CN110376753B - High-performance polarization beam splitter and design method thereof - Google Patents
High-performance polarization beam splitter and design method thereof Download PDFInfo
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- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
- G02B27/283—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising used for beam splitting or combining
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/125—Bends, branchings or intersections
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/126—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind using polarisation effects
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
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- G02B6/26—Optical coupling means
- G02B6/27—Optical coupling means with polarisation selective and adjusting means
- G02B6/2726—Optical coupling means with polarisation selective and adjusting means in or on light guides, e.g. polarisation means assembled in a light guide
- G02B6/2733—Light guides evanescently coupled to polarisation sensitive elements
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- G—PHYSICS
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12133—Functions
- G02B2006/1215—Splitter
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Abstract
The invention discloses a high-performance polarization beam splitter and a design method thereof. The high-performance polarization beam splitter comprises n +1 cascade directional couplers, n beam combiners and n phase shifters (n is more than or equal to 2). Each directional coupler or beam combiner comprises two S-bend input waveguides, a coupling region and two S-bend output waveguides, the coupling region comprises two parallel single-mode straight waveguides, and m sub-wavelength structures (m is more than or equal to 2) are arranged in parallel between the two single-mode straight waveguides. One ends of the two S-shaped bent input waveguides are respectively connected with one ends of the two single-mode straight waveguides in the coupling region; the other ends of the two single-mode straight waveguides in the coupling region are respectively connected with one ends of the two S-shaped output waveguides. The invention can realize the design of ultrahigh extinction ratio or ultrahigh bandwidth polarization beam splitting in a communication waveband by setting the length of a coupling area of the directional coupler and the length of the phase shifter.
Description
Technical Field
The invention relates to the field of integrated optoelectronic devices, in particular to a polarization beam splitter and a design method thereof.
Background
The polarization beam splitter is applied to the field of optical communication, is a key device for multiplexing and demultiplexing different polarization signals in optical waveguides, and is also an important component for regulating and controlling polarization related devices of high-refractive-index-difference materials. In the research of the past decade, researchers have proposed various polarization beam splitter structures, including multimode interference coupler, mach-zehnder interferometer, grating coupler, asymmetric directional coupler, etc., and the extinction ratio is at 20dB level in the report of better performance at present, the working wavelength bandwidth is about 100nm, and the loss is 1 dB.
But for higher extinction ratios, such as greater than 35dB, only stay near the center wavelength. In addition, in recent years, further utilization of spectrum in optical communication, especially improvement of on-chip optical interconnection communication capacity, adoption of coarse wavelength division multiplexing of more channels, and higher requirements on operating wavelength bandwidth are put forward, and the polarization beam splitter must also meet the same operating band, for example, in the application of polarization and wavelength division multiplexing technology.
Disclosure of Invention
In order to overcome the defects of the prior art and meet the requirement of higher extinction ratio of polarization beam splitting in a specific waveband, for example, the extinction ratio is more than 35dB in a C waveband; or a larger working bandwidth, such as greater than 300nm, is achieved with polarization beam splitter insertion loss and extinction ratio that meet the application of integrated optoelectronic systems. According to the requirements of different application occasions, the corresponding parameters of the polarization beam splitter can be designed. The invention aims to provide a polarization beam splitter and a design method thereof.
The invention provides a high-performance polarization beam splitter, which comprises n +1 cascade directional couplers, n beam combiners and n phase shifters (n is more than or equal to 2); the upper output end of the directional coupler D1 is connected with the upper input end of the next-stage directional coupler D2, and so on until the upper output end of the directional coupler Dn is connected with the upper input end of the next-stage directional coupler Dn + 1; the lower output end of the coupler Dn +1 is connected with the upper input end of the beam combiner Hn; the upper output end of the beam combiner Hn is connected with the upper input end of the beam combiner Hn-1, and so on until the upper output end of the beam combiner H2 is connected with the upper input end of the beam combiner H1; and the lower output end of the directional coupler Di is connected with one end of a phase shifter Si, and the other end of the phase shifter Si is connected with the lower input end of a beam combiner Hi (i =1,2, …, n).
