A curved waveguide array structure optical chip and a preparation method thereof

Abstract

The application discloses a kind of curved waveguide array structure optical chip and preparation method thereof, applied to optical chip technical field: waveguide array structure and substrate;The waveguide array structure is prepared on the substrate;The waveguide array structure is a plurality of parallel composite curved track, the composite curved track is the circular arc bending that a plurality of periodic bends are formed, and the reconstruction period and reconstruction evolution process are discretely controlled by changing the period and amplitude of periodic bending in composite curved track.Light signal transmission evolution in waveguide array is controlled, and a new type of on-chip curved waveguide array structure that can realize light signal period reconstruction is proposed.The structure can realize the discrete regulation and control of light signal reconstruction period and reconstruction process, and is simple to prepare, has small bending curvature, is robust, and has potential application prospects in the field of light signal transmission and processing and super-resolution imaging.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical chip, more particularly to a curved waveguide array structure optical chip and a preparation method thereof. BACKGROUND

[0002] As the feature size of integrated circuit chip has approached its physical limit, the development of electrical chip is trapped in a bottleneck, thus failing to meet the demand of people for further miniaturization and improvement of information transmission performance. Recently, integrated optical chip has attracted extensive attention due to its high speed, large bandwidth, low loss and high integration, and is expected to become a promising development direction of high-capacity and high-speed information system. Integrated optical circuit is an important component of integrated optical chip, and has shown the potential of integrating passive and active optical devices in a chip in an expandable manner, and has important applications in the fields of optical communication, optical computing, optical sensing, astrophotonics and quantum information processing. The faithful transmission of optical signals in a high-density integrated optical circuit is the basis for realizing the above-mentioned applications. However, when the distance between waveguides in the integrated optical circuit is reduced to a certain extent, the mode in the waveguide will be coupled into the adjacent waveguide, causing crosstalk of the transmission signal, thereby limiting the improvement of the chip integration. At present, there are mainly two ways to realize the faithful transmission of optical signals, the first way is to reduce the crosstalk and confine the optical signal in a single waveguide, and the second way is to realize the periodic reconstruction of the optical signal to reproduce the initial optical signal after a specified transmission distance. The main method for realizing the reconstruction of optical signals in the integrated optical circuit in the prior art is to use a periodically curved optical waveguide array, and the optical signal satisfying the dynamic localization resonance condition can realize the periodic reconstruction of the optical signal. However, this method has the following defects, the change of the periodic curvature amplitude will destroy the periodic reconstruction of the optical signal, so this structure is not adjustable, the evolution process of the optical signal reconstruction cannot be controlled, and it is difficult to realize the wideband optical signal reconstruction, which is not conducive to practical application. Therefore, designing a structure-adjustable optical signal reconstruction device to realize flexible control of the optical signal transmission evolution process is the long-term goal pursued by researchers in the field of integrated optical technology. SUMMARY

[0003] Therefore, the present application provides a curved waveguide array structure optical chip and a preparation method thereof to solve the problems in the background art.

[0004] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0005] On the one hand, the present application discloses a curved waveguide array structure optical chip, comprising: a waveguide array structure and a substrate; the waveguide array structure is directly written on the substrate;

[0006] The waveguide array structure is a plurality of parallel composite curved tracks, and the composite curved track is an arc curve composed of a plurality of periodic curves.

[0007] Preferably, in the above-mentioned curved waveguide array structure optical chip, the reconstruction period and the reconstruction evolution process are discretely controlled by changing the period and the amplitude of the periodic bending in the composite bending trajectory.

[0008] Preferably, in the above-mentioned curved waveguide array structure optical chip, the composite bending trajectory is a circular arc bending superimposed with a plurality of periodic bendings.

[0009] Preferably, in the above-mentioned curved waveguide array structure optical chip, the substrate is a fused quartz substrate.

[0010] Preferably, in the above-mentioned curved waveguide array structure optical chip, the expression of the composite bending trajectory is: x(z) = x arc (z) + x cos (z).

[0011] wherein x arc (z) is a circular arc bending trajectory, x cos (z) = A cos(2πz / T) is a periodic cosine bending trajectory, A is a bending amplitude, and T is a bending period.

[0012] In another aspect, the present application discloses a preparation method of a curved waveguide array structure optical chip, and the specific steps are as follows:

[0013] The substrate is fixed on a three-dimensional moving platform, and the surface of the substrate is perpendicular to the incident direction of the femtosecond laser;

[0014] A single bending trajectory of the curved waveguide array is designed in the moving platform control software, and a plurality of parallel composite bending trajectories of the waveguide array are obtained by copying and translating the single bending trajectory a plurality of times; the composite bending trajectory is a circular arc bending composed of a plurality of periodic bendings;

[0015] The femtosecond laser is focused inside the substrate through an objective lens, and the three-dimensional moving platform is controlled to move the substrate along the designed processing trajectory, and the positive refractive index modification region induced in the substrate by the femtosecond laser pulse constitutes a waveguide core layer.

