Output power optimization method of ytterbium-doped pulse fiber laser

Abstract

The invention provides an output power optimization method of an ytterbium-doped pulse fiber laser, and relates to the field of laser design, and the method comprises the steps: building a dynamic transmission model of the ytterbium-doped fiber laser in a bidirectional pumping mode, and researching the power improvement factor of signal light in the transmission process of the ytterbium-doped fiber. A dynamic rate and power transmission equation of the Yb3 +-doped pulse fiber laser is established according to a two-energy-level simplified model of Yb3 + and the propagation characteristic of laser in the fiber, and finally a laser output power equation is obtained. According to a dynamic transmission rate equation of an ytterbium-doped fiber laser, power distribution conditions of pump light and signal light in the length direction of a gain fiber under different pump modes, influences of pump power on signal light gain output and influences of different gain fiber parameters on amplifier output are simulated and analyzed; and the optimization design method of the ytterbium-doped pulse fiber laser is obtained.

Description

Technical Field

[0001] The present application relates to the field of laser design, and in particular to a method for optimizing the output power of an ytterbium-doped pulsed fiber laser. Background Art

[0002] As a core research direction in high-energy laser technology, ytterbium-doped pulsed fiber lasers occupy an important position in the fields of precision machining and space communications due to their near-diffraction-limited beam quality, electro-optical conversion efficiency exceeding 70%, modular and compact structural design, and excellent thermal stability. Particularly in industrial applications, ytterbium-doped fiber laser systems in the 1μm band have become the mainstream configuration. Their core advantages are: ytterbium ions have an energy level structure with quantum defects as low as 8%, completely avoiding the energy loss caused by ground-state absorption and excited-state absorption; the upper energy level lifetime is as long as 0.8ms, which is conducive to energy storage and release; the absorption spectrum covers the 900-980nm band, with a broad absorption band and narrow absorption peaks at 915nm and 976nm, respectively, which perfectly match the characteristics of semiconductor pump sources. More importantly, ytterbium-doped fibers can achieve doping levels as high as 1026ions / m3 without quenching effects, and when combined with end-pumping technology, achieve a pump conversion efficiency of over 80%.

[0003] Therefore, in-depth research on the optimal design method of ytterbium-doped pulsed fiber lasers has both theoretical and practical significance. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for optimizing the output power of an ytterbium-doped pulse fiber laser in order to fill the research gap in the output power of an ytterbium-doped pulse fiber laser.

[0005] The above-mentioned purpose of this application is achieved through the following technical solutions:

[0006] S1: Constructing a dynamic transmission model of ytterbium-doped pulsed fiber laser;

[0007] S2: The laser output power equation is obtained through the dynamic transmission model and the simplified two-level model of Yb3+;

[0008] S3: Perform simulation analysis through the laser output power equation to determine the output power optimization strategy of the fiber laser and complete the optimized design of the fiber laser.

[0009] Optionally, step S1 includes:

[0010] Set the length of the Yb3+-doped gain fiber of the ytterbium-doped pulse fiber laser to L, z=0 represents the starting end of the Yb3+-doped gain fiber, and z=L represents the end of the Yb3+-doped gain fiber;

[0011] Considering the influence of ASE spontaneous emission on amplifier performance, the emission spectrum of ASE is divided into multiple small channels, each of which has a central wavelength λ k The center is Δλ, the bandwidth is k=1,2,3…K.

[0012] Optionally, step S2 includes:

[0013] According to the simplified two-level model of Yb3+ ions and the propagation characteristics of laser in optical fiber, combined with the dynamic transmission model, the dynamic rate and power transmission equations of Yb3+-doped pulsed fiber laser are obtained:

[0014]

[0015] N1+N2=N (2)

[0016]

[0017] Among them, N1 and N2 are the number of particles in the lower and upper energy levels respectively; represents the forward and reverse transmission pump light intensity, ± represents the forward and reverse transmission of light; v is the frequency of light propagating in the optical fiber; g represents the optical gain coefficient; Γ p represents the effective superposition factor of the pump light and the doped ion region; σ pe represents the emission cross section of the pump light; σ pa represents the absorption cross section of the pump light; α p represents the attenuation coefficient of the pump light in the optical fiber; P p Indicates the intensity of the pump light; P s represents the intensity of the signal light, Γ s represent the effective superposition factor of the signal light and the doped ion region, σ se represent the emission cross section of the signal light, σ sa Represent the absorption cross section of the signal light, α s are the attenuation coefficients of the signal light in the optical fiber; P ASEk The wavelength is λ k ASE power, ± represents the forward and reverse transmission of light; σ ka and σ ke The wavelength is λ k The absorption and emission cross sections of ASE light; h represents the Planck constant;

