Method for reducing line width of semiconductor quantum dot laser on silicon substrate

Abstract

The invention provides a method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate, which comprises the following steps of: selecting a master laser and a slave laser to be optimized, and adopting a current pumping source as a driving source; calculating the optical injection locking area range of the slave laser according to the related parameters of the master laser and the slave laser; the injection laser power range and the injection laser wavelength range of the master laser are adjusted under different bias currents, meanwhile, the spectral line width of the slave laser is calculated, and finally the optimal line width value within the optical injection locking area range of the slave laser can be obtained under different bias currents. The method has the beneficial effects that the line width of the slave laser can be obviously reduced, the jumping phenomenon of the ground state line width of the slave laser near an excited state threshold is inhibited, and meanwhile, the re-broadening phenomenon of the line width of two energy states is inhibited.

Description

Technical Field

[0001] The invention relates to the field of semiconductor optoelectronic technology, and in particular to a method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate. Background Art

[0002] In recent decades, optoelectronics has been the driving force behind the development of the modern information society. With the emergence of technologies such as 5G, cloud computing, and artificial intelligence, and people's pursuit of higher network speeds, the surge in information volume has brought unprecedented challenges to the telecommunications field. The "Moore's Law" followed by microelectronic chips states that the number of transistors that can be accommodated on an integrated circuit will double approximately every 18 months. The improvement in integration is based on the continuous reduction of micro-machining dimensions. However, there is a limit to reducing the size, so new ways must be found to increase the rate and capacity of information. Silicon-based optoelectronic chips are developing rapidly because of their low cost, small space, high energy efficiency, and high integration density. They are considered to be the most promising solution for mainstream data transmission in the next generation of data centers. Driven by the needs of the new generation of communications and computing, silicon-based optoelectronic technology has made great progress and has become the core technology of the post-Moore era, characterized by the deep integration of optoelectronics and microelectronics.

[0003] As the core component of the optical communication system, semiconductor laser plays a vital role in the performance of the entire system. Low-cost, low-power, high-performance small semiconductor laser light sources are ideal light sources for the new generation of high-speed optical communication networks. Zero-dimensional quantum dot (QD) materials have the characteristics of discrete energy level distribution, which makes them insensitive to dislocation defects. QD lasers have been proven to have low threshold current density, high temperature operating characteristics, strong anti-reflection and other characteristics, and are expected to become the most ideal light source in photonic integrated circuits (PICs). Noise characteristics are an important indicator for evaluating on-chip light sources, and low-noise light sources are urgently needed not only for PICs, but also for optical transmitters for low-cost data transmission in super data centers and metropolitan data links.

[0004] Optical noise in semiconductor lasers includes relative intensity noise and frequency noise, the latter of which is usually converted into spectral line width. In current semiconductor laser applications, even without applied current modulation, random carrier and photon recombination and generation events will produce instantaneous time changes in carrier and photon density. Changes in photon density lead to changes in output power magnitude, thus generating background noise, and changes in carrier density lead to changes in output wavelength, thus creating a limited spectral line width for the laser mode.

[0005] Narrow linewidth lasers are important for applications such as coherent communications and free-space optical communications. Digital coherence technology is also a key element of optical communications (including data centers and access networks). In principle, coherent systems are able to retrieve amplitude and phase information of optical signals, but at the cost of being sensitive to the phase noise of the transmitter and the local oscillator. In order to maintain stable heterodyne detection, narrow linewidth semiconductor lasers are required. Semiconductor lasers must strongly suppress amplified spontaneous emission noise to achieve narrow linewidth operation in these applications. Exploring the impact of optical injection locking operation on the linewidth characteristics of silicon-based lasers is of great significance for improving the performance of silicon-based QD lasers.

