On-chip integrated multi-frequency narrow-linewidth semiconductor laser optical pulse device and preparation method thereof

Abstract

The invention relates to an on-chip integrated multi-frequency narrow-linewidth semiconductor laser optical pulse device and a preparation method thereof. The device comprises a silicon substrate; the laser signal processing device is positioned on the silicon substrate and is processed and prepared through a semiconductor technology; the laser signal processing device comprises a silicon-based waveguide grating, a silicon-based optical switch structure, a silicon-based frequency shifter structure and a silicon-based beam combining structure which are connected in sequence; the single-mode output semiconductor laser is processed and prepared through a semiconductor technology and connected to the silicon substrate through heterogeneous bonding, the waveguide structure is a single-mode waveguide, the semiconductor laser is connected to the silicon substrate through heterogeneous bonding, and the semiconductor laser is coupled with the silicon-based waveguide grating through an end face. The method comprises the following steps: preparing a laser signal processing device; processing and preparing a semiconductor laser through a semiconductor technology; the two devices are placed on a silicon substrate. According to the invention, external elements are not needed, the loss of light in the transmission process is small, and the process complexity is not improved in the packaging process.

Description

Technical Field

[0001] This disclosure relates to semiconductor laser pulses, and in particular to an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device and its fabrication method. Background Technology

[0002] A multi-frequency optical pulse generation module typically refers to a device or system capable of generating optical pulses of multiple frequencies. This technology is widely used in the fields of optics and lasers, including optical communication, lidar, and spectral analysis.

[0003] The principle of existing multi-frequency optical pulse modules is to modulate the original laser with external equipment to generate new laser pulses with frequencies different from the original laser, thereby achieving multi-frequency optical output. The "multi-frequency" in a multi-frequency laser refers to the multi-frequency nature of the output laser, which is independent of the original laser. Therefore, the original laser can be either single-frequency or multi-frequency. According to modulation techniques, existing multi-frequency optical pulse generation methods mainly include multi-frequency light generation through nonlinear optical effects and multi-frequency light generation through tuned lasers.

[0004] Nonlinear optics technology has wide applications in the generation of multi-frequency optical pulses. Under high-intensity electromagnetic fields, the optical response of a nonlinear crystal is no longer linearly related to the intensity of incident light, exhibiting nonlinear behavior dependent on light intensity, which is called the nonlinear effect. When the nonlinear effect occurs, the incident single-frequency or multi-frequency laser will produce phenomena such as mixing and self-phase modulation, and the phase of the frequency changes with the light intensity, thus achieving spectral broadening of the output optical pulse. Mainstream nonlinear optical technologies include self-phase modulation, wavelength division multiplexing (e.g., Chinese patent CN102412894A, "Method and Apparatus for Multi-Frequency Probe Time-Division Multiplexed Coherent Optical Time-Domain Reflectometer"), Raman scattering, passive mode-locking, and optical frequency combs (e.g., Chinese patent CN114628978A, "Method for Generating Spectral Flat Broadband Optical Frequency Combs Based on Multi-Pumped Microcavities"). Since nonlinear systems are mostly external cavity lasers, commonly used systems typically involve multiple nonlinear technologies simultaneously to ensure narrower linewidths and wider spectra (e.g., Chinese patent CN106030934A, "Adjustable Mid-Infrared Supercontinuum Generator Using a Tunable Femtosecond Oscillator"). Nonlinear optical technologies themselves achieve frequency mixing or conversion using nonlinear optical crystals, generally requiring external optical components to assemble them into external cavity lasers. This necessitates additional consideration of cost for other optical components, results in a larger size, and makes them more susceptible to external influences on stability.

