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The terahertz communications display an important role in high-speed wireless communications, the security threat from the eavesdroppers in the terahertz communications has been gaining attention recently. The true randomness in the physical layer can ensure one-time-pad encryption for secured terahertz communications, however, physical layer security schemes like the quantum key distribution methods suffer from device imperfections that limit the desirable signal rate and link distance. Herein, we present the quantum noise secured terahertz wireless communications with photonic terahertz signal generation schemes. With the high-order diffusion algorithms, the signal is masked by the quantum noise ciphers to the eavesdroppers and cannot be detected because the inevitable randomness by quantum noise measurement will cause physical measurement errors. In the experiment, we demonstrate 16 Gbits(-1) quantum noise secured terahertz wireless communications with the conventional optical communication realms and devices, operating at 300 GHz terahertz frequency. This quantum noise secured terahertz communication approach is a significant step toward high-security wireless communications., QC 20221223

The sixth-generation (6G) mobile networks must increase coverage and improve spectral efficiency, especially for cell-edge users. Distributed multiple-input multiple-output (D-MIMO) networks can fulfill these requirements provided that transmission/reception points (TRxPs) of the network can be synchronized with sub-nanosecond precision, however, synchronization with current backhaul and fronthaul digital interfaces is challenging. For 6G new services and scenarios, analog radio-over-fiber (ARoF) is a prospective alternative for future mobile fronthaul where current solutions fall short to fulfill future demands on bandwidth, synchronization, and/or power consumption. This paper presents an experimental validation of coherent joint transmissions (CJTs) in a two TRxPs D-MIMO network where ARoF fronthaul links allow to meet the required level of synchronization. Results show that by means of CJT a combined diversity and power gain of +5 dB is realized in comparison with a single TRxP transmission., Part of ISBN 9798350311020QC 20230831

Silicon photonics (SiP) is a key enabling technology for high-baudrate communication. It is a key technology for future 800 Gbps and 1.6 Tbps solutions to meet the ever-increasing demands. The 800G pluggable multi-source agreement (MSA) suggests that intensity-modulated direct-detection (IM/DD) is the most sustainable way forward [1]. The high operational bandwidth of each transceiver component is essential. An ultra-compact SiP slow light modulator with record-high bandwidth of 110 GHz shows the potential [2]. Therefore, both multilevel pulse amplitude modulation (PAM) and on-off keying (OOK) should be considered. SiP offers excellent production yield and has a substantial role in optical interconnects. SiP ring resonator modulators (RRM) have unique advantages like a small footprint, simple driver configuration, low power consumption, and suitability for multichannel applications. On the other hand, the SiP Mach-Zehnder modulator (MZM) offers differential drive benefits., Part of ISBN 9798350303032QC 20230919

We demonstrate a record 240 Gbaud on-off keying, 150 Gbaud 4-level pulse amplitude modulation, and 100 Gbaud 6-level pulse amplitude modulation SiP MZM-based transmitter with performance below the 6.25% overhead HD-FEC threshold. We also show a 160 Gbaud on-off keying SiP RRM-based transmitter., Part of ISBN 9781665486552QC 20230712

We experimentally demonstrate an O-band single-lane 200 Gb/s intensity modulation direct detection (IM/DD) transmission system using a low-chirp, broadband, and high-power directly modulated laser (DML). The employed laser is an isolator-free packaged module with over 65-GHz modulation bandwidth enabled by a distributed feedback plus passive waveguide reflection (DFB+R) design. We transmit high baud rate signals over 20-km standard single-mode fiber (SSMF) without using any optical amplifiers and demodulate them with reasonably low-complexity digital equalizers. We generate and detect up to 170 Gbaud non-return-to-zero on-off-keying (NRZ-OOK), 112 Gbaud 4-level pulse amplitude modulation (PAM4), and 100 Gbaud PAM6 in the optical back-to-back configuration. After transmission over the 20-km optical-amplifier-free SSMF link, up to 150 Gbaud NRZ-OOK, 106 Gbaud PAM4, and 80 Gbaud PAM6 signals are successfully received and demodulated, achieving bit error rate (BER) performance below the 6.25%-overhead hard-decision (HD) forward-error-correction code (FEC) limit. The demonstrated results show the possibility of meeting the strict requirements towards the development of 200 Gb/s/lane IM/DD technologies, targeting 800 Gb/s and 1.6 Tb/s LR applications., QC 20230704

