Optical spectral modulator device

Abstract

The invention relates to an optical spectral modulator device (1) comprising: • - at least one optical fibre (2) comprising optical functionalisation means (4) having a reflection spectrum of a portion of light radiation travelling through the fibre; • - a deformable element (10) having a length L; • - a first mechanical element (8) and a second mechanical element (14) that are attached to the deformable element (10) and capable of undergoing a relative deformation or a relative displacement as a result of this deformable element (10), wherein the optical fibre is attached to the mechanical elements at two attachment points (16, 18) arranged on either side of the optical functionalisation means (4), wherein the distance d between the first attachment point and the second attachment point is shorter than the length L of the deformable element, and wherein the ratio L / d is at least equal to 5.

Description

Description Title of the invention: OPTICAL SPECTRUM MODULATOR DEVICE TECHNICAL FIELD AND PRIOR ART

[0001] The invention relates to the field of devices for controlling the transmission or reflection properties of radiation in an optical fiber.

[0002] We know the implementation of discrete components, for example MEMS or crystal type, to realize optical functions, for example switches or modulators.

[0003] However, assemblies using such components are complex. The problem arises of having simpler components, for example fully fibered ones.

[0004] In addition, more flexibility is sought regarding the transparency of the reflective elements used: in particular, MEMS type mirrors that are either 100% reflector or 100% transmitter, which leaves little flexibility of use.

[0005] In particular, in some cases, we seek to control the transmission or reflection functions independently depending on the wavelengths. For example, we may want to let one wavelength pass and block another. However, a mirror of the type presented above cannot fulfill this function.

[0006] Furthermore, document WO 2022 / 243639 discloses a device for spectral interrogation of Bragg wavelengths.

[0007] Such a device is shown schematically in [Fig.1],

[0008] It comprises a broad spectral band radiation source 103, an optical circulator 123, a measuring optical fiber 105, at least one reflection optical fiber 107, a detector 109, an optical switch 111 and a configurable driver 112. The measuring optical fiber comprises a series of successive Bragg gratings 115, configured to reflect a light signal 113 according to different wavelengths.

[0009] The reflection optical fiber 107 comprises a total reflection element 119, for example a totally reflecting mirror.

[0010] The optical switch 111 is controlled by the driver 12, so as to switch the passage of the light signal between the optical source 103, the measuring optical fiber 115, the reflection fiber 107 and the detector 109 (via the circulator 123).

[0011] But the presence of the 111 switch induces losses at each passage of the light, which limits the number of possible passages, because we also want to maintain the optical power above a certain detection threshold.

[0012] Additionally, an 111 switch requires at least two input arms: a first arm is connected to the interrogator and a second is connected to the fixed mirror. However, having two arms makes integration complex.

[0013] Here again, we are trying to simplify this type of device. Statement of the invention

[0014] The invention aims to solve all or part of the problems set out above or in the remainder of this application.

[0015] According to a first aspect, the invention relates to an optical spectrum modulator device, comprising:

[0016] -at least one optical fiber comprising optical functionalization means, presenting a reflection spectrum of a part of light radiation circulating in the fiber;

[0017] - a deformable element, having a length L;

[0018] -a first mechanical element and a second mechanical element fixed to the deformable element and capable of undergoing relative deformation or relative displacement under the action of this deformable element, said optical fiber being fixed to the first mechanical element at a first fixing point and to the second mechanical element at a second fixing point, these 2 fixing points being arranged on either side of the optical functionalization means, the distance (d) between the first fixing point and the second fixing point being preferably less than the length (L) of the deformable element, the ratio L / d being at least equal to 5.

[0019] The invention therefore relates to a device which implements an optical spectrum modulator mechanically controlled by a deformable or mobile element.

[0020] The spectrum is generated by functionalization of at least one optical fiber, for example a Bragg grating or a Fabry-Pérot cavity.

[0021] Since the fiber is mechanically connected to the deformable or mobile element, the spectrum is modified when the latter is deformed or set in motion.

[0022] The mechanical element includes, for example, a piezoelectric element or a MEMS.

[0023] According to one embodiment, the fiber(s) is / are arranged outside the deformable element. For example, the first mechanical element comprises a first lateral surface and the second mechanical element comprises a second lateral surface, aligned with each other and parallel to the direction of extension of the deformable element and the fiber(s), the first attachment point being located on the first lateral surface and the second attachment point being located on the second lateral surface, these two lateral surfaces being separated by a distance (D) less than the distance (d) which separates the attachment points.

