Silver-based chalcohalide anti-perovskites (CAP), Ag_3BC (B = S, Se; C = Cl, Br, I), represent an emerging family of energy materials with intriguing optoelectronic, vibrational and ionic transport properties. However, the structural features and phase stability of CAP remain poorly investigated to date, hindering their fundamental understanding and potential integration into technological applications. Here we employ theoretical first-principles methods based on density functional theory to fill this knowledge gap. Through crystal structure prediction techniques, ab initio molecular dynamics simulations, and quasi-harmonic free energy calculations, we unveil a series of previously overlooked energetically competitive phases and temperature-induced phase transitions for all CAP. Specifically, we identify a new cubic P2_13 structure as the stable phase of all CAP containing S both at zero temperature and T ≠ 0 K conditions. Consequently, our calculations suggest that the cubic Pm3m phase identified in room-temperature X-ray diffraction experiments is likely to be metastable. Furthermore, for CAP containing Se, we propose different orthorhombic (Pca2_1 and P2_12_12_1) and cubic (I2_13) structures as the ground-state phases and reveal several phase transformations induced by temperature. This theoretical investigation not only identifies new candidate ground-state phases and solid-solid phase transformations for all CAP but also provides insights into potential stability issues affecting these highly anharmonic superionic materials.

We present an initial evaluation of the two main technologies for $200 G$ optical access networks: IMDD and coherent. We consider the emerging requirements from operators and review how both options meet them.

Discovering novel families of materials composed of earth-abundant elements and characterized by non-toxicity, high thermodynamic stability, and simple low-temperature synthesis processes, is paramount for the advancement of urgently needed energy storage and conversion technologies. Pnictogen chalcohalides, represented by the general formula ABC (A = Bi, Sb; B = S, Se; C = I, Br), emerge as a promising class of energy materials particularly well-suited for photovoltaic applications. However, the compositional landscape of BixSb1 - xSySe1 - yIzBr1 - z is vast and remains largely unexplored, with traditional experimental and theoretical exploration techniques facing limitations in covering the entire solid-solution range due to their labor-intensive and time-consuming nature. Here, an integrated bottom-up approach that combines first-principles calculations, machine learning models, experiments, and device optimizations is introduced to provide a comprehensive fundamental understanding of pnictogen chalcohalides with arbitrary composition and to expedite the design of high-performance multi-junction solar cells. The synergistic investigations unveil a broad and continuous spectrum of bandgaps and optical absorption coefficients ranging from 1.2 to 2.1 eV and from 2.5 105 to 6.6 105 cm-1, respectively, across a wide variety of thermodynamically stable compounds. Additionally, a tandem BiSBr-BiSeI device is identified as an optimal multi-junction solar cell, exhibiting a maximum short-circuit current density of 18.65 mA cm-2 under intensity-matching conditions. The introduced bottom-up materials design approach may facilitate an unprecedented and rapid translation of basic knowledge into the most demanded solar cell applications. An integrated bottom-up approach that combines first-principles calculations, machine learning models, experiments, and device optimizations is introduced to provide a comprehensive fundamental understanding of pnictogen chalcohalides with arbitrary composition and to expedite the design of high-performance multi-junction solar cells. image

Ag3SX (X = I, Br) possess a unique anti-perovskite structure (similar to perovskites but switching anions by cations and vice-versa). Here, we propose a new low-cost low-temperature synthesis methodology based on thiol-amine molecular ink deposition.

In a first system configuration, a dedicated 50G-PON module was incorporated into the OLT, seamlessly coexisting with commercial G-PON and XGS-PON. The coexistence of the three generations of PONs is done here without adding any loss (filter) in existing ODNs, the 50G-PON being inserted on a 2:2 splitter at the CO. Furthermore, the possibility to extend the reach and place the 50G-PON OLT in a remote CO is evaluated. The second system uses a MPM at the OLT that includes the three PON generations. To our knowledge, this is the first full G-PON, XG(S)-PON, 50G-PON system prototype that provides an optical budget of 29 dB, and we demonstrate the possibility of extending the budget to 35 dB using SOAs.

Coherent PON is a promising candidate for the next generation VHSP-PON systems, which could support net data rates beyond 200Gb/s per wavelength, maintain coexistence with previous generations, and enable new services.

We evaluate TDEC and Rx sensitivity in a negative dispersion regime with 25G-class DML and EML modulated at 50 Gb/s. Results show that TDEC can effectively predict the performance of both transmitters for 50G-PON upstream.

