Tunable photonic unit for generating frequency converted and / or squeezed light and photonic apparatus comprising a plurality of such devices

Abstract

The invention relates to a photonic device (1) for generating frequency converted and / or squeezed light. The device (1) comprises an optical waveguide (6) that has a plurality of regions (8) arranged one behind the other in the direction of light propagation. In this way, the optical waveguide (6) varies accordingly in regions in a property that influences a light property of the light passing through the optical waveguide (6). The device (1) further comprises a unit (7) for controllably influencing, in regions, the refractive index of the material of the optical waveguide (6) for the light passing through in at least one selection of the regions (8). The invention also relates to a photonic apparatus that comprises a plurality of such photonic devices.

Description

[0001] Tunable photonic device for generating frequency-converted and / or squeezed light and photonic device comprising a plurality of such devices

[0002] The present invention relates to a photonic device for generating squeezed light and to a photonic device comprising such a photonic device.

[0003] Frequency or wavelength conversion of light can be used, for example, in communications engineering to derive the wavelengths of carrier signals from a laser wavelength. Squeezed light, i.e., light in corresponding quantum states, can be useful for various applications in quantum computers or in sensor technology to improve phase sensitivity. Various approaches already exist to realize corresponding light sources for generating squeezed light. However, the actually resulting optical quantum states can be sensitively dependent on minimal manufacturing-related variations in the components or materials of the corresponding light sources, which are within the scope of currently achievable manufacturing tolerances. This can limit the quality of the quantum states or even the practicality of corresponding applications. Therefore, there is a need for further improvements in this area.

[0004] The object of the present invention is to improve the usability of influenced, in particular frequency-converted and / or squeezed, light in photonic applications.

[0005] The object is achieved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the subclaims, the description and the drawing. Features, advantages and possible embodiments that are set out in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages and possible embodiments of the respective subject matter of the other independent claims and of any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims. The photonic device according to the invention serves to generate frequency-converted and / or squeezed light in comparison to an initial state, for example of light generated in the device or supplied to the device on the input side.For this purpose, the device has at least one optical fiber made of a material with non-vanishing, i.e. non-zero, second-order nonlinear susceptibility. This optical fiber comprises several regions arranged one behind the other in the optical fiber or through the optical fiber along a specified direction of light propagation. The optical fiber varies accordingly in at least one property, i.e. across these several regions, in at least one property. This is a property by which at least one light property, such as the wavelength or the light wavelength composition or the propagation or phase velocity or the frequency conversion behavior or the phase adaptation to a predetermined target frequency of the light, is influenced or determined by the light passing through the optical fiber.Such properties can be, for example, the crystal orientation or the geometry or the refractive index of the material of the corresponding regions of the optical waveguide or the like. In each case, a region of the optical waveguide can have a specific value or a specific characteristic of this property. Likewise, the property or its value or characteristic can vary within a region. In this case, the property can vary in different ways in at least two regions, so that these two regions can then differ from one another accordingly when viewed as a whole. The optical waveguide can therefore comprise at least two regions that differ from one another in this property. In addition, the optical waveguide can comprise two or more regions that are identical in this property and therefore do not differ from one another in this regard.In particular, the regions can be designed and arranged in such a way that the property alternates between two different values ​​or characteristics along the intended direction of light propagation, i.e., switches back and forth. Other configurations are also possible.

[0006] According to the invention, the photonic device also comprises at least one device for selectively, i.e., controlled or controllable, influencing the refractive index of the material of the optical waveguide in the respective region for the intended light passing through in at least one selection, i.e., at least some of the regions. In other words, by appropriate operation or control of the device, the refractive index can be adjusted or adjusted in at least one region of the optical waveguide.

[0007] The device according to the invention can be configured, for example, as a photonic chip or PIC (Photonic Integrated Circuit). The device can, in particular, be manufactured entirely or partially using semiconductor manufacturing methods. The device can, for example, also comprise a laser or pump light source, such as a diode or semiconductor laser or the like. This can also be integrated, i.e., arranged, for example, on the same chip or circuit board as the optical waveguide and the device for influencing the refractive index. Thus, the device according to the invention can be configured or manufactured particularly compactly and robustly.

[0008] To generate the light influenced by the device, i.e., frequency-converted and / or squeezed, light radiated into the optical waveguide at a given wavelength can be converted into light of a different wavelength. Different materials or material systems can be used for this purpose. For example, lithium niobate can be used as the material for the optical waveguide. Other possible materials can be or include, for example, lithium tantalate, barium titanate, silicon nitride, electro-optically active polymers, or the like. The present invention can enable maximization of the conversion rate and / or optimization of the resulting wavelength for a particular application by controlling the refractive index, i.e., appropriate tuning or tunability in this regard.This can be particularly useful when the photonic device is used as a single or sole squeezed light source in the application.

[0009] For quantum computing applications, for example, it can be useful to use multiple light sources in parallel, especially for squeezed light, to enable the superposition or interaction of squeezed light with other squeezed light, or the superposition or interaction of multiple corresponding optical quantum states, as easily as possible. For such an interaction of multiple optical quantum states based on squeezed light, these quantum states should ideally be indistinguishable. Accordingly, multiple corresponding light sources would have to produce indistinguishable quantum states, in particular, squeezed light of exactly the same wavelength with exactly the same conversion rate.This is not easily achievable in practice due to virtually unavoidable minimal manufacturing-related variations between multiple light sources, such as geometric deviations or material defects, etc. Even for applications that require a specific wavelength that can practically only be generated through frequency or wavelength conversion, geometric and / or material- or manufacturing-related deviations can be problematic.

