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    • 专利摘要:
    The invention relates to an optoelectronic device for generating a frequency comb comprising: a laser source (2); an optical micro-resonator (3) comprising a resonant ring (20); at least one waveguide (30) optically coupled to the resonant ring (20) having an effective index associated with a fundamental optical mode supported by the filter guide (30) equal to an effective index associated with an optical mode of higher order supported by the resonant ring (20).
    公开号:FR3061776A1
    申请号:FR1750164
    申请日:2017-01-09
    公开日:2018-07-13
    发明作者:Marco CASALE；Houssein EL DIRANI；Corrado SCIANCALEPORE
    申请人:Commissariat a lEnergie Atomique CEA；Thales SA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    © Holder (s): ATOMIC AND ALTERNATIVE ENERGY COMMISSIONER Public establishment, THALES Public limited company.
    O Extension request (s):
    © Agent (s): INNOVATION COMPETENCE GROUP.
    (54) OPTOELECTRONIC DEVICE FOR GENERATING A COMBINED FREQUENCY COMB.
    FR 3,061,776 - A1 (© The invention relates to an optoelectronic device for generating a frequency comb comprising:
    - a laser source (2);
    - an optical micro-resonator (3), comprising a resonant ring (20);
    - at least one waveguide (30) optically coupled to the resonant ring (20), having an effective index associated with a fundamental optical mode supported by the filtering guide (30) equal to an effective index associated with an optical mode of higher order supported by the resonant ring (20).

    OPTOELECTRONIC DEVICE FOR GENERATING A COMBINED FREQUENCY COMB
    TECHNICAL FIELD [001] The field of the invention is that of optoelectronic devices for generating a frequency comb.
    STATE OF THE PRIOR ART Optoelectronic devices exist which make it possible to generate frequency combs. A frequency comb is a representation of an optical signal in the frequency domain whose spectrum is composed of a discrete sum of frequencies. The amplitude can be weighted by a spectral envelope centered on the frequency w P of a pump signal. Such optoelectronic devices find their application in particular in the field of optical telecommunications, for example coherent data transmission networks, signal generation, fast spectroscopy, or even time reference systems.
    Figure IA illustrates an example of such an optoelectronic device 1, described in the publication of Levy et al. titled CMOS-compatible multiple-wavelength oscillator for on-chip optical interconnects, Nature Photon. 4, 37-40 (2010), this optoelectronic device 1 being produced by microelectronics methods of the CMOS type. It includes a laser source 2 and an optical micro-resonator 3 in a ring. The laser source 2 is adapted to emit an optical signal Sin called a pump, continuous and monochromatic with wavelength λ Ρ . The micro-resonator 3 comprises a first waveguide 10 having an input coupled to the laser source 2 and an output which provides an optical signal Sout whose spectrum forms the frequency comb generated. It further comprises an optical cavity formed by a second waveguide 20, called the resonant ring, made of a material with third order nonlinear optical properties, here silicon nitride.
    The optical micro-resonator 2 forms an optical parametric oscillator. The pump signal Sin, the spectrum of which is represented in FIG. 1B, resonantly couples by evanescent wave to a fundamental mode of the resonant ring 20. Insofar as the material of the resonant ring 20 is optically not linear of order three, that is to say that it has an electrical susceptibility of order three, a phenomenon called mixing in four cascade waves appears which generates, starting from the fundamental mode supported by the resonant ring 20, a frequency comb, an example of which is shown in FIG. Furthermore, since such an optical micro-resonator has a high quality factor Q, it is not necessary for the power of the pump signal to be large for the parametric gain to be greater than the optical losses present in the resonant ring, which initiates the amplification of the waves generated.
    The publication of Kordts et al. titled Higher order mode suppression in high-Q anomalous dispersion SiN microresonators for temporal dissipative Kerr soliton formation, Opt. Lett. 41, 452 (2016), describes another example of an optoelectronic device making it possible to generate here a coherent frequency comb, in which the resonant ring made of SiN exhibits an abnormal dispersion regime at the pump wavelength λ Ρ . Due to the anomalous dispersion and the third order nonlinear properties of the material of the resonant ring, dissipative temporal so-called Kerr solitons are formed, which generate a frequency comb by mixing in four cascade waves. The optoelectronic device makes it possible in particular to generate a comb of frequencies whose amplitude and frequency noise is reduced.