[0018] Formula (1) describes the rate of change of the number concentration of upper energy level particles in the optical fiber, Formula (2) shows the conservation of the total number of upper and lower energy level particles, Formulas (3) and (4) respectively represent the changes in the optical power of the pump light and signal light during transmission in the optical fiber, and Formula (5) is the change in the optical power of K wavelengths of light in the optical fiber during the transmission process;

[0019] In formulas (1)-(5), Hpa 、H pe 、W sa 、W se 、A e The meaning is shown in formulas (6)-(10):

[0020]

[0021] A e =1 / τ 21 (10)

[0022] Among them, A eff represents the effective mode field area, τ 21 is the survival time of the upper energy level particle, is its spontaneous emission rate.

[0023] Optionally, step S2 further includes:

[0024] Equations (1)-(5) form a nonlinear partial differential equation system, whose boundary conditions are as follows:

[0025] P s (0,t)=P s0 F(t) (11)

[0026]

[0027]

[0028] Among them, P p1 and P p2 is the initial power of the forward and reverse pump light, P S0 is the initial power of the signal light;

[0029] When the pump light is transmitted to position z in the optical fiber, the distribution of the upper energy level Yb3+N2(z) in the optical fiber can be expressed as:

[0030]

[0031] Among them, σ ap represents the pump light absorption cross section; σ as represents the signal light absorption cross section; v p represents the pump light frequency; A represents the cross-sectional area of the double-clad fiber core; v s represents the signal light frequency; σ ep represents the emission cross section of the pump light; σ es represents the emission cross section of the signal light; N represents the ytterbium ion doping concentration;

[0032] Equations (17) and (18) describe the relationship between the forward and reverse pump light and the upper energy level Yb3+ density and the forward and reverse signal light, respectively.

[0033] Optionally, step S2 further includes:

[0034] Since the ASE optical power transmitted backward in the optical fiber is much smaller than the signal optical power, it can be ignored. According to the boundary conditions, we know that:

[0035]

[0036] The gain at point z in the fiber is expressed as:

[0037]

[0038] Where I(z) represents the light intensity at position z;

[0039] From formula (21), the gain at the optical fiber L can be obtained as:

[0040]

[0041] When the gain and loss in the laser resonator reach a steady state, we have:

[0042] R1R2e 2Gs(L) =1 (23)

[0043] Where R1 and R2 represent the reflectivity of the input and output end mirrors;

[0044] Combining equation (22) and equation (23) we can get:

[0045]

[0046] signal light With pump light The output power in saturation state can be expressed as:

[0047]

[0048] Combining equations (16)-(26), the rate equation of the quasi-three-level structure Yb3+-doped laser can be obtained:

[0049]

[0050] The left side of equation (28) represents the effect of the signal light on the upper energy level Yb3+ number N2(z), and the second term on the right side of the equation represents the effect of the pump light on N2(z). Since N2(z) is much smaller than N, equation (28) can be expressed as:

[0051]

[0052] Where K represents the net gain coefficient.

[0053] Optionally, step S2 further includes:

[0054] Combining equations (17), (18), (24) and (29), we can obtain:

[0055]

[0056] The laser output power equation can be obtained by integrating the forward laser and multiplying it with the transmittance of the rear cavity mirror to the laser, as follows:

[0057]

[0058] An electronic device includes a processor, a memory, a user interface, and a network interface. The memory is used to store instructions. The user interface and the network interface are used to communicate with other devices. The processor is used to execute the instructions stored in the memory so that the electronic device performs a method for optimizing the output power of an ytterbium-doped pulsed fiber laser.

[0059] A computer-readable storage medium stores instructions. When the instructions are executed, a method for optimizing the output power of an ytterbium-doped pulsed fiber laser is performed.

[0060] The beneficial effects of the technical solution provided by this application are:

[0061] 1. The optimization design method for ytterbium-doped pulsed fiber lasers provided by the present invention has more outstanding effects in improving signal light output and other aspects, and has wide versatility. The method is simple and effective and has a certain guiding role in the optical path design of fiber lasers.

