Waveguide structure for generating complex coupling strength and design method thereof

Abstract

The invention discloses a waveguide structure for generating complex coupling strength and a design method thereof, and belongs to the technical field of integrated optoelectronic devices, and the method comprises the steps: designing a waveguide structure meeting the requirement of a complex coupling coefficient according to an expression of an equivalent coupling coefficient caused by an artificial standard field of a double-waveguide coupling system transmitted along a z direction; and according to the obtained waveguide function meeting the complex coupling coefficient requirement, constructing different waveguide structures, and carrying out modeling simulation on the constructed different waveguide structures. Artificial standard field modulation is introduced into a waveguide structure, and a direct coupling coefficient between optical waveguides is expanded from a real number domain to a complex number domain; the artificial standard field is used for carrying out geometric structure modulation on the optical system so as to influence photon transmission in the optical system; a proper optical waveguide structure is designed by using an equivalent coupling coefficient calculation formula, and a complex coupling coefficient is obtained, so that complex photon state conversion and light intensity regulation and control in the optical waveguide array can be realized by using the complex coupling coefficient.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated optoelectronic devices, and in particular relates to a waveguide structure for generating complex coupling strength and a design method thereof. Background Art

[0002] As the basic structure of integrated optoelectronic devices, the development of optical waveguide arrays is driving the progress of optoelectronic technology and providing a foundation for the realization of high-speed communications and complex optical systems. It plays a pivotal role in the realization of various functional devices such as lasers, modems, wavelength division multiplexers / demultiplexers, optical switches, etc. The coupling between optical waveguides is an important mechanism for realizing optical signal transmission and processing in optical systems, which enables the optical signal in one waveguide to be partially or completely transferred to another waveguide through the propagation and interference of light.

[0003] However, there are some limitations to the coupling between optical waveguides. The coupling coefficient can effectively regulate the properties of the photon state (including symmetry, light intensity distribution, etc.), but the coupling coefficient between common optical waveguides is generally limited to positive real numbers, which greatly limits the richness of photon state transmission in the waveguide. At the same time, the control method of the light intensity transmitted by different waveguides in the waveguide array is also relatively simple. There is no waveguide structure that can produce a complex coupling coefficient in the existing technology. Summary of the invention

[0004] In view of the deficiency that there is no waveguide structure capable of generating complex coupling coefficients in the prior art, the present invention provides a waveguide structure for generating complex coupling strength and a design method thereof; the present invention extends the direct coupling coefficient between optical waveguides from real numbers to complex numbers by introducing artificial gauge field modulation in the waveguide structure; the so-called artificial gauge field is to modulate the geometric structure of the optical system to affect the photon transmission in the optical system; by designing a suitable optical waveguide structure using an equivalent coupling coefficient calculation formula, the complex coupling coefficient is obtained, and then the complex coupling coefficient can be used to realize complex photon state conversion and light intensity control in the optical waveguide array. The method of the present invention is beneficial to further enrich the functions of the optical waveguide array, greatly enriches the regulation of the photon state in the waveguide, and can also better regulate the transmission of light in the waveguide, that is, the directional transmission of light can be realized by designing the complex coupling coefficient between the waveguides, thereby providing a basis for the design of various functional devices such as directional couplers and optical switches.

[0005] The present invention is achieved through the following technical solutions:

[0006] A design method for a waveguide structure for generating complex coupling strength comprises the following steps:

[0007] Step 1: According to the expression of the equivalent coupling coefficient caused by the artificial gauge field in the dual-waveguide coupling system transmitting along the z direction, design a waveguide structure that meets the complex coupling coefficient requirements; specifically, it includes the following contents:

[0008] The expression of the equivalent coupling coefficient of the dual-waveguide coupling system transmitted along the z direction caused by the artificial gauge field is as follows:

[0009]

[0010] in, Parameter κ eff is the calculated equivalent coupling coefficient between waveguides, parameter κ is the straight waveguide coupling coefficient, which is a positive real number, P is the period, which represents the length of one period of the function corresponding to the designed waveguide, d is the center distance between the two waveguides, λ is the wavelength of the light propagating in the waveguide, n0 is the ambient refractive index, Represents the partial derivative of the function x(z) with respect to the variable z.

