Methods and applications of reducing total loss in three-dimensional optical waveguides using femtosecond laser variable-speed scanning

Abstract

This invention discloses a method and application for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning, belonging to the field of laser processing technology. The method first fabricates a straight waveguide using uniform femtosecond laser scanning. The insertion loss versus length relationship is obtained by testing the waveguide using the truncation method, thus yielding processing parameters for low-coupling-loss and low-propagation-loss waveguides. These parameters are then used for femtosecond laser variable-speed scanning processing, achieving a simultaneous reduction in both coupling and transmission losses. Compared to traditional methods for reducing optical waveguide losses, this method of processing waveguides using femtosecond laser variable-speed scanning can simultaneously reduce both coupling and transmission losses; moreover, it is independent of the waveguide's geometry or size, making this arrangement applicable to various types and paths of waveguides.

Description

Technical Field

[0001] This invention belongs to the field of laser processing technology, specifically relating to a method and application of reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable speed scanning. Background Technology

[0002] As the most basic and important component in integrated photonic chips, the optical waveguide (hereinafter referred to as "waveguide") is a high-refractive-index region covered by a low-refractive-index cladding. Loss is the most fundamental property of a waveguide, and reducing waveguide loss is of great significance. For example, in the field of optical communication, low-loss waveguides can ensure efficient signal transmission over long distances and reduce the risk of data errors and loss; in the fields of optical sensing and high-performance optical device manufacturing, low-loss waveguides help improve signal quality and device performance. However, during light propagation, due to factors such as the intrinsic absorption of materials and the waveguide's own ability to confine light, the signal strength will attenuate to a certain extent, resulting in loss. Waveguide loss mainly includes coupling loss, transmission loss, and bending loss. Currently, researchers are maximizing optical coupling efficiency and reducing waveguide coupling loss by designing optical waveguide structures, combining surface treatment techniques, utilizing gratings and lenses or using fiber optic plugs, and customizing coupling structures. They are also improving waveguide transmission efficiency and reducing transmission loss by using materials with low light absorption and scattering, compensating for transmission loss during optical signal transmission with optical amplifiers, and optimizing optical transmission characteristics by controlling waveguide temperature to adjust its refractive index. Finally, they are employing curvature compensation devices or techniques to compensate for optical phase near bending regions, and using low-loss connectors or joints in the bending regions of the waveguide to reduce the impact of bending on light, thereby reducing bending loss.

[0003] However, the above methods still have the problem of only primarily reducing certain types of losses. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to provide a method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning. This method involves fabricating a straight waveguide using femtosecond laser uniform-speed scanning, obtaining the relationship between its insertion loss and length by testing the waveguide using the truncation method, thereby obtaining the processing parameters for low-coupling-loss waveguides and low-propagation-loss waveguides, and then using these parameters for femtosecond laser variable-speed scanning processing, thereby achieving the effect of simultaneously reducing waveguide coupling loss and transmission loss.

[0005] This invention is achieved through the following technical solution:

[0006] The method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning specifically includes the following steps:

[0007] Step 1: Preparation before processing;

[0008] First, preheat the laser on the processing platform to stabilize the laser output; next, clean the glass sample to be processed to prevent surface contaminants from affecting the focusing of the femtosecond laser beam; then, fix the sample on the sample stage.

[0009] Step 2: Leveling the sample stage;

[0010] First, adjust the laser beam path to focus the laser onto the glass sample surface. Then, focus the LED illumination light through mirror M2 onto the CCD and connect the CCD to a PC to monitor the leveling process of the sample stage in real time. Next, adjust the X and Y tilt angles of the sample stage to make it horizontal. Finally, when the CCD imaging system displays a uniform minimum reflective spot on the glass sample surface, it indicates that the sample stage is perpendicular to the focused laser beam, thus completing the leveling of the sample stage.

[0011] Step 3: The femtosecond laser is used to scan the straight waveguide at a constant speed, and the insertion loss as a function of waveguide length is obtained by using the truncation method.