[0016] Preferably, in the above-mentioned preparation method of the curved waveguide array structure optical chip, the single bending trajectory processing trajectory is obtained by splicing a plurality of straight line segments, and the shorter the straight line segment, the closer the processing trajectory to the theoretical bending trajectory.

[0017] Compared with the prior art, the application provides a curved waveguide array structure optical chip and a preparation method thereof, which can regulate the reconstruction process of the optical signal without changing the optical signal reconstruction period, is simple to prepare, has small bending curvature, is robust, and has potential application prospects in the fields of optical signal transmission and processing and super-resolution imaging. The structure can realize periodical reconstruction of any complex optical signal; the function form and bending amplitude of the periodical bending term in the composite bending track of the structure do not affect the period of the optical signal reconstruction, so the structure is robust, and the periodical reconstruction of the optical signal can be realized by using a waveguide array with small bending curvature; the period and process of the optical signal reconstruction can be regulated separately; the structure is prepared in fused quartz by using a femtosecond laser direct writing method, has low cost, stable performance and high flexibility. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of the provided drawings.

[0019] Figure 1 Optical microscope photo of the curved waveguide array prepared by the present application;

[0020] Figure 2 Schematic diagram of preparing the waveguide array by using femtosecond laser direct writing technology;

[0021] Figure 3 Schematic diagram of the device for characterizing the transmission evolution of the light beam in the waveguide array;

[0022] Figure 4 Measurement result of the optical signal transmission when a single waveguide in the waveguide array is excited by incident light;

[0023] Figure 5 Measurement result of the optical signal transmission when multiple waveguides in the waveguide array are excited by incident light;

[0024] Figure 6 Variation of the optical signal reconstruction period with the cosine bending period in the composite bending track;

[0025] Figure 7 Variation of the FBO amplitude in the optical signal reconstruction process with the cosine bending amplitude in the composite bending track.

[0026] 11 - fused quartz substrate; 12 - waveguide; 13 - waveguide spacing; 14 - circular arc bending track; 15 - cosine bending period T; 16 - twice the cosine bending amplitude 2A;

[0027] 21—Femtosecond laser; 22—Femtosecond laser beam; 23—Objective lens; 24—3D moving platform;

[0028] 31—Helium-neon laser; 32—Helium-neon laser beam; 33—Second objective lens; 34—Second three-dimensional moving platform; 35—Objective lens; 36—Waveguide fluorescence; 37—CMOS camera; 38—Third three-dimensional moving platform. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] An embodiment of the present invention discloses a curved waveguide array structure optical chip, such as... Figure 1 As shown, it includes: a waveguide array structure and a substrate; the waveguide array structure is directly written on the substrate;

[0031] The waveguide array structure consists of multiple parallel composite bending trajectories, which are circular arcs composed of several periodic bends.

[0032] Specifically, such as Figure 1 The image shown is an optical microscope image of the curved waveguide array proposed in this invention, fabricated on a fused silica substrate 11 using femtosecond laser direct writing technology. The scale bar in the x-direction is 30 μm, and the scale bar in the z-direction is 10 mm. The total length of the curved waveguide 12 in the z-direction is 90 mm, and the spacing 13 between the curved waveguides is 16 μm. The bending trajectory of the curved waveguide is a composite trajectory composed of circular arc bending and periodic cosine bending; the radius of the circular arc bending 14 is 1108 mm, corresponding to an optical BO period TBO of 30 mm for a transmission beam at a wavelength of 633 nm; the bending period T15 and the bending amplitude 2A16 of the cosine bending are 22.5 mm and 27 μm, respectively.

[0033] To further optimize the above technical solution, the reconstruction period and reconstruction evolution process are controlled separately by changing the period and amplitude optical signals of the periodic bending in the composite bending trajectory.

[0034] To further optimize the above technical solution, the composite bending trajectory is formed by superimposing circular arc bending and several periodic bending.

[0035] To further optimize the above technical solution, the substrate is a fused silica substrate.

[0036] To further optimize the above technical solutions, the composite bending trajectory expression is: x(z) = x arc (z) + x cos (z);

[0037] Wherein x arc (z) is a circular arc bending trajectory, x cos (z) = A cos(2πz / T) is a periodic cosine bending trajectory, A is a bending amplitude, and T is a bending period.

