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In this paper, a filterless 32-tupling millimeter wave generation scheme based on eight MZMs is proposed. The system has an upper and lower parallel two-branch structure. The upper branch consists of two subsystems Sub-A and Sub-B in cascade, each subsystem contains four MZMs, and the MZMs are all operating at maximum transfer point (MATP). Sub-A mainly generates ±8th order optical sideband signal as the incident light signal of Sub-B. After modulation of Sub−B, the output signal is mainly ±16th order optical sideband signal containing the central optical carrier component. The optical attenuator (OATT) and optical phase shifter (OPS) of the lower branch are used to regulate the phase and amplitude of the optical carrier. The upper and lower branches are coupled, and the central optical carrier component is superimposed and cancelled so only the ±16th order optical sideband signal is retained. Finally, the 32-tupling frequency millimeter is generated by the photodiode (PD) receiver after photoelectric detection which receives and generates a 32-tupling frequency millimeter wave signal. The simulation results show that the 160 GHz millimeter wave signal can be obtained by driving the MZM with a 5 GHz RF signal, and the optical sideband suppression ratio (OSSR) and the RF sideband suppression ratio (RFSSR) are 52.6 dB and 44.75 dB, respectively. Theoretical analysis and simulation experiments are carried out for the proposed scheme which proves the feasibility of the scheme. [ABSTRACT FROM AUTHOR]

In the field of optical communication, laser and its modulation bandwidth and modulation rate are very important for optical wireless communication. There are two main modulation modes for semiconductor laser signal: internal modulation and external modulation. These two modulation technologies have their own characteristics and are suitable for different fields of optical fiber communication. Internal modulation laser, also known as direct modulation laser, has become a cost-effective light source for the Fifth Generation Mobile Communication Technology (5G) fronthaul and data center because of its high-speed transmission and low cost. There is no additional Chirp of light source in external modulation laser, so the Composite Second Beat (CSB) distortion caused by fiber dispersion can be effectively overcomed. On the basis of reviewing the development history of communication laser and its modulation technology, this paper introduces the work and main progress made by Xi’an University of Technology in this field. This paper discusses the internal and external factors of nonlinear distortion of semiconductor laser, simulates the effects of various parameters of response characteristics, linearization compensation method and power control system on the output light source of light emitting device, and analyzes the influence of temperature fluctuation on the output power of laser and modulation device. Based on the basic theory of refractive index ellipsoid and numerical analysis, the variation trend of emitted light intensity with temperature is discussed under the longitudinal and transverse modulation, respectively. The results show that the variation trend of outgoing light intensity with temperature under longitudinal modulation is only related to the refractive index of Lithium Niobate (LN) crystal. Under transverse modulation, the variation trend of outgoing light intensity with temperature is affected not only by the refractive index of the crystal, but also by the crystal size and its expansion coefficient. Therefore, the special size crystal can be used to improve the temperature stability of the electro-optic modulator.

In this paper, a filterless 32-tupling millimeter wave generation scheme based on eight MZMs is proposed. The system has an upper and lower parallel two-branch structure. The upper branch consists of two subsystems Sub-A and Sub-B in cascade, each subsystem contains four MZMs, and the MZMs are all operating at maximum transfer point (MATP). Sub-A mainly generates ±8th order optical sideband signal as the incident light signal of Sub-B. After modulation of Sub−B, the output signal is mainly ±16th order optical sideband signal containing the central optical carrier component. The optical attenuator (OATT) and optical phase shifter (OPS) of the lower branch are used to regulate the phase and amplitude of the optical carrier. The upper and lower branches are coupled, and the central optical carrier component is superimposed and cancelled so only the ±16th order optical sideband signal is retained. Finally, the 32-tupling frequency millimeter is generated by the photodiode (PD) receiver after photoelectric detection which receives and generates a 32-tupling frequency millimeter wave signal. The simulation results show that the 160 GHz millimeter wave signal can be obtained by driving the MZM with a 5 GHz RF signal, and the optical sideband suppression ratio (OSSR) and the RF sideband suppression ratio (RFSSR) are 52.6 dB and 44.75 dB, respectively. Theoretical analysis and simulation experiments are carried out for the proposed scheme which proves the feasibility of the scheme.

