Electronic dispersion precompensation of direct-detected NRZ using analog filtering

We demonstrate (in real-time) electrical dispersion compensation in direct detection links using analog transmit side filtering techniques. By this means, we extend the fiber reach using a low complexity solution while avoiding digital preprocessing and digital-to-analog converters (DACs) which are commonly used nowadays. Modulation is done using an IQ MachZehnder modulator (MZM) which allows straightforward compensation of the complex impulse response caused by chromatic dispersion in the fiber. A SiGe BiCMOS 5-tap analog complex finite impulse response (FIR) filter chip and/or a delay between both driving signals of the MZMs is proposed for the filter implementation. Several link experiments are conducted in C-band where transmission up to 60 km of standard single-mode fiber (SSMF) of direct detected 28Gb/s NRZ/OOK is demonstrated. The presented technique can be used in applications where low power consumption is critical

InP-on-Si DFB laser diode with distributed reflector for improved power efficiency

A heterogeneously integrated InP-on-Si DFB laser diode with an active distributed reflector is demonstrated. The goal is to improve the power efficiency of the laser, by reducing the threshold current, and obtaining similar 3-dB modulation bandwidth with similar optical output power levels to previously demonstrated lasers, at lower injected current values. The device was first fabricated as a standard single-section DFB laser, then electrically isolated in two sections with unequal lengths. The shorter section is pumped and acts as an active laser section, while the other section is not pumped and acts as an absorbing distributed reflector. The threshold current was reduced from 17 mA to 9 mA, and the bias current required to achieve similar 3-dB modulation bandwidth to previously demonstrated lasers was reduced from 100 mA to 45 mA. Transmission of a 28 Gbps NRZ-OOK signal for both a back-to-back configuration and over 2 km of NZ-DS fiber is demonstrated, with bit-error-rate below the hard-decision forward-error-correction threshold

Maximally flat and least-square co-design of variable fractional delay filters for wideband software-defined radio

This paper describes improvements in a Farrow-structured variable fractional delay (FD) Lagrange filter for all-pass FD interpolation. The main idea is to integrate the truncated sinc into the Farrow structure of a Lagrange filter, in order that a superior FD approximation in the least-square sense can be achieved. Its primary advantages are the lower level of mean-square-error (MSE) over the whole FD range and the reduced implementation cost. Extra design parameters are introduced for making the trade-off between MSE and maximal flatness under different design requirements. Design examples are included, illustrating an MSE reduction of 50% compared to a classical Farrow-structured Lagrange interpolator while the implementation cost is reduced. This improved variable FD interpolation system is suitable for many applications, such as sample rate conversion, digital beamforming and timing synchronization in wideband software-defined radio (SDR) communications

Distributed multi-user MIMO transmission using real-time sigma-delta-over-fiber for next generation fronthaul interface

To achieve the massive device connectivity and high data rate demanded by 5G, wireless transmission with wider signal bandwidths and higher-order multiple-input multiple-output (MIMO) is inevitable. This work demonstrates a possible function split option for the next generation fronthaul interface (NGFI). The proof-of-concept downlink architecture consists of real-time sigma-delta modulated signal over fiber (SDoF) links in combination with distributed multi-user (MU) MIMO transmission. The setup is fully implemented using off-the-shelf and in-house developed components. A single SDoF link achieves an error vector magnitude (EVM) of 3.14% for a 163.84 MHz-bandwidth 256-QAM OFDM signal (958.64 Mbps) with a carrier frequency around 3.5 GHz transmitted over 100 m OM4 multi-mode fiber at 850 nm using a commercial QSFP module. The centralized architecture of the proposed setup introduces no frequency asynchronism among remote radio units. For most cases, the 2 x 2 MU-MIMO transmission has little performance degradation compared to SISO, 0.8 dB EVM degradation for 40.96 MHz-bandwidth signals and 1.4 dB for 163.84 MHz-bandwidth on average, implying that the wireless spectral efficiency almost doubles by exploiting spatial multiplexing. A 1.4 Gbps data rate (720 Mbps per user, 163.84 MHz-bandwidth, 64-QAM) is reached with an average EVM of 6.66%. The performance shows that this approach is feasible for the high-capacity hot-spot scenario

26 GHz carrier frequency 10 Gbit/s radio-over-fiber link based on a directly modulated III-V/Si DFB laser

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Electronic-photonic board as an integration platform for Tb/s multi-chip optical communication

Chip-on-board silicon photonics O-band wavelength-division multiplexing transceivers have been developed that will eventually enable high-throughput on-board optical communication for multi-socket on-board communication. This direct, any-to-any configuration yields low-latency, low-power optical communication among multiple compute nodes on the board. Silicon photonic transceiver chips are flip-chipped on a polymer waveguide containing an electro-optical circuit board using adiabatic coupling and then completed with driver and amplifier electronic chips. A transceiver assembly based on wire-bond technology verifies 50 Gb/s operation per channel, and the flip-chip version demonstrates the chip on-board assembly techniques for compact on-board transceivers