Micro-ring assisted DBR external cavity laser

Abstract

The application relates to the technical field of external cavity lasers, and particularly provides a micro-ring assisted DBR external cavity laser, which comprises a reflective semiconductor optical amplifier and a photonic chip, the photonic chip comprises a phase shifter, a micro-ring resonator and a ridge waveguide Bragg grating; wherein the Bragg grating is etched in the ridge waveguide flat plate area of the photonic chip, the ridge waveguide Bragg grating serves as an on-chip mirror, and the reflective semiconductor optical amplifier and the ridge waveguide Bragg grating constitute a Fabry-Perot resonant cavity; the phase shifter and the micro-ring resonator change the refractive indexes of the phase shifter and the micro-ring resonator based on the thermo-optic effect, thereby synchronously changing the resonant wavelengths of the micro-ring resonator and the resonant cavity, the resonant wavelengths of the micro-ring resonator and the resonant cavity are kept aligned and moved, and mode-hop-free wavelength tuning is realized. The application solves the defects of high process requirement, small process tolerance, limited mode-hop-free tuning range, limited power and limited line width in the manufacturing process of the traditional external cavity laser.

Description

Technical Field

[0001] This invention belongs to the field of external cavity laser technology, and particularly relates to a micro-ring assisted DBR external cavity laser. Background Technology

[0002] The development of quantum information technology has placed unprecedentedly stringent demands on the performance of coherent light sources. In cutting-edge fields such as cold atom quantum computing, ion trap quantum simulation, quantum networks, and precision measurement, lasers are not only the core tools for exciting and manipulating qubits, but also directly determine the fidelity of quantum state preparation, coherence retention time, and measurement accuracy. Specifically, quantum technology scenarios require laser sources to simultaneously possess narrow linewidths, ultra-low frequency noise, long-term frequency stability, precise wavelength tuning capabilities, and multi-wavelength collaborative operation capabilities. However, traditional solutions face fundamental contradictions: while commercially available distributed feedback lasers are small in size, their linewidths are only in the MHz range, making it difficult to meet the requirements of quantum coherent manipulation; while bulk external cavity semiconductor lasers can achieve kHz-level narrow linewidths, their large size, alignment sensitivity, and cost bottlenecks severely restrict the engineering and large-scale deployment of quantum systems.

[0003] Hybrid integrated tunable external cavity lasers address these challenges by achieving sub-micron precision alignment between a III-V group gain chip and a high-quality silicon-based / silicon nitride passive cavity, constructing a composite resonant system. This approach fully leverages the high efficiency of the gain chip and the ultra-low loss characteristics of the silicon photonics platform, extending the effective cavity length to the centimeter level and narrowing the linewidth by two orders of magnitude to the sub-kHz level. Simultaneously, utilizing the tuning mechanism of the microring resonator, it achieves wide-range mode-hopping-free tuning while maintaining single-mode stability, with tuning precision controlled at the megahertz level by thermo-optical or electro-optical effects. Crucially, the hybrid integrated architecture compresses the volume to the cubic centimeter level through chip-level packaging and achieves frequency stability with an Allen variance of <10⁻¹² @1s through stress isolation design, meeting the stringent requirements of long-term coherence in quantum systems.

[0004] In quantum technology applications, this technology exhibits unique advantages: its ultra-high side-mode suppression ratio ensures the purity of qubit manipulation; its fast wavelength tuning capability supports time-varying Hamiltonian manipulation in quantum simulations; and its multi-channel integration potential provides a feasible path for achieving parallel addressing of large-scale qubit arrays. For example, in neutral atom-based quantum computing architectures, hybrid integrated lasers can achieve high-fidelity two-qubit gate operations by precisely tuning to specific Rydberg state transition lines; in ion trap systems, its narrow linewidth characteristics can significantly suppress off-center optical frequency shifts caused by laser frequency noise, reducing the quantum logic gate error rate to 10-1. -4Below the order of magnitude. Furthermore, by integrating thin-film lithium niobate (TFLN) electro-optic modulation, this technology is approaching the quantum limits of megahertz-level tuning speed and hertz-level frequency resolution, providing a core light source solution for building scalable, programmable quantum information processing platforms.