[0011] Design the waveguide function expression x(z) of different structures, select the appropriate waveguide spacing, take the amplitude as the independent variable, and calculate the ratio of the equivalent coupling coefficient to the straight waveguide coupling coefficient corresponding to the waveguide spacing κ eff κ is the dependent variable. MATLAB is used to plot the curve of the equivalent coupling coefficient of the waveguide structure corresponding to different waveguide functions as a function of amplitude according to the above expression. eff The real and imaginary parts of κ are plotted separately, and the change curve is used to determine whether it is a waveguide function that meets the requirements of the complex coupling coefficient;

[0012] Step 2: Based on the waveguide function that meets the complex coupling coefficient requirements obtained in step 1, different waveguide structures are constructed, and modeling and simulation are performed on the constructed different waveguide structures. By setting up a monitor to detect the light intensity during the propagation of light in each waveguide structure, the waveguide structure with the smallest loss is selected and compared with the theoretical calculated value.

[0013] Furthermore, in step one, the different waveguide functions include symmetric and asymmetric functions in the form of sine and cosine, and symmetric and asymmetric functions in the form of broken lines, and corresponding waveguide structures are constructed respectively.

[0014] Furthermore, the function expression x(z) in the form of sine and cosine includes a function of the central position x of the dual waveguides of the symmetrical structure changing with the z period and a function of the central position x of the dual waveguides of the asymmetrical structure changing with the z period;

[0015] The function of the central position x of the dual waveguides of the symmetrical structure changing with the z period is:

[0016] The function of the central position x of the dual waveguides of the asymmetric structure changing with the z period is:

[0017]

[0018] Where A is the amplitude and P is the length of one period of the waveguide function.

[0019] Furthermore, the function expression x(z) in the form of a broken line includes a function of the central position x of the dual waveguides of the symmetrical structure changing with the z period and a function of the central position x of the dual waveguides of the asymmetrical structure changing with the z period;

[0020] The function of the central position x of the dual waveguides of the symmetrical structure changing with the z period is:

[0021] The function of the central position x of the dual waveguides of the asymmetric structure changing with the z period is:

[0022]

[0023] Furthermore, in step 1, when the imaginary part curve of the equivalent coupling coefficient corresponding to the waveguide function no longer always remains at 0, it is a waveguide function that meets the requirements of the complex coupling coefficient.

[0024] Furthermore, in step 2, the constructed waveguide structure is modeled and simulated using Rsoft simulation software.

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] 1. A design method for a waveguide structure for generating complex coupling strength of the present invention extends the coupling coefficient between waveguides to the complex domain through artificial gauge field, i.e., waveguide shape adjustment, and selects a suitable structure to minimize the loss of light propagating in the waveguide, thus enriching the means of photon state regulation and light intensity regulation in the waveguide array;

[0027] 2. The coupling coefficient is indirectly characterized by light intensity. When the coupling coefficient is a real number, the normalized light intensity of the light in the dual waveguides is 0.5. When the coupling coefficient is a complex number, the normalized intensity of light transmitted in the waveguide changes periodically with the light intensity of 0.5 as the dividing line, and the number of cycles is closely related to the size of the coupling coefficient. The larger the modulus of the complex coupling coefficient, the more cycles there are. The accuracy and rationality of the design are verified by comparing the consistency between the theoretical calculation results and the actual modeling simulation of the dual waveguide light intensity distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0029] Figure 1 The curve of the equivalent coupling coefficient corresponding to the sine-cosine structure design in the present invention as a function of the amplitude;

[0030] Among them: (a) The curve of the equivalent coupling coefficient of the sine-cosine symmetrical structure changing with the amplitude;

