In this Letter, we experimentally demonstrate an unamplified analog RoF distribution of 60 GHz 5G signals. The system entails the heterodyning of two optical tones from an externally injected gain switched laser (EI-GSL) based optical frequency comb to generate a millimeter wave (mmW) signal. A fixed frequency separation and a high level of phase correlation, between the EI-GSL comb lines, results in the generation of a high-quality signal. An active demultiplexer is used to filter and amplify two comb tones, thus alleviating the need for an external optical amplifier to boost the low power comb tones. Furthermore, the same demultiplexer is also used to modulate one of the tones with a 64-QAM UF-OFDM signal. Such an approach enables the remote generation of a mmW downlink data signal as well as an unmodulated RF carrier that could be used to downconvert the mmW signals to an intermediate frequency. Using the abovementioned scheme, we demonstrate the distribution of the downlink signal over 25 km of fiber, achieving a BER of 2.4e-3 (below the HD-FEC limit of 3.8e-3) and only a 0.5 dB penalty at the FEC limit in comparison to the BtB case.
Experimental methods are being developed to enable quantum communication systems research in testbeds. We describe testbed architectures for emerging quantum technologies and how they can integrate with existing fibre optical testbeds, specifically OpenIreland.
Using phase-modulation-induced potential gradient whose period is synchronized to a microwave optoelectronic oscillator, dissipative Kerr solitons generated in a crystalline optical microresonator are trapped by the soliton tweezing effect, exhibiting a stabilized soliton repetition rate. In the meantime, side-mode suppression of the microwave signal is enabled by the photodetection of the soliton train. Substantiated both experimentally and theoretically, the hybrid system produces a drift-reduced microcomb and a spectrum-purified optoelectronic oscillator simultaneously, yielding a low-cost toolkit for microwave and optical metrology.
Optical frequency combs (OFCs) were well documented by early reports in the 60's and 70's [1] including the Nobel lecture by Hansch [2] and Hall [3]. During the last decade, there has been an immense amount of research activity focused on OFCs and their wide range of applications. These range from molecular spectroscopy [4], astronomy [5] to RF photonics [6], optical clocks [7], arbitrary waveform generation [8] and high speed optical communications [9]. An OFC can be defined, as a series of equally spaced discrete spectral lines [10]. There are various parameters that could be used to characterise an OFC, including frequency and amplitude stability, occupied bandwidth, free spectral range (repetition rate), spectral flatness, phase noise, phase correlation etc. However, the choice of optimum OFC parameters depends on the nature of the application. This work focuses on the parameter requirements for OFCs employed in next generation optical communication systems. Emerging broadband applications and bandwidth hungry services are driving the evolution of optical networks. Next generation short and long reach communication networks would be required to provide data rates of multiple Tb/s. Such high line rates are not feasible using a single wavelength channel, as the bandwidth of electronics will act as a bottleneck. However, the multi-Tb/s transmission capacity can be achieved by utilising highly parallel wavelength division multiplexing (WDM), with tens or hundreds of channels, in combination with spectrally efficient advanced modulation formats. Through such an approach, symbol rates can be maintained at levels that are compliant with the electrical bandwidth of energy-efficient CMOS driver circuitry [11]. One of the factors that has been attracting a lot of attention, with the move to higher line-rates, is maximizing the information spectral density (ISD) achieved at the transmitter. With the available spectral bandwidth becoming an extremely precious commodity, enhancing the ISD beyond what is achievable through the employment of the advanced modulation formats, becomes of paramount importance. Current optical WDM systems, using a large array of laser transmitters, require inter-channel guard bands to avoid cross channel interference/cater for the wavelength drift of the free running lasers. However, OFCs portray precise frequency spacing thereby making them an invaluable asset to densely packed communication systems. Hence, the use of OFCs for advanced multicarrier transmission techniques, like Nyquist wavelength division multiplexing (NWDM) [12], coherent optical orthogonal frequency division multiplexing (CO-OFDM) [13, 14] or time frequency packing (TFP) [15], have been investigated to realize terabit transponders. The authors will present the major benefits and shortcomings of the most commonly used techniques [16-22] that are available for the generation of OFCs. Focus will be placed on the inherent advantageous properties exhibited by the different techniques, while attention will also be paid to ways of overcoming some of the shortcomings [23-25].
The side mode suppression ratio of self-seeded, gain-switched optical pulses is shown to be a vital parameter in wavelength division multiplexed communications systems. Experiments carried out on a 2-channel wavelength multiplexed set-up using tunable self-seeded gain-switched pulse sources at 2.5 GHz, have demonstrated the cross-channel interference effects which may be encountered if the side mode suppression ratio of one of the sources becomes degraded.
We demonstrate a novel directly modulated transmitter, based on a six-section photonic integrated circuit. The device uses a unique master-slave configuration with a variable optical attenuator in between, allowing decoupling of cavities and independent control of the injection power. The VOA also provides the ability to find an optimum injection level that balances the trade-off between the extinction ratio and the chirp of the transmitted signal. Using the device, an error-free transmission of a 10 Gb/s non-return-to-zero signal over 25 km and 50 km standard single mode fibre is achieved.
The authors present a novel technology for uplink transmission in radio over fiber (RoF) distribution systems. The technique employs remote downconversion of the uplink data to intermediate frequency (IF) in the base station (BS). The local oscillator (LO) signal for the downconversion is optically generated in the central station (CS) and sent to the BS via optical fiber. The IF uplink data is then modulated onto an optical carrier and sent to the CS, where the baseband conversion takes place. By employing this method of uplink connection simplicity and cost efficiency of the BS is achieved.
Developing broadband access networks is one of the most urgent needs in the telecommunications world. The wireless systems provide an efficient solution to address the requirements for last mile connectivity of data, Internet and voice services Radio systems using millimetre-wave frequencies can supply home users with capacities in the order of 50-200 Mbit/s Such bit rates allow the transmission of broadband applications including digital TV, video-on-demand etc In order to provide the massive capacities that are required for the distribution of such broadband data between Central Station and Base Stations, optical fiber can be employed The enormous transmission bandwidth and low loss of the fiber ensure that high capacity microwave signals can be encoded on an optical carrier and successfully transmitted from a Central to Base Station.
The goal of this project was to develop and test a radio over fiber communication system This involved investigating the generation of microwave optical signals for transmission in optical fiber, followed by an examination of the effect of fiber propagation on the microwave optical signals.
'/%3e%3cpath d='M200 752.362h200v300H200z' style='fill:%23fff;fill-opacity:1;stroke:none' transform='translate(0 -752.362)'/%3e%3cpath d='M400 752.362h200v300H400z' style='fill:%23ff883e;fill-opacity:1;stroke:none' transform='translate(0 -752.362)'/%3e%3c/svg%3e)
