CN113770515B - Method for resetting coupling coefficient of directional coupler by femtosecond laser secondary direct writing and application - Google Patents

Method for resetting coupling coefficient of directional coupler by femtosecond laser secondary direct writing and application Download PDF

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CN113770515B
CN113770515B CN202111128012.9A CN202111128012A CN113770515B CN 113770515 B CN113770515 B CN 113770515B CN 202111128012 A CN202111128012 A CN 202111128012A CN 113770515 B CN113770515 B CN 113770515B
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laser
sample
coupling
directional coupler
waveguide
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CN113770515A (en
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孙洪波
余峰
田振男
陈岐岱
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Jilin University
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/03Observing, e.g. monitoring, the workpiece
    • B23K26/032Observing, e.g. monitoring, the workpiece using optical means
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0643Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising mirrors
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0648Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising lenses
    • GPHYSICS
    • G03PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03FPHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70Microphotolithographic exposure; Apparatus therefor
    • G03F7/70383Direct write, i.e. pattern is written directly without the use of a mask by one or multiple beams

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Abstract

本发明公开了一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法及应用,属于激光加工技术领域,包括玻璃样品的清洁;激光加工光路的搭建及待加工样品的调平;飞秒激光第二次直写器件;首先关闭光闸,并将玻璃样品移动到起始加工位置;然后转动半波片,调节激光功率;最后操控软件直接运行预先写好的加工程序,在耦合区两根波导的加工区域内分别进行二次直写;加工结束后对样品进行抛光,得到与原有波导耦合间距不同的两根新波导;所述加工区域为距离原有波导的中轴线上下0μm‑3μm的区域内。本发明的方法可以实现定向耦合器初始分束比的修复以及重新分配,从而解决利用飞秒激光制备定向耦合器及集成芯片过程中存在的制造误差问题。

Figure 202111128012

The invention discloses a method and application for resetting the coupling coefficient of a directional coupler by using femtosecond laser secondary direct writing, belonging to the technical field of laser processing, including cleaning of glass samples, construction of laser processing optical paths and leveling of samples to be processed ;Femtosecond laser direct writing device for the second time; firstly close the shutter and move the glass sample to the initial processing position; then rotate the half-wave plate to adjust the laser power; finally, the control software directly runs the pre-written processing program, in the In the processing area of the two waveguides in the coupling area, secondary direct writing is performed respectively; after the processing, the sample is polished to obtain two new waveguides with different coupling distances from the original waveguides; the processing area is distanced from the central axis of the original waveguides Within the area of 0μm-3μm above and below. The method of the invention can realize the repair and redistribution of the initial beam splitting ratio of the directional coupler, thereby solving the problem of manufacturing errors existing in the process of using the femtosecond laser to prepare the directional coupler and the integrated chip.

Figure 202111128012

Description

一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法 及应用A Method of Resetting Coupling Coefficient of Directional Coupler Using Femtosecond Laser Secondary Direct Writing and applications

技术领域technical field

本发明属于激光加工技术领域,具体涉及利用飞秒激光二次直写来修改飞秒激光第一次直写的定向耦合器的耦合间距,达到初始定向耦合器耦合系数重置的目的。通过对初始器件耦合系数的重置,实现了定向耦合器分束比的重新分配,解决了利用飞秒激光制备光子器件过程中存在着的不可避免的制造误差问题,达到基础单元器件以及集成芯片制造误差修复的目的。The invention belongs to the technical field of laser processing, and specifically relates to modifying the coupling distance of a directional coupler in the first direct writing of the femtosecond laser by using the second direct writing of the femtosecond laser, so as to achieve the purpose of resetting the coupling coefficient of the initial directional coupler. By resetting the coupling coefficient of the initial device, the beam splitting ratio of the directional coupler is redistributed, which solves the inevitable manufacturing error problem in the process of preparing photonic devices using femtosecond lasers, and achieves basic unit devices and integrated chips. Manufacturing bug fix purposes.

技术背景technical background

近年来,飞秒激光直写技术因为其真三维加工能力和无掩模快速加工的特点,逐渐成为制备光子量子集成芯片的重要手段。光子量子集成芯片出色的计算能力,强烈依赖于定向耦合器等基础单元器件的制造精度。然而,受到加工过程中脉冲激光与物质复杂相互作用、激光功率浮动和环境稳定性等因素的影响,这些基础单元器件存在着不可避免的制造公差。为了解决上述器件制作公差的问题,人们提出了两类可以实现非完美器件分束比重置的调控方案。第一类是基于基底材料热光效应或者电光效应的电极调控方案,尽管这些依赖电极的动态调控方法在重置定向耦合器分束比,实现器件修复方面取得了很大的进步,但是不可避免地产生了芯片集成度受限和需要额外功耗等新问题。为了达到误差器件分束比修复的目的,又不引入额外的功耗和复杂的外部电极调控线路的前提下,一种基于飞秒激光多次扫描来改变波导基本性质的静态调控方案受到关注。目前使用静态调控的方法中,主要是利用飞秒激光多次扫描定向耦合器中一条耦合臂使其传播常数发生变化,造成耦合区两条耦合臂传播常数的失谐,从而达到器件分束比重置的目的。这种重置定向耦合器中波导传播常数的方法,尽管也能进行器件分束比的重置,但是存在两个的缺点:一方面,由于传播常数的失谐,其中一个波导中的能量不能完全转移到另一根波导中去,从而难以实现分束比为0:1的特殊器件的制备;另一方面,由于传播常数失谐的范围有限,难以实现器件分束比在较大范围内被重置。上述两个缺点严重限制了该方法在集成芯片误差修复中的应用,因此亟需一种新的静态调控方法来解决器件误差修复的问题,提高集成芯片的成品率。In recent years, femtosecond laser direct writing technology has gradually become an important means of preparing photonic quantum integrated chips because of its true three-dimensional processing capability and the characteristics of fast maskless processing. The excellent computing power of photonic quantum integrated chips strongly depends on the manufacturing precision of basic unit devices such as directional couplers. However, affected by factors such as the complex interaction between pulsed laser and matter, laser power fluctuation, and environmental stability during processing, there are unavoidable manufacturing tolerances in these basic unit devices. In order to solve the above-mentioned problem of device manufacturing tolerance, two types of control schemes that can realize the reset of the splitting ratio of imperfect devices have been proposed. The first type is the electrode control scheme based on the thermo-optic effect or electro-optic effect of the substrate material. Although these dynamic control methods relying on electrodes have made great progress in resetting the beam splitting ratio of the directional coupler and realizing device repair, it is inevitable However, new problems such as limited chip integration and the need for additional power consumption have arisen. In order to achieve the purpose of repairing the beam splitting ratio of error devices without introducing additional power consumption and complicated external electrode control circuits, a static control scheme based on multiple scanning of femtosecond lasers to change the basic properties of waveguides has attracted attention. In the current method of static control, the femtosecond laser is used to scan one coupling arm of the directional coupler multiple times to change the propagation constant, resulting in the detuning of the propagation constants of the two coupling arms in the coupling area, so as to achieve the beam splitting ratio of the device. purpose of setting. This method of resetting the propagation constant of the waveguides in the directional coupler, although it can also reset the splitting ratio of the device, has two disadvantages: On the one hand, due to the detuning of the propagation constant, the energy in one of the waveguides cannot It is completely transferred to another waveguide, so it is difficult to realize the preparation of special devices with a beam splitting ratio of 0:1; on the other hand, due to the limited range of propagation constant detuning, it is difficult to achieve a wide range of device beam splitting ratios is reset. The above two shortcomings severely limit the application of this method in integrated chip error repair, so a new static control method is urgently needed to solve the problem of device error repair and improve the yield of integrated chips.

发明内容Contents of the invention

针对现有技术的不足,本发明要解决的技术问题是:提供一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法,实现定向耦合器初始分束比的修复以及重新分配,从而解决利用飞秒激光制备定向耦合器及集成芯片过程中存在的制造误差问题。针对现有定向耦合器的耦合区中的两根第一波导和第二波导,利用飞秒激光分别在第一波导和第二波导中轴线附近区域进行二次直写新的拼接波导,得到两根具有不同耦合间距的新的组合第三波导和第四波导,从而实现定向耦合器耦合系数及分束比的重置。由于二次直写的拼接波导与原第一波导和第二波导高度重叠,因此形成的两根新的组合第三波导和第四波导实际为原第一波导和第二波导分别与二次直写的拼接波导融合而成。Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is: to provide a method for resetting the coupling coefficient of the directional coupler by secondary direct writing with a femtosecond laser, so as to realize the restoration and redistribution of the initial beam splitting ratio of the directional coupler , so as to solve the manufacturing error problem existing in the process of using femtosecond laser to prepare directional coupler and integrated chip. For the two first waveguides and the second waveguides in the coupling region of the existing directional coupler, the femtosecond laser is used to write a new spliced waveguide directly in the area near the central axis of the first waveguide and the second waveguide respectively, and the two waveguides are obtained. A new combination of the third waveguide and the fourth waveguide with different coupling spacings is used to realize the resetting of the coupling coefficient and beam splitting ratio of the directional coupler. Since the spliced waveguide of the secondary direct writing overlaps the original first waveguide and the second waveguide highly, the two new combined third waveguides and fourth waveguides formed are actually the original first waveguide and the second waveguide and the second direct waveguide respectively. Written by splicing waveguide fusion.

