A wavelength division multiplexer

Abstract

The application discloses a wavelength division multiplexer, which comprises an input waveguide group, an output waveguide, a free transmission zone flat waveguide, a diffraction grating and a reflection grating. The input waveguide group and the output waveguide are located on the same side of a Rowland circle of the free transmission zone flat waveguide. The diffraction grating is arranged on a grating circle of the free transmission zone flat waveguide. The reflection grating is located on a side, away from the free transmission zone flat waveguide, of the diffraction grating, and the reflection grating is matched with the diffraction grating. A grating tooth surface of the diffraction grating is located on the grating circle, and a grating period of the diffraction grating continuously changes along an arc length direction of the grating circle, thereby forming a chirp distribution. The reflection grating is a two-dimensional Bragg reflection grating composed of alternating medium strips, which is used for reflecting light diffracted by the diffraction grating back to the free transmission zone flat waveguide and focusing the light on the output waveguide respectively. The application can efficiently reflect light signals of different wavelengths in a wide range of incident angles, thereby supporting a large bandwidth requirement of multi-band combining.

Description

Technical Field

[0001] This invention relates to the field of integrated optical device technology, and more specifically to a wavelength division multiplexer. Background Technology

[0002] Wavelength division multiplexing (WDM) is a key optical communication technology that can multiplex light of different wavelengths into the same transmission channel, or separate light of different wavelengths within a single channel into different channels for transmission. This significantly improves the utilization efficiency of optical fibers and saves fiber resources. This technology is not only widely used in optical communication but also plays an important role in applications such as spectral detection. In on-chip spectrometer applications, laser chips typically have narrow bandwidths, and even when using superluminescent diodes (SLEDs), multiple SLEDs are required to cover the entire wavelength band. This places special requirements on the WDM structure.

[0003] Diffraction etched gratings offer advantages such as insensitivity to temperature changes and compact structure, making them suitable for multi-wavelength applications. However, traditional etched diffraction gratings struggle to meet the bandwidth requirements of spectrometer applications. Summary of the Invention

[0004] This invention aims to address, to a certain extent, one of the technical problems in related technologies. To this end, this invention provides a wavelength division multiplexer.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a wavelength division multiplexer, comprising an input waveguide group, an output waveguide, a free transmission region planar waveguide, a diffraction grating, and a reflection grating, wherein the input waveguide group and the output waveguide are located on the same side of the Rowland circle of the free transmission region planar waveguide, the input waveguide group is used to input light of different wavelengths into the free transmission region planar waveguide, characterized in that the diffraction grating is disposed on the grating circle of the free transmission region planar waveguide, the reflection grating is located on the side of the diffraction grating away from the free transmission region planar waveguide, and the reflection grating is matched with the diffraction grating; The grating teeth of the diffraction grating are located on the grating circle, and the grating period of the diffraction grating changes continuously along the arc length of the grating circle to form a chirped distribution, which is used to enable the light arriving at the diffraction grating to achieve diffraction and convergence at the target position. The reflection grating is a Bragg reflection grating composed of alternating dielectric strips, used to reflect the light diffracted by the diffraction grating back to the free transmission region planar waveguide, and focus it onto the output waveguide.

[0006] Optionally, the reflective grating includes a plurality of alternatingly stacked first dielectric strips and second dielectric strips, wherein the refractive index of the first dielectric strips is greater than that of the second dielectric strips; the alternating arrangement of the first dielectric strips and the second dielectric strips forms a periodic refractive index modulation structure to reflect incident light based on the Bragg reflection principle; The first dielectric strip includes multiple connected first dielectric segments, with a transition between adjacent first dielectric segments; the second dielectric strip includes multiple connected second dielectric segments, with a transition between adjacent second dielectric segments; the boundary profile between the first dielectric strip and the second dielectric strip exhibits a continuous alternating convex and concave shape along the grid line direction.

