A narrow-band reflector waveguide and reflector based on edge-coupled Bragg grating resonators

Abstract

This invention discloses a narrowband reflector waveguide and reflector based on a side-coupled Bragg grating resonant cavity, relating to the field of optoelectronics. It includes a main waveguide and a resonant cavity waveguide arranged in parallel. The main waveguide supports TE0 mode transmission, while the resonant cavity waveguide supports both TE0 and TE1 mode transmission. The main waveguide and the resonant cavity waveguide form an asymmetric directional coupling region through side coupling. A first resonant mode and a second resonant mode are formed within the resonant cavity waveguide. A TE0 mode optical signal is input to the main waveguide and coupled to the resonant cavity waveguide, where it is converted into a TE1 mode optical signal. Under the synergistic effect of the first and second resonant modes, the TE1 mode optical signal generates narrowband reflected light of the desired wavelength in TE1 mode. This TE1 mode narrowband reflected light is coupled back to the main waveguide and converted into TE0 mode narrowband reflected light, which is then output from the main waveguide. This narrowband reflector exhibits high reflectivity, narrow linewidth, high side-mode suppression ratio, and good process robustness.

Description

Technical Field

[0001] This invention relates to the field of optoelectronics technology, and in particular to a narrowband reflector waveguide and reflector based on a side-coupled Bragg grating resonator. Background Technology

[0002] The birth and development of fiber optic communication is an inevitable result of the modern information society's pursuit of higher efficiency and greater capacity communication. In the era of traditional metal cable communication, electrical signal transmission was limited by inherent bottlenecks such as narrow bandwidth, high loss, susceptibility to electromagnetic interference, and large weight and size, making it difficult to meet the ever-increasing global data transmission demands. In fiber optic communication systems, high-performance narrowband light sources are key to achieving high-speed, high-capacity information transmission, and external cavity lasers (ECLs) have become the preferred solution due to their excellent spectral characteristics. Their performance is highly dependent on the performance of external feedback components; however, existing feedback schemes all have significant limitations, restricting further improvements in system performance and large-scale integrated applications.

[0003] Among existing feedback schemes, traditional volume diffraction gratings, while offering high-precision wavelength selection and high sidelobe suppression, suffer from a major bottleneck: their bulky three-dimensional optical structure is difficult to integrate monolithically with semiconductor laser chips. This necessitates complex offline alignment and mechanically stabilized packaging, significantly increasing module size, cost, and power consumption, and limiting their practical application in compact optoelectronic systems. Fiber Bragg gratings (FBGs), another common feedback element, offer excellent filtering characteristics, but as fiber optic devices, their coupling with on-chip semiconductor laser sources introduces significant end-face reflections and mode-field mismatch losses. This requires additional lens systems or mode-field converters for efficient optical power transmission, greatly increasing packaging complexity and reliability risks, hindering low-cost, mass production. Microring resonators (MRRs) are a promising integrated optical solution in recent years, offering advantages such as small size and high Q-value, enabling extremely narrowband feedback. However, its drawbacks are also quite prominent: First, in order to achieve stable single-mode operation and wavelength selection, vernier caliper effect tuning is usually required, which requires precise coupling of at least two microrings and complex thermal or electrical tuning, significantly increasing the design difficulty and power consumption of the drive circuit; Second, MRR is extremely sensitive to process fluctuations, and its resonant wavelength is prone to drift with process deviations, resulting in mismatch with the laser gain spectrum, forcing the system to be equipped with a real-time wavelength locking circuit, further increasing the system complexity and cost; In addition, if a cascaded microring structure is used to improve performance, more insertion loss and crosstalk will be introduced, which will have an adverse effect on the output power and side-mode rejection ratio of the laser.

