A method of simulating the effective reflectivity of a bent waveguide

Abstract

The application provides a method for simulating effective reflectivity of a curved waveguide, and the method comprises the following steps: using an equivalent refractive index method to equivalently convert a multilayer semiconductor structure into a three-layer flat plate waveguide structure; the core layer waveguide of the three-layer flat plate waveguide structure is arranged between two cladding layers; the core layer waveguide comprises a straight waveguide and a curved waveguide; an auxiliary waveguide is added between the cladding layer and the core layer waveguide by using Lumerical FDTD simulation software, and an absorption area is added to the light field leakage area of the cladding layer at the junction of the straight waveguide and the curved waveguide; a light source is arranged at the front end of the straight waveguide in the simulation area, and power monitors are arranged at the front end of the light source in the simulation area, the rear end of the light source and the light output surface of the curved waveguide respectively; and the reflectivity is calculated by using the power monitors. Through cooperation of the auxiliary waveguide and the cladding absorption area, the method can eliminate the reflection of light leakage at the junction of the straight waveguide and the curved waveguide on the cavity surface, so that the simulation result, namely the simulated reflectivity, is more in line with the actual situation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of simulation of optical modes in optical waveguide, and particularly relates to a method for simulating reflectivity of a curved waveguide. BACKGROUND

[0002] In the field of optoelectronics, especially in the field of integrated optics, curved waveguide is a commonly used device to change the direction of light beam propagation; on the other hand, curved waveguide can reduce the effective reflectivity of the mode, which is commonly used in the preparation of superluminescent diodes and semiconductor optical amplifiers. If the reflectivity of the waveguide device is too large, it will form a lasing mode instead of a superluminescent mode. If the reflectivity is too small, it will also result in too small power. Therefore, controlling the reflectivity is important for the power and spectrum of the superluminescent diode. However, the research on curved waveguide mainly focuses on reducing its transmission loss, radiation loss, and mode conversion loss, and there is less research on the reflectivity of curved waveguide.

[0003] The invention patent with application number 202110690109.2 discloses an S-shaped curved waveguide with offset and groove, which includes an input straight waveguide, two curved waveguide segments with opposite curvature and same radius, an output straight waveguide, an offset at the connection of each waveguide, and a groove filled with air. The S-shaped curved waveguide structure introduces a certain offset at the connection of the input straight waveguide and the first curved waveguide segment, the connection of the two curved waveguide segments, and the connection of the second curved waveguide segment and the output straight waveguide segment, respectively. Two grooves with the same shape are added outside the two curved arc segments, and the grooves are filled with air medium. The core width of the waveguide structure is consistent, the refractive index difference between the waveguide core layer and the cladding layer is 0.01, the bending radius of the curved waveguide segment is 1000-5000 μm, the groove width is 0-5 μm, and the distance between the inner side of the groove and the outer side of the waveguide is 0-20 μm. The above invention significantly reduces the bending loss of the low refractive index difference S-shaped waveguide by introducing the optimal offset at each waveguide segment of the low refractive index difference S-shaped waveguide and adding air grooves outside the curved arc segments. By adjusting the offset, the distance between the groove and the waveguide, and the groove width, low-loss transmission of the low refractive index difference polymer waveguide can be achieved at a small bending radius. However, the focus of the above application is to minimize the transmission loss of the curved waveguide by offsetting and filling different refractive index materials in the curved waveguide. However, the present application is a method for simulating when designing a superluminescent diode. The present application does not require that the loss of the curved waveguide be as small as possible, and focuses on the residual reflectivity of the curved waveguide. SUMMARY

[0004] In view of the technical problem that the prior art cannot simulate the reflectivity of the curved waveguide, the present application provides a method for simulating the reflectivity of the curved waveguide, which simulates the reflectivity of the curved waveguide by using the FDTD simulation software, and can quickly and accurately calculate the reflectivity and loss of the curved waveguide.

