Coupling connector for transmitting light signals

Abstract

The invention relates to a coupling connector for transmitting light signals between an optical fiber (11) and a semiconductor circuit (15), wherein the coupling connector comprises a liquid crystal element (12) for steering a light beam incoming via the optical fiber (11), which element is configured to couple the incoming light beam into a light coupling unit (14) arranged in the semiconductor circuit.

Description

[0001] Description

[0002] Coupling plug for transmitting light signals

[0003] The present invention relates to a coupling connector for transmitting light signals between an optical fiber and a semiconductor circuit, which can be used, for example, for a photonic radar system. The present invention further relates to a photonic arrangement with such a coupling connector, a radar system with such a photonic arrangement, and a vehicle comprising a radar system with such a photonic arrangement.

[0004] For driver assistance and safety systems in fully automated driving, the safest possible perception of the surroundings is essential. This is achieved by using sensors such as radar, lidar, and camera sensors integrated into the vehicle to capture the environment. Based on the collected sensor data, an environmental model can then be created. While cameras provide detailed visual information and enable the recognition of traffic signs, lane markings, and colors, for example, they deliver poor results in unfavorable lighting conditions, fog, or glare, and provide only inadequate distance information. Lidar-based systems, while capable of precise distance measurement, are expensive and susceptible to weather conditions. Radar sensors, on the other hand, deliver reliable and fail-safe data in all weather conditions.However, the resolution of radar sensors currently in series production in the automotive sector is limited.

[0005] Currently under development are so-called photonic radar systems, in which driver signals in the GHz range can be distributed to a multitude of radar sensors via one or more optical fibers using an optical carrier signal in the THz frequency range. This allows for the co-integration of electronic and photonic components on a single semiconductor chip, enabling extremely compact form factors for individual radar sensors and, consequently, arrays with numerous such radar sensors integrated into the vehicle. When transmitting signals from an optical fiber into photonic structures on a semiconductor chip, the coupling of optical signals, particularly with single-mode fibers, is extremely sensitive to translational beam misalignment, rotation, and polarization of the incident light beam due to the small fiber core diameter.Several techniques are known for coupling electromagnetic radiation onto the coupling structure of a semiconductor chip. In edge coupling, the fiber end with its core is brought close to a waveguide embedded in the semiconductor, so that the electromagnetic radiation, after emission at the fiber end, is focused onto the waveguide and coupled into the semiconductor. Another technique for fiber-to-chip coupling uses a grating coupler. Here, the fiber is directed at the chip at a precisely maintained angle. The chip contains an optical grating structure that couples the electromagnetic radiation into the waveguide integrated within the semiconductor. The high degree of accuracy required in positioning the fiber relative to the chip, as well as the tight tolerances in angular acceptance, necessitates highly precise positioning methods to achieve all six degrees of freedom.Because the methods used iteratively optimize the positioning, they are very time-consuming.

[0006] Furthermore, it is known to transmit light signals from an optical fiber to a semiconductor chip using liquid crystals (LC) located on the chip. However, integrating an LC element onto a semiconductor requires additional steps in semiconductor manufacturing, thus significantly increasing manufacturing complexity. A semiconductor chip with an integrated optical coupling grating, in which a switchable liquid crystal polarizing grating directs a light beam arriving from the optical fiber into the optical coupling grating, is described in EP2823343 A1.

[0007] It is an object of the invention to provide a connection of optical fibers to semiconductor circuits such as photonic or electronic-photonic semiconductor chips, which eliminates the aforementioned disadvantages.

[0008] This problem is solved by the independent claims. Preferred embodiments of the invention are the subject of the dependent claims.

[0009] According to one aspect of the invention, a coupling connector is provided for transmitting light signals between an optical fiber and a semiconductor circuit, wherein the coupling connector comprises a liquid crystal element for beam control of a light beam entering via the optical fiber, which is configured to couple the incoming light beam into a light coupling unit arranged in the semiconductor circuit.

[0010] This enables fiber-to-chip coupling with high coupling tolerance. When optical fibers are automatically connected to semiconductor circuits such as photonic or electro-photonic semiconductor chips, the time required for low-loss coupling can be significantly reduced. This can result in considerable time savings and thus significant cost advantages, especially when using devices manufactured in high-volume series production.

