External cavity lasers and lidar

Abstract

This application provides an external cavity laser and a lidar. The external cavity laser includes an active multimode gain chip and a passive optical chip. The active multimode gain chip and the passive optical chip are coupled together. The active multimode gain chip provides a multimode beam, which is then fed back to a single-mode source and output by the passive optical chip. The lidar includes a light source, a beam splitter, a phased array antenna, and a detection module, and includes the aforementioned external cavity laser. This application solves the technical problem of low power output in external cavity lasers in related technologies, thereby improving the power output of external cavity lasers.

Description

Technical Field

[0001] This application relates to the field of lidar, and more specifically, to an external cavity laser and lidar. Background Technology

[0002] Currently, applications such as laser detection and ranging (LIDAR), wavelength division multiplexing (CWDM) for optical communication, laser sensing, and machine vision require high-power, high-performance, low-cost, miniaturized, and mass-producible semiconductor lasers. External-cavity semiconductor lasers, due to their unique and advanced structure, possess the characteristics of high-performance laser output and can meet the performance requirements of most application scenarios. An external-cavity semiconductor laser integrates an active multimode gain chip and a passive optical chip to form a large, unified resonant cavity. It utilizes the gain provided by the active multimode gain chip and the low-loss propagation and wavelength selective feedback characteristics of the optical chip to achieve high-performance laser output on a chip-level platform.

[0003] Typically, three main performance indicators are considered for external cavity lasers: power, WPE (Wall-Plug Efficiency, also known as electro-optical conversion efficiency), and coherence. For external cavity lasers, achieving high power output requires high gain power. However, achieving high gain power in active multimode gain chips requires large current pumping (i.e., high pump current), which leads to increased heat generation, especially under high current pumping conditions. This, in turn, causes a sharp decrease in the overall WPE of the laser due to thermal effects, thus limiting the high power output of the external cavity laser. This phenomenon is particularly pronounced in small-sized active multimode gain chips.

[0004] It is evident that external cavity lasers in related technologies suffer from low power output. Summary of the Invention

[0005] This application provides an external cavity laser and a lidar to at least solve the technical problem of low power output of external cavity lasers in related technologies.

[0006] According to one aspect of the embodiments of this application, an external cavity laser is provided, the external cavity laser comprising: an active multimode gain chip and a passive optical chip; wherein the active multimode gain chip is docked and coupled to the passive optical chip; the active multimode gain chip is used to provide a multimode beam, the multimode beam passing through the passive optical chip to form partial single-mode optical feedback and single-mode optical output.

[0007] In one exemplary embodiment, the passive optical chip includes: an end-face mode field converter and a wavelength selective feedback module. The wavelength selective feedback module includes an input waveguide, a wavelength selective feedback device, and an output waveguide. The active multimode gain chip is coupled to the passive optical chip via the end-face mode field converter. The multimode beam is transmitted from the active multimode gain chip to the passive optical chip via the end-face mode field converter and converted into a single-mode beam. The beam is then transmitted to the wavelength selective feedback device via the input waveguide. A portion of the single-mode beam passes through the wavelength selective feedback device and enters a resonant cavity composed of the active multimode gain chip and the passive optical chip to form the single-mode optical feedback. Another portion of the single-mode beam passes through the wavelength selective feedback device and is output via the output waveguide to form the single-mode optical output.

[0008] In one exemplary embodiment, the end-face mode field converter is a positive conical coupling structure or a multi-end-face coupling structure.

[0009] In one exemplary embodiment, the passive optical chip further includes a phase shifter, the end-face mode field converter is connected to the left waveguide of the phase shifter, and the right waveguide of the phase shifter is connected to the input waveguide of the wavelength selection feedback module; the phase shifter is used to modulate the single-mode beam.

[0010] In one exemplary embodiment, the passive optical chip is fabricated using one of the following materials: silicon, silicon nitride, thin-film lithium niobate, and the phase shifter is one of the following: a thermo-optical phase shifter, an electro-optical phase shifter.

[0011] In one exemplary embodiment, the wavelength selective feedback device includes at least one of the following: a distributed Bragg grating, a microring resonator.

[0012] In one exemplary embodiment, the wavelength selective feedback device is a microring resonator, and the wavelength selective feedback module further includes an on-chip Sagnac mirror.

[0013] In one exemplary embodiment, the microring resonator includes at least one of the following: an all-through microring resonator, an uplink / downlink microring resonator, a structure composed of cascaded microring resonators, and a tunable microring resonator with applied electrodes.

[0014] In one exemplary embodiment, the active multimode gain chip includes at least one of the following: a multimode Fabry-Perot laser, a multimode reflective semiconductor optical amplifier.

[0015] According to another aspect of the embodiments of this application, a lidar is also provided, comprising: a light source, a beam splitter, a phased array antenna, and a detection module, wherein the light source comprises any of the external cavity lasers described above.

[0016] This application achieves a solution by incorporating an active multimode gain chip and a passive optical chip on an external cavity laser, with the active multimode gain chip and passive optical chip being docked and coupled. The active multimode gain chip provides a multimode beam, which is then fed back to a single-mode optical source and output by the passive optical chip. By introducing a multimode gain chip with a wide waveguide, the electro-optical conversion efficiency (socket efficiency) of the active gain chip under high current pumping can be improved, thereby increasing the power output of the external cavity laser and solving the technical problem of low power output in external cavity lasers in related technologies. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an optional external cavity laser according to an embodiment of this application;

[0018] Figure 2 This is a schematic diagram of an optional active multimode gain output power and an external cavity laser output power according to an embodiment of this application;

[0019] Figure 3 This is a schematic diagram of the output spectrum of an optional external cavity laser according to an embodiment of this application;

[0020] Figure 4 This is a schematic diagram of another optional external cavity laser according to an embodiment of this application;

[0021] Figure 5 This is a schematic diagram of a wavelength selection feedback module for an optional external cavity laser according to an embodiment of this application;

[0022] Figure 6 This is a pattern field distribution diagram of multiple transverse modes present on an optional end face according to an embodiment of this application;

[0023] Figure 7 This is a schematic diagram illustrating the conversion efficiency from an optional fundamental mode TE0 mode to various higher-order lateral modes according to an embodiment of this application.

