Hybrid integrated semiconductor laser and bandwidth increasing method

Abstract

The invention provides a hybrid integrated semiconductor laser and a bandwidth increasing method, and relates to the field of optoelectronic devices. The hybrid integrated semiconductor laser comprises a semiconductor laser chip and a silicon nitride outer cavity chip, an optical feedback regulation and control structure is integrated in the silicon nitride outer cavity chip, active control over feedback light is achieved, photon-photon resonance and detuning loading effects are further introduced, and the modulation bandwidth of a directly modulated laser is cooperatively improved. The hybrid integrated semiconductor laser provided by the invention not only is simple in structure and high in preparation yield, but also can carry out secondary improvement on the bandwidth of a finished laser, and has the advantages of flexible regulation and control, easy integration and wide applicability.

Description

Technical Field

[0001] The invention belongs to the field of optoelectronic device technology, and in particular relates to a hybrid integrated semiconductor laser and a method for improving bandwidth. Background Technology

[0002] With the explosive growth of cloud computing, the Internet of Things (IoT), and artificial intelligence (AI), the demand for network data capacity and transmission rates continues to rise, and 400G / 800G Ethernet technology is becoming the mainstream solution for next-generation data centers. Against this backdrop, directly modulated semiconductor lasers, as an irreplaceable light source for data centers, present a key challenge in improving their modulation bandwidth and speed. However, traditional directly modulated lasers are limited by relaxation oscillations and chip parasitic parameters, typically making it difficult to exceed 25GHz in bandwidth.

[0003] While existing technologies have achieved bandwidth improvements through the introduction of detuning loading effects and photon-photon resonance effects, these solutions typically employ monolithically integrated composite cavity structures, which suffer from low yield rates and sensitivity to changes in chip structure parameters and the environment. Therefore, they have not been widely adopted in the commercial field. Currently, commercially available direct-modulated lasers still primarily rely on traditional bandwidth enhancement methods. Due to the difficulty in achieving breakthroughs in bandwidth, coupled with continuously increasing market demands for communication speeds, there is a significant backlog of low-bandwidth laser chip inventory.

[0004] On the other hand, hybrid integration technology can use silicon nitride-based waveguide structures as external cavities for lasers. This technology has been applied in areas such as narrow-linewidth laser coherent optical communication, frequency-modulated continuous-wave lidar, and wide-range laser wavelength tuning. However, most current research still focuses on using silicon nitride external cavities to achieve narrow linewidth and wavelength tuning. Only a few studies have attempted to use external cavities to increase the bandwidth of directly modulated lasers. Moreover, these schemes are usually based on complex self-injection locking mechanisms, which have the problem of difficulty in precisely controlling the intensity of feedback light. However, the control of optical feedback is precisely the key to realizing the photon-photon resonance effect.

[0005] In summary, existing technologies suffer from drawbacks such as complex structures, low yield rates, and inflexible feedback control. Therefore, there is an urgent need for a hybrid integrated solution that is simple in structure, flexible in control, has a high yield rate, and can effectively improve the bandwidth of directly modulated lasers. Summary of the Invention

[0006] In view of this, the invention provides a hybrid integrated semiconductor laser and a method for improving bandwidth, which aims to flexibly introduce photon-photon resonance and detuning loading effects by utilizing an optical feedback control structure in a silicon nitride external cavity chip, so as to improve the bandwidth of the finished laser.

[0007] The technical solution of the invention is implemented as follows: An embodiment of the invention provides a hybrid integrated semiconductor laser, which includes a semiconductor laser chip and a silicon nitride external cavity chip. An optical feedback modulation structure is integrated on the silicon nitride external cavity chip. The optical feedback modulation is used to control the intensity and phase of the optical signal from the silicon nitride external cavity chip to the semiconductor laser chip. The optical feedback is weak feedback, with a proportion of less than or equal to 10%, to introduce photon-photon resonance and detuning loading effects into the semiconductor laser chip, thereby improving its modulation bandwidth.

