Planar optical element, sensor element and method for producing the same

Description

[0001] The invention relates to a planar optical element comprising at least one photonic component arranged in at least one carrier containing or consisting of at least one polymer. Furthermore, the invention relates to a method for producing such a planar optical element.

[0002] WO 2011 / 089244 A2 discloses the use of a fiber optic sensor with a plurality of fiber Bragg gratings for detecting temperatures and / or mechanical stresses. The light reflected by the fiber Bragg gratings is detected using a spectrometer, which can be arranged as a planar optical filter element on a silicon substrate. However, the disadvantage is the considerable complexity involved in manufacturing the planar optical filter element on a silicon substrate.

[0003] DE 41 30 550 A1 describes optical elements with an embossed surface structure, in which the embossed surface consists of a transparent composite material which has a three-dimensional framework of inorganic or organically modified inorganic components in the form of nanoscale particles in a polymer matrix.

[0004] WO 2006 / 014582 A2 discloses an optical connection with a polymer waveguide. The core contains a polymer material with a nanoparticle filler having a particle size of less than one-tenth of the shortest wavelength relevant for the optical connection.

[0005] EP 1 886 802 A2 discloses an optical device consisting of a mixture or composite of polymer-inorganic particles. The inorganic particles may be phosphorescent, exhibit nonlinear optical properties, or possess piezoelectric properties.

[0006] US 2003 / 0031438 discloses mixtures of polymers and inorganic particles. The particles are incorporated into structures that generally have interfaces with additional materials that can be advantageously used to manufacture desired devices. In some embodiments, the structures are optical structures and the interfaces are optical interfaces.

[0007] JP H 11109155 (A) discloses carbon fiber plates with low thermal expansion coefficients. These are densely arranged on the surfaces of an optical waveguide. Since the contraction of the optical waveguide due to temperature change is minimized, the temperature change in the optical path length of the optical waveguide can be suppressed.

[0008] Japanese Patent Application Publication No. 2006-208982 (A) discloses an optical waveguide film with low thermal expansion. It comprises a transparent base plate consisting of a fiber-reinforced composite material containing fibers with an average diameter of 4 to 200 nm and a matrix material.

[0009] Based on this prior art, the invention is therefore based on the object of providing a planar optical filter element which can be produced cost-effectively and easily in large quantities and which can be easily integrated into other components or parts.

[0010] The object is achieved according to the invention by a planar optical element according to claim 1 and a method according to claim 8.

[0011] According to the invention, it is proposed to integrate at least one photonic component on a carrier or a substrate. The photonic component can, for example, be a passive optical component. In some embodiments of the invention, the passive optical component can be selected from a waveguide, a fiber Bragg grating, a coupler, or an arrayed waveguide grating. The planar optical element or the proposed sensor element contains at least one such photonic component. In some embodiments of the invention, several photonic components can also be integrated on the carrier, resulting in an integrated photonic component that can perform a plurality of functions or at least one complex function.In some embodiments of the invention, the photonic component can be a multi-channel spectrometer, allowing the intensity of incoming light to be determined in a predefined spectral range. Such spectrometers can be used, for example, for the readout of fiber optic sensors or for signal readout or signal generation in optical communications.

[0012] According to the invention, it is now proposed to use a multilayer polymer material as the carrier. The polymer material can, for example, contain or consist of polymethyl methacrylate, polycarbonate and / or polyimide. The carrier has a first layer with a first side and an opposite second side, as well as at least one second layer with a first side and an opposite second side. The two layers are firmly bonded to one another, for example by gluing, welding or lamination, so that the first side of the second layer lies on the second side of the first layer. The photonic components are arranged in the first layer and can be produced, for example, by a printing process, by photolithographic structuring or by material modification by laser radiation. In the latter case, material modification by femtosecond laser pulses can advantageously be used.To minimize losses due to light scattering or refraction in the first layer, the first layer is free of inclusions or material inhomogeneities, at least in the partial areas where the photonic components are arranged. However, this leads to a larger thermal expansion coefficient, so that a change in temperature leads to a change in the size of the photonic components. This can change the optical properties of at least one photonic component.

