An active optical fiber for generating a single high-order transverse mode laser

Abstract

The application discloses an active optical fiber for generating single high-order transverse mode laser, comprising an active core region, a passive background region, a double-layer anti-resonance unit region, an inner cladding region and an outer cladding region; the double-layer anti-resonance unit region comprises a first anti-resonance region and a second anti-resonance region; the first anti-resonance region is composed of six first capillaries which are symmetrically distributed along the y-axis, and the included angle between the line connecting the center of the adjacent first capillary on the same side of the y-axis and the midpoint of the core is alpha; the second anti-resonance region is composed of two second capillaries with the center on the y-axis and four second capillaries which are symmetrically distributed along the y-axis, the refractive index of the two second capillaries with the center on the y-axis is greater than that of the other four second capillaries, the included angle between the line connecting the center of the second capillary on the same side of the y-axis and the midpoint of the core is alpha, and the center of the second capillary is located on the midline of the line connecting the centers of the adjacent first capillaries in the first anti-resonance region; the wall thickness of all the capillaries in the double-layer anti-resonance unit region satisfies the anti-resonance condition.

Description

Technical Field

[0001] This invention relates to the field of active optical fibers, and more particularly to an active optical fiber for generating a single high-order transverse mode laser. Background Technology

[0002] High-order transverse-mode fiber lasers (LP lasers) possess unique mode field distributions compared to traditional fundamental transverse-mode fiber lasers, offering broad application prospects in mode-division multiplexing optical communication, optical tweezers, fiber optic sensing, high-resolution imaging, and materials processing. 11 The mode is one of the most common operating modes in high-order transverse-mode fiber lasers. It can be generated by devices such as spatial light modulators, fiber gratings, and mode selection couplers, but these devices are all used in LP (Lithium-Laser Laser) systems. 11 The passive generation of modes is due to the lack of passive devices. Limited by the power handling capacity of the devices, the power level of the generated high-order mode lasers is relatively low. Furthermore, the generated high-order mode lasers may propagate in free space, resulting in poor system integration and stability, or they may propagate in few-mode fibers, where the mode purity deteriorates significantly with the fiber transmission length, making it difficult to meet the actual application requirements.

[0003] Microstructured fiber design has demonstrated unique advantages in realizing active and passive fibers with large mode field areas. Among them, antiresonant fibers have attracted widespread attention for their wide operating wavelength range of fundamental transverse mode, large mode field area, and low-loss transmission, and have achieved important applications in high-power laser power transmission fibers, gas Raman fiber lasers, and gas sensors. However, the aforementioned applications are mostly limited to hollow-core antiresonant fibers. Although solid-core antiresonant fibers have been studied to some extent in recent years, they are only used for the generation and transmission of fundamental transverse mode lasers. Summary of the Invention

[0004] This invention provides an active optical fiber for generating a single high-order transverse mode laser, which addresses the shortcomings of conventional methods for generating LP lasers. 11 The limitations of the mode can be overcome by selecting appropriate materials and designing the fiber optic structure to achieve the target band LP. 11 This single-mode laser generation and low-loss transmission can be applied to high-power fiber lasers and amplifiers with special mode field distributions, as detailed below:

[0005] An active optical fiber for generating a single high-order transverse mode laser, the active optical fiber comprising: an active core region, a passive background region, a double-layer anti-resonant unit region, an inner cladding region, and an outer cladding region;

[0006] The active fiber core region is a rare earth ion doped region; the passive background region is a mode leakage region with a refractive index higher than that of the active fiber core region.

[0007] The double-layer anti-resonance unit region includes: a first anti-resonance region and a second anti-resonance region;

[0008] The first anti-resonance region consists of six first capillaries symmetrically distributed along the y-axis. The angle between the line connecting the center of the adjacent first capillaries and the midpoint of the fiber core on the same side of the y-axis is α.

[0009] The second anti-resonance region consists of two circles centered on the y-axis and four second capillaries symmetrically distributed along the y-axis. The refractive index of the two second capillaries centered on the y-axis is greater than that of the other four second capillaries. The angle between the line connecting the center of the second capillaries on the same side of the y-axis and the midpoint of the fiber core is α, and the center of the capillaries is located on the perpendicular bisector of the line connecting the centers of adjacent first capillaries in the first anti-resonance region.

[0010] The wall thickness of all capillaries in the double-layer anti-resonance unit region satisfies the anti-resonance condition.

[0011] The material of the inner cladding region is a high refractive index material that forms a double-layer FP etalon with the passive background region and satisfies the anti-resonance condition.

[0012] The material of the outer cladding region is a material with a refractive index lower than that of the passive background region.

[0013] The refractive index relationship of different parts of the active optical fiber is as follows:

[0014] The inner cladding region and the two second capillaries on the y-axis > the first and second anti-resonance regions and the remaining ten capillaries > the passive background region > the active fiber core region > the outer cladding region. Among them, the inner cladding region and the two second capillaries on the y-axis have no refractive index relationship, which can be adjusted appropriately.

[0015] Furthermore, the cross-section of the active optical fiber is symmetrical along both the x-axis and y-axis.