[0008] In one embodiment, the optical feedback control structure includes a first tapered waveguide, a straight waveguide, a phase-shift heater, a multimode interferometer, a microring, and a microring heater; the phase-shift heater is integrated on the straight waveguide and is used to control the phase of the feedback light; the microring is provided with a microring heater for adjusting the resonant wavelength of the microring.

[0009] In one embodiment, the multimode interference coupler is used to split the optical signal incident on the silicon nitride chip into two paths, which are then coupled to the waveguides on the upper and lower sides of the microring, respectively, and the coupling strength between the microring and the waveguides on both sides is consistent.

[0010] In one embodiment, the circumference of the microring is set in the range of 1-5 mm so that the resonant frequency of the microring matches the target photon-photon resonant frequency.

[0011] In one embodiment, the optical feedback control structure includes a first tapered waveguide, a straight waveguide, a phase-shifting heater, a directional coupler, a Mach-Zehnder interferometer, a Sagnac ring, and a Mach-Zehnder interferometer heater; the Mach-Zehnder interferometer heater is integrated on one arm of the Mach-Zehnder interferometer for controlling the intensity of the feedback light through interference effects.

[0012] In one embodiment, the semiconductor laser chip is a direct modulation laser chip, which includes at least a DFB laser and a DBR laser, and the operating band of the direct modulation laser chip covers at least the C-band or the O-band.

[0013] In one embodiment, the semiconductor laser chip and the silicon nitride external cavity chip are coupled through the first tapered waveguide structure, and the light-emitting end face of the semiconductor laser chip is cut with an 8° tilt angle to reduce reflection.

[0014] This invention also provides a method for improving bandwidth, the method being based on a hybrid integrated semiconductor laser, the hybrid integrated semiconductor laser comprising a semiconductor laser chip and a silicon nitride external cavity chip; the silicon nitride external cavity chip integrates an optical feedback modulation structure, the optical feedback modulation being used to control the intensity and phase of the optical signal from the silicon nitride external cavity chip to the semiconductor laser chip, and the optical feedback being weak feedback, the weak feedback accounting for less than or equal to 10%, to introduce photon-photon resonance effect and detuning loading effect in the semiconductor laser chip, thereby improving its modulation bandwidth; the bandwidth improvement method includes: The phase and intensity of the optical signal fed back to the semiconductor laser chip are controlled by the optical feedback control structure, thereby exciting the photon-photon resonance effect and providing a basic gain for bandwidth enhancement. By combining the frequency chirp characteristics generated during the direct modulation process of semiconductor laser chips, and utilizing the reflectivity difference of silicon nitride external cavity chips at different wavelengths, a detuning loading effect on the laser is achieved. The inherent bandwidth limitation of the semiconductor laser chip is removed through the synergistic effect of the photon-photon resonance effect and the detuning loading effect, thereby improving its modulation bandwidth.

[0015] In one embodiment, the small-signal -3dB modulation bandwidth of the hybrid integrated semiconductor laser is higher than the inherent bandwidth of the semiconductor laser chip.

[0016] The present invention has the following beneficial effects: 1. This invention provides a hybrid integrated semiconductor laser and a method for improving bandwidth, which can achieve a secondary improvement in the bandwidth of the finished laser.

[0017] 2. This invention provides a hybrid integrated semiconductor laser and a method for increasing bandwidth, offering two typical optical feedback control methods with strong implementation flexibility and applicability.

[0018] 3. This invention provides a hybrid integrated semiconductor laser and a method for improving bandwidth. By controlling the feedback light of the optical feedback control structure in the silicon nitride external cavity chip, the introduction and control of photon-photon resonance and detuning loading effects are realized, thereby improving the bandwidth. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1This is a schematic diagram of the bandwidth enhancement method for the hybrid integrated semiconductor laser and bandwidth enhancement method proposed in this invention. Figure 2 This is a schematic diagram of the structure of a first embodiment of the hybrid integrated semiconductor laser and the method for increasing bandwidth proposed in this invention; Figure 3 The reflectivity of the external cavity reflection spectrum of the hybrid integrated semiconductor laser and the bandwidth enhancement method proposed in this invention, as well as the main mode of the semiconductor laser chip, are shown. Figure 4 This is the small-signal response of Embodiment 1 of the hybrid integrated semiconductor laser and bandwidth enhancement method proposed in this invention; Figure 5 This is a schematic diagram of the structure of Embodiment 2 of the hybrid integrated semiconductor laser and bandwidth enhancement method proposed in this invention; Figure 6 The external cavity reflection spectrum of the hybrid integrated semiconductor laser and the bandwidth enhancement method proposed in this invention is the reflectivity of the heater voltage of a Mach-Zehnder interferometer under different Mach-Zehnder interferometer voltages. Figure 7 This is the small-signal response of Embodiment 2 of the hybrid integrated semiconductor laser and bandwidth enhancement method proposed in this invention.

