Advancing LWIR FSO communication through high-speed multilevel signals and directly modulated quantum cascade lasers.

This study investigates the potential of long-wave infrared (LWIR) free-space optical (FSO) transmission using multilevel signals to achieve high spectral efficiency. The FSO transmission system includes a directly modulated-quantum cascade laser (DM-QCL) operating at 9.1 µm and a mercury cadmium telluride (MCT) detector.

Unipolar quantum optoelectronics for high speed direct modulation and transmission in 8-14 µm atmospheric window.

The large mid-infrared (MIR) spectral region, ranging from 2.5 µm to 25 µm, has remained under-exploited in the electromagnetic spectrum, primarily due to the absence of viable transceiver technologies. Notably, the 8-14 µm long-wave infrared (LWIR) atmospheric transmission window is particularly suitable for free-space optical (FSO) communication, owing to its combination of low atmospheric propagation loss and relatively high resilience to turbulence and other atmospheric disturbances.

Silica micro-rod resonator-based Kerr frequency comb for high-speed short-reach optical interconnects.

Conventional data center interconnects rely on power-hungry arrays of discrete wavelength laser sources. However, growing bandwidth demand severely challenges ensuring the power and spectral efficiency toward which data center interconnects tend to strive. Kerr frequency combs based on silica microresonators can replace multiple laser arrays, easing the pressure on data center interconnect infrastructure.

Editorial for the Special Issue on Broadband Terahertz Devices and Communication Technologies.

The remarkable explosion of wireless devices and bandwidth-consuming Internet applications have boosted the demand for wireless communications with ultra-high data rate [...

Optical amplification-free deep reservoir computing-assisted high-baudrate short-reach communication.

An optical amplification-free deep reservoir computing (RC)-assisted high-baudrate intensity modulation direct detection (IM/DD) system is experimentally demonstrated using a 100G externally modulated laser operated in C-band. We transmit 112 Gbaud 4-level pulse amplitude modulation (PAM4) and 100 Gbaud 6-level PAM (PAM6) signals over a 200-m single-mode fiber (SMF) link without any optical amplification. The decision feedback equalizer (DFE), shallow RC, and deep RC are adopted in the IM/DD system to mitigate impairment and improve transmission performance.

High bitrate data transmission in the 8-14 µm atmospheric window using an external Stark-effect modulator with digital equalization.

High bitrate mid-infrared links using simple (NRZ) and multi-level (PAM-4) data coding schemes have been realized in the 8 µm to 14 µm atmospheric transparency window. The free space optics system is composed of unipolar quantum optoelectronic devices, namely a continuous wave quantum cascade laser, an external Stark-effect modulator and a quantum cascade detector, all operating at room-temperature. Pre- and post-processing are implemented to get enhanced bitrates, especially for PAM-4 where inter-symbol interference and noise are particularly detrimental to symbol demodulation.

Simultaneous modulation format identification and OSNR monitoring based on optoelectronic reservoir computing.

An approach for simultaneous modulation format identification (MFI) and optical signal-to-noise ratio (OSNR) monitoring in digital coherent optical communications is proposed based on optoelectronic reservoir computing (RC) and the signal's amplitude histograms (AHs) obtained after the adaptive post-equalization. The optoelectronic RC is implemented using a Mach-Zehnder modulator and optoelectronic delay feedback loop. We investigate the performance of the proposed model with the number of symbols, bins of AHs and the hyperparameters of optoelectronic RC.

Human recognition with the optoelectronic reservoir-computing-based micro-Doppler radar signal processing.

Current perception and monitoring systems, such as human recognition, are affected by several environmental factors, such as limited light intensity, weather changes, occlusion of targets, and public privacy. Human recognition using radar signals is a promising direction to overcome these defects; however, the low signal-to-noise ratio of radar signals still makes this task challenging. Therefore, it is necessary to use suitable tools that can efficiently deal with radar signals to identify targets.

Hybrid fiber-THz fronthaul supporting up to 16384-QAM-OFDM with the delta-sigma modulation.

