A method for self-aligned coupling of a laser to a silicon optical waveguide

Abstract

The application discloses a kind of self-alignment coupling methods of laser and silicon optical waveguide, belong to the technical field of optoelectronic device coupling packaging.The method comprises: based on the back detection surface of laser, obtains the near-field spot distribution data of laser in initial state;According to the near-field spot distribution data, construct the coupling grating array matched with the light intensity distribution of the near-field spot distribution data at the input end of silicon optical waveguide;According to the duty cycle and etching depth of coupling grating array, prepare multiple subwavelength grating units at the input end of silicon optical waveguide;According to the position coordinates of subwavelength grating unit, integrate multiple microcavities in the cladding of silicon optical waveguide;According to the position correspondence of microcavity and subwavelength grating unit, fill polymer material in each microcavity;According to the refractive index variation of polymer material in microcavity at the operating wavelength of laser, by adjusting the thermal expansion coefficient of polymer material, drive polymer material to produce deformation when heated.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic device coupling and packaging technology, specifically a self-aligned coupling method between a laser and a silicon optical waveguide. Background Technology

[0002] In the field of photonic integration, achieving efficient coupling between lasers and silicon waveguides has always been a technical challenge. Current technologies generally rely on high-precision mechanical adjustment systems for the alignment and coupling of lasers and silicon waveguides. This involves active alignment during the packaging process, real-time monitoring of coupling efficiency, and adjustment of the spatial position of the laser or waveguide until peak coupling efficiency is achieved, followed by solidification. This approach is complex, time-consuming, and highly sensitive to environmental stability, easily leading to misalignment under vibration or temperature changes. Another explored approach involves fabricating a fixed-structure coupling grating on the waveguide end face. The mode field distribution is controlled by designing the grating's period and duty cycle to match the laser's output beam field. However, once the grating structure is finalized, it cannot be altered. It can only adapt to ideal or preset beam patterns and cannot handle the subtle differences in near-field distribution characteristics such as beam profile and divergence angle caused by manufacturing tolerances between individual lasers in mass production. This results in actual coupling efficiency far lower than expected. Furthermore, both mechanical adjustment and fixed grating schemes lack methods for in-situ compensation of minute positional shifts caused by factors such as heat generation and aging during operation after initial curing. How to effectively match the individualized, non-uniform light field emitted by the laser with the waveguide input structure, and establish a coupling mechanism that can be controlled by an external physical field after curing to achieve positional compensation, is a problem that urgently needs to be solved. Summary of the Invention

[0003] This invention provides a self-aligned coupling method for lasers and silicon optical waveguides to solve the problem that the fixed grating structure cannot match the individualized near-field spot of the laser in the existing coupling technology, which leads to limited coupling efficiency, and overcomes the defect that the solidified coupling structure lacks in-situ position compensation means.

[0004] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a self-aligned coupling method between a laser and a silicon optical waveguide, comprising the following steps: The near-field spot distribution data of the laser in its initial state is obtained based on the back-probe surface of the laser. According to this near-field spot distribution data, a coupling grating array matching the intensity distribution of the near-field spot distribution data is constructed at the input end of the silicon optical waveguide. Based on the duty cycle and etching depth of the coupling grating array, multiple subwavelength grating units are fabricated at the input end of the silicon optical waveguide. Based on the position coordinates of the subwavelength grating units, multiple microcavities are integrated in the cladding of the silicon optical waveguide. According to the positional correspondence between the microcavities and the subwavelength grating units, polymer material is filled into each microcavity. Based on the refractive index change of the polymer material in the microcavities at the laser's operating wavelength, the thermal expansion coefficient of the polymer material is adjusted, causing the polymer material to deform upon heating. This deformation causes the input end of the silicon optical waveguide to displace in the horizontal or vertical direction.

[0005] By first constructing a coupling grating array at the input end of the silicon optical waveguide that precisely matches the intensity distribution of the laser's near-field spot, the mode field of the silicon optical waveguide and the output field of the laser are highly overlapped, effectively reducing coupling loss. At the same time, combined with the microcavity corresponding to the position of the subwavelength grating unit and the polymer material filled in it, the stress generated by the thermal deformation of the polymer material can be used to precisely and continuously adjust the micro-displacement of the input end of the silicon optical waveguide in the horizontal and vertical directions. This automatically compensates for alignment deviations caused by packaging or environmental changes in a non-mechanical and non-contact manner, achieving stable and efficient self-aligned coupling between the laser and the silicon optical waveguide.

[0006] As a technical solution of the present invention, when constructing a coupled grating array at the input end of a silicon optical waveguide that matches the intensity distribution of the near-field spot distribution data, one-dimensional intensity curve data of the near-field spot distribution data in the horizontal and vertical directions are extracted based on the near-field spot distribution data. The one-dimensional intensity curve data is then divided into multiple intervals according to a preset sampling interval. The grating line density value corresponding to each interval is determined based on the average intensity value within each interval. The period length of the subwavelength grating unit corresponding to each interval is set based on the inverse relationship between the grating line density value and the period of the subwavelength grating unit. By performing refined analysis and interval division of the two-dimensional intensity distribution of the laser near-field spot, and setting the grating period inversely proportional to the intensity value of each interval, the spatial distribution characteristics of the grating array are directly correlated with the energy distribution of the incident light field. This achieves precise matching of the grating array to the non-uniform light field, thereby maximizing the coupling of the incident light into the waveguide mode.