[0004] On the other hand, on-chip reflectors based on Bragg gratings also face multiple challenges. To obtain sufficient reflectivity and narrow bandgap, traditional distributed feedback gratings often require lengths of hundreds of micrometers or even millimeters, which not only occupy valuable chip area but are also prone to spectral degradation due to nanoscale waveguide width inhomogeneity during manufacturing, causing reflection peak distortion and linewidth broadening. Although some studies have proposed using a compact structure of π-phase-shifted antisymmetric gratings cascaded with uniform gratings to shorten device size, this approach faces severe challenges in actual fabrication: the Bragg wavelengths of the two grating segments must be highly matched, and any slight deviation in etching depth, period, or waveguide size will lead to reflection spectrum splitting and a sharp decline in performance; at the same time, such structures typically have limited sidelobe suppression capabilities (generally around 10 dB), and high sidelobes can introduce multi-wavelength feedback, leading to laser mode competition and mode hopping, severely deteriorating the signal-to-noise ratio and stability of the output optical signal, making it difficult to meet the stringent requirements of high-end coherent communication systems for light source purity. Summary of the Invention

[0005] To address the aforementioned problems and technical requirements, the inventors have proposed a narrowband reflector waveguide and reflector based on a side-coupled Bragg grating resonator. The technical solution of this invention is as follows: A narrowband reflector waveguide based on a side-coupled Bragg grating resonant cavity is characterized in that it includes a main waveguide and a resonant cavity waveguide arranged in parallel, wherein the main waveguide supports TE0 mode transmission and the resonant cavity waveguide supports both TE0 mode and TE1 mode transmission. The main waveguide and the resonant cavity waveguide form an asymmetric directional coupling region through side coupling to achieve coupling conversion between the TE0 mode optical signal in the main waveguide and the TE1 mode optical signal in the resonant cavity waveguide; a first resonant mode and a second resonant mode are formed in phase coupling within the resonant cavity waveguide; After the TE0 mode optical signal is input into the main waveguide, it is coupled to the resonant cavity waveguide and converted into a TE1 mode optical signal. Under the synergistic effect of the first resonant mode and the second resonant mode, the TE1 mode optical signal generates TE1 mode narrowband reflected light of the required wavelength. The TE1 mode narrowband reflected light is coupled back to the main waveguide and converted into TE0 mode narrowband reflected light, which is then output from the main waveguide.

[0006] A further technical solution is that the main waveguide includes a first straight waveguide segment, a second straight waveguide segment, and a curved waveguide segment connecting the first straight waveguide segment and the second straight waveguide segment; The resonant cavity waveguide is sequentially fabricated with a first antisymmetric Bragg grating, a uniform Bragg grating, and a second antisymmetric Bragg grating along its length, wherein the phase difference between the first antisymmetric Bragg grating and the second antisymmetric Bragg grating is π.

[0007] A further technical solution is that the curved waveguide segment protrudes in the direction of the resonant cavity waveguide and forms an asymmetric directional coupling region with the section containing the uniform Bragg grating in the resonant cavity waveguide through edge coupling.

[0008] A further technical solution is that, within the resonant cavity waveguide, the first resonant mode is used to realize the conversion between the forward TE1 mode optical signal and the reverse TE0 mode optical signal; The second resonant mode is used to realize the conversion between the forward TE0 mode optical signal and the reverse TE1 mode optical signal.

[0009] A further technical solution is that, within the resonant cavity waveguide, the uniform Bragg grating achieves coupling between the first resonant mode and the second resonant mode by reflecting the TEO mode optical signal.

[0010] A further technical solution is that a tapered waveguide is provided at each end of the resonant cavity waveguide, the width of the tapered waveguide is not greater than the width of the resonant cavity waveguide and gradually decreases in the direction away from the resonant cavity waveguide.

[0011] A further technical solution is that the first antisymmetric Bragg grating, the uniform Bragg grating, and the second antisymmetric Bragg grating are fabricated on the sidewall, surface, or interior of the resonant cavity waveguide.

[0012] A narrowband reflector based on a side-coupled Bragg grating resonator includes a substrate, a lower cladding, and an upper cladding arranged sequentially from bottom to top, with the aforementioned narrowband reflector waveguide based on the side-coupled Bragg grating resonator fabricated between the lower cladding and the upper cladding.

[0013] A further technical solution includes a thermal tuning device, which is disposed on the upper cladding and is used to adjust the reflection wavelength of the narrowband reflector.

[0014] A further technical solution is that the narrowband reflector is integrated with the laser as an external cavity feedback device to form a narrowband laser.

[0015] The beneficial technical effects of this invention are: The narrowband reflector provided by this invention employs an innovative structure with a UBG (Uniform Bragg Grating) coupled dual resonant mode in the resonant cavity waveguide. Compared with existing cascaded structures, it can break free from the dependence on the Vernier effect tuning mechanism. At the same time, thanks to the wide bandwidth characteristics of UBG, there is no need to perform stringent and precise alignment of the Bragg wavelength of ASBG (Anti-symmetric Bragg Grating) with UBG. It has good manufacturability and process tolerance, significantly reducing the requirements and control difficulty of the manufacturing process.

