WO2013124502A1 - Waveguide coupling device and method for designing same - Google Patents

Waveguide coupling device and method for designing same Download PDF

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Publication number
WO2013124502A1
WO2013124502A1 PCT/ES2013/000048 ES2013000048W WO2013124502A1 WO 2013124502 A1 WO2013124502 A1 WO 2013124502A1 ES 2013000048 W ES2013000048 W ES 2013000048W WO 2013124502 A1 WO2013124502 A1 WO 2013124502A1
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waveguides
network
wavelength
variation
coupling
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PCT/ES2013/000048
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Spanish (es)
French (fr)
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Robert Halir
Alejandro Maese Novo
Alejandro ORTEGA MOÑUX
Iñigo MOLINA FERNANDEZ
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Universidad De Malaga
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/34—Optical coupling means utilising prism or grating
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2808—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs
    • G02B6/2813—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs based on multimode interference effect, i.e. self-imaging

Definitions

  • the present invention pertains to the field of telecommunications and integrated optics, and more specifically to light couplers between waveguides.
  • the main object of the present invention is a waveguide coupler device, which stands out for having a considerable bandwidth, without implying an oversizing of the device, and without negatively affecting its response in phase.
  • the design method of said coupling device is another object of the invention.
  • coupling devices or waveguide couplers are known, which constitute the fundamental elements in integrated photonic circuits (PIC).
  • Said devices fulfill among others the functions of dividing or combining power between said guides and imposing specific offset between the waves coupled to each waveguide.
  • Said waveguide couplers are used, among other applications, in wavelength demultiplexers, switches, coherent receivers and biosensors.
  • AD directional couplers
  • MMI multi-modal interference couplers
  • the shake length (L K ) indicates the distance a light beam must travel to be fully transferred from one waveguide to another waveguide.
  • this beat length (L var ⁇ a ) varies with the wavelength of said light beam, so that the bandwidth in the coupler is limited.
  • AD directional coupler
  • multimodal interference couplers these consist of several input and output waveguides and a coupling zone (ZA M MI), which guides various modes ( ⁇ , ⁇ 2 , ⁇ 3 , ...), as shown in Figure 2.
  • Such interference couplers multimodal (MM) generally have a polarization-dependent behavior; In what follows we will focus without loss of generality on a specific polarization state, for example a horizontal (quasi-TE) or vertical (quasi-TM) polarization.
  • a ray of light is launched in one of the input waveguides and excites various modes ( ⁇ , ⁇ 2 , ⁇ 3 , ...) in the coupling zone (ZAMM I ), which propagate with different constants of propagation ( ⁇ , ⁇ 2> ⁇ 3> ).
  • the modes ( ⁇ , ⁇ 2 , ⁇ 3 , ..) interfere forming one or more images of the input excitation.
  • the output waveguides are placed in the position of these images, so that the light is coupled to them.
  • Multimodal interference couplers have a bandwidth greater than directional couplers (AD), but such bandwidth is still limited by the variation of the beat length (L n ) with the wavelength.
  • the bandwidth of multimodal interference couplers (MMI) decreases as the number of inputs and / or outputs increases (P. Besse et al, "Optical bandwidth and fabrication tolerances of multimode interference couplers", 1994).
  • the above-mentioned technical problem is solved by providing a waveguide coupler device that presents a considerable increase. of its bandwidth with respect to the current devices, without this implying an increase in the size of the device, and without its phase response being degraded.
  • the coupling device object of the invention is of the type comprising at least one input waveguide in which a light beam, at least one output waveguide, and a coupling zone located between said waveguides is injected input and output, said coupling zone being configured to couple the light beam of the input waveguide to the output waveguide.
  • the coupling device mainly stands out for presenting in the coupling area at least one network consisting of a substrate, a core and a coating, said network having a period less than half of the wavelength less than the operating range of the coupler device (it is understood that each coupler device works for a certain range of wavelengths), divided by the lower indexes of refraction of the substrate, the core and the lining of the network, and ensuring that no phenomena of diffraction (radiation and reflection are negligible for practical purposes),
  • a network of these characteristics will be called simply a network.
  • the modes that support these networks have periodic field distributions and are called Floquet modes or Bloch modes; Hereinafter they will simply be called modes.
  • Said network is configured to modify the variation of the propagation constants ( ⁇ 1; ⁇ 2 ) of the first and second order modes ( ⁇ ⁇ , ⁇ 2 ) of the coupling area with respect to the wavelength, so that the variation of the beat length with the wavelength is reduced, thus increasing the bandwidth of the coupling device.
  • said network comprises a segmented waveguide whose elements are arranged periodically, perpendicular to the direction of propagation of the light beam, and with a period less than the first order Bragg period.
  • the present invention proposes the use of the dispersive properties of said networks, that is, the variation of their properties with the operating wavelength of the device.
  • uniform waveguide will be used here to refer to conventional waveguides, in order to distinguish them from those guides that use networks.
  • the waveguides described herein can be designed for a given range of wavelengths; and that the input and output waveguides can be uniform waveguides or networks.
  • the coupling device of the invention further comprises in the area of coupling at least two guides uniform waves, where the network is configured to modify the variation of the propagation constants ( ⁇ , ⁇ 2) the first and second order modes ( ⁇ , ⁇ 2 ) in the coupling area as a function of the wavelength, so that the variation of the beat length with the wavelength is reduced, thus increasing the width of device band, working in this case as a directional coupler, with a predefined division ratio.
  • the network is arranged essentially perpendicular to the uniform waveguides.
  • the duty cycle and the lateral extension of the network are configured so that the excitation of the third order mode ( ⁇ 3 ) that produces an unwanted power transfer between the guides is reduced of uniform waves.
  • the network of the coupling zone is adapted to support at least two guided modes of the same polarization (quasi-TE or quasi-TM), where the network is configured to modify the variation with the length wavelength of the propagation constants of the modes in the coupling area, so that the variation of the beat length with the wavelength is reduced, thereby increasing the bandwidth of the device, which in this case works as a multimodal interference coupler.
  • the coupling device thus configured has smaller modal phase errors than a conventional multimodal interference coupler, that is, the propagation constants of the higher modes better follow the parabolic law required to form high quality images.
  • the design method of the coupling device described above comprises at least the following steps: a) it is based on a waveguide where its design parameters and materials are defined for the substrate, the core and the coating,
  • the period of the network is adjusted to a slightly lower value than the first order Bragg period, so that diffraction phenomena do not occur
  • step d) if in step d) it has been possible to reduce the variation of the beating length, the period of the network is adjusted again by reducing it slightly,
  • step e) if in step e) it has not been possible to reduce the beating length, the value of the period for which said beating length had been reduced is chosen, and
  • the complete coupling device is designed for the period value of step e2), for which a maximum increase in its bandwidth is obtained.
  • the parameters set in phase a) is at least one selected from: period, duty cycle, gap, thickness, engraving depth, width, distance, and lateral extension. DESCRIPTION OF THE DRAWINGS
  • Figure 1. Shows a schematic view of a conventional directional coupler.
  • Figure 2. Shows a schematic view of a conventional multimodal interference coupler.
  • Figure 4.- Shows a graph that represents the variation of the beat length with respect to the wavelength using a conventional directional coupler.
  • Figure 5. Shows a view of the coupling device of the invention configured to work as a directional coupler, according to a first preferred embodiment.
  • Figure 6. Shows another graph that represents the variation of the beat length with respect to the wavelength using now the directional coupler device according to the first embodiment of the invention.
  • Figure 7. Shows a graph where the insertion losses of the directional coupler device of the invention are simulated, compared with the insertion losses of a conventional directional coupler.
  • Figures 8a, 8b.- Show the simulated phase response of the directional coupler device of the invention.
  • Figure 9. Shows a graph that represents the variation of the beat length with respect to the wavelength using a conventional multimodal interference coupler.
  • Figure 10. Shows a view of the coupling device of the invention configured to work as a multimodal interference coupler, according to a second preferred embodiment.
  • Figure 11.- Shows a graph that represents the variation of the beat length with respect to the wavelength using the multimodal interference coupling device according to the second embodiment of the invention.
  • Figures 12a, 12b.- They show the performance of the multimodal interference coupling device according to the second preferred embodiment of the invention, compared with those of a conventional multimodal interference coupler.
  • Figure 13 Shows a schematic view of a multimodal interference coupling device according to the present invention, presenting a 2x4 configuration.
  • FIGS 14a, 14b, 14c, 14d.- show the performance of the 2x4 multimodal interference coupling device of Figure 13.
  • Figure 15.- Shows a view of the coupling device of the invention configured for work as a broadband polarization separator, according to a third preferred embodiment.
  • the coupling device (1) and the network (31) it contains are designed with a substrate (2) formed by silicon dioxide, a silicon core (3), and a polymer coating (4) SU-8.
  • the refractive indices at the free space wavelength of 1.55 ⁇ are , 58 respectively.
  • quasi-TE horizontal polarization is assumed (in the direction of the x-axis).
  • the coupling device (1) of the invention configured as a directional coupler is described below.
  • the length of the coupling zone is set at LJ2 at the center wavelength, that is, at 1, 55 ⁇ .
  • the beat length (L Subject) changes and the device is no longer tuned. Therefore, in order to increase the bandwidth of the device it is necessary to reduce the variation of the beat length (L z ) with the wavelength.
  • Figure 5 shows the coupling device (1) configured according to the present invention to work as a directional coupler and by means of which it is possible to reduce the variation of the beat length (L réelle) with the wavelength, thereby increasing the bandwidth of the coupling device (1).
  • a 2x2 configuration of the coupling device (1) is observed with two input waveguides (10a, 10b) and two output waveguides (20a, 20b) between which is a coupling zone (30).
  • Said coupling area (30) has a network (31).
  • the lateral extension (t) of the network (31) has been increased on both sides of the waveguides (10a, 10b, 20a, 20b). In this particular case a lateral extension ⁇ > 0.4 ⁇ has been found to be sufficient to reduce said excitation in the third order mode ( ⁇ 3 ).
  • the variation of the beat length (L K ) with the wavelength is controlled using the dispersive properties of the network (31), that is, the variation with the wavelength of the propagation constants ( ⁇ 1? ⁇ 2 ) of the first and second order modes ( ⁇ 1? ⁇ 2 ).
  • These dispersive properties can be configured with the period (A) and the duty cycle (DC) of the network (31), which in turn control the Bragg wavelength of the network (31).
  • the variation of the beat length (L rt ) with the wavelength is significantly reduced, as represented in the graph in the figure 6.
  • the beat length (L, i) of the coupling device (1) object of the invention varies only by 8% in the wavelength band from 1.5 ⁇ to ⁇ , ⁇ , which means a reduction by a factor five compared to a conventional directional coupler.
