Paolo Pintus

Magnetic field sensors with high sensitivity and spatial resolution have profoundly impacted diverse applications ranging from geopositioning and navigation to medical imaging, materials science, and space exploration. However, the use of high-precision magnetometers is often limited due to their bulky size or low energy efficiency. In this work, we present the design, modeling, and an experimental demonstration of an all-optical magnetometer based on silicon integrated photonics heterogeneously integrated with a magneto-optic thin film. By bonding a thin cerium–yttrium iron garnet layer onto an integrated silicon photonic interferometer, small magnetic field fluctuations can be detected through the nonreciprocal phase shift in the sensor. This strategy enables more than 80 dB of dynamic range with better than 40pT/Hz sensitivity at room temperature. Importantly, by leveraging silicon photonics, the core platform is scalable through foundry manufacturing, and the ultra-low-power requirements enable complete system integration with on-chip lasers, detectors, and quantum elements for enhanced sensitivity. This work provides a path for realizing a compact, scalable, room-temperature magnetometer based on integrated photonic systems, opening new opportunities for ultra-sensitive and ultra-efficient magnetic field detectors.

In the past decade, remarkable advances in integrated photonic technologies have enabled table-top experiments and instrumentation to be scaled down to compact chips with significant reduction in size, weight, power consumption, and cost. Here, we demonstrate an integrated continuously tunable laser in a heterogeneous gallium arsenide-on-silicon nitride (GaAs-on-SiN) platform that emits in the far-red radiation spectrum near 780 nm, with 20 nm tuning range, 40 dB side-mode suppression ratio. The GaAs optical gain regions are heterogeneously integrated with low-loss SiN waveguides. The narrow linewidth lasing is achieved with an extended cavity consisting of a resonator-based Vernier mirror and a phase shifter. Utilizing synchronous tuning of the integrated heaters, we show mode-hop-free wavelength tuning over a range larger than 100 GHz (200 pm). To demonstrate the potential of the device, we investigate two illustrative applications: (i) the linear characterization of a silicon nitride microresonator designed for entangled-photon pair generation and (ii) the absorption spectroscopy and locking to the D1 and D2 transition lines of 87Rb. The performance of the proposed integrated laser holds promise for a broader spectrum of both classical and quantum applications in the visible range, encompassing communication, control, sensing, and computing.

Metal halide perovskites have emerged as promising materials for low‐threshold lasers, ideally suited for integrated optical circuits due to their easy fabrication, tunable wavelength, and seamless on‐chip integration. Exciton lasing, electron‐hole population inversion, polariton condensation and superfluorescence have been proposed to explain the low threshold. Fundamental to discriminate lasing mechanisms is the knowledge of the material's absorption/gain spectrum in the stimulated emission regime, a difficult experimental task in microcavities and metasurfaces. In this study, femtosecond tandem spectroscopy applied to MAPbBr₃ planar waveguides enables the measurement of material absorption and gain spectra at any carrier density, as well as directly monitoring the matter component of hybrid excitations. Results demonstrate that stimulated emission always involves hybrid electron‐hole‐photon excitations in the absence of photon gain, even at the highest excitations when the exciton resonance is completely bleached, a characteristic almost unique in the landscape of photonic materials. Parameter‐free numerical simulations show that MAPbBr₃ waveguides support electromagnetic modes with an exciton‐polariton‐like dispersion below the bandgap at all investigated carrier densities. These excitations combine the advantages of hybrid light‐matter states‐ namely, lower stimulated emission thresholds and higher nonlinearities‐ with the robustness of photon amplification, seamlessly extending potential applications from low to high carrier densities.

Processing information in the optical domain promises advantages in both speed and energy efficiency over existing digital hardware for a variety of emerging applications in artificial intelligence and machine learning. A typical approach to photonic processing is to multiply a rapidly changing optical input vector with a matrix of fixed optical weights. However, encoding these weights on-chip using an array of photonic memory cells is currently limited by a wide range of material- and device-level issues, such as the programming speed, extinction ratio and endurance, among others. Here we propose a new approach to encoding optical weights for in-memory photonic computing using magneto-optic memory cells comprising heterogeneously integrated cerium-substituted yttrium iron garnet (Ce:YIG) on silicon micro-ring resonators. We show that leveraging the non-reciprocal phase shift in such magneto-optic materials offers several key advantages over existing architectures, providing a fast (1 ns), efficient (143 fJ per bit) and robust (2.4 billion programming cycles) platform for on-chip optical processing.

We present recent progress in cryogenic optical modulators for data links from cryogenic to room temperature environments, which can have applications in emerging cryogenic classical and quantum computing systems. Two efficient solutions based on III-V alloys and Ce:YIG are presented, utilizing the electro-optic and magneto-optic effects, respectively.

Continuously tunable lasers with a narrow linewidth are at the core of a large number coherent optical systems. Integration of these devices on a single chip will enable a large number of applications that require minimal size, weight, power, and cost. In this work, we demonstrate a 3 nm-continuously tunable laser operating around 1550 nm with a narrow intrinsic linewidth of 5.7 kHz. The device is fully integrated on a silicon-on-insulator platform and the optical gain is provided by a bonded III-V layer. The narrow laser linewidth is attained with an extended cavity that consists of a Vernier ring-based mirror and a passive waveguide. To reach the record continuous (mode-hop-free) tuning range of 3 nm (375 GHz), we demonstrate a method for synchronously tuning the Vernier resonances together with the cavity longitudinal modes, both thermally controlled. In the current laser, the mode-hop-free tuning range is limited by the maximum heating power, but it can be extended over more than 10 nm (1.25 THz) by optimizing the integrated heater design.

Integrated magneto‐optic (MO) modulators are an attractive but not fully explored alternative to electro‐optic (EO) modulators. They are current driven, structurally simple, and could potentially achieve high efficiency in cryogenic and room temperature environments where fJ bit⁻¹optical interfaces are needed. In this paper, the performance and energy efficiency of a novel MO modulator at room temperature are for the first time assessed. First, a model of the micro‐ring‐based modulator is implemented to investigate the design parameters and their influence on the performance. Then, a fabricated device is experimentally characterized to assess its performance in terms of bit rate and energy efficiency. The model shows efficient operation at 1.2 Gbps using a 16 mA drive current, consuming only 155 fJ bit⁻¹. The experimental results show that the MO effect is suitable for modulation, achieving error‐free operation above 16 mA with a power consumption of 258 fJ bit⁻¹at a transient limited data rate of 1.2 Gbps.