阅读说明：本技术 一种基于微环的矩形光滤波器及其设计方法 (Micro-ring-based rectangular optical filter and design method thereof ) 是由 李佳琛 陈明华 于 2019-11-01 设计创作，主要内容包括：公开了一种基于微环的矩形光滤波器,其能够免去独立调谐多腔的困扰,结构简单,尺寸小,调谐简便,对于制造误差不敏感,具有良好的通带平坦度和矩形系数,能够获得相比于普通微环大约两倍的群延时。该基于微环的矩形光滤波器具有第一端口(In)、第二端口(Through)、第三端口(Drop)、第四端口(Add),在双臂耦合微环的波导上添加亚波长大小的微结构来构成反射点,激励起反向传播的模式,顺时针和逆时针的两种传播方向的模式通过添加的微结构构成反射点而引起背向散射相互耦合,新的谐振峰在原有谐振峰的位置处发生谱峰分裂,通过控制耦合的强弱来调整通带的平坦程度而获得矩形光滤波器。还提供了设计方法。(Disclosed is a micro-ring-based rectangular optical filter which can eliminate the trouble of independent tuning of multiple cavities, has a simple structure, a small size, simple and convenient tuning, is insensitive to manufacturing errors, has good pass band flatness and rectangular coefficients, and can obtain approximately twice the group delay compared with a common micro-ring. The rectangular optical filter based on the micro-ring is provided with a first port (In), a second port (Through), a third port (Drop) and a fourth port (Add), a micro-structure with a sub-wavelength size is added on a waveguide of the double-arm coupling micro-ring to form a reflection point, a mode of back propagation is excited, modes In two propagation directions of clockwise and anticlockwise form the reflection point Through the added micro-structure to cause back scattering mutual coupling, a new resonance peak is subjected to spectral peak splitting at the position of the original resonance peak, and the flatness degree of a pass band is adjusted by controlling the coupling strength to obtain the rectangular optical filter. A design method is also provided.)

1. A kind of rectangle optical filter based on micro-ring, characterized by that: the rectangular optical filter based on the micro-ring is provided with a first port (In), a second port (Through), a third port (Drop) and a fourth port (Add), a micro-structure with a sub-wavelength size is added on a waveguide of the double-arm coupling micro-ring to form a reflection point, a mode of back propagation is excited, modes In two propagation directions of clockwise and anticlockwise form the reflection point Through the added micro-structure to cause back scattering mutual coupling, a new resonance peak is subjected to spectral peak splitting at the position of the original resonance peak, and the flatness degree of a pass band is adjusted by controlling the coupling strength to obtain the rectangular optical filter.

2. The micro-ring based rectangular optical filter of claim 1, wherein: the micro-structure is a circular, strip-shaped or fracture type sub-wavelength structure.

3. The micro-ring based rectangular optical filter of claim 2, wherein: a fracture type microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the fracture length of the microstructure is 0.2um-0.4 um.

4. The micro-ring based rectangular optical filter of claim 3, wherein: a fracture type microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the fracture length of the microstructure is 0.3 um.

5. The micro-ring based rectangular optical filter of claim 1, wherein: the rectangular optical filter based on the micro-ring is arranged on a 200nm silicon nitride platform, the width of a waveguide is 1.4um, the radius of the micro-ring is 500um, and the coupling distance of the micro-ring is 0.8 um; a fracture type microstructure is arranged in the center of the micro-ring, and the fracture length of the microstructure is 0.2 um; light is input from a first port (In), a part of light is coupled In modes with opposite propagation directions every time the light passes through the microstructure, when the light is reflected and coupled for many times In the micro-ring, two stable modes with opposite rotation directions exist, spectral peak splitting occurs after the two modes are coupled with each other, and the flatness of a pass band is adjusted by controlling the coupling strength of the two modes; the third port (Drop) and the fourth port (Add) have optical outputs, and compared with the fourth port (Add), the extinction ratio of the fourth port (Add) is larger, the passband is flatter, and the fourth port (Add) is used as an output port to obtain a rectangular filter.

6. The micro-ring based rectangular optical filter of claim 1, wherein: the rectangular optical filter based on the micro-ring is arranged on a 100nm silicon nitride platform, the width of a waveguide is 2.8um, the radius of the micro-ring is 600um, and the coupling distance of the micro-ring is 1.1 um; the center of the micro-ring is provided with a strip-shaped microstructure, and the size of the microstructure is 0.5um to 0.2 um; light is input from a first port (In), a part of light is coupled In modes with opposite propagation directions every time the light passes through the microstructure, when the light is reflected and coupled for many times In the micro-ring, two stable modes with opposite rotation directions exist, spectral peak splitting occurs after the two modes are coupled with each other, and the flatness of a pass band is adjusted by controlling the coupling strength of the two modes; the third port (Drop) and the fourth port (Add) have optical outputs, and compared with the fourth port (Add), the extinction ratio of the fourth port (Add) is larger, the passband is flatter, and the fourth port (Add) is used as an output port to obtain a rectangular filter.

