CN113725711B - Optical vortex optical fiber laser based on double vortex wave plates - Google Patents

Abstract

The invention discloses an optical vortex optical fiber laser based on double vortex wave plates, which comprises an annular cavity, wherein the annular cavity comprises a wavelength division multiplexer, a gain optical fiber, a space optical portion and a plurality of single-mode optical fibers which are sequentially connected end to end, the input end and the output end of the space optical portion are both connected with optical fiber collimators, the wavelength division multiplexer is connected with a light source, an optical isolator is connected on an optical fiber light path in the annular cavity or a space light path of the space optical portion, a polarization control module is integrated on the optical fiber light path or the space light path, the space optical portion comprises a plurality of vortex wave plates, and an output mirror is arranged between the vortex wave plates. The invention inserts the double vortex wave plate into the laser cavity of the fiber laser, on one hand, the unstable factor caused by the backward reflected light returning to the optical fiber light path is greatly reduced, on the other hand, the utilization rate of the light beam in the cavity is greatly improved, and the use of few-mode fiber and mode selection devices is avoided, thereby obtaining the ultrashort pulse cylindrical vector light beam and vortex light beam with high purity and high utilization rate.

Description

An optical vortex fiber laser based on a double vortex wave plate

technical field

The invention relates to the field of novel vector light field control, in particular to an optical vortex fiber laser based on a double vortex wave plate.

Background technique

的新型结构光束，其单个光子携带

的轨道角动量(Orbital Angular Momentum,OAM)，因为又被称为OAM光束。OAM光束的中心存在相位奇点，也表现为中心光强为零的环状光强分布。携带轨道角动量以及环状光强分布的特性使涡旋光束在轨道角动量复用光纤通信、粒子操控、激光微纳加工等领域具有广泛的应用前景。随着学者们的深入研究，光学涡旋的各种新应用层出不穷，对光学涡旋激光器有着强烈的需求。Optical vortex is a new type of structured beam. Typical optical vortex includes cylindrical vector beam and vortex beam. Among them, the cylindrical vector beam has a rotationally symmetric polarization distribution, and typical cylindrical vector beams include radially polarized beams and angularly polarized beams. There is a polarization singularity in the center of the cylindrical vector beam, which is manifested as a ring-shaped light intensity distribution with the central light intensity being zero. The anisotropy of the polarization state and the characteristics of the annular light intensity distribution make the cylindrical vector beam widely used in laser processing, particle acceleration, surface plasmon excitation, super-resolution optical microscopy, optical tweezers and other fields; and the vortex beam means that the wavefront has

A novel structured beam of which a single photon carries

Orbital Angular Momentum (OAM), because it is also called OAM beam. There is a phase singularity in the center of the OAM beam, which also appears as a ring-shaped light intensity distribution with zero central light intensity. The characteristics of carrying orbital angular momentum and annular light intensity distribution make vortex beams have broad application prospects in the fields of orbital angular momentum multiplexing optical fiber communication, particle manipulation, and laser micro-nano processing. With the in-depth research of scholars, various new applications of optical vortex emerge in an endless stream, and there is a strong demand for optical vortex lasers.

Contents of the invention

Purpose of the invention: The purpose of the present invention is to provide an optical vortex fiber laser based on a double vortex wave plate, inserting two identical optical vortex wave plates in the cavity of the fiber laser, by adjusting the polarization state in the laser cavity, respectively Realize the output of cylindrical vector beam (including radial and angular polarization beam) and vortex beam.

Technical solution: The present invention includes a ring cavity, and the ring cavity includes a wavelength division multiplexer, a gain fiber, a spatial light part and a plurality of single-mode fibers connected end to end in sequence, and the input end and the output end of the space light part are both An optical fiber collimator is connected, the wavelength division multiplexer is connected to the light source, an optical isolator is connected to the optical fiber optical path in the annular cavity or the spatial optical path of the spatial light part, and the optical fiber optical path or the spatial optical path A polarization control module is integrated on the road, and the spatial light part includes a plurality of vortex wave plates, and output mirrors are arranged between the vortex wave plates.

The input end of the spatial light part is connected with a second fiber collimator, and the output end is connected with a first fiber collimator.

The spatial light part includes a first vortex wave plate and a second vortex wave plate, and an output mirror is arranged between the first vortex wave plate and the second vortex wave plate, wherein the first vortex wave plate The wave plate is placed on the side of the second fiber collimator, and the second vortex wave plate is placed on the side of the first fiber collimator.

