CN101938080B - An active optical fiber with single-mode output TM01 mode characteristics - Google Patents

Abstract

The invention discloses an active optical fiber with single-mode output TM ₀₁ mode characteristics, and relates to an active optical fiber with an active optical fiber. The active optical fiber includes: doped rare earth ion core (1) and cladding (4). A non-doped rare earth ion annular core (2) is arranged between the doped rare earth ion core (1) and the cladding (4). Introduce axisymmetrically distributed rectangular air holes (3) or circular air hole arrays (5) along the radial direction in the non-doped rare earth ion annular core (2), and the angle between adjacent air holes is 360/m degrees , 12<m<30, m is an integer. It solves the problem of simplifying the structure of the single-mode output _TM01 mode fiber laser system and improving the working stability. Finally, the TM ₀₁ mode in the fiber laser occupies a dominant position in the mode competition. The output signal light with high radial polarization purity can be obtained by using the active optical fiber, without additionally introducing a mode selection device in the resonant cavity.

Description

An active optical fiber with single-mode output TM₀₁ mode characteristics

technical field

The invention relates to an active optical fiber with single-mode output TM ₀₁ mode characteristics.

Background technique

The radially polarized laser is different from linearly polarized light and circularly polarized light. The direction of the electric field is distributed along the radial direction, and the electric field vector and field amplitude are both axisymmetric. Compared with linear (circular) polarization, the radially polarized laser can obtain a smaller spot by focusing through a lens with a high numerical aperture, so it can be used as a super-resolution microscopic light source. In addition, it is used in efficient metal cutting, electron acceleration and biological optical tweezers It also has important application value in other fields. Lasers that obtain radially polarized mode output are mainly classified into solid-state lasers, gas lasers, and fiber lasers. Compared with solid-state and gas lasers, fiber lasers have the advantages of small size, good heat dissipation and high beam quality. Therefore, using fiber lasers to output radial polarization modes has become a research hotspot in recent years. At present, the method of using fiber laser to output radial polarization mode, that is, TM ₀₁ mode, is mainly as follows:

1. A Brewster biconical prism is introduced into the fiber laser resonator. According to Brewster's law, only the radially polarized TM ₀₁ mode has the smallest loss when passing through the prism, and other modes have the polarization component of the vertical incident plane. Emission occurs, resulting in a large loss, and finally the fiber laser acquires the characteristics of a single-mode output TM ₀₁ mode.

2. The fiber amplifier uses the active polarization maintaining fiber as the gain medium, and the linearly polarized seed signal light is injected into the active polarization maintaining fiber at an appropriate angle, so as to maximize the excitation of the LP ₁₁ mode and suppress the LP ₀₁ mode. The optical fiber applies pressure, and its direction is at an angle of 45 degrees to the main axis. By precisely adjusting the pressure and angle, the two orthogonally polarized LP ₁₁ modes are synthesized into TM ₀₁ mode in phase.

The above two methods have their own shortcomings. The former needs to introduce discrete optical components into the laser resonator to reduce the output efficiency of the laser. The latter needs to use auxiliary tools to accurately adjust the incident angle of the seed light source and apply it to the active polarization maintaining fiber The size and direction of the upper pressure not only increase the complexity of the system, but also bring instability to the laser.

Contents of the invention

The technical problem to be solved by the present invention is to simplify the single-mode output _TM01 mode fiber laser system structure and improve the working stability, and propose an active optical fiber with single-mode output _TM01 mode characteristics.

Technical scheme of the present invention:

An active optical fiber with single-mode output TM ₀₁ mode characteristics, the active optical fiber includes: a doped rare earth ion core and a cladding; a non-doped rare earth ion annular fiber is arranged between the doped rare earth ion core and the cladding core.

Axisymmetrically distributed air holes are introduced into the non-doped rare earth ion annular core along the radial direction, and the angle between adjacent air holes is 360/m degrees, 12<m<30, m is an integer.

In the non-doped rare earth ion annular core, the air holes distributed axially symmetrically along the radial direction are introduced into a rectangular hole or a circular hole array.

Beneficial results of the present invention:

The present invention provides an active optical fiber with single-mode output TM ₀₁ mode characteristics, which is achieved by introducing a ring-shaped non-doped core between the doped rare earth ion core and the cladding, and introducing axisymmetrically distributed rectangular air Holes or circular hole arrays to obtain radial birefringence, resulting in confinement loss of TM ₀₁ mode much smaller than TE ₀₁ mode and HE ₂₁ mode, and finally make TM ₀₁ mode dominate in the mode competition in fiber lasers. Using the active fiber with single-mode output TM ₀₁ mode characteristics can obtain output signal light with high radial polarization purity, and does not need to introduce additional mode selection devices in the resonator, thus simplifying the system of single-mode output TM ₀₁ mode fiber laser The structure improves the working stability.

