CN117130098B - Compact adiabatic optical isolator - Google Patents

Abstract

The present invention belongs to the field of integrated optical technology, and specifically relates to a compact adiabatic optical isolator. The present invention comprises a first cladding, a second cladding, a third cladding, a first silicon core and a second silicon core; the first silicon core and the second silicon core are respectively arranged at the upper end of the first cladding; the second cladding is arranged around the first silicon core and the second silicon core; the third cladding is arranged at the upper end of the first silicon core and the second silicon core; along the propagation direction of the light beam, the first silicon core is a wide waveguide, and the second silicon core is a narrow waveguide, and the first silicon core and the second silicon core both comprise an input end, a first adiabatic coupler transition structure, an adiabatic coupler conversion structure, a second adiabatic coupler transition structure and an output end connected in sequence; the first adiabatic coupler transition structure is used to realize the adiabatic transmission of the TE ₀ mode in the narrow waveguide at the input end; the adiabatic coupler conversion structure converts the TE ₀ mode in the narrow waveguide into the TM ₀ mode in the wide waveguide; the second adiabatic coupler transition structure is used to realize the adiabatic transmission of the TM ₀ mode in the wide waveguide.

Description

A compact adiabatic optical isolator

Technical Field

The invention belongs to the technical field of integrated optics, and in particular relates to a compact adiabatic optical isolator.

Background Art

In integrated photonic circuits, reflected light in the opposite direction of the forward transmission light may be generated for various reasons. For example, when an optical signal is transmitted between different structures, reflected light in the opposite direction of the original transmission direction will be generated at the connection, leading to the excitation of other modes or radiation modes, thereby destroying the transmission stability and causing various adverse effects on the device. Optical isolators reduce signal noise and maintain system stability by blocking reflected light from reaching the laser cavity while ensuring forward transmission of light. They are usually placed between the laser source and subsequent devices and are widely used in optical communication systems. In the paper D. Jalas, A. Petrov, M. Eich, W. Freude, S. Fan, Z. Yu, R. Baets, M. This is reflected in A.Melloni, JD Joannopoulos, M.Vanwolleghem, CR Doerr, and H.Renner, “What is—and what is not—an optical isolator,” Nature Photon, 7(8), 579–582 (2013).

At present, optical isolators are discrete devices with large device size, high cost and difficult packaging. With the development of integrated optical technology, optical isolators need to be integrated on a single chip to reduce device size, improve integration and reliability, and reduce cost. Adiabatic devices based on adiabatic mode evolution have a very wide bandwidth and good manufacturing tolerance. Adiabatic devices play an important role in large-scale photonic integrated chips. This is reflected in the paper T.-L. Liang, Y. Tu, X. Chen, Y. Huang, Q. Bai, Y. Zhao, J. Zhang, Y. Yuan, J. Li, F. Yi, W. Shao, and S.-T. Ho, "A Fully Numerical Method for Designing Efficient Adiabatic Mode Evolution Structures (Adiabatic Taper, Coupler, Splitter, Mode Converter) Applicable to Complex Geometries," J. Lightw. Technol., 39 (17), 5531-5547 (2021). However, in order to ensure the evolution of the adiabatic mode and thus not excite other modes, the adiabatic optical isolator requires a large device size, which runs counter to the development trend of photonic integrated chips towards higher integration.

Summary of the invention

The purpose of the present invention is to provide a compact adiabatic optical isolator, which can achieve optical isolation and conversion between different modes, and can also achieve the transmission of mode energy between different waveguides. The problem of "large size and low integration" of the current optical isolator is solved, and the purpose is to design an optical isolator with small size, low loss, high transmission efficiency and simple structure.

In order to achieve the above-mentioned invention object, the technical scheme adopted by the present invention is as follows: a compact adiabatic optical isolator comprises a first cladding, a second cladding, a third cladding, a first silicon core and a second silicon core; the first silicon core and the second silicon core are respectively arranged at the upper end of the first cladding; the second cladding is arranged around the first silicon core and the second silicon core; the third cladding is arranged at the upper end of the first silicon core and the second silicon core; along the propagation direction of the light beam, the first silicon core is a wide waveguide, and the second silicon core is a narrow waveguide, and the first silicon core and the second silicon core each comprise an input end, a first adiabatic coupler transition structure, an adiabatic coupler conversion structure, a second adiabatic coupler transition structure and an output end connected in sequence; the first adiabatic coupler transition structure is used to realize the adiabatic transmission of the TE ₀ mode in the narrow waveguide at the input end; the adiabatic coupler conversion structure converts the TE ₀ mode in the narrow waveguide into the TM ₀ mode in the wide waveguide; the second adiabatic coupler transition structure is used to realize the adiabatic transmission of the TM ₀ mode in the wide waveguide.

