scispace - formally typeset
Search or ask a question

Showing papers on "Modulation published in 2006"


Proceedings ArticleDOI
01 Oct 2006
TL;DR: A new transmission approach, called spatial modulation, is presented that entirely avoids ICI and requires no synchronization between the transmitting antennas while maintaining high spectral efficiency and results in a vast reduction in receiver complexity.
Abstract: The multiplexing gain of multiple antenna transmission strongly depends on transmit and receive antenna spacing, transmit antenna synchronization, and the algorithm used to eliminate interchannel interference (ICI) at the receiver. In this paper, a new transmission approach, called spatial modulation, that entirely avoids ICI and requires no synchronization between the transmitting antennas while maintaining high spectral efficiency is presented. A block of information bits is mapped into a constellation point in the signal and the spatial domain, i.e. into the location of a particular antenna. The receiver estimates the transmitted signal and the transmit antenna number and uses the two information to de-map the block of information bits. For this purpose, a novel transmit antenna number detection algorithm called iterative-maximum ratio combining (i-MRC) is presented. Spatial modulation is used to transmit different number of information bits and i-MRC is used to estimate both the transmitted signal and the transmit antenna number. The results are compared to ideal V-BLAST (vertical-Bell Lab layered space-time) and to MRC. Spatial modulation outperforms MRC. The (bit-error-ratio) BER performance and the achieved spectral efficiency is comparable to V-BLAST. However, spatial modulation results in a vast reduction in receiver complexity.

567 citations


Journal ArticleDOI
TL;DR: In this article, the authors compared the performances of optical millimeter-wave generation or up-conversion using external modulators based on different modulation schemes and found that the OCS modulation scheme has the highest receiver sensitivity, highest spectral efficiency and smallest power penalty over long-distance delivery.
Abstract: We have experimentally compared the performances of optical millimeter-wave generation or up-conversion using external modulators based on different modulation schemes. The generated or up-converted optical millimeter wave using the optical carrier suppression (OCS) modulation scheme shows the highest receiver sensitivity, highest spectral efficiency, and smallest power penalty over long-distance delivery. Moreover, the OCS modulation scheme has a simple configuration and low-frequency bandwidth requirement for both electrical and optical components. Employing an OCS modulation scheme, 16-channel dense wavelength-division multiplexing signals at 2.5-Gb/s per channel have been up-converted to a 40-GHz carrier simultaneously.

501 citations


Patent
24 May 2006
TL;DR: In this article, a system and method for stimulating a nerve was proposed, which included a first waveform generator adapted to generate a first and carrier waveforms having a frequency capable of passing through tissue of the mammal, a modulation device electrically coupled to the first and second waveform generators and adapted to modulate the first waveforms to create a modulated waveform.
Abstract: A system and method for stimulating a nerve, wherein the system includes a first waveform generator adapted to generate a first waveform having a frequency capable of stimulating a predetermined nerve of the mammal, a second waveform generator adapted to generate a carrier waveform having a frequency capable of passing through tissue of the mammal, a modulation device electrically coupled to the first and second waveform generators and adapted to modulate the first and carrier waveforms to create a modulated waveform, and an electrode electrically coupled to the modulation device and positioned substantially adjacent to skin of the mammal, and adapted to apply the modulated waveform thereto.

442 citations


Journal ArticleDOI
TL;DR: This paper presents a form of digital multicarrier modulation which is referred to as overlapped discrete multitone, or discrete wavelet multitone (DWMT), modulation, which is based on the application of M-band wavelet filters, and designed to achieve a combination of subchannel spectral containment and bandwidth efficiency that is fundamentally better than with other forms of multicarriers modulation.
Abstract: Multicarrier modulation possesses several properties which make it an attractive approach for high speed copper wire communication networks. Among these properties are the ability to efficiently access and distribute multiplexed data streams, and a reduced susceptibility to impulsive, as well as to narrowband channel disturbances. In digital implementations of multicarrier modulation, subcarrier generation and data modulation are accomplished digitally using orthogonal transformations of data blocks. These implementations are particularly efficient with regard to bandwidth utilization and transceiver complexity. In this paper, we present a form of digital multicarrier modulation which we refer to as overlapped discrete multitone, or discrete wavelet multitone (DWMT), modulation. For DWMT modulation, which is based on the application of M-band wavelet filters, the pulses for different data blocks overlap in time, and are designed to achieve a combination of subchannel spectral containment and bandwidth efficiency that is fundamentally better than with other forms of multicarrier modulation. We show that, as a result of the spectral containment feature, DWMT gives a high level of robustness with regard to noise environments and channel variations that are encountered in practice