[0024] According to another embodiment of a device according to the invention, the device comprises a single fiber or several fibers, this / these fiber(s) being partly arranged inside the deformable element, which makes the device particularly compact.

[0025] For example :

[0026] - the first mechanical element comprises a semi-cylindrical core forming a first internal surface for positioning the optical fiber, the first fixing point being located on this first internal positioning surface;

[0027] - the second mechanical element comprises an elongated part which penetrates inside the deformable element and which comprises an internal channel for receiving a first part of the optical fiber, this elongated part comprising a semi-cylindrical end part forming a second surface for positioning a second part of the fiber, the second fixing point being located on this second internal positioning surface, aligned with the first internal positioning surface, the two positioning surfaces being separated by a distance less than the distance which separates the fixing points.

[0028] Whatever the implementation envisaged, the optical functionalization means can present a reflection spectrum:

[0029] - which totally or partially reflects light in a spectral band between the two wavelengths Xi and X 2 ;

[0030] - and / or which has a front which varies with the wavelength.

[0031] This reflection spectrum will vary depending on the constraints applied to it by the deformable element.

[0032] A device according to the invention may further comprise means for controlling the deformable element, for example means capable of controlling the deformable element at a frequency less than or equal to 100 kHz or 500 kHz or 1 MHz or even above 1 MHz. Thus, the reflection spectrum (and the transmission spectrum) of the optical functionalization means will vary at the same frequency.

[0033] Whatever the planned achievement:

[0034] - The first mechanical element may be movable relative to the undeformed position of the deformable element and the second mechanical element may be fixed relative to the first mechanical element;

[0035] - or the first mechanical element may be movable relative to the undeformed position of the deformable element and the second mechanical element also movable relative to the first mechanical element.

[0036] In a spectral modulation device according to the invention, the relative variation Ad / d of the portion of the fiber located between the fixing points is greater than 0.2% or 0.3%, and for example less than 3%. It can therefore be much greater than the usual values ​​which are of the order of 0.15% or 0.2%.

[0037] The invention also relates to an optical device comprising:

[0038] - a spectral modulation device according to the invention;

[0039] - a source of radiation at at least one wavelength which is reflected by the spectral modulation device in a first state thereof, and which is not reflected by the spectral modulation device in a second state thereof.

[0040] Such an optical device may further comprise:

[0041] - a plurality of Bragg gratings, arranged at the output of the spectral modulation device;

[0042] - a detection device, capable of receiving radiation reflected by at least one of said Bragg gratings and transmitted by the spectral modulation device when the latter is in the second state.

[0043] Such a device forms a Bragg wavelength spectral interrogation device.

[0044] Such a device may further comprise means, for example an optical circulator, for directing radiation emitted by the source at the input of the spectral modulation device and for directing radiation reflected by a Bragg grating arranged at the output of the spectral modulation device towards the detection device.

[0045] Such a device can operate in the following phases:

[0046] - in a first phase, the modulator is on: the radiation from the source goes towards the spectrum modulator then towards the Bragg gratings;

[0047] - in a second phase, the modulator is reflective: the radiation of the back and forths between the Bragg gratings and the modulator;

[0048] - in a 3 èmephase, the modulator is again on: the radiation returns for example to the detection device via the means for directing the reflected radiation towards the detection device.

[0049] The invention also relates to a method for modulating an optical spectrum, implementing a device according to the invention, as described above or in the remainder of the present application.

[0050] In particular, the invention also relates to a method of modulating the transmission of radiation by an optical fiber of a device according to the invention, in which:

[0051] - in a first state of the deformable element, the functionalization means have a first reflection spectrum;

[0052] - in a second state of the deformable element, the functionalization means have a second reflection spectrum, different from the first reflection spectrum. BRIEF DESCRIPTION OF THE FIGURES

[0053] [Fig. 1] represents a device according to the prior art;

[0054] Figures 2A and 2B represent a device according to one embodiment of the invention;

[0055] [Fig.2C] represents a variant of a device according to another embodiment of the invention;

[0056] Figures 3A and 3B represent steps of mounting a device according to the invention;

[0057] Figures 4A and 4B represent a device according to another embodiment of the invention;

[0058] [Fig.5A], [Fig.5B], [Fig.5C], [Fig.5D], [Fig.5E] and [Fig.5F] represent steps of mounting a device according to the invention;

[0059] Figures 6A-6D show examples of reflection spectra of a Bragg mirror;

[0060] [Fig.7] represents an example of a reflection spectrum of a Fabry-Pérot cavity;

[0061] Figures 8 A - 8B represent the reflection spectrum of a modulator, in two different states;