[0024] Figure 8 This is a schematic diagram of an optional end-face mode field converter according to an embodiment of this application;

[0025] Figure 9 This is a schematic diagram of another optional external cavity laser according to an embodiment of this application;

[0026] Figure 10 This is a schematic diagram of another optional external cavity laser according to an embodiment of this application;

[0027] Figure 11 This is a schematic diagram of an optional distributed Bragg grating according to an embodiment of this application;

[0028] Figure 12 This is a schematic diagram of the transmittance and reflectance of an optional wavelength selection feedback device according to an embodiment of this application;

[0029] Figure 13 This is a schematic diagram of an optional on-chip Sagnac mirror according to an embodiment of this application;

[0030] Figure 14 This is a schematic diagram of an optional microring resonator according to an embodiment of this application;

[0031] Figure 15 This is a schematic diagram of another optional microring resonator according to an embodiment of this application;

[0032] Figure 16 This is a schematic diagram of another optional external cavity laser according to an embodiment of this application;

[0033] Figure 17 This is a schematic diagram of another optional external cavity laser according to an embodiment of this application;

[0034] Figure 18 This is a schematic diagram of another optional external cavity laser according to an embodiment of this application;

[0035] Figure 19 This is a schematic diagram of another optional external cavity laser according to an embodiment of this application;

[0036] Figure 20 This is a schematic diagram of an optional lidar according to an embodiment of this application. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0038] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0039] According to one aspect of the embodiments of this application, an external cavity laser is provided. Optionally, the external cavity laser can be applied to lidar, such as optical phased array lidar, or to other terminals or devices. The development of big data, artificial intelligence, and intelligent vehicles has driven rapid progress in optical communication and integrated photonics, leading to a large demand for lasers, especially semiconductor lasers that can meet the requirements of large-scale production and low cost. For applications such as laser detection and ranging (LIDAR), wavelength division multiplexing (CWDM) in optical communication, laser sensing, and machine vision, high-power, high-performance, low-cost, miniaturized, and mass-producible semiconductor lasers have always been a necessity. External cavity semiconductor lasers, due to their special and advanced structure, possess the characteristics of high-performance laser output and can meet the performance requirements of most application scenarios.

[0040] An external cavity laser integrates an active gain chip and a passive optical chip to form a large, unified resonant cavity. Utilizing the gain provided by the active gain chip and the low-loss propagation and wavelength-selective feedback characteristics of the optical chip, a high-performance external cavity laser with laser output can be achieved on a chip-level platform. The active gain chip can be a Fabry-Perot (FP) laser or a Reflective Semiconductor Optical Amplifier (RSOA), among other semiconductor laser types.

[0041] Typically, external cavity lasers are considered for three main performance indicators: power, wavelength-to-earnings ratio (WPE), and coherence. Introducing a high-performance passive optical chip effectively increases the overall cavity length of the laser resonator, thereby improving the coherence of the laser output. However, for external cavity lasers, achieving high power output requires high gain power. But for active gain chips, achieving high gain power requires large current pumping (i.e., high pump current). For currently used narrow-waveguide single-mode gain chips, high current pumping leads to increased device heat, which in turn causes a sharp decrease in the overall WPE of the laser due to thermal effects, thus limiting the high power output of the external cavity laser. This phenomenon is particularly pronounced in small-sized active gain chips.

[0042] In external cavity lasers, to obtain laser output with high coherence characteristics, the active gain chip typically needs to maintain a single transverse mode output. This necessitates the use of narrow-width, highly confined single-mode gain waveguides, which have high resistance and thermal resistance, making the aforementioned phenomenon particularly pronounced in narrow-waveguide single-mode gain chips. Although feedback provided by an external passive optical chip can confine the final output mode to a single longitudinal mode, and the laser current density can be reduced by increasing the area, the overall power and WPE of the external cavity laser are still limited by the active gain chip. Therefore, the power output of external cavity lasers is generally low.

[0043] Furthermore, active multimode gain chips and high-performance passive optical chips are typically integrated together via docking coupling. This involves docking coupling losses between the active and passive optical chips, primarily due to power losses in mode-field conversion during docking coupling caused by the mismatch in near-field mode spot sizes between different chips, thus reducing the overall power output of the external cavity laser. To compensate for the reduced power output of the external cavity laser, an external SOA (Semiconductor Optical Amplifier) ​​can be connected to the output end to achieve high-power external cavity laser output. However, this sacrifices cost and size, increases complexity, and fails to meet the requirements of low cost and miniaturization.

[0044] To at least partially solve the above-mentioned technical problems, in this embodiment, the external cavity laser includes an active multimode gain chip and a passive optical chip. By introducing a multimode gain chip with a wide waveguide, the WPE of the active gain chip under high current pumping can be improved, thereby increasing the high power output of the external cavity laser.

[0045] As an optional implementation method, Figure 1 This is a schematic diagram of an optional external cavity laser according to an embodiment of this application, as shown below. Figure 1As shown, the external cavity laser 100 includes an active multimode gain chip 101 and a passive optical chip 102; wherein, the active multimode gain chip 101 and the passive optical chip 102 are coupled together; the active multimode gain chip 101 is used to provide a multimode beam, and the multimode beam passes through the passive optical chip 102 to form partial single-mode optical feedback and single-mode optical output. Here, the active multimode gain chip has a wide waveguide, and by utilizing the high WPE under high current of the wide waveguide multimode active gain, the external cavity laser can have the advantages of high power and high performance.

[0046] Here, the waveguide in an external cavity laser primarily serves to transmit and feedback light, amplifying the optical field and enabling the selection of specific wavelengths. The width of the waveguide directly affects the laser's output characteristics and performance parameters. A wider waveguide may support more propagation modes, making the laser's output modes more complex and potentially increasing the linewidth. Conversely, a narrower waveguide helps limit the laser's propagation modes, making it easier for the laser to achieve single-mode output with a narrower linewidth.

