Binary Phase Modulation Research Articles

Investigation of Multilevel Phase and Amplitude Modulation Formats in Combination With Polarization Multiplexing up to 240 Gb/s

We present experimental investigations of the receiver sensitivity and dispersion tolerance of multilevel optical communication systems with a symbol rate of 40 Gbaud. Four- and eight-level communication is obtained by combining binary amplitude modulation with either binary or quadrature differential phase modulation. We experimentally compare the dispersion tolerance, and show that multilevel modulation formats offer much better dispersion tolerance compared to binary formats. By combining multilevel modulation with polarization multiplexing, bit rates up to 240 Gb/s were obtained. We demonstrate transmission over 50-km fiber span with no power penalty for a pseudorandom binary sequence length of 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> -1 bits

Viewing angle enhancement for two- and three-dimensional holographic displays with random superresolution phase masks

Holographic displays employing binary phase modulation have been demonstrated to be attractive on the grounds of efficiency and miniaturization, and they offer a plausible approach to two-dimensional (2D) and three-dimensional (3D) image projection and display. A novel algorithm--one-step phase retrieval--and corresponding hardware architecture have recently been proposed, providing the performance required for real-time holographic display. However, since viewing angle varies inversely with pixel size, very small display pixels are required to achieve a wide field of view. This is particularly problematic for 3D displays, as the requirement for a large display with small pixels has hitherto necessitated an unachievably large electrical bandwidth. We present a novel approach, utilizing fixed random pixelated quaternary phase masks of greater resolution than the displayed hologram, to dramatically increase the viewing angle for 2D and 3D holographic displays without incurring a bandwidth penalty or significantly degrading image quality. Furthermore, an algorithm is presented to generate holograms accounting for the presence of such a phase mask, so that only one mask is required.

Generation of hollow beams by using a binary spatial light modulator

We demonstrate the generation of hollow laser beams by using a binary spatial light modulator and compare the results with those for a continuous modulator. The binary phase modulator produces beams that have continuous, azimuthally varying phase profiles and can be dynamically changed with kilohertz refresh rates. The intensity and phase profiles are recorded through the focus of an imaging lens and are compared with scalar diffraction theory. We highlight properties of the beams relevant to optical dipole traps.

Pulse shaping of octave spanning femtosecond laser pulses

Characterization and pulse shaping of octave spanning femtosecond lasers poses a significant challenge. We have constructed a grating-based pulse shaper for an ultra-broad-bandwidth (620-1020 nm)femtosecond laser, and used it to compensate the phase distortions of the laser, spatial-light modulator and optics within 0.1 rad accuracy accross the entire bandwidth using Multiphoton Intrapulse Interference Phase Scan (MIIPS) without a precompressor. The compensated transform limited pulses generated a second harmonic spectrum with a 12,260 cm(-1) spectral width. Binary phase modulation was introduced by this pulse shaping system to demonstrate high resolution control of the second harmonic generation spectrum.

Space-time trellis code design with binary CPM

Binary continuous phase modulation (CPM) is considered with space-time trellis codes (STTCs) for multiple-input multiple-output systems. Single-h CPM with rectangular, raised cosine and half cycle sinusoid is considered. The upper bound on the minimum product distance of this signalling scheme is determined over a quasi-static Rayleigh fading channel. Based on the rank and determinant criterion, best STTC/CPM combinations are identified for two transmit and an arbitrary number of receive antennas.

Dielectric phase-switched screen

Conventional radar absorbent materials rely on the absorption and conversion into heat of the electromagnetic energy incident upon them. In an alternative approach, the phase-switched screen (PSS) uses a switchable resistive layer to apply binary phase modulation to the reflected signal so that its energy is redistributed into sidebands that lie outside the receiver passband. Here, the characteristics of an alternative type of PSS, whose efficacy depends on periodic changes in the permittivity or permeability of a dielectric layer, are considered. This leads to the concept of the pseudo-multi-layer dielectric PSS, which mimics the performance of a multi-layer absorber but comprises of only a single layer.

Supplementary Proof for “Exact and Approximate Construction of Digital Phase Modulations by Superposition of AMP” by P. A. Laurent

In this letter, we supplement the derivation in Laurent's paper by mathematically proving that combining binary continuous phase modulation (CPM) signals in different bit durations results in the decomposed CPM expression consisting of a set of continuous amplitude-modulated pulse functions.

Common-path interferometry with one-dimensional periodic filters.

