Tunable photonic device for generating frequency-converted and / or squeezed light and photonic device with several 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) having several regions (8) arranged one behind the other in the direction of light propagation. The optical waveguide (6) varies accordingly in a region with respect to a property of the light passing through it. The device (1) further comprises a device (7) for selectively controlling the refractive index of the material of the optical waveguide (6) for the passing light in at least one selection of the regions (8). The invention also relates to a photonic device comprising several such photonic devices.

Description

[0001] The present invention relates to a photonic device for generating squeezed light and to a photonic device comprising such a photonic device.

[0002] Frequency and wavelength conversion of light can be used, for example, in telecommunications 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. Several approaches already exist for realizing suitable light sources to generate squeezed light. However, the resulting optical quantum states can be highly dependent on manufacturing-related minute variations in the components or materials of the light sources, variations that fall within the range of currently achievable manufacturing tolerances. This can limit the quality of the quantum states or the practicality of corresponding applications. Therefore, there is a need for further improvements in this area.

[0003] The object of the present invention is to improve the usability of influenced, in particular frequency-converted and / or squeezed, light in photonic applications.

[0004] The problem is solved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the dependent claims, the description, and the drawings. Features, advantages, and possible embodiments set forth 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, as well as of any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the dependent claims.

[0005] The photonic device according to the invention serves to generate frequency-converted and / or squeezed light compared to an initial state, for example, light generated in the device or supplied to the device at the input. For this purpose, the device comprises at least one optical waveguide made of a material with a non-zero, i.e., non-zero, second-order nonlinear susceptibility. This optical waveguide includes several regions arranged one after the other along a defined direction of light propagation within or through the optical waveguide. The optical waveguide varies accordingly in at least one property across these regions, i.e., when viewed across these multiple regions. This property is such that at least one light property, such as the wavelength, is affected.The wavelength composition of light, its propagation or phase velocity, or its frequency conversion behavior (phase adjustment to a predetermined target frequency) are all factors that influence or determine the light passing through the optical waveguide. Such properties can include, for example, the crystal orientation, geometry, or refractive index of the material in the corresponding regions of the optical waveguide. A specific region of the optical waveguide can exhibit a particular value or characteristic of this property. Likewise, the property, its value, or its characteristic can vary within a region. In this case, the property can vary differently in at least two regions, so that these two regions, when considered as a whole, can differ from each other accordingly.The optical waveguide can therefore comprise at least two regions that differ from each other in this property. Additionally, the optical waveguide can comprise two or more regions that are identical in this property, meaning they do not differ from each other in this respect. In particular, the regions can be designed and arranged such that the property alternates between two different values ​​or characteristics along the intended direction of light propagation, i.e., it switches back and forth between them. Other configurations are also possible.

[0006] According to the invention, the photonic device also comprises at least one device for selectively influencing the refractive index of the optical waveguide material in the respective area for the light passing through it as intended, in at least one selection, i.e., at least a part of the areas. In other words, the refractive index in at least one area of ​​the optical waveguide can be set or adjusted by appropriate operation or control of the device.

[0007] The device according to the invention can, for example, be configured as a photonic chip or PIC (Photonic Integrated Circuit). In particular, the device can be manufactured wholly or partially using semiconductor fabrication methods. The device can, for example, also include 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. This allows the device according to the invention to be designed and manufactured in a particularly compact and robust manner.

[0008] To generate the light influenced by the device, i.e., frequency-converted and / or squeezed, light with a predetermined wavelength incident on the optical waveguide can be converted into light of a different wavelength. Various 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 include, for example, lithium tantalate, barium titanate, silicon nitride, electro-optically active polymers, or the like. The present invention can enable the conversion rate and / or the resulting wavelength to be maximized and / or optimized for a specific application by controlling the refractive index, i.e., by appropriate tuning or adjustment in this respect.This can be particularly useful when the photonic device is used as the single or only source of squeezed light in the respective application.

