阅读说明：本技术 一种宽波段高消光比片上集成偏振器及设计方法 (Broadband high-extinction-ratio on-chip integrated polarizer and design method ) 是由 毛玉政 陈琳 王少华 袁钊 谢良平 于 2021-08-27 设计创作，主要内容包括：本发明属于集成光子学、光传感技术领域,具体涉及一种宽波段高消光比片上集成偏振器及设计方法。本发明宽波段高消光比片上集成偏振器包括衬底6、上包层5、以及设置在衬底和上包层之间的波导芯层,所述波导芯层按光传播方向顺次分成三部分,分别为输入直波导芯层(1)、倾斜光栅波导芯层(2)及输出直波导芯层(3),其中,设置在输入直波导芯层(1)与输出直波导芯层(3)之间的倾斜光栅波导芯层(2)包含若干个周期且相互倾斜平行设置。本发明提供的偏振器结构简单、工艺实现难度低,同时利用一维光子晶体能带理论设计倾斜光栅参数,可得到较大的工作带宽,具有较大加工误差容限,同时可保证TM模式低损透射而TE模式高效反射,实现超高偏振消光比。(The invention belongs to the technical field of integrated photonics and optical sensing, and particularly relates to an on-chip integrated polarizer with a wide waveband high extinction ratio and a design method. The integrated polarizer on the broadband high extinction ratio chip comprises a substrate 6, an upper cladding 5 and a waveguide core layer arranged between the substrate and the upper cladding, wherein the waveguide core layer is sequentially divided into three parts according to the light propagation direction, namely an input straight waveguide core layer (1), an inclined grating waveguide core layer (2) and an output straight waveguide core layer (3), wherein the inclined grating waveguide core layer (2) arranged between the input straight waveguide core layer (1) and the output straight waveguide core layer (3) comprises a plurality of periods and is arranged in parallel in an inclined mode. The polarizer provided by the invention has the advantages of simple structure and low process realization difficulty, and simultaneously designs inclined grating parameters by utilizing the energy band theory of the one-dimensional photonic crystal, so that a larger working bandwidth can be obtained, a larger processing error tolerance is realized, meanwhile, the low-loss transmission of a TM mode and the high-efficiency reflection of a TE mode can be ensured, and the ultrahigh polarization extinction ratio is realized.)

1. The integrated polarizer is characterized by comprising a substrate 6, an upper cladding 5 and a waveguide core layer arranged between the substrate and the upper cladding, wherein the waveguide core layer is sequentially divided into three parts according to the light propagation direction, namely an input straight waveguide core layer (1), an inclined grating waveguide core layer (2) and an output straight waveguide core layer (3), and the inclined grating waveguide core layer (2) arranged between the input straight waveguide core layer (1) and the output straight waveguide core layer (3) is in a plurality of periods and is arranged in parallel in an inclined mode.

2. The integrated polarizer of claim 1, wherein the input straight waveguide core layer (1) and the tilted grating waveguide core layer (2) are parallel to the output straight waveguide core layer (3) near the end face of the output straight waveguide core layer (3).

3. The integrated polarizer of claim 1, wherein the input straight waveguide core layer (1) and the output straight waveguide core layer (3) have the same structure, and the projection of the etching depth and width of the tilted grating waveguide core layer (2) in the transmission direction is the same size as the input straight waveguide core layer (1)/the output straight waveguide core layer (3).

4. The integrated polarizer of claim 1, wherein the refractive index of the input straight waveguide core (1), the tilted grating waveguide core (2) and the output straight waveguide core (3) are the same and larger than the refractive index of the upper cladding (5) in the gap between them.

5. The integrated polarizer of claim 1, wherein the tilt angle of the tilted grating waveguide core layer (2) is not larger than

6. A design method of the integrated polarizer on the broadband high extinction ratio chip according to any one of claims 1 to 5, characterized in that the normalized frequencies of the TE and TM modes are calculated by using the one-dimensional photonic crystal energy band theoryChinese angelica root and stemNormalized wave vector k₁Selecting the overlapped boundary of two band gaps of TE mode forbidden band and TM conduction band to determine the inclination angle, gap and grating period of the inclined grating.

