Multilayer signal conduction structure and method for operating a multilayer signal conduction structure

Abstract

Described is a multilayer signal conducting structure comprising: a plurality of layers, wherein the plurality of layers comprises at least two waveguide layers which extend along an extension direction and which serve to couple in an electromagnetic signal, and at least one intermediate layer arranged between the at least two waveguide layers; at least two cover layers, wherein the at least two waveguide layers are arranged partially or completely between the at least two cover layers, wherein the at least one intermediate layer comprises a magneto-optical material, MO, and / or the at least two cover layers comprise a magneto-optical material, MO. Furthermore, a method for operating a multilayer signal conducting structure is described.

Description

The present invention describes a multi-layer signal conducting structure and a method of operating a multi-layer signal conducting structure. A principle of efficient signal routing is described, which is used in particular in switches, circulators and isolators.Data centers are essential components in today's digital landscape and serve as centralized nodes for the processing, storage and distribution of data. The wide spread of mobile applications as well as the increasing complexity of these applications have resulted in a significant increase in data traffic. This increase may be attributed to factors such as increasing user binding with smartphones, augmented reality applications, high-resolution video streaming, and the Internet of Things. As a result, data centers are challenging to meet the increasingly increasing data throughput requirements, requiring continued development of the hardware and software infrastructure. Datacenter design optimization, including the introduction of high performance computers, energy efficient cooling solutions, and advanced network protocols, has become indispensable to ensure uninterrupted data flow, minimize latencies, and address the ecological impact of increased energy consumption.Photonics is a promising instrument in addressing the increasing challenges of data traffic in data centers. Photonic integrated circuits (PICs; PIC= Photo Integrated Circuits) offer the potential to reduce both power consumption and footprint. In recent decades, continuous efforts have been made to develop photonic components with different functionalities. To direct data traffic, efficient and chip integrable switches and circulators are of great importance. Moreover, PICs that require integrated or external lasers require the use of optical isolators to block any signals that travel to the source that could degrade performance. To date, the bulky configurations proposed are demanding and involve many technological steps for chip integration. On the other hand, waveguiding solutions suffer from high insertion losses (hereinafter also abbreviated as I.L; I.L=insertion loss) and have an unsatisfactory insulation ratio (hereinafter also abbreviated as I.R; I.R=insulation ratio).In recent decades, digital communication and information exchange have grown exponentially. There is an increasing need to develop circuits that provide improved functionality. The advancement of components such as switches, circulators, and isolators, which play a central role in enabling efficient and seamless data flow across various applications, is a need.To achieve these functionalities, a medium that breaks spatial and temporal symmetry is required [1].Over the last decades, these components have been demonstrated both experimentally and theoretically. Various mechanisms with different architectures have been proposed and widely studied based on magneto-optics (MO), electro-optics (EO), acousto-optics (AO), optomechanics (OM), photonic junctions (PT), photonic crystals (PhC) and piezoelectric (PZT) interactions.For switches, microring resonator (MRR) and Mach-Zehnder interferometer (MZI) configurations were studied and evaluated. In the MRR case, a microring provides resonance at a particular wavelength (λ 0). When an external magnetic field is applied in the clockwise (CW) and counterclockwise (CCW), the resonance is shifted red or blue. With the use of such a device, an extinction ratio of 21 dB at λ 0=1,561 μm was achieved at a wavelength shift of 0.14 nm [2].MZI-based MO-al switches have also been studied. They are usually composed of a combination of an unbalanced MZI, MMI couplers, an unbalanced phase bias voltage and an MO-al phase shifter. At λ 0=1,541 μm and a device length of 1.2 mm and a current of ±400 mA, an extinction ratio of 25 dB was observed with an energy loss of I.L=10 dB [2].Another approach has been presented in [3]. The design comprises two tapered multimode sections in which the transverse electric modes TE 0 and TE 1 are excited equally, the TE 1- mode then being converted into a transverse magnetic mode TM. In the central waveguide of the MO phase shifter, the TM mode experiences a phase shift. The phase difference between the TE and TM modes determines the interference between the TE 0- and TE 1- modes of the output half-mode converter. When the TM mode experiences a phase shift of ±π / 2, the output port of the light signal is selected by changing the magnetization. For a device with L=950 μm, an energy loss of I.L=6.7 dB and an insulation ratio of I.R=19.9 dB were obtained at λ 0=1,5753 μm.For MO circulators, in [4] three waveguides were coupled with a metal nano-rod heterostructure placed in a uniformly magnetized MO material. At λ 0=1,43 μm, the system has a sharp plasmonic resonance and the structure redistributes the input power between the link arms, with up to 63% of the power being transmitted through one of the output ports and the other output port being almost completely isolated.Magneto-PhCs were also theoretically used to demonstrate circulators. When working in a uniform external magnetic field, the researchers showed a marked splitting of the natural frequencies of the two counterpropagating modes. Using three PhC waveguides coupled to an MO cavity, an isolation ratio (I.R) of 20 dB at λ 0=1,3 μm was calculated [5]. Similarly, in [6], I.R=30 dB was found for λ 0=0,633 μm and λ 0=1,55 μm.In the isolators, one of the first attempts was to reproduce the principle of solid Faraday isolators. Low forward and high reverse energy losses (I.L.) are the features of this massive insulator that is not compatible with PICs. This isolator requires the integration of polarizers into the system, which must be done first. From here, attempts are made to realize insulators in waveguiding configuration [7].Among the various MO effects, the TMOKE (Transverse Magneto-Optic Kerr effect) appears to be the most compatible solution because it has the advantage of not affecting the polarization of the input light.In the case of NRL (Non-Reciprocal Loss), the combination of an optical semiconductor amplifier (SOA; SOA= Semi Optical Amplifier) with a ferromagnetic coating is investigated. By injecting a current into the SOAs, the forward losses can be compensated. The polarization dependent design configures the imaginary component of the effective refractive index, resulting in unequal losses in the opposite propagation directions. In the TM configuration [8], at λ 0=1,3 μm, the design was validated and showed about an insulation ratio of I.R=99 dB / cm. In the TE configuration [9], the design was validated at λ 0=1,55 μm and showed I.R=14.7 dB / mm.In the NRPS (non-reciprocal phase shift) effect, a change in the real part of the effective refractive index is observed, resulting in a phase difference between the forward and reverse signals. Here, an MZI is covered with a magnetic rare garnet. In this passive design, the light would interfere constructively in the forward direction and destructively in the reverse direction. Many research groups have used NRPS; an isolation ratio of I.R=19 dB was achieved at a wavelength of λ 0=1,54 μm with a waveguide having a length of L=8 mm

[10] .In resonator devices, many groups have developed highly resonant microrings. The lugs varied in geometry (radius) and placement (fill material: in the disc, cladding material: deposited on the resonator). For the first scenario, an isolation ratio of I.R=20 dB was measured, along with I.L of less than 0.1 dB and a bandwidth of 0.4 nm

[11] . As for the sheath solution, a first demonstrator exhibited an insulation ratio I.R=19.5 dB for L=290 μm

[12] , while a second 9 dB reached 1.R at λ 0=1,55 μm

[13] .Magneto-plasmonic insulators based on the TMOKE effect have also been studied. In this case garnets and metals have been integrated to make use of the SPP (surface plasmon polariton) limitation along the metal / dielectric interface. In the design of magnetoplasmonic MZIs, researchers achieved an isolation ratio of I.R=22.82 dB at low energy loss I.L

[14] . Others used a magnetoplasmonic slot conductor to excite an LRSPP mode (LRSSP is an abbreviation of the English for Long-Range Surface Plasmon Polariton) with the aid of a cone. This resulted in an isolation ratio of I.R=30 dB at a wavelength of λ 0=1.55 μm

