Photonic integrated circuit for free space optical communication and method

Abstract

A photonic integrated circuit for free space optical communication is provided, comprising a controller coupled to an optical antenna array (OAA), which comprises N antenna elements. The OAA receives a light beam and transmits N first optical signals to the controller, each being associated to one antenna element. The controller is configured to: define a plurality of M sectors of the OAA, with M≤N, each sector comprising one or more of the N antenna elements; combine the first optical signals of each sector to generate a second optical signal that is associated to the respective sector; combine the M second optical signals to generate an output optical signal that is associated to the M sectors; generate an electrical signal for each sector, which is associated to a power of the sector; extract information about data transmitted by the light beam, and extract information about a position of the light beam.

Description

[0001] PHOTONIC INTEGRATED CIRCUIT FOR FREE SPACE OPTICAL COMMUNICATION AND METHOD

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a photonic integrated circuit for free space optical communication that comprises an optical antenna array (OAA) controlled by a controller, the controller being for example a programmable optical processor (POP). The disclosure further provides a method for the photonic integrated circuit, and a computer program to perform the method steps as performed by the controller.

[0004] BACKGROUND

[0005] Free space optical (FSO) communication is an optical communication technology that uses light propagating in free space to wirelessly transmit data for telecommunications or computer networking.

[0006] In contrast to communication based on optical fiber cables, the light transmitted and received in FSO systems is prone to degradation due to optical turbulence. Thus, high-accuracy pointing between a transmitter and a receiver of the communication system is of paramount importance for FSO. Inaccurate alignment on FSO links provides degradation in both transported capacity and limitation of the maximum distance spanned due to loss of received power.

[0007] In conventional FSO systems, terminal (i.e. , transmitter or receiver) misalignment correction has been approached using beacon signals. Beacon-aided systems, however, increase the number of laser sources needed on each terminal, impacting equipment complexity, cost, power consumption and weight. Further, the wavelength of the beacon signal is different from that of data channels to avoid disturbances. Thus, propagation at different optical wavelengths can be very different in a turbulent medium (e.g., atmosphere), particularly over long link distances; hence, turbulence-induced wandering might affect the beacon and the data beam differently, resulting in errors in estimating the misalignment of the data beam.

[0008] Beaconless solutions have also been proposed, which use the data signal itself to obtain information about misalignment between terminals (e.g., caused by building and support deformation and deflection) and wandering of the beam induced by atmospheric turbulence. However, conventional beaconless FSO systems require using additional devices, for example beam splitters or spatial light modulators, thereby increasing costs and complexity.

[0009] SUMMARY

[0010] In view of the above, this disclosure aims to improve conventional solutions for FSO systems. An objective is to solve the problem of received light spot drift estimation for pointing and tracking in beaconless FSO communication by improving the detection accuracy.

[0011] These and other objectives are achieved by the solutions of this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

[0012] According to a first aspect, a photonic integrated circuit for free space optical communication is provided. The photonic integrated circuit comprises a controller coupled to an optical antenna array, OAA. The OAA comprises N antenna elements, wherein N is an integer number and N>2, and the OAA is configured to receive a light beam, and to transmit N first optical signals to the controller, each first optical signal being associated to one of the N antenna elements. The controller is configured to: define a plurality of M sectors of the OAA, with M<N, each sector comprising one or more of the N antenna elements; combine the first optical signals of the one or more antenna elements of each sector to generate a second optical signal, each second optical signal being associated to the respective sector; combine the M second optical signals to generate an output optical signal, the output optical signal being associated to the M sectors; generate an electrical signal for each of the M sectors, each electrical signal being associated to a power of the respective sector; extract, from the output optical signal, information about data transmitted by the light beam received by the OAA; and extract, from the M electrical signals, information about a position of the light beam received by the OAA.

[0013] The photonic integrated circuit may easily recover information about the position of the incoming beam in the OAA plane, thereby facilitating terminal alignment. At the same time, the photonic integrated circuit may directly provide the data signal containing the information transmitted in the light beam.

[0014] In an implementation form of the first aspect, the M sectors are symmetrically arranged with respect to a center of the OAA.

[0015] In an implementation form of the first aspect, the plurality of M sectors comprises a same number of antenna elements. Alternatively, the plurality of M sectors comprises a different number of antenna elements.

[0016] In an implementation form of the first aspect, the controller comprises a coherent optical adder, and the controller is configured to combine the optical signals of the one or more antenna elements of each sector to generate the second optical signal by using the coherent optical adder.

[0017] In an implementation form of the first aspect, the controller further comprises a plurality of optical detectors, each optical detector being coupled to the coherent optical adder. Each optical detector is configured to detect a beam power of the respective second optical signal, and the controller is configured to generate the electrical signal for each of the M sectors as being the detected beam power of each optical detector.

[0018] In an implementation form of the first aspect, the coherent optical adder comprises a plurality of first waveguides and an output waveguide, and the coherent optical adder is configured to combine the first optical signals of the one or more antenna elements of each sector into one of the first waveguides to generate the respective second optical signal, and to combine the M second optical signals of the M first waveguides into the output waveguide to generate the output optical signal. Each optical detector is coupled to one of the first waveguides, and each optical detector is further configured to detect the beam power of the respective second optical signal transmitted by the respective first waveguide.

[0019] In an implementation form of the first aspect, the controller is configured to extract, from the M electrical signals, the information about the position of the light beam received by the OAA by determining, based on the M electrical signals, whether the light beam received by the OAA is centered at the OAA.