[0010] The present invention makes it possible, through appropriate operation or control of the device for influencing the refractive index in a specific area, to specifically influence or tune the respective light source for frequency-converted and / or squeezed light in such a way that a plurality of such light sources can be coordinated with one another. This makes it possible to ensure that these plurality of coordinated light sources generate, for example, light of exactly the same frequency or wavelength or squeezed light in indistinguishable optical quantum states. The present invention therefore makes it possible to compensate for individual production-related properties or variations, i.e. deviations from the ideal light sources, by means of the device. This makes it possible to implement correspondingly complex applications which require a plurality of light sources which are as identical as possible orrequire indistinguishable quantum states, or can be implemented more robustly than conventional approaches.

[0011] In one possible embodiment of the present invention, the property in which the optical waveguide varies across the regions is or comprises a dispersion-influencing geometry of the regions. In other words, one or more of the regions can be shaped such that, due to their shape, they influence or enable the propagation of light therein in a frequency- or wavelength-dependent manner. Furthermore, the device for influencing the refractive index of the material of the optical waveguide is or comprises at least one heating device for thermo-optically influencing this material. By means of the heating device, the optical waveguide or its material can therefore be heated or tempered in certain regions. In this way, the refractive index of the material can be set or adapted in certain regions by utilizing the thermo-optical effect. In particular, this orThe corresponding influence on the phase condition, for example for light of different wavelengths, can be carried out here in certain areas by means of several heating devices or individual heating elements.

[0012] In the embodiment of the present invention proposed here, the optical waveguide can be manufactured particularly simply. For example, the optical waveguide can be manufactured consistently homogeneously with regard to the material used or its material properties.

[0013] For example, a layer made of the material of the optical waveguide can be applied to a carrier layer. This carrier layer can, for example, form an intermediate layer between the optical waveguide and a substrate. Silicon or a metallic material can be used as the substrate, for example. The carrier layer can be made of silicon dioxide, for example. To form the actual optical waveguide, parts of the layer made of the material of the optical waveguide can be removed laterally, for example by etching or mechanical or micromechanical processing or the like. If necessary, the substrate can be removed in places or regions, for example to enable more efficient or faster heating of the optical waveguide and / or to install a - possibly additional - heating device or heating element there instead of the corresponding region of the substrate.a heating element, such as a heating electrode or the like, for applying the thermo-optical effect. Likewise, one or more trenches, i.e., depressions or recesses in the carrier layer and / or the substrate, can be arranged between several different sections of the optical waveguide or between different optical waveguides provided as part of the photonic device. This can improve thermal insulation between the optical waveguides or the optical waveguide sections, thus preventing or reducing thermal crosstalk. This can enable more isolated, faster, and more precise temperature control.

[0014] In a further possible embodiment of the present invention, the property in which the optical waveguide varies across the regions is or comprises a crystal direction or crystal orientation of the material of the optical waveguide. In other words, a crystal structure of the material of the optical waveguide can be aligned or oriented in different, in particular different, directions in different regions. The optical waveguide, in particular a nonlinear crystal used as such here, can be at least partially periodically or aperiodically poled with regard to its crystal orientation. Such polarization can optimize phase matching and thus increase the conversion efficiency of the passing light.Due to the varying crystal orientation, the light passing through the various regions can be influenced differently, for example due to corresponding anisotropic optical properties of the material. For example, PPLN (Periodically Poled Lithium Niobate) can be used as the material for the optical waveguide. The embodiment of the present invention proposed here enables particularly efficient conversion of the light passing through the optical waveguide. The poling period, i.e., the spatial period with which the crystal orientation changes along the intended direction of light propagation, can be important for this. This poling period can be determined by the conditions of phase matching, for example between light of different wavelengths, and can be influenced by the device.For example, the device can be used to change the effective optical path that the light takes or must traverse in the respective area. This makes it possible to control which wavelength of the passing light is converted with which conversion efficiency. This can be achieved in particular by applying an electric field using the device, i.e. by exploiting the electro-optical effect. By appropriately designing the optical waveguide, the change in crystal orientation along the direction of light propagation can, for example, lead to a change in the phase of the light by TT, so that the conditions for phase matching can be met for specific wavelengths. In practice, however, this is typically only achieved approximately due to manufacturing tolerances. Corresponding deviations can then be compensated for using the device.The periodic poling of the ferroelectric domains of a nonlinear crystal can be achieved during production of the nonlinear crystal, for example, by means of a periodically structured electrode or by means of several separate electrodes. This at least one electrode used for the initial poling can be different from the device mentioned for influencing the refractive index of the crystal in certain areas, i.e., trimming the refractive index of the crystal or for tuning the light conversion process during later operation, which device can also have one or more electrodes. With a suitable design or by a corresponding electrode arrangement, however, both processes - namely the initial poling during production and the later tuning of the various refractive indices during operation - can be realized with the same electrodes. For example, coupled or separate electrodes can be used initially for poling.connected electrodes are used, which can be electronically separated for later influencing or tuning of the respective refractive index.

