Bragg diffraction grating device integrated in a waveguide and use of same

Abstract

The present invention relates to a Bragg diffraction grating device integrated in a waveguide, wherein the Bragg diffraction grating comprises corrugations that repeat periodically along the opposite sides of the Bragg diffraction grating, wherein two consecutive corrugations in the Bragg diffraction grating are arranged on opposite sides of the Bragg diffraction grating with respect to each other. The invention also relates to a use of the device according to a first aspect of the invention to filter a Bragg wavelength value (λB) in the range of 450-1750 nm. Lastly, the invention further relates to a use of the device according to the first aspect of the invention in telecommunication systems, spectral filtering systems, laser systems and / or optical detection systems.

Description

[0001] BRAGG DIFFRACTION GRATING DEVICE INTEGRATED IN A WAVEGUIDE AND ITS USE

[0002] FIELD OF INVENTION

[0003] The present invention relates to integrated photonics devices. More specifically, the invention relates to a Bragg grating device integrated into a waveguide with alternating corrugations.

[0004] BACKGROUND OF THE INVENTION

[0005] The field of integrated photonics encompasses the fabrication and integration of various photonic components onto a common planar substrate. Such photonic components include, among others, beam splitters, diffraction gratings, wave couplers, polarizers, and interferometers. Typically, these components are incorporated into the fabrication of more complex devices that can perform a wide range of functions, with applications in telecommunications systems, LiDAR, instrumentation, or sensors.

[0006] In this context, optical waveguides are key elements of integrated photonics, where they are used not only for guiding optical signals, but also for coupling, switching, splitting, multiplexing, and / or demultiplexing them. Among the integrated photonics devices based on waveguides are integrated Bragg gratings (IBGs), where the effective refractive index changes periodically along the light-guiding direction of the waveguide. Due to this periodic change in the refractive index, an IBG is configured to reflect certain wavelengths.In particular, the IBG is configured to reflect those components of light that propagate inside it, and whose wavelength is included in a bandwidth centered on a value known as the Bragg wavelength (XB), which is given by AB=2 n. e f A, where n ef is the effective refractive index mentioned above, and A is the grating period of the Bragg grating. In the previous context, the grating period (A) is the length along the light guiding direction of each period of the Bragg grating where the effective refractive index of the grating changes. Thus, IBGs are generally used as reflectors or filters of specific wavelengths. For example, in IBGs used in telecommunications systems, their operational wavelength is generally around 1550 nm. This is because, around this wavelength, the loss during information transmission is remarkably low (around 0.2 dB / km) in the optical fibers that typically make up said telecommunications systems.

[0007] An example of IBGs are corrugated IBGs, where the periodic variation of the effective refractive index (n ef) is typically achieved by forming a plurality of periodic corrugations in a light-guiding substrate (i.e., a waveguide) that entail a periodic change in the width and / or thickness of said substrate. Typically, photolithographic techniques are used in the manufacture of this type of IBGs, that is, techniques that use light to transfer a pattern from a photomask to the surface of a substrate. Commonly, said substrate is composed of materials such as silicon and / or silicon nitride, among others. In this context, the effective refractive indices (n e f) in Bragg grating (BGR) devices obtained with lithographic methods on commonly used substrates (e.g., n e f = 2.2 on silicon substrates, n ef = 1 ,6 on silicon nitride substrates) require generating IBGs with grating periods (A) around 350 nm and 500 nm, so that the value of the Bragg wavelength (XB) of said IBG is around the 1550 nm characteristic of the telecommunications systems mentioned above. However, the dimensions of the corrugations and the separation between them according to what is described above may become incompatible with the minimum sizes that can be achieved with today's photolithographic techniques.

[0008] There are numerous proposals for the design and optimization of the structure and profile of IBGs that seek to obtain spectral responses appropriate to previously established requirements. Examples of such proposals are found, for example, in patent applications CN 114063216 A, CN 114675371 A and WO 2023065010 A1 , and in the articles R. Cheng et al., “Spectral Design of Silicon Integrated Bragg Gratings: A Tutorial'', Journal of Lightwave Technology, vol. 39, no. 3, R. Cheng et al., “Apodization of Silicon Integrated Bragg Gratings Through Periodic Phase Modulation", IEEE Journal of Selected Topics in Quantum Electronics, vol. 26, no. 2, and S. Kaushal et al., “Design of Ultra-Compact On-Chip Discrete Phase Filters for Broadband Dispersion Management', Journal of Lightwave Technology, vol. 39, No. 21. Some of these proposals mention the difficulties and resolution limitations that exist in the photolithography methods used to manufacture IBGs.However, none of the above proposals provide a solution that can be adapted to applications around wavelengths of 1500-1750 nm, nor to other lower wavelength bands such as 800-1310 nm or 480-650 nm.