328 citations


Journal ArticleDOI
TL;DR: Optical Orthogonal frequency division multiplexing (OOFDM) is shown to outperform RZ-OOK transmission in high-speed optical communications systems in terms of transmission distance and spectral efficiency.
Abstract: Optical Orthogonal frequency division multiplexing (OOFDM) is shown to outperform RZ-OOK transmission in high-speed optical communications systems in terms of transmission distance and spectral efficiency. The OOFDM in combination with the subcarrier multiplexing offers a significant improvement in spectral efficiency of at least 2.9 bits/s/Hz.

326 citations


Journal ArticleDOI
TL;DR: The effects of the nonideal performance parameters of commercial diode lasers are especially important away from the line center of discrete spectra, and these contributions become more pronounced for 2f signals with the large modulation depths needed for WMS at elevated pressures.
Abstract: Tunable diode laser absorption measurements at high pressures by use of wavelength-modulation spectroscopy (WMS) require large modulation depths for optimum detection of molecular absorption spectra blended by collisional broadening or dense spacing of the rovibrational transitions. Diode lasers have a large and nonlinear intensity modulation when the wavelength is modulated over a large range by injection-current tuning. In addition to this intensity modulation, other laser performance parameters are measured, including the phase shift between the frequency modulation and the intensity modulation. Following published theory, these parameters are incorporated into an improved model of the WMS signal. The influence of these nonideal laser effects is investigated by means of wavelength-scanned WMS measurements as a function of bath gas pressure on rovibrational transitions of water vapor near 1388 nm. Lock-in detection of the magnitude of the 2f signal is performed to remove the dependence on detection phase. We find good agreement between measurements and the improved model developed for the 2f component of the WMS signal. The effects of the nonideal performance parameters of commercial diode lasers are especially important away from the line center of discrete spectra, and these contributions become more pronounced for 2f signals with the large modulation depths needed for WMS at elevated pressures.

298 citations


Journal ArticleDOI
TL;DR: It is demonstrated that its truncated version of order 4 or 6 provides a very good approximation in the evaluation of the error probability for PSK and QAM in the presence of ICI.
Abstract: The focus of this paper is on the performance of orthogonal frequency division multiplexing (OFDM) signals in mobile radio applications, such as 802.11a and digital video broadcasting (DVB) systems, e.g., DVB-CS2. The paper considers the evaluation of the error probability of an OFDM system transmitting over channels characterized by frequency selectivity and Rayleigh fading. The time variations of the channel during one OFDM symbol interval destroy the orthogonality of the different subcarriers and generate power leakage among the subcarriers, known as inter-carrier interference (ICI). For conventional modulation methods such as phase-shift keying (PSK) and quadrature-amplitude modulation (QAM), the bivariate probability density function (pdf) of the ICI is shown to be a weighted Gaussian mixture. The large computational complexity involved in using the weighted Gaussian mixture pdf to evaluate the error probability serves as the motivation for developing a two-dimensional Gram-Charlier representation for the bivariate pdf of the ICI. It is demonstrated that its truncated version of order 4 or 6 provides a very good approximation in the evaluation of the error probability for PSK and QAM in the presence of ICI. Based on Jakes' model for the Doppler effects, and an exponential multipath intensity profile, numerical results for the error probability are illustrated for several mobile speeds

297 citations


Journal ArticleDOI
TL;DR: Direct time-domain observations are reported of a low-power, self-induced modulation of the transmitted optical power through a high-Q silicon microdisk resonator, attributed to a nonlinear interaction between competing free-carrier and phonon populations within the microdisk.
Abstract: Direct time-domain observations are reported of a low-power, self-induced modulation of the transmitted optical power through a high-Q silicon microdisk resonator. Above a threshold input power of 60 μW the transmission versus wavelength deviates from a simple optical bistability behavior, and the transmission intensity becomes highly oscillatory in nature. The transmission oscillations are seen to consist of a train of sharp transmission dips of width approximately 100 ns and period close to 1 μs. A model of the system is developed incorporating thermal and free-carrier dynamics, and is compared to the observed behavior. Good agreement is found, and the self-induced optical modulation is attributed to a nonlinear interaction between competing free-carrier and phonon populations within the microdisk.