[0020] In an implementation form of the first aspect, the determining, based on the M electrical signals, whether the light beam received at the OAA is centered at the OAA, comprises: when the beam powers detected by the M photonic detectors are equal to each other, the controller is configured to determine that the light beam received by the OAA is centered at the OAA. Alternatively, the determining, based on the M electrical signals, whether the light beam received at the OAA is centered at the OAA, comprises: when the beam power detected by at least one of the photonic detectors is different than the beam powers detected by the remaining photonic detectors, the controller is configured to determine that the light beam received at the OAA is not centered at the OAA and / or to estimate a drift of the light beam received at the OAA with respect to the center of the OAA. In an implementation form of the first aspect, when the number N of antenna elements is equal to an integer multiple of M plus one antenna element, the controller is further configured to define the M sectors by excluding one antenna element, the one antenna element being at the center of the OAA, wherein each of the M sectors comprises the same number of (N- 1 ) / M antenna elements.

[0021] In an implementation form of the first aspect, the controller comprises other coherent optical adder that is configured to combine the first optical signal of the one antenna element into the output waveguide to generate the output optical signal. The output optical signal is then associated to the one antenna element and to the M sectors.

[0022] In an implementation form of the first aspect, each of the optical detectors comprises at least one detector that is coupled to one or more optical splitters. Alternatively, each of the optical detectors comprises at least one in-line power monitor, the at least one in-line power monitor comprising a Contactless Integrated Photonic Probe (CLIPP) and / or a plasmonic detector.

[0023] In an implementation form of the first aspect, the controller is a POP.

[0024] This provides the advantage of using the typical components the POP, e.g., waveguides and / or splitters, to combine the first optical signals to generate the second optical signals, and to combine the generated M second optical to generate the output optical signal.

[0025] Moreover, the structure and components of the POP may simplify the integration of the one or more optical detectors, thereby further facilitating the generation of the M electrical signals that are associated to each sector.

[0026] Further, since the POP is a photonic coherent combiner, it can be controlled and reconfigured in real-time to retrieve the data transmitted in the light beam and to recover information about the position of the incoming beam in the OAA plane.

[0027] According to a second aspect, a method for a photonic integrated circuit for free space optical communication is provided. The photonic integrated circuit comprises a controller coupled to an OAA, and the OAA comprises N antenna elements, wherein N is an integer number and N>2. The method comprises: receiving, with the OAA, a light beam; transmitting, with the OAA, N first optical signals to the controller, each first optical signal being associated to one of the N antenna elements; defining, with the controller, a plurality of M sectors of the OAA, with M<N, each sector comprising one or more of the N antenna elements; combining, with the controller, the first optical signals of the one or more antenna elements of each sector to generate a second optical signal, each second optical signal being associated to the respective sector; combining, with the controller, the M second optical signals to generate an output optical signal, the output optical signal being associated to the M sectors; generating, with the controller, an electrical signal for each of the M sectors, each electrical signal being associated to a power of the respective sector; extracting from the output optical signal, with the controller, information about data transmitted by the light beam received by the OAA; and extracting from the M electrical signals, with the controller, information about a position of the light beam received by the OAA.

[0028] In an implementation form of the second aspect, the M sectors are symmetrically arranged with respect to a center of the OAA.

[0029] In an implementation form of the second aspect, the plurality of M sectors comprises a same number of antenna elements. Alternatively, the plurality of M sectors comprises a different number of antenna elements. In an implementation form of the second aspect, the controller comprises a coherent optical adder, and the method comprises combining, with the controller, the optical signals of the one or more antenna elements of each sector to generate the second optical signal by using the coherent optical adder.

[0030] In an implementation form of the second aspect, the controller further comprises a plurality of optical detectors, each optical detector being coupled to the coherent optical adder, and the method further comprises: detecting, with each optical detector, a beam power of the respective second optical signal; and generating, with the controller, the electrical signal for each of the M sectors as being the detected beam power of each optical detector.

[0031] In an implementation form of the second aspect, the coherent optical adder comprises a plurality of first waveguides and an output waveguide, and the method further comprises: combining, with the coherent optical adder, the first optical signals of the one or more antenna elements of each sector into one of the first waveguides to generate the respective second optical signal, and combining, with the coherent optical adder, the M second optical signals of the M first waveguides into the output waveguide to generate the output optical signal. Each optical detector is coupled to one of the first waveguides, and the method further comprises detecting, with each optical detector, the beam power of the respective second optical signal transmitted by the respective first waveguide.

[0032] In an implementation form of the second aspect, the method further comprises extracting, with the controller from the M electrical signals, the information about the position of the light beam received by the OAA by determining, based on the M electrical signals, whether the light beam received by the OAA is centered at the OAA.

[0033] In an implementation form of the second aspect, the determining, based on the M electrical signals, whether the light beam received at the OAA is centered at the OAA, comprises: when the beam powers detected by the M photonic detectors are equal to each other, determining, with the controller, that the light beam received by the OAA is centered at the OAA. Alternatively, the determining, based on the M electrical signals, whether the light beam received at the OAA is centered at the OAA, comprises: when the beam power detected by at least one of the photonic detectors is different than the beam powers detected by the remaining photonic detectors, determining, with the controller, that the light beam received at the OAA is not centered at the OAA and / or estimating, with the controller, a drift of the light beam received at the OAA with respect to the center of the OAA.

[0034] In an implementation form of the second aspect, when the number N of antenna elements is equal to an integer multiple of M plus one antenna element, the method further comprises defining, with the controller, the M sectors by excluding one antenna element, the one antenna element being at the center of the OAA, wherein each of the M sectors comprises the same number of (N-l ) / M antenna elements.

[0035] In an implementation form of the second aspect, the controller comprises other coherent optical adder, and the method further comprises combining, with the coherent optical adder, the first optical signal of the one antenna element into the output waveguide to generate the output optical signal. The output optical signal is then associated to the one antenna element and to the M sectors.

