Optical coupling system compatible with wide mode field and debugging method

Abstract

The application provides an optical coupling system compatible with wide mode field and a debugging method. The optical coupling system comprises a laser, a collimating lens, an optical isolator and a converging lens which are sequentially fixed along an optical path. The light beam emitted by the laser is collimated and isolated, and then focused by the converging lens to the end face of an edge coupler. By optimizing the focal length and aspheric coefficient of the converging lens and other parameters, the diameter of the focused light spot is controlled within the range of 6.5-7.0 μm, and the focal depth is extended to ±7 μm, and the in-coupling efficiency is still higher than 90%. Simulation verification shows that when the mode field diameter of the edge coupler changes from 4 μm to 9 μm, the coupling efficiency of the fixed optical path structure is higher than 0.78, and the peak value reaches 0.97. The application can realize a set of optical path compatible with various mode field sizes of chips without precise active alignment, significantly reduces the packaging cost, and improves the production yield.

Description

Technical Field

[0001] This invention relates to the field of integrated photonics packaging, and in particular to an optical coupling system and debugging method compatible with wide mode fields. Background Technology

[0002] In the field of optical communication, the transmission of optical signals inside and outside the chip is a crucial process, and edge couplers are typically chosen as the transmission device in this process. For example... Figure 1 As shown, the laser generates a laser signal, which is focused onto the edge coupler after passing through the spatial light device, and then transmitted to the chip via the edge coupler. The chip can perform different specific functions by receiving the highly coherent laser signal.

[0003] However, when laser signals are applied to chips made of different materials, different edge couplers are required to receive them. This process necessitates continuous adjustments to the spatial optical path to ensure compatibility, thus consuming significant human and material resources. This is because the mode field diameters of edge couplers on different material platforms (such as silicon, silicon nitride, and indium phosphide) vary significantly, typically ranging from 4µm to 9µm, making it difficult for existing coupling systems to accommodate all these differences.

[0004] Therefore, how to provide an optical coupling system and debugging method compatible with a wide mode field, so that spatial light signals can have optimal coupling efficiency with multiple mode fields, has become one of the technical problems that urgently need to be solved by people in this field.

[0005] It should be noted that the above description of the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of the present invention and facilitating understanding by those skilled in the art. It should not be assumed that the above technical solutions are known to those skilled in the art simply because they have been described in the background section of this invention. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an optical coupling system and debugging method compatible with wide mode fields, so as to solve the problem that edge couplers with different mode field sizes need to be debugged separately in the prior art.

[0007] To achieve the above and other related objectives, the present invention provides an optical coupling system compatible with a wide mode field. The optical coupling system includes at least: a laser, a collimating lens, an isolator, a focusing lens, and a coupler, which are sequentially fixedly arranged. The laser generates a laser signal. The collimating lens is disposed after the optical path of the laser to collimate the laser signal. The isolator is disposed after the optical path of the collimating lens to prevent the focused light signal from being transmitted to the collimating lens and the laser. The focusing lens is disposed after the optical path of the isolator to focus the collimated laser signal to generate a focused light signal. The coupler is an edge coupler, and the mode field diameter of the coupler is in the range of 4μm-9μm. The coupling efficiency of the optical coupling system to the coupler is greater than 78%.

[0008] Optionally, the ratio of the effective focal length f2 of the focusing lens to the effective focal length f1 of the collimating lens, f2 / f1, is 2.0 to 2.5.

[0009] Optionally, the coupler is an edge coupler integrated on a silicon, silicon nitride, or indium phosphide chip.

[0010] Optionally, within the defocus range of ±7μm of the focused optical signal, the coupling efficiency between the focused optical signal and any coupler is greater than or equal to 90%.

[0011] Optionally, the size of the focused optical signal at an intensity of 1 / e² is 6.5–7.0 μm, where e is a natural constant.

