Modulated Optical Pulse Research Articles

A novel fiber nonlinearity suppression method in DWDM optical fiber transmission systems with an all-optical pre-distortion module

In this paper a novel all-optical scheme is proposed to reduce fiber nonlinear distortions in high-speed dense wavelength division multiplexed (DWDM) optical fiber communication systems by applying time-domain fractional Fourier transform (FRFT) based on the time–space duality theory. The modulated optical pulses will be pre-distorted by an FRFT module before being launched into fiber links. It has been validated that the pre-distorted signal performs better fiber nonlinearity tolerance compared to that without pre-distortion. Simulation results show that the received bit error rate (BER) is improved by several orders of magnitude for a 40Gbit/s carrier-suppressed return-to-zero on-off keying (CSRZ-OOK) DWDM system, which can be used in a current 40Gbit/s system easily to improve the nonlinearity effect tolerance.

Surface plasmon polariton induced optical amplitude and phase modulation in sub-wavelength apertures

We report on the amplitude and phase modulation of picosecond optical pulses, near λ = 800 nm, transmitted through sub-wavelength rectangular apertures in thin gold films with thicknesses of λ/10 at per-pulse energies of <0.3 nJ or 9 pJ per aperture. Due to the excitation and strong confinement of surface plasmon polaritons in the apertures, the leading edge of a pulse causes a rapid heating of the electrons and lattice to modulate its falling edge. By comparing cross-correlation frequency resolved optical gating measurements with simulations, the thermal effects responsible for the induced pulse dynamics are identified.

Multiple carrier ultra-wideband systems using an optical pulse modulation scheme

This study proposes a new optical pulse modulation scheme for multiple carrier ultra-wideband (MC-UWB) wireless systems to achieve a reliable high-bit-rate transmission. The scheme can decrease the system complexity and lowering cost. Moreover, the UWB receiver is adapted with a modified single-user correlation detector to recover original data signal by a narrow carrier spacing. Finally, we set up a practical experimental system to prove our proposed scheme. Experiment results demonstrate that the scheme can provide high spectral efficiency and reduce interference noise for MC-UWB wireless communications. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2735–2738, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25584

A new coding technique in serial data transmission and demodulation with Josephson junctions array

We have developed a coding technique to drive an overdamped Josephson junction array (JJA) using modulated optical pulses for voltage standard applications. Our system is composed of a multi-channel pulse pattern generator (PPG), a LiNbO3 (LN) modulator with an electrical multiplexer (MUX), a photodiode (PD), and an over-damped JJA cooled with 4 K GM cryocooler. The modulated optical pulses are transmitted via an optical fiber to a PD that is installed close to the JJA on a cold stage, and they are then converted into an electrical current pulse train in order to drive the JJA. To avoid a problem in our LN modulator system, i.e., the duty-ratio dependence of the output pulse waveform, pseudo signals that maintain the duty ratio at approximately 50% are inserted in the original bit stream. We demonstraited that this technique is applicable for arbitrary return-to-zero (RZ) binary bit streams.

A performance study of a logical gate using PPM optical pulse modulation for TDM systems

In this paper we propose the operation of an all-optical logical gate based in an acousto optical tunable filter (AOTF) operating with a pulse position modulation (PPM). The performance of an AOTF realizing two-input AND/OR logical functions, which can be applied in transmission and processing of signals in all-optical form in TDM systems, was examined. This novel integrated acousto optical logical gate operates with two ultrashort soliton light pulses (2ps), which are modulated in agreement with the technique of pulse position modulation (PPM). Initially, we evaluated the effect resulting of an increment in the acousto optical interaction length, for the temporal position of the output pulse, considering the anomalous group velocity dispersion (GVD), nonlinear self phase modulation (SPM) and without loss propagation regime of TE and TM input pulses not modulated. We have analyzed the four possible situations for the two-input logical gate, modulating the TE and TM input pulses through temporal displacement and allowing a variation in the coding parameter offset (ε). We can conclude that is possible to get AND/OR logical operations for the modes TM or TE, without to insert PPM error, since a phase control (Δϕ) exists (applied on the TM input pulse) in agreement with each situation in the truth table. Finally we defined the truth table, considering the adequate phase difference and coding parameter offset for the operation of the AND/OR logical gate based in the AOTF.