[0038] In another aspect, the application discloses a preparation method of a curved waveguide array structure optical chip, and the specific steps are as follows:

[0039] Fix the substrate on the three-dimensional moving platform, and make the surface of the substrate perpendicular to the incident direction of the femtosecond laser;

[0040] Design a single bending trajectory of the curved waveguide array in the control software of the moving platform, copy and translate the single bending trajectory multiple times to obtain multiple parallel composite bending trajectories of the waveguide array; the composite bending trajectory is a circular arc bending composed of a plurality of periodic bendings.

[0041] Focus the femtosecond laser on the inside of the substrate through the objective lens, and control the three-dimensional moving platform to move the substrate along the designed machining trajectory; the positive refractive index modification region induced by the femtosecond laser pulse in the substrate constitutes a waveguide core layer.

[0042] To further optimize the above technical solutions, the single bending trajectory machining trajectory is obtained by splicing a plurality of straight line segments, and the shorter the straight line segment, the closer the machining trajectory to the theoretical bending trajectory.

[0043] Further, referring to Figure 2 , the machining device for preparing the curved waveguide array by the femtosecond laser direct writing has the following operation method:

[0044] Fix the fused quartz substrate 11 after end face grinding and polishing on the three-dimensional moving platform 24, and make the surface (x-z plane) of the fused quartz substrate perpendicular to the transmission direction of the femtosecond laser beam 22;

[0045] Design the machining trajectory of the curved waveguide array in the control software of the three-dimensional moving platform 24, including but not limited to the trajectory shown in Figure 1 .

[0046] Turn on the femtosecond laser 21, and focus the femtosecond laser beam 22 on the surface of the fused quartz substrate below through the objective lens 23;

[0047] Control the three-dimensional moving platform 24 to move the substrate 11 along the designed waveguide array machining trajectory, and continuously expose the fused quartz to the femtosecond laser in the substrate to induce modification, so that the positive refractive index modification region constitutes a waveguide core layer; after the movement is completed, the curved waveguide array structure can be obtained.

[0048] Further, see Figure 3 The measurement device characterizing the propagation evolution of a beam in a curved waveguide array is operated as follows:

[0049] The fused silica substrate 11 with the curved waveguide array structure processed above is placed on the second three-dimensional moving platform 34. The helium-neon laser 31 is turned on, and the helium-neon laser beam 32 with a wavelength of 633nm is focused after passing through the second objective lens 33. The second three-dimensional moving platform 34 is adjusted so that the helium-neon laser beam 32 is vertically focused on the waveguide section. At this time, the helium-neon laser beam 32 is coupled into the waveguide of the array.

[0050] When a 633nm helium-neon laser propagates in a fused silica waveguide fabricated by femtosecond laser direct writing, it excites a 650nm fluorescence 36. The fluorescence 36 is collected by a CMOS camera 37 through an objective lens 35. During the collection process, a filter is used to remove stray light at the 633nm wavelength, thereby obtaining a fluorescence image with a high signal-to-noise ratio. Since the intensity of the fluorescence 36 is proportional to the intensity of the transmitted light in the waveguide, the fluorescence image can be used to characterize the propagation distribution of light in the waveguide.

[0051] The CMOS camera 37 is fixed on the third three-dimensional moving platform 38. Moving the third three-dimensional moving platform 38 allows the CMOS camera 37 to scan the entire curved waveguide array. By stitching the scanned images in sequence, an image of the transmission evolution of light in the entire curved waveguide array can be obtained.

[0052] To more intuitively present the propagation evolution of light in a curved waveguide array, digital image processing can be performed on the stitched optical propagation evolution image. During processing, coordinate transformation is used to map the circular curvature in the optical propagation evolution image to straight lines, thus obtaining... Figure 4 and Figure 5 The experimental results are shown.

[0053] like Figure 4 The figure shows the measurement results of optical transmission evolution when a single waveguide in a bent waveguide array is excited by a helium-neon laser. The structural parameters of the bent waveguide array in the left figure are the same as those in the right figure. Figure 1 The only difference is the parameter of the cosine bending. The bending period T of the cosine bending is 10mm, and the bending amplitude A is 6μm. It can be seen that the optical signal reconstruction period T FBO It is 30mm; the right image is... Figure 1 The measurement results for the curved waveguide array shown are: T = 22.5 mm, A = 13.5 μm. It can be seen that the optical signal reconstruction period T... FBO It is 90mm.

[0054] like Figure 5The figure shows the measured results of the light transmission evolution when multiple waveguides in the Helium Neon laser excited curved waveguide array are excited. The curved waveguide arrays in the left and right figures are the same as those shown in the figure Figure 4 , and the periodic reconstruction of the incident light signal will also occur. The light signal reconstruction period T FBO in the left figure is still 30 mm; and the light signal reconstruction period T FBO in the right figure is still 90 mm.