[0015] In a further possible embodiment of the present invention, the device is or comprises an electrode arrangement for generating different electric fields in the different regions. This allows, for example, electric fields with different field directions and / or electric field strengths to be generated in different regions. The electrode arrangement can comprise several individual electrodes, in particular at least three electrodes. If, for example, a large-area electrode extending across all regions were used instead, an electric field could still be generated in the different regions, thus influencing the refractive index there or the optical path of the passing light.However, since the various regions differ in at least one property, as described, the refractive index could then, for example, be increased in one region and decreased in another region by the electric field, so that overall there would be no effective change in the optical path across these two regions, i.e. no net effect. By means of the embodiment of the present invention proposed here, however, different regions of the optical waveguide can be subjected to or influenced by different electric fields. This makes it possible to achieve a net change in the optical properties even across several different regions. For example, the electric fields or the resulting influence on the material of the optical waveguide can bring about an additional phase change or phase shift of the light passing through.This allows the phase condition or phase adjustment to be set precisely despite the optical fiber not being manufactured with absolute precision.

[0016] For this purpose, the device can, for example, have at least two different or separate electrodes, which can be arranged on the same side of the optical waveguide, in particular on a side of the optical waveguide facing away from the substrate mentioned elsewhere. The device can then be designed to apply or supply different voltages or potentials to these different electrodes. A common counterelectrode or several separate counterelectrodes can be arranged on the opposite side of the optical waveguide, for example on an underside of the substrate facing away from the optical waveguide. If the optical waveguide comprises several regions that are identical with regard to the property influencing the light property, one electrode can, for example, extend over several of these identical regions.This makes it particularly easy to achieve a uniform electric field strength in these multiple identical regions. Likewise, an individual electrode can be provided or arranged for each region, particularly on the side of the optical waveguide facing away from the substrate mentioned elsewhere.

[0017] In a possible further development of the present invention, the electrodes for generating the various electric fields are also designed as heating electrodes or heating elements. Thus, the same electrodes can be used or operated both for generating the various electric fields and simultaneously as heating elements for additional thermo-optical influencing of the material in the various regions. The electrodes then heat up when a voltage is applied and thus function as heating elements. At the same time, the applied voltage induces an electric field strength between the counterelectrode, arranged, for example, on the underside of the substrate facing away from the optical waveguide, and the electrode arranged on the opposite side of the optical waveguide.This allows both thermo-optical and electro-optical effects to be used simultaneously, allowing the optical properties to be influenced particularly effectively and efficiently. For example, a lower electric field strength may be sufficient to achieve a specific change in the refractive index in the material of the various regions. The design or effect of the electrodes as heating electrodes or heating elements can, for example, be achieved or supported by a shape and / or material selection of the electrodes designed for high heating output or heating effect, i.e., heat generation. Likewise, the electrodes may, for example, be not thermally insulated, or be less thermally insulated, on their side facing the optical fiber than on their side facing away from the optical fiber.Likewise, the electrodes can be thermally connected directly or indirectly to the optical fiber, for example by means of a thermally conductive material, such as a thermal paste or a thermally conductive pad or a thermally conductive adhesive or the like.

[0018] In a possible further development of the present invention, the regions have alternating crystal orientations along the intended direction of light propagation. The crystal orientations can thus alternate along the direction of light propagation, i.e., change back and forth from region to region between two, in particular exactly two, different, in particular opposing, orientations. The device is then configured to generate the electric fields in the regions with field directions correlated to the crystal orientations by means of the electrodes. The field directions of the electric fields can thus, for example, always correspond to the crystal orientation or a corresponding crystal direction, or always be opposite to it.This makes it particularly easy and reliable to change the refractive index in the same direction across all regions, for example, by increasing or decreasing it in all regions permeated by one of the electric fields. The respective strength or magnitude of this change can be adjusted or adjusted by appropriately controlling the device, i.e., by adjusting the electric field strengths accordingly. This allows the optical behavior of the optical fiber or photonic device as a whole to be adjusted particularly effectively and efficiently, for example, by setting a specific phase condition or phase adjustment.

[0019] In a possible development of the present invention, the device comprises a continuous voltage divider extending across multiple regions of the optical fiber for generating an electric field strength that continuously varies across these regions. For this purpose, various voltage sources or potentials, for example, at least three different potentials applied at different locations, can be used. Such a continuous voltage divider enables particularly precise or flexible tuning. This allows, for example, systematic, manufacturing-related deviations of the optical fiber from an ideal target value that continuously vary spatially in the same direction to be compensated for particularly easily and effectively.