[0005] The tuning principles of existing hybrid integrated tunable external cavity lasers mainly rely on dual-microring vernier filters and single-microring self-injection locking. The dual-microring vernier filter type hybrid integrated tunable external cavity laser uses a semiconductor optical amplifier as the gain chip and couples it to a passive external cavity chip. The external cavity chip has two microring resonators of slightly different sizes. The free spectral ranges of the two microring resonators are different, and they are connected in series to form a vernier filter, which can expand the free spectral range and achieve single-mode lasing. Furthermore, by modulating the refractive index of the microring resonators and phase shifters, the free spectral ranges of the two microring resonators can overlap in different locations, thus achieving wide-range wavelength tuning. Simultaneously, the longer external cavity and the resonance enhancement effect of the microrings can achieve narrow linewidth output. The single-microring self-injection locking external cavity laser uses a distributed feedback or distributed Bragg reflector laser as the gain chip and couples it to a passive external cavity chip. The gain chip used is usually a high-quality resonator that injects single-mode lasing into the external cavity chip. The external high-quality resonator feeds a portion of the light back to the gain chip to narrow the linewidth. Furthermore, by modulating the refractive index of the micro-ring resonator in the external cavity chip, its resonant wavelength can be changed, thereby achieving mode-skipping-free tuning within a certain range.

[0006] However, the self-injection locking principle, which uses a distributed feedback laser or a distributed Bragg reflector laser as the optical gain chip, inherently possesses mode selection capabilities. The emitted light is typically a single longitudinal mode, and locking via external resonant cavity feedback can only occur within that single longitudinal mode of the emitted light from the gain chip. This limits the laser's tuning range. Furthermore, due to the high refractive index of silicon, single-mode waveguides based on silicon are small in size, thus requiring sophisticated etching processes with small tolerances for silicon waveguides. In addition, the high inherent loss and two-photon absorption effect of silicon also limit the laser's power and linewidth. Summary of the Invention In view of this, the present invention aims to provide a micro-ring assisted DBR external cavity laser, which uses a reflective semiconductor optical amplifier as the gain chip, and combines micro-rings on a silicon nitride platform with a planar Bragg grating for filtering. It also incorporates a two-dimensional synchronous tuning mechanism of a dual-zone phase shifter and a micro-ring resonator. While simplifying the process, it achieves a wide range of mode-hopping-free tuning and narrow linewidth output, solving the defects of traditional external cavity laser manufacturing processes such as high process requirements, small process tolerance, limited mode-hopping-free tuning range, and limited power and linewidth.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows: This invention provides a microring-assisted DBR external cavity laser, comprising: Reflective semiconductor optical amplifiers are used to provide the gain medium; In addition, a photonic chip with thermo-optical effect, the photonic chip including a phase shifter, a micro-ring resonator and a ridge waveguide Bragg grating; Among them, the reflective semiconductor optical amplifier is connected to the end face of the photonic chip; The ridge waveguide Bragg grating is etched in the ridge waveguide plate area of ​​the photonic chip. The ridge waveguide Bragg grating serves as an on-chip mirror and forms a Fabry-Perot resonant cavity with the reflective semiconductor optical amplifier, and is used for wavelength selection of laser light. The phase shifter and the microring resonator are equipped with heaters. By applying a time-varying voltage signal with a specific relationship to the heaters of the phase shifter and the microring resonator, heating is achieved. Based on the thermo-optic effect, the refractive index of the phase shifter and the microring resonator is changed, thereby synchronously changing the resonant wavelength of the microring resonator and the Fabry-Perot resonator. The resonant wavelengths of the microring resonator and the Fabry-Perot resonator remain aligned and shifted, achieving mode-hopping-free wavelength tuning.

[0008] Preferably, the reflective semiconductor optical amplifier includes a low-reflectivity end face and a high-reflectivity end face, with the low-reflectivity end face being directly coupled to the end face of the photonic chip; the high-reflectivity end face and the ridge waveguide Bragg grating form a Fabry-Perot resonant cavity.

[0009] Preferably, one end of the reflective semiconductor optical amplifier is coated with an anti-reflection film to form a high-reflectivity end face; the other end is coated with an anti-reflection film to form a low-reflectivity end face.

[0010] Preferably, the waveguide layer of the photonic chip is made of silicon nitride.

[0011] Preferably, the photonic chip further includes a first mode size converter, which is used to thermally transfer the output light field of the reflective semiconductor optical amplifier into the photonic chip.

