber (1) to make the core expansion area (2), and then corrode the core expansion in the radial direction with HF solution In the middle of the zone (2), a corrosion zone (3) is formed; heating methods include: electric spark discharge, CO ₂ laser focusing or flame heating; The diameter of the optical fiber (1) is D ₁ , the maximum diameter of the core expansion zone (2) is D ₂ , the length of the core expansion zone (2) is 2L ₁ +L ₂ , the length of the corrosion zone (3) is L ₂ , and the depth is H ; D ₁ =50～500μm; D ₂ =1.1D ₁ ~10D ₁ ; L ₁ = 0.5D ₁ ~ 10D ₁ ; L ₂ =0.5L ₁ ~5L ₁ ; 0.1D ₂ ≤ H<0.5D ₂ .