本发明中涉及到的重置定向耦合器耦合系数的基本原理为:根据耦合模理论,两根波导耦合系数的大小与耦合间距负相关,即耦合系数随耦合间距增加而减小;其中,耦合间距指耦合区两根波导横截面几何中心的间距(即中轴线间距)。因此,改变耦合区两根波导的耦合间距即可实现定向耦合器耦合系数的重置。此外,由于定向耦合器的分束比与耦合系数和耦合区波导长度两个参数直接相关,并与这两个参数的乘积满足正弦函数变化趋势。因此,在定向耦合器的耦合长度不变的条件下,通过重置耦合系数的方式实现定向耦合器分束比的重置。The basic principle of resetting the coupling coefficient of the directional coupler involved in the present invention is: according to the coupling mode theory, the size of the coupling coefficient of the two waveguides is negatively correlated with the coupling distance, that is, the coupling coefficient decreases with the increase of the coupling distance; wherein, the coupling The spacing refers to the spacing between the geometric centers of the cross-sections of the two waveguides in the coupling area (ie, the spacing between the central axes). Therefore, the coupling coefficient of the directional coupler can be reset by changing the coupling distance between the two waveguides in the coupling area. In addition, since the beam splitting ratio of the directional coupler is directly related to two parameters, the coupling coefficient and the waveguide length in the coupling region, and the product of these two parameters satisfies the changing trend of a sinusoidal function. Therefore, under the condition that the coupling length of the directional coupler remains unchanged, the resetting of the splitting ratio of the directional coupler is realized by resetting the coupling coefficient.

本发明通过如下技术方案实现:The present invention realizes through following technical scheme:

一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法,具体步骤如下:A method for resetting the coupling coefficient of a directional coupler by secondary direct writing with a femtosecond laser, the specific steps are as follows:

(1)玻璃样品的清洁;(1) Cleaning of glass samples;

(2)激光加工光路的搭建及待加工样品的调平;(2) The construction of laser processing optical path and the leveling of samples to be processed;

(3)飞秒激光第二次直写器件;(3) Femtosecond laser direct writing device for the second time;

具体步骤为:首先关闭光闸,并将步骤(1)中的玻璃样品移动到起始加工位置;然后转动半波片,调节激光功率;最后操控软件直接运行预先写好的加工程序,在耦合区两根波导的加工区域内分别进行二次直写;加工结束后对样品进行抛光,得到与原有波导耦合间距不同的两根新波导;所述加工区域为距离原有波导的中轴线上下0μm-3μm的区域内。The specific steps are: first close the shutter, and move the glass sample in step (1) to the initial processing position; then turn the half-wave plate to adjust the laser power; finally, the control software directly runs the pre-written processing program, and Secondary direct writing is carried out in the processing area of the two waveguides in the area; after the processing, the sample is polished to obtain two new waveguides with different coupling spacing from the original waveguide; the processing area is up and down from the central axis of the original waveguide In the region of 0μm-3μm.

进一步地,步骤(1)中所述玻璃样品为已经完成第一次飞秒激光加工的包含初始定向耦合器的样品;其中,第一次飞秒激光加工参数为:扫描速度1mm/s-60mm/s;激光功率140mw-300mw,初始定向耦合器的耦合区长度为0-20mm;耦合间距d0为8μm-15μm。Further, the glass sample described in step (1) is a sample containing an initial directional coupler that has completed the first femtosecond laser processing; wherein, the first femtosecond laser processing parameters are: scanning speed 1mm/s-60mm /s; the laser power is 140mw-300mw, the length of the coupling area of the initial directional coupler is 0-20mm; the coupling distance d 0 is 8μm-15μm.

进一步地,步骤(2)中所述激光加工光路具体为:首先,飞秒激光由飞秒激光器出射后,经过半波片、偏振分束器后激光功率被调整;然后经过第一反射镜被反射,经过第一凹透镜和第二凸透镜后激光被扩束;然后扩束后的激光经过光阑选出能量分布均匀、且光斑直径与物镜入口尺寸相同的激光光束;然后激光经过第二反射镜和第三反射镜反射后进入物镜;然后激光经过物镜聚焦于样品表面或内部;样品放置于样品台上,样品台与气浮运动平台相连,可进行三维运动;激光经过物镜汇聚在样品表面或内部以后会有一部分激光反射,反射激光经过物镜后,穿过第三反射镜,由第四反射镜反射,经过第三凸透镜汇聚后在成像相机上成像,根据成像相机中光斑形貌可以判断经过物镜聚焦后的激光焦点处于样品表面还是内部。Further, the laser processing optical path described in step (2) is specifically as follows: first, after the femtosecond laser is emitted by the femtosecond laser, the laser power is adjusted after passing through the half-wave plate and the polarization beam splitter; Reflection, the laser beam is expanded after passing through the first concave lens and the second convex lens; then the expanded laser beam passes through the diaphragm to select a laser beam with uniform energy distribution and the same spot diameter as the entrance size of the objective lens; then the laser beam passes through the second reflector After being reflected by the third mirror, the laser beam enters the objective lens; then the laser beam is focused on the surface or inside of the sample through the objective lens; There will be a part of the laser reflection in the interior. After the reflected laser passes through the objective lens, it passes through the third reflector, is reflected by the fourth reflector, and is imaged on the imaging camera after being converged by the third convex lens. According to the shape of the spot in the imaging camera, it can be judged After the objective lens is focused, the laser focus is on the surface or inside of the sample.

进一步地,步骤(2)中所述的飞秒激光的波长为500-1064nm,脉冲频率100KHZ-2000KHz,脉冲宽度130fs-400fs,激光器出射功率为3W-20W;使用的物镜倍数为20-100倍。Further, the wavelength of the femtosecond laser described in step (2) is 500-1064nm, the pulse frequency is 100KHZ-2000KHz, the pulse width is 130fs-400fs, and the output power of the laser is 3W-20W; the multiple of the objective lens used is 20-100 times .

进一步地,步骤(2)中所述待加工样品的调平具体为:Further, the leveling of the sample to be processed described in step (2) is specifically:

将待激光加工的玻璃样品平放在二维倾角平台上,二维倾角平台固定在三维气浮运动平台中心位置;调节气浮运动平台的XY轴,使物镜处于样品左上角位置;然后,调节气浮运动平台的Z轴使物镜和样品之间的间距每间隔10μm-100μm缩短一次,并且观察成像相机中,直到有“十字”型的反射光斑出现;然后移动气浮运动平台的Y轴,使物镜位于样品左下角正上方,调节二维倾角调平台的θx旋钮使成像相机中再次出现“十字”型的光斑;反复在左上角和左下角的两个顶点来回切换,并依据光斑判断高度,反复调节θx旋钮直到两个顶点同时出现“十字”型的光斑,证明样品在Y轴方向水平;同理,反复调节左上角和右上角两个顶点处于同一水平位置;同时调节左上角、左下角和右上角三个顶点处于同一水平位置后;最后,移动气浮运动平台到样品右下角的顶点,观察此时成像相机中光斑状态,如果第四个顶点的反射光斑也同时处于“十字”型则证明整个样品处于水平状态,可以等待后续加工使用;其中,调平过程中的激光功率P0为20mw-80mw。Place the glass sample to be laser processed flat on the two-dimensional tilt platform, and the two-dimensional tilt platform is fixed at the center of the three-dimensional air-floating motion platform; adjust the XY axes of the air-floating motion platform so that the objective lens is at the upper left corner of the sample; then, adjust The Z-axis of the air-floating motion platform shortens the distance between the objective lens and the sample at intervals of 10 μm-100 μm, and observes the imaging camera until a "cross"-shaped reflection spot appears; then move the Y-axis of the air-floating motion platform, Make the objective lens directly above the lower left corner of the sample, and adjust the θx knob of the two-dimensional inclination adjustment platform to make the "cross"-shaped spot appear again in the imaging camera; repeatedly switch back and forth between the two vertices in the upper left corner and lower left corner, and judge the height according to the spot , adjust the θx knob repeatedly until a "cross"-shaped spot appears at the two vertices at the same time, which proves that the sample is horizontal in the Y-axis direction; similarly, repeatedly adjust the two vertices in the upper left corner and upper right corner to be at the same horizontal position; adjust the upper left corner and lower left corner at the same time After the three apexes in the corner and the upper right corner are at the same horizontal position; finally, move the air-floating motion platform to the apex in the lower right corner of the sample, and observe the state of the light spot in the imaging camera at this time. If the reflected light spot of the fourth apex is also in the "cross" The model proves that the entire sample is in a horizontal state and can be used for subsequent processing; wherein, the laser power P 0 in the leveling process is 20mw-80mw.

进一步地,步骤(3)中起始加工位置的确定方法具体如下:Further, the method for determining the initial processing position in step (3) is specifically as follows:

调平结束后,移动气浮运动平台的XY轴,使物镜处于样品左上角;然后每间隔10μm-100μm移动一次X轴,直到成像相机中的“十字”型反射光斑消失,证明物镜处于样品X轴的边缘位置;同理,每间隔10μm-100μm移动一次Y轴,直到光斑消失,证明物镜处于样品的左上角位置;经过上述两个步骤,则激光焦点处于样品最左上角位置;此时,将左上角的位置作为起始加工位置,并设置运动平台软件将此处坐标归零,即(0,0,0)点。After leveling, move the XY axis of the air bearing motion platform so that the objective lens is in the upper left corner of the sample; then move the X axis every 10μm-100μm until the "cross" type reflection spot in the imaging camera disappears, proving that the objective lens is in the X position of the sample. The edge position of the axis; similarly, move the Y axis every 10μm-100μm until the spot disappears, which proves that the objective lens is at the upper left corner of the sample; after the above two steps, the laser focus is at the upper left corner of the sample; at this time, Use the position of the upper left corner as the initial processing position, and set the motion platform software to reset the coordinates here to zero, that is, point (0, 0, 0).

进一步地,步骤(3)中二次直写所使用的功率为140mw-300mw,扫描速度为1mm/s-60mm/s;激光聚焦深度为50um-1000um。Further, the power used in the second direct writing in step (3) is 140mw-300mw, the scanning speed is 1mm/s-60mm/s; the laser focus depth is 50um-1000um.

