Phase Modulation Research Papers - Academia.edu (original) (raw)

In this paper, we experimentally investigate a peak-to-average power ratio (PAPR) reduction technique based on a constant envelope orthogonal frequency division multiplexing (CE-OFDM) approach in direct-detection optical OFDM (DDO-OFDM) systems. In comparison to conventional DDO-OFDM, our results show a 6.37 dB performance gain in terms of error vector magnitude (EVM) with a 5 Gb/s DDO-CE-OFDM transmission system over 40 km of uncompensated standard single-mode fiber (SSMF) at an optical injection power of 5 dBm.

- by
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- Optical physics, Optical Fiber Technology, Phase Modulation

Two-dimensional electronic coherence spectroscopy ͑ECS͒ is an important method to study the coupling between distinct optical modes of a material system. Such studies often involve excitation using a sequence of phased ultrashort laser pulses. In conventional approaches, the delays between pulse temporal envelopes must be precisely monitored or maintained. Here, we introduce a new experimental scheme for phase-selective nonlinear ECS, which combines acousto-optic phase modulation with ultrashort laser excitation to produce intensity modulated nonlinear fluorescence signals. We isolate specific nonlinear signal contributions by synchronous detection, with respect to appropriately constructed references. Our method effectively decouples the relative temporal phases from the pulse envelopes of a collinear train of four sequential pulses. We thus achieve a robust and high signal-to-noise scheme for phase-selective ECS to investigate the resonant nonlinear optical response of photoluminescent systems. We demonstrate the validity of our method using a model quantum three-level system-atomic Rb vapor. Moreover, we show how our measurements determine the resonant complex-valued third-order susceptibility.

- by Patrick Tekavec
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- Engineering, Mathematics, Physical Chemistry, Electronics

This work considers PSK with noncoherent demodulation. It is shown that by performing noncoherent demodulation over an increased observation interval, the performance approaches that of coherent PSK. This block demodulation technique of PSK is a natural generalization of differentially coherent detection and yields improved SNR performance. PSK with noncoherent block demodulation could be very attractive for harsh channels wich are power and bandwidth limitted, such as in Mobile Digital Cellular systems. reference used in demodulation is simply the previous received symbol.

- by P. Pasupathy
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- Computer Science, Fading, Degradation, Demodulation

Experiments with an acoustooptic phase modulator for single-mode optical fibers are described. The device, which operates in the 500-MHz frequency range, uses a zinc oxide transducer sputter deposited on top of a gold fim evaporated on the fiber. The device was heat cooled and partially acoustically terminated by gallium, which was also used as the top electrode of the zinc oxide transducer. The maximum modulation observed on a 2-mm length of fiber was 2 rad with an input power of 2 W.

- by Butrus Khuri-Yakub
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- Optical fiber sensors, Zinc Oxide, Frequency, Optical physics
- by Le Binh
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- First-Order Logic, Optical physics, Tunable Filter, First Order Logic

The low frequency rf linacs and bunch compressors in the NLC are heavily loaded by beam currents up to 0.9 A. Beam loading generates bunch-to-bunch energy deviations, which need to be compensated to operate with long bunch trains in the linear collider. There are two basic compensation techniques, namely T and F schemes. The F scheme is operationally straightforward but requires additional rf systems which are powered at slightly different frequencies. In contrast, the T scheme does not require any additional rf and is thus expected to be less expensive. Here, the loading compensation is realized by early injection combined with rf phase and amplitude modulation. The phase/amplitude modulation is performed with fast phase shifters at low rf power before amplification by the klystrons. With combined phase and amplitude modulation, the T scheme can be applied to both the accelerator and compressor linacs. In this paper, we present simulations of the T compensation scheme for the NLC low rf accelerator and compressor linacs. We discuss different rf configurations using the T scheme as well as some issues related to phase/amplitude modulations in such layouts.