[0012] First, a femtosecond laser is focused onto a preset processing position on a glass sample by controlling a precision three-dimensional motion platform. Then, the half-wave plate (HWP) in front of the laser is rotated to adjust the femtosecond laser processing power. Next, a processing program is loaded into a PC, and the PC is used to control the precision three-dimensional motion platform to make the femtosecond laser focus scan uniformly along the X-direction within the glass sample to obtain a straight waveguide structure. Following this, the waveguide end faces are polished, and the insertion loss of waveguides of different lengths is tested using the truncation method. Finally, the experimental data are linearly fitted to obtain the insertion loss versus waveguide length curve.

[0013] Step 4: Femtosecond laser variable-speed scanning to process low-loss straight waveguides;

[0014] First, select the processing parameters for variable-speed laser scanning. Then, by controlling the precision three-dimensional motion platform, focus the femtosecond laser onto the preset processing position of the glass sample to be processed. Next, adjust the processing power of the femtosecond laser by rotating the half-wave plate HWP in front of the laser. Then, load the processing program into the computer PC and use the computer PC to control the precision three-dimensional motion platform to make the femtosecond laser focus perform variable-speed scanning along the X direction within the glass sample, thereby processing a straight waveguide structure in the glass sample.

[0015] Furthermore, in step two, the leveling of the sample stage specifically includes the following:

[0016] The femtosecond laser emitted from the laser is expanded by the first concave lens L1 and the second convex lens L2, and then sequentially passes through the spatial light modulator SLM, the second convex lens L3, and the third convex lens L4. Next, the laser enters the objective lens OL. The optical axis of the half-wave plate HWP at the laser exit is rotated so that the laser energy behind the reflecting mirror M1 and before the entrance pupil of the objective lens OL is 50mW. Subsequently, the objective lens OL focuses the laser onto the surface of the glass sample on the sample stage. The CCD imaging system connected to the PC is turned on, and the specific leveling process is as follows: Define the two mutually perpendicular sides of the sample as the X-axis and... Using the PC, adjust the precision three-dimensional motion platform to move in the X direction while simultaneously adjusting the X-axis leveling knob. Repeat this process until the laser moves along the X direction and the CCD imaging system displays a uniform minimum reflective spot on the glass sample surface. At this point, the X-axis leveling is complete. Similarly, make the sample stage horizontal in the Y direction. Finally, use the PC to adjust the three-dimensional motion platform to move the laser along the edge of the glass sample clockwise or counterclockwise. The CCD imaging system will then display a uniform minimum reflective spot on the glass sample surface, indicating that the sample stage is now perpendicular to the focused laser beam, thus completing the sample stage leveling.

[0017] Furthermore, in step three, the femtosecond laser power before the entrance pupil of the objective lens OL is 200-500mW, the repetition frequency is 0.5-2MHz, the femtosecond laser scanning speed is 3-40mm / s, and the processing depth is 0.1-0.2mm.

[0018] Furthermore, in step three, the insertion loss of waveguides of different lengths is tested using the truncation method, specifically including the following:

[0019] Define the waveguide transmission loss as A dB / m, the length as X, and the coupling loss as C dB. Its insertion loss S(X) is expressed as: S(X) = A*X n +C, during the test, by changing X n The insertion loss for different waveguide lengths is obtained. Through linear fitting, the line intercept C and slope A are obtained, thus yielding the waveguide coupling loss and transmission loss; where X... n It is 5-50mm.

[0020] Furthermore, in step four, the selection of processing parameters specifically includes:

[0021] First, based on the waveguide insertion loss versus length curve obtained in step three, the processing speed of the waveguide with the lowest coupling loss, the processing speed of the waveguide with the lowest unit transmission loss, and the processing parameters of the waveguide with the lowest insertion loss are obtained; the processing parameters of the waveguide with the lowest insertion loss include processing power and repetition frequency; then, the processing speed of the waveguide with the lowest coupling loss is selected as the starting speed V1 of the femtosecond laser variable speed scanning, the processing speed of the waveguide with the lowest unit transmission loss is selected as the ending speed V2 of the femtosecond laser variable speed scanning, and the processing parameters of the waveguide with the lowest insertion loss are selected as the processing parameters of the femtosecond laser variable speed scanning.