[0005] In order to achieve the above object, the technical solution of the present invention is implemented as follows: a method for simulating the reflectivity of a curved waveguide, the steps of which are as follows:

[0006] Step 1: Using the equivalent refractive index method, the multi-layer semiconductor structure is equivalent to a three-layer planar waveguide structure; the three-layer planar waveguide structure includes a core waveguide and two cladding layers, and the core waveguide is arranged between the two cladding layers; the core waveguide includes a straight waveguide and a curved waveguide, the straight waveguide is connected to the curved waveguide, and the straight waveguide is arranged at the front end of the curved waveguide;

[0007] Step 2: Use Lumerical FDTD simulation software to add an auxiliary waveguide between the cladding and core waveguides, and add an absorption region to the cladding at the junction of the straight waveguide and the curved waveguide where the light field leaks along the straight waveguide direction;

[0008] Step 3: Select the area including the core waveguide, cladding, auxiliary waveguide and absorption zone as the simulation area, set the light source in the area where the straight waveguide is located in the simulation area, set power monitors at the front and back ends of the light source in the simulation area and at the light output of the bent waveguide. The power monitor value at the back end of the light source is used as the light source power during the simulation process, and the reflectivity is calculated using the power monitors at the front and back ends of the light source and at the light output of the bent waveguide.

[0009] Preferably, the two claddings are respectively an upper cladding and a lower cladding, the auxiliary waveguide is arranged between the upper cladding and the core waveguide, and the auxiliary waveguide just wraps the core waveguide; the auxiliary waveguide includes a straight auxiliary waveguide and a curved auxiliary waveguide, and the straight auxiliary waveguide is connected to the curved auxiliary waveguide.

[0010] Preferably, the absorption region is arranged in the upper cladding layer directly above the bent auxiliary waveguide.

[0011] Preferably, the material setting of the cladding absorption zone is to add an imaginary part of the refractive index, and the imaginary part of the refractive index of the material is not set to 0; the cladding outside the leakage zone adopts non-absorbing material, that is, the imaginary part of the refractive index of the material is 0.

[0012] Preferably, the simulation area has a width smaller than the cladding and larger than the core waveguide and the auxiliary waveguide layer; the left boundary of the simulation area is in the straight waveguide, and the right boundary of the simulation area is larger than the length of the core waveguide; the upper boundary of the simulation area is above the auxiliary waveguide, and the lower boundary of the simulation area is below the core waveguide.

[0013] Preferably, the upper and lower boundaries of the simulation area are located within the cladding layer, with the upper boundary being 5 μm higher than the auxiliary waveguide layer and the lower boundary being 10 μm lower than the core waveguide layer.

[0014] Preferably, the boundary condition of the simulation area is set to a perfect matching layer, and the number of layers of the perfect matching layer is 50.

[0015] Preferably, the method for calculating the reflectivity using power monitors at the front end of the light source, the rear end of the light source, and the light output of the bending waveguide is as follows: the power monitored at the rear end of the light source is used as the incident power p_in during the entire simulation process, the monitor power at the front end of the light source is p_r, the reverse power at the light output of the bending waveguide is p_b, and p_r / p_b is the reflectivity.

[0016] Preferably, the three power monitors are placed 10 μm in front of the light source, 10 μm behind the light source, and at the exit of the bending waveguide.

[0017] Compared with existing technologies, the present invention offers the following advantages: During simulation, an auxiliary waveguide is added between the core layer and the cladding, and a cladding absorption zone is added at the straight and curved waveguides. The use of the auxiliary waveguide and the absorption zone, combined with their coordination, eliminates reflections at the cavity surface caused by light leakage at the junction of the straight and curved waveguides. This results in simulation results, specifically the simulated reflectivity, that are more consistent with reality. This simulation result can effectively guide the development and production of curved waveguide devices. The present invention can quickly and accurately simulate the reflectivity and loss of curved waveguides. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 FIG. 4 is a schematic cross-sectional view of a superluminescent diode according to an embodiment of the present invention.

[0020] Figure 2 FIG. 1 is a top view of a superluminescent diode according to an embodiment of the present invention, which is equivalent to a three-layer structure.