[0012] Preferably, the phase shifter includes a first phase shifter and a second phase shifter, which are respectively disposed on both sides of the micro-ring resonator. The first phase shifter and the second phase shifter are respectively provided with heaters and electrodes, and heating is performed by applying a time-varying voltage signal to the electrodes.

[0013] Preferably, the microring resonator includes: a ring optical waveguide based on strip silicon nitride, and straight-bus silicon nitride optical waveguides disposed on the upper and lower sides of the ring optical waveguide. The ring optical waveguide and the straight-bus silicon nitride optical waveguide include, in sequence: a silicon substrate, a silicon dioxide buried oxide layer, a silicon nitride thin film, a silicon dioxide upper cladding layer, a heater, and an electrode layer.

[0014] Preferably, the radius of the ring waveguide is 100-120nm, the distance between the straight-bus silicon nitride waveguide and the ring waveguide is 600-950nm, and the straight-bus silicon nitride waveguide and the ring waveguide are evanescent wave coupled.

[0015] Preferably, the ridge waveguide Bragg grating has a period of 450-500nm, a ripple amplitude of 100-300nm, a duty cycle of 30%-50%, and a 3dB bandwidth of its reflection spectrum that is less than twice the free spectral range of the micro-ring resonator. The distance between the ridge waveguide Bragg grating and the ridge region of the ridge waveguide of the photonic chip is 250-400nm.

[0016] Preferably, the photonic chip further includes a second mode size converter, which is disposed between the second phase shifter and the ridge waveguide Bragg grating, for thermally transitioning the filtered and phase-modulated laser to the ridge waveguide Bragg grating.

[0017] Compared with the prior art, the present invention can achieve the following beneficial effects: This invention employs a reflective semiconductor optical amplifier coupled to a silicon nitride photonic chip via end-face coupling to form a hybrid integrated external cavity tunable laser. The external cavity chip contains only a mode size converter, a bus waveguide, a micro-ring resonator, and a ridge waveguide Bragg grating. It features a simple structure, flexible design, and low loss, and solves the defects of traditional external cavity laser manufacturing processes, such as high process requirements, small process tolerance, limited non-mode-hopping tuning range, and limited power and linewidth. It is also beneficial for coupling packaging and mass production.

[0018] This invention uses a reflective semiconductor optical amplifier as the gain chip, whose gain bandwidth is much greater than that of distributed feedback semiconductor lasers and distributed Bragg reflection semiconductor lasers. Combined with the wide reflection spectrum of the ridge waveguide Bragg grating, and through the synchronous tuning mechanism of the micro-ring and phase shifter, it ensures that the longitudinal modes are always aligned when the wavelength changes continuously, thereby achieving a wide range of mode-hopping-free tuning on the order of tens of GHz.

[0019] This invention innovatively etches a Bragg grating onto the planar region of a ridge waveguide, achieving weak coupling by controlling the ripple amplitude and grating period. Compared to traditional grating processes, this design eliminates the need for complex and precise weak coupling control, has lower precision requirements for the etching process, and offers greater process tolerance, thus significantly improving production yield. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1This is a structural diagram of a microring-assisted DBR external cavity laser provided according to an embodiment of the present invention; Figure 2 This is a cross-sectional view of a ridge waveguide Bragg grating provided according to an embodiment of the present invention; Figure 3 This is a top view of a ridge waveguide Bragg grating provided according to an embodiment of the present invention.

[0021] The reference numerals in the figures include: 1. Reflective semiconductor optical amplifier; 101. Antireflective coating; 102. 2. Photonic chip; 3. First mode size converter; 4. Input waveguide; 5. First phase shifter; 6. Micro-ring resonator; 7. Second mode size converter; 8. Ridge waveguide Bragg grating; 9. Output waveguide; 10. Ring waveguide 601, straight bus silicon nitride waveguide 602; Flat area A, ridge area B. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and do not constitute a limitation thereof. Similar elements in different embodiments are referred to by associated similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the invention. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, some operations related to the invention are not shown or described in the specification. This is to avoid obscuring the core parts of the invention with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; the relevant operations can be fully understood based on the description in the specification and general technical knowledge in the art.

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined to form various implementations. Furthermore, the order of the steps or actions in the method description can be changed or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various orders in the specification and drawings are merely for the clear description of a particular embodiment and do not imply a mandatory order, unless otherwise stated that a particular order must be followed.