- by T. Raubenheimer
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- Artificial Intelligence, Low Frequency, Large Hadron Collider, Power Generation

In this paper, we deal with the subject of cross-gain modulation (XGM) and cross-phase modulation (XPM) semiconductor optical amplifier-based wavelength conversion of optical channels carrying subcarrier multiplexing signals in a comprehensive way. The equations and models that describe the conversion process and the resulting harmonic and intermodulation distortions are obtained showing the superior performance of XPM over XGM in terms of second-and third-order distortion and contrast ratio. Experimental results for XGM-based wavelength conversion that confirm the results predicted by our theoretical models are presented, and finally, we consider the specific application of wavelength conversion of optical channels carrying full frequency plans such as that of cable television applications.

- by Bruce Leonardo Oliva Ortega
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- Mathematics, Optics, Medical Imaging, Fiber Optics

We present coherent phase modulation detection for laser phase noise measurements with delayed self-heterodyne method. The technique is demonstrated for the first time with the distributed feedback laser and external cavity laser. The... more

- by Liam Barry
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- Optical physics, Phase Modulation, Noise Measurement, Phase Noise

The atomic force microscope (AFM) has a unique capability of allowing the high-resolution imaging of biological samples on substratum surfaces in physiological solutions. Recent technological progress of AFM in biological research has resulted in remarkable improvements in both the imaging rate and the tip force acting on the sample. These improvements have enabled the direct visualization of dynamic structural changes and dynamic interactions occurring in individual biological macromolecules, which is currently not possible with other techniques. Therefore, high-speed AFM is expected to have a revolutionary impact on biological sciences. In addition, the recently achieved atomic-resolution in liquids will further expand the usefulness of AFM in biological research. In this article, we first describe the various capabilities required of AFM in biological sciences, which is followed by a detailed description of various devices and techniques developed for high-speed AFM and atomic-resolution in-liquid AFM. We then describe various imaging studies performed using our cutting-edge microscopes and their current capabilities as well as their limitations, and conclude by discussing the future prospects of AFM as an imaging tool in biological research.

- by Atsushi Miyagi
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- Condensed Matter Physics, Chemistry, Imaging, Atomic Force Microscopy

This paper presents a new blind equalization algorithm called multimodulus algorithm (MMA). This algorithm combines the benefits of the well-known reduced constellation algorithm (RCA) and constant modulus algorithm (CMA). In addition, MMA provides more flexibility than RCA and CMA, and is better suited to take advantage of the symbol statistics of certain types of signal constellations, such as nonsquare constellations, very dense constellations, and some wrong solutions.

- by Eli Mozeson
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- Aerospace Engineering, Signal Processing, OFDM, Geomatic Engineering

We propose a theory and experimentally verify ultraflat comb generation by dual-sine-wave phase-only modulation. This novel approach requires a single optical element and is very practical and efficient in terms of both power budget and bandwidth. Using this approach, we have generated two optical spectra, one with 11 comb lines and 1.9-dB flatness and the other with 9 comb lines and 0.8-dB flatness.

A technique is presented for determining the frequency modulation transfer function of a laser. The method is based on a Mach-Zehnder interferometer, with a significant difference in the optical path lengths of the two arms. A frequency-modulated laser beam incident on the interferometer produces a phase-modulated photocurrent signal with an effective modulation index that is related to the amplitude of the optical frequency modulation. Techniques for determining both the amplitude and the phase of the optical frequency modulation from the photocurrent signal are described. PACS 42.60.Fc; 42.55.Px; 07.60.Ly

- by Terry Mcrae
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- Mechanical Engineering, Semiconductor Lasers, Transfer Function, Optical physics

Industrial applications often require a number of variable speed electric drives. In the majority of cases, these multi-motor drive systems require independent control of individual motors. Over the past decade, research efforts have been made to reduce the number of power electronic devices required in multi-motor drive systems in order to reduce the overall complexity and hence cost of the drive. It has been shown recently that it is possible to independently control two three-phase induction machines using a five-leg voltage source inverter (VSI) as the supply, with one inverter leg being common to both machines. The existing pulse-width modulation (PWM) methods for this supply topology either limit the amount of DC bus voltage available to each machine or lead to uneven and increased switching frequency across five legs of the VSI. A new PWM method that effectively utilises the standard three-phase modulators in conjunction with appropriate modifications to generate modulation signals for all five legs of the VSI is presented. It enables an arbitrary distribution of the available DC bus voltage between the two machines. The considered supply topology, when utilised in conjunction with the developed PWM technique, is well suited to constant power applications such as centre-driven winders. Verification of the developed modulation method and its applicability to winder systems are demonstrated by experimental testing that includes both steady state and transient operation.

