WO2003052864A1

WO2003052864A1 - A multi-mode interference optical attenuator

Info

Publication number: WO2003052864A1
Application number: PCT/CN2002/000768
Authority: WO
Inventors: Lin Yang; Yuliang Liu; Qiming Wang
Original assignee: Institute Of Semiconductors Chinese Academy Of Sciences
Priority date: 2001-12-17
Filing date: 2002-10-30
Publication date: 2003-06-26
Also published as: CN1188740C; CN1427290A

Abstract

This invention relates to a multi-mode interference optical attenuator. The attenuator includes a input waveguide region, two tapered transition regions, two multi-mode interference regions, two double-tapered transition regions, a modulating region and a output waveguide region, wherein a front end of the tapered transition region connects to a tail end of the output waveguide region, a tail end of the tapered transition region connects to a front end of the modulating region, a front end of another double-tapered transition region connects to a tail end of the modulating region, a tail end of another double-tapered transition region connects to a front end of the multi-mode interference region, a front end of another tapered transition region connects to a tail end of the multi-mode interference regions, and a tail end of another tapered transition region connects to a front end of the output waveguide region.

Description

Multimode interference optical attenuator TECHNICAL FIELD

The present invention relates to a waveguide-type optical attenuation device with optical signal intensity modulation. The invention relates specifically to the use

The principle of the Mach-Zender interferometer uses the plasma dispersion effect or the thermo-optic effect to realize the modulation of the phase of the optical signal. The multi-mode interference coupler is used to complete the beam splitting and combining functions of the optical signal, and the multi-mode waveguide is used. Waveguide-type optical attenuation devices as input and output waveguides. Background technique

With the rapid development of the Internet, which has come from the popularity of personal computers, the revolution in conventional communications triggered by digital mobile communication services leading to personal communication, and the emergence of multimedia communication services. The explosion of information has stimulated the rapid growth of communication services. The most direct result of this growth is the so-called "fiber exhaustion" phenomenon. On the one hand, the early investment in optical fiber communication systems is very large, mainly due to the laying of optical cable lines. The cost is high; on the other hand, the existing optical fiber communication system only occupies a small part of the low-loss optical window of the optical fiber; in order to make full use of the existing optical cable facilities to achieve maximum expansion, it is generally considered that dense wavelength division multiplexing System (DWDM) is the best way to solve this problem. Commercial fiber communication systems currently under construction or to be constructed are basically wavelength division multiplexing systems.

As the number of channels increases, the problems inherent in DWDM systems are exposed. Its main problems are manifested in the following aspects:

1. As far as the current level of laser technology is concerned, it is still difficult to achieve stable and consistent power levels for optical signals of different wavelengths from different lasers.

2. Because the absorption coefficients of optical waveguide materials and optical fiber materials are wavelength-dependent, the power loss of optical signals of different wavelengths transmitted in optical devices and optical fibers is different.

3. Since the current gain flatness problem of erbium-doped fiber amplifiers has not been well solved, the gains of optical signals of different channels through erbium-doped fiber amplifiers are also different.

4. If an interference filter is used as the demultiplexer, the optical power loss of each channel will be different due to the different times of reflection of optical signals of different wavelengths.

Therefore, the power levels of the optical signals in the channels in the DWDM system are different. How to solve the power equalization problem of each channel is a problem that must be solved first when the DWDM system becomes practical. If a device is used to attenuate the power of the optical signal with a higher power in each channel, then the power equalization of the optical signal in each channel can be achieved. Such a device is an optical attenuator. There are many commercially available optical attenuators, mainly including the following four −

1. Displacement type optical attenuator: The basic principle is to use a stepping motor to drive the optical fiber to make horizontal or vertical relative movement. The purpose of adjusting the optical signal intensity is to change the relative distance between the two fibers in the horizontal or vertical direction.

2. Coated optical attenuator: Adjust the intensity of the optical signal by plating a metal absorption film or reflection film on the end face of the optical fiber.