In a further specific embodiment, each directional coupler or beam combiner includes two S-bend input waveguides, a coupling region and two S-bend output waveguides, the coupling region includes two parallel single-mode straight waveguides, and m sub-wavelength structures (m ≧ 2) are disposed in parallel between the two single-mode straight waveguides. One ends of the two S-shaped bent input waveguides are respectively connected with one ends of the two single-mode straight waveguides in the coupling region; the other ends of the two single-mode straight waveguides in the coupling region are respectively connected with one ends of the two S-shaped output waveguides.
In a further specific embodiment, the coupling region of each directional coupler or beam combiner includes two parallel single-mode straight waveguides with the same width and m parallel sub-wavelength structures (m ≧ 2) placed between the two single-mode straight waveguides; the sub-wavelength structures are equal in width and spacing, and the length of the sub-wavelength structures is 3.5 times of the width of each of the left and right long waveguides of the two single-mode straight waveguides.
In a further specific embodiment, the directional couplers D1 and D2 are added to an n + 1-stage cascade directional coupler composed of directional couplers Dn +1, and their coupling region lengths are respectively equal to the beat length of TM polarized light at different wavelengths.
In a further specific embodiment, the polarization beam splitters, the beam combiner H1 and the beam combiner H2 are increased to the beam combiner Hn as the TM polarization beam combiner, and the structure of the beam combiner Hi and the directional coupler Di is the same (i =1,2, …, n).
In a further embodiment, the length of the phase shifter Si is set such that the TM polarized light is coupled from the beam combiner Hi
When the upper input terminal and the lower input terminal are input, the output can be output from the upper output terminal (i =1,2, …, n).
In still further embodiments, the S-bend waveguide, the coupling region straight waveguide, and the sub-wavelength structure comprise a high-refractive index
A rectangular core layer of low refractive index, an upper cladding layer of low refractive index, and a lower cladding layer of low refractive index.
In addition, the present invention provides a design method of the above high performance polarization beam splitter: the upper output end of the directional coupler D1 is connected with the upper input end of the next-stage directional coupler D2, and so on until the upper output end of the directional coupler Dn is connected with the upper input end of the next-stage directional coupler Dn + 1; the lower output end of the coupler Dn +1 is connected with the upper input end of the beam combiner Hn; the upper output end of the beam combiner Hn is connected with the upper input end of the beam combiner Hn-1, and so on until the upper output end of the beam combiner H2 is connected with the upper input end of the beam combiner H1; and the lower output end of the directional coupler Di is connected with one end of a phase shifter Si, and the other end of the phase shifter Si is connected with the lower input end of a beam combiner Hi (i =1,2, …, n).
In a further specific embodiment, when the TE polarized light is input from the input end of the directional coupler D1, no coupling occurs in the coupling region, and the TE polarized light is directly output from the output end of the directional coupler D2, enters the input end of the next stage of the directional coupler D2, and so on until the TE polarized light is output from the output end of the directional coupler Dn + 1.
In a further embodiment, when TM polarized light is input from the upper input end of the directional coupler D1, the beat length at a specific wavelength is equal to the length of the coupling region, light at that wavelength will be coupled out from the lower output port, light at other wavelengths will be output from the upper output port and enter the upper input end of the directional coupler D2 of the next stage, and so on, TM polarized light at different wavelengths will be output from the lower output ends of different directional couplers Di (i =1,2, …, n + 1).
In a further specific embodiment, the coupling region of each directional coupler or beam combiner is composed of two parallel single-mode straight waveguides with the same width and m parallel sub-wavelength structures (m is greater than or equal to 2) placed between the two single-mode straight waveguides; the sub-wavelength structures are equal in width and spacing, and the length of the sub-wavelength structures is 3.5 times of the width of each of the left and right long waveguides of the two single-mode straight waveguides. The m sub-wavelength structures are equivalent to anisotropic materials, so that the coupling of TE polarized light between the two single-mode straight waveguides can be prevented, and the coupling of TM polarized light between the two single-mode straight waveguides can be enhanced.
