Self-injection locking frequency stabilization system based on quantum dot laser

Abstract

A quantum dot laser-based self-injection locking frequency stabilization system provided by the present invention comprises a quantum dot laser, a light splitting element and a reflection unit, the quantum dot laser is internally provided with a laser cavity, the two ends of the quantum dot laser can output laser, and the light splitting element and the reflection unit are sequentially arranged along the laser emission direction of one end of the quantum dot laser. The quantum dot laser, the light splitting element and the reflection unit are connected through optical fibers or waveguides, and a part of laser beams output from one end of the quantum dot laser can be separated by the light splitting element and reflected back into the laser cavity through the reflection unit to be output from the other end of the quantum dot laser. The quantum dot laser has the beneficial effects that the output frequency stability and high-precision control of the quantum dot laser are improved, the structure is simple, the cost is low, the radio frequency spectrum line width of the quantum dot laser is optimized, and the time jitter performance of the pulse of the quantum dot laser is improved.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor optoelectronics, and in particular to a self-injection locking frequency stabilization system based on quantum dot lasers. Background Art

[0002] With the rapid development of optical communications, optical frequency synthesis, microwave photonics and other fields, the performance requirements for pulsed lasers are increasing, especially in terms of frequency stability and time jitter. Traditional lasers often require complex modulation technology and external equipment to achieve frequency locking and stabilization, which not only increases the complexity and cost of the system, but also limits the application scope of lasers.

[0003] Semiconductor lasers have many advantages in on-chip integrated applications, but they still face some challenges in practical applications. Among them, a key issue is the stability of the laser's output frequency. In the absence of external feedback or locking mechanism, the laser's output frequency is easily affected by environmental disturbances and internal noise, resulting in increased frequency drift and time jitter. This not only affects the performance of the laser, but also limits its application in high-precision measurement and communication systems. In order to solve this problem, researchers have proposed a variety of frequency stabilization technologies, including active frequency stabilization of electronic servo control systems, optical injection locking, and external optical feedback (EOF). Among them, external optical feedback technology is favored because of its simple structure, easy implementation and high cost-effectiveness. By introducing external optical feedback, the noise and disturbance inside the laser can be effectively suppressed, thereby achieving output frequency stability and linewidth compression.

[0004] However, there are still some problems in the application of existing external optical feedback technology in semiconductor lasers. For example, excessive feedback conditions may induce chaotic behavior of the laser, leading to output spectrum broadening and nonlinear oscillation of the RF spectrum. In addition, precise control of feedback intensity and phase is also a key challenge to achieve stable locking, which is difficult to control and requires complex modulation technology and external equipment to achieve. Summary of the invention

[0005] In order to solve the problems in the prior art, the present invention provides a self-injection locking and frequency stabilization system based on quantum dot lasers. By arranging a quantum dot laser, a spectroscopic element and a reflection unit that cooperate with each other in the self-injection locking and frequency stabilization system based on quantum dot lasers, a part of the laser beam output from one end of the quantum dot laser can be separated by the spectroscopic element and reflected back into the laser cavity through the reflection unit and output from the other end of the quantum dot laser, thereby optimizing the radio frequency spectrum line width of the quantum dot laser, improving the time jitter performance of the quantum dot laser pulse, and solving the problem in the prior art that the output frequency of the laser is easily affected by environmental disturbances and internal noise.

[0006] The present invention provides a self-injection locking frequency stabilization system based on a quantum dot laser, comprising a quantum dot laser, a spectroscopic element and a reflection unit, wherein a laser cavity is arranged inside the quantum dot laser, both ends of the quantum dot laser can output laser, the spectroscopic element and the reflection unit are sequentially arranged along the direction in which the laser is emitted from one end of the quantum dot laser, the quantum dot laser, the spectroscopic element and the reflection unit are connected through an optical fiber or a waveguide, and a part of the laser beam output from one end of the quantum dot laser can be separated by the spectroscopic element and reflected back to the laser cavity through the reflection unit and output from the other end of the quantum dot laser.

