Abstract:
The invention explains, inter alia, integrated waveguide arrangements in which a waveguide with glass core and glass sheath is arranged in a waveguide layer consisting of glass. A foreign region made from a material other than glass extends in the vicinity of the waveguide. A temperature-adjustment unit is used to heat and/or cool the foreign region. The foreign region is integrated in the waveguide region.

Description:
TECHNICAL FIELD 
     The invention relates to an integrated waveguide arrangement which includes a waveguide region, a foreign region and a temperature-adjustment unit. 
     BACKGROUND ART 
     Typically, the waveguide region consists of glass, for example SiO 2 , and includes a waveguide with glass core and glass sheath. The refractive index of the glass cores is greater than the refractive index of the glass sheath. The waveguide is such that it carries an electromagnetic wave with low losses. The foreign region consists of a material other than glass and extends in the vicinity of the waveguide. A typical distance between foreign region and waveguide is, for example, 1 micrometer (μm) or 2 μm. 
     The temperature-adjustment unit is used to heat and/or cool the foreign region, so that it is possible to influence the wave propagation in the waveguide. A typical working range of the temperature-adjustment unit is between −40° C. and 150° C. 
     A waveguide arrangement of this type is known form the article “Hybrid switches offer the best of both worlds”, fiber systems, 05/2000, Vol.4, No.4, p.15, by Pauline Rigby. The wave arrangement explained in that document includes two waveguides made from glass which are connected by a waveguide made from polymer. 
     When producing waveguides from glass, the procedure is usually as follows: 
     1. An intermediate layer of silicon dioxide, which is known as a buffer layer, is applied to a silicon substrate. 
     2. A core layer, the refractive index of which is greater than the refractive index of the silicon dioxide layer, is applied to the silicon dioxide layer. The core layer likewise consists of silicon dioxide. 
     3. Regions at which there are to be no waveguide cores are removed from the core layer, usually by dry-chemical etching. 
     4. The remaining waveguide cores of the core layer and those areas of the intermediate layer which have been exposed in the previous process step are coated with a sheath coating of silicon dioxide which has the same refractive index as the silicon dioxide of the intermediate layer. This process is also known as cladding. 
     The known integrated waveguide arrangement is hybrid in the sense that it includes a waveguide made from glass and a waveguide made from polymer. Waveguides made from glass are distinguished by low transmission losses when carrying the waves. By contrast, waveguides made from polymer have a significantly higher thermo-optical coefficient than waveguides made from glass and are therefore more suitable for switching operations with the aid of the temperature-adjustment unit. The thermo-optical coefficient is a measure of the change in the refractive index as a function of the change in temperature of a material. For SiO 2 , the thermo-optical coefficient is approximately dn/dT=1e−6/K. On account of using both materials, the hybrid approach exploits both advantages. The result is a switching element which operates with a low switching power and low transmission losses. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an integrated waveguide arrangement which is of simple structure and in which the advantages of the hybrid structure are retained. Moreover, it is intended to provide a process for producing a waveguide arrangement of this type. 
     The object relating to the waveguide arrangement is achieved by means of a waveguide arrangement having the features of patent claim 1. Refinements are given in the subclaims. 
     The invention is based on the discovery that the good properties of a polymer waveguide with regard to the high temperature coefficient are retained even if only the waveguide core consists of polymer. The waveguide sheath can be produced from glass without the transmission properties being changed significantly. Furthermore, the discovery is based on the consideration that materials other than glass, for example polymer, have a better capacity to conduct heat. When using a waveguide core made from a material other than glass in a region consisting of glass, the energy emitted by the temperature-adjustment unit can be concentrated in a smaller area, since less heat is dissipated via the waveguide sheath. 
     In the waveguide arrangement according to the invention, in addition to the features listed in the introduction, the foreign region is integrated or embedded in the waveguide region. The foreign region forms the region in which switching operations take place with the aid of the temperature-adjustment unit. In the waveguide arrangement according to the invention, waveguides are made from glass apart from the foreign region and therefore have low transmission losses. The foreign region itself consists of a material other than glass, which therefore has a higher thermal conductivity and a greater thermo-optical coefficient. 
     The integration of the foreign region in the waveguide region facilitates production of the waveguide arrangement. In addition to the process steps listed in the introduction, the following steps are carried out: 
     5. A trench is etched into the sheath layer. 
     6. The entire structure is coated with a polymer, for example by means of spinning. 
     Therefore, during production of the waveguide arrangement according to the invention it is simply necessary to apply a polymer layer. The manufacturing tolerances are low, because a trench of defined depth can be etched with very great accuracy. 
     The advantages of the hybrid approach are retained in the waveguide arrangement according to the invention. In addition, however, the effect is achieved that the heat which is dissipated by the temperature-adjustment unit is concentrated on the waveguide core made from polymer, since a glass sheath is being used. Also, during cooling operations, heat is initially extracted only from the foreign region. This leads to a reduction in the switching power required. 
     The refractive index of the material in the foreign region is not critical, since the high thermo-optical coefficient means that it can be set within wide limits with the aid of the temperature-adjustment unit. 
     The integrated waveguide arrangement according to the invention opens up the route to a large number of new types of waveguide components. Depending on the arrangement of the foreign region with regard to a glass waveguide or with regard to a plurality of glass waveguides, it is possible, inter alia, to construct switching units, coupling units, attenuators and radiators. 
