Multi-soliton-state adjustable fiber laser based on time delay polarization multiplexing structure

Abstract

The invention belongs to the technical field of optical fiber lasers, and discloses a multi-soliton-state adjustable optical fiber laser based on a time delay polarization multiplexing structure. The fiber laser comprises a laser pumping source, a wavelength division multiplexer, an erbium-doped gain fiber, a polarization independent isolator, a mode locking device based on a carbon nanotube saturable absorber, a polarization beam splitter, a polarization beam combiner and an output coupler which are sequentially connected through a single-mode fiber. A time delay polarization multiplexing structure of the optical fiber laser adopts a combination of a polarization beam splitter, a single-mode optical fiber and a polarization beam combiner, and the lengths of the single-mode optical fibers on two branches are obviously different. Therefore, traditional solitons conforming to independent mode locking of the long and short cavities can be output, and long-cavity or short-cavity-dominated master-slave soliton equally-spaced soliton beams and long-cavity and short-cavity periodic alternately-spaced pulse output can be generated. According to the invention, by introducing a time delay polarization multiplexing structure, the limitation of a traditional annular cavity is broken through, and a new solution is provided for the generation and dynamic regulation of multiple soliton states.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber lasers, and in particular to a multi-soliton state tunable optical fiber laser based on a time-delay polarization multiplexing structure. Background Art

[0002] Passively mode-locked fiber lasers are widely used in fiber-optic communications, precision micromachining, biomedical imaging and other fields due to their advantages such as simple structure, ultrashort pulses and high stability. In traditional ring cavity structures, the formation of solitons mainly depends on the balance between nonlinear effects and dispersion management, but the polarization state and time delay effects in the cavity are often not fully utilized. The output mode of this type of laser is single, and it is difficult to flexibly control the generation and evolution of multiple soliton states. In addition, due to the fixed cavity length, the interaction mode of solitons is limited, making it difficult to achieve complex soliton states with different time slot intervals or alternating soliton outputs. Although some studies have manipulated soliton characteristics by introducing nonlinear polarization rotation or birefringence filtering effects, these methods usually rely on fine polarization adjustment, have poor stability, and make it difficult to achieve precise control of multiple soliton states.

[0003] To address these issues, the present invention proposes a multi-soliton tunable fiber laser based on a time-delay polarization multiplexing structure. By combining beam separation and nonlinear synergy in a dual-polarization path structure, this laser can flexibly control the output of multiple soliton states while ensuring stable mode locking, reducing reliance on complex control. By introducing a polarization multiplexing structure and combining it with an asymmetric cavity length design, this invention overcomes the limitations of traditional ring cavities and provides a new solution for the generation and dynamic control of multiple soliton states. Summary of the Invention

[0004] Purpose of the invention:

[0005] To address the shortcomings and drawbacks of existing technologies, the present invention provides a multi-soliton tunable fiber laser based on a time-delay polarization multiplexing structure. By introducing a dual-path time-delay polarization multiplexing structure, the laser can generate stable outputs of various soliton states under the control of a polarization controller. These include traditional solitons mode-locked independently by the long and short cavities, equally spaced soliton beams of master and slave solitons dominated by either the long or short cavity, and alternating pulses with adjacent pulses separated by the round-trip time of the long and short cavities, respectively.

[0006] Technical solution:

[0007] The multi-soliton state generation and control fiber laser based on the time-delay polarization multiplexing structure described in the present invention includes a laser pump source, a wavelength division multiplexer, an erbium-doped gain fiber, a polarization-independent isolator, a carbon nanotube-based saturable absorber mode-locked device, a polarization controller 1, a time-delay polarization multiplexing structure composed of a polarization beam splitter, a polarization beam splitter polarization-maintaining pigtail connected to a polarization controller 2 with a single-mode fiber pigtail, a time-delay single-mode fiber, a polarization combiner, and an output coupler, and is sequentially connected through a single-mode fiber to form a laser resonant cavity.

[0008] Furthermore, the laser pump source adopts 976nm band laser, which has good stability and adjustable power; the wavelength division multiplexer couples the 976nm pump light with the C-band light wave and inputs them into the resonant cavity.

[0009] Furthermore, the erbium-doped gain fiber has a length of 0.6 m, and its unique energy level structure and excitation form contribute to the gain of C-band light waves and broadband light wave transmission.

[0010] Furthermore, the carbon nanotube-based saturable absorber mode-locked device is composed of two optical fiber connectors and a carbon nanotube saturable absorber film in the middle, and utilizes the ultrafast recovery time of carbon nanotubes to generate ultrashort pulses.

[0011] Furthermore, the polarization-independent isolator ensures unidirectional transmission of laser light in the optical resonant cavity; the polarization controller 1 and the polarization controller 2 are used to adjust the polarization state of light in the resonant cavity.

[0012] Furthermore, the long cavity and short cavity lengths of the laser resonant cavity are 14.7 m and 11.7 m respectively. The fundamental periods of the long and short cavity output pulses measured by an oscilloscope are 73 ns and 57 ns respectively.