[0007] The present invention is further improved in that a phase control unit is provided between the beam splitting element and the reflection unit, and the phase control unit can adjust the phase of the laser light beam separated by the beam splitting element to match the light field in the laser cavity.

[0008] The present invention is further improved in that an intensity control unit is provided between the beam splitting element and the reflection unit, and the intensity control unit can adjust the intensity of the laser light beam separated by the beam splitting element to match the light field in the laser cavity.

[0009] The present invention is further improved in that the manufacturing material of the quantum dot laser is InAs / GaAs quantum dot material or InAs / InP quantum dot material.

[0010] The present invention is further improved in that the substrate of the quantum dot laser is an intrinsic substrate or a silicon-based substrate or a germanium-based substrate.

[0011] The present invention is further improved, and the structure of the quantum dot laser is a quantum dot micro-disk laser or a vertical cavity surface emitting quantum dot laser or a quantum dot distributed feedback laser or a distributed Bragg reflection laser.

[0012] The present invention is further improved in that the light splitting element is a polarization light splitting prism or a fiber coupler or an integrated directional coupler, and the reflection unit is a plane reflector or a Faraday rotator or a micro-ring reflector.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a self-injection locking frequency stabilization system based on quantum dot lasers. By arranging mutually coordinated quantum dot lasers, spectroscopic elements and reflection units in the self-injection locking frequency stabilization system based on quantum dot lasers, a laser beam output from one end of the quantum dot laser can be separated by the spectroscopic element, and a part of the laser beam is reflected back into the laser cavity through the reflection unit and output from the other end of the quantum dot laser, that is, the frequency stability and high-precision control of the quantum dot laser output are improved through external optical feedback. The present invention has a simple structure and low cost, optimizes the radio frequency spectrum line width of the quantum dot laser, and improves the time jitter performance of the quantum dot laser pulse. The present invention is suitable for optical communication, optical frequency synthesis and microwave photonics fields with high requirements for frequency stability and time jitter, and solves the problem in the prior art that the output frequency of the laser is easily affected by environmental disturbances and internal noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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.

[0015] Figure 1 This is a principle block diagram of the self-injection locking frequency stabilization system based on quantum dot lasers of the present invention;

[0016] Figure 2 Schematic diagram of the change of line width of quantum dot laser with the intensity of feedback laser beam;

[0017] Figure 3 Schematic diagram of the change of line width of quantum dot laser with external cavity delay time;

[0018] Figure 4 This is the spectrum diagram of quantum dot laser when there is no feedback laser beam;

[0019] Figure 5 This is the spectrum diagram of the quantum dot laser under -6.3dB external cavity feedback laser beam;

[0020] Figure 6 This is the spectrum diagram of the quantum dot laser near the fundamental frequency (10.2GHz). DETAILED DESCRIPTION

[0021] 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.

[0022] 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.

[0023] 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.

