Method for compressing spectral line width of laser, local oscillator and coherent detection system

Abstract

The invention provides a method for compressing the spectral line width of a laser, a local oscillator and a coherent detection system, and belongs to the technical field of coherent light communication. The method for compressing the spectral line width of the silicon-based quantum dot laser is realized by reducing the external carrier noise of the pumping source, so that the frequency noise of the silicon-based quantum dot laser is reduced, and the phase fluctuation of output light is reduced; and the method for compressing the spectral line width of the silicon-based quantum dot laser can be used for preparing a coherent detection local oscillator light source. The silicon-based quantum dot laser has the beneficial effects that the line width of the silicon-based quantum dot laser is remarkably reduced, the re-broadening phenomenon is inhibited, the performance of the silicon-based laser is greatly optimized, and the output stability and reliability of the silicon-based quantum dot laser are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coherent optical communication, and in particular to a method for compressing the spectral line width of a silicon-based quantum dot laser, and also to a local oscillator and a coherent detection system using the method for compressing the spectral line width of a silicon-based quantum dot laser. Background Art

[0002] With the continuous development of information technology, the demand for data traffic has grown rapidly, and traditional communication technologies have begun to face limitations in transmission capacity and speed. Coherent optical communication is particularly important in this context, and it effectively addresses these challenges by using coherent detection technology. Coherent optical communication is able to handle high-speed and large-capacity data transmission, support higher modulation complexity and spectrum utilization, making it an ideal choice for meeting modern communication needs. In addition, coherent optical communication can improve the flexibility and adaptability of the system by precisely controlling the phase and amplitude of the optical signal. This makes it possible to maintain stable performance in complex network environments, such as in long-distance transmission with significant multipath interference and signal attenuation. At the same time, coherent optical communication also has excellent bit error rate performance, which is essential to ensure the reliability and accuracy of data transmission.

[0003] In coherent communication systems, the performance and quality of the local oscillator (LO) are critical to the efficiency and performance of the entire system. LO needs to generate extremely stable and pure light waves to ensure that it can be effectively mixed with the received signal light, which is the core of achieving accurate coherent detection. Therefore, LO must have a very stable frequency, low phase noise, high spectral purity and spectral linewidth below 200kHz, and provide appropriate output power to match system requirements.

[0004] The preparation of high-quality LO involves complex technical processes, including precise optical design, advanced electronic control systems, and strict manufacturing environment control. These requirements make the preparation of LO a difficult task, requiring the integration of advanced optical and electronic engineering technologies, while also being carried out in an environment with little dust and good temperature and humidity control to ensure that the performance of LO meets the design standards. Therefore, it is not easy to manufacture LO that meets all these performance requirements, but this is crucial to ensure the efficient operation and high-quality communication of coherent communication systems.

[0005] The quantum dot (QD) structure has a strong three-dimensional quantum confinement effect, which makes QD lasers ideal as LOs in coherent detection. This three-dimensional confinement not only quantizes the energy levels of electrons and holes, but also significantly improves the emission wavelength stability and spectral purity of the laser. The light emitted by QD lasers has a very narrow linewidth, which is crucial to improving the coherence of the system because the narrow linewidth can reduce phase fluctuations and improve the demodulation quality of the signal. At the same time, QD lasers can also provide high output power and fast modulation response at low energy consumption, meeting the needs of high-speed data transmission. These combined characteristics enable QD lasers to ensure stable signal transmission and high-quality demodulation in high-precision and high-efficiency coherent communication systems.

