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We design and simulate a Si-Ge avalanche photodetector secured by a deep trench for effective shielding from thermal crosstalk. Further, the effective photocurrent, dark current, and bandwidth parameters for such detectors are thoroughly analyzed.

We present a laser phase noise (PN) induced effect of a phase-modulation-to-intensitymodulation conversion noise and noise pedestals underneath each of the orthogonal frequency division multiplexing (OFDM) subcarriers in a selfcoherent optical OFDM transmission using a self-homodyne technique. We provide a statistical analysis on the received symbols using a histogram to demonstrate the effect of a phase rotation term and inter-subcarrier interference individually and collectively. The PN is then compensated using a simple time delay to realign the phase walk-off of the subcarriers relative to the carrier. Significant quadrature improvements of 6.82 dB using 5 MHz laser linewidth over a 720 km transmission length and 5.38 dB using 20 MHz over 240 km have been obtained with 16 quadrature amplitude modulation (QAM) over 15 GHz OFDM signal bandwidth. The technique also significantly reduced an optical-signal-tonoise ratio requirement at the bit error rate of 1 × 10−3 by 16.15 dB for 64-QAM over 160 km. With the delay, the system can tolerate three times the chromatic dispersion-length product..

We present a broadband coherent orthogonal frequency-division multiplexing (OFDM) transceiver based on orthogonal sampling and low bandwidth electronic analog signal processing. Wideband superchannels, without any guardband are aggregated from low bandwidth OFDM channels in the time domain by orthogonal Nyquist sinc-pulse sequences with a rectangular bandwidth. Therefore, the method is called OFDM-Nyquist-time division multiplexing (TDM). Simulation and experimental results will be discussed for optical systems. However, with some modifications the same principle can be used for wireless or THz signals. In simulations, we show a 40 GHz bandwidth, 160 Gbps, 16-QAM, 128 OFDM x 5-Nyquist-TDM transceiver based on 4 GHz electronics for the digital-to-analog (DAC), analog-to-digital (ADC) conversion and for the digital signal processing, including Fourier transform. For the experiment, we verify the processing of a 24 GHz bandwidth, 48 Gbps QPSK, 512 OFDM x 3-Nyquist-TDM signal with a 4 GHz transmitter and receiver. Since the proposed method drastically decreases the sampling rate and bandwidth requirements for the Fourier processing, the DAC and ADC, it can be a promising alternative for future communication systems with the highest possible symbol rate.

To cope with the exponential increase in internet services and corresponding data traffic, especially data centers and access networks require new high data rate transmission methods with low cost, very small package and low energy consumption. In this paper, we demonstrate a filterless, agnostic Nyquist wavelength division multiplexing (ANy-WDM) transmission system based on cascaded ring modulators and a comb source. The single ring modulator acts as a filter, filtering one of the n WDM lines, generated by the comb. The same ring modulator modulates k time division multiplexed (TDM) channels on the single wavelength. Since each WDM channel, consisting of k time domain channels, has a rectangular bandwidth, the aggregated symbol rate of the superchannel modulated by this system corresponds to the optical bandwidth of all n WDM channels together. The approach is very simple and compact. Since no optical filters, delay lines or other special photonics or high bandwidth electronics is needed, an integration into any photonics platform is straightforward. Thus, the proposed method might enable very compact, ultrahigh data rate transmission devices for future data centers and access networks.INDEX TERMS Integrated photonics, Nyquist transmission, ring modulators, WDM.