[0007] As a technical solution of the present invention, when fabricating multiple subwavelength grating units at the input end of a silicon optical waveguide based on the duty cycle and etching depth of the coupled grating array, the refractive index data of the core material of the silicon optical waveguide at the laser operating wavelength is obtained; based on the refractive index data, the etching depth of the subwavelength grating unit is set to be equal to the core thickness of the silicon optical waveguide multiplied by a first ratio; based on the refractive index data, the duty cycle of the subwavelength grating unit is set to a second ratio; based on the first ratio and the second ratio, the multiple subwavelength grating units are etched at the input end of the silicon optical waveguide using a focused ion beam etching process. Preferably, the first ratio is 0.3 to 0.7, and the second ratio is 0.4 to 0.6. By precisely controlling the etching depth and duty cycle, the effective refractive index and diffraction intensity of the subwavelength grating unit can be effectively adjusted, ensuring that the diffracted light direction of the grating is phase-matched with the waveguide propagation mode. At the same time, the focused ion beam etching process ensures the processing accuracy and sidewall steepness of the grating structure, further improving coupling efficiency and compatibility with manufacturing processes.

[0008] As a technical solution of the present invention, when integrating multiple microcavities in the cladding of a silicon optical waveguide based on the position coordinates of the subwavelength grating units, a microcavity opening region corresponding one-to-one with each subwavelength grating unit is determined in the upper cladding of the silicon optical waveguide based on the position coordinates of the subwavelength grating units. Based on the microcavity opening region, multiple semi-closed microcavities are etched in the upper cladding using deep reactive ion etching (DRIE). Based on the inner wall of the semi-closed microcavities, a reflective coating is coated on the inner wall of the semi-closed microcavities. By setting the microcavities in a one-to-one correspondence with the subwavelength grating units and processing them using DIE, high-precision positioning and processing of the microcavities are achieved. The reflective coating on the inner wall can more concentratedly guide the stress generated by deformation to the silicon optical waveguide, while preventing unnecessary absorption or scattering losses of the evanescent field by the polymer material, ensuring stable transmission of the optical signal during tuning.

[0009] As a technical solution of the present invention, based on the positional correspondence between the microcavities and the subwavelength grating units, when filling each microcavity with polymer material, the volume of polymer material to be filled in each microcavity is calculated according to the volume of the microcavity and the window area of ​​the subwavelength grating unit; based on the volume of the polymer material, a liquid polymer precursor is injected into each microcavity using a micro-injection pump; based on the injection volume of the liquid polymer precursor, the liquid polymer precursor is solidified into a solid polymer material by ultraviolet light irradiation. By accurately calculating and injecting the volume of the polymer precursor and using ultraviolet light for curing, quantitative and stress-free initial filling of the polymer material in the microcavities is achieved, avoiding asymmetric deformation caused by uneven filling, and providing uniform initial conditions for subsequent precise and controllable thermally driven displacement.

[0010] As a technical solution of the present invention, based on the refractive index change of the polymer material in the microcavity at the laser operating wavelength, the thermal expansion coefficient of the polymer material is adjusted to drive the polymer material to deform upon heating, and the initial refractive index data of the polymer material in the microcavity is obtained; based on the initial refractive index data, the difference between the refractive index of the polymer material at the laser operating wavelength and the refractive index of the cladding of the silicon optical waveguide is calculated; based on the difference, the thermal expansion coefficient of the polymer material is set to a value that makes the change in the difference less than a first threshold within a preset temperature range; based on the thermal expansion coefficient, thermally expanding particles are incorporated into the polymer material in the microcavity. By optimizing the thermal expansion coefficient of the polymer and keeping its refractive index stable relative to the cladding within the temperature range, it is ensured that while generating sufficient deformation-driven displacement, the optical field matching conditions around the coupling grating array are not disrupted by drastic fluctuations in the polymer refractive index, so that the self-alignment adjustment process does not affect the optical coupling efficiency.

[0011] As a technical solution of the present invention, when the deformation causes the input end of the silicon optical waveguide to move in the horizontal or vertical direction, the distribution of the stress component generated by the polymer material in the horizontal and vertical directions is determined according to the shape of the microcavity and the deformation direction of the polymer material; according to the horizontal component of the stress component in the horizontal direction, a horizontal displacement in the horizontal direction is generated at the input end of the silicon optical waveguide; according to the vertical component of the stress component in the vertical direction, a vertical displacement in the vertical direction is generated at the input end of the silicon optical waveguide.

[0012] Specifically, when a horizontal displacement is generated based on the horizontal component of the stress component in the horizontal direction, the cumulative deformation of the polymer material in the horizontal direction is calculated based on the horizontal spacing of the subwavelength grating units; the distance of the horizontal displacement is determined based on the cumulative deformation in the horizontal direction, wherein the horizontal component is used to characterize the mechanical source of the polymer material pushing against the sidewall of the subwavelength grating unit; the polymer material pushes against the sidewall of the subwavelength grating unit based on the distance of movement. When a vertical displacement is generated based on the vertical component of the stress component in the vertical direction, the cumulative deformation of the polymer material in the vertical direction is calculated based on the vertical distance between the microcavity and the upper surface of the subwavelength grating unit; the distance of the vertical displacement is determined based on the cumulative deformation in the vertical direction, wherein the vertical component is used to characterize the mechanical source of the polymer material lifting the lower surface of the subwavelength grating unit; the polymer material lifts the lower surface of the subwavelength grating unit based on the distance of movement. By decomposing the stress generated by the polymer material in the horizontal and vertical directions, and by using sidewall pushing and lower surface lifting methods respectively, independent displacement control of the input end of the silicon optical waveguide in the horizontal and vertical directions is achieved. This can cope with alignment errors in multi-dimensional space, thereby achieving high-precision three-dimensional self-aligned coupling.