[0005] Tuned lasers generate multi-frequency light by changing the resonator length, the characteristics of the gain medium, or by using tuning elements (piezoelectric devices, grating fibers, etc.) to adjust the output wavelength (see Chinese patents CN105981238A, "Tunable Mid-Infrared Fiber Laser for Nonlinear Imaging Applications"; CN117154516A, "A Fiber Laser with Selectable Wavelength or Simultaneous Output of Multiple Wavebands"; CN117543335A, "An Integrated Tuned External Cavity Ultra-Narrow Linewidth DBR Laser"; and CN112688150A, "A Dual-Wavelength Fiber Laser Based on a Mode Interferometer"). When external current, temperature, etc., change, the resonant cavity length and the refractive index characteristics of the gain medium of the laser are affected, resulting in a frequency shift in the output spectrum, thus achieving the phenomenon of single-frequency light spectral broadening. Because characteristics such as current and temperature directly affect the gain medium of a laser, the gain of the laser will fluctuate during tuning, which can lead to unstable power in tuned lasers. For some tuned lasers that rely on external tuning components, the additional components increase cost and system complexity, both of which limit the practicality, reliability, and stability of the device.

[0006] There are many variations of tunable lasers. These devices do not alter the output properties of the seed source or pump source laser, nor do they directly affect the laser itself. Instead, they process the laser output from the source laser. This includes using optical frequency combs (Chinese patent CN113534106A, "A Microcavity Optical Comb Laser, Ranging Device and Ranging Method"), nonlinear crystals, etc., to achieve nonlinear spectral broadening. Other variations include using external modulation devices to change the phase and intensity of the laser (Chinese patent CN112697181A, "A Phase-Sensitive Optical Time-Domain Reflectometer Device and Method Based on Frequency Modulation," and Chinese patent CN102571200A, "Multi-Frequency Probe Optical Coherent Time-Domain Reflectometer Method and Device"), thereby broadening the spectrum of the source laser. These variations are all systems formed by external coupling, transmission, and packaging based on the source laser. Light incurs additional losses during transmission, and the packaging process increases the complexity of the manufacturing process. Summary of the Invention

[0007] Therefore, it is necessary to provide an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device and its fabrication method to address the problems of needing external components and high light loss during transmission.

[0008] To solve the above problems, the present disclosure adopts the following technical solution: In a first aspect, this disclosure provides an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device, comprising: silicon substrate; A laser signal processing device located on the silicon substrate and fabricated by semiconductor technology, the laser signal processing device comprising: a silicon-based waveguide grating, a silicon-based optical switch structure, a silicon-based frequency shifter structure and a silicon-based beam combiner structure connected in sequence; A single-mode output semiconductor laser is heterobonded to a silicon substrate. The semiconductor laser is fabricated using semiconductor technology. The waveguide structure of the semiconductor laser is a single-mode waveguide. The semiconductor laser is coupled to the silicon-based waveguide grating through an end face.

[0009] In a preferred embodiment, the semiconductor laser is an indium phosphide-based laser.

[0010] In a preferred embodiment, the semiconductor laser includes, from bottom to top, an N-electrode layer, an N-type substrate layer, an N-type cladding layer, an N-waveguide layer, an active region, a P-waveguide layer, a P-type cladding layer, a P-type capping layer, and a P-electrode layer, wherein the N-electrode layer is located on a silicon substrate.

[0011] Secondly, this disclosure provides a method for fabricating an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device, comprising: A laser signal processing device is fabricated using semiconductor technology. The laser signal processing device includes: a silicon-based waveguide grating, a silicon-based optical switch structure, a silicon-based frequency shifter structure, and a silicon-based beam combiner structure connected in sequence. A single-mode output semiconductor laser is fabricated using semiconductor technology, wherein the waveguide structure of the semiconductor laser is a single-mode waveguide. The laser signal processing device is placed on a silicon substrate, the semiconductor laser is connected to the silicon substrate by heterobonding, and the semiconductor laser and the silicon-based waveguide grating are coupled end-to-end.

[0012] In a preferred embodiment, the semiconductor laser is an indium phosphide-based laser.

