Caterina Taddei

Silicon nitride microwave photonic circuits.

We present an overview of several microwave photonic processing functionalities based on combinations of Mach-Zehnder and ring resonator filters using the high index contrast silicon nitride (TriPleX™) waveguide technology. All functionalities are built using the same basic building blocks, namely straight waveguides, phase tuning elements and directional couplers. We recall previously shown measurements on high spurious free dynamic range microwave photonic (MWP) link, ultra-wideband pulse generation, instantaneous frequency measurements, Hilbert transformers, microwave polarization networks and demonstrate new measurements and functionalities on a 16 channel optical beamforming network and modulation format transformer as well as an outlook on future microwave photonic platform integration, which will lead to a significantly reduced footprint and thereby enables the path to commercially viable MWP systems.

Compact and reconfigurable silicon nitride time-bin entanglement circuit

Photonic-chip-based time-bin entanglement has attracted significant attention because of its potential for quantum communication and computation. Useful time-bin entanglement systems must be able to generate, manipulate, and analyze entangled photons on a photonic chip for stable, scalable, and reconfigurable operation. Here we report the first time-bin entanglement photonic chip that integrates pump time-bin preparation, wavelength demultiplexing, and entanglement analysis. A two-photon interference fringe with 88.4% visibility is measured (without subtracting any noise), indicating the high performance of the chip. Our approach, based on a silicon nitride photonic circuit, which combines low loss and tight integration features, paves the way for scalable real-world quantum information processors.

On-chip microwave photonic beamformer circuits operating with phase modulation and direct detection

We propose and experimentally demonstrate the working principles of two novel microwave photonic (MWP) beamformer circuits operating with phase modulation (PM) and direct detection (DD). The proposed circuits incorporate two major signal processing functionalities, namely a broadband beamforming network employing ring resonator-based delay lines and an optical sideband manipulator that renders the circuit outputs equivalent to those of intensity-modulated MWP beamformers. These functionalities allow the system to employ low-circuit-complexity modulators and detectors, which brings significant benefits on the system construction cost and operation stability. The functionalities of the proposed MWP beamformer circuits were verified in experimental demonstrations performed on two sample circuits realized in Si(3)N(4)/SiO(2) waveguide technology. The measurements exhibit a 2 × 1 beamforming effect for an instantaneous RF transmission band of 3‒7 GHz, which is, to our best knowledge, the first verification of on-chip MWP beamformer circuits operating with PM and DD.

Ring resonator-based on-chip modulation transformer for high-performance phase-modulated microwave photonic links

In this paper, we propose and experimentally demonstrate a novel wideband on-chip photonic modulation transformer for phase-modulated microwave photonic links. The proposed device is able to transform phase-modulated optical signals into intensity-modulated versions (or vice versa) with nearly zero conversion of laser phase noise to intensity noise. It is constructed using waveguide-based ring resonators, which features simple architecture, stable operation, and easy reconfigurability. Beyond the stand-alone functionality, the proposed device can also be integrated with other functional building blocks of photonic integrated circuits (PICs) to create on-chip complex microwave photonic signal processors. As an application example, a PIC consisting of two such modulation transformers and a notch filter has been designed and realized in TriPleX(TM) waveguide technology. The realized device uses a 2 × 2 splitting circuit and 3 ring resonators with a free spectral range of 25 GHz, which are all equipped with continuous tuning elements. The device can perform phase-to-intensity modulation transform and carrier suppression simultaneously, which enables high-performance phase-modulated microwave photonics links (PM-MPLs). Associated with the bias-free and low-complexity advantages of the phase modulators, a single-fiber-span PM-MPL with a RF bandwidth of 12 GHz (3 dB-suppression band 6 to 18 GHz) has been demonstrated comprising the proposed PIC, where the achieved spurious-free dynamic range performance is comparable to that of Class-AB MPLs using low-biased Mach-Zehnder modulators.

