MOPA pulse fiber laser for laser communication

Abstract

The invention relates to the field of laser communication, and discloses a laser communication-oriented MOPA pulse fiber laser, which comprises a seed source, a first pumping source, a second pumping source, a primary amplification module and a secondary amplification module, pump light emitted by the first pumping source enters the first-stage amplification module and the second-stage amplification module after being subjected to beam splitting through the coupler. Signal light emitted by a seed source and pump light after beam splitting pass through a first beam combiner in a first-stage amplification module, and first-stage amplification is carried out on the signal light through an ytterbium-doped gain optical fiber, so that first amplified signal light is obtained; the amplified first signal light enters a secondary amplification module, is subjected to secondary amplification through the ytterbium-doped gain fiber again, and passes through a second beam combiner together with the beam-split pump light and the pump light emitted by the second pump source again to obtain final signal light output; the method can be widely applied to the fields of laser communication, laser marking, laser welding, laser medical treatment and the like; the implementation scheme is low in cost.

Description

Technical Field

[0001] The invention relates to the field of laser communication, and in particular to a MOPA pulse fiber laser for laser communication. Background Art

[0002] Fiber laser is a laser that uses doped ions as the medium in the gain fiber. The waveguide structure of the optical fiber will cause the pump light to continuously reflect in the inner cladding of the gain fiber and enter the core to excite the gain ions therein. After absorbing the energy of the pump light, the ground state gain ions are stimulated to transition to an excited state, achieving a reversal of the number of particles at the upper and lower energy levels. When the signal light passes through, the excited state ions produce stimulated radiation and release photons, so that the signal light absorbs photons in this process and is amplified.

[0003] Compared with traditional solid-state lasers, fiber lasers have the advantages of small quantum loss, high pumping efficiency, good heat dissipation, reliable working performance, long service life, and small structure volume; compared with traditional semiconductor lasers, fiber lasers have the advantages of good output spot quality and narrow system output spectral bandwidth. In recent years, they have attracted much attention from scientific researchers and achieved rapid development.

[0004] Master Oscillator Power Amplifier (MOPA) technology is to couple the seed light signal into the core of the double-clad gain fiber and use a semiconductor pump source to amplify the seed light. The advantage of using this method for light amplification is that the pulse width and repetition frequency of the output signal light are determined by the seed light source, the pulse shape of the output signal light is basically the same as the pulse shape of the seed light, and the seed light and the pump light are controlled by two different driving circuits, and the two do not interfere with each other. The optical path design is relatively flexible, the average power and peak power of the seed light after amplification are high, the output light pulse width can be adjusted in a wide range, and the output light spot quality is high. At present, the research on MOPA fiber lasers is mainly aimed at laser marking, laser cleaning and other fields, and there is little research on MOPA fiber lasers in the field of laser communication. Summary of the invention

[0005] The purpose of the present invention is to propose a MOPA pulse fiber laser for laser communication, so as to solve the technical problem that the prior art lacks relevant research on MOPA pulse fiber laser in the field of laser communication.

[0006] Specifically, the present invention provides a MOPA pulse fiber laser for laser communication, comprising:

[0007] A seed source, a first pump source, a second pump source, a primary amplification module and a secondary amplification module;

[0008] The pump light emitted by the first pump source is split by the coupler and enters the primary amplification module and the secondary amplification module respectively;

[0009] The signal light emitted by the seed source and the split pump light pass through the first beam combiner in the first-stage amplification module, and the signal light is first-stage amplified through the ytterbium-doped gain fiber to obtain the amplified first signal light;

[0010] The amplified first signal light enters the secondary amplification module and is again amplified through the ytterbium-doped gain fiber. At the same time, it passes through the second combiner again with the split pump light and the pump light emitted by the second pump source to obtain the final signal light output.