7. A method for designing a rectangular optical filter based on microrings according to claim 1, wherein: the sub-wavelength micro-structure is etched out by single exposure through layout design in the waveguide.

8. The method of claim 7, wherein: the central wavelength of the rectangular optical filter is tuned through the heating electrode, the heating electrode is grown and etched on the surface of the chip, the local temperature around the heating electrode is changed by changing the voltage of the heating electrode, the heat is diffused to the waveguide to correspondingly change the refractive index of the waveguide, and further the central wavelength of the rectangular optical filter is changed.

Technical Field

The invention relates to the technical field of optical communication and photoelectron, in particular to a rectangular optical filter based on a micro-ring and a design method of the rectangular optical filter based on the micro-ring.

Background

The rectangular optical filter based on the micro-ring has important application in the aspects of wavelength division multiplexing and flat group delay realization. The related micro-ring based rectangular optical filter structure includes: multiple rings coupled in series, multiple rings coupled in parallel, etc.

The biggest disadvantage of this structure is that it needs to use a plurality of independent tuning units (such as heating electrodes) to perform post-compensation for errors introduced by the manufacture of each micro-ring, and is inconvenient to control and use. Secondly, the size of the whole device is also increased, which is not favorable for dense integration.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a rectangular optical filter based on a micro-ring, which can avoid the trouble of independently tuning multiple cavities, has simple structure, small size, simple and convenient tuning, is insensitive to manufacturing errors, has good pass band flatness and rectangular coefficient, and can obtain about twice group delay compared with the common micro-ring.

The technical scheme of the invention is as follows: the rectangular optical filter based on the micro-ring is provided with a first port (In), a second port (Through), a third port (Drop) and a fourth port (Add), wherein a micro-structure with sub-wavelength size is added on a waveguide of the double-arm coupling micro-ring to form a reflection point, a mode of backward propagation is excited, modes In two propagation directions of clockwise and anticlockwise form the reflection point Through the added micro-structure to cause back scattering mutual coupling, a new resonance peak generates spectrum peak splitting at the position of the original resonance peak, and the flatness of a pass band is adjusted by controlling the coupling strength to obtain the rectangular optical filter.

According to the invention, a reflection point is formed by adding a micro structure with a sub-wavelength size on a waveguide of a double-arm coupling micro-ring, a mode of reverse propagation is excited, modes in two propagation directions of clockwise and anticlockwise form the reflection point through the added micro structure to cause back scattering mutual coupling, a new resonance peak is subjected to spectrum peak splitting at the position of the original resonance peak, and the flatness of a pass band is adjusted by controlling the coupling strength to obtain the rectangular optical filter, so that the trouble of independently tuning multiple cavities can be avoided because the micro-structure is formed by only one micro-ring; because a sub-wavelength micro-structure is added on the existing micro-ring waveguide, the rectangular optical filter has the advantages of simple structure, small size, simple and convenient tuning and insensitivity to manufacturing errors; because of the line standing wave mode formed in the micro-ring, the light output from the fourth port has the optical path which is twice of the light output from the third port of the original output end, so the group delay and the extinction ratio are correspondingly changed into twice of the original output, the extinction ratio is higher, and the passband is flatter, which means that the rectangular coefficient of the optical filter is better.

The design method of the rectangular optical filter based on the micro-ring is also provided, and the micro-structure with the sub-wavelength is etched out through single exposure by performing layout design in the waveguide.

Drawings

Fig. 1 shows a schematic structural diagram of a rectangular optical filter based on microrings according to the present invention.

FIG. 2a shows a circular microstructure; FIG. 2b shows a microstructure in the form of a bar; fig. 2c shows a microstructure of the fracture type.

Fig. 3 shows the proportion of back-scattered and forward-transmitted light caused by the reflection points as a function of the fracture length.

Fig. 4 shows the optical loss due to the reflection point as a function of the break length.

Fig. 5 shows a schematic structural diagram of a specific rectangular optical filter based on microrings according to the present invention.

Fig. 6 shows transmission responses of the third port (Drop) and the fourth port (Add) of the micro-ring based rectangular optical filter of fig. 5.

Fig. 7 shows a schematic structural diagram of another specific rectangular optical filter based on microrings according to the present invention.