[15] , although promising results were shown, but for a complete device with input / output couplers, the isolator would have an isolation ratio of I.L >10 dB.The principles and performance of MO and non-MO isolators published since 1988 are summarized in Table 1 below.Table 1: Summary of the various types of optical isolators, MO (dark gray) and non-MO (light gray), their operating polarization, their conductive material, their operating wavelength λ 0 and their properties I.R, I.L, L.FR-based designs (FR for Faraday rotation-based isolator) are bulky and not suitable for integration on the chip. NRL and NRPS designs require additional SOAs with complex technological processes and have a high energy loss (I.L.). Resonator structures offer a large isolation ratio (IR), but are greatly limited due to their narrow bandwidth. Magnetoplasmonic designs offer satisfactory performance, however, absorption due to the metal can severely affect the intensity of the output signal. Non-MO-based devices suffer from large footprint and moderate I.R.DE 26 14 141 A1 discloses an optical waveguide. DE 38 33 413 A1 discloses 3D-integrated optical semiconductor components.An object of the present invention is to provide a multilayer signal conducting structure and a method for operating a multilayer signal conducting structure with efficient signal conduction, in which / in particular a low energy loss and a good insulation ratio can be measured.The object is achieved by a multilayer signal conducting structure according to claims 1 to 3 and a method for operating a multilayer signal conducting structure according to claim 30.The scope of protection is defined by the appended claims.According to the proposal, the multilayer signal guide structure comprises a plurality of layers, wherein the plurality of layers comprises at least two, in particular dielectric, waveguide layers which extend along an extension direction and which serve for coupling in an electromagnetic signal, and at least one, in particular dielectric, intermediate layer which is arranged between the at least two waveguide layers. The multilayer signal guiding structure further comprises at least two, in particular dielectric, cover layers, wherein the at least two waveguide layers are partially or completely arranged between the at least two cover layers. According to the proposal, the at least one intermediate layer comprises a magneto-optical material, MO, and / or the at least two cover layers (30) comprise a magneto-optical material, MO. An external magnetic field can be applied or is applied to the multilayer signal guiding structure, as a result of which a transverse magnetic mode, TM mode, and / or a transverse electrical mode, TE mode, of the electromagnetic signal coupled into the at least two waveguide layers experiences a change in its electromagnetic field profile aligned along the direction of extent of the at least two waveguide layers. When an external magnetic field is applied, at least one TM / TE mode propagates along the direction of extent in at least one waveguide layer of the at least two waveguide layers, wherein at least one even TM / TE mode is described by a first propagation constant β e and an odd TM / TE mode by a second propagation constant β o wherein the at least two waveguide layers are each described by the further propagation constants β a, β b wherein a maximum power transmission takes place at a ratio of the propagation constants, where β a is the propagation constant of the fundamental mode of the first waveguide layer of the at least two waveguide layers and β b is the propagation constant of the fundamental mode of the second waveguide layer of the at least two waveguide layers.The at least two waveguide layers are preferably positioned parallel to one another in the multilayer signal guide structure. In particular, an air layer can also serve as the cover layer or various materials as described herein can be used. The at least one intermediate layer may be formed as an air layer or various materials as described herein may be used. In particular, a plurality of multi-layer signal conducting structures can be used on top of one another, i.e. stacked (horizontally or vertically, i.e. along the y-direction and / or along the z-direction), in order to define signal guidance in an efficient manner. By way of example, the multi-layer signal routing structure will be described with reference to five layers to facilitate understanding of the derivation of the principles of the proposed technical teaching for the reader of the present application. However, the proposed multi-layer signal conducting structure may have more than five layers. In particular, an external magnetic field can be applied to the multilayer signal conducting structure, as a result of which electromagnetic signals, i.e. electromagnetic waves, can be directed in a targeted manner in a predefined direction or in a plurality of predefined directions when using the multilayer signal conducting structure. While a flow of the electromagnetic signals in another direction can be suppressed or reduced in a targeted manner. When using the multi-layer signal conducting structure in an external magnetic field, signals in the multi-layer signal conducting structure can be efficiently guided in one or more predetermined directions substantially without great energy loss.Further proposed multi-layer signal conducting structures are defined in claims 2 and 3.According to a further aspect, a method for operating a multilayer signal conducting structure is described. In the proposed method, a multi-layer signal conducting structure as described herein is used. The method comprises providing a multi-layer signal structure comprising a plurality of layers, wherein the plurality of layers comprises at least two waveguide layers which extend along an extension direction and which serve for coupling an electromagnetic signal, and at least one intermediate layer which is arranged between the at least two waveguide layers. In addition, the multi-layer signal guiding structure comprises at least two cover layers, wherein the at least two waveguide layers are partially arranged between the at least two cover layers, wherein the at least one intermediate layer comprises a magneto-optical material, MO, and / or the at least two cover layers comprise a magneto-optical material, MO. The method further comprises applying an external magnetic field to the multi-layer signal guiding structure, whereby a transverse magnetic mode, TM mode, of an electromagnetic signal introduced into the multi-layer signal guiding structure experiences a change in its magnetic field profile aligned along an extension direction of the at least two waveguide layers, wherein depending on an alignment of the external magnetic field to the multi-layer signal guiding structure, a concentration of the electromagnetic signal takes place in only one of the at least two waveguide layers.The disclosure of the multi-layer signal conducting structure also applies to the disclosed method, wherein the details are not repeated for redundancy reasons. Rather, reference is made to the description of the multilayer signal conducting structure.The proposed invention describes a novel method and a novel multi-layer signal guiding structure for signal guidance that could be implemented to achieve efficient photonic switches, circulators and isolators with negligible energy loss I.L. and low power usage. The components developed are simple and uncomplicated; all designs are based on a multilayer magneto-optical (MO) heterostructure, which is illustrated in the figures in particular in five layers, or else signal guiding structure, in which coupled optical modes, in particular in parallel dielectric waveguides, exchange power in the presence of an MO material which is magnetized externally.The proposed invention relates in particular to three optical components, namely: switches, circulators and isolators, which are constructed in particular completely in dielectric format and on the basis of MO-s, in order to enable the PIC integration.The proposed invention does not require complex technological steps for production and has the advantage of simple integration into PICs. Moreover, for each MO material (level of gyrotropy), 100% performance can be achieved by modifying the geometric dimensions of the heterostructure or also called signal conducting structure. In contrast to other designs, this does not affect the performance of the component, since the input signal here propagates in the, in particular dielectric, waveguides without great interaction with the MO material itself, making the design tolerable with respect to an energy loss I.L., which can be estimated to be less than a few db / cm. Finally, these components require, in use, an external mag field applied to the signal conducting structure, which is applied to the signal conducting structure in the TMOKE configuration. The external magnetic field may be provided via a rare earth magnet or an electromagnet.Preferred embodiments of the present invention will be explained in detail below with reference to the accompanying drawings. The following are shown: FIG. 1 shows a plan view of a first configuration of the multilayer signal conducting structure, wherein the MO material is arranged between the at least two, in particular parallel, waveguiding layers; FIG. 2 shows a plan view of a second configuration of the multilayer signal conducting structure, wherein the MO material is arranged on two of the at least two, in particular parallel, waveguiding layers; FIGS. 3 a, b show a plan view of a third configuration of the multilayer signal conducting structure, wherein the MO material is arranged on two of the at least two, in particular parallel, waveguiding layers and wherein the MO material is arranged between the at least two, in particular parallel, waveguiding layers (see FIGS. 3 aand 3 b ); FIG. 4 is a top view of a first partition of the multi-layer signal conducting structure with only one waveguiding layer, i.e. waveguide a. FIG. 5 is a top view of a further partition of the multi-layer signal conducting structure with only one waveguiding layer, i.e. waveguide b. FIG. 6 shows a ratio (ratio) which was calculated for different gyrotropy values (g=0.1; 0.05; 0.01) and as a function of the varying width of the at least one intermediate layer (gap width); FIG. 7 shows coupling length representations (coupling length) calculated for different gyrotropy values g (g=0.1; 0.05; 0.01) as a function of the variation width of the at least one intermediate layer (gap width); FIG. 8 shows a ratio (ratio) which was calculated for different gyrotropy values (g=0.01; 0.005; 0.001) and as a function of the varying width of the at least one intermediate layer (gap width); FIG. 9 shows coupling length representations (coupling length) calculated for different gyrotropy values g (g=0.01; 0.005; 0.001) as a function of the variation width of the at least one intermediate layer (gap width); FIG. 10 shows the power P in the at least two waveguiding layers (waveguides a (black) and b (gray)) of the multilayer signal guiding structure as a function of the coupling length Lc, which is used, for example, in a switch or a circulator; FIG. 11 shows the power P in the at least two waveguiding layers (waveguides a (black) and b (gray)) of the multilayer signal guiding structure in the forward direction as a function of twice the coupling length 2Lc, which is used, for example, in an isolator; FIG. 12 shows the power P in the at least two waveguiding layers (waveguides a (black) and b (gray)) of the multilayer signal guiding structure in the reverse direction as a function of twice the coupling length 2Lc, which is used, for example, in an isolator; FIG. 13 is a flow diagram of a method for operating the multi-layer signal conducting structure; FIG. 14 is a plan view of a dielectric MO switch with an inwardly directed external magnetic field, with light entry through a first input connection port I 1 and light exit through a second output connection port O 1; FIG. 15 is a plan view of a dielectric MO switch with an external magnetic field directed outwards, with light entering through a first input connection port I 1 and light exiting through a second output connection port O 2; FIG. 16 is a plan view of a dielectric MO circulator with light entry through a first input terminal Port I 1 and light exit through a second output terminal Port O 2; FIG. 17 is a plan view of a dielectric MO circulator with light entry through a second input terminal Port I 2 and light exit through a third output terminal Port O 3; FIG. 18 is a plan view of a dielectric MO circulator with light entry through a third input terminal Port I 3 and light exit through a first output terminal Port O 1; FIG. 19 is a plan view of a MO dielectric isolator with light moving in a forward propagation direction; and FIG. 20 is a plan view of a MO dielectric isolator with light moving in the backward propagation direction.Individual aspects of the invention described herein are described below in Figures 1-20. In the present application, like reference numerals refer to like or identically functioning elements, and not all reference numerals need to be redewined in all drawings, provided they are repeated.When a component is described herein as "configured to do something", it is intended that the component be correspondingly designed structurally and physically so that the components perform what it is intended.In the present case, the term signal means an electromagnetic wave. The terms signal and electromagnetic wave are used interchangeably. Likewise, the terms waveguiding layer and waveguide are used interchangeably.The proposed multilayer signal guiding structure 100 comprises a plurality n of layers, wherein the plurality n of layers comprises at least two waveguide layers 10, in particular a first waveguide layer a and a second waveguide layer b, which extend along an extension direction x and which serve for coupling in an electromagnetic signal, and at least one intermediate layer 20 arranged between the at least two waveguide layers 10. The multi-layer signal guiding structure 100 further comprises at least two cover layers 30, wherein the at least two waveguide layers 10 are partially or completely arranged between the at least two cover layers 30. According to the proposal, the at least one intermediate layer 20 comprises a magneto-optical material, MO, and / or the at least two cover layers 30 comprise a magneto-optical material, MO. These three possible configurations of the multi-layer signal conducting structure 100 are schematically shown in Figures 1 to 3. The MO material can also be a ferromagnetic metal, for example. The at least two waveguide layers 10 can be, for example: a dielectric such as silicon Si, silicon nitride SiN, polymer or epoxy or a hybrid consisting of a dielectric and a metal.The at least one intermediate layer 20 can consist of ferromagnetic metals such as copper CU or iron FE, silicon dioxide or polymers doped with iron nanoparticles, or garnets such as YIG, BIG, TIG, GGG, which can be further doped to enhance their MO effects. However, dielectric materials are preferred for the layers 10, 20, 30. The at least two cover layers can be provided, for example, by SiO2or air, but not by a metal.FIG. 1 shows a plan view of a first configuration of the multilayer signal conducting structure 100, wherein the MO material is arranged between the at least two, in particular parallel, waveguiding layers 10. According to the first configuration, the at least one intermediate layer 20 includes the MO material. FIG. 2 shows a plan view of a second configuration of the multilayer signal conducting structure, wherein the MO material is arranged on two of the at least two, in particular parallel, waveguiding layers. According to the second configuration, the at least two capping layers 30 include the MO material. FIGS. 3 aand 3 b show a plan view of a third configuration of the multilayer signal guiding structure, wherein the MO material is arranged on two of the at least two, in particular parallel, waveguiding layers and wherein the MO material is arranged between the at least two, in particular parallel, waveguiding layers.According to the third configuration, the at least one intermediate layer 20 comprises a second MO material and the at least two cover layers 30 comprise a first MO material. The first and second MO materials may be different from each other. In particular, the first and the second MO material have different gyrotropy values g. In particular, the external magnetic fields applied to the first and second MO materials are oppositely directed. For this purpose, two magnetic fields oriented opposite to one another are applied to the two identical or different MO materials by permanent magnets being deposited locally on the MO materials in a corresponding manner.In FIGS. 1 to 3a, 3b, a coordinate system (x, y, z) is shown. As can also be seen from FIGS. 1 to 3 a, 3 b, the direction of extension extends along the x-axis. The different layers 10, 20, 30 have a length along the direction of extension along the x-axis. Along the z-axis, the layers 10, 20, 30 each have a thickness. A single waveguiding layer 10, a, bhas a thickness d. A single intermediate layer 20 in FIGS. 1 to 3 a, 3 bhas a thickness 2 a. A single cover layer 1 to 3a, 3b has a thickness D.The layers 10, 20, 30 are preferably arranged directly one on top of the other, as can be seen from FIGS. 1 to 3, 3b.An external magnetic field can be applied or applied to the multilayer signal guiding structure 100, as a result of which an optical mode, for example a transverse magnetic mode, TM mode, and / or a transverse electrical mode, TE mode, of the electromagnetic signal coupled into