[0013] In a preferred embodiment, the fabrication of the single-mode output semiconductor laser specifically involves: fabricating an N-electrode layer, fabricating an N-type substrate layer on the N-electrode layer, fabricating an N-type cladding layer on the N-type substrate layer, fabricating an N-waveguide layer on the N-type cladding layer, fabricating an active region on the N-waveguide layer, fabricating a P-waveguide layer on the active region, fabricating a P-type capping layer on the P-type cladding layer, and fabricating a P-electrode layer on the P-type capping layer; wherein the N-electrode layer is used to connect to the silicon substrate and is located on the silicon substrate.

[0014] In a preferred embodiment, the step of fabricating a single-mode output semiconductor laser includes: determining the epitaxial structure, waveguide width, and etching depth of the semiconductor laser according to the requirements of the output spot and divergence angle, and fabricating the semiconductor laser accordingly; The fabrication of the laser signal processing device includes: determining the duty cycle, period, and number of periods of the grating of the laser signal processing device according to the output linewidth requirements, and fabricating a silicon-based waveguide grating accordingly.

[0015] This disclosure presents an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device and its fabrication method. The device integrates a single-mode output semiconductor laser and a laser signal processing device. The laser signal processing device comprises a silicon-based waveguide grating, a silicon-based optical switch structure, a silicon-based frequency shifter structure, and a silicon-based beam combiner structure connected in sequence. Signal processing using the laser signal processing device realizes multi-frequency narrow-linewidth semiconductor laser pulses. Both the semiconductor laser and the laser signal processing device are fabricated using semiconductor processes. The semiconductor laser and laser signal processing device are integrated on a silicon substrate, with the semiconductor laser and silicon-based waveguide grating end-face coupled, reducing losses during optical transmission. This method eliminates the need for external tuning elements and mechanical connections, and avoids the external coupling, transmission, and packaging required for conventional external cavity lasers. It ensures mechanical structural stability and the miniaturization and integration of the overall device, avoiding the complexity of packaging processes and overcoming the disadvantages associated with external tuning elements. This disclosure offers lower cost and simpler fabrication. Since this disclosure does not employ nonlinear effects, it does not suffer from the disadvantages caused by nonlinear effects. Attached Figure Description

[0016] Figure 1 This is a simplified structural diagram of an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device according to one embodiment of the present disclosure; Figure 2 This is a three-dimensional structural schematic diagram of an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device according to one embodiment of the present disclosure; Figure 3 This is a front view schematic diagram of an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device according to one embodiment of the present disclosure; Figure 4 This is a schematic diagram of the structure of a semiconductor laser in one embodiment of an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device.

[0017] Among them, 10 is a silicon substrate; 20 is a laser signal processing device; 21 is a silicon-based waveguide grating; 22 is a silicon-based optical switch structure; 23 is a silicon-based frequency shifter structure; 24 is a silicon-based beam combiner structure; 30 is a semiconductor laser; 31 is an N-electrode layer; 32 is an N-type substrate layer; 33 is an N-type cladding; 34 is an N-waveguide layer; 35 is an active region; 36 is a P-waveguide layer; 37 is a P-type cladding; 38 is a P-type capping layer; and 39 is a P-electrode layer. Detailed Implementation

[0018] The technical solutions of this disclosure will now be described in detail with reference to the accompanying drawings and preferred embodiments.

[0019] See Figures 1 to 3 This disclosure provides an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device, the device comprising: Silicon substrate 10; A laser signal processing device 20 located on the silicon substrate 10 and fabricated by semiconductor technology includes a silicon waveguide grating 21, a silicon optical switch structure 22, a silicon frequency shifter structure 23 and a silicon beam combiner structure 24 connected in sequence. A single-mode output semiconductor laser 30 is connected to a silicon substrate 10 via heterobonding. The semiconductor laser 30 is fabricated using semiconductor technology. The waveguide structure of the semiconductor laser 30 is a single-mode waveguide. The semiconductor laser 30 is welded to a laser signal processing device 20 and coupled to a silicon-based waveguide grating 21.

[0020] In this embodiment, the semiconductor laser 30 is heterobonded to the silicon substrate 10 and is located on the silicon substrate 10. The semiconductor laser 30 and the silicon waveguide grating 21 are coupled to each other at the end face (coupling enables light propagation).