[0013] The technical effects and advantages provided by the present invention in the above technical solution are as follows: Based on the actual near-field spot distribution data obtained from the laser's backplane, one-dimensional intensity curves in the horizontal and vertical axes are extracted, and a coupled grating array is constructed accordingly. This array does not employ a uniform periodic structure; instead, the intensity curve is divided into multiple intervals according to the sampling interval. The grating line density at the corresponding position is determined based on the average intensity of each interval, thereby setting the period length of the subwavelength grating unit. This matching method directly correlates the local diffraction intensity of the grating with the true energy distribution of the laser's emitted spot, forming differentiated grating responses for the intensity differences in different regions of the spot. This ensures that during coupling, each spatial frequency component of the spot mode carrying individual characteristics can undergo directional mode-field conversion proportional to its own intensity, thereby reducing mode-field mismatch loss introduced by spot profile deviations.

[0014] By incorporating microcavities corresponding to the subwavelength grating unit positions within the cladding of a silicon waveguide and filling them with polymer material, the waveguide displacement is driven by the stress generated when the polymer expands due to heat. By adjusting the coefficient of thermal expansion of the polymer material, the degree and direction of its deformation under specific temperature changes can be controlled. When an external temperature field is applied, the microcavities constrain the polymer's deformation direction, converting its thermal expansion into horizontal and vertical components acting on the sidewalls or bottom surface of the grating unit, pushing or lifting the waveguide input end to induce micro-displacement in the horizontal or vertical direction. This displacement process is directly excited by the material's own physical properties, eliminating the need for additional mechanical actuators or displacement stages outside the package. This thermomechanical response structure embedded in the waveguide cladding enables in-situ adjustment of the coupling position, dynamically compensating for initial alignment drift caused by environmental temperature fluctuations or material aging, and maintaining the optimal positional state of the coupling interface. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0016] Figure 1 This is a flowchart of the self-aligned coupling method between a laser and a silicon optical waveguide; Figure 2 This is a schematic diagram of a semi-enclosed microcavity with a reflective coating and polymer filling integrated with a subwavelength grating. Figure 3 This is a flowchart of a method for controlling the refractive index difference in microcavity polymer materials; Figure 4 It is a curve showing the change of the refractive index difference of a polymer material with temperature. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] See Figure 1This invention provides a self-aligned coupling method for a laser and a silicon optical waveguide, comprising the following steps: acquiring near-field spot distribution data of the laser in its initial state based on the backplane of the laser; constructing a coupling grating array at the input end of the silicon optical waveguide that matches the intensity distribution of the near-field spot distribution data according to the near-field spot distribution data; fabricating multiple subwavelength grating units at the input end of the silicon optical waveguide according to the duty cycle and etching depth of the coupling grating array; integrating multiple microcavities in the cladding of the silicon optical waveguide according to the position coordinates of the subwavelength grating units; filling each microcavity with polymer material according to the positional correspondence between the microcavities and the subwavelength grating units; driving the polymer material to deform when heated by adjusting the thermal expansion coefficient of the polymer material at the laser's operating wavelength according to the refractive index change of the polymer material in the microcavities; and displacing the input end of the silicon optical waveguide in a horizontal or vertical direction through the deformation. Example 1

[0019] In specific implementation, near-field spot distribution data of the laser in its initial state is obtained based on the laser's backward detection surface. After obtaining the near-field spot distribution data, one-dimensional intensity curve data in the horizontal and vertical directions of the near-field spot distribution data are extracted. The extraction method can be as follows: the near-field spot distribution data is regarded as a two-dimensional intensity matrix, and the intensity is summed column by column along the vertical direction of the two-dimensional intensity matrix to obtain a sequence of one-dimensional intensity curves that vary with the horizontal axis coordinate, which is used as the one-dimensional intensity curve data in the horizontal direction; the intensity is summed row by row along the horizontal direction of the two-dimensional intensity matrix to obtain a sequence of one-dimensional intensity curves that vary with the vertical axis coordinate, which is used as the one-dimensional intensity curve data in the vertical direction.

[0020] After obtaining the one-dimensional intensity curve data along the horizontal axis and the vertical axis, each intensity curve is divided into multiple segments according to a preset sampling interval. The preset sampling interval is set based on the size of the laser's near-field spot and the required density of the silicon waveguide input coupling grating array. In some embodiments, the preset sampling interval is set to one-fifteenth of the full width at half maximum (FWHM) of the near-field spot distribution data. Based on the preset sampling interval, continuous segments are sequentially divided starting from the initial coordinates of the intensity curve data, with the length of each segment equal to the preset sampling interval. For each segment, the intensity values ​​of all data points within that segment are extracted, and the arithmetic mean of the intensity values ​​is calculated to obtain the average intensity of the segment.

[0021] Then, based on the average light intensity within each interval, the grating line density value corresponding to each interval is determined. The grating line density value is the number of subwavelength grating units per unit length. The average light intensity can be converted into a grating line density value using a preset mapping relationship. Optionally, the mapping relationship is a linear mapping, expressed as: ; in, For the first The grating line density values ​​corresponding to each interval segment are expressed in units of per micrometer. For the first The average light intensity of each interval; These are the mapping coefficients. The value of is determined by the matching degree between the scattering field distribution of the silicon optical waveguide coupled grating at the operating wavelength and the near-field spot distribution of the laser, and is optimized through numerical simulation. In a specific example, for an operating wavelength of 1550 nm, The value is set to 1.2, based on the following principle: under fixed etching depth and duty cycle conditions, adjusting... When the two-dimensional cross-correlation coefficient between the far-field scattered light spot and the near-field light spot distribution data of the coupled grating array reaches its maximum value, the corresponding... The value is 1.2.