[0011] According to one embodiment of the invention, the optical fiber is connected to the coupling connector, wherein in the coupling connector one end of the optical fiber is arranged in front of the liquid crystal element in such a way that the incoming light beam is coupled into the liquid crystal element via the optical fiber transversely to the liquid crystal element arranged opposite each other in the coupling connector and the light coupling unit of the semiconductor circuit.

[0012] Preferably, electrodes are arranged in the coupling connector which are configured to apply an electrical voltage to the liquid crystal element, whereby the refractive index changes depending on the applied voltage by changing the orientation of liquid crystals in the liquid crystal element.

[0013] In particular, applying an electrical voltage to the electrodes allows the refractive index of the liquid crystals in the liquid crystal element to be adjusted to the refractive index of a wall of the liquid crystal element in the direction of the semiconductor circuit, which enables signal transmission into the optical coupling unit of the semiconductor circuit.

[0014] Furthermore, the power of the light signal coupled into the optical coupling unit can advantageously be optimized by regulating the electrical voltage applied to the electrodes.

[0015] According to a further aspect of the invention, a photonic arrangement is provided which comprises a coupling connector according to the invention and a semiconductor circuit, wherein the electrodes arranged in the coupling connector are designed such that an electrical control signal can be transmitted to the liquid crystal element by contacting electrodes of the semiconductor circuit and wherein the refractive index of the liquid crystal element can be controlled based on the electrical control signal.

[0016] Preferably, in such a photonic arrangement, the coupling connector is connected to the semiconductor circuit or a carrier for electronic components on which the semiconductor circuit is arranged by means of a fastening means.

[0017] In particular, the semiconductor circuit can be designed as an electronically-photonically cointegrated chip, in which several electronic and photonic components are integrated in one integrated circuit.

[0018] According to a further aspect of the invention, a radar system is provided which comprises one or more radar sensors and a central unit which exchange signals via an optical fiber, wherein the radar sensors and / or the central unit are connected to the optical fiber via a coupling connector according to the invention.

[0019] Finally, the invention also includes a vehicle that has such a radar system.

[0020] Further features of the present invention will become apparent from the following description and the claims in conjunction with the figures. These show:

[0021] Fig. 1 a schematic representation of a fiber-to-chip coupling using a liquid crystal element with guiding of the coupled electromagnetic radiation in the liquid crystal element (A) and coupling into an adjacent electronically-photonically cointegrated chip (B);

[0022] Fig. 2 shows a schematic representation of a coupling plug according to the invention;

[0023] Fig. 3 shows a schematic representation of a compact embodiment of a coupling plug according to the invention;

[0024] Fig. 4 shows a schematic representation of a coupling connector attached to an electronically-photonically cointegrated chip by means of adhesive; Fig. 5 shows a schematic representation of a coupling connector attached to an electronically-photonically cointegrated chip by means of mechanical fastening; and

[0025] Fig. 6 shows a schematic representation of a control loop integrated in an electronically-photonically cointegrated chip for optimal coupling of the optical signal.

[0026] To better understand the principles of the present invention, embodiments of the invention are explained in more detail below with reference to the figures. It is understood that the invention is not limited to these embodiments and that the described features can also be combined or modified without departing from the scope of protection of the invention as defined in the claims.

[0027] Figure 1 schematically illustrates the basic principle of fiber-to-chip coupling using a liquid crystal element. The coupling connector according to the invention is not shown in this figure, but is explained in detail in connection with the other figures.

[0028] The end of an optical fiber 11 for optical data transmission is connected to a liquid crystal element 12 or arranged in the immediate vicinity in front of the liquid crystal element 12, wherein the liquid crystal element 12 is provided on or in a semiconductor circuit 15.

[0029] The semiconductor circuit 15 can, in particular, be an electronically-photonically cointegrated chip (EPIC). Silicon photonics technology can be used for the cointegration of the electronic and photonic components, enabling the monolithic integration of photonic devices, high-frequency electronics, and digital electronics on a single chip. The integration of optical components into the chip can be implemented, for example, using so-called silicon-on-insulator (SOI) regions, while the integration of electronic components can be achieved using so-called bulk silicon regions. In SOI regions, a thin silicon layer is separated from the silicon substrate by an insulating layer, for example, made of silicon dioxide.Since silicon is transparent in the near-infrared at the common wavelengths used in optical communication technology, and since the refractive indices of silicon and silicon dioxide differ significantly in this wavelength range, various optical components can be implemented using SOI structures. This allows for high signal quality with low parasitic interference, especially at high data rates. Alternatively, other integration methods, such as hybrid integration using separate photonic and electronic chips, can also be implemented.

