阅读说明：本技术 一种基于msm结构的耗散孤子锁模光纤激光器 (Dissipation soliton mode locking fiber laser based on MSM structure ) 是由 金亮 张贺 徐英添 李卫岩 李永平 于 2020-06-01 设计创作，主要内容包括：本申请提供一种基于MSM结构的耗散孤子锁模光纤激光器,包括：包括泵浦源、波分复用器、增益光纤、偏振无关隔离器、输出耦合器、色散补偿光纤、偏振控制器、两个多模单模多模结构；所述泵浦源、波分复用器、增益光纤、偏振无关隔离器、输出耦合器、色散补偿光纤、偏振控制器、两个多模单模多模结构依次连接形成环形谐振腔。本发明通过调整偏振控制器调节腔内传输光的偏振态,实现了稳定耗散孤子锁模脉冲的输出。(The application provides a dissipation soliton mode locking fiber laser based on MSM structure includes: the system comprises a pumping source, a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, an output coupler, a dispersion compensation fiber, a polarization controller and two multimode single-mode multimode structures; the pump source, the wavelength division multiplexer, the gain fiber, the polarization-independent isolator, the output coupler, the dispersion compensation fiber, the polarization controller and the two multimode single-mode multimode structures are sequentially connected to form an annular resonant cavity. The invention realizes the output of stable dissipation soliton mode locking pulse by adjusting the polarization state of the light transmitted in the cavity through adjusting the polarization controller.)

1. A dissipation soliton mode-locked fiber laser based on MSM structure, characterized by, includes: the system comprises a pumping source (1), a wavelength division multiplexer (2), a gain fiber (3), a polarization-independent isolator (4), an output coupler (5), a dispersion compensation fiber (6), a polarization controller (7) and two multimode single-mode multimode structures (8) connected in series;

the pump source (1), the wavelength division multiplexer (2), the gain fiber (3), the polarization-independent isolator (4), the output coupler (5), the dispersion compensation fiber (6), the polarization controller (7) and the two multimode single-mode multimode structures (8) which are connected in series are sequentially connected to form an annular resonant cavity.

2. The dissipative soliton mode-locked fiber laser based on MSM structure of claim 1, wherein the multimode single mode multimode structure (8) is comprised of a single mode fiber and a graded index multimode fiber welded together at intervals.

3. The dissipative soliton mode-locked fiber laser based on an MSM structure according to claim 1, wherein the two multimode, single mode multimode structures (8) fulfill the condition:

when light is transmitted clockwise and passes through the multimode optical fiber wound into the polarization controller for the first time, the phase difference among the excited modes of each order meets m pi, and m is an odd integer; the generated pulse passes through a second single-mode multimode single-mode structure, the phase difference between high-order modes in the multimode fiber meets n pi, and n is an even integer.

Technical Field

The invention relates to the technical field of optical fibers, in particular to a dissipative soliton mode-locked fiber laser based on an MSM structure.

Background

Dissipative solitons, a common class of output pulses for fiber lasers, are formed in a dissipative system within a positively dispersive resonator, and are then referred to as dissipative solitons. The soliton has high non-linear tolerance because it is formed in a dissipative system, and when the pulse energy is high, the pulse can not be split to reduce the stability of the laser. Compared with the defects that the traditional soliton formed by negative dispersion cannot bear too high nonlinearity, and when the pulse energy is higher, the energy dispersion is caused by pulse forming and splitting, and high-energy pulse cannot be obtained, the method has great advantages. Dissipative solitons have wide applications in the industrial field due to their high energy properties.

