Abstract Next generation wireless communications systems are rapidly penetrating higher RF frequency bands together with massive Multiple-Input-Multiple-Output (MIMO) communication schemes, requiring processing units to perform at millimeter-wave RF carriers while supporting high-bandwidth and highly scalable configurations. However, operating electronic MIMO processing units at such high-frequency and high-bandwidth system requirements becomes extremely challenging when targeting beneficial energy consumption metrics. Photonic processors emerge as a promising alternative to tackle channel interference encountered in MIMO systems, with the main argumentation building on the large available bandwidth and favorable energy efficiency credentials of Photonic Integrated Circuit (PIC) technologies. However, photonic MIMO processors that support more than 2 channels are currently entirely missing; moreover, their architectural framework relies exclusively on matrix decomposition algebra, raising significant concerns about their scalability potential. In this paper, we present a scalable silicon photonic (SiPho) MIMO processor architecture that exploits the coherent crossbar (Xbar) interferometric layout and demonstrates experimentally its successful performance in proof-of-concept MIMO setups. The zero-forcing photonic processor can cancel channel interference and compensate for phase offsets in the received signals. The experimental validation of the proposed system is performed through a 4×4 SiPho Xbar chip, demonstrating 3×3 and 4×4 MIMO processing with phase offset compensation capabilities for both single-tone and data-modulated RF channels, transmitted through arbitrary linear channels. This work presents, to the best of our knowledge, the largest demonstrated photonic MIMO processor, utilizing the SiPho Xbar linear optical circuit architecture and bearing the promise of scaling to more than 32 high-RF frequency and mmWave wireless channels.
Complex-valued double-sideband direct detection (DD) can reconstruct the optical field and achieve a high electrical spectral efficiency (ESE) comparable to that of a coherent homodyne receiver, and DD does not require a costly local oscillator laser. However, a fundamental question remains if there is an optimal DD receiver structure with the simplest design to approach the performance of the coherent homodyne detection. This study derives the optimal DD receiver structure with an optimal transfer function to recover a quadrature amplitude modulation (QAM) signal with a near-zero guard band at the central frequency of the signal. We derive the theoretical ESE limit for various detection schemes by invoking Shannon’s formula. Our proposed scheme is closest to coherent homodyne detection in terms of the theoretical ESE limit. By leveraging a WaveShaper to construct the optimal transfer function, we conduct a proof-of-concept experiment to transmit a net 228.85-Gb/s 64-QAM signal over an 80-km single-mode fiber with a net ESE of 8.76 b/s/Hz. To the best of our knowledge, this study reports the highest net ESE per polarization per wavelength for DD transmission beyond 40-km single-mode fiber. For a comprehensive metric, denoted as 2<sup>ESE</sup>×Reach, we achieve the highest 2<sup>ESE</sup>×Reach per polarization per wavelength for DD transmission.
Zhe Zhang, Min Zhou, Chao Wang, Yingying Wang · 7 authors
A new approach to conquer the thermal phase drift of an optical fiber Fabry-Perot interferometer (FPI) sensor is proposed and experimentally demonstrated. By employing a hollow-core anti-resonant fiber (HC-ARF) and optimizing the fusion splicing (includes mode field adaptation) between the lead-in single-mode fiber (SMF) and the HC-ARF, a high spectral resolution ( λ /Δ λ ≈ 3.8 × 10 4 ) optical fiber air-cavity FPI sensor with a fringe visibility higher than 7 dB is constructed. To eliminate the thermal phase drift (i.e. temperature crosstalk) of the sensor that originates from the intrinsic thermal expansion effect of the silica material of the HC-ARF, the FPI air cavity is connected to the external environments, by which the effect of air expelling from the cavity with temperature increasing can well compensate the temperature-induced cavity elongation. As a result, the thermal phase drift of the FPI is reduced to zero at a temperature range of ∼ 80–110 °C and within the temperature range of 40–80 °C, the thermal phase drift is still halved compared with the sealed FPI cavity. The nearly zero thermal phase drift of a FPI at such a temperature range has never been achieved before, to our best knowledge. As a proof of concept, a temperature-immune fiber-optic strain sensor is demonstrated. This work offers a new and efficient approach to eliminate the thermal phase drift (i.e. temperature crosstalk) of a fiber-optic device, which may significantly improve the measurement accuracy and detection limit of fiber-optic FPI sensors. Furthermore, the principle and schema can be generalized to a wide variety of fiber-optic devices.
As blockchain technology and cryptocurrency become increasingly mainstream, ever-increasing energy costs required to maintain the computational power running these decentralized platforms create a market for more energy-efficient hardware. Photonic cryptographic hash functions, which use photonic integrated circuits to accelerate computation, promise energy efficiency for verifying transactions and mining in a cryptonetwork. Like many analog computing approaches, however, current proposals for photonic cryptographic hash functions that promise similar security guarantees as Bitcoin are susceptible to systematic error, so multiple devices may not reach a consensus on computation despite high numerical precision (associated with low photodetector noise). In this paper, we theoretically and experimentally demonstrate that a more general family of robust discrete analog cryptographic hash functions, which we introduce as LightHash, leverages integer matrix-vector operations on photonic mesh networks of interferometers. The difficulty of LightHash can be adjusted to be sufficiently tolerant to systematic error (calibration error, loss error, coupling error, and phase error) and preserve inherent security guarantees present in the Bitcoin protocol. Finally, going beyond our proof-of-concept, we define a ``photonic advantage'' criterion and justify how recent developments in CMOS optoelectronics (including analog-digital conversion) provably achieve such advantage for robust and digitally-verifiable photonic computing and ultimately generate a new market for decentralized photonic technology.
An ultra-long distance distributed intrusion detecting system assisted with power amplification and sensitivity enhancement is proposed and demonstrated. First, through introducing multiple bidirectional amplifiers into the unbalanced Mach-Zehnder/Sagnac interferometer-based fiber sensing link, the sensing distance is remarkably extended, and second, the signal-to-noise ratio of this sensing system is significantly improved from less than 2 to 6-8 dB by coating the sensing fiber with organic silicone polymer. Furthermore, the high-order downtrend fitting function is adopted to implement the intrusion locating of ultralong distance sensing; the zero-padding fast Fourier transform algorithm and multiple-averaging method are jointly utilized for the improvement of the locating accuracy. Experimentally, a proof-of-concept distributed intrusion detecting system is constructed with the employment of bidirectional amplification. In particular, the ultra-long sensing distance up to 226.337 km is implemented, which is the reported longest distributed sensing system to the best of our knowledge.