High-efficiency vertical coupling large-angle PLC optical branching chip and preparation method thereof

Abstract

The invention belongs to the technical field of integrated photonic devices, and discloses an efficient vertical coupling large-angle PLC optical branching chip and a preparation method thereof. The optical fiber comprises a quartz substrate layer, a core region layer and a cladding layer, the cladding layer is located on the quartz substrate layer, the core area layer is located between the quartz substrate layer and the cladding layer, and a micro lens is etched on the upper surface of the cladding layer; a total reflection angle is arranged at an output waveguide of the PLC optical branching chip, and when a light beam is transmitted to the output waveguide in the core area layer along the horizontal direction, the light beam corresponds to the central position of the micro lens in the vertical direction after being reflected by the total reflection angle arranged at the output waveguide. According to the PLC optical branching chip provided by the invention, a micro lens is processed on the cladding surface of a total reflection optical path by utilizing a semiconductor technology, and the micro lens can realize focusing of light beams in the vertical direction and reduce the size of the light beams, so that most of light beam energy can be received by a photosensitive surface of a detector, and the coupling efficiency is improved.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of integrated photonic devices, and in particular to a high-efficiency vertically coupled large-angle PLC optical splitter chip and a preparation method thereof. Background Art

[0002] At present, the methods for most PLC optical splitter chips to achieve large-angle vertical coupling are mainly divided into optical evanescent wave coupling, coupling using discrete devices (mirrors, gratings), and end-face polishing large-angle coupling.

[0003] Optical evanescent wave coupling utilizes the energy transfer of the evanescent field between adjacent waveguides to achieve coupling. The coupling efficiency is controlled by adjusting the waveguide spacing and refractive index difference. Its advantages include a compact structure, the absence of additional components, and the ability to achieve wavelength-selective coupling. However, its disadvantages are significant. First, the evanescent field intensity decays exponentially with the incident angle, so the angular tolerance of evanescent wave coupling is typically less than ±15°, resulting in high angular sensitivity. Second, this coupling method requires the waveguide spacing to be controlled within ±10nm, requiring stringent process precision and making mass production difficult. Third, due to the different evanescent field decay rates in the TE and TM modes, the polarization-dependent loss (PDL) is greater than 0.5dB, resulting in a strong polarization dependence of this coupling method.

[0004] Vertical coupling can be achieved by using discrete components and integrating micro-mirrors or grating structures to redirect light. This approach offers advantages in terms of wide angular tolerance, with the mirror solution specifically supporting incident angles of ±25°. Furthermore, CMOS-compatible deep silicon etching technology allows for the mass production of high-precision mirrors, making this coupling method relatively mature. However, this coupling approach also presents challenges such as high insertion loss, high wavelength sensitivity, and difficulty in three-dimensional alignment.

[0005] The high-angle coupling method, achieved through end-face grinding and polishing, uses mechanical grinding or laser polishing to create a waveguide end face at a specific angle, exploiting a sudden change in refractive index to deflect the optical path. For example, the waveguide end face of the optical splitter chip can be ground and polished to refract the light path, achieving vertical coupling. This coupling method is cost-effective, but coupling efficiency is affected by the size of the photosensitive surface of the optical receiver chip. In a PLC optical splitter, after the output optical waveguide is polished at a high angle, the light enters the upper cladding layer of the optical waveguide and then enters the air medium. Upon entering the air, the light signal undergoes diffraction, causing the beam to broaden. When coupling to a high-speed photodetector, due to the small aperture of the detector's photosensitive surface, the broadened light beam has little energy reaching the detector, significantly reducing the coupling efficiency. Currently, there are two main methods to improve the coupling efficiency of this structure: one is to reduce the width of the output waveguide, thereby reducing the size of the initial light beam before entering the air layer, thereby increasing the light signal energy received by the detector; the other is to reduce the distance between the cladding and the detector to reduce the spectral broadening caused by diffraction in the air layer. However, method one reduces the width of the output waveguide, which will cause the chip output spectral bandwidth to become smaller and deteriorate the chip performance; method two requires reducing the distance between the chip and the detector, but in actual module packaging operations, the risk of contact between the PLC chip and the detector's photosensitive surface will be greatly increased, making the process operation extremely difficult.