[0036] In an implementation form of the second aspect, each of the optical detectors comprises at least one detector that is coupled to one or more optical splitters. Alternatively, each of the optical detectors comprises at least one in-line power monitor, the at least one in-line power monitor comprising a CLIPP and / or a plasmonic detector.

[0037] In an implementation form of the second aspect, the controller is a POP. The method according to the second aspect and its implementation forms provide the same advantages and effects of the device of the first aspect and its respective implementation forms.

[0038] According to a third aspect, a computer program is provided. The computer program includes instructions which, when the program is executed by a computer, cause the computer to carry out the method steps of the controller in the method according to the second aspect and its implementation forms.

[0039] The computer program according to the third aspect provides the same advantages and effects for the actions performed by the controller according to the second aspect and its respective implementation forms.

[0040] The advantages of the solutions according to this disclosure can be summarized as follows: The disclosure integrates into the same device, with the same technology and a unique mode of operation, both the capability of recovering the information data signal and the ability to extract information to be used for pointing and tracking, from the data signal itself, everything in the optical domain. This is cost-effective in terms of power consumption, hardware, and complexity, since the proposed solutions can reduce the number of components and devices to be used for the pointing detection and tracking functions in FSO equipment.

[0041] It has to be noted that all devices, elements, units and means described in the present disclosure could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the this disclosure as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

[0042] BRIEF DESCRIPTION OF DRAWINGS

[0043] The above-described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

[0044] FIG. 1 schematically depicts a photonic integrated circuit for FSO communication, according to this disclosure;

[0045] FIG. 2 schematically depicts other photonic integrated circuit for FSO communication, according to this disclosure;

[0046] FIG. 3 schematically depicts another photonic integrated circuit for FSO communication, according to this disclosure;

[0047] FIG. 4 schematically depicts another photonic integrated circuit for FSO communication, according to this disclosure;

[0048] FIG. 5 schematically depicts another photonic integrated circuit for FSO communication, according to this disclosure; FIG. 6 schematically depicts an exemplary implementation of a photonic integrated circuit for FSO communication, according to this disclosure;

[0049] FIG. 7 schematically depicts another photonic integrated circuit for FSO communication, according to this disclosure;

[0050] FIG. 8 schematically depicts another photonic integrated circuit for FSO 1 communication, according to this disclosure;

[0051] FIG. 9 schematically shows a method for a photonic integrated circuit for FSO communication, according to this disclosure.

[0052] Same elements shown in the figures are labeled with the same reference signs, and may be implemented likewise. It is emphasized that the various features in the figures are not necessarily drawn to scale.

[0053] DETAILED DESCRIPTION OF EMBODIMENTS

[0054] FIG. 1 shows an exemplary embodiment of a photonic integrated circuit 100 for FSO communication according to this disclosure. The photonic integrated circuit 100 can be implemented in, or can be a part of, a receiver in a FSO system.

[0055] The photonic integrated circuit 100 comprises a controller 110 and an OAA 120 that are coupled to each other.

[0056] The OAA 120 comprises N antenna elements 121, alternatively N optical radiators, where N is an integer number and N>2. The OAA 120 can be, for example, a two-dimensional (2D) OAA.

[0057] The OAA 120 is configured to receive a light beam 130, for example from a transmitter of the FSO system. The OAA 120 is further configured to transmit N first optical signals 122 to the controller 110. Each of the first optical signals 122 is associated to one of the N antenna elements 121.

[0058] The controller 110 is configured to define a plurality of M sectors 123 of the OAA 120, where M is an integer number and M<N. Each sector 123 comprises one or more of the N antenna elements 121. That is, each sector 123 may comprise at least one of the N antenna elements 121 of the OAA.

[0059] In other words, the controller 110 is configured to divide the N antenna elements 121 of the OAA 120 into the M sectors.

[0060] For example and not as a limitation, FIG. 1 depicts four sectors, i.e., an example in which M=4, exemplary sectors 123-1, 123-2, 123-3 and 123-4. However, a total number of sectors is not limited to M=4.

[0061] The M sectors 123 are symmetrically, or substantially symmetrically, arranged with respect to a center of the OAA 120.

[0062] Further, the plurality of M sectors 123 comprises a same number of antenna elements 121, or comprises a different number of antenna elements 121. In other words, each sector 123 may comprise the same number of the antenna elements 122, said same number of the antenna elements 121 being equal to NZM, or the sectors 123 may comprise each a different number of antenna elements 122.

[0063] Then, the controller 110 is configured to combine the first optical signals 122 of the one or more antenna elements 121 of each sector 123, received from the OAA 120, to generate a second optical signal 124. Thus, each of the M second optical signals 124 is associated to the respective sector 123.

[0064] For example and not as a limitation, FIG. 1 depicts the second optical signal 124-1 associated to the first sector 123-1, the second optical signal 124-2 associated to the second sector 123-2, the second optical signal 124-3 associated to the third sector

[0065] 123-3, and the second optical signal 124-4 associated to the fourth sector 123-4.

[0066] The controller 110 is then configured to combine the M second optical signals 124, exemplary signals 124-1, 124-2, 124-3 and

[0067] 124-4, to generate an output optical signal 125. The output optical signal 125 is thus an optical signal associated to all the M sectors 123.

[0068] Further, the output optical signal 125 may be a data signal containing the information transmitted (e.g., from the transmitter in the FSO system) by the light beam 130 received at the OAA 120.

[0069] Further, the controller 110 is configured to generate an electrical signal 126 for each of the M sectors 123. That is, the controller may generate one of the electrical signals 126 for each of the M second optical signals 124. Thus, each electrical signal 126 is associated to a power of the respective sector 123.