[0062] 2. Based on the analysis of the power distribution of pump light and signal light along the length of the gain fiber under different pumping modes, the influence of pump power on the signal light gain output, and the influence of different gain fiber parameters on the amplifier output, selecting appropriate optical device parameters can significantly improve the output performance of the fiber laser.

[0063] 3. The optimized design and implementation method of the ytterbium-doped pulse fiber laser provided by the present invention has low cost, few process steps, and easy-to-control implementation process, which has certain practical significance for laser industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The present application will be further described below with reference to the accompanying drawings and embodiments, in which:

[0065] Figure 1 It is a dynamic transmission model diagram in the embodiment of the present application;

[0066] Figure 2 is a distribution diagram of the pump light and signal light intensities in the embodiment of the present application;

[0067] Figure 3 is a signal light gain diagram under different pump powers in the embodiment of the present application;

[0068] Figure 4 is a diagram of the output power of signal light at different gain fiber lengths in an embodiment of the present application;

[0069] Figure 5 1 is a distribution diagram of signal light and pump light in an optical fiber at different doping concentrations in an embodiment of the present application;

[0070] Figure 6 is a diagram showing the effect of different numerical apertures on signal light output in an embodiment of the present application;

[0071] Figure 7 It is a schematic diagram of the structure of an electronic device in an embodiment of the present application. DETAILED DESCRIPTION

[0072] In order to have a clearer understanding of the technical features, purposes and effects of this application, the specific implementation methods of this application are now described in detail with reference to the accompanying drawings.

[0073] The embodiments of the present application provide a method for optimizing the output power of an ytterbium-doped pulsed fiber laser.

[0074] Please refer to Figure 1 , Figure 1 This is a dynamic transmission model diagram of an output power optimization method for an ytterbium-doped pulsed fiber laser in an embodiment of the present application, including:

[0075] S1: Constructing a dynamic transmission model of ytterbium-doped pulsed fiber laser;

[0076] As an example, in order to study the factors that affect the power increase of signal light during transmission in ytterbium-doped fiber, it is necessary to model and analyze the laser transmission in ytterbium-doped pulsed fiber laser. Figure 1 shown.

[0077] S2: The laser output power equation is obtained through the dynamic transmission model and the simplified two-level model of Yb3+;

[0078] S3: Perform simulation analysis through the laser output power equation to determine the output power optimization strategy of the fiber laser and complete the optimized design of the fiber laser.

[0079] Step S1 includes:

[0080] Set the length of the Yb3+-doped gain fiber of the ytterbium-doped pulse fiber laser to L, z=0 represents the starting end of the Yb3+-doped gain fiber, and z=L represents the end of the Yb3+-doped gain fiber;

[0081] Considering the influence of ASE spontaneous emission on amplifier performance, the emission spectrum of ASE is divided into multiple small channels, each of which has a central wavelength λ k The center is Δλ, the bandwidth is k=1,2,3…K.

[0082] In a specific embodiment of the present application, in a Yb3+-doped gain fiber with a length of L, the signal light wavelength is λ s The incident light is at z = 0, and the wavelength of the pump light is λ p , where the forward pump light is coupled into the inner cladding of the optical fiber from z = 0, and the backward pump light is coupled into the optical fiber from z = L. Due to the wide fluorescence spectrum of Yb3+, during the propagation of the signal light and pump light in the optical fiber, the ASE laser light close to the wavelength of the signal light will inevitably be amplified. When the pump power is high, the impact of ASE (spontaneous emission) on the performance of the amplifier must be considered. When analyzing ASE, a common method is to divide the emission spectrum of ASE into multiple small channels, each of which is centered at a certain wavelength λ. k The power characteristics of the overall ASE are analyzed by studying the light waves in these small wavelength ranges.