[0012] To achieve the above and other related objectives, the present invention provides a method for debugging a wide-mode-field compatible laser signal, used to obtain the aforementioned wide-mode-field compatible optical coupling system. The coupling method for the wide-mode-field compatible laser signal includes at least the following steps: S1: providing a laser signal, which is collimated, isolated, and focused to generate a focused light signal; S2: acquiring mode field data of at least two edge couplers, wherein the mode field diameter of the edge couplers is between 4μm and 9μm, calculating and adjusting the aberration and spot size of the focused light signal to maximize the total coupling efficiency between the focused light signal and all couplers; S3: coupling the focused light signal to any edge coupler, with a coupling efficiency greater than 78%.

[0013] Optionally, in step S1, the wavelength of the laser signal and the size of the emitted spot are determined based on the mode field diameter of the coupler to be coupled.

[0014] Optionally, in step S2, the aberration and spot size of the focused optical signal are iterated based on the host computer, and the optimal aberration and optimal spot size of the focused optical signal under the maximum total coupling efficiency are obtained; the focused optical signal is actually adjusted to the optimal aberration and the optimal spot size.

[0015] Optionally, in step S2, the aberration and spot size of the focused light signal are adjusted by adjusting any one or a combination of two or more of the following: the distance between the laser and the collimating lens, the radius of curvature of the collimating lens, the conic coefficient of the collimating lens, the center thickness of the collimating lens, the distance between the collimating lens and the isolator, the distance between the isolator and the focusing lens, the radius of curvature of the focusing lens, the conic coefficient of the focusing lens, the center thickness of the focusing lens, and the distance between the focusing lens and the coupler.

[0016] Optionally, in step S2, the total coupling efficiency , ;

[0017] Here, a one-to-one corresponding mode field is obtained based on the edge coupler, where n represents the number of types of mode fields, and i is a natural number between 1 and n. They represent The calculation weights, This represents the coupling efficiency between the focused optical signal and the i-th mode field. This represents the overlap area between the focused optical signal and the i-th mode field. This represents the light field distribution of the focused light signal. Let x represent the light field distribution of the i-th mode field, where x represents the X coordinate and y represents the Y coordinate.

[0018] As described above, the optical coupling system and debugging method compatible with wide mode fields of the present invention have the following beneficial effects:

[0019] 1. This invention, by adjusting the aberrations and spot size of the focused optical signal, enables the focused optical signal to maintain a coupling efficiency higher than 78% with multiple mode fields in the range of 4µm to 9µm, achieving a leap from "single-point optimal" to "range optimal".

[0020] 2. The present invention adopts a fixed optical path structure, which can be compatible with edge couplers of various mode field sizes without precise active alignment, significantly simplifying the packaging process, reducing production costs, and improving production yield.

[0021] 3. The long focal depth characteristic of this invention (efficiency ≥90% within ±7µm focal length range) makes it insensitive to assembly errors and temperature changes, and has good dynamic tolerance and engineering applicability. Attached Figure Description

[0022] Figure 1 The diagram shows a schematic of an optical system and an edge coupler.

[0023] Figure 2 The diagram shown is a structural schematic of the optical coupling system compatible with wide mode fields according to the present invention.

[0024] Figure 3 The diagram shows a flowchart illustrating the debugging method for a wide-mode-field compatible laser signal according to the present invention.

[0025] Figure 4 The diagram shows three types of couplers according to the present invention.

[0026] Figure 5 The diagram shows the coupling efficiency between the focused optical signal and the first mode field coupler of the present invention.

[0027] Figure 6 The diagram shows the coupling efficiency between the focused optical signal and the coupler of the second mode field according to the present invention.

[0028] Figure 7 The diagram shows the coupling efficiency between the focused optical signal and the third mode field of this invention.

[0029] Figure 8 The diagram shows the coupling efficiency curves of the focused optical signal and various couplers according to the present invention.

[0030] Figure 9 The table shown is a schematic diagram illustrating the coupling efficiency of the focused optical signal and various couplers according to the present invention.

[0031] Figure 10 The diagram shows the coupling efficiency of the focused light signal at different focal depths according to the present invention.

[0032] Figure 11 This diagram illustrates the coupling efficiency of a focused light signal in an optical system at different focal depths.