     In a refinement of the waveguide arrangement according to the invention, the waveguide region is arranged on a planar substrate. On the side which is remote from the substrate, the waveguide region forms a surface which lies approximately parallel to the interface between substrate and waveguide region. The waveguide arrangement can be produced using the technically highly developed lithographic processes. When using the process steps 1 to 4 listed in the introduction, therefore, the waveguide region includes the intermediate layer, parts of the core layer, specifically the waveguide cores made from glass and the sheath covering. On account of flow processes during its application to the side remote from the substrate, the sheath covering has a surface which is approximately parallel to the substrate surface. 
     In a subsequent refinement, the foreign region is produced from a material with a thermo-optical coefficient, the magnitude of which differs significantly from the magnitude of the thermo-optical coefficient of the glass. By way of example, coefficients which in terms of magnitude are 100 times greater than the thermo-optical coefficient of glass are used. The reference temperature selected, by way of example, is room temperature, i.e. 20° C. 
     In a further configuration, the material used in the foreign region is a plastic, for example, a polymer. An example of a polymer with a positive thermo-optical coefficient is a fluoroacrylate polymer which contains pentafluorostyrene (PFS), trifluoroethylmethacrylate (TFM) and glycidylmethacrylate (GMA). An example of a polymer with a negative thermo-optical coefficient is benzocyclobutene resin (RCB), which is marketed by the Dow Chemical Company under the CYCLOTENE trademark. This is a polymer which is polymerized from divinyldisiloxane-bis-benzocyclobutene monomers (B stage). The choice of polymer depends on what is required at the “normal” switching state. A polymer with a thermo-optical coefficient which overall requires a lower heating capacity is selected. 
     In one configuration, the foreign region extends from that surface of the waveguide region which is remote from the substrate to close to the waveguide. This arrangement is a result of the production technology employed. It is possible to introduce a trench from that surface of the waveguide region which is remote from the substrate. When the material of the foreign region is then introduced into the trench, it extends as far as the edge of the trench or beyond it. 
     In another configuration, the waveguide core has a higher refractive index than the waveguide sheath, and the refractive index of the material in the foreign region is dependent on the temperature which is generated by the temperature-adjustment unit and, for the same waveguide arrangement, may, depending on the operating mode, be less than, equal to or greater than the refractive index of the waveguide sheath. This method of selecting refractive indices makes it possible to construct waveguide arrangements for different tasks. Examples of different components and the refractive indices required therefore are given below. 
     In a refinement, a damping component which operates thermo-optically is formed as a result of the foreign region extending into the waveguide core. Depending on the temperature in the foreign region, a wave is transmitted from that part of the waveguide made from glass which lies on one side of the foreign region, through the foreign region, into that part of the waveguide made from glass which lies on the other side of the foreign region. If the foreign region is at a temperature which leads to a refractive index which corresponds to the refractive index of the waveguide core made from glass, a wave is passed unchanged through the foreign region. By contrast, if the foreign region is at a temperature which leads to a refractive index which is lower than the refractive index of the glass material surrounding the foreign region, a wave cannot pass through the foreign region and is radiated into the waveguide sheath and the surrounding waveguide region. In this case, only a wave which has been attenuated to a greater or lesser extent is present in the waveguide core on the other side of the foreign region. This component is suitable for signal matching, for example upstream of a sensor element. 
     In other refinements, the foreign region extends approximately parallel to the glass waveguide. Since waveguide and foreign region are arranged so close together that a wave which is propagating in the waveguide is influenced, the extent of this influence is dependent both on the length of the distance over which foreign region and waveguide lie approximately parallel to one another and on the refractive index in the foreign region which is brought about by the temperature. Numerous control options and switching principles are opened up. 
     In a further configuration, the foreign region is arranged outside a region which lies between the glass waveguide and a substrate. When using lithographic processes to etch the trench for the foreign region, this measure does not entail any risk of the waveguide region being involuntarily destroyed, as would be the case if the trench had to be etched directly via the waveguide. In this case, the waveguide would be arranged within the region which lies between foreign region and substrate. An offset arrangement of the foreign region allows greater tolerances to be set when etching the trench. 
     A thermo-optical attenuator which operates according to a different principle is formed if the waveguide is curved along the direction of propagation of the waves. The foreign region is arranged at the curved regions of the waveguide. Depending on the temperature of the temperature-adjustment unit, a wave which is propagating within the glass waveguide will be drawn to a greater or lesser extent into the foreign region, from where it will be radiated into the waveguide sheath. 
     If, in a further configuration, glass waveguide and foreign region are of approximately the same cross section, they are suitable as waveguides for carrying the same type of wave. A wave can be transferred with relatively low transmission losses out of the glass waveguide into the foreign region or in the opposite direction. This forms the basis for numerous switching operations. 
     A thermo-optical reversing switch is formed in a waveguide arrangement in which the waveguide region includes two waveguides which run approximately parallel and between which the foreign region is arranged. The foreign region can be so small that, depending on the temperature, it transmits a wave transmitted in one waveguide into the other waveguide. With a small foreign region, the transmission losses in the polymer remain low. It is not necessary for the wave to be guided in the foreign region itself. 
