Soiton dynamics simulation method of 9-shaped cavity fiber laser

Abstract

A soliton dynamics simulation method of a 9-shaped cavity optical fiber laser is suitable for the 9-shaped cavity optical fiber laser, the applicability and feasibility of the method are not affected by the arrangement sequence of optical fibers and optical fiber devices in a laser cavity, the operation sequence corresponding to the optical fibers and the optical fiber devices can be adjusted according to the actual situation, and the detection precision and reliability are both good. And meanwhile, the method becomes a reliable means for researching abundant soliton dynamics phenomena occurring in the mode locking process, is convenient for a user to operate and observe, and not only greatly helps theoretical simulation research for verifying experimental phenomena, but also robust design for engineering application.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber lasers, and particularly relates to a method for simulating soliton dynamics of a "9"-shaped cavity fiber laser. Background Art

[0002] Benefiting from the advantages of integratability, stability and high cost performance of ultrafast mode-locked fiber lasers, this type of laser has attracted extensive attention and research in recent decades and plays a key role in many applications, such as precision metrology, nonlinear optics and ultrafine material processing. As a light source for optical frequency combs, mode-locked lasers have opened up a new era of technologies applied in rich fields. There are various mode-locking techniques, and their basic principle is to forcibly lock thousands or tens of thousands of longitudinal modes together through a real or equivalent saturable absorber. The commonly used passive mode-locking mechanisms are mainly two types, namely real saturable absorber mode-locking, such as semiconductor saturable absorber mirror (SESAM), and equivalent saturable absorber, such as nonlinear polarization evolution (NPE), nonlinear optical loop mirror (NOLM) or nonlinear amplifying loop mirror (NALM).

[0003] Considering future space applications, the SESAM mode-locking structure is simple, but its relaxation time is in the picosecond order of magnitude and there is a risk of optical damage; the NPE mode-locking has excellent performance, but it is difficult to achieve a fully polarization-maintaining structure and is greatly affected by environmental changes. In comparison, the NALM mode-locking method, due to the introduction of a non-reciprocal phase shifter, effectively solves the problems of repetition frequency improvement and self-starting, and is easy to achieve a fully polarization-maintaining structure. Especially for specific scenarios with strict environmental adaptability requirements, it has now become the most promising technical solution. It should be noted that an important aspect of the research on mode-locking technology is the study of the rich soliton dynamics involved in the mode-locking process.

[0004] Since the simulations adopted in existing patents and related technical reports are mostly for the NPE mode-locking mechanism, and the simulation operations generally use the saturable absorber model as an equivalent substitute for the mode-locking process, although it can conveniently simulate the formation process of laser pulses, for the "9"-shaped cavity fiber laser, this simulation method lacks many key parameters. Especially in recent years, especially in the technical background where the "9"-shaped cavity is increasingly favored in engineering applications such as non-laboratory environments, an in-depth study of its mode-locking mechanism also requires a real and reliable simulation method as a support. Summary of the Invention

[0005] Aiming at the above problems, the purpose of the present invention is to provide a method for simulating soliton dynamics of a "9"-shaped cavity fiber laser, so as to solve the problem that there is no simulation method for the "9"-shaped cavity fiber laser at present.

[0006] To achieve the above purpose, the technical solutions adopted by the present invention include:

[0007] A soliton dynamics simulation method for a "9"-shaped cavity fiber laser, comprising the following steps:

[0008] S1. Define an initial input signal (1), input the initial input signal (1) into a first single-mode fiber (2), and after performing operations using the NLSE equation, solve to obtain a first input signal S in_k , and input the first input signal S in_k into a fiber coupler (3) from a first port (3-1) of the fiber coupler (3);

[0009] wherein, in an initial state, k = 1;

[0010] S2. Perform fiber coupler 3 simulation operations using a transfer matrix. The first input signal S in_k is split by the fiber coupler (3) to obtain a clockwise transmission signal S cw_k and a counterclockwise transmission signal S acw_k in the ring cavity, and they are respectively output from a second port (3-2) and a fourth port (3-4) of the fiber coupler (3);

[0011] S3. The clockwise transmission signal S cw_k obtained in S2 sequentially passes through a second single-mode fiber (4), a gain fiber (5), and a non-reciprocal phase shifter (6) to obtain a clockwise output signal S cw_k ', and at the same time, the counterclockwise transmission signal S acw_k obtained in S3 sequentially passes through the non-reciprocal phase shifter (6), the gain fiber (5), and the second single-mode fiber (4) to obtain a counterclockwise output signal S acw_k ';