[0062] Figures 9A - 9B represent another reflection spectrum of a modulator, in 2 different states;

[0063] [Fig.10A] and [Fig.10B] represent another reflection spectrum of a modulator, in 2 different states and relative to a line of a laser source;

[0064] Figures 11 A - 1 IB represent another reflection spectrum of a partially reflective and partially transparent modulator, in two different states and relative to a line of a laser source;

[0065] Figures 12A - 12B represent a rising edge of another reflection spectrum of a modulator, in two different states and relative to a line of a laser source;

[0066] Figures 13A - 13B represent another reflection spectrum of a modulator, in 2 different states and with respect to two lines of two laser sources;

[0067] [Fig.l4A] represents a spectral interrogation device according to the invention;

[0068] Figures 14B - 14D represent the reflection spectrum of a modulator of a spectral interrogation device according to the invention, in different states, relative to the spectrum of the radiation source;

[0069] Figures 15A - 15C represent the different operating phases of a spectral interrogation device according to the invention;

[0070] [Fig. 16] shows in an enlarged view means for functionalizing an optical fiber within the framework of the present invention.

[0071] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0072] Figures 2A and 2B represent a first example of embodiment of a device 1 according to the invention, comprising at least one fiber 2 extending at least partly along an axis XX', this fiber 2 being fixed to the outside of an element 10 deformable or movable in a direction parallel to the same axis XX'.

[0073] Fiber 2 is functionalized by means 4, for example a Bragg grating or a Fabry-Pérot cavity, each having light reflection properties depending on the wavelength, properties which will evolve depending on the deformation of the element 10.

[0074] The device further comprises a first support or mechanical element 8 and a second support or mechanical element 14. The two supports or mechanical elements are movable relative to each other: in this example, the first support or mechanical element 8 is fixed and the second support or mechanical element 14 is movable, but any configuration with two supports or mechanical elements movable relative to each other can also be used, as illustrated in [Fig.2C].

[0075] Each of these two supports or mechanical elements is linked on the one hand to the deformable or mobile element 10 and on the other hand to a part of the optical fiber 2, so that the means 4 are arranged between a first point 16 for fixing or anchoring the fiber to the support 8 and a second point 18 for fixing or anchoring the fiber to the support 14.

[0076] The deformable or mobile element 10 is preferably of the piezoelectric type, which makes it possible to modulate the spectrum at high rates: up to several hundred kHz or even more (for example at frequencies less than or equal to 500 kHz or 1 MHz or even beyond 1 MHz; in fact the resonance frequency depends on the size of the piezoelectric element). For example, this piezoelectric element deforms longitudinally, along the axis XX', parallel to the optical fiber 2. An example of such a piezoelectric element 10 is illustrated in [Fig.2B], It can be controlled or commanded by means (or an electrical circuit) 55, which will make it possible to control the voltage and its frequency applied to the terminals of the piezoelectric element.Alternatively (in this embodiment or in the other embodiments described in this application), the deformable or mobile element 10 may comprise a MEMS, or a motor, or a translation element (for example a plate), or a worm screw, or a spring.

[0077] For example, a fiber 2 can be attached to a MEMS in order to deform it. We can refer in particular to the following articles:

[0078] - Gierl C, Gründl T, Paul S, Zogal K, Haidar MT, Meissner P, Amann MC, Küppers F. Temperature characteristics of surface micromachined MEMS-VCSEL with large tuning range. Opt Express. 2014 Jun 2;22(11): 13063-72. doi:10.1364 / OE.22.013063. PMID: 24921503;

[0079] - Christian Gierl, Karolina Zogal, Sandro Jatta, Hooman A. Davani, Franko Küppers, Peter Meissner, Tobias Gründl, Christian Grasse, Markus-Christian Amann, Aidan Daly, Brian Corbett, Benjamin Kogel, Asa Haglund, Johan Gustavsson, Petter Westbergh, Anders Larsson, Pierluigi Debernardi, and Markus Ortsiefer "Tuneable VCSEL aiming for the application in interconnects and short haul systems", Proc. SPIE 7959, Optical Metro Networks and Short-Haul Systems III, 795908 (24 January 2011); https: / / doi.org / 10.1117 / 12.881247.

[0080] In the example of [Fig.2A], the fixed mechanical support 8 preferably has a parallelepiped shape, with:

[0081] - a flat lateral face 8b parallel to the direction XX' of extension of at least part of the fiber 2 and against which the latter can be fixed;

[0082] - a main face 8a, facing the piezoelectric element 10, which may have in its middle a hollow 8c forming a receiving volume into which one end of this element 10 can penetrate in order to ensure solid fixing of the latter with the support 8.