[0016] Meanwhile, this reflector can achieve high reflectivity, narrow linewidth, and extremely high sidelobe suppression ratio. Its reflection spectrum is non-Lorentzian and can present a more ideal box-shaped reflection spectrum response through parameter adjustment. It can maintain functional stability even when there is a slight chirp in the laser wavelength. The resonant wavelength shift caused by manufacturing errors can be compensated by a thermal tuning device. Furthermore, by adjusting design parameters such as grating period and waveguide width, it can be flexibly applied to different communication bands such as O-band and L-band, demonstrating excellent scalability and application potential. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an embodiment of a narrowband reflector based on a side-coupled Bragg grating resonator provided by the present invention.

[0018] Figure 2 This is a schematic diagram of the internal optical path of an embodiment of a narrowband reflector waveguide based on a side-coupled Bragg grating resonator provided by the present invention.

[0019] Figure 3 This is a schematic diagram of the Bragg grating fabrication location provided by the present invention.

[0020] Figure 4 This is a cross-sectional schematic diagram of an embodiment of a narrowband reflector based on a side-coupled Bragg grating resonator provided by the present invention.

[0021] Figure 5 This is a schematic diagram of an embodiment of a narrowband laser formed by integrating a narrowband reflector as an external cavity feedback device with a laser, as provided by the present invention. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0023] To address the common problems in existing on-chip narrowband reflector (NBR) technology, such as the need for complex tuning mechanisms (e.g., Vernier effect), low process tolerance, difficulty in accurately aligning Bragg wavelengths, insufficient sidelobe suppression ratio, and complex device structure, this invention provides a narrowband reflector waveguide and reflector based on a side-coupled Bragg grating resonator (BGR).

[0024] Please refer to Figure 1The narrowband reflector waveguide includes a main waveguide 101 and a resonant cavity waveguide arranged in parallel. The main waveguide 101 is a single-mode waveguide that supports TE0 mode (transverse electric field fundamental mode) transmission. The resonant cavity waveguide is a multimode waveguide that supports TE0 mode and TE1 mode (first-order mode) transmission. The main waveguide 101 and the resonant cavity waveguide form an asymmetric directional coupling region through side coupling (also known as lateral coupling) to realize the coupling conversion between the TE0 mode optical signal in the main waveguide 101 and the TE1 mode optical signal in the resonant cavity waveguide; a first resonant mode and a second resonant mode are formed in phase coupling within the resonant cavity waveguide. When the aforementioned reflector waveguide is in operation, the TE0 mode optical signal is input into the main waveguide 101 and coupled to the resonant cavity waveguide, where it is converted into a TE1 mode optical signal. Under the synergistic effect of the first resonant mode and the second resonant mode, the TE1 mode optical signal generates TE1 mode narrowband reflected light of the required wavelength. The TE1 mode narrowband reflected light is coupled back to the main waveguide 101 and converted into TE0 mode narrowband reflected light, which is then output from the main waveguide 101.

[0025] Specifically, the main waveguide 101 serves as both the input and output channel for the entire device. It is designed with the typical width of a single-mode waveguide to ensure that only TE0 mode transmission is supported. The main waveguide 101 is used to guide external optical signals from the input end into the asymmetric directional coupling region, enabling the conversion and energy exchange between the TE0 mode in the main waveguide 101 and the TE1 mode in the resonant cavity waveguide. It also guides transmitted optical signals not coupled to the resonant cavity waveguide from the transmission end. Simultaneously, the main waveguide 101 is also used to output narrowband reflected light, enhanced by resonance in the resonant cavity waveguide, from the input end.

[0026] The asymmetric directional coupling region can also be considered as forming an asymmetric directional coupler (ADC). The core function of this region is to selectively and efficiently couple the TE0 mode in the main waveguide 101 to the resonant cavity waveguide and convert it to the TE1 mode, based on the principle of asymmetric mode phase matching, while suppressing other unnecessary mode coupling. This design enables controllable transmission of optical power between two different modes and different waveguides, which is a prerequisite for exciting the resonant modes in the resonant cavity. It should be noted that both the main waveguide 101 and the resonant cavity waveguide are designed with uniform width. To form an effective asymmetric directional coupling region, the widths of the main waveguide 101 and the resonant cavity waveguide need to be configured so that the effective refractive index of the TE0 mode in the main waveguide 101 is equal to the effective refractive index of the TE1 mode in the resonant cavity waveguide, thus satisfying the asymmetric mode phase matching condition and achieving selective coupling and conversion between the TE0 and TE1 modes.

