Device for narrowing line width of laser and expanding tuning range

Abstract

The invention discloses a device for narrowing the line width of a laser and expanding the tuning range. The device comprises a laser used for generating single-mode signal light for communication; the input end of the spot size converter is connected with the output end of the laser, and the spot size converter is used for matching the mode field of the laser with the mode field of the output waveguide; the input end of the 1 * N splitter is connected with the output end of the spot size converter, and the 1 * N splitter is used for distributing the optical signals to the N paths of output waveguides; the first phase shifter is deposited on the connecting waveguide between the output end of the spot size converter and the input end of the 1 * N splitter; and N runway type micro-ring resonators, each runway type micro-ring resonator is coupled with one path of output waveguide, and the N runway type micro-ring resonators and the N paths of output waveguides form an equivalent parallel coupling structure. The problem that in the prior art, in order to give consideration to the narrow linewidth and the wide tunable range of the laser, a scheme with high structural complexity and complex production process requirements is adopted, and consequently the cost is too high is solved.

Description

Technical Field

[0001] This application relates to the field of lasers, and more specifically, to an apparatus for narrowing the linewidth of a laser and expanding its tuning range. Background Technology

[0002] Narrow-linewidth lasers, as the core light source of modern precision optoelectronic systems, have become enabling technologies in cutting-edge fields such as quantum technology, high-speed communication, and precision measurement due to their ultra-narrow spectral linewidth and long coherence length. Currently, external cavity-based narrow-linewidth lasers remain the mainstream choice, but they face the challenge of simultaneously achieving a wide tunable range and narrow linewidth. Even though various structural and process optimization schemes have been proposed in existing technologies to achieve both narrow linewidth and wide tunable range, their high structural complexity and complex manufacturing requirements result in excessively high costs.

[0003] There is currently no effective solution to the above problems. Summary of the Invention

[0004] This application provides a device for narrowing the linewidth of a laser and expanding its tuning range, thereby at least solving the problem of excessively high costs caused by the use of highly complex structural and manufacturing processes in the prior art to balance the narrow linewidth and wide tuning range of the laser.

[0005] According to one aspect of the embodiments of this application, an apparatus for narrowing the linewidth of a laser and expanding its tuning range is provided, comprising: a laser for generating single-mode signal light for communication; a mode converter, the input of which is connected to the output of the laser, for matching the mode field of the laser with the mode field of an output waveguide; a 1×N splitter, the input of which is connected to the output of the mode converter, for distributing the optical signal to N output waveguides; and a first phase shifter deposited between the output of the mode converter and the input of the 1×N splitter. The waveguide is connected to N racetrack-shaped microring resonators, each of which is coupled to one of the output waveguides. The N racetrack-shaped microring resonators and the N output waveguides form an equivalent parallel coupling structure. N is an integer greater than or equal to 2, and the resonant cavity lengths of any two racetrack-shaped microring resonators are configured to be unequal to obtain N distinct free spectral ranges. The least common multiple of the N distinct free spectral ranges is taken as the extended maximum tunable range.

[0006] Optionally, in this embodiment, the method further includes: introducing a micro-adjustment structure array in the uncoupled region of each of the racetrack-shaped microring resonators, wherein the micro-adjustment structure array is configured to: generate reflected light; superimpose the reflected light through the equivalent parallel coupling structure to form feedback light; inject the feedback light into the laser after phase matching through the first phase shifter; and achieve narrowing of the linewidth of the laser and acquisition of an equivalent free spectral range by self-injection locking through the laser, wherein the coupling region of the racetrack-shaped microring resonator refers to the region where the racetrack-shaped microring resonator and the output waveguide are arranged parallel to each other and the spacing is closest, and the uncoupled region of the racetrack-shaped microring resonator refers to the region other than the coupling region.

[0007] Optionally, in the embodiments of this application, the method further includes: the relative position parameters between the output waveguide and the racetrack-shaped microring resonator coupled to the output waveguide are adjustable and configured to satisfy the critical coupling condition.

[0008] Optionally, in an embodiment of this application, the method described above is further enhanced by ensuring that the optical signals of any two output waveguides in the N output waveguides have the same energy and phase.

[0009] Optionally, in an embodiment of this application, the method described above is further included by: each racetrack-shaped microring resonator having a second phase shifter integrated in its coupling region, the second phase shifter being configured to dynamically adjust the wavelength and phase of the racetrack-shaped microring resonator.

[0010] Optionally, in an embodiment of this application, the method described above is further included in that the micro-adjustment structures in the micro-adjustment structure array are arranged periodically.

[0011] Optionally, in this embodiment of the application, the method described above is further improved by including, but not limited to, the shape of the micro-adjustment structure as a circle or a polygon.