Due to the wide application prospect of dissipative solitons, scientific research personnel are concerned, so that methods for generating dissipative solitons are more and more abundant, two types of commonly used methods for obtaining dissipative solitons are available, one is based on a real saturable absorber, and the common real saturable absorber is made of two-dimensional materials such as graphene, topological insulators, transition metal sulfides and the like; the other type of the optical fiber saturable absorber is a similar saturable absorber, a common mode is a nonlinear polarization rotation and nonlinear amplification optical fiber ring mirror, and the similar saturable absorber is frequently applied to practical application. The generated pulse has instability due to the characteristics of smaller damage threshold and oxidation resistance of a true saturable absorber, and the generated pulse has stability due to the fact that the damage threshold is higher and no oxidation problem exists because the saturable absorber is composed of optical fibers. However, this type of saturable absorber still has disadvantages, namely: because the pulse obtaining mode depends on the nonlinearity of the optical fiber, the anti-interference capability to the external environment is poor. Therefore, a new mode locking mode is developed, which needs to have high damage threshold and oxidation resistance, is not sensitive to the external environment, and has strong anti-interference capability. The new mode locking mode has great significance.

However, the new mode locking structure is composed of a single-mode multimode single-mode fiber (SMS), and the mode locking mode has an excellent mode locking effect in a negative dispersion resonant cavity, but when the mode locking structure is placed in a positive dispersion resonant cavity, the unstable mode locking pulse envelope problem occurs. Namely: the pulse generated in the positive dispersion fiber laser is dissipation solitons, and the dissipation soliton formation needs the four of intracavity nonlinearity, dispersion, gain and loss to achieve balance acquisition. The intra-cavity energy is in real-time variation during soliton formation. On the other hand, the mode interference effect is generated from the imaging position and is related to the power in the cavity, so that the coupling efficiency of the multi-mode fiber output end coupled into the single-mode fiber can be changed in the soliton forming process, and the output peak values of the solitons are inconsistent. In other words, the presence of the multimode fiber further modulates the generated pulses, thereby outputting a pulse envelope phenomenon.

Disclosure of Invention

The invention aims to solve the defects in the prior art, and the problem of unstable mode-locked pulse envelope in a positive dispersion resonant cavity is solved based on the mode-locking mode of the existing SMS structure.

A dissipative soliton mode-locked fiber laser based on an MSM structure comprises: the system comprises a pumping source, a wavelength division multiplexer, a gain fiber, a polarization-independent isolator, an output coupler, a dispersion compensation fiber, a polarization controller and two multimode structures connected in series;

the pump source, the wavelength division multiplexer, the gain fiber, the polarization-independent isolator, the output coupler, the dispersion compensation fiber, the polarization controller and the two multimode single-mode multimode structures which are connected in series are sequentially connected to form an annular resonant cavity.

Further, as described above, the dissipative soliton mode-locked fiber laser based on the MSM structure, the multimode single-mode multimode structure is formed by welding a single-mode fiber and a graded-index multimode fiber at intervals.

Further, as described above for the dissipative soliton mode-locked fiber laser based on the MSM structure, the two multimode single-mode multimode structures satisfy the following conditions:

when light is transmitted clockwise and passes through the multimode optical fiber wound into the polarization controller for the first time, the phase difference among the excited modes of each order meets m pi, and m is an odd integer; the generated pulse passes through a second single-mode multimode single-mode structure, the phase difference between high-order modes in the multimode fiber meets n pi, and n is an even integer.

Has the advantages that:

the mode-locked fiber laser based on the multimode, single-mode and multimode structure is used for stably dissipating soliton mode-locked pulse output, and has the advantages of full fiber structure, high damage threshold, simplified mode-locked structure, compact structure and high robustness. The mode-locked fiber laser with the structure has the advantages that the practicability is enhanced, and the application is wider. The invention realizes the output of stable dissipation soliton mode locking pulse by adjusting the polarization state of the light transmitted in the cavity through adjusting the polarization controller.

The invention utilizes the anti-saturation absorption effect of the multimode structure, provides an optical amplitude limiting mechanism in the laser, and utilizes the optical amplitude limiting mechanism to perform loss feedback on the laser resonant cavity, thereby achieving the effect of stabilizing pulses and realizing stable pulse output. Since the multimode, single-mode and multimode structure has the reverse saturable absorption characteristic, the characteristic has the effects that high-energy pulses are lost and low-energy pulses pass through without loss. This characteristic is used to achieve a stable laser action. Because the output pulse is further modulated to cause the inconsistent peak power, the peak value of the pulse is homogenized through the anti-saturation characteristic, and stable pulse output is realized.