[0027] In this embodiment, the main waveguide 101 includes a first straight waveguide segment, a second straight waveguide segment, and a curved waveguide segment connecting the first straight waveguide segment and the second straight waveguide segment; a first antisymmetric Bragg grating 102 (ASBG1), a uniform Bragg grating 103 (UBG), and a second antisymmetric Bragg grating 104 (ASBG2) are sequentially fabricated along the length direction on the resonant cavity waveguide. The Bragg wavelengths of the first antisymmetric Bragg grating 102 and the second antisymmetric Bragg grating 104 are the same, and the phase difference is π.

[0028] Please refer to Figure 1 In this embodiment, the curved waveguide segment protrudes towards the resonant cavity waveguide and forms an asymmetric directional coupling region (i.e., the area within the dashed box in the figure) with the section containing the uniform Bragg grating 103 within the resonant cavity waveguide through edge coupling. The curved waveguide segment can be composed of two S-shaped curved waveguides connected together, and the lateral translation of the main waveguide is achieved through a double circular arc transition, ensuring low bending loss while achieving a compact layout.

[0029] Furthermore, the resonant cavity waveguide forms a composite grating cavity that supports multimode resonance. ASBG1 and ASBG2 are responsible for forming the first and second resonant modes, realizing coupling and conversion between forward and reverse TE1 and TE0 modes. Specifically, the first resonant mode is used to convert between forward TE1 mode optical signals and reverse TE0 mode optical signals; the second resonant mode is used to convert between forward TE0 mode optical signals and reverse TE1 mode optical signals. The uniform Bragg grating 103 achieves coupling and energy cycling between the first resonant mode (RM1, Resonance Mode 1) and the second resonant mode (RM2, Resonance Mode 2) by reflecting the TE0 mode optical signal. Ultimately, through the synergistic effect of mode conversion and reflection mechanisms, the resonant cavity waveguide generates a high suppression ratio and narrow linewidth reflection response at a specific wavelength, i.e., it generates narrowband reflected light.

[0030] Figure 2 A schematic diagram of the optical path routing inside the reflector waveguide is shown, as follows: Figure 2As shown, the optical signal is injected into the input terminal of the main waveguide 101 in TE0 mode. It is efficiently coupled to the resonant cavity waveguide in the asymmetric directional coupling region and converted into the forward TE1 mode. When the forward TE1 mode propagates to the second antisymmetric Bragg grating 104, it is reflected and converted into the reverse TE0 mode. After that, the optical path splits into two branches: most of the reverse TE0 mode light passes through the uniform Bragg grating 103 to reach the first antisymmetric Bragg grating 102, is reflected again and converted back to the forward TE1 mode, and then is transmitted back to the second antisymmetric Bragg grating 104 through the uniform Bragg grating 103, forming the first resonant mode (RM1); the other part of the reverse TE0 mode light is reflected by the uniform Bragg grating 103 and converted into the forward TE0 mode. After being reflected by the second antisymmetric Bragg grating 104, it becomes the reverse TE1 mode, forming the second resonant mode (RM2). The optical signal, after being reflected by the second antisymmetric Bragg grating 104, becomes the reverse TE1 mode and propagates to the uniform Bragg grating 103. Finally, it is coupled back to the main waveguide 101 through the asymmetric directional coupling region and converted into the reverse TE0 mode, then reflected from the original input port of the main waveguide 101. The resonant cavity waveguide achieves coupling of the two resonant modes through the reflection of the TE0 mode by the UBG, and achieves mode selection through the phase difference between ASBG1 and ASBG2, so as to realize efficient narrowband reflection of a single wavelength.