Description of drawings

Figure 1 Schematic diagram of the active optical fiber structure of the single-mode output TM ₀₁ mode with a rectangular air hole angle of 30 degrees;

Figure 2 is a schematic diagram of the structure of an active optical fiber with a single-mode output TM ₀₁ mode with a rectangular air hole at an angle of 20 degrees;

Figure 3 is a schematic diagram of the active optical fiber structure of the single-mode output TM ₀₁ mode with a rectangular air hole angle of 12 degrees;

Figure 4 is a schematic diagram of the active optical fiber structure of the single-mode output TM ₀₁ mode with a circular air hole array at an angle of 30 degrees;

Reference numerals: 1 - doped rare earth ion core, 2 - non-doped rare earth ion annular core, 3 - rectangular air hole, 4 - cladding, 5 - circular air hole array.

Detailed ways

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

An active optical fiber with single-mode output TM ₀₁ mode characteristics, the active optical fiber includes: doped rare earth ion core 1 and cladding 4 . A non-doped rare earth ion annular core 2 is arranged between the doped rare earth ion core 1 and the cladding 4 .

Axisymmetrically distributed rectangular air holes 3 or circular air hole arrays 5 are introduced into the non-doped rare earth ion annular core 2 along the radial direction, and the angle between adjacent air holes is 360/m degrees, 12 <m<30, m is an integer.

The refractive indices of the doped rare earth ion core 1, the non-doped rare earth ion annular core 2 and the cladding 4 are expressed as n ₁ , n ₂ and n ₄ respectively.

Embodiment one

An active optical fiber with single-mode output TM ₀₁ mode characteristics, as shown in Figure 1, consists of a rare earth ion doped core 1, a non-doped rare earth ion annular core 2 and a cladding 4.

The diameter of the rare earth ion-doped core 1 is 8 μm, and the refractive index n ₁ =1.4573.

The distribution of rare earth ions in the rare earth ion-doped core 1 is as follows: the concentration of rare earth ions in the circular region with a middle radius of 2.35 μm is 0, and the concentration of rare earth ions in other regions is 1.8×10 ²⁶ m ^-3 .

The outer diameter of the non-doped rare-earth ion annular core 2=20 μm, the air holes introduced into the axisymmetric distribution along the radial direction in the non-doped rare-earth ion annular core 2 are rectangular air holes 3, and the size of the rectangular air holes 3 is wide The sum and length are respectively: 0.1 μm and 6 μm, the angle between adjacent rectangular air holes 3 is 360/12 degrees = 30 degrees, the refractive index n 3 of the rectangular air holes ₃ = 1; Refractive index n ₂ =1.449.

The refractive index n 4 of the cladding ₄ =1.4508.

Embodiment two

Embodiment 2, as shown in Figure 2, is different from Embodiment 1:

The refractive index n ₁ of the core 1 doped with rare earth ions is 1.464.

The outer diameter of the non-doped rare-earth ion annular core 2=20 μm, the air holes introduced into the axisymmetric distribution along the radial direction in the non-doped rare-earth ion annular core 2 are rectangular air holes 3, and the adjacent rectangular air holes 3 The included angle is 360/18 degrees = 20 degrees, the refractive index n 3 of the rectangular air hole ₃ = 1; the refractive index n 2 of the non-doped rare earth ion annular core ₂ = 1.46.

The refractive index n _{4 of the cladding 4} =1.4573.

Embodiment Three

Embodiment 3, as shown in Figure 3, is different from Embodiment 1:

The refractive index n ₁ of the core 1 doped with rare earth ions is 1.4415.

The outer diameter of the non-doped rare earth ion annular core 2 is 16 μm, and the refractive index n ₂ of the non-doped rare earth ion annular core 2 is 1.421.

In the non-doped rare earth ion annular core 2, the air holes distributed axially symmetrically along the radial direction are rectangular air holes 3. The width and length of the rectangular air holes 3 are respectively: 0.1 μm and 4 μm, and the adjacent rectangular air holes 3 The included angle is 360/30 degrees=12 degrees, and the refractive index n ₃ of the rectangular air hole 3 is 1.