[0021] Explanation of reference numerals in the attached figures: 1. Semiconductor laser chip; 2. Silicon nitride external cavity chip; 21. Optical feedback control structure; 211. First tapered waveguide; 212. Straight waveguide; 213. Phase shift heater; 214. Multimode interferometer; 215. Microring; 216. Microring heater; 217. Directional coupler; 218. Mach-Zehnder interferometer; 219. Sanjack ring; 220. Mach-Zehnder interferometer heater; 221. Second tapered waveguide. Detailed Implementation

[0022] The technical solutions of the embodiments of the invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the invention, and not all of them. Based on the embodiments of the invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the invention.

[0023] It should be noted that if the embodiments of the invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0024] Furthermore, if the embodiments of the invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of a person skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the invention.

[0025] Figure 1 This diagram illustrates the basic principle of this invention for improving bandwidth. The feedback light is actively modulated through an optical feedback control structure within the silicon nitride external cavity chip. The optical feedback should be weak and not exceed 10%. The optical feedback control structure includes, but is not limited to: using a micro-ring heater to change the free spectral position of the micro-ring, thereby adjusting the reflectivity to a fixed wavelength; or using a Mach-Zehnder interferometer heater to control interference, achieving constructive or destructive interference, and thus controlling the intensity of the feedback light. Based on this, by precisely controlling the phase and intensity of the feedback light, a photon-photon resonance effect is excited; simultaneously, combined with the frequency chirp generated during the modulation of the semiconductor laser, the difference in reflectivity of the external cavity chip at different wavelengths is used to achieve a detuning loading effect. The synergistic effect of these two effects can increase the modulation bandwidth of the laser.

[0026] Among them, the weak feedback characteristic of optical feedback is crucial, and its proportion is strictly controlled to be less than or equal to 10%. This design is to effectively introduce photon-photon resonance effect and detuning loading effect into semiconductor laser chip, while avoiding the adverse effects of excessive feedback on laser stability.

[0027] The photon-photon resonance effect is achieved by introducing optical feedback at a specific frequency (such as around 15 GHz) into a semiconductor laser chip, which causes coherent superposition and energy redistribution of photon states within the cavity, thereby forming a resonance peak at a specific frequency and providing an additional gain mechanism for improving the modulation bandwidth of the laser.

[0028] The detuning effect refers to the frequency chirping of the output optical signal during direct modulation of a semiconductor laser chip due to changes in the injected current; that is, different modulation frequencies correspond to different wavelength shifts. The reflection spectrum of a silicon nitride external cavity chip has a specific wavelength dependence. When the wavelength of the laser output light changes due to frequency chirping, the reflectivity of the external cavity chip for different wavelengths of light varies. This difference causes the intensity of the optical signal fed back to the laser chip to change with the modulation frequency, which is equivalent to applying a frequency-dependent "detuning" feedback to the laser.