[0033] Component designation explanation

[0034] 1 laser

[0035] 2 collimating lenses

[0036] 3-Focusing Lens

[0037] 4 Couplers

[0038] 5 isolators Detailed Implementation

[0039] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] Please see Figures 1-11 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0041] like Figure 1 As shown, each time an edge coupler is replaced, the spatial optical path of the laser signal needs to be adjusted to achieve compatibility between the laser signal and the edge coupler, thus presenting a complex adjustment problem. Analysis revealed that the reason for adjusting the spatial optical path after coupler replacement is the excessive pursuit of perfect coupling efficiency between the coupler and the laser signal. If this single-point optimization approach is transformed into a range optimization approach—that is, replacing aberration elimination with controlling aberrations within a certain range—the spatial optical path can be made compatible with different edge couplers. However, during range optimization, the laser signal is prone to defocusing and severe mode mismatch on different edge couplers.

[0042] Therefore, in order to solve the above problems, this invention proposes an optical coupling system and debugging method compatible with wide mode fields, the specific technical solution of which is as follows:

[0043] Example 1

[0044] like Figure 2 As shown, this embodiment provides an optical coupling system compatible with a wide mode field, including a laser 1, a collimating lens 2, an isolator 5, a focusing lens 3, and a coupler 4, which are fixedly arranged sequentially along the optical path.

[0045] Laser 1 is used to generate laser signals. In this embodiment, the center wavelength of laser 1 is 1550 nm, and the output light is a multimode beam with fast axis and slow axis divergence angles (FWHM) of approximately 25° and 20°, respectively. The relative distance between laser 1 and collimating lens 2 is constant.

[0046] The collimating lens 2 is positioned after the optical path of the laser 1 to collimate the laser signal.

[0047] Isolator 5 is placed after the optical path of the collimating lens to prevent the focused light signal from being transmitted to the collimating lens and the laser; focusing lens 3 is placed after the optical path of isolator 5 to focus the collimated laser signal to generate a focused light signal.

[0048] Specifically, in this embodiment, both the collimating lens 2 and the focusing lens 3 are aspherical lenses. The front surface of the collimating lens 2 is a plane (with an infinite radius of curvature), and the rear surface is aspherical with a radius of curvature of approximately 1100 (±5%) μm, a conicity of -4.15±1.5, and a center thickness of 0.5±0.025 mm. The front surface of the focusing lens 3 is aspherical with a radius of curvature of 2120 (±5%) μm, a conicity of -0.56±1.5, and a center thickness of 0.5±0.025 mm. The effective focal length f1 of the collimating lens is 0.439 mm, and the effective focal length f2 of the focusing lens is 0.855 mm. The ratio of f2 / f1 is 1.947, falling between 1.5 and 2.0. The isolator 5 has a center band coverage of 1550 nm, an isolation of ISO ≥ 35 dB, and an insertion loss IL < 0.35 dB. In this embodiment, the spacing between each component is optimized and then fixed, specifically: the distance d1 between the laser 1 and the collimating lens 2 is 0.30±0.02mm; the distance d2 between the collimating lens 2 and the isolator 5 is 0.20±0.02mm; the distance d3 between the isolator 5 and the focusing lens 3 is 0.20±0.02mm; and the distance d4 between the focusing lens 3 and the end face of the edge coupler 4 is 0.707±0.02mm. These values ​​are all fixed and together constitute the fixed optical path structure, i.e., the laser, collimating lens, isolator, focusing lens, and coupler are fixedly arranged in sequence.

[0049] In this embodiment, the mode field diameter of the edge coupler 4 is in the range of 4µm to 9µm. Throughout the entire mode field diameter range, the coupling efficiency between the focused optical signal and the edge coupler is greater than or equal to 78%. When the mode field diameter of the edge coupler 4 is 6µm, the coupling efficiency is higher than 95%, with a peak value of 96.8%.

