An on-chip integrated narrow linewidth high power laser

Abstract

The application discloses a kind of narrow linewidth high-power lasers integrated on chip, all structures of the device are integrated on the same photonic integrated chip, including semiconductor laser, optical power distribution unit, coupling straight waveguide, micro-ring resonant cavity and Sagnac on-chip mirror in sequence, wherein: semiconductor laser: as light source, generates initial laser.Light path power distribution unit: laser is divided into two ways-one is directly led out as output light, another enters subsequent feedback loop as feedback light.Coupling straight waveguide: feedback light is coupled into micro-ring resonant cavity.Micro-ring resonant cavity: as main resonant unit, for realizing the core resonance of self-injection locking.By using the application, by designing special light path power distribution structure, the power distribution of feedback light and output light is accurately controlled, and stable output of narrow linewidth high-power laser is realized.The application can be widely applied in the technical field of semiconductor laser.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more particularly to an on-chip integrated narrow-linewidth high-power laser. Background Technology

[0002] Narrow-linewidth semiconductor lasers possess extremely high spectral purity, extremely high peak spectral density, ultra-long coherence length, and extremely low phase noise. As a core light source, they have important applications in precision measurement, optical atomic clocks, low-noise microwave generation, and time-frequency transmission. In these applications, to support long-distance transmission and detection, overcome high link losses, and improve the signal-to-noise ratio, there is an urgent need for high power, narrow linewidth, and fast tuning performance of lasers.

[0003] Laser self-injection locking technology combines a semiconductor laser with an external feedback microcavity, re-injecting the optical signal fed back from the microcavity into the semiconductor laser to achieve significant compression of the output linewidth and effective noise suppression. However, self-injection locking technology still faces the challenge of balancing linewidth reduction with output power: the linewidth reduction factor depends on the optical feedback strength. When the feedback is too weak, it is insufficient to effectively suppress the phase noise of the pump laser itself, resulting in limited linewidth reduction; while excessively strong optical feedback can induce oscillations in carrier concentration and photon density inside the semiconductor laser, causing the system to cross a critical threshold and enter the "coherent collapse" region, manifested as a sharp deterioration in linewidth, power jitter, and multimode oscillations. Although recent work has used cascaded tunable mirrors (such as Sagnac rings) to adjust the feedback strength, this "serial" post-feedback architecture has inherent physical limitations, as the optical feedback path and the main output path remain highly coupled. This architecture forces all the laser's energy to interact with the microcavity. When the laser self-injects and locks into the microcavity, most of the laser energy is clamped inside, resulting in a significant reduction in the final effective output power. Furthermore, when pursuing higher power output, the rapidly increasing photon density within the microcavity easily triggers stimulated Raman scattering, thermal nonlinear effects, the Kerr effect, and photorefractive effects in lithium niobate microcavities. This becomes a bottleneck limiting the maximum output power of the laser. Ultimately, microcavity-based self-injected lasers face a trade-off between narrow linewidth and output power. It is necessary to find the optimal operating point for the self-injection locking feedback strength while avoiding coherent collapse and nonlinear effects. This process often cannot simultaneously achieve high-speed tuning, high power, and narrow linewidth on-chip laser output, which is the core challenge currently facing self-injection locking technology. Summary of the Invention

[0004] In view of this, in order to address the technical shortcomings of existing narrow-linewidth high-power lasers that cannot simultaneously achieve narrow linewidth, high power, and high-speed tuning, this invention proposes an on-chip integrated narrow-linewidth high-power laser. This on-chip integrated laser adopts a self-injection locking structure, and the components work together in the following manner: Semiconductor laser: As a light source, it generates the initial laser beam.

[0005] Optical power distribution unit: splits the laser into two paths - one path is directly output as output light, and the other path is used as feedback light to enter the subsequent feedback loop.

[0006] Coupled straight waveguide: Couples the feedback light into the micro-ring resonator.

[0007] Micro-ring resonant cavity: as the main resonant unit, used to achieve core resonance with self-injection locking.

[0008] Sagnac on-chip mirror: used to feed the pump light back to the distributed feedback laser to achieve self-injection locking; Based on the above structure, its working principle is as follows: The optical power distribution unit integrates thermo-optical modulation electrodes to dynamically adjust the power distribution ratio between the feedback and output light. When the feedback light power is too high and the system approaches the coherent collapse boundary, the electrode voltage is finely adjusted through the thermo-optical effect to reduce the proportion of feedback light, thereby reducing the number of photons injected into the micro-ring resonator. This keeps the photon density fed back to the laser below the nonlinear threshold, suppressing the chaotic state caused by carrier density oscillations and preventing coherent collapse. When the feedback light power is insufficient and phase noise suppression is inadequate, leading to laser linewidth broadening, the proportion of feedback light is increased through the thermo-optical modulation electrodes. This enhances the stimulation of the laser's master mode, prolongs photon lifetime, and achieves linewidth compression. This adjustment mechanism is based on the Lang-Kobayashi rate equation and controls the feedback power within the optimal range.

