Proc. SPIE. 10559, Broadband Access Communication Technologies XII
KEYWORDS: Mathematical modeling, Digital signal processing, Polarization, Birefringence, Signal attenuation, Numerical simulations, Single mode fibers, Distortion, Charge-coupled devices, Picosecond phenomena
Multi-core fiber transmissions provide great capacity scalability for future optical backbone and access networks. Unfortunately, the polarization-mode dispersion has not been experimentally investigated so far in single-mode multi-core fibers. In this scenario, the differential group delay may present a time-varying nature in each core because of the temporal fluctuations of the optical medium. In order to investigate this phenomenon, we present a coupled-mode theory based on local modes to simulate numerically the polarization-mode dispersion in such optical media and we report extensive experimental measurements of the time-varying differential group delay using a homogeneous 4-core multi-core fiber considering three different months. Our results indicate that the differential group delay presents a similar, but not identical, temporal evolution in the four cores.
Broadband access in optical domain usually focuses in providing a pervasive cost-effective high bitrate communication in a given area. Nowadays, it is of utmost interest also to be able to provide a secure communication to the costumers in the area. Wireless access networks rely on optical domain for both fronthaul and backhaul of the radio access network (C-RAN). Multicore fiber (MCF) has been proposed as a promising candidate for the optical media of choice in nextgeneration wireless. The capacity demand of next-generation 5G networks makes interesting the use of high-capacity optical solutions as space-division multiplexing of different signals over MCF media. This work addresses secure MCF communication supporting C-RAN architectures. The paper proposes the use of one core in the MCF to transport securely an optical quantum key encoding altogether with end-to-end wireless signal transmitted in the remaining cores in radio-over-fiber (RoF). The RoF wireless signals are suitable for radio access fronthaul and backhaul. The theoretical principle and simulation analysis of quantum key distribution (QKD) are presented in this paper. The potential impact of optical RoF transmission crosstalk impairments is assessed experimentally considering different cellular signals on the remaining optical cores in the MCF. The experimental results report fronthaul performance over a four-core optical fiber with RoF transmission of full-standard CDMA signals providing 3.5G services in one core, HSPA+ signals providing 3.9G services in the second core and 3GPP LTEAdvanced signals providing 4G services in the third core, considering that the QKD signal is allocated in the fourth core.
Multi-core fiber (MCF) has been one of the main innovations in fiber optics in the last decade. Reported work on MCF has been focused on increasing the transmission capacity of optical communication links by exploiting space-division multiplexing. Additionally, MCF presents a strong potential in optical beamforming networks. The use of MCF can increase the compactness of the broadband antenna array controller. This is of utmost importance in platforms where size and weight are critical parameters such as communications satellites and airplanes. Here, an optical beamforming architecture that exploits the space-division capacity of MCF to implement compact optical beamforming networks is proposed, being a new application field for MCF. The experimental demonstration of this system using a 4-core MCF that controls a four-element antenna array is reported. An analysis of the impact of MCF on the performance of antenna arrays is presented. The analysis indicates that the main limitation comes from the relatively high insertion loss in the MCF fan-in and fan-out devices, which leads to angle dependent losses which can be mitigated by using fixed optical attenuators or a photonic lantern to reduce MCF insertion loss. The crosstalk requirements are also experimentally evaluated for the proposed MCF-based architecture. The potential signal impairment in the beamforming network is analytically evaluated, being of special importance when MCF with a large number of cores is considered. Finally, the optimization of the proposed MCF-based beamforming network is addressed targeting the scalability to large arrays.