7. The design method of the integrated polarizer on the chip with the wide waveband and the high extinction ratio as claimed in claim 6, wherein the effective refractive index of the inclined grating waveguide core layer (2) is n₁With refractive index n of the upper cladding in the gap₂And both widths are a₁、a₂According to the one-dimensional photonic crystal energy band theory, the normalized frequency of the TE and TM energy band structures can be respectively calculated by using a transmission matrix methodAnd normalized wave vector k₁Distribution of the planes.

8. The method of claim 7, wherein the method comprises normalizing the frequency of the polarizer to obtain a normalized valueNormalized wave vector k₁Relation straight lineThe overlapping of the energy band structure can determine the overlapping area of two band gaps of the TE mode forbidden band and the TM conduction band.

9. The integrated polarizer of claim 8, wherein the upper and lower boundaries of the overlapped region of the two band gaps of the TE mode forbidden band and the TM conduction band are determined according to the TE mode forbidden bandCalculating and obtaining the straight grating period

10. The method of claim 9, wherein the period d of the straight grating, the period a of the tilted grating, and the width a of each dielectric layer are used₁And a₂The parameters are determined.

Technical Field

The invention belongs to the technical field of integrated photonics and optical sensing, and particularly relates to an on-chip integrated polarizer with a wide waveband high extinction ratio and a design method.

Background

In many fields of optical fiber communication and optical sensing systems, such as optical switches, integrated optical gyroscopes, polarization coherent detection, etc., in order to suppress polarization-dependent errors, only single-mode optical transmission is allowed, and therefore, a polarization control function is essential. The on-chip polarization control device has attracted attention because of its advantages of small size, stable performance, mass production and the like. In recent years, Polarization control devices based on different structural principles have been implemented including a Polarization Beam Splitter (PBS), a Polarization Rotator (PR), and an on-chip polarizer. Among them, a polarizing beam splitter based on a curved Directional Coupler (DC) and a polarizer based on a surface plasmon waveguide are reported in a great deal of research. The polarization beam splitter based on the DC structure can realize the separation of TE and TM modes, has a relatively simple structure, is relatively sensitive to wavelength and temperature, and needs to design a bending structure in order to realize higher extinction ratio, thereby increasing the size and the loss of a device; and the polarizer based on the surface plasma waveguide mainly utilizes the attenuation of TM mode light in the surface transmission of mixed plasma, and the TE mode transmission in the dielectric waveguide is hardly influenced, so that extremely high polarization extinction ratio (more than 30 dB) can be obtained. But the structure is complex, and a metal film with negative refractive index needs to be deposited to form surface plasma elements, so that the process difficulty is increased; and the structure requires the phase matching of the dielectric waveguide and the surface plasma waveguide mode, so the structure is very sensitive to the size change of the waveguide, and the higher requirement is also provided for the etching precision. The two polarization control structures have defects in the aspects of bandwidth, extinction ratio, process difficulty and the like, and the application and popularization of the two polarization control structures in the field of photonic integration are greatly limited.

Disclosure of Invention

Aiming at the defects of the existing structural design, the invention provides a design of an integrated polarizer on a wide-band high-extinction-ratio chip with a compact structure and large processing error tolerance. In order to achieve the purpose, the invention adopts the following technical scheme:

the technical scheme of the invention is as follows: the integrated polarizer comprises a substrate 6, an upper cladding 5 and a waveguide core layer arranged between the substrate and the upper cladding, wherein the waveguide core layer is sequentially divided into three parts according to the light propagation direction, namely an input straight waveguide core layer 1, an inclined grating waveguide core layer 2 and an output straight waveguide core layer 3, wherein the inclined grating waveguide core layers 2 arranged between the input straight waveguide core layer 1 and the output straight waveguide core layer 3 are a plurality of and are mutually inclined and parallel.

The end surfaces of the input straight waveguide core layer 1 and the inclined grating waveguide core layer 2, which are adjacent to the output straight waveguide core layer 3, are parallel to the output straight waveguide core layer 3, so that efficient diffraction of the grating is realized.

The input straight waveguide core layer 1 and the output straight waveguide core layer 3 have the same structure, and the projection of the etching depth and width of the inclined grating waveguide core layer 2 in the light transmission direction is the same as the dimension of the input straight waveguide core layer 1/the output straight waveguide core layer 3, so that the insertion loss of the polarizer is effectively reduced.

