Flip chip soldered longitudinal stack light coupling device

Abstract

The application discloses a flip soldering type longitudinal stacking light coupling device and relates to the technical field of semiconductor optoelectronic integrated packaging, which comprises a photonic chip, an electric chip, a light path calibration layer, a heat sink layer, a heat sink layer and a closed-loop feedback control system, the upper surface of the photonic chip is provided with a light coupling area, the light coupling area contains a grating coupler, the electric chip is located above the photonic chip, and the lower surface of the electric chip is provided with flip soldering micro-bumps; the integrated monitoring photoelectric detector is used for monitoring the coupled light power in real time, the micro-displacement sensor is used for monitoring the position of the reflector in real time, the local heater is used for locally heating and softening the transparent packaging layer, and the control circuit is used for realizing closed-loop feedback control; when the light power is detected to decrease, the reflector constraint can be automatically removed, the position is finely adjusted at nanometer level, the reflector is fixed again, the light coupling device has self-maintenance ability in the whole life cycle, and the problem that long-term reliability cannot be guaranteed in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic integrated packaging technology, and in particular to a flip-chip vertically stacked optical coupling device. Background Technology

[0002] With the rapid development of cloud computing, big data, and artificial intelligence technologies, data centers and high-speed communication networks are placing increasingly higher demands on the transmission rates of optical modules. Currently, optical communication systems are evolving from 400G to 800G and even 1.6T. Traditional two-dimensional packaging methods, where electrical and photonic chips are placed side-by-side on a substrate and interconnected via gold wire bonding, are no longer sufficient to meet the demands of high-speed signal transmission. The parasitic inductance and capacitance introduced by gold wire bonding severely degrade signal integrity, becoming a bottleneck restricting the improvement of transmission rates. To solve this problem, the industry widely adopts flip-chip vertical stacking packaging structures, where the driver electrical chip is directly flip-chip bonded to the photonic chip via microbumps, achieving three-dimensional vertical interconnection. This structure significantly shortens the electrical path, effectively reduces parasitic parameters, and ensures the integrity of high-speed electrical signals, making it the mainstream packaging solution for high-speed silicon photonic engines.

[0003] However, existing flip-chip vertically stacked optical coupling devices still have significant drawbacks in practical applications. Because the electrical chip completely covers the optical coupling area of ​​the photonic chip, once the flip-chip reflow process is complete, the grating couplers and alignment marks on the photonic chip surface are permanently obscured, making it impossible to detect or adjust the optical path coupling state from outside the device. If the coupling efficiency decreases due to thermal mismatch, process deviations, or minor displacements during solder reflow, the entire device must be scrapped, as online calibration or fine-tuning is impossible. Furthermore, this tightly stacked structure faces severe thermal management challenges: the electrical chip, as the primary heat source, directly conducts heat to the underlying photonic chip, causing changes in the waveguide refractive index and resulting in optical signal drift; simultaneously, the difference in thermal expansion coefficients between the electrical and photonic chip materials generates thermomechanical stress within the stack, which couples to the optical waveguide layer through microbumps, triggering photoelasticity and further deteriorating optical performance. Existing solutions lack effective thermo-mechanical-optical coordinated control methods and struggle to support the parallel alignment requirements of multi-channel optical coupling devices, severely restricting mass production yield and long-term product reliability.

[0004] To address these issues, the present invention proposes a flip-chip welded longitudinally stacked optical coupling device. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention is proposed.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a flip-chip welded longitudinally stacked optical coupling device, comprising:

[0007] A photonic chip having an optical coupling region on its upper surface, wherein the optical coupling region contains a grating coupler;

[0008] An electrical chip is located above the photonic chip. The lower surface of the electrical chip is provided with flip-chip bonding microbumps. The electrical chip is vertically stacked and electrically connected to the photonic chip through the flip-chip bonding microbumps. A vertical optical detection window is formed on the electrical chip. The projection of the vertical optical detection window in the vertical direction covers at least a portion of the grating coupler.

[0009] An optical path calibration layer is located above the electrical chip. The optical path calibration layer includes a micro-mirror and a driving mechanism. The micro-mirror has a reflective surface, and the driving mechanism is connected to the micro-mirror.