the at least two waveguide layers 10 experiences a change in its magnetic field profile aligned along the direction of extent of the at least two waveguide layers 10. The change in the magnetic field profile (i.e. a resulting magnetization) has an effect on a measured power P, as can be seen, for example, in FIGS. 10, 11 and 12, which will be described in greater detail below. In FIGS. 1 to 3 a, 3 b, for example, the orientation of the magnetic field can be seen schematically. In Fig. 1, it can be seen that the magnetization is directed inwardly.In FIG. 1, the at least one intermediate layer 20 comprises the MO material, whereby the external magnetic field is directed inward (see x in circle in layer 20 in FIG. 1 ). In FIG. 2, the at least two capping layers 30 comprise the MO material, whereby a magnetization is also directed inward in this case.In FIGS. 3 aand 3 b, the layers 20 (at least one intermediate layer) and 30 (the at least two covering layers) comprise the MO material, in particular the layers 20 and 30 consist of the MO material. The applied external magnetization is directed in the opposite direction (inward and outward or outward and inward). Depending on the orientation of the external applied magnetic field, the magnetization in the MO material is oriented outwards (layers 30 and inwards (layer 20) (FIG. 3 a ) or inwards (in layers 30) and outwards (in layer 20) (FIG. 3 b ). According to FIG. 3 b, the magnetization of the at least two cover layers is directed inward. The magnetization of the at least one intermediate layer 20 is directed outwards. Magnetization is in opposite directions in layers 20 and 30. Accordingly, according to FIG. 3 a, the magnetization of the at least two cover layers 30 is directed outwards. The magnetization of the at least one intermediate layer 20 is directed inward. The magnetization in the layers 20 and 30 also runs in opposite directions in FIG. 3 a. In other words, the local external magnetic field acting on the MO material in the center is opposite to that acting on the MO outside the waveguides. The magnetization consequently runs in the opposite direction in the layers 20 and 30.Opposing magnetic fields in the at least two MO layers can be generated by depositing magnets on the different MO layers and controlling the magnets independently of each other. Permanent magnets or also non-permanent magnets can be arranged on the MO layers.In magneto-optical materials, the direction of magnetization is influenced by a magnetic field applied from the outside. The term "magnetization direction" typically refers to the orientation of the magnetic moments within the MO material. Without an external magnetic field, the magnetic moments may be randomly oriented or follow the crystallographic axes of the material.If an external magnetic field is applied to the MO material or materials, the external magnetic field may induce (align) a preferred orientation of the magnetic moments. The orientation of the magnetic moments affects the optical properties of the MO material or materials, such as the ability of the MO material to rotate the plane of polarization of the light, which is the basis for magneto-optical effects. In summary, it can thus be stated that the magnetization of the material and the applied external magnetic field are hand-held, the magnetization of the layer does not exist without the magnetic field applied from the outside.In physics, the representation of vectors, e.g. in a magnetic field, is frequently used to show their orientation with respect to the image plane. If a vector represented as a circle with a point is indicated, this means that it points into the image plane. If the vector is represented as a circle with a cross, it points out of the image plane.The at least two waveguide layers 10 and / or at least one intermediate layer 20 and / or the at least two covering layers 30 are preferably dielectric. In this case, the multilayer signal conducting structure is a multilayer dielectric signal conducting structure. The multilayer signal conducting structure described above could comprise at least one dielectric layer 10, 20, 30. It is also conceivable for each of the layers 10, 20, 30 to be dielectric.The external magnetic field may be a rare earth magnet or an electromagnet configured to saturate the MO material. The electromagnet is preferably used. The electromagnet may comprise a thin metal layer arranged directly on the MO material or on one of the at least two cover layers 30. Referring to FIG. 1, the electromagnet (not shown in FIG. 1 ) could be arranged on the MO material of the at least one intermediate layer 20 or on the at least two cover layers 30.A wave propagation of the electromagnetic signal coupled into the at least two waveguide layers 10 is described in each case by a propagation constant β, β b wherein the propagation constants β a, β b of the at least two waveguide layers 10 are different, β a ≠ β b. The fact that the propagation constants β a, β b are different is due to the presence of the MO layer, resulting in breakage of the spatial symmetry. Whenever at least one MO material is present in one of the three configurations, the propagation constants β a, β b in the individual waveguiding layers 10, a, b differ from one another.When an external magnetic field is applied, at least one, in particular optical, TM mode propagates along the direction of extent in at least one waveguide layer 10, a, b, of the at least two waveguide layers 10, a, b, wherein at least one, in particular even, TM mode is described by a first propagation constant β e and one, in particular optical, odd TM mode is described by a second propagation constant β o wherein the at least two waveguide layers 10, a, b are each described by the further propagation constants β a, β b, which have already been described, wherein a maximum power transmission takes place at a ratio of the propagation constants, wherein β a is the propagation constant of the, in particular optical, TM mode, TM mode of the first waveguide layer 10, a of the at least two waveguide layers 10 and β b is the propagation constant of the, in particular optical, TM mode of the second waveguide layer 10, b of the at least two waveguide layers 10Each waveguide layer 10, a, b defines a coupling length on account of its nature, such that the coupled modes introduced into the waveguide layer 10, a, bare decoupled in C after the coupling length L has been covered. In addition, these modes should propagate over a distance called "coupling length" in order to decouple, so that only one mode remains at the end of them, the power of which is concentrated exclusively in one of the, in particular parallel, waveguides a, b. The coupling length L C is a function of the first and second even and odd mode propagation constants β e, β o and is given by:Each MO material used in the multi-layer signal structure 100 has one gyrotropic level or different gyrotropic levels. According to the first configuration, in which the multi-layer signal conducting structure 100 comprises an MO material in the at least one intermediate layer 20, the MO material has a single gyrotropic level. According to the second configuration, in which the multi-layer signal conducting structure 100 comprises an MO material in the at least two cover layers 30, two different gyrotropic levels may be present. However, the external magnetization should point in the same direction, respectively. According to the third configuration, in which the at least one intermediate layer 20 and the at least two cover layers 30 each comprise an MO material, up to three different gyrotropic levels may be present.However, the external magnetic field in the at least one intermediate layer should be opposite to the external magnetic field in the at least two cover layers 30. Preferably, the at least two cover layers 30 each have the same gyrotropic level, which however can differ from the gyrotropic level in the at least one intermediate layer 20. However, it is also conceivable for all three gyrotropic levels to be the same.A length L, in particular geometric, of the at least two waveguide layers 10 and a length L', in particular geometric, of the at least one intermediate layer 20 are preferably of the same length. In particular, the geometric length L corresponds to a multiple of the coupling length L C. The coupling length L C for example, depends on many different factors, such as the wavelength of the electromagnetic signal and / or on a length-thickness index of the waveguiding layer 10 and / or the used MO material or materials. The length-thickness index of the waveguiding layer 10 means the geometric length L and the geometric thickness of the waveguiding layer 10. In the case of an insulator, for example, the geometric length L preferably corresponds to twice the coupling length L C. This is because the light incident into the waveguiding layers 10 must decouple and then couple again. In the case of a switch, however, the geometric length L preferably corresponds to the simple coupling length L C. This is because the light incident into the waveguiding layers 10 only has to decouple.FIG. 6 shows a relationship of the two propagation constants β a, β b and the even and odd modes β e, β o. The ratio was calculated for a constant thickness d (d indicates the width along the z-direction of a waveguide a, b) of the at least two waveguide layers 10 as a function of the at least one intermediate layer 20 (2a, gap width) for different gyrotropia values g. This ratio is shown in FIG. 6 versus that of the width 2 aof the at least one intermediate layer 20 (gap width) for different gyrotropia values g. FIG. 7 shows, in a manner corresponding to FIG. 6, a representation of the coupling length (coupling length) calculated for different gyrotropia values g as a function of the variation thickness 2 aof the at least one intermediate layer 20 (gap width). The various gyrotropy values g in Figs. 6 and 7 are g=0.1 and g=0.05 and g=0.01.FIG. 8 shows a relationship of the two propagation constants β a, β b and the even and odd modes β e, β o. The ratio was calculated for a constant thickness d (d indicates the width along the z-direction of a waveguide a, b) of the at least two waveguide layers 10 as a function of the at least one intermediate layer 20 (2a, gap width) for different gyrotropia values g. This ratio is shown in FIG. 8 versus that of the width 2 aof the at least one intermediate layer 20 (gap width) for different gyrotropia values g. FIG. 9 shows, in a manner corresponding to FIG. 8, a representation of the coupling length Lc (coupling length) calculated for different gyrotropia values g as a function of the variation thickness 2 aof the at least one intermediate layer 20 (gap width). The various gyrotropy values g in Figs. 8 and 9 are g=0.01 and g=0.005 and g=0.001.It can be seen from FIGS. 6 and 8 that the ratio for all gyrotropy values g varies between 0 and 1. For a given interlayer width 2a, this size reaches 0.707107, which is the width at which complete power exchange takes place between waveguides a and b.It can be seen from FIGS. 7 and 9 that the variable Lc increases with increasing intermediate width 2 afor all gyrotropia values. Considering a single gyrotropy case, when the width 2a of the intermediate layer reaches a certain value at which the calculated ratio is 0.707107, and when the input optical modes, i.e. the TM optical modes entering a waveguide layer 10, travel a distance Lc, a complete power exchange takes place between the waveguides a and b.The following values could be calculated: For g=0.1 against Lc=50.7 μmFor g=0.05 against Lc=101.4 μmFor g=0.01 against Lc=506.9 μmFor g=0.005 against Lc=1013.75 μmFor g=0.001 against Lc=5063.45μm )It can thus be seen from FIGS. 6 to 9 that the coupling length extends from approximately Lc=50 μm for g=0.1 over Lc=500 μm for g=0.01 to after Lc=5000 μm for g=0.001.A preferred thickness d of one of the at least two waveguiding layers 10 is between 0.1 μm and 4 μm, in particular in the two-dimensional (2D) and in the three-dimensional (3D). The preferred thickness d of one of the at least two waveguiding layers 10 depends, for example, on the wavelength at which the multilayer signal conducting structure 100 is operated. The preferred thickness d of one of the at least two waveguiding layers 10 also depends, for example, on the materials used in the at least two waveguiding layers 10. Single-mode waveguiding layers 10 are preferably used. In single-mode waveguiding layers 10, a single mode concentrates in the corresponding waveguiding layer 10, provided that an electromagnetic signal is transmitted into the corresponding waveguiding layer 10.A thickness D of the MO material in the form of the at least two capping layers 30 or a thickness 2 aof the MO material in the form of the at least one intermediate layer 20 may depend on the deposition technique used. A thickness can be between 50 nm and 500 nm.In the present case, the term thickness 2 a, dor D is understood to mean a thickness in the three-dimensional form. The term thickness 2 a, dor D a thickness can also be understood as a diameter along the z-axis. In the figures shown, however, the thickness 2a, d or D is only shown two-dimensionally.The at least two waveguide layers 10 preferably run parallel to one another along the direction of extent. In the present case, "parallel to one another" is to be understood in the sense of the possibility of producing waveguide layers 10 aligned as parallel to one another as possible. Production-related fabrication errors of the at least two waveguide layers 10 can therefore also be understood as "parallel to one another".A thickness 2 aof the at least one intermediate layer 20 is between 0.01 μm and 10 μm. The thickness 2 aof the at least one intermediate layer 20 depends on the gyrotropy value g of the MO material used in each of the three configurations described, provided an MO material is used for the at least one intermediate layer 20. In FIGS. 7 and 9, for example, the thickness 2 aof the at least one intermediate layer 20 is 2 a=0.6 μm for g=0.1 or 2 a=0.95 μm for g=0.01 or 2 a=1.3 μm for g=0.001. In FIGS. 6 to 9, the size "gap width" (German gap width) on the x-axis thus denotes the thickness 2 aof the at least one intermediate layer 20.The at least one intermediate layer 20 can also be provided by an air layer or SiO 2. Air is not an MO material, however. In other words, air does not have a gyrotropy value g. The at least one intermediate layer 20 can also be provided by an air layer or SiO2or epoxy resin when using the configuration shown in FIG. 2.In particular, the at least one intermediate layer 20 does not exceed a thickness 2 aof 100 μm. The value of 2 a=100 μm can be understood as the maximum value of the thickness 2 aof the at least one intermediate layer 20. Above such a value, coupled optical modes occur. The value of 2 a=0.01 μm can be understood as a minimum value of the thickness 2 aof the at least one intermediate layer 20. In particular, the minimum value may be any thickness 2a greater than zero.A thickness D of one of the cover layers 30 is between 0.0 μm and 50 μm, in particular in the case of a chip, or between 0.0 μm to infinity, in particular if the multilayer signal conducting structure 100 is not installed in a chip. The at least two covering layers 30 can also be designed as an air layer. In this case, the thickness D may be infinite. In the case of a dielectric cover layer 30, the thickness D is at a minimum value greater than zero, for example D=0.01 μm, up to a maximum value of D=50 μm. In particular, the evanescent field of a corresponding mode extends no longer than over a length of 5 μm into the dielectric cover layer 30.The multilayer signal guiding structure 100 preferably comprises at least one input port 120 for introducing the electromagnetic signal and at least one output port 140 for diverting an output signal, wherein the input port 120 is configured to introduce coupled modes of the electromagnetic signal into the at least two waveguide layers 10 and the at least one output port 140 is configured to re-couple the modes decoupled in the at least two waveguide layers 10 along the direction of extension. The at least one input port 120 and the at least one output port 140 are shown, for example, in FIGS. 14 to 20.The multilayer signal guide structure 100 can be configured, by virtue of its structure, to provide insulation for, in particular optical, TM modes of an electromagnetic wave introduced into the at least two waveguide layers 10 (as illustrated, for example, in FIGS. 19 and 20 ) and / or to let the, in particular optical, TM modes propagate in a predefined direction in the at least two waveguide layers 10 (see FIG. 19 ) and to prevent propagation in the direction opposite to the predefined direction (as illustrated, for example, in FIGS. 14 and 15 ) and / or to let the, in particular optical, TM modes circulate in the at least two waveguide layers 10 (as illustrated, for example, in FIGS. 16 to 18 ). The term structure is understood here to mean a geometric and physical structure. It should be noted here that in 2D, only TM modes exhibit this phenomenon, while in 3D, TM and TE modes exhibit this phenomenon.In 2D, the switching, circulating and isolator effects are present when using the TM optical modes. In the 3D mode, on the other hand, the operating mode can also comprise the optical TE mode depending on the thickness of the MO layer and the waveguiding layers in the y direction. In FIG. 3D, the TE and TM modes propagating in the at least two waveguide layers 10 depend on the geometric configuration of the multilayer signal line structure 100. This means that if the MO material has a small thickness in the y direction, then the functionality is better developed in the TE mode than in the TM