进一步地,步骤(3)中所述的抛光具体步骤如下:将加工好的样品取下,利用砂纸对波导端面所在的样品侧面进行粗略抛光,砂纸目数100目-7000目;然后将样品放置于含有抛光液的抛光机上进行精细抛光,抛光液颗粒度为50nm-14um,每一侧的抛光时间为40分钟-300分钟;样品抛光结束后,擦干净等待测试。Further, the specific steps of polishing described in step (3) are as follows: remove the processed sample, use sandpaper to roughly polish the side of the sample where the end face of the waveguide is located, and the number of sandpaper is 100 mesh-7000 mesh; then place the sample Perform fine polishing on a polishing machine containing a polishing liquid, the particle size of the polishing liquid is 50nm-14um, and the polishing time for each side is 40 minutes to 300 minutes; after the sample is polished, wipe it clean and wait for the test.

本发明还提供了一种利用飞秒激光二次直写重置定向耦合器耦合系数在器件分束比重置方面的应用,可以实现定向耦合器的初始分束比到任意最终分束比的重置。The present invention also provides an application of resetting the coupling coefficient of the directional coupler by secondary direct writing of the femtosecond laser in resetting the beam splitting ratio of the device, which can realize the resetting of the initial beam splitting ratio of the directional coupler to any final beam splitting ratio place.

与现有技术相比,本发明具有以下优点:Compared with the prior art, the present invention has the following advantages:

(1)、可提高芯片集成度;提出了通过飞秒激光二次直写技术来修改定向耦合器耦合间距,实现耦合系数的重新配置,从而达到器件分束比重置的目的,可以解决芯片中器件制造误差的问题;该方法与现有的电极调控方法一样均可实现器件分束比的修复,但该方法不需要额外的电极,因此可提高芯片集成度,并且减小不必要的功耗;(1) It can improve the integration of the chip; it is proposed to modify the coupling spacing of the directional coupler through the femtosecond laser secondary direct writing technology to realize the reconfiguration of the coupling coefficient, so as to achieve the purpose of resetting the beam splitting ratio of the device, which can solve the problem of in-chip The problem of device manufacturing error; this method can realize the restoration of the device beam splitting ratio as the existing electrode regulation method, but this method does not require additional electrodes, so it can improve chip integration and reduce unnecessary power consumption ;

(2)、可进行三维芯片修复;与现有电极调控方法中电极只能制备于样品表面而进行浅层器件调控的现状相比,该方法依靠飞秒激光特有的三维加工优势,可以实现三维光子回路的定点定量的调控;(2) Three-dimensional chip repair can be carried out; compared with the current situation in which the electrode can only be prepared on the surface of the sample for shallow device regulation in the existing electrode regulation method, this method relies on the unique three-dimensional processing advantages of the femtosecond laser to achieve three-dimensional Fixed-point quantitative regulation of photon circuits;

(3)、可进行全周期调控;与现有的基于飞秒激光多次扫描的同类型的静态调控方法相比,该方法通过调控定向耦合器的耦合系数来实现器件分束比的重置,可以实现器件从任意初始分束比到任意终态分束比的重置,即可以实现器件分束比全周期的调控,可满足任意光量子芯片的需求。(3) Full-cycle control is possible; compared with the existing static control method of the same type based on femtosecond laser multiple scanning, this method realizes the reset of the device beam splitting ratio by adjusting the coupling coefficient of the directional coupler , can realize the reset of the device from any initial beam splitting ratio to any final state beam splitting ratio, that is, can realize the full-cycle regulation of the device beam splitting ratio, and can meet the needs of any optical quantum chip.

附图说明Description of drawings

图1为本发明的一种利用飞秒激光二次直写重置定向耦合器耦合系数的激光加工光路示意图;Fig. 1 is a schematic diagram of the laser processing optical path of the present invention using femtosecond laser secondary direct writing to reset the coupling coefficient of the directional coupler;

图2为本发明的一种利用飞秒激光二次直写技术重置定向耦合器耦合系数的方法的原理示意图;Fig. 2 is a schematic diagram of the principle of a method for resetting the coupling coefficient of a directional coupler using femtosecond laser secondary direct writing technology of the present invention;

其中:飞秒激光第一次直写的初始波导用灰色条形表示;飞秒激光第二次直写的拼接波导用虚线条形表示;初始波导和拼接波导融合后组成新的组合波导用灰色叠加虚线条形表示。初始器件的耦合间距由初始第一波导和初始第二波导的中轴线间距定义为d0,耦合区的耦合长度为L0(a);在二次直写区域进行二次直写拼接波导后,器件耦合间距由组合后的新第三波导和波导4的中轴线中心定义为d1(在耦合区内侧二次直写)(b)或者d2(在耦合区外侧二次直写),耦合长度为L0(c);Among them: the initial waveguide of the femtosecond laser direct writing for the first time is represented by a gray bar; the spliced waveguide of the femtosecond laser direct writing for the second time is represented by a dotted line; the initial waveguide and the spliced waveguide are fused to form a new combined waveguide in gray Superimposed dotted line representation. The coupling spacing of the initial device is defined by the central axis spacing of the initial first waveguide and the initial second waveguide as d 0 , and the coupling length of the coupling region is L 0 (a); , the device coupling spacing is defined by the central axis center of the combined new third waveguide and waveguide 4 as d 1 (secondary direct writing inside the coupling region) (b) or d 2 (secondary direct writing outside the coupling region), The coupling length is L 0 (c);

图3为本发明的一种利用飞秒激光二次直写重置定向耦合器耦合系数的二次直写前后耦合区的波导端面显微镜图和模场重叠图;Fig. 3 is a micrograph of waveguide end face and mode field overlap diagram of the coupling region before and after secondary direct writing of a second direct writing using femtosecond laser to reset the coupling coefficient of the directional coupler according to the present invention;

其中:a为初始器件的耦合区两根波导的端面图,耦合间距为d0;b和c分别为利用第二次直写在初始耦合区内侧和外侧进行二次直写后的耦合区两根波导的端面图,耦合间距为d1和d2;d、e和f分别是a、b和c图对应的耦合区模场重叠图;Among them: a is the end view of the two waveguides in the coupling region of the initial device, and the coupling distance is d 0 ; b and c are the two direct writing in the coupling region after the second direct writing on the inside and outside of the initial coupling region, respectively. The end view of the root waveguide, the coupling spacing is d 1 and d 2 ; d, e and f are the mode field overlap diagrams of the coupling region corresponding to a, b and c respectively;

图4为本发明的一种利用飞秒激光二次直写重置定向耦合器耦合系数的二次直写前后耦合系数的变化趋势图;Fig. 4 is a change trend diagram of the coupling coefficient before and after the secondary direct writing of the present invention using femtosecond laser secondary direct writing to reset the coupling coefficient of the directional coupler;

其中:初始器件的耦合间距为8μm,耦合系数为0.89rad/mm;被修改后的耦合间距为5μm-11μm;耦合系数为0.47rad/mm-2.1rad/mm。Among them: the coupling spacing of the initial device is 8 μm, and the coupling coefficient is 0.89rad/mm; the modified coupling spacing is 5 μm-11 μm; the coupling coefficient is 0.47rad/mm-2.1rad/mm.

图5为本发明的一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法进行定向耦合器分束比重置的应用示意图;Fig. 5 is an application schematic diagram of resetting the beam splitting ratio of the directional coupler by using a method of resetting the coupling coefficient of the directional coupler by secondary direct writing of the femtosecond laser according to the present invention;

其中:初始器件的耦合间距为8μm,耦合长度为3.5mm均为固定值,利用二次直写技术重置耦合系数的方法来调控器件分束比;Among them: the coupling spacing of the initial device is 8 μm, and the coupling length is 3.5 mm, both of which are fixed values. The method of resetting the coupling coefficient by the secondary direct writing technology is used to control the splitting ratio of the device;

图6为本发明的一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法进行定向耦合器分束比重置的测试结果图;Fig. 6 is a test result diagram of resetting the beam splitting ratio of the directional coupler by using a femtosecond laser secondary direct writing method of the present invention to reset the coupling coefficient of the directional coupler;

其中:初始器件的分束比为46.1:53.9;圆形数据点和正方形数据点分别代表在初始器件耦合区内侧和外侧进行二次直写的结果。Among them: the beam splitting ratio of the initial device is 46.1:53.9; the circular data points and square data points represent the results of secondary direct writing on the inside and outside of the coupling region of the initial device, respectively.

具体实施方式Detailed ways

下面结合附图对本发明做进一步地说明。The present invention will be further described below in conjunction with the accompanying drawings.