[0083] The movable mechanical support 14 preferably has an overall “U” shape, the lateral branches 14b, , 14b 2 of the “U” being parallel to each other and to the direction XX' of extension of at least a part of the fiber 2 and of displacement of the element 10. As a variant (not shown in the figures), the mobile mechanical support 14 has a single lateral branch 14bl (therefore no branch 14b2). The presence of an elbow or a branch 14b 2 (which, if it extends 360° around the AA' axis, forms a crown) allows one or more additional optical fiber(s) to be positioned and the technical effects to be parallelized.

[0084] Thus, the distance D between the movable mechanical support 14 and the fixed mechanical support 8 is less than the distance d which separates the fixing points 16, 18 of the optical fiber against the surfaces 8b and 14b. The fiber is fixed against the outer wall 14b of the branch 14b located on the same side, relative to the deformable element 10, as the surface 8b against which the fiber is fixed. This movable mechanical support 14 may have in its middle a stud 14a which penetrates into the piezoelectric element 10 in order to ensure a solid fixing of the latter with the support 14.

[0085] The outer surface 14b of the mechanical support 14 and the surface 8b of the fixed mechanical support 8 against which the fiber 2 is fixed are flat and aligned in the same plane.

[0086] Fiber 2 is made solid:

[0087] - on the one hand of the fixed mechanical support 8 by means of a first means of fixing or anchoring at the first point 16;

[0088] - on the other hand of the mobile mechanical support 14 by means of a second means of fixing or anchoring at the second point 18.

[0089] Each anchoring means is for example a glue, or a cement, or an adhesive tape, or thermal projections, or any means allowing the fixing of the fiber.

[0090] In the example of [Eig.2C], the second mobile mechanical support 14' has for example the same structure as the mobile mechanical support 14: it preferably has a overall “U” shape, lateral branches 14'bi, 14'b 2 of the “U” being parallel to each other and to the direction XX' of extension of at least a part of the fiber 2 and of displacement of the element 10. As a variant (not shown in the figures), the mobile mechanical support 14' has a single lateral branch I4'b, (therefore no branch 14'b 2 ). The presence of a 14'b elbow 2allows several optical fibers to be positioned and phenomena to be parallelized.

[0091] Figures 3A-3B represent assembly steps of a device as illustrated in [Eig.2A],

[0092] First ([Eig.3A]), one end of the piezoelectric element 10 is positioned in the receiving volume 8c, if the latter is present; this end can be glued into the fixed mechanical support 8.

[0093] The mobile mechanical support 14, comprising its lateral branches l4b 14b 2 and its central pad 14a is fixed to the other end of the piezoelectric element; more precisely, the central pad 14a, if present, can be introduced into a hollow 10a made in this other end; this pad 14a can be fixed there for example by gluing, so that the surfaces 14b and 8b are aligned.

[0094] Finally ([Eig.3B]), the functionalized fiber 2 (therefore comprising a Bragg grating or an Eabry Perrot cavity 4) is positioned against the lateral surfaces 8b and 14b on which it is fixed as explained above, the means 4 being arranged between the 2 fixing or anchoring points 16, 18.

[0095] Steps for assembling a device as illustrated in [Eig.2C] are similar to those of figures 3A-3B for the moving part.

[0096] Figures 4A and 4B represent a second exemplary embodiment of a device 1' according to the invention, in which the fiber 2, which extends at least partly along an axis XX', passes inside the deformable or mobile element 10 along the same axis XX'.

[0097] As previously, fiber 2 is functionalized by means 4, for example a Bragg grating or an Eabry-Pérot cavity.

[0098] The device further comprises a fixed support or mechanical element 38 and a mobile support or mechanical element 34, in the shape of a “T”, comprising a head 34 and an elongated body 34a; as a variant (not shown), it is possible to have, as in the case of [Fig. 2C], two mobile supports or mechanical elements.

[0099] Each of these two supports or mechanical elements is linked on the one hand to the deformable or mobile element 10 and on the other hand to a part of the optical fiber 2, so that the means 4 are arranged between a first point 26 for fixing or anchoring the fiber to the support 38 and a second point 28 for fixing or anchoring the fiber to the support 34.