[0050] Because the focused optical signal in this embodiment has a large depth of focus, the coupling efficiency between the focused optical signal and the edge coupler is still greater than or equal to 90% within a defocus range of ±7μm, indicating that the system has good tolerance for axial assembly errors. Meanwhile, the spot size of the focused optical signal at 1 / e² intensity is 6.5–7.0μm. This moderate size ensures that the overlap rate between the focused optical signal and different mode fields within the 4–9μm range remains high, thereby achieving optimal coupling efficiency within the range.

[0051] Example 2

[0052] like Figure 3As shown, this embodiment provides a method for debugging laser signals compatible with wide mode fields, including the following steps:

[0053] like Figure 3 As shown, in step S1, a laser signal is provided, and the laser signal is collimated, isolated, and focused to generate a focused light signal.

[0054] Specifically, in this embodiment, the laser signal emitted by laser 1 is collimated by collimating lens 2, isolated by isolator 5, and then focused by focusing lens 3, generating a focused light signal near the focal point of focusing lens 3. Simultaneously, mode field data for at least two edge couplers with mode field diameters ranging from 4μm to 9μm are acquired. This embodiment uses three edge couplers with mode field diameters of 4μm (typical value for silicon photonics chips), 6μm (typical value for silicon nitride / indium phosphide chips), and 9μm (typical value for large mode field couplers) as examples for illustration, but the debugging method of this invention is not limited to these.

[0055] like Figure 3 As shown, in step S2, at least two types of edge couplers are acquired, with the mode field diameter of the edge couplers ranging from 4μm to 9μm. The aberrations and spot size of the focused light signal are calculated and adjusted to maximize the total coupling efficiency between the focused light signal and all couplers.

[0056] Specifically, in this embodiment, a one-to-one corresponding mode field is obtained based on the edge coupler, that is, one edge coupler yields one mode field, and the total coupling efficiency between the focused optical signal and all mode fields is... , Where n represents the number of types of model fields (e.g., ... Figure 4 As shown in this embodiment, n=3), and i is a natural number between 1 and n. They represent The calculation weights are set according to the requirements for coupling efficiency of different mode fields. This represents the coupling efficiency between the focused optical signal and the i-th mode field, calculated based on the optical parameters of the focused optical signal and the optical parameters of the mode field. This represents the overlap area between the focused optical signal and the i-th mode field, that is, the area where the spot of the focused optical signal overlaps with the coupler 4 corresponding to the i-th mode field. This represents the light field distribution of the focused light signal. Let x represent the light field distribution of the i-th mode field, where x represents the X coordinate and y represents the Y coordinate.

[0057] Furthermore, aberrations and spot size have a significant impact on the optimal coupling efficiency within the interval. Therefore, the aberrations and spot size of the focused optical signal are used as optimization variables to perform global optimization with the goal of maximizing the overall coupling efficiency. During the optimization process, the aberrations and spot size of the focused optical signal are controlled by adjusting any one or more combinations of the following parameters: distance d1 between laser 1 and collimating lens 2, radius of curvature of collimating lens 2, conic coefficient of collimating lens 2, center thickness of collimating lens 2, distance d2 between collimating lens 2 and isolator 5, distance d3 between isolator 5 and focusing lens 3, radius of curvature of focusing lens 3, conic coefficient of focusing lens 3, center thickness of focusing lens 3, and distance d4 between focusing lens 3 and end face of edge coupler 4.

[0058] In this embodiment, the optimization objective is to maximize the worst coupling efficiency among the three points: 4μm, 6μm, and 9μm. In practice, target values ​​(all approaching 1) are set for the three points in the Zemax optical simulation software, with a higher weight assigned to 6μm and appropriate weights assigned to 4μm and 9μm. A global optimization algorithm is then used for iterative convergence.

[0059] Furthermore, in order to improve work efficiency, the aberration and spot size of the focused light signal are continuously iterated on the host computer (such as a computer running Zemax simulation software) to optimize the total coupling efficiency and obtain the optimal aberration and optimal spot size of the focused light signal when the total coupling efficiency reaches its maximum. Then, the focused light signal in the actual optical system is adjusted to the optimal aberration and optimal spot size.