[0083] Step S2 includes:

[0084] According to the simplified two-level model of Yb3+ ions and the propagation characteristics of laser in optical fiber, combined with the dynamic transmission model, the dynamic rate and power transmission equations of Yb3+-doped pulsed fiber laser are obtained:

[0085]

[0086] N1+N2=N (2)

[0087]

[0088] Among them, N1 and N2 are the number of particles in the lower and upper energy levels respectively; represents the forward and reverse transmission pump light intensity, ± represents the forward and reverse transmission of light; v is the frequency of light propagating in the optical fiber; g represents the optical gain coefficient; Γ p represents the effective superposition factor of the pump light and the doped ion region; σ pe represents the emission cross section of the pump light; σ pa represents the absorption cross section of the pump light; α p represents the attenuation coefficient of the pump light in the optical fiber; P p Indicates the intensity of the pump light; P s represents the intensity of the signal light, Γ s represent the effective superposition factor of the signal light and the doped ion region, σ serepresent the emission cross section of the signal light, σ sa represent the absorption cross section of the signal light, σ s are the attenuation coefficients of the signal light in the optical fiber; P ASEk The wavelength is λ k ASE power, ± represents the forward and reverse transmission of light; σ ka and σ ke The wavelength is λ k The absorption and emission cross sections of ASE light; h represents the Planck constant;

[0089] Formula (1) describes the rate of change of the number concentration of upper energy level particles in the optical fiber, Formula (2) shows the conservation of the total number of upper and lower energy level particles, Formulas (3) and (4) respectively represent the changes in the optical power of the pump light and signal light during transmission in the optical fiber, and Formula (5) is the change in the optical power of K wavelengths of light in the optical fiber during the transmission process;

[0090] In formulas (1)-(5), H pa 、H pe 、W sa 、W se 、A e The meaning is shown in formulas (6)-(10):

[0091]

[0092] A e =1 / τ 21 (10)

[0093] Among them, A eff represents the effective mode field area, τ 21 is the survival time of the upper energy level particle, is its spontaneous emission rate.

[0094] Optionally, step S2 further includes:

[0095] Equations (1)-(5) form a nonlinear partial differential equation system, whose boundary conditions are as follows:

[0096] P s (0,t)=P s0 F(t) (11)

[0097]

[0098] Among them, P p1 and P p2 is the initial power of the forward and reverse pump light, P S0 is the initial power of the signal light;

[0099] When the pump light is transmitted to position z in the optical fiber, the distribution of the upper energy level Yb3+N2(z) in the optical fiber can be expressed as:

[0100]

[0101]

[0102] Among them, σ ap represents the pump light absorption cross section; σ as represents the signal light absorption cross section; v p represents the pump light frequency; A represents the cross-sectional area of the double-clad fiber core; v s represents the signal light frequency; σ ep represents the emission cross section of the pump light; σ es represents the emission cross section of the signal light; N represents the ytterbium ion doping concentration;

[0103] Equations (17) and (18) describe the relationship between the forward and reverse pump light and the upper energy level Yb3+ density and the forward and reverse signal light, respectively.

[0104] Step S2 further includes:

[0105] Since the ASE optical power transmitted backward in the optical fiber is much smaller than the signal optical power, it can be ignored. According to the boundary conditions, we know that:

[0106]

[0107] The present application provides an embodiment as follows. According to equations (19) and (20), the influence of Yb3+ doping concentration N and fiber length on forward and reverse pump light power is obtained, thereby optimizing the optical path design of the laser.

[0108] The gain at point z in the fiber is expressed as:

[0109]

[0110] Where I(z) represents the light intensity at position z;

[0111] From formula (21), the gain at the optical fiber L can be obtained as:

[0112]

[0113] When the gain and loss in the laser resonator reach a steady state, we have:

[0114] R1R2e 2Gs(L) =1 (23)

[0115] Where R1 and R2 represent the reflectivity of the input and output end mirrors;

[0116] Combining equation (22) and equation (23) we can get:

[0117]

[0118] signal light With pump light The output power in saturation state can be expressed as:

[0119]

[0120] Combining equations (16)-(26), the rate equation of the quasi-three-level structure Yb3+-doped laser can be obtained:

[0121]

[0122] The left side of equation (28) represents the effect of the signal light on the upper energy level Yb3+ number N2(z), and the second term on the right side of the equation represents the effect of the pump light on N2(z). Since N2(z) is much smaller than N, equation (28) can be expressed as:

[0123]

[0124] Where K represents the net gain coefficient.

[0125] Step S2 further includes:

[0126] Combining equations (17), (18), (24) and (29), we can obtain:

[0127]

[0128] The laser output power equation can be obtained by integrating the forward laser and multiplying it with the transmittance of the rear cavity mirror to the laser, as follows:

[0129]

[0130] This application provides an embodiment as follows. From the laser output power equation, it can be found that factors such as pump light power, resonant cavity reflectivity, Yb3+ doping concentration in the optical fiber, and optical fiber length will all affect the output power of the laser. Next, we will simulate and analyze the output characteristics of the pulsed ytterbium-doped fiber laser by selecting appropriate parameter values, and then optimize the design of the fiber laser to obtain high-power pulsed light output.

