Influence of guard band on performance of absolute polar duty cycle division multiplexing over a single wavelength and wavelength division multiplexing system

For the first time to the best of our knowledge the effect of guard band (GB) on the performance of 40 Gb/s Absolute Polar Duty Cycle Division Multiplexing (AP-DCDM) over a single wavelength and wavelength division multiplexing (WDM) are investigated and reported. It is demonstrated that the spectral width occupied by 40 Gb/s AP-DCDM with GB is 100 GHz (with minimum spectral efficiency of 0.4 b/s/Hz) whereas, this value can be reduced to around 80 GHz for AP-DCDM without GB (with minimum spectral efficiency of 0.5 b/s/Hz). In addition to better spectral efficiency, this amount of saving in the spectral width leads to ～60 ps/nm improvement in chromatic dispersion tolerance. In this paper, characteristics of AP-DCDM with and without GB over WDM system are compared at the speed of 40 Gbit/s per WDM channel, for the tolerance to narrow optical filtering and minimum allowed channel spacing. The AP-DCDM without GB has narrower spectral width than AP-DCDM with GB, which makes its implementation in WDM system advantageous.     

Experimental investigation on gain-dependent chromatic dispersion of the semiconductor optical amplifier

Using a chromatic-dispersion analysis method based on K–K transformation of the gain spectrum, we experimentally investigated the chromatic dispersion of semiconductor optical amplifier in detail within the wavelength range from 1530 nm to 1610 nm. Experimental results demonstrate that there are three typical dispersion regions, which are abnormal dispersion, flatten dispersion and normal dispersion region, and three zero-dispersion points, which exist around 1550 nm, 1580 nm and 1600 nm, over the wide wavelength range of 80 nm. With an increase in bias current on SOA, wavelengths of the three zero dispersion points all had a blue shift and the three near-zero dispersion regions corresponding became wider. However, the three near-zero dispersion regions corresponding became narrower when the input optical power increased. Therefore, the dispersion of SOA can be flexibly adjusted by changing the bias current and input optical power to SOA.     

Performance analysis of dense wavelength division multiplexing secure communications with multiple chaotic optical channels

The performance of dense wavelength division multiplexing secure communications with multiple chaotic optical channels is numerically analyzed in this paper. Taking the multiplexing of three chaotic optical channels as an example, we investigate the effects of second-order dispersion coefficient and nonlinear coefficient of fiber, channel spacing, message amplitude and bit rates on chaotic synchronization and multiplexing communications. Chaotic synchronization quality and Q-factor of the recovered message decrease with the increasing fiber length. A 1.25 Gbits/s non-return-to-zero (NRZ) sequence can be securely transmitted up to 60 km under the influence of the other two chaotic optical channels. Compared with the fiber dispersion, the cross-phase modulation is the primary factor which deteriorates the quality of communications. The results also show that the quality of communications is unlimited to the channel spacing as long as chaotic synchronization can be maintained. In addition, the effect of the amplitude of encrypted message on Q-factor and the confidentiality is demonstrated.     

10 Gb/s optical carrier distributed network with W-band (0.1 THz) short-reach wireless communication system

Millimeter-wave (mm-wave) operated in W-band (75 GHz–0.11 THz) is of particular interests, since this frequency band can carry signals at much higher data rates. We demonstrate a 10 Gb/s optical carrier-distributed network with the wireless communication system. The mm-wave signal at carrier frequency of 0.1 THz is generated by a high speed near-ballistic uni-traveling carrier photodiode (NBUTC-PD) based transmitter (Tx), which is optically excited by optical short pulses. The optical pulse source is produced from a self-developed photonic mm-wave waveform generator (PMWG), which allows spectral line-by-line pulse shaping. Hence these optical pulses have high tolerance to fiber chromatic dispersion. The W-band 10 Gb/s wireless data is transmitted and received via a pair of horn antennas. The received 10 Gb/s data is envelope-detected and then used to drive an optical modulator at the remote antenna unit (RAU) to produce the upstream signal sending back to the central office (CO). 20 km single mode fiber (SMF) error free transmission is achieved. Analysis about the optimum repetition rate of the optical pulse source and the transmission performance of the upstream signal are also performed and discussed.     