The single-mode fiber includes a first single-mode fiber and a second single-mode fiber, one end of the first single-mode fiber is connected to the first fiber collimator, the other end is connected to the second single-mode fiber, and the second single-mode fiber The other end of the mode fiber is connected with a wavelength division multiplexer.

A mode-locking device is provided between the first single-mode fiber and the second single-mode fiber, and the mode-locking device includes a first fiber jumper and a second fiber jumper, wherein the second fiber jumper is the same as the first fiber jumper A single-mode optical fiber is connected, and the first optical fiber jumper is connected to the second single-mode optical fiber.

The mode-locking device is integrated into the fiber optical path or placed in the spatial optical path.

The first fiber jumper and the second fiber jumper are connected by a fiber coupler, and a saturable absorber is arranged between the first fiber jumper and the second fiber jumper.

The optical isolator is a spatial optical isolator placed in the spatial optical path in the cavity or a fiber isolator placed in the optical fiber optical path in the cavity.

The polarization control module adopts a fiber optic polarization controller placed in the optical fiber path or a combination of a half-wave plate and a quarter-wave plate placed in the spatial light path, and the half-wave plate and quarter-wave The plates are arranged sequentially along the optical path, wherein the half-wave plate is placed on one side of the second fiber collimator, and the other side of the quarter-wave plate is provided with the first vortex wave plate.

The gain fiber is a rare-earth-doped gain fiber, and the wavelength of light radiated by the gain fiber should be greater than the cut-off frequency of the single-mode fiber in the device, so that the single-mode fiber works in a single-mode transmission state.

Working principle: By inserting two identical vortex half-wave plates into the laser cavity of the ring fiber laser, the transverse mode in the laser cavity can realize the conversion of Gaussian beam-vortex beam/cylindrical vector beam-Gaussian beam, thus obtaining Cylindrical vector and vortex beams with continuously adjustable polarization.

Beneficial effects: the present invention inserts the double vortex wave plate into the laser cavity of the fiber laser, on the one hand, solves the strong Fresnel reflection effect caused by the combination of the single-sided vortex wave plate and the mirror in the past, and greatly reduces It prevents the back-reflected light from returning to the optical fiber path and causing instability. On the other hand, it greatly improves the utilization rate of the beam in the cavity. Under the premise of ensuring that the light in the optical fiber path is all the fundamental mode, a cylinder is obtained in the cavity. Vector beams and vortex beams avoid the use of few-mode fibers and mode selection devices, thereby obtaining ultrashort pulse cylindrical vector beams and vortex beams with high purity and high utilization rate.

Description of drawings

1 is a schematic diagram of a pulsed optical vortex beam fiber laser based on a double vortex wave plate in the present invention;

2 is a schematic diagram of a continuous optical vortex beam fiber laser based on a double vortex wave plate in the present invention;

Figure 3(a) Gaussian beam after passing through the double vortex wave plate;

The angular vector polarized light beam output in Fig. 3(b);

The radial vector polarized light beam of Fig. 3 (c) output;

Figure 3(d) output left-handed circularly polarized vortex beam;

45° cylindrical vector beam output in Fig. 3(e);

Figure 3(f) Output 30° cylindrical vector beam.

Detailed ways

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

In the present invention, two identical vortex wave plates are inserted into the cavity of the ring fiber laser, one side is used to convert the Gaussian beam in the cavity into a cylindrical vector beam or a vortex beam and then output out of the cavity, and the other side is used to convert the cylindrical vector beam Or the vortex beam is converted into a Gaussian beam, which is coupled into the fiber again. By adjusting the polarization state in the laser cavity, the outputs of cylindrical vector beams (including radially and angularly polarized beams) and vortex beams are respectively realized. At the same time, adding a mode-locking device in the cavity can generate ultrashort pulse cylindrical vector beams and vortex beams. The device has the advantages of high electro-optic efficiency, compact structure and the like.

Example 1

As shown in Figure 1, the present invention includes a pumping source 1 for pumping a gain fiber, the pumping source includes but is not limited to a fiber-coupled output semiconductor laser, the output wavelength of the semiconductor laser is 976nm, and the pumping power is adjustable from 0 to 600mW . The pump source 1 is connected to the wavelength division multiplexer 2 to couple the pump light into the ring cavity. The wavelength division multiplexer 2 includes but not limited to 980nm/1064nm or 980nm/1310nm or 980nm/1550nm wavelength division multiplexer, Its coupling wavelength should be consistent with the stimulated emission wavelength of the gain fiber 3 . The other end of the wavelength division multiplexer 2 is connected to the gain fiber 3, the gain fiber 3 is used as the working substance of the ring cavity, and is a rare earth doped gain fiber, including but not limited to doped fibers such as ytterbium and erbium doped fibers, and the gain fiber 3 is excited The radiated light wavelength should be greater than the cut-off frequency of the single-mode fiber in the device, so that the single-mode fiber works in a single-mode transmission state.