3. Attenuator-type optical attenuator: The intensity of the optical signal is adjusted by the stepper motor driving the rotation of the attenuator.

4. Liquid crystal type optical attenuator: The property of changing the crystal orientation of the liquid crystal under the action of an electric field is used to change the relative angle of the two crystal orientations by changing the voltage to achieve the purpose of adjusting the intensity of the optical signal.

However, these optical attenuators are generally large in size, and the device production process used is completely incompatible with existing semiconductor processes, so they cannot be integrated with other optoelectronic devices, and they cannot achieve continuous online attenuation of optical signals, or have poor stability. (Such as the poor environmental performance of the liquid crystal type optical attenuator), it cannot meet the requirements of the existing communication technology for device miniaturization, integration and high environmental stability.

However, waveguide optical attenuators made using planar optical waveguide technology and using the principle of Mach-Zehnder interferometer are completely free of these restrictions. Optical attenuators made with this technology can not only achieve miniaturization of the device, but also The conventional semiconductor process is easy to integrate with other optoelectronic devices. Because carrier dispersion or thermo-optic effect is achieved by carrier injection or heating, it is easy to achieve continuous online attenuation of optical signals. Through reasonable design, it can also be inserted. Optical attenuator with low loss and low power consumption. The object of the present invention is not only to provide a variable optical attenuator with the above advantages, but also to adopt a structure of a multi-mode interferometer, so that it has a more compact device structure and a device than a general waveguide-type optical attenuator. The advantages of larger production tolerance and wider working bandwidth. In addition, since multi-mode input and output waveguide structures are used, the insertion loss of the device can also be made smaller. Summary of the Invention

An object of the present invention is to provide a multi-mode chirped optical attenuator, which has the advantages of high integration, small volume, and high environmental stability. .

A multi-mode interference optical attenuator of the present invention is characterized in that: the multi-mode interference optical attenuator package Including an input waveguide region, two tapered transition regions, two multi-mode interference regions, two double-tapered transition regions, a modulation region, and an output waveguide region, a total of nine parts are included. The tail end of the input waveguide region is connected, its tail end is connected to the front end of the multi-mode interference region, the front end of a double-tapered transition region is connected to the tail end of the multi-mode interference region, its tail end is connected to the front end of the modulation region, and the other The front end of the double-tapered transition area is connected to the tail end of the modulation area, and its tail end is connected to the front end of the multi-mode interference area. The front end of the other tapered transition area is connected to the tail end of the multi-mode interference area, and its tail end is connected to the output. The front ends of the waveguide regions are connected.

The input waveguide area is composed of an input waveguide, which is a multimode waveguide capable of carrying multiple modes. The basic requirements of the multimode waveguide are low coupling loss with single-mode fiber, and the length of the optical waveguide is relatively short.

A tapered transition region is used between the input waveguide region and the multi-mode interference region. The front end of the tapered transition region is connected to the input waveguide region, and the tail end is connected to the multi-mode interference region. The shape of the tapered transition waveguide is similar to that of the input waveguide, and the cross-sectional dimension of the tail end is the same as that of the multi-mode waveguide in the multi-mode interference region.

The front end of the multimode interference region is connected to the tapered transition region, and the tail end is connected to the biconical transition region. The multimode interference region is composed of a multimode waveguide capable of carrying at least three waveguide modes. The mutual interference between the two modes divides the input light coupled from the tapered transition waveguide into two images of equal intensity and phase, and completes the function of splitting a beam of light into two beams.

The front end of the double-tapered transition area is connected to the multi-mode interference area, and the tail end is connected to the modulation area. The double-tapered transition area is composed of two tapered transition waveguides. The double image formed in the multi-mode interference region is low-loss coupled into two single-mode waveguides in the modulation region. The width of the starting ends of the two tapered transition waveguides is half the width of the multi-mode waveguide in the multi-mode interference region The cross-sectional dimension of the tail end is the same as that of the single-mode waveguide in the modulation region.

