WO2022012434A1

WO2022012434A1 - High-density integrated optical waveguide

Info

Publication number: WO2022012434A1
Application number: PCT/CN2021/105519
Authority: WO
Inventors: 李涛; 宋万鸽; 祝世宁
Original assignee: 南京大学
Priority date: 2020-07-17
Filing date: 2021-07-09
Publication date: 2022-01-20
Also published as: CN111708116B; GB202204438D0; GB2602757A; CN111708116A

Abstract

A high-density integrated optical waveguide. The optical waveguide is provided on a waveguide substrate, and comprises a plurality of curved waveguides; a rectangular coordinate system is established by using the curving direction of the curved waveguides as a y-axis and using a propagation direction of light as an x-axis; on the basis of the rectangular coordinate system, the curved waveguides are periodically curved in the propagation direction according to the curving direction; the plurality of curved waveguides are arranged in parallel in the y-axis direction, and the curved waveguides are perpendicular to the y-axis direction, so as to form a curved waveguide array; and an optical waveguide signal transmission function or an optical waveguide directional coupling function of the optical waveguide is achieved by adjusting an coefficient of coupling between the curved waveguides. Such an optical waveguide avoids sensitivity and dependency of parameters such as a gap between waveguides and wavelength in the condition of high-density integration, and thus has structural robustness and broadband characteristics.

Description

A high-density integrated optical waveguide

This application claims the priority of the Chinese patent application with the application number 202010690095.X and the invention title "a high-density integrated optical waveguide" filed with the China Patent Office on July 17, 2020, the entire contents of which are incorporated herein by reference Applying.

technical field

The invention relates to the field of integrated photonics, in particular to a high-density integrated optical waveguide.

Background technique

With the rise of the modern Internet of Things, big data and other industries, the human society's demand for information processing such as higher speed, larger broadband network capacity, and stronger confidentiality has grown rapidly, and electrical chips have obviously reached a bottleneck stage. In the same way as the development idea of integrated circuits, two or more discrete optical components are integrated on a small substrate (below the centimeter level) to form an integrated optical chip system that realizes a certain function. The advantages of high-density integration are expected to become a promising development direction for large-capacity, high-speed information systems.

Silicon-on-insulator (SOI) has become one of the most widely used platforms in integrated photonics, and based on this, many photonic devices with a wide range of applications have been developed, such as waveguides, directional couplers, etc. However, in a high-density integrated chip, the existence of the diffraction limit increases the crosstalk between components, thus limiting the further improvement of the chip integration degree. On the other hand, these integrated photonic devices generally exhibit structure and wavelength sensitivity. Therefore, how to realize crosstalk-free transmission and broadband coupling of signals in a high-density integrated chip in a wide band is an urgent problem to be solved in the current chip industry.

Regarding low crosstalk transmission, there are currently two main methods. The first is to adjust the width of the waveguide to increase the mode mismatch to reduce the crosstalk. This method requires the width of the waveguide to be designed; the second is to adjust the width of the waveguide. Several auxiliary small waveguides are inserted between them to reduce the crosstalk by reducing the width of the waveguide mode. Since the size of the auxiliary waveguides is often small, it is also a challenge for large-scale processing. Regarding broadband coupling, there are currently two mainstream schemes. One is to introduce the compensation process of the Mach-Zehnder interferometer, which can adjust the phase on one arm of the interferometer through thermal effects, electro-optic effects, etc., so as to realize the dynamic modulation of the coupling distance. ; however, in large-scale integration, it is very power-hungry and has great technical difficulty, and is large in size. The other is to use adiabatic design, again, the size of this solution is also large. In addition, there are several other schemes, such as the use of surface plasmon design, this scheme can reduce the size of the device, but will introduce large metal losses. Asymmetric waveguide design can also be used. This solution has little loss and small size, but has limited improvement in bandwidth. Recently, erasable directional couplers have been reported based on the use of a localized laser annealing process, which does provide a solution for on-demand fabrication, however, it will inevitably introduce more losses and make the overall process more cumbersome . Based on the above demand background and technical status, it can be seen that under the current design paradigm of straight waveguide, some important performance indicators such as high-density integration, low crosstalk, high efficiency, robustness, and broadband are Satisfaction of performance will inevitably sacrifice some other performances, so that the current integrated chips dominated by straight waveguides cannot get rid of the sensitivity and dependence on parameters such as waveguide spacing and wavelength under high-density integration. How to achieve high-density integration, low crosstalk, high efficiency, robustness, and broadband integrated devices at the same time is a long-standing goal of researchers in the field of integrated optics technology.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a high-density integrated optical waveguide to solve the problem that the current integrated chip mainly based on straight waveguides cannot get rid of the sensitivity and dependence on parameters such as waveguide spacing and wavelength under high-density integration.

For achieving the above object, the present invention provides the following scheme:

A high-density integrated optical waveguide, the optical waveguide is arranged on a waveguide substrate, comprising: a plurality of curved waveguides;

A rectangular coordinate system is established with the bending direction of the curved waveguide as the y-axis and the propagation direction of the light as the x-axis; and based on the rectangular coordinate system, the curved waveguide is periodic along the propagation direction in the bending direction sexual bending;

A plurality of curved waveguides are arranged in parallel along the y-axis direction, and the curved waveguides are perpendicular to the y-axis direction to form a curved waveguide array; the optical waveguide is realized by adjusting the coupling coefficient between the curved waveguides Optical waveguide signal transmission function or optical waveguide directional coupling function.