[0047] To achieve high power output, external cavity lasers require high gain power, which necessitates high pump current. For currently used narrow-waveguide single-mode gain chips, the overall power efficiency (WPE) decreases sharply under high-current pumping due to thermal effects, thus limiting the high-power output of the external cavity laser. WPE refers to the energy conversion efficiency from electrical energy to laser light. A higher WPE indicates a higher efficiency in converting electrical energy to light, meaning less energy is lost during the conversion. With the same electrical input, a laser with a higher WPE can produce a stronger laser output. Furthermore, a higher WPE also means less heat generated during laser operation. Therefore, a lower WPE leads to a decrease in the output power of the external cavity laser under the same electrical input.

[0048] To prevent a decrease in WPE, in this embodiment, an active multimode gain chip with a wide waveguide can be used to improve the WPE of the external cavity laser under high current pumping, enabling the external cavity laser to output high power. The multimode beam output from the active multimode gain chip passes through a passive optical chip, which can form partial single-mode optical feedback and single-mode optical output.

[0049] An active multimode gain chip is a semiconductor chip containing active optical elements. When current passes through it, it can generate a multimode beam. That is, an active multimode gain chip can generate and modulate a multimode beam. A passive optical chip is a chip that does not contain active optical elements. It does not generate a laser beam, but it may contain waveguides, optical fibers, or other structures. It can be used to guide the transmission of laser beams between the active multimode gain chip and other components. In addition, passive optical chips can also be used to process laser beams, such as filtering, splitting, combining, or isolating different laser beams.

[0050] Optionally, the passive optical chip may include a wavelength selective feedback device. This device can be used to select a specific wavelength of light from the laser resonant cavity. When the wavelength of the light matches the resonance condition constructed within the wavelength selective feedback device, the light is significantly amplified and reflected back to the laser resonant cavity; conversely, light that does not match the resonance condition is attenuated. By adjusting or selecting the parameters of the wavelength selective feedback device, the selected wavelength range can be adjusted. Furthermore, the passive optical chip may include other components capable of wavelength selective feedback. In this embodiment, the method by which the passive optical chip processes multimode beams is not limited, as long as it can form partial single-mode optical feedback and single-mode optical output.

[0051] Optionally, to reduce the docking coupling loss between the active and passive multimode gain chips (which leads to power loss and thus affects the overall power output of the external cavity laser), in this embodiment, a mode-size converter (SSC) is also integrated on the passive optical chip. This improves the coupling efficiency with the active multimode gain chip, thereby achieving high power output of the external cavity laser. The mode-size converter is a key technology for optimizing optical systems. By adjusting the mode field size and shape of the beam, it matches the mode field size differences between different devices, reducing beam loss and scattering during coupling, thereby improving the coupling efficiency between the passive optical chip and the active multimode gain chip.

[0052] For example, the output power of a high-power, high-performance external cavity laser can be as shown in formula (1):

[0053] P out =(κ) c ∑ l ρ l η l T out )P mm (1)

[0054] Among them, the output power of the high-power, high-performance external cavity laser is P. out κ c ρ is the coupling coefficient between the active multimode gain chip and the passive optical chip. l η represents the proportion of the corresponding pattern. l For the conversion efficiency between the corresponding mode and the basic transverse mode TE0 mode, T out For the output transmittance of the wavelength selection feedback module, P mm This represents the output power of the active multimode gain. The wavelength-selective feedback device has a κ = 100m. -1 κ c When ≈0.8, the output power P of the active multimode gain mmand high-power, high-performance external cavity laser output power P out The curve showing the change in current is as follows: Figure 2 As shown, and the final output laser spectrum is as follows. Figure 3 As shown.

[0055] According to the embodiments provided in this application, the external cavity laser includes an active multimode gain chip and a passive optical chip; wherein the active multimode gain chip and the passive optical chip are docked and coupled; the active multimode gain chip is used to provide a multimode beam, and the multimode beam passes through the passive optical chip to form partial single-mode optical feedback and single-mode optical output, which can solve the technical problem of low power output of external cavity lasers in related technologies and improve the power output of external cavity lasers.

[0056] In one exemplary embodiment, such as Figure 4 As shown, the passive optical chip 102 includes an end-face mode-field converter 110 and a wavelength selection feedback module 130. The wavelength selection feedback module 130 includes an input waveguide, a wavelength selection feedback device 131, and an output waveguide. The end-face mode-field converter 110 (i.e., the aforementioned mode-field converter) is used to achieve end-face coupling matching between the gain waveguide and the inorganic waveguide, and can be used to convert the multimode beam provided by the active multimode gain chip 101 into a single-mode beam. The wavelength selection feedback module 130 provides precise wavelength selection and wavelength tuning functions.

[0057] The wavelength selection feedback module 130 can be implemented in various ways, including but not limited to: a Y-branch, a directional coupler, and a 1*2 multimode interference coupler; or, a Y-branch, a directional coupler, and a 2*2 multimode interference coupler. For example, as... Figure 5 As shown, 133A is the Y-branch, 133B is the directional coupler, 133C is the 1*2 multimode interference coupler, and 133D is the 2*2 multimode interference coupler.

[0058] The active multimode gain chip 101 is coupled to the passive optical chip 102 via the end-face mode field converter 110. The multimode beam is transmitted from the active multimode gain chip 101 to the passive optical chip 102 through the end-face mode field converter 110, and is converted into a single-mode beam. It is then transmitted to the wavelength selective feedback device 131 through the input waveguide. Part of the single-mode beam enters the resonant cavity composed of the active multimode gain chip 101 and the passive optical chip 102 after passing through the wavelength selective feedback device 131 to form single-mode optical feedback, and another part of the single-mode beam is output through the output waveguide after passing through the wavelength selective feedback device 131 to form single-mode optical output.

[0059] In this embodiment, one end of the active multimode gain chip 101 is coated with an antireflection film, while the other end may be coated with a high-reflectivity film or left uncoated. The end of the active multimode gain chip 101 coated with the antireflection film is mated and coupled to the passive optical chip 102. When one end of the active multimode gain chip 101 is coated with an antireflection film and the other end is uncoated, the laser from the external cavity laser can also be output from the uncoated end. The antireflection film can reduce reflected light and enhance transmitted light, thereby improving light transmittance and clarity; while the high-reflectivity film can increase the reflectivity of the optical device.

