Manufacturing process for an optical coupling element for use in a vehicle, optical coupling element for a laser scanner, laser scanner, vehicle with a laser scanner, computer program and computer-readable medium

Abstract

Manufacturing process for an optical coupling element (1) intended for use in a vehicle, wherein the coupling element (1) is configured for coupling laser light from at least one fiber (2) into at least one waveguide (3), wherein the manufacturing process comprises the following process steps: - providing at least one fiber (2), at least one waveguide (3) and a support substrate (4) (100); - attaching the at least one fiber (2) and the at least one waveguide (3) to a surface of the support substrate (4) forming a space between at least one fiber exit (2a) of the at least one fiber (2) and at least one waveguide inlet (3a) of the at least one waveguide (3) (200);- Applying a polymer spacer (5) into the space on the surface of the support substrate (4) such that the polymer spacer (5) is in direct contact with the at least one fiber output (2a) and the at least one waveguide input (3a) (300); and - Structuring, by means of a laser, a 3D waveguide (6) into the polymer spacer (5), wherein the 3D waveguide (6) extends from the at least one fiber output (2a) to the at least one waveguide input (3a) and connects the at least one fiber output (2a) with the at least one waveguide input (3a) (400).;

Description

The present invention relates to a manufacturing method for an optical coupling element intended for use in a vehicle, wherein the coupling element is configured for coupling laser light from at least one fiber into at least one waveguide. The coupling element can, for example, be used to couple light into a laser scanner, which is used in the vehicle to detect properties of the vehicle's environment. The present invention also relates to an optical coupling element produced by steps of the manufacturing process. Furthermore, the present invention relates to a vehicle with the optical coupling element, as well as a laser scanner with the optical coupling element. Furthermore, the present invention relates to a computer program comprising instructions which, when the computer program is executed by a computer, cause it to perform steps of the manufacturing process. Furthermore, the present invention relates to a data carrier signal that transmits the computer program. Furthermore, the present invention relates to a computer-readable medium comprising instructions which, when executed by a computer, cause it to perform steps of the manufacturing process. DE 10 2016 118 539 A1 discloses a taper as a coupling element for coupling laser light into a waveguide as a deflection unit for a laser scanner. The coupling element is used for a system consisting of a scanning unit for an optical transmitter and an optical detection device. The scanning unit comprises at least one beam-controlling device for deflecting at least one light beam emitted into an inlet of the scanning unit and at least one coupler for introducing the at least one light beam into the at least one beam-controlling device. The at least one coupler has or consists of at least one beam-constricting device for narrowing the cross-section of the at least one light beam. When using a taper as a coupling element in the state of the art, aligning optical components is required when introducing the taper into the overall optical system, which complicates the manufacturing process. Further state of the art is known from US 2014 / 0334768 A1 and US 2005 / 0238277 A1. Based on the aforementioned prior art, the invention is thus based on the objective of providing an improved manufacturing process for an optical coupling element for use in a vehicle, an improved optical coupling element, a vehicle with such an improved coupling element, a correspondingly improved computer program, a correspondingly improved data carrier signal, and a correspondingly improved computer-readable medium. In particular, the manufacturing process for the optical coupling element for use in the vehicle should be simpler. The problem is solved according to the invention by the features of the independent claims. Advantageous embodiments of the invention are specified in the dependent claims. According to the invention, a manufacturing process for an optical coupling element intended for use in a vehicle is thus specified, wherein the coupling element is configured for coupling laser light from at least one fiber into at least one waveguide, and wherein the manufacturing process comprises the following process steps: providing at least one fiber, at least one waveguide, and a support substrate; attaching the at least one fiber and the at least one waveguide to a surface of the support substrate, forming a gap between at least one fiber exit of the at least one fiber and