[0031] This resonant cavity waveguide structure eliminates the need for the reflection peaks formed by ASBG and UBG to satisfy the vernier caliper effect, thus solving the problem of precisely controlling the phase matching between feedback light and the internal optical field of the laser in cascaded micro-ring resonators and Salic ring resonators. Furthermore, the obtained reflection spectrum greatly suppresses the generation of side lobes other than the main resonance peak, solving the problem of its influence when used in laser external cavity feedback or high-precision sensing systems, and improving the coherence and stability of single-mode.

[0032] Furthermore, the two resonant modes, RM1 and RM2, share the same resonant cavity waveguide but have different mode compositions and propagation paths. The two resonant modes exchange energy and couple phase through reflection of the TEO mode via the UBG, forming a non-Lorentzian line-shaped reflection spectrum. This dual-mode interference mechanism differs from the Lorentzian line-shaped interference of a single resonant cavity, exhibiting higher tolerance to wavelength drift and laser chirp. The resonant frequencies of RM1 and RM2 are similar, appearing as two adjacent resonant peaks in the spectrum. The coupling strength of the two resonant modes can be controlled by adjusting the length of the UBG. When the UBG length is optimized to an appropriate value, the frequency interval of the two resonant peaks matches their respective linewidths, resulting in interference superposition and forming a box-shaped reflection spectrum with a flat-topped characteristic, thereby further improving its tolerance to wavelength drift and laser chirp.

[0033] Furthermore, such as Figure 3As shown, the first antisymmetric Bragg grating 102, the uniform Bragg grating 103, and the second antisymmetric Bragg grating 104 are fabricated on the sidewall of the resonant cavity waveguide. Figure 3 301), surface ( Figure 3 (303) or internal ( Figure 3 (See section 302). The Bragg grating can be fabricated in three ways: 1) on the sidewalls of the resonant cavity waveguide, where a periodic rectangular grating structure is formed on both sides of the waveguide through etching, with the grating depth roughly equal to the waveguide height; 2) inside the resonant cavity waveguide, where a volume grating is formed by periodically creating circular or elliptical through-holes; and 3) on the waveguide surface, where a surface grating is formed by etching or depositing periodic stripes on the upper surface of the waveguide. All three structures utilize the periodic refractive index distribution introduced by the periodic structure to achieve the gating, reflection, and other modulation functions of the Bragg grating for specific wavelength optical signals. The appropriate method can be flexibly selected based on the specific fabrication conditions.

[0034] In this embodiment, the optical waveguide adopts a strip waveguide configuration, meaning the optical signal is confined within a silicon-based waveguide region with a rectangular cross-section. The first and second straight waveguide segments are parallel to the resonant cavity waveguide. The first antisymmetric Bragg grating 102, the uniform Bragg grating 103, and the second antisymmetric Bragg grating 104 are fabricated on the sidewall of the resonant cavity waveguide. The main waveguide 101 has a width of 730 nm and a height of 400 nm; the resonant cavity waveguide has a width of 1770 nm and a height of 400 nm; the sidewall gratings have a grating tooth width of 150 nm; the two antisymmetric Bragg gratings (102, 104) each have a length of 227 μm and a period of 468 nm; the uniform Bragg grating 103 has a length of 22.8 μm and a period of 451 nm; and the maximum distance between the main waveguide 101 and the resonant waveguide is 820 nm.

[0035] The wavelength of the narrowband reflected light is primarily determined by the Bragg wavelengths of the two antisymmetric Bragg gratings (102, 104), and finely adjusted by coupling with the uniform Bragg grating 103. In practice, the dimensions of each grating can be flexibly set using existing simulation methods according to the desired reflected light wavelength to obtain the desired reflected light wavelength. The lengths of the antisymmetric Bragg gratings (102, 104) can be flexibly adjusted according to different materials and grating tooth widths, while the length of the uniform Bragg grating 103 can be adjusted accordingly based on the distance between the main waveguide and the resonant cavity waveguide.

[0036] Furthermore, a tapered waveguide 105 is respectively provided at both ends of the resonant cavity waveguide. The width of the tapered waveguide 105 is no greater than the width of the resonant cavity waveguide and gradually decreases along the direction away from the resonant cavity waveguide. The tapered waveguide 105 is used to dissipate transmitted light that has not been resonated and reflected. In this embodiment, the width of the tapered waveguide 105 gradually decreases from the width of the resonant cavity waveguide along the direction away from the resonant cavity waveguide, thus achieving a smooth connection with the resonant cavity waveguide.

