FR2816062A1 - Fibre optic telecommunications optical filter manufacture, having thin substrate deposited layer with inserted shaped sections forming pass band filter near normal incidence - Google Patents

Abstract

The optical component structure has a thin deposited layer (14) on a substrate (13). There is a structure or resonant network with a number of shaped sections (15,16) in the thin layer. The shaped sections form a pass band filter for a thin layer incidence near to the normal angle.

Description

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Optical filter, its method of manufacture by ion doping and its use for a multiplex system
The present invention relates to an optical filter, to its method of manufacture by ion doping and to its use for an optical multiplex system with wavelength division.

 The technical field of the invention is that of the manufacture of telecommunications systems by optical fibers.

In order to increase the transport capacity of cable fiber-optic networks, it is known to multiplex several channels to make them transit simultaneously in a fiber, then to demultiplex them; when the multiplexing is carried out by division of the transmission band (in wavelength) of the fiber, one generally speaks about system WDM v) for Wavetength Division Multiplex; in order to increase the number of channels capable of being multiplexed in order to increase the capacity of a fiber while remaining within a determined wavelength range, it is necessary to have a multiplexer (and a demultiplexer) capable of processing (mix or separate) several beams whose wavelengths are very close; there is therefore a need for optical filtration components having a very narrow bandwidth (of the order of 10-9 meters) and a very high rejection rate.

surface adapté à la longueur d'onde de la diode ; dans le cas d'un démultiplexeur, les diodes laser et leurs réseaux de diffraction associés sont remplacés par des photodiodes ; le réseau diffractant courbe est réalisé par lithographie à faisceau d'électrons, sous la forme d'un chenal étroit s'étendant en dent de scie le long d'un contour courbe ; les US Patent 5,355,237 has proposed a multiplexer device comprising several input waveguides, a diffracting grating extending along a concave curve, and an output waveguide, one of which face is coupled to an optical fiber; the device comprises laser diodes, which extend orthogonally to the axis of the fiber, and to each of which is associated a diffraction grating of

surface adapted to the wavelength of the diode; in the case of a demultiplexer, the laser diodes and their associated diffraction gratings are replaced by photodiodes; the curved diffracting grating is produced by electron beam lithography, in the form of a narrow channel extending in a sawtooth fashion along a curved contour; the

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 disadvantages of this type of device are their high cost, their poor efficiency and their high sensitivity to temperature and to the polarization of the incident beam.

 US Patent 5,216,680 discloses a mathematical method for analyzing resonance phenomena in a waveguide and suggests applying the results thereof to the design of a resonant optical filter for laser, without however describing the filter; US Patent 6,035,089 explains that this method can be used to design a filter made up of bands hollowed out in a waveguide supported by a substrate, then filled with a material capable of obtaining a resonant structure, in particular at 533, 4 nm.

 It is also known to produce optical filters (passband in transmission) by stacking many thin layers of thickness and determined refractive index, to transmit a determined wavelength.

 It is also known to make Bragg filters photoinscribed in a fiber; these filters work in reflection.

 The present invention aims to provide an improved optical filter, a multiplexer (and a demultiplexer) incorporating this filter, and its manufacturing process.

résonance est obtenue par la construction d'un réseau de motifs à la surface et le cas échéant dans l'épaisseur d'au moins un guide d'onde constitué par une couche mince ou un empilement de couches minces ; la résonance résulte d'un couplage électromagnétique par le réseau entre une onde incidente sensiblement selon la normale à la surface du guide d'onde et/ou des couches minces, et un mode guidé du guide d'onde : la résonance est observée lorsque des fréquences temporelle et spatiale de l'onde incidente sont sensiblement égales à celles correspondant à un mode propre de la structure ; à cet effet, on prévoit According to the invention, resonant structures are used at a determined wavelength and under a determined incidence; a

resonance is obtained by the construction of a network of patterns on the surface and if necessary in the thickness of at least one waveguide constituted by a thin layer or a stack of thin layers; the resonance results from an electromagnetic coupling by the network between an incident wave substantially according to the normal to the surface of the waveguide and / or thin layers, and a guided mode of the waveguide: the resonance is observed when temporal and spatial frequencies of the incident wave are substantially equal to those corresponding to a specific mode of the structure; to this end, provision is made

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 generally patterns whose dimensions are close to the desired wavelength, and generally smaller than these.