[0013] According to the invention, it is now proposed to reinforce the second layer of the carrier with nanowires to compensate for the temperature-induced expansion. The nanowires can be introduced into the second layer by coextrusion, lamination, a sol-gel process, or other processes not specified here. The nanowires can absorb and counteract tensile stresses in the material, so that the thermal expansion of the second layer can be considerably lower than the thermal expansion of the first layer alone. In some embodiments of the invention, the second layer can have a negative temperature coefficient in certain temperature ranges, i.e., instead of thermal expansion, the second layer contracts with increasing temperature.

[0014] By bonding the first layer and the second layer, the second layer can compensate or at least reduce the temperature expansion of the first layer, so that the photonic components on the carrier function reliably even when there are temperature changes in at least one predeterminable temperature range.

[0015] Even though the present description describes only three layers as part of the carrier, it should be noted that in some embodiments of the invention, a larger number of layers may also be present. For example, multiple first layers may be provided in order to arrange a larger number of photonic components one above the other in the carrier. In other embodiments of the invention, a layer may be composed of multiple layers, thus forming a multilayer system. This allows the material properties of the layer to be even better adapted to predeterminable target values.

[0016] In some embodiments of the invention, the second film layer can be provided with nanowires over its entire surface, so that the carrier has the required low temperature coefficient over its entire surface.

[0017] In other embodiments of the invention, only a partial area of ​​the second film layer can be provided with nanowires, resulting in surface areas in which the photonic components are protected from inadmissibly large thermal expansion and other surface areas of the carrier have a different, usually larger, temperature coefficient.

[0018] According to the invention, the nanowires can contain or consist of zinc oxide and / or titanium dioxide and / or carbon nanotubes. These materials are suitable for ensuring the desired low thermal expansion of the support and can also be easily incorporated into the conventional polymer materials used to produce the support.

[0019] In some embodiments of the invention, the nanowires can be produced using wet chemical methods. This allows for cost-effective, large-scale production of the nanowires.

[0020] In other embodiments of the invention, the nanowires can be generated from a plasma. Due to the resulting non-equilibrium conditions, even thermodynamically unstable materials can be processed into nanowires.

[0021] According to the invention, the nanowires can have a diameter of approximately 100 nm to approximately 1000 nm. These dimensions have proven to be effective in achieving a sufficient reduction in the thermal expansion of the carrier, while also allowing the nanowires to be easily manufactured and processed.

[0022] In some embodiments of the invention, the first film layer can contain nanoparticles and / or dopants. Such nanoparticles can be used in addition to or alternatively to dopants to achieve predeterminable optical properties of the first film layer. In some embodiments of the invention, nanoparticles and / or dopants can be used to adapt the refractive index of the first film layer to predeterminable values.

[0023] In some embodiments of the invention, only a partial area of ​​the first film layer or a partial volume of the film layer can be provided with nanoparticles. This allows the optical properties of the material to be adapted in specific spatial regions or for specific photonic components. Other photonic components, however, can be arranged in other surface regions, which in turn have different optical properties.

[0024] In some embodiments of the invention, the first film layer can contain nanoparticles containing or consisting of titanium dioxide and / or zinc oxide and / or silicon dioxide. It has been shown that these materials are easy to produce, disperse well in the polymer materials of the first film layer, and have a positive influence on the optical properties for predefined wavelengths or wavelength ranges.

[0025] In some embodiments of the invention, the first film layer may contain nanoparticles having a diameter of about 10 nm to about 500 nm or having a diameter of about 100 nm to about 800 nm.