[0007] Optionally, the reflective grating has multiple sub-periodic units defined at different positions. The sub-periodic units are used to characterize the local periodic structure of the reflective grating, and the local grating line orientation of the reflective grating changes with position. Each sub-periodic unit includes a first dielectric segment and a second dielectric segment arranged alternately along its periodic normal direction. The grating line direction and the periodic normal direction perpendicular to the grating line direction of each sub-periodic unit are set according to the incident light direction and the desired reflection direction, so that the main reflection direction of the reflective grating points to the output waveguide.

[0008] Optionally, the stacking period of the reflective grating can be in the range of 0.2 μm. The first dielectric strip has a thickness of 0.7 μm and a duty cycle of 0.3 in the periodic direction. 0.7.

[0009] Optionally, the diffraction grating has a plurality of grating teeth, which are numbered sequentially as k∈K (K={-K1,……,0,……K2}), where K1 and K2 are positive integers and may be unequal; the grating tooth numbered k=0 is a reference grating tooth; the center point P(x,y) of the reflecting surface of any grating tooth numbered k satisfies the following formula (1): (1) Where P(x, y) is the position of the center point of the reflecting surface of the kth grating tooth; The center wavelengths of the several different wavelengths of light to be input. For planar waveguides in The effective refractive index; m represents the optical path difference being m times the wavelength and taking an integer value; O is the position of the center point of the reflecting surface of the reference grating teeth, I is the input position, and D is the output position. Let be the total geometric path of the incident and reflected light from the reflecting surface of the k-th grating tooth. It is the total geometric path of the incident light plus the reflected light of the reference grating teeth.

[0010] Optionally, the center point of the reflecting surface of the kth grating tooth also satisfies the following formula (2): (2) Where R is the radius of the Rowland circle, the position of the center point of the reflecting surface of the kth grating tooth is obtained according to formula (1) and formula (2).

[0011] Optionally, the grating tooth interference cancellation point corresponding to number k satisfies the following formula (3): (3) Among them, P d For the k-th interference cancellation point, the k-th interference cancellation point P on the grating is obtained according to formulas (3) and (2). d The coordinates of the point P are... d The points where the incident light ray intersects with the reflecting surfaces of two adjacent grating teeth are the head edge point and the tail edge point of the reflecting surfaces of the two adjacent grating teeth.

[0012] Optionally, the angle bisector of the incident and reflected rays of the reflective surface of each of the grating teeth coincides with the normal of the reflective surface of the grating tooth.

[0013] Optionally, the input waveguide group includes multiple input waveguides, each of which includes a straight input waveguide and an input tapered waveguide connected in sequence. One end of the straight input waveguide is an optical signal input end, and the other end of the straight input waveguide is connected to one end of the tapered input waveguide. The other end of the tapered input waveguide is disposed on the Rowland circle circumference of the free transmission region planar waveguide and is connected to the free transmission region planar waveguide.

[0014] Optionally, the output waveguide includes an output tapered waveguide and an output straight waveguide connected in sequence. One end of the output tapered waveguide is disposed on the Rowland circle circumference of the free transmission region planar waveguide and is connected to the free transmission region planar waveguide. The other end of the output tapered waveguide is connected to one end of the output straight waveguide, and the other end of the output straight waveguide is an optical signal output terminal.

[0015] The wavelength division multiplexer provided by this invention firstly adopts a continuous strip directional Bragg reflection grating in its core structure. The alternating dielectric strips form a periodic refractive index modulation to achieve Bragg reflection. Since a continuous strip structure is used instead of a discrete grating structure, there are no tiny gaps between discrete grating regions, which reduces the requirements for photolithography resolution, etching consistency and alignment accuracy. As a result, it still has good manufacturability under lower process capabilities, and improves device consistency and production yield.

[0016] Secondly, the local strip orientation is optimized and fine-tuned in the design of the reflection grating so that the reflected main lobe can still be guided in the predetermined direction under different angle conditions, thereby maintaining high reflection efficiency in a wide angle range and effectively reflecting the light back to the free transmission region planar waveguide and coupling it to the corresponding output port.