[0030] A light signal arriving via the optical fiber 11 is coupled into the liquid crystal element 12 and propagated within the liquid crystal element, as indicated in Figure 1A by the propagating light beam 13. The light is guided through the liquid crystal element by total internal reflection at the walls of the liquid crystal element.

[0031] Below the liquid crystal element is a light coupling unit 14 arranged in the semiconductor circuit 15. The light coupling unit 14 can be configured, in particular, as a grating coupler, which can couple the electromagnetic radiation into a waveguide integrated in the semiconductor circuit. Such a grating coupler consists of a regular grid structure, for example in the form of lines or holes, on the surface of the chip. When light strikes this grid structure, it is diffracted towards the optical waveguide on the semiconductor circuit. For the light to be efficiently transferred from the grid to the waveguide, the angle of incidence of the light must be chosen such that it constructively interferes with the waveguide and is then transmitted there with minimal losses.Diffraction and interference are strongly dependent on the angle of the coupled light; even small angular deviations on the order of just a few degrees can lead to significant coupling losses. A small error in the angle of incidence causes the phase of the diffracted light to change, thus weakening constructive interference. If the angle deviates too much from the ideal value, destructive interference occurs, resulting in poor or no coupling of the light into the waveguide.

[0032] If the refractive index of the liquid crystal element in the area of ​​the light coupling unit 14 is suitably changed and thereby adapted to the refractive index of the adjacent material, the radiation can couple into the waveguide integrated in the semiconductor, as shown in Figure 1 B by the propagating light beam 13'.

[0033] This process utilizes the property of liquid crystals that when a voltage is applied, the liquid crystal molecules align, thereby changing the refractive index for transmitted light. This is due to the anisotropy of the liquid crystal molecules, which results from their elongated shape and means that their physical properties, such as the refractive index, depend on the orientation of the molecules. When a voltage is applied, the electric field exerts a force on the molecules, changing their orientation. In the resting state, i.e., without an applied voltage, the molecules in the illustrated example are oriented parallel to the surface of the liquid crystal element. The light propagating through the liquid crystal element strikes the liquid crystal molecules at a specific angle and experiences a refractive index corresponding to the orientation of the liquid crystal molecules.

[0034] When a voltage is applied to the liquid crystal element, the elongated liquid crystal molecules align themselves with the resulting electric field, with the change in orientation increasing with increasing voltage. This change in the orientation of the liquid crystal molecules affects the refractive index for the transmitted light, so that by precisely adjusting the voltage, the effective refractive index can be continuously changed, thus influencing the propagation of light within the material. If the refractive index in the liquid crystal is matched to the refractive index of the adjacent material, a process also known as index matching, the light can pass through unimpeded. In this way, in the arrangement shown in Figure 1B, the electromagnetic radiation can be coupled into the light coupling unit 14, for example in the form of a grating coupler, in the semiconductor circuit 15.By appropriately generating a locally varying electric field, the direction of propagation of the light and thus the angle of incidence of the light into the grating coupler can also be varied in the liquid crystals and adapted to the optimal angle of incidence.

[0035] The following figures schematically illustrate various embodiments of a coupling connector according to the invention, which is based on the integration of a liquid crystal element within the coupling connector. For clarity, a coupling connector for a connection with a single optical fiber is described, but the invention is equally applicable to a connection with multiple optical fibers. The optical fiber can be, in particular, a single-mode or multi-mode optical fiber.

[0036] Figure 2 schematically depicts a first embodiment of a coupling connector according to the invention, which is connected to a semiconductor circuit, for example in the form of an electronically-photonically cointegrated chip. An optical fiber 11 is arranged in a housing 21 of the coupling connector and is secured by a fixing means 22, for example by bonding it to the cladding of the optical fiber, such that it does not move and its position is precisely determined. At least one liquid crystal element 12 is integrated into the coupling connector to couple the optical signals transmitted by the optical fiber into the light coupling unit 14 of the semiconductor circuit 15 and to adjust the propagation direction of these signals.In this case, additional optical elements not shown, for example for focusing the light exiting the optical fiber onto the entrance surface of the liquid crystal element, can be arranged between the end of the optical fiber 11 and the liquid crystal element 12.