- by Drazen Dujic
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- Power Electronics, Motor Control, Steady state, Voltage

We report on results from the characterization of the frequency chirp characteristics of distributed feedback (DFB) lasers under direct modulation conditions. Parameters describing transient and adiabatic chirp effects are measured for a DFB laser from the ratio of phase to amplitude modulation factors when modulated with sine waves using a high-resolution optical spectrum analyzer. Transient and adiabatic chirp effects produced under digital non-return to zero (NRZ) amplitude modulation are also analyzed using the emitted optical spectrum. Finally, results from the measurement technique are compared with those obtained from measured optical spectra.

- by Alain Pumir
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- Applied Mathematics, Mathematical Sciences, Physical sciences, CHEMICAL SCIENCES

A 2.4-GHz half-sine shaping O-QPSK transmitter (TX) which supports IEEE 802.15.4 standard is reported. This TX employs a RF phase modulator which incorporates a semi-digital FIR filter for waveform shaping. Fabricated in a 0.18-m CMOS process, the TX, including a PLL, draws 10 mA from a 1.5-V supply and delivers an output power of -3 dBm. It achieves an EVM of 6.2% when operating at 2-Mcps chip rate.

- by Yao-Hong Liu
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- FIR filter, Phase Modulation, Finite Impulse Response (FIR), Phase Lock Loop

We derive an analytic expression for the signal distortion that results from the effects of group-delay ripple (GDR). When reduced to its simplified first-order form, our expression provides a clear physical picture of how the signal is affected by the ripple period, magnitude, and how the mean signal frequency is located with respect to the ripple peaks. We also find the optical signal-to-noise ratio penalty associated with the ripple to be dependent on the phase relationship among the signal bits. Particular analysis on the impact of GDR in differential phase-shift keying transmission is presented.

- by xing wei
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- First-Order Logic, Optical physics, Wavelength Division Multiplexing, Phase Modulation

A two-channel multibit CA audio digital-to-analogconverter (DAC) with on-chip digital phase-locked loop and sample-rate converter is described. The circuit requires no oversampled synchronous clocks to operate and rejects input sample clock jitter above 16 Hz at 6 dB/octave. A second-order modulator with a multibit quantizer, switched-capacitor (SC) DAC, and single-ended second-order SC filter provides a measured out-ofband noise of -63 dBr with less than 0.1' phase nonlinearity.

- by Robert Adams
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- Jitter, Interpolation, Second Order, Switched Capacitor Filters

This paper provides a new look at the mechanisms underlying pulse width modulation (PWM). A simple approach to analyze the behavior of a single-sided pulse width modulator is presented. By using elementary methods, the pulse-width-modulated waveform is written as the sum of two sawtooth functions and the original modulating waveform. Simply applying the well-known Fourier series expansion of the sawtooth function, an equivalent model of the pulse width modulator, which shows that it is in essence a sequence of phase modulators, is derived. This model provides a clear understanding of the nonlinearities involved in the PWM process. It is shown how the superposition of modulating waveforms in the time-domain translates into the convolution of the sidebands in the frequency domain. Finally, the interaction of the pulse width modulator and a sample-and-hold register is studied and a general expression for the Fourier transform of a regular-sampled PWM waveform is derived. The analysis applies to periodic as well as aperiodic modulating waveforms.

- by Bruno Putzeys
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- Harmonic Analysis, Mathematical Model, Fourier transform, Phase Modulation

Absrract-The very broad bandwidth of low-loss optical transmission in a single-mode fiber and the recent improvements in single-frequency tunable lasers have stimulated significant advances in dense wavelength division multiplexed optical networks. This technology, including wavelength-sensitive optical switching and routing elements and passive optical elements, has made it possible to consider the use of wavelength as another dimension, in addition to time and space, in network and switch design. The independence of optical signals at different wavelengths makes this a natural choice for multiple-access networks, for applications which benefit from shared transmission media, and for networks in which very large throughputs are required.

