WO2015158882A2 - Resonant-cavity wavelength-selective transmission filter - Google Patents

Resonant-cavity wavelength-selective transmission filter

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Publication number
WO2015158882A2
WO2015158882A2 PCT/EP2015/058362 EP2015058362W WO2015158882A2 WO 2015158882 A2 WO2015158882 A2 WO 2015158882A2 EP 2015058362 W EP2015058362 W EP 2015058362W WO 2015158882 A2 WO2015158882 A2 WO 2015158882A2
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Prior art keywords
filter
side
wavelength
cg
vertical
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PCT/EP2015/058362
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French (fr)
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WO2015158882A3 (en )
Inventor
Olivier Gauthier-Lafaye
Antoine MONMAYRANT
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Centre National De La Recherche Scientifique
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    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/20Filters
    • G02B5/28Interference filters
    • G02B5/284Interference filters of etalon type comprising a resonant cavity other than a thin solid film, e.g. gas, air, solid plates
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS, OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/18Diffraction gratings
    • G02B5/1866Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
    • G02B5/1871Transmissive phase gratings

Abstract

The invention relates to a wavelength-selective resonant-cavity transmission filter (10) comprising: a planar central portion (PC) extending in a horizontal plane XY, comprising: a coupling grating (CG) having a first periodic variation in dielectric permittivity; first and second lateral phase zones (ZL1, ZL2) devoid of periodic permittivity, and placed on either side of the coupling grating (CG) and adjacent to the latter; first and second vertical phase zones (ZV1, ZV2) devoid of periodic permittivity and placed on either side of the coupling grating (CG); first and second lateral high-reflectivity structures (HRL1, HRL2) placed on either side of the central portion (PC), adjacent to the first and second lateral phase zones, respectively, in order to laterally confine the localized mode (Ol); and first and second vertical high-reflectivity structures (HRV1, HRV2) placed on either side of the central portion (PC), for vertically confining the localized mode (Ol) and for reflecting an incident wave (Oinc) having wavelengths belonging to a spectral reflection band (Δλ) comprising the resonant wavelength, said filter forming a resonant cavity for the localized mode (Ol).

Description

Selective transmission filter long wavelength

Resonant cavity

FIELD OF INVENTION

The present invention relates to the field of selective networks in wavelength, and more particularly in transmission networks using a resonance effect to the selectively transmitted wavelength.

The present invention is applicable to wavelengths of the visible optical region, infrared and microwave, typically between 400 nm and 500 μηι.

STATE OF THE ART selective optical filter wavelength typically used in the industry fall into three main categories:

optical filters of colored glass. These filters are characterized by very good optical rejection (absorption of unwanted wavelengths of the order of 10 "4-10" 8). These filters are not spectrally narrow hand.

interferential optical filters. These filters consist of a stack of several thin layers. They can be spectrally narrow, and their filtering performance can be optimized based on need. For a complex filter function, a very large number of layers is required, typically from 100 to 1500 thin layers.

Optical filters "dispersive" network filters or type prism. This type of filtering is to be integrated in complex optical system to function. Apart from these three great industrial families, many research works have focused in recent years on the filters resonant referred GMRF networks "Guided Mode Resonant Filter" in English terminology, as described in US 5,598,300. these components may function in reflection or in transmission, and consist of a core network acting as resonant guide, included in a multilayer dielectric structure, each layer having a thickness of λ / 2 or λ / 4. In transmission, an optimal function is obtained when the network is in a structure of plane of symmetry. These filters achieve an ultrathin spectral filtering typically λ / Δλ equal to a few hundred to several thousand for a transmission filter. A drawback of these filters is a small angular tolerance, which means a dependence of the filtered wavelength depending on the angle of incidence.

More recently, a resonant cavity filter, named CRIGF for "Cavity-Resonator-Integrated Guided-mode-Resonance Filter" according to English terminology operating in reflection was described in the patent application JP2012098513, the publication of K. Kintaka T. Majima, J. Inoue, K. Hatanaka, J. Nishii, and S. Ura, "Cavity-resonator-integrated guided mode resonant filter for aperture miniaturization," opt. Express 20, 1444-1449 (2012), and is shown schematically in Figure 1.