Optionally, the coupling coefficient is adjusted according to the bending amplitude of the bending waveguide, the bending period, the incident wavelength of the incident light, the refractive index of the waveguide substrate, and the period interval of the bending waveguide.

Optionally, the expression of the coupling coefficient is: c=c ₀ J ₀ (4π ² An ₀ d/Pλ);

Wherein, c is the coupling coefficient between the curved waveguides; c ₀ is the coupling coefficient between straight waveguides, c ₀ >0, the straight waveguide is the first straight waveguide or the second straight waveguide; A is the bending amplitude; P is the bending period; d is the periodic interval of the waveguide arrangement, d=w+gap, w is the width of the waveguide, and the gap is the spacing between the waveguides; λ is the incident wavelength; n ₀ is the substrate refractive index.

Optionally, let J ₀ (4π ² An ₀ d/Pλ) be less than 0, the coupling coefficient is less than 0, and the optical waveguide further includes: a first straight waveguide array and a second straight waveguide array;

The first straight waveguide array includes a plurality of first straight waveguides arranged in parallel along the y-axis; the second straight waveguide array includes a plurality of second straight waveguides arranged in parallel along the y-axis; the The coupling coefficient between the first straight waveguides is equal to the coupling coefficient between the second straight waveguides, and the coupling coefficient between the first straight waveguides and the coupling coefficient between the second straight waveguides are both greater than 0;

The output end of the first straight waveguide array is butted with the input end of the curved waveguide array, the output end of the curved waveguide array is butted with the input end of the second straight waveguide array, the first straight waveguide array, The curved waveguide array and the second straight waveguide array form a three-level cascade structure; the incident light enters the three-level cascade structure from the input end of the first straight waveguide array, and the incident light is in the three-level cascade structure. The first straight waveguide array diverges due to coupling, and the curved waveguide array re-converges the divergent light to the second straight waveguide array due to negative coupling. The negative coupling strength is matched to realize the optical waveguide signal transmission function of broadband and low crosstalk.

Optionally, the optical waveguide includes a plurality of the three-stage cascade structures; and the plurality of the three-stage cascade structures are arranged in parallel in the x-axis direction.

Optionally, let J ₀ (4π ² An ₀ d/Pλ) be equal to 0, the coupling coefficient is equal to 0, the incident light is transmitted in the curved waveguide array, and the optical waveguide signal transmission function of broadband and low crosstalk is realized.

Optionally, let J ₀ (4π ² An ₀ d/Pλ) be less than 0, the coupling coefficient is less than 0, and the curved coupling array specifically includes two curved waveguides; the two curved waveguides are along the y-axis direction Arranged in parallel to realize the directional coupling function of optical waveguides in a wide band.

Optionally, the periodic bending expression of the curved waveguide is:

Wherein, y(x) is the periodic bending function of the bending waveguide; A is the bending amplitude; P is the bending period;

It is the initial phase of bending.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the present invention provides a high-density integrated optical waveguide, a plurality of curved waveguides are arranged on a waveguide substrate to form a curved waveguide array, and the curved waveguides are adjusted by adjusting the curved waveguides. The coupling coefficient between the waveguides realizes the optical waveguide signal transmission function or the optical waveguide directional coupling function of the optical waveguides.

The invention utilizes the regulation of the coupling by the curved waveguide, realizes the broadband low crosstalk transmission and robust coupling under high-density integration, exhibits quite good robustness to structural deviation and wavelength change, and improves the processing error tolerance, thereby Save processing costs.

At the same time, the optical waveguide provided by the present invention does not require further adjustment and correction after processing, thereby avoiding additional energy consumption and loss; it is fully compatible with the current manufacturing process, does not bring additional processing difficulties, and is easy to scale Production requires low production accuracy.

Instruction drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings required in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the present invention. In the embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without any creative effort.

1 is a schematic diagram of a cascaded positive-coupling straight waveguide array and a negative-coupling curved waveguide array for realizing broadband low-crosstalk optical waveguide transmission;

2 is a schematic diagram of a zero-coupling curved waveguide array for realizing broadband low-crosstalk optical waveguide transmission;

3 is a schematic diagram of a negatively coupled curved waveguide for realizing directional coupling of broadband robust optical waveguides;

4 is a schematic diagram of a straight waveguide array of N waveguides and a curved waveguide array of N waveguides;

5 is a schematic diagram of a three-stage cascade structure formed by cascading two straight waveguide arrays and a curved waveguide array together;

Figure 6 shows the initial phase of the curved waveguide

and the first phase

Schematic diagram of connection with straight waveguide in two cases;

FIG. 7 is a graph showing the variation of the coupling coefficient c between the waveguides with wavelength in the case of different bending amplitudes A=0 and A=0.74 μm in the cascade structure;

8 is a graph showing the relationship between the transmission efficiency of the transmission port and the crosstalk port as a function of wavelength when N=2 in the cascade structure;

FIG. 9 is a schematic diagram of the propagation of the optical field in the waveguide at 100 μm and 200 μm under the corresponding different wavelengths in the cascade structure;

