CN115951451B - Be applicable to TM 1 And TE (TE) 2 Adiabatic mode converter for mode conversion - Google Patents
Be applicable to TM 1 And TE (TE) 2 Adiabatic mode converter for mode conversion Download PDFInfo
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Abstract
The invention discloses a method suitable for TM 1 And TE (TE) 2 Adiabatic mode converter for mode conversion, comprising a silicon coreAnd a cladding; the silicon core is of a ridge waveguide structure and consists of a bottom silicon core and a top silicon core; the width of the bottom silicon core is kept unchanged along the propagation direction of the light beam; the input end and the output end of the top silicon core are parallel plate waveguides respectively, and the width W of the input end L <1.80 μm, width W of output end R >2.0 μm; along the beam propagation direction, the top silicon core between the input end and the output end consists of 11 continuous segments from segment a to segment k; the adiabatic mode converter of the present invention selects the length of each segment based on the equilibrium mode conversion power loss in the mode propagation direction, and by such an arrangement, an efficient and compact adiabatic mode converter is realized.
Description
Technical Field
The present invention relates to an adiabatic mode converter.
Background
Silicon waveguides based on silicon-on-insulator structures have attracted considerable attention due to their advantages in terms of low cost, compact footprint and compatibility with complementary metal oxide semiconductor processing techniques. Nanoscale silicon waveguides are important for their potential use in photonic integrated circuits. Adiabatic devices are an essential component of photonic integrated chips. In addition to waveguide loss, substrate loss, optical confinement and space occupation, polarization issues must be addressed when designing adiabatic devices. In a vertically asymmetric waveguide, mode mixing can be used for switching between TM mode and TE higher order modes in a ridge waveguide.
Adiabatic mode converters are very important for integrated optical applications because they have a wide bandwidth and high tolerance to manufacturing variations. Furthermore, adiabatic mode converters are key elements in polarization diversity circuits for achieving a unipolar state in a photonic integrated chip. Adiabatic mode converters are used to perform mode conversion between two waveguides having different cross sections, such as conversion between TE and TM modes. In optical waveguides with high refractive index contrast, mode mixing is important for certain specific waveguide widths. Thus, mode conversion may occur in the ridge waveguide. Thus, the use of adiabatic mode converters requires that a particular TM be realized by changing the guided wave structure from input to output 1 Mode evolution to TE 2 Mode, or TE 2 Mode evolution to TM 1 A mode. In the design of adiabatic mode converters, adiabatic mode conversion can be achieved by slowly increasing/decreasing the size of the device cross section. Furthermore, when the change is slow enough, the modes in the adiabatic mode converterThe conversion may be considered lossless, but requires a long length.
In designing TM 1 And TE (TE) 2 These two modes are particularly sensitive to changes in device geometry when transitioning between modes, and thus designing an adiabatic mode converter is very complex and difficult. The existing design methods are all direct linear connection of the input end and the output end, namely, the waveguide structure is simply changed linearly to obtain the device length required under the specific mode conversion efficiency, but the device length obtained by the method can be obviously beyond the required length.
Disclosure of Invention
The invention aims to: in view of the above prior art, a compact adiabatic mode converter is proposed to implement TM 1 And TE (TE) 2 Mode transition between modes.