     If, in a further configuration, an intermediate layer made from a material which prevents the optical field from reaching the temperature-adjustment unit is present between the temperature-adjustment unit and foreign region, waves can be transmitted with relatively low losses in the foreign region. 
     In an alternative configuration, however, the temperature-adjustment unit is arranged directly on the foreign region. As a result, the temperature-adjustment unit attenuates a wave which is propagating in the foreign region and therefore, in addition to emitting or absorbing heat, has a dual function. The absorption of a wave is for many applications better than diffuse radiation of the energy into the waveguide region. It is possible to construct an attenuator in which, on the one hand, the temperature-adjustment unit absorbs the wave which is propagating in the foreign region and in which, on the other hand, the material of the foreign region is selected in such a way that it has a poor transmission capacity. The drawback of the polymer, i.e. that it has higher transmission losses than a glass waveguide, can therefore be utilized as an advantage for an attenuator. 
     The invention also relates to a process for producing an integrated waveguide arrangement comprising the process steps given in patent claim  15 . These process steps lead to the waveguide arrangement according to the invention. Therefore, the technical effects which have been listed above for the waveguide arrangement and for its configurations and refinements also apply to the process. In configurations of the process, it is modified in such a way that waveguide arrangements in accordance with the modifications referred to above are formed. 
     The invention relates furthermore to thermo-optical components, namely a thermo-optical radiation unit, a thermo-optical switching unit and a thermo-optical absorption unit in accordance with patent claims  16 ,  17  and  18 , respectively. These components are closely technically related to the waveguide arrangement according to the invention and the process according to the invention. 
     The thermo-optical radiation unit is constructed in such a way that the foreign region interrupts the glass waveguide core. The foreign region is therefore introduced directly above the waveguide core and extends into this core or even closer to the substrate. Since the foreign region may be very small, it is possible to construct radiation units with short switching times. 
     The thermo-optical switching unit includes at least two waveguides which run parallel to one another at least in a section. The foreign region extends between the waveguides and lies parallel thereto. When this switching unit is being constructed, it is possible to select high manufacturing tolerances, since there is no risk of damage to the glass waveguide cores. The result is a compact thermo-optical switching unit which is simple to produce. The foreign region may be very small. This enables a switching unit with a short switching time to be produced. 
     In the thermo-optical absorption unit, the temperature-adjustment unit bears directly against the foreign region and absorbs a wave which is propagating in the foreign region. The temperature-adjustment unit therefore has a double function. The drawback of the material in the foreign region, namely that its transmission capacity is worse than that of glass, is in this case an advantage, since a high degree of attenuation is desired. Materials which have a high attenuation coefficient are selected for the foreign region. The thermo-optical component which is formed in this way can be used, for example, for level adapting ahead of sensor elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the text which follows, exemplary embodiments of the invention are explained with reference to the appended drawings, in which: 
     FIG. 1 shows a plan view of a thermo-optical attenuator, 
     FIGS. 2A to  2 C show the thermo-optical attenuator shown in FIG. 1 in three operating modes, 
     FIG. 3 shows the cross section through a thermo-optical attenuator with curved waveguide, 
     FIGS. 4A and 4B show the thermo-optical attenuator shown in FIG. 3 in two operating modes, 
     FIG. 5 shows a plan view of a thermo-optical reversing switch, 
     FIGS. 6A and 6B show the thermo-optical reversing switch shown in FIG. 5 in two operating modes, 
     FIGS. 7A,  7 B and  7 C illustrate cross sections through a thermo-optical switch in three operating modes, 
     FIGS. 8A,  8 B and  8 C illustrate cross sections through a thermo-optical absorber in three operating modes. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a plan view of a thermo-optical attenuator  10 , which includes waveguide cores  14  and  16  which have been introduced into a waveguide layer  12 . The waveguide layer  12  consists of silicon dioxide and has a refractive index n 1  equal to 1.442. In the waveguide layer  12 , the waveguide cores  14  and  16  are embedded on all sides. The waveguide cores  14  and  16  likewise consist of silicon dioxide, but have a refractive index n 3  of 1.448. A polymer region  18  lies between the waveguide cores  14  and  16 . The waveguide cores  14 ,  16  and the polymer region  18  are of the same dimension transversely with respect to the propagation direction of a wave in the waveguide cores  14 ,  16 . The polymer region  18  extends from the surface of the waveguide layer  12  to the surfaces of the waveguide cores  14 ,  16  which face a substrate (not shown). At room temperature, the polymer region  18  has a refractive index n 2  of 1.5. The refractive index n 2  can be changed within wide ranges with the aid of a heater element (not shown) arranged above the polymer region  18 , as explained below with reference to FIGS. 2A to  2 C. The polymer region  18  consists of the CYCLOTENE™ material. The CYCLOTENE™ material has a very high negative temperature coefficient. 
     An abscissa axis  19   a  shows the length dimensions of the attenuator  10  in the x direction. An ordinate axis  19   b  shows length dimensions in the z direction. Therefore, the width of the waveguide core  14  is approximately 8 μm. The attenuator  10  is approximately 900 μm long. 