[0070] Each electrical signal 126 is proportional to a beam power coupled from free space to the respective sector 123. In other words, each of the electrical signals 126 may be related to the power crossing the respective sector, or section, of the OAA 120.

[0071] For example and not as a limitation, FIG. 1 depicts four electrical signals 126 for the exemplary case with M=4 sectors: the electrical signal 126-1 for the second optical signal 124-1, which in turn is associated to the first sector 123-1, the electrical signal 126-2 for the second optical signal 124-2 that is associated to the second sector 123-2, the electrical signal 126-3 for the second optical signal 124-3 that is associated to the third sector 123-3, and the electrical signal 126-4 for the second optical signal 124-4 that is associated to the first sector 123-4. This is not limiting in this disclosure, as the total number M of sectors is not limited to M=4.

[0072] The controller 110 is then configured to extract, from the output optical signal 125, information about data transmitted by the light beam 130 that is received by the OAA 120.

[0073] Further, the controller 110 is configured to extract, from the M electrical signals 126, information about a position of the light beam 130 that is received by the OAA 120.

[0074] The controller 110 may be appropriately configured, via hardware and / or software, to process the output optical signal 126 so that the controller can extract the information about the data transmitted by the light beam 130.

[0075] The controller 110 may be appropriately configured, via hardware and / or software, to process each output optical signals 126 to determine the power associated to the respective sector 123, and to further process the determined M powers so that the controller 110 can extract the information about the position of the light beam 130 received by the OAA 120. Then, the controller 110 may further provide the output optical signal 125 and / or the M electrical signals 126 and / or the information about the data transmitted by the light beam 130 and / or the information about the position of the light beam 130 as a result.

[0076] The controller 110 is further configured to extract, from the M electrical signals 126, the information about the position of the light beam received by the OAA 120 by determining, based on the M electrical signals 126, whether the light beam 130 received by the OAA 120 is centered, or substantially centered, at the OAA 120. This may comprise the following: The controller 110 may be configured to determine that the light beam 130 received by the OAA 120 is centered or is substantially centered at the OAA 120, when the beam powers detected in the M electrical signals 126 are equal to each other. Alternatively, when the beam power detected in at least one of the M electrical signals 126 is different than the beam powers detected by the remaining electrical signals 126, the controller 110 is configured to determine that the light beam 130 received at the OAA 120 is not centered, or substantially centered, at the OAA 120.

[0077] In other words, from the power associated to each of the M electrical signals 126, the controller 110 can determine where a centroid of the incoming beam 130 is located. For example, if the power determined by all the electrical signals 126 is the same, or substantially the same, the beam 130 is centered, or substantially centered, at the OAA 120 and no alignment of the OAA 120 (alternatively of the receiver of the FOS system) is needed. Otherwise, if one of the electrical signals 126 is significantly larger than one or more of the other electrical signals 126, an alignment of the OAA (or of the receiver) is required.

[0078] The controller 110 may be additionally or alternatively configured to estimate a drift of the light beam 130 received at the OAA 120 with respect to the center of the OAA 120.

[0079] When the controller 100 also estimates the drift, the controller 110 may further provide the output optical signal 125 and / or the M electrical signals 126 and / or the information about the data transmitted by the light beam 130 and / or the information about the position of the light beam 130 and / or of the light beam 130 received at the OAA 120 as the result.

[0080] In this disclosure, the controller 110 may be implemented as, or may be, a POP with appropriately designed connections that enables the above-described combination of the first optical signals 122 of the one or more antenna elements 121 of each sector 123 to generate the second optical signal 124, and the combination of the M second optical signals 124 to generate the output optical signal 125.

[0081] That is, the POP, i.e. the controller 110, may be a photonic coherent combiner that can be controlled and reconfigured in real-time to retrieve the transmitted data and recover information about the position of the incoming beam in the OAA plane.

[0082] Once the POP 110 is configured to combine all the second optical signals 124 to obtain the output optical signal 125, the controller 110 can then generate the M electrical signals 126, which are proportional to a beam power coupled from free space to the respective sector 123. Then, by appropriately processing the detected powers, the information about the position of the beam spot on the OAA plane can be obtained.

[0083] The photonic integrated circuit 100 according to this disclosure may comprise a processor or processing circuitry (not shown) configured to perform, conduct or initiate the various operations of the photonic integrated circuit 100 described herein. The processing circuitry may comprise hardware and / or the processing circuitry may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The photonic integrated circuit 100 may further comprise memory circuitry, which stores one or more instructions) that can be executed by the processor or by the processing circuitry, in particular under control of the software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processor or the processing circuitry, causes the various operations of the photonic integrated circuit 100 to be performed. The processing circuitry may comprise one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the photonic integrated circuit 100 to perform, conduct or initiate the operations or methods described herein.

[0084] Further, the controller 110 according to this disclosure may comprise a processor or processing circuitry (not shown) configured to perform, conduct or initiate the various operations of the controller 110 described herein. The processing circuitry may comprise hardware and / or the processing circuitry may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application- specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The controller 110 may further comprise memory circuitry, which stores one or more instructions) that can be executed by the processor or by the processing circuitry, in particular under control of the software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processor or the processing circuitry, causes the various operations of the controller 110 to be performed. The processing circuitry may comprise one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the controller 110 to perform, conduct or initiate the operations or methods described herein.

[0085] The OAA 120 according to this disclosure may comprise a processor or processing circuitry (not shown) configured to perform, conduct or initiate the various operations of the OAA 120 described herein. The processing circuitry may comprise hardware and / or the processing circuitry may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or multi-purpose processors. The OAA 120 may further comprise memory circuitry, which stores one or more instruction(s) that can be executed by the processor or by the processing circuitry, in particular under control of the software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processor or the processing circuitry, causes the various operations of the OAA 120 to be performed. The processing circuitry may comprise one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the OAA 120 to perform, conduct or initiate the operations or methods described herein.

