In this paper, we analyzed the system power penalty induced by the coherent crosstalk components as the dominant crosstalk channel in WDM-OXC, and present a simple expression, which can be readily calculated by popular software. We also present an expression of the power penalty when both incoherent and coherent crosstalks are presented. The simulation results show that by introducing a bit pattern mismatch method in a WDM-OXC, the extra penalty caused by the coherent crosstalk can be distinctively suppressed.
Measured and simulated power penalties were compared for 10Gbit/s NRZ loop experiments for cascaded AWG filters with 50GHz and 100GHz channel spacings. The results show that spectral flatness of cascaded filters can strongly influence the performance of high-speed systems with small channel spacing.
An optical low coherence interferometer was built and used to characterize the optical performance of planar arrayed-waveguide grating (AWG) devices. The phase error and amplitude distributions of individual waveguides in an AWG were extracted by sectioning individual interferograms from the low coherence interferometer. Using a large amount of oversampling to improve signal-to-noise in combination with Hilbert transformation method, phase errors of less than λ/300 in our AWG’s were achieved and correlated to fabrication variations from the waveguide device design. This was subsequently used to improve the performance of our devices. In addition, the group delay (GD) and chromatic dispersion (CD) were also derived from the measured phase error using a Fourier transform method. The derived GD and CD matched well with those directly measured from commercial chromatic dispersion equipment based on the phase modulation method. The relationship between the phase and amplitude errors with different frequencies and the variation of GD or CD will be discussed.
Reconfigurable optical network, the way of the future, can encounter serious packet loss problem during optical level reconfiguration. This paper presents a novel buffering scheme for GMPLS optical networks that minimizes packet loss during reconfiguration of optical nodes, consisting of both a reconfigurable optical cross-connects (OXCs), or an optical add-drop multiplexers (OADMs), and a packet-capable layer-two switch [1]. In this scheme, buffering takes place whenever an optical path is altered due to either a node reconfiguration or protection/restoration. Packets are buffered in a distributed manner starting from the first O/E/O-capable node before the reconfigured optical node all the way to the ingress node, if needed. In the worst-case scenario, where the path is all-optical or buffers are full along the path, all incoming packets are buffered at the ingress node, or the edge router. Buffering is carried out at layer two so that the interruption of service is kept at a minimum (less than 50ms, if possible). Furthermore, if buffers are overflowed, packets dropping will be carried out in accordance with the QoS levels, which further ensure that QoS of the network is maintained. It is shown by both analysis and simulation methods that this scheme performs quite well on either a general local area network, such as the UMBC WDM optical testbed, or the MCI backbone network. It is also cost-effective in that, even at the worst-case scenario, the required buffer is quite small.
The crosstalk performance of an arrayed-waveguide grating (AWG) multi-/demultiplexer is
primarily caused by random optical phase errors introduced in the arrayed-waveguides. Since the layout of
waveguides on a wafer is patterned by photomask through photolithography process, the resolution of a
photomask has a direct influence on the phase errors of an AWG. This paper presents a theoretical analysis
on the phase error caused by photomask resolution along with other basic design parameters. Both
calculation and measurement results show that a high-resolution photomask (better than 25 nm) is a critical
requirement to produce low-crosstalk (less than -30 dB) AWG demultiplexers. We also investigated the
non-ideal power distribution in the array waveguides since it contributes considerable phase errors when
material impurity is not well controlled during wafer fabrication. Basic criteria of power profile truncation,
number of grating waveguides, and material index variation are summarized in this paper as well.
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