Colm Browning

WDM-OFDM-PON Based on Compatible SSB Technique Using a Mode Locked Comb Source

We report on a wavelength division multiplexed-orthogonal frequency division multiplexed-passive optical network (WDM-OFDM-PON), for downstream transmission, based on a tunable mode locked comb source. The 12.75 Gb/s compatible single side-band (SSB) OFDM signal is used to modulate 10 comb tones separated by 10 GHz. Net spectral efficiencies of 1.12 and 1 bit/s/Hz were achieved in conjunction with the use of low complexity electronics. Transmission over 50 and 87 km of standard single mode fiber was successfully demonstrated. The incurred penalty after transmission over 50 km was at a bit error rate (BER) of 3×10-3, relative to the back-to-back case. All channels after 87 km transmission achieved performance below the 20% forward error correction (FEC) limit.

Integrated Two-Section Discrete Mode Laser

The authors present the design and characterization of a novel integrated two-section discrete mode index patterned diode laser source. The two slotted regions etched into the laser ridge waveguide are formed in the same fabrication step as the ridge, thus avoiding the requirement for complex lithography and regrowth steps. The laser is encased in a temperature-controlled butterfly package, which simplifies the static and dynamic measurements. Initial static characterization of this two-section laser shows that the injection, from the master laser to the slave laser, enhances the slaves emission side-mode suppression ratio from 30 dB to over 50 dB and its relative intensity noise is reduced from about -129.3 dB/Hz to -142.6 dB/Hz. Subsequent dynamic characterization then shows that the modulation bandwidth of the laser can be improved via injection to about three times the inherent free-running bandwidth. Hence, optical injection from master section into slave section enables the improvement of various parameters, which makes this two-section device attractive as a transmitter in optical communication systems.

Quantum Dash Mode-Locked Lasers for Data Centre Applications

The authors demonstrate single-polarisation WDM transmission with capacities higher than 400 Gb/s and 1 Tb/s, and show the possibility of obtaining capacity in excess of 4 Tb/s for interconnect applications within and between data centres, based on a single laser source. Quantum Dash (Q-Dash) passively mode-locked lasers (PMLLs), with free spectral ranges of 82.8, 44.7, and 10.2 GHz, were used for the generation of a large number of carriers, enabling high data rate transmission. The terabit per second transmission using Q-Dash MLLs was demonstrated in this paper, and was enabled using intensity modulated and directly detected (IM/DD) single-side band orthogonal frequency-division multiplexed signals. The system performance was investigated for a propagation distance of 3 and 50 km of standard single mode fibre indicating the potential for interconnect applications within and between data centres. The relative intensity noise (RIN) of all Q-Dash devices was characterised, and the effect of RIN on the system performance was investigated by examining the error-vector magnitude of OFDM subcarriers over the desired frequency range.

Performance Investigation of IM/DD Compatible SSB-OFDM Systems Based on Optical Multicarrier Sources

The authors investigate and compare the performance of three different optical frequency comb sources in an intensity modulated and directly detected compatible SSB OFDM system. The influence of relative intensity noise and carrier-to-noise ratio of the different multicarrier sources, on the performance of a 12.5 Gb/s compatible SSB OFDM system, were investigated experimentally and by simulation. The results obtained show that, system performance depends significantly on the relative intensity noise and carrier-to-noise ratio levels of the specific multicarrier optical source employed. However, it is shown that optical multicarrier sources with low relative intensity noise and high carrier-to-noise ratio levels can assure very good performance in a WDM-OFDM system.

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.

Performance improvement of 10Gb/s direct modulation OFDM by optical injection using monolithically integrated discrete mode lasers

Performance improvement of a directly modulated 10Gb/s OFDM system by optical injection is shown experimentally over differing fibre lengths. The modulation and optical injection is performed using monolithically integrated Discrete Mode lasers.

Dynamic Linewidth Measurement Method via an Optical Quadrature Front End

This letter describes a dynamic linewidth characterization method using an optical quadrature front end. The phase noise of the laser is recorded using a real-time oscilloscope in the time domain and the linewidth of the laser can be estimated statistically offline. The major advantage of this technique compared with conventional linewidth measurements in the frequency domain, is that this method enables the dynamic phase noise characterization which is increasingly important for fast wavelength tunable and switched networks employing advanced modulation formats. The dynamic linewidth of an sampled grating distributed Bragg reflector (SG-DBR) laser is characterized by using this method.

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.

Optical burst-switched SSB-OFDM using a fast switching SG-DBR laser

The application of orthogonal frequency-division multiplexing (OFDM) in an optical burst-switched system employing a single fast switching sample grating-distributed Bragg reflector (SG-DBR) laser isdemonstrated experimentally. The effect of filter profiles compatible with 50, 25, and 12.5 GHz wavelength-division multiplexing grids on the system is investigated with system performance examined in terms of error vector magnitude per subcarrier for OFDM burst data beginning at various times after a switching event. Additionally the placement of the OFDM training sequence within the data burst and its effect on the system is investigated.

Software-defined control-plane for wavelength selective unicast and multicast of optical data in a silicon photonic platform

We demonstrate a programmable control-plane based on field programmable gate array (FPGA) with a power-efficient algorithm for optical unicast, multicast, and broadcast functionalities in a silicon photonic platform. The platform includes a silicon photonic 1×8 microring array chip which in conjunction with a fast tunable laser over the C-band is capable of delivering software controlled wavelength selective functionality on top of spatial switching. We characterize the thermo-optic response of microring resonators and extract key parameters necessary for the development of the control-plane. The performance of the proposed architecture is tested with 10 Gb/s on-off keying (OOK) optical data and error-free operation is verified for various wavelength and spatial switching scenarios. Lastly, we evaluate electrical power and energy consumption required to reconfigure the silicon photonic device for all possible wavelength operations and output ports combinations and show that unicast, multicast of two, three, four, five, six, seven, and broadcast functions are achieved with energy overheads of 0.02, 0.07, 0.18, 0.49, 0.76, 1.01, 1.3, and 1.55 pJ/bit, respectively.