Introduction. Designers of modern on-board systems for communication, radar, and radio monitoring face the problem of improving their qualitative characteristics, including the operating frequency, instantaneous bandwidth, receiver sensitivity, and electromagnetic compatibility. In addition, the dimensions, weight, and power of such systems, as well their cost, should be minimized. However, the current semiconductor microwave electronics has reached its limits in terms of frequency and dynamic characteristics. A possible solution consists in the implementation of microwave photonic transmission lines in the design of on-board systems for communication, radar, and radio monitoring on the basis of modulation of laser radiation by means of electro-absorption.Aim. To study the transfer characteristics and noise figure of a microwave photonic transmission line realized based on the modulation of laser radiation by means of electro-absorption. To compare the results of theoretical calculations and experimental investigations.Materials and methods. The research methodology involved external modulation using an electro-absorption modulator (EAM), mathematical representation of the transmission coefficient, as well as comparison of the theoretical and practical results.Results. Theoretical values of the transmission coefficient and noise figure for a microwave photonic transmission line based on the external modulation method using an EAM were obtained. Experimental values of the transmission coefficient and noise figure for a microwave photonic line in the frequency range from 100 MHz to 16 GHz were presented. The obtained data were compared with those of the nearest mass-produced products of foreign production and those presented in domestic publications on microwave photonic signal transmission lines.Conclusion. The use of an EAM, whose main advantage consists in the possibility of integration with a laser emitter, allowed the authors to design and manufacture a small-sized industrial prototype of a radio-photonic transceiver, capable of transmitting a radio signal over tens of kilometers in the frequency range from 100 MHz to 12 GHz with a transmission coefficient of at least −3 dB and a noise figure no more than 36 dB at the upper operating frequency. At the same time, the closest analogue manufactured by Emcore with similar dimensions has a transmission coefficient of −30 dB and uses direct modulation of laser radiation as a transmission method, which significantly reduces the transmission range of the microwave signal.

A photonics-assisted scheme for generating various microwave waveforms has been investigated in this paper. In the proposed scheme, two phase modulation to intensity modulation (PM-IM) conversions are realized using two cascaded Sagnac interferometers (SIs) to manipulate light in the optical domain. From the first SI, by adjusting the amplitude of the microwave signal and time delay of the tunable optical delay line (TODL), both half duty cycle square and full duty cycle triangular waveforms can be generated from the photodetector (PD) and balanced photodetection (BPD). Using the second SI and applying microwave signals with appropriate amplitudes and phases, as well as the BPD process, results in full duty cycle sawtooth and reversed sawtooth waveforms. Detailed theoretical analyses are presented and results are verified by simulations. In the simulations, square-, triangular- and sawtooth-shaped (or reversed sawtooth-shaped) waveforms are obtained successfully. To complete the simulation results, the effects of non-ideal microwave hybrid coupler and optical couplers on the performances of the proposed scheme have been studied and no destructive effects were observed. The proposed structure does not include any optical or electrical filters which result in a wide operational bandwidth.

This paper presents the analytical research and characterization of optical Binary Phase Shift Keying (BPSK) for single-tone sinusoidal and digital signals. The mathematical analysis and simulation for optimal modulation depth are proposed in this paper for maximum efficiency of the output modulated signal. The modulation depth is analysed with suitable Radio Frequency (RF) drive voltage for message signal and the effect of modulation depth on carrier suppression and higher order harmonics over fundamental tone is analysed theoretically and with simulation. To achieve phase modulation in this work, an external modulation technique via the Mach-Zehnder Modulator (MZM) is used, and an optical source using a narrow line width Distributed Feed Back (DFB) laser is used to minimise phase noise. The simulation and characterization results strongly support the mathematical analysis of the proposed criteria for suitable RF drive over half wave voltage for optimal detection and maximum message signal efficiency. [ABSTRACT FROM AUTHOR]

This paper presents the development and characterization of high-speed ON-OFF Keying (OOK) Optical Transmitter up to 12 Gbps using External Modulation Technique that comprises Continuous Wave (CW) laser, Mach-Zehnder Modulator (MZM), and ultra-high bandwidth driver amplifier for MZM. The CW laser driver and high bandwidth modulator driver amplifier has been designed and integrated with the modulator which is biased for OOK modulation scheme. This work includes Direct Current (DC), Optical and Radio Frequency (RF) characterization of MZM modulator; selection of suitable bias point for modulator to achieve OOK modulation format, design and development of wideband driver amplifier in microstrip configuration on 25-mil alumina using Hittite device. The biasing circuit for distributed feedback laser is designed as an unmodulated CW optical signal to feed optical modulator. In this work, the assembly and characterization of optical transmitter is also carried out and performance is analyzed in terms of different parameters such as Extinction ratio and Signal-to-Noise Ratio (SNR) etc. [ABSTRACT FROM AUTHOR]

An improved photonic generation of full-duty-cycle triangular waveforms based on external modulation and orthogonal polarization control is proposed. The external modulation configuration consists a dual-parallel Mach–Zehnder modulator (DP-MZM) and a remodulation structure. After external modulation, four main sidebands with uniform frequency interval existed in the optical spectrum. To obtain the target triangular waveform, the modulation indices of modulators need to be carefully adjusted to guarantee the amplitude ration of inner-sideband and outer- sideband is desired 9.5 dB. Subsequently, polarization control is utilized to eliminate the coherent interference of different sidebands. Based on our proposal, triangular waveforms at 10 GHz, 20 GHz, 30 GHz and 40 GHz are achieved. The proposal might be attractive since that the generated signal repetition rate is frequency-tunable and frequency-quadrupled.