[0017] Then, in terms of diffraction grating design, this invention is compatible with chirped diffraction gratings and the "one-point method," accurately calculating the position of each diffraction grating unit so that the center of its reflecting surface satisfies the constructive interference condition to maximize diffraction efficiency, while the edges satisfy the destructive interference condition, thus ensuring optimal light energy utilization in principle. Furthermore, the start and end positions of each grating unit (i.e., the edges of the grating tooth reflecting surface) are precisely defined to ensure the entire grating structure is in a spatially optimal state, thereby optimizing spectral response and energy utilization and improving light energy efficiency.

[0018] Finally, at the system-level design level, the input and output shaping waveguides were optimized. This design expands the bandwidth by actively increasing crosstalk and significantly enhances tolerance to input signal deviations and process variations, further improving the overall robustness of the product and meeting the high bandwidth requirements of multi-band multiplexing.

[0019] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. The preferred embodiments or means of the present invention will be shown in detail in conjunction with the accompanying drawings, but are not intended to limit the technical solutions of the present invention. In addition, each of these features, elements and components appearing in the following text and drawings is a plurality of, and different symbols or numbers are used for convenience of representation, but all represent parts with the same or similar construction or function. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the structure of the present invention.

[0021] Figure 2 This is the optical path diagram of the present invention.

[0022] Figure 3 This is a schematic diagram showing the position of the reflecting surface of the diffraction grating of the present invention.

[0023] Figure 4 for Figure 1 A magnified view of a portion of point A (i.e., a schematic diagram of the structure of the diffraction grating and reflection grating of the present invention).

[0024] Figure 5 for Figure 4 A magnified view of a section at point B in the middle.

[0025] Figure 6 This is a schematic diagram of the input shaping waveguide of the present invention.

[0026] Figure 7 This is a schematic diagram illustrating the flattening effect of the input-shaped waveguide spectral lines in this invention.

[0027] Figure 8 This is the combined spectrum of the present invention.

[0028] Among them, 10 is the input waveguide group; 11 is the input straight waveguide; 12 is the input tapered waveguide; 20 is the output waveguide; 21 is the output straight waveguide; 22 is the output tapered waveguide; 30 is the free transmission region planar waveguide; 41 is the reflection grating; 410 is the second dielectric strip; 411 is the first dielectric strip; and 42 is the diffraction grating. Detailed Implementation

[0029] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described are intended to explain the present invention and should not be construed as limiting the invention.

[0030] The terms "an embodiment," "example," or "trademark" used in this specification refer to a particular feature, structure, or characteristic described in connection with the embodiment itself that may be included in at least one embodiment disclosed in this patent. The phrase "in an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0031] Currently, there are several main technical approaches for on-chip wavelength division multiplexing (WDM) architectures.

[0032] Arrayed waveguide gratings (AWGs) are susceptible to temperature changes, are polarization sensitive, and require high manufacturing precision.

[0033] Cascaded MZI (Mach-Zehnder Interferometer) structures offer good channel isolation, but this advantage is primarily applicable to optical communications. For spectrometers requiring wavelength separation, this becomes a disadvantage. As the number of wavelengths to be separated increases, the number of cascades also increases, leading to more complex device structures and larger sizes, which is detrimental to integrated applications.

[0034] Etched diffracted gratings (EDGs) offer advantages such as insensitivity to temperature changes and compact structure, making them suitable for multi-wavelength applications. However, traditional etched diffracted gratings struggle to meet the bandwidth requirements of spectrometer applications, and their integrated Bragg gratings for reflection require extremely high process precision, resulting in high manufacturing costs and low yields.

[0035] In existing research, the perfectly matched concave diffraction grating proposed by MAO Y et al. (article title: Perfectmatching of concave diffraction grating with continuously circular Braggmirrors on SOI platform) achieves a gapless design between Bragg gratings. However, because the circular Bragg grating they used requires a strict match between the period and duty cycle of the Bragg grating and the period and duty cycle of the etched diffraction grating, the period and duty cycle of the etched diffraction grating are uniform and consistent. This makes it impossible to use the "one-point method" or chirped diffraction grating design, which is not the optimal design and limits further improvement of device performance.