[0012] S4. The clockwise output signal S cw_k ' and the counterclockwise output signal S acw_k ' obtained in S3 are respectively input from the fourth port (3-4) and the second port (3-2) and assigned to the transfer matrix of the fiber coupler (3) to obtain a laser output signal S out_k and a reflection arm input signal S reflected_k , and they are respectively output from the first port (3-1) and the third port (3-3);

[0013] S5. The reflection arm input signal S reflected_k obtained in S4 is transmitted by a third single-mode fiber (7), and after performing operations using the NLSE equation, a first transmission signal S reflected_k ' of the reflection arm is obtained;

[0014] S6. The first transmission signal S reflected_k ' of the reflection arm obtained in S5 is reflected by a reflector (8) to obtain a second transmission signal ηS reflected_k ' of the reflection arm, and the second transmission signal ηSreflected_k is transmitted to the third single-mode optical fiber (7), and after being operated by the NLSE equation, the second input signal S is obtained in_k’ The second input signal S in_k’ is input into the optical fiber coupler (3) from the third port (3-3);

[0015] where k' = k + 1;

[0016] S7, the second input signal S in_k’ is used as the input signal for the next round of operation and the loop of S2 - S6 is repeatedly executed to obtain multiple laser output signals S out_k ;

[0017] The number of times of repeated loop execution is the preset number of loop times n.

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] (1) The soliton dynamics simulation method of the "9"-shaped cavity fiber laser of the present invention is applicable to the "9"-shaped cavity fiber laser, and its applicability and feasibility are not affected by the arrangement order of the optical fibers and optical fiber devices in the laser cavity. The corresponding operation order of the optical fibers and optical fiber devices can be adjusted according to the actual situation, and both the authenticity and reliability are excellent.

[0020] (2) The soliton dynamics simulation method of the "9"-shaped cavity fiber laser of the present invention becomes a reliable means for studying the rich soliton dynamics phenomena occurring during the mode-locking process, which is convenient for users to operate and observe. It is not only helpful for the theoretical simulation research to verify experimental phenomena, but also of great help for the robust design for engineering applications.

[0021] (3) The soliton dynamics simulation method of the "9"-shaped cavity fiber laser of the present invention performs step-by-step simulation operations on the signal according to the real physical transmission process based on the pulse tracking method. The traversal operation of the real signal transmission process is more helpful for studying the influence of key device parameters and external input conditions, and can flexibly realize the operation of the generation and evolution process of the rich soliton dynamics phenomena in the cavity. Description of the Drawings

[0022] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation to the present invention. In the drawings:

[0023] Figure 1 is a schematic flow chart of a soliton dynamics simulation method for a "9"-shaped cavity fiber laser of the present application;

[0024] Figure 2 are the evolution results of different soliton dynamics phenomena obtained by using the simulation method of the present application. Detailed implementation manners

[0025] The invention is not limited to the following specific embodiments. Any equivalent transformation made on the basis of the technical solution of this application falls within the protection scope of the present invention. All components and devices in the present invention, unless otherwise specified, are all components and devices known in the prior art.

[0026] Embodiment

[0027] This embodiment discloses a method for simulating soliton dynamics of a "9"-shaped cavity fiber laser.

[0028] Before the simulation, global parameters of the fiber laser are first assigned. The global parameters include simulation operation parameters and key parameters of the fiber laser; the simulation operation parameters include time-domain sampling period, central wavelength, step length of the split-step Fourier method, and number of operation cycles. The key parameters of the fiber laser include the splitting ratio α of the fiber coupler 3, the phase shift value of the non-reciprocal phase shifter 6, and the reflectivity η of the reflector 8;

[0029] Set the main parameters of all the optical fibers in the fiber laser, including the lengths and corresponding transmission attenuation coefficients, dispersion parameters, and nonlinear parameters of the first single-mode optical fiber 2, the second single-mode optical fiber 4, and the third single-mode optical fiber 7, and also include the length of the gain fiber 5 and its corresponding transmission attenuation coefficient, dispersion parameter, nonlinear parameter, small-signal gain coefficient, and gain saturation energy;

[0030] Confirm whether it is necessary to simulate the tuning of the pump power of the gain fiber. If so, the small-signal gain coefficient of the gain fiber 5 is assigned in segments according to the number of operation cycles.

[0031] The specific steps are as follows:

[0032] S1. Define the initial input signal 1. Input the initial input signal 1 into the first single-mode optical fiber 2. After operation by the NLSE equation, the first input signal S in_k , and the first input signal S in_k is input into the fiber coupler 3 from the first port 3-1 of the fiber coupler 3; where, in the initial state, k = 1.