In a further specific embodiment, the directional couplers D1 and D2 are gradually increased to an n + 1-stage cascade directional coupler composed of directional couplers Dn +1, and the lengths of their coupling regions are respectively equal to the beat lengths of TM polarized light at different wavelengths, and the selected wavelength is determined by the designed operating band range.
In a further embodiment, the beam combiner (H1), the beam combiner (H2) are incremented to the beam combiner (Hn) as a TM polarization beam combiner, and the beam combiner (Hi) and the directional coupler (Di) have the same structure (i =1,2, …, n).
In a further specific embodiment, the length of the phase shifter Si is set such that TM polarized light can be output from the upper output terminal when input from the upper input terminal and the lower input terminal of the beam combiner Hi (i =1,2, …, n).
In a further specific embodiment, the S-bend waveguide, the coupling region straight waveguide and the sub-wavelength structure are formed by wrapping a low-refractive-index upper cladding layer and a low-refractive-index lower cladding layer outside a high-refractive-index rectangular core layer.
The invention has the beneficial effects that:
(1) the equivalent anisotropic material is added in the middle of the coupling area of the directional coupler or the beam combiner, and a single directional coupler or beam combiner can more effectively separate TE polarized light from TM polarized light, and the extinction ratio at the central wavelength is high;
(2) the invention utilizes the cascade directional coupler, and can realize ultrahigh extinction ratio (more than 35 dB) by the polarization beam splitter in a specific wave band range, such as C wave band, on the premise of keeping lower insertion loss;
(3) the invention utilizes the cascade directional coupler, and the polarization beam splitter can realize the ultra-large working bandwidth (more than 300 nm) under the condition that the insertion loss and the extinction ratio of the polarization beam splitter meet the application of an integrated optoelectronic system;
any technical scheme of the invention does not necessarily achieve all the above beneficial effects.
Drawings
FIG. 1 is a schematic diagram of a high performance polarizing beam splitter according to the present invention;
FIG. 2 is a schematic structural diagram of a directional coupler or combiner for use in the high performance polarization beam splitter of the present invention;
FIG. 3 is a cross-sectional view of a directional coupler or combiner coupling region;
FIG. 4 is a schematic diagram of a phase shifter for use in the high performance polarization beam splitter of the present invention;
fig. 5 is a schematic structural diagram of a polarization beam splitter in a three-stage cascade, that is, when n =2 according to an embodiment of the present invention;
FIG. 6 is a diagram showing the optical field of TE polarized light with a wavelength of 1.55 μm transmitted in the polarization beam splitter with ultra-high extinction ratio in embodiment 2 of the present invention;
FIG. 7 is a diagram of the optical field of TM polarized light with a wavelength of 1.55 μm transmitted in the polarization beam splitter with ultra-high extinction ratio in embodiment 2 of the present invention;
FIG. 8 is a diagram of the optical field of TE polarized light with a wavelength of 1.6 μm transmitted in the ultra-large bandwidth polarization beam splitter in embodiment 3 of the present invention;
FIG. 9 is a diagram of the optical field of TM polarized light with a wavelength of 1.45 μm transmitted in the ultra-large bandwidth polarization beam splitter of embodiment 3 of the present invention;
FIG. 10 is a diagram of the optical field of TM polarized light with a wavelength of 1.6 μm transmitted in the ultra-large bandwidth polarization beam splitter of embodiment 3 of the present invention;
FIG. 11 is a diagram of the optical field of TM polarized light with a wavelength of 1.75 μm transmitted in the ultra-large bandwidth polarization beam splitter of embodiment 3 of the present invention.
Detailed Description
The invention is further illustrated below with reference to the figures and examples.
Example 1
As shown in FIG. 1, the polarization beam splitter comprises n +1 cascaded directional couplers, n beam combiners and n phase shifters (n ≧ 2); the upper output end of the directional coupler D1 is connected with the upper input end of the next-stage directional coupler D2, and so on until the upper output end of the directional coupler Dn is connected with the upper input end of the next-stage directional coupler Dn + 1; the lower output end of the coupler Dn +1 is connected with the upper input end of the beam combiner Hn; the upper output end of the beam combiner Hn is connected with the upper input end of the beam combiner Hn-1, and so on until the upper output end of the beam combiner H2 is connected with the upper input end of the beam combiner H1; and the lower output end of the directional coupler Di is connected with one end of a phase shifter Si, and the other end of the phase shifter Si is connected with the lower input end of a beam combiner Hi (i =1,2, …, n).