Telemetry system and method for acoustic arrays

A telemetry system includes a plurality of acoustic sensors for receiving acoustic information and generating analog signals based on the received acoustic information. A first plurality of subsystems is coupled to at least a subset of the plurality of acoustic sensors. The first plurality of subsystems is configured to receive the analog signals from the acoustic sensors and generate digital values based on the received analog signals. The system includes a first optical splitter. A first optical transmitter transmits a first set of optical pulses to the first optical splitter. The first optical splitter is configured to transmit the first set of optical pulses to each subsystem in the first plurality of subsystems. Each subsystem in the first plurality of subsystems is configured to modulate the first set of optical pulses based on the generated digital values and thereby generate a modulated optical pulse stream. A first optical combiner receives and combines the modulated optical pulse stream from each subsystem in the first plurality of subsystems, thereby generating a combined modulated optical pulse stream. A first optical receiver receives the combined modulated optical pulse stream from the first optical combiner. The first optical receiver is configured to generate electrical signals based on the received combined modulated optical pulse stream.

Analytical study of the optical spectrum shift in a modulating channel

In this work, an analytical model of the frequency shift experienced by an optical signal passing through a traveling wave modulating channel is derived. The model starts from the well-known coupled-mode theory but holds for an arbitrary temporal envelope of the optical signal and for any time dependence of the slowly varying modulating field; it provides an analytical and accurate explanation of various effects such as those due to losses or microwave-optical group velocity mismatch. The practical example of a modulated optical Gaussian pulse is provided.

Millimeter-wave and microwave signal generation by low-bandwidth electro-optic phase modulation

We propose, analyze and numerically illustrate a photonic-based technique for waveform generation of electrical signals approaching the 50 GHz bandwidth with time apertures as large as a few nanoseconds, by low-frequency, up to 2 GHz, electro-optic phase modulation of time-stretched optical pulses. Synthesis of the electrical waveform relies on phase-to-amplitude conversion of the modulated signal by a group delay dispersion circuit designed to behave as a transversal filter with N taps. Although arbitrary waveform generation capabilities are limited, a wide variety of user-defined signals are numerically demonstrated by appropriately designing the low-frequency signal driving the electro-optical modulator. Frequency upshifting is controlled by the chirp of the stretched pulse which provides an additional degree of freedom. Finally, optical-to-electrical conversion allows for the user-defined electrical waveform. Simulations are given for square waveform generation demonstrating the high resolution and wide-band capabilities of the technique.

Serrodyne frequency translation of continuous optical signals using ultrawide-band electrical sawtooth waveforms

Serrodyne frequency translation of continuous optical signals by /spl plusmn/1.28 GHz is reported, significantly exceeding the highest previously published serrodyne shifts. To achieve these shifts, an ultrawide-band high-power electrical sawtooth created by spectral modulation of dispersed optical pulses was used. Its amplification involved a novel predistortion technique to compensate for the gain and phase ripple in the amplifier bandwidth.

Optical beat noise reduction in WDM-SCM access networks using modulated optical pulse train

We proposed a new method to suppress the optical beat interference (OBI) in wavelength-division-multiplexing/subcarrier-multiple-access network. The proposed scheme uses the modulated optical pulse train that has broad bandwidth in frequency domain. Since the OBI noise is inversely proportional to the optical bandwidth of beating optical signals, the generated OBI noise by beating of optical pulse train signals from several optical network units (ONUs) spreads over wide frequency range. In addition, the chance of optical beating is low because optical pulse trains from different ONU have different pulse timing. We have demonstrated the proposed idea experimentally. In beating experiment, the carrier-to-noise ratio was obtained over 30 dBc regardless of optical beating. In addition, 6-Ms/s 16 quadrature amplitude modulator data at 0.7 GHz was successfully transmitted up to 20 km with an average error-vector-magnitude of 4.5% in presence of optical beating.

Pulse trains produced by phase-modulation of ultrashort optical pulses: tailoring and characterization

In this paper, creation of pulse doublets and pulse trains by spectral phase modulation of ultrashort optical pulses is investigated. Pulse doublets with specific features are generated through step-like and triangular spectral phase modulation, whereas sequences of pulses with controllable delay and amplitude are produced via sinusoidal phase modulations. A temporal analysis of this type of tailored pulses is exposed and a complete characterization with the SPIDER technique (Spectral Phase Interferometry for Direct Electric-field Reconstruction) is presented.

High-temporal-resolution, single-shot characterization of terahertz pulses.

A technique for noncollinear cross correlation of electro-optic modulated optical pulses is presented for the single-shot characterization of terahertz waveforms and is compared to established electro-optic terahertz characterization methods. This technique is free from the limitations on time resolution and faithful reproduction of previously demonstrated single-shot amplitude modulation spectral encoding.