[0060] In this embodiment, the active multimode gain chip 101 is coupled to the passive optical chip 102 via an end-face mode field converter 110. The end-face mode field converter 110 is connected to the input waveguide of the wavelength selective feedback module 130. Light is transmitted from the active multimode gain chip 101 to the passive optical chip 102 via the end-face mode field converter 110, and then transmitted to the wavelength selective feedback module 130 via the input waveguide. After passing through the wavelength selective feedback device 131, part of the light is fed back, and after passing through the input waveguide of the wavelength selective feedback module 130 and the end-face mode field converter 110, it is transmitted back to the active multimode gain chip 101, forming a resonant cavity with a longer cavity length. Part of the light passes through the output waveguide of the wavelength selective feedback module 130 to form laser output. Here, the final laser output is a single-mode light output.

[0061] In this embodiment, a multimode beam is transmitted to the passive optical chip and converted into a single-mode beam by the end-face mode field converter of the passive optical chip. The wavelength selection feedback module realizes single-mode light feedback and single-mode light output, which can reduce the loss and scattering of the beam during the coupling process, thereby improving the coupling efficiency between the passive optical chip and the active multimode gain chip.

[0062] In an exemplary embodiment, the end-face mode field converter is mainly used to convert light containing multiple modes input from an active multimode gain device into a single-mode TEO mode transmitted in a passive optical chip. Its structure can be a positive cone coupling structure or a multi-end-face coupling structure.

[0063] Taking a positive conical coupling structure as an example, for such Figure 6 The transverse multimode shown, after passing through a conical structure, has conversion efficiencies from the fundamental TE0 mode to various higher-order transverse modes as follows: Figure 7 As shown.

[0064] To confine the multimode light output from the active multimode gain chip 102 to a single mode in the lateral dimension, the end-face mode-field converter 110 is a conical coupling structure or a multi-end-face coupling structure. For example, Figure 8 As shown, Figure 8The diagram illustrates the conical coupling structure and multi-end-face coupling structure of the end-face mode field converter 110. The conical coupling structure has a gradually narrowing conical end face, transitioning from the wider end face of the multimode fiber to the narrower end face of the single-mode fiber. When multimode light enters the conical coupling structure, the beam is restricted in its lateral dimension due to the gradual narrowing of the conical end face, and the light of multiple modes is gradually filtered and focused. Ultimately, only light that meets the transmission conditions of single-mode fiber can pass through, thus realizing the conversion from multimode to single-mode. The multi-end-face coupling structure contains multiple end faces with different sizes and shapes for matching with different fiber modes. When multimode light enters the multi-end-face coupling structure, each end face couples with a specific fiber mode. Through optical effects such as reflection, refraction, or diffraction, different modes in the multimode light are separated and guided to the corresponding output end, thereby selectively transmitting light that meets the single-mode conditions.

[0065] For example, taking the end-face mode field converter 110 as a positive conical coupling structure, a multimode beam can be output from the active multimode gain chip 101, and transmitted from the active multimode gain chip 101 to the passive optical chip 102 through the end-face mode field converter 110. Through the positive conical coupling structure of the end-face mode field converter 110, the multimode light with active multimode gain (i.e., the multimode light after being amplified by the active multimode gain chip 101) is restricted to single mode in the lateral dimension. Due to the waveguide thickness of the passive optical chip 102, it is also restricted to single mode in the longitudinal dimension. Then, the aforementioned single-mode beam enters the wavelength selective feedback device 131 through the input waveguide, is confined to a single longitudinal mode, passes through the end-face mode field converter 110, and is transmitted back to the active multimode gain chip 101. It is then reflected by the high-reflectivity film of the active multimode gain chip 102, thereby forming a resonant cavity with a longer cavity length, including the active multimode gain chip 101, the end-face mode field converter 110, and the wavelength selective feedback device 131. This forms a self-injection lock, allowing another part of the light to pass through the output waveguide to form a high-performance laser with narrow linewidth and high coherence characteristics, and this high-performance laser is a single-mode light.

[0066] Through this embodiment, the special structural design of the end-face mode field converter can confine multimode light with active multimode gain to single-mode, thereby achieving single-mode light output.

[0067] In one exemplary embodiment, the external cavity laser may or may not include a phase shifter. When the external cavity laser includes a phase shifter, such as... Figure 9 As shown, the passive optical chip 102 also includes a phase shifter 120. The end-face mode field converter 110 is connected to the left waveguide of the phase shifter 120, and the right waveguide of the phase shifter 120 is connected to the input waveguide of the wavelength selection feedback module 130. The phase shifter 120 is used to modulate the single-mode beam.

[0068] The phase shifter 120 can be a thermally modulated phase shifter based on silicon waveguides, a thermally modulated phase shifter based on silicon nitride waveguides, a PN electro-optic phase shifter based on silicon waveguides, a PIN electro-optic phase shifter based on silicon waveguides, a thermally modulated phase shifter based on lithium niobate thin film waveguides, an electro-optic phase shifter based on lithium niobate thin film waveguides, etc., and this embodiment does not limit it.

[0069] In this embodiment, the phase shifter 120 is connected to the end-face mode-field converter 110 and the wavelength selection feedback module 130, respectively. The phase shifter 120 can be used to adjust the overall intracavity phase, thereby achieving the function of adjusting the laser output wavelength. In addition, different types of modulation can be applied to the phase shifter 120 to meet different application requirements.

[0070] For example, taking an external cavity laser including a phase shifter 120 as an example, the active multimode gain chip 101 is coupled to the passive optical chip 102 via an end-face mode field converter 110. The end-face mode field converter 110 is connected to the left waveguide of the phase shifter 120, and the right waveguide of the phase shifter 120 is connected to the input waveguide of the wavelength selective feedback module 130. Light is transmitted from the active multimode gain chip 101 to the passive optical chip 102 through the end-face mode field converter 110, then transmitted to the phase shifter 120 through the left waveguide, output through the right waveguide of the phase shifter 120, and then output through the input of the wavelength selective feedback module. The light is transmitted through the waveguide to the wavelength selective feedback module 130. After passing through the end-face mode-field converter 110, the light is transmitted from the active multimode gain chip 101 to the passive optical chip 102. Then, it is transmitted through the input waveguide of the wavelength selective feedback module 130 to the wavelength selective feedback module 130. After passing through the wavelength selective feedback device 131, part of the light is fed back. After passing through the input waveguide of the wavelength selective feedback module 130, the phase shifter 120, and the end-face mode-field converter 110, it is transmitted back to the active multimode gain chip 101 to form a resonant cavity with a longer cavity length. Part of the light is transmitted through the output waveguide of the wavelength selective feedback module 130 to form laser output.