[0131] The output power optimization strategy specifically includes: Through the analysis of the gain of the signal light under different pump powers, it can be seen that before reaching gain saturation, increasing the pump power can improve the gain of the signal light, and when the pump light is sufficient, increasing the pump power will have a greater gain for the high-power signal light.

[0132] Analysis of the effects of different gain fiber lengths on amplifier output reveals that for single-mode optical output, when the fiber length is below the optimal value, the pump light cannot be fully absorbed, resulting in insufficient population of upper-level particles and limited signal light gain. Furthermore, when the fiber length exceeds the optimal value, the pump light is almost completely depleted in the rear section of the fiber, resulting in an extremely low population of upper-level particles in this region, making it impossible to effectively amplify the signal light. The signal light output power may even decrease due to fiber loss and reabsorption. Therefore, in order to maximize the signal light output power, it is necessary to select the gain fiber length.

[0133] By analyzing the effects of different doping concentrations on amplifier output in gain fibers, we can see that as the doping concentration increases, the peak power of the signal light increases significantly, while the fiber length required to reach the peak power decreases significantly. Therefore, when selecting a gain fiber, it is necessary to choose an appropriate doping concentration.

[0134] By analyzing the impact of different numerical apertures of gain fibers on amplifier output, it is known that, given the same gain fiber core diameter, increasing the numerical aperture (NA) significantly improves the fiber's light collection efficiency, thereby increasing the power of the output signal light. The larger the core-to-cladding diameter ratio, the higher the coupling efficiency of the pump light into the core. Therefore, when designing and building a fiber laser, it is necessary to comprehensively consider the numerical aperture and core diameter of the gain fiber and select gain fiber parameters that balance high power output and good beam quality.

[0135] In one embodiment, in order to study the power distribution of pump light and signal light along the length direction of the gain fiber of a Yb3+-doped fiber laser under different pumping modes, forward pumping and backward pumping were tested under the conditions of pump light power of 10W and signal light power of 80mW. The power distribution results are shown in Figure 2. Figure 2 shown.

[0136] Figure 2 In the figure, the blue curve represents the power distribution of the forward pump light in the gain fiber, the green curve represents the power distribution of the reverse pump light in the gain fiber, and the red curve represents the power distribution of the signal light in the gain fiber. Figure 2 (a) shows the power variation curve of the pump and signal light during forward pumping. At the beginning of the fiber, the signal light power rises sharply, while the pump light power decreases rapidly. When the fiber length increases to approximately L = 6m, the growth rate of the signal light power begins to slow. As the fiber length increases further, the signal light power continues to rise, reaching a maximum at approximately L = 10m. At this point, the rate of decrease of the forward pump light power also gradually slows down until it reaches almost zero at the end of the fiber. Figure 2(b) shows the variation in reverse pump power. At the beginning of the fiber, the pump light power is at its minimum. As the fiber length increases, the pump light power gradually increases, reaching its maximum at the end. The signal light power, on the other hand, grows more slowly in the initial stages of the fiber transmission. After a certain distance, the signal light power begins to increase rapidly, eventually reaching its peak at the end of the fiber.

[0137] In order to study the effect of pump power on the signal light gain output in Yb3+-doped fiber laser, the experiment injected signal light with optical power of 10mW and 100mW respectively, and used gain fiber with lengths of 4m, 6m, 8m, and 10m respectively. The pump light power was changed by forward pumping to test the signal light gain output. The results are as follows Figure 3 shown.

[0138] Figure 3 (a) shows the gain curves for different pump powers at different gain fiber lengths when the signal light injection power is 10mW. As the pump power increases, the signal light gain gradually increases at each fiber length, but the increase trend gradually becomes flat. When the pump power continues to increase, the gain curve shows no obvious increase trend. For a 10m fiber length, when the pump power is 2W, the signal light gain increases rapidly; when the pump power reaches 3.5W, the signal light gain approaches saturation; when the pump power increases to 5W, the signal light gain only increases by 1.1dB compared to 3.5W. For a 4m fiber length, when the pump power is 1W, the gain is still rising; when the pump power reaches 1.5W, it approaches gain saturation. When the pump power continues to increase to 5W, the signal light gain only increases by 0.9dB compared to 1.5W. When the pump power is in the range of 1.5W to 5W, the signal light gain increases with increasing fiber length at the same pump power. When the pump power is 0.5W, the signal light gain generated by a 10m long gain fiber is lower than that of a 6m or 8m long gain fiber, but higher than that of a 4m long gain fiber. When the gain fiber is 4m long, the pump is not fully absorbed, the number of particles in the upper energy level in the gain fiber is small, and the gain for the signal light is low.