  • Figures 8a and 8b show the phase response of the 2x2 directional coupler device (1) of Figure 5. More specifically in Figure 8a, the offset between the light beams in the output waveguides (20a, 20b) is shown. ) when a light beam is injected into the input waveguide (10a). Thus, it is observed that the offset is very close to the ideal value of 90 ° in the entire band of wavelengths considered, that is, from 1, 5 ⁇ to ⁇ , ⁇ ⁇ ⁇ .
  • Figure 8b shows the differential lag with which Light waves from the input waveguides (10a, 10b) are combined in the output waveguides (20a, 20b). It is observed that the differential offset is very close to the ideal value of 180 ° in the entire wavelength band considered.
  • the reflection of the directional coupler device (1) of the present invention is maintained below -15dB in the entire band of wavelengths considered, from 1.5 ⁇ to ⁇ , ⁇ .
  • the coupling device (1) of the invention configured to work as a multimodal interference coupler, hereinafter referred to as "MMI" coupler, is described.
  • Figure 9 shows a graph showing the variation of the beat length ( ⁇ , ⁇ ) with respect to the wavelength of a conventional MMI coupler.
  • a conventional MMI coupler uniform input and output waveguides with a separation distance (s) of 2 ⁇ and a width (WMMI) of 6 ⁇ have been considered, see figure 2.
  • s separation distance
  • WMMI width
  • the wavelength of the coupling zone (30) has been set to optimize the device to the central wavelength, that is, at 1 , 48 ⁇ .
  • the beat length (L n ) changes and the device is tuned, worsening its performance.
  • Figure 10 shows a coupler device (1) 2x2, with two input waveguides (10a, 10b) and two output waveguides (20a, 20b), configured according to the present invention to work as an MMI coupler, by presenting in the coupling area (30) a network (31) that allows to reduce the variation of the beat length ( ⁇ ⁇ ) with respect to the wavelength at which the device operates, resulting in an increase in its bandwidth.
  • the MMI coupling device (1) is shown in a 2x2 configuration, however it is provided that it can be configured according to any other configuration, such as 1x2, 1x4, 2x2, 2x3, 3x3 and 2x4, always presenting the area of coupling (30) at least one network (31).
  • the MMI coupling device (1) By properly configuring the period ( ⁇ ) and the duty cycle (DC) of the network (31), you can control the variation with the wavelength of the propagation constants ( ⁇ , ⁇ 2 ) of the first and second order modes ( ⁇ , ⁇ 2 ) of the coupling area (30). In fact, choosing a coupling area width (30) of 6 ⁇ , and a duty cycle (DC) of 50% and a period of it is possible to reduce the variation of the shake length (L n ) to approximately 10%, as shown in Figure 1 1. Note that although in the present embodiment only the shake length ( n ) of the two first and second order modes ( ⁇ ⁇ 5 ⁇ 2 ) of the coupling zone (30), the MMI coupling device (1) also has excellent performance for other relevant modes of the coupling zone (30).
  • FIG. 12a shows a graph in which the insertion losses (PI) and the imbalance (Unb) of a MMI 2x2 coupling device (1) according to the invention are simulated, comparing them with those of a conventional MMI coupler. All simulations include the effect of material dispersion.
  • the coupling device (1) MMI of the invention has a bandwidth of 500nm, from 1.25 ⁇ to 1.75 ⁇ , with an imbalance below 0.6dB, which is almost five times more bandwidth than a conventional MMI.
  • phase error that is, the deviation of the 90 ° offset that is ideally between the output waveguides (20a, 20b
  • EF phase error
  • a conventional MMI coupler has a phase error (EF with v) as small as that of the invention only in a width of 150nm band
  • a coupling device (1) MMI of 2x4 configuration is shown in Figure 13, with two input waveguides (10a, 10b) and four output waveguides (20a, 20b, 20c, 20d), based on the concept of the present invention, and where the network (31) is arranged essentially perpendicular to said input and output waveguides (10a, 10b, 20a, 20b, 20c, 20d).
  • This device is of particular interest because it is a key component for coherent reception systems.
  • FIG. 14a shows the imbalance between the outputs of the coupling device (1) MMI of the invention for each of the two inputs, which is below 1, 6dB in a 200nm bandwidth of 1 , 45 ⁇ to 1.65 ⁇ .
  • a conventional MMI coupler is shown in the graph of Figure 14b, which has an imbalance below 1, 6dB only in a band of lOOnm.
  • figures 14c and 14d show graphs of the differential offset with which the light waves of the input waveguides (10a, 10b) are combined in the output waveguides (20a, 20b, 20c, 20d ).
  • the coupling device (1) operates with a single polarization, specifically horizontal polarization (quasi-TE), along the x-axis.
  • coupler devices (1) that operate with vertical polarization (quasi-TM) can also be configured.
  • the coupler device (1) is configured to work as a broadband polarization separator.
  • the network (31) existing in the coupling area (30) is configured in such a way that the variation of the beat length (L *) is reduced with the wavelength for both polarizations (quasi-TE, quasi -TM).
  • the values of the shake lengths (L n ) for each of said polarizations are quite different due to the strong birefringence of the networks (31).
  • the length (L) of the coupling zone (30) is configured so that when a light beam of a polarization (quasi-TE or quasi-TM) is injected, into an input waveguide (10) , said light beam is completely coupled to one of the output waveguides (20a), while if a light beam with opposite polarization is injected through the input waveguide (10) said Light beam is fully coupled to the other output waveguide (20b), as shown in Figure 15.
  • a polarization quadrati-TE or quasi-TM

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  • General Physics & Mathematics (AREA)
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Abstract

According to the invention, the bandwidth of the device can be increased, without its dimensions being increased and without the phase response thereof being degraded. The coupling device (1) is characterised in that the coupling zone (30) thereof contains at least one grating (31) with a period (Λ) that guarantees that no diffraction phenomena are generated, said grating (31) being configured to alter the variation of the propagation constants (βι, β2) of the first and second order modes (Φι, Φ2) of the coupling zone (30) in relation to the wavelength, such as to reduce the variation of the beat length (Lπ)) with the wavelength, thereby increasing the bandwidth of the coupling device (1).

Description

DISPOSITIVO ACOPLADOR DE GUÍAS DE ONDA. Y MÉTODO DE DISEÑO DE  WAVE GUIDE COUPLING DEVICE. AND DESIGN METHOD OF
DICHO DISPOSITIVO  SUCH DEVICE
OBJETO DE LA INVENCIÓN OBJECT OF THE INVENTION
La presente invención pertenece al campo de las telecomunicaciones y la óptica integrada, y más concretamente a dispositivos acopladores de luz entre guías de onda. The present invention pertains to the field of telecommunications and integrated optics, and more specifically to light couplers between waveguides.
El objeto principal de la presente invención es un dispositivo acoplador de guías de onda, que destaca por presentar un ancho de banda considerable, sin que ello suponga un sobredimensionamiento del dispositivo, y sin que ello afecte negativamente a su respuesta en fase. Asimismo, es otro objeto de la invención el método de diseño de dicho dispositivo acoplador.  The main object of the present invention is a waveguide coupler device, which stands out for having a considerable bandwidth, without implying an oversizing of the device, and without negatively affecting its response in phase. Likewise, the design method of said coupling device is another object of the invention.
ANTECEDENTES DE LA INVENCIÓN BACKGROUND OF THE INVENTION
En la actualidad son conocidos los dispositivos de acoplo o dispositivos acopladores de guías de onda, los cuales constituyen los elementos fundamentales en circuitos fotónicos integrados (PIC). Dichos dispositivos cumplen entre otras las funciones de dividir o combinar potencia entre dichas guías e imponer desfases específicos entre las ondas acopladas a cada guía de onda. Dichos acopladores de guías de onda se usan, entre otras aplicaciones, en demultiplexadores de longitud onda, conmutadores, receptores coherentes y biosensores. At present, coupling devices or waveguide couplers are known, which constitute the fundamental elements in integrated photonic circuits (PIC). Said devices fulfill among others the functions of dividing or combining power between said guides and imposing specific offset between the waves coupled to each waveguide. Said waveguide couplers are used, among other applications, in wavelength demultiplexers, switches, coherent receivers and biosensors.
Más en particular, en óptica integrada se usan generalmente dos tipos de acopladores: acopladores direccionales (AD) y acopladores de interferencia multi-modal (MMI). Los primeros tienen las ventajas de un diseño sencillo y de ratios de división arbitrarios, mientras que los segundos ofrecen generalmente mejores tolerancias de fabricación y un mayor ancho de banda.  More particularly, in integrated optics, two types of couplers are generally used: directional couplers (AD) and multi-modal interference couplers (MMI). The former have the advantages of a simple design and arbitrary division ratios, while the latter generally offer better manufacturing tolerances and greater bandwidth.
Respecto a los acopladores direccionales (AD), su funcionamiento se basa esencialmente en colocar dos guías de ondas lo suficientemente juntas como para que las ondas luminosas que viajan por ellas interactúen, y así se transfiera potencia de una guía de onda a la otra, ver figura 1. En general este proceso es dependiente de la polarización de la onda luminosa; en adelante nos centraremos, sin pérdida de generalidad, en una polarización específica, como por ejemplo polarización horizontal (cuasi-TE), o vertical (cuasi-TM).  With regard to directional couplers (AD), their operation is essentially based on placing two waveguides close enough so that the light waves traveling through them interact, and thus transfer power from one waveguide to the other, see Figure 1. In general this process is dependent on the polarization of the light wave; from now on we will focus, without loss of generality, on a specific polarization, such as horizontal (quasi-TE), or vertical (quasi-TM) polarization.
COPIA DE CONFIRMACIÓN El proceso de acoplamiento entre guías de onda puede describirse en términos de los modos de primer y segundo orden (Φι, Φ2) de dos guías acopladas, y sus respectivas constantes de propagación (β1? β2). Se entiende por "modos" aquellas distribuciones de campo que al propagarse por una guía de onda no modifican su forma. El campo de entrada (Φύ excita los modos (Φι, Φ2) en la región central de acoplo o zona de acoplamiento (ZAAD), y debido a la diferencia entre sus constantes de propagación (β! y β2) la potencia luminosa se transfiere de una guía a la otra. Dicha transferencia de potencia luminosa es máxima a la longitud de batido (LK) de los supermodos:
Figure imgf000004_0001
CONFIRMATION COPY The coupling process between waveguides can be described in terms of the first and second order modes (Φι, Φ 2 ) of two coupled guides, and their respective propagation constants (β 1? Β 2 ). "Modes" means those field distributions that, when propagated by a waveguide, do not change their shape. The input field (Φύ excites the modes (Φι, Φ 2 ) in the central coupling region or coupling area (ZAAD), and due to the difference between their propagation constants (β ! And β 2 ) the light output is transfers from one guide to the other.This luminous power transfer is maximum to the beat length (L K ) of the supermodes:
Figure imgf000004_0001
La longitud de batido (LK) indica la distancia que debe recorrer un haz de luz para que sea totalmente transferido de una guía de onda a otra guía de onda. Sin embargo, esta longitud de batido (L¾) varía con la longitud de onda de dicho haz luminoso, de manera que el ancho de banda en el acoplador está limitado. The shake length (L K ) indicates the distance a light beam must travel to be fully transferred from one waveguide to another waveguide. However, this beat length (L varía ) varies with the wavelength of said light beam, so that the bandwidth in the coupler is limited.