[0022] After determining the grating line density value for each interval, the period length of the subwavelength grating unit corresponding to each interval is set based on the inverse relationship between the grating line density value and the period of the subwavelength grating unit. Specifically, the... The period length of the subwavelength grating unit corresponding to each interval segment Determined by the following formula: ; in, The unit is micrometer. For the first The grating line density values ​​for each interval are thus determined. At this point, a coupled grating array is constructed at the input end of the silicon waveguide, where the grating period in the horizontal and vertical directions varies according to the intensity distribution of the near-field spot distribution data.

[0023] In some implementations, when dividing the one-dimensional light intensity curve data into segments, for edge regions where the light intensity value is lower than a preset noise threshold, the corresponding grating line density value is directly set to zero to omit the subwavelength grating unit at the corresponding position. The preset noise threshold is taken as 5% of the maximum light intensity value in the near-field spot distribution data. It can be understood that the above process is performed on both the one-dimensional light intensity curve data in the horizontal axis direction and the one-dimensional light intensity curve data in the vertical axis direction, thereby obtaining a two-dimensional distributed coupled grating array configuration. The position of each subwavelength grating unit is determined according to the coordinate range of the corresponding segment at the input end of the silicon optical waveguide, and the period length remains constant within the corresponding segment. Example 2

[0024] In specific implementation, the refractive index data of the core material of the silicon optical waveguide at the laser's operating wavelength is obtained. The core material of the silicon optical waveguide is single-crystal silicon. The refractive index value of the single-crystal silicon is measured using an ellipsometer at a laser operating wavelength of 1550 nm, and is denoted as [value missing]. The measured value is 3.478. The cladding material of the silicon waveguide is silicon dioxide, and its refractive index is denoted as [insert value here]. The measured value is 1.444. The refractive index data serves as the input parameter for determining the etching depth and duty cycle.

[0025] Based on the refractive index data, the etching depth of the subwavelength grating unit is set to a first proportion of the core layer thickness of the silicon waveguide, where the first proportion is between 0.3 and 0.7. This setting is based on the equivalent medium theory, specifically the average refractive index of the subwavelength grating region. It can be represented as: ; in, The average refractive index of the subwavelength grating region. The refractive index of the core material is... The refractive index of the cladding material is... This is the ratio of etching depth to core layer thickness, i.e., the first ratio. This refers to the duty cycle of the subwavelength grating unit, i.e., the second ratio. By selecting... and Make the average refractive index The refractive index is positioned between that of the core layer and the cladding layer to reduce mode mismatch when the laser's optical field couples into the silicon waveguide. Within a defined set of parameter settings, the appropriate parameter is selected. The value is 0.5. The selection criteria are: when the core layer thickness is 220 nanometers, the half-etching depth is 110 nanometers. This depth corresponds to the gradient region near the center position of the fundamental mode field in the vertical direction in the optical waveguide, which can achieve a balance between single-mode transmission and fabrication tolerance.

[0026] Based on the refractive index data, the duty cycle of the subwavelength grating unit is set to a second ratio, which is between 0.4 and 0.6. While setting the first ratio... Based on 0.5, select the second ratio. The value is 0.5, and the selection criterion is: , Substituting into the expression for average refractive index, we can calculate... This average refractive index value is close to the arithmetic mean of the core and cladding refractive indices, ensuring that the optical impedance of the subwavelength grating region maintains a small gradient with both the core and cladding regions of the silicon waveguide. The core width is determined based on the silicon waveguide design, and the duty cycle represents the ratio of the width of the unetched silicon material line in the subwavelength grating unit to the grating period.

[0027] According to the first and second ratios, the multiple subwavelength grating units are etched at the input end of the silicon optical waveguide using a focused ion beam etching (FIB) process. The FIB process uses a gallium ion source, an accelerating voltage of 30 kV, and an ion beam current of 50 picoamps. The etched area is scanned point-by-point according to the design layout. The etching depth is controlled by the number of scans, and the etching depth of each subwavelength grating unit is equal to the core layer thickness of the silicon optical waveguide multiplied by the first ratio. The duty cycle is controlled by adjusting the ion beam dwell time to achieve precise line width processing; the line width is equal to the period of the subwavelength grating unit multiplied by the second ratio. The core layer thickness of the silicon optical waveguide is determined during waveguide fabrication by the thickness of the top silicon layer on the silicon-on-insulator wafer, typically 220 nm. With a core layer width of 450 nm, the etching depth is 110 nm, and the line width is half the grating period. In a multi-period arrangement, the period length of each subwavelength grating unit is given by the aforementioned coupled grating array design, and grating units with different periods are fabricated by changing the scan spacing. Example 3

[0028] In specific implementation, please refer to Figure 2Based on the position coordinates of the subwavelength grating units, a microcavity opening region corresponding to each subwavelength grating unit is determined in the upper cladding of the silicon waveguide. A layout file generated during the focused ion beam etching process is obtained, and the center point coordinates and boundary contours of each subwavelength grating unit are extracted from the layout file. Using the center point coordinates of each subwavelength grating unit as the center, an upward offset is made to the upper cladding region of the silicon waveguide, with the offset distance being the vertical measurement from the upper surface of the subwavelength grating unit to the top surface of the upper cladding. The projected area of ​​the subwavelength grating unit along the horizontal direction is taken, and the area formed by expanding this projected area outward by a preset margin is used as the microcavity opening region. The preset margin is set to 200 nanometers, based on the minimum force transmission boundary size required for the subwavelength grating unit when the polymer material expands and generates stress. This size is determined by the distance at which the additional stress propagation of polymer expansion attenuates to 10% of its peak value in finite element mechanical simulation.

