CN112968347B - Method for inhibiting stimulated Raman scattering, high-power optical fiber laser and all-solid-state microstructure optical fiber - Google Patents

Abstract

The invention provides a method for suppressing stimulated Raman scattering, a high-power fiber laser and an all-solid-state microstructure fiber. The all-solid-state microstructure fiber comprises a core and a microstructure cladding, wherein the core is a solid core and the microstructure The cladding is wrapped around the periphery of the fiber core, and the microstructure cladding is located on the germanium rod and the solid substrate in the regular hexagonal lattice. The regular hexagonal lattice is distributed with multiple layers from the inside to the outside. The center spacing of any two adjacent points is equal, the fiber core is located at the center of the regular hexagonal lattice, and a plurality of germanium rods are arranged in a sparse structure on each layer of the regular hexagonal lattice, and a solid substrate is filled between the germanium rods. . When the propagation constant is constant, by adjusting the diameter and refractive index of the germanium rod, when the all-solid-state microstructure fiber transmits high-power fiber laser, the high-power laser quasi-single-mode long-distance transmission can be realized and stimulated Raman scattering can be suppressed.

Description

Method for suppressing stimulated Raman scattering, high-power fiber laser and all-solid-state microstructure fiber

technical field

The invention mainly relates to the technical field of laser optical fibers, in particular to a method for suppressing stimulated Raman scattering, a high-power optical fiber laser and an all-solid-state microstructure optical fiber.

Background technique

High-average power lasers have been widely used in various fields such as metal cutting, material cladding, laser welding, and laser ignition due to their natural advantages such as energy concentration, flexible transformation, and small heat-affected zone. In recent years, thanks to the development of high-brightness pump sources, key optical components, laser materials, pump coupling, beam synthesis and other technologies, various types of lasers such as high-power fiber lasers, gas lasers, solid-state lasers, and semiconductor lasers Remarkable progress has been made in power improvement. Taking high-power fiber laser (HPFL) as an example, kilowatt-level fiber oscillator and amplifier technologies at home and abroad have become increasingly mature, and 10,000-watt fiber laser test prototypes and industrial-grade products have also been launched and gradually entered the market.

In the process of high-power laser (HPL) applications, the energy-transferring fiber provides the possibility of flexible single-mode transmission of the high-power laser beam from the laser source to the working platform. Taking conventional laser processing applications as an example, high-power laser beams are usually required to travel several meters, tens of meters, or even hundreds of meters from the light source to the work platform. However, due to the increase of optical power density and the limited area of the fiber mode field, high-brightness beams in the hundreds of watts or kilowatts will inevitably induce nonlinear effects during long-distance transmission, such as stimulated Brillouin scattering (SBS), Stimulated Raman Scattering (SRS) etc. Generally speaking, the spectral broadening caused by SBS is the primary problem that needs to be solved for narrow linewidth lasers, and the signal optical power fluctuation and efficiency reduction caused by the SRS Stokes shift are the main problems of all laser oscillators and amplifiers. common problems faced. Industrial continuous wave HPL usually has a wide output spectral bandwidth, so the main obstacle restricting the length of its energy transmission fiber is stimulated Raman scattering.

其中A_eff为模场面积、g_R(Ω)为拉曼增益系数、L_eff为光纤长度。为了克服SRS以实现高功率激光束的远距离传输通常需要增大光纤的纤芯尺寸，也就是所谓的大模场(LMA)光纤。然而，LMA光纤的使用会不可避免地造成光纤多模运转从而导致输出光束质量下降。为了尽可能保证光纤的单模运转特性，通常要求其数值孔径(NA)随着纤芯尺寸的增大而减小，而过小的NA则会导致光纤模场面积对于弯曲的敏感程度较高，不利于其实际应用。与此同时，部分微结构光纤如光子晶体光纤、泄露通道光纤、多芯光纤、空芯光纤的出现固然能够使光纤兼备大模场面积、低NA、恒稳单模运转的特性，但是此类光纤制备成本较高、传输损耗和弯曲敏感性较大，一般不适用于工业应用中的柔性传输。伴随着HPL的进一步功率提升，传能光纤本身的模式特性、传导特性、光谱特性和机械性能也面临更大的考验。The length of the fiber itself and the mode field area directly determine the threshold power of the SRS, which satisfies the

where A _eff is the mode field area, g _R (Ω) is the Raman gain coefficient, and L _eff is the fiber length. In order to overcome SRS for long-distance transmission of high-power laser beams, it is usually necessary to increase the core size of the fiber, so-called large mode field (LMA) fiber. However, the use of LMA fibers will inevitably lead to multimode operation of the fiber, resulting in the degradation of the output beam quality. In order to ensure the single-mode operation characteristics of the fiber as much as possible, the numerical aperture (NA) of the fiber is usually required to decrease with the increase of the core size, and too small NA will cause the fiber mode field area to be more sensitive to bending. , which is not conducive to its practical application. At the same time, the emergence of some microstructured fibers such as photonic crystal fibers, leaky channel fibers, multi-core fibers, and hollow-core fibers can make the fibers have the characteristics of large mode field area, low NA, and stable single-mode operation. Optical fibers are generally not suitable for flexible transmission in industrial applications due to their high fabrication cost, large transmission loss and bending sensitivity. With the further power improvement of HPL, the mode characteristics, conduction characteristics, spectral characteristics and mechanical properties of the energy transmission fiber itself are also facing greater challenges.