Actualmente, se han propuesto varias técnicas para mejorar el ancho de banda de los dispositivos acopladores direccionales (AD). Una de ellas consiste en conectar varios acopladores en un interferómetro "Mach-Zehnder", de manera que sus respuestas se compensen (B. Little et al, "Design rules for maximally fíat wavelength-insensitive optical power dividers using Mach-Zehnder structures", 1997). Sin embargo esta técnica presenta el inconveniente de que aumenta considerablemente el tamaño del dispositivo, con los problemas y costes asociados que ello conlleva.  Currently, several techniques have been proposed to improve the bandwidth of directional coupler (AD) devices. One of them consists of connecting several couplers in a "Mach-Zehnder" interferometer, so that their responses are compensated (B. Little et al, "Design rules for maximally fiat wavelength-insensitive optical power dividers using Mach-Zehnder structures", 1997). However, this technique has the disadvantage that the size of the device increases considerably, with the problems and associated costs that this entails.
Por otra parte, en dispositivos acopladores basados en la conversión adiabática de modos, el ancho de banda se mejora usando formas específicas de variación gradual de la geometría de las guías de ondas en la región de acoplo. Sin embargo, esta técnica lleva ligada igualmente un aumento considerablemente del tamaño del dispositivo (Y. Shani et al "Integrated optic adiabatic devices on silicon," 1991).  On the other hand, in coupling devices based on adiabatic mode conversion, the bandwidth is improved using specific forms of gradual variation of the waveguide geometry in the coupling region. However, this technique also has a considerable increase in the size of the device (Y. Shani et al. "Integrated optic adiabatic devices on silicon," 1991).
Por último, se sabe que curvando el acoplador completo se puede incrementar su ancho de banda, pero esta técnica presenta el inconveniente de que degrada la respuesta en fase del dispositivo (C. Doerr et al, "Bending of a planar lightwave circuit 2x2 coupler to desensitize it to wavelength, polarization, and fabrication changes," 2005).  Finally, it is known that bending the entire coupler can increase its bandwidth, but this technique has the disadvantage that it degrades the response in phase of the device (C. Doerr et al, "Bending of a planar lightwave circuit 2x2 coupler to desensitize it to wavelength, polarization, and fabrication changes, "2005).
Respecto a los acopladores de interferencia multimodal (M ), éstos constan de varias guías de ondas de entrada y salida y una zona de acoplamiento (ZAMMI), que guía varios modos (Φι, Φ2, Φ3,...), tal y como se representa en la figura 2. Dichos acopladores de interferencia multimodal (MM) presentan generalmente un comportamiento dependiente de la polarización; en lo que sigue nos centraremos sin pérdida de generalidad en un estado de polarización específico, por ejemplo una polarización horizontal (cuasi-TE) o vertical (cuasi-TM). Regarding multimodal interference couplers (M), these consist of several input and output waveguides and a coupling zone (ZA M MI), which guides various modes (Φι, Φ 2 , Φ 3 , ...), as shown in Figure 2. Such interference couplers multimodal (MM) generally have a polarization-dependent behavior; In what follows we will focus without loss of generality on a specific polarization state, for example a horizontal (quasi-TE) or vertical (quasi-TM) polarization.
Un rayo de luz es lanzado en una de las guías de onda de entrada y excita varios modos (Φι, Φ2, Φ3,...) en la zona de acoplamiento (ZAMMI), los cuales se propagan con diferentes constantes de propagación (βι, β2> β3>...). A unas determinadas distancias desde el plano de entrada, los modos (Φι, Φ2, Φ3, ..) interfieren formando una o varias imágenes de la excitación de entrada. Las guías de onda de salida se colocan en la posición de estas imágenes, de manera que la luz se acopla a ellas. La distancia a la que se forman las imágenes depende en esencia de la longitud de batido Lv) de los modos de primer y segundo orden (Φ1? Φ2) de la zona de acoplamiento: Ln=n/( βι-β2). A ray of light is launched in one of the input waveguides and excites various modes (Φι, Φ 2 , Φ 3 , ...) in the coupling zone (ZAMM I ), which propagate with different constants of propagation (βι, β 2> β 3> ...). At certain distances from the input plane, the modes (Φι, Φ 2 , Φ 3 , ..) interfere forming one or more images of the input excitation. The output waveguides are placed in the position of these images, so that the light is coupled to them. The distance at which the images are formed depends essentially on the beat length L v ) of the first and second order modes (Φ 1? Φ 2 ) of the coupling area: L n = n / (βι-β 2 ).
Además, para que se formen imágenes de alta calidad las constantes de propagación (βή,) de los modos de la zona de acoplamiento tienen que seguir la ley parabólica:  In addition, for high quality images to be formed, propagation constants (βή,) of the modes of the coupling zone must follow the parabolic law:
Los acopladores de interferencia multimodal (MM) tienen un ancho de banda mayor que los acopladores direccionales (AD), pero dicho ancho de banda sigue estando limitado por la variación de la longitud de batido (Ln) con la longitud de onda. De hecho, el ancho de banda de los acopladores de interferencia multimodal (MMI) disminuye conforme se aumenta el número de entradas y/o salidas (P. Besse et al, "Optical bandwidth and fabrication tolerances of multimode interference couplers", 1994). Multimodal interference couplers (MM) have a bandwidth greater than directional couplers (AD), but such bandwidth is still limited by the variation of the beat length (L n ) with the wavelength. In fact, the bandwidth of multimodal interference couplers (MMI) decreases as the number of inputs and / or outputs increases (P. Besse et al, "Optical bandwidth and fabrication tolerances of multimode interference couplers", 1994).
Por tanto, el problema técnico que aquí se plantea es conseguir un dispositivo acoplador de guías de ondas que ofrezca un ancho de banda lo más grande posible, sin que ello tenga como consecuencia una ampliación de sus dimensiones, y sin que su respuesta en fase se vea afectada.  Therefore, the technical problem that arises here is to achieve a waveguide coupler device that offers as large a bandwidth as possible, without resulting in an extension of its dimensions, and without its phase response being See affected.
DESCRIPCIÓN DE LA INVENCIÓN DESCRIPTION OF THE INVENTION
Mediante la presente invención se resuelve el problema técnico anteriormente planteado proporcionando un dispositivo acoplador de guías de onda que presenta un aumento considerable de su ancho de banda con respecto a los dispositivos actuales, sin que ello suponga un aumento del tamaño del dispositivo, y sin que su repuesta en fase se vea degradada. By means of the present invention, the above-mentioned technical problem is solved by providing a waveguide coupler device that presents a considerable increase. of its bandwidth with respect to the current devices, without this implying an increase in the size of the device, and without its phase response being degraded.
El dispositivo acoplador objeto de invención es del tipo que comprende al menos una guía de onda de entrada en la cual está destinado a inyectarse un haz luminoso, al menos una guía de onda de salida, y una zona de acoplamiento localizada entre dichas guías de onda de entrada y salida, estando dicha zona de acoplamiento configurada para acoplar el haz luminoso de la guía de onda de entrada a la guía de onda de salida.  The coupling device object of the invention is of the type comprising at least one input waveguide in which a light beam, at least one output waveguide, and a coupling zone located between said waveguides is injected input and output, said coupling zone being configured to couple the light beam of the input waveguide to the output waveguide.
Más concretamente, el dispositivo acoplador destaca fundamentalmente por presentar en la zona de acoplamiento al menos una red constituida por un sustrato, un núcleo y un revestimiento, presentando dicha red un periodo inferior a la mitad de la longitud de onda menor del rango de operación del dispositivo acoplador (se entiende que cada dispositivo acoplador trabaja para un determinado rango de longitudes de onda), dividida entre el menor de los índices de refracción del sustrato, el núcleo y el revestimiento de la red, y que garantice que no se producen fenómenos de difracción (la radiación y reflexión son despreciables a efecto prácticos), De aquí en adelante una red de estas características se denominará simplemente red. Los modos que soportan estas redes tienen distribuciones de campo periódicas y se denominan modos Floquet o modos Bloch; de aquí en adelante se denominarán simplemente modos.  More specifically, the coupling device mainly stands out for presenting in the coupling area at least one network consisting of a substrate, a core and a coating, said network having a period less than half of the wavelength less than the operating range of the coupler device (it is understood that each coupler device works for a certain range of wavelengths), divided by the lower indexes of refraction of the substrate, the core and the lining of the network, and ensuring that no phenomena of diffraction (radiation and reflection are negligible for practical purposes), Hereafter a network of these characteristics will be called simply a network. The modes that support these networks have periodic field distributions and are called Floquet modes or Bloch modes; Hereinafter they will simply be called modes.
Dicha red está configurada para modificar la variación de las constantes de propagación (β1; β2) de los modos de primer y segundo orden (Φ\, Φ2) de la zona de acoplamiento respecto a la longitud de onda, de manera que se reduce la variación de la longitud de batido con la longitud de onda, consiguiendo aumentar así el ancho de banda del dispositivo acoplador. Preferentemente, dicha red comprende una guía de onda segmentada cuyos elementos se disponen de forma periódica, perpendicularmente a la dirección de propagación del haz luminoso, y con un periodo inferior al periodo de Bragg de primer orden. Said network is configured to modify the variation of the propagation constants (β 1; β 2 ) of the first and second order modes (Φ \ , Φ 2 ) of the coupling area with respect to the wavelength, so that the variation of the beat length with the wavelength is reduced, thus increasing the bandwidth of the coupling device. Preferably, said network comprises a segmented waveguide whose elements are arranged periodically, perpendicular to the direction of propagation of the light beam, and with a period less than the first order Bragg period.
En la presente invención se propone la utilización de las propiedades dispersivas de dichas redes, esto es, la variación de sus propiedades con la longitud de onda de operación del dispositivo.  The present invention proposes the use of the dispersive properties of said networks, that is, the variation of their properties with the operating wavelength of the device.