[0029] The hybrid integrated semiconductor laser provided by this invention includes a semiconductor laser chip and a silicon nitride (SiN) external cavity chip. An optical feedback control structure is integrated on the SiN external cavity chip. This optical feedback control is used to regulate the intensity and phase of the optical signal from the SiN external cavity chip to the semiconductor laser chip. The optical feedback is weak, with a weak feedback ratio of less than or equal to 10%, to introduce photon-photon resonance and detuning loading effects into the semiconductor laser chip, thereby improving its modulation bandwidth. The hybrid integrated semiconductor laser provided by this invention achieves flexible control of the intensity and phase of the optical signal fed back to the semiconductor laser chip by hybrid integrating the semiconductor laser chip and the SiN external cavity chip and utilizing the optical feedback control structure integrated on the SiN external cavity chip. By strictly controlling the optical feedback within the weak feedback range (ratio less than or equal to 10%), it can effectively excite the photon-photon resonance effect, providing a basic gain for bandwidth improvement, and also combine the frequency chirp characteristics of direct modulation by the semiconductor laser chip to achieve a detuning loading effect by utilizing the reflectivity difference of the SiN external cavity chip at different wavelengths. The synergistic effect of these two effects can, to some extent, remove the inherent bandwidth limitations of semiconductor laser chips, thereby increasing their modulation bandwidth and alleviating the problem of low-bandwidth laser chip inventory backlog.

[0030] Example 1: This embodiment provides a hybrid integrated semiconductor laser structure based on a microring resonator. Figure 2 The schematic diagram shows its structure. It includes: a semiconductor laser chip 1, a silicon nitride external cavity chip 2, and an optical feedback control structure 21 integrated on the silicon nitride external cavity chip 2. The optical feedback control structure 21 includes a first tapered waveguide 211, a straight waveguide 212, a phase-shift heater 213, a multimode interferometer 214, a micro-ring 215, and a micro-ring heater. After the laser is output from the semiconductor laser chip 1, it is coupled into the silicon nitride external cavity chip 2 via the first tapered waveguide 211.

[0031] Semiconductor laser chip 1 is a traditional direct-modulation semiconductor laser with a communication band, such as C-band or O-band, and its structure can be in the form of DFB laser or DBR, etc.

[0032] The C-band refers to the communication window of 1530-1565nm, which has low fiber loss and dispersion characteristics and is widely used in long-distance fiber optic communication systems. The O-band refers to the communication window of 1260-1360nm, which has extremely low fiber dispersion and is suitable for short-distance, high-speed communication scenarios.

[0033] DFB lasers, short for distributed feedback lasers, achieve single-mode output by introducing a periodic grating structure in the active region and utilizing the Bragg reflection principle. They offer advantages such as high wavelength stability and narrow linewidth, and are widely used in high-speed optical communication systems. DBR lasers, on the other hand, are distributed Bragg reflection lasers. Their gratings are located outside the active region, and wavelength tuning can be achieved by adjusting the injection current or temperature in the grating region, offering greater flexibility.

[0034] After laser coupling into the silicon nitride external cavity chip 2, the laser sequentially passes through a first tapered waveguide 211, a straight waveguide 212, a multimode interferometer 214, a microring 215, and back to the first tapered waveguide 211. Above the straight waveguide is a phase-shift heater 213, which controls the phase delay by applying a voltage. Above the microring 215 is a microring heater 216, which shifts the free spectral position of the microring 215 by applying a voltage, thereby changing the center wavelength of the reflection spectrum. Figure 3 As shown.

[0035] The operating wavelength of the silicon nitride external cavity chip 2 should be the same as that of the semiconductor laser chip 1.

[0036] The laser input end can be tilted at an 8° angle to reduce reflected light during laser coupling.

[0037] The primary purpose of the first tapered waveguide 211 is to improve coupling efficiency, allowing more energy from the laser output by the semiconductor laser chip 1 to enter the silicon nitride external cavity chip 2.

[0038] Multimode interferometer 214 splits the incident light into two paths, which are coupled to the waveguides on the upper and lower sides of microring 215, respectively. The coupling strength between microring 215 and the waveguides on both sides is consistent, ensuring symmetrical transmission of the optical field. By adjusting the voltage of microring 215, the effective refractive index of microring 215 can be changed, thereby shifting the center wavelength of its reflection spectrum. When the center wavelength of the reflection spectrum is located on the long-wavelength side of the main mode of semiconductor laser chip 1, the detuning loading effect can be effectively excited; at the same time, by controlling the phase of the feedback light through phase-shift heater 4, the photon-photon resonance effect can be further enhanced, such as... Figure 4 As shown.