at least one waveguide input of the at least one waveguide; applying a polymer spacer to the gap on the surface of the support substrate such that the polymer spacer is in direct contact with the at least one fiber exit and the at least one waveguide input;and structuring, by means of a laser, a 3D waveguide into the polymer intermediate, wherein the 3D waveguide extends from the at least one fiber output to the at least one waveguide input and connects the at least one fiber output to the at least one waveguide input.; According to the invention, an optical coupling element, e.g. for a laser scanner, in a vehicle, having properties produced by manufacturing process steps described above or subsequently mentioned as advantageous, is also specified. Furthermore, a vehicle with the optical coupling element is specified according to the invention. Preferably, the vehicle is a driver's ego vehicle. Furthermore, a laser scanner with the optical coupling element is specified according to the invention. Furthermore, the invention provides a computer program comprising instructions that, when executed by a computer, cause the computer to perform steps of the manufacturing process. A computer program is a collection of instructions for performing a specific task, designed to solve a particular class of problems. The instructions of a program are designed to be executed by a computer, and it is necessary for a computer to be able to execute programs in order for the program to function. Furthermore, according to the invention, a data carrier signal is specified that transmits the computer program. Furthermore, according to the invention, a computer-readable medium is provided, comprising instructions which, when executed by a computer, cause it to perform steps of the manufacturing process. The basic idea of ​​the present invention is therefore to produce a coupling element for coupling laser light into a waveguide, e.g., as a deflection unit for a laser scanner. In particular, laser light from a fiber is coupled into the waveguide by means of the coupling element. In this process, the fiber and waveguide are arranged on a common substrate. A suitable polymer is applied to the substrate between the fiber and the waveguide, with the polymer being in direct contact with the fiber exit and the waveguide input. Subsequently, the 3D waveguide is written into the polymer using a laser. 3D waveguides are structures embedded in a transparent material, for example, at wavelengths in the range of 750 nm to 850 nm. These structures are created by local heating and the resulting local change in the refractive index of the transparent material. For example, 3D waveguides can be created by focusing femtosecond pulsed laser radiation into a volume of the transparent material. The energy of the laser radiation is absorbed by nonlinear processes in a small volume within the beam focus. This causes a volume of the transparent material, limited to a few cubic micrometers, to be heated intensely for a short time, locally melting the material. After solidification, a region with a higher refractive index than the surrounding material can result.When the focus of the laser radiation is moved within the volume of the transparent material, three-dimensional structures with an increased refractive index are created, which act as light guides. These light guides are 3D waveguides. The 3D waveguide, for example, is a monomodal polymer waveguide, i.e., a single-mode polymer waveguide. To produce a single-mode polymer waveguide with sufficient refractive index contrast, a polymer of the type described below is locally cured by three-dimensional direct laser writing (DLW), and then a lower-index guest monomer is diffused into an uncured photopolymer matrix. For the manufacturing concept described above, an epoxy-based photopolymer is used, for example. Its main component is an oligomer based on a bisphenol A diglycidyl ether. In addition to a photoinitiator, the photopolymer also contains a γ-butyrolactone (GBL) solvent, which enables the formation of defect-free layers when the polymer film is uniformly distributed on the substrate, e.g., by spin coating.The polymer film is highly transparent at 780 nm but sensitive to 365 nm light. UV curing at a wavelength of 365 nm reduces the refractive index of the uncured film by 0.003. To achieve sufficient index contrast for optical fibers, external diffusion of an aliphatic guest monomer is used, resulting in a further decrease in the refractive index of 0.016. This reduction is due to the lower index of the guest monomer (e.g., in the range of 1.45) compared to the carrier oligomer (e.g., in the range of 1.59). Furthermore, the index of the cured film hardly changes after the diffusion of the guest monomer. In other words, the gaseous monomer barely diffuses into the polymerized, cross-linked film.The concept