    However, as Kordts 2016 explains, the dimensioning of such a resonant ring in order to obtain an abnormal dispersion regime results in making the resonant ring multimode. However, it appears that the different modes supported by the resonant ring can interfere with each other, which can degrade the abnormal dispersion regime and thus disturb the formation of Kerr's time solitons. One solution then consists in locally modifying the resonant ring to form a locally monomode portion, adapted to filter the higher order modes.
    PRESENTATION OF THE INVENTION The aim of the invention is to at least partially remedy the drawbacks of the prior art, and more particularly to propose an optoelectronic device for generating a coherent frequency comb which is more efficient. Another object of the invention is to provide an optoelectronic device for generating a coherent frequency comb whose optical losses are limited. Another object is to propose an optoelectronic device which limits or even eliminates the optical disturbances liable to degrade the formation of time dissipative Kerr solitons. For this, the object of the invention is an optoelectronic device for generating a frequency comb comprising a laser source adapted to emit a so-called pump, continuous and monochromatic optical signal of a so-called pump wavelength, and an optical ring microresonator.
    The optical micro-resonator comprises:
    a first waveguide, comprising an input optically coupled to the laser source, and an output intended to supply the frequency comb generated;
    a second multimode ring waveguide, called a resonant ring, optically coupled to the first waveguide to generate a so-called fundamental optical mode in the resonant ring, the resonant ring being formed from a material, called a core material, optically nonlinear order three whose refractive index depends on the intensity of an optical signal passing through it and which has transverse dimensions such that it has an abnormal dispersion regime associated with said fundamental optical mode. In other words, the transverse dimensions of the resonant ring, for example the width and / or the thickness of the resonant ring, are chosen so that the dispersion parameter D, at the wavelength of the fundamental mode, is positive.
    According to the invention, the optoelectronic device further comprises at least a third waveguide, said filter guide, optically coupled to the resonant ring, having an effective index associated with a fundamental optical mode supported by the filter guide equal to an effective index associated with a higher order optical mode supported by the resonant ring.
    Some preferred but non-limiting aspects of this optoelectronic device are as follows.
    The filter guide may include a coupling portion optically coupled to the resonant ring, and formed of a material called core, the refractive index of the core material and transverse dimensions being chosen so that a effective index associated with the fundamental optical mode of the filter guide is equal to an effective index associated with the higher-order optical mode of the resonant ring.
    The filter guide may have a single-mode coupling portion.
    The filter guide can be made of a material, called a heart, identical to that of the resonant ring.
    The filter guide may include a coupling portion spaced from the resonant ring by a distance between 200nm and 300nm.
    The filter guide may include a coupling portion and an end portion, the end portion having transverse dimensions which decrease as one moves away from the coupling portion.
    The resonant ring can be formed from a core surrounded by a sheath, the core material being silicon nitride.
    The resonant ring may have an average thickness greater than or equal to 700nm, and an average width greater than or equal to 1200nm.
    BRIEF DESCRIPTION OF THE DRAWINGS Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of nonlimiting example, and made with reference to the accompanying drawings, in addition to FIGS. IA-IC already described, in which:
    Figure IA is a top view, schematic and partial, of an optoelectronic device for generating a frequency comb according to an example of the prior art; FIGS. 1B and 1C respectively illustrate an example of a wavelength spectrum of the optical pump signal and an example of a frequency comb generated;
    FIG. 2A is a top view, schematic and partial, of an optoelectronic device for generating a frequency comb according to one embodiment; Figure 2B is a cross-sectional view of the resonant ring and the filter guide along a plane A-A;
    FIGS. 3A and 3B respectively illustrate an example of the wavelength spectrum of the optical pump signal and an example of frequency comb generated by the optoelectronic device shown in FIG. 2A;
    FIGS. 4A and 4B are schematic and partial top views of the resonant ring and the filter guide, illustrating the filtering of the higher order mode supported by the resonant ring by the filter guide (FIG. 4A) and the absence of filtering of the fundamental mode supported by the resonant ring (fig.4B);
    FIGS. 5A-5C illustrate an example of the influence of the distance d separating the filter guide from the resonant ring on the value of the dispersion parameter D (FIG. 5A); on the optical coupling for the higher order mode supported by the resonant ring and filtered by the filter guide (fig.5B); on the optical losses of the fundamental mode supported by the resonant ring (fig.5C); and FIG. 5D illustrates the evolution of the optical coupling for the higher order mode supported by the resonant ring and filtered by the filter guide as a function of the wavelength for a fixed distance d.
    DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS In the figures and in the following description, the same references represent the same or similar elements. In addition, the different elements are not shown to scale so as to favor the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and can be combined with one another. Unless otherwise indicated, the terms "substantially", "approximately", "in the order of" mean to the nearest 10%.
    The invention relates to an optoelectronic device for generating a coherent frequency comb. It comprises an optical micro-resonator which forms an optical parametric oscillator, in which a coherent frequency comb is generated by a non-linear phenomenon of order three of mixing in four cascade waves, associated with the formation of dissipative temporal solitons of the type Kerr. The frequency comb is said to be coherent when all or part of the frequency lines are in phase relationship with one another. The consistency of the frequency comb is linked here to the presence of Kerr-type dissipative temporal solitons.
    An optical parametric oscillator is a coherent light source which is based on a parametric amplification in an optical resonator. The optical resonator here comprises an optical cavity produced in a non-linear medium of the third order, that is to say comprising an electrical susceptibility χ ^ 3 ) of order three, allowing the mixing with four cascaded waves to take place, thus generating a frequency comb.
    The cascaded four-wave mixing is a third order nonlinear phenomenon in which two photons of pump frequency w P are converted without loss of energy into a signal photon of frequency w s and a complementary photon (idler , in English) of frequency w c . It is said to be cascaded insofar as the photons generated are also at the origin of the generation of other signal and complementary photons by mixing with four waves.
    The optical Kerr effect is a non-linear phenomenon of order three which expresses the dependence of the refractive index of a medium on the intensity of the optical signal which passes through it. This dependence can be formalized by the relation: n = no + Π2.Ι where n is the refractive index of the material, no = (1 + χ (1) ) 1/2 , where χ <Τ is the electrical permittivity d order 1, Π2 is the nonlinear index which depends on the electrical permittivity χ ( 3 ) of order 3, and where I is the intensity of the optical signal which crosses the medium.
    As detailed below, to allow the formation of Kerr's dissipative temporal solitons, the optical cavity of the micro-resonator is further adapted to present an abnormal dispersion regime associated with the fundamental optical mode that it supports. The dispersion is said to be abnormal when the dispersion parameter D is positive. This parameter D, expressed in ps / (nm.km), is defined as the product of a quantity β2 and -2πο / λ 2 where λ is the wavelength of the fundamental mode supported by the resonant ring, equal here at the pump wavelength λ Ρ . The quantity β2, also called group velocity dispersion (GVD, for Group Velocity Dispersion, in English), corresponds to the fact that the group speed of the optical signal is dependent on the wavelength of the signal. The quantity β2 is defined as being equal to the derivative of the inverse of the group speed of the optical signal: β 2 = = ° ù v § es t the group speed of the optical signal considered, w the frequency and k the number wave. In other words, it corresponds to the second derivative of 3 (w) with respect to w, at the pump wavelength λ Ρ . β is the propagation constant, which depends on the optical field of the mode and the dimensional characteristics of the waveguide.
    FIG. 2A is a top view, schematic and partial, of an optoelectronic device 1 for generating a coherent frequency comb according to one embodiment. This optoelectronic device 1 comprises a laser source 2 adapted to emit a continuous monochromatic optical signal, an optical micro-resonator 3 in a ring, and at least one filtering waveguide 30. FIG. 2B is a sectional view of the ring resonant 20 and the filter guide 30 along a plane AA illustrated in FIG. 2A.
    In the following description, a three-dimensional orthogonal coordinate system (Χ, Υ, Ζ) is defined where the axes X and Y form a plane parallel to the plane on which the waveguides of the optoelectronic device rest, and where l Z axis is oriented along the thickness dimension of the waveguides.
    The laser source 2 is adapted to emit an optical signal called pump Sin. This optical signal is continuous and monochromatic, of wavelength λ Ρ . The pump wavelength λ Ρ is chosen to be able to excite a fundamental mode supported by a ring waveguide 20 of the optical micro-resonator 3. As an example, it can be equal to l , 55pm in the case of a so-called telecom application, or even equal to 1.3 lpm for a so-called datacom application, or even also be a wavelength of the visible or the infrared, in particular the mid-infrared. The power of the pump signal is chosen so as to be greater than the optical losses present in the optical micro-resonator, so that the parametric gain is greater than the optical losses and that the amplification of the optical signal in the micro-resonator 3 in ring can generate a frequency comb by mixing four waves in cascade.