[0100] For the reasons already explained above, the deformable or movable element 10 is preferably of the piezoelectric type, but the variants already mentioned above (MEMS, or motor, or element (for example a plate) of translation, or worm screw, or a spring) can be implemented. It deforms longitudinally, along the axis XX'. An example of such a piezoelectric element has already been given above in [Fig.2B]; it is also represented in [Fig.5D],

[0101] The fiber 2 is positioned in an inner channel 34c of the movable mechanical support and in an inner channel 38c (see Figures 5E and 5F) of the fixed mechanical support. The end 34d of the elongated body 34a is not solid and comprises a solid half-cylinder and a hollow half-cylinder, as illustrated in Figures 5B and 5C, so that a flat surface 34e, in the conduit extension 34c into which the fiber is introduced, forms a receiving surface for the latter, on which it can be fixed.

[0102] Thus, the distance D' between the mobile mechanical support 34 and the fixed mechanical support 38 is less than the distance d which separates the fixing points 26, 28 of the optical fiber against these supports, more precisely against the surfaces 34e and 38e (see below).

[0103] Figures 5A-5E show various parts of the device of [Fig.4A],

[0104] The piezoelectric element ([Fig.5D]) is of elongated shape, and comprises an internal channel 10a inside which the body 34a of the movable mechanical support can be introduced.

[0105] The fixed mechanical support 38 (figures 5E and 5F) preferably has a cylindrical shape, with:

[0106] - an internal channel 38c parallel to the direction of extension of the fiber 2 and into which the latter can be inserted;

[0107] - a main face 38a, facing the piezoelectric element 10, which may have in its middle a hollow 38d forming a receiving volume into which one end of the element 10 can penetrate in order to ensure solid fixing of the latter with the support 38.

[0108] The inner end of this support 38 is hollowed out to form a half-cylinder, as illustrated in FIGS. 5E and 5F, so that a flat surface 38e forms a receiving surface 38e for the fiber, on which it can be fixed.

[0109] For the assembly of the device, the surfaces 34e and 38e are arranged so as to be located in the same plane, so that the fiber 2 can be positioned and fixed on these 2 surfaces.

[0110] More precisely, fiber 2 is made solid:

[0111] - on the one hand of the surface 34e of the mobile mechanical support 34 by means of an anchoring means 28;

[0112] - on the other hand of the surface 38e of the fixed mechanical support by means of an anchoring means 26.

[0113] Each anchoring means 26, 28 is for example a glue, or a cement, or an adhesive tape, or thermal projections, or any means allowing the fiber to be fixed.

[0114] During assembly, the movable mechanical support 34 is introduced into the channel 10a of the element 10. Then the fiber 2, equipped with its functionalization element 4, is introduced into the channel 34c, along the surface 34e. The structure of [Fig.4B] is thus obtained.

[0115] The free end of the element 10 is then introduced into the hollow part 38d of the fixed mechanical support, the free end of the fiber enters the channel 38c and runs along the surface 38e.

[0116] Then the 34th and 38th surfaces are aligned with each other.

[0117] An anchoring point 28 makes it possible to fix the fiber on the surface 34e and an anchoring point 26 makes it possible to fix the fiber on the surface 38e. The means 4 are arranged between these two points of fixing or anchoring of the fiber.

[0118] In the embodiments of figures 4A, 4B, 5A - 5F, it is possible to increase the number of fibers (which are then in parallel) by making several grooves on the fixed and mobile supports.

[0119] In the embodiments presented above, the distance d between the points 16, 18 or 26, 28 for fixing the fiber, on the one hand on the fixed mechanical support and on the other hand on the mobile mechanical support, is small, less than the extension L of the piezoelectric element itself; in particular, it is possible to have a ratio L / d at least equal to 5 or 10, the exact ratio depending on the desired tunability. [Fig.16] shows schematically the part of the fiber 2 comprising the element 4 as well as the fixing points 16, 18, on either side of the latter and separated by the distance d.

[0120] Consequently, when activating the element 10, the relative variation Ad / d of the portion of the fiber located between these fixing points is much greater (from 10 to 20 times) than in the case where these points are separated by a distance substantially equal to the length of the element 10; for example Ad / d can be between 0 and 3%, in particular be greater than the usual values ​​which are of the order of 0.15% or 0.2%; the Ad / d of a device according to the invention can therefore be greater than 0.2% or 0.3%, and less than 3%). These variations will affect the optical properties of the functionalization element 4, for example a Bragg grating or a Fabry Pérot cavity. These properties will now be presented.

[0121] A Bragg grating is used to generate a bandpass filter, which can completely reflect (up to about 100%) light in a certain region of the spectrum and completely let (up to about 100%) light pass elsewhere (outside of said region).