The technical scheme is as follows: be applicable to TM 1 And TE (TE) 2 An adiabatic mode converter for mode conversion, comprising a silicon core and a cladding 3; the silicon core is of a ridge waveguide structure and consists of a bottom silicon core 1 and a top silicon core 2; the width of the bottom silicon core 1 is kept unchanged along the propagation direction of the light beam; the input end and the output end of the top silicon core 2 are parallel plate waveguides respectively, and the width W of the input end L <1.80 μm, width W of output end R >2.0 μm, the top silicon core 2 between the input and output ends is composed of 11 consecutive segments, segment a-segment k, along the beam propagation direction, segment a being the straight line connection width W L And W is 1 Length l=1.75 μm a = 28.116 μm; segment b is joined by a straight line of width W 1 =1.75 μm and W 2 =1.80 μm, length L b = 38.928 μm; segment c is joined by a straight line of width W 2 =1.80 μm and W 3 =1.84 μm, length L c = 59.460 μm; segment d is connected by a straight line with width W 3 =1.84 μm and W 4 =1.86 μm, length L d = 33.788 μm; segment e is connected by a straight line with width W 4 =1.86 μm and W 5 =1.88 μm, length L e = 53.236 μm; segment f is connected by a straight line with width W 5 =1.88 μm and W 6 =1.90 μm, length L f = 58.568 μm; fragmentsg is connected by a straight line with the width W 6 =1.90 μm and W 7 =1.92 μm, length L g = 56.312 μm; segment h is joined by a straight line of width W 7 =1.92 μm and W 8 =1.96 μm, length L h = 81.220 μm; segment i is connected by a straight line with width W 8 =1.96 μm and W 9 =2.00 μm, length L i = 54.136 μm; segment j is connected by a straight line with width W 9 =2.00 μm and W 10 =2.05 μm, length L j = 33.068 μm; segment k is connected by a straight line with width W 10 =2.05 μm and W R Length L k ＝28.344μm。
The beneficial effects are that: the adiabatic mode converter of the present invention selects the length of each segment based on the equilibrium mode conversion power loss in the mode propagation direction, and by such an arrangement, an efficient and compact adiabatic mode converter is realized. Comparing the design of the present invention with the design of the straight line connection case as shown in fig. 2, the mode conversion efficiency of both cases is shown in fig. 6. It can be seen from the figures that the design of the present invention is far better in efficiency than the case of a straight connection. For example, when 96% transmission efficiency is to be achieved, the design of the present invention requires only a length of 82 μm, whereas the straight line connection case requires a length of 230 μm. Therefore, when 96% of power transmission is required, the length required for the straight line case is 2.8 times that required for the design of the present invention, i.e., the present invention greatly reduces the size of the adiabatic mode converter, and a compact design in the photonic integrated chip is realized.
Drawings
FIG. 1 is a schematic cross-sectional view of an adiabatic mode converter of the present invention;
FIG. 2 is a schematic top view of a conventional structure with a straight line connection;
FIG. 3 shows the TM at the input of an adiabatic mode converter 1 A pattern diagram;
FIG. 4 is a TE view of the output of an adiabatic mode converter 2 A pattern diagram;
FIG. 5 is a schematic top view of a top silicon die of the adiabatic mode converter of the present invention;
FIG. 6 is a graph comparing the mode conversion efficiency curve of an adiabatic mode converter of the present invention with a straight line connection.
Detailed Description
The invention is further explained below with reference to the drawings.
As shown in FIG. 1, one is suitable for use with a TM 1 And TE (TE) 2 An adiabatic mode converter for mode conversion comprises a silicon core and a cladding 3. Refractive index n of silicon core Si = 3.455 the silicon core is a ridge waveguide structure, consisting of a bottom silicon core 1 and a top silicon core 2. Thickness h of bottom silicon core 1 2 Along the beam propagation direction, the width of the bottom silicon core 1 remains w =220 nm 0 Unchanged; thickness h of top silicon core 2 3 =280 nm. The material of the cladding 3 is silicon dioxide, and the refractive index n SiO2 =1.445, thickness h 1 >(h 2 +h 3 ) Width W 0 >w 0 . The incident beam wavelength was set to 1550nm.
In the conventional structure, the linear connection mode of the width change of the top silicon core 2 is shown in fig. 2. The left end a is the input end of the adiabatic mode converter and the right end c is the output end of the adiabatic mode converter. The device length obtained by the straight line connection mode can obviously exceed the required length, so the invention aims to design an efficient and compact geometric structure to realize the conversion between different modes. FIG. 3 is a schematic diagram of the TM input to an adiabatic mode converter 1 Mode, FIG. 4 is TE at the output 2 A mode.