[0022] Furthermore, in step four, the femtosecond laser variable-speed scanning specifically includes the following:

[0023] First, the femtosecond laser starts at an initial scanning speed of V1 with a scanning length of S1, accelerates to V2, and then accelerates for another length of S2. After acceleration, it continues scanning at speed V2 for a length of S3. L is the total length of the waveguide.

[0024] Furthermore, there are two ways to accelerate the scanning speed of a femtosecond laser from V1 to V2:

[0025] A1: Scanning speed and acceleration length are linearly related;

[0026] A2: The scanning speed and acceleration length have a non-linear relationship.

[0027] Furthermore, the waveguide length L is 20-60 mm.

[0028] On the other hand, the present invention also provides the application of a method for reducing the total loss of a three-dimensional optical waveguide by using femtosecond laser variable-speed scanning in quantum communication.

[0029] Thirdly, the present invention also provides the application of a method for reducing the total loss of a three-dimensional optical waveguide by using femtosecond laser variable-speed scanning in fiber optic waveguide coupling devices.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] (1) The present invention utilizes a femtosecond laser variable speed scanning method to process waveguides, which, compared with traditional methods for reducing optical waveguide losses, can simultaneously reduce coupling loss and transmission loss.

[0032] (2) The method of the present invention does not depend on the geometry or size of the waveguide, and this layout is applicable to waveguides of various types or paths. Attached Figure Description

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0034] Figure 1 This is a schematic diagram of an optical path for a femtosecond laser variable-speed scanning straight waveguide according to the present invention;

[0035] Among them, HWP represents half-wave plate, PBS represents polarizing beam splitter, L1 represents concave lens, L2, L3, L4, and L5 represent convex lens, SLM represents spatial light modulator, M1 and M2 represent mirrors, OL represents objective lens, CCD represents camera, LED represents illumination source, and PC represents computer.

[0036] Figure 2 This is a schematic diagram of the processing structure utilizing femtosecond laser variable speed scanning according to the present invention;

[0037] Where L represents the total length of the fabricated waveguide, S1 represents the initial scan length of the femtosecond laser, S2 represents the accelerated length of the femtosecond laser, S3 represents the scan length at a constant speed of V2, V1 represents the initial scan speed of the femtosecond laser, and V t V1 represents the speed of the femtosecond laser scanning speed during the acceleration phase, and V2 represents the speed of the femtosecond laser after the scanning length S1+S2.

[0038] Figure 3 This is a schematic diagram of the photonic chip packaging of the present invention;

[0039] The optical fiber and the waveguide are bonded together with UV-curable adhesive.

[0040] Figure 4 This invention utilizes the truncation method to test a straight waveguide and obtain the insertion loss as a function of waveguide length (H-polarized light);

[0041] Wherein, the slope of the line represents propagation loss, and the intercept represents coupling loss;

[0042] Figure 5 This invention utilizes the truncation method to test a straight waveguide and obtain the insertion loss as a function of waveguide length (V-polarized light);

[0043] Wherein, the slope of the line represents propagation loss, and the intercept represents coupling loss;

[0044] Figure 6 This is a schematic diagram illustrating the linear relationship between speed and length of the femtosecond laser using the first acceleration method of the present invention;

[0045] Figure 7This is a schematic diagram illustrating the nonlinear relationship between velocity and length of the femtosecond laser using the second acceleration method of the present invention;

[0046] Figure 8 The graph shows the relationship between the acceleration length and insertion loss of the femtosecond laser of the present invention at the starting speed V1 = 3 mm / s and the ending speed V2 = 10 mm / s, and the relationship between the speed and insertion loss obtained by uniform scanning with an initial speed of [3 10] mm / s (H-polarized light).