[0122] Such a Bragg grating makes it possible to generate very different spectral profiles, for example example :

[0123] - a profile showing several peaks in reflection over a range of wavelengths between Xi and X 2 ; the case of two peaks, one at X and the other at X' 2 is illustrated in [Fig.ôA], and the case of a multitude of peaks at X'i (i=l, .. n) is illustrated in [Fig.ôB]; such a filter completely reflects the light at X' 1 and X'2 ([Fig.ôA]) or at each X'i (i=l, n) ([Fig.ôB]), the light being in fact reflected on a narrow spectral band around each of the wavelengths X' 1, X'2, X'i since each peak has a certain spectral width;

[0124] - or a broadband filter profile, between X and X' 2 for example as illustrated in [Fig.ôC]; such a filter completely reflects the light between X' 1 and X'2 and transmits the light outside this spectral band;

[0125] - or a profile comprising a single reflection peak at X , for example as illustrated in [Fig.ôD]; such a filter completely reflects the light at X' 1 (or on a small spectral band around X' 1).

[0126] The shape of the reflection or transmission spectrum of a Bragg grating and / or the various wavelengths XX 2 , X' X' 2 , X'ides figures 6A-6D can be adapted according to the physical properties of the network, for example according to the inscription pitch and / or the inscription energy (various types of networks can be implemented, for example bubble networks, planar networks, filament networks). For example the spectral width X'2 - X'i of [Fig.ôC] is configurable and is for example between a dozen or a few dozen nanometers and a hundred nm, for example between 10 nm and 100 nm.

[0127] A Bragg grating can therefore have a single reflection peak, or several reflection peaks, or form a broadband filter.

[0128] Thus, it is possible to obtain a bandpass filter with configurable width (for example up to several tens of nanometers of spectral width).

[0129] A Fabry-Pérot cavity also makes it possible to generate very varied spectral profiles, for example of the type illustrated in [Fig.7],

[0130] Here again, the shape of the reflection or transmission spectrum of a Fabry-Pérot cavity can be adapted or modulated according to its properties (for example its length and / or reflectivity, etc.).

[0131] A functionalizing element 4 forms an optical element or component in reflection or transmission or of the bandpass filter type, which can completely or partially reflect (up to X%, X = 100 or X < 100) the light in a certain region of the spectrum and completely or partially let (up to (100- X)%) the light pass elsewhere (outside said region).

[0132] In the case of a modulation device according to the invention, each modulation of length Ad between the fixing points, on either side of the element 4, imposed by element 10 also affects element 4 whose optical properties are in turn modulated.

[0133] It is thus possible:

[0134] - in the case of an element 4 having at rest (or in a first state) a reflection spectrum between 2 wavelengths Xi and X 2([Fig.8A]), to modulate the spectrum so that in an “excited” state (or second state) of element 4 the reflection spectrum is shifted between 2 other wavelengths X 3 and X 4 ([Fig.8B]); thus the radiation from a laser source having a spectrum located outside the reflection window of the modulator, but between the wavelengths X 3 and X 4 , is first transmitted ([Fig.lOA], first state of the modulator) then, when the modulator is excited (second state of the modulator), is reflected, the modulator then acting as an open switch (blocking for the laser wavelength);

[0135] - in the case of an element 4 having at rest (or in a first state) a reflection spectrum around a single wavelength Xi ([Fig.9A]), to modulate this spectrum so that in an “excited” state (or second state) of the element 4 the reflection spectrum is shifted around another wavelength X 2([Fig.9B]), element 4 becoming at least partially transparent for the wavelength

[0136] - in the case of a partially reflective element 4, having at rest (or in a first state) a spectrum in partial reflection at X% (0 < X ​​< 100) between two wavelengths Xi and X 2 ([Fig.11 A]), to modulate the spectrum so that in an “excited” state (or second state) of element 4 the spectrum in partial reflection is shifted between two other wavelengths X 3 and X 4 ([Fig.l lB]); thus the radiation from a laser source having a spectrum located outside the reflection window of the modulator, but between the wavelengths X 3 and X 4, is first transmitted ([Fig.l IA], first state of the modulator) then, when the modulator is excited (second state of the modulator), is partially reflected and partially (100-X)% transmitted; the modulator then acts as a partially open switch (partially blocking for the laser wavelength);

[0137] - in the case of an element 4 having at rest (or in a first state) a reflection spectrum having an increasing front between two wavelengths Xi and X 2([Fig.l2A]), then a constant value for X > X2 , to modulate the spectrum so that, in an "excited" state (or second state) of element 4, this front is displaced between two other wavelengths X3 and X4 ([Fig.l2B]); thus the radiation from a laser source having a spectrum initially within the reflection window of the modulator, but between wavelengths X3 and X4, is first reflected ([Fig.12A], first state of the modulator) then, when the modulator is excited (second state of the modulator), partially transmitted, at X%, the modulator then acting as a variable analog modulator (modulating the proportion of laser radiation transmitted).