[0009] Based on the above scheme, the present invention provides an on-chip integrated narrow linewidth high-power laser. Through a unique structural design and implementation method, combined with the Lang-Kobayashi equation to precisely control the feedback optical power, and with the high-quality factor micro-ring resonator, the laser linewidth can be narrowed to below kHz. At the same time, a high power output of ~20mW can be achieved through the optical path power distribution unit, breaking through the bottleneck of the trade-off between narrow linewidth and high power, and achieving synergistic output. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the structure of an on-chip integrated narrow linewidth high-power laser according to the present invention; Figure 2 A schematic diagram showing the variation of output optical power and linewidth narrowing factor under different power allocation ratios; Figure 3 A schematic diagram illustrating the laser linewidth variation under different feedback optical powers for the tuning optical path power distribution unit; Figure 4 This is a schematic diagram of the spectral characterization of the output light of the present invention. Detailed Implementation

[0011] Addressing the aforementioned technical bottlenecks, this invention, through unique structural design and implementation methods, completely solves the core problem that current self-injection locking technology cannot simultaneously achieve high-power and narrow-linewidth laser output on a thin-film lithium niobate integrated platform. Ultimately, it stably realizes on-chip laser output with high-speed tuning, high power, and narrow linewidth. This core achievement is not only the innovative value of this invention but also a key advantage that distinguishes it from existing technologies.

[0012] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0013] It should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. Unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0014] Furthermore, flowcharts are used in this application to illustrate the operations performed by the system according to embodiments of this application. It should be understood that the preceding or following operations are not necessarily performed precisely in sequence. Instead, the steps can be processed in reverse order or simultaneously. Additionally, other operations can be added to these processes, or one or more steps can be removed from them.

[0015] Reference Figure 1 This is a schematic diagram of an optional example of the on-chip integrated narrow-linewidth high-power laser proposed in this invention. All structures of this device are integrated on the same photonic integrated chip, and sequentially include: a semiconductor laser, an optical power distribution unit, a coupled straight waveguide, a high-quality factor microring resonator, and a Sagnac on-chip mirror. The optical power distribution structure is the core functional structure, used to achieve precise distribution of laser power, providing the foundation for narrow-linewidth high-power output. The connection relationships and functions of each component are as follows: Semiconductor laser: used to output initial laser light as a laser source; employs a distributed feedback laser with no built-in isolator, and has an output power of not less than 100mW.

[0016] Optical power distribution unit: Connected between the laser and the coupled straight waveguide, it adopts a 1×2 coupling ratio design (power distribution ratio 50:50) to split the laser light entering the optical waveguide into two paths. One path is transmitted to the micro-ring resonator to provide feedback light for self-injection locking to narrow the linewidth; the other path serves as the high-power output light. A thermo-optic modulation electrode is installed on it, which changes the refractive index of the material through the thermo-optic effect, thereby precisely controlling the power distribution between the feedback and output light. This avoids coherence collapse caused by excessive feedback and excitation of nonlinear effects, or excessive linewidth caused by insufficient feedback. This optical power distribution structure is integrated on the photonic chip, eliminating the need for additional external beam splitting components, simplifying the integrated structure, and providing high beam splitting accuracy, which is key to achieving both narrow linewidth and high power.

[0017] Coupled Straight Waveguide: Connected between the optical path power distribution unit and the high-quality factor micro-ring resonator, it is used to efficiently couple the feedback light split from the optical path power distribution structure into the micro-ring resonator. Its length and coupling spacing are optimized according to the self-injection locking theoretical model to achieve the optimal self-injection locking effect and reduce the power loss of the feedback light.

[0018] High-quality factor microring resonator: serving as the main resonant unit, it is used to achieve the core resonance function of self-injection locking, enabling narrowing of laser linewidth. Electro-optic modulation electrodes are set on the microring for high-speed frequency tuning.