Performance analysis of optical network based on optical add drop multiplexers with different MZI techniques

This paper presents an investigation on the performance of an optical network in terms of crosstalk based on optical add drop multiplexers with Mach–Zehnder interferometer (MZI), MZI-semiconductor optical amplifier (SOA) and MZI-fiber Braggs gratings (FBG) techniques obtained at 8 × 10 Gbps with 0.1 nm channel spacing wavelength division multiplexing (WDM) transmission with optical add drop multiplexer (OADM) placed at the 20 km point of a 40 km link. It is found that the signal can be transmitted with least BER and better Q-factor with MZI-FBG based OADM and the worst case is found with the MZI-SOA based OADM.     

Simulation of 16 × 10 Gb/s WDM system based on optical amplifiers at different transmission distance and dispersion

In this paper, the 16 channel WDM systems at 10 Gb/s have been investigated for the various optical amplifiers and hybrid optical amplifiers and the performance has been compared on the basis of transmission distance and dispersion. The amplifiers EDFA and SOA have been investigated independently and further compared with hybrid optical amplifiers like RAMAN-EDFA and RAMAN-SOA. It is observed that hybrid optical amplifier RAMAN-EDFA provides the highest output power (12.017 and 12.088 dBm) and least bit error rate (10^?40 and 9.08 × 10^?18) at 100 km for dispersion 2 ps/nm/km and 4 ps/nm/km respectively.     

Simultaneous demodulation and dispersion compensation of WDM DPSK channels using optical ring resonator

We have introduced and comprehensively analyzed a novel scheme of simultaneous demodulation and dispersion compensation of wavelength division multiplexed (WDM) non-return-to zero (NRZ) differential phase shift keying (DPSK) optical link using an optical ring resonator (ORR) based filter. Using extensive numerical simulation we have demonstrated the transmission of 10.7 Gb/s WDM DPSK channels having 50 GHz and 100 GHz spacing over 400 km of unrepeatered reach at 20 dB optical-signal-to-noise-ratio (OSNR) to achieve a bit error rate (BER) of 10^? 3.     

Optimization of Super Dense WDM systems for capacity enhancement

We investigate the performance of the Super Dense Wavelength Division Multiplexed (SDWDM) systems with high spectral efficiency and narrow spacing of the channels and optimization in terms of bit rate up to 15 Gbps, channel spacing as low as 12.5 GHz, number of channels up to 64 and repeater less transmission distance up to 100 km and report high capacity SDWDM systems. We demonstrate the minimal allowed channel spacing and provide recommendations for future SDWDM solutions. The simulation results have shown that the minimum channel spacing for 15 Gbps, 32 channel system need to be not less than 0.35 nm and that for a 10 Gbps system it should be not less than 0.25 nm. The 5 Gbps system gives acceptable results at spacing of 0.1 nm for maximum up to single span of 80 km.     

Impact of PMD induced penalties on 40 Gb/s duobinary optical communication system for fixed and variable scattering section dispersion

In this paper, we evaluate the performance of 40 Gb/s duobianry optical transmitter for different scattering section dispersion and polarization-mode dispersion coefficient of single mode fiber. We observe that the variable scattering section dispersion considerably improves the performance of duobinary optical system as compared to fixed scattering section dispersion where the Q value fluctuates over wide frequency range. Also, duobinary system observes pulse delay of 7 ps for the fixed scattering section dispersion while there is no delay in the received output signal if variable scattering section dispersion is considered.     

An optical OFDM multiplexer and 16 × 10 Gb/s OOFDM system using serrodyne optical frequency translation based on LiNbO3 phase modulator

This paper proposes an all-optical orthogonal frequency division multiplexing (OFDM) multiplexer based on sawtooth wave driving LiNbO₃ phase modulators by using serrodyne optical frequency translation. This multiplexer has high integration ability. The designing concept and implementation method have been discussed. A 16 × 10 Gb/s optical OFDM system is designed based on this multiplexer. Transmission characteristics, including tolerances of polarization mode dispersion (PMD) and nonlinear impairments have been studied numerically. Simulations show that the PMD tolerance is about 42 ps. The spectral efficiency reaches 1 bit/s/Hz with binary modulation format.     