[0060] like Figure 3 As shown, in step S3, the focused light signal adjusted in step S2 is coupled to any edge coupler, and the coupling efficiency is greater than 78%.

[0061] Specifically, in this embodiment, the focused light signal optimized in step S2 has optimal aberration and optimal spot size (spot diameter approximately 6.8 μm, efficiency >90% within a focal depth ±7 μm), and can maintain a coupling efficiency higher than 78% with any edge coupler with a mode field diameter in the range of 4 μm to 9 μm. As an example, such as... Figure 4 As shown, three edge couplers with mode field diameters of 4μm, 6μm, and 9μm were selected. After optimization in step S2, the spot size of the focused optical signal was 6.8μm. Figure 5 As shown, under a 4μm mode field, the spot size is slightly larger than the mode field diameter, but the central energy is highly concentrated, and most of the energy can still enter, resulting in a coupling efficiency of 84.7%. Figure 6 As shown, under a 6μm mode field, the spot size is close to the mode field diameter, resulting in optimal overlap and a coupling efficiency of 96.8%; Figure 7As shown, under a 9μm mode field, the spot size is completely contained within the mode field, with no overflow loss, and the coupling efficiency is 78.5%. Figure 8 and Figure 9 As shown, this example exhibits high coupling efficiency and low coupling loss (approximately 0.72 dB, 0.14 dB, and 1.05 dB, respectively) in all three mode fields.

[0062] It should be noted that this embodiment can obtain the optical coupling system of Embodiment 1, that is, the various edge couplers with mode field diameters of 4μm-9μm that were debugged in this embodiment are within the range of edge couplers with mode field diameters of 4μm-9μm in Embodiment 1.

[0063] Comparative Example

[0064] To highlight the technical effects of this invention, a set of traditional single-point optimization schemes are provided as comparative examples. The comparative examples use the same optical path topology (laser, collimating lens, isolator, focusing lens) as this embodiment, but the difference is that they only optimize the selection and position parameters of the focusing lens for the edge coupler with a mode field diameter of 4μm, pursuing the highest coupling efficiency at this single point, without considering the compatibility of 6μm and 9μm mode fields.

[0065] Simulation results show that the coupling efficiency of the comparative example reaches approximately 94% at 4μm, but when the receiver mode field size is set to 6μm and 9μm, the coupling efficiency is less than 0.7. Meanwhile, the defocus curve of the comparative example shows that within a defocus range of ±7μm, its coupling efficiency drops below 80%, and the depth of focus is significantly shorter than that of the present invention.

[0066] The above comparison results show that the traditional single-point optimization scheme can only achieve high efficiency for a single mode field. Once the mode field deviates from the optimization value, the efficiency drops sharply and is sensitive to the assembly position. In contrast, the present invention, through the fixed optical path and multi-mode field collaborative optimization design, improves the coupling efficiency at 4μm and 9μm to more than 78% while maintaining high coupling efficiency at 6μm, and has a longer depth of focus and better assembly tolerance.

[0067] Figure 10 The coupling efficiency of the two methods under axial defocus conditions is further demonstrated. Within a defocus range of ±7μm, the coupling efficiency of the present invention remains above 90%, exhibiting excellent long depth of focus characteristics; while the comparative example, within the same defocus range, shows a rapid drop in coupling efficiency to below 80%, such as... Figure 11 As shown.

[0068] The above comparison results clearly show that, compared with the traditional scheme that can only optimize for a single mode field, the present invention, through fixed optical path and multi-mode field collaborative optimization design, significantly improves the system's tolerance to mode field changes and assembly errors while maintaining high coupling efficiency.

[0069] It should be noted that this embodiment can be used to debug the laser 1, collimating lens 2, isolator 5, and focusing lens 3 arranged in sequence, and to obtain an optical coupling system with the total coupling efficiency of multiple edge couplers with a mode field diameter in the range of 4μm to 9μm. That is, the optical coupling system described in Embodiment 1 can be obtained, or any optical coupling system with the same or similar concept as this invention can be obtained.