[0011] The beneficial effects provided by the present invention are:

[0012] An all-fiber structure single-mode pulse MOPA fiber laser optical path is designed, and the implementation scheme and the selected seed source wavelength, pump source wavelength, double-clad fiber doping ions, etc. are provided. Through the two-stage amplification of the optical path, the signal light with an average output power of about 4.6W is finally obtained. The feasibility of this scheme in the field of laser communication is verified by comparing the output waveforms of the pulse seed source before and after amplification. Compared with traditional solid-state lasers, it has the advantages of small quantum loss, high pumping efficiency, good heat dissipation, reliable working performance, long service life, and small structure volume; compared with traditional semiconductor lasers, it has the advantages of good output spot quality and narrow system output spectrum bandwidth;

[0013] Secondly, the pulse width and repetition frequency of the fiber laser pulse seed source provided by the present invention are adjustable, the output beam quality is good, and the output light waveform characteristics are excellent. It can be widely used in laser communication, laser marking, laser welding, laser medical treatment and other fields; the fiber laser implementation scheme provided by the present invention is low-cost, has fewer process flows, and the implementation process is easy to control, which has certain practical significance for laser industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structure of the laser of the present invention;

[0015] Figure 2 is the spectrum of the pulse seed source;

[0016] Figure 3 It is a schematic diagram of single pulse and multi-pulse waveforms of pulse seed source;

[0017] Figure 4 This is a schematic diagram of the effect of different gain fiber lengths on the spectral signal-to-noise ratio of the signal light output during the first stage amplification process;

[0018] Figure 5 Schematic diagram of the effect of different pump pulse widths on the spectrum during the first stage amplification process;

[0019] Figure 6 It is a schematic diagram of the power obtained after the signal light is amplified in the first stage at different pumping times;

[0020] Figure 7 It is the spectrum curve under different gain fiber lengths in the second stage amplification process;

[0021] Figure 8 It is the spectrum diagram of different pump pulse widths in the secondary amplification process;

[0022] Fig. 9 It is the output power change of the signal light during the second amplification process as the pumping time changes;

[0023] Fig.10 It is the pulse waveform output after the signal light is amplified in two stages. DETAILED DESCRIPTION

[0024] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0025] Before formally describing the present invention, the scheme of the present invention is first generally described for easy understanding.

[0026] Please refer to Figure 1 The present invention provides a MOPA pulse fiber laser for laser communication, comprising:

[0027] A seed source, a first pump source, a second pump source, a primary amplification module and a secondary amplification module;

[0028] The pump light emitted by the first pump source is split by the coupler and enters the primary amplification module and the secondary amplification module respectively;

[0029] The signal light emitted by the seed source and the split pump light pass through the first beam combiner in the first-stage amplification module, and the signal light is first-stage amplified through the ytterbium-doped gain fiber to obtain the amplified first signal light;

[0030] The amplified first signal light enters the secondary amplification module and is again amplified through the ytterbium-doped gain fiber. At the same time, it passes through the second combiner again with the split pump light and the pump light emitted by the second pump source to obtain the final signal light output.

[0031] It should be noted that a first isolator and a circulator are provided in sequence between the seed source and the first beam combiner.

[0032] It should be noted that the final signal light obtained by the second beam combiner needs to pass through a high-performance isolator before being output.

[0033] It should be noted that the seed source, the first pump source and the second pump source adopt an electric pulse modulation method.

[0034] As an embodiment, the seed source is a semiconductor laser with a central wavelength of 1064 nm. The first pump source and the second pump source are both pump lasers with a wavelength of 915 nm.

[0035] Example:

[0036] In order to test the feasibility of the pulse laser constructed by the present invention in the field of laser communication, the present invention conducted an experimental analysis on the relevant characteristics of the laser, as follows.

[0037] First, the pulse seed source is modulated, the rate of change within the laser is analyzed, and the output spectrum and waveform are obtained.

[0038] The seed source and pump source modulation technology used in this experiment is an electric pulse modulation technology. The electric pulse generated by the signal source directly drives the seed source laser and the pump laser to generate corresponding light pulses. Under the modulation of the driving power supply, electron transitions occur at the PN junction of the laser, and stimulated radiation generates photons. As the number of current-carrying electrons in the active region continues to increase, when the gain of the photons is greater than the loss, it begins to emit light. The carrier density and photon density in single-mode light can be reflected by the following equations to reflect their rate of change:

[0039]

[0040] Where N is the density of carriers, S is the density of photons, τ N is the survival time of carriers in the resonant cavity, τ ρ is the photon survival time in the resonant cavity, ε is the gain saturation factor, g is the maximum gain coefficient of the mode field, Γ is the light confinement factor, β is the spontaneous radiation factor, and V is the volume of the active layer.