This work investigates the performance enhancement achieved for an optical communication link designed using co-simulation platform provided by Optisystem and OptiSPICE. A passive optical network with a single channel is designed that employs external Mach–Zehnder modulator at the transmitter and direct detection at the receiver end. The design is first simulated at 2.5 Gbps with Optisystem v.13 only. Externally modulated laser circuit is then designed in OptiSPICE v.5 and this circuit's co-simulation is done with a design made in Optisystem. The simulation results validate the superior performance obtained when optical components are designed using OptiSPICE that provides more control over user adjustable parameters for different components. The same design parameters can be emulated for practical implementation of Passive optical Network system. [ABSTRACT FROM AUTHOR]

The nonlinear degradations and chromatic dispersion induced bandwidth penalty are critical obstacles for implementing the analog radio-over-fiber (A-RoF) technique in future mobile fronthaul (MFH). In this paper, we propose an analog multiple intermediate-frequency-over-fiber (multi-IFoF) MFH system with blind linearity improvement and flexible dispersion-induced bandwidth penalty mitigation. The bias adjustment of a single-electrode driven dual-drive Mach–Zehnder modulator is used to compensate the bandwidth penalty arising from the dispersion-induced power fading of fiber links in different lengths. This operation can increase the available bandwidth for the MFH system free of even-order intermodulation distortions (IMDs). At the receiver, a self-adaptive digital post-processing algorithm is introduced to blindly improve the linearity of the IFoF MFH system by suppressing the residual odd-order IMDs, with no need of training signals or prior knowledge of the transmission channel. In the proof-of-concept experiments, the transmission of 64-QAM-OFDM signals in 1 to 12 IF channels with a 500-MHz bandwidth has been demonstrated over standard single-mode fibers (SSMFs) of 20, 50, and 100 km. For the 50-km (or 100-km) SSMF, the bandwidth penalty for a broadband signal with a bandwidth of 4.5 GHz (or 2.5 GHz) is fully compensated. In addition, the proposed post-processing algorithm can significantly suppress the odd-order IMDs and thus improve the linearity by greater than 5.4 dB in terms of the input RF power range which retains an acceptable error-vector-magnitude (EVM) performance for the 64-QAM-OFDM signal. [ABSTRACT FROM AUTHOR]

Nonlinearities implanted by refractive index and scattering degrade the performance of optical networks. In this paper, FWM (Four Wave Mixing) has been analyzed for four different channels with 10 nm spacing. Due to the presence of resonant frequency, FWM interface of different channels in WDM (Wavelength Division Multiplexing) hinders the performance of the system. The system is affected by nonlinear cross talk. A system with the bandwidth of 10 Gbps has been investigated using External Modulation and an optical rectangle filter as a key parameter to improve the system performance with respect to FWM effect

This study presents the external modulation and direct detection of duobinary signal in optical access networks at 25 and 50 Gb/s with the use of first‐order optical equaliser at the transmitter output (pre‐equalisation) to compensate the waveform distortion induced by fibre dispersion. The first‐order optical equaliser is then replaced by second‐order optical equaliser to further improve the bit error rate (BER) performance and extend the maximum transmission distance by compensating the residual dispersion for the first time. The authors explain the enhancement in the BER by analysing the eye diagrams and optical spectra. The authors also investigate non‐return‐to‐zero signal with similar setup parameters for reference. [ABSTRACT FROM AUTHOR]

A system involving W-band (75-110 GHz) optical millimeter (mm)-wave generation using the external optical modulator (EOM) in a radio-over-fiber (RoF) link is presented for satisfying the requirements for multi-gigabit-per-second data rates. A 90-GHz mm-wave signal was generated by a nonupling (nine times) increase in only a 10-GHz local oscillator by biasing the EOM at its zero level and choosing an appropriate modulation index. To achieve a fast transmission speed wirelessly, high spectral efficiency (SE), and better transmission performance, orthogonal frequency-division multiplexing (OFDM) is used. The bit error rate (BER) and error vector magnitude (EVM) of the system were measured for three different fiber lengths and for a wireless distance of 1-5 m. The results show that the system with the SE of ~4 (b/s)/Hz and 16-ary quadrature amplitude modulation (QAM) 40-GB/s OFDM signals can be received by the end user with BER less than 3.8 × 10-3 and EVM less than 25% over a 50-km optical fiber and 3-m wireless link.