[0039] The laser in the microring 215 needs to meet the requirement that the round-trip phase is an integer multiple of 2π to resonate, and its length is preferably between 1-5mm to ensure that its resonant frequency matches the photon-photon resonant frequency.

[0040] When the circumference of the microring 215 is within this range, its corresponding free spectral range can match the relaxation oscillation frequency of the semiconductor laser chip 1, thus providing suitable frequency conditions for the generation of photon-photon resonance effect. In actual operation, the laser output from the semiconductor laser chip 1 is coupled into the straight waveguide 212 of the silicon nitride external cavity chip 2 via the first tapered waveguide 211. At this time, the phase-shift heater 213 starts working, changing the phase of the light transmitted in the straight waveguide 212 by controlling the voltage applied to it. Next, the optical signal enters the multimode interferometer 214, which uniformly splits the incident light signal into two paths, which are then coupled to the waveguides on the upper and lower sides of the microring 215, respectively. Because the coupling strength between the microring 215 and the waveguides on both sides is designed to be consistent, the optical field can achieve symmetrical transmission within the microring 215, ensuring the stability and symmetry of the resonance process. Subsequently, the micro-ring heater 216 functions, adjusting its voltage to change the temperature of the micro-ring 215, thereby adjusting the effective refractive index of the micro-ring 215 and ultimately controlling the resonant wavelength of the micro-ring 215. Figure 3 As shown, by changing the voltage of the micro-ring heater 216, the center wavelength of the reflection spectrum of the micro-ring 215 shifts. When the center wavelength of the reflection spectrum is tuned to the long-wavelength side of the main mode of the semiconductor laser chip 1, the detuning loading effect can be achieved by utilizing the reflectivity difference of the silicon nitride external cavity chip 2 at different wavelengths, combined with the frequency chirp characteristics generated during the direct modulation process of the semiconductor laser chip 1. This detuning loading effect works synergistically with the photon-photon resonance effect excited by the phase modulation of the feedback light phase by the phase-shift heater 213, jointly removing the inherent bandwidth limitation of the semiconductor laser chip 1 originally constrained by relaxation oscillations and chip parasitic parameters. Figure 4 The small-signal response curve of Embodiment 1 clearly shows that after adopting this hybrid integrated structure based on microring resonators, the small-signal -3dB modulation bandwidth of the hybrid integrated semiconductor laser is significantly improved, which is significantly higher than the inherent bandwidth of the semiconductor laser chip 1 itself, fully verifying the effectiveness of this structure in improving the modulation bandwidth.

[0041] Example 2: This embodiment provides a hybrid integrated laser structure based on a Sagnac ring and a Mach-Zehnder interferometer, such as Figure 5 As shown. The difference from Embodiment 1 lies in the optical feedback control structure 21 in the silicon nitride external cavity chip 2. The optical feedback control structure 21 includes a first tapered waveguide 211, a straight waveguide 212, a phase-shift heater 213, a directional coupler 217, a Mach-Zehnder interferometer 218, a Sanigauch ring 219, and a Mach-Zehnder interferometer heater 220.

[0042] After the laser is coupled into the silicon nitride external cavity chip 2, it is split into two paths by the directional coupler 217, which respectively enter the two arms of the Mach-Zehnder interferometer 218. After reflection by the Sanigauch ring 219, the beam is recombined and finally output through the second tapered waveguide 221. One arm of the Mach-Zehnder interferometer 218 is equipped with a Mach-Zehnder interferometer heater 220. By adjusting the voltage of the Mach-Zehnder interferometer heater 220, the phase of the arm can be changed, thereby achieving constructive or destructive interference and controlling the intensity of the feedback light, such as... Figure 6 As shown.

[0043] The Sagnac ring 219, as a key reflective element in the optical feedback path, is structurally designed to ensure stable transmission and reflection of the optical signal within the ring. When the optical signal enters the Sagnac ring 219 from the two arms of the Mach-Zehnder interferometer 218, it propagates along the clockwise and counterclockwise directions of the ring. Due to the arc-shaped structure of the Sagnac ring 219, these two counter-propagating beams travel the same optical path within the ring and then re-converge at the directional coupler 217. By adjusting the voltage of the Mach-Zehnder interferometer heater 220, the phase difference between the two arms of the Mach-Zehnder interferometer 218 can be controlled, thereby achieving modulation of the intensity of the feedback light after convergence.