[0006] Silicon-based optoelectronic integration technology realizes the monolithic integration of optoelectronic devices and microelectronic devices through traditional microelectronic CMOS processes. It is a silicon-based large-scale integration technology that studies and develops photons and electrons as information carriers. In the past decade, the research on key materials, devices and chips for silicon-based optoelectronic integration has attracted widespread attention from the scientific and industrial communities. The narrow linewidth laser on a silicon-based chip aims to miniaturize and integrate the traditional bulky laser system, reduce the energy consumption, volume and manufacturing cost of the system, and improve stability and scalability. The development of high-performance narrow linewidth silicon-based light sources has posed new challenges to integrated semiconductor materials, low-loss micro-nano optical manufacturing, and even the entire basic physical optics. Due to the lattice mismatch and different polarity between the III-V group materials and silicon materials used to make semiconductor lasers, silicon-based lasers produce a higher dislocation density during the manufacturing process, which inevitably reduces the luminous efficiency and light quality of the device, resulting in a larger spectral linewidth. The linewidth of traditional semiconductor quantum well lasers is at the MHz level. Compared with quantum well materials, the discrete distribution characteristics of quantum dot (QD) materials make them more tolerant to epitaxial growth defects. They can effectively deflect or clamp defects to prevent loop formation, and at the same time position carriers to prevent lateral diffusion or non-radiative recombination, thereby greatly reducing the impact of dislocation defects on the optical properties of the laser. Therefore, the linewidth of QD lasers can reach the kHz level. Therefore, silicon-based QD lasers can be the best choice for coherent communication LO.

[0007] In order to further reduce the line width of silicon-based QD lasers to meet the requirements of coherent communication, the laser line width can be reduced by changing the shape of the laser resonant cavity, adding frequency-selective gratings, and other methods. The laser cavity is designed to be ring-shaped, aiming to reduce the line width by increasing the cavity length and the cycle time of photons in the laser cavity. The ring cavity narrow line width laser has a variable structure. Compared with the linear cavity structure, it can eliminate the spatial hole burning effect, but because the ring cavity laser is an all-fiber structure, it is easily affected by the environment. In order to improve the stability of the laser system, the researchers also proposed a laser cavity structure that combines the Bragg grating with the active region, and introduced a phase shift region in the middle position of the Bragg grating to convert the multi-longitudinal mode output into a single longitudinal mode output, thereby reducing the laser line width. This structure has a higher degree of integration, stronger integrity, and better stability, but the manufacturing process is complex, requires high-precision lithography and etching technology, and has a high manufacturing cost. In addition to the above-mentioned methods of improving the laser itself, external control methods such as external optical feedback, light injection, and photoelectric feedback can also be used, but these external control methods require precise control and have high requirements for control elements.

[0008] External optical feedback refers to the reflection of part of the light emitted by the laser back into the laser cavity. In this process, two key parameters, the external cavity round-trip time and the optical feedback intensity, play a decisive role. The distance between the laser and the reflector is defined as the external cavity length, and the external cavity round-trip time is proportional to the external cavity length. In the active region of the laser, the re-injected light causes a disturbance in the photon density, resulting in fluctuations in the carrier density and optical gain, which in turn causes fluctuations in the output phase of the QD laser. Therefore, the presence of optical feedback causes the laser to exhibit complex nonlinear dynamic behavior, resulting in significant changes in the output light width. In the feedback space composed of the external cavity length and the optical feedback intensity, only a very small part of the area can reduce the spectral linewidth of the laser. Although optical feedback is expected to be used to reduce the spectral linewidth of QD lasers, its adjustment process is extremely difficult and requires precise control of the optical feedback parameters to achieve the desired effect.

[0009] The external light injection locking technology is to inject the output light of a tunable laser into the QD laser, thereby increasing the photon lifetime in the laser, thereby reducing the frequency noise and stabilizing the light source output. By adjusting the injection intensity and frequency detuning, the output characteristics of the QD laser can be effectively controlled and the output spectrum linewidth can be significantly improved. Compared with the optical feedback method, external light injection is easier to adjust, but the requirements for the tunable laser are extremely high: only when its output light has a high stability can the goal of reducing the spectrum linewidth of the QD laser be achieved.