As shown in FIG. 2, the directional coupler or combiner of the present invention is composed of an upper input S-bend waveguide 1, a lower input S-bend waveguide 2, a pair of parallel single-mode straight waveguides 3 and 4, an upper output S-bend waveguide 5, a lower output S-bend waveguide 6, and m sub-wavelength structures (m ≧ 2) parallel to the straight waveguides. The two input S-shaped curved waveguides are respectively connected with one end of each of the two parallel single-mode straight waveguides, the other end of each of the two parallel single-mode straight waveguides is connected with the two output S-shaped curved waveguides, the sub-wavelength structure is located between the two single-mode straight waveguides, and the whole directional coupler or beam combiner structure is symmetrical about a horizontal central line and a vertical central line.
As shown in FIGS. 2 and 3, the subwavelength structure has a width WmThe length of the subwavelength structure, i.e. the length of the coupling region, is LcThe space between the sub-wavelength structure and the straight waveguide and the space between the sub-wavelength structure are both G, and the widths of the S-shaped curved waveguide and the straight waveguide are both WwgThe S-bend waveguide has a transverse span length of LsLongitudinal span length of WsThe length of the straight waveguides 3 and 4 is 7 times smaller than the length of the subwavelength structure, i.e. L, than the width of the straight waveguidesc-7*WwgThe different directional couplers or combiners described in this invention have coupling zone lengths LcDifferent.
As shown in FIG. 4, the phase shifter aimed at in the present invention is composed of a two-stage tapered cone 10, a straight waveguide11 and a gradual change tapered device 12, wherein the gradual change tapered device 10 is connected with the straight waveguide 11, and the other end of the straight waveguide 11 is connected with the gradual change tapered device 12. The input and output waveguides are all W in widthwgThe lengths of the gradual taper devices are LtThe width of the straight waveguide 11 is WpLength of Lp。
As shown in fig. 3, all waveguides and subwavelength structures described in the present invention use high refractive index material as core layer, and have a thickness H, and further have a low refractive index upper cladding layer 8 and a low refractive index lower cladding layer 9.
The working principle of the invention is that TE or TM polarized light is input from the input end of the directional coupler D1 by adjusting the width W of the sub-wavelength structure 7mAnd a distance G, so that the evanescent wave of TE polarization is better confined to the vicinity of the waveguide, the coupling between the two waveguides is greatly reduced, the TE polarized light is output from the upper output end of the directional coupler D1 and enters the upper input end of the next-stage directional coupler D2, and the like, and the TE polarized light is finally output from the upper output end of the directional coupler Dn + 1. the sub-wavelength structure is equivalent to an anisotropic cladding material, and for the TM polarized light, more evanescent wave is diffused to the sub-wavelength structure area, so that the coupling between the two waveguides is enhancedc1，Lc2，…，Lcn+1. This allows TM polarized light of different wavelengths to be output from the lower output of the directional coupler (D1, D2, …, Dn + 1). The structure of the beam combiner (H1, H2, …, Hn) is the same as that of the directional coupler (D1, D2, …, Dn), and the working process of the beam combiner is the reverse process of the directional coupler. For example, TM polarized light at the upper output end of the directional coupler Dn enters the upper input end of the beam combiner Hn after passing through the directional coupler Dn +1, and TM polarized light at the lower output end of the directional coupler DnTM polarized light enters the lower input end of the beam combiner Hn through the phase shifter, coherent beam combination is carried out on the upper input end and the lower input end of the beam combiner Hn to be output to the upper output end by adjusting the length of the phase shifter Sn, the phase shifters Si of all levels are adjusted by parity of reasoning, and the lengths of the marked phase shifters are L respectivelyp1，Lp2，…，Lpn+1So that the two paths of TM polarized light output by the directional coupler Di are combined and output at the beam combiner Hi (i =1,2, …, n), and the TM polarized light is finally output at the output end of the beam combiner H1.
