CN112230338B - Ultra-wideband on-chip polarization beam splitting rotator based on reverse biconical asymmetric coupler - Google Patents

Abstract

The invention discloses an ultra-wideband on-chip polarization beam splitting rotator based on reverse biconical asymmetric coupling, and belongs to the field of photonic integrated waveguides (PICs) based on SOI platforms. The polarization beam splitting rotator is based on a standard SOI wafer structure and comprises a substrate (1) and input and output waveguides on top of the substrate; the input guide waveguide (2), the output guide waveguide (3), the input tapered waveguide (4) and the output tapered waveguide (5) of the silicon material form an inverse double-cone asymmetric waveguide structure in a polarization mode coupling region (6). Based on the reverse double-cone asymmetric waveguide structure, in a wider working waveband, the insertion loss of two input polarized lights TE0 and TM0 is lower, the polarization conversion efficiency and crosstalk are better, and tolerance analysis shows that the polarization beam splitting-rotating device still has a higher working wavelength range from the O waveband to the U waveband in the current optical fiber communication.

Description

Ultra-wideband on-chip polarization beam splitting rotator based on reverse double-cone asymmetric coupler

Technical Field

The invention relates to the technical field of optical fiber communication, in particular to an ultra-wideband on-chip polarization beam splitting rotator.

Background

Silicon photonic devices compatible with CMOS (complementary metal-oxide-semiconductor) processes have received much attention over the past decades, with SOI (Silicon-on-insulator) platform based photonic integrated waveguides (PICs) taking the leading position in the scientific research field. The high refractive index contrast and sub-micron structure of SOI materials result in SOI-based PIC devices with very high birefringence, which causes polarization dependent loss and polarization mode dispersion, limiting the applications of SOI devices in the optical communication direction. The current solution to this problem is to design a polarization transparent photonic integrated loop or on-chip polarization diversity system, which consists mainly of a Polarization Beam Splitter (PBS), a Polarization Rotator (PR), and a polarization beam splitter-rotator (PSR). The current principle for realizing the PSR can be divided into two types, namely asymmetrical directional coupling and mode evolution, wherein the cross section of the waveguide is fixed and unchanged along the light transmission direction, and the former method introduces optical asymmetry into the waveguide, and comprises the steps of adopting a straight waveguide with an asymmetrical section, an optical path matched curved waveguide, a sub-wavelength grating auxiliary structure and the like, so that energy transfer is generated between two specific orthogonal polarization modes, and the polarization beam splitting-rotation function is realized under a specific length. Since the coupling coefficient can be influenced by the wavelength of incident light and process errors, the PSR has narrow working bandwidth, small manufacturing tolerance and large insertion loss caused by scattering. The waveguide section of the mode evolution type PSR is gradually changed along the optical transmission direction, and mode mixing occurs in the whole coupling interval, so that certain adaptability exists to different optical wavelengths and process errors, the working bandwidth is wider, and the PSR has larger manufacturing tolerance and lower insertion loss and is widely concerned.

Due to the limitation of the manufacturing process, the width of the SOI waveguide is generally larger than the height of the waveguide, and the effective refractive index difference between the TE0 mode and the TM0 mode is larger, so the current mode evolution type PSR generally consists of two cascaded parts, namely a TM0-TE1 polarization rotator and a TE1-TE0 mode converter. For example, using an adiabatic graded waveguide as the TM0-TE1 polarization rotator, an Asymmetric Directional Coupler (ADC), a Y-branch, a multimode interferometer (MMI) as the PSR of the TE1-TE0 mode-converting beam splitter; or a staggered gradual waveguide (bi-level taper) is used as a TM0-TE1 polarization rotator, and an ADC is used as a TE1-TE0 mode conversion beam splitter. The above-described cascade structure makes the PSR structure complicated, resulting in an increase in manufacturing cost.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a novel reverse biconic asymmetric ultra-wideband PSR based on a mode evolution principle, which can separate an input optical signal TE0 from a TM0, convert a TM0 mode into a TE0 mode and output the TE0 mode, and has the advantages of simple structure and high process feasibility.