In this work we propose and evaluate experimentally the performance of IEEE 802.11ac WLAN standard signals in radio-over-fiber (RoF) distributed-antenna systems based on multicore fiber (MCF) for in-building WLAN connectivity. The RoF performance of WLAN signals with different bandwidth is investigated considering up to IEEE 802.11ac maximum of 160 MHz per user. We evaluate experimentally the performance of WLAN signals employing different modulation and coding schemes achieving bitrates from 78 Mbps to 1404 Mbps per user in distances up to 300 m in a 4-core MCF. The performance of the wireless standard multiple-input multiple-output (MIMO) processing algorithms included in WLAN signals applied to the RoF transmission in MCF optical systems is also evaluated. The impact on the quality of the signal from one of the cores in the MIMO processing is investigated and compared with the results achieved with single-input single-output (SISO) transmission in each core. We measured the error vector magnitude (EVM) and the OFDM data burst information of the received WLAN signals after RoF transmission for different distributed-antenna systems with uni- and bi-directional MCF communication. Finally, we compare the received EVM of a single-antenna system (SISO arrangement) with WLAN systems using two antennas (2×2 MIMO) and four antennas (4×4 MIMO).
The Asymmetric Directional Coupler (ADC) based on SOI (Silicon-on-Insulator) technology converts and couples the fundamental mode to the first higher order mode. The ADC is designed to achieve phase-matching condition, which is accomplished when both propagation constants are equal in each waveguide arm. Devices are fabricated in a SOI wafer with a 220 nm thick silicon layer. The refractive indexes of Si and SiO<sub>2</sub> are n<sub>Si</sub>=3.47 and n<sub>Si02</sub>=1.46 respectively. The access waveguides (W<sub>1</sub>=0.45 μm) have been designed to propagate just the fundamental mode, TE<sub>0</sub>. The optimum width for the second waveguide was chosen to achieve the phase-matching condition for the TE<sub>1</sub> mode, which corresponds to W<sub>2</sub>=0.962 μm. The coupling to the input and output waveguides is achieved through grating couplers. The input grating coupler will need to couple the LP<sub>01</sub> mode from the SSMF (Standard Single-Mode Fiber) to the TE<sub>0</sub> mode in the SOI waveguide; thus a typical design for a SOI coupler can be used. However, the output coupler must simultaneously couple the TE<sub>0</sub> and TE<sub>1</sub> modes in the SOI wide waveguide to the LP<sub>01</sub> and LP<sub>11</sub> modes in the FMF (Few-Mode Fiber). Input gratings are designed to have an area of 12x12 μm<sup>2</sup> and a period of Λ=610 nm in order to maximize the optical power coupled between the fiber and the waveguide for an incident angle of 10 degrees. Output gratings are designed with the same period but distinct area (12.5x12.5 μm<sup>2</sup>) to correctly couple the LP<sub>01</sub> and LP<sub>11</sub> modes in the FMF.
Multicore fiber (MCF) systems have been proposed for high capacity optical transmission applications ranging from the access network to long haul. In this paper we critically review the application of MCF-based systems in optical fronthaul technology with the simultaneous radio-over-fiber (RoF) transmission of 3GPP LTE-Advanced signals in downlink and uplink directions. The experimental study evaluates the quality of the received signals in terms of error vector magnitude (EVM) of the LTE-Advanced signal and of each channel frame according to the 3GPP wireless standard. The suitability of the 3GPP MIMO processing algorithms is also investigated experimentally evaluating two-antenna and four-antenna system configuration and compared with single-antenna (SISO) transmission in a 4-core MCF.
Proc. SPIE. 9807, Optical Technologies for Telecommunications 2015
KEYWORDS: Radar, Transceivers, Radio optics, Radio over Fiber, Signal processing, Optical communications, Signal generators, Wireless communications, Fiber optic communications, Orthogonal frequency division multiplexing, RF communications
Ultra-Wide Band (UWB) technology for wireless multiple access communications are receiving great interest for the last five years due to its unique features such as spectrum coexistence with other wireless services, RF front-end simplicity (enabling potential low cost terminals), good radio wave propagation (robust against multi-path fading, material penetration) and high bitrate. Low-cost UWB technology can be employed to provide simultaneous communications and vehicular radar capabilities. In this paper, the application of vehicle-to-vehicle (C2C), infrastructure-to-vehicle (I2C), communication and vehicular radar (VRAD) based on UWB technology are proposed altogether the required fiber-optics infrastructure, with the advantage of being flexible, cost-effective, reliable, fast and secure. The experimental validation and comparison for the optical generation of UWB signals combined with radio-over-fiber transmission is also reported in this work applied to vehicular communications. Both impulse-radio (IR-UWB) and orthogonal frequency division multiplexing (OFDM-UWB) signals are generated and their performance are evaluated experimentally in the 3.1-10.6 GHz frequency range. Up-conversion in the 60 GHz wireless band is also herein reported.