[0010] In order to further cater to the development trend of large-scale and highly integrated optoelectronic chips, coherent detection LO urgently needs an easy-to-integrate, low-cost, narrow-linewidth light source. Summary of the invention

[0011] In order to solve the problems in the prior art, the present invention provides a method for compressing the spectral line width of a silicon-based quantum dot laser, and also provides a local oscillator and a coherent detection system using the method for compressing the spectral line width of a silicon-based quantum dot laser.

[0012] The method of compressing the spectral line width of a silicon-based quantum dot laser of the present invention is achieved by reducing the external carrier noise of a pump source. The method of reducing the external carrier noise of a pump source is as follows:

[0013] Adjusting the injection current output by the pump current source so that the pump current electron distribution presents a sub-Poisson or quasi-sub-Poisson distribution;

[0014] The injection current acts on the silicon-based quantum dot laser.

[0015] Furthermore, the specific processing method implemented by reducing the external carrier noise of the pump source includes the following steps:

[0016] S1: Building a quantum dot laser model, which consists of three energy states: a two-dimensional carrier reservoir RS, an excited state ES, and a ground state GS;

[0017] S2: Build the quantum dot laser model with the number of carriers N RS 、N ES 、N GS , photon number S GS and the light field phase φ GS The kinetic rate equations, each of which contains a noise source associated with the corresponding current source;

[0018] S3: determining the autocorrelation of the current source noise within the time period based on the five kinetic rate equations in step S2;

[0019] S4: establishing a frequency noise function of the quantum dot laser, obtaining a frequency noise spectrum, and obtaining the spectral line width of the silicon-based quantum dot laser from the frequency noise spectrum;

[0020] S5: Based on the autocorrelation relationship and the frequency noise function of the quantum dot laser, determine the relationship between the frequency noise of the quantum dot laser and the spectral line width of the silicon-based quantum dot laser and the external carrier noise of the pump source;

[0021] S6: Compressing the spectral linewidth of silicon-based quantum dot lasers by reducing the external carrier noise of the pump source.

[0022] Furthermore, in step S2, the number of carriers N RS 、N ES 、N GS , photon number S GS and the light field phase φ GSThe kinetic rate equation is expressed as:

[0023]

[0024] Where I is the pump current, 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, are the capture time, relaxation time and escape time of external carriers, respectively. are the spontaneous radiative recombination time of external carriers in each state, τ SRH is the non-radiative recombination lifetime of silicon-based quantum dot lasers, g RS ,g ES ,g GS are the material gains of each energy state, respectively, and the calculation formula is:

[0025]

[0026] Among them, a RS ,a ES ,a GS is the differential gain, ε is the optical confinement factor, N B is the total number of quantum dots, V B is the volume of the active region, D RS is the number of RS states, V RS is the volume of RS, ρ RS , ES , GS are the carrier occupancy rates of RS, ES, and GS, respectively, and F RS ,F ES ,F GS ,F S ,F φ are the kinetic rate equation noise sources for carriers, photons, and phase, respectively.

[0027] Furthermore, in step S3, the correlation strength relationship of the noise sources at two moments is: <F i (t)F j (t')>=U i,j δ(t-t'), where i, j refers to the correlation intensity U of the noise source of the kinetic rate equation at two times t and t' in RS, ES, GS, S, Φ i,j is δ-related, and the correlation strength is specifically expressed as:

[0028]

[0029] U RS,GS =URS,S =U RS,φ =U ES,S =U ES,φ =U GS,φ =U S,φ =0

[0030] RS, ES, and GS are respectively H The contribution of factors.