[0086] FIG. 2 shows an exemplary embodiment of a photonic integrated circuit 100 for FSO communication, which builds on the photonic integrated circuit 100 shown in FIG. 1. Same elements are labelled with the same reference signs. Hereinafter, only the differences between FIG. 1 and FIG. 2 are explained.

[0087] In the exemplary embodiment according to FIG. 2, the controller 110 comprised in the photonic integrated circuit 100 comprises a coherent optical adder 240, and the controller 110 is configured to combine the optical signals 122 of the one or more antenna elements 121 of each sector 123 to generate the second optical signal 124 by using the coherent optical adder 240. That is, the controller 110 may be configured combine in phase the one or more first optical signals 122, exemplary first signals 122-1, 122-2, 122-3 and 122-4, of each sector 123, exemplary sectors 123-1, 123-2, 123-3 and 123-4, by using the coherent optical adder 240.

[0088] In this exemplary embodiment, the controller 110 further comprises a plurality of optical detectors 241. Each optical detector 241 is coupled to the coherent optical adder 240, and each optical detector 241 is configured to detect the beam power of a respective one second optical signal 124, exemplary second optical signals 124-1, 124-2, 124-3, and 124-4.

[0089] Each optical detector 241 may be configured to measure the optical power crossing the respective sector (or section) of OAA 120. In other words, the controller 110 may be configured to control each optical detector 241 to monitor the coupled power in the respective sector 123.

[0090] Then, the controller 110 is configured to generate the electrical signal 126 for each of the M sectors 123 as being equal to the beam power detected by the respective optical detector 241.

[0091] Further, the controller 110 is configured to extract, from the M electrical signals 126, the information about the position of the light beam received by the OAA 120 by determining, based on the M electrical signals 126, whether the light beam 130 received by the OAA 120 is centered, or substantially centered, at the OAA 120.

[0092] In this exemplary embodiment, the determining based on the M electrical signals 126, whether the light beam 130 received at the OAA 120 is centered, or substantially centered, at the OAA 120, comprises: When the beam powers detected by the M photonic detectors 241 are equal to each other, the controller 110 is configured to determine that the light beam 130 received by the OAA 120 is centered at the OAA 120: otherwise, when the beam power detected by at least one of the photonic detectors 241 is different, or substantially different, than the beam powers detected by the remaining photonic detectors 241 , the controller 110 is configured to determine that the light beam 130 received at the OAA 120 is not centered at the OAA 120 and / or to estimate a drift of the light beam 130 received at the OAA 120 with respect to the center of the OAA 120.

[0093] FIG. 3 shows an exemplary embodiment of a photonic integrated circuit 100 for FSO communication, which builds on the photonic integrated circuit 100 shown in FIG. 2. Same elements are labelled with the same reference signs. Hereinafter, only the differences between FIG. 2 and FIG. 3 are explained.

[0094] In the exemplary embodiment according to FIG. 3, the coherent optical adder 240 comprises a plurality of first waveguides 342 and an output waveguide 343.

[0095] In this exemplary embodiment, that the controller 110 is configured to combine the optical signals 122 of the one or more antenna elements 121 of each sector 123 to generate the second optical signal 124 by using the coherent optical adder 240 comprises the following: The coherent optical adder 240 is configured to combine the first optical signals 122 of the one or more antenna elements 121 of each sector 123 into one of the first waveguides 342 to generate the respective second optical signal 124.

[0096] Next, the coherent optical adder 240 is configured to combine the M second optical signals 124 of the M first waveguides 342 into the output waveguide 343 to generate the output optical signal 125.

[0097] The coherent optical adder 240 may further comprise one or more first phase shifters (not shown), and the coherent optical adder 240 may be further configured to combine in phase the one or more first electrical signals 122 of each sector 123 into the first optical waveguides 342 using one or more of the first phase shifters to generate the respective second optical signal 124. Additionally or alternatively the coherent optical adder 240 may be configured to combine in phase the M second optical signals 124 of the M first waveguides 342 into the output waveguide 343 using one or more of the first phase shifters to generate the output optical signal 125.

[0098] Each of the optical detectors 241 is coupled to one of the first waveguides 342, and each optical detector 241 is further configured to detect the beam power of the respective second optical signal 124 that is transmitted by the respective first waveguide 342.

[0099] Further, determining with the controller 110, based on the M electrical signals 126, whether the light beam 130 received by the OAA 120 is centered, or substantially centered, at the OAA 120 comprises: When the beam powers detected by the M photonic detectors 241 are equal to each other, the controller 110 is configured to determine that the light beam 130 received by the OAA 120 is centered, or substantially centered, at the OAA 120. Alternatively, when the beam power detected by at least one of the photonic detectors 241 is different, or substantially different, than the beam powers detected by the remaining photonic detectors 241, the controller 110 is configured to determine that the light beam 130 received at the OAA 120 is not centered, or substantially centered, at the OAA 120.

[0100] Additionally or alternatively, the controller 110 is configured to estimate a drift of the light beam 130 received at the OAA 120 with respect to the center of the OAA 120.

[0101] Each of the optical detectors 241 may comprise at least one detector that is coupled to one or more optical splitters. Alternatively, each of the optical detectors 241 may comprise at least one in-line power monitor, the at least one in-line power monitor comprising a CLIPP and / or a plasmonic detector.