Proc. SPIE. 9772, Broadband Access Communication Technologies X
KEYWORDS: Optical fibers, Optical amplifiers, Radio optics, Modulation, Polarization, Radio over Fiber, Wavelength division multiplexing, Multiplexing, Single mode fibers, Transmittance, Antennas, Optical networks, Space division multiplexing, Chemical elements, Signal detection
This paper reports the experimental demonstration of a multicore fiber (MCF) system employing space-division multiplexing for the combined transmission of radio-over-fiber full-standard LTE-Advanced and WiMAX signals in a 4-core MCF optical fronthaul on a PON access network. Combining MCF fronthaul and PON access with RoF transmission enables the simultaneous transmission of downstream and upstream services in different cores. In this work, we propose and demonstrate a MCF fronthaul system providing combined fully-standard LTE-A and WiMAX signals using radio-over-fiber (RoF) transmission in a 4-core MCF media. The impact of the inter-core crosstalk in RoF transmissions is also evaluated and we studied the possibility of mitigating the crosstalk impairments with MIMO processing. The experimental performance of the PON access overlay employing optical polarization multiplexing is also reported.
Proc. SPIE. 9772, Broadband Access Communication Technologies X
KEYWORDS: Optical fibers, Refractive index, Optical amplifiers, Radio optics, Modulation, Signal attenuation, Complex systems, Radio over Fiber, Kerr effect, Single mode fibers, Monte Carlo methods, Nonlinear optics, Space division multiplexing, Stochastic processes
Optical transmission in multi-core optical media has the potential of great capacity and scalability for current and future optical networks. Optical fronthaul networks are expected to employ relatively high optical intensity levels when a large number of cores are connected to a large number of antennas. In this paper, the crosstalk characteristics of multi-core fiber operating in non-linear regime are identified, indicating advantageous performance in optical fronthaul radio-overfiber transmission. The nonlinear coupled-mode and coupled-power theories are revisited to demonstrate theoretically that the underlying Kerr effect mismatches the phase constant of the core modes reducing the mean and variance of the crosstalk when nonlinear regime is employed. This theoretical analysis is validated experimentally in this work using a homogeneous 4-core optical fiber in radio-over-fiber transmission for LTE fronthaul applications. In addition, the impact of the linear and nonlinear inter-core crosstalk in the error vector magnitude (EVM) is evaluated with the optical transmission of fully-standard LTE-Advanced signals using MIMO and SISO configurations operating in both linear and nonlinear power regimes.
Proc. SPIE. 9387, Broadband Access Communication Technologies IX
KEYWORDS: Optical fibers, Radio optics, Networks, Radio over Fiber, Integrated optics, Optical networks, Orthogonal frequency division multiplexing, Signal detection, Standards development, Phase only filters
Deep integrated optical access networks target to provide great capillarity and multiple ONTs for cost- and energy-efficient pervasive connectivity seamless supporting integrated wireless. Several key optical technologies are herein reported supporting integrated deep optical access: Bundled radio-over-fiber transmission is proposed and demonstrated for the provision of quintuple-play services achieving 125 km SSMF optical reach. Bend-insensitive fiber in-building distribution is also proposed and demonstrated supporting joint legacy coaxial transmission. Multimode POF is also proposed and demonstrated suitable for joint in-building distribution of MATV and SMATV broadcasting signals. Optical comb technology us is also demonstrated suitable for mm-wave radio generation of multiband OFDM wireless signals. Finally, multicore fiber transmission is also proposed and demonstrated suitable for the transmission of LTE and WIMAX in wireless fronthaul applications in a minimized inter-core crosstalk penalty configuration.