[0021] It is understood that the laser signal processing device 20 is a silicon-based laser signal processing device 20.

[0022] In this embodiment, the laser signal processing device 20 is fabricated using photolithography, and the silicon-based waveguide grating 21, silicon-based optical switch structure 22, silicon-based frequency shifter structure 23 and silicon-based beam combiner structure 24 are fabricated in one step.

[0023] In this embodiment, the silicon-based bundle combiner structure 24 adopts a silicon-based MMI bundle combiner structure (silicon-based multimode interference bundle combiner structure). It can be understood that, depending on the different application scenarios and application requirements, it can be replaced with a star coupler according to different channel numbers and different design requirements.

[0024] In this embodiment, both the semiconductor laser 30 and the laser signal processing device 20 are soldered onto the silicon substrate 10.

[0025] In this embodiment, the semiconductor laser 30 is a single-mode output 1550nm semiconductor laser chip. To achieve the gain function, the epitaxial structure of the chip needs to be designed; please refer to the structure of the semiconductor laser 30. Figure 4 , including, along Figure 2The following layers are arranged sequentially in the z-axis upward direction (usually from bottom to top): N-electrode layer 31, N-type substrate layer 32, N-type cladding layer 33, N-waveguide layer 34, active region 35, P-waveguide layer 36, P-type cladding layer 37, P-type capping layer 38, and P-electrode layer 39. The N-electrode layer 31 is located on the silicon substrate 10.

[0026] The N-electrode layer 31 is used for injecting negative charges and is one of the current injection terminals of the semiconductor laser 30. The N-type substrate layer 32 serves as a mechanical support and crystal template for the epitaxial growth of other semiconductor layers. The N-type cladding layer 33, through its low refractive index, forms an optical waveguide structure with the waveguide layer, confining light laterally and preventing light energy leakage. The N-waveguide layer 34, together with the P-waveguide layer 36, tightly confines the optical field near the active region 35, enhancing the interaction efficiency between photons and charge carriers. The active region 35 is responsible for stimulated emission, generating optical gain. The P-waveguide layer 36 works in conjunction with the N-waveguide to complete the longitudinal confinement of the optical field, ensuring the stability of the optical mode field. The P-type cladding layer 37, symmetrically confining light and charge carriers with the N-type cladding layer 33, is the other half of the key structure for achieving efficient optical field confinement. The P-type capping layer 38 achieves low-resistance ohmic contact with the P-electrode, greatly reducing the potential barrier and power consumption for hole injection. The P-electrode layer 39, through which holes are injected, serves as a positive input terminal for population inversion.

[0027] To achieve narrow linewidth laser output, the semiconductor laser 30 (also known as a semiconductor gain chip) must have a single-mode waveguide structure (including near-single-mode waveguides), typically achieved using a narrow ridge refractive index waveguide. However, this structure is too small to achieve high power output. To improve single-mode output power while maintaining mode control and a low divergence angle, this embodiment employs a wide transverse waveguide structure. With a lateral width (i.e., in the z-direction) comparable to that of a common ridge laser, increasing the transverse mode size effectively increases the transverse mode size. Figure 2 The dimensions along the x-axis enable low divergence angle and large spot size output, while simultaneously increasing the longitudinal cavity length (i.e., Figure 2 The resonant cavity size in the y-axis direction is used to reduce the linewidth.

[0028] The semiconductor laser 30 is an InP-based laser, meaning it uses an indium phosphide (InP) single crystal wafer as a substrate, and all epitaxial layers are lattice-matched to it. Specifically, except for the N-type substrate layer 32 and the N-type cladding layer 33 and P-type cladding layer 37, which are primarily made of indium phosphide (InP), the other functional layers utilize different III-V compounds depending on their function. like Figure 2 and Figure 3As shown, along the y-axis outwards are a silicon-based waveguide grating 21, a silicon-based optical switch structure 22, a silicon-based frequency shifter structure 23, and a silicon-based MMI combiner structure. Figure 3 The sections are separated by dashed lines for better illustration. The silicon-based waveguide grating 21 is a Bragg grating.

