Biological tissue is non-homogeneous in nature. It is difficult to measure its optical properties due to non-uniformity throughout the tissue being tested. To obtain the spatial distribution of optical parameters, conventional approaches use an array of light sources and detectors to reconstruct the image, thus, there is very limited spatial resolution. In contrast, solutions that provide high resolution have a high computational complexity. In this paper, we propose a fast, simple scheme to resolve the effective attenuation profile from the spatial diffuse reflectance. Rather than giving one single value for the absorption and reduced scattering coefficients, a novel algorithm is proposed for the reconstruction of an effective attenuation profile in 2-dimension from a diffuse reflectance curve. This technique is applied to the reconstruction of a 2-D effective attenuation profile. By obtaining the diffuse reflectance image from a camera and using the algorithm developed here, fast imaging of the effective attenuation profile with relatively high spatial resolution can be achieved.
KEYWORDS: Transmitters, Signal generators, Tolerancing, Modulators, Signal detection, Single mode fibers, Clocks, Eye, High speed electronics, Telecommunications
We propose and demonstrate a simple chirp-free optical Manchester signal transmitter that consists of a single-drive
Mach-Zehnder modulator and a passive electronic power combiner. A 5-Gb/s optical Manchester signal is generated and
its dispersion tolerance enhancement is investigated. The bandwidth of the modulator and driving circuit is reduced by
half.
Optical properties of biological tissue such as reduced scattering and absorption coefficients can be determined from the
temporal or spatial reflectance curve of the diffusion process. Owing to its non-homogenous nature, the assumption of
uniform optical parameters may not be valid in practice. We propose a new scheme to resolve the optical effective
attenuation profile from the spatial reflectance curve of a non-homogeneous tissue. The algorithm reconstructs the linear
attenuation profile along the line of measurement, rather than giving one single value for the coefficient for each
reflectance curve. The technique was applied to the reconstruction of a 2-dimensional attenuation image.
We propose and demonstrate the use of 10-Gb/s inverse-RZ data as downstream signal in WDM-PON to injection-lock a directly modulated Fabry-Perot laser used for the upstream signal at 1Gb/s.
We review some of the recent developments of optical performance monitoring (OPM) in various aspects: (i) the
enhancement of monitoring resolution, (ii) multi-impairment monitoring, and (iii) OPM network optimization. In
particular, some of the studies on the optimization of performance monitoring networks to achieve the optimal
monitoring locations and number of monitoring probes are discussed.
In this paper, different kinds of optical performance monitoring (OPM) techniques, in particular the optical signal-to-noise ratio (OSNR) monitoring and chromatic dispersion (CD) monitoring, are reviewed. Then recent trend of multiple-parameter simultaneous monitoring is examined.
Recently, optical differential phase shift keying (DPSK) has attracted much interest in high-speed optical transmission systems. It features constant intensity and thus is less vulnerable to the fiber nonlinearities. In addition to high-speed data transmission, it is desirable to carry relatively low-speed supervisory information simultaneously to facilitate the system monitoring and network management. In this paper, we propose and investigate an orthogonal modulation scheme for carrying relatively low bit-rate supervisory amplitude shift keying (ASK) data on a high-speed (10-Gb/s) optical DPSK data stream. The supervisory data is amplitude-modulated onto the constant intensity optical DPSK signal, thus no dedicated time slots are needed and this eliminates the bandwidth overhead. We investigate both experimentally and numerically the optimized operation conditions for such orthogonal modulation. The results suggest the design guidelines of the proposed ASK/DPSK orthogonal modulation for supervisory information dissemination.
With the recent explosive growth of Internet traffic, optical networks with high
connectivity and large capacity are indispensable. This can be achieved by
multi-dimensional optical routing networks, which can offer fine bandwidth granularity
and a large number of channels. In this paper, a trunk switched model is used to study the performance of multi-dimensional optical routing networks. The
closed-form network utilization is derived and compared to that of one-dimensional
optical routing networks. The network utilization gain is found to be closely
related to the link correlation and be insensitive to the network size. Besides,
based on this analytical model, the closed-form conversion gains are derived for
both partially and fully convertible cases. These results provide crucial
information in performance optimization of multi-dimensional optical routing networks.