[0009] Therefore, there is a need in the state of the art to provide integrated diffraction gratings (IBGs), where said integrated diffraction gratings contain structural elements that can be easily fabricated by means of the commonly available photolithographic fabrication methods and which as indicated may be difficult for applications in the 1500-1750 nm range but even impossible for other lower wavelength bands such as 800 nm-1310 nm in telecommunications or in sensor applications in the visible band (480 nm - 650 nm).

[0010] BRIEF DESCRIPTION OF THE INVENTION

[0011] The present invention provides a solution to the aforementioned need in the prior art. Thus, the present invention consists of an integrated Bragg diffraction grating comprising a plurality of corrugations. In particular, the arrangement of the corrugations in the integrated Bragg diffraction grating of the present invention is such that the number of corrugations is reduced and the separation between them is increased compared to Bragg diffraction gratings known in the prior art, while maintaining the phase condition (i.e., the Bragg wavelength (XB) of the diffraction grating) characteristic of said known integrated Bragg diffraction gratings.

[0012] Thus, in a first aspect the invention relates to a Bragg diffraction grating device integrated in a waveguide configured to guide a light beam inside the same in a light guiding direction (z), where said waveguide comprises in at least one region of said waveguide at least one Bragg diffraction grating with a grating period (A), such that said Bragg diffraction grating is divided in the light guiding direction into a plurality of sections, where the length of each section in the light guiding direction is substantially equal to the length of the grating period (A) for said section, where

[0013] - the Bragg diffraction grating comprises a first side and a second side where the second side is opposite the first side along the light guiding direction, such that each section of the Bragg diffraction grating comprises a portion of the first side and a portion of the second side of the Bragg diffraction grating; - the first and second sides of the Bragg diffraction grating each comprise a plurality of corrugations that are periodically repeated along the light guiding direction;

[0014] - each section of the Bragg diffraction grating comprises a single corrugation;

[0015] - the two corrugations included in two consecutive sections of the Bragg diffraction grating are located relative to each other on opposite sides of the Bragg diffraction grating; and

[0016] - the separation distance (g) between two consecutive corrugations in the light guiding direction on each side of the Bragg grating is greater than the grating period (A) of the Bragg grating.

[0017] In a second aspect, the invention relates to a use of the device according to the first aspect of the invention for filtering a Bragg wavelength value (XB) that is comprised in the range 450 nm-1750 nm.

[0018] Finally, in a third aspect, the invention relates to a use of the device according to the first aspect of the invention in telecommunications systems, spectral filtering systems, integrated dispersion compensation devices, integrated laser devices, and integrated optical sensors.

[0019] DESCRIPTION OF THE FIGURES Uniform standard integrated Bragg diffraction grating according to the state of the art. Uniform integrated Bragg diffraction grating according to a particular embodiment of the invention. Results of simulations with uniform standard integrated Bragg diffraction gratings according to the state of the art. Results of simulations with uniform integrated Bragg diffraction gratings according to a particular embodiment of the invention.

[0020] DETAILED DESCRIPTION OF THE INVENTION As indicated above, the invention consists of an integrated Bragg diffraction grating comprising a plurality of corrugations. In particular, the arrangement of the corrugations in the Bragg diffraction gratings of the present invention is such that the number of corrugations is reduced and the separation between them is increased compared to Bragg diffraction gratings known in the state of the art, while maintaining the phase condition (i.e., the Bragg wavelength (AB) of the diffraction grating) characteristic of said known integrated Bragg diffraction gratings.

[0021] Thus, in a first aspect, the invention relates to a Bragg diffraction grating device integrated in a waveguide configured to guide inside the same a light beam in a light guiding direction (z), where said waveguide comprises in at least one region of said waveguide at least one Bragg diffraction grating with a grating period (A), such that said Bragg diffraction grating is divided in the light guiding direction into a plurality of sections, where the length of each section in the light guiding direction is substantially equal to the length of the grating period (A) for said section, where

[0022] - the Bragg diffraction grating comprises a first side and a second side, where the second side is opposite the first side along the light guiding direction, such that each section of the Bragg diffraction grating comprises a portion of the first side and a portion of the second side of the Bragg diffraction grating;

[0023] - the first and second sides of the Bragg diffraction grating each comprise a plurality of corrugations that are periodically repeated along the light guiding direction;

[0024] - each section of the Bragg diffraction grating comprises a single corrugation;

[0025] - the two corrugations included in two consecutive sections of the Bragg diffraction grating are located relative to each other on opposite sides of the Bragg diffraction grating; and

[0026] - the separation distance (g) between two consecutive corrugations in the light guiding direction on each side of the Bragg grating is greater than the grating period (A) of the Bragg grating.