[0012] Optionally, in an embodiment of this application, the method further includes: integrating two third phase shifters on a racetrack-shaped microring resonator having the maximum resonant cavity length described above. The third phase shifter is configured to adjust the resonant wavelength and phase of the light wave coupled to the racetrack-shaped microring resonator via the thermo-optic effect.

[0013] In this embodiment, N output waveguides are designed, each coupled to a racetrack-shaped microring resonator. The cavity lengths of the N racetrack-shaped microring resonators are unequal. A micro-adjustment structure array is introduced on each racetrack-shaped microring resonator to capture reflected light. An equivalent free spectral range is obtained through an equivalent parallel structure, avoiding the problems of insertion loss accumulation and sensitivity to process deviations in series structures, thus significantly reducing the manufacturing complexity. This approach, with its lower loss and relatively simple structure and process, solves the problem of excessively high costs caused by high structural complexity and complex manufacturing processes required in existing technologies to balance the narrow linewidth and wide tunable range of lasers. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of an optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application; Figure 2 This is a schematic diagram of another optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application; Figure 3 This is a schematic diagram of another optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application; Figure 4 This is a schematic diagram of another optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application; Figure 5 This is a schematic diagram of another optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application; Figure 6 This is a schematic diagram of another optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application; Figure 7 This is a schematic diagram of another optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application; Figure 8 This is a schematic diagram of another optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application; Figure 9 This is a schematic diagram of another optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application; Figure 10 This is a schematic diagram of another optional method for narrowing laser linewidth and expanding tuning range according to an embodiment of this application.

[0015] In the picture: 1—Laser; 2—Pattern converter; 3—First phase shifter; 4-1×N splitter; 5—Output waveguide; 6—Runway-shaped microring resonator; 7—Second phase shifter; 8—Micro-adjustable structure array; 9-Third phase shifter. Detailed Implementation

[0016] 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.

[0017] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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 the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0018] 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 communication of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. In the following description, specific details such as particular system structures and technologies are presented for illustrative purposes rather than for limiting purposes, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art should understand that this application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of this application with unnecessary details. It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or collections thereof. It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0019] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0020] Optionally, as an alternative implementation, the aforementioned means for narrowing the laser linewidth and expanding the tuning range includes: S1, Laser 1, used to generate single-mode signal light for communication; Mode converter 2, whose input end is connected to the output end of the laser, used to match the mode field of the laser with the mode field of the output waveguide 5; 1×N splitter 4, whose input end is connected to the output end of the mode converter, used to distribute the optical signal to N output waveguides; First phase shifter 3, which is deposited on the connecting waveguide between the output end of the mode converter and the input end of the 1×N splitter; N racetrack-shaped microring resonators 6, each racetrack-shaped microring resonator is coupled to one output waveguide, and the N racetrack-shaped microring resonators and the N output waveguides form an equivalent parallel coupling structure; where N is an integer greater than or equal to 2, and the resonant cavity lengths of any two racetrack-shaped microring resonators are configured to be unequal to obtain N distinct free spectral ranges, and the least common multiple of the N distinct free spectral ranges is taken as the extended maximum tunable range.

[0021] S2, a micro-adjustment structure array 8 is introduced into the uncoupled region of each racetrack-shaped microring resonator. The micro-adjustment structure array is configured to: generate reflected light; make the reflected light superimposed by an equivalent parallel coupling structure to form feedback light; inject the feedback light into the laser after phase matching through a first phase shifter; the laser, mode converter, first phase shifter, 1×N splitter and equivalent parallel coupling structure achieve narrowing of the linewidth of the laser and obtain equivalent free spectral range through self-injection locking. The coupling region of the racetrack-shaped microring resonator refers to the region where the racetrack-shaped microring resonator and the output waveguide are arranged parallel to each other and the spacing is the closest. The uncoupled region of the racetrack-shaped microring resonator refers to the region other than the coupling region.

[0022] Optionally, in the embodiments of this application, the method of narrowing the laser linewidth and expanding the tuning range can be applied to the fields of optoelectronics and optical communication. Narrowing the laser linewidth can improve coherence and measurement accuracy, while expanding the tuning range can adapt to the wavelength requirements of multiple scenarios. The two work together to realize the application value of lasers in communication, sensing, quantum technology and other fields that combine high precision and flexibility.

[0023] Optionally, in the embodiments of this application, the linewidth of a laser refers to the frequency (or wavelength) width of the optical power distribution in the output laser spectrum, usually expressed as full width at half maximum (FWHM). Linewidth is a key indicator for measuring laser monochromaticity (spectral purity); the narrower the linewidth, the better the monochromaticity of the laser. Tuning range typically refers to the range within which the resonant wavelength can be continuously shifted through external control. The tuning range usually needs to be smaller than the free spectral range to avoid mode jumps. The wider the tuning range, the wider the applicable scenarios for the laser.