Spectral efficient hybrid wireless optical broadband access network (WOBAN) based on transmission of wireless MIMO OFDM signals over WDM PON

In this paper, a spectral efficient hybrid wireless optical broadband access network (WOBAN) is proposed and demonstrated based on the transmission of wireless multi-input multi-output orthogonal frequency division multiplexing (MIMO OFDM) signals over wavelength division multiplexing passive optical network (WDM PON). By using radio over fiber (ROF) techniques, the optical fiber is well adapted to propagate multiple wireless services having different carrier frequencies. It is a known fact that multiple wireless signals having the same carrier frequency cannot propagate over a single optical fiber at the same time, such as MIMO signals feeding multiple antennas in fiber wireless (FiWi) system. A novel optical single-sideband frequency translation technique is designed and simulated to solve this problem. This technique allows four pairs of wireless MIMO OFDM signals with the same carrier frequency for each pair to be transmitted over a single optical fiber by using one optical source per wavelength. The crosstalk between the different MIMO channels with the same frequency is eliminated, since each channel is upconverted on specified wavelength with enough channel spacing between them. Also the maximum crosstalk level between the different MIMO channels with different frequencies is very low around ?76 dB. The physical layer performance of the proposed WOBAN is analyzed in terms of the bit error rate (BER), error vector magnitude (EVM), and signal-to-noise ratio (SNR). The proposed WOBAN achieves 7.68 Gb/s data rate for 20 km for the optical back-end and 240 Mb/s for the outdoor wireless front-end.     

Improving the performance of three level code division multiplexing using the optimization of signal level spacing

In order to optimize the performance of three level code division multiplexing (3LCDM) at 2×20 Gb/s data rate, signal level spacing technique is investigated in this paper. The 3LCDM performance is improved considerably using both electrical and optical level spacing optimization configurations. The results demonstrate that by optimization, in conditions of the optical signal-to-noise ratio, an improvement of around 4.5 dB can be achieved in both approaches as well as 3.3 dB in the electrical configuration and 3.5 dB in the optical configuration can be accomplished for the 3LCDM in terms of the receiver sensitivity.     

Reduction of nonlinear impairments in fiber transmission system using fiber and/or transmitter diversity

A multi-fiber architecture is proposed to mitigate the nonlinear impairments in fiber-optic systems. The power launched to each fiber is reduced in multi-fiber architecture as compared to the case of single fiber leading to reduction in nonlinear impairments. The optical pulses propagating in the fibers undergo different amount of phase shifts and timing delays. Optical and electrical equalization techniques to compensate for these channel effects are discussed. Our numerical simulation results show that for unrepeatered systems, the performance (Q factor) is improved by 6.2 dB using 8-fiber configuration as compared to single-fiber system. In addition, for multi-span system, the transmission reach at a bit error rate (BER) of 2.1 × 10^? 3 is quadrupled in 8-fiber configuration.     

Arrayed waveguide grating-based demultiplexer with two central wavelengths

In this paper we have presented an arrayed waveguide grating with two central wavelengths, 1550.12 nm and 1310.12 nm. Introducing a novel architecture for outputs of system, if input light to arrayed waveguide grating consists of wavelengths around 1550.12 nm, proposed system will act as 16 channels demultiplexer with channel spacing of 1.6 nm. On the other hand when input wavelengths are distributed around 1310.12 nm, the same arrayed waveguide grating will divide the input to 27 channels with channel spacing of 0.68 nm.     

Proposal for a 4-channel all optical demultiplexer using 12-fold photonic quasicrystal

In this work, 12-fold photonic quasicrystal (PQC) with cross section equals to 138 μm² has been used to design a 4-channel optical demultiplexer. The size of structure promises its applications in optical integrated circuits (OICs) and also, wavelength division multiplexing (WDM) communication devices. Finite difference time domain (FDTD) method has been employed in order to investigate the structure's band gap and output waveforms of each channel. Four channels, with spacing less than 1 nm and cross-talk level better than ? 2.8 dB have been separated by introducing defects in L-shaped and line defect waveguides (LDWs) in the crystal's structure. It has been shown that, L-shaped waveguides (LWs) are quite more frequency selective than line defect waveguides. Also, it has been found that the exact tuning of the central wavelength of each channel is possible by making use of defects with different radiuses and sites in the waveguides.     

