阅读说明：本技术 一种四通道硅基阵列波导光栅波分复用器 (Four-channel silicon-based array waveguide grating wavelength division multiplexer ) 是由 陈远祥 付佳 韩颖 黄雍涛 李凯乐 余建国 于 2020-05-29 设计创作，主要内容包括：本发明实施例提供了一种四通道硅基阵列波导光栅波分复用器,其中阵列波导光栅中的过渡波导中第二端过渡段的宽度较小部分占过渡波导整个长度的比例更高,则使有效折射率变化更加缓慢,可以有效降低器件的插入损耗；而过渡波导中第一端过渡段的宽度较大部分占过渡波导整个长度的比例有所减少,其对有效折射率的变化不大,也可减少不必要的第一端过渡段长度,减少了尺寸,并且其损耗相较于直线型过渡方式的损耗低。(The embodiment of the invention provides a four-channel silicon-based arrayed waveguide grating wavelength division multiplexer, wherein the proportion of the smaller width part of a second end transition section in a transition waveguide in an arrayed waveguide grating in the whole length of the transition waveguide is higher, so that the change of the effective refractive index is slower, and the insertion loss of a device can be effectively reduced; the proportion of the larger width part of the first end transition section in the transition waveguide in the whole length of the transition waveguide is reduced, the change of the effective refractive index is not large, the unnecessary length of the first end transition section can be reduced, the size is reduced, and the loss of the transition waveguide is lower than that of a linear transition mode.)

1. A four-channel silicon-based arrayed waveguide grating wavelength division multiplexer, comprising:

an arrayed waveguide grating, wherein the arrayed waveguide grating comprises: the waveguide device comprises a channel waveguide, a slab waveguide, an array waveguide and a transition waveguide, wherein the transition waveguide is respectively coupled between the channel waveguide and the slab waveguide and between the slab waveguide and the array waveguide, and comprises: a first end, a second end opposite to the first end and smaller than the first end, and a transition section between the first end and the second end, the first end facing the slab waveguide; the transition section consists of a second end transition section and a first end transition section, and the first end transition section accounts for half or less than half of the transition section;

the transition section comprises a section of a smooth curve, the smooth curve is a smooth curve which is non-linearly and monotonically increased from the second end to the first end and is guided everywhere, wherein the smooth curve is a smooth curve which is concave towards the inside of the transition waveguide or a smooth curve which is convex towards the outside of the transition waveguide;

the channel waveguides include an input channel waveguide and four output channel waveguides, and the slab waveguides include an input slab waveguide and an output slab waveguide.

2. The quad silicon-based arrayed waveguide grating multiplexer of claim 1 wherein said smooth curve is a power function curve, said smooth curve that is concave inward of said power function curve and said smooth curve that is convex outward of said transition waveguide is a convex-concave curve in said power function curve.

3. The quad-channel silicon-based arrayed waveguide grating multiplexer of claim 2, wherein the argument in the power function curve has a value in the range of [0,1], and the power number has a value in the range of (1, 7).

4. The quad silicon-based arrayed waveguide grating multiplexer of any one of claims 1 to 3, wherein the transition waveguide comprises: a first transition waveguide, a second transition waveguide, a third transition waveguide and a fourth transition waveguide; wherein the content of the first and second substances,

the output end of the input channel waveguide is coupled with the second end of the first transition waveguide in a one-to-one correspondence manner, the first end of the first transition waveguide is coupled with the input end of the input slab waveguide, the output end of the input slab waveguide is coupled with the first end of the second transition waveguide, the second end of the second transition waveguide is coupled with the input end of the array waveguide, the output end of the array waveguide is coupled with the second end of the third transition waveguide, the first end of the third transition waveguide is coupled with the input end of the output slab waveguide, the output end of the output slab waveguide is coupled with the first end of the fourth transition waveguide, and the second end of the fourth transition waveguide is coupled with the four output channel waveguides in a one-to-one correspondence manner.

5. The quad-channel silicon-based arrayed waveguide grating multiplexer of any one of claims 1 to 3, wherein the channel waveguide, the slab waveguide, the arrayed waveguide, and the transition waveguide are monolithically integrated on a substrate of a same chip using planar optical waveguide technology;

the channel waveguide, the array waveguide and the transition waveguide are respectively embedded waveguides, each embedded waveguide is composed of a core layer and a cladding layer, the height of the core layer is within the range of [4 microns, 4.5 microns ], and the width of the core layer is within the range of [4 microns, 4.5 microns ];

the number of the arrayed waveguides takes an integer value in a range of [11,20 ];

the diffraction order of the four-channel silicon-based array waveguide grating wavelength division multiplexer is an integer value within the range of [8,20 ];

the distance of the array waveguide is within the range of [5 μm,10 μm ];

the distance of the input channel waveguide is within the range of [5 μm,12 μm ];

the distance between the output channel waveguides is within the range of [5 μm,12 μm ].

6. The quad-channel silicon-based arrayed waveguide grating multiplexer of any one of claims 1 to 3, wherein the input channel waveguide, the output channel waveguide, and the arrayed waveguide are each tapered.

Technical Field

The invention relates to the technical field of optical communication, in particular to a four-channel silicon-based arrayed waveguide grating wavelength division multiplexer.

Background

With the rapid increase of global communication traffic, people put higher demands on communication bandwidth, and it is difficult for traditional communication technologies to meet the increasing demand of communication bandwidth. In order to increase the capacity of an optical fiber communication system greatly and increase the physical limit of information transmitted by one optical fiber by one to several times, a WDM (Wavelength division multiplexing, abbreviated as WDM) technology can be used in a Wavelength Division Multiplexing (WDM) transmission system, so that two or more optical Wavelength signals can transmit information through different optical channels in the same optical fiber.