[0026] In some embodiments of the invention, the planar optical element can contain a third film layer having a first side and an opposite second side, wherein the third film layer contains nanowires at least in a partial area. The first side of the third film layer can be fully bonded to the second side of the second film layer, for example by gluing, welding, or lamination. In this way, in some embodiments of the invention, further improved stability and thus a lower susceptibility of the photonic components to thermal expansion and / or the action of mechanical stresses on the carrier result.

[0027] In some embodiments of the invention, the nanowires can have a predeterminable orientation. Such an orientation can be achieved, for example, by applying an electric and / or magnetic field, so that the nanowires align along a desired direction before the polymer material solidifies. In some embodiments of the invention, the orientation of the nanowires can deviate from the desired orientation by less than 20°, less than 15°, less than 5°, or less than 3°. This makes it possible to provide a carrier that exhibits anisotropic thermal expansion behavior.

[0028] In some embodiments of the invention, the orientation of the nanowires of the third film layer may differ from the orientation of the nanowires of the second film layer. In some embodiments of the invention, the nanowires of the third film layer and the second film layer may be arranged approximately orthogonally to each other. This allows for a particularly stable support that locks in the different expansion behavior of the layers, similar to laminated wood or plywood.

[0029] In some embodiments, the planar optical element can contain a fiber optic sensor having at least one waveguide, which in turn has at least one core made of a first material with a first refractive index and a cladding surrounding the core made of a second material with a second refractive index. In this way, an optical wave can be totally reflected at the interface between the first material and the second material, so that the optical power is guided in the core. At least one fiber Bragg grating can be incorporated in the core. The fiber Bragg grating reflects part of the coupled optical power and transmits the other part. The wavelength or wavelength distribution of the reflected light depends on the grating constant of the fiber Bragg grating.The grating constant, in turn, is defined by the grating constant originally intended during the manufacture of the fiber Bragg grating, as well as its change due to thermal expansion and / or mechanical stress. Thus, by analyzing the spectral distribution of the reflected light, one of several fiber Bragg gratings can be selected, and the temperature and / or force prevailing at this fiber Bragg grating can be determined.

[0030] By integrating such a sensor element onto the carrier, a component can be created that integrates both the sensor element and the spectrometer required for readout. One or more sensors can cover a larger area, enabling the area-wide measurement of force or temperature. For use, the carrier simply needs to be glued to the component to be monitored or laminated into it.

[0031] In some embodiments of the invention, the component to be provided with the sensor can be a battery or a battery housing. In other embodiments of the invention, the component to be monitored can be a mechanical component, for example, the blade of a wind turbine, a wing, an engine nacelle, or an aircraft fuselage element, a tire, or another component not mentioned here made of a fiber-reinforced plastic, a thermoplastic, a thermoset, or a rubber. The proposed sensor element can be particularly easily embedded into these material systems during primary molding.

[0032] The invention will be explained in more detail below with reference to figures without limiting the general inventive concept. Figure 1 shows a planar optical element according to an embodiment of the invention. Figure 2 shows a sensor element. Figure 3 shows a battery housing with a sensor element.

[0033] Figure 1 shows a planar optical element 1 according to an embodiment of the invention. In the illustrated embodiment, the planar optical element 1 has a carrier 2, which is composed of a first layer 21, a second layer 22, and a third layer 23. The first layer 21, the second layer 22, and the third layer 23 each contain a polymer as the base material. In the first layer 21, at least one partial area or a partial volume can also be provided with nanoparticles containing, for example, TiO 2. This can influence the optical properties of the first layer 21.

[0034] The second layer 22 and the third layer 23 contain, in addition to the base material, nanowires 3. The nanowires 3 are introduced in each layer with a preferred direction, ie the longitudinal extensions of the individual nanowires 3 run approximately parallel to one another and approximately parallel to a predetermined desired direction.

