WO2021175969A1

WO2021175969A1 - System with optical carrier distribution

Info

Publication number: WO2021175969A1
Application number: PCT/EP2021/055418
Authority: WO
Inventors: Stephan Kruse; Johannes Christoph SCHEYTT
Original assignee: Universität Paderborn
Priority date: 2020-03-04
Filing date: 2021-03-04
Publication date: 2021-09-10
Also published as: DE102020202771A1; CN115349230A

Abstract

The invention relates to a system with optical carrier distribution with a return channel without local oscillator, having a base station with a laser source (LD), with light of the laser source (LD) being distributed among one or more distant front-end devices, the front-end device furthermore having an output device which outputs a transmission signal under control by the received laser light of the laser source (LD), and a recording device which records a backscattered transmission signal, wherein part of the received laser light of the laser source (LD) is made available at an optical IQ generator for generating phase-shifted signals, wherein the received backscattered transmission signal is mixed with the signals of the IQ generator and returned to an evaluation device in the base station. The invention furthermore relates to a system with optical carrier distribution with a return channel without local oscillator, having a base station with a laser source (LD), with light of the laser source (LD) being distributed among one or more distant front-end devices, the front-end device furthermore having a recording device which records a reception signal, wherein part of the received laser light of the laser source (LD) is made available at an optical IQ generator for generating phase-shifted signals, wherein the reception signal is mixed with the signals of the IQ generator and returned to an evaluation device in the base station.

Description

System with optical carrier distribution

The invention relates to a system with optical carrier distribution.

background

In many areas of technology, signals are received from a front end and transmitted to a base station via a connection.

Using the example of wireless group antennas, a number of problems will be discussed below, which can also be at least partially present in other systems, e.g. from communications engineering, and for which the invention can likewise provide advantageous solutions.

From a number of publications, for example from "Demonstration of a microwave photonic synthetic aperture radar based on photonic-assisted signal generation and Stretch Processing," by Li et al, in Opt. Express 25, 14334-14340 (2017), "A. Fully Photonics-Based Coherent Radar System, "by Ghelfi et al, in Nature, vol. 507, pp. 341 EP -, Mar 2014, "Optical Signal Generation and Distribution for Large Aperture Radar in Autonomous Driving," by Preusler et al., In 12th German Microwave Conference (GeMiC), Stuttgart, Germany, 2019, pp. 154-157, and "Photonics-based broadband radar for high-resolution and real-time inverse synthetic aperture imaging", by Zhang et al, in Opt. Express 25, 16274-16281 (2017) are wireless systems with phased array antennas known on wireless RF transmitting and receiving circuits which are partially synchronized with an optical carrier which is generated in a base station. The signal processing of the received data also takes place in this base station. The analog signal path from the HF receiver to the base station is made with a glass fiber. From US Pat. No. 9,823,540 B2 a system for the optical transmission of IQ signals is known which uses a separate laser diode for each IQ path.

The disadvantage of such systems is that one laser is required for each HF receiver in order to generate the IQ signal. The IQ generation was also implemented using a DSP and phase shifter. Since the DSP works with digital signals, whereas the phase shifters require analog signals, a digital to analog converter (DAC) and an analog to digital converter (ADC) are required. Thus, N + 1 laser diodes are required for the entire system, where N is the number of RF receivers.

From the document "A Fully Photonics-Based Coherent Radar System" mentioned at the beginning, a system with an optical carrier is known that uses a coaxial line for the path from the RF receiver to the base station.

The disadvantage of such systems is that coaxial cables are heavy and contain comparatively expensive materials. In addition, coaxial cables also have high attenuation and are also susceptible to electromagnetic interference. The manufacture and wiring of coaxial cables is also expensive. Furthermore, the rapid degradation caused by environmental influences is a major problem for signal transmission.

A system with optical carriers is known from the document mentioned at the beginning, "Demonstration of a microwave photonic synthetic aperture radar based on photonic-assisted signal generation and stretch processing," that the data for the path from the RF receiver to the base station is transmitted via an optical return channel sends. A second laser was used to implement the optical carrier for the return channel. In order to have both the transmitted and the received signal in the base station, the laser signal was divided into two paths, the two paths being polarized by 90 ° to one another. A coherent detection based on the polarization of the laser light then took place in the base station. Thus, N + 1 laser diodes are required for the entire system, where N is the number of RF receivers. The disadvantage of such systems is that the system requires a further local oscillator (LO) laser per HF receiver. Since these LO lasers cannot be monolithically integrated into the chip, the costs for the overall system increase. Furthermore, the power dissipation is high in a solution with multiple lasers. In addition, the method of coherent detection by means of polarization mentioned in the document is not suitable for integration in, for example, silicon photonic circuits, since only TE-polarized light can propagate in silicon-based photonic circuits.