实施例1Example 1

耦合间距是影响耦合系数的重要参数之一,对定向耦合器中耦合间距的修改可实现对器件耦合系数的重置。在加工参数相同的情况下,定向耦合器中两条耦合臂的尺寸和截面形貌等所有基本性质均基本相同,器件的耦合间距可以被认为是两根波导的中轴线间距。因此,重置定向耦合器耦合系数的问题可以被认为是重新构成波导几何中心的问题。利用飞秒激光二次直写的方式,在初始波导中轴线间隔很近的位置二次直写出第二条拼接波导,则初始波导与第二条拼接波导会融合成为一条新的组合波导。由于组合波导由初始波导和拼接波导融合而成,所以组合波导的中心是初始波导与拼接波导几何中心的中间值,这样重新构成的组合波导的几何中心相对于初始波导的几何中心发生了偏移,即实现了波导几何中心的重新构成。利用这种方法修改初始器件的耦合区域,即可得到由两条新波导构成的新的耦合区域,由于新波导具有新的几何中心,因此耦合间距会因耦合区域波导几何中心的偏移而发生改变。进一步地,拼接波导处于耦合区内侧,即新波导的几何中心偏向耦合区内侧时,耦合间距会减小,而耦合系数会增大;相反地,拼接波导处于耦合区外侧,新波导的几何中心偏向耦合区外侧时,耦合间距会增大,而耦合系数会减小;以此,来实现对器件耦合系数的重新配置。The coupling distance is one of the important parameters affecting the coupling coefficient, and the modification of the coupling distance in the directional coupler can reset the coupling coefficient of the device. In the case of the same processing parameters, all basic properties such as the size and cross-sectional shape of the two coupling arms in the directional coupler are basically the same, and the coupling spacing of the device can be considered as the central axis spacing of the two waveguides. Therefore, the problem of resetting the coupling coefficients of a directional coupler can be considered as a problem of reconstructing the geometric center of the waveguide. Using the femtosecond laser secondary direct writing method, the second spliced waveguide is directly written at the position where the central axis of the initial waveguide is very close, and the initial waveguide and the second spliced waveguide will be fused into a new combined waveguide. Since the combined waveguide is formed by the fusion of the original waveguide and the spliced waveguide, the center of the combined waveguide is the intermediate value of the geometric center of the original waveguide and the spliced waveguide, so the geometric center of the reconstructed combined waveguide is offset relative to the geometric center of the original waveguide , which realizes the reconstruction of the geometric center of the waveguide. Using this method to modify the coupling region of the initial device, a new coupling region composed of two new waveguides can be obtained. Since the new waveguide has a new geometric center, the coupling distance will occur due to the offset of the geometric center of the coupling region waveguide. Change. Furthermore, when the spliced waveguide is inside the coupling area, that is, when the geometric center of the new waveguide is biased to the inside of the coupling area, the coupling distance will decrease, but the coupling coefficient will increase; on the contrary, if the spliced waveguide is outside the coupling area, the geometric center of the new waveguide When it is biased to the outside of the coupling region, the coupling distance will increase and the coupling coefficient will decrease; in this way, the reconfiguration of the coupling coefficient of the device is realized.

一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法,具体步骤如下:A method for resetting the coupling coefficient of a directional coupler by secondary direct writing with a femtosecond laser, the specific steps are as follows:

(1)制备待加工样品:(1) Prepare the sample to be processed:

取一片待加工的25mm*25mm*0.7mm尺寸的样品放在滤纸上,使用镊子依次夹起丙酮棉球、乙醇棉球对样品先后擦拭一次,擦拭时沿着同一个方向避免污染样品;用镊子夹起经过丙酮和乙醇处理后的样品,使用去离子水进行冲洗一次;最后使用洗耳球沿着一个固定角度将样品吹干,并放在干净的样品盒中备用;Take a 25mm*25mm*0.7mm sample to be processed and put it on the filter paper, use tweezers to pick up the acetone cotton ball and the ethanol cotton ball to wipe the sample successively, and wipe along the same direction to avoid contamination of the sample; use tweezers Pick up the sample treated with acetone and ethanol, rinse it with deionized water once; finally use the ear washing ball to dry the sample along a fixed angle, and put it in a clean sample box for later use;

(2)激光加工光路的搭建及确定激光调平功率:(2) Construction of laser processing optical path and determination of laser leveling power:

飞秒激光加工系统如图1所示,飞秒激光波长为1064nm,脉冲频率2000KHz,脉冲宽度400fs,激光初始功率为3W。激光由激光器出射后,经过半波片、偏振分束器后激光功率被调整。半波片被安放在一个可以旋转的步进电机上,通过软件控制使步进电机旋转起来,即可实现半波片的旋转,进而使透过偏振分束器之后的激光功率得到定量调整。穿过偏振分束器之后的激光经过第一反射镜被反射,经过第一凹透镜和第二凸透镜后激光被扩束,第一凹透镜焦距为-7.5mm,第二凸透镜焦距为30mm,扩束倍数为4倍,扩束后激光光斑直径由原来的3mm增大为12mm。扩束后的激光经过光阑选出能量分布均匀,且光斑直径与物镜入口尺寸相同的激光光束。本次实验中选择的物镜是20倍奥林巴斯干式物镜,物镜入口尺寸为7mm,因此穿过光阑后的激光光束直径也为7mm。然后激光经过第二反射镜和第三反射镜反射后进入物镜;然后激光经过物镜聚焦于样品表面;样品放置于样品台上,样品台与气浮运动平台相连,可进行三维运动;激光经过物镜汇聚在样品表面或内部以后会有一部分激光反射。反射激光经过物镜后穿过第三反射镜,并由第四反射镜反射后,经过焦距为50mm的第三凸透镜汇聚在成像相机上成像。根据成像相机中光斑形貌可以判断经过物镜聚焦后的激光焦点处于样品表面还是内部。The femtosecond laser processing system is shown in Figure 1. The femtosecond laser wavelength is 1064nm, the pulse frequency is 2000KHz, the pulse width is 400fs, and the initial laser power is 3W. After the laser is emitted from the laser, the laser power is adjusted after passing through a half-wave plate and a polarizing beam splitter. The half-wave plate is placed on a rotatable stepping motor, and the stepping motor is rotated through software control to realize the rotation of the half-wave plate, thereby quantitatively adjusting the laser power after passing through the polarization beam splitter. After passing through the polarizing beam splitter, the laser beam is reflected by the first mirror, and the laser beam is expanded after passing through the first concave lens and the second convex lens. The focal length of the first concave lens is -7.5mm, and the focal length of the second convex lens is 30mm. After beam expansion, the laser spot diameter increases from 3mm to 12mm. The expanded laser beam passes through the aperture to select a laser beam with uniform energy distribution and the same spot diameter as the entrance size of the objective lens. The objective lens selected in this experiment is a 20x Olympus dry objective lens, and the entrance size of the objective lens is 7mm, so the diameter of the laser beam after passing through the diaphragm is also 7mm. Then the laser is reflected by the second reflector and the third reflector and then enters the objective lens; then the laser is focused on the surface of the sample through the objective lens; the sample is placed on the sample stage, which is connected with the air-floating motion platform and can move in three dimensions; the laser passes through the objective lens Part of the laser light will be reflected after converging on the surface or inside of the sample. The reflected laser light passes through the objective lens, passes through the third reflector, is reflected by the fourth reflector, passes through the third convex lens with a focal length of 50mm, and converges on the imaging camera for imaging. According to the shape of the light spot in the imaging camera, it can be judged whether the focus of the laser beam focused by the objective lens is on the surface or inside of the sample.

由于调平需要使激光聚焦在样品表面进行后续操作,而过高的激光功率会烧蚀样品,因此实验中尽量使调平功率尽可能低。具体地,在第三反射镜和物镜之间放置一个功率计,调节步进电机软件,控制半波片旋转角度,使得功率计读数为20mw,作为调平功率。Because leveling needs to focus the laser on the sample surface for subsequent operations, and too high laser power will ablate the sample, so try to keep the leveling power as low as possible in the experiment. Specifically, place a power meter between the third mirror and the objective lens, adjust the stepper motor software, and control the rotation angle of the half-wave plate, so that the power meter reads 20mw as the leveling power.

(3)调平样品:(3) Leveling samples:

调平的原理是:根据三点确定一个平面的原则,调节样品三个顶点位于同一水平高度,即可使样品水平。具体展开解释为,由图1可知,激光经过物镜聚焦之后会汇聚为一个焦点,调节三维位移运动平台使焦点刚好处于样品顶点的表面时,焦点位置的激光经过样品表面反射后,经过第三凸透镜汇聚后进入成像相机,此时成像相机中会出现一个“十字”型的光斑,即此时证明是将激光聚焦到样品表面;调节样品台倾角的旋钮使得样品三个顶点的反射光斑都是“十字”型的光斑,证明三个顶点处于同一水平高度,即调平结束。依据上述原理,具体地实验操作如下:The principle of leveling is: according to the principle of determining a plane by three points, adjust the three vertices of the sample to be at the same level to make the sample level. The specific explanation is as shown in Figure 1. After the laser is focused by the objective lens, it will converge into a focal point. When the three-dimensional displacement motion platform is adjusted so that the focal point is just on the surface of the apex of the sample, the laser at the focal point is reflected by the sample surface and passes through the third convex lens. After converging, it enters the imaging camera. At this time, a "cross"-shaped spot will appear in the imaging camera, which proves that the laser is focused on the surface of the sample at this time; the knob for adjusting the inclination angle of the sample stage makes the reflected spots of the three vertices of the sample all " The "cross"-shaped spot proves that the three vertices are at the same level, that is, the leveling is over. According to the above principles, the specific experimental operation is as follows:

将待激光加工的玻璃样品固定在气浮运动平台上方的样品架上;调节气浮运动平台的XY轴,使物镜处于样品左上角位置;然后,调节Z轴使物镜和样品之间的间距每间隔100微米缩短一次,并且观察成像相机中是否有反射光斑出现;根据光斑形貌判断焦点位置是在表面以上(上移)还是在表面以下(下移);根据焦点上移时反射光斑中心区能量变弱直径变大,焦点下移时反射光斑环带数量增多且直径变大,这两个明显的判断标准可以使物镜和样品之间的间距控制在正负1微米的误差范围内,足以满足调平需求;根据上述判断标准,移动运动平台Z轴使左上角的反射光斑在成像相机中刚好出现“十字”型的光斑;后续移动运动平台Y轴23厘米,使物镜位于样品左下角正上方,此时样品可能不平整,因此成像相机中的光斑不再是“十字”型的光斑,需要焦点上移和下移的光斑判断标准确定此时物镜和样品左下角之间的间距是变大还是变小,然后调节二维倾角调平台的θx旋钮使成像相机中再次出现“十字”型的光斑;由于样品的左上角可能不在调平台的中心位置,调节θx旋钮后,左上角的高度也发生了变化,因此需要移动运动平台Y轴-23厘米返回左上角;此时左上角光斑极大可能也发生了变化,再次调节二维倾角条平台的θx旋钮使成像相机中再次出现“十字”型的光斑;后续反复在左上角和左下角两个顶点来回切换,并依据光斑判断高度,反复调节θx旋钮一直到两个顶点同时出现“十字”型的光斑,证明样品在Y轴方向水平;同理,可以反复调节左上角和右上角两个顶点处于同一水平位置;同时调节左上角、左下角和右上角三个顶点处于同一水平位置后,可以初步认为样品处于水平状态;最后,移动运动平台到样品右下角的顶点,观察此时成像相机中光斑状态,如果第四个顶点的反射光斑也处于“十字”型则证明整个样品确实处于完美的水平状态,可以等待后续加工使用。Fix the glass sample to be laser-processed on the sample holder above the air-floating motion platform; adjust the XY axes of the air-floating motion platform so that the objective lens is at the upper left corner of the sample; then, adjust the Z axis to make the distance between the objective lens and the sample every The interval of 100 microns is shortened once, and observe whether there is a reflection spot in the imaging camera; judge whether the focus position is above the surface (moving up) or below the surface (moving down) according to the shape of the spot; according to the central area of the reflection spot when the focus moves up The energy becomes weaker and the diameter becomes larger, and the number of reflection spot rings increases and the diameter becomes larger when the focus moves down. These two obvious criteria can make the distance between the objective lens and the sample controlled within the error range of plus or minus 1 micron, which is enough Meet the leveling requirements; according to the above judgment criteria, move the Z-axis of the motion platform so that the reflected light spot in the upper left corner just appears in the imaging camera as a "cross" type of light spot; subsequently move the Y-axis of the motion platform 23 cm, so that the objective lens is positioned at the lower left corner of the sample. Above, the sample may be uneven at this time, so the spot in the imaging camera is no longer a "cross" spot, and the spot judgment standard of moving the focus up and down is required to determine the distance between the objective lens and the lower left corner of the sample at this time. Larger or smaller, then adjust the θx knob of the two-dimensional inclination adjustment platform to make the "cross"-shaped spot appear again in the imaging camera; since the upper left corner of the sample may not be in the center of the adjustment platform, after adjusting the θx knob, the height of the upper left corner It has also changed, so it is necessary to move the Y-axis of the motion platform -23 cm to return to the upper left corner; at this time, the light spot in the upper left corner may also have changed, adjust the θx knob of the two-dimensional inclination bar platform again to make the "cross" appear again in the imaging camera ""-shaped light spot; then repeatedly switch back and forth between the two vertices in the upper left corner and lower left corner, and judge the height according to the light spot, and repeatedly adjust the θx knob until a "cross"-shaped light spot appears at the two vertices at the same time, proving that the sample is horizontal in the Y-axis direction ; Similarly, you can repeatedly adjust the two vertices of the upper left corner and the upper right corner to be at the same horizontal position; after adjusting the three vertices of the upper left corner, lower left corner and upper right corner to be at the same horizontal position at the same time, you can preliminarily consider the sample to be in a horizontal state; finally, move Move the platform to the vertex in the lower right corner of the sample, and observe the state of the light spot in the imaging camera at this time. If the reflected light spot at the fourth vertex is also in the "cross" shape, it proves that the entire sample is indeed in a perfect horizontal state and can wait for subsequent processing.

(4)确定起始加工位置:(4) Determine the initial processing position:

调平结束后,移动运动平台XY轴,使物镜处于样品左上角;然后每间隔100微米移动一次X轴,一直到成像相机中的“十字”型反射光斑消失,证明物镜处于样品X轴的边缘位置;同理,每间隔100微米移动一次Y轴,一直到光斑消失,证明物镜处于样品真正的左上角位置。此时,将左上角的位置作为起始加工位置,并设置运动平台软件将此处坐标归零,即(0,0,0)点。After leveling, move the XY axis of the moving platform so that the objective lens is at the upper left corner of the sample; then move the X axis every 100 microns until the "cross" type reflection spot in the imaging camera disappears, proving that the objective lens is at the edge of the sample X axis Position; Similarly, move the Y axis every 100 microns until the spot disappears, which proves that the objective lens is in the real upper left corner of the sample. At this time, take the position of the upper left corner as the initial processing position, and set the motion platform software to reset the coordinates here to zero, that is, point (0, 0, 0).

(5)确定激光加工功率:(5) Determine the laser processing power:

将功率计放置于第三反射镜和物镜之间,控制旋转步进电机的软件使半波片转动,直到功率计读数为300mw;此时该功率作为第一次和第二次直写的加工功率。Place the power meter between the third reflector and the objective lens, and the software that controls the rotating stepper motor makes the half-wave plate rotate until the power meter reads 300mw; at this time, the power is used as the processing of the first and second direct writing power.

(6)第一次直写初始器件:(6) Write the initial device directly for the first time:

初始器件是由耦合长度逐渐递增的、其它参数均一致的定向耦合器构成;如图2中(a)所示,定向耦合器的宽度为127微米,器件总长度为25厘米,拐弯区的曲率半径为60毫米,初始耦合间距是8微米,器件的直写速度为60毫米每秒;根据上述的具体参数和要求,完成加工程序的制作;将写好的第一次加工程序加载到三维运动平台的软件中,点击运行,制备初始器件。The initial device is composed of a directional coupler whose coupling length is gradually increasing and other parameters are consistent; as shown in Figure 2 (a), the width of the directional coupler is 127 microns, the total length of the device is 25 cm, and the curvature The radius is 60 mm, the initial coupling spacing is 8 microns, and the direct writing speed of the device is 60 mm per second; according to the above specific parameters and requirements, the production of the processing program is completed; the written first processing program is loaded into the three-dimensional motion In the software of the platform, click Run to prepare the initial device.

(7)第二次直写器件:(7) The second direct write device:

为了实现耦合区中波导几何中心的偏移,采用如图2(b)和(c)所示的结构。飞秒激光第一次直写的初始定向耦合器由初始第一波导和初始第二波导组成,第一波导和第二波导在图中用深灰色区域表示。利用飞秒激光二次直写技术在第一波导或者第二波导中轴线附近的位置二次直写拼接波导,在图中用虚线框表示,拼接波导和初始波导中轴线距离为Δd为±(0μm-3μm)。由于拼接波导与初始第一波导(2)距离很近,因此这两根波导融合成为一根新的组合第三波导(4)。可以发现,初始波导和拼接波导的几何中心并不重合,所以它们重新构成的组合波导的形状在水平方向会增加,也就是说相比于初始波导而言,组合波导的横向尺寸增大了。进一步发现,由于拼接波导和初始波导的加工参数一致,因此组合波导的几何中心是拼接波导和初始波导几何中心的中间值,即组合波导的几何中心相对于初始波导来说就发生了偏移。根据上述方法,初始器件经过飞秒激光二次直写后,其耦合区中两根波导的几何中心被修改(偏移)。由于耦合间距是根据耦合区中两根波导的中轴线间距(几何中心间距)定义,因此,波导几何中心的偏移会直接引起耦合间距的变化,从而进一步影响到耦合系数的变化;如图2(b)所示,当第二次直写的拼接波导在耦合区内侧时,根据两根新的组合波导的几何中心来定义,新的耦合间距为d1,相比初始间距d0明显缩小;如图2(c)所示,当第二次直写的拼接波导在耦合区外侧时,新的耦合间距为d2,耦合间距相比初始间距d0明显增大;实验中,第二根波导偏离第一根波导的范围在0-3微米,因此d1最小值为5微米,而d2最大值为11微米;使第二次直写的波导与第一次直写的初始波导具有相同的长度,则耦合区完全由新的组合波导构成,具有一个新的耦合系数;根据上述方式,书写第二次加工的加工程序,即程序根据第一次的程序以及起始加工位置来定位二次直写的坐标,扫描速度依旧为60毫米每秒,保留第一组作为对照组,对其它组的定向耦合器进行二次直写;将运动平台移动至(0,0,0)点后,点击加工程序,进行二次加工。In order to realize the offset of the geometric center of the waveguide in the coupling region, the structures shown in Fig. 2(b) and (c) are adopted. The initial directional coupler of femtosecond laser direct writing for the first time consists of an initial first waveguide and an initial second waveguide, which are represented by dark gray areas in the figure. Use the femtosecond laser secondary direct writing technology to directly write the spliced waveguide at the position near the central axis of the first waveguide or the second waveguide, which is represented by a dotted line box in the figure, and the distance between the spliced waveguide and the initial waveguide central axis is Δd is ±( 0μm-3μm). Since the spliced waveguide is very close to the original first waveguide (2), the two waveguides are merged into a new combined third waveguide (4). It can be found that the geometric centers of the original waveguide and the spliced waveguide do not coincide, so the shape of the combined waveguide reconstructed by them will increase in the horizontal direction, that is to say, the lateral dimension of the combined waveguide increases compared with the original waveguide. It was further found that since the processing parameters of the spliced waveguide and the original waveguide are consistent, the geometric center of the combined waveguide is the intermediate value of the geometric center of the spliced waveguide and the original waveguide, that is, the geometric center of the combined waveguide is offset relative to the original waveguide. According to the above method, after the initial device is directly written by femtosecond laser twice, the geometric centers of the two waveguides in the coupling region are modified (shifted). Since the coupling spacing is defined according to the central axis spacing (geometric center spacing) of the two waveguides in the coupling area, the offset of the geometric center of the waveguide will directly cause the change of the coupling spacing, which further affects the change of the coupling coefficient; as shown in Figure 2 As shown in (b), when the spliced waveguide of the second direct writing is inside the coupling region, it is defined according to the geometric center of the two new combined waveguides, and the new coupling distance is d 1 , which is significantly smaller than the initial distance d 0 ; As shown in Figure 2(c), when the spliced waveguide of the second direct writing is outside the coupling region, the new coupling spacing is d 2 , and the coupling spacing is significantly larger than the initial spacing d 0 ; in the experiment, the second The root waveguide deviates from the first waveguide in the range of 0-3 microns, so the minimum value of d 1 is 5 microns, and the maximum value of d 2 is 11 microns; make the waveguide of the second direct writing and the initial waveguide of the first direct writing have the same length, the coupling area is completely composed of a new combined waveguide, and has a new coupling coefficient; according to the above method, the processing program for the second processing is written, that is, the program is based on the first program and the initial processing position. Locate the coordinates of the secondary direct writing, the scanning speed is still 60 mm per second, keep the first group as the control group, and perform secondary direct writing on the directional couplers of other groups; move the motion platform to (0, 0, 0) After clicking, click on the processing program to perform secondary processing.