[0070] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An optical coupling system compatible with wide mode fields, characterized in that, The optical coupling system includes at least: a laser, a collimating lens, an isolator, a focusing lens, and a coupler, which are fixedly arranged in sequence. The laser is used to generate laser signals; The collimating lens is disposed after the optical path of the laser and is used to collimate the laser signal; The isolator is positioned after the optical path of the collimating lens to prevent the focused light signal from being transmitted to the collimating lens and the laser. The focusing lens is disposed after the optical path of the isolator and is used to focus the collimated laser signal to generate a focused light signal; The coupler is an edge coupler, and the mode field diameter of the coupler is in the range of 4μm-9μm; the coupling efficiency of the optical coupling system to the coupler is greater than 78%.

2. The optical coupling system compatible with wide mode fields according to claim 1, characterized in that: The ratio of the effective focal length f2 of the focusing lens to the effective focal length f1 of the collimating lens, f2 / f1, is 2.0 to 2.

5.

3. The optical coupling system compatible with wide mode fields according to claim 1, characterized in that: The coupler is an edge coupler, integrated on a silicon, silicon nitride, or indium phosphide chip.

4. The optical coupling system compatible with wide mode fields according to any one of claims 1-3, characterized in that: Within the defocus range of ±7μm of the focused optical signal, the coupling efficiency between the focused optical signal and any coupler is greater than or equal to 90%.

5. The optical coupling system compatible with wide mode fields according to any one of claims 1-3, characterized in that: The size of the focused light signal at an intensity of 1 / e² is 6.5–7.0 μm, where e is a natural constant.

6. A method for debugging a wide-mode-field compatible laser signal, used to obtain the wide-mode-field compatible optical coupling system as described in any one of claims 1-5, characterized in that, The coupling method for the laser signal compatible with wide mode fields includes at least the following steps: S1: Provides a laser signal, which is collimated, isolated, and focused to generate a focused light signal; S2: Obtain mode field data for at least two edge couplers, wherein the mode field diameter of the edge couplers is between 4μm and 9μm; calculate and adjust the aberration and spot size of the focused light signal to maximize the total coupling efficiency between the focused light signal and all couplers. S3: Couple the focused optical signal to any edge coupler, with a coupling efficiency greater than 78%.

7. The method for debugging a laser signal compatible with a wide mode field according to claim 6, characterized in that: In step S1, the wavelength of the laser signal and the size of the emitted spot are determined based on the mode field diameter of the coupler to be coupled.

8. The method for debugging a laser signal compatible with a wide mode field according to claim 6, characterized in that: In step S2, the aberration and spot size of the focused optical signal are iterated based on the host computer, and the optimal aberration and optimal spot size of the focused optical signal under the maximum total coupling efficiency are obtained; the focused optical signal is actually adjusted to the optimal aberration and optimal spot size.

9. The method for debugging a laser signal compatible with a wide mode field according to any one of claims 6-8, characterized in that: In step S2, the aberration and spot size of the focused light signal are adjusted by adjusting any one or a combination of two or more of the following: the distance between the laser and the collimating lens, the radius of curvature of the collimating lens, the conic coefficient of the collimating lens, the center thickness of the collimating lens, the distance between the collimating lens and the isolator, the distance between the isolator and the focusing lens, the radius of curvature of the focusing lens, the conic coefficient of the focusing lens, the center thickness of the focusing lens, and the distance between the focusing lens and the coupler.

10. The method for debugging a wide-mode-field compatible laser signal according to any one of claims 6-8, characterized in that: In step S2, the total coupling efficiency , ; Here, a one-to-one corresponding mode field is obtained based on the edge coupler, where n represents the number of types of mode fields, and i is a natural number between 1 and n. They represent The calculation weights, This represents the coupling efficiency between the focused optical signal and the i-th mode field. This represents the overlap area between the focused optical signal and the i-th mode field. This represents the light field distribution of the focused light signal. Let x represent the light field distribution of the i-th mode field, where x represents the X coordinate and y represents the Y coordinate.

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