242 citations


Proceedings ArticleDOI
05 Mar 2006
TL;DR: Simulations show orthogonal frequency division multiplexing with optical single sideband modulation can adaptively compensate for dispersion in 4000-km 32×10Gbps WDM SMF links with 40% spectral efficiency.
Abstract: Simulations show orthogonal frequency division multiplexing (OFDM) with optical single sideband modulation can adaptively compensate for dispersion in 4000-km 32×10Gbps WDM SMF links with 40% spectral efficiency. OFDM requires no reverse feedback path so can compensate rapid plant variations.

240 citations


Journal ArticleDOI
TL;DR: In this paper, a full-duplex radio-over-fiber system using a single light source at the central station (CS) was demonstrated, where the optical carrier suppression modulation scheme was employed to generate 40GHz optical millimeter wave and up-convert the baseband signal simultaneously at CS for downlink transmission while the same optical carrier was reused at base station for uplink connection.
Abstract: We have experimentally demonstrated a full-duplex radio-over-fiber system using a single light source at central station (CS). Optical carrier suppression modulation scheme was employed to generate 40-GHz optical millimeter wave and up-convert the baseband signal simultaneously at CS for downlink transmission while the same optical carrier was reused at base station for uplink connection. The bidirectional full-duplex 2.5-Gb/s data was successfully transmitted over 40-km standard single-mode fiber (SMF-28) for both upstream and downstream channels with less than 2-dB power penalty. This system shows simple cost-efficient configuration and good performance over long-distance delivery

231 citations


Journal ArticleDOI
TL;DR: In this article, the optical phase modulation to intensity modulation conversion is achieved by reflecting the phase modulated light at the slopes of the fiber Bragg grating (FBG) that serves as a frequency discriminator.
Abstract: We propose a novel approach to generating ultrawideband impulse radio signals in the optical domain. The proposed system consists of a laser source, an electrooptic phase modulator (EOPM), a fiber Bragg grating (FBG), and a photodetector (PD). The light source is phase modulated by an electrical Gaussian pulse train via the EOPM. The optical phase modulation to intensity modulation conversion is achieved by reflecting the phase modulated light at the slopes of the FBG that serves as a frequency discriminator. Electrical monocycle or doublet pulses are obtained at the output of the PD by locating the wavelength of the optical carrier at the linear or the quadrature slopes of the FBG reflection spectrum. The use of the proposed configuration to implement pulse polarity and pulse shape modulation in the optical domain is discussed. Experimental measurements in both temporal and frequency domains are presented

Journal ArticleDOI
TL;DR: In this article, the authors have demonstrated intensity modulation of light with light in a silicon-polymer integrated waveguide device, based on the all-optical Kerr effect -the same ultrafast effect used in four-wave mixing.
Abstract: Although Gigahertz-scale free-carrier modulators have been previously demonstrated in silicon, intensity modulators operating at Terahertz speeds have not been reported because of silicon's weak ultrafast optical nonlinearity. We have demonstrated intensity modulation of light with light in a silicon-polymer integrated waveguide device, based on the all-optical Kerr effect - the same ultrafast effect used in four-wave mixing. Direct measurements of time-domain intensity modulation are made at speeds of 10 GHz. We showed experimentally that the ultrafast mechanism of this modulation functions at the optical frequency through spectral measurements, and that intensity modulation at frequencies in excess of 1 THz can be obtained in this device. By integrating optical polymers through evanescent coupling to high-mode-confinement silicon waveguides, we greatly increase the effective nonlinearity of the waveguide for cross-phase modulation. The combination of high mode confinement, multiple integrated optical components, and high nonlinearities produces all-optical ultrafast devices operating at continuous-wave power levels compatible with telecommunication systems. Although far from commercial radio frequency optical modulator standards in terms of extinction, these devices are a first step in development of large-scale integrated ultrafast optical logic in silicon, and are two orders of magnitude faster than previously reported silicon devices.

Journal ArticleDOI
TL;DR: In this paper, a 10-Gb/s transmitter subsystem is described for single-mode fiber (G.652) single-input single-output (SISO) networks.
Abstract: We introduce digital precompensation for optical nonlinearities. A 10-Gb/s transmitter subsystem is described. Experimental results, across 320 and 1280 km of standard single-mode fiber (G.652) without any optical compensators, show substantial elimination of self-phase modulation. Some of the limits of this method are explored.