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

[0010] The present invention makes it possible, through appropriate operation or control of the device for selectively influencing the refractive index, to selectively influence or tune the respective light source for frequency-converted and / or squeezed light in such a way that several such light sources can be coordinated. This makes it possible to achieve, for example, that these several coordinated light sources generate light of exactly the same frequency or wavelength, or squeezed light in indistinguishable optical quantum states. The present invention thus makes it possible to compensate for individual manufacturing-related properties or variations, i.e., deviations from the ideal of the light sources, by means of the device. This enables correspondingly complex applications that require several as identical as possible orindistinguishable quantum states require, enable, or can be realized more robustly compared to conventional approaches.

[0011] In one possible embodiment of the present invention, the property in which the optical waveguide varies across its regions comprises a dispersion-influencing geometry of the regions. In other words, one or more of the regions can be shaped such that their shape influences or enables the propagation of light within them in a frequency- or wavelength-dependent manner. Furthermore, the device for influencing the refractive index of the optical waveguide material comprises at least one heating device for thermo-optical manipulation of this material. By means of the heating device, the optical waveguide or its material can thus be heated or tempered region by region. This allows the refractive index of the material to be adjusted or adapted region by utilizing the thermo-optical effect. In particular, this can be achieved by...The corresponding influence on the phase condition, for example for light of different wavelengths, can be achieved 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 with a homogeneous material throughout, with respect to the material used and its material properties.

[0013] For example, a layer of optical fiber material can be deposited onto a substrate. This substrate can, for instance, form an intermediate layer between the optical fiber and a substrate. Silicon or a metallic material can be used as the substrate. The substrate itself can be made of silicon dioxide, for example. To form the actual optical fiber, portions of the optical fiber material layer can be removed laterally, for example, by etching, mechanical or micromechanical processing, or similar methods. If necessary, the substrate can be partially or completely removed, for example, to enable more efficient or faster heating of the optical fiber and / or to replace the corresponding area of ​​the substrate with a heating element (possibly an additional one).A heating element, such as a heating electrode or similar device, can be arranged to apply the thermo-optical effect. Similarly, one or more grooves, 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 included in the photonic device. This improves thermal insulation between the optical waveguides or 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 its regions is, or comprises, a crystal direction or crystal orientation of the optical waveguide material. In other words, the crystal structure of the optical waveguide material can be aligned or oriented in different, particularly different, directions in different regions. The optical waveguide, especially a nonlinear crystal used here as such, can be at least partially periodically or aperiodically polarized with respect to its crystal orientation. Such polarization can optimize the phase matching and thus increase the conversion efficiency of the transmitted light.The varying crystal orientation—for example, due to corresponding anisotropic optical properties of the material—can affect the light passing through different regions in different ways. For instance, PPLN (Periodically Polarized Lithium Niobate) can be used as the material for the optical waveguide. The proposed embodiment of the present invention enables particularly efficient conversion of the light passing through the optical waveguide. The polarization 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 polarization period can be determined by the phase matching conditions, for example, between light of different wavelengths, and can be influenced by the device.For example, the effective optical path that the light takes or must traverse in a given area can be altered using this device. It is therefore possible to control which wavelength of the transmitted light is converted with which conversion efficiency. This can be achieved, in particular, by applying an electric field using the device, thus utilizing the electro-optic 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 π, so that the conditions for phase matching for specific wavelengths can be met. In practice, however, this is typically only achieved approximately due to manufacturing tolerances. Such deviations can then be compensated for using this device.The periodic polarization of the ferroelectric domains of a nonlinear crystal can be achieved during the crystal's fabrication, for example, using a periodically structured electrode or several separate electrodes. This electrode, used for the initial polarization, can be different from the device used for selectively influencing the crystal's refractive index or for fine-tuning the light conversion process during subsequent operation, which can also include one or more electrodes. With suitable design or an appropriate electrode arrangement, both processes—the initial polarization during fabrication and the subsequent adjustment of the various refractive indices during operation—can be accomplished using the same electrodes. For example, electrodes coupled to the polarization process can be used to create a new, more complex system.Connected electrodes are used, which can be electronically separated for subsequent adjustment or tuning of the respective refractive index.