This filter comprises a waveguide 2 deposited on a substrate 8, a core network coupling 1 is arranged on the guide and two side DBR networks, realizing a type of Bragg reflection function distributed (DBR in English terminology for Distributed Bragg Reflector). Two phase regions 3 are disposed between the core network and the side networks. An incident wave 4 of the filter is divided into a reflected portion 5 and a transmitted portion 6. The switching network allows to couple the incident wave 4 to 7 a guided mode which propagates in the guide 2 and is reflected on the mirrors DBR. The phase regions are dimensioned so as to bring the phase of the guided modes propagating and contrapropagatif to obtain a single peak spectral resonance in reflection. For such phase zone two situations arise according to the wavelength of the incident wave. Off-resonance, the wave does not couple to the propagating guided modes and contrapropagatif and is substantially transmitted. At resonance, the wave couples to the guided modes which are then retransmitted in reflection.

The core network is arranged outside the guide to ensure a non-zero overlap but weak and perturbative between the guided modes propagating and contrapropagatif and the core network, which ensures a narrow resonance peak in reflectivity.

These selective reflective wavelength filters can be used as mirrors in a VCSEL type laser device for Vertical Cavity Surface Emitting Laser in English terminology or in a diode laser device in an extended cavity (or ECDL Extended Cavity Diode Laser in English terminology).

These filters work in reflection at normal incidence and therefore can not be integrated directly into the optics of detection system. Their use requires separate incident beam back beam by an optical device, typically a beamsplitter cube. The aim of the invention is to remedy the aforementioned drawbacks, and more particularly to realize a selective filter cavity wavelength résonantefonctionnant transmission. DISCLOSURE OF INVENTION

The present invention relates to a filter transmission to selective resonant cavity wavelength comprising:

-a planar central portion in a horizontal XY plane comprising:

-a coupling network having a first periodic variation in dielectric permittivity,

-a first and a second lateral zones phase devoid of periodic permittivity, and disposed on either side of the coupling network and adjacent thereto,

-a first and a second vertical phase areas devoid of periodic permittivity, and disposed on either side of the coupling network and adjacent thereto along an axis Z perpendicular to the XY plane, - the coupling network and phase regions being configured to provide a coupling of an incident wave resonant wavelength propagating in the filter with a localized mode of same wavelength,

-a first and a second lateral high reflectivity structures disposed on either side of the central portion, adjacent to the first and second side phase regions, to laterally confine the localized mode,

-a first and a second vertical high reflectivity structures disposed on either side of the central portion, adjacent to the first and second vertical phase regions to confine vertically localized mode and for reflecting an incident wave having lengths d wave belonging to a spectral reflection band including the resonance wavelength,

said filter forming a resonating cavity for the localized mode, capable of radiating a wave resonance wavelength that interferes with the incident and reflected waves constructively in a propagating direction and destructively in a contrapropagatif direction, so that the transmitted wave at the resonant wavelength is maximized.

Advantageously, the localized mode is a standing wave having the extrema and electric field of zeros, two successive extrema having an opposite sign, and wherein the coupling network is arranged such that the dielectric permittivity maxima coincide with extrema of same sign of electric field.

Advantageously, an optical thickness of the central portion in the vertical direction corresponds to a whole odd multiple of the quarter of the resonance wavelength.

According to one embodiment, the filter according to the invention comprises a third and a fourth side regions phase and third and fourth high-reflectivity side structures, and a switching network having a two-dimensional periodic variation in dielectric permittivity, the filter forming a three-dimensional resonant cavity. Advantageously, the filter of the invention has a plane of symmetry. Advantageously, at least one high reflectivity vertical structure comprises a stack of dielectric layers with an optical thickness substantially equal to a quarter of the resonance wavelength. According to one embodiment at least one high reflectivity vertical structure comprises a periodic structure having a period shorter than the resonance wavelength.

Alternatively, at least one high side reflectivity structure comprises a network side having a second periodic variation in dielectric permittivity substantially equal to the half of the first periodic variation in dielectric permittivity.

According to one embodiment, at least a high-reflectivity side structure comprises a polished face having a high reflectivity treatment. According to one embodiment, the coupling network comprises an alternation of a strong material and index of a medium in gas or liquid phase, the medium being able to flow into the filter.

According to one embodiment, the filter according to the invention comprises a plurality of core portions and side high reflectivity structures associated, arranged on a same substrate, each center portion having a resonant wavelength selected.

Alternatively, the coupling network has a continuous variation of the periodicity of the dielectric permittivity according to X or Y dimension According to another aspect, the invention provides a photodetector comprising a plurality of elementary detectors and comprising a plurality of filters according to the invention positioned upstream of the elementary detectors, a filter being associated with an elementary detector and having a resonant wavelength selected in a detection band of the associated elementary detector.