[0016] In this system, the wall thickness of the first and second capillaries in the double-layer anti-resonance unit region is equal; the refractive index and inner diameter of all first capillaries in the first anti-resonance region are equal; the inner diameter of all second capillaries in the second anti-resonance region is equal, the refractive indices of the two second capillaries on the y-axis are equal, and the refractive indices of the remaining four second capillaries are equal.

[0017] In the first anti-resonance region, the outer walls of all the first capillaries are tangent to the fiber core; in the second anti-resonance region, the centers of the two second capillaries on the y-axis are located on the same circumference, and the centers of the remaining four second capillaries are located on another circumference.

[0018] The beneficial effects of the technical solution provided by this invention are:

[0019] 1. This invention increases the refractive index of capillaries excluding LP by introducing two high-refractive-index capillaries with their centers on the y-axis in the anti-resonance region and adjusting the angle α between the lines connecting the centers of adjacent capillaries and the midpoint of the fiber core on the same side of the y-axis in the two anti-resonance regions. 11The losses of modes other than the main mode can be used not only for the generation of a single high-order transverse mode, but also for its low-loss transmission, thus compensating for the losses in LP modes based on mode selection couplers. 11 The optical fibers used in mode fiber lasers do not have the capability for long-distance, high-mode-purity transmission of LP. 11 Defects of modal lasers;

[0020] 2. This invention employs a unique double-layer anti-resonant unit and double-layer FP etalon design, which can still guarantee LP over a wide wavelength range even with a large mode field area. 11 The optical fiber enables low-loss transmission of high-order transverse mode lasers, while other modes have higher losses, thus achieving the unique capability of transmitting large-mode-area single high-order transverse mode lasers through optical fibers. In addition, the solid fiber structure design facilitates the full fiberization of high-order transverse mode lasers, which is beneficial for improving system integration and operational stability.

[0021] 3. This invention can be fabricated using a stacking-drawing method, which is simple in structure and easy to implement. Furthermore, the optical fiber has advantages such as low nonlinear effects, wide transmission bandwidth, and high damage threshold, and can be applied to the field of high-power special fiber laser technology. Attached Figure Description

[0022] Figure 1 A schematic diagram of the cross-sectional structure of an active optical fiber that generates a single high-order transverse mode laser.

[0023] Figure 2 LP in an active fiber for generating a single high-order transverse mode laser 01 LP 11a LP 11b Loss characteristics of the three modes in the 1550nm band;

[0024] Figure 3 For an active fiber that generates a single high-order transverse mode laser at 1550 nm, LP 01 LP 11a LP 11b LP 21a LP 21b LP 02 Electric field diagrams for six modes and two polarization directions.

[0025] Appendix Figure 1 The list of components represented by each number is as follows:

[0026] 1: Active fiber core area;

[0027] 2: Passive background area;

[0028] 3: All the first capillaries in the first anti-resonance region;

[0029] 4: The two second capillaries whose centers are on the y-axis in the second anti-resonance region;

[0030] 5: The remaining four second capillaries in the second anti-resonance region;

[0031] 6: Inner cladding area;

[0032] 7: Outer layer area. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0034] Figure 1 This is a schematic diagram of the cross-sectional structure of an active optical fiber that generates a single high-order transverse mode laser. The fiber structure is symmetrical along the x and y directions (centrosymmetric about the fiber core). Part 1 represents the active fiber core region, with a diameter of d. c =50μm, material refractive index 1.45; Part 2 is the passive background region, distributed around the active core region, material refractive index 1.45055; Part 3 consists of six first capillaries in the first anti-resonance region, with an inner diameter of d1 = 16.5μm and a material refractive index of 1.48; Part 4 consists of two second capillaries in the second anti-resonance region, centered on the y-axis, with a distance of T3 = 15μm from the core and a material refractive index of 1.495; Part 5 consists of the remaining four second capillaries in the second anti-resonance region, with a distance of T1 = 26μm from the core and a distance of T2 = 23μm from the inner cladding, material refractive index 1.48; Parts 4 and 5 The inner diameter of the six second capillaries is d2 = 36.5 μm. The wall thickness of all capillaries in parts 3, 4, and 5 is t = 3.92 μm, which is the second-order anti-resonance wall thickness at 1550 nm. The angle between the line connecting the center of the adjacent capillaries on the same side of the y-axis in parts 3 and 5 and the midpoint of the fiber core is α = 49°. Part 6 is the inner cladding region with a thickness of t1 = 6.5 μm and a refractive index of 1.495. Parts 6 and 2 constitute a double-layer FP etalon and satisfy the anti-resonance condition. Part 7 is the outer cladding region with a thickness of t2 = 10 μm and a refractive index of 1.3757. Composite materials such as acrylic resin and polyimide can be selected. The double-layer FP etalon is well known to those skilled in the art, and will not be described in detail in this embodiment.

[0035] The active fiber design scheme for generating a single high-order transverse mode laser proposed in this embodiment is not limited to the materials and fiber structure parameters selected in this embodiment. Different materials and structure parameters can be used to meet other requirements.