[0031] Furthermore, through small signal analysis, the kinetic rate equation is linearized to:

[0032]

[0033] in,

[0034]

[0035] In step S4 and step S5, the calculation formula of the frequency noise FN of the silicon-based quantum dot laser is established:

[0036]

[0037] where δφ(ω) is the phase fluctuation in the frequency domain, j is the imaginary unit, ω is the angular frequency,

[0038] Spectral line width Δυ of silicon-based QD lasers OL Extracted from the FN spectrum at a frequency of 1MHz, the extraction formula is:

[0039] Δυ OL =2πFN| f＝1MHz

[0040] According to the calculation formula of the frequency noise FN of silicon-based quantum dot laser and the extraction formula of the spectral line width of silicon-based quantum dot laser, the correlation intensity U RS,RS It is a key parameter that correlates RIN and external carrier noise. By reducing or eliminating the external carrier noise of the pump source, the spectral line width of the silicon-based quantum dot laser can be reduced.

[0041] The present invention also provides a local oscillator, wherein the local oscillator adopts a silicon-based quantum dot laser to provide local oscillation light, and the silicon-based quantum dot laser adopts the method of compressing the spectral line width of the silicon-based quantum dot laser to generate local oscillation light.

[0042] Furthermore, the electron distribution of the pump current of the local oscillator presents a sub-Poisson or quasi-sub-Poisson distribution.

[0043] The present invention also provides a coherent detection system, including a local oscillator, an optical mixer, an optical amplifier, an optical detector and an electrical signal processing module, wherein the local oscillator is used to output local oscillator light as reference light, the optical mixer is used to receive signal light and local oscillator light of the local oscillator and perform mixing, the optical amplifier is used to amplify the signal output by the optical mixer, the optical detector is used to convert the optical signal output by the optical amplifier back into an electrical signal, and identify and reconstruct the original information of the signal based on the reference light, and the electrical signal processing module is used to receive the signal from the optical detector and perform coherent detection processing.

[0044] Compared with the prior art, the present invention has the following beneficial effects: by adjusting the injection current output by the pump current source, the present invention effectively reduces the external carrier noise of the pump source, significantly reduces the spectrum linewidth of the silicon-based QD laser, and also suppresses the phenomenon that the spectrum linewidth appears to be broadened again as the pump current increases, while meeting the LO spectrum linewidth requirements of coherent detection, and providing a sufficiently large output power to match the system requirements. Compared with methods such as optical feedback and external light injection, the present invention does not require precise regulation, and is simple and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the present invention or the solutions in 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 invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0046] Figure 1 Schematic diagram of silicon-based QD laser working under pump source;

[0047] Figure 2 Statistical diagram of noise power, time domain intensity noise and intensity distribution of time domain noise under normal pump and low noise pump with current variation;

[0048] Figure 3 A schematic diagram showing the comparison of the RIN spectra of the pump source of the present invention and the QD laser driven by a normal pump;

[0049] Figure 4 A schematic diagram showing the comparison of the low-frequency RIN of a silicon-based QD laser under the pump source of the present invention and normal pumping conditions;

[0050] Figure 5 Schematic diagram of the comparison of line width enhancement factors of silicon-based QD lasers at 1.5-10 times the threshold;

[0051] Figure 6 Schematic diagram of the coherent detection system structure. DETAILED DESCRIPTION

[0052] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs; the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of the present invention or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

[0053] Reference to "embodiments" in the present invention 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 invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it mutually exclusive, independent, or alternative to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.

[0054] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings.

[0055] The present invention provides a method for compressing the spectral line width of a silicon-based quantum dot laser. The method for compressing the spectral line width of a silicon-based quantum dot laser is achieved by reducing the external carrier noise of a pump source. The method for reducing the external carrier noise of a pump source is as follows:

[0056] Adjusting the injection current output by the pump current source so that the pump current electron distribution presents a sub-Poisson or quasi-sub-Poisson distribution;

[0057] The injection current acts on the silicon-based quantum dot laser.

[0058] The present invention significantly reduces the spectral line width of silicon-based quantum dot lasers and suppresses the re-broadening phenomenon by effectively reducing the external carrier noise of the laser pump source. Compared with optical feedback and external light injection, the present invention does not require precise regulation, greatly optimizes the performance of silicon-based lasers, and improves the stability and reliability of their output. This innovative technology provides an efficient and stable light source solution for photonic integrated circuits, data centers and other fields, fully demonstrating its wide application potential in modern optoelectronic systems.