[0036] In view of this, such as Figures 1 to 8 As shown, an embodiment of the present invention provides a wavelength division multiplexer, including an input waveguide group 10, an output waveguide 20, a free transmission region planar waveguide 30, a diffraction grating 42, and a reflection grating 41. The input waveguide group 10 and the output waveguide 20 are located on the same side of the Rowland circle of the free transmission region planar waveguide 30. The input waveguide group 10 is used to input light of different wavelengths into the free transmission region planar waveguide 30. The diffraction grating 42 is disposed on the grating circle of the free transmission region planar waveguide 30. The reflection grating 41 is located on the side of the diffraction grating 42 away from the free transmission region planar waveguide 30, and the reflection grating 41 is matched with the diffraction grating 42. The grating teeth of the diffraction grating 42 are located on the grating circle, and the grating period of the diffraction grating 42 changes continuously along the arc length of the grating circle to form a chirped distribution. This is used to ensure that the diffracted light at the design center wavelength achieves strict phase alignment at the target position, so that the light achieves diffraction convergence at the target position and reduces aberrations.

[0037] The reflection grating 41 is a continuous strip directional Bragg reflection grating composed of alternating dielectric strips, used to reflect the diffracted light from the diffraction grating 42 back to the free transmission region planar waveguide 30, and focus it onto the output waveguide 20.

[0038] like Figure 2 As shown, the Rowland circle has a radius of R, and the input and output units are arranged on the circumference of the Rowland circle. The grating circle has a radius of 2R and is tangent to the Rowland circle at point O. The gratings are arranged on the grating circle, and the free propagation region is the area shown in ABCE. The waveguides are made of silicon material, and the number of input waveguides in the input waveguide group is not limited to the three shown in the figure and can be adjusted according to actual needs.

[0039] In some embodiments, such as Figure 3As shown, the reflective grating 41 includes a plurality of alternatingly stacked first dielectric strips 411 and second dielectric strips 410, wherein the refractive index of the first dielectric strip 411 is greater than the refractive index of the second dielectric strip 410; The first dielectric strip 411 includes multiple first dielectric segments connected in sequence, with a transition between two adjacent first dielectric segments; the second dielectric strip 410 includes multiple second dielectric segments connected in sequence, with a transition between two adjacent second dielectric segments; the boundary contour between the first dielectric strip and the second dielectric strip presents a continuous alternating convex and concave shape along the grid line direction.

[0040] Specifically, the first dielectric strip 411 is made of silicon, a high-refractive-index material, and the second dielectric strip 410 is made of silicon dioxide, a low-refractive-index material. The period d and duty cycle a satisfy the Bragg reflection conditions for the required reflection band. With the designed number of Bragg grating periods N, it can achieve reflection for the required band with a reflectivity greater than 0.9. This strip structure increases the equivalent width of the Bragg grating and improves the bandwidth of Bragg reflection. Simultaneously, the dielectric strip is composed of multiple sequentially connected dielectric segments to accommodate local orientation changes within the reflection grating region, enabling effective light reflection back to the free transmission region's planar waveguide and coupling to the corresponding output port. Traditional etched diffraction gratings have gaps between adjacent discrete Bragg gratings. This continuous strip-type directional Bragg reflection grating is a continuous whole, without the tiny gaps between discrete grating regions. All dimensions meet the 130nm process requirements, offering low-cost processing capabilities and excellent reflection performance. In some embodiments, such as Figure 4 and Figure 5 As shown, the reflective grating 41 has multiple sub-periodic units defined at different positions. The sub-periodic units are used to describe the local periodic structure of the reflective grating 41, and the local grating line orientation of the reflective grating 41 changes with position. Each sub-periodic unit includes a first dielectric segment and a second dielectric segment arranged alternately along its periodic normal direction. The grating line direction and the periodic normal direction perpendicular to the grating line direction of each sub-periodic unit are set according to the incident light direction and the desired reflection direction, so that the main reflection direction of the reflective grating 41 points to the output waveguide.

[0041] In some embodiments, the stacking period of the reflective grating 41 ranges from 0.2 μm. The first dielectric strip 411 has a thickness of 0.7 μm and a duty cycle of 0.3 μm in the periodic direction. 0.7.