A novel architecture of bidirectional gigabit signal transport system over long-haul single-mode fiber (SMF) using wavelength division multiplexed passive optical network technique is proposed and demonstrated. In order to offer multimedia services of high bandwidth, four signals of 5 Gbps data rates are externally modulated and transmitted through four channels over 100-km SMF in uplink and downlink. In our proposed scheme, an excellent bit error rate, good Q-factor and clear eye diagrams are observed for both 100-km uplink and downlink transmission. This architecture has potential to transmit 4 × 5 Gbps over long-haul fiber backbone and it will be useful in future broadband communications. [ABSTRACT FROM AUTHOR]

A novel pre-coding scheme for modified optical duobinary signals was proposed.It could be applied to trans-mit high speed data rate signals（≥ 10Gbit/s）.Through analyzing the process of coding and decoding,It was demon-strated that modified optical duobinary signals have capability in reduction of pulse-to-pulse interaction,and could be di-rectly measured through a conventional binary intensity modulation direct detection（IM-DD） receiver.Two modified op-tical duobinary signals’ formats were simulated to generate.Simulation results show that MD-NRZ and MD-RZ signals’ formats can avoid the eye diagrams’ distortion for long-distance transmission,if the dispersion can be compensated in each amplifier span.Moreover,the MD-RZ signal has lower BER than the MD-NRZ signal after long-distance commu-nication.

ABSTRACT Selective delivery of gigabit-per-second wireless and wired services is demonstrated in an integrated fiber-wireless access network using the millimeter-wave (mm-wave) radio-over-fiber (RoF) system employing the dual-sideband optical carrier suppression technique. A dual-electrode Mach-Zehnder modulator is used in this technique to generate 40 GHz carrier to distribute 1.25 Gbps data via direct modulation (DM) over a 20 km RoF system. The results show that selective signal delivery can be achieved using a low-cost DM laser diode drive current of 20 mA. The advantage of the proposed system is that it provides versatility to control the gigabit-per-second (Gbps) signal delivery in an integrated ROF-PON system with a common high frequency oscillator shared for the whole system. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1768-1773, 2016 [ABSTRACT FROM AUTHOR]

This paper is regarding the concept and development of a photonics-based tunable and broadband radio frequency converter (PBRC). It employs an external modulation technique to generate and reconfigure its output frequency, a digital circuit to manage the modulators' bias voltages, and an optical interface for connecting it to optical-wireless networks based on radio-over-fiber technology. The proposed optoelectronic device performs photonics-based upconversion and downconversion as a function of the local oscillator frequency and modulators' bias points. Experimental results demonstrate a radiofrequency (RF) carrier conversion with spectral purity over the frequency range from 750 MHz to 6.0 GHz, as well as the integration of the photonics-based converter with an optical backhaul based on a 1.5-km single-mode fiber from a geographically distributed optical network. Low phase noise and distortion absence illustrate its applicability for convergent and reconfigurable optical wireless communications. A potential application relies on the use of PBRC in convergent optical wireless networks to dynamically provide RF carriers as a function of the telecom operator demand and radio propagation environment. [ABSTRACT FROM AUTHOR]

Nonlinearities implanted by refractive index and scattering degrade the performance of optical networks. In this paper, FWM (Four Wave Mixing) has been analyzed for four different channels with 10 nm spacing. Due to the presence of resonant frequency, FWM interface of different channels in WDM (Wavelength Division Multiplexing) hinders the performance of the system. The system is affected by nonlinear cross talk. A system with the bandwidth of 10 Gbps has been investigated using External Modulation and an optical rectangle filter as a key parameter to improve the system performance with respect to FWM effect. [ABSTRACT FROM AUTHOR]

A simple and affordable 10 GHz intermediate frequency (IF) over fiber system with direct detection and up conversion at the base station (BS) was designed. Its central station (CS) output signal performance was evaluated. In the proposed system, quadrature phase-shifting keying (QPSK) with a data rate of 5 Gbit/s was used to enhance the spectral efficiency of the analog transmitted signal. For the downlink transmission, the CS consists of an IQ mixer, radio frequency (RF) amplifiers, a distributed feedback (DFB) laser, an amplitude modulator (AM) and a local oscillator (LO). At the BS, detected IF by photodiode was upconverted to 60 GHz carrier frequency and wirelessly transmitted to the mobile station (MS). The CS was assembled on a printed circuit board (PCB) process using commercially available components ensuring low cost. Prior to the PCB layout design; the CS schematic was simulated using optical systems simulator VPItransmissionMaker and RF components simulator AWR Microwave Office. Looking at the CS, from the PRBS data source to the input of electrical to optical amplitude modulation, the system has a low noise figure of 2.5 dB and a total gain of 24 dB. The AM has a maximum rated power input of 24 dBm. In phase (I) and Quadrature (Q) inputs in the IQ mixer have 2 GHz bandwidth. The fabricated PCB with four SMA edge connectors is integrated with a DFB laser source for the transmitter testing and performance analysis. The power consumed by the CS (without DFB laser) is estimated to be less than 1.5 W. [ABSTRACT FROM AUTHOR]

