Eslam El-Fiky

A Silicon Photonic PAM-4 Modulator Based on Dual-Parallel Mach–Zehnder Interferometers

We present a silicon photonic dual-parallel Mach-Zehnder modulator (MZM) operating near 1550 nm used for four-level pulse amplitude modulation (PAM-4). The differential and integral nonlinearities of the device are investigated. A driving scheme and a biasing method that improves the linearity and PAM operation of the device are presented. The measured second harmonic distortion and two-tone, third-order intermodulation spurious-free dynamic range are 75 dB · Hz1/2 and 86 dB · Hz3/2, respectively. We further investigate the performance of the device in a short-reach transmission system. We report a successful 50-Gbaud single-wavelength transmission of PAM-4 over 2 km of single-mode fiber (SMF) below hard decision pre forward error correction (pre-FEC) threshold of 4.4 × 10-3.

Experimental parametric study of 128 Gb/s PAM-4 transmission system using a multi-electrode silicon photonic Mach Zehnder modulator

We present an experimental study and analysis of a travelling wave series push-pull silicon photonic multi-electrode Mach-Zehnder modulator (ME-MZM) and compare its performance with a single-electrode travelling wave Mach-Zehnder modulator (TWMZM). Utilizing the functionality of the ME-MZM structure plus digital-signal-processing, we report: 1) the C-band transmission of 84 Gb/s OOK modulated data below the KP4 forward error correction threshold with 2 Vpp drive voltage over a distance of 2 km; 2) the transmission of a 128 Gb/s optical 4-level pulse amplitude modulated signal over 1 km of fiber; and 3) the generation of a 168 Gb/s PAM-4 signal using two electrical OOK signals. By comparing the transmission system performance measurements for the ME-MZM with measurements performed using a similar series push-pull TWMZM, we show that the ME-MZM provides a clear advantage in achieving higher baud PAM-4 generation and transmission compared to a TWMZM.

High-speed low-chirp PAM-4 transmission based on push-pull silicon photonic microring modulators

We report a silicon photonic modulator based on the use of dual parallel microring modulators (MRMs) inserted in a Mach-Zehnder interferometer (MZI). It is operated in a push-pull configuration for low-chirp transmission at approximately 1550 nm. The chirp parameters of the device are measured using 10 Gb/s on-off keying (OOK) transmission over 20 km of standard single mode fiber (SSMF), and they are less than 0.01, showing the low-chirp characteristic of the modulator. We further demonstrate four-level pulse amplitude modulation (PAM-4) transmission at 92 Gb/s over 1 km of SSMF and at 40 Gb/s over 20 km of SSMF. The measured bit error rates (BERs) are below the hard-decision (HD) forward error correction (FEC) threshold of 3.8 × 10-3.

Single wavelength 480 Gb/s direct detection over 80km SSMF enabled by Stokes vector Kramers Kronig transceiver

We propose 4D modulation with directed detection employing a novel Stokes-Vector Kramers-Kronig transceiver. It shows that employing Stokes vector receiver, transmitted digital carrier and Kramers-Kronig detection offers an effective way to de-rotate polarization multiplexed complex double side band signal without using a local oscillator at receiver. The impact of system parameters and configurations including carrier-to-signal-power ratio, guard band of the digital carrier, oversampling ratio and real MIMO is experimentally investigated. Finally, a record 480 Gb/s data rate over 80 km SSMF is achieved in a 60 Gbaud PDM-16QAM single carrier experiment with a BER below the threshold of 2.0x10-2

Silicon Photonic Ring-Assisted MZI for 50 Gb/s DAC-Less and DSP-Free PAM-4 Transmission

We present the design and characterization of a silicon photonic ring-assisted Mach–Zehnder interferometer for four-level pulse amplitude modulation (PAM-4) short-reach transmission without the use of digital-to-analog converter (DAC) or digital signal processing (DSP). The PAM-4 optical signals are generated by driving two microring modulators with independent 2-level radio frequency signals. The device is operated at 25 Gbaud and the PAM-4 optical signals are transmitted over 2 km of standard single mode fiber. The bit error rate is estimated to be lower than the hard-decision forward error correction threshold of

Novel polarization beam splitter based on p-i-n structure for an indium phosphide platform

3.8 \times 10^{-3}

Intensity directed equalizer for the mitigation of DML chirp induced distortion in dispersion-unmanaged C-band PAM transmission

, showing a successful DAC-less and DSP-free PAM-4 transmission at 50 Gb/s.

A silicon-on-insulator 120° Optical hybrid based on 3× multimode interference coupler

In this paper, a polarization beam splitter (PBS) based on the indium phosphide (InP) platform is presented. The main advantage of the device is that the tight fabrication tolerances of fully passive devices can be overcome by adjusting two voltages in an easy calibration. To produce the splitting function, the Pockels effect and the plasma dispersion effect are exploited in the phase shifters of a symmetric 1×2 Mach-Zehnder interferometer (MZI). The experimental results show that such a device operating at 1550 nm has an on-chip loss of 3.5 dB and a polarization extinction ratio better than 15 dB.

Broadband sub-wavelength grating coupler for O-band application

The directly modulated laser (DML) is one of the most cost-effective transmitter options in optical communication systems, but it introduces an additional impairment caused by the interaction between frequency chirp and chromatic dispersion for C-band transmission. In this paper, we propose a low-complexity intensity directed equalizer based on feedforward equalizer and decision feedback equalizer (FFE/DFE) to mitigate the chirp induced distortions, and remarkably improve the transmission performance of PAM signals generated by DML. The equalizer is based on the fact that the directly modulated PAM symbols with different intensity levels have different chirp frequencies, which will lead to different inter-symbol interference (ISI) contributions to their adjacent symbols due to the velocity difference caused by chromatic dispersion. To address this phenomenon, the proposed equalizer employs multiple sets of tap coefficients according to the intensity levels of PAM signals. With this equalizer and a commercial 16.8GHz DML, we demonstrate a 56Gb/s PAM4 transmission over a record 43km SSMF in the C-band without optical dispersion compensation under the 3.8 × 10−3 HD-FEC BER threshold.

Self-homodyne system for next generation intra-datacenter optical interconnects

A 120° optical hybrid based on 3× multimode interference coupler is reported. The device exhibits less than 10° phase deviation over 55 nm in the C- and L-band.