[0006] Although the relative intensity noise floor can be reduced by increasing the bias current of the laser source, this will bring unnecessary additional energy consumption. Although the line width can also be reduced through external optical feedback, the feedback intensity needs to be precisely controlled, otherwise the optical feedback will cause the laser to be unstable, produce chaos, coherent collapse and other states, which is very troublesome to operate. Summary of the invention

[0007] In order to solve the problems in the prior art, the present invention provides a method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate. By using an external laser injection operation and adjusting the injected laser power and the injected laser wavelength of a master laser, the line width of a slave laser can be significantly reduced, and the jumping phenomenon of the ground state line width of the slave laser near the excited state threshold is suppressed. At the same time, the line width re-broadening phenomenon of the two energy states is suppressed, so that the semiconductor quantum dot laser on a silicon substrate can maintain a narrow line width operation within a large current range, solving the problems in the prior art of increasing the bias current of the laser source to reduce the line width with high energy consumption and the difficulty of accurately controlling the external optical feedback intensity to reduce the line width operation.

[0008] The present invention provides a method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate, comprising:

[0009] Step 1, build an optical injection-locked semiconductor laser system, select a master laser and a slave laser to be optimized, and use a current pump source as a driving source for the master laser and the slave laser;

[0010] Step 2, calculating the optical injection locking region range of the slave laser, and calculating the optical injection locking region range of the slave laser according to the relevant parameters of the master laser and the slave laser, that is, the injection laser power range and the injection laser wavelength range in which the master laser optical injection coupling reduces the slave laser line width;

[0011] Step 3, obtain the optimal line width value within the optical injection locking region of the slave laser, adjust the injection laser power range and injection laser wavelength range of the master laser under different bias currents, and calculate the spectral line width of the slave laser at the same time, and finally obtain the optimal line width value within the optical injection locking region of the slave laser that can be obtained by repeatedly adjusting the injection laser power range and injection laser wavelength range of the master laser under different bias currents, and the calculation method is as follows:

[0012] The simplified three-level rate equation model of the electronic structure of the two-state silicon-based semiconductor quantum dot laser consists of a two-dimensional carrier pool RS and a quantum dot ensemble in the active region. The active region includes two energy levels, a quadruple degenerate excited state ES and a doubly degenerate ground state GS. This model assumes that there is only one quantum dot in the active region, and does not consider the non-uniform broadening of the gain distribution due to the uneven size of the dots. Electrons and holes are considered to be neutral excitons. External carriers are directly injected into the two-dimensional carrier pool RS. The carriers first move at a time The carriers are captured from the two-dimensional pool RS to the excited state ES, and then relax with a relaxation time From the excited state ES to the ground state GS, due to the thermal effect, the carrier escapes with a time Thermal relaxation from the ground state GS to the excited state ES is also based on the escape time The process of thermal relaxation from the excited state ES to the two-dimensional carrier pool RS is determined by the Fermi distribution of the quasi-equilibrium state. In addition, the carriers also emit spontaneous radiation at a time Spontaneous recombination, non-radiative recombination of each energy level is determined by τ SRH Indicates that the model also includes the optical injection term S inj , establish the following description of the carrier number N RS，ES，GS , photon number S ES，GS and the electric field phase φ ES，GS The rate equation for kinetics,

[0013]

[0014] Where I is the bias current from the laser's current pump source, q is the electron charge, and Γ p is the optical confinement factor, υ g is the group velocity, τ p is the photon lifetime, β sp is the spontaneous emission factor, is the contribution of the ground state GS to the line width enhancement factor, are coefficients related to the contributions of excited states ES and two-dimensional carrier pool RS, respectively, and F RS，ES，GS , is Langevin noise, representing carrier, photon and phase noise sources respectively. When performing light injection operation, add optical injection terms to equations (2-4) to (2-7). At this time, the formula should be written as:

[0015]

[0016] Among them, S inj The number of photons injected into the main laser is defined as R inj =S inj / S0 is the injection ratio, S0 is the number of photons from the laser when it is free running, Δω inj is the frequency detuning amount, defined as the frequency difference between the master laser and the slave laser, i.e. Δω inj =ω master -ω slaυe , k c The coupling coefficient between the master laser and the slave laser is defined as L is the laser cavity length, R is the cavity surface reflectivity, and through small signal analysis and using Cramer's law, the final calculation formula from the laser line width FN is as follows:

[0017]

[0018] Among them, δφ(ω) is the phase fluctuation, which is expressed by the formula , use low-frequency FN to approximate the intrinsic linewidth of the laser.