(8)抛光待测试的样品:(8) Polish the sample to be tested:

将加工好的样品取下,用手拿住样品,给波导端面所在的两个样品侧面进行砂纸抛光,先用400目的砂纸快速抛掉边缘不需要的位置,两个侧面用掉一页砂纸即可;然后分别使用1000目和2000目的砂纸进行细抛;然后使用抛光机进行精抛,样品放置于抛光机的夹具上,使用50纳米的抛光液进行抛光,每一侧的抛光时间为40分钟;样品抛光结束后,擦干净等待测试。Take down the processed sample, hold the sample by hand, and polish the two sides of the sample where the end face of the waveguide is located. First use 400-grit sandpaper to quickly throw away the unnecessary position on the edge, and use one page of sandpaper on the two sides. Yes; then use 1000-mesh and 2000-mesh sandpaper for fine polishing; then use a polishing machine for fine polishing. The sample is placed on the fixture of the polishing machine and polished with a 50-nanometer polishing solution. The polishing time for each side is 40 minutes ; After polishing the sample, wipe it clean and wait for the test.

(9)测试样品:(9) Test samples:

对器件二次直写前和二次直写后的耦合区进行表征,利用显微镜观察耦合区的波导端面发现,初始器件的耦合区由两根彼此分开的初始波导构成,如图3(a)所示,初始第一波导和初始第二波导的横向尺寸为5微米,把穿过两根初始波导几何中心的两条竖直线分别称作初始波导中心线1和初始波导中心线2,并且在图中用粗的竖直线表示。根据耦合间距的定义(即耦合区中两根波导的几何中心的间距)可知,初始器件的耦合间距是初始波导中心线1和初始波导中心线2的间距,记作d0。在实验中,给初始器件的耦合间距设计为8微米,也就是d0等于8微米。当利用本发明的一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法时,其效果如图3(b)和图3(c)所示。先讨论图3(b),飞秒激光第一次直写的两根初始波导仍然用粗的竖直线表示,和图3(a)中一样其中心间距仍然是d0;对器件耦合间距重新构成的过程如下:在耦合区内侧靠近初始波导中心3微米的位置(也就是初始中心线1和初始波导中心线2之间的区域,并与初始中心线1或者初始中心线2间距3微米的位置),利用飞秒激光第二次直写的策略制备出一条拼接波导;由于拼接波导和初始波导距离很近且仅3微米,所以初始波导和拼接波导融合成为一根新的组合波导,并且组合波导仍然支持810nm单模传输;由于组合波导由初始波导和拼接波导构成,所以其横向尺寸相比于初始波导来说增加了,在图3(b)中用椭圆形虚线描绘其边缘轮廓;进一步地,由于初始波导和拼接波导的加工参数一样,所以组合波导的几何中心是这两根波导几何中心的中间值,如图3(b)中用组合波导中心线1和组合波导中心线2描述组合波导的几何中心位置(即椭圆形的中线竖直中心线位置);可以很清楚的看见,组合波导中心线1和初始中心线1是不重合的,也就是说经过飞秒激光二次直写后耦合区中波导的几何中心发生了偏移,根据耦合间距是由两根耦合波导地几何中心距离定义,那么新的耦合间距就是d1;进一步地,由于是在耦合区内侧进行地二次直写,组合波导中心线1和组合波导中心线2更加向中间靠拢,所以可以很明显地看见耦合间距d1小于初始耦合间距d0;进一步地,由于拼接波导距离初始第三波导微米,所以中间值就是1.5微米,也就是说组合波导中心线1相比于初始波导中心线1向耦合区内侧偏移了1.5微米。同理组合波导中心线2也是向内侧偏移了1.5微米。那么在组合第一波导和组合第二波导的几何中心同时向内偏移1.5微米的情况下,修改后的耦合间距d1是5微米。根据图3(b)中同样的方式,在图3(c)中,利用飞秒激光在初始波导外侧直写出拼接波导后,组合波导的中心线相比于初始波导中心线向耦合区外侧偏移1.5微米,这样新的耦合间距d2就增大为11微米。从图3(a)、(b)和(c)可以很清楚地得到耦合区被修改后,耦合间距可以变小和变大的结论;而耦合区间距被修改后,其对耦合系数的影响如何,需要对耦合区进行模场重叠程度测试。在定向耦合器的输入口通入810纳米的激光,使用单模分析仪进行观测,得到耦合区模场交叠情况;如图3(d)所示,初始器件两根波导的模场交叠程度为44.1%,也就是说图3(a)中的初始器件的模场交叠程度为44.1%;如图3(e)所示,利用飞秒激光二次直写策略在耦合区内侧对器件进行二次直写后,器件两根新波导的模场交叠程度增大为56.7%,也就是说图3(b)中的被修改后器件的模场交叠程度为56.7%;结合图3(b)中得出的耦合间距d1比耦合间距d0变小的结论一起分析,可以知道耦合间距变小以后,耦合区两根耦合波导的模场交叠程度变大,根据耦合模理论,这样光波能量在两根波导中的振荡频率变快,就可以使得耦合系数增大;同理,如图3(f)所示,利用飞秒激光二次直写策略在耦合区外侧进行二次直写后,器件两根新波导的模场交叠程度减小为24.4%,也就是说图3(c)中的被修改后器件的模场交叠程度为24.4%,同理分析可以知道,模场交叠程度变小,会引起耦合系数减小;综上所述,利用飞秒激光二次直写的方法,可以改变波导的几何中心位置,进一步改变耦合间距,进一步影响模场交叠程度,最后引起耦合系数的变化。上述是对耦合系数可以被该发明重置的理论上的讨论,如何得到耦合系数重置后的具体实验数值,需要进行更加精确的测试;接下来对芯片上的多组定向耦合器进行分束比的测量,并拟合数据得到如图4所示的结果;横坐标表示被二次直写后的器件的耦合间距,横坐标不同的数值表示利用飞秒激光二次直写策略制备的拼接波导与初始波导的位置和间距不同,8微米时是初始器件的耦合间距,当拼接波导处于耦合区内侧或者外侧并且距离3微米时,耦合间距有最小值5微米或者最大值11微米(之前已经详细介绍过);纵坐标是耦合系数。根据图中数据点,不难发现,当二次直写的拼接波导处于耦合区内侧时,耦合间距d1变小,耦合系数增大,最大可以增加到2.1rad/mm;相反地,耦合系数减小,最小可以减小到0.47rad/mm;经过分析,初始器件的耦合系数可以被重置的范围是0.47-2.1rad/mm;综上,证明了初始器件经过二次直写后可以实现耦合系数的重置,即本发明提供了一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法。Characterize the coupling region of the device before and after the second direct writing, and use a microscope to observe the waveguide end face of the coupling region. It is found that the coupling region of the initial device is composed of two initial waveguides separated from each other, as shown in Figure 3(a) As shown, the lateral dimensions of the initial first waveguide and the initial second waveguide are 5 microns, and the two vertical lines passing through the geometric centers of the two initial waveguides are called the initial waveguide centerline 1 and the initial waveguide centerline 2, respectively, and It is indicated by a thick vertical line in the figure. According to the definition of the coupling spacing (that is, the spacing between the geometric centers of the two waveguides in the coupling region), the coupling spacing of the initial device is the spacing between the initial waveguide centerline 1 and the initial waveguide centerline 2, denoted as d 0 . In the experiment, the coupling pitch for the initial device is designed to be 8 microns, that is, d 0 is equal to 8 microns. When using a method of resetting the coupling coefficient of the directional coupler by using the femtosecond laser secondary direct writing of the present invention, the effect is shown in Fig. 3(b) and Fig. 3(c). Let’s discuss Figure 3(b) first. The two initial waveguides written by the femtosecond laser for the first time are still represented by thick vertical lines, and the distance between their centers is still d0 as in Figure 3(a); The formation process is as follows: 3 microns near the center of the initial waveguide inside the coupling region (that is, the area between the initial centerline 1 and the initial waveguide centerline 2, and a distance of 3 microns from the initial centerline 1 or initial centerline 2 position), a spliced waveguide was prepared by using the femtosecond laser direct writing strategy for the second time; since the spliced waveguide and the initial waveguide are very close and only 3 microns, the initial waveguide and the spliced waveguide are fused into a new combined waveguide, and The combined waveguide still supports 810nm single-mode transmission; since the combined waveguide is composed of the original waveguide and the spliced waveguide, its lateral dimension is increased compared to the original waveguide, and its edge outline is depicted by an elliptical dashed line in Figure 3(b); Furthermore, since the processing parameters of the initial waveguide and the spliced waveguide are the same, the geometric center of the combined waveguide is the intermediate value of the geometric centers of the two waveguides, as shown in Figure 3(b) with combined waveguide centerline 1 and combined waveguide centerline 2 Describe the geometric center position of the combined waveguide (that is, the vertical centerline position of the centerline of the ellipse); it can be clearly seen that the centerline 1 of the combined waveguide and the initial centerline 1 are not coincident, that is to say, after the second femtosecond laser After direct writing, the geometric center of the waveguide in the coupling area has shifted. According to the coupling spacing is defined by the geometric center distance of the two coupling waveguides, then the new coupling spacing is d 1 ; In the second direct writing, the combined waveguide centerline 1 and the combined waveguide centerline 2 are closer to the middle, so it can be clearly seen that the coupling distance d1 is smaller than the initial coupling distance d0; further, since the distance between the spliced waveguide and the initial third waveguide is microns, so The middle value is 1.5 microns, that is to say, the central line 1 of the composite waveguide is shifted 1.5 microns to the inner side of the coupling region compared with the central line 1 of the original waveguide. Similarly, the centerline 2 of the combined waveguide is also shifted inward by 1.5 microns. Then in case the geometric centers of the combined first waveguide and the combined second waveguide are simultaneously shifted inwards by 1.5 microns, the modified coupling spacing d1 is 5 microns. According to the same method in Fig. 3(b), in Fig. 3(c), after using the femtosecond laser to directly write the spliced waveguide on the outside of the initial waveguide, the centerline of the combined waveguide is to the outside of the coupling region compared to the centerline of the initial waveguide Offset by 1.5 microns, the new coupling spacing d2 increases to 11 microns. From Figure 3(a), (b) and (c), it can be clearly concluded that after the coupling region is modified, the coupling spacing can be reduced and increased; and after the coupling region spacing is modified, its influence on the coupling coefficient However, it is necessary to test the degree of mode field overlap in the coupling region. The 810nm laser is fed into the input port of the directional coupler, and the single-mode analyzer is used to observe the mode field overlap in the coupling region; as shown in Figure 3(d), the mode fields of the two waveguides of the initial device overlap The degree is 44.1%, which means that the mode field overlap degree of the initial device in Figure 3(a) is 44.1%; After the device is directly written twice, the mode field overlap degree of the two new waveguides of the device increases to 56.7%, which means that the mode field overlap degree of the modified device in Figure 3(b) is 56.7%; combined with Analyzing together the conclusion that the coupling spacing d1 is smaller than the coupling spacing d0 in Figure 3(b), it can be known that after the coupling spacing becomes smaller, the degree of mode field overlap of the two coupled waveguides in the coupling area becomes larger. According to the coupling mode theory , so that the oscillation frequency of the light wave energy in the two waveguides becomes faster, which can increase the coupling coefficient; similarly, as shown in Figure 3(f), the femtosecond laser secondary direct writing strategy is used to perform secondary After the second direct writing, the mode field overlap degree of the two new waveguides of the device is reduced to 24.4%, that is to say, the mode field overlap degree of the modified device in Figure 3(c) is 24.4%. The same analysis can be It is known that the smaller the degree of mode field overlap, the smaller the coupling coefficient will be; in summary, the use of femtosecond laser secondary direct writing method can change the geometric center position of the waveguide, further change the coupling distance, and further affect the mode field The degree of overlap finally causes a change in the coupling coefficient. The above is a theoretical discussion on how the coupling coefficient can be reset by the invention. How to obtain the specific experimental value after the coupling coefficient is reset requires a more accurate test; next, split the beams of multiple groups of directional couplers on the chip Ratio measurement, and fitting the data to get the results shown in Figure 4; the abscissa indicates the coupling spacing of the device after the secondary direct writing, and the different values of the abscissa indicate the splicing prepared by the femtosecond laser secondary direct writing strategy The position and spacing of the waveguide and the original waveguide are different. 8 microns is the coupling spacing of the initial device. When the spliced waveguide is inside or outside the coupling area and the distance is 3 microns, the coupling spacing has a minimum value of 5 microns or a maximum value of 11 microns (previously Introduced in detail); the ordinate is the coupling coefficient. According to the data points in the figure, it is not difficult to find that when the spliced waveguide of the secondary direct writing is inside the coupling area, the coupling distance d1 becomes smaller and the coupling coefficient increases to a maximum of 2.1rad/mm; on the contrary, the coupling coefficient decreases Small, the minimum can be reduced to 0.47rad/mm; after analysis, the coupling coefficient of the initial device can be reset in the range of 0.47-2.1rad/mm; in summary, it proves that the initial device can achieve coupling after secondary direct writing Coefficient reset, that is, the present invention provides a method for resetting the coupling coefficient of a directional coupler by using femtosecond laser secondary direct writing.