Se empleará aquí el término "guía de ondas uniformes" para referirse a las guías de onda convencionales, con objeto de poder distinguirlas de aquellas guías que utilizan redes. Además, se ha previsto que las guías de onda aquí descritas puedan diseñarse para un rango determinado de longitudes de onda; y que las guías de onda de entrada y salida puedan ser guías de ondas uniformes o redes. De acuerdo con una primera realización preferente, el dispositivo acoplador de la invención comprende adicionalmente en la zona de acoplamiento al menos dos guías de ondas uniformes, donde la red está configurada para modificar la variación de las constantes de propagación (βι, β2) de los modos de primer y segundo orden (Φι, Φ2) en la zona de acoplamiento en función de la longitud de onda, de manera que se reduce la variación de la longitud de batido con la longitud de onda, consiguiendo aumentar así el ancho de banda del dispositivo, trabajando en este caso como un acoplador direccional, con un ratio de división predefinido. Además, preferentemente, la red está dispuesta esencialmente perpendicular a las guías de onda uniformes. The term "uniform waveguide" will be used here to refer to conventional waveguides, in order to distinguish them from those guides that use networks. In addition, it is envisioned that the waveguides described herein can be designed for a given range of wavelengths; and that the input and output waveguides can be uniform waveguides or networks. According to a first preferred embodiment, the coupling device of the invention further comprises in the area of coupling at least two guides uniform waves, where the network is configured to modify the variation of the propagation constants (βι, β 2) the first and second order modes (Φι, Φ 2 ) in the coupling area as a function of the wavelength, so that the variation of the beat length with the wavelength is reduced, thus increasing the width of device band, working in this case as a directional coupler, with a predefined division ratio. Furthermore, preferably, the network is arranged essentially perpendicular to the uniform waveguides.
Asimismo, se ha previsto que en esta primera realización, el ciclo de trabajo y la extensión lateral de la red estén configurados de modo que se reduce la excitación del modo de tercer orden (Φ3) que produce una transferencia de potencia indeseada entre las guías de ondas uniformes. Likewise, it is envisaged that in this first embodiment, the duty cycle and the lateral extension of the network are configured so that the excitation of the third order mode (Φ 3 ) that produces an unwanted power transfer between the guides is reduced of uniform waves.
De acuerdo con una segunda realización preferente, la red de la zona de acoplamiento está adaptada para soportar al menos dos modos guiados de la misma polarización (cuasi-TE o cuasi-TM), donde la red está configurada para modificar la variación con la longitud de onda de las constantes de propagación de los modos en la zona de acoplamiento, de manera que se reduce la variación de la longitud de batido con la longitud de onda, aumentando así el ancho de banda del dispositivo, el cual trabaja en este caso como un acoplador de interferencia multimodal. Además, el dispositivo acoplador así configurado presenta unos errores de fase modal menores que un acoplador de interferencia multimodal convencional, esto es, las constantes de propagación de los modos superiores siguen mejor la ley parabólica requerida para formar imágenes de alta calidad.  According to a second preferred embodiment, the network of the coupling zone is adapted to support at least two guided modes of the same polarization (quasi-TE or quasi-TM), where the network is configured to modify the variation with the length wavelength of the propagation constants of the modes in the coupling area, so that the variation of the beat length with the wavelength is reduced, thereby increasing the bandwidth of the device, which in this case works as a multimodal interference coupler. In addition, the coupling device thus configured has smaller modal phase errors than a conventional multimodal interference coupler, that is, the propagation constants of the higher modes better follow the parabolic law required to form high quality images.
Finalmente, de acuerdo con una tercera realización preferente, la red está configurada para reducir la variación de la longitud de batido respecto a la longitud de onda tanto para polarizaciones horizontales cuasi-TE como para polarizaciones verticales cuasi-TM, y donde la longitud de la zona de acoplamiento es un múltiplo par de la longitud de batido para el haz luminoso con polarización cuasi-TE y un múltiplo impar de la longitud de batido para el haz luminoso con polarización cuasi-TM. No obstante se ha previsto que pueda ser al contrario, múltiplo par para polarización cuasi-TM, y múltiplo impar para polarización cuasi-TE. En este caso, el dispositivo acoplador de la presente invención trabajaría como un separador de polarización de banda ancha, que puede estar basado tanto en un acoplador direccional o en un acoplador de interferencia multimodal. Finally, according to a third preferred embodiment, the network is configured to reduce the variation of the beating length with respect to the wavelength for both quasi-TE horizontal polarizations and quasi-TM vertical polarizations, and where the length of the The coupling zone is an even multiple of the beat length for the light beam with quasi-TE polarization and an odd multiple of the beat length for the light beam with quasi-TM polarization. However, it is expected that it may be the opposite, even multiple for quasi-TM polarization, and odd multiple for quasi-TE polarization. In this case, the coupling device of the present invention would work as a broadband polarization separator, which may be based on either a directional coupler or a multimodal interference coupler.
De acuerdo con otro objeto de la invención, se describe a continuación el método de diseño del dispositivo acoplador descrito anteriormente. Dicho método de diseño comprende al menos las siguientes etapas: a) se parte de una guía de onda donde se definen sus parámetros y materiales de diseño para el sustrato, el núcleo y el revestimiento,  According to another object of the invention, the design method of the coupling device described above is described below. Said design method comprises at least the following steps: a) it is based on a waveguide where its design parameters and materials are defined for the substrate, the core and the coating,
b) se ajusta el periodo de la red a un valor ligeramente inferior al periodo de Bragg de primer orden, de manera que no se produzcan fenómenos de difracción,  b) the period of the network is adjusted to a slightly lower value than the first order Bragg period, so that diffraction phenomena do not occur,
c) se determina, por simulación, la variación de las constantes de propagación (βι, β2) de los modos de primer y segundo orden (Φι, Φ2) de la zona de acoplamiento, c) determining, by simulation, the variation of the propagation constants (βι, β 2) modes of first and second order (Φι, Φ 2) of the coupling region,
d) se comprueba si la variación de la longitud de batido con respecto a la longitud de onda se ha reducido,  d) it is checked whether the variation of the beat length with respect to the wavelength has been reduced,
el) si en la etapa d) se ha conseguido reducir la variación de la longitud de batido se ajusta de nuevo el periodo de la red reduciéndolo ligeramente,  el) if in step d) it has been possible to reduce the variation of the beating length, the period of the network is adjusted again by reducing it slightly,
e2) si en la etapa e) no se ha conseguido reducir la longitud de batido se escoge el valor del periodo para el que se había conseguido reducir dicha longitud de batido, y  e2) if in step e) it has not been possible to reduce the beating length, the value of the period for which said beating length had been reduced is chosen, and
f) se diseña el dispositivo acoplador completo para el valor del periodo de la etapa e2), para el cual se obtiene un aumento máximo de su ancho de banda.  f) the complete coupling device is designed for the period value of step e2), for which a maximum increase in its bandwidth is obtained.
Preferentemente los parámetros ajustados en la fase a) es al menos uno seleccionado entre: periodo, ciclo de trabajo, hueco, grosor, profundidad de grabado, anchura, distancia, y extensión lateral. DESCRIPCIÓN DE LOS DIBUJOS Preferably the parameters set in phase a) is at least one selected from: period, duty cycle, gap, thickness, engraving depth, width, distance, and lateral extension. DESCRIPTION OF THE DRAWINGS
Para complementar la descripción que se está realizando y con objeto de ayudar a una mejor comprensión de las características de la invención, de acuerdo con un ejemplo preferente de realización práctica de la misma, se acompaña como parte integrante de dicha descripción, un juego de dibujos en donde con carácter ilustrativo y no limitativo, se ha representado lo siguiente: To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation thereof, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented:
Figura 1.- Muestra una vista esquemática de un acoplador direccional convencional. Figura 2.- Muestra una vista esquemática de un acoplador de interferencia multimodal convencional. Figure 1.- Shows a schematic view of a conventional directional coupler. Figure 2.- Shows a schematic view of a conventional multimodal interference coupler.
Figura 3.- Muestra una vista de perfil esquemática de una red.  Figure 3.- Shows a schematic profile view of a network.
Figura 4.- Muestra una gráfica que representa la variación de la longitud de batido con respecto a la longitud de onda empleando un acoplador direccional convencional.  Figure 4.- Shows a graph that represents the variation of the beat length with respect to the wavelength using a conventional directional coupler.
Figura 5.- Muestra una vista del dispositivo acoplador de la invención configurado para trabajar como un acoplador direccional, según una primera realización preferente.  Figure 5.- Shows a view of the coupling device of the invention configured to work as a directional coupler, according to a first preferred embodiment.
Figura 6.- Muestra otra gráfica que representa la variación de la longitud de batido con respecto a la longitud de onda empleando ahora el dispositivo acoplador direccional de acuerdo con la primera realización de la invención.  Figure 6.- Shows another graph that represents the variation of the beat length with respect to the wavelength using now the directional coupler device according to the first embodiment of the invention.
Figura 7.- Muestra una gráfica donde se simulan las pérdidas de inserción del dispositivo acoplador direccional de la invención, comparadas con las pérdidas de inserción de un acoplador direccional convencional.  Figure 7.- Shows a graph where the insertion losses of the directional coupler device of the invention are simulated, compared with the insertion losses of a conventional directional coupler.
Figuras 8a, 8b.- Muestran la respuesta de fase simulada del dispositivo acoplador direccional de la invención.  Figures 8a, 8b.- Show the simulated phase response of the directional coupler device of the invention.
Figura 9.- Muestra una gráfica que representa la variación de la longitud de batido con respecto a la longitud de onda empleando un acoplador de interferencia multimodal convencional.  Figure 9.- Shows a graph that represents the variation of the beat length with respect to the wavelength using a conventional multimodal interference coupler.
Figura 10.- Muestra una vista del dispositivo acoplador de la invención configurado para trabajar como un acoplador de interferencia multimodal, según una segunda realización preferente.  Figure 10.- Shows a view of the coupling device of the invention configured to work as a multimodal interference coupler, according to a second preferred embodiment.
Figura 11.- Muestra una gráfica que representa la variación de la longitud de batido con respecto a la longitud de onda empleando el dispositivo acoplador de interferencia multimodal de acuerdo con la segunda realización de la invención.  Figure 11.- Shows a graph that represents the variation of the beat length with respect to the wavelength using the multimodal interference coupling device according to the second embodiment of the invention.
Figuras 12a, 12b.- Muestran las prestaciones del dispositivo acoplador de interferencia multimodal según la segunda realización preferente de la invención, comparadas con las de un acoplador de interferencia multimodal convencional.  Figures 12a, 12b.- They show the performance of the multimodal interference coupling device according to the second preferred embodiment of the invention, compared with those of a conventional multimodal interference coupler.