As a further preferred technical solution of the present invention, the wavelength of the incident light beam is set to 1550nm; the refractive index of the first silicon core and the second silicon core is n _Si =3.455, and the thickness is h ₂ =220nm; the input end and the output end are parallel plate waveguides; in the direction of the input end, the width of the first silicon core is W _I =0.54μm; the width of the second silicon core is w _I =0.46μm, where W _I +w _I =1μm, and the gap between the first silicon core and the second silicon core is G =150nm; in the direction of the output end, the width of the first silicon core is W _O =0.7μm, the width of the second silicon core is w _O =0.3μm, where W _O +w _O =1μm, and the gap between the first silicon core and the second silicon core is G =150nm. The selection of the lengths of these two ends has no effect on the entire structure and can be selected arbitrarily.

Further as a preferred technical solution of the present invention, the material of the first cladding is SiO ₂ , with a refractive index of n _{SiO 2} =1.445, a thickness of h ₁ , and a width of W ₀ >W _I +w _I +G; the material of the second cladding is Air, with a refractive index of n _Air =1, and a thickness of h ₂ =220 nm; the material of the third cladding is Ce:YIG, with a refractive index of n _Ce:YIG =2.2, a thickness of h ₃ , and a width of W ₀ .

Further as a preferred technical solution of the present invention, the first adiabatic coupler transition structure comprises a segment in the beam propagation direction, connected by a straight line with widths W ₁ =0.54 μm and W ₂ , wherein 0.54 μm<W ₂ <0.595 μm, and length L _t1 =13.696 μm.

Further, as a preferred technical solution of the present invention, the adiabatic coupler conversion structure comprises ten segments in the beam propagation direction: segment one is connected by a straight line with a width of _W2 and _Wa =0.595μm and a length of _L1 =43.57μm; segment two is connected by a straight line with a width of _Wa =0.595μm and _Wb =0.597μm and a length of _L2 =68.592μm; segment three is connected by a straight line with a width of _Wb =0.597μm and _Wc =0.598μm and a length of _L3 =167.485μm; segment four is connected by a straight line with a width of _Wc =0.598μm and _Wd =0.599μm and a length of _L4 =137.295μm; segment five is connected by a straight line with a width of _Wd =0.599μm and _We =0.60μm and a length of _L5 =167.485μm. =151.88μm; segment six is connected by a straight line with a width of _We =0.60μm and _Wf =0.601μm, and a length of _L6 =143.955μm; segment seven is connected by a straight line with a width of _Wf =0.601μm and _Wg =0.602μm, and a length of _L7 =81.77μm; segment eight is connected by a straight line with a width of _Wg =0.602μm and _Wh =0.604μm, and a length of _L8 =75.125μm; segment nine is connected by a straight line with a width of _Wh =0.604μm and _Wk =0.608μm, and a length of _L9 =38.488μm; segment ten is connected by a straight line with a width of _Wk =0.608μm and _W3 , and a length of _L10 =12.982μm. The total length of segments one to ten _{is Lt2} =921.142μm.

Further as a preferred technical solution of the present invention, the second adiabatic coupler transition structure comprises a segment in the beam propagation direction, connected by a straight line with widths W ₃ and W ₄ = 0.70 μm, wherein 0.608 μm<W ₃ <0.7 μm, and length L _t3 = 2.813 μm.

Further, as a preferred technical solution of the present invention, W ₂ =0.59 μm.

Further, as a preferred technical solution of the present invention, W ₃ =0.63 μm.

The compact adiabatic optical isolator of the present invention adopts the above technical solution and has the following technical effects compared with the prior art:

(1) The adiabatic coupler conversion structure of the compact adiabatic optical isolator of the present invention converts the TE ₀ mode in a narrow waveguide into the TM ₀ mode in a wide waveguide, realizing the conversion connection between the TE ₀ mode and the TM ₀ mode between different waveguides, which not only realizes the conversion between different modes, but also realizes the transmission of mode energy between different waveguides.