- by faim uddin
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- Distributed Computing, Optical Switch, Millimeter Wave Antennas, Oscillations

Burst transmission of digital data and voice has become commonplace, particularly in satellite communication systems employing time-division multiple-access (TDMA) and packet demand-assignment mnltiple-access (DAMA) techniques. In TDMA systems particularly, phase estimation on each successive burst is a requirement, while bit timing and carrier frequency can be accurately tracked between bursts. A class of nonlinear estimation algorithms is described to estimate the unknown phase of a carrier which is fully modulated by m-ary PSK modulation. Performance of the method is determined in closed form and compared to the Cramer-Rao lower bound for the variance of the estimation error in the phase of an unmodulated carrier. Results are also obtained when the carrier frequency is imprecisely known. Finally, the effect of quantization and finite read-only-memory (ROM) implementation of the nonlinearity are determined by computer simulation.

The theoretical/experimental work done in the area of digital phase-locked loops (DPLL) from 1960 to 1980 is surveyed. The survey is motivated by the fact that microprocessor technology is advancing rapidly to the extent that sophisticated and flexible signal processing algorithms for communications and control can be realized in the digital domain. It is anticipated that the use of this signal processing technology will continue to expand rapidly in the development of advanced communications and tracking receivers, for example, digital modems.

- by chak chie
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- Biomedical Engineering, Signal Processing, Digital Signal Processing, Network Analysis

Microwave photonics (MWP) is an emerging field in which radio frequency (RF) signals are generated, distributed, processed and analyzed using the strength of photonic techniques. It is a technology that enables various functionalities which are not feasible to achieve only in the microwave domain. A particular aspect that recently gains significant interests is the use of photonic integrated circuit (PIC) technology in the MWP field for enhanced functionalities and robustness as well as the reduction of size, weight, cost and power consumption. This article reviews the recent advances in this emerging field which is dubbed as integrated microwave photonics. Key integrated MWP technologies are reviewed and the prospective of the field is discussed.

- by photon 2013
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- Quantum Physics, Signal Processing, Photonic Integrated Circuits, Silicon Photonics

This paper presents a novel direct current-fed interleaved phase-modulated single-phase unfolding inverter for fuel-cell applications. Two active-clamped zero-voltage switching current-fed half-bridge isolated converters are interleaved in parallel input and series output configuration. Phase modulation is proposed to control these two converter cells, which generate a rectified sinusoidal pattern at the dc link. A simple H-bridge unfolding dc-ac inversion is used to produce single-phase sine voltage at line frequency switching using square-wave control. This not only simplifies the inversion stage in terms of modulation but also reduces the switching losses. Direct front-end current-fed based unfolding inverter is not reported in literature yet. Detailed analysis and design of the proposed direct current-fed single-phase unfolding inverter has been presented. Simulation waveforms using PSIM 9.0.4 are given to verify the presented analysis and design. Experimental results on a laboratory prototype rated at 200 W are demonstrated to support the investigation, to validate the accuracy of the proposed analysis and design, and to test the performance.

- by Hadi Moradi
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- Phase Modulation

Holographic interferometry (HI) techniques are powerful tools for experimental mechanics which can be used to assess displacement fields on a loaded object surface. Used with no contact and high resolution HI can be combined with image methods for data analysis. Nevertheless, the speckle should be fully resolved by the image detector to digitally record an interferogram. This leads to a noisy recording which difficult it's post-processing. Each measurement with HI ends normally in a phase map computation representing the object displacement. Phase calculation algorithms are based on spatial or temporal phase modulation and lead to wrapped phase maps. To obtain the continuous phase distribution several solutions have been implemented. This paper describes the main filtering and unwrapping algorithms available and compares it´s performance to solve discontinuities in noisy phase maps.