[0071] In this embodiment, by setting a phase shifter in a passive optical chip, the modulation of a single-mode beam can be achieved, ensuring the reliability of the signal output.

[0072] In one exemplary embodiment, the passive optical chip is fabricated using one of the following materials: silicon, silicon nitride, thin-film lithium niobate, and the phase shifter is one of the following: thermo-optical phase shifter, electro-optical phase shifter.

[0073] The passive optical chip is fabricated using one of the following materials: silicon, silicon nitride, or lithium niobate thin film. In addition to the above materials, other materials can also be selected as the fabrication materials for the passive optical chip in the aforementioned frequency-modulated continuous wave lidar.

[0074] Here, the passive optical chip fabricated using silicon can be a silicon waveguide-based optical chip. Silicon waveguide-based optical chips can utilize the high refractive index and excellent waveguide properties of silicon to guide light waves propagation within the chip, exhibiting good transparency and low absorption loss. However, silicon-based waveguides have significant bending losses, which may require additional design considerations for applications demanding high-precision waveguide bending and bifurcation.

[0075] Passive optical chips fabricated using silicon nitride can be based on silicon nitride waveguides. Silicon nitride, a wide-bandgap material, provides excellent transparency for optical signals ranging from the visible to the infrared spectrum. Silicon nitride waveguides exhibit low bending loss and good optical field confinement, making them suitable for high-precision wavelength-selective feedback devices. Furthermore, they allow for seamless integration with silicon waveguides.

[0076] Here, the passive optical chip fabricated using lithium niobate thin film can be an optical chip based on a lithium niobate thin film waveguide. Lithium niobate is a nonlinear optical material exhibiting electro-optic and photoelastic effects, and can be used to fabricate optical modulators and optical switches. Optical chips based on lithium niobate thin film waveguides have unique advantages in modulation and frequency selection, enabling high-speed and efficient optical modulation, suitable for optical communication and optical signal processing. They can achieve low-loss, high-speed phase modulation, suitable for precise control of laser output frequency in FMCW lidar systems. Furthermore, lithium niobate material also has good temperature stability, maintaining high-precision optical wave modulation over a wide temperature range.

[0077] The phase shifter can be selected based on the application scenario, and it can be, but is not limited to, one of the following: electro-optic phase shifter, thermo-optic phase shifter. Compared with other phase shifters, electro-optic phase shifters and thermo-optic phase shifters have higher modulation efficiency and higher compatibility with FMCW lidar. Furthermore, the phase shifter can be a silicon waveguide-based thermally modulated phase shifter, a silicon nitride waveguide-based thermally modulated phase shifter, a silicon waveguide-based PN electro-optic phase shifter, a silicon waveguide-based PIN electro-optic phase shifter, a lithium niobate thin-film waveguide-based thermally modulated phase shifter, an electro-optic phase shifter based on a lithium niobate thin-film waveguide, etc. This embodiment does not limit the type of phase shifter.

[0078] In this embodiment, various factors such as integration level, cost, optical loss, temperature stability, and compatibility with the system's operating wavelength can be comprehensively considered to configure a suitable passive optical chip for the aforementioned frequency-modulated continuous wave lidar, thereby improving the overall performance of the lidar system.

[0079] In one exemplary embodiment, the wavelength selective feedback device 131 includes at least one of the following: a distributed Bragg grating, a microring resonator.

[0080] For wavelength selective feedback devices, different components can be configured as needed. Depending on the application requirements, different wavelength feedback devices can be selected, including at least one of the following: distributed Bragg gratings (DBRs) and microring resonators. Optionally, the wavelength selective feedback device can be designed with multiple DBRs, multiple microring resonators, or at least one DBR and at least one microring resonator. A switching mechanism selects different wavelengths for the feedback device, achieving more flexible wavelength selection and modulation capabilities.

[0081] A distributed Bragg grating is a periodic optical element composed of alternating layers of materials with different refractive indices. The refractive index differences between these layers cause light waves of specific wavelengths to be reflected, while other wavelengths are transmitted. Its working principle is based on Bragg reflection; that is, when light propagates through multiple layers of medium, if the Bragg condition is met (i.e., the difference in reflection path length in the medium is an integer multiple of the wavelength), strong reflection will occur. Distributed Bragg gratings can effectively reflect light of specific wavelengths, thereby improving the wavelength selectivity and output power of lasers. It should be noted that the aforementioned... Figure 4 and Figure 9 The wavelength selective feedback device 131 in the image is a distributed Bragg grating.

[0082] A microring resonator is a ring structure composed of tiny optical waveguides, typically on the order of micrometers. When light propagates within the microring, a strong resonance occurs if the resonance condition is met (i.e., the path length of the light wave within the ring is an integer multiple of its wavelength). This resonance, generated through the ring structure, produces a high Q-value, enhancing light of a specific wavelength while suppressing other wavelengths. Optionally, this selectivity can be adjusted by the size and refractive index of the microring. Microring resonators allow for the precise selection and filtering of specific wavelengths. Furthermore, microring resonators can be used in applications such as optical switches, optical modulators, and optical sensors. For example, as... Figure 10 As shown, Figure 10 The wavelength-selective feedback device in the design is a micro-ring resonator 132.