[0027] In the context of the invention, the term “Bragg grating device” refers to a device that, by the phenomenon of Bragg diffraction, is configured to selectively reflect and / or diffract a wavelength bandwidth of the radiation propagating inside said device. Specifically, the Bragg grating device of the present invention is integrated into a waveguide. Typically, these devices are known as integrated Bragg gratings (IBGs). In the context of the invention, the term “waveguide” refers to a transparent structure that provides a refractive index contrast between the interior of said structure and the exterior thereof, such that the structure is configured to guide a light beam inside it in a light guiding direction.In embodiments of the invention, the waveguide is surrounded by a surrounding material. In particular embodiments of the invention, the waveguide is composed of silicon (Si) with surrounding silicon oxide (SIO2) or Silicon On Insulator (SOI), by silicon nitride (SiSN^ with surrounding silicon oxide (S¡O2), by non-stoichiometric silicon nitride (S¡N. X ) with surrounding S¡02, by S¡02 doped with GeÜ2 in the core and S¡02 as surrounding material (silica technology), by polymers, and / or by semiconductor materials, preferably materials from groups III-V or groups I1-VI. The guides based on polymer and / or semiconductor materials may be in air, or alternatively surrounded by a surrounding material. As used herein, the term “core” is understood to mean the guide itself. That is, in the case of Si surrounded by S¡02 the guide is the rectangular section which is normally made of Si.

[0028] The waveguide comprises at least one Bragg diffraction grating in at least one region thereof. Specifically, in the present invention, the diffraction grating comprises periodic perturbations generated on the inner or outer side of the waveguide. In this sense, the perturbation can be generated internally, during the manufacture of the waveguide itself (core), or externally, that is, in the cover. Thus, in embodiments of the invention, the perturbation could be created on the "exterior" of the guide at a certain distance from the core by inserting voids filled with the core material such that the beam guided by the core, which also travels along the outside, is equally affected, although less weakly. These IBGs are used when less interaction of the light beam with the perturbation is required.Thus, the Bragg grating is a region inside or outside the waveguide comprising a first side and a second side, where the first side is opposite the second side along the light guiding direction, where the first and second sides of the Bragg grating each comprise a plurality of perturbations (i.e., a plurality of corrugations) that are repeated alternately on the first side and the second side, such that two consecutive corrugations in the Bragg grating are located relative to each other on opposite sides of the Bragg grating. Said Bragg grating comprises a plurality of sections, where the length of each section in the light guiding direction is substantially equal to the so-called grating period (A).In this sense, the above expression "substantially equal" refers to the fact that said length is equal to the grating period (A), except for deviations inherent to the generation process (i.e., manufacturing) of the Bragg diffraction grating. In a particular embodiment of the invention, the Bragg diffraction grating is generated by a photolithographic method. On the other hand, in particular embodiments of the invention, the number of sections comprised in the Bragg diffraction grating is between 200 and 10000, preferably between 200 and 4000. In particular embodiments of the invention, the number of sections comprised in the Bragg diffraction grating is 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4200, 4400, 4600, 4800, 5000, 5200, 5400, 5600, 5800, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, or 10000.

[0029] In the above context, the plurality of corrugations of the Bragg diffraction grating is equivalent to producing a periodic perturbation of the effective refractive index (n e f) from the interior of the waveguide in the region thereof comprising the Bragg diffraction grating. Consequently, the Bragg diffraction grating device is configured to reflect those components of the radiation propagating within it, the wavelength of which is included in a bandwidth centered on a value known as the Bragg wavelength (AB), which is given by the following equation: AB = 2 n e f A, where n ef is the effective refractive index in the region of the waveguide comprising the Bragg grating, and A is the grating period of said Bragg grating. In the context of the invention, guides that propagate a single mode, the fundamental mode, are usually used. If other modes exist, then they could be reflected according to the same equation where n e f would be the effective index of each mode, which is distinct. Furthermore, it is necessary to consider whether the mode is even or odd. If it is odd, the contributions from the "first side" are subtracted from the contributions from the "second side" and cancel each other out, which also occurs in standard IBGs.