The enormous traffic growth sets a stringent requirement to upgrade short-reach optical links to 1.6 TbE capacity in an economically viable way. The power consumption and latency in these links should be as low as possible, especially for high-speed computing. This is possible to achieve using high baudrate on-off keying links thanks to a better noise tolerance and a relaxed requirement on linearity for electronics and photonics. In this regard, we demonstrate a 200 Gbaud on-off keying link without any optical amplification using an externally modulated laser with 3.3 dBm of modulated output power operating at 1541.25 nm wavelength. We achieve transmission over 200 meters of single-mode fiber with performance below 6.25% overhead hard-decision forward error correction threshold for each baudrate and all selection of modulation formats. We also show 108 Gbaud on-off keying link with superior performance without decision feedback equalizer up to 400 meters of single-mode fiber. In addition, we benchmark the short-reach optical link with 112 Gbaud four-level pulse amplitude modulation and 100 Gbaud six-level pulse amplitude modulation. For 108 Gbaud on-off keying and 112 Gbaud four-level pulse amplitude modulation, we can achieve an even lower bit error rate., QC 20230613

Since about one and half centuries ago, at the dawn of modern communications, the radio and the optics have been two separate electromagnetic spectrum regions to carry data. Differentiated by their generation/detection methods and propagation properties, the two paths have evolved almost independently until today. The optical technologies dominate the long-distance and high-speed terrestrial wireline communications through fiber-optic telecom systems, whereas the radio technologies have mainly dominated the short- to medium-range wireless scenarios. Now, these two separate counterparts are both facing a sign of saturation in their respective roadmap horizons, particularly in the segment of free-space communications. The optical technologies are extending into the mid-wave and long-wave infrared (MWIR and LWIR) regimes to achieve better propagation performance through the dynamic atmospheric channels. Radio technologies strive for higher frequencies like the millimeter-wave (MMW) and sub-terahertz (sub-THz) to gain broader bandwidth. The boundary between the two is becoming blurred and intercrossed. During the past few years, we witnessed technological breakthroughs in free-space transmission supporting very high data rates, many achieved with the assistance of photonics. This paper focuses on such photonics-assisted free-space communication technologies in both the lower and upper sides of the THz gap and provides a detailed review of recent research and development activities on some of the key enabling technologies. Our recent experimental demonstrations of high-speed free-space transmissions in both frequency regions are also presented as examples to show the system requirements for device characteristics and digital signal processing (DSP) performance., QC 20220614

Error vector magnitude (EVM) is a metric for assessing the quality of m-ary quadrature amplitude modulation (mQAM) signals. Recently proposed deep learning techniques, e.g., feedforward neural networks (FFNNs) -based EVM estimation scheme leverage fast signal quality monitoring in coherent optical communication systems. Such a scheme estimates EVM from amplitude histograms (AHs) of short signal sequences captured before carrier phase recovery (CPR). In this work, we explore further complexity reduction by proposing a simple linear regression (LR) -based EVM monitoring method. We systematically compare the performance of the proposed method with the FFNN-based scheme and demonstrate its capability to infer EVM from an AH when the modulation format information is known in advance. We perform both simulation and experiment to show that the LR-based EVM estimation method achieves a comparable accuracy as the FFNN-based scheme. The technique can be embedded with modulation format identification modules to provide comprehensive signal information. Therefore, this work paves the way to design a fast-learning scheme with parsimony as a future intelligent OPM enabler., QC 20221213

Error vector magnitude (EVM) is commonly used for evaluating the quality of m-ary quadrature amplitude modulation (mQAM) signals. Recently proposed deep learning techniques for EVM estimation extend the functionality of conventional optical performance monitoring (OPM). In this article, we evaluate the tolerance of our developed EVM estimation scheme against various impairments in coherent optical systems. In particular, we analyze the signal quality monitoring capabilities in the presence of residual in-phase/quadrature (IQ) imbalance, fiber nonlinearity, and laser phase noise. We use feedforward neural networks (FFNNs) to extract the EVM information from amplitude histograms of 100 symbols per IQ cluster signal sequence captured before carrier phase recovery. We perform simulations of the considered impairments, along with an experimental investigation of the impact of laser phase noise. To investigate the tolerance of the EVM estimation scheme to each impairment type, we compare the accuracy for three training methods: 1) training without impairment, 2) training one model for all impairments, and 3) training an independent model for each impairment. Results indicate a good generalization of the proposed EVM estimation scheme, thus providing a valuable reference for developing next-generation intelligent OPM systems., QC 20220530