实施例2一种利用飞秒激光二次直写重置定向耦合器耦合系数的应用:Embodiment 2 An application of using femtosecond laser secondary direct writing to reset the coupling coefficient of the directional coupler:

(1)制备待加工样品:同实施例1。(1) Prepare the sample to be processed: Same as Example 1.

(2)确定激光调平功率:同实施例1。(2) Determining laser leveling power: Same as Embodiment 1.

(3)调平样品:同实施例1。(3) Leveling sample: same as embodiment 1.

(4)确定起始加工位置:同实施例1。(4) Determining the initial processing position: same as embodiment 1.

(5)确定激光加工功率:同实施例1。(5) Determining laser processing power: same as embodiment 1.

(6)第一次直写初始器件:(6) Write the initial device directly for the first time:

初始器件是由耦合长度固定的一系列相同的定向耦合器构成,定向耦合器的宽度为127微米,器件总长度为25厘米,拐弯区的曲率半径为60毫米,初始耦合间距是8微米,器件的直写速度为60毫米每秒;根据实施例1中初始器件的分束比变化趋势可以得知,耦合长度为3.5毫米时,器件初始分束比约为50:50;根据上述的具体参数和要求,完成加工程序的制作;将写好的第一次加工程序加载到三维运动平台的软件中,点击运行,制备初始器件。The initial device is composed of a series of identical directional couplers with a fixed coupling length. The width of the directional couplers is 127 microns, the total length of the device is 25 cm, the radius of curvature of the turning area is 60 mm, and the initial coupling spacing is 8 microns. The device The direct writing speed is 60 millimeters per second; according to the variation trend of the beam splitting ratio of the initial device in Example 1, it can be known that when the coupling length is 3.5 mm, the initial beam splitting ratio of the device is about 50:50; according to the above specific parameters and requirements, complete the production of the processing program; load the written first processing program into the software of the three-dimensional motion platform, click to run, and prepare the initial device.

(7)第二次直写以实现器件分束比的重置:(7) The second direct writing to reset the splitting ratio of the device:

在实施例1中第一次制备的初始器件,耦合长度固定为3.5毫米、耦合间距固定为8微米时,定向耦合器的分束比约为50:50;利用上述加工参数在另外一个芯片上去重新加工定向耦合器时,理论上仍然会得到50:50的分束比,然而由于制造误差的存在,后续加工的定向耦合器的分束比尽管非常接近理想值,但多少会存在一些偏差,这种偏差经过多个器件的累积之后将会影响芯片的性能;为了解决上述问题,本发明提出了一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法来实现定向耦合器分束比的重置,使之回复到理论值;理论上,器件的分束比与耦合系数和耦合区耦合长度两个因素密切相关,并且分束比和上述两个参数之积满足正弦函数平方的变化趋势。然而,对于一个已经制备完成的器件来说,其耦合长度是无法再改变的,因此可以通过改变耦合系数的方式实现其分束比的重置。在实施例1中已经展示了重置定向耦合器耦合系数的方法,现在利用这种方法来实现定向耦合器分束比的重置;由实施例1可知,当对耦合区整体进行二次直写时,耦合系数为K1,而初始耦合系数为K0;现在设计了一种可以多次改变器件耦合系数地方式,如图5(a)所示,在耦合区内侧的其中一部分耦合区进行二次直写,修改的部分为K1,没有进行修改的部分仍然为K0;器件耦合区的耦合系数由K1和K0共同组成,那么器件的平均耦合系数K01将介于K0和K1之间,并且随着二次直写长度Ls地逐渐增加,K01会逐渐趋近于K1;根据上述耦合系数和分束比的关系,耦合系数每次被重置时都会引起器件分束比的重置,那么利用飞秒激光二次直写多次改变二次直写波导的长度,即可多次重置耦合系数K01,进一步实现器件分束比的多次重置;同理,如图5(b)所示,在耦合区外侧的其中一部分耦合区进行二次直写,被修改的部分为K2,没有进行修改的部分为K0;由于K2小于K0,那么器件的平均耦合系数K02将介于K2和K0之间,并且随着二次直写长度Ls地逐渐增加,K02会逐渐趋近于K2;同理,利用飞秒激光二次直写多次重置耦合系数K02,则可以实现器件分束比的多次重置。实验中,在耦合区内侧距离初始第一波导中轴线微米的位置进行不同长度的二次波导的直写,如图5(a)所示;在耦合区外侧距离初始第一波导微米进行不同长度的二次直写,如图5(b)所示;按照上述要求书写好加工程序,在软件中加载程序并开始运行。For the initial device prepared for the first time in Example 1, when the coupling length is fixed at 3.5 mm and the coupling spacing is fixed at 8 microns, the beam splitting ratio of the directional coupler is about 50:50; When the directional coupler is reprocessed, the beam splitting ratio of 50:50 can still be obtained in theory. However, due to the existence of manufacturing errors, although the beam splitting ratio of the subsequent processed directional coupler is very close to the ideal value, there will be some deviations. This deviation will affect the performance of the chip after the accumulation of multiple devices; in order to solve the above problems, the present invention proposes a method of resetting the coupling coefficient of the directional coupler by using femtosecond laser secondary direct writing to realize the directional coupler Reset the beam splitting ratio to restore it to the theoretical value; theoretically, the beam splitting ratio of the device is closely related to the coupling coefficient and the coupling length of the coupling region, and the product of the beam splitting ratio and the above two parameters satisfies the sine function squared trend. However, for a fabricated device, its coupling length cannot be changed, so the beam splitting ratio can be reset by changing the coupling coefficient. The method for resetting the coupling coefficient of the directional coupler has been shown in Embodiment 1, and now this method is used to realize the resetting of the beam splitting ratio of the directional coupler; When writing, the coupling coefficient is K1, and the initial coupling coefficient is K0; now a method that can change the device coupling coefficient multiple times is designed, as shown in Figure 5(a), a part of the coupling area inside the coupling area performs secondary The second direct writing, the modified part is K1, and the unmodified part is still K0; the coupling coefficient of the device coupling area is composed of K1 and K0, then the average coupling coefficient K01 of the device will be between K0 and K1, and with the With the gradual increase of the secondary direct writing length Ls, K01 will gradually approach K1; according to the above relationship between the coupling coefficient and the beam splitting ratio, every time the coupling coefficient is reset, the device beam splitting ratio will be reset, then using Femtosecond laser secondary direct writing can change the length of the secondary direct writing waveguide multiple times, and the coupling coefficient K01 can be reset multiple times, further realizing multiple resets of the device beam splitting ratio; similarly, as shown in Figure 5(b) It shows that the secondary direct writing is performed on a part of the coupling area outside the coupling area, the modified part is K2, and the unmodified part is K0; since K2 is less than K0, the average coupling coefficient K02 of the device will be between K2 and K0 Between, and as the secondary direct writing length Ls gradually increases, K02 will gradually approach K2; similarly, using femtosecond laser secondary direct writing to reset the coupling coefficient K02 multiple times, the device beam splitting ratio can be achieved multiple resets. In the experiment, the direct writing of secondary waveguides of different lengths is carried out at the position of micrometers away from the central axis of the initial first waveguide inside the coupling region, as shown in Figure 5(a); Secondary direct writing, as shown in Figure 5(b); write the processing program according to the above requirements, load the program in the software and start running.