With the progress of high-capacity radio access networks, ultra-dense small cells are rapidly being deployed in urban areas. As a result, the deployment of a large number of optical fibers in urban areas becomes a severe issue. In this Letter, we propose a hybrid fiber-terahertz (THz) mobile fronthaul system supporting flexible and high-order wireless signal transmission with the delta-sigma modulation.

Integrated dual-laser photonic chip for high-purity carrier generation enabling ultrafast terahertz wireless communications.

Photonic generation of Terahertz (THz) carriers displays high potential for THz communications with a large tunable range and high modulation bandwidth. While many photonics-based THz generations have recently been demonstrated with discrete bulky components, their practical applications are significantly hindered by the large footprint and high energy consumption. Herein, we present an injection-locked heterodyne source based on generic foundry-fabricated photonic integrated circuits (PIC) attached to a uni-traveling carrier photodiode generating high-purity THz carriers.

Nonlinearity-aware optoelectronic terahertz discrete multitone signal transmission with a zero-bias diode.

The terahertz band has been recognized as a promising candidate to support future rate-greedy applications such as 6G communications. Optoelectronic terahertz communications are beneficial for the realization of high-speed transmission. In this Letter, we propose and experimentally demonstrate an optoelectronic terahertz transmission system with intensity modulation and direct detection, where a discrete multitone (DMT) waveform with high-order quadrature amplitude modulation (QAM) is used.

Kernel mapping for mitigating nonlinear impairments in optical short-reach communications.

Nonlinear impairments induced by the opto-electronic components are one of the fundamental performance-limiting factors in high-speed optical short-reach communications, significantly hindering capacity improvement. This paper proposes to employ a kernel mapping function to map the signals in a Hilbert space to its inner product in a reproducing kernel Hilbert space, which has been successfully demonstrated to mitigate nonlinear impairments in optical short-reach communication systems. The operation principle is derived.

Multi-channel collision-free reception for optical interconnects.

A multi-channel reception scheme that allows each node to receive an arbitrary set of wavelengths simultaneously (i.e., collision-free) is proposed for optical interconnects.

Real-time 100 Gbps/λ/core NRZ and EDB IM/DD transmission over multicore fiber for intra-datacenter communication networks.

A BiCMOS chip-based real-time intensity modulation/direct detection spatial division multiplexing system is experimentally demonstrated for both optical interconnects. 100 Gbps/λ/core electrical duobinary (EDB) transmission over 1 km 7-core multicore fiber (MCF) is carried out, achieving KP4 forward error correction (FEC) limit (BER < 2E-4). Using optical dispersion compensation, 7 × 100 Gbps/λ/core transmission of both non-return-to-zero (NRZ) and EDB signals over 10 km MCF transmission is achieved with BER lower than 7% overhead hard-decision FEC limit (BER < 3.

Spectrally efficient digitized radio-over-fiber system with k-means clustering-based multidimensional quantization.

We propose a spectrally efficient digitized radio-over-fiber (D-RoF) system by grouping highly correlated neighboring samples of the analog signals into multidimensional vectors, where the k-means clustering algorithm is adopted for adaptive quantization. A 30  Gbit/s D-RoF system is experimentally demonstrated to validate the proposed scheme, reporting a carrier aggregation of up to 40 100 MHz orthogonal frequency division multiplexing (OFDM) channels with quadrate amplitude modulation (QAM) order of 4 and an aggregation of 10 100 MHz OFDM channels with a QAM order of 16384. The equivalent common public radio interface rates from 37 to 150  Gbit/s are supported.

Nonlinearity-aware 200 Gbit/s DMT transmission for C-band short-reach optical interconnects with a single packaged electro-absorption modulated laser.

We experimentally demonstrate the transmission of a 200 Gbit/s discrete multitone (DMT) at the soft forward error correction limit in an intensity-modulation direct-detection system with a single C-band packaged distributed feedback laser and traveling-wave electro absorption modulator (DFB-TWEAM), digital-to-analog converter and photodiode. The bit-power loaded DMT signal is transmitted over 1.6 km standard single-mode fiber with a net rate of 166.