[0044] For example, when a voltage is applied to create a π phase difference between the two arms, destructive interference can be achieved, resulting in the minimum intensity of the feedback light; while when the phase difference is 0, constructive interference is achieved, maximizing the intensity of the feedback light. This control over the intensity of the feedback light provides an important guarantee for exciting the photon-photon resonance effect. Simultaneously, by combining the phase-shift heater 213 with the adjustment of the feedback light phase, the synergistic effect of the photon-photon resonance effect and the detuning loading effect can be further optimized. The laser output from the semiconductor laser chip 1 is efficiently coupled through the first tapered waveguide 211 into the straight waveguide 212 of the silicon nitride external cavity chip 2. After the phase-shift heater 213 performs preliminary phase adjustment on the transmitted light, the optical signal enters the directional coupler 217. The directional coupler 217 splits the optical signal into two paths at a certain ratio (e.g., 50:50), which are injected into the two waveguide arms of the Mach-Zehnder interferometer 218, respectively. In the Mach-Zehnder interferometer 218, the Mach-Zehnder heater 220 on one arm changes the effective refractive index of that arm by applying different voltages, thereby adjusting the optical path difference between the two arms. The optical signal output from the Mach-Zehnder interferometer 218 enters the Sagnac ring 219, is reflected within the ring, and returns to the Mach-Zehnder interferometer 218 along the original path. At this point, the two returning optical signals interfere again within the Mach-Zehnder interferometer 218, and the interference result is determined by the previously set phase difference between the two arms. The interfered optical signals are combined via the directional coupler 217 and fed back to the semiconductor laser chip 1 through the second tapered waveguide 221. By adjusting the voltage of the Mach-Zehnder interferometer heater 220, such as... Figure 6As shown, the feedback light intensity can be continuously adjusted over a wide range. When the feedback light intensity and phase are tuned to appropriate values, a photon-photon resonance effect can be excited, and a detuning loading effect can be achieved by utilizing the wavelength-selective reflection of the external cavity and the frequency chirp characteristics of the laser. Figure 7 The small-signal response curve of Example 2 shows that the hybrid integrated structure based on the Sagnac ring and the Mach-Zehnder interferometer can also significantly improve the modulation bandwidth of the laser, and its feedback intensity control method is more direct and linear, providing another effective way to optimize bandwidth in different application scenarios.

[0045] This invention, through the two aforementioned structural embodiments, achieves active control of optical feedback, thereby effectively stimulating the photon-photon resonance effect and the detuning loading effect. For example... Figure 3 and Figure 6 As shown, by adjusting the heater voltage, the external cavity reflectivity can be flexibly controlled, thereby optimizing the bandwidth expansion effect. Figure 4 and Figure 7 As shown, the method proposed in this invention can increase the -3dB modulation bandwidth of the laser while maintaining a good frequency response.

[0046] This invention also provides a method for increasing bandwidth, which is based on the hybrid integrated semiconductor laser provided in the above embodiments. The method for increasing bandwidth includes: By controlling the phase and intensity of the optical signal fed back to the semiconductor laser chip through an optical feedback control structure, a photon-photon resonance effect is excited, thereby providing a basic gain for bandwidth enhancement.

[0047] By combining the frequency chirp characteristics generated during the direct modulation process of semiconductor laser chips, and utilizing the reflectivity difference of silicon nitride external cavity chips at different wavelengths, a detuning loading effect on the laser is achieved.

[0048] By leveraging the synergistic effect of photon-photon resonance and detuning loading, the inherent bandwidth limitation of semiconductor laser chips is removed, thereby enhancing their modulation bandwidth.