- by Mário Vaz
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- Data Analysis, High Resolution, Phase Modulation

The aim of this paper is to present a review of recently used current control techniques for three-phase voltagesource pulsewidth modulated converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes proportional integral stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on-line optimization. New trends in the current control-neural networks and fuzzy-logicbased controllers-are discussed, as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.

- by Marian Kazmierkowski
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- Engineering, Fuzzy Logic, Neural Networks, Neural Network

In this paper, a filtering technique based upon two-dimensional continuous wavelet transform (2D-CWT) is used to eliminate the low frequency components of fringe patterns. The filtered fringe patterns are subsequently demodulated using a standard Fourier transform profilometry (FTP) algorithm. This image pre-filtering stage improves the noise performance of the FTP algorithm and enables the FTP method to demodulate fringe patterns with larger bandwidths. Also, the 2D-CWT technique reduces speckle noise significantly. Moreover, only a single fringe pattern is required in this technique. The 2D-CWT algorithm is capable of separating low frequency terms from the high frequency terms that contain phase-modulated fringe information, even when both interfere, greatly, in the frequency domain. The proposed algorithm is tested, both via computer simulation and using real fringe patterns. This revealed the robustness of this algorithm and also demonstrably enables the demodulation of a wider range of fringe patterns using the FTP technique.

- by munther gdeisat
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- Image Processing, Low Frequency, High Frequency, Phase Retrieval

| This paper presents an overview of the potential of free space optical technology in information security, encryption, and authentication. Optical waveform posses many degrees of freedom such as amplitude, phase, polarization, spectral content, and multiplexing which can be combined in different ways to make the information encoding more secure. This paper reviews optical techniques for encryption and security of two-dimensional and three-dimensional data.

Spatial light modulators (SLM) are devices used to modulate amplitude, phase or polarization of a light wave in space and time. Current SLMs are based either on MEMS (micro-electro-mechanical system) or LCD (liquid crystal display) technology. Here we report on the parameters, trends in development and applications of phase SLMs based on liquid crystal on silicon (LCoS) technology. LCoS technology was developed for front and rear projection systems competing with AMLCD (active matrix LCD) and DMD (Digital Mirror Device) SLM. The reflective arrangement due to silicon backplane allows to put a high number of pixels in a small panel, keeping the fill-factor ratio high even for micron-sized pixels. For coherent photonics applications the most important type of LCoS SLM is a phase modulator. In the paper at first we describe the typical parameters of this device and the methods for its calibration. Later we present a review of applications of phase LCoS SLMs in imaging, metrology and beam manipulation, developed by the authors as well as known from the literature. These include active and adaptive interferometers, a smart holographic camera and holographic display, microscopy modified in illuminating and imaging paths and active sensors.

- by Chang Hwan Park
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- Optics, Digital Holography, Optical Metrology, Phase Modulation

Whatever may be the material used to build the engineering structures, they are bound to undergo damage at some point in their lifetime. The damage could develop because of continuous usage, degradation, environmental factors, earthquakes or man-made disasters. Structural health monitoring (SHM) has emerged as an important area that has attracted intensive research attention in the recent time. Smart materials like piezoceramics (e.g. lead zirconate titanate or PZT) and fibre optical sensors (FOSs) based effective SHM tools are rapidly developing. Especially, the FOSs offer great potential as monitoring sensors due to their small size, immunity to electromagnetic interference, robustness and survivability in harsh environment. Conventional FOSs use phase modulation techniques for sensing. In spite of the above advantages, they are dependent heavily on source intensity fluctuations and coupling loses. However the fibre Bragg grating (FBG) sensors developed from FOSs are immune to source intensity fluctuations, thus addressing some potential problems of the conventional FOSs. This paper presents a review on the current development of FBG based monitoring techniques and their applications.