[0037] Furthermore, the present invention also provides a narrowband reflector based on a side-coupled Bragg grating resonator. Figure 4 This is a schematic diagram of the cross-sectional structure of the narrowband reflector provided by the present invention, as shown below. Figure 4 As shown, the narrowband reflector includes a substrate 401, a lower cladding layer 402, and an upper cladding layer 404 arranged sequentially from bottom to top. A narrowband reflector waveguide 403 based on a side-coupled Bragg grating resonator is fabricated between the lower cladding layer 402 and the upper cladding layer 404. The specific structure of the reflector waveguide 403 is consistent with that described above and will not be repeated here.

[0038] The substrate 401 and its upper and lower cladding layers can be made of SiO2, and the narrow-linewidth reflector waveguide 403 can be made of silicon nitride. Generally, a 4μm thick SiO2 lower cladding layer 402 can be pre-prepared on the substrate 401. A Si3N4 core layer is deposited on the SiO2 lower cladding layer 402 using low-pressure chemical vapor deposition (LPCVD) to provide basic support for optical mode confinement. Subsequently, electron beam lithography (EBL) is used for patterning to ensure the consistency of key structural parameters with sub-100-nanometer precision in the Bragg grating of the narrow-band reflector. Then, inductively coupled plasma (ICP) etching is used to complete the Si3N4 layer pattern transfer, ensuring the dimensional accuracy of the waveguide and grating structures. Finally, plasma-enhanced chemical vapor deposition (PECVD) is used. Deposition: A 3μm thick SiO2 cladding layer 403 is deposited to ensure refractive index uniformity and achieve physical protection; finally, chip annealing is performed to optimize optical transmission performance and alleviate cladding loss.

[0039] Furthermore, the reflector also includes a thermal tuning device 405, which is disposed on the upper cladding 404 and is used to adjust the reflected wavelength of the narrowband reflector. The thermal tuning device 405 covers at least the corresponding area above the reflector waveguide 403, and is used to fine-tune the reflected wavelength of the narrowband reflector through thermal tuning to compensate for wavelength shifts caused by manufacturing errors, ensuring that the reflector outputs reflected light of the required wavelength, and further improving the reliability of the device.

[0040] Furthermore, the narrowband reflector can be integrated with the laser as an external cavity feedback device to form a narrowband laser. For example... Figure 5 As shown, this invention provides an application embodiment of a narrowband laser formed by using a narrowband reflector as an external cavity feedback device. In this embodiment, the narrowband laser includes a cascaded mode converter 501, a 3-dB directional coupler 502, and a narrowband reflector 503. The reflecting end and the incident end of the cascaded mode converter 501 are optically coupled to the directional coupler 502. The directional coupler 502 and the main waveguide 101 of the narrowband reflector 503 are connected by end-face coupling. The transmitting end of the cascaded mode converter 501 is coupled to the transmitting end of the main waveguide 101. The specific optical transmission process is as follows: The optical signal output from the gain chip (not shown) is input from the input end, coupled to a 3-dB directional coupler 502 via a cascaded mode converter 501, and then guided to a narrowband reflector 503 by the directional coupler 502; the reflected light generated after the action of the narrowband reflector 503 is transmitted to the reflection end of the cascaded mode converter 501 via the 3-dB directional coupler 502; simultaneously, the optical signal not resonantly reflected by the narrowband reflector 503 is output from the transmission port after coupling with the cascaded mode converter 501. The cascaded mode converter 501 is compatible with both vertical input and edge-parallel input optical input modes. The structure of the narrowband reflector is consistent with the above, and the specific forms of the cascaded mode converter 501 and the 3-dB directional coupler 502 can be consistent with existing technologies.

[0041] In summary, this invention achieves single-mode narrowband reflection without Vernier alignment through the synergistic design of asymmetric directional coupling and a composite Bragg grating resonator, significantly reducing the alignment accuracy requirements and improving the system's tolerance to wavelength drift. The device incorporates a thermal tuning mechanism to compensate for manufacturing errors, balancing fabrication tolerance and operational stability. This approach combines high reflectivity, narrow linewidth, high side-mode suppression ratio, and process robustness, making it flexible and adaptable to different communication bands. It is suitable for various applications such as narrow-linewidth laser external cavity feedback and high-precision fiber optic sensing.