A system with optical carriers is known from the publication "Photonics-based broadband radar for high-resolution and realtime inverse synthetic aperture imaging" mentioned at the beginning, which uses an optical return channel for the path from the RF receiver to the base station.

The disadvantage of such systems is that an optical bandpass is required in the return channel from the RF receiver to the base station. Since each path requires a separate bandpass, this solution is very costly for discrete systems. Furthermore, the carrier has to be recovered from the phase-modulated signal by means of complex processing in order to get the IQ signal, which is very computationally intensive and therefore consumes a lot of power. Furthermore, fast analog-to-digital converters are required, which are also cost-intensive. However, it must also be taken into account here that fast phase shifters and their drivers or a wavelength control must be available, since the signal in the HF range must be sent back to the base station. Therefore, the frequency band in which the wireless system can operate is limited by the speed of the phase shifter. If the wavelength of the laser is changed, a lot of energy is also required, since the change in wavelength is achieved by heating the laser.

The invention has set itself the task of avoiding one or more problems from the prior art, in particular of offering a cost-effective solution.

The object is achieved by a system with optical carrier distribution according to one of the independent claims. Advantageous configurations are the subject of the dependent claims, the description and the figures.

The invention is explained in more detail below with reference to the figures. In this shows: Fig. 1 is a block diagram of a (wireless) system according to the invention with optical carrier distribution (for phase-controlled group antennas) with IQ return channel without local oscillator according to embodiments of the invention,

Fig. 2 is a block diagram of a (wireless) system according to the invention with optical carrier distribution with IQ return channel without local oscillator according to a wide Ren embodiments of the invention

3 shows a first embodiment of an optical IQ generator with optical directional couplers and phase shifters for fine tuning according to embodiments of the invention; and

4 shows a second embodiment of an optical IQ generator with 1x2 MMI and phase shifters according to embodiments of the invention.

The invention will be illustrated in more detail below with reference to the figures. It should be noted that different aspects are described that can be used individually or in combination. That is, any aspect can be used with different embodiments of the invention unless explicitly shown as a pure alternative.

Furthermore, for the sake of simplicity, reference will generally only be made to one entity in the following. Unless explicitly noted, the invention can also have several of the entities concerned. In this respect, the use of the words “a”, “an” and “an” is only to be understood as an indication that at least one entity is used in a simple embodiment.

Insofar as methods are described below, the individual steps of a method can be arranged and / or combined in any order, unless the context explicitly results in something different. Furthermore, the processes can be combined with one another, unless expressly indicated otherwise.

Figures with numerical values are generally not to be understood as exact values, but also include a tolerance of +/- 1% up to +/- 10%. References to standards or specifications are to be understood as referring to standards or specifications that apply at the time of filing and / or - if priority is claimed - at the time of filing for priority. However, this is not to be understood as a general exclusion of applicability to the following or replacing standards or specifications.

FIG. 1 shows a (wireless) system 1 with optical carrier distribution (for phase-controlled group antennas) with a return channel without a local oscillator.

The (wireless) system has a base station with a laser source LD. Light from the laser source LD can be distributed to one or more remote front-end devices FEi ... FEN. The laser source LD can be a suitable laser, for example a semiconductor laser diode, which provides, for example, light of approximately 1310 nm or 1550 nm.

The front-end devices FEi ... FE _N each have, for example, at least one output device ANTtc which, controlled by the received laser light from the laser source LD, outputs a transmission signal. The transmission signal can also be amplified by means of a power amplifier PA. The delivery device ANTTX can be, for example, a transmitting antenna.

Without loss of generality, the transmission signal can also be modulated, e.g. using IQ data. Without restricting the generality, the transmission signal can also include an up-mixing of the received signal.

_{Without loss of generality, the light ELD of the laser source LD can be modulated E M} z in the base station BS before it is distributed to one or more remote front-end devices (FEI... _N).

Furthermore, the front-end devices FEi ... FE _N each have at least one recording device ANTRX, which records a received signal. The receiving device ANTRX can be, for example, a receiving device. By means of a suitable structure and wiring, it can also be provided that a single antenna is used as a transmitting antenna and as a receiving device in an alternating manner. In other words, at a first point in time / time period the antenna is used as a transmitting antenna ANT ™ and at a second point in time / time period the antenna is used as a receiving device ANTRX. As an alternative to this, an embodiment would also be possible in which, for example, as in the case of a circulator, a single antenna can act simultaneously as a transmitting antenna and as a receiving device.