An ultra-wideband on-chip polarization beam splitting rotator based on reverse biconic asymmetric coupling comprises a substrate and input and output waveguides arranged at the top of the substrate; wherein the substrate is an SOI structure, and is characterized in that:

the input and output waveguides comprise input guide waveguides, output guide waveguides, input tapered waveguides and output tapered waveguides, and are all made of silicon materials; the input guide waveguide and the output guide waveguide are parallel to each other in a polarization mode coupling region, and the input tapered waveguide and the output tapered waveguide are positioned in the polarization mode coupling region and are respectively and correspondingly formed at the tops of the input guide waveguide and the output guide waveguide; the taper width of the input tapered waveguide is gradually narrowed along the input direction, and the taper width of the output tapered waveguide is gradually widened along the input direction, so that when a TM0 mode is injected, the effective refractive indexes of the input end TM0 mode and the cross end TE0 mode are equal on a certain section of the waveguide due to opposite trend of the effective refractive index curve change of the two modes.

Further, the input guide waveguide and the output guide waveguide are separated by taking an air gap as a medium.

Further, let the length of the polarization mode coupling region be L _c An input guide waveguide, an output guide waveguide, and an input tapered waveguide and an output tapered waveguide, the input guide waveguide having a width W _s1 The width of the output guide waveguide is W _s2 The taper width of the input tapered waveguide is W _t1 The taper width of the output tapered waveguide is W _t2 W on the input port _t1 And W _s1 Equal, decreasing linearly along the Z direction through a length L _c Then, W _t1 Becomes zero; cross port upper W _t2 Linearly widening from zero along the Z direction, over a length L _c Then, W _t2 And W _s2 Are equal.

Further, the thickness H of the silicon layer of the substrate _co 220nm, the underlying buried oxide thickness is 2 μm.

Further, the bottom layer buried oxide is silicon dioxide.

Further, the input tapered waveguide and the output tapered waveguide are formed by etching based on the input guide waveguide and the output guide waveguide respectively, and the maximum etching depths are all H _t 。

Further, the overall height of the input guide waveguide and the input tapered waveguide, and the overall height of the output guide waveguide and the output tapered waveguideAll height of the body is H _co 。

Further, the width W of the input guide waveguide _s1 1 μm, width W of the output guide waveguide _s2 0.35 μm, length L of the polarization mode coupling region _c 520 μm, thickness H of input and output tapered waveguides _t 0.07 μm, a gap W between the input guide waveguide and the output guide waveguide (3) _g ＝0.12μm。

The technical scheme provided by the embodiment of the invention has the following beneficial effects:

in the present invention, based on a standard SOI wafer structure, the bottom buried oxide (BOX, SiO2) is formed above the input and output guide waveguides and a silicon layer based on an inverse biconic asymmetric structure. The structure forms the ultra-wideband on-chip polarization beam splitting rotator of the reverse biconical asymmetric coupler, so that in an incident wavelength range of 500nm (1250nm-1750nm), for an incident TE basic mode loss IL is less than 0.05dB, mode energy is output from a Through port, and meanwhile, the ultra-wideband on-chip polarization beam splitting rotator has very low crosstalk and very high polarization extinction ratio (PER is more than 60dB and CT is less than-60 dB), for an incident TM basic mode, the mode energy is output from a Cross port, and the polarization conversion efficiency is higher than 95% (IL is less than 0.2dB), and meanwhile, the ultra-wideband on-chip polarization beam splitting rotator has high polarization extinction ratio (PER is more than 15dB) and low crosstalk (CT is less than-20 dB). The tolerance analysis shows that when the parameters of the coupling region of the device deviate from +/-1%, the device keeps high polarization conversion efficiency (IL <0.4dB) in a 400nm bandwidth, and has the advantages of large manufacturing tolerance, simple structure, high process feasibility and potential application value in the field of on-chip photonic integration.