Example 2
As shown in FIG. 5, a polarization beam splitter consisting of three cascaded directional couplers D1-D3, two beam combiners H1-H2 and two phase shifters S1-S2 is selected, namely n =2, wherein the output end of the directional coupler D1 is connected with the input end of the directional coupler D2 through a straight waveguide 13, and the length L of the straight waveguide 13 isz1=12 μm, the output end of the directional coupler D2 is connected with the input end of the directional coupler D3 via an S-bend waveguide 14, and the transverse span length of the S-bend waveguide 14 is Ls1=15 μm, longitudinal span length Ws1=2.09 μm, the lower output end of the directional coupler D3 is directly connected with the upper input end of the beam combiner H2, the upper output end of the beam combiner H2 is connected with the upper input end of the beam combiner H1 through the straight waveguide 15, and the length L of the straight waveguide 15z4=12 μm, the lower output end of the directional coupler D2 and the lower input end of the beam combiner H2 are sequentially connected through a phase shifter S2 and a straight waveguide 18, and the length of the phase shifter S2 is Lp2=45 μm, length L of straight waveguide 18z2=3.3 μm, the lower output end of the directional coupler D1 and the lower input end of the beam combiner H1 are connected in turn by an S-bend waveguide 16, a phase shifter S1, a straight waveguide 17 and an S-bend waveguide 19, and the length of the phase shifter S1 is Lp1=46 μm, length L of straight waveguide 17z3=31.7 μm, and the S-bend waveguides 16 and 19 are L long in lateral spans2=30 μm, longitudinal span length Ws2With the wavelength range of 1.52-1.58 μm, the directional couplers D1-D3 have lengths of L respectivelyc1=19.5μm，Lc2=20.7μm，Lc3=21.3 μm, the beam combiners H1-H2 have the same structures as the directional couplers D1-D2, respectively, and the other parameters of the directional couplers and the beam combiners are W as shown in FIG. 2wg=0.55μm，Wm=60nm，G=60nm，Ws=0.5μm，Ls=8 μm. The core layer material of the whole polarization beam splitter is silicon, the thickness H =220nm, and the upper and lower cladding layers are made of silicon dioxide.
Through numerical simulation of a Finite Difference Time Domain (FDTD) method, in a wave band range of 1.52-1.58 μm, when TE polarized light and TM polarized light are input, the extinction ratios between two output ends are respectively larger than 35dB and 41.5dB, the insertion losses are respectively smaller than 0.1dB and 0.36dB, and the high extinction ratio is achieved while the small insertion loss is kept in a 60nm wave band. Fig. 6 shows the electric field amplitude distribution of the optical transmission when the light with TE polarization and wavelength of 1.55 μm is input by the design. Fig. 7 shows the electric field amplitude distribution of the optical transmission of this design when TM polarization and light with a wavelength of 1.55 μm are input.