In a front-end device FEi ... FEN, part of the received laser light from the laser source LD is made available to an optical IQ generator OIQ for generating phase-shifted signals.

The received signal can now be mixed in the front-end device FEi ... FE _N with the signals from the IQ generator OIQ and fed back to an evaluation device in the base station BS. Received signals can be amplified using a low-noise amplifier LNA.

It should be noted at this point that the front-end device FEi ... FE _N can be both a concentrated device, as shown. Alternatively, however, it is also possible _{to distribute the front-end device FEi ... FE N} so that, for example, one sub-device has components of the transmission branch and another sub-device has components of the reception branch.

That means, unlike before, only a single laser source LD is now required for a large number of front-end devices FEi ... FEN, which is also available for the return channel. In addition to the lower hardware expenditure that results from this, there are also lower operating costs and further advantages, as will be explained below.

The architecture presented in Fig. 1 or 2 sends IQ data from a (eg wireless) front-end device FEi ... FE _N optically back to the base station BS without having to own a LO laser itself. The laser signal of the optical carrier distribution is used again for this purpose. For this purpose, the optical carrier is divided between the various front-end devices FEi ... FEN at (5) in the base station BS. In Each front-end device FEi ... FEN is divided in (3) the optical signal on the transmitter part with the photodiode and the return channel.

In the return channel, the reused carrier signal can be converted into an IQ signal in the optical IQ generator OIQ. The signals Ei and EQ are multiplied with their corresponding electrical signals Vi and V _Q, for example in Mach Zehnder interferometers (abbreviated to MZI) and added in (4) in order to then return the signals to the base station, for example via a glass fiber.

Furthermore, the system can also be implemented in silicon photonic circuits, since the system can work with purely TE-polarized light in addition to mixed polarized light. In addition, no fast analog-digital converters or digital-analog converters are required, since the optical signal to be detected is only in the bandwidth of the electrical LO signal.

This embodiment is suitable, for example, for radar systems.

In a further embodiment of the invention, which is of interest, for example, for communications engineering, a (wireless) system 1 with optical carrier distribution with a return channel without a local oscillator according to FIG. 2 is again provided.

The system in turn has a base station BS with a laser source LD, with light from the laser source LD being distributed to one or more remote front-end devices FEi ... FE _N , the front-end device FEi ... FE _N also _{having a receiving device ANT RX} , which picks up a received signal, part of the received laser light from the laser source LD being made available to an optical IQ generator OIQ for generating phase-shifted signals, the received signal being mixed with the signals from the IQ generator OIQ and sent to an evaluation device in the base station BS is returned.

It should be noted again at this point that the front-end device FEi ... FEN can be both a concentrated device, as shown. Alternatively, however, it is also possible to distribute the front-end device FEi ... FEN, so that, for example, one sub-device has components of the transmission branch and another sub-device has components of the reception branch. In configurations of the embodiments, the light from the laser source LD is distributed _{to the remote front-end devices FEi... FE N via a glass fiber or a free space connection.} It is also possible, as an alternative or in addition, to route the signal in the reverse direction to the base station BS from the front-end devices FEi ... FEN via a glass fiber or a free space connection.

In a further refinement of the embodiments, part of the laser light from the laser source LD is branched off in the base station BS and made available to the evaluation device AE.

In a further development of this embodiment, the base station BS furthermore has a phase shifter which makes the branched off part of the laser light from the laser source LD available to the evaluation device AE with a phase shift.

In (1) a part of the optical carrier can be derived and made available as a source signal for the signal Es. The splitting off can take place before, after or during the splitting for the different receiving paths, e.g. in (5).

Thus, only one single laser LD is necessary for the entire system with any number of front-end devices FEi ... FE _N. A coherent detection can then take place in the base station BS.

This is a simple implementation possible, since only the phase offset between the base station BS and the front-end device FEi ... FE _N and back needs to be compensated. The electrical in- and quadrature-phase signals are regenerated from the signal Eo in the photodiodes PD and the transimpedance amplifier (abbreviated to TIA).

This has the advantage that only the phase offset from the base station BS to the respective front-end device FEi ... FEN and back to the base station BS has to be compensated for. In addition, there is no need to compensate for a frequency offset between different lasers. This also makes it possible to dispense with computationally intensive carrier recovery, for example by means of DSP. In addition, no costly and complex wavelength regulation of the laser is required. That is, the inventive The system makes it possible to implement a coherent IQ modulation between front-end devices FEi ... FE _N and base station BS in a cost-effective manner.