The gain optical fiber 3 is connected with the optical isolator, and the optical isolator makes the optical path in the annular cavity unidirectional. The optical isolator can adopt a spatial optical isolator to place the optical path in the cavity, or an optical fiber isolator 5 can be used to place the optical path in the cavity. The fiber optic path in the cavity is shown in Figure 1 and Figure 2. The other end of the optical fiber isolator 5 is connected to the polarization control module. The polarization control module can adopt a fiber optic polarization controller 62 in the optical fiber path, as shown in FIG. A combination of wave plates 74, as shown in Figure 2. The fiber polarization controller 62 can control the polarization state in the cavity, thereby controlling the output light to be a cylindrical vector beam or a common vortex beam; the other end of the fiber polarization controller 62 is connected to a second fiber collimator 82, and the second fiber collimator 82 outputs the light beam in the optical fiber to the spatial light part 7. Since there is a strong Fresnel reflection between the spatial light and the fiber collimator, the FC/APC connector can be used to access the collimator during actual operation, so as to Reduce the unstable factors caused by back-reflected light returning to the optical path; in the spatial light part 7, along the direction of the optical path are the first vortex wave plate 72, the output mirror 73, and the second vortex wave plate 71, and the output mirror 73 is used for The output of ultrashort pulse cylindrical vector beam or vortex beam has no effect on the polarization distribution in the cavity, including but not limited to 45° beam splitting flat plate, non-polarizing beam splitting cube, etc.

Taking the output vortex beam as an example, it is assumed that the light output by the second fiber collimator 82 is right-handed circularly polarized light 21; after being transmitted to the first vortex wave plate 72, it becomes a left-handed circularly polarized vortex beam 22, see FIG. 3 (d) is a left-handed circularly polarized vortex beam, the left-handed circularly polarized vortex beam 22 outputs a part of the second vortex beam 25 through the output mirror 73, and transmits a part of the first vortex beam 23, and the first vortex beam 23 passes through the second vortex beam again Two vortex wave plates 71, after transmission, become right-handed circularly polarized Gaussian light 24, referring to FIG. 3(a), which is a Gaussian beam after passing through two vortex wave plates. In the actual operation process, if the topological charge of the vortex wave plate is relatively large, the focus and collimation module can be used to focus and collimate the light beam and then couple it into the first single-mode fiber 4 through the first fiber collimator 81; The other end of a single-mode optical fiber 4 is connected to the mode-locking assembly 33, and the mode-locking assembly 33 is used to form an ultrashort pulse, including a first optical fiber jumper 31 and a second optical fiber jumper 32, wherein the second optical fiber jumper 32 is connected to the first single-mode optical fiber 4; the first fiber jumper 31 and the second fiber jumper 32 are connected with a fiber coupler, and a saturable absorber is placed between the two jumpers to form an ultrashort pulse in the cavity; The other end of a fiber jumper 31 is connected to the wavelength division multiplexer 2 through the second single-mode fiber 12 to form a ring cavity.

The mode-locking mode used in Fig. 1 is real insurable and absorber mode-locking, and the device of the present invention can also be artificially available with nonlinear polarization rotation (NPR), nonlinear loop magnifier (NALM) and nonlinear optical fiber loop mirror (NOLM) Paul and absorber mode-locking. The mode-locking device can be integrated into the optical fiber path or placed in the spatial light path. The methods of integration into the fiber optic path include but are not limited to drop-coating jumper head, D-shaped or tapered fiber deposition, photonic crystal fiber filling, etc. The mode-locking device can be removed to realize the generation of continuous cylindrical vector beams and vortex beams, as shown in Figure 2.