    The optical micro-resonator 3 in a ring comprises a first waveguide 10 and a second waveguide 20 in a ring, called the resonant ring.
    The first waveguide 10 has an input 11 and an output 12, which also form the input and the output of the optical micro-resonator 3. The input 11 is optically coupled to the laser source 2 to receive the pump signal Sin emitted by the latter, and the output 12 is adapted to supply the frequency comb generated. It comprises a coupling zone 13 intended to be optically coupled, by evanescent wave, to the resonant ring 20.
    The first waveguide 10 is made of a material, called a heart, with a high refractive index. More precisely, it comprises a core formed from the material of high refractive index surrounded by a sheath formed from at least one material of low refractive index. The heart rests on a surface of a substrate (not shown) whose material participates in forming the sheath. For example, the core material can be silicon nitride SiN, for example S13N4, and the cladding material can be silicon oxide SiO, for example S1O2.
    The waveguide 10 extends longitudinally between the inlet 11 and the outlet 12, with a shape which can be arbitrary. Generally, each waveguide has an upper face opposite the surface of the substrate, and lateral flanks which extend from the upper face to the surface of the substrate. It has transverse dimensions of height and width. By height is meant the average distance of the waveguide, and more precisely of the heart, along the axis Z orthogonal to the plane of the substrate, between the upper face and the surface of the substrate. By width is meant the average distance between the lateral flanks of the waveguide, and more precisely of the core, in a plane parallel to the plane of the substrate. The height and the width are substantially constant along the longitudinal extent of the waveguide. For example, for a pump length of 1.55pm, the transverse dimensions of the heart can range from a few hundred nanometers to several micrometers. The first waveguide can be singlemode or multimode. In this example, it is preferably single mode and supports a TE type mode (electrical transverse).
    The second waveguide 20, called the resonant ring, forms the optical cavity of the micro-resonator 3. As with any optical parametric oscillator of the Kerr type, it comprises a non-linear material of order three making it possible to generate waves optical wavelengths different from the pump wavelength by a phenomenon of four-cascade mixing. In addition, the resonant ring 20 has an abnormal dispersion regime for the fundamental optical mode, thus allowing the formation of dissipative time solitons of the Kerr type contributing, with the four-wave cascade mixture, to the generation of the coherent frequency comb. .
    The resonant ring 20 is a ring-shaped waveguide. It has an optical coupling zone allowing it to be coupled by evanescent wave to the first waveguide. It can extend in the form of a circle, an oval or the like. In this example, it has a circle shape whose radius r is defined from a longitudinal line extending along the transverse barycenter of the heart of the resonant ring 20.
    The resonant ring 20 is made of a high index material with nonlinear optical properties of order three. More specifically, it comprises a core 21 made of the material of high refractive index and a sheath made of a material of low refractive index. The heart 21 has an upper face 22 opposite the surface of the substrate on which it rests, and lateral flanks 23 which extend from the upper face 22 to the substrate. It has a thickness e ga and a width l ga substantially constant along its longitudinal extent.
    The resonant ring 20 is adapted to be optically coupled to the first waveguide 10. Thus, it is dimensioned so that there is phase agreement between the fundamental optical mode, here TEoo, supported by the first guide 10 and the fundamental optical mode, here TEoo, supported by the resonant ring 20. In other words, the propagation constant of the fundamental mode TEoo supported by the resonant ring 20 is equal to the propagation constant of the fundamental mode TEoo supported by the first guide 10, which results here in the equality between the effective index of the fundamental mode TEoo supported by the resonant ring 20 with that of the fundamental mode TEoo supported by the first guide 10.
    In general, the effective index n e ff of a mode of a waveguide is defined as the product of the propagation constant β and λ / 2π. The propagation constant β depends on the wavelength λ and the mode of the optical signal, as well as on the properties of the waveguide (refractive indices and geometry). The effective mode index corresponds, in a certain way, to the refractive index of the guide 'seen' by the optical mode. It is usually between the index of the heart and the index of the sheath of the waveguide.