Journal ArticleDOI
TL;DR: In this paper, a carrier-based modulation method for a matrix converter is proposed, which is equivalent to the so-called space vector pulsewidth modulation method, which uses a new point of view to understand the matrix converter modulation method such as the voltage source inverter modulation method.
Abstract: This paper presents a carrier-based modulation method for a matrix converter. By using the offset voltage and changing the slope of carrier, it is possible to synthesize the sinusoidal input currents with the unity power factor and desired output voltages. The proposed method is equivalent to the so called space vector pulsewidth modulation method. The proposed method uses a new point of view to understand the matrix converter modulation method such as the voltage source inverter (VSI) modulation method. Using the proposed method, this paper presents the two-phase/three-phase modulation method and dynamic/steady-state overmodulation method for the matrix converter. These methods are well developed in the study of a VSI. By the proposed steady-state overmodulation method, it is possible to synthesize the fundamental component of output voltage to be equal to that of input voltage at the cost of some distortion of input current. The feasibility of the proposed modulation method has been verified by a computer simulation and experimental results. These results show that the proposed carrier-based modulation method can be implemented easily without any tables. It can be used for the application where a higher voltage transfer ratio is essential

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the optimum carrier-to-sideband ratio (CSR) for maximizing the transmission performance of an optically modulated millimeter-wave signal in a fiber-wireless system via experiment, theory, and simulation.
Abstract: In this paper, we investigate the optimum carrier-to-sideband ratio (CSR) for maximizing the transmission performance of an optically modulated millimeter-wave signal in a fiber-wireless system via experiment, theory, and simulation. We present a simple analytical model to assess the performance enhancement resulting from optical CSR variations. The model is capable of analyzing systems incorporating binary phase-shift keyed and quaternary phase-shift keyed modulation formats. We quantify the optical CSR of a point-to-point fiber-radio link and establish that the performance of the fiber-wireless links can be significantly improved when the optical signal is transmitted at the optimum CSR of 0 dB. The analysis further shows that the optimum optical CSR is independent of transmission bit rates.

Patent
18 Apr 2006
TL;DR: In this paper, a system and method of transmitting and receiving RF service signals between a base transceiver station (BTS) of a wireless communication system and subscriber units within a structure is presented.
Abstract: A system and method of transmitting and receiving RF service signals between a base transceiver station (BTS) of a wireless communication system and subscriber units within a structure. In the forward link, the system demodulates the RF service signal from a BTS to recover a digital service signal; conditions the digital service signal for transmission via the powerline of a structure; and modulates an RF carrier with the digital service signal to generate the RF service signal for wireless transmission to subscriber units within the structure. In the reverse link, the system demodulates the RF service signal from subscriber unit(s) to generate a digital service signal; conditions the digital service signal for transmission via the powerline; and modulates an RF carrier with the digital service signal to generate the RF service signal for transmission to the BTS. Another embodiment eliminates the modulation of an RF carrier with the digital service signal to generate an RF service and vice-versa at the BTS.

Journal ArticleDOI
TL;DR: Spectral and temporal measurements of the single-chip pulse generator are presented with an illustration of the modulation effects on the power spectral density (PSD).
Abstract: This paper presents a single-chip pulse generator developed for Ultra Wide Band (UWB) wireless communication systems based on impulse radio technology. The chip has been integrated in a CMOS 130-nm technology with a single supply voltage of 1.2 V. The basic concept is to combine different delayed edges in order to form a very short duration "logical" pulse, and then filter it, so as to obtain an UWB pulse. It is possible to vary the output pulse shape, and thus the corresponding spectrum, just by acting on the delayed edge combination. Furthermore, the pulse generator supports both position modulation (2-PPM) and polarity modulation (BPSK modulation) in order to convey data through the air. Its power consumption remains less than 10 mW for a raw data rate of up to 160 Mb/s. Spectral and temporal measurements of the single-chip pulse generator are presented with an illustration of the modulation effects on the power spectral density (PSD)