mode. If the MO material has a sufficient thickness in the y direction, the functionality is better developed in the TM mode than in the TE mode.The terms small thickness and sufficient thickness are understood here as follows. In FIG. 3D, the functionality of the multi-layer signal conducting structure 100 depends on the MO material used. For example, some suppliers may deposit MO material having a thickness along the Y-axis of less than 100 nm. With such a thickness (small thickness) along the y-axis, the signal guiding structure 100 works better with TE modes. Other suppliers may deposit 500 nm from the MO material along the Y-axis. With such a thickness (sufficient thickness) along the y-axis, the signal guiding structure 100 works better with TM modes. In summary, depending on the thickness of the MO material along the y-axis, a TE mode or a TM mode may preferably be used to effect switching or isolation.The proposed design of the multi-layer signal guiding structure 100 can be used for both TE modes and TM modes in an isolator or in a switch or in a circulator. If necessary, polarization converters positioned before or after the respective components may be used to convert the electromagnetic signal into a desired signal accordingly. The multilayer signal guide structure 100 can preferably be designed as a switch (see FIGS. 14 and 15 ), or as a circulator (FIGS. 16 to 18 or as an isolator.A multi-port switching may be performed by stacking at least two multi-layered signal line structures 100 in parallel in the Z direction. In order to reduce the design footprint, stacking such signal line structures 100 in the y-direction could also be a possibility to make use of these. Such a device could be of great interest in data centers, for example. Stacked multi-layer signal conducting structures 100 are not shown in the accompanying figures.The MO material may be partially or fully etched to provide room for a ridge waveguide format and / or a ridge waveguide format: garnet MO materials are considered hard materials. It is a delicate work to etch completely onto the substrate to create a waveguiding structure. For this reason, rib waveguide constructions could also be a possible solution instead of ridge waveguides. In the rib configuration, the TMOKE acts in the same manner on the coupled even and odd optical modes and changes the intensity profile of the magnetic field. Ridge waveguides are rectangular waveguides. Ridge waveguides are rectangular waveguides with an additional layer of waveguiding material under the waveguide.A single waveguide layer 10 comprises, for example, silicon and / or silicon nitride and / or silicon dioxide and / or a polymer and / or sol-gel. A single waveguide layer 10 can consist, for example, of only one of the substances mentioned. A single waveguide layer 10 can also consist of several of the substances mentioned or comprise several of the substances mentioned as heterostructure.The MO material may comprise garnet or doped garnet or doped silicon dioxide or sol-gel or ferromagnetic material or consist thereof. Each layer 20 and / or 30 comprises or consists in each case of one of the materials mentioned. In particular, the at least two cover layers 30 consist of or comprise the same MO material. The at least two cover layers 30 can comprise an MO material with different, in particular opposite, magnetization directions or consist of the MO material with different, in particular opposite, magnetization directions as the at least one intermediate layer 20, with the proviso that the applied external magnetization is oriented in the opposite direction in the two regions.(For example, as shown in FIGS. 3 aand 3 b, the MO material MO 1 and the MO material MO 2 may be made of the same MO material or MO 1 includes a different MO material from MO 2. In any case, the external magnetic field in MO1 and MO2 should be opposite to each other in both cases.A capping layer 30 may comprise or consist of silicon dioxide, SiO 2, and / or air and / or polymethyl methacrylate, PMMA and / or PVA and / or SU-8. A single cover layer 30 can consist, for example, of only one of the substances mentioned. A single covering layer 30 can also consist of several of the substances mentioned or comprise several of the substances mentioned as a heterostructure. SU-8 is an epoxy-based photoresist material. The name is not intended to be something of a particular one, but is a product name of the manufacturer MicroChem who has developed this material.The multi-layer signal conducting structure 100 is preferably arranged between a decoupling structure 110 for dividing an input signal at an input of the multi-layer signal conducting structure 100 into signals of the same amplitude and a coupling structure 130 for re-coupling an output signal at an output of the multi-layer signal conducting structure 100. The decoupling structure 110 may include the input port 120. The decoupling structure 110 comprises a distributor which makes it possible to split the input signal into signals of equal amplitude. Suitable distributors for the decoupling structure are, for example, a Y connection (Y junction) or a multimode interference coupler (MMI), etc. The coupling structure 130 likewise comprises a distributor which makes it possible to re-couple the output signal which comprises decoupled modes of the multilayer signal guiding structure 100. Suitable distributors for the coupling structure 130 are, for example, a Y-junction (Y-junction) or a multimode interference coupler (MMI), etc.Typically, the input signal follows the path in the signal routing structure 110:1) In a switch or circulator: from the input port 210, P I1 to the distributor (MMI, Y port...), then, a simple coupling length Lc is set back in the waveguiding layers 10, and then, an output signal is output to the output ports 220, O1, O22) In an isolator: from input port 210, P I1 to the splitter (MMI, Y port...), then returning twice the coupling length 2Lc in the waveguiding layers 10, then to the coupler (inverse MMI, INVERSEY port...) and then outputting an output signal to output port 220, O1, O2The decoupling structure 110 and the coupling structure 130 can each be configured as a multimode interference coupler (MMI) or as a Y connection (Y junction) or as a tree coupler (tree coupler) or as a star coupler or as a directional coupler. In this case, the decoupling structure 110 and the coupling structure 130 can each both be of the same type, i.e. in each case a multimode interference coupler (MMI) or a Y connection (Y junction) or a tree coupler (tree coupler) or a star coupler or a directional coupler. However, the decoupling structure 110 and the coupling structure 130 can also be of different types. For example, decoupling structure 110 could be multimode interference couplers (MMI) and coupling structure 130 could be directional couplers. Any combination of the mentioned decoupling / coupling structures is possible.Preferably, the decoupling structure 110 and the coupling structure 130 comprise an adiabatic coupler C 1 which is designed such that back reflections are avoided. Adiabatic couplers C 1 are shown in Figs. 14 to 20. An operating wavelength range of adiabatic couplers is known to be very large, meaning that they could function optimally along a large wavelength spectrum, thereby being suitable for applicationsAs used herein, nomenclature means that the coupler (whether combiner or distributor) may have rearward reflections that may originate from both arms of the coupler. The R therefore stands for the rearward reflection, C1 for the first coupler, and a1 and b1 stand for the waveguides. Nomenclature is also applicable to where T is the transfer of power.A waveguide layer 10 is preferably formed as a waveguide running straight along the direction of extension, in particular along the x-axis, or as a bent waveguide or as a slot waveguide or as a SWG waveguide or as a PhC waveguide or as a hybrid waveguide.The theory behind the proposed invention is considered below. For simplicity and without limitation of generality, only five layers will be considered below. The above-described multi-layer signal conducting structure 100 may include five layers or more than five layers.Each of the configurations described herein yields similar results.The physical phenomena resulting from such geometry can be explained as follows: In conventional coupled waveguides (without MO materials or effects), there are usually even and odd coupled modes that do not exchange power when moving simultaneously. When applying an external magnetization in TMOKE (transverse magneto-optical Kerr effect) to the five-layer signal guiding structure, which could also be referred to as heterostructure, coupled even and odd optical modes lose their conventional electromagnetic symmetric / anti-symmetric intensity profiles and become asymmetric and anti-asymmetric, respectively.Due to an imbalanced intensity distribution, when the even mode concentrates in the waveguide a, the odd mode, on the other hand, concentrates in the waveguide b. In addition, these modes should propagate over a distance called the "coupling length" in order to decouple themselves, leaving only one of them at the end, whose power is concentrated exclusively in one of the waveguides, in particular in parallel with one another.The switch component (as shown for example in Figures 14 and 15) plays a decisive role in the forwarding and management of data in optical networks and thereby enables efficient and fast switching of optical signals between different paths. They are used in telecommunications, data centers, etc. Here, switches can be designed with a waveguide as input port, which accommodates the TM mode (fundamental modes or higher-order optical modes), in particular optical ones. A second element, a (de)coupler: Y-splitter, MMI-coupler etc. (see above) divides the input waveguide into two, in particular parallel, waveguides with MO material in between. At this point there are even and odd modes coupled in the system, decoupling at the end of the structure. Depending on the orientation of the external magnetization, the light is concentrated in one of the waveguides, a or b. Up to now, the multilayer, in particular five-layer, signal-conducting structure enables complete control over the light propagation direction by manipulating the alignment of the external magnetization.It is noteworthy that an additional degree of freedom is the phase of the optical mode in the waveguides a and b. The straight-asymmetric mode has modal lobes which are in phase with each other, the higher intensity lobe being concentrated in the waveguide a. The odd anti-asymmetric mode has phase shifted modal lobes (π), with the higher intensity lobe concentrated in the waveguide b. That is, if the input modes are in phase (when excited by the basic TM optical mode), the even asymmetrical mode appears in the waveguide a at the output port. If, on the other hand, the input modes are phase shifted (when excited by a second-order TM optical mode), the odd anti-asymmetrical mode appears in the waveguide b at the output port. Thus, besides using the external magnetic field direction for switching the light guide, the initial phase can also be used. In both cases, these modes should propagate for decoupling over a distance described as "coupling length" L c herein, so that only one mode of which the power is concentrated exclusively in one of the parallel waveguides remains at the end of them.FIG. 14 is a plan view of a MO dielectric switch in which the direction of the applied external magnetic field is directed inward. FIG. 15 is a plan view of a MO dielectric switch in which the magnetization direction is directed outward. Inward or outward means a direction into the MO material or from the MO material in which the magnetization resulting from the external magnetic field is directed. When the direction of the external magnetic field is reversed, the magnetization also reverses. This has the result that the light then propagates in the waveguide b instead of in the waveguide a. The switches of Figures 14 and 15 each have one input port 110 and two output ports 130. In addition, the switches from FIGS. 14 and 15 each have a decoupling structure 120 and two coupling structures 140. Furthermore, the switches from FIGS. 14 and 15 each have an adiabatic coupler C 1. The reference numerals of the multilayered signal conducting structure correspond to the reference numerals of FIGS. 1 to 3, which is not repeated again at this point. It should be noted that in the switch of FIGS. 14 and 15, a cover layer 30 is partially arranged between the two signal conducting layers 10, namely where no MO material is arranged between the two signal conducting layers.A circulator as shown in, for example, Figs. 16, 17 and 18 is similar in functionality to a switch, but differs by accommodating a larger number of ports. The extended capacity of a circulator allows efficient management of multiple connections with increased versatility. It can be designed, for example, by placing three switches at 120° angles to each other. The description for the switches from FIGS. 14 and 15 therefore also applies to the circulators from FIGS. 16, 17 and 18 and is not repeated again.FIG. 16 is a plan view of a dielectric MO circulator with light entry through a first port I 1. FIG. 17 is a plan view of a dielectric MO circulator with light entry through a second port I 2. FIG. 18 is a plan view of a dielectric MO circulator with light entry through a third port I 3.When the direction of the input light is switched from forward to backward, the light is concentrated in the waveguide b as if the orientation of the external magnetization were switched. This concept enables the construction of optical isolators.Optical isolators (such as shown in FIGS. 19 and 20) act as a one way road for light that allows signal motion from the input to the output, but prevents light from being reflected back into the source, i.e., in the opposite direction. Optical isolators are indispensable in various applications, for example, laser systems, fiber optic communication networks, and optical instruments. By ensuring signal integrity and preventing destabilization of the laser, they contribute to the general reliability and performance of optical systems.Fig. 19 is a plan view of a dielectric MO isolator with light moving in the forward propagation direction, i.e., from zero to +x. Fig. 20 is a plan view of a dielectric MO isolator with light moving in the backward propagation direction, i.e., from -x to zero.For the development of an isolator, an input waveguide 210, a (de)coupler C1, a multi-layer, in particular five-layer, signal conducting structure 100, a coupler C2 and an output waveguide 220 are used. The optical TM mode is decoupled and fed back to the output again. In this design, the input light (TM optical mode) is confined forward to the waveguide a, particularly a waveguide a, and backward to the waveguide b, particularly a waveguide b. Finally, the power collected at the input and output ports 110, 130 must be unequal so as not to be reciprocal. To achieve this, the use of any element that generates a disturbance so that it does not cause back reflections is sufficient. A radiating SWG waveguide (SWG=sub-wavelength grating) is proposed. The SWG waveguide is preferably placed in the center of the waveguide b to diffract the light outward. In this connection, ring resonators can also be used for deflecting light, which offer a versatile mechanism for deflecting the light towards the rear.When the SWG waveguide is at the proper pitch with respect to the waveguide b and the proper fill factor demand, the SWG waveguide operates in a radiation mode. That is, the light outside a guide region SG is diffracted by the SWG waveguide (SG in FIGS. 19 and 20 ). If the ring resonator is carefully designed and has the correct dimensions, the ring resonator can efficiently guide light out of the waveguide.With this arrangement, the forward light can pass undisturbed while backward light is scattered outward, resulting in imbalance in power collected at the opposing input and output ports 110, 130. The SWG is an array of grids having geometric properties that can be merged by division and fill factor. The ring resonator is a high quality resonator defined by parameters such as radius, perimeter, coupling coefficient.In summary, the MO effect on the coupled optical modes allows selection of the light propagation direction, whereby switches / circulators can be provided. When combined with additional elements such as SWGs or resonators, these emit the backward-running signal outwards and thus form an isolator. As will now be apparent, the proposed invention is a highly efficient solution for integratable optical switches / circulators and isolators in PICs. The design promising 100% circuit / circulation and / or isolation when it is used.The various elements forming the switch, circulator and isolator are of low complexity. The theory behind straight waveguides (input and output) and couplers (regular or inverse) is already known and clear and will not be described in detail at this point. The segment debearing most attention is the core region, namely, the multi-layer signal conducting structure 100.A theoretical approach for the multi-layer signal conducting structure 100 is presented below.Modal AnalysisThe work performed for this invention was theoretically performed using the Maxwell equations and supported by FDTD and FEM simulations (FDTD for Finite Element Modulation Method in the English). As discussed in detail above, the use of MO materials is an efficient way to break the time symmetry. Almost all MO phenomena are a direct consequence of the Zeeman effect.The dielectric tensor of such an MO material may be represented in the form