Drawings

FIG. 1 is a schematic cross-sectional view of an ultra-wideband on-chip polarization beam splitting rotator based on an inverse biconic asymmetric coupler provided by the invention: (a) a three-dimensional view; (b) a cross-section; (c) a top view;

fig. 2 shows that when the wavelength is 1250nm, 1350nm, 1450nm, 1550nm, 1650nm and 1750nm under the specific geometric parameters of the reverse biconical asymmetric structure provided by the invention, the waveguide input port is etched in a tapered manner by comparing the cross sections of different tapered waveguides: (a) TE0 mode; (b) effective refractive index dependence of TM0 mode;

FIG. 3 is a diagram showing the gamma of the mixed mode in the waveguide when the TM0 mode and TE0 mode with 1550nm wavelength are input at the input end under the specific geometrical parameters of an inverse biconical asymmetric structure provided by the invention _x A curve changing along with the width of the top conical region and an electric field distribution diagram of a mixed mode under different sections of the waveguide coupling region;

FIG. 4 shows an inverse biconical asymmetric structure provided by the present invention under specific geometric parameters (a) L _c ；(b) H _t Polarization conversion efficiency curve at the input of TM0 of (1);

FIGS. 5 (a) - (f) show the magnetic field distribution in xoz plane when the incident light wavelength is 1250nm, 1550nm, 1750nm, respectively, and the TM0 mode and TE0 mode are input;

fig. 6 (a) is a transmittance curve of the TE fundamental mode and the TM fundamental mode output from each port when the TE0 mode is input.

Fig. 6 (b) is a transmittance curve of the TE fundamental mode and the TM fundamental mode output from each port when the TM0 mode is input;

FIGS. 7 (a) - (b) show the waveguide height change Δ H at TM0 mode incidence according to the present invention _co 10nm and Δ H _co Transmission curve of-10 nm for each port fundamental mode.

FIGS. 7 (c) - (d) illustrate the input waveguide width error Δ W provided by the present invention _s1 = 10nm and Δ W _s1 The transmission curve is output by the basic mode of each port when the wavelength is-10 nm.

FIGS. 7 (e) - (f) illustrate the input waveguide error Δ W provided by the present invention _s2 +3nm and Δ W _s2 The transmission curve is output by the base mode of each port when the wavelength is equal to-3 nm.

FIGS. 7(g) - (H) illustrate the input waveguide error Δ H provided by the present invention _t Not greater than +10nm and Δ H _t And when the wavelength is equal to-10 nm, the fundamental mode of each port outputs a transmittance curve.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of an ultra-wideband on-chip polarization beam splitting rotator based on an inverted double-cone asymmetric coupler provided by the invention. Referring to fig. 1, the inverse biconic asymmetric optical waveguide includes: the substrate 1, the substrate 1 adopts the silicon dioxide insulating layer; input and output waveguides are provided on top of the substrate 1; the input and output waveguides include: the input guide waveguide 2, the output guide waveguide 3, the input tapered waveguide 4 and the output tapered waveguide 5, in the polarization mode coupling region 6, the taper width of the input end waveguide gradually narrows along the Z direction, and the taper width of the output end gradually widens along the Z direction, namely the coupling region is composed of two reverse double-cone asymmetric waveguides, and the waveguides are all made of silicon.

It should be noted that, with the rapid development of the information society, the PSR structure is more complex based on the general cascade structure under the mode evolution PSR principle, which leads to an increase in manufacturing cost. Therefore, the invention provides a novel ultra-wideband PSR based on the mode evolution principle, which can separate the input optical signal TE0 from the TM0 and convert the TM0 mode into the TE0 mode for output. Polarization beam splitter-rotators have received much attention because they have both beam splitting and rotation capabilities. The device can be regarded as the combination of PR and PBS, when an input optical signal is decomposed into two orthogonal polarization direction components, the polarization direction of one light beam is rotated by 90 degrees, the information carried by the two orthogonal polarization signals is respectively reserved, and only one polarization state exists in a line, so that the polarization-dependent dispersion and the polarization-dependent loss are avoided.