[0010] A heat sink layer covers the optical path calibration layer, and a laser entrance hole is opened on the heat sink layer corresponding to the position of the micro-reflector;

[0011] A transparent encapsulation layer is filled around the micro-mirror, and the transparent encapsulation layer contacts the micro-mirror and fixes the micro-mirror in place;

[0012] The closed-loop feedback control system includes a monitoring photodetector, a micro displacement sensor, a local heater, and a control circuit. The monitoring photodetector is integrated on a photonic chip and positioned adjacent to the grating coupler to output a detection signal characterizing the coupled light power. The micro displacement sensor is integrated on the optical path calibration layer and connected to the micro mirror to output a displacement signal characterizing the position of the micro mirror. The local heater is integrated inside the heat sink layer and located directly above the micro mirror. The control circuit is electrically connected to the driving mechanisms of the monitoring photodetector, the micro displacement sensor, the local heater, and the micro mirror.

[0013] As a preferred embodiment of the flip-chip bonded vertically stacked optical coupling device of the present invention, wherein: the vertical optical detection window is a stepped through-hole structure, the vertical optical detection window includes a wide aperture area at the top and a narrow aperture area at the bottom, a stepped surface is formed between the wide aperture area and the narrow aperture area, and an annular electrode pad is provided on the stepped surface; the optical path calibration layer further includes a microlens, the microlens is embedded in the wide aperture area and located between the micro-mirror and the photonic chip; an annular bonding structure is provided at the bottom of the micro-mirror, and the annular bonding structure is in contact with the annular electrode pad.

[0014] As a preferred embodiment of the flip-chip welded longitudinally stacked optical coupling device of the present invention, wherein: the driving mechanism is a composite driving mechanism, which includes an electrothermal driving unit and an electrostatic comb driving unit; the electrothermal driving unit is a dual-material cantilever beam structure, which includes a first material layer and a second material layer with different coefficients of thermal expansion, and the first material layer and the second material layer are compositely connected; the electrostatic comb driving unit is an interdigitated comb structure, which includes movable comb teeth and fixed comb teeth, and the movable comb teeth and the fixed comb teeth are alternately opposed.

[0015] As a preferred embodiment of the flip-chip welded longitudinally stacked optical coupling device of the present invention, wherein: the electrothermal driving unit has a proximal end and a distal end, the proximal end is connected to the annular electrode pad through an annular bonding structure, and the distal end is connected to the side of the micro-reflector; the movable comb teeth of the electrostatic comb driving unit are connected to the bottom of the micro-reflector, and the fixed comb teeth of the electrostatic comb driving unit are fixed to the step surface through anchor points.

[0016] As a preferred embodiment of the flip-chip bonded longitudinally stacked optical coupling device of the present invention, wherein: the transparent encapsulation layer is made of an optically transparent material with a low glass transition temperature, the transparent encapsulation layer is solid when the temperature is below the glass transition temperature, and the transparent encapsulation layer is liquid when the temperature is above the glass transition temperature.

[0017] As a preferred embodiment of the flip-chip welded longitudinally stacked optical coupling device of the present invention, wherein: a global heating element is also integrated inside the heat sink layer, and the global heating element is electrically connected to the control circuit; a gap is left between the heat sink layer and the micro-reflector, and the height of the gap in the vertical direction is greater than the maximum displacement of the drive mechanism.

[0018] In a preferred embodiment of the flip-chip soldering longitudinally stacked optical coupling device of the present invention, the control circuit includes a storage unit, a comparison unit, and a trigger unit; the storage unit is connected to a monitoring photodetector and a micro displacement sensor, and stores a reference optical power value and a reference displacement value; the comparison unit is connected to the monitoring photodetector and the storage unit, compares the detection value output by the monitoring photodetector with the reference optical power value, and outputs a comparison result signal; the trigger unit is connected to the comparison unit, a local heater, and a drive mechanism, and when the comparison result signal indicates that the difference between the detection value and the reference optical power value exceeds a preset difference, the trigger unit outputs a trigger signal to the local heater and the drive mechanism.

[0019] In a preferred embodiment of the flip-chip bonded vertical stacked optical coupling device of the present invention, the number of vertical optical detection windows, micro-mirrors, and local heaters are all multiple and arranged in an array, and the multiple vertical optical detection windows, multiple micro-mirrors, and multiple local heaters correspond one-to-one with multiple optical coupling channels on the photonic chip.

[0020] As a preferred embodiment of the flip-chip welded longitudinally stacked optical coupling device of the present invention, wherein: the laser incident hole is an inclined through-hole penetrating the heat sink layer, and the angle between the central axis of the inclined through-hole and the vertical direction matches the angle of the reflective surface of the micro-mirror; the inner wall of the laser incident hole is provided with an anti-reflection film, and the aperture of the laser incident hole is larger than the diameter of the reflective surface of the micro-mirror.

