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In this study, we propose a novel wavelength shift keying (WSK) technique that is combined with the conventional intensity modulation scheme for the transmission of point-to-point bidirectional data at the rate of 10 Gbps in each direction. We observe that WSK technique has not been investigated for implementation in point-to-point free space optical (FSO) links. Therefore, to the best of our knowledge, our study is the first one to perform this investigation. Our proposed link uses WSK in the downlink direction while we re-use the optical carriers for the transmission of uplink data. The use of WSK in the downlink direction enables us to perform balanced detection at the receiver, resulting in 3 dB improvement in receiver sensitivity compared to simple direct detection. We present bit error rate (BER) results for the signals transmitted in both the directions under different turbulence conditions and FSO link lengths. It was observed that the downlink signals generally perform better compared to the uplink due to the use of balanced detection and higher intensity fluctuations induced over the re-used optical carrier transmitted in the uplink direction.Please check and confirm that all the author names (given name, family name) and initials are correctly identified. The author names and initials are CORRECT. [ABSTRACT FROM AUTHOR]

In this paper, a high-speed short-reach free space optical (FSO) transmission system is proposed for data center interconnect (DCI). This system supports the transmission of 400 Gbps over a single wavelength by employing spatial vertical cavity surface emitting lasers. Space division multiplexing along with polarization division multiplexing of the Laguerre–Gaussian (LG) modes (LG 00 and LG 01 ) are exploited to achieve higher capacity over FSO channel. Intensity modulation direct detection scheme is used in the proposed system for cost-efficiency. Least mean square equalization is applied to the received data signals to mitigate the FSO channel's impairments. The performance of the proposed system is evaluated by observing the bit error ratio (BER) for weak, moderate and strong turbulences at different weather dynamics. The effects of polarization induced crosstalk and aperture misalignment induced crosstalk on BER degradation are also investigated. FSO channel lengths of 700 m, 500 m and 150 m are achieved for weak, moderate and strong turbulences, respectively. The receiver sensitivities at forward error correction limit of 3.8 × 10 - 3 for each FSO channel length are compared with back to back configuration. A penalty of 2.5 dB is observed for strong turbulence whereas 2 dB and 0.6 dB penalties are obtained for moderate and weak turbulences, respectively. The proposed FSO-DCI could be used to provide high aggregate transmission capacity of 800 Gbps and 1.6 Tbps for future DCI by adding more LG modes or other wavelengths. [ABSTRACT FROM AUTHOR]

A multi-hop free space optical link based on all-optical relays is presented. All-optical relays are either composed of simple optical amplifiers or optical regenerators. It has been shown that after a certain number of hops, the amplifier based relay cannot extend the range of the free space optical link. Therefore, we have investigated the use of a self phase modulation based regenerator as a substitute for simple amplifier based relay. By employing the regenerative relay, a 10 Gbps optical signal having pulse width of 7 ps is transmitted over a distance of 8 km of free space optical link. The free space optical link is modeled on the basis of Gamma-Gamma channel model in the strong turbulence regime. The performance of the link is observed on the basis of bit error rate analysis. It has been shown that under strong turbulence and accumulation of amplifier noise, the range of the link can only be extended by employing an optical regenerator. [ABSTRACT FROM AUTHOR]

We have proposed a novel multi-channel regeneration scheme for wavelength division multiplexed systems, which is based on four wave mixing in a highly nonlinear fiber. A 40-channel wavelength division multiplexed signal having data rate of 10 Gbps per channel is divided into five groups. Each group is composed of eight channels and requires a single pump laser source and two segments of highly nonlinear fibers to regenerate the eight channels. Therefore, our proposed scheme requires four times lesser number of highly nonlinear fibers compared to the previously proposed techniques. The regeneration performance for all the forty channels is presented through bit error rate analysis at low optical signal to noise ratio of 15 dB. Simulation results show that an average improvement of 4.246 dB, 3.935 dB, 3.72 dB, 2.71 dB and 2.593 dB in receiver sensitivities has been observed for all the five groups of channels, respectively. [ABSTRACT FROM AUTHOR]