Fully reconfigurable coupled ring resonator-based bandpass filter for microwave signal processing

We propose and demonstrate an integrated coupled resonator optical waveguide (CROW)-based bandpass filter in TriPleX™ technology for microwave photonic signal processing. The system principle allows the selection of a channel in a dense-frequency-division subcarrier satellite communication system. Using tunable phase shifters for each resonator and tunable power couplers, every time a power coupler is needed, is possible to achieve full programmability and full reconfigurability for the realized device. These characteristics allow a center frequency tunability over a full free spectral range (FSR) and a bandwidth tunability, which can be as small as tens of MHz. Furthermore, the device can be easily integrated with other functional building blocks in photonic integrated circuits to realize an on-chip complex microwave photonic signal processor.

Integrated microwave photonic splitter with reconfigurable amplitude, phase, and delay offsets

This work presents an integrated microwave photonics splitter with reconfigurable amplitude, phase, and delay offsets. The core components for this function are a dual-parallel Mach-Zehnder modulator, a deinterleaver, and tunable delay lines, all implemented using photonic integrated circuits. Using a demonstrator with an optical free spectral range of 25 GHz, we show experimentally the RF splitting function over two continuous bands, i.e., 0.9-11.6 GHz and 13.4-20 GHz. This result promises a deployable solution for creating wideband, reconfigurable RF splitters in integrated forms.

Programmable optical processor chips: toward photonic RF filters with DSP-level flexibility and MHz-band selectivity

Abstract Integrated optical signal processors have been identified as a powerful engine for optical processing of microwave signals. They enable wideband and stable signal processing operations on miniaturized chips with ultimate control precision. As a promising application, such processors enables photonic implementations of reconfigurable radio frequency (RF) filters with wide design flexibility, large bandwidth, and high-frequency selectivity. This is a key technology for photonic-assisted RF front ends that opens a path to overcoming the bandwidth limitation of current digital electronics. Here, the recent progress of integrated optical signal processors for implementing such RF filters is reviewed. We highlight the use of a low-loss, high-index-contrast stoichiometric silicon nitride waveguide which promises to serve as a practical material platform for realizing high-performance optical signal processors and points toward photonic RF filters with digital signal processing (DSP)-level flexibility, hundreds-GHz bandwidth, MHz-band frequency selectivity, and full system integration on a chip scale.

Enhanced coverage though optical beamforming in fiber wireless networks

Integrated microwave photonics (IMWP) is a novel field in which the fast-paced progress in integrated, on-chip, optics is harnessed to provide breakthrough performances in well-established microwave photonic processing functions, which are traditionally realized using discrete optoelectronic components. A field where IMWP can have a strong impact is the one of Antenna Arrays for 5G networks. Such arrays offer a number of attractive characteristics, including a conformal array profile, electronic beamforming (beam shaping and beam steering), interference nulling and the capability to generate multiple antenna beams simultaneously. In many cases, however, the performance of a phased array is limited by the characteristics of the beamforming network (BFN) used. It is generally desired to realize beamformers with broad instantaneous bandwidth, continuous amplitude, and delay tunability while, at the same time, capable of feeding large arrays. This, however, is very challenging to achieve using only electronics. For this reason, in the last few years, an increasing amount of research has been directed to beamforming in the optical domain using, integrated microwave photonics solutions. Besides antenna array applications, opportunities for cost effective use of IMWP in switched delay lines has become feasible due to the continuous improvement of optical chips, particularly the achieved record-low propagation losses in Si3N4/SiO2-based-chips combined with the high integration density.

Waveguide filter-based on-chip differentiator for microwave photonic signal processing

We propose and demonstrate a waveguide filter-based on-chip differentiator for microwave photonic signal processing. The system principle allows the operation of arbitrary-order differentiation. The realized device is constructed using the basic building blocks of photonic integrated circuits, and features scalability and full reconfigurability. The waveguide architecture allows this functionality to be incorporated in more complex on-chip signal processing systems, which manifests the potentials of a fully integrated microwave photonic signal transmitter.

Ring resonator-based on-chip PM-IM convertor for high-performance microwave photonic links

We propose and demonstrate a novel wideband photonic PM-IM convertor for performance improvement of phase-modulated microwave photonic links, which uses a simple architecture based on ring resonators. The full programmability of the proposed device allows arbitrary optical amplitude and phase manipulations required for broadband PM-IM conversion. Moreover, the device can be integrated with other functional building blocks in photonic integrated circuits to realize on-chip complex microwave photonic signal processors.