The time-dependent barrier passage of an activated rate process is studied where the heat bath in the system-reservoir coupling environment is modulated by an external fluctuation. For a thorough inspection on the barrier recrossing dynamics, the Kramers rate and effective transmission coefficient are calculated of the reactive flux method. In the particular case of a δ-correlated noise activated Ornstein-Uhlenbeck process, it is found that, the external modulation can in some cases result in an maximum effective transmission coefficient. This reveals a maximum net flux and can be obtained from the minimum barrier recrossing resulted from appropriate external modulation. [ABSTRACT FROM AUTHOR]

ABSTRACT A scheme of high-dense wavelength-division-multiplexing light source based on external mixing-modulated Fabry-Perot laser diode (FP-LD) is investigated in this article. A 10-GHz spaced 22-channel optical carrier supply module is achieved by cascading a multiple-longitudinal mode FP-LD with two types of external modulators. Then a 110-channel extendable light source scheme is proposed. This scheme has potential application prospect in future optical access network. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:403-406, 2015 [ABSTRACT FROM AUTHOR]

A system involving W-band (75-110 GHz) optical millimeter (mm)-wave generation using the external optical modulator (EOM) in a radio-over-fiber (RoF) link is presented for satisfying the requirements for multi-gigabit-per-second data rates. A 90-GHz mm-wave signal was generated by a nonupling (nine times) increase in only a 10-GHz local oscillator by biasing the EOM at its zero level and choosing an appropriate modulation index. To achieve a fast transmission speed wirelessly, high spectral efficiency (SE), and better transmission performance, orthogonal frequency-division multiplexing (OFDM) is used. The bit error rate (BER) and error vector magnitude (EVM) of the system were measured for three different fiber lengths and for a wireless distance of 1-5 m. The results show that the system with the SE of ∼4 (b/s)/Hz and 16-ary quadrature amplitude modulation (QAM) 40-GB/s OFDM signals can be received by the end user with BER less than 3:8 × 10-3 and EVM less than 25% over a 50-km optical fiber and 3-m wireless link. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, optical upconverted microwave frequency generation was experimentally demonstrated using a frequency quadrupling technique based on two types of baseband signal modulation in a radio-over-fiber (RoF) system. The measured results revealed that an error-free transmission could be achieved without causing the periodic power fading affect, and that clear eye diagrams were obtained after a 20-km transmission by using baseband/RF mixed-signal external modulation. The proposed method is a feasible technique for generating a 622 Mbps (1.25 Gbps)/15 GHz frequency quadrupling RoF signal without using narrow-band optical notch filters or sophisticated optical modulators. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1603-1610, 2014 [ABSTRACT FROM AUTHOR]

Abstract: This study experimentally demonstrates the performance of optical frequency quadrupling generation and base-band signal up-conversion techniques based on the cascaded single-electrode Mach–Zehnder modulator (SEMZM) using different signal modulation schemes. The optical signals in microwave band with double-sideband suppressed-carrier (DSB-SC) modulated format exhibit that the receiver sensitivity and the spectral efficiency are maximized and the power penalty over long-distance delivery is minimized. A simple configuration and low-frequency bandwidth requirement for both electrical and optical components in the proposed schemes also are demonstrated. [Copyright &y& Elsevier]

A dual parallel Mach?Zehnder modulator (DPMZM) used for electro-optic conversion of multi-band orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) radio signals in intensity modulated direct detection optical communication systems is optimized theoretically and through numerical simulation. The optimum DPMZM parameters that allow simultaneous mitigation of the second and third order distortion components created by the joint electro-optic converter and photodiode nonlinearities are identified. The corresponding minimum optical signal-to-noise ratio (OSNR) required to achieve a bit error ratio of 10-9 is also evaluated. An analytical expression showing the relation between the optimum DPMZM parameters under extended voltage levels of the OFDM-UWB signals applied to the DPMZM is proposed and validated. It is shown that the DPMZM performance presents high robustness to deviations from the optimum DPMZM parameters identified. Additionally, it is shown that similar minimum required OSNR levels are obtained with the optimized DPMZM and when the electro-optic conversion is realized by a single MZM. [ABSTRACT FROM PUBLISHER]