The refractive index n 4 of the cladding ₄ =1.43385.

Embodiment Four

Embodiment 4, as shown in Figure 4, is different from Embodiment 1:

The refractive index n ₁ of the core 1 doped with rare earth ions is 1.4573.

The outer diameter of the non-doped rare earth ion annular fiber core 2: 20 μm, the air holes introduced into the non-doped rare earth ion annular fiber core 2 along the radial direction and distributed axisymmetrically are circular air hole arrays 5, and the diameter of the circular air holes is 0.1 micron, the size width and length of the circular air hole array 5 are respectively: 0.1 μm and 6 μm, the angle between adjacent circular air hole arrays 5 is 360/12 degrees=30 degrees 30 degrees, the circular air holes The refractive index of = 1.

The refractive index n ₂ of the non-doped rare earth ion annular core 2 is 1.4515.

The refractive index n _{4 of the cladding 4} =1.451.

Design steps of active optical fiber parameters with single-mode output TM ₀₁ mode characteristics:

1. Set the basic parameters of the active optical fiber, that is, the diameter and refractive index of the doped rare earth ion core 1; the outer diameter of the non-doped rare earth ion annular core 2 and the size of the rectangular air hole, and the diameter of the adjacent air hole included angle; cladding index of refraction.

2. Setting and adjusting the refractive index of the non-doped rare earth ion annular core 2, so that the limiting loss of the TM ₀₁ mode is much smaller than that of the TE ₀₁ mode and the HE ₂₁ mode.

3. Optimize the rare earth ion distribution in the doped rare earth ion core 1, so that the mode field distribution and the integral value of the gain region of TM ₀₁ and fundamental mode HE ₁₁ reach the maximum and minimum values respectively, thus resulting in the TM ₀₁ mode in the fiber laser Dominance in the model competition.

Claims (2)

1. one kind has single mode output TM ₀₁The Active Optical Fiber of mode characteristic, this Active Optical Fiber comprises: doping with rare-earth ions fibre core (1) and covering (4); It is characterized in that: non-doping with rare-earth ions annular fibre core (2) is set between doping with rare-earth ions fibre core (1) and the covering (4);

Wherein the diameter of doping with rare-earth ions fibre core (1) is 8 μ m, its refractive index n ₁=1.4573, the rare earth ion in this doping with rare-earth ions fibre core (1) is distributed as: middle radius is that the border circular areas middle rare earth ion concentration of 2.35 μ m is 0, and all the other regional rare earth ion concentrations are 1.8 * 10 ²⁶m ^-3

The external diameter of non-doping with rare-earth ions ring-type fibre core (2) is 20 μ m, in non-doping with rare-earth ions annular fibre core (2), introduce the rectangle airport (3) that axial symmetry distributes along radial direction, the size of rectangle airport (3) is wide and long to be respectively: 0.1 μ m and 6 μ m, the angle of adjacent two rectangle airports (3) are 30 degree; The refractive index n of rectangle airport (3) ₃=1; The refractive index n of non-doping with rare-earth ions annular fibre core (2) ₂=1.449;

The refractive index n of covering (4) ₄=1.4508.

2. one kind has single mode output TM ₀₁The Active Optical Fiber of mode characteristic, this Active Optical Fiber comprises: doping with rare-earth ions fibre core (1) and covering (4); It is characterized in that: non-doping with rare-earth ions annular fibre core (2) is set between doping with rare-earth ions fibre core (1) and the covering (4);

Wherein the diameter of doping with rare-earth ions fibre core (1) is 8 μ m, its refractive index n ₁=1.4573, the rare earth ion in this doping with rare-earth ions fibre core (1) is distributed as: middle radius is that the border circular areas middle rare earth ion concentration of 2.35 μ m is 0, and all the other regional rare earth ion concentrations are 1.8 * 10 ²⁶m ^-3

The external diameter of non-doping with rare-earth ions ring-type fibre core (2) is 20 μ m, in non-doping with rare-earth ions annular fibre core (2), introduce the circular airport array (5) that axial symmetry distributes along radial direction, wherein circular airport diameter is 0.1 micron, the size of this circle airport array (5) is wide and long to be respectively: 0.1 μ m and 6 μ m, the angle of adjacent two circular airport arrays (5) is 30 degree, the refractive index n of circular airport ₃Be 1; The refractive index n of non-doping with rare-earth ions annular fibre core (2) ₂=1.4515;

The refractive index n of covering (4) ₄=1.451.

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