[0083] For example, taking a distributed Bragg grating as the wavelength selective feedback device, light is output from an active multimode gain device, transmitted from the active multimode gain chip to the passive optical chip through an end-face mode field converter, and the multimode light of the active multimode gain is restricted to single mode in the lateral dimension by the positive conical structure. Due to the waveguide thickness of the passive optical chip, it is also restricted to single mode in the longitudinal dimension. The light is then transmitted through the left waveguide of the phase shifter to the phase shifter, output through the right waveguide of the phase shifter, and then through the left waveguide of the distributed Bragg grating (DBR) back into the DBR. Due to the wavelength selectivity of the DBR, the light is confined to a single longitudinal mode. Then, part of the light is reflected back by the DBR and transmitted back to the active multimode gain chip through the left waveguide of the DBR, the phase shifter, and the end-face mode-field converter. It is then reflected by the high-reflectivity film of the active multimode gain chip, thus forming a resonant cavity with a longer cavity length that includes the active multimode gain chip, the end-face mode-field converter, the phase shifter, and the DBR. Part of the light is output as laser light through the right waveguide of the DBR.

[0084] like Figure 11 As shown, the wavelength selection feedback device is a distributed Bragg grating, and the transmittance at the output end of the distributed Bragg grating is as shown in formula (2):

[0085]

[0086] The reflectivity at the reflecting end is shown in formula (3):

[0087]

[0088] Where, γ 2 =κ 2 +[α-iδ] 2 κ=πΔn / λ0 is the grating coupling coefficient, α is the grating transmission loss, δ is the phase detuning, Δn is the grating refractive index difference, and λ0=2n eff ×Λ0 is the Bragg wavelength, n eff The effective refractive index is given by Λ0, and the grating period is given by κ = 100m. -1 n eff When λ = 1.5459 and Λ0 = 530 nm, the transmittance and reflectance of the wavelength selective feedback device 131 are as follows: Figure 12 As shown.

[0089] Through this embodiment, wavelength selection feedback devices can be selected from distributed Bragg gratings and microring resonators as needed, enabling precise wavelength selection and feedback control of laser output light, thereby improving the overall resolution and stability of the system.

[0090] In one exemplary embodiment, the wavelength selection feedback device is a microring resonator, and the wavelength selection feedback module further includes an on-chip Sagnac mirror. The on-chip Sagnac mirror is an optical device based on the Sagnac effect, utilizing the structural characteristics of the microring resonator to achieve light reflection and interference.

[0091] Furthermore, the Sagnac mirror may include a phase shifter, which includes at least one of the following: a thermally modulated phase shifter based on a silicon waveguide, a thermally modulated phase shifter based on a silicon nitride waveguide, a PN positive-negative electro-optic phase shifter based on a silicon waveguide, a PIN positive intrinsically negative electro-optic phase shifter based on a silicon waveguide, a thermally modulated phase shifter based on a lithium niobate thin-film waveguide, and an electro-optic phase shifter based on a lithium niobate thin-film waveguide. Here, the phase shifter in the Sagnac mirror can be used to adjust the reflectivity of the Sagnac mirror. For example, as... Figure 13 As shown, Figure 13 The middle section shows the structure of the on-chip Sagnac mirror, and the on-chip Sagnac mirror including the phase shifter 140.

[0092] It should be noted that for external cavity lasers with on-chip Sagnac mirror phase shifters, they are different from those on passive optical chips. The phase shifter on the on-chip Sagnac mirror can be called the first phase shifter, and the phase shifter on the passive optical chip can be called the second phase shifter.

[0093] In this embodiment, when the wavelength selection feedback device is a microring resonator, an on-chip Sagnac mirror is installed in the microring resonator, which can achieve precise control of the reflected light through reflection.

[0094] In one exemplary embodiment, the microring resonator includes at least one of the following: an all-through microring resonator, a upload / download microring resonator, a structure composed of cascaded microring resonators, and a tunable microring resonator with applied electrodes.

[0095] In this embodiment, the microring resonator (MRR) can be an all-through MRR, a upload / download MRR, a structure composed of cascaded MRRs, or a tunable MRR with electrodes. The structure of an all-through MRR is as follows: Figure 14 As shown, the structure of upload / download type MRR is as follows: Figure 15 As shown.

[0096] For example, taking a wavelength selective feedback device (MSR) as an upload / download type MRR, and including an on-chip Sagnac mirror with a first phase shifter, light is output from an active multimode gain chip, transmitted from the active MMR to a passive optical chip via an end-face converter. Through a conical structure, the multimode light from the active MMR is confined to a single mode in the lateral dimension. Due to the waveguide thickness of the passive optical chip, it is also confined to a single mode in the longitudinal dimension. Then, it is transmitted through the left waveguide of the second phase shifter to the second phase shifter, output through the right waveguide of the second phase shifter, and then input into the upload / download type MRR. Due to the wavelength selectivity formed by the MRR's resonance, the light is confined to a single longitudinal mode. Then, part of the light is output from the download end of the upload / download type MRR and transmitted to the input end of the on-chip Sagnac mirror. By adjusting the first phase shifter of the Sagnac mirror, the reflectivity of the mirror can be adjusted. The reflected light is then transmitted through the input end of the Sagnac mirror. The light is sent to the download end of the upload / download type MRR, then input into the MRR, then output from the input end of the upload / download type MRR, then through the second phase shifter and the end face mode field converter, and finally transmitted back to the active multimode gain chip. It is then reflected by the high-reflection film of the active multimode gain chip, thus forming a longer resonant cavity that includes the active multimode gain chip, the end face mode field converter, the second phase shifter, the upload / download type MRR, and the on-chip Sagnac mirror. The other part of the light passes through the output end of the on-chip Sagnac mirror to form laser output.

[0097] This embodiment allows for the selection of microring resonators from various options, including all-through microring resonators, upload / download microring resonators, structures composed of cascaded microring resonators, and tunable microring resonators with electrodes, to enhance the flexibility of external cavity laser configuration.

[0098] In one exemplary embodiment, the active multimode gain chip includes at least one of the following: a multimode Fabry-Perot laser, a multimode reflective semiconductor optical amplifier.

[0099] Both multimode Fabry-Perot lasers and multimode reflective semiconductor optical amplifiers are optical devices based on the Fabry-Perot cavity structure. The resonant cavity of a multimode Fabry-Perot laser is composed of two cleaved surfaces of a semiconductor material. Multimode Fabry-Perot lasers can support multiple modes of laser oscillation and achieve high power output through multiple reflections and superpositions. Multimode reflective semiconductor optical amplifiers can amplify incident light signals by utilizing the stimulated emission effect of semiconductor materials. They can support multiple modes of optical signal amplification, are suitable for the transmission and processing of multimode optical signals, and can achieve high optical gain.

