CN104852116B - A kind of surface phasmon directional coupler and its control method independent of polarization - Google Patents
A kind of surface phasmon directional coupler and its control method independent of polarization Download PDFInfo
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- CN104852116B CN104852116B CN201510256468.1A CN201510256468A CN104852116B CN 104852116 B CN104852116 B CN 104852116B CN 201510256468 A CN201510256468 A CN 201510256468A CN 104852116 B CN104852116 B CN 104852116B
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Abstract
The invention discloses a kind of surface phasmon directional coupler and its control method independent of polarization.Asymmetric defective small structure is processed in present invention proposition on the ridge waveguide of sub-wavelength, and realization p-polarization and s polarized incident light directional couples go out SPP mode；Ridge waveguide only supports single pattern；Due to the influence of defect, the incident light of p-polarization and s polarizations can directionally be coupled out the SPP mode propagated along ridge waveguide；By adjusting the geometric parameter of defect, the SPP mode that the incident light that p-polarization and s are polarized is coupled out both can also be propagated in opposite direction along identical；In the case where propagating in same direction, the intensity of the SPP mode being coupled out of the incident beam modulated of s polarizations always can be made full use of；In the case where propagating in opposite direction, the information of the incident light of polarization encoder is just retained, it is achieved thereby that the coupling process of SPP mode is independent of polarization.
Description
Technical field
The present invention relates to nanophotonics field, more particularly to a kind of surface phasmon directional couple independent of polarization
Device and its control method.
Background technology
Surface phasmon SPPs is the horizontal magnetic TM mode of electromagnetic waves being strapped on metal-dielectric interface.Because its is excellent
Sub-wavelength field containment and strong field enhancement effect, SPPs is considered as potential of future generation information carrier.Free space optical
It is coupled to SPPs most important to the performance for studying phasmon device.In terms of this has expedited the emergence of out many SPP unidirectional couplings devices
Research.Free space optical can be efficiently coupled on metal flat or ridged waveguide structure by unidirectional couplings device,
Along the SPPs specified or direction interested is propagated.However, the polarization independent characteristic (TM polarizations) due to SPPs in itself, only
The incident light of p-polarization (magnetic direction of the magnetic vector parallel to SPPs) can be coupled into SPPs.So (magnetic vector hangs down s polarizations
Directly in SPPs magnetic direction) carry energy and information just lost completely.Recently, having been reported that can with the incident light of circular polarization
To overcome the dependence in SPPs coupling process to polarization to a certain extent.Because the incident light of any polarization can be decomposed
Into two mutually perpendicular linear polarization compositions, this can for explain many optical phenomenas and effect (including optical Kerr effect,
Optical birefringence, electrooptic effect).So, going out SPPs with p-polarization or s the incident light directional couple polarized may be with more real
Border meaning.But due to SPPs p-polarization dependency characteristic, the incident light directional couple polarized with s, which goes out SPPs and is one, severe chooses
War.
The content of the invention
The problem of existing for above prior art, the present invention is proposed a kind of to be machined with the ridge waveguide of sub-wavelength
The small structure of defect, realize p-polarization and s polarized incident lights can directional couple go out SPPs so that it is inclined to solve SPP directional couples
Shake dependence the problem of.
It is an object of the present invention to provide a kind of surface phasmon directional coupler independent of polarization.
The surface phasmon directional coupler of the present invention includes：Metallic film, aperture, ridge waveguide and projection nanometer
Grain；Wherein, aperture is provided with metallic film；On metallic film and positioned at aperture two ends positional symmetry set two
The width of ridge waveguide, ridge waveguide width and aperture, by adjusting the width w and height h of ridge waveguide, can be made with inconsistent
Obtain ridge waveguide and only support single SPP mode；Projection nano particle, projection are set on metallic film and positioned at the side of aperture
The edge of the endless all standing aperture of nano particle, forms defective small structure；Incident light is defective small from back side illuminaton
Pore structure, electric charge is accumulated in the corner region of defective small structure and forms focus (hot spots)；For p-polarization
Incident light, electric charge is accumulated in the corner region of ridge waveguide and forms focus, and the radiation field of focus is coupled into along ridge waveguide
The SPP mode of propagation, so that the incident light of p-polarization is coupled into the SPP mode propagated along ridge waveguide；The incidence polarized for s
Light, electric charge is accumulated in the corner region of projection nano particle and forms focus, and the radiation field of focus is coupled into along ridge waveguide
The SPP mode of propagation, so that the incident light of s polarizations can also be coupled into along ridge waveguide and propagate SPP mode, is realized independent of polarization
Surface phasmon coupler.