SUMMARY OF THE INVENTION

In view of the defects existing in the prior art, the present invention provides a method for suppressing stimulated Raman scattering, a high-power fiber laser and an all-solid-state microstructure fiber, which can realize high-power laser quasi-single-mode long-distance transmission and can suppress stimulated pull Mann scattering.

For realizing the above-mentioned technical purpose, the technical scheme of the present invention is:

Methods to suppress stimulated Raman scattering include:

Design an all-solid microstructure optical fiber, wherein the all-solid microstructure optical fiber includes a core and a microstructure cladding, the core is a solid core, the microstructure cladding is clad on the periphery of the core, and the microstructure cladding includes The germanium rod and solid substrate are located in the regular hexagonal lattice. The regular hexagonal lattice is distributed with multiple layers from the inside to the outside. The center distance Λ of any two adjacent points in the regular hexagonal lattice is equal, and the fiber core is located on the regular hexagon. At the center of the lattice lattice, a plurality of germanium rods are arranged in a sparse structure on each layer of regular hexagonal lattice, and a solid substrate is filled between the germanium rods;

The all-solid-state microstructure fiber is spliced on the output pigtail of the high-power fiber laser as a long-distance transmission fiber; when the all-solid-state microstructure fiber transmits the high-power fiber laser, the germanium rod in the microstructure cladding is generated due to anti-resonant coupling. The photonic band gap effect, the multiple interference between the scattered light in a specific frequency range makes its intensity weakened and cannot pass through the microstructure cladding, and finally restricts the transmission in the core of the fiber, this specific frequency range is called the photonic band gap frequency range. For the signal wavelength laser, there is multiple interference between the scattered light falling within the frequency range of the photonic band gap, so that its intensity is weakened and cannot pass through the microstructure cladding, and finally limited to the stable transmission in the fiber core, realizing high-efficiency single-frequency laser light at the signal wavelength. Mode low-loss transmission; at the same time, the Stokes wavelength of stimulated Raman scattering (SRS) that falls outside the photonic band gap frequency range presents high loss and cannot be stably transmitted. This all-solid-state microstructure fiber can suppress high-power fiber lasers for long distance Stimulated Raman scattering effects during transmission.

As a further improvement of the present invention, the regular hexagonal lattice has four layers, which are the first layer of regular hexagonal lattice, the second layer of regular hexagonal lattice, and the third layer of regular hexagonal lattice from inside to outside. And the fourth layer of regular hexagonal lattice.

As a further improvement of the present invention, the first layer of regular hexagonal lattice is provided with 12 points and all the points are distributed with germanium rods, and the second layer of regular hexagonal lattice is provided with 18 points and located at each There are germanium rods distributed on the two points in the middle of the edge, there are 24 points on the third layer of regular hexagonal lattice, and four points at both ends of each edge are distributed with germanium rods, and the fourth layer of regular hexagonal There are 30 points on the lattice, and germanium rods are distributed on two points located at both ends of each side and two points located at the center of each side. That is, in the second layer of regular hexagonal lattices, no germanium rods are set on the points located at the vertices of the hexagons; in the second layer of regular hexagonal lattices, no germanium rods are set on the points at the center of each side; No germanium rods are provided on the second and fourth points on each side of the lattice. These dot positions where no germanium rods are provided and the gaps between the germanium rods are filled with a solid quartz substrate. In this way, the bending loss of the high-order mode is increased while ensuring the low loss of the fundamental mode of the signal laser, so as to realize the quasi-single-mode operation of the fiber.

As a further improvement of the present invention, the core material is solid quartz. The solid substrate is a solid quartz substrate.

As a further improvement of the present invention, all germanium rods have the same structure and size, and the germanium rods include a high-refractive-index germanium-doped region located in the center and a low-refractive-index cladding region located in the outer layer, wherein the high-refractive index germanium-doped region is refracted The rate is parabolically graded or step-type refractive index distribution. The high-refractive-index germanium-doped region and the low-refractive-index cladding region have a certain core-to-clad ratio, and the ratio can be arbitrarily set according to requirements, for example, set to 1:2.5.

As a further improvement of the present invention, there is a refractive index difference Δ between the high-refractive-index germanium-doped region and the low-refractive-index cladding region of the germanium rod, which satisfies Δ=(n _high ² -n _low ² )/(2×n _high ² ), where n _high and n _low are the maximum refractive index of the germanium-doped region with high refractive index and the refractive index of the cladding region with low refractive index, respectively.

As a further improvement of the present invention, the refractive index difference Δ satisfies 1.5%≤Δ≤3%. When the refractive index difference Δ is determined, the distribution of the photonic band gap is only related to the diameter d of the germanium rod, and is related to the arrangement of the germanium rod Regardless of the manner, the suppression of the stimulated Raman scattering effect can be achieved by increasing or decreasing the diameter d of the germanium rod.

As a further improvement of the present invention, the low-refractive-index cladding region of the germanium rod can be made of a low-refractive-index material such as solid quartz or fluorine-doped solid quartz.