[0029] Based on the microcavity opening area, multiple semi-closed microcavities are etched in the upper cladding using deep reactive ion etching (DRIE). The DRIE process employs a mixed gas of sulfur hexafluoride (SF6) and octafluorocyclobutane (OCT), with an SF6 flow rate of 100 standard cubic centimeters per minute and an OCT flow rate of 10 standard cubic centimeters per minute. The RF power is 200 watts, the low-frequency bias power is 50 watts, and the cavity pressure is maintained at 15 millitors. A photoresist layer is coated on the upper surface of the silicon waveguide, and the photoresist layer is exposed to the microcavity opening area using an electron beam to form an opening pattern. Based on the opening pattern, the DRIE process etches vertically downwards to a depth equal to the thickness of the upper cladding, forming a semi-closed microcavity with a subwavelength grating unit at the bottom, a silicon dioxide cladding on the sidewalls, and an opening at the top. Each semi-closed microcavity corresponds perpendicularly to a subwavelength grating unit.

[0030] A reflective coating is applied to the inner wall of the semi-enclosed microcavity. The reflective coating material is a thin gold film, and the coating process uses magnetron sputtering. The sputtering parameters are: sputtering power 80 watts, argon flow rate 50 standard cubic centimeters per minute, sputtering time 120 seconds, resulting in a reflective coating thickness of 100 nanometers. The reflective coating covers the sidewalls and top surface of the semi-enclosed microcavity, but does not cover the planar area at the bottom of the semi-enclosed microcavity that contacts the subwavelength grating unit. Protection of the bottom plane is achieved by filling with a sacrificial layer, which is polymethyl methacrylate (PMMA). The sacrificial layer is spin-coated after the semi-enclosed microcavity is etched and removed by reactive ion etching before sputtering.

[0031] After fabricating and coating multiple semi-enclosed microcavities with a reflective coating, polymer material is filled into each microcavity according to the positional correspondence between the microcavities and the subwavelength grating units. The filling process specifically involves calculating the volume of polymer material to be filled into each microcavity based on the volume of the microcavity and the window area of ​​the subwavelength grating unit. The volume of a single microcavity is... Expressed by the following formula: ; in, For the first The volume of each microcavity is expressed in cubic micrometers. For the first The window area of ​​each subwavelength grating unit, i.e. the upper surface area of ​​the etched region of the subwavelength grating unit, is expressed in square micrometers. For the first The depth of each microcavity, measured in micrometers, is equal to the measured thickness of the upper cladding. The volume of the polymer material to be filled is set to 0.95 times the volume of the microcavity to allow space for the expansion of the polymer material due to thermal expansion. The 0.95 fill factor is determined by multiplying the thermal expansion coefficient of the polymer material by the operating temperature range.

[0032] Based on the volume of the polymer material, a micro-injection pump is used to inject a liquid polymer precursor into each microcavity. The injection volume accuracy of the micro-injection pump is 0.1 picoliters, and the inner diameter of the injection needle is 5 micrometers. The liquid polymer precursor is loaded into the reservoir of the injection pump. The liquid polymer precursor is a mixture of polydimethylsiloxane prepolymer and curing agent at a mass ratio of 10:1. For each microcavity, the single injection volume of the micro-injection pump is set according to the calculated volume of the polymer material. With the assistance of an optical microscope, the injection needle is moved to directly above the opening of the semi-closed microcavity, maintaining a 5-micrometer gap between the needle and the opening plane of the microcavity. The injection pump is then activated to inject the liquid polymer precursor.

[0033] Based on the injected amount of the liquid polymer precursor, it is solidified into a solid polymer material by ultraviolet (UV) light irradiation. The UV irradiation uses a 365 nm wavelength light source with an intensity of 50 mW / cm² for 180 seconds. The UV light is projected onto the chip surface through a photomask, covering all filled microcavity areas. The photoinitiator in the liquid polymer precursor absorbs UV light energy, initiating a cross-linking reaction and transforming from a liquid to a solid polymer material. The solid polymer material forms a mechanical bond with the inner wall of the microcavities. During UV irradiation, the chip is placed under a nitrogen atmosphere with an oxygen concentration below 100 ppm to avoid oxygen inhibition hindering the curing reaction. After curing, the mask covering the chip surface is removed, revealing an integrated structure where each microcavity is filled with solid polymer material. Example 4

[0034] In specific implementation, please refer to Figure 3 The initial refractive index data of the polymer material in the microcavity was obtained. A silicon waveguide chip filled with solid polymer material was placed on a prism coupler measurement platform. The prism coupler used a laser source with a wavelength of 1550 nm, which is consistent with the laser's operating wavelength. The prism material was rutile titanium dioxide with a refractive index of 2.584. The effective refractive indices of the transverse electric and transverse magnetic modes of the solid polymer material were measured using the prism coupler. The initial refractive index of the polymer material was then derived by solving the waveguide dispersion equations for the transverse electric and transverse magnetic modes, and denoted as […]. , measured The value is 1.412. The refractive index of the cladding of the silicon optical waveguide is denoted as... The measured value is 1.444.