[0041] The modulation method has low environmental requirements and is easy to implement, and can modulate the pulse width, repetition frequency, high and low levels of the generated signal light pulse according to actual needs. The present invention mainly discusses the pulse MOPA fiber laser for laser communication. Due to the influence of factors such as communication rate and communication distance, the present invention will use an electric pulse with a high level of 1.7V, a low level of 0V, a pulse width of 20ns, and a repetition frequency of 1MHZ to drive the seed source to generate pulse light.

[0042] The seed source laser is a semiconductor laser with a central wavelength of 1064nm.

[0043] The above method uses the signal source electric pulse to drive the seed source to obtain a seed light power of about 2.88mW without amplification. The spectrum of the pulse seed source is as follows: Figure 2 As shown, the pulse seed source single pulse and multi-pulse waveforms are as follows Figure 3 shown.

[0044] It can be seen from the above figure that the pulse interval of the pulse seed light modulated by the electrical signal pulse is 1us, corresponding to its repetition frequency of 1MHZ, the pulse waveform is not distorted, the unamplified seed source spectrum is good, the signal-to-noise ratio is high, there is only a central wavelength of 1064nm, and no stray light of other wavelengths appears near the central wavelength.

[0045] The above process verifies the feasibility of the electrical pulse modulation method and verifies that the seed source itself has good performance and its output pulse waveform is suitable for laser communication.

[0046] On the other hand, the present invention is based on Yb 3+ The multi-level structure of ions and the transmission characteristics of signal light in gain fiber are used to establish the dynamic rate of pulsed fiber lasers and related parameter equations of optical fibers.

[0047] Specifically, Yb-doped 3+ The equations for the dynamic rate and power of a pulsed fiber laser are shown below:

[0048]

[0049] N=N1(z,t)+N2(z,t)

[0050]

[0051] Where c is the speed of light, h is Planck's constant, z is the axial position of a point in the gain fiber, and N is the unit length Yb in the gain fiber. 3+ The doping concentration of ions, N1 and N2 are the number of particles at the upper and lower energy levels, Γ p and Γ are the transmission modes of pump light and signal light and the filling factor of doping ions, respectively. ± (z,t,λ k ) is the ASE laser light power, is the pump light power, the superscript indicates the forward and reverse transmission, ν p and ν represent the group velocity of the pump light and ASE light in the optical fiber, σ a (λ p ) and σ e (λ p ) represents the absorption cross section and emission cross section of the pump light, σ a (λ k ) and σ e (λ k ) represents the absorption cross section and emission cross section of the signal light, A is the gain fiber core area, S is the core capture factor, λ k and λ p are the wavelengths of the signal light and the pump light, αRS is the Rayleigh scattering coefficient, α(λ p ) and α(λ k ) represents the attenuation coefficient of pump light and signal light, and τ is the survival time of the upper energy level particles.

[0052] The beam quality of the system output light is closely related to the mode field distribution in the gain fiber, among which the beam quality of the fundamental mode is the best. As the number of transmitted light modes increases, the beam quality will decrease accordingly.

[0053] The number of modes in a gain fiber is determined by the numerical aperture of the core and the core diameter. The numerical aperture of the core can be expressed as n1 and n2 are the refractive indices of the fiber core and inner cladding respectively. NA is the numerical aperture. The larger the numerical aperture, the stronger the light receiving ability of the fiber. The number of modes can be expressed as:

[0054]

[0055] V is the normalized cutoff frequency, which can be expressed as:

[0056]

[0057] α is the core radius of the optical fiber. The larger the normalized frequency V is, the more modes that can be transmitted in the optical fiber. The normalized transverse phase parameter U can describe the transverse electric field distribution in the optical fiber:

[0058]

[0059] k0 is the wave number in vacuum, β is the longitudinal distribution constant of the mode, and the normalized transverse attenuation constant of the inner cladding is:

[0060]

[0061] W represents the attenuation rate of the optical waveguide in the cladding. The larger its value, the faster the attenuation. In double-clad optical fibers, usually only the effects of the core and cladding are considered. By converting the equations into a cylindrical coordinate system through the Maxwell equations, the electric field and magnetic field in the optical fiber core and the corresponding light intensity can be characterized as:

[0062]

[0063] Substituting the above formula into Maxwell's equations, we can get the electric field on the z component as:

[0064]