[40] .Each pair of these non-diagonal elements is equal in size and of opposite sign (ε xy= - ε yx, ε xz= - ε zx, ε y z = -ε zy). In the absence of an external magnetic field, this tensor could be written as a diagonal in which the three elements are equal to each other (ε xx= ε yy= ε zz).The off-diagonal element is given by: where: g is the gyrotropic MO parameter, ε d is the dielectric constant, λ is the wavelength of operation, and θ F is the associated Faraday rotation coefficient. The parameter g is usually very small at optical wavelength (<10 -2). Bismuth-iron garnet (BIG), for example, has g≈0.06

[41] . Referring to Figs. 6 to 9, g is also referred to as gyrotropic level.For simplicity, in the theoretical derivatives, analyses and numerical simulations, and without loss of generality, it is assumed that the system is a two-dimensional structure, i.e. without field variations in the y-direction. Note that in the present analysis, the material permittivity is considered regardless of frequency. This does not represent a limitation of the proposed concept, since the dispersion of the material parameters can easily be incorporated into the original design of the system if necessary.Using the Maxwell's equations, the generalized dispersion relations are derived. A plan view of the multilayer signal conducting structure 100 in the form of a five-layer signal conducting structure is illustrated in FIG. 1. FIG. 1 shows an MO material having the width / thickness 2 aand two, in particular dielectric, waveguides a and b of the width d, respectively. This type of structure can accommodate the even and odd coupled modes. These eigenmodes arise from evanescent coupling between the optical modes supported by the individual waveguides a and b propagating in the x-direction.In a Cartesian coordinate system, the electromagnetic fields can be represented as follows: where and the amplitude vectors are with complex valued components. β is the propagation constant of the moving waves and corresponds to the component of the wave vector in the propagation direction and ω=2πf is the angular frequency of the incident wave.By selecting suitable modal field functions in each region of the waveguide a, b and applying the electromagnetic field constraints, the modal field solution and characteristic equation can be obtained. The magnetic field components in the five layers under consideration can be written in the following form, where 2a represents the thickness of the at least one intermediate layer 20 and d represents the thickness of a waveguiding layer 10:By substituting H y of each layer into the wave equation, one can find the expression for the wave vectors in each layer of the structure under consideration, where:Finally, when the continuity of the electromagnetic fields E x, H y and E z is applied at the various limits (-a - d, -a, +a, +a +d), the complex dispersion relationship for this wave is written as follows: wherein:In the second equation, the two solutions resulting from the "plus" and "minus" signs correspond to the propagation constants of the even and odd modes β e,o. From the ratio of A 3 to A 4 it can be seen that the amplitudes of the H y( z) component corresponding to each of the coupled modes, A 2 and A 5 in the waveguides a and b, respectively, are different. From this we can conclude that the even and odd coupled modes lose their traditional symmetric behavior and become asymmetric and anti-asymmetric about the z-axis, respectively.If the width of the MO layer becomes too large, the system can be divided into two areas. FIGS. 4 and 5 show the two divisions.FIG. 4 shows a plan view of a first partition of the multilayer signal guiding structure 100 with only one waveguiding layer 10, i.e. waveguide a. FIG. 5 shows a plan view of a further partition of the multilayer signal guiding structure 100 with only one waveguiding layer 100, i.e. waveguide b.For the three-layered signal conducting structure in Fig. 4, the magnetic field components in the waveguide a may be written in the following form:Dispersion relation:β a represents the propagation constant of the fundamental mode of the waveguide a.For the three-layer signal guide structure 100 in FIG. 5, the magnetic field components in the waveguide b may be written in the following form:Dispersion relation:β b represents the propagation constant of the fundamental mode of the waveguide b.The derived relationships show that the propagation constants are different in both cases, β a ≠ β b. This is indeed due to the presence of the MO layer, leading to a breakage of the spatial symmetry.Theory of Coupled Modes in the Multilayer, in particular Five-Layer, Signal Conducting StructureCoupled-mode theory (CMT) is useful to understand the coupling mechanisms in parallel waveguides. The CMT assumes that the coupled modes can be expressed as a linear combination of the individual modes in the uncoupled waveguides a, b, and involves solving a series of equations for determining the amplitudes and propagation constants of the coupled modes. The coupling between the modes is described by the coefficients K ab and K ba, which quantify the strength of the interaction. It is sufficient to use the equations of