Van der Waals chalcogenides and chalcohalides have the potential to become the next thin film PV breakthrough, owing to the earth-abundancy and non-toxicity of their components, and their stability, high absorption coefficient and quasi-1D structure, which leads to enhanced electrical anisotropic properties when the material is oriented in a specific crystalline direction. However, quasi-1D semiconductors beyond Sb2(S,Se)3, such as SbSeX chalcohalides, have been scarcely investigated for energy generation applications, and rarely synthesised by physical vapor deposition methodologies, despite holding the promise of widening the bandgap range (opening the door to tandem or semi-transparent devices), and showing enticing new properties such as ferroelectric behaviour and defect-tolerant nature. In this work, SbSeI and SbSeBr micro-columnar solar cells have been obtained for the first time by an innovative methodology based on the selective halogenation of Sb2Se3 thin films at pressure above 1 atm. It is shown that by increasing the annealing temperature and pressure, the height and density of the micro-columnar structures grows monotonically, resulting in SbSeI single-crystal columns up to 30 μm, and tuneable morphology. In addition, solar cell prototypes with substrate configuration have shown remarkable Voc values above 550 mV and 1.8 eV bandgap.

This work presents a comprehensive set of experiments for the multipoint-to-point coherent passive optical network (PON), where the wavelength locking between the optical network unit (ONU) and optical line termination lasers is critical, especially if operating in burst mode. Here, we test the performance of continuous multiple access in a splitter-based PON with both an ultra-dense wavelength division multiplexing and RF-subcarrier multiplexing configuration, with simple distributed feedback (DFB) lasers along non-return to zero and pulse amplitude modulation of four levels. Most interestingly, we test a spectrally efficient heterodyne receiver with image-frequency rejection and polarization independence based on the ${{3}} \times {{3}}$ optical front-end. Two users at the same intermediate frequency are detected simultaneously avoiding image frequency interference while minimizing complexity, with transmissions of 2.5 Gb/s. We provide comparison with an asynchronous homodyne receiver. The achieved results demonstrate the feasibility of continuous multiple access using thermally controlled ONUs with conventional DFBs as an enhanced alternative to commercial time division multiplexing access.

We analyze the metrology of transmitter and dispersion eye closure (TDEC) as defined in a 50G passive optical network (50G-PON) for assessing transmitter quality. First, we present a theoretical evaluation for adapting TDEC to 50G-PON, where equalized bandwidth limited avalanche-photodiode-based receivers are expected. We optimize the parameters for a proper numerical evaluation and provide some guidelines for implementing the metric. We also show that TDEC can be measured with both sampling and real-time oscilloscopes provided that there are enough samples for the latter. A comparison of two techniques, one noiseless and one considering noise enhancement, for computing the coefficients of the equalizer is also provided. Finally, an experimental comparison between a Mach–Zehnder modulator and an electroabsorption-modulated-laser-based transmitter is carried out with different extinction ratios and fiber lengths, showing that TDEC can effectively predict the receiver sensitivity penalty.

Optical access networks are seeing growing applications for use cases beyond residential, for example in campus and as Industry 4.0 intra-factory networks, which introduce different requirements in terms of bandwidth delivery and latency. We present an uplink access system with simultaneous transmission and detection of several users by means of frequency division multiplexing (FDM). We demonstrate a multiple uplink access system with differential binary phase shift keying (DBPSK) signals and coherent detection that targets a low and deterministic latency. We achieve receiver (Rx) sensitivities of -43.5dBm, -40dBm, and -34dBm at a pre forward error correction (FEC) bit error ratio (BER) of 10 -3 at 2.5 GBaud, 5 GBaud, and 8 GBaud respectively after 20km of fibre with coherent detection. Furthermore, we show the possibility of employing time-division multiplexing (TDM) within the frequency bands. We also present real-time services showing that the system can allow latency-sensitive and best-effort applications to share the network.

The growing demand for broadband access networks keeps motivating research for higher capacity in both wired and wireless access networks. Recently, the recommendation for 50G-PON with conventional NRZ modulation has been published. Bidirectional point-to-point access networks, also known as BiDi, used in mobile xHaul, are standardized up to 50 Gb/s with PAM-4 as modulation format. The evolution in view of a next generation 6G wireless encourages research towards higher bitrates for fronthaul systems. Hence, there is interest for having single channel BiDi links with a bitrate of at least 100 Gb/s. In this paper we experimentally evaluate four possible IMDD transceiver schemes suitable for optical access applications in the O-Band that can cover BiDi link losses up to a bitrate of 100 Gb/s using PAM-4. We employ an EML with either a 25G-based APD or an optically preamplified p-i-n photodiode (PD) with low-complexity FFE equalization and achieve a real-time power budget of 23.7 dB, just above BiDi B- loss class. By adding an optical booster, we demonstrate up to 34 dB power budget, exceeding with enough margin the highest BiDi class B loss of 25 dB.