In the present embodiment, as shown in FIG. 5, the input end and the output end of the top silicon core 2 are parallel plate waveguides, respectively, and the width W of the input end L Width W of output end =1.65 μm R The top silicon core 2 between the input and output ends, along the beam propagation direction, is composed of 11 consecutive segments, segment a-segment k, each segment having a width W and length designed as follows: segment a is connected by a straight line with width W L =1.65 μm and W 1 Length l=1.75 μm a = 28.116 μm; segment b is joined by a straight line of width W 1 =1.75 μm and W 2 =1.80 μm, length L b = 38.928 μm; segment c is joined by a straight line of width W 2 =1.80 μm and W 3 =1.84 μm, lengthIs L c = 59.460 μm; segment d is connected by a straight line with width W 3 =1.84 μm and W 4 =1.86 μm, length L d = 33.788 μm; segment e is connected by a straight line with width W 4 =1.86 μm and W 5 =1.88 μm, length L e = 53.236 μm; segment f is connected by a straight line with width W 5 =1.88 μm and W 6 =1.90 μm, length L f = 58.568 μm; segment g is joined by a straight line of width W 6 =1.90 μm and W 7 =1.92 μm, length L g = 56.312 μm; segment h is joined by a straight line of width W 7 =1.92 μm and W 8 =1.96 μm, length L h = 81.220 μm; segment i is connected by a straight line with width W 8 =1.96 μm and W 9 =2.00 μm, length L i = 54.136 μm; segment j is connected by a straight line with width W 9 =2.00 μm and W 10 =2.05 μm, length L j = 33.068 μm; segment k is connected by a straight line with width W 10 =2.05 μm and W R =2.15 μm, length L k = 28.344 μm. The selection of adiabatic mode converter length of the present invention is based on the balanced mode conversion power loss along the mode propagation direction. Through simulation and analog calculation, the lengths selected by the fragments correspond to the same mode conversion power loss. By the above structural arrangement, the adiabatic mode converter proposed by the present invention can achieve very high mode conversion efficiency.
At present there is also TM 0 And TE (TE) 1 The design of the conversion between modes, while seemingly changing in geometric parameters, is quite different in physical properties from mode to mode, and the physical properties involved in the design of the conversion between modes, the degree of refinement required for the division, and the scene applied are also different, so that the design of the invention is applicable to a TM 1 And TE (TE) 2 The means of switching between adiabatic mode coupler and other modes of mode switching is not merely a change in geometric parameters.
The initial width W of the top silicon core 2 L And end width W R Is not unique and needs to satisfy W L <1.80 μm and W R >2.0 μm. Adiabatic mode converterThe material of the cladding 3 may also be air.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (1)
1. Be applicable to TM 1 And TE (TE) 2 Adiabatic mode converter for mode conversion, characterized by comprising a silicon core and a cladding (3); the silicon core is of a ridge waveguide structure and consists of a bottom silicon core (1) and a top silicon core (2); the width of the bottom silicon core (1) is kept unchanged along the light beam propagation direction; the input end and the output end of the top silicon core (2) are parallel plate waveguides respectively, and the width W of the input end L <1.80 μm, width W of output end R In the beam propagation direction, the top silicon core (2) between the input and output ends is composed of 11 consecutive segments, segment a-k, segment a being the straight line connection width W L And W is 1 Length l=1.75 μm a = 28.116 μm; segment b is joined by a straight line of width W 1 =1.75 μm and W 2 =1.80 μm, length L b = 38.928 μm; segment c is joined by a straight line of width W 2 =1.80 μm and W 3 =1.84 μm, length L c = 59.460 μm; segment d is connected by a straight line with width W 3 =1.84 μm and W 4 =1.86 μm, length L d = 33.788 μm; segment e is connected by a straight line with width W 4 =1.86 μm and W 5 =1.88 μm, length L e = 53.236 μm; segment f is connected by a straight line with width W 5 =1.88 μm and W 6 =1.90 μm, length L f = 58.568 μm; segment g is joined by a straight line of width W 6 =1.90 μm and W 7 =1.92 μm, length L g = 56.312 μm; segment h is joined by a straight line of width W 7 =1.92 μm and W 8 =1.96 μm, length L h = 81.220 μm; segment i is connected by a straight line with width W 8 =1.96 μm and W 9 =2.00 μm, length L i = 54.136 μm; segment j is connected by a straight lineWidth W 9 =2.00 μm and W 10 =2.05 μm, length L j = 33.068 μm; segment k is connected by a straight line with width W 10 =2.05 μm and W R Length L k ＝28.344μm。
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