Atomic and Molecular Physics, and Optics, Signal Processing
7
Scopus Publications
Scopus Publications
Flexible All-Optical Remote Frequency Conversion of 5G Signals to FR1 and FR2 Bands Employing an Optical Comb and Multi-Core Fiber for Next-Generation C-RAN Fronthaul Vicente Fito, Maria Morant, Roberto Llorente IEEE Access, 2025 The rapid deployment of 5G wireless networks demands efficient, high performance, dynamically reconfigurable solutions for seamless multi-band frequency conversion and connectivity provision. Efficient centralized radio access networks (C-RAN) can benefit from an all-optical signal conversion and remoting employing optical frequency combs and multicore fiber (MCF) as optical source and transmission media respectively. This paper proposes and evaluates experimentally an all-optical frequency conversion approach based on an optical frequency comb (OFC) generated using a dual-drive Mach-Zehnder modulator (DD-MZM) and transmitted through MCF. The proposed method enables seamless frequency up- and down-conversion across sub-6 GHz and millimeter-wave (mm-wave) bands, leveraging optical heterodyning to achieve low-distortion signal transmission in next-generation C-RAN fronthaul implementations. The performance of the system is evaluated in terms of signal-to-noise ratio (SNR) and error vector magnitude (EVM) of the frequency-converted 5G signals. The results demonstrate that frequency-converted replicas exhibit minimal EVM degradation, with values consistently below 10.5%, ensuring compliance with 3GPP 5G NR standards. Additionally, we analyze how the modulation order affects the 5G performance, finding that lower-order orthogonal frequency division multiplexing (OFDM) schemes (e.g., QPSK) maintain robust performance at lower SNRs, while higher-order OFDM schemes (e.g., 64QAM and 256QAM) require higher SNRs for satisfactory performance meeting 3GPP threshold recommendations. Furthermore, we explore the role of multiple modulated optical carriers over the MCF media, showing that increasing the number of modulated carriers improves SNR and reduces the fluctuation of the received EVM. The EVM fluctuation is measured for different configurations, using one or two modulated optical carriers. The maximum access network reach is calculated by measuring the power margin available using the same receiver. Considering the propagation losses and expected crosstalk-induced SNR penalty of a 7-core MCF, a 23.6 km extension could be reached when using two modulated carriers for optical heterodyning compared with a single modulated carrier without frequency conversion. Finally, the impact of power balance of the optical carriers used for optical heterodyning is also evaluated in terms of EVM and SNR of the original and upconverted signals. These findings highlight the potential of MCF networks using an OFC for the transmission of 5G signals as a scalable solution for next-generation C-RAN supporting agile reconfiguration in multiple frequency bands.
All-Optical Multi-Frequency Conversion 5G NR Analog-Radio-over-Fiber Fronthaul with Enhanced Performance over Digitised Implementations Vicente Fito, Maria Morant, Roberto Llorente Optical Fiber Communication Conference in Proceedings Optical Fiber Communication Conference Ofc 2025 and Optical Fiber Communication Conference Ofc Postdeadline Papers 2025, 2025 This work demonstrates all-optical frequency conversion for 5G NR by heterodyning two lines of an optical comb transmitted in multicore fiber, which outperforms conventional digital fronthaul systems considering SNR, and achieves long-range 58.8 km reach.