[0024] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] Please see Figure 1 In one embodiment of the present invention, a microring-assisted DBR external cavity laser is provided, comprising: A reflective semiconductor optical amplifier 1 is used to provide the gain medium; And, a photonic chip 2 with thermo-optical effect, the photonic chip 2 including a phase shifter, a micro-ring resonator 6 and a ridge waveguide Bragg grating 9; Among them, the reflective semiconductor optical amplifier 1 is end-to-end coupled to the photonic chip 2; The ridge waveguide Bragg grating 9 is etched in the ridge waveguide plate area of ​​the photonic chip 2. The ridge waveguide Bragg grating 9 serves as an on-chip mirror and together with the reflective semiconductor optical amplifier 1, it forms a Fabry-Perot resonant cavity and is used for wavelength selection of laser light. The phase shifter and the microring resonator 6 are equipped with heaters. By applying a time-varying voltage signal with a specific relationship to the heaters of the phase shifter and the microring resonator 6, heating is achieved. Based on the thermo-optic effect, the refractive index of the phase shifter and the microring resonator 6 is changed, thereby synchronously changing the resonant wavelength of the microring resonator 6 and the Fabry-Perot resonator. The resonant wavelengths of the microring resonator 6 and the Fabry-Perot resonator 6 remain aligned and shifted, achieving mode-hopping-free wavelength tuning.

[0028] The reflective semiconductor optical amplifier 1 serves as the gain unit of the entire laser, providing the gain medium for laser excitation. The reflective semiconductor optical amplifier 1 can be a directly adopted existing reflective semiconductor optical amplifier chip. It is coupled to the end face of the photonic chip 2 via end-face coupling. Alternatively, micro-transfer technology can be used to achieve heterogeneous integration of the reflective semiconductor optical amplifier 1 and the photonic chip 2. The reflective semiconductor optical amplifier 1 includes two end faces, a front and a rear, with the rear end face coupled to the photonic chip 2. The front end face of the reflective semiconductor optical amplifier 1 is coated with an anti-reflection film, forming a high-reflectivity end face with a reflectivity of 90%. This end face serves as a mirror in the entire laser resonant cavity, forming a Fabry-Perot resonant cavity together with the ridge waveguide Bragg grating 9 at the other end. The rear end face of the reflective semiconductor optical amplifier 1 is coated with an anti-reflection film, forming a low-reflectivity end face with a reflectivity of 0.01%, thereby eliminating end-face reflection, preventing unnecessary self-oscillations within the resonant cavity, and ensuring efficient, unidirectional coupling of light into the silicon nitride photonic chip 2. Compared to existing DFB or DBR lasers, the reflective semiconductor optical amplifier 1 used in this embodiment of the invention has an extremely wide gain spectrum, which can provide a gain basis for wide-range wavelength tuning. Furthermore, during the excitation light circulation process in the cavity, it is amplified every time it passes through the reflective semiconductor optical amplifier 1 to compensate for losses and ensure that the laser has sufficiently high output power.

[0029] The photonic chip 2 is made of silicon nitride and is used to realize functions such as wavelength selection, phase adjustment, feedback reflection, and laser output. The optical transmission unit of the photonic chip 2 is mainly a silicon nitride optical waveguide. The silicon nitride optical waveguide is a multilayer dielectric film structure. The silicon nitride optical waveguide is a strip waveguide with a height of 400nm and a width of 800-1000nm. From bottom to top, it includes a silicon substrate, a silicon dioxide buried oxide layer, a silicon nitride thin film, a silicon dioxide top cladding, a microheater, and an electrode layer. Along the waveguide structure of the photonic chip 2, the following components are integrated in sequence: a first mode size converter 3, an input waveguide 4, a first phase shifter 5, a micro-ring resonator 6, a second phase shifter 7, a second mode size converter 8, a ridge waveguide Bragg grating 9, and an output waveguide 10. Among them, the first mode size converter 3 is a transition structure between the reflective semiconductor optical amplifier 1 and the photonic chip 2, and it thermally transitions the output light field of the reflective semiconductor optical amplifier 1 to the photonic chip 2. Because the mode size of the reflective semiconductor optical amplifier 1 differs from that of the input waveguide 4 by orders of magnitude, direct docking would result in significant mode mismatch loss. Therefore, a first mode size converter 3 is used to achieve mode matching between the reflective semiconductor optical amplifier 1 and the input waveguide 4, thereby reducing reflection and scattering losses.