Two-beam interferogram intensity modulation decoding using spatial carrier phase shifting interferometry is discussed. Single frame recording, simplicity of experimental equipment, and uncomplicated data processing are the main advantages of the method. A comprehensive analysis of the influence of systematic errors (spatial carrier miscalibration, nonuniform average intensity profile, and nonlinear recording) on the modulation distribution determination using automatic fringe pattern analysis techniques is presented. The results of searching for the optimum calculation algorithm are described. Extensive numerical simulations are compared with laboratory findings obtained when testing vibrating silicon microelements under various experimental conditions.

- by Krzysztof Patorski and +1
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- Mechanical Engineering, Numerical Simulation, VIBRATION ANALYSIS, Applied Optics

We present the characterization of a ferro-electric liquid crystal spatial light modulator and of a nematic liquid crystal spatial light modulator. It is shown that the nematic device can be compensated for its phase distortions and a method is proposed for increasing its frame rate while maintaining a maximum phase modulation of 2π. Several applications in information processing are presented with experimental results.

Purpose of this paper is to highlight the principles of the nonlinear signal-noise interaction (NSNI) in dispersion-managed long-haul optical links and provide a quantitative understanding of the system parameters for which NSNI sets the nonlinear performance of the most popular intensity and phase modulation formats, namely on-off keying, differential binary and quadrature phase-shift keying and coherent quadrature phase-shift keying.

- by Paolo Serena
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- Telecommunications, Nonlinear dynamics, Artifacts, Optical physics

A novel cognitive receiver for modulation format recognition with reconfigurable carrier recovery scheme is proposed and experimentally demonstrated for phase modulated radio-over-fibre links. Demodulation of burst-mode mixed modulation... more

- by Darko Zibar
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- Radio over fiber, Phase Modulation

A new method for laser cavity dumping using an antiresonant ring laser cavity and an electrooptic phase modulator has been demonstrated on a COz laser at 10.6 pm. Experimental results are summarized and the cavity and modulator design considerations for this type of cavity dumping are reviewed in this paper. Although the initial experiments were done at 10.6 pm, the antiresonant ring technique may be particularly advantageous for high-power lasers such as ruby and Nd:giass in the visible and near IR. A modified form of the antiresonant ring for accomplishing extremely fast phase switching is also proposed.

- by R. Trutna
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- Carbon Dioxide, Optical physics, High Power, Infrared

Pulse compression is used in radar systems to improve range resolution while maintaining a high duty cycle. In addition to practical implementation constraints, the key issues for the selection of a pulse-compression waveform are mismatch loss, peak / integrated range sidelobes, and Doppler tolerance. While much progress has been made in the design of nonlinear frequency modulated (FM) chirp waveforms satisfying these requirements, the corresponding performance for binary phase-coded waveforms is often inadequate. In order to improve the range sidelobes achieved with phase-coded waveforms, specially designed mismatched pulse compression filters can be used. Several such approaches have been described in the literature since 1959. This paper review these techniques and highlight a particular approach using infinite impulse response (IIR) filters, which has received little attention in the past. Using this technique the performance for a number of binary phase codes of different length have been determined and their Doppler tolerance is investigated.

- by Vilhelm Gregers-Hansen
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- Coding, Nonlinear Systems, Frequency, Resolution
- by Milica Stojanovic
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- Design, Signal Processing, Underwater Acoustics, Modulation

The performance of filtered analog photonic links, useful in signal processing applications, is analyzed along with techniques for compensation of distortion. We analyze the attributes of various link configurations and compare the performance of filtered coherent-detection links with intensity-modulated-direct-detection links. Experimental results on the dynamic range and the compensation of nonlinearities using predistortion compensation are presented for a filtered coherent link. We demonstrate suppression of third-order nonlinearity by 20 dB. In addition to supporting signal processing operations such as filtering and arbitrary intermediate frequency downconversion, at the same detected power, we find filtered coherent links to have up to 9 dB noise figure advantage over unfiltered direct-detection links, dependent on the limits of the operating optical power in the link.