Further, the center of projection nano particle is not on the center of aperture side, so as to form along ridged
The asymmetric defective small structure of wave guide direction, the ridge waveguide of aperture one end is away from projection nano particle, and aperture
The ridge waveguide of the other end is close to projection nano particle.For the incident light of p-polarization, electricity is accumulated in the corner region of ridge waveguide
Lotus simultaneously forms focus (hot spots).And the focus formed on the ridge waveguide away from projection nano particle be more than by
The focus number formed on the ridge waveguide of nearly projection nano particle, so that the main edge of SPP mode of the incident optical coupling of p-polarization
The ridge waveguide away from projection nano particle to propagate；The incident light polarized for s, tires out in the corner region of projection nano particle
Accumulated charge simultaneously forms focus, and the geometric structure diamete of projection nano particle can influence the radiation field direction of focus, so that s polarizations
The SPP mode propagated along ridge waveguide that incident light can be directionally coupled into.Therefore using asymmetric defective small
Pore structure, can realize the surface phasmon directional coupler independent of polarization in sub-wavelength waveguide.
The geometric structure diamete of projection nano particle can influence the field distribution of focus, therefore the geometry knot of projection nano particle
Structure size influences the intensity of SPP mode.Due to the asymmetry of small structure, the intensity of the SPP mode of opposite direction is to differ
Sample, therefore the intensity of SPP mode can be adjusted by adjusting the geometric structure diamete of projection nano particle.By adjusting projection
The proportion of the intensity of the SPP mode of the geometric structure diamete of nano particle, regulation p-polarization and s polarization coupleds.
Further, the geometric parameter of projection nano particle is adjusted so that p-polarization and the SPP mode of s polarized incident optical couplings
Propagated along equidirectional on ridge waveguide.Can be by rotating the angle of polarization of incident light hence for incident linearly polarized light
Degree, it is easy to the intensity for the SPP mode that ground regulation is coupled out.The geometric parameter of projection nano particle includes：Cross section geometry
And the position away from small hole center axle.
The thickness of metallic film is more than 300nm；The width and height of ridge waveguide are all higher than 50nm；The length of aperture exists
Between 200nm~2 μm；The size of projection nano particle is more than 50nm.
It is another object of the present invention to provide a kind of control of the surface phasmon directional coupler independent of polarization
Method processed.
The control method of the surface phasmon directional coupler of the present invention, comprises the following steps：
1) aperture is provided with metallic film, on metallic film and positioned at aperture two ends positional symmetry set two
Individual ridge waveguide, the width of ridge waveguide is consistent with the width of aperture need not be consistent, by adjust ridge waveguide width w and
Height h so that ridge waveguide only supports single SPP mode, projection is set on metallic film and positioned at the position of aperture side
Nano particle, the edge of the endless all standing aperture of projection nano particle；
2) incident light is from the defective small structure of back side illuminaton, and electric charge tires out in the corner region of defective small structure
Accumulate and form focus (hot spot)；
3) for the incident light of p-polarization, electric charge is accumulated in the corner region of ridge waveguide and forms focus, the radiation of focus
Field is coupled into the SPP mode propagated along ridge waveguide, so that the incident light of p-polarization is coupled into what is propagated along ridge waveguide
SPP mode；
4) incident light polarized for s, electric charge is accumulated in the corner region of projection nano particle and forms focus, focus
Radiation field is coupled into the SPP mode of ridge waveguide propagation, so that the incident light of s polarizations can also be coupled into what is propagated along ridge waveguide
SPP mode, realizes that the surface phasmon independent of polarization is coupled.
The control method of the surface phasmon directional coupler of the present invention also includes, by adjusting projection nano particle
The proportion of the intensity of the SPP mode of geometric parameter, regulation p-polarization and s polarization coupleds.
Further, the geometric parameter of projection nano particle is adjusted so that the SPP mode of p-polarization coupling is along identical side
Propagated on ridge waveguide.Hence for incident linearly polarized light, coupling can be adjusted by rotating the polarization angle of incident light
The intensity of the SPP mode closed out.