[0037] Furthermore, one or more electrodes 23 are integrated into the coupling connector. These electrodes 23 allow an electrical control signal to be transmitted to the liquid crystal element 12 by contacting the coupling connector with electrodes 24 on the semiconductor circuit 15. Based on this electrical control signal, the liquid crystal element 12 can be controlled to regulate the electric field generated within it. Signal coupling can be optimized by means of an electrical connection 25 to a downstream control circuit. For this purpose, an electro-optical feedback loop, described below, can be used in the semiconductor circuit, whereby the offset of the optical radiation in all three axes and the three solid angles can be changed to ensure optimal coupling into the semiconductor circuit.

[0038] The coupled light signal can then be supplied to one or more photonic components (not shown) that are also integrated in the semiconductor circuit 15 via a waveguide 26 integrated in the semiconductor circuit 15.

[0039] Figure 3 shows a second embodiment of a coupling connector according to the invention. The integrated components correspond to those of the first embodiment and are therefore provided with the same reference numerals and are not explained again in detail.

[0040] In the second embodiment, the optical fiber 11 and the liquid crystal element 12 are also integrated into the coupling connector, but they are arranged differently relative to each other. Here, too, the optical fiber is connected to the coupling connector by means of a fixing element. In the coupling connector, the end of the optical fiber is positioned in front of the liquid crystal element 12 such that the incoming light beam is coupled into the liquid crystal element 12 perpendicular to the opposing liquid crystal element and the optical coupling unit of the semiconductor circuit. Compared to the first embodiment, this results in the coupling of the light signal transmitted by the optical fiber into the liquid crystal element 12 at a 90° angle.In this way, a particularly compact design is achieved, making this embodiment particularly suitable, for example, for coupling a large number of antenna chips of a photonic radar system with a central unit of this radar system.

[0041] The coupling connector can be attached to the semiconductor circuit in various ways. An advantageous embodiment, in which the coupling connector is attached to an electronically-photonically cointegrated chip 15 using adhesive 41, is shown in Figure 4. The adhesive can completely cover the housing 21 of the coupling connector and a portion of the optical fiber 11, thus significantly reducing the risk of the optical fiber being pulled out or kinked. Such an adhesive bond offers further advantages. It provides a permanent, stable mechanical connection, minimizing disruptive effects that could arise from mechanical movements such as vibrations or temperature fluctuations.Since the bonding does not require any additional adapters or brackets, it allows for a compact design and can be mass-produced more easily and cost-effectively than other joining methods.

[0042] Another advantageous embodiment, in which the coupling connector is mechanically attached to an electronically-photonically cointegrated chip 15 by means of a holder 51, is shown in Figure 5. The holder 51 can, for example, be designed as a clamp-shaped housing that is open on one side. The coupling connector is arranged on the inside of the housing, with the optical fiber 11 passing through the corresponding side of the housing. The housing can then be mechanically connected to a carrier for electronic components 52, on which the electronically-photonically cointegrated chip 15 is arranged. The carrier for electronic components 52 can, for example, be designed as a semiconductor substrate, a printed circuit board (PCB), or a flexible printed circuit board (FPC). Such a mechanical connection also offers numerous advantages.This allows for easier disassembly or removal compared to adhesive bonding, thus simplifying systems that require regular maintenance or component replacement. With a suitable material selection for the mechanical connection, it is less susceptible to failure than adhesive bonding, as it avoids cracks or stresses caused by temperature fluctuations. Since no curing time is required for adhesive bonding, the connection can be made more quickly during manufacturing. Figure 6 schematically shows a control loop integrated into an electronically-photonically cointegrated chip for optimal coupling of the optical signal. Here, a portion of the optical signal coupled into the electronically-photonically cointegrated chip via a liquid crystal element is used to control the liquid crystal element through a control circuit.In the figure, electrical connections are represented by solid lines and optical connections, for example by waveguides, are represented by dashed lines for differentiation.