The present invention provides a high-power fiber laser, comprising a laser generating unit for generating high-power fiber laser, and an output pigtail of the laser generating unit is fused with an all-solid-state microstructure fiber as a long-distance transmission fiber; The solid microstructure optical fiber includes a core and a microstructure cladding, the core is a solid core, the microstructure cladding is clad on the periphery of the core, and the microstructure cladding includes germanium located in a regular hexagonal lattice Rods and solid substrates, the regular hexagonal lattice is distributed with multiple layers from the inside to the outside, the center distance Λ of any two adjacent points in the regular hexagonal lattice is equal, and the fiber core is located at the center of the regular hexagonal lattice. The germanium rods are arranged on each layer of regular hexagonal lattice in a sparse structure, and a solid substrate is filled between the germanium rods. The various further optimized design solutions about the all-solid-state microstructured optical fiber are the same as those described above, and will not be repeated here. All-solid-state microstructured fiber is used as a long-distance transmission fiber for high-power fiber lasers. When the all-solid-state microstructured fiber transmits high-power fiber lasers, the germanium rod in the microstructure cladding produces a photonic band gap effect due to anti-resonance coupling, and enters the microstructure cladding. The beam of the layer undergoes multiple scattering, and there is multiple interference between the scattered light falling within the frequency range of the photonic band gap, so that the intensity is weakened and cannot pass through the microstructure cladding, and is finally limited to stable transmission in the fiber core, achieving high signal wavelength laser. Efficient single-mode transmission; at the same time, the all-solid-state microstructured fiber can suppress the stimulated Raman scattering effect during long-distance transmission of high-power fiber lasers.

The invention provides an all-solid microstructure optical fiber, comprising a core and a microstructure cladding, wherein the core is a solid fiber core, the microstructure cladding is clad on the periphery of the core, and the microstructure cladding comprises a The germanium rod and solid substrate in the hexagonal lattice, the regular hexagonal lattice is distributed with multiple layers from the inside and the outside, the center distance Λ of any two adjacent points in the regular hexagonal lattice is equal, and the fiber core is located at the regular hexagonal point At the center of the array, a plurality of germanium rods are arranged in a sparse structure on each layer of regular hexagonal lattice, among which a solid substrate is filled between the germanium rods, and all the germanium rods have the same structure and size.

The microstructure cladding provided by the present invention produces a photonic band gap effect due to anti-resonance coupling, and the light beam entering the microstructure cladding undergoes multiple scattering under the action of the microstructure, and the multiple interference between the scattered lights in a specific frequency range makes it The strength is weakened to pass through the microstructured cladding, ultimately limiting transmission in the core. In the case of a certain propagation constant, the relative position distribution of the photonic band gap with wavelength can be controlled by adjusting the diameter and refractive index of the germanium rod, so that the stimulated Raman scattering (SRS) Stokes falling outside the frequency range of the photonic band gap can be controlled. The Si wavelength band (1110nm-1130nm) shows high loss and cannot be transmitted stably, and the light falling in the signal wavelength band (1060nm-1080nm) within the photonic bandgap frequency range is repelled by the cladding and presents low loss and is better confined to the core. Stable transmission, macroscopically showing a certain spectral filtering effect.

Further, the fiber core in the all-solid-state microstructured optical fiber is composed of a single quartz rod, or is formed by a plurality of quartz rods arranged closely in a periodical manner. According to the number n of quartz rods used to form the core, the core type is defined as n-cell core, and the core diameter is 4Λ-d.

Compared with the prior art, the beneficial effects of the present invention at least include:

1. The all-solid-state microstructured fiber of the present invention utilizes the photonic bandgap effect generated by the microstructure cladding structure itself to directly show low confinement loss in the laser signal band, and show low confinement loss at the stimulated Raman scattering Stokes wavelength. For high confinement loss, the natural stimulated Raman scattering suppression effect can be obtained without other technical means such as bending and writing inclined gratings.

2. The all-solid-state microstructured fiber of the present invention has a larger core diameter and mode field area than the traditional step-index fiber (SIF), which in principle improves the nonlinear effect threshold, including stimulated Raman fiber. A variety of high-power laser nonlinear effects, including scattering and stimulated Brillouin scattering, have a certain inhibitory effect.

3. The all-solid microstructure optical fiber of the present invention, because the germanium rods are arranged in a sparse structure on the regular hexagonal lattice of each layer, that is, no germanium rods are provided on some points on the regular hexagonal lattice, and no germanium is provided. The spot locations of the rods and the gaps between the germanium rods are filled with a solid quartz substrate. In this way, the bending loss of the high-order mode is increased while ensuring the low loss of the fundamental mode of the signal laser, so as to realize the quasi-single-mode operation of the fiber. Specifically, except that a circle of germanium rods is arranged strictly according to the regular hexagon at each point in the first layer of regular hexagonal lattices close to the fiber core, the germanium rods in the other regular hexagonal lattices are arranged in a sparse structure That is, selectively no germanium rods are provided on some points on the regular hexagonal lattice of the remaining layers, and the positions of the points where no germanium rods are provided and the gaps between the germanium rods are filled by the solid quartz substrate. In this way, the bending loss of the high-order mode is much larger than that of the fundamental mode, so the quasi-single-mode operation of the high-power laser can be ensured within a certain range of coil diameters.

4. By reasonably setting the structural parameters of the germanium rod, the stimulated Raman scattering (SRS) Stokes wavelength band (1110nm-1130nm) that falls outside the band gap can exhibit high loss and cannot be stably transmitted, but falls in the photonic band. The light in the signal wavelength band (1060nm-1080nm) in the gap is repelled by the cladding and presents a low loss, so that it is better restricted to the core for stable transmission, showing a certain spectral filtering effect macroscopically.

5. Compared with other types of complex microstructure fibers such as hollow core fibers and air hole photonic crystal fibers, the microstructure fibers of the present invention are all solid-state structures, and the difficulty of preform preparation and fiber drawing is relatively low. The difficulty of splicing with the laser output pigtail is low, which is beneficial to practical high-power laser transmission applications.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained according to the structures shown in these drawings without creative efforts.