[0019] The present invention is further improved, in step 1, the slave laser to be optimized is a semiconductor quantum dot laser on a silicon substrate whose line width needs to be reduced.

[0020] The present invention is further improved, in step 1, the master laser is a single-mode tunable laser with a narrow spectral linewidth.

[0021] The present invention is further improved. In the step 2, the relevant parameters of the slave laser include the output power range, the output laser wavelength range, the optical parameters and the line width of the slave laser, the relevant parameters of the master laser include the output power range and the output laser wavelength range, and the optical injection locking region range of the slave laser is the injection laser power range and the injection laser wavelength range of the master laser optical injection after coupling to reduce the slave laser line width.

[0022] The present invention is further improved. In the step 2, the dynamic characteristics of the optical injection locked laser in which the light of the master laser is coupled to the slave laser depend on the injection ratio and the frequency detuning. The injection ratio is the ratio of the power of the master laser to the power of the slave laser when running freely under the same bias current. The frequency detuning is the frequency offset between the master laser and the slave laser. The injection ratio and the frequency detuning can be adjusted by adjusting the injection laser power range and the injection laser wavelength range of the master laser.

[0023] The present invention is further improved. In step 3, by changing the bias current I of the current pump source of the slave laser, the spectral linewidth of the injection parameter space under different bias currents is calculated, so that the optimal linewidth value can be extracted within the optical injection locking region of the slave laser.

[0024] The present invention is further improved, that in step 3, the magnitude of the optimal line width value extracted from the optical injection locking region of the laser can reach the millihertz magnitude.

[0025] The present invention is further improved, in step 3, the low-frequency FN is the low-frequency frequency noise, that is, the intrinsic line width of the laser.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate. By using an external laser injection operation and adjusting the injected laser power and injected laser wavelength of a master laser, the line width of a slave laser can be significantly reduced, and the jumping phenomenon of the ground state line width of the slave laser near the excited state threshold is suppressed, and the line width re-broadening phenomenon of the two energy states is suppressed, so that the semiconductor quantum dot laser on a silicon substrate can maintain narrow line width operation within a large current range. Compared with the existing method of increasing the bias current of a laser source and the method of accurately controlling the external optical feedback intensity, the optimization effect is not only better, but also the energy consumption is low and the operation is simpler, which solves the problems of high energy consumption in increasing the bias current of a laser source to reduce the line width and great difficulty in accurately controlling the external optical feedback intensity to reduce the line width in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the solutions in the present application or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 A flow chart of a method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate according to the present invention;

[0029] Figure 2 is a schematic diagram of a coherent optical communication system;

[0030] Figure 3 is a schematic diagram of an optical injection system of the present invention;

[0031] Figure 4 The figure shows the influence of the non-radiative recombination effect on the photocurrent characteristics of GS and ES of the present invention, as well as the threshold currents of GS (blue) and ES (red) under different non-radiative recombination lifetimes, and the corresponding ES-GS threshold ratio;

[0032] Figure 5 is a graph showing the variation of the spectral line width of GS and ES of the present invention with the normalized bias current at different non-radiative recombination lifetimes;

[0033] Figure 6 A block diagram showing the principle of the optical injection locking process of the present invention;

[0034] Figure 7 A schematic diagram of the electronic structure and carrier dynamics of the semiconductor quantum dot laser on a silicon substrate of the present invention;

[0035] Figure 8 Graph showing the variation of the spectral linewidth of the GS and ES of the present invention with the normalized bias current under free-running (blue) and optical injection locking (red) operations. DETAILED DESCRIPTION