In a PSR device based on an SOI platform and a mode evolution principle reported in the past, a TE0 mode in cross end waveguide and an input end TM0 mode are difficult to meet a phase matching condition, a TE1 mode needs to be introduced as a transition state auxiliary mode for evolution, and a polarization beam splitting-rotating process follows a TM0-TE 1-TE0 process. Namely, in the light transmission direction, the PSR is divided into two sections to realize polarization rotation of TM0-TE1 and mode conversion of TE1-TE0, respectively.

When a TM0 mode is injected, because the structural characteristics of two waveguides are gradually inverted along with the transmission length, the change trends of effective refractive index curves of an input end TM0 mode and a cross end TE0 mode are opposite, the effective refractive indexes of the two modes can be equal on a certain section of the waveguide, an X-shaped curve is formed, and the PSR achieves the condition of phase matching in a wide band. When the structural parameters of the coupling region of the device deviate from +/-1%, the device keeps high polarization conversion efficiency (IL <0.4dB) in a wide wave band, and the device is simple in structure and high in process feasibility.

The refractive index of the silicon dioxide substrate layer at the wavelength of 1550nm is 1.445 as nSiO 2.

The input guide waveguide 2 and the output guide waveguide 3 are separated by an air gap as a medium, and both are made of silicon having a refractive index n at 1550nm _Si 3.455; the input guide waveguide 2 and the output guide waveguide 3 are separated by air.

The taper width of the input tapered waveguide 4 is gradually narrowed in the Z direction, and the taper width of the output tapered waveguide 5 is gradually widened in the Z direction.

Silicon layer thickness H in standard-based SOI wafer structure _co The underlying buried oxide (BOX, SiO2) thickness was 2 μm, 220 nm.

The input guide waveguide 2, the output guide waveguide 3, and the cross end on the left side have a width W _s2 The width of the right input end is W _s1 。

The etching depths of the input conical waveguide 4 and the output conical waveguide 5 are both H _t Height of waveguide H _co The waveguide coupling region has a length L _c ，W _g Is a waveguide gap, W _t2 And W _t1 The widths of the left and right tapered waveguides are respectively.

Right tapered waveguide on input port W _t1 And W _s1 Equal, linearly decreasing along the Z direction through a length L _c Rear, taper width W _t1 Becomes zero; cross end taper width W _t2 The trend of change is opposite, the width is changed from the zero line along the Z direction and passes through the length L _c Then, W _t2 And W _s2 And are equal.

The parameters of the standard-based SOI wafer structure of the embodiment shown in FIG. 1 are set to W, respectively _s1 ＝1μm， W _s2 ＝0.35μm，W _t1 ，W _t2 Are all in a linear gradual change structure L _c ＝520μm，H _t ＝0.07μm，W _g 0.12 μm. Under the above parameter settings, the polarization beam splitting rotator on the ultra-wideband chip can realize two input polarized lights TE0 and TM0 in a wider (500nm) working waveband, and the insertion loss is lower, and the polarization conversion efficiency and crosstalk are better. Tolerance analysis shows that the polarization beam splitter-rotator still has a higher working wavelength range from the O band to the U band in the current optical fiber communication.