1 is a schematic cross-sectional structure diagram of an embodiment;

2 is a schematic diagram of the arrangement of the germanium rods in FIG. 1, wherein the dotted circle in the regular hexagonal lattice represents the point position where the germanium rod is not provided, and the solid line dotted circle represents the point position where the germanium rod is provided;

3 is a schematic diagram of a cross-sectional structure of a germanium rod used in an embodiment;

4 is a schematic diagram of the refractive index distribution of germanium rods used in Example 1;

5 is a schematic diagram of the intensity distribution of the eigenmodes of the signal band of the all-solid-state microstructured optical fiber provided in Example 1, wherein (a) is a schematic diagram of the intensity distribution corresponding to the LP ₀₁ mode of the all-solid-state microstructured optical fiber at 1070 nm signal light, (b) ) Schematic diagram of the intensity distribution corresponding to the LP _11o mode of the all-solid-state microstructured fiber at 1070 nm signal light, (c) schematic diagram of the intensity distribution corresponding to the LP _11e mode of the all-solid-state microstructured fiber at 1070 nm signal light;

6 is a schematic diagram of the wavelength-dependent loss of the all-solid-state microstructured optical fiber provided in Example 1 in a straight fiber and a bent state;

7 is a schematic diagram of the fundamental mode loss of the all-solid-state microstructure optical fiber signal band wavelength under different bending radii provided in Example 1;

8 is a schematic diagram of the fundamental mode and the minimum loss high-order mode bending loss of the all-solid-state microstructure optical fiber provided in Example 1;

9 is a schematic diagram of the refractive index distribution of germanium rods used in Example 2;

10 is a schematic diagram of the wavelength-dependent loss of the all-solid-state microstructured optical fiber provided in Example 2 in a straight fiber state and the signal band loss under different bending radii;

11 is a schematic diagram of the change of the signal band mode field area of the all-solid-state microstructured optical fiber provided in Example 2 under different bending radii;

12 is a schematic diagram of the bending loss of the fundamental mode and the minimum loss high-order mode of the all-solid-state microstructured optical fiber provided in Example 2;

FIG. 13 is a schematic structural diagram of Embodiment 4. FIG.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Referring to FIG. 1, the present invention provides an all-solid microstructure optical fiber, the optical fiber includes a core and a microstructure cladding, the core 1 is a solid core, and the microstructure cladding is wrapped around the periphery of the core 1, so The microstructure cladding includes germanium rods 2 and solid substrates 3 located in a regular hexagonal lattice. The regular hexagonal lattice is distributed with multiple layers from the inside to the outside. The center distance between any two adjacent points in the regular hexagonal lattice is Λ is equal, the fiber core 2 is located at the center of the regular hexagonal lattice, and a plurality of germanium rods 2 are arranged on each layer of the regular hexagonal lattice in a sparse structure, and a solid substrate 3 is filled between the germanium rods 2 . The selected materials for the fiber core 1 and the solid substrate 3 are all quartz (Silica).

Referring to Figure 1 and Figure 2, the regular hexagonal lattice has four layers, from the inside to the outside are the first regular hexagonal lattice, the second regular hexagonal lattice, the third regular hexagonal lattice and the third regular hexagonal lattice Four-layer regular hexagonal lattice. Except that a circle of germanium rods is arranged strictly according to the regular hexagon at each point in the first layer of regular hexagonal lattice close to the fiber core, the germanium rods in the other regular hexagonal lattices are arranged in a sparse structure, that is, select In fact, no germanium rods are provided on some points on the regular hexagonal lattice of the remaining layers, and the positions of the points where no germanium rods are provided and the gaps between the germanium rods are filled by the solid quartz substrate. In this way, the bending loss of the high-order mode is much larger than that of the fundamental mode, so the quasi-single-mode operation of the high-power laser can be ensured within a certain range of coil diameters. Specifically, there are 12 points on the regular hexagonal lattice on the first layer and germanium rods 2 are distributed on all the points, and there are 18 points on the regular hexagonal lattice on the second layer, and two dots located in the middle of each side are provided. There are germanium rods 2 distributed on each point, the third layer of regular hexagonal lattice is provided with 24 points, and the four points located at both ends of each edge are distributed with germanium rods 2, and the fourth layer of regular hexagonal lattice is distributed with germanium rods 2 There are 30 points on it, and two points located at both ends of each side and two points located at the center of each side are distributed with germanium rods 2 . That is, in the second layer of regular hexagonal lattices, no germanium rods are set on the points located at the vertices of the hexagons; in the second layer of regular hexagonal lattices, no germanium rods are set on the points at the center of each side; There are no germanium rods on the second and fourth points on each side of the lattice, as shown in Figure 2, where the dotted circles in the regular hexagonal lattice represent the positions where no germanium rods are set, and the solid lines represent Sets the point position of the germanium rod. On the one hand, the arrangement of germanium rods in the above microstructure cladding ensures that the optical fiber has a small fundamental mode bending loss (BL<0.1dB/m) in the signal wavelength band (1060nm-1080nm), and on the other hand ensures a large high-order mode. Bending loss (BL>5dB/m).