of this difference in index contrast generation in the uncured and cured film is an exemplary possibility for the fabrication of 3D buried waveguides using multiple photon lithography, also called multiphoton lithography. Multiphoton lithography is also known as direct laser lithography or direct laser writing. Similar to standard photolithography, the structuring is achieved by illuminating negative or positive-toned photographic films with light of a precisely defined wavelength. The invention has the advantage that no optical system is required. Furthermore, no alignment of optical components is necessary, since the positions of the fiber and the waveguide are determined during the fabrication of the optical coupling element, e.g., as part of a system-on-a-chip (SoC). The fabrication process on an SoC is also called an in-situ process. Moreover, the manufacturing process is easily industrialized. The coupling structure of the optical coupling element can be flexibly designed. For example, the structure can be designed as a waveguide, a distributor, or a cone. Finally, the structure is written three-dimensionally with full freeform capability and can be adapted as desired to the positioning, orientation, and design of the fiber exit and the waveguide input. According to an advantageous embodiment of the invention, the at least one fiber is part of a fiber laser, wherein at least one light-emitting surface of the fiber laser is arranged on the surface of the substrate, forming the space between the fiber laser and at least one waveguide input. A fiber laser is a solid-state laser. The fiber laser comprises, for example, a doped core of an optical fiber as the active medium. Fiber lasers are optically pumped, for example, by coupling radiation from diode lasers into the fiber cladding or into the fiber core in parallel with the fiber core. For example, erbium, ytterbium, and neodymium are used for doping the laser-active fiber core. Fiber lasers have electro-optical efficiencies of up to 30%, a beam quality with M2 < 1.1 for single-mode fiber lasers or M2 < 1.2 for double-clad fibers, and long lifetimes exceeding 20,000 years.They can have a lifespan of 000 hours and a compact, maintenance-free, and robust design. Fiber lasers can be operated in pulsed mode down to the femtosecond range. According to an advantageous embodiment of the invention, the waveguide is part of a system-on-a-chip (SoC), wherein the SoC is arranged on the surface of the substrate, forming the space between the at least one fiber exit of the at least one fiber and at least one light entry surface of the SoC. A system-on-a-chip is a system in which all or some of the functions of a programmable electronic system are integrated on a single chip. The aforementioned advantageous embodiment enables a compact design and also facilitates assembly. According to an advantageous embodiment of the invention, the following steps are performed to apply the polymer intermediate to the support substrate: applying a monolithic polymer film to the support substrate; uniformly distributing the polymer film over the support substrate; and solidifying the polymer film, in particular for at least one hour, while the support substrate rests on a heating plate. Conventional fabrication systems for applying and solidifying polymer films can be used in the steps described above, thus enabling cost-effective production. According to an advantageous embodiment of the invention, the following steps are performed to structure the 3D waveguide: structuring a core trajectory in the polymer spacer using 3D laser lithography with multiphoton absorption; at least partial curing of the polymer spacer by baking at 60 °C for 10 minutes; treatment of the polymer spacer in a chamber such that external diffusion of a gaseous monomer occurs in an uncured part of the polymer spacer; UV exposure of the polymer spacer with radiation having a wavelength of 365 nm; and hard baking such that the polymer spacer and the support substrate are stabilized. In other words, the manufacturing steps described above are part of a rapid prototyping process in which the manufacturing steps can be programmed by a computer and thus reproduced. According to an advantageous embodiment of the invention, the coupling element is configured as a deflection unit for a laser scanner. In another advantageous embodiment, the laser scanner is a LiDAR scanner. LiDAR (light detection and ranging), also known as Ladar (laser detection and ranging), is a radar-related method for optical distance and velocity measurement, as well as for remote sensing of atmospheric parameters. LiDAR systems emit laser pulses and detect the backscattered light. The distance to the point of scattering is calculated from the time of flight of the signals. According to an advantageous embodiment of the invention, the 3D waveguide is