(2) The adiabatic optical isolator proposed in the present invention only requires a total length of 108 μm to achieve a power conversion efficiency of 90%, while the traditional design requires 1540 μm to achieve a power transmission efficiency of 90%. The device size of the adiabatic optical isolator of the present invention is shortened by 14 times compared with the existing design, which can push the integration level to a higher level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of an input end of an adiabatic optical isolator according to an embodiment of the present invention;

FIG2 is a schematic diagram of an output end of an adiabatic optical isolator according to an embodiment of the present invention;

3 is a schematic diagram of the effective refractive index of each mode corresponding to each waveguide width W of the adiabatic optical isolator according to an embodiment of the present invention;

FIG4 is a top view of a first silicon core and a second silicon core of an adiabatic optical isolator according to an embodiment of the present invention;

FIG5 is a schematic diagram showing a comparison of the mode conversion efficiency of the present invention and the conventional design, i.e., a linear shape connection;

Among them, the figure markings are: 1-first cladding; 2-second cladding; 3-third cladding; 4-first silicon core; 5-second silicon core; 6-input end; 7-first adiabatic coupler transition structure; 8-adiabatic coupler conversion structure; 9-second adiabatic coupler transition structure; 10-output end.

DETAILED DESCRIPTION

The present invention is further explained below in detail with reference to the accompanying drawings so that those skilled in the art can more deeply understand the present invention and be able to implement it. However, the following reference examples are only used to explain the present invention and are not intended to limit the present invention.

As shown in Fig. 1-2, a compact adiabatic optical isolator comprises a first cladding 1, a second cladding 2, a third cladding 3, a first silicon core 4 and a second silicon core 5; the first silicon core 4 and the second silicon core 5 are respectively arranged at the upper end of the first cladding 1; the second cladding 2 is arranged around the first silicon core 4 and the second silicon core 5; the third cladding 3 is arranged at the upper end of the first silicon core 4 and the second silicon core 5; along the propagation direction of the light beam, the first silicon core 4 is a wide waveguide, and the second silicon core 5 is a narrow waveguide, and the first silicon core 4 and the second silicon core 5 each comprise an input end 6, a first adiabatic coupler transition structure 7, an adiabatic coupler conversion structure 8, a second adiabatic coupler transition structure 9 and an output end 10 connected in sequence; the first adiabatic coupler transition structure 7 is used to realize the adiabatic transmission of the TE ₀ mode in the narrow waveguide of the input end 6; the adiabatic coupler conversion structure 8 converts the TE ₀ mode in the narrow waveguide into the TM ₀ mode in the wide waveguide; the second adiabatic coupler transition structure 9 is used to realize the adiabatic transmission of the TM ₀ mode in the wide waveguide.

The wavelength of the incident light beam is set to 1550nm; the refractive index of the first silicon core 4 and the second silicon core 5 is n _Si =3.455, and the thickness is h ₂ =220nm; the input end 6 and the output end 10 are parallel plate waveguides; in the direction of the input end 6, the width of the first silicon core 4 is W _I =0.54μm; the width of the second silicon core 5 is w _I =0.46μm, where W _I + w _I =1μm, and the gap between the first silicon core 4 and the second silicon core 5 is G =150nm; in the direction of the output end 10, the width of the first silicon core 4 is W _O =0.7μm, the width of the second silicon core 5 is w _O =0.3μm, where W _O + w _O =1μm, and the gap between the first silicon core 4 and the second silicon core 5 is G =150nm. The selection of the length of these two ends has no effect on the entire structure and can be selected arbitrarily.

As shown in FIG3 , the present invention calculates the change of the width W of the wide waveguide, which is the first silicon core 4, from the input end width W _I = 0.54 μm to the output end width W _O = 0.7 μm, and the change of the width w of the narrow waveguide, which is the second silicon core 5, from the input end width W _I = 0.46 μm to the output end width W _O = 0.3 μm, and the effective refractive index change curve corresponding to each mode, which shows the change of the effective propagation refractive index of the TE ₀ mode and the TM ₀ mode in the wide waveguide first silicon core 4 and the narrow waveguide second silicon core 5 with the waveguide width W. It can be seen from the black solid line in the figure that the TE ₀ mode in the narrow waveguide is converted into the TM ₀ mode in the wide waveguide near the width W = 0.6 μm.

In order to realize the conversion between the TE ₀ mode in the narrow waveguide and the TM ₀ mode in the wide waveguide: the first step is to design a "first adiabatic coupler transition structure 7" to realize the adiabatic transmission of the TE ₀ mode in the narrow waveguide; second, to design an "adiabatic coupler conversion structure 8" to convert the TE ₀ mode in the narrow waveguide into the TM ₀ mode in the wide waveguide; third, to design a "second adiabatic coupler transition structure 9" to realize the adiabatic transmission of the TM ₀ mode in the wide waveguide. Through the above three-step design, optical isolation can be achieved, that is, the TE ₀ mode in the narrow waveguide can be transmitted to the TM ₀ mode in the wide waveguide: not only the conversion between different modes is realized, but also the transmission of mode energy between different waveguides is realized. At the same time, in order to improve the integration of photonic integrated chips and achieve a smaller size to meet the needs of the development of new generation information technology, an adiabatic optical isolator as short as possible is designed to convert the TE ₀ mode in the narrow waveguide into the TM ₀ mode in the wide waveguide.