[0100] This embodiment demonstrates how using an active multimode gain chip that can provide high power output or high optical gain can improve the output power of an external cavity laser.

[0101] The external cavity laser in this embodiment will be explained below with reference to optional examples. The external cavity laser in this optional example includes an active multimode gain chip and a passive optical chip. The passive optical chip includes an end-face mode field converter and a wavelength selection feedback module. The passive optical chip may or may not include a phase shifter. The wavelength selection feedback module can be a distributed Bragg grating or a microring resonator.

[0102] In one alternative example, an external cavity laser is provided, such as Figure 16 As shown, the external cavity laser 100 includes an active multimode gain chip 101 and a passive optical chip 102. The passive optical chip 102 includes an end-face mode field converter 110 and a wavelength selection feedback module 130. The wavelength selection feedback module 130 includes a wavelength selection feedback device 131, which is a distributed Bragg grating.

[0103] Light is output from the active multimode gain chip 101, and transmitted from the active multimode gain chip to the passive optical chip 102 through the end-face mode field converter 110. Through the positive cone structure, the multimode light of the active multimode gain is restricted to single mode in the lateral dimension. Due to the waveguide thickness of the passive optical chip 102, it is also restricted to single mode in the longitudinal dimension. The light then passes through the left waveguide of the wavelength selective feedback device 131 (i.e., the distributed Bragg grating) and is input into the distributed Bragg grating. Due to the wavelength selective characteristics of the distributed Bragg grating, the light is confined to a single longitudinal mode. Subsequently, part of the light is reflected by the distributed Bragg grating and fed back through the left waveguide of the distributed Bragg grating and the end-face mode-field converter 110, and then transmitted back to the active multimode gain chip 101. It is then reflected by the high-reflection film of the active multimode gain chip, thus forming a resonant cavity with a longer cavity length that includes the active multimode gain chip 101, the end-face mode-field converter 110, and the wavelength selective feedback device 131. This forms a self-injection lock, allowing another part of the light to output a high-performance laser with narrow linewidth and high coherence characteristics through the right waveguide of the distributed Bragg grating.

[0104] In another alternative example, a variant of the external cavity laser is provided, such as Figure 17 As shown, the external cavity laser 100 includes an active multimode gain chip 101 and a passive optical chip 102. The passive optical chip 102 includes an end-face mode field converter 110, a phase shifter 120, and a wavelength selection feedback module 130. The wavelength selection feedback module 130 includes a wavelength selection feedback device 132 and a directional coupler 133B. The wavelength selection feedback device 132 is a upload / download type MRR.

[0105] Light is output from the active multimode gain chip 101, passes through the end-face mode-field converter 110, and is transmitted from the active multimode gain chip to the passive optical chip 102. Through a conical structure, the multimode light from the active multimode gain is confined to single-mode in the lateral dimension. Due to the waveguide thickness of the passive optical chip 102, it is also confined to single-mode in the longitudinal dimension. The light is then output to the left waveguide of the phase shifter 120, and from the right waveguide of the phase shifter 120 to the wavelength selective feedback module 130. From the lower left waveguide of the directional coupler 133B, and from the lower right waveguide of the directional coupler 133B, the light is input to the input waveguide of the wavelength selective feedback device 132 (i.e., the upload / download type MRR), thus entering the MRR. Then, part of the light is output from the download end of the upload / download type MRR and output to the upper right waveguide of the directional coupler 133B, while part of the light is fed back from the lower left waveguide of the directional coupler 133B. The light passes through the phase shifter 120 and the end-face mode field converter 110, and is transmitted back to the active multimode gain chip 101. It is then reflected by the high-reflectivity film of the active multimode gain chip, thus forming a longer resonant cavity containing the active multimode gain chip 101, the end-face mode field converter 110, the phase shifter 120, the directional coupler 133B, and the wavelength selective feedback device 132. Combined with the resonance effect of MRR, self-injection locking is formed, so that another part of the light is output through the upper left waveguide of the directional coupler 133B to produce a high-performance laser with narrow linewidth and high coherence characteristics.

[0106] In yet another optional example, a different variant of the external cavity laser is provided, such as Figure 18 As shown, the external cavity laser 100 includes an active multimode gain chip 101 and a passive optical chip 102. The passive optical chip 102 includes an end-face mode field converter 110 and a wavelength selection feedback module 130. The wavelength selection feedback module 130 includes a Y branch 133A and a wavelength selection feedback device 131, which is a distributed Bragg grating.

[0107] Light is output from the active multimode gain chip 101, and transmitted from the active multimode gain chip to the passive optical chip 102 through the end-face mode field converter 110. Through the positive cone structure, the multimode light of the active multimode gain is restricted to single mode in the lateral dimension. Due to the waveguide thickness of the passive optical chip 102, it is also restricted to single mode in the longitudinal dimension. Afterwards, the light is input through the left waveguide of the Y-branch 133A, and then output from the upper right waveguide of the 133A to the left waveguide of the wavelength selective feedback device 131 (i.e., the distributed Bragg grating). The light is input into the distributed Bragg grating. Due to the wavelength selective characteristics of the distributed Bragg grating, the light is confined to a single longitudinal mode. Then, part of the light is reflected by the distributed Bragg grating and fed back through the left waveguide of the distributed Bragg grating, the upper right waveguide and the left waveguide of the Y-branch 133A, and the end-face mode field converter 110. It is then transmitted back to the active multimode gain chip 101 and reflected again by the high-reflection film of the active multimode gain chip. This forms a longer resonant cavity containing the active multimode gain chip 101, the end-face mode field converter 110, the Y-branch 133A, and the wavelength selective feedback device 131. This forms a self-injection lock, allowing another part of the light to output a high-performance laser with narrow linewidth and high coherence characteristics through the lower right waveguide of the Y-branch 133A.