[0024] Optionally, in this embodiment, the laser is mainly used to provide a single-mode light source; the mode converter is mainly used to efficiently couple the output mode field of the laser into the waveguide to reduce the loss caused by mode mismatch; the first phase shifter is mainly used to adjust the phase of the feedback light to achieve optimal self-injection locking, which is a metal thin film heated electrode deposited on the surface of the connecting waveguide, and modulates the phase through the thermo-optic effect, wherein the connecting waveguide refers to the waveguide between the output end of the mode converter and the input end of the 1×N splitter; the 1×N splitter is mainly used to divide the optical signal into N output waveguides, where N is an integer greater than or equal to 2; the output waveguide mainly realizes the function of transmitting and outputting optical signals, and serves as the connection channel of each component to ensure efficient integration of the optical path; N racetrack-shaped micro-ring resonators with micro-adjustment structure arrays serve as wavelength selection and feedback elements, which mainly realize linewidth narrowing and extended tuning range.

[0025] Optionally, in this embodiment, single-mode signal light for communication refers to a single-mode optical signal used in an optical fiber communication system and transmitted in a single-mode optical fiber. It possesses characteristics of a single transmission mode, low loss, and high bandwidth, enabling high-speed, high-capacity, and long-distance communication. The mode field refers to the transverse electric field distribution when a light wave propagates in a waveguide (such as an optical fiber or optical chip waveguide), i.e., the spatial intensity distribution of the light field. In optical devices, the mode field describes the distribution characteristics of light energy on the cross-section of the waveguide, and its size is usually quantified by the mode field diameter. The purpose of mode field matching in a mode field converter is to maximize optical power coupling efficiency and avoid insertion loss and reflection loss caused by mode field mismatch. It mainly adjusts the mode field size and shape.

[0026] Optionally, in the embodiments of this application, when the runway-shaped microring resonator waveguide and the output waveguide are laterally coupled structures, the coupling region of the runway-shaped microring resonator is located in the section where the runway-shaped microring resonator waveguide and the output waveguide are arranged in parallel and are very close together.

[0027] Optionally, in this embodiment, self-injection locking is a technique that actively stabilizes the laser frequency, narrows the linewidth, or locks the phase by feeding back a portion of the laser's output light into its own resonant cavity, utilizing the optical feedback effect. Its core function is to suppress the laser's frequency noise using the interference effect of its own light, thereby improving the laser's performance. The feedback light is injected into the laser after phase matching through a first phase shifter to achieve optimal self-injection locking. The laser, mode converter, first phase shifter, 1×N splitter, and equivalent parallel coupling structure achieve narrowing of the laser's linewidth while maintaining an equivalent free spectral range through self-injection locking.

[0028] Optionally, in the embodiments of this application, the coupling between the output waveguide and the racetrack-shaped microring resonator is direct coupling. The output waveguide directly transmits light or energy to the racetrack-shaped microring resonator through physical contact or field overlap at a very close distance, without the need for an intermediate medium.

[0029] Optionally, in the embodiments of this application, when designing and determining the resonant radius of each racetrack-shaped microring resonator, parameters such as waveguide thickness and waveguide width need to be comprehensively considered; when designing and determining the coupling length and coupling gap, critical coupling must be ensured. Figure 8 The structure shown uses silicon nitride as the material for the racetrack-shaped microring resonator to narrow the laser linewidth and expand the tuning range. The waveguide thickness and width are both 0.8 μm. One racetrack-shaped microring resonator has a radius of 50 μm, and the other has a radius of 52 μm. The coupling length of each resonator is 10 μm. The cavity length is L = 2πR + 2L. C (R is the radius, L) C (This refers to the coupling length). Other materials can also be used for racetrack-shaped microring resonators, but the appropriate material must be selected based on the required length of the resonant cavity, and the appropriate waveguide thickness must be selected based on the material, loss, and manufacturing difficulty. The waveguide width must be selected to ensure single-mode transmission.

[0030] Optionally, in this embodiment, the resonant cavity lengths of any two racetrack-shaped microring resonators among the N racetrack-shaped microring resonators are configured to be unequal, and the difference in resonant cavity length ΔL = |L2-L1| between any two racetrack-shaped microring resonators in the same level must satisfy the conditions: 1% ≤ (ΔL / L1) ≤ 5%, and 1% ≤ (ΔL / L2) ≤ 5%. "Same level" refers to racetrack-shaped microring resonators sharing the same 1×N splitter. For example... Figure 8 It contains two racetrack-shaped microring resonators, which share the same 1×2 splitter, so Figure 8 The two racetrack-shaped microring resonators in the image belong to the same level; such as Figure 9 It contains three racetrack-shaped microring resonators, which share the same 1×3 splitter. Figure 9 The three racetrack-shaped microring resonators in the image belong to the same level; such as Figure 10 It contains four racetrack-shaped microring resonators. The top two racetrack-shaped microring resonators share the same 1×2 splitter, so the top two racetrack-shaped microring resonators belong to the same level. The bottom two racetrack-shaped microring resonators also share the same 1×2 splitter, so the bottom two racetrack-shaped microring resonators belong to the same level. Therefore, the top two racetrack-shaped microring resonators and the bottom two racetrack-shaped microring resonators do not belong to the same level.