Proceedings ArticleDOI
TL;DR: In this paper, a four-element fiber array has demonstrated 470 watts of coherently phased, linearly polarized light energy in a single far-field spot, each element consists of a single-mode fiber-amplifier chain.
Abstract: A four-element fiber array has demonstrated 470 watts of coherently phased, linearly polarized light energy in a single far-field spot. Each element consists of a single-mode fiber-amplifier chain. Phase control of each element is achieved with a Lithium-Niobate phase modulator. A master laser provides a linearly polarized, narrow linewidth signal that is split into five channels. Four channels are individually amplified using polarization maintaining fiber power amplifiers. The fifth channel is used as a reference arm. It is frequency shifted and then combined interferometrically with a portion of each channel's signal. Detectors sense the heterodyne modulation signal, and an electronics circuit measures the relative phase for each channel. Compensating adjustments are then made to each channel's phase modulator. This effort represents the results of a multi-year effort to achieve high power from a single element fiber amplifier and to understand the important issues involved in coherently combining many individual elements to obtain sufficient optical power for directed energy weapons. Northrop Grumman Corporation and the High Energy Laser Joint Technology Office jointly sponsored this work.

Journal ArticleDOI
TL;DR: The capacity of multiple-input multiple-output (MIMO) systems using multidimensional phase-shift keying/quadratic-amplitude modulation signal sets is evaluated and it was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and that of the additive white Gaussian noise channel.
Abstract: In this contribution, the capacity of multiple-input multiple-output (MIMO) systems using multidimensional phase-shift keying/quadratic-amplitude modulation signal sets is evaluated. It was shown that transmit diversity is capable of narrowing the gap between the capacity of the Rayleigh-fading channel and that of the additive white Gaussian noise channel. However, because this gap becomes narrower when the receiver diversity order is increased, for higher order receiver diversity, the performance advantage of transmit diversity diminishes. A MIMO system having full multiplexing gain has a higher achievable throughput than the corresponding MIMO system designed for full diversity gain, although this is attained at the cost of a higher complexity and a higher signal-to-noise ratio. The tradeoffs between diversity gain, multiplexing gain, complexity, and bandwidth are studied.

Patent
21 Sep 2006
TL;DR: In this paper, a first radio station receives a message in a first frequency band from a second radio station and passes the message to a third radio station in a second frequency band, where the width of the first band differs from the width in the second band.
Abstract: A first radio station receives a message in a first frequency band from a second radio station and passes the message to a third radio station in a second frequency band, where the width of the first frequency band differs from the width of the second frequency band. The modulation of the data in the message is maintained unchanged and the first radio station is not required to perform decoding of the message.

Journal ArticleDOI
TL;DR: In this article, the compensation of nonlinear phase noise by a midlink optical phase conjugation (OPC) is studied and a proof-of-principle experiment is presented showing an over 4dB improvement in Q factor when OPC is employed in a differential phase-shift-keying (DPSK) system.
Abstract: Nonlinear phase noise (Gordon-Mollenauer phase noise) can limit the transmission distance for phase-shift-keyed modulation formats. In this paper, the compensation of nonlinear phase noise by a midlink optical phase conjugation (OPC) is studied. A proof-of-principle experiment is presented showing an over 4-dB improvement in Q factor when OPC is employed in a differential phase-shift-keying (DPSK) system. Also, an ultra long-haul OPC-based differential quadrature phase-shift-keying (DQPSK) transmission experiment is studied to show the impact of self-phase modulation (SPM)-induced impairments, including nonlinear phase noise, in a transmission line. OPC results in a 44% increase in transmission distance when compared to a "conventional" transmission system using dispersion compensating fiber (DCF) for chromatic dispersion compensation.

Proceedings ArticleDOI
01 Nov 2006
TL;DR: It is shown that ACO- OFDM with 4-QAVI subcarrier modulation has the same bandwidth efficiency but requires 2 dB less energy per bit than on-off keying, andACO-OFDM with larger constellation sizes gives higher bandwidth efficiencies and lower optical power than other modulation schemes.
Abstract: Orthogonal frequency division multiplexing (OFDM) is used in many wired and wireless broadband communication systems because of its resilience in the presence of signal dispersion or multipath distortion. OFDM has not been used in practical optical communication systems because the bipolar waveform cannot be used in intensity-modulated direct detection (IM/DD) systems. A new unipolar form of OFDM, asymmetrically clipped optical OFDM (ACO-OFDM), has recently been developed. For the case of an AWGN channel, we compare ACO- OFDM and other modulation schemes. It is shown that ACO- OFDM with 4-QAVI subcarrier modulation has the same bandwidth efficiency but requires 2 dB less energy per bit than on-off keying. ACO-OFDM with larger constellation sizes gives higher bandwidth efficiencies and lower optical power than other modulation schemes. Unlike existing methods, the performance of ACO-OFDM is limited by the bandwidth of the transmitter and receiver not the dispersion of the channel.