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field of this application; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit the application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0037] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0038] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0039] like Figure 2 As shown, narrow linewidth lasers are important for applications such as coherent optical communications and free-space optical communications. Figure 2 The schematic diagram of the coherent optical communication system is shown. At the transmitting end, the signal is modulated onto the optical carrier by external modulation to generate the input signal light. When the signal light reaches the receiving end, it is first coherently coupled with the local oscillator light signal, and then detected by the balanced receiver. Coherent optical communication can be divided into heterodyne detection and homodyne detection according to whether the local oscillator light frequency is unequal or equal to the signal light frequency. In the former, the intermediate frequency signal is obtained after the photoelectric conversion of the optical signal, and it needs to be demodulated twice before it can be converted into a baseband signal. In the latter, the optical signal is directly converted into a baseband signal after photoelectric conversion without secondary demodulation, but it requires that the local oscillator light frequency strictly matches the signal light frequency, and that the local oscillator light and the signal light are phase-locked. In addition, in coherent detection, frequency noise will increase the bit error rate of signal detection, limit the system transmission rate, and require the local oscillator spectrum linewidth to be less than 200kHz. Therefore, we propose that the linewidth of the local oscillator laser, that is, the linewidth of the semiconductor quantum dot laser on the silicon substrate, can be reduced by optical injection. The other parameters of the semiconductor quantum dot laser on the silicon substrate are shown in the following table:

[0040] Table 1. Materials and optical parameters of semiconductor quantum dot lasers on silicon substrates

[0041]

[0042]

[0043] like Figure 4 As shown, unlike quantum well lasers that emit light in a single ground state, a unique feature of semiconductor quantum dot lasers on silicon substrates is that they can emit both ground state (GS) and excited state (ES) simultaneously when the bias current is increased. In addition to single GS emission and simultaneous emission of GS and ES, semiconductor quantum dot lasers on silicon substrates can also emit single ES. For dual-state emission quantum dot lasers, Figure 4 The variation of the photon number of GS and excited ES with the bias current under different non-radiative recombination lifetimes is described. It can be seen that after ES emission, the efficiency of GS emission decreases, and the growth of GS photon number is slower than that of single-state emission. The corresponding threshold current and ES-GS threshold ratio are shown in Figure 4 , the threshold current of GS changes from τ SRH = 125mA drops to τ when 0.5ns SRH = 52mA at 10ns, the threshold current of ES is from τ SRH = 412mA at 0.5ns drops to τ SRH =287mA at 10ns, and the corresponding threshold ratio of ES to GS increases from 3.3 to 5.4. It can be seen that for the free-running laser, the increase in defect density leads to an increase in threshold current, and the ES-GS threshold ratio decreases, making ES easier to emit light, which is undesirable in practical applications.

[0044] Figure 5 The variation of the spectral linewidth of the two energy states with the normalized threshold current at different non-radiative recombination lifetimes is shown. Below the ES threshold, the spectral linewidth of GS decreases rapidly with the increase of the bias current. Near the ES threshold, the spectral linewidth of GS increases sharply by about 0.6-1.4MHz and then gradually decreases. This indicates that ES emission also affects the spectral linewidth of GS. However, with the continuous increase of the bias current, the spectral linewidths of ES and GS become wider again. In addition, higher defect density will lead to linewidth jumps of GS and re-broadening of the spectral linewidths of the two energy states at lower normalized bias currents.

[0045] Therefore, the present invention provides a method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate. By using an external laser injection operation and adjusting the injected laser power and injected laser wavelength of a master laser, the line width of a slave laser can be significantly reduced, and the jumping phenomenon of the ground state line width of the slave laser near the excited state threshold is suppressed. At the same time, the line width re-broadening phenomenon of the two energy states is suppressed, so that the semiconductor quantum dot laser on a silicon substrate can maintain narrow line width operation within a large current range.

[0046] like Figure 1-8 As shown, the present invention provides a method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate, comprising:

[0047] Step 1, build an optical injection-locked semiconductor laser system, select a master laser and a slave laser to be optimized, and use a current pump source as the driving source of the master laser and the slave laser; wherein the slave laser to be optimized is a semiconductor quantum dot laser on a silicon substrate whose line width needs to be reduced, and the master laser is a single-mode tunable laser with a narrow spectral line width.