Properties of Bi2O3 thin films prepared via a modified Pechini route

Thin bismuth oxide films have been prepared by a modified Pechini route on glass substrate and annealed at temperatures ranging between 400 °C and 700 °C using bismuth nitrate as raw material. The thin films were then characterized for structural, surface morphological, optical and electrical properties by means of X-ray diffraction (XRD), Atomic force microscopy (AFM), scanning electron microscopy (SEM), optical absorption and d.c. two-probe, respectively. Structural investigations indicated that as-prepared bismuth oxide films were polycrystalline and multiphase, and annealing temperatures played a key role in the composition and optical properties of these films. AFM and SEM images revealed well defined particles which are highly influenced by annealing temperatures. The optical studies showed a direct band gap which varied with annealing temperatures between 3.63 eV and 3.74 eV. The electrical measurement showed that the electrical resistivity increased with annealing temperatures and the films were typical semiconductors. As catalyst, bismuth oxide films annealed at 550 °C had the best photocatalytic performance for photodegradation of methyl orange.     

Flat and compact switchable dual wavelength output at 1060 nm from ytterbium doped fiber laser with an AWG as a wavelength selector

A dual-wavelength ytterbium doped fiber laser with a narrowest spacing of 0.53 nm and widest spacing of 12.2 nm at 1064 nm is presented in this paper. An arrayed waveguide grating (AWG) together with an optical channel selector (OCS) have also been incorporated in the proposed setup that works as a switchable mechanism giving 23 different wavelength tunings. Producing an average output power of ?8 dB m and side mode suppression ratio (SMSR) of 59.65 dB, this dual-wavelength fiber laser is quite stable with an output power variance as low as 0.47 dB giving it an advantage due to its switching ability and stable dual-wavelength output powers.     

Wavelength tunable,high energy femtosecond laser pulses directly generated from large-mode-area photonic crystal fiber

Wavelength tunable high energy ultrashort laser pulses are generated from a large-mode-area photonic crystal fiber in anomalous dispersion (AD) regime. A simplified laser cavity design with one fine polished facet of the fiber as a cavity mirror is used. The intra-cavity dispersion compensation is achieved by a grating pair, the spatial dispersed light from which also have optical spectrum filtering effects combined with the limited aperture of the fiber core. The laser system is able to generate ultrashort pulses ranging from 494 fs (with 56 nJ pulse energy) to 1.24 ps (with 49 nJ pulse energy) at 55 MHz repetition rate. The filtering mechanism benefits the generation of high energy pulses with narrowing pulse duration in AD regime. An undulation in frequency and time domain is also observed with the increase of the pump power. Furthermore, this laser system is directly used as seed for supercontinuum generation.     

A novel OCS millimeter-wave generation scheme with data carried only by one sideband and wavelength reuse for uplink connection

We propose a novel optical carrier suppression (OCS) millimeter-wave generation scheme with data carried only by one sideband using a dual-drive Mach–Zehnder modulator (MZM) in radio-over-fiber system, and the transmission performance is also investigated. As the signal is transmitted along the fiber, there is no time shifting of the codes caused by chromatic dispersion. Simulation results show that the eye diagram keeps open and clear even when the optical millimeter-waves are transmitted over 110 km and the power penalty is about 1.9 dB after fiber transmission distance of 60 km. Furthermore, due to the +1 order sideband carrying no data, a full duplex radio-over-fiber link based on wavelength reuse is also built to simplify the base station. The bidirectional 2.5 Gbit/s data is successfully transmitted over a 40 km standard single mode fiber with less than 0.8 dB power penalty in the simulation. Both theoretical analysis and simulation results show that our scheme is feasible and we can obtain a simple cost-efficient configuration and good performance over long-distance transmission.     

Optical and physical characteristics of In-doped ZnO nanorods

In this paper the effect of indium dopants on structure, optical, electrical and mechanical properties of ZnO nanorods are studied. The average surface potentials and the surface currents of ZnO:In nanorods were 0.25–0.84 mV and 2.2–200 MΩ-cm, respectively. The turn-on threshold field for the vertical ZnO nanorods was around 2–16 V μm⁻¹. Emission current densities of 3.3–911.4 mA cm⁻² were obtained for an electrical field of 60–160 V μm⁻¹. The photoluminescence (PL) spectrum measured at 15–300 K showed that the intensity of the peak at 2.06 eV increased with decreasing temperature, while the peak at 2.06 eV further red shifted and the peak at 3.39 eV blue shifted.