Other features, objects and advantages of the present invention appear on reading the detailed description which follows and from the accompanying drawings given as non-limiting examples and in which:

FIG 1 shows schematically a resonant cavity filter in reflection according to the prior art.

FIG 2 shows schematically a filter according to the invention. 3 illustrates the position of the extrema of the electric field localized mode in the resonant cavity for an optimized filter.

4 illustrates the position of the extrema of the electric field localized mode in the cavity resonator for a filter not working.

5 illustrates a first variant of a filter according to the invention with a one-dimensional variation of the dielectric permittivity of the coupling network.

6 illustrates a second variant of a filter according to the invention with a two-dimensional variation of the dielectric permittivity of the coupling network.

7 illustrates a variant in which the studs of the coupling network have a rectangular shape.

8 illustrates an embodiment wherein the vertical HR structures include a stack of dielectric layers.

9 illustrates another variant in which the vertical HR structures comprise a periodic sub wavelength structure.

FIG 10 shows schematically an alternative filter according to the invention having a plane of symmetry.

-The Figure 1 1 illustrates an exemplary filter according to the invention having side structures comprising side networks.

FIG 12 illustrates the distribution of the envelope of the electric field the localized mode.

FIG 13 illustrates the spectral performance of a filter according to the invention. DETAILED DESCRIPTION OF THE INVENTION

A filter 10 according to the invention is shown diagrammatically in Figure 2. This filter has a transmission maximum at a resonant wavelength λθ and a high reflection for a spectral band Δλ around λθ. The filter according to the invention works for wavelengths included in the optical band visible, infrared and microwave, typically for wavelengths between 400 nm and 500 μηι.

In describing operation of the filter 10 is considered a wave incident on the filter Oinc, which propagates in the filter 1 0. The filter generates from the Oinc wave interference by superimposition, a reflected wave and a transmitted wave Or Ot which propagate in the filter and then come out.

The filter 10 includes a central portion PC planar geometry according to an XY plane. Figure 2 is a sectional plan as for example a plane YZ. The PC core comprises a CG coupling network having a first periodic variation in dielectric permittivity Δε (χ). The central portion PC also includes a first side region of ZL1 phase and a second side region of ZL2 phase. These areas are devoid of periodic permittivity, arranged on either side of the CG coupling network and adjacent thereto. The central portion further comprises a first vertical zone ZV1 phase and a second vertical zone ZV2 phase also devoid of periodic permittivity, arranged on either side of the CG and adjacent coupling network thereto along an axis Z perpendicular to the XY plane.

CG coupling network and the phases areas ZL1, ZL2, ZV1, ZV2 are configured to provide coupling of a Oinc incident wave resonance wavelength λθ propagating in the filter with a localized mode Oi of the same length λθ wave. The way to get optimum coupling is detailed further.

Folder 1 0 also includes a first upper sideband reflectivity nature HRL1 interference structure adjacent the first side ZL1 phase zone, and a second lateral high-reflectivity structure HRL2 such interference adjacent the second lateral ZL2 phase zone. The HRL1 HRL2 structures and are arranged on either side of the central portion PC, and have the function of laterally confining the localized mode Oi (role side mirror).

Folder 1 0 also includes a first vertical high-reflectivity structure HRV1 adjacent the first vertical phase zone ZV1, and a second vertical high-reflectivity structure HRV2 adjacent to the second vertical ZV2 phase zone. The HRV2 HRV1 structures and are arranged on either side of the central portion PC in a vertical plane, and serve to confine vertically localized mode 0 |.

Thus the core network CG and ZL1 phase regions, ZL2, ZV1, ZV2 allow to couple, that is to say to excite a localized mode Oi in the central portion PC from the incident wave Oinc. This localized mode is confined laterally and vertically by the high reflectivity structures HRL1, HRL2, HRV1, HRV2. It is in the presence of a "dual chamber", a horizontal cavity defined by the structures and HRL1 HRL2, and a vertical cavity defined by the structures and HRV1 HRV2.

Three conditions are necessary to obtain a resonant coupling.

A first condition is that the vertical high reflectivity structures HRV1 HRV2 and are configured to reflect an incident wave Oinc over a spectral reflection band Δλ comprising the resonance wavelength λθ.

And off-resonance, i.e. for an incident wave Oinc (A) λ wavelength in the band Δλ λθ but different from, the filter is equivalent to a conventional high reflectivity interference structure. Preferably the resonant wavelength λθ is located in the center of the band Δλ, localized mode vertically by the vertical cavity then being perfectly antiresonant relative the horizontal cavity.