The influence of the Mach-Zehnder modulator (MZM) bias and driving voltages on the transmission performance of multiband orthogonal frequency division multiplexing ultrawideband radio signals is analyzed theoretically and experimentally. Particularly, the optical signal-to-noise ratio (OSNR) required to achieve a given bit error probability is evaluated for a bias voltage close to the minimum power transmission of the MZM characteristic. In addition, the required OSNR obtained for that bias voltage is compared with the OSNR required when the MZM is biased at the quadrature point. The analysis is performed for different fiber lengths indicated for long-reach passive optical networks (LR-PONs). It is shown that lower OSNR is required when the modulator is biased at the quasi-minimum point than when it is biased at the quadrature point, for all the fiber reaches analyzed. This is due to the compromise between additional distortion induced by the modulator and lower carrier-to-signal-power ratio when the quasi-minimum bias point is employed. In addition, it is also shown that, as for the quadrature bias point, similar optimum driving voltages are obtained for the different LR-PONs reaches analyzed, when the quasi-minimum bias point is employed. [ABSTRACT FROM PUBLISHER]

Purpose: Previous studies have suggested that cognitive tasks modulate (provoke or inhibit) the epileptiform electroencephalography (EEG) discharges (EDs) in patients with juvenile myoclonic epilepsy (JME). Their inhibitory effect was found to be especially frequent (64-90%). These studies arbitrarily defined modulation as a >100% increase or >50% decrease of the EDs compared with baseline, which may not sufficiently distinguish from spontaneous fluctuations. The aim of our study was to assess the modulation of EDs and the precipitation of myoclonic seizures by cognitive tasks and by conventional provocation methods, taking into account also the spontaneous fluctuation of EDs. Method: Sixty patients with JME underwent video-EEG recordings including 50-min baseline, sleep, hyperventilation, intermittent photic stimulation (IPS), and cognitive tasks. To account for spontaneous fluctuations of the EDs we divided the baseline period into 5-min epochs and calculated the 95% confidence interval for the baseline EDs in each patient. Modulation was assumed when the number of EDs during any 5-min test period was outside the 95% confidence interval. Key Findings: Using the arbitrary method, our results were similar to previous publications: Cognitive tasks seemed to inhibit the EDs in 94% of the patients, and to provoke them in 22%. However, when the spontaneous fluctuations were accounted for, inhibition was found in only 29% of the patients and provocation in 18%. A nonspecific effect of any cognitive task seemed to account for the observed significant inhibition in two-thirds of the cases, but was observed in only one of the patients with significant provocation. Photoparoxysmal response was observed in 23% of the patients. When accounting for the spontaneous occurrence of EDs, IPS had provocative effect in 10% of the patients. Hyperventilation and sleep had provocative effect on EDs to an extent similar to the cognitive tasks (hyperventilation: 22%; sleep: 18%). The conventional provocation methods tended to be more efficient in patients who were not seizure free. Myoclonia were recorded most often during the cognitive tasks (10 patients). Significance: Spontaneous fluctuations of EDs account for most of the previously described inhibitory effect of the cognitive tasks. The provocative effect of the cognitive tasks is task-specific, whereas the inhibitory effect seems to be related to cognitive activation in general. [ABSTRACT FROM AUTHOR]

Integrating an ultrawideband-over-fiber (UWBoF) system into a wavelength division multiplexing passive optical network (WDM-PON) is of great interest due to the high potential to provide high data-rate and flexible wired and wireless services with a favorable cost. In this paper, we perform a comprehensive study on an impulse radio UWBoF system compatible with the WDM-PON architecture implemented based on a photonic microwave bandpass filter. The bandpass filter is a two-tap delay-line filter implemented using either a polarization modulator (PolM) or a phase modulator (PM), which is used to simultaneously shape an electrical Gaussian-like pulse to an optical UWB pulse and reduce the out-band noise and interference. The features of the photonic microwave bandpass filters are theoretically studied. The photonic microwave bandpass filter based on a PolM would produce a chirp-free UWB signal, while the one based on a PM would generate a UWB signal that is insensitive to fiber dispersion. A single-channel UWBoF system with ON–OFF keying, biphase modulation, and pulse-position modulation without and with time hopping are experimentally studied. The experimental results agree well with the theoretical predictions. A four-channel UWBoF broadcasting network as well as a hybrid WDM-PON network to provide both wireless and wired services is also experimentally investigated. Results show that a conventional WDM-PON network could be easily upgraded to provide UWB services by incorporating the proposed photonic microwave bandpass filter. [ABSTRACT FROM PUBLISHER]

Abstract: A general model of analog microwave photonic links employing cascaded amplitude and phase external modulation is theoretically derived. Chromatic dispersion is also included in the model showing a different dispersion induced attenuation response in comparison to pure phase or amplitude modulation. Thus, hybrid modulation can be used to increase the bandwidth of radio over fiber links without the need of single-sideband modulation or dispersion compensation. Experimental results agreeing with the derived theory are also provided. [Copyright &y& Elsevier]

