Tien-Thang Pham

System Wide Implementation of Photonically Generated Impulse Radio Ultra-Wideband for Gigabit Fiber-Wireless Access

In this paper, we comprehensively review our research work on system wide implementation of photonically generated IR-UWB signals based on relaxation oscillations of a semiconductor laser. Firstly, we present our novel approach as a flexible method for photonic generation of high speed impulse radio ultra-wideband (IR-UWB) signals at 781.25 Mbps with on-off keying (OOK) and binary phase shift keying (BPSK) modulation formats. We further advance the state-of-the-art to include multi-Gigabit IR-UWB signal generation. Both OOK and BPSK signals comply with the Federal Communications Commission (FCC) regulation. Secondly, we implement UWB fiber transmission systems and study hybrid fiber-wireless transmission performance at a system level. This is accomplished by employing our digital signal processing (DSP) assisted receiver. The photonic generation method is superior to the state-of-the-art electronic generation method in terms of transmission bit-error rate performance. Moreover, photonic IR-UWB generation is shown to be capable of longer wireless reach due to its lower bandwidth limitation. Finally, we experimentally demonstrate the integration of a relaxation oscillations-based UWB photonic generation system into existing wavelength division multiplexing passive optical networks (WDM-PON) infrastructure. This provides converged Gigabit indoor wireless and wireline access services.

SC-FDE for MMF short reach optical interconnects using directly modulated 850 nm VCSELs

We propose the use of single-carrier frequency-domain equalization (SC-FDE) for the compensation of modal dispersion in short distance optical links using multimode fibers and 850 nm VCSELs. By post-processing of experimental data, we demonstrate, at 7.9% overhead, the error-free transmission (over a 4 Mbit sequence) of OOK-modulated 5 Gbps over 2443 meters of OM3 fiber (with a nominal 3300 MHz×km bandwidth). The proposed solution may be applied as a low cost alternative for data center and supercomputer interconnects.

Sub-cycle QAM modulation for VCSEL-based optical fiber links.

QAM modulation utilizing subcarrier frequency lower than the symbol rate is both theoretically and experimentally investigated. High spectral efficiency and concentration of power in low frequencies make sub-cycle QAM signals attractive for optical fiber links with direct modulated light sources. Real-time generated 10-Gbps 4-level QAM signal in a 7.5-GHz bandwidth utilizing subcarrier frequency at a half symbol rate was successfully transmitted over 20-km SMF using an un-cooled 1.5-µm VCSEL. Only 2.5-dB fiber transmission power penalty was observed with no equalization applied.

Quad 14Gbps L-band VCSEL-based system for WDM migration of 4-lanes 56 Gbps optical data links

We report on migrating multiple lane link into a single WDM L-band VCSEL-based system. Experimental validation successfully achieves 10 km of SMF reach with 4×14Gbps and less than 0.5dB inter-channel crosstalk penalty.

Comparison of carrierless amplitude-phase (CAP) and discrete multitone (DMT) modulation

We compare the transmission of 1.25 Gb/s CAP-16 and 909.2 Mb/s 16-QAM-DMT modulation formats over 2.4 km of MMF with 850 nm DM-CSELs. CAP displays 0.7-1.1 dB better sensitivity than DMT in this experiment.

Energy-efficient VCSEL-based multiGigabit IR-UWB over fiber with airlink transmission system

We propose VCSEL based impulse-radio ultra-wideband technology for energy efficient high-speed wireless networks; with full passive signal distribution, from the central office to the home with high-speed wireless connection to the final user.