[0065] After simplification, the electric field and magnetic field components in the z direction of the optical fiber are:

[0066]

[0067] Where l is the order of the Bessel function, and The first and second Bessel functions are the first and second Bessel functions. In the weak waveguide fiber transmission process, the mode characteristic equation can be expressed as:

[0068]

[0069] The above process shows the reasons for selecting the relevant parameters of the gain fiber and the advantages of using single-mode double-clad gain fiber in fiber lasers for laser communications. The mode field in the single-mode double-clad gain fiber is evenly distributed and mainly concentrated in the core area. It has good mode and power symmetry, high output beam quality, and a high optical power density that can be detected on the detector target after transmission through the atmosphere.

[0070] It should be noted that the present invention also performs a first-stage optical amplification on the seed light and analyzes its output performance.

[0071] After being isolated and filtered by an isolator and a filter, the pulse seed source is optically coupled with the pump light through an MPC combiner, and the signal light is amplified in the first stage through a single-mode gain fiber. During the amplification process, optical feedback will be generated in the gain fiber. The length of the gain fiber and the concentration of the doping medium in the fiber will have a significant impact on the output wavelength of the system. Their relationship can be expressed by the following equation:

[0072]

[0073] Among them, Z u and Z l are the family distribution functions of the upper and lower energy bands of the laser, E ul is the energy level difference between the upper and lower energy levels of the gain ion, h and c are Planck constant and the speed of light respectively, K is the Boltzmann constant, T is the temperature, σ ap and σ ep are the absorption and emission cross sections of the gain ions, I p (0) is the intensity of the pump light, I c is its saturation intensity, L is the length of the gain fiber, N t is the concentration of doping ions in the gain fiber.

[0074] In this experiment, the signal-to-noise ratio and signal light intensity of the output spectrum at different fiber lengths during the signal light amplification process are compared by cutting gain fibers of different lengths, and the gain and spectrum of the signal light at different pumping times are compared by adjusting the pump pulse width of the pump laser.

[0075] This experiment uses synchronous pulse pumping technology to pump and amplify the signal light. Therefore, when selecting different pumping times, attention should also be paid to the delay time of the pump signal to ensure that each pump light pulse covers the corresponding light pulse to ensure maximum gain. The influence of different gain fiber lengths on the spectral signal-to-noise ratio of the signal light output during the first stage amplification process is shown in Figure 2. Figure 4 shown.

[0076] Depend on Figure 4 It can be seen that the intensity of the signal light and the signal-to-noise ratio first increase and then decrease with the length of the gain fiber, and reach the highest at 4.5M. This is because when the fiber length is too short, the gain ions do not absorb the pump light sufficiently, resulting in less signal light generated by stimulated radiation and low light-to-light conversion efficiency. When the fiber length exceeds 4.5M, the central wavelength intensity gradually decreases with the increase of the fiber length, and the signal-to-noise ratio gradually deteriorates. This is because the excessively long gain fiber will cause the signal light to be absorbed by the fiber core twice during the amplification process, and will produce an amplified spontaneous emission effect (ASE) during the amplification process. ASE laser light will be generated in the same and opposite directions as the pump light. The forward ASE laser light is generated at the input end of the signal light, has the same transmission direction as the pump light, and is amplified during this transmission process. The backward ASE laser light is generated at the output end of the signal light and is transmitted in the opposite direction of the pump light. In the process of amplifying the seed light signal, the generation of ASE laser light will seriously interfere with the signal light, and ASE laser light will consume the excited state doping ions in the gain fiber, reducing the efficiency of converting pump light into signal light. Therefore, in the process of amplifying weak signal light, it is necessary to optimize the length of the gain fiber to reduce the decrease in spectral signal-to-noise ratio caused by ASE laser light and the decrease in signal light gain caused by too long a gain fiber.

[0077] In the process of signal light amplification, synchronous pulse pumping technology is used. The effects of different pumping times on the signal light gain and system signal-to-noise ratio are also completely different. Figure 5 This is the effect of different pump pulse widths on the spectrum during the first stage amplification process.