[0030] Input waveguide 4 is positioned at the rear end of the first mode-size converter 3 for optical field transmission. A first phase shifter 5 is positioned between the input waveguide 4 and the micro-ring resonator 6 to adjust the optical length of the laser resonator cavity for the first time, thereby changing the laser optical phase. A second phase shifter 7 is positioned between the micro-ring resonator 6 and the second mode-size converter 8, with the micro-ring resonator 6 positioned between the first phase shifter 5 and the second phase shifter 7. The second phase shifter 7 is used for a second adjustment of the optical length of the laser resonator cavity, combining with the first phase shifter 5 to change the laser optical phase. The total length of the first phase shifter 5 and the second phase shifter 7 is 500-1500 micrometers, maximizing the mode-skipping-free tuning range while considering chip size, and working with the micro-ring resonator 6 to achieve mode-skipping-free tuning. This two-stage phase tuning design can compensate for errors introduced by environmental fluctuations through two adjustments, compensating for minor phase mismatches that occur during tuning, and ensuring that the phase delay after one round trip within the cavity strictly meets the resonance condition.

[0031] The micro-ring resonator 6 adopts a symmetrical all-through structure, including: a ring optical waveguide 601 based on strip-shaped silicon nitride, and straight-bus silicon nitride optical waveguides 602 disposed on the upper and lower sides of the ring optical waveguide 601. The ring optical waveguide 601 and the straight-bus silicon nitride optical waveguide 602 include, in sequence: a silicon substrate, a silicon dioxide buried oxide layer, a silicon nitride thin film, a silicon dioxide upper cladding, a heater, and an electrode layer. In this embodiment, the radius of the ring optical waveguide 601 is 100-120 nm, and the straight-bus silicon nitride optical waveguide 602 and the ring optical waveguide 601 are coupled via evanescent wave coupling, with a certain coupling distance between them, which can be designed to be 600-950 nm. The micro-ring resonator 6 is the main resonant wavelength selection element in the resonant cavity. Only wavelengths that meet the resonance conditions of the micro-ring resonator 6 will enter the subsequent optical path through the straight-bus silicon nitride optical waveguide 602 and the ring optical waveguide 601; light of other wavelengths is suppressed. The narrowband filtering characteristics of the micro-ring resonator 6 effectively limit the number of longitudinal modes of the laser, while its resonance enhancement effect extends the lifetime of photons in the cavity, realizing narrow linewidth single longitudinal mode output.

[0032] In this embodiment of the invention, phase modulation and wavelength selection are achieved by combining the first phase shifter 5, the micro-ring resonator 6, and the second phase shifter 7. On the upper surface of the photonic chip 2, the first phase shifter 5, the micro-ring resonator 6, and the second phase shifter 7 are each provided with a corresponding heater and electrode. By applying a time-varying voltage signal with a specific relationship to the heater above the micro-ring resonator 6, the silicon nitride optical waveguide of the micro-ring resonator 6 is heated. The thermo-optical effect of the silicon nitride material is used to change the refractive index of the waveguide, causing the resonant wavelength of the micro-ring resonator 6 to redshift. At the same time, a current signal is applied to the heater of the first phase shifter 5 and the second phase shifter 7 in a specific ratio, and the effective optical length of the laser resonant cavity is changed by the thermo-optical effect, so that the longitudinal mode of the cavity is synchronously redshifted and always aligned with the resonant wavelength of the micro-ring resonator 6, realizing wide-range mode-skipping-free tuning.

[0033] The second mode size converter 8 is disposed between the second phase shifter 7 and the ridge waveguide Bragg grating 9, and is used to connect the strip waveguide and the ridge waveguide of the ridge waveguide Bragg grating 9 region within the photonic chip 2. The laser, after being filtered and phase-modulated by the first phase shifter 5, the micro-ring resonator 6, and the second phase shifter 7, undergoes an adiabatic transition to the ridge waveguide Bragg grating 9 via the second mode size converter 8. Specifically, in this embodiment of the invention, the second mode size converter 8 is a tapered mode size converter, realizing an adiabatic transition from the strip waveguide eigenmode to the ridge waveguide eigenmode. The ridge width of the ridge waveguide in the ridge waveguide Bragg grating 9 region is consistent with the width of the strip waveguide, and the width of the ridge waveguide plate region is greater than the width of the strip waveguide, connected to the strip waveguide via a tapered structure.