A roadmap for future wireless communications is expected to exploit all transmission-suitable spectrum bands, from the microwave to the optical frequencies, to support orders of magnitude faster data transfer with much lower latency than the deployed solutions nowadays. The currently under-exploited mid-infrared (mid-IR) spectrum is an essential building block for such an envisioned all-spectra wireless communication paradigm. Free-space optical (FSO) communications in the mid-IR region have recently attracted great interest due to their intrinsic merits of low propagation lass and high tolerance of atmospheric perturbations. Future development of viable mid-IR FSO transceivers requires a semiconductor source to fulfill the high bandwidth, low energy consumption, and small footprint requirements. In this context, quantum cascade laser (QCL) appears as a promising technological choice. In this work, we present an experimental demonstration of a mid-IR FSO link enabled by a 4.65-mu m directly modulated (DM) QCL operating at room temperature. We achieve a transmission data rate of up to 6 Gbps over a 0.5-m link distance. This achievement is enabled by system-level characterization and optimization of transmitter and receiver power level and frequency response and assisted with advanced modulation and digital signal processing (DSP) techniques. This work pushes the QCL-based FSO technology one step closer to practical terrestrial applications, such as the fixed wireless access and the wireless mobile backhaul. Such a QCL-based solution offers a promising way towards the futuristic all-spectra wireless communication paradigm by potentially supporting the whole spectrum from the MIR to the terahertz (THz)., QC 20220429

Foreseen requirements and use cases of future beyond fifth-generation (B5G) and sixth-generation (6G) mobile networks have shown that current mobile networks implementations must be reconsidered. Analog radio-over-fiber (ARoF) is a prospective solution for future mobile fronthaul of certain applications where current solutions fall short to fulfill future demands on bandwidth and power consumption. This paper provides a complete New-Radio (NR) conformance testing of ARoF fronthaul links in full accordance with the 3rd Generation Partnership Project (3GPP) technical specifications. We experimentally verified that the adjacent channel leakage power ratio (ACLR) and the error vector magnitude (EVM) transmitter requirements are fulfilled validating ARoF links as a suitable solution for next-generation mobile fronthaul. Wireless transmissions results are also provided., Part of ISBN 9781665421218QC 20230801

We demonstrate a 200 Gbps IM/DD link without any optical amplification using C-band externally modulated laser with 3.3 dBm of modulated output power and O-band directly modulated laser with 7.3 dBm of modulated output power., Part of ISBN 9784885523366QC 20230614

Short reach optical communication technologies are increasingly demanded in several fast-evolving application scenarios in both telecom and datacom. Low-cost and low-complexity intensity modulation and direct detection (IM/DD) technologies are challenged to scale up the link rate beyond 400 Gbps by increasing the single-lane rate towards 200 Gbps, to maintain a low lane count in client-side optics. Limited by the bandwidth of both electronics and optoelectronics, and the more pronounced chromatic dispersion in the fiber, such high baud rate systems require the use of digital signal processing techniques with forward error correction (FEC) coding. Therefore, in this work, we first summarize a few potential alternative technologies to the IM/DD for future development and then focus on extending the IM/DD systems towards 200 Gbps lane rate. We study both their capability and their performance limits using numerical simulations and transmission experiments., QC 20210916

We report our recent studies in photonics-assisted free-space transmissions in both the lower (0.3-0.5 THz) and upper- (similar to 64.5 THz) terahertz bands. We adopt the hybrid electro-optical approach for the lower-THz signal transmission, whereas a directly modulated quantum cascade laser is used for the upper-THz band., Part of proceedings: ISBN 978-1-6654-3868-1QC 20220810

