Claudio Porzi

We report on the performance of a monolithically integrated silicon photonics $\sim$100 GHz-carrier synthesizer, and its application in a radio transmission system. The photonic integrated circuit (PIC) includes an optical frequency comb generation stage driven by a $\sim$ 20-GHz reference clock, followed by an innovative multi-resonant distributed feedback resonator-based optical filter for selecting the two comb components generating the target $\sim$ 100 GHz-carrier wave in an off-chip photodiode. Phase noise (PN) characterization of the synthesized W-band signal indicates operation in agreement with ideal frequency multiplication of the employed reference clock. In addition, the flat-tops spectral feature of the photonic integrated filter allows the output frequency to be tuned in the range 96 — 100 GHz without significant PN degradation. A 97-GHz optical local oscillator is then used to up-convert and succesfully transmit broadband wireless data signals with different complex modulation formats, including single-carrier and orthogonal frequency division multiplexed (OFDM) QPSK and 16-QAM, with net information rate up to 4 Gb/s.

A packaged silicon photonics radio-frequency (RF) synthesizer operating in the millimeter (mm-) wave band suitable for clock signal distribution in b5G/6G radio access networks is realized and experimentally characterized. The assembly include a photonic integrated circuit (PIC) acting as a frequency multiplier for a local oscillator (LO) reference at microwave frequencies and a printed circuit board (PCB) hosting a custom bias tee designed to provide a wideband matching condition over more than 6 GHz around 20 GHz for the input LO signal and supporting high power levels for efficient frequency multiplication operation. Phase noise (PN) measurements performed on a 100 GHz generated RF carrier via five-fold multiplication of a LO wave at 20 GHz indicate a low PN of -97 dBc/Hz at 10 kHz from the carrier with a small excess timing jitter of less than 2 fs with respect to the LO signal, making the circuit operating nearly as an ideal frequency multiplier.

Multi-static SARs from LEO orbits allow the single-pass high-resolution imaging and detection of moving targets. A coherent MIMO approach requires the generation of multi-band, thus orthogonal, signals, the fusion of which increases the system resolution. Up to now the synchronization capability of SAR signals of different satellites is critical. Here, we propose the use of photonics to generate, receive and distribute the radar signals in a coherent multi-static SAR constellation. Photonics overcomes issues in the implementation of MIMO SAR, allowing for the flexible generation of multi-band signals and centralized generation in a primary satellite with coherent distribution to all the secondary satellites of the SAR signals over FSO links. The numerical analysis shows the proposed system has a NESZ < −29.6 dB, satisfying the SAR system requirements. An experimental proof of concept based on COTS, for both signal up- and down-conversion, is implemented to demonstrate the system functionality, showing performance similar to the simulations. The implementation of the proposed systems with integrated technologies could reduce the system SWaP and increase robustness to vibrations. A design based on the consolidated SOI platform with the transfer printing-based hybrid integration of InP semiconductor optical amplifiers is proposed. The amplifiers compensate for the losses of the passive SOI waveguides, decreasing the overall conversion loss. The polarization multiplexing of the modulated and unmodulated combs to be sent from (to) the primary to (from) the secondary satellite over the FSO links avoids complex space-consuming optical filters requiring several control signals.

We report of a silicon photonics (SiP) flat-top bandpass microwave photonic (MWP) filter with large out-of-band power rejection (OBPR) of up to more than 40 dB and exhibiting central frequency tunability over a range as large as 70 GHz, while still guaranteeing a minimum full-span OBPR larger than 25 dB. Furthermore, the RF bandpass transfer function can be widely configured without sacrificing the filter performance. In the present realization, a continuous bandwidth tuning from 5 to 10 GHz (corresponding to a 100% of bandwidth variation) is demonstrated. The operation is based on optical-to-RF mapping the response of a tunable and bandwidth reconfigurable photonic integrated optical filter, realized with a high-order distributed feedback resonator (DFBR) waveguide Bragg grating structure. A high level of functional integration is provided in a compact footprint of less than 2 mm ² by embedding within the circuit a SiP phase modulator generating the modulation sideband scanning the DFBR filter, and a tunable optical splitter optimizing the MWP filter performance. Possibility of further extending system integration for monolithic on-chip operation is also investigated.