The optical IQ generator can be designed in a suitable analog or digital manner. Two analogous variants are presented below, but without being restricted to these.

In a further refinement of the embodiments, the optical IQ generator OIQ has optical directional couplers RK and phase shifter PS. Such an implementation is shown as a principle sketch in FIG. Again, all components of the optical IQ generator OIQ can be integrated on one chip. Since the optical directional coupler already generates a phase difference of 90 °, with this type of optical IQ generation OIQ the phase shifters only have to compensate for environmental influences and therefore the expected control voltage is small.

In an alternative configuration of the embodiments, the optical IQ generator OIQ has a multi-mode interferometer (MMI) and phase shifter. Such an implementation is shown as a principle sketch in FIG. Again, all components of the optical IQ generator OIQ can be integrated on one chip. Since a 1x2 MMI does not generate a phase difference between the two outputs, the phase shifters must generate the phase difference of 90 ° with this type of optical IQ generation.

In a further embodiment, the embodiments of the removed front terminals FEi ... FE _N is changed a part of the received laser light from the laser source LD before the recycling to the evaluation in the base station by mixing and / or modulating in at least one order, for example an IQ modulation with or without realizing data.

In a further embodiment, the phase position can be set, preferably in the base station BS, for example by means of a phase shifter PS. However, it would also (alternatively or additionally) be possible to influence the phase position in a front-end device FEi ... FEN with an effect on the returned signals. In this case, for example, the necessary phase setting information would have to reach the associated front-end device FEi... FE _N via a further signal from the base station BS for coherent reception. In yet another embodiment of the invention, light from the laser source LD, which is intended for distribution to one or more remote front-end devices (FE1... N), is amplified by an amplifier device, for example a fiber amplifier. The invention makes it possible, by means of a single laser LD, to _{synchronize any number of front-end devices FEi ... FE N} ZU, and at the same time to implement an optical IQ path from the receiver to the base station BS. Furthermore, a coherent detection can take place in the base station BS, as a result of which the IQ signals can be regenerated again from the single laser signal. Without restricting the generality, the invention is also not restricted to wireless systems.

Rather, it can also be used in wired systems.

Claims

1. System (1) with optical carrier distribution with return channel without local oscillator, comprising a base station (BS) with a laser source (LD), with light from the laser source (LD) being sent to one or more remote front-end devices

are distributed, the front-end device further comprising an output device (ANT c) which, controlled by the received laser light from the laser source (LD), outputs a transmission signal, and a recording device (ANTRX) which picks up a backscattered transmission signal, with part of the received laser light from the laser source (LD) is made available to an optical IQ generator (OIQ) for generating phase-shifted signals, the received backscattered transmission signal being mixed with the signals from the IQ generator (OIQ) and being sent to an evaluation device (AE) in the base station ( BS) is returned.

2. System (1) with optical carrier distribution with return channel without local oscillator, comprising a base station (BS) with a laser source (LD), with light from the laser source (LD) being sent to one or more remote front-end devices

are distributed, the front-end device further comprising a receiving device

which picks up a received signal, part of the received laser light from the laser source (LD) being made available to an optical IQ generator (OIQ) for generating phase-shifted signals, the received signal being mixed with the signals from the IQ generator (OIQ) and is fed back to an evaluation device in the base station.

3. System according to claim 1 or 2, characterized in that light from the laser source (LD) is distributed to the remote front-end devices via a glass fiber or a free space connection.

4. System according to one of claims 1 to 3, characterized in that the base station further branches off part of the laser light from the laser source (LD) and makes it available to the evaluation device.

5. System according to claim 4, characterized in that the base station furthermore has a phase shifter which makes the branched part of the laser light from the laser source (LD) available to the evaluation device in a phase-shifted manner

6. System according to one of the preceding claims, characterized in that the optical IQ generator has optical directional couplers, MMIs and phase shifters.

7. System according to one of the preceding claims 1 to 5, characterized in that the optical IQ generator has a multi-mode interferometer (MMI) and phase shifter.

8. System according to one of the preceding claims, characterized in that in at least one of the remote front-end devices, part of the received laser light from the laser source (LD) is changed by mixing and / or modulating before it is returned to the evaluation device in the base station.

9. System according to one of the preceding claims, characterized in that the light from the laser source (LD) is modulated _{to one or more remote front-end devices (FE I} ... _{N) before the distribution).}

10. System according to one of the preceding claims, characterized in that the phase position in the base station (BS) is adjustable.

11. System according to any one of the preceding claims, characterized in that the light

Laser source (LD) for distribution to one or more remote front-end devices (FEI ... _N ) is amplified by an amplifier device.