[0031] (b) Curve of the equivalent coupling coefficient of the asymmetric structure in the form of sine and cosine as a function of amplitude;

[0032] Figure 2 The curve of the equivalent coupling coefficient changing with the amplitude corresponding to the broken line structure design in the present invention;

[0033] Among them: (a) Curve of the equivalent coupling coefficient of the symmetrical structure in the form of a broken line versus the amplitude;

[0034] (b) Curve of the equivalent coupling coefficient of the asymmetric structure in the form of a broken line versus amplitude;

[0035] Figure 3 A schematic diagram of the optical waveguide structure that generates complex coupling in the present invention, including a function of the waveguide center position x changing with the z period and a single-period actual structure diagram;

[0036] Where: (a) is the function curve of the waveguide center position x changing with z, P represents one period and P = 2mm, A represents the amplitude and A = 5.5um;

[0037] (b) Schematic diagram of a single period of structure prepared in an optical glass chip using femtosecond laser direct writing technology;

[0038] Figure 4 A diagram showing the simulation results of the dual waveguide system constructed in the present invention;

[0039] Figure 5 Schematic diagram of the light intensity distribution (a) obtained by simulating the Rsoft waveguide constructed in the present invention and the light intensity distribution of the complex coupling coefficient calculated theoretically (b). DETAILED DESCRIPTION

[0040] In order to clearly and completely describe the technical solution and its specific working process of the present invention, the specific implementation methods of the present invention are as follows in conjunction with the accompanying drawings of the specification:

[0041] Example 1

[0042] This embodiment provides a design method for a waveguide structure for generating complex coupling strength. By designing the periodic bending change of the waveguide along the propagation direction, an artificial gauge field and a complex coupling coefficient are introduced, and a structure prepared in an optical glass chip using femtosecond laser direct writing technology is selected; the expression of the equivalent coupling coefficient caused by the artificial gauge field in the dual-waveguide coupling system transmitting along the z direction is considered: in, The parameters in the expression are period P = 2 mm, center spacing of the dual waveguides d = 7 um, wavelength λ = 0.81 um, and ambient refractive index n0 = 1.504. Substitute the parameters in the expression using Matlab, taking amplitude as the independent variable, and the equivalent coupling coefficient κ eff κ is the dependent variable, and the equivalent coupling coefficient of different structures is plotted against the amplitude, such as Figure 1 As shown. Among them, the symmetric function 1 of the dual waveguide center position x of the symmetrical structure changes with the z period is: The asymmetric function 2 of the double waveguide center position x of the asymmetric structure changes with the z period is:

[0043]

[0044] When the function corresponding to the structure is a symmetric function in the form of sine and cosine, the corresponding relationship between the equivalent coupling coefficient and the amplitude is as follows: Figure 1 As shown in (a), it can be seen that the equivalent coupling coefficient does not have an imaginary part, but changes positively and negatively with the amplitude. When the function corresponding to the structure is an asymmetric function, the corresponding equivalent coupling coefficient changes with the amplitude as shown in Figure 1 As shown in (b), the coupling coefficient has an imaginary part. It can be seen that the asymmetric function 2 is selected as the waveguide function that generates the complex coupling coefficient, and the actual waveguide structure is constructed based on it. For this waveguide structure, a 7-period waveguide with a total length of 1.4 cm is selected for modeling. According to the loss calculation formula The calculated loss of light propagating in the waveguide is 4.54 dB.

[0045] Example 2

[0046] This embodiment introduces a waveguide structure and a design method for generating complex coupling strength, by designing the periodic bending change of the waveguide along the propagation direction, introducing an artificial gauge field and a complex coupling coefficient. At this time, the symmetric function form and the asymmetric function form selected are both broken line forms. Considering the expression of the equivalent coupling coefficient caused by the artificial gauge field in the dual waveguide coupling system transmitted along the z direction, the parameter selection in the expression is consistent with that in Example 1. Substitute the parameters in the formula using Matlab, take the amplitude as the independent variable, and the equivalent coupling coefficient κ eff κ is the dependent variable, and the equivalent coupling coefficient of different structures is plotted against the amplitude, such as Figure 2 As shown. Among them, the function 3 of the change of the center position x of the dual waveguide of the symmetrical structure with the z period is:

[0047]

[0048] The function 4 of the center position x of the dual waveguide of the asymmetric structure changes with the z period is:

[0049]

[0050] When the function corresponding to the structure is a symmetrical function in the form of a broken line, the corresponding relationship between the equivalent coupling coefficient and the amplitude is as follows: Figure 2 As shown in (a), it can be seen that the equivalent coupling coefficient does not have an imaginary part, but changes positively and negatively with the amplitude. When the function corresponding to the structure is an asymmetric function, the corresponding equivalent coupling coefficient changes with the amplitude as shown in Figure 2 As shown in (b), the coupling coefficient has an imaginary part. It can be seen that the asymmetric function 4 is selected as the waveguide function that generates the complex coupling coefficient, and the actual waveguide structure is constructed based on it. For this waveguide structure, a 7-period waveguide with a total length of 1.4 cm is selected for modeling and the calculated loss of light propagating in the waveguide is 12.68 dB.

[0051] It can be seen that the asymmetric waveguide structure will cause light loss during propagation in the waveguide, and the asymmetric structure of the sine and cosine deformation function will have relatively small losses compared to other asymmetric structures including broken lines. Therefore, the asymmetric function 2 is selected as the waveguide function that generates the complex coupling coefficient and the waveguide structure is constructed.

[0052] Example 3

[0053] This embodiment introduces a method for constructing a waveguide model with an asymmetric function structure and verifying its coupling coefficient. According to the above discussion, an asymmetric function obtained by deforming the sine and cosine functions is selected because the loss of light transmitted in the waveguide in this form is small. The amplitude when the real part and the imaginary part of the equivalent coupling coefficient are close is selected, so the asymmetric waveguide amplitude A is selected to be 5.5um. Figure 3Taking the amplitude of 5.5um as an example, a schematic diagram of the function of the waveguide center position x changing with the z period in the asymmetric structure and a schematic diagram of the actual structure of a single period are given. The total length of the established simulation model is 3cm. Open the Rsoft simulation software, click Edit Globel Settings, select the Beampro module, select Fiber in 3D Struct Type, enter 0.81 in Free SpaceWavelength, enter 1.504 in Background Index, enter 0.004 in Component Delta-N, enter 6 in Component width, enter 6 in Component height, click Edit symbol and then click New Symbol, enter length as the name, and the expression is 2000. Click Accept Symbol. Click Seqment to model in the blank space of Rosft. Its basic structure is the same as Figure 2 Consistent, and repeat 15 cycles, the center distance between the two waveguides is 7. Click EditsPathways, select all waveguides on the left as path one, click New, repeat the operation to select all waveguides on the right as path two, and click OK. Click Edits Lanuch to build two Lanuchs, Lanuch1 and Lanuch2, and set the Power in Lanuch1 and Lanuch2 to 1. In order to monitor the intensity of light transmitted in the two waveguides, a monitor is needed. Click Edit Pathway Monitors, select Fiber Mode Power for Type, select 1 for Pathway, and set the monitor to monitor the light intensity of the first waveguide; in the same way, set the monitor for the light intensity of the second waveguide, and select 2 for Pathway. Click Simulation to simulate, and the simulation results are as follows Figure 4 as shown in .

[0054] The light intensity detected by the monitor of the dual waveguide system after modeling and simulation is different from the theoretically calculated light intensity. Figure 4 . The intensity information of the complex coupling coefficient can be characterized by the period of light intensity variation. The period of light intensity variation calculated theoretically using the complex coupling coefficient is the same as the period of the simulation result, which proves that the actual coupling intensity is basically consistent with the theoretical result. In addition, the reason why the light intensity monitored by the monitor in the simulation model gradually decreases is that in actual situations, there will be losses when light is transmitted in the asymmetric structure waveguide, which does not need to be considered in the theoretical calculation. The simulation results are basically consistent with the theoretical results in form and the number of periods is basically the same, which confirms the existence of the complex coupling coefficient and also shows the rationality of this verification method.