In a WDM transmission system, a wavelength division multiplexer/demultiplexer is a core device thereof. The wavelength division multiplexer/demultiplexer completes the wave combination task at the transmitting end and completes the wave combination at the receiving end. The technologies for manufacturing the above-described wavelength division multiplexer/demultiplexer are many, and mainly, there is a diffraction grating method. The diffraction Grating method is divided into a fiber Grating method and an Arrayed Waveguide Grating method, and the wavelength division multiplexer/demultiplexer used in the WDM transmission system may be an Arrayed Waveguide Grating (AWG for short), and because the structure has a bidirectional symmetrical multiplexing/demultiplexing function, the method becomes an optimal choice for a large port number, such as a channel number greater than 32. But the conventional AWG has higher loss.

Disclosure of Invention

The embodiment of the invention aims to provide a four-channel silicon-based arrayed waveguide grating wavelength division multiplexer, which is used for solving the technical problem that the traditional AWG in the prior art has higher loss. The specific technical scheme is as follows:

the embodiment of the invention provides a four-channel silicon-based array waveguide grating wavelength division multiplexer, which comprises:

an arrayed waveguide grating, wherein the arrayed waveguide grating comprises: the waveguide device comprises a channel waveguide, a slab waveguide, an array waveguide and a transition waveguide, wherein the transition waveguide is respectively coupled between the channel waveguide and the slab waveguide and between the slab waveguide and the array waveguide, and comprises: a first end, a second end opposite to the first end and smaller than the first end, and a transition section between the first end and the second end, the first end facing the slab waveguide; the transition section consists of a second end transition section and a first end transition section, and the first end transition section accounts for half or less than half of the transition section;

the transition section comprises a section of a smooth curve, the smooth curve is a smooth curve which is non-linearly and monotonically increased from the second end to the first end and is guided everywhere, wherein the smooth curve is a smooth curve which is concave towards the inside of the transition waveguide or a smooth curve which is convex towards the outside of the transition waveguide;

the channel waveguides include an input channel waveguide and four output channel waveguides, and the slab waveguides include an input slab waveguide and an output slab waveguide.

Further, the smooth curve is a power function curve, the smooth curve recessed towards the inside of the transition waveguide is a concave curve in the power function curve, and the smooth curve protruding towards the outside of the transition waveguide is a convex curve in the power function curve.

Furthermore, the independent variable in the power function curve takes values in the range of [0,1], and the power times take values in the range of (1, 7).

Further, the transition waveguide comprises: a first transition waveguide, a second transition waveguide, a third transition waveguide and a fourth transition waveguide; wherein the content of the first and second substances,

the output end of the input channel waveguide is coupled with the second end of the first transition waveguide in a one-to-one correspondence manner, the first end of the first transition waveguide is coupled with the input end of the input slab waveguide, the output end of the input slab waveguide is coupled with the first end of the second transition waveguide, the second end of the second transition waveguide is coupled with the input end of the array waveguide, the output end of the array waveguide is coupled with the second end of the third transition waveguide, the first end of the third transition waveguide is coupled with the input end of the output slab waveguide, the output end of the output slab waveguide is coupled with the first end of the fourth transition waveguide, and the second end of the fourth transition waveguide is coupled with the four output channel waveguides in a one-to-one correspondence manner.

Further, the channel waveguide, the slab waveguide, the array waveguide and the transition waveguide are monolithically integrated on a substrate of the same chip by adopting a planar optical waveguide technology;

the channel waveguide, the array waveguide and the transition waveguide are respectively embedded waveguides, each embedded waveguide is composed of a core layer and a cladding layer, the height of the core layer is within the range of [4 microns, 4.5 microns ], and the width of the core layer is within the range of [4 microns, 4.5 microns ];

the number of the arrayed waveguides takes an integer value in a range of [11,20 ];

the diffraction order of the four-channel silicon-based array waveguide grating wavelength division multiplexer is an integer value within the range of [8,20 ];

the distance of the array waveguide is within the range of [5 μm,10 μm ];

the distance of the input channel waveguide is within the range of [5 μm,12 μm ];

the distance between the output channel waveguides is within the range of [5 μm,12 μm ].

Further, the input channel waveguide, the output channel waveguide, and the array waveguide are respectively in a tapered structure.

The embodiment of the invention has the following beneficial effects:

according to the four-channel silicon-based arrayed waveguide grating wavelength division multiplexer provided by the embodiment of the invention, the proportion of the smaller width part of the second end transition section in the transition waveguide to the whole length of the transition waveguide is higher, so that the change of the effective refractive index is slower, and the insertion loss of a device can be effectively reduced; the proportion of the larger width part of the first end transition section in the transition waveguide in the whole length of the transition waveguide is reduced, the change of the effective refractive index is not large, the unnecessary length of the first end transition section can be reduced, the size is reduced, and the loss of the transition waveguide is lower than that of a linear transition mode.

Of course, not all of the advantages described above need to be achieved at the same time in the practice of any one product or method of the invention.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of a star coupler for an arrayed waveguide grating according to an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of a transition waveguide with a concave transition mode according to an embodiment of the present invention;

FIG. 3 is a schematic cross-sectional view of a transition waveguide with a convex transition according to an embodiment of the present invention;

FIG. 4 is an exemplary illustration of an arrayed waveguide grating in accordance with an embodiment of the invention;

fig. 5 is a schematic three-dimensional structure diagram of a transition waveguide in a concave transition manner according to an embodiment of the present invention;

FIG. 6 is a schematic three-dimensional structure diagram of a transition waveguide with a convex transition mode according to an embodiment of the present invention;

FIG. 7 is a schematic representation of a smooth curve as a power function curve in a cross-section of a transition waveguide in accordance with an embodiment of the present invention;

FIG. 8 is a schematic illustration of a smooth curve as an exponential function curve in a cross-section of a transition waveguide in accordance with an embodiment of the present invention;

FIG. 9 is a first schematic of insertion loss according to an embodiment of the present invention;

FIG. 10 is a second schematic illustration of insertion loss according to an embodiment of the present invention;

FIG. 11 is a schematic view of a 1 × 4 arrayed waveguide grating according to an embodiment of the present invention;

FIG. 12 is a schematic cross-sectional view of a waveguide in accordance with an embodiment of the present invention;

FIG. 13 is a schematic illustration of output channel waveguide spacing versus bandwidth for an embodiment of the present invention;

FIG. 14 is a graphical representation of the relationship between the number of diffraction orders m and Δ L, R, FSR for an embodiment of the present invention;

FIG. 15 is a schematic illustration of an arrayed waveguide grating transmission for different numbers of arrayed waveguides in accordance with an embodiment of the present invention;

FIG. 16 is a graph showing the relationship between the number of arrayed waveguides and the insertion loss according to an embodiment of the present invention;

FIG. 17 is a diagram illustrating the relationship between the number of arrayed waveguides and the bandwidth according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, belong to the protection scope of the present invention.