[0013] Furthermore, the time-delay polarization multiplexing structure adopts a polarization splitter and a polarization combiner, both of which have 1m polarization-maintaining fiber pigtails, and the functions of the two are to perform polarization splitting and combining of light pulses respectively; the single-mode fiber pigtail and the time-delay single-mode fiber of the polarization controller 2 are 1m and 4m in length respectively, which can make the light transmitted along the two branches have obvious time difference when reaching the polarization combiner, thereby introducing a controllable time delay difference and the asymmetric nonlinear effect of the two branches, realizing the generation and dynamic regulation of multiple soliton states.

[0014] Furthermore, the output coupler splits the laser light at a power ratio of 7:3, wherein 30% of the light signal is output as the laser and 70% of the light signal returns to the resonant cavity for circulation.

[0015] Furthermore, by adjusting the polarization controllers of the main and branch paths, when the optical pulse enters the polarization multiplexing structure, it is split by the polarization beam splitter into two orthogonal polarization components that propagate along the fast and slow axes of the polarization beam splitter. During transmission, the optical pulse undergoes different paths and polarization state transitions before being polarization-combined by the polarization beam combiner and output through the output coupler. This invention achieves the output of conventional solitons in which the long and short cavities are independently mode-locked, master-slave solitons dominated by either the long or short cavity, and alternating pulses with intervals between adjacent pulses equal to the round-trip time of the long and short cavities, respectively.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The present invention achieves dynamic switching and stable output of three soliton states through a time-delay polarization multiplexing structure, combined with dual path length differences (short cavity and long cavity) and polarization control: traditional solitons that conform to independent mode locking of long and short cavities, soliton beams of equally spaced master and slave solitons dominated by long or short cavities, and solitons with periodic alternating intervals between long and short cavities.

[0018] 2. The present invention only requires adjusting the polarization controller or pump power to switch the soliton state, which reduces manufacturing cost and operational complexity compared to the complex external cavity modulation (such as acousto-optic devices) or parallel connection of multiple lasers usually required to achieve multi-soliton state output. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a schematic structural diagram of the multi-soliton state tunable fiber laser based on the time-delay polarization multiplexing structure of the present invention. 1 is a laser pump source, 2 is a wavelength division multiplexer, 3 is an erbium-doped gain fiber, 4 is a polarization-independent isolator, 5 is a carbon nanotube saturable absorber mode-locked device, 6 is a polarization controller 1, 7 is a polarization beam splitter, 8 is a polarization controller 2, 9 is a time-delay single-mode fiber, 10 is a polarization combiner, and 11 is an output coupler.

[0021] Figure 2 (a) is a traditional soliton mode-locked pulse sequence diagram only by short cavity mode-locking; Figure 2 (b) is a diagram of the traditional soliton mode-locked pulse sequence only by long cavity mode-locking.

[0022] Figure 3 (a) is a soliton beam pulse sequence diagram with uniform master and slave soliton intervals dominated by a short cavity; Figure 3(b) is a soliton beam pulse sequence diagram with uniform master and slave soliton spacing dominated by a long cavity.

[0023] Figure 4 This is the output pulse sequence diagram with alternating long and short cavity periods. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0025] Example 1

[0026] The purpose of the present invention is to change the path selection of optical pulses in a time-delay polarization multiplexing structure and adjust the nonlinear interference phase of dual-path light by regulating the polarization controller. This multi-dimensional regulation capability realizes dynamic multi-soliton state output and high environmental adaptability.

[0027] Figure 1 This is a schematic diagram of the structure of the multi-soliton tunable fiber laser based on the time-delay polarization multiplexing structure provided by the present invention. The laser pump source 1, wavelength division multiplexer 2, erbium-doped gain fiber 3, polarization-independent isolator 4, carbon nanotube saturable absorber mode-locked device 5, polarization controller 1 6, polarization beam splitter 7, polarization controller 2 8, time-delay single-mode fiber 9, polarization beam combiner 10, and output coupler 11 are connected in sequence to form a ring laser resonator.

[0028] The laser pump 1 uses a 976nm band laser, which has strong stability and adjustable power, and is a key factor in regulating the soliton morphology and stabilizing the mode-locked operation.

[0029] The function of the wavelength division multiplexer 2 is to couple the 976nm pump light with the C-band light wave and input them into the resonant cavity.

[0030] The erbium-doped gain fiber 3 has a length of 0.6 m, and its unique energy level structure and excitation form contribute to the gain of C-band light waves and broadband light wave transmission.

[0031] The polarization-independent isolator 4 ensures unidirectional transmission of laser light in the optical resonant cavity.

[0032] The carbon nanotube saturable absorber mode-locked device 5 promotes pulse narrowing by periodically modulating the intra-cavity loss, and ultimately forms a stable ultrashort pulse sequence.

[0033] Polarization controller 1 (6) and polarization controller 2 (8) alter the polarization direction of light input to the polarization beam splitter, thereby controlling the optical power ratio of the light split within the polarization beam splitter. They also optimize the nonlinear accumulation of the two paths and compensate for polarization crosstalk caused by axial deviation of the polarization-maintaining fiber. Polarization controller 1 manages global polarization and ensures mode-locking stability, while polarization controller 2 independently optimizes long and short path characteristics.