Figura 13.- Muestra una vista esquemática de un dispositivo acoplador de interferencia multimodal según la presente invención, presentando una configuración 2x4.  Figure 13.- Shows a schematic view of a multimodal interference coupling device according to the present invention, presenting a 2x4 configuration.
Figuras 14a, 14b, 14c, 14d.- Muestran las prestaciones del dispositivo acoplador de interferencia multimodal 2x4 de la figura 13.  Figures 14a, 14b, 14c, 14d.- They show the performance of the 2x4 multimodal interference coupling device of Figure 13.
Figura 15.- Muestra una vista del dispositivo acoplador de la invención configurado para trabajar como un separador de polarización de banda ancha, según una tercera realización preferente. Figure 15.- Shows a view of the coupling device of the invention configured for work as a broadband polarization separator, according to a third preferred embodiment.
REALIZACIÓN PREFERENTE DE LA INVENCIÓN PREFERRED EMBODIMENT OF THE INVENTION
Se describen a continuación varios ejemplos de realizaciones preferidas, haciendo mención a las figuras arriba citadas, sin que ello suponga limitación alguna en el ámbito de protección de la presente invención. Several examples of preferred embodiments are described below, with reference to the aforementioned figures, without any limitation in the scope of protection of the present invention.
Para los siguientes ejemplos, el dispositivo acoplador (1) y la red (31) que contiene, se diseñan con un sustrato (2) formado por dióxido de silicio, un núcleo (3) de silicio, y un revestimiento (4) de polímero SU-8. Los índices de refracción a la longitud de onda de espacio libre de 1 ,55μηι son
Figure imgf000010_0001
,58 respectivamente. Asimismo, se asume polarización horizontal cuasi-TE (en dirección del eje x). For the following examples, the coupling device (1) and the network (31) it contains are designed with a substrate (2) formed by silicon dioxide, a silicon core (3), and a polymer coating (4) SU-8. The refractive indices at the free space wavelength of 1.55μηι are
Figure imgf000010_0001
, 58 respectively. Also, quasi-TE horizontal polarization is assumed (in the direction of the x-axis).
En la figura 3 se muestra una vista en perfil de una red (31), donde "g" es el hueco entre los elementos de la red (31), y el ciclo de trabajo (DC) se define como DC=(A-g)/A. El grosor del núcleo (3) de la guía de onda, representada por "H", tiene en los siguientes ejemplos un valor de Η=0.26μπι. Asimismo, la profundidad de grabado en el núcleo (3) representada con la letra "D", es en este caso prácticamente igual al grosor (H) del mismo, pudiendo no obstante tomar cualquier valor.  A profile view of a network (31) is shown in Figure 3, where "g" is the gap between the elements of the network (31), and the duty cycle (DC) is defined as DC = (Ag) /TO. The thickness of the core (3) of the waveguide, represented by "H", has in the following examples a value of Η = 0.26μπι. Also, the engraving depth in the core (3) represented with the letter "D", is in this case practically equal to the thickness (H) thereof, however, it can take any value.
De acuerdo con una primera realización preferente, se describe a continuación el dispositivo acoplador (1) de la invención configurado como un acoplador direccional.  According to a first preferred embodiment, the coupling device (1) of the invention configured as a directional coupler is described below.
En la gráfica de la figura 4 se puede apreciar la variación de la longitud de batido (L ) de un acoplador direccional "convencional" con la longitud de onda. Se observa que en el rango de longitudes de onda entre 1 ,5μπι y Ι ,όμπι, la longitud de batido (L„) varía de forma prácticamente lineal con la longitud de onda, cambiando su valor en aproximadamente un 40%.  In the graph of figure 4 the variation of the beat length (L) of a "conventional" directional coupler with the wavelength can be seen. It is observed that in the range of wavelengths between 1.5μπι and Ι, όμπι, the beat length (L „) varies practically linearly with the wavelength, changing its value by approximately 40%.
Para obtener, por ejemplo, un acoplador direccional simétrico con un ratio de división de potencia de salida de 50/50, la longitud de la zona de acoplamiento se ha fijado en LJ2 a la longitud de onda central, esto es, a 1 ,55μπι. Conforme varía la longitud de onda la longitud de batido (L„) cambia y el dispositivo deja de estar sintonizado. Por tanto, para incrementar el ancho de banda del dispositivo es necesario reducir la variación de la longitud de batido (Lz) con la longitud de onda. En dicho acoplador direccional convencional, ver figura 1 , se han empleado guías de ondas uniformes con una anchura de =0,45μιη y separadas una distancia 8=0,3μηι en la zona de acoplamiento (ZAAD)-To obtain, for example, a symmetric directional coupler with an output power split ratio of 50/50, the length of the coupling zone is set at LJ2 at the center wavelength, that is, at 1, 55μπι . As the wavelength varies the beat length (L „) changes and the device is no longer tuned. Therefore, in order to increase the bandwidth of the device it is necessary to reduce the variation of the beat length (L z ) with the wavelength. In said conventional directional coupler, see figure 1, they have used uniform waveguides with a width of = 0.45μιη and separated a distance 8 = 0.3μηι in the coupling area (ZAAD) -
En la figura 5 se muestra el dispositivo acoplador (1) configurado según la presente invención para trabajar como acoplador direccional y mediante el cual se consigue reducir la variación de la longitud de batido (L„) con la longitud de onda, incrementando por tanto el ancho de banda del dispositivo acoplador (1). Más concretamente en dicha figura 5 se observa una configuración 2x2 del dispositivo acoplador (1) con dos guías de onda de entrada (10a, 10b) y dos guías de onda de salida (20a, 20b) entre las cuales se encuentra una zona de acoplamiento (30). Dicha zona de acoplamiento (30) presenta una red (31). En este caso particular el periodo (Λ) de la red (31) es A=271nm, lo que impide que se produzca difracción en el rango de longitudes de onda de 1,5μιη a Ι,όμηι. Figure 5 shows the coupling device (1) configured according to the present invention to work as a directional coupler and by means of which it is possible to reduce the variation of the beat length (L „) with the wavelength, thereby increasing the bandwidth of the coupling device (1). More specifically in said figure 5 a 2x2 configuration of the coupling device (1) is observed with two input waveguides (10a, 10b) and two output waveguides (20a, 20b) between which is a coupling zone (30). Said coupling area (30) has a network (31). In this particular case the period (Λ) of the network (31) is A = 271nm, which prevents diffraction in the wavelength range from 1.5μιη to Ι, όμηι.
Además, en dicha figura 5 puede apreciarse que en la zona de acoplamiento (30) del dispositivo acoplador (1) existe un modo de tercer orden (Φ3), que puede excitarse y producir transferencia de potencia indeseada. Este modo de tercer orden (Φ3) también está presente en los acopladores convencionales donde su excitación es, sin embargo, despreciable. En el dispositivo acoplador (1) de la invención dicha excitación producida por el modo de tercer orden (Φ3) se reduce usando dos mecanismos. Furthermore, in said figure 5 it can be seen that in the coupling zone (30) of the coupling device (1) there is a third order mode (Φ 3 ), which can be excited and produce unwanted power transfer. This third order mode (Φ 3 ) is also present in conventional couplers where its excitation is, however, negligible. In the coupling device (1) of the invention said excitation produced by the third order mode (Φ 3 ) is reduced using two mechanisms.
En primer lugar, la extensión lateral (t) de la red (31) se ha aumentado a ambos lados de las guías de onda (10a, 10b, 20a, 20b). En este caso particular una extensión lateral ί>0.4μιη ha resultado ser suficiente para reducir dicha excitación del modo de tercer orden (Φ3). En segundo lugar, el ciclo de trabajo (DC) de la red (31), definido anteriormente como DC=(A-g)/A, se mantiene por debajo de un determinado umbral, que es aproximadamente un 25% en este caso particular. De esta manera se consigue que la potencia acoplada al modo de tercer orden (Φ3) disminuya conforme el ciclo de trabajo (DC) de la red (31) se reduce, y, para esta configuración particular, dicha potencia acoplada es despreciable para ciclos de trabajo (DC) por debajo del 25%. Cabe señalar que este es un comportamiento general que se observa para diferentes periodos (A) de la red (31). First, the lateral extension (t) of the network (31) has been increased on both sides of the waveguides (10a, 10b, 20a, 20b). In this particular case a lateral extension ί> 0.4μιη has been found to be sufficient to reduce said excitation in the third order mode (Φ 3 ). Secondly, the duty cycle (DC) of the network (31), previously defined as DC = (Ag) / A, remains below a certain threshold, which is approximately 25% in this particular case. In this way it is achieved that the power coupled to the third order mode (Φ 3 ) decreases as the duty cycle (DC) of the network (31) is reduced, and, for this particular configuration, said coupled power is negligible for cycles Working (DC) below 25%. It should be noted that this is a general behavior observed for different periods (A) of the network (31).
La variación de la longitud de batido (LK) con la longitud de onda se controla usando las propiedades dispersivas de la red (31), esto es, la variación con la longitud de onda de las constantes de propagación (β1 ? β2) de los modos de primer y segundo orden (Φ1? Φ2). Estas propiedades dispersivas pueden ser configuradas con el periodo (A) y el ciclo de trabajo (DC) de la red (31), que a su vez, controlan la longitud de onda de Bragg de la red (31). Usando 1 Ü este concepto, y para una distancia (s) de separación entre guías de ondas uniformes en la zona de acoplamiento (30) de
Figure imgf000012_0001
un periodo de A=271nm y un ciclo de trabajo de DC=22.5%, la variación de la longitud de batido (Lrt) con la longitud de onda se reduce de manera significativa, tal y como se representa en la gráfica de la figura 6. Así, la longitud de batido (L,i) del dispositivo acoplador (1) objeto de invención varía sólo en un 8% en la banda de longitudes de onda de 1 ,5μηι a Ι ,όμηι, lo que supone una reducción por un factor cinco en comparación con un acoplador direccional convencional. The variation of the beat length (L K ) with the wavelength is controlled using the dispersive properties of the network (31), that is, the variation with the wavelength of the propagation constants (β 1? Β 2 ) of the first and second order modes (Φ 1? Φ 2 ). These dispersive properties can be configured with the period (A) and the duty cycle (DC) of the network (31), which in turn control the Bragg wavelength of the network (31). Using 1 Ü this concept, and for a separation distance (s) between uniform waveguides in the coupling area (30) of
Figure imgf000012_0001
A period of A = 271nm and a duty cycle of DC = 22.5%, the variation of the beat length (L rt ) with the wavelength is significantly reduced, as represented in the graph in the figure 6. Thus, the beat length (L, i) of the coupling device (1) object of the invention varies only by 8% in the wavelength band from 1.5μηι to Ι, όμηι, which means a reduction by a factor five compared to a conventional directional coupler.