[0043] The optical signal is fed into the electronically-photonically integrated chip 15 via the liquid crystal element 12 to an optical beam splitter or switch 61, which splits the optical signal into two partial beams. One partial beam is then fed to one or more components 62 of the electronically-photonically integrated chip 15 to process the signal content transmitted with the optical signal. The second partial beam is fed to a photodiode 63 to convert the split partial beam into an electrical signal. The output signal of the photodiode is then fed to a control unit 64, which generates a control signal for optimal coupling of the optical signal into the electronically-photonically integrated chip 15.The control unit 64 then transmits a corresponding electrical control signal via electrodes on the semiconductor circuit to the liquid crystal element 12 in order to correct unintended changes in intensity, frequency, and / or phase in a control loop. This allows, for example, coupling losses caused by vibrations or temperature changes to be compensated for, thus ensuring stable operation over the long term, even under changing conditions. Furthermore, the control signal can be made available to other electrical components via another output of the control unit 64, such as a central processing unit for data generated by various vehicle sensors.

[0044] The coupling connectors according to the invention can be used in various technical fields where light signals need to be efficiently transmitted from an optical fiber to photonic circuits. In particular, the coupling connectors according to the invention can also be used for photonic radar systems integrated into any road vehicle, such as passenger cars, commercial vehicles, trucks, or buses. Application in conjunction with other vehicle sensors is also possible. (List of reference numerals)

[0045] Optical fiber

[0046] Liquid crystal element, 13' light beam

[0047] Light coupling unit

[0048] Semiconductor circuit

[0049] Housing

[0050] Fixative

[0051] electrode

[0052] electrode electrical connection

[0053] Waveguide

[0054] Adhesive bonding, mechanical fastening

[0055] Carrier for electronic components, optical beam splitter, chip component

[0056] Photodiode

[0057] Control unit

Claims

Patent claims 1. Coupling connector for transmitting light signals between an optical fiber (11) and a semiconductor circuit (15), wherein the coupling connector comprises a liquid crystal element (12) for beam control of a light beam entering via the optical fiber (11), which is configured to couple the incoming light beam into a light coupling unit (14) arranged in the semiconductor circuit.

2. Coupling connector according to one of the preceding claims, wherein the optical fiber is connected to the coupling connector and in the coupling connector an end of the optical fiber is arranged in front of the liquid crystal element (12) such that the incoming light beam is coupled into the liquid crystal element (12) via the optical fiber (11) transversely to the liquid crystal element (12) arranged opposite each other in the coupling connector and the light coupling unit (14) of the semiconductor circuit.

3. Coupling connector according to claim 1 or 2, wherein electrodes are arranged in the coupling connector which are configured to apply an electrical voltage to the liquid crystal element (12), wherein, depending on the applied voltage, the refractive index changes by changing the orientation of liquid crystals in the liquid crystal element (12).

4. Coupling connector according to claim 3, wherein by applying the electrical voltage to the electrodes an adjustment of the refractive index of the liquid crystals in the liquid crystal element to the refractive index of a wall of the liquid crystal element in the direction of the semiconductor circuit takes place, which enables signal transmission into the light coupling unit (14) of the semiconductor circuit.

5. Coupling plug according to claim 4, wherein the power of the light signal coupled into the light coupling unit (14) is optimized by regulating the electrical voltage applied to the electrodes.

6. Photonic arrangement comprising a coupling connector according to one of claims 3 to 5 and a semiconductor circuit, wherein the electrodes arranged in the coupling connector are designed such that an electrical control signal can be transmitted to the liquid crystal element (12) by contacting electrodes of the semiconductor circuit and wherein the refractive index of the liquid crystal element (12) can be controlled based on the electrical control signal.

7. Photonic arrangement according to claim 6, wherein the coupling connector is connected by a fastening means to the semiconductor circuit or a carrier for electronic components on which the semiconductor circuit is arranged.

8. Photonic arrangement according to claim 6 or 7, wherein the semiconductor circuit is designed as an electronically-photonically cointegrated chip in which several electronic and photonic components are integrated in one integrated circuit.

9. Radar system comprising one or more radar sensors and a central unit which exchange signals via an optical fiber (11), wherein the radar sensors and / or the central unit are connected to the optical fiber via a coupling connector according to one of claims 1 to 5.

10. Vehicle comprising a radar system according to claim 9.

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