[0030] As described above, the grating period (A) of the Bragg diffraction grating determines the value of the Bragg wavelength (AB) thereof, and, consequently, determines the spectral selectivity of said Bragg diffraction grating. In particular embodiments of the invention, the grating period (A) of the Bragg diffraction grating is between 100 nm and 500 nm.In particular embodiments of the invention, the red period (A) of the Bragg diffraction grating is substantially equal to 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, 195 nm, 200 nm, 205 nm, 210 nm, 215 nm, 220 nm, 225 nm, 230 nm, 235 nm, 240 nm, 245 nm, 250 nm, 255 nm, 260 nm, 265 nm nm, 270 nm, 275 nm, 280 nm, 285 nm, 290 nm, 295 nm, 300 nm, 305 nm, 310 nm, 315 nm, 320 nm, 325 nm, 330 nm, 335 nm, 340 nm, 345 nm, 350 nm, 355 nm, 360 nm, 365 nm, 370 nm, 375 nm, 380 nm, 385 nm, 390 nm, 395 nm, 400 nm, 405 nm, 410 nm, 415 nm, 420 nm, 425 nm, 430 nm, 435 nm, 440 nm, 445 nm, 450 nm, 455 nm, 460 nm, 465 nm, 470 nm, 475 nm, 480 nm, 485 nm, 490 nm, 495 nm, or 500 nm.In the above context, the expression “substantially equal” means that the grating period (A) is equal to the corresponding value, except for deviations inherent in the Bragg grating generation process. The value for the grating period (A) in a specific device will be determined by the wavelength of the specific application (which will determine AB) and by the technology / material from which the waveguide is manufactured (which will determine n). e f). In particular embodiments of the present invention, the value of the grating period (A) may be constant in the Bragg diffraction grating, or it may be variable in the Bragg diffraction grating, A(z), along the light guiding direction (z). Such that the invention is compatible with frequency modulated (chirp) Bragg diffraction gratings or with any other type of amplitude or phase design, as explained below.

[0031] On the other hand, the Bragg diffraction grating has a duty cycle (DC), which is given by the ratio between the perturbation width (p) and the grating period (A), where the perturbation width (p) is the length of the perturbation in the light-guiding direction (z). Thus, the duty cycle can be represented by the equation DC=p / A. For a grating with DC=0.5, the maximum effect of the perturbations is obtained, while for DC<0.5 and DC>0.5 the effect is reduced. In this way, the strength of a BGI can be "modulated" in such a way that a greater or lesser reflectivity or intensity of the reflected signal in AB is produced. In particular embodiments of the invention, the duty cycle of the Bragg diffraction grating is substantially equal to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%.In a particular embodiment of the invention, the duty cycle of the Bragg diffraction grating is substantially equal to 50%. In the previous context, the expression “substantially equal” refers to said duty cycle being equal to the corresponding value, except for deviations inherent to the generation of the Bragg diffraction grating. In the context of the invention, a duty cycle of the Bragg diffraction grating equal to 50% implies a separation distance (g) between two consecutive corrugations in the light guiding direction that is substantially equal to 1.5 times the grating period (A). In general, g = A*(2-DC) where DC belongs to the interval (0, 1). Thus, if DC=0.5, then g=1.5 A; if DC=0.2, then g=1.8 A; etc.Thus, the separation distance (g) between two consecutive corrugations in the light guiding direction on each side of the Bragg diffraction grating is greater than the grating period (A) of the Bragg diffraction grating, and less than twice the grating period (A). In particular embodiments of the invention, said separation distance (g) is 1, 1; 1, 2; 1, 3; 1, 4; 1, 5; 1, 6; 1, 7; 1, 8; or 1, 9 times the grating period (A). In a particular embodiment of the invention, the separation distance (g) between two consecutive corrugations in the light guiding direction is substantially equal to 1, 5 times the grating period (A). In this sense, the above expression “substantially equal” refers to the separation distance (g) between two consecutive corrugations in the light guiding direction being equal to the corresponding value, except for deviations inherent to the Bragg diffraction grating generation process.In the context of the invention, the duty cycle (DC) can be variable along the light guiding direction (z), i.e., DC(z) along the IBG. This modification would be equivalent to the case of frequency-modulated (“chirped”) Bragg gratings and is equally applicable to eliminating alternating disturbances. The variation of DC(z) is called “windowing” or “apodization” and is used to provide the IBG with certain improved performance in the shape of its spectrum.

[0032] Likewise, in particular embodiments of the invention, the effective refractive index (n e f) in at least one region of the Bragg diffraction grating, is between 1.5 and 2.5. In particular embodiments of the invention, the effective refractive index (n ef) in at least one region of the Bragg diffraction grating is substantially equal to 1 , 5, 1 , 6, 1 , 7, 1 , 8, 1 , 9, 2.0, 2, 1 , 2.2, 2.3, 2.4, or 2.5. In this sense, the expression “substantially equal” refers to said effective refractive index (n e f) is equal to the corresponding value, except for deviations inherent to the generation of the Bragg grating.