[0035] As the cross-section through the carrier 2 shows, the first side 211 of the first layer 21 forms the surface of the carrier 2. The second side 212 of the first layer 21 lies on the first side 221 of the second layer 22. The interface can be connected over its entire surface by welding, gluing, or lamination. In the same way, the second side 222 of the second layer 22 lies on the first side 232 of the third layer 23. A fully adhesive connection can also be provided at this interface. The second side 223 of the third layer 23 forms the underside of the carrier 2. As is also indicated in the cross-section, the longitudinal extents of the nanowires 3 in the second layer 22 run approximately orthogonal to the longitudinal extent of the nanotubes 3 of the third layer 23. This results in mechanical stabilization ora stabilization against thermal expansion in both spatial directions, so that the photonic component 4 on the carrier 2 is little influenced by thermal expansion or force.

[0036] The nanowires 3 can be arranged over the entire surface of the carrier 2, so that the entire carrier 2 is insensitive to thermal expansion, i.e., the change in length or width as a function of temperature is small. The first layer 21, the second layer 22, and the third layer 23 can each have a thickness of approximately 25 µm to approximately 250 µm or of approximately 50 µm to approximately 125 µm. At least one of the layers 21, 22, or 23 can be produced by extrusion, rolling, or wet chemical deposition.

[0037] An arrayed waveguide grating 43 is shown as an example of a photonic component 4. The arrayed waveguide grating can be used as an optical microspectrometer, i.e., input signals of different wavelengths are imaged at different locations of the output.

[0038] The optical input signal is fed to the planar optical element 1 via an optical waveguide 50, which can be provided with an optional connector 51. The input signal is transmitted via the waveguide 50 into the integrated waveguide 41. The waveguide 41 forwards the input signal to the free propagation region 431 of the arrayed waveguide grating 43. The free propagation region 431 has an approximately triangular base area.

[0039] At the end of the free propagation region 431, a plurality of waveguides 432 are located. The waveguides 432 have different lengths and guide the optical input signal from the propagation region 431 to the interference region 433. There, the different wavelengths are caused to interfere. At the output of the interference region 431, an interference pattern is formed, with different wavelengths being imaged at different locations.

[0040] At each of the interference maxima there are additional waveguides which transport the output signal to the output of the planar optical element.

[0041] The individual components of the arrayed waveguide grating 43 can be introduced into the first layer 21, for example, by a nanoprinting process. In other embodiments of the invention, the components can be created in the first layer 21 by material modification with a laser or by conventional photolithography.

[0042] A conventional polymer carrier would expand or contract with changes in temperature, causing the geometric dimensions of the arrayed waveguide grating 43 to change. This would impair the performance of the arrayed waveguide grating 43. By reinforcing the substrate according to the invention with nanowires 3, which are arranged in the second layer 22 and the optional third layer 23, sufficient mechanical stabilization of the carrier 2 can be achieved, so that the arrayed waveguide grating 43 always exhibits full performance or improved performance compared to known polymer carriers, even at fluctuating temperatures. At the same time, the carrier 2 made of a polymer material offers the advantage over known silicon substrates that even very large carriers can be produced cost-effectively, so that large photonic components or many photonic components can be produced cost-effectively.An arrayed waveguide grating with larger dimensions can have improved channel spacings, for example, more than 400 GHz, more than 600 GHz or more than 1 THz.

[0043] In the same way as in Figure 1 As shown for an arrayed waveguide grating 43, additional or other photonic components can be arranged on the carrier 2. For example, couplers, fiber Bragg gratings, fiber optic sensors, or waveguides and components derived therefrom can be produced in the first layer 21.

[0044] Figure 2 shows an embodiment of a sensor element which is arranged on a carrier 2. The carrier 2 can be composed of at least two layers, as described above with reference to Figure 1 has already been explained. In the example according to Figure 2The carrier 2 has a partial surface 225 reinforced with nanowires 3. For reasons of clarity, only a few nanowires 3 are shown with their orientation. Of course, however, the nanowires 3 can occupy the entire partial surface 225 and be arranged in several different orientations in one or more layers. It is only essential that the nanowires 3 achieve a sufficiently small expansion for at least one temperature range so that the components arranged in the surface region 225 are not unduly influenced by acting forces and / or temperature fluctuations.