[0048] Step 2, calculate the optical injection locking region range of the slave laser, and calculate the optical injection locking region range of the slave laser according to the relevant parameters of the master laser and the slave laser, that is, the injection laser power range and the injection laser wavelength range in which the optical injection coupling of the master laser reduces the line width of the slave laser; wherein the dynamic characteristics of the optical injection locking laser in the slave laser coupled to the master laser depend on the injection ratio and the frequency detuning, the injection ratio is the ratio of the power of the master laser to the power of the slave laser when running freely under the same bias current, the frequency detuning is the frequency offset between the master laser and the slave laser, and the injection ratio and the frequency detuning can be adjusted by adjusting the injection laser power range and the injection laser wavelength range of the master laser; the relevant parameters of the slave laser include the output power range, the output Laser wavelength range, optical parameters and line width of slave lasers. Relevant parameters of the master laser include output power range and output laser wavelength range. The optical injection locking region range of the slave laser is the injection laser power range and injection laser wavelength range of the master laser after optical injection coupling to reduce the line width of the slave laser. By adjusting the injection laser power range and injection laser wavelength range of the master laser, relative intensity noise values ​​under a series of injection conditions can be obtained in the injection ratio and frequency detuning parameter space. By analyzing the obtained noise values, the injection laser power and injection laser wavelength range required for stable injection locking can be obtained, that is, the optical injection locking region range of the slave laser is the injection laser power range and injection laser wavelength range of the master laser after optical injection coupling to reduce the line width of the slave laser.

[0049] Step 3, obtain the optimal line width value within the optical injection locking region of the slave laser, adjust the injection laser power range and injection laser wavelength range of the master laser under different bias currents, and calculate the spectral line width of the slave laser at the same time, and finally obtain the optimal line width value within the optical injection locking region of the slave laser that can be obtained by repeatedly adjusting the injection laser power range and injection laser wavelength range of the master laser under different bias currents, and the calculation method is as follows:

[0050] The simplified three-level rate equation model of the electronic structure of the two-state silicon-based semiconductor quantum dot laser consists of a two-dimensional carrier pool RS and a quantum dot ensemble in the active region. The active region includes two energy levels, a quadruple degenerate excited state ES and a doubly degenerate ground state GS. This model assumes that there is only one quantum dot in the active region, and does not consider the non-uniform broadening of the gain distribution due to the uneven size of the dots. Electrons and holes are considered to be neutral excitons. External carriers are directly injected into the two-dimensional carrier pool RS. The carriers first move at a time The carriers are captured from the two-dimensional pool RS to the excited state ES, and then relax with a relaxation time From the excited state ES to the ground state GS, due to the thermal effect, the carrier escapes with a time Thermal relaxation from the ground state GS to the excited state ES is also based on the escape time The process of thermal relaxation from the excited state ES to the two-dimensional carrier pool RS is determined by the Fermi distribution of the quasi-equilibrium state. In addition, the carriers also emit spontaneous radiation at a time Spontaneous recombination, non-radiative recombination of each energy level is determined by τ SRH Indicates that the model also includes the optical injection term S inj , establish the following description of the carrier number N RS，ES，GS , photon number S ES，GS and the electric field phase φ ES，GS The rate equation for kinetics,

[0051]

[0052]

[0053] Where I is the bias current from the laser's current pump source, q is the electron charge, and Γ p is the optical confinement factor, υ g is the group velocity, τ p is the photon lifetime, β sp is the spontaneous emission factor, is the contribution of the ground state GS to the line width enhancement factor, are coefficients related to the contributions of excited states ES and two-dimensional carrier pool RS, respectively, and F RS，ES，GS , is Langevin noise, representing carrier, photon and phase noise sources respectively. When performing light injection operation, add optical injection terms to equations (2-4) to (2-7). At this time, the formula should be written as:

[0054]