    The resonant ring 20 is more suitable for ensuring parametric conversion of frequencies by mixing four waves in cascade. For this, the material with a high index of the core has non-linear optical properties allowing the optical Kerr effect, and thus has a refractive index which depends on the intensity of the optical signal traversing it. Four-wave mixing by optical Kerr effect is then possible. Preferably, the material of the resonant ring, and more precisely that of the core 21, is silicon nitride SiN, for example S13N4. The sheath material can be a silicon oxide SiO, for example S1O2.
    The resonant ring 20 is more suitable for forming dissipative time solitons called Kerr. By definition, a soliton is a solitary optical wave which propagates without deformation in a non-linear and dissipative medium. These solitons are said to be of Kerr type insofar as they are generated in a third order nonlinear material by optical Kerr effect.
    Insofar as the solitonic regime can only appear in an optical cavity where the dispersion is abnormal, the resonant ring 20 is adapted so that the dispersion is abnormal for the fundamental mode, here Teoo, supported by the resonant ring 20. For this, as shown in the publication by Okawachi et al entitled Octave-spanning frequency comb generation in a silicon nitride chip, Opt. Lett. 36,3398 (2011), the transverse dimensions of height and / or width of the resonant ring 20, and more precisely of the heart 21 of the resonant ring 20, are adapted so that it has an associated abnormal dispersion regime in fundamental mode, here Teoo. In the case where the core material is a silicon nitride, this then results in the fact that the thickness and / or width dimensions of the resonant ring 20 become greater than the wavelength λ Ρ of the signal pump, the resonant ring 20 can then support several different optical modes (multimode guide). The resonant ring 20 can thus support TEoo fundamental mode and at least one higher order mode, for example TE01 mode. By way of example, in the case of a pump wavelength λ Ρ equal to approximately 1.55 μm, and for a material of the core of the resonant ring 20 made of silicon nitride, the height e ga is preferably greater than or equal to 700 nm and the width l ga is preferably greater than or equal to 1200 nm.
    The filter guide 30 is optically coupled to the resonant ring 20 so as to filter a higher order mode, here for example the TE01 mode, supported by the resonant ring 20. It thus makes it possible to limit the interactions between the different optical modes within the resonant ring 20, these interactions being capable of degrading the abnormal regime of the dispersion D and therefore of disturbing the formation of the dissipative temporal solitons.
    For this, the filter guide 30 includes a coupling portion 31 optically coupled to the resonant ring 20.  The dimensions and the refractive index of the filter guide 30, more precisely of the heart 34 of the filter guide 30, are chosen so that there is phase agreement between the optical mode of higher order to be filtered, here TEoi, supported by the resonant ring 20, and the fundamental optical mode TEoo supported by the filter guide 30.  In other words, the propagation constant of the higher order mode to be filtered TEoi supported by the resonant ring 20 is equal to the propagation constant of the fundamental mode TEoo supported by the filter guide 30, which results here in equality between the effective index of the higher order mode TEoi of the resonant ring 20 with that of the fundamental mode TEoo of the filter guide 30.  Thus, the filter guide 30 is able to filter the higher order mode of the resonant ring 20.  In addition, since there is phase agreement between these two optical modes, there is no phase agreement between the filter guide 30 and the fundamental mode TEoo of the resonant ring 20, so that the presence of the filter guide 30 does not substantially induce disturbances in the fundamental mode of the resonant ring 20.
    The filter guide 30 is formed of a heart 34 made of at least one high index material surrounded by a sheath made of at least one low index material. The high index material is preferably identical to that of the resonant ring 20, for example silicon nitride SiN, for example S13N4. The sheath material can be a silicon oxide SiO, for example S1O2. The filter guide 30 has a constant thickness e g f and a width l g f at the coupling portion 31. The filter guide 30 is spaced from the resonant ring 20 by a distance d, corresponding to the minimum distance separating the coupling portion of the filter guide 30 of the resonant ring 20. The distance d is measured from the lateral flanks facing the resonant ring 20 and the filter guide 30. The distance d can be l '' a few hundred nanometers or even a few microns. It can thus be between 100 nm and 800 nm, preferably between 100 nm and 400 nm, and preferably between 200 nm and 300 nm, for example equal to approximately 250 nm.
    The waveguide 30 comprises a so-called end portion 35 located in the extension of the coupling portion 31 in the direction of propagation of the fundamental optical mode, which has a gradual decrease in its transverse dimensions, and here of its width, as one moves away from the coupling portion 31. One thus achieves a gradual decrease in the effective index of the guided mode, resulting in an optical leak of the mode by diffractive radiation in the substrate.