[0033] The NLSE equation disclosed in this embodiment is the nonlinear Schrödinger equation, and its expression is:

[0034]

[0035] In the formula, A represents the slow-varying envelope amplitude, z is the transmission distance, α represents the optical fiber loss, β 2 is the group velocity dispersion of the optical fiber, iγ|A| 2 A represents the self-phase modulation term of the optical fiber nonlinear effect, where γ is the optical fiber nonlinear parameter. T is the introduced group velocity vg The reference frame that moves with the pulse (i.e., the so-called delay system) is the definition of the time coordinate system for the entire formula, and there is

[0036] The specific solution method uses the split-step Fourier method. Specifically, the optical fiber length microelement is divided into N segments, and the operation is carried out segment by segment with the set step value. The signal obtained by solving based on the previous optical fiber length microelement is used as the input for the next length microelement, and the calculation is iterated until the entire optical fiber length is solved. The solution signal of the last microelement is the first input signal S in_k 。

[0037] S2, the simulation operation of the optical fiber coupler 3 is carried out using the transfer matrix. The first input signal S in_k is split by the optical fiber coupler 3 to obtain the clockwise transmission signal S cw_k and the counterclockwise transmission signal S acw_k in the ring cavity, and they are respectively output from the second port 3-2 and the fourth port 3-4 of the optical fiber coupler 3.

[0038] The simulation operation expression in this embodiment of S2 is:

[0039]

[0040] S3, the clockwise transmission signal S obtained from S2 cw_k successively passes through the second single-mode optical fiber 4, the gain optical fiber 5, and the non-reciprocal phase shifter 6 to obtain the clockwise output signal S cw_k ’, and at the same time, the counterclockwise transmission signal S obtained from S3 acw_k successively passes through the non-reciprocal phase shifter 6, the gain optical fiber 5, and the second single-mode optical fiber 4 to obtain the counterclockwise output signal S acw_k ’.

[0041] In this embodiment, for the clockwise transmission signal S cw_k and the counterclockwise transmission signal S acw_k both pass through the second single-mode optical fiber 4 in the ring. The operation implementation is the same as that of the first single-mode optical fiber 2 in S1, and will not be elaborated here.

[0042] In this embodiment, the amplification transmission process of the gain optical fiber 5 is described by the Ginzburg-Laudau equation, and the equation expression is:

[0043]

[0044] where g is the gain coefficient (calculated based on the small-signal gain coefficient and the gain saturation energy), and T 2 is the dipole relaxation time. The specific solution method of the above equation is the same as that of S1, using the split-step Fourier method to iteratively calculate the amplification transmission process of the signal in the gain optical fiber.

[0045] The non-reciprocal phase shifter 6 of this embodiment introduces a preset phase offset amount. The phase shift processing of the signal in the operation is as shown in the following formula:

[0046]

[0047] Where S ps represents the input signal of the non-reciprocal phase shifter 6, and S' ps represents the output signal of the non-reciprocal phase shifter 6. exp(*) represents the shift operation, and i is the imaginary unit. represents the phase shift difference caused by the non-reciprocal phase shifter.

[0048] The clockwise output signals S cw_k ' and the counterclockwise output signals S acw_k ' are respectively input from the fourth port 3-4 and the second port 3-2 and assigned to the fiber coupler 3 to obtain the laser output signal S out_k and the reflection arm input signal S reflected_k which are respectively output from the first port 3-1 and the third port 3-3;

[0049] S4 is similar to S2. The simulation operation expression in the fiber coupler 3 is:

[0050]

[0051] The reflection arm input signal S reflected_k obtained from S5 and S4 is transmitted by the third single-mode fiber 7. After being operated by the NLSE equation, the first transmission signal S reflected_k ' of the reflection arm is obtained;

[0052] The solution method of this embodiment is the same as that of S1, and will not be elaborated here;

[0053] The first transmission signal S reflected_k ' of the reflection arm obtained from S6 and S5 is reflected by the reflector 8 to obtain the second transmission signal ηS reflected_k ' of the reflection arm, which is transmitted to the third single-mode fiber 7. After being operated by the NLSE equation, the second input signal S in_k’ is obtained. The second input signal S in_k’ is input into the fiber coupler (3) from the third port (3-3); where k' = k + 1

[0054] Up to S6, the simulation method completes one traversal operation.