[0033] Each corrugation in a Bragg diffraction grating has a width (AW). In the context of the present invention, the “width” (AW) of a corrugation refers to its maximum length in the direction perpendicular to the light guiding direction. The width of the corrugations in a Bragg diffraction grating determines the intensity (“strength”) of said diffraction grating, i.e., it determines the reflectivity of the Bragg-directed grating. In the context of the invention, the term “reflectivity” refers to the ratio of the energy of the radiation entering the Bragg diffraction grating to the energy of the radiation reflected therefrom. In particular embodiments of the invention, the width (AW) of the corrugations within the Bragg diffraction grating is between 50 nm and 600 nm.In particular embodiments of the invention, the width of the corrugations comprised in the Bragg grating is substantially equal to 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, or 600 nm. In the above context, the expression “substantially equal” refers to said width (AW) being equal to the corresponding value, except for deviations inherent in the generation of the Bragg diffraction grating. In embodiments of the invention, all corrugations have the same width (AW). In alternative modes of the invention, the corrugations may be of variable width (AW). That is, each corrugation can have a different width (AW).

[0034] Furthermore, in particular embodiments of the invention, the corrugations may have a rectangular shape or smoothed flanks, depending on the type of manufacturing process. In a particular embodiment of the invention, the corrugations within the Bragg diffraction grating have a substantially rectangular shape. In the above context, the term "substantially rectangular" refers to the fact that said corrugation has a rectangular shape, except for deviations inherent in the generation of the Bragg diffraction grating. In certain embodiments, all corrugations have the same shape. In alternative embodiments, the corrugations may have a variable shape, with different AW(z) values ​​along the Bragg diffraction grating, which generally vary "slowly" with respect to z compared to A.This is what is called apodization or windowing of the disturbance and is typically used to reduce the amplitude of the secondary lobes in the spectral response or the ripple of the group delay in linear frequency modulated (chirp) diffraction gratings with applications for example in chromatic dispersion compensation.

[0035] Thus, in particular embodiments of the invention, the Bragg grating is a uniform Bragg grating, or an apodized and / or frequency-modulated Bragg grating. In the above context, the term “uniform Bragg grating” refers to the effective refractive index (n ef), the perturbation width AW and the Bragg period A are substantially equal throughout the region of the waveguide comprising the Bragg grating. In the previous context, the expression “substantially equal” refers to the fact that the cited parameters are equal (i.e., constant) throughout that region, except for deviations inherent to the generation of the Bragg grating. On the other hand, in the context of the present invention, the term “apodized” Bragg grating refers to the fact that the value of AW in the region of the waveguide comprising the Bragg grating varies gradually along said region. In particular embodiments of the invention, the apodized Bragg grating is a Gaussian apodized Bragg grating.Furthermore, in the context of the present invention, the term “chirp Bragg grating” refers to the fact that the value of the Bragg period (A) varies along the Bragg grating. In this case, the Bragg period in the frequency modulated Bragg grating typically varies with A(z) where n. e f constant. Alternatively, A may be constant and n e f(z) variable, since in both cases the AB = 2 n e f A is modified AB(Z).

[0036] In particular embodiments of the present invention, the waveguide of the device comprises more than one Bragg diffraction grating, where each Bragg diffraction grating is comprised in a different region in the z propagation direction of said waveguide. In particular embodiments of the invention, the value of the Bragg wavelength (AB) is substantially the same for all of the more than one Bragg diffraction grating comprised in different interior regions of said waveguide. In the previous context, the expression “substantially the same” refers to the corresponding value being the same, except for deviations inherent in the generation of the Bragg diffraction grating.In particular embodiments of the invention, the value of the Bragg wavelength of at least one of the more than one Bragg diffraction grating comprised in different interior regions of said waveguide is different with respect to the value of the Bragg wavelength of the rest of the more than one Bragg diffraction grating comprised in different interior regions of said waveguide. In particular embodiments of the invention, the value of the grating period (A) of at least one of the more than one Bragg diffraction grating comprised in different interior regions of said waveguide is different with respect to the value of the grating period (A) of the rest of the more than one Bragg diffraction grating comprised in different interior portions of said waveguide. That is, the Bragg diffraction gratings may have the same value of the grating period (A), or they may have a different value of the grating period (A) from one another.