Example 3
As shown in FIG. 5, a polarization beam splitter consisting of three cascaded directional couplers D1-D3, two beam combiners H1-H2 and two phase shifters S1-S2 is selected, namely n =2. Wherein the output end of the directional coupler D1 and the input end of the directional coupler D2 pass through a straight line
Waveguide 13 connected, straight waveguide 13 length Lz1=12 μm, the output end of the directional coupler D2 is connected with the input end of the directional coupler D3 via an S-bend waveguide 14, and the transverse span length of the S-bend waveguide 14 is Ls1=15 μm, longitudinal span length Ws1=2.09 μm, the lower output end of the directional coupler D3 is directly connected with the upper input end of the beam combiner H2, the upper output end of the beam combiner H2 is connected with the upper input end of the beam combiner H1 through the straight waveguide 15, and the length L of the straight waveguide 15z4=12 μm, the lower output end of the directional coupler D2 and the lower input end of the beam combiner H2 are sequentially connected through a phase shifter S2 and a straight waveguide 18, and the length of the phase shifter S2 is Lp2=75 μm, length L of straight waveguide 18z2=4.8 μm, the lower output end of the directional coupler D1 and the lower input end of the beam combiner H1 are connected in turn by an S-bend waveguide 16, a phase shifter S1, a straight waveguide 17 and an S-bend waveguide 19, and the length of the phase shifter S1 is Lp1=80 μm, length L of straight waveguide 17z3=35.8 μm, and the S-bend waveguides 16 and 19 are L long in lateral spans2=30 μm, longitudinal span length Ws2=3.5 μm. At 1.4 μm toThe design of realizing super-large bandwidth in a wave band range of 1.8 mu m is taken as an example, the lengths of the directional couplers D1-D3 are Lc1=11.5μm，Lc2=24μm，Lc3=52.8 μm, the beam combiners H1-H2 have the same structure as the directional couplers D1-D2, respectively, and the other parameters of the directional couplers and the beam combiners are W as shown in FIG. 2wg=0.55μm，Wm=60nm，G=60nm，Ws=0.5μm，Ls=8 μm. The core layer material of the whole polarization beam splitter is silicon, the thickness H =220nm, and the upper and lower cladding layers are made of silicon dioxide.
Through numerical simulation of a Finite Difference Time Domain (FDTD) Time Domain method, in a wave band range of 1.42-1.765 mu m, when TE polarized light and TM polarized light are input, the extinction ratio between two output ends is respectively larger than 13dB and 14dB, the insertion loss is respectively smaller than 1.5dB and 0.26dB, the insertion loss and the extinction ratio in 345nm ultra-large bandwidth meet the application requirement of an integrated optoelectronic system, and the integrated optoelectronic system has ultra-large working bandwidth. Fig. 8 shows the electric field amplitude distribution of the optical transmission when the TE polarization and the light with the wavelength of 1.6 μm are input by the design, and the electric field distribution patterns at other wavelengths are similar. FIGS. 9-11 show the electric field amplitude distribution of the optical transmission when light with TM polarization and wavelength of 1.45 μm, 1.6 μm, and 1.75 μm is input.
Claims (10)
1. A high-performance polarization beam splitter is characterized in that the polarization beam splitter comprises n +1 cascade directional couplers, n beam combiners and n phase shifters (n is more than or equal to 2); the upper output end of the directional coupler D1 is connected with the upper input end of the next-stage directional coupler D2, and so on until the upper output end of the directional coupler Dn is connected with the upper input end of the next-stage directional coupler Dn + 1; the lower output end of the coupler Dn +1 is connected with the upper input end of the beam combiner Hn; the upper output end of the beam combiner Hn is connected with the upper input end of the beam combiner Hn-1, and so on until the upper output end of the beam combiner H2 is connected with the upper input end of the beam combiner H1; the lower output end of the directional coupler Di is connected with one end of a phase shifter Si, and the other end of the phase shifter Si is connected with the lower input end of a beam combiner Hi (i =1,2, …, n);
each directional coupler or beam combiner comprises two S-shaped bent input waveguides, a coupling area and two S-shaped bent output waveguides, the coupling area comprises two parallel single-mode straight waveguides, and m sub-wavelength structures (m is more than or equal to 2) are arranged in parallel between the two single-mode straight waveguides; one ends of the two S-shaped bent input waveguides are respectively connected with one ends of the two single-mode straight waveguides in the coupling region; the other ends of the two single-mode straight waveguides in the coupling region are respectively connected with one ends of the two S-shaped bent output waveguides; the phase shifter is composed of a gradual change conical device, a straight waveguide and a gradual change conical device.
2. The high performance polarization beam splitter of claim 1, wherein the coupling region of each directional coupler or beam combiner comprises two parallel single-mode straight waveguides with the same width and m parallel sub-wavelength structures (m ≧ 2) placed between the two single-mode straight waveguides; the width and the interval of the sub-wavelength structures are equal, the length of the sub-wavelength structures is the length of the coupling region, is respectively equal to the beat length of TM polarized light under different wavelengths, and is 3.5 times of the width of each long waveguide at the left and the right of the two single-mode straight waveguides.