Passive optical networks (PONs) have recently emerged to be a promising approach to enhance the penetration of fiber towards the subscriber side, thus further enables delivery of higher data-rate services to the subscribers. They feature easy network maintenance as there is no active component at the remote node (RN). However, in conventional PONs, both upstream and downstream bandwidths have to be time-shared among all optical network units (ONUs). By applying WDM technique to PONs, the total system capacity can be further enhanced. Each ONU enjoys a dedicated bandwidth and resolves the ranging problem as in PONs.
In both conventional PON and WDM-PON, little work has been done to offer protection capability though fiber fault detection methods have been extensively studied. We propose a novel network architecture for WDM-PON which offers 1:1 protection capability. In case of any fiber cut between remote node and ONUs, the affected ONU can re-route the wavelength channels via the adjacent ONU and can still maintain normal bidirectional traffic.
In our paper, we present a heuristic method for maximizing the utilization of a survivable multi-ring DWDM network without wavelength conversion. We assume that the network is supporting packet and circuit based services simultaneously. The idea is that we can provide ample bandwidth or even dedicated channels to packet based services by sharing the resources in the protection ring under normal conditions. In case of a ring failure, the packet based channels can be compressed into fewer channels to yield protection bandwidth to circuit based services. Packet ring technologies such as Resilient Packet Ring (RPR) or IEEE 802.17 will ensure that all packet connections are still maintained in a fair manner under such condition. The main contribution in this work is to jointly consider the effect of packet and optical connection services on DWDM rings to enhance wavelength utilization.
Recent advances in optical devices greatly enhance the feasibility of optical code-division multiplexing/wavelength-division multiplexing (CDM/WDM) network. In this paper, the performance in blocking probability in a two-dimension code/wavelength routing network is investigated. Facilitated by the optical code and wavelength conversion, the capability in reconfigurability, restoration and protection of the optical layer is enhanced. The network blocking performances under various conversion capabilities are investigated and the blocking probabilities are given in closed-form expressions. Under certain conditions, the analysis of the two-dimension routing network can be extended to N-dimension routing network by iterative decomposition procedure. Numerical results are obtained to show the performance improvement from the optical code conversion in terms of code conversion gain. With wavelength conversion provided in the network, the addition of the code conversion achieves a conversion gain as high as 104 even when the code conversion is provided with a low placement density of 0.2.
In this paper, we propose and demonstrate a novel and effective wavelength-matching scheme for wavelength grating routers to match their transmission peaks to the wavelength assignment of the data channels without any reference sources. The unused portion of the amplified spontaneous emission (ASE) power of the Erbium doped fiber amplifiers is utilized as the monitoring light source and fiber Bragg gratings of a particular center reflection wavelength is used as the wavelength reference. The scheme supports in- service monitoring and will not degrade the performance of the data channels. It is also insensitive to dynamic ASE power variations arising form channel ad-drop. We have experimentally demonstrated the proposed wavelength-matching scheme for WGR and analyzed the scheme numerically for design optimization.
KEYWORDS: Homodyne detection, Signal to noise ratio, Optical networks, Interference (communication), Receivers, Information operations, Modulation, Lead, Telecommunications, Signal attenuation
Homodyne crosstalk causes severe system performance degradation in optical networks by beating with the desire signal. While Gaussian approximation overestimates the performance degradation, for a single dominant crosstalk source, the exact noise probability distribution and closed- form error probability is derived in this paper.
KEYWORDS: Modulation, Data modeling, Switching, Switches, Linear filtering, Transmittance, Optical switching, Modulators, Receivers, Signal attenuation
We propose and experimentally demonstrate a novel variable bit-rate limiter (BRL) for ASK optical transmission systems. The BRL operates on the sampling principle with an optical switch inserted anywhere between the terminals in the fiber link. To facilitate the design of the BRL, a theoretical model of bit-error-rate for the proposed BRL is developed, and shows good agreement with the experimental data.
Tunable-channel multi-access (TCMA) networks are a new class of multi-channel networks that employ local channel tuning to reduce the node complexity. These networks are hybrids of switching networks and multiaccess networks and are vary suitable for high-speed multimedia integrated networking. Various distributed network protocols for these TCMA networks based on star, bus and ring topologies are discussed, including two particularly promising protocols, ACTA and EQEB. Both are based on bus/ring topologies, compatible to ATM, have simple design, high throughput, low delay and a performance that is independent of the round-trip delay. Various multiplexing strategies (space-division, wavelength-division, time-division and subcarrier) employing regenerative and non-regenerative implementations are also discussed.
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