(8)抛光待测试的样品:同实施例1。(8) Polishing the sample to be tested: Same as in Example 1.

(9)测试样品:(9) Test samples:

在步骤(7)中介绍了按照实施例1中的加工参数,器件的初始分束比理论上应该为50:50,但是由于制造误差的存在,其具体的分束比为46.1:53.9,如图6中C0点所示;为了实现器件分束比的修复,采用本发明的一种利用飞秒激光二次直写重置定向耦合器耦合系数的方法来进行实验;图6中圆形数据点和方形数据点分别代表在耦合区内侧和外侧二次直写后,器件分束比的变化趋势;在耦合区内侧和外侧二次直写以修改器件时,耦合系数得到重置,而分束比也被重置为新的数值;由图可知,一个已经被制备完成的器件经过飞秒激光二次直写重置其耦合系数之后,器件的分束比不仅可以修复为非常接近理想值50:50,甚至可以被重置为包括0:100和100:0等分束比在内的任意数值;这种利用飞秒激光二次直写重置定向耦合器耦合系数的方法在实现器件分束比重置的方面得到了很好的应用,为解决飞秒激光制备光量子芯片时存在的误差问题提供了一个很好的解决途径。In step (7), it is introduced that according to the processing parameters in Example 1, the initial beam splitting ratio of the device should be 50:50 in theory, but due to the existence of manufacturing errors, its specific beam splitting ratio is 46.1:53.9, such as Shown in C0 point among Fig. 6; In order to realize the repair of device beam splitting ratio, adopt a kind of method of the present invention to utilize femtosecond laser secondary direct writing to reset the coupling coefficient of directional coupler to carry out experiment; In Fig. 6 circular data The dots and square data points respectively represent the change trend of the splitting ratio of the device after the second direct writing inside and outside the coupling region; when the device is modified by the second direct writing inside and outside the coupling region, the coupling coefficient is reset, and the splitting ratio The beam ratio is also reset to a new value; it can be seen from the figure that after the coupling coefficient of a fabricated device is reset by femtosecond laser direct writing, the beam splitting ratio of the device can not only be restored to be very close to the ideal value 50:50, and can even be reset to any value including 0:100 and 100:0 equal beam splitting ratio; this method of resetting the coupling coefficient of the directional coupler by using femtosecond laser secondary direct writing is very important in realizing the device The aspect of resetting the beam splitting ratio has been well applied, which provides a good solution for solving the error problem existing in the preparation of optical quantum chips by femtosecond laser.

以上结合附图详细描述了本发明的优选实施方式,但是,本发明并不限于上述实施方式中的具体细节,在本发明的技术构思范围内,可以对本发明的技术方案进行多种简单变型,这些简单变型均属于本发明的保护范围。The preferred embodiment of the present invention has been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the specific details of the above embodiment, 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, These simple modifications all belong to the protection scope of the present invention.

另外需要说明的是,在上述具体实施方式中所描述的各个具体技术特征,在不矛盾的情况下,可以通过任何合适的方式进行组合,为了避免不必要的重复,本发明对各种可能的组合方式不再另行说明。In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way if there is no contradiction. The combination method will not be described separately.

此外,本发明的各种不同的实施方式之间也可以进行任意组合,只要其不违背本发明的思想,其同样应当视为本发明所公开的内容。In addition, various combinations of different embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the idea of the present invention, they should also be regarded as the disclosed content of the present invention.

Claims (7)

1. A method for resetting the coupling coefficient of a directional coupler by femtosecond laser secondary direct writing is characterized by comprising the following specific steps:
(1) Cleaning a glass sample;
(2) Building a laser processing light path and leveling a sample to be processed;
(3) The femtosecond laser second direct writing device;
the method comprises the following specific steps: firstly, closing the optical gate, and moving the glass sample in the step (1) to an initial processing position; then, rotating the half-wave plate and adjusting the laser power; finally, the control software directly runs the pre-written processing program, and respectively carries out secondary direct writing in the processing areas of the two waveguides in the coupling area; polishing the sample after the processing is finished to obtain two new waveguides with different coupling distances from the original waveguides; the processing area is an area which is 0-3 mu m above and below the central axis of the original waveguide;
wherein, the glass sample in the step (1) is a sample which is already finished with the first femtosecond laser processing and comprises an initial directional coupler; wherein the first femtosecond laser processing parameters are as follows: the scanning speed is 1mm/s-60mm/s; the laser power is 140mw-300mw, the length of the coupling region of the initial directional coupler is 0-20mm, and the coupling distance d 0 Is 8 to 15 mu m.
2. The method for resetting the coupling coefficient of the directional coupler by using femtosecond laser twice direct writing as set forth in claim 1, wherein the laser processing optical path in the step (2) is specifically: firstly, after the femtosecond laser is emitted by a femtosecond laser device, the laser power is adjusted after the femtosecond laser passes through a half-wave plate and a polarization beam splitter; then the laser beam is reflected by a first reflector, and the laser beam is expanded after passing through a first concave lens and a second convex lens; then, the expanded laser passes through a diaphragm to select laser beams with uniform energy distribution and the same spot diameter and size of the objective lens inlet; then the laser enters an objective lens after being reflected by a second reflector and a third reflector; then laser is focused on the surface or the interior of the sample through an objective lens; the sample is placed on a sample table, and the sample table is connected with an air floatation motion platform and can perform three-dimensional motion; the laser is converged on the surface or inside of the sample through the objective lens to reflect a part of the laser, the reflected laser passes through the third reflector after passing through the objective lens, is reflected by the fourth reflector, is converged through the third convex lens to form an image on the imaging camera, and the laser focus focused by the objective lens can be judged to be positioned on the surface or inside of the sample according to the appearance of light spots in the imaging camera.
3. The method for twice direct-writing resetting of the coupling coefficient of the directional coupler by using the femtosecond laser as claimed in claim 2, wherein the wavelength of the femtosecond laser is 500-1064nm, the pulse frequency is 100KHZ-2000KHz, the pulse width is 130fs-400fs, and the emergent power of the laser is 3W-20W; the objective lens multiple used is 20-100 times.
4. The method for resetting the coupling coefficient of the directional coupler by twice direct writing of the femtosecond laser as set forth in claim 1, wherein the method for determining the initial processing position in the step (3) is specifically as follows:
after leveling is finished, moving an XY axis of the air floatation motion platform to enable the objective lens to be positioned at the upper left corner of the sample; then moving the X axis once every 10-100μm until the cross-shaped reflection light spots in the imaging camera disappear, and proving that the objective lens is at the edge position of the X axis of the sample; similarly, moving the Y axis once at intervals of 10-100 mu m until the light spots disappear, and proving that the objective lens is located at the upper left corner of the sample; after the two steps, the laser focus is positioned at the uppermost left corner of the sample; at this time, the position of the upper left corner is taken as the initial processing position, and the motion platform software is set to zero the coordinates of the position, namely the (0,0,0) point.
5. The method for resetting the coupling coefficient of the directional coupler by the femtosecond laser secondary direct writing as set forth in claim 1, wherein the power used for the secondary direct writing in the step (3) is 140mw to 300mw, and the scanning speed is 1mm/s to 60mm/s; the laser focusing depth is 50um-1000um.
6. The method for twice direct-writing resetting of the coupling coefficient of the directional coupler by using the femtosecond laser as set forth in claim 1, wherein the polishing in the step (3) is specifically performed by the following steps: taking down the processed sample, and roughly polishing the side surface of the sample where the waveguide end surface is positioned by using abrasive paper, wherein the mesh number of the abrasive paper is 100-7000 meshes; then, placing the sample on a polishing machine containing polishing solution for fine polishing, wherein the granularity of the polishing solution is 50nm-14um, and the polishing time of each side is 40-300 minutes; and after the sample polishing is finished, wiping the sample clean and waiting for testing.
7. The use of the method of any one of claims 1-6 for resetting the coupling coefficient of the directional coupler using femtosecond laser direct writing twice in resetting the splitting ratio of the device.
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