Partha Pratim Sahu

Review and Performance Analysis on Routing and Wavelength Assignment Approaches for Optical Networks

Abstract For the past several years, traffic especially, Internet traffic has been increased tremendously and this growth demands for a high-speed communication network such as optical network. Routing and Wavelength Assignment (RWA) is one of the key tasks for the optical network, due to its information transparency and wavelength reuse characteristics. In this paper, we discuss different conventional RWA approaches in the wavelength-routed optical networks and compare them with our proposed Priority-based RWA (PRWA) scheme under wavelength continuity constraint. The performance analysis of different conventional RWA approaches including our PRWA scheme is conducted in terms of blocking probability. Finally, we address a number of research issues that appear to us to be both important and challenging.

All-optical switch using optically controlled two mode interference coupler

In this paper, we have introduced optically controlled two-mode interference (OTMI) coupler having silicon core and GaAsInP cladding as an all-optical switch. By taking advantage of refractive index modulation by launching optical pulse into cladding region of TMI waveguide, we have shown optically controlled switching operation. We have studied optical pulse-controlled coupling characteristics of the proposed device by using a simple mathematical model on the basis of sinusoidal modes. The device length is less than that of previous work. It is also seen that the cross talk of the OTMI switch is not significantly increased with fabrication tolerances (±δw) in comparison with previous work.

Theoretical Investigation of All Optical Switch Based on Compact Surface Plasmonic Two Mode Interference Coupler

In this paper, an optical controlled surface plasmonic two mode interference (SPTMI) structure based on silicon waveguide has been proposed for all optical switching. We have shown cross and bar state switching characteristics depending on additional phase between the excited SPP modes propagating through the silicon core obtained due to refractive index modulation of GaAsInP cladding with incidence of optical pulse of width ~1 ps. It is also seen that the coupling length of the proposed device is ~33 times compact than that of the existing multimode interference-directional coupler. The deviation of crosstalk of the SPTMI switch with increase of fabrication tolerances (±δw) is also almost to that of previously reported all optical switch.

Priority Based Dispersion-Reduced Wavelength Assignment for Optical Networks

Dispersion in optical fiber degrades the quality of signal in optical networks. Although the use of dispersion compensating fiber (DCF) reduces the effects of dispersion, it is expensive and has more propagation loss compared to step-index fiber (SIF). In this paper, we propose a priority based dispersion-reduced wavelength assignment (PDRWA) scheme to reduce overall dispersion in optical network. In this scheme, the connection requests having a same source-destination (s-d) pair are groomed first to avoid intermediate optical-electrical-optical (O/E/O) conversation and then these groomed connection requests with longer lightpath are assigned the wavelengths having lesser dispersion and the wavelengths having a higher dispersion are assigned to the lightpaths with shorter distance. If the connection requests are assigned to the wavelengths using such constraint on dispersion, the overall dispersion in the network can be reduced to a great extent, which will in turn lead to better performance of the network in terms of overall signal quality (Q-factor) without increasing network setup cost. The performance analysis of the proposed scheme using SIF is conducted with different channel speeds (10, 40 and 100 Gbps) in terms of total dispersion and compared the same with the use of DCF. Furthermore, we have studied the overall Q-factor in the network with different channel speeds and considering polarization mode dispersion (PMD) effect using SIF and DCF.

New traffic grooming approaches in optical networks under restricted shared protection

In this paper, two traffic grooming approaches based on alternate path routing are proposed to accommodate a greater number of connections in optical networks. In the first approach (called as Source_SWG), the connections of same source and different destinations along a path are groomed in a wavelength channel, whereas in the second approach (called as Des_SWG), the connections of the same destination and different sources along a path are groomed in a wavelength channel. These approaches are compared with existing heuristic traffic grooming algorithms based on fixed routing. It is found that both the approaches provide less wavelengths than the existing heuristic traffic grooming algorithms for establishment of all the connections present in the network. The comparative studies of these approaches are also made under restricted shared protection. It is seen that in case of Source_SWG, the number of wavelengths required for establishment of all the connections present in the network is less than that for Des_SWG.

Compact integrated optical devices using high index contrast waveguides

In this paper, we have demonstrated two mode interference (TMI) coupler using the material SiO2/SiON having index contrast (Deltan) of 2% and 5% and the corresponding compact beat lengths are observed as ~103 mum and ~50 mum, respectively. The reduction of the beat length with Deltan and the corresponding width of the coupling zone are analyzed and compared with the experimental results. We also analyzed the coupling coefficients for the TMI couplers and the directional couplers (DC) and observed that the coupling coefficient of a DC with small gap (les 0.02 mum) is same to that of a TMI coupler. We have demonstrated a DC with small gap (<1 mum) and Deltan of 2% and the corresponding beat length is ~207 mum. The wavelength multiplexing/demultiplexing using the TMI couplers is also discussed

A Novel Versatile Precision Full-Wave Rectifier

In this paper, we have proposed and realized a novel precision full-wave rectifier using an all-pass filter as a 90° phase shifter. The circuit gives a dc output voltage that is almost the same as the peak input voltage over a frequency range of 50 Hz-1 MHz with a very low ripple voltage and low harmonic distortion. Oscilloscope traces of the rectified waveform for the proposed circuit show a ripple voltage of 12 mV obtained with an input voltage of amplitude 1 V and frequency 100 kHz.

A Compact Optical Multiplexer Using Silicon Nano-Waveguides

An ultracompact optical-multiplexer-based two-mode interference (TMI) coupler has been designed for the first time using a mathematical model based on sinusoidal modes and implemented with silicon nano-waveguides. The multiplexing characteristics of the device are verified with the beam propagation method and are also demonstrated experimentally. The coupling length for the TMI coupler for multiplexing of wavelength channels of spacing ~10 nm is five times less than that of a conventional multimode interference (MMI) coupler of width 660 nm. The effect of fabrication tolerance on crosstalk of the TMI coupler is found to be less than that of conventional MMI couplers and of TMI coupler based on tooth-shaped grating structure.

All-optical compact surface plasmonic two-mode interference device for optical logic gate operation

In this paper, we have proposed an ultra-compact surface plasmonic two-mode interference (SPTMI) coupler having a silicon core, silver upper and lower cladding, and GaAsInP left and right cladding for basic logic gate operations. By modulating the refractive index of the GaAsInP cladding with incidence of optical pulse energy, we have shown coupling characteristics depending on additional phase change ΔΦ(E) between the excited surface plasmon polariton modes propagating through the silicon core. By using applied optical pulse dependent coupling behavior of the proposed SPTMI device, the operations of NOT, AND, and OR logic gates are shown. It is also seen that the coupling length of the proposed device is 32.3 times more compact than that of a multimode interference-directional coupler.

A Tapered Structure for Compact Multimode Interference Coupler

A new tapered structure based on general interference has been proposed and realized by using silica waveguides with a silicon oxinitride (SiON) core for the reduction of coupling length of the 2times2 multimode interference (MMI) coupler. The coupling characteristics of the proposed structure are compared with those of conventional MMI structures using a simple mathematical model based on sinusoidal modes. The beat length for the proposed tapered MMI coupler is reduced by 45% of that of a conventional MMI coupler. The effect of power imbalance on fabrication tolerance of the proposed tapered MMI coupler are also studied and compared with other tapered MMI couplers.