The refractive indexes of the input straight waveguide core layer 1, the inclined grating waveguide core layer 2 and the output straight waveguide core layer 3 are the same and are larger than that of the upper cladding layer 5 arranged in the gap between the input straight waveguide core layer and the inclined grating waveguide core layer, so that the process is low in implementation difficulty and easy to implement.

The tilt angle of the tilted grating waveguide 2 is not more thanThereby reducing the total reflection of the TM mode.

A design method of the integrated polarizer on the broadband high extinction ratio chip calculates the relationship between the normalized frequency and the normalized wave vector of two modes of TE and TM by utilizing a one-dimensional photonic crystal energy band theory, selects a band gap with overlapped band gaps of two parts of the TE mode forbidden band and the TM conduction band to determine the inclination angle, the gap and the grating period of the inclined grating so as to realize efficient reflection of the TE mode and efficient transmission of the TM mode, and further realize ultrahigh polarization extinction ratio in a broadband range.

Effective refractive index of core layer 2 of tilted grating waveguideIs n₁With refractive index n of the upper cladding in the gap₂And both widths are a₁、a₂According to the one-dimensional photonic crystal energy band theory, the normalized frequency of the TE and TM energy band structures can be respectively calculated by using a transmission matrix methodAnd normalized wave vector k₁Distribution of the planes.

According to normalized frequencyNormalized wave vector k₁Relation straight lineAt normalized frequency with band structureAnd normalized wave vector k₁The overlapping of the plane distribution can determine the overlapping area of two band gaps of the TE mode forbidden band and the TM conduction band.

And calculating and obtaining the period d of the straight grating according to the upper and lower boundaries of the two band gap overlapping regions of the TE mode forbidden band and the TM conduction band.

Using the period d of the straight grating, the period a of the inclined grating and the width a of each dielectric layer₁And a₂The parameters are determined.

Compared with the prior art, the invention has the following beneficial effects:

the polarizer provided by the invention has a simple structure and low process realization difficulty, simultaneously designs inclined grating parameters by utilizing the one-dimensional photonic crystal energy band theory, can obtain larger working bandwidth, has free parameter selection and larger processing error tolerance, and simultaneously selects the overlapping band gap design of a TM conduction band and a TE forbidden band, can ensure the low-loss transmission of the TM mode and the high-efficiency reflection of the TE mode, thereby realizing the ultrahigh polarization extinction ratio of more than 30 dB.

Drawings

FIG. 1 is a schematic diagram of a tilted grating waveguide polarizer according to the present invention;

FIG. 2 is a schematic diagram of a planar straight grating structure;

FIG. 3 is a diagram of the band structure of a grating;

FIG. 4 is a field profile for TE mode and TM mode;

fig. 5 is an output spectrum of the polarizer.

Detailed Description

In order to make the technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be described in detail and completely 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, but not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention is described in further detail below with reference to the accompanying drawings:

referring to fig. 1, the polarizer on a broadband high extinction ratio chip of the invention mainly comprises an input straight waveguide core layer 1, an inclined grating waveguide core layer 2 and an output straight waveguide core layer 3. The etching depths of the input straight waveguide core layer 1, the inclined grating waveguide core layer 2 and the output straight waveguide core layer 3 are the same, and the width of the projection of the inclined grating waveguide core layer 2 in the transmission direction is the same as the width of the input straight waveguide core layer 1/the width of the output straight waveguide core layer 3. TE and TM mixed mode light enters from the input straight waveguide core layer 1 and is transmitted through the inclined grating core layer 2, wherein the TE mode light is efficiently reflected, and the TM mode light is transmitted in the output straight waveguide core layer 3 continuously in a low-loss mode.

Inclined grating waveguide core layer 2 according to refractive index n₁、n₂And width a₁、a₂Periodically and alternately arranged, and has a fixed included angle theta with the transmission direction and a core layer refractive index n₂The refractive index of the upper cladding layer is same as that of the upper cladding layer 5. Tilted grating period a ═ a₁+a₂The method can be obtained by one-dimensional photonic crystal band theory calculation.