[0108] In yet another alternative example, a further variation of the external cavity laser is provided, such as Figure 19 As shown, the external cavity laser 100 includes an active multimode gain chip 101 and a passive optical chip 102. The passive optical chip 102 includes an end-face mode field converter 110, a phase shifter 120, and a wavelength selection feedback module 130. The wavelength selection feedback module 130 includes a wavelength selection feedback device 132 and an on-chip Sagnac mirror 135. The wavelength selection feedback device 132 is a upload / download type MRR, and the on-chip Sagnac mirror 135 includes a phase shifter 140. In this case, the phase shifter on the passive optical chip is the phase shifter 120.

[0109] Light is output from the active multimode gain device 101, passes through the end-face mode-field converter 110, and is transmitted from the active multimode gain chip 101 to the passive optical chip 102. Through a conical structure, the multimode light from the active multimode gain is confined to single-mode in the lateral dimension. Due to the waveguide thickness of the passive optical chip, it is also confined to single-mode in the longitudinal dimension. Then, it passes through the left waveguide of the phase shifter 120 to the phase shifter, and then through the right waveguide of the phase shifter to the input waveguide of the wavelength selection feedback device 132 (i.e., the upload / download type MRR), thus being input into the MRR. Next, a portion of the light is output from the download end of the upload / download type MRR and transmitted to the input end of the on-chip Sagnac mirror 135. By adjusting the phase shifter 140 on the Sagnac mirror 135, the reflectivity of the mirror can be adjusted. The reflected light passes through the input end of the Sagnac mirror 135 to the download end of the upload / download type MRR 132, and then back into the MRR, and then through the upload / download type... The input of the MRR132 is output, then passes through the phase shifter 120 and the end-face mode-field converter 110, and is transmitted back to the active multimode gain chip 101. It is then reflected by the high-reflectivity film of the active multimode gain chip 101, thus forming a longer resonant cavity that includes the active multimode gain chip 101, the end-face mode-field converter 110, the phase shifter 120, the upload / download type MRR132, and the on-chip Sagnac mirror 135. Combined with the resonance effect of the MRR, self-injection locking is formed, so that another part of the light is output through the output waveguide of the on-chip Sagnac mirror 135 to produce a high-performance laser with narrow linewidth and high coherence characteristics.

[0110] This optional example demonstrates how high WPE under high current is achieved through a wide waveguide active multimode gain, a passive optical chip mode field converter design, and a high-performance wavelength selection feedback device on the passive optical chip, thereby realizing high-power, high-performance laser output.

[0111] According to another aspect of the embodiments of this application, a lidar is also provided. As an optional implementation, such as... Figure 20 As shown, Figure 20 This is a schematic diagram of the structure of a lidar according to an embodiment of this application, as shown below. Figure 20 As shown, the lidar includes: a light source 2001, a beam splitter 2002, a phased array antenna 2003, and a detection module 2004, wherein the light source 2001 includes an external cavity laser in any of the above embodiments. As already described, it will not be repeated here.

[0112] It should be noted that if the external cavity laser already includes some of the structures in the beam splitter, phased array antenna, and detection module, then there is no need to repeat the above structures outside the external cavity laser.

[0113] Obviously, those skilled in the art should understand that the modules or steps of this application described above can be implemented using general-purpose computing devices. They can be centralized on a single computing device or distributed across a network of multiple computing devices. They can be implemented using computer-executable program code, and thus can be stored in a storage device for execution by a computing device. In some cases, the steps shown or described can be performed in a different order than those presented here, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. Thus, this application is not limited to any particular combination of hardware and software.

[0114] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the protection scope of this application.

Claims

1. An external cavity laser, characterized by, include: Active multimode gain chips and passive optical chips; among them, The active multimode gain chip is docked and coupled to the passive optical chip; the active multimode gain chip is used to provide a multimode beam, and the multimode beam is fed by the passive optical chip to form a partial single-mode optical feedback and a single-mode optical output.

2. The external cavity laser according to claim 1, characterized in that, The passive optical chip includes: an end-face mode field converter and a wavelength selection feedback module, wherein the wavelength selection feedback module includes an input waveguide, a wavelength selection feedback device and an output waveguide; The active multimode gain chip is coupled to the passive optical chip via the end-face mode field converter. The multimode beam is transmitted from the active multimode gain chip to the passive optical chip via the end-face mode field converter and converted into a single-mode beam. It is then transmitted to the wavelength selective feedback device via the input waveguide. Part of the single-mode beam enters the resonant cavity composed of the active multimode gain chip and the passive optical chip after passing through the wavelength selective feedback device to form the single-mode optical feedback. Another part of the single-mode beam is output through the output waveguide after passing through the wavelength selective feedback device to form the single-mode optical output.

3. The external cavity laser according to claim 2, characterized in that, The end-face mode field converter is a positive cone coupling structure or a multi-end-face coupling structure.

4. The external cavity laser according to claim 2, characterized in that, The passive optical chip also includes a phase shifter. The end-face mode field converter is connected to the left waveguide of the phase shifter, and the right waveguide of the phase shifter is connected to the input waveguide of the wavelength selection feedback module. The phase shifter is used to modulate the single-mode beam.

5. The external cavity laser according to claim 4, characterized in that, The passive optical chip is made of one of the following materials: silicon, silicon nitride, thin-film lithium niobate, and the phase shifter is one of the following: thermo-optical phase shifter, electro-optical phase shifter.

6. The external cavity laser according to claim 2, characterized in that, The wavelength selective feedback device includes at least one of the following: a distributed Bragg grating, a microring resonator.

7. The external cavity laser according to claim 2, characterized in that, The wavelength selective feedback device is a micro-ring resonator, and the wavelength selective feedback module also includes an on-chip Sagnac mirror.

8. The external cavity laser according to claim 7, characterized in that, The microring resonator includes at least one of the following: a full-pass microring resonator, a upload / download microring resonator, a structure composed of cascaded microring resonators, and a tunable microring resonator with electrodes.

9. The external cavity laser according to any one of claims 1 to 8, characterized in that, The active multimode gain chip includes at least one of the following: a multimode Fabry-Perot laser, a multimode reflective semiconductor optical amplifier.

10. A lidar, characterized in that, The lidar includes a light source, a beam splitter, a phased array antenna, and a detection module, wherein the lidar comprises an external cavity laser as described in any one of claims 1 to 9.

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