[0059] In this example, the pump current source is referred to as low-noise pump. In the specific implementation process, this example builds a quantum dot laser model and explores the relationship between the pump source noise and frequency noise of the silicon-based quantum dot laser and the spectral line width of the QD laser, thereby effectively compressing the spectral line width of the silicon-based quantum dot laser.

[0060] The working principle of the present invention is described in detail below.

[0061] Step S1: constructing a quantum dot laser model, wherein the quantum dot laser model consists of three energy states: a two-dimensional carrier reservoir RS, an excited state ES and a ground state GS.

[0062] In this example, when building a quantum dot laser model, two pump current sources with different external carrier noise are represented: a normal pump with a Gaussian carrier distribution (the commonly used pump source) and a low-noise pump with a sub-Poissonian carrier distribution (the pump source of the present invention). The model describes the QD carrier dynamics by considering a three-level system, assuming that the silicon-based QD laser is a single-mode laser and that there is only one QD ensemble in the active region.

[0063] like Figure 1 As shown in Figure 1, the silicon-based QD laser model consists of a two-dimensional carrier reservoir (RS), an excited state (ES), and a ground state (GS). The carriers are first trapped in the Captured from RS into ES, and then with relaxation time Relaxation from ES to GS, stimulated emission finally occurs at GS. Due to the effect of heat, the carrier escapes with a time Return from GS to ES to escape time From ES back to RS, this process is determined by the Fermi distribution of the quasi-equilibrium state. In addition, the carriers will spontaneously radiate and recombine in each state, and the time is respectively Since the laser model is a silicon-based QD laser, the non-radiative recombination lifetime τ SRH .

[0064] Step S2: Build the quantum dot laser model with carrier number N RS 、N ES 、N GS , photon number S GS and the light field phase φ GS The kinetic rate equations each contain a noise source associated with the corresponding current source.

[0065] This example describes the carrier number N RS 、N ES 、N GS , photon number S GS and the light field phase φ GSThe kinetic rate equation is expressed as:

[0066]

[0067] Where I is the pump current, 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, g RS ,g ES ,g GS are the material gains of each energy state, respectively, and the calculation formula is:

[0068]

[0069] Among them, a RS ,a ES ,a GS is the differential gain, ε is the optical confinement factor, N B is the total number of quantum dots, V B is the volume of the active region, D RS is the number of RS states, V RS is the volume of RS, ρ RS , ES , GS are the carrier occupancies of RS, ES, and GS, respectively, and the calculation formula is: RS, ES, and GS are respectively H The contribution of the factor. Given, where T D is the dephasing time, ω RS,ES,GS is the angular frequency of each energy state.

[0070] Step S3: determining the autocorrelation of the current source noise within the time period based on the five kinetic rate equations in step S2.

[0071] F RS ,F ES ,F GS ,F S ,F φ are the kinetic rate equation noise sources of carriers, photons, and phases, respectively. The correlation intensity relationship of the noise sources at two different times t and t' is: <F i (t)F j (t')>=U i,j δ(t-t'), where i, j refers to the correlation intensity U of the noise source of the kinetic rate equation at two times t and t' in RS, ES, GS, S, Φ i,j is δ-related, and the correlation strength is specifically expressed as:

[0072]

[0073] U RS,GS =U RS,S =U RS,φ =U ES,S =U ES,φ =U GS,φ =U S,φ =0

[0074] Through small signal analysis, the rate equation is linearized to obtain:

[0075]

[0076] in,

[0077]

[0078] where a and a p Considering the gain compression under high photon number, dg = adN GS -a p dS GS The other parameter values ​​of silicon-based QD laser can refer to Table 1.