    The operation of the optoelectronic device according to the embodiment is now described, with reference to Figures 3A-3B and 4A-4B.
    The laser source 2 emits an optical signal Sin from a continuous and monochromatic pump of wavelength λ Ρ , a spectrum of which is illustrated in FIG. 3A. This pump signal Sin is transmitted by the first waveguide 10 towards the output 12 of the guide. Insofar as the first waveguide 10 is single-mode in this example, the pump signal corresponds to a fundamental mode of the guide 10, for example TEoo.
    By optical coupling of evanescent type between the first waveguide 10 and the resonant ring 20, the pump signal Sin of TEoo mode excites the fundamental mode TEoo of the resonant ring 20. More specifically, the optical coupling is achieved by the phase agreement between the fundamental mode TEoo of the first guide 10 and the fundamental mode TEoo of the resonant ring 20. Thus, part or all of the optical signal Sin is transmitted from the first guide 10 into the ring resonant 20.
    Insofar as the resonant ring 20 is made of a third order non-linear material allowing the optical Kerr effect on the one hand, and that it has an abnormal dispersion regime on the other hand, solitons Kerr dissipative temporals are formed which generate a coherent frequency comb by mixing four cascaded waves.
    The generation of the coherent frequency comb is made more robust in so far as the formation of dissipative solitons is not disturbed by possible couplings or interference between the fundamental mode TEoo and at least one optical mode of higher order, here TEoi mode.
    Indeed, as illustrated in Figure 4A, the higher order optical mode TEoi supported by the resonant ring 20 is filtered and therefore substantially removed from the resonant ring 20 by the optical coupling between the resonant ring 20 and the filter guide 30. This optical filtering is obtained by the phase agreement between the higher order mode, here TEoi, of the resonant ring 20 and the fundamental mode TEoo of the filter guide 30. Thus, the optical power TEoi mode present in the resonant ring 20 is transmitted to TEoo fundamental mode of the filter guide 30.
    In addition, as illustrated in FIG. 4B, the filtering of the higher order mode TEoi does not impact the fundamental mode TEoo (nor its dispersion) of the resonant ring 20, insofar as it does not there is no phase agreement between the fundamental mode TEoo of the resonant ring 20 and that of the filter guide 30.
    Thus, at the output of the first waveguide, a coherent frequency comb is obtained. It presents a constant free spectral interval, that is to say a constant value of spacing between the successive frequency lines, as well as a low noise of frequency and / or amplitude. In addition, the amplitude of the frequency lines is weighted by a spectral envelope of the hyperbolic sine type squared (sinh 2 ) centered on the wavelength λ Ρ of the pump, thus translating the coherence of the frequency comb.
    The optoelectronic device 1 thus has reduced optical losses compared to the example of the prior art mentioned above, insofar as the resonant ring 20 does not have a filtering portion. The optical micro-resonator 3 then has a reduced oscillation threshold, in the sense of an optical parametric oscillator, making it possible to obtain a frequency comb of the same intensity for a reduced power of the pump signal, or a frequency comb of higher intensity for an identical pump signal strength.
    In addition, the optoelectronic device is made more robust in so far as the dispersion regime remains of abnormal type over the entire length of the resonant ring 20, thus limiting the disturbances liable to degrade the formation of dissipative temporal solitons from Kerr type.
    Purely by way of illustration, the optoelectronic device 1 may include a laser source 2 adapted to emit a continuous monochromatic pump optical signal, with a wavelength equal to 1.55pm. The pump signal is guided in the first waveguide 10, which is single mode and supports the TEoo fundamental mode.
    The resonant ring 20 is made of S13N4 which is a material with an optical Kerr effect. It has a radius r of approximately 115pm, a thickness e ga of 710nm and a width ga l, approximately 6pm. The resonant ring 20 is therefore multimode at 1.55 pm and supports the TEoo fundamental mode as well as at least one higher order mode, for example the TE01 mode. Independently of the filter guide 30, the resonant ring 20 has a chromatic dispersion parameter D associated with the fundamental mode TEoo at 1.55pm equal to 82.2 ps / (nm.km). This chromatic dispersion value being positive, the resonant ring 20 is indeed in an abnormal dispersion regime for this optical signal.