[0021] In a preferred embodiment of the flip-chip welded longitudinal stacked optical coupling device of the present invention, an alignment groove is provided on the step surface, a positioning protrusion is provided on the outer edge of the microlens, and the alignment groove and the positioning protrusion are engaged.

[0022] The beneficial effects of this invention are:

[0023] 1. By integrating a monitoring photodetector to monitor the coupled optical power in real time, a micro displacement sensor to monitor the position of the reflector in real time, a local heater to locally heat and soften the transparent encapsulation layer, and a control circuit to achieve closed-loop feedback control, the reflector constraint can be automatically released when a decrease in optical power is detected, and the position can be finely adjusted with nanometer-level precision to re-solidify and fix it. This enables the optical coupling device to have self-maintenance capabilities throughout its entire life cycle, thus solving the problem that the long-term reliability of existing technologies cannot be guaranteed.

[0024] 2. The electrothermal drive unit and the electrostatic comb drive unit are integrated into a composite drive mechanism, which are distributed around the micro-reflector and work together: During initial calibration, the electrothermal drive unit is energized to generate bending displacement, which pushes the micro-reflector to perform a large-stroke coarse adjustment at the micrometer level, quickly adjusting the reflector to the approximate position; then the electrostatic comb drive unit is energized to generate electrostatic force, which pulls the micro-reflector to perform a high-precision fine adjustment at the nanometer level, achieving the best coupling efficiency based on the dual feedback from the displacement sensor and the optical power detector; during adaptive maintenance, the electrostatic comb drive unit performs closed-loop fine adjustment to compensate for small displacement deviations, thus solving the technical contradiction that a single drive method cannot simultaneously achieve both stroke and accuracy.

[0025] 3. By using an optically transparent material with a low glass transition temperature as the encapsulation layer, and with the heating control of local heaters and global heating elements, the reversible conversion between the solid and liquid states of the encapsulation layer is achieved. This allows the micro-mirrors to be readjusted when needed and then re-cured and fixed. At the same time, the vertical optical detection window, micro-mirrors, and local heaters are arranged in an array, corresponding one-to-one with the multiple optical coupling channels on the photonic chip. The monitoring photodetector, micro-displacement sensor, and local heater of each channel work independently, enabling precise maintenance of a single channel. This allows the optical path to still be detected and adjusted after stacking. In case of a single channel failure, only the faulty channel is maintained without affecting other channels, significantly improving the mass production yield and maintainability of the device. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of the photonic chip in this invention;

[0028] Figure 2 This is a schematic diagram of the structure of the electrical chip in this invention;

[0029] Figure 3 This is a schematic diagram of the optical path calibration layer in the figure of the present invention;

[0030] Figure 4 This is a schematic diagram of the structure of the miniature reflector in this invention;

[0031] Figure 5 This is a schematic diagram of the structure of the heat sink layer in this invention.

[0032] Explanation of reference numerals in the attached figures: 100, photonic chip; 110, optical coupling region; 111, grating coupler; 112, alignment mark array; 200, electrical chip; 210, flip-chip microbump; 220, vertical optical detection window; 230, annular electrode pad; 300, optical path calibration layer; 310, microlens; 311, positioning protrusion; 320, miniature mirror; 321, annular bonding structure; 330, electrothermal drive unit; 340, electrostatic comb drive unit; 400, heat sink layer; 410, laser entrance aperture; 500, monitoring photodetector; 600, miniature piezoresistive displacement sensor. Detailed Implementation

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0036] Reference Figures 1-5 As shown, this embodiment provides a flip-chip bonded longitudinally stacked optical coupling device, including:

[0037] The photonic chip 100 is a silicon-based photonic chip. Its upper surface has an optical coupling region 110, which contains grating couplers 111 and multiple optical coupling channels arranged in an array. Each optical coupling channel is used to independently process the coupling and transmission of one optical signal. The optical coupling region 110 includes an array of grating couplers 111 and an alignment mark array 112. The grating coupler array 111 consists of multiple grating couplers 111, each corresponding to an optical coupling channel, used to couple externally input optical signals into the optical waveguide inside the photonic chip 100. The alignment mark array 112 is used to assist alignment during manufacturing. A built-in monitoring photodetector 500 is integrated beside the optical coupling region 110 to monitor the optical power coupled into the grating couplers 111 in real time.