[0020] In a further possible embodiment of the present invention, the device is designed or configured to influence the refractive index to different degrees in different regions of the optical waveguide. This means that, for example, not only different field directions of the electric field can be set in different or different regions of the optical waveguide, but also, for example, different field strengths or field magnitudes or voltage amplitudes. When using a heating device to utilize the thermo-optical effect, different temperatures or temperature gradients or temporal temperature curves can be set in different or different regions. For this purpose, the device can comprise a plurality of separate or independently controllable electrodes or heating elements. In this way, particularly precise and flexible adaptation orTuning can be made possible. This, in turn, can ultimately lead to or contribute to a particularly precise fulfillment or adjustment of the phase condition or phase adaptation. This can, for example, achieve a particularly high conversion rate or a particularly high quality of the generated optical quantum states. It can also be used to respond robustly and flexibly to changes in the optical waveguide in certain regions, which can arise during operation, for example, due to different distances of the regions to a hotspot or a cooling device of the photonic device or in its surroundings or to a source of an external electric field, or the like. Likewise, in the embodiment of the present invention proposed here, the fill factor can be detuned, set or adapted, for example, within a poling period.For example, when using PPLN as material for the optical waveguide, a poling period can comprise two, in particular directly adjacent or contiguous, regions of the optical waveguide with different, in particular mutually opposite, crystal orientations.

[0021] In a further possible embodiment of the present invention, the optical waveguide comprises a plurality of sections. At least a selection or a portion of these sections comprises a plurality of regions that differ from one another in the property influencing the at least one light property. The device is then designed and configured to influence the property differently in each section. The device can therefore, for example, have separately controllable electrodes or electrodes to which a voltage can be individually applied for several or all such sections, or separately or individually controllable heating elements or the like. Accordingly, the device can then, for example, have a plurality of separate or individually controllable voltage supplies for the various sections.Within a section, for example, all regions or the regions of the respective section that have the same properties can be influenced jointly, for example, using the same electrode or the same heating element. The embodiment of the present invention proposed here can thus represent or enable a simplified design or implementation of the device, for example, compared to a completely individual influenceability of each individual region. At the same time, however, it can be taken into account that different parts, i.e., different sections of the optical fiber, can have different properties or must be influenced in different ways to achieve a specific effect.This can apply, for example, if different materials are used for the optical fiber in the different sections, or if the different sections of the optical fiber have different shapes, for example, different curvature radii, etc. This allows a particularly good compromise between maximum flexibility and the simplest possible design to be achieved, whereby in practice, effective or sufficient adjustability or tunability can be achieved to realize the described advantages.

[0022] In a further possible embodiment of the present invention, the optical waveguide is shaped straight in some sections and curved in some sections, viewed along the intended direction of light propagation. The optical waveguide can therefore have at least one straight and at least one curved region or section. For example, the optical waveguide can have a stadium or racetrack shape. There, i.e. in these different sections, regions or sections, the optical waveguide varies in different ways in the at least one property that influences the light properties of the light passing through. For example, when using PPLN as the material for the optical waveguide, it can have different polarization periods on the straight section or in the straight section on the one hand and in the curved section or in the curved section on the other.By designing the optical waveguide in this way, which varies section by section or depending on the shape or path of the optical waveguide, the conversion efficiency can be improved or maximized. This can ultimately benefit the generation of particularly high-quality optical quantum states. In particular, the device can be designed to influence the optical waveguide separately, i.e., independently of one another, in the at least one straight section and the at least one curved section.

[0023] In a further possible embodiment of the present invention, it is provided that the regions of the optical waveguide are embedded in an optical resonator or at least form part of an optical resonator. This allows the light to traverse the optical waveguide in the resonator multiple times. This can enable a particularly compact and efficient design of the photonic device. By means of the device, the total optical length of the resonator, i.e. the light path through the resonator, can be effectively adapted or adjusted in such a way that, for example, constructive interference of the light at the pump wavelength, i.e. the wavelength of the fed-in light, and the produced or generated wavelength, i.e. the wavelength of the light after conversion in the optical waveguide, is enabled. This allows corresponding photonic applications to be implemented particularly effectively and robustly.

[0024] In a possible development of the present invention, the device or the optical waveguide comprises a further optical waveguide optically coupled to the optical resonator in a light-conducting coupling region, or a corresponding section of the optical waveguide, i.e., a light feed and / or light output. The device is then configured or arranged to controllably influence the refractive index in this coupling region, in particular individually or independently of the other regions of the optical waveguide. The coupling region can thus be an optical waveguide section or region in which light supplied by a light source can be coupled into the optical resonator and / or light can be coupled out of the optical resonator for forwarding to another location or to another functional unit or the like.This coupling region may therefore have specific requirements to enable the most effective, efficient, robust, and flexible generation and use of the frequency-converted light and / or the optical quantum states of the squeezed light. These requirements can be met or realized by controllable manipulation in the coupling region. For example, by appropriately controlling the device, the coupling region or its optical properties can be adjusted or tuned to compensate for the light loss during a pass through the optical resonator at the pump wavelength.

[0025] In a possible development of the present invention, the photonic device is designed to supply light to the optical resonator in a plurality of directions, i.e. two or more different, in particular mutually opposite, directions. For this purpose, the device can have a plurality of corresponding light feeds, i.e. corresponding further optical waveguides or optical waveguide sections. These can impinge on the optical resonator or on a region of the optical waveguide that is embedded in the optical resonator or forms part of the optical resonator at the same point or at different points. For example, a double-sided supply of light to the optical resonator can be provided, whereby two or more optical quantum states that are as identical as possible can be generated particularly easily and particularly reliably. This can be based on the fact that different light feeds orLight coupled into the optical resonator from different directions can pass through the same optical resonator independently of each other and thus possible differences or mismatches between different optical resonators can be avoided or circumvented.