Advantages of the present invention：
The present invention is proposed to process asymmetric defective small structure on the ridge waveguide of sub-wavelength, realized inclined with p
Shake and go out SPP mode with s polarized incident light directional couples；In view of the single mode operation condition in photon circuit, the ridged of sub-wavelength
Waveguide has been optimized to only support single pattern；Due to the influence of defect, the incident light of p-polarization and s polarizations can be directionally
It is coupled out the SPP mode propagated along ridge waveguide；By the incident optical coupling for adjusting the geometric parameter of defect, p-polarization and s polarizations
The SPP mode gone out both can also be propagated in opposite direction along identical., can be abundant in the case where propagating in same direction
The intensity of the SPP mode being coupled out of the incident beam modulated polarized using s always.In the case where propagating in opposite direction, polarization
The information of the incident light of coding is just retained.So, in this extra small defective small structure, p-polarization and s
The incident light of polarization is coupled into the SPP mode propagated along ridge waveguide with being directed, so the coupling process of SPP mode
Being can be independent of polarization.
Brief description of the drawings
Fig. 1 is the structural representation of the surface phasmon directional coupler independent of polarization of the present invention, wherein, (a)
For the schematic diagram of defective small structure, (b) is the profile of ridge waveguide, and (c) is the SPP mode that ridge waveguide is supported
Field pattern, (d) schemes for the Scanning Electron microscope SEM of the sample of flawless small structure, and (e) is defective small
The Scanning Electron microscope figure of the sample of pore structure；
Fig. 2 be incident light from back side illuminaton when, flawless small structure with the present invention defective small structure coupling
The SPP mode comparison diagram of conjunction, wherein, (a) and (b) are respectively that the incident light of p-polarization and s polarizations is flawless small from back side illuminaton
The distribution map of the electric field of pore structure, (c) and (d) is respectively that the incident light of p-polarization and s polarizations in experiment is defective from back side illuminaton
The distribution map of the electric field of small structure, (e) and (f) are respectively that the incident light of theoretical calculation p-polarization and s polarizations has scarce from back side illuminaton
The distribution map of the electric field of sunken small structure；
Fig. 3 is obtained p-polarization and the s polarization of the surface phasmon directional coupler independent of polarization of the present invention
The interference pattern of the SPP mode of coupling, wherein, (a) is the linearly polarized light and ridged ripple that the incident light compositing that p-polarization and s are polarized is obtained
45 ° of angles are led, (b) is that the linearly polarized light that the incident light compositing that p-polarization and s are polarized is obtained has -45 ° of angles, (c) with ridge waveguide
The field pattern obtained for the numerical computations of 45 ° of angles, the field pattern that (d) obtains for the numerical computations of -45 ° of angles, (e) line
The intensity for the SPP mode that polarised light is coupled out and the relation of polarization direction, the intensity for the SPP mode that (f) linearly polarized light is coupled out
With the relation of polarization direction；
Fig. 4 polarizes the electric field intensity map of the SPP mode of bidirectional couple for the p-polarization and s of embodiment two, wherein, (a) is embodiment
Two Scanning Electron microscope figure, (b) and (c) is distributed as the electric field that incident light λ=780nm p-polarization and s polarization coupleds are obtained
CCD schemes, and (d) and (e) is respectively the field pattern that numerical computations are obtained；
During Fig. 5 (a) to (c) is respectively embodiment three, change the structural parameters w of projection nano particledAnd Ld, numerical computations
Obtained p-polarization and the intensity of the SPP mode of s polarization coupleds, Fig. 5 (d) to (f) is respectively that two defect sturctures are symmetrically disposed at
Change the structural parameters w of projection nano particle during aperture both sidesdAnd Ld, p-polarization and the SPP of s polarization coupleds that numerical computations are obtained
The intensity of pattern；
During Fig. 6 is embodiment one, SPP mode excites figure when incident light is circular polarization, wherein, (a) and (b) is several respectively
Value calculate the incident light of obtained dextrorotation and Left-hand circular polarization from back side illuminaton sample when, the energy flow point above waveguide at 100nm
Cloth, image when (c) and (d) is the dextrorotation that CCD is obtained and left-handed elliptical polarization incidence respectively, (e) and (f) is corresponding numerical value
Calculate the energy flow distribution at 100nm in obtained waveguide；
Fig. 7 is the Spectral Extinction of the SPP mode in embodiment two, wherein, (a) and (b) are respectively the incident light that experiment is obtained
The delustring collection of illustrative plates of SPP mode when being polarized for p-polarization and s, (c) and (d) is respectively that to calculate obtained incident light be p-polarization and s
The Spectral Extinction of SPP mode during polarization；
Fig. 8 is the schematic diagram of p-polarization and s polarization coupled mechanism, wherein, (a) is the schematic diagram of focus, and (b) is p-polarization
Field strength pattern, (c) is the field strength pattern that s is polarized；
Fig. 9 is the intensity map of SPP mode when two defect sturctures are symmetrically disposed at aperture both sides；
Figure 10 is analyzing analysis chart, wherein, (a) and (b) is that Glan-Taylor prism is p-polarization, and incident light is respectively p inclined
Shake the image of CCD when being polarized with s, and (c) and (d) is that Glan-Taylor prism is s polarizations, and incident light is respectively p-polarization and s polarizations
When CCD image.