[0079]

[0080]

[0081] Table 1 Materials and optical parameters of silicon-based QD lasers

[0082] Step S4: establishing a frequency noise function of the quantum dot laser, obtaining a frequency noise spectrum, and obtaining the spectral line width of the silicon-based quantum dot laser from the frequency noise spectrum.

[0083] According to Cramer's law, the calculation formula of the frequency noise FN of the silicon-based quantum dot laser is established:

[0084]

[0085] where δφ(ω) is the phase fluctuation in the frequency domain, j is the imaginary unit, ω is the angular frequency,

[0086] The spectral line width Δυ of the silicon-based QD laser in this example OL It can be extracted from the FN spectrum at a frequency of 1MHz. The extraction formula is:

[0087] Δυ OL =2πFN| f＝1MHz .

[0088] Step S5: Based on the autocorrelation relationship and the frequency noise function of the quantum dot laser, determine the relationship between the frequency noise of the quantum dot laser and the spectral line width of the silicon-based quantum dot laser and the external carrier noise of the pump source.

[0089] According to the calculation formula of the frequency noise FN of silicon-based quantum dot laser and the extraction formula of the spectral line width of silicon-based quantum dot laser, the correlation intensity U RS,RS It is a key parameter that correlates RIN and external carrier noise. By reducing or eliminating the external carrier noise of the pump source, the spectral line width of the silicon-based quantum dot laser can be reduced.

[0090] Step S6: Compressing the spectral line width of the silicon-based quantum dot laser by reducing the external carrier noise of the pump source.

[0091] In this example, when a normal pump is used to drive the QD laser, RS,RS Add the pump current source noise term to When a low-noise pump is used to drive a QD laser, the external carrier noise will affect the lasing of the active region of the QD laser. RS,RS Remove the pump current source noise term from It is assumed that external carrier noise has no effect on the laser. By adjusting the external carrier noise, the line width of the silicon-based quantum dot laser can be effectively compressed.

[0092] Test verification:

[0093] The present invention conducts experimental measurements on the noise power and time domain noise of the low noise pump of the present invention and the existing ordinary pump, such as Figure 2 As shown in Figure (a), the frequency domain noise power of the low-noise pump is about 30dB lower than that of the ordinary pump. Figure 2 As shown in the time domain diagram of Figure (b), the low-noise pump has a lower noise intensity and shows a narrow range of jitter, indicating that the noise intensity is relatively concentrated. In contrast, the normal pump shows a wider range of jitter values ​​and higher noise intensity, indicating that the distribution of noise intensity over time is more dispersed. Figure 2 The statistical distribution in Figure (c) on the right more intuitively shows the difference in noise levels between the two pump sources.

[0094] In order to verify the effect of the present invention, the present invention further compares and verifies the spectral line width of the low-noise pump of the present invention and the existing common pump based on the above method.

[0095] like Figure 3As shown, in this example, according to the above principles and formulas, the FN spectra of the QD laser driven by different pump sources at 5.5 times the threshold current are obtained. It can be seen that the present invention can significantly reduce the FN of the silicon-based QD laser by low-noise pumping that reduces the external carrier noise of the pump source, so that the output optical power of the laser is more stable in the time domain.

[0096] like Figure 4 As shown, the present invention consists of Δυ OL =2πFN f＝1MHz The line width of the silicon-based QD laser under the two pumping conditions of the low-noise pump of the present invention and the conventional pump of the prior art is obtained and shown in the figure. Figure 4 It can be seen that under normal pumping, the output light width of the laser will first decrease with the increase of the pump current, and then increase accordingly, resulting in a re-broadening phenomenon. The low-noise pump of the present invention not only has a lower line width than ordinary pumping under the same pump current, but also effectively suppresses the occurrence of the re-broadening phenomenon. Even under a high pump of 10 times the threshold current, the line width still shows a decreasing trend. In this example, at 10 times the threshold current, the line width of the QD laser under low-noise pumping is 139kHz, which fully meets the requirements of the coherent detection LO, and because the laser is pumped by a large current, the generated laser power is high enough to fully match the system communication requirements for the laser power. Compared with low-noise pumping, when using normal pumping, the line width of the laser is 536kHz, the phase fluctuation is large, and the spectral line width is wide. If used for coherent detection, it will reduce the accuracy of the communication system and cannot achieve high-quality and stable signal transmission.