[0026] In a possible development of the present invention, the photonic device comprises a plurality of optical resonators that are optically coupled to one another. Thus, a light path can lead to a first optical resonator, through it, out of it, and then to a second optical resonator. Such a configuration of the photonic device can enable particularly flexible generation of different quantum states or particularly extensive tunability, since, for example, a maximum influence per unit length of the optical waveguide can be limited and / or the various optical resonators can be optimized for different properties or requirements.

[0027] In a further possible embodiment of the present invention, the optical waveguide comprises at least one intermediate region arranged between two adjacent regions of the optical waveguide, which influence the at least one light property. Compared to these regions, however, the intermediate region does not influence the light property of the light passing through it in the intended light propagation, or influences it differently, in particular less strongly. The intermediate region can thus be a neutral region in this respect or a more neutral region compared to the other regions, or an interruption, for example, in the regions of the optical waveguide that are poled with respect to crystal orientation.For this purpose, the intermediate region can, for example, have an individual crystal orientation to minimize its influence on the light passing through, or be made of a different material than the other regions of the optical waveguide, or the like. The device is then designed or configured to controllably influence the refractive index in this at least one intermediate region independently of the other regions of the optical waveguide. By appropriately influencing this intermediate region, the conversion of the light can be optimized, since this can, for example, make it particularly easy and effective to avoid destructive interference or to adjust it only for certain wavelengths. The use of such an intermediate region can enable particularly flexible shaping orThe overall design of the optical waveguide can be independent of the degree or extent of the influence on the light properties of the light passing through the optical waveguide. This can therefore enable particularly flexible optimization of the photonic device for various requirements.

[0028] The present invention also relates to a photonics device comprising a plurality of parallel photonic devices according to the invention, in particular as separate or parallel light sources for frequency-converted and / or squeezed light. The photonics device according to the invention can be configured to generate a uniform frequency or wavelength and / or indistinguishable quantum states of the frequency-converted and / or squeezed light generated by means of the various photonic devices through coordinated control of the devices of the photonic devices. In other words, in the photonics device according to the invention, in particular simultaneously, by means of the plurality of photonic devices, for example, a plurality of instances or wave trains of squeezed light, i.e. a plurality of corresponding optical quantum states, can be generated. These can then be superimposed or combined with one another, for example, likewise on or in the photonics device.to interact with each other. The optical quantum states can, for example, function as qubits to perform correspondingly complex photonic functions, such as optical quantum computations. Depending on the application, the photonic device can comprise additional components, such as one or more light sources, switching or control logic, connections, or

[0029] Connecting cables and / or the like.

[0030] Further features of the invention can be derived from the following description of the figures and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures alone, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0031] The drawing shows:

[0032] Fig. 1 is a partial schematic perspective view of a photonic device;

[0033] Fig. 2 is a partial schematic plan view of the photonic device;

[0034] Fig. 3 is a partial schematic plan view of the photonic device in a stadium configuration;

[0035] Fig. 4 is a partial schematic plan view of the photonic device in a ring resonator configuration with two-sided light supply;

[0036] Fig. 5 is a partial schematic plan view of the photonic device in a ring resonator configuration with a first electrode configuration; and

[0037] Fig. 6 is a partial schematic plan view of the photonic device in a ring resonator configuration with a second electrode configuration.

[0038] Identical or functionally equivalent elements are provided with the same reference numerals in the figures. For the sake of clarity, only a representative selection of identical or similar elements may be explicitly identified in the figures.

[0039] In photonic applications, the indistinguishability of these states is important for the interaction of multiple optical quantum states based on squeezed light. For example, there may be a requirement that multiple chip-integrated light sources for squeezed light should generate optical states of the same wavelength with the same conversion rate. This cannot be easily achieved with previously known manufacturing processes due to unavoidable minimal manufacturing-related geometric deviations within the various light sources. However, corresponding deviations in the geometry or the optical properties can be compensated for by additional measures to adapt the optical properties. Fig. 1 shows a partial schematic perspective view of a photonic device 1. This device is manufactured here in a layered structure, for example, using methods known from semiconductor or microchip manufacturing.On the underside of the device 1 there is a base electrode 2, for example in the form of a metal layer. Above this there is a substrate 3, which in this case can be a layer of silicon, for example. An intermediate layer 4 is applied to the substrate 3. This intermediate layer 4 can be made of an electrically insulating material, such as silicon dioxide. A waveguide layer 5 is applied to the intermediate layer 4, which in this case can be made entirely or partially of lithium niobate, for example. This waveguide layer 5 is shaped or structured to form a light guide or waveguide 6. The intermediate layer 4 can have a lower refractive index than the waveguide layer 5 arranged above it and the substrate 3 arranged below it, so that no light passes from the waveguide 6 into the substrate 3. The waveguide layer 5 orthe waveguide 6 can be covered by a protective layer, for example made of silicon dioxide, which is not shown here for the sake of clarity.