[0047] Figure 9 The graph shows the relationship between the acceleration length and insertion loss of the femtosecond laser of the present invention at the starting speed V1 = 3 mm / s and the ending speed V2 = 10 mm / s, as well as the relationship between the speed and insertion loss obtained by uniform scanning with an initial speed of [3 10] mm / s (V polarized light). Detailed Implementation

[0048] To clearly and completely describe the technical solution and its specific working process of the present invention, the specific embodiments of the present invention are as follows, in conjunction with the accompanying drawings:

[0049] Example 1

[0050] This embodiment provides a method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning. This method utilizes a femtosecond laser uniform-speed scanning mode, employing different processing power, repetition frequency, and scanning speed parameters to fabricate straight waveguides. The insertion loss versus waveguide length curve is obtained through truncation testing, yielding the processing parameters for low-coupling-loss and low-transmission-loss waveguides. The specific steps are as follows:

[0051] (1) Preparations before processing;

[0052] First, the laser on the processing platform is preheated to stabilize the laser output. The laser's output wavelength is 1030 nm, the pulse width is 239 fs, and the repetition frequency is 1 MHz. Next, the glass sample to be processed is cleaned with acetone and ethanol to prevent surface contamination from affecting the focusing of the femtosecond laser beam. Then, an adhesive is used to fix the glass sample to the sample stage.

[0053] (2) Leveling the sample stage;

[0054] First, such as Figure 1As shown, the femtosecond laser emitted from the laser is expanded by a first concave lens L1 and a second convex lens L2, and then sequentially passes through a spatial light modulator (SLM), a second convex lens L3, and a third convex lens L4. Next, the laser enters the objective lens OL. The optical axis of the half-wave plate HWP at the laser exit is rotated so that the laser energy behind the reflecting mirror M1 and before the entrance pupil of the objective lens OL is 50mW. The focal length of the first concave lens L1 is -8cm, the focal length of the second convex lens L2 is 32cm, and the focal length of the third convex lens L4 is... The focal length of the first lens is 60cm, and the focal length of the fourth convex lens L4 is 35cm. The distance from the spatial light modulator (SLM) LCD panel to the entrance pupil of the objective lens OL is 190cm. The working distance of the objective lens OL is 0.51mm, NA = 0.75, and magnification × 40. The objective lens OL then focuses the laser onto the surface of the glass sample on the sample stage. Illumination is then provided by an LED light source fixed to the frame of the reflector M1 and a CCD camera on the right side of the reflector M2. To focus the femtosecond laser onto the glass sample surface, the Z-axis of the precision three-dimensional motion platform is adjusted to lower the objective lens OL to the working distance. Simultaneously, CCD imaging is observed during the descent of the objective lens OL. After finding the sample surface, the sample stage is leveled, and the leveling process is monitored in real time using the CCD imaging system. The specific steps are as follows: Turn on the CCD imaging system connected to the PC. The specific leveling process is as follows: Define the two mutually perpendicular sides of the sample as the X-axis and Y-axis. Adjust the precision three-dimensional motion platform in the X-direction using the PC, while simultaneously adjusting the X-direction leveling knob. Repeat this process until the femtosecond laser moves along the X-direction and the CCD imaging system displays a uniform minimum reflective spot on the glass sample surface. At this point, the X-direction leveling is complete. Similarly, make the sample stage horizontal in the Y-direction. Finally, adjust the three-dimensional motion platform using the PC to move the laser along the edge of the glass sample clockwise (or counterclockwise). The CCD imaging system displays a uniform minimum reflective spot on the glass sample surface, indicating that the sample stage is perpendicular to the focused laser beam, thus completing the sample stage leveling.

[0055] (3) The insertion loss curve as a function of waveguide length was obtained by uniformly scanning the straight waveguide with a femtosecond laser and using the truncation method.