We discuss a spatial filtering interferometry setup that employs a periodic spatial filter with either cosine transmittance or binary phase modulation. The setup's input plane is formed by two separate windows, one of which supports a phase object and the other, a reference beam. Using the appropriate frequency and orientation of the filter produces an interference pattern of the two input fields at the output plane of the system. The main attributes and advantages of the setup are discussed and experimentally illustrated with the example of a binary phase periodic filter implemented with a spatial light modulator.

PHASE MODULATION TIME DEPENDENCE MEASUREMENT

Phase modulation using liquid crystals has wide-ranging applications including correlation [1] and telecommunications [2,3]. At present, relatively slow (order 5ms) nematic cells demonstrate the advantage of continuous phase modulation but are sensitive to polarisation of the input light [4,5]. The alternative is to use faster ferroelectric cells which exhibit polarisation insensitivity but show only binary phase modulation [2]. This work demonstrates a novel technique for measuring the phase response time, which allows evaluation of different cell topologies. Rise and fall times are calculated in the Fourier plane from a wave-front splitting interferometer. Phase modulation measurements of in-house cells have been made for planar and hybrid aligned liquid crystal cells using nematic liquid crystals. The results demonstrate the capabilities of in-house cells, and also show agreement with theoretical predictions of cell behaviour.

Modelling of binary phase modulation in surface stabilized ferroelectric liquid crystal spatial light modulators

Modelling of binary phase modulation is required for optimal performance of ferroelectric liquid crystals (FLC) on silicon SLMs when used in coherent optical systems. This paper presents a modelling technique by which an HSpice model can be provided for characterization of phase modulation properties for designing FLC-on-silicon SLMs. The simulation and experimental measurements of phase modulation are described. For the theoretical model simulation, FLC parameter measurements are described. We experimentally verify the modelled prediction of phase modulation by investigating reflective FLC test cells. We have shown reasonable agreement within 9% between the measured and simulated values of phase modulation.

Optical Comparator Based on an FLC over Silicon SLM

Optics provides the potential medium to deal with information at‘the speed of light’, hence it is a logical progression from the current electronic state of the art. By exploiting the inherent parallelism of free-space optics, it is possible to design and build optical image processors capable of analysing thousands of two-dimensional images every second. By using ferroelectric liquid crystal (FLC) spatial light modulators (SLMs) as two dimensional light modulation devices, it is possible to build either a binary phase only matched filter (BPOMF)[1] or a joint transform correlator (JTC)[2]. Both architectures exploit the fact that FLCs can be used for binary phase modulation which is independent of both tilt angle and cell thickness and is capable of switching speeds in excess of 10μsec. A further advancement is the development of FLC over silicon VLSI SLMs[3,4], which allow the integration of circuitry with the FLC over mirrors to make an active backplane high speed binary phase modulator with very low pixel pitches. Hence, miniaturisation of the correlator is possible. In the case of the BPOMF, it is possible to make a very compact correlator[5], however it will always be limited by the optomechanical system used to make the correlator. This is not such a major issue with the JTC and can be completely eliminated by adopting the binary phase l/f JTC architecture[6].

Binary phase modulation using electrically addressed transmissive and silicon backplane spatial light modulators

The operation and performance of a 128-by-128 matrix elec- trically addressed ferroelectric liquid crystal (FLC) multiplexed transmis- sive spatial light modulator (SLM) and a 320-by-240 reflective silicon- backplane SLM are described. The two-dimensional multiplexed FLC SLM is probably the only device that exists to date optimized for l 51.55-mm operation. The spatial and temporal measurements of the binary phase modulation of the two devices are discussed. For the spa- tial measurements, a novel idea regarding the effects of the LC modula- tion characteristics in the interpixel deadspace of the silicon backplane on the quality of the binary phase modulation is described. For the tem- poral measurements, two addressing schemes for holographic beam- steering applications are described and compared experimentally with the silicon-backplane SLM. The limitation in performance for these two devices is briefly stated, and an indication given of future devices that will be possible using this rapidly advancing technology. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)01609-3)

Blind self-noise-free frequency detectors for a subclass of MSK-type signals

Frequency offset due to Doppler shift and/or oscillator instabilities degrade the receiver performance. A family of frequency detectors for frequency offset estimation and compensation in digital receivers is introduced. The proposed detectors are best suited for frequency offset compensation of a subclass of binary continuous phase modulation with h=1/2 that includes modulation schemes with nonnegative frequency pulses. For the considered modulation schemes, the modulation-induced self-noise term is absent from the variance of the frequency estimate. The estimator is nondata- and nontiming-aided and its estimation range is either half or a quarter of the bit rate (R). With larger frequency offsets, the estimators that have a /spl plusmn/R/2 estimation range introduce a frequency ambiguity of R that is of no relevance to the performance of a differential detection based receiver.