[0040] For the aforementioned adaptation of the optical properties, the device 1 comprises an influencing device 7. This influencing device 7 here, for example, comprises several electrodes for generating electric fields. These electrodes can also be designed or serve as heating elements for influencing the temperature in the waveguide 6, which is also permeated by the electric fields, in order to enable combined electro-optical and thermo-optical influencing using the same electrodes, i.e., without additional heating elements. Likewise, the influencing device 7 could - in addition to or alternatively to the electrodes - have heating elements for influencing the waveguide 6 using the thermo-optical effect. The electrodes are arranged here above the waveguide layer 5 or the waveguide 6 along a predetermined light propagation direction for the waveguide 6.

[0041] In particular, the electrodes or heating elements of the influencing device 7 can rest on or be arranged on the aforementioned protective layer (not shown here). This can prevent the material of the electrodes or heating elements from causing losses, in particular light losses, i.e. losses of an optical signal transported by the waveguide 6. The waveguide 6 has a plurality of waveguide regions 8 arranged one behind the other along the intended direction of light propagation. The waveguide regions 8 can differ in their crystal orientations 9, indicated schematically here by corresponding arrows. The crystal orientations 9 can alternate from one of the waveguide regions 8 to the next waveguide region 8 along the intended direction of light propagation.The electrodes of the influencing device 7 can each be designed and arranged to correspond to one of the waveguide regions 8. Thus, a respective electric field can be generated between each of the electrodes and the base electrode 2, which permeates the respective waveguide region 8. By appropriate polarity or voltage supply to the electrodes, it can be adjusted or achieved that a respective field direction 10 of the electric fields, also indicated schematically here by arrows, is correlated with the crystal orientation 9 present in the respective waveguide region 8, i.e., for example, corresponds to it.

[0042] Thus, a specific and modular design of multiple electrically conductive electrodes is proposed, which interact with different parts of the waveguide 6 and change the refractive index there in specific regions. This ultimately allows multiple corresponding light sources for frequency-converted and / or squeezed light to be combined on a microchip and, for example, coordinated with one another in such a way that the resulting optical quantum states of these multiple light sources become indistinguishable. Likewise, when using a single light source, it is possible to optimize the conversion rate and wavelength of the light guided in the waveguide 6 for a specific application by appropriately controlling the influencing device 7, i.e., by appropriately designing or adjusting the electric fields and thus the respective refractive index in different waveguide regions 8.

[0043] The parallel generation and interaction of high-quality, squeezed light states can be useful, for example, for applications in quantum computing or in sensor technology to improve phase sensitivity. Chip-integrated optical quantum circuits can be used for this purpose, which are intended to generate indistinguishable optical quantum states using several parallel chip-integrated light sources. These optical quantum states can function as qubits or symbolize qubits that, after their generation, can interact with each other in optical quantum circuits. For this purpose, light of a predefined wavelength can be coupled into the waveguide 6 and converted there into light of a different wavelength. Different materials or material systems can be used to realize such chip-integrated light sources. For example, lithium niobate can be used, particularly for the waveguide 6.Lithium niobate can be particularly useful and effective due to its particularly large second-order nonlinear susceptibility, which is based on its crystalline structure. This allows, for example, particularly high conversion efficiency and a particularly high quality of the generated light or quantum states to be achieved.

[0044] As shown here, a thin lithium niobate layer can be applied to a silicon-based wafer (including an intermediate layer, not shown) and formed by appropriate structuring of the waveguide 6. The waveguide 6 can be designed, for example, as a ridge or rib, i.e., as an elongated structure or elevation or the like in the intended direction of light propagation. The waveguide layer 5 or the waveguide 6 can be periodically poled for an optimized conversion process. This means that the crystal orientation 9 is modified or alternates in certain regions. This can enable a particularly efficient conversion process for light that passes through several or many correspondingly differently poled waveguide regions 8.An important factor for the conversion is the poling period, i.e., the period with which the crystal orientations 9 change along the intended direction of light propagation. The poling period can be determined by the phase matching conditions and influenced by the application of electric fields. Since the ideal state is only approximately achieved due to unavoidable manufacturing tolerances, the influencing device 7 can be used to compensate for corresponding deviations or tolerances. Thus, a corresponding tunability with regard to the phase conditions can be realized.

[0045] For further illustration, Fig. 2 shows a partial schematic plan view of the or a corresponding photonic device 1. Here, two electrodes of the influencing device 7 can be seen as an example. In this case, one of the two electrodes overlaps or covers all waveguide regions 8 that have the same crystal orientation 9. For the sake of better recognizability, the electrodes only partially cover the waveguide regions 8 here. In practice, this coverage can be greater, or complete coverage of the waveguide regions 8 by the respective electrode can be provided. The intended direction of light propagation can run in the plane of the drawing or parallel to the plane of the drawing.

[0046] Fig. 3 shows a partial schematic top view of the photonic device 1 or a corresponding one. Here, the waveguide 6 and the influencing device 7 with multiple electrodes are also shown. The waveguide 6 comprises variously shaped waveguide regions 8, which are arranged in straight sections 11 and curved sections 12 connecting these at the ends. Thus, the waveguide 6 has an overall stadium or racetrack shape. The waveguide 6 forms an optical resonator 13.

[0047] In addition, another optical waveguide is indicated here as a light guide 14. Light guided through this light guide 14 can be coupled into the waveguide 6, i.e., into the resonator 13, in a coupling region 15.

