CN1632629A - "One" shape polarization maintaining optical fiber and production method thereof - Google Patents

Abstract

This invention relates to 'l'shape bias fiber, which has the structure from inner to outer of basic tube layer, outer cover layer, stress action area, inner layer and core layer. It is characterized by the 'l' shape of long bar action area. This invention also relates to a 'l' shape of bias fiber process method.

Description

"One" shape polarization maintaining optical fiber and production method thereof

1. Technical field:

The invention relates to a polarization-maintaining optical fiber, in particular to a "one"-shaped polarization-maintaining optical fiber and a production method thereof.

2. Background technology:

Polarization maintaining fiber, also known as polarization maintaining fiber, is a kind of special fiber. It has a wide range of applications in the field of wavelength division multiplexing communication systems and fiber optic sensors. Especially in the field of fiber optic sensors, it is the core sensing component of military sensors such as fiber optic gyroscopes, fiber optic hydrophones, and optical integrated devices.

According to the different cross-sectional structures, there are four common types of polarization-maintaining optical fibers commercially available in the world, namely: panda type, bow tie type, elliptical jacket type and elliptical core type. The first three types belong to the stress-induced type, while the latter type belongs to the shape-determined type.

At present, silica optical fiber is generally produced by first manufacturing a preform (the preform of polarization-maintaining optical fiber is also called polarization-maintaining optical rod), and then drawing the preform, and polarization-maintaining optical fiber is no exception.

Stress-induced polarization-maintaining rods are generally doped or placed around the fiber core with substances with high expansion coefficients (such as boron, aluminum, germanium, etc.), and through some special treatment, these doped or placed The area becomes a non-circularly symmetrical stress application area.

Since the expansion coefficient of boron is greater than that of silicon, even greater than that of germanium, after boron doping, during the cooling process after collapsing into a rod, and during the cooling process of the optical fiber after drawing, the stress action area will produce tensile stress on the core layer and inner cladding. . Since the stress action area is anisotropic, the stress on the core layer is different along different radial directions of the fiber, resulting in different refractive indices of the core layer in different radial directions, which is the so-called birefringence phenomenon. When light propagates in such an optical fiber, the speed of propagation in each direction is also different, forming a corresponding fast axis and slow axis.

Linearly polarized light is injected into a certain axis of the polarization-maintaining fiber core layer, and after a certain transmission distance, its polarization state can still be basically maintained. The fast axis and slow axis generally coincide with the long and short axes of the stress action zone. The parameter that characterizes the performance of polarization maintenance is polarization crosstalk or extinction ratio. The smaller the polarization crosstalk (it is generally a negative number) and the larger its absolute value, the better the polarization-maintaining performance of the fiber.

Since the transmission of light energy in the optical fiber is not limited to the core layer, a considerable part of the optical power is transmitted in the inner cladding layer adjacent to the core layer, and boron has a large attenuation in the working wavelength range (1200-1600nm) of the silica fiber. Therefore, the inner cladding is generally introduced into several kinds of stress-induced polarization-maintaining optical fibers, which can greatly reduce the attenuation of the optical fiber, and make the attenuation level of the optical fiber reach the applicable level below 2.0dB/km.

For ordinary panda-type and bow-tie-type polarization-maintaining fibers, to meet the requirements of sensors such as fiber optic gyroscopes, the ratio of the area of the stress action area to the cross-sectional area of the fiber is generally greater than 10%, and the proportion of some products even exceeds 15%. The stress action area is often doped with boron and other expensive substances. If the stress action area is too large, not only the manufacturing cost will increase obviously, but also the manufacturing difficulty will become greater. In addition, if the area of the stress action area is too large, it will also cause problems in the performance of the polarization-maintaining fiber in terms of environmental temperature adaptability, bending resistance, mechanical strength, etc., resulting in poor overall performance of the polarization-maintaining fiber.

Although the relative area of the stress action area of some elliptical jacket-type polarization-maintaining fibers is relatively small, the technical indicators such as the beat length of these elliptical-jacket-type polarization-maintaining fibers at some operating wavelengths (such as 1310nm or 1550nm) are difficult to meet the requirements of fiber optic gyroscopes. and other sensor requirements.

