Future 100Gbaud DSP-enabled optical coherent transceivers [1] will need 100GS/s DACs with an analog bandwidth (BW) of at least 50GHz to support advanced modulation schemes. CMOS-based DACs are preferred because they support monolithic integration of the DSP and DAC, but the achievable sampling rate and BW is limited [2]. To increase the sampling rate, multiple DACs can be passively or actively combined. A passive combiner using a distributed topology [3] increases the DAC sampling rate to 100GS/s with an analog BW of 13GHz. A 200GS/s linear active combiner with 44GHz analog BW is demonstrated in [4] using a bipolar process. Such linear combiner schemes [3], [4] extend their spurious-free dynamic range by adding the outputs of two complementary clocked DACs and cancelling the images in the even Nyquist zones, however, fundamentally their output analog BW cannot extend beyond the Nyquist frequency of the sub-DACs. Alternatively, time domain interleaving of DACs can be used. A 2-to-1 analog multiplexer (AMUX) using 130nm SiGe BiCMOS is reported in [5] with an analog BW >67GHz. Its measured sampling rate is 56GS/s. The 2-to-1 AMUX from [6] achieved>110GHz analog BW at 180GS/s using a 0.25μm InP HBT process, however it requires digital pre-processing to compensate the limited switching speed [7]. We report a 4-to-1 interleaver with an analog BW beyond Nyquist at sampling rates up to 100GS/s using SiGe BiCMOS. The interleaver is based on the generation and summation of return-to-zero (RZ) signals from analog input signals. The advantage of the architecture is that it can simultaneously perform equalization to e.g. compensate interconnect losses at its output and cancels clock feedthrough.
We present a 6-bit 56-GSa/s digital-to-analog converter (DAC), implemented in 55 nm SiGe BiCMOS. It consumes 2.36 W of which 0.77 W is utilized in the DAC core. Experiments show an analog 3-dB bandwidth exceeding 28 GHz and an effective number of bits (ENOB) of 3.9. We demonstrate transmission of 112 Gb/s four-level pulse-amplitude modulation (PAM-4) and 168 Gb/s PAM-8 over a channel consisting of an electrical probe and 20 cm RF cables. With pre-equalization compensating the channel loss, we achieve a 0.59 Vpp signal swing.
In-band full-duplex (FD) wireless communication allows the simultaneous transmission and reception of data at the same frequency band, effectively doubling the spectral efficiency and data rate while reducing the latency. Previously published designs mostly target the self-interference (SI) cancellation in conventional wireless systems. In this paper, we focus on real-time SI cancellation for short-reach wireless FD systems. The superior signal quality of a point-to-point short-reach wireless system, allows the utilization of wideband communications to achieve a high throughput. Besides, in such wireless systems, the impacts of phase noise and nonlinear distortions are largely reduced, easing the SI cancellation. Moreover, the degradation of signal reception quality due to FD operation is experimentally evaluated in different environments. Experimental results of a prototype implementation show that a combination of antenna isolation and digital cancellation can already achieve an overall SI cancellation performance of 72.5 dB over a bandwidth of 123 MHz. This prototype can support a high-data-rate FD communication link of close to 1 Gbps up to 300 cm with an error vector magnitude lower than -26 dB in a typical indoor environment.
10Gb/s, 28GHz radio-over-fiber transmission using a directly-modulated single-mode C-band VCSEL is demonstrated over 2km.The chirp of the VCSEL is translated into intensity modulation to extend the fiber-reaches and increase the power budget with 10dB.
The demand for compute capacity is currently doubling every 3.4months. This has accelerated the need for Terabit optical transceivers for data centre applications. Scaling options, and photonic and electronic technologies that can meet such demand are presented.
This paper shows how to estimate an extended polynomial matrix description of a non-linear MIMO system. Both linear and non-linear impulse responses are obtained by transmitting pseudo random binary sequence (PRBS) test-patterns and can be easily separated thanks to the shift-and-add property of PRBS. Further on, a method to equalize such nonlinear systems based on this extended polynomial matrix and the result is compared with a linear zero-forcing equalizer for different channel impairments and in a VPI simulation. This proves the presented approach is suited to cancel self-phase modulation in coherent optical communication systems.