[0042] In some embodiments, such as Figure 2 and Figure 3As shown, the optical path difference of the light with the center wavelength of the input band starts from the input position I on the Rowland circle, passes through the center of the adjacent grating reflector, and then converges to the output position D on the Rowland circle. The optical path difference is an integer multiple of the wavelength. The diffraction grating 42 has a number of grating teeth, which are numbered k∈K (K={-K1,……,0,……K2}), that is, K is a set containing all consecutive integers from -K1 to K2, where K1 and K2 are positive integers and may not be equal. The grating tooth numbered k=0 is the reference grating tooth; for any grating tooth numbered k, the center point of the reflector satisfies the following formula (1): (1) Where P(x, y) is the position of the center point of the reflecting surface of the kth grating tooth; The center wavelengths of the several different wavelengths of light to be input. For planar waveguides in The effective refractive index; m represents the optical path difference being m times the wavelength and taking an integer value; O is the position of the center point of the reflecting surface of the reference grating teeth, I is the input position, and D is the output position. Let be the total geometric path of the incident and reflected light from the reflecting surface of the k-th grating tooth. It is the total geometric path of the incident light plus the reflected light of the reference grating teeth.

[0043] Meanwhile, the center point of the reflecting surface of the kth grating tooth also satisfies the following formula (2): (2) Where R is the radius of the Rowland circle, the position of the center point of the reflecting surface of the kth grating tooth is obtained according to formulas (1) and (2). When the radius R of the Rowland circle, the input and output positions and other parameters are determined, the position P of the grating can be obtained by the system of equations composed of formulas (1) and (2). The position parameters of each grating are obtained by successively changing the value of k.

[0044] The size of each grating reflective surface is determined by the position of interference cancellation, and the interference cancellation point of the grating tooth corresponding to number k satisfies the following formula (3): (3) Among them, P d For the k-th interference cancellation point, the k-th interference cancellation point P on the grating is obtained according to formulas (3) and (2). d The coordinates of the point P are... d The points where the incident light ray intersects with the reflecting surfaces of two adjacent grating teeth are the head edge point S2 and the tail edge point S1 of the reflecting surfaces of the two adjacent grating teeth.

[0045] Combining equations (3) and (2), we can obtain the point P on the grating where interference cancels out.d The coordinates of the point P through which the interference cancels out. d The points where the incident ray intersects with two adjacent reflecting surfaces are the beginning and end edge points S2 and S1 of the two reflecting surfaces, determining the size of the reflecting surfaces. To illustrate the determination of the interference cancellation point, suppose point P is located at the grating position (k=1), and point O is the position of the reference grating (k=0). The calculated P... d The point of interference cancellation, S1, is the end point of the reference grating reflecting surface, as shown below. Figure 3 As shown, point S2 is the starting point of the grating with k=-1. The position of each grating and the size of its reflecting surface can be obtained by analogy. Once the position of each grating and the size of its reflecting surface are determined, the entire basic etching diffraction grating is determined. This type of grating is a chirped grating, which greatly improves the light energy utilization rate.

[0046] The input positions for other wavelengths are obtained from the chromatic dispersion relation, and the dispersion formula is as follows: (4) in It is the angle between the center wavelength ray and the grating normal, i.e. Figure 2 The angle between the IO axis and the x-axis, where It is the angle between light rays of other wavelengths and the grating normal. That is, planar waveguide in group refractive index, To determine the wavelength at the input position. , , , , Given a specific value, the wavelength can be obtained using the formula. From this, we can obtain the angle between the wavelength and the center wavelength, and thus the input position of the wavelength.

[0047] In some embodiments, the angle bisector of the incident and reflected rays of the reflective surface of each grating tooth coincides with the normal of the reflective surface of that grating tooth.

[0048] In some embodiments, such as Figure 6 As shown, the input waveguide group 10 includes multiple input waveguides, each including a straight input waveguide 11 and a tapered input waveguide 12 connected in sequence. One end of the straight input waveguide 11 is an optical signal input end, and the other end of the straight input waveguide 11 is connected to one end of the tapered input waveguide 12. The other end of the tapered input waveguide 12 is disposed on the Rowland circle circumference of the free transmission region planar waveguide 30 and is connected to the free transmission region planar waveguide 30.