The front end of the modulation region is connected to the biconical transition region, and the tail end is connected to another biconical transition region. The modulation region is composed of two single-mode waveguides. The two single-mode waveguides are required to have a relatively strong restriction on the optical field. The polarization correlation is good, and the distance between the two single-mode waveguides is large enough to ensure that there is no electromagnetic field energy coupling between the two single-mode waveguides. Plasma is used in one or both of the two single-mode waveguides. Volume dispersion effect or thermo-optic effect is used to realize modulation of optical signal phase.

The front end of the double-tapered transition area is connected to the modulation area, and its tail end is connected to the multi-mode interference area. The double-tapered transition area is composed of two nano-shaped tapered transition waveguides, and the light fields from the two single-mode waveguides The two tapered transition waveguides in the double-tapered transition region are coupled into the multi-mode waveguide in the multi-mode interference region. The basic requirements of these two tapered transition waveguides are: For each tapered transition waveguide, the cross-sectional size of its input end Same cross-section dimensions as single-mode waveguides, The cross-sectional width of the output end is half of the width of the multimode waveguide in the multimode interference region.

The front end of the multimode interference region is connected to the biconical transition region, and the tail end is connected to the output waveguide region. The multimode interference region is composed of a multimode waveguide capable of carrying at least three waveguide modes. The mutual interference between the modes converts the two input light beams coupled through the two tapered transition waveguides into a beam of light to complete the beam combining function.

The front end of the tapered transition region is connected to the multi-mode interference region, and its tail end is connected to the output waveguide region. The tapered transition region is composed of a tapered transition waveguide, and the multi-mode interference region is connected by this tapered transition waveguide. The image formed in the medium is coupled into the output waveguide region with low loss. The basic requirements of this tapered transition waveguide are: the cross-sectional size of the input end is the same as that of the multi-mode waveguide in the multi-mode interference region, and the cross-sectional size of the output end is The cross-sectional dimensions of the output waveguides in the output waveguide region are the same.

The output waveguide area consists of an output waveguide, which is composed of a multimode waveguide capable of carrying multiple waveguide modes. The basic requirements of the output waveguide are low coupling loss with single-mode fiber, and the length of the optical waveguide is also shorter.

The cross section of the entire multimode interference optical attenuator can adopt a waveguide structure with a rectangular cross section or a ridge cross section. BRIEF DESCRIPTION OF THE DRAWINGS

In order to introduce the present invention in detail, the following describes the present invention in detail with reference to the accompanying drawings, in which- FIG. 1 is a three-dimensional (XYZ three-dimensional) schematic diagram of a multi-mode interference optical attenuator having a ridge cross section according to the principle of the present invention, In order to be more visible, the upper cladding of the waveguide is not shown in the figure;

FIG. 2 is a three-dimensional (X-Y-Z three-dimensional) schematic diagram of a multimode interference-type optical attenuator with a rectangular cross-section according to the principles of the present invention. In order to be more visible, the upper cladding of the waveguide is not shown in the figure;

FIG. 3 is a schematic cross-sectional view (XY plane) of a multi-mode interference optical attenuator using a ridge-shaped cross-section structure. Except that the cross-section of the single-mode waveguide modulation region 105 in FIG. The cross-sections can be schematically shown in the figure, the difference is that the width of the ridge region has changed, but this does not affect the understanding of this specification;

4 is a schematic cross-sectional view (X-Y plane) of a single-mode waveguide modulation region 105 of a multimode interference-type optical attenuator using a ridge-shaped structure;

FIG. 5 is a schematic cross-sectional view (XY plane) of a multi-mode interference optical attenuator with a rectangular cross-sectional structure. Except for the cross-section of the single-mode waveguide modulation region 105 in FIG. Cut All the faces can be simply illustrated with this figure, the difference is that the width of the section has changed;

FIG. 6 is a schematic cross-sectional view (X-Y) of a single-mode waveguide modulation region 105 of a multimode interference-type optical attenuator using a rectangular cross-sectional structure. detailed description

The structure of a multimode interference optical attenuator of the present invention. The basic structure of the device is a Mach-Zehnder interferometer. The difference is that it uses a 1x2 multimode interference beam splitter and a 2x1 multimode interference type. The beam combiner replaces the two Y-branch structures of the Mach-Zehnder interferometer. It is different from the general 1x2 multimode interference beam splitter and 2x1 multimode interference beam combiner. For the beam splitter, it The input end is a multimode waveguide instead of a single mode waveguide; for a combiner, its output end is a multimode waveguide instead of a single mode waveguide.