3. Technical content:

In view of the above-mentioned shortcomings of other structures of polarization-maintaining optical fibers, the purpose of the present invention is to provide a polarization-maintaining optical fiber with a new shape of the stress application area and a smaller ratio of the area of the stress application area to the cross-sectional area of the optical fiber.

The technical content of the present invention is: a new type of polarization-maintaining optical fiber, its cross-sectional structure from outside to inside is: base tube layer, outer cladding, stress action area, inner cladding and core layer, which is characterized by: stress action area The shape is "one" long strip.

The main components of each layer of the "one" shape polarization maintaining fiber are as follows:

Substrate layer: silica;

Outer cladding: silicon dioxide, doping elements: phosphorus and fluorine;

Stress action area: silicon dioxide, doping elements: boron, germanium, etc.;

Inner cladding: silicon dioxide, can also be properly doped with germanium and fluorine;

Core layer: silicon dioxide, doping element: germanium.

The structure and manufacturing method of the Chinese patent elliptical jacket-type optical fiber preform and polarization-maintaining optical fiber, the publication number is CN1410375A, discloses the structure and manufacturing method of the elliptical jacket-type optical fiber preform and polarization-maintaining optical fiber. The structure of the "one"-shaped polarization-maintaining optical fiber of the present invention is similar to that of the elliptical jacket-shaped polarization-maintaining optical fiber: that is, the stress action area has both a major axis and a short axis; the difference is that the "one"-shaped polarization-maintaining fiber of the present invention The minor axis of the stress action zone of the polarization maintaining fiber is very thin compared with that of the stress action area of the elliptical jacket type polarization maintaining fiber, which can significantly improve important performance indicators such as beat length and polarization crosstalk of the polarization maintaining fiber.

The proportion of the area of the stress acting area of the "one"-shaped polarization maintaining optical fiber to the cross-sectional area of the optical fiber is less than 10%, and the proportion of some models can even be less than 5%.

Another object of the present invention is to provide a production method of "one"-shaped polarization maintaining optical fiber.

At present, silica optical fiber is generally produced by first manufacturing a preform and then drawing the preform, and polarization maintaining optical fiber is no exception.

The "one"-shaped polarization-maintaining optical fiber is made of the "one"-shaped polarization-maintaining rod using the known drawing technology, that is, the polarization-maintaining rod is thinned into a quartz fiber, and two layers of acrylic paint are immediately coated on its periphery for protection. The coating is then cured by ultraviolet light to produce a "one"-shaped polarization-maintaining optical fiber.

Since the "one"-shaped polarization-maintaining optical fiber is made from the "one"-shaped polarization-maintaining optical rod, the cross-sectional structure of the "one"-shaped polarization-maintaining optical rod should also be: base tube layer, outer cladding 1. The stress action area, the inner cladding and the core layer, the shape of the stress action area is a "one" long strip shape, and the area of the stress action area accounts for less than 10% of the cross-sectional area of the optical rod.

The MCVD method is a well-known method for producing preforms. Using this method, the production of "one"-shaped polarization-maintaining rods is basically the same as the production of bow-tie-type polarization-maintaining rods. The etching process of the light rod carves the stress action area on both sides of the inner wall of the substrate very transparently, so that the stress action area of the collapsed polarization maintaining light rod is bow tie-shaped; The etching process does not completely penetrate the stress action area on both sides of the inner wall of the substrate tube, so that the stress action area there is left with a little thickness, even if the stress layer deposited in the base tube is not completely separated, so that the collapsed preservation The stress action area of the polarizer is in the shape of a "one" long strip.

The main steps of known manufacturing bow-tie type polarization maintaining optical fiber are:

1. Pretreat the base tube first, which can achieve the effect of preheating the base tube and effectively eliminating impurities and air bubbles on the inner wall of the base tube;

2. The deposition process is carried out subsequently, and the deposition process is followed by outer cladding deposition, stress layer deposition, inner cladding deposition and core layer deposition; where the etching process is carried out after the stress layer deposition process is completed, so that the stress inside the substrate tube at the heated place The layer is gradually etched through;

3. After the deposition is completed, perform forward and reverse collapse on the base tube to make a solid bow-tie type polarization-maintaining light rod;

4. After the collapse, the polarization-maintaining light rod is polished to obtain a quartz-like transparent bow-tie type polarization-maintaining light rod.