[0034] A ridge waveguide Bragg grating 9 is positioned at the rear end of the second mode size converter 8, serving as an on-chip mirror. It forms a Fabry-Perot resonant cavity with the high-reflectivity end face of the reflective semiconductor optical amplifier 1. The ridge waveguide Bragg grating 9 also provides secondary wavelength selection, ensuring that only wavelengths satisfying the Bragg condition are strongly reflected. Due to the periodic comb-like filtering characteristics of the micro-ring resonator 6, more than one longitudinal mode may exist. After filtering by the micro-ring resonator 6, a series of longitudinal modes are selected. The ridge waveguide Bragg grating 9 can cover one of the multiple resonance peaks of the micro-ring, returning only one longitudinal mode along its original path to form a single-mode oscillation. The overlap region between the narrowband resonance peak of the micro-ring resonator 6 and the reflection spectrum of the ridge waveguide Bragg grating 9 determines the final lasing wavelength, thus collaboratively achieving single-mode lasing. The single-mode laser is output through the output waveguide 10 at the rear end of the ridge waveguide Bragg grating 9. The ridge waveguide Bragg grating 9 is a ridge waveguide structure, etched into the ridge waveguide planar region of the photonic chip 2, used for lateral confinement of the optical field. Figure 2 and Figure 3 As shown, the ridge waveguide region of the photonic chip 2 includes a planar region A and a ridge region B. Unlike traditional sidewall gratings, the ridge waveguide Bragg grating 9 of this embodiment is etched in the planar region A, not on the sidewall of the ridge region B. The distance between the ridge waveguide Bragg grating 9 and the ridge region B of the ridge waveguide of the photonic chip is 250-400 nm, and the ripple amplitude is 100-300 nm, which creates a weak perturbation to the optical field to achieve a low coupling coefficient, thereby achieving a narrow-band reflection spectrum. The period of the ridge waveguide Bragg grating 9 is 450-500 nm, which places the reflection spectrum near 1550 nm, with a duty cycle of 30%-50%, achieving a weak grating coupling coefficient. The 3dB bandwidth of the reflection spectrum of the ridge waveguide Bragg grating 9 is less than twice the free spectral range of the micro-ring resonator 6, typically 2-4 nm. The wide reflection spectrum characteristics of the ridge waveguide Bragg grating 9 enable a relatively stable feedback intensity within the laser wavelength (frequency) tuning range, avoiding discontinuities in output spectrum and power caused by mode jumping. The ridge waveguide Bragg grating 9 uses a first-order grating, eliminating the need for a long grating length. Compared to traditional methods that require precise etching of deep submicron gratings on the ridge sidewalls, etching the grating in the planar region has lower precision requirements for photolithography and etching processes, offers greater process tolerance, and improves production yield.

[0035] The micro-ring assisted DBR external cavity laser of this invention achieves wide-range mode-hopping-free tuning based on the wide gain spectrum of the reflective semiconductor optical amplifier 1 and the wide reflection spectrum of the ridge waveguide Bragg grating 9; it achieves narrow linewidth output based on the narrowband filtering and resonance enhancement effect of the micro-ring resonator 6 and the ultra-low loss of the silicon nitride waveguide. In terms of fabrication, it eliminates the need for a weakly coupled extended Bragg grating, thus reducing process requirements and eliminating the need for an ultra-long grating length to achieve the target reflectivity. The micro-ring assisted DBR external cavity laser of this invention features high integration, small chip size, simple fabrication, low cost, and superior device performance. Compared to other tunable external cavity lasers, this invention offers advantages such as a large mode-hopping-free tuning range, simple control, and simple fabrication.

[0036] As an optional embodiment, the waveguide material of the photonic chip 2 can also be silicon or lithium niobate.

[0037] As an alternative embodiment, the reflective semiconductor optical amplifier 1 can also be replaced with a non-reflective optical amplifier, but the coating on the high reflectivity end face of the reflective semiconductor optical amplifier 1 needs to be replaced with a Sangnac ring mirror, and the function of the reflective semiconductor optical amplifier 1 can be realized by combination.