[0055] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0056] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0057] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for designing a waveguide structure for generating a complex coupling strength, characterized in that: The specific steps include: Step 1: According to the expression of the equivalent coupling coefficient caused by the artificial gauge field in the dual-waveguide coupling system transmitting along the z direction, design a waveguide structure that meets the complex coupling coefficient requirements; specifically, it includes the following contents: The expression of the equivalent coupling coefficient of the dual-waveguide coupling system transmitted along the z direction caused by the artificial gauge field is as follows: in, Parameter κ eff is the calculated equivalent coupling coefficient between waveguides, parameter κ is the straight waveguide coupling coefficient, which is a positive real number, P is the period, which represents the length of one period of the function corresponding to the designed waveguide, d is the center distance between the two waveguides, λ is the wavelength of the light propagating in the waveguide, n0 is the ambient refractive index, Represents the partial derivative of the function x(z) with respect to the variable z. Design the waveguide function expression x(z) of different structures, select the appropriate waveguide spacing, take the amplitude as the independent variable, and calculate the ratio of the equivalent coupling coefficient to the straight waveguide coupling coefficient corresponding to the waveguide spacing κ eff / κ is the dependent variable. MATLAB is used to plot the curve of the equivalent coupling coefficient of the waveguide structure corresponding to different waveguide functions as a function of amplitude according to the above expression. eff / The real and imaginary parts of κ are plotted separately, and the change curve is used to determine whether it is a waveguide function that meets the requirements of the complex coupling coefficient; Step 2: Based on the waveguide function that meets the complex coupling coefficient requirements obtained in step 1, different waveguide structures are constructed, and modeling and simulation are performed on the constructed different waveguide structures. By setting up a monitor to detect the light intensity during the propagation of light in each waveguide structure, the waveguide structure with the smallest loss is selected and compared with the theoretical calculated value.

2. A method for designing a waveguide structure for generating a complex coupling strength according to claim 1, characterized in that: In step 1, the different waveguide functions include symmetric and asymmetric functions in the form of sine and cosine, and symmetric and asymmetric functions in the form of broken lines, and corresponding waveguide structures are constructed respectively.

3. A method for designing a waveguide structure for generating a complex coupling strength according to claim 2, characterized in that: The function expression x(z) in the form of sine and cosine includes the function of the center position x of the dual waveguides of the symmetrical structure changing with the z period and the function of the center position x of the dual waveguides of the asymmetrical structure changing with the z period; The function of the central position x of the dual waveguides of the symmetrical structure changing with the z period is: The function of the central position x of the dual waveguides of the asymmetric structure changing with the z period is: Where A is the amplitude and P is the length of one period of the waveguide function.

4. A method for designing a waveguide structure for generating a complex coupling strength as claimed in claim 2, characterized in that: The function expression x(z) in the form of a broken line includes the function of the central position x of the dual waveguides of the symmetrical structure changing with the z period and the function of the central position x of the dual waveguides of the asymmetrical structure changing with the z period; The function of the central position x of the dual waveguides of the symmetrical structure changing with the z period is: The function of the central position x of the dual waveguides of the asymmetric structure changing with the z period is:

5. A method for designing a waveguide structure for generating a complex coupling strength according to claim 1, characterized in that: In step 1, when the imaginary part curve of the equivalent coupling coefficient corresponding to the waveguide function no longer always remains at 0, it is a waveguide function that meets the requirements of the complex coupling coefficient.

6. A method for designing a waveguide structure for generating a complex coupling strength according to claim 1, characterized in that: In step 2, the constructed waveguide structure is modeled and simulated using Rsoft simulation software.

7. A waveguide structure for generating a complex coupling strength, characterized in that: Obtained by the design method according to any one of claims 1 to 6.

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