[0031] To further illustrate, such as Figure 1As shown, the laser is connected to a 1×N splitter via a mode converter. A first phase shifter is deposited on the connecting waveguide between the output of the mode converter and the input of the 1×N splitter. The 1×N splitter divides the optical signal into N output waveguides, each coupled to a racetrack-shaped microring resonator, resulting in a total of N racetrack-shaped microring resonators. These N resonators form an equivalent parallel microring array. The resonant cavity lengths of any two of the N racetrack-shaped microring resonators in the array are different, resulting in N distinct FSRs (Free Spectral Ranges). A second phase shifter 7 is integrated into the coupling region of each racetrack-shaped microring resonator, while a micro-adjustment structure array is introduced into the uncoupled region. (The text abruptly ends here.) Figure 2 As shown, the introduction of a micro-adjustment structure array (three rectangular micro-adjustment structures) on the racetrack-shaped micro-ring resonator excites backscattering (forward mode). The ring structure is periodic; even if a single micro-adjustment structure is small and its reflection is weak, this weak backscattering, enhanced by the array, can still form constructive interference of the forward mode. Similarly, due to the periodicity of the ring structure, the forward mode can also be reflected back to the inverse wave mode. The forward and inverse modes couple to form a new resonant mode with mixed forward / inverse properties. Finally, the resonantly enhanced forward mode propagates in the reverse direction along the output waveguide, forming feedback light injected into the laser. Figure 3 As shown, after the input light 302 is coupled into the racetrack-shaped microring resonator with a micro-adjustment structure array through the output waveguide, part of the energy is reflected by the micro-adjustment structure array to form reflected light 306, and the remaining energy 304 includes directly transmitted light and the reverse mode light of the micro-adjustment structure array; after the reflected light is reverse-transmitted and phase-matched by the first phase shifter, the linewidth is narrowed by the self-injection locking effect.

[0032] In this embodiment, by setting N racetrack-shaped microring resonators with different resonant cavity lengths, the equivalent FSR is obtained by using the vernier effect. By setting a micro-adjustment structure array on each racetrack-shaped microring resonator, the microring array formed by the N racetrack-shaped microring resonators can narrow the laser linewidth and obtain reflected light. The relatively simple structural design reduces the manufacturing difficulty and is easy to produce.

[0033] As an alternative, the relative position parameters between the output waveguide and the racetrack-shaped microring resonator coupled to the output waveguide can be adjusted and configured to satisfy the critical coupling condition.

[0034] Optionally, in this embodiment, the relative position parameters, in addition to the coupling gap and coupling length, also include lateral offset, vertical alignment, coupling zone curvature, and cone angle. The critical coupling condition refers to the coupling strength between the output waveguide and the racetrack-shaped microring resonator being exactly equal to the internal loss of the racetrack-shaped microring resonator, ensuring that all incident light energy is absorbed by the racetrack-shaped microring resonator. Ideally, the output waveguide achieves zero transmission (complete extinction) at the resonant wavelength. In other words, when designing the relative position between the output waveguide and the racetrack-shaped microring resonator coupled to it, the relative position parameters can be varied and adjusted, but the critical coupling condition must be met during these adjustments.

[0035] Through the embodiments of this application, the relative position parameters between the output waveguide and the racetrack-shaped microring resonator coupled to the output waveguide can be adjusted, but the critical coupling condition must be met. This structural design is relatively flexible, and the N racetrack-shaped microring resonators and N output waveguides form an equivalent parallel coupling structure, so the entire device will not collapse due to the detuning of a single racetrack-shaped microring resonator.

[0036] As an alternative, the optical signals of any two output waveguides in the N-way output waveguides have the same energy and phase.

[0037] Optionally, in the embodiments of this application, Figure 8 The device includes a 1×2 splitter, which splits the optical signal into two output waveguides. The optical signals in these two output waveguides have the same energy and phase, and the total energy is normalized to 1. That is to say, the energy of each output waveguide accounts for 1 / 2 of the total energy. Figure 9 The device includes a 1×3 splitter, which divides the optical signal into three output waveguides. The optical signals in these three output waveguides have the same energy and phase, and the total energy is normalized to 1. That is to say, the energy of each output waveguide accounts for 1 / 3 of the total energy. Figure 10 The device contains three 1×2 splitters. The first 1×2 splitter evenly distributes the optical signal to two output waveguides, with each output waveguide accounting for 1 / 2 of the total energy. The second and third 1×2 splitters then evenly distribute their respective 1 / 2 of the energy to two output waveguides, resulting in a total of four output waveguides. These four output waveguides have the same energy and phase, each accounting for 1 / 4 of the total energy, and the total energy is normalized to 1.