This paper presents an electrooptic vector digital-to-analog converter (EO-DAC) for coherent synthesis of optical multilevel signals, such as quadrature-amplitude modulation (QAM) signals. For generation of an optical multilevel/QAM signal, the inphase (I) and quadrature (Q) components of a carrier lightwave should be orthogonally modulated in multilevels. Conventionally, inphase–quadrature (IQ) orthogonal modulators have been utilized for this purpose. In the scheme, however, the symbol rate available for multilevel/QAM signals is limited, and it is difficult to obtain a clear constellation because of the difficulty involved in handling with electrical multilevel signals. The EO-DAC employing multiparallel modulator, described in this paper, can be used to synthesize multilevel signals through the combination of binary data streams. Using this proposed technology, multilevel signals can be coherently synthesized at a high bit rate, and clearer constellations can be obtained. Further, because of its flexibility, and versatility, the EO-DAC can be used for the several types of multilevel modulation formats. In this paper, we describe the EO synthesis of optical multilevel signals especially focusing on the method based on the EO-DAC, along with comparisons with other conventional methods. [ABSTRACT FROM PUBLISHER]

UWB over fiber (UWBoF) technique has been proposed to increase the area of coverage for UWB communication systems. In this paper, the transmission performance of impulse UWB signals over optical fiber is analyzed. Three types of UWB signals generated based on three different techniques are considered. Since optical signals with different optical spectra would have different tolerances to fiber dispersion, the transmission performance of the three types of UWB signals is studied. First, the impact of fiber chromatic dispersion on UWB waveforms and their spectra is evaluated. Then, the transmission performance of data-modulated UWB signals in an optical fiber is investigated, with a general model to analyze the signal power spectral density (PSD) being developed. The PSD of an UWB signal with on-off keying (OOK), bi-phase modulation (BPM) and pulse position modulation (PPM) schemes is calculated. Evolution of the PSD as a function of transmission distance is then performed. The suitability of the three types of UWB signals for UWBoF applications is also evaluated. The study provides a guideline for the design and development of a practical UWBoF system. [ABSTRACT FROM AUTHOR]

An optimization technique is presented for the radio over fiber (ROF) wireless local area network (WLAN) transmission in IM/DD optical link. The results show that with minimal optimization, directly modulated ROF WLAN 802.11g signal at 2.4 GHz and externally modulated 1.25 Gbps baseband signal can coexist in the 2 km IM/DD optical link with a power penalty of 3 dB. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:812–815, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25029 [ABSTRACT FROM AUTHOR]

Optical glass fiber shows great advantages over coaxial cables in terms of electromagnetic interference, thus, it should be considered a potential alternative for magnetic resonance imaging (MRI) receive coil interconnection, especially for a large number coil array at high field. In this paper, we propose a 4-channel analog direct modulation optical link for a 1.5-T MRI coil array interconnection. First, a general direct modulated optical link is compared to an external modulated optical link. And then the link performances of the proposed direct modulated optical link, including power gain, frequency response, and dynamic range, are analyzed and measured. Phantom and in vivo head images obtained using this optical link are demonstrated for comparison with those obtained by cable connections. The signal-to-noise (SNR) analysis shows that the optical link achieves 6%-8% SNR a improvement over coaxial cables by elimination of electrical interference between cables during MR signal transmission. [ABSTRACT FROM AUTHOR]

We have proposed and demonstrated a novel radio-over-fiber (ROF) architecture by using only one phase modulator and one optical filter to generate DWDM optical millimeter (mm) signals and realize wavelength reuse for upstream data connection. There is no additional laser source for the upstream data generation in the base station and no dc-bias controller for phase modulator. By this method, we simplify the configuration of the DWDM ROF system and reduce the cost of the system. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2146–2149, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23616 [ABSTRACT FROM AUTHOR]

In this paper we examine the transmission of two types of ultra-wideband (UWB) signals, multiband orthogonal frequency division multiplexing (MB-OFDM) and impulse radio ultra-wideband (IR-UWB), over single mode fiber at 1550 nm. In order to investigate the impact of optical components such as laser diode, external modulator and single mode fiber on UWB signals, we develop mathematical models for these components. These models are experimentally verified and corresponding numerical parameter values are obtained by experiment. Using these models we discuss the transmission of two types of UWB signals over single mode fiber. A new figure of merit namely distortion factor is defined. Using this figure of merit the direct modulation of distributed feedback (DFB) laser diode and the external modulation with Mach-Zehnder modulator (MZM) are compared in terms of their impact on UWB signals. Using intensive simulation we also compare MB-OFDM and IR-UWB in terms of their sensitivity to the distortions of a UWB over fiber link using error vector magnitude (EVM) as a figure of merit. An EVM measurement is accomplished for a MB-OFDM over fiber link. The impact of IR-UWB pulse shape on its resistance to the nonlinearity of modulation transfer function is also investigated. [ABSTRACT FROM PUBLISHER]