     The thermo-optical attenuator  10  attenuates a wave which is initially transmitted in the waveguide core  14  as a function of the temperature of the polymer region  18  or transmits this wave to the waveguide core  14 . The waveguide core  14  is therefore an input and the waveguide core  16  an output. The precise way in which the thermo-optical attenuator functions is explained below with reference to FIGS. 2A to  2 C. 
     FIGS. 2A,  2 B and  2 C show the attenuator  10  in three operating modes Ia, IIa and IIIa. In all three operating modes Ia, IIa, IIIa, a wave is introduced into the waveguide core  14 . This wave propagates in the direction toward the polymer region  18 . In FIGS. 2A,  2 B and  2 C, intensity distributions are in each case illustrated in a plane which lies parallel to the substrate and in the center of the waveguide cores  14 ,  16 . The intensity results from the sum of the squares of the components of the electric field strength. 
     FIG. 2A shows the operating mode Ia, in which the polymer region has not yet been heated and is at a temperature T 1   a . In operating mode Ia, the refractive index n 2  of the polymer region  18  is higher than the refractive index n 3  and therefore also higher than the refractive index n 1 . The refractive index n 2  of the polymer region  18  is therefore higher than that of the material surrounding the polymer region  18 , which has the refractive index n 1 . The polymer region  18  is therefore able to transmit a wave which is introduced as input wave  20 . However, since the refractive index n 2  of the polymer region  18  differs from the refractive index n 3  of the waveguide core  14  or of the waveguide core  16 , the boundaries between the polymer region  18  and the waveguide core  14  or the waveguide core  16  form dislocations which lead to transmission losses. Therefore, a scattered wave  22  of low intensity compared to the input wave  20  arriving from the waveguide core  14  is radiated into the waveguide layer  12 . However, most of the input wave is transmitted through the polymer region  18  and is passed on as output wave  24  with the aid of the waveguide core  16 . 
     Operating mode Ia is in practice used as an intermediate stage between operating modes IIa and IIIa which are explained with reference to FIGS. 2B and 2C. 
     FIG. 2B shows the attenuator  10  in operating mode IIa. The temperature T 2   a  of the polymer region  18  in operating mode IIa is higher than temperature T 1   a . Therefore, in operating mode IIa the refractive index n 2  of the polymer region  18  is equal to the refractive index n 3  of the waveguide core  14  and of the waveguide core  16 . This means that the polymer region  18  is matched to the waveguide core  14  and the waveguide core  16 . An input wave  26  is introduced into the waveguide core  14  and is transmitted virtually without losses via the polymer region  18  to the waveguide core  16 , appearing as output wave  28  at the output of the attenuator  10 . 
     In operating mode IIa, therefore, the thermo-optical attenuator works as a waveguide which transmits virtually without losses. 
     FIG. 2C shows the thermo-optical attenuator  10  in an operating mode IIIa, in which the polymer region  18  has been heated to an even greater extent than in operating mode IIa. The temperature T 3   a  of the polymer region  18  is higher than the temperature T 2   a . Consequently, the refractive index n 2  of the polymer region  18  is lower than the refractive index n 1  and therefore also lower than the refractive index n 3 . Since the refractive index n 2  of the polymer region  18  is lower than the refractive index n 1  of the surrounding medium, in operating mode IIIa the polymer region  18  cannot act as a waveguide. An input wave  30  which is introduced at the input of the attenuator  10  is almost completely radiated into the surrounding medium at the interface between waveguide core  14  and polymer region  18 , and in this surrounding medium propagates as a scattered wave  32  of high intensity. Only a residual wave  34  which has been greatly attenuated compared to the input wave  30  and to the scattered wave  32  and which emerges at the output of the attenuator  10  passes into the waveguide core  16 . 
     In operating mode IIIa, the attenuator  10  has its greatest influence on the incoming wave. By way of example, if a sensor element is situated at the output of the attenuator  10 , in operating mode IIIa the lowest amount of energy reaches the sensor element. 
     FIG. 3 shows a cross section through a thermo-optical attenuator  50  which, in a waveguide layer  52 , includes a waveguide core  54  which curves along the propagation direction of the waves, cf. FIGS. 4A and 4B. The waveguide layer  52  consists of silicon dioxide with a refractive index n 1  of 1.447. The waveguide core  54  likewise consists of silicon dioxide, but has a refractive index n 3  of 1.45. The waveguide core  54  is rectangular in cross section and its dimensions are such that a light wave with a wavelength of 1550 nanometers (nm) is transmitted virtually without losses. 
     To illustrate the dimensions of the attenuator  50 , an abscissa axis  56  shows length values in the horizontally running x direction. An ordinate axis  58  shows length values in the y direction, which is perpendicular to the x direction. Length values in μm are plotted on the abscissa axis  56  and the ordinate axis  58 . In the x direction, the extent of the waveguide core  52  is approximately 6 μm, and in the y direction the extent of the waveguide core  52  is approximately 6 μm. 
     A polymer region  60  which is rectangular in cross section is offset in both the x direction and the y direction with respect to the waveguide core  54 . The polymer region  60  runs parallel to a section of the waveguide core  54  in the propagation direction of the waves, cf. FIGS. 4A and 4B. In the y direction, the polymer region  60  is situated further away from a substrate (not shown) than the waveguide core  54 . A distance d between the top left-hand edge of the waveguide core  54  and the bottom right-hand edge of the polymer region  60  is only a few μm, for example 2 μm. Since the wave is transmitted both in the waveguide core  54  and in the regions which immediately adjoin this waveguide core  54 , its propagation can be influenced by the polymer region  60 . 