Digital mobile fronthaul employing differential pulse code modulation with suppressed quantization noise.

A differential pulse code modulation (DPCM) based digital mobile fronthaul architecture is proposed and experimentally demonstrated. By using a linear predictor in the DPCM encoding process, the quantization noise can be effectively suppressed and a prediction gain of 7~8 dB can be obtained. Experimental validation is carried out with a 20 km 15-Gbaud/λ 4-level pulse amplitude modulation (PAM4) intensity modulation and direct detection system.

Gigabit free-space multi-level signal transmission with a mid-infrared quantum cascade laser operating at room temperature.

Gigabit free-space transmissions are experimentally demonstrated with a quantum cascaded laser (QCL) emitting at mid-wavelength infrared of 4.65 μm, and a commercial infrared photovoltaic detector. The QCL operating at room temperature is directly modulated using on-off keying and, for the first time, to the best of our knowledge, four- and eight-level pulse amplitude modulations (PAM-4, PAM-8).

Laser Frequency Noise in Coherent Optical Systems: Spectral Regimes and Impairments.

Coherent communication networks are based on the ability to use multiple dimensions of the lightwave together with electrical domain compensation of transmission impairments. Electrical-domain dispersion compensation (EDC) provides many advantages such as network flexibility and enhanced fiber nonlinearity tolerance, but makes the system more susceptible to laser frequency noise (FN), e.g.

Impact of local oscillator frequency noise on coherent optical systems with electronic dispersion compensation.

A theoretical investigation of the equalization-enhanced phase noise (EEPN) and its mitigation is presented. We show with a frequency domain analysis that the EEPN results from the non-linear inter-mixing between the sidebands of the dispersed signal and the noise sidebands of the local oscillator. It is further shown and validated with system simulations that the transmission penalty is mainly due to the slow optical frequency fluctuations of the local oscillator.

Phase noise tolerance study in coherent optical circular QAM transmissions with Viterbi-Viterbi carrier phase estimation.

We present a performance evaluation of a non-conventional approach to implement phase noise tolerant optical systems with multilevel modulation formats. The performance of normalized Viterbi-Viterbi carrier phase estimation (V-V CPE) is investigated in detail for circular m-level quadrature amplitude modulation (C-mQAM) signals. The intrinsic property of C-mQAM constellation points with a uniform phase separation allows a straightforward employment of V-V CPE without the need to adapt constellation.

Gigabit close-proximity wireless connections supported by 60 GHz RoF links with low carrier suppression.

We present an experimental investigation of the 60 GHz optical carrier suppressed radio over fiber systems with less than 5 dB carrier suppression. As a case study, the 60 GHz RoF signal is generated using a 12.5 Gb/s commercially available Mach-Zehnder modulator biased at its minimum point.

High phase noise tolerant pilot-tone-aided DP-QPSK optical communication systems.

In this paper we experimentally demonstrate a novel, high phase-noise tolerant, optical dual polarization (DP) quadrature phase-shift keying (QPSK) communication system based on pilot-tone-aided phase noise cancellation (PNC) algorithm. Vertical cavity surface emitting lasers (VCSELs) with approximate 300 MHz linewidth are used as transmitters and local oscillators for coherent detection of optical DP-QPSK signals. The proposed system, with central wavelength at 1540.

2x2 MIMO-OFDM Gigabit fiber-wireless access system based on polarization division multiplexed WDM-PON.

We propose a spectral efficient radio over wavelength division multiplexed passive optical network (WDM-PON) system by combining optical polarization division multiplexing (PDM) and wireless multiple input multiple output (MIMO) spatial multiplexing techniques. In our experiment, a training-based zero forcing (ZF) channel estimation algorithm is designed to compensate the polarization rotation and wireless multipath fading. A 797 Mb/s net data rate QPSK-OFDM signal with error free (<1 × 10(5)) performance and a 1.