[0056] First, adjust the laser pulse repetition frequency to 500kHz, rotate the half-wave plate HWP to make the laser power in front of the objective lens OL at 200mW; next, load the processing program on the computer PC, so that the femtosecond laser scans relative to the three-dimensional displacement platform at a speed of [3 5 7 9 10 20 30 40mm / s], the scanning length is 50mm, and the processing depth is 0.1-0.2mm. Similarly, straight waveguides were fabricated by sequentially changing the laser output power and laser pulse repetition frequency. Next, the fabricated waveguide end faces were polished, with the following specific steps: First, using polishing disc 1, a suspension of white corundum polishing powder W7 was used to roughly grind and polish the input and output end faces of the fabricated photonic chip. The purpose was to quickly remove the unstable waveguide structure at the edge of the femtosecond laser-written chip. Then, polishing disc 2 was used, and a suspension of cerium oxide polishing powder was used to finely grind and polish the input and output end faces of the fabricated photonic chip. Next, using a six-axis precision alignment fiber optic testing platform, 852nm horizontally polarized light (H-light) was coupled into the input end of the photonic chip through a 780nm fiber. A ×50 objective lens was used to collect the beam emitted from the output end of the photonic chip, and the power was read using a power meter. By finely adjusting the six-axis precision motion platform, the power of the beam focused by the objective lens was maximized, and the maximum power of each waveguide was recorded. Insertion loss is calculated using the formula: Insertion Loss = -10 × lg(Output Power / Input Power), where output power represents the maximum output power of each waveguide obtained from the power meter, and input power represents the laser power emitted from the fiber without a waveguide. Following this, according to the experimental method mentioned in the published article by Frank, Milan, et al.—the truncation method—diamond wire cutting is used to cut the waveguide from the output end of the photonic chip, with a cutting length of 3-5 mm. The newly cut waveguide end face is polished, and insertion loss is tested again. This process is repeated 4-6 times. The experimental data is then analyzed using S(X) = A*X. n By performing linear fitting with +C, the intercept C and slope A can be obtained. The experimental results are as follows: Figure 4 As shown in the figure. The experimental results show that when the waveguide coupling loss is the lowest, the processing power is 400mW, the repetition frequency is 1MHz, and the processing speed is 3mm / s; when the waveguide transmission loss is the lowest, the processing power is 400mW, the repetition frequency is 1MHz, and the processing speed is 10mm / s.

[0057] (4) Femtosecond laser variable speed scanning process for low-loss straight waveguides;

[0058] Select processing parameters: Based on the waveguide insertion loss variation curve with length in step (3), the processing speeds of the waveguide with the lowest coupling loss and the waveguide with the lowest transmission loss are obtained. The processing speed with the lowest coupling loss is taken as the starting speed V1 of the femtosecond laser variable speed scanning, and the processing speed with the lowest transmission loss is taken as the ending speed V2 of the femtosecond laser variable speed scanning. Except for the processing speed, the processing parameters of the waveguide with the lowest insertion loss obtained in step (3) are used as the processing parameters of the femtosecond laser variable speed scanning. First, rotate the half-wave plate HWP so that the femtosecond laser power in front of the objective lens OL is 400mW. Next, use the computer PC to load the program for processing. The scanning wavelength L = 20mm is as follows: The femtosecond laser scans relative to the three-dimensional displacement platform at the starting speed V1. The scanning length of this process is S1 = 1 / 25mm. Then, the femtosecond laser accelerates to V2 with V1 as the initial scanning speed. The acceleration length is S2 = [4 8 12 16mm]. Finally, it scans at a constant speed V2. The scanning length is S3 = L - (S1 + S2). There are two acceleration methods for accelerating from V1 to V2, one of which is as follows: Figure 6 As shown, the scanning speed and acceleration length have a linear relationship; another method is as follows: Figure 7 As shown, the scanning speed and acceleration length have a non-linear relationship. A schematic diagram of the processing structure is shown below. Figure 2 As shown. After polishing the end face of the fabricated photonic chip, an 852nm horizontally polarized light (H-light) was coupled into the input end of the photonic chip through a 780nm fiber using a six-axis precision-aligned fiber test platform. A ×50 objective lens was used to collect the beam emitted from the output end of the photonic chip, and the insertion loss of the photonic chip was calculated using power meter readings. The experimental results are shown below. Figure 8 When the H-beam of an 852nm laser is input into an optical fiber, the insertion loss is lowest at 0.9408dB when the scanning start speed is 3mm / s, the scanning end speed is 10mm / s, and the acceleration length is 4mm.

[0059] The principle of the method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning in this embodiment is as follows:

[0060] The propagation of light in an optical waveguide follows the Helmholtz equations, and in cylindrical coordinates, the solution can be written as:

[0061] Ψ(r,φ)=AJ m (κr)cos(mθ),r<a

[0062] Ψ(r,φ)=BK m (σr)cos(mθ),r>a

[0063] in, α is the waveguide radius, β is the propagation constant, and J m K mLet be the Bessel functions of the first and second kind, respectively, where m = 0, 1, 2... represents the order of the mode, and θ is a variable. The solution of the entire function describes how the wavefunction changes with the spatial angle. For the fundamental mode with m = 0, its wavefunction does not change with the spatial angle and exhibits centrosymmetry. It can be seen that the waveguide radius α and the change in refractive index Δn = n1 - n2 jointly affect the mode field size.