[0015] In a further possible embodiment of the present invention, the device comprises an electrode arrangement for generating different electric fields in the various areas. This allows, for example, the generation of electric fields with different field directions and / or electric field strengths in different areas. The electrode arrangement can comprise several individual electrodes, in particular at least three electrodes. If, for example, a single large-area electrode extending across all areas were used instead, an electric field could also be generated in the different areas, thereby influencing the refractive index or the optical path of the passing light.Since the different regions differ in at least one property, as described, the refractive index could, for example, be increased in one region and decreased in another by the electric field, resulting in no net change in the optical path across these two regions. In contrast, the proposed embodiment of the present invention allows different regions of the optical waveguide to be subjected to or influenced by different electric fields. This enables a net change in the optical properties to be achieved even across several differing regions. For example, the electric fields, and the resulting influence on the optical waveguide material, can induce an additional phase change or phase shift of the transmitted light.This allows the phase condition or phase adjustment to be set exactly, even if the optical fiber is not manufactured with absolute precision.

[0016] 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 configured to apply or supply these different electrodes with different voltages or potentials. On the opposite side of the optical waveguide, for example on an underside of the substrate facing away from the optical waveguide, a common counter electrode or several separate counter electrodes can be arranged. If the optical waveguide comprises several regions with the same property influencing the light properties, an electrode can, for example, extend over several of these same regions.This makes it particularly easy to achieve a uniform electric field strength in these several identical areas. Likewise, an individual electrode can be provided or arranged for each area, especially 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 both to generate the various electric fields and simultaneously as heating elements for the additional thermo-optical modification of the material in the different areas. 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 counter electrode, located, for example, on the underside of the substrate facing away from the optical waveguide, and the electrode located on the opposite side of the optical waveguide.This allows both thermo-optical and electro-optical effects to be used simultaneously, enabling particularly effective and efficient manipulation of optical properties. For example, a lower electric field strength may be sufficient to achieve a specific change in the refractive index of the material in different areas. The design and function of the electrodes as heating electrodes or heating elements can be achieved or enhanced by selecting a shape and / or material optimized for high heating power and / or heat generation. Similarly, the electrodes can be less thermally insulated, or not at all, on the side facing the optical fiber than on the side facing away from it.Similarly, the electrodes can be thermally connected directly or indirectly to the optical fiber, for example by means of a thermally conductive material such as thermal paste, thermal pad, thermal adhesive, or the like.

[0018] In a possible embodiment of the present invention, the regions along the intended direction of light propagation exhibit alternating crystal orientations. The crystal orientations can thus alternate along the direction of light propagation, i.e., switch back and forth between two, in particular exactly two, different, especially opposing, orientations or alignments from region to region. The device is then configured to generate 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 therefore, 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 ensure that the refractive index is changed in the same direction in all areas, for example, increasing or decreasing it in all areas exposed to one of the electric fields. The magnitude of this change can be adjusted by controlling the device, i.e., by adjusting the electric field strengths. This allows for particularly effective and efficient adjustment of the optical behavior of the optical waveguide or the photonic device as a whole, for example, setting a specific phase condition or phase adjustment.