[0024] like Figure 1-Figure 6 As shown, the present invention provides a self-injection locking frequency stabilization system based on a quantum dot laser, including a quantum dot laser, a spectroscopic element and a reflection unit. A laser cavity is provided in the quantum dot laser. Both ends of the quantum dot laser can output lasers. The spectroscopic element and the reflection unit are arranged in sequence along the direction of laser emission from one end of the quantum dot laser. The quantum dot laser, the spectroscopic element and the reflection unit are connected through an optical fiber or a waveguide. A portion of the laser beam output from one end of the quantum dot laser can be separated by the spectroscopic element and reflected back into the laser cavity through the reflection unit and output from the other end of the quantum dot laser. A phase control unit is also provided between the spectroscopic element and the reflection unit. The phase control unit can adjust the phase of the laser beam separated by the spectroscopic element to match the light field in the laser cavity. An intensity control unit is also provided between the spectroscopic element and the reflection unit. The intensity control unit can adjust the intensity of the laser beam separated by the spectroscopic element to match the light field in the laser cavity. The spectroscopic element is a polarization spectroscopic prism or an optical fiber coupler or an integrated directional coupler. The reflection unit is a plane reflector or a Faraday rotator or a micro-ring reflector. In this embodiment, Figure 1The figure describes how the laser beam emitted by a quantum dot laser is fed back into the laser cavity after being processed by multiple functional units, and how it is output. The figure depicts in detail the starting point of the light source - the quantum dot laser from left to right. The laser beam emitted by the quantum dot laser is first divided into two parts by a spectroscopic unit, one part of the laser beam enters the feedback process, and the other part of the laser beam is directly output; the laser beam entering the feedback process first passes through a phase control unit to adjust the phase of the laser beam to ensure that it matches the light field in the quantum dot laser; then, the laser beam enters an intensity control unit to adjust the intensity of the laser beam to optimize the performance of the quantum dot laser and prevent damage; finally, the adjusted laser beam is reflected back into the laser cavity through a reflection unit to complete the external light feedback control. This process is crucial to reducing the RF linewidth and stabilizing the time jitter of the laser pulse. In this system, the most important thing is the quantum dot laser and reflection unit used. Even without using a phase control unit and an intensity control unit, self-injection locking can be achieved to improve performance compared to the free-running state. Quantum dot lasers with different structures can also have single-port output or dual-port output. The former can use a spectroscopic element to generate laser output, and the latter can output directly at the other port. The design of the entire system not only enhances the performance of the quantum dot laser, especially in terms of frequency stability, but also provides a high-quality light source for high-tech application scenarios such as precision measurement and data transmission by precisely controlling the phase and intensity of the laser beam.

[0025] The self-injection locking frequency stabilization system based on quantum dot laser proposed in the present invention has the following advantages:

[0026] First, from the perspective of frequency stability, the present invention achieves high stability in the output frequency of the quantum dot laser by introducing an external optical feedback mechanism. In traditional laser systems, the output frequency of the laser is often difficult to maintain constant due to slight fluctuations in environmental factors or interference from internal noise in the laser, which poses a challenge to application scenarios that require high-precision frequency control. The self-injection locked frequency stabilization system of the present invention locks the laser output frequency at a specific value by controlling the phase and intensity of the external feedback laser beam, thereby effectively suppressing the frequency drift phenomenon. Experimental data show that at maximum feedback intensity, the RF spectrum line width is greatly compressed, from tens of megahertz during free operation to the kilohertz level. This significant improvement provides a more reliable frequency reference for the application of quantum dot lasers in optical communications, optical frequency synthesis and other fields.

[0027] Secondly, in terms of time jitter performance, the present invention also shows extraordinary effects. Time jitter is one of the key indicators to measure the stability of laser pulse output. For high-speed optical communication systems, lasers with low time jitter can significantly improve the accuracy and reliability of signal transmission. Traditional lasers often rely on complex modulation technology and external compensation equipment for time jitter control, which not only increases the complexity and cost of the system, but also may introduce new unstable factors. The self-injection locking frequency stabilization system of the present invention achieves effective suppression of pulse time jitter by optimizing the optical feedback path and phase locking mechanism inside the laser. Experimental results show that under the maximum feedback intensity, the pulse time jitter is reduced from hundreds of femtoseconds during free operation to tens of femtoseconds or even lower levels. This performance improvement is of great significance to improving the overall performance of the system.

[0028] In addition, the self-injection locked frequency stabilization system of the present invention also has the advantages of simple structure and low cost. Compared with traditional frequency stabilization technology, this technology does not need to introduce additional complex components such as modulators or filters. It only needs to add a laser beam feedback loop outside the quantum dot laser to achieve frequency stabilization and line width compression. This design not only simplifies the system structure, reduces production costs and maintenance difficulties, but also helps to improve the stability and reliability of the system. At the same time, since the quantum dot laser itself has the advantages of low material cost and mature preparation process, the implementation of the present invention is expected to further promote the application and popularization of quantum dot lasers in a wider range of fields.