[0037] In embodiments of the present invention, the value of the Bragg wavelength (AB) of the at least one Bragg diffraction grating is in the range 450 nm-1750 nm. In particular embodiments of the invention, the value of the Bragg wavelength (AB) of the at least one Bragg diffraction grating is in the range 480 nm-650 nm covering the visible range, or is in the range between 800 nm and 1750 nm covering the O, E, S, C, L and U bands of the infrared in the context of optical communications.In particular embodiments of the invention, the value of the Bragg wavelength (AB) of the at least one Bragg diffraction grating is in the range 1260-1360 nm (O Band, Original), in the range 1360-1460 nm (E Band, Extended), in the range 1460-1530 nm (S Band, Short Wavelength), in the range 1530-1565 nm (C Band, Conventional), in the range 1565-1625 nm (L Band, Long Wavelength), or in the range 1625-1675 nm (U Band, Ultra Long Wavelength). Thus, in a second aspect, the invention relates to a use of the device according to the first aspect of the invention for filtering a Bragg wavelength value (AB) that is comprised in the range 450 nm-1750 nm, preferably that is comprised in the range 480 nm-650 nm covering the visible range, or preferably that is comprised in the range between 800 nm and 1750 nm covering the O, E, S, C, L and U bands of the infrared in the context of optical communications.In accordance with the foregoing, the spectral selectivity of the waveguide-based Bragg grating device according to the present invention allows its use in a wide variety of systems. Thus, a third object of the present invention relates to the use of the waveguide-based Bragg grating device according to any of the embodiments of the invention described herein, in telecommunications systems, spectral filtering systems, integrated dispersion compensation devices, integrated laser devices, and integrated optical sensors.For example, in non-limiting embodiments, the waveguide-based Bragg grating device according to the present invention may be employed as a filter, a multiplexer, and / or a demultiplexer in telecommunications systems, or as a filtering reflector element as part of an External Cavity Laser (ECL).

[0038] All of the terms and embodiments described above are applicable to any aspect and embodiment of the invention. In accordance with the present invention, the singular term "the," "a," "one," "an," equally refers to its plural counterpart, "the," "the," "some," "somes," unless it is clear from the context that the term clearly refers to a species in the singular. The term "comprises" or "comprising," as used herein, also describes "consists of" or "consisting of" in accordance with generally accepted patent practice. EXAMPLES

[0039] The following invention is described by means of the following examples, which should be interpreted as merely illustrative and not limiting the scope of the invention.

[0040] Figure 1 shows an example of a standard integrated Bragg grating (IBG), where a uniform standard Bragg grating is included in a region of a waveguide according to the prior art. Said standard Bragg grating is manufactured such that it is divided into a plurality of sections of length equal to a grating period (A) in the light guiding direction of said waveguide. Furthermore, the standard Bragg grating comprises a first side and a second side opposite each other, which run in parallel with respect to said light guiding direction.

[0041] On the other hand, both the first side and the second side of the standard Bragg grating each comprise a plurality of rectangular corrugations. The width (AW) of all corrugations in Figure 1 is the same along the entire Bragg grating. Furthermore, the separation (W) in the direction perpendicular to the light guiding direction between a portion of the first side of the Bragg grating of Figure 1 and an opposite portion of the second side thereof that does not comprise corrugations is the same along the entire standard Bragg grating. Furthermore, on each side of the standard Bragg grating, the separation distance (g) between two consecutive corrugations is equal to 0.5 times the grating period (A).Likewise, each region of the standard Bragg grating comprises a corrugation on each side of the grating, such that each corrugation on the first side of the standard Bragg grating is faced by a corrugation on the second side of the grating.

[0042] In the previous context, when in Figure 1 a light beam is guided from left to right in the standard Bragg diffraction grating, in each periodic section, the different modes included in said beam interact with the corrugation (perturbation) of the first side and with the corrugation of the second side. Consequently, among the components of different optical frequencies of the light beam that are guided inside the waveguide, those whose wavelength is included in a bandwidth centered on the Bragg wavelength (XB) are reflected by the standard Bragg diffraction grating, according to the equation: AB = 2 n e f A, where n ef is different for each mode. That is, the waves experience small reflections at discontinuities (called perturbations) that cause the light beams to deviate from their normal course and radiate in other directions, giving rise to many types of Bragg gratings. In this case, those that couple light in exactly the opposite direction according to the famous formula AB = 2 n are described here. e f A.

[0043] Figure 2 shows, in contrast, an IBG where a uniform Bragg grating is comprised in a portion of a waveguide according to a particular embodiment of the present invention. Analogously to the Bragg grating of Figure 1 , the Bragg grating of Figure 2 is divided into a plurality of sections of length equal to a grating period (A) in the light guiding direction of the waveguide. Furthermore, the Bragg grating of Figure 2 also comprises a first side and a second side opposite with respect to said light guiding direction, where both the first side and the second side thereof each comprise a plurality of rectangular corrugations. The width (AW) of all the corrugations of Figure 2, is the same along the entire Bragg grating.Also, in Figure 2 the separation (W) in the direction perpendicular to the light guiding direction between a portion of the first side of the Bragg grating and an opposite portion of the second side of the same that does not comprise corrugations, is the same along the entire Bragg grating.

[0044] However, unlike the standard Bragg grating in Figure 1 , each Bragg grating region comprises a single corrugation, and the two corrugations in two consecutive Bragg grating regions lie on opposite sides of each other. Specifically, in Figure 2, the separation distance (g) between two consecutive corrugations on either side of the Bragg grating is equal to 1.5 times the grating period (A) since for this particular example the duty cycle is 50% (DC=0.5).