Example 1:

为0.4，纤芯直径4Λ-d为43.2μm。其中纤芯由7根石英棒周期紧密排列而形成。The structure of the all-solid-state microstructure optical fiber provided in an embodiment of the present invention is shown in FIG. 1, and its parameters include: the diameter d of the germanium rod is 4.8 μm, the center distance Λ of any two adjacent points in the regular hexagonal lattice 12μm, fiber characteristic parameters

is 0.4, and the core diameter 4Λ-d is 43.2 μm. The fiber core is formed by 7 quartz rods arranged closely in a periodical manner.

The cross-sectional structure diagram of the germanium rod used in this embodiment is shown in FIG. 3 . The germanium rod 2 includes a high-refractive-index germanium-doped region 4 located in the center and a low-refractive-index cladding region 5 located in the outer layer, wherein the high-refractive-index germanium-doped region 5 The refractive index of zone 4 exhibits a parabolic graded refractive index profile, as shown in FIG. 4 . The outer low-refractive-index cladding region 5 adopts a quartz cladding. There is a refractive index difference Δ between the high-refractive-index germanium-doped region 4 and the low-refractive-index cladding region 5 of the germanium rod, which satisfies Δ=(n _high ² -n _low ² )/(2×n _high ² ), where n _high , n _low is the maximum value of the high-refractive-index germanium-doped region and the refractive index of the low-refractive-index cladding region, respectively. In this embodiment, the refractive index difference between the central high-refractive-index germanium-doped region and the outer low-refractive-index cladding region of the germanium rod is Δ=2%, and the diameter of the central high-refractive-index germanium-doped region and the outer low-refractive-index cladding The ratio of the outer diameter of the layer area is 1:2.5.

The eigenmode field distribution of the all-solid-state microstructured fiber in the signal band provided in this embodiment is shown in Figure 5, where (a) is a schematic diagram of the intensity distribution corresponding to the LP ₀₁ mode of the all-solid-state microstructured fiber in the signal light at 1070 nm, (b) Schematic diagram of the intensity distribution corresponding to the LP _11o mode of the all-solid-state microstructured fiber at 1070 nm signal light, (c) schematic diagram of the intensity distribution corresponding to the LP _11e mode of the all-solid-state microstructured fiber at 1070 nm signal light. The confinement loss of the straight fiber and the mode field area of the fundamental mode corresponding to each eigenmode at this wavelength are shown in Table 1 below. It can be seen from the table that the confinement loss of the fiber to the fundamental mode is extremely low and the mode field area is 567μm ² , so the fiber It must have a large mode field area and the ability to stably transmit the signal wavelength laser, which meets the basic application requirements of energy transmission fibers.

Table 1 The effective refractive index and the mode field area of the fundamental mode corresponding to each eigenmode

Specifically, the wavelength-dependent loss of the all-solid-state microstructured optical fiber provided in the above embodiment in a straight optical fiber and a 20 cm bending state is shown in FIG. 6 . Whether it is a straight fiber or a bent state, the fundamental mode loss at the signal band can be less than 0.1dB/m, while the fundamental mode loss at the SRS Tox wavelength (1120nm-1130nm) is greater than 20dB/m, ensuring that the SRS wavelength is effective. ability to inhibit.

Specifically, when the signal band wavelength laser (take 1060nm and 1070nm as an example) is transmitted in the all-solid microstructure fiber provided by the above embodiment, the fundamental mode loss under different bending radii (15-20cm) is shown in Figure 7. The bending loss increases slightly as the bending radius decreases, but remains below 0.1 dB/m, ensuring a low bending sensitivity of the signal band.

Specifically, for the all-solid-state microstructure optical fiber provided in this embodiment, in addition to the wavelength-dependent loss, the mode-dependent bending loss of the signal-band wavelength laser transmission should also be considered according to its practical application. Only by controlling the wavelength-dependent loss of the fiber can it have the function of SRS suppression; only by controlling the mode-dependent bending loss, the quasi-single-mode transmission of high-power lasers can be realized. In order to realize the quasi-single-mode operation of the fiber, it is necessary to ensure a large bending loss of the high-order mode and a small bending loss of the fundamental mode at the same time, and filter out the high-order mode that may exist in the fiber by the method of bending mode selection. As shown in FIG. 8 , the all-solid-state microstructured fiber provided in this embodiment can ensure that the fundamental mode bending loss of the signal band is less than 0.1 dB/m, and the bending loss of the high-order mode is greater than 5 dB/m under a bending radius of 20 cm. The high-order mode loss corresponds to The high-order mode with the smallest loss is calculated, so the quasi-single-mode transmission of high-power laser can be guaranteed to a certain extent.

Example 2:

为0.38，纤芯直径4Λ-d为50.5μm。其中纤芯由7根石英棒周期紧密排列而形成。The structure of the all-solid-state microstructure optical fiber provided in an embodiment of the present invention is shown in FIG. 1, and its parameters include: the diameter d of the germanium rod is 5.3 μm, the center distance Λ of any two adjacent points in the regular hexagonal lattice is 13.95μm, fiber characteristic parameters

is 0.38, and the core diameter 4Λ-d is 50.5 μm. The fiber core is formed by 7 quartz rods arranged closely in a periodical manner.