     The polymer region  60  consists of CYCLOTENE™ and at room temperature, i.e. at 20° C., has a refractive index n 2  of approximately 1.5. 
     The polymer region  60  adjoins a polymer layer  62  which lies on the surface of the waveguide layer  52 . On the polymer layer  62 , in the region of the polymer region  60 , there is an electrode  64  which is designed as a heater element. 
     Depending on the temperature in the polymer region  60  which is generated by the electrode  64 , the attenuator  50  operates in one of two operating modes Ib and IIb, which are explained below with reference to FIGS. 4A and 4B. 
     FIGS. 4A and 4B show the thermo-optical attenuator  50  in two operating modes Ib and IIb. A plan view of a plane through the attenuator  50  which lies parallel to the substrate surface is shown in FIGS. 4A and 4B. The figures also illustrate the intensity distribution within the attenuator  50 , resulting from an input wave which has been introduced at an input  66  of the attenuator  50 , in the different operating modes Ib and IIb. Moreover, FIGS. 4A and 4B each show an abscissa axis  68  and an ordinate axis  70 , on which length details are plotted using the unit μm. By way of example, the polymer region  60  has a length of approximately 500 μm in the z direction. 
     The waveguide core  54  is curved twice as it runs from the input  66  to an output  72  of the attenuator  50 . The first curve runs to the right and lies in the region of the polymer region  60 . Then, the waveguide core  54  is curved to the left. In the region of this curve, there is a further polymer region  74 , which likewise consists of a polymer of refractive index n 2 . The polymer regions  60  and  74  each lie on the convex side in the curved profile of the waveguide core  54 . 
     An electrode (not shown) for presetting the temperature in the polymer region  74  is also situated above the polymer region  74 . 
     FIG. 4A shows the attenuator  50  in operating mode Ib. In operating mode Ib, no voltage is applied to the electrode  64  and the electrode arranged above the polymer region  74 . Therefore, the electrodes are not providing any heat. T 1   b  denotes the temperature in the polymer regions  60  and  74 . In operating mode Ib, the refractive index n 2  of the polymer regions  60  and  74  is higher than the refractive index n 1  and the refractive index n 3 . Therefore, the polymer regions  60  and  74  can act as waveguides. An input wave  76  which is introduced at the input  66  is drawn almost completely into the polymer layer  60 , where it propagates. Scattered waves  78  occur at the edges of the polymer region  60  and propagate diffusely in the waveguide layer  12 . Only a wave of low intensity emerges at the output  72 . 
     The polymer region  74  further attenuates a residual wave transmitted in the waveguide core  54 . 
     Operating mode Ib is used, by way of example, if a sensor element arranged at the output  72  is to be in the at-rest state. 
     FIG. 4B shows the attenuator  50  in operating mode IIb. In operating mode IIb, the electrode  64 , cf. FIG. 3, and the electrode arranged above the polymer region  74  are carrying voltage and heat the polymer regions  60  and  74  to a temperature T 2   b  which lies above the temperature T 1   b  of operating mode Ib. Consequently, the value of the refractive index n 2  falls compared to the operating mode Ib. In operating mode IIb, the refractive index n 2  is lower than the refractive index n 1  of the waveguide layer  52  and therefore also lower than the refractive index n 3 . Since the refractive index n 2  of the polymer regions  60  and  74  is less than or equal to the refractive index of the surrounding medium of the waveguide layer  52 , the polymer regions  60  and  74  cannot operate as waveguides. An input wave  80  which is introduced at the input  66  is transmitted along the waveguide core  54  substantially without interference to the output  72 , where it appears as output wave  82 . 
     Therefore, in the switched-on state, i.e. in operating mode IIb, the attenuator  50  transmits the input wave  80 . In operating mode Ib, i.e. in the switched-off state of the attenuator  50 , by contrast, an input wave  76  is radiated into the waveguide layer  52 . In this way, the attenuator  50  can also be used as a switch. 
     FIG. 5 shows a plan view of a thermo-optical reversing switch  100 , which in a waveguide layer  102  includes two waveguide cores  104  and  106  which run parallel to one another in a region  108 . The waveguide layer  102  consists of silicon dioxide with a refractive index n 1  of 1.442. The waveguide cores  104  and  106  likewise consist of silicon dioxide but have a refractive index n 3  of 1.448. The waveguide core  104  runs from an input  110  to a working output  112 . The waveguide core  106  runs from the section  108  to a neutral output  114 . 
     In the region of the section  108 , there is a polymer region  116  made from CYCLOTENE™, which at room temperature (20° C.) has a refractive index n 2  of 1.5, is located between the waveguide cores  104  and  106 . The polymer region  116  extends on the one hand parallel to the waveguide cores  104  and  106 . On the other hand, the polymer region  116  extends from the surface of the waveguide layer  102  to a depth to which the waveguide cores  104  and  106  also reach. However, unlike the polymer region  116 , the waveguide cores  104  and  106  are completely surrounded by the silicon dioxide of the waveguide layer with the refractive index n 1 . 