[0038] An electrical chip 200, serving as a driver chip, is located above the photonic chip 100. The lower surface of the electrical chip 200 has flip-chip microbumps 210. The electrical chip 200 is vertically stacked and electrically connected to the photonic chip 100 via the flip-chip microbumps 210. The flip-chip microbumps 210 are arrayed metal bumps located between the lower surface of the electrical chip 200 and the upper surface of the photonic chip 100, made of copper pillars or gold-tin solder, used to achieve short-range interconnection of high-speed electrical signals. The electrical chip 200 has vertical optical detection windows 220 arranged in an array. These windows correspond to multiple optical coupling channels on the photonic chip 100. The vertical projection of the vertical optical detection windows 220 covers at least a portion of the grating coupler 111, allowing incident light to be vertically transmitted to the grating coupler 111 via the vertical optical detection windows 220. The vertical optical detection window 220 has a stepped through-hole structure, comprising a wide-aperture area at the top and a narrow-aperture area at the bottom, forming a stepped surface between them. A ring-shaped electrode pad 230 is provided on the stepped surface, comprising multiple independently powered sectors for subsequent multi-degree-of-freedom control of the micromirror 320. Alignment grooves are provided on the stepped surface for precise assembly of the microlens 310. The non-window area of ​​the electrical chip 200 is covered with a metal shielding layer to reduce electromagnetic interference.

[0039] The optical path calibration layer 300, located above the photonic chip 200, includes a micromirror 320 and a driving mechanism. The micromirror 320 has a reflective surface to deflect the obliquely incident calibration laser and transmit it vertically downwards, through the vertical optical detection window 220, and then couple it into the grating coupler 111. The driving mechanism is connected to the micromirror 320 and drives its movement. The optical path calibration layer 300 also includes microlenses 310, which are embedded in the wide aperture area and located between the micromirror 320 and the photonic chip 100. Each microlens 310 corresponds to a vertical optical detection window 220 for focusing the calibration beam. A positioning protrusion 311 is provided on the outer edge of the microlens 310, which engages with an alignment groove on the stepped surface to achieve passive alignment. The microlenses 310 are initially fixed in the wide aperture area using UV-curable adhesive.

[0040] Furthermore, the bottom of the miniature reflector 320 is provided with an annular bonding structure 321, which contacts the annular electrode pad 230 and achieves temporary mechanical fixation and electrical connection through thermocompression welding. The miniature reflector 320 adopts a hollow structure and is filled with phase change heat storage material to absorb transient thermal shocks and play a thermal buffering role.

[0041] Furthermore, the annular bonding structure 321 is an annular metal layer located at the bottom of the micro-mirror 320, which contacts the annular electrode pad 230 and achieves temporary mechanical fixation and electrical connection through thermo-pressure welding.

[0042] A heat sink layer 400 covers the optical path calibration layer 300. The laser entrance aperture 410 is an inclined through-hole that penetrates the heat sink layer 400. The angle between the central axis of the inclined through-hole and the vertical direction matches the angle of the reflective surface of the micro-reflector 320. The calibration laser enters the laser entrance aperture 410 from above the heat sink layer 400 at an inclined angle, passes through the heat sink layer 400, and reaches the micro-reflector 320. An anti-reflection film is provided on the inner wall of the laser entrance aperture 410. The aperture of the laser entrance aperture 410 is larger than the diameter of the reflective surface of the micro-reflector 320.

[0043] Furthermore, the reflective surface of the micro-mirror 320 is optimized according to the incident light direction, and its angle matches the tilt angle of the laser entrance aperture 410. This ensures that the calibration laser, incident obliquely from above, is reflected by the reflective surface into a precisely vertically downward direction. This vertical beam continues to propagate downwards, passing sequentially through the microlens 310, converging through the vertical optical detection window 220, and finally coupling into the grating coupler 111. The inner wall of the laser entrance aperture 410 is coated with an anti-reflection film to reduce light energy loss. The diameter of the laser entrance aperture 410 is larger than the diameter of the reflective surface of the micro-mirror 320, ensuring that the beam passes through without obstruction.

[0044] The heat sink layer 400 is made of a high thermal conductivity material to quickly conduct and dissipate the heat generated by the electrical chip 200 and the optical path calibration layer 300. The high thermal conductivity material can be aluminum nitride, copper tungsten alloy, or other materials.

[0045] A transparent encapsulation layer surrounds the micromirror 320, contacting and securing it. The encapsulation layer is made of an optically transparent material with a low glass transition temperature, such as modified acrylate or epoxy resin. The encapsulation layer is solid below its glass transition temperature, firmly securing the micromirror 320, and liquid above its glass transition temperature, allowing the micromirror 320 to be repositioned. Its glass transition temperature ranges from 40°C to 80°C.

[0046] The closed-loop feedback control system includes a monitoring photodetector 500, a miniature displacement sensor, a local heater, and control circuitry.