- by Anjali Agarwal
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- Signal Processing, Radio Frequency, Microwave Photonics, Optical physics

Programmable diffractive optical elements ͑DOEs͒ with axial response have many interesting applications, including diffractive lenses, axicons, and optical tweezers. In all these cases, it is essential to properly select the modulation configuration of the spatial light modulator ͑SLM͒ where the DOE is displayed, in order to avoid the undiffracted zero order component that appears on axis and overlaps the desired axial response. However, in general, the chromatic dispersion in liquid crystal SLMs prevents the cancellation of the zero order for a broadband light source, thus limiting the possibilities for polychromatic programmable axial DOEs. We operate a ferroelectric liquid crystal on silicon display with polychromatic illumination and with a specific polarization configuration that provides binary -phase modulation for all wavelengths. Since this type of modulation cancels the undiffracted zero order, we use this SLM to display DOEs with axial response. Moreover, chromatic control is achieved by time-multiplexing sequences of properly scaled DOEs with the corresponding selection of the input wavelength by means of an electronically controlled color-filter wheel. The presented experimental results include wavelength-controlled diffraction gratings, axicons, and vortex-producing lenses. © 2010 Society of Photo-Optical Instrumentation Engineers.

- by Pascuala García-Martínez
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- Optical Engineering, Optical, Spatial Light Modulator, Optical physics

The performance of deep-space telemetry signals that employ a residual carrier modulation technique is compared in the presence and absence of a subcarrier. When the subcarrier is present, the performance for the resulting pulse-coded modulatiodphase-shift keydphase-modulated (PCM/PSK/PM) scheme is evaluated for both sine-wave and square-wave subcarriers and non-return-to zero (NRZ) data. When the subcarrier is absent, the performance for the resulting PCM/PM technique is evaluated for both the NRZ and the bi-phase data format.

- by Tien Nguyen
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- Telemetry, Error Analysis, Symbol error rate, Interference

We present the design, fabrication, and results from the first monolithically integrated optical phase-locked loop (OPLL) photonic integrated circuit (PIC) suitable for a variety of homodyne and offset phase locking applications. This InP-based PIC contains two sampled-grating distributed reflector (SG-DBR) lasers, semiconductor optical amplifiers (SOAs), phase modulators, balanced photodetectors, and multimode interference (MMI)-couplers and splitters. The SG-DBR lasers have more than 5 THz of frequency tuning range and can generate a coherent beat for a wide spectrum of frequencies. In addition, the SG-DBR lasers have large tuning sensitivities and do not exhibit any phase inversion over the frequency modulation bandwidths making them ideal for use as current controlled oscillators in feedback loops. These SG-DBR lasers have wide linewidths and require high feedback loop bandwidths in order to be used in OPLLs. This is made possible using photonic integration which provides low cost, easy to package compact loops with low feedback latencies. In this paper, we present two experiments to demonstrate proof-of-concept operation of the OPLL-PIC: homodyne locking and offset locking of the SG-DBR lasers.

- by ashish bhardwaj
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- Optics, Medical Imaging, Fiber Optics, Telecommunications

POLICRYPS (an acronym of polymer liquid crystal polymer slices) is a nano/microcomposite structure made of slices of almost pure polymer alternated with films of well aligned nematic liquid crystal (NLC). The structure is obtained by irradiating a homogeneous syrup of NLC, monomer and curing agent molecules with an interference pattern of UV/visible light under suitable experimental and geometrical conditions; the spatial periodicity can be easily varied from an almost nanometric (200 nm) to a micrometric (15 µm) scale. Where the effect on an impinging reading light beam is concerned, the POLICRYPS can be utilized either in a transmission or a reflection configuration (depending on the geometry and substrate used) with negligible scattering losses, while the effect of spatial modulation of the refractive index (from polymer to NLC values) can be switched on and off by applying an external electric field of the order of few V µm-1. In this paper, we start by reviewing the general features of the POLICRYPS structure, that is the 'recipe' to fabricate it, along with a chemical-diffusive model that indicates the right physical and chemical conditions to make samples exhibiting good morphological, optical and electro-optical properties. We then show some possible utilizations of POLICRYPS with a light beam impinging almost perpendicularly to the structure: a switchable diffraction grating and a switchable optical phase modulator. Furthermore, we put into evidence that POLICRYPS channels can become an array of mirrorless optical micro-resonators for lasing effects. Finally, we report about utilization of POLICRYPS with a light beam impinging parallel to the structure and perpendicular to the channels, demonstrating that, in this case, the structure becomes a tuneable Bragg filter. Performances exhibited in all above applications put the POLICRYPS structure at the top level of the state of art of application oriented research in optics of liquid crystalline composite materials.

