During my career spanning over twenty-four years, I have worked mainly in the area of Optical and wireless communication systems and networks, which mainly deals with transmission impairments for optical systems and Wavelength Division Multiplexed (WDM) networks. The significant contributions include the original research work in the field of broadband optical systems and Networks, WDM-systems & -networks and Radio-over-Fiber (RoF) systems for broadband wireless applications. The brief about the work done during past years is highlighted below.
- Long distance broadband optical fiber links were realized by compensating the most limiting factor pulse spreading due to GVD (chromatic dispersion) using differential time delay and fiber nonlinearities. Results establish that for realistic systems the dispersionless propagation distance enhanced to 3.5 and 4.5 times, if dispersion is compensated by using the combined second- and third-order and the third- and fourth-order dispersion terms together, respectively. In second approach, combined effects of higher-order (second-, third-, and fourth-order) dispersion terms all along on RMS phase deviation, dimension free chirp parameter and figure of merit have been evaluated for ideal and realistic optical communication systems in order to achieve accurate results. Further, the work has extended to obtain the power penalty for all the above-mentioned approaches to indicate the power penalty at varied chirp for realistic and ideal systems. My innovative contributions in the dispersion compensation are practically suitable at very high bit-rate 20 or 40 Gb/s using integrated interferometers or optical filters.
- An analysis describing the propagation of signal and noise through a lossless linear dispersive single-mode fiber near zero higher-order dispersion wavelengths was modified using small-signal approach. Here, my contribution resulted the modified analysis for a phase and intensity modulating signal propagating through a dispersive medium, yielding the generalized conversion matrix including the influence of N number of higher-order dispersion parameters to obtain frequency response and Relative Intensity Noise (RIN) for laser diode.
- Further, I have contributed by investigating the Chromatic Dispersion Compensation for the dispersion-induced bit-delay associated with parallel data (WDM systems and networks) in fiber. The relative bit-delay caused by different wavelengths in byte-wide WDM optical systems is investigated around low loss transmission windows (1.3 and 1.5 mm). Moreover, an algorithm is developed for compensating bit-delay caused by wavelength drift at source (transmitter) and for shift of group delay curves and change in fiber length without prior knowledge of fiber parameters. In addition, an optical receiver design is proposed which automatically compensates the bit-delay among byte-wide WDM channels and is applicable for any zero dispersion wavelength and fiber. Bit-delay compensation scheme has been suggested for Optical Line Terminal Equipment (OLTE).
- I have addressed the limitations due to fiber nonlinearities on the performance of optical communication systems including the influence of higher-order dispersion parameters. The crosstalk due to Cross Phase Modulation and Stimulated Raman Scattering has been studied including higher-order dispersion effects. The four wave mixing (FWM) effect and its suppression methods are illustrated through computer simulations using OptSim and OptiSystem. Though my work includes different methods of FWM suppression, I have reported one of the methods where break through has taken place in terms of filling a patent jointly with Centre of Opto-electronics and Optical Communication, University of North Carolina, Charlotte, USA. Here we have proposed a novel method by using alternate channel negative and positive pre-chirped laser (±0.6) source to reduce the impact of FWM in 8-channel DWDM and WDM transmission link. It is shown that there is significant improvement in the FWM suppression by using the proposed method.
- The system designing and simulation was carried using OptSim to observe the performance of RZ, NRZ, CRZ, CSRZ single and multi-channel optical links at 10 Gb/s, 20Gb/s and 40 Gb/s using pre-, post- and symmetrical-dispersion compensation and it was proved that the symmetrical-dispersion compensation is the best choice. The performance metrics like the bit error rate (BER); eye diagrams and eye-closure penalty at the output were studied by simulating the different configurations. It was investigated and recommended that the CSRZ is the dispersion tolerant electric derive and is suitable for dispersive optical systems.
- Further, my investigations have been focused to the issues related to Radio-over-Fiber (RoF) which is the promising candidate to fulfill the growing demand of bandwidth of wireless end users. A RoF system capable of generating modulated wireless LAN microwave carrier with optical frequency multiplication (OFM) set up was designed and analyzed. It was indicated that it is a cost effective approach for reducing the radio system cost as it simplifies the remote antenna sites and enhances the sharing of expensive radio equipment located at appropriately sited Central Office. The designed ROF is able to transmit and down-, up-convert radio signals having data modulation such as ASK, BPSK, as well as QAM. It is suggested that ROF using OFM is the promising technology for the current as well as future wireless mobile and broadband services for the both service user and provider. Using similar approach system modeling for ODSB and OSSB Sub-Carrier Multiplexed (SCM) transmission links applicable for Fiber-to-the-Home has been investigated using QPSK and DPSK modulation. The investigations establish that the SCM link can be used to explore the potential bandwidth capabilities of fiber at microwave frequencies.
- Recently, my research has been focused on the WDM Networks, RoF, QoS issues related to wireless LAN and wireless sensor networks. The investigations have been carried out using OptSim, OptiSystem, OPNET, OMNeT++ and NS2.