[0047] The monitoring photodetector 500 is integrated on the photonic chip 100 and is located near the grating coupler 111. It is used to monitor the optical power coupled into the grating coupler 111 in real time and output a detection signal characterizing the coupled optical power.

[0048] The miniature displacement sensor is integrated on the optical path calibration layer 300 and connected to the miniature reflector 320. The miniature displacement sensor is a miniature piezoresistive displacement sensor 600, which is used to monitor the position of the miniature reflector 320 in real time and output a displacement signal characterizing the position of the miniature reflector 320.

[0049] The local heater is integrated inside the heat sink layer 400 and located directly above the micro reflector 320. The local heater is an embedded thin-film resistance heating element. Each local heater is set at the position of one micro reflector 320. The control circuit is electrically connected to the monitoring photodetector 500, the micro displacement sensor, the local heater and the drive mechanism of the micro reflector 320 respectively.

[0050] In one embodiment, the driving mechanism is a composite driving mechanism, which includes an electrothermal driving unit 330 and an electrostatic comb driving unit 340.

[0051] The electrothermal drive unit 330 is a dual-material cantilever beam structure, including a first material layer with a large coefficient of thermal expansion and a second material layer with a small coefficient of thermal expansion. The first material layer and the second material layer are connected in a composite manner. Through Joule heating, the electrothermal drive unit 330 generates bending displacement to achieve micron-level large stroke coarse adjustment.

[0052] The electrostatic comb drive unit 340 has an interdigitated comb structure, which includes movable comb teeth and fixed comb teeth. The movable comb teeth and fixed comb teeth are alternately opposed. Electrostatic force is generated by applying voltage. The electrostatic comb drive unit 340 is used to achieve nanometer-level precision adjustment.

[0053] In one embodiment, the electrothermal drive unit 330 has a proximal end and a distal end, the proximal end being connected to the annular electrode pad 230 via an annular bonding structure 321, and the distal end being connected to the side of the micro-reflector 320.

[0054] The movable comb teeth of the electrostatic comb drive unit 340 are connected to the bottom of the micro-reflector 320, and the fixed comb teeth of the electrostatic comb drive unit 340 are fixed to the step surface by anchor points.

[0055] In one embodiment, the heat sink layer 400 also integrates a global heating element, which is a thin-film resistance heating element electrically connected to the control circuit via leads and independently controlled by the control circuit. The global heating element is used to heat the entire heat sink layer 400 as a whole, working in conjunction with the local heaters.

[0056] A gap is left between the heat sink layer 400 and the micro reflector 320. The height of the gap in the vertical direction is greater than the maximum displacement of the drive mechanism to ensure that the micro reflector 320 does not interfere with the heat sink layer 400 during the adjustment process.

[0057] In one embodiment, the control circuit includes a storage unit, a comparison unit, and a trigger unit; the storage unit is connected to the monitoring photodetector 500 and the miniature displacement sensor, and stores the reference optical power value and the reference displacement value.

[0058] The comparison unit is connected to the monitoring photodetector 500 and the storage unit, and is used to compare the detection value output by the monitoring photodetector 500 with the reference optical power value. When the difference between the detection value and the reference optical power value exceeds the preset difference, a trigger signal is output.

[0059] The trigger unit is connected to the comparison unit, the local heater, and the drive mechanism. After receiving the trigger signal, it outputs the trigger signal to the local heater and the drive mechanism, causing the corresponding channel to enter the maintenance mode.

[0060] Furthermore, there are multiple vertical optical detection windows 220, micro mirrors 320, and local heaters arranged in an array, with each of the multiple vertical optical detection windows 220, multiple micro mirrors 320, and multiple local heaters corresponding one-to-one with multiple optical coupling channels on the photonic chip 100.

[0061] Working Principle: The initial calibration phase is performed after the optical coupling assembly is completed and before final encapsulation. The control circuit first supplies power to the integrated global heating element inside the heat sink layer 400, raising its temperature above the glass transition temperature of the transparent encapsulation material. The heat is conducted downwards, causing the transparent encapsulation layer surrounding the micromirrors 320 to reversibly soften from a solid state. At this point, the constraints around all micromirrors 320 are released, allowing for free adjustment. The calibration laser source enters the laser entrance aperture 410 from above the heat sink layer 400 at a preset tilt angle. The laser entrance aperture 410 is an inclined through-hole penetrating the heat sink layer 400, ensuring the beam accurately reaches the reflecting surface of the micromirrors 320 after passing through the heat sink layer 400. The angle of the reflecting surface of the micromirrors 320 matches the tilt angle of the laser entrance aperture 410, causing the obliquely incident calibration laser to be reflected vertically downwards. The vertical beam continues to propagate downwards, first passing through a microlens 310 embedded in the wide-aperture region of a stepped through-hole. The microlens 310 converges the beam, reducing its divergence angle and improving subsequent coupling efficiency. The converged beam continues downwards, passing through a vertical optical detection window 220 on the photonic chip 200. This window is a stepped through-hole structure, and its narrow aperture provides an unobstructed transmission path for the beam. The vertically downward beam finally reaches the grating coupler 111 of the photonic chip 100. The grating coupler 111 utilizes diffraction to convert the vertically incident free-space light into a horizontal direction, transforming it into guided mode light propagating along the internal optical waveguide of the photonic chip 100.