     FIGS. 6A and 6B show two operating modes Ic and IIc of the thermo-optical reversing switch  100 . The figures illustrate the intensity distribution of the electrical component of an electromagnetic wave in a plane laid through the center axes of the waveguides  104  and  106 . In the longitudinal direction of the waveguide cores  112  and  114 , length details are given in micrometers on the left-hand side of the plane. The excerpt shown lies at z positions from 0 micrometers to approximately 1350 micrometers. Length details in the x direction in micrometers are shown at the lower edge of the plane. The center axis of the waveguide core  112  lies at 0 micrometers. The planes shown in FIGS. 6A and 6B extend from approximately −40 micrometers to approximately 60 micrometers in the x direction. 
     FIG. 6A shows the operating mode Ic, in which the polymer region  116  is being heated by the electrodes (not shown) at a temperature T 1   c . At temperature T 1   c , the refractive index n 2  of the polymer region  116  is less than or equal to the refractive index n 1  of the polymer layer  102  surrounding the polymer region  116  and the waveguide cores  112  and  114 . On account of its low refractive index n 2 , the polymer region  116  cannot function as a waveguide. An input wave  118  which is introduced at the input  110  of the reversing switch  100  is transmitted virtually unchanged through the waveguide core  112  to the working output  112 , where it appears as output wave  120 . In operating mode Ic, there is no wave at the neutral output  114 . 
     FIG. 6B shows the thermo-optical reversing switch  100  in operating mode IIc, in which the polymer region  116  is not being heated, i.e. the reversing switch  100  is in the neutral state. In operating mode IIc, the reversing switch  100  works at a temperature T 2   c  which is lower than temperature T 1   c . On account of the negative thermo-optical coefficient of the polymer region  116 , the refractive index n 2  at temperature T 2   c  is higher than at temperature T 1   c . In operating mode IIc, the refractive index n 2  of the polymer region  110  is higher than the refractive index n 3  of the waveguide cores  112  and  114  and therefore also higher than the refractive index n 1  of the waveguide layer  102 . On account of this relationship between the refractive indices, the polymer region  116  is able to influence a wave which is propagating in the waveguide core  112 . The polymer region  116  operates as a coupling region between the waveguide cores  112  and  114 . In the region of the polymer region  116 , an input wave  122  at the input  110  is transferred into the waveguide core  114 , and appears at the neutral output  114  as output wave  124 . In operating mode IIc, only a small part of the input wave  122  appears as residual wave  126  at the working output  112 . The intensity of the residual wave  126  is lower by orders of magnitude than the intensity of the output wave  124 . 
     FIGS. 7A,  7 B and  7 C show cross sections through a thermo-optical attenuator  150 . The attenuator  150  includes, on a silicon substrate (not shown), a waveguide layer  152  made from silicon dioxide with a refractive index n 1  of 1.442 at room temperature, i.e. at 20° C. A waveguide core  154 , which has a square cross section, illustrated in distorted form, and likewise consists of silicon dioxide, but with a refractive index n 3  of 1.448, is embedded in the waveguide layer  152 . A trench which ran parallel to the waveguide core  154  was etched into the waveguide layer  154 . The trench was then filled with the polymer CYCLOTENE™, so that a polymer region  156  is formed. In the direction which runs transversely with respect to the propagation direction of waves, the polymer region  156  has the same cross-section as the waveguide core  154 . At room temperature, i.e. at 20° C., the polymer region  156  has a refractive index n 2  of 1.5. However, the polymer region  156  only runs next to the waveguide core  154  for a relatively short section, for example for a distance of 500 micrometers. A thin layer of TEFLON™, a durable and slippery polymer manufactured by E.I. du Pont de Nemours and Company,  158  with a height of approximately 2 micrometers is applied above the polymer region  156  and above the waveguide layer  152 . The TEFLON™ layer  158  ahs a refractive index which approximately corresponds to the refractive index n 1 . As a result, the TEFLON™ layer  158  has a refractive index which approximately corresponds to the refractive index n 1 . As a result, the TEFLON™ layer  158  prevents waves from the polymer region  156  from reaching a heating electrode  160  which is arranged above the polymer region  156  on the TEFLON™ layer  158 . 
     In FIGS. 7A,  7 B and  7 C, length details are plotted in micrometers in the vertical x direction and in the vertical y direction. The surface of the TEFLON™ layer  158  lies at 0 micrometers in the y direction. The waveguide core  154  and the polymer region  156  each have an extent of approximately 6 micrometers in the x direction and also have an extent of approximately 6 micrometers in the y direction. In the x direction, the polymer region  156  is offset by an offset Vx of approximately 9 micrometers (from center to center). In the y direction, there is likewise an offset Vy of approximately 9 micrometers. Therefore, the shortest distance between waveguide core  154  and polymer region  156  is only a few micrometers. This means that the propagation of a wave in the waveguide core  154  and in the region of the waveguide layer  152  which lies directly around the waveguide core  154  can be influenced with the aid of the polymer region  156 . 