[0029] A Bragg grating and the back cavity surface of an InP-based laser form a resonant cavity, enabling single-longitudinal-mode (i.e., single-wavelength or single-frequency) laser output. Simultaneously, through grating feedback and back cavity surface resonance of the InP-based laser, the cavity length is effectively increased, improving photon lifetime. The increased cavity length also narrows the laser linewidth, facilitating narrow-linewidth output. Furthermore, by adjusting the grating period, duty cycle, and other conditions, the center reflection wavelength can be controlled, achieving stable laser wavelength output.

[0030] To achieve controllable multi-frequency optical output, the lasing beam is split and first passes through a silicon-based optical switch structure 22. This structure, primarily a PIN junction, is responsible for switching and controlling the multiple laser beams. When a voltage is applied to the PIN junction, the carrier concentration changes, leading to a change in the effective refractive index and consequently a phase shift in the optical mode. When the phase difference between the two branch waveguides is an odd multiple of π, destructive interference occurs, and the channel is turned off. Constructive interference occurs when the phase difference is 0 or an even multiple of π, resulting in superposition and transmission of optical energy, thus enabling conduction.

[0031] Then, a silicon-based frequency shifter structure 23 (silicon-based PIN frequency shifter) is used to individually control the frequency shift of each laser path to obtain multi-frequency lasers. Its core is based on single-sideband modulation technology of dual parallel Mach-Zehnder interferometer (DP-MZM) to achieve high-purity and high-precision shift of laser frequency.

[0032] Its working principle is as follows: A radio frequency (RF) local oscillator signal first passes through a 90° bridge and is decomposed into two RF signals with equal amplitude and orthogonal phase. These two signals drive two parallel sub-Mach-Zehnder modulators inside the DP-MZM. By precisely controlling the DC bias points of these two sub-modulators to make them operate at the quadrature transmission points, and by finely adjusting the relative amplitude and phase of the two RF signals, carrier-suppressed single-sideband modulation can be achieved in the optical domain.

[0033] In this ideal operating state, most of the power of the input optical carrier is transferred to a specific first-order sideband (e.g., the +1 sideband), while the optical carrier itself, another sideband (-1), and other higher-order sideband components are greatly suppressed by the interference principle. Through optimization, it can be ensured that the power ratio of the desired sideband to all other stray frequency components is better than 40 dB, thereby outputting a frequency-pure new optical carrier with a precise frequency shift relative to the input light. The frequency shift of the output light ( It is numerically exactly equal to the frequency of the driving RF signal. This scheme plans to use a radio frequency (RF) signal of f_RF = 50 MHz to generate a multi-frequency laser with a precise frequency interval of 50 MHz. The key advantage of this method is that the frequency offset is entirely defined by the electrical RF signal, allowing for flexible and continuous adjustment of the RF frequency through programming, thus achieving real-time and precise control of the output laser frequency. This characteristic can be directly used to compensate for inherent manufacturing process deviations in downstream optical frequency selection devices (such as gratings). By fine-tuning the RF frequency, the channel wavelength offset caused by minute differences in the grating period can be corrected, ultimately ensuring high long-term stability and consistency of the wavelength interval of the multi-frequency laser output by the entire system.

[0034] To facilitate fiber coupling and encapsulation of multi-frequency output light, this embodiment also employs a silicon-based multimode interference (MMI) beam combining waveguide structure to combine the frequency-shifted multiple laser beams into a single output. The beam combining mechanism of MMI is the self-mirror effect generated by the mutual interference between waveguide modes. Its working principle is that the input field excites multiple modes in the multimode waveguide, and the mutual interference between the modes generates an output field in the direction of wave propagation, realizing beam combining in the waveguide. After coupling with a single-mode fiber, high-power, high-brightness laser output is achieved.