[0019] The key difference between this invention and traditional self-injection locking schemes lies in the construction of a precise control mechanism for feedback optical power through the dynamic tuning of a unique optical path power distribution unit. This fundamentally resolves the core contradiction between "insufficient feedback leading to excessively wide linewidth" and "excessive feedback causing coherent collapse or nonlinear effects." Traditional on-chip self-injection locking laser schemes employ a "serial" structure, where feedback intensity and output power are intrinsically coupled and cannot be independently controlled. This results in either insufficient feedback, making it difficult to effectively suppress phase noise and narrow the linewidth to below the kHz level, or excessive feedback causing the laser to enter the coherent collapse region, manifesting as chaotic linewidth broadening, multimode oscillation, and single-mode output power that is difficult to exceed 10mW. Simultaneously, high intracavity photon density triggers parasitic nonlinear effects such as stimulated Raman scattering and the Kerr effect, further degrading output stability. This invention, through the design of a unique optical path power distribution structure, completely decouples the feedback channel and the output channel, enabling independent control of the feedback optical power and the output optical power. It successfully achieves an intrinsic linewidth of ~350Hz and an output power of ~20mW. At the same time, relying on the efficient electro-optic effect of the lithium niobate microcavity, the tuning rate is significantly improved, approximately 1000 times higher than that of commercial DFB lasers, thus significantly improving the overall performance of the laser.

[0020] The optical power distribution unit adjusts the power distribution ratio through thermo-optic modulation electrodes to precisely allocate the power proportion of the feedback light and the output light. When the feedback light power is too high, the system approaches the coherent collapse boundary. At this point, the electrode voltage is finely adjusted through the thermo-optic effect to reduce the proportion of the feedback light, thereby reducing the number of photons injected into the micro-ring resonator. This keeps the photon density fed back into the laser cavity below the nonlinear threshold, avoiding the chaotic state caused by carrier density oscillations and thus suppressing coherent collapse. When the feedback light power is insufficient, the self-injection locking effect of the micro-ring resonator cannot be fully utilized, and phase noise cannot be effectively suppressed, resulting in an excessively wide laser linewidth. In this case, the proportion of the feedback light is increased through the thermo-optic modulation electrodes, increasing the feedback light power and enhancing the stimulated emission of the laser's main mode, extending photon lifetime, effectively compressing the laser linewidth, and ultimately narrowing the linewidth to below the kHz level.

[0021] Through simulation and experimental verification using a self-injection locking theoretical model based on the Lang-Kobayashi rate equation, the optimal feedback power range was determined. At this range, the feedback optical power satisfies the linewidth compression requirements of self-injection locking while ensuring that coherence collapse and nonlinear effect thresholds are not reached, while the output light retains sufficient power. The thermo-optical modulation electrodes of the optical path power distribution structure can respond in real-time to changes in the feedback optical power, dynamically fine-tuning the power distribution ratio to ensure stable system operation within this optimal range. This achieves a synergistic output of narrow linewidth and high power, an active control mechanism that traditional fixed feedback ratio self-injection locking schemes cannot achieve.

[0022] This invention employs a distributed feedback laser without a built-in isolator, with an output power of 100mW and an output wavelength of 1550nm. Its output end is connected to the optical waveguide through a lens, and the coupling loss is controlled within 2dB.

[0023] The laser enters the integrated optical power distribution unit, which splits the laser into two paths through a 1×2 independent optical path design. One path is a feedback light transmitted to the coupled straight waveguide, and the other path is a direct output light. The power ratio of the two laser paths is precisely controlled through the thermo-optic effect to ensure that the output light retains sufficient power, while the feedback light meets the self-injection locking requirements, thereby realizing high-power narrow-linewidth laser output.

[0024] A coupled straight waveguide is used to couple the laser into the micro-ring resonator with a coupling spacing of 600 nm and a coupling efficiency of ≥90%. The design is optimized based on the self-injection locking theoretical model to ensure that the feedback light is efficiently coupled into the micro-ring resonator.

[0025] By utilizing the high quality factor characteristics of lithium niobate microring resonators, stimulated emission of the master mode of the laser cavity is enhanced through self-injection locking technology, thereby extending the equivalent cavity length of the laser and prolonging the photon lifetime. This results in significant compression of the output linewidth of the semiconductor laser and effective suppression of noise.

[0026] By utilizing the electro-optic modulation electrode on the lithium niobate microring resonator and relying on the efficient electro-optic effect of lithium niobate material, high-speed tuning and rapid frequency sweep of the laser frequency are achieved, with a tuning rate reaching the MHz level. At the same time, through the dynamic control of the optical path power distribution unit, the output optical power is maintained at a stable level of ~20mW, and the side-mode rejection ratio is ≥60dB.