5. Thinning the polarization-maintaining rod to obtain a bow-tie type polarization-maintaining optical fiber.

The production method of "one"-shaped polarization-maintaining optical fiber, the production steps are as follows:

1. Pretreatment of the substrate tube, to preheat the substrate tube and effectively eliminate impurities and bubbles on the inner wall of the substrate tube;

2. Carry out the deposition process. The deposition process is followed by outer cladding deposition, stress layer deposition, inner cladding deposition and core layer deposition; where after the stress layer deposition process is finished, directional etching is carried out, so that the stress layer inside the substrate tube at the heated place It is gradually etched, and the stress action area at this place is not completely etched, so that the stress action area at this place has a little thickness, and the stress layer deposited in the substrate tube is not completely separated; directional etching is to make the substrate tube not Rotate again, there is fluorine-containing corrosive gas in the base tube; outside the base tube, use a bunch of fire heads or two fire heads that burn on both sides to move back and forth along the axis of the base tube;

3. Perform forward collapse and reverse collapse on the base tube to make a solid "one"-shaped polarization-maintaining light rod;

4. Polish the polarization-maintaining light rod to obtain a quartz transparent "one"-shaped polarization-maintaining light rod;

5. Thin the polarization-maintaining light rod into a quartz optical fiber, and immediately coat two layers of acrylic paint on its periphery for protection, and the coating is then cured by ultraviolet light to obtain a "one"-shaped polarization-maintaining optical fiber.

In the above production method, when a bundle of fire heads is used outside the substrate tube during directional etching, the bundle of fire heads moves back and forth along the axial direction of one side of the substrate tube. After one side is etched, the substrate tube is turned 180 degrees, and then The other side of the tube is etched.

In the above production method, when two beams of fire heads are used on both sides of the substrate tube for directional etching, the two beams of fire heads will go back and forth on both sides of the substrate tube symmetrically along the axis of the substrate tube in the plane passing through the center of the substrate tube. Move to heat the tube walls.

With the continuous improvement of MCVD equipment, the substrate tubes that can be used are getting thicker and thicker, and the wall thickness of the substrate tubes is also allowed to be larger. It is also longer and longer, the production cost can be significantly reduced, and the uniformity of various parameters of a single batch of optical fibers can be significantly improved.

The present invention can use base tubes with multiple outer diameters (the maximum outer diameter can reach more than 30mm), multiple wall thicknesses and multiple cross-sectional areas as polarization maintaining rods. The range of the outer diameter of the base tube is 12-35mm, and the range of the wall thickness 1.5-3.5mm, and the cross-sectional area ranges from 70-300mm ² .

The advantages that the present invention has are:

1. The "one"-shaped polarization maintaining fiber has the characteristics of small stress action area.

2. The "one" shape polarization maintaining fiber has good polarization maintaining performance, environmental temperature adaptability, bending resistance and mechanical strength.

4. Description of drawings:

Fig. 1 is a schematic diagram of the cross-sectional structure of the "one"-shaped polarization-maintaining optical fiber of the present invention.

Fig. 2 is a schematic diagram of the manufacturing process of the "one"-shaped polarization-maintaining light rod of the present invention.

Five, specific embodiment:

As shown in Figure 1, the "one"-shaped polarization maintaining fiber has a cross-sectional structure from the outside to the inside: the base tube layer 11, the outer cladding layer 12, the stress action area 13, the inner cladding layer 14 and the core layer 15. The stress The shape of the active area 13 is a long strip of "one".

Embodiment 1, as shown in Figure 2, the pretreatment of the base pipe, the deposition of the outer cladding, the deposition of the stress layer, the directional etching, the deposition of the inner cladding, the deposition of the core layer, forward collapse, reverse collapse and In the polishing process, a "one"-shaped polarization-maintaining light rod is obtained, and the area of the stress action area accounts for 4% of the cross-sectional area of the light rod; the outer diameter of the base tube is 30mm, the wall thickness is 2.5mm, and the cross-sectional area is 216mm ² ; During the directional etching process, the sulfur hexafluoride corrosive gas is passed into the substrate tube; outside the substrate tube, two beams of fire heads that are fired on both sides are symmetrically placed on the substrate tube along the axis of the substrate tube in the plane passing through the center of the substrate tube. The two sides of the tube move back and forth to heat the tube wall so that the stress layer inside the substrate tube at the heated place is gradually etched, and a little thickness is left in the stress action zone at the place.