Simulation of Ultrafast Cross-Gain Modulation in Optically-Pumped GaN/AlN Intersubband Optical Amplifiers

Cross-gain modulation (XGM) of sub-picosecond optical pulses in optically-pumped GaN/AlN intersubband optical amplifiers (ISOA) has been analyzed by a one-dimensional finite-difference time-domain (FDTD) model. The calculated signal gain at 1.544 µm was about 20 dB at a pumping power of 6–7 W. A 10-dB gain suppression was predicted at a control pulse energy of 100 fJ. This switching energy is one order of magnitude smaller than that in saturable-absorber switches utilizing the intersubband-transition in GaN/AlN quantum wells. The simulation suggested that the XGM switches operate without serious pattern effect even at 1 Tb/s.

Experimental investigation of a 4‐FBG TDM sensor array with a tunable laser source

AbstractThe performance of a time‐division‐multiplexed fiber Bragg grating sensor array that uses a tunable laser source has been investigated. It was found that the wavelength detection accuracy is affected by the extinction ratio of the optical pulse modulator used for input pulse generation. Experiments with a 4‐FBG sensor array demonstrated a strain resolution of 0.7 με with an optical pulse modulator of −24‐dB extinction ratio. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 435–437, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10343

Characterization of crosstalk of a TDM FBG sensor array using a laser source

The crosstalk characteristics of a time-division multiplexing fiber Bragg grating sensor array that uses a laser source are examined. The system performance is found to be limited by the extinction ratio of the input optical pulse modulation and can be improved significantly by properly modulating the laser wavelength.

Analysis of the dynamic behavior and short-pulse modulation scheme for laterally coupled diode lasers

A theoretical investigation of the high-speed coupling phenomena of two laterally coupled diode lasers (LCDL) is presented. The analysis is centered on the spatiotemporal dynamics of the LCDL when coupling between emitters is varied, We have obtained the dynamic behavior of these devices showing high resonance frequencies beyond the well-known resonance frequency of a single diode laser. In this paper, we have presented a new modulation scheme by asymmetric switching of the injected current in both stripes, showing short optical output pulse modulation with a high repetition rate.

Performance analysis of a time-division-multiplexed fiber Bragg grating sensor array by use of a tunable laser source

The results of an investigation of the performance of a time-division-multiplexed (TDM) fiber Bragg grating (FBG) sensor array using a tunable laser source are reported. The system performance is found limited by the extinction ratio of the optical pulse modulator used for pulse amplitude modulation. Formulas that relate the crosstalk to the extinction ratio of the optical pulse modulator, the modulation parameters of the tunable laser, and the optical path differences among sensing channels are derived. Computer simulation shows that an array of 20 FBG sensors with 3 /spl mu//spl epsi/ resolution can be realized with a commercially available single Mach-Zehnder type optical pulse modulator of -35-dB extinction ratio.

Ultrafast nonlinear absorption of quantum well excitons periodically distributed in a Bragg reflector

Ultrafast absorptive nonlinearity of excitons is enhanced in a Bragg reflector in which quantum wells are periodically distributed. Absorptive excitonic nonlinearity in the exciton Bragg reflector is characterised by femtosecond transient transmission and reflectance measurements with e–h pair density far above the exciton saturation density. The absorptive excitonic nonlinearity is dominated by two-photon absorption enhanced under the optical confinement in this Bragg reflector. Optical frequency shift caused by ultrafast refractive index change due to the enhanced two-photon absorption, is evaluated from frequency-resolved absorption transients. Spectral modulation of optical pulses and the resultant pulse chirping are produced by this frequency shift and the optical pulses reflected from the exciton Bragg reflector are compressed by compensating the pulse chirping.

Ultrafast image transmission by optical time-to-two-dimensional-space-to-time-to-two-dimensional-space conversion

We propose an optical time-to-two-dimensional (2-D)-space-to-time-to-2-D-space conversion technique for ultrafast image transmission with ultrashort-pulse lasers. The proposed technique is based on the concepts of the time–space transform, the spatial time–frequency transform, and their inverses. We describe and analyze the proposed technique for ultrafast all-optical processors that can convert an input 2-D spatial object into a modulated ultrafast optical pulse sequence and can retrieve the original 2-D spatial image from the temporal signals transmitted through the optical fiber channel with ultrahigh bandwidth. To verify the proposed technique, we report preliminary experimental results.

An optical pulse modulator based on an all-fiber mirror

An optical pulse modulator based on an all-fiber mirror