10 is a graph showing the relationship between the transmission efficiency of the transmission port and the crosstalk port as a function of wavelength when N=7 in the cascade structure;

FIG. 11 is a schematic diagram of the propagation of the corresponding optical field at different wavelengths by 100 μm in the cascade structure;

Figure 12 shows the relationship between the coupling coefficient c between the waveguides as a function of wavelength when the bending amplitude A=0.51 μm for a zero-coupling curved waveguide;

Fig. 13 is a graph of the relationship between the transmission efficiency of the transmission port and the crosstalk port as a function of wavelength in the case of the zero-coupling curved waveguide N=2;

Fig. 14 is a schematic diagram of the propagation of the optical field in the waveguide of 100 μm at different wavelengths corresponding to the zero-coupling curved waveguide;

Fig. 15 is a graph of the relationship between the transmission efficiency of the transmission port and the crosstalk port as a function of wavelength in the case of the zero-coupling curved waveguide N=7;

Fig. 16 is a schematic diagram of the propagation of the corresponding optical field of 100 μm under different wavelengths of the zero-coupling curved waveguide;

17 is a graph showing the relationship between the coupling coefficient c between the waveguides as a function of wavelength under the condition of different bending amplitudes A;

Figure 18 is a graph showing the variation of coupling degree with wavelength;

Figure 19 is a graph showing the variation of isolation with wavelength;

Figure 20 is a graph showing the change of directivity with wavelength;

Figure 21 is a schematic diagram of the propagation of the optical field in the waveguide under different wavelengths of the straight waveguide;

22 is a schematic diagram of the propagation of the optical field in the waveguide under different wavelengths of the curved waveguide;

FIG. 23 is a graph showing the relationship between the coupling coefficient c between the waveguides and the spacing between the waveguides under the condition of different bending amplitudes A;

Figure 24 is a graph showing the variation of coupling degree with the spacing of the waveguides;

FIG. 25 is a graph showing the variation of isolation with the spacing of the waveguides;

FIG. 26 is a graph showing the change of directivity with the spacing of the waveguides;

Fig. 27 is a graph showing the propagation of the optical field in the waveguide under different waveguide spacings of the curved waveguide;

FIG. 28 is a graph showing the propagation of the optical field in the waveguide under different waveguide spacings of the curved waveguide.

Symbol explanation: 1 is a cascade structure of straight waveguide and curved waveguide (including multiple cascades); 2 is a curved waveguide array with zero coupling; 3 is two curved waveguides.

detailed description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The purpose of the present invention is to provide a high-density integrated optical waveguide, which adopts the positive and negative coupling cascades brought by straight waveguides and curved waveguides to realize broadband low-crosstalk optical waveguide transmission; To achieve broadband low-crosstalk optical waveguide transmission, Figure 2 is a schematic diagram of a zero-coupling curved waveguide array for broadband low-crosstalk optical waveguide transmission; the negative coupling brought by the curved waveguide is used for the stability of structure and wavelength to achieve robustness And broadband optical waveguide directional coupling, as shown in FIG. 3 is a schematic diagram of a negatively coupled curved waveguide for realizing broadband robust optical waveguide directional coupling.

In order to make the above objects, features and advantages of the present invention more clearly understood, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

A high-density integrated optical waveguide, the optical waveguide is arranged on a waveguide substrate, comprising: a plurality of curved waveguides; a rectangular coordinate system is established with the bending direction of the curved waveguide as the y-axis and the propagation direction of the light as the x-axis ; and based on the Cartesian coordinate system, the curved waveguide is periodically bent in the bending direction along the propagation direction; a plurality of curved waveguides are arranged in parallel along the y-axis direction, and the curved waveguide is parallel to the direction of the y-axis. The y-axis directions are perpendicular to each other to form a curved waveguide array; the optical waveguide signal transmission function or the optical waveguide directional coupling function of the optical waveguide is realized by adjusting the coupling coefficient between the curved waveguides.

The curved waveguide is periodically curved along the propagation direction y in the x direction, for example, the curved shape is a trigonometric function:

where A is the bending amplitude, P is the bending period,

is the initial phase of bending, representing the initial state of the curved waveguide, as shown in Figure 6, showing the initial phase of the curved waveguide

and the first phase

Schematic diagram of the connection with the straight waveguide in both cases. N is the total number of waveguides in the waveguide array, indicating the number of signal paths to be transmitted; M is the number of cascades, and M can be an integer greater than 1. If it is a three-level cascade structure, M=3; d is the period of the waveguide arrangement Gap; w is the width of the waveguide, gap is the distance between the waveguides, satisfying d=w+gap; λ is the incident wavelength, n is the refractive index of the waveguide, n ₀ is the refractive index of the substrate, and c is the coupling coefficient between the curved waveguides , c is related to _{parameters such as A, n 0} , d, P and λ.

The coupling coefficient is adjusted according to the bending amplitude of the bending waveguide, the bending period, the incident wavelength of the incident light, the refractive index of the waveguide substrate, and the period interval of the bending waveguide.