Specifically, the schematic diagrams of the cross-sectional structure and the refractive index distribution of the germanium rod used in this embodiment are shown in Figures 3 and 9, respectively. The germanium rod 2 includes a high-refractive-index germanium-doped region 4 located in the center and a low-refractive index package located in the outer layer. The layer region 5, wherein the refractive index of the high-refractive-index germanium-doped region 4 is a parabolic graded index distribution. The low-refractive-index cladding region 5 of the outer layer adopts a quartz cladding. There is a refractive index difference Δ between the high-refractive-index germanium-doped region 4 and the low-refractive-index cladding region 5 of the germanium rod, which satisfies Δ=(n _high ² -n _low ² )/(2×n _high ² ), where n _high , n _low is the maximum value of the high-refractive-index germanium-doped region and the refractive index of the low-refractive-index cladding region, respectively. In this embodiment, the difference in refractive index between the central high-refractive-index germanium-doped region 5 of the germanium rod and the outer low-refractive-index cladding region 6 is Δ=1.7%. The ratio of the outer diameter of the cladding region 5 is 1:2.5.

Specifically, the wavelength-dependent loss of the all-solid-state microstructured optical fiber provided in this embodiment and the signal band loss in a 25 cm bending state are shown in FIG. 10 . Whether it is a straight fiber or a bent state, the fundamental mode loss at the signal band can be less than 0.1dB/m, while the fundamental mode loss at the SRS Tox wavelength (1120nm-1130nm) is greater than 40dB/m, ensuring that the SRS wavelength is effective. ability to inhibit.

Specifically, the mode field area change of the signal band (1040nm-1070nm) of the all-solid-state microstructure optical fiber provided in this embodiment is shown in FIG. 11 under different bending radii (50cm, 25cm). Under a bending radius greater than 25 cm, the all-solid-state microstructured optical fiber described in this embodiment can ensure a mode field area of more than 740 μm ² for the signal band laser.

Specifically, for the all-solid-state microstructure optical fiber provided in this embodiment, in addition to the wavelength-dependent loss, the mode-dependent bending loss of the signal-band wavelength laser transmission should also be considered according to its practical application. Only by controlling the wavelength-dependent loss of the fiber can it have the function of SRS suppression; only by controlling the mode-dependent bending loss, the quasi-single-mode transmission of high-power lasers can be realized. In order to realize the quasi-single-mode operation of the fiber, it is necessary to ensure a large bending loss of the high-order mode and a small bending loss of the fundamental mode at the same time, and filter out the high-order mode that may exist in the fiber by the method of bending mode selection. As shown in FIG. 12 , the all-solid-state microstructured optical fiber provided in this embodiment can ensure that the fundamental mode bending loss of the signal band is less than 0.1 dB/m, and the bending loss of the high-order mode is greater than 5 dB/m under a bending radius of 20 cm. The high-order mode loss corresponds to The high-order mode with the smallest loss is calculated, so the quasi-single-mode transmission of high-power laser can be guaranteed to a certain extent.

The microstructure cladding designed by the present invention produces a photonic band gap effect due to anti-resonance coupling, and the optical fiber structure designed by the present invention enables the signal light wavelength to be located on the photonic band gap and the Stokes wavelength to fall outside the photonic band gap, The all-solid-state microstructure fiber has the characteristics of stable transmission of signal laser and high suppression of stimulated Raman scattering; through the sparse structure arrangement design of the outer germanium rods, the high-order mode bending loss is increased while ensuring the low loss of the fundamental mode of the signal laser. , so that the all-solid-state microstructure fiber has the characteristic of effectively suppressing high-order modes, and ensures the quasi-single-mode operation in the process of high-power laser transmission. In conclusion, the present invention can meet the application requirements of high-power laser quasi-single-mode and long-distance, and can further ensure the application effect of high-power laser in medical, industrial, national defense and other fields.

Example 3:

This embodiment provides a method for suppressing stimulated Raman scattering, including:

Design an all-solid-state microstructure fiber, wherein the structure of the all-solid-state microstructure fiber is shown in Figure 1, including a core and a microstructure cladding, the core is a solid core, and the microstructure cladding is clad on the periphery of the core , the microstructure cladding includes germanium rods and solid substrates located in a regular hexagonal lattice, the regular hexagonal lattice is distributed with multiple layers from the inside out, and the center distance between any two adjacent points in the regular hexagonal lattice is Λ is equal, the fiber core is located in the center of the regular hexagonal lattice, and a plurality of germanium rods are arranged on each layer of the regular hexagonal lattice in a sparse structure, and a solid substrate is filled between the germanium rods. Specifically, the regular hexagonal lattice has four layers, which are the first layer of regular hexagonal lattices, the second layer of regular hexagonal lattices, the third layer of regular hexagonal lattices, and the fourth layer of regular hexagonal lattices. shaped lattice. Except that a circle of germanium rods is arranged strictly according to the regular hexagon at each point in the first layer of regular hexagonal lattice close to the fiber core, the germanium rods in the other regular hexagonal lattices are arranged in a sparse structure, that is, select In fact, no germanium rods are provided on some points on the regular hexagonal lattice of the remaining layers, and the positions of the points where no germanium rods are provided and the gaps between the germanium rods are filled by the solid quartz substrate. In this way, the bending loss of the high-order mode is much larger than that of the fundamental mode, so the quasi-single-mode operation of the high-power laser can be ensured within a certain range of coil diameters. Specifically, there are 12 points on the regular hexagonal lattice on the first layer and germanium rods 2 are distributed on all the points, and there are 18 points on the regular hexagonal lattice on the second layer, and two dots located in the middle of each side are provided. There are germanium rods 2 distributed on each point, the third layer of regular hexagonal lattice is provided with 24 points, and the four points located at both ends of each edge are distributed with germanium rods 2, and the fourth layer of regular hexagonal lattice is distributed with germanium rods 2 There are 30 points on it, and two points located at both ends of each side and two points located at the center of each side are distributed with germanium rods 2 .