[0045] The remaining surface area of ​​the carrier 2 is provided with fiber optic sensors 45a, 45b, and 45c. The invention does not teach the use of exactly three fiber optic sensors 45. Rather, the selected number can be greater or lesser, for example, from 1 to approximately 50.

[0046] Each of the fiber optic sensors 45 has a core 411 whose refractive index is greater than the refractive index of the first layer 21 of the carrier 2. This guides light in the core 411, resulting in a waveguide 41. In the illustrated embodiment, the waveguides are arranged in a straight line. Of course, meandering or spiral arrangements of at least one waveguide 41 can also be realized.

[0047] At least one fiber Bragg grating 44 is arranged in the core 411 of the waveguide 41. In the illustrated embodiment, each core 41 has seven fiber Bragg gratings 44. In other embodiments of the invention, the number may be greater or lesser. Furthermore, different numbers of fiber Bragg gratings 44 may be arranged in different waveguides 41.

[0048] The optical waveguide 41 and / or the fiber Bragg gratings 44 can be produced in the carrier 2 by laser material processing and / or nanoprinting.

[0049] Since the carrier 2 does not contain any stabilizing nanowires in the area of ​​the fiber optic sensors 45, the lattice constant of the fiber Bragg gratings 44 changes when force and / or temperature are applied. This changes the spectrum reflected by the respective gratings 40.

[0050] The light reflected by the fiber Bragg gratings 44 is analyzed by the spectrometer arranged in the surface area 225. A connecting waveguide 50 with an optional connector 51, via which the light from a superluminescent diode or a tunable semiconductor laser can be coupled, is used to generate the optical signal 45. The light is expanded by two couplers 42a and 42b into three optical paths, each of which is connected to a fiber optic sensor 45.

[0051] The light reflected by the fiber Bragg gratings 44 is guided via further couplers 42c, 42d, and 42e to three arrayed waveguide gratings 43a, 43b, and 43c. These provide an optical signal at the output waveguides 435, which can be converted into electrical signals, for example, via a CCD array or a photodiode array. The magnitude of the optical signal is thus a measure of the intensity of the light reflected by the respective fiber Bragg grating 44 and thus a measure of the temperature and / or force prevailing at the location of the respective grating 44. If the same temperature acts on the region 225, the spectrometer remains essentially unaffected, since the nanowires 3 provide mechanical stabilization of this partial area of ​​the carrier 2.

[0052] The invention thus discloses for the first time the integration of a fiber optic sensor and the associated signal readout on a carrier 2.

[0053] Figure 3 shows a possible application of the sensor element from Figure 2 or the planar optical element according to Figure 1 . Figure 3 shows a battery housing 6, which can contain a plurality of battery cells to provide a battery with a predeterminable electrical voltage and / or a predeterminable current delivery capacity. The battery housing 6 has at least two connection contacts 61 and 62 on its exterior, via which current can be drawn from the battery or a charging current can be supplied.

[0054] To monitor the temperature of the battery cells in the housing 6, a fiber optic sensor 45 can be provided, which contains a plurality of fiber Bragg gratings 44, as described above with reference to Figure 2The battery housing 6 can be configured accordingly so that the temperature of the battery cells can be determined at the respective location of the fiber Bragg grating 44. The fiber optic sensor 45 is formed on a carrier 2, which is glued to the battery housing 6 or embedded in the material of the battery housing 6. As described above, the carrier 2 has a surface area 225, which is stabilized by nanowires 3. Located in this area is a planar optical spectrometer in the form of an arrayed waveguide grating 43. The light for querying the respective lattice constants of the arrayed waveguide gratings 44 can be coupled in via the waveguide 41 and the coupler 42, as described above. Thus, the proposed sensor element only requires the connection of a light source and an electronic evaluation circuit to monitor the temperature of a plurality of battery cells.The sensor element and the spectrometer required for readout can be embedded on the carrier 2 in the material of the housing 6, resulting in a mechanically robust structure that can withstand even harsh operating conditions, such as those found in vehicles. Furthermore, the materials used are inexpensive to manufacture, making mass market use easy.