Cylindrical vector beams can be obtained by adjusting the polarization state in the cavity. See Figure 3(b), which is angular vector beams; see Figure 3(c), which is radial vector beams. Both beams are special cylindrical vector beams. It is also possible to output other cylindrical vector beams, referring to Fig. 3(e), for the cylindrical vector beams when the angle with each point of the standard radially polarized light is 45°, only need to adjust the polarization module 62 to make the output of the fiber collimator 82 The angle between the polarization angle of the linearly polarized light and the zero-degree fast axis of the vortex wave plate 72 is 45°; in the same way, see Fig. 3(f) for the cylinder when the angle with each point of the standard radially polarized light is 30° Vector light beam.

Example 2

As shown in Figure 2, the mode-locking component 33 in Figure 1 can be removed to output a continuous cylindrical vector beam or a common vortex beam. The difference from Embodiment 1 is that the polarization control module in Figure 2 is set In the space light path part. The continuous cylindrical vector beam or common vortex beam generating device includes a pump source 1 for pumping the gain fiber; a wavelength division multiplexer 2 for coupling the pump light into the gain fiber; used as the working substance of the laser cavity The gain fiber 3; the optical isolator 5 used to make the optical path in the ring cavity unidirectional; the fiber collimators 81 and 82 used to couple the light in the fiber with the spatial light; used to control the polarization state in the cavity A quarter-wave plate 74 and a half-wave plate 75; vortex wave plates 71 and 72 for interconverting intracavity beam modes; output mirrors for outputting ultrashort pulse cylindrical vector beams or vortex beams 73; single-mode optical fibers 4 and 12 for connecting the entire optical path.

The pump source 1 is connected to the wavelength division multiplexer 2, and the pump light is coupled into the ring cavity; the end of the wavelength division multiplexer 2 is connected to the gain fiber 3, and the gain fiber 3 is used as the working substance of the ring cavity; the gain fiber 3 The other end is connected with the optical fiber isolator 5, and the optical fiber isolator 5 makes the optical path in the annular cavity have unidirectionality; The light beam in is output to the spatial light part 7. Due to the strong Fresnel reflection between the spatial light and the fiber collimator, the FC/APC connector can be used to connect to the collimator during actual operation to reduce back reflection The light returns to the optical path and causes unstable factors; in the space light part, along the direction of the optical path, there are half-wave plate 75, quarter-wave plate 74, first vortex wave plate 72, output mirror 73, and second vortex wave plate. Plate 71; Consistent with Embodiment 1, the polarization state distribution in the cavity can be controlled by rotating the half-wave plate 75 and the quarter-wave plate 74, thereby selecting the mode of the output light, if the topological charge of the vortex wave plate Larger, you can also use a focusing and collimating module to focus and collimate the light beam and couple it into the first single-mode fiber 4 through the first fiber collimator 81; the other end of the first single-mode fiber 4 passes through the second single-mode fiber 12 is connected with the wavelength division multiplexer 2 to form an annular cavity.

In the following, the Jones vector is used to deduce the beam transverse mode transformation of the spatial light path.

Assuming that the Gaussian beam output by the fiber collimator is right-handed circularly polarized light, the process of the beam passing through the first vortex wave plate can be expressed by Jones matrix as:

为涡旋波片特定位置的半径和0°快轴夹角；θ为涡旋波片0°快轴与光束偏振角度夹角。通过上式可见，第一涡旋波片输出为拓扑荷数为m的涡旋光束，可参见附图3(d)。将此光束一部分反射输出腔外，使另一部光透射再次回到腔内。回到腔内的涡旋光束，通过第二涡旋波片可用琼斯矩阵表示为：Among them, m is the topological charge number of the vortex wave plate;

is the angle between the radius of a specific position of the vortex wave plate and the 0° fast axis; θ is the angle between the 0° fast axis of the vortex wave plate and the beam polarization angle. It can be seen from the above formula that the output of the first vortex wave plate is a vortex beam with a topological charge m, as can be seen in Figure 3(d). A part of the light beam is reflected out of the cavity, and another part of the light is transmitted back into the cavity again. The vortex beam returning to the cavity can be expressed by the Jones matrix through the second vortex wave plate:

被抵消，再次转化成了右旋圆偏振高斯光束。当涡旋波片的拓扑荷数较大时，可用聚焦准直模块将双涡旋波片转换的高斯光束聚焦并耦合进光纤中。It can be seen from the above formula that after the generated vortex beam passes through the second vortex wave plate, its helical phase factor

is canceled out and transformed again into a right-handed circularly polarized Gaussian beam. When the topological charge of the vortex wave plate is large, the Gaussian beam converted by the double vortex wave plate can be focused and coupled into the optical fiber by the focusing and collimating module.