[0064] The main losses in waveguides include coupling loss, propagation loss, and bending loss. Coupling loss originates from the longitudinal coupling between the optical fiber and the waveguide, primarily consisting of mode mismatch loss and Fresnel reflection loss. For mode mismatch loss, the smaller the overlap integral of the mode fields of the optical fiber and the waveguide, the greater the mode matching loss. Fresnel reflection loss, on the other hand, is only related to the refractive index of the medium between the optical fiber and the waveguide, and can be described by the reflectivity at normal incidence.

[0065]

[0066] Where R is reflectivity, n eff Let be the effective refractive index within the optical waveguide, and n be the refractive index of the medium between the optical fiber and the optical waveguide. Propagation loss mainly originates from the intrinsic absorption of light by the material and the scattering by impurities and defects as light propagates in the optical waveguide, which are inherent properties of the optical waveguide.

[0067] Regarding the conditions for femtosecond laser processing of optical waveguides, when a femtosecond laser acts on the material to fabricate the waveguide, the material experiences internal thermal accumulation under high-frequency laser irradiation, and the temperature increases with exposure time. The scanning speed determines the accumulated femtosecond laser irradiation intensity; the scanning speed V... S With focus diameter D, single pulse energy E P The repetition frequency R together determine the irradiance I per unit volume of a femtosecond laser. V Or it can be called (RNF):

[0068]

[0069] The heat Q generated inside the focal point is:

[0070]

[0071] Where Ee is the energy of the free electron, and n e The free electron density, W, is used to describe the photoionization process, and it is related to the irradiation intensity I. V The single-photon energy hw is related to the material bandgap Δ. When the material is heated, it expands, generating a shock wave that originates from the focal point and spreads rapidly outward. The shock wave creates strong compression from the center to the outside of the material, making the waveguide edge material more compact. A relatively compact material has a higher refractive index.

[0072] Therefore, by controlling the scanning speed of the femtosecond laser to control the internal thermal effects of the material, the compression during the shock wave diffusion process can be affected, thereby achieving the goal of controlling the waveguide mode field size and the amount of change in refractive index, and thus controlling the waveguide loss performance.

[0073] Example 2

[0074] This embodiment provides an application of a method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning in quantum communication. The test was conducted using 852nm vertically polarized light (V-beam), and the specific steps are as follows:

[0075] The photonic chip fabricated in step (3) was tested using the truncation method. First, the end face of the photonic chip was polished. Then, using a six-axis precision alignment optical core testing platform, 852nm vertically polarized light (V-beam) was coupled into the input end of the photonic chip through a 780nm optical fiber. A ×50 objective lens was used to collect the beam emitted from the output end of the photonic chip, and the insertion loss of the photonic chip was calculated using a power meter reading. Next, a 3-5mm section was cut from the output end of the photonic chip using diamond wire cutting, followed by polishing and loss testing. This process was repeated 4-6 times. The experimental data were then fitted to obtain... Figure 5 It can be seen that the lowest coupling loss is achieved when the processing power is 400mW, the repetition frequency is 1MHz, and the processing speed is 3mm / s; and the lowest transmission loss is achieved when the processing power is 400mW, the repetition frequency is 1MHz, and the processing speed is 10mm / s.

[0076] The optimized speeds of 3 mm / s and 10 mm / s were selected as the initial velocity V1 and the final velocity V2 of the femtosecond laser variable-speed scanning, respectively. The lowest insertion loss waveguide processing parameters were used as the femtosecond laser variable-speed scanning processing parameters. A photonic chip was obtained using femtosecond laser variable-speed scanning. After polishing the waveguide end face, 852 nm vertically polarized light (V-beam) was coupled into the input end of the photonic chip through a 780 nm fiber using a six-axis precision alignment optical core testing platform. The beam emitted from the output end of the photonic chip was collected using a ×50 objective lens. The insertion loss of the photonic chip was calculated using power meter readings. The test results are as follows: Figure 9 As shown, the insertion loss is lowest at 1.18887 dB when the femtosecond laser scanning start speed is 3 mm / s, the scanning end speed is 10 mm / s, and the acceleration length is 8 mm.