Embodiment
Below in conjunction with the accompanying drawings, by embodiment, the present invention will be further described.
Embodiment one
As shown in figure 1, the metallic film of the present embodiment, aperture, ridge waveguide and projection nano particle；Wherein, metal foil
The thickness of film is t, and aperture is provided with metallic film；On metallic film and positioned at aperture two ends positional symmetry set
Two ridge waveguides, the width of ridge waveguide and the width of aperture can be with inconsistent, by the width w and height that adjust ridge waveguide
Spend h so that ridge waveguide only supports single SPP mode；Projection nanometer is set on metallic film and positioned at the side of aperture
Grain；The edge of the endless all standing aperture of projection nano particle, forms defective small structure.
First, ridge waveguide, w=290nm, h=300nm are set on metallic film, and metallic film uses golden film, ridged
Shown in the field distribution such as Fig. 1 (c) for the SPP mode that waveguide is supported.Now, lambda1-wavelength λ=780nm, corresponding golden dielectric
Constant is εAu=-22.5+1.4i30.It can be seen that, electromagnetic field is held onto well, and electric field is mainly vertical metal
Surface, explanation is TM polarizations.In order in incident light from back side illuminaton in the case of be coupled out SPP mode, set on metallic film
A rectangular apertures are put, the edge for being close to aperture sets projection nano particle, shown in such as Fig. 1 (a).Wherein rectangular apertures
Length is L, and the width and length of projection nano particle are respectively wdAnd Ld.In order to sample process convenience, projection nano particle and
The overlapping Δ L distance of ridge waveguide.Due to the influence of projection nano particle, the incident light of p-polarization and s polarizations can be oriented
Ground is coupled out the SPP mode propagated along ridge waveguide.
Experimentally, with focused ion beam FIB in the thick golden films of 450nm (deposition on the glass substrate, and centre has one
Titanium adhesion layer thick layer 30nm) it machined defective small structure.Fig. 1 (d) and (e) are that the Scanning Electron of sample is micro- respectively
Mirror SEM image, wherein Fig. 1 (d) are the common apertures on ridged waveguide structure, and Fig. 1 (e) is defective small on ridge waveguide
Pore structure.The flawless small structure that also machined no defect sturcture simultaneously is used as reference sample.Defective aperture knot
The details of structure is shown in Fig. 1 (e) right half part.During FIB is processed, a ridge waveguide, ripple are first machined in golden film
The width led is w.In order to process projection nano particle, a small rectangular area has been stayed not during ridge waveguide is processed
Processing.Then, the position that projection nano particle is close on ridge waveguide processes the aperture of a rectangle.According to the knot of measurement
Really, the structural parameters of total are approximately as w=290nm, L=600nm, wd=300nm, Ld=360nm, and Δ L=
60nm, the cross section of ridge waveguide is 290 × 300nm2Rectangle.So the area of total is about 0.28 μm2(<λ2/
2).Facilitate far field detection in order to which SPP mode is scattered into free space, machined 6 μm long respectively in the both sides of ridge waveguide
Grating (cycle 800nm, 31.2 μm of spacing).
In order to prove dependence of the coupling to polarization of SPP mode on ridged waveguide structure, first with λ=780nm p-polarization
The laser of (magnetic vector is perpendicular to ridge waveguide) is from common aperture of the back side illuminaton as reference sample.Can be with after back side illuminaton
Eliminate the noise that incident light is introduced.The SPP mode that the optical coupling of back surface incident goes out can be propagated along ridge waveguide, then by grating
Scattering.With long reach object lens (Mitutoyo, 100 ×, NA=0.5) collect scattered light, and be imaged on CCD.Due to general
Logical small structure is symmetrical, so the intensity of the light gone out from left side and right side grating scattering is essentially identical, such as shown in Fig. 2 (a).