A high-speed external modulation scheme for optical continuous-phase frequency-shift keying (CPFSK) is presented. In external frequency-shift keying (FSK) modulation using single-sideband modulation technology, an optical upper/lower sideband (USB/LSB) component with respect to a carrier frequency is selectively generated. However, the FSK-modulated signal has phase discontinuities at the timings of frequency shifts. To overcome the problem, we propose a synchronous control technique that enables continuous phase modulation. In the external CPFSK modulation, the USB/LSB is allowed to shift to the other state when their phases coincide with each other. It is shown that CPFSK with a zero-to-peak frequency deviation of 0.5times(bit rate) is achieved with this synchronous control. Occupant bandwidth is less than half that of the externally modulated incoherent FSK with phase discontinuities. At a modulation speed of 10 Gb/s, higher order sidelobes are highly suppressed by more than 20 dB at the 20-GHz offset, comparing to a conventional binary phase-shift keying (BPSK). By the use of a Mach-Zehnder interferometer with balanced photodetection, receiver sensitivity is 3-dB greater than that of an on-off keying, as well as a BPSK. In this paper, we report on the experimental demonstration of CPFSK modulation/demodulation. A six-channel wavelength-division-multiplexed, 10-Gb/s CPFSK modulation/demodulation was successfully demonstrated [ABSTRACT FROM PUBLISHER]

In this paper, the model and implementation of an optical transmission system using a multi-longitudinal mode optical source and a dispersive optical channel are described. Such a system exhibits multi-bandpass transmission windows, as a result of a combination of the wideband optical spectrum and chromatic dispersion on the optical channel. As shown in this paper, the band-pass windows are centered at frequencies that depend on the spectral free range of the optical source and optical channel length. In the telecommunications domain, band-pass transmission windows can be used for multiplexing analog and/or digital signals, as an alternative way for transmitting baseband and modulated subcarriers, through optical-fiber links. To show such a potential application, the multiplexed transmission of two microwave signals, using two adjacent band-pass windows, is also described in this paper. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 202–206, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10720 [ABSTRACT FROM AUTHOR]

The status and prospects of semiconductor light sources for 40-Gb/s transmission systems are reviewed in regard to the following three topics: direct modulation, external modulation, and pulse sources for return-to-zero format. Included are discussions on direct modulation of a 1.3-μm distributed feedback laser for 40-Gb/s very-short-reach optical links, progress made in developing external modulators based on electroabsorption of multiple quantum wells, and mode-locked lasers for carrier-suppressed return-to-zero modulation format. [ABSTRACT FROM PUBLISHER]

The architecture of fiber-radio mm-wave wireless access systems critically depends upon the optical mm-wave generation and transport techniques. Four optical mm-wave generation and transport techniques: 1) optical self-heterodyning, 2) external modulation, 3) up- and downconversion, and 4) optical transceiver, will be assessed. From the technical viewpoints, their advantages and disadvantages are discussed. The economical assessment, focusing on the cost of a base station BS ( ), will suggest that the optical transceiver looks the most promising in the long run, but in the near future, however, the external modulation will be cost-effective. The experimental results of 60 GHz testbeds using the external modulation will support the conclusion. [ABSTRACT FROM AUTHOR]

The presence of relatively short time constants (<20 nS) in the impulse response of the thermal chirp of directly modulated DFB lasers is shown to significantly reduce the deleterious effects of interferometric noise in fiber-optic systems with multipaths. Compared with the chirp-free case of external modulation, thermal chirp can improve crosstalk tolerance by as much as 5 dB for eight interferers at 622 Mb/s and 13 dB at 80 Mb/s. This improvement was studied both theoretically and experimentally for several lasers. Simulations results match the experimental data, while two simplified semi-analytical models provide qualitative description [ABSTRACT FROM PUBLISHER]

The fiber optic communication is the one where the wired and the wireless communication systems are integrated to have high bandwidth, low cost, and high data rate with high user density. The RoF technology brings about high-performance network and the guaranteed quality of service for the increased demand for multimedia services. The RoF faces problems like distortion and chromatic dispersion in the RoF link, reducing the quality of the signal at receiver. To enhance the quality of the signal at the receiver side, several techniques have been reported. Those techniques concentrated on the RoF link and the modulation schemes used in the technology. This article reviews the complete RoF technology, which includes the challenges that limit the RoF network along with its compensation scheme and the RoF in the PON services with security. Along with that, the comparative study on the problems faced by the RoF and its mitigation schemes, such as linearization techniques and compensation for chromatic dispersion, are discussed. The linearization schemes will analyze the different pre-distortion circuits used to linearize the transmitting signal such that the signal received by the mobile unit is free of distortion. When these problems are reduced, the RoF with PON has faced another major problem of insecure transmission. Hence the performance of the existing encryption schemes is compared. [ABSTRACT FROM AUTHOR]