Journal Article
TL;DR: A DSP-based phase-estimation scheme consists of a simple and demultiplexable architecture that allows the system to reach significantly higher performance than conventional optical delay detection and various kinds of postprocessing of the received signal become possible.
Abstract: This paper describes a phase-diversity homodyne receiver that which can cope with multilevel modulation formats. The carrier phase drift is estimated with digital signal processing (DSP) on the homodyne-detected signal, entirely restoring the complex amplitude of the incoming signal. Our DSP-based phase-estimation scheme consists of a simple and demultiplexable architecture that allows the system to reach significantly higher performance than conventional optical delay detection. Since the whole optical signal information is preserved with our receiver, various kinds of postprocessing of the received signal become possible. For example, we can demultiplex wavelength-division/optical time-division multiplexed channels and compensate for group velocity dispersion of fibers as well as the nonlinear phase noise in the electrical domain. We also experimentally evaluate the performance of our receiver. Our offline bit-error rate experiments show the feasibility of transmitting polarization-multiplexed 40-Gb/s quadrature phase-shift keying signals over 200 km with channel spacing of 16 GHz, leading to spectral efficiency of 2.5 b/s/Hz

Patent
18 Dec 2006
TL;DR: In this paper, a phase reference pilot symbol of which a modulation amplitude is suppressed to zero, and an amplitude reference pilot signal obtained through modulation performed by using an amplitude known to a reception end are transmitted from a transmission end, and the transmission characteristic of the transmission channel is estimated and compensated by using the phase-reference pilot signal and the amplitude-specific pilot signal at the reception end.
Abstract: An object is to generate a pilot signal for estimating transmission characteristic of a transmission channel which is suitable for the OFDM/OQAM multicarrier modulation. A phase reference pilot symbol of which a modulation amplitude is suppressed to zero, and an amplitude reference pilot signal obtained through modulation performed by using an amplitude known to a reception end are transmitted from a transmission end, and the transmission characteristic of the transmission channel is estimated and compensated by using the phase reference pilot signal and the amplitude reference pilot signal at the reception end. Thus, it is possible to simplify frame generation process performed at the transmission end, and reduce transmission power for the phase reference pilot signal.

Journal ArticleDOI
TL;DR: In this article, a phase-diversity homodyne receiver is proposed to cope with multilevel modulation formats, where the carrier phase drift is estimated with digital signal processing (DSP) on the signal, entirely restoring the complex amplitude of the incoming signal.
Abstract: This paper describes a phase-diversity homodyne receiver that which can cope with multilevel modulation formats. The carrier phase drift is estimated with digital signal processing (DSP) on the homodyne-detected signal, entirely restoring the complex amplitude of the incoming signal. Our DSP-based phase-estimation scheme consists of a simple and demultiplexable architecture that allows the system to reach significantly higher performance than conventional optical delay detection. Since the whole optical signal information is preserved with our receiver, various kinds of postprocessing of the received signal become possible. For example, we can demultiplex wavelength-division/optical time-division multiplexed channels and compensate for group velocity dispersion of fibers as well as the nonlinear phase noise in the electrical domain. We also experimentally evaluate the performance of our receiver. Our offline bit-error rate experiments show the feasibility of transmitting polarization-multiplexed 40-Gb/s quadrature phase-shift keying signals over 200 km with channel spacing of 16 GHz, leading to spectral efficiency of 2.5 b/s/Hz

Journal ArticleDOI
01 Apr 2006
TL;DR: In this paper, a cross-modulation effect consisting of the modulation transfer from an intensive, initially slowly amplitude-modulated stronger (pump) excitation to the probe signal is discussed.
Abstract: Novel nonlinear-modulation methods for crack detection are discussed. The approach is based on the so-called cross-modulation effect consisting of the modulation transfer from an intensive, initially slowly amplitude-modulated stronger (pump) excitation to the probe signal. Advantage of this technique is a very flexible choice of the operation frequencies, since their ratio for both carriers and the modulation may be rather arbitrary. This in its turn allows one to effectively use the sample resonances in order to achieve the necessary level of the pump excitation and to ameliorate conditions for detection of the modulation sidelobes for the probe wave. Unlike higher harmonic-generation methods the initial nonlinear distortions of the pump and probe excitations (e.g. due to nonlinearities in the electronics) are not critical for this technique. In the paper we summarise results of recent test experiments that indicated high sensitivity of the new technique.

