The dynamic switching of channels to adapt the capacity to the actually occurring traffic load is a promising method to improve the energy efficiency in optical networks. However, this approach is ...limited by the possible generation of optical power transients, which are able to disturb the transmission of the remaining channels. In transparent networks, spreading of transients can occur across several nodes. In this paper, we demonstrate the restrictions of the dynamic channel switching by the consideration of optical power transients and shows how to minimize these limitations.
Silicon oxycarbide deposited by plasma enhanced chemical vapor deposition is investigated regarding its application as a material for optical waveguides. The dependence of the infrared absorption, ...the refractive index, and the surface roughness on the precursor gas flow ratios is studied by Fourier transform infrared spectroscopy, ellipsometry, and atomic force microscopy, respectively. Results show that the refractive index can be tuned over a significant wider range compared to silicon oxynitride. Fabricated waveguides with a refractive index contrast of 0.05 show waveguide attenuation from about 0.3 dB/cm to 0.4 dB/cm for wavelengths between 1480 nm and 1570 nm. These low values were achieved without using a high temperature annealing process.
Erbium-doped fiber amplifiers are a promising solution for the signal amplification in long-haul mode-division multiplexed transmission systems. In order to minimize signal degradations by these ...amplifiers, low mode dependent gain and noise figures are desirable. We propose a scalable mode dependent gain equalization scheme for the 1480-nm pump wavelength. Contrary to the 980-nm pump wavelength, each signal mode has a maximum overlap with only one pump mode. Due to this, a scalable mode selective gain control is achievable by adjusting the pump modes. In this letter, we demonstrate the scalability of our approach with the number of signal modes by numerical simulation. Furthermore, we propose a two-stage amplifier setup in which the mode dependent gain of both stages is compensated in the second stage, pumped at a wavelength of 1480 nm.
For the realization of multi-mode optical fiber based long haul transmission systems with space division multiplexing, new erbium doped amplifiers have to be developed. Accurate amplifier simulation ...models are indispensable tools for this development task. We investigate the impact of mode beating effects on amplifier characteristics. The impact of mode beating is caused by the nonlinear dependence of the population densities on the power densities. Gain and noise figure values, calculated taking the impact of pump mode beating on population inversion into account, are compared with values where interference has been neglected and only power addition has been used. We compare results calculated with the exact waveguide modes with results obtained using linearly polarized modes for pumping and find that occurring beat lengths between fiber modes of one mode group have a noticeable impact on the amplifier performance. We study this effect by investigating how this impacts population inversion along the doped fiber of the amplifier.
Cost and energy efficient optical amplifiers are key components for capacity increase in fiber based optical transmission systems by space division multiplexing. We focus on the scaling of the mode ...count in multi-mode erbium-doped fiber amplifiers, which we identified as the most promising candidate.
A novel OTDR-system is introduced, which enables a significant reduction of measurement times in TDM- and WDM-PON measurements compared to a conventional λ-OTDR. It has the ability to measure ...multiple wavelengths simultaneously with just one receiver photodiode. The working principle is similar to a code division multiplexing transmission system. Furthermore, the measurement time is not only reduced by the simultaneous measurements on different wavelengths but also by means of coding gain, which reduces the OTDR averaging time. The coding gain has its origin in the correlation of signals based on complete complementary codes. In an experiment, measurements were performed, which provided results 15 times faster than with a conventional λ-OTDR. Further improvements are possible with different measurement parameters.
Silicon-oxynitride waveguides fabricated by plasma-enhanced chemical vapor deposition are very attractive for passive optical components used in optical networks. We use a combination of an ...high-index contrast and compact core dimensions for the realization of small bending radii. To achieve the high quality requirements with the desired waveguide design the layer deposition and the waveguide fabrication are optimized. Furthermore, we discuss the interface of the high-index optical components to standard single-mode fiber (SSMF) and coupling tolerances, which is more difficult compared to common fiber-mode-matched wave guides. We show results of fabricated Mach-Zehnder interferometer-switches, tunable ring resonators and present a solution to reduce the waveguide birefringence by adjusting the mechanical stress of the cover layer.
In high-capacity metro networks, fiber Bragg gratings (FBGs) offer a potentially cost-effective solution for compensation of chromatic dispersion (CD). However, FBGs suffer from stochastic variations ...of their group delay, the so-called group delay ripple (GDR). We propose a novel statistical model to describe the effects of stochastic variations of GDR. The statistical properties of our model are verified by comparison to measurement data and Monte Carlo simulations as well as Multicanonical Monte Carlo (MMC) simulations. Results indicate that without further measures to counteract the GDR distortions, very large penalties (>; 10 dB) for the optical signal-to-noise ratio (OSNR) occur frequently at a bitrate of 112 Gbit/s. Thus, we investigated the performance of short and cost-effective optical finite and infinite impulse response equalizer structures to mitigate the GDR distortions and to enhance the signal quality. With the use of optical equalizers (which can be realized as planar lightwave circuits) we were able to reduce the mean OSNR penalty due to the GDR to less than 0.1 dB. We also demonstrate that the same filter structures can efficiently be used to mitigate all-order PMD distortions as well.
We present a comprehensive study on how to design and fabricate low loss electro-optic phase shifters based on an electro-optic polymer and the silicon nitride and silicon oxynitride waveguide ...material systems. The loss mechanisms of phase shifters with an electro-optic (EO) polymer cladding are analyzed in detail and design solutions to achieve lowest losses are presented. In order to verify the low loss design a proof of concept prototype phase shifter was fabricated, which exhibits an attenuation of 0.8 dB/cm at 1550 nm and an electro-optic efficiency factor of 27%. Furthermore, the potential of this class of phase shifters is evaluated in numerical simulations, from which the optimal design parameters and achievable figures of merit were derived. The presented phase shifter design has its potential for application in fast adaptive multi stage devices for optical signal processing.
Data transport capacities of fiber based optical transmission systems with conventional phase insensitive optical amplification and phase sensitive parametric amplification are compared using the ...Shannon capacity formula to identify the better suited amplifier concept. Due to lower noise figures of phase sensitive amplifiers, up to 3 dB higher signal-to-noise ratios at the link output can be achieved with phase sensitive amplification than with phase insensitive amplification in the same link configuration. Thus, phase sensitive parametric amplification enables a transmission of more bit/s/Hz in the signal channels, but it also requires additional bandwidth for the transmission of idler channels. Different application scenarios are studied and guidelines are derived for the selection of the better suited lumped linear amplifier concept for the respective system type.
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