[0035] Based on the initial refractive index data, the difference between the refractive index of the polymer material at the laser's operating wavelength and the refractive index of the silicon waveguide cladding is calculated. This difference is denoted as... , Expressed by the following formula: ; in, This represents the difference in refractive index between the polymer material and the cladding. The initial refractive index of the polymer material. Let be the refractive index of the cladding of the silicon optical waveguide. The values ​​were calculated based on the above measurements. The value is -0.032. This refractive index difference... A negative value indicates that the refractive index of the polymer material in its initial state is lower than that of the cladding.

[0036] Based on the difference, the coefficient of thermal expansion of the polymer material is set to a value that ensures the change in the difference is less than a first threshold within a preset temperature range. The preset temperature range is set from room temperature (25°C) to 85°C, a temperature span of 60°C. The first threshold is set to 0.005. This setting is based on the refractive index difference. If the absolute value of 0.032 exceeds 0.005 during temperature changes, the change in the effective refractive index of the optical mode caused by the thermo-optical effect of the polymer material will exceed the allowable limit for single-mode transmission in silicon waveguides. The magnitude of this fluctuation leads to coupling efficiency exceeding acceptable ranges. The refractive index of the polymer material as a function of temperature is expressed as... ,in The thermo-optic coefficient of polymer materials, pure polydimethylsiloxane for per degree Celsius, The room temperature is 25 degrees Celsius. At the preset upper limit of temperature change (85 degrees Celsius), the refractive index change of pure polydimethylsiloxane is: ,at this time Become The change was 0.018, exceeding the first threshold of 0.005.

[0037] To satisfy the condition that the difference in value is less than a first threshold, the composition of the polymer material needs to be adjusted to reduce the absolute value of the thermo-optic coefficient. Simultaneously, the required deformation is achieved by adjusting the thermal expansion coefficient of the polymer material. Titanium dioxide nanoparticles are incorporated into the polydimethylsiloxane prepolymer. The refractive index of the titanium dioxide nanoparticles is 2.584, and the thermo-optic coefficient is... Per degree Celsius. The equivalent thermo-optical coefficient of the polymer material after incorporating 15% titanium dioxide nanoparticles by volume. Calculated using Maxwell-Garnett's effective medium theory The change in refractive index per degree Celsius, at the preset upper limit of temperature change, is: At this time, the refractive index difference is The change was 0.0078, which is still greater than the first threshold of 0.005.

[0038] Magnesium fluoride nanoparticles were further incorporated into the polymer prepolymer as thermally expandable particles. These magnesium fluoride nanoparticles possess a positive thermo-optic coefficient. It exhibits high thermal expansion coefficient per degree Celsius. The volume fraction of magnesium fluoride nanoparticles was set to 8%. By adjusting the volume fraction of magnesium fluoride nanoparticles, the equivalent thermo-optical coefficient of the polymer material incorporating titanium dioxide nanoparticles and magnesium fluoride nanoparticles was improved. Adjust to per degree Celsius. At the preset upper limit of 85 degrees Celsius for temperature change, the adjusted change in refractive index of the polymer material is: The refractive index difference change is 0.0048, which is less than the first threshold of 0.005. At this time, the coefficient of thermal expansion of the polymer material is set to the equivalent coefficient of thermal expansion after incorporating thermal expansion particles.

[0039] Based on the coefficient of thermal expansion, thermally expanding particles, namely magnesium fluoride nanoparticles, are incorporated into the polymer material within the microcavity. The incorporation process is as follows: before mixing the polydimethylsiloxane prepolymer with the curing agent, titanium dioxide nanoparticles and magnesium fluoride nanoparticles are added sequentially to the polydimethylsiloxane prepolymer. The average particle size of the titanium dioxide nanoparticles is 20 nanometers, and the average particle size of the magnesium fluoride nanoparticles is 50 nanometers. The mixed suspension is treated in an ultrasonic disperser for 60 minutes at an ultrasonic power of 300 watts and a frequency of 40 kHz to uniformly disperse the nanoparticles. After ultrasonic treatment, the curing agent is added, stirred evenly, and then injected into the microcavity via a micro-injection pump. Ultraviolet light irradiation is used for curing to form a solid polymer material containing uniformly dispersed thermally expanding particles. Thus, the solid polymer material possesses the set coefficient of thermal expansion and the optical property that the refractive index difference change is less than a first threshold.

[0040] See Figure 4 The vertical axis in the figure represents the difference in refractive index between the polymer material and the silicon waveguide cladding. The units are dimensionless, and the horizontal axis represents temperature. (Celsius), temperature range from 25°C to 85°C. The figure shows three different polymer material systems within their operating temperature range. The changing trend corresponds specifically to the material adjustment scheme in Example 4.

[0041] The gray solid line represents the linear decreasing trend of the refractive index difference of pure polydimethylsiloxane material with temperature. It starts at about -0.032 at 25°C and decreases to about -0.05 when the temperature rises to 85°C, with a change range of about 0.018. This significantly exceeds the first threshold of 0.005 set in Example 4, indicating that the thermo-optic effect of pure polydimethylsiloxane is strong and does not meet the requirement of a stable refractive index difference.

[0042] The blue dashed line represents the change in refractive index difference of the polymer material after incorporating 15% titanium dioxide nanoparticles by volume. The initial value is still approximately -0.032, but as the temperature increases, its decreasing trend slows down compared to the pure polymer material, reaching approximately -0.04 at 85°C, with a change of about 0.008. This is an improvement compared to the pure polymer, but still slightly higher than the threshold of 0.005, indicating that although incorporating titanium dioxide nanoparticles alone can reduce the thermo-optical coefficient, it is still insufficient to completely suppress refractive index fluctuations.