configured as a splitter and / or a taper. A splitter, also called a beam splitter, is an optical component that divides a single light beam into two partial beams. A taper is an optical component that connects two optical waveguides with different radii. The power transfer of a taper between waveguides of the same numerical aperture (NA) in the direction of the smaller radius occurs such that light from a waveguide with a large core cross-section is removed from the waveguide with the smaller cross-section that cannot fit into the waveguide with the smaller cross-section. This also applies to conical tapers. Conversely, all light from a thinner waveguide can pass into a thicker waveguide with the same NA. According to an advantageous embodiment of the invention, the 3D waveguide is configured as at least one of the following elements and / or comprises the following elements: a waveguide array; a fan-shaped input and output coupling, which is configured in particular with three or four channels; and / or an optical router. In other words, any adaptation of the 3D waveguide to the optical connections of the fiber and the waveguide is possible. According to an advantageous embodiment of the invention, the material of the polymer intermediate is a resin or a photopolymer. The photopolymer can be of the type described above. The aforementioned types of polymer are particularly suitable for the fabrication of a 3D waveguide. The invention is explained in more detail below with reference to the accompanying drawing and preferred embodiments. The features shown can represent an aspect of the invention, either individually or in combination. Features of different embodiments are transferable from one embodiment to another. Fig. 1 shows a flowchart according to an embodiment of the manufacturing process according to the invention, Fig. 2 shows a schematic top view of a coupling element in a first stage of the manufacturing process, Fig. 3 shows a schematic top view of a coupling element in a second stage of the manufacturing process and Fig. 4 shows a schematic top view of a coupling element in a third stage of the manufacturing process. Fig. 1 shows a flowchart according to an embodiment of the manufacturing process according to the invention for an optical coupling element 1 (see Fig. 4 for a possible embodiment of a coupling element 1, which is shown schematically in this figure) for use in a vehicle. The coupling element 1 is configured for coupling laser light from at least one fiber 2 into at least one waveguide 3. The manufacturing process comprises the following manufacturing process steps: First, in step “100”, at least one fiber 2, at least one waveguide 3 and a support substrate 4 are provided (see also Fig. 2, in which fiber 2 and waveguide 3 are already arranged on the support substrate 4). Subsequently, in step “200”, the at least one fiber 2 and the at least one waveguide 3 are attached to a surface of the support substrate 4, forming a space between at least one fiber output 2a of the at least one fiber 2 and at least one waveguide input 3a of the at least one waveguide 3. Then, in step “300”, a polymer spacer 5 is applied to the space on the surface of the support substrate 4 such that the polymer spacer 5 is in direct contact with the at least one fiber output 2a and the at least one waveguide input 3a (see also Fig. 3). Finally, in step “400”, a 3D waveguide 6 is structured into the polymer intermediate 5 using a laser, wherein the 3D waveguide 6 extends from the at least one fiber output 2a to the at least one waveguide input 3a and connects the at least one fiber output 2a with the at least one waveguide input 3a (see also Fig. 4 ). In particular, the manufacturing process provides that at least one fiber 2 is part of a (not shown) fiber laser, wherein the fiber laser would be arranged on the surface of the support substrate 4 forming the space between the fiber laser and at least one waveguide input 3a. In the embodiment of the coupling element 1 of Fig. 4, the waveguide 3 is part of a single-chip system (SoC), wherein the SoC 7 is arranged on the surface of the substrate 4, forming the space between at least one fiber outlet 2a and the SoC 7 (see Fig. 2 and Fig. 3). In the embodiment of Fig. 2, Fig. 3 to Fig. 4, the space is formed between a single fiber outlet 2a of the fiber 2 and a single light entry surface of the SoC 7. Furthermore, it is provided that the following steps are carried out in step "300" to apply the polymer intermediate 5 to the support substrate 4: According to step "310", a monolithic polymer film is applied to the support substrate 4. According to step "320", the polymer film is evenly distributed on the support substrate 4. According to step "330", the polymer film is solidified for at least one hour while the support substrate 4 rests on a heating plate. To structure the 