[42] . Expressed in a matrix form:There are two eigenvalues for β: namely β e and β o for the even (β e where e stands for even) and odd modes (β o where o stands for odd):The coupling length can be written as a function of the even and odd mode propagation constants:In the presence of MO material, at x=0, the optical power is incident on both waveguides, i.e. P 1(0) = P 2(0) = 0.5. The power at any point along the propagation axis (i.e. along the direction of extension) can be extracted from the matrix:The maximum power transmission between the waveguides a and b occurs at L c, where ψx=π / 2. if it is assumed that the transmitted power is complete, the ratio of normalized power difference can be written as follows:If the respective term is used, and after simplification, the following is obtained:That is, when the ratio is 0.707107, complete power transmission takes place. To illustrate the principle, the following values for material and geometric parameters were assumed.The variables d and 2 adescribe the thickness 2 aof the intermediate layer 20 and the thickness d of a waveguiding layer 10. The value n Mantel indicates a refractive index of a capping layer 30. The value n MO indicates a refractive index of the intermediate layer 20, which comprises the MO material in the present example. The value nwaveconductorindicates a refractive index of a waveguiding layer 10, a, b. In the present case, the terms waveguide and waveguiding layer are used interchangeably. The derivation given here was made for the first configuration of Fig. 1. For the second and third configurations, the derivation is performed in an analogous manner and leads to similar results. In particular, the ratio and the coupling length Lc result for these further configurations in each case in the same equation which has been derived in the present case.Table 1 lists parameters which were used to generate the graphs shown from FIGS. 6 to 9. These parameters indicate typical values for the cap layers 30, the waveguiding layers 10 and the MO materials. Table 1: Variables and possible values of the five-layer heterostructure. Table 1: Variables and possible values of the five-layer heterostructure.n Mantel1,45n waveguides3,48n MO2,3g g g g g g g g g g0,001, 0,05, 0,01, 0,05, 0.12a[0,2-1,7] μmd d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d d0,3 μmNumerical methods can be used to solve the dispersion relations shown above and to derive the propagation constants β a,b and β e,o. To avoid complicated presentation, the results were divided into two quantities, for g, varying between [0.1-0.01] and [0.01-0.001]. These results are shown in FIGS. 6 to 9.It can thus be seen from FIGS. 6 to 9 that the coupling length extends from approximately Lc=50 μm for g=0.1 over Lc=500 μm for g=0.01 to after Lc=5000 μm for g=0.001.The results from FIGS. 6 to 9 show that for all g values the ratio (ratio) increases with increasing intermediate layer 20, which could also be referred to as gap widths (gap width). For each value of g, the ratio reaches 0.707107 (see Figures 7 and 9) at a particular width. With larger gap widths, β e,o grow closer together, which means that a larger coupling length Lcis required to reach the point of complete power transfer, especially at Lc=506.9 μm, as seen in Figures 7 and 9. For MO materials similar to BIG or Ce:YIG, g≈0.06, for which the ratio reaches the required value for 2a=0.72 μm, this corresponds to an L c ≈100 μm. The use of such a structure can result in I.R > 30 dB with minimum I.L < 1 dB.For even lower g, L c continues to increase, but this has no effect on I.L., when silicon or silicon nitride is used as the waveguide material, the losses are in the range of a few db / cm.Optical Switch / CirculatorThe optical switches 1 a(see FIG. 14 ) and 1 b(see FIG. 15 ) refer to the inward and outward orientation of the external magnetization. The optical circulators 2a, 2b and 2c are shown in Figs. 16, 17 and 18. Figures 14 to 18 each show a 2D plan view of the proposed design as well as the path of electromagnetic signal propagation (see bold arrows in Figures 14 to 18) in each case.In the optical switch 1a of Fig. 14, the applied external magnetic field is directed inwardly. The signal starts from a region I 1 which could be, for example, a laser source or a PIC. In the transition from the input region to the input waveguide 210, IW 1 with dimensions μm through the port P I1 negligible back reflections (B.R) are assumed, which can be quantified as R I1. The remaining normalized signal, T I1 is split into two equal signals using an adiabatic coupler C 1, particularly of the dimension. The coupler should be designed to avoid B.R, which may occur at this interface. The uniformly divided signals enter the waveguides a and b having the dimensions μm and μm, respectively. Here, the MO material in the intermediate layer 20 is located outside between the waveguides a, b of dimension μm and the cladding layers 30, also called Cl cladding layer. This is the interaction region in which the even and odd coupled modes exchange power. At the end, i.e. after propagation over a distance corresponding to the coupling length, a maximum, in particular the entire, power concentrates in the waveguide a, and a minimum, in particular no, power remains in the waveguide b. B. R can also be expected as R O1 when T O1 passes from the output waveguide OW 1 having the dimensions μm through the port P O1 to the output region O 1.When the external magnetization is switched and oriented from inside to outside, the same phenomenon occurs (see FIG. 15 ). In this case, however, the light is concentrated after propagation through a coupling path in the waveguide b. The output signal T O2 passes from the output waveguide OW 2 having the dimensions through the port P O2 to the output region O 2,FIG. 10 shows the power P in the at least two waveguiding layers 10 (i.e. waveguides a (black) and b (gray)) of the multilayer signal guiding structure 100 as a function of the coupling length Lc in the forward direction, in particular which is used, for example, in a switch or a circulator. It can be seen from FIG. 10 that as the coupling length Lc increases, the concentration of the power P in the waveguide a increases, while at the same time it decreases in the waveguide. With a coupling length of approximately Lc=500 μm, the power P is maximum in the waveguide a and minimum in the waveguide b.In the case of a circulator (see FIGS. 16 to 18 ), there are three ports with a fixed external magnetization orientation. Following the same description as the switch, the input signal of P I1 is outputted by P O2. When the second port, P I2 is energized, the output signal from P O3 is collected. Finally, when the third port, P I3 is energized, the output of P O1 is collected. For reasons of redundancy, a further description of the circulators is omitted, since the description of the switches can be applied analogously.Optical isolatorThe optical isolator, 3a (see Figure 19) and 3b (see Figure 20), has a forward and backward propagation direction, respectively, the forward direction being represented in Figure 19 by the bold arrows along the +x axis and the backward direction being represented in Figure 20 by the bold arrows along the -x axis. Figures 19 and 20 each show a 2D plan view of the proposed design as well as the path of electromagnetic signal propagation (see bold arrows) in each sense.In the forward sense, the signal starts from a region I 1, which may be a laser source or a PIC. In the transition from the input region to the input waveguide 210, IW 1 with dimensions μm through the port P I1 negligible B.R are provided and can be quantified as R I1. The remaining normalized signal, T I1 is split into two equal signals using an adiabatic coupler C 1 having dimensions μm. The coupler should be designed to avoid B.R, which may also occur at this interface. The uniformly divided signals enter the waveguides a and b having the dimensions μm and μm, respectively. Here, the MO material of the intermediate layer 20 is placed between the waveguides 10, a, b of the dimension μm and the cladding layers 30, or also called Cl cladding layer, on the outside. This is the interaction region in which the even and odd coupled modes are exchanging power in the presence of external magnetization. In the middle, after the first coupling length LC, all the power concentrates in the waveguide a. After propagation by another coupling length, the signal evanescently couples back into the waveguide b. At this point, the signals are of equal intensity and combine into a single signal by the second coupler C 2 having the dimensions μm. B.R can also be expected by recombination of the signals. Then, T O2 passes from the output waveguide 220, OW 2 having dimensions μm through the port P O2 to the output region O 2, which may be another optical component or a PIC. Assuming that there is no I.L through the dielectric waveguides and the B.R is minimal, the forward transmission isIn the backward-forward sense, the signal starts in a region I 1, which may be, for example, an optical component or a PIC. In the transition from the input region to the input waveguide 210, IW 1 with dimensions μm through the port P I1 negligible B.R are provided and can be quantified as R I1. The remaining normalized signal, T I1 is split into two equal signals using an adiabatic coupler C 1 having dimensions μm. The coupler should be designed to avoid B.R, which may also occur at this interface. The uniformly divided signals enter the waveguides a and b having the dimensions μm and μm, respectively. Here, the multi-layer, in particular five-layer, signal structure is formed, wherein the MO material is placed in the intermediate layer 20 between the waveguides 10, a, b of the dimension μm and the cladding layers 30, which could also be referred to as Cl cladding layer, outside. This is the interaction region in which the even and odd coupled modes are exchanging power in the presence of external magnetization. In the middle, after the first coupling length, all the power concentrates in the waveguide b. In this area a SWG or resonator SG with the dimensions (SG w, SG l) μm is placed. With proper selection of the division and fill factor, the SG radiates the optical mode to the outside. In this way, no light couples in C 2 and no light reaches the output waveguide and port system. Assuming that the light is fully radiated from the gratings, the reverse transmission isAs can be seen, the forward and reverse transmission are different from each other. This results in a component with high efficiency: high I.R, low I.L and low B.R. In FIG. 11, the power P in the at least two waveguiding layers (waveguides a (black) and b (gray)) of the multilayer signal guiding structure 100 in the forward direction is shown as a function of the double coupling length 2Lc, which is used, for example, in an isolator. It can be seen from FIG. 11 that when the simple coupling length Lc (at approximately 500 μm) is reached, the power P is at a maximum in the waveguide a, i.e. is concentrated, while the line P is at a minimum in the waveguide b. At twice the coupling length 2Lc, the waveguide a and the waveguide b have an equal power. In FIG. 12, the power P in the at least two waveguiding layers (waveguides a (black) and b (gray)) of the multilayer signal guiding structure 100 in the reverse direction is illustrated as a function of twice the coupling length 2Lc, which is used, for example, in an isolator.A further aspect of the present invention relates to a method 1300 for operating a multi-layer signal conducting structure 100, in particular having a multi-layer signal conducting structure 100 described herein. The method 1300 is depicted in FIG. 13 as a flow chart. The method 1300 comprises, in step 1310, providing a multi-layer signal structure comprising: a plurality n of layers, wherein the plurality n of layers comprises at least two waveguide layers 10 which extend along an extension direction and which serve for coupling an electromagnetic signal, and at least one intermediate layer 20 which is arranged between the at least two waveguide layers 10; and at least two cover layers 30, wherein the at least two waveguide layers 10 are arranged partially between the at least two cover layers 30, wherein the at least one intermediate layer 20 comprises a magneto-optical material, MO, and / or the at least two cover layers (30) comprise a magneto-optical material, MO. In particular, in step 1310, a multi-layer signal conducting structure 100 described herein is provided. All the explanations already made regarding the multilayer signal conducting structure 100 can be interpreted as method step 1310, which, however, are not described again as method steps below for redundancy reasons. The method 1300 comprises, in step 1320, applying an external magnetic field to the multi-layer signal guiding structure 100, whereby a transverse magnetic mode, TM mode, of an electromagnetic signal introduced into the multi-layer signal guiding structure 100 experiences a change in its magnetic field profile aligned along an extension direction of the at least two waveguide layers 10. Step 1310 is to be performed prior to step 1320. In the case of the proposed mode, coupled modes are first decoupled and concentrated alone or predominantly in a waveguiding layer 10, for example in waveguide a. The decoupled modes are finally coupled again in the form of an output signal. The output signal can then be further processed.Depending on an orientation of the external magnetic field to the multi-layer signal guiding structure 100, the electromagnetic signal is concentrated in only one of the at least two waveguide layers 10.FIG. 10 shows the power P in the at least two waveguiding layers 10 (i.e. waveguides a (black) and b (gray)) of the multilayer signal guiding structure 100 as a function of the coupling length Lc in the forward direction, in particular which is used, for example, in a switch or a circulator. It can be seen from FIG. 10 that as the coupling length Lc increases, the concentration of the power P in the waveguide a increases, while at the same time it decreases in the waveguide. With a coupling length of approximately Lc=500 μm, the power P is maximum in the waveguide a and minimum in the waveguide b.In FIG. 11, the power P in the at least two waveguiding layers (waveguides a (black) and b (gray)) of the multilayer signal guiding structure 100 in the forward direction is illustrated as a function of twice the coupling length 2Lc, which is used, for example, in an isolator. It can be seen from FIG. 11 that when the simple coupling length Lc (at approximately 500 μm) is reached, the power P is at a maximum in the waveguide a, i.e. is concentrated, while the line P is at a minimum in the waveguide b. At twice the coupling