Eamonn P. Martin

25-Gb/s OFDM 60-GHz Radio Over Fiber System Based on a Gain Switched Laser

A 25-Gb/s OFDM 60-GHz radio over fiber (RoF) transmission system employing a gain switched DFB laser for millimeter-wave generation is demonstrated. Transmission performance below the 7% FEC limit is achieved over 50 km of fiber initially by employing precompensation. This precompensation overcomes phase noise caused by the optical phase decorrelation induced by chromatic dispersion on the two optical channels separated by 60 GHz. An externally injected gain switched laser is subsequently employed to eradicate the need for the precompensation, thus reducing phase noise and increasing the tolerance to the induced time delay between the optical tones. Transmission performance below the 7% limit is achieved over 25 km of fiber with 2-m wireless transmission in this case.

All-Analogue Real-Time Broadband Filter Bank Multicarrier Optical Communications System

This paper studies the key aspects of an optical link which transmits a broadband microwave filter bank multicarrier (FBMC) signal. The study is presented in the context of creating an all-analogue real-time multigigabit orthogonal frequency division multiplexing electro-optical transceiver for short range and high-capacity data center networks. Passive microwave filters are used to perform the pulse shaping of the bit streams, allowing an orthogonal transmission without the necessity of digital signal processing (DSP). Accordingly, a cyclic prefix that would cause a reduction in the net data rate is not required. An experiment consisting of three orthogonally spaced 2.7 Gbaud quadrature phase shift keyed subchannels demonstrates that the spectral efficiency of traditional DSP-less subcarrier multiplexed links can be potentially doubled. A sensitivity of -29.5 dBm is achieved in a 1-km link.

Chromatic Dispersion-Induced Optical Phase Decorrelation in a 60 GHz OFDM-RoF System

We propose and demonstrate a 25-Gb/s 16-quadrature amplitude modulation orthogonal frequency division multiplexing 60-GHz radio over fiber transmission system based on a gain-switched optical comb source. The impact of the phase noise caused by the optical phase decorrelation due to the chromatic dispersion is theoretically studied and experimentally investigated by employing a high linewidth comb source and transmitting over a 50-km standard single-mode fiber reel. A time delay precompensation is deployed based on the study of phase noise in order to reduce the phase noise impact, and thereby improve system performance.

Terahertz-bandwidth coherence measurements of a quantum dash laser in passive and active mode-locking operation

This research carries out coherence measurements of a 42.7 GHz quantum dash (QDash) semiconductor laser when passively, electrically, and optically mode-locked. Coherence of the spectral lines from the mode-locked laser is determined by examining the radio frequency beat-tone linewidth as the mode spacing is increased up to 1.1 THz. Electric-field measurements of the QDash laser are also presented, from which a comparison between experimental results and accepted theory for coherence in passively mode-locked lasers has been performed.

Polarization insensitive all-optical wavelength conversion of polarization multiplexed signals using co-polarized pumps.

We study and experimentally validate the vector theory of four-wave mixing (FWM) in semiconductor optical amplifiers (SOA). We use the vector theory of FWM to design a polarization insensitive all-optical wavelength converter, suitable for advanced modulation formats, using non-degenerate FWM in SOAs and parallelly polarized pumps. We demonstrate the wavelength conversion of polarization-multiplexed (PM)-QPSK, PM-16QAM and a Nyquist WDM super-channel modulated with PM-QPSK signals at a baud rate of 12.5 GBaud, with total data rates of 50 Gbps, 100 Gbps and 200 Gbps respectively.

DM-DD OFDM-RoF System With Adaptive Modulation Using a Gain-Switched Laser

We propose a 60-GHz orthogonal frequency division multiplexing (OFDM) radio over fiber system based on direct modulation-direct detection using an externally injected gain-switched DFB laser with adaptive modulation format. Power fading due to chromatic dispersion is mitigated by optimizing the bias current. Adaptive modulation for OFDM is used to improve the signal transmission performance. A 15.31-Gb/s 60-GHz OFDM signal generation and transmission over 25-km standard single-mode fiber is experimentally demonstrated.

Long reach UDWDM PON with SCM-QPSK modulation and direct detection

We demonstrate a 100km un-repeated downstream transmission based on a 12.5GHz wavelength tunable comb source with 1.25GBd SSB-SCM-QPSK data. The pilot tone enables direct detection and phase noise independence with error free performance at -20dBm.

WDM Orthogonal Subcarrier Multiplexing

Electro-optical transceivers can be implemented employing all-analog signal processing in order to achieve low values of power consumption and latency. This paper shows that the spectral efficiency of such solutions can be increased by combining orthogonal multicarrier techniques and off-the-shelf microwave components. A real-time 108-Gbit/s experiment was performed emulating a wavelength division multiplexing (WDM) system composed of five optical channels. The optical carriers were provided by an externally injected gain switched optical frequency comb. Each optical channel transmitted a 21.6-Gbit/s orthogonal subcarrier multiplexing (SCM) signal that was modulated and demodulated in the electrical domain without the requirement for digital signal processing. The net data rate remained higher than 100 Gbit/s after taking into account forward error correction overheads. The use of orthogonally overlapping subchannels achieves an unprecedented spectral efficiency in all-analog real-time broadband WDM/SCM links.

100 Gbit/s real-time all-analogue filter bank OFDM based on a gain-switched optical comb

A real-time 5×21.6 Gbit/s WDM electro-optical transceiver is presented. Optical carriers were spaced by 20 GHz and each one transmitted four orthogonally overlapping broadband subcarriers. Only analogue electronics were employed, achieving an unprecedented spectral efficiency in DSP-less SCM links.

60-GHz Direct Modulation-Direct Detection OFDM-RoF System Using Gain-Switched Laser

We propose a 60-GHz orthogonal frequency-division multiplexing radio over fiber system based on direct modulation-direct detection using an externally injected gain-switched distributed feedback (DFB) laser. External injection from a master laser into the gain-switched DFB laser is used to mitigate chirp in the directly modulated DFB laser and 25-km fiber transmission is investigated. Power fading due to multipath transmission induced by fiber chromatic dispersion is theoretically analyzed and experimentally demonstrated.