The structure of the multi-mode interference optical attenuator according to the principles of the present invention is described in detail below with reference to FIGS. 1-6. The perspective view of the entire device is shown in FIG. 1 (having a ridge cross-section structure) or FIG. 2 (having a rectangular cross-section structure). As can be seen in the figure, the entire device can be divided into the following nine parts: input waveguide region 101, tapered transition region 102, multi-mode interference region 103, double cone transition region 104, modulation region 105, and double cone transition region 106 , A multi-mode interference region 107, a tapered transition region 108, and an output waveguide region 109. Now introduce each part separately:

1. Input waveguide area 101: This area is composed of the input waveguide 113, which is mainly used to couple the optical signal in the optical fiber into the waveguide-type optical attenuator. The lower the coupling loss with the optical fiber, the better. Since the input fiber is generally a single-mode fiber, its core diameter is generally about 9 microns, and its outer diameter is 125 microns. Since the refractive index difference between its outer and core layers is small, its mode field radius is generally about 5 Microns. For example: Coming SMF-28 fiber has a core diameter of 8.2 microns and an outer diameter of 125 microns. For general materials, such as: Si, Si0 _2, etc., the use of a single mode waveguide structure is adopted regardless of ridge waveguide structure (FIG. 3) or a rectangular waveguide structure (FIG. 5), the cross-sectional dimension of the cross section of single mode fiber The size is very different, so the coupling loss between the fiber and the input waveguide 113 is large, which increases the insertion loss of the entire device. Therefore, we use the input structure of a multimode waveguide, which makes it easy to find the coupling loss with a single-mode fiber. The small size greatly reduces the insertion loss of the entire device.

2. Conical transition region 102: This region is composed of a tapered waveguide 114, whose input end is the same width as the input waveguide 113, and whose tail end is the same width as the multimode waveguide 115. Select such a section Instead of directly connecting the input waveguide 113 to the multimode waveguide 115, the tapered transition waveguide 114 is intended to reduce the energy loss of the optical signal.

3. Multimode interference region 103: This region is composed of a multimode waveguide 115 capable of carrying multiple modes. The mutual interference between multiple modes in the multimode waveguide 115 is used to form one or more images of the input field in the multimode waveguide 115. This is the so-called self-mapping principle. Here, the multi-mode waveguide 115 is used to form a double image of the input field. The formed double images are equal in intensity and have the same phase. That is to say, the input beam is divided by the multi-mode interference region 103. Two beams with the same intensity and the same phase realize the beam splitting function.

4. Double-tapered transition area 104: This area is composed of two nabbed tapered transition waveguides 116, which are symmetrical with respect to the plane of X = 0. If a multimode waveguide The width of 115 is represented by W _mmi , then the two tapered waveguides 116 are located at x iW ^ / 4, and the width at the beginning is half the width of the multi-mode waveguide 115, and the width of the output is the same as that of the single-mode of the modulation region 105. The width of the waveguide 117 is the same. The purpose of doing this is also to reduce the energy loss of the optical signal.

5. Modulation area 105: The modulation area 105 is composed of two single-mode waveguides 117. These two single-mode waveguides 117 are located separately. The basic requirements are that the field-limiting capability is strong and the polarization correlation is good. If the length is properly selected, the electromagnetic field at the end of the single-mode waveguide 117 should be the fundamental mode field of the single-mode waveguide 117. This is because other waveguide modes cannot stably propagate in the single-mode waveguide 117, and the leakage mode Loss of form. If one single-mode waveguide 117 or two single-mode waveguides 117 are heated with a hot electrode at the same time, an additional phase difference will be introduced according to the thermo-optic effect; or carrier injection through a PN junction will be based on the plasma The dispersion effect can also realize the modulation of the optical signal phase. In short, the basic function of this modulation area is to realize the modulation of the phase of the optical signal.