[0038] In the embodiments of this application, the optical signals of any two output waveguides in the N-way output waveguides have the same energy and phase. This is to achieve controllable interference effects, symmetrical power distribution, or serve as a reference for phase modulation, so as to meet high-precision functional requirements.

[0039] As an alternative, a second phase shifter 7 is integrated in the coupling region of each racetrack-shaped microring resonator. The second phase shifter is configured to dynamically adjust the resonant wavelength and phase of the racetrack-shaped microring resonator.

[0040] Optionally, in the embodiments of this application, dimensional deviations or temperature changes during the manufacturing process of the racetrack-shaped microring resonator may cause a shift in the resonant wavelength of the racetrack-shaped microring resonator. The second phase shifter integrated on the racetrack-shaped microring resonator can compensate for these errors through phase adjustment.

[0041] In the embodiments of this application, a second phase shifter is integrated in the coupling region of each racetrack-shaped microring resonator. The second phase shifter is used to dynamically adjust the wavelength and phase of the racetrack-shaped microring resonator to compensate for wavelength and phase errors.

[0042] As an alternative approach, the micro-adjustment structures in the micro-adjustment structure array are arranged periodically.

[0043] Optionally, in the embodiments of this application, the micro-adjustment structure introduced in the racetrack-shaped microring resonator can be geometric deformation, material change, etc. Multiple micro-adjustment structures are integrated on each racetrack-shaped microring resonator, and these structures are arranged periodically to form an array. For example... Figure 4 The figure shows the transmittance (reverse transmittance) at the reflective end under critical coupling conditions in a racetrack-shaped microring resonator without the introduction of a micro-adjustment structure array. The horizontal axis represents wavelength in μm, and the vertical axis represents transmittance. Figure 5 The figure shows the transmittance (reverse transmittance) at the reflecting end under critical coupling conditions when a single micro-adjustment structure (rectangular, 0.1μm × 0.2μm) is introduced onto a racetrack-shaped microring resonator. The horizontal axis represents wavelength in μm, and the vertical axis represents transmittance. Figure 6 The figure shows the transmittance (reverse transmittance) at the reflective end under critical coupling state when three identical micro-adjustment structures (all three micro-adjustment structures are rectangular, each with a size of 0.1μm × 0.1μm, and arranged in a certain periodic manner) are introduced on a racetrack-shaped micro-ring resonator. The horizontal axis in the figure represents the wavelength in μm, and the vertical axis represents the transmittance. Figure 4 , Figure 5 and Figure 6 The racetrack-shaped microring resonators involved all have a resonant cavity length of 50μm, a coupling length of 10μm, a waveguide thickness of 0.8μm, and a waveguide width of 0.8μm.

[0044] Transmittance represents the ratio of output optical power to input optical power transmitted from the input port to the output port. When light passes through the coupling region, some light enters the racetrack-shaped microring resonator, and some light is directly transmitted. Transmittance reflects the proportion of light that passes directly without being captured by the racetrack-shaped microring resonator. When the transmittance value is 1, it indicates that the light passes completely without coupling with the racetrack-shaped microring resonator. When the transmittance value is 0, it indicates that the light is completely absorbed or reflected by the racetrack-shaped microring resonator. The minimum value in the transmittance versus wavelength curve corresponds to the resonant mode of the racetrack-shaped microring resonator, and its depth and linewidth are determined by the coupling strength and loss. The critical coupling state represents the state where the coupling strength and loss of the racetrack-shaped microring resonator are balanced. Ideally, the transmittance at the resonant wavelength is reduced to the minimum, at which point the light energy is completely absorbed or scattered by the racetrack-shaped microring resonator, and there is no transmission.