The mode locking device of the laser is an optical fiber device, and the optical fiber material has a high damage threshold, so that the mode locking device still has the mode locking capability under the condition that the laser is not damaged, and has the high damage threshold.

In addition, the laser mode locking device provided by the invention is a section of multi-mode optical fiber with the length of dozens of centimeters, and the multi-mode optical fiber is wound in the polarization controller, so that the multi-mode optical fiber part is not greatly influenced under the interference of an external environment, and the stability is very strong, and the robustness is high.

Drawings

FIG. 1 is a schematic diagram of a multimode, single mode, Multimode Structure (MSM); wherein, SMF is single mode fiber; the GIMF is a graded-index multimode fiber;

FIG. 2 is a schematic diagram of a multimode-structure-based mode-locked fiber laser;

reference numerals:

1-a pump source; 2-wavelength division multiplexer; a 3-gain optical fiber; 4 polarization independent isolators; 5-an output coupler; 6-a dispersion compensating fiber; 7-a polarization controller; 8-multimode, single-mode, multimode structure.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention are described clearly and completely below, and it is obvious that the described embodiments are some, not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, the multimode, single-mode and multimode structure provided by the present invention is composed of a single mode and a graded-index multimode fiber, and is formed by welding the single-mode fiber to two ends of two graded-index multimode fibers and welding them together, and winding two multimode fiber parts in the welded structure into two polarization controllers.

As shown in fig. 2, the mode-locked fiber laser based on the multimode, single-mode and multimode structure includes a pump source 1, a wavelength division multiplexer 2, a gain fiber 3, a polarization-independent isolator 4, an output coupler 5, a dispersion compensation fiber 6, a polarization controller 7, and a multimode, single-mode and multimode structure 8.

The pumping source 1 is connected with the wavelength division multiplexer 2; the wavelength division multiplexer 2 is connected with a gain optical fiber 3; the gain fiber 3 is connected with a polarization-independent isolator 4; the polarization-independent isolator 4 is connected with the output coupler 5; the output coupler 5 is connected with a dispersion compensation optical fiber 6; the dispersion compensation fiber 6 is connected with a single-mode fiber, and the single-mode fiber is wound into a polarization controller 7; said single mode fiber is connected to a multimode, single mode structure 8. The connection is connected by using an optical fiber fusion splicer in a fusion mode, and the device is connected with the device by a single mode fiber to form an annular resonant cavity.

The pump source 1 provides a basic light source for exciting laser for the optical fiber laser; the wavelength division multiplexer 2 is used for integrating light with two wavelengths into one optical fiber, namely integrating the pump source 1 and the excited laser into the same optical fiber; the gain fiber 3 is used for exciting substances in the gain fiber 3 through light emitted by the pumping source 1 to enable the gain fiber 3 to generate laser; the polarization-independent isolator 4 is used for enabling light in the resonant cavity to be transmitted in a single direction, the output coupler 5 is used for splitting a beam of light, one part of the light is output to be observed, one part of the light returns to the cavity to be subjected to continuous oscillation feedback, for example, one beam of light with energy of 1 is split into two beams of light with energy of 0.1 and 0.9 respectively according to the ratio of 1: 9; the dispersion compensation fiber 6 compensates for intra-cavity negative dispersion so that the net dispersion of the resonant cavity is positive, and positive dispersion is a necessary condition for forming dissipative solitons. The polarization controller 7 is used to adjust the polarization characteristics of the intracavity transmitted light to achieve better beam quality. The multimode single-mode multimode structure 8 is used for mode locking and loss feedback in the resonant cavity and modulating output pulses.

The pump source provides a basic light source for exciting laser for the optical fiber laser;

the wavelength division multiplexer is used for integrating light with two wavelengths into one optical fiber, namely integrating a pumping light source and excited laser into the same optical fiber;

the gain fiber is used for exciting substances in the gain fiber through light emitted by the pumping source to enable the gain fiber to generate laser;

the polarization-independent isolator is used for enabling the transmission light in the annular cavity to carry out unidirectional transmission

The output coupler is used for splitting a beam of light, wherein part of the light is output for observation, and part of the light returns to the cavity for continuous oscillation feedback;

the dispersion compensation fiber is used for adjusting the intra-cavity dispersion into positive dispersion;

the polarization controller is used for changing the polarization state of the transmitted light in the cavity;

the multimode single-mode multimode structure is used for realizing mode locking pulse output and regulating the loss in a cavity and inhibiting the appearance of unstable mode locking pulse envelopes.