The material of the first cladding layer 1 is SiO ₂ , with a refractive index of n _{SiO 2} =1.445, a thickness of h ₁ , and a width of W ₀ >W _I +w _I +G; the material of the second cladding layer 2 is Air, with a refractive index of n _Air =1, a thickness of h ₂ =220 nm; the material of the third cladding layer 3 is Ce:YIG, with a refractive index of n _Ce:YIG =2.2, a thickness of h ₃ , and a width of W ₀ .

As shown in FIG4 , the wide waveguide of the adiabatic optical isolator is a first silicon core 4 and the narrow waveguide is a second silicon core 5 in a connection manner in which the widths thereof vary. Only the connection manner in which the wide waveguide is the first silicon core 4 is given below, and the width of the narrow waveguide being the second silicon core 5 can be calculated by those skilled in the art.

The first adiabatic coupler transition structure 7 comprises a segment in the beam propagation direction, connected by a straight line with widths W ₁ =0.54 μm and W ₂ , where 0.54 μm<W ₂ <0.595 μm, and a length L _t1 =13.696 μm, and W ₂ =0.59 μm.

The adiabatic coupler conversion structure 8 comprises ten segments in the beam propagation direction: segment one is connected by a straight line with a width of _W2 and _Wa =0.595 μm and a length of _L1 =43.57 μm; segment two is connected by a straight line with a width of _Wa =0.595 μm and _Wb =0.597 μm and a length of _L2 =68.592 μm; segment three is connected by a straight line with a width of _Wb =0.597 μm and _Wc =0.598 μm and a length of _L3 =167.485 μm; segment four is connected by a straight line with a width of _Wc =0.598 μm and _Wd =0.599 μm and a length of _L4 =137.295 μm; segment five is connected by a straight line with a width of _Wd =0.599 μm and _We =0.60 μm and a length of _L5 =151.88 μm; segment six is connected by a straight line with a width of _We =0.60μm and _Wf =0.601μm, length _L6 =143.955μm; segment seven is connected by a straight line with a width of _Wf =0.601μm and _Wg =0.602μm, length _L7 =81.77μm; segment eight is connected by a straight line with a width of _Wg =0.602μm and _Wh =0.604μm, length _L8 =75.125μm; segment nine is connected by a straight line with a width of _Wh =0.604μm and _Wk =0.608μm, length _L9 =38.488μm; segment ten is connected by a straight line with a width of _Wk =0.608μm and _W3 , length _L10 =12.982μm, and the total length of segments one to ten is _Lt2 =921.142μm.

The second adiabatic coupler transition structure 9 comprises a segment in the beam propagation direction, connected by a straight line with widths W ₃ and W ₄ =0.70 μm, where 0.608 μm<W ₃ <0.7 μm, and a length L _t3 =2.813 μm. W ₃ =0.63 μm.

The selection of the length of the adiabatic optical isolator in the present invention is based on the typical adiabatic beam propagation theory - balanced mode conversion power loss along the beam propagation direction. Through simulation calculation, the length selected for each segment corresponds to the same mode conversion power loss.

Figure 5 shows the power conversion efficiency of the adiabatic optical isolator designed in this embodiment, and compares it with the traditional design (linear shape connection). It can be seen from the figure that for the same conversion efficiency, the device length designed by the present invention is much shorter than the device length required by the traditional design. For example, when the power transmission efficiency is 90%, the length required for the design of the present invention is 108μm, while the traditional design requires 1540μm. Therefore, when a power transmission efficiency of 90% is required, the length required for the traditional design is more than 14 times the length required for the design of the present invention, which fully proves that the adiabatic optical isolator proposed by the present invention has the advantage of small size, helping photonic chips to develop in the direction of higher integration.

The specific implementation scheme described above further describes in detail the purpose, technical scheme and beneficial effects of the present invention. It should be understood that the above is only a specific implementation scheme of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes and modifications made by any technician in the field without departing from the concept and principle of the present invention should fall within the scope of protection of the present invention.