[0036] Figure 2 An active fiber LP that generates a single high-order transverse mode laser.01 LP 11a LP 11b Loss characteristics of the three modes in the 1550nm band; LP in the 1544–1579nm band 11a The loss of the first mode is less than 0.1 dB / m, while the losses of the other two modes are greater than 10 dB / m, indicating that this fiber can achieve LP wavelengths greater than 30 nm in the 1550 nm wavelength range. 11a Single-mode low-loss transmission.

[0037] By adjusting the fiber structure parameters and selecting different materials, the active optical fiber proposed in this embodiment of the invention can achieve LP in other bands. 11a Single-mode transmission.

[0038] Figure 3 For an active fiber that generates a single high-order transverse mode laser at 1550 nm, LP 01 LP 11a LP 11b LP 21a LP 21b LP 02 Electric field diagrams for six modes in both x (top) and y (bottom) polarization directions. Except for LP. 11a Outside of the mode, the light field of other modes leaks a lot of energy into the background region, with losses all exceeding 10dB / m.

[0039] In summary, the active optical fiber proposed in this invention for generating a single high-order transverse mode laser can achieve LP over a wide wavelength range under conditions of large mode field area. 11a Single-mode laser generation and low-loss transmission, i.e., LP 11a The transmission loss of a single mode is less than 0.1 dB / m, while the transmission loss of other modes is greater than 10 dB / m. This embodiment of the invention introduces two high-refractive-index capillaries centered on the y-axis and adjusts their distance from the active fiber core, thus ensuring LP (Limited Fiber) transmission loss. 11a Under the premise of low transmission loss in the mode, the loss of other modes is increased, thereby realizing the ability of the invented optical fiber to suppress other modes, and realizing the generation of a single high-order mode and low-loss transmission.

[0040] The embodiments of the present invention compensate for the fact that the optical fibers used in high-order transverse mode fiber lasers, represented by mode selection coupler-based solutions, do not inherently possess the ability to transmit LP over long distances with high mode purity. 11 The laser itself cannot generate high-power LP due to its limited ability to modulate. 11 Inherent defects such as patterned lasers.

[0041] Unless otherwise specified, the model numbers of the various devices in this embodiment of the invention are not limited, and any device that can perform the above functions is acceptable.

[0042] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An active optical fiber for generating a single high-order transverse mode laser, characterized in that, The active optical fiber includes: an active core region, a passive background region, a double-layer anti-resonant unit region, an inner cladding region, and an outer cladding region; The active fiber core region is a rare earth ion doped region; the passive background region is a mode leakage region with a refractive index higher than that of the active fiber core region. The double-layer anti-resonance unit region includes: a first anti-resonance region and a second anti-resonance region; The first anti-resonance region consists of six first capillaries symmetrically distributed along the y-axis. The angle between the line connecting the center of the adjacent first capillaries and the midpoint of the fiber core on the same side of the y-axis is α. The second anti-resonance region consists of two circles centered on the y-axis and four second capillaries symmetrically distributed along the y-axis. The refractive index of the two second capillaries centered on the y-axis is greater than that of the other four second capillaries. The angle between the line connecting the center of the second capillaries on the same side of the y-axis and the midpoint of the fiber core is α, and the center of the capillaries is located on the perpendicular bisector of the line connecting the centers of adjacent first capillaries in the first anti-resonance region. The wall thickness of all capillaries in the double-layer anti-resonance unit region satisfies the anti-resonance condition. The material of the inner cladding region is a high refractive index material that forms a double-layer FP etalon with the passive background region and satisfies the anti-resonance condition. The material of the outer cladding region is a material with a refractive index lower than that of the passive background region; The six first capillaries in the first resonant region are located in the inner region closer to the fiber core, while the six second capillaries in the second resonant region are located in the outer region farther from the fiber core.

2. The active optical fiber for generating a single high-order transverse mode laser according to claim 1, characterized in that, The refractive index relationship of different parts of an active optical fiber is as follows: The inner cladding region and the two second capillaries on the y-axis > the first and second anti-resonance regions and the remaining ten capillaries > the passive background region > the active fiber core region > the outer cladding region. Among them, the inner cladding region and the two second capillaries on the y-axis have no refractive index relationship, which can be adjusted appropriately.

3. An active optical fiber for generating a single high-order transverse mode laser according to claim 1, characterized in that, The cross-section of active optical fiber is symmetrical along both the x-axis and y-axis.

4. An active optical fiber for generating a single high-order transverse mode laser according to claim 1, characterized in that, The wall thicknesses of the first and second capillaries in the double-layer anti-resonant unit region are equal; In the first anti-resonance region, all first capillaries have the same refractive index and inner diameter; in the second anti-resonance region, all second capillaries have the same inner diameter, the two second capillaries on the y-axis have the same refractive index, and the remaining four second capillaries have the same refractive index.

5. An active optical fiber for generating a single high-order transverse mode laser according to claim 1, characterized in that, The outer walls of all the first capillaries in the first anti-resonance region are tangent to the fiber core; The second anti-resonance region has two second capillaries on the y-axis whose centers are located on the same circumference, while the centers of the other four second capillaries are located on another circumference.

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