6. Double-tapered transition region 106: It is composed of two tapered transitional waveguides 118 in the shape of a nap. The two tapered transitional waveguides 118 are symmetrical with respect to the plane of X = 0. If the width of the multi-mode waveguide 117 is \ ¥ ^ to indicate, then these two tapered waveguides 118 are located at x-iW ^ M. For each tapered transition waveguide, its input end is the same width as the single-mode waveguide 117 of the modulation region 105, and its output end is The width of the multi-mode waveguide 119 of the multi-mode interference region 107 is half, and the purpose of doing so is to reduce the energy loss of the optical signal.

7. Multimode interference area 107: It is composed of a multimode waveguide 119 capable of carrying multiple waveguide modes. This area is identical in geometry to the multimode interference area 103. The only difference is the way of entering and exiting the light. In the multi-mode interference region 107, two beams of light enter the multi-mode waveguide 119 at the same time, and then a beam of light enters the output waveguide 121 through a tapered transition waveguide 120 through mutual interference between multiple modes in the multi-mode waveguide 119. The physical process occurring in this area is exactly the opposite of the physical process occurring in the multi-mode interference area 103, that is, the physical process in the multi-mode interference area 107 can be regarded as the inverse process of the physical process in the multi-mode interference area 103.

8. Conical transition region 108: It is composed of a tapered transition waveguide 120, which is a tapered transition waveguide.

The cross-sectional size of the input end of 120 is the same as that of the multi-mode waveguide 119 of the multi-mode interference region 107, and its output The cross-sectional size of the end is the same as that of the output waveguide 121 of the output waveguide region 109. This can reduce the energy loss of the optical signal.

9. Output waveguide area 109: It is composed of output waveguide 121, and the cross-sectional size of the output waveguide is the same as that of the input waveguide 113 in the input waveguide area 101. The basic requirement is that the lower the coupling loss with the single-mode optical latent, the better.

The material used to make the variable optical attenuator can be silicon material or silicon dioxide material, or mv group compound materials such as indium phosphide, etc. The cross section of the device can use a ridge waveguide structure (as shown in Figures 1 and 3). (Shown) or a rectangular cross-section structure (as shown in Figure 2 and Figure 4). What needs to be explained here is that when the ridge cross-section structure is used, due to the limitation of the actual etching process, the bottom angle of the corrosion generally deviates from the right angle to a certain extent. A ridge-shaped waveguide structure is used for illustration. The waveguide structure is composed of four parts: a substrate 112, an under cladding layer 111, a waveguide layer 110, and an upper cladding layer 301. The formation process can be described as an example of an SOI ridge waveguide: A layer of silicon dioxide is formed on the silicon substrate by oxidation or ion implantation, and then a thick layer of silicon is formed thereon by epitaxial methods, and then the silicon layer is etched by dry etching or wet etching. A structure with a ridge-shaped cross-section is etched, and then a layer of silicon dioxide is formed as the upper cladding layer 301 by a high-temperature thermal oxidation method or a chemical vapor deposition method, so that an SOI ridge waveguide structure is formed. The refractive index is larger than that of silicon dioxide. According to the effective refractive index method, it can be known that the optical signal will be mainly localized near the ridge region. Depending on the physical effects used, the fabrication of the electrodes is accomplished in different ways. If the thermo-optic effect is used, a layer of metal is further sputtered or thermally evaporated over the silicon oxide layer to heat the electrodes and electrode leads. If the plasma dispersion effect is used, N-type and P-type doped regions and electrode leads must be formed before forming silicon dioxide.