Nótese que la variación de la longitud de batido (LK) con la longitud de onda sólo se reduce en la zona de acoplamiento (30) del dispositivo acoplador (1) direccional, donde existe la red (31) de periodo (Λ) inferior a la longitud de onda, pero no se reduce en las regiones de entrada (I) y de salida (O), las cuales están desacopladas. Además, cabe indicar que dependiendo del número de periodos (P) de la red (31) se obtienen diferentes ratios de acoplamiento. Note that the variation of the beat length (L K ) with the wavelength is only reduced in the coupling zone (30) of the directional coupling device (1), where the network (31) of the lower period (Λ) exists to the wavelength, but it is not reduced in the input (I) and output (O) regions, which are decoupled. In addition, it should be noted that depending on the number of periods (P) of the network (31) different coupling rates are obtained.
Para mostrar la mejora del ancho de banda del dispositivo acoplador (1) direccional de la invención comparado con un acoplador direccional convencional nos centraremos, a modo de ejemplo, en un acoplador simétrico 2x2 50/50 (3dB) que se obtiene con una red (31) con P=71 periodos. En la figura 7 se muestran las pérdidas de inserción del dispositivo acoplador (1) direccional de la invención, comparándolas con las de un acoplador direccional convencional. Tanto simulaciones 2D con una herramienta basada en un método de expansión modal, como simulaciones completas 3D con el método FDTD, muestran que la diferencia de potencia entre las dos regiones de salida (O) varía en tan sólo ±0.6dB en el rango considerado de longitudes de onda de 1 ,5μη a Ι ,όμη , es decir una banda ancha de lOOnm, tal y como se puede apreciar en dicha figura 7. Por su parte, el acoplador direccional convencional únicamente cubre con estas mismas prestaciones un ancho de banda de 20nm, lo que confirma el incremento del ancho de banda conseguido con el dispositivo acoplador (1) direccional de la invención en un factor de cinco.  To show the improvement in the bandwidth of the directional coupler device (1) of the invention compared to a conventional directional coupler, we will focus, for example, on a symmetric coupler 2x2 50/50 (3dB) that is obtained with a network ( 31) with P = 71 periods. Figure 7 shows the insertion losses of the directional coupler device (1) of the invention, comparing them with those of a conventional directional coupler. Both 2D simulations with a tool based on a modal expansion method, and full 3D simulations with the FDTD method, show that the power difference between the two output regions (O) varies by only ± 0.6dB in the range considered wavelengths of 1.5μη to Ι, όμη, that is to say a broad band of lOOnm, as can be seen in said figure 7. For its part, the conventional directional coupler only covers a bandwidth of these same features 20nm, which confirms the increase in bandwidth achieved with the directional coupling device (1) of the invention by a factor of five.
En las figuras 8a y 8b se muestra la respuesta de fase del dispositivo acoplador ( 1) direccional 2x2 de la figura 5. Más concretamente en la figura 8a se representa el desfase entre los haces luminosos en las guías de onda de salida (20a, 20b) cuando se inyecta un haz luminoso en la guía de onda de entrada (10a). Así, se observa que el desfase está muy próximo al valor ideal de 90° en toda la banda de longitudes de onda considerada, esto es, de 1 ,5μηι a Ι,όμηι. Por otra parte, en la figura 8b se muestra el desfase diferencial con el que las ondas luminosas procedentes de las guías de onda de entrada (10a, 10b) se combinan en las guías de onda de salida (20a, 20b). Se observa que el desfase diferencial está muy cercano al valor ideal de 180° en toda la banda de longitudes de onda considerada. Por último, cabe señalar que la reflexión del dispositivo acoplador (1) direccional de la presente invención se mantiene por debajo de -15dB en toda la banda de longitudes de onda considerada, de 1,5μιη a Ι ,όμηι. Figures 8a and 8b show the phase response of the 2x2 directional coupler device (1) of Figure 5. More specifically in Figure 8a, the offset between the light beams in the output waveguides (20a, 20b) is shown. ) when a light beam is injected into the input waveguide (10a). Thus, it is observed that the offset is very close to the ideal value of 90 ° in the entire band of wavelengths considered, that is, from 1, 5μηι to Ι, όμ η ι. On the other hand, Figure 8b shows the differential lag with which Light waves from the input waveguides (10a, 10b) are combined in the output waveguides (20a, 20b). It is observed that the differential offset is very close to the ideal value of 180 ° in the entire wavelength band considered. Finally, it should be noted that the reflection of the directional coupler device (1) of the present invention is maintained below -15dB in the entire band of wavelengths considered, from 1.5μιη to Ι, όμηι.
A continuación, de acuerdo con una segunda realización preferente, se describe el dispositivo acoplador (1) de la invención configurado para trabajar como un acoplador de interferencia multimodal, en adelante acoplador "MMI".  Next, according to a second preferred embodiment, the coupling device (1) of the invention configured to work as a multimodal interference coupler, hereinafter referred to as "MMI" coupler, is described.
La figura 9 muestra una gráfica donde se representa la variación de la longitud de batido (Ι,π) con respecto a la longitud de onda de un acoplador MMI convencional. Para este acoplador MMI convencional se han considerado unas guías de ondas uniformes de entrada y salida con una distancia (s) de separación de 2μηι y una anchura (WMMI) de 6μηι, ver figura 2. Nótese que en comparación con el dispositivo acoplador (1) direccional arriba descrito, ahora se está considerando un ancho de banda mayor de 1,26μηι a 1,7μηι. En esta banda la longitud de batido (L„) del dispositivo varía aproximadamente en un 40%. Figure 9 shows a graph showing the variation of the beat length (Ι, π ) with respect to the wavelength of a conventional MMI coupler. For this conventional MMI coupler, uniform input and output waveguides with a separation distance (s) of 2μηι and a width (WMMI) of 6μηι have been considered, see figure 2. Note that compared to the coupling device (1 ) directional described above, a bandwidth greater than 1.26μηι to 1.7μηι is now being considered. In this band the shake length (L „) of the device varies by approximately 40%.
Para obtener, por ejemplo, un acoplador MMI simétrico 2x2 con potencia de salida 50/50, la longitud de onda de la zona de acoplamiento (30) se ha fijado para optimizar el dispositivo a la longitud de onda central, esto es, a 1 ,48μηι. De forma análoga al caso anterior, conforme varía la longitud de onda, la longitud de batido (Ln) cambia y el dispositivo se de- sintoniza, empeorando sus prestaciones. To obtain, for example, a 2x2 symmetric MMI coupler with 50/50 output power, the wavelength of the coupling zone (30) has been set to optimize the device to the central wavelength, that is, at 1 , 48μηι. Similarly to the previous case, as the wavelength varies, the beat length (L n ) changes and the device is tuned, worsening its performance.
En la figura 10 se muestra un dispositivo acoplador (1) 2x2, con dos guías de onda de entrada (10a, 10b) y dos guías de onda de salida (20a, 20b), configurado según la presente invención para trabajar como acoplador MMI, presentando en la zona de acoplamiento (30) una red (31) que permite reducir la variación de la longitud de batido (ίπ) con respecto a la longitud de onda a la que opera el dispositivo, lo que resulta en un aumento de su ancho de banda. En dicha figura 10 se muestra el dispositivo acoplador (1) MMI en una configuración 2x2, no obstante se ha previsto que pueda configurarse según cualquier otra configuración, tal como 1x2, 1x4, 2x2, 2x3, 3x3 y 2x4, presentando siempre la zona de acoplamiento (30) al menos una red (31). Figure 10 shows a coupler device (1) 2x2, with two input waveguides (10a, 10b) and two output waveguides (20a, 20b), configured according to the present invention to work as an MMI coupler, by presenting in the coupling area (30) a network (31) that allows to reduce the variation of the beat length (ί π ) with respect to the wavelength at which the device operates, resulting in an increase in its bandwidth. In said figure 10 the MMI coupling device (1) is shown in a 2x2 configuration, however it is provided that it can be configured according to any other configuration, such as 1x2, 1x4, 2x2, 2x3, 3x3 and 2x4, always presenting the area of coupling (30) at least one network (31).
Configurando adecuadamente el periodo (Λ) y el ciclo de trabajo (DC) de la red (31), se puede controlar la variación con la longitud de onda de las constantes de propagación (βι, β2) de los modos de primer y segundo orden (Φι, Φ2) de la zona de acoplamiento (30). De hecho, eligiendo un ancho de la zona de acoplamiento (30) de 6μιη, y un ciclo de trabajo (DC) del 50% y un periodo de
Figure imgf000014_0001
se consigue reducir la variación de la longitud de batido (Ln) a aproximadamente un 10%, tal y como se representa en la figura 1 1. Nótese que aunque en la presente realización sólo se ha ajustado la longitud de batido ( n) de los dos modos de primer y segundo orden (Φΐ5 Φ2) de la zona de acoplamiento (30), el dispositivo acoplador (1) MMI presenta también unas prestaciones excelentes para otros modos relevantes de la zona de acoplamiento (30). By properly configuring the period (Λ) and the duty cycle (DC) of the network (31), you can control the variation with the wavelength of the propagation constants (βι, β 2 ) of the first and second order modes (Φι, Φ 2 ) of the coupling area (30). In fact, choosing a coupling area width (30) of 6μιη, and a duty cycle (DC) of 50% and a period of
Figure imgf000014_0001
it is possible to reduce the variation of the shake length (L n ) to approximately 10%, as shown in Figure 1 1. Note that although in the present embodiment only the shake length ( n ) of the two first and second order modes (Φ ΐ5 Φ 2 ) of the coupling zone (30), the MMI coupling device (1) also has excellent performance for other relevant modes of the coupling zone (30).
Para mostrar el incremento de ancho de banda que ofrece el dispositivo acoplador (1) MMI de la presente invención nos centraremos a continuación, a modo de ejemplo, en acopladores MMI en configuración 2x2 y 2x4, ya que éstos son de particular interés para la recepción coherente.  To show the increase in bandwidth offered by the MMI coupler device (1) of the present invention, we will now focus, for example, on MMI couplers in 2x2 and 2x4 configuration, since these are of particular interest for reception coherent.