    Furthermore, the filter guide 30 is also made of S13N4. It has a coupling portion with a thickness e g f of approximately 710 nm, substantially equal to that of the resonant ring 20, and with a width l g f of approximately 660 nm. In addition to the refractive index of the filter guide 30, the transverse dimensions of its coupling portion 31 are chosen so that there is phase agreement between the higher order mode TE01 supported by the resonant ring 20 and the mode TEoo fundamental supported by the filter guide 30. In other words, the effective index of the higher order mode TE01 supported by the resonant ring 20 is substantially equal to the effective index of the TEoo fundamental mode supported by the filter guide. 30: (n e ff, TE01) g a = (n e ff, TE00) g f.
    As illustrated in FIG. 5A, it appears that the value of the dispersion parameter D associated with the fundamental mode TEoo supported by the resonant ring 20 at the pump wavelength l, 55pm is modified by the presence of the filter guide 30, and that it is in particular a function of the distance d separating the filter guide 30 from the resonant ring 20. Thus, the value of the parameter D decreases as the filter guide 30 is brought closer to the ring resonant 20. It is thus 78 ps / (nm.km) at a distance d of 650nm and decreases continuously to a value of 15 ps / (nm.km) at a distance d of 200nm. Thus, whatever the value of the distance d between the filter guide 30 and the resonant ring 20, the value of the dispersion parameter D remains positive, thus reflecting the presence of an abnormal dispersion regime for the fundamental TEoo mode supported. by the resonant ring 20 at the pump wavelength 1.55pm.
    As illustrated in FIG. 5B, the coupling rate K by evanescent wave between the higher order mode TEoi supported by the resonant ring 20 and the TEoo mode supported by the filter guide 30 depends on the distance d separating the filter guide 30 of the resonant ring 20. While the coupling rate K decreases as the distance d increases, it appears that it has an optimum at approximately 250 nm, where the coupling rate is equal to approximately 90% . Thus, the distance d is preferably less than or equal to about 400 nm to ensure a coupling rate greater than or equal to 50%, and preferably is less than or equal to 350 nm, and preferably between 200 nm and 300 nm to ensure a rate of coupling greater than or equal to 80%, and more preferably still equal to approximately 250 nm.
    As illustrated in FIG. 5C, the optical losses L of the fundamental mode TEoo supported by the resonant ring 20, due to the presence of the filter guide 30, remain very low, thus reflecting the low impact of the filter guide 30 on this optical mode. The filter guide 30 then makes it possible to correctly filter the higher order mode TEoi present in the resonant ring 20 without disturbing the fundamental mode TEoo. The optical losses decrease as the distance d increases, but they remain very small. They are thus less than 0.03 dB for a distance d greater than 200nm and drop to about 0.01 dB for a distance d of 250nm. They are therefore negligible, even almost zero.
    FIG. 5D illustrates the coupling rate K 'between the higher order mode TEoi supported by the resonant ring 20 and the TEoo mode supported by the filter guide 30 as a function of the wavelength, for a distance d equal to approximately 250nm. In other words, this figure illustrates the spectral behavior of the filter guide 30 between the resonant ring 20 and the filter guide 30 at a distance d of approximately 250 nm. The coupling rate K has a maximum value of 90% for a wavelength of l, 585pm approximately. The bandwidth of the filter, at 3 dB, is approximately 430nm. Such a filter guide 30 thus makes it possible to limit the phase tuning constraints between the optical modes of the resonant ring 20 and of the filter guide 30.
    Specific embodiments have just been described. Different variants and modifications will appear to those skilled in the art. Thus, the higher order mode to filter mentioned previously is TEoi mode but it could be TEio mode 5 or even another type of mode. If several higher order modes are present in the resonant ring 20, several filter guides can be provided, which are each adapted to filter a given higher order mode. In addition, the examples of optical modes mentioned above are TE (transverse electric) modes, but they could be TM (transverse magnetic) modes.
    权利要求:
    Claims (8)
    [1" id="c-fr-0001]
    1. Optoelectronic device (1) for generating a frequency comb, comprising:
    o a laser source (2) adapted to emit an optical signal called a pump, continuous and monochromatic with a wavelength called a pump;
    o an optical micro-resonator (3) in a ring, comprising:
    a first waveguide (10), comprising an input (11) optically coupled to the laser source (2), and an output (12) intended to supply the frequency comb generated;
    a second multimode ring waveguide (20), called a resonant ring, optically coupled to the first waveguide (10) to generate a so-called fundamental optical mode in the resonant ring (20), the resonant ring (20 ) being formed of a material, said to be of the heart, optically nonlinear of order three whose refractive index depends on the intensity of an optical signal traversing it and which has transverse dimensions such that it has a regime of abnormal dispersion associated with said fundamental optical mode;
    characterized in that it comprises:
    o at least a third waveguide (30), said filter guide, optically coupled to the resonant ring (20), having an effective index associated with a fundamental optical mode supported by the filter guide (30) equal to an index effective associated with a higher order optical mode supported by the resonant ring (20).