 According to the invention, each of the patterns consists of a thin layer region whose index is locally modified by the implantation of ions in the thin layer; this implantation is obtained by subjecting the thin layer to ion bombardment, by an ion beam delivered by a particle accelerator, an ion gun and / or an ion implanter.

le niobium, le titane, le silicium, le phosphore ou le germanium. This implantation operation uses a known technique in particular for doping a semiconductor material with doping materials. For the application of this technique to the invention, a material chosen from erbium will generally be used as doping material,

niobium, titanium, silicon, phosphorus or germanium.

 In order to dope only certain regions of the thin layer to form the doped patterns, a thin layer masking technique such as that used for etching is preferably used: the thin layer to be doped is covered with a "perforated" mask. of a shape complementary to that of the network of patterns to be formed; the mask thus prevents the parts of the thin layer which it covers from being subjected to ionic flux; it therefore allows the preservation, in the thin layer which it covers, of undoped areas surrounding the doped regions.

d'exposition des parties non masquées de la couche mince au faisceau d'ions, on peut faire varier la configuration ionique des motifs dopés, en particulier la densité volumique d'ions implantés et/ou la profondeur d'implantation, afin d'obtenir une configuration de forme (profil) et/ou d'indice déterminé. Furthermore, by varying the intensity and / or the duration

exposure of the unmasked parts of the thin layer to the ion beam, the ion configuration of the doped patterns can be varied, in particular the volume density of implanted ions and / or the implantation depth, in order to obtain a configuration of shape (profile) and / or determined index.

 It is also possible to anneal the structure after doping to modify, in a controlled manner, by migration of the ions in the layer.

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 thin, the index and / or ionic population gradient in the doped patterns.

 According to another aspect of the invention, said structure and / or said network is biperiodic or pluriperiodic: it (it) comprises a plurality of identical first patterns, regularly spaced in two directions parallel to the waveguide, and according to a first step ; it (it) further comprises a plurality of second identical patterns regularly spaced in said directions and in said first pitch, which are arranged nested with said first patterns and which are of configuration and / or dimensions different from those of the first patterns. Thus, said first patterns form a first sub-network which is nested with a second sub-network constituted by said second patterns.

 Generally, and as a result of this nesting, a first pattern and a second pattern adjacent to the first pattern will be separated by a distance equal to half of said pitch; in a preferred embodiment, the resonant network can comprise more than two sub-networks, in particular 3 or 4 nested sub-networks to form a multi-period network.

 Such a structure makes it possible to provide a bandpass filtering in reflection, which has a high rejection rate and which allows an inclination (of low value) of the incident wave relative to the normal to the surface of the layers. thin of the waveguide, this inclination being desirable for separating the reflected beam from the incident beam, without requiring the use of a semi-reflecting plate or an interference system.

 Such a structure makes it possible to obtain improved performance for variations in the angle of incidence, the opening angle, or the polarization of the incident beam.

 According to another aspect of the invention, an optical component is used comprising several thin layers superimposed on a

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 substrate and incorporating two such resonant structures, which are preferably arranged symmetrically with respect to a median plane, and which are identical and / or resonant at the same wavelength; a passive bandpass filter in transmission is thus obtained which has a high rejection rate, and which is simple to manufacture.

 The production of a component incorporating two resonant networks can be carried out by implanting the two networks on two portions of a thin layer resting on a common substrate; the substrate can then be cut into two parts which can be assembled to form the component; assembly can be carried out by bringing the two parts into contact through the face on which the network is provided; this assembly can be obtained by molecular adhesion, alternately the two parts can be assembled by their respective portions of the substrate, if necessary by bonding.

 According to an alternative embodiment, it is possible to carry out doping on the surface of each of two stacks of thin layers provided on each of the two faces of a substrate common to the two stacks.

 Preferably, the network is installed in an anti-reflective structure comprising at least one thin layer.