Aiming at the problem that the loss of the traditional AWG is higher in the prior art, the embodiment of the invention provides a four-channel silicon-based arrayed waveguide grating wavelength division multiplexer, wherein the proportion of the smaller width part of the second end transition section in the transition waveguide to the whole length of the transition waveguide is higher, so that the change of the effective refractive index is slower, and the insertion loss of a device can be effectively reduced; the proportion of the larger width part of the first end transition section in the transition waveguide in the whole length of the transition waveguide is reduced, the change of the effective refractive index is not large, the unnecessary length of the first end transition section can be reduced, the size is reduced, and the loss of the transition waveguide is lower than that of a linear transition mode.

The following first introduces a quad-channel silicon-based arrayed waveguide grating wavelength division multiplexer provided in an embodiment of the present invention.

As shown in fig. 1, in the four-channel silicon-based arrayed waveguide grating multiplexer provided in the embodiment of the present invention, the multiplexer may include the following components:

an arrayed waveguide grating, wherein the arrayed waveguide grating comprises: the waveguide structure comprises a channel waveguide 1, a slab waveguide 2, an array waveguide 3 and a transition waveguide 4, wherein the transition waveguides are respectively coupled between the channel waveguide and the slab waveguide and between the slab waveguide and the array waveguide. The transition waveguide includes: a first end 411, a second end 421 opposite to the first end 411 and smaller than the size of the first end 411, and a transition between the first end 411 and the second end 421, the first end 411 facing the slab waveguide; the transition section is composed of a second end transition section 422 and the first end transition section 412, and the first end transition section 412 occupies half or less than half of the transition section, as shown in fig. 2 and 3, although fig. 2 and 3 are only for convenience of illustrating the transition waveguide, and are not limited herein, and any transition waveguide capable of implementing the following structure according to the embodiment of the present invention is within the protection scope of the embodiment of the present invention. The method comprises the following specific steps: the transition section comprises a section of a smooth curve, the smooth curve is a smooth curve which is in nonlinear monotonic increasing and is guided everywhere from the second end to the first end, wherein the smooth curve is a smooth curve which is concave towards the inside of the transition waveguide or a smooth curve which is convex towards the outside of the transition waveguide, and the smooth curve is a power function curve;

referring to fig. 4, the channel waveguides include an input channel waveguide 11 and four output channel waveguides 12, and the slab waveguides include an input slab waveguide 21 and an output slab waveguide 22. Wherein, the number of the array waveguides 3 is a value in the range of [11,20 ]; the number of transition waveguides is determined by the number of channel waveguides and array waveguides.

It should be noted that, because the port sizes of the channel waveguide and the slab waveguide are different, and the port sizes of the slab waveguide and the array waveguide are different, the transition waveguide is used to implement matching between two waveguides with different port sizes. The transition waveguide may be coupled between the channel waveguide and the slab waveguide or between the slab waveguide and the arrayed waveguide, and is used for realizing transmission of light between the channel waveguide and the slab waveguide or between the slab waveguide and the arrayed waveguide. The channel waveguide, the slab waveguide, the arrayed waveguide and the transition waveguide of the arrayed waveguide grating are mutually matched for completing the transmission of light.

The coupling of the various waveguides of the arrayed waveguide grating described above refers to any connection, coupling, linking, etc., and the optical coupling refers to coupling such that light is transferred from one element to another. Such coupled components need not be directly connected to one another, but may be separated by intermediate components that manipulate or modify such signals. Also, as used in connection with embodiments of the present invention, the terms "directly coupled" or "directly optically coupled" refer to any optical connection that allows light to be transmitted from one element to another without intervening components, such as optical fibers.

Compared with the linear transition waveguide in the related art, the slope of the linear transition waveguide changes along with the slope of the linear transition waveguide, if the slope is large, the waveguide formed by the transition edges which conform to the linear change can enable the effective refractive index to change greatly, and further the insertion loss of the device after the waveguide coupling structure is increased. If the slope is small, the effective refractive index of the waveguide formed by the transition edges following the linear change does not change much, but the length of the entire waveguide is increased. Therefore, the waveguide formed by the transition edge which is in line type change is difficult to realize, the insertion loss of a device added with the transition waveguide can be reduced, and the length of the whole transition waveguide can be shortened. Based on this, the embodiment of the present invention adopts the transition waveguide to change in a smooth curve, so as to simultaneously satisfy the requirements of reducing the insertion loss of the device and reducing the size of the device.

With the above and fig. 4, the input channel waveguide transmits input light, the input slab waveguide allows light to freely propagate therein, and has a function of dispersing light incident from the input channel waveguide into the slab waveguide, the arrayed waveguide means that a plurality of waveguides are arranged side by side, the output slab waveguide has the same structure as the input slab waveguide, and the output channel waveguides are arranged side by side. The input slab waveguide connects the input channel waveguide and the arrayed waveguide, also known as an input star coupler; an output slab waveguide connects the output channel waveguide and the arrayed waveguide, also known as an output star coupler. The number of input channel waveguides may be 1 or more, the number of arrayed waveguides may be many, and the number of output channel waveguides is typically more than two, such as four.