According to a second condition, resonance, i.e. for an incident wave Oinc (AO) of λθ wavelength Oi localized mode is excited in the central PC partite and laterally and vertically confined by the high reflectivity structures . The localized mode takes the form of a standing wave in all directions of the space located in the central part.

The resonant wavelength λθ is function of the pitch Λ of the CG coupling network. Indeed, typically the vectors associated with the switching network, to the incident wave Oinc and Oi localized mode check law networks which results in an approximate formula that: 2π / Λ "2π n eff / A0

n eff being the effective index associated with localized mode which is calculated from the indices layers, their thicknesses and the form of the network and corresponds to an equivalent index.

Preferably, the core network CG is a network of second order for the localized mode of Oi λθ wavelength. It allows to ensure resonant coupling between the incident wave and the localized mode Oinc 0 |. According to a third condition, the horizontal resonant cavity is along the axis of the waveguide, which leads to the condition:

Leff x 2TT / n eff = n. π integer n

The effective length Leff is the geometric length of the horizontal cavity including side phase zone to which is added the penetration depth of the localized wave in the reflecting structures and HRL1 HRL2.

All of these conditions provides the necessary resonant coupling with the invention, comprising a verticlale antiresonant cavity with respect to a horizontal resonant cavity.

The phase zone ZL1, ZL2, ZV1 ZV2 and are adjusted so that the coupling coefficient K between the incident wave and the localized mode is non-zero and maximized.

K is defined as:

K

Figure imgf000011_0001
E moc dV i e (1)

Where Eincident is the incident field of the incident wave Oinc, E m0 d e is the field of localized mode and Oi e Δ varying dielectric permittivity. Note that this coefficient K is here intrinsically low value given the exponential attenuation of the incident wave formed by the vertical structure HRV1 HRV2.

We will now describe the manner in which the high reflectivity structures and phase regions forming the cavity on the one hand, and the second switching network are arranged to ensure an optimum coupling of the incident wave length Oinc of λθ wave with localized mode Oi in the central portion PC. Firstly it is appropriate that the vertical optical path or the optical PC of the central portion thickness (including the central portion and the areas of vertical phases ZV1, ZV2) corresponds to an integral odd multiple of the quarter wavelength resonance (A0 / 4) to ensure that the vertical stack behaves as a high reflectivity reflector for all wavelengths outside the resonance Δλ reflectivity band. Thus, if one disregards the CG coupling network and the localized mode in the central part, the overall stack behaves as a HR mirror over the entire band Δλ.

This condition also has the consequence that the overlap between the incident wave and the Oinc variation of Ae dielectric permittivity is low, the vertical structure HR ensuring an exponential attenuation of the incident wave during its penetration into the structure, which ensures the a spectral filter fineness of the resonance peak.

If the vertical optical path is chosen so that it corresponds to an even number of times λΟ / 4, the filter does not work, it loses its single mode character and finesse. Indeed a range of wavelengths in the vicinity of λθ is transmitted through the whole stack by Fabry-Pérot effect. The existence of these modes disrupts the functioning of the filter, in particular, this can make the highly multimode.

Concerning the lateral optimization, Figure 3 illustrates two cases of optimum arrangement, a first illustrated case 3a and a second case illustrated in Figure 3b.

The localized mode is a standing wave in all directions having Mv extrema (or antinodes) and zeros (or nodes) of the electric field E fixed, i.e. non-mobile in space.

At time t arbitrary given two extrema (or belly) have successive opposite sign, and we denote by Mv "corresponding bellies with negative periods and Mv + bellies corresponding to Positive.

If one disregards the CG network, the lateral position of the extremum and zero of the standing wave in the cavity is determined by the lateral optical thickness DL of the resonant cavity between the side structures HR CG network exhibits a change Periodical dielectric permittivity e. In the central part PC, so there are 30 zones where the dielectric permittivity e is maximum, corresponding to maximum index.

To obtain maximum coupling, it is necessary to arrange the CG coupling network so that the maxima 30 of dielectric permittivity coincide with the electric field of extrema of the same sign as shown in Figure 3a for extrema Mv + and 3b for Mv extrema ". this maximizes the overlap integral between Oi standing wave (e m0 d e) and CG coupling network (Δ e), thus maximizing the coupling coefficient K defined by the equation ( 1) (the product in

Δ G. E ^ Ocle) -

On the contrary in document JP201 3 209 851, the value of the coupling coefficient K is controlled and limited to a small value by moving the guided mode coupling grating or decreasing in the integral of the relation between E 1 recovery m0 Δ e d and e.