[0049] In implementing this bandwidth enhancement method, it is first necessary to ensure that the operating wavelengths of the semiconductor laser chip and the silicon nitride external cavity chip are matched, for example, both are set in the communication C-band or O-band. After the laser is output from the semiconductor laser chip, it is efficiently coupled into the external cavity system through the first tapered waveguide on the silicon nitride external cavity chip. Inside the silicon nitride external cavity chip, the optical feedback control structure begins to operate. Taking the microring resonator structure of Embodiment 1 as an example, the phase shift heater adjusts the phase of the transmitted light in the straight waveguide to meet the phase conditions required for the photon-photon resonance effect; at the same time, the microring heater adjusts the center wavelength of its reflection spectrum by changing the microring temperature, so that it is located on the long-wavelength side of the main mode of the semiconductor laser chip, thereby introducing a detuning loading effect by utilizing the difference in reflectivity of the microring for different wavelengths of light when the laser is directly modulated to generate frequency chirp. For the Saniac ring and Mach-Zehnder interferometer structure in Example 2, the phase difference between the two arms is adjusted by the Mach-Zehnder interferometer heater to control the feedback light intensity. Combined with phase-shifting heaters to modulate the phase, the excitation of photon-photon resonance and detuning loading effects is also achieved. Throughout the process, the optical feedback intensity must be strictly controlled within a weak feedback range (less than or equal to 10%) to avoid excessive feedback affecting the laser's stability. Simultaneously, it must be ensured that the two effects work synergistically to effectively overcome the bandwidth limitations imposed by the semiconductor laser chip's relaxation oscillation frequency and parasitic parameters, ultimately achieving a significant increase in modulation bandwidth. By precisely controlling the voltage of each heater in the optical feedback control structure, the intensity of the two effects can be flexibly optimized, thereby obtaining the best bandwidth expansion effect under different operating conditions.

[0050] In one embodiment, the small-signal -3dB modulation bandwidth of the hybrid integrated semiconductor laser is higher than the inherent bandwidth of the semiconductor laser chip.

[0051] The small-signal -3dB modulation band refers to the modulation frequency range corresponding to when the output optical power drops to √2 / 2 (approximately 70.7%) of the maximum output power in the small-signal modulation response of a laser. It is a key indicator for measuring the high-speed modulation capability of a laser. This indicator directly reflects the laser's ability to maintain signal integrity under high-frequency modulation. The higher the bandwidth, the greater the amount of data transmitted by the laser per unit time, and the better it meets the signal transmission rate requirements of high-speed optical communication systems. This invention effectively breaks through the bandwidth bottleneck of traditional semiconductor laser chips through the synergistic effect of photon-photon resonance and detuning loading, resulting in a significant improvement in the small-signal -3dB modulation bandwidth of the hybrid integrated laser compared to the inherent bandwidth of the chip itself. This provides a practical technical solution for solving the application limitations of low-bandwidth laser chips and improving their applicability in the field of high-speed communication.

[0052] The inherent bandwidth of a semiconductor laser chip refers to the maximum modulation bandwidth determined solely by the physical structure and material properties of the semiconductor laser chip itself, without introducing any external optical feedback or special control structures. It is primarily limited by the relaxation oscillation frequency caused by the carrier lifetime in the active region of the chip, as well as by parameters such as parasitic capacitance and inductance introduced by the chip packaging and internal structure. Typically, the inherent bandwidth of traditional directly modulated semiconductor laser chips is relatively low, making it difficult to meet the demands of high-speed optical communication systems for ultra-high-capacity data transmission. This is the fundamental reason why this invention improves its modulation bandwidth through a hybrid integrated external cavity structure.

[0053] In practical applications, this bandwidth enhancement method can effectively improve the performance of semiconductor laser chips with limited modulation bandwidth. For example, for a DFB laser chip with an inherent -3dB modulation bandwidth of 25GHz, after adopting the hybrid integrated structure and bandwidth enhancement method of this invention, its -3dB modulation bandwidth can be increased to over 35GHz. Furthermore, the frequency response curve is relatively flat and has minimal fluctuations throughout the entire modulation bandwidth range, meeting the stringent requirements of high-speed optical communication systems for laser modulation bandwidth. In addition, this method is simple to operate; precise control of the feedback light phase and intensity can be achieved by applying different voltages to the heater on the silicon nitride external cavity chip, without requiring complex structural modifications to the semiconductor laser chip itself. This reduces manufacturing difficulty and cost, demonstrating strong practicality and operability. Simultaneously, due to the excellent optical properties and thermal stability of silicon nitride, the hybrid integrated semiconductor laser maintains stable performance during operation and is less affected by changes in ambient temperature, further expanding its application range.