The expression of the coupling coefficient is: c=c ₀ J ₀ (4π ² An ₀ d/Pλ); wherein, c is the coupling coefficient between the curved waveguides; c ₀ is the coupling coefficient between the straight waveguides, c ₀ >0, the straight waveguide is the first straight waveguide or the second straight waveguide; A is the bending amplitude; P is the bending period; d is the periodic interval of the waveguide arrangement, d=w+gap, w is the waveguide width, gap is the spacing between the waveguides; λ is the incident wavelength; n ₀ is the substrate refractive index.

As an optional implementation manner, the optical waveguide further includes: a first straight waveguide array and a second straight waveguide array; the first straight waveguide array includes a plurality of first straight waveguides arranged in parallel along the y-axis a waveguide; the second straight waveguide array includes a plurality of second straight waveguides arranged in parallel along the y-axis; the coupling coefficient between the first straight waveguides is equal to the coupling coefficient between the second straight waveguides, And the coupling coefficient between the first straight waveguides and the coupling coefficient between the second straight waveguides are both greater than 0; the output end of the first straight waveguide array is docked with the input end of the curved waveguide array, so The output end of the curved waveguide array is butted with the input end of the second straight waveguide array, and the first straight waveguide array, the curved waveguide array and the second straight waveguide array form a three-stage cascade structure; the The incident light enters the three-stage cascade structure from the input end of the first straight waveguide array, the incident light diverges due to coupling in the first straight waveguide array, and the curved waveguide array will diverge due to negative coupling The light is re-converged to the second straight waveguide array, since the positive coupling strength in the three-stage cascade structure matches the negative coupling strength, the optical waveguide signal transmission function of broadband and low crosstalk is realized.

The optical waveguide includes a plurality of the three-stage cascade structures; and the plurality of the three-stage cascade structures are arranged in parallel in the x-axis direction.

The formation method of the structure is described in detail below by taking the three-level structure as an example: First, N straight waveguides are arranged in parallel along the y direction to form a straight waveguide array structure, as shown in Figure 4, and then the straight waveguides in the straight waveguide array are arranged The waveguide is bent to form a curved waveguide array structure, and then the two straight waveguide arrays and one curved waveguide array are butted along the x-direction to form a three-level cascade structure as shown in FIG. 5 . Other multi-level cascade structures can be completed by connecting multiple straight waveguide arrays and curved waveguide arrays. Each waveguide in the waveguide array is a channel for transmitting optical signals. Ideally, the optical signal entering from a certain waveguide can be output from the waveguide at the output end, while the waveguide without optical signal input is at the output end. There will be no optical signal output. However, due to the evanescent wave coupling effect between the waveguides, the signals will interact with each other. Sometimes a waveguide without signal input will also have a signal at the output, which is a crosstalk signal, and the smaller the waveguide array spacing, the more serious this crosstalk phenomenon will be, especially in the case of high-density integration (d ~ λ/ 2). Here, by introducing the curved waveguide, the crosstalk phenomenon generated in the straight waveguide structure can be eliminated. At the same time, because this effect is broadband, low crosstalk or no crosstalk transmission under high-density integration can be realized in the broadband wavelength range. .

By bending the waveguides, the coupling between the waveguides can be effectively reduced. If the waveguide system satisfies the conditions for weak coupling of weak guides, the relationship between the coupling coefficient c and other parameters between the curved waveguides can be approximately written as: c= c ₀ J ₀ (4π ² An ₀ d/Pλ), where c ₀ is the coupling coefficient between straight waveguides, generally c ₀ >0; J ₀ is the lowest-order Bessel function of the first kind. Therefore, when A, P, d, λ, and n ₀ take appropriate parameters, the function J ₀ (4π ² An ₀ d/Pλ) can be made to be less than 0, so the coupling coefficient c between the waveguides can take a negative value. It is worth noting that under the condition of high-density integration, the condition of weak conduction if coupled will not be satisfied, so the coupling coefficient between curved waveguides will not strictly satisfy the formula c=c ₀ J ₀ (4π ² An ₀ d/ Pλ), but in a more complex form. However, the negative coupling effect caused by the curved waveguide still exists, and the relationship between the coupling coefficient between the curved waveguides and some of the parameters can be obtained by means of simulation, as shown in Figure 7.

In order to realize the transmission of multi-channel signals, it is first considered to arrange N straight waveguides in parallel along the y direction to form a straight waveguide array. gap, as shown in Fig. 1, the coupling coefficient c ₀ between straight waveguides is greater than zero. Consider another waveguide array. The parameters of this waveguide array are exactly the same as those of the straight waveguide array just described, but each waveguide is bent to obtain a curved waveguide array. The coupling coefficient in this array is a negative number. Then, several of the curved waveguide arrays and straight waveguide arrays are butted together in the propagation direction (x direction) to form a multi-level cascade structure, as shown in FIG. 1 . Light diverges due to coupling in a straight waveguide, but converges due to negative coupling in a curved waveguide, so the light will re-converge to the waveguide where the incident port is located at a specific propagation distance to complete the signal transmission function. At the same time, since the strength of the positive and negative coupling is kept matched in a long wavelength range, the low crosstalk transmission function in a wide band can be realized.