We report on an experimental demonstration of a mid-infrared free-space communication link enabled by a directly modulated quantum cascade laser operating at room temperature. A record high transmission rate up to 6 Gbps over 50-cm link distance is demonstrated at 4.65 mu m wavelength., QC 20220811Part of proceedings: ISBN 978-1-6654-3868-1

Robustness against the large linewidth semiconductor laser-induced impairments in coherent systems is experimentally demonstrated for a feedforward neural network-enabled EVM estimation scheme. A mean error of 0.4% is achieved for 28 Gbaud square and circular QAM signals and linewidths up to 12.3 MHz., QC 20220815Part of proceedings: ISBN 978-1-6654-3868-1

Nonlinearity is one of the key issues that hinder the development of high-capacity optical short reach systems. This paper proposes three variants of kernel affine projection (KAP) algorithms, all of which combine kernel mapping and affine projection in a reproducing kernel Hilbert space for compensating nonlinear impairments in optical short reach systems. An intensity modulation/direct detection system with a single digital-to-analogue converter, a packaged externally modulated laser and a packaged InP photo-detector is used for experimental demonstration, achieving 238-Gbps (net rate 222-Gbps). Experimental results show that the KAP algorithms can mitigate nonlinear impairments in short-reach communications while maintaining low complexity in reproducing kernel Hilbert space., QC 20201110

Quantum key distribution (QKD) is regarded as an alternative to traditional cryptography methods for securing data communication by quantum mechanics rather than computational complexity. Towards the massive deployment of QKD, embedding it with the telecommunication system is crucially important. Homogenous optical multi-core fibers (MCFs) compatible with spatial division multiplexing (SDM) are essential components for the next-generation optical communication infrastructure, which provides a big potential for co-existence of optical telecommunication systems and QKD. However, the QKD channel is extremely vulnerable due to the fact that the quantum states can be annihilated by noise during signal propagation. Thus, investigation of telecom compatibility for QKD co-existing with high-speed classical communication in SDM transmission media is needed. In this paper, we present analytical models of the noise sources in QKD links over heterogeneous MCFs. Spontaneous Raman scattering and inter-core crosstalk are experimentally characterized over spans of MCFs with different refractive index profiles, emulating shared telecom traffic conditions. Lower bounds for the secret key rates and quantum bit error rate (QBER) due to different core/wavelength allocation are obtained to validate intra- and inter-core co-existence of QKD and classical telecommunication., QC 20200603

The article analyzes the total cost of ownership (TCO) of 5G fronthauling solutions based on analog and digital radio-over-fiber (RoF) architectures in cloud radio access networks (C-RANs). The capital and operational expenditures (CAPEX, OPEX) are assessed, for a 10-year period, considering three different RoF techniques: intermediate frequency analog RoF (IF-A-RoF), digital signal processing (DSP) assisted analog RoF (DSP-A-RoF), and digital RoF (D-RoF) based on the common public radio interface (CPRI) specifications. The greenfield deployment scenario under exam includes both fiber trenching (FT) and fiber leasing (FL) options. The TCO is assessed while varying (i) the number of aggregated subcarriers, (ii) the number of three-sector antennas located at the base station, and (iii) the mean fiber-hop length. The comparison highlights the significance that subcarrier aggregation has on the cost efficiency of the analog RoF solutions. In addition, the analysis details the contribution of each cost category to the overall CAPEX and OPEX values. The obtained results indicate that subcarrier aggregation via DSP results in high cost efficiency for a mobile fronthaul network, while a CPRI-based architecture together with FL brings the highest OPEX value., QC 20210125

We experimentally demonstrate a net-rate 503.61-Gbit/s discrete multitone (DMT) transmission over 10-km 7-core fiber with 1.5-mu m single mode VCSEL, where low-complexity kernel-recursive-least-squares algorithm is employed for nonlinear channel equalization., Part of proceedings ISBN 978-1-5386-4862-9QC 20220926

We report on a 116 Gb/s on-off keying (OOK), four pulse amplitude modulation (PAM) and 105-Gb/s 8-PAM optical transmitter using an InP-based integrated and packaged externally modulated laser for high-speed optical interconnects with up to 30 dB static extinction ratio and over 100-GHz 3-dB bandwidth with 2 dB ripple. In addition, we study the tradeoff between power penalty and equalizer length to foresee transmission distances with standard single mode fiber., QC 20210825