CN102023318A - Composition and preparation method of ultra-large mode area silicate optical fiber - Google Patents

Abstract

The invention provides a composition of a silicate optical fiber with an ultra-large mode area and a preparation method thereof. The fiber comprises a fiber core part and a fiber cladding part, wherein the formula comprises silicon oxide, boron oxide, aluminum oxide, lead oxide, potassium oxide, lanthanum oxide, yttrium oxide and rare earth oxide, the structure of the fiber is gain guide-refractive index reverse guide, the diameter of the fiber core of the gain guide-refractive index reverse guide fiber is far larger than that of the fiber core (4-10 mu m) of a common single mode fiber, and the area of a mode field can reach tens of thousands of square microns. The core diameter is within the range of 100-500 um; the cladding consists of multi-component glass, and the diameter of the cladding is about 250-650 um; the refractive index difference delta n between the fiber core and the cladding is less than 0.05-0.28%, and the problems of more than 100 mu m of mode field diameter and single-mode transmission characteristic are solved.

Description

Composition and preparation method of ultra-large mode area silicate optical fiber

technical field

The invention belongs to the field of optical materials and laser technology, and in particular relates to the composition and preparation method of an ultra-large modulus area silicate optical fiber.

Background technique

High-power fiber amplifiers and lasers are widely used in laser processing and other fields. Under high-power pumping, when the fiber core diameter is small, the fiber core and fiber end face are prone to catastrophic optical damage; when the fiber core diameter is large, the fiber due to stimulated Raman scattering and stimulated Brillouin scattering Serious nonlinear effects will be produced, which will affect the beam quality of the laser output.

Using optical fiber combining technology or large mode field fiber can theoretically avoid the constraints caused by the above factors, but the core diameter of the step-type large mode field fiber that has been realized so far for single-mode laser output is only 40 μm, while the photonic crystal fiber The maximum core diameter is 100 μm. When the core diameter is larger than 100 μm, near-field diffraction will seriously affect the beam quality of the laser.

In addition, the fiber bundle technology has not made a breakthrough. Therefore, it is of great significance to develop a super-large mode area, single-mode laser output fiber.

In traditional technology, methods such as reducing the numerical aperture and designing the refractive index distribution of the fiber are mainly used to realize the large mode field fiber. Reducing the numerical aperture will lead to weaker light guiding effect and increased loss; designing the refractive index distribution of the fiber may cause multi-mode oscillation problems; these two methods are to obtain a large mode field area by designing the fiber structure, which can currently be achieved The mode field area is only a few hundred square microns. Therefore, to achieve a mode field diameter of more than 100 μm and satisfy the single-mode transmission characteristics at the same time, it is difficult to realize the traditionally designed optical fiber structure.

In 2003, Siegman proposed a new concept of optical fiber, that is, gain-guided - index-antiguided optical fiber (gain-guided, index-antiguided, GG+IAG). The core refractive index of this fiber is smaller than the cladding refractive index (Δn<0), while the core refractive index of ordinary single-mode fiber is greater than the cladding refractive index.

Therefore, at the interface between the core and the cladding of the GG+IAG fiber, light cannot be transmitted according to the principle of total internal reflection. Most of the light transmitted by the core in the GG+IAG fiber leaks into the cladding, and the gain medium in the core amplifies the optical signal to compensate for the leakage loss.

In 2006, Nd ³⁺ phosphate GG+IAG fiber was developed abroad, and in 2007, side-pumped and end-pumped single-mode laser output was realized, with a core diameter of 100 μm to 400 μm.

Contents of the invention

The invention provides a composition and a preparation method of an ultra-large mode area silicate optical fiber, which mainly solves the problem that the optical fiber in the prior art cannot satisfy the mode field diameter of more than 100 μm and the single-mode transmission characteristic at the same time.

Technical solution of the present invention is as follows:

The core of the silicate optical fiber, its formula contains:

The above-mentioned more suitable formula of the present invention contains by mole percentage:

The above-mentioned preferred formula of the present invention contains by mole percentage:

The silicon oxide, aluminum oxide, and lead oxide mentioned above are introduced as oxides, boron oxide is introduced as boric acid, and potassium oxide is introduced as potassium nitrate. The purity of each oxide or compound is greater than 99.6%; the purity of lanthanum oxide and yttrium oxide is greater than 99.99%. , the rare earth oxide is any one of ytterbium oxide, erbium oxide, neodymium oxide or thulium oxide, preferably ytterbium oxide, with a purity greater than 99.99%.

