Varughese Mathew

Bio: Varughese Mathew is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Time domain & Laser linewidth. The author has an hindex of 2, co-authored 2 publications receiving 10 citations.

200G system with PDM-16QAM: Performance evaluation and trade-offs

Abstract: Realization of increased spectral efficiency with polarization multiplexing and advanced modulation formats require performance optimization at the transmitter and the receiver, considering the laser linewidth, chromatic dispersion, polarization mode dispersion and nonlinear effects. This paper addresses the performance optimization of a 200G system using PDM-16QAM. DSP algorithms for the mitigation of the phase noise of the laser, drifts in modulator bias, frequency drifts of the transmitter and receiver lasers are discussed in detail. Frequency domain and a time domain approach is discussed to compensate for the impairments introduced due to chromatic dispersion and polarisation mode dispersion. The performance of a complete 200G system in the presence of different impairments and the associated trade-offs are discussed in detail.

Dispersion and Nonlinearity Distortion Compensation of the QPSK/16QAM Signals Using Optical Phase Conjugation in Nonlinear SOAs

Abstract: We experimentally demonstrate the simultaneous compensation of both dispersion and nonlinear effects in a 100 km optical fiber link using optical phase conjugation of a 21 GB aud QPSK and 16QAM signal with nonlinear SOAs. Error-free performance is recorded for a launched power of up to 12 dBm, without any digital signal processing to compensate for distortions due to chromatic dispersion and nonlinear effects in fiber. The performance is verified for operation across the C-band.

Investigation of Tolerable Laser Linewidth for Different Modulation Formats in CO-OFDM Systems

Abstract: The ideal behavior of communication system requires a single frequency carrier In optical communication system, light is used as a carrier Practical laser source has a finite linewidth due to variations in the frequency of operation, hence, resulting in undesired phase perturbations in the signal whereas the ideal requirement is the delta function spectral shape at the carrier frequency The spectral shape gets broadened due to phase noise and is modeled as lorentzian shape Linewidth is a measure of stability of laser phase noise with time Coherent Optical Orthogonal frequency division multiplexing (CO-OFDM) along with the spectrally efficient Quadrature Amplitude Modulation (QAM) formats is emerging as one of the best solutions for future high speed fiber transmission systems Though the coherent, receivers have advantages in terms of sensitivity and selectivity, laser phase noise is the main limitation of such systems as the laser phase noise further causes common phase rotation of all the subcarriers per symbol and also results in inter carrier interference QAM formats are also susceptible to laser phase noise Phase noise in coherent systems is governed by laser linewidth Hence, it is very important to investigate the impact of laser linewidth in CO-OFDM systems This paper investigates the tolerable laser linewidths for different QAM formats in a 40 Gbps COOFDM system

Electrochemical reduction of S(IV) species in aqueous medium by glassy carbon electrodes modified with polymeric copper(II)tetra-aza-annulene complexes

Abstract: The electrocatalytic reduction of SO2 in aqueous media was studied as a function of the pH at a glassy carbon electrode modified with poly[Cu(II)-5,7,12,14-tetramethyldinaphtho[b,i]-1,4,8,11-tetraaza[14]annulene] film. The best amperometric response was obtained at pH = 1 and the activity decreased upon pH increasing. The SO2 reduction potential in this condition was shifted ca. 220 mV in the anodic direction compared to the value observed in bare glassy carbon. The Tafel slope, 278.64 mV dec−1, and the charge transfer coefficient, 0.18, are consistent with some interaction between SO2 and the modified electrode. The amperometric response is linear up to a 0.1 mM SO2 concentration, the detection limit being 0.02 mM under optimized conditions.