[0045] In the previous context, the Bragg diffraction grating of Figure 2 is equivalent to alternatively “eliminating” on each side the corrugations of the Bragg diffraction grating of Figure 1 , without modifying the grating period (A) thereof. Thus, when in Figure 2 a light beam is guided from left to right in the Bragg diffraction grating according to the present invention, in each region the different modes comprised in said beam interact with a single corrugation of the Bragg diffraction grating. Consequently, the intensity of said interaction is reduced by half compared to Figure 1 , but the components of the light beam reflected by the Bragg diffraction grating of Figure 2 are also those whose wavelength is comprised in a bandwidth centered on the Bragg wavelength (AB), that is, a bandwidth centered on AB = 2 n e f A.

[0046] 2: Results of diffraction grating simulations

[0047] Figure 1 shows an example of a standard integrated Bragg grating (IBG) while Figure 3 shows a graph of the results of FDTD (Finite Domain Time Difference) simulations simulating the guiding of a light beam through five grating periods in a standard IBG device, analogous to the one shown in Figure 1. In particular, in said simulations the standard Bragg gratings comprise more sections than the standard Bragg grating of said Figure 1 , namely 200 periodic sections with a grating period (A) of 404.6 nm. Furthermore, the standard Bragg gratings comprise rectangular corrugations on either side of each standard Bragg grating, where the separation distance (g) between two consecutive corrugations on each side is equal to 0.5 times the grating period (A). Consequently, the duty cycle of said standard Bragg gratings is equal to 50%.On the other hand, along each standard Bragg grating, the separation (W) in the direction perpendicular to the light progradation direction between a portion of the first side of the standard Bragg grating and an opposite portion of the second side thereof which does not comprise corrugations, is the same along the entire standard Bragg grating and equal to 1 .m. Furthermore, the effective refractive index (n. ef) of the waveguide width W is equal to 1.9112 (according to the materials used in the simulation example), so that for a target Bragg wavelength of 1545 nm the aforementioned Bragg period (A=404.6 nm) has been set. Thus, the standard Bragg gratings of each simulation differ in the width (AW) of the corrugations, so that in the first standard Bragg grating this width (AW) is equal to 100 nm, in the second it is equal to 150 nm, in the third it is equal to 200 nm, in the fourth it is equal to 400 nm, and in the fifth it is equal to 600 nm.

[0048] In this context, Figure 3 shows the reflectivity as a function of wavelength (A) of a simulated light beam guided from left to right in the standard IBGs device described above. As expected, the reflectivity maxima are located around the target Bragg wavelength (AB) for simulating these gratings (1545 nm). Furthermore, the reflectivity around the Bragg wavelength (AB) increases with the corrugation width (AW).

[0049] Figure 2 shows, in contrast, an IBG where a uniform Bragg grating is comprised in a portion of a waveguide according to a particular embodiment of the present invention, while Figure 4 shows in a graph the results of FDTD simulations simulating the guiding of a light beam in an IBG device according to the present invention, analogous to that shown in Figure 2. In said simulations, the Bragg gratings comprise 200 sections of length equal to a grating period (A) of 404.6 nm, and rectangular corrugations on either side of each Bragg grating. However, the separation distance (g) between two consecutive corrugations on either side is equal to 1.5 times the grating period (A). Consequently, the duty cycle of said Bragg gratings is equal to 50%.On the other hand, as for the standard gratings in the simulations of Figure 3, the separation (W) in the direction perpendicular to the light progradation direction between a portion of the first side of the Bragg grating and an opposite portion of the second side that does not comprise corrugations, is the same along each Bragg grating and is equal to 1 .m. Likewise, the effective refractive index (n. e f) is equal to 1.89. Furthermore, the Bragg diffraction gratings of each simulation differ again in the width (AW) of the corrugations, so that in the first Bragg grating this width (AW) is equal to 100 nm, in the second it is equal to 150 nm, in the third it is equal to 200 nm, in the fourth it is equal to 400 nm, and in the fifth it is equal to 600 nm.