The polarization of incident light is rotated by 90 ° (s is polarized, and magnetic vector is parallel to ridge waveguide), any scattered light is now can't see at grating,
SPP mode can not be coupled out by illustrating the incident light of s polarizations, shown in such as Fig. 2 (b).This phenomenon and the SPP mode reported before
The dependence coupled to polarization is also what is be consistent.However, just different for defective small structure situation.Due to structure
Symmetry is broken, as incident light λ=780nm, the incident light of p-polarization from back side illuminaton when, the grating in left side is substantially
Dark, and the grating on right side then brightens, such as shown in Fig. 2 (c).The SPP mode that this explanation is coupled out is mainly along ridge waveguide
(direction away from projection nano particle) is propagated to the right.Moreover, go out in defective small structure from right side grating scattering
Light intensity is about 1.8 times of common sample, and this explanation is in defective small structure, and the intensity of SPP mode is added.It will enter
The polarization for penetrating light is rotated by 90 ° (s polarizations), similar when phenomenon and the incident p-polarization shown in Fig. 2 (c), such as shown in Fig. 2 (d).This says
Bright, in the structure shown here, the incident light of s polarizations can also be coupled out SPP mode.Further it can be seen that the area of scattering hot spot is remote
Less than the area of scattered grating, dashed rectangle in such as Fig. 2 (a) to (d).What this two kinds of mutually perpendicular incident light of explanation was coupled out
SPP mode is all strapped on ridge waveguide, rather than propagated along metal surface well.Numerical computations are obtained when p is inclined
Shake incident light defective from the back side illuminaton small structure polarized with s when, distribution such as Fig. 2 (e) and (f) of electric field are shown.From
It can see in this two width figure, the incident light of p-polarization and s polarizations can be coupled out the SPP mode propagated along specific direction, this
With the experimental result as shown in Fig. 2 (c) and (d) meet it is fine.So, in defective small structure, SPP mode both may be used
With with p-polarization, the incident optical coupling that can also be polarized with s, and the intensity for the SPP mode being coupled out can obtain with common aperture
The intensity arrived is comparable.
Next, study in defective ridged waveguide structure, it is dry between the SPP mode that p-polarization and s polarization coupleds go out
Relate to.Consider two kinds of special circumstances.As shown in arrow in Fig. 3 (a), when intensity identical p-polarization and the s incident light compositing polarized are obtained
When having the linearly polarized light of 45 ° of angles to magnetic vector and ridge waveguide, SPP mode that the incident light of p-polarization is coupled out and s polarizations
The SPP mode coherent subtraction that incident light is coupled out.So scattered light is there is no at grating, the CCD figures as shown in Fig. 3 (a)
Picture.In Fig. 3 (b) shown in arrow, when the magnetic vector and ridge waveguide of the line polarisation of synthesis have -45 ° of angles, the incidence of p-polarization
The SPP mode coherent phase that the incident light for SPP mode and the s polarization that optical coupling goes out is coupled out is long, so the intensity of SPP mode can increase
Plus.This can significantly increase the intensity of scattered light at grating, and shown in such as Fig. 3 (b), now the intensity of scattered light is common aperture
5.2 times of scattered light intensity.Shown in field distribution such as Fig. 3 (c) and (d) that corresponding numerical computations are obtained, meet with experimental result
Very well.So, the SPP intensity being coupled out can be effectively modulated using the s polarized components of incident light.And measure and calculate
The intensity for the SPP mode that the linearly polarized light of same intensity is coupled out and the relation of polarization direction, as a result such as Fig. 3 (e) and (f) institute
Show.It can be seen that, experiment [Fig. 3 (e)] and numerical computations [Fig. 3 (f)] result meet it is fine.It was found from Fig. 3 (e) and (f),
By rotating the polarization angle of incident light, the intensity for the SPP mode being coupled out can be readily adjusted.In addition, rotatory polarization is incident
When, the unidirectional couplings of SPP mode experimentally also demonstrate that, and with numerical result meet it is fine.
During Fig. 6 is embodiment one, SPP mode excites figure when incident light is circular polarization, wherein, (a) and (b) is several respectively
Value calculate the incident light of obtained dextrorotation and Left-hand circular polarization from back side illuminaton sample when, the energy flow point above waveguide at 100nm
Cloth, image when (c) and (d) is the dextrorotation that CCD is obtained and left-handed elliptical polarization incidence respectively, (e) and (f) is corresponding numerical value
The energy flow distribution at 100nm in obtained waveguide is calculated, annular arrow represents electric vector, and dashed rectangle represents the position of scattered grating
Put.