[0077] Therefore, this method significantly reduces the insertion loss of straight waveguides, which is beneficial for on-chip integration and thus promotes the development of integrated photonic chips. Simultaneously, using UV-curable adhesive and a UV light source, the optical fiber is bonded to the waveguide with the lowest insertion loss, reducing Fresnel reflection loss at the waveguide end face to achieve the fabrication of a low-loss three-dimensional optical link. The specific steps are as follows: First, prepare UV-curable adhesive, a UV light source, and a clean optical fiber end face; then, connect the optical fiber to the waveguide with the lowest insertion loss; next, apply UV-curable adhesive to the optical fiber end face, slowly bringing it closer to the waveguide end face until contact is established; then, turn on the UV light source to allow the UV-curable adhesive to solidify. During this process, adjust the UV light source irradiation angle as needed to maximize the waveguide output power. Each exposure lasts approximately 15 minutes, and the UV-curable adhesive is applied repeatedly 4-5 times; finally, the optical fiber and waveguide are connected and moved to a glass substrate, where they are left for approximately 5 hours to complete the fiber-waveguide bonding. A schematic diagram of the photonic chip packaging is shown below. Figure 3 As shown.

[0078] In summary, by using the above processing methods and parameters, the total loss of the three-dimensional optical link can be reduced to 0.8108 dB.

[0079] Example 3

[0080] This embodiment provides an application of a method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning in fiber optic waveguide coupling devices. First, the pre-processing steps are as described in Example 1 (1) and (2). Then, a photonic chip is fabricated by gradually varying the femtosecond laser scanning speed using an adiabatic conversion method. The end face of the photonic chip is then polished. Next, an ultraviolet-cured adhesive and an ultraviolet light source are used to bond the optical fiber to the photonic chip, completing the chip encapsulation. The encapsulated chip is then connected to a Mach-Zehnder interferometer (MZI), a directional coupler (DC), a beam splitter, an optical switch, etc., to fabricate a waveguide coupler. This method results in lower overall loss of the encapsulated device, improves the integration of the photonic chip, and enables effective optical modulation, giving it broad application potential in optical communication, optical sensing, and optical computing.

[0081] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0082] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0083] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning, characterized in that, Specifically, the steps include the following: Step 1: Preparation before processing; First, preheat the laser on the processing platform to stabilize the laser output; next, clean the glass sample to be processed to prevent surface contaminants from affecting the focusing of the femtosecond laser beam; then, fix the sample on the sample stage. Step 2: Leveling the sample stage; First, adjust the laser beam path to focus the laser onto the glass sample surface. Then, focus the LED illumination light through mirror M2 onto the CCD and connect the CCD to a PC to monitor the leveling process of the sample stage in real time. Next, adjust the X and Y tilt angles of the sample stage to make it horizontal. Finally, when the CCD imaging system displays a uniform minimum reflective spot on the glass sample surface, it indicates that the sample stage is perpendicular to the focused laser beam, thus completing the leveling of the sample stage. Step 3: The femtosecond laser is used to scan the straight waveguide at a constant speed, and the insertion loss as a function of waveguide length is obtained by using the truncation method. First, a femtosecond laser is focused onto a preset processing position on a glass sample by controlling a precision three-dimensional motion platform. Then, the half-wave plate (HWP) in front of the laser is rotated to adjust the femtosecond laser processing power. Next, a processing program is loaded into a PC, and the PC is used to control the precision three-dimensional motion platform, causing the femtosecond laser focus to scan uniformly along the X-axis within the glass sample to obtain a waveguide structure. Following this, the waveguide end faces are polished, and the insertion loss of waveguides of different lengths is tested using the truncation method. Finally, the experimental data are linearly fitted to obtain the insertion loss versus waveguide length curve. Step 4: Femtosecond laser variable-speed scanning to process low-loss straight waveguides; First, select the processing parameters for variable-speed laser scanning; then, by controlling the precision three-dimensional motion platform, focus the femtosecond laser onto the preset processing position of the glass sample to be processed; next, adjust the processing power of the femtosecond laser by rotating the half-wave plate HWP in front of the laser; next, load the processing program into the computer PC, and use the computer PC to control the precision three-dimensional motion platform to make the femtosecond laser focus perform variable-speed scanning along the X direction within the glass sample, thereby processing a waveguide structure in the glass sample; The femtosecond laser variable speed scanning specifically includes the following: Based on the waveguide insertion loss versus length curve obtained in step three, the minimum coupling loss waveguide fabrication speed is determined. Minimum unit transmission loss waveguide processing speed The fabrication parameters of the lowest insertion loss waveguide; the fabrication parameters of the lowest insertion loss waveguide include fabrication power and repetition frequency; the fabrication parameters of the lowest insertion loss waveguide are selected as the femtosecond laser variable-speed scanning fabrication parameters; the femtosecond laser uses... The initial scan speed is [value], and the scan length is [value]. Accelerate to acceleration length is After acceleration, at speed Continue scanning length ;in, , L is the total length of the waveguide.