[0049] In some embodiments, the output waveguide 20 includes an output tapered waveguide 22 and an output straight waveguide 21 connected in sequence. One end of the output tapered waveguide 22 is disposed on the Rowland circle circumference of the free transmission region planar waveguide 30 and connected to the free transmission region planar waveguide 30. The other end of the output tapered waveguide 22 is connected to one end of the output straight waveguide 21, and the other end of the output straight waveguide 21 is the optical signal output end. Both the input and output waveguides are specially designed and optimized shapes that can guide the transmission of light, spatially shape the light field, significantly improve the transmission efficiency of the optical system, increase the tolerance to input signal deviations and process fluctuations, further achieve spectral flatness and increase bandwidth, and the coupling effect of adjacent waveguides can increase crosstalk. The spectral flatness effect is as follows: Figure 7 As shown.

[0050] Light of three wavelengths enters the free propagation region planar waveguide 30 after passing through three input waveguides 11 and undergoing optical field shaping via input shaping waveguide 12. Kirchhoff diffraction occurs in the free propagation region planar waveguide 30, propagating to the diffraction grating 42. Because a continuous strip-type directional Bragg reflection grating is located behind the diffraction grating, the light is reflected. The parameters of the etched diffraction grating and the reflection grating are designed to converge the diffracted and reflected light of the three wavelengths to the same output position. After passing through the output tapered waveguide and the output waveguide, the combined light is output, and the spectrum is as follows: Figure 8 As shown.

[0051] It should be noted that, based on the design scheme of this invention, if the input and output of light are interchanged, this structure can also be used as a beam splitter to achieve wavelength demultiplexing.

[0052] This invention features easy fabrication and a continuous, gapless integral structure, eliminating the minute gaps between traditional discrete waveguide Bragg gratings. This reduces the requirements for lithography resolution, etching consistency, and alignment accuracy, eliminating the need for high-precision processes. It is compatible with medium-to-low precision processes such as 90nm and 130nm, thus maintaining good manufacturability even with lower process capabilities. This improves device consistency and production yield, while reducing processing costs and yield risks. High reflection efficiency: The design of the reflection grating optimizes and fine-tunes the local strip orientation, ensuring that the reflected main lobe is guided in a predetermined direction under different diffraction angles. This maintains high reflection efficiency over a wide angle range and effectively reflects the light back to the free transmission region planar waveguide and couples it to the corresponding output port. Wideband Adaptability: The continuous strip directional Bragg grating design increases the reflection bandwidth; it is compatible with the chirped structure of diffraction grating groups, ensuring phase matching of light reaching the target position for perfect imaging, further improving light energy utilization. This surpasses the limitations of circular Bragg grating (in the article title: Perfect matching of concave diffraction grating with continuously circular Bragg mirrors on SOI platform) on light reflection at specific angles, and the non-chirped diffraction grating form, improving light energy utilization and supporting the high bandwidth requirements of multi-band beam combining. A periodic structure with a high refractive index difference between silicon and silicon dioxide, combined with an optimal number of periods N, is used based on the Bragg reflection principle. This ensures a full-band reflectivity greater than 0.9 and a maximum reflectivity greater than 0.95, reducing optical signal leakage and improving light energy utilization. The wavelength division multiplexer provided by this invention firstly adopts a continuous strip directional Bragg reflection grating in its core structure. The alternating dielectric strips form a periodic refractive index modulation to achieve Bragg reflection. Since a continuous strip structure is used instead of a discrete grating structure, there are no tiny gaps between discrete grating regions, which reduces the requirements for photolithography resolution, etching consistency and alignment accuracy. As a result, it still has good manufacturability under lower process capabilities, and improves device consistency and production yield.