Claims (4)

1. The compact heat-insulating optical isolator is characterized by comprising a first cladding (1), a second cladding (2), a third cladding (3), a first silicon core (4) and a second silicon core (5); the upper end of the first cladding (1) is provided with a first silicon core (4) and a second silicon core (5) respectively; the periphery of the first silicon core (4) and the periphery of the second silicon core (5) are respectively provided with a second cladding (2); the upper ends of the first silicon core (4) and the second silicon core (5) are provided with a third cladding (3); along the light beam propagation direction, the first silicon core (4) is a wide waveguide, the second silicon core (5) is a narrow waveguide, and the first silicon core (4) and the second silicon core (5) comprise an input end (6), a first thermal insulation coupler transition structure (7), a thermal insulation coupler transition structure (8), a second thermal insulation coupler transition structure (9) and an output end (10) which are sequentially connected; the first thermal insulation coupler transition structure (7) is used for realizing thermal insulation transmission of TE ₀ modes in the narrow waveguide of the input end (6); the adiabatic coupler conversion structure (8) converts TE ₀ modes in a narrow waveguide to TM ₀ modes in a wide waveguide; the second adiabatic coupler transition structure (9) is used for realizing adiabatic transmission of TM ₀ modes in a wide waveguide;

The wavelength of the incident beam is set to 1550nm; the refractive indexes n _Si = 3.455 of the first silicon core (4) and the second silicon core (5) are respectively h ₂ = 220nm; the input end (6) and the output end (10) are parallel plate waveguides; in the direction of the input end (6), the width of the first silicon core (4) is W _I = 0.54 μm; the width of the second silicon core (5) is W _I =0.46 μm, wherein W _I+w_I =1 μm, and the gap g=150 nm between the first silicon core (4) and the second silicon core (5); in the direction of the output end (10), the width of the first silicon core (4) is W _O =0.7 μm, the width of the second silicon core (5) is W _O =0.3 μm, wherein W _O+w_O =1 μm, and the gap g=150 nm between the first silicon core (4) and the second silicon core (5);

the first thermally insulating coupler transition structure (7) comprises a segment in the beam propagation direction, with a straight line connecting widths W ₁ =0.54 μm and W ₂, wherein 0.54 μm < W ₂ <0.595 μm, length L _t1 = 13.696 μm;

the adiabatic coupler transfer structure (8) comprises ten segments in the direction of beam propagation: segment one connects width W ₂ and W _a =0.595 μm by straight line, length L ₁ =43.57 μm; segment two is connected by a straight line with a width W _a =0.595 μm and a length W _b =0.597 μm, a length L ₂ = 68.592 μm; Segment three is connected by a straight line with a width W _b =0.597 μm and a length W _c =0.598 μm, a length L ₃ = 167.485 μm; segment four is connected by a straight line with a width W _c =0.598 μm and a length W _d =0.599 μm, length L ₄ = 137.295 μm; segment five is connected by a straight line with a width W _d =0.599 μm and a length W _e =0.60 μm, length L ₅ = 151.88 μm; segment six is connected by a straight line with a width W _e =0.60 μm and a length W _f =0.601 μm, length L ₆ = 143.955 μm; Segment seven is formed by connecting straight lines with a width W _f =0.601 μm and a length W _g =0.602 μm, and a length L ₇ =81.77 μm; segment eight is connected by a straight line with width W _g =0.602 μm and W _h =0.604 μm, length L ₈ = 75.125 μm; Segment nine is connected by a straight line with a width W _h =0.604 μm and a length W _k =0.608 μm, length L ₉ = 38.488 μm; Segment ten is connected by a straight line with widths W _k =0.608 μm and W ₃, lengths L ₁₀ = 12.982 μm, total lengths of segment one to segment ten L _t2 = 921.142 μm;

The second adiabatic coupler transition structure (9) comprises a segment in the direction of beam propagation, with a linear connection width W ₃ and W ₄ =0.70 μm, where 0.608 μm < W ₃ <0.7 μm, and a length L _t3 = 2.813 μm.

2. A compact adiabatic optical isolator as claimed in claim 1, characterized in that the material of the first cladding (1) is SiO ₂, the refractive index n _SiO2 =1.445, the thickness is h ₁, the width is W ₀>W_I+w_I +g; the material of the second cladding layer (2) is Air, the refractive index n _Air =1 and the thickness h ₂ =220 nm; the material of the third coating layer (3) is Ce, YIG, the refractive index n _Ce:YIG =2.2, the thickness is h ₃, and the width is W ₀.

3. A compact adiabatic optical isolator as claimed in claim 1, wherein W ₂ = 0.59 μm.

4. A compact adiabatic optical isolator as claimed in claim 1, wherein W ₃ = 0.63 μm.