[0102] The controller 110 may extract, for example, 10% of the optical power from each second signal 124. The remaining signals (i.e., 90%) may be coherently added by the POP 110 so that all the information coupled by the antenna elements 121 can be retrieved at the output optical signal 125 of the POP 110.

[0103] Further, from an output of each of the optical detectors 241, the controller 110 may determine where the centroid of the incoming beam 130 is located. For example, if the power received by all the optical detectors 241 is the same, or substantially the same, the light beam 130 is centered or substantially centered at the OAA 120 and no alignment is needed. Nevertheless, if one of the optical detectors 241 is significantly larger than that of its pairs, an alignment of the receiver or of the OAA 120 is required.

[0104] When the controller 110 is implemented as the POP 110, then the coherent optical adder 240 and / or the first waveguides 342 may be, or may form, a part of the components inherent to the POP, thereby reducing costs, hardware, and complexity of the photonic integrated circuit 100.

[0105] Moreover, the POP can be appropriately configured to combine the one or more first optical signals 122 into the first waveguides 342 to generate the M second optical signals 124, and to further combine the M second optical signals 124 into the output waveguide 343 to generate the output optical signal 125. That is, the inherent connections and operation of the POP 110 can be suitably controlled in order to generate the first optical signals 122, the second optical signals 124, and the output optical signal 125. Further, the POP 110 can be suitably configured to process the power detected by each of the optical detectors 241, i.e., to suitably process the M electrical signals 126, to extract the information about the location of the light beam 130.

[0106] FIG. 4 shows an exemplary embodiment of a photonic integrated circuit 100 for FSO communication, which builds on the photonic integrated circuit 100 shown in FIG. 3. Same elements are labelled with the same reference signs. Hereinafter, only the differences between FIG. 3 and FIG. 4 are explained.

[0107] In the exemplary embodiment according to FIG. 4, the number N of antenna elements 121 of the OAA 120 is equal to an integer multiple of M plus one antenna element 121.

[0108] The controller 110 is then configured to define the M sectors 123 by excluding one antenna element 121 , where the one antenna element 121 is at the center, or substantially the center, of the OAA 120, and each of the M sectors 123 comprise the same number of (N-l ) / M antenna elements 121.

[0109] In this exemplary embodiment, the controller 110 comprises other coherent optical adder 450 being configured to combine the first optical signal 122 of the one antenna element 121 into the output waveguide 343 of the coherent optical adder 240 to generate the output optical signal 125.

[0110] Thus, in this exemplary embodiment, the output optical signal 125 is to the M sectors 123 and is further associated to the one antenna element 121 (i.e., to the antenna element 121 at the center or substantially the center of the OAA 120).

[0111] The other coherent optical adder 450 may comprise one or more second waveguides (not shown), additionally or alternatively one or more second phase shifters (not shown), the second optical waveguides and / or the second phase shifters being configured to combine the optical signal 122 of the one antenna element 121 with the M second optical signals 124, to generate the output optical signal 125.

[0112] FIG. 5 shows an exemplary embodiment of a photonic integrated circuit 100 for FSO communication, which builds on the photonic integrated circuit 100 shown in FIG. 4. Same elements are labelled with the same reference signs. Hereinafter, only the differences between FIG. 4 and FIG. 5 are explained.

[0113] In this exemplary embodiment, the coherent optical adder 240 may be configured to combine the M second optical signals 124, exemplary second optical signals 124-1, 124-2, 124-3 and 124-4, of the M first waveguides 342 into the output waveguide 343 to generate a third optical signal 544 that is associated to the M sectors 123, exemplary sectors 123-1, 123-2, 123-3 and 123-4, and to further provide it to the other coherent optical adder 450.

[0114] Then, the other coherent optical adder 450 may be configured to combine the third optical signal 544 and the first optical signal 122 received from the one antenna element 121 (i.e., the one at the center or substantially the center of the OAA 120) to generate the output optical signal 125.

[0115] The other coherent optical adder 450 may comprise, for example, a third waveguide (not shown), additionally or alternatively one or more third phase shifters (not shown), the third optical waveguide and / or the phase shifters being configured to combine the optical signal 122 of the one antenna element 121 with third optical signal 544 to generate the output optical signal 125.

[0116] Thereby, the output optical signal 125 is associated to both the one antenna element 121 and to the M sectors 123. FIG. 6 shows an exemplary implementation of the photonic integrated circuit 100 for FSO communication according to the embodiments shown in FIG. 3, FIG. 4 or FIG. 5. Same elements are labelled with the same reference signs.

[0117] This example depicts that the POP 110 may be suitably configured to perform the combination of the N first optical signals 122 using the plurality of first waveguides 342. Said first waveguides 342 are show as being externally located to the POP 110 for the sake of clarity.

[0118] Further, FIG. 6 shows that the different elements inherent to the POP 110 can be used to suitably combine the M second optical signals until the output optical signal 125 is generated.

[0119] FIG. 6 further depicts that the plurality of optical detectors 241 can be readily integrated within the different elements comprised in the POP 110, so that the M electrical signals 126 are generated and subsequently processed by the POP 110 to extract the information about the position of the light beam 130.

[0120] FIG. 7 shows an exemplary embodiment of a photonic integrated circuit 100 for FSO communication, which builds on the photonic integrated circuit 100 shown in FIG. 1. Same elements are labelled with the same reference signs. Hereinafter, only the differences between FIG. 1 and FIG. 7 are explained.

[0121] In this exemplary embodiment, the controller 110 may be configured to control the OAA 120 to generate the second optical signals 124 by combining the first optical signals 122 of the one or more antenna elements 121 defined in each sector 123, exemplary sectors 123-1 to 123-M, and to further transmit the M second optical signals 124 to the controller 110..