In this paper a spectral crosstalk monitoring technique is proposed and demonstrated. The technique is based on optically perform a real-time continuous Fourier Transform (OFT) comprising the whole set of transmitted wavelengths. This approach does not require to stop the channel operation. Once the spectral information has been brought to time domain, the basic parameters as amplitude (channel power) or central wavelength can be evaluated. This technique is theoretically developed and demonstrated in a three channel DWDM system at 10 GBit/s channel bitrate in a proof-of-concept experiment.
In this paper is proposed a novel high spectral efficiency modulation scheme using time-squared pulses forming an orthogonal wavelength division multiplexing. Experimental results show a significant reduction of the interchannel linear crosstalk-induced penalty compared with Gaussian RZ modulation. Simulation studies are in good agreement with experimental results and show the system performance dependence on several multiplexing impairments inherent to this technique. The proposed modulation technique allows a maximum spectral efficiency of 1 bit/s/Hz without any other spectral efficiency enhancement technique like polarisation division multiplexing.
The parallel analysis of Cy5 fluorophore micro-arrays over polycarbonate and polymethyl metacrilate substrates is reported. Sequential printing of biochemical samples, CCD detection, enhanced analysis by signal processing and assay results recording as digital data on a consolidated substrate is demonstrated. The developed equipment finds its application in low-cost high throughput screening of massive chemical, biochemical or cellular agents.
Future multi-terabit/s optical core networks require optical technologies capable of managing ultra-high bit rate OTDM/DWDM (optical time division multiplexing/dense wavelength division multiplexing) channels at 160 Gbit/s or higher bit rates. The key functionalities in ultra-high speed network nodes are all-optical wavelength conversion, 3R-regeneration and demultiplexing of OTDM signals. Advanced optical networking techniques (optical add-drop multiplexing and optical routing) are studied in simulations and their performance evaluated considering 160 Gbit/s OTDM/DWDM channels. Performance comparison results for both OADM (optical add-drop multiplexer) and OXC (optical cross-connect) node networking functionalities are shown considering different technologies: semiconductor-optical-amplifier-based symmetric Mach-Zehnder interferometers (SOA-MZI) for wavelength conversion, signal regeneration and demultiplexing, electroabsorption-modulator-based demultiplexers, and wavelength converters based on four-wave mixing in dispersion-shifted fiber. The simulation results show that the SOA-MZI is a promising technology for all-optical signal processing in network nodes mainly due to its signal regeneration capability. At ultra-high bit rates, however, the relaxation time of SOAs considerably limits the operation. A solution to mitigate this problem is to use a differential scheme at the input of the device. Error-free wavelength conversion, signal regeneration and demultiplexing of 160 Gbit/s OTDM signals employing a SOA-MZI with a differential scheme is demonstrated by means of simulations. Furthermore, the parameters of this architecture are optimized to obtain the best performance for each optical networking functionality in OADM and OXC network nodes.
There is an increasing interest in performing many key networking functions in the optical domain to achieve bit rate transparency. Optical header processing is one such key function that may enable fast reading and forwarding of optical packets in the future all-optical packet-switched core network. Many of these optical header processing functions are enabled through the use of all-optical logic gates. The logic XOR gate is of key importance in decision and comparator circuits. A novel architecture of an N-bit logic XOR gate based on a Mach-Zehnder interferometer with feedback is proposed and its performance evaluated by means of simulations. Basically, this architecture consists of an integrated semiconductor-optical-amplifier-based Mach-Zehnder interferometer (SOA-MZI), an optical pulsed control signal, a differential transmission scheme for the input data sequences, and a feedback network. The simulation results show error-free operation at 40 Gbit/s for 16-bit-length words with extinction ratio values better than 16 dB. Furthermore, simulation results of the data power threshold needed for obtaining error-free operation as a function of the peak power of the control pulses are also presented, showing an optimum operating point at about 8 mW. An important application for the proposed SOA-MZI architecture is label processing directly at the optical domain in high-speed all-optical label swapping networks.