- by Giuseppe Strangi and +1
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- Refractive Index, Composite Material, Optical physics, Microstructures

This paper reports the current status of the DARPA Quantum Network, which became fully operational in BBN's laboratory in October 2003, and has been continuously running in 6 nodes operating through telecommunications fiber between Harvard University, Boston University, and BBN since June 2004. The DARPA Quantum Network is the world's first quantum cryptography network, and perhaps also the first QKD systems providing continuous operation across a metropolitan area. Four more nodes are now being added to bring the total to 10 QKD nodes. This network supports a variety of QKD technologies, including phase-modulated lasers through fiber, entanglement through fiber, and freespace QKD. We provide a basic introduction and rational for this network, discuss the February 2005 status of the various QKD hardware suites and software systems in the network, and describe our operational experience with the DARPA Quantum Network to date. We conclude with a discussion of our ongoing work.

- by Henry Yeh
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- Quantum Physics, Quantum Cryptography, Quantum Network Theory, Software Systems

We report the first experimental demonstration of simultaneous multi-impairment monitoring of phase-modulated 40 Gbit/s nonreturn to zero differential phase-shift keying (NRZ-DPSK) and 640 Gbit/s return-to-zero (RZ)-DPSK optical signals. Our approach exploits the femtosecond response time of the Kerr nonlinearity in a centimeter-scale, highly nonlinear, dispersion engineered chalcogenide planar waveguide to perform THz bandwidth RF spectrum analysis. The features observed on the radio-frequency (RF) spectrum are directly utilized to perform simultaneous group velocity dispersion and in-band optical signal-to-noise ratio (SNR) monitoring. We also numerically investigate the measurement accuracy of this monitoring technique, highlighting the advantages, and suitability of the chalcogenide rib waveguide.

The paper addresses the problem of demodulating Continuous Phase Modulation (CPM) signals embedded in Gaussian noise. The paper introduces a description of CPM signals by a state-space model. Based on this model, a noncoherent demodulation method of CPM signals, that uses an Extended Kalman Filter (EKF), was developed. The performances of the demodulation method were tested on two types of CPM modulated signals, embedded in noise: Minimum Shift Keying (MSK) and Gaussian Minimum Shift Keying (GMSK). The results, obtained from simulations performed in MATLAB, leaded to the conclusion that, for moderately low Signal to Noise Ratios (SNR), the EKF algorithm provides satisfactorily even good results in noncoherent demodulation of CPM signals.

- by Ioan Nafornita and +1
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- Minimum shift keying, Phase Modulation, Extended Kalman Filter
- by Ljubisa Stankovic
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- Computer Science, Signal Processing, Image Registration, Image Quality

We present a new multisectional model for high-speed electrooptic modulators, fully integrated within the framework of a microwave circuit computer-aided design (CAD) suite (MWOFFICE [1]). Starting from geometrical and layout parameters, the model allows both simple (traveling-wave) and complex (phase reversal, periodically loaded) structures to be assembled, analyzed, and optimized from the standpoint of the electrical and electrooptic response (including chirp effects) both in small-signal (analog) and in large-signal (digital) operation, exploiting standard simulator tools. At no additional effort, parasitic and passive elements (such as optical or electrical delay paths) can be directly included in the modulator schematic, and the effect of transitions and package parasitics can be readily accounted for at a circuit level. Moreover, model integration within a circuit CAD suite enables one to seamlessly perform driver and modulator design and optimization within the same monolithic or hybrid circuit environment. Comparisons with experimental and literature data and design examples are presented to validate the approach and stress its potential in the design of high-speed electrooptic modulators.

- by Federica Cappelluti
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- Harmonic Analysis, Optics, Medical Imaging, Fiber Optics