4 illustrates the case wherein the regions 30 of maximum index of the CG network are positioned on the nodes of stationary field mode. In this case the integral overlap between Emode and Ae is zero and therefore the coupling is zero the localized mode is never excited in the cavity regardless of the wavelength of the incident wave. The structure behaves as if the central portion did not bear any stationary mode and has no peak resonant transmission. A wave resonance wavelength λθ is radiated by the cavity in the form of losses. This radiated wave interferes with the incident wave Oinc, the transmitted wave and the reflected wave Ot Or by high reflectivity vertical structures. The coupling achieved by the network and the phase regions is configured so that interference between the radiated wave and the impact wave are constructive (wave propagating in the direction) and that the interference between the wave and the wave radiated reflected are destructive (contrapropagatif wave in a direction). The wave transmitted Ot Following these constructive interference is thus maximized at the resonant wavelength λθ, while other wavelengths of the spectral band Δλ are reflected by the highly reflective structures (HR) and vertical HRV1 HRV2. And the coupling is at the origin of the excitation of the stationary mode by the incident wave and is also responsible for the "losses" that ensure consistent reissue this stationary mode. Due to the combination of resonance phenomena and interference filter of the invention has a high spectral finesse, and a large angle of deflection greater than the interference filters and filters resonant cavity by reflection.

In addition, the value of the resonance wavelength and the fineness thereof are independent of the angle of incidence on the filter of the wavelength to be filtered. Transmission is maximum at normal incidence.

Large combined angular tolerance transmissive operation makes use of the filter compatible with a focused beam, and therefore with the insertion of the filter according to the invention in the focal plane of an optical imaging or detection system, or directly before a detection system. The filter is also feasible on small surfaces and has a planar geometry, allowing the arrangement of a plurality of filters with different resonance wavelengths 2D matrix.

Moreover the filter comprises few layers (see examples below) compared to the interference filters of the same spectral finesse, which allows a simpler manufacture and a more reliable and robust filter.

According to a first variant illustrated in Figure 5, the change in permittivity Δε (χ) of the CG coupling network is one-dimensional, such as X. The resonant cavity realizes here a two-dimensional confinement (in directions x and z).

In a second variant illustrated in Figure 6, the variation of the dielectric permittivity CG coupling network is two-dimensional A {x, y), the network having for example a studded structure 40, typically hexagonal or square. An advantage of two-dimensional structures is their insensitivity to polarization of the incident wave. Alternatively, the permittivity variation may of course be three-dimensional with A {x, y, z).

Also Figure 6 is illustrated a third embodiment in which the filter further comprises:

-a third lateral area of ​​ZL3 phase and a third high side reflectivity structure associated HRL3

-a fourth side region of ZL4 phase and a fourth high-reflectivity side HRL4 associated structure. The filter here forms a cavity providing a three-dimensional confinement. The coupling network CG then has two directions of periodicity for driving the same mode guided independently of the polarization of the incident wave, as these two periodicity directions. High lateral reflectivity structures used to horizontally confine the cavity mode in these two directions, the vertical confinement being provided by the HRV1 areas and HRV2.

This geometry is particularly suitable for an arrangement of a plurality of filters in a matrix structure, sharing the same vertical and lateral HR structures, and the same substrate.

Thus, in one embodiment, the filter according to the invention comprises a plurality of core portions and side high reflectivity structures associated, arranged on a same substrate, each center portion having a resonant wavelength selected by varying for each filter the pitch of the coupling network. Different selected resonance wavelengths are of course included in the spectral band of reflectivity of the vertical HR structure Δλ. The change is not such discreet.

According to another embodiment, the filter is made tunable in wavelength by performing a network not continuously variable, that is to say that the coupling network has a continuous variation of the periodicity of the dielectric permittivity depending on a dimension, X or Y, such as a network fan-shaped for one-dimensional structure. Change filter wavelength / resonance is obtained by translation of the filter relative to the incident wave.

According to a variant illustrated in Figure 7 the pads 50 have a rectangular shape. This structure allows the cavity to resonate in two lengths resonance waves MO, λ20. The two periodicity directions are used to excite each mode depending on its direction, the two modes are at different wavelengths. Each cavity direction is then independently adjusted to resonate at a specific wavelength.