Fig. 8 shows transmission responses of the third port (filter 1 port) and the fourth port (filter 2 port) of the micro-ring based rectangular optical filter of fig. 7.

Detailed Description

As shown In fig. 1, the rectangular optical filter based on the micro-ring has a first port In, a second port Through, a third port Drop, and a fourth port Add, wherein a sub-wavelength micro-structure is added to a waveguide of the double-arm coupled micro-ring to form a reflection point, a mode of backward propagation is excited, modes In two propagation directions of clockwise and counterclockwise form the reflection point to cause back scattering mutual coupling, a new resonance peak is subjected to spectral peak splitting at the position of the original resonance peak, and the flatness of a pass band is adjusted by controlling the coupling strength to obtain the rectangular optical filter.

According to the invention, a reflection point is formed by adding a micro structure with a sub-wavelength size on a waveguide of a double-arm coupling micro-ring, a mode of reverse propagation is excited, modes in two propagation directions of clockwise and anticlockwise form the reflection point through the added micro structure to cause back scattering mutual coupling, a new resonance peak is subjected to spectrum peak splitting at the position of the original resonance peak, and the flatness of a pass band is adjusted by controlling the coupling strength to obtain the rectangular optical filter, so that the trouble of independently tuning multiple cavities can be avoided because the micro-structure is formed by only one micro-ring; because a sub-wavelength micro-structure is added on the existing micro-ring waveguide, the rectangular optical filter has the advantages of simple structure, small size, simple and convenient tuning and insensitivity to manufacturing errors; due to the standing wave mode formed in the micro-ring, the light output from the fourth port Add has the optical path which is twice of the light output from the third port Drop of the original output end, so that the group delay and the extinction ratio are correspondingly changed into twice of the original output light, the extinction ratio is higher, the pass band is flatter, and the rectangular coefficient of the optical filter is better.

Preferably, the shape of the sub-wavelength reflection point is arbitrary in the case where the processing condition is satisfied. For example, the microstructures are circular (as shown in fig. 2 a), stripe-shaped (as shown in fig. 2 b), or broken (as shown in fig. 2 c) subwavelength structures.

Specific subwavelength reflecting dot shapes and sizes need to be designed according to specific integration platforms and requirements. The scattering condition introduced by the reflection point is characterized by a coupling coefficient and loss. The coupling coefficient represents the proportion of the clockwise (anticlockwise) light converted into the anticlockwise (clockwise) light after passing through the defect point once, namely the coupling strength of the two kinds of light with rotation directions and determines the splitting degree (pass band flatness) of the resonance peak; loss means loss introduced by light passing through a defect point (scattering in other directions) in addition to light converted into two handedness. Moreover, the coupling coefficient and the loss are always in a positive correlation relationship, that is, the stronger the optical coupling of the two types of rotation directions, the larger the size of the reflection point is required to be, the more energy is lost at the same time, and the Q value is correspondingly reduced for the micro-ring. Therefore, the shape and size of the defect needs to be carefully designed in order to obtain sufficient reflected energy while reducing the additional loss of light energy.

Preferably, the micro-ring based rectangular optical filter is: a fracture type microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the fracture length of the microstructure is 0.2um-0.4 um.

Specifically, the rectangular optical filter based on the microring is as follows: a fracture type microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the fracture length of the microstructure is 0.3 um.

Or, the micro-ring based rectangular optical filter is: a circular microstructure is arranged in the center of a silicon nitride micro-ring waveguide which is 1.4um wide and 0.2um thick, and the radius of the microstructure is equal to 0.2 um.

Assuming a fracture-type microstructured reflection point in the center of a 1.4um wide, 0.2um thick silicon nitride waveguide, the relationship between the fraction of light that is backscattered and transmitted in the forward direction due to this reflection point and the fracture length can be obtained as shown in fig. 3.

As can be seen from fig. 3 and 4, it can be seen that as the size of the reflection spot increases, the through transmission ratio decreases while the back scattering ratio remains substantially constant. However, when the size of the reflection point is too large, the scattering rate in other directions increases, and the loss increases because light escapes from the waveguide more.

One specific example is as follows.