[0048] In particular, the coupling region 15 can also be detuned electro-optically and / or thermo-optically using at least two elements, i.e., electrodes and / or heating elements or the like. Thus, the refractive index of the light guide 14 and / or the waveguide 6 in the coupling region 15 can be controlled, i.e., adjusted, or modified separately from the rest of the waveguide 6. This allows the phase condition for the light conversion in the waveguide 6 and the coupling coefficients for coupling the light into the waveguide 6 or into the resonator 13 to be influenced, controlled, or adjusted. At least one further element, i.e., at least one further electrode or at least one further heating element, can be arranged in the resonator 13 or partially covering it. This can serve to fine-tune the phase condition of the critical coupling, which depends on the optical path of a complete revolution of the light in the resonator 13.

[0049] The significance of the aforementioned poling period is also present when the correspondingly poled waveguide regions 8 are embedded in an optical resonator 13 or form such an optical resonator 13. Further aspects may then be important for generating the highest possible optical quantum states. For example, a different poling period can be realized in the curved sections 12 than in the straight sections 11. Although not explicitly shown here for the sake of clarity, the influencing device 7 may have additional separately controllable elements for influencing the waveguide regions 8 in the curved sections 12. Such separate or independent influencing of the material of the waveguide regions 8 in the straight sections 11 on the one hand and in the curved sections 12 on the other hand can enable improved conversion efficiency overall.Likewise, the coupling region 15 can be designed so that it can be influenced or tuned separately or individually. In addition, the optical path of the light in a complete pass through the resonator 13 can be adjustable or tuned by means of the influencing device 7 in order to achieve a critical coupling in the resonator 13 at certain predetermined wavelengths. In this case, by appropriately controlling the influencing device 7, in particular in the coupling region 15, it can be achieved that the light loss during a pass through the resonator 13 at the coupled-in wavelength is just compensated. In this case, the respective field direction 10 of the electric fields used for tuning can also be adapted to the respective local or region-specific crystal orientation 9 and / or geometric shape of the waveguide regions 8. Overall, the photonic device 1 can therefore have different sections orRegions whose optical properties can be tuned separately or individually for optimal operation of a corresponding chip-integrated light source.

[0050] Possible interruptions of the waveguide regions 8 poled with respect to the crystal orientation 9, in particular in the resonator 13, can also be designed as a group so as to be separately or individually tunable, i.e., influenceable, for example by arranging there a further individually controllable or controllable electrode of the influencing device 7 or the like.

[0051] The resonator 13 can also be shaped differently, for example as a ring resonator. This is indicated by way of example in a partial schematic representation in Fig. 4. In addition, a double-sided light feed 14 is indicated here, although this is not restricted to the ring shape of the resonator 13 shown here. Here, in the light feed 14 or in the light feeds 14, in particular simultaneously, light can be fed both in a first light feed direction 17a (shown schematically here) and in a second light feed direction 17b (likewise shown schematically) and coupled into the resonator 13 in order to generate two optical quantum states that are as identical as possible in the resonator 13. The light fed in or fed out in the first light feed direction 17aAfter passing through the resonator 13, the coupled-in light can be output and forwarded in a first light output direction 18a via another optical fiber, indicated here as light output 16. Similarly, the light supplied or input in the second light supply direction 17b can be output in a second light output direction 18b after passing through the resonator 13 and forwarded in the light output 16.

[0052] An unstructured z-cut LNOI wafer, for example, can be used as the basis for producing the photonic device 1. In this case, or when using a z-cut electrode arrangement, an additional upper intermediate layer can be provided. This upper intermediate layer can be deposited on top of the waveguide layer 5—which may not yet have been structured to form the actual waveguide 6—before or after structuring the waveguide layer 5, i.e., after producing the actual waveguide 6, for its protection, for example, with a layer thickness of between 100 nm and 3 pm. A conductive, structured metal layer can be applied thereon, which is structured to define the various poled waveguide regions 8. The upper intermediate layer can therefore be produced, in particular, before structuring or before applying this metal layer.In order to generate the different polarities in the various waveguide regions 8, a sufficiently high voltage can be applied between the metal layer and the substrate 3. The metal layer can then be removed and, if this has not already been done, the waveguide 6 can be structured, i.e. shaped. A passivation layer or the protective layer mentioned elsewhere, for example a silicon dioxide layer with a thickness of between 0.5 pm and 3 pm, can be applied to the waveguide 6 structured in this way or, if appropriate, to the upper intermediate layer. The influencing device 7, for example its electrodes, can then be arranged at a predefined distance of, for example, at least 1 pm from the lithium niobate layer, i.e. the waveguide layer 5, on the passivation or

[0053] protective layer can be arranged or created.

[0054] With a closed, ring-shaped waveguide 6, leads to electrodes arranged within the ring, i.e., in a region enclosed by the resonator 13, can be realized from an edge of the device 1 or a corresponding chip, for example, using an additional metal layer. If crossovers occur, for example, between the leads or connecting lines for different electrodes, multiple electrically conductive or metallic layers or plies with an insulating intermediate layer and vias (through-hole contacts) arranged between them can be used.