The cladding formulation of this silicate optical fiber contains, in molar percentages:

Above-mentioned preferred formula contains by molar percentage:

The method for preparing an ultra-large mode area silicate optical fiber comprises the following steps:

(1) Preparation of fiber core preform

After mixing the raw materials evenly, add them to the quartz crucible and heat them one by one. The heating temperature is 900-980°C, and the heating time is 1.0-1.5h. After stirring, clarification, and homogenization for 2.5 to 3.5 hours, high-temperature homogenized molten glass is obtained; after the temperature is lowered to 890°C, the high-temperature homogenized molten glass is poured into the mold, and precision annealing is carried out after pouring. The annealing temperature After the annealing is completed, the temperature is lowered to room temperature at 1.5-2°C/min, and the silicate optical fiber core preform is obtained after treatment;

(2) Preparation of cladding preform

Determine the raw material of the cladding preform according to the raw materials selected for the preparation of the core preform, and after mixing the raw materials evenly, prepare the cladding preform according to the preparation method for preparing the core preform in step (1);

(3) synthetic fiber

The core preform and the cladding preform will be sleeved, fused, surface processed and drawn to obtain a silicate optical fiber.

In the above step (3) drawing process of the synthetic optical fiber, the drawing temperature is 780-820° C., the feeding speed is 1-2 mm/min, and the drawing speed is 5-10 cm/min.

When the above-mentioned step (1) is used to prepare the gain core preform, the heating is first put into a quartz crucible and heated by a silicon carbide rod, the heating temperature is 900-980°C, and the heating time is 1.0-1.5h; The inside of the crucible is heated by silicon carbide rods, the heating temperature is 1100-1150°C, and the heating time is 2.5-3.5h.

The advantages of the present invention are:

1. The structure of the silicate optical fiber provided by the present invention is gain guiding-refractive index anti-guiding, and the core diameter of the gain guiding and refractive index anti-guiding fiber is much larger than that of a common single-mode optical fiber (4-10 μm ), the mode field area can reach tens of thousands of square microns.

2. The core material of the silicate optical fiber provided by the present invention is composed of rare earth ions with gain activity, and the core diameter is in the range of 100-500um; the cladding is composed of multi-component glass, and the cladding diameter is about 250-650um; the core - The refractive index difference between the cladding layers Δn<0.05%-0.28%.

3. The silicate optical fiber provided by the present invention has excellent thermal properties, optical properties, mechanical properties and mechanical properties, and is expected to be used in high-power fiber lasers.

4. The core of the silicate optical fiber provided by the present invention contains a gain medium, so when the core gain coefficient is large enough, the core gain of the GG+IAG optical fiber can partially compensate for the leakage mode transmission from the core layer to the cladding , partly used to realize LP ₀₁ -mode oscillation.

Description of drawings

Fig. 1 The transmission process of light gain-guiding in a refractive index anti-guiding fiber;

Fig. 2 is the end face of the single-mode optical fiber with large core diameter of the present invention;

Fig. 3 shows the output quality of the large mode field single-mode fiber laser involved in the present invention.

Detailed ways

this invention

Table 1-1: Fiber core glass composition: (by mole percentage)

Table 1-2: Composition of cladding glass: (by mole percentage)

The silicate optical fiber prepared according to Group 1 to Group 12 has high process stability, super large mode area, and is a single-mode optical fiber, which is suitable for large-scale production.

The purpose of adding PbO in the formula is to improve the glass structure and enhance the spectral characteristics of the glass; the purpose of adding K ₂ O is to reduce the viscosity of the glass and make the glass easy to melt.

Since the fiber core contains a gain medium (that is, a gain-guiding fiber), the signal light can be amplified, thereby compensating for the loss of light leakage. When the gain coefficient of the fiber core is large enough, a part of the energy can compensate the leakage mode transmission from the core to the cladding, and another part of the energy can be used to realize the transmission of the LP ₀₁ mode. At this time, the gain coefficient of the GG+IAG fiber does not reach the LP ₁₁ mode. The laser oscillation threshold of , thus realizing the single-mode laser output.

The optical fiber prepared by the formula of the silicate optical fiber and the preparation method thereof has a structure of gain guiding-refractive index anti-guiding (GG+IAG), that is, the core refractive index of the optical fiber is smaller than the cladding refractive index Δn<0( Refractive index anti-guiding fiber), therefore, the transmission of light between the core and the cladding interface does not use the principle of total internal reflection. In the GG+IAG fiber, except for a small amount of grazing light, most of the light transmitted by the core leaks into the cladding, as shown in Figure 1; The output quality of the large mode field single-mode fiber laser is shown in Figure 3.

Because the optical fiber has excellent thermal properties, optical properties and mechanical properties, it is expected to be used in important fields such as high-energy fiber lasers and amplifiers, and the information industry.