[0035] This disclosure provides a method for fabricating an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device, comprising the following steps: A laser signal processing device 20 is fabricated using semiconductor technology. The laser signal processing device 20 includes: a silicon-based waveguide grating 21, a silicon-based optical switch structure 22, a silicon-based frequency shifter structure 23, and a silicon-based beam combiner structure 24 connected in sequence. A single-mode output semiconductor laser 30 is fabricated using semiconductor technology, wherein the waveguide structure of the semiconductor laser 30 is a single-mode waveguide. The laser signal processing device 20 is placed on the silicon substrate 10, the semiconductor laser 30 is connected to the silicon substrate 10 by heterobonding, and the semiconductor laser 30 and the silicon waveguide grating 21 are docked and coupled, that is, connected by end face coupling, for the propagation of light.

[0036] In this embodiment, the semiconductor laser 30 and the laser signal processing device 20 are welded together in the method.

[0037] In this embodiment, the connection between the laser signal processing device 20 and the silicon substrate 10 is specifically fabricated on the silicon substrate 10 using a mature semiconductor processing technology.

[0038] In this embodiment, the semiconductor laser 30 is an indium phosphide-based laser; the laser signal processing device 20 is specifically fabricated by photolithography.

[0039] In this embodiment, the fabrication of the single-mode output semiconductor laser 30 specifically involves: fabricating an N-electrode layer 31, fabricating an N-type substrate layer 32 on the N-electrode layer 31, fabricating an N-type cladding layer 33 on the N-type substrate layer 32, fabricating an N-waveguide layer 34 on the N-type cladding layer 33, fabricating an active region 35 on the N-waveguide layer 34, fabricating a P-waveguide layer 36 on the active region 35, fabricating a P-type capping layer 38 on the P-type cladding layer 37, and fabricating a P-electrode layer 39 on the P-type capping layer 38; the N-electrode layer 31 is used to connect to the silicon substrate 10 and is located on the silicon substrate 10.

[0040] In this embodiment, the epitaxial structure, waveguide width and etching depth of the semiconductor laser 30 are determined according to the requirements of the output spot and divergence angle, and the semiconductor laser 30 is fabricated accordingly. The end face is the connection end face between the semiconductor laser and the laser signal processing device. Based on the output linewidth requirements, the duty cycle, period, number of periods, and other conditions of the grating of the laser signal processing device 20 are determined, and the silicon-based waveguide grating 21 is fabricated accordingly.

[0041] In this embodiment, the optical path is disconnected and connected through a silicon-based optical switching structure 22. This device is a Mach-Zehnder interferometer-type electro-optic switch, fabricated on a silicon platform. Its core is a PN junction phase modulator with a built-in traveling wave electrode, serving as one interferometer arm of the MZI.

[0042] In this embodiment, a silicon-based frequency shifter structure 23 is used to individually control the frequency shift of each laser path to obtain multi-frequency lasers. This is combined with a silicon-based optical switching structure 22 and a silicon-based beam combining structure 24 (multimode interference coupler) to achieve multi-frequency optical output. This disclosure provides an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device and its fabrication method. The device includes a single-mode output semiconductor laser 30 and a laser signal processing device 20. The laser signal processing device 20 includes a silicon-based waveguide grating 21, a silicon-based optical switch structure 22, a silicon-based frequency shifter structure 23, and a silicon-based beam combiner structure 24 connected in sequence. The multi-frequency narrow-linewidth semiconductor laser pulse is realized by signal processing using the laser signal processing device 20. Meanwhile, both the semiconductor laser 30 and the laser signal processing device 20 are fabricated using semiconductor processes. The semiconductor laser 30 and the laser signal processing device 20 are integrated on the silicon substrate 10. The semiconductor laser 30 is coupled to the silicon-based waveguide grating 21, reducing losses during optical transmission. This system does not rely on external tuning elements, the mechanical connections of conventional external cavity lasers, or external coupling, transmission, and packaging based on a source laser. This ensures mechanical structural stability and the miniaturization and integration of the overall device, resulting in high practicality, reliability, and stability. It avoids the complexity of packaging processes and overcomes the disadvantages associated with external tuning elements. This disclosure offers lower cost and simpler fabrication. Since this disclosure does not employ nonlinear effects, it avoids the disadvantages associated with nonlinear effects.

