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A spectrum-sliced (SS) Wavelength division multiplexing (WDM) based Free-space optical (FSO) communication system at a data rate of 2.5 Gbps per optical carrier is proposed in this research article. Utilizing the broadening of the spectrum by means of supercontinuum generation in a highly non linear Fiber (HNLF), an SS-WDM based FSO system is designed. The narrow spectrum of laser light source is broadened by means of self phase modulation (SPM). The proposed work reveals that the DQPSK based SS-WDM FSO system has higher performance compared to intensity modulation formats as well as other differential phase modulation formats. Considering various values of FSO link distances, antenna diameters of transmitter and receiver, beam divergence and thus, determining the values of performance metrics such as Q-factor and bit error rate (BER), differential quadrature phase shift keying (DQPSK) based SS-WDM FSO system is simulated. The same process is repeated for dual channel FSO system for DPSK and DQPSK.

In this paper, a photonic crystal based ultra-compact Optical XOR gate followed by an optical half-subtractor is proposed. Plane wave expansion is used to evaluate the photonic bandgap of the devised structure. The output and efficiency of logical circuits can be improved by maintaining distinct thresholds for the output logic states, thereby enabling the design to operate even in low power inputs. Reliability of the structure is enhanced by retaining a threshold for the output value. The performance of the proposed circuit is examined using the Finite Difference Time Domain method. The output is considered as logic 1 when the power level exceeds 0.7 μW and logic ‘0’ if it is below 0.35 μW. The proposed logical circuit has high contrast ratio. The XOR gate has a contrast ratio of about 12.55 dB, and the half subtractor has 7.78 dB and 11.76 dB for Difference and Borrow respectively. These devices work at 1550 nm wavelength and are ultra-compact in size. The proposed structure of logic gates will be suitable for photonic integrated circuits due to its ultra-small and simple design.

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Visible Light Communication (VLC) is a well known emerging technology for indoor communication that has drawn more attention in recent years. The name itself indicates that the medium to transfer data in VLC technology is the light that travels in free space. During VLC Inter-Symbol Interference (ISI) in free space channel occurs due to reflectivity of surfaces like walls and ceiling. In order to overcome this problem an inverse filter called equalizer is placed. Equalizers are feasible solution to improve the transmission performance. In this paper, the performance of VLC system is analyzed with various pre-equalization techniques using Optisystem V.16 simulation tool for a practically measured parameters since the spectrum of LED required equalization. This simulation is carried out by placing various equalizers such as Spaced Feed Forward Equalizer, Fractionally Spaced Feed Forward Equalizer, Decision Feedback Equalizer, Combination of both Feed Forward and Decision Feedback Equalizer and Adaptive Equalizer at transmitter side for different bitrates and different link ranges. With adaptive pre-equalization, this VLC system can support 2 Gbps data rate up to 5 m range with a Q factor of 8.52. Under the influence of external white light (noise) of power − 80dBm and below, the proposed system works well. Above − 80dBm, the modulated light is disturbed, so that the data obtained is slightly degraded.