[0021] Figure 3 Schematic diagram of a simulated device after adding inappropriate auxiliary waveguides and absorption regions according to an embodiment of the present invention.

[0022] Figure 4 Schematic diagram of a simulation device after adding appropriate auxiliary waveguides and absorption regions according to an embodiment of the present invention.

[0023] Figure 5 This is a schematic diagram of an embodiment of the present invention after adding a simulation area, a light source, and a power detector.

[0024] Figure 6The calculated light field distribution schematic diagram of adding the material refractive index imaginary part (material does not absorb to the wavelength) for the embodiment of the present application.

[0025] Figure 7 The calculated light field distribution schematic diagram of adding the refractive index imaginary part of the whole cladding region for the embodiment of the present application.

[0026] Figure 8 The calculated light field distribution schematic diagram of adding the inappropriate auxiliary waveguide for the embodiment of the present application.

[0027] Figure 9 The calculated light field distribution schematic diagram of using the appropriate auxiliary waveguide for the embodiment of the present application. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0029] A method for simulating the reflectivity of a curved waveguide, the steps of which are as follows:

[0030] Step one: using the equivalent refractive index method to equivalently convert the multilayer semiconductor structure into a three-layer flat waveguide structure.

[0031] Figure 1 The cross-sectional schematic diagram of the super radiation light emitting diode for the embodiment of the present application. Like the traditional semiconductor light emitting device, it is a multilayer material structure, but in the simulation simulation, the calculation of the multilayer, three-dimensional device will seriously affect the calculation speed, so the equivalent refractive index method is used to equivalently convert the multilayer structure into a three-layer flat waveguide, wherein 101 is the core layer waveguide, the equivalent refractive index is n1; 102 and 103 are cladding layers, the equivalent refractive index is n2, n1>n2. The core layer waveguide is wrapped by the cladding layer.

[0032] Figure 2 The top view schematic diagram of the super radiation light emitting diode for the embodiment of the present application. Wherein 104 is the core layer waveguide region equivalently converted by the multilayer semiconductor structure, 105 and 106 are the equivalent cladding layers. 107 and 108 are straight waveguides and curved waveguides respectively, and the cavity surface of the curved waveguide 108 is the light emitting surface.

[0033] The three-layer slab waveguide structure consists of two cladding layers with a core waveguide located between them. The two cladding layers are an upper cladding and a lower cladding, with the core layer located between them. The core layer includes a straight waveguide and a curved waveguide, which are connected to each other. The light field is confined and propagated within the core layer. Light is totally internally reflected at the interface between the core and cladding, zigzagging forward.

[0034] Step 2: Use Lumerical FDTD simulation software to add an auxiliary waveguide between the upper cladding and the core waveguide, and add an absorption region in the area where the cladding light field leaks along the straight waveguide direction.

[0035] In order to accurately calculate the reflectivity and loss of the curved waveguide, the present invention uses Figure 4 The auxiliary waveguide 114 and cladding absorption region 115 are located between the upper cladding and the core waveguide. The cladding absorption region 115 is located in the upper cladding directly above the curved auxiliary waveguide. This ensures that the optical mode remains unchanged and propagates within the core waveguide while absorbing any leaking light at the bend. Like the core waveguide, the auxiliary waveguide 114 comprises a straight waveguide and an auxiliary waveguide. The auxiliary waveguide precisely encloses the core waveguide, effectively confining the light field within the core and auxiliary waveguides, maintaining the optical field mode unchanged. The width of the auxiliary waveguide 114 is the cross-sectional width of the fundamental mode of the optical field (the fundamental mode width of the optical field). Due to the inconsistent mode matching between the straight waveguide and the curved waveguide, the optical field may leak at the junction of the straight waveguide and the curved waveguide. To more closely resemble the internal conditions of a real laser, a cladding absorption region 115 is added to the exterior of the auxiliary waveguide at the junction of the straight and curved waveguides during simulation (the imaginary part of the refractive index is added to the material settings during simulation). This represents light absorption and reduces the impact of stray light reflection on the reflectivity. During simulation, a cladding absorption region is added to the light leakage area of ​​the straight and curved waveguides in the upper cladding layer, with the imaginary part of the refractive index set to non-zero to simulate material absorption. The cladding absorption region absorbs light leaking from the bend.