[0027] Based on the overall structure and working principle of the on-chip integrated narrow-linewidth high-power laser described above, the beneficial effects of this invention also include: relying on integrated photonic materials with efficient electro-optic effects, high-speed tuning and rapid frequency sweeping at the MHz level are achieved through electro-optic modulation electrodes on the micro-ring resonant cavity, which improves the tuning rate by 1000 times compared to commercial DFB lasers, meeting the rapid response requirements of scenarios such as lidar and coherent optical communication; all structures are integrated on the same photonic chip, eliminating the need for additional external beam splitting or control components, simplifying the structure, reducing fabrication difficulty and large-scale application costs; at the same time, the integrated design reduces external environmental interference, resulting in high purity of the output laser spectrum (side-mode suppression ratio ≥60dB), and stable adaptation to various harsh operating environments such as ocean, plateau, and high temperature; it is compatible with various on-chip thin-film microcavity materials, including but not limited to lithium niobate, lithium tantalate, BTO, and other on-chip thin-film materials with high-speed electro-optic efficiency, eliminating the need for structural reconstruction for specific materials, greatly expanding the application scenarios and adaptability of the technology, and breaking the limitations of existing technologies on microcavity materials.

[0028] Reference Figure 2 As the power split ratio increases, the feedback light gradually strengthens, resulting in a significant linewidth narrowing effect. However, this also leads to a decrease in laser power due to more optical power being allocated to the feedback path. Further adjusting the split ratio to increase the feedback light intensity to the coherence collapse boundary causes a sharp deterioration in laser linewidth performance, while the laser output power continues to decline. Therefore, the system exhibits optimal noise suppression before the coherence collapse boundary, achieving optimal self-injection locking and enabling high-power, narrow-linewidth on-chip laser output simultaneously.

[0029] Reference Figure 3 As can be seen, the present invention precisely optimizes the feedback intensity at the end of region II (near the coherent collapse boundary), at which point the frequency noise of the laser is significantly suppressed, achieving the optimal self-injection locking state.

[0030] Reference Figure 4 As can be seen, the laser spectrum output by this invention has extremely high purity, and the side-mode suppression ratio reaches 60dB.

[0031] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. An on-chip integrated narrow-linewidth high-power laser, characterized in that, The components, in sequence, include a semiconductor laser, an optical power distribution unit, a coupled straight waveguide, a micro-ring resonator, and a Sagnac on-chip mirror, wherein: The semiconductor laser is used to output the initial laser beam; The optical power distribution unit is used to split the initial laser into two transmission paths, one as feedback light and the other as output light; The coupled straight waveguide is used to couple the feedback light to the micro-ring resonant cavity; The micro-ring resonant cavity, as the main resonant unit, is used to achieve self-injection locked core resonance; The Sagnac on-chip mirror is used to feed the pump light back to the distributed feedback laser, achieving self-injection locking.

2. The on-chip integrated narrow-linewidth high-power laser according to claim 1, characterized in that, The semiconductor laser is a distributed feedback laser with an output power of not less than 100mW and an output wavelength of 1550nm.

3. The on-chip integrated narrow-linewidth high-power laser according to claim 1, characterized in that, The optical power distribution unit adopts a 1×2 coupling ratio design.

4. The on-chip integrated narrow-linewidth high-power laser according to claim 3, characterized in that, The optical path power distribution unit is equipped with a thermo-optic modulation electrode, which changes the refractive index of the material through the thermo-optic effect to control the power distribution between the feedback light and the output light.

5. The on-chip integrated narrow-linewidth high-power laser according to claim 1, characterized in that, An electro-optic modulation electrode is provided on the micro-ring resonant cavity.

6. The on-chip integrated narrow-linewidth high-power laser according to claim 1, characterized in that, Its working principle is as follows: The optical path power distribution unit adjusts the power distribution ratio through thermo-optic modulation electrodes to allocate the power ratio of feedback light and output light; When the feedback light power is too high, the system approaches the coherent collapse boundary. At this time, the electrode voltage is finely adjusted through the thermo-optic effect to reduce the proportion of feedback light and reduce the number of photons injected into the micro-ring resonator, so that the photon density fed back into the laser cavity is maintained below the nonlinear threshold, avoiding the chaotic state caused by carrier density oscillation and suppressing the occurrence of coherent collapse. When the feedback light power is insufficient, phase noise cannot be suppressed, resulting in an excessively wide laser linewidth. In this case, the proportion of feedback light is increased by using a thermo-optic modulation electrode to enhance the feedback light's effect on stimulated emission of the laser's main mode, thereby extending photon lifetime and compressing the laser linewidth.

7. The on-chip integrated narrow-linewidth high-power laser according to claim 6, characterized in that, Its working principle also includes: The optimal feedback power range was determined based on the Lang-Kobayashi rate equation.

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