Embodiment two
By adjusting the structural parameters of projection nano particle, the SPP mode that p-polarization and s polarization coupleds are obtained can be divided
Open and propagate in opposite direction.In the present embodiment, the width of projection nano particle is decreased to 60nm.Corresponding SEM image and
Shown in detail view such as Fig. 4 (a).Other structural parameters of defective small structure are as follows：W=260nm, L=560nm, Ld
=240nm, h=350nm, and Δ L=60nm.Electric field ccd image such as Fig. 4 (b) and (c) institute that incident light λ=780nm is obtained
Show.From ccd image it can be seen that, the SPP mode that the incident light of p-polarization is coupled out mainly is propagated to the right along ridge waveguide, accordingly
Extinction ratio be about (IR/IL)p≈ 5.1, so right side grating is illuminated, such as shown in Fig. 4 (b).And the incident optical coupling of s polarizations
The SPP mode gone out is propagated to the left mainly along along ridge waveguide, and corresponding extinction ratio is about (IL/IR)s≈ 3.3, so left side light
Grid are illuminated, such as shown in Fig. 4 (c).Herein, extinction ratio (IR/ILOr IL/IR) be defined as at two scattered grating scatterings
The intensity ratio of light.Subscript R and L are represented to the right or to the left.The SPP mode propagated to the right that the incident light of p-polarization is coupled out
Intensity be about s polarizations be coupled out twice of the SPP mode propagated to the left of incident light.What corresponding numerical computations were obtained
Shown in field distribution such as Fig. 4 (d) and (e), and experimental result meet it is fine.So, in defective small structure, two kinds are partially
The SPP mode that the mutually perpendicular incident light that shakes is coupled out can be sufficiently separated, and the information that incident light is carried is retained
.Because the SPP mode that two mutually perpendicular linearly polarized lights are coupled out is propagated in opposite direction, so any polarization state
Incident light can be coupled out the SPP mode propagated along ridge waveguide.Importantly, two mutually perpendicular linearly polarized lights are taken
The information of band can be individually modulated in chip.
Fig. 7 is the Spectral Extinction of the SPP mode in embodiment two, wherein, (a) and (b) are respectively the incident light that experiment is obtained
The delustring collection of illustrative plates of SPP mode when being polarized for p-polarization and s, (c) and (d) is respectively that to calculate obtained incident light be p-polarization and s
The Spectral Extinction of SPP mode during polarization.
Embodiment three
In the present embodiment, defective small structure is calculated with COMSOL Multiphysics to SPP on ridge waveguide
The influence of Mode Coupling.The structural parameters of calculating formula, ridge waveguide and aperture use sample shown in Fig. 1 experimentally to measure
Obtained result, parameter is respectively w=290nm, L=600nm, h=300nm, Δ L=60nm.Change projection nano particle
Structural parameters wdAnd LdShown in the intensity of obtained SPP mode such as Fig. 5 (a) to (c).It can be seen that, the incidence that p-polarization is polarized with s
Dependence of the intensity of the SPP mode of optical coupling to structural parameters is different.