The star coupler of fig. 1 is formed of a circular slab waveguide having a rowland and connected thereto an input channel waveguide and an array waveguide. Or, it is composed of a rowland circular plate waveguide, and the output channel waveguide and array waveguide connected with it, the channel waveguide includes: input channel waveguide/output channel waveguide. The end faces of the input channel waveguides/output channel waveguides are called ports, which are equally spaced d_iGround is arranged on the rowland circumference and towards the central array waveguide. The two ends of the array waveguide are at equal interval d_oThe central array waveguide is arranged on the circumferences of the two gratings and is opposite to the circle center of the grating circle, the central array waveguide is positioned at the tangent point of the grating circle and the Rowland circle, and the adjacent array waveguides have a fixed length difference delta L. The Rowland circle diameter is R, i.e. the radius of the grating circle is also R. Since different tapered Taper structures have different differences in the performance of the arrayed waveguide grating, in order to collect optical power as much as possible, thereby effectively increasing transmission efficiency and reducing insertion loss, the more arrayed waveguides are, the more diffracted light of the input channel waveguide can be collected to the maximum, and the input channel waveguide, the output channel waveguide, and the arrayed waveguide respectively have a tapered structure, that is, a tapered structure. Therefore, the input channel waveguide, the output channel waveguide and the array waveguide are all in a tapered structure, so that loss can be reduced, and channel crosstalk can be reduced.

Compared with the linear transition waveguide in the prior art, in the embodiment of the invention, the proportion of the smaller width part of the second end transition section in the transition waveguide to the whole length of the transition waveguide is higher, so that the change of the effective refractive index is slower, and the insertion loss of a device can be effectively reduced; the proportion of the larger width part of the first end transition section in the transition waveguide in the whole length of the transition waveguide is reduced, the change of the effective refractive index is not large, the unnecessary length of the first end transition section can be reduced, the size is reduced, and the loss of the transition waveguide is lower than that of a linear transition mode.

The first end may be a large end surface, the second end may be a small end surface, the first end may be a large port, and the second end may be a small port. The second end is for concentrating the incoming light beams together and the first end is for the concentrated light output. When the transition waveguide is coupled with other components, and the transition waveguide and the other components are positioned on the same horizontal plane, the section of the transition section containing a smooth curve is the cross section of the transition waveguide, and the corresponding transition section contains the section containing only a straight line is the longitudinal section of the transition waveguide. Similarly, when the transition waveguide is coupled with other components, and the transition waveguide and the other components are in the same vertical plane, the section of the transition section containing the smooth curve is the longitudinal section of the transition waveguide, and the corresponding transition section contains the section containing only the straight line and is the cross section of the transition waveguide.

Referring to fig. 5 and 6, when the transition waveguide 4 is coupled with other components 5, the other components 5 may be referred to as channel waveguides or arrayed waveguides. The transition waveguide and other components are all in the same horizontal plane, and the longitudinal cross-sectional area of the second end is the cross-sectional width (width, w) multiplied by the cross-sectional height (h), that is, the longitudinal cross-sectional area of the rectangular waveguide. That is, the cross-sectional area of the first end is the cross-sectional width Wit multiplied by the cross-sectional height h, or the cross-sectional area of the first end is the cross-sectional width Wot multiplied by the cross-sectional height h, where Wot represents the tapered waveguide flare width of the arrayed waveguide and Wit represents the tapered waveguide flare width of the output channel waveguide. Thus, the cross-sectional area varies from small to large from the second end to the first end. Among them, since the channel waveguide and the array waveguide may be formed in a rectangular shape, they may be referred to as rectangular waveguides.

The transition section is composed of a second end transition section and a first end transition section, the first end transition section occupies half or less than half of the transition section, the proportion of the wide part of the first end transition section in the transition waveguide occupying the whole length of the transition waveguide is reduced, the change of the effective refractive index is not large, the unnecessary length of the first end transition section can be reduced, the size is reduced, and the loss is low compared with that of a linear transition mode.

Since the effective refractive index is an important and commonly used parameter in the optical waveguide, and its value is related to the sectional shape of the waveguide and the refractive index of the waveguide material, once the sectional shape and material of the waveguide are determined, the effective refractive index of the waveguide will also be determined, and the specific value can be calculated by simulation software. The change of the smooth curve can be measured from the effective refractive index, the size and the light receiving capacity of the waveguide, wherein the smooth curve is a smooth curve which is concave towards the inside of the transition waveguide and can be called a concave transition mode, as shown in fig. 2 and fig. 5. The smooth curve protruding outward the transition waveguide may be referred to as a convex transition, as shown in fig. 3 and 6. Compared with the inward concave transition mode, the special outward convex transition mode enhances the light receiving capacity, enables more light to be absorbed or output into the waveguide connected with the special outward convex transition mode, enhances the optical power of the channel, and reduces the loss, and the outward convex transition mode and the inward concave transition mode both reduce the size.

The smooth curve in the cross section of the transition waveguide can be a smooth curve which is nonlinearly monotonically increased and is guided everywhere from the second end to the first end. In one possible smooth curve, the smooth curve may be a power function curve, i.e., satisfying f (x) ═ f^a,>1, where a is 1,2,3,4,5,6,7,8, the curve a is a power, x is a normalization of the length of the waveguide in the direction of light transmission, and f (x) is a normalized variation in a power function with respect to x, as shown in fig. 7, that is, a power function satisfying a square function, a cubic function, and the like. The concrete description is as follows:

referring to fig. 2 and 5, the smooth curve recessed into the transition waveguide is a concave curve in the power function curve. Compared with the exponential type, the proportion of the part of the power function type with smaller width at the second end transition section in the whole length is higher, so that the change of the effective refractive index is slower, and the insertion loss of the device can be effectively reduced; the proportion of the part with larger width of the first end transition section in the whole length is reduced, the change of the effective refractive index is not large, the unnecessary length of the first end transition section can be reduced, the size is reduced, and the loss is lower compared with the loss of a linear transition mode. The number of times of the power function cannot be increased infinitely because the higher the number of times of the power function, the more obvious the concavity thereof, the higher the length of the whole waveguide occupied by the portion of the second end having the smaller width, the more approximate a rectangle having the width of the second end, which is contrary to the object of reducing the loss, and also causes the reflection of light, thereby increasing the loss.