[0138] Alternatively, shown in [Fig.l3A] and 13B, the modulator may act as a wavelength selector; for example, in the case of a first laser source having a spectrum located in a transmission zone of a modulator, between two wavelengths X3 and X4 and a second laser source having a spectrum located in a reflection zone of the modulator, between two wavelengths X1 and X2:

[0139] - in a first state ([Fig.13 A]), the first laser source is located in the transmission zone of the modulator and the second laser source is located in the reflection zone of the latter; the modulator then acts as a closed (passing) switch for the first laser source and as an open switch for the second laser source;

[0140] - in a second state ([Fig.13B]), the first laser source is in the reflection zone of the modulator and the second laser source is in the transmission zone of the latter; the modulator then acts as a closed (passing) switch for the second laser source and as an open switch for the first laser source.

[0141] In other words, the modulator will allow a selection of the transmitted wavelength.

[0142] Generally speaking, various combinations of the operating modes set out above can be implemented; for example, a modulator can be combined with a wavelength selector.

[0143] A spectral modulator according to the invention makes it possible to produce an interrogator, as explained below in connection with figures 14A - 15C.

[0144] An example of an interrogator is illustrated in Figures 14A-14D. It includes:

[0145] - a light source 50, which may be a broadband source (for example of the type SUED or ASE, with a spectral width between X^ and Xmax), adapted to emit radiation which can be detected by a detector 52;

[0146] - means, for example a circulator 54, which make it possible to direct the light from the source 50 towards a modulator 1 (or 1') according to the invention, which forms a bandpass filter between two wavelengths Xi and X 2 , the spectral width X 2 -Xi being greater than that of X max - X min of the laser source (with in addition X^^Xi andX max <X 2 ); thus, we understand from [Fig.l4B], the spectrum of the source 50 is entirely included in the reflection spectrum of the modulator;

[0147] - a plurality of Bragg gratings 56, 58, 60 arranged at the output of the modulator 1, 1'; these different gratings are configured to reflect in spectral bands or at peaks of wavelengths different from each other.

[0148] The modulator may be of the type described above, with fiber on the outside (as described in connection with Figures 2A-3B) or with fiber on the inside (as described in connection with Figures 4A-5F). It is controlled or driven by means or a circuit electric 55.

[0149] When the modulator is excited into a state that shifts its reflection spectrum between two wavelengths X 3 And / M .the radiation from source 50 is completely transmitted ([Fig.l4C]).

[0150] The light is reflected by one or more of the Bragg gratings 56, 58, 60 and returns to the modulator 1, 1' which has returned to its initial state and therefore reflects the radiation which returns to it ([Fig.l4D]).

[0151] Thus, the radiation from the source will travel back and forth between the modulator and the Bragg gratings. These back and forths will increase the delays between the Bragg peaks. Once a sufficient delay is reached, the modulator returns to the through state and lets the light pass through, which will arrive at the detector 52.

[0152] Figures 15A-15C illustrate the three phases described above:

[0153] - in a first phase ([Fig.15A]), the modulator is passing: the radiation from the source 50 goes towards the spectrum modulator then towards the Bragg gratings 56-60;

[0154] - in a second phase ([Fig.15B]), the modulator is reflective: the radiation goes back and forth between the Bragg gratings 56-60 and the modulator;

[0155] - in a 3 ème phase ([Fig.l5C]), the modulator is again on: the radiation returns to the detector 52 via the circulator 54.

[0156] The invention therefore makes it possible to simply control the delay between the pulses by means of a spectrum modulator which will switch from through mode to mirror (reflector) mode.

[0157] Whatever the embodiment, it is possible to transfer the movement (deformation, displacement) of the mechanical element 10 to the means 4 of the functionalized zone of the optical fiber. It is thus possible to modulate or shift the optical spectrum in reflection or transmission of the means 4, that is to say that the rate of reflected or transmitted light depends on the state of stress applied by the means 10 to the means 4.

[0158] It is possible to quantify by calibration the spectral shift of element 4 as a function of the deformation or displacement of element 10.