[0045] from Figure 4 and Figure 5 As can be seen, the reverse transmittance of a racetrack-shaped microring resonator with a single micro-adjustment structure at the resonant wavelength is significantly higher than that of a racetrack-shaped microring resonator without such an adjustment structure. Figure 5 and Figure 6 It can be seen that, with the same racetrack-shaped microring resonator structure, the resonant wavelength reverse transmittance of the micro-tuning structure array formed by introducing three micro-tuning structures is higher than that of the resonant wavelength reverse transmittance of the same racetrack-shaped microring resonator with a single micro-tuning structure, and the transmittance of the three resonant peaks is basically the same; among them, Figure 6 The introduced micro-adjustment structure size should be smaller than Figure 5 The introduced micro-adjustment structure size is crucial. In other words, for racetrack-shaped microring resonators with the same structure, the reverse transmittance of a racetrack-shaped microring resonator with a single micro-adjustment structure is significantly higher than that without. Furthermore, the reverse transmittance of a racetrack-shaped microring resonator with an array of three micro-adjustment structures (0.1μm × 0.1μm) is higher than that with a single micro-adjustment structure (0.1μm × 0.2μm). The size of the micro-adjustment structures within the array is smaller than that of a single micro-adjustment structure; smaller sizes result in lower scattering loss, and the transmittance of the three resonance peaks is essentially the same. By introducing a relatively small array of micro-adjustment structures, the intensity of reflected light is ensured with lower loss, and the problem of large differences in transmittance among the resonance peaks of individual micro-adjustment structures is solved.

[0046] In the embodiments of this application, the micro-adjustment structures are periodically arranged in the micro-adjustment structure array introduced in the uncoupled region of each racetrack-shaped microring resonator. That is, by introducing a relatively small array of micro-adjustment structures, scattering loss is reduced while a certain intensity of reflected light is obtained, thereby achieving the goal of narrowing the laser linewidth.

[0047] As an alternative, the shape of the micro-adjustment structure includes circles and polygons.

[0048] Optionally, in this embodiment, the shape of the micro-adjustment structure can be circular, or it can be any polygon such as a rectangle, triangle, or rhombus. When multiple micro-adjustment structures are introduced on a single racetrack-shaped microring resonator, the shapes of the multiple micro-adjustment structures included on the same racetrack-shaped microring resonator can be the same or different, and the dimensions of the multiple micro-adjustment structures included on the same racetrack-shaped microring resonator can be the same or different. The number of micro-adjustment structures introduced on any two racetrack-shaped microring resonators can be the same or different. The shapes of the micro-adjustment structures introduced on any two racetrack-shaped microring resonators can be the same or different, and the dimensions of the micro-adjustment structures introduced on any two racetrack-shaped microring resonators can be the same or different. Figure 7 As shown, three rectangular micro-adjustment structures are introduced on the racetrack-shaped micro-ring resonator. At the same time, a second phase shifter is also integrated on the racetrack-shaped micro-ring resonator. The three rectangular micro-adjustment structures are arranged in an array in the uncoupled region of the racetrack-shaped micro-ring resonator.

[0049] By defining the shape of the micro-adjustment structure as a circle or any kind of polygon through the embodiments of this application, the structural design can be more flexible, and the appropriate shape of the micro-adjustment structure can be selected according to different scenarios, thereby improving the fabrication yield and reliability of the device.

[0050] As an alternative, two third phase shifters 9 are integrated on a racetrack-shaped microring resonator with the maximum resonant cavity length. The third phase shifters are configured to adjust the resonant wavelength and phase of the light wave coupled to the racetrack-shaped microring resonator via the thermo-optic effect.

[0051] Optionally, in this embodiment, the feedback light injected into the laser will sequentially pass through a mode converter, a first phase shifter, a 1×N splitter, and an output waveguide to be coupled to a racetrack-shaped microring resonator. The racetrack-shaped microring resonator with the largest resonator cavity length will adjust the resonant wavelength and phase of the light wave coupled to the racetrack-shaped microring resonator through the thermo-optic effect.

[0052] Optionally, as an alternative implementation, the above method is explained and illustrated by the following steps: like Figure 8The diagram shows a structure containing two racetrack-shaped microring resonators. The laser is connected to a 1×2 splitter via a mode converter. The 1×2 splitter distributes the optical signal to two output waveguides. The first output waveguide is coupled to the first racetrack-shaped microring resonator, and the second output waveguide is coupled to the second racetrack-shaped microring resonator. The resonant cavity lengths of the first and second racetrack-shaped microring resonators are different.

[0053] like Figure 9 The diagram shows a structure containing three racetrack-shaped microring resonators. The laser is connected to a 1×3 splitter via a mode converter. The 1×3 splitter distributes the optical signal to three output waveguides. The first output waveguide is coupled to the first racetrack-shaped microring resonator, the second output waveguide is coupled to the second racetrack-shaped microring resonator, and the third output waveguide is coupled to the third racetrack-shaped microring resonator. The resonant cavity lengths of any two of the first, second, and third racetrack-shaped microring resonators are different.

[0054] like Figure 10 The diagram shows a structure containing four racetrack-shaped microring resonators. The laser is connected to a 1×4 splitter via a mode converter. The 1×4 splitter distributes the optical signal to four output waveguides. The first output waveguide is coupled to the first racetrack-shaped microring resonator, the second output waveguide is coupled to the second racetrack-shaped microring resonator, the third output waveguide is coupled to the third racetrack-shaped microring resonator, and the fourth output waveguide is coupled to the fourth racetrack-shaped microring resonator. The resonant cavity lengths of any two of the first, second, third, and fourth racetrack-shaped microring resonators are different.