[0019] In a possible further development of the present invention, the device comprises a continuous voltage divider extending over several regions of the optical fiber for generating a continuously varying electric field strength across these regions. Various voltage sources or potentials, for example at least three different potentials applied at different locations, can be used for this purpose. Such a continuous voltage divider enables particularly precise or flexible adjustment. This allows, for example, systematic, spatially continuous deviations in the optical fiber from an ideal target value, caused by manufacturing processes and changing 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 and configured to influence the refractive index to varying degrees in different regions of the optical waveguide. This allows, for example, not only the setting of different field directions of the electric field in different regions of the optical waveguide, but also, for example, different field strengths, field magnitudes, or voltage amplitudes. When using a heating device to utilize the thermo-optical effect, different temperatures, temperature gradients, or time-dependent temperature curves can be set in different regions. For this purpose, the device can comprise several separate or independently controllable electrodes or heating elements. In this way, particularly precise and flexible adjustment is possible.This enables precise adjustment of the phase condition. This, in turn, can ultimately lead to or contribute to a particularly accurate fulfillment or adjustment of the phase condition or phase matching. This allows, for example, a particularly high conversion rate or a particularly high quality of the generated optical quantum states to be achieved. Likewise, it allows for a robust and flexible response to localized changes in the optical waveguide, which can occur during operation, for example, due to varying distances of the sections to a hotspot or cooling device of the photonic device or in its vicinity, or to a source of an external electric field, or similar factors. Similarly, in the embodiment of the present invention proposed here, the fill factor can be detuned, adjusted, or adapted, for example, within a polarization period.For example, when using PPLN as the material for the optical waveguide, a polarization period can comprise two, in particular immediately adjacent or adjoining, areas of the optical waveguide with different, in particular opposite, crystal orientations.

[0021] In a further possible embodiment of the present invention, the optical waveguide comprises several sections. At least a selection or part of these sections comprises several areas that differ from one another in the property influencing at least one optical property. The device is then designed and configured to influence this property differently in each section. The device can, for example, have separately controllable electrodes or heating elements, or the like, for several or all such sections. Accordingly, the device can then, for example, have several separate or individually controllable voltage supplies for the different sections.Within a section, for example, all areas or areas of the respective section with the same properties can be influenced together, i.e., by means of 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 completely individual control of each individual area. At the same time, however, it can be taken into account that different parts, i.e., different sections of the optical waveguide, may 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 different sections, or if the different sections of the optical fiber have different shapes, such as different radii of curvature. This allows for a particularly good compromise between maximum flexibility and the simplest possible design, resulting in effective and sufficient adjustability or tunability in practice to realize the described advantages.

[0022] In another possible embodiment of the present invention, the optical waveguide is shaped as follows: in some sections it is straight and in others it is curved, when viewed along the intended direction of light propagation. The optical waveguide can therefore have at least one straight and at least one curved section. For example, the optical waveguide can have a stadium or racetrack shape. The optical waveguide varies in these different sections or areas with respect to at least one property that influences the light properties of the transmitted light. For example, when using PPLN as the material for the optical waveguide, it can have different polarization periods on the straight section and on the curved section.By varying the optical waveguide's design in sections or segments, depending on its shape or path, the conversion efficiency can be improved or maximized. This can ultimately benefit the generation of particularly high-quality optical quantum states. The device can be specifically designed to influence the optical waveguide separately, i.e., independently of each other, in at least one straight section and at least one curved section.

[0023] In a further possible embodiment of the present invention, the optical waveguide sections are embedded in an optical resonator or at least form part of one. This allows the light to pass through the optical waveguide multiple times within the resonator. This can enable a particularly compact and efficient design of the photonic device. The device allows the overall optical length of the resonator, i.e., the light path through the resonator, to be effectively adjusted or set so that, for example, constructive interference between the light at the pump wavelength (i.e., the wavelength of the injected light) and the generated wavelength (i.e., the wavelength of the light after conversion in the optical waveguide) is achieved. This allows for the particularly effective and robust implementation of corresponding photonic applications.

[0024] In a possible embodiment of the present invention, the device or optical waveguide comprises a further optical waveguide or a corresponding section of the optical waveguide, i.e., a light input and / or light output, optically coupled to the optical resonator in a light-conducting coupling region. The device is then configured or arranged to control the refractive index in this coupling region, in particular individually or independently of the other regions of the optical waveguide. The coupling region can therefore 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 transmission to another location or to another functional unit, or the like.Specific requirements may therefore exist for this coupling region 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 here through controllable manipulation within the coupling region. For example, by appropriately controlling the setup, the coupling region or its optical properties can be adjusted or set so that the light loss during a pass through the optical resonator at the pump wavelength is compensated.