    [2" id="c-fr-0002]
    2. Device (1) according to claim 1, wherein the filter guide (30) comprises a coupling portion (31) optically coupled to the resonant ring (20), and formed of a material called heart, the refractive index of the core material and of the transverse dimensions being chosen such that an associated effective index of the fundamental optical mode of the filter guide (30) is equal to an effective index associated with the higher order optical mode of the resonant ring (20).
    [3" id="c-fr-0003]
    3. Device (1) according to claim 1 or 2, wherein the filter guide (30) has a coupling portion (31) single mode.
    [4" id="c-fr-0004]
    4. Device (1) according to any one of claims 1 to 3, wherein the filter guide (30) is made of a material, called heart, identical to that of the resonant ring (20).
    [5" id="c-fr-0005]
    5. Device (1) according to any one of claims 1 to 4, wherein the
    5 filter guide (30) has a coupling portion (31) spaced from the resonant ring (20) by a distance (d) between 200nm and 300nm.
    [6" id="c-fr-0006]
    6. Device (1) according to any one of claims 1 to 5, in which the filter guide (30) comprises a coupling portion (31) and an end portion (35), the end portion (35 ) with transverse dimensions which
    10 decrease as one moves away from the coupling portion (31).
    [7" id="c-fr-0007]
    7. Device (1) according to any one of claims 1 to 6, in which the resonant ring (20) is formed by a core (21) surrounded by a sheath, the core material being silicon nitride .
    [8" id="c-fr-0008]
    8. Device (1) according to any one of claims 1 to 7, in which the resonant ring (20) has an average thickness greater than or equal to
    700nm, and an average width greater than or equal to 1200nm.
    1/4 ι
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    EP3346328B1|2019-08-28|
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    US6940878B2|2002-05-14|2005-09-06|Lambda Crossing Ltd.|Tunable laser using microring resonator|
    US8519803B2|2010-10-29|2013-08-27|Hewlett-Packard Development Company, L.P.|Resonator systems and methods for tuning resonator systems|
    US9128246B2|2011-10-17|2015-09-08|University Of Maryland, College Park|Systems, methods, and devices for optomechanically induced non-reciprocity|
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    WO2015012915A2|2013-04-22|2015-01-29|Cornell University|Parametric comb generation via nonlinear wave mixing in high-q optical resonator coupled to built-in laser resonator|
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    WO2018081824A1|2016-10-31|2018-05-03|The Regents Of The University Of California|Adiabatic dispersion-managed frequency comb generation|
    FR3064078B1|2017-03-17|2020-07-24|Commissariat Energie Atomique|OPTOELECTRONIC DEVICE FOR GENERATING A FREQUENCY COMB|FR3064078B1|2017-03-17|2020-07-24|Commissariat Energie Atomique|OPTOELECTRONIC DEVICE FOR GENERATING A FREQUENCY COMB|
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    法律状态:
    2017-12-21| PLFP| Fee payment|Year of fee payment: 2 |
    2018-07-13| PLSC| Search report ready|Effective date: 20180713 |
    2020-01-30| PLFP| Fee payment|Year of fee payment: 4 |
    2021-10-08| ST| Notification of lapse|Effective date: 20210905 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1750164|2017-01-09|
    FR1750164A|FR3061776B1|2017-01-09|2017-01-09|OPTOELECTRONIC DEVICE FOR GENERATING A COMBINED FREQUENCY COMB|FR1750164A| FR3061776B1|2017-01-09|2017-01-09|OPTOELECTRONIC DEVICE FOR GENERATING A COMBINED FREQUENCY COMB|
    US15/862,173| US10261391B2|2017-01-09|2018-01-04|Optoelectronic device for generation of a coherent frequency comb|
    EP18150511.6A| EP3346328B1|2017-01-09|2018-01-05|Optoelectronic device for generating a coherent frequency comb|
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