There is a wedge angle in defective small structure, shown in such as Fig. 1 (a), when incident light irradiation, electric charge easily exists
These regions accumulate and form focus.To the incident light of p-polarization, three focuses are occurred in that altogether in the sharp corner of ridge waveguide, such as
Shown in Fig. 8 (a).In addition, the ridge waveguide edge on the right is also very bright.The focus at the edge of these wedge angles and ridge waveguide it is strong
Radiation field can be coupled into the SPP mode propagated along ridge waveguide, then interfere.It is right due to the influence of projection nano particle
The hot spot region of the ridge waveguide at end is much larger than the ridge waveguide of left end, shown in such as Fig. 8 (b).So, the SPP moulds propagated to the right
The intensity of formula is always greater than the SPP mode propagated to the left, and dotted line in such as Fig. 5 (a) to (c) and shown in solid illustrates coupling
SPP mode is mainly propagated to the right along ridge waveguide.The incident light polarized to s, a very strong heat is occurred in that in the wedge angle of defect
Shown in point, such as Fig. 8 (c).10 times of intensity of hot spots when now the intensity of focus is about p-polarization incidence.Moreover, the radiation of focus
Field can be coupled to ridge waveguide up.Here it is the reason for incident light of s polarizations can couple SPP mode.Because aperture
Central field it is most strong, so when the wedge angle of defect sturcture is nearer from the center of aperture, the intensity of focus is stronger.In addition, numerical value meter
Calculate result and show that the width of projection nano particle can influence the field distribution of focus, so the width and length of projection nano particle
The intensity of SPP mode can be influenceed, as shown in Fig. 5 (a) to (c) dotted line and chain-dotted line.Due to the asymmetry of structure, phase
The intensity of the SPP mode of opposite direction is different, and its intensity can be adjusted by adjusting the parameter of projection nano particle
Section.For example, when the parameter of projection nano particle is wd=100nm and LdDuring=260nm, the SPP moulds of the incident optical coupling of s polarizations
Formula is mainly propagated to the left along ridge waveguide, as shown in the dotted line erected in Fig. 5 (a).When the parameter of defect sturcture is wd=300nm and
LdDuring=360nm, the SPP mode of the incident optical coupling of s polarizations is mainly propagated to the right along ridge waveguide, the void erected in such as Fig. 5 (c)
Shown in line.These numerical results and experimental result before all meet very well.It is further to calculate discovery, p-polarization and s
The proportion for the SPP intensity that polarization coupled goes out can be adjusted by adjusting the structural parameters of defect sturcture.Wherein, IL PAnd IR PRespectively
Represent the SPP mode to the left and to the right of the incident light of p-polarization, IL SAnd IR SRespectively represent s polarization incident light to the left and to
Right SPP mode.
In order to support these analysis, SPP moulds when two defect sturctures are symmetrically disposed at aperture both sides are further study
The intensity of formula.The incident light polarized to s, two defect sturctures can introduce two focuses, as shown in Figure 9.But the two are hot
Point is inverting each other, so coupling obtained SPP mode coherent subtraction by this focus.Therefore, the incident light that now s is polarized
SPP mode can not be coupled out, as shown in Fig. 5 (d) to (f) dotted line and chain-dotted line, this is consistent with analysis above.
Figure 10 is analyzing analysis chart, wherein, (a) and (b) is that Glan-Taylor prism is p-polarization, and incident light is respectively p inclined
Shake the image of CCD when being polarized with s, and (c) and (d) is that Glan-Taylor prism is s polarizations, and incident light is respectively p-polarization and s polarizations
When CCD image.
Sum it up, by processing defective small structure on the ridge waveguide of sub-wavelength, what p-polarization and s were polarized
Incident light is coupled out the single SPP mode of ridge waveguide support in which can have direction.This overcomes free space optocoupler completely
Close dependence of the SPP mode process to polarization.In the corner region of aperture, p-polarization and s polarizations can produce focus.Due to lacking
The destruction of structural symmetry is fallen into, the radiation field of focus is coupled into SPP mode with being directed.By adjusting the parameter of defect, p
The SPP mode that is coupled out of incident light of polarization and s polarizations is identical or opposite backpropagation can be realized along waveguide.It is shown,
It is that polarization is unrelated to be coupled out along the SPP mode that ridge waveguide is propagated, and this has weight in following phasmon loop and system
Apply.
It is finally noted that, the purpose for publicizing and implementing mode is that help further understands the present invention, but ability
The technical staff in domain is appreciated that：Without departing from the spirit and scope of the invention and the appended claims, it is various replacement and
Modification is all possible.Therefore, the present invention should not be limited to embodiment disclosure of that, the scope of protection of present invention with
The scope that claims are defined is defined.
Claims (10)
1. a kind of surface phasmon directional coupler, it is characterised in that the directional coupler includes：Metallic film, aperture,
Ridge waveguide and projection nano particle；Wherein, aperture is provided with metallic film；On metallic film and positioned at aperture two ends
Positional symmetry two ridge waveguides are set, by the width w and height h that adjust ridge waveguide so that ridge waveguide is only propped up
Hold single SPP mode；Projection nano particle is set on metallic film and positioned at the side of aperture, projection nano particle is incomplete
The edge of aperture is covered, defective small structure is formed；Incident light is having from the defective small structure of back side illuminaton, electric charge
The corner region of the small structure of defect is accumulated and forms focus；For the incident light of p-polarization, wedge angle of the electric charge in ridge waveguide
Zone-accumulation simultaneously forms focus, the radiation field of focus is coupled into the SPP mode propagated along ridge waveguide, so that p-polarization enters
Penetrate the SPP mode that optocoupler synthesis along ridge shape waveguide is propagated；The incident light polarized for s, wedge angle of the electric charge in projection nano particle
Zone-accumulation simultaneously forms focus, and the radiation field of focus is coupled into the SPP mode propagated along ridge waveguide, thus s polarization enter
Penetrate optocoupler synthesis along ridge shape waveguide and propagate SPP mode, realize the surface phasmon directional coupler independent of polarization.