A mmWave-over-fiber distributed antenna system (DAS), in combination with highly efficient air-filled substrate-integrated-waveguide (AFSIW) remote antenna units (RAUs), proves to be a prime candidate to counter the harsh propagation conditions that arise at mmWave frequencies. This paper proposes a system-level model to accurately analyze the link quality of a downlink mmWave-over-fiber wireless link in a time-efficient way. The model includes a realistic antenna description, fiber losses, and non-linear effects of the opto-electrical/electro-optical transducers and the electrical amplifiers. This provides in-depth insight into the signal quality at each stage of the link and enables offline link optimization. In addition, the modular nature allows incorporating more advanced wireless channel models/measurements, which can be used to optimize RAU placement in the future. Finally, the model is validated by means of a measurement campaign, demonstrating good agreement.
A cost-effective, compact, and high-performance antenna element for beamforming applications in all fifth-generation (5G) New Radio bands in the [24.25–29.5] $ \,$ GHz spectrum is proposed in this letter. The novel antenna topology adopts a square patch, an edge-plated air-filled cavity, and an hourglass-shaped aperture-coupled feed to achieve a very high efficiency over a wide frequency band in a compact footprint ( $\boldsymbol{{0.48} \lambda _0 \times \text{0.48}\lambda _0}$ ). Its compliance with standard printed circuit board (PCB) fabrication technology, without complex multilayer PCB stack, ensures low-cost fabrication. The antenna feedplane offers a platform for compact integration of active electronic circuitry. Two different modular 1 $ \boldsymbol{\times }$ 4 antenna arrays were realized to demonstrate its suitability for broadband multiantenna systems. Measurements of the fabricated antenna element and the antenna array prototypes revealed a $-$ 10 dB impedance bandwidth of 7.15 GHz (26.8%) and 8.2 GHz (30.83%), respectively. The stand-alone antenna features a stable peak gain of 7.4 $ \,\pm \,$ 0.6 $ \,$ dBi in the [24.25–29.5] $ \,$ GHz band and a measured total efficiency of at least 85%. The 1 × 4 array provides a peak gain of 10.1 $ \,\pm \,$ 0.7 $ \,$ dBi and enables grating-lobe-free beamsteering from ${-}\text{50}^\circ$ to $ \text{50}^\circ$ .
The article describes a numerical approach for Massive MIMO channel modeling that accounts for the effects of electromagnetic coupling between a user and the receiving device. The modeling is performed by a combination of the Finite-Difference Time-Domain and the Ray-Tracing methods, supplemented with a stochastic geometry model of the propagation environment. The influence of user-coupling on the channel properties was studied statistically using the singular value spread and matrix power ratio metrics of the channel correlation matrix. The time-averaged Poynting vector distribution in the near-field of the receiver was evaluated using a realistic human phantom model and the Maximum Ratio Transmission precoding scheme in the downlink. The average enhancement of the time-average Poynting vector magnitude at the receiver location, compared to the surrounding area, was found to be around 10 dB when using 36 antenna elements at the base station. The electromagnetic field exposure of the phantom was assessed in terms of the 10g-average peak-spatial Specific Absorption Rate and compared with the existing public guidelines. Comparison of the EMF and exposure results provides a new perspective on the future regulatory procedures.
Integrated photonic systems require fast modulators to keep up with demanding operation speeds and increasing data rates. The silicon nitride integrated photonic platform is of particular interest for applications such as datacom, light detection and ranging (LIDAR), quantum photonics, and computing owing to its low losses and CMOS compatibility. Yet, this platform inherently lacks high-speed modulators. Heterogeneous integration of lithium niobate on silicon nitride waveguides can address this drawback with its strong Pockels effect. We demonstrate the first high-speed lithium niobate modulator heterogeneously integrated on silicon nitride using micro-transfer printing. The device is 2 mm long with a half-wave voltage Vπ of 14.8 V. The insertion loss and extinction ratio are 3.3 and 39 dB, respectively. Operation beyond 50 GHz has been demonstrated with the generation of open eye diagrams up to 70 Gb/s. This proof-of-principle demonstration opens up possibilities for more scalable fabrication of these trusted and performant devices.