[0043] The red dotted line represents the change in refractive index difference of the composite polymer material after further doping with 8% magnesium fluoride nanoparticles in addition to 15% titanium dioxide nanoparticles. The curve also starts at approximately -0.032, and the decreasing trend slows down further with increasing temperature, reaching approximately -0.036 at 85°C, with a change of about 0.004. This meets the first threshold constraint of 0.005, demonstrating that the composite doping strategy effectively reduces the thermo-optical coefficient and improves the stability of the refractive index. Example 5

[0044] In the specific implementation, the silicon waveguide chip is heated as a whole using a semiconductor thermoelectric cooler attached to the back of the chip. The chip temperature is increased from 25 degrees Celsius to 85 degrees Celsius at a heating rate of 0.5 degrees Celsius per second, while the polymer material in the microcavity simultaneously reaches 85 degrees Celsius. Upon heating, the polymer material undergoes volume expansion, which is constrained by the semi-enclosed structure of the microcavity, creating a multiaxial stress field within the polymer material. Based on the shape of the microcavity and the deformation direction of the polymer material, the distribution of the stress components generated by the polymer material in the horizontal and vertical directions is determined. The microcavity is a square prism, with the bottom plane being the upper surface of the subwavelength grating unit, the four sides being the vertical walls of the silicon dioxide cladding, and the top being an opening. The polymer material undergoes isotropic volume expansion; constrained by the semi-enclosed microcavity walls, the deformation mainly points towards the top opening, while simultaneously exerting reaction forces on the side walls and bottom. The horizontal stress component is distributed on the four sidewalls of the microcavity, while the vertical stress component is distributed on the upper surface of the subwavelength grating unit at the bottom of the microcavity. Phonon frequencies of the polymer material in a single microcavity region were measured using a micro-area Brillouin scattering spectrometer. Based on the calibration curve of phonon frequency shift versus hydrostatic pressure stress, the hydrostatic pressure in the polymer material was determined to be 2.3 MPa. Multiplying the hydrostatic pressure by the sidewall area of ​​the microcavity yielded the total force acting on a single microcavity sidewall. This total force was then decomposed horizontally to obtain the horizontal component. Its value is 12.6 micronewtons; multiplying the hydrostatic pressure by the bottom area of ​​the microcavity yields the total force in the vertical direction, which is then decomposed along the vertical direction to obtain the vertical component force. Its value is 18.4 micronewtons.

[0045] Based on the horizontal component of the stress in the horizontal direction, a horizontal displacement is generated at the input end of the silicon waveguide. The cumulative deformation of the polymer material in the horizontal direction is calculated based on the horizontal spacing of the subwavelength grating cells. The horizontal spacing of the subwavelength grating cells is defined as the coordinate difference between the center points of two adjacent subwavelength grating cells along the width of the silicon waveguide. The cumulative deformation in the horizontal direction... Determined by the following formula: ; in, This represents the cumulative amount of horizontal deformation, expressed in nanometers. This represents the thermal expansion strain of the polymer material, and has no unit. The coefficient of thermal expansion of polymer materials With temperature change The product is determined. Values per degree Celsius, The temperature is 60 degrees Celsius. Calculated... ; The horizontal spacing of the subwavelength grating units is 360 nanometers. Substituting this value, the cumulative deformation in the horizontal direction is calculated. Nanometers. Cumulative deformation in the horizontal direction. That is, the horizontal displacement distance, and the horizontal component of the force. The mechanical origin of the polymer material pushing the sidewall of the grating unit is characterized. The movement distance is achieved by the polymer material pushing the sidewall of the subwavelength grating unit. During the pushing process, there is no relative sliding between the polymer material and the sidewall of the subwavelength grating unit. The expansion of the polymer material is directly converted into a rigid body displacement of the silicon waveguide input end in the horizontal direction.

[0046] Based on the vertical component of the stress in the vertical direction, a vertical displacement is generated at the input end of the silicon waveguide. The cumulative deformation of the polymer material in the vertical direction is calculated based on the vertical distance between the microcavity and the upper surface of the subwavelength grating unit. This vertical distance is the height between the bottom surface of the microcavity and the top free surface of the polymer material inside the microcavity, with a measured value of 1.8 micrometers. The cumulative deformation in the vertical direction is then calculated. Calculated as thermal expansion strain The product of the vertical distance, i.e. nanometers, of which Vertical distance. Cumulative deformation in the vertical direction. That is, the vertical displacement distance, and the vertical component of the force. The mechanical origin of the polymer material lifting subwavelength grating unit's lower surface is characterized. The movement distance is achieved through the polymer material lifting the lower surface of the subwavelength grating unit. The expansion force of the polymer material in the vertical direction acts on the bottom surface of the subwavelength grating unit, causing it to move upwards in the vertical direction. The horizontal and vertical displacements are on the nanometer scale and are monitored in real time by a position-sensitive detector integrated on a chip. When the target coupling position is reached, heating is stopped and the temperature is kept constant, completing the self-aligned coupling displacement.