[0043] Specifically, this disclosure discloses an on-chip integrated external cavity laser that utilizes a silicon-based waveguide array to process the input laser, achieving both integration and miniaturization while avoiding nonlinear effects and overcoming their disadvantages. Firstly, regarding the overall device design, although it is an external cavity laser and does not directly alter the properties of the laser source, all structures in this disclosure are fabricated using on-chip technology. The semiconductor laser 30 and the laser signal processing device 20 are connected via chip-level coupling, without relying on the mechanical connections of conventional external cavity lasers. This ensures the stability of the mechanical structure and the miniaturization and integration of the overall device, while minimizing losses during optical transmission. Secondly, this invention also differs from conventional on-chip tunable lasers. Conventional on-chip tunable lasers fabricate all structures on a single substrate. To ensure proper laser emission, GaAs, InP, or GaN are commonly chosen as substrates. The advantage of integrating the laser emitter and processor onto a single chip is that the process is slightly more convenient. However, the disadvantage is that these processes are not compatible with mature CMOS processes, which prevents them from being mass-produced like silicon-based processes, especially in the manufacture of large-size wafers. Furthermore, the purification and manufacturing costs of these commonly used laser substrate materials are high, and their heat dissipation performance is not as good as that of silicon-based materials. This disclosure overcomes the problems of high cost, poor heat dissipation, and incompatibility of conventional on-chip integrated tunable lasers by separately fabricating the semiconductor laser 30 and the laser signal processing device 20. The laser part continues the design of a conventional on-chip tunable laser, but without fabricating tuning and mode-selection elements such as gratings; it leverages its power advantage solely through waveguides and arrays (si-based materials are difficult to achieve high-efficiency light emission due to material bandgap limitations). The laser signal processing part uses a silicon substrate to fabricate a passive waveguide processing module, integrating the waveguide grating, optical switch structure, frequency shifter structure, and beam combiner structure onto the silicon substrate. These four structures are fabricated in a single photolithography step, significantly reducing process complexity. Simultaneously, the high thermal conductivity, lower optical loss, lower cost, and more compatible integration mode of the silicon substrate improve the overall device performance and competitiveness. Since the entire device does not utilize nonlinear optical effects, it is not affected by the disadvantages of nonlinear effects, ensuring the device can operate at higher speeds. This disclosure offers advantages such as wide tuning, narrow linewidth, integration, small size, simple fabrication, and stable output for the multi-frequency light generation module.

[0044] This disclosure achieves both high power and narrow linewidth while maintaining high integration and miniaturization. Traditional on-chip tunable lasers are limited by size, heat dissipation, and other factors, making it difficult to achieve high power, which restricts the application of on-chip integrated tunable lasers under high-power and ultra-high-power conditions. External-cavity tunable lasers and systems using nonlinear optics require numerous external devices to adjust and optimize output, also making integration and miniaturization difficult. The on-chip integrated system proposed in this invention employs a wide transverse waveguide structure on a semiconductor gain chip to achieve low divergence angle and large spot output, while simultaneously increasing the longitudinal cavity length to reduce linewidth. In the second part of the design, a resonant cavity is formed using a silicon-based waveguide grating 21 (Bragg grating) and the rear cavity surface of an InP-based laser to achieve single-longitudinal-mode laser output. Through grating feedback and resonance of the rear cavity surface of the InP-based laser, the cavity length is effectively increased, improving photon lifetime and facilitating narrow linewidth output. By controlling the center reflection wavelength of the grating, stable laser wavelength output is achieved.

[0045] The present invention has low manufacturing cost and mature process, uses an on-chip integrated external cavity system, uses a traditional on-chip laser to generate a light source, and uses a silicon substrate for the laser signal processing device 20. Passive waveguide devices can be fabricated in one photolithography process, which is compatible with mature CMOS process. Compared with traditional on-chip tunable lasers, silicon-based materials have lower cost, higher thermal conductivity, more mature process, lower processing cost, and support mass production of large-size wafers.