Example 1:

According to the structural characteristics of GG+IAG optical fiber, take the first group of formulas in Table 1-1 and Table 1-2 for processing.

In the raw materials, silicon oxide, aluminum oxide, and lead oxide are introduced in the form of oxides, boron oxide is introduced in boric acid, potassium oxide is introduced in potassium nitrate, and the purity of each oxide or compound is greater than 99.6%; the purity of lanthanum oxide and yttrium oxide is greater than 99.99%, The rare earth oxide is any one of ytterbium oxide, erbium oxide, neodymium oxide or thulium oxide, preferably ytterbium oxide, with a purity greater than 99.99%. Yb3+ doped silicate glass was prepared by high temperature melting process.

After mixing the raw materials evenly, add them to the quartz crucible and heat them one by one. The heating temperature is 910°C and the heating time is 1.0h, and then pour the melt into the Pt crucible for heating. , clarification, and homogenization to obtain high-temperature homogenized molten glass; after the temperature is lowered to 890°C, pour the high-temperature homogenized molten glass into the mold, and perform precision annealing after pouring. The annealing temperature is 450°C. The temperature is lowered to room temperature at 1.5-2° C./min, and the silicate optical fiber core preform is obtained through treatment.

On the basis of the preparation process of the core glass, the corresponding process parameters are adjusted to obtain the inner cladding glass and the outer cladding glass.

The optical fiber is drawn by rod and tube method. First, the core glass rod, the inner cladding glass rod, and the outer cladding glass rod are processed into the actual geometric structure and external dimensions required by the optical fiber drawing process by mechanical processing.

The processed preform is drawn on a wire drawing machine, the drawing temperature is 780° C., the feeding speed is 1 mm/min, and the drawing speed is 7.5 cm/min.

The core refractive index n1=1.57387 of the large-core-diameter single-mode optical fiber prepared according to the above method, the core diameter is 100 μm; the inner cladding refractive index n2=1.57432, and the inner cladding diameter is 250 μm; the outer cladding refractive index n3 is 1.50613; The refractive index difference with the inner cladding is Δn=-0.0045.

Example 2:

According to the structural characteristics of GG+IAG optical fiber, take the sixth group formula in Table 1-1 and Table 1-2 for processing.

In the raw materials, silicon oxide, aluminum oxide, and lead oxide are introduced in the form of oxides, boron oxide is introduced in boric acid, potassium oxide is introduced in potassium nitrate, and the purity of each oxide or compound is greater than 99.6%; the purity of lanthanum oxide and yttrium oxide is greater than 99.99%, The rare earth oxide is any one of ytterbium oxide, erbium oxide, neodymium oxide or thulium oxide, preferably ytterbium oxide, with a purity greater than 99.99%. Yb3+ doped silicate glass was prepared by high temperature melting process.

After mixing the raw materials evenly, add them to the quartz crucible and heat them one by one. The heating temperature is 940°C and the heating time is 1.5h, and then pour the melt into the Pt crucible for heating. , clarification, and homogenization to obtain high-temperature homogenized molten glass; after the temperature is lowered to 890°C, pour the high-temperature homogenized molten glass into the mold, and perform precision annealing after pouring. The annealing temperature is 450°C. Cool down to room temperature at 1.5-2°C/min, and obtain a silicate optical fiber core preform after treatment;

On the basis of the preparation process of the core glass, the corresponding process parameters are adjusted to obtain the inner cladding glass and the outer cladding glass.

The optical fiber is drawn by rod and tube method. First, the core glass rod, the inner cladding glass rod, and the outer cladding glass rod are processed into the actual geometric structure and external dimensions required for the optical fiber drawing process by mechanical processing.

The processed preform is drawn on a wire drawing machine, the drawing temperature is 800° C., the feeding speed is 1.5 mm/min, and the drawing speed is 5 cm/min.

The core refractive index _n1 of the large-core diameter single-mode fiber prepared according to the above method is 1.57224, and the core diameter is 300 μm; the inner cladding refractive index _n2 is 1.57318, and the inner cladding diameter is 460 μm; the outer cladding refractive index _n3 is 1.50552 , the diameter of the outer cladding is 520 μm; the refractive index difference between the core and the inner cladding is -0.00094.

Example 3:

According to the structural characteristics of GG+IAG optical fiber, take the formula of Group 10 in Table 1-1 and Table 1-2 for processing.