Performance Evaluation of Dual-Drive Mach-Zehnder Modulator and Optomechanical Crystal Cavity Comb Generation for All-Optical Band Conversion in 5G-Advanced Cellular Systems Vicente Fito, Raúl Ortiz, Maria Morant, Laura Mercadé, Alejandro Martínez, Roberto Llorente IEEE Photonics Journal, 2025 Multiband operation is a key aspect of emerging 5G-Advanced cellular systems, also named 5.5G, which target seamless provision of multi-gigabit per second connectivity employing sub-6 GHz and mm-wave overlapping coverage. All-optical frequency conversion gives flexibility due to the feasible high-speed reconfiguration in broad bands and large radio signal bandwidth. Optical frequency combs, featuring a spectrum of discrete, equally spaced coherent frequency lines, are crucial for high-precision metrology, spectroscopy, and telecommunications. Their effectiveness in all-optical frequency conversion depends on their stability in terms of frequency drift, phase noise, and power distribution across the comb lines. This paper evaluates experimentally the generation of optical frequency combs employing two distinct technologies: a dual-driven Mach-Zehnder modulator (DD-MZM) and an optomechanical crystal cavity (OMCC), and experimentally compares their performance for all-optical frequency conversion of 5G data streams. The DD-MZM implementation generates a comb with flexible line spacing and comprising several spectrum-flat lines with low phase noise (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-88.5$</tex-math></inline-formula> dBc/Hz at 1 kHz offset and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-108.3$</tex-math></inline-formula> dBc/Hz at 100 kHz offset). The OMCC implementation provides a reduced footprint (182 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu \mathrm{m}^{2}$</tex-math></inline-formula>) since it is implemented on a silicon chip and has the extra advantage of generating an optical comb without an external local oscillator, which reduces its power requirements (under 1 mW) while providing a phase noise of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-38.3$</tex-math></inline-formula> dBc/Hz at 1 kHz offset and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-97.1$</tex-math></inline-formula> dBc/Hz at 100 kHz offset. The polarization stability and jitter of both implementations are also evaluated. The experimental demonstration evaluates the error vector magnitude (EVM) of frequency-converted 3GPP 5G NR signals using both implementations, confirming the successful transmission with EVM smaller than 12.01% for DD-MZM up to the third harmonic and EVM smaller than 17.36% with the OMCC first harmonic.
Experimental Evaluation of All-Optical Up- and Down-Conversion of 3GPP 5G NR Signals Using an Optomechanical Crystal Cavity Frequency Comb Vicente Fito, Raúl Ortiz, Maria Morant, Laura Mercadé, Roberto Llorente, Alejandro Martínez Journal of Lightwave Technology, 2024 Optomechanical crystal cavities (OMCCs) allow the interaction between localized optical and mechanical modes through the radiation-pressure force. Driving such cavities with blue-detuned lasers relative to the optical resonance can induce a phonon lasing regime where the OMCC supports self-sustained mechanical oscillations. This dynamic state results in a narrow and stable microwave tone that modulates the laser at integer multiples of the mechanical resonance frequency, creating an optomechanical (OM) frequency comb suitable for microwave photonics applications. OMCCs enable compact, low-cost power-efficient all-photonic processing of multiple microwave signals, crucial for current and future beyond-5G systems, whilst being compatible with silicon integrated photonic circuits. This work reports the demonstration of all-optical up- and down-conversion of 3GPP 5G new-radio (NR) signals from the low- to mid- and extended-mid bands using the first and second harmonics of the frequency comb generated in a silicon OMCC. The OM comb generates up to 6 harmonics in the K-band, which is suitable for microwave photonic applications. The experimental demonstration also evaluates the impact of the phase-noise and the signal-to-noise ratio (SNR) in the frequency-converted 5G NR signals when the first and second OMCC harmonics are employed for frequency conversion.
Design requirements for mm-wave integrated optical beamforming networks Vicente Fito, Maria Morant, Roberto Llorente Proceedings of SPIE the International Society for Optical Engineering, 2023 This paper proposes a mm-wave cellular flexible architecture based on a photonic beamformer network. An overview of integrated optical beamformer technology state-of-the-art is reported considering different implementations, fabrication technologies and the associated design requirements and limitations. A network architecture based on multicore-fiber (MCF) is proposed to operate as fronthaul or backhaul depending on the network configuration and user capacity dynamics. Multi-wavelength operation is achieved employing an optical frequency comb generator capable of providing several phase-correlated optical lines. Following new-radio 5G specifications, both NR 5G frequency ranges (FR) are considered in the proposed network, including FR1 at sub-6 GHz frequency bands, and FR2 in the mm-wave range from 24 to 100 GHz. The work analyses the main subsystems of the integrated photonics beamformer: the laser source which comprises an optical comb, the optical filtering and induced delay subsystems, the arrangement of MCF media to feed different antenna elements and the mm-wave generation subsystem, where optical heterodyning is proposed. The performance of these key subsystems is evaluated experimentally and analyzed by simulation when necessary to assess the proper photonic beamforming network operation.