[0025] In a possible further development of the present invention, the photonic device is configured to supply light to the optical resonator in several directions, i.e., two or more different directions, particularly opposite directions. For this purpose, the device can have several corresponding light feeds, i.e., corresponding additional optical waveguides or optical waveguide sections. These can meet the optical resonator at the same location or at different locations, or at a region of the optical waveguide embedded in or forming part of the optical resonator. For example, a double-sided supply of light to the optical resonator can be provided, which allows two or more optical quantum states that are as similar as possible to be generated particularly easily and reliably. This can be based on the fact that the light is supplied via different light feeds or...Light coupled into the optical resonator from different directions can pass through the same optical resonator independently of each other, thus avoiding or circumventing any differences or mismatches between different optical resonators.

[0026] In a possible further development of the present invention, the photonic device comprises several optical resonators that are optically coupled to one another. Thus, a light path can lead to a first optical resonator, through and 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, the maximum influence per unit length of the optical waveguide can be limited and / or the different 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 that influence at least one optical property. In contrast to these regions, the intermediate region does not influence the optical property of the light passing through it in the intended propagation, or does so differently, in particular to a lesser extent. The intermediate region can therefore be a region that is neutral in this respect, or more neutral compared to the other regions, or it can be an interruption, for example, in the regions of the optical waveguide that are polarized with respect to the crystal orientation.For example, the intermediate section can have a unique crystal orientation to minimize its influence on the transmitted light, or be made of a different material than the other sections of the optical waveguide, or similar features. The device is then designed or configured to control the refractive index in this intermediate section independently of the other sections of the optical waveguide. By appropriately manipulating this intermediate section, the light conversion can be optimized, as this allows, for example, destructive interference to be avoided particularly easily and effectively, or for the conversion to be set only for specific wavelengths. The use of such an intermediate section allows for particularly flexible shaping and / or…The design of the optical waveguide can be completely independent of the degree or extent to which the optical properties of the light passing through it are affected. This allows for particularly flexible optimization of the photonic device for various requirements.

[0028] The present invention also relates to a photonic device comprising several parallel photonic devices according to the invention, in particular as separate or parallel light sources for frequency-converted and / or squeezed light. The photonic 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 produced by the various photonic devices through coordinated control of the photonic devices. In other words, several instances or wave trains of squeezed light, i.e., several corresponding optical quantum states, can be generated in the photonic device according to the invention, particularly simultaneously, by means of the several photonic devices. These can then be superimposed on or within the photonic device, for example.They can be brought into interaction with each other. In this process, the optical quantum states can, for example, function as qubits to perform correspondingly complex photonic functions, such as optical quantum calculations. Depending on the application, the photonic device can include further components, such as one or more light sources, switching or control logic, connections or connecting cables, and / or the like.

[0029] Further features of the invention may become apparent 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 themselves, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention.

[0030] The drawing shows in: Fig. 1 a partial schematic perspective view of a photonic device; Fig. 2 a partial schematic top view of the photonic device; Fig. 3 a partial schematic top view of the photonic device in a stadium configuration; Fig. 4 a partial schematic top view of the photonic device in a ring resonator configuration with two-sided light supply; Fig. 5 a partial schematic top view of the photonic device in a ring resonator configuration with a first electrode configuration; and Fig. 6 A partial schematic top view of the photonic device in a ring resonator configuration with a second electrode configuration.

[0031] Identical or functionally equivalent elements are marked with the same reference symbols in the figures. For the sake of clarity, only a representative selection of identical or similar elements is explicitly marked in the figures, at least in part.

[0032] In photonic applications, the indistinguishability of multiple optical quantum states based on squeezed light is crucial for their interaction. For example, it may be necessary for several chip-integrated light sources to generate optical states of the same wavelength with the same conversion rate for squeezed light. This is not readily achievable with current manufacturing methods due to unavoidable, minimal manufacturing-related geometric deviations between the different light sources. However, such deviations in geometry or optical properties can be compensated for by additional measures to adjust the optical properties. This is demonstrated in [reference to relevant section]. Fig. Figure 1 shows a partial schematic perspective view of a photonic device 1. This device is manufactured using a layered structure, for example, with methods known from semiconductor or microchip manufacturing. A base electrode 2, for example, in the form of a metal layer, is located on one underside of the device 1. Above this is a substrate 3, which in this case could be, for example, a layer of silicon. 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, which in this case could be made entirely or partially of lithium niobate, is applied to the intermediate layer 4. This waveguide layer 5 is shaped or structured to form an optical 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 from the waveguide 6 passes into the substrate 3. The waveguide layer 5 or the 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.