Se parte de un acoplador MMI convencional 2x2, con P=122 periodos en la zona de acoplamiento. En la figura 12a se muestra una gráfica en la que se simulan las pérdidas de inserción (PI) y el desbalanceo (Desb) de un dispositivo acoplador (1) MMI 2x2 según la invención, comparándolas con las de un acoplador MMI convencional. Todas las simulaciones incluyen el efecto de la dispersión del material. En dicha figura 12a se puede observar que el dispositivo acoplador (1) MMI de la invención presenta un ancho de banda de 500nm, de 1,25μπι a 1 ,75μιη, con un desbalanceo por debajo de 0,6dB, lo que es casi cinco veces más ancho de banda que un MMI convencional. Por otro lado, en la figura 12b se puede observar que el error de fase (EF), esto es, la desviación de los 90° de desfase que hay idealmente entre las guías de onda de salida (20a, 20b), está por debajo de ±5° en el rango de las longitudes de onda de 1 ,25μηι a 1 ,75μηι En comparación, un acoplador MMI convencional presenta un error de fase (EFconv) tan reducido como el de la invención tan sólo en un ancho de banda de 150nm. It starts from a conventional 2x2 MMI coupler, with P = 122 periods in the coupling area. Figure 12a shows a graph in which the insertion losses (PI) and the imbalance (Unb) of a MMI 2x2 coupling device (1) according to the invention are simulated, comparing them with those of a conventional MMI coupler. All simulations include the effect of material dispersion. In said figure 12a it can be seen that the coupling device (1) MMI of the invention has a bandwidth of 500nm, from 1.25μπι to 1.75μιη, with an imbalance below 0.6dB, which is almost five times more bandwidth than a conventional MMI. On the other hand, in Fig. 12b it can be seen that the phase error (EF), that is, the deviation of the 90 ° offset that is ideally between the output waveguides (20a, 20b), is below ± 5 ° in the range of wavelengths from 1.25μηι to 1.75μηι In comparison, a conventional MMI coupler has a phase error (EF with v) as small as that of the invention only in a width of 150nm band
En la figura 13 se muestra un dispositivo acoplador (1) MMI de configuración 2x4, con dos guías de onda de entrada (10a, 10b) y cuatro guías de onda de salida (20a, 20b, 20c, 20d), basado en el concepto de la presente invención, y donde la red (31) está dispuesta esencialmente perpendicular a dichas guías de onda de entrada y salida (10a, 10b, 20a, 20b, 20c, 20d). Este dispositivo es de particular interés porque es un componente clave para los sistemas de recepción coherentes.  A coupling device (1) MMI of 2x4 configuration is shown in Figure 13, with two input waveguides (10a, 10b) and four output waveguides (20a, 20b, 20c, 20d), based on the concept of the present invention, and where the network (31) is arranged essentially perpendicular to said input and output waveguides (10a, 10b, 20a, 20b, 20c, 20d). This device is of particular interest because it is a key component for coherent reception systems.
En las figuras 14a, 14b, 14c, 14d se comparan las prestaciones del dispositivo acoplador (1) MMI 2X4 con un acoplador MMI convencional. Más concretamente en la figura 14a se muestra el desbalanceo existente entre las salidas del dispositivo acoplador (1) MMI de la invención para cada una de las dos entradas, que está por debajo de l,6dB en un ancho de banda de 200nm, de 1,45μηι a 1,65μηι. Por otro lado, en la gráfica de la figura 14b se muestra un acoplador de MMI convencional, el cual presenta un desbalanceo por debajo de l,6dB sólo en una banda de lOOnm. The device features are compared in figures 14a, 14b, 14c, 14d coupler (1) MMI 2X4 with a conventional MMI coupler. More specifically, Figure 14a shows the imbalance between the outputs of the coupling device (1) MMI of the invention for each of the two inputs, which is below 1, 6dB in a 200nm bandwidth of 1 , 45μηι to 1.65μηι. On the other hand, a conventional MMI coupler is shown in the graph of Figure 14b, which has an imbalance below 1, 6dB only in a band of lOOnm.
Además, en las figuras 14c y 14d se muestran gráficas de representación del desfase diferencial con que las ondas luminosas de las guías de onda de entrada (10a, 10b) se combinan en las guías de onda de salida (20a, 20b, 20c, 20d).  In addition, figures 14c and 14d show graphs of the differential offset with which the light waves of the input waveguides (10a, 10b) are combined in the output waveguides (20a, 20b, 20c, 20d ).
Más en particular, en la figura 14c se observa que los desfases diferenciales con los que los haces luminosos procedentes de las guías de onda de entrada (10a, 10b) se combinan en las guías de onda de salida (20a, 20b, 20c, 20d), es cercano al valor ideal de 90° entre los pares de guías de onda de salida (20a-20b, 20b-20d, 20d-20c), desviándose de dicho valor ideal de 90° en menos de 20° en todo el ancho de banda de 200nm considerado. Por su parte, en la gráfica de la figura 14d se muestra el desfase diferencial de un acoplador MMI convencional, el cual se desvía hasta 90° de su valor ideal para el mismo ancho de banda considerado, de 1,45μηι a 1,65μιη.  More particularly, in Figure 14c it can be seen that the differential gaps with which the light beams coming from the input waveguides (10a, 10b) are combined in the output waveguides (20a, 20b, 20c, 20d ), is close to the ideal value of 90 ° between the pairs of output waveguides (20a-20b, 20b-20d, 20d-20c), deviating from that ideal value of 90 ° in less than 20 ° across the entire width 200nm band considered. On the other hand, in the graph of figure 14d the differential offset of a conventional MMI coupler is shown, which deviates up to 90 ° from its ideal value for the same bandwidth considered, from 1.45μηι to 1.65μιη.
En los ejemplos de realización descritos hasta ahora se ha asumido que el dispositivo acoplador (1) opera con una sola polarización, concretamente polarización horizontal (cuasi- TE), a lo largo del eje x. No obstante, se ha previsto que puedan configurarse igualmente dispositivos acopladores (1) que operen con polarización vertical (cuasi-TM).  In the embodiments described so far, it has been assumed that the coupling device (1) operates with a single polarization, specifically horizontal polarization (quasi-TE), along the x-axis. However, it is envisioned that coupler devices (1) that operate with vertical polarization (quasi-TM) can also be configured.
De acuerdo con una tercera realización preferente, mostrada en la figura 15, el dispositivo acoplador (1) está configurado para trabajar como un separador de polarización de banda ancha. Para esta aplicación la red (31) existente en la zona de acoplamiento (30) se configura de tal manera que se reduce la variación de la longitud de batido (L*) con la longitud de onda para ambas polarizaciones (cuasi-TE, cuasi-TM). Los valores de las longitudes de batido (Ln) para cada una de dichas polarizaciones son bastante diferentes debido a la fuerte birrefringencia de las redes (31). Por tanto, la longitud (L) de la zona de acoplamiento (30) se configura de modo que cuando se inyecta un haz luminoso de una polarización (cuasi-TE o cuasi-TM), en una guía de onda de entrada (10), dicho haz luminoso se acopla completamente a una de las guías de onda de salida (20a), mientras que si se inyecta un haz luminoso con polarización opuesta a través de la guía de onda de entrada (10) dicho haz luminoso se acopla completamente a la otra guía de onda de salida (20b), tal y como muestra en la figura 15. According to a third preferred embodiment, shown in Figure 15, the coupler device (1) is configured to work as a broadband polarization separator. For this application, the network (31) existing in the coupling area (30) is configured in such a way that the variation of the beat length (L *) is reduced with the wavelength for both polarizations (quasi-TE, quasi -TM). The values of the shake lengths (L n ) for each of said polarizations are quite different due to the strong birefringence of the networks (31). Therefore, the length (L) of the coupling zone (30) is configured so that when a light beam of a polarization (quasi-TE or quasi-TM) is injected, into an input waveguide (10) , said light beam is completely coupled to one of the output waveguides (20a), while if a light beam with opposite polarization is injected through the input waveguide (10) said Light beam is fully coupled to the other output waveguide (20b), as shown in Figure 15.

Claims

R E I V I N D I C A C I O N E S
1. - Dispositivo acoplador (1) de guías de onda, que comprende: 1. - Coupler device (1) of waveguides, comprising:
- al menos una guía de onda de entrada (10a, 10b) en la cual está destinado a inyectarse un haz luminoso,  - at least one input waveguide (10a, 10b) in which a light beam is intended to be injected,
- al menos una guía de onda de salida (20a, 20b, 20c, 20d), y  - at least one output waveguide (20a, 20b, 20c, 20d), and
- una zona de acoplamiento (30) localizada entre dichas guías de ondas de entrada y salida (10a, 10b, 20a, 20b, 20c, 20d), y que está configurada para acoplar el haz luminoso de la guía de onda de entrada (10a, 10b) a la guía de onda de salida (20a, 20b, 20c, 20d),  - a coupling zone (30) located between said input and output waveguides (10a, 10b, 20a, 20b, 20c, 20d), and which is configured to couple the light beam of the input waveguide (10a , 10b) to the output waveguide (20a, 20b, 20c, 20d),
caracterizado porque la zona de acoplamiento (30) comprende al menos una red (31) constituida por un sustrato (2), un núcleo (3) y un revestimiento (4), presentando dicha red (31) un periodo (Λ) inferior a la mitad de la longitud de onda menor del rango de operación del dispositivo acoplador (1), dividida entre el menor de los índices de refracción del sustrato (2), el núcleo (3) y el revestimiento (3) de la red (31), y que garantice que no se producen fenómenos de difracción, estando dicha red (31) configurada para modificar la variación de las constantes de propagación (β1? β2) de los modos de primer y segundo orden (Φ1; Φ2) de la zona de acoplamiento (30) respecto a la longitud de onda, de manera que se reduce la variación de la longitud de batido (L„) con la longitud de onda, aumentando así el ancho de banda del dispositivo acoplador (1). characterized in that the coupling area (30) comprises at least one network (31) constituted by a substrate (2), a core (3) and a coating (4), said network (31) having a period (Λ) of less than half of the smaller wavelength of the operating range of the coupling device (1), divided by the smaller of the refractive indexes of the substrate (2), the core (3) and the lining (3) of the network (31) ), and to ensure that no diffraction phenomena occur, said network (31) being configured to modify the variation of the propagation constants (β 1? β 2 ) of the first and second order modes (Φ 1; Φ 2 ) of the coupling area (30) with respect to the wavelength, so that the variation of the beat length (L „) with the wavelength is reduced, thereby increasing the bandwidth of the coupling device (1) .
2. - Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 1, caracterizado porque la red (31) comprende una guía de onda segmentada cuyos elementos se disponen de forma periódica, perpendicularmente a la dirección de propagación del haz luminoso, y con un periodo (Λ) inferior al periodo de Bragg de primer orden. 2. - Waveguide coupler device (1), according to claim 1, characterized in that the network (31) comprises a segmented waveguide whose elements are arranged periodically, perpendicular to the direction of propagation of the light beam , and with a period (Λ) less than the first order Bragg period.
3. - Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 1, caracterizado porque las guías de ondas de entrada y salida (10a, 10b, 20a, 20b, 20c, 20d) son guías de ondas uniformes. 3. - Waveguide coupler device (1), according to claim 1, characterized in that the input and output waveguides (10a, 10b, 20a, 20b, 20c, 20d) are uniform waveguides.
4.- Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 1, caracterizado porque las guías de ondas de entrada y salida (10a, 10b, 20a, 20b, 20c, 20d) comprenden redes (31). 4. Coupler device (1) of waveguides, according to claim 1, characterized in that the input and output waveguides (10a, 10b, 20a, 20b, 20c, 20d) comprise networks (31).
5.- Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 1, caracterizado porque comprende adicionalmente al menos dos guías de ondas uniformes en la zona de acoplamiento (30), estando la red (31) configurada para modificar la variación de las constantes de propagación (βι, β2) de los modos de primer y segundo orden (Φι, Φ2) en la zona de acoplamiento (30) en función de la longitud de onda, de manera que se reduce la variación de la longitud de batido (Ln) con la longitud de onda, trabajando el dispositivo acoplador (1) como un acoplador direccional, con un ratio de división predefinido. 5. Coupler device (1) of waveguides, according to claim 1, characterized in that it additionally comprises at least two uniform waveguides in the coupling area (30), the network (31) being configured to modify the variation of the propagation constants (βι, β 2 ) of the first and second order modes (Φι, Φ 2 ) in the coupling area (30) as a function of the wavelength, so that the variation in the beat length (L n ) with the wavelength, the coupling device (1) working as a directional coupler, with a predefined division ratio.
6.- Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 5, caracterizado porque la red (31) está dispuesta esencialmente perpendicular a las guías de onda uniformes. 6. Coupler device (1) of waveguides, according to claim 5, characterized in that the network (31) is arranged essentially perpendicular to the uniform waveguides.
7. - Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 5, caracterizado porque la red (31) presenta un ciclo de trabajo (DC) y una extensión lateral (t) configurados para reducir la excitación del modo de tercer orden (Φ3) que produce una transferencia de potencia indeseada entre las guías de ondas uniformes. 7. - Waveguide coupler device (1), according to claim 5, characterized in that the network (31) has a duty cycle (DC) and a lateral extension (t) configured to reduce the excitation of the mode of third order (Φ 3 ) that produces an unwanted power transfer between the uniform waveguides.
8. - Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 1, caracterizado porque la red (31) está adaptada para soportar al menos dos modos (Φ\, Φ2) guiados de la misma polarización (cuasi-TE o cuasi-TM), estando la red (31) configurada para modificar la variación con la longitud de onda de las constantes de propagación (βι, β2) de los modos (Φι, Φ2) en la zona de acoplamiento (30) de manera que se reduce la variación de la longitud de batido U) con la longitud de onda, trabajando el dispositivo acoplador (1) como un acoplador de interferencia multimodal. 8. - Waveguide coupler device (1) according to claim 1, characterized in that the network (31) is adapted to support at least two guided modes (Φ \ , Φ 2 ) of the same polarization (quasi- TE or quasi-TM), the network (31) being configured to modify the variation with the wavelength of the propagation constants (βι, β 2 ) of the modes (Φι, Φ 2 ) in the coupling area (30 ) so that the variation of the beat length U) with the wavelength is reduced, the coupling device (1) working as a multimodal interference coupler.
9. - Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 8, caracterizado porque la red (31) está dispuesta esencialmente perpendicular a las guías de onda de entrada (10a, 10b) y las guías de onda de salida (20a, 20b, 20c, 20d). 9. - Waveguide coupler device (1) according to claim 8, characterized in that the network (31) is arranged essentially perpendicular to the input waveguides (10a, 10b) and the output waveguides (20a, 20b, 20c, 20d).
10.- Dispositivo acoplador (1) de guías de onda, de acuerdo con una cualquiera de las reivindicaciones 5 u 8, caracterizado porque comprende dos guías de onda de entrada (10a, 10b) y dos guías de onda de salida (20a, 20b), y donde el desfase entre los haces luminosos en las i ( guías de onda de salida (20a, 20b) es aproximadamente 90°. 10. Coupler device (1) of waveguides, according to any one of claims 5 or 8, characterized in that it comprises two input waveguides (10a, 10b) and two output waveguides (20a, 20b ), and where the gap between the light beams in the i (output waveguides (20a, 20b) is approximately 90 °.
11.- Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 8, caracterizado porque comprende dos guías de onda de entrada (20a, 20b) y cuatro guías de onda de salida (20a, 20b, 20c, 20d), y donde los desfases diferenciales con los que los haces luminosos procedentes de las guías de onda de entrada (10a, 10b) se combinan en las guías de onda de salida (20a, 20b, 20c, 20d) es aproximadamente de 90°, entre los pares de guías de onda de salida (20a-20b, 20b-20d, 20d-20c)11.- Coupler device (1) of waveguides, according to claim 8, characterized in that it comprises two input waveguides (20a, 20b) and four output waveguides (20a, 20b, 20c, 20d) , and where the differential gaps with which the light beams from the input waveguides (10a, 10b) are combined in the output waveguides (20a, 20b, 20c, 20d) is approximately 90 °, between The pairs of output waveguides (20a-20b, 20b-20d, 20d-20c)
12.- Dispositivo acoplador (1) de guías de onda, de acuerdo con la reivindicación 1 , caracterizado porque la red (31) está configurada para reducir la variación de la longitud de batido (L„) respecto a la longitud de onda tanto para polarizaciones horizontales cuasi-TE como para polarizaciones verticales cuasi-TM, y donde la longitud (L) de la zona de acoplamiento (30) es un múltiplo par de la longitud de batido (LK) para el haz luminoso con polarización cuasi-TE, y un múltiplo impar de la longitud de batido (Ln) para el haz luminoso con polarización cuasi- TM, o viceversa, trabajando el dispositivo acoplador (1) como un separador de polarización de banda ancha.. 12.- Waveguide coupler device (1), according to claim 1, characterized in that the network (31) is configured to reduce the variation of the beat length (L „) with respect to the wavelength for both quasi-TE horizontal polarizations as for quasi-TM vertical polarizations, and where the length (L) of the coupling area (30) is an even multiple of the beating length (L K ) for the light beam with quasi-TE polarization , and an odd multiple of the beating length (L n ) for the light beam with quasi-polarization, or vice versa, the coupling device (1) working as a broadband polarization separator.
13.- Método de diseño del dispositivo acoplador (1) descrito en una cualquiera de las reivindicaciones anteriores, caracterizado porque comprende al menos las siguientes etapas: a) se parte de una guía de onda donde se definen sus parámetros y materiales de diseño para el sustrato (2), el núcleo (3) y el revestimiento (4), 13.- Design method of the coupling device (1) described in any one of the preceding claims, characterized in that it comprises at least the following steps: a) it is based on a waveguide where its design parameters and materials are defined for substrate (2), core (3) and coating (4),
b) se ajusta el periodo (Λ) de la red a un valor ligeramente inferior al periodo de Bragg de primer orden, de manera que no se produzcan fenómenos de difracción,  b) the period (Λ) of the network is adjusted to a value slightly lower than the first order Bragg period, so that diffraction phenomena do not occur,
c) se determina, por simulación, la variación de las constantes de propagación (βΐ5 β2) de los modos de primer y segundo orden (Φΐ5 Φ2) de la zona de acoplamiento (30), c) the variation of the propagation constants (β ΐ5 β 2 ) of the first and second order modes (Φ ΐ5 Φ 2 ) of the coupling area (30) is determined by simulation,
d) se comprueba si la variación de la longitud de batido (L*) con respecto a la longitud de onda se ha reducido,  d) it is checked whether the variation of the beat length (L *) with respect to the wavelength has been reduced,
el) si en la etapa d) se ha conseguido reducir la variación de la longitud de batido (L%) se ajusta de nuevo el periodo (Λ) de la red (31) reduciéndolo ligeramente, el) if in step d) it has been possible to reduce the variation of the shake length (L % ), the period (Λ) of the network (31) is adjusted again by reducing it slightly,
e2) si en la etapa e) no se ha conseguido reducir la longitud de batido (L ) se escoge el valor del periodo (Λ) para el que se había conseguido reducir dicha longitud de batido (LK), y f) se diseña el dispositivo acoplador (1) completo para el valor del periodo (Λ) de la etapa e2), para el cual se obtiene un aumento máximo de su ancho de banda. e2) if in step e) it has not been possible to reduce the shake length (L), the value of the period (para) for which it was possible to reduce said shake length (L K ) has been chosen, and f) the complete coupling device (1) is designed for the period value (Λ) of step e2), for which a maximum increase in its bandwidth is obtained.
14. - Método de diseño de acuerdo con la reivindicación 13, caracterizado porque los parámetros ajustados en la fase a) es al menos uno seleccionado entre: 14. - Design method according to claim 13, characterized in that the parameters set in phase a) is at least one selected from:
- periodo (Λ),  - period (Λ),
- ciclo de trabajo (DC),  - duty cycle (DC),
- hueco (g),  - hole (g),
- grosor (H),  - thickness (H),
- profundidad de grabado (D),  - engraving depth (D),
- anchura (W),  - width (W),
- distancia (s), y  - distance (s), and
- extensión lateral (t).  - lateral extension (t).
15. - Método de diseño de acuerdo con la reivindicación 13, caracterizado en la fase a) se parte de una red (1) que comprende un sustrato (2) de dióxido de silicio, un núcleo (3) de silicio, y un revestimiento (4) de polímero SU-8. 15. - Design method according to claim 13, characterized in phase a) is part of a network (1) comprising a substrate (2) of silicon dioxide, a core (3) of silicon, and a coating (4) SU-8 polymer.
PCT/ES2013/000048 2012-02-23 2013-02-22 Waveguide coupling device and method for designing same WO2013124502A1 (en)

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ES2736899B2 (en) 2018-06-29 2020-05-11 Univ Malaga WAVE GUIDE, METHOD OF MANUFACTURE OF SUCH WAVE GUIDE AND POLARIZATION DIVIDER THAT MAKES USE OF SUCH WAVE GUIDE

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Title
ORTEGA-MONUX A ET AL.: "High-Performance Multimode Interference Coupler in Silicon Waveguides With Subwavelength Structures", IEEE PHOTONICS TECHNOLOGY LETTERS, vol. 23, no. 19, 1 October 2011 (2011-10-01), PISCATAWAY, NJ, US, pages 1406 - 1408, XP011360072 *
ROELKENS G ET AL.: "Grating-Based Optical Fiber Interfaces for Silicon-on-Insulator Photonic Integrated Circuits", IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, vol. 17, no. 3, 1 May 2011 (2011-05-01), PISCATAWAY, NJ, US, pages 571 - 580, XP011326458 *

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