 Improved performance (narrow band and high rejection) is obtained by implanting the doped patterns of each network in a (so-called external) layer with an index (for example close to 1.5) lower than that (for example close to 2) of the layer on which the outer layer is deposited, which leads to an anti-reflection structure.

 In addition, the use of circular contour patterns and / or with an implantation profile inclined relative to normal to thin layers, improves the resistance to opening.

 To increase the rejection rate of the optical filter obtained, it is also possible to provide several superimposed resonant networks.

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 The components according to the invention have the advantage of requiring a reduced number of thin layers, compared with conventional thin layer filters.

d'onde sur laquelle est centré le filtre, ayant une largeur spectrale inférieure à un nanomètre et réfléchissant ou transmettant environ 100 % du faisceau incident-en dehors de la bande passante-, même lorsque le faisceau incident est doté d'une incidence (par rapport à la normale) pouvant atteindre plusieurs degrés et/ou d'une ouverture de quelques mrd, en particulier de 5 à 20 mrd. In addition, they make it possible to obtain narrower filters which are therefore better suited to dividing a transmission band into a large number of channels. In practice two or three thin layers may suffice to construct a bandpass filter having a high rejection rate for wavelengths far from the length.

wave on which the filter is centered, having a spectral width of less than one nanometer and reflecting or transmitting about 100% of the incident beam - outside the bandwidth - even when the incident beam has an incidence (for example compared to normal) which can reach several degrees and / or an opening of a few bn, in particular from 5 to 20 bn.

d'ajuster la longueur d'onde centrale après réalisation du réseau : ce décalage peut en particulier être obtenu en recouvrant le réseau d'une couche mince d'indice et d'épaisseur adaptés, ou bien en modifiant la géométrie du réseau, par exemple par une étape postérieure de gravure par faisceau d'électrons. Since the position of the central wavelength is essentially determined by the geometry of the grating which extends over the external face (s) of the component, it is easy to offset and / or

to adjust the central wavelength after completion of the network: this offset can in particular be obtained by covering the network with a thin layer of suitable index and thickness, or else by modifying the geometry of the network, for example by a later step of electron beam etching.

 The thin layers can be produced by depositing a material chosen from metals such as AI, Ni, Ag, Au, oxides such as TiO2, Sei02, Ta205, fluorides (such as MgF2), sulfides (such as ZnS ) or nitrides; each thin layer has a thickness generally ranging from 10 nm to 10 μm; the thickness of the thin layer covering the grating to offset the central wavelength may be less than these values: it can range from 1 to 10 nm (nanometer).

 By comparison, the substrate has a greater thickness, for example of the order of 0.5 mm; it is made of a material

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transparent pour les longueurs d'ondes considérées, en particulier les longueurs d'ondes voisines de 1, 5 um, te) que de la silice.

transparent for the wavelengths considered, in particular the wavelengths close to 1, 5 μm, te) than silica.

 Other advantages and characteristics of the invention will be understood through the following description which refers to the accompanying drawings, which illustrate without any limiting nature of the preferred embodiments of the invention.

 Figure 1 is a schematic perspective view of part of a component according to a first embodiment.

 Figure 2 is a schematic cross-sectional view of part of a component according to a second embodiment.

 Figure 3 is a schematic plan view of an eight-way demultiplexer incorporating bandpass filters in transmission according to the invention.

 FIG. 4 illustrates in plan view the arrangement of the doped patterns of square contour of a pluriperiodic network.

 Figure 5 is a schematic sectional view through a plane transverse to the planes of the layers, which shows a doped pattern of a network whose transverse index profile is inclined and curved.

 Figure 6 is a schematic plan view of a four-way demultiplexer incorporating four components forming reflection bandwidth filters.

 With reference to Figures 3 and 6, the demultiplexer 1,2 comprises eight filters 3 (respectively four filters 4) bandpass centered on eight (respectively four) different wavelengths corresponding to the eight (respectively four) channels to be separated.