Example 2. The "one"-shaped polarizing rod obtained in Example 1 was thinned into a quartz optical fiber with a diameter of 125 μm, and immediately coated with two layers of acrylic paint on its periphery for protection. After curing treatment, a "one"-shaped polarization-maintaining fiber with a diameter of 125 μm was obtained, and the area of the stress action area of the polarization-maintaining fiber accounted for 4% of the cross-sectional area of the polarization-maintaining fiber; the "one"-shaped polarization-maintaining fiber The main technical indicators are shown in Table 1.

Table 1 Indicator name performance specification Working wavelength(nm) 1310 cut-off wavelength(nm) 1100-1300 Mode Field Diameter (μm)(@1310nm) 6±1 Attenuation (dB/km) (@1310nm) ≤1.5 Fiber Diameter (μm) 125±1 Core/clad concentricity (μm) ≤1.0 Coating diameter (μm) 245±10 Screening Strength (kpsi) 100 Beat length(mm)(@1310nm) ≤3 Polarization Crosstalk (Extinction Ratio) (dB) ≤-23(1km optical fiber) Working temperature (℃) -45--+70

Claims (7)

1. The "one"-shaped polarization-maintaining optical fiber has a cross-sectional structure from the outside to the inside: the base tube layer (11), the outer cladding layer (12), the stress action area (13), the inner cladding layer (14) and the core layer ( 15), it is characterized in that: the shape of the stress action area (13) is a long strip shape of "one". 2. The polarization maintaining optical fiber according to claim 1, characterized in that the area of the stress action region (13) accounts for less than 10% of the cross-sectional area of the optical fiber. 3. The cross-sectional structure of the "one"-shaped polarization maintaining rod is: base tube layer, outer cladding layer, stress action area, inner cladding layer and core layer from the outside to the inside. It is characterized by: the shape of the stress action area is " One" is a long strip. 4. The polarization maintaining optical rod according to claim 4, characterized in that the area of the stress acting region accounts for less than 10% of the cross-sectional area of the optical rod. 5. The production method of "one"-shaped polarization-maintaining optical fiber, the production steps are as follows: (1) Pretreatment of the substrate tube, to preheat the substrate tube and effectively eliminate impurities and air bubbles on the inner wall of the substrate tube; (2) Depositing, the deposition process is followed by outer cladding deposition, stress layer deposition, inner cladding deposition and core layer deposition; where after the stress layer deposition process is finished, directional etching is carried out to make the stress layer inside the substrate tube at the heated place It is gradually etched, and the stress action area at this place is not completely etched, so that the stress action area at this place has a little thickness, and the stress layer deposited in the substrate tube is not completely separated; directional etching is to make the substrate tube not Rotate again, there is fluorine-containing corrosive gas in the base tube; outside the base tube, use a bunch of fire heads or two fire heads that burn on both sides to move back and forth along the axis of the base tube; (3) Perform forward collapse and reverse collapse on the base tube to make a solid "one"-shaped polarization-maintaining light rod; (4) polishing the polarization-maintaining light rod to obtain a "one"-shaped polarization-maintaining light rod in the transparent shape of quartz; (5) Thin the polarization-maintaining light rod into a silica fiber, and immediately coat two layers of acrylic paint on its periphery for protection, and the paint is cured by ultraviolet light to obtain a "one"-shaped polarization-maintaining fiber. 6. The production method of polarization maintaining optical fiber according to claim 5, characterized in that during directional etching, a bunch of torches are used outside the substrate tube to move back and forth along the axial direction of one side of the substrate tube, and after one side is etched, the base tube The tube is flipped 180 degrees, and then the other side of the substrate tube is etched. 7. The method for producing polarization-maintaining optical fiber according to claim 5, characterized in that during directional etching, two beams of torches fired on opposite sides are used on the outside of the substrate tube, symmetrically along the axis of the substrate tube in the plane passing through the center of the substrate tube A back and forth movement is made on both sides of the substrate tube to heat the tube walls.

Images