[0029] It is worth mentioning that the self-injection locking frequency stabilization system of the present invention also has good compatibility and scalability. The system is not only applicable to different types of quantum dot lasers, but can also be combined with the existing quantum dot laser preparation process. The manufacturing material of the quantum dot laser can be InAs / GaAs quantum dot material or InAs / InP quantum dot material; the substrate of the quantum dot laser can be an intrinsic substrate or a silicon-based substrate or a germanium-based substrate; the structure of the quantum dot laser can be a quantum dot micro-disk laser (QD micro-disk laser) or a vertical cavity surface emitting quantum dot laser (QD VCSEL) or a quantum dot distributed feedback laser (QD DFB laser) or a distributed Bragg reflection laser (QD DBR laser), and the frequency stability can be achieved without major modifications to the structure of the quantum dot laser. This compatibility enables the technology to be quickly applied to actual production to meet the diverse needs of high-performance lasers in different fields. At the same time, with the continuous development and progress of quantum dot laser material science and preparation technology, the frequency stabilization technology of the present invention is also expected to be continuously optimized and improved, further improving the performance and application potential of the laser.

[0030] like Figure 2 and Figure 3As shown, in the study of self-injection locking, the feedback laser beam intensity and the feedback laser beam phase difference have a significant influence on the linewidth compression effect of the quantum dot laser. Figure 2 and Figure 3 The trend of the RF line width variation of the output laser under different conditions is shown, which can help us understand this phenomenon. First, the greater the feedback laser beam intensity, the better the line width compression effect of the quantum dot laser. The feedback laser beam intensity refers to the proportion of light fed back to the laser cavity of the quantum dot laser. Figure 2 In the figure, we can see that when the feedback laser beam intensity increases from -35dB to -10dB, the 3-dB RF linewidth decreases significantly from about 0.8MHz to about 0.3MHz. This shows that increasing the feedback laser beam intensity can effectively compress the linewidth of the quantum dot laser and improve the purity of the output spectrum. This is because stronger feedback can enhance the coherence of the light field inside the quantum dot laser, thereby reducing the broadening of the spectrum. At this point, the anti-feedback characteristics of the quantum dot laser enable it to remain stable under strong feedback, thereby obtaining a better self-injection frequency stabilization effect. Secondly, the phase of the feedback laser beam also has an important influence on the linewidth compression effect, which can be studied by changing the external cavity delay time. The compression effect is best when the round-trip time of the external cavity is an integer multiple of the round-trip time of the internal cavity. This conclusion can be seen from Figure 3 This has been verified in the figure, which shows the change of the RF linewidth of the quantum dot laser with the delay time. In the figure, when the delay time is around 150ps and 250ps, the RF linewidth of the quantum dot laser increases significantly, reaching about 370kHz. At other time points, the RF linewidth of the quantum dot laser remains at a low level of about 320kHz. This shows that a specific delay time can weaken the interference effect of the light field, resulting in the broadening of the spectrum of the quantum dot laser. Therefore, the rational design of the length of the external cavity so that its round-trip time is exactly an integer multiple of the round-trip time of the inner cavity can suppress this broadening to the greatest extent, thereby achieving the best linewidth compression effect. At the same time, it can be found that the feedback laser beam phase has little effect on the quantum dot laser, and the range of change of the RF linewidth does not exceed 20%. Therefore, this scheme based on quantum dot lasers does not require sophisticated external cavity length control means and has high practical value. Based on the above analysis, the following conclusions can be drawn: when using a self-injection locking system based on quantum dot lasers, increasing the feedback intensity can significantly improve the pulse frequency stability of the laser. At the same time, no additional external cavity length control is required, which can provide a stable and reliable light source for high-precision optical measurement and communication applications.