Fig. 1 shows the structure of the designed PSR, where the whole PSR is composed of input and output guide waveguides and a polarization mode coupling region, and the coupling region is composed of two gradually-changed ridge waveguides, where the ridge width of the input end waveguide gradually narrows along the Z direction, and the ridge width of the output end gradually widens along the Z direction. W _s2 Width of cross end waveguide on left side, W _s1 The width of the waveguide at the right input end and the etching depth of the waveguide are H _t Height of waveguide H _co The waveguide coupling region has a length L _c ，W _g Is a waveguide gap, W _t2 And W _t1 Width of the left and right waveguide ridge regions, W on the input port _t1 And W _s1 Equal, linearly decreasing along the Z direction through a length L _c Back, ridge width W _t1 Becomes zero; cross end ridge width W _t2 The change trend is opposite, the width is changed from the zero line along the Z direction and the length is L _c Then, W _t2 And W _s2 And are equal. Standard-based SOI wafers (silicon layer thickness H) are designed herein _co 220nm with a 2 μm thickness of underlying buried oxide (BOX, SiO2), the refractive indices of Si and SiO2 being n, respectively, at a wavelength of 1550nm _Si 3.455 and n _SiO2 1.445. To increase the refractive index asymmetry in the vertical direction of the device, air is used as cladding, n _Air 1. The gap width between the two waveguides is determined as W according to the accuracy limitations of the existing deep ultraviolet lithography process _g ＝120nm。

Fig. 2 shows that a waveguide coupling region section exists at a selected wavelength to make the effective refractive indexes of two modes equal, thereby satisfying the condition of complete energy coupling, and supposing that the incident TM0 modes in the wavelength range of 1250nm to 1750nm all follow the rule. When the TE0 mode is injected, since the width-to-height ratio of the through-end waveguide is relatively large, the change in the top-layer taper has little effect on the effective refractive index of the TE0 mode in the waveguide, resulting in a large difference between the input TE0 mode and the effective refractive index of the mode existing in the cross-end waveguide. This can be further explained by (b) in fig. 2. In the figure, the effective refractive index of the input end TE0 mode and the effective refractive index of the cross end waveguide TE0 mode have no intersection point, the minimum value of the refractive index difference between the two modes is 0.23, and the minimum value is positioned at the tail end of a coupling area when a 1250nm mode is input, so that coupling cannot occur at the moment, obvious phase mismatch exists between the two modes, energy is limited in a through waveguide, and the polarization beam splitting-rotating effect is achieved.

FIG. 3 shows the gamma-ray of the mixed mode in the waveguide when TM0 mode and TE0 mode with 1550nm wavelength are input at the input end respectively _x The curve changing with the width of the ridge region at the top, and the electric field distribution of the mixed mode under different sections of the waveguide coupling region. It can be seen from the figure that when the input is injected into the TE0 mode, γ _x Almost constant with the change of the waveguide structure, and when inputting TM0, gamma is _x The secondary gamma is completed in the whole area _x < 5% to gamma _x > 95% change, integrated gamma _x And electric field distribution, the input TM0 mode will shift throughout the span to the TE0 mode on the cross waveguide. And gamma in a cross section of the coupling region _x 50%, this represents a complete hybridization of the modes, by choosing a suitable coupling length L _c The polarization state rotation can be efficiently completed.

FIG. 4 calculates the optical propagation characteristics in the waveguide using the method of mode expansion (EME), and calculates the L-dependent coupling length for the case where the input TM0 mode is converted into the Cross port TE0 mode _c And polarization conversion efficiency with a change in wavelength λ of incident light. FIG. 4 (a) shows the analysis of the polarization conversion efficiency with the etching depth L of the ridge region under the condition _c And a change in wavelength λ of the incident light. From whichIt can be seen that following L _c To increase the conversion efficiency of the input TM0 mode from 1250nm to 1750nm as much as possible, Lc is selected to be 520 μm although L is increased _c The operating bandwidth can be further extended toward shorter wavelengths, but the performance of operation in the 1500nm-1700nm wavelength range is degraded. Similarly, (b) in fig. 4 shows that the polarization conversion efficiency was analyzed under this condition as a function of the ridge region etching depth Ht and the incident light wavelength λ. It shows that the influence of the taper etching depth of the device on the conversion efficiency is small when the taper etching depth is 70nm +/-10 nm, and the influence on the performance is serious after the taper etching depth exceeds the performance, so that the taper etching depth Ht is selected to be 70nm, and all structural parameters defining the PSR are obtained: w is a group of _s1 ＝1μm，W _s2 ＝0.35μm， W _t1 ，W _t2 Are all linear gradual change structures L _c ＝520μm，H _t ＝0.07μm，W _g ＝0.12μm。