[0055] For further illustration, Fig. 5 shows a partial schematic representation of the or a corresponding photonic device 1 with another possible electrode configuration. Here, two differently polarized electrodes of the influencing device 7 are arranged next to the resonator 13, i.e. next to the actual waveguide 6. The waveguide regions 8 are alternately electrically connected to one of the electrodes via a contacting line 19 each. In this configuration, particularly few actual electrodes are required, which can enable a particularly simple design of a corresponding voltage supply. However, the required contacting lines 19 can then sometimes be relatively long or lead over at least one waveguide region 8 that is not contacted by them. To avoid this, a different electrode configuration can be used. For this purpose, Fig.Figure 6 shows a partial schematic representation of the photonic device 1 or a corresponding photonic device 1 with such a different electrode configuration. Here, two differently polarized electrodes of the influencing device 7 are arranged on either side of the resonator 13. These are also alternately connected to the waveguide regions 8 via corresponding contact lines 19.

[0056] Overall, the described examples demonstrate how a tunable source for squeezed light states can be realized, enabling the parallel and efficient generation of multiple indistinguishable optical quantum states in a very small space, for example, integrated on a single microchip.

[0057] 1 device

[0058] 2 base electrode

[0059] 3 Substrat

[0060] 4 Intermediate layer

[0061] 5 waveguide layer

[0062] 6 waveguides

[0063] 7 Influencing device

[0064] 8 waveguide regions

[0065] 9 Crystal orientation

[0066] 10 Field direction

[0067] 11 straight section

[0068] 12 curved section

[0069] 13 Resonator

[0070] 14 Light supply

[0071] 15 Coupling area

[0072] 16 Light dissipation

[0073] 17a first light supply direction

[0074] 17b second light supply direction

[0075] 18a first light emission direction

[0076] 18b second light emission direction

[0077] 19 contact lines

Claims

PATENT CLAIMS 1. Photonic device (1) for generating frequency-converted and / or squeezed light, comprising an optical waveguide (6) made of a material with a second-order non-linear susceptibility different from zero, which comprises a plurality of regions (8) arranged one behind the other along a designated light propagation direction, wherein the optical waveguide (6) varies accordingly in regions in at least one property influencing a light property of the light passing through the optical waveguide (6), and a device (7) for controllably influencing the refractive index of the material for the light passing through in at least one selection of the regions (8).

2. Photonic device (1) according to claim 1, characterized in that the property is a dispersion-influencing geometry of the regions (8) and the device (7) is a heating device for thermo-optically influencing the material.

3. Photonic device (1) according to one of the preceding claims, characterized in that the property is a crystal orientation (9) of the material of the regions (8).

4. Photonic device (1) according to one of the preceding claims, characterized in that the device (7) comprises an electrode arrangement for generating different electric fields (10) in the different regions (8).

5. Photonic device (1) according to claim 4, characterized in that the electrode arrangement has electrodes which serve both to generate the various electric fields (10) and are designed as heating electrodes and thus serve to thermo-optically influence the material of the various regions (8).

6. Photonic device (1) according to claims 3 and 4 or 3 and 5, characterized in that the regions (8) have alternating crystal orientations (9) along the intended light propagation direction and the device (7) is designed to generate the electric fields with field directions (10) correlated to the crystal orientations (9) by means of the electrodes.

7. Photonic device (1) according to one of claims 3 to 6, characterized in that the device (7) comprises a continuous voltage divider extending over a plurality of regions (8) for generating an electric field strength varying continuously over these regions (8).

8. Photonic device (1) according to one of the preceding claims, characterized in that the device (7) is designed to influence the refractive index in different regions (8) to different degrees.

9. Photonic device (1) according to one of the preceding claims, characterized in that the optical waveguide (6) comprises a plurality of sections (11, 12) which at least partially comprise a plurality of regions (8) differing from one another in terms of their properties, and the device (7) is designed to influence the properties differently in sections.

10. Photonic device (1) according to one of the preceding claims, characterized in that the optical waveguide (6) is shaped so as to be straight in sections and curved in sections along the intended light propagation direction and varies there in different ways in one property.

11. Photonic device (1) according to one of the preceding claims, characterized in that the regions (8) of the optical waveguide (6) are embedded in an optical resonator (13) or form at least part of an optical resonator (13).

12. Photonic device (1) according to claim 11, characterized in that the device (1) comprises a further optical waveguide (6) optically coupled to the optical resonator (13) in a light-conducting coupling region (15), and the device (7) is also designed to controllably influence the refractive index in the coupling region, in particular independently of the other regions (8) of the optical waveguide (6).

13. Photonic device (1) according to claim 11 or 12, characterized in that the device (1) is designed to supply light to the optical resonator (13) in several different, in particular mutually opposite, directions (17a, 17b).

14. Photonic device (1) according to one of claims 11 to 13, characterized in that the photonic device (1) comprises a plurality of such optical resonators (13) which are optically coupled to one another.

15. Photonic device (1) according to one of the preceding claims, characterized in that the optical waveguide (6) comprises at least one intermediate region arranged between the regions (8) influencing the one light property, which intermediate region influences this light property of the light passing through it in the intended light propagation direction to a lesser extent, and the device (7) is designed to controllably influence the refractive index in this intermediate region independently of the other regions (8) of the optical waveguide (6).

16. A photonic device comprising a plurality of parallel photonic devices (1) according to any one of the claims.

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