[0055] Figure 8 , Figure 9 and Figure 10 Each component includes multiple racetrack-shaped microring resonators, and the resonant cavity lengths of any two racetrack-shaped microring resonators are different, thus allowing for multiple distinct free spectral ranges. The specific implementation process is explained in detail using the following formulas.

[0056] (1) (2) (3) (4) (5) (6) In formula (1) This represents the resonant cavity length of the i-th racetrack-shaped microring resonator; This represents the radius of the i-th racetrack-shaped microring resonator; This represents the length of the straight waveguide section connecting the semicircular curved waveguide in the i-th racetrack-shaped microring resonator. In formula (2) It is expressed as the effective refractive index, which describes the propagation characteristics of light in a waveguide; The wavelength is represented by λ; m represents the resonance order, which is a positive integer (m=1,2,3,...). λ represents the optical path difference matching condition satisfied when light propagates in the racetrack-shaped microring resonator, that is, the optical path difference after the light circles the racetrack-shaped microring resonator once (2πR) must be an integer multiple of the wavelength (m×λ). ). n in formula (3) g represents the group refractive index, which describes the group velocity of a light pulse and is used to correct the effect of dispersion on the FSR. In formula (4) The free spectral range of the i-th racetrack-shaped microring resonator represents the frequency or wavelength interval between adjacent resonant peaks (i.e., m and m+1 orders), reflecting the spectral periodicity of the resonant cavity. In formula (5), FSR_ver represents the equivalent FSR calculated by the vernier effect for the two racetrack-shaped microrings. In formula (6) Approximately The least common multiple of the numbers is much larger than the value of any single number. The value of .

[0057] In the initial state (untuned), the resonant peak of each racetrack-shaped microring resonator appears periodically at the wavelength. Because the resonant cavity lengths of the racetrack-shaped microring resonators are different, this leads to… They are all different. Figure 8 Taking the double-ring structure as an example, the waveguide thickness and width of the two racetrack-shaped microring resonators are both 0.8 μm, and their radii are R1=50 μm and R2=52 μm, respectively. C Both are 10μm, and the resonant cavity length meets the condition: ΔL=|L2-L1|. The values ​​of ΔL / L1 and ΔL / L2 must be between 1% and 5%, because too small a value will result in an excessively small vernier peak spacing, while too large a value will reduce the extinction ratio. At a resonant wavelength of 1.55μm, n g If the value is 2.15, then from formula (4), we can obtain FSR1 = 3.34 nm, FSR2 = 3.22 nm, and |ΔFSR| = 0.12 nm. The total transmission spectrum is the superposition of the individual transmission spectra of the racetrack-shaped microring resonators, exhibiting a complex shape. The resonance peak value after superposition is determined according to... (That is, the wavelengths of the periodically aligned resonant peaks are initially adjusted to the same resonant wavelength through their respective second phase shifters, and the difference between the wavelengths of the resonant peaks and the initial aligned resonant wavelengths appears periodically. From formula (6), we can obtain FSR_ver ≈ 89.65nm, which is much larger than the tuning range of a single microring. The superimposed resonant value narrows the linewidth through self-injection locking, while other secondary peaks cannot achieve the self-injection locking effect due to insufficient light intensity, thus suppressing the secondary peaks.

[0058] The equivalent parallel coupling of N racetrack-shaped microring resonators results in a total transmission spectrum that is the result of the interaction of all microring resonance peaks. A high-transmittance reflected light peak only appears when all parallel microrings resonate simultaneously. This occurs when the resonance peaks of different microrings coincide at the same frequency (wavelength), i.e., the equivalent FSR follows... (That is, the wavelengths of each microring resonant peak periodically aligned, initially adjusted to the same resonant wavelength by their respective second phase shifters, and the difference between the wavelengths of the second resonant alignment and the initial aligned resonant wavelengths) appear periodically, approximately the same as those of each racetrack-shaped microring resonator. The least common multiple of the least common multiple, even if the FSR of each racetrack-shaped microring resonator is small, as long as there is a small difference in the FSR between each racetrack-shaped microring resonator (according to formula (4), by setting ΔL, the difference in FSR between different microrings can be set, but ΔL / L i and ΔL / L i+1 Between 1% and 5%, ΔL = |L i+1 -L i |), the least common multiple will be much larger than a single digit. This significantly increases the equivalent FSR. The superimposed resonance value narrows the linewidth through self-injection locking, while other secondary peaks cannot achieve the self-injection locking effect due to insufficient light intensity, thus suppressing the secondary peaks. Through the equivalent parallel coupling structure, there is no loss accumulation of the series structure, so the insertion loss is relatively low and the extinction ratio is high.