2. directional coupler as claimed in claim 1, it is characterised in that further, the center of projection nano particle is not small
On the center of hole side, so as to form the asymmetric defective small structure along ridge waveguide direction, aperture
The ridge waveguide of one end is away from projection nano particle, and the ridge waveguide of the aperture other end is realized not close to projection nano particle
Rely on the surface phasmon directional coupler of polarization.
3. directional coupler as claimed in claim 2, it is characterised in that for the incident light of p-polarization, in the ridge waveguide
Corner region stored charge and form focus, and the focus formed on the ridge waveguide away from projection nano particle is more than
The focus number formed on the ridge waveguide close to projection nano particle, so that the SPP mode master of the incident optical coupling of p-polarization
To be propagated along the ridge waveguide away from projection nano particle.
4. directional coupler as claimed in claim 2, it is characterised in that the incident light polarized for s, in projection nano particle
Corner region stored charge and form focus, the geometric structure diamete of projection nano particle influences the radiation field direction of focus,
So as to which the s incident lights polarized are directionally coupled into the SPP mode propagated along ridge waveguide.
5. directional coupler as claimed in claim 1, it is characterised in that the geometric structure diamete shadow of the projection nano particle
The intensity of SPP mode is rung, by the SPP for adjusting the geometric structure diamete of projection nano particle, regulation p-polarization and s polarization coupleds
The proportion of the intensity of pattern.
6. directional coupler as claimed in claim 1, it is characterised in that the geometry chi of the adjustment projection nano particle
It is very little so that p-polarization and the SPP mode of s polarized incident optical couplings are propagated along equidirectional on ridge waveguide, for incidence
Linearly polarized light, by rotating the polarization angle of incident light, adjusts the intensity for the SPP mode being coupled out.
7. a kind of control method of surface phasmon directional coupler, it is characterised in that the control method includes following step
Suddenly：
1) aperture is provided with metallic film, on metallic film and positioned at aperture two ends positional symmetry two ridges are set
Shape waveguide, by the width w and height h that adjust ridge waveguide so that ridge waveguide only supports single SPP mode, in metal foil
Projection nano particle, the edge of the endless all standing aperture of projection nano particle are set on film and positioned at the position of aperture side；
2) incident light is from the defective small structure of back side illuminaton, and electric charge is accumulated simultaneously in the corner region of defective small structure
Form focus；
3) for the incident light of p-polarization, electric charge is accumulated in the corner region of ridge waveguide and forms focus, the radiation field coupling of focus
The SPP mode propagated along ridge waveguide is synthesized, so that the incident light of p-polarization is coupled into the SPP moulds propagated along ridge waveguide
Formula；
4) incident light polarized for s, electric charge is accumulated in the corner region of projection nano particle and forms focus, the radiation of focus
Field is coupled into the SPP mode of ridge waveguide propagation, so that the incident light of s polarizations is coupled into the SPP mode propagated along ridge waveguide,
Realize the surface phasmon directional couple independent of polarization.
8. control method as claimed in claim 7, it is characterised in that the center of the projection nano particle is not in aperture side
Center on, so as to form the asymmetric defective small structure along ridge waveguide direction, aperture one end
Ridge waveguide is away from projection nano particle, and the ridge waveguide of the aperture other end is close to projection nano particle.
9. control method as claimed in claim 8, it is characterised in that by the geometry chi for adjusting projection nano particle
It is very little, the proportion of the intensity of the SPP mode of regulation p-polarization and s polarization coupleds.
10. control method as claimed in claim 8, it is characterised in that further, adjusts the geometry of projection nano particle
Size so that p-polarization and the SPP mode of s polarization coupleds are propagated along identical direction on ridge waveguide, for incident line
Polarised light, by rotating the polarization angle of incident light, adjusts the intensity for the SPP mode being coupled out.
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| Ultracompact surface plasmon polariton unidirectional generator based on asymmetric single-nanoslit;Zhi Li et al.;《Lasers and Electro-Optics(CLEO), 2011 Conference》;20110506;1-2 * |
| 基于电光聚合物的表面等离激元调制器;陈建军等;《物理学报》;20080930;第57卷(第9期);5893-5898 * |
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