[0050] Thus, Figure 4 shows the reflectivity as a function of wavelength (A) of a simulated light beam being guided from left to right through the IBG device according to the present invention described above. Indeed, comparing the results in Figures 3 and 4, it can be seen that the reflectivity of the simulated light beam in Bragg gratings according to the present invention is lower than in standard gratings. However, as described above, the reflectivity maxima in Figure 4 are located around the same Bragg wavelength (AB) targeted in the simulation as those in Figure 3 (1545 nm). On the other hand, again, the reflectivity around the Bragg wavelength (AB) is higher the wider the corrugations (AW).In Figure 4, a shift to the right is observed as AW increases because the corrugations / disturbances themselves have a certain influence on the average refractive index experienced by the propagating beam. That is, n. e f increases slightly with increasing AW. This is a normal and well-known phenomenon in Bragg gratings. There are methods to compensate for this effect. However, the simulation in Figure 4 did not use such methods to keep the model simpler. To give you an idea, a 20 nm shift at 1550 nm represents 20 / 1550 = 1.2%, i.e., n e f increases from 1.89 (unperturbed guide) to 1.91 due to the presence of perturbations. This is much less the case with the IBGs of the invention, where the IBGs are "decimated" because there are fewer perturbations and they affect the beam less, although a slight shift is also observed.

Claims

CLAIMS 1. A Bragg diffraction grating device integrated in a waveguide configured to guide a light beam inside the waveguide in a light guiding direction (z), wherein said waveguide comprises in at least one region of said waveguide at least one Bragg diffraction grating with a grating period (A), such that said Bragg diffraction grating is divided in the light guiding direction into a plurality of sections, where the length of each section in the light guiding direction is substantially equal to the length of the grating period (A) for said section, where - the Bragg diffraction grating comprises a first side and a second side, where the second side is opposite the first side along the light guiding direction, such that each section of the Bragg diffraction grating comprises a portion of the first side and a portion of the second side of the Bragg diffraction grating; - the first and second sides of the Bragg diffraction grating each comprise a plurality of corrugations that are periodically repeated along the light guiding direction; - each section of the Bragg diffraction grating comprises a single corrugation; - the two corrugations included in two consecutive sections of the Bragg grating are located relative to each other on opposite sides of the Bragg grating; and - the separation distance (g) between two consecutive corrugations in the light guiding direction on each side of the Bragg grating is greater than the grating period (A) of the Bragg grating.

2. The device according to claim 1, wherein the length of the grating period (A) of the Bragg diffraction grating is between 100 nm and 500 nm.

3. The device according to any one of claims 1 to 2, wherein on each side of the Bragg diffraction grating, the separation distance (g) between two consecutive corrugations in the light guiding direction is substantially equal to 1.5 times the grating period (A) of the Bragg diffraction grating.

4. The device according to claim 3, wherein the duty cycle of the Bragg diffraction grating is substantially equal to 50%.

5. The device according to any one of claims 1 to 4, wherein the number of sections comprised in the Bragg diffraction grating is between 200 and 10000.

6. The device according to any one of claims 1 to 5, wherein the effective refractive index (n e f) in at least one region of the Bragg diffraction grating, it is between 1.5 and 2.

5.

7. The device according to any one of claims 1 to 6, wherein the waveguide is composed of silicon (Si) with surrounding silicon oxide (SIO2) or Silicon On Insulator (SOI), by silicon nitride (ShN4) with surrounding silicon oxide (SÍÜ2), by non-stoichiometric silicon nitride (S¡N X ) with surrounding S¡O2, by GeÜ2-doped S¡O2 in the core and SÍÜ2 as surrounding material, by polymers, and / or by semiconductor materials, preferably materials from groups III-V or groups II-VI.

8. The device according to any one of claims 1 to 7, wherein the width (AW) of the corrugations comprised in the Bragg diffraction grating is between 50 nm and 600 nm.

9. The device according to any one of claims 1 to 8, wherein the corrugations comprised in the Bragg diffraction grating are substantially rectangular.

10. The device according to any one of claims 1 to 9, wherein the Bragg diffraction grating is a uniform Bragg diffraction grating, or an apodized and / or frequency modulated Bragg diffraction grating.

11. The device according to claim 10, wherein the apodized Bragg diffraction grating is a Gaussian apodized Bragg diffraction grating.

12. Use of the device according to any one of claims 1 to 11, for filtering a Bragg wavelength value (XB) that is comprised in the range 450 nm-1750 nm.

13. Use of the device according to claim 12, for filtering a Bragg wavelength value (XB) that is comprised in the range 480 nm-650 nm covering the visible range, or that is comprised in the range between 800 nm and 1750 nm covering the O, E, S, C, L and U bands of the infrared in the context of optical communications.

14. Use of the device according to claim 13, for filtering a Bragg wavelength value (XB) that is comprised in the range 1260-1360 nm (O Band, Original), in the range 1360-1460 nm (E Band, Extended), in the range 1460-1530 nm (S Band, Short Wavelength), in the range 1530-1565 nm (C Band, Conventional), in the range 1565-1625 nm (L Band, Long Wavelength), or in the range 1625-1675 nm (U Band, Ultra-Long Wavelength).

15. Use of the device according to any one of claims 1 to 11, in telecommunications systems, spectral filtering systems, integrated dispersion compensation devices, integrated laser devices, and integrated optical sensors.

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