3. The high performance polarization beam splitter of claim 1 wherein the beam combiner H1, the beam combiner H2 to the beam combiner Hn are configured as TM polarization beam combiners, and the beam combiner Hi and the directional coupler Di are configured identically (i =1,2, …, n).
4. The high-performance polarization beam splitter according to claim 1, wherein the phase shifter Si is configured to have a length such that TM polarized light can be output from the upper output end (i =1,2, …, n) when input from the upper input end and the lower input end of the beam combiner Hi.
5. The high performance polarizing beam splitter of any one of claims 1-4 wherein the S-bend input waveguides, S-bend output waveguides, coupling region straight waveguides and subwavelength structures comprise a high index rectangular core layer, a low index upper cladding layer and a low index lower cladding layer.
6. A design method of a high-performance polarization beam splitter according to claim 1 is characterized in that n +1 cascaded directional couplers, n beam combiners and n phase shifters (n is more than or equal to 2) form the polarization beam splitter, the upper output end of a directional coupler D1 is connected with the upper input end of a next-stage directional coupler D2, and so on until the upper output end of a directional coupler Dn is connected with the upper input end of the next-stage directional coupler Dn + 1; the lower output end of the coupler Dn +1 is connected with the upper input end of the beam combiner Hn; the upper output end of the beam combiner Hn is connected with the upper input end of the beam combiner Hn-1, and so on until the upper output end of the beam combiner H2 is connected with the upper input end of the beam combiner H1; the lower output end of the directional coupler Di is connected with one end of a phase shifter Si, and the other end of the phase shifter Si is connected with the lower input end of a beam combiner Hi (i =1,2, …, n);
when TE polarized light is input from the input end of the directional coupler D1, coupling can not occur in a coupling area, the TE polarized light is directly output from the upper output end of the directional coupler D2, enters the upper input end of the next-stage directional coupler D2, and so on until the TE polarized light is output from the upper output end of the directional coupler Dn + 1;
when TM polarized light is input from the upper input end of the directional coupler D1, the beat length at a specific wavelength is equal to the length of the coupling region, light at the wavelength will be coupled out from the lower output port, light at other wavelengths will be output from the upper output port and enter the upper input end of the directional coupler D2 at the next stage, and so on, TM polarized light at different wavelengths will be output from the lower output ends of different directional couplers Di (i =1,2, …, n + 1).
7. The design method of claim 6, wherein the coupling region of each directional coupler or beam combiner consists of two parallel single-mode straight waveguides with the same width and m parallel sub-wavelength structures (m ≧ 2) placed between the two single-mode straight waveguides; the width and the interval of the sub-wavelength structure are equal, the length of the sub-wavelength structure is that the length of the coupling region is respectively equal to the beat length of TM polarized light under different wavelengths and is 3.5 times of the width of each long waveguide at the left and the right of the two single-mode straight waveguides; the m sub-wavelength structures are equivalent to anisotropic materials, so that the coupling of TE polarized light between the two single-mode straight waveguides can be prevented, and the coupling of TM polarized light between the two single-mode straight waveguides can be enhanced.
8. The design method as claimed in claim 6, wherein the beam combiner H1, the beam combiner H2 are increased to the beam combiner Hn as TM polarization beam combiner, and the structure of the beam combiner Hi and the directional coupler Di is the same (i =1,2, …, n).
9. The design method according to claim 6, wherein the length of the phase shifter Si is set such that TM polarized light can be output from the upper output terminal when input from the upper input terminal and the lower input terminal of the beam combiner Hi (i =1,2, …, n).
10. The design method of claim 6, wherein the S-bend input waveguide, the S-bend output waveguide, the coupling region straight waveguide and the sub-wavelength structure are surrounded by a low refractive index upper cladding layer and a low refractive index lower cladding layer outside the high refractive index rectangular core layer.
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| CN111999957B (en) * | 2020-07-17 | 2022-08-05 | 宁波大学 | Polarization insensitive photosensitive switch based on assistance of germanium antimony tellurium compound phase change material |
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