3D waveguide 6 in step "400", the following steps are also performed: According to step "410", a core trajectory is structured in the polymer intermediate 5 using 3D laser lithography with multiphoton absorption. According to step "420", the polymer intermediate 5 is baked at 60 °C for 10 minutes to at least partially cure. According to step "430", the polymer intermediate 5 is treated in a chamber such that external diffusion of a gaseous monomer occurs in an uncured part of the polymer intermediate 5. According to step "440", the polymer intermediate 5 is exposed to UV radiation with a wavelength of 365 nm. According to step "450", a hard baking process is carried out such that the polymer intermediate 5 and the support substrate 4 are stabilized. The manufacturing process described above will be explained in detail below. A multiphoton lithography technique is used to structure the 3D waveguide 6. One example of a lithography technique of the aforementioned type is two-photon lithography. This is a rapid prototyping technique that enables the fabrication of submicron 3D structures in photographic films, such as a photopolymer. In two-photon lithography, erbium-doped fiber lasers are used, for example, which emit ultrashort pulses of 100 femtoseconds at a wavelength of 780 nm with a repetition rate of 80 MHz. An acousto-optic modulator (AOM) is used to control the optical power to a maximum of 70 mW. The laser beam is expanded before being split into a lens and a detector array. The former is a lens with a 63x magnification and a numerical aperture of 0.75. The latter detects sample interfaces and corrects its tilt angles via the intensity of the reflected light.A piezoelectric 3D scanning stage drives the sample and tracks the coordinates specified by the computer. The depth of the laser focus inside the film is calculated taking into account aberration correction and diffraction at the air / paint surface, which is done using calculation methods known to those skilled in the art, in particular using Snell's law. The manufacturing process of the 3D waveguide includes, for example, the following steps: casting, three-dimensional direct laser writing, heat treatment, external monomer diffusion and flood UV exposure with hard baking. After spin coating onto a 2-inch silicon wafer, the gel-like polymer is solidified on a hot plate for several hours. The film adheres to silicon wafers without an adhesion promoter. Subsequently, the time and temperature for a soft-bake step are selected to control the solvent concentration and provide a tack-free surface. Two-photon lithography then follows a programmed trajectory, initiating crosslinking to form the waveguide core. Baking at 60°C for 10 minutes after exposure accelerates crosslinking in an exposed volume of the film. The writing speed varies from 0.1 to 1 mm / s, and the input laser intensity ranges from 5 to 40 mW, resulting in different doses for the crosslinking process.Subsequently, an external diffusion of a gaseous, low-index monomer into the uncured encapsulation takes place in a closed chamber at room temperature. The diffusion time varies from 96 to 168 h for diffusion depths in the range of 40–70 micrometers. UV flood exposure at 365 nm crosslinks the diffused monomer and host oligomer via single-photon absorption. Finally, hard baking of the sample at 140°C for 10 min completely cures the encapsulation and stabilizes the embedded waveguides. The incorporation of the guest monomer (e.g., with a refractive index of nD 1.445) into the host oligomer matrix (with a refractive index of nD 1.59) reduces the refractive index of the encapsulation, resulting in increased index contrast between the core and encapsulation for light guidance. This manufacturing process offers several advantages over other waveguide manufacturing methods. It requires only a single layer of a single material. Multilayer waveguides can be labeled in a single writing step without stacking or alignment. Finally, this rapid prototyping technique eliminates the need for masks, contact printing, or wet chemical process steps such as wet etching. Reference symbol list 1 Coupling element 2 Fiber 2a Fiber output 3 Waveguide 3a Waveguide input 4 Substrate 5 Polymer spacer 6 3D waveguide 7 Single-chip system 100 Providing at least one fiber, at least one waveguide, and one substrate 200 Attaching the at least one fiber and the at least one waveguide to a surface of the substrate 300 Applying a polymer spacer to the space on the surface of the substrate 310 Applying a monolithic polymer film to the substrate 320 Distributing the polymer film evenly on the substrate 330 Solidifying the polymer film for at least one hour while the substrate rests on a hot plate 400 Structuring, using a laser,410 Structuring a core trajectory in the polymer intermediate using 3D laser lithography with multiphoton absorption 420 Baking at 60 °C for 10 minutes to at least partially cure the polymer intermediate 430 Treating the polymer intermediate in a chamber 440 UV exposure of the polymer intermediate with radiation with a wavelength of 365 nm 450 Hard baking,