Considering the general case, that is, M waveguide arrays are cascaded in M stages in the propagation direction x, and the length and coupling coefficient of the i-th waveguide array are L _i and c _i , respectively. In general, _ci can be written as a function _ci (λ,x) of wavelength λ and propagation distance x. The total length of the device is L=L ₁ +L ₂ +...+L _i +..., with x=0 as the input end, then x=L as the output end, the N waveguides at the input end can input N different signals arbitrarily.

If:

Then the light will perfectly obtain the N signals at the output end x=L. Perfect means that the signal at the output end x=L is completely consistent with the signal strength and phase distribution at the input end x=0, thus completing the signal transmission. Features. For convenience, let the coupling coefficient not change with the propagation x, the above formula can be simplified as

c ₁ (λ)L ₁ +c ₂ (λ)L ₂ +…+c _i (λ)L _i +…=0, (2)

In general, the coupling coefficient between dielectric straight waveguides is positive, and the magnitude of the coupling varies with wavelength. Therefore, to satisfy equation (2), one way is that there are both positive coupling and negative coupling in the cascade structure; the other way is that all coupling coefficients are equal to zero. In addition, if the transmission function of broadband is to be realized, then (2) must still be satisfied or approximately satisfied in a certain band.

In order to obtain zero coupling and negative coupling, the curved waveguide is analytically modeled as follows:

A curved waveguide is periodically bent in the y direction along the propagation direction x, for example, a bend in the shape of a trigonometric function:

where A is the bending amplitude, P is the bending period,

For the curved initial phase.

The value of , has little effect on the result, so let

is equal to π (or 0), as shown in Figure 6. Because the slope of the bending is zero at this time, the light can enter the bending waveguide system without loss.

By bending the waveguides, the coupling between the waveguides can be effectively reduced, and even zero or negative values can be taken. At this time, the positive-coupling straight waveguides and the negatively-coupling curved waveguides are cascaded together to form a cascade structure. In straight waveguides, it diverges due to coupling, and in curved waveguides, it converges due to negative coupling, thereby realizing the transmission function. Alternatively, the transmission function can also be achieved with zero coupling.

When A, P, d, λ, and n ₀ take appropriate parameters, Equation (2) can be satisfied in a certain band. For the positive and negative coupling cascade scheme or the zero coupling scheme, broadband optical waveguide transmission function can be realized. .

As an optional implementation manner, the incident light is transmitted in the curved waveguide array, so as to realize the optical waveguide signal transmission function of broadband and low crosstalk.

Arrange N curved waveguides in parallel along the y direction. By bending the waveguides, the coupling effect between the waveguides can be eliminated. The optical signal entering from a certain waveguide will not be coupled to the adjacent waveguides, thereby eliminating crosstalk and achieving low crosstalk. transmission. At the same time, this effect is broadband, so the low crosstalk transmission function can be realized in the broadband wavelength range.

By bending the waveguides, the coupling between the waveguides can be effectively reduced. If the waveguide system satisfies the conditions for weak coupling of weak guides, the relationship between the coupling coefficient c and other parameters between the curved waveguides can be approximately written as: c= c ₀ J ₀ (4π ² An ₀ d/Pλ), where c ₀ is the coupling coefficient between straight waveguides; J ₀ is the lowest-order Bessel function of the first kind. Therefore, when A, P, d, λ, and n ₀ take appropriate parameters, the function J ₀ (4π ² An ₀ d/Pλ) can be made to be 0, so the coupling coefficient c between the waveguides can be zero. It is worth noting that under the condition of high-density integration, the condition of weak conduction if coupled will not be satisfied, so the coupling coefficient between curved waveguides will not strictly satisfy the formula c=c ₀ J ₀ (4π ² An ₀ d /Pλ), but in a more complex form. However, the effect of zero coupling caused by the curved waveguide still exists, and the relationship between the coupling coefficient between the curved waveguides and some of the parameters can be obtained by means of simulation, as shown in Figure 12.

In order to realize the transmission of multi-channel signals, it is first considered to arrange N bending waveguides in parallel along the y direction to form a single bending waveguide array. The coupling coefficient in this array is zero, and can be approximately equal to zero in a certain band range. Light entering the waveguide array with zero coupling coefficient will not be coupled into adjacent waveguides, so a single curved waveguide array structure can also realize the function of low crosstalk transmission in a wide band.

As an optional implementation manner, let J ₀ (4π ² An ₀ d/Pλ) be less than 0, the coupling coefficient is less than 0, and the curved coupling array specifically includes two of the curved waveguides; The waveguides are arranged in parallel along the y-axis direction to realize the directional coupling function of the optical waveguides in a wide band.

This structure is formed by arranging two curved waveguides in parallel along the y direction. By bending the waveguides, a broadband coupling effect between the waveguides can be achieved, that is, the optical signal entering from a certain waveguide can be in the broadband wavelength range. It is stably coupled to the adjacent waveguide to realize the broadband directional coupling function.