According to one embodiment illustrated in Figure 8, at least one vertical HR structure, the two (HRV1 and HRV2) in Figure 8, comprises a stack of dielectric layers with an optical thickness substantially equal to a quarter of the wavelength resonance or A0 / 4. The stack consists of alternating layers of different index n a, n b .... This alternation is a high-reflectivity structure for all incident wave wavelength in the range Δλ around λθ and incident at an angle of incidence close to normal.

Areas of vertical phases ZV1, ZV2 are, for example layers of a thickness optimized consist of neighbor index n b material. The central portion outside the phase regions comprises a sorting structure Ec layer. CG coupling grating formed on a substrate having an index n and C c is arranged between two layers C1 and C2 having the same index

For the localized mode is confined in the central part, the central part must achieve a waveguide when it is inserted inside the stack. A solution for this is that C n c n and PC are higher than all the clues present in the stack. Another solution is that PC or n G n c is greater than the lowest index present in the stack and that the thickness of this high index layer is greater than the thicknesses of other layers present in the stack.

According to an embodiment also shown in Figure 8, at least one side HR structure (both HRL1 and HRL2 structures in Figure 8), comprises a lateral array having a second periodic variation in dielectric permittivity substantially equal to the half of the first variation Periodical dielectric permittivity, that is to say the pitch of the network side is substantially equal to Λ / 2. Indeed preferably, the network side is a first order network for localized mode to the λθ wavelength. The realization of the lateral HR structures in the form of identical networks not near to the core network this coupling the advantage of providing the central portion and the side HR structures in a single planar manufacturing step.

The side phase areas are areas of constant index, for example equal to the index n PC or n C G, the thickness of these zones in the direction of the change in permittivity of the core network is determined to optimize the coupling , as explained above. According to another embodiment, at least a high-reflectivity side structure comprises a polished face having a high reflectivity treatment.

Figure 9 illustrates another variant of the filter according to the invention, wherein at least one high reflectivity vertical structure (both HRV1 structures, HRV2 in Figure 9) comprises a periodic structure having a period δ less than the length of λθ wave resonance. These components referred to as sub-wavelength gratings are known, the wave incident on these structures is broken down into Bloch modes destructively interfere depending on the incidence direction of propagation and thus achieving a high-reflectivity structure on a large spectral range and with a wide angular tolerance.

Figure 10 diagrammatically shows a preferred embodiment of filter according to the invention having a plane of symmetry Ps.

A filter having this symmetry can be made from two identical parts each formed on a substrate which are then connected, for example by cons-bonding of substrates. The two half structures may thus be manufactured simultaneously on a single substrate which is subsequently divided into two, the two half structures are subsequently pasted against face to face. This ensures a perfect symmetry, in particular a perfect match HRV1 HRV2 and multilayer, of the phase regions, both in thickness and composition as well as positioning of the coupling network in the center of the vertical stack.

Table I below illustrates an example of stacking for a filter according to the invention resonance wavelength λθ 6 = 81 nm based on a glass stack (index 1 .47) / Nitride (index 2.04) as schematically Figure 10.

Material Thickness (nm) Name Function

Glass - substrate

Nitride 104 ¼ waveplate stack 144 HRV1 Silica blade ¼ wave

Nitride 104 Blade ¼ wave

Blade 144 silica ¼ wave

Nitride 120 ZV1 PC core comprising the coupling network and thickness

Silica 100 total optical network layer wave ¾ to achieve

Nitride 120 HR ZV2 a stack.

Silica 144 ¼ waveplate stack HRV2

Nitride 104 Blade ¼ wave

Blade 144 silica ¼ wave

Nitride 104 Blade ¼ wave

infinite glass substrate

Table I

The vertical phase regions ZV1 ZV2 and consist of a thick nitride layer 120 nm.

Ec central layer is a silica layer formed in at least one direction X and / or Y of a silica alternation (index 1 .54) and air (index 1) of identical thickness (filling rate of 50%) so as to form the core network and the network side, as illustrated in Figure 1 1 a (sectional view) and Figure 1 1b (top view in the XY plane of the networks). The period Λ of the network is equal to 485 nm.

It has:

2 x 120 nm x 100 nm x 2.04 + 1 .22 = 612 nm = 3 x 1/4 x 81 6 nm

With 1 .22 average index of the network layer silica / air.