     In an operating mode Id, the attenuator  150  is heated, with the aid of the heating electrode  160 , by supplying a maximum heating power Pmax, to a temperature T 1   d . At this temperature, the refractive index n 2  of the polymer region is equal to the refractive index n 1 , i.e. 1.442, i.e. the same as the refractive index of the waveguide layer  52  which surrounds the polymer region  156 . Therefore, in operating mode Id, the polymer region  156  cannot act as a waveguide. A wave which is introduced into the waveguide core  154  propagates without obstacle and is not influenced by the polymer region  156 . Equi-intensity lines of a wave of this type are also shown in FIG. 7A, for example the equi-intensity line  162 . 
     FIG. 7B shows the thermo-optical attenuator  150  in an operating mode IId. In this operating mode IId, the heating electrode  160  is supplied with a heating power PH which is lower than the maximum heating power Pmax of the heating electrode  160 . Consequently, in operating mode IId the temperature T 2   d  of the polymer region  156  is lower than temperature T 1   d . On account of the changed temperature, in operating mode IId the refractive index n 2  of the polymer region  156  is higher than the refractive index n 1  of the waveguide layer  152  surrounding the polymer region  156 . In operating mode IId, the refractive index n 2  is equal to the refractive index n 3  of the waveguide core  154 . This leads to the polymer region  156  “sucking out” a part of the wave which is propagating in the waveguide core  156 . Equi-intensity lines  164  and  166  comprise both the waveguide core  154  and the polymer region  156 . This “sucking out” attenuates the intensity of a wave which is propagating in the waveguide core  154 . 
     FIG. 7C shows the thermo-optical attenuator  150  in an operating mode IIId in which the heating electrode  160  is in the voltage-free state. The heating power PH is 0 watts. The temperature T 3   b  of the polymer region  156  is lower than temperature T 2   d . Consequently, the refractive index n 2  of the polymer region  156  is higher than the refractive index n 3  of the waveguide core  154  and is also higher than the refractive index n 1  of the waveguide layer  152 , which also surrounds the polymer region  156 . Therefore, in operating mode IIId, the polymer region  156  is better able to carry a wave than the waveguide core  154 . The cross section shown in FIG. 7C lies at the end of the polymer region  152  which is reached by a wave entering the attenuator  150  later than the other end of the polymer region  156 . A wave which propagates in the waveguide core, up to the cross section illustrated in FIG. 7C, is introduced in its entirety from the waveguide core  154  into the polymer region  156 . Therefore, equi-intensity lines  168  encompass only the polymer region  156 . 
     The attenuator  150  illustrated in FIGS. 7A,  7 B and  7 C can therefore be used, by way of example, as a switch. In operating mode Id, a wave passes through the attenuator  150  without being influenced. By contrast, in operating mode IIId the “switch” is open and an incoming wave cannot pass through the waveguide region  154 , since it is transferred into the polymer region  168 . 
     If the attenuator  150  is used for signal matching, all three operating modes Id, IId and IIId are utilized. A sensor element is situated, by way of example, at the output of the waveguide core  154 . In operating mode Id, a wave which enters the waveguide core is transferred without obstacle to the sensor element. In operating mode IId, only a part of the wave which is introduced into the waveguide core  154  reaches the sensor element. In operating mode IIId, by contrast, a wave which propagates in the waveguide core  154  cannot reach the sensor element. 
     FIGS. 8A,  8 B and  8 C show cross sections through a thermo-optical absorber  170 . On a silicon substrate (not shown), there is a waveguide layer  172  made from silicon dioxide with a refractive index n 1  of 1.442 at 20° C. A waveguide core  174  has been embedded in the waveguide layer  172  with the aid of the process steps described in the introduction. The waveguide core  174  likewise consists of silicon dioxide, but has a refractive index n 3  of 1.448. The waveguide core  174  has a square cross section which, however, appears rectangular on account of the distorted illustration in FIGS. 8A,  8 B and  8 C. A polymer region  176  was introduced into the waveguide layer  172  in the immediate vicinity of the waveguide core  174 . To do this, firstly a trench was etched parallel to the path of the waveguide core  176 , over a length of approximately 300 micrometers. Then, a spinning process was used to introduce a polymer, for example CYCLOTENE™, into the trench. The result was the formation of a polymer layer  178  on the surface of the waveguide layer  172 . The polymer region  176  and the polymer layer  178  have a refractive index n 2  of 1.5 at room temperature of 20° C. 
     In FIGS. 8A,  8 B and  8 C, details of dimensions for the horizontal x direction and the vertical y direction in micrometers are plotted at the lower edge and at the left-hand edge, respectively. The waveguide core  174  and the polymer region  176  have a square cross section of 6 micrometers by 6 micrometers. The polymer region  176  is offset by in each case 9 micrometers in the x direction and in the y direction (center to center) with respect to the waveguide core  174 . Therefore, the polymer region  176  is situated so close to the waveguide core  174  that a wave which is transmitted with the aid of the waveguide core  174  can be influenced depending on the refractive index n 2  of the polymer region  176 . 
     FIG. 8A shows an operating mode Ie of the thermo-optical absorber  170 , in which a heating electrode  180  is being operated with a maximum heating power Pmax. The heating electrode  180  is located directly above the polymer region  176  on the polymer layer  178 . In operating mode Ie, the polymer region  176  is heated at a temperature T 1   e . At this temperature, the polymer region  176  has a refractive index n 2  which is equal to the refractive index n 1 . Therefore, the polymer region n 2  cannot act as a waveguide in operating mode Ie. In operating mode Ie, a wave which is introduced into the waveguide core  174  is guided past the polymer region  176  without being influenced by the latter. Therefore, equi-intensity lines  182  encompass only the waveguide core  174 . 