Referring to fig. 1, fig. 1 is a schematic diagram of a structure of a multimode single-mode multimode fiber, a single multimode fiber can be used as a saturable absorber for mode-locked pulse output, and a single-mode multimode single-mode structure is additionally introduced into the single-mode multimode single-mode structure for intra-cavity loss feedback to suppress a pulse envelope phenomenon formed by dissipative soliton mode locking formed by the single multimode fiber. In the figure, SMF is a single mode fiber and GIMF is a GI multimode fiber.

When fundamental transverse mode light is coupled into a multimode fiber through a single mode fiber, the fundamental transverse mode light excites high-order transverse modes in the multimode fiber, the high-order transverse mode light is transmitted in the multimode fiber, nonlinear phase shifts of different degrees can be accumulated between the fundamental mode and the high-order transverse modes due to dispersion and nonlinearity, when the nonlinear phase shift difference accumulated between the high-order transverse mode light and the fundamental transverse mode is an odd integral multiple of pi, the transmittance between the single mode multimode single mode fiber presents a nonlinear relation, so that the single mode multimode single mode structure has saturable absorption characteristics, can be used for realizing mode locking, and forms the saturable absorption characteristics to have a harsh condition, namely only when the output end of the multimode fiber just meets the odd integral multiple of pi, the effect can be utilized, so that the multimode is wound into a polarization controller, and the nonlinear phase shift difference of the transmission light in the multimode fiber is changed by using the polarization controller, so that it meets the condition just at the multimode output. Then one multimode fiber is used to form the mode-locked pulse at this time.

However, when the cavity is adjusted to have positive dispersion by using the dispersion compensation fiber, the laser cannot form stable mode-locked pulses, and an unstable mode-locked pulse envelope is formed, which is very disadvantageous for practical use. Analysis shows that when the resonant cavity only contains one multimode fiber, the laser forms dissipation soliton mode locking, but when the dissipation soliton mode locking is formed, the loss in the cavity is reduced due to nonlinear effect, so that the formed dissipation soliton is further modulated into mode locking pulse envelope. Therefore, another multimode fiber is introduced to carry out loss modulation in a laser resonant cavity, and the mode-locked pulse envelope phenomenon is restrained. The second multimode optical fiber has a different function from the multimode optical fiber for mode-locked pulse output, and is used for a sideband filter. Research shows that when the phase of a high-order transverse mode and the phase of a basic transverse mode of light transmitted in the multimode optical fiber meet pi/2 and 3 pi/2, the single-mode multimode single-mode structure can be respectively used for a low-pass filter and a high-pass filter. Low pass filtering can achieve high energy light loss, low energy light transmission, and high pass filtering in contrast. Because of the restriction of phase difference conditions, the same multimode fiber cannot simultaneously meet two conditions, so that the multimode fiber is made into a multimode single-mode multimode structure, and two multimode fibers respectively perform corresponding functions, so that the two multimode fibers can be freely regulated and controlled without mutual interference.

Specifically, the method comprises the following steps: the light is transmitted clockwise, and when the light passes through the multimode optical fiber wound into the polarization controller for the first time, the phase difference between the excited modes of each order should satisfy m pi (m is an odd integer). At the moment, the single-mode multimode single-mode structure has a saturable absorption effect and can be used as a mode locking device, and mode locking pulse output can be obtained through the structure. The generated pulse passes through a second single-mode multi-mode single-mode structure, the phase difference between high-order modes in the multi-mode optical fiber meets n pi (n is an even integer), and the single-mode multi-mode single-mode structure has an anti-saturation absorption effect and can realize pulse modulation to obtain stable pulse output.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.