[0122] That is, the controller 110 may be configured to receive from the OAA 120 the M second optical signals 124, each second optical signal 124 being associated to the respective sector 123.

[0123] FIG. 8 shows an exemplary embodiment of a photonic integrated circuit 100 for FSO communication, which builds on the photonic integrated circuit 100 shown in FIG. 5. Same elements are labelled with the same reference signs. Hereinafter, only the differences between FIG. 5 and FIG. 8 are explained.

[0124] In this exemplary embodiment, the number N of antenna elements 121 of the OAA 120 may be equal to an integer multiple of M plus one antenna element 121. In FIG. 8, only the one antenna element 121 at the center, or substantially the center, of the OAA 120 is depicted for the sake of clarity.

[0125] The controller 110 is then configured to define the M sectors 123, just as an example and not as a limitation sectors 123-1, 123-2, 123-3 and 123-4, by excluding one antenna element 121, the one antenna element 121 being at the center, or substantially at the center, of the OAA 120, and each of the M sectors 123 comprise the same number of (N-l) / M antenna elements 121.

[0126] In the example depicted in FIG. 8, the same number of antenna elements is N / 4. This is not limited in this disclosure

[0127] Then, the controller 110 may be configured to control the OAA 120 to combine the first optical signals 122 of the one or more antenna elements 121 of each sector 123 to generate the M second optical signals 124, and to further transmit the M second optical signals 124 to the controller 110. The controller 110 may comprise a coherent optical adder 840 and a plurality of optical detectors 841 coupled to the coherent optical adder 840. In FIG. 8 the plurality of optical detectors 841 are depicted as a single block for the sake of clarity; however, this is not limiting in this disclosure.

[0128] Each of the plurality of optical detectors 841 may be configured to generate the respective electrical signal 126, each electrical signal 126 being associated to the power of the respective sector 123.

[0129] The controller 110 may be configured to combine the M second optical signals 124 by using the coherent optical adder 840 to generate the third optical signal 844, the third optical signal 844 being associated to the M sectors 123.

[0130] Further, the controller 110 may comprise other coherent optical adder 850. The other coherent optical adder 850 may be configured to combine the optical signal 122 of the one antenna element 121 with the third optical signal 844 to generate the output optical signal 125, which is associated to the M sectors 125 and to the one antenna element at the center, or substantially the center, of the OAA 120.

[0131] FIG. 9 shows an exemplary embodiment of a method 900 for a photonic integrated circuit 100 for free space optical communication, according to this disclosure. The photonic integrated circuit 100 comprises a controller 110 coupled to an OAA 120, and the OAA 120 comprises N antenna elements 121, wherein N is an integer number and N>2.

[0132] The method 900 may be performed by the exemplary embodiments of the photonic integrated circuit 100 according to FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 7, and FIG. 8 as disclosed above.

[0133] The method 900 comprises a step 901 of receiving, with the OAA 120, a light beam 130.

[0134] Then, the method 900 comprises a step 902 of transmitting, with the OAA 120, N first optical signals 122 to the controller 110, each first optical signal 122 being associated to one of the N antenna elements 121.

[0135] The method 900 further comprises a step 903 of defining, with the controller 110, a plurality of M sectors 123 of the OAA 120, with M<N. Each sector 123 comprises one or more of the N antenna elements 121.

[0136] Further, in a step 904, the method comprises combining, with the controller 110, the first optical signals 122 of the one or more antenna elements 121 of each sector 123 to generate a second optical signal 124. Each second optical signal 124 is associated to the respective sector 123.

[0137] Next, in a step 905, the method comprises combining, with the controller 110, the M second optical signals 124 to generate an output optical signal 125. The output optical signal 125 is associated to the M sectors 123.

[0138] The method comprises a step 906 of generating, with the controller 110, an electrical signal 126 for each of the M sectors 123. Each of the electrical signals 126 is associated to a power of the respective sector 123.

[0139] Then, in a step 907, the method comprises extracting from the output optical signal 125, with the controller 110, information about data transmitted by the light beam 130 received by the OAA 120.

[0140] Further, the method comprises a step 908 of extracting from the M electrical signals 126, with the controller 110, information about a position of the light beam 130 received by the OAA 120. The method 900 may further comprise actions according to the exemplary embodiments of the photonic integrated circuit 100 of FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, FIG. 7, and FIG. 8. Hence, the method 900 achieves the same advantages as the photonic integrated circuit 100.

[0141] This disclosure further provides a computer program comprising instructions for carrying out, when the program is executed by a processor and / or a computer, the steps performed by the controller 110 in the method 900, and its implementation forms. The computer program may be included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), a 15 EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

[0142] Additionally or alternatively, this disclosure may further provide a computer program comprising instructions for carrying out, when the program is executed by a processor and / or a computer, the steps performed by the OAA 120 in the method 900, and its implementation forms. The computer program may be included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), a 15 EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

[0143] The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. A photonic integrated circuit (100) for free space optical communication, comprising a controller (110) coupled to an optical antenna array (120), OAA, wherein: the OAA (120) comprises N antenna elements, (121) wherein N is an integer number and N>2, and the OAA (120) is configured to:- receive a light beam (130); and- transmit N first optical signals (122) to the controller (110), each first optical signal (122) being associated to one of the N antenna elements (121); and the controller (110) is configured to:- define a plurality of M sectors (123) of the OAA (120), with M<N, each sector (123) comprising one or more of the N antenna elements (121);- combine the first optical signals (122) of the one or more antenna elements (121) of each sector (123) to generate a second optical signal (124), each second optical signal (124) being associated to the respective sector (123);- combine the M second optical signals (124) to generate an output optical signal (125), the output optical signal (125) being associated to the M sectors (123);- generate an electrical signal (126) for each of the M sectors (123), each electrical signal (126) being associated to a power of the respective sector (123);- extract, from the output optical signal (125), information about data transmitted by the light beam (130) received by the OAA (120); and- extract, from the M electrical signals (126), information about a position of the light beam (130) received by the OAA (120).