[0006] In summary, in order to achieve efficient coupling between the PLC optical splitter chip and other optical chips, it is urgent to propose a new PLC chip design and preparation method to realize a new coupling mode, while also taking into account the requirements of mass production and low cost. Summary of the Invention

[0007] To address the technical problem of low photoelectric conversion efficiency when coupling vertically with the detector's photosensitive surface after end-face polishing, existing PLC optical splitter chips exhibit low photoelectric conversion efficiency. This present invention proposes a high-efficiency, vertically coupled, large-angle PLC optical splitter chip and its fabrication method. The proposed PLC optical splitter chip utilizes semiconductor processing to create a microlens on the cladding surface of the total internal reflection optical path. This microlens focuses the light beam vertically, reducing its size and ensuring that the majority of the beam energy is received by the detector's photosensitive surface, thereby improving coupling efficiency.

[0008] To achieve the above object, the present invention provides a high-efficiency vertically coupled large-angle PLC optical splitter chip, comprising a quartz substrate layer, a core layer and a cladding layer; The cladding is located on the quartz substrate layer, the core layer is located between the quartz substrate layer and the cladding, and a microlens is etched on the upper surface of the cladding; A total reflection angle is set at the output waveguide of the PLC optical splitter chip. When the light beam is transmitted horizontally in the core layer to the output waveguide, it is reflected by the total reflection angle set at the output waveguide and corresponds to the center position of the microlens in the vertical direction.

[0009] Furthermore, the core layer is a silicon dioxide layer doped with germanium, and the cladding layer is a silicon dioxide layer doped with boron and phosphorus.

[0010] Furthermore, the degree of the total reflection angle is set to 41°.

[0011] The present invention also provides a method for preparing a high-efficiency vertically coupled large-angle PLC optical splitter chip, comprising the following steps: Step 1: Grow a silicon dioxide layer on the quartz substrate to form a core layer, and transfer the PLC optical branching waveguide pattern to the core layer through a photolithography process; Step 2: growing a silicon dioxide layer on the surface of the core layer formed in step 1 to form a cladding layer; Step 3: coating the surface of the cladding layer formed in step 2 with photoresist to obtain a photoresist layer; Step 4: Transfer the pattern on the microlens mask to the photoresist layer formed in step 3 through a photoresist development process; Step 5: The photoresist layer formed in step 4 is deformed into a hemispherical structure by a high-temperature reflow process; Step 6: Using the photoresist layer with the hemispherical structure formed in step 5 as a mask, perform ICP etching to etch a microlens pattern on the cladding surface to obtain a cladding integrated microlens; Step 7: Perform total reflection angle grinding and polishing on the output waveguide of the PLC optical splitter chip so that the polished output waveguide end face is aligned with the center position of the microlens in the vertical direction.

[0012] Furthermore, the core layer in step 1 is a silicon dioxide layer doped with germanium, and the cladding layer in step 2 is a silicon dioxide layer doped with boron and phosphorus.

[0013] Furthermore, in step 3, the thickness of the photoresist layer is greater than 20 μm.

[0014] Furthermore, in step 5, the reflux temperature of the high-temperature reflux process is 120° C., and the reflux constant temperature time is 45 minutes.

[0015] Furthermore, in step 6, the curvature radius of the microlens is adjusted by the etching selectivity ratio of the photoresist layer and the cladding layer, and the curvature radius of the microlens corresponds to the coupling distance between the detector and the PLC optical branching chip.

[0016] Furthermore, the degree of the total reflection angle in step 7 is set to 41°.

[0017] Beneficial effects: The cladding surface of the PLC chip provided by the present invention is prepared with a microlens. When the light beam propagates horizontally in the core layer of the PLC chip to the output waveguide, it is reflected by the total reflection angle at the output waveguide, and the light beam passes through the cladding in the vertical direction. It is focused by the microlens on the cladding corresponding to the core layer. The size of the light beam is reduced, so that most of the light beam energy can be received by the photosensitive surface of the detector, avoiding the problem of reduced coupling efficiency due to beam broadening, and can greatly improve the light coupling efficiency. Moreover, the presence of the microlens makes it unnecessary to reduce the assembly distance between the PLC chip and the detector. The coupling distance between the PLC chip and the detector is large, thereby reducing the difficulty of coupling packaging and improving the coupling efficiency. In addition, the PLC chip preparation method proposed by the present invention adopts traditional semiconductor process steps, can be prepared in large quantities, has a high yield rate, and can greatly reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic side view of a high-efficiency vertically coupled large-angle PLC optical splitter chip according to an embodiment of the present invention (partially enlarged end face); Figure 2 Schematic diagram (side view) of a high-efficiency vertically coupled large-angle PLC optical splitter chip and a detection coupler according to an embodiment of the present invention; Figure 3 This is a top view schematic diagram of a high-efficiency vertically coupled large-angle PLC optical splitter chip involved in an embodiment of the present invention (taking a 1-to-4 PLC chip as an example).