In the raw materials, silicon oxide, aluminum oxide, and lead oxide are introduced in the form of oxides, boron oxide is introduced in boric acid, potassium oxide is introduced in potassium nitrate, and the purity of each oxide or compound is greater than 99.6%; the purity of lanthanum oxide and yttrium oxide is greater than 99.99%, The rare earth oxide is any one of ytterbium oxide, erbium oxide, neodymium oxide or thulium oxide, preferably ytterbium oxide, with a purity greater than 99.99%. Yb3+ doped silicate glass was prepared by high temperature melting process.

After mixing the raw materials evenly, add them to the quartz crucible and heat them one by one. The heating temperature is 960°C and the heating time is 1.5h. Then pour the molten body into a Pt crucible and heat it. , clarification, and homogenization to obtain high-temperature homogenized molten glass; after the temperature is lowered to 890°C, pour the high-temperature homogenized molten glass into the mold, and perform precision annealing after pouring. The annealing temperature is 450°C. The temperature is lowered to room temperature at 1.5-2° C./min, and the silicate optical fiber core preform is obtained through treatment.

On the basis of the preparation process of the core glass, the corresponding process parameters are adjusted to obtain the inner cladding glass and the outer cladding glass.

The processed preform is drawn on a wire drawing machine, the drawing temperature is 810° C., the feeding speed is 1.5 mm/min, and the drawing speed is 6 cm/min.

The core refractive index _n1 of the large-core single-mode leaky-mode optical fiber prepared according to the above method is 1.57286, and the core diameter is 200 μm; the inner cladding refractive index _n2 is 1.57402, and the inner cladding diameter is 320 μm; the outer cladding refractive index _n3 is 1.50564, and the diameter of the outer cladding is 340 μm; the refractive index difference between the core and the inner cladding is -0.00116.

Claims (9)

1. the fibre core of a silicate fibers, its prescription contains by mole number percent:

2. the fibre core of silicate fibers according to claim 1 is characterized in that, described prescription contains by mole number percent:

3. the fibre core of silicate fibers according to claim 2 is characterized in that, described prescription contains by mole number percent:

4. according to the fibre core of the arbitrary described silicate fibers of claim 1 to 3, it is characterized in that: described monox, aluminium oxide, massicot are introduced with oxide form, boron oxide is introduced with boric acid, and kali is introduced with potassium nitrate, and each oxide or compound purity are all greater than 99.6%; Lanthana, yttria purity are greater than 99.99%, and described rare earth oxide is the arbitrary replacement of ytterbium oxide, erbium oxide, neodymia or thulium oxide, are good with ytterbium oxide, and purity is greater than 99.99%.

5. the covering of a silicate fibers is characterized in that, described prescription contains by mole number percent:

6. the covering of silicate fibers according to claim 5 is characterized in that, described prescription contains by mole number percent:

7. a method for preparing the long-pending silicate fibers of super large die face is characterized in that, may further comprise the steps:

(1) preparation fibre core prefabricated rods

Add in the silica crucible one by one after raw material mixed and heat, heating-up temperature is 900～980 ℃, be 1.0～1.5h heat time heating time, and then molten mass poured in the Pt crucible heat, heating-up temperature is 1100～1150 ℃, be 2.5～3.5h heat time heating time, obtains the glass metal of high temperature homogenizing through stirring, clarification, homogenizing; After temperature is reduced to 890 ℃, the glass metal of high temperature homogenizing is cast in the mould, carries out fine annealing behind the casting complete and handle, annealing temperature is 450 ℃, after finishing, annealing is cooled to room temperature with 1.5～2 ℃/min again, the treated silicate fibers fibre core prefabricated rods that obtains;

(2) preparation covering prefabricated rods

Determine the raw material of covering prefabricated rods according to preparing the selected raw material of fibre core prefabricated rods, after raw material is mixed, according to the preparation method of step (1) preparation fibre core prefabricated rods, preparation covering prefabricated rods;

(3) synthetic fibre-optical

To carry out socket, fusion, surface working and wire drawing processing to fibre core prefabricated rods and covering prefabricated rods, obtain silicate fibers.

8. the method for preparing silicate fibers according to claim 7 is characterized in that: during the wire drawing of described step (3) synthetic fibre-optical was handled, wire-drawing temperature was 780～820 ℃, and charging rate is 1～2mm/min, and drawing speed is 5～10cm/min.

9. according to claim 7 or the 8 described methods that prepare silicate fibers, it is characterized in that: during described step (1) preparation gain core prefabricated rods, put into silica crucible earlier and heated by Elema, heating-up temperature is 900～980 ℃, and be 1.0～1.5h heat time heating time; After put into the Pt crucible and heat by Elema, heating-up temperature is 1100～1150 ℃, be 2.5～3.5h heat time heating time.