Journal ArticleDOI
TL;DR: In this article, the authors present a theoretical analysis of a silicon all-optical modulator based on free-carrier injection by two-photon absorption (TPA) in a highly light-confining structure.
Abstract: This paper presents a theoretical analysis of a silicon all-optical modulator based on free-carrier injection by two-photon absorption (TPA) in a highly light-confining structure. In spite of the weak optoelectronic properties of silicon, strong light confinement allows high modulation depths in very compact devices requiring low-energy pump pulses. This analysis is applied to 1-5 mum radius silicon ring resonators with the pump pulse coupled on-chip and including in the model the scattering loss due to sidewall roughness originating from the fabrication process. The calculations show that using this scheme, modulation depths greater than 80% can be achieved, with no more than 3 pJ of pump pulse energy, at speeds on the order of 10 GHz

Journal ArticleDOI
TL;DR: In this paper, the bandpass-modulation characteristics of a ring resonator-based traveling-wave modulator using an electrooptic polymer AJL8/APC were reported.
Abstract: The authors report the bandpass-modulation characteristics of a ring resonator-based traveling-wave modulator using an electrooptic polymer AJL8/APC. The use of the traveling-wave electrode makes it possible to achieve an efficient modulation around 28 GHz, which is the free spectral range of the resonator, with a 3-dB bandwidth of 7 GHz. The modulation sensitivity is evaluated by defining an equivalent half-wave voltage of ring modulators. It is shown that the modulator has a potential in the microwave and millimeter-wave photonics applications

Proceedings ArticleDOI
01 Sep 2006
TL;DR: In this article, a pilot-tone-based receiver design for zero-padded OFDM transmissions is proposed for underwater acoustic channels, which performs carrier frequency offset compensation, channel estimation, and data demodulation on the basis of individual OFDM block.
Abstract: Existing coherent underwater acoustic communication systems rely on single carrier transmission and adaptive decision feedback equalization to deal with time-varying and highly dispersive underwater acoustic (UWA) channels. Equalization complexity prevents any substantial rate improvement with the existing single-carrier approach, as the channel frequency selectivity increases considerably when the symbol rate increases. Multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM), on the other hand, converts a frequency selective channel into a set of parallel frequency-flat subchannels, thus greatly simplifying receiver equalization. Motivated by the success of OFDM in radio channels, we investigate its use for underwater acoustic channels. In this paper, we develop a pilot-tone based receiver design for zero-padded OFDM transmissions, and test it in a real underwater acoustic channel. Our proposed receiver performs carrier frequency offset compensation, channel estimation, and data demodulation on the basis of individual OFDM block. This approach is appealing to applications with short data bursts, or fast varying channels, as it does not rely on channel dependence across OFDM blocks.

Patent
Esko Jarvinen1
01 Feb 2006
TL;DR: In this paper, an envelope elimination and restoration (EER) RF transmitter includes at least one power RF amplifier having the input terminal for receiving the phase modulated signal to be transmitted on the RF carrier, and further including an input power node for receiving a modulated voltage for amplitude modulating the RF ''carrier''.
Abstract: A RF transmitter has at least one amplifier having an input terminal for receiving a phase modulated signal to be transmitted on an RF carrier and an input node for receiving a modulation signal for amplitude modulating the RF carrier. The RF transmitter further includes an amplitude modulator having an output coupled to the input node of the power amplifier through a low-pass filter. The low-pass filter includes at least one variable filter component for varying a bandwidth of the low-pass filter. In a preferred embodiment an envelope elimination and restoration (EER) RF transmitter includes at least one power RF amplifier having the input terminal for receiving the phase modulated signal to be transmitted on the RF carrier, and further including an input power node for receiving a modulated voltage for amplitude modulating the RF `carrier. The EER RF transmitter further includes a class-S modulator having a variable bandwidth low-pass filter having an output coupled to the input power node and including at least one first variable capacitance.