[0055] Among them, S inj The number of photons injected into the main laser is defined as R inj =S inj / S0 is the injection ratio, S0 is the number of photons from the laser when it is free running, Δω inj is the frequency detuning amount, defined as the frequency difference between the master laser and the slave laser, i.e. Δω inj =ω master -ω slaυe , k c The coupling coefficient between the master laser and the slave laser is defined as L is the laser cavity length, R is the cavity surface reflectivity, and through small signal analysis and using Cramer's law, the final calculation formula from the laser line width FN is as follows:

[0056]

[0057] Among them, δφ(ω) is the phase fluctuation, which is expressed by the formula , using low-frequency FN, that is, low-frequency frequency noise, to approximate the intrinsic line width of the slave laser. Among them, by changing the bias current I of the current pump source of the slave laser, the spectral line width of the injection parameter space under different bias currents is calculated, and the optimal line width value can be extracted within the optical injection locking region of the slave laser. The order of magnitude of the optimal line width value extracted within the optical injection locking region of the slave laser can reach the millihertz order. In this embodiment, if Figure 8 As shown in Figure 1, the spectral linewidth of the injection parameter space under different bias currents is calculated, and the optimal linewidth value can be extracted in the stable optical injection locking region. Figure 8 The comparison of the spectral linewidth values ​​of GS and ES after optical injection and under free-running operation under different normalized bias currents is shown. From the results in the figure, it can be seen that optical injection can obtain a spectral linewidth of the millihertz order, greatly reducing the linewidth value of the dual-state quantum dot laser, suppressing the sudden increase of the GS linewidth near the ES threshold and the re-broadening of the spectra of the two laser states. It ensures that the QD laser can maintain narrow linewidth operation even at high currents.

[0058] As can be seen from the above, the present invention provides a method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate. By using an external laser injection operation and adjusting the injected laser power and injected laser wavelength of a master laser, the line width of a slave laser can be significantly reduced, and the jumping phenomenon of the ground state line width of the slave laser near the excited state threshold is suppressed. At the same time, the line width re-broadening phenomenon of the two energy states is suppressed, so that the semiconductor quantum dot laser on a silicon substrate can maintain a narrow line width operation within a large current range. Compared with the existing method of increasing the bias current of a laser source and the method of accurately controlling the external optical feedback intensity, the optimization effect is not only better, but also the energy consumption is low and the operation is simpler, which solves the problems of high energy consumption in increasing the bias current of a laser source to reduce the line width and great difficulty in accurately controlling the external optical feedback intensity to reduce the line width in the prior art.

[0059] The specific implementation modes described above are preferred implementation modes of the present invention, and are not intended to limit the specific implementation scope of the present invention. The scope of the present invention includes but is not limited to the specific implementation modes, and all equivalent changes made according to the present invention are within the protection scope of the present invention.