[0034] The polarization beam splitter 7 separates the incident light according to orthogonal polarization states and outputs the light to the long and short paths respectively.

[0035] The time-delayed single-mode optical fiber 9 causes a time difference between the two paths of light arriving at the polarization beam splitter, reflecting the propagation difference between the two paths, thereby promoting the generation of multiple soliton states.

[0036] The polarization beam combiner 10 recombines two orthogonal polarized lights transmitted through long and short paths, and forms a composite light field through coherent interference.

[0037] The output coupler 11 splits the laser light into two beams at a power ratio of 7:3, with 30% of the light signal being output as laser light.

[0038] Example 2

[0039] In this example, the performance of the laser of the present invention (the laser in Example 1) was tested. The pump power was fixed at 225 mW, and different soliton state outputs were obtained by adjusting polarization controller 1 and polarization controller 2. The optical signal was converted into an electrical signal using a photodetector, and the laser output pulse shape and pulse period were measured using an oscilloscope.

[0040] Figure 2 (a) is the pulse sequence diagram of independent mode locking in the short cavity path, with a pulse interval of 57 ns; Figure 2 (b) shows the pulse sequence diagram of the long cavity path independently mode-locked, with a pulse interval of 73 ns. In this case, the two paths independently satisfy the soliton conditions of the nonlinear Schrödinger equation, and the period is determined by the respective cavity lengths.

[0041] Figure 3 (a) shows a pulse sequence diagram of a short cavity-dominated pulse with uniform master-slave soliton spacing. The pulse period is 57 ns, and the master-slave soliton spacing of each soliton beam is 16 ns, which is the difference between the soliton spacings of the long and short cavities when they are independently mode-locked. Figure 3 (b) shows a pulse sequence diagram of a long cavity-dominated pulse with uniform master-slave soliton spacing. The pulse period is 73 ns, and the master-slave soliton spacing in each soliton beam is also 16 ns. This is caused by the non-dominant path affecting the dominant path pulse through cross-phase modulation, forming an energy-asymmetric soliton beam.

[0042] Figure 4This is a pulse sequence diagram showing alternating long and short cavity periods. Light pulses are output periodically at intervals of 57ns and 73ns. This is due to asynchronous interference between the short cavity pulses (57ns period) and the long cavity pulses (73ns period) at the polarization beam combiner, which then outputs them alternately.

[0043] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas. At the same time, for those skilled in the art, modifications or replacements based on the scheme of this application will cause corresponding changes in actual operation and use areas, which are all covered within the scope of the requirements of this specification.

Claims

1. A multi-soliton tunable fiber laser based on a time-delay polarization multiplexing structure, characterized in that: The invention comprises a laser pump source (1), a wavelength division multiplexer (2), an erbium-doped gain fiber (3), a polarization-independent isolator (4), a carbon nanotube-based saturable absorber mode-locked device (5), a polarization controller (6), a time-delay polarization multiplexing structure composed of a polarization beam splitter (7), a polarization beam splitter polarization-maintaining pigtail connected to a polarization controller (8) having a single-mode fiber pigtail, a time-delay single-mode fiber (9), and a polarization combiner (10), and an output coupler (11), and the laser resonant cavity is formed by sequentially connecting the structures through the single-mode fiber.

2. The multi-soliton tunable fiber laser based on a time-delay polarization multiplexing structure according to claim 1, characterized in that: The laser pump source (1) uses a 976nm band laser; the erbium-doped gain optical fiber (3) has a length of 0.6m; and the carbon nanotube-based saturable absorber mode-locking device (5) is composed of two optical fiber connectors and a carbon nanotube saturable absorber film in the middle.

3. The multi-soliton tunable fiber laser based on a time-delay polarization multiplexing structure according to claim 1, characterized in that: The laser pump source (1) emits laser light through a 980 / 1550 nm wavelength division multiplexer (2); the polarization-independent isolator (4) ensures unidirectional transmission of the laser light in the optical resonant cavity; and the polarization controller 1 (6) and the polarization controller 2 (8) are used to adjust the polarization state of light in the resonant cavity.

4. The multi-soliton tunable fiber laser based on a time-delay polarization multiplexing structure according to claim 1, characterized in that: The long cavity and short cavity lengths of the laser resonant cavity are 14.7m and 11.7m respectively.

5. The multi-soliton tunable fiber laser based on a time-delay polarization multiplexing structure according to claim 1, characterized in that: The time-delay polarization multiplexing structure adopts a polarization beam splitter (7) and a polarization beam combiner (10), both of which have 1m polarization-maintaining optical fiber pigtails; the length of the single-mode optical fiber pigtail of the second polarization controller (8) is 1m, and the length of the time-delay single-mode optical fiber (9) is 4m.

6. The multi-soliton tunable fiber laser based on a time-delay polarization multiplexing structure according to claim 1, characterized in that: The output coupler (11) divides the laser light into two beams according to a power ratio of 7:3, wherein 30% of the light signal is output as the laser and 70% of the light signal is returned to the resonant cavity for circulation.

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