[0159] Thus, it is possible to have on a single functionalized fiber (coupled with a mechanical element and an anchoring system) a mirror whose reflection is controlled mechanically.

Claims

Claims

1. Optical spectrum modulator device (1, 1'), comprising: - at least one optical fiber (2) extending at least partly along an axis (XX') and comprising optical functionalization means (4), presenting a spectrum in reflection of a part of light radiation circulating in the fiber; - an element (10) deformable in a direction parallel to the same axis (XX') and having a length L; -a first mechanical element (8) and a second mechanical element (14) fixed to the deformable element (10) and capable of undergoing relative deformation or relative displacement under the action of this deformable element (10), said at least one optical fiber being fixed to the first mechanical element (8, 38) at a first fixing point (16, 26) and to the second mechanical element (14, 34) at a second fixing point (18, 28), these two fixing points being arranged on either side of the optical functionalization means (4), the distance (d) between the first fixing point and the second fixing point being less than the length (L) of the deformable element (10), the ratio L / d being at least equal to 5.

2. Device according to claim 1, said functionalization means (4) comprising a Bragg grating and / or a Fabry-Pérot cavity.

3. Device according to one of claims 1 or 2, the deformable element (10) comprising a piezoelectric type element, or a MEMS or a motor, or a translation element, or a worm screw, or a spring.

4. Device according to one of claims 1 to 3, one or more fibers (2) being arranged outside the deformable element (10).

5. Device according to claim 4, the first mechanical element (8) comprising a first lateral surface (8b) and the second mechanical element (14) comprising a second lateral surface (14b), aligned with each other and parallel to the direction of extension of the deformable element (10) and of the fiber(s), the first fixing point (16) being located on the first lateral surface (8b) and the second fixing point (18) being located on the second lateral surface (14b), these two lateral surfaces being separated by a distance (D) less than the distance (d) which separates the fixing points.

6. Device according to one of claims 1 to 3, said at least one fiber (2) being partly arranged inside the deformable element (10).

7. Device according to claim 6: - the first mechanical element (8) comprising a semi-cylindrical core forming a first internal surface (38e) for positioning the optical fiber, the first fixing point (26) being located on this first internal positioning surface (38e); - the second mechanical element (14) comprising an elongated portion (34a) which penetrates inside the deformable element (10) and which comprises an internal channel (34c) for receiving a first portion of the optical fiber (2), this elongated portion comprising a semi-cylindrical end portion (34d) forming a second surface (34e) for positioning a second portion of the fiber (2), the second fixing point (28) being located on this second internal positioning surface (34e), aligned with the first internal positioning surface (38e), the two positioning surfaces being separated by a distance (D') less than the distance (d) which separates the fixing points.

8. Device according to one of claims 1 to 7, the optical functionalization means (4): - having a reflection spectrum which totally or partially reflects light in a spectral band between the two wavelengths Xi and X2; - and / or having a reflection spectrum which includes a front which varies with the wavelength.

9. Device according to one of claims 1 to 8, the first mechanical element (8) being movable relative to the undeformed position of the deformable element (10) and the second mechanical element (14) being fixed relative to the first mechanical element (8).

10. Device according to one of claims 1 to 8, the first mechanical element (8) being movable relative to the undeformed position of the deformable element (10) and the second mechanical element (14) being movable relative to the first mechanical element (8).

11. Device according to one of claims 1 to 10, further comprising means (55) for controlling the deformable element (10).

12. Optical device comprising: - an optical spectrum modulator device (1, 1') according to one of claims 1 to 11; - a source (50) of radiation at at least one wavelength which is reflected by the optical spectrum modulator device (1, 1') in a first state thereof, and which is not reflected by the spectral modulation device in a second state thereof.

13. An optical device according to claim 12 further comprising: - a plurality of Bragg gratings (56, 58, 60), arranged at the output of the optical spectrum modulator device (1, 1'); - a detection device (52), capable of receiving radiation reflected by at least one of said Bragg gratings and transmitted by the optical spectrum modulator device (1, 1') when the latter is in the second state.

14. Device according to claim 13, further comprising means (54) for directing radiation emitted by the source (50) at the input of the spectral modulation device and for directing radiation reflected by a Bragg grating arranged at the output of the spectral modulation device towards the detection device (52).

15. Method for modulating the transmission of radiation by an optical fiber (2) of a device according to one of claims 1 to 14, in which: - in a first state of the deformable element (10), the functionalization means (4) have a first reflection spectrum; - in a second state of the deformable element (10), the functionalization means (4) have a second reflection spectrum, different from the first reflection spectrum.

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