[0019] Description of reference numerals: 1 is the quartz substrate layer; 2 is the core layer; 3 is the cladding layer; 4 is the microlens; 5 is the detector. DETAILED DESCRIPTION

[0020] like Figures 1 to 3 As shown, the present invention provides a high-efficiency vertically coupled large-angle PLC optical splitter chip and a preparation method thereof. Figure 1 Schematic side view of a high-efficiency vertically coupled large-angle PLC optical splitter chip according to an embodiment of the present invention (partially enlarged end face); Figure 2 Schematic diagram (side view) of a high-efficiency vertically coupled large-angle PLC optical splitter chip and a detection coupler according to an embodiment of the present invention; Figure 3 This is a top view schematic diagram of a high-efficiency vertically coupled large-angle PLC optical splitter chip involved in an embodiment of the present invention (taking a 1-to-4 PLC chip as an example). Example 1

[0021] This embodiment proposes a high-efficiency vertically coupled large-angle PLC optical splitter chip, which is used to avoid the problem that after the end face of the PLC optical waveguide is polished, the optical signal enters the air medium through the upper cladding layer and diffracts, thereby widening the light beam and causing a decrease in coupling efficiency. It can greatly improve the coupling efficiency between the PLC optical splitter chip and the high-speed photodetection chip. At the same time, when performing coupling assembly, there is no need to reduce the distance between the chip and the detector chip, the coupling process has a large tolerance, and the production yield is high. The general principle block diagram of this chip can be referred to Figure 1 , Figure 1 This is a side view schematic diagram (partially enlarged end view) of a high-efficiency vertically coupled, large-angle PLC optical splitter chip according to an embodiment of the present invention, including: 1 is a quartz base layer, which is made of silicon dioxide.

[0022] 2 is the core layer, which is made of silicon dioxide doped with germanium. The core layer is located between the base layer and the cladding layer, and the light beam passes through it; Reference numeral 3 denotes a cladding layer, which is made of a silicon dioxide layer doped with boron and phosphorus. Micro lenses corresponding to the light beam passing through the core layer are etched on the cladding layer.

[0023] 4 is a microlens, which focuses the light beam after total reflection from the core layer through the waveguide end face, reduces the size of the light beam, and enables most of the light beam energy to be coupled to the photosensitive surface of the detector.

[0024] It should be further explained that the relationship between the quartz substrate layer 1, core layer 2, and cladding layer 3 of the high-efficiency vertically coupled, large-angle PLC optical splitter chip provided in this embodiment is as follows: cladding layer 3 is located above substrate layer 1, while core layer 2 is located between substrate layer 1 and cladding layer 3. A microlens 4 corresponding to the light beam passing through core layer 2 is etched on the upper surface of cladding layer 3. A total reflection angle of 41° is set at the output waveguide of the entire chip. After reflection from the end face of the output waveguide, the light beam in core layer 2 is vertically aligned with the center position of the microlens. When the light beam propagates horizontally within core layer 2 to the chip's output waveguide, it is reflected at a 41° angle at the output waveguide and then vertically passes through cladding layer 3. It is focused by microlens 4 on cladding layer 3 corresponding to the core layer. After focusing, the beam size is reduced, allowing most of the beam's energy to be received by the photosensitive surface of detector 5, thereby improving coupling efficiency.

[0025] At the same time, due to the presence of the microlens 4, the distance between the PLC optical branch chip and the detector 5 does not need to be shortened, and a larger coupling distance is left between the PLC chip and the detector, which can reduce the difficulty of coupling packaging and improve coupling efficiency. Example 2

[0026] A method for preparing a high-efficiency vertically coupled large-angle PLC optical splitter chip comprises the following steps: Step 1: A germanium-doped silicon dioxide layer is grown on a quartz substrate layer made of silicon dioxide to form a core layer. The PLC optical branching waveguide pattern is transferred to the core layer through photolithography and etching processes. Step 2: growing a silicon dioxide layer doped with boron and phosphorus on the surface of the core layer formed in step 1 to form a cladding layer; Step 3: coating the cladding layer obtained in step 2 with a photoresist to obtain a photoresist layer, wherein the thickness of the photoresist layer should be greater than 20 μm; Step 4: Transfer the pattern on the microlens mask to the photoresist layer formed in step 3 through a photolithography development process; Step 5: The photoresist layer obtained in step 4 is subjected to a high-temperature reflow process (reflow temperature 120° C., reflow constant temperature time 45 min) to deform into a hemispherical structure; Step 6: Using the photoresist layer with the hemispherical structure formed in step 5 as a mask, perform ICP etching to etch a microlens pattern on the cladding surface to obtain a cladding integrated microlens; Step 7: Perform total reflection angle grinding and polishing on the output waveguide of the chip so that the polished output waveguide end face is aligned with the center position of the microlens in the vertical direction.