[0055] For S7, the second input signal S in_k’ is used as the input signal for the next round of operation, and S2 - S6 are repeatedly executed in a loop. Finally, multiple laser output signals S out_k are obtained;

[0056] The number of times of the repeated loop execution is a preset loop number n, that is, k = [1, 2, 3, …, n].

[0057] At this time, it is determined whether the operation continues or ends according to the preset loop number n of the operation. If k' = n, the operation ends; if k' < n, the operation continues, and the second input signal S obtained in S6 in_k’ is input into the fiber coupler 3 from the third port 3-3, that is, the second input signal S in_k’ is assigned to the transmission matrix as the input of the fiber coupler 3, and the clockwise transmission signal S transmitted in the ring cavity in a new round is obtained by solving cw_k and the counterclockwise transmission signal S acw_k . At this time, k = 2, and S2 - S6 is executed to obtain the laser output signal S out_k and the third input signal S of the next round of operation in_k’ ,, until k' = n, the simulation ends.

[0058] The simulation operation of the transmission matrix of the fiber coupler 3 in S7 disclosed in this embodiment is as follows:

[0059]

[0060] According to this example, by using the simulation verification method of the present invention and establishing a simulation platform based on Mat l ab software to analyze the rich soliton dynamics phenomena of this type of fiber laser, the following can be obtained Figure 2 as the shown simulation process.

[0061] The method of this application becomes a reliable means for studying the rich soliton dynamics phenomena occurring in the mode-locking process, which is convenient for users to operate and observe. It not only helps in the theoretical simulation research to verify experimental phenomena, but also is of great help for the robust design for engineering applications.

[0062] The preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings. However, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept scope of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0063] In addition, it should be noted that, among the various specific technical features described in the above specific embodiments, they can be combined in any appropriate manner without conflict. To avoid unnecessary repetition, the present disclosure does not separately describe various possible combination methods.

[0064] In addition, any combination can be made between various different embodiments disclosed in this solution as long as it does not violate the idea of the present disclosure, and it should also be regarded as the content invented by the present disclosure.

Claims

1. A soliton dynamics simulation method for a "9" cavity fiber laser, characterized in that: The steps include: S1, define the initial input signal (1), input the initial input signal (1) into the first single-mode optical fiber (2), and after the NLSE equation is calculated, the first input signal S is obtained in_k , and the first input signal S in_k Inputting the optical fiber coupler (3) through the first port (3-1) of the optical fiber coupler (3); Among them, k = 1 in the initial state; S2, using the transmission matrix to perform simulation operation of the optical fiber coupler 3, the first input signal S in_k After the optical fiber coupler (3) splits the beam, the clockwise transmission signal S in the ring cavity is obtained. cw_k and counterclockwise transmission signal S acw_k and are outputted from the second port (3-2) and the fourth port (3-4) of the optical fiber coupler (3) respectively; S3, S2 get the clockwise transmission signal S cw_k The clockwise output signal S is obtained by sequentially passing through the second single-mode optical fiber (4), the gain optical fiber (5) and the non-reciprocal phase shifter (6). cw_k ', and at the same time S3 obtains the counterclockwise transmission signal S acw_k The counterclockwise output signal S is obtained by sequentially passing through the non-reciprocal phase shifter (6), the gain optical fiber (5) and the second single-mode optical fiber (4). acw_k '; S4, S3 get the clockwise output signal S cw_k ' and counterclockwise output signal S acw_k 'The fourth port (3-4) and the second port (3-2) are input and assigned to the fiber coupler (3) transmission matrix to obtain the laser output signal S out_k and the reflection arm input signal S reflected_k , are outputted by the first port (3-1) and the third port (3-3) respectively; S5, S4 get the reflection arm input signal S reflected_k The first transmission signal S of the reflector arm is obtained by transmitting through the third single-mode optical fiber (7) and calculating through the NLSE equation. reflected_k '; S6, S5 obtained by the first transmission signal S of the reflection arm reflected_k 'After being reflected by the reflector (8), the second transmission signal ηS of the reflector arm is obtained reflected_k ', the second transmission signal ηS of the reflector arm reflected_k 'Transmitted to the third single-mode optical fiber (7), the second input signal S is obtained after the NLSE equation is calculated in_k’ The second input signal S in_k’ Inputting into the optical fiber coupler (3) through the third port (3-3); Where k'=k+1; S7, the second input signal S in_k’ As the input signal of the next round of operation, S2-S6 is repeatedly executed to obtain multiple laser output signals S out_k ; The number of times the repeated cycle is executed is a preset number of cycles n.

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