[0078] Depend on Figure 5 It can be seen that the intensity of the signal light increases with the increase of the pump signal pulse width, but at the same time, too high a pump power will cause a significant increase in ASE lasing light, resulting in a broadening of the output spectrum, a deterioration of the system signal-to-noise ratio, and a serious thermal effect that affects the stability of the system performance. Therefore, when increasing the pump signal pulse width to increase the pump power, attention should be paid to selecting a suitable pulse width to avoid the generation of a large amount of ASE lasing light. The power of the signal light after the first stage amplification at different pump times is shown in Figure 2. Figure 6 shown.

[0079] Depend on Figure 6It can be seen that the signal light power increases rapidly with the increase of pump time during the first stage amplification process. When the pump time is 500NS, the signal light output power is only 23mW. When the pump time increases to 800NS, the signal light output power is about 280mW, which is about 10dB higher than when the pump time is 500NS. It can be concluded that increasing the pump power during the signal light amplification process can increase the amplification factor of the signal light power.

[0080] 4.5M was selected as the length of the first-stage gain fiber, 650NS was selected as the pulse width of the pump signal, and the average power of the signal light after the first amplification was measured to be 110mW. It should be noted that when splicing the gain fiber, a layer of low-refractive-index coating liquid should be applied at the input end of the pump light to reduce the leakage loss caused by the pump light during splicing. When the pump light is transmitted in the cladding of the gain fiber, it will be absorbed by the doped ions and produce a population inversion, but a portion of the pump light that is not completely absorbed by the doped ions will remain in the cladding. The excess pump light will degrade the spectral output characteristics, and the high-power pump light will increase the power density of the fiber end face, and even damage the fiber end face. Therefore, a layer of high-refractive-index coating liquid should be applied at the splicing point at the output end of the pump light to leak the excess pump light into it, which effectively reduces the influence of the pump light on the output spectrum and the power density of the fiber end face, and improves the signal-to-noise ratio of the system.

[0081] It should be noted that the present invention also performs a second-stage optical amplification on the seed light and analyzes its output performance.

[0082] After the first amplification of the signal light, the isolator should be fused to prevent the reverse light from damaging the device, and the filter should be fused to filter out the stray light in the spectrum. When the signal light is amplified for the second time, a longer gain fiber should be selected to increase the gain of the signal light, and reverse pumping should be used to improve the pump conversion efficiency and suppress the occurrence of nonlinear effects. Figure 7 It is the spectral curve under different gain fiber lengths during the second stage amplification process.

[0083] Depend on Figure 7It can be seen that the signal light intensity changes with the gain fiber length in the second stage amplification process similarly to the first stage amplification process, first increasing and then decreasing, and reaching the highest at 6M. Compared with the first amplification process, it can be found that the ASE lasing light of the signal light in the second stage amplification process is significantly reduced. This is because the signal light intensity is weak in the first stage amplification process. When the pump light passes through, the number of inversion particles consumed by the signal light is small, thus causing a large amount of ASE lasing light. In the second stage amplification process, the signal light intensity becomes higher than that of the first stage amplification, so that the pump light enters the fiber core and induces excited state ions to amplify the signal light. The advantage of the signal light in the competition of the longitudinal mode of the fiber core is improved, and the spontaneous radiation of high-energy particles begins to decrease. However, high-power signal light will interact with the medium to produce nonlinear effects, and the spectrum will be broadened. Figure 8 Spectra of different pump pulse widths during the secondary amplification process.

[0084] In the second-stage amplification process, the impact of different pumping times on the system spectrum is similar to that in the first-stage amplification process. Similarly, as the pump power increases, the signal light intensity gradually increases, and a large amount of ASE laser light is also brought about. From this, it can be concluded that whether in the amplification process of small signals or large signals, increasing the pump power will inevitably lead to an increase in ASE laser light. Therefore, it is necessary to select a suitable pump pulse width to reduce the impact of ASE laser light on the system.

[0085] The output power of the signal light changes with the pumping time during the second amplification process as shown in Fig. 9 As shown in the figure, the change trend of the signal light in the second amplification process is similar to that in the first stage amplification. It increases rapidly with the increase of pump time. When the pump time is 500NS, the final output power of the signal light is only 0.6W. When the pump time is increased to 800NS, the final output power of the signal light is amplified to about 4.6W.

[0086] Fig.10 This is the pulse waveform of the signal light after two-stage amplification. It can be seen that the pulse waveform of the seed light is almost unchanged after being amplified twice by the system, and only the amplitude and power are improved. It is particularly suitable for use in OOK modulated laser communications.