2. The photonic integrated circuit (100) according to claim 1, wherein the M sectors (123) are symmetrically arranged with respect to a center of the OAA (120).

3. The photonic integrated circuit (100) according to claim 1 or 2, wherein the plurality of M sectors (123) comprises a same number of antenna elements (121); or wherein the plurality of M sectors (123) comprises a different number of antenna elements (121).

4. The photonic integrated circuit (100) according to one of the claims 1 to 3, wherein the controller (110) comprises a coherent optical adder (240), and the controller (110) is configured to combine the optical signals (122) of the one or more antenna elements (121) of each sector (123) to generate the second optical signal (124) by using the coherent optical adder (240).

5. The photonic integrated circuit (100) according to one of the claims 1 to 4, wherein the controller (110) further comprises a plurality of optical detectors (241), each optical detector (241) being coupled to the coherent optical adder (240); wherein: each optical detector (241) is configured to detect a beam power of the respective second optical signal (124); and the controller (110) is configured to generate the electrical signal (125) for each of the M sectors (123) as being the detected beam power of each optical detector (241).

6. The photonic integrated circuit (100) according to one of the claims 1 to 5, wherein the coherent optical adder (240) comprises a plurality of first waveguides (342) and an output waveguide (343); wherein the coherent optical adder (240) is configured to:- combine the first optical signals (122) of the one or more antenna elements (121) of each sector (123) into one of the first waveguides (342) to generate the respective second optical signal (124);- combine the M second optical signals (124) of the M first waveguides (342) into the output waveguide (343) to generate the output optical signal (125); and wherein each optical detector (241) is coupled to one of the first waveguides (342); and each optical detector (241) is further configured to detect the beam power of the respective second optical signal (124) transmitted by the respective first waveguide (342).

7. The photonic integrated circuit (100) according to one of the claims 1 to 6, wherein the controller (110) is configured to extract, from the M electrical signals (126), the information about the position of the light beam received by the OAA (120) by: determining, based on the M electrical signals (126), whether the light beam (130) received by the OAA (120) is centered at the OAA (120).

8. The photonic integrated circuit (100) according to claim 7, wherein the determining, based on the M electrical signals (126), whether the light beam (130) received at the OAA (120) is centered at the OAA (120), comprises: when the beam powers detected by the M photonic detectors (241) are equal to each other, the controller (110) is configured to determine that the light beam (130) received by the OAA (120) is centered at the OAA (120); or when the beam power detected by at least one of the photonic detectors (241) is different than the beam powers detected by the remaining photonic detectors (241), the controller (110) is configured to determine that the light beam (130) received at the OAA (120) is not centered at the OAA (120) and / or to estimate a drift of the light beam (130) received at the OAA (120) with respect to the center of the OAA (120).

9. The photonic integrated circuit (100) according to one of the claims 1 to 8, wherein when the number N of antenna elements (121) is equal to an integer multiple of M, plus one antenna element (121), the controller (110) is further configured to define the M sectors (123) by excluding one antenna element (121), the one antenna element (121) being at the center of the OAA (120); wherein each of the M sectors(123) comprise the same number of (N-l) / M antenna elements (121).

10. The photonic integrated circuit (100) according to claim 9, wherein the controller (110) comprises other coherent optical adder (450) being configured to: combine the first optical signal (122) of the one antenna element (121) into the output waveguide (343) to generate the output optical signal (125), wherein the output optical signal (125) is associated to the one antenna element (121) and to the M sectors (123).

11. The photonic integrated circuit (100) according to one of the claims 1 to 10, wherein each of the optical detectors (241 ) comprises at least one detector that is coupled to one or more optical splitters; or wherein each of the optical detectors (241 ) comprises at least one in-line power monitor, the at least one in-line power monitor comprising a Contactless Integrated Photonic Probe, CLIPP, and / or a plasmonic detector.

12. The photonic integrated circuit (100) according to one of the claims 1 to 11, wherein the controller (110) is a programmable optical processor, POP.

13. A method (900) for a photonic integrated circuit (100) for free space optical communication, the photonic integrated circuit (100) comprising a controller (110) coupled to an optical antenna array (120), OAA, the OAA (120) comprising N antenna elements (121), wherein N is an integer number and N>2, wherein the method (900) comprises: receiving (901), with the OAA (120), a light beam (130); transmitting (902), with the OAA (120), N first optical signals (122) to the controller (110), each first optical signal(122) being associated to one of the N antenna elements (121); defining (903), with the controller (110), a plurality of M sectors (123) of the OAA (120), with M<N, each sector(123) comprising one or more of the N antenna elements (121); combining (904), with the controller (110), the first optical signals (122) of the one or more antenna elements (121) of each sector(123)to generate a second optical signal (124), each second optical signal (124) being associated to the respective sector (123); combining (905), with the controller (110), the M second optical signals (124) to generate an output optical signal (125), the output optical signal (125) being associated to the M sectors (123); generating (906), with the controller (110), an electrical signal (126) for each of the M sectors (123), each electrical signal (126) being associated to a power of the respective sector (123); extracting (907) from the output optical signal (125), with the controller (110), information about data transmitted by the light beam (130) received by the OAA (120); and extracting (908) from the M electrical signals (126), with the controller (110), information about a position of the light beam (130) received by the OAA (120).

14. A computer program comprising instructions which, when the program is executed by a processor, cause the processor to carry out the steps of the controller (110) in the method (900) according to claim 13.

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