The Transmitter and Dispersion Eye Closure (TDEC) is a metric originally introduced by IEEE 802.3 for short reach optical transmission in datacenters and later adopted for 50G-PON in ITU-T Recommendation G.9804.3. TDEC evaluates the performance of a transmission system as a penalty due to eye-diagram closure, comparing it to a reference ideal transmitter. To this end, the standard defines a procedure to be followed involving filtering, equalization and the definition of time windows inside the eye diagram. The purpose of this article is to show the correlation between TDEC and the Optical Modulation Amplitude receiver sensitivity in 50G-PON scenario using optical amplifiers either as booster at transmitter side (for the downstream direction) or as pre-amplifiers at receiver (in the upstream direction).

Kesterite materials are among the most promising emerging photovoltaic absorbers, despite the number of challenging issues this technology presents. The use of soft thermal post-deposition treatments (PDT) is key to improving the CdS/kesterite interface quality. Thermal treatments can result in a low-temperature phase transition which affects the optoelectronic properties. In this work, the effects of applied voltage during a full device thermal PDT above the critical temperature of the phase transition are explored. The applied voltage modifies the formation energy and drives in-depth migration of ionized defects, which can generate a shallow doping density gradient (SDDG). Supporting the experimental findings, the effects of an SDDG on the current-voltage curves and the external quantum efficiency are modelled using drift-diffusion calculations. The presence of bulk recombination centers in the modelling is a key aspect to precisely reproduce the experimental results. The SDDG in opposite directions precisely matches the experimental results for opposite voltage polarizations. The effects on the band structure of the device are presented proving this as a promising strategy for improving charge carrier selectivity. In this sense, the results and their thorough physical interpretation will potentially open new perspectives in the field of materials engineering.

We present a demo for a multiple uplink access system with real-time services. Several terminals transmit and are detected simultaneously through FDMA. The system can allow latency-sensitive and best-effort applications to share the network.

We demonstrate a UD-WDM PON using DML transmitters with multilevel intensity modulation, both in base-band and RF, and a spectrally-efficient heterodyne receiver. We provide comparison with a homodyne receiver. Two users at the same IF are detected simultaneously avoiding image frequency interference while minimizing complexity.

We experimentally demonstrate in real-time a 34dB PON power budget, exceeding E1 ODN class, with 100Gb/s PAM4 modulation using an amplified O-Band EML plus receiver-side optical amplification and only low complexity FFE equalization.

We evaluate TDEC in a 50G-PON downstream through experiments and show the relation with receiver sensitivity at different fiber lengths and ER. The results show that TDEC effectively follows the penalty induced by transmission impairments.

We perform real-time 50Gb/s transmission targeting the HS-PON standard. An SOA shared at OLT enables 30dB optical budget and 50km upstream burst-mode transmission. The SOA's XGM impact from upstream to downstream is studied. © 2022 The Author(s)

Sb2Se3 is a quasi-one-dimensional (1D) semiconductor, which has shown great promise in photovoltaics. However, its performance is currently limited by a high Voc deficit. Therefore, it is necessary to explore new strategies to minimize the formation of intrinsic defects and thus unlock the absorber's whole potential. It has been reported that tuning the Se/Sb relative content could enable a selective control of the defects. Furthermore, recent experimental evidence has shown that moderate Se excess enhances the photovoltaic performance; however, it is not yet clear whether this excess has been incorporated into the structure. In this work, a series of Sb2Se3 thin films have been prepared imposing different nominal compositions (from Sb-rich to Se-rich) and then have been thoroughly characterized using compositional, structural, and optical analysis techniques. Hence, it is shown that Sb2Se3 does not allow an extended range of nonstoichiometric conditions. Instead, any Sb or Se excesses are compensated in the form of secondary phases. Also, a correlation has been found between operating under Se-rich conditions and an improvement in the crystalline orientation, which is likely related to the formation of a MoSe2 phase in the back interface. Finally, this study shows new utilities of Raman, X-ray diffraction, and photothermal deflection spectroscopy combination techniques to examine the structural properties of Sb2Se3, especially how well-oriented the material is.