     FIG. 8B shows an operating mode IIe in which the electrode  180  is operated with a heating power PH which is lower than the maximum heating power Pmax. Therefore, a temperature T 2   e  of the polymer region  176  in operating mode IIe is lower than temperature T 1   e . On account of the lower temperature T 2   e , a refractive index n 2  which is equal to the refractive index n 3  and therefore also greater than the refractive index n 1  is established in the polymer region  176 . 
     On account of these refractive indices, the polymer region  176  is able to guide a wave and extracts a part of a wave which is being transported with the aid of the waveguide core  164 , cf. equi-intensity line  184  and  186 , encompassing both the polymer region  176  and the waveguide core  174 . However, the wave which is guided in the polymer region  176  is absorbed by the heating electrode  180 . The absorption of the wave with the aid of the heating electrode  180  leads to less energy being radiated into the waveguide layer  172  than with the thermo-optical attenuator  150  which was explained with reference to FIGS. 7A,  7 B and  7 C. 
     FIG. 8C shows an operating mode IIIe in which the heating electrode  180  is free of voltage and is therefore switched off. The heating power PH is therefore 0 watts. In operating mode IIIe, T 3   e  denotes the temperature in the polymer region  176 . Temperature T 3   e  is lower than temperature T 2   e  in operating mode IIe. On account of the lower temperature T 3   e , in operating mode IIIe the refractive index n 2  of the polymer region  176  is higher than the refractive index n 3  in the waveguide core  174  and is also higher than the refractive index n 1  of the waveguide layer  172 . On account of these refractive indices, the polymer region  176  is more suitable for transporting a light wave of, for example, 1550 nanometers than the waveguide core  174 . If a wave is introduced into the waveguide core  174  at the input of the absorber  170 , in the cross section at the end of the polymer region  176 , which is shown in FIG. 8 c , this wave has been almost completely transferred into the polymer region  176 , cf. equi-intensity lines  188  which encompass only the polymer region  176 . The wave which is being guided in the polymer region  176  is almost completely absorbed by the heating electrode  180 . The radiation into the waveguide layer  172  is low. 
     In other exemplary embodiments of the components which have been explained with reference to FIGS. 3,  4 A,  4 B;  7 A,  7 B,  7 C;  8 A,  8 B and  8 C, polymers which strongly attenuate waves are used in the polymer region  60 ,  74 ,  156 ,  176 . Consequently, the attenuation which is achieved with the components is increased further. 
     In other exemplary embodiments, polymers with other properties, for example with a positive thermo-optical coefficient, are used. In this way, it is possible to reverse the switching behavior in the neutral state and in the operating state of the component in question. 
     LIST OF REFERENCE SYMBOLS 
       10  Thermo-optical attenuator 
       12  Waveguide layer 
       14 ,  16  Waveguide core 
     n 1 , n 2 , n 3  Refractive index 
       18  Polymer region 
     Ia, IIa, IIIa Operating mode 
     T 1   a , T 2   a , T 3   a  Temperature 
       19   a  Abscissa axis 
       19   b  Ordinate axis 
       20  Input wave 
       22  Scattered wave 
       24  Output wave 
       26  Input wave 
       28  Output wave 
       30  Input wave 
       32  Scattered wave 
       34  Residual wave 
       50  Thermo-optical attenuator 
       52  Waveguide layer 
       54  Waveguide core 
       56  Abscissa axis 
       58  Ordinate axis 
       60  Polymer region 
     d Distance 
       62  Polymer layer 
       64  Electrode 
     Ib, IIb Operating mode 
     T 1   b , T 2   b  Temperature 
       66  Input 
       68  Abscissa axis 
       70  Ordinate axis 
       72  Output 
       74  Polymer region 
       76  Input wave 
       78  Scattered wave 
       80  Input wave 
       82  Output wave 
       100  Thermo-optical reversing switch 
       102  Waveguide layer 
       104 ,  106  Waveguide core 
       108  Section 
       110  Input 
       112  Working output 
       114  Neutral output 
       116  Polymer region 
     Ic, IIc Operating mode 
     T 1   c , T 2   c  Temperature 
       118  Input wave 
       120  Output wave 
       122  Input wave 
       124  Output wave 
       126  Residual wave 
     Id, IId, IIId Operating mode 
     T 1   d , T 2   d , T 3   d  Temperature 
       150  Thermo-optical attenuator 
       152  Waveguide layer 
       154  Waveguide core 
       156  Polymer region 
       158  Teflon layer 
       160  Heating electrode 
     Vx, Vy Offset 
       162  Equi-intensity lines 
     PH Heating power 
     Pmax Maximum heating power 
       164 ,  166 ,  168  Equi-intensity lines 
       170  Thermo-optical absorber 
     Ie, IIe, IIIe Operating mode 
     T 1   e , T 2   e , T 3   e  Temperature 
       172  Waveguide layer 
       174  Waveguide core 
       178  Polymer layer 
       180  Heating electrode 
       182  to  188  Equi-intensity lines