Claims

1. A method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate, characterized in that: include: Step 1, build an optical injection-locked semiconductor laser system, select a master laser and a slave laser to be optimized, and use a current pump source as a driving source for the master laser and the slave laser; Step 2, calculating the optical injection locking region range of the slave laser, and calculating the optical injection locking region range of the slave laser according to the relevant parameters of the master laser and the slave laser, that is, the injection laser power range and the injection laser wavelength range in which the master laser optical injection coupling reduces the slave laser line width; Step 3, obtain the optimal line width value within the optical injection locking region of the slave laser, adjust the injection laser power range and injection laser wavelength range of the master laser under different bias currents, and calculate the spectral line width of the slave laser at the same time, and finally obtain the optimal line width value within the optical injection locking region of the slave laser that can be obtained by repeatedly adjusting the injection laser power range and injection laser wavelength range of the master laser under different bias currents, and the calculation method is as follows: The simplified three-level rate equation model of the electronic structure of the two-state silicon-based semiconductor quantum dot laser consists of a two-dimensional carrier pool RS and a quantum dot ensemble in the active region. The active region includes two energy levels, a quadruple degenerate excited state ES and a doubly degenerate ground state GS. This model assumes that there is only one quantum dot in the active region, and does not consider the non-uniform broadening of the gain distribution due to the uneven size of the dots. Electrons and holes are considered to be neutral excitons. External carriers are directly injected into the two-dimensional carrier pool RS. The carriers first move at a time The carriers are captured from the two-dimensional pool RS to the excited state ES, and then relax with a relaxation time From the excited state ES to the ground state GS, due to the thermal effect, the carrier escapes with a time Thermal relaxation from the ground state GS to the excited state ES is also based on the escape time The process of thermal relaxation from the excited state ES to the two-dimensional carrier pool RS is determined by the Fermi distribution of the quasi-equilibrium state. In addition, the carriers also emit spontaneously with a time Spontaneous recombination, non-radiative recombination of each energy level is determined by τ SRH Indicates that the model also includes the optical injection term S inj , establish the following description of the carrier number N RS，ES，GS , photon number S ES，GS and the electric field phase φ ES，GS The rate equation for kinetics, Where I is the bias current from the laser's current pump source, q is the electron charge, and Γ p is the optical confinement factor, v g is the group velocity, τ p is the photon lifetime, β sp is the spontaneous emission factor, is the contribution of the ground state GS to the line width enhancement factor, are coefficients related to the contributions of excited states ES and two-dimensional carrier pool RS, respectively, and F RS，ES，GS , F SES，GS , F φES，GS is Langevin noise, representing carrier, photon and phase noise sources respectively. When performing light injection operation, add optical injection terms to equations (2-4) to (2-7). At this time, the formula should be written as: Among them, S inj The number of photons injected into the main laser is defined as R inj =S inj / S0 is the injection ratio, S0 is the number of photons from the laser when it is free running, Δω inj is the frequency detuning amount, defined as the frequency difference between the master laser and the slave laser, i.e. Δω inj =ω master -ω slave , k c The coupling coefficient between the master laser and the slave laser is defined as L is the laser cavity length, R is the cavity surface reflectivity, and through small signal analysis and using Cramer's law, the final calculation formula from the laser line width FN is as follows: Among them, δφ(ω) is the phase fluctuation, which can be expressed by the formula Δv OL =2πFN| (f＝1MHz) , use low-frequency FN to approximate the intrinsic linewidth of the laser.

2. The method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate according to claim 1, characterized in that: In step 1, the slave laser to be optimized is a semiconductor quantum dot laser on a silicon substrate whose line width needs to be reduced.

3. The method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate according to claim 2, characterized in that: In step 1, the master laser is a single-mode tunable laser with a narrow spectral linewidth.

4. The method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate according to claim 3, characterized in that: In step 2, the relevant parameters of the slave laser include the output power range, the output laser wavelength range, the optical parameters and the line width of the slave laser, the relevant parameters of the master laser include the output power range and the output laser wavelength range, and the optical injection locking region range of the slave laser is the injection laser power range and the injection laser wavelength range for reducing the line width of the slave laser after optical injection coupling of the master laser.

5. The method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate according to claim 4, characterized in that: In step 2, the dynamic characteristics of the optical injection locked laser in which the light of the master laser is coupled to the slave laser depend on the injection ratio and the frequency detuning. The injection ratio is the ratio of the power of the master laser to the power of the slave laser when running freely under the same bias current. The frequency detuning is the frequency offset between the master laser and the slave laser. The injection ratio and the frequency detuning can be adjusted by adjusting the injection laser power range and the injection laser wavelength range of the master laser.

6. The method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate according to claim 5, characterized in that: In step 3, by changing the bias current I of the current pump source of the slave laser and calculating the spectral linewidth of the injection parameter space under different bias currents, the optimal linewidth value can be extracted within the optical injection locking region of the slave laser.

7. The method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate according to claim 6, characterized in that: In step 3, the order of the optimal line width value extracted from the optical injection locking region of the laser can reach the millihertz order.

8. The method for reducing the line width of a semiconductor quantum dot laser on a silicon substrate according to claim 7, characterized in that: In step 3, the low-frequency FN is the low-frequency frequency noise, that is, the intrinsic line width of the laser.

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