In this paper a review on different signal generation techniques for Radio over Fiber systems is presented. Radio over fiber has become a conspicuous contender in upcoming high data rate demands from ...household and enterprises users. Radio signals or waves can be generated back from optical signals at RAU (radio access unit) so that they may be transmitted to mobile stations. This generation is first assembled into different categories on the basis of some similar parameters, various aspects of each category are given and then a comparison between different aspect of each technique is summarized in table. Analysis of these techniques on the basis of ranges of radio frequencies that can be generated is also proposed in this paper.
The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a widespread and destructive pest of cruciferous crops. Owing to its increasing resistance to conventional pesticides, ...new strategies need to be developed for diamondback moth control. Here, we investigated factors that modulate juvenile hormone esterase (JHE) activity and jhe (Px004817) transcription, and determined the effects of these factors on subsequent growth and development in diamondback moth. Starvation inhibited JHE activity and jhe transcription, increased mortality, and decreased the rate of molting from the third- to the fourth-instar stages. Larvae kept at 32°C molted earlier and showed increased JHE activity and jhe transcription after 24-h treatment. Exposure to 1,325 mg/liter OTFP (3-octylthio-1,1,1-trifluoro-2-propanone) delayed molting and pupation, increased pupal weight, and decreased JHE activity and jhe transcription at both 24 and 48 h. Treatment with 500 mg/liter pyriproxyfen delayed molting, completely suppressed pupation, and significantly increased JHE activity at 48 h and jhe transcription at 24 and 48 h. A combination of OTFP (1,325 mg/liter) and pyriproxyfen (500 mg/liter) induced the highest mortality, delayed molting, completely suppressed pupation, and significantly increased JHE activity at 48 h and jhe transcription at 24 and 48 h. These effects on JHE activity and jhe transcription were similar to those in insects treated only with pyriproxyfen. The results demonstrated that JHE and jhe (Px004817) were involved in the responses of diamondback moth to external modulators and caused changes in growth and development. The combination of OTFP and pyriproxyfen increased the effectiveness of action against diamondback moth.
The performance degradation caused by transmission along dispersive single-mode fibers of optically generated millimeter-wave signals using up-conversion is theoretically assessed and validated by ...numerical simulation. Up-conversion techniques based on optical double sideband, optical single sideband, and optical carrier suppression are considered. The generation of 60 GHz by frequency tripling using the optical single sideband is shown to be particularly tolerant to the fiber dispersion. The practical imbalance of Mach-Zehnder modulators is taken into account for optical carrier suppression modulation, where the finite extinction ratio is found to increase tolerance to fiber dispersion.
We present a microwave photonic filter featuring the highest Q ever reported The filter structure is based on a modified gratings and Erbium Doped Fiber based structure. Q factors over 3000 are ...demonstrated when a tuned modulator is used in combination with the recirculating approach. Also comb RF filters for specific applications have been implemented. Finally, we investigate the possibility of using lasing from the cavity to feed the recirculating structure. This opens the path for RF filters with higher selectivity and low cost since no external source is required. Experimental measurements illustrate other interesting effects in these systems, which are generally employed to optimize the RF filter response.
The performance of wireless local area networks (WLANs) over fiber systems is investigated under multipath fading for different external modulators and optical system imperfections. Systems employing ...LiNbO/sub 3/ based Mach Zehnder modulators, polymer based Mach Zehnder modulators and electro-absorption modulators are presented. The benefits of wireless transmitter diversity, to deal with the optical domain imperfections, are examined.
A large energy shift of excitonic absorption peaks in quaternary InGaAlAs quantum wells operating in the 1.5 µm wavelength region has been demonstrated in a waveguide configuration. Shifts of up to ...30 meV (600 Å) and 17 meV (270 Å) have been achieved for the electron-to-heavy-hole and the electron-to-light-hole exciton absorption peaks, respectively. These shifts were obtained using a reverse bias of 6 V and without causing large broadening of exciton features. These values agree well with the calculated values.
The past few decades have witnessed a substantial increase in terahertz (THz) research. Utilizing THz waves to transmit communication and imaging data has created a high demand for phase and ...amplitude modulation. However, current active THz devices, including modulators and switches, still cannot meet THz system demands. Double-channel heterostructures, an alternative semiconductor system, can support nanoscale two-dimensional electron gases (2DEGs) with high carrier concentration and mobility and provide a new way to develop active THz devices. In this Letter, we present a composite metamaterial structure that combines an equivalent collective dipolar array with a double-channel heterostructure to obtain an effective, ultrafast, and all-electronic grid-controlled THz modulator. Electrical control allows for resonant mode conversion between two different dipolar resonances in the active device, which significantly improves the modulation speed and depth. This THz modulator is the first to achieve a 1 GHz modulation speed and 85% modulation depth during real-time dynamic tests. Moreover, a 1.19 rad phase shift was realized. A wireless free-space-modulation THz communication system based on this external THz modulator was tested using 0.2 Gbps eye patterns. Therefore, this active composite metamaterial modulator provides a basis for the development of effective and ultrafast dynamic devices for THz wireless communication and imaging systems.
We have experimentally demonstrated a novel transmission system for seamless integration of ROF with centralized lightwave OFDM-WDM-PON based on an integrated external modulator. At the one of two ...arms of the integrated external modulator, the optical carrier suppression (OCS) is realized to generate 40-GHz optical millimeter-wave (mm-wave) and up-converted baseband data signal as wireless signal. In another arm of the integrated external modulator, 16 quadrature amplitude modulation intensity-modulated OFDM signals at 10 Gbit/s are used for downstream transmission as wired signal based on double sideband modulation. By using one intensity modulator (IM), the downstream RF OFDM signal is remodulated for upstream on-off keying (OOK) data at 2.5 Gbit/s because of its downstream RZ shape waveform. The 10-Gbit/s wired signal, 2.5-Gbit/s wireless signal, and 2.5-Gbit/s upstream signal have been transmitted over 20-km single mode fiber (SMF) successfully.
•A scheme of ROF system with 18-tuple frequency optical millimeter-wave is proposed.•90 GHz optical millimeter-wave is generated and transmitted over 20 km SMF.•The impacts of SOA’s current on SR and ...system performance are also studied.
In this paper, we have reported a radio-over-fiber (ROF) system with 18-tuple frequency optical millimeter-wave using external modulator and four-wave mixing (FWM) in semiconductor optical amplifier (SOA). Signal lightwave and pump with frequency interval of 6fRF are generated by adjusting the parameters of the Mach-Zehnder modulator (MZM). After FWM in SOA and filtering, 18-tuple frequency millimeter-wave signal is generated. Based on the proposed scheme, a 90 GHz optical millimeter-wave is generated only using 5 GHz RF by numerical simulation. The simulation results show that our proposed scheme can provide 20 km single-mode fiber (SMF) transmission. In addition, the impact of SOA’s current on the sideband ratio (SR) and the system performance are also studied.
We have proposed a novel radio-over-fiber architecture to reduce the system cost at both central office (CO) and base station (BS). In this architecture, by incorporating the proper dc bias and ...optical filtering techniques in CO, the optical millimeter- wave (mm-wave) carriers are generated with four times frequency of the local oscillator signal. The BS is simplified by using the separated optical carrier along with downlink mm-wave signals to carry the upstream data. We have experimentally demonstrated optical mm-wave carrier generation up to 64-GHz, and both down- and upstream signal delivery over 20 km fiber with 1-dB power penalty.