The all-solid-state microstructure fiber is spliced on the output pigtail of the high-power fiber laser as a long-distance transmission fiber; when the all-solid-state microstructure fiber transmits the high-power fiber laser, the germanium rod in the microstructure cladding is generated due to anti-resonant coupling. Photonic band gap effect. The light beam entering the microstructured cladding undergoes multiple scattering, and the multiple interference between the scattered light in a specific frequency range makes its intensity weakened and cannot pass through the microstructured cladding, and is finally restricted to transmit in the core of the fiber. This specific frequency range is called the photonic band slot frequency range. ; For the signal wavelength laser, there is multiple interference between the scattered light falling within the frequency range of the photonic band gap, so that its intensity is weakened and cannot pass through the microstructure cladding, and finally limited to stable transmission in the fiber core, achieving high efficiency of the signal wavelength laser Single-mode low-loss transmission; meanwhile, the stimulated Raman scattering Stokes wavelength that falls outside the photonic bandgap frequency range exhibits high loss and cannot be transmitted stably. This all-solid-state microstructure fiber can suppress the long-distance transmission process of high-power fiber lasers Stimulated Raman scattering effect in .

The structure and size of all germanium rods are the same. The germanium rods include a high-refractive-index germanium-doped region in the center and a low-refractive-index cladding region located in the outer layer, wherein the high-refractive-index germanium-doped region has a parabolic graded index of refraction. distributed. There is a refractive index difference Δ between the high-refractive-index germanium-doped region and the low-refractive-index cladding region of the germanium rod, which satisfies Δ=(n _high ² -n _low ² )/(2×n _high ² ), where n _high and n _low are respectively It is the maximum value of the high-refractive-index germanium-doped region and the refractive index of the low-refractive-index cladding region. The refractive index difference Δ satisfies 1.5%≤Δ≤3%. When the refractive index difference Δ is determined, the distribution of the photonic band gap is only related to the diameter d of the germanium rod, and has nothing to do with the arrangement of the germanium rod. Suppression of the effect can be achieved by increasing or decreasing the diameter d of the germanium rod. The low-refractive-index cladding region of the germanium rod is made of solid quartz or fluorine-doped solid quartz.

Example 4,

13, the present embodiment provides a high-power fiber laser, including a laser generating unit 301, the laser generating unit is used to generate a high-power fiber laser, and the output pigtail 302 of the laser generating unit is fused with an all-solid-state microstructure fiber 303 As a long-distance transmission fiber, the final signal laser is transmitted to the collimator 305 through the relay fiber 304 for output; wherein the all-solid microstructure fiber is the all-solid microstructure fiber described in any of the above embodiments.

When the all-solid-state microstructure fiber transmits high-power fiber laser, the germanium rod in the microstructure cladding produces a photonic band gap effect due to anti-resonant coupling, and the light beam entering the microstructure cladding undergoes multiple scattering, and the scattered light within a specific frequency range is scattered. The multiple interference between them weakens the intensity and cannot pass through the microstructure cladding, and finally restricts the transmission in the fiber core. This specific frequency range is called the photonic bandgap frequency range. For the signal wavelength laser, there is multiple interference between the scattered light falling within the frequency range of the photonic band gap, so that its intensity is weakened and cannot pass through the microstructure cladding, and finally limited to the stable transmission in the fiber core, realizing high-efficiency single-frequency laser light at the signal wavelength. Mode low-loss transmission; at the same time, the Stokes wavelength of stimulated Raman scattering (SRS) that falls outside the photonic band gap frequency range presents high loss and cannot be stably transmitted. This all-solid-state microstructure fiber can suppress high-power fiber lasers for long distance Stimulated Raman scattering effects during transmission.

In summary, although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person of ordinary skill in the art, without departing from the spirit and scope of the present invention, can make various modifications. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims (6)