[0033] For the aforementioned adjustment of the optical properties, the device 1 comprises an influencing device 7. This influencing device 7 includes, by way of example, several electrodes for generating electric fields. These electrodes can simultaneously be configured 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 as an alternative to the electrodes—have heating elements for influencing the waveguide 6 by means of the thermo-optical effect. The electrodes are arranged above the waveguide layer 5 or the waveguide 6 along a predetermined direction of light propagation for the waveguide 6. In particular, the electrodes orThe heating elements of the influencing device 7 rest on or are arranged on the aforementioned protective layer (not shown here). This prevents 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.

[0034] The waveguide 6 has several waveguide regions 8 arranged one after the other along the intended direction of light propagation. The waveguide regions 8 can differ by their crystal orientations 9, which are schematically indicated here by corresponding arrows. The crystal orientations 9 can alternate along the intended direction of light propagation from one waveguide region 8 to the next. The electrodes of the influencing device 7 can each be designed and arranged corresponding to one of the waveguide regions 8. Thus, an electric field can be generated between each of the electrodes and the base electrode 2, which penetrates the respective waveguide region 8. By appropriately adjusting the polarity or supplying voltage to the electrodes, the field can be set or adjusted.It is achieved that a respective field direction 10 of the electric fields, which is also schematically indicated here by arrows, is correlated with the crystal orientation 9 given in the respective waveguide region 8, i.e., corresponds to this, for example.

[0035] Here, a specific and modular design of several electrically conductive electrodes is proposed, which interact with different parts of the waveguide 6 and change the refractive index in specific regions. This allows several corresponding light sources for frequency-converted and / or squeezed light to be combined on a single microchip and, for example, coordinated 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 shaping or adjusting the electric fields and thus the respective refractive index in different waveguide regions 8.

[0036] The parallel generation and interaction of high-quality, squeezed light states can be useful, for example, in quantum computing applications or in sensor technology to improve phase sensitivity. Chip-integrated optical quantum circuits can be used for this purpose, generating indistinguishable optical quantum states using multiple parallel chip-integrated light sources. These optical quantum states can function as qubits or symbolize qubits that, after their generation in optical quantum circuits, can interact with each other.

[0037] Light of a predefined wavelength can be coupled into the waveguide 6 and converted there into light of a different wavelength. Various materials or material systems can be used to implement such chip-integrated light sources. For example, lithium niobate can be used, particularly for the waveguide 6. Due to its exceptionally high second-order nonlinear susceptibility, which stems from its crystalline structure, lithium niobate can be particularly useful and effective. This allows, for example, a particularly high conversion efficiency and a particularly high quality of the generated light or quantum states to be achieved.

[0038] As shown here, a thin lithium niobate layer can be deposited onto a silicon-based wafer (including an intermediate layer, not shown) and shaped by appropriate structuring of the waveguide 6. The waveguide 6 can, for example, be designed as a ridge or rib, i.e., as a longitudinally extended structure or elevation, or the like, in the intended direction of light propagation. The waveguide layer 5 or the waveguide 6 can be periodically polarized 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 passing through several or many differently polarized waveguide regions 8.An important factor for the conversion is the polarization period, i.e., the period with which the crystal orientations 9 change along the intended direction of light propagation. The polarization period can be determined by the phase matching conditions and influenced by applying electric fields. Since the ideal state can only be approximated due to unavoidable manufacturing tolerances, the influencing device 7 can be used to compensate for corresponding deviations or tolerances. This allows for appropriate tuning of the phase conditions.