Fig. 5 (a) - (f) show the magnetic field distribution in the xoz plane when the incident light wavelength is 1250nm, 1550nm, 1750nm, respectively, the TM0 mode is input, and the TE0 mode is input, and it can be observed that most of the energy of the input TM0 mode is transferred to the cross end, the magnetic field distribution position at the cross end is different at different wavelengths, and the evolution mode will occur at different sections of the waveguide at different wavelengths in the corresponding FDE analysis; on the other hand, for the injection TE0 mode, no energy transfer between waveguides is observed, and finally the TE0 mode is output at the through end. Namely, the device realizes the function of polarization beam splitting rotation in the working bandwidth.

In fig. 6, (a) shows the transmittance curve of the TE fundamental mode and the TM fundamental mode output from each port when the TE0 mode is input, the insertion loss is less than 0.05dB in the 1200nm-1800nm band, the crosstalk is lower than-60 dB, and the polarization extinction ratio is higher than 60 dB. Since no mode conversion occurs in the TE0 mode at the Through end, the loss is low. The case of the input TM0 mode is plotted in (b) of fig. 6, and it can be seen that most of the energy is coupled into the cross-terminal TE0 mode, the polarization extinction ratio reaches 15dB at 1250nm and remains higher than 15dB within 1250nm-1750nm, the insertion loss in this segment is lower than 0.2dB, and the crosstalk is lower than-30 dB, showing good performance within the designed wavelength range.

The modern DUV photoetching process can generally achieve the purposes that the flatness of the line width on a chip is superior to 0.6nm, the flatness of the line width on the chip is superior to 2.6nm, and the nonuniformity in a 200mm SOI wafer is less than 1 percent, so that the maximum tolerance value in the width direction is 1 percent of the width, and the maximum tolerance value in the height direction is 10 nm.

FIGS. 7 (a) - (b) show the waveguide height error change Δ H at TM0 mode incidence _co 10nm and Δ H _co Normalized energy of fundamental mode of each port at-10 nm, yielding polarization conversion efficiency for TM0 mode in both cases>91％(IL<0.4dB) of the incident wavelength range of 1270nm to 1720nm, with a PER in this wavelength range>11dB，CT<15dB, which means that the PSR can be within the waveguide top layer height error | Δ H _co When the | is less than 10nm, the normal work is carried out in the wave band range of 1350nm to 1720 nm. FIGS. 7 (c) - (d) show the input waveguide width error Δ W _s1 = 10nm and Δ W _s1 Normalized energy output for each port fundamental mode at-10 nm, in both cases polarization conversion efficiency for TM0 mode>91％(IL<0.4dB) of the incident wavelength range of 1310nm to 1710nm, with a PER in this wavelength range>13dB，CT<-15 dB; waveguide error Δ W according to input ends in (e) to (f) in FIG. 7 _s2 +3nm and Δ W _s2 Normalized energy output by each port fundamental mode at-3 nm, polarization conversion efficiency for TM0 mode>91％(IL<0.4dB) of the incident wavelength range of 1270nm to 1670nm, while having a PER in this wavelength range>12dB，CT<-14 dB. Input end waveguide error Δ H _t 10nm and Δ H _t The transmission spectra at-10 nm are plotted in fig. 7(g) - (h), in both cases for TM0 mode polarization conversion efficiency>95％(IL<0.22dB) of 1250nm to 1750nm, and a PER in this wavelength range>15dB，CT<-25 dB. This indicates that the current PSR inherently maintains good performance over a very wide band (1350nm-1670nm) within the tolerance allowed by the manufacturing process.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (8)