[0031] like Figure 4 and Figure 5As shown in the figure, the frequency stabilization principle of quantum dot laser under self-injection locking is based on feedback and interference phenomena. By feeding back a part of the output light into the laser cavity of the quantum dot laser, the frequency stability and spectral purity of the quantum dot laser are improved. During the self-injection locking process, part of the laser beam is reflected back to the laser cavity through an external optical path to form optical feedback. The feedback laser beam interferes with the light field in the laser cavity to form a new steady-state light field. This interference phenomenon causes the phase relationship of the light field to change, thereby affecting the frequency of the quantum dot laser. By locking the light field in the laser cavity of the quantum dot laser with the feedback laser beam, the output frequency of the laser can be stabilized. In addition, self-injection locking can also suppress the mode hopping phenomenon in the quantum dot laser. Under normal circumstances, the frequency of the quantum dot laser will jump due to temperature changes or driving current fluctuations, resulting in spectrum instability. Through the self-injection locking technology, the interference effect of the feedback laser beam can effectively suppress this mode hopping, so that the quantum dot laser can still maintain a stable output frequency under different environmental conditions. This is of great significance for applications requiring high frequency stability, such as optical communications and high-precision spectral analysis. In this embodiment, the use of quantum dot lasers as the self-injection locked light source is an important core point. Quantum dot lasers have a unique gain medium, and their quantum dot structure can provide a wide gain spectrum and fast carrier dynamics, so that they can maintain excellent performance over a wide temperature range. This characteristic makes quantum dot lasers have strong anti-feedback capabilities. Using a single-cavity quantum dot laser according to Figure 1 The system is built with the structure shown in the figure. The spectrum of the quantum dot laser under the non-feedback laser beam and the -6.3dB external cavity feedback laser beam is shown as follows: Figure 4 and Figure 5 As shown, the quantum dot laser is in a stable pulse operation state because no chaotic oscillation is maintained.

[0032] like Figure 6 The figure shows the spectrum signal of the quantum dot laser near the fundamental frequency (10.2GHz). Black is without feedback, red is with feedback and the feedback intensity is -6.3dB. The RF signal is greatly compressed and the signal line width is reduced. The line width of the RF signal is calculated using Gaussian fitting, and the line width of the quantum dot laser under the non-feedback laser beam and the -6.3dB external cavity feedback laser beam is 10.5MHz and 249kHz respectively. For a pulsed laser with a high repetition rate, the time jitter between two adjacent pulses can be calculated by the following formula:

[0033]

[0034] Where ν0 is the repetition frequency and Δν is the RF line width. Therefore, the time jitter of the quantum dot laser without feedback and with -6.3dB external cavity optical feedback is 1248fs / cycle and 192fs / cycle respectively.

[0035] The higher the intensity of the feedback laser beam in the external cavity, the lower the RF linewidth, the better the self-injection locking effect, and the more stable the pulse frequency. Since the critical feedback intensity of traditional quantum well lasers is generally below -20dB, quantum dot lasers are used as the basic light source of self-injection locking lasers in practical applications, and extremely strong external cavity feedback can be used to achieve the ultimate frequency stabilization effect. The external cavity delay time is related to the phase difference between the feedback laser beam and the laser cavity light field. The locking effect is best when the phase difference is near 0, and the linewidth increases when the phase difference is ±π. Note that the difference between the two is small, not exceeding 20%, so in practical applications, quantum dot lasers are used as the basic light source of self-injection locking lasers, which can simplify the optimization of the phase in the external cavity length. The frequency stabilization working principle of quantum dot lasers under self-injection locking mainly depends on the interference between the feedback laser beam and the light field in the cavity. Normally, this frequency stabilization effect is greatly affected by the feedback strength and phase in the external cavity. However, the use of quantum dot lasers can take advantage of their feedback insensitivity, without having to consider the laser instability caused by strong feedback, and avoid the phase matching problem caused by external cavity feedback. Therefore, the anti-feedback characteristics of quantum dot lasers make them more suitable as locked lasers for self-injection locking.