[0027] In step 6, the curvature radius of the microlens is adjusted by the etching selectivity of the photoresist layer and the cladding layer. The curvature radius of the microlens corresponds to the coupling distance between the detector and the PLC optical branch chip.

[0028] The full emission angle in step 7 is set to 41°.

[0029] The present invention proposes a high-efficiency vertically coupled large-angle PLC optical splitter chip and a preparation method. The PLC optical splitter chip proposed in the present invention uses a semiconductor process to process a microlens on the cladding surface of the total reflection optical path. The microlens can focus the light beam in the vertical direction, reduce the beam size, and enable most of the light beam energy to be received by the photosensitive surface of the detector, thereby improving the coupling efficiency.

[0030] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent replacements for some of the technical features therein. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-efficiency vertically coupled large-angle PLC optical splitter chip, characterized in that: Includes quartz base layer, core layer and cladding; The cladding is located on the quartz substrate layer, the core layer is located between the quartz substrate layer and the cladding, and a microlens is etched on the upper surface of the cladding; The output waveguide of the PLC optical branching chip is provided with a total reflection angle. When the light beam is transmitted to the output waveguide along the horizontal direction in the core layer, it is reflected by the total reflection angle set at the output waveguide and corresponds to the center position of the microlens in the vertical direction.

2. The high-efficiency vertically coupled large-angle PLC optical splitter chip according to claim 1 is characterized in that: The core layer is a silicon dioxide layer doped with germanium, and the cladding layer is a silicon dioxide layer doped with boron and phosphorus.

3. The high-efficiency vertically coupled large-angle PLC optical splitter chip according to claim 1 or 2, characterized in that: The total reflection angle is set to 41°.

4. A method for preparing a high-efficiency vertically coupled large-angle PLC optical splitter chip, characterized in that: The following steps are involved: Step 1: Grow a silicon dioxide layer on the quartz substrate to form a core layer, and transfer the PLC optical branching waveguide pattern to the core layer through a photolithography process; Step 2: growing a silicon dioxide layer on the surface of the core layer formed in step 1 to form a cladding layer; Step 3: coating the surface of the cladding layer formed in step 2 with photoresist to obtain a photoresist layer; Step 4: Transfer the pattern on the microlens mask to the photoresist layer formed in step 3 through a photoresist development process; Step 5: The photoresist layer formed in step 4 is deformed into a hemispherical structure by a high-temperature reflow process; Step 6: Using the photoresist layer with the hemispherical structure formed in step 5 as a mask, perform ICP etching to etch a microlens pattern on the cladding surface to obtain a cladding integrated microlens; Step 7: Perform total reflection angle grinding and polishing on the output waveguide of the PLC optical splitter chip so that the polished output waveguide end face is aligned with the center position of the microlens in the vertical direction.

5. The method for preparing a high-efficiency vertically coupled large-angle PLC optical splitter chip according to claim 4, characterized in that: The core layer in step 1 is a silicon dioxide layer doped with germanium, and the cladding layer in step 2 is a silicon dioxide layer doped with boron and phosphorus.

6. The method for preparing a high-efficiency vertically coupled large-angle PLC optical splitter chip according to claim 4, characterized in that: The thickness of the photoresist layer in step 3 is greater than 20 μm.

7. The method for preparing a high-efficiency vertically coupled large-angle PLC optical splitter chip according to claim 4, characterized in that: In step 5, the reflux temperature of the high-temperature reflux process is 120° C., and the reflux constant temperature time is 45 minutes.

8. The method for preparing a high-efficiency vertically coupled large-angle PLC optical splitter chip according to claim 4, characterized in that: In step 6, the curvature radius of the microlens is adjusted by the etching selectivity of the photoresist layer and the cladding layer. The curvature radius of the microlens corresponds to the coupling distance between the detector and the PLC optical branch chip.

9. The method for preparing a high-efficiency vertically coupled large-angle PLC optical splitter chip according to claim 4, characterized in that: In step 7, the total reflection angle is set to 41°.

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