[0039] To further illustrate this, shows Fig. 2 A partial schematic top view of the photonic device 1 or a corresponding photonic device. Two electrodes of the influencing device 7 are shown as examples. Each of the two electrodes overlaps or covers all waveguide regions 8 that have the same crystal orientation 9. For the sake of clarity, the electrodes only partially cover the waveguide regions 8 here. In practice, this overlap can be greater, or complete coverage of the waveguide regions 8 by the respective electrode may be provided. The intended direction of light propagation can run in the plane of the drawing or parallel to the plane of the drawing.

[0040] Fig. Figure 3 shows a partial schematic top view of the photonic device 1, or a corresponding photonic device. The waveguide 6 and the influencing device 7 with multiple electrodes are also shown. The waveguide 6 comprises differently shaped waveguide sections 8, arranged in straight sections 11 and curved sections 12 connecting them at their ends. Thus, the waveguide 6 has an overall stadium or racetrack shape. The waveguide 6 forms an optical resonator 13.

[0041] Furthermore, another optical waveguide is indicated here as a light feed 14. Light introduced into this light feed 14 can be coupled into the waveguide 6, i.e., into the resonator 13, in a coupling region 15.

[0042] In particular, the coupling region 15 can be detuned electro-optically and / or thermo-optically with at least two elements, i.e., electrodes and / or heating elements or the like. This allows the refractive index of the light guide 14 and / or the waveguide 6 in the coupling region 15 to be controlled, i.e., adjusted or changed, separately from the rest of the waveguide 6. This allows the phase condition for 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 overlapping it.This can be used for fine-tuning the phase condition of the critical coupling, which depends on the optical path of a total revolution of the light in the resonator 13.

[0043] The significance of the aforementioned polarization period is also given when the correspondingly polarized waveguide sections 8 are embedded in or form such an optical resonator 13. Further aspects can then be important for generating the highest possible quality of optical quantum states. For example, a different polarization period can be implemented 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 can include further separately controllable elements for influencing the waveguide sections 8 in the curved sections 12. Such separate or independent influencing of the material of the waveguide sections 8 in the straight sections 11 on the one hand and in the curved sections 12 on the other can enable an overall improvement in conversion efficiency.Likewise, the coupling region 15 can be designed to be separately or individually controllable or tunable. Furthermore, the optical path of the light during a complete pass through the resonator 13 can be adjusted or tuned by means of the control device 7 in order to achieve critical coupling in the resonator 13 at certain predetermined wavelengths. By appropriately controlling the control device 7, particularly in the coupling region 15, it can be ensured that the light loss during a pass through the resonator 13 at the coupled wavelength is precisely compensated. Here, too, the respective field direction 10 of the electric fields used for tuning can 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 or...regions that can be separately or individually tuned, i.e., influenced in their optical properties, for optimal operation of a corresponding chip-integrated light source.

[0044] Possible interruptions of the waveguide regions 8 polarized with respect to the crystal orientation 9, in particular in the resonator 13, can also be designed to be tunable as a group separately or individually, i.e. influenceable, for example by arranging another individually controllable or controllable electrode of the influencing device 7 or the like there.

[0045] The resonator 13 can also be shaped differently, for example as a ring resonator. This is illustrated in a partial schematic representation in Fig. 4 is indicated. Furthermore, a double-sided light feed 14 is indicated here, although this is not limited to the ring shape of the resonator 13 shown here. Here, light can be introduced into the light feed 14 or feeds 14, particularly simultaneously, in both a first light feed direction 17a (schematically indicated here) and a second light feed direction 17b (also schematically indicated) 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 introduced or coupled in the first light feed direction 17a can, after passing through the resonator 13 via a further optical waveguide, indicated here as a light output 16, be coupled out and forwarded in a first light output direction 18a. Analogously, the light introduced or coupled in the second light feed direction 17b can be coupled out or forwarded in a first light output direction 18a.After passing through the resonator 13, the coupled light is coupled out in a second light discharge direction 18b and forwarded in the light discharge 16.