[0139] Figure 3 (b) is the gain curve of different pump powers for different gain fiber lengths when the signal light injection power is 100mW. As the pump power increases, the signal light gain change curve under each gain fiber length gradually increases and the trend gradually flattens until the gain is saturated. However, in contrast, Figure 3(a) shows that when the pump power is less than 1.5W, the pump light gain for a 10mW signal is much higher than the gain for a 100mW signal at the same gain fiber length. As the pump power continues to increase, the gain for a 10mW signal gradually reaches saturation. When the pump power increases to 3.5W, the gain for a 100mW signal exceeds that for a 10mW signal at all gain fiber lengths, approaching gain saturation. For a 10m fiber length, at a 5W pump power, the gain for a 10mW signal is 28.6dB, while the gain for a 100mW signal is 31dB, a 3.4dB improvement.

[0140] In order to study the amplifier output under different gain fiber parameters in Yb3+-doped fiber lasers, amplification experiments were carried out using single-mode gain fiber. The advantage of using single-mode fiber to amplify signal light is that there will be no change in mode field output power and degradation of beam quality due to coupling of multiple mode lights. Figure 4 Figure 3 is the relationship between the output power of the 1064nm signal light and the gain fiber length when the pump power is 0.5W, 1W, 1.5W, and 2W, respectively.

[0141] From the data comparison in the figure, it can be seen that under the condition of fixed fiber length, as the pump light power increases, the output power also increases accordingly. In addition, all curves show a trend of first rising to a peak and then gradually decreasing. This phenomenon shows that for any signal light, there is an optimal gain fiber length that can maximize the output power. Specifically, when the pump power is 0.5W, the signal light output power reaches its maximum value when the fiber length is 4.5m, so the optimal gain fiber length is L = 4.5m; when the pump power is 1W, 1.5W and 2W respectively, the optimal gain fiber length is approximately 5m, 5.5m and 6m, respectively.

[0142] The concentration of doped ions in the gain fiber is also an important parameter in the signal light amplification process. Figure 5 The distribution of signal light and pump light in the gain fiber using forward pumping when the pump power is 2 W and the doping ion concentrations are N=3.8, N=4.5, and N=5.2, respectively.

[0143] from Figure 5As shown in (a), the signal light power distribution curves of gain fibers with different doping concentrations show that the gain characteristics of the signal light are closely related to the doping concentration. As the doping concentration increases, the peak power of the signal light increases significantly, while the fiber length required to reach the peak value is significantly shortened. In addition, the signal light power in highly doped fibers increases faster in the initial section. However, when the fiber length exceeds the optimal value, the pump light is almost completely depleted, resulting in the inability to effectively amplify the signal light in the subsequent section of the gain fiber. At this point, the loss effect of the fiber dominates, causing the signal light power to gradually decrease.

[0144] Figure 5 (b) is the distribution curve of pump light along the length of the fiber in gain fibers with different doping concentrations. It can be found from the figure that the higher the doping concentration, the faster the pump light power decreases in the gain fiber. This is opposite to the trend of the signal light power. This is because the higher the doping concentration, the more pump light participates in stimulated recombination in the gain fiber, the faster the pump light consumption rate is, and the higher the gain for the signal light is. When N = 5.2, the pump light power drops rapidly in the initial stage. Figure 5 (a) It can be seen that the signal light gain reaches its maximum when the gain fiber length is approximately 4.5m. When the gain fiber length reaches 7m, the pump light is completely consumed and the signal light power begins to decline rapidly. When N = 3.8, the pump light power decreases slowly in the initial stage, and the gain to the signal light is also low, and the signal light power increases slowly. When the gain fiber length is approximately 6m, the signal light gain reaches its maximum, and at this time, there is still a lot of pump light remaining in the gain fiber. As the gain fiber length continues to increase, the signal light power begins to decline. When the gain fiber length reaches 9m, a lot of pump light still remains, and the remaining pump light will interfere with the laser performance during the subsequent amplification process.