[0055] As shown in the figure Figure 6 , a graph of the function relationship between the light signal reconstruction period T FBO , the Bloch oscillation period T BO , and the cosine curvature period T is shown. Theoretically, the light signal reconstruction period T FBO is the minimum extended common multiple of T BO and T, keeping T BO unchanged and changing the cosine curvature period T can change the light signal reconstruction period T FBO . The experimental measurement results are in good agreement with the theory.

[0056] As shown in the figure Figure 7 , a graph of the function relationship between the FBO amplitude A FBO , the cosine curvature period T, and the amplitude A is shown. Here, the FBO amplitude A FBO is defined as the mean square value of the excited waveguide when the light beam is transmitted in the z direction for a distance of T FBO / 2. The round dots and square dots shown in the figure are experimental measurement results, and the connecting lines between the round dots and square dots are theoretical calculation results. It can be seen that the experimental results and the theory are in good agreement. As can be seen from the figure, the size of the FBO amplitude A FBO during the light signal reconstruction process can be regulated by the amplitude A of the cosine period curvature.

[0057] The working principle of the present application is as follows:

[0058] When light is transmitted in the curved waveguide array, the bending of the curved waveguide array will generate an equivalent electric field acting on the transmitted light beam, so that the transmitted light beam can simulate the complex motion phenomenon of the electrons in the crystal lattice under the action of the applied electric field. Under the action of the equivalent superimposed electric field, the light beam will be periodically reconstructed when transmitted, and the signal reconstruction period is the minimum extended common multiple of the optical BO period T BO and the period curvature period T. This phenomenon is also called Floquet-Bloch oscillation (FBO). In addition, changing the amplitude A of the period curvature will not change the signal reconstruction period (FBO period T FBO ), but will affect the amplitude of the light signal evolution during the reconstruction process (FBO amplitude A FBO ). Therefore, the signal reconstruction period T FBOand the FBO amplitude A FBO control.

[0059] The various embodiments described in this specification are presented for the purpose of illustration and description. Each of the embodiments highlights a different aspect of the disclosure. The embodiments are not mutually exclusive, and some aspects of the embodiments can be combined with each other without departing from the scope of the disclosure. The embodiments disclosed herein are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations are possible in light of the disclosure.

[0060] The above description of disclosed embodiments is intended to be illustrative and not restrictive. Many embodiments of the present application will be apparent to those of ordinary skill in the art upon reviewing this description. The scope of the application should, therefore, be determined not with reference to the above description, but instead with reference to the appended claims, along with their full scope of equivalents. All publications and patent documents cited herein are incorporated by reference in their entirety for the purpose of explaining and defining the terms used herein.

Claims

1. An optical chip with a curved waveguide array structure, characterized in that, include: Waveguide array structure and substrate; the waveguide array structure is directly written on the substrate; The waveguide array structure consists of multiple parallel composite bending trajectories, and the composite bending trajectory is a circular arc composed of several periodic bends. The composite bending trajectory is formed by the superposition of circular arc bending and several periodic bending; The expression for the composite bending trajectory is: x ( z )= x arc ( z )+ x cos ( z ); in x arc (z) represents the trajectory of the circular arc. x cos (z)=Acos(2πz / T) is the periodic cosine bending trajectory, where A is the bending amplitude and T is the bending period.

2. The optical chip with a curved waveguide array structure according to claim 1, characterized in that, The reconstruction period and reconstruction evolution process of the optical signal are controlled by separately changing the period and amplitude of the periodic bending in the composite bending trajectory.

3. The optical chip with a bent waveguide array structure according to claim 1, characterized in that, The substrate is a fused silica substrate.

4. A method for fabricating an optical chip with a bent waveguide array structure, characterized in that, The method for fabricating the curved waveguide array structure optical chip according to any one of claims 1 to 3, wherein the specific steps of the fabrication method are as follows: The substrate is fixed on a three-dimensional moving platform with its surface perpendicular to the incident direction of the femtosecond laser. In the mobile platform control software, a single bending trajectory of a curved waveguide array is designed, and the single bending trajectory is copied and translated multiple times to obtain multiple parallel composite bending trajectories of the waveguide array; the composite bending trajectory is an arc bending composed of several periodic bends. A femtosecond laser is focused onto the interior of a substrate through an objective lens, while a three-dimensional moving platform is controlled to move the substrate along a designed processing trajectory. The positive refractive index modification region induced by the femtosecond laser pulse in the substrate constitutes the waveguide core layer.

5. The method for fabricating a curved waveguide array structure optical chip according to claim 4, characterized in that, Using the concept of infinite division, a single curved trajectory is obtained by splicing together multiple straight line segments. The shorter the straight line segments, the closer the processed trajectory is to the theoretical curved trajectory.

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