 The demultiplexer comprises an interface 5 for optical coupling with an optical fiber 6 transporting the radiation to be divided; the incident beam 7 delivered by the fiber 6 forms with the normal 8 at the

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face 9 du filtre un angle 10 d'incidence, dont la valeur est la plus faible possible afin de limiter les perturbations susceptibles d'en résulter.

face 9 of the filter an angle of incidence 10, the value of which is as low as possible in order to limit the disturbances liable to result therefrom.

qui a été réfléchie par le filtre 4 correspondant. The demultiplexer 2 in FIG. 6 comprises four output collimators 11 respectively associated with the four filters 4, which serve to direct the portion of the incident beam 7 which corresponds to the wavelength associated with the corresponding channel to an output optical fiber 110, and

which has been reflected by the corresponding filter 4.

 Similarly, the demultiplexer 1 in FIG. 3 comprises eight output collimators 11; each demultiplexer 1,2 may include an integrated input collimator to limit the opening of the incident beam 7 coming from the fiber. Filters 3 and 4 have a plate structure such as that respectively illustrated in FIGS. 1 and 2.

 Each output collimator 11 can be constituted by the doped end of the corresponding output fiber 110; the end of the input fiber 6 can also be doped to form a collimator 5.

 Each demultiplexer 1,2 comprises an input waveguide 100 which is formed in a layer deposited on a substrate, and which is extended by other guides 101; this layer is provided with grooves substantially transverse to the longitudinal axis of the guides 100, 101, each groove receiving a filter disposed transversely to the wave guide portions 100, 101; thus the spectral component of the beam 7 propagating in the guides 100, 101, which corresponds to the wavelength on which the filter is centered, passes through it in the case of FIG. 3 or on the contrary is reflected by the filter in the case of figure 6.

 This filtered component is transmitted by an output waveguide 102 to the output fiber 110; in the case of FIG. 6, the end of the guide 102 is doped to form the output collimator 11.

 The filter 3 in FIG. 1 extends in a symmetry with respect to its median plane 12: it comprises, on either side of this plane, a substrate 13 covered with a thin layer 14 in the thickness of which have been

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 formed, by ion implantation, doped patterns 15,16 forming a resonant network.

This network comprises on the one hand a plurality of first patterns
15, of cylindrical shape along axes parallel to normal 8 to the upper external face 9 and to the lower external face 17 of the component 3, and of circular cross section (or contour); the network also comprises a plurality of second patterns 16 of also cylindrical shape and parallel to the normal 8 to the plane 12.

 The patterns 15 are of identical shape and size and are regularly spaced in two orthogonal directions perpendicular to the normal 8 to form a first square mesh.

 The patterns 16 are also of identical shape and size and are spaced along said orthogonal directions perpendicular to the normal 8 to form a second square mesh, which is nested with the first square mesh.

 The patterns 15, 16 thus form a two-dimensional two-dimensional network which extends inside the layer 14.

 For this purpose, the longitudinal 21 and transverse steps 18 of the two meshes are identical, but the diameter 19.20 and / or the respective height of the patterns 15.16 is (are) different.

 Component 3 thus comprises two identical networks respectively provided on its upper external face 9 and on its external lower face 17, so as to form a bandpass filter in transmission; the central frequency (wavelength) of this filter is calculated by the usual methods in the matter, according to the optical and geometric characteristics of the patterns 15, 16 and of the layer 14 in which these patterns are formed; this layer constitutes a waveguide endowed with its own frequencies (temporal and spatial) of resonance.

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According to the alternative embodiment illustrated in FIG. 2, the passband filter 4 in reflection can consist of several resonant structures stacked along the axis 8 (of normal incidence) which is perpendicular to the faces of the layers: this filter comprises a substrate 13 covered with 'a thin layer 14 in the thickness of which is implanted a first resonant network; a layer 22 forming a substrate (or spacer spacer) covers the layer 14 and is itself coated with a thin layer 23 comprising a second resonant network; a layer 24 similar to layer 22 covers layer 23 and is coated with a thin layer 25 comprising a third resonant network.

With reference to FIG. 5, the lateral faces (or flanks) 36, 37 of the pattern 38 of a network formed under the surface 9 of the thin layer 40, are inclined, with respect to a normal 8a at the surface 9, d 'an angle 41.

 In the case of a demultiplexer 2 using reflecting filters 4 (FIG. 6), the filters can be aligned along the axis 50, their respective planes 12a being arranged parallel to each other and regularly spaced apart by a pitch 51.