[0145] The numerical aperture NA of an optical fiber is calculated from the refractive index of the core and the refractive index of the inner cladding, and is expressed as , which reflects the optical fiber's ability to focus light. Light with an incident angle less than can achieve total reflection in the optical fiber and propagate longitudinally along the core. Therefore, the larger the numerical aperture, the stronger the optical fiber's focusing ability, and the larger the superposition factor. Currently, the double-clad Yb3+-doped optical fiber used in the engineering field generally has a core numerical aperture between 0.05 and 0.15. Double-clad gain fibers with core / cladding diameters of 8 / 130μm, 10 / 130μm, and 12 / 130μm, respectively, are selected. When the pump power is 2W, the gain fiber length is 6m, and the Yb3+ doping particle concentration is N=4.5, a comparative study is conducted on the effects of different numerical apertures on the signal light output characteristics. The results are as follows: Figure 6 shown.

[0146] As can be seen from the data in the figure, when the gain fiber core diameter remains the same, an increase in the numerical aperture (NA) can significantly improve the optical fiber's light collection efficiency, thereby increasing the power of the output signal light. In addition, the larger the ratio of the core to the cladding diameter, the higher the coupling efficiency between the pump light and the core, and more pump light can enter the core, which in turn causes the signal light power to increase rapidly when the pump power increases. However, although larger numerical apertures and core diameters help achieve higher signal light output power, they also increase the number of modes transmitted in the core, resulting in a decrease in the output beam quality. In order to maintain high beam quality under large core diameter conditions, the method of reducing the numerical aperture is usually used to limit the number of modes, thereby effectively suppressing the negative impact of multimode effects on beam quality.

[0147] This application also discloses an electronic device. Figure 7 , Figure 7 Schematic diagram of the structure of an electronic device disclosed in an embodiment of the present application. The electronic device 500 may include: at least one processor 501, at least one network interface 504, a user interface 503, a memory 505, and at least one communication bus 502.

[0148] The communication bus 502 is used to implement the connection and communication between these components.

[0149] The user interface 503 may include a display screen, and the optional user interface 503 may also include a standard wired interface or a wireless interface.

[0150] The network interface 504 may optionally include a standard wired interface or a wireless interface (such as a WI-FI interface).

[0151] The present application also discloses a computer-readable storage medium storing a plurality of instructions suitable for loading by a processor to execute the above-mentioned method for optimizing the output power of an ytterbium-doped pulsed fiber laser.

[0152] The above are merely exemplary embodiments of the present disclosure and are not intended to limit the scope of the present disclosure. In other words, any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure.

[0153] This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary techniques in the art not described herein. The description and examples are to be considered as exemplary only, and the scope and spirit of the present disclosure are to be defined by the claims.

Claims

1. A method for optimizing the output power of an ytterbium-doped pulsed fiber laser, characterized in that: The method comprises the following steps: S1: Constructing a dynamic transmission model of ytterbium-doped pulsed fiber laser; S2: The laser output power equation is obtained through the dynamic transmission model and the simplified two-level model of Yb3+; S3: Perform simulation analysis through the laser output power equation to determine the output power optimization strategy of the fiber laser and complete the optimized design of the fiber laser.

2. The method for optimizing the output power of an ytterbium-doped pulsed fiber laser according to claim 1, wherein: Step S1 includes: Set the length of the Yb3+-doped gain fiber of the ytterbium-doped pulse fiber laser to L, z=0 represents the starting end of the Yb3+-doped gain fiber, and z=L represents the end of the Yb3+-doped gain fiber; Considering the influence of ASE spontaneous emission on amplifier performance, the emission spectrum of ASE is divided into multiple small channels, each of which has a central wavelength λ k The center is Δλ, the bandwidth is k=1,2,3…K.