By bending the waveguides, the coupling between the waveguides can be effectively reduced. If the waveguide system satisfies the condition of weak coupling of weak guides, the relationship between the coupling coefficient c between the curved waveguides and other parameters can be approximately written as: c= c ₀ J ₀ (4π ² An ₀ d/Pλ), where c ₀ is the coupling coefficient between straight waveguides; J ₀ is the lowest-order Bessel function of the first kind. Therefore, when A, P, d, λ, and n ₀ take appropriate parameters, the function J ₀ (4π ² An ₀ d/Pλ) can be made to be less than 0, so the coupling coefficient c between the waveguides can take a negative number. It is worth noting that under the condition of high-density integration, the condition of weak conduction if coupled will not be satisfied, so the coupling coefficient between curved waveguides will not strictly satisfy the formula c=c ₀ J ₀ (4π ² An ₀ d /Pλ), but in a more complex form. However, the effect of zero coupling caused by the curved waveguide still exists, and the relationship between the coupling coefficient between the curved waveguides and some of the parameters can be obtained by means of simulation, as shown in Figure 17. Unlike the positive coupling between straight waveguides, which is sensitive to wavelength and structural parameters, this negative coupling can maintain a small change over a long wavelength range and a wide range of waveguide spacing variations. Therefore, two curved waveguide structures are formed by arranging the two curved waveguides together in parallel along the y-direction. The coupling effect of light between two curved waveguides can realize the directional coupling function of the waveguide, and maintain the directional coupling function in a very long wavelength band and a large change in the waveguide spacing.

After the negative coupling is realized by bending the waveguide, it is found that when A, P, d, λ, and n ₀ take appropriate parameters, the coupling between the waveguides remains small in a long wavelength range and a large range of changes in the waveguide spacing. change, that is

c(λ+Δλ)≈c(λ), (4)

c(gap+Δgap)≈c(gap), (5)

Among them, Δλ and Δgap are the changes in wavelength and waveguide spacing, respectively.

Generally, under the condition of high-density integration, the coupling in equations (4) and (5) takes a negative number. That is, stable negative coupling properties can be maintained in a large wavelength band or a large structural parameter variation range. At this time, a broadband optical waveguide directional coupling function with structural robustness can be realized.

It is worth noting that the previous solution to achieve optical transmission with zero coupling was obtained by formula (2). But in fact, the zero-coupling scheme can also be considered as a special case of (4) and (5), that is, when A, P, d, λ, and n ₀ take appropriate parameters, it can make

c(λ+Δλ)≈c(λ)=0, (6)

c(gap+Δgap)≈c(gap)=0, (7)

The stable zero-coupling property can be maintained in a large waveband or a large range of structural parameters. At this time, a broadband optical waveguide transmission function with structural robustness can be realized.

In a word, bending the waveguide can realize the flexible regulation of the coupling effect between the waveguides. By controlling the parameters of the bending, the above-mentioned different functions such as broadband low crosstalk transmission and broadband directional coupling can be realized.

For a better understanding of the present invention, further explanations are given below in conjunction with the examples.

Without loss of generality, in this embodiment, a curved waveguide is designed for a silicon waveguide on an alumina substrate in the near-infrared wavelength band in an air environment, and the invention is also applicable to other wavelength bands and material systems. As shown in Figure 1, the optical waveguide transmission technology is based on two schemes: (1) Cascade structure of straight waveguides and curved waveguides (including multiple cascades), where a straight waveguide array is used to connect the curved waveguide array to the straight waveguide array Take the three-level cascade structure as an example; (2) a single curved waveguide array structure. The optical waveguide directional coupling technology is based on (3) two curved waveguides. The width w of the silicon waveguide is 400 nm, and the period of bending modulation is P=10 μm. In this example, COMSOL Multiphysics is used to simulate and test the device performance.

Figures 7-11 show the simulation results of cascading straight waveguides and curved waveguides to achieve broadband low crosstalk transmission. During the simulation, the fundamental mode TE mode supported by the waveguide is used. In the case of d=760nm, the coupling situation under different bending amplitudes A and different wavelengths λ is simulated. When A=0, the curved waveguide degenerates into a straight waveguide. It can be seen that in the case of straight waveguides, as the wavelength increases, the coupling coefficient between the two waveguides gradually increases. When A gradually increases from 0 to 0.74 μm, that is, the straight waveguide becomes a curved waveguide, it is found that the coupling coefficient between the two waveguides becomes negative, and the absolute value of the coupling coefficient at this time is similar to that of the straight waveguide. are equal, and this equality can be maintained over a very long wavelength band, that is, c ^A=0 (λ)≈-c ^{A=0.74 μm} (λ). Since the widths of the straight waveguide and the curved waveguide are the same, w=400 nm, they can be cascaded together. Considering the three-stage cascade structure of straight waveguide-curved waveguide-straight waveguide, when the total length is L, the length of the two straight waveguides is selected as L/4, and the length of the middle curved waveguide is selected as L/2, so that (2 ) can be satisfied. Figure 8 calculates the transmission and crosstalk as a function of wavelength for two waveguides with N=2 and different lengths L (L=100 μm, 200 μm). It can be seen that the device (L=100μm) can maintain high transmission efficiency (>-0.1dB) and low crosstalk (<-20dB) in a very long wavelength range (>200nm). If the length increases to 200μm, although the crosstalk increases, it can still maintain a high transmission efficiency (>-0.19dB) in a very long wavelength band (>200nm). Figure 9 shows the propagation of the light field in the waveguide with different wavelengths of 100 μm and 200 μm. It can be seen that the light field can maintain high transmission efficiency and low crosstalk in a long wavelength band. Figures 10 and 11 show simulation results for transmitting multiplex signals using array N=7. Take 7 waveguides as an example to perform multi-channel signal transmission, such as "1011010", where "1" represents signal transmission, and "0" represents no signal transmission. Figure 10 calculates the variation of transmission efficiency and crosstalk with wavelength for different channels for the case of length L=100 μm. It can be seen that the device can maintain high transmission efficiency (-0.46-0.27dB) and low crosstalk (<-20.3dB) in a very long wavelength range (1300-1450nm). Figure 11 shows the propagation of the light field in the waveguide of this structure for 100 μm under different wavelengths. It can be seen that the light field can maintain high transmission efficiency and low crosstalk in a long wavelength band.