[0097] Figure 5 This further explains why the QD laser spectral line width re-broadening phenomenon behaves differently under the two pumping conditions. As the pump current increases, the influence of the carriers of ES on GS increases gradually under normal pumping, making α H The factor increases, and the spectral line width increases. The influence of ES carriers on GS is suppressed during low-noise pumping, making α H The factor hardly changes with the pump current, so there is no spectrum re-broadening phenomenon, which broadens the pump current range of the QD laser and can obtain sufficient output power without increasing the line width, which is conducive to matching the output requirements of the coherent detection system. This result proves that the method of compressing the line width of the QD laser by reducing external carrier noise is feasible and effective. The present invention does not require improvement of the structure of the QD laser, making it easier to operate.

[0098] The present invention also provides a local oscillator, wherein the local oscillator uses a silicon-based quantum dot laser to provide local oscillation light, and the silicon-based quantum dot laser uses the method of compressing the spectral line width of the silicon-based quantum dot laser to generate local oscillation light. This example reduces the line width while suppressing the re-broadening phenomenon of the spectrum line width of the QD laser, ensuring that the output power of the laser is large enough, so that the line width meets the needs of coherent detection, and the power can match the communication system.

[0099] like Figure 6 As shown, the present invention also provides a coherent detection system including the local oscillator. The signal light carrying the information from the transmitting end first enters the optical mixer, where the signal light is mixed with the light from the local oscillator LO, and the LO provides a stable narrow linewidth reference light source. After mixing with the signal light, the phase and amplitude information of the signal light can be extracted by comparing the interference patterns of the two lights. The mixed optical signal is then sent to the optical amplifier, the purpose of which is to enhance the strength of the signal and ensure the quality and stability of the signal in the subsequent transmission process. The amplified signal light enters the optical detector, which is responsible for converting the optical signal back into an electrical signal. During this conversion process, the optical detector uses the reference light previously obtained from the LO to identify and reconstruct the original information of the signal, and then sends it to the electrical signal processing module, thereby completing the accurate reception and processing of the data. In the above-mentioned coherent detection process, LO is the core of realizing accurate coherent detection. The quality of the local oscillator light emitted by the LO determines the accuracy of the recovered signal. The present invention does not require precise regulation to meet the requirements of the coherent detection for the LO spectrum linewidth.

[0100] 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 compressing the spectral line width of a silicon-based quantum dot laser, characterized in that: This is achieved by reducing the external carrier noise of the pump source. The method to reduce the external carrier noise of the pump source is: Adjusting the injection current output by the pump current source so that the pump current electron distribution presents a sub-Poisson or quasi-sub-Poisson distribution; The injection current acts on the silicon-based quantum dot laser.

2. The method for compressing the spectral line width of a silicon-based quantum dot laser according to claim 1, characterized in that: The steps include: S1: Building a quantum dot laser model, which consists of three energy states: a two-dimensional carrier reservoir RS, an excited state ES, and a ground state GS; S2: Build the quantum dot laser model with the number of carriers N RS 、N ES 、N GS , photon number S GS and the light field phase φ GS The kinetic rate equations, each of which contains a noise source associated with the corresponding current source; S3: determining the autocorrelation of the current source noise within the time period based on the five kinetic rate equations in step S2; S4: establishing a frequency noise function of the quantum dot laser, obtaining a frequency noise spectrum, and obtaining the spectral line width of the silicon-based quantum dot laser from the frequency noise spectrum; S5: Based on the autocorrelation relationship and the frequency noise function of the quantum dot laser, determine the relationship between the frequency noise of the quantum dot laser and the spectral line width of the silicon-based quantum dot laser and the external carrier noise of the pump source; S6: Compressing the spectral linewidth of silicon-based quantum dot lasers by reducing the external carrier noise of the pump source.