3. The method for optimizing the output power of an ytterbium-doped pulsed fiber laser according to claim 2, wherein: Step S2 includes: According to the simplified two-level model of Yb3+ ions and the propagation characteristics of laser in optical fiber, combined with the dynamic transmission model, the dynamic rate and power transmission equations of Yb3+-doped pulsed fiber laser are obtained: N1+N2=N (2) Among them, N1 and N2 are the number of particles in the lower and upper energy levels respectively; represents the forward and reverse transmission pump light intensity, ± represents the forward and reverse transmission of light; v is the frequency of light propagating in the optical fiber; g represents the optical gain coefficient; Γ p represents the effective superposition factor of the pump light and the doped ion region; σ pe represents the emission cross section of the pump light; σ pa represents the absorption cross section of the pump light; α p represents the attenuation coefficient of the pump light in the optical fiber; P p Indicates the intensity of the pump light; P s represents the intensity of the signal light, Γ s represent the effective superposition factor of the signal light and the doped ion region, σ se represent the emission cross section of the signal light, σ sa Represent the absorption cross section of the signal light, α s are the attenuation coefficients of the signal light in the optical fiber; P ASEk The wavelength is λ k ASE power, ± represents the forward and reverse transmission of light; σ ka and σ ke The wavelength is λ k The absorption and emission cross sections of ASE light; h represents the Planck constant; Formula (1) describes the rate of change of the number concentration of upper energy level particles in the optical fiber, Formula (2) shows the conservation of the total number of upper and lower energy level particles, Formulas (3) and (4) respectively represent the changes in the optical power of the pump light and signal light during transmission in the optical fiber, and Formula (5) is the change in the optical power of K wavelengths of light in the optical fiber during the transmission process; In formulas (1)-(5), H pa 、H pe 、W sa 、W se 、A e The meaning is shown in formulas (6)-(10): A e =1 / t 21 (10) Among them, A eff represents the effective mode field area, τ 21 is the survival time of the upper energy level particle, is its spontaneous emission rate.

4. The method for optimizing the output power of an ytterbium-doped pulsed fiber laser according to claim 3, wherein: Step S2 further includes: Equations (1)-(5) form a nonlinear partial differential equation system, whose boundary conditions are as follows: P s (0,t)=P s0 F(t) (11) Among them, P p1 and P p2 is the initial power of the forward and reverse pump light, P S0 is the initial power of the signal light; When the pump light is transmitted to position z in the optical fiber, the distribution of the upper energy level Yb3+N2(z) in the optical fiber can be expressed as: Among them, σ ap represents the pump light absorption cross section; σ as represents the signal light absorption cross section; v p represents the pump light frequency; A represents the cross-sectional area of the double-clad fiber core; v s represents the signal light frequency; σ ep represents the emission cross section of the pump light; σ es represents the emission cross section of the signal light; N represents the ytterbium ion doping concentration; Equations (17) and (18) describe the relationship between the forward and reverse pump light and the upper energy level Yb3+ density and the forward and reverse signal light, respectively.

5. The method for optimizing the output power of an ytterbium-doped pulsed fiber laser according to claim 4, wherein: Step S2 further includes: Since the ASE optical power transmitted backward in the optical fiber is much smaller than the signal optical power, it can be ignored. According to the boundary conditions, we know that: The gain at point z in the fiber is expressed as: Where I(z) represents the light intensity at position z; From formula (21), the gain at the optical fiber L can be obtained as: When the gain and loss in the laser resonator reach a steady state, we have: R1R2e 2Gs(L) =1 (23) Where R1 and R2 represent the reflectivity of the input and output end mirrors; Combining equation (22) and equation (23) we can get: signal light With pump light The output power in saturation state can be expressed as: Combining equations (16)-(26), the rate equation of the quasi-three-level structure Yb3+-doped laser can be obtained: The left side of equation (28) represents the effect of the signal light on the upper energy level Yb3+ number N2(z), and the second term on the right side of the equation represents the effect of the pump light on N2(z). Since N2(z) is much smaller than N, equation (28) can be expressed as: Where K represents the net gain coefficient.

6. The method for optimizing the output power of an ytterbium-doped pulsed fiber laser according to claim 5, wherein: Step S2 further includes: Combining equations (17), (18), (24) and (29), we can obtain: The laser output power equation can be obtained by integrating the forward laser and multiplying it with the transmittance of the rear cavity mirror to the laser, as follows:

7. An electronic device, characterized in that: It includes a processor, a memory, a user interface and a network interface, the memory is used to store instructions, the user interface and the network interface are used to communicate with other devices, and the processor is used to execute the instructions stored in the memory so that the electronic device executes the method according to any one of claims 1 to 6.

8. A computer-readable storage medium, characterized in that The computer-readable storage medium stores instructions, and when the instructions are executed by a computer, the method according to any one of claims 1 to 6 is executed.

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