[0062] During this process, a monitoring photodetector 500, integrated on the photonic chip 100 and located adjacent to the grating coupler 111, monitors the optical power coupled into the grating coupler 111 in real time and transmits the detection signal to the control circuit. Based on the feedback from the monitoring photodetector 500, the control circuit first applies a driving voltage to the electrothermal drive unit 330. The electrothermal drive unit 330 is a dual-material cantilever beam structure, composed of a first material layer with a larger coefficient of thermal expansion and a second material layer with a smaller coefficient of thermal expansion. When current passes through, Joule heating causes the temperature of the dual-material beam to rise. Due to the different coefficients of thermal expansion of the two materials, the cantilever beam bends towards the side with the smaller coefficient of thermal expansion. Its distal end is connected to the side of the micro-reflector 320. The bending displacement pushes the micro-reflector 320 to move over a large range at the micrometer level, quickly adjusting the reflector to a roughly correct position.

[0063] After the coarse adjustment is completed, the control circuit applies a driving voltage to the electrostatic comb drive unit 340. The electrostatic comb drive unit 340 has an interdigitated comb structure. When a voltage is applied between the fixed comb teeth and the movable comb teeth, the two carry opposite charges and generate electrostatic force, attracting the movable comb teeth to swing towards the fixed comb teeth, pulling the micro-reflector 320 to perform nanometer-level high-precision fine adjustment.

[0064] During the fine-tuning process, a micro-displacement sensor integrated on the optical path calibration layer 300 and connected to the micro-reflector 320 monitors the precise position of the micro-reflector 320 in real time, while the photodetector 500 monitors the coupled optical power in real time. The control circuit continuously adjusts the driving voltage of the electrostatic comb drive unit 340 based on the dual feedback from the displacement sensor and the optical power detector until the coupled optical power reaches its maximum value, at which point the micro-reflector 320 is in the optimal coupling position. The control circuit stores the current optical power value as the reference optical power value and the current displacement sensor value as the reference displacement value in the control circuit's storage unit. Each optical coupling channel independently completes the above calibration process and stores its own reference value. After all channels are calibrated, the control circuit stops supplying power to the global heating element, the temperature of the heat sink layer 400 gradually decreases to room temperature, and the transparent encapsulation layer cools and re-solidifies, firmly fixing the micro-reflector 320 in the optimal coupling position. The drive mechanism is then de-energized, and the optical coupling device enters a standby state.

[0065] During normal operation, the externally input optical signal is transmitted along the same optical path as during calibration. The optical signal enters the laser entrance aperture 410 at an angle from above the heat sink layer 400, is reflected vertically downwards by the micro-reflector 320, converges through the microlens 310, passes through the vertical optical detection window 220 on the photonic chip 200, and finally reaches the grating coupler 111. After being turned horizontal by the grating coupler 111, it enters the optical waveguide inside the photonic chip 100 for subsequent processing. During the optical signal transmission, the monitoring photodetector 500 continuously monitors the optical power coupled into the grating coupler 111. The monitoring photodetector 500 for each optical coupling channel works independently, transmitting the real-time detection value to the control circuit. The comparison unit in the control circuit continuously compares the real-time optical power value of each channel with the stored reference optical power value. As long as the required real-time value is not lower than the reference optical power value minus a set difference, the control circuit does not take any action, and the optical coupling device maintains normal operation. During normal operation, the drive mechanism is completely de-energized, and neither the electric heating drive unit 330 nor the electrostatic comb drive unit 340 works. The miniature reflector 320 is mechanically fixed by the solidified transparent encapsulation layer, without consuming any electrical energy.