According to the graph of the power function, if the independent variable takes on values in the range of [0,1], when the power number is larger than 7, the range of the function value is approximate to the initial value and occupies about half of the range of the independent variable. Therefore, the transition waveguide is provided with the second end transition section which occupies half of the whole transition waveguide, so that the performance is not obviously improved, and the loss is slightly increased. Therefore, the number of times of selecting the power function of the concave transition mode is set to be within the range of (1, 7), that is, the length of the second end transition section is ensured to be less than half of the length of the whole transition section.

Referring to fig. 3 and 6, the smooth curve protruding outward from the transition waveguide is an outward convex curve in the power function curve. Compared with the inward concave transition mode, the outward convex transition mode enhances the light receiving capacity, enables more light to be absorbed or output to the waveguide connected with the outward convex transition mode, enhances the optical power of the channel, and reduces the loss, and the outward convex transition mode and the inward concave transition mode both reduce the size. However, the number of times of the power function cannot be increased infinitely, because the higher the number of times of the power function is, the larger the degree of convexity thereof is, the larger the shape of the transition waveguide is, the larger the portion of the first end width thereof occupies the entire length of the waveguide is, the more approximate the rectangle with the width of the first end is, which is contrary to the goal of optimizing the size, and the mode fields between the adjacent waveguides are partially overlapped, so that the signals of the optical field are coupled into the adjacent waveguides, thereby increasing the crosstalk between the adjacent channels.

According to the graph of the power function, if the independent variable takes on values in the range of [0,1], when the power number is larger than 7, the range of the function value is approximate to the initial value and occupies about half of the range of the independent variable. Therefore, what appears on the transition waveguide is that the first end transition section occupies half of the entire transition waveguide, and at this time, the performance is not significantly improved, but the crosstalk is slightly increased. Therefore, the number of times of selecting the power function of the convex-concave transition mode in the embodiment of the invention is a value in the range of (1, 7), that is, the length of the first end transition section is ensured to be less than half of the length of the whole transition section.

In another possible smooth curve, the smooth curve may be an exponential function curve, i.e.,where b is a curve of 1.5, b is a curve of 2, b is a curve of 3, b is a base number, x is a normalization of the length of the waveguide in the light transmission direction, and g (x) is a normalized variation in an exponential function with respect to x, as shown in fig. 8. For the transition waveguide with the exponential function curve, the width of the second end transition section in the transition waveguide is higher than the whole length of the transition waveguide, so that the change of the effective refractive index is relatively slow, and the insertion loss can be effectively reduced; the width of the transition section at the first end in the transition waveguide is lower than the whole length of the transition waveguide, so that the length of the device can be effectively reduced, the change of the effective refractive index is not large, and the insertion loss of the device cannot be greatly increased. The concrete description is as follows:

and the smooth curve sunken towards the inside of the transition waveguide is an inward concave curve in the exponential function curve. Based on the above linear analysis, the ratio of the smaller width part of the second end transition section of the exponential type to the whole length is improved, so that the change of the effective refractive index is relatively slow, and the insertion loss of the device can be effectively reduced; the proportion of the part with larger width of the first end transition section in the whole length is reduced, the change of the effective refractive index is not large, the unnecessary length of the first end transition section can be reduced, the size is reduced, and the loss is lower compared with the loss of a linear transition mode.

The smooth curve protruding to the outside of the transition waveguide is an external convex curve in the exponential function curve. Compared with the inward concave transition mode, the outward convex transition mode enhances the light receiving capacity, enables more light to be absorbed or output to the waveguide connected with the outward convex transition mode, enhances the optical power of the channel, and reduces the loss, and the outward convex transition mode and the inward concave transition mode both reduce the size.

The parameters are illustrated based on fig. 5 and 6 as follows:

(1) about the width W of the first end of the transition waveguide connected to the input channel waveguide/output channel waveguide_it：

The AWG is an optical imaging device in which each arrayed waveguide has its ends facing the central input channel waveguide/output channel waveguide ports. By adjusting the width of the first end of the transition waveguide connected to the input channel waveguide/output channel waveguide, light can be efficiently coupled directly into the arrayed waveguide, improving bandwidth and insertion loss, etc. FIGS. 5 and 6 illustrate the width W of the first end of the transition waveguide in connection with the input channel waveguide/output channel waveguide_itThe effect on the insertion loss of both channels. When the rectangular waveguide width W of the output channel waveguide was 4.5 μm, the embodiment of the present invention tested W_itIncreasing from 5 μm to 14 μm. Both example output ports #1 and #3 from the four output ports have similar trends. When W is_itIncreasing from 6 to 9 μm, the insertion loss gradually decreases, as W_itAbove 10 μm, the insertion loss increases slightly, see FIG. 9. Therefore, the width of the first end of the transition waveguide connected to the input channel waveguide/output channel waveguide cannot be excessively increased. Otherwise, the channel bandwidth is continuously widened, the problem of mutual overlapping of the tapered waveguides occurs, and the crosstalk level is obviously increased. Embodiment of the invention selects W_itAt 8 to 10 μm.