Figures 12-16 show simulation results of zero-coupling curved waveguides for broadband low-crosstalk transmission. In the case of d=760nm, it is found that when A=0.51μm, the coupling coefficient between the two waveguides is approximately zero, and can remain zero in a very long wavelength band, that is, equation (6) can be satisfied. Figure 13 calculates the transmission and crosstalk as a function of wavelength for a propagation of 100 μm at N=2. It can be seen that the device can maintain high transmission efficiency (>-0.138dB) and low crosstalk (<-15dB) in a longer wavelength range (~100nm). Figure 14 shows the propagation of the light field in the waveguide of this structure under different wavelengths. It can be seen that the light field can maintain high transmission efficiency and low crosstalk in a long wavelength band. Figures 15 and 16 show the simulation results of transmitting multiplex signals using array N=7. Take 7 waveguides as an example to perform multi-channel signal transmission, such as "1011010", where "1" represents signal transmission, and "0" represents no signal transmission. Figure 15 calculates the variation of transmission efficiency and crosstalk with wavelength for different channels for the case of length L=100 μm. It can be seen that the device can maintain high transmission efficiency (-0.85-0.63dB) and low crosstalk (<-9.8dB) in a very long wavelength range (1300-1450nm). Figure 16 shows the propagation of the light field in the waveguide of this structure for 100 μm under different wavelengths. It can be seen that the light field can maintain high transmission efficiency and low crosstalk in a long wavelength band.

Figures 17 to 22 show the simulation results of the bending waveguide to achieve broadband coupling. In the case of gap=200nm, that is, d=600nm, the coupling situations under different bending amplitudes A and different wavelengths λ are simulated. When A=0, it is the traditional straight waveguide coupling situation. It can be seen that the coupling size changes with the change of wavelength at this time. When the length is fixed, the energy distribution of the output port will also change. When considering the curved waveguide, that is, A>0, it is found that the coupling coefficient between the two waveguides gradually becomes negative, and the coupling gradually slows down with the change of wavelength. In particular, when A=0.9 μm, the coupling coefficient at this time hardly changes with the change of wavelength, that is, equation (4) can be satisfied. Figures 18 to 20 calculate the coupling, isolation and directivity at different wavelengths for the straight waveguide (A=0) and the curved waveguide (A=0.9 μm), respectively. The length of the device was chosen to be 15.6 μm for the straight waveguide and 34.8 μm for the curved waveguide. It can be seen that, compared with the traditional straight waveguide coupler, the curved waveguide coupler has a lower coupling degree and a large bandwidth, and the bandwidth reaches nearly 200nm at a coupling degree of 1dB. In addition, the curved waveguide coupler is superior to the traditional straight waveguide directional coupler in terms of isolation and directivity. Figure 21 and Figure 22 intuitively show the propagation of the optical field in the straight waveguide coupler and the curved waveguide coupler. It can be seen that the optical field can be well coupled to another waveguide in the 1350-1550 nm band. In contrast, the performance of conventional straight-waveguide couplers varies dramatically with wavelength.

Figures 23-28 show the simulation results of structurally robust coupling achieved by curved waveguides. In the case of λ=1550nm, the coupling situation under different bending amplitudes A and different waveguide spacing gaps is simulated. When A=0, it is the traditional straight waveguide coupling situation. It can be seen that the coupling size changes with the change of the waveguide spacing. When the length is fixed, the energy distribution of the output port will also change. When considering the curved waveguide, that is, A>0, it is found that the coupling coefficient between the two waveguides gradually becomes negative, and the coupling gradually slows down with the change of the spacing. In particular, when A=0.9 μm, the coupling coefficient at this time hardly changes with the change of the pitch, that is, the formula (5) can be satisfied. Figures 24-26 calculate the coupling, isolation, and directivity at different wavelengths for the straight waveguide (A=0) and the curved waveguide (A=0.9 μm), respectively. The length of the device was chosen to be 23 μm for the straight waveguide and 34.5 μm for the curved waveguide. It can be seen that compared with the traditional straight waveguide coupler, the curved waveguide coupler has a lower coupling degree, and the coupling degree can still be maintained less than 1dB under the change of the waveguide spacing near 200nm. In addition, the curved waveguide coupler is superior to the traditional straight waveguide coupler in terms of isolation and directivity. Figures 27 and 28 intuitively show the propagation of the optical field in the straight waveguide coupler and the curved waveguide coupler. It can be seen that even if the gap varies in a wide range from 200nm to 400nm, the optical field can still be well coupled to another root waveguide, while the performance of traditional straight-waveguide couplers varies drastically with the spacing of the waveguides.