[0046] This disclosure achieves high stability while maintaining high-speed operation. Traditional systems employing nonlinear optics technology, in pursuit of high efficiency, must utilize bulk nonlinear crystals and precise phase-matching techniques, directly resulting in large system size and complex structure. Large systems inevitably suffer from poor stability and are extremely sensitive to environmental disturbances (temperature drift, vibration). Maintaining stability requires additional control and cooling systems, further exacerbating system complexity, power consumption, and cost. Similarly, external cavity tuned lasers, relying on numerous external devices for laser tuning, also suffer from reduced overall system stability and reliability. The on-chip integrated external cavity system of this disclosure uses silicon-based semiconductor gain chips for coupling, enabling it to achieve the same high-speed frequency tuning, integration, and reliability as on-chip systems.

[0047] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0048] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. An on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device, characterized in that, include: silicon substrate; A laser signal processing device located on the silicon substrate and fabricated by semiconductor technology, the laser signal processing device comprising: a silicon-based waveguide grating, a silicon-based optical switch structure, a silicon-based frequency shifter structure and a silicon-based beam combiner structure connected in sequence; A single-mode output semiconductor laser is heterobonded to a silicon substrate. The semiconductor laser is fabricated using semiconductor technology. The waveguide structure of the semiconductor laser is a single-mode waveguide. The semiconductor laser is coupled to the silicon-based waveguide grating through an end face.

2. The on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device according to claim 1, characterized in that, The semiconductor laser is an indium phosphide-based laser.

3. An on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device according to claim 1 or 2, characterized in that, The semiconductor laser includes, from bottom to top, an N-electrode layer, an N-type substrate layer, an N-type cladding layer, an N-waveguide layer, an active region, a P-waveguide layer, a P-type cladding layer, a P-type capping layer, and a P-electrode layer, wherein the N-electrode layer is located on a silicon substrate.

4. A method for fabricating an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device, characterized in that, include: A laser signal processing device is fabricated using semiconductor technology. The laser signal processing device includes: a silicon-based waveguide grating, a silicon-based optical switch structure, a silicon-based frequency shifter structure, and a silicon-based beam combiner structure connected in sequence. A single-mode output semiconductor laser is fabricated using semiconductor technology, wherein the waveguide structure of the semiconductor laser is a single-mode waveguide. The laser signal processing device is placed on a silicon substrate, the semiconductor laser is connected to the silicon substrate by heterobonding, and the semiconductor laser and the silicon-based waveguide grating are coupled end-to-end.

5. The method for fabricating an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device according to claim 4, characterized in that, The semiconductor laser is an indium phosphide-based laser.

6. The method for fabricating an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device according to claim 4, characterized in that, The specific steps for fabricating a single-mode output semiconductor laser are as follows: fabricating an N-electrode layer, fabricating an N-type substrate layer on the N-electrode layer, fabricating an N-type cladding layer on the N-type substrate layer, fabricating an N-waveguide layer on the N-type cladding layer, fabricating an active region on the N-waveguide layer, fabricating a P-waveguide layer on the active region, fabricating a P-type capping layer on the P-type cladding layer, and fabricating a P-electrode layer on the P-type capping layer; wherein the N-electrode layer is used to connect to the silicon substrate and is located on the silicon substrate.

7. The method for fabricating an on-chip integrated multi-frequency narrow-linewidth semiconductor laser pulse device according to claim 4, characterized in that, The steps for preparing a single-mode output semiconductor laser include: determining the epitaxial structure, waveguide width, and etching depth of the semiconductor laser according to the requirements of the output spot and divergence angle, and preparing the semiconductor laser accordingly; The fabrication of the laser signal processing device includes: determining the duty cycle, period, and number of periods of the grating of the laser signal processing device according to the output linewidth requirements, and fabricating a silicon-based waveguide grating accordingly.

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