[0053] Secondly, the local strip orientation is optimized and fine-tuned in the design of the reflection grating so that the reflected main lobe can still be guided in the predetermined direction under different angle conditions, thereby maintaining high reflection efficiency in a wide angle range and effectively reflecting the light back to the free transmission region planar waveguide and coupling it to the corresponding output port.

[0054] Then, in terms of diffraction grating design, this invention is compatible with chirped diffraction gratings and the "one-point method," accurately calculating the position of each diffraction grating unit so that the center of its reflecting surface satisfies the constructive interference condition to maximize diffraction efficiency, while the edges satisfy the destructive interference condition, thus ensuring optimal light energy utilization in principle. Furthermore, the start and end positions of each grating unit (i.e., the edges of the grating tooth reflecting surface) are precisely defined to ensure the entire grating structure is in a spatially optimal state, thereby optimizing spectral response and energy utilization and improving light energy efficiency.

[0055] Finally, at the system-level design level, the input shaping waveguide was optimized. This design expands the bandwidth by actively increasing crosstalk and significantly enhances tolerance to input signal deviations and process variations, further improving the overall robustness of the product and meeting the high bandwidth requirements of multi-band multiplexing.

[0056] This invention presents a low-cost, high-performance continuous strip directional Bragg grating: employing a continuous Bragg reflection grating structure, its core advantage lies in significantly reducing fabrication difficulty and cost. This design eliminates the problem of tiny gaps between traditional discrete Bragg gratings, enabling stable fabrication even with lower process capabilities, while ensuring superior reflection performance and high reliability; it also increases the reflection bandwidth, thereby improving the device bandwidth. Optimized grating positioning for optimal light energy utilization: By precisely determining the local strip orientation of each reflection grating, the main lobe of the Bragg reflection grating is oriented in a predetermined direction, improving reflection efficiency. Simultaneously compatible with the "one-point method" chirped grating design, the start and end positions of each diffraction grating (i.e., the edge of the grating tooth reflection surface) are precisely determined, ensuring that each grating unit is in a spatially optimal structure. This method causes constructive interference of light waves at the center of the grating tooth reflection surface and destructive interference at the edges, thereby maximizing light utilization efficiency. Robust system-level performance enhancement: The optimized input shaping waveguide expands the bandwidth by actively increasing crosstalk and enhances tolerance to input signal deviations and process variations. This feature effectively reduces the extreme dependence on machining precision, thereby improving the overall robustness and production yield of the product and ensuring the stable performance of the system under non-ideal conditions.

[0057] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A wavelength division multiplexer, comprising an input waveguide group (10), an output waveguide (20), a free-transmission region planar waveguide (30), a diffraction grating (42), and a reflection grating (41), wherein the input waveguide group (10) and the output waveguide (20) are located on the same side of the Rowland circle of the free-transmission region planar waveguide (30), and the input waveguide group (10) is used to input light of different wavelengths into the free-transmission region planar waveguide (30), characterized in that, The diffraction grating (42) is disposed on the grating circle of the free transmission region planar waveguide (30), and the reflection grating (41) is located on the side of the diffraction grating (42) away from the free transmission region planar waveguide (30), and the reflection grating (41) is matched with the diffraction grating (42). The grating teeth of the diffraction grating (42) are located on the grating circle, and the grating period of the diffraction grating (42) changes continuously along the arc length direction of the grating circle to form a chirped distribution, which is used to make the light arriving at the diffraction grating (42) diffract and converge at the target position. The reflection grating (41) is a Bragg reflection grating composed of alternating dielectric strips, used to reflect the light diffracted by the diffraction grating (42) back to the free transmission region planar waveguide (30) and focus it onto the output waveguide (20).

2. The wavelength division multiplexer according to claim 1, characterized in that, The reflective grating (41) includes a plurality of alternatingly stacked first dielectric strips (411) and second dielectric strips (410), wherein the refractive index of the first dielectric strip (411) is greater than the refractive index of the second dielectric strip (410); the alternating arrangement of the first dielectric strips and the second dielectric strips forms a periodic refractive index modulation structure to reflect incident light based on the Bragg reflection principle. The first dielectric strip (411) includes multiple connected first dielectric segments, with a transition between two adjacent first dielectric segments; the second dielectric strip (410) includes multiple connected second dielectric segments, with a transition between two adjacent second dielectric segments; the boundary contour between the first dielectric strip (411) and the second dielectric strip (410) presents a continuous alternating convex and concave shape along the grid line direction.