[0038] In summary, the above description is merely a preferred embodiment of this specification and is not intended to limit the scope of protection of this specification. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this specification should be included within the scope of protection of this specification.

[0039] The systems, apparatuses, modules, or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, a computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0040] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0041] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

Claims

1. A microring-assisted DBR external cavity laser, characterized in that, include: Reflective semiconductor optical amplifiers are used to provide the gain medium; And a photonic chip with thermo-optical effect, the photonic chip comprising a phase shifter, a micro-ring resonator, and a ridge waveguide Bragg grating; The reflective semiconductor optical amplifier is coupled face-to-face with the photonic chip. The ridge waveguide Bragg grating is etched into the ridge waveguide plate region of the photonic chip. The ridge waveguide Bragg grating serves as an on-chip mirror and together with the reflective semiconductor optical amplifier, it forms a Fabry-Perot resonant cavity and is used for wavelength selection of laser light. The phase shifter and the microring resonator are equipped with heaters. By applying a time-varying voltage signal with a specific relationship to the heaters of the phase shifter and the microring resonator, heating is achieved. Based on the thermo-optic effect, the refractive index of the phase shifter and the microring resonator is changed, thereby synchronously changing the resonant wavelength of the microring resonator and the Fabry-Perot resonator. The resonant wavelengths of the microring resonator and the Fabry-Perot resonator remain aligned and shifted, achieving mode-hopping-free wavelength tuning.

2. The microring-assisted DBR external cavity laser according to claim 1, characterized in that, The reflective semiconductor optical amplifier includes a low-reflectivity end face and a high-reflectivity end face. The low-reflectivity end face is in-line coupled to the end face of the photonic chip. The high-reflectivity end face and the ridge waveguide Bragg grating form a Fabry-Perot resonant cavity.

3. The microring-assisted DBR external cavity laser according to claim 1, characterized in that, One end of the reflective semiconductor optical amplifier is coated with an anti-reflection film to form a high-reflectivity end face; the other end is coated with an anti-reflection film to form a low-reflectivity end face.

4. The microring-assisted DBR external cavity laser according to claim 1, characterized in that, The waveguide layer of the photonic chip is made of silicon nitride.

5. The microring-assisted DBR external cavity laser according to claim 1, characterized in that, The photonic chip also includes a first mode size converter, which is used to thermally transfer the output light field of the reflective semiconductor optical amplifier into the photonic chip.

6. The microring-assisted DBR external cavity laser according to claim 5, characterized in that, The phase shifter includes a first phase shifter and a second phase shifter, which are respectively disposed on both sides of the micro-ring resonator. The first phase shifter and the second phase shifter are respectively provided with heaters and electrodes, and are heated by applying a time-varying voltage signal to the electrodes.

7. The microring-assisted DBR external cavity laser according to claim 1, characterized in that, The microring resonator includes: a ring optical waveguide based on strip silicon nitride, and straight bus silicon nitride optical waveguides disposed on the upper and lower sides of the ring optical waveguide. The ring optical waveguide and the straight bus silicon nitride optical waveguide include, in sequence: a silicon substrate, a silicon dioxide buried oxide layer, a silicon nitride thin film, a silicon dioxide upper cladding layer, a heater, and an electrode layer.

8. The microring-assisted DBR external cavity laser according to claim 7, characterized in that, The radius of the ring optical waveguide is 100-120nm, the distance between the straight bus silicon nitride optical waveguide and the ring optical waveguide is 600-950nm, and the straight bus silicon nitride optical waveguide and the ring optical waveguide are evanescent wave coupled.

9. The microring-assisted DBR external cavity laser according to claim 1, characterized in that, The ridge waveguide Bragg grating has a period of 450-500nm, a ripple amplitude of 100-300nm, and a duty cycle of 30%-50%. Its 3dB bandwidth of reflection spectrum is less than twice the free spectral range of the micro-ring resonator. The distance between the ridge waveguide Bragg grating and the ridge region of the ridge waveguide of the photonic chip is 250-400nm.

10. The microring-assisted DBR external cavity laser according to claim 6, characterized in that, The photonic chip also includes a second mode size converter, which is disposed between the second phase shifter and the ridge waveguide Bragg grating, for adiabatic transition of the filtered and phase-modulated laser to the ridge waveguide Bragg grating.

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