The invention relates to a design method of the integrated polarizer on the broadband high extinction ratio chip, which is beneficial toCalculating the normalized frequency of two modes of TE and TM by using one-dimensional photonic crystal energy band theoryAnd normalized wave vector k₁Selecting a band gap with overlapped band gaps of two parts of band gaps of a TE mode forbidden band and a TM conduction band to determine the inclination angle, the gap and the grating period of the inclined grating so as to realize efficient reflection of the TE mode and efficient transmission of the TM mode, thereby realizing ultrahigh polarization extinction ratio in a wide band range, and the detailed process is as follows:

step 1, as shown in FIG. 2, a straight grating structure, n₁The effective refractive index of the grating waveguide core layer is in structural relation with the inclined grating: the period d is a multiplied by sin theta, the included angle phi between light and the normal of an incident plane and the inclination angle theta meet the relation phi + theta is 90 degrees, and the etching layer width scaling factor f is defined as d 2/d;

step 2, according to the one-dimensional photonic crystal energy band theory, respectively calculating the alternative refractive indexes of the TE mode light and the TM mode light as n respectively by using a transmission matrix method₁And n₂The band structure of the periodic dielectric layer structure with the width scale factor f is related to the normalized frequencyAnd normalized wave vector k₁See fig. 3 for the photonic band structure;

and 3, according to the normalized frequency and the wave vector definition:k₁＝k_yv. (2 π/d), usingNormalized frequencyNormalized wave vector k₁Relationships between

Step 4, utilizing the relation to respectively normalize the frequencies of the TE mode and the TM mode when the incident angle is phi in the photon energy band structureNormalized wave vector k₁The relation straight lines are respectively intersected with the photon energy band boundaries to obtain the overlapped part of the TE mode forbidden band and the TM mode conduction band under the phi angle incidence;

step 5, selecting the lower boundary of the TE mode forbidden bandThe upper boundary of the A point and the TM mode conduction band in FIG. 3Calculating the grating structure parameters according to the band gap between points B in FIG. 3The wavelength boundary corresponding to the selected energy band boundary can be calculatedDesign center wavelength λ ═ λ₁+λ₂) /2, obtaining the period

Step 6, according to the geometrical relationship theta being 90-phi, a being d/sin theta, f being d₂/d＝a₂A, obtaining the inclination angle theta of the grating, the period a of the inclined grating and the width a of each medium layer₁And a₂And determining the grating structure.

And finishing the design.

Example (b):

in order to better embody the advantages of the present invention, we have designed a tilted grating waveguide type polarizer based on a platform of silicon-on-insulator SOI material according to the solution of the present invention. Designing the central wavelength lambda of the device as 1550nm and the refractive index n of the silicon material₁＝3.47，SiO₂Refractive index n of material₂3.47 straight waveguide rulerInch is 500nm × 220 nm. The effective refractive index n of the two-dimensional planar waveguide can be obtained by calculation_eff2.848. Selecting the width ratio f of the dielectric layer to be 0.75, the incident angle phi to be 25 degrees, and calculating the photon energy band structure to obtain the productThus, d was 426.7 nm. Obtained by using the geometric relationship of theta 65 DEG, a 470.8nm, a₁＝353.1nm，a₂＝117.7nm。

By utilizing the parameter modeling simulation, the distribution of the TE mode and the TM mode at the central wavelength is obtained, and obviously, the TE mode is almost completely reflected, and the TM mode is transmitted with low loss. The TE mode transmittance is 0.000285 and the TM mode transmittance is 0.867, thus a high polarization-dependent ratio of 34.8dB can be obtained. As can be seen from FIG. 5, the polarizer structure can achieve high extinction ratios above 30dB over a large bandwidth of 360nm in the wavelength band from about 1340nm to about 1700 nm.

In conclusion, the integrated polarizer on the broadband high extinction ratio chip has a simple structure and low process realization difficulty, and simultaneously designs inclined grating parameters by utilizing the one-dimensional photonic crystal energy band theory, so that a larger working bandwidth can be obtained, a larger processing error tolerance is realized, and meanwhile, the low-loss transmission of a TM mode and the high-efficiency reflection of a TE mode can be ensured, and the ultrahigh polarization extinction ratio is realized.

The foregoing is a detailed description of the present invention, which is only a specific embodiment of the present invention, and is not intended to be exhaustive or to be a substitute for the conventional art. The scope of the present invention is not limited thereto, and any changes or substitutions that can be easily made by those skilled in the art within the technical scope of the present invention will be covered by the scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.