3. The method for compressing the spectral line width of a silicon-based quantum dot laser according to claim 2, characterized in that: In step S2, the number of carriers N RS 、N ES 、N GS , photon number S GS and the light field phase φ GS The kinetic rate equation is expressed as: Where I is the pump current, 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, are the capture time, relaxation time and escape time of external carriers, respectively. are the spontaneous radiative recombination time of external carriers in each state, τ SRH is the non-radiative recombination lifetime of silicon-based quantum dot lasers, g RS ,g ES ,g GS are the material gains of each energy state, respectively, and the calculation formula is: Among them, a RS ,a ES ,a GS is the differential gain, ε is the optical confinement factor, N B is the total number of quantum dots, V B is the volume of the active region, D RS is the number of RS states, V RS is the volume of RS, ρ RS , ES , GS are the carrier occupancy rates of RS, ES, and GS, respectively, and F RS ,F ES ,F GS ,F S ,F φ are the kinetic rate equation noise sources for carriers, photons, and phase, respectively.

4. The method for compressing the spectral line width of a silicon-based quantum dot laser according to claim 3, characterized in that: In step S3, the correlation strength relationship between the noise sources at two times t and t' is: <F i (t)F j (t')>=U i,j δ(t-t'), where i, j refers to the correlation intensity U of the noise source of the kinetic rate equation at two times t and t' in RS, ES, GS, S, Φ i,j is δ-related, and the correlation strength is specifically expressed as: IN RS,GS =U RS,S =U RS,φ =U ES,S =U ES,φ =U GS,φ =U S,φ =0 RS, ES, and GS are respectively H The contribution of factors.

5. The method for compressing the spectral line width of a silicon-based quantum dot laser according to claim 4, characterized in that: Through small signal analysis, the kinetic rate equation is linearized to: in, In step S4 and step S5, the calculation formula of the frequency noise FN of the silicon-based quantum dot laser is established: where δφ(ω) is the phase fluctuation in the frequency domain, j is the imaginary unit, ω is the angular frequency, Spectral line width Δυ of silicon-based QD lasers OL Extracted from the FN spectrum at a frequency of 1MHz, the extraction formula is: Two OL =2πFN| f＝1MHz According to the calculation formula of the frequency noise FN of silicon-based quantum dot laser and the extraction formula of the spectral line width of silicon-based quantum dot laser, the correlation intensity U RS,RS It is a key parameter that correlates RIN and external carrier noise. By reducing or eliminating the external carrier noise of the pump source, the spectral line width of the silicon-based quantum dot laser can be reduced.

6. A local oscillator, characterized in that: The local oscillator uses a silicon-based quantum dot laser to provide local oscillation light, and the silicon-based quantum dot laser uses the method for compressing the spectral line width of a silicon-based quantum dot laser as described in any one of claims 1-5.

7. The local oscillator according to claim 6, characterized in that: The electron distribution of the pump current of the local oscillator exhibits a sub-Poisson or quasi-sub-Poisson distribution.

8. A coherent detection system, comprising the local oscillator according to claim 6, characterized in that: It also includes an optical mixer, an optical amplifier, an optical detector and an electrical signal processing module, wherein the local oscillator is used to output local oscillator light as reference light, the optical mixer is used to receive signal light and local oscillator light of the local oscillator and perform mixing, the optical amplifier is used to amplify the signal output by the optical mixer, the optical detector is used to convert the optical signal output by the optical amplifier back into an electrical signal, and identify and reconstruct the original information of the signal based on the reference light, and the electrical signal processing module is used to receive the signal from the optical detector and perform coherent detection processing.

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