Claims

Manufacturing process for an optical coupling element (1) intended for use in a vehicle, wherein the coupling element (1) is configured for coupling laser light from at least one fiber (2) into at least one waveguide (3), wherein the manufacturing process comprises the following process steps: - providing at least one fiber (2), at least one waveguide (3) and a support substrate (4) (100); - attaching the at least one fiber (2) and the at least one waveguide (3) to a surface of the support substrate (4) forming a space between at least one fiber exit (2a) of the at least one fiber (2) and at least one waveguide inlet (3a) of the at least one waveguide (3) (200);- Applying a polymer spacer (5) into the space on the surface of the support substrate (4) such that the polymer spacer (5) is in direct contact with the at least one fiber output (2a) and the at least one waveguide input (3a) (300); and - Structuring, by means of a laser, a 3D waveguide (6) into the polymer spacer (5), wherein the 3D waveguide (6) extends from the at least one fiber output (2a) to the at least one waveguide input (3a) and connects the at least one fiber output (2a) with the at least one waveguide input (3a) (400).; Manufacturing method according to claim 1, wherein the at least one fiber (2) is part of a fiber laser, wherein the fiber laser is arranged on the surface of the support substrate (4) forming the space between at least one light-emitting surface of the fiber laser and the at least one waveguide input (3a). Manufacturing method according to claim 1 or 2, wherein the waveguide (3) is part of a single-chip system, SoC, (7), wherein the SoC (7) is arranged on the surface of the support substrate (4) forming the space between at least one fiber exit (2a) and at least one light entry surface of the SoC (7). Manufacturing process according to at least one of the preceding claims, wherein the following steps are carried out to apply the polymer intermediate (5) to the support substrate (4) (300): - applying a monolithic polymer film to the support substrate (4) (310); - uniformly distributing the polymer film on the support substrate (4) (320); and - solidifying the polymer film, in particular for at least one hour, when the support substrate (4) rests on a heating plate (330). Manufacturing process according to at least one of the preceding claims, wherein the following steps are carried out to structure the 3D waveguide (6) (400): - structuring a core trajectory in the polymer spacer (5) using 3D laser lithography with multiphoton absorption (410); - to at least partially cure the polymer spacer (5), baking at 60 °C for 10 minutes (420); - treating the polymer spacer (5) in a chamber (430) such that external diffusion of a gaseous monomer occurs in an uncured part of the polymer spacer (5); - UV exposure of the polymer spacer (5) with radiation having a wavelength of 365 nm (440); and - hard baking (450) such that stabilization of the polymer spacer (5) and the support substrate (4) occurs. Manufacturing method according to at least one of the preceding claims, wherein the coupling element (1) is designed as a deflection unit for a laser scanner. Manufacturing method according to at least one of the preceding claims, wherein the 3D waveguide (6) is designed as a splitter and / or as a taper. Manufacturing method according to at least one of the preceding claims, wherein the 3D waveguide (6) is configured as at least one of the following elements and / or comprises the following elements: a waveguide array; a fan coupling, which is configured in particular with three or four channels; and / or an optical router. Manufacturing process according to at least one of the preceding claims, wherein the material of the polymer intermediate (5) is a resin or a photopolymer. Optical coupling element (1) for a laser scanner in a vehicle, having properties generated by process steps according to at least one of the preceding claims. Vehicle comprising a laser scanner with an optical coupling element (1) according to the aforementioned claim. Laser scanner with the optical coupling element (1) intended for use in a vehicle according to claim 10. Computer program comprising instructions which, when executed by a computer, cause the computer to execute a manufacturing process according to at least one of claims 1 to 9. Data carrier signal that the computer program transmits according to the aforementioned claim. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to execute a manufacturing process according to at least one of claims 1 to 9.

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