[0042] In the description of this specification, the terms "first," "second," "third," "fourth," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0043] The use of terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example, which is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0044] In the description of this application, if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application 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. Therefore, they should not be construed as limitations on this application.

[0045] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0046] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0047] The above description is merely a preferred embodiment disclosed in this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of protection involved in this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-disclosed concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this disclosure. Furthermore, although several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of this disclosure.

Claims

1. A narrowband reflector waveguide based on a side-coupled Bragg grating resonator, characterized in that, It includes a main waveguide and a resonant cavity waveguide arranged in parallel. The main waveguide supports TE0 mode transmission, and the resonant cavity waveguide supports both TE0 mode and TE1 mode transmission. The main waveguide and the resonant cavity waveguide form an asymmetric directional coupling region through side coupling to achieve coupling conversion between the TE0 mode optical signal in the main waveguide and the TE1 mode optical signal in the resonant cavity waveguide; a first resonant mode and a second resonant mode are formed in phase coupling within the resonant cavity waveguide; After the TE0 mode optical signal is input into the main waveguide, it is coupled to the resonant cavity waveguide and converted into a TE1 mode optical signal. Under the synergistic effect of the first resonant mode and the second resonant mode, the TE1 mode optical signal generates TE1 mode narrowband reflected light of the required wavelength. The TE1 mode narrowband reflected light is coupled back to the main waveguide and converted into TE0 mode narrowband reflected light, which is then output from the main waveguide.

2. The narrowband reflector waveguide based on a side-coupled Bragg grating resonator cavity according to claim 1, characterized in that, The main waveguide includes a first straight waveguide segment, a second straight waveguide segment, and a curved waveguide segment connecting the first straight waveguide segment and the second straight waveguide segment; The resonant cavity waveguide is sequentially fabricated with a first antisymmetric Bragg grating, a uniform Bragg grating, and a second antisymmetric Bragg grating along its length, wherein the phase difference between the first antisymmetric Bragg grating and the second antisymmetric Bragg grating is π.

3. The narrowband reflector waveguide based on a side-coupled Bragg grating resonator cavity according to claim 2, characterized in that, The curved waveguide segment protrudes in the direction of the resonant cavity waveguide and forms an asymmetric directional coupling region with the section containing the uniform Bragg grating in the resonant cavity waveguide through edge coupling.

4. The narrowband reflector waveguide based on a side-coupled Bragg grating resonator according to claim 2, characterized in that, Within the resonant cavity waveguide, the first resonant mode is used to realize the conversion between the forward TE1 mode optical signal and the reverse TE0 mode optical signal; The second resonant mode is used to realize the conversion between the forward TE0 mode optical signal and the reverse TE1 mode optical signal.

5. The narrowband reflector waveguide based on a side-coupled Bragg grating resonator cavity according to claim 2, characterized in that, Within the resonant cavity waveguide, the uniform Bragg grating achieves coupling between the first resonant mode and the second resonant mode by reflecting the TEO mode optical signal.

6. The narrowband reflector waveguide based on a side-coupled Bragg grating resonator cavity according to claim 1, characterized in that, A tapered waveguide is provided at each end of the resonant cavity waveguide. The width of the tapered waveguide is not greater than the width of the resonant cavity waveguide and gradually decreases in the direction away from the resonant cavity waveguide.

7. The narrowband reflector waveguide based on a side-coupled Bragg grating resonator cavity according to claim 3, characterized in that, The first antisymmetric Bragg grating, the uniform Bragg grating, and the second antisymmetric Bragg grating are fabricated on the sidewall, surface, or inside of the resonant cavity waveguide.

8. A narrowband reflector based on a side-coupled Bragg grating resonator, characterized in that, It includes a substrate, a lower cladding layer, and an upper cladding layer arranged sequentially from bottom to top, and a narrowband reflector waveguide based on a side-coupled Bragg grating resonator as described in any one of claims 1-7 is fabricated between the lower cladding layer and the upper cladding layer.

9. The narrowband reflector based on a side-coupled Bragg grating resonator according to claim 8, characterized in that, It also includes a thermal tuning device disposed on the upper cladding for adjusting the reflected wavelength of the narrowband reflector.

10. The narrowband reflector based on a side-coupled Bragg grating resonator according to claim 9, characterized in that, The narrowband reflector is integrated with the laser as an external cavity feedback device to form a narrowband laser.

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