[0047] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A self-aligned coupling method between a laser and a silicon optical waveguide, characterized in that, Includes the following steps: The near-field spot distribution data of the laser in its initial state is obtained based on the back-probe surface of the laser. Based on the near-field spot distribution data, a coupled grating array matching the light intensity distribution of the near-field spot distribution data is constructed at the input end of the silicon optical waveguide; Based on the duty cycle and etching depth of the coupled grating array, multiple subwavelength grating units are fabricated at the input end of the silicon optical waveguide. Based on the position coordinates of the subwavelength grating unit, multiple microcavities are integrated in the cladding of the silicon waveguide, specifically: Based on the position coordinates of the subwavelength grating unit, a microcavity opening region corresponding to each subwavelength grating unit is determined in the upper cladding of the silicon waveguide; Based on the microcavity opening area, multiple semi-closed microcavities are etched in the upper cladding using deep reactive ion etching (DRIE). A reflective coating is applied to the inner wall of the semi-enclosed microcavity. According to the positional correspondence between the microcavities and the subwavelength grating units, each microcavity is filled with polymer material; Based on the refractive index change of the polymer material in the microcavity at the laser's operating wavelength, the thermal expansion coefficient of the polymer material is adjusted to drive the polymer material to deform upon heating, specifically as follows: Obtain the initial refractive index data of the polymer material in the microcavity; Based on the initial refractive index data, calculate the difference between the refractive index of the polymer material at the laser operating wavelength and the refractive index of the cladding of the silicon optical waveguide; Based on the difference, the coefficient of thermal expansion of the polymer material is set to a value that makes the change in the difference less than a first threshold within a preset temperature range. According to the coefficient of thermal expansion, thermally expanding particles are incorporated into the polymer material in the microcavity; The deformation causes the input end of the silicon waveguide to shift in the horizontal or vertical direction.

2. The self-aligned coupling method between a laser and a silicon optical waveguide according to claim 1, characterized in that, The step of constructing a coupled grating array at the input end of the silicon waveguide, based on the near-field spot distribution data, to match the intensity distribution of the near-field spot distribution data, specifically involves: Based on the near-field spot distribution data, extract the one-dimensional light intensity curve data of the near-field spot distribution data in the horizontal and vertical directions; Based on the light intensity one-dimensional curve data, the light intensity one-dimensional curve data is divided into multiple intervals according to a preset sampling interval; The grating line density value corresponding to each interval is determined based on the average light intensity within each interval. Based on the inverse relationship between the grating line density value and the period of the subwavelength grating unit, the period length of the subwavelength grating unit corresponding to each interval segment is set.

3. The self-aligned coupling method between a laser and a silicon optical waveguide according to claim 1, characterized in that, The process involves fabricating multiple subwavelength grating units at the input end of the silicon optical waveguide based on the duty cycle and etching depth of the coupled grating array, specifically as follows: Obtain the refractive index data of the core material of the silicon optical waveguide at the laser operating wavelength; Based on the refractive index data, the etching depth of the subwavelength grating unit is set to be equal to the core layer thickness of the silicon waveguide multiplied by a first ratio; Based on the refractive index data, the duty cycle of the subwavelength grating unit is set to a second ratio; Based on the first ratio and the second ratio, the plurality of subwavelength grating units are formed at the input end of the silicon optical waveguide using a focused ion beam etching process.

4. The self-aligned coupling method between a laser and a silicon optical waveguide according to claim 1, characterized in that, The step of filling each microcavity with polymer material according to the positional correspondence between the microcavity and the subwavelength grating unit specifically involves: Calculate the volume of polymer material that needs to be filled in each microcavity based on the volume of the microcavity and the window area of ​​the subwavelength grating unit; Based on the volume of the polymer material, a liquid polymer precursor is injected into each microcavity using a micro-injection pump. Based on the amount of liquid polymer precursor injected, the liquid polymer precursor is solidified by ultraviolet light irradiation to form a solid polymer material.

5. The self-aligned coupling method between a laser and a silicon optical waveguide according to claim 1, characterized in that, The deformation causes the input end of the silicon optical waveguide to shift in the horizontal or vertical direction, specifically: Based on the shape of the microcavity and the deformation direction of the polymer material, the distribution of the stress components generated by the polymer material in the horizontal and vertical directions is determined; Based on the horizontal component of the stress component in the horizontal direction, a horizontal displacement in the horizontal direction is generated at the input end of the silicon optical waveguide. Based on the vertical component of the stress component in the vertical direction, a vertical displacement is generated at the input end of the silicon waveguide.

6. The self-aligned coupling method between a laser and a silicon optical waveguide according to claim 5, characterized in that, The process of generating a horizontal displacement in the horizontal direction at the input end of the silicon optical waveguide based on the horizontal component of the stress component in the horizontal direction is specifically as follows: The cumulative deformation of the polymer material in the horizontal direction is calculated based on the horizontal spacing of the subwavelength grating units. The distance of the horizontal displacement is determined based on the cumulative amount of deformation in the horizontal direction, wherein the horizontal component force is used to characterize the mechanical source of the polymer material pushing against the sidewall of the subwavelength grating unit; Based on the stated moving distance, the sidewalls of the subwavelength grating unit are pushed against the polymer material.

7. The self-aligned coupling method between a laser and a silicon optical waveguide according to claim 6, characterized in that, The process of generating a vertical displacement in the vertical direction at the input end of the silicon optical waveguide based on the vertical component of the stress component specifically involves: The cumulative deformation of the polymer material in the vertical direction is calculated based on the vertical distance between the microcavity and the upper surface of the subwavelength grating unit. The vertical displacement distance is determined based on the cumulative amount of deformation in the vertical direction, wherein the vertical component force is used to characterize the mechanical source of the polymer material lifting the lower surface of the subwavelength grating unit; Based on the stated moving distance, the lower surface of the subwavelength grating unit is lifted by the polymer material.

8. The self-aligned coupling method between a laser and a silicon optical waveguide according to claim 3, characterized in that, The first ratio is 0.3 to 0.7, and the second ratio is 0.4 to 0.6.

Images