[0036] The light field of the upper cladding is leaked along the straight waveguide direction, and the cladding absorption area is added to the non-leaking area. Figure 6 and Figure 8 By comparison, we can see that the leakage area is at the junction of the straight waveguide and the curved waveguide, along the straight waveguide direction. The lower cladding is made of non-absorbing material, which means that the imaginary part of the refractive index is not set.

[0037] In order to compare the key roles of the auxiliary waveguide layer and the absorption region, Figure 3 It is a schematic diagram of the structure in which inappropriate auxiliary waveguides and absorption regions are set, wherein 109 is the core layer, 110 is the auxiliary waveguide layer, 111 is the cladding layer, and 112 and 113 are material absorption regions. Figure 8 yes Figure 3The simulation results of the simulated device. After the bent waveguide emits light, reflection occurs at the interface between the lower auxiliary waveguide and the lower cladding absorption region, which affects the calculation of the simulated reflectivity.

[0038] Step 3: Select a simulation area that includes the upper cladding, lower cladding, core waveguide, auxiliary waveguide, and cladding absorption area. Set a light source in the straight waveguide area of ​​the simulation area. Set a power monitor at the front end of the light source and at the light output of the bent waveguide in the simulation area. The method for calculating the reflectivity is: the power monitored at the back end of the light source is used as the incident power p_in during the entire simulation process, the power of the monitor at the front end of the light source is p_r, and the reverse power at the light output of the bent waveguide is p_b. p_r / p_b is the reflectivity.

[0039] Figure 5 This diagram shows a simulation region, light source, and power detector. Light source 201 is a mode light source located in a straight waveguide region. The light source includes power parameters. Its width is greater than the core waveguide and smaller than the cladding. Power monitor 202 measures the power transmitted through it to calculate the loss and reflectivity of the curved waveguide. The power monitor to the left of light source 201 is used to calculate reflectivity, while the power monitor at the exit of the curved waveguide is used to calculate the loss of the curved waveguide. The three power detectors are located 10 μm in front of the light source, 10 μm behind the light source, and at the exit of the curved waveguide. Simulation region 203 is narrower than the cladding and wider than the core. Its left boundary is within the straight waveguide, and its right boundary extends beyond the right interface of the simulated structure. The boundary conditions for the simulation region are set to 50 perfectly matched layers (PMLs), which completely absorb incident light. The upper and lower boundaries of the simulation region are located between the cladding and core waveguides, with the upper boundary 5 μm above the cladding waveguide and the lower boundary 10 μm below the core waveguide.

[0040] Figure 6 To not add material absorption area (in simulation Figure 4 The light field distribution calculated from the simulation results (no imaginary part of the material refractive index is set in the middle cladding absorption region 115) indicates that when the light mode is transmitted from the straight waveguide to the curved waveguide, a large amount of light leaks out of the curved waveguide. This leaked light is reflected at the interface between the right semiconductor and the air. The reflected light is transmitted along the core waveguide to the monitor in front of the light source, affecting the power p_r result and the final reflectivity calculation.

[0041] Figure 7 The optical field distribution is calculated by adding the imaginary part of the refractive index to the entire cladding region (i.e., the entire cladding region absorbs at the simulation wavelength). Because the optical mode cannot be completely confined to the core waveguide, a certain amount of energy penetrates the cladding, causing light to be absorbed by the cladding after a very short transmission distance, seriously affecting the calculation results.