length 2Lc, the waveguide a and the waveguide b have an equal power.In FIG. 12, the power P in the at least two waveguiding layers (waveguides a (black) and b (gray)) of the multilayer signal guiding structure 100 in the reverse direction is illustrated as a function of twice the coupling length 2Lc, which is used, for example, in an isolator.It can be seen in FIGS. 10 to 12 that for an MO material with, for example, a gyrotropic level of g≈0.01 used, for which the ratio (ratio) reaches a required value of 2a=0.97 μm, which corresponds to a coupling length of Lc=500 μm, I.R>30 dB will be achieved with an I.L<1 dB. For this case, the power P is shown in the waveguides a, b through LC (for a switch or circulator in FIG. 10 ) and through 2LC (for forward and reverse isolators in FIGS. 11 and 12 ).As seen in Figs. 10 and 11, after covering the simple coupling length Lc, the power P of the input signal is completely transferred into only one waveguide a, while no power remains in the other waveguide b. For Lc, a switch or circulator can direct the signal in a desired direction by controlling the orientation of the external magnetic field.In FIG. 11, which shows the line distribution in the forward direction in an isolator, it can be seen that between 0 μm and Lc the power transmission of the power P takes place completely from the waveguide b (gray) into the waveguide a (black). After a distance Lx traveled by the input signal of more than the simple coupling length Lc, the power is partially transferred back into the waveguide b (see in FIG. 11 the x-axis in the range Lc>X>Lc). At the output port at 2Lc, the power P in the two waveguides a, b, in turn, corresponds to the output line in the two waveguides a, b at Lx=0. After twice the coupling length has been travelled at Lx=2Lc, both waveguides have their original power P.In Fig. 12, which shows the backward line distribution in an isolator, it can be seen that between 0 μm and Lc, the power transfer from the waveguide a (black) to the waveguide b (gray) occurs. The input signal, i.e. the power P, is completely transferred into the waveguide b (see FIG. 12, range between 0 μm and Lc at 500 μm).Whenever an additional structure SG (see FIGS. 19 and 20 ) is placed complementarily in the waveguide b to scatter or absorb light at Lx=Lc, the backward propagating signal is completely lost, as seen in FIG. 12 between Lc and 2Lc. The additional structure SG may be a cut-to-size SWG-s or an absorbing metal or resonator or the like.In view of FIGS. 11 and 12, it can be summarized that the difference in amplitude between the forward and backward propagating signals results in a high performance of the isolator with a high isolation ratio and very low insertion loss and low back reflectionAt this point it should be noted that for a low gyrotropic level g the coupling length Lc at which maximum power transfer can take place increases. However, this does not have any consequences for the power transfer I. L. If, for example, silicon and / or silicon nitride and / or epoxy resin and / or polymer is used in the waveguiding layers 10, the loss is a few dB / cm.The method 1300 may further include attaching an input port 110 to the multi-layer signal guiding structure 100 to introduce coupled modes of the electromagnetic signal into the at least two waveguide layers 10, in particular into the waveguides a and b. Furthermore, the method 1300 may include attaching an output port 130 for deriving an output signal comprising coupled modes. In particular, the output port 130 may be configured to re-couple decoupled modes to define the output signal.The method 1300 may further comprise splitting the coupled modes of the electromagnetic signal onto the at least two waveguide layers 10, in particular onto the waveguides a and b, as has already been described with reference to FIGS. 10 to 12. The method 1300 may further comprise decoupling the modes during a course of the coupled modes in the at least two waveguide layers 10, in particular along the X axis in the direction of extension, such that at one end of the at least two waveguide layers 10, in particular after a length corresponding to the coupling length Lc, decoupled modes are present in one of the at least two waveguide layers 10, and a subsequent re-coupling of the decoupled modes at or in the output port to generate an output signal. Finally, the method 1300 may include deriving the output signal. The output signal may be forwarded or further processed.The proposed technical solution has the following advantages over the prior art:• The proposed design for the switch / circulator and isolator is simple and requires only minimal engineering interventions for integration into PICs.• Satisfactory switching, circulating and insulating effects can be realized in a versatile manner by using MO materials with any gyrotropic level. The critical factors for achieving these effects are primarily the geometric parameters, in particular the length and width of the signal conducting structure.• This innovative design is very promising in the area of lossless components, since the primary signal propagation takes place predominantly in, in particular dielectric, waveguides and thus undesirable absorption effects are avoided.• The applied external magnetic field operates with low power consumption, wherein a rare earth magnet or an electromagnet can saturate the MO material.• In contrast to Faraday rotators, the proposed technical teaching is distinguished by its taught compact base area.• Compared to conventional NRL and NRPS devices, the design has a distinct advantage because it does not cause a higher I.L. even with a longer propagation length.• Compared to resonator-based structures, this novel design is characterized by superior performance characterized by a wider bandwidth. This improvement results from the gyrotropy exhibited by the MO material over the entire wavelength spectrum.• The design can provide switching / circulating and isolation, in the form of isolators, for TM and TE modes.• Design compliance is also evident in the option of replacing conventional straight waveguides with SWGs or PhC-s. This exchange effectively reduces the required coupling length to allow seamless power transmission between different waveguides.• Circuit effects can be achieved by controlling the orientation of the external magnetic field and / or by controlling the phases of the input signals.• MO materials may be used according to the third configuration, wherein a different orientation of the external magnetic field may be used to reduce the space requirement of the signal conducting structure.The matching of these properties makes this innovative design attractive for on-chip applications, for example.The three components described herein-the switch, the circulator and the isolator-rely on the multilayer, in particular five-layer, signal structure as core, which comprises at least one MO layer (see first to third configurations). In the proposed multi-layer signal conducting structure 100, power exchange takes place and the various propagating signals take different paths and pass through different processes. Although the components look similar to MZIs, they differ greatly from each other by the modes that pass inside. In comparison with conventional MZIs, in which the arms are far from each other and the modes are not coupled, in the present case the intermediate layer 20 does not exceed a certain width and the modes remain coupled in the entire signal guiding structure from the input to the output. The signal routing structure 100 could be further utilized to achieve optimal performance. The determined width of the intermediate layer 20 is to be selected such that decoupling of the even and odd modes can take place in the waveguiding layers 10. The determined width is material-dependent and geometry-dependent.It should be emphasized once again at this point that the derivation of the theory for the proposed technical teaching has been limited to five layers for the sake of simplicity.Instead of the five-layer signal structure, n-layers, in particular in the z-direction and / or y-direction, can be used, for example, to increase or decrease the number of output channels in any direction or to exchange power with different waveguides.Materials with different indices can also be integrated into the signal structure: for example, placed at the sides of the waveguide in order to increase the mode limitation in the waveguides and / or placed in the middle of the signal guiding structure in order to press the light more towards the waveguides. In addition, more than one signal conducting structure can be stacked in order to also obtain modes coupled in the y-direction.Also, the location of the MO layer(s) may result in different design configurations: a) The MO material may be placed as an intermediate layer 20 between the two waveguides a and b (first configuration according to FIG. 1 ). b) The MO material may be placed on the opposite sides of the waveguides, a and b, in the capping layers 30 (second configuration according to FIG. 2 ). c) The MO material may be placed as an intermediate layer 20 between the two waveguides a and b and on the opposite sides of the waveguides, a and b, in the capping layers 30 (third configuration according to FIG. 3 ) d) The MO material may be partially or completely etched, To make room for ridge and ridge waveguide formats (not shown in the Figures).Without an applied external magnetic field, the intensities in the signal conducting structure 100 are the same at the two ports. In this case, no exchange of power takes place. Therefore, the intensity recorded after any propagation length should be equal in both arms.In the case of an inward external magnetic field in which the MO material is saturated, imbalance between the outputs is detectable (see FIGS. 10 to 12 ). The unequal amplitudes depend on the length of the signal guiding structure 100, the waveguide material of the waveguiding layers 10 and the design. In this case, for example, after a coupling length propagation, the intensity in the waveguide a should be higher.In the case of an outward magnetic field where the MO material is saturated, an imbalance between the outputs is detectable. The unequal amplitudes depend on the length of the signal guide structure 100, the waveguide material in the waveguiding layers 10 and the design. In this case, for example, after a coupling length propagation, the intensity in the waveguide b should be higher.Optical switches, circulators and isolators are important components in modern optical networks and specify specific requirements for the efficient management and routing of optical signals.Optical switches are configured to selectively control the path of optical signals within a network. They meet the need for dynamic and flexible redirection of optical signals, thereby allowing flexible network reconfiguration and wavelength switching. Optical switches play an important role in improving network efficiency and reliability by enabling a quick response to changing traffic requirements, fault tolerance, and wavelength management. Their ability to redirect optical signals to different output ports or fibers makes them indispensable to network operators who want to optimize resource utilization and improve the overall performance of optical communication systems. At present, these switches are widely used in PICs for programmable photonics, neuromorphic computing, etc. In summary, optical circulators and switches contribute to the robustness and adaptability of modern optical communication systems. Similarly, optical circulators are used to direct signals of different wavelengths to particular targets. This allows for the transmission of multiple data streams over a single optical fiber, thereby increasing the data capacity of the communication network.Such a switch design may also be used to sense the intensity of the applied external magnetic field. This has wide application in the field of magnetometry. In this case, the properties of the external magnetic field can be derived from the output of the connections one and two by back engineering.Optical isolators find substantial applications in various fields because of their ability to control and manage the light flux in one direction while blocking it in the other direction. An important application is use in fiber optic communication systems. In these systems, optical isolators play a crucial role in avoiding back scattering and B.R., which can degrade signal quality. By isolating the incoming and outgoing light paths, they help maintain signal integrity and minimize signal losses, which ensures reliable data transmission over long distances. Additionally, optical isolators are used in laser systems to protect sensitive laser components from feedback damage that can destabilize the laser output. This application ensures stable and efficient laser operation in various fields including medical equipment, telecommunications and research laboratories.Although some aspects have been described in connection with a device or a method, it is understood that these aspects also represent a description of a corresponding method or a device, so that a block or a component of a device or a system is also to be understood as a corresponding method step or as a feature of a method step and vice versa. A complete representation of the present invention in the form of method steps or in the form of device features is omitted here for redundancy reasons.In the foregoing detailed description, various features have been partially grouped together in examples to rationalize the disclosure. This type of disclosure is not to be interpreted as the intention that the claimed examples have more features than are expressly recited in each claim. Rather, as the following claims reflect, subject matter may reside in less than all features of a single disclosed example. Accordingly, the following claims are hereby incorporated into the Detailed Description, and each claim may stand as a separate example. While each claim may stand as a separate example of its own, it should be noted that although dependent claims refer in the claims to a specific combination with one or more other claims, other examples also include a combination of dependent claims with the subject matter of any other dependent claim or a combination of each feature with other dependent or independent claims. Such combinations are intended to be included unless it is stated that a specific combination is not intended. Furthermore, it is intended that a combination of features of a claim with any other independent claim be included, even if this claim is not directly dependent on the independent claim.References[1] Jalas, D. et al. 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Claims