[0036] In summary, the self-injection locking frequency stabilization system based on quantum dot lasers proposed in the present invention has shown significant advantages and positive effects in many aspects such as frequency stability, time jitter performance, system complexity, cost-effectiveness and application prospects. This technology not only provides strong support for the application of quantum dot lasers in the field of optoelectronics, but also promotes technological progress and industrial development in related fields. In the future, with the continuous maturity of quantum dot laser technology and the in-depth promotion and application of the present invention, it is believed that quantum dot lasers will show their unique charm and broad application prospects in more fields.

[0037] As can be seen from the above, the present invention provides a self-injection locking frequency stabilization system based on quantum dot lasers. By arranging a quantum dot laser, a spectroscopic element and a reflection unit that cooperate with each other in the self-injection locking frequency stabilization system based on quantum dot lasers, a laser beam output from one end of the quantum dot laser can be separated by the spectroscopic element, and a part of it is reflected back into the laser cavity through the reflection unit and output from the other end of the quantum dot laser, that is, the frequency stability and high-precision control of the quantum dot laser output are improved through external light feedback. The structure is simple and the cost is low. The radio frequency spectrum linewidth of the quantum dot laser is optimized, and the time jitter performance of the quantum dot laser pulse is improved. The system is suitable for optical communication, optical frequency synthesis and microwave photonics fields that have high requirements for frequency stability and time jitter, and solves the problem in the prior art that the output frequency of the laser is easily affected by environmental disturbances and internal noise.

[0038] 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 self-injection locking frequency stabilization system based on quantum dot laser, characterized by: The invention comprises a quantum dot laser, a spectroscopic element and a reflecting unit. The quantum dot laser is provided with a laser cavity. Both ends of the quantum dot laser can output laser. The spectroscopic element and the reflecting unit are sequentially arranged along the direction of laser emission from one end of the quantum dot laser. The quantum dot laser, the spectroscopic element and the reflecting unit are connected through an optical fiber or a waveguide. A part of the laser beam output from one end of the quantum dot laser can be separated by the spectroscopic element and reflected back to the laser cavity through the reflecting unit and output from the other end of the quantum dot laser.

2. The self-injection locking frequency stabilization system based on quantum dot laser according to claim 1, characterized in that: A phase control unit is further provided between the beam splitting element and the reflecting unit, and the phase control unit can adjust the phase of the laser light beam separated by the beam splitting element to match the light field in the laser cavity.

3. The self-injection locking frequency stabilization system based on quantum dot laser according to claim 2, characterized in that: An intensity control unit is also provided between the beam splitting element and the reflecting unit, and the intensity control unit can adjust the intensity of the laser light beam separated by the beam splitting element to match the light field in the laser cavity.

4. The self-injection locking frequency stabilization system based on quantum dot laser according to claim 3, characterized in that: The manufacturing material of the quantum dot laser is InAs / GaAs quantum dot material or InAs / InP quantum dot material.

5. The self-injection locking frequency stabilization system based on quantum dot laser according to claim 4, characterized in that: The substrate of the quantum dot laser is an intrinsic substrate or a silicon-based substrate or a germanium-based substrate.

6. The self-injection locking frequency stabilization system based on quantum dot laser according to claim 5, characterized in that: The structure of the quantum dot laser is a quantum dot micro-disk laser, a vertical cavity surface emission quantum dot laser, a quantum dot distributed feedback laser, or a distributed Bragg reflection laser.

7. The self-injection locking frequency stabilization system based on quantum dot laser according to claim 6, characterized in that: The beam splitting element is a polarization beam splitting prism, a fiber coupler, or an integrated directional coupler, and the reflection unit is a plane reflector, a Faraday rotator, or a micro-ring reflector.

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