[0042] Figure 8 To add inappropriate auxiliary waveguides ( Figure 3 The optical field distribution calculated using a simulated device (Figure 2). Because an auxiliary waveguide is added between the core and lower cladding, and the lower cladding is provided with material absorption, the reflected light from the curved waveguide is reflected when it reaches the interface between the lower auxiliary waveguide and the lower cladding. This reflected light then passes through the core waveguide, interfering with the light traveling along the core waveguide to the monitor at the front end of the light source. This affects p_r, resulting in inaccurate calculated reflectivity of the curved waveguide.

[0043] Figure 9 To use the correct auxiliary waveguide ( Figure 4 The leakage light from the straight waveguide is absorbed by the cladding absorption region, ensuring the correctness of the calculated reflectivity.

[0044] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for simulating reflectivity of a curved waveguide, characterized in that: The steps are as follows: Step 1: Using the equivalent refractive index method, the multi-layer semiconductor structure is equivalent to a three-layer planar waveguide structure; the three-layer planar waveguide structure includes a core waveguide and two cladding layers, and the core waveguide is arranged between the two cladding layers; the core waveguide includes a straight waveguide and a curved waveguide, the straight waveguide is connected to the curved waveguide, and the straight waveguide is arranged at the front end of the curved waveguide; Step 2: Use Lumerical FDTD simulation software to add an auxiliary waveguide between the cladding and core waveguides, and add an absorption region to the cladding at the junction of the straight waveguide and the curved waveguide where the light field leaks along the straight waveguide direction; Step 3: Select the region containing the core waveguide, cladding, auxiliary waveguide, and absorption region as the simulation region. Set up a light source in the straight waveguide region of the simulation region. Set up power monitors at the front and back ends of the light source and at the light output of the bent waveguide in the simulation region. The power monitor value at the back end of the light source is used as the light source power during the simulation. Use the power monitors at the front and back ends of the light source and at the light output of the bent waveguide to calculate the reflectivity. The two claddings are respectively an upper cladding and a lower cladding, the auxiliary waveguide is arranged between the upper cladding and the core waveguide, and the auxiliary waveguide just covers the core waveguide; the auxiliary waveguide includes a straight auxiliary waveguide and a curved auxiliary waveguide, and the straight auxiliary waveguide is connected to the curved auxiliary waveguide; The absorption region is arranged in the upper cladding layer directly above the bent auxiliary waveguide.

2. The method for simulating reflectivity of a curved waveguide according to claim 1, wherein: The material of the cladding absorption area is set to add an imaginary part of the refractive index and the imaginary part of the refractive index of the material is set to not be 0; the cladding outside the leakage area adopts non-absorbing material, that is, the imaginary part of the refractive index of the material is 0.

3. The method for simulating reflectivity of a curved waveguide according to claim 2, wherein: The simulation area has a width smaller than the cladding and larger than the core waveguide and the auxiliary waveguide layer; the left boundary of the simulation area is in the straight waveguide, and the right boundary of the simulation area is larger than the length of the core waveguide; the upper boundary of the simulation area is above the auxiliary waveguide, and the lower boundary of the simulation area is below the core waveguide.

4. The method for simulating reflectivity of a curved waveguide according to claim 3, wherein: The upper boundary and the lower boundary of the simulation area are both located between the cladding layers, and the upper boundary is 5 μm higher than the auxiliary waveguide, and the lower boundary is 10 μm lower than the core waveguide.

5. The method for simulating reflectivity of a curved waveguide according to claim 3 or 4, characterized in that: The boundary condition of the simulation region is set to be a perfect matching layer, and the number of perfect matching layers is 50.

6. The method for simulating reflectivity of a curved waveguide according to claim 5, wherein: The reflectivity is calculated using power monitors at the front and back ends of the light source, as well as at the output of the bending waveguide: the power monitored at the back end of the light source is used as the incident power p_in throughout the simulation, the power monitored at the front end of the light source is p_r, the reverse power at the output of the bending waveguide is p_b, and p_r / p_b is the reflectivity.

7. The method for simulating reflectivity of a curved waveguide according to claim 6, wherein: The three power monitors are placed at positions 10 μm in front of the light source, 10 μm behind the light source, and at the exit of the bending waveguide.

Images