(2) About the width W of the first end of the transition waveguide connected to the arrayed waveguide_ot：

To prevent light from leaking through the gaps between the arrayed waveguides, transition waveguides may be used at the interfaces of the arrayed waveguides coupled to the slab waveguide to enhance the light intensity in the arrayed waveguides. FIGS. 5 and 6 illustrate the width W of the first end of the transition waveguide coupled to the arrayed waveguide_otThe effect on the insertion loss of both channels. When the rectangular waveguide width W of the arrayed waveguide is 4.5 μm, the embodiment of the present invention tests W in two star couplers_otWhile increasing from 6 μm to 14 μm. Both example output ports #1 and #3 from the four ports have similar trends. When W is_otIncreasing from 6 to 8 μm, the insertion loss gradually decreases, see fig. 10. When W is_otAbove 10 μm, the insertion loss is slightly higherAnd (5) rising. Embodiment of the invention selects W_otAt 7 to 9 μm.

(3) About the length L of the transition waveguide_tThe value is within 400-500 μm.

Referring to fig. 5 and 6, the heights of the transition waveguide, the input channel waveguide/output channel waveguide, and the array waveguide are all equal to each other, and are all h; the width of the second end of the transition waveguide is equal to the width of the input channel waveguide/output channel waveguide and the array waveguide, and is w; w for width of first end of transition waveguide at connection of input channel waveguide/output channel waveguide and slab waveguide_itRepresents; w for width of first end of transition waveguide at junction of array waveguide and slab waveguide_otAnd (4) showing.

Based on the introduction of the channel waveguide, the slab waveguide, the arrayed waveguide, and the transition waveguide, the embodiment of the present invention introduces the following overall connection relationship of the arrayed waveguide grating:

referring to fig. 11, the transition waveguide 4 includes: a first transition waveguide, a second transition waveguide, a third transition waveguide and a fourth transition waveguide; wherein the content of the first and second substances,

the output end of the input channel waveguide 11 is coupled to the second end of the first transition waveguide in a one-to-one correspondence manner, the first end of the first transition waveguide is coupled to the input end of the input slab waveguide 21, the output end of the input slab waveguide 21 is coupled to the first end of the second transition waveguide, the second end of the second transition waveguide is coupled to the input end of the arrayed waveguide 3, the output end of the arrayed waveguide 3 is coupled to the second end of the third transition waveguide, the first end of the third transition waveguide is coupled to the input end of the output slab waveguide 22, the output end of the output slab waveguide 22 is coupled to the first end of the fourth transition waveguide, and the second end of the fourth transition waveguide is coupled to the four output channel waveguides 12 in a one-to-one correspondence manner.

Based on the above-described overall connection relationship of the arrayed waveguide grating, the embodiment of the present invention further introduces the following working principle of the multiplexer:

the light beam propagates through the AWG device with four transitions:

(1) the rectangular waveguide mode is converted into a flat waveguide mode which is limited in the direction vertical to the waveguide and freely diverged in the width direction;

(2) because the function of the input slab waveguide/the output slab waveguide is similar to that of a lens, the light field is input to different array waveguide input ends to excite the array waveguide light field;

(3) because the adjacent arrays have a constant length difference delta L, a corresponding constant phase factor is introduced into a mode field output by the array waveguide, and diffraction is generated at the input end of the output slab waveguide;

(4) the light field is diffracted on the output flat waveguide and focused on a Rowland circle, different wavelength phases are converged to different positions of an image plane, and finally the light field is output through an output channel waveguide.

The demultiplexing realization process of the AWG device comprises the following steps: after being output through the central input channel waveguide, the multi-wavelength multiplexing signal light reaches the input concave grating through the diffraction of the input flat waveguide and is coupled into the array waveguide. Because the end face of the arrayed waveguide is on the circumference of the grating circle, the phases of the optical signals reaching the input end of the arrayed waveguide are the same. Since the length difference Δ L between adjacent arrayed waveguides is set to be a fixed value, the phase difference generated after the signal light with the same wavelength is transmitted through the arrayed waveguidesThe same applies. By

It is easy to know that the phase difference of the signal light with different wavelengths reaching the output concave grating after being transmitted by the array waveguide is also different. Therefore, the light with different wavelengths is focused to different output channel waveguides for output after being diffracted by the output slab waveguide.

The multiplexing implementation process of the AWG device is as follows: and respectively inputting the optical signals with different wavelengths from the output channel waveguides corresponding to the right side, and outputting the optical signals from the central waveguide on the left side to complete the multiplexing of the optical signals.

With reference to fig. 11, a diagram is shown according to the above descriptionThe operating principle and structure of the AWG multiplexer, the selection of device parameters in the embodiment of the invention will determine the performance of the device. In order to obtain a four-channel AWG, first, the thickness a and the width b of the core layer of the waveguide need to be designed; then according to the channel central wavelength lambda required by design target₀And a wavelength interval lambda₀Designing the waveguide spacing d of adjacent input or output channels respectively_iArray waveguide spacing d_oParameters such as the length difference delta L of adjacent array waveguides, the diffraction order M, a Free Spectral Range (FSR for short), the focal length of a planar waveguide, the diameter of a Rowland circle, the length R of a flat waveguide, the number M of array waveguides and the like; and finally, the loss is reduced by increasing the number of the array waveguides and optimizing the channel geometric dimension. Thus, the parameters of the device of an embodiment of the invention are illustrated as follows:

the channel waveguide, the slab waveguide, the array waveguide and the transition waveguide are monolithically integrated on a substrate of the same chip by adopting a planar optical waveguide technology;

the channel waveguide, the array waveguide and the transition waveguide are respectively embedded waveguides, each embedded waveguide is composed of a core layer and a cladding layer, the height of the core layer is within a range of [4 μm and 4.5 μm ], and the width of the core layer is within a range of [4 μm and 4.5 μm ], which is shown in fig. 12; the core means a width and a height of the core shown in a longitudinal section of the buried waveguide, that is, a section including only straight lines. In order to reduce the birefringence effect, the width and thickness of the core layer of the rectangular waveguide and the thickness of the core layer of the slab waveguide may also be made the same, but not limited thereto.