1. An ultra-wideband on-chip polarization beam splitting rotator based on reverse biconic asymmetric coupling comprises a substrate (1) and input and output waveguides arranged at the top of the substrate (1); wherein the substrate (1) is of an SOI structure, characterized in that:

the input waveguide and the output waveguide comprise an input guide waveguide (2), an output guide waveguide (3), an input tapered waveguide (4) and an output tapered waveguide (5), and are all made of silicon materials; the input guide waveguide (2) and the output guide waveguide (3) are parallel to each other in a polarization mode coupling region (6), and the input tapered waveguide (4) and the output tapered waveguide (5) are positioned in the polarization mode coupling region and are correspondingly formed at the tops of the input guide waveguide (2) and the output guide waveguide (3) respectively; the taper width of the input tapered waveguide (4) is gradually narrowed along the input direction, and the taper width of the output tapered waveguide (5) is gradually widened along the input direction, so that when a TM0 mode is injected, the effective refractive indexes of the input end TM0 mode and the cross end TE0 mode are equal on a certain section of the waveguide due to the fact that the effective refractive index curves of the two modes are opposite in change trend;

the polarization mode coupling region is composed of two gradually-changed ridge waveguides, wherein the ridge width of the input end waveguide is gradually narrowed along the Z direction, and the ridge width of the output end waveguide is gradually widened along the Z direction.

2. The ultra-wideband on-chip polarization beam splitting rotator based on inverse biconic asymmetric coupling as claimed in claim 1, wherein the input guide waveguide (2) and the output guide waveguide (3) are separated by a medium of air gap.

3. The ultra-wideband on-chip polarization splitting rotator based on inverse biconic asymmetric coupling of claim 1, wherein assuming that the length of the polarization mode coupling region (6) is L c, the input guide waveguide (2), the output guide waveguide (3), and the input tapered waveguide (4) and the output tapered waveguide (5), the width of the input guide waveguide (2) is W s1, the width of the output guide waveguide (3) is W s2, the taper width of the input tapered waveguide (4) is W t1, and the taper width of the output tapered waveguide (5) is W t2, then W t1 and W s1 on the input port are equal, decrease linearly along the Z direction, and after the length of L c, W t1 becomes zero; cross port W t2 widens linearly in the Z direction from zero and, after a length Lc, W t2 equals W s 2.

4. The ultra-wideband on-chip polarization beam splitting rotator based on inverse biconic asymmetric coupling as claimed in claim 1, wherein the substrate (1) has a silicon layer thickness hco of 220nm and an underlying buried oxide thickness of 2 μm.

5. The ultra-wideband on-chip polarization beam splitting rotator based on inverse biconic asymmetric coupling as claimed in claim 4, wherein the bottom buried oxide is silicon dioxide.

6. The ultra-wideband on-chip polarization beam splitting rotator based on the inverse biconic asymmetric coupling as claimed in claim 1, wherein the input tapered waveguide (4) and the output tapered waveguide (5) are formed by etching based on the input guide waveguide (2) and the output guide waveguide (3), respectively, and the maximum etching depth is H t.

7. The ultra-wideband on-chip polarization beam splitting rotator based on the inverse biconic asymmetric coupling as claimed in claim 1, wherein the overall height of the input guide waveguide (2) and the input tapered waveguide (4), and the overall height of the output guide waveguide (3) and the output tapered waveguide (5) are all H co.

8. The ultra-wideband on-chip polarization beam splitting rotator based on the inverse biconic asymmetric coupling as claimed in claim 1, wherein the width W s1 of the input guide waveguide (2) is 1 μm, the width W s2 of the output guide waveguide (3) is 0.35 μm, the length L c of the polarization mode coupling region (6) is 520 μm, the thicknesses H t of the input tapered waveguide (4) and the output tapered waveguide (5) are 0.07 μm, and the gap W g between the input guide waveguide (2) and the output guide waveguide (3) is 0.12 μm.

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