 In the demultiplexer 1 illustrated in FIG. 3, the transmitter filters 3 extend in two planes 12b, 12c parallel and are regularly spaced apart by a step 52.

 With reference to FIG. 4, the network 60 comprises a plurality of square meshes 61 of width 62 which are arranged side by side and extend in two orthogonal directions contained in the plane of the figure.

 In each mesh are provided four doped patterns delimited by contours of square section: - two first patterns 631, 632 whose square section has a side of width 64,

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 - A second pattern 65 whose square section has a side of width 66, - a third pattern 67 whose square section has a side of width 68, the values of said widths being different while being close.

est égale à la largeur 62 de la maille ; les motifs 632 sont également espacés entre eux du même pas, ainsi que les motifs 65 entre eux d'une part et de même que les motifs 67 entre eux d'autre part. The patterns 63 are regularly spaced apart by a step whose value

is equal to the width 62 of the mesh; the patterns 632 are also spaced apart by the same pitch, as well as the patterns 65 between them on the one hand and just as the patterns 67 between them on the other hand.

dont le côté 70 correspond à la moitié du côté 62 de la maille 61.The four doped patterns of each mesh are arranged so that their respective centers are arranged at the top of a square

whose side 70 corresponds to half of the side 62 of the mesh 61.

Claims (11)

 CLAIMS 1. Optical component (3,4) comprising at least one thin layer (14,23, 25,29, 30,40) deposited on a substrate (13,28), characterized in that it comprises at least one structure or a pluriperiodic resonant network comprising a plurality of patterns (15,16, 31,32, 38,63, 65,67) or doped regions regularly spaced in two directions, so as to form a passband filter under incidence close to normal for thin layers.  2. Component according to claim 1, in which the resonant structure or network (60) comprises: - a plurality of first doped patterns or regions (15) having a first ion configuration common to all of said first patterns or regions, - a plurality of second doped patterns or regions (16) having a second ion configuration common to all of said second patterns or regions, said second ion configuration being different from said first ion configuration.  3. Component according to claim 1 or 2, which comprises: - a first pluriperiodic resonant network (15,16, 31,32, 38) implanted in at least one first thin layer, - a second pluriperiodic resonant network implanted in at least one second thin layer, - at least a third thin layer forming a first coupling and decoupling region associated with the first network.  4. Component according to claim 3, which further comprises: - at least a fourth thin layer forming a second coupling and decoupling region associated with the second network, - at least one thick layer forming said substrate. <Desc / Clms Page number 13>  5. Component according to any one of claims 1 to 4 which comprises two resonant structures or networks arranged symmetrically with respect to the median plane (12,12b, 12c) of the component, so as to form a band-pass filter (3) transmission.  6. Component according to any one of claims 1 to 5, wherein said patterns or regions have a substantially circular or square section.  7. Component according to any one of claims 1 to 6, in which the patterns or regions of the network are implanted in an external thin layer whose index is lower than that of the layer supporting said external thin layer.  8. Component according to any one of claims 1 to 7, whose resonant structure comprises a network of patterns (38) whose transverse index profiles (36,37) are inclined.  9. Component according to any one of claims 1 to 8, which comprises at least three resonant networks provided in three thin layers (14, 23, 25) superimposed, which comprises less than ten thin layers, and whose bandwidth is centered on a wavelength close to 1.5 microns.  10. Optical multiplexer or demultiplexer (1,2) with wavelength division, which comprises a plurality of components, in particular from 8 or 16 to 256 components (3,4) according to any one of claims 1 to 9 , preferably in which said components (3,4) are mechanically integral with each other, the respective central wavelengths of which are preferably different, and extend substantially parallel to each other, and which also comprises a collimation means (11) associated with each component (3,4), and where appropriate a collimation means (5) or waveguide suitable for the optical coupling of the multiplexer or demultiplexer with the tip of a fiber ( 6) optical.  11. A method of manufacturing a component according to any one of claims 1 to 9, in which one deposits from 1 to 10 <Desc / Clms Page number 14>  thin layers on a substrate, and in which an array is implanted on a thin layer by an ion beam delivered by an ion implanter.