The number of the arrayed waveguides takes an integer value in a range of [11,20 ];

the diffraction order of the four-channel silicon-based array waveguide grating wavelength division multiplexer is an integer value within the range of [8,20 ];

the distance of the array waveguide is within the range of [5 μm,10 μm ];

the distance of the input channel waveguide is within the range of [5 μm,12 μm ];

the distance between the output channel waveguides is in the range of [5 μm,12 μm ], so that for the output channel waveguides, the coupling between the waveguides can enable the optical power of any channel to be received by the waveguides of other channels, thereby increasing the crosstalk of the device; for arrayed waveguides, coupling between waveguides can cause phase errors, which can also increase device interference.

The array waveguide grating with one channel input and four channels output has central channel wavelengths of 1271nm, 1291nm, 1311nm and 1331nm and central channel wavelength interval of 20 nm.

Based on the above different parameter ranges, the embodiments of the present invention provide the following examples:

1. regarding the size and loss characteristics of AWG devices in relation to the selection of the relative refractive index difference, Δ n, of the waveguide core and cladding, the waveguide core and cladding refractive indices are determined as follows, table 1:

TABLE 1 SiO with different refractive index differences₂Dimensional parameters and loss characteristics of optical waveguides

	Is low in	In	Height of	Super high
					Relative refractive index difference Δ n (%)	0.3	0.45	0.75	1.5～2.0
Waveguide core rulerInch (mum)	8×8	7×7	6×6	4.5×4.5～3×3
					Radius of curvature (μm)	25	15	5	2
Transmission loss (dB/cm)	<0.01	0.02	0.04	0.07

According to table 1, when the refractive index difference is low, the selected waveguide core size and bend radius are large, but the transmission loss is small; when the refractive index difference is high, the waveguide core size and bend radius are selected to be small, but the transmission loss is large. Therefore, for the selection of the refractive indexes of the waveguide core and the waveguide cladding, the transmission loss is ensured to be in a relatively reasonable range, the size of the device is also considered, and the miniaturized device is favorable for the integration and application of the device.

FIG. 12 is a schematic cross-sectional view of a waveguide according to an embodiment of the present invention, in which a relative refractive index difference Δ n between a core and a cladding of a four-channel AWG is 1.5%, and a central wavelength of SiO corresponding to the central wavelength is selected₂Material refractive index is cladding refractive index n₂According to the formula of the relative refractive index difference,

obtaining refractive index n of core layer₁。

2. Regarding the size and spacing of the input channel waveguides, the output channel waveguides, and the arrayed waveguides:

the waveguide structures in the AWG are all symmetrical waveguides, and when the width and the height of the waveguide core are different, the birefringence influence is brought, so that in order to reduce the influence, the width and the thickness of the core layer of the rectangular waveguide and the thickness of the core layer of the slab waveguide are the same, and the size of the core layer can be but is not limited to the embedded waveguide with the size of 4.5 mu mx4.5 mu m.

Input channel waveguide or output channel waveguide spacing d_iArray waveguide spacing d_oThe minimum distance that the adjacent waveguide crosstalk meets the design requirement is provided, and the symmetrical AWGs are equal. Due to the existence of the exponentially decaying optical field at the edge of the waveguide, the outward extension of the optical field may partially overlap with the mode field of the adjacent waveguide, so that the signal of the optical field is coupled into the adjacent waveguide, and coupling occurs. For the output channel waveguide, the coupling between the waveguides can lead the optical power of any channel to be received by the waveguides of other channels, thereby increasing the crosstalk of the device; for arrayed waveguides, coupling between waveguides can cause phase errors, which can also increase device interference.

As the waveguide spacing becomes larger, the overlap of the exponentially decaying portion of the waveguide mode field with the adjacent waveguide mode field becomes smaller, and the corresponding coupling becomes smaller and the crosstalk becomes lower. However, as the spacing between the waveguides increases, the overall size of the device also increases, and the greater the optical loss of light coupled into the arrayed waveguide from the slab waveguide, the greater the insertion loss of the device. Because the value of the distance between the input channel waveguide/output channel waveguide and the array waveguide does not have a fixed formula, when the distance between the waveguides is selected, the embodiment of the invention comprehensively considers the contradiction generated by the size of the device, the insertion loss and the crosstalk requirement, carries out reasonable optimization and selects the minimum waveguide distance meeting the requirement.

The bandwidth is an important index for measuring the spectral utilization rate of the AWG, the embodiment of the invention mainly focuses on the 1dB bandwidth and the 3dB bandwidth, and the spectral bandwidth is related to the distance between the input channel waveguide and the output channel waveguide. When the distance between the input channel waveguide and the output channel waveguide is larger, the bandwidth is smaller; the bandwidth is larger when the input channel waveguide/output channel waveguide spacing is smaller.

The arrayed waveguide grating designed by the embodiment of the invention can be a 1 × 4 arrayed waveguide grating, and four inputs and one output are realized during multiplexing, namely four input channel waveguides and one output channel waveguide; when demultiplexing, the input channel waveguide is one-way output, and the output channels are four-way output, namely one input channel waveguide and four output channel waveguides. Therefore, when the relationship between the input channel waveguide/output channel waveguide spacing and the bandwidth is studied, it is only necessary to study the relationship between the input channel waveguide spacing and the bandwidth during multiplexing and the relationship between the output channel waveguide spacing and the bandwidth during demultiplexing.

FIG. 13 shows the 1dB bandwidth versus output channel waveguide spacing and the 3dB bandwidth versus output channel waveguide spacing for an array waveguide derivative of 12 and an array waveguide spacing of 5 μm. In the range shown in fig. 13, the 1dB bandwidth and the 3dB bandwidth decrease with increasing output channel waveguide spacing, and the trend of variation becomes slower. As the output channel waveguide spacing increases from 5 μm to 15 μm, the 1dB per channel bandwidth decreases by about 5nm and the 3dB per channel bandwidth decreases by about 9 nm. Through tests, when the array waveguide spacing is within the range of 5-10 μm, the relationship between the bandwidth and the output channel waveguide spacing is not greatly different from that in FIG. 13. Therefore, when the array waveguide spacing is within the range of 5-10 μm, the value of the input channel waveguide/output channel waveguide spacing can be flexibly set according to relevant conditions, and the value of the input channel waveguide/output channel waveguide spacing is within the range of 5-12 μm.