The on-chip optical waveguide transmission and coupling based on curved waveguides can be expressed as:

1) The optical signal input from a certain waveguide port can realize the signal transmission function of wide band and low crosstalk through the cascade structure of positive coupling straight waveguide and negative coupling curved waveguide.

2) The optical signal input from a certain waveguide port passes through the zero-coupling curved waveguide, which can realize the signal transmission function of wide band and low crosstalk.

3) The negative coupling realized by the curved waveguide can realize the directional coupling function of the optical waveguide in a wide band.

To sum up, the present invention adopts the positive and negative coupling cascading brought by straight waveguide and curved waveguide cascade to realize broadband low crosstalk optical waveguide transmission; adopts the zero coupling brought by the curved waveguide to the stability of wavelength to realize broadband low crosstalk optical waveguide transmission ; Adopting the stability of structure and wavelength due to the negative coupling brought by the curved waveguide to achieve robust and broadband optical waveguide directional coupling.

The present invention is fully compatible with the current manufacturing process, does not bring additional processing difficulties, is easy to mass-produce, and does not require high precision.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other.

The principles and implementations of the present invention are described herein using specific examples. The descriptions of the above embodiments are only used to help understand the method and the core idea of the present invention; meanwhile, for those skilled in the art, according to the present invention There will be changes in the specific implementation and application scope. In conclusion, the contents of this specification should not be construed as limiting the present invention.

Claims

A high-density integrated optical waveguide, the optical waveguide is arranged on a waveguide substrate, characterized in that it comprises: a plurality of curved waveguides;

A rectangular coordinate system is established with the bending direction of the curved waveguide as the y-axis and the propagation direction of the light as the x-axis; and based on the rectangular coordinate system, the curved waveguide is periodic along the propagation direction in the bending direction sexual bending;

A plurality of curved waveguides are arranged in parallel along the y-axis direction, and the curved waveguides are perpendicular to the y-axis direction to form a curved waveguide array; the optical waveguide is realized by adjusting the coupling coefficient between the curved waveguides Optical waveguide signal transmission function or optical waveguide directional coupling function.
The high-density integrated optical waveguide according to claim 1, wherein the coupling coefficient is based on the bending amplitude of the bending waveguide, the bending period, the incident wavelength of the incident light, the refractive index of the waveguide substrate, and The periodic interval of the curved waveguide is adjusted.
The high-density integrated optical waveguide according to claim 2, wherein the expression of the coupling coefficient is: c=c 0 J 0 (4π 2 An 0 d/Pλ);

Wherein, c is the coupling coefficient between the curved waveguides; c 0 is the coupling coefficient between straight waveguides, c 0 >0, the straight waveguide is the first straight waveguide or the second straight waveguide; A is the bending amplitude; P is the bending period; d is the periodic interval of the waveguide arrangement, d=w+gap, w is the width of the waveguide, and the gap is the spacing between the waveguides; λ is the incident wavelength; n 0 is the substrate refractive index.
The high-density integrated optical waveguide according to claim 3, wherein, if J 0 (4π 2 An 0 d/Pλ) is less than 0, the coupling coefficient is less than 0, the optical waveguide further comprises: a first a straight waveguide array and a second straight waveguide array;

The first straight waveguide array includes a plurality of first straight waveguides arranged in parallel along the y-axis; the second straight waveguide array includes a plurality of second straight waveguides arranged in parallel along the y-axis; the The coupling coefficient between the first straight waveguides is equal to the coupling coefficient between the second straight waveguides, and the coupling coefficient between the first straight waveguides and the coupling coefficient between the second straight waveguides are both greater than 0;

The output end of the first straight waveguide array is butted with the input end of the curved waveguide array, the output end of the curved waveguide array is butted with the input end of the second straight waveguide array, the first straight waveguide array, The curved waveguide array and the second straight waveguide array form a three-level cascade structure; the incident light enters the three-level cascade structure from the input end of the first straight waveguide array, and the incident light is in the three-level cascade structure. The first straight waveguide array diverges due to coupling, and the curved waveguide array re-converges the divergent light to the second straight waveguide array due to negative coupling. The negative coupling strength is matched to realize the optical waveguide signal transmission function of broadband and low crosstalk.
The high-density integrated optical waveguide according to claim 4, wherein the optical waveguide comprises a plurality of the three-level cascade structures; and the plurality of the three-level cascade structures are arranged in parallel along the x-axis direction.
The high-density integrated optical waveguide according to claim 3, wherein, let J 0 (4π 2 An 0 d/Pλ) be equal to 0, the coupling coefficient is equal to 0, and the incident light is in the curved waveguide array It can realize the optical waveguide signal transmission function of broadband and low crosstalk.
The high-density integrated optical waveguide according to claim 3, wherein J 0 (4π 2 An 0 d/Pλ) is smaller than 0, the coupling coefficient is smaller than 0, and the curved coupling array specifically includes two The curved waveguide; the two curved waveguides are arranged in parallel along the y-axis direction to realize the directional coupling function of the optical waveguide with a wide band.
The high-density integrated optical waveguide according to any one of claims 1-7, wherein the periodic bending expression of the curved waveguide is:

Wherein, y(x) is the periodic bending function of the bending waveguide; A is the bending amplitude; P is the bending period;
It is the initial phase of bending.