The Gaussian beam from the single-mode fiber is coupled into the device through the input waveguide 113, and then enters the multi-mode waveguide 115 through the tapered transition waveguide 114. Due to the mutual interference between multiple modes in the multi-mode waveguide 115, the Two beams of equal intensity and the same phase are formed at the ends. The two beams of equal intensity enter a two-mode waveguide 117 of the modulation region 105 through a tapered transition waveguide 116, and most of the energy is converted into a single-mode waveguide. The energy of the fundamental mode field in in, other energy is converted into the energy of the leakage mode and lost. Expressed mathematically as follows:

The sum is the electric field distribution in the two single-mode waveguides 117, ω is the frequency of the optical signal, A is the amplitude of the electric field of the optical signal, and t is time. Since the two single-mode waveguides 117 are symmetrically distributed, and the two single-mode waveguides are of interest here, The relative phase of the optical signal in the mode waveguide 117 changes, so the phase portion related to the propagation distance is not shown. If the effective refractive index of one or two of the single-mode waveguides 117 is changed, the light beam propagating therein will introduce an additional phase difference. Generally, the refractive index of the material can be changed by two physical effects, one is plasma Volume dispersion effect, one is the thermo-optic effect. The so-called plasma dispersion effect refers to the phenomenon that the refractive index of a material changes with changes in the carrier concentration, which can be achieved by means of doping or electrical injection; the other is the thermo-optic effect, which refers to the refraction of a material The phenomenon that the rate changes with temperature can be achieved by heating. The two beams of light are coupled into the multimode waveguide 119 with low loss through the two tapered transition waveguides 118. Due to the mutual interference between multiple modes in the multimode waveguide 119, a single spot is formed and coupled into the output through the tapered transition waveguide 120 In the waveguide 121, the purpose of adjusting the intensity of the output light can be achieved by adjusting the intensity of the thermo-optic effect or the plasma dispersion effect. Expressed mathematically as:

E! = {ΑΙ). Χρ [ϊ (ωί + Αφ)]

Ε ₂ = (Α / ΐ). Exp [i (<yt + Αφ ₂ )]

I \ {Α I / 2). Exp [z '(iyt + Δ ^,)] + (Α / ϊ)-& χρ [ί (ωί + Αφ ₂ )] 1

2

= /., cos ² (A ^ / 2) where% represents the additional phase difference introduced by the two single-mode waveguides 117 due to modulation. If modulation is performed on only one of the single-mode waveguides 117, then two One of them is zero. Where Δ = Δ-Δρ ₂ , /. ,,, is the light intensity of the output light field, is the light intensity of the input light field, and its value is. Therefore, by changing the size of ip, the output light intensity with continuously changing intensity can be obtained, so as to achieve the purpose of modulating light intensity.

Claims

1. A multi-mode chirped optical attenuator, characterized in that the multi-mode interference-type optical attenuator includes an input waveguide region, two tapered transition regions, two multi-mode interference regions, and two double cones. The transition region, a modulation region, and an output waveguide region have nine parts. The front end of a tapered transition region is connected to the tail end of the input waveguide region, and the tail end is connected to the front end of the multimode interference region. A double-tapered transition The leading end of the region is connected to the trailing end of the multi-mode interference region, the trailing end of which is connected to the leading end of the modulation region, and the leading end of the other biconical transition region is connected to the trailing end of the modulation region. Connected, the front end of the other tapered transition region is connected to the tail end of the multi-mode interference region, and the tail end is connected to the front end of the output waveguide region.

2. The multimode interference optical attenuator according to claim 1, wherein the input waveguide region is composed of an input waveguide, the input waveguide is a multimode waveguide capable of carrying multiple modes, and the basic of the multimode waveguide is The requirement is that the coupling loss with single-mode fiber is low, and the length of the optical waveguide is relatively short.

3. The multimode interference optical attenuator according to claim 1, characterized in that: a tapered transition region is used between the input waveguide region and the multimode interference region, and the front end of the tapered transition region is connected to the input waveguide region. The tail end is connected to the multi-mode interference region. The tapered transition region is composed of a tapered tapered transition waveguide. The cross-sectional size of the starting end of the tapered transition waveguide is the same as the cross-sectional size of the input waveguide. It has the same cross-sectional dimensions as the multimode waveguide in the multimode interference region.