ZL1 and ZL2 phase areas separate the core network side network and are made of the same material as a material constituting the network by the silica. Their thickness is equal to 0.13.Λ (Λ period CG network) is 63.05 nm. The optical thickness of these zones, optimized to obtain a wedging of the same sign of field maxima on areas of high permittivity of the CG network as explained above, is a function of the optical network layer thickness and phase areas vertical. Figure 12 illustrates the envelope of the electric field 90 of the wave coupled into the vertical stack according to Z of the filter, corresponding to Oi localized mode wavelength λθ 6 = 81 nm. The curve 91 shows the distribution value of the vertical stack of the filter according Z. The field is located in the central portion PC.

13 illustrates the spectral performance of the filter of Table I, the transmitted intensity Τ (λ) of the transmitted wave Ot in Figure 13a and the reflected intensity R (A) of the wave reflected Or in Figure 13b , when illuminated by a focused incident wave on the filter with an incidence of 1 +/- .55 ​​° cone. It is noted that the filter has a very high spectral selectivity in transmission, despite a non-incident plane wave, with a spectral width of resonance:

δλ / λθ = 0.04% (0.33 to 81 nm 6 nm).

The very low value of δλ is due to the resonant effect of the cavity. The optical coupling therewith adds to the reflectivity of a resonant Fano whose spectral width varies proportionally with the coupling factor. The realization of a transmissive filter of the same spectral width is not possible according to a type of drawing CRIGF "Cavity-Resonator-Integrated Guided-mode- resonance Filter". The embodiment Drawing Type GMRF "Guided Resonant Filter Mode" is possible but said filter would have an angular tolerance to well below 0.5 °. Finally, obtaining the same spectral finesse GMRF according to a type of drawing request the production of a stack of a larger number of layers, the fineness of the resonance of the invention is increased by the three-dimensional waveguiding mode located. Broadband Δλ around λθ greater than +/- 15 nm is reflected by the HR vertical structure, the central portion PC is configured to be an integral part of the vertical structure HR off-resonance.

The resonant wavelength of the filter λο component is tunable by changing the period of the considered systems, for a given vertical HR structure. For example, the wavelength tunability is obtained by a modification of the central portion: mechanical change in the size of the phase zone ZL1, ZL2, ZV1, ZV2 for example, or changing the period of the networks, for example by contraction / expansion, typically thermal, networks, or modification of the effective index of the localized mode (electro-optical effect on the index of the network layer for example).

The resonant wavelength and the spectral width λο δλ resonance are insensitive to angle of incidence of the incident wave 0 |. The spectral width of the resonance filter δλ is adjustable by changing the coupling K between the network, the incident wave and the localized mode, that is to say for example by changing the index contrast between the two materials constituting the teeth and the recesses of the coupling network, or the network of the filling factor (that is to say the ratio of the lengths of teeth and hollow), or the positioning of the CG network with respect to the localized extrema mode. When the angle of incidence is not normal to the filter, only the maximum transmission is impacted: Tmax = T (A0) decreases and thus Rmin = R (A0) increases.

According to another variant, the CG coupling grating and side networks where appropriate comprises an alternation of high-index material and a medium in gas or liquid phase (typically including index between 1 and 1 .7), the medium liquid or gas being able to circulate in the filter. The flow of liquid or gas makes it possible to make the variable index (by modifying the type or composition of the liquid / gas flowing, for example). The variation of the index of the liquid / gas then allows tunability of the filter resonance wavelength. This type of filter is to be applied as tunable filter, or to probe the optical index of the liquid / gas and thus its composition. Finally, the absorption of the liquid / gas to the resonance wavelength may alter consistently the optical response of the component. The filter component according to the invention can be used in this case as a measure of the absorption medium.

According to another aspect, the invention relates to a photodetector including a plurality of elementary detectors and comprising a plurality of filters according to the invention positioned upstream of the elementary detectors, a filter being associated with an elementary detector and having a wavelength resonance selected from a detection band of the associated elementary detector. Photodetector according to the invention finds application in spectroscopy systems or hyperspectral imaging.