3. Regarding the diffraction order m:

the number of diffraction orders m is an important parameter in designing an arrayed waveguide grating. After the number of diffraction orders is determined, other parameters, such as: the focal length R of the planar waveguide and the length difference delta L, FSR between the adjacent arrayed waveguides are also determined. When the number of diffraction orders is large, the device will achieve higher resolution, but a corresponding reduction in the array wave derivative will affect the cross talk of the device. Therefore, in the embodiment of the present invention, an appropriate value should be selected for the derivation stage, taking crosstalk and device size into consideration.

4. Regarding the planar waveguide focal length R, the adjacent array waveguide length difference Δ L, FSR:

(1) regarding FSR:

when the incident angle and the emergent angle are the same, a plurality of groups of m and lambda can satisfy the grating equation, namely, output light waves with the same incident angle and different wavelengths are output from the same output port. The free spectral range is the wavelength range between two diffraction peaks, namely the wavelength interval range of light waves with the same incident angle and different wavelengths and with the same diffraction order m after being diffracted by the array waveguide.

Wherein λ is₀Is the channel center wavelength, n_cIs the effective refractive index of the arrayed waveguide, n_gIs the group index of the arrayed waveguides.

(2) Regarding the planar waveguide focal length R, the adjacent array waveguide length difference Delta L:

when the length difference Delta L between adjacent arrayed waveguides is constant, light intensity diffraction can occur in the output slab waveguide, and after the diffraction order m is determined, Delta L and R are also determined. The focal length of the planar waveguide is also called the Rowland circle diameter, and the value is determined mainly considering the maximum number of channels and the uniformity of the channel loss. The relationship between Δ L, R and m is obtained from the grating equation:

wherein n is_sEffective refractive index of slab waveguide, d_iFor input or output channel waveguide spacing, d_oIs the array waveguide pitch, n_gΔ λ is the wavelength interval for the group index of the arrayed waveguides.

As shown in FIG. 14, as the number m of diffraction orders increases, the focal length R and FSR of the planar waveguide and the length difference Δ L of the adjacent arrayed waveguides increase, the influence of the three aspects and the limiting factor of the maximum channel wave derivative on the device are comprehensively considered, and the number of diffraction orders is taken to be between 8 and 20.

5. With respect to the array wave derivative M:

the array wave derivative is not a critical parameter but affects the device loss and imaging quality. If the number is too small, the diffraction efficiency is lowered, and the diffraction loss becomes too large. Therefore, the number of arrayed waveguides can be designed to be large enough, so that the numerical aperture of the arrayed waveguide is larger than that of the output channel waveguide, and the diffracted light of the input channel waveguide can be completely received by the arrayed waveguide, namely, the narrower the diffraction fringes are, the stronger the brightness is, and the darker the background light is, so that the coupling efficiency can be increased, and the crosstalk and loss among channels can be reduced. Wave derivative M due to minimum array_minThe linear inverse relation with the diffraction order m is formed, and the small number of the array waveguides can cause the input optical field to be partially truncated, so that the sidelobe crosstalk is caused. Therefore, the number of the arrayed waveguides can be increased appropriately to increase the coupling degree and reduce the loss. In this regard, the embodiments of the present invention have studied the substantial influence of different numbers of arrayed waveguides on the arrayed waveguide grating.

In the embodiment of the present invention, a channel corresponding to 1311 μm is selected for observation, and as shown in fig. 15, the output channel waveguide pitch and the array waveguide pitch are both 8 μm. As shown in fig. 16, when the number M of arrayed waveguides increases, the insertion loss thereof becomes smaller to some extent, while crosstalk is also reduced. The increase of the number of the arrayed waveguides increases the optical power received by the arrayed waveguides, thereby reducing the insertion loss of the device; and the increase of the number of arrayed waveguides suppresses secondary peaks of a diffraction far field, thereby reducing channel crosstalk. Therefore, the number of arrayed waveguides can be increased appropriately to achieve reduction in channel crosstalk and insertion loss. However, the number of arrayed waveguides cannot be increased without limit, and the crosstalk of the device is also increased by considering phase errors caused in actual process manufacturing. Therefore, in the arrayed waveguide grating designed by the embodiment of the invention, the number of selectable arrayed waveguides is 11-20.

Fig. 17 shows the bandwidth versus the number of arrayed waveguides, with embodiments of the invention observing primarily 1dB and 3dB bandwidths. In the range shown in fig. 17, the bandwidth decreases as the number of arrayed waveguides increases. According to the test, when the number of arrayed waveguides exceeds 25, the bandwidth hardly changes. When the number of arrayed waveguides was increased from 8 to 20, the 1dB bandwidth per channel was reduced by about 3.2nm and the 3dB bandwidth per channel was reduced by about 4.5 nm.

The embodiment of the invention researches the basic working principle, related parameters and main performance indexes of the arrayed waveguide grating, analyzes the influence of important parameters such as the input channel waveguide/output channel waveguide distance, the arrayed waveguide distance, the number of arrayed waveguides and the like on the related performance indexes, provides the basic design idea of the arrayed waveguide grating, designs the Taper structures of the input channel waveguide, the output channel waveguide and the arrayed waveguide in the arrayed waveguide grating, and provides the optimized design scheme of the four-channel arrayed waveguide grating. The embodiment of the invention optimally designs the four-channel arrayed waveguide grating according to the simulation result by comparing the influence of different parameters of the arrayed waveguide grating on the performance, reduces the size of the arrayed waveguide grating, improves the loss and crosstalk performance of the arrayed waveguide grating and increases the bandwidth to a certain extent.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.