1. A method for suppressing stimulated Raman scattering, comprising: Design an all-solid microstructure optical fiber, wherein the all-solid microstructure optical fiber includes a core and a microstructure cladding, the core is a solid core, and the microstructure cladding is clad on the periphery of the core, and the microstructure cladding includes The germanium rod and solid substrate are located in the regular hexagonal lattice. The regular hexagonal lattice has four layers from the inside to the outside. array, the third layer of regular hexagonal lattice and the fourth layer of regular hexagonal lattice; the center distance Λ of any two adjacent points in the regular hexagonal lattice is equal, the fiber core is located in the center of the regular hexagonal lattice, the first There are 12 points on a regular hexagonal lattice on the first layer and germanium rods are distributed on all the points, and there are 18 points on the second regular hexagonal lattice and two points located in the middle of each side are evenly distributed. There are germanium rods, there are 24 points on the third layer of regular hexagonal lattice and four points at both ends of each side are distributed with germanium rods, and the fourth layer of regular hexagonal lattice is provided with 30 points and Two points located at both ends of each edge and two points located at the center of each edge are distributed with germanium rods, and a solid substrate is filled between the germanium rods; the high-refractive-index germanium-doped regions and the low-refractive-index packets of the germanium rods There is a refractive index difference Δ in the layer region, which satisfies Δ=(n _high ² -n _low ² )/(2×n _high ² ), where n _high and n _low are the maximum and The refractive index of the low-refractive index cladding region, the refractive index difference Δ satisfies 1.5%≤Δ≤3%, when the refractive index difference Δ is determined, the distribution of the photonic band gap is only related to the diameter d of the germanium rod, and is related to the arrangement of the germanium rod Regardless of the method, the suppression of the stimulated Raman scattering effect can be achieved by increasing or decreasing the diameter d of the germanium rod; The all-solid-state microstructure fiber is spliced on the output pigtail of the high-power fiber laser as a long-distance transmission fiber; when the all-solid-state microstructure fiber transmits the high-power fiber laser, the germanium rod in the microstructure cladding is generated due to anti-resonant coupling. Photonic band gap effect; for the signal wavelength laser, there is multiple interference between the scattered light falling within the frequency range of the photonic band gap, so that its intensity is weakened and cannot pass through the microstructure cladding, and is ultimately limited to stable transmission in the fiber core, realizing the signal wavelength High-efficiency single-mode low-loss transmission of laser light; at the same time, the stimulated Raman scattering Stokes wavelength that falls outside the photonic bandgap frequency range exhibits high loss and cannot be transmitted stably. This all-solid-state microstructured fiber can suppress high-power fiber lasers. Stimulated Raman scattering effects during long-distance transmission. 2 . The method for suppressing stimulated Raman scattering according to claim 1 , wherein the core material is solid quartz, and the solid substrate is a solid quartz substrate. 3 . 3. The method for suppressing stimulated Raman scattering according to claim 2, wherein the structure and size of all germanium rods are the same, and the germanium rods comprise a high-refractive-index germanium-doped region located in the center and a low-refractive-index germanium-doped region located in the outer layer. The refractive index cladding region, wherein the refractive index of the high-refractive-index germanium-doped region exhibits a parabolic gradient or step-type refractive index distribution. 4 . The method for suppressing stimulated Raman scattering according to claim 1 , wherein the low refractive index cladding region of the germanium rod is made of solid quartz or fluorine-doped solid quartz. 5 . 5. A high-power fiber laser, characterized in that it comprises a laser generating unit, the laser generating unit is used to generate a high-power fiber laser, and the output pigtail of the laser generating unit is fused with an all-solid-state microstructure fiber as a long-distance transmission fiber; wherein The all-solid-state microstructure optical fiber includes a core and a microstructure cladding, the core is a solid core, the microstructure cladding is clad on the periphery of the core, and the microstructure cladding includes For the germanium rod and solid substrate, the regular hexagonal lattice is distributed with four layers from the inside to the outside. The lattice and the fourth layer of regular hexagonal lattice; the center distance Λ of any two adjacent points in the regular hexagonal lattice is equal, the core is located at the center of the regular hexagonal lattice, and the first layer of the regular hexagonal lattice is on the There are 12 points and germanium rods are distributed on all points, there are 18 points on the second layer of regular hexagonal lattice, and germanium rods are distributed on two points located in the middle of each edge, and the third layer is regular six There are 24 points on the polygonal lattice, and germanium rods are distributed on the four points located at both ends of each edge. The fourth layer of regular hexagonal lattice is provided with 30 points and two located at the two ends of each edge. There are germanium rods distributed on the point and the two points located in the center of each edge. The solid substrate is filled between the germanium rods. There is a refractive index difference Δ between the germanium-doped region with high refractive index and the cladding region with low refractive index. Satisfy Δ=(n _high ² -n _low ² )/(2×n _high ² ), where n _high and n _low are the maximum refractive index of the germanium-doped region with high refractive index and the refractive index of the cladding region with low refractive index, respectively , the refractive index difference Δ satisfies 1.5%≤Δ≤3%. When the refractive index difference Δ is determined, the distribution of photonic band gap is only related to the diameter d of the germanium rod, and has nothing to do with the arrangement of the germanium rod. Suppression of the scattering effect can be achieved by increasing or decreasing the diameter d of the germanium rod. 6. An all-solid-state microstructure optical fiber, characterized in that it comprises a fiber core and a microstructure cladding, the fiber core is a solid fiber core, the microstructure cladding is wrapped around the periphery of the fiber core, and the microstructure cladding is It includes germanium rods and solid substrates located in a regular hexagonal lattice. The regular hexagonal lattice is distributed with four layers from the inside to the outside. lattice, the third layer of regular hexagonal lattice and the fourth layer of regular hexagonal lattice; the center spacing Λ of any two adjacent points in the regular hexagonal lattice is equal, and the fiber core is located at the center of the regular hexagonal lattice, There are 12 points on the first layer of regular hexagonal lattice, and germanium rods are distributed on all the points, and there are 18 points on the second layer of regular hexagonal lattice, and the two points located in the middle of each side are both. There are germanium rods distributed, there are 24 points on the third layer of regular hexagonal lattice, and germanium rods are distributed on the four points at both ends of each side, and there are 30 points on the fourth layer of regular hexagonal lattice And two points located at both ends of each edge and two points located at the center of each edge are distributed with germanium rods, among which a solid substrate is filled between the germanium rods, all the germanium rods have the same structure and size, and the germanium rods are There is a refractive index difference Δ between the high-refractive-index germanium-doped region and the low-refractive-index cladding region, which satisfies Δ=(n _high ² -n _low ² )/(2×n _high ² ), where n _high and n _low are respectively high refraction The maximum value of the refractive index of the germanium-doped region and the refractive index of the low-refractive index cladding region, the refractive index difference Δ satisfies 1.5%≤Δ≤3%, when the refractive index difference Δ is determined, the distribution of the photonic band gap is only the same as that of the germanium rod. The diameter d is related to the arrangement of the germanium rods, and the suppression of the stimulated Raman scattering effect can be achieved by increasing or decreasing the diameter d of the germanium rods.

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