[0055] Of course, the invention is not limited to the embodiments illustrated in the figures. The above description is not to be considered restrictive, but rather explanatory. Features of different embodiments can be combined with one another. The following claims are to be understood in such a way that a named feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define "first" and "second" features, this designation serves to distinguish between two similar features without establishing a priority.

Claims

1. Planar optical element (1) having at least one photonic component (4), which is arranged in at least one substrate (2), characterized in that the substrate (2) includes at least a first film layer (21) having a first side (211) and an opposite second side (212) and a second film layer (22) having a first side (221) and an opposite second side (222), the first film layer (21) and the second film layer each containing or consisting of at least one polymer and the first side (221) of the second film layer (22) being arranged on the second side (212) of the first film layer (21), at least a sub-surface (225) of the second film layer (22) containing nanowires (3) which contain or consist of zinc oxide and have a diameter of about 100 nm to about 1000 nm and the photonic component (4) being arranged in the first film layer (21).

2. Planar optical element according to claim 1, characterized in that the nanowires (3) have a length of about 1 µm to about 10 µm.

3. Planar optical element according to claim 1 or 2, characterized in that first film layer (21) further contains nanoparticles.

4. Planar optical element according to claim 3, characterized in that the nanoparticles contain or consist of TiO2 and / or ZnO and / or SiO2.

5. Planar optical element according to any one of claims 1 to 4, characterized in that the photonic component (4) in the first film layer is selected from at least one waveguide (41) and / or at least one coupler (42) and / or at least one arrayed waveguide grating (43) and / or at least one fiber Bragg grating (44) and / or at least one fiber-optic sensor (45).

6. Planar optical element according to any one of claims 1 to 5, further containing a third film layer (23) having a first side (231) and an opposite second side (232), wherein at least a sub-surface (225) of the third film layer (23) contains nanowires.

7. Planar optical element according to any one of claims 1 to 6, characterized in that the nanowires (3) have a predeterminable orientation.

8. Method for producing a planar optical element (1) containing the steps of: - providing a first film layer (21) having a first side (211) and an opposite second side (212), the first file layer (21) containing a polymer; - providing a second film layer (22) having a first side (221) and an opposite second side (222), the second film layer (22) containing a polymer and, in at least a sub-surface (225), nanowires (3) which contain or consist of zinc oxide and have a diameter of about 100 nm to about 1000 nm, - connecting the first side (221) of the second film layer (22) to the second side (212) of the first film layer (21), - producing at least one photonic component (4) in the first film layer (21) by modifying the material using layer radiation and / or nanoprinting and / or photolithography, wherein - the photonic component (4) in the first film layer (21) is selected from at least one waveguide (41) and / or at least one coupler (42) and / or at least one arrayed waveguide grating (43) and / or at least one fiber Bragg grating (44) and / or at least one fiber-optic sensor (45).

9. Method according to claim 8, further containing the steps of: - providing a third film layer (23) having a first side (231) and an opposite second side (232), wherein at least a sub-surface (225) of the third film layer (23) contains nanowires (3), - laminating the first side (231) of the third film layer (23) to the second side (222) of the second film layer (22).

10. Method according to claim 8 or 9, wherein the first film layer (21) further contains nanoparticles or wherein the first film layer (21) further includes nanoparticles which contain or consist of TiO2 and / or ZnO and / or SiO2.

11. Method according to any one of claims 8 to 10, wherein the nanowires (3) have a predeterminable orientation.

12. Method according to any one of claims 8 to 11, wherein the nanowires (3) have a length of about 1 µm to about 10 µm.