[0059] Figure 8 , Figure 9 and Figure 10 In the racetrack-shaped microring resonator, three rectangular micro-adjustment structures are introduced into the uncoupled region. The reflected light caused by the micro-adjustment structures is phase-matched by the first phase shifter, and the laser linewidth is narrowed through self-injection locking. The specific principle is as follows: Figure 2As shown in the diagram, the laser input light is a single-mode signal light for communication, with a normalized total energy of 1. The mode converter couples the laser output light to the waveguide. Each of the N output waveguides has the same signal energy and phase, but the 1×N splitter needs optimization to ensure the loss is within a reasonable range. The relative position between each output waveguide and its corresponding racetrack-shaped microring resonator is not fixed, but all must meet the critical coupling condition. The resonant cavity length of the racetrack-shaped microring resonator is matched with the material and thickness, and the waveguide width meets the single-mode transmission condition.

[0060] It should be noted that for the aforementioned method embodiments, for the sake of simplicity, they are all expressed as a series of action combinations, but those skilled in the art should be aware that this application is not limited by the order of the actions described, because according to this application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by this application.

[0061] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0062] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0063] In the embodiments provided in this application, it should be understood that the disclosed devices / electronic devices and methods can be implemented in other ways. For example, the device / electronic device controller embodiments described above are merely illustrative. For instance, the division of modules or units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0064] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0065] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

[0066] The scope of protection of this invention is not limited thereto. Any variations or substitutions of technical solutions that can be conceived without inventive effort should be included within the scope of protection of this invention. The scope of protection of this invention is determined by the claims.

Claims

1. A device for narrowing the linewidth of a laser and expanding its tuning range, characterized in that, include: Laser (1), used to generate single-mode signal light for communication; The mode field converter (2) is connected to the output of the laser (1) and is used to match the mode field of the laser (1) with the mode field of the output waveguide (5). A 1×N splitter (4) is connected to the output of the mode converter (2) for distributing optical signals to N output waveguides (5). The first phase shifter (3) is deposited on the connecting waveguide between the output of the mode converter (2) and the input of the 1×N splitter (4); N racetrack-shaped microring resonators (6), each of the racetrack-shaped microring resonators (6) is coupled to one of the output waveguides (5), and the N racetrack-shaped microring resonators and the N output waveguides form an equivalent parallel coupling structure; Wherein, N is a positive integer greater than or equal to 2, and the resonant cavity lengths of any two of the N racetrack-shaped microring resonators (6) are configured to be unequal to obtain N distinct free spectral ranges, and the least common multiple of the N distinct free spectral ranges is taken as the extended maximum tunable range.

2. The apparatus according to claim 1, characterized in that, A micro-adjustment structure array (8) is introduced into the uncoupled region of each racetrack-shaped microring resonator (6). The micro-adjustment structure array (8) is configured to: generate reflected light; make the reflected light superimposed by the equivalent parallel coupling structure to form feedback light; inject the feedback light into the laser (1) after phase matching by the first phase shifter (3); the laser (1), the mode converter (2), the first phase shifter (3), the 1×N splitter (4) and the equivalent parallel coupling structure achieve narrowing of the linewidth of the laser (1) and obtain an equivalent free spectral range through self-injection locking; The coupling region of the runway-shaped microring resonator (6) refers to the region where the runway-shaped microring resonator (6) and the output waveguide (5) are arranged in parallel and are closest to each other, while the non-coupling region of the runway-shaped microring resonator (6) refers to the region other than the coupling region.

3. The apparatus according to claim 1, characterized in that, The relative position parameters between the output waveguide (5) and the racetrack-shaped microring resonator (6) coupled to the output waveguide (5) are adjustable and configured to satisfy critical coupling conditions.

4. The apparatus according to claim 1, characterized in that, The energy and phase of the optical signals of any two of the N output waveguides (5) are the same.

5. The apparatus according to claim 1, characterized in that, Each of the racetrack-shaped microring resonators (6) has a second phase shifter (7) integrated in its coupling region, the second phase shifter (7) being configured to dynamically adjust the wavelength and phase of the racetrack-shaped microring resonator (6).

6. The apparatus according to claim 2, characterized in that, The micro-adjustment structures in the micro-adjustment structure array (8) are arranged periodically.

7. The apparatus according to claim 6, characterized in that, The shape of the micro-adjustment structure includes circles and polygons.

8. The apparatus according to claim 1, characterized in that, Two third phase shifters (9) are integrated on the racetrack-shaped microring resonator having the maximum resonant cavity length. The third phase shifters (9) are configured to adjust the resonant wavelength and phase of the light wave coupled to the racetrack-shaped microring resonator via the thermo-optic effect.

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