[0046] For example, an unstructured z-cut LNOl wafer can be used as the basis for fabricating the photonic device 1. In this case, or when using a z-cut electrode array, an additional upper intermediate layer can be provided. This upper intermediate layer can be deposited on the top side of the waveguide layer 5—or, if necessary, on the waveguide layer 5 (which may not yet be structured to form the actual waveguide 6)—before or after the structuring of the waveguide layer 5, i.e., the fabrication of the actual waveguide 6, for protection purposes. The layer thickness can be, for example, between 100 nm and 3 µm. A conductive, structured metal layer can then be applied to this, structured to define the different polarized waveguide regions 8. The upper intermediate layer can therefore be produced, in particular, before the structuring or before the application of this metal layer.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 not already 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 between 0.5 µm and 3 µm, can then be applied to the structured waveguide 6 or, if applicable, to the upper intermediate layer. The influencing device 7, i.e., its electrodes, can then be arranged or created at a predefined distance of, for example, at least 1 µm from the lithium niobate layer, i.e., the waveguide layer 5, on the passivation or protective layer.

[0047] In the case of a ring-shaped closed form of the waveguide 6, leads to electrodes arranged inside the ring, i.e., in an area enclosed by the resonator 13, can be implemented from an edge of the device 1 or a corresponding chip, for example, by means of an additional metal layer. If crossings occur, for example, between the leads or connecting leads for different electrodes, several electrically conductive or metallic layers or layers with an insulating intermediate layer and vias (through-holes) can be used.

[0048] To further illustrate this, shows Fig. Figure 5 shows a partial schematic representation of the 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 sections 8 are alternately electrically connected to one of the electrodes via a contact line 19. In this configuration, very few actual electrodes are required, which can enable a particularly simple design of the corresponding power supply. However, the required contact lines 19 can then be relatively long in some cases or extend over at least one waveguide section 8 that is not connected. To avoid this, a different electrode configuration can be used. Figure 5 shows this configuration. Fig.Figure 6 shows a partial schematic representation of the photonic device 1 with such a different electrode configuration. Here, two differently polarized electrodes of the influencing device 7 are arranged on each side of the resonator 13. These are also alternately connected to the waveguide sections 8 via corresponding contact lines 19.

[0049] Overall, the described examples show how a tunable source for squeezed light states can be realized, thus enabling the parallel and efficient generation of several indistinguishable optical quantum states in the smallest space, for example, integrated on a single microchip. REFERENCE MARK LIST 1 Device 2 Base electrode 3 Substrat 4 Intermediate layer 5 Waveguide layer 6 waveguides 7. Influence device 8 waveguide sections 9 Crystal orientation 10 Field direction 11 straight section 12 curved section 13 Resonator 14 Light supply 15 coupling range 16 Light discharge 17a first light supply direction 17b second light supply direction 18a first direction of light emission 18b second direction of light emission 19 contact lines

Claims

[1] Photonic device (1) for generating frequency-converted and / or squeezed light, comprising an optical waveguide (6) made of a material with a non-zero second-order non-linear susceptibility, 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 by 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 by 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 by 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 by 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 bythat 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 by that the device (7) comprises a continuous voltage divider extending over a plurality of regions (8) for generating an electric field strength which varies continuously over these regions (8). [8] Photonic device (1) according to one of the preceding claims, characterized by that the device (7) is designed to influence the refractive index in different areas (8) to different degrees. [9] Photonic device (1) according to one of the preceding claims, characterized bythat 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 each section. [10] Photonic device (1) according to one of the preceding claims, characterized by that the optical waveguide (6) is shaped so as to be straight in sections and curved in sections along the intended direction of light propagation and varies there in different ways in one property. [11] Photonic device (1) according to one of the preceding claims, characterized by that the regions (8) of the optical waveguide (6) are embedded in an optical resonator (13) or at least form part of an optical resonator (13). [12] Photonic device (1) according to claim 11, characterized bythat 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 by 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 by 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 bythat the optical waveguide (6) comprises at least one intermediate region arranged between the regions (8) influencing a 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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