100-Gb/s per channel optical transport technology development has experienced a long journey from purely
academic interests to commercially viable solutions. In near future, 100-Gb/s channel will be one of the major
building blocks for the next generation transport network. Beyond 100 Gb/s optical channel designs may, however,
experience a paradigm change. So far, almost all commercially available optical channels, with capacity up to 100
Gb/s, are single-optical-carrier ETDM (electrical time domain multiplexing) channels. Optical channels with
capacities beyond 100 Gb/s, however, will most likely be a superchannel with multiple optical carriers based on our
In this paper the history of channel speed development of optical transport networks, from a few MbI/s to beyond
100 GbI/s, is reviewed. A new channel type categorization, which divided various channel designs into only three
basic channel types, has been proposed. Based on the new categorization distinguishable performances of the three
types of channels are analyzed and the future direction of optical channel designs is predicted.
A novel bandwidth- and center-wavelength-tunable interleaver structure based on birefringent materials is proposed. This device can provide network designers more flexibility in their design work and reduce system upgrading and modification costs. Since the proposed structure is a kind of finite-impulse-response filter, the interleaver can be designed to be dispersion-free. Moreover, it can be implemented without moving parts to increase reliability. These two features make the proposed device attractive for increasing design flexibility and network efficiency. Simulation and experimental results are presented to verify the fundamental idea.
The impact of cascaded spectral Slicers on network performance is investigated in this paper. For a dispersive spectral Slicer, its dispersion is inversely proportional to the square of its channel spacing. When many narrow-band spectral Slicers are cascaded together, the total dispersion can cause significant penalty on system performance. We demonstrated the deleterious effects on system performance caused by the dispersion of cascaded spectral Slicers. To solve this problem, we applied a signal processing technique to design theoretically dispersion-free spectral Slicers. The design principle and simulation results of dispersion-free spectral Slicers are presented. Based on this signal processing technique, six dispersion-free 50-GHz Slicers were made and cascaded together. The total group delay ripples across spectrum within ±12GHz around center frequencies are less than ±0.8ps, which are much less than the group delay variation of ±14ps within the same bandwidth for dispersive Slicers. The power penalty of cascade dispersion-free Slicers is investigated by deploying them in a 16-channel OC-192 WDM (wavelength-multiplexing division) link. The measurement result shows no noticeable power penalty.
We describe a series of experiments on solutions of the inorganic metal cluster molecules Mo2Ag4S8(PPh3)4 and compare them with data on a suspension of carbon particles in liquid (ink). The optical limiting behavior is measured using both single picosecond 532 nm pulses and nanosecond long trains of these picosecond pulses. Both materials show reduced transmittance for increasing fluence (energy per unit area). We also perform picosecond time-resolved pump-probe measurements. We find that the observed pump-probe data is nearly identical for the metal cluster solution and the carbon particle suspension (CBS), and we conclude that the nonlinear mechanisms are the same for the two materials. Our previous studies have shown that the nonlinear losses are due to scattering and absorption by microplasmas formed after thermionic emission from heated particles of carbon or inorganic clusters.
We describe several methods for optimizing optical limiters, including a modification to existing geometries called the stepped limiter. We show that a stepped limiter may have a performance close to that of a fully optimized limiter with a graded molecular density. Given the difficulty in making a graded molecular density, the stepped limiter may be an attractive approach toward making practical devices. We also discuss the importance of damage threshold of the nonlinear limiting material on the limiter design and performance. Liquids have high damage thresholds and for this reason we may use tandem limiting geometries for devices based on nonlinear absorber molecules in liquid solutions. With currently available materials, this is still the best approach. Our experimental results on a tandem limiter based on Zn:tetra((rho) -methoxyphenyl) tetrabenzporphyrin show the best limiting performance to date.
Transient energy transfer or two-beam coupling is demonstrated in CS2 and other transparent Kerr liquids using frequency chirped, 17 picosecond (HW1/eM) 532 nm pulses with several polarization combinations. As the temporal delay between pulses in a standard pump-probe geometry is varied within the coherence time, the first pulse always loses energy while the second pulse gains this energy. Scattering from phase gratings can lead to coherent energy coupling only if the nonlinearity has a finite relaxation time. This two-beam coupling in Kerr media such as CS2 is associated with stimulated Rayleigh-wing scattering (SRWS). The frequency difference needed for beam coupling can be achieved with chirped pulses or with short pulses in nonlinear materials if irradiance dependent phase shifts are being developed during the laser pulse due to self and cross-phase modulation. Here we consider the interaction between linearly chirped pulses obtained from our modelocked, Q-switched Nd:YAG laser. This leads to an energy transfer linearly proportional to irradiance, so that the signal can be observed at irradiances lower than those needed for induced phased modulation. The measurements are performed on CS2 but the results are valid for any Kerr liquid that has a nonlinear index of refraction with a relaxation time on the order of the laser pulse width. We demonstrate that the interaction follows the polarization dependence of SRWS. The only parameters needed for the theoretical fittings are the nonlinear index n2, its relaxation time and the linear chirp of the laser pulse. The first two are well known for CS2 and the laser chirp is independently measured using first and second order autocorrelations.
The damage threshold of five different types of quartz glass obtained from NSG Precision Cells, Inc. was determined using nanosecond pulses at 532 nm. It was found that the damage threshold of one of the glasses is more than twice that of others.
The EZ-scan, an improved Z-scan technique, shows a sensitivity for measuring nonlinearly induced wavefront distortion of approximately equals (lambda) /104. We show that the nonlinear refraction and nonlinear absorption coefficients can be determined separately by a single EZ-scan measurement. We describe application of this technique to several organic thin films.
Experimental and theoretical results are given for studies of optical limiters designed to increase the functional range without incurring optical damage. In particular, we investigate a tandem geometry with two passive nonlinear elements, one placed in the focal plane of a lens and the second placed `upstream' of the focal position to protect the material at focus from damage. To provide a proof-of-principle demonstration of this geometry, simple limiters consisting of combinations of reverse saturable absorber dyes and a carbon black suspension in thin cells were tested. Our results show that a substantial increase in device performance can be achieved by use of a tandem limiter geometry. Simple modelling predicts that the dynamic range of a separate- element tandem limiter is given by the product of the dynamic ranges of the individual component limiting elements, in agreement with our experimental results. We also describe our numerical beam propagation code, which must be applied for thick limiting elements and in other cases where simple modelling is invalid.