As shown in fig. 5, the rectangular optical filter based on micro-ring is disposed on a 0.2um thick silicon nitride platform (the platform can be other, and herein, it is only used for illustration and not meant to be limiting), the width of the waveguide is 1.4um, the radius of the micro-ring is 500um, and the coupling pitch of the micro-ring is 0.8 um; a fracture type microstructure is arranged in the center of the micro-ring, and the fracture length of the microstructure is 0.2 um; light is input from the first port In, a part of light is coupled In a mode with opposite propagation directions every time the light passes through the microstructure, when the light is reflected and coupled for many times In the micro-ring, two stable modes with opposite rotation directions exist, spectral peak splitting occurs after the two modes are coupled with each other, and the flatness degree of a pass band is adjusted by controlling the coupling strength of the two modes; the third port Drop and the fourth port Add both have optical outputs, and compared with the fourth port Add, the extinction ratio of the third port Drop and the fourth port Add is larger, the passband is flatter, and the rectangular filter is obtained by using the fourth port Add as an output port.

If the micro-ring waveguide does not have the reflection point, the micro-ring waveguide is a pure micro-ring filter, light is output from the third port Drop, transmission lines meet a Lorentzian type, and the fourth port Add does not output light; however, after the reflection point is added, a small part of light can be coupled to the mode in the opposite propagation direction after passing through once, when the light is reflected and coupled for many times in the micro-ring, two stable modes with opposite rotation directions exist, the two modes are coupled with each other to generate spectral peak splitting, and the flatness of the passband can be controlled by controlling the coupling strength of the two modes. At this time, both the fourth port Add and the third port Drop will have light output, compared to the fourth port Add, which has a larger extinction ratio and flatter passband. Therefore, an optical rectangular filter can be obtained by using the fourth port Add as an output port. The transmission response of both ports is shown in fig. 6.

After the addition of the reflection point, it can be seen that the microring also has a light output at the fourth port Add. The insertion loss of this port is 8dB and the bandwidth is about 7 GHz. It is clear that the transmission line of the fourth port Add has a flat passband and steeper edges. Compared with the common micro-ring Lorentz type transmission line (the rectangular coefficient of 20dB/3dB is about 9.8), the rectangular coefficient of the transmission line of the fourth port Add can reach 2.8. Compared with the common micro-ring, the group delay of the external cavity is doubled, which is equivalent to obtaining longer equivalent cavity length with the same device size. In addition, the center wavelength of the micro-ring filter can be tuned by heating the electrode. The problem of independently tuning multiple cavities can be avoided because the micro-ring is only formed by one micro-ring. The optical filter based on the sub-wavelength reflection point micro-ring has the advantages of simple structure, small size, simple and convenient tuning and insensitivity to manufacturing errors; the pass band flatness and the rectangular coefficient are good; approximately twice the group delay compared to a normal micro-ring can be achieved. Therefore, the structure has excellent performance as a rectangular optical filter and a flat-top time delay structure.

Fig. 7 shows another specific embodiment. The rectangular optical filter based on the micro-ring is arranged on a 100nm silicon nitride platform, the width of a waveguide is 2.8um, the radius of the micro-ring is 600um, and the coupling distance of the micro-ring is 1.1 um; the center of the micro-ring is provided with a strip-shaped microstructure, and the size of the microstructure is 0.5um to 0.2 um; light is input from the first port In, a part of light is coupled In a mode with opposite propagation directions every time the light passes through the microstructure, when the light is reflected and coupled for many times In the micro-ring, two stable modes with opposite rotation directions exist, spectral peak splitting occurs after the two modes are coupled with each other, and the flatness degree of a pass band is adjusted by controlling the coupling strength of the two modes; the third port Drop and the fourth port Add both have optical outputs, and compared with the fourth port Add, the extinction ratio of the third port Drop and the fourth port Add is larger, the passband is flatter, and the rectangular filter is obtained by using the fourth port Add as an output port.

This reflection point gives rise to a reflection coefficient of 2.72e-4, and the energy lost per pass of the reflection point is about 0.2%.

Due to this reflection point, there will also be a light output at the "filter 2 end", as shown in fig. 8. Compared with the 'filtering 1 end' and the 'filtering 2 end', the extinction ratio is larger, the pass band is flat, and therefore the rectangular coefficient is better. The insertion loss of the filter 2 end is 9dB, the Q value reaches 4.8e5, and the rectangular coefficient is 3. It is also well suited as a rectangular optical filter.

The design method of the rectangular optical filter based on the micro-ring is also provided, and the micro-structure with the sub-wavelength is etched out through single exposure by performing layout design in the waveguide.

Preferably, the central wavelength of the rectangular optical filter is tuned through the heating electrode, the heating electrode is grown and etched on the surface of the chip, the local temperature around the heating electrode is changed by changing the voltage of the heating electrode, the heat is diffused to the waveguide, the refractive index of the waveguide is correspondingly changed, and the central wavelength of the rectangular optical filter is further changed.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications, equivalent variations and modifications made to the above embodiment according to the technical spirit of the present invention still belong to the protection scope of the technical solution of the present invention.