A multi-layer signal guiding structure (100) comprising: a plurality of layers, wherein the plurality of layers comprises at least two waveguide layers (10) which extend along an extension direction and which serve for coupling an electromagnetic signal, and at least one intermediate layer (20) which is arranged between the at least two waveguide layers (10); at least two cover layers (30), wherein the at least two waveguide layers (10) are arranged partially or completely between the at least two cover layers (30), wherein the at least one intermediate layer (20) comprises a magneto-optical material (MO) and / or the at least two cover layers (30) comprise a magneto-optical material (MO), wherein an external magnetic field can be applied or is applied to the multi-layer signal guiding structure (100), whereby a transverse magnetic mode, TM mode, and / or a transverse electric mode, TE mode of the electromagnetic signal coupled into the at least two waveguide layers (10) experiences a change in its electromagnetic field profile aligned along the direction of extent of the at least two waveguide layers (10), wherein, when an external magnetic field is applied, at least one TM and / or TE mode propagates along the direction of extent in at least one waveguide layer (10) of the at least two waveguide layers (10), wherein at least one even TM and / or TE mode is described by a first propagation constant β e and an odd TM and / or TE mode is described by a second propagation constant β o wherein the at least two waveguide layers (10) are respectively described by the further propagation constants β a, β b, wherein a maximum power transmission takes place at a ratio of the propagation constants of V e r h a%0020̈ l t n i s = β a - β b β e - β o = 1 2 wherein β a is the propagation constant of the fundamental mode of the first waveguide layer of the at least two waveguide layers (10) and β b is the propagation constant of the fundamental mode of the second waveguide layer (10) of the at least two waveguide layers (10).A multi-layer signal guiding structure (100) comprising: a plurality of layers, wherein the plurality of layers comprises at least two waveguide layers (10) extending along an extension direction and serving for coupling an electromagnetic signal and at least one intermediate layer (20) arranged between the at least two waveguide layers (10); at least two cover layers (30), wherein the at least two waveguide layers (10) are arranged partially or completely between the at least two cover layers (30), wherein the at least one intermediate layer (20) comprises a magneto-optical material (MO) and / or the at least two cover layers (30) comprise a magneto-optical material (MO), wherein a wave propagation of the electromagnetic signal coupled into the at least two waveguide layers (10) is respectively determined by a propagation constant β a, β b wherein the propagation constants β a, β b of the at least two waveguide layers (10) are different, β a ≠ β b, wherein the coupling length L c is a function of the first and second propagation constants β e, β o of even and odd modes and is given by: L c = π β e - β o A multi-layer signal guiding structure (100) comprising: a plurality of layers, wherein the plurality of layers comprises at least two waveguide layers (10) extending along an extension direction and serving for coupling an electromagnetic signal and at least one intermediate layer (20) arranged between the at least two waveguide layers (10); at least two cover layers (30), wherein the at least two waveguide layers (10) are partially or completely arranged between the at least two cover layers (30), wherein the at least one intermediate layer (20) comprises a magneto-optical material (MO) and / or the at least two cover layers (30) comprise a magneto-optical material (MO), wherein at least two multi-layer signal guiding structures (100) are stacked to obtain coupled modes perpendicular to the extension direction.The multi-layer signal guiding structure (100) according to claim 2 or 3, wherein an external magnetic field can be applied or is applied to the multi-layer signal guiding structure (100), whereby a transverse magnetic mode, TM mode, and / or a transverse electric mode, TE mode, of the electromagnetic signal coupled into the at least two waveguide layers (10) experiences a change of its electromagnetic field profile aligned along the extension direction of the at least two waveguide layers (10).The multi-layer signal guiding structure (100) according to any of the preceding claims, wherein the at least two waveguide layers (10) and / or at least one intermediate layer (20) and / or the at least two cladding layers (30) are dielectric.The multi-layer signal conducting structure (100) according to any of the preceding claims, wherein the external magnetic field is given by a rare earth magnet or by an electromagnet configured to saturate the magneto-optical material (MO).The multi-layer signal conducting structure (100) according to claim 6, wherein the electromagnet is formed as a metal layer which is positioned directly on the magneto-optical material (MO) or on the at least one cover layer (30).The multi-layer signal guiding structure (100) according to any one of claims 1 or 3 to 7, wherein a wave propagation of the electromagnetic signal coupled into the at least two waveguide layers (10) is respectively described by a propagation constant β a, β b wherein the propagation constants β a, β b of the at least two waveguide layers (10) are different, β a # β b.The multi-layer signal guiding structure (100) according to any one of claims 2 to 8, wherein, when an external magnetic field is applied, at least one TM and / or TE mode propagates along the extension direction in at least one waveguide layer (10) of the at least two waveguide layers (10), wherein at least one even TM and / or TE mode is described by a first propagation constant (β e) and an odd TM and / or TE mode is described by a second propagation constant (β o) wherein the at least two waveguide layers (10) are respectively described by the further propagation constants β a, β b, wherein a maximum power transmission takes place at a ratio of the propagation constants of V e r h a%0020̈ l t n i s = β a - β b β e - β o = 1 2 wherein β a is the propagation constant of the fundamental mode of the first waveguide layer of the at least two waveguide layers (10) and β b is the propagation constant of the fundamental mode of the second waveguide layer (10) of the at least two waveguide layers (10).The multi-layer signal guiding structure (100) according to any of the preceding claims, wherein each waveguide layer (10) defines a coupling length due to its nature, such that the coupled modes introduced into the waveguide layer (10) are decoupled C after traversing the coupling length L.The multi-layer signal conducting structure (100) of claim 8, wherein the coupling length L C is a function of the first and second even and odd mode propagation constants β e, β o and is given by: L c = π β e - β o The multi-layer signal conducting structure (100) according to any of the preceding claims, wherein each magneto-optical material used in the multi-layer signal structure has one or different gyrotropic levels.The multi-layer signal guiding structure (100) according to any one of the preceding claims, wherein a length (L) of the at least two waveguide layers (10) and a length (L') of the at least one intermediate layer (20) are formed to be of equal length.The multi-layer signal guiding structure (100) according to any of the preceding claims, wherein a thickness (d) of the at least two waveguide layers (10) is between 0.1μm and 4μm.The multi-layer signal guiding structure (100) according to any one of the preceding claims, wherein the at least two waveguide layers (10) extend parallel to each other along the extension direction.The multi-layer signal conducting structure (100) according to any of the preceding claims, wherein a thickness (2a) of the at least one intermediate layer (20) is between a value greater than 0 μm and 10 μm.The multi-layer signal conducting structure (100) according to any of the preceding claims, wherein a thickness (D) of one of the cover layers (30) is between a value greater than 0 μm and 50 μm or between 0.0 μm and infinity.The multi-layer signal guiding structure (100) according to any one of the preceding claims, wherein the multi-layer signal guiding structure (100) comprises at least one input port for introducing the electromagnetic signal and at least one output port for discharging an output signal, wherein the input port is configured for introducing coupled modes of the electromagnetic signal into the at least two waveguide layers (10) and the at least one output port is configured for re-coupling the modes decoupled in the at least two waveguide layers (10) along the extension direction.The multi-layer signal guiding structure (100) according to any one of the preceding claims, wherein the multi-layer signal guiding structure (100) is formed by its structure to provide insulation for TM and TE modes of an electromagnetic wave introduced into the at least two waveguide layers (10) and / or to let the TM and TE modes propagate in a predetermined direction in the at least two waveguide layers (10) and to prevent propagation in the direction opposite to the predetermined direction and / or to let the TM and TE modes circulate in the at least two waveguide layers (10).The multi-layer signal guiding structure (100) according to any one of the preceding claims, wherein the multi-layer signal guiding structure (100) is formed as a switch, or as a circulator or as an isolator.The multi-layer signal guiding structure (100) according to any one of claims 1, 2 or 4 to 20, wherein at least two multi-layer signal guiding structures (100) are stacked to obtain coupled modes perpendicular to the extension direction.The multi-layer signal conducting structure (100) of any preceding claim, wherein the magneto-optical material is partially or fully etched to provide space for a ridge waveguide format and / or a ridge waveguide format.The multi-layer signal guiding structure (100) according to any of the preceding claims, wherein a waveguide layer (10) comprises silicon and / or silicon nitride and / or silicon dioxide and / or a polymer and / or sol-gel and / or hybrid plasmonic-dielectric.The multi-layer signal conducting structure (100) according to any of the preceding claims, wherein the magneto-optical material comprises a garnet or a doped garnet or doped silicon dioxide or sol-gel or ferromagnetic material.The multi-layer signal conducting structure (100) according to any of the preceding claims, wherein a capping layer (30) comprises silicon dioxide, SiO 2, and / or air and / or polymethylmethacrylate, PMMA, and / or PVA and / or SU-8.The multi-layer signal conducting structure (100) according to any of the preceding claims, wherein the multi-layer signal conducting structure (100) is arranged between a decoupling structure (110) for splitting an input signal at an input of the multi-layer signal conducting structure (100) into signals of equal amplitude and a coupling structure (120) for re-coupling an output signal at an output of the multi-layer signal conducting structure (100).The multi-layer signal guiding structure (100) according to claim 23, wherein a decoupling structure (110) and a coupling structure (120) are formed as a multimode interference coupler or as a Y-junction or as a tree coupler or as a star coupler or as a directional coupler.The multi-layer signal guiding structure (100) of claim 23 or 24, wherein a coupling structure (129) comprises an adiabatic coupler configured to avoid back reflections.The multi-layer signal guiding structure (100) according to any one of the preceding claims, wherein a waveguide layer (10) is formed as a waveguide running straight along the extension direction or as a bent waveguide or as a slot waveguide or as a SWG waveguide or as a PhC waveguide or as a plasmonic-dielectric hybrid waveguide.Method for operating a multi-layer signal guiding structure (100), in particular according to one of claims 1 to 25, comprising: providing a multi-layer signal structure (100) comprising: a plurality of layers, wherein the plurality of layers comprises at least two waveguide layers (10), which extend along an extension direction and which serve for coupling an electromagnetic signal, and at least one intermediate layer (20), which is arranged between the at least two waveguide layers (10); at least two cover layers (30), wherein the at least two waveguide layers (10) are arranged partially between the at least two cover layers (30), wherein the at least one intermediate layer (20) comprises a magneto-optical material (MO) and / or the at least two cover layers (30) comprise a magneto-optical material (MO); Application of an external magnetic field to the multilayer signal guiding structure (100), whereby a transverse magnetic mode, TM mode, or a transverse electric mode, TE mode, of an electromagnetic signal introduced into the multilayer signal guiding structure (100) experiences a change in its magnetic field profile aligned along an extension direction of the at least two waveguide layers (10), wherein, depending on an alignment of the external magnetic field to the multilayer signal guiding structure (100), the electromagnetic signal is concentrated in only one of the at least two waveguide layers (10).The method of claim 30, comprising: attaching to the multi-layer signal guiding structure (100) an input port (110) to introduce coupled modes of the electromagnetic signal into the at least two waveguide layers (10), and attaching an output port (130) to derive an output signal comprising coupled modes.The method of claim 30 or 31, wherein the method comprises: splitting the coupled modes of the electromagnetic signal onto the at least two waveguide layers (10); decoupling the modes during a course of the coupled modes in the at least two waveguide layers (10), such that decoupled modes are present in one of the at least two waveguide layers (10) at an end of the at least two waveguide layers (10), subsequently re-coupling the decoupled modes at the output port to the output signal; and deriving the output signal.

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