[0054] The above description is merely an exemplary embodiment of the invention and does not limit the patent scope of the invention. Any equivalent structural transformations made using the contents of the invention specification and drawings under the technical concept of the invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the invention.

Claims

1. A hybrid integrated semiconductor laser, characterized in that, include: Semiconductor laser chips and silicon nitride external cavity chips; The silicon nitride external cavity chip integrates an optical feedback control structure. The optical feedback control is used to control the intensity and phase of the optical signal from the silicon nitride external cavity chip to the semiconductor laser chip. The optical feedback is weak feedback, and the weak feedback accounts for less than or equal to 10%, so as to introduce photon-photon resonance effect and detuning loading effect in the semiconductor laser chip to improve its modulation bandwidth.

2. The hybrid integrated semiconductor laser according to claim 1, characterized in that, The optical feedback control structure includes a first tapered waveguide, a straight waveguide, a phase-shift heater, a multimode interferometer, a microring, and a microring heater; the phase-shift heater is integrated on the straight waveguide and is used to control the phase of the feedback light; the microring is equipped with a microring heater for adjusting the resonant wavelength of the microring.

3. The hybrid integrated semiconductor laser according to claim 2, characterized in that, The multimode interference coupler is used to split the optical signal incident on the silicon nitride chip into two paths, which are then coupled to the waveguides on the upper and lower sides of the microring, respectively, and the coupling strength between the microring and the waveguides on both sides is consistent.

4. The hybrid integrated semiconductor laser according to claim 2, characterized in that, The circumference of the microring is set in the range of 1-5mm so that the resonant frequency of the microring matches the target photon-photon resonant frequency.

5. The hybrid integrated semiconductor laser according to claim 1, characterized in that, The optical feedback control structure includes a first tapered waveguide, a straight waveguide, a phase-shifting heater, a directional coupler, a Mach-Zehnder interferometer, a Sagnac ring, and a Mach-Zehnder interferometer heater; the Mach-Zehnder interferometer heater is integrated on one arm of the Mach-Zehnder interferometer and is used to control the intensity of the feedback light through interference effect.

6. The hybrid integrated semiconductor laser according to claim 2 or 5, characterized in that, The semiconductor laser chip and the silicon nitride external cavity chip are coupled through the first tapered waveguide structure. The light-emitting end face of the semiconductor laser chip is cut with an 8° tilt angle to reduce reflection.

7. The hybrid integrated semiconductor laser according to claim 1, characterized in that, The semiconductor laser chip is a direct modulation laser chip, which includes at least a DFB laser and a DBR laser, and the operating band of the direct modulation laser chip covers at least the C-band or the O-band.

8. A method for increasing bandwidth, characterized in that, Based on the hybrid integrated semiconductor laser according to any one of claims 1 to 7, the method for increasing bandwidth includes: The phase and intensity of the optical signal fed back to the semiconductor laser chip are controlled by the optical feedback control structure, thereby exciting the photon-photon resonance effect and providing a basic gain for bandwidth enhancement. By combining the frequency chirp characteristics generated during the direct modulation process of semiconductor laser chips, and utilizing the reflectivity difference of silicon nitride external cavity chips at different wavelengths, a detuning loading effect on the laser is achieved. The inherent bandwidth limitation of the semiconductor laser chip is removed through the synergistic effect of the photon-photon resonance effect and the detuning loading effect, thereby improving its modulation bandwidth.

9. The method for increasing bandwidth according to claim 8, characterized in that, The small-signal -3dB modulation bandwidth of the hybrid integrated semiconductor laser is higher than the inherent bandwidth of the semiconductor laser chip.

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