2. The method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning as described in claim 1, characterized in that, Step two, the leveling of the sample stage, specifically includes the following: The femtosecond laser emitted from the laser passes through the first concave lens Second convex lens The beam is expanded and then passed sequentially through a spatial light modulator (SLM) and a second convex lens. and the third convex lens Next, the laser enters the objective lens OL, and the optical axis of the half-wave plate HWP at the laser exit is rotated, causing the reflecting mirror... The laser energy before the objective lens OL enters the pupil is 50mW. Then, the objective lens OL focuses the laser onto the surface of the glass sample on the sample stage. The CCD imaging system connected to the PC is turned on, and the leveling process is as follows: Define the two mutually perpendicular sides of the sample as the X-axis and Y-axis. Adjust the precision three-dimensional motion platform in the X-direction using the PC, while simultaneously adjusting the X-direction leveling knob. Repeat this process until the femtosecond laser moves along the X-direction and the CCD imaging system displays a uniform minimum reflective spot on the glass sample surface; at this point, X-direction leveling is complete. Similarly, make the sample stage horizontal in the Y-direction. Finally, adjust the three-dimensional motion platform using the PC to move the laser along the edge of the glass sample clockwise or counterclockwise. The CCD imaging system displays a uniform minimum reflective spot on the glass sample surface, indicating that the sample stage is perpendicular to the focused laser beam, thus completing the sample stage leveling.

3. The method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning as described in claim 1, characterized in that, In step three, the femtosecond laser power in front of the objective lens OL entrance pupil is 200-500mW, the repetition frequency is 0.5-2MHz, the femtosecond laser scanning speed is 3-40mm / s, and the processing depth is 0.1-0.2mm.

4. The method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning as described in claim 1, characterized in that, Step three involves testing the insertion loss of waveguides of different lengths using the truncation method, specifically including the following: Define the waveguide transmission loss as A dB / m, the length as X, and the coupling loss as C dB. Its insertion loss S(X) is expressed as: During the test, by changing The insertion loss for different waveguide lengths was obtained. Through linear fitting, the line intercept C and slope A were obtained, thus yielding the waveguide coupling loss and unit transmission loss. It is 5-50mm.

5. The method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning as described in claim 1, characterized in that, The scanning speed of femtosecond lasers is from Accelerate to The scanning speed is linearly related to the acceleration length.

6. The method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning as described in claim 1, characterized in that, The scanning speed of femtosecond lasers is from Accelerate to The scanning speed and acceleration length have a non-linear relationship.

7. The method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning as described in claim 1, characterized in that, The waveguide length L is 20-60mm.

8. The application of the method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning as described in claim 1 in quantum communication.

9. The application of the method for reducing the total loss of a three-dimensional optical waveguide using femtosecond laser variable-speed scanning as described in claim 1 in fiber optic waveguide coupling devices.

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