3. The wavelength division multiplexer according to claim 2, characterized in that, The reflective grating (41) has multiple sub-periodic units defined at different positions. The sub-periodic units are used to describe the local periodic structure of the reflective grating (41). The local grating line orientation of the reflective grating (41) changes with position. Each sub-periodic unit includes a first dielectric segment and a second dielectric segment arranged alternately along its periodic normal direction. The grating line direction and the periodic normal direction perpendicular to the grating line direction of each sub-periodic unit are set according to the incident light direction and the desired reflection direction, so that the main reflection direction of the reflective grating (41) points to the output waveguide.

4. The wavelength division multiplexer according to claim 2, characterized in that, The stacking period of the reflective grating (41) ranges from 0.2 μm. 0.7 μm, the duty cycle of the first dielectric strip (411) in the periodic direction is 0.

3. 0.

7.

5. The wavelength division multiplexer according to any one of claims 1-4, characterized in that, The diffraction grating (42) has a number of grating teeth, each numbered sequentially as k∈K (K={-K1,……,0,……,K2}), where K1 and K2 are positive integers and may be unequal; the grating tooth numbered k=0 is the reference grating tooth; for any grating tooth numbered k, the center point P(x,y) of the reflecting surface satisfies the following formula (1): （1） Where P(x, y) is the position of the center point of the reflecting surface of the kth grating tooth; The center wavelengths of the several different wavelengths of light to be input. For planar waveguides in The effective refractive index; m represents the optical path difference being m times the wavelength and taking an integer value; O is the position of the center point of the reflecting surface of the reference grating teeth, I is the input position, and D is the output position. Let be the total geometric path of the incident and reflected light from the reflecting surface of the k-th grating tooth. It is the total geometric path of the incident light plus the reflected light of the reference grating teeth.

6. The wavelength division multiplexer according to claim 5, characterized in that, The center point of the reflecting surface of the kth grating tooth also satisfies the following formula (2): （2） Where R is the radius of the Rowland circle, the position of the center point of the reflecting surface of the kth grating tooth is obtained according to formula (1) and formula (2).

7. The wavelength division multiplexer according to claim 6, characterized in that, The interference cancellation point corresponding to the grating tooth numbered k satisfies the following formula (3): （3） Among them, P d For the k-th interference cancellation point, the k-th interference cancellation point P on the grating is obtained according to formulas (3) and (2). d The coordinates of the point P are... d The points where the incident light ray intersects with the reflecting surfaces of two adjacent grating teeth are the head edge point and the tail edge point of the reflecting surfaces of the two adjacent grating teeth.

8. The wavelength division multiplexer according to claim 5, characterized in that, The angle bisector of the incident and reflected rays of the reflective surface of each of the grating teeth coincides with the normal of the reflective surface of that grating tooth.

9. The wavelength division multiplexer according to claim 1, characterized in that, The input waveguide group (10) includes multiple input waveguides, each of which includes a straight input waveguide (11) and a tapered input waveguide (12) connected in sequence. One end of the straight input waveguide (11) is an optical signal input end, and the other end of the straight input waveguide (11) is connected to one end of the tapered input waveguide (12). The other end of the tapered input waveguide (12) is located on the Rowland circle of the free transmission region planar waveguide (30) and is connected to the free transmission region planar waveguide (30).

10. The wavelength division multiplexer according to claim 1, characterized in that, The output waveguide (20) includes an output tapered waveguide (22) and an output straight waveguide (21) connected in sequence. One end of the output tapered waveguide (22) is disposed on the Rowland circle of the free transmission region planar waveguide (30) and connected to the free transmission region planar waveguide (30). The other end of the output tapered waveguide (22) is connected to one end of the output straight waveguide (21), and the other end of the output straight waveguide (21) is the optical signal output end.

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