Reconfigurable radiofrequency (RF) signal generation in the 30 – 300 GHz range is attractive for many applications. W-band (75 – 110 GHz) is currently targeted by both wireless and satellite communications and similar frequency ranges are employed for on-board automotive radar systems. Distribution of high-precision and high-frequency synchronization signals in modern centralized radio access networks might be addressed by radio-over-fiber solutions, but the stringent phase noise (PN) requirements in case of broadband signals with high subcarriers density are not easily attainable through conventional electric-domain solutions. This article reports on the performance of a monolithically integrated silicon photonics (SiP) circuit employed for RF carrier synthesis. Up to sixfold frequency multiplication of an 18.5 GHz reference clock is demonstrated with low additional phase noise. The circuit includes a high-speed electro-optic phase modulator employed for optical frequency comb (OFC) generation and a tunable distributed feedback resonator (DFBR) filter for selecting the desired OFC harmonic. The beating of the OFC tone with the input laser mode in an off-chip photodiode generates the target RF carrier wave. By tuning the reference clock and the DFBR filter, reconfigurable frequency generation up to W-band and beyond is achieved. PN and time jitter (TJ) of the generated RF carriers are experimentally measured, demonstrating a similar performance as of an ideal frequency multiplier. The effect of the noise of DC sources employed for filter tuning is assessed and a counteracting solution is implemented. TJ robustness versus laser drifting is analyzed and the potential for up to elevenfold frequency multiplication (203.5 GHz) is shown.

This paper reports the development, the complete characterization, and the first outdoor field trial of a coherent dual-band photonics-based radar implemented through integrated photonic circuits. The dual band radar transceiver has been implemented on a silicon-on-insulator platform, and is capable of operating up to the Ku-band. It has been packaged and engineered on a printed circuit board for its use in a complete radar system. The electronic RF front-end in S- and X-bands and the digital baseband equipment have been developed in order to guarantee performance aligned with the state of the art of conventional radars. The developed apparatus has been characterized in S- and X-band in terms of sensitivity, linearity, phase noise, and conversion efficiency, both at chip and system level. The impact and issues related to the used fabrication platform and to the packaged approach have been analyzed. The outdoor field trial has been carried out in a relevant maritime environment close to the port of Livorno (Italy). First, X-band radar acquisitions of a complex maritime scene using a rotating antenna has allowed to verify the radar behavior by comparing the detected scene with official data provided by the automatic identification system mounted on the observed ships. A false alarm probability of 2×10 ⁻⁵ has been demonstrated, aligned with radar state of the art. Then, S- and X-band range/velocity acquisitions allowed to confirm the coherent dual band operation, posing the basis for the next step: the development of adapted coherent data fusion algorithms for target imaging.

Currently, due to the 6G revolution, applications ranging from communication to sensing are experiencing an increasing and urgent need of software-defined ultra-wideband (UWB) and tunable radio frequency (RF) apparatuses with low size, weight, and power consumption (SWaP). Unfortunately, the coexistence of ultra-wideband and software-defined operation, tunability and low SWaP represents a big issue in the current RF technologies. Recently, photonic techniques have been demonstrated to support achieving the desired features when applied in RF UWB transmitters, introducing extremely wide operation and instantaneous bandwidth, tunable filtering, tunable photonics-based microwave mixing with very high port-to-port isolation, and intrinsic immunity to electromagnetic interferences. Moreover, the recent advances in photonics integration also allow to obtain very compact devices. In this article, to the best of our knowledge, the first example of a complete tunable software-defined RF transmitter with low footprint (i.e., on photonic chip) is presented exceeding the state-of-the-art for the extremely large tunability range of 0.5–50 GHz without any parallelization of narrower-band components and with fast tuning (<200 μs). This first implementation represents a breakthrough in microwave photonics.

This paper reports the advancements on a recently presented silicon photonic chip implementing a photonics-based coherent multiband radar transceiver. In this work, the chip has been packaged and engineered for its use in a complete radar system capable of operating up to the X band. The electronic RF frontend and the digital baseband equipment have been developed in order to guarantee performance aligned with the state of the art of conventional radars. A first indoor field trial has been carried out in X band. Range/Velocity acquisitions allow to confirm the radar system effectiveness, posing the base for the next step: the multiband field trial and coherent data fusion.

We report on the characterization of a photonic integrated circuit (PIC) for the generation of a RF carrier in the millimeter-wave band up to the sub-THz region. The circuit is implemented in silicon waveguides through a standard multi project wafer service, and exploits an innovative filtering technique for effectively selecting two tones out of an input optical frequency comb (OFC) driven by a local oscillator at a sub-multiple frequency of the system output RF signal. Experimental results confirm a large suppression ratio of RF spurious tones up to more than 30 dB for generated carrier frequencies ranging from 20 GHz to 126 GHz with input OFC frequency spacing between 10 GHz and 20 GHz. Additionally, the unfiltered input OFC tones are recovered in the scheme with negligible loss, enabling efficient comb reuse for minimizing optical and RF equipment in future wireless communications and sensing networks systems. Design strategies for further improving the circuit performances are finally presented.