[0087] The key points of the present invention are:

[0088] 1. An all-fiber structure single-mode pulsed MOPA fiber laser optical path is designed, and the implementation scheme and the selected seed source wavelength, pump source wavelength, double-clad fiber doping ions, etc. are provided.

[0089] 2. By analyzing the change rate inside the semiconductor laser, Yb-doped 3+The dynamic rate of the pulse fiber laser and the related parameters of the optical fiber were tested on the constructed optical path. The influence and reasons of different gain fiber lengths and pumping time on the spectrum of the pulse seed source during the first and second stage amplification were analyzed through experimental data. The matters that should be paid attention to during the signal light amplification experiment were explained.

[0090] 3. Through two-stage amplification of the optical path, a signal light with an average output power of about 4.6W was finally obtained. The feasibility of this scheme in the field of laser communication was verified by comparing the output waveforms of the pulse seed source before and after amplification.

[0091] The beneficial effects of the present invention are:

[0092] An all-fiber structure single-mode pulse MOPA fiber laser optical path is designed, and the implementation scheme and the selected seed source wavelength, pump source wavelength, double-clad fiber doping ions, etc. are provided. Through the two-stage amplification of the optical path, the signal light with an average output power of about 4.6W is finally obtained. The feasibility of this scheme in the field of laser communication is verified by comparing the output waveforms of the pulse seed source before and after amplification. Compared with traditional solid-state lasers, it has the advantages of small quantum loss, high pumping efficiency, good heat dissipation, reliable working performance, long service life, and small structure volume; compared with traditional semiconductor lasers, it has the advantages of good output spot quality and narrow system output spectrum bandwidth;

[0093] Secondly, the pulse width and repetition frequency of the fiber laser pulse seed source provided by the present invention are adjustable, the output beam quality is good, and the output light waveform characteristics are excellent. It can be widely used in laser communication, laser marking, laser welding, laser medical treatment and other fields; the fiber laser implementation scheme provided by the present invention is low-cost, has fewer process flows, and the implementation process is easy to control, which has certain practical significance for laser industrial production.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A MOPA pulse fiber laser for laser communication, characterized by: include: A seed source, a first pump source, a second pump source, a primary amplification module and a secondary amplification module; The pump light emitted by the first pump source is split by the coupler and enters the primary amplification module and the secondary amplification module respectively; The signal light emitted by the seed source and the split pump light pass through the first beam combiner in the first-stage amplification module, and the signal light is first-stage amplified through the ytterbium-doped gain fiber to obtain the amplified first signal light; The amplified first signal light enters the secondary amplification module and is again amplified through the ytterbium-doped gain fiber. At the same time, it passes through the second combiner again with the split pump light and the pump light emitted by the second pump source to obtain the final signal light output.

2. A MOPA pulse fiber laser for laser communication as claimed in claim 1, characterized in that: A first isolator and a circulator are arranged in sequence between the seed source and the first beam combiner.

3. A MOPA pulse fiber laser for laser communication as claimed in claim 1, characterized in that: The final signal light obtained by the second combiner needs to pass through a high-performance isolator before being output.

4. A MOPA pulse fiber laser for laser communication as claimed in claim 1, characterized in that: A second isolator is further arranged between the first beam combiner and the second beam combiner.

5. A MOPA pulse fiber laser for laser communication as claimed in claim 1, characterized in that: The seed source, the first pump source and the second pump source adopt an electric pulse modulation method.

6. A MOPA pulse fiber laser for laser communication as claimed in claim 1, characterized in that: The seed source is a semiconductor laser with a central wavelength of 1064nm.

7. A MOPA pulse fiber laser for laser communication as claimed in claim 1, characterized in that: The first pump source and the second pump source are both pump lasers with a wavelength of 915 nm.

8. A MOPA pulse fiber laser for laser communication as claimed in claim 5, characterized in that: The formula of the electrical pulse modulation method is as follows: Where N is the density of carriers, S is the density of photons, τ N is the survival time of carriers in the resonant cavity, τ ρ is the photon survival time in the resonant cavity, ε is the gain saturation factor, g is the maximum gain coefficient of the mode field, Γ is the light confinement factor, β is the spontaneous radiation factor, and V is the volume of the active layer.

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