4. The multi-mode interference-type optical attenuator according to claim 1, characterized in that: the front end of the multi-mode interference region is connected to the tapered transition region, and the tail end thereof is connected to the double-tapered transition region, the multi-mode interference region It consists of a multimode waveguide capable of carrying at least three waveguide modes, and uses the mutual interference between multiple modes in the multimode waveguide to split the input light coupled from the tapered transition waveguide into two images of equal intensity and phase. , Complete the function of splitting a beam of light into two beams.

5. The multi-mode interference optical attenuator according to claim 1, characterized in that: the front end of the double-cone transition area is connected to the multi-mode interference area, and the rear end thereof is connected to the modulation area; It consists of two tapered transition waveguides in the shape of a tap. The two tapered transition waveguides are used to couple the double image formed in the multi-mode interference region with low loss to two single-mode waveguides in the modulation region. The width of the start end of each tapered transition waveguide is half of the width of the multimode waveguide in the multimode interference region, and the cross-sectional size of the tail end thereof is the same as that of the single-mode waveguide in the modulation region.

6. The multi-mode interference optical attenuator according to claim 1, characterized in that: the front end of the modulation area is connected to the double-cone transition area, and the rear end thereof is connected to the other double-cone transition area, and the modulation area is composed of two A single-mode waveguide is required. The two single-mode waveguides are required to have a strong ability to confine the light field, and the polarization correlation is good. The spacing between the waveguides must be large enough to ensure that there is no electromagnetic field energy coupling between the two single-mode waveguides. Plasma dispersion or thermo-optic effects are used to implement optical signals in one or both of the two single-mode waveguides. Phase modulation.

7. The multi-mode interference-type optical attenuator according to claim 1, characterized in that: the front end of the double-tapered transition area is connected to the modulation area, and the rear end thereof is connected to the multi-mode interference area. It consists of two tapered transition waveguides in the shape of a cone. The light field from the two single-mode waveguides is coupled into the multi-mode waveguide in the multi-mode interference region through the two tapered transition waveguides in the double-tapered transition region. The basic requirements of the shape transition waveguide are: For each tapered transition waveguide, the cross-sectional size of the input end is the same as that of the single-mode waveguide, and the cross-sectional width of the output end is half the width of the multi-mode waveguide in the multi-mode interference region.

8. The multi-mode interference optical attenuator according to claim 1, characterized in that: the front end of the multi-mode interference region is connected to the double-cone transition region, and the tail end thereof is connected to the output waveguide region, and the multi-mode interference region is formed by A multi-mode waveguide capable of carrying at least three waveguide modes. By using the mutual interference between multiple modes in the multi-mode waveguide, the two input light beams coupled through the two tapered transition waveguides are turned into a beam of light. Beam function.

9. The multi-mode interference optical attenuator according to claim 1, characterized in that: a front end of the tapered transition region is connected to the multi-mode interference region, and a tail end thereof is connected to the output waveguide region, and the tapered transition region is formed by a The tapered transition waveguide is composed of a nano-shaped cone, and the image formed in the multi-mode interference region is coupled to the output waveguide region with low loss through this tapered transition waveguide. The basic requirements of this tapered transition waveguide are: the cross-sectional size of its input end The cross-sectional size of the multi-mode waveguide in the multi-mode interference region is the same, and the cross-sectional size of its output end is the same as that of the output waveguide in the output waveguide region.

10. The multimode interference optical attenuator according to claim 1, wherein the output waveguide region is composed of an output waveguide, and the output waveguide is composed of a multimode waveguide capable of carrying a plurality of waveguide modes. The basic requirement is that the coupling loss with single-mode fiber is relatively low, and the length of the optical waveguide is also relatively short.

11. The multi-mode interference optical attenuator according to claim 1, characterized in that the cross section of the entire multi-mode interference optical attenuator can be a waveguide structure with a rectangular cross section or a ridge cross section.