Assuming that the Gaussian beam output by the fiber collimator is any linearly polarized light, the process of the beam passing through the first vortex wave plate can be expressed by Jones matrix as:

Where α is the angle between the linearly polarized light and the x-axis. It can be seen from the above formula that the output of the first vortex wave plate is a cylindrical vector beam. When α is 45°, the output light can be seen in Figure 3(e); when α is 30°, the output light can be seen in Figure 3(f ). The polarization angle between its polarization state and the standard radially polarized light in each direction is α, and a part of the light beam is reflected out of the cavity, and the other part of the light is transmitted back into the cavity again. The vortex beam returning to the cavity can be expressed by the Jones matrix through the second vortex wave plate:

It can be seen from the above formula that after the generated cylindrical vector beam passes through the second vortex wave plate, its polarization state singularity is canceled and transformed into a linearly polarized Gaussian beam again, and the polarization state is the same as that incident on the first vortex wave plate The beam polarization state of the wave plate is consistent.

Claims (8)

1. The optical vortex optical fiber laser based on the double vortex wave plates is characterized by comprising an annular cavity, wherein the annular cavity comprises a wavelength division multiplexer (2), a gain optical fiber (3), a space optical portion (7) and a plurality of single-mode optical fibers which are sequentially connected end to end, the input end and the output end of the space optical portion (7) are both connected with an optical fiber collimator, the wavelength division multiplexer (2) is connected with a light source, an optical isolator is connected to an optical fiber light path in the annular cavity or a space light path of the space optical portion, a polarization control module is integrated on the optical fiber light path or the space light path, the space optical portion comprises a plurality of vortex wave plates, and an output mirror (73) is arranged between the vortex wave plates;

the spatial light part (7) comprises a first vortex wave plate (72) and a second vortex wave plate (71), an output mirror (73) is arranged between the first vortex wave plate (72) and the second vortex wave plate (71), the first vortex wave plate (72) is arranged on one side of a second optical fiber collimator (82), and the second vortex wave plate (71) is arranged on one side of a first optical fiber collimator (81);

the polarization control module adopts an optical fiber polarization controller (62) arranged in an optical fiber light path or a combination of a half-wave plate (75) and a quarter-wave plate (74) arranged in a space light path, the half-wave plate (75) and the quarter-wave plate (74) are sequentially arranged along the light path, wherein the half-wave plate (75) is arranged on one side of a second optical fiber collimator (82), the other side of the quarter-wave plate (74) is provided with a first vortex wave plate (72), and the output of cylindrical vector beams and vortex beams is respectively realized by regulating and controlling the polarization state in a laser cavity.

2. The optical vortex fiber laser based on double vortex plate according to claim 1, characterized in that the input end of the space light part (7) is connected with the second optical fiber collimator (82), and the output end is connected with the first optical fiber collimator (81).

3. The optical vortex fiber laser based on the double vortex wave plate according to claim 1, wherein the single mode fiber comprises a first single mode fiber (4) and a second single mode fiber (12), one end of the first single mode fiber (4) is connected with the first fiber collimator (81), the other end of the first single mode fiber is connected with the second single mode fiber (12), and the other end of the second single mode fiber (12) is connected with the wavelength division multiplexer (2).

4. The optical vortex fiber laser based on the double vortex wave plates according to claim 3, wherein a mode locking device (33) is arranged between the first single mode fiber (4) and the second single mode fiber (12), the mode locking device (33) comprises a first optical fiber jumper (31) and a second optical fiber jumper (32), the second optical fiber jumper (32) is connected with the first single mode fiber (4), and the first optical fiber jumper (31) is connected with the second single mode fiber (12).

5. The optical vortex fiber laser based on double vortex plate as claimed in claim 4, characterized in that said mode locking device (33) is integrated into the optical fiber path or placed in the spatial path.

6. The optical vortex fiber laser based on the double vortex wave plates according to claim 4, characterized in that the first optical fiber jumper (31) and the second optical fiber jumper (32) are connected by an optical fiber coupler, and a saturable absorber is arranged between the first optical fiber jumper and the second optical fiber jumper.

7. The optical vortex fiber laser based on the double vortex wave plate as claimed in claim 1, wherein the optical isolator is a spatial optical isolator disposed in the intracavity spatial optical path or a fiber isolator (5) disposed in the intracavity fiber optical path.

8. The optical vortex fiber laser based on double vortex wave plate according to claim 1, characterized in that the gain fiber (3) is rare earth doped gain fiber.

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