We are investigating to utilize multi-core fiber for increasing the concentration of optical fiber and the density of optical connector. Until now, from the viewpoint of optical mounting, the bending loss and the crosstalk of the multi-core fiber in a short distance range have not been investigated so much. In this report, we propose low-loss and easily bendable multi-core fiber with a novel double core taper structure to realize highly efficient optical coupling to a silicon photonics integrated circuit, and compact fiber mounting with small bending radius. By BPM simulation, we confirmed that it is possible to suppress the bending loss of less than 0.5 dB and the inter-channel crosstalk to -20 dB or less when the radius of curvature is 3 cm. Based on this result, we fabricated an optical fiber with the double core taper structure in order to verify the characteristics. As a result, the coupling loss was realized within 1.5 dB with low radiation loss. It is therefore considered that the double core taper structure can be sufficiently applied to the multi-core fiber.
KEYWORDS: Radio over Fiber, WDM-PON, Signal to noise ratio, Antennas, Computer simulations, Time division multiplexing, Receivers, Radio optics, Hybrid fiber radio, Wavelength division multiplexing
This paper addresses the wireless channel capacity in small cells provided by RoF-DAS over WDM-PON that can increase the capacity in a small cell with RoF entrance link and MIMO distributed antenna. Considering the SNR of the RF signal transmitted in the RoF entrance network and the interferences among wireless cells, computer simulation results show the optimized cell size to maximize the MIMO channel capacity.
KEYWORDS: WDM-PON, Radio over Fiber, Antennas, Wavelength division multiplexing, Signal to noise ratio, Wireless communications, Time division multiplexing, Local area networks, Telecommunications, Channel projecting optics
Radio on fiber (RoF) - distributed antenna system (DAS) over wavelength division multiplexing - passive
optical network (WDM-PON) with multiple - input multiple - output (MIMO) has been proposed as a next
generation radio access network (RAN). This system employs optical time division multiplexing (OTDM)
over one WDM channel to multiplex and transmit various types of wireless interfaces such as 3.9G, Wireless
LAN and WiMAX. A combination of star and bus topologies has employed to cover a wider service area. The
optical transmission loss is caused notably at remote base stations (RBSs) quipped on a WDM bus link. The
loss is relatively small, but at the RBS far from the center station (CS), the RBS suffers the large accumulated
loss, so the reduction of cell size provides the increasing of the number of RBSs, causes the degradation of the
SNR of RoF link. This paper addresses this trade-off problem, and considers the application to the actual
service area by the channel capacity investigation of RoF-DAS over WDM-PON with computer simulation.
Then, this paper focuses on the flexibility of RoF-DAS over WDM-PON, considers the adaptive wireless cell
configuration according to population fluctuations of day and night, or densely populated areas and sparsely
populated areas, respectively.
KEYWORDS: Quadrature amplitude modulation, Phase shift keying, Modulation, Stars, Signal attenuation, Thick film dielectric electroluminescent technology, Modulators, Semiconductor lasers, Systems modeling, Digital signal processing
In this paper, we study the performance of star quadrature amplitude modulation (QAM) signals with various
constellations for hierarchically-modulated PON systems that overlay an over 20-Gbps PSK signal on a 10-Gbps on-off
keying (OOK) signal; previous work examined only the performance of an 8-star QAM signal. A star QAM signal
consists of a PSK signal with lower amplitude (inner-PSK signal) and a PSK signal with higher amplitude (outer-PSK
signal). We propose to decrease the modulation level of the inner-PSK signal and increase that of the outer-PSK signal
with the goal of improving the bit error rate performance in some conditions. Simulations indicate the minimum required
received power for the various constellations examined: it is shown that effective design depends on the extinction ratio.
For example, 10-star QAM improves the minimum required received power by 3 dB compared to 8-star QAM when the
extinction ratio is 12 dB.
We describe a novel architecture of broadband ubiquitous femto-cell network with MIMO distributed antenna systems
accommodated in WDM-PON. A technical convergence of WDM-PON and time division multiplexed RoF techniques
can realize the universality of base stations with various types of broadband air interfaces, the increase of wireless access
throughput, and the scalability of service area covered by MIMO distributed antenna systems. We discuss the
configuration of MIMO antenna systems, transmission scheme of MIMO RF signals over WDM-PON, and
configurations of center station and base stations. The preliminary experiments of proposed network architecture are
demonstrated.
The investigation of next-generation optical access network (NG-OAN) systems as well as the corresponding
standardization activities has been steadily progressing. In the near future, whenever such a NG-OAN system is deployed
to meet the bandwidth demands, the smooth migration from the existing system is indispensable because current PON
systems such as 1G-EPON/G-PON have been massively deployed all over the world. NGA systems should be deployed
so as not to interrupt existing system operation or degrade in-service user availability. I introduce recent technical topics
related to co-existence with 1G/10G-EPON as an example. In particular, a 1G/10G dual-rate dynamic bandwidth
allocation (DBA) technique and a 1G/10G dual-rate burst-mode transceiver are key technologies enabling 1G- and 10Gdata
to be handled simultaneously. Furthermore, from the CAPEX/OPEX reduction viewpoint, longer lifetime system is
preferable. NGA systems will, therefore, be more flexible to meet later bandwidth demands, wide coverage requirement,
and energy-efficient operation. WDM technology is an attractive approach to meeting these goals.
In this paper, we propose a wavelength locker free, simple and cost effective wavelength setting and monitoring method that estimates wavelength on a software basis. This method uses preliminarily measured wavelengths at selected sets of drive current and device temperature, which are stored in the memory of the transceiver module. We then determine the relationship among the wavelength, the drive current, and the device temperature as a linear function. This function enables us to estimate the wavelength by setting and monitoring the drive current and device temperature. The same procedure is done for output power estimation. We measured the wavelength estimation accuracy using two practical DFB-LDs and confirmed that the discrepancy between the estimated wavelength and the measured wavelength was less than ±1 GHz.
Fiber to the home (FTTH) is now the most popular fixed Internet access service in Japan; it has been attracting far more
customers than ADSL since early 2005. Gigabit-capable passive optical networks (PONs) have been proven to be the
most promising approach since they realize not only point-to-multipoint bidirectional connections for broadband data
communication but also video distribution in a very cost effective manner. This paper first reviews such PON
technologies as well as other optical technologies to support the massive deployment of these PONs in terms of further
reducing the cost, especially with regard to operation/installation and to further increasing user friendliness towards the
full-scale FTTH era. It next discusses possible technical directions for future optical access networks (OANs), and
review recent research towards them. Wavelength-division multiplexing (WDM) is one of the important technologies in
realizing the future OANs.
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