Claims

1. Filter (1 0) transmission to selective resonant cavity wavelength comprising:
-a central portion (PC) planar along a horizontal XY plane comprising:
-a coupling grating (CG) having a first periodic variation in dielectric permittivity,
-a first and a second lateral zones phase (ZL1, ZL2) devoid of periodic permittivity, and disposed on either side of the coupling grating (CG) and adjacent thereto,
-a first and a second vertical phase zones (ZV1, ZV2) devoid of periodic permittivity, and disposed on either side of the coupling grating (CG) and adjacent thereto along an axis Z perpendicular to the XY plane ,
- the coupling network (CG) and the phase zones (ZL1, ZL2, ZV1, ZV2) being configured to provide a coupling of an incident wave (Oinc) resonance wavelength (λθ) propagating in the filter with a localized mode (Oi) of the same wavelength (λθ)
-a first and a second lateral high-reflectivity structure (HRL1, HRL2) arranged on either side of the central part (PC), respectively adjacent to first and second side phase regions, to laterally confine the localized mode (Oi )
-a first and a second high reflectivity vertical structures (HRV1, HRV2) arranged on either side of the central part (PC), respectively adjacent to the first and second vertical phase regions to confine vertically localized mode (Oi ) and for reflecting an incident wave (Oinc) having wavelengths belonging to a spectral reflection band (Δλ) comprising the resonance wavelength,
said filter forming a resonating cavity for the localized mode (Oi), capable of radiating a wave resonance wavelength (λθ) that interferes with the incident and reflected waves constructively in a propagating direction and destructively in a contrapropagatif direction, so that the transmitted wave (Ot) at the resonant wavelength (λθ) is maximized.
2. The filter of claim 1 wherein the localized mode (Oi) corresponds to a standing wave having the extrema (Mv) and the electric field of zeros, two successive extrema having an opposite sign, and wherein the coupling network (CG ) is arranged so that the maxima (30) of dielectric permittivity coincide with the same sign extrema (Mv ", Mv +) electric field.
3. Filter according to one of the preceding claims wherein an optical thickness of the central portion (PC) in the vertical direction (Z) corresponds to a whole odd multiple of the quarter of the resonance wavelength (λθ).
4. Filter according to one of the preceding claims further comprising a third and a fourth (ZL3, ZL4) lateral zones phase and a third and a fourth (HRL3, HRL4) side high-reflectivity structure, and a coupling network ( CG) having a two-dimensional periodic variation of dielectric permittivity, said filter forming a three-dimensional resonant cavity.
5. Filter according to one of the preceding claims having a plane of symmetry (Ps).
6. Filter according to one of the preceding claims wherein at least one high reflectivity vertical structure (HRV1, HRV2) comprises a stack of dielectric layers with an optical thickness substantially equal to a quarter of the resonance wavelength.
7. Filter according to one of the preceding claims wherein at least one high reflectivity vertical structure (HRV1, HRV2) comprises a periodic structure having a period shorter than the resonance wavelength (λθ).
8. Filter according to one of the preceding claims wherein at least one high-reflectivity side structure comprises a network side having a second periodic variation in dielectric permittivity substantially equal to the half of the first periodic variation in dielectric permittivity.
9. Filter according to one of the preceding claims wherein at least one high-reflectivity side structure comprises a polished face having a high reflectivity treatment.
10. Filter according to one of the preceding claims wherein the coupling network comprises an alternation of a strong material and index of a medium in gas or liquid phase, said medium being adapted to flow through the filter.
January 1. Filter according to one of the preceding claims comprising a plurality of central portions and side high reflectivity structures associated, arranged on a same substrate, each center portion having a resonant wavelength selected.
12. Filter according to one of the preceding claims wherein the coupling network has a continuous variation of the periodicity of the dielectric permittivity in one dimension X or Y.
13. Photodetector comprising a plurality of elementary detectors and comprising a plurality of filters according to the invention positioned upstream of the elementary detectors, a filter being associated with an elementary detector and having a resonant wavelength selected in a detection band associated elementary detector.
PCT/EP2015/058362 2014-04-17 2015-04-17 Resonant-cavity wavelength-selective transmission filter WO2015158882A3 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5598300A (en) 1995-06-05 1997-01-28 Board Of Regents, The University Of Texas System Efficient bandpass reflection and transmission filters with low sidebands based on guided-mode resonance effects
JP2012098513A (en) 2010-11-02 2012-05-24 Kyoto Institute Of Technology Wavelength selection filter, and filter device and laser device provided with the same

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5598300A (en) 1995-06-05 1997-01-28 Board Of Regents, The University Of Texas System Efficient bandpass reflection and transmission filters with low sidebands based on guided-mode resonance effects
JP2012098513A (en) 2010-11-02 2012-05-24 Kyoto Institute Of Technology Wavelength selection filter, and filter device and laser device provided with the same

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
K. KINTAKA; T. MAJIMA; J. INOUE; K. HATANAKA; J. NISHII; S. URA: "Cavity-resonator-integrated guided-mode resonance filter for aperture miniaturization", OPT. EXPRESS, vol. 20, 2012, pages 1444 - 1449, XP032712921, DOI: doi:10.1109/IPCon.2014.6995466

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