Analysis and design of vertical cavity binary-phase modulators

The Fabry-Perot equation used to model asymmetric Fabry-Perot cavity reflection mode modulators can be considered as a bilinear transformation between the amplitude reflectivity of the modulator and the optical parameters of the cavity. Conformal mapping of this transformation into a suitable plane is used to visualise the operation of such a device working as a binary-phase modulator and to evaluate the tolerance of points of operation towards changes in the physical or operational parameters. Operation away from cavity resonance is shown to be less sensitive to parameter variations than conventional on-resonance operation.

Space-variant optical correlation by the use of random binary phase modulation

Space-variant optical correlation by the use of random binary phase modulation

Space-variant optical correlation by the use of random binary phase modulation

A simple method to achieve space-variant pattern recognition is proposed with a typical VanderLugt arrangement, in which the input pattern is modulated by a random binary phase function. The output correlation location can be programmed into the filter function. With the introduction of random binary phase modulation, the impulse response of either phase-only or binary phase-only filter function is not edge enhanced, resulting in higher Horner efficiency. Computer simulations are conducted to verify the proposed method.

Effects of dead zones in multiple-quantum-well binary-phase modulators on optical interconnections

We investigate the effects of inactive regions [dead zones (DZ's)] in multiple-quantum-well binary-phase modulators used for free-space dynamic optical interconnection applications. Results, however, have implications for other types of pixelated spatial light modulators (SLM's). To our knowledge, the effects of DZ's in SLM's have not before been thoroughly studied in a context other than optical correlation. We investigate the DZ's (considered to be either opaque or transmissive) as a feature that may be exploited in system design, calculating light efficiency and fidelity as a function of DZ fractional width. It is shown that in particular cases an appropriate choice of DZ width would lead to an optical interconnection with substantially improved cross-talk performance.

Scale invariant correlation with truncated phase-only radial harmonic filters

The classical radial harmonic filter is discussed first, to determine the best harmonic order and expansion center. The phase-only concept is then applied. The improved performances versus the number of discrete phase levels are then studied with computer simulations, showing that the optical implementation on spatial light modulators is optimal with 16 phase levels, and even possible on binary phase modulators. To compensate for the lack of noise filtering with phase-only filters, the new concept of truncated filter is introduced, restricting the region of support of the filter in the frequency domain without loss on the correlation peak value.

Hartley holograms

Binary holograms have become more interesting since spatial light modulators, capable of binary phase modulation, were developed. The primary restriction of these dynamic elements when used with the Fourier transform is the symmetry of the hologram reconstruction. I describe a new type of hologram that uses the Hartley transform instead of the Fourier transform. Despite their binary form, Hartley holograms offer maximal efficiency (theoretically 100%). Thus they can be presented as high diffraction-efficiency programmable elements. For practical reasons, I also propose a modified version for Hartley holograms that is easy to use. A theoretical analysis as well as experimental results are given.

An ambiguity‐function‐based method for analysis of Doppler decompressed radar signals applied to EISCAT measurements of oblique UHF‐VHF meteor echoes

Binary phase modulation using Barker codes as the modulating sequences is often used as a pulse compression technique in incoherent scatter radar measurements of the ionospheric E region. Demodulation of the compressed signal is usually accomplished by matched filtering techniques. If the target has appreciable velocity, the resulting Doppler shift detunes the scattered signal relative to the filter, and the target response spreads over a large range interval. The paper describes the development of a new data analysis method, based on an ambiguity function description of radar total‐power measurements, which uses the characteristic Doppler decompression signatures to identify, extract, and analyze high‐velocity events from conventional Barker‐coded power profile type incoherent scatter (IS) measurements. Data sets recorded with the European Incoherent Scatter UHF (931 MHz) and VHF (224 MHz) radars during the 1990‐1991 Geminid and 1993 Perseid showers are shown to contain many events which are associated with individual meteors crossing the radar beams over a wide range of aspect angles, including a few near‐radial cases. Line‐of‐sight velocities and effective cross sections are derived for some of the best dual radar events. The cross sections are very small and increase with decreasing wavelength, something not observed before. It is suggested that this is indicative of a scattering mechanism different from the one operating at near‐normal incidence at VHF, and Rayleigh scatter from compact “balls” of plasma contained within the meteor coma is proposed as a possible candidate, in qualitative agreement with the observations. Finally, some signal‐processing related aspects of the method are discussed. It is shown that most IS radars should be able to apply it to their existing programs with very little effort and without having to compromise the performance in normal E region applications. The method could therefore become a powerful tool for studies of meteor statistics at UHF frequencies.