<div>We demonstrate a broadband and continuously tunable 1×4 optical beamforming network (OBFN), based on the hybrid integration of indium phosphide (InP) components in the silicon nitride (Si3N4) platform. The photonic integrated circuit (PIC) comprises a hybrid InP-Si3N4 external cavity laser, a pair of InP phase modulators, a Si3N4 optical single-sideband full carrier (SSBFC) filter followed by four tunable optical true time delay lines (OTTDLs), and four InP photodetectors. The performance of the OBFN-PIC is experimentally characterized by measuring the link gain, noise figure, and spurious free dynamic range of the microwave photonics links. Moreover, we assess its beamforming capabilities assuming that the OBFN-PIC is part of a wireless system operating in the downlink direction and feeds a multielement antenna array. Using microwave signals at 5 and 10 GHz with quadrature amplitude modulation (QAM) formats at 500 Mbaud, we evaluate the performance of the OBFN-PIC under various configurations. An error-free performance is achieved for all the experimental cases validating the potential of the proposed OBFN-PIC for high-quality beamforming performance. To our best of knowledge, this is the first thorough performance evaluation of a fully integrated OBFN-PIC.</div>
We demonstrate a broadband and continuously tunable 1×4 optical beamforming network (OBFN), based on the hybrid integration of indium phosphide (InP) components in the silicon nitride (Si3N4) platform. The photonic integrated circuit (PIC) comprises a hybrid InP-Si3N4 external cavity laser, a pair of InP phase modulators, a Si3N4 optical single-sideband full carrier (SSBFC) filter followed by four tunable optical true time delay lines (OTTDLs), and four InP photodetectors. Each OTTDL consists of eight cascaded thermo-optical micro-ring resonators (MRRs) that impose tunable true time delay on the propagating optical signals. The OBFN-PIC is designed to facilitate the steering of a microwave signal with carrier frequency up to 40 GHz over a continuous set of beam angles. We evaluate the performance of the OBFN-PIC to handle and process microwave signals, measuring the link gain, the noise figure (NF), and the spurious-free dynamic range (SFDR) parameters. Moreover, we assess its beamforming capabilities assuming that the OBFN-PIC is part of a wireless system operating in the downlink direction and feeds a multielement antenna array. Using microwave signals at 5 and 10 GHz with quadrature amplitude modulation (QAM) formats at 500 Mbaud, we evaluate the performance of the OBFN-PIC under various configurations. We show that error-free performance can be achieved at both operating frequencies and for all the investigated beam angles ranging from 45° to 135°, thus validating its potential for high-quality beamforming performance. Index Terms-Microwave photonics, optical beamforming network, optical true-time delay lines, photonic integrated circuits.
We demonstrate the generation, of a mmWave signal via the injection of an optical frequency comb (OFC) into an integrated tunable dual distributed Bragg reflector (DBR) laser as well as the fiber transmission and the processing of this signal by an optical beamforming network (OBFN). The dual DBR laser is based on a hybrid indium phosphide (InP)polymer photonic integrated circuit (PIC). Two different cases have been examined in which the microwave signal is centered around 39 GHz and 60 GHz respectively, carrying quadrature amplitude modulation (QAM) formats at 0.5 Gbaud. In this proof-of-concept scenario, the OBFN consists of two optical paths, where the relative true time delay is induced by an optical delay line (ODL). Extensive comparison between the back-toback (B2B) case and scenarios with transmission over 25 km of standard single-mode fiber (SSMF) has been made using the error-vector magnitude (EVM) and the bit-error ratio (BER) as evaluation criteria. In all cases, error-free transmission was suggested for all QPSK signals, whereas a worst-case EVM of 11.8% was observed for 16-QAM transmission, successfully showcasing the concept's potential. The generated microwave signal's frequency can be set arbitrarily high, provided that highspeed photodetection equipment is available for the detection and down-conversion of the signal. Extension to higher antenna elements (AEs) numbers is straight-forward, relying only on the number of available photodetectors.
Optoelectronic technology is expected to be the cornerstone of sub-THz communication systems, enabling access to and use of the vast frequency resources found in this portion of the spectrum. In this work we demonstrate a photonics-enabled sub-THz wireless link operating in real-time settings, using a PIN-PD-based THz emitter, and a THz receiver based on an ultra-fast photoconductor. The real-time generation and detection of the information signal is performed by an intermediate frequency (IF) unit based on a commercially available mmWave platform, operating at 1.6 GBaud. The evaluation of our setup takes place on two phases. Firstly, a homodyne scenario is demonstrated, where the same pair of lasers is used at the transmitter and receiver side. Secondly, we demonstrate a heterodyne scheme, employing optical phase locking techniques at the receiver. Errorfree operation was achieved in both scenarios at a bit rate of 3.2 Gb/s, over 1 m of free-space with ambient air. The broadband characteristics of our setup were validated, achieving error-free transmission over a 0.22 THz range, spanning from 90 up to 310 GHz. Finally, the stability of our real-time link was successfully demonstrated, showing stable SNR performance at the receiver with adaptive capabilities, over a time period of 5 min and 22 sec.
Photonic integrated circuits (PICs) are one of the key enablers for beyond 5G networks. A novel generation of fully integrated photonic-enabled transceivers operating seamlessly in W-D-and THz-bands is developed within the EU funded project TERAWAY. Photonic integration technology enables key photonic functionalities on a single PIC including photonic up/down conversion. For efficient down-conversion at the photonic integrated receiver, we develop the first waveguide-fed photoconductive antenna for THz communications. Finally, we report on the experimental implementation of a fully photonic-enabled link operating across W-D-and THz-bands.
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