Summary: In this article, a full‐duplex millimeter wave (mm‐wave) enabled radio‐over‐fiber architecture is proposed for distributed antenna systems. This architecture is capable of achieving transmission of 16 × 16 optical multiple input multiple output spatial streams at 12 Gbps per spatial stream by employing wavelength division multiplexing and exploiting its other degrees of freedom such as polarization states and modes of wavelengths. A single laser source based multiwavelength comb and wavelength reuse techniques along with plastic optical fiber are employed to make the proposed architecture cost efficient. Optical heterodyne detection is performed at the radio access unit to generate mm‐wave carrier frequency at 60 GHz. Channel equalization is achieved for pulse amplitude modulation data signal by employing least mean square equalizer to mitigate the optical fiber channel effects. Our proposed system supports 16 × 12 Gbps for downlink (DL) and uplink (UL) transmissions. To evaluate the performance of the proposed system, we compare the receiver sensitivities at forward error correction limit of 3.8 × 10−3 of bit error ratio of back to back system, employing no fiber effects, with its counterparts. We show that acceptable power penalties for the fiber lengths of 200 and 400 m are achieved for both LP01 and LP11 modes in DL and UL directions. [ABSTRACT FROM AUTHOR]

Ultrawideband (UWB) signals have low allowable transmission powers. To enhance the coverage and capacity of UWB signals, a cost-efficient solution for the access network has been proposed and simulated. The access network is based on gamma-gamma free-space optical channel model, which is employed between the central unit and the four different carrier-free radio access units (RAUs). All-optical generation and transmission of UWB signals at a rate of 1.5 Gbps to each RAU are demonstrated. Bit error rate results are obtained to observe the performance of the UWB signals received at the mobile stations. The proposed architecture requires minimum deployment cost and gives acceptable bit error rate results. [ABSTRACT FROM AUTHOR]

We demonstrate a method for all-optical multi-wavelength regeneration based on four-wave mixing. Three wavelength division multiplexed signals, each having a data rate of 10 Gbps and a fixed wavelength spacing of 1 nm, are modulated with a sinusoidal signal of 25 GHz. The resultant sidebands of the modulated signal are filtered at a variable wavelength spacing and combined with a pump signal. The combined signal is passed through a highly non-linear fiber to generate multiple carriers at different wavelengths through four-wave mixing. Filtering the data modulated carriers obtained at the output of the highly non-linear fiber results in signals having lesser noise contribution. Two different optical signal-to-noise ratios (OSNRs) of 16.5 and 19 dB at the input of the regenerator are considered to evaluate the system performance. In both cases, a significant improvement in the bit error rate (BER) of the signals is observed. Simulation results show an average improvement of 2.537 and 1.335 dB in received optical power at BER of 10 − 9 in case of 16.5 and 19 dB OSNRs, respectively. [ABSTRACT FROM AUTHOR]

This work proposes a novel technique for transmission of data from two different sources by using a combination of wavelength shift keying (WSK) and pulse position modulation (PPM) over a free space optical (FSO) link. It has been shown that the proposed technique has potential of improving the physical layer security of FSO links, which is a growing concern due to considerable interest in the employment of FSO for high data rate applications. The proposed technique transmits at a combined data rate of 20 Gbps over a single pulse per bit slot. The wavelength and position in time of the pulse is varied according to the combination of bits received from the two different data sources. Gamma–Gamma channel model is used to simulate the FSO link whose length has been varied from 0.5 km to 3 km to observe the bit error rate (BER) performance. The BER has also been observed for different time delays induced over the optical pulse for implementing the PPM technique. It has been shown that the proposed technique can work under different time delays, hence making it difficult for an eavesdropper to sample the optical pulses at the correct instant for information extraction. Furthermore, this scheme allows us to perform balanced detection, resulting in wider eye opening at the receiver. [ABSTRACT FROM AUTHOR]