[0066] During the adaptive maintenance phase, when the comparison unit of the control circuit detects that the difference between the real-time optical power value of a certain channel and the reference optical power value exceeds a set difference, the trigger unit immediately identifies the faulty channel and records its corresponding channel number. The control circuit independently supplies power to the local heater corresponding to the faulty channel. After power-on, Joule heating is rapidly generated, and the heat is conducted downwards, only locally heating the transparent encapsulation layer around the channel. When the temperature rises above the glass transition temperature of the transparent encapsulation material, the transparent encapsulation layer in this area reversibly changes from a solid state to a softened state, while the transparent encapsulation layers of adjacent channels remain solid and unaffected.

[0067] After the transparent encapsulation layer softens, the constraints around the miniature reflector 320 in the faulty channel are released, and the control circuit re-supplyes power to the drive mechanism of that channel, restoring the miniature reflector 320 to its adjustable state. The control circuit first reads the reference displacement value of the channel from the storage unit and applies a driving voltage to the electrostatic comb drive unit 340. Based on real-time feedback from the miniature displacement sensor, the electrostatic comb drive unit 340 precisely adjusts the miniature reflector 320 to the stored reference displacement value using electrostatic force, allowing the reflector to quickly return to its optimal position during initial calibration. After the position is restored, the control circuit fine-tunes the electrothermal drive unit 330 based on real-time feedback from the monitoring photodetector 500. The electrothermal drive unit 330, when energized, generates a slight bending displacement, pushing the miniature reflector 320 for fine adjustment until the optical power value detected by the monitoring photodetector 500 returns to the set range of the reference value.

[0068] After the optical power is restored, the control circuit maintains the power supply to the local heater for a set time, allowing the transparent encapsulation layer to remain in a softened state for a sufficient period of time to ensure the stability of the miniature reflector 320 in its new adjusted position. After the maintenance time ends, the control circuit stops supplying power to the local heater, the local heater stops heating, and the temperature of the transparent encapsulation layer in that area gradually decreases. When the temperature drops below the glass transition temperature, the transparent encapsulation layer re-solidifies, firmly fixing the miniature reflector 320 in its new adjusted position.

[0069] The control circuit uses the adjusted new optical power value as the new reference optical power value and the adjusted new displacement value as the new reference displacement value, updates the corresponding data of that channel in the storage unit, and then cuts off the power supply to the faulty channel drive mechanism. The device returns to normal operating mode, and the monitoring photodetector 500 continues to monitor the optical power in real time. The global heating element and the local heater work together. During initial calibration, the global heating element performs overall heating to complete batch coarse calibration. During adaptive maintenance, the local heater performs precise heating of individual channels to achieve independent maintenance of a single channel. This enables adaptive optical path maintenance throughout the entire life cycle of the device, effectively compensating for coupling state drift caused by factors such as device aging, temperature cycling, and stress release.

[0070] Finally, the following points should be noted: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installation", "connection", and "linkage" should be interpreted broadly, and can be mechanical or electrical connections, or internal connections between two components, or direct connections. "Up", "down", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may change.

[0071] Secondly: The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.

[0072] In conclusion, 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 within the protection scope of the present invention.

Claims

1. A flip-chip welded longitudinally stacked optical coupling device, characterized in that, include: A photonic chip (100) has an optical coupling region (110) on its upper surface, and the optical coupling region (110) contains a grating coupler (111). An electrical chip (200) is located above the photonic chip (100). The lower surface of the electrical chip (200) is provided with flip-chip bonding microbumps (210). The electrical chip (200) is vertically stacked and electrically connected to the photonic chip (100) through the flip-chip bonding microbumps (210). A vertical optical detection window (220) is provided on the electrical chip (200). The projection of the vertical optical detection window (220) in the vertical direction covers at least a portion of the grating coupler (111). An optical path calibration layer (300) is located above the electrical chip (200). The optical path calibration layer (300) includes a micro mirror (320) and a driving mechanism. The micro mirror (320) has a reflective surface, and the driving mechanism is connected to the micro mirror (320). A heat sink layer (400) is provided on top of the optical path calibration layer (300), and a laser entrance hole (410) is provided on the heat sink layer (400) at the position corresponding to the micro mirror (320). A transparent encapsulation layer is filled around the micro-mirror (320), and the transparent encapsulation layer contacts the micro-mirror (320) and fixes the micro-mirror (320); The closed-loop feedback control system includes a monitoring photodetector (500), a micro displacement sensor, a local heater, and a control circuit. The monitoring photodetector (500) is integrated on a photonic chip (100) and located adjacent to the grating coupler (111) for outputting a detection signal characterizing the coupled light power. The micro displacement sensor is integrated on the optical path calibration layer (300) and connected to the micro reflector (320) for outputting a displacement signal characterizing the position of the micro reflector (320). The local heater is integrated inside the heat sink layer (400) and located directly above the micro reflector (320). The control circuit is electrically connected to the driving mechanisms of the monitoring photodetector (500), the micro displacement sensor, the local heater, and the micro reflector (320).

2. The flip-chip welded longitudinally stacked optical coupling device as described in claim 1, characterized in that: The vertical optical detection window (220) is a stepped through-hole structure. The vertical optical detection window (220) includes a wide aperture area at the top and a narrow aperture area at the bottom. A stepped surface is formed between the wide aperture area and the narrow aperture area. An annular electrode pad (230) is provided on the stepped surface. The optical path calibration layer (300) also includes a microlens (310). The microlens (310) is embedded in the wide aperture area and located between the micro mirror (320) and the photonic chip (100). An annular bonding structure (321) is provided at the bottom of the micro mirror (320). The annular bonding structure (321) is in contact with the annular electrode pad (230).

3. The flip-chip welded longitudinally stacked optical coupling device as described in claim 2, characterized in that: The driving mechanism is a composite driving mechanism, which includes an electrothermal driving unit (330) and an electrostatic comb driving unit (340); the electrothermal driving unit (330) is a dual-material cantilever beam structure, which includes a first material layer and a second material layer with different coefficients of thermal expansion, and the first material layer and the second material layer are compositely connected; The electrostatic comb drive unit (340) is an interdigitated comb structure, which includes movable comb teeth and fixed comb teeth, with the movable comb teeth and fixed comb teeth being alternately opposed.

4. The flip-chip welded longitudinally stacked optical coupling device as described in claim 3, characterized in that: The electrothermal drive unit (330) has a proximal end and a distal end. The proximal end is connected to the annular electrode pad (230) through an annular bonding structure (321), and the distal end is connected to the side of the micro-reflector (320). The movable comb teeth of the electrostatic comb drive unit (340) are connected to the bottom of the micro-reflector (320), and the fixed comb teeth of the electrostatic comb drive unit (340) are fixed to the step surface through anchor points.

5. The flip-chip welded longitudinally stacked optical coupling device as described in claim 4, characterized in that: The transparent encapsulation layer is made of an optically transparent material with a low glass transition temperature. The transparent encapsulation layer is solid when the temperature is below the glass transition temperature and liquid when the temperature is above the glass transition temperature.

6. The flip-chip welded longitudinally stacked optical coupling device as described in claim 5, characterized in that: The heat sink layer (400) also integrates a global heating element, which is electrically connected to the control circuit; a gap is left between the heat sink layer (400) and the micro reflector (320), and the height of the gap in the vertical direction is greater than the maximum displacement of the drive mechanism.

7. The flip-chip welded longitudinally stacked optical coupling device as described in claim 6, characterized in that: The control circuit includes a storage unit, a comparison unit, and a trigger unit. The storage unit is connected to a monitoring photodetector (500) and a miniature displacement sensor, and stores a reference optical power value and a reference displacement value. The comparison unit is connected to the monitoring photodetector (500) and the storage unit, compares the detection value output by the monitoring photodetector (500) with the reference optical power value, and outputs a comparison result signal. The trigger unit is connected to the comparison unit, a local heater, and a drive mechanism. When the comparison result signal indicates that the difference between the detection value and the reference optical power value exceeds a preset difference, the trigger unit outputs a trigger signal to the local heater and the drive mechanism.

8. The flip-chip welded longitudinally stacked optical coupling device as described in claim 7, characterized in that: The vertical optical detection window (220), the micro mirror (320), and the local heater are all multiple and arranged in an array. Each of the multiple vertical optical detection windows (220), the multiple micro mirrors (320), and the multiple local heaters corresponds to a multiple optical coupling channel on the photonic chip (100).

9. The flip-chip welded longitudinally stacked optical coupling device as described in claim 8, characterized in that: The laser incident hole (410) is an inclined through hole that penetrates the heat sink layer (400). The angle between the central axis of the inclined through hole and the vertical direction matches the angle of the reflective surface of the micro-reflector (320). The inner wall of the laser incident hole (410) is provided with an anti-reflection film. The aperture of the laser incident hole (410) is larger than the diameter of the reflective surface of the micro-reflector (320).

10. The flip-chip welded longitudinally stacked optical coupling device as described